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Marine Biological Laboratory Library

Woods Hole, Mass.

Presented by

Dr. Wm. Amber son

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HUMAN PHYSIOLOGY

BY

PROF. LUIGI LUCIANI

TRANSLATED BY

FRANCES A. WELBY

WITH A PREFACE BY

PROF. J. X. LANGLEY, F.R.S.
In 5 vols. Illustrated. 8vo.

Vol. I. Circulation and Respiration. 18s. net.

Vol. II. Internal Secretion Digestion Excretion The

Skin. 18s. net.

Vol. III. Muscnlar and Nervous Systems.
Vols. IV. and V. [In the Press.

LONDON : MACMILLAN AND CO., LTD.

HUMAN PHYSIOLOGY

MACMILLAN AND CO., LIMITED

LONDON BOMBAY CALCUTTA
MELBOURNE

THE MACMILLAN COMPANY

NEW YORK BOSTON CHICAGO
DALLAS SAN FRANCISCO

THE MACMILLAN CO. OF CANADA, LTD.

TORONTO

HUMAN
PHYSIOLOGY

BY

PROFESSOR LUIGI LUCIANI

DIRECTOR OF THE PHYSIOLOGICAL INSTITUTE OF THE ROYAL UNIVERSITY OF ROMK

TRANSLATED BY

FEANCES A. WELBY

WITH A PREFACE BY

J. K LANGLEY, F.E.S.

PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OP CAMBRIDGE

IN FIVE VOLUMES
VOL. Ill

EDITED BY

GORDON M. HOLMES, M.D.

MUSCULAR AND NERVOUS SYSTEMS

MACMILLAN AND CO., LIMITED
ST. MARTIN'S STREET, LONDON"

1915

COPYRIGHT

NOTE

THE third volume of Professor Luciani's Human Physiology,
which deals with the muscular and nervous systems, has been
translated from the fourth Italian edition, which has appeared
since the publication of the English translation of Vols. I. and II.

This edition, in which the third and fourth volumes have
been enlarged and corrected in places by Professor Luciaui, w r as
brought out in 1913 on which occasion a commemorative medal
and an album containing the autographs of almost all the world's
most eminent physiologists were presented to the Author.

The English translation of the preceding volumes was edited
by Dr. M. Camis, but as he was unable to act again in this
capacity the Editorship of the present volume has been under-
taken by Dr. Gordon Holmes.

LONDON, 1914.

CONTENTS

CHAPTER I

PAGE

GENERAL PHYSIOLOGY OF MUSCLE . . . . .1

1. Skeletal muscles ; excitability and the conditions which regulate
it. 2. Curves of muscular contraction. 3. Theory of contraction in
tetanus ; the muscle sound. 4. Propagation of excitatory wave along
the muscle on exciting with induced or constant currents. 5. Minute
structure of striated muscle fibres : changes during contraction. 6.
Muscular tone,contracture, and capacity of muscle for active elongation.
7. Chemical composition of muscle in rest and activity. 8. Metabolism
in muscle and sources of the energy developed. 9. Muscular work and
muscular energy. 10. Heat production in muscle. 11. Electrical
changes during rest and activity. 12. Origin of muscular activity.
Bibliography.

CHAPTER II

MECHANICS OF LOCOMOTOR APPARATUS . . . .96

1. General remarks on the structure of the bones and their articula-
tions. 2. Form, attachments, and mechanics of muscles in relation to
bones. 3. Line and centre of gravity of the body in different postures.
4. Mechanics of equilibration in different postures. 5. Movements of
the body in walking. 6. Movements of the body in running. 7. Move-
ments of the body in swimming. Bibliography.

CHAPTER III

PHONATION AND ARTICULATION . . . . .129

1. General observations on the fundamental characters of sounds,
and their formation by different musical instruments. 2. Structure
of larynx as a musical instrument ; functions of laryngeal muscles.

vii

viii PHYSIOLOGY

PAGE

3. Nerves and centres of phonation. 4. Mechanical conditions for the
production of laryngeal sounds ; function of different parts of the
phonatory system. 5. Principal characteristics of the singing voice.
6. Difficulties and natural imperfections of singing. 7. The vowel
system in phonetic language. 8. Theory of physical nature of vowel
tones. 9. System of semivowels or sounding consonants, middle conso-
nants, and mute consonants. 10. Composition of syllables and words.
11. Writing, or graphic language. Bibliography.

CHAPTER IV

GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM . .175

1. Structural elements of the nervous system. Theory of inde-
pendent neurones, or continuity of neuro-fibrils. 2. Conditions, laws,
and phenomena of conduction in nerve. 3. Rate of conductivity :
diphasic character of the impulse arousing it. 4. Metabolism of nerve :
electromotive phenomena during rest and excitation ; demarcation
current, action current. 5. Excitation of nerve. Natural stimuli and
artificial (chemical, mechanical, electrical) stimuli. 6. Factors in life
and death of nerve : conditions of excitability. 7. Polar effects of
constant current (electrotonus) : correlative changes in excitability and
conductivity. 8. Excitatory action of electrical currents. Laws of
excitation. 9. Theories as to origin of neural activity. 10. General
functions of nerve-centres. Ganglion cells and central fibrillary net-
work. Bibliography.

CHAPTER V

SPINAL CORD AND NERVES. . . .278

1. Grey and white matter of the spinal cord. 2. Extra- and intra-
spinal nerve-cells ; their connections with the root-fibres and tracts
which make up the spinal columns. 3. Spinal roots. Bell-Magendie
law of localisation of sensory and motor tracts. Waller's law of
degeneration after section. 4. Functional relations between afferent
and efferent roots. 5. Segmental arrangement of spinal roots. 6.
Reflex activity of segments of cord ; shock after section of cord. 7.
Short and long spinal reflexes ; laws of reflex spread. 8. Genesis of
spinal reflexes ; central factors that inhibit or promote them. 9. Tonic
and automatic functions of spinal cord ; " knee-jerk " or patellar reflex.
10. Trophic functions of spinal cord. 11. Sensory functions and
Pfliiger's " spinal soul." 12. Spinal cord an instrument of the brain ;
spino-cerebral and cerebro-spinal paths of conduction. 13. Localisation
of principal spinal centres ; phenomena of spinal deficiency (dogs with
amputated cord, Goltz). Bibliography.

CONTENTS ix

CHAPTER VI

PAGE

SYMPATHETIC SYSTEM ...... 359

1. Anatomy and histology of fibres and ganglia of sympathetic
system. 2. Peripheral distribution of sympathetic system to the
organs which it innervates. 3. Physiological arrangement of con-
stituent parts of sympathetic system ; origin and course of efferent
iibres. 4. Origin and course of afferent fibres, o. Function of peripheral
ganglia. Bibliography.

CHAPTER VII

THE MEDULLA OBLONGATA AND CEREBRAL NERVES . . 380

1. General anatomy of the brain : the medulla oblongata. 2. Motor
functions of hypoglossus nerve. 3. Vago- accessory group ; motor
functions of eleventh nerve. 4. Different functions of vagus nerve.
5. The glosso-pharyngeal exclusively a nerve of taste. 6. Functions of
the facial and acoustic nerves. 7. Functions of the oculomotor and
trigeminal nerves. 8. The medulla oblongata as a motor centre. 9.
The medulla oblongata as the central organ of locomotion and posture.
10. The medulla oblongata as a sensory centre. Bibliography.

CHAPTER VIII
THE HIND-BRAIN . . . . ... .419

1. Anatomy of hind-brain : ati'erent and efferent tracts of the
three cerebellar peduncles. 2. Preliminary observations on cerebellar
functions. 3. Dynamic phenomena immediately incident on removal
of cerebellum. 4. Cerebellar ataxy in dogs and monkeys after removal
of half the cerebellum. 5. Cerebellar ataxy after total removal of
cerebellum. 6. Cerebellar ataxy. 7. The cerebellum as the centre of
equilibrium ; 8. And the co-ordinating organ of voluntary movements-;
9. And the organ of subconscious sensations, exercising constant
reinforcing action upon the other nerve-centres. 10. Localisation of
cerebellar 'functions. Bibliography.

CHAPTER IX

MID-BRAIN AND THALAMENCEPHALON . . . .486

1. General structure of the mesencephalon. 2. The thalamen-
cephalon. 3. Effects of total extirpation of fore-, inter-, and mid-
brain in fishes ; 4. In amphibia ; 5. In birds ; 6. In mammals. 7.
Effects of stimulating the mesencephalon. 8. Effects of extirpating
the corpora quadrigemina alone. 9. Effects of dividing the whole or
half the brain stem at level of the mid-brain. 10. Effects of incom-
plete or total removal of optic thalami. Bibliography.

x PHYSIOLOGY

CHAPTER X

PAGE

THE FORE-BRAIN . . . . .526

1. General anatomy of telencephalon. 2. Structure of the cerebral
cortex or pallium. 3. History of cerebral localisation. 4. Excitable
zone of the cerebral cortex ; localisation in dog, monkey, man. 5.
Physiological analysis of motor reactions of cerebral cortex. 6. Inhibi-
tory reactions. 7. Organic reactions of cortical origin. 8. Epilepsy
from cortical excitation. 9. The sensory-motor area, deduced from
effects of partial or total destruction of excitable cortex. 10. Functions
of basal ganglia or corpora striata (caudate and lenticular nuclei).
11. Visual area. 12. Auditory area. 13. Olfactory and gustatory
areas. 14. Association areas ; division of cortex into thirty-six areas,
according to Flechsig's embryological method. 15. Physiological analysis
of speech disorders of cerebral origin. 16. General theory of the
psycho- physical functions of the brain. Bibliography.

INDEX OF SUBJECTS . . . . . .637

INDEX OF AUTHORS 651

EEEATA

Page 24, par. 4, line 5, for " idea- muscular" read " idio-muscular."
,, 38, ,, 3, ,, 6, for " zanthine, hypozanthine " read " xanthine, hypo-

xanthine."

,, 102, ,, 3, ,, 5, for " hypoglossus " read " hyoglossus. "
,, 130, ,, 4, ,, 6, for "phonation (speech) " read "phonation (voice)."
,, 144, ,, 2, ,, 14, for "pitch " read "timbre."
,, 345, Fig. 192, for "dorsal" read "thoracic vertebra."
,, 349, ,, 5, ,, 2, for "controlateral" read "contralateral."
,, 510, ,, 3, ,, 3, for " Macacus rheus" read " Macacus rhesus. "
,, 514, ,, 5, ,, 1, for " opistothonus " read " opisthotonus."

CHAPTEE I

GENERAL PHYSIOLOGY OF MUSCLE

CONTENTS. 1. Skeletal muscles; excitability and the conditions which
regulate it. 2. Curves of muscular contraction. 3. Theory of contraction in
tetanus ; the muscle sound. 4. Propagation of excitatory wave along the muscle
on exciting witli induced or constant currents. 5. Minute structure of striated
muscle fibres ; changes during contraction. 6. Muscular tone, contracture, and
capacity of muscle for active elongation. 7. Chemical composition of muscle in
rest and activity. 8. Metabolism in muscle and sources of the energy developed.
9. Muscular work and muscular energy. 10. Heat production in muscle.
11. Electrical changes during rest and activity. 12. Origin of muscular activity.
Bibliography.

FROM the physiological standpoint the higher animal organism
may be treated as a system of blood-forming organs, at the service
of a sensory-motor system. The first of these the vegetative or
involuntary system subserves the internal life of the body, and
its function is to prepare and keep approximately constant the
mass and constituents of the blood and lymph which provide the
common nutriment : the second the organic or voluntary system-
subserves the phenomena of external life, and maintains and regu-
lates the relations between the organism and its environment.

But this distinction, proposed by Xavier Bichat, has little
intrinsic value, however useful it may be in the classification of
functions. The two systems do not constitute two separate
organisms, like the two primitive layers of the blastoderm, but
form a single complex indivisible organism, in which the specific
functions of both systems are sharply differentiated and localised.
Bones, tendons, and other forms of connective tissue participate
in the structure of the organs and mechanisms of animal life, and
although they remain passive during the activity of the muscles
and nervous system they make the functions of the latter possible,
and are thus important constituents of the sensory-motor system.
On the other hand motor and sensory elements contribute to
the structure of the organs and systems of vegetative life ; among
the former are amoeboid cells, ciliated epithelia and muscle
fibres, among the latter not only the nerve plexuses of the
VOL. in 1 B

2 PHYSIOLOGY CHAP.

sympathetic, but also the nerve-paths and centres of the cerebro-
spinal system.

Nevertheless the muscular and nervous elements which play
a direct part in the functions of vegetative life have usually
certain morphological and functional characters which distinguish
them from those which make up the organs of animal life, and
regulate the relations of the organism with the external world :

(a) Voluntary or skeletal muscles are almost always striated ;
involuntary muscles, i.e. those of vegetative life, are almost always
non-striated.

(&) The former are controlled by the will, and only come into
play in response to nervous impulses ; the latter are nearly always
independent of the will, and may even function independently
of the central and peripheral nervous systems.

(c) The voluntary muscles consist of long fibres, grouped into
large masses, each of which is an anatomical unit ; the involuntary
fibres, which are not grouped into separate muscles, almost always
form smooth layers that line vessels or tubes, or constitute sheaths
that surround certain special cavities.

(f/) Finally (and this appears the most important), the first
are almost always skeletal muscles, attached by tendons to bony
levers, by which they can lift weights and overcome resistance,
i.e. perform actual mechanical work ; the second, on the con-
trary, are nearly all visceral muscles, and perform work that is
entirely confined to the interior of the body.

The nerves that control the involuntary system, again, present
certain characters which distinguish them from those that
innervate the voluntary muscles. The latter consist of medullated
fibres which come directly from the spinal roots ; the former are
exclusively non-medullated, and come principally from the sym-
pathetic system, and make at the periphery an exceedingly fine
fibrillary network which surrounds the separate muscle cells.

I. The skeletal muscles constitute the principal mass of the
body. Each muscle is an anatomical unit, a separate organ,
which can assume the most various shapes and sizes, but usually
consists of an elongated mass provided with tendons by which
it is attached to the skeleton. Each muscle consists of fibres
which are generally arranged parallel to its long axis, and converge
more or less towards the tendinous attachments. The muscle
fibres are united into bundles of varying size by connective
tissue, which is connected with the sheath or perimysium that
surrounds the whole muscle ; the blood and lymph vessels and
the nerves run through this connective tissue.

The length and the diameter of the muscle fibres vary con-
siderably. On an average, the length does not exceed 30-40 mm.,
but according to some authors it may reach 30 cm. The diameter
varies considerably even in the same muscle, and still more in

i GENERAL PHYSIOLOGY OF MUSCLE 3

different muscles, as it ranges from O'l to O'Ol mm. The fibres are
cylindrical or prismatic in form, with rounded angles and conical
ends. They consist of a striated substance of soft consistency
(the structure of which we shall presently examine) enclosed in
a tubular, apparently homogeneous elastic sheath, called the
sarcolemma; this is continued at both ends of the fibre into
connective tissue fibrils, which join the tendon or the septa of
the perirnysium.

The muscle fibres alone become active when the muscle
contracts ; the sarcolemma, the connective tissue of the perimysium
and its intermuscular septa, and the tendons remain passive.
During contraction each fibre pulls upon the tendon, either
directly or by means of the interfascicular connective tissue
which is continued into the tendon.

Each muscle has rnedullated and non-medullated nerve fibres ;
the former innervate its fibres, the latter the walls of the blood-
vessels : every muscle fibre is provided with at least one nerve
fibre, which usually forms an end-plate near its middle.

Under normal conditions the skeletal muscles are thrown
into activity by their nerves, and after section of these all move-
ment of the muscle is arrested ; this indicates that neither the
muscles nor the nerves by which they are innervated are capable
of automatic activity. But after dividing the nerve and exposing
the muscle an effective mechanical, thermal, chemical or electrical
stimulus, applied either to the nerve or directly to the muscle,
evokes a contraction of the latter in response ; so that both
nerves, when severed from their centre, and voluntary muscles
manifest irritability or excitability, i.e. a power of reacting by an
explosion of energy to external impulses (Vol. I. p. 44). The
active reaction, or contraction, of the muscle is expressed in its
rapid change of form and displacement ; excitation of the nerve,
on the contrary, is not accompanied by any direct visible change,
and consists solely, as we shall see, in a molecular vibration, by
which the excitatory impulse is transmitted to the muscle.

Since the natural excitation of a muscle is always the effect
of an excitation through its nerve, it is legitimate to assume that
the reaction produced artificially by its direct stimulation is also
due to stimulation of the nerve fibres that run between the
muscle bundles. Many authors, from Borelli and Willis onwards,
have regarded the muscles as the passive instruments of the
nerves, though A. Haller maintained the opposite view in his
famous theory of muscular irritability, which was based on
fallacious arguments (Vol. I. p. 299). Although Haller's view
has now only an historical interest, it is instructive to sum up
briefly the most striking arguments that were, and still might be,
adduced in support of the theory of direct or autonomous excita-
bility of the voluntary muscles.

4 PHYSIOLOGY CHAP.

In 1841, Longet resorted to a very simple method of deciding
the question, by cutting the nerves to a limb of a mammal, and
testing the direct and indirect excitability of its muscles, at
various intervals after the operation. He found that the nerves
lost their excitability to all stimuli (mechanical, chemical,
electrical) after the fourth day ; while the muscles to which these
nerves were distributed reacted to direct stimulation as long as
twelve weeks after the operation. To this argument in favour
of autonomous muscular excitability it was objected that the
degeneration and loss of excitability in the nerve is propagated in
a centrifugal direction, i.e. from the point of section towards the
nerve-endings, and that the end-plates might consequently retain
their excitability after total degeneration of the corresponding
fibres. Microscopical investigation, however, shows that the small
muscular nerves are already altered eight to ten days after the
section, and it would therefore be illogical to suppose that the
end-plates can remain intact several months longer. Clinical ob-
servations confirm this fact ; the muscles of the face, for instance,
preserve their direct excitability several years after the facial
nerve has been paralysed (C. Richet).

Another more effective method of showing that muscular
excitability is independent of the corresponding nerves was dis-
covered in 1850 by Cl. Bernard, and almost simultaneously by
Ko'lliker. The strongest stimuli applied to the nerves of
animals paralysed by curare are unable to excite any contraction
of the skeletal muscles ; but the muscles preserve their direct
excitability. Curare neither paralyses the sensory nerves nor
the nerve-centres, its paralysing action being limited (except
with excessive doses) to the motor nerve -endings. In fact, if
the sciatic nerve of a frog is exposed on the right side, and that
leg, leaving out the sciatic, is ligatured, and curare is then injected
under the skin of the back, the right leg reacts when its sciatic
nerve is stimulated ; but when the left sciatic is stimulated no
reaction of the muscles on that side is obtained because the poison
has been circulating through them, while there are reflex move-
ments from the right leg. The section of a motor nerve abolishes
excitability from the point of section to the periphery, but the
toxic action of curare begins by paralysing the motor end-plates,
and then extends centripetally along the nerve. Curare does not
therefore alter the excitability of the muscle perceptibly (at any
rate in small doses and in the early stages of its action), but it
paralyses motor nerves, by abolishing the conductivity of the motor
end-plates, and thus interrupts the normal link between the nerve
and its muscle.

A simpler and no less conclusive argument was brought
forward by Kiihne (1859). He observed that the sartorius muscle
of the frog has no nerve fibres near its end, for about ^ of its

i GENERAL PHYSIOLOGY OF MUSCLE 5

total length. Yet the muscle reacts by a twitch if it is stimulated
by pinching it with forceps at a point at which there are no nerve
fibres.

Another sound argument for the autonomous excitability of
muscle is the so-called idio- muscular contraction observed by
Schiff. This is seen in fatigued or degenerating muscle, in which
conductivity is lowered. On stroking the exposed muscle obliquely
to the direction of its fibres with a blunt object, or tapping it
with a scalpel, a ridge of contraction appears at the point of
contact. This is obviously a local muscular reaction, independent
of the nerve.

These direct arguments for the independent excitability of
voluntary muscles are confirmed by observations which demonstrate
the automatic and reflex excitability of involuntary muscle fibres.
(See Vol. I. pp. 305-12.)

Muscular excitability, independent of the nerves, is controlled
by the circulation which supplies the muscle with the nutrient
material and oxygen indispensable to its metabolism, and removes
the waste products as fast as these accumulate. Nicolas Stensen
(1687) first observed that after tying the abdominal aorta in
mammals paralysis of the posterior limbs rapidly set in, and dis-
appeared again if the artery were reopened after a short period.
In this experiment, however, the paralysis depends not only on the
fall of muscular excitability, but also on the anaemia of the lumbar
cord which is supplied by the aorta (Schiffer). If instead of the
aorta the iliac and crural arteries of one limb are tied, the ex-
citability of the muscles cut off from the .circulation survives for
many hours (Brown -Sequard) ; as the vitality of the muscle
diminishes it shortens, and finally becomes rigid (rigor mortis).
If the circulation is re-established before the onset of complete
rigor, the excitability of the muscles may be recovered.

Brown-Sequard demonstrated by a long series of experiments
that, after death, excitability persists for a longer or shorter time
in different muscles of the same animal ; that, generally speaking,
it survives longer if the external temperature is low, although the
contrary has been affirmed ; and that the longer the muscles pre-
serve their excitability after death, the longer are they capable
of recovering it on the artificial circulation of arterial blood.

Claude Bernard stated that during muscular contraction in
the living animal the blood flowing away from the muscles is
highly venous. Ludwig further observed that during tetanisation
of the muscles of any limb, by stimulation of its nerves, the flow
of blood from the muscle was accelerated, owing to the active
dilatation of the vessels. Chauveau noted an acceleration of the
circulation in the masticator muscles of calves during mastication,
which was due not only to nervous influence but also to the active
dilatation of the muscular vessels, and to the impetus given to the

6 PHYSIOLOGY CHAR

venous stream by each contraction of the muscles. But in curar-
ised animals also direct excitation of the muscles dilates the
vessels and may produce minute capillary extravasations owing to
excess of tension.

The nutrition of the muscles, and indirectly their excitability,
also depend on the trophic influence continually exercised upon
them by the nervous system. After cutting the motor nerves the
muscles degenerate as well as the peripheral end of the nerves
severed from their centre. Their excitability falls in the first three
or four days, but then rises to mechanical and galvanic excitation
(Erb's reaction of degeneration^), while it decreases still further to
faradic stimulation; after seven weeks muscular excitability is much
reduced, and within six to seven mouths it has disappeared. During
the first week after section fibrillary contractions are observed in
the degenerating muscle, which are due to the excitation of the
contractile elements by intrinsic chemical changes (Schiff).

Use and disuse again have great influence upon the nutrition,
and thus upon the excitability and work-capacity, of muscle. It
is a common observation that exercise develops and strengthens
the muscles, while disuse and a sedentary life render them weak
and flabby. Absolute enforced rest causes the muscles in time to
degenerate and atrophy.

II. The physiology of muscle was not really known till after
the ingenious researches of E. Weber (1846) on the relations
between contractility and elasticity ; and till Helinholtz (1850-52)
applied the graphic method to its study by means of his myograpli,
which traces the entire curve of a muscular contraction (myogram)
and indicates the exact moment of the application of the stimulus
to the nerve or to the muscle.

A Myograpli is an apparatus designed to show by a tracing on a smoked
plate or revolving cylinder the changes in length (or thickness) which a
muscle undergoes during excitation, i.e. the active state into which it is
thrown as the effect of .stimulation.

There are a great variety of these instruments, invented by the different
authors who have occupied themselves with the mechanical functions of the
muscles. One of the oldest is that of Pfliiger, which again is only a simpli-
fication of the original rnyograph devised by Helmholtz. Pfliiger's apparatus
(Fig. 1) consists of an arm LL which moves round a horizontal axis, and can
be brought into equilibrium by the counterpoise C. The other end of the arm
is fitted witli a lever, which also rotates round an axis and ends in a metal
point P, which writes on a moving smoked plate or drum that can be rotated
at varying speeds. The writing-point is kept in contact with the recording
surface by a small weight or spring, but can be drawn back by a thread
fastened to the wheel c. A freshly excised muscle is clamped at the top, and
attached below by a thread and hook to the middle of the lever. Below the
point at which the muscle is attached is a small scale-pin />, on which different
weights can be placed to examine the influence of different loading on the
contractility of the muscle. The latter is kept moist in a glass chamber con-
taining a little wet filter paper.

Instruments of this class give an imperfect record because the myograms

GENEEAL PHYSIOLOGY OF MUSCLE

do not correspond with the true movements of the excited muscle. Owing,
to the weight of the lever and the distance from the axis of the load appliec
to the muscle, tin- entire mass
is accelerated on the rapid con-
traction of the muscle, and the
curve altered, because the ten-
sion in the muscle due to the
load is greater at first, and then
gradually diminishes instead
of being constant. To avoid this
the mass raised by the muscle
and the height to which it is
lifted must be lessened, so as
to obviate changes of tension
during the contraction. This
is done by using a very light-
lever, and making the height
to which the weight is raised
as small as possible by attach-
ing it, close to the fulcrum, to
a thread which passes over a
wheel fixed at the axis of the
lever. By this arrangement
the acceleration imparted to
the weight becomes negligible,
no matter how rapid and ample
the movement of the lever, and
the passive tension of the muscle
remains constant throughout
the experiment.

Fig. 2 (which is only a modi-

FIG. 1. Pfliiger's myograph. Explanation in text.

fication of Waller's myograph) gives one of many that have been constructed
on this principle. It is adapted to show on the same muscle the effects

FIG. 2. Myograph for comparing direct and indirect excitation on the same muscle loaded or
unloaded. (Luciani.) The frog's gastrocnemius muscle is fixed horizontally over the surface
nf the mercury contained in a hollow of the cork plate. It is connected by a thread with a
jointed lever II, the axis of which carries a small wheel ; a thread passes round this to hold
the scale-pan for the weight ji, which is to load the muscle. The vertical arm of the aluminium
lever, cm which the muscle pulls directly, works the movements of the much longer horizontal
arm, which consists of a straw ending in a writing-point, by which the movement is traced
on a revolving cylinder. The relations between the two arms can be easily adjusted. The
electrodes from the secondary coil of an induction apparatus can be applied by a Pohl's
commutator without cross-wires to the muscle or the nerve, according as the bridge is thrown
over to the left M, or right N.

not only of direct and indirect excitation, but also of different weights
applied to the muscle, from the minimal load of a fine straw employed as

8

PHYSIOLOGY

CHAP.

the lever to progressively increasing weights suspended from the thread and
wheel at the axis.

The errors inseparable from the use of a lever (inertia, etc.) have more
recently been eliminated by employing the photographic method (Blix, 1895 ;

Brodie and Richardson, 1897 ; Lucas,
1903, etc.) The principle is that the

contracting muscle deflects a small

I Te^V IL ^"X. mirror, from which a beam of light is

reflected on to a travelling sensitive
surface so that the movement of con-
traction is photographed.

The myograms best suited for
analysis and study are those ob-
tained from " nerve -muscle pre-
parations " of the frog or other

Fio. 3. Frog's nerve -muscle preparation. Cold-blooded animal, ill which the

muscle; n, sciatic exc it a bility of the nerves and

t.a.

nerve, with all the branches cut except
that to the muscle ; /, femur ; p, clamp to
fix upper end of muscle with femur ; (.a.,
tenclo Achillis with hook to attach lower
end of muscle to myograph ; c.s/i., extreme
end of spinal cord.

muscles lasts much longer than
in warm-blooded animals (Fig. 3).
Whatever the nature of the
stimulus applied to the muscle or

its nerve, the contraction which is recorded by the myograph may

assume the form of a twitch or of tetanus. The twitch is the

simplest and most rapid form of muscular contraction ; tetanus is

a more complex and persistent contraction which results from the

fusion of a greater or less number of twitches in rapid succession.
Fig. 4 gives the myogram of a simple twitch, obtained on the

momentary stimulation of the frog's gastrocneinius by a break

shock from the secondary coil of an induction apparatus. In

order to determine the exact moment at which the shock is

thrown into the muscle the

recording cylinder itself, at a

certain point of its revolution,

is arranged to open a contact

(Helmholtz), or else an electric

signal which is interposed in

the circuit marks the exact

moment of stimulation upon

the recording surface (Marey

and others).

In Fig. 4 three different

periods can be distinguished:

(a) The interval a b, in

which no visible change takes place in the muscle ; this is the
time lost between the application of the stimulus and the com-
mencement of the contraction, which Helmholtz termed the period
of latent excitation or latent period.

(b) The interval b c, during which the muscle shortens, at first

PIG. 4. Myogram of contraction of frog's gastm-
cnemius. Time tracing from tuning-fork, giving
10U vibrations per second, n, li, latent period ;
li, <, phase of contract-ion ; <, d, phase of re-
laxation.

GENERAL PHYSIOLOGY OF MUSCLE 9

slowly, then more rapidly, then more slowly again, which repre-
sents the contraction period.

(c) The interval c d, during which the muscle relaxes and
lengthens, slowly at first, then more rapidly, then again slowly,
which is the expansion or elongation period.

According to Helmholtz' first results the latent period in the
voluntary muscles of the frog is about O'Ol sec., but later work has
shown it to be much shorter. According to Yeo it is 0'005 sec. ;
according to Burdou-Sanderson 0'0025 sec. ; lastly, according to
Tigerstedt (who made many comparative experiments on the
frog's gastrocnemius under a variety of conditions) it varies between
0-004 to 0-006 sec,, but is generally (41 per cent) 0'005 sec.

From the theoretical standpoint it is more than probable that
there is really no appreciable interval between the direct stimula-
tion of a muscle and the commencement of contraction, and that
the apparent latency of excitation depends on the fact that the
contraction does not begin simultaneously throughout the mass of
the muscle, but advances gradually like a wave, so that the fibres
which first contract pull upon, and passively extend, the fibres
that have not yet contracted, and thus nullify the mechanical
effect. It is only when, with the advance of the contraction wave,
the active shortening of the mass of muscle exceeds its passive
elongation that the lever attached to the muscle begins to rise
from the abscissa (Gad).

Apart from the latent period, the active reaction or excitation
of the muscle consists in a diphasic process, with distinct phases
of contraction and of expansion, which may vary considerably
under different circumstances. For instance :

(it) Tracings of a muscle twitch vary considerably in the
duration or velocity of the total movement and that of the two
separate phases, according to the character of the muscles which
are under observation. As regards speed of reaction, there is an
enormous difference between the plain muscles, which react so
slowly that both phases are visible to the eye, and the striated
muscles, which react so quickly that the graphic method is indis-
pensable for their demonstration. The cardiac muscle cells come
midway as regards rate of response between the unstriated visceral
and the striated skeletal muscles. The duration of the contraction
of skeletal muscles is variable, not only in the muscles of different
animals, but even in the different muscles of the same animal.

Contraction is most rapid in insects, less rapid in birds, slower
still in mammals (about O'l sec. on an average), slowest of all in
the cold-blooded animals, especially in the tortoise.

Eauvier (1874) first noted that in certain birds and mammals
two kinds of muscles can be distinguished, red and pale, and that
the latter contract more rapidly than the former, an important
fact subsequently confirmed by other experimenters.

10 PHYSIOLOGY CHAP.

According to Griitzner (1883) each muscle contains rapidly
contracting and slowly contracting fibres, which cannot always be
distinguished by their colour. Speaking generally, he holds that
the latter, which are less excitable and less easily fatigued, are
richer in sarcoplasm, darker and thinner ; the former, on the
contrary, are more excitable and more easily fatigued, less rich in
sarcoplasm, lighter and thicker. Easier (1904-5), in Griitzner's
laboratory, afterwards confirmed and extended these researches.

Paukul (1904), who examined the forms of twitch from almost
every muscle of the rabbit, came to the conclusion that the
different modes of contraction depend on the arrangement of the
muscle fibrils and the intervening sarcoplasm ; those muscles in
which fibrils lie uniformly and are surrounded by little sarcoplasm
contract rapidly, while those in which the fibrils are arranged in

FIG. 5. Influence of temperature on amplitude of muscular contraction. (A. D. Waller.) 1, con-
traction of normal gastrocnemius ; 2, of same muscle, slightly cooled ; 3, of same muscle, much
cooled.

groups and separated by a large amount of sarcoplasm contract
more slowly.

(6) Temperature, either higher or lower than the normal, has
a marked influence upon the course of the muscular contraction.
Cooling always lengthens the contraction, and raises its height
when the degree of cooling is moderated, but lowers it if more
marked (Fig. 5). Warming constantly accelerates contraction
and increases its height when moderate in degree, but lowers it
when more pronounced. Gad and Heymans found the maximum
height of contraction at 30 C. It is diminished as tbe tempera-
ture falls to 19 C, and subsequently rises again at C.

Patrizi examined muscular contraction in the marmot, both
in the hibernating and in the waking state, which are, of course,
distinguished by great differences of temperature. He found that
contraction is about three times more rapid when the animal is
awake than in hibernation ; and determined the latent period and
duration of the different phases of the twitch, and the stimulation
frequency required to produce tetanus, in both these states, that is,
with both the high and the low body-temperature.

i GENERAL PHYSIOLOGY OF MUSCLE 11

While cold diminishes muscular excitability and renders the
muscle less easily fatigued and more resistent, heat, after a brief
rise of excitability, leads to easy exhaustion. When the rise of
temperature exceeds 40-50 0. the muscle enters into thermal rigor,
in which it gives its maximal contraction, and does not relax again.

(c) The duration and form of the muscle twitch also depend on
the degree of fatigue. If a series of twitches from a frog's muscle,
uniformly loaded and excited at equal intervals (1-2 sees.), with
uniform shocks from make or break induction currents are recorded
on the drum of the myograph, a fatigue curve will be obtained which
shows a gradual retardation and weakening of muscular activity,
preceded by a short phase of augmentation. Fig. 6 shows that in
a preliminary period, consisting of some ten twitches, the tracings
rise in height, and the duration of both contraction and elongation
is lengthened. In a second much longer period the height drops,

I ;. ti. Curve of fatigue, with direct stimulation of frog's gastrocnemius. (A. D. Waller.) Tracing
of 125 maximal contractions at H sees, interval. The experiment was stopped before the muscle
became fully exhausted.

while the duration of both phases increases, but particularly that
of relaxation.

Kronecker (1871) showed that when a frog's muscle, excited
at regular intervals with maximal induction shocks, is loaded
only at the moment at which it commences its contraction (after
loading}, the apex of the twitches forms a straight line, which
drops more rapidly towards the abscissa in proportion as the
interval between the single stimulations diminishes. In repro-
ducing Kronecker's experimental conditions it is necessary first
to test the excitability of the muscle in order to find the least
stimulus that will produce a maximal effect ; next, the single
stimuli must succeed each other at long intervals, so that the
muscle shall not be excited again before the phase of relaxation is
fully completed, which takes longer and longer as the fatigue
increases. The apparent rise of activity, often seen at the com-
mencement of muscular fatigue, is probably due to the fact that,
owing to the lengthening of the phase of relaxation, the muscle
receives the next shock before it has completely relaxed. In
this case each new excitation summates with the residue of the
previous contraction, and the level of the myogram rises in conse-
quence (Fr. W. Frohlich, 1905).

12

PHYSIOLOGY

CHAP.

The study of fatigue phenomena in muscle is simplified and
made more complete if, instead of sending in the excitations at
regular intervals, the muscle is stimulated by a make induction
shock directly it has relaxed. The apparatus can be arranged so
that the contraction of the muscle breaks the exciting circuit, and
its relaxation closes it again. The muscle thus contracts and
relaxes continuously (Wundt, 1858 ; Novi, 1879).

Fig. 7 shows the curve of muscular fatigue passing into
complete exhaustion. It exhibits the initial phases that are to
be seen in Waller's incomplete curve, followed by a much longer

Km. 7. Complete tracing of muscular fatigue from frog's gastrocnemins ; series of successive
contractions which vary in frequency with the varying duration of the contraction. (I. Novi.)
Lines 1, 2, 3, 4 represent successive parts of one tracing, a, b, first, very brief phase con-
sisting of extremely rapid contractions of increasing height ; b, <:, second phase, four to five
times longer, rapid contractions decreasing in height ; c, d, third phase, less rapid contractions,
approximately equal in height ; </, c, fourth phase, longer than preceding, contractions becoming
slower and higher ; e, f, fifth phase, the longest of all, contractions decrease regularly in height,
and become increasingly slower; x, y, slowest of all ; y, /, minimum height, contractions
gradually die away.

final phase, in which the height of the twitches regularly decreases
in a straight line, as shown by Kronecker.

By Novi's method it is easier to analyse the changes in the
functions of muscle which are due to fatigue, and the variations
of the curve of fatigue with variations of temperature, and under
the influence of different drugs and poisons.

When fatigue has been pushed to complete exhaustion by
very frequent stimulation the muscle often fails to regain its
normal length, and remains more or less contracted, thus approxi-
mating to the state of rigor that signalises its death.

If the muscle is left to itself for a certain time after its
excitability is so exhausted that it no longer reacts to stimuli,
it gradually recovers, i.e. regains its excitability. In the living

i GENEEAL PHYSIOLOGY OF MUSCLE 13

body the tired muscle rapidly recovers with rest, owing to the
blood circulation ; but excised muscle, too, is capable of a partial
restoration, although it is cut off from the circulating tissue fluids.
Fatigue is the effect of two factors which act simultaneously
upon contractile protoplasm the consumption of the dynamogenic
materials of muscle, and the accumulation of waste matters or
decomposition products. Recovery depends on the supply of
further nutritive material and removal of the waste products, as
we shall presently see in discussing muscular metabolism.

(d~) The height of the twitch also depends on the form or
strength of the stimulus. It is advisable in studying these
relations to employ the make or break shocks of an induced
current, which can be easily graduated. If a muscle is rhythmic-
ally excited by break shocks of gradually increasing strength,
it begins to respond only when the stimulus reaches a certain
intensity, the so-called threshold of stimulation. If the exciting
current is then further strengthened, a series of contractions
result that increase in height, step by step, up to a certain point,
after which they no longer increase with the strength of the
stimulus. Stimulation is therefore distinguished as effective and
ineffective according as it produces or does not produce a reaction ;
effective stimuli, again, may be minimal, median, maximal, or
super -maximal. The gradation of the stimuli alters, moreover,
according as the muscle is directly or indirectly excited. When
the muscle is directly excited the interval between the minimal
and maximal stimulus is greater, but as this interval is very small
it requires only a slight increase of the stimulus above the threshold
to elicit a maximal contraction. The gradation of the response to
an increasing stimulus is not, therefore, easy to demonstrate.
Certain muscles, e.g. cardiac muscle, either do not respond at all
or respond to each shock by a maximal contraction Bowditch's
Law of " all or nothing " (Vol. I. p. 318).

According to Fick's first researches (1862) on the gradation of
response to indirect stimulation of skeletal muscle, the increase
in height of the contractions is approximately proportional to the
increase in strength of the stimulus ; but Tigerstedt has shown,
with direct stimulation of curarised muscles, that with regular
increase in the strength of the current the contractions at first
increase rapidly, and afterwards more slowly, till they become
maximal. The ascending line of the contractions is thus not a
straight line but a hyperbola.

At the maximum height of the muscle twitch obtained on
exciting a fresh frog's muscle with a maximal or supermaximal
stimulus the muscle shortens by \ of its length, as measured in
the resting state.

(e) The height, duration, and form of the contraction are
considerably influenced by the load carried by the muscle, i.e.

14 PHYSIOLOGY CHAP.

the resistance it encounters during its contraction. Generally
speaking, it is said that the weight applied to the muscle impedes
contraction while it facilitates relaxation. It is further assumed
that a muscle which carries no load i.e. is not influenced by
external resistance, as when it floats on mercury shortens with
an induced shock, and remains contracted without resuming its
initial length. If this were accepted unconditionally it would be
in open contradiction with a number of experimental observations,
which prove that both contraction and relaxation are active states
of the muscle. Kaiser (1900) showed that if the frog's sartorius
muscle is carefully dissected out without pulling on it, and dipped
in olive oil before being placed on the mercury to minimise friction,
it responds to each shock of an induced - current by a single
diphasic contraction, i.e. after contracting it relaxes at its normal
rate. After the first indirect stimulation the muscle regularly

^D

FIG. 8. Diagram of isotonic myograph. L, lever connected with the muscle at point A, traces the
movements with writing-point p on the recording surface. The weight P that pulls on the
muscle is fastened by a thread to a little wheel attached to axis of the lever.

becomes longer than it was before ; but if the stimuli are
applied frequently the expansion is less complete a muscle, for
instance, 35 mm. long in the initial resting state fails to attain
its original length, but becomes successively shorter by 1, 2, or
3 mm.

It may be said in general that the greater the load or the
resistance opposed to the contractile phase of muscular activity
the less is the shortening and the greater the degree of tension
in the muscle, so that shortening and muscular tension are in
inverse ratio. On stimulating a muscle clamped at both ends,
the tension can be increased to a maximum without any shortening ;
conversely, when a muscle, clamped at one end only and loaded
at the other with a small weight, is stimulated, it contracts
maximally with the least possible increase of tension. A. Fick
(1887) first analysed these two functions of muscular activity,
and devised a comparatively simple method by which it was
possible to a large extent to eliminate the alterations of tension,
while the curve of shortening was simultaneously recorded, or
vice versa to minimise the alterations in the length of the muscle

i GENERAL PHYSIOLOGY OF MUSCLE 15

and at the same time record the curve of muscular tension. To
the first he gave the name of isotonic, to the second of isometric
curves.

Isotonic curves are recorded with a very light lever, the weight being
applied near the fulcrum by a thread that runs over a wheel during the
contraction (Fig. R).

The free end of the muscle is attached by a hook and thread to a point of
the lever at greater or less distance from the fulcrum. The movements of
the muscle are magnified by the writing-point according as the muscle is
fixed nearer the fulcrum. Under these conditions the acceleration of the
weight is negligible, no matter what the amplitude and speed of the move-
ment, and the tension of the muscle remains approximately constant through-
out its contraction.

To obtain relatively perfect isometric curves, the shortening of the muscle
must be reduced to a minimum by causing its lower end to work against a
strong elastic resistance, and magnifying the excursion of the lever by a long
arm (Fig. 9). The muscle is fixed at its upper extremity, and is connected
by a long inextensible thread with a metal wheel, to which a steel spring

M

FIG. 9. Diagram of isometric myograph. The muscle is directly connected with the wheel, which
carries the spring .V; by pressing on the supports this considerably reduces the rotary
movement A, although the latter is magnified by the long arm of the lever L which records it.

is attached, which rests on a support at its free end. When the muscle
pulls on the thread the wheel moves slightly round the axis and the spring is
stretched against the support. The least movement of the wheel is magnified
by a long light lever, the point of which traces a curve upon a rotating
drum that almost perfectly expresses the tension of the muscle during
excitation, but not its change of form.

Various isotonic and isometric myographs have been invented, but the
principle is the same as in Figs. 8 and 9.

When the tension of the muscle remains approximately constant
during the course of the contraction (isotonic] the height of the
latter generally increases with diminution of the load, at first
rapidly, then more slowly, i.e. not in proportion with the load,
while the work done by the muscle, calculated from the weight
multiplied by the height to which it is raised, increases within
certain limits with each increment of weight (Santesson).

There are, indeed, exceptions to this rule. According to the
observations originally made by Fick, and afterwards confirmed
by others, when the weight applied to the muscle is not great,
and particularly when an elastic resistance is opposed to the
muscle, so that its tension increases constantly during contraction,

16 PHYSIOLOGY CHAP.

the shortening is greater when the weight and the initial resist-
ance are increased. This paradoxical phenomenon is a specific
property of the substance of living muscle, and shows that the
sudden pull of the muscle and increase of tension during shortening
act as a stimulus on the contractile substance, and increases the
effect of the electrical stimulation.

With the isometric method the tension of the muscle pre-
vented from shortening is far greater in the excited than in the
resting state. Comparison of the curves of isotonic and isometric
contraction, obtained from the same muscle under uniform con-
ditions of stimulation, show that the two curves differ very little
at medium temperature. When, on the contrary, the temperature
of the atmosphere is lowered to about 5 C. the two tracings

present distinctive char-
acters. Fig. 10 plainly
shows that the isometric
curve reaches its maximum
more rapidly than the iso-
tonic curve, and that in
the former maximal tension
persists for a certain time,
while in the second it passes
suddenly from the height of
the contraction phase to the

FIG. 10. Comparison of isotonic (a) and isometric (/-) phase of relaxation.

inyograms from the same muscle. (Gad.) The eor.iv.o-nn /"I QOJA cfnrliprl

isometric curve is reversed because in Gad's myo- \J.yw) &LUI

graph the lever is pulled down instead of up by foe influence of the load
increasing tension of the muscle.

upon isometric curves by

submitting the muscle to sudden changes of tension during its
contraction. Such changes, whether a temporary or permanent
increase or decrease, always induce marked diminution of tension
in the muscle in a degree which depends not on the magnitude,
but on the abruptness of the change, and is more pronounced
the later the alteration in tension occurs in the contraction.
In the body these conditions of isotonia and isometria are, of
course, seldom realised. A certain amount of contraction is nearly
always needed to overcome the resistance that diminishes or
increases during the course of excitation. The muscles, in other
words, are almost always employed in carrying out an external
mechanical task under various conditions, which differ from the
experimental conditions of isotonia and isometria. The isometric
method is an analytic means of eliminating the complications of
changes of form and internal friction, so as to obtain the simpler
curve of the changes of tension or of longitudinal molecular attrac-
tion, which are the fundamental effects of muscular excitation.

III. The activity of skeletal muscle in the body differs in
another respect from that above described. Under natural

i GENEEAL PHYSIOLOGY OF MUSCLE 17

conditions the movements of our body are not the effects of
simple muscular contraction, due to isolated and instantaneous
stimulations, but almost invariably result from a series of rapidly
succeeding stimuli, which produce in the muscle the state of
permanent and apparently uniform contraction known as tetanus.

Volta (1792) was the first who recognised that frequently
repeated stimuli were able to produce persistent contraction in
muscle. Matteucci (1838) first termed this state of contraction
tetanus, and the interrupted currents which produce it, tetanising
currents. Helmholtz (1854) first demonstrated that tetanus of
the skeletal muscles is the effect of the summation and fusion of
a rapid succession of simple contractions.

On sending two shocks from an induced current into the
nerve of a muscle at very brief intervals, so that the second
stimulus falls 011 the muscle during the period of latent excitation,
the resulting curve does not differ from that produced by a single
shock if the current is maximal, but if, on the contrary, the

Fin. 11. Diagrammatic superposition of two contractions. (Helmholtz.) The curves a b c and
</ i: / represent two distinct contractions excited by two shocks rr'. The curve a g h i k
represents the superposition and fusion of the two preceding, as if the contractions <l ef rose
from the abscissa line g i, and not from d /.

current is moderate or hardly effective, the height of the curve
is different. Accordingly, two shocks of medium strength act
in this case like a single maximal or supra -maximal stimulus,
showing that there is summation of the two excitations (Helm-
holtz). In the crab's muscles it is possible also to observe latent
summation of several shocks, each of which is ineffective in itself,
that is, incapable of producing any visible sign of excitation
(Richet).

If the interval between two stimuli is such that the second
induction shock falls on the muscle during the contraction
induced by the first, the second shock is superposed upon the
former, as if the muscle were at the moment of its application in
the natural state of rest (Helmholtz). In this case, accordingly,
the two contractions fuse into a single one of greater height and
duration (Fig. 11).

If the interval between the two stimulations is such that the
second contraction is sent in when the muscle is at the height of
the contraction produced by the first, the fusion of the two will be
maximal, i.e. almost double that of the simple twitch. This

VOL. in c

18 PHYSIOLOGY CHAP.

maximal effect of the fusion of the two contractions takes place
when the interval between the two shocks is about oV of a second
(Sewall and others).

Summation of contractions takes place not only with currents
of medium strength, but also with maximal or supra-maximal
stimulation. The maximal contraction of a muscle is therefore
not obtained with a single stimulation, however strong, but only
with repeated stimuli in rapid succession, owing to the summation
of excitation. The interpretation of this phenomenon will be
given later in speaking of Contracture.

When a series of stimuli act upon a muscle in rapid succession,
it reaches the maximum degree of % shortening, owing to summation
of the stimuli, and remains in the state of persistent contraction
known as tetanus so long as the stimuli act upon it. The minimal

.:*. '-.. ':,;

-

.-;' s

Fin. 12. Comparison of tetanus curves from a red (;) and pale (yi) muscle of rabbit. (Kroneckor
and Stirling.) At A both muscles were excited by ten induced shocks per second ; at B by
six shocks per second.

stimulation frequency necessary to produce complete tetanus
varies in the muscles of different animals. As a rule it is less
in proportion as the active phase of the muscular contraction is
slower. 12-30 stimuli per second suffice for frog muscles, while
20-30 are required for those of mammals. The red muscles of the
rabbit, according to Kronecker and Stirling, may be almost com-
pletely tetanised with 10 stimuli per second, while the pale muscles
of the same animal are only thrown into tetanus with 20-30
stimuli per second. With 6 stimuli per second the pale muscles
exhibit a series of almost wholly isolated contractions, while
the same frequency throws the red muscles into a tremulous
contraction closely resembling tetanus (Fig. 12).

All conditions that make muscular contraction slower, as
fatigue, fall of temperature, etc., diminish the stimulation
frequency necessary for complete tetanus. On the cessation of
the series of stimuli that induced tetanic contraction, the muscle
never resumes its original length, but remains a little shortened
in consequence of the fatigue and the abnormal changes which the

i GENERAL PHYSIOLOGY OF MUSCLE 1.9

contractile protoplasm has suffered. The degree of this residual
shortening is, of course, in definite relation with the duration of
the tetanus.

It follows from the theory of summation of contractions that
in tetanus the shortening of the muscle, and thus the work it is
able to accomplish, is greater than in a simple contraction. To
this rule there is, however, one exception ; according to von Frey
a lightly loaded muscle contracts equally both to a single shock,
and to a tetanisiug current.

The degree of shortening and the yield of work from the
tetanised muscle depend on the frequency and strength of the
tetanising current. When the stimulation frequency exceeds
300 per second, and the current is sufficiently weak, no tetanus
results (Harless, Heidenhain), or at most a single initial twitch
(Bernstein). In order to produce tetanus the current must be
strengthened ; this is due to the fact that after the first stimulation
the excitability of the muscle drops, and consequently it no longer
reacts to subsequent stimuli so long as these remain minimal.
According to Salomonson (1904), on the contrary, this is merely
a physical phenomenon.

The upper limit of the stimulation frequency that can produce
tetanus has not yet been ascertained. Bernstein obtained it with
an acoustic interrupter that sent 2000-3000 induction shocks into
the muscle per second : Kronecker with 20,000 shocks per second.

Tesla and d'Arsonval discovered that high frequency alternating
currents sufficiently intense to render a carbon filament in-
candescent fail to excite a muscle or nerve. While a constant
current of 5 milliamperes excites both at break and at make
of the circuit, an alternating current of 5 amperes, of high
frequency (about one million per second), produces no effect, motor
or sensory. By a special contrivance this current can be passed
through one or more persons and at the same time through a
series of incandescent lamps ; the lamps light up, while the
individuals included in the circuit feel neither sensation nor
motion. Eiuthoven (1900) subsequently demonstrated that it is
possible to evoke muscular contractions by means of indirect
stimulation, even with alternating currents of the highest frequency
(up to a million per second), provided the strength of the current
is enormously increased in proportion with its frequency.

Comparison of the rate of the muscular contractions produced
by an instantaneous shock from an induced current with the slow
persistent contractions by which the skeletal muscles are usually
thrown into voluntary contraction, has led to the conclusion that
the latter are tetanic in character, i.e. are the effects of a series of
impulses from the nerve centres. To support this theory of the
discontinuity of excitation in voluntary contraction, Wollaston
(1810) adduced the sound developed by the muscle in contracting,

20

PHYSIOLOGY

CHAP.

in which one tone predominates. On introducing one finger into
the auditory meatus and then forcibly contracting the muscles of
the arm, a dull murmur is heard similar to that from a distant
vehicle moving rapidly along the surface of a road. He regarded
the tremor often noticed in the muscular movements of old people
as the effect of an abnormal slowing of the muscular vibrations
due to debility and age. From his studies of voluntary muscular
contraction Wollaston concluded that the sound in the contracting
muscle corresponds to a frequency that oscillates between 14 and
15 per second at the minimum, 35 and 36 at the maximum.

Helmholtz (1864) investigated the subject of the muscle sound
with better methods. He observed that if in the dead of night
the auditory meatuses are stopped and the masseters forcibly
contracted, a murmur is heard in which there is a ground tone
that lasts as long as the voluntary contraction, and does not
change materially with increase of muscular tension.

n
s

,VAV/ fsrsfW\W't*w AMAA AAA*WWy / A- AM/ ./AAA/NAA/ / A/. W\ '/ //v%A'V////>lAA''/-'////y/'^/yA' l AA/-/Wyv/v/yv.// 1 A/W

Fn:. 13. Vibrations of biceps muscle of rabbit's femur on stimulating the spinal cord or sciatic
nerve with forty-two induction shocks per second. (Kronecker and Stanley Hall.) The middle
line s gives the vibrations of a tuning-fork in T J n sec. ; the upper line n is the tracing of the
vibration of the muscle during stimulation of the sciatic ; the lower line in, the vibrations of
the muscle during stimulation of the cord. Both tracings were obtained by applying a
sensitive lever to the surface of the exposed muscle.

