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THE INTERNATIONAL SCIENTIFIC .SERIES.

GENERAL PHYSIOLOGY

OF

MUSCLES AND NERVES.

BY

DR. I. ROSENTHAL,

PROCESSOR OF PHYSIOLOGY IN THE UNIVEKStTY 0F ERLANGEN.

WITH SEVENTY-FIVE WOODCUTS.

NEW YORK:

APPLETON AND COMPANY,
1, 3, AND 5 BOND STREET.
1881.

A

ic o 3

THIS BOOK IS DEDICATED

TO

HIS VENERATED MASTER
EMIL DU BOIS-REYMOND

BY

THE AUTHOR

PEE FACE.

THIS attempt at a connected account of the General
Physiology of Muscles and Nerves is, as far as I know,
the first of its kind. The necessary data for this
branch of science have been gained only within the
last thirty years, and even now many of the facts are
uncertain and have been insufficiently studied. Under
these circumstances it might well be asked if the time
has yet come for such an account as this. But any-
one who endeavours to gain an idea of this branch of
knowledge from the existing text-books of Physiology
will probably labour in vain. Moreover, the subject
is one which has many points of interest not only for
the specialist, but also for the physicist, for the psy-
chologist, and indeed for every cultivated man ; and as
regards the gaps in our knowledge, they are scarcely
greater than those in any other branch of the science
of life.

There being no previous writers on the same sub-
ject, I have been obliged to d peiid entirely on myself
in the matter of the arrangement, in the selection
of important points and the rejection of those of less
importance, and as to the form in which the subject

vi

is presented. From tin- experience gained liy teach-
ing during more than fifteen years, 1 believe that I
have ;ic(juircd sufficient clearness of ( xpre -ion, even in
treating of more difficult matters, to be intelligible
when studied carefully even by tlu.se who are not
specialists. In crrtain cases it lias been impossible to
avoid somewhat long explanations of physical and.
especially, of electric phenomena. But these have
been confined to the narrowest possible limits, and I
must refer those who require further details to my
Elektridtdtslehre //'//• .lAr-//,'//^/- (lierlin, Ilirschwald).
It has also been unavoidable in giving an account of
one branch of Physiology to indicate the connection
with other branches, though it has been impossible to
enter into the details of these. To those who feel
inclined to follow these matters further, I recommend
the study of Huxley's ' Elementary Physiology.' Cer-
tain details, which would have detained the course of
the text too long, I have relegated to the Notes and
Additions at the end of the book.

In accordance with the title of the book, I have
omitted too scientific proofs, references, &<•. The
names of men of science to whom the discovery of the
facts is due have only been occasionally introduced.
In this matter no fixed rule has been followed, but it
did not seem riidit to omit occasional mention of the
names of the chief founders of this branch of know-
ledge I'd. Weber, K. du Bois-Reymond, and II. Ilelm-
holtz.

Kia.\Noi:\ : April 15, 1677.

CONTENTS.

TAGR

PREFACE vii

CHAPTER I.

L Introduction : Motion and sensation as animal charac-
teristics ; 2. Movement in plants; 3. Molecular motion;
4. Simplicity of the lowest organisms ; 5. Protoplasmic
motion and amoeboid motion; 6. Elementary organisms
and gradual differentiation of the tissues; 7. Ciliary
motion . 1

CHAPTER II.

1. Muscles, their form and structure; 2. Minute structure of
striated muscle-fibres ; 3. Connection of muscles and
bones ; 4. Bones and bone-sockets ; 5. The law of elasticity :
6. The elasticity of the muscles 12

CHAPTER III.

1. Irritability of muscle; 2. Contraction and tetanus; 3.
Height of elevation and performance of work ; 4. Internal
work during tetanus ; 5. Generation of heat and muscle-
tone : 6. Alteration in form during contraction ... 28

CHAPTER IV.

1. Alteration in elasticity during contraction; 2. Duration of
contraction; the myograpb ; 3. Determination of electric

X (.'MINIS.

PAQB

time; I. Applicaii'ii of this to muscular puKati"ii: ."».
HurdeM ami o\rr-l>urdeH, muscular force; (!. Ill-termina-
tion of muscular force la man; 7. Allrra'ion in muscular
force il-.. • r ic! i"M 47

CHAPTER V.

. inii-al ].]• !(•:•>-. -s within the muscle; 2. General ion of
warmth durini: contraction; 3. Exhaustion and recovery J
4. Source of muscle-force; 5. Death of the muscle : r..
Death-stiffening (J?ty0r m0r£i«) 72

CHAPTER VI.

). l-'nrmsiif mu.-M'lc : L'. At larhnn-nt of muscles t<> tin- Imiics ; 3.
Kla<tir irii>imi; I. Smniith musclf-tiliri-s : .". l'i-rislalt ic
motion; <;. Voluntary and involuntary motion . . . '.'1

CHA1TKK VII.

1. Nerve-fibres and nerve-cells ; 2. Irritability of nerve-fibre;

3. Traiismij-siiin of the irritation; I. Isnlatnl tratismis-
sir.n ; .",. In italiility ; d. The curve of irritation; 7. Ex-
haust ion and recovery, death ...... 103

CHAPTER VIII.

I, Kli -etroii ini- : L'. Modifications of excitaliility ; '.'>. I.a\v of
jiiiNat imi> : 4. i 'oimec.tion of electrotonus \\ith excjta-
liiliiy; :>. Coiidiiinn of excitalality in elect |-..t, ,ims ; 6.
Kxplanal ion of the law of j.ulsat ion.- ; 7. tiei:eral law of

nerve-excitemehl ......... !•_'.">

( 1IAITKK IX.

1. Kler'ric phenomena ; L'. Klect ric li>li.-s ; :;. Kleet ric oivans ;

4. Multiplier and tangent ^alvanonu ter ; .". 1 litliculty of

the study; (i. Homogeneous diverting vessels; 7. Klectro-

nioti\r |.,!c. : s. Kh-etric fall; '.>. Ten.'.ioii in the clOSll

ai oh . . . 153

CONTENTS. Xi

CHAPTER X.

PAGE

1. Diverting arches; 2. Current-curves and tension-curves;
3. Diverting cylinders ; 4. Method of measuring tension
differences by compensation 17G

CHAPTER XL

1. A regular muscle-prism; 2. Currents and tensions in a
muscle-prism ; 3. Muscle-rhombus ; 4. Irregular muscle-
rhombi ; 5. Current of m. gastrocnemius .... 189

CHAPTER XII.

1. Negative variation of the muscle-current ; 2. Living muscle
is alone electrically active ; 3. Parelectronomy ; 4. Secon-
dary pulsation and secondary tetanus ; 5. Glands and their
currents . 202

CHAPTER XIII.

1. The nerve-current ; 2. Negative variation of the nerve-
current ; 3. Duplex transmission in the nerve ; 4. Eate of
propagation of negative variation ; 5. Electrotonus ; 6.
Electric tissue of electric fishes ; 7. Electric action in plants 21 o

CHAPTER XIV.

1. General summary; 2. Fundamental principles; 3. Com-
parison of muscle-prism and magnet; 4. Explanation of
the tensions in muscle-prisms and muscle-rhombi ; 5.
Explanation of negative variation and parelectronomy ; 6.
Application to nerves ; 7. Application to electric organs
and glands 226

CHAPTER XV.

1. Connection of nerve and muscle ; 2. Isolated excitement of
individual muscle-fibres j 3. Discharge-hypothesis ; 4. Prin-

XU CONTEXTS.

PAliB

ciple uf tin' dispersion of forces; ~>. Independent irrita-
bility of muscle-substance; <">. Curare; 7. Chemical irri-
tants; 8. Theory of the activity of the nerves . . . 244

CHAPTER XVI.

1. Various kinds of nerves ; L'. Absence of indicable differences
in the fibres ; ;?. Characters of nerve-cells ; 4. Various kincl>
of nerve-cells; 5. Voluntary and automatic motion; 6. Ke-
tlex motion and c .i-ivlative sensation; 7. Sensation and
consciousness; 8. Itetardation ; *). Specific energies of
nerve-cells; 10. Conclusion 2G1

NOTES AND ADDITIONS.

1. (iraphical \'<-\ >rescntat ion. ^latheniat ie.al inunction . . '_".':'•

2. Irritation of Muscle-Fibres, Height of Elevation and Per-

formance of Work ........ L",i7

;;. Ivxcitaliility and Strength of Irritant. Combination of

Irritants .......... ^'.'c,t

4. Curve of Excitability. Resistance to Transmission . . :ton

~>. Influence of the Length of Irritated Portion of Nerve . 303

6. Difference between closing and opening Inductive Cur-

rents. Helmholtz's Arrangement ..... :!<>t

7. Effect of Currents of Short Duration . . ... ::n7

8. Unipolar Irritation ........ 3()!»

;i. Tan •_'•<• nt Galvanometer ........ I'.lo

in. Tensions in Conduotora ....... :;ii

11. l)ii]ile.\ Transmission. Degeneration, Hogcneralion, and

Hcalitigof llisocted Nerves ...... :il'J

12. Negative Variation and Excitement ... . ."KJ
]:;. |-;ic, -trot onus. S«'( ..... dary J'ulsatioiis dlViM i-<l by Neivea,

Paradoxical I'uNatioii ....... .'ill

II. rarclcctronomy . . ....... I!!.".

]',. I li^charLTe llypol ln'.-i.> and Isolated Traii-inis>ion inNcr\c-

|MH;X

LIST OF WOODCUTS.