The same tone is heard on firmly contracting the eye-muscles
or applying the stethoscope to the arm-muscles during voluntary
contraction. Helmholtz pointed out that the vibrations which
give rise to the sounds did not follow in regular sequence like
those of a musical tone. To determine the frequency objectively,
he applied watch springs or strips of paper to the muscles which
were vibrating in unison, and found the vibrations to be 18-20
per second. He confirmed the fact previously observed by Du Bois-
Keymond, that vibrations of the same frequency as those of
voluntary contraction are produced when a tetanising current of
high frequency is applied not only to the nerve or muscle but
also to the spinal cord of an animal. Subsequently, Helmholtz
pointed out (1864) that the tone perceived by the ear corresponds
not to the effective number of muscular vibrations, but to the
resonance tone proper to the ear of the observer, which corresponds
with the first over-tone or the octave of the fundamental tone of
the muscle, and is difficult to determine, because it lies at the limit
of the perceptible tones. He stated in effect that the tone heard
on voluntary contraction of the masseter muscles corresponds to

i GENERAL PHYSIOLOGY OF MUSCLE 21

36-40 vibrations, while the natural vibration of the human muscles is
only 18-20 per second. Similar results were obtained by Kronecker
and Stanley Hall (1879), who registered the oscillations in the
mass of the exposed femoral biceps of the rabbit by applying the
lever of a Marey's tambour to its surface, and tetanising the spinal
cord with an induced current of 43 shocks per second (Fig. 13).

Later work on this subject, particularly by Loven, von Kries,
Schafer, Wedensky, and Stern (1900), however, yielded different
and apparently contradictory conclusions in certain particulars,
while confirming the fact that all voluntary contractions, and
those due to strychnine and to reflex or direct stimulation of the
cerebral centres, are discontinuous phenomena, i.e. are due to the
summation of a series of impulses emanating from the centres and
transmitted to the muscles.

It is difficult on the generally accepted theory of Helmholtz,
that the sound heard from a muscle either in tetanus or in per-
sistent voluntary muscular contraction depends essentially on the
displacement of the contractile substance, to explain the fact that
simple twitches or contractions, such as the cardiac systole, can
give rise to a murmur.

Lastly, it should be added that Briinings (1903) made an
accurate analysis of the muscle sound produced by direct and
indirect stimulation with faradic currents of varying frequency.
He found that it always has the character of a simple tone, and
that its frequency never differs from that of the stimulus. But if
on direct stimulation the frequency of the faradic currents is
constantly increased, the intensity of the muscle sound grows
proportionately less, until it disappears altogether after reaching a
certain limit of frequency, though the tetanus still continues.
This maximal limit is higher in proportion to the strength of the
stimulus and the freshness and the temperature of the muscle.
Its relation to the temperature in particular is surprisingly
regular. While, e.g., at Y'5 C. 3 stimuli per second is the maximum
at which an isorhythmic murmur can be obtained, no sound being
heard at any higher frequency, at 35 C. the highest perceptible
tone is observed with 435 vibrations.

IV. To complete the analysis of the mechanical effects of
excitation we must further consider the variations in thickness of
the muscle and the propagation of excitation along its fibres. In
excitation the long axis of the muscle shortens, and its transverse
axis increases, while the surface of the muscle diminishes during
the contraction and increases in relaxation. But the question was
long disputed as to whether the volume of the muscle also varied
during contraction, and diminished during tetanus. This question
was experimentally investigated long since by Borelli, Glisson,
Swammerdam, and subsequently with better methods by Barzel-
lotti, Erinan, Joh. Mu'ller, E. Weber, and many others. The

22

PHYSIOLOGY

CHAP.

results were contradictory. Many observers were unable to dis-
cover any variation in the volume of the muscle, while others saw
a more or less marked diminution in volume during tetanus.

Among the former we must

mention Barzellotti (1795-96),
who invented the method of
introducing the muscles of a
frog into a closed vessel full of
water, which carried a capillary
tube: among the latter, Erman
(1812), who with the same
method observed a marked
diminution in volume. An

Fin. 14. Myograph suitable for man, to record
increased bulk of the muscles. (Marey.) Con-
sists of a capsule covered with a rubber mem-
brane, pulled out by a spiral spring. A metal

rane, pue ou y a spra sprng. mea , . 11

button in the centre of the membrane carries the exhaustive research by

exciting current to the skin immediately above /1oq7\ w Vir> riprfppfpH "

the muscle to be explored. The compression of V iO ' )> wn

the air in the capsule flunns the contraction lis lottl's method with nce a-

tiansimtted by a rubber tube to the lever of a . .,

recording tambour. JUStUientS, aiSO jailed to Obtain

even minimal variations of
volume in a muscle during tetanisation.

The muscle therefore changes in form and extent of surface,
but not in density and volume, during activity. Were they not
sanctioned by use it would be better to give up the inappropriate
expressions " contraction " and " relaxation," to indicate the two
phases of muscular activity.

The state of contraction in a muscle can also be studied by
tracings of the area of its cross-section. Marey invented special
myographs for this purpose which can be applied to man in
physiological and clinical research. The simplest of these are
shown in Figs. 14 and 15. Curves of simple contraction and of

FIG. 15. Exploring tambour that can lie used as a myograph to transmit the phases of increasing
thickness of a contracting muscle to a tambour with writing lever.

tetanus recorded by this method closely resemble those we have
already analysed in the corresponding changes in the length of a
muscle. But there is one important difference ; while the former
record the algebraic sum of the changes in length in all tbe
different parts of the muscle, the latter only trace the changes in

i GENEKAL PHYSIOLOGY OF MUSCLE 23

thickness of the particular portion of the muscle to which the
myograph is applied.

The rate of propagation of the contraction wave can be calcu-
lated from the interval between the contraction of two different
points of an isolated muscle, traced by two myograph levers placed
on the muscle at a known distance from each other, and writing
on the same drum. The sartorius muscle of the frog, in which
the fibres were parallel to one another, is the most suitable for
this purpose. Before dissecting it out, the frog should be curarised
to eliminate the action of the stimulus upon the intramuscular
nerves. When an induced shock is applied to one end of the
muscle, the contraction spreads in wave-form to the other end, at
a velocity which can be calculated by means of the two curves.

Fig. 16 shows that the second curve rises about - 06 sec.
after the commencement of the first curve : in passing over the

Fir,. 16. Two myograms of thickening from the same frog's muscle, obtained by applying two
/(/'/UTS myographiqves at a distance of 15 mm. to measure the velocity of the excitation wave.
(Marey.) Time tracing in T n sec.

part of the muscle between the two rnyographs the wave of con-
traction therefore occupied 0'06 sec. As the distance between the
two levers was 15 mm., the wave travelled at a rate of about 1 m.
per second.

The length of the wave can also be calculated from the
duration of the thickening of the fibres (in Fig. 16 about seven
vibrations of the tuning-fork = O07 sec.), and from the rate at
which the wave is propagated. Bernstein stated that the duration
of the twitch in any segment of the muscle (which must be dis-
tinguished from the duration of the twitch of the whole muscle,
which usually takes longer) is from 0'05 to 01 sec. Assuming
Bernstein's calculations of the rate at which the wave travels
3-4 m. per second, to be correct then the length of the wave, or
the part of the muscle over which it passes in O'05-O'l sec., is on
an average 200-300 mm.

As the length of each muscle fibre rarely exceeds 40 mm. the
entire length of each fibre is usually involved in the contraction.
It is only at the beginning and towards the end of the contraction
that one or other end of the fibre is not active; throughout the

24 PHYSIOLOGY CHAP.

greater part of the duration of the wave, each segment of the
fibre will be in some phase of activity, which is more advanced in
the segments nearer to, less advanced in those more distant from,
the points at which the stimulus is applied.

The rate of propagation varies considerably in the muscles of
the same animal according to the method adopted. According to
Aeby (1860), who first applied the graphic method to this research
in the gracilis and semi-membranosus muscles of the frog, it is
about 1 m. per second (1'2-1'G in.). Yon Bezold's and Marey's
results were much the same, while Bernstein, who compared the
moments at which successive waves, travelling in the same
direction from different points, reached a particular spot at a
known distance from each of them, obtained much higher values
(3'2-4'4 m. per second). Hermann who excited the two sartorius
muscles in a curarised frog at two different points, and simultane-
ously, gave the rate as 2 - 7 m. per second.

Just as the velocity of the muscle twitch differs considerably
in the muscles of different animals (cold-blooded and warm-
blooded), and in different muscles (pale or red, quick or torpid), so
the velocity at which the wave of excitation or contraction travels
also varies. In the retractor collis muscle of the tortoise the rate
at which excitation is transmitted varies between 05 and T8 m.
(Hermann and Aeby) ; while in the sterno-mastoid muscle of the
dog it is equal to 3-6 m. (Bernstein and Steiner).

The rate of propagation of the wave may v/iry greatly in the
same muscle with the strength of stimulus, still more with the
state of its excitability, which varies largely according to fatigue
and with the temperature. Schiff (1856-58) first studied the
interesting phenomenon known as the ideo-muscular contraction,
which directly shows the transmission of a contraction excited by
mechanical stimuli along mammalian muscles exposed shortly
after death. A ridge or weal forms when the muscle is tapped
or stroked with a blunt object, and persists for a certain time ;
two contractile waves start from it, and spread towards the
two ends of the muscle, where they are reflected back towards
the spot stimulated, and collide with secondary waves from the
weal. As the excitability of the tissue is exhausted, the velocity
of this wave conduction also diminishes.

These observations on the propagation of the contraction wave
through the muscle refer to artificial direct stimulation at one
end. With natural or indirect stimuli, when the excitation
reaches the muscle through the end-plates of the motor nerves that
lie towards the middle of each fibre, the contraction must invade
the total length of the fibres in a much shorter time. In fact we
assume that the contraction is propagated from the end-plates in
two opposite directions towards the two ends of the fibres, and
therefore has only to traverse half its length.

GENERAL PHYSIOLOGY OF MUSCLE

25

When, instead of using make and break shocks from an
induction coil, a muscle is excited with the constant current,
it contracts at each closure or opening of the current, but is
relaxed during the passage of the current. This law usually holds
good if a current of medium strength is employed, but if the
strength of the current exceeds certain limits, the make or break
of the current is immediately followed by a tetanus (closure or
opening tetanus). This fact, which was first noted by Wundt,
can also be observed on man, by sending a strong galvanic current
into a muscle, or even a comparatively weak current when the
muscle is degenerated.

Curarised muscles react more readily to the closure and open-
ing of a constant current than to the
more transitory make and break shocks
of an induced current. Hence in ex-
amining the rate of transmission of
contraction, the constant current is pre-
ferable.

The excitation at make of the con-
stant current is greater than at break,
as can be seen by varying the amount
of current passed through the muscle,
by means of a rheochord.

Von Bezold, Engelmann, and Hering
showed that the "law of contraction"
which Pfliiger formulated for nerve (see
Chap. IV.) holds for muscle also : the
closing contraction always starts from
the negative pole, while the opening
contraction is set up at the positive
pole ; in other words the make excita-
tion is kathodal, the break excitation is

anodal. This law may be demonstrated by placing two myograph
levers far apart on a curarised muscle, to the two ends of which
the two electrodes are applied. At make and break of the
current the two contractions are recorded at brief intervals, but
the kathodal always precedes the anodal at the closure, and the
anodal the kathodal at the opening, of the current.

V. In order to understand the changes in form which the
muscle undergoes during activity, it is necessary to examine the
structure of the muscle fibre under the microscope, and the
changes which it undergoes during contraction.

Each muscle fibre consists of soft protoplasm enclosed in an
elastic tubular sheath, the sarcolemma. This membrane is so
resistant that it is uninjured by a pull strong enough to rupture
the muscle substance (Fig. 17). Oval nuclei parallel with the
long axis of the fibre generally lie immediately under the sarco-

Fi

}. 17. Sarcolemma of mammalian
muscle. (Schafer.) Highly magni-
fied. The sarcolemma is left clear,
owing to rupture of the muscular
substance.

26

PHYSIOLOGY

CHAP.

lemma, but they belong to the muscle substance, and not to the
sarcolemma. Each muscle fibre may be regarded as a very
elongated cell, provided with several nuclei, the sarcolemma
representing the cell membrane. The diameter of the fibres
usually varies from 30 to 40 /*, but may be greater or less in
different classes of animals.

The substance proper or protoplasm of the fibre presents a
double striation, longitudinal and transverse, owing to the fact
that it consists of a bundle of numerous primitive fibrils arranged
parallel, each of which has a complex transverse structure.

On examining a fibre in cross-section, each primitive fibril
appears as a rounded spherical granule, comparatively dark in
colour, surrounded by a lighter non-differentiated substance the
sarcoplasm. The amount of sarcoplasm may vary considerably in

s ,

Fio. 18. Traiivi'rsi- section of two striated muscle fibres of rabbit. (S/.ymonowk-z.) Magnified
1000 diameters. At A the primitive fibrils (.S) are equally distributed in the sarcoplasm (S^).
At B they form polyliedric segments known as Cohnlu-im's areas (Cc).

different muscles, just as the mode of division or grouping of the
primitive fibrils within the sarcoplasm also differs (Fig. 18).

On examination of a fre^h muscle fibre in serum, a longi-
tudinal striation is seen owing to the parallel arrangement of the
primitive fibrillae. A series of light and dark striae at right
angles to the longitudinal axis of the fibre are also visible, which
are due to a double series of light and dark parallel bands that
alternate regularly through the entire length of the fibre. The
dark striae are broader than the light, and show at the boundary
of the clear bands a darker layer which seems to consist of a series
of dots.

On teasing out dead muscle fibres hardened in alcohol, it is
possible to separate the primitive fibrils. This is easiest in
animals which have the most abundant sarcoplasm (Fig. 20).
Under a high power, each fibril is seen to consist of alternating
light and dark bands of approximately uniform width. But in
the middle of the clear band there is a very fine dark line,

GENERAL PHYSIOLOGY OF MUSCLE

27

which was first described by Aniici, but is generally known as
Krause's membrane. Krause regarded this as a delicate little
membrane, dividing the fibrils into a series of segments which he
called sarcomeres. In the muscles of certain insects as well as
those of some mammals, a further differentiation is visible with
strong magnification in both light and dark bands, for the
description of which the reader must refer to text-books of modern
histology.

From the physiological point of view the different refracting

:::::::- .

:, !;ij;;;;;;;

is

iiffjj in I,

tmfl &aiwis
ii-j 3 !MwFfi ;

Dun --/(({"'V't'/
jllHll '."iinimTf/ -,
-.'!'!'.' BjrnjHifijf /'
ufff unniTinm /

FIG. 19. (Left.) Muscular fibre of a mammal examined fresh in .serum. (Schiifer.) Highly
magnified.

FIG. 20. (Right.) Fragment of frog's muscle fibre in which a few fibres have been isolated.
(Szymonowicz.) Magnified about 650 diameters, n, nucleus ; fp, primitive fibril ; is,
isotropous layer; an, anisotropous layer; A, Amici's striae or intermediate disc.

power of the respective light or dark bands of muscle fibres is
more important. Boeck of Christiania was the first who pointed
out that certain tissues, among them the muscles, were doubly
refracting or anisotropous, but Briicke (1857) showed that the
whole fibre is not anisotropous, a portion of its substance being
singly refracting or isotropous. When the fibres are viewed by
polarised light, the dark striae show up light on the black ground
formed by crossed Nicol prisms : the light striae, on the contrary,
appear dark. The former are doubly, the latter singly refracting.
To obtain a clear idea of the changes which the striatiou of
the muscle fibre undergoes during contraction, it is necessary to
fix the muscle as the contraction wave crosses it, in order to study

PHYSIOLOGY CHAP.

all the details of its appearance under the microscope. This is
easily accomplished if a fresh muscle from an insect's leg is
dropped into absolute alcohol or solution of osmic acid. These
reagents excite a series of waves in the muscle fibre, and fix it at
the same time, so that on teasing out some bundles of fibres for a
few minutes and examining them under the high power, the so-
called "fixed wave of contraction " can be seen in the form of
nodes or fusiform swellings. In some fibres it is also possible to
see the so-called " lateral waves," due to contraction of one surface
of a fibre which is relaxed on the opposite side, and intermediate
parts between the two surfaces show gradations of all the
intermediate stages between the phases of contraction and of
relaxation.

Engelmann (1878) made the most important contributions to
this subject. He found in the muscle fibres of an insect (Thele-
pliorus melanurus) treated as above, that the optical properties
and the breadth of the isotropous and anisotropous bands altered
inversely to the changes in the form of the fibres during contrac-
tion. As shown by Fig. 21 the isotropous layers become ?is a
whole more refracting, i.e. more compact and darker, while the
anisotropous layers become less refractive, i.e. more fluid and
Lighter. The breadth of both layers diminishes during contraction,
but more rapidly in the isotropous than in the anisotropous bands,
so that the latter increase in volume at the expense of the former.
Thus, according to Engelmann, we must assume that during
contraction the anisotropous substance subtracts water from the
isotropous.

The same fact is more evident in Fig. 22, which represents a
lateral contraction wave, observed by Eollet near a motor end-plate.

Ranvier (1880) employed an ingenious method for determining
which bands of the sarcoplasm contracted, and which behaved
passively, when stimulated. He put two muscles of a frog or
rabbit into a condition of absolute isometry, and then fixed them
by absolute alcohol while one was inactive, the other in tetanus
produced by an induced current. On then comparing the muscles
under the microscope, he found a reduction in the breadth of the
dark anisotropous discs in the fibres of the tetanised muscle, which
were now perceptibly equal to the clear isotropons discs, while
in the inactive muscle they were considerably broader. He
further pointed out that there was in the fibres of the tetanised
muscle a considerable increase of the interfibrillar sarcoplasm,
which appeared to break up the fibre into fibrils.

According to Eanvier, therefore, the layers of anisotropous
substance diminished in volume. Contrary to Engelmann's
results, water does not pass from the isotropous to the anisotropous
substance during tetanic tension, but diffuses from the latter into
the interfibrillary substance.

GENEKAL PHYSIOLOGY OF MUSCLE

29

Since the experimental conditions adopted by the two authors
are essentially different, these apparently contradictory conclusions
may not be irreconcilable.

Both Engelmaim and Eanvier agree, though from different

FIG. 21. (Left.) Fixed wave of contraction in muscular fibre of insect. (Engelmann.) The right
half of the figure shows the fibre examined under polarised light; the doubly refracting bands
look light on a dark ground with crossed Nicols. R, segment of fibre at rest ; //, segment
beginning to contract ; C, contracted segment, a, intermediate disc of Amici ; b, accessory
disc of clear or isotropous layer ; c, dark or anisotropous layer.

Fio. 2'2. (Right.) Fixed wave of lateral contraction near a motor end-plate (Pin) obtained by
Rollett from a muscle fibre of Cassida eifuestris. Very high magnification.

reasons, in regarding the anisotropous disc as the only contractile
part of the muscle fibre. Engelmann based this conclusion on a
long series of observations which showed that contractility and
double refractivity appear simultaneously during the ontogeiietic
development of the muscle cells, and that the contractile force is
greater in proportion as the double refractivity is more intense.

30 PHYSIOLOGY CHAP.

Kanvier draws the same conclusions from the fact brought out
directly by his experiments, viz. that the anisotropous discs are
the only ones that change in form and diminish in volume during
the state of isomeric tetanisation.

More recently Schafer (1891) and Hiirthle (1901-4) have
studied the microscopic variations in the muscle fibres during
contraction, by photography and cinematography. Schiller's
observation in particular, according to which minute canals,
parallel with one another, run in the anisotropous layer in the
direction of the fibres, is important. During contraction the
isotropous substance penetrates these canaliculi, which dilate so
that the muscular segment becomes wider and shorter.

It is in any case certain that the transverse striatiou due to
the separation of the doubly refracting from the singly refracting
tibres is not indispensable to the contractility of the elements,
because the unstriated muscle cells are contractile although much
more sluggishly so than the striated fibres. Kanvier assumes in the
latter that the separation of the doubly refracting substance into
distinct masses facilitates and makes possible a quicker displace-
ment of the fluid from the surrounding parts into the contractile
layers.

VI. We must next consider the phase of relaxation, in which
the shortened muscle elongates and describes a curve which
closely resembles the curve of contraction. The sole difference
between contraction and relaxation lies in the fact that the latter
is, generally speaking, more variable in its duration and rate of
drop towards the abscissa.

Formerly the elongation of the contracted muscle was regarded
as a physiologically passive phenomenon, due to the cessation of
the process of contraction. Very few admitted that both the
shortening and the lengthening of the muscle were due to
converse physiological processes : yet this theory of the con-
tractive and expansive activity of skeletal muscle, which we have
maintained since 1871, agrees with the corresponding theory of
the properties of amoeboid protoplasm, cardiac muscle, and the
musculature of the vessels and gut, which was discussed at length
in Vol. I.

The length of any skeletal muscle in the resting state is not
constant, but varies under different intrinsic and extrinsic
conditions.

When any muscle or the tendon by which it is attached to
the bone is divided in the living animal, the two segments draw
apart or retract,- as though the muscle were normally in elastic
tension and the distance from the points of its insertion were
greater than the natural length.

Cut muscles also retract after death, so that the tension of
normal skeletal muscle is partly an effect of the elasticity of the

i GENEEAL PHYSIOLOGY OF MUSCLE 31

muscle and the stretching to which it is mechanically subjected.
One advantage of this extension is that, even if fully relaxed, the
muscle on contraction immediately approximates its two points
of insertion, without any loss through mechanical causes.

The elastic tension of the resting muscle under normal con-
ditions is not, however, explained solely by this passive traction.
During life it undergoes marked oscillations under various
conditions. This tension of the muscle, which is not passively
determined by the distance between its points of insertion but
is the expression of muscular activity, is known as its tone.

Many facts show that the natural length of the resting
muscle, on which its natural tone depends, is directly dependent
on the nervous system. We shall elsewhere study the mechanism
of this constant tonic influence which the nerve exercises upon
the muscle : here we must confine ourselves to describing the
classical experiment of Brondgeest (1860) which demonstrates it.
If the lumbar plexus of a frog is cut on one side, after its spinal
cord has been divided higher up so as to paralyse voluntary
movements, and the animal is suspended vertically by its head,
the two hind-limbs of the animal take up essentially different
positions. The leg of the side on which the nerves were cut
hangs fully extended, i.e. the muscles are flaccid, while that of
the other side, on which the nerves are intact, is slightly flexed
owing to the tone of the muscles. A similar phenomenon is
observed on man in the fairly frequent cases of facial paralysis ;
the distortion of the mouth and nose, which is very pronounced
in speaking, is also obvious even in the state of absolute inactivity
of all the facial muscles ; it is due to loss of tone in the muscles
of the paralysed side and its persistence in the muscles of the
sound side, owing to which the latter pull on the former.

In certain abnormal conditions of the nervous system as in
hysteria, somnambulism, and hemiplegia of long standing the
tone of the muscles may be enormously exaggerated and become
contractured (Brissaud and Eichet). This condition is essentially
different from tetanus, which is due, as we have seen, to summation
and fusion of muscular contraction. Simple twitches and even
a true tetanus can be obtained from contractured muscles, by
suitable electrical stimulation, as in the normal resting muscle :
and the characteristic muscle sound can be heard during tetanus,
that is absent in simple contracture (Brissaud and Boudet).

Independently, again, of the nervous system, contracture may
result from intrinsic alterations in the muscle, caused by certain
poisons. This is a tonic state, quite distinct from the rapid
contractions which can also be evoked from the muscle by means
of make or break shocks during contracture. Among the poisons
capable of producing this phenomenon, veratrin has been the
most studied, particularly by von Bezold, Fick, Bohm, and others.

PHYSIOLOGY CHAP.

If one muscle of a lightly veratrinised animal (frog or toad)
is detached, fixed to the myograph, and stimulated with an
induction shock, the resulting curve will be very different from
that of the normal twitch (in Fig. 23), as the rapid contraction is
followed by a long contracture which slowly diminishes.

Fick endeavoured to explain this phenomenon by assuming
that the rapid primary contraction depends on the indirect
excitation of the muscle transmitted by the intramuscular nerves,
and the subsequent contracture on the direct excitation by the
poison. f But this interpretation is contradicted by the fact that
it is possible to obtain the same form of curve from animals that
have previously been curarised. Griitzner proposes another
explanation, and suggests that the rapid primary and slow
secondary contraction depend on two distinct species of fibres

FIG. 23. Contracture of gastrocnemius muscle of veratrinised toad, produced by simple break
shock from an induced current. (Bottazzi.) The tracing shows that the veratrin contracture
is preceded by an ordinary contraction, which is suddenly interrupted at the commencement
of the relaxation. Time tracing in half-seconds.

(pale and red, rapid and torpid) in the muscle. This hypothesis
is contradicted by the later observations of Carvallo and Weiss,
according to which both the pale muscles and the red exhibit
the characteristic veratrin contracture. The most probable
explanation is that of Bottazzi, who regards the coexistence of a
rapid and a slow contraction as due to the presence in the
muscle fibres of two distinct contractile materials, endowed with
different degrees of excitability anisotropous and isotropous
substance.

The hypothesis that the singly refracting substance of the
sarcoplasrn is capable of causing positive and negative variations
in the tone of the muscle, independently of the simultaneous
rhythmical excitation of the doubly refracting substance, explains
the phenomenon discovered by Fano in the auricular musculature
of Emys europea (Vol. I. p. 319), which exhibits rhythmical
oscillations of tone, on which the ordinary cardiac rhythm is
superposed. The plain muscles of the oesophagus in toad, fowl,

i GENERAL PHYSIOLOGY OF MUSCLE

Aplysia (Bottazzi), aud those of the dog's stomach also show
automatic rhythmic oscillations of tone, similar to those in the
tortoise auricle, and may be explained by contractility of the
sarcoplasrn, which certainly predominates in these muscles.

More recently (1901) Bottazzi lias endeavoured to extend his
hypothesis to all contractile protoplasm, including the striated
muscles of the skeleton. Why, he asked, should the muscular
tetanus due to the fusion of elementary twitches reach a height
considerably greater than that of a single twitch obtained from
the same muscle with maximal stimulation ? This is explained
by assuming that owing to the tetauising stimulus and the
weight applied to the muscle the muscular tone is exaggerated
into a contract ure, which represents a form of " internal support "
maintained as long as the muscle remains shortened, while the
rhythmical contractions rise above the level of this contracture
(v. Kries, v. Frey, Griitzner). v. Frey (1877) had demonstrated

Fin. 24. Myogram of frog's gastrocnemius loaded with 10'5 grins, (v. Frey.) t, t, myograms of
tetanus; *. i. , s.i. , myograms of .simple contractions obtained with single shock of the same
induced current; x.in.s., myograms of a group of contractions obtained with the muscle
supported, i.e. relieved of the weight during relaxation.

that on exciting the muscle of a frog by a series of induction
shocks, while the muscle is so supported that in relaxing it is not
stretched by the weight which it lifts in contracting, the con-
tractions rise in proportion as the lever-support is raised by a
screw, till they eventually reach the same height as the tetanus
of the same muscle, loaded and not supported (Fig. 24).

But v. Frey's explanation is not sufficient. We still ask-
on what does the contracture depend '{ It cannot be due to
activity of the same contractile substance as that on which muscle
twitches depend, for it would then be unable to function as an
internal stimulus. Bottazzi holds that it can only he interpreted
on his hypothesis of the contractility of the sarcoplasm. He
assumes that the rhythmical faradic stimuli (and in our opinion
the weight which stretches the muscle as well) are capable, in
addition to the rapid twitches that su inmate in the curve of
tetanus, of evoking a further excitation and contracture of the
sarcoplasm, which constitutes an internal support. If after induc-
ing " veratrin contracture " in a muscle it is excited with a maximal
induction shock, the resulting twitch rises above the level of

VOL. Ill D

34 PHYSIOLOGY CHAP.

contracture to the same height to which it rose above the abscissa
of the base line, previous to contracture (Fig. 25). Probably,
therefore, the rapid shortening of the muscle in contraction is
independent of the slow and persistent shortening in contracture.
The former, depends on the activity of the anisotropous, the latter
on that of the isotropous substance.

The fact that the tetanus-curve of a muscle rises normally
above the maximal twitch is, however, capable of a far more simple
interpretation. We have seen that the excitation spreads over
the muscle like a wave. Hence even after a maximal shock all parts
of the muscle cannot be simultaneously thrown into contraction.
On the contrary, the parts first excited already begin to relax before
the others reach the maximum of contraction (Fig. 16, p. 23). So
that with maximal shocks the extent of the muscular shortening

FIG. 25. Two contractions of toad's gastrocnemius, before (1) and after (2) veratrin contracture
(I') on exciting by maximal induction shocks. (Bottazzi.)

depends on the point of excitation, the rate at which the contrac-
tion wave travels, and the rapidity with which the individual
portions of the muscle contract and relax. If, on the other hand,
a series of excitation-waves are sent in rapid succession through
the muscle, all its parts will finally be in maximal contraction at
the same time, which must obviously result in a much more
pronounced contraction (Fr. W. Frohlich).

The general conclusion that can be deduced from this discussion
of the tone of the skeletal muscles is that tonicity may undergo
positive or negative oscillations, which are probably the expression
of corresponding changes in the elastic forces intrinsic to the
muscular protoplasm. These changes may be due to the tonic
influence exercised by the nerves 011 the muscles, or to stimuli
acting directly on the latter. After section or paralysis of the
nerves or motor end-plates the tone of the skeletal muscles is
abolished ; it is normal in healthy individuals in whom the
antagonist muscles exert reciprocal traction ; it becomes more or
less strongly exaggerated under certain special abnormal conditions

i GENERAL PHYSIOLOGY OF MUSCLE 35

of the nervous system, some of which may also he produced
artificially in healthy subjects, and by curtain poisons which act
directly upon muscle.

It should be added that muscle tone may be inhibited under
special conditions ; i.e. it may suffer a negative variation in which
the length of the muscle is exaggerated beyond the normal.

An interesting example of obvious lengthening of the muscles
after direct excitation of their motor nerves was first observed by
Eichet (1882) on the muscles of the crab's claw. This organ for
the capture of prey and weapon of offence and defence consists of
two arms, one of which is fixed, the other movable by means of
two muscles of antagonist action, the one a very delicate abductor,
the other a much thicker and stronger adductor. If the rigid
branch of the claw be fixed in a clamp, and a thread attached to
the movable arm, it is easy (either by direct transmission to a
writing-lever, or by indirect transmission through a couple of
Marey's tambours joined together) to record on a moving drum
the reactions of the claw-muscles to induced or constant currents,
acting directly on the nerves of the claw, or on one or other of the
muscle.?.

On exciting the nerve with a weak current, Eichet saw that
the claw opened ; on exciting with a strong current, on the
contrary, it closed. In the first case the action of the abductor
prevailed, in the second, of the adductor.

Eichet's observation was confirmed by Luchsinger, and
elucidated by further experiments of Biedermann (1887-88). If
the abductor is divided before exciting the nerve of the claw, the
result is the same as in Eichet's experiments ; with weak stimula-
tion the claw opens, with stronger excitation it closes. In the
first case, therefore, there is elongation or relaxation of the adductor,
in the second, contraction. If, on the contrary, the adductor be
cut, a weak current causes opening of the claw, or contraction of
the abductor, a stronger current closing of the claw and lengthen-
ing of the muscle. The elongation of the muscle apparent in the
first experiment with weak stimulation, in the second with strong,
was interpreted by Biedermann as an inhibition of muscle tone,
similar to that produced in cardiac muscle by excitation of the
vagus.

Piotrow r ski (1893) confirmed the fact already noted by Bieder-
mann that to produce the inhibitory effect it is essential that the
preparation should be in a state of considerable tonic excitation ;
in fact it can never be obtained in summer, when the tone of the
muscles is low. He noted further that the same current may
evoke now contraction and now inhibition, according as the tone
of the preparation is low or high. Temperature has a marked
effect on the phenomenon ; high temperatures abolish the
inhibitory effect ; low temperatures favour it ; the optimum for

36 PHYSIOLOGY CHAP.

obtaining the inhibitory effect is about 8 C. For both claw
muscles he saw that the latent period of the inhibition produced
by a minimal stimulus is shorter than that which precedes con-
traction evoked by a similar stimulus. Lastly, he found on
stimulating the nerve with simple induction shocks that when the
tone of the muscle was very pronounced the contraction was
preceded by a brief depression of tone. The same was noted by
(lad, and later by Nagy von Eegeczy and by Cowl, for nerve-
muscle preparations of the frog under special conditions.

All these researches on the reaction of striated crustacean
muscles to stimuli present numerous analogies with the phenomena
of cardiac muscle. Certain histological observations of Biedermann
justify the conjecture that there are two different species of nerve-
fibres in the crab's claw-muscles, as in the heart, some of which
may excite the assimilatory or anabolic processes, others dis-
similatory or katabolic changes. The former function like the
vagus fibres, the latter like the sympathetic fibres, on the heart.
Mangold (1905) has recently confirmed this hypothesis of a double
in nervation of these muscles.

VII. Alterations of form (contraction and relaxation, positive
and negative variations in tone) are only the external expression
of the physiological processes that take place within the muscle.
To obtain a clear idea of these, we must next investigate the
chemical composition of muscle, and the changes which it under-
goes during activity and in rest.

Muscle undergoes a profound physico-chemical alteration after
death, which is termed rigor mortis. Muscles excised from the
body of the living animal, or merely cut off from the circulation,
become rigid after a certain time (varying from ten minutes to
several hours) i.e. they are less soft and elastic, less extensible and
at the same time shorter, thicker, darker, and less transparent.
Their alkaline or neutral reaction becomes acid. As early as 1833
Sommer regarded cadaveric rigidity as a coagulation phenomenon.
Briicke accepted the same theory, but proof was afforded for the
first time in 1859 by Kiibne. He showed that when the living
muscles of the frog were completely deprived of blood by an
endovascular injection of salt solution, and gradually cooled to
- 7 C. rubbed into fragments and squeezed under high pressure, it
was possible at a temperature of to separate off a fluid which
filtered slowly, was of syrupy consistency and slightly alkaline
reaction, which he termed muscle plasma.

At the temperature of the air, muscle plasma clots as easily as
blood plasma, and takes on a gelatinous consistency. A fluid
afterwards separates out, owing to the contraction of the clot.
The substance that clots was termed my o sin by Kiihne, and the
liquid that separates off, muscle serum. Muscle plasma, like blood
plasma, begins to clot at the points of contact, and the process of

i GENERAL PHYSIOLOGY OF MUSCLE 37

coagulation is accelerated by agitation and by rise of temperature.
Cold checks coagulation ; above C. it proceeds very slowly ; at
higher temperatures it becomes faster, and at 40 very rapid.
Addition of distilled water or acids causes instantaneous co-
agulation.

It is obvious that the coagulation of muscle plasma corresponds
to the rigor that develops after the death of the muscle. Muscle
plasma indeed contains the whole of the soluble proteins of living
muscle, and as on cooling muscle to - 7 C. its excitability is not
abolished, but merely becomes latent, it may reasonably be
concluded that extraction of muscle plasma at a low temperature
destroys its structure, but produces no chemical alteration in the
substance of living muscle.

Kiihne's discoveries on frog's muscle were extended to the
muscles of warm-blooded animals by Halliburton (1887), who nob
only employed cooling to check the coagulation of muscle plasma,
but also added neutral salts (sodium chloride, sodium and
magnesium sulphate), as in the preparation of salted blood
plasma (Vol. I. Chap. V.) The addition of water to salted muscle
plasma causes it to coagulate like blood plasma when the fluid
is at body temperature, while it does not clot at C. When
coagulation sets in the reaction of the plasma becomes acid. In
blood plasma fibrin is formed from fibrinogen by the action of an
enzyme, and similarly in muscle plasma myosin is formed by the
action of an analogous enzyme from a mother-substance, which
Kiilme and Halliburton termed myosinogen. As in blood,
fibrinogen, not fibrin, is pre-existent, so in muscle myosinogen pre-
exists, not myosin. 0. v. Fiirth (1902-3), however, denies this
analogy between the coagulation of blood and of muscle, as he
failed to obtain experimental proof that the rigor mortis of muscle
depends on the action of any ferment.

Myosin has the same chemical composition as globulin ; it is
insoluble in distilled water, soluble in solutions of neutral salts
(sodium chloride, sodium and magnesium sulphate), and it coagu-
lates at a temperature of 55-60 C. Myosin when dissolved in
neutral salts has all the properties of myosinogen, and can easily
be reconverted into myosin on simple dilution (Halliburton).

The fact that myosin dissolved in a weak salt solution at a low
temperature is doubly refracting in polarised light, justifies the
assumption that the anisotropous discs that are actively concerned
in muscular contraction are principally composed of myosinogen
(C. Schipiloff and A. Danilewsky).

Halliburton succeeded by means of fractional heat coagulation,
and by salt solutions of different concentrations, in separating five
different proteins from the muscle plasma, four of which are
coagulable at different degrees of temperature, and one is un-
coagulable. This last is a proteose, and is apparently identical

38 PHYSIOLOGY CHAP.

with the eozyme which effects the coagulation or transformation
of myosinogen into myosin. Of the four coagulable proteins, two
(inyosinogen and the paramyosinogen or musculin of Hammarsten)
form the clot, while the two found in the muscle serum (myo-
globulin and -myoalbumiii) closely resemble or are identical with
those present in blood serum.

Muscle serum holds the pigments to which the muscles owe
their colour in solution. The normal pigment of the red muscles
is due to haemoglobin, identical with that of the erythrocytes, as
was proved by Kiihne (1865) from the spectrum of muscles
(diaphragm) that had been entirely freed from blood by prolonged
washing with saline. MacMunn (1884-87) afterwards investi-
gated the muscles of different classes of vertebrates and inverte-
brates, and found that they exhibited a variety of absorption
spectra, due in his opinion to a group of pigments which he
named myohae matin. According, however, to Hoppe-Seyler and
Levy (1889) myohaematin is only a decomposition product of the
haemoglobin of the muscle. That haemoglobin is an intrinsic
product of the muscle cells or fibres is shown by the fact that it
exists in the muscles of invertebrates which have no haemoglobin
in their circulating fluids.

When the muscles of recently killed animals are treated with
boiling water the proteins coagulate, and the extract contains all
the soluble nitrogenous and non-nitrogenous organic substances of
the muscle. The first form a group of compounds which represent
different disintegration products of the proteins (creatine and
creatinine zanthine, hypozanthine, carnine, uric acid and urea
taurine and glycocoll). The second belong to the carbohydrate
group and its derivatives (glycogen, dextrin, glucose, maltose,
inosite, lactic acid, and lactates).

Quantitatively speaking, creatine and glycogen (which we have
already discussed, Vol. II. pp. 391, 310) predominate among these
groups of substances in the muscle.

Nothing definite is known at present about the physiological
importance of creatine and creatinine. They are certainly formed
by katabolic processes from the proteins in the muscle. In fact
they are more abundant in muscles which have been overworked
previous to the death of the animal (Monari, 1888) than in muscles
analysed after rest. Nawrocki and Sarokin, however, found that
the creatine-content is no larger in tetanised than in resting
muscle. Another striking fact was discovered by Demant (1879)
in Hoppe-Seyler's laboratory. In the muscles of pigeons starved
until they have consumed all the non-nitrogenous reserve materials
contained in the muscles, so that metabolism proceeds at the
expense of protein disintegration, the content of creatine and
creatinine amounts to three times that in normal pigeon muscle.

Glycogen and its derivatives are the principal reserve material

i GENERAL PHYSIOLOGY OF MUSCLE 39

utilised by the muscle during work. Nasse (1869) first poiuted
this out, as he found that the glycogen content of muscle is in
inverse ratio with the work performed. The best evidence for it
lies in the fact that all muscles prevented from working by section
of their nerves or tendinous attachments contain an excess of
glycogen, as compared with the symmetrical muscles that have
remained intact (MacDonnel, Chandelon, Manche, Weiss, E.
Krauss). At the same time it is a striking fact that muscular
glycogen diminishes far more slowly than hepatic glycogen in
fasting (Weiss, Aldehoff, Luchsinger) ; this is not due to the fact
that the liver normally supplies the muscles with glycogen, since
even when the liver has been excised the glycogen-content of the
muscles can be increased by feeding with cane-sugar. Muscles
have therefore an amylogenic and glycogenic function which is
perfectly independent of that of the liver (Prausnitz).

Helmholtz (1845) observed that during tetanus the extractives
of muscle which are soluble in water diminish, while those soluble in
alcohol increase, which depends at least in part on the reduction of
glycogeu and increase of glucose coincident with muscular activity.

Lactic (or sarcolactic) acid is an important constituent of
muscle; during rigor mortis it may amount to O'l-l'O percent
(Bohm, Demant). Living, resting muscle has a neutral or feebly
alkaline reaction, while rigid muscle has a distinctly acid reaction.
Muscle plasma, too, is first neutral or feebly alkaline, and becomes
acid after coagulation. The cause of this reaction has been the
subject of much controversy. Some authors have tried to replace
Liebig's early theory (1847) that it is due to a development of
lactic acid, by the hypothesis that the acidity of muscle is caused
exclusively by mono-phosphate of potassium. This can only be
proved by excluding the formation of lactic acid during the life of
the muscle. It may, however, be assumed that the free lactic
acid, acting on the potassium bi-phosphate of normal living
muscles, is converted into potassium lactate, by reduction of the
neutral into acid phosphate, which may partly account for the
acidity of dead muscle.

It was formerly, and is still sometimes held (Araki), that
lactic acid arises from disintegration of the glycogen. But this
is obviously controverted by the work of Bohni and of Demant.
Bohm (1880) showed that the amount of lactic acid formed during
the death of the cat's muscle is in no relation with the glycogen
content, since the latter gradually disappears during starvation,
while the proportion of lactic acid is not less than normal. Demant
(1879) showed that glycogen entirely disappears in the pectoral
muscle of pigeon after eight days of fasting, while there is a free
formation of lactic acid. From these results they concluded that
the mother-substances of the lactic acid formed by muscle must
be sought in its proteins.

40 PHYSIOLOGY CHAP.

Lactic acid has been proved experimentally to be one of the
normal katabolites of muscle, formed not only in dead but also
in living muscle during rest, and still more during work. On
artificially circulating defibrinated blood for three hours through
the muscles of the lower limbs of a dog, the amount of lactic acid
that can be extracted from the blood that has repeatedly passed
through the resting muscle amounts to about 1-5 grms. Tetanisa-
tion of living muscle certainly increases lactic acid formation ;
the amount of lactates present in the blood (Spiro) or excreted by
the kidneys (Colasanti and Moscatelli) increases. The muscles
do not, however, acquire an acid reaction, because the lactic acid
is given off as fast as it is formed to the blood - stream, where
it is saturated with alkali. When, on the contrary, a group of
muscles previously cut off from the circulation is tetanised they
become acid owing to accumulation of lactic acid, while the
corresponding, non-excited muscles of the opposite side remain
neutral or alkaline and contain little lactate (Marcuse, Werther).
In excised frog's muscle slight electrical excitation, which causes
no violent contraction, suffices to convert the neutral into an acid
reaction (Gotschlich).

From these and other experimental researches it may be con-
cluded that the formation of lactic acid is associated with the life
of muscle, and not with its death, as many believe. The con-
vincing evidence of this lies in the fact that when a muscle with
normal circulation is tetanised, then excised, it forms less acid
during its death than the corresponding muscle which was not
excited, showing that the mother-substance of the acid has been
used up, and that the amount of acid developed by a muscle in
dying corresponds with the quantity of mother-substance con-
tained in it.

In addition to protein and glycogen the fats may be regarded
as reserve materials; these are found not only in the inter-
muscular connective tissue, but also within the fibres and in the
sarcoplasm, and especially in the fibres of the red muscles, in the
form of droplets which give them a turbid appearance (Ph. Knoll).
Some of these droplets stain black with osmic acid, others remain
unstained and probably consist of lecithin. During starvation
they disappear, and return on feeding. In morbid degenerative
changes, as after phosphorus poisoning, the amount of fat in-
creases enormously, and it must therefore be due not to storage,
but to regressive metamorphosis of the proteins.

The part played by the fats in muscular metabolism is un-
known. The small fat-content of normal fibres is no reason for
regarding it as unimportant, since in all probability fat does not
accumulate normally because it is consumed as soon as formed.
According to Bogdanow the fat of muscle-substance is richer in
volatile fatty acids than that of the interniuscular connective

i GENERAL PHYSIOLOGY OF MUSCLE 41

tissue. It seems to us uot improbable that tbe development of
latty acids contributes to the acidification of muscle during its
death.

The inorganic compounds of muscle are water and the salts
contained in the ash.

The amount of water in human muscle is not less than 70 per
cent and may rise to 72-74 per cent. It varies to some extent
in different classes of muscle. Generally speaking, embryonic
muscles and those of young persons are richer in water than
those of adults and old people. During starvation the water
diminishes considerably ; it is increased, on the contrary, by work,
which suggests that during the discharge of the energy accumu-
lated in the muscle water is one of the end-products of the carbo-
hydrate metabolism.

Of the mineral salts contained in the ash of muscle the pre-
dominance of potash over soda among the bases, and of phosphoric
acid among the acids, is remarkable. According to Bunge the
ash of 100 parts of muscle contains on an average :

K,0 . . . 4-407 Fe.,0 3 . . . O057

Na.,0 . . . 0-790 P.,6 3 . . . 4-612

C.,0" . . . 0-079 01 ... 0-682

MgO . . . 0-396 S0 3 . . . 0-100

It is certain that in living muscle these mineral compounds are
not all present in the form of simple solutions, but are in organic
combination. The sulphuric acid is formed from the sulphur of
the proteins during combustion. The phosphoric acid is only pre-
existent to a very small extent in living muscle, the greater part
arises from the combustion of the lecithin and the nucleins.
The ferric oxide results from the disintegration of the muscular
haemoglobin.

The gases of muscle consist in a considerable amount of carbon
dioxide and traces of nitrogen. The mercury pump has failed
to separate any trace of oxygen from muscles when carefully
washed free of blood, obviously because the oxygen combined with
the haemoglobin is dissociated and carried away in the washing.
According to Hermann (1867), 2 - 74 per cent free, and 1*95
per cent combined C0 2 can be extracted from muscle which is
bled, minced up, and triturated previous to the onset of rigor.
Stiutzing found that on prolonged boiling of muscle another
substance decomposes, which gives rise to a free development of
CO.,. It is probable that the carbonic acid developed in tetanus
and" during rigor is derived from the same substance as is decom-
posed by boiling.

We have already reviewed the principal facts of muscular
respiration (Vol. I. p. 393). The important fact is that the gas
exchanges of muscle are exaggerated during activity, i.e. both

42 PHYSIOLOGY CHAP.

elimination of C0 2 and absorption of 2 are increased ; but the

CO

value of the respiratory quotient p increases also, because the

2

output of C0 9 is greater than the intake of 0., (Ludwig and
Sczelkow, 1862, Ludwig and Schmidt, 1868, v. Frey, 1885).

Hans Winterstein (1907) demonstrated that the rigor mortis
of mammalian muscle is essentially due to the loss of oxygenation,
owing to arrest of the vascular circulation ; it is thus an asphyxia
phenomenon. In fact, if a mammalian muscle, excised from the
body, is kept in Einger's solution at an oxygen pressure of 2-4
atmospheres, at a temperature of 36-38 C., its excitability may
be preserved for twenty-seven hours after dissecting it out, with
no appearance of rigor. If rigor sets in, it may be kept off by
successive strong doses of oxygen. When it is once established,
however, further oxygenation is useless.

VIII. There can be no doubt that the chemical processes
which come into play during the activity of muscle are the source
of the physical energy which the muscle develops, and the external
mechanical work which it performs. This is a direct corollary to
the law of the conservation of energy. Muscular excitation is the
most classical instance in the living world of the explosive dis-
charge of energy, i.e. the rapid transformation of potential chemical
energy iuto kinetic energy, in the form of work, heat, and
electricity. As in the steam-engine the mechanical work depends
on the combustion of coal, so the mechanical work of the muscular
machine results from the katabolic processes of disintegration and
oxidation of the organic compounds which build up the muscle.

Having now discussed the chemical changes that go on in
living muscle during rest and in activity, we must next turn to
the problem of the origin of muscular energy, that is, which of the
food stuffs introduced into the body and assimilated by the muscles
furnishes the necessary energy for their activity.

Starting from the fact that proteins represent the chief con-
stituents of muscle, and that a full meat-diet increases the work-
capacity of muscle, while a diet poor in protein depresses it,
Liebig (1857-70) assumed that the source of muscular energy
must be sought in the proteins. There can be no doubt that the
nitrogenous exchanges of muscle are very active, much protein
being consumed both in rest and in activity ; but Liebig showed
no direct experimental proof that the activity of muscle depends
mainly upon increased protein metabolism.

Bischoff and Voit (1860) thought the question could be solved
by comparing the urea content and the total nitrogen content
of urine during hard muscular work, with that eliminated during
rest, the same quantity and quality of food stuffs being ingested.
In both man and dogs they obtained a nitrogenous equilibrium after
a few days of uniform dieting, i.e. equivalence between the nitrogen

r GENEKAL PHYSIOLOGY OF MUSCLE 43

introduced and that eliminated with the urine. They found that
this equilibrium was not much affected by days of rest, as com-
pared with working days, i.e. no perceptibly greater quantity of
nitrogenous substances was consumed during work.

This result was confirmed by the later and more accurate
researches of Voit (1870-81). He found not only in dogs kept on
a constant diet, but in starving animals also, that the amount of
nitrogen excreted was not much increased by work, and that the
increment was in no case in ratio with the amount of work done.

Experiments made on themselves by Fick and Wislicenus
(1685) supported this result. They climbed the Faulhorn, 1906 m.,
in six hours, during which time they collected all the urine passed.
During the twelve hours preceding the climb and on the ascent
they took no nitrogenous foods, and lived solely on starch, fat, and
sugar. From the amount of nitrogen contained in the urine they
deduced the amount consumed during the climb. They further
calculated the amount of mechanical work accomplished by the
leg muscles of each, multiplying the body-weight by the height of
the mountain ; the work done by the other muscles was not calcu-
lated. From the combustion heat of the protein consumed during
the ascent they calculated the maximal yield that could be
obtained if the whole of the protein in the body were burned up.
The result showed that the work done on the climb far exceeded
that which could be performed by the decomposition and oxida-
tion of the protein consumed. From this they concluded that the
non-nitrogenous substances introduced with the food or stored in
the body as reserve materials supply energy which can be utilised
during work.

The direct proof that it is principally the non-nitrogenous
substances (carbohydrates and fats) that are consumed during
work is derived from experiments on the respiratory gas-exchanges,
which show that while the elimination of nitrogen does not
increase perceptibly the excretion of carbonic acid and absorption
of oxygen do increase considerably during work (Pettenkofer and
Voit, 1866, and others). This agrees perfectly with what was
stated above in regard to the consumption of glycogen and fat in
muscular activity.

What part, then, does the protein of muscle play in the per-
formance of its functions ? Since muscle consists principally of
proteins, which are the fundamental substrate of all living tissues,
it must be recognised that these substances play an active part in
all the internal processes that go on in muscle.

Traube suggested that the proteins of living matter have the
task of carrying oxygen to the nou- nitrogenous combustible
materials, but are not themselves decomposed. This agrees with
PHiiger's general theory of the oxidation processes of the animal
body, according to which the intra-molecular oxygen, chemically

44 PHYSIOLOGY CHAP.

bound up in the molecules of living matter, is the source of the
disintegrative and oxidising changes that go on in all the tissues.
We may therefore assume that the proteins of muscle absorb and
combine with oxygen during rest, and pass it on during activity
to nitrogen-free molecules, while they once more take up fresh
oxygen in the resting period which follows. On this hypothesis
the proteins of muscle fulfil the same function as an enzyme
during work. But the inadequacy of this explanation is evident
from the fact that muscle, independently of rest or activity, is the
seat of an active nitrogenous metabolism, which must therefore be
heightened during work. Further, intense muscular work is
possible on an exclusively flesh diet. Voit showed that dogs can
be kept alive under normal conditions on an exclusive diet of
meat. In his latest researches (1892) Ffliiger fed a great Dane
of 30 kgrm. for nine months on horseflesh, which was almost free
of fat, and made it do hard work for weeks by dragging a heavy
cart for 13 km. in two to three hours. During this time the
animal remained exceptionally well and vigorous. Under these
conditions almost the whole of the energy developed in the
animal's muscles must be derived from disintegration of protein,
since the small quantity of glycogen and fat ingested is negligible.

Nevertheless, on comparing the amount of nitrogen given off
by the animal in periods of work and of rest, Pfliiger could only
confirm the fact that it did not vary conspicuously, and that the
increase was never in proportion with the work performed.

To explain this fact he assumed that the excretion of nitrogen
does not increase definitely after work, because though the muscles
consume more protein, other tissues consume less, by a sort of
adaptation due to the lesser amount of protein circulated.

Verworn, however, pointed out that this hypothesis cannot
explain Voit's observation on the dog, that even in the fasting
state when the amount of circulating protein at the disposal
of the muscles and other tissues is minimal, nitrogen elimination
does not increase proportionately with hard work (making a wheel
revolve on its axis).

Pfliiger suggested later that the increased disintegration of
protein effected by the muscle during work does not show a
larger excretion of nitrogen in the urine, because the nitrogenous
waste products are regenerated synthetically into the complex
molecules of protein, by combining with non-nitrogenous atoms
lost during the work, at the expense of nutrition, or of the reserve
materials. In other words, it is possible and even probable that
the nitrogenous products of proteolysis, which is increased in
muscular work, do not leave the body like the non-nitrogenous
products, which are excreted principally in the form of carbohydrate
and water, but are stored up and partially utilised again in the
synthetic regeneration of protein : this is to some extent analogous

i GENERAL PHYSIOLOGY" OF MUSCLE 45

to the process by which the proteoses and peptones are regenerated
into protein by the intestinal epithelium, and the amino-acids
(which are the final products of the digestive decomposition of the
proteins) restore and build up the tissues, after being reabsorbed
into the lymph and blood. So that muscular proteolysis, which
is stimulated or increased by work, in its turn promotes the
genesis of protein and consequently the quantity of nitrogenous
products in the urine does not materially increase during work.