FIQ. PAGIt

1. Amcebre 6

2. White Blood-Corpuscles from a Guinea-Pig .... 7
MI. Ciliate Cells situated with the other Cells on a Mem-
brane . . . . . . . . . .10

3&. A single Ciliate Cell, greatly magnified, of somewhat

abnormal form 10

4. Striated Muscle-Fibres 13

5. The Double-headed Calf-Muscle («. gaetrocncmi-us) with

its Tendons 17

6. The Bones of the Arm . .... 19

7. Du Bois-Reyinond's Apparatus for studying the Elastic

Extension in Muscle . . . . . . . 25

8. The Simple Myograph ... 26

9. Du Bois-Reymond's Muscle-Telegraph 29

10. Induction Coil 31

11. Electric Wheel 33

12. Wagner's Hammer 34

13. Du Bois-Reymond's Sliding Inductive Apparatus . 35

14. Du Bois-Reymond's Tetanising Key 36

15. Heights of Elevation with different Weights . . . . 38

16. The Changes in Elasticity during Contraction ... 48

17. Helmholtz's Myograph 52

18. The Curve of Pulsation of a Muscle . .... 56

19. Measurement of small Angles of Deflection with Mirror

and Lens 57

20. Apparatus for measuring the Duration of Muscle-Contrac-

tion GO

21. End of the Lever of the Time-determining Apparatus with

Capsule of Quicksilver 61

22. Diagram of Experiment for measuring Electric Time . 62

23. Diagram of the Flexor Appara1 us of the Forearm . . 68

24. Dynamometer .69

Xiv LIST OF WOODCUTS.

I'A'iK

25. Smooth Muscle-Fibres 97

lit;. Nrrvr-Filiivs 101

'-'7. Ganglion-Cells with Nerve-F lOfi

28. Spring .My<>_r;i|ili i't' K. du Bois-K"\ mond . . . . 112

l".'. rrop:r_';iti'.n ni' the Excitement in the Nerve . . . lit

30. Electron >mi;$ 127

31. Elnctrotonna under the influence of Currents of varying

Strength 130

:•!•_'. Rhcochord 133

:;:;. Klectrotonus 140

34. Series of Magnetic Needles representing Nerve-Particles . 117

86. Kheochord 149

3G. Electric Current . . . ... I.V.'

37. Multiplier . ... . .161

38. Reflecting Galvanometer. ... ...

:'.'.!. Du Bois-Bcymond's homogeneous Diverting Vessel . .

40. Distribution of Currents in [rregular Conductors . • . . 170

41. Electric Fall ' . .172

42. Fall in different Wires . . . . 171!

43. Current-Paths in a Conductor .... . 17">

44. Current-Curves and Tension-Curves . . . . 1"S
4.'. Dn Bois-Beymond's Diverting Cylinders . . 181
4(5. Measurement by Compensation of Differences in Tension . 184

47. Du Bois-Beymond's Bound Compensator .... 186

48. Diagram of Electric Measurement by Hound ' Compensator 187

49. A Regular Muscle-Prism ... . 1I>0

50. Currents in a Muscle-Prism . . . . 192

51. Tensions on the Longitudinal HI id Cross Sections of a

);< irubr MiiM-li'-Prism ... . 193

52. Tensions in a Begular Muscle-Bhombns . .
:,:;. Currents in a Begular Muscle-Bhombus . . .

:,t. Currents in the Graatxocnemius . . . -""

:.:,. Muscle-Current during Pulsation . -"'•'•
B6. Deflection of the Magnetic Needle by the ^Till . .
B7 and 58. Secondary Pulsation . .
:,;i. TI-IIMOII in Nerves .

CO. Changes in Tension during Electrotonus . . 220

c,l. Tli.M.ry of M.T_rnrti.Mii . -'•'•<)

r,L'. Diagram of a Piece of Muscle-Fibre . . -'31

,;;;. ] )j;, _, ,-;,„, ,,f il,c Electric Action in an \ gl j.'ition of

.Mii>.-l«'-Kli-iiii-nts

r,i. Diagram of an oblique Cross-Section ., . . . -34

LIST OF WOODCUTS. XV

PAGE

Go. Magnetic Induction • 242

66. Magnetic Induction 243

67. Nerve-Terminations in the Muscles of a Guinea-Pig . . 245

68. Ganglion-Cells from the Human Brain .... 266

69. Graphical Representation of Muscle-Extension . . . 295

70. Representations of Positive and Negative Values . . 296

71. Action of Oblique Muscle-Fibres 297

72. The Sciatic Nerve and Calf-Muscle of a Frog . . . 302

73. Duration of Inductive Currents 305

74. Helmholtz's Arrangement with a Sliding Inductive Appara-

tus 307

75A,JB,C. Secondary Pulsation from the Nerves . . . 315

GENEKAL PHYSIOLOGY

OP

MUSCLES AND NEEVES.

CHAPTER I.

1. Introduction: — Movement and sensation as animal charac-
teristics; 2. Movement in plants; 3. Molecular movements;
4. Simplicity of the lowest organisms ; 5. Protoplasmic and
amoeboid movements ; 6. Elementary organisms, and the gradual
differentiation of the tissues ; 7. Ciliary movement.

1. The student who has elected to study the pheno-
mena of life probably meets with no more attractive, and
at the same time no harder task than that of explaining
motion and sensation. It is especially in these pheno-
mena that the distinction lies between animate and
inanimate objects, between animals and plants. It is
true that movements can be detected even in inanimate
objects, and, indeed, according to the modern conception,
all natural phenomena depend on motion, either on that
of entire masses, or on that of the smallest particles
of the masses. But the movements of animals are

2 rilY.SIOLOGY OF MUSCLES AND NHKVES.

of a different kind. The contraction of a p"lyp when
touched and the voluntary movement °f tac human
arm are phenomena of a peculiar kind, and result from
circumstances quite other than those which cause the
fall of a stone or the attraction and repulsion exercised
between magnetic or electric masses. Moreover, sensa-
tion, such as we are conscious of in ourselves, and of the
existence of which in other men and in animals we learn
either from the statements or from the conduct of those
others, seems to be entirely unrepresented in inanimate
nature ; it even appears doubtful if it occurs in plants.
Upon this task, hard as it is, physiological research has
thrown much light; it is the knowledge which has thus
already been gained which will form the subject of the
following explanations.

2. Although even in plants movements occur similar
to those observable in animals, yet there seems to be an
essential difference between the two. For instance, in
most animals we find that special organs are formed to
serve principally for movement. Such are the muscles,
which form what is ordinarily railed flesh. Organs
of this sort have never yet been seen in plants. But
not all the movements of the animal body are accom-
plished by the muscles, and some forms of mot ion occur
in exactly the same way in the plant as in the animal
organism.

These movements are most e\ident.and are mo>(
easily explained in the sensitive planl ( Mim".-<ii //"<//'<•</).

The stem and 1. randies of the sensitive plant bear leaf-
stalks, each of \\liicli again bears secondary leaf-stalks,
to \\hich latter the individual leaflets are attached. If
the plant is shaken, the leaf-stalks suddenly bend and
sink, the upper surfaces of t he t wo halves of each lea Met

MOLECULAR MOVEMENTS. 3

meeting together as do the two halves of a sheet of
paper when folded. This movement may be excited in
any individual stalk, most easily by touching or softly
rubbing the under surface of that part of it which is
immediately attached to the branch. At this point the
leaf-stalk is attached to the branch by a lump-like thick-
ening or node. Similar nodes occur at the bases both of
the secondary leaf-stalks and of the leaflets. If one of
these nodes is cut through, a bundle of fibres is observ-
able in the centre, round which there is a layer of cells,
very full of sap, the walls of which are thicker on the
upper, thinner on the lower side. Between the cells
are spaces filled with air. Now, it can be shown that
the bending movement is due to the fact that part of
the fluid matter passes out of the cells into the inter-
mediate spaces, so thatthe cellular tissue becomes weaker
and less able to support the stalk.

Motion of this sort is, however, very different from
the motion peculiar to animals, in that in the latter,
as we shall presently see, it serves to counteract the
pressure of opposed weights ; while in the Mimosa the
pressure of the leaf-stalk is downward when the under
side of the node becomes slack. Before, however, we
examine minutely the motion peculiar to animals, men-
tion must be made of certain other phenomena of
motion which occur partly in the vegetable, partly in
the animal world, but which can scarcely be observed
without the aid of the microscope, as the efficient forces
in these cases are too slight to produce perceptible
movements of the larger parts of the mass.

3. Among these forms of motion we do not include
the so-called molecular, or Brownian movements, to
which the celebrated English botanist Brown first called

4 PHYSIOLOGY OF MUSCLES AM> NKRVES.

attention. If portions of vegetable or animal bodies
are observed under high magnifying powers, small
granules or similar bodies are seen to be engaged in a
peculiar tremulous motion. Whence does this arise?
That it is not a vital phenomenon is sufficiently shown
liy the fact thai perfectly inanimate bodies, for instance,
( lie carbon particles of finely rubbed Indian ink, exhibit
the same movement. The effect is, in fad. due merely
to currents in the fluid, by which the light particles
suspended in the fluid are carried away. Such current-;
are easily engendered in any fluid, sometimes in con-
sequence of uneven temperature, sometimes in conse-
quence of evaporation, sometimes, also, as the result of
the unavoidable shaking of the microscope. Weak as
these currents may be, the disturbance caused by them,
when seen under strong microscopic power, seems con-
siderable, and is often hardly distinguishable from those
movements which are caused by the vital act ivit ies of
the particles. Sometimes this molecular motion may
be detected within parts of living bodies; in which case
small granules swim about in a clear fluid within larger
or smaller cavities in these parts of living bodi

4. If a drop of pond water is placed under the
microscope, many living objects, some of which shoot
quickly about in all directions, are usually discernible
in the water. Side by side with these occur certain
oblong, or rod-shaped Indies. mo\ ing t ivmnlon.-ly about
with greater or le.-s rapidity. It is often hard to
distinguish whether the motion seen in these latter is
independent or molecular. It must lie observed whet her
of these bodies t \\ o contiguous indi\ iduals always pa —
along in the same direction, or whether their move-
ment- appear independent of each other. In the latter

SIMPLICITY OF THE LOWEST ORGANISMS. 5

case it is impossible to suppose that they are only hur-
ried along by currents, and it is safe to conclude that
even these simplest organisms are gifted with the
power of independent motion. Of the nature of this
power nothing is very certainly known. The organisms
of which we are speaking belong to the lowest rank of
the organic world. They are living beings, for they
move, they grow, and they multiply ; they can be
killed, for instance, by boiling water, and their inde-
pendent motion then ceases. This is nearly all that is
known of them. Next to them rank organisms which
are somewhat more complex in structure. They are
small lumps of semi-fluid, granular matter, which is
called protoplasm.1 This semi-fluid condition — inter-
mediate between a liquid and a solid state — is charac-
teristic of all organic matter. It is due to the absorp-
tion of water into the pores of a solid mass, which in
consequence swells and undergoes an intimate mixture
with the water, and in which the molecules can then
change their positions in the same way, though perhaps
not quite so easily, as otherwise is possible only in liquids.
A thin jelly-like clay would afford the best representa-
tion of this condition of aggregation of protoplasm.
A small lump of protoplasm of this sort may in itself
represent an independent living being, exhibiting vital
phenomena of such a kind that it is impossible to refuse
to call it an ' animal.' It moves by its own force, and,
as it would seem, voluntarily ; it imbibes matter for its
own nutrition from the surrounding liquid ; it grows, it
multiplies its kind, and it dies. The most evident mo-

1 Sometimes, but not always, in addition to these fine granules, a
larger, bladder-like body, called the kernel or nucleus, is seen within
the mass.

() PHYSIOLOGY OF MTSCI.KS AM> M.KVKS.

tion in this case occurs in two ways. Sometimes single
processes are seen to protrude from the whole mass;
thc-e processes gradually affect the whole granular
mass, so that the whole body is displaced, and a genuine
change of position happens to the animal ; or the pro-
cesses being again retracted, other similar processes are
protruded from another part of the body, in such a wav
that the direction of motion is changed ; in short, the
animal creeps about on the glass plate on which it is ob-
served by means of these proc<>-«--. .Meanwhile currents
of granules can be seen within the mass; closer obser-
vation, however, shows that the motion in this case is
only passive, and that it is the result of a continuous
wave like displacement of the protoplasm.

1

Fit;. I. AAKKII.K.

n. Anni-ti:i vi -rrnci'i-;!. /•. Anm-l a |«irnvta.

."). .Movements entirely similar to those in these
independent living animal>, called Aiunhn, occur in

PROTOPLASMIC AND AMCEBOID MOVEMENTS. 7

more highly organised beings, vegetable as well as ani-
mal. All living beings are fundamentally composed of
just such lumps of protoplasm as we see in the Amoeba?.
Most of these lumps of protoplasm have, however,
essentially changed their appearance, and, at the same
time, their qualities, so that it is only from the evolu-
tion of the parts that we know them to have originated
from such lumps. Moreover, even in developed organ-
isms separate parts always occur which are in all re-
spects similar to such lumps of protoplasm as the
Amoeba', and which move like the latter. It is a well-
known fact, that when a drop of blood is placed under

FIG. 2. WHITE BLOOD-CORPUSCLES FROM A GUINEA-PIG.

a, b, c. Various forms assumed by ouc and the same corpuscle.

the microscope, a very large number of small red bodies,
to which the red colour of the blood is due, are seen
within it. And scattered about among these red blood-
corpuscles are seen colourless or white blood-corpuscles,
round or jagged in form, and containing granular pro-
toplasm with a kernel or nucleus. If the blood has
been placed on a warmed glass, and if it is observed
at a temperature of from 35 to 40 degrees C., these
blood-corpuscles exhibit active movements entirely
similar to those of the Amoeba', and which have, there-
fore, been called Amoeboid movements. The corpuscles
send out processes and again retract them ; they creep
about on the glass ; and, in short, they behave exactly

8 PHYSIOLOGY OF MUSCLKS AND NERVES.

like Arna'bcc, and like the latter they even absorb mutter,
such as granules of any colouring substance which may
have been added, from the blood-fluid — they ear, that
is — and after a time they again reject this matter.
.Moreover, the other form of motion described above,
the protoplasmic movements or granule currents, mav
also be seen in parts of compound organisms. If the
tiny hairs of the stinging nettle are placed under the
microscope, it appears that each hair consists of a closrd
sac or pouch, over the inner surface of which protoplasm
is spread in a thin layer. Even this represents a much
moreadvanced modification of the protoplasmic mass, but
yet the protoplasm still retains its power of indepen-
dent motion. Wave-like movements are seen to pa-
over the mass of the protoplasm, and by this, just as in
the Amoeba, a current is apparently produced among
the granules. For a time the movement continues
in one direction ; then it suddenly ceases and begins
again in an opposite direction; sometimes one c-ir-
rent separates itself into two, others unite, mid so on.
If the protoplasm dies — and this may be artificial! v
caused by the application of heat — all motion ceases.
It is inseparably hound up with the vital powers of the
cells.

I!. The free protoplasmic mass, as seen in the
Amoeba, is one of the simplest of organic forms. Such
masses sometimes occur in groups, ^hich thus repre-
sent colonies of organisms, each of the components
of which, however, retains conipleje independence,
and i.- exactly like every ol her. Snnet inies, however,
modification takes place amount these; and \\heii
these modifications advance at an unequal rate in
the separate members of the colony, a composite or-

ELEMENTARY ORGANISMS ; DIFFERENTIATION OF TISSUES. I)

ganism with variously formed parts is the result. Each
part is originally a completely independent organism of
equal value with all the others, and each has, therefore,
been very aptly called an elementary organism. But
together with the modification in the form, a change
usually takes place in the qualities. Of the various
qualities possessed by the protoplasm in its original
form, some are lost, others are especially developed.
A colony of uniform elementary organisms may be
likened to a society in the lowest stage of civilisation,
in which each member still personally performs all the
tasks necessary to life 5 but a composite organism, with
variously developed and modified elementary organisms,
may be likened to a modern state of which the various
members perform very different tasks. The more highly
developed plants and animals are of this sort. They
originate from a number of elementary organisms — or
cells, as they are also called — originally uniform; but
these develop in very different ways— differentiate, as
is technically said, and then acquire very different ap-
pearance and purpose. In some the power of causing
motion, which is originally common to all protoplasm,
is especially developed ; others effect sensation, which
power was possibly or probably present even in the
simple protoplasm. These will be fully discussed in the
following chapters. But before doing this, a few words
must be said as to one form of these modified cells, in
which the power of generating motion is already de-
veloped in a very noticeable degree, and serves partly
for the independent movement of the cell-body, or of
the animal of which the cell is a part; partly, when
occurring in fixed bodies, to move foreign matter— that
is, for the drawing in of food.

10

OF MC.<CI.I:S AM> N

7. If ;i light powder — such. for in>t;iiifr. ;is finely
powdered charcoal is spread over the skin of the
palate of a living or a recently killed fn>g, the pn\\der
is seen to advance with some speed inwards the gullet.
Microscopic examination shows thai this >kin is studded
with a dense layer of cylindrical cells standing, palisade-
like. side liy side. The free surface of each of these
cells is studded with a large number <>{ delicate hairs

a

a. Ciliatnl roll>,

:ill(l. With

:iti:n-hi-i| In tliL- iin-iii

brane.