This hypothesis appears to us acceptable in view of recent
researches on the complex structure of the proteins which build
up living matter, and the different cleavage products that can be
isolated by the action of enzymes. Pick's studies (1899) on the
proteolytic products into which fibrin can split under the action
of pepsin are of first importance. Of these products he was able
to isolate :

(a) A proteoalbumose, which contains no carbohydrate group, but
has much tyrosine and indole, gives off no glycocoll among its
decomposition products, and holds sulphur only in unstable
equilibrium.

(&) A heteroalbumose, which contains no carbohydrate group
and hardly any tyrosiue and indole, is rich in leuciue, with some
glycocoll, and holds sulphur only in unstable combination.

(c) A deuteroalbumose, which contains no carbohydrates.

(V) Two deuteroalbuminoses rich in carbohydrates.

(e) Two peptones containing carbohydrates.

The importance of these results consists in the fact that it is
comparatively easy to separate the protein molecule from the
carbo-hydrate group (which is oxidised during muscular work)
without loss of the fundamental chemical properties of the pro-
teins, which therefore retain their capacity for synthetic regenera-
tion into protein under the influence of the anabolic activity of
the living tissue -cells. If we admit an anabolic proteogenic
activity in the intestinal epithelium, it seems reasonable also to
assume that it exists in muscle (Vol. II. p. 328).

IX. We have said that muscular contraction is the most
classical and hence the best investigated instance of an explosive
discharge of energy in the living world. The potential chemical
energy stored up in the muscle is converted during excitation
into kinetic energy, which appears in the forms of mechanical
work, heat, and electricity, each of which must be considered
separately.

The work done by muscle is measured by the product of the
weight raised by the muscle into the height to which it is raised,
w x h. If, therefore, the muscle contracts without lifting a weight
or overcoming any resistance, it performs no mechanical work.
This supposition is, however, purely theoretical since the muscle
always has to carry its own weight, which may indeed be reduced

46

PHYSIOLOGY

CHAP.

to a minimum if the muscle is laid horizontally on mercury, after
first dipping it into oil to diminish the surface friction.

Again, the muscle does 110 work when it is loaded with such
a heavy weight that it is unable to raise it. In the first case the
energy developed by the excitation is exhausted in the contraction,
in the second in the tension of the muscle ; but in both cases
no external mechanical work, but only internal mechanical work
is done.

On calculating the external work done by a muscle in raising
regularly increasing weights, it is found that it increases quickly
at first, and then more slowly, until it reaches a certain maximum,
after which it diminishes again and finally becomes nil on reaching
the weight which the muscle is unable to lift.

Fig. 26 illustrates

grms.

i 50

.. 100

.. <50

.. 200

.' 250

" 300

.. 350

i 400

.. 450

>, 500

min. 5

6
5

4
3

2 5
2

grin. mm.

.. 550

.. 700

.. 900

,.000

N<000

> i. 900

" 675

ii ., 800

,,675

,, BOO

Fio. 26. Diagram showing work done by muscle frog's gastrocnemius. (A. D. Waller.)

these experimental results, which can be verified on every muscle
that is loaded and stretched before contraction, or merely while it
contracts.

It may thus be stated that there is a given weight for every
muscle, at which it reaches its maximal yield of work, and that
with diminution or increase of the load the work becomes
gradually less till it finally reaches zero. This law of course
applies also to all groups of muscles which co-operate in the work
performed.

The resistances encountered by the different muscles concerned
in complicated action vary ; the degree of shortening which they
undergo varies also. Generally speaking, the strength of a muscle,
i.e. the weight it is able to lift, increases in proportion to its
diameter, that is, the number of fibres it contains. Since work is
the product of the weight and the height to which it is raised, it
follows that, other things being equal, the work of a muscle is in
proportion with the product of its length and cross-section, viz.

GENEKAL PHYSIOLOGY OF MUSCLE

47

the volume or mass of the muscle. These relations between the
size of a muscle and the energy it is capable of developing :

between the length of a muscle consisting of parallel fibres and its
degree of contraction ; and finally between the weight of the
muscle and the useful work it is capable of yielding were all
noted by Borelli in the early half of the eighteenth century, and
were fully considered and cleared up by Weber in 1845.

The absolute force of a muscle is measured by the minimal
weight that it is unable to lift under maximal excitation (Weber).
Since it is proportional to the cross-section or diameter of the
muscle, a universal standard is obtained by calculating the absolute
force of a square centimetre of the muscle section. The absolute
force of the muscles varies in
different animals and even in
different muscles of the same
animal. It varies for a square
cm. of frog's muscle between 7
and 8 kgrms. (Henke and Knorz)
or even 9 and 10 k grins. (Koster,
Haughton).

Attempts have also been made
to determine the absolute force
of a sq. cm. of human muscle by
measuring the cross -section on
a dead subject of the same
physique and muscular develop-
ment as the subject of experi-
ment. Here, again, the values
obtained were very different :
2-8-3 kgrms. (Eosenthal), 5-10
kgrms. (other experimenters). It
should be noted, however, that these experiments on man were made
not with artificial tetanisation, but with a voluntary yield of work,
in which the energy developed may be double, or at least a third
more than that developed on stimulation with a tetanising current.

From the clinical point of view, investigation of the relative
strength of certain groups of human muscles is far more practicable.
The dynamometer is usually employed for this purpose. It consists
of a strong oval steel spring, which is compressed by the hand, while
an index moves along an empirically graduated scale to indicate
the amount of compression and thus of the power developed in the
group of muscles which come into play when the hand is closed.

The figures obtained by this instrument are, however, of little
value, since they can be modified by practice, attention on the part
of the subject, and, above all, degree of voluntary effort, which may
vary considerably, even independently of the conscious will of the
subject.

FIG. 27. Dynamograph. (A. D. Waller.)

48

PHYSIOLOGY

CHAP.

Morselli added a contrivance for air- transmission, which made
it possible to record the compression of the spring upon a revolving
cylinder, and which transformed the dynamometer into a dynamo-
graph, by which the tracing of a series of maximal voluntary
contractions of the flexor muscles of the hand, at regular intervals
measured by the beats of a metronome, can be recorded. Such

FIG. 28. Tracing from Waller's dynainograph, to show elli-cls of fatigue and recovery.

curves show not only the comparative force of the muscles, but
also their resistance, or the ease with which they become fatigued.
Still more simple is Waller's dynarnograph (Fig. 27), in which
the pull of the hand upon a strong steel spring is registered
directly by a long lever. Fig. 28 shows the tracing of six groups
of maximal contractions, at regular intervals ; between each group

Fn.. '_".!. Mosso'x c] i;oi;Tapli.

there is a uniform pause for rest. The drop in the
line uniting the apices in each group shows the
fatigue of the muscle ; the return to the original
executed height in the next group represents its
recovery during rest.

The dynamographs of Morselli and Waller are
based on the isometric method, and consequently record the maxi-
mal tensions of the flexors of the hand, and the correlative internal
work ; Mosso's ergograph (Fig. 29) is an instrument based on the
isotonic method, and it records the maximal contraction of the

GENEEAL PHYSIOLOGY OF MUSCLE

49

flexors of the middle tinger, on loading with a given weight, and
therefore the external work (in kilogranimetres) performed during
maximal voluntary effort. The arm is placed in the supine position
and h'xed to a horizontal support. A leather ring is applied to the
middle finger, which carries a string that runs over a pulley and is
weighted at the end. Raising the weight displaces a lever, the
point of which records the amount of flexion of the finger. Mosso
attached a supporting screw or stop to the indicator of the ergo-
graph, by which the flexor muscle of the finger can be relieved of
its load during rest, and the weight only pulls on the muscle
during its contractions.

FIG. 30. Two tracings of different types from Mosso's ergograph, taken from two boys of the same
age and habit ; in both a weight of 3 kgrms. was lifted every two seconds.

The most striking results obtained in the earliest researches
of Mosso and his collaborators (1890) by the study of the ergograph
tracings in a series of voluntary maximal efforts at regular intervals
are as follows :

(a) There is no common type for the ergograph fatigue curve,
but each individual has a personal type i.e. under good physio-
logical conditions, in a state of repose, with a given load and
definite rate, each individual even at long intervals exhibits
the same fatigue curve, although the amount of external mechanical
work may vary widely (Fig. 30).

(6) The personal type of the fatigue curve persists even when
the fatigue is produced, not by voluntary effort, but by rhythmic
electrical stimulation of the nerve or muscle.

(c) Pronounced mental fatigue or fatigue of all the muscles of

VOL. in E

50 PHYSIOLOGY CHAP.

the body produces rapid exhaustion on the ergograph, even if the
curve is obtained by electrical excitation.

(oT) Ergograph work may alter the elasticity of the muscle,
increasing or diminishing it ; in certain individuals it may excite
contracture, which is the more readily produced in proportion with
the strength and frequency of the stimulus, and the weight the
muscle has to raise.

The ergograph curve depends on the combined effects of
fatigue of the nerve-centres and fatigue of the muscle, though the
latter always predominates. " The characteristic phenomena,"
Mosso writes, " are peripheral, since the muscle exhibits its char-
acteristic fatigue curve even with artificial stimulation. ... It is
not the will nor the nerves, but the muscle that is weakened after
arduous brain-work."

Maggiora subsequently brought out the great importance of
the varying conditions under which external mechanical work is
performed on the ergograph :

(a) There is a certain weight which elicits the maximum of
utility ; with weights below a certain value, no sign of fatigue is
perceptible.

(6) With every load, the slower the rhythm of contraction the
more external work can be performed, and the more the onset of
fatigue is delayed. For any given weight there is a rate at which
the contractions can proceed for a long time with no trace of
fatigue.

(c) If a muscle is contracting at a given rate slow enough to
allow of its complete recovery at each contraction, and the load is
then doubled, it is not sufficient to reduce the rate to half its
original frequency in order to obtain the same yield of mechanical
work from the muscle.

(d) The interval which must elapse between two ergo-
graphic curves in order to obtain normal fatigue curves during
the whole day is from 1| to 2 hours. The weight of the load is a
matter of indifference between certain limits (2-4 kgrms.).

(e) The work performed by a muscle that is already fatigued is
far more injurious to that muscle than a greater amount of work
performed under normal conditions.

In these studies Mosso, Maggiora, and other investigators, in
calculating the work effected by the muscle, neglected the end
part of the tracing which consists of low, long-drawn-out con-
tractions. Lombard (1890) investigated this terminal phase,
and discovered that when the ergogram appeared to stop, it
usually continues as a new series of contractions, in which the
rise and fall of the curve were approximately regular. According
to Lombard these periods are only to be seen in the voluntary
ergogram, and are due to spinal fatigue.

Owing to the ease with which the ergograph can be used it is

i GENERAL PHYSIOLOGY OF MUSCLE 51

employed by psychologists and clinicians as well as physiologists.
The method is universally allowed to make functional isolation of
a limited group of muscles possible ; average weights (.'5-4 kgrms.)
should be used to ensure the better graduation of the work and
curves that are neither too short nor too long ; and it is assumed
that the output of work with this load and under the right experi-
mental conditions for the ergograph is a true expression of the
physiological capacity of the muscle in relation to the weight.
Above all, psychologists and psychiatrists sought - - on the
strength of Mosso's results, and obviously going farther than he
originally attempted to emphasise that both central and peri-
pheral or muscular fatigue were shown in the curve. Kraepelin
affirmed that in the ergographic curve the height of lift expresses
muscular fatigue ; the number of contractions, on the contrary,
gives the measure of mental fatigue. This proposition includes
the conception that the cessation of the ergograph curve is due to
muscular exhaustion, i.e. functional incapacity of the nerve-muscle
apparatus, caused in all probability by the curarising action
of the fatigue products, owing to which the psychical impulses
encounter an increasing resistance.

In fact, the experiments of many workers upon the influence
on the ergograph curve of different external conditions (as
temperature, pressure, time of day, etc.), as well as of many internal
states (state of nutrition, period of digestion, special diet, exhibi-
tion of stimulating agents, of organic extracts, etc.), have always
yielded very uncertain results. The output of external mechanical
work never varied perceptibly from the ordinary physiological
limits.

U. Mosso attempted by a series of experiments to determine
whether the administration of foods sugar in particular could
restore the potential capacity of the muscle depressed by work.
The most definite conclusion was that the action of sugar was only
beneficial with the ergograph when the individual was in a condition
of extreme fatigue.

Generally speaking, the ergograph is not suitable for solving
these questions Zuntz and his pupils utilised it, but only as an
index to the state of fatigue on certain occasions when the subject
was executing a definite piece of work that involved the musculature
of the whole body. If the subject is made to do a known quantity
of work in the interval between the ergographic records, a per-
ceptible recovery is seen in the next ergogram if small quantities
of food are administered.

The value of the ergograph curve as an index of muscular
fatigue on the one hand and mental fatigue on the other, as
Kraepelin has used it, is very doubtful.

In 1898 Treves, working in the Physiological Institute of
Turin on the laws of muscular activity in man and animals, made

52

PHYSIOLOGY

CHAP.

certain modifications in the methods of investigation, and obtained
results which frequently contradicted previous conclusions. His
first experiments were carried out on the rabbit, with direct and
indirect excitations of the muscles once a second. The tendon of
the muscle was not separated from its insertions, but the resistance

cjr. 1150

Fio. 31. Ergogram of rabbit's gastrocnemius, loaded with 1150 gnus, (maximal weight). The
sciatic was excited every two seconds. (Treves.)

of the weight was transmitted to the muscle by means of the
natural bony lever of the rabbit's leg, the end of which is connected
with the writing point of the ergograph. He used maximal
tetauising stimuli of very brief duration, in imitation of voluntary
impulses. Before taking the ergograph curves, Treves ascertained
at what weight the muscle was able to contract, with maximal

FIG. 32. Ergograph tracings from same muscle as preceding figure. The initial maximal weight was
gradually diminished so as to determine the maximal terminal weight at which the rhythmic
lifts no longer make a descending curve, but form a horizontal line (constant phase of ergogram).
(Treves.)

excitation, so as to serve up maximal work. As he did away with
the supporting screw of Mosso's ergograph, the weight pulled
continuously upon the muscle, and not merely during contraction.
Under these conditions Treves obtained an ergogram in which
the height of the contractions regularly diminished, but more and
more slowly, till they became almost inappreciable, and below

GENERAL PHYSIOLOGY OF MUSCLE

53

this they showed no tendency to further diminution (Fig. 31).
On the usual interpretation of ergograph curves it would be said
that the muscle had become incapable of any further work at this
point. But this is not the case ; the muscle is still capable of
serving up a considerable amount of external work. For if the
weight is gradually reduced, the height of the contraction again
increases until a new maximal weight is found which yields

Fn:. 33. Ergograph tracing of rabbit's gastrocnemius, after ten minutes' rest, during phase

of constant work. (Treves.)

the maximum of work (Fig. 32) and corresponds to about
400 grms., i.e. much less than the original weight, which was
1150 grms. If the rhythmical maximum excitation is continued
with this new load (which may be called the terminal maximal
load), an endless series of contractions is obtained, which correspond
with the production of constant work. The series of contractions
following on a falling curve exhibits similar constancy, irrespective
of the load which is carried. Fig. 32 reproduces a few cm. only
of the tracings obtained with different loads in testing for the

Fin. 34. Ergogram of rabbit's gastrocnemius, loaded with 600 grms., after twenty minutes' rest,
during phase of constant work. (Treves.) Before resting the muscle gave at each lift a
constant yield of 400 grms. x 4 mm. = 1600 grm. mm. After resting the maximal work was
600 grms. x 11 mm. =6600 grm. mrn.

terminal maximal load in the second phase of the ergogram.
This constant phase may preserve its regularity at a rhythm of
1 sec. for over 2000 consecutive contractions, each representing
work that may amount to 2500 gr. mm.

If the muscle is allowed a longer or shorter pause for rest
during the period of constant work, the maximal work of which it
is capable at each contraction increases again, in proportion as the
resting-pause has been longer. This partial recovery of power is
shown in the capacity of the muscle to trace a new ergogram with

54 PHYSIOLOGY CHAP.

diminishing heights of contraction which is followed by the
constant phase with uniform values (Figs. 33 and 34).

If the falling portion of the ergogram is obtained with a
sub-maximal load, the tracing passes into the constant phase
without altering the weight, in which case each contraction
represents a sub-maximal yield of work (Fig. 35).

The level of constant work may be maintained for several hours
without any sign of the characteristic modifications of fatigue

Fn;. 3.x Kilogram of gastrocnemius showing decreasing and constant phase, at a
sub-maximal load. (Treves.)

(Fig. 36), but finally there comes a moment at which the muscle can
no longer yield any mechanical work owing to the gradual onset of

rigor.

In the ergogram of the gastrocnemius obtained with electrical
stimulation and an initial maximal load, the curve of the contraction
heights sinks rapidly to zero, or to a very low level., because after
a certain number of contractions the load becomes super-maximal.
If the weight could be gradually adjusted as the muscle weakens
so as to be maximal at each fresh contraction, the ergogram would
show no intervening stage of complete or almost complete cessation
of work, which is solely due to imperfect mechanical conditions.
A more important curve would stand out as a whole namely the

FIG. 36. Ergograph tracing of rabbit's gastrocnemius (phase of constant work) after two hours'
rhythmical maximal excitation. (Treves.) The tracing shows a slight irregularity of the base
line of the contractions, but the work remains fairly constant.

work curve, represented by a series of rhythmical contractions
executed under conditions of maximal work. Treves endeavoured
to approximate to such conditions in his experiments, and con-
structed a diagrammatic work curve} the course of which recalls
the form of a muscle twitch, with an ascending and a descending
phase, passing gradually into the period of constant work.

Treves was the first to apply these methods of research to the
human subject. He did away with the support of the ergograph
lever, and made the subject lift a weight of 4-5-6 kgrms. (accord-
ing to the individual) every two seconds by a voluntary maximal
effort. In consequence the constant level was always obtained on

GENERAL PHYSIOLOGY OF MUSCLE 55

the ergogram, and forms an essential part of it. This proves that
supporting of the ergograph lever creates artificial work conditions,
which, together with the variations in elasticity and tone which
the muscle suffers during work, cause a more or less rapid
decline in the successive contractions, and shorten the ergogram
prematurely.

In extending his investigation to voluntary work, Treves found
it necessary to alter his system of loading, and to apply the
principle of maximal loading in this case also that is of gradually
altering the weight as the muscular power declines. In this study
he employed the flexor muscles of the forearm, and invented a
new ergograph for the purpose which may be studied in his
original memoir.

A minute analysis of Treves' results is beyond the scope of
this text-book. We must confine ourselves to a few of the most
important principles that can be deduced from them :

(a) During voluntary work on the ergograph the height of
contraction remains constant so long as the conditions of work are
favourable, and above all so long as the load is not excessive.

(6) The maximal load that can be raised by voluntary effort
corresponds with the load which necessitates the maximum of work.

(c) The maximum load diminishes gradually in a hyperbolic
curve till it reaches a value which varies with the rate of work, but
is practically constant. The curve of voluntary work, like that
obtained by artificial stimulation, consists of two phases a
descending and a constant part. The differences seen in the two
curves arise from the fact that in the case of work elicited by
artificial stimuli the stimulus is constant ; in voluntary work, on
the contrary, the effort varies since it diminishes independently of
the will, according to the resistance experienced in carrying out
the movement.

(d} The ergograph tracing consists of a series of vertical lines
approximately equal in height, with no feature characteristic of
the individual or of the experimental conditions. The true
ergogram is the line according to which the work diminishes with
the maximal load.

(e) The main factor which determines the rapid fall of the
curve with a constant load is the appearance of unfavourable
mechanical conditions. To obviate this the muscles must be left
perfectly free to contract, and the contraction of other muscles
connected with those under investigation must not be hindered.
It suffices to see that the graphic apparatus records only the
movements of the bony lever in question. Further, the normal
conditions under which the muscle acts must be respected, and
the gradual unloading of the muscle during contraction permitted,
as would happen by the displacement of the bony lever on which
the muscle naturally works.

56 PHYSIOLOGY CHAP.

(/) The will as a psychical factor has no influence on the fall
of the curve with a constant load. Directly the load is adjusted
the tracing is prolonged by an unlimited number of contractions
with a considerable production of work. All other hypotheses are
superfluous, on which the functional incapacity which appears in
the ergograph curve only with the constant load has been
explained by assuming a sort of antagonism between the height
and the number of the contractions.

(<?) In order to elicit the whole work of which a muscle is
capable, in regard both to time and to amount, care must be taken
that the muscle is always engaged in maximal work. At whatever
load the work begins, the time necessary for attaining a constant
level is always the same. Still the muscle working under the
influence of the will with sub-maximal loads economises part of
the materials at its disposal, and may accumulate a fresh supply.

(h~) Given uniform conditions, the value of the initial maximal
load is constant in the same person on different days, and the
height of the contractions varies but little. The work curves
vary very slightly in the amount of work that can be obtained
with the initial maximal load, the terminal maximal load, and,
lastly, the total amount of work.

(i) Fasting does not perceptibly alter the value of the initial
maximal load, but it accelerates the fall of the curve, and lowers
the value of the terminal maximal load considerably. Practice
and training, on the contrary, render the muscle capable of accom-
plishing much more work. After practice the initial maximal
load increases within limits, while the value of the terminal
maximal load increases from day to day, without, however, delaying
the fall of the curve to the constant level.

(A-) If the work is begun with the maximal terminal load
as determined by the previous experiments, the ergograph curve
forms a horizontal line. From this we must not conclude that
work under these conditions produces no appreciable fatigue in
the nerve-muscle apparatus. Fatigue, according to Treves, can
be studied simultaneously with the production of external work,
by determining the manner in which the nervous energy
diminishes. This is represented by the product of a given weight
into the time in seconds for which the weight can be held up by
the voluntary tetanus, continued to exhaustion, of a given group
of muscles. The line indicating the alterations of nervous energy
falls much more rapidly than that showing the variations of
the maximal load, and is in a marked degree independent of the
production of external work.

At the Fifth International Congress of Physiology at Turin
Treves proposed certain modifications of his original ergograph,
by which he w r as enabled to control these observations and to
extend his research to the flexor muscles of the fingers (Fig. 37).

GENERAL PHYSIOLOGY OF MUSCLE

57

In the first place he investigated the conditions which determine
the spontaneous rhythm of contraction in voluntary ergograph
work. This rhythm depends essentially upon perception of resist-
ance, and not upon the amount of work accomplished by the
subject nor his state of fatigue.

Fie. 37. Treves' new ergograph, in which the weight can be gradually reduced, to obtain a tracing
under constant conditions of maximal load and maximal work. Platform (a) to support the
forearm, and Mosso's recording apparatus (l>) are retained, but the contrivances for fixing the
arm and fingers that are not working are discarded. The arrangement for applying the weight
is altered. The cord passes over the pnlley d, the axis of which ends in a small crank which
revolves round the axis with the flexion of the middle finger. The lower part of the apparatus
serves to graduate the weight h and keep it maximal by running it along a metal bar one metre
long, which moves upon the axis k. It is obvious that the resistance opposed to the flexion of
the finger must decrease regularly, in proportion as the weight is farther from the point 100,
and nearer the zero at axis /,-.

The " constant phase " of the work curve was investigated by
other authors, and appreciated at its proper value. Some physio-
logists, however, while recognising the theoretical accuracy of the
isotonic method and Treves' application of the principle of the
maximal load, regard the isometric method as more practical and
better adapted to the study of voluntary muscular activity.

58 PHYSIOLOGY

CHAP.

Schenck justly remarks of Treves' method that, while it corrects
certain faults of the original ergograph, it introduces new corn-
plications. Obviously, as Treves himself admits, contractions
against different loads cannot be compared, because with variations
of the weight raised the energy of inner vation must also vary,
other conditions being equal.

Schenck resumed the study of muscular fatigue (1900) in
voluntary effort by applying the isometric method to the abductor
of the index finger. For this purpose he used the apparatus
devised by Fick in 1887 (Spannungszeichner), with the addition
of certain useful modifications. The subject, working by the
beats of a metronome, throws this muscle into maximal tension
for one second, and relaxes it for the next second. Each series
lasts for twenty-five minutes, and therefore consists of 750 alter-
nate contractions and relaxations.

The results of these researches may be summed up as follows :
The curve of the isometric contractions of the abductor indicis,
made with maximal voluntary effort, generally presents three
distinct stages :

(a) In the first stage the tension which the muscle reaches in
the first contractions (which may exceed 14 kgrms.) diminishes
rapidly, and drops to about two-thirds (i.e. to 8400 grms.) after
about five minutes.

(&) In a second much longer period (about fourteen minutes)
the tension reached by the muscle is approximately constant.

(c) In a third period the tension drops again, but slightly (to
about 7700 grms.)to the end of the series, which may exceed twenty-
five minutes, without any further evidence of fatigue in the muscle.

If these results are compared with those of Treves, it is seen
at once that Schenck's first stage corresponds with the descending
phase of Treves' ergogram, and the second stage with the constant
phase which Treves obtained with the so-called " terminal maximal
load," with this difference, that in Schenck's method the maximal
energy of innervation is exerted from the beginning to the end,
while in Treves' method the energy of innervatiou gradually
declines. Accordingly, there is never any sign of fatigue after
the constant phase, and the third stage, which is prominent in
the isometric method, does not appear.

The functional constancy, that is, the comparative non-fatigu-
al >ility and inexhaustibility of muscle, contracting rhythmically
both with Treves' ergographic and Schenck's isometric method,
recalls the continuous rhythmic activity of the heart and respira-
tory muscles. This certainly depends on the blood-supply that
restores the muscle and nerve-centres as fast as they become
fatigued, and carries off the waste-products. In fact, when excised
muscles of the frog are used, the so-called fatigue curve passes
into complete exhaustion (Fig. 7, p. 12).

i GENERAL PHYSIOLOGY OF MUSCLE 59

This exhaustion depends on the absence of a proper supply of
oxygen and nutrient material to repair the waste of substance in
the active muscle and nerve-centres, and to the accumulation of
metabolites which paralyse the tissue owing to the arrest of the
blood and lymph circulation. Ranke, in fact, showed that, on
merely circulating a saline solution that contained no nutrient
restorative matters through fatigued frog-muscle, the signs of
fatigue disappeared. If, on the other hand, an aqueous extract of
the fatigued muscle of one frog were circulated through the fresh
muscle of another, fatigue phenomena at once set in.

Mosso continued these researches on warm-blooded animals,
and showed that transfusion of the blood of a fatigued into the
vessels of a normal dog induced symptoms of respiratory, cardiac,
and general fatigue in the latter. Clearly, therefore, the waste
products of muscular activity act as toxic substances, and cause
muscular fatigue and exhaustion.

The inexhaustibility of the flexor muscles of the middle finger
or the abductors of the index linger, under the experimental
conditions adopted by Treves, Schenck, and others, is not sur-
prising, and seems indirectly to confirm Eanke's theory of the
causes of muscular fatigue and exhaustion.

X. Only a small part of the potential energy liberated in
muscular contraction is used up in the form of external work ;
the other, considerably larger, part is converted into internal work,
which is accompanied by the development of heat.

It is a common observation that after vigorous effort or
repeated contractions of the muscles the temperature of the body
rises ; every one knows that muscular activity is the best way of
warming oneself in cold weather. In walking and running the
rectal temperature may rise some tenths of a degree. In tetanus
the fever may reach a high degree (45 '3 C., according to Wunder-
lich). The same is seen in strychnine poisoning (44 C., Vulpian).

On the other hand it has long been known that in a state of
absolute muscular rest, as in sleep, the internal temperature falls
about half a degree centigrade, and rises again rapidly on waking.
The mere immobilisation of an animal, or its curarisation, cools it
to 30 - 7 C. (Ricliet), and a subsequent injection of strychnine is
no longer able to evoke spasms or to raise the temperature, which
must therefore depend on the tetanising action of the strychnine.

Since the muscles represent about 40 per cent of the total body
weight in vertebrates, and after removal of the skeleton (which
can only develop a negligible amount of heat) certainly represent
more than 50 per cent, and since katabolism is more active in
muscle than in any other tissue, we are justified in assuming
that the muscles have a preponderating influence on the heat pro-
duction of the body, in comparison with that of all other tissues.

We shall elsewhere discuss thermogenesis and the thermal

60

PHYSIOLOGY

CHAP.

balance of the organism as a whole ; here we must confine our-
selves to the study of muscle as a thermogenic organ by the direct
examination of its temperature both during contraction and in the
resting state.

The first observations were made in 1835 by Becquerel and
Brechet. They attached one couple of a thermo-electric battery
to the biceps muscle of a human arm, while the second couple
was kept at constant temperature. After a few contractions the
temperature of the muscle was raised 05, and after five minutes
of energetic alternate contraction and relaxation (working a saw)
1 C. Gierse (1842) was the first who noted in the dog, with the

v_

Fio. 38. D'Arsonval's thermo-electric couples with sheathed junctions, to avoid the electrical
currents liable to be set up by the contact of two different metals with fluid. 1, Section of
finely-pointed conical tube of German silver, into which an iron wire has been soldered ; 2,
section of cylindrical tube of German silver, closed and pointed at one end at the junction
with an iron wire, and protected above this by a non-conducting sheath ; 3 and 4, a pair of
thermo-electric needles composed of two wires, iron and German silver, soldered together at
the points, and covered with an insulating varnish.

thermometer, that the cutaneous temperature of a limb rose during
the contraction of its muscles. Zienissen (1857) and Bee-lard
(1860-61) observed the same on man. The objection that the
rise of temperature depends on increased flow of blood to the skin
may be met by saying that the skin becomes warmer, but not
redder, during the contraction of the subjacent muscles. Another
objection, that the heating may depend on the hyperaernia of the
muscle during its contraction, is less easily met.

The ordinary thermometric or thermo-electric methods are used in investigat-
ing muscular thermogenesis. If the bulb of a highly sensitive thermometer
covered with a thick layer of non-conducting material (cotton-wool) to prevent
the dispersion of heat is applied to the human skin above the muscle to be
examined ; or better, if the bulb of the thermometer is inserted between the
muscles of the animal, it is possible to measure the alterations of temperature.

i GENERAL PHYSIOLOGY OF MUSCLE 61

Baudin has recently carried tlie construction of mercury thermometers with
small bull >s for physiological purposes to such perfection that he has obtained
a scale in which each degree is divided into fifty parts. But even with an
ordinary clinical thermometer, divided into tenths of a degree, it is possible
on reading the scale under the microscope to estimate differences of a hundredth
of a degree.

The thermo-electric method has, as compared with the thermometric
method, the great advantage of almost instantaneously indicating rapid
alterations in the temperature of the muscle. On the other hand it is more
difficult and delicate of application, and may lead to fallacies if not employed
very cautiously.

The thermo-electric method is founded on the following principle : If two
different metals united by two junctions are included in the circuit of a
low resistance galvanometer, the heating or cooling of one of the junctions
gives rise to an electric current, which deflects the needle of the galvanometer
in the positive or negative direction, in proportion with the rise or fall of
temperature in the first junction, if that of the second remains unchanged.
To investigate muscular therniogenesis it is best to take needle-shaped
thermo-electric couples (Fig. 38), which are plunged into two symmetrical
muscles of the frog, one of which is at rest, the other contracting (Helmholtz).

(HUM

mmn^nmx^f "^""^'^^^tHasnr:

FIG. 39. Photograph of positive and negative variations of temperature obtained with two
thermo-electric needles pushed into the two gastrocnemius muscles of a frog, and connected
with a low resistance galvanometer ; the sciatic nerve was excited alternately on either side.
(A. D. Waller.) The excursions of the galvanometer mirror are photographed by a beam of light
reflected on to the sensitive surface of a moving drum. Each tetanising excitation of the
sc-iatics, respectively, lasted one minute as indicated by the break of the abscissa line. During
tetanus the curve falls or rises, according as the right or left sciatic was excited.

To measure the rise of temperature developed in a simple twitch a Melloni's
thermopile is used, which consists of several elements, the two muscles of
the frog being placed in contact with the two surfaces at which are the
junctions of the elements of the pile (Heidenhain).

If a mirror is attached to the magnet of the galvanometer, its deflections
can be photographed by the reflection of a ray of light upon a sensitive
surface (Waller, Fig. 39).

The first experiments that proved incontestably that muscle
is concerned in the production of heat as well as motion were
performed on cold-blooded animals by Helmholtz (1847). By
employing the thermo-electric method he saw that the muscles of
the frog's thigh developed heat during indirect or direct tetanisa-
tion (0-14-0-18 C.).

In later experiments (1864) Heidenhain measured the rise of
temperature (1-5 hundredths of a degree) in the isolated gastro-
cnemius of the frog after a simple twitch.

There is therefore no doubt that muscular contraction is
accompanied by a development of heat, which is due to an increase
of exothermal processes within the contractile organ, by which the
greater part of the store of accumulated energy is dispersed.

62 PHYSIOLOGY CHAP.

Even in rest, however, muscle develops more heat thaii other
tissues. An indirect proof of this is obtained from the experi-
ments in which Claude Bernard attempted to estimate the oxygen
content of the hlood flowing respectively to and from the muscle,
in rest and during tetanus. According to Bernard the blood of
the artery of the anterior rectus muscle of the dog's leg carries
9'31 c.c. oxygen, the blood that flows from the veins 8'21 c.c. when
the muscle is at rest, 3'31 during tetanus. During its activity,
therefore, the muscle consumes much more oxygen than during
rest ; but even in the resting state it consumes a certain amount,
and must therefore develop heat.

These results were confirmed in Ludwig's laboratory by Meade
Smith (1881), who made numerous direct estimations of tempera-
ture, both on the blood of the artery and vein of the muscle, and
on the resting or tetanised muscle itself. The general conclusion
was that the temperature in the artery is less than in the vein
and in the muscle in the resting state, and that the difference
increases considerably during tetanus.

Beclard was the first who studied heat production in muscle
from the point of view of the mechanical theory of heat (1861).
He tried first on the frog by the thermo-electric method, and then
on his own biceps muscle, to estimate with an air-thermometer,
graduated in fiftieths of a degree, the amount of heat developed
during static (isometric) contraction, in which the mechanical work
is nil, with that produced during dynamic (isotonic) contraction,
which is accompanied by mechanical work that can be measured
in kilogrammetres. He stated positively that when the muscular
contraction results in muscular work, much less heat is evolved in
the muscle than when a contraction of the same strength is not
accompanied by external mechanical effects.

This fact, despite the imperfections of Beclard's method, proves
that muscular activity is subject to the great law of the conserva-
tion of energy. When the whole of the energy liberated by the
muscle is expressed in the form of heat, more heat is evolved than
when part of the energy is converted into muscular work.

Beclard further demonstrated that the amount of energy trans-
formed into mechanical work during the lifting of the weight by
the muscle is reconverted into heat when the raising is succeeded
by the lowering of the weight, i.e. when the positive is followed
by negative work. The experiment consists in comparing the
heat developed when a certain weight is held up for a given time
by the static contraction of the biceps, with that developed during
the same time when the arm loaded with the same weight makes
up and down movements. Under these conditions (according to
Beclard) the development of heat indicated by the thermometer is
equal, whether the arm be kept in equilibrium or executes move-
ments. The positive work of raising the weight is therefore

GENERAL PHYSIOLOGY OF MUSCLE

03

cancelled by the negative work of lowering it, so that in this case
the heat production in static contraction is equal to that in dynamic
contraction.

But apart from the imperfections of the method Beclard's
results were incomplete. He neglected the influence exerted by
differences of load on muscular thermogenesis, as well as the degree
of stimulation and the state of fatigue of the muscles. In 1864
Heidenhain investigated the question again from a wider point of
view and by more exact methods. He employed the isolated
muscles of the frog, with different loads, and recorded the height
of the contractions, from which he calculated the work, and
measured the changes of temperature with a thermo-electric pile.

Since we know that with increase of load the mechanical work
of the muscle increases within certain limits (Fig. 26, p. 46) it
seems natural to suppose that the simultaneous development of
heat takes place inversely and diminishes with increment of work,
so that the sum of energy liberated by the katabolic processes in
the muscle remains constant for the same stimulus, its division
into work and heat alone being variable. Heidenhain's researches,
however, demonstrated that when the intensity of the stimulus
remains constant, the sum of energy developed by the muscle
increases up to a certain point with increase of load, i.e. the
increase of work is accompanied by increased heat-production.

This important conclusion is represented by the following
table, which gives Heidenhain's data from one of his experiments
on the gastrocuemius of the frog loaded with different weights :

Increased warmth

Number
of test.

Weights applied
to the muscle.

Summated
height of three
contractions.

Mechanical
work of the three
contractions.

of the muscle
expressed in
degrees of the scale
of the thernio-

multiplier.

1

grms.
10

mm.
10-6

gr. mm.
106

8-5

2

30

10-4

312

11-5

3

90

8-5

761

18-0

4

60

9-6

573

11-5

5

30

10-6

318

9-5

6

10

10-8

108

7-0

During three successive contractions the muscle was loaded
with the weight during both contraction and relaxation ; thus the
mechanical work given out by the muscle during contraction was
restored to it in the form of heat during relaxation. The rise of
temperature shown in the table therefore expresses the total sum
of the energy developed by the muscle during the three successive
contractions. This is not a constant but varies with the external
mechanical work : it increases with the increment of this work

64 PHYSIOLOGY CHAP.

and declines with its decrement. The facts collected by Heiden-
haiu, however, show that the rise and fall of temperature in the
muscle are not strictly proportionate to the increase and
diminution of the mechanical work which it performs ; generally
speaking, the thermal increase is much less than the increase of
work. This proves that the muscle works more economically
when it lifts a moderate weight than when it lifts a lighter one.

The property which the muscle possesses of adjusting the
quantity of energy which it develops under a constant stimulus
to the greater or less resistance which it has to overcome, is very
important. If the strength of its reaction depended only on the
strength of the stimulus, and was independent of the load, then
the development of muscular energy the nerve impulses remain-
ing uniform would not be in proportion with the external work
that had to be performed. Heidenhaiu's discovery that the total
sum of energy developed by the muscle depends on the degree of
tension due to the resistance it encounters in contracting, shows
that it possesses a mechanism in itself which is capable inde-
pendently of the nervous impulses of partially regulating its
intrinsic metabolism according to the needs of the moment.

Again, when the load remains constant, and the strength of
stimulation is progressively increased, the development of heat
increases within certain limits with the height of the con-
tractions and the mechanical work performed, till it reaches a
maximum. So that the metabolism and heat production of
muscle are regulated not only by tension, but also by the nervous
system, owing to the varying intensity of the impulses which it
transmits to the muscle.

It should, however, according to the results of Heidenhain and
Nawalichin, be observed that, just as we have seen with constant
stimulus and increasing load, so too with a constant load and a
progressively increased stimulus, the increase in heat and work
development are not parallel, but the maximum production of heat
is always reached before the maximum of work, i.e. the heat pro-
duction increases more rapidly than the height of the contractions.
This proves that the muscle works more economically whenever it
is more strongly excited from the nerve, and forced to do more
work.

But when the same amount of work is performed by a muscle,
on the one hand by many small contractions, on the other by
fewer but larger contractions, less heat, according to Heidenhain,
is developed in the first case than in the second. This agrees
with the common observation that it is more fatiguing to ascend a
rapid incline with long steps, than a less steep slope of the same
height, with shorter steps.

Heidenhaiu brought out another interesting fact which is not
easy to explain. When the same amount of work is performed by

i GENERAL PHYSIOLOGY OF MUSCLE 65

a fresh muscle and a fatigued muscle, the former develops more
heat than the latter, as if the chemical activity necessary for
developing the same amount of useful external work were greater
in the fresh muscle and less in the fatigued. In a series of
successive contractions of equal height, carried out by a muscle
loaded with the same weight, so that each contraction performs
the same amount of work, the development of heat diminishes
between the first and the last of the series. This shows that
fatigue can be detected in the diminished heat-production before
it becomes evident in the lessened height of contraction. Accord-
ingly, as it becomes fatigued, the muscle functions more economi-
cally i.e. a less amount of energy is transformed into heat.

When the impulses that reach the muscle follow so rapidly as
to give rise to tetanic fusion of the contractions, the production of
heat increases progressively up to a certain maximum, in propor-
tion to the increasing height to which the weight is raised.

The heat developed in tetanus increases with increment of the
load and corresponding tension of tjhe muscle. When the weight
is so great as to inhibit contraction altogether, more heat is
developed than when the load is less and the muscle can shorten
a little. During the development of tension the heat production
is greater than when the tetanic rise is complete. During a brief
tetanus the same amount of heat is liberated at each instant. But
during the contraction, and possibly during the relaxation, that
precede and follow tetanus, a much larger quantity of heat is
developed.

Heidenhain's work on muscular thermogeuesis was extended
and completed by Fick and his pupils. Fick in his first experi-
ments (1884) resumed the study of the question already investigated
by Beelard. Heidenhain's discovery that the sum of the energy
(work and heat) developed by the muscle is proportional to its
tension during its activity, does not contradict Beclard's view, as
Hermann also pointed out, that with constant tension the sum of
energy developed by the muscle (work and heat) is in direct ratio
with the intensity and duration of its activity, so that, caeteris
paribiis, the energy liberated in the form of work is inversely
proportional to that liberated in the form of heat conformably
with the law of conservation of energy.

In order to prove this theory experimentally, Fick employed
Heidenhain's method on the excised muscles of the frog. To
compare the thermal production in useful work with that of con-
traction by which no external work was performed, he invented
an ingenious apparatus which he termed " Arbeitssammler." This
is a small windlass which the muscle turns on contracting 'against
the constant resistance of a weight, which can be prevented from
dropping again during relaxation by putting a brake on the wheel
(Fig. 40). When this is applied the muscle is unloaded, i.e. freed

VOL. in F

66

PHYSIOLOGY

CHAr.

from the weight, when it begins to relax, and the work done in
contraction is utilised ; when the break is removed, the work done
is cancelled and converted into heat when the muscle relaxes.

Tick's results confirmed Beclard's hypothesis. In a series of
contractions produced by stimuli of uniform strength, while the
muscle is performing useful work, less heat is evolved than in a

Fir.. 40. Kick's Arbeitssammler, by which the muscle is loader! with a weight during contraction,
and unloaded during relaxation. While contracting, the muscle (frog's gastrocnemius) lifts
the lever r rj, which in itself offers little resistance, as it is almost balanced by the small
counterpoise /. But owing to the support /(, which presses on the edge of the graduated disc
m M (which revolves round the same axis as the lever), the disc turns as the lever rises, along
with the concentric pulley that carries the thread to which the weight is attached. The
muscle is thus loaded during contraction, and lifts the. weight to a height that can be exactly
measured by the degree of rotation of the disc shown on the scale ./'. In relaxing, the muscle
is freed from its load, because the disc and pulley cannot drop back owing to the stop /ij.
The weight remains up, and the lever sinks to its original position owing to the slight pre-
ponderance of arm r over arm )-j. At each succeeding contraction the weight is lifted higher,
so that from the total rotation of the disc it is easy to calculate the total sum of work per-
formed by the muscle in a given number of contractions. When the stop /ij is removed from
the edge of the disc, the apparatus can be used as a simple isotonic lever. At each contraction
the muscle rotates the disc and lifts the weight ; but at each successive relaxation the work
done is cancelled, because the disc retracts with the lever owing to the pull of the weight.

second series of uniform contractions, produced by stimuli of the
same strength, in which the muscle performs no useful work.

The later work of Danilewsky, Blix, and Chauveau leads to the
same conclusion.

On comparing the heat developed by a series of maximal
muscular contractions in a given time without useful work, with
that developed by the same muscle in the same time with maximal

i GENERAL PHYSIOLOGY OF MUSCLE 67

stimuli so frequent as to produce complete tetanus, Fick observed
that in the first case there was a much greater development of heat
than in the second. From this he concluded:

(a) That the amount of heat developed at each contraction
during tetanus is in inverse ratio to the frequency of the stimuli.

(b) That in a series of single contractions due to momentary
stimuli, the theriiiogenetic effect of each twitch far exceeds that
of each contraction of a series of such frequency as to result in
tetanus.

Fick tried to express the amount of heat liberated during
muscular activity in absolute values. He found that the maximum
heat which a gram of muscle may develop during a simple con-
traction may reach the value of 3'1 microcalories, a microcalorie
being the amount of heat required to raise the temperature of
1 mgrm. of water 1 C. With his pupils he determined the relative
rates at which the development of heat and of work increased, by
a series of tests on frog muscle excited with maximal stimuli, and
loaded with regularly increasing weights.

The general result as a rule was that the greater part of the
potential chemical energy liberated by the muscle during its
activity appeared in the form of heat. But with increase of load
the ratio between heat and work alters regularly, as an increasingly
larger part of the potential chemical energy is set free in the form
of work, and a comparatively smaller part as heat. This proves
that the muscle in doing more work functions more economically
than in doing little work.

Zuntz, Lehmann, and Hagemann (1889) tried to ascertain what
proportion of the total energy developed in the muscles of warm-
blooded animals is utilised in the form of mechanical work. This
question has only been solved approximately by calculating the
total chemical energy developed by the estimation of the reciprocal
gas-exchanges which take place in any given work of the muscles.
It was shown by experiments on horses that about J of the
energy is transformed into work, and f into heat. If we con-
sider that in the best steam-engines man is able to construct
only jL or T V part of the energy liberated can be utilised in
mechanical work, all the rest being lost in the form of heat, we
see that the muscle is a living machine which functions more
economically than any steam-engine. On the other hand, an
electric motor fed from a battery is capable of utilising y 9 ^
of the energy developed by the oxidisation of the zinc of the cell
in external mechanical work, so that it is a more perfect machine
than the muscle. We must not, however, forget that in homoio-
thermic animals the development of heat must not be regarded as
a loss, since it is as useful to the organism as mechanical work.
A muscle is not merely an apparatus for the production of external
work, but it also serves to heat the body of warm-blooded

68 PHYSIOLOGY CHAP.

animals, and raise their temperature to a given height, inde-
pendently of the variations of external temperature. From this
physiological standpoint it may be held that the muscle utilises
all the energy which it develops, either in the form of work or of
heat.

XL A portion of the potential chemical energy liberated
during the activity of the muscle appears not as heat, but as
electricity.

A discovery of great importance in physics galvanism, and in
physiology animal electricity, originated in Galvani's observations
that muscles of a recently killed frog were thrown into convulsions
on closing the circuit between the muscles and the nerves by
means of two metals. From this Galvaiii concluded that the
muscles of the frog were normally charged like a Leyden jar, with
positive electricity inside and negative electricity outside each
muscle. Hence he assumed that on making connection between

the inside and outside of a
muscle, a current was produced
which gave rise to the con-
traction.

Volta at once recognised
that this interpretation was
erroneous, because the circuit

FIG. 41. Galvani's second experiment, without j- t i

metais. comprising two different metals

in itself contained a source of

electromotive force. The long controversy between Volta, who
affirmed the existence of metallic currents, and Galvani, who
maintained the contrary and endeavoured to explain everything
by muscle currents, is certainly one of the most remarkable
incidents in the history of experimental science. The contrary
statements of the two protagonists were true ; their negations
were false. Volta's theory led to the discovery of the pile ;
Galvani's to the first demonstration that living tissues in general,
and the muscles in particular, may, under given conditions, be the
seat of the development of electrical currents.

The observation of Galvani and his nephew Aldini was
based on the fact that contraction takes place in the muscles of
a recently killed frog, not only when a circuit is made between a
muscle and its nerve by a bridge consisting of two metals or even
of one metal, but also though in a less degree when the circuit
is made without any metal. This experiment, famous in the
annals of medicine, consists in laying the nerve-muscle preparation
of a frog upon a glass plate (Fig. 41), and bringing the surface of
the muscle into contact with the end of the freshly-cut nerve by
a glass rod. At the moment of contact the muscle contracts.
Eepeated and confirmed by Valli (1794) and Alexander v.
Humboldt (1798), this experiment underlies the general theory

i GENEEAL PHYSIOLOGY OF MUSCLE 69

that living tissues are under special conditions the seat of
electromotive forces, which may excite muscular contractions on
the closure of non-metallic circuits.

Direct proof of this was not available till after the invention
of the galvanometer by Nobili (1824), when it became possible
not only to demonstrate the existence of the comparatively
weak currents present in living tissues, but also to measure them.
In 1827 Nobili made use of Schweigger's rnultiplicator to demon-
strate the so-called " natural current " of the frog, directed from
the foot towards the head.

On repeating and varying Nobili's experiment in different
ways, Matteucci (1838-40) discovered the phenomenon known
later as the "current of rest" in muscle. He amputated the
thigh of a skinned frog by a transverse incision, and brought it
into the circuit of a galvanometer, by applying one electrode to
the cut surface and the other to the outer surface of the thigh
muscles. On closing the current the galvanometer needle was

Fin. 42. Matteucci's experiment of secondary contraction and tetanus.

deflected, showing a current in the muscle from within outwards,
i.e. from the cut surface to the natural surface of the muscle, in
the galvanometer circuit from the natural to the cut surface. 1

In 1842 Matteucci communicated to the Academic des Sciences
in Paris another discovery, which Biedermann reckons among the
most important in experimental physiology. When the nerve of
a frog's leg is placed on the muscle of the opposite leg, and the
nerve of the latter is excited by certain stimuli, a vigorous primary
contraction results in the muscles of this excited limb, accom-
panied by a less vigorous secondary contraction in the muscles of
the other limb (Fig. 42).

This observation was the first demonstration of an electrical
phenomenon concomitant with the state of muscular activity.
Matteucci interpreted it wrongly ; the true explanation was only
possible after the law of the current of rest in muscle and its
negative variation had been discovered by du Bois-Keymond (1843).

1 To avoid the confusion that frequently arises between the current in the
outer (galvanometer) circuit and that flowing within the tissue, it might be well,
as suggested by Waller, to replace the ambiguous term " negative " (more correctly
" electro-positive ") by the term "zincative," which would serve as a reminder that
the current flows from the excited to the unexcited portion of the tissue, as from
zinc to copper in a Daniell cell. Translator.

70 PHYSIOLOGY CHAP.

Du Bois-Keymond's researches began in 1841, shortly after

Fin. 43. Thomson's galvanometer. To the left is the galvanometer, in the centre a .shunt, to the
right the scale, illuminated by a beam reflected from a lamp to the galvanometer mirror.

those of Matteucci.

Jl

FIG. 44. Diagram of galvano-
meter, n s and s n, pair of
magnets with opposite poles,
circular mirror fixed to upper
magnet ; 1 1, end of wire that
surrounds the magnets ; N S,
third magnet, which controls
the two lower magnets.

equilibrium

theory ").

He devoted many years to the study of
animal electricity, and his great merit lies
in the introduction of exact methods. His
discovery of unpolarisable electrodes, com-
bined with the method of compensating
by means of a rheochord, enabled him to
separate the tissue currents from those of
metallic origin, and to measure them, both
in the resting state of the muscles and
nerves and during their activity.

In 1807 Hermann's investigations
opened up a new chapter in electro-
physiology. He overthrew clu Bois-
Reymond's theory, according to which
electrical currents are pre - existent in
normal living tissues in the resting state
(" pre-existence theory"]. By the experi-
ments we are about to discuss, which were
to a large extent confirmed by subsequent
observers (Hering, Engelmaun, Bieder-
mann, and others), Hermann proved that
muscles and other tissues, so long as
they are at rest and intact, give off no
currents to the galvanometer. When
currents appear they are due solely to
the effects of artificial alteration of the
tissues, or to the disturbance of chemical
which accompanies functional activity (" alteration

GENEEAL PHYSIOLOGY OF MUSCLE

71

Owing to (lie high resistance of animal tissues (which is millions of times
greater than the resistance of metals) and their low potential, it is necessary
in electrophysiological research to employ galvanometers or multipliers with

FIG. 45. Various forms of unpolarisable electrodes. D and C, du Bois-Reymond's pattern ;
E, Burden-Sanderson's ; B, von Fleischl's ; A, d'Arsouval's.

astatic magnets, so as to render the vibrations as

have a high internal resistance
the instrument can be decreased

These galvanometers

of

,9,99

1 oTFu

many coils and with
a-periodic as possible.
(5,000-20,000 ohms). The sensitiveness
by a shunt, which cuts off -j 9 ^, -fifa, or
of the current. The principle on which gal-
vanometers are constructed is that a magnet,
suspended and surrounded by a conducting
wire, is deflected in the direction of a current
passing through the wire, in proportion to
the strength of the current.

Both in Wiedemann's (with detachable
and interchangeable spools) and in Thomson's
galvanometer (Figs. 43, 44) the deflections of
the magnet suspended by a thread of raw silk
are more or less magnified by a mirror which
reflects a ray of light on to a horizontal scale.
These deflections can be photographed on a
moving sensitive surface.

The ends of the galvanometer wires must
not be directly applied to the tissues, on
account of their polarisability. Unpolarisable
electrodes are indispensable in experimenting
with muscle and nerve (du Bois-Eeymond).
These usually consist of a little rod or disc of
amalgamated zinc dipping into solution of
zinc sulphate in a glass tube, the other end
of which is closed by a plug of china clay
saturated with physiological saline, which is in contact with
protects it from the caustic action of the zinc sulphate (Fig. 45).