Fi... ::.

!»•- b. A

riliutc'l cell.
.I and
wlmt mop uii^liiiL-.l form.

or cilia1, which are in cnut iniial motion in a definite
direction in >nch a way that they propel all such liquid,
together with <he ]i:irt ides contained in this, as adheres
to (heir upper surface in that direction. This is called
ciliarv motion. It occurs very frequently in t lie animal
liody. e.<r. iii the windpipe and its branches where the
motion is upward, serving to propel the phlegm to the
lar\n\, from which it can be thrown out by coughing.

CILIARY MOVEMENT. 1 1

111 many fixed animals of low order a crown of cilise
encircles the mouth-opening, producing a current
which brings water, together with particles floating in
the latter, to the animal as food. Other aquatic ani-
mals have the whole or a part of their upper surface
studded with cilia?, by means of which they rotate in
the water. Finally, there are bodies which, instead of
the delicate ciliate hairs, possess only a larger and
stronger whip-like process by the sinuous motions of
which these animals move themselves about in the
water, as a boat may be moved by the quick motion of
the rudder, or as a water-newt propels itself by the
sinuous motion of its tail.

No'ne of these motions are, however, equal in force
and effectiveness to those which are produced by muscles,
In higher animals, muscles occur in two forms, — either
as smooth muscle-fibres, or as striated muscle-fibres. The
former are spindle-shaped cells which have grown out
in a longitudinal direction, and which have rod-shaped
kernels (nuclei") and pointed ends, sometimes twisted
like a corkscrew. The latter are produced by the coa-
lescence and amalgamation of several cells, the contents
of which have undergone an important change. These,
and the qualities of these, will be fully discussed in
the following chapters.

12 PHYSIOLOGY OF MUSCLKS AND .NKKY1.S.

CHAPTER II.

1. Muscles, their form and structure; 2. Minute structure of
striated muscle-fibres; 3. Connection of muscles and bones;
4. Bones and bone-sockets; 5. The law of elasticity; C. Elas-
ticity of the musclt-s.

1. Muscles are elastic structures capable of altering
their form — that is, of becoming shorter and thicker.
In the bodies of the more highly developed animals
they constitute those masses which are commonly called
flesh. The flesh, when carefully studied, is found to
consist of bundles of fibres, the ends of which are pr»-
duced into white cords, most of which are attached to
bones. When one of these muscles shortens, it exerts
a strain, by means of these white cords, on the bones ;
and these latter, being movable the one against the
other, are flms put in motion by the shortening of the
muscle. All muscles are not, however, arranged in this
way; some ring-shaped muscles form the walls of sacs
or pouches, and these, by contracting, decrease tin-
space within these cavities, so that the contents of tin-
latter are thus forced onward. In any case, muscles
always serve to produce movement — either of the limits
in opposition to each other, or of the whole animal, or
of the substances contained within the cavities.

AVe must first confine our attention to those muscles
which are attached to Imiies, and which are

FORM AND STRUCTURE OF MUSCLES.

13

called skeleton muscles. These muscles occur in various
forms. Sometimes they are flat, thin bands, and some-
times cylindrical cords, some of which are of considerable
length. Others again are thicker in the middle than at
the ends ; in these cases the middle is called the trunk,
the ends are spoken of as the head and tail, of the muscle.
Some muscles have two or more heads — that is, two or
more ends — springing from different points on the bone,

easseoooos

FlG. 4. SxitlATED Ml'SfLK-FIDRKS.

a. Two fibres cut through in the middle, and passing, on the left, into tendons, b. A
single muscle-fibre deprived of its discs, ami separating into fibrillse. c. Two
single fibrilla;. d. A muscle-fibre separating into its discs.

and uniting in a common trunk. But these muscles,
whatever their external shape, always consist of several
fibres, united into a bundle, and together forming the
muscle as a whole. One of these fibres, when isolated,
will be found to be very minute, and scarcely visible to
the naked eye ; when seen, enlarged from 250 to 300
times, under the microscope, it appears as a pouch,
consisting of a firm, solid wall, with certain contents ;
and this contained matter exhibits alternate lighter and

LJ

14 PHYSIOLOGY OF MUSCLES AND NERVES.

darker streaks, placed at right angles to the longitudinal
direction of the fibres. For this reason, these muscle-
fibres are called streaked or striated muscles, in order
to distinguish them from certain others of which we
shall presently learn. In order to obtain an approxi-
mate idea of the appearance of one of these fibres, we
may imagine it as a roll of coins, the separate pieces of
which are, however, transparent and alternately lighter
and darker. Some observers have indeed assumed that
a muscle-fibre really consists of discs of this sort, ranged
side by side. The fibres, when treated with certain
chemical re-agents, separate into these discs, and while
some of them yet remain attached to each other, the
fibre very closely resembles a roll of coins the pieces of
which are falling away from each other. But there are
other re-agents which split up the fibre in a longitudinal
direction, so that it separates into extremely delicate
smaller fibres or fibrilloK each of which still exhibits the
alternation of lighter and darker parts, which, in the
entire fibre, produce the transverse striation. More-
over it can be shown that a muscle-fibre when recently
taken from the living animal must, in reality, be of a
fluid, or, at least, of a semi-fluid nature. So that it is
impossible to affirm that either the discoid or the fibril-
It >id structure actually exist in the muscle-fibre itself;
it must ratln-r be assumed that both forms of structure
;nv really the result of the application of re-agents
which solidify the originally fluid mass and split it up
in a Longitudinal or transverse direction.

2. it is hard to say what the true character of the
fresh, or, as \\c may also call it, the living muscle-fibre
"really is. Jveceiit observations by means of very much
improved and very highly-magnifying microscopes, have

MINUTE STRUCTURE OF STRIATED MUSCLE-FIBRES. 15

brought to light other differences besides that of the
mere alternation of lighter and darker streaks. Of
the highest importance as explaining the structure of
muscle-fibres are the researches of E. von Briicke into
the phenomena exhibited by muscle-fibres in polarised
light. According to modern physical views, light de-
pends on the vibrations of ether, an impalpable matter
spread throughout the universe and present in all bo-
dies. These vibrations always proceed at right angles
to the direction in which motion is propagated. With-
in this imaginary plane at right angles to the ray of
light, an ether particle may vibrate in the most diverse
directions. Under certain circumstances, however, they
all vibrate in one and the same plane, in which case
the ray exhibits certain peculiarities, and is said to be
polarised.1 Certain crystals have the power of polaris-
ing such rays of light as pass through them. A few,
at the same time, separate each ray of light into two
rays which move separately from the original ray.
Such crystals are called double-refracting bodies. Ice-
land spar or, as it is also called, double spar, is the best-
known example of such a double-refracting body.
Briicke has shown that of the two substances which
form the alternate layers of striated muscle, the one
transmits light unchanged, the other is possessed of
double-refracting powers. But, as has already been
said, the contents of a living muscle-fibre must be re-
garded not as solid but rather as fluid, or at least as
semi-fluid; and observations made on living muscle-
fibres show that the streaks are not incapable of modi-
fication in their breadth and in their distance from

1 This circumstance is treated in more detail in Lommel's The
Nature of Light (International Scientific Series, Vol. XVIII.)

Hi PHYSIOLOGY OF MUSCLES AND NERVES,

cadi ••flier. Briicke, therefore, supposes that tin- muscle

substance i- in itself homogeneous or uniform, luil that
iu it a iv in-erted small particles \vliich are <>(' double-

refracting power. When these particles are massed in
lar^e numbers, and arc regularly arranged, they refract
the linT.t doubly, so that the whole of that particular
part seems to refract doubly, while the inieriuediate
parts, since they contain few or none of the particles
in question, continue i» refract simply. Tlie-e latter
parts, however, when seen under ordinary un polarised
light, so that it is impossible to judge of their powers
of double refraction, appear lighter, Avhile the former
appear darker ; and so toget her they cause the striated
appearance of the nuix-le.

3. In one of these muscle-fibres it is ne.v.-sary (,,
di-tiiiinil>h the contained matter and the containing
pouch. The latter is called the muscle-fibre pouch, or
MI fi;>ti ,,uiia. In it, especially after the addition of
aci-tic arid, \\hich causes the whole fibre to swell ;:nd
become more transparent, a number of longish pointed
kernels (nuclei) are seen, and similar kernels occur also
in parts within the muscle-fibre. To the ends of the
muscle-fibre, which are rounded and are very uniformly
enclosed by the pouch, which must therefore be re-
garded as a lon^r closed sac, the white cords mentioned
;;lio\e attach themselves, and these are completely
coalescent with the sarcolemma.

They consist of strong slender threads of the naf lire
of the so-called connective fi>Hie. As a considerable
number of muscle- fibres constitute the trunk of the

muscle, these threads also unite into cords which are

called the miix-le-teiidons. They are sometimes ,-hort .
sometime- loiiL,r, thicker or thinner according to the

CONNECTION OF MUSCLES AND BONES.

17

size of the muscle, and they serve to attach the muscles
firmly to the bones, to which, acting like ropes, they
transmit the tension of the muscles. One of the two
bones to which a muscle is attached is usually less
mobile than the other, so that
when the muscle shortens,
the latter is drawn down
against the former. In such
a case the point of attach-
ment of the muscle to the
less mobile bone is called its
origin, while the point to
which it is fixed on the more
mobile bone is called its at-
tachment (epiphysis). For
instance, there is a muscle
which, originating from the
shoulder-blade and collar-
bone, is attached to the
upper arm-bone ; when this
muscle is shortened, the arm
is raised from its perpen-
dicular pendant position in-
to a horizontal position. A
muscle is not always ex-
tended between two con-
tiguous bones. Occasionally
passing over one bone, it at-
taches itself to the next. This is the case with several
muscles which, originating from the pelvic bone, pass
across the upper thigh-bone, and attach themselves to
the lower thigh-bone. In such cases the muscle is
capable of two different movements : it can either

FIG. 5. THE i

CALF MUSCLE
minx), WITH
UONS.

(J/. gaslrocne-
ITS TWO TEN-

„, „. Tlie two liea-ls. c. The com-
mrnc^ment of the tendon which at
k is attached to the heel-bone.

18 PHYSIOLOGY OF MUSCLES AND NERVES.

stretch the ki , previously bent, so that the u]>]» i

and the lower thigh-hones an- in a >traidit line; or it
can rai-e ihc whole extended leg yet higher and brin^-
it nearer to the pelvis. J'nt the points of origin and
of attachment of muscles may exchange olh'ces. When
both legs stand firmly on the ground, the above-men-
tioned muscles are unable to raise the thigh ; instead,
on shortening, they draw down the pelvis, which now
presents the more mobile point, and thus bend forward
the whole upper part of the body. In order, therefore,
to understand the action of the skeleton, the separate
bones of the skeleton and their connection must first be
studied.

4. All bones are classified according as they are
flat, short, or long. Flat bones, as their name indicates,
are expanded chielly in two directions ; they form thin
plates. Short bones are expanded almost equally and
but slightly in all three directions. In long bon
finally, the expansion in the longitudinal direction con-
siderably exceeds that in the other two directions. The
extremities, the arms and legs, are chiefly formed of
these long bones. The arm, for instance, consists of
the long bone of the upper arm, to which are attached,
first, two other long bones (called the dhow bone and
the radius), which together form the lore-arm; and
secondly, by means of several shorter bones, which con-
stitute the \\rist. the hand itself; this latter consists of
the fi\e bones of the pa 1 m and the live fingers, of which

theiirsi has two, the others each have three di\ i-ions.

In all these bones, with the exception of (ho>e of the

wrist, a 1 >ng middle part, or shaft, \\ith two thickened
• •nds, are noticeable. A- this shaft is hollow, the-e
bones are also spoken of as cylindrical. The expanded

BONES AND THEIR SOCKETS.

19

ends are rounded and are provided with a smooth car-
tilaginous covering. The smooth ends of two contiguous
bones fit into each other, so that when the surfaces of
the two ends glide the one over the other, the two
bones are capable of motion
in opposite directions. The
point of attachment between
two bones is called the socket ;
and the surfaces of the two
ends of the bones where they
touch each other are called the
socket surfaces. The motion
which these bones have the
power of exercising in opposite
directions varies with the form
of these socket surfaces. When
the surface of the socket is of
semi-spherical form, the motion
is most free, and can be exert-
ed backward or forward in any
direction. The socket in this
case is called a ball- or nut-
socket. An example of this sort
may be seen at the upper end
of the bone of the upper arm, FIG. 6. THE BONES OF THE
where it ends in a ball-shaped

,, , . •, . v J (>• Bones of the upper-arm. A.

Surface Which IS applied tO a Elbowbone. B. Bfulius. by.

-.. i c The cormectkm of the bones at

corresponding socket surface in the socket of the eibow.
the shoulder blade. In other

cases motion can only take place in a definite direc-
tion, as, for instance, in the case of the socket con-
necting the upper and fore arms. These are called
hinge-sockets. They serve to increase or decrease the

20 I'HYsl.iUHiY (IF MUSCLES ANN NERVES.

angle lift \\een <]ic two parts. To Jin-lit i.iii all tli«'
various form- of BOcketfl and the movements which they
all..\\- \\ould lend us too far; it is sufficient to have

,-hoWU that the action of the lllliseles is affected by the
liones between wllicll they ai'e extended. Ill order, \\n\\-

ever, to examine the contractile power of muscles, the
latter maybe detached from the bones and examined
bv themselves.

•/

The muscles of warm-blooded animals are but ill-
adajited for this purpose ; fortunately, however, those of
cold-blooded animaU not only possess the same qualities,
but retain the power of contraction long after their re-
moval from tlie animal, a circumstance which renders
them \ery valuable for purposes of study. The frog is
most frequently used in such experiments, both on
account of it> common occurrence and of the power of
its mu-cles. If a frog is beheaded and an cut ire muscle
is cut from either its upper or lower thigh, one of the
tendons of this muscle may be fixed in a vice, and
its other tendon may be connected with a lever, re-
present ing- as it were the bone, by the motion of which
the contraction of the muscle may be studied.1 "Weights
may also be attached to this lever in such a way that
the burden which the muscle i- capable of lifting may

be Studied. It Will at ollce be •)! (Served that t he muscle

is extended when such weights are attached, and is
extruded more in proportion as the weight attached

is heavier. This n .-nit - from the elastic qualities of
muscle ; and before examining the contraction of muscles

it will be nece—arv carefully to study their ela>ti -ity.

1 In unlrr to fasten the nmsc'lr ni'.n- ,. it is irnirnilly

\\i-ll t» lt-;i\c :i -ln;ill piei-e ut' the l).ine ;it eillier eml ;il t;idie«l tn I

tendons, and \<-> last en the muscle by these.

LAW OF ELASTICITY. 21

5. Those bodies which alter their form under the
influence of external forces, and resume their original
form on the cessation of these external forces, are called
elastic. The greater these alterations are, the greater
is the elasticity of the body. The external force pro-
ducing the alterations may be either tension, extending / ;
the body in one particular direction ; or it may be pres-
sure, compressing the body into a smaller space ; or,
again, it may be tension combined with pressure, bend-
ing the body. We are only concerned with the force
of tension, which acting on the body in a longitudinal
direction extends it ; that is to say, we are about to
study the elasticity of muscle tension. Physicists
have experimented on elastic tension in bodies of the
most diverse kinds. But bodies of regular shape, rods
or threads, the length of which considerably exceeds
the thickness, are best adapted for such experiments.

On firmly fastening a body of this kind, for instance
a steel wire or a glass thread, to a beam in the ceiling,
and, after accurately measuring its length, attaching
weights to the lower end, it will be found that the ex-
tension caused by these weights is greater in the first
place in proportion as the weights causing the extension
are greater, and in the second place in proportion as the
body which is extended is longer. And, on the con-
trary, with any given weight and length, the extension
will be found to be less in proportion as the body is
thicker, or, in other words, the larger is its cross-section.
This latter circumstance may be easily understood by
assuming that the rod or thread consists 'of a number
of smaller rodlets or tiny threads which lie evenly side by
side. If, for instance, we select for this experiment a
steel rod, the cross-section of which measures exactly

22 PHYSIOLOGY <>F Mrsu. K- AND NF.KVES.

one square cent imet r<\ we may a — nine that this

ta of a Inimln-il n>dh 'ts of equal length, lying >ide by
si !<•. tin- Cross-Section of cadi of \\hich mea-mvs ex-
actly one square millimetre. On attaching a weight ,,f
one kilogramme ( = 1000 gr.) to this r<><l, each one of the
hunili-c;! thin r< •• ll« •( s would have to bear a weight of
but ten graiiiincs. ('tunj)aring with tin's the tension of
another steel rod of the same length, but of which the
cross-sect ion measures twice as much, we may assume
that this second rod is composed of two hundred minute
n>d let <, the cross-section of each of which niea.-uivs unc
millimetre. The weight being now distributed between
two hundred of these rodlcts, each has to support a
weight of onU live grammes. This explains why the
tension by the same \\eight is only half as great in a
rod of double thickness. That the extension is pro-
portionate to the length of the extended rod can be
explained in the following way. According to the \iews
of modern ph\>iei-ls every body consists of a number
of -mall molecules or ] (articles which are held at definite
distances from each other by attractive and repulsive
forces. On fastening a rod by its upper end and at-
taching a weight- to its lower end, the molecules are
bv these means slightly separated from each other.
The sum of all these small separations represents that
whole extension mea-nrable at the end. The longer
any given bodv is the greater is the number of these
small particles which occur in its whole length, and

con^eiplelltly tin- greater lllll-t itse\tellMoH be, pl'e-

vided all otlyr circumstance- are eijiial.