Nowadays, however, all these imperfect electrodes may be replaced by the
so-called "normal electrodes" of Ostwald, in which potassium chloride is

FIG. 46. Ostwald's normal electrode,
adapted to physiological research
by Oker Blom.

the tissue and

PHYSIOLOGY

CHAP.

substituted for sodium chloride. A suitable adaptation of these to physio-
logical purposes is the model of Oker Blom (1900). Two glass tubes are
sealed at the bottom in the flame, with a little mercury on the base, by which
contact is made with two platinum wires that pass through the sealed ends.
Pure calomel is placed on the mercury, and above that physiological salt
solution, which is brought into contact with the muscle by a tag of cotton
saturated with the solution (Fig. 46).

The galvanometer can be replaced by Lippmann's capillary electrometer,
which has the advantage of reacting to very rapid oscillations of current, with

FN;. 47. Lippmamf s capillary electrometer. A, viewed as a whole (pressure bulb, capillary, and
microscope) ; 1', tube (Hg) and capillary (<) which dips into the tube of sulphuric acid
(HoSO.|) ; C, mercury in capillary tube under the microscope.

no lost time and no periodic vibrations. Moreover, as the resistance in the
capillary is enormous and the current passing through it is practically abolished,
nnpolarisable electrodes can be dispensed with. As seen in Fig. 47, the
instrument consists of a glass tube drawn out in the flame at one end to a
capillary 20-30 mm. diameter. This tube is filled with mercury and joined to
an apparatus by which the pressure can be regulated. The open end of the
capillary dips into 10 per cent sulphuric acid solution. Two platinum wires con-
nect the mercury and sulphuric acid, respectively, to the points of the organ under
investigation. Under the microscope the excursions of the mercury meniscus
which is brought into the field by means of the pressure apparatus can be
seen plainly on closure of the circuit. The meniscus advances or recedes towards
the end of the capillary according as the potential rises or falls on the side of
the mercury tube, and vice versa as regards the reservoir of sulphuric acid.
In the capillary electrometer the excursions of the meniscus do not

i GENERAL PHYSIOLOGY OF MUSCLE 73

indicate the strength of current, but the electromotive force or <li (Terence of
potential between the two electrodes. It is thus an electrical manometer,
the sensitiveness of which is so great that it reacts to TUT&UTT volt. The dis-
placements of the mercury surface can be photographed.

Eiiithoven (1905-6) introduced the string galvanometer which has distinct
advantages over its predecessors.

This instrument has a fine thread of silvered quartz or platinum stretched
between the two poles of a strong magnet. On passing a weak current
through the string, it moves laterally in proportion to the strength of the
current. The poles of the magnet are pierced by holes so that the thread may
be illuminated by an electric light from the one side, and observed from the
other by means of a microscope ; or a magnified image may be thrown on a
screen, or moving sensitive surface on which it is photographed.

Einthoven devised this apparatus for the special purpose of studying
the electrical variations of the human heart. But it may be substituted
advantageously for all purposes instead of the apparatus described above.

We will briefly consider the principal electromotive phenomena
in muscle, keeping distinct the electrical manifestations of the
resting and the active states.

When a muscle with parallel fibres, e.g. the frog's sartorius, is
dissected out, and the tendinous end trimmed neatly with a razor,
a regular cylinder of muscle substance is obtained, with a natural
longitudinal surface and two artificial cross-sections. If any two
points of this muscle are connected with the galvanometer by
unpolarisable electrodes there is nearly always a deflection of the
galvanometer needle, showing that the two points led off are not
isoelectric, but that there is a difference in potential.

If the electrodes are applied to points on the natural
longitudinal and the artificial transverse surfaces, the former is
found to be " positive" in relation to the latter, which is " negative."
Du Bois-Keymond made a minute study of the different degrees
to which the galvanometer needle was deflected by altering the
position of the electrodes upon the muscle cylinders, and drew up
the following laws of the muscle current :

(a) Strong currents appear on leading off to the galvano-
meter from the natural longitudinal surface and artificial cross-
section of the muscle. The current is strongest when a point in
the equatorial median line of the longitudinal surface is connected
with the axial point of an artificial cross-section, and decreases
regularly with increased distance from these points.

(&) Weak currents are obtained when two points at unequal
distance from the equator of the longitudinal section are united ;
still weaker currents when two points of the cross-section at un-
equal distances from the ends of its axis are connected.

(c) No current is obtained on connecting two points of the
equator or any two points at equal distance from the same ; nor on
connecting the two axial points of the cross-section, or any two
points of the cross - section equidistant from the axial points
(Fig. 48).

74

PHYSIOLOGY

CHAP.

These observations show that the natural surface of the muscle
has a positive electrical charge, which is maximal along the
equatorial Hue and decreases regularly away from it; and that the
two artificial cross-sections have a negative electrical charge which
decreases regularly from the axial point of the muscle cylinder,

4-

f

! +

t

Fie. 48. Diagram of direction of currents that
can be led off to a galvanometer from
different points of the surface of a muscle
cylinder.

-f

Fia. 4;t. Distribution of positive electrical
charge on natural longitudinal, and negative
electrical charge on artificial transverse
sections of a muscle cylinder.

where it is maximal, to the more peripheral points of the cross-
section (Fig. 49).

If the section is made obliquely through the muscle cylinder,
the potential at the different points of the natural surface and the
artificial surfaces varies according to another law. The galvano-
meter shows that the most positive points of the longitudinal
surface lie much nearer the obtuse angles of the rhombus, and the
more negative points close to the acute angles. The strongest
current is obtained on leading-off from these opposite points ; on

4-

\

FIG. 50. Diagram of direction of currents led
off from surface of a muscle rhombus.

-f- +

Kici. 51. Positive and negative electrical
charges at longitudinal and transverse
sections of a muscle rhombus.

connecting points more remote from these the currents become
increasingly weaker ; lastly, there is no current on joining up
honionymous points on the natural or artificial surfaces (Fig. 50).

There is thus in the oblique muscle cylinder a displacement of
the isoelectric equatorial and axial points in the direction indicated
in Fig. 51.

The longitudinal surface of a muscle shows a positive charge

i GENEKAL PHYSIOLOGY OF MUSCLE 75

as compared with the artificial transverse or oblique section, even
when it is not the natural external surface covered with periinysium,
but the surface of a bundle of fibres artificially dissected out, but
otherwise intact. On the other hand, the natural transverse or
oblique section, consisting of the ends of the fibres where they are
connected with the tendon or aponeurosis, is not like the artificial
surface produced by a cut negative to the longitudinal surface.
The negative charge first makes its appearance after removal of
the tendon, i.e. on the formation of an artificial cross-section.

The gastrocnemius muscle, which is generally employed for a
nerve-muscle preparation from the frog, shows marked differences
of potential at different points of its natural surface, which do not
altogether conform, to the laws of the current of rest in straight or
oblique muscle cylinders. This is due to the complicated structure

Fio. 52. Measurement of electromotive force of current of rest in muscle by method of compensa-
tion. V ), rectilinear rheochord (monochord) consisting of a long wire connected at the ends
to the battery. The runm-r * is movable along it, so that any fraction of the battery current
can be thrown into the galvanometer to compensate the muscle current which is opposite
in direction.

of the muscle, which consists not of parallel fibres, but of fibres that
run obliquely (Kosenthal).

The electromotive force which a frog's muscle is capable of
developing may be measured by the compensation method, i.e. by
introducing into the circuit that connects the two oppositely
charged points of the muscle with the galvanometer a current
from a Daniell cell in the direction opposite to, and of the same
strength as, the muscle current. This is easily effected by means of
a rheochord (Fig. 52). The electromotive force has been known to
exceed O'OS volt (du Bois-Eeymond, Chapman). But it may be
concluded that the portion of the current led off to the galvano-
meter is only a small fraction of the total current developed
within the muscle, which we are not in a position to measure
(Bernstein).

The electrical phenomena of the resting muscle depend on the
state of vitality of the tissues. Muscles that are dead or in rigor
mortis are electrically inactive. Muscles treated with ether vapour,

76 PHYSIOLOGY CHAP.

or swollen with water, which are totally inexcitable and apparently
dead do, on the contrary, manifest differences of electrical
potential.

Another important fact discovered by Hermann and confirmed
by Biedermann and others is that wholly uninjured muscles
are isoelectric, i.e. manifest no difference in potential at their
surface in the resting state. When the hind -leg of a frog is
very carefully skinned, precaution being taken to avoid contact
between the cutaneous secretion and the exposed surface of the
muscle, no current can be led off from the latter to the galvano-
meter. When, on the contrary, an exposed muscle is injured at
any point of its surface by cauterisation, chemical burns, partial
poisoning with potassium salts, mechanical crushing, etc., the
injured spot invariably becomes negative to the intact parts of the
surface. So that injured points react like transverse or oblique
surfaces produced by section. Hermann, therefore, formulated the
general law which is applicable to all cases, that " In every injured
muscle fibre the surface of demarcation between the living and
dead portions of the fibre is the seat of an electromotive force
directed towards the living part." He gave the name of demarca-
tion current to the so-called " current of rest," because it does not
pre-exist in the normal muscle, but first appears when any part of
the latter suffers alteration. [Current of injury : Hering.]

Another phenomenon brought out by Hermann is that a
general rise of temperature increases the strength of the demarca-
tion current up to a certain limit, beyond which it decreases
again, till it disappears with the onset of heat rigor. A drop in
the temperature, on the contrary, lowers the e.m.f. Again, in
intact muscle heated points are electro-positive to cooler parts
(Hermann and Worm-Mliller). Finally, fatigue from protracted
muscular activity weakens the demarcation current (Eb'ber), and
abolishes it if pushed as far as rigor.

Another fact in favour of Hermann's views is that in muscle
prisms or cylinders freshly cut with a razor and connected with
the galvanometer the demarcation current is absent, or almost
absent, during the first moments, but increases rapidly to its
maximum. This phenomenon can only be explained by assuming
that the surface of the section alters with exposure to air, and
that its negative potential increases in proportion with this
change. The alteration shown in the acidification of- the muscle
gradually extends over the whole, till it becomes perfectly rigid.
The demarcation current as shown on the galvanometer suffers
a parallel slow diminution, till it eventually disappears.

We must next study the phenomena of active muscle. If the

nerve of a muscle-nerve preparation that is showing a demarcation

current on the galvanometer is tetanised, the current is diminished

the galvanometer needle swings back towards the zero of the

i GENERAL PHYSIOLOGY OF MUSCLE 77

scale during the tetanus. This is the " negative variation " referred
to above. On a sensitive galvanometer it can be shown during
single twitches as well as in tetanus. If the current of rest is
compensated, and the nerve is then excited, the negative variation
will appear on the galvanometer as an autonomous current, in
the opposite direction to the current of rest showing that the
e.m.f. of the muscle is diminished by excitation (du Bois-Pieyrnond).

The phenomena of secondary contraction, or induced contraction
as it was termed by Matteucci, and secondary tetanus, which can
be seen in a frog's leg when its nerves are laid across the muscles
of another leg, so that the muscle current produced in the latter
on contraction passes through the nerves of the former (Fig. 42),
depend, as du Bois-Eeymond showed, on the exciting action of
the negative variation of the current. The secondary twitch is
the simplest and most convincing proof that a single contraction
can elicit a negative variation of sufficient intensity to stimulate
the nerve. Secondary tetanus further shows that the negative
variation of the primary tetanus is a discontinuous process,
although the variations in the current are too rapid to be
followed by the galvanometer needle, and their mean value only
is recorded.

The oscillating character of the muscle current in tetanus can
also be demonstrated by the telephone, which Hermann regards
as more sensitive than the " galvanoscopic leg." When the
muscle current is led off to a telephone, a sound is heard during
tetanisation which results, as Bernstein and Wedensky demon-
strated, from a number of vibrations equal to the rate of the break
or make shocks of the tetanising current.

Bernstein was able by an ingenious apparatus known as the
differential rheotome to analyse the negative variation during a
simple contraction.

The negative variation in a nerve-muscle preparation during
tetanus can be photographed by reflecting a beam of light from
the galvanometer magnet on to a sensitive surface moving by
clockwork. Fig. 53 records the tetanic contraction and accom-
panying negative variation.

The galvanometer does not react quickly enough to show the
oscillations that accompany tetanus, but if the capillary electro-
meter is used, they can be photographed by letting the shadow
of the meniscus fall on a slit behind the sensitive paper, which
travels in a direction vertical to the oscillations of the mercury
(Burdon-Sanderson and others).

The negative variation increases to a maximum with the
intensity of the tetanising current. According to Bernstein it
never reaches the zero point, i.e. never cancels the demarcation
current. According to Gotch and Sanderson, on the contrary,
the negative variation may pass beyond the zero point, and

78

PHYSIOLOGY

CHAP.

exceed the value of the demarcation current ; for instance, the
demarcation current may equal O04 volt, the negative variation
0'08 volt. The negative variation also increases up to a certain
maximum with increase of the elastic tension or load of the
muscle, parallel with the development of work and of heat.

In order to understand the nature of the negative variation
of the demarcation current in muscle when the nerve is tetanised,

FIG. 53. Myogram of tetanic contraction of frog's gastrocnemius (white line on black ground) ,-md
simultaneous photograph of negative variation (black line on white ground). (A. D. Waller.)
u, gradually diminishing demarcation current; &, its sudden decrease during tetanus (negative
variation) ; c, subsequent positive variation on cessation of tetanus ; d, return of slowly
declining demarcation current.

it must be remembered that in consequence of stimulation the
whole mass of the muscle undergoes an explosive chemical change
associated with the passage from the state of rest to the state of
activity, which is greater in the normal than in the altered parts
of the muscle. This effect of excitation sets up a difference of
electrical potential and gives rise to the action current, which
neutralises the demarcation current, and may even exceed it
(Gotch and Sanderson).

GENEEAL PHYSIOLOGY OF MUSCLE

In studying the current of action developed by stimulation
it is best to employ an intact muscle with no current of rest,
for as this would pass in the opposite direction, it would be
unfavourable to the demonstration of the action current, which
would then seem to be only the negative variation of the current
of rest. When the galvanometer electrodes are applied to both
ends of an intact and freshly excised muscle, as in Fig. 54, A, B,
and the muscle is stimulated at C by an induction shock, the
reaction does not take place simultaneously all over the muscle,
but it is propagated, as we saw above (Fig. 16, p. 23), like a wave
from the point stimulated to the more distant points. So that
the end A of the muscle which is near the point of application of

B

Fir:. 54. Apparatus for study of diphasic-
action current.

FIG. 55. Myogram of a contraction of frog's gastro-
enrmius, in m, and simultaneous photograph of
diphasic electrical variation, e e. (A. D. Waller.)

the stimulus C will be thrown into activity first, and the end B
last. Since the active points of the muscle become galvano-
metrically negative to the inactive points, the galvanometer needle
reacts in a diphasic oscillation. In the first phase A will be
negative to B, in the second phase B will be negative to A. The
first phase coincides with the transmission of the contractile wave
from A to B ; the second phase coincides with the contraction of
B, as A begins to relax. The slower the transmission of the
wave along the muscle, the more prolonged will be the negativity
of A at the beginning, and of B at the close of the contraction.
Hence the diphasic variation of the action current is more easily
demonstrated on the frog's heart, where the systolic wave is
propagated on an average at O'l m. per second, than in skeletal
muscle, where the wave of contraction is propagated at about
1 m. per second.

Pig. 55 gives the myogram of a contraction produced in the
frog's gastrocneuiius when an induction shock is sent through

80

PHYSIOLOGY

CHAP.

the sciatic nerve, with a synchronous photograph of the diphasic
current of action. In this case the muscle was indirectly stimu-
lated, and the contractile wave started from the end-plates which
usually lie about midway in the fibres, and spread from there
towards the two ends, one electrode connected with the sulphuric

Fir;. 56. Cardiogram of spontaneous beat of frog's heart, It, and simultaneous photograph of
diphasic variation, e. (A. D. Waller.)

acid of the electrometer being applied near the middle of the
muscle, and the other, connected with the mercury, to the
tendinous end. Fig. 56 gives the spontaneous cardiogram of the
frog's heart with a synchronous photograph of the diphasic
variation, the sulphuric acid electrode being applied to the apex

FIG. 57. Apparatus for leading off diphasic action current from the muscles of the human fore-
arm. (Hermann.) To light of figure an unpolarisable bracelet electrode ; r, ', points of
stimulation of brachial plexus.

of the heart, and the mercury electrodes to the base of the
ventricle. In the first experiment there is a positive oscillation
of the electrometer at the first phase, and a negative oscillation
at the second phase, because in the first phase the end of the
muscle is positive to its middle part, which was first thrown
into contraction negative to it in the second phase. In the

GENERAL PHYSIOLOGY OF MUSCLE

81

experiment on the heart, on the contrary, there is a negative
oscillation in the first phase, which expresses the negativity of
the base to the apex at the commencement of systole, and a
positive oscillation in the second phase, which expresses the
positivity of base to apex at the close of systole and commence-
ment of diastole.

Hermann succeeded in demonstrating the diphasic variation in

I

I

Fie;. 58. Distribution of electrical potential to different parts of the human body at the moment
at which the diphasic action current of the heart arises. (A. D. Waller.) A, apex ; B, base of
ventricles ; 0, equatorial line or plane in which the electrical potential is nil ; a, a, a and
6, ft, b are the equipotential curves of A and L.

the muscles of the fore-arm of a man by stimulating the brachial
plexus in the axilla. The current was led off by special electrodes,
applied one between the middle and upper third of the fore-arm,
the other to the wrist or elbow (Fig. 57).

In the first case there is a descending-ascending, in the second
case an ascending-descending diphasic current, as shown by
arrows 1, 2 of the diagram. This diphasic action current is the
only electrical phenomenon which can be positively demonstrated
for skeletal muscle on living man.

The ascending current in the arm after a voluntary contraction
of the muscles (du Bois-Eeymond) is not a muscular action

VOL. Ill G

82

PHYSIOLOGY

CHAP.

current, but a secretory skin current, as was shown by Hermann
and Lucb singer.

A. D. Waller succeeded in demonstrating the electrical changes
that accompany contraction of cardiac muscle in intact animals
and man. He used Lippmann's capillary electrometer, by which
he was able to record not only the diphasic variation that accom-
panies the beats of the human heart, but also the simultaneous
distribution of electrical potential in the remainder of the body.
In connecting the different points of the cutaneous surface witli
the capillary electrometer, he obtained the results shown in
Fig. 58. If the two electrodes are placed on the two points A
and B, or other more remote points ab, situated at either side of
the oblique equatorial line 00, along which the potential is zero,
the mercury of the capillary moves synchronously with the beats

FIG. 59. Cardiograms of human heart, c c, and simultaneous diphasic variations. (A. D. Waller.)
Time tracing, 1 1, in T \, sec. The electrode connected with the sulphuric acid went to the
mouth, that with the mercury to the left foot.

of the heart. This does not occur if the electrodes are applied to
two points on the same side of the equatorial plane. If the
oscillations of the mercury are closely watched or photographed
it can be seen that a diphasic variation corresponds with each
systole (Fig. 59).

We have elsewhere described Gaskell's important discovery on
the cardiac muscle of the tortoise when arrested by Stanuius'
upper ligature (Vol. I. p. 332). He found on leading off a
demarcation current excited by injury of the surface to the
galvanometer, and then exciting a branch of the vagus, that the
variation was not negative, but positive, i.e. the demarcation
current was reinforced, not weakened. From this observation he
concluded that the vagus has an anabolic action on the heart, as
opposed to the katabolic action of the sympathetic. As dis-
integrative explosive stimuli produce a negative potential in the
active segments of the tissue as compared with the non-active, so
integrative processes which spread as a wave of inhibition, after

GENERAL PHYSIOLOGY OF MUSCLE

83

stimulation of the diastolic nerves, produce a positive potential in
the inhibited segments in relation to those at rest.

At the International Congress of Physiology in Turin (1901)
Fano communicated another interesting observation on the tortoise
heart, which agrees well with Gaskell's theory, and also helps to
interpret the diphasic character of the current of action. If while
the photograph of the normal diphasic current or electrical beat
of the heart is being recorded the vagus is excited by a slight
stimulus, which does not arrest the heart completely but only

FIG. 60. Electrical beat of right auricle of tortoise heart, and its reversal during excitation of
vagus. (Fano.) Ad, photograph of beat of right auricle ; Pe, photograph of its electrical beat
or diphasic variation ; Vd, line showing duration of gentle stimulation of right vagus.

slows down the beat and diminishes the amplitude of the systole,
there is usually a profound alteration in the form of the photo-
graph, which consists in the marked diminution, sometimes the
almost total disappearance, of the negative phase, with a simul-
taneous increase in the second or positive phase. There is, in fact,
a complete reversal of the electrical beat of the heart (Fig. 60).

The same sometimes occurs after, instead of during, the
stimulation of the vagus, when the systolic wave is gradually
increasing towards its normal.

This reversal of the electrical beat during or after vagus
excitation depends on the inhibitory or diastolic action of this
nerve, since it does not occur after the application of atropine to
the heart.

84 PHYSIOLOGY CHAP.

According to Fano the reversal of the diphasic curve proves
that it does not depend solely, as is usually assumed, on a wave of
negativity spreading from the near points to those more remote
from the stimulus, but is due to a wave of positivity immediately
following the former. In the normal electrical tracing, too, the
relations between the two phases, negative and positive, vary
the first predominating in some cases, the second in others. It is
not improbable that these different types of the electrical curve
depend on the relations between the katabolic and anabolic
processes of cardiac muscle, and that stimulation of the vagus
exaggerates the latter.

XII. The innumerable physical, chemical, and histological
researches 011 muscle which have thus been briefly summarised
have yielded an extraordinary wealth of physiological data, from
which some solution of the difficult problem of the origin of
muscular force may be constructed some hypothesis able to
explain the internal mechanism on which the contraction and
relaxation of the muscle depends, or more generally, its capacity
for passing suddenly from the state of comparative rest to that of
activity, and vice versa.

An exhaustive theory of the mechanism of muscular excita-
bility must cover a series of difficult problems, among which are
the following :

(a) How is the excitation of the nerve end-plate transmitted
to the muscle fibre ?

(6) On what does the sudden contraction (isotonic) and elastic
tension (isometric) depend ?

(c) What process gives rise to the sudden relaxation of the
muscle, i.e. the cessation of the elastic tension on which shortening
depends and the production of the elastic tension to which lengthen-
ing is due ?

(rf) How are the excitatory impulse and the wave of contraction
and relaxation conducted along the muscle fibre ?

Speaking generally, it may be said that these and other
problems have at present received no proper scientific solution,
so we must confine ourselves to a critical investigation of the
principal hypotheses that have been put forward.

It is now universally agreed that the physiological combustion
of certain chemical constituents of the tissue which are bound up
with the protein molecule or intimately connected with it, are the
prime source of muscular energy, and that the transformation of
potential chemical energy into mechanical energy, either in the
form of elastic tension or in that of external work, is performed
according to the law of the conservation of energy. There is a
general tendency to consider the chemical state of the resting
muscle substance as one of unstable equilibrium, in which the
atoms of oxygen and the groups of combustible atoms which form

i GENERAL PHYSIOLOGY OF MUSCLE 85

part of the great protein molecule are so close together that a very
weak stimulus suffices to bring about an explosion, in which most,
of the oxygen atoms combine with atoms of carbon and hydrogen
to form carbonic acid and water. It is more difficult to explain
why the explosion is confined to a small part of the explosive
mass instead of discharging it completely, as in the case of a
loaded tire-arm. But the universally accepted principle is that
the potential chemical energy of the muscle substance is the primary
source of muscular energy in all its manifestations.

How does the explosive reaction of the muscle produce its
shortening or elastic tension ? The answers to this question are
by no means unanimous, and physiologists differ, according as the
one or the other sign of muscular activity receives the more con-
sideration from them.

We need not discuss the earlier hypotheses which are collected
in the classical text-books of Haller (1792) and Johannes Miiller
(1844), but may confine ourselves to the later and more probable
theories, commencing with that of E. Weber.

Schwann had already suggested that muscle acts by elastic
forces, but Weber was the first to clear up the obscurity that
prevailed as to contractility and elasticity in his classic work on
Muskelphysik, published 1846. According to the theory formulated
by Eontana elasticity is an inherent physical property which tends
to preserve the natural form of the muscle, and thus acts in the
contrary sense to contractility, i.e. it limits the contraction and
brings the muscle back to equilibrium as soon as the active state
ceases. But Weber pointed out that the natural form of the
muscle which depends on its elastic equilibrium is not constant,
but rnrii-s freely with the external and internal conditions of the
life of the muscle. As a metal rod lengthens when heated, and
shortens again on cooling, because different degrees of temperature
alter the equilibrium of its atoms and produce a reaction of its
elastic forces which expand in the first case and contract in the
second, so the molecular arrangement differs in the muscle accord-
ing as it is at rest or excited, and its external form differs
accordingly. The active muscle is short and thick, the inactive
long and thin, and in suddenly passing from one state to the
other the muscle contracts or expands, not against the elasticity,
but by an elastic reaction in order to assume the natural form of
equilibrium which corresponds to its active or inactive state. On
Weber's view the extension of a muscle by a weight is not com-
parable with the shortening due to a stimulus : the weight stretches
the muscle against its elastic forces ; the stimulus, on the contrary,
causes a sudden alteration in its chemical equilibrium, and therefore
in the elastic forces, which are the immediate cause of contraction.

Weber was the first who submitted the elasticity of muscle,
and the changes it undergoes in various conditions, to strict

86

PHYSIOLOGY

CHAP.

investigations. He found that muscle has a low but perfect
elasticity ; it can be readily extended by small weights, but
promptly returns, under normal conditions, to its initial length,
when the extending force ceases to act on it. He recognised
that, unlike inorganic, but like certain organic substances, the
elongation of the muscle is not proportional to the weight, and
becomes less so as the load increases ; so that the curve of extensi-
bility obtained when the weights are plotted on the abscissae,
and the elongations taken as ordinates, is not a straight line but
a curve, which Wertheim subsequently recognised as a hyberbola.
Weber compared the elasticity of the resting hyoglossus
muscle of the frog with that of the same frog 'when tetanised, by

m

FIG. 61. Diagram to show elasticity of muscle in rest and in activity. A B, length of unloaded
resting muscle ; A b, same muscle in activity. A' B', A" B", length of resting muscle loaded
with regularly increasing weights ; A' b', A" b", length reached by active muscle loaded with
same weights. The line B B' B" . . . y x gives the elasticity curve of resting, b If b" . . . y, of
contracting muscle.

comparing the curves of extensibility to regularly increasing
weights during rest and in tetanus. He found that the active
muscle is less elastic, i.e. more extensible than the inactive
(Fig. 61). '^Therefore the extensibility curve of active muscle
falls more rapidly than that of resting muscle. With progressive
increase of load a point is reached at which the two curves meet.
This happens when the weight is sufficiently great to hinder
contraction, i.e. when the elastic tension in the muscle due to
the weight is in complete equilibrium with the opposite elastic
tension which is actively set up by the stimulus. If, after
reaching this point, the muscle is further overloaded and then
stimulated, there will not only be no contraction, but, on the
contrary, a certain degree of elongation due to the decrease in
muscular elasticity after stimulation, so that the elasticity curve
of the active state crosses the elasticity curve of the resting state
(Weber). But this has not been confirmed by later workers, who

i GENEEAL PHYSIOLOGY OF MUSCLE 87

hold with Tick that the two curves tend to converge asymptotic-
ally without meeting.

These studies of Weber on the elasticity curve of resting and
active muscle were subsequently confirmed and extended with
better methods by Marey (1868) and Blix (1874) on excised frog
muscles ; by Bonders and Van Mansvelt (1863) and by Chauveau
and Laulanie (1899) on human muscles.

Other work on muscular elasticity has shown that it varies
under the influence of different toxic and medicinal substances.
In this connection Eossbach's and Anrep's observations (1880) on
the frog are striking. These showed that the changes which the
elasticity of muscles loaded with low weights (2 grms.) undergoes
by the action of certain poisons may be utilised as a good method
of toxicological analysis. They found that curare and cocaine,
which paralyse the motor or sensory nerve -endings, produce
elongation of the muscle (lowering of tone) without perceptibly
affecting elasticity ; pliysostigmine, in addition, causes an increase
of elasticity by acting on the contractile substance ; digitaline
causes elongation of the muscle and increase of its elasticity,
independent of the action of the nerves, i.e. by direct action on
the contractile substance ; veratrin (injected in doses of 1-5 mgrms.)
produces first elongation, then contracture of the muscle, inde-
pendently of the nerve, and in both stages depresses the elasticity
and makes it imperfect ; lastly, potassium salts shorten the muscle
and simultaneously increase its excitability, while sodium salts in
the same dose and same concentration produce no visible change
either in the length or the elasticity of the muscle.

Progressive muscular fatigue, too, alters elasticity in the same
way as poisons, raising it in the first stage, and subsequently
decreasing it in proportion as contracture sets in. After death,
when rigor mortis begins, muscle is highly elastic, that is, but little
extensible, and its elasticity simultaneously diminishes, for when
the traction is removed it no longer returns to its initial length.

All these and other experimental observations confirm Weber's
theory, and show that elasticity is not a constant physical property
of the muscle, but is perhaps the most variable and least stable of
all its properties.

But Weber's assertion that the contraction of the muscle
is only the result of a sudden change in its elasticity, due to
the chemical changes produced by excitation, is no more than
a schematic restatement, whatever its theoretical value. Its
simplicity, however, signalises a considerable advance in mechanical
notions of muscular activity ; for, by excluding Fontana's theory,
which assumes contractility and elasticity to be two opposite or
antagonistic properties, it leads on logically to the formulation of
a more exact idea, harmonising better with the facts, of the process
by which relaxation follows on the contraction of the muscle.

PHYSIOLOGY CHAP.

By many authors muscular relaxation has been, and still is,
regarded as a simple effect of the cessation of contraction. This
is Fontana's theory that contraction throws the muscle into
elastic tension, so that when the contraction ceases the muscle
lengthens owing to its elasticity. But if contraction is not con-
trary to elasticity, it is plain that the muscle can only relax by a
chemical process which is opposed to that of contraction, owing
to which its form changes in a direction opposite to that of the
contraction phase. As early as 1874 \\e pointed out this logical
consequence of Weber's theory, and added further, " If the con-
traction, which is due to a fresh molecular arrangement to which
a shorter natural form of the muscle corresponds, be termed actin ,
we are equally justified in calling the elongation of the muscle
active, since it too is associated with a new molecular equilibrium
which accompanies the process of relaxation." Years after (1887)
Gaskell made the important discovery that electrical phenomena
accompany the inhibition of cardiac muscle by the vagus, and
disproved the hypothesis that the contraction of this muscle is
due to kat<tl>/ir and its relaxation to un<tl>uli<: chemical processes
(Vol. I. p. 332). More recently Fano (1901) extended this theory
(see p. 83), which in our opinion applies not merely to the heart,
but to all other muscular tissues.

No special advance upon Weber's hypothesis has been made
by the physiologists who refer the transformation of the potential
chemical energy developed in muscle after excitation into
mechanical energy, to the direct effect of a special form of
chemical alteration. Pfliiger, in his famous memoir, 1 accepts
this theory of the origin of muscular energy without enlarging
on it. Pick 2 expresses himself more clearly, and states that " the
chemical forces of attraction must a 2'iori be more or less pre-
disposed in the direction of the mechanical action which is to
follow, and participate directly in the same." Chauveau 3 remarks
that "muscular contraction is a derivative of chemical work."

This theory seems no less artificial than that of Weber.
According to Engelmann, moreover, it is irreconcilable with the
fact that during contraction an infinitely small portion of the
muscle substance is chemically active as compared with the total
mass of the muscle which remains passive. He points out that
the muscle contains 70-80 per cent water, and that the greater
part of the 20-30 per cent of the organic substances and minerals
of which it is composed take no chemical part in the process. Of
the carbo-hydrate group associated with the protein molecule,
which gives rise during excitation to the formation of C0 2 and
H.,0, only small proportions are simultaneously affected. On

1 Ueber die pJiysiologische Verbrennung in den lebcndif/en Organismen (1875).

2 Mechanische Arbeit und Wcirmeentwickluny lei der Muskcltatiykeit (1882).

3 Publications on Muscular Work and Energy (1891).

i GENEKAL PHYSIOLOGY OF MUSCLE 89

Engelmanu's calculation the source of the energy necessary to
produce a contraction amounts to about four uiillionths of the
entire mass of the muscle. It is inconceivable to Engelmann
that the movement of the relatively enormous mass of inert
substance should be effected by the direct chemical attraction of
this minimal fraction of active substance, no matter what the
natural form or magnitude of the vibrations or the particular
arrangement of the few active molecules. He further objects that
the hypothesis of direct chemical attraction does not take into
account the tibrillary structure of the contractile apparatus, the
differentiation of the fibrils into isotropous and anisotropous
portions, the opposite variations in volume, form, refrangibility,
extensibility, etc., of these parts, and a number of other facts
which are in more or less open contradiction to it.

Engelmaun holds the thermodynamic theory propounded by
J. K. Mayer (1845), according to which the muscle is compared
with a steam engine which transforms the heat evolved in com-
bustion into mechanical work, to be far more probable.

In reply to Solway's criticism that the muscle works more
economically than any engine, Engelmann remarks that the
muscle is an apparatus whose combustible materials burn in
direct contact with the parts that perform the mechanical work,
so that it works under far more favourable conditions than Watt's
thermodynamic machine.

Another, apparently more serious, objection to the theory of
the thermal origin of muscular energy put forward by Fick (1882),
and repeated by Gad, is that it is irreconcilable with the second
of Glausius' fundamental laws of thermodynamics. According to
this law, heat can only perform work when it passes from a warmer
body (A} to a cooler body (B}, and its potential is proportional to
the difference of temperature between A and B. So that before
we can assume that muscle works like a thermodynamic machine,
we must first prove that there is in it a marked difference between
A and B, or between the source of heat and the surrounding
medium.

Fick held that this is not the case with muscle, which only
exhibits slight differences of temperature, proving conclusively
that it does not act as a thermodynamic motor.

Engelmann replied to this objection that Pflliger had already
pointed out in 1875 that body-temperature is only an arithmetic
mean which comprises innumerable very different temperatures
at innumerable different points of an organ, and that the molecules
formed in physiological combustion have, at least at the moment
of formation, an extremely high temperature, which they lose at
once by giving off heat to the cooler matter that surrounds them.

Pfliiger's conclusions in so far as muscle is concerned are con-
firmed, according to Engelmann, by the fact that the combustion

90

PHYSIOLOGY

CHAP.

of a comparatively small number of molecules suffices to produce
contraction, which can only be explained on the assumption that
at the moment of oxidation they acquire a temperature so high
that their minute size and low number are perhaps the only reason

why they do not appear
b incandescent. The rise of

temperature in the total
mass of the muscle, even
granting that it only
amounts to O'OOl C. for
one contraction, is when we
consider the great specific
heat of the muscle sub-
stance--i.e. the large
quantity of heat necessary
to raise its temperature-
conceivable only on the
supposition that each heat-
producing molecule has at
its birth an enormous tem-
perature in comparison
with the immense mass of
substance able to conduct
and permeable to heat, by
which it is surrounded.
In this assumption it is
implicitly recognised that
the muscle presents to a
high degree the funda-
mental condition for the
conversion of heat into
mechanical work. This
conversion according to
Engelmann is effected by
the anisotropous substance
which forms the positive,
doubly refracting elements
with one axis parallel to
the direction of contraction
which he terms inotagmata.
He supposes that in mus-
cular excitation the inotag-
mata, warmed by the heat

generated in the thermogenic molecules, swell up and shorten,
owing to imbibition of the more fluid isotropous substance that
surrounds them. This alternate swelling and shortening of the
inotagmata arranged in longitudinal series results in the whole

Fio. 62. Engelmann's apparatus for imitating the con-
traction and relaxation of muscle on a violin string.
A string 5 cm. long soaked in water is fixed by its
lower end a to a rigid support b, and connected above
by a strong silk thread to the short arm of the lever
H, which moves round the axis c. By means of the
movable weights d and d' the string can be thrown
into the desired tension, and the position of the lever
regulated by screw e. The string is surrounded by a
thin platinum wire /, which turns spirally round it,
and is soldered at the end to thick copper wires con-
nected with the poles of two Grove or Bunsen cells.
The string, platinum wire, and support are placed in
a wide low beaker filled with water, into which a
thermometer is introduced. When stretched by at
weight of 25-50 grms. the string after a few minutes
ceases to expand, and the end of the lever remains
steady. If a current is then passed through the
spiral for a few seconds, the lever rises at once with
great rapidity, and on breaking the circuit it returns
almost to its original level, while the thermometer is
either stationary or shows a hardly appreciable rise
of temperature.

i GENERAL PHYSIOLOGY OF MUSCLE 91

muscle in the formation and propagation of the contraction wave,
by which a part of the heat is transformed into mechanical work.

To strengthen this ingenious hypothesis Engelmann devised
an experiment, in which the contraction of the muscle, owing to the
swelling and shortening of doubly refracting particles in the long
axis in accordance with the therrnodynamic law, is imitated on
a violin string. He started from the fact that the property of
contracting in heat is not peculiar to muscle, but is inherent in
different degrees in all living tissues, and even in other organic
substances that contain a doubly refracting substance, e.g. a violin
string or specially prepared string of non- vulcanised indiarubber.
Engelmann's model is shown in Fig. 62. He proved that under
definite experimental conditions a moistened violin string, thrown
into tension by a weight, thickens and shortens and does a certain
amount of work when heated by a coil of platinum wire traversed
by an electrical current, and lengthens again on cooling when
the current is interrupted. In this experiment the violin string
which contains the doubly refracting substance represents the
inotagma or anisotropous element of the muscle ; the vessel
filled with water the aqueous, isotropous muscle substance; the
platinum coil the thermogenic molecules; the closure of the
galvanic current the excitation of the inotagrnata which gives
rise to contraction ; the opening of the circuit the cessation of
excitation from which relaxation results. Nothing but the
transmission of excitation along the series of inotagmata which
causes the transmission of the contractile wave is absent in this
ingenious model.

On recording the contractions and subsequent elongations of
the violin string on a revolving drum, Engelmann obtained
chordogra/ns which resemble myograms to a surprising degree
(Fig. 63). This proves that they depend on a cyclic process as
after the warming which leads to shortening, the string lengthens
and returns (at least approximately) to its initial state on cooling.

It may be objected to Engelmann's theory that it takes no
account of the electrical phenomena that occur in the muscle.
Before meeting this objection it is well to consider the different
hypotheses that have been put forward in favour of an electrical
origin of muscular energy.

Prevost and Dumas, Meyer and Amici compared the muscle,
owing to its striated structure, with a Volta's pile, which also
consists of discs. Voit, starting from the negative variation,
assumes that the muscle current diminishes in contraction, because
a part of the electricity developed in the muscle is transformed
into movement. Krause and Kiihne compared the motor end-
plates to the electrical organs of Torpedo, and the action of nerve
on muscle to the discharge of a Leyden jar. According to du
Bois-Reymond, on the contrary, it is the wave of negative

92

PHYSIOLOGY

CHAP.

variation (i.e. the current of action) which causes the transmission
of excitation from the nerve to the muscle, and the spread of the
contraction in the latter. According to d'Arsonval the thermal
phenomenon and mechanical work of the muscle are the effects of
the electrical phenomenon ; the chemical energy is transformed

FIG. 63. Chordograms obtained by Engelmann with the apparatus described in preceding figui '<',
with the violin string loaded with 50 grins, and a lever that magnified fifty times. /, At a a
strong current was passed through the spiral for 2-3 sees. ; at b a weak current for a longer
time, a shows a shorter latent period, a sharper and more rapid rise, and a steeper descent
than b. II and ///, Uniform strength of current, but the temperature of the water was 35 C.
in //, 45 C. in ///. IV, After removing the water the warmth of the spiral was conveyed to
the string by the air which was at a temperature of 1S C. At a a stronger current was passed
than at b. As the cooling of the string had been accelerated, it expanded more rapidly.
]', The curve falls still more rapidly, owing to accelerated cooling of the string due to a
stronger current of air. Time marking = 0'5 sec.

into electrical energy, and this again into thermal and mechanical
energy.

All these hypotheses are too vague and indefinite, and they
neglect certain well-established experimental facts.

G. E. Miiller of Gottingen (1889) put forward a pyro-electrical
theory of the origin of muscular force, which, although partially

i GENERAL PHYSIOLOGY OF MUSCLE 93

founded on arbitrary hypotheses, is certainly more definite. He
attributes the contraction of the muscle to the electrical attraction
and repulsion of the doubly refracting crystalloids, the poles of
which undergo a change of electrical state owing to the heat that
is generated. On this theory the muscle shortens as its tempera-
ture rises ; and when the temperature of the crystalloids becomes
constant it lengthens, because the electrical changes subside.
Engelmann's experiments show, however, that the length of the
muscle does not depend on the rate at which the temperature
rises, but on the absolute temperature present at the moment in
the doubly refracting discs. They further show that when the
temperature in these discs is constant, the muscle does not
lengthen, but remains indefinitely shortened.

Certain well-authenticated facts prove that there is a direct
association between the electrical and mechanical phenomena in
muscle. As long ago as 1855 Helmholtz showed by an exact
chronometric method that the electrical wave precedes the
mechanical in skeletal muscle. The same fact was demonstrated
in 1856 by Kiilliker and H. Miiller by the experiment of secondary
contraction, and by Bernstein with his differential rheotome. In
the nerve-fibres, in which no sign of mechanical phenomena can
be detected, and little heat development or chemical activity,
electrical phenomena similar to those of the muscle occur, which
proves them to be quite independent of the phenomena of con-
tractility. Certain important researches of Biederniann (1880)
favour the same conclusion, since they prove that frog muscles
which have lost their power of contracting by imbibition of water
or the effect of ether vapour preserve their electrical excitability
and capacity for conducting intact. From this Biederrnanu
concludes that the capability of actively changing its form at the
seat of direct stimulation is not an indispensable condition of the
excitation of muscle.

The independence of the electrical phenomena from muscular
contractility is also demonstrated by the fact that the majority
of electric and pseudo-electric organs develop at the expense of
the striated muscle fibres, and that during this development,
according to Ewart, contractility is gradually lost, while the
electromotive function develops in proportion. According to
Baglioni (1906) the chemical composition of the electrical organs
differs fundamentally from that of the muscles.

On the strength of all these facts Engelmann founded his
hypothesis that in muscle the particles on which the development
of the electrical phenomena depends are quite distinct from those
which supply heat by combustion (thermogenic], and those which
subserve mechanical work (inogenic particles').

The first are solely concerned with excitation and its con-
duction and propagation, as Hermann also concluded from the

94 PHYSIOLOGY CHAP.

fact that the wave of negativity at the point of the muscle
stimulated appears hefore and precedes the wave of contraction.
These particles probably lie chiefly in the isotropous layers which
take no active part in contraction. The thermogenic particles,
on the contrary, are in close contiguity with the inogcnic particles,
which are represented by the doubly refracting elements of the
anisotropous layers, on which the specific function of the muscle,
i.e. contraction, depends. According to Engelinann's theory this
is due to the conversion of heat into work.

Verworn (1895), starting from a hypothesis put forward by
Berthold (1886), has formulated another theory of contraction,
which includes all the movements of all forms of living matter,
from amoeba to muscle. On this theory movement is due to
changes in the surface tension of the histological elements of
which the muscle fibrils consist (isotropous and anisotropous
discs) ; these changes in surface tension are due, according to
Verworn, to chemical processes.

A similar theory, by which muscular contraction is referred to
changes of surface tension, has been put forward by other physio-
logists, as d'Arsonval, Imbert, Bernstein, Jensen, and Galeotti.
Galeotti holds (1906) that the changes in surface tension of the
different muscle elements are due to electrochemical phenomena.

None of these theories, however, take into account the whole
of the active changes concomitant with muscular activity.

BIBLIOGRAPHY

Structure of Muscle and its Visible Changes during Activity :

ENGELMANN. Pfliiger's Archiv, xi., 1875, xxv., 1881.

RANVIER. Lemons d'anatoniie gunerale sur le systeme musculaire. Paris, 1880.

ROLLET. Denkschr. der AViener Akademie, xlix. and li., 1885, Iviii. 1891.

Mechanical, Thermal, and Electrical Activity of Muscle:

HERMANN. Handbuch der Physiologic, i. 1879.

CH. RICHET. Physiologic des muscles et des nerfs. Paris, 1882.

BIEDERMANN. Elektrophysiologie. Jena, 1895. (English translation by F. A.

Welby, 1896.) Ergebnisse d. Physiol., II. Part 2, 1903.
A. FICK. Mechan. Arbeit und Warmeentwickelung bei der Muskeltatigkeit.

Internat. wiss. Bibliothek, 1882.

ROSENTHAL. Allgemeine Physiol. der Muskeln und Nerven. Leipzig, 1899.
W. EINTHOVEN. Pfliiger's Archiv, lx., 1905 ; Arch, intern, d. Physiol., iv. 1906.
I. BERNSTEIN. Pfliiger's Archiv, Ixxxi., 1901.
G. GALEOTTI. Zeitschr. f. allg. Physiol., vi., 1906.
HOFMANN. Pfliiger's Arch., xciii., xcv., ciii., 1902-4.
BORUTTAU. Pfliiger's Arch., cv., 1904.
0. FRANK. Thermodynamik des Muskels. Ergeb. d. Physiol., III. Part 2, 1904.

Chemical Composition and Metabolism of Muscle :

HALLIBURTON. Text-book of Chemical Physiology and Pathology, 1891.

NEUMEISTER. Lehrbuch der physiologischen Chemie, 1895.

H. WINTERSTEIN. Pfliiger's Archiv, cxx., 1907.

v. FURTH. Ergeb. d. Physiol., I. Part 1, 1902 ; II. Part 1, 1903.

i GENEKAL PHYSIOLOGY OF MUSCLE 95

Ergograph work :

A. Mosso. Arch. ital. de biologic, xiii., 1890.

A. MAGGIORA. Ibidem.

P. W. LOMBARD. Ibidem.

PATUIZI. Archives ital. de biologic, 1892, 1893, 1901.

Z. TREVES. Ibidem, xxix., xxx., xxxi., 1898-1900.

F. SCHENCK. Pfliiger's Archiv, Ixxxii., 1900.

General Theory of the Genesis of Muscular Force, in addition to the treatise by
Hermann, see :

TH. W. ENGELMANN. Snr 1'origine de la force mnsculaire. Archives neerlandaises,

xxvii., 1893.

VERWORN. Allg. Physiologie, 4th Ed. Jena, 1903.
JENSEN. Pfliiger's Arch., Ixxx. , 1900.
BERNSTEIN. Pfliiger's Arch., Ixxxi., 1901 ; cv., 1905. Die Krafte der Bevvegung

in der lebenden Substanz. Brunswick, 1902.
GALEOTTI. Zeitschr. f. allg. Physiol., vi. , 1906.

Recent English Literature :

MAoDoNALD. The Structure and Function of Striated Muscle. Quart. Journ. of
Experiment. Physiol., 1909, ii. 5.

LANGLEY. On the Contraction of Muscle, chiefly in relation to the Presence of
"Receptive" Substances. Journ. of Physiol., 1907, xxxvi., 347; 1908,
xxxvii. 165 and 285 ; 1909, xxxix. 235.

KEITH LUCAS. On the Refractory Period of Muscle and Nerve. Journ. of Physiol.,

1909, xxxix. 331.

KEITH LUCAS. All-or-None Contraction of the Amphibian Skeletal Muscle Fibre.

Journ. of Physiol., 1908, xxxviii. 113.
KEITH LUCAS. On the Relation between the Electric Disturbance in Muscle and

the Propagation of the Excited State. Journ. of Physiol., 1909, xxxix. 207.
A. V. HILL. The Absolute Mechanical Efficiency of the Contraction of an Isolated

Muscle. Journ. of Physiol., 1913, xlvi. 435.
BANCROFT.. The Electrical Stimulation of Muscle as dependent upon the Relative

Concentration of the Calcium Ions. Journ. of Physiol., 1909, xxxix. 1.
LILLIE. The Relation of Ions to Contractile Processes. Amer. Journ. of

Physiol., 1909, xxiv. 459.
KEITH LUCAS. Summation of Adequate Stimuli in Muscle and Nerve. Journ. of

Physiol., 1910, xxxix. 461.

MINES. Summation of Contractions. Journ. of Physiol., 1913, xlvi. 1.
KEITH LUCAS. On the Transference of the Propagated Disturbance from Nerve to

Muscle, with special reference to the apparent Inhibition described by

Wedensky. Journ. of Physiol., 1911, xliii. 46.
MAcDouoALL. Mental and Muscular Fatigue. Reports, 80th Meeting, British

Assoc., 1911, 292.
BURRIDGE. An Inquiry into some Chemical Factors of Fatigue. Journ. of Physiol.,

1910, xli. 285.

KEITH LUCAS. On the Recovery of Muscle and Nerve after the Passage of a

Propagated Disturbance. Journ. of Physiol., 1910, xli. 368.
A. V. HILL. The Energy degraded in the Recovery Processes of Stimulated Muscle.

Journ. of Physiol., 1913, xlvi. 28.
HILL. The Heat produced in Contraction and Muscular Tone. Journ. of Physio!.,

1910, xl. 389.
MEIGS. Heat Coagulation of Smooth Muscle. Amer. Journ. of Physiol,, 1909,

xxiv. 1.

CHAPTER II

MECHANICS OF LOCOMOTOR APPARATUS

CONTENTS. 1. General remarks on the structure of the bones and their
articulations. 2. Form, attachments, and mechanics of muscles in relation to
bones. 3. Line and centre of gravity of the body in different postures.
4. Mechanics of equilibration in different postures. 5. Movements of the body
in walking. 6. Movements of the body in running. 7. Movements of the body
in swimming. Bibliography.

THE muscles are the active organs the bones, cartilages, ligaments,
etc., which build up the skeleton to which the muscles are attached
represent the passive organs of a highly complex system to which
Marey correctly applied the term animal machine. In industrial
machines also it is usual to distinguish between the active parts
which are the seat of the production or development of the energy
destined to be transformed into useful work, and the passive parts
which transmit it, and which consist as in the animal machine
of levers, pulleys, inclined planes, pumps, etc.

Our principal task in this chapter will be to study the complex
motor apparatus, consisting of an elaborate system of skeletal
muscles, on the co-ordinated action of which depend the loco-
motor movements, i.e. the different forms of displacement of the
body as a whole. These are distinguished from the partial move-
ments or displacements of the limbs, by which the relations of the
different mobile parts of the body are altered. In the former the
base of the body is displaced ; in the latter it may remain immobile.

In the study of these motor functions the physiologist's task is
to a large extent linked with that of the anatomist. It is, in fact,
impossible to form a clear conception of the mechanism of a move-
ment carried out by the active participation of many different
muscles without first knowing the points of attachment of each
muscle as well as the form and articulation of the bones, which act
passively as the levers. But while the anatomist is occupied more
particularly with the mechanical action of each muscular unit, the
physiologist supplements this by the synthetic study of the co-
ordination of the various muscular forces which combine in the
accomplishment of each separate motor act.

96

CHAP, ii MECHANICS OF LOCOMOTOR APPARATUS 97

I. Historical investigation into the action of the muscles on
the skeleton, aiid the mechanism of posture and locomotion, com-
menced with Borelli's classic De motu animalium, published in
1680. The writings of Barthez (1798) and of Gerdy (1832) con-
tain no real advance on the work of Borelli. Poisson (1833)
first attempted to calculate the work which a man performs in
walking. Eeal progress in this direction was made in the classical
publication of W. and E. Weber, Die Mechanik der menschlichen
Gehwerkzeuge, which appeared in 1836. The second half of the
nineteenth century brought many anatomical studies on the form
of the articular surfaces, and the significance of the ligaments, the
articular capsules, fascia, etc., more especially from Henke, Langer,
and H. Meyer. Among standard works Duchenne's Pliysiologie
des mouvements deserves mention, owing to the positive character
of the research and the accuracy of the descriptions, although it
does not compare in originality with the epoch-making researches
of Borelli and the Webers. After the application of the graphic
methods, more particularly by Marey and Carlet (1872), the study
of locomotion was carried to greater perfection. Still greater
advances were made after instantaneous photography had been
applied to the study of the successive phases of movement in man
and other animals, first by Muybridge, subsequently by Marey
(1882) and his successors with more perfect kinernatographic
methods.

As a preliminary we require a general notion of the structure
of the bones, the passive organs, and the action of the muscles,
which are the active organs of movement.

Taken as a whole, the bones may be regarded as rigid organs
in comparison with the forces which act on them during the
movements of the body. The ribs are an exception to this rule,
since (Vol. I. p. 407) they undergo a slight degree of flexion and
torsion round their long axis during thoracic inspiration.

To the student of animal mechanics the histological structure
of the bones, which is more particularly of morphological interest,
appeals less than their architecture, which is such as to combine
the greatest amount of rigidity with the greatest possible lightness,
as first pointed out by H. Meyer in 1867. All the long bones
are hollow, which does not lessen their rigidity, since a hollow
cylinder presents the same resistance to pressure and traction as a
solid cylinder of the same 'diameter and identical material. The
marrow which fills the bony cavity contributes to the comparatively
light weight of bone, since it is rich in fat. The trabeculae which
constitute the spongy part of the extremities of the long bones are
so arranged as to support the surfaces destined to bear the greatest
pressure.

The application of this mechanical principle is to be found in
all bones, but it is specially obvious in the femurs.

VOL. in H

98 PHYSIOLOGY CHAP.

The head of the femur is united obliquely by its neck to the
shaft of the bone, at an angle which usually diminishes during the
period of growth under the influence of the weight of the body, and
varies in the adult from 110 to 140. In the shaft of the femur,
which is by far the larger portion, the compact bone forms a tube
with thick, solid walls, filled with marrow which is largely fat.

Fin. M. Section through the end of a femur. (Zaaijnr.)

But at the upper end of the femur, including the head, neck,
and trochanters, in consequence of the obliquity of the head to the
longitudinal axis of the bone the conditions for obtaining the
necessary strength become extremely complex, since the compact
substance of the tube extends (Fig. 64) into a system of lamellae
arranged fanlike so as to support the surfaces destined to bear the
greatest pressure.

It should be noted that when from pathological conditions, for

ii MECHANICS OF LOCOMOTOE APPARATUS 99

instance, articular anchylosis, and after amputations or resections,
the mechanical requirements to which the bones naturally conform
are changed, the systems of lamellae of the spongy substance alter
considerably.

The enlargements usually presented at the ends of the long
bones, the ridges, tuberosities, and spines are for the purpose of
giving the muscles large and adequate surfaces of attachment.

The bones of which the skeleton is made up are united rigidly
together, or in such a manner as to permit a more or less extensive
displacement and movement on each other. The bones united by
sutures (sytiarthroses), as those which compose the cranium, are
perfectly immobile ; those united by means of cartilages (synchon-
droses) are semi-mobile, or admit of very limited movements. Such
are the syrnphyses of the pubis and innominate bone and the
synchondroses of the ribs and vertebrae. Finally, the bones
united by articular capsules are semi- mobile (ampliiartlirose},
mobile (artlirose), or very mobile (diarthrose*), according to the
form of the articulation. The articulations of the carpal and
tarsal bones belong to the first category ; the elbow, knee, and ankle
to the second ; the shoulder and hip-joints to the last.

In all these true articulations the heads of the bone are covered
with a layer of cartilage, to the edges of which the fibrous articular
capsule, which connects the two bones and surrounds the articular
cavity, is attached. Each capsule is covered internally by a pave-
ment epithelium which extends over the joint cartilage, and
secretes the synovia, a colourless, transparent, viscous fluid, formed
by the mucous metamorphosis of the epithelium, which is destined
to lubricate the articular surfaces and enable them to move easily
one upon the other.

Externally, fibro-elastic ligaments strengthen the capsule, and
prevent or limit to a greater or less extent the movements of the
articular heads.

From the physiological point of view, articulations can be
subdivided into the classes proposed by A. Fick. The first
comprises the synchondroses (ribs and vertebrae) and the
arnphiarthroses (joints between the tarsus and carpus). In these
articulations the bony surfaces never change their relations,
and can only be fixed or moved to a limited extent by the
elasticity of the interpolated fibro-cartilages, or pericapsular liga-
ments. The bones thus united are in stable equilibrium, to which
they return immediately when any external cause which has
displaced them from their normal position ceases to act. The
arthroses and diarthroses form the second class, as the articular
surfaces change their relations while moving. The bones thus
articulated are in unstable equilibrium, that is, they remain in
whatever position they are placed by external causes, until this is
removed by some force working in the opposite direction. A

100 PHYSIOLOGY CHAP.

comparatively slight force is consequently able to produce move-
ments of the bones.

In articulations of the second class (arthroses and diarthroses),
which more especially concern us, the bones have articular heads
which are approximately cylindrical or spherical in shape. The
former constitute the hinge joints which move in a single axis ;
one of the articular surfaces is concave, the other convex. Both
are shaped like a section of a cylinder, or more exactly like a cone,
an ovoid, or an ellipse. The articulations of the elbow, knee,
and ankle belong to this class. In the second class of articula-
tions with round heads, the bones can rotate round a single axis,
as in the humero-radial and the atlanto-epistropheal joints, or
round many axes, as in the ball-and-socket joints, represented by
the scapulo-humeral and the hip-joints.

From these articulations with one or many axes, we must
distinguish the articulations with two axes at right angles to
one another, represented by the saddle joints and the con-
dyloid joints. The articular saddle surfaces are convex in one
direction and concave in the plane vertical to it. Such is
the joint between the metacarpal bone of the thumb and the
trapezium bone of the carpus, which permits not only of flexion
and extension, but also of adduction and abduction in two almost
perpendicular axes. The joint between the radius and the bones
of the carpus, which permits the flexion and extension of the
hand, and its abduction and adduction in two axes vertical to
each other, is also a condyloid bi-axial articulation.

In most articulations the surfaces of the bones are not in
complete apposition. There is only a small area of contact
between the head of the femur and the hollow of the acetabulum,
because, as Konig showed, their surfaces are not geometrically
complementary. The gap between the articular surfaces where
there is no direct contact is filled either by the synovia or by
introflexion of the capsular membrane due to external pressure.
These capsular introflexions always have excrescences known as
synovial villosities, which are rich in vessels and lined with
epithelium, to which the formation of synovia is mainly due.
There are consequently no true articular cavities.

However small the area of contact of the articular heads,
it was formerly supposed that it was invariably present, but
Konig found an exception in the scapulo-humeral articulation.
On dissecting frozen subjects he discovered that there was
always a layer of congealed synovia between the two articular
surfaces.

An important but difficult question is, what forces intervene
to resist displacements of the articular surfaces ? E. Weber
attributed this to atmospheric pressure only. He saw that if all
the muscles surrounding the hip-joint in a suspended corpse

ii MECHANICS OF LOCOMOTOR APPARATUS 101

were divided, and the capsular membrane and accessory ligaments
of the articulation were then cut oft* the head of the femur remained
in the acetabulum, and was not apparently displaced. In this
case the entire weight of the lower limb is effectively supported
by atmospheric pressure, which is equivalent to admitting that
a column of air the height of the atmosphere and section equal
to that of the acetabular cavity, would be heavier than the lower
limb, which weighs about 22 kgrms. Weber tried a control ex-
periment. On the same subject he made a small opening from
the internal surface of the pelvis to the acetabulum, and allowed
the air to enter into the joint ; the head of the femur no longer
remained in the cavity, and the limb fell directly the air was
admitted, because the contact of the articular surfaces at the
point of perforation was not so intimate as at the edges of the
acetabulum, where there is a cartilaginous ring which exactly fits
the head of the femur, and consequently the air rapidly penetrated
between the surfaces.

It is, however, known that the results of these experiments are
not applicable to other articulations : if the fingers are stretched
by a traction of not more than 500 grrns., the articular surfaces
of the rnetacarpal-phalaugeal joints come apart. The separation
produces a characteristic sound, and the articular capsule and
surrounding tissue are intraflected to fill the space left by the
displacement of the surfaces of contact.

Besides the atmospheric pressure, the contact of the articular
surfaces is aided by the ligaments which are attached chiefly to
the capsule. This is apparent in the amphiarthrosis of the carpus
and tarsus, which, owing to the shortness, strength, and tension
of the accessory ligaments which strengthen the capsules as well
as to the complex and irregular form of the articular surfaces, are
movable only to a very limited extent. In the arthroses and
diarthroses, on the contrary, which are more freely movable, the
capsules and ligaments serve, not to keep the articular heads in
contact, but rather to limit the movements. In fact they are not
tense when the muscles are at rest, but are thrown into tension
when the moving limb reaches a certain extreme position. In
order to understand the mechanism of the articulations in general,
it is also necessary to take into consideration the tone and state
of contraction of the muscles which surround the joints. Even
in the resting state the muscles are never so relaxed in the normal
individual, as not to contribute to the support of the joints. The
articular contact is opposed by the weight of the limb, as well as
by the pressure at which the synovial juice is secreted, which
cannot be less than that at which the blood circulates in the
capillaries of the synovial tissue. And there must always be
equilibrium between these antagonistic forces. It is not possible
to calculate exactly to what extent atmospheric pressure helps to

102 PHYSIOLOGY CHAP.

support a joint and keep its articular surfaces in contact, although
it is undeniable that this pressure is a considerable factor.

Owing to their conformation the joints and the soft parts
which surround them (muscles, capsules, ligaments) not only
serve to connect the segments of the limbs, but also limit their
movements. Thus the olecranon of the ulna during the extension
of the forearm comes in contact with the dorsal surface of the
humerus, and prevents further extension. The same function
is exerted by the so - called ligaments of arrest ; the lateral
ligaments of the knee-joint, which run from the internal and
external condyles of the femur to the internal condyle of the
tibia and the head of the fibula, are stretched during the extension
of the leg, and limit this movement to 180.

II. The discussion on the physiology of muscle in Chapter I.
refers particularly to bundles of parallel fibres of uniform
length, in which the total action represents the sum of the
actions of each fibre. But muscles with parallel fibres like
the sartorius and the frog's hypoglossus are rare ; the structure
of the muscle is usually less simple. In addition to long muscles
and short muscles, cylindrical, and spindle-shaped, and flat muscles,
anatomists distinguish fan-shaped muscles, semipennate muscles,
and pennate muscles, according to the direction of the fibres, the
form of the tendons, and the manner in which the muscle bundles
are inserted.

In fan-shaped muscles the different parts may act separately
or all together. The deltoid is a classical example. This muscle
raises the arm forward, backward, or from the side, according
as only the front or back portion or the whole acts. In the
latter case the movement (as occurs when several forces act
simultaneously in different directions) follows the diagonal given
by the parallelogram of the forces, which causes the arm to be
raised in the lateral plane.

Semipennate and pennate muscles are more common. In
these a tendon penetrates deep into the belly of the muscle, and the
muscular fibres run out from it obliquely in one or more directions.
In such muscles the line of junction of the points of attachment
does not coincide with the direction of the fibres, and when the
whole muscle contracts, the effect is the sum of the values,
calculated for each fibre separately. The gastrocnemius, the
biceps, and brachialis anticus, and the flexors for the arm, are
examples of pinnate muscles.

Generally speaking, in muscles with parallel fibres, the
diameter and cross -section is proportional to their strength,
while their length is proportional to the range of the movements
they can produce. But in pennate muscles the strength and
range of the movements cannot be deduced from their section
and apparent length : there are short muscles which appear to be

ii MECHANICS OF LOCOMOTOE APPARATUS 103

long, thick muscles which appear thin. The energy these are
capable of developing is measured, not by the area of the section
vertical to their long axis (anatomical section), but by the area
of a section vertical to the direction of the bundles of fibres
(physiological section) ; and the range of their action is measured,
not by their anatomical length, but by their physiological length,
i.e. the mean length of the muscle bundles of which they consist.

All muscles are not inserted into the bones. The fibres of the
visceral organs as the heart, bladder, intestines, uterus, as well as
the circular fibres of the oral, pyloric, and anal sphincters are
only inserted into one another or into the surrounding soft parts.

Other muscles are attached to the bone by one end, and
terminate at the other in soft parts, either on the skin or in the
raucous membrane. Such are the azygos uvulae, the levator
palati, the muscles of the face, the stylo -glossus, the stylo-
pharyngeus, etc. The muscles of the face exert a mutual traction,
making equilibrium with the symmetrical muscles of the other
side ; when the muscles on one side of the face are paralysed, the
mouth consequently becomes oblique.

All the other skeletal muscles are composed of straight fibres,
the two ends of which are generally inserted into tendons of
greater or less length, by which they are attached to two distinct
bones of the skeleton. The majority of the muscles cross only
one joint, that is, they are attached by their two ends to two
contiguous bones, and are therefore uni- articular muscles.
Certain muscles, however, cross two or more articulations, and
are attached to more or less distant bones : these are bi- or multi-
articular muscles. The anterior brachial muscle is uni-articular,
the semi-tendinous is bi-articular, as well as the long head of the
biceps and certain muscles of the leg. In these cases the muscles
and tendons are unusually long, and as they can shorten con-
siderably are able to move two or more articulations simultaneously.

When two bones are connected by a movable articulation, and
a muscle passes from one to the other, this forms a lever. The
skeleton is built up of a vast number of levers, the movements
of which combine among themselves in the most various and
complex forms. The centre of gravity of each limb represents
the point of application of the resistance, that is the weight of
the bony lever, of the soft parts by which this is covered, and
of any extrinsic load which may be carried by the limb. The
point of insertion of a muscle or muscles upon the movable
segment represents the point of application of the force. Finally,
the fulcrum of the lever is represented by the articular surface
of the moving bone upon the articular surface of the fixed bone,
or by the ground, or any other fixed support on which the
limb rests.

It is rare to find that one of two interarticulated bones is

104

PHYSIOLOGY

CHAP.

absolutely rigid and the other movable ; much more frequently
both the bones are movable, but in different degrees. The muscle
or muscles attached to the two bones exert in contraction an
equal traction upon the two points of insertion and tend to dis-
place the two bones equally, but since the resistances opposed to
the displacement of the two bones differ, it follows that they are
unequally displaced. The distinction of fixed and movable in-
sertions of a muscle really has only a very relative value. As a
rule, however, one of the muscular insertions is less displaced
than the other, generally that which is nearer the axis of the
trunk, or the root of the limb.

FIG. 65. A, Flexor movements of forearm for contraction of anterior brachial, which causes
backward rotation of arm in scapulo-humeral articulation. (O. Fischer.) B, Extensor move-
ments of forearm produced by triceps, and associated with forward rotation of arm in
scapulo-humeral articulation. (O. Fischer.) The two diajn'ams represent an experiment made
on a mechanical model.

To demonstrate the mobility of the points of insertion of the
muscle, Fischer (1895) employed a wooden model to represent
the humerus and ulna articulating together, flexed by contrac-
tion of the anterior brachial muscles, and extended by the con-
traction of the triceps. He found that the movement of flexion
is associated with the backward displacement of the humerus, and
the movement of extension with its forward displacement (Fig.
65, A, B).

The relation between the movements of the shoulder and of
the elbow joints which occur in consequence of the contraction
of the flexor or extensor muscles of the elbow varies when the
mass of the limb is increased. If, for instance, a weight is held
in the hand, and the elbow is flexed, the movement at the shoulder
is increased.

II

MECHANICS OF LOCOMOTOE APPAEATUS 105

These statements refer not merely to the flexor and extensor
muscles of the forearm, but have a general value. When the
knee is bent, not only does the leg move backward, but the thigh
bends simultaneously forward. Generally speaking, it may be
stated that a uni-articular muscle produces a movement in the
neighbouring articulation in the opposite direction to that which
occurs in the articulation lying between its points of insertion.

The whole of the force on the muscles

is not utilised in the movements of the ^

skeleton. This occurs only in the case
when the insertion of the muscles is
approximately at right angles to the bone,
as in the masseters which are able to em-
ploy their full strength in bringing the
jaws together. But the great majority
of the muscles are inserted more or less
obliquely, the direction of their fibres
forming a more or less acute angle with
the principal axis of the bone. In all
these cases a great part of the traction
force of the muscle is lost in the move-
ment. This disadvantage is frequently
diminished by the fact that many bones
have prominences at the point of attach-
ment of the muscles over which the tendons
of the muscles pass as over a pulley, and
become attached to the bone at a favour-
able angle.

In every case, whatever the form and
size of the angle of insertion of a muscle
upon the bone, it is possible by resolving
the total traction force into its components,
according to the law of the parallelogram
of forces, to estimate how much is utilised

T i . , , , Fio. t>6. Diagram of the resolu-

m displacing the moving bone, Supposing tion ofi muscular force into

the other bone to be rigid.

Let it be supposed that AC and AB in
Fig. 66 represent the long axes of two bones, which are movable
round the axis A perpendicular to the plane of the figure ; that
MM' are the points of insertion of a muscle, M being fixed, M'
movable ; lastly, that the line M'D represents the total traction
force of which the muscle is capable. If we resolve the line M'D
into its two components M'E and M'F, which are vertical to each
other, then M'E represents the force utilised by the muscle in
moving the joint A, called by mechanicians the moment of force,
while M'F is the amount of force that is spent in pressing the two
articular surfaces at A against one another, so as to render the

its components. Explanation
in text.

106

PHYSIOLOGY

CHAP.

articulation more solid. The more obtuse the angle BAG formed
by the two bones, the smaller will be the components M'E, i.e. the
force utilised in the movement. The smaller this angle becomes,
the greater will be the proportion of the force employed in the
movement.

Since movable bones may be regarded as levers, the laws

which govern the action of
levers can be applied to them.
When the object is to attain
considerable speed rather than
have great force, the force is
applied to the shorter arm of
the lever ; when, on the con-
trary, a high resistance has to
be overcome, and less speed
of movement is required, the
force is applied to the longer
arm. In the animal body the
arm of the lever to which the
force is applied is shorter than
that which causes resistance,
i.e. the majority of the muscles
are inserted nearer the articu-
lations than is the centre of
gravity of the movable part.

This arrangement is advan-
tageous for the speed of the
movement,butdisadvantageous
owing to loss of force. The
loss is, however, compensated
by the fact that a less amount
of muscular shortening is re-
quired to effect a given range
of movement (Fig. 67).

It is important to note that
during movement the length
of the arm to which the force
applied, and that which

FIG. C7. Diagram showing the various degrees of
muscular shortening required for a given move-
ment, according as the lever arm varies for
Eower and for the load. (Luciani.) When the
iver AC rotating on the axis A reaches AC", the
muscle MM only shortens slightly (Mm'), because
the lever arm AM i.s shorter than that of the
load MC ; the muscle MM', on the contrary, has
to shorten much more (to Mm") to execute the
same movement, because the arm AM' is much
longer than that of the load M'l '.

IS

carries the weight, often vary
in proportion with the range of
the movement, so that the load diminishes during work. When,
for instance, the body is raised from the bent knee, this movement
is accompanied by the unloading of the muscles which actively
extend the knee. In this position the arm that carries the load
is represented by the horizontal distance of the axis of the knee-
joint from the line of gravity of the body, i.e. from the perpen-
dicular taken from its centre of gravity. During the rise this

ii MECHANICS OF LOCOMOTOK APPARATUS 107

distance becomes gradually less, and iu the erect posture is almost
negligible. On the other hand, the working line of the quadriceps
muscle which extends the knee remains at approximately the same
distance from the axis of the knee-joint during the movement.

III. Leaving the study of the various positions that may be
assumed and the different movements that may be performed
by each part of the skeleton, we must here confine ourselves to
studying the different postures and movements of the body as a
whole in progression.

In both standing and walking the position and the displace-
ment of the centre of gravity and of the line of action of gravity
of the whole body are of great importance.

Every part of the body gravitates according to the vertical
line that falls from it to the earth. This infinite number of
perpendiculars which only meet at the centre of the earth, and
niay therefore be regarded as parallels, may be replaced by one
single perpendicular line representing the sum of the component
forces ; this is known as the line of gravity. Whatever position
is assumed by the body, so long as it preserves the same form,
the lines of gravity corresponding with each posture intersect
at the same point which is known as the centre of gravity.

In all bodies which are not geometrical in form and consist
of a heterogeneous mass, the centre of gravity can only be deter-
mined by experiment. This is done by suspending the body by a
cord successively in two different positions ; the directions of the
cord prolonged through the body give two lines of gravity, and
the point at which they intersect is the centre of gravity. The
exact determination of the centre of gravity of the human body
is much more difficult, since it is not a rigid body, and undergoes
changes of form.

Borelli (1679) and the Webers, starting from the assumption that
in well-formed individuals the line of gravity must lie in the median
sagittal plane, or the plane of symmetry of the body, attempted
merely to ascertain the height of the centre of gravity, that is, its
distance from the sole of the foot and apex of the head, without
defining its position on the transverse vertical plane. For this
purpose they laid a man on his back upon a board supported on
a metal wedge, and placed the whole in equilibrium like the arms
of a balance. The vertical plane perpendicular to the length of
the body through the wedge that supports the board must pass
through the centre of gravity. They found that this plane was
nearer the crown of the head than the sole of the foot. If the
total height of a man be taken as 1000, the centre of gravity
would be found at 570 from the sole and at 430 below the crown.

These observations were controlled by Harless and by Meyer,
who found values that did not vary more than 3 per cent from
those of the earlier observers. Harless found that in woman the

108

PHYSIOLOGY

CHAP.

centre of gravity is placed lower than in man ; in children, on the
contrary, it is higher, owing to the relatively greater or less
development of the pelvis.

In order to ascertain the centre of gravity in the antero-
posterior plane of the body, Meyer placed a naked subject in the
erect and rigid posture, and then made him bend forward on the
front of his feet and his heels as far as possible without falling.
By means of a plumb line he determined the lines of gravity in
the two most extreme postures, and the points of intersection of

Fin. 68. Normal position. (Braune ami
Fischer.) In this position the centres of
rotation of the principal articulations fall
in the same vertical plain- indicated by the
line.

FIG. 60. Military position or "stand at
ease." (Braune and Fischer.) In this
position the centres of rotation for the
lower limbs lie behind the vertical line that
passes through the centre of gravity.

these lines in the body represent its centre of gravity in the given
erect and rigid posture.

More recently Braune and Fischer have applied the same
method to the dead body frozen and extended on its back upon a
board. The rigid and invariable form of the body enabled them
to determine exactly the point of intersection of three perpen-
dicular lines of gravity obtained by successively suspending the
body in three different positions.

According to Weber the centre of gravity of the whole body
in the erect position is at about the level of the sacral promontory ;
according to Meyer it lies at about the upper border of the second
sacral vertebra inside the spinal canal ; according to Braune and
Fischer it is considerably farther forward, at the level of the upper
border of the third sacral vertebra.

ii MECHANICS OF LOCOMOTOE APPAEATUS 109

The centre of gravity of the trunk may lie determined on the
dead subject in the same manner after exarticulating all the
limbs. It lies in the plane between the lower extremity of
the sternum or the ensiform cartilage and the tenth dorsal
vertebra, and in a vertical transverse plane that passes somewhat
behind the axes of rotation of the heads of the femurs. We shall
presently see the importance of this fact.

The position of the centre of gravity for the whole body is
important in determining the positions of more or less stable
equilibrium of the body. Braune and Fischer denned the normal
erect posture (Normdl-Stdlung} as that in which the axes of
rotation of the principal articulations fall in the same vertical
transverse plane as the line of gravity (Fig. 68). From this
they distinguish the military or " stand-at-ease " position (Bequeme
Hal tuny} in which the line of gravity falls 4 cm. in front of

FIG. 70. The base of support and the line of gravity in different postures. At A tin 1 base of
support is represented by the area <>''<'/, and </ is the point through which the line of gravity
passes ("attention attitude"). At B the base of support comprises ulinl, i/ being the point
through which the line of gravity passes ("normal position").

the line of junction of the articular heads of the femurs (Fig. 69).
In the first posture the line of gravity falls near the posterior
margin of the base of support ; in the second it falls considerably
more forward (Fig. 70). Obviously this last posture represents a
more stable condition of equilibrium.

In each different posture assumed by the body resting on the
soles of both feet there is a new displacement of the centre of gravity
(Fig. 71). If the individual carries a weight he is constrained to
modify his position because the system is thrown out of equilibrium,
unless the centre of gravity lies within the common base of
support. If the load is placed on the back he must lean forward,
if the weight is placed in front, backward. If a weight is held up
with the right arm the body inclines to the left ; if with the left
arm, to the right. Heavier weights can be borne on the head, as
then the normal posture of the trunk may be but little changed,
and the line of gravity little displaced, but the centre of gravity
is raised, which renders the equilibrium less stable, though the
base of support is unchanged.

110

PHYSIOLOGY

CHAP.

In order to increase the base of support and to obtain more
stable equilibrium it is only necessary to set the feet further apart
upon the ground. This is often done where the erect posture has
to be long maintained.

From these forms of symmetrical vertical posture we must dis-
tinguish the asymmetrical vertical posture, in which almost the
whole weight of the body falls upon one leg, the other being
slightly flexed and placed in advance. In this posture (Jianchee]
the line of gravity falls through the extended limb which supports

FIG. 71. Displacement of centre of gravity in postures a, &, c. (Braune and Fischer.)
Centres of gravity shown as black dots on the vertical lines.

the body, and the trunk consequently inclines towards this side.
The different forms of this posture, which is very natural and
instinctive, are determined by the angle formed by the longi-
tudinal axes of the two limbs or by the distance between the
two soles of the feet.

IV. We should next consider briefly the mechanism of
equilibration in the different postures of the human body, but
must here confine ourselves to the horizontal posture, the sitting
posture, and the common erect attitudes.

The horizontal posture is the easiest to maintain because
it unites as completely as possible the two conditions of stable
equilibrium, i.e. an extensive base of support, and the maximum
approximation of the centre of gravity to it. As muscular con-

ii MECHANICS OF LOCOMOTOE APPAEATUS 111

tractions are not necessary for maintaining equilibrium in lying
down, that is therefore the position of rest and sleep. We may
distinguish between the sternal, sterno-costal, lateral and dorsal
postures. This last is almost confined to man, as in no other
vertebrate is the back sufficiently flat to support the weight of the
body conveniently.

In the sitting posture, if the trunk is leaning against the back
of the seat, all the muscles are in repose, except the elevators of
the head which keep it in the vertical position. In fact, in
sleeping while seated the head drops forward towards the chest,
which shows that the centre of gravity for the head is placed in
front of the occipito-atlantoid articulation.

When seated on a stool with no support for the back, the base
of support is represented by the line that connects the outer
margins of the sciatic tuberosities and of the feet which rest on
the ground. In order to maintain the centre of gravity of the
head and trunk within this base, it is necessary to obtain the
antero-posterior balance by the alternate activity of the dorsal,
the lumbar, and the psoas-iliac muscles.

In the erect posture, with the two feet set square, the centre
of gravity of the body is brought much higher from the base of
support, and this base is much smaller; it would therefore be
natural to assume that a much greater muscular force would be
necessary to preserve equilibrium. Meyer, on the contrary,
demonstrated that in the most comfortable erect posture, the
muscular activity necessary to preserve equilibrium is small, as this
is due principally to the tension of the ligaments, especially the
ileo-femoral ligaments.

As its articulations are mainly synchondroses, the vertebral
column may be regarded as an elastic bar, capable of supporting
the entire weight of the head, trunk, and upper limbs. It has
various curvatures ; it is convex forwards in the cervical and
lumbar regions, and concave in the thoracic and sacral regions
(Fig. 72). It is wholly immobile in the sacral region owing to the
fusion of the vertebrae, but little movable and flexible in the
lumbar region, much more mobile and flexible in the dorsal
part, and in the cervical region it is remarkably flexible in all
directions. The neck muscles fix the head, and therefore make
the cervical spine relatively rigid.

The line of gravity of the trunk and head in the easy (or
military) position shown in Fig. 69 falls behind the line of
junction of the ileo-femoral articulations. The trunk would
primarily fall back, but for the resistance, as Meyer showed, of the
strong ligament which runs from the anterior inferior iliac spine
to the anterior intertrochanter line of the femur ; the balancing
of the trunk on the heads of the femur is chiefly due to the
elastic tension of this ileo-femoral ligament, but this is aided by

112

PHYSIOLOGY

CHAP.

the alternate activity of the psoas-iliac muscles, which tend to
bend the trunk forward, and the dorsal and lumbar muscles, which
tend to incline it backward.

The common line of gravity of the head, trunk, and thighs, also
passes behind the knee-joints; and some arrangement is necessary

when the individual is in the upright
posture to prevent falling backwards
owing to flexion of the knees. This is
provided for by the tension of the ileo-
fernoral ligaments which rotate the
femora inwards, and thus prevents the
slight external rotation which is neces-
sary for the flexion of the knees. The
hip- and knee-joints are thus both fixed
by the weight of the trunk, which
throws the ileo-femoral ligaments into
tension. Owing to this mode of fixation
of the knee-joints, the active interven-
tion of the extensor quadriceps muscle
is not necessary, and indeed the patellar
ligament does not seem to be more tense
in the vertical posture than in other
positions.

The line of gravity of the whole body
falls on the ground in a plane somewhat
anterior to the line between the two
tibio-astragalic articulations, and the
body tends to fall forwards. This is
avoided by the fact that the plane of
flexion in this joint is very oblique with
that of the other side ; the two planes
of flexion form an angle of 60 open to
the front. In order that flexion at
these two joints should be possible, it
is therefore necessary for the two knees
to be moved apart from each other, and
flexed. When flexion of the knees is
prevented, falling forward owing to
flexion of the tibio-astragalic articula-
tions is also prevented. As the fixation
of the hip-joint determines the fixation of the knee, the fixation
of this joint leads to the fixation of the ankle. Here again the
gastrocnemius, soleus, posterior tibial, and posterior peroneal
muscles also take part in maintaining fixation.

The tarsal and metatarsal bones, which constitute the skeleton
of the foot, form an arch which rests on the ground by the
tuberosity of the heel, and the heads of the first and fifth meta-

Fio. 72. Curve normally presented
by the anterior median profile of
the vertebral column in the
military posture. (G. H. Meyer.)
it, tuberculum anterius of atlas ;
b, lower border of 6th cervical
vertebra ; c, upper border of 9th
dorsal vertebra ; /, lower border
of 2nd lumbar vertebra ; p, pro-
montorium ; s, symphysis ossium
pubis ; d, angle of 3rd sacral
vertebra ; e, coccyx.

ii MECHANICS OF LOCOMOTOE APPARATUS 113

tarsal bones. Owing to the strength of the plantar ligaments
the arch of the foot can carry heavy weights without giving way.
Flat foot, owing to abnormal relaxation of these ligaments, is un-
favourable to the maintenance of equilibrium in the erect posture
and in walking.

Owing to the formation of the skeleton and the arrangement
of its ligaments, the erect posture can therefore be maintained
with a comparatively slight expenditure of muscular energy.
But when it is necessary to remain standing for a long time,
an asymmetrical posture is generally preferred, in which the
main part of the weight of the body is thrown on one leg, while
the other is held in a forward and semi-flexed position.

Vierordt, by an extremely simple graphic method, registered
the oscillations of the head in different positions, with the object
of determining the most natural posture, i.e. that which induces
the least fatigue and provides the greatest stability of the body.
The method consisted in attaching a pen to the head by a suitable
cap, which traced on a paper fixed horizontally from above the
oscillations of the principal axis of the body in different postures,
each being maintained for three minutes. He found that the
antero-posterior and lateral oscillations are considerably greater
in the symmetrical military posture than when the weight was
thrown upon one leg (asymmetrical). The latter posture is
accordingly the most natural, and preference is given to it in
sculpture and painting.

According to Vierordt the advantages of the asymmetrical
posture are as follows :

(a) Greater rigidity of the hip- and knee-joints, due to almost
the whole weight of the body falling on the limb which serves
as support ; this produces increased tension of the ligaments,
particularly of the ileo-femoral.

(&) The calf muscles of only one side are active, and less
work is thrown upon these than in the symmetrical posture.

(c) The advanced limb, which does not bear the weight of the
body, exerts a slight pressure on the ground, so that when the
quadriceps extensor of the knee comes actively into play to hinder
the body from falling forwards, it works under favourable con-
ditions. In the symmetrical posture, on the contrary, the calf
muscles on both sides work under a heavy load to attain the
same end.

(d) The appreciation of pressure by the sole of the advanced
limb, and the muscle sense generally, are under the most advan-
tageous conditions in the asymmetrical posture, so that oscillations
of the centre of gravity are more readily perceived, and promptly
compensated by muscular reaction.

And, as in the asymmetrical attitude, the muscles of one
limb only become fatigued, it is possible to remain longer
VOL. Ill I

114

PHYSIOLOGY

CHAP.

standing, by throwing the weight of the body alternately on the
two feet.

V. In locomotion there is a great and more or less rapid dis-
placement of the centre of gravity of the body and its base of
support. The movements performed by man in different forms
of locomotion are extremely complicated. But the principles of
mechanics by which we have explained the maintenance of
equilibration help to solve the fundamental problems of human
locomotion.

The ordinary forms of locomotion are walking and runniny.

In both the body is thrown
forward by the rhythmic and
alternate muscular contractions,
specially by the muscles of the
lower limbs. In walking the
body never leaves the ground,
but in running the whole body
is momentarily in the air.

According to the description
of the Webers the lower limbs
are alternately active in walk-
ing ; while the one which is
applied to the ground sustains
the entire weight of the body
and throws the centre of gravity
forward, the other swings pass-

ively.

Each step begins with plac-

ment of the step. (Kick.) a, passive right in g the active limb with its Sole

leg winch touches ground with big toe only; on the ground, the foot and
db, left foot with whole sole resting on ,~

ground; c, centre of rotation for hip-joint; knee being SOlliewhat flexed,
IKY/, rectangular triangle, in which the passive -\ , i -i , p , i 1,1

limb forms the hypotenuse, the ground and ailQ 1116 Weigilb 01 DOCly

catheter ' accor(lin 8 to the falls on the sole, while the

passive limb lies behind with
its great toe on the ground. At this stage the centres of the
femoral heads and the extremes of the two limbs form a rect-
angular triangle with the ground, two sides being formed by the
active limb and the ground, and the hypotenuse by the passive
limb (Fig. 73).

In the next stage of the step, the knee of the active limb
is extended and the heel raised, throwing the centre of gravity
forward and slightly raising it, while at the same time the passive
leg is lifted from the ground and swung forwards till it once
more touches the ground and takes the weight of the body.

According to the Webers each step in walking may be con-
sidered as a movement of falling forward, which is arrested by
advancing the passive limb and throwing the weight upon it.

S a!

FIG. 73. Position of lower limbs at commence

II

MECHANICS OF LOCOMOTOE APPARATUS 115

In order to swing forward without hitting the ground the
passive lirub must shorten slightly. But according to the Webers'
theory this is not due to contraction of the flexors of the thigh
or knee, for the lower limb may be regarded as a compound
pendulum which in oscillating becomes slightly flexed at its
articulations. Eecent investigation has, however, modified much
in this theory.

It is not correct to say that the limb lifted from the ground
and swinging forwards is totally passive. Duchenne, by his
clinical observations, demonstrated the
necessity in regular walking of the
active intervention of the flexors of the
thigh, the tensor fasciae, the psoas-iliac
and the sartorius muscles to shorten
the limb and avoid contact with the
ground during the swing. Marey, too,
showed that the swing of this limb
could not be regarded as passive, since
it consists in a progressively acceler-
ated movement, and must therefore be
associated with, and partly dependent
on, muscular force.

In order to obtain a more exact idea
of the complex movements of walking,
the way the feet are lifted and set
down, and the position assumed by
the limbs at their principal articula-
tions in each phase of the step, graphic
and chronophotographic methods must

hp rp^nrrprl in FIG. 74. Pedestrian in exploring si s

which record the pressure applied
to the ground upon a portable

Marey and Carlet were the first who apparatus. (Marey.)
applied the graphic method to the study

of the complex movements of walking and running. Of the different
instruments which Marey invented, the most important are the shoes, which
register the pressure applied to the ground by the individual who walks or
runs. The sole of these shoes contains an air-chamber communicating by a
tube with a recording tambour, which writes upon a portable revolving
cylinder, held in the hand of the individual who performs the experiment
(Fig. 74). The air-chamber lies in the front part of the sole, near the end
of the metatarsus. Accordingly it only registers the pressure exerted upon
the anterior part of the foot (Fig. 75). Carlet obtained better tracings by em-
ploying soles with two intercommunicating air-chambers placed one lu-ar
the heel, the other near the front of the metatarsus.

Along with these tracings of the pressure exerted by the feet while
resting on the ground, Marey and Carlet registered the vertical oscillations
of the head, or the horizontal oscillations of the pelvis (Figs. 75, 79), by
means of special tambours.

The chronophotographic method which Marey applied to walking
consists in recording on one fixed plate the successive images of a person
walking. The photographic apparatus has a lens, and a man is made to

116

PHYSIOLOGY

CHAP.

walk past a black ground with a white net on his back which is vividly
illuminated by direct sunlight. While he walks a rotating apparatus lets
light into the camera obscura at regular intervals. At each instantaneous
exposure an image of the subject in different postures is thrown upon the
successive parts of the plate (Figs. 82 and 84). In order to obtain more
images at each cycle, and at the same time to avoid the confusion resulting
from their superposition, Marey invented the ingenious method of partial

Km. 7-j. Curve of walking. (Marry.) />, movements of right foot ; 5, of left foot ;

II, vertical oscillations.

which consists in suppressing the images of the left side of
the body, photographing only the right half of the walker. For this
purpose the left half is clothed in black, the right in white (Fig. 76).
The figures of each step can similarly be multiplied in walking or run-
ning by increased simplification of the images. For this the subject is
clothed entirely in black, six brilliant metal buttons being placed on the
head and over the articulations of the shoulder, elbow, thigh, knee, and foot, as
well as five shining bands over the bone of the arm, forearm, thigh, leg,
and edge of the foot (Fig. 77). By photographing the subject as he walks
forward strongly illuminated by the sun, the chronophotogram is obtained,
as shown in Fig. 78, where, for the sake of simplification, the tracing of the

Fiii. 76. Photographs of right half of body of a subject walking slowly iiasl the camera. (Marey.)

head is omitted, since it shows only vertical oscillations which are perfectly
comparable at every step with those of the dots on the shoulder and thigh,
as shown on the figure.

A later improvement on Marey's method was introduced by Braune and
Fischer, who substituted for the dots and metal bands on the black coat of
the subject, upright Geissler's tubes, connected with the conducting wires
of a circuit which included a big Ruhmkorf induction apparatus. The
circuit was interrupted at equal intervals, which lasted O0383 parts of a
second. By photographing the subject as he w r alked not only along a plane
parallel with the sensitive plate but also along other planes, Fischer was

II

MECHANICS OF LOCOMOTOK APPARATUS 117

able to construct a curve of the movements of various joints and of the head,
as also of the, movements of the trunk, etc.

Fig. 80 is a diagram of the cycle of walking constructed by Zimmerman
from tlie dmmophotographs of Fischer.

The tracing (Fig. 79) obtained by Carlet with his exploring
shoes shows that in the usual mode of walking the heel is first
applied to the ground, then the whole sole of the foot, and lastly
the ball of the toes only ; that the time during which both feet
are on the ground is less than half the
period that each alone rests on it ; that
the time of the rise and swing of one
leg is always shorter than that of the
opposite limb. Carlet demonstrated by
the same method that the pressure exer-
cised by the foot upon the ground during
a step is not equal to the weight of the
body, but that in the last stage of the
step an additional pressure dependent
on the muscular forces, which raises the
body and propels it forward, is added.
According to Carlet the additional incre-
ment of pressure varies with the length
of the steps and never exceeds 20 kgrms.

The length of the step depends on
the length of the lower limbs and the
degree in which the knee of the limb
which bears the weight of the body at
the commencement of the step is flexed.
Fig. 73, which shows diagrammatically
the position of the lower limbs at the
commencement of the step, makes it
plain that the length of step can only
increase when the length of the hypo-
tenuse (i.e. the length of the extended
limb) is increased, or when the flexion
of the knee of the limb on which the weight of the body
falls is increased. People who have long legs and long feet
naturally take longer steps than short people ; and if they walk
together the latter are obliged to quicken their step by a voluntary
effort ; this is done by increasing the flexion of the knee and
dropping the centre of gravity. If the knee is kept rigid and
extended, only very short steps are possible, and a greater expendi-
ture of energy than usual is required.

It is also possible to vary the rate of the step, which depends
on the duration of the application of one or both feet to the ground,
that is, on the forward swing of the inactive limb. The duration of
the double application depends on the will ; the more hurried the

ing. ChronophotograpMc method.
(Marey.)

118

PHYSIOLOGY

CHAP.

gait, the shorter it becomes, and according to the Webers in very
rapid walking its duration is reduced to zero, i.e. one leg is raised
as soon as the other touches the ground. This, however, is contra-
dicted by Carlet, who found a brief period in which both feet were
on the ground, even in the most rapid gait. The rate of swing
of the relatively passive limb depends on the stature or the length
of limb. The shorter the limb, the more rapid the swing.

The speed of walking depends upon the length and duration
of the steps, i.e. the distance traversed in the time unit. Numerous

FIG. 78. Chronophotograph of walking ; shows the successive positions taken up by the joints
"and bones of the limbs in the step. (Marey.)

experiments of the "Webers show that as an individual increases
the length of his steps their duration diminishes, so that when
walking at full speed the duration of the steps is minimal and their
length maximal. This can be verified from the figures given by
the Webers in the following table :

Duration of Step
in Seconds.

Length of Step
in Millimetres.

Speed of Walking
in Metres per Sec.

0-335

851

2-397

0-417

804

1-928

0-480

790

1-646

0-562

724

1-288

0-604

668

1-106

0-668

629

0-942

0-846

530

0-627

0-966

448

0-464

1-050

398

0-379

This law of the inverse ratio between length and duration of
steps only holds, according to Marey, up to a certain point. When

II

MECHANICS OF LOCOMOTOE APPARATUS 119

the number of steps exceeds 150 per minute, i.e. when the duration
of the step becomes less than 0'4 second, the speed of walking
does not increase because the length of step diminishes.

The force of walking depends on the extensor muscles of the
thigh, leg, and foot.

Fig. 80 gives an exact idea of the position of the principal
articulations not only of the lower limbs, but also of the upper
limbs and the head at the different moments of the step cycle.

123 4 567 g- 91011

T23 4 567

Fi<:. 79. Tracings of the pressure applied to the ground in walking. (Carlet.) I'd, right foot;
P*. left foot; Or, vertical oscillations; On, horizontal oscillations. 1, 2, 3 = period of double
application; 3, 4, 5 = period of single application; l-7 = period of application of left foot;
5-11 = period of application of right lout ; 1-3 and 5-7 = application of heel of left or right foot ;
4-5 and 8-'.i = application of point of left or liuht foot.

The cycle begins at the instant in which the left leg is raised
from the ground and swings forward, while the heel of the right
leg rests upon the ground.

Each step is divided into 10 successive phases of equal duration,
and at every 10th phase the right leg is in the position originally
occupied by the left, and vice versa. From the 1st to the 5th
phase, which include the first half of the step, the left knee
becomes flexed, while the right becomes extended, so that the thigh
and shoulder joints (represented by the junctions of the black and
red lines) and the vertex of the head (represented by the big dots
marked on the upper part of the figure) are somewhat raised.
From the 6th to the 10th phase, which include the second half of

i 1

120

PHYSIOLOGY

CHAP.

the step, the left leg is extended forward till the heel touches the

o

~~.

to

5

30

a

o

S

00

ground, while the right leg first rests upon the ground with the

ii MECHANICS OF LOCOMOTOE APPARATUS 121

whole sole of the foot, but later, as the heel rises, on the point of the
foot only. In the first half of the step owing to the extension
of the right knee there is an upward vertical oscillation of the
hip, shoulder, and head ; while in the second half of the step there
is a downward movement owing to forward flexion of the right
ankle, and parti} 7 also of the knee on the same side. So that at
each step there is a douhle vertical oscillation of the hip, shoulder,
and head, as clearly shown by the figure. According to the Webers
these vertical oscillations attain a height of 32 mm., according to
Carlet of 37 mm., in persons of average height, during fairly rapid
walking; they increase in proportion to the length of the steps.

Besides these vertical oscillations, the top of the head and the
shoulders and hips show lateral horizontal oscillations during
walking, which are very apparent on looking down from a height,
for instance from a window, upon a person walking in the street.
While the vertical oscillations coincide with the length of a step,
the horizontal oscillations correspond to the double steps or a whole
step cycle. These lateral horizontal oscillations reach their maximum
at the same moment as the vertical oscillations. In the diagram
of Fitj. 80 the maximal lateral oscillation therefore falls to the

O

right at the 5th phase, and the maximum of lateral oscillation to
the left at the 15th phase. The further apart the limbs are in
walking, the more pronounced are these lateral oscillations, which
evidently depend upon the degree of abduction at which the feet
are planted upon the ground.

The oscillations of the shoulders and hips round a vertical axis
should also be noted ; these accompany the lateral oscillations of
the trunk. At each step the leg that is moving forward is accom-
panied by a forward movement of the hips and a backward move-
ment of the shoulders, i.e. a slight twist of the trunk round a
vertical axis. This torsion may be so exaggerated as to become
very apparent, but it is present to a slight extent even in normal
walking, especially in women with a large pelvis. The forward
movement of the hips is also due to the swing forward of the
lower limb of the corresponding side and the active contraction of
the lumbar muscles ; the backward inclination of the shoulders is
produced by the swing forward of the upper limb of the opposite
side, which, according to Duchenne, is not purely passive, as it
depends partly on contraction of the deltoid muscle. Fig. 80 shows
plainly that while the left leg swings forwards, the right arm
becomes more and more flexed at the elbow, and is raised and
advanced. This torsion of the trunk and active oscillation of the
upper limbs, which balance the body, increase in rapid walking.

These simultaneous and opposite movements of the upper and
lower limbs in the ordinary gait of man correspond with the
alternate movement of the four limbs in the ordinary gait of the
quadrupeds.

122 PHYSIOLOGY CHAP.

Lastly, it should be noted that the torsion of the trunk is
always accompanied (particularly in hurried walking and climbing)
by a rhythmical forward movement of the trunk and head at each
stride. This movement, which overcomes the resistance of the air
and economises the power of the limbs by throwing the centre of
gravity forward, is probably the effect of the activity of various
muscles, especially of the ilio-psoas.

VI. After this account of the complex mechanism of walking
there is little to add in regard to running. As we have already
pointed out, the two feet are never on the ground at the same
moment in running, and one foot never comes in contact with the
ground till the other has been raised from it ; the entire body is
consequently suspended for a moment in the air. This is shown
by the tracing taken with the exploring shoes (Fig. 81). It can
also be seen with instantaneous photographs upon a fixed plate,

FIG. 81. Curves nf luiiniim, traced with m-onliim shoes. (Matey.) D, movements of rijjlit font :
S, movements of left tout : n. \n t iciil oscillations. The ai'plieation of the foot to the ground
lie-ins at. the moment at which tin- cuive tises; its removal, at. the moment at wliich tin-
curve drops.

when the exposures occur at a rhythm corresponding with that of
the two phases of the step in running (Fig. 82).

This essential difference between walking and running depends
upon the fact that in running the extension of the limb upon the
ground and of forward displacement of the body is more marked,
so that the body is thrown forward and raised from the ground.
During the moment while the body is unsupported in the air the
two legs swing forward. The leg which gives the forward impulse
is a little behind during the swing, and a little forward while the
other leg touches the ground.

The contact of each foot on the ground is shorter in running
than in walking, and its duration is inversely proportional to the
force with which each foot is applied to the ground ; this increases
with the rate of running. The frequency of contact increases
with the pace, but only within certain limits, beyond which the
space covered in a certain time depends more on the length of the
steps than on their number.

The absolute duration of the period in which neither foot is on
the ground varies very little with the variations of the speed of
running ; but its relative duration increases considerably, since,

ii MECHANICS OF LOCOMOTOH APPARATUS 123

as was said above, the duration of the contact diminishes with
increased speed.

In order to form a true conception of the mechanism of
running it is very instructive to ascertain the exact moment at
which the vertical oscillations of the body reach their maximum
upward excursion. The Webers held that this occurred as the
body is projected upward and forward by the force of the impulse
given by the rapid extension of the limb in contact with the
ground. Marey's tracings show, on the contrary, that the body
attains the maximum of its vertical ascents as one foot conies to

FIG. 82. Instantaneous photograph of running on a fixed plate. (Marey.)

the ground. As shown by curve 0, Fig. 81, the head begins to
rise at the moment at which the foot touches the ground, and
reaches its maximum height midway through the period of
contact, after which it descends and reaches its minimum at the
moment when the foot leaves the ground, and before the other
foot comes into contact with it, i.e. during the phase of suspension.
This proves that the suspension is due essentially not to the
sudden extension of the leg but to its subsequent flexion, which
suddenly withdraws it from the ground after giving the upward
and forward thrust to the body.

Both the leg on the ground and also the swinging leg are
much more active in running than in walking. The muscles of
the upper limbs also contribute to the forward thrust of the body,
since they oscillate alternately with the homologous lower limbs.

The torsion of the trunk round a vertical axis and inclination

124 PHYSIOLOGY CHAP.

of the shoulders are less marked in running than in walking. On
the other hand the inclination of the trunk forward in the first
period of the contact, and backward in the second half, is much
more pronounced in running.

The speed of running, according to the statement of the
Webers, may exceed 4'5 m. per second ; anything beyond these
limits can only be kept up for a short distance.

Galloping differs from walking and running, in which there is
a regular alternation of the movements of the limbs on the two
sides, which are placed on the ground at regular intervals.
Galloping deserves a short mention, although it is not a normal
form of locomotion in man. According as the gallop to the
right or to the left is imitated, the right or left foot is put forward
at each step, like a galloping horse. In Fig. 83, which represents

Fio. 83. Tracing of galloping to the right. (After Marey.) D, movements of right foot;
N, of left foot ; 0, vertical oscillations.

a tracing obtained by Marey with recording shoes, four phases can
be distinguished in the gallop. The left foot, the more posterior,
firsb touches the ground with a firm and prolonged pressure ;
while the left foot is still on the ground the right foot is placed in
a more advanced position (double contact), but with less and
shorter pressure ; the second contact is at once followed by
elevation of the left foot (simple contact) ; and finally conies the
rise of the right foot also (suspension), which lasts a perceptible time
before the tap of the left foot begins the second cycle. Line of
the figure shows that the two taps are followed by two slight
elevations of the head, followed in turn by two depressions, most
of which coincide with the phase in which the whole body is
unsupported in the air.

Jumping consists essentially in the rapid and energetic
extension of one or both lower limbs, preceded by a pronounced
flexion, by which means the body is thrown upward and forward.
The mechanism of jumping varies considerably according to its
purpose.

Chronophotographs on a fixed plate of the successive positions
of an individual who is jumping over a hedge or ditch (Fig. 84)
show that during the spring and the upward and forward thrust

ii MECHANICS OF LOCOMOTOK APPAEATUS 125

of the body, the movement is much more rapid than in coming
down again. While rising, the arms are pushed forward in order
to raise the centre of gravity and increase the impulse in the
direction of the leap ; during the descent, on the contrary, they
are thrown back to lessen the momentum of the body at the
moment at which it touches the ground. As soon as the feet
come in contact with the ground the knees are flexed to lessen
the counter-blow and the shock.

In order to understand the essential features of the different
gaits which we have been discussing the diagram suggested by
Marey is useful. In this the duration of the contacts of the right
foot is shown by white lines, of the left foot by shaded lines, the
duration of the elevation of either limb in the air by the iuter-

FIG. 84. Instantaneous photographs of a long jump on fixed plate. (Mai^y.)

veiling black area. It is a kind of simplified notation, less
complete than that of the graphic method because it does not
indicate the pressure exercised by the foot upon the ground and
its variations ; but it is much clearer and shows at a glance the
fundamental difference between the different gaits (Figs. 85, 86).
This form of notation is almost indispensable in differentiating the
various gaits of quadrupeds.

VII. Swimming differs from terrestrial locomotion inasmuch as
the body does not rest on the ground, but is immersed in water,
which is a fluid medium.

The body floating in water may be compared to a body
resting upon a supporting plane, formed by the buoyancy of the
fluid. This is due to a great number of parallel forces which
act vertically from below upward on the lower surface of the
swimming body. The resultant of these forces is called the centre
of buoyancy, which corresponds to the centre of gravity of the
liquid mass displaced. The floating body may thus be regarded as

126

PHYSIOLOGY

CHAP.

suspended by its centre of buoyancy, and to be in equilibrium it is
necessary that the centre of gravity and the centre of buoyancy
shall be on the same vertical plane. And for the equilibrium to
be stable the centre of gravity of the floating body must be below
the centre of buoyancy. Ships are all constructed on this

Fio. S5. Diagram of four different gaits, from man. (After Marey.) 1, walking on Hat ground ;
2, walking uphill and upstairs ; 3, running ; 4, fast running.

principle, i.e. so that their centre of gravity shall be as low as
possible in comparison with the centre of buoyancy. The same
principle has recently been applied to dirigible airships and
aeroplanes.

On an average the human body as a whole is heavier than fresh
water (I/O 10), but its gravity differs little from, and is even some-
what less than, that of salt water. While lying on his back, so

Fio. 86. Diagram of galloping and jumping. (Marey.) 1, galloping to the left ; 2, to the right ;
3, series of rhythmical jumps on both feet ; hops on right foot alone.

that only his mouth and nose are above the water, an adult man
(especially if very fat) can easily float on the sea, if he keeps all
his muscles relaxed. Thin people, however, whose average specific
gravity is rather higher than that of salt water, are unable to
float in the supine position without the help of slight impulsive
movements of the feet, produced by rhythmical extension of the
legs. In order to move in this position it is necessary to supple-

ii MECHANICS OF LOCOMOTOK APPARATUS 127

ment the movements of the legs by slight rowing movements with
the arms.

Swimming with the abdomen downwards is more difficult,
either because the centre of gravity is above the centre of dis-
placement or because, as the head and neck are out of water, the
weight of the body is consequently greater than that of the water
displaced.

The mechanism of swimming consists essentially in exercising
pressure upon the water rhythmically from above downwards, and
from before backwards with the surface of the hands and feet, so
as to cause a reaction of the water displaced, which is able to raise
the body, prevent it from sinking, and impel it forward in the
required direction.

The details of the mechanism of swimming have been little
studied since graphic methods cannot be applied, and chrono-
photography is difficult. Moreover, swimming is not natural to
man, but is an art which he learns and perfects by practice.
Accordingly there is no fixed and constant mode of swimming,
and the movements of the upper and lower limbs adopted by
different swimmers are not exactly alike. Generally speaking,
there is an initial thrust forward on the surface of the water by a
rapid extension and adduction of the legs, on which the water is
displaced backwards and toward the bottom by the feet, producing
a reaction which raises the body of the swimmer and jerks it
forward. This movement of the lower limbs is accompanied with
a forward thrust of the arms, which are brought together in front.
The arms are then moved outwards, backwards, and slightly
downwards, this being perhaps more efficacious in swimming
than the initial movement of the lower limbs. This movement
is associated with retraction and abduction of the legs, which
completes the natatory cycle.

If the swimming movements are too strong and rapid, they
are fatiguing and of little use. Both hands and feet, which act as
the blades of an oar, press on the water with the maximum available
surface, and return to the starting position with a slower move-
ment, and at the same time present the smallest possible surface
to the water.