From the-e .ih-e|-\:ii ions may be deduced a la\\ fa
to ela-lic teii-i"ii, which is fnrt her continued by accurate
Sj and this law is that tin tension i* <lin'clh/

ELASTICITY OF MUSCLES. 23

proportionate to the length of the body extended, and
to the amount of the extending weights ; and that it
is also proportionate in inverse ratio to the diameter
of the extended body. This is called the law of elas-
ticity, of Hook and S'Grravesande. In order, however,
to find the tension of a particular body, another factor
connected with the nature of the body itself must be
known ; for, under otherwise equal conditions, the ten-
sion, for instance, of steel, as found by actual experiment,
differs from that of glass, and that of the latter from
that of lead, and so on. In order, therefore, to be able
to calculate the tension in the case of all bodies, the
tension, experimentally found, must be reduced to the
units of length and diameter of the weighted bodies,
and to units of the weight applied. This gives a figure
which expresses the tension of a body of a given nature
of one millimetre in length, and with a cross-section
measuring one square centimetre when supporting a
weight of one kilogramme. This result, which is con-
stant in the case of every substance, whether it be steel,
glass, or aught else, is the co-efficient of elasticity of
that substance.

6. Similar researches have been made in the case
of organic bodies also, such as caoutchouc, silk, muscle,
&c., and in so doing certain peculiarities have been
observed which are of course of great importance to us.
In the first place, all these bodies — which we may also
call soft, to distinguish them from those rigid bodies of
which, up to the present, we have been speaking — ex-
hibit a much greater extensibility. That is to say, soft,
organic bodies are capable of far greater extension than
are rigid, inorganic bodies of equal length and diameter,
and under the application of equal weight. But the

'J4 PHYSIOLOGY OF Ml SCLKS .\M> NKKVES.

former also exhibil another peculiarity. If a weight is

attached to a steel wire, or some other similar body,
the latter extends, and retains its new length so long
) as the weight acts upon it ; but as soon as tin- weight
' is removed tin- strrl resumes its original length. It i-
not so in the case of inorganic bodies. For instance,
if a weight is attached to a caoutchouc thread it will be
found that the latter is immediately extended to a
certain length; but if the weight is not removed, it
will be found that the caoutchouc thread extends yet
more, and the weight continues to sink, though, indeed,
but slowly, and, as time goes on, with ever decreasing
speed. But even at the end of twenty-four hours a
slight additional extension of the thread is observable.
If the weight is then removed, the thread immediately
becomes considerably shorter, but does not entirely re-
vert to its original length; it attains the latter very
gradually and in the course of many hours. This phe-
nomenon is known as the </i-<t<ln<i! <;ri<'ii*'n>n of organic
liin/ii'8. It takes place in very considerable degree in
muscle, and naturally increases the difficulty of deter-
mining the extensibility of muscles, in that the mea-
surements differ according to the moment at which they
are read. It is safest to take into consideration only
that extension which occurs instantaneously, without
regard to that which gradually follows.

Various apparatus have been produced for examina-
tion of ii.u-ciilar extension. The latter can be m»-{
aceiiratel\ read by means of the apparatu- invented by
dil Bois-Keyiiioud, represented in fig. 7. The muscle
is firmly fastened to ;i fixed bearer, it> upper tendon
being fixed in a \ ice. A small, finely graduated rod is
fa.-tencd to tin- louer tendon by means of a small hook.

ELASTICITY OF MUSCLES.

25

Below the graduations the rod branches into two
arms, which again re -unite at a lower point, and within
the space thus formed a scale-
plate is fixed for the reception
of the weights which it is de-
sired to apply. Finally the rod
ends in two vertical plates of
thin talc standing at right
angles to each other, and these
are immersed in a vessel filled
with oil, so that, while offering
no obstacle to the upward and
downward motion of the ap-
paratus, they prevent any lateral
movement. In order to deter-
mine the extension of the muscle,
the graduated rod attached to
it must be observed through a
lens, and it must be noted which
divisional line of the graduated
rod corresponds with a thread
stretched horizontally across the
lens ; weights must then be ap-
plied, and the increase in length,
which declares itself by an alter-
ation in the relative position
of the graduated rod and the
thread, must be observed. Of

course, in calculating the ex-

FIG. 7. Di; Boi£-R KYMOND'S

Al'PAKATrs Foil Till']

STUDY OF ELASTIC EX-
TENSIOX IN MUSCLE.

tensibility from the figures thus
obtained, the weight of the ap-
paratus attached to the muscle must be taken into
consideration.

• <>F Mr.-n.F.s .\M) M:I;\KS.

Kx peri men ts in muscular elasticity may also be made
with the apparat us briefly described above, by measuring
the e\ten-ion< of i he mii-de 1 ,y the variations of a lever
attach.'.! to it. The easiest way to do this is by t'a.-t.-n-
ing an indicating apparatus to the lever in such a way

lie. 8. M \iri.i MI IM.I: Aril.

that it tra :i - the movements of the lever on a plate of
smoked glass placed in front of it. This apparatus is
called a iiii/<>i/r<i/ili< or muscle-writer- Fig. S represents
it in the Simplified form adopted by I'lliiger. The body,
1 1n- elasticity of \\hich is to be examined, is 1 irmly fixed

ELASTICITY OF MUSCLES. 27

in the vice C, and is connected with the lever E E, the
point of which touches the plate of smoked glass. The
weight of the lever is held in equipoise by the balance
II. When weights are placed in the scale-pan at F, the
lever moves upward, and its point marks a straight line
which affords opportunity for measuring the amount of
the extension.

But in whatever way examined, muscle, in common
with all other soft bodies, exhibits another variation
from the bearing of rigid bodies. We have seen that
in steel or similar bodies the extension is exactly pro-
portionate to the weight applied ; that is to say, if a
given steel wire is extended one millimetre by one
kilogramme, then the amount of extension caused by
two kilogrammes is two millimetres, that by three kilo-
grammes is three millimetres, and so on. It is not so
in the case of muscle and other soft bodies. They are
comparatively more extensible by light than by heavy
bodies. For instance, if the extension of a muscle
when carrying ten grammes is five millimetres, when
carrying a weight of twenty grammes it is, not ten
millimetres, but perhaps only eight; when carrying
thirty grammes it is only ten millimetres, and so on.
The extension, therefore, becomes continually less as
the weight increases, and finally becomes unnoticeable
by the time that the point at which the muscle is torn
by the applied weights is reached. This behaviour is
of importance, because the conditions of elasticity play
an important part in muscular operations. The muscle
on contracting is capable of lifting aweigh.t. The same
weight, however, extends the muscle, and the co-opera-
tion of the two forces— the contractile tendency and
the elastic extension — produces, as we shall find, the
final operation on which labour depends.

28 PHYSIOLOGY OF MUSCLlv- AM" M-UVES.

CHAPTER III.

1. Jrrit.-il.ilil y of muscle; 2. Contraction and tetanus; ,'?.

of elevation and performance of \\nrk; -I. Internal work during
tetanus; 5. Generation of heat and muscle-tone ; (',. Altrratimi
in form d.uriny o ml faction.

1. If a muscle is cut from the body of a frog, and
i- fastened into the myograph just d< -scribed, it never
shortens spontaneously. If tin's docs seem to happen, it

may safely be assumed that some accidental and uu-
pereeived external cause lias influenced it. A muscle
may, however, always be induced to shorten by
pinching it with tweexcrs, by smearing it with strong
acid, or by bringing certain other external influences,
the nature of which vie shall presently learn, to bear
upon it. Muscle, therefore, never shortens sponta-
neously, hut it can always be induce;! to do so. This
quality of muscle enables us to produce the state
of contract i. .11 at pleasure, and to examine accurately
(lie nature and method of tin; condition, \\hi,-h give
ri-e to it and the phenomena by which it i> accom-
panied.

The myograph which, by means of the indicator
attached to it. marks the contraction of the muscle mi
the smoked glass plate, and at the. same time affords

opport unity for measuring the extenl of the contraction,

will presently prove of yet greater service. 1'ut for

29

i

w
M

a

P

O

a

CO

O

a

d

en

a

H

30 PHYSIOLOGY OF MI-< !.!> .\NI> NKIiYES.

our present purpose uhich is to discover whether or
not contraction take- place under certain circumstances
— it is hardly adapted. It may, therefore, be replaced
by another ajiparat us. arranged l,y du Bois-Reymond
espe, iall\ - 1', n- experiments during Lectures, and called by
him the muscle-telegraph. The muscle is fixed in a
vice; its other end is connected by a hook \vith a
thread running1 over a reel. The reel supports a long
indicating liand to which a coloured disc is attached.
The nuiM-le in shortening turns the wheel and lifts the
disc; and this is easily seen e\en from a considerable
distance. A second thread, slung over the reel, sup-
ports a brass vessel which may be filled with shot, so as
to apply any desired weight to the muscle.