BIBLIOGRAPHY

BORELIJ. De motu animalium, etc. Rome, 1680.

ED. and W. WEBER. Mechanik der menschlichen Gehwerkzeuge. Guttingen, 1836.
DUCHENNK.. Phys. des mouvements, 1867.
CARLET. fitude sur la locomotion humaiiie, 1872.
MAREY. La machine animale, 1879.

G. H. MEYER. Die Statik und Mechanik des menschlichen Knochengeriistes, 1873.
PETTIGREW. La locomotion chez les animaux, 1874.
A. FICK. Hermann's Handbuch der Physiol., I., 1879.

W. BRAUNE and 0. FISCHER. Abhandlungen der rnath.-phys. Klasse der konig.
sachs. Gesellsch. der Wissenschat'ten, 1885-1904.

128 PHYSIOLOGY CHAP, n

MAREY. Developpement de la methode grafique par 1'emploi de la photographic.

Paris, 1885. Le mouvement, 1894.

0. FISCHER. Arch. f. Anat. und PhysioL, Anat. Abt., 1S96.
R. DU BOIS-REYMOND. Ergebnisse d. PhysioL, II., Part ii., 1903. (Contains

many references. ) Spezielle Muskel physiologic oder Bewegungslehre. Berlin,

1903.

Recent English Literature :

SHERRINGTON. Remarks on the Reflex Mechanism of the Step. Brain, 1910,

xxxiii. 1.
GRAHAM BROWN. The Intrinsic Factors in the Act of Progression in the Mammal.

Proc. Roy. Soc., London, 1911, B. Ixxxiv. 308.
GRAHAM BROWN. Note on the Movements of Progression in Man. Journ. of

PhysioL , 1912, xlv. p. xvii.
GRAHAM BROWN. Dynamic Principles involved in Progression. Brit. Mt>d.

Journ., 1912, ii. 285.

CHAPTER III

PHONATION AND ARTICULATION

CONTENTS. 1. General observations on the fundamental characters of sounds,
and their formation by different musical instruments. 2. Structure of larynx as
a musical instrument ; functions of laryngeal muscles. 3. Nerves and centres of
phonation. 4. Mechanical conditions for the production of laryngeal sounds ;
function of different parts of the phonatory system. 5. Principal characteristics
of the singing voice. 6. Difficulties and natural imperfections of singing.
7. The vowel system in phonetic language. 8. Theory of physical nature of
vowel tones. 9. System of semivowels or sounding consonants, middle consonants
and mute consonants. 10. Composition of syllables and words. 11. Writing, or
graphic language. Bibliography.

BOTH in animals and man movement may be regarded, broadly
speaking, as the external, conscious or unconscious, manifestation
of the mental state. But it is essential to discriminate between
the movements which betray only instinct and feeling, and the
expressional movements which are the means of intellectual
communication.

These expressional movements and attitudes taken as a
whole constitute natural language, and are of special artistic and
psychological interest. From the physiological point of view
they present no difficulties ; they can be explained on simple
anatomical principles, and by the general laws of mechanics,
which were discussed in the last chapter.

The natural language and the vocal expression of animals
constitute our only objective basis for the construction of a
comparative psychology. This language consists of gestures,
ejaculatory sounds or noises, and physiognomic attitudes, which
are partly imitative (onomatopoeic) and to a far larger extent
instinctive, developed according to the laws of heredity and
atavism. In this language there is nothing conventional ; it is
intelligible to all, without instruction or effort. Without such
a language animals would be unable to herd together, unite in
families and societies, defend themselves from their enemies,
migrate in flocks at certain seasons, etc.

As a general rule it may be said that natural language is
most complete in the more intelligent animals. In different

VOL. Ill 129 K

130 PHYSIOLOGY CHAP.

animals, again, different organs or parts have the task of expression.
In the higher mammals it is the face which by the mobility of
its muscles lie trays most expression, and in many mammals but
not in man the ears contribute greatly to expression by their
varied movements ; the nose, lips, and mouth play a considerable
part in physiognomy. In some animals, again, the movements of
the tail and feet are significant. Lastly, the different postures of
the body as a whole play a great part in expression. Painters,
sculptors, actors, all make special studies of the natural language,
both in animals and man. They devote themselves to observing
and minutely analysing postures and deciphering their psycho-
logical significance, in order to reproduce them effectively in
works of art or dramatic representations.

I Hit the chief means by which the animal expresses its feelings,
wants, and passions is the voice, i.e. the inarticulate or scarcely
articulate sounds and noises which are characteristic of different
species.

In deaf mutes the language of gesture attains a high develop-
ment, and is able to fulfil all the needs of social life. But under
normal conditions the mimetic language of man is almost always
accompanied by phonetic language, or speech, and merely serves
to reinforce and elucidate expression.

Voice production is not the direct effect of muscular activity,
but is due to the vibrations produced in a particular apparatus,
the larynx, which is a true musical instrument. Nevertheless, as
it is muscular contraction which produces the degree of tension
in the vocal cords that is essential to the formation of the different
sounds, the study of phonation (speech) is closely connected with
the study of movements.

The formation of words, i.e. articulate speech, is a more
complex process, which is not limited to the larynx, but also
depends on the production of non-musical noises by the current
of expired air as it passes through the pharynx, buccal cavity,
and nasal fossae. Consequently, laryiigeal phonation is not in-
dispensable to conversation, any more than verbal articulation is
necessary to singing. It is possible to whisper without using
the vocal cords, and to sing vocally without words.

I. Since the voice is an acoustic phenomenon with musical
characters, the organ which produces it may be considered as a
musical instrument. In order to understand its function in
speech, it is well to glance briefly at the fundamental principles
of the production and characteristics of tones in general.

All elastic, solid, fluid, or gaseous bodies are capable of
vibrating so as to produce auditory sensations, that is, tones or
noises. A tone, according to Helmholtz, is any auditory sensation
produced by regular rhythmical vibrations ; a noise is a sensation
due to irregular and non-rhythmical vibrations.

in PHONATION AND ARTICULATION 131

Simple sounds or tones are composed of pendular vibrations,
i.e. to-and-fro movements of the vibrating molecules which follow
the same laws of motion as a pendulum. These vibrations only
differ in amplitude and duration : the amplitude is directly pro-
portional to the loudness of the sounds ; the duration is inversely
proportional to the number of vibrations per second, on which the
pitch of the sound depends. The form of the pendular vibrations
is constant and invariable. They can be graphically recorded
by making a tuning-fork trace its vibrations on a revolving
cylinder.

Helmholtz distinguishes "simple tones" or sounds (Ton) from
" compound tones " (.Klang), which are an aggregate of the simple
tones produced by simple, pendular vibrations. While, the form
of vibration in simple tones is always the same, that of compound
tones varies considerably, and depends on. the algebraic sum of the
component tones. The deepest of these tones is called the prime
tone, and the rest are the harmonics, or over-tones. The vibration
frequency of the prime tone to that of the partial tones is in the
ratio of 1 : 2 : 3, etc.

The number of partials which make up a compound tone, and
their relative strength, differs considerably for different musical
instruments, even when the prime tone is the same. This difference
gives rise to the quality (timbre, Klangfarbe] of a note, which
depends on the particular form of the vibration of the tone, due to
the relative number and strength of its harmonic overtones.

A compound tone can be resolved into its partial tones by
means of resonators. All sounding bodies have their own note ;
when made to vibrate, they invariably give out a note of a certain
pitch, which corresponds with a certain frequency of vibration per
second. When the surrounding air transmits to the sounding
body a number of vibrations corresponding to its proper note, it
begins to vibrate in unison. When, on the contrary, the vibration
frequency does not correspond with the frequency of its own note,
it remains at rest, or vibrates very feebly. Given a series of hollow
metal chambers (resonators) tuned to different notes of the musical
scale, it is possible to analyse compound tones into their partials.
When one ear is stopped, and the other is applied to the aperture
of a resonator, each resonator reinforces its own note and cuts
out all the rest (Helmholtz). Konig's manometric flame method,
described in text-books of physics, renders visible the partials
contained in a compound tone.

Another mode of analysing complex sounds is based on the
phonautographic curves traced by means of the thin membranes
used in phonographs with a very light lever, or a small mirror
that reflects a beam of light 011 to a travelling sensitive surface
(Hermann's

Musical instruments can be classified according to the

132 PHYSIOLOGY CHAP.

way in which their sounds are produced ; the principal forms are
stringed instruments, wind instruments, and reed pipes.

In stringed instruments the notes produced by the vibrations
of the strings are enormously reinforced by the resonance boxes.
The pitch varies with the length, tension, density, and thickness
of the stretched string.

The frequency of vibration per second, on which the pitch
depends, is inversely proportional to the length of the string. A
string vibrating over its whole length gives out the deepest note ;
if the length is halved, the frequency of vibration is doubled, and
the pitch is raised an octave ; with a third of its length the
frequency will be three times as great, i.e. a twelfth, and so on.

The frequency of vibration varies directly as the square root
of its stretching force. In order to raise by an octave the pitch
of the note given by the string, the tension would require to be
increased four times.

The frequency of vibration varies inversely as the mass of unit-
lengths of the string. Thicker and heavier strings vibrate less
rapidly and therefore have a deeper tone.

Wind instruments differ from stringed, since the air is here the
resonant body, and the walls of the pipe in which the air vibrates
affect only the timbre, i.e. the number and strength of the partials.
The pitch of the fundamental tone depends on the dimensions of
the pipe, and the strength of the blast of air passing through its
aperture. The narrower and shorter the pipe, the higher is the
pitch ; the greater the tension of the vibrating air molecules, the
more rapid are the vibrations, and the higher the frequency per
second.

Eeed instruments (oboe, clarinet, bassoon) only differ from
other wind instruments by the fact that their aperture is not
fixed and constant, but is formed of two vibrating tongues, which
rhythmically enlarge and reduce the opening by which the air
penetrates into the tube. According to Helruholtz the vibrations
of the tongues are pendular, and they can only give out simple
tones. The compound tones of these instruments depend on the
vibration of the air in the pipes ; the tongues merely regulate the
entrance of the air blast by rhythmically alternating the diameter
of the opening, which breaks up the column of air into a series of
rapid blasts.

Instruments with rigid tongues must be distinguished from
those with soft or membranous tongues, which are represented in
brass instruments (trumpets, horns, etc.) by the lips of the performer.
In these instruments the number of the vibrations is inversely
proportional to the length and diameter of the vibrating membrane,
and directly proportional to its tension and elasticity and to the
strength of the air-current thrown into vibration. The width of
the aperture does not appear to influence the pitch of the note

Ill

PHONATION AND AKTICULATION

133

produced by membranous tongues, but its formation is easier
in proportion as the slit is narrower. The extra tubes which
form the body of these instruments have a great influence on pitch
and timbre ; the tones become deeper as the body is longer, but
never drop an octave as is the case in instruments with rigid lips.
As a musical instrument the larynx has many points of
resemblance with tongued instruments. The formation of laryn-
geal sounds depends on the passage of air through a slit (opening
of the glottis) which is rhythmically altered in width by the
vibration of membranous tongues (the vocal cords) so as to break
up the air blast that passes through it. The wind-pipe is formed
by the bronchi and trachae,
as in brass instruments ; the
sounding -pipe or resonator
by the cavities lying above
the glottis, i.e. the larynx and
pharynx, the mouth and the
nose. On the other hand
the vocal apparatus is dis-
tinguished from all tongued
musical instruments by the
fact that the vocal cords
which represent the tongues
can change at any moment
in length, breadth, diameter,
and tension, even independ-
ently of the pressure of the

air blast which thrOWS them Fl - S7. Laryngeal cartilages, seen from behind.

(Henle.) t, thyroid cartilage: Cs, i.'l, its superior
and inferior horns; Pm, Pr, processus muscnlus
and vocalis of arytenoid cartilage ; co, cartilage
of Santorini ; <;, cricoid cartilage.

cr

into vibration.

A clear idea of the con-
struction of the larynx is
essential in order to understand the complex mechanism of
phonation.

II. The larynx consists of a cartilaginous skeleton which is only
partially ossified. The laryngeal cartilages are united by fibrous
membranes, ligaments, small articular capsules, and by a series of
small muscles, which constrict or dilate the glottis, stretch or relax
the vocal cords, and regulate the thickness of their vibrating
portions.

The cricoid cartilage is shaped like a signet ring with its narrow
part forward, and its face backward. Its lateral surface articulates
with the inferior cornua of the thyroid cartilage. The two
cartilages can rotate round the horizontal axis of these articular
surfaces, the anterior surface of the thyroid may be displaced
forwards and downwards, or the front part of the cricoid cartilage
may be pushed up towards the thyroid. The triangular bases of
the two arytenoid cartilages articulate at the upper margin of the

K 1

134

PHYSIOLOGY

CHAP.

cricoid plate on both sides of the median line by oval saddle-shaped
joints, which allow of their rotation on their base, and the dis-
placement of the base inward or outward. The stout crico-
arytenoid ligament controls the back to front movement of the
arytenoids. At the summit of the latter comes the articulation of
the two little cartilages of Santorini (Figs. 87, 88, 89).

The thyroid cartilage is attached to the hyoid bone, which lies
above it, by a fibrous membrane, the thyro-hyoid (known in its
middle portion as the ligamentuni thyreo-hyoideum lateralis), and
by the lateral thyro-hyoid ligament, which runs from the superior
cornua of the thyroid to the great cornua of the hyoid. By means

-Cs

Pi 3

FIG. 88. (Left.) t, thyroid, and cc, cricoid cartilages, from the side. (Henle.)

FIG. 89. (Right.) Laryngeal cartilages divided through the median -sagittal plane, and viewed
from within. (Henle.) /, thyroid cartilage ; Cs, its upper horn ; Pi', processus vocalis of
arytenoid ; co, cartilage of Santorini ; er, cricoid cartilage.

of these membranes and ligaments the whole larynx can be drawn
upwards.

Behind the thyro-hyoid membrane is the epiglottis, which is
attached below the thyro-epiglottidean ligament to the median
notch of the thyroid, and projects into the pharyngeal cavity in the
form of a tongue which is folded back in swallowing and forms a
lid for the upper opening of the larynx (Figs. 90, 91, 92).

On both sides of the free portion of the epiglottis the mucous
membrane forms a fold that unites the upper margin of this
cartilage with the cartilages of Sautorini. In the depth of this
aryteiio-epiglottidean fold there is a group of mucous glands and a
nodule known as the cuneiform cartilage, or cartilage of Wrisberg.
The aryteno-epiglottidean fold limits the upper opening of the
larynx ; it is oval in form and is inclined backwards and downwards.

The laryngeal cavity narrows into the glottis or rima glottidis.

Ill

PROBATION AND AKTICULATION

135

Here the mucous membrane forms on each side two thick trans-
verse ridges which extend from the base of the epiglottis backwards
to the vocal processes of the arytenoids. The two upper ridges are
known as the false, and the two lower as the true vocal cords. The
former project less towards the median line of the glottis than the
latter. Between the true and false vocal cords are two recesses,
known as the ventricle of Morgagni (Fig. 94).

The elastic fibres of the submucosa are highly developed in the

fas

tat

J. f -

FIG. 90. Laryngeal cartilage with fascia, ligaments, and insertions of certain muscles. (Henle.)
Oli, hyoid bone; e, epiglottis; Cs, superior horn of thyroid cartilage; he, hyo-epiglottic
ligament ; Jitl, lateral hyo-thyroid ligament ; tr, cartilage tritica ; tc, thyro-epiglottie cartilage ;
ca, crico - arytenoid cartilage: tas, tai, superior and inferior thyro - arytenoid ligaments;
Cap', Cap", insertions of posterior crico-arytenoid muscle ; Lp, insertion of laryngo-pharyngeal
muscle.

true vocal cords, and form compact bands which run through their
whole length ; they are wedge-shaped in cross-section, and covered
by a layer of non-ciliated pavement epithelium. In the false vocal
cords the elastic connective tissue is much less abundant, and the
mucous membrane that covers it is rich in adenoid tissue, which is
even more plentiful in the laryngeal ventricles and on the posterior-
inferior surface of the epiglottis. The mucous membrane of these
parts soon becomes oedematous from accumulation of lymph in the
lymph-spaces, which may obstruct respiration and cause suffocation
by closure of the glottis.

Owing to their elasticity the true vocal cords extend and con-
tract without falling into folds, and their delicate free edges,

136

PHYSIOLOGY

CHAP.

which are thrown into vibration by the expiratory blast, remain
regular.

The two true vocal cords which extend from their anterior
insertion on the thyroid to the vocal processes of the arytenoids,
into which they are inserted posteriorly, form the pars vocalis of
the glottis, the average length of which in the adult male is 18 '2
mm. according to Miiller, 17'5 mm. according to Harless, in the
female 12'6 mm. according to Miiller, 13 - 5 mm. according to Harless.
The posterior part of the glottis, which is 7 -8 mm. long, and

FK;. 91. Larynx from behind, after removing a portion of the aryepiglottidean fold and upper
posterior portion of left thyroid cartilage. (Henle.) Taep, thyro-ary-epiglottidean muscle ;
Cap, posterior crico - ary tenoid muscle; A, arytenoid muscle; x, kerato - cricoid muscle;
kcps, posterior, superior, kerato-crieoid ligament ; co, cartilage of Santorini ; *, mucous glands
iu tlie aryepiglottic fold.

extends from the posterior ends of the vocal cords to the intra-
arytenoid fold, is bounded by the arytenoids, and is known as the
rirna glottidis respiratoria or intercartilaginea.

The laryngeal muscles dilate and constrict the glottis, and
extend and relax the vocal cords. These effects for the most, part
depend not on the action of a single muscle, but on the co-ordinated
play of several, which makes it harder to obtain any exact know-
ledge of the function of each separate muscle when they are
working together.

The two posterior crico-aryteuoid muscles are the chief, if not
the only dilators of the glottis ; owing to their attachments
and the oblique course of their fibres they rotate the bases of the

Ill

PHONATION AND AKTICULATK >X

137

arytenoids round their vertical axis, and, therefore, draw the two
muscular processes of the arytenoids down and back, and con-
sequently further from the median line, and at the same time
raise the two vocal processes. Isolated contraction of these
muscles must therefore abduct the vocal cords and dilate the rima
glottidis ; their paralysis must, on the other hand, produce in-
spiratory dyspnoea owing to abnormal constriction of the rima, but
it does not cause appreciable disturbance of phonation.

The constriction of the glottis is produced chiefly by the

Oh

.} tr

cl

FIG. M. Larynx and hyoid bone, from the front. (Henle.) Oh, hyoid bone; litl, lateral hyo-
thyroid ligament ; if, cartilage tritica ; htm, median hyo-thyroid ligament ; ct, crieo-thyroid
ligament; Pp, inferior extremity of palato-pharyngeal muscle; Th, thyro-hyoid muscle; Cir,
erico-thyroid muscle divided into three bundles ; the vertical bundle on the left side has been
removed to show the crico-thyroid ligament i:t.

transverse arytenoid muscle, which runs between the outer
posterior borders of the arytenoids, and by contracting draws the
two bases of these cartilages towards the middle line, and their
mesial surfaces together, so that the intercartilaginous glottis
is closed. When this muscle is divided in any animal, the
posterior portion of the glottis remains fully open.

Other muscles also are concerned in the active closure of the
glottis ; they co-operate with the transverse arytenoids to form
a kind of laryngeal sphincter. Among these are the thyro-
aryepiglottidean, and the thyro-arytenoid muscles. The two first
run from their point of attachment on the inner surface of the
thyroid obliquely backwards over the two posterior surfaces of

138

PHYSIOLOGY

CHAP.

the arytenoids, where they cross in the median line, and then
run along in the aryteno-epiglottidean fold to be inserted in
the base of the epiglottis. The two latter start from the lower
part of the internal angle of the thyroid, and turn backwards
and upwards to the muscular processes of the arytenoid. The
chief function of these muscles is to constrict the glottis, and
reinforce the transverse arytenoid muscle.

The lateral crico-arytenoid muscle also aids in the abduction
of the vocal cords. This muscle runs obliquely from behind and

CO

M cap

Fin. 93. Side view of larynx, utter exarticula-
tion and removal of left plate of thyroid
cartilage. (Henle.) Sat, articular surface of
thyroid with cricoid ; (jap and ( 'al, crico-
arytenoid muscles, posterior and lateral ;
co, cartilage of Santorini, below which the
arytenoid and thyro-epiglottidean muscles
(Fig. 91) are seen in profile.

ct

Fie. 94. Frontal section of larynx, the anterior
half viewed from behind. (Henle.) t, thyroid;
cr, cricoid ; a, plica ary-epiglottica ; Taep,
thyro-ary-epiglottidean muscle ; Toe and
Tai, thyro-aryitenoid muscles, external and
internal : 1, tubercle of epiglottis ; 2, 3, ven-
tricle ; 4, plica thyreo-arytaenoidea superior
or false vocal cord; 5, plica thyreo-ary-
taenoidea inferior, or true vocal cord.

above, forward and downward, viz. in the opposite direction to the
posterior crico-arytenoid or abductor of the glottis.

The tension of the vocal cords is especially due to the crico-
thyroid muscles, which in contracting raise the front part of the
cricoid towards the thyroid, and depress the posterior part of
the cricoid and consequently of the two arytenoids which rest
upon it (Longet). The effect of this rotation of the cricoid on
its transverse horizontal axis is to increase the distance between
the points of insertion of the vocal cords and thus to stretch
them. In order that the vocal cords may be stretched, it is necessary
that the two arytenoid cartilages should be firmly fixed, so that

Ill

PHONATION AND AETICULATION

139

Tae

Tan

they cannot be drawn forward. This is effected by the combined
action of the dilatators and constrictors of the glottis, viz. the
posterior crico-arytenoids (dilatators), the transverse and oblique
arytenoids, the external thyro-arytenoids, and the lateral crico-
arytenoids (constrictors). If the posterior crico-arytenoids alone
contracted with the crico-thyroids, the vocal cords would be
stretched and abducted and the glottis dilated. But it is
essential for the formation of sounds that the cords shall be not
only tense, but also approximated to each other, so that they can be
thrown into vibration by the expiratory air-current. These two
conditions are realised when the constrictors of the glottis are
thrown into action simultaneously with the dilatators.

According to C. Meyer and Griitzner, the genio-hyoid and
thyro-hyoid muscles con-
tribute to the tension of
the vocal cords, as they
raise the thyroid upwards
and forwards in the direc-
tion of the chin, and sup-
plement the action of the
crico- thyroid muscles by
which the rotation of the
crico- thyroid articulations
round the transverse hori-
zontal axis is effected.

The relaxation of the
vocal cords is due to
simple elastic reaction
when the extensor muscles
cease to act. Active re-
laxation of the cords can,

however, be produced by the internal thyro-arytenoids, which
are perhaps the most important muscles for phonation. They
are triangular muscles, which extend with the vocal cords from
the inner angle of the thyroid to the vocal processes of the
arytenoids, but some of their bundles are inserted in the elastic
substance of the cords. When these muscles contract they pro-
duce an opposite effect to the crico-thyroids, and bring the vocal
processes of the arytenoid nearer to the thyroid, which relaxes
the cords. But it is conceivable that contraction of the isolated
bundles inserted into the elastic tissue of the cords may produce
tension of some parts and relaxation of others.

It is very probable that the true function of the internal
thyro-arytenoids in phonation is to regulate the tension and
thickness of the vibrating portion of the vocal cords, by which
a rapid succession of tones of different pitch is made possible.

The internal thyro-arytenoids almost always co-operate in

Km. '.15. Transverse section of larynx through bone of
arytenoid cartilages. (Henle.) t, thyroid ; PC, pro-
cessus vocalis of arytenoid ; .?//, sinus pyriformis ;
Th, section through thyro-hyoid muscle; A, ary-
tenoid muscle; Toe, Tai, thyro - arytenoid muscles,
internal and external ; Taep, thyro-ary-epiglottidean
muscle ; *, anterior cord of glottis.

140

PHYSIOLOGY

CHAP.

phonation with other laryngeal muscles. If we assume that
during contractions of the muscles which stretch the vocal cords,
the internal thyro-arytenoids which tend to relax them are also
contracting, it is easy to understand the functions of the latter,
which regulate the delicate changes in position of the larynx
and vocal cords necessary in a gradual succession of tones that
differ little in strength and pitch from each other. The feeling
of tension in the larynx in singing with the chest register fully

open shows that in singing all
the laryngeal muscles may be
more or less active, and that the
formation of different musical
notes, gradations of their pitch,
and rise and fall in the scale,
depend on the delicate co-ordina-
tions of their activity, and par-
ticularly on the internal thyro-
arytenoids, which are in direct
and intimate relation with the
vibrating vocal cords, and have
justly been named the " vocal
muscles."

III. The nerves to the larynx
are the two laryngeal branches
of the vagus (Fig. 96). The
superior laryngeal certainly con-
tains more sensory than .motor
fibres ; the former are distributed
by the rainus internus to the
mucous membrane of the larynx
FIG. 96. Laryngeal nerves from behind, and to the laryngeal muscles as

(Sappey.)l, Superior laryngeal nerve; 2, its flU vp( , n f mnqmilflv cprmp rhp

external branch ; 3, 4, 5, twigs to mucous HDrCS UlUSCUJdl SenbC , tilt

membrane of larynx ; 6 filaments that con- mo tor fibres paSS through the
nect lett superior and interior laryngeal

nerves; 7, same nn the right: 8, 8, inferior ramUS externUS to innervate the

laryngeal nerves; !>, branches to posterior ,1 -j -i ,1 i

cricp-arytenoid muscles; 10, branch to Cl'lCO-thyrOld mUSClCS, partly alSO

arytenoid muscle ; 11, 12, branches to crico- t-U c q r -irfemnirl rnnenlp
aryteiioid and thyro-arytenoid muscles. B dry ten O. SOie.

The inferior laryngeal, or

nervus recurrens, is a purely motor branch which supplies all
the muscles of the larynx except the crico-thyroid.

As Claude Bernard observed complete aphonia in cats after
extirpation of the spinal accessory, it was generally held that
the motor fibres of the larynx came from the ramus interims
(accessorius vagi) of this nerve, although they ran in the vagus.
But the later work of Grabower (1890) showed that the motor
branches to the larynx originate in the vagus, and more
particularly from its lower roots.

Section of both laryngeal nerves produces relaxation of all

in PHONATION AND ARTICULATION 141

the muscles of the larynx, so that the vocal cords assume the
position of elastic equilibrium as in the dead body. Under
these conditions the glottis is moderately open, in the form of
mi isosceles triangle, with the angle of the apex towards the
attachments of the vocal cords on the inner surface of the thyroid.
Contraction of the laryngeal muscles is therefore not required
to hold the glottis open, as it must be in respiration. Laryngo-
scopic observations show, however, that during quiet respiration
when no voluntary influence is exerted upon the laryngeal
muscles the glottis is more widely open than after death. In
quiet respiration the glottis has an average width of 14 mm. in
the adult man, and about 11 mm. in a woman, while on the dead
subject it is about 5 mm. and 4 mm. respectively. This striking
difference shows that in life the posterior crico-arytenoid muscle
is kept continuously in a state of semi-contraction by the reflex
or automatic tonic activity of a centre, which acts exclusively
or predominatingly upon those fibres of the recurrens which
innervate the abductors of the vocal cords.

In many animals this tonic contraction of the abductors of
the glottis varies with the rhythm of the respiratory muscles ;
at each inspiration the glottis dilates, and at each expiration
it is slightly constricted. In man, however, laryngoscopical
observation shows that during quiet breathing these respiratory
oscillations of the glottis do not occur in the great majority of
cases (Sernon), and only appear during forced or dyspnoeic
respiration (see Vol. I. p. 421).

After section of the recurrent laryngeal nerve this respiratory
rhythm ceases, and the cords take up the paralytic position of
moderate separation which is seen after death.

Section of one recurrent nerve alone deforms the glottis owing
to disappearance of the tone of the muscles on the paralysed side,
which brings the vocal cord of that side nearer the median line.
This deformation or asymmetry of the glottis increases during
forced respiration.

The most important effect of section of the recurrent nerves is
the aphonia first described by Galen. Total loss of the voice is
not, however, constant. Haller, J. Miiller, Magendie, and others
noted that many dogs continue to bark after section of the
recurrent nerves, while others are still capable of emitting high
notes, especially when suffering acute pain. Longet confirmed this
fact, and found that the power of uttering high sounds was ob-
served only in dogs a few months old, in which the tension of the
vocal cords produced by the action of the crico-thyroid muscles,
which are not paralysed by section of the recurrent nerves,
suffices for the formation of high sounds, the inter-cartilaginous

O t O

portion of the glottis not being fully developed, owing to the almost
total absence of the vocal processes, so that the cords are kept

142 PHYSIOLOGY CHAP.

sufficiently close together, even when the arytenoid muscles are
paralysed.

Stimulation of the peripheral branch of a recurrent nerve
brings the cord of the same side nearer the median line than does
simple section of this nerve, while stimulation of both recurrent
nerves causes the cords to come together and the glottis to close.
So that normally the effect of the recurrent nerves which contain
fibres for both the abductors and the adductors of the glottis is
domiiiantly on the dilatators ; when, on the other hand, they are
stimulated artificially the effect on the adductors of the glottis pre-
dominates. The explanation of these phenomena seems to be as
follows : Normally, only those fibres of the recurrent nerves which
are connected with a centre intimatelv related with the bulbar

b

respiratory centre exert a constant tonic influence which maintains
the inspiratory dilatation of the glottis ; when, on the contrary, the
two recurrent nerves are artificially excited, all the laryngeal
muscles concerned in voluntary phonatioii (except the anterior
crico-thyroids) contract, and the contraction of the adductors
consequently predominates.

Section of the superior laryngeal nerve on one or both sides
does not appreciably affect the glottis, but it makes the voice
raucous and prevents the formation of high notes owing to the
loss of function of the crico-thyroid muscles which keep the cords
in tension. Longet demonstrated that the peculiar harshness
which ensues on paralysis of the superior laryngeal nerve depends
wholly on its external branch, which gives fibres to the crico-
thyroid. Isolated section of this nerve produces the same effect
as section of the whole nerve. He found, too, that the hoarseness
of the voice can be made to disappear by bringing the cricoid
artificially nearer the thyroid ; it is therefore obviously due solely
to relaxation of the vocal cords. After cutting the internal
branch of the inferior laryngeal, Longet could detect no appreci-
able change in the animal's voice, and electrical stimulation of
this branch produced no effect on the laryngeal muscles, though
Magendie held that the ramus interims contains motor fibres for
the arytenoid muscle.

The centres of the laryngeal fibres, both those which maintain
the laryngeal respiratory rhythm and those which control phona-
tion, lie in the bulb or medulla oblongata.

The centre for respiratory rhythm is closely connected with
the respiratory centre, but is distinct and independent of it. We
saw that the glottis, during quiet respiration, is kept constantly
dilated by the tonic action of the recurrent nerves. Semon and
Horsley, experimenting on cats, further showed that stimulation
of the upper portion of the floor of the fourth ventricle produces
marked widening of the glottis, but the thoracic respiratory move-
ments continue ; the bulbar centre for the laryngeal respiratory

in PHONATION AND ARTICULATION 143

movements can therefore be excited independently of the centre
for the thoracic respiratory movements. Unilateral stimulation
of this centre invariably produces bilateral effects, i.e. abduction
of both vocal cords and widening of the glottis.

The movements of phonation have also a separate centre in the
bull). After separating the brain from the bulb, Vulpian was able
renexly to elicit cries, as though the animal still reacted to the
painful effects of stimulation. Semon and Horsley on stimulating
the ala cinerea and upper margin of the calamus scriptorius,
obtained energetic closure of the glottis, or adduction of both
vocal cords, when the animal was not too profoundly narcotised.

Since phonation is a voluntary act, perfected by practice, it is
regulated by special cortico- cerebral centres which control the
action of the bulbar laryngeal centres.

The cortical centres in the Macacus monkey lie in the lowest
part of the pre-central or ascending frontal convolution ; and in
doo-s, in the lowest part of the pre-crucial part of the sigmoid
gyrus. Electrical stimulation of this area, in either hemisphere,
produces adduction of both vocal cords which lasts as long as the
stimulation (Semon and Horsley). But if this is unduly pro-
tracted the need of breathing causes a pronounced dilatation
of the glottis, which momentarily interrupts its closure.

In man the area of phonation and articulate language is far
more developed ; it lies at the foot of the third frontal convolution,
and acquires a much higher functional significance in the left
hemisphere than in the right. This important subject will be
discussed more fully in Chapter IX.

Extirpation of both cortical speech centres does not paralyse
the glottis in animals. After unilateral extirpation stimulation
of the centre in the other hemisphere produces the same effect-
closure of the glottis as was previously obtained.

Unduly strong or protracted stimulation of the cortical centre
of phonation may induce an epileptic attack which begins in the
vocal cords, and then spreads to the muscles of the face, neck, and
limbs. The scream with which ordinary epileptic attacks begin
probably depends on the initial excitation of this centre in
the cortex.

IV. Ferrein (1741) was the first who attempted acoustic
experiments on the excised larynx of recently killed dogs, by
bringing the walls of the glottis artificially together, and blowing
forcibly through the trachea.

Johannes Miiller (1839) successfully resumed the study of the
formation of sounds in the larynx of dead bodies. He fixed
threads to the two arytenoid cartilages so that he could alter
the width of the glottis by bringing them more or less closely
together, and produced different degrees of tension in the vocal
cords by pulling the thyroid cartilage forward by weights.

144 PHYSIOLOGY CHAP.

The trachea was connected to a bellows, and the different
pressures at which the air traversed the glottis were measured
by a manometer.

With this method Miiller carried out a long series of experi-
ments which, though less valuable to-day owing to the laryngo-
scopical observations now made on the living subject, were of
epoch-making importance in the history of physiology. When
the cords were brought together, their tension being unchanged,
the laryngeal sounds became higher ; on moving the cords apart,
the sounds were deeper. With increased tension of the cords, the
note could be raised two octaves. With increased air pressure, the
tension of the cords being unchanged, the strength and pitch of
the laryngeal note could be raised a fifth. Lastly, he found that
everything above the true vocal cords could be removed without
altering the pitch of the sounds, and that the office of the accessory
tube, the pharyngo-buccal and nasal cavities, was limited to
altering the pitch.

J. Miiller first constructed an artificial larynx with one or two
membranous tongues of elastic material or arterial wall stretched
across the mouth of a wooden pipe, 011 which he studied the
mechanical conditions for the production of sound and of variations
in pitch, strength, and timbre. But in his conclusions he fell into
the same error as Ferrein, who first compared the vocal cords to
the strings of a violin, and regarded their vibrations as the primary
source of the sounds, the air blast as the bow which threw them
into vibration, and the thorax and lungs as the hand that moves
the bow. Miiller supported this theory, even after W. Weber had
demonstrated by his classical experiments that the sounds of
tongued instruments are essentially due to explosions of air, viz.
to the periodic increments and decrements of pressure as it passes
through the slit that lies between the vibrating tongues.

Direct observation on the living subject of the position of the
glottis during the formation of sounds was an immense advance
in the study of the mechanism of the laryngeal sounds.

Magendie (1816) was the pioneer in this research. He
recognised that it is necessary for the emission of vocal sounds
that the arytenoids and vocal cords be brought together,
while the opening of the inter-cartilaginous glottis does not
prevent the formation of sounds. His method consisted in
exposing the glottis in dogs by an incision between the hyoid
bone and thyroid cartilage. The same method was adopted by
the surgeon Malgaigne (1831), who corrected certain errors in
Magendie's observations, and showed that only the pars niena-
branacea of the glottis is concerned in voice formation.

The human glottis has also been directly observed in persons
who have attempted suicide by cutting the throat above the vocal
cords (Mayo, 1883, and others). Such observations confirm the

Ill

PHONATION AND AKTICULAT ION

145

fact that there is adduction of the vocal cords in the formation
of sounds, so that the glottis assumes the form of a slit.

The discovery of the laryngoscope by the famous singing-
master Manuel Garcia (1854) made it possible to observe the
human glottis directly under normal conditions, during the
emission of laryngeal sounds of different pitch.

The original laryngoscope used by Garcia was a simple metal mirror
fixed to a handle at a suitable angle. After warming it gently over a spirit
lamp to prevent the deposition of moisture, it was introduced into the isthmus
of the fauces, so that a beam of light could be thrown on to the glottis, which
thus becomes visible to the observer, who is looking into the mirror. The

F I0 . 07. Examination of larynx by laryngoscope, u, b, two metal mirrors ; illuminated by a lamp,
which is reflected from a mirror with a central aperture which is fixed in front of the
observer's eye.

latter may be directly illuminated by sunlight, which was Garcia's original
method, or by a lamp at the side of the observer in front of which a large
lens is placed to increase the strength of the illumination ; or by a lamp
placed behind the shoulder of the person observed, which illuminates a
concave mirror, and reflects a beam of light upon the mirror of the laryngo-
scope. The observer watches the latter through a central aperture in the
concave mirror (Fig. 97).

Oertel employed a rapidly intermittent illumination by placing a Mach's
stroboscopic disc in front of the lamp. It is then possible to follow the
vibration of the vocal cords by direct vision.

Szimanowsky obtained instantaneous photographs of the glottis during
the production of the different tones by substituting a photographic apparatus
for the eye of the observer.

The whole of the laryngeal vestibule cannot be seen simultaneously on
the laryngoscopic mirror, but by moving the mirror it is possible to see the
different parts in succession (Fig. 98).

Laryngoscopical observation shows that voice production is
VOL. in L

146

PHYSIOLOGY

CHAP.

preceded by closure of the whole glottis, or of the pars mem-
branacea (Fig. 98). 1 Now the emission of tones coincides with
the rapid opening and vibration of the vocal cords by the blast of
air forced through the glottis by the expiratory muscles. The
vibrations of the cords are not limited to their narrow margins,
but extend more or less through their entire mass. At the same
moment the epiglottis is somewhat raised, particularly in high
notes ; the aryteno-epiglottidean folds are stretched ; and the false
vocal cords are drawn slightly nearer together and stretched, but
they do not vibrate. At the same moment the whole larynx
becomes more or less firmly fixed by the action of the extrinsic
muscles (thyro-hyoid, sterno-thyroid, pharyngeal, etc.), and rises
with the emission of the high notes, and falls with the low notes.
During the production of high notes the tongue contracts
energetically, the tip being drawn back, and the base lifted. The
soft palate is raised towards the posterior wall of the pharynx,

FIG. '.is. Positions of glottis previous to production of the voice.

and the pillars of the fauces approximate and narrow its opening.
In deep notes, on the contrary, the tongue contracts slightly and
remains flat ; the soft palate is raised, and the pillars of the fauces
move apart. But the most important of all these changes in the
voice-producing apparatus are the vibration of the vocal cords
and the form of the membranous glottis, which varies considerably
with the pitch, intensity, and register of the voice.

In order that the vocal cords should vibrate, it is necessary
for the air- current passing through them to be at a certain
pressure, sufficient to displace them from their position of
equilibrium. In a case of tracheal fistula in a woman, Cagnard-
Latour, by fitting a manometer into the mouth of the fistula, was
able to measure the pressure of the blast of air during the
production of sounds of different pitch. He found a pressure of
160 mm. H 2 necessary for sounds of medium pitch, of 200 mm.
for high, and of 945 mm. for the highest notes. Griitzner
obtained approximately the same figures in a young man on
whom tracheotomy had been performed.

Adduction of the vocal cords and narrowing of the glottis

1 This is not in agreement with some later observations. F. A. W.

in PHONATION AND ARTICULATION 147

obstructs the passage of air, and increases the pressure in the
trachea necessary for throwing the vocal cords into vibration.
The loss of voice when the trachea is opened depends on the fall
of the pressure of the expiratory air below the minimum necessary
for the vibration of the vocal cords.

But the pressure of the expiratory air would in itself produce
no musical effect if the vocal cords were not thrown into a proper
degree of tension by their tensor muscles. As we have seen,
paralysis of the anterior crico-thyroid muscles makes the voice
hoarse, and hinders the formation of high tones.

The following general laws of the mechanism of the production
of laryngeal sounds may be deduced from experiments on animals
and observations on man :

(a) The membranous glottis is the exclusive seat of voice
production. Lesions of the vocal cords render voice production
impossible.

(b) The vocal cords acting as membranous tongues are thrown
into vibration by the pressure of the expiratory blast, and vibrate
synchronously with the air-current. The vibrations of the vocal
cords certainly produce a note, but its intensity is very low, hardly
to be compared with that of the tones arising from the larynx.
The true sounding body is the air, but the vibrations of the air
are determined by the vibrations of the vocal cords.

(c) The vibrations of the air which are started in the glottis
are transmitted to the mass of air lying below as well as above
the vocal cords. The vibrations of air in the windpipe, bronchi,
and lungs are communicated to the thoracic wall, and can easily
be detected by applying the hand to the chest. This resonance
of the chest must certainly produce increased intensity of the
laryngeal notes, though it is difficult to appreciate its importance.

(d) The resonator proper consists of the parts lying above the
vocal cords, the laryngeal vestibule, and upper portions of the
pharynx, mouth, and nose. It is on the vibrations of the air in
this tube that the special qualities which characterise the human
voice depend. The necessary coincidence between the vibration
of the vocal cords and that of the air in the resonator is obtained
by the varying tension of the walls, and the alterations in length,
breadth, and shape of the cavity, by upward and downward move-
ments of the larynx, and alterations of the tongue, soft palate,
pillars of fauces, cheeks, and lips.

(e) Moro-agni's ventricles are of little importance as resonators,
but they give space for the free vibration of the vocal cords, and
produce a secretion by which the laryngeal mucous membrane is
kept moist.

(/) The false vocal cords can alter the form of the laryngeal
vestibule by their approximation towards the middle line, and
thus change the character of the tone produced by the vibrations

148 PHYSIOLOGY CHAP.

of the true vocal cords. It is doubtful whether they can act as
dampers by dropping to the level of the true vocal cords.

(g) The function of the epiglottis in voice production is also
uncertain. But the positions it takes up must certainly contribute
to altering the character and quality of the voice.

(A) Abundant proof of the great influence on the character of
the voice of the different forms which may be assumed by the
pharyngo-buccal cavity owing to the various positions of the soft
palate, tongue, and lips, will be shown when we come to discuss
language and particularly the formation of the vowels.

V. The sounds produced by the human voice are all comprised
in the interval of three and a half octaves, or a little more, but no
one individual possesses such an extensive vocal range. Few
indeed, and only after long practice, succeed in acquiring a range
of even three octaves, and in these rare cases the end-notes of the
scale are deficient in strength and clearness. The average compass
of a well-developed singer seldom exceeds two octaves.

The range of voice within the limits of the two octaves
depends principally upon the dimensions of the larynx, which
differs considerably in the sexes. In either sex musicians dis-
tinguish three different varities soprano, mezzo-soprano, and
contralto, for the female voice ; tenor, baritone, and bass, for the
male voice. The soprano voice is about an octave higher than
the tenor ; the contralto about an octave above the bass. A few
notes between G and F of the third octave of the piano are
common to baritone and soprano. The table, p. 149, shows the
range of voice usually met with in different singers. Opposite
each note is the number of simple vibrations which correspond
to it according to the international concert pitch a 1 = 435 (see
Chap. V. of Vol. IV.).

At puberty there is a rapid development of the larynx which
alters the range of the voice. Owing to the elongation of the
cords the voice generally falls an octave in the male and about
two notes in girls. A boy's soprano voice usually changes to a
tenor, an alto to a baritone. While changing, the voice becomes
harsh, uneven, and guttural ; this is due to a transitory hyperaernia
and swelling of the vocal cords which accompanies the growth of
the whole organ.

In eunuchs the voice of childhood is usually retained, but it
becomes stronger and fuller.

The upper limit of the vocal tones is reached at about the age
of eleven years. Children's voices may reach the highest notes of
the fifth octave, which are very seldom attained by the highest
sopranos.

The range of a child's voice varies, according to Engel, from
three whole toues to two full octaves. Paulsen (1895) found on
examining a large number of children that the compass of the

III

PHONATION AND ARTICULATION

149

voice in the sixth year was about an octave, by eleven it was
twice as great, by fourteen still more extended. Girls' voices
reach their widest range at the thirteenth, boys' voices at the
fourteenth year.

In advanced life the upper tones gradually weaken, and
ultimately disappear. A soprano voice nearly always turns into
a mezzo-soprano, and a tenor often becomes a baritone. These
changes, unlike those of puberty, come on gradually, and are due
to loss of elasticity, caused by calcification of the laryngeal

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cartilages, which begins about middle age, and increases with old
age. The thyroid ossifies first ; then the cricoid ; much later the
arytenoids. In old age the compass of the voice shrinks, and its
resonance diminishes and becomes tremulous, owing to retrogressive
changes in the neuro-muscular apparatus of the larynx and the
expiratory muscles.

Voices differ not only in their relative position in the scale, but
also in quality or timbre. Just as it is easy to distinguish the tone
of a basso concerto from a violoncello, and that of a clarinet from
an oboe, so a practised ear can distinguish a bass from a baritone
or tenor, and a contralto from a soprano, even when they are
singing the same notes.

Generally speaking, " bright " voices can be distinguished from

150

PHYSIOLOGY

CHAP.

" dull " voices, while others are " full," i.e. of medium, normal
timbre. With bright timbre the larynx is raised, the resonance
cavity is short, the mouth wide open, the glottis constricted ; with
dull timbre the larynx is lowered, the resonance tube long, the
oral opening constricted, the glottis rather wider. The difference
in quality is most distinct if the same note is sung with the two
vowels A and U.

It is an important fact that the voice can be varied in the
same individual by altering the position of the vocal organ.
When the scale is sung from the lowest to the highest note the
voice retains the same quality between certain limits, the pitch
only being altered. But in rising gradually to higher notes the
voice is not only raised hut also changes in quality. The voice is
usually divided into three registers, in analogy with the registers
of an organ : these are the chest register, the middle register, and
the head register, or falsetto.

A B

Fie. 9; i. Aperture of glottis during emission of low notes (A), and liigh notes (B),

with chest register.

Laryngoscopical observations show that each register corre-
sponds to a particular position of the larynx, which is constant for
all notes comprised in that register, the tension of the cords alone
being altered according to the height of the notes. In passing
from one register to another the position of the larynx changes
abruptly.

The exact positions of the larynx in correspondence with the
different vocal registers is a subject of discussion among the
laryngologists.

It is generally admitted that in the chest register the vocal
cords vibrate over their whole length ; the aperture of the glottis
is elliptical and wide or narrow, according to the pitch of the
sounds ; the intercartilaginous portion of the glottis is also more or
less widely open ; and, lastly, the vibrations of the cords, which can
be clearly seen by the laryngoscope, are transmitted to the chest
walls, hence the name of " chest " register (Fig. 99).

In singing with a head register, or falsetto, the vocal cords are
shorter and narrower; the intercartilaginous portion of the glottis
is completely closed ; the membranous glottis, on the contrary, is

Ill

PHONATION AND AETICULATION

151

open, Itut only in the middle part, where it forms a comparatively
wide space through which the expired air can readily escape
(Garcia) ; this produces greater resonance in the pharyngo-huccal
cavity, and vibrations of the cranial bones (hence "head" voice);
the false vocal cords are tensely stretched, and approach the true
cords, or, according to some authors, actually come into contact
with them; the vibrations of the cords are only visible in the
most forward part of their free edges (Fig. 99)- Other observers.,
on the contrary, state that in the head register the glottis is open
in its entire length, although it is reduced to a linear slit (French).
Possibly all singers do not employ the same laryngeal mechanism
in the different registers.

Among the contradictory interpretations of the fundamental
differences between the chest register and the head register, that
of Lehfeldt (1835) found wide acceptance, and was adopted by

Fit;. 99a. Aperture of glottis during emission of lii.^h notes (C), with chest register ; and of
highest notes (D), with head register. (Mandl.)

Job. Miiller and many other physiologists. He assumed that in
the falsetto voice only the free edges of the vocal cords are thrown
into vibration, while in the chest voice the whole of the cords
vibrate. Bonders held that in the chest register the musculus
vocalis (internal thyro-aryteuoid), being contracted and tense,
participates in the vibrations of the cords, and that its weight
drags down the pitch. In the falsetto register, on the other hand,
as the musculus vocalis is relaxed, the vibratory movement is con-
fined to the edges of the cords; the pitch consequently becomes
higher owing to the reduction of the vibrating mass. The relaxa-
tion of the musculus vocalis accounts for the comparative breadth
of the glottis and the more rapid absorption of the reserve air, as
well as the more marked fatigue and greater vibration of the head.
After Oertel's laryngoscopical observations (1882) by Mach's
stroboscope method (intermittent illumination of the glottis) this
theory lost ground, and was gradually replaced by another,
according to which, when the falsetto voice is produced, nodal lines
are formed in the vocal cords parallel to their free borders. The
increased height of the falsetto notes is therefore due, not to

152 PHYSIOLOGY CHAP.

decreased depth and breadth of the vibrating portion but to the
subdivision of the vocal cords into two vibrating sections, by a
nodal line which runs parallel with their edges. When the
musculus vocalis is tense and contracted like the edge of the cord
in which it is embedded, it vibrates with them, and this prevents
the formation of nodal points, and the chest voice consequently
results.

The change from the chest register to falsetto is on this new
theory due principally to the relaxation of the musculus vocalis.
This change is usually easier and less apparent in women than in
men.

The singer's art is largely directed to equalising the resonance
and timbre of the voice in different notes of the scale, so as to pass
smoothly from one register to another. Many important exercises,
again, aim at facility in altering the strength of a tone without
changing its pitch i.e. at singing crescendo and decrescendo. The
strength of the laryngeal notes depends on the amplitude of the
vibrations of the vocal cords, due in its turn to the pressure of the
expiratory current. But when the position of the glottis and the
tension of the vocal cords remain unchanged it is possible by
increasing the pressure of the air-blast to raise the height of a
tone a fifth ; consequently, to produce a crescendo on the same note
there must be a compensatory alteration of the vocal cords in order
to preserve the same number of vibrations. Compensation in the
opposite direction is necessary to produce a decrescendo. These
compensations are obtained by decrease or increase of the tension
in the vocal cords (relaxation or contraction of the crico-thyroid
muscles), or by increase or decrease in the mass of the vibrating
parts (contraction or relaxation of the musculus vocalis). Laryngo-
scopical observation confirms sometimes the one, sometimes the
other interpretation. Both are difficult adjustments, which are
easily executed even by experienced singers, and are only learned
by long practice.

" Expression " depends on these modulations of the strength of
a note without altering its pitch. No musical instrument is better
adapted than the larynx to give expression in singing, for the
larynx is a living instrument, brought into direct relation with the
emotional and motor centres of the performer by means of its
sensory and motor nerves.

VI. The power of utilising the larynx as a musical instrument
is not common as a natural endowment, not only because few people
possess the range, volume, and quality of voice that is indispensable
for singing, but also because many people do not understand the
right use of the larynx as a musical organ, though every one is more
or less capable of using it as an organ of speech.

In former days, particularly towards the end of the eighteenth
century, the difference between the singing voice and the speaking

ni PHONATION AND ARTICULATION 153

voice was much discussed. The voice used for speaking is
commonly held to be different from that used in singing. But
this is a mistake. In compass the only difference is that the tones
used in speaking are generally comprised within half an octave,
while those employed in singing extend over two octaves. A more
important difference lies in the fact that in speaking many sounds
(consonants) are used, so that the tones and the intervals between
the tones are not so plain as in singing. There are not therefore
two different voices but rather two modes of using the same voice ;
dramatic recitation and lyrical declamation stand midway between
speaking and singing.

Owing to these differences between the singing voice and the
speaking voice, mistakes in the correct pronunciation of words, and
in the true intonation, modulation, and accentuation of phrases
and periods, are often tolerated in speaking because they are less
offensive ; in singing, on the contrary, false intonation and wrong
notes produce a sense of discomfort which is unbearable to the
trained ear.

Longet distinguishes three different causes for the very common
failure to sing in tune, which amounts, in some cases, to a total
incapacity :

1. The individual " has no ear," i.e. his sense of hearing is not
acute enough to enable him to distinguish between the different
tones. No one with this defect can sing. In fact, auditory
sensations are at least as necessary to the adequate function of the
organ of phonation as are visual and tactile sensations in the
movements of the body and limbs. The actual development of
the voice is dependent on the functioning of the organ of hearing ;
dumbness is associated with congenital deafness, and is almost
always due to lack of auditory sensations and not to defects in the
voice-producing apparatus.

2. The individual does not sing well because his tone-memory
is defective, i.e. notes do not leave clear and distinct traces in his
memory, from which he can easily revive the corresponding tones.
He is quite capable of singing in tune to an instrument, or with
other true singers, but when left to himself he cannot hit or keep
up the correct note, and is aware that he sings out of tune. In
these cases the musical memory can be developed gradually by
careful training, so that the faults in singing are reduced or
disappear.

3. The individual cannot sing correctly because his larynx
cannot produce true notes in response to volitional impulses. l A his
not uncommon peculiarity is due not to anomalous conformation
of the larynx, but to some imperfection of the nervous mechanism
by which the tactile and muscular sensations are transmitted
centripetally to the centre, or the motor impulses centrifugally to
the laryngeal muscles.

154 PHYSIOLOGY CHAP.

The ability to sing depends not on the construction of the
larynx, but on the possession of the proper nervous mechanism, by
which both the auditory sensations and the tactile and muscular
sensations are capable of guiding the volitional impulses in such a
way that these are promptly and accurately transmitted to the
corresponding muscles. Congenital delects in these nervous
mechanisms can also, to some extent at least, be overcome by long
and steady practice, just as a violin player is able in a wonderful
way to cultivate the nervous mechanisms which move the muscles
of his hands. A perfect singer is not born, but trained, as a
concert player is developed after long practice ; but of course in
either case a favourable congenital predisposition is indispensable
to the mastery of the art.