The influences which car.se the contraction of the
muscle, such as pinching or smearing with acid, are
called irrifiinfx, and the muscle is said to be irritable,
because cont raei j, >n can he induced in it by these means.
The irritants already spoken of are mechanical and
chemical ; they labour under a disadvantage in that the
muscle, at least at the point touched, is destroyed, or
at least is so changed that it is no longer irritable.
There is, however, another form of irritant which is
free from this disadvantage. If the vice which holds
the upper end of the nmsele and the hook to which tin-
lower end is attached are fastened to the two coatii,
of a charged Kleistian or Leydeii jar, the charge acts at
the moment at \\hich the Connection is formed, and
an electric shot k traverses the muscle. At the same
instant the muscle is seen to contract . and the disc
passes abruptly upward. In order to repeat the experi-
ment it would be necessary to re-charge the Klei-tian
jar. But similar electric shocks may be more con-

IRRITABILITY OF MUSCLES 31

Yoniently produced by means of so-called induction.
Let us take two coils of silk-covered copper wire and
attach the two ends of one of these to a muscle. An
electric current from a battery must now be passed
through the other coil A. The two coils being com-
pletely isolated from each other, the current passing
through A can in no way enter into B or into the muscle
attached to B. If, however, the electric current in A is
suddenly interrupted, an electric shock immediately
arises in 5, a so-called inductive shock ; and this passes
through and irritates the muscle ; that is to say, a

FIG. 10. INDUCTION COIL.

The coil A is connected with the battery by means of the wires x and y ; the other
coil, B, is connected with the muscle by means of wires fixed at q and p.

sudden contraction of the muscle is observable at the
instant of the opening of the current in coil A ; and
this suddenly lifts the disc attached to the muscle.
The same thins: occurs when the current in the coil A

O

is again closed ; so that this electric irritant affords an

O 7

easy and simple means of causing this sudden con-
traction of the muscle at pleasure. This contraction
may be called a pulsation; and it will be perceived
from the description of the above experiments that a
^simple electric shock, such as is afforded by the dis-
charge of a Kleistian jar, or any similar inductive
shock, is the most convenient means of producing such
a pulsation as often as it is required.

:V_> rilY.-InI.o.,Y <>F MTSCLES ANI> NKKVi

All el.-ctric em-rent from the hat t ery it self is also
capable of acting as an irritanl «'n muscle. lfthepoi,->

of tin- 1 lattery are c< >nnected with the muscle, a con-taut
current pa.-.-es through it. If OIK- of the connecting
\\ires consists of t\vo parts, a capsule filled with quick-
silver may l>e inserted between the cut ends. One end
of the wire must be allowed to remain immersed in the
quicksilver ; the other end must be bent into the form
•A a hunk st.) as to allow it to be easily immersed in, ;md
again withdrawn from, the quicksiher. This make-,
it easy to close the current \\ithin the mu-cle, and
to interrupt it again at pleasure. At the moment
at which the current is dosed, a pulsation is observed
entirely similar to that which would be produced hy
an electric shock. The mii-cle contracts, and the disc
is jerked upward and then falls a-ain. But it does
not return quite to its original portion; it remains
somewhat raised, thus showing that the muscle is now
continuously contracted; and this contraction lasts a-
long as the current passes uninterruptedly through the
muscle.

If the current is interrupted, a pulsation which
jerks the lever up\\;.rd i- sometimes but not always
oh.-ervablc ; the muscle then, however, resumes its
original length, which it retains until it is irritated

->
anew.

2. The.-e experiments show that muscle exhihits
two forms of contract ion : the one, which we ealh d pul-
sat ion, is of short durat ion ; the other, \\hicli is produced
by a con-taut electric current, endures longer. Tin's
more enduring form of con! ract i..n may, moreover, he
yet more conveniently produeed hy allou ing an irritant
as in itself would only prodiiee a single pukiti.ui

PULSATION AND TETANUS. 33

to operate repeatedly in quick succession. An inductive
current is most suitable for this purpose, for it can
be produced at will by the closing and opening of an-
other current. Once more turning to the coils A and
B (fig. 10, p. 31), let A be connected with a chain,
B with the muscle. Within the circuit of the chain
which includes A, we can insert an apparatus capable
of repeatedly and rapidly shutting or opening the
current. For this purpose a so-called electric wheel
is used. The wheel Z is made of some conducting
substance, such as copper,
and its circumference is cut
into teeth like that of the
ratchet-wheel of a watch.
The copper wire rests on
this circumference. The
axis of the wheel and the

7 T .,-, IMG. 11. ELECTRIC WHKEK.

wire o are connected with

the conducting wires by means of the screws d and/.
When the click rests on one tooth of the circumference
of the wheel, the current is enabled to pass through
the wheel, and thus also through coil A ; it is, how-
ever, interrupted during the interval which intervenes
while the click springs from one tooth to the other.
Therefore, by turning the wheel on its axis the current
in coil A is alternately closed and opened. Conse-
quently, inductive currents constantly occur in the
adjacent coil B, and these pass in rapid succession
through the muscle. Each of these currents irritates
the muscle ; and since they occur in such quick suc-
cession, the muscle has no time to relax in the intervals,
but continues permanently contracted. Enduring con-
3

PHYSIOLOGY OF MCSCI.KS ANU NERVES.

traction nf tliis sort i< called (,f<ntnx of the muscle to
distimnii-h it from ;i serie- of di-t iu.-t pul-at ion-.

Another method of frequently and n-peatedlv do-
sing and opening the current is by means of a self-
acting apparatus which is put in motion by the current
itself. This, \\hich is called Warner's hanuner, is re-
presented in ti^-. 1^. The current of the chain i- con-
ducted through the column
represented on the ri^ht to
the ( ierman silver spring <;.
A small platinum plate c is
soldered on to the latter, and
is pressed against the point
above it by the elastic force
of the spring. The cun'ent
passes from this to the coil-;
of a small electro-magnet,
and, after pas-in^ through
this, back to the chain

through the clamp connected with it on I he left. An
armature of soft iron, /,, fastened on to the <prin^
O o, i- >u-pended over the poles of the electro-magnet.
This iron beiu^ at t ract ed by the electro-magnet, the
>mall plate <• is forced away from the point and the cur-
rent i< thus interrupted. In so doin^. h:>\\e\er, the
electro-magnel parts with its magnetism, and conse-
quently relinquishes it- hold upon the armature; the
plate is thus a«rain prosed by the action ,,f the
sj)riiiL( against the point. The current being thus again
c!o>ed, the electro-magnet reco\crs its force, a ^a i ii at-
tract- the armat lire, and a^ain interrupts the current ;
and these processes are e.intinued as I 'in^ as the chain
remain-- inserted between tin- column on the rififhi and

FIG. 12. WAGSKK'S HAM.MKU.

PULSATION AND TETANUS.

35

the clamp on the left. In order to use this hammer for
the production of inductive currents, the one coil, A, of
the apparatus (shown in fig. 10, p. 31), must be inserted
between the two clamps shown on the right.1

Wagner's hammer in a more simple form may be
permanently connected with coil A. In this case it is
best to place the second coil B on a sliding-piece which
is so arranged that it can be moved along a groove to a

FlG. 13. THE SLIDING INDUCTIVE AITAli-ATCS.

(As used by du Bois-Reymond.)

greater or less distance from coil A. This enables the
operator to regulate the strength of the inductive current
generated in it. Fig. 13 represents an apparatus of this
sort. The secondary coil, in which the inductive currents
originate, is in this case indicated by i ; the primary coil,
through which the constant currents pass, by c ; b is the
electro-magnet ; h the armature of the hammer ; / is
a small screw, at the point of contact of which with the

1 In order to set Wagner's hammer itself in motion, these damps
must be connected by a wire through which alone the connection
from the point to the coils of the electro-magnet is made.

36

PHYSIOLOGY OK MIS( l.KS AND NT.UYFS.

small plate soldered mi 1.) the surface of thederman
silver spring the currenl i> closed :nnl interrupted. A"n
;i|)]):ir;itus of lliis kind is called a sliding inductorium.
It is only neees-ary to attach the ends of tin- mil / to

the muscle, and to insert the chain between the columns
(/ ;ind //. The action of the hammer then at once

commences; the inductive cur-

rents n'eni -rat cd in <• pass t hnm^h
the muscle, \vhich contracts te-

tanically.

Instead of connect \\\<^ coil c
immediately with the muscle-, it
is better to carry the wires from
the coil to the two clamps // and
c in the apparatus shown in tiij.
14, which is call, d a l< t<t H'IX'I n<i
/•«•//. Two other wires pass from
t hese same clamj)s !> and r to the
muscle. Wlienthe induct i\'e ;i]>-
]>arat us is in action the muscle is
put intoa tetanic condition. 1'ut
as soon as the lever </ is jiressed
down, so as to connect l> and c
together, the current of coil / is

KM;. 11. TETASISINO KBY OF cnaliled to pass through this le-

Di- i:<ns Ki vM(.\i.. ,.,, , , , - ~

ver. 1 he lever </ being made of

a short and thick pice.- ,.(' l>ra<s, \\hich otVers hanllv anv
resistance to the current, while the nui-cle on the con-
trary of t'ers L,nvat re-i-taiice, \-ery little of the current
passes through the mu>ele, luit nearly all throiiu-h the
lever </. The muscle, therefore, remains at rest. As
soon, however, as the lever </ is a^ain raised, the in-

duct i\ e current s must a^ain

throuh the mu>cle.