It is possible by minute and careful analysis of the voice to
detect comparative correctness or faults of its formation, as well as
of the different notes of the musical scale which it is able to
produce.

A voice is " true " when the vibration numbers of its notes
correspond exactly to their place on the scale ; it is " false " when
the vibration numbers are greater or less than those of the notes.
Rising (crescenti) voices are the more usual ; falling (calandi) voices
less common, except in a singer whose voice is worn out. It is
often the case that certain notes are false, while others are in tune.
Minor keys are more difficult to sing correctly than major keys.

Hen sen by Konig's manometric flames, Kliinder by the
phonautographic method which records the vibrations of the
original tone and the note sung in unison with it, made interest-
ing researches on the accuracy of the voice. They discovered that
it is very difficult to hold a note with a constant number of
vibrations for a given time. Owing to positive or negative
variations in the tension of the vocal cords, the truest voices
fluctuate in vibration frequency above and below the normal
mean. The mean error for any particular note is not more than
0'35 per cent ; but in holding on a note, or in singing crescendo
or diminuendo it may amount to 1*54 per cent, owing to the
difficulty of compensation, even in the larynx of a professional
singer with long practice, in forming and holding on the notes.
This slight natural imperfection of the voice in keeping on the
notes is due not to want of ear, but to the larynx and its vocal
muscles (thyro-arytenoid muscles), which are incapable no matter
how much they are exercised of keeping up the exact, degree of
tension required for the several notes of the scale, without slight
periodic variations. The slight imperfections in the formation
and emission of tones, perceptible even in expert singers, depend
more on the ear than on the larynx, and are due to defective
sharpness in the memory traces of the respective tones.

VII. Articulate language is limited to man, and is one of the

in PHONATION AND AETICULATION 155

highest faculties by which he is distinguished from the rest of
the animal kingdom. From the physical point of view it consists
in a series of special expiratory and sometimes inspiratory sounds
produced in the resonance cavity of the pharynx, mouth, and nose,
which may be, but need not be, combined with the laryngeal
tones. In talking aloud the laryngeal tones are combined with
the pharyugo-buccal sounds into articulate speech, but in whisper-
ing, i.e. speech without voice, there are no laryngeal tones. It is
even possible to speak sotto voce without a glottis, as after loss of
the larynx by surgical operation. The resonator is therefore of
fundamental importance to the formation of words, while in
singing it is of secondary importance.

The vocal apparatus has rigid parts, such as the hard palate
and nostrils, and mobile parts, such as the lips, tongue, and soft
palate. It is the changes in form of the resonating cavity due to
the movements of these soft parts which give rise to the different
articulate sounds. Sometimes these changes do not interrupt the
continuity of the vocal instrument ; at other times they constrict
or close it, rendering the escape of the expired air difficult or
impossible. This constriction or occlusion may occur in certain
regions, as in the glottis, in the isthmus of the fauces, between the
soft palate and dorsum of the tongue, between the hard palate or
alveolar arches and the tip of the tongue, or at the lips. These
are known as the regions of articulation.

The number of elementary sounds which in different combina-
tions build up a language or dialect is limited, but it varies
considerably in different languages and dialects. The sounds are
distinguished as vowels and consonants in the grammar of every
language. The value of this distinction has been much discussed,
and many erroneous definitions have been made, showing that
there cannot be any absolute difference between vowels and
consonants, by which they can invariably be recognised. One
group of consonants, in fact, has the character of vowels, and
these sounds are frequently referred to as the semi- vowels.

Speaking generally, it may be said that the vowels are laryn-
geal sounds, which assume their specific character in the resonating
cavity owing to the predominance there of one or two tones of a
given pitch. The consonants, on the contrary, are sounds which
are almost invariably formed in the resonating cavity, and may
or may not be combined with laryngeal tones.

The vowel a (ah) is often regarded as the foundation from
which all the other vowels may theoretically be derived. It does
in fact represent a laryngeal sound as little modified as may be
by the resonating cavity, which remains as widely open as possible.
C. Hellvvag in his Deformatione loquelae (1781) distinguishes three
typical vowels, which produce the maximal difference to the ear.
These three are the only vowels found in hieroglyphs, and in

156 PHYSIOLOGY CHAP.

Indian, Gothic, and Arabic writing. They are i (ee\ a (ah), u (00).
All other vowels used in modern languages and dialects are inter-
mediate, and are derived from these three typical vowels.

The system of distinct vowels used in different languages and
dialects is represented in the following diagram of Briicke (after
Hellwag) :

A

A e A

E a A oe O

E E O

I I u U 1 U

The angles of the triangle are occupied by three typical vowels ; at
the sides and within the triangle are the intermediate vowels, many
of which are not represented in written language by special signs.

The mouth takes up a definite position for each vowel according
as it is pronounced aloud or whispered. These positions of course
differ most for the three typical vowels.

As shown by Fig. 100 the larynx is most raised at i (ee), the
lips are drawn back and the oral aperture is widened transversely,
the teeth are brought close together, and the tongue is raised
from the floor of the mouth and brought near the palate so as
to leave only a narrow opening for the air. With u (oo), on >the
contrary, the larynx is lowered as far 'as possible, the oral aperture
is brought forward and constricted, the lips forming an almost
circular opening, owing to contraction of the orbicularis, and the
tongue is dropped towards the floor of the mouth and raised
behind towards the soft palate. Lastly, with a (ah) the vocal
tube has a length intermediate between i (ee) and u (oo), the
larynx is least displaced, the mouth is wide open and rounded,
and the whole tongue is drawn back towards the floor of the
mouth so as to form a funnel-shaped cavity.

Certain authors distinguish a (ah,) as pharyngeal, i (ee) as
palatal, u (oo) as velar (Fig. 100), but these terms have little
physiological value. The phonic characters of the different vowels
depend essentially on the position and special form of the whole
resonance cavity, and not merely on the different regions in which
it becomes constricted.

In the intermediate vowels the different movable parts of the
resonator take up intermediate positions : e (eh), e a (e = let), a e
(a = hat) are formed between i (ie) and a (ah) ; o (oh), o a ( = or),
a (6 = shot) between u (oo) and a (ah).

The pure vowels are pronounced with the soft palate raised,
and the nasal cavities more or less completely closed (Fig. 100).
When the soft palate is not raised the vowel has a nasal sound,
and if the nostrils are closed this is intensified, because the air
in the nasal cavity is better able to vibrate in unison with the
air of the pharyngo-buccal cavity.

Ill

THONATION AND AETICULA.TION

157

In pronouncing the fundamental vowel a (ah), where the
oral aperture is maximal, the soft palate is least raised
(Czermak) ; 011 dropping from a to the end-vowels u and i the
soft palate is raised and the nasal cavity more perfectly closed
in proportion as the oral cavity is constricted. This agrees with
the fact that a, o, e are easily rendered nasal, which is difficult
for i and u.

The complete series u (oo) . . . a (oh) ... i (re) corresponds to

FIG. 100. Shape of oral cavity in the production of the three fundamental vowels (Grutzner.)

the progressive rise in pitch when the vowels are pronounced with
the ordinary breath. Although the several vowels can be pro-
nounced on different musical notes it is very difficult to enunciate
u clearly in the highest soprano, and i in the deepest bass.

U... i really represent the vowel -limits. In uttering these
the canal is most constricted ; at u the opening of the lips is
narrowest, at i the oral cavity is smallest, owing to the rise of
the tongue which divides it into two. Beyond these limits the
character of the vowel sounds is obscured, and approximates to
that of the consonants.

158 PHYSIOLOGY CHAP.

The fact that the vowel limits are reached when the resonating
cavity is most restricted, and blocks the passage of the air, agrees
with the fact that it is impossible to sing u and i very long and
loud like the other vowels. According to Wolf u can only be
heard distinctly at 280 paces, i at 300, while a is quite audible 360
paces distant.

On the other hand the vibrations of the walls of the resonance
cavity produced by the vibration of the air is maximal with the
vowels u and i, minimal with a. On stopping the ears, u and i
sound very loud to the ear, a much less so. On applying the palm
of the hand to the head, the cranial bones are felt to be vibrating
at u, still more strongly at i, and not at all at a, e, o. This fact has
been utilised in teaching deaf mutes to pronounce i, which they find
the most difficult.

The diplitliongs should not be confused with the intermediate
vowels. Grunmaeh erroneously regards a, u, o as diphthongs ; in
our opinion it is more correct to define them with Goidanich, as
organic alterations of the normal vowels. All the intermediates
represent special vowel sounds due to special positions of the phona-
tory apparatus. In diphthongs, on the contrary, as Brticke noted,
there is a rapid passage from the position of one vowel to that of
the next, the first being almost always accentuated. In the
diphthongs au ( = how), ai ( = high'), etc., the first vowel functions
as the sonant, the second as a consonant.

VIII. The formation of the different vowels is thus funda-
mentally due to the special positions assumed by the pharyugo-
buccal cavity acting as a resonator, and we next have to determine
the physical nature of the vowels, i.e. the partial tones of which
they are composed, and the relations of intensity on which their
timbre or quality depends. This problem is more complicated
than appears at first sight.

Generally speaking, the sound of any musical instrument is
a compound, in which one fundamental tone, the deepest and
strongest, and several harmonic over-tones, weaker in proportion
as their pitch is higher, can be distinguished. But this theory is
not applicable to the human voice, especially not to the complex
sounds in which we can distinguish the specific characters of the
different vowels. This is evident from the following facts :

(a) The different vowels can be recognised even when they are
whispered, that is, uttered without any laryngeal voice.

(&) The different vowels can be uttered either in speaking or
singing to the same musical note.

(c) Any vowel may be sung to different notes of the scale, and
recognised for each note.

These three points suggest that the complicated laryngeal
sounds acquire their special vowel character from the pharyngo-
buccal cavity, which acts as a resonator, and reinforces certain

in PHONATTON AND AETICULATION 159

partials, while others are excluded, according as it assumes the
position for saying or singing one or other of the vowels.

The earliest experiments on the physical nature of vowel tones
were made by Willis (1829), and Wheatstone (1837), who con-
structed a theory of vowel tones which remained unnoticed for
twenty years. Douders (1857) first showed clearly that the cavity
of the mouth for different vowels is tuned to different pitches. It
forms a resonator which can be tuned to the different sounds
characteristic of different vowels.

In order to ascertain the tones which characterise the several
vowels, Donders cut out the laryngeal sounds which usually
accompany them, by whispering them one after the other ; under
these conditions sounds are produced in which the ear can re-
cognise a definite pitch in the dominating tone, which varies for
the different vowels, but is approximately constant in all persons
of the same sex and age. These sounds are caused by the air-blast
in the oral cavity, where the tones are reinforced so that it is
possible to recognise the different vowels, although they are
w r eaker than the normal voice. In speaking or singing the
sounds given out by the resonator are associated with the laryngeal
sounds, and the specific partials of the different vowels are greatly
reinforced, and give the laryngeal sounds their characteristic
timbre.

In his classical work Die Lehre von den Tonempfindungen
Helmholtz placed his theory of vowel-tones on a strict scientific
basis, and extended Bonders' hypothesis. According to Helmholtz
" the vowels of speech are in reality tones produced by membranous
tongues (the vocal cords) with a resonance chamber (the mouth)
capable of altering in length, width, and resonant pitch, and hence
capable also of reinforcing at different times different partials of
the compound tone to which it is applied." J

In order to determine what partial tones of the mouth cavity
give their vowel character to the laryngeal tones Helmholtz
employed a more accurate method than that of Donders. He
struck tuning-forks of different pitch, and held them before the
open mouth arranged for the pronunciation of each vowel in turn.
The pitch of the fork which then sounded loudest gave the proper
tone to which the mouth was tuned. Helmholtz found that the
pitch of the vowels rises progressively from u (oo) to a (ah) and
from a (nil} to i (ee). In u, o, a he only distinguished a single
note ; in a e , e, i, o c , u' two different notes, because the mouth cavity
is divided in the pronunciation of these vowels by the rise of the
tongue (Fig. 101). He maintained that the vowel notes are the
same in men, women, and children. The least change in the
position of the oral cavity modifies the quality of the tone, and
thus gives rise to the intermediate vowels which are so common

1 Sensations of Tone, Helmholtz, tr. Ellis from 3rd ed., p. 153, 1875.

160

PHYSIOLOGY

CHAP.

in the Franco-Italian and Anglo-Saxon languages. This fact,
according to Helmholtz, explains why the vowel tones as fixed
by Bonders and also by Merkel, Auerbach, Krinig, and other

n f :

9-

r

>
*-

f-

v,

VL *

rrr\r i f

vy 1

f

9

y d A A
*

E r <
i

'.
[)

T

ri

FIG. 101. Pitch of vowels according to Helmholtz.

later observers differ in certain respects from those which he
obtained.

He finally concluded that " vowel qualities of tone consequently
are essentially distinguished from the tones of most other musical
instruments by the fact that the loudness of their partial tones

FIG. 102. Kcinig's apparatus for illustrating the quality of vowel tones by a manometric flame.
Above, the figure shows a section of Konig's manometric capsule and the rubber membrane
which divides the stream of gas from the air of the tube that is sung into.

does not depend upon the numerical order, but upon the absolute
pitch of those partials." l

Helmholt/ attempted to demonstrate the correctness of his
view by synthetically combining the tones of certain tuning-forks

1 Page 172, Ellis' tr., q.v.

Ill

PHONATION AND ARTICULATION

1G1

in his well-known vowel apparatus. He obtained the sound of u (oo)
by combining the fundamental tone I 1 \vith/& 2 ; the sound of u (oh)
by combining the same fundamental tone with & 3 ; the sound of a
(ah) by combining b l with I 4 . He was, however, unable to repro-
duce the highest tones of e (ch) and i (re) by the tuning-forks.

The vowel tones were also studied by Ko'nig with the aid of
his mauometric flame apparatus (Fig. 102). This method is very
useful in analysing the complex nature of the vowel tones, since it
shows the difference in the form of sound-wave not only for the

IT

Fio. 103. Flame pictures of the vowels a (ah), o (oh), u (oo), in three different keys.

separate vowels, but for the same vowel at a different pitch. The
duration of the wave-periods is, however, the same for the different
vowels sung to the same note (Fig. 103). The alteration of the
form of the wave while the period is constant must be due to the
superposition of tones developed in the mouth, characteristic of
the vowels upon the tones emitted by the larynx. But it is not
possible from the simple wave-form shown by the flames to
determine the number, pitch, and strength of the partial tones
from which the different sung vowels result.

Hallock (1896) employed a method founded on that of Ko'nig.
He connected eight resonators in harmonic series with as many
Konig's man om etric capsules, sang a vowel in front of them, and
then photographed the reflection of the flames in a mirror. From

VOL. Ill M

162 PHYSIOLOGY CHAP.

these photographs the partials present in any vowel tone within
the range of the resonators could be detected.

Edison's invention of the phonograph (1877), and its perfection
by himself, by Graham Bell and others, reopened the whole
question of vowel tones, to which Fleeming-Jenkm, Ewing,
Hermann, Hensen, Pipping, Boeke, Lloyd, M'Kendrick, and others,
have contributed in the controversy. The chief question has been
whether each word has an absolute or a relative pitch, and whether
on changing the prime tone to which a vowel is sung, its principal
over-tones change too, as is the case with ordinary musical instru-
ments ; or whether the height of the partial tones which give the
vowel its character always remains the same, independent of the
pitch of the prime tone to which it is sung.

The method employed for solving this difficult problem con-
sisted in taking graphic tracings of the vowel sounds, or vowel
phonograms, and then analysing the complex curves of these
sounds into the simple curves of the component tones by means of
Fourier's theorem.

Bonders (1870) first applied the phonautograpli of Leon Scott
to the investigation of vocal phonograms. In 1878 Fleeming-
Jenkin and Ewing employed Edison's tin-foil phonograph for
this purpose, although it was too imperfect to produce the sounds
of all the vowels clearly. These authors came to the conclusion
that both relative and absolute factors entered into the composition
of the vowels an intermediate theory already accepted by
Auerbach and by Helmholtz in later editions of his book.

Hermann took up the subject about 1890, by the improved
wax-cylinder phonograph, and photographed the curves by a
beam of light, reflected from a small mirror attached to the
vibrating disc of the phonograph. The curves thus obtained,
representing the wave forms of the vowel tones, were then
analysed by Fourier's method.

Hermann found that the phonograph only reproduces the
sung vowels accurately when the cylinder rotates at the same
rate as that at which they were recorded, and that the quality
of a vowel varies considerably with the rate of the cylinder.
He maintains the fixed-pitch theory, and states that there is
for each vowel a characteristic tone which he terms the formant.
He further assumes (and in this his theory differs from all others)
that the formant need not necessarily be a partial tone of the
fundamental. The pitch of the formant may vary considerably ;
with the same prime it may vary in certain cases as much as
several semitones. Fig. 104 shows in musical notation the pitch
of the vowel according to Hermann.

Pipping's results in the main agree with those of Hermann.
He collected and analysed the vowel curves by means of Hensen's
gramograph.

Ill

PHONATION AND AKTICULATION

163

Sauberschwartx with Griitzner (1895) investigated the subject
by an ingenious application of the laws of the interference of
sounds. The vowels were sung into the mouthpiece of a long
tube, to which other short tubes of definite length were attached.
By closing the outer end of certain of these tubes various partials
could be extinguished by interference, and the listener at the
other end of the tube observed an alteration in the quality of
the vowel. Sauberschwartz, generally speaking, supports Hermann.

Later researches by Boeke, M'Kendrick and others added
new facts to the analysis of vowel sounds. At the Fifth
International Physiological Congress at Turin, Hensen stated
that the resonance tones of the oral cavity arranged for the
pronunciation of different vowels are variable within certain
limits, as had been established by Pipping. But he also showed
that the pitch of the laryngeal tones produces a rise in the oral
resonance tones. At a they may rise from 940 to 1175 ; at o

1

!

1

j j

L

J

i

i

-#

ff

j

j

~]r *

i

J 5^

^

ln\

i

v Is

*

t -A-

f

u o

FIG. 104. Pitch of the vowels according to Hermann.

from 498 to 552 double vibrations. The problem of vowel sounds
is therefore more complicated than was supposed, and still awaits
its final solution.

In conclusion, Bonders' theory, which assumes that the oral
cavity is tuned for each vowel to a tone of fixed and unalterable
pitch, whatever the fundamental laryngeal note to which it is
sung, is certainly too restricted. Each vowel, however, undoubtedly
has one or more predominating partial tones, formed by the oral
cavity, on which the specific character of that vowel depends. Since
the form of the mouth varies with the individual and the race, and
the positions it assumes in different dialects and even in different
individuals in the pronunciation of the several vowels are not
and cannot be identical, it is easy to see why the formants of
any vowel are not identical in all cases. They approximate,
however, in certain common characters, by which it is possible
to identify a vowel, however differently it may be formed by
different individuals. It is also certain that the resonating
cavity varies very little when a musical scale is sung to a single
vowel. The ear is always able to recognise the vowel sung,
whatever its pitch ; each vowel, however, has a special register
in which its quality is best ; the soprano is best adapted to the

164 PHYSIOLOGY CHAP.

end- vowel i, the bass to the end-vowel u. Finally, the clearness
and purity of vowel-formation varies considerably in different
languages. It is generally admitted that the sung or spoken
vowels are purest in the Italian tongue, and least so in English.
Italians, moreover, prefer the fundamental vowel sounds a, i, u,
which He at the extremes of the natural system ; they also admit
the middle vowels e and 6, b and 6 (open and closed), but reject
all other intermediate vowels. The English, on the other hand,
not only prefer these, but have further developed a whole series
of vowels characterised by imperfect formation, which makes
them very difficult to recognise and classify.

IX. 1 It is difficult to draw up any rational classification of
consonants. The most satisfactory would be based on their
objective, physical nature, but we have no means for the physical
analysis of elementary consonant sounds, such as enables us to
determine the physical nature of musical tones. Hermann found
himself at a loss after some introductory experiments. We
can only fall back on the physiological classification, which
is founded on the mode of producing the consonant sounds and
their subjective acoustic character.

Hermann made a primary division of consonants into two
groups, voiced and voiceless, according as the sounds formed are
accompanied by laryngeal tones or not. Voiced consonants are
much more numerous than voiceless consonants ; they are sub-
divided into semivowels, or liquids (which can function either as
consonants or vowels, and can be pronounced alone, independent
of other vowel sounds), and sounding consonants.

It is indispensable to the perfect formation of vowel sounds
that the pharyngeal cavity should be closed off from the nasal
fossae. When this does not take place, the quality of the vowels
alters and they become nasal, since the expiratory current passes
through the nose as well as the mouth. On closing the nostrils
the nasal character is intensified and may be more prolonged.
This nasal quality characterises the French language, but is also
present in Italian, Spanish, and all other languages.

The nasal vowels an, en, 6n represent the transition between
the vowels and the liquids or semivowels.

The semivowels are in, n, ng, I, and r. They have the
character of vowels because they are always uttered with the
voice, i.e. they are accompanied by vibrations of the glottis
(except when whispered), and sometimes carry the accent, when
they function as pure vowels. They approximate to consonants
because they are pronounced with the mouth partly or entirely
closed, and in the majority of cases the accent does not fall on
them, so that they mostly play the part of consonants.

1 This section has been considerably abridged from the Italian text, which
contains more detail than is required by the physiological student. ED.

Ill

PHONATION AND ARTICULATION

165

The sounds in, n, n<j, constitute a distinct group of nasal
semivowels (rhinophones) characterised by the expulsion of the
expired air through the nose, where the laryngeal tone acquires
a characteristic resonance, while the mouth is closed in a definite
position. For m the mouth is closed with the lips pressed
together (labial articulation). For n the oral cavity is generally
closed by applying the tip of the tongue to the upper alveolar
arch (alveolar articulation) or to the hard palate (palatal articu-
lation) (Figs. 105 and 106). In ng (represented in Sanskrit
by a special symbol) the mouth is closed by the approxi-

Fio. 105. Articulation of >i".
(Luciani and Baglioni.)

FIG. 106. Articulation of gna.
(Luciani and Baglioni.)

Impression left by the tongue stained by cocoa powder previous to articulation.

mation of the dorsum of the tongue to the soft palate, either
more to the front (when preceded by e and i as in Engel,
thing} or more to the back (if preceded by a and o, as in
Wange, long].

The semivowels / and r are distinguished from these nasal
sounds by the fact that their resonance comes from the mouth,
and not from the nasal cavities which are closed by elevation
of the soft palate. Several kinds of I can be distinguished
according to the seat of articulation, the most usual being formed
by bringing the tip and lateral edges of the tongue into contact
with the alveolar and dental arches, while the air escapes
through two lateral openings between the premolars (Fig. 107).

M i

166

PHYSIOLOGY

CHAP.

This is the so-called alveolar I used in most European languages.
Besides this there is also an apical I, which is easily formed by
applying the tip of the tongue to the hard palate, above the
alveolar border. This is the / of the English will, well, hall,
etc. It is also found in Norwegian and Polish.

r differs from / because the tip of the tongue is rapidly and
intermittently applied to the palate, which gives a vibratory
character to the laryngeal tone. The labial r (brr) is not in
written language, but is often formed by children, and is also
an interjection e.g. to express cold. In Germany coachmen use

FIG. 107. Articulation of Za.
(Luciani and Baglioni.)

FIG. 108. Articulation of glia.
(Luciani and Baglioni.)

it to stop their horses. Gael states that it occurs in the language
of the savages on an island near New Guinea. The most common
forms of the anterior and alveolar-palatal are formed by vibrating
the tip of the tongue against the dental and alveolar arches,
and by applying it in the apical position to the hard palate.
The velar or uvular r, formed by applying the dorsum of the
tongue to the uvular portion of the soft palate, is less vibrant,
and is known as the French r because it is characteristic of that
language. Lastly, there is a laryngeal r caused by the tremulous
closure of the glottis, with a deep, soft tone as in the English
girl, bird, or the higher and harsher gli of Arabic.

The physical nature of the semivowels has not been determined,
owing to the difficulties which their study presents. According
to Hermann and Matthias there are formants in the sounds

Ill

PHONATION AND AKTICULATION

1G7

m, n, I, which can be recognised in phonautographic curves. The
phonograms of r, according to Hensen and Winckler, exhibit
a rhythmical crescendo and decrescendo like the modemto beats of
a musical tempo.

Consonants proper are distinguished from semivowels in being
invariably composed of sounds, while the accent never falls on
them, i.e. they never act as syllabic sonants. They form two
subgroups, according as they are accompanied by distinct laryngeal
tones, or not ; the first are called sounding (or median) consonants,

FIG. 109. Articulation of da and gia.
(Luciani and Baglioni.)

Km. 110. Articulation of co and ga.
(Luciani and Baglioni.)

the second mutes. Both may be subdivided into occlusives or
explosives, and fricatives or spirants.

Explosive consonants are produced by the sudden opening of
the oral cavity, owing to the pressure of the expiratory air.
Their formation accordingly involves the closure of the pharyngo-
buccal cavity at a certain point, in which sense only they are
occlusive or dosing sounds. Some authors maintain that they
should be called explosive when followed by a vowel or semivowel
(as in ba, pi, de, te, bra,^>la, dro, knu), and occlusive when preceded
by a vowel or semivowel (ab, ip, ed, ot, arb, alp, ord, onk). But
this a fallacy. Every one can demonstrate that even when
preceded by vowels or semivowels, the characteristic sound of an
explosive consonant is heard, not at the closure, but at the
reopening, of the cavity which has been momentarily closed.

168

PHYSIOLOGY

CHAP.

Fricative consonants are produced by sounds of friction as
the expiratory current passes through the constricted oral cavity,
and are consequently continuous or liquid sounds like the semi-
vowels, unlike the explosives which are instantaneous.

The explosive consonants b, d, g ; , g", are formed with the
glottis open, and may be preceded and accompanied by a laryngeal
tone ; in p, t, c', k, the glottis is fully closed, and the expulsion of
the air is not accompanied by vibrations of the vocal cords.

The labials & and p are always formed by the opening of both
lips. In the alveolars, </, <f, t, c' the position of the tongue varies ;

FIG. 111. Articulation of i and en'.
(Luciani and Baglioni.)

FIG. 112. Articulation of jet.
(Luciani and Baglioni.)

hence their sound differs more or less noticeably. The same holds
for the palatals g a and k (Figs. 109, 110).

Fricative or spirant consonants are formed when the expiratory
blast of air is driven with a certain force through a confined
passage. Unlike the explosives the fricatives are preceded, not
By the closure, but simply by the constriction of the pharyngo-
buccal cavity. They may or may not be accompanied by laryngeal
tones, i.e. may be voiced or voiceless, w, v, the French and Italian
j, are pronounced with the voice ; /, the German ch and sell, and
French ch, without the voice ; with or without, s, z and the
English tli. Grammarians term the sounding s and z lenes, and
the mute s and z fortes. But the true physiological difference is
that the former are accompanied by laryngeal sounds.

The only consonant which is necessarily voiceless is h ; it may

Ill

rHONATION AND AETICULATION

109

be tennis, due to the slight sound that accompanies the opening
of the glottis previous to the utterance of a vowel (spiritus lenis
of the Greeks, aleph of the Hebrews, hamze of the Arabs), or
t'ortis (spiritus asper, Greek; he, Arabic). The latter sound is
'absent in Italian, but exists in many languages (harp, house,
Hans}. The mute h is sometimes represented (as a historical
reminder) in Italian, French, and English, but is frequently
omitted in written language.

In pronouncing s the constriction is usually produced by
contact of the lateral edges of the tongue with the entire dental

]'!<. 113. Articulation of sa. (Griitzner.) FK;. 114. Articulation of scia. (GriitziuT.)

Impression left by the tongue stained with carmine previous to articulation.

arcade, except the small anterior median space opposite the two
incisor teeth (Fig. 113) ; the sound is due to the escape of air
through this narrow passage.

The English tk is formed by applying the tip of the tongue
above the lower incisors till it lightly touches the lower lip
(interdental articulation).

Both s and th may be pronounced without the voice (thick,
thing}, or with the voice (those, that). The mute th corresponds
to 6a and the sounding th to 8a of modern Greek.

The fricative which the Germans write sch, the French ch,
and the Italians sci, is distributed through all known languages,
and is really a simple consonant, although in a few languages
(Sanskrit, Hebrew/ Cyrillian and Glagolitic dialects of Slav) it

170 PHYSIOLOGY CHAP.

is expressed by a special sign. It is not, in fact, a series of sounds,
but a single continuous sound very similar to s, formed by con-
striction of different parts of the oral cavity. It is due to
application of the lateral edges of the tongue to the hard palate,
alveoli, molar teeth, allowing an escape of air through a median
passage between the tip of the tongue and palate, which is wider
and more posterior than in s (Figs. 113, 114).

X. The words of a language result from the different combina-
tions of the elementary sounds we have been dealing with
vowels, semivowels, sounding and mute consonants. One or two
vowels, alone or accompanied by semivowels or consonants so as
to make a continuous phonetic unity, form the so-called syllables.
The phonetic continuity of the syllable depends on its being
pronounced in one uninterrupted breath, which is only possible
when its elements are capable of fusion or agglutination. When
the successive sounds are not capable of agglutination, so as to
be uttered in a single, continuous, expiratory effort,' a short
interruption or pause (the hiatus) is interposed between them, by
which the sound is divided into two or more syllables.

The coherence of two vowels forms a diphthong ; when they
make a single syllable, i.e. fuse together so that the voice is
not interrupted in the rapid transition from the position for the
first to that for the second vowel ; when, on the contrary, two
vowels follow without agglutinating, so that the voice is interrupted
in passing from one to the other, they do not form part of the same
syllable and do not constitute a diphthong (aid, poetry}. The
division of two normally agglutinated vowels by the interposition
of a hiatus is known as diuresis ; the fusion of two separate vowels
which form part of two successive syllables, as synaresis. Tn the
first case one of the syllables is made into tw T o, in the second two
syllables are fused into one.

More frequently the syllable consists of one vowel or diphthong
and one, two, or three semivowels or consonants, and vice versa.
Two laws must be observed for the adhesion of a vowel with
semivowels and consonants : (a) Vowels readily adhere to semi-
vowels, imperfectly to explosives and fricatives; () Both
semivowels and consonants agglutinate perfectly with vowels to
form single syllables.

The combination of several syllables constitutes polysyllabic
words, in which the phonetic unity is interrupted once or oftener,
according as it consists of two or more syllables. The break
is produced by the discontinuity of the outgoing expiratory
blast due either to occlusion or narrowing- of the resonating

o o

cavity at some point along its course glottis, soft palate, hard
palate, or lips. The interruption may be more or less appreci-
able according as it is more or less prolonged, and is not always
a complete silence, but may be a light aspiration the tennis

in PHONATION AND AKTICULATION 171

h, or spirit-us lewis of Greek which is not usually marked in
writing.

In each syllable accent and yuaiUity have to be distinguished.
" Accent " means the loudness and pitch of tone with which the
.syllable is pronounced. In syllables which consist of one or two
vowels combining with one, two, or three semivowels or consonants,
the accent falls on the sound which is uttered in the strongest
and highest voice : this is the sonant of the syllable. The rest
of the elements associated with the sonant and pronounced in a
weaker and lower voice, whether vowels, semivowels, sounding
consonants, or dumb consonants form the consonants.

irrd accent, again, must be distinguished from syllabic accent;
it falls on those syllabic sonants which are pronounced in the
loudest, highest voice. Physiologically the accent may be suit-
divided as pJton-ic and tonic according to its strength or pitch.
Practically this distinction is rarely made, because the accent
generally, depends on the higher pitch at which the syllable is
uttered.

The " quantity " of the syllables depends on their brevity or
length, i.e. the physiological duration of the expiratory breath in
which they are uttered, which varies according to the different
vowels, semivowels, and consonants. In Greek and Latin the
quantity of the syllable was regularly distinguished and used as
the base of metric poetry. Modern languages attach little weight
to the quantity i.e. brevity or length of the syllables, since
this is dominated by the accent, which has become the base of
modern metrical poetry. Even when imitating classical metres
we emphasise the accent, not the length of the syllables a
splendid example of this being the work of the Italian poet,
Carducci.

The combination of syllables leads to the formation of sentences
which are divided by pauses of different length, marked in writing
by commas, semicolons, etc. The words of which they consist are
variously accentuated. There is also a sentence accent, which
falls on the words we emphasise in speaking, and sometimes
underline in writing. The pitch of the ordinary speaking voice
varies within the limits of a half-octave. In European languages
the different tones of the language colour the phrases and alter
their expression. Correct diction and accent is a special gift with
which different individuals are very variously endowed. This
may not make their speech more intelligible, but it certainly
renders it more effective and agreeable.

XI. The development of speech in children closely follows
their anatomical development and the physiological exercise of
the speech organs. They begin by vocalising, and utter high-
pitched vocal sounds, i, a, e, which constitute the cries and in-
articulate sounds of infancy. The child's first articulate utterances

172 PHYSIOLOGY CHAP.

are those that are most easily formed, viz. semivowels and labial
consonants ( pa, ba, ma, Iru, Ira, pra\ which require only a single
action of the lips that are perfectly formed from birth and capable
of function. A little later conies the formation of the alveolar
consonants (da, to) winch cannot be uttered till the jaws are well
developed and the teeth protruding. The palatals and volars are
acquired later, 1 toth because they are harder to form, and because
the development of the soft palate is completed. Ca (ka) is easier
than ga, which does not occur in primitive languages, as g was a
later modification of c. The ga sound is often replaced by children
with ta. The semivowel r is harder to pronounce than m, n, and
/. Many children and adults lisp, i.e. are unable to utter the
alveolar r, and substitute I for it.

Up to a certain point there is a parallelism between the
ontogenetic and phylogenetic development of language in the
different races. Some primitive languages are very rich in vowels ;
but after a certain point of development they employ many
consonants. Up to the present there has been no comprehensive
study of the development of primitive idioms, but it may be stated
generally that languages, like individuals, evolve until they reach a
certain point of development, after which they suffer a slow but
persistent transformation, for worse or for better.

It is well known that the dialects of savage races may undergo
such modifications in the course of a few years that they are
hardly recognisable. Writing and written language play an
important part in checking or hindering the natural tendency of
every language to transformation, but this is largely promoted
by contact between the several dialects and vernaculars, as well
as by intercourse between peoples who employ different idioms.

The great historical transformation of Latin into the modern
Romance languages may perhaps be taken as an illustration of the
above. Even before the fall of the Roman Empire it was favoured
by the predominating influences of the unlettered popular dialects
during the early part of the Middle Ages, over the fixed idiom of
the Latin Codices. The metamorphosis took place more rapidly
in France than in Italy, which was the centre of Roman civilisation.
And French literature was, for this very reason, nearly two
centuries ahead of Italian literature.

But while written literature may check the natural evolution
of a language, it can never arrest it, for its development is the
work of the people, not of the writers. This is plain from the
discrepancy between any language in the strict sense, and its
literature--*.^ between spoken and written language. The
difference is greatest in the English language, in which the written
or printed words are not so much a symbolic representation of the
different tones and sounds of which they are built up, as mere
mnemonic signs a little plainer and more expressive than the

in PHONATION AND AETICULATION 173

hieroglyphics of the ancients. Among the different Teutonic
idioms the German language is the most faithfully represented in
its writing.

Of the Neo-Latin languages, French has certainly retained its
archaic form in writing more closely than the others ; because the
evolutionary transformations of the language spoken by the people
were not adopted in the written form, owing to the prejudices of
the grammarians. In Italian and Spanish, on the contrary, the
written language is a more faithful transcript of the pronunciation.

BIBLIOGRAPHY

For this subject the student may consult articles by JON. MULLER, LONGET,
GRUTZNER (iu Hermann's Handbuch), BRUCKE, GAD and HEYMAN.S, SCHAEFKK.

The principal Monographs and Memoirs are :

LISKOVIUS. Phys. d. Menschl. Stimnie, 1846.

HARLESS. Art. Stimnie i. d. Wagners's Handwort. d. Physiol., 1853.

LEPSIUS. Das allgemeine liuguistische Alphabet. Berlin, 1855.

DONPER.S. Arch. f. d. holland. Beitrage f. Nat. u. Heilk., 1857.

CZERMAK. Der Kehlkopfspiegel, etc. Leipzig, 1860.

THAI*SING. Das natiirliche Lautsystem. Leipzig, 1863.

MKRKEL. Anat. u. Physiol. d. menschl. Stimni- und Sprachorgans, 1856. Antro-

pophonik. Leipzig, 1857. Physiol. d. menschl. Sprache. Leipzig, 1866.
FOURNIE. Physiologic de la voix et de la parole. Paris, 1866.
RUMPELT. Das natiirliche System d. Sprachlante. Halle, 1869.
KONIG. Annal. d. Physik, vii. , 1876; cxxxxvi. , 1872.

SIEVEKS. Grundziige der Lautphysiologie. Leipzig, 1879. (Now in its 5th ed.)
BUUECKE. Grundziige d. Physiol. u. Systematik d. Sprachlaute. Wien, 1836.

(Now in its 5th ed.)

GAVARRET. Phenomenes physiques de la phonation et de 1'audition. Paris, 1877.
HELMHOLTZ. Die Lehre von den Tonempfindungen. Braunschweig, 1877.

(Tr. by Ellis from 3rd ed., 1875.)
AUERBACH. Ann. d. Physik, iii., 1878.
GARCIA. Mem. sur la voix humaiue, 1855-1861-1878.
SCHNEEBELI. Arch, des sc. phy. et nat. i., 1879.

OERTEL. Ueber d. Median, des Brust- und Falsett-Register. Stuttgart, 1882.
BELL, A. M. Sounds and their Relations. London, 1882.
TECHMER. Phouetik. Leipzig, 1880. International Zeitschr. f. allgemeine

Sprachwissensch. i., 1884.

SWEET. A Primer of Phonetics. Oxford, 1890.
SEMON. Brit. Med. Journ. London, 1886.
FRENCH. Verhamll. d. intern. Congr. Berlin, 1890.
STORN, J. Englische Philologie. Leipzig, 1892. (Vol. i. contains a critical review

of all the important works on phonetics published between 1840 and 1880.)
WYLLIE. Disorders of Speech. 1894.
PIPPING. Zeitschr. f. Biol., xxvii., xxxi., 1890-94.
BREYMANN, H. Die phon. Literatur von 1876-1895. Leipzig, 1897.
HERMANN. Arch. f. d. ges. Physiol. Ixi., 1895 ; Ixxxiii., 1900.
HALLOCK. Am. Ann. Photogr. ' 1896.

FLEEMING-JENKIN and EWING. Trans. Roy. Soc. Edin. vol. xxxviii., 1897.
HENSEN. Arch. ital. de biol., 1901.
ROUSSELOT. Principes de pnonetique experimental e. Paris, 1897-1901. Les

Modifications phonetiques du langage. Paris, 1891.
G. ASCOLI. Archivio glottologico italiano, vol. i., 1873.
SCRIPTURE, E. W. Elements of Experimental Phonetics. New York and London,

1902.
JESPERSEN, 0. Lehrbuch d. Phon. Leipzig, 1904.

174 PHYSIOLOGY CHAP, in

SCRIPTURE, E. W. Speech Curves. Washington, 1906.

PANCONCELLI-CALZIA. Bibliographia phonetica. (Published regularly since 1906

in Medizinisch-piidagogische Monatschrift f. d. Sprachheilkunde. (References

to recent works on phonetics).
PASSY, P. Expose des principes de 1'association phon. internationale. Leipzig,

1908.

GUTZMANN, H. Phys. d. Stimme u. Sprache. Brunswick, 1909.
LUCIANI, L. Par la ritbrnia ortografica (Estr. Atti d. Soc. it. per il progr. delle

Scienze iv. Riunione. Naples, ottobre 1910.
LUCIANI, L. Di una ril'orma ortografica basata sulla fonetica fisiologica (Estr.

Rivista pedagogica, a. iv., v. i., 1910).
GOIDANICH, P. C. Rivista pedagogica, 3rd year, vol. ii. Modena, 1910. Archivio

glottologico italiano, vol. xvii., 1910. Miscellanea di studi in onore di Attilio

Hortis. Trieste, 1910.
POIROT, J. Die Phonetik (Hb. d. phys. Methodik di R. TIEGERSTEDT, iii. Bd. vi.

Abt.). Leipzig, 1911.

Recent English Literature :

MOTT, F. AV. The Brain and the Voice in Speech and Song. London and New

York, 1910.
AIKIN, \V. A. The Voice An Introduction to Practical Phonology. London,

1910.

CHAPTER IV

GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM

CONTENTS. 1. Structural elements of the nervous system. Theory of in-
dependent neurones, or continuity of neuro-fibrils. 2. Conditions, laws and
phenomena of conduction in nerve. 3. Rate of conductivity : diphasic character
of the impulse arousing it. 4. Metabolism of nerve ; electromotive phenomena
during rest and excitation : demarcation current, action current. 5. Excitation
of nerve. Natural stimuli and artificial (chemical, mechanical, electrical) stimuli.
6. Factors in life and death of nerve : conditions of excitability. 7. Polar effects
of constant current ( electro tonus) : correlative changes in excitability and con-
ductivity. 8. Excitatory action of electrical currents. Laws of excitation.
9. Theories as to origin of nerve activity. 10. General functions of nerve-centres.
Ganglion cells and central fibrillary network. Bibliography.

THE Nervous System, which is the real centre of the functions of
animal life, controls the activities of the organs of involuntary
or vegetative life, as well as those of the muscles. By means of
the sensory mechanisms it correlates the several organs among
themselves, and brings the organism as a whole into relation with
the external world, while it is able by means of the motor
mechanisms to vary these relations and adapt them to change of
circumstances.

In order that it may fulfil these important functions, the
nervous system is built up of morphological elements which
establish a functional link between the different organs, inde-
pendent of their juxtaposition or distance, and control the
circulation of the tissue fluids, so that when a given change takes
place in one part, other phenomena necessarily ensue in other
remote parts, e.g. in the skin and the muscles, the mucous
membrane and the glands, etc. It is the nervous system that
presides over those complex relations between distant organs
which the ancients termed "sympathies." It represents the
physiological unity, the reciprocal dependence of parts, on which
the psychological unity, expressed in the phenomena of the ego or
consciousness, is founded.

The most elementary organisms, while they possess no differ-
entiated nervous and muscular systems, nevertheless exhibit
essential animal characteristics of sensibility and motility, albeit

175

176 PHYSIOLOGY CHAP.

in a rudimentary and ill-defined form : to explain this fact we
must assume a common protoplasmic basis for both these
elementally functions and those evolved in the more perfect
organisms 'by gradual morphological and functional differentiation
intfc %r?e**nervous and muscular systems.

The organs of the nervous system, of which the general
physiology will be considered in this chapter, represent the highest
grade of morphological and functional differentiation, both in the
ontogenetic development of the individual and in the phylogenetic
development of the lowest forms of the animal kingdom.

I. The nervous system in man and other vertebrates consists
of: (a) a compact mass the cerebrospinal axis; (&) nerves which
are given off from this axis the cerebral and spinal nerves and
distributed, by successive division, into smaller and smaller bundles
and branches, to nearly all the organs and tissues of the body ;
(c) a vast number of ganglia or nervous nodes, intercalated along
the course of the nerves at greater or less distance from the cerebro-
spinal axis, many of which form two lateral chains, and constitute
the splanchnic or great sympathetic system.

To the naked eye the nervous system consists of two dissimilar
substances the white matter and the f/rey matter. Under the
microscope both are seen to be made up of fibres and nerve-
cells, the fibres predominating in the white matter, the cells in
the grey.

Apart from their minute histological structure, the nerve-cells
of the cerebrospinal axis and ganglia have long been regarded as
the central, and the nerve-fibres as the peripheral, parts of the
I system. The cells more particularly serve the storage, elaboration,
I transformation, and development of the specific energies of the
system ; the fibres more especially conduct and transmit these
energies from the periphery to the centre (centripetal or afferent
nerves), and from the centre to the periphery (centrifugal or efferent
nerves). The inclination to differentiate between the physiological
functions of the ganglion cells and of the nerve fibres, which are
filiform processes of the cells, became more definite after the
discovery of the telegraph by Morse (1837), which to many minds
suggested a parallel between the functions of the nervous system
and the telegraphic installation of a State. The cells were com-
pared to the telegraph apparatus, the fibres to the conducting
wires, the cerebrospinal axis to the great central telegraph station,
the conglomerated ganglia of the sympathetic system to the inter-
mediate exchanges, the peripheral ganglia to the local offices of
country towns and villages.

But despite the apparent analogy between the two systems,
which both consist of distant apparatus brought into direct relation
by conducting wires, there are huge internal differences in the
nature and function of the elements of which the two systems,

iv GENEEAL PHYSIOLOGY OF NEEVOUS SYSTEM 177

respectively, are composed. The physiological data we are about
to discuss will emphasise these differences.

In reviewing our present knowledge of the minute structure of
the histological elements of the nervous system, it should be noted
that the data are all comparatively recent. Notwithstanding the
number and ability of the investigators and the delicacy and
variety of the methods employed, the facts are not yet sufficiently
clear and unequivocal to admit of the construction of any universal
and authoritative morphological theory.

The first exact account of the existence of specific nerve-cells
dates from 1833, when Ehreuberg described the cells of the spinal
ganglia of the frog. In 1838 Eemak first discovered in the
sympathetic of vertebrates that the nerve-fibres are a prolongation
of the processes of the cells, which was confirmed in 1842 by
Helmholtz and Hannover on invertebrates. Deiters was the first
to demonstrate, in a monograph published after his death by
Schultze (1863), that two different kinds of processes can be
distinguished in the central nerve-cells nerve-fibres proper, and
protoplasmic processes. He proved the continuity of the former
with the axis-cylinders of medullated nerve-fibres, but left the
destination and physiological function of the latter undetermined.

Gerlach in 1871, by the gold chloride method, demonstrated
the existence in the grey matter of the cerebrospinal axis of a
diffuse fibrillary network, which he interpreted as the result of
an anastomosis or concrescence of the finest ramifications of the
protoplasmic processes of the ganglion cells. To this he ascribed
the important function of bringing the ganglion cells of the central
mass of the nervous system into direct interrelation.

In 1873 Golgi discovered his method of staining nerve-cells and
fibres black with salts of silver which led to a great advance in our
knowledge of the minute structure of the nervous system. He
showed that at a certain distance from the cells the nerve pro-
longations or axons give off collateral rami which branch from the
trunk, mostly at a right angle. Like Gerlach he admitted the
existence of a diffuse network of nerve-fibrils which conduct the
excitation ; but denied that it was formed by the dendritic
ramifications of the protoplasmic processes, which he held to be
simple nutrient paths from the cell body, with free endings.
Golgi maintained that the ganglion cells were united by a fibrillary
network formed of the finest ramifications of the axis-cylinders.

Subsequent researches made by Eamon y Cajal after 1888, with
Golgi's methods, led this author to deny the existence of any such
diffuse fibrillary network : Cajal concluded that both the dendrites
and the axons terminate free ; and that each ganglion cell, with
the whole of its protoplasmic and axis-cylinder processes, represents
an elementary organism in itself, connected with the others not by
anastomosis nor continuity, but by simple contact or contiguity.

VOL. 1IT N

-13

mm

, j

R

B

II

c

FIG. 115. A, Bipolar nei ve-cell with poles prolonged into medullated nerve-fibres. (Rey and
Retzius.) The cut in' cell is invested with the neurilemma. li R, nodes of Ranvier.
B, Portions of two nerve-tibres stained with osinic acid (from a yonm; rabbit); diagrammatic,
425 diameters. (Schafer.) R R, nodes of Ranvie.r, with axis : cylinder passing through ;
a, neurilemma ; c, nucleus and ]irotoplasm lying between the neuiilemma and the medullary
sheath. C, Mednllated nei vr-liln i- treated with osmic acid. (Rey and Retzius.) E, node of
Ranvier ; K, nucleus. The myelin of the medullary sheath is incompletely interrupted so as
to form conico-cylindrical segments.

CH.IV GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 179

Cajal's observations found general support and were repeated
and confirmed by Ko Hiker, Lenhossok, and van Gehuchten with
Golgi's method ; by Eetzius, Biedermanu, and others with
Ehrlich's method (intra vitn-m, staining with methylene blue).

Waldeyer gave the name of neurone (from vtvpov, point of
contact of many nerve threads) to the elementary units of
which the nervous system is built up, which term found great
favour with the neurologists, and contributed not a little to

Kl'.. 11(1. Phylogenetic and onto^enetic development of neurones with loiix axons from pyramidal
cells of cerebral cortex. (Ramon y Cajal.) The upper series represents the phylogenetic
development of these cells : .4, in fro;; ; Jl, newt ; (.', rat ; D, man. The lower series shows the
ontogenetic development of the neuroblasts of those cells in live successive phases, a, b. c, "'. e.

popularise the " neurone theory " in the medical world. The
protoplasmic processes were termed dendrites, the nerve process
neurite, axon, or axis-cylinder. The dendrites differ from the
axons in various structural characters, some of which had been
described by Deiters, others were discovered by Golgi with his
method. In many neurones the dendrites exhibit minute lateral
processes spines or gemmules along their course which are
never seen on the axons.

Some nerve-cells are wholly destitute of dendrites, e.g. the
typical cells of spinal ganglia and the corresponding ganglia of
the cranial nerves. On the other hand some nerve-cells have no

N 1

180

PHYSIOLOGY

CHAP.

\

true axis-cylinder process, e.g. those of the stratum granulosum of
the olfactory bulb. The cells of the spinal ganglia of Teleosteans and
the cells of the cochlear ganglion are bipolar or bineural, i.e. have
two axons (Fig. 115, A), and in the molecular layer of the cerebral
cortex, according to Ramon y Cajal, Eetzius, and others, there
are nerve -cells with two or three axons. Veratti, however,
contests this statement, and gives a totally different interpreta-
tion to the data on

which it
According

is based,
to Gok r i

o o

the cells of the cere-
bral cortex which give
origin to the so-called
pyramidal tracts, and
still more those of the
ventral horns of the
spinal cord, have long
axis-cylinder processes
which give off col-
lateral rami, while
they preserve their
individuality for a
long distance ; the
latter are continued
in the ventral root-
fibres of the spinal
nerves (Fig. 116).
The cells of the dorsal
horns of the cord, on
the contrary, and
many cells in the grey
matter of the large

FIG. 117. Large ceUs with short axons. Golgi s second type, 6

found in the nuclear layer of the cat's cerebellum, high Cerebral Centres, have

magnification. (Golgi.) In order to distinguish the proto- , , -i >

plasmie processes from the nerve processes or axis-cylinders, SllOr b aXIS - Cylinders,

the former are printed in black, the latter with their rami- ,,7 V, i r - l-i v o T> o o f a A 1 \T

tications in red. 11V

divide and subdivide,

and soon lose their individuality (Fig. 117). It is, however, very
doubtful whether the presumably different functions of these
various forms of neurones are connected with the morphological
differences indicated by the appearance of their axis-cylinders.

The neurone theory, which regards the elementary components
of the nervous system as morphologically distinct, is not based
on any conclusive evidence. Even after the observations of
Ramon y Cajal and his numerous adherents, Golgi and his pupils
still insisted on the theory of a diffuse; nervous network, formed
of the collateral rami given off from the axons in the vicinity
of the ganglion cells. Golgi demonstrated this diffuse nervous

iv GENEEAL PHYSIOLOGY OF NEEVOUS SYSTEM 181

network more particularly in certain parts of the central nervous
system, e.g. the fascia dentata of the hippocampus (Fig. 118)
and the cerebellar cortex (Fig. 119).

The neurone theory, on the other hand, harmonises perfectly
with the embryological observations of His (1887), who believed

Fin. IIS. Fascia dentata of pes hippocampi major. (Golgi.) Between the processes coming from
the upper layer of nerve-cells and the lower of nerve-fibres there is an intervening zona reticulari.s
composed of nerve-libres which interlace repeatedly, so that they lose their individuality and
constitute what Golgi calls the diffuse nerve network.

that he had demonstrated the genesis of the nerve elements from
the special germinal cells of ectodermal origin, which are inter-
posed between the epithelial cells of which the walls of the
primitive neural tube are composed. A-polar and rounded in
an early stage, they subsequently become piriform ; next they
send out a nerve process and become uni-polar ; finally the
dendrites appear also (Fig. 116, a, b, c, d, e]. During their growth

N 2

182

PHYSIOLOGY

CHAP.

the neuroblasts gradually move away from the wall of the neural
canal towards the exterior. Many of them remain in the central
grey matter ; others wander out to form the cerebrospinal ganglia,
sympathetic ganglia, etc.

But this theory of His, in so far as it conceives the nerves
to be only appendages of the ganglion cells, is contradicted by
the observations of Balfour, Beard, Dohrn, Kupfer, and Eaffaele

FIG. IIP. Cerebellar cortex showing relations between the small cells of the molecular layer and
the body of Pnrkinje's cells. (Golgi.) The nerve-fibres descending from the small cells of the
molecular layer partially embrace the large body of the Purkinje cells, partially pass between
these, and then subdivide repeatedly belowjthem to form another diffuse network

on fishes, and the more recent work of Bethe, Paladiuo, Fragnito,
and Capobianco on chick embryos. According to these observers
the axis - cylinders of the peripheral nerves and of the white
matter of the central organs are not (from the histogenetical
point of view) composed of prolongations of the axons and
dendrites of the ganglion cells, but are derived from the fusion
of many cells arranged in series, and only contract relations with
the ganglion cells at a later time. The problem is still unsolved,
since some authors (Harrison in the first place) confirm the
view of His, while others take the polygenetic theory as proven.

iv GENERAL PHYSIOLOGY OF NEEVOUS SYSTEM 183

Whatever the value of these conflicting statements, and how-
ever certain it is that during their histogenetic development
the constituent elements of the nervous system are morphologi-
cally distinct and independent, it is far from proved that in
fully developed tissues the so-called " neurone " represents a
true morphological unit, and is not a fusion of many elements,
or syncytiutn ; nor that these neurones do not enter into close
relation by direct continuity of their protoplasmic substance ;
nor, lastly, is the idea of a diffuse fibrillary network which, both
in the central grey matter and at the periphery, knits the several
neurones into a single unitary system, comparable with the
vascular system, by any means excluded.

This modern view of the minute structure of the nervous
system is founded on the work of Apathy,- Bethe, Nissl, and
others, who, by new methods of staining, have brought out new
facts which are in more or less open contradiction with the
neurone theory. We must confine ourselves to a brief survey of
the principal data supplied by these researches.

While the method used by Golgi and his numerous followers
in the study of the minute structure of the nervous system has
added greatly to our positive knowledge in this difficult subject,
it is by no means the best adapted to show up the microscopic
structure of the nerve-cells and processes. With too intense
impregnation with silver, both cells and processes are stained
uniformly black. In order that this method may bring out the
fine structure of the body of the nerve -cell, as in the figures
obtained by Golgi, it is necessary to make repeated experiments,
for which no general rules can be given.

Again, there is grave reason to suspect, on the strength of the
facts established by Apathy for the nervous system of the leech,
that the silver method which only shows up certain elements of the
system, leaving the rest unstained and therefore undifferentiated, is
inadequate for the demonstration of the finest ramifications of the
dendrites and axis-cylinders. We have seen that Golgi himself
pointed out that the free endings discovered by Ramon y Cajal,
upon which the whole neurone theory is based, are not indisput-
able, but result from an inherent defect in the method of staining.

In 1871, in describing the ganglion cells of the spinal cord,
Max Schultze recognised the fibrillary nature of their protoplasm
and of the protoplasmic and nerve processes. Both in fresh
preparations and in those treated with osmic acid, he observed
distinct fibrils which run in various directions through the cell
body, giving it the appearance of a network or reticulum, and
are in direct connection with the elementary fibrils of which both
the axons and the dendrites are composed. He further assumed
the existence of a finely granular substance, which fills the
inter fibrillary spaces.

184

PHYSIOLOGY

CHAP.

This point of view was adopted by Erik Miiller, Boll, Schwalbe,
and Eanvier, and was subsequently carried further by Flemming
(1895), who on staining with hamiatoxylin described independent
fibrils in the dendrites which were continued into the cell body,
though he could not trace them distinctly into the centre of the
cell, where they seemed to anastomose to form a network.

The theory of the fibrillary nature of the protoplasm of the
nerve-cells was disputed by v. Lenhossek, but it was adopted and
defended by Dogiel, Donaggio, Becker, Marinesco, Held, and
Lugaro. In 1896, Donaggio, with a special method of elective

FIG. 120. Peripheral network of nerve-cells from flop's spinal conl. (Dona.ugio.)

staining, observed and described a fibrillary network that per-
vades both the interior and the periphery of the nerve-cells, and
in which the fibrils from the surrounding tissue terminate
(Fig- 120).

Lugaro (1897) convinced himself, with the same haeniatoxylin
method as Flemniing employed, of the fibrillary structure of the
spinal ganglion cells of dogs poisoned with arsenic, which totally
destroyed the chromatic substance at the periphery of the cell
body. The fibrils, according to Lugaro, anastomose among them-
selves, forming a very delicate reticulum in certain types of cells,
a coarser network in others. He made analogous observations
upon the cells of the nerve-centres of animals subjected to ex-
perimental hyperthermia.

iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 185
Levi, Luo-aro's collaborator, obtained similar results from the

O

ganglion cells of frogs during hibernation, in which state the
chromatic subtance is very scanty, so that the achromatic fibrillary
part is more conspicuous.

The existence of fibrils in the nerve-cell and its processes may
be regarded as fully established by Apathy's work on the nervous
system of the Anellidac (1897). He demonstrated definite fibrils
by a special method of staining the ganglion cells with gold
chloride. As shown by Fig. 121, these fibrils penetrate from the
dendrites into the cell body, where they form a wide -meshed
network, and then collect into a single bundle, and leave by the
axis-cylinder. The fibrillary network (Apathy) assumes different

FIG. 121. <i;t]r_li'>n cell of ventral cord of Lmnliriciit, showing an endoeellular fibrillary network,
which is continuous with the afferent fibrils of the dendrites, and with one larger, effVii-nt
fibre of the axon. (Apathy.)

forms according to the nature of the ganglion cells. The small
fibres brought out by the gold stain are shown to be bundles of
very delicate elementary fibrils, which escape observation owing
to their size and the inadequacy of the staining methods. These
are the conducting elements proper of the nervous system.

Any one who has studied the preparations obtained with
Apathy's method must admit that they exhibit astonishingly
clear details of structure, which may be of fundamental import-
ance to physiology. At the same time it must be remembered
that Apathy's positive results relate solely to the nerve-cells of
the lower animals (Hirudo and Lumbricus), and that in spite
of prolonged experiments, nothing exactly corresponding has so
far been obtained in vertebrates.

Bethe, in a series of interesting observations (1897-1890),
endeavoured by other special methods of elective staining of the

186

PHYSIOLOGY

CHAP.

fibrils to extend to vertebrates the morphological facts and con
ceptions which Apathy developed for Anellidae. According to
Bethe the fibrils in the ganglion cells remain independent,
without anastomosing among themselves to form a network,
except in the cells of the spinal ganglia, in which he found the
network to consist of coarser fibrils, with larger meshes, than had
been observed by other methods. Bethe's fibrils pass in every
direction from one process to another, and between different
branches of the dendrites.

Golgi also investigated the minute structure of the nerve-cell

JSlPii Jim

^

~

Fie. 1:22. Kibrillary ut-twoik of a fell of the do^'s spinal curd, obtained by Dona.u.uio with
his spi'dal mi-thud uf fli-cth>- staining.

after his classical work on the general structure of the nervous
system referred to above. His own publications and those of
his pupil Veratti (1898-1900) demonstrated for almost every
form of nerve-cell : () an endocellular reticulum ; (&) a fibrillary
structure of the peripheral zone of the cell; (c) a kind of peri-
cellular network.

The nature and function of the endocellular reticulum are
still undetermined. As between the two hypotheses now in the
field, according to which it is either a nervous network (Apathy)
or a system of nutritive canaliculi (Holmgren), Golgi does not
attempt to decide.

The nervous character of the fibrils which constitute the
fibrillary structure of the peripheral zone of the ganglion cell

iv GENERAL PHYSIOLOGY OF NERYOUS SYSTEM 187

:i

3

o

p

is proved by their continuity with the axis-cylinder
process. Golgi has hitherto failed to discover any
relation between these peripheral fibrils and the
endocellular reticulum, which appears to be an
argument in favour of Holmgren's hypothesis,
although Golgi's reluctance to accept this inter-
pretation is easily understood.

The pericellular network described by Golgi
for different cells of the cerebellum, cerebrum, and
spinal cord consists, in his opinion, of neuro-keratiu,
and he believes its function to be one of insulation,
as he considers it entirely different to and distinct
from the diffuse nervous network described above.

This fibrillary network on the surface of the
nerve -cells is admirably shown up by Bethe's
method, and probably corresponds with the peri-
pheral network observed by Donaggio and by Cajal
in 1896.

Donaggio obtained excellent preparations of
vertebrate nerve-cells by his special method. As
seen in Fig. 122, the cells are not only penetrated
at the periphery by longitudinal fibrils which pre-
serve their individuality without anastomosing, as
stated by Bethe, but in addition a great number of
fibrils can be seen which are directed to the centre
of the cell, and there divide minutely to form a
dense network which is not stained by Bethe's and
Golgi's methods. The fibrillary network
nected on the one side with the
fibrils that penetrate from the
dendrites, on the other with
the fibrils that form the axis-
cylinder.

Donaggio's more recent pre-
parations (1904) show still more
plainly that the fibrils of which
the axis - cylinder is composed
are derived directly from the
endocellular fibrillary network
(Fig. 123). The mode of origin
varies according to two cellular
types, indicated by Donaggio.

On tracing out the course of
a sensory fibre, Apathy found
that it breaks up within the
central nervous system into an
elementary fibrillary network (JElementargitter), which suggests

is con-

I!*'"''

188 PHYSIOLOGY CHAP.

the diffuse nervous network of Gerlach and Golgi, inasmuch as
it is continuous with the fibrils that enter from the periphery,
and those which leave in the axis of the single process of the
nerve-cells of Hirudo. The filaments of this network are therefore
in direct continuity with the sensory or motor fibrils that enter and
leave the ganglion cells, and which form the intracellular fibrillary
network referred to above. All the ganglion cells are thus directly
connected among themselves by the continuity of the fibrils, which,
according to Apathy, are the essential* elements of nerve con-
ductivity. At the periphery of the system again, both in the
epithelial cells and in the sensory cells and muscles, the fibres
never exhibit free endings but anastomose among themselves to
form a network, in the same way as the arteries and veins form a
single continuous system by means of the capillary network.

Bethe confirmed Apathy's results in the most essential points,
for vertebrates as well as for invertebrates, by another method, viz.
elective staining of the fibrils. He finds that very different re-
lations prevail in different classes of animals between the ganglion
cells and the fibrils. In Arthropoda the extracellular fibrillary
network is well developed, while comparatively few h'brils enter or
leave the ganglion cells to form an intracellular network. In
vertebrates, on the other hand, most of the fibrils pass through the
cell, without forming a network within it ; on the contrary an
extracellular network is formed by the anastomosing of the fibrils
that surround the cell.

This last statement of Bethe's is contradicted, as we have seen,
by the most recent work of Golgi, Donaggio, and Semi Meyer,
which shows that the methods employed by Bethe bring out
only the coarser fibrils, leaving the more delicate intra- and peri-
cellular fibrils unstained. Bethe, on the strength of his own
observations, and of an experimental argument which we shall
examine below, reduces the importance of the ganglion cells, and
holds them to be mere stations for the passage and reinforcement
of the nerve current, while the central activity of the system is
developed outside the cell in the intercellular elementary network
of the grey matter ; Donaggio, on the contrary, holds that the
cell probably represents the true centre for the reception of the
excitatory impulse and for its synthesis and transformation.

As regards the theory of the unitary structure of the nervous
system of vertebrates, Held supports Bethe in essentials, on the
strength of his own observations ; Golgi, Veratti, Donaggio main-
tain an absolute reserve ; Semi Meyer and Lugaro, while they
admit the importance of Bethe's observations, deny that these prove
the applicability to vertebrates of Apathy's results for inverte-
brates, so as to overthrow the neurone theory, according to which
the relation of the separate elements of the system is merely one
of contact. Lugaro admits as a possibility, in regard to the question

iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 189

of inter-neuronal anastomosis, that the nature of the connection
between the elements of the system may have developed in two
opposite directions in the course of phylogenetic evolution. He
accepts the theory of Apathy for invertebrates, but maintains that
of Ramon y Cajal for vertebrates, so long as the continuity of the
fibrils which compose the central and peripheral elementary net-
work is not positively demonstrated.

The most emphatic and certainly one of the most reliable
supporters of the theory of Apathy and Bethe, for both in-

FIG. 124. Two cells from ventral horn of human spinal cord. (Nissl's method.) The chromatic
sul .stance is collected into small masses, which give a speckled appearance to the cytoplasm.
Each cell, besides the nucleus and nucleolus, contains a distinct mass of stainable granules.

vertebrates and vertebrates, is Nissl, although his own work does
not refer specially to the fibrillary structure of the nervous
system. In 1893 he discovered the existence in many ganglion
cells of peculiar granules which stain with basic aniline dyes,
particularly with rnethylene blue and toluidine blue. These
which are now generally referred to as Nissl's granules or chromato-
phile granules are present in small masses throughout the body
of the cell and in the larger dendrites (Fig. 124).

Nissl holds that since the fibrillary nature of the achromatic
part of the ganglion cell has been established, the theory of the
nerve unit (neurone*) is no longer tenable. He concludes, on the
strength of the researches of Apathy, Bethe, and Held, which

190

PHYSIOLOGY

CHAP.

demonstrated the fusion of the axis -cylinder fibrils into an
intracellular elementary network, that the nervous system is
constructed of ganglion cells and of a fibrillary nerve substance,
the latter being a specifically differentiated cell protoplasm,
present in the cells as fibrils, and outside them as grey matter,
which last apparently consists of a close and very delicate
network of elementary fibrils. So that Nissl, like Bethe, considers
the grey matter to be the most important constituent of the
nervous system.

Another method, which brings out the fibrillary character of
the nerve-cells, is that discovered by Ramon y Cajal ; it depends
on the reduction of silver nitrate, and is known as the photo-
graphic method. According to Golgi the results obtained by
it are of the utmost importance and are easy of demonstration.

FIG. 125. Tin cr nri \v-cells and processes showing presence and course of neuro-tibrils.
Rtimon y Cajal's photographic method.

Cajal's method (Fig. 125) shows up every detail, so that the
course of the fibrils can be followed both within the cell body
and in the processes. Among its other advantages is the fact
that, unlike any that preceded it, it brings out the fibrillary
structure of the nerve elements during their earliest development.
Jaederholm, nevertheless, remarks with regard to the signifi-
cance and theoretical value of these histological observations :
" In my opinion the reticular formations within the cells must
be regarded as artificial products due to agglutination. Such a
reticular formation may be simulated, because the cytoplasm,
coagulated in the form of a network, stains along with the
fibrils ; this happens most frequently with Donaggio's method ;

iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 191

less often with that of Cajal, more rarely still with those of
Bethe and of Bielschowsky."

It is curious and instructive to note that while for Ramon
y Cajal (1908) the results obtained by his method and its
modifications afford a positive proof of the neurone theory since
he has never been able to convince himself of the existence of
anastomosing intercellular fibrils for Golgi (1910) none of the
data adduced in regard to the anatomical structure of the nervous
system offer a definite proof either of the theory of independent
cell-units (neurones), or of the unitary fibrillary theory.

Nevertheless, from the present state of our knowledge, Golgi
rejects the view according to which the nerve-cell is deposed,
and the chief functional value attributed to the fibrils. " I
should feel as though I were breaking faith if I faltered in
my firm conviction that the nerve-cells are the central organs
of the specific psychical and sensory activities which we ascribe to
the nervous system, provided we admit that they too come under
the concept that is valid for the whole of the cell theory, viz.
that the nerve-cells, while endowed with a certain autonomy,
are more or less dependent on their anatomical and functional
inter-relations. It is hardly necessary to point out that this
statement does not entirely exclude the participation in psychical
and sensory actions of all the other factors that enter into the
complex organisation of the nervous system.

" In regard to the functional mechanism of the nerve elements,
far from being able to accept the idea of the independence
implied in the concept of the neurone, I can but once more state
my conviction that the nerve-cells exhibit collective activity,
in the sense that larger or smaller groups of them exert a
collective action upon the peripheral organs, through bundles of
fibres and through the diffuse nervous network. This concept of
course includes that of the analogous opposite action in regard
to sensory functions.

" However much my position may conflict with the view of
separate anatomical units, I cannot renounce the idea of a
unitary action of the nervous system, nor feel disturbed if this
brings me back to the earlier conception of the mode in which
the nervous system functions."

Golgi's views on the functional activity of the central nervous
system, which are based on anatomical investigations, and parti-
cularly on the existence of a diffuse nervous network, are, how-
ever, opposed to the best-established facts of the physiology of the
sense organs. They are more particularly at variance with the
authentic and easily demonstrated observations of isolated con-
duction and perception of tactile sensations at various points
of the skin, and of elementary retinal sensations, which we
shall discuss in treating of the physiology of these sense organs.

192 PHYSIOLOGY CHAP.

In 1885 Golgi wrote at the beginning of his celebrated mono-
graph : " As regards the central organs of the nervous system,
the main task of modern anatomy must be to answer the
most pressing of the problems propounded by physiology." The
neurone theory, while it harmonises with the cell theory, un-
doubtedly corresponds best with the postulates of physiology,
although it is far from solving them all adequately.

Whatever the final solution of this important controversy
as to the structure and mode of activity of the central and
peripheral nervous systems, it must be admitted that the wealth
of physiological facts that have accumulated in this important
field have developed quite independently of the prevailing theories
of their exact constitution. If the contents of the present
chapter are considered without prejudice and we recommend
them more particularly to the attention of histologists, it must
be admitted that the physiology of the nervous system is far
in advance of its anatomy.

II. In discussing the general physiology of the skeletal
muscles we saw that they are normally thrown into activity
by the agency of their nerves alone ; when these are cut, all
movement instantly ceases. Nerves are no less excitable than
muscles ; but while in muscle active reaction to stimuli, i.e.
"excitation," is apparent as contraction or relaxation, the active
response of the nerve is not visible, but consists in the simple
transmission or conduction of the excitation from the point
stimulated to the end-organ. The excitability of nerve is therefore
manifested in its conductivity, i.e. its capacity for transmitting
the effect of local stimulation at one point along its entire
length. The excitatory impulse in muscle is also, as we know,
propagated along the muscle fibres by physiological conduction,
but conductivity assumes a special development in the nerve,
and may be considered as its specific function, depending on
the particular differentiation and constitution of its protoplasm.
Nerve conduction consists not in the propagation of fluid
or gaseous materials, as was formerly supposed, but in the
transmission of excitation, that is, of the active state of the nerve
substance, the conditions, laws, and characteristics of which we
must now investigate.

The fundamental condition of conductivity in a nerve-fibre
is its anatomical continuity and integrity. If after dividing a
mixed nerve the two ends are brought into perfect contact, we
obtain physical continuity, but not the anatomical continuity
which is imperative for conduction ; stimuli applied above the
section are not transmitted in an efferent direction to the muscles,
nor those sent in below in an afferent direction to the centres.
An effect identical with that of section is produced by crushing,
cauterisation, scalding, and by the action of certain poisons,

iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 193

n

I

localised to one point of the nerve. Lastly, as was known to
the ancients, the simple tying of a nerve prevents physiological
conduction along its fibres.

Fontana (1797) was the first who observed that the gradual
compression of a nerve may abolish its conductivity without any
concomitant excitatory phenomena. But the subsequent experi-
ments of E. H. Weber, Schiff, and others, threw doubt upon his
conclusions. They found that the paralysis due to compression of
the nerve is preceded by a
state of increased excita-
bility of the nerve and
motor phenomena in the
muscle. The subject, which
is important to clinical
medicine, was methodically
investigated by Liideritz
(1881), Zederbaum (1883),
and Efron (1886), who con-
firmed the observations of
Schiff. They saw that when
the compression of the nerve
has not been too severe, nor
too prolonged, its conduc-
tivity may be gradually re-
established. According to
Liideritz, gradual compres-
sion abolishes conductivity
first in motor and later in
sensory fibres ; but this
observation was contra-
dicted by Zederbaum and
Efron. In their experi-
ments on the nerves of
amphibia and of mammals,
these authors noted that
a pressure of some hundred
grammes is always required before conductivity is abolished.

These experiments were resumed by Ducceschi (1900) in
Ewald's laboratory by another method, i.e. compression of a very
limited area of the nerve by means of a silk thread (about 0'3
mm. thick) ; this is passed round the nerve as it lies upon a
metal plate through two small holes made in the latter, so that it
can be gradually drawn down by a weight (Fig. 126).

By means of this little apparatus Ducceschi succeeded in
diminishing or abolishing conduction in the frog's sciatic by the
compression caused by a weight of a few grammes, without any
preceding signs of excitation, as already observed by Fontana.

VOL. in

FIG. 12G. Apparatus for measurable compression of
frog's nerve by a silk thread. (Uucceschi.) 1, metal
plate pierced with two small holes ; , sciatic nerve ;
/, silk thread ; b, balance to carry weights ; , support
moved by screw v to allow the weight to be applied
gradually.

194

PHYSIOLOGY

CHAP.

He saw that conductivity returned a few seconds after the pressure
was removed, provided it had not been excessive nor unduly pro-

Fni. 127. Myograms of frog's gastrocnemius (1) with electrical stimulation ; (2) with break shocks
at an interval of 4 sees. (Ducceschi.) In both tracings a weight was applied at ^ the value
being marked in grammes ; at -^- the compression ceased.

longed (Fig. 127). If, while the frog's gastrocnemius was being
tetanised by an interrupted current applied to the sciatic, the
nerve was compressed below the point of excitation, the trans-
mission of the impulses was partially inhibited, and the almost

FIG. 128. The marks on these tracings correspond to those of the preceding figure.
At b and c the nerve was tetanised.

tonic contraction of the muscle was transformed into a clonic
contraction (Fig. 128). The effects of graduated compression on
conductivity differed according as chemical, mechanical, or electrical

iv GENEKAL PHYSIOLOGY OF NEEVOUS SYSTEM 195

stimuli were employed, owing probably to their different intensity.
When excitation from chemical stimuli (glycerol or hypertonic
salt solution) was no longer able to pass the compressed point,
excitation from mechanical stimuli was able to get through ; when
the latter was blocked by the compression, electrical stimuli were
still effective (Fig. 129). It is an interfering fact that reflex
spinal excitation is arrested by a minimal degree of compression
such as blocks the transmission of chemipal stimuli.

A frog's nerve ceases to conduct when its diameter is reduced
to one-third or one-fourth of the normal ; it then becomes trans-
parent, as the fluid contained in the myelin sheath is pushed back
above and below the point of compression. Histological inspection
of the nerve compressed by a silk thread shows that there is
no blackening of the myelin
sheath by osinic acid near the
point of compression, but the
axis-cylinder (the conducting
element) is reduced in size.

After D ucceschi, Signorina
Calugareanu (1901) experi-
mented iu Dastre's laboratory,
by a somewhat different
method, on the effects of
mechanical compression of
the nerve of the electrical

Organ Of Torpedo, the frog's Fio. 129. The very rapid contractions at the begin-

, -i ,1 11 ,> ning of the tracing were due to chemical stimula-

SCiatlC, and the rabbit S VagUS. tion with glycerol, applied to the upper part of

She also obtained diminution the nerve - At ^ the nerve was compressed by

P i , ., .I 25 grms. At </ it was stimulated above the point

01 COlldllCtlVlty WltbOUt any of compression with break shocks.

previous rise of excitability,

and found that the injurious influence of compression was

not manifested immediately, but after a certain time (about 1

minute).

Bethe, too (1903), studied the effect of compression on frog's
nerve by a method similar to that of Ducceschi, with reference
more particularly to the histological changes. He found that by
a degree of compression which did not abolish conductivity to
electrical stimuli the axis-cylinder may be considerably reduced
in diameter, at the cost not of the neuro- fibrils which compose it,
but of the perifibrillar substance (or neuroplasin). According to his
calculations the amount of perifibrillar substance in the normal
fibre is to that of a compressed fibre which is still capable of con-
ducting, as 654 : 1. This, he says, proves that conductivity is a
function of the neuro-fibrils and not of the perifibrillar substance.
Bethe further noted that when the nerve-fibres are rendered
incapable of conducting by compression, they also lose their
capacity for primary staining, i.e. staining with basic dyes in the

\

\

196 PHYSIOLOGY CHAP.

fresh state, or when dehydrated only, which returns when con-
ductivity is re-established.

One of the most important facts, which may rank as a funda-
mental law of nerve conduction, is that each fibre of a nerve
conducts the excitatory impulse from the periphery to the centre,
or from the centre to its terminal ramifications, without spread of
the excitation by contact to the neighbouring fibres. In the case
of a mixed nerve the motor fibres can be excited along their
course without simultaneously producing sensations, or the sensory
fibres without simultaneous production of movements. The most
convincing proof of isolated conduction of the active state in
individual fibres is afforded by the delicacy of localisation, both of
movements and, still more, of sensations. It is possible to stimulate
the small bundle of fibres that form the motor roots of the
sciatic separately so as to produce localised contractions in the
individual muscles or portions of muscles which they innervate,
without diffusion of the impulse to the whole group of muscles
that are thrown into action by stimulating the trunk of the sciatic.
The excessively delicate localisation of tactile sensations, the
sharpness of outlines and shading of colours in visual images,
would be quite impossible if each fibre of a peripheral or optic
nerve were not an isolated conductor.

This localisation of movements and sensations, with which we
are all familiar, has so far received no mechanical explanation. It
has been thought on good evidence that the sheaths, and particularly
the myelin sheath, are mainly responsible for the complete insula-
tion of the axis-cylinder ; but the fact that this insulation holds
good for the non-medullated nerve-fibres as well leads one to
conjecture that it is a property inherent in the axis -cylinder,
though we are ignorant of the cause to which it is due. That
insulated conduction does not depend > on the medullary sheath
is further proved by the fact established by Ducceschi, that when
the frog's sciatic is so compressed as to rupture the sheath without
blocking the conductivity of the nerve, isolated contraction of the
separate muscles of the foot can be obtained by stimulating single
branches of the lumbro-sacral plexus.

The new theory of the minute structure of the nervous system,
according to which the axis-cylinder and the dendrites are con-
sidered not as elementary nerve-fibres but as bundles of separate
fibrils forming an elementary network, naturally raises the question
whether the law of insulated conduction is applicable to the pro-
cesses (dendrites and axons) of the ganglion cells as a whole, or
to the individual fibrillary elements of which these seem to
consist. It must be confessed that science is not yet ready to
solve this problem, which needs a more complete knowledge of
their anatomical relations. We can only say that many ramifica-
tions of nerve-fibres are merely dissociations of distinct fibrils

iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 197

united into bundles, and that the true ramifications of the con-
ducting elements probably exist only in the terminal and peripheral
organs, where distinction and localisation of the physiological
effects of the excitation transmitted along the conducting filaments
is no longer necessary.

Another fundamental fact of nerve conduction is what William
James, the psychologist, termed the forward direction. Conduction
is normally centripetal, i.e. from the periphery to the centre in
sensory fibres and afferent fibres in general, and centrifugal, from
centre to periphery, in the motor fibres and efferent fibres in
general. Again, when the nerves are artificially stimulated along
their course, the effect is expressed in movement for motor nerves,
in sensation for the sensory. We shall see, in fact, in discussing
the physiology of the special nerve roots, that on stimulating the
central stump of a root that contains motor fibres only all sensory
reaction fails, and on stimulating the peripheral stump of a root
containing only sensory fibres no motor reactions are obtained.

This fact at first sight justifies the conjecture that sensory
nerves can only conduct the excitation in an afferent direction
when excited along their course, and motor nerves only in an
efferent direction, as though there were some valvular mechanism
which allows the transmission of the impulse in one direction and
blocks it in the other. Certain experimental facts, however, show
this hypothesis to be untenable, and indicate that nerves in
general, when artificially excited at any point of their course, are
capable of conducting in both directions, but the effect is manifested
only at the centre for sensory nerves, and at the periphery for
motor nerves.

The best argument for double conduction appears from the
study of the electrical phenomena that accompany the excitation
of nerve. This will be discussed in a separate section. When a
nerve is stimulated midway, while the two ends are joined up to
two galvanometers, the so-called negative variation is seen on
both. This occurs not only with a mixed nerve, which contains
both sensory and motor fibres, but also, as Du Bois Reymond
pointed out, with a nerve which contains only motor (efferent)
fibres, e.g., the ventral spinal roots.

Gotch and Horsley repeated and varied this experiment, both
with efferent and afferent nerves. They divided a ventral root of
the sciatic plexus in the cat ; connected it with a highly sensitive
galvanometer, and then excited the trunk of the sciatic. A double
reaction followed -of the muscles of the limb, which proved
centrifugal conduction in the motor fibres, and of the galvano-
meter, which showed centripetal conduction in the same motor
fibres. Similar effects were obtained with sensory nerves. On
exciting a dorsal root and connecting the central end of the
divided sciatic with the galvanometer, the negative variation

198 PHYSIOLOGY CHAP.

appeared, which is a proof of centrifugal conduction in the sensory
fibres.

Many other attempts have been made to demonstrate the
possibility of reversal of the normal passage of excitation along a
nerve. Schwann divided the sciatic of a frog, and allowed the
two ends to unite. He then stimulated the sensory roots of the
nerve, and saw that its excitation produced no contraction in the
muscles of the limb. From this he concluded against the theory
of conduction in a double direction, since it seemed to him im-
probable that each afferent or efferent fibre of the two stumps
should be able to unite with a fibre of its own kind. But the
fact that normal sensibility and motility is recovered after nerve
section shows that what Schwann thought so impossible really
does take place. His experiments, which Steinbriick confirmed in
1838, do not therefore overthrow the theory of conduction in
both directions.

Bidder (1841) attempted to connect the peripheral end of the
hypoglossal (motor nerve) with the central end of the lingual
(sensory nerve), but he only managed to unite trunks of the same
kind, as in Schwann's experiments. Union of heterouomous
stumps was, however, obtained by the subsequent experiments
of Gluge and Thiernesse (1859), Philipeaux and Vulpian (1860),
Roseuthal (1864), and Bidder himself (1865). It was found that
when the two nerves above mentioned had united, stimulation of
the lingual produced movements of the tongue, and stimulation
of the hypoglossal (united to the central end of the lingual) elicited
signs of pain.

These results seemed to be positive evidence for conduction in
I both directions ; subsequent researches, however, proved them
capable of a different interpretation. The symptoms of pain when
the hypoglossal was stimulated can, according to Arloing and
Tripier, be interpreted as a phenomenon of recurrent sensibility in
the stump of the hypoglossal, and the movements of the tongue
on stimulating the lingual may, according to Vulpian's last work,
depend on excitation of the fibres of the chorda tympani, which is
an efferent nerve. If, on the other hand, the hypoglossal on one
side be cut so that it degenerates completely, and the peripheral
stump of the freshly divided lingual nerve is then excited, a slow
contraction of the tongue follows, which is due to the chorda
tympani and is accompanied by vascular dilatation. The mechanism
of this phenomenon is very obscure, since the chorda tympani has
no direct anatomical connection with the tongue muscles, and
produces no motor effect under normal conditions, i.e. when the
hypoglossal is uninjured. So that none of these experiments are
of any account for the question of double conductivity in nerve.

Nor can any greater value be assigned to the experiments which
Paul Bert carried out on rats by suturing the tip of the tail to the

iv GENERAL PHYSIOLOGY OF NEEVOUS SYSTEM 199

skin of the back, and dividing it when healed close to the root.
As he elicited signs of pain on exciting this inverted tail, he
concluded that conduction in the nerve had been reversed. But
till we know what phenomena of degeneration and regeneration
take place in the nerve, after transplanting the tail, it is impossible
to give any positive explanation of the results of this experiment,
and it cannot be invoked in favour of the law of double conduction.

Kiihne (1859) attempted by another method to prove con-
duction in both directions. He divided the broad end of a freshly
dissected frog's sartorius into two strips with scissors, and found
that mechanical stimulation of one of the strips produced h'brillary
contractions which were not confined to the segment of muscle
that was directly excited, but spread also to the strip that had
not been excited. According to Klihne this phenomenon can only
be explained on the assumption that the excited and non-excited
segments of muscle contain nerve-fibres which come from the
bifurcation of the axis-cylinders of the principal nerve. The
excitation is transmitted centripetally in the nerves of the first
strip, and then spreads centrifugally to the nerves of the second
strip.

Babuchin repeated this experiment on the electrical organ of
Malapterwrus which has a single gigantic many-branching nerve-
fibre. He found that excitation of a single twig of this fibre
suffices to produce a discharge of the whole electrical organ.

Hermann attached great importance to these experiments of
Ktihne and Babuchin as evidence for the law of conduction in
both directions. Other authorities, on the contrary, make strong
objections, for which we have not space, particularly as Kiihne,
in a memoir of 1886, published a long series of new experiments
on the pectoral and gracilis muscles of the frog which lend them-
selves better to the solution of the problem.

If the pectoral muscle of the frog is divided as shown in Fig.
130, by leaving a bridge (Z~] which carries the nerve and a few
muscle fibres, mechanical, chemical, or electrical stimulation of
this bit of tissue will cause the whole of the remainder of the
preparation (J/) to contract. This contraction is not fibrillary as
in the sartorius, but diffuse and simultaneous in all the fibres of
the muscle, so that it can be graphically recorded and shown to
exhibit the characteristics of a single twitch. The experiment of
Fig. 131 is still more decisive. It shows that retrograde con-
duction of the nerve impulse along the motor fibres may also
occur between two parts of the same muscle (K and L], united
only by the nerve (&), on stimulating one portion of the nerve (Z),
so that any direct intervention of the muscle fibres in causing
the phenomenon is excluded.

Kiihne ascertained by a minute histological examination of
the nerves of the frog's pectoral and gracilis muscles that the

200

PHYSIOLOGY

CHAP.

dichotomous branchings of the nerve-fibres occur principally at
the points at which the nerve enters the muscle, and in the
extramuscular part of the same nerve. This dichotomous division
of the nerve-fibres is brought about by the separation of the fibrils
of which, according to Schultze, the axis-cylinders are composed.
Hence the experiments of Kiihne not only yield a direct proof
of double conductivity, but they also imply that the isolated con-
duction which Johannes Miiller showed to be a property of the
axis-cylinder does not hold as between the fibrils of which each
axis-cylinder is composed.

Kiihne employed the same method to demonstrate unequivocally
that the paralysing action of curare is localised in the end-plates
of the muscular nerves, and does not spread to the motor fibres

Z

...

1'lUv

rTXiF

I
ft

I ^

p" '

f !

i ' L

N

FIG. 130. Killing's experiment on frog's pectoral
muscle. -Y, iirrvt- which supplies the right
half (in) of the muscle ; the left half is cut
away leaving only the bridge Z, which con-
tains the part of the nerve that is mechanic-
ally stimulated.

PIG. 131. Kiihne's experiment on the gracilis
muscle. N, nerve that gives off branches
to the two separate parts of the muscle
A' and L and to the bridge of muscle Z,
which is mechanically excited.

(see Chapter I.). He employed the gracilis muscle of the frog,
which can be divided by a ligature into two portions, in only one
of which the poisoned blood circulates. The muscle thus treated
can be cut so that the nerve forms the only connection between
the curarised and non-curarised portions (Fig. 132). Under normal
conditions the mechanical stimulus applied at N, Z, or K pro-
duces a contraction of the entire muscle according to the law
of the backward conduction of excitation ; but in the curarised
muscle mechanical stimulation of the nerve at N and at k will
only cause contraction of the part K, i.e. the non-curarised portion
of the muscle, the same effect being produced by exciting the
branches / and I' of the curarised portion. This proves that the
nerve-fibres have not been paralysed by the curare, since con-
duction in a centripetal direction takes place in them, as under
normal conditions.

It may be argued logically from the law of double conduction
that the motor and sensory nerves do not differ fundamentally in

iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 201

their internal constitution. That under normal conditions the
former conduct centrifugally and the latter centripetally depends
not ou any intrinsic difference, but on the specific nature of the
organ with which they are related at the centre or the periphery,
and to which they transmit the excitation. If experimental efferent
excitation of sensory nerves and afferent excitation of motor
nerves produces no perceptible motor or sensory effects, there must
at the peripheral end of the former and central end of the latter
be some apparatus, as to the nature of which we are entirely
ignorant, which hinders the excitation from being propagated, as
a system of valves determines the direction of flow of a current.
There is thus no intrinsic contradiction
between the law " of the forward direc-
tion of normal excitations " and that " of
the double direction of experimental
Vexcitation," i.e. such as is artificially
produced along the course of the nerve.
Intimately connected with this law
is the other which Hermann (1879)
termed "law of the constant effect of
nervous excitation." Whether a nerve
be excited at its end or at any point
along its course, the effect on the organ
of reaction is invariably the same, viz.

I muscular movement for motor nerves,

sensation for sensory nerves. The local- F io. 132. -Kuime's experiment
isation and character of the muscular
movement are determined not by the
site of stimulation, but by the number
of fibres excited and their peripheral
distribution to the muscle. So, too,
the location and specific quality of
the sensation, e.g. pressure, heat, and
pain, which occurs on stimulating a sensory cutaneous nerve
at any point, is identical with that produced by the action
of natural stimuli upon the end-organ in the skin. The most
striking example that can be adduced in proof of this law is that
observed when a limb has been amputated. " When the member to
which a nerve trunk is distributed," says Johannes Miiller, " is
removed by amputation, the stump of the nerve which contains
the whole of the shortened nerve-fibres is capable of the same

\sensations as if the amputated limb were still present. This
persists all through life." If the stump becomes inflamed, such
persons complain of sharp pains in the entire lost limb. Upon
recovery they have the same sensations that normal people feel in
a healthy limb, and there is often a persistent sensation of itching,
or discomfort, which appears to be localised in the limb that no

frog's graeilis muscle, halt' of which
had been poisoned with curare and
then severed, so that only the
nerve was left as a connecting
bridge. N, nerve that gi\es
branches to the poisoned L and
non - poisoned K, halves of the
muscle ; k, connecting bridge ;
Z, nerve -muscle biidgr that is
mechanically excited.

202 PHYSIOLOGY CHAP.

longer exists. Many persons eventually become accustomed to
these sensations, and cease to notice them ; but they surge up
again when attention is focussed upon them, and are often felt
distinctly in the fingers, sole of the foot, or hand. The sensation
is more acute when pressure is exerted on the stump.

The symptoms of anaesthesia dolorosa are no less important
to the demonstration of the peripheral projection of sensations.
Traumatic paralysis from compression or section of a nerve trunk,
in which more or less extensive cutaneous areas become totally in-
sensitive to the strongest stimuli, though the patient still complains
of intense pain in them owing to the irritable state of the nerve
trunk, is not infrequent. In surgery, division of the nerve may
fail to cure neuralgia, as it merely interrupts the conduction of
external peripheral excitations to the centre, but cannot suppress
the conduction of central irritation in the nerve, which gives
origin to sensations projected to the periphery similar to those
produced by extrinsic local stimulation.

The phenomenon of the peripheral projection of sensations can
easily be demonstrated under normal conditions by mechanical
excitation of one's own ulnar nerve in the groove of the internal
condyle at the elbow, where it is accessible ; this produces a prick-
ing in the palm and back of the hand, and in the third and fourth
fingers. Pressure on the infraorbital nerve, where it issues from
its foramen, produces pricking at many points of the cheek and
upper lip.

III. Johannes Miiller in 1844 declared the problem of the
velocity of nerve conduction to be insoluble, and compared it with
that of light. " The time," he writes, " in which a sensation
passes from the exterior to the brain and spinal cord, and thence
back to the muscle so as to produce a contraction, is infinitely
small and immeasurable." Only six years later, in 1850,
Helmholtz was able by exact physical methods to determine the
rate of propagation in a frog's nerve, and to demonstrate that it
is infinitely slow in comparison with the propagation of physical
energy. Electricity traverses a space of 464 million metres in a
second, light 300 million, sound 332 metres; the excitatory
impulse in nerve, on the contrary, is transmitted at a rate so
much lower that it may be compared with the speed of a loco-
motive or the flight of an eagle.

The first exact measurement of the velocity of conduction in
nerve was made by Helmholtz on a frog's nerve-muscle preparation
(Fig. 3). If the time-interval between the stimulation of the
nerve and the contraction of the muscle (latent period) is measured,
it is found to be greater when the motor nerve is stimulated at a
point remote from the muscle than when it is stimulated near the
muscle. The difference in the time-interval is also, carteris paribus,
proportional to the length of nerve between the two points excited.

iv GENEEAL PHYSIOLOGY OF NEEVOUS SYSTEM 203

From the difference in time and the length of the nerve as
measured the rate of conductivity is easily calculated.

Helmholtz employed two methods for determining the time that elapses
between the (electrical) stimulation of the nerve and the reaction of the muscle.
The first method, invented by Pouillet, consists in measuring the duration
of an electrical current, sent through a galvanometer at the moment of excit-
ing the nerve, and interrupted at the moment at which the muscle contracts
(for details of the application of this method see Biedermann). 1 The second
method, employed after Helmholtz by all physiologists, is a special applica-
tion of the graphic method. The times of nerve excitation and muscle con-
traction are recorded by a myograph on the smoked paper of a drum or plate,
which is moving very rapidly, the time being marked on the same surface
by means of a tuning-fork. The difference in time can thus be measured
exactly between the first stimulation of the nerve close to the muscle and the
commencement of the muscular contraction, and the second stimulation
farther from the muscle and commencement of the second: contraction.
When the times of the two successive stimulations are recorded at the same
point of the revolving drum (as in Fig. 133), the distance between the initial

Fir.. 133. Velocity of nerve conduction, as measured by Marey on himself. 1, myogram traced on
exciting the nerve close to the muscle ; 2, myogram on exciting the nerve 30 cms. from the
muscle ; D, time tracing from a tuning-fork at 250 double vibrations per second. The interval
between the two contractions occupies about 2-5 vibrations, corresponding to O'Ol sec. in
which the impulse traverses 30 cms. = 30 m. per second.

point of the two contractions is all that is required to calculate the rate of
conductivity, when the length of nerve between the two points of excitation
is known.

From an average of the experiments made by Helmholtz on
the frog's nerves the velocity of nerve conduction was found to be
27'25 metres per second, which is much less than the velocity of
the propagation of sound in air, but greater than the propagation
of the contraction wave in the muscle of the same animal, this
being, as we have seen, about 1 metre per second.

Helmholtz and Baxt also determined the rate of conductivity
in the motor nerves of man. They recorded the myograms of the
thumb-muscle upon a rotating cylinder by placing a sensitive
lever on the thenar eminence, and exciting the median nerve
either in the axilla or near the wrist joint, through the previously
moistened skin. The rate obtained was somewhat higher than for
frog nerves, i.e. 30-35 in. per second.

Helmholtz and many other investigators have also attempted
to determine the rate at which the impulse is propagated in the

1 Electro-Physiology, English translation by F. A. Welby, 1896, ii. 59.

204 PHYSIOLOGY CHAP.

sensory nerves of man, but the resulting data are discordant and
unconvincing. The method consists in determining the reaction-
time to tactile sensations sent in at two points on the skin of the
arm, at different distances from the centres. As soon as the
subject perceived the sensation he pressed a button which marks
the moment of reaction upon a revolving cylinder. It was
formerly assumed that the reaction-time for two approximately
identical sensations, evoked at two points of the skin at different
distances from the centres, differed only in proportion to the
different length of nerve through which the impulse has to
pass before reaching the centres. The discrepancy of results
obtained by various experimenters, which ranges from 26 to more
than 100 m. per second, however, shows that the lost time at
the centres, where the afferent excitation is transformed into a
motor impulse passing down the efferent nerve, must vary con-
siderably, according to the site of stimulation, the state of fatigue
and degree of attention of the subject, with other less appreciable
conditions. It is probable, judging from other experiments to be
described later, that the rate of conductivity is the same in
sensory nerves as in motor.

Considerable differences in rate of conductivity are found in
the lower animals, and even in different kinds of nerve in the
same animal. Fredericq and van de Velde found for the nerves
of the claw of the sea-crab a velocity varying from 6 to 12 metres
per second when the temperature varied between 19 and 20 C.
v. Uexkiill found variations of O'4-l m. per second for the nerves of
the mantle of Cephalopoda ; Chauveau found in the vagus fibres
that innervate the smooth muscle cells of the oesophagus of large
mammals a velocity averaging 8'2 rn. per second, while in the
vagus fibres that innervate the striated muscles of the larynx it
averaged 66'7 m. per second. According to Chauveau -this rate
is not uniform for all parts of the nerve, but falls in the parts
nearest the muscle.

From some of Gotch's work, again, it seems highly probable
that the rate of transmission of the motor impulse is much lower
in the terminal branches of the nerve than it is in the principal
trunks. In experiments on the electrical organ of Malapterurus,
in which a gigantic nerve-fibre terminates in a very free arborisa-
tion, he measured the difference of latent period obtained on
exciting the organ -directly or through the nerve, and found that a
non-negligible fraction of time (0'003-0'005 per second) was lost
in the transmission of the impulse along the twigs of the nerve.
On repeating the experiments of Babuchin on the same nerve
(see p. 199) to see if the retrograde centripetal conduction of
the impulse proceeded at the same rate as the centrifugal, his
results led him to conclude that the velocity of conduction did not
alter with the ascending or descending direction of the impulse.

iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 205

The influence of temperature on rate of conduction in nerve is
very apparent. Helmholtz, experimenting with the motor nerves I
of frog, found that their conductivity diminished considerably
on cooling, and increased on warming to 25 C. Gotch and
Macdonald made a careful research, exciting the same nerve at
regular intervals with minimal or nearly minimal stimuli. They
found that on cooling the nerve to 5 C. the muscular response
diminished or disappeared, while on warming it to 35 C. it was
increased and became maximal. So that cooling diminishes not
only the velocity of conduction, but the intensity of the effect trans-
mitted by the nerve as well ; heating produces the opposite effect.

Helmholtz and Baxt further observed that both the rate of
conduction and the intensity of the effect transmitted vary
with alterations in the strength of the stimulus. This result,
obtained on the brachial nerve of man, was confirmed by
Vintschgau for the motor nerves of frog, and by Fick for the non-
medullated nerves of Anodonta. It was, however, always disputed
by Rosenthal and Lautenbach, and it is in any case doubtful
whether it applies to mechanical and chemical excitation as well
as to electrical stimuli. It should further be noted that the
shortened latent period obtained on stimulating the nerve with a
stronger induction current may be apparent only, which is due
to the fact that in this case the current spreads further and
stimulates points of the nerve which lie nearer to the muscle.

We shall later discuss the alterations in the conductivity of
the nerve caused by electrotonus.

Fr. W. Frohlich (1904), in studying the oxygen demand, and
the effects of narcosis on the frog's sciatic (infra], showed by the
myographic method that the rate of transmission of the nervous
impulse undergoes a local diminution during asphyxia and
narcosis in the part of the nerve affected, and that this became
more marked in proportion to the length of nerve involved. This
delay in conduction is perceptible even in a state of narcosis or
asphyxia in which conductivity seems by other methods to be
unaltered.

According to Ch. Richet the experimental results arrived at
by the various authors as to the velocity of transmission of the
excitation or active state of the nerve may be summarised as
follows :

(r/,) In the frog the mean velocity of the nervous vibration (as
he terms the active or excited state of the nerve) is from 20 to
26 m. per second.

(&) In warm-blooded animals this velocity is 30-34 m. per
second.

(c) It varies with a number of factors, particularly with the
temperature.

It is not identical in every part of the nerve.

206 PHYSIOLOGY CHAP.

From these facts we derive the important conclusion that
fthe internal excitatory process, or active state of the nerve,
Us transmitted at a rate that is, comparatively speaking, so low
that it must undoubtedly consist in a physico-chemical change of
the living substance of the axis cylinder, propagated by contiguity
from one part to the next. The conduction of excitation in the
nerve is analogous to the transmission of excitation in the muscle,
although it occurs much more rapidly. We may assume with
Pfliiger that potential energy is liberated during activity in nerve
as in muscle, this chemical process being propagated from segment
to segment till it reaches the muscle, where it excites the
mechanical process of contraction just as the spark of a match
produces an explosion when it reaches the powder in a mine.

As in muscle so in nerve, it can be proved that excitation
is a diphasic cyclic process, whatever concept be formed of the
hitherto unknown chemical changes aroused by the stimulus.
Just as in muscle the phase of relaxation follows the phase of
contraction, and the whole cycle of muscular excitation results
from these two factors, so in nerve the active state results, as can
be demonstrated, from a physico-chemical, presumably katabolic,
change, followed after a brief interval by the opposite (anabolic)
change, which represents the return of the protoplasm of the
nerve to the molecular equilibrium proper to the resting state.
Our physiological analysis of the phenomena of excitation will
yield constant confirmation of this law.

IV. We have seen that the excitation or active state of a
muscle is expressed in three orders of effects ; in mechanical,
chemical, and electrical phenomena. The active state of a
nerve induced by various stimuli is, on the contrary, so far as we
know, expressed solely by alteration of its electrical potential.

The chemical composition of the axis-cylinder (the only really
and specifically active part of a nerve) is totally unknown to us.
Under the microscope it gives the xanthroproteic reaction and
other indications of a protoplasmic character. From this single
fact we may conclude, with Foster, that there is a generic
analogy between the chemical composition of the active sub-
stance of muscle and that of nerve, and conjecture that the
transmission of excitation along the nerve-fibre is accompanied
by chemical changes similar to those which take place in the
muscle fibre. It is, however, certain that the nutritive exchanges
and metabolic phenomena which are theoretically probable in
nerve must be extremely small, since it has so far been impossible
to obtain any direct demonstration of them.

A. D. Waller, starting from the observation (which we shall
discuss below) that there is a relation between the functional
capacity of the nerve and the variations produced experimentally
in the CO., content of the surrounding atmosphere, concludes that

iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 207

the nerve produces carbonic acid during its activity ; but there is
so far no direct demonstration of this fact. It has, indeed, as we
shall see, been demonstrated of late years by the school of Verworn
(H. v. Baeyer, Fr. W. Frohlich) that the nerve requires a supply
of oxygen to keep up its vitality. Thunberg succeeded in
measuring the quantity of oxygen absorbed and of carbonic acid
given off. But no one has yet proved that this respiratory gas
exchange depends directly upon the state of rest or activity of
the nerve. Funke found that the normally alkaline reaction was
converted into an acid reaction in a nerve treated with strychnine,
owing to its exaggerated activity, but this observation has not
been confirmed by other workers. Rohmann, who experimented
on the nerves of the electrical organ of Torpedo, using acid fuchsin
as his reagent, failed to obtain any positive result.

The exceedingly slow character of nerve metal lolisrn can also ,
be detected in the fact that, unlike the grey matter, which is
irrigated by a rich network of blood capillaries, the vascularisa-
tion of nerve is very little developed. But the best argument, of
which we shall give experimental proof later on, is the fact that
nerve, unlike the nerve-centres, is practically inexhaustible, i.e. it
shows no visible signs of fatigue, even when thrown into a state I
of activity for several hours.

Thermal phenomena, again, such as are due to katabolic
processes, are very small and insignificant in the active nerve.
Schiff found a slight increase in heat development when he
applied the thermo-electric pile to nerve. But the same method
yielded negative results in the hands of other expert observers
(Helmholtz, Heidenhain). Nor did Rolleston arrive at any
positive result with Callender's extremely sensitive method.

It seems impossible to doubt that metabolism is very low in
nerve-fibre, even after strong and persistent stimulation, which
evidently means that the work the nerve has to perform is
inconsiderable. Both when the excitation is propagated from the
periphery to the centre (afferent nerves) and when it travels from
the centre to the periphery (efferent nerves), the nerve only needs
to send a slight impulse, a tiny spark, to the end - organ with
which it is connected in order to effect a vigorous process and
marked explosion of energy, owing to the great irritability of
that organ.

Yet, however slight it may be, the process of excitation and
conduction in the nerve-fibre must involve a certain consumption
of energy. That the products of chemical dissociation and the
correlative development of heat are not demonstrable even after
strong and protracted stimulation, suggests that the chemical i
dissociation is rapidly compensated by a process of restitution. '
Gad, in formulating this notion more precisely, assumes that the
restitution of the substance that has been altered by excitation

208 PHYSIOLOGY CHAP.

in any part of a nerve is accomplished instantaneously at the
expense of the next part, and that upon this the propagation of
the excitatory impulse depends.

An indirect proof of this theory is afforded by the study of
the electrical phenomena exhibited by nerve in the state of rest
and of activity, which need only a brief description, since they are
almost exactly identical with those already discussed for muscle
(vide Chapter L, sec. XL, p. 68).

The discovery of the so-called current of rest in nerve was
made by du Bois-Beymond (1845). Any bit of nerve cut out
of the body presents approximately the same electromotive
phenomena as muscle, and these may be summed up as follows :

(a) Two symmetrical points on the longitudinal surface and of
the two cross-sections of a nerve are as a rule iso-electric, i.e.
equipotential.

(6) Two points at different distances from the sections show a

FIG. 134. Diagram <>f demarcation currents in a length of mixed nerve excised from the animal.
Direction ni currents indicated by arrows; e, physiological equator at the centre of the bit
of nerve.

difference in potential, in the sense that the point nearest the
cross -section is electrically negative, on the galvanometer, as
compared with the other point.

(c) Generally speaking, the surface of a transverse section is
negative to the natural or longitudinal surface, and the greatest
difference in potential, i.e. the maximum deflection of the galvano-
meter needle, is obtained on placing one unpolarisable electrode
on the cut surface and the other on the middle of the longitudinal
surface.

The diagram in Fig. 134 is a representation of these pheno-
mena. They are all comprised under the general law that in
i excised nerve the longitudinal surface represents the positive pole
' or anode, and the transverse surface the negative pole or kathode.

The currents that can be led off to a galvanometer from an
artificial cross-section and from any given point of the natural
longitudinal surface of a nerve, decline rapidly, especially in
warm-blooded animals. In the frog's sciatic the value of the
current may fall by one-half in two to four hours, especially in
summer. But the difference of potential may increase again, and
the current may regain its original force, if a new section is made

iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 209

near the first. This fact seems to us important, because it
corroborates Engelrnarm's theory that the strength of the current
corresponds with the intensity of the lesion in the injured nerve,
and that this process of injury is arrested at the next node of
Ranvier. It also gives support to Hermann's theory that the
uninjured cell elements are incapable of developing electromotive
phenomena, and that the critical points of demarcation between
the healthy tissue and that injured by the section are determined
by these nodes.

Nerves that are wholly dead are incapable of giving currents.
Any lesion of a nerve along its course, by cauterising, crushing,
compression, etc., renders it negative to the normal p