ACCOMPLISHMENT OF LABOUR. 37

A slight pressure on the handle of the lever d is, there-
*fore, sufficient to produce or to put an end to the te-
tanic condition at the will of the operator, thus allowing
more accurate study of the muscle processes.

We have now noticed muscle in two conditions : in
the ordinary condition in which it usually occurs either
within the body or when taken from the body, and in
the contracted condition which results from the appli-
cation of certain irritants. The former condition may
be spoken of as the rest of the muscle, the latter as the
action of the muscle. Muscular action occurs in two
forms, one of which is a sudden temporary shortening
or pulsation, while the other is an enduring contraction
or tetanus. The latter, on account of its longer dura-
tion, is more easily studied. In many cases it is a
matter of indifference whether pulsating or tetanised
muscle is examined. In the following investigations
we shall therefore employ sometimes one, sometimes
the other, method of irritation.

3. On attaching weights to a muscle, the latter is
capable of raising these weights so soon as it is set in
motion. It raises the weight to a certain height, and
thus accomplishes labour which, in accordance with
mechanical principles, can be expressed in figures by
multiplying together the weight raised and the height
to which it is raised. This height to which the weight
can be raised, which may be called the height of ele-
vation of the muscle, can be measured by means of the
myograph already described. On attaching a weight
to the lever of the myograph, the muscle is imme-
diately extended. The pencil must now be brought in
contact with the glass plate of the myograph, and
the muscle must be made to contract by opening the

ov Misi u:> AND M:I;\I:S.

key so as to allow the induct ive currents to have access
to the muscle. The latter at once shortens, and its
height of elevation is indicated by a vertical stroke on
the smoked glass plate. On instituting a series of
experiments with the same muscle but with various
weights, it will be found that the muscle is not able
to raise all weights to the same height. When the
\\ e>ht is small the height to which it is raised is gnat .
As a rule, as tin- weight increases, the height to which
it is raised becomes less, and finally, when a certain
weight is reached, it ben unes unuoticeablc. Fig. 15

0

50

100

150

200

250

FlG. 15. IIl-llClIT OF KI.F.VATION C< iNSK.QU KNT ON Till-: ATPI ICATIoN OP

YAKY1NU WEIGHTS.

slmws the result of a series of experiments of this sort.
The figures under each of the vertical strokes represent
in grammes the anmunt of the weight raised ; the height
of the strokes is double the real height of elevat inn,
t In- ajijiarat us employed in t he experiment representing
them twice their natural si/.e. Jlet \\eeii each two of

the experiments th" ^lass plate was pushed on a little

further in order that the separate experiments might
be indieated side by side. Jn tinding the first of
t hese height - of el e\ a t i-ni, under which stands an 0, no
weight. A\as applied, and e\en the \\eight of the indi-
caling le\er \\as neiit ralised l>y an cimix'aleiit weight.
It appear-, therefore, that the height ,,f elevation is

INTERNAL WORK DURING TETANUS. 39

greatest in this case. Each of the succeeding heights
begins from a somewhat lower point in consequence of
the extension of the muscle by the applied weights.
But each also rises to a less height than that which
preceded it ; and, finally, a weight of 250 grammes
being applied, the height of elevation is naught.

From this series of experiments it is evident that,
as the weight increases, the height to which it is raised
continually decreases. The following conclusion must,
therefore, be drawn as to the work accomplished by the
muscle. When no weight is applied, the height of
elevation is great ; but as no weight is raised in this
casej the amount of work accomplished, therefore, also
equals 0. When 250 grammes, the greatest weight, is
applied, the height of elevation equals 0, so that in
this case also no work is accomplished. It was only on
the application of the intermediate weights that the
muscle accomplished work ; and this, moreover, at first
increased until a weight of 150 grammes was reached,
and then gradually decreased. On calculating the
amount of work accomplished during each of the pul-
sations in question, the following results are found : —

Weight applied. . 0 50 100 150 200 250 gr.
Height of elevation .14 9 7 5 2 0 mm.

Work accomplished . 0 450 700 750 400 0 mm.

The same results may be obtained with any other
muscle. So that it may be stated as a very general
proposition, that for each muscle there is a definite
weight, on the application of which the greatest amount
of work is accomplished by that muscle ; when greater
or less weight is applied, the amount of work accom-
plished is less. But the height of elevation correspond-
ing with the application of one and the same weight is

•K) rilY.-KM.txiY OF MUSCLES AND M'KYKS.

IP it al way- 1 lie .-ill i ic ill the ruse i >f different muscles. Ou

comparing thick with thin muscles, il appears, in the first

J)l: ice. thill (he extension in the case of thick muscles he-
ciii ncs less in |)ni]nirt Ion as the Weighl :i]i|»lic(l increases ;
;ind that tlie decrease in the height of elevation corre-
-pondingto the iiicrea-e in the weight applied proceeds
less rapidly ; so t hat much greater weights can be raised
by thick than hy thin muscles. On the other hand, it
appears that in the case of muscles of eipial thickness
the height of elevation is greater in proportion as
the muscle-fibres are longer. I'nder an equal weight
the height of elexation increase's proportionately with
the length of the in iisde-fil ires. They decrease with
increased weight; and they do this more rapidly in the
case of thin than of thick muscles.

4. In calculating the amount of work accomplished
liy a mii-cle, only the raising of the weight is taken into
consideration. When, however, the ordinary method
of irritating the muscle is applied, the weight which
is raised sinks hack after each pulsation to its former
height. The muscular work accomplished at each pul-
sation is, therefore, cancelled. It [s probably converted
into warmth. It is, however, possible, to retain the
\\eii_dit at the height to which il was raised by t he muscle.
A. Kick accomplished this very ingeniously liy can-ing
t he muscle to act on a light Lever, which moves a wheel

each time it rises, but leases the same wh-el undis-
turbed when it again .-inks. A thread, on which the
\\eight han^.-, p iver the axis of the wheel. The

etlect of t his arrangement is that the muscle at each
pulsation turns the \\hed slightly, and lhu> slowly
rai-es the \\ejnht. If the muscle is made to pulsate
frequently, the weighi is rai-ed somewhat higher each

GENERATION OF WARMTH. 41

time, and the final result is the sum of the work
accomplished by the separate pulsations. Fick calls
this apparatus a labour-accumulator (Arbeitsammler).
It represents the method by which the whole work of
all muscular efforts is summarised. When labourers
lift a weight by means of a winch or windlass, a cog-
wheel and drag-hook is applied to the axis in such
a way that the wheel is free to revolve in one direc-
tion but not in the other. This gives cumulative
effect to the separate muscular efforts which raise the
weight ; and the labourer is even able to make longer
or shorter pauses without the result of the work already
accomplished being cancelled by the falling back of the
weight.

In tetanus the case is not the same as in separate
pulsations. In the former the muscle at first accom-
plishes work by raising the weight, and then prevents
it from falling by its own exertion. In addition to
the height of elevation, it is, therefore, possible to
distinguish also the carried height, that is to say, the
height at which the weight is permanently supported.
In doing this the muscle does not really accomplish
any work in the mechanical sense ; for work consists
only in the raising of weight. In lifting a stone to the
height of the table I accomplish definite work ; the
stone being placed on the table presses by its own
weight on the latter ; but the table though it prevents
the stone from falling, cannot be said in so doing to ac-
complish work. So it is in the case of muscle. On raising
a weight by means of the muscles of my arm to the
height of my shoulder, and then holding out my arm
horizontally, the muscles of the arm prevent the weight
from falling ; they act just as the table, and, therefore,

4U niY.-aoLoiiY or MUSCLES AND M.UYKS.

they accomplish no work in a mechanical sense. Yet
everyone- kno\\> the difficulty of holding a weight long
in this position; the sense of weariness which verv
soon make.- itself frit, shows that work in ;i phvsiologjeal
smse is really done. The kind of work thus accom-
plished may be spoken of as the i nh-nml work of the
iiiii>ele, as distinguished from the external work accom-
plished in the raising of weights.

5. We must now inquire on what the labour accom-
plished by the muscle as a whole depends. We are
justified in assuming that here also, as in other cases,
the work done does not originate in itself, but comes
into existence in consequence of the exercise of some
force. On examining a muscle during its active con-
dition, we find that chemical processes occur within it
which, though the details are not indeed fully known,
must, since they are connected with the production
of warmth and the evolution of carbonic acid, depend
on the oxidation of a portion of the muscle-substance.
Thus, the muscle art > like a steam-engine, in which work
is accomplished in the same way by the evolution of
warmth and the production of carbonic acid. So far all
is clear; a portion of the substances of which the
muscle is composed is oxidised during its artive state,
and the energy released by this chemical process is
(lie source of the work accomplished by the muscle.
The production of warmth in a muscle can be shown
even during a single pupation; but, this production
of \\armth is far more noticeable during tetanu- :
and as warmth is but another form of motion, we jnav
infer from this that the \\lmle force resulting from

the rheiuieal proccs- i - r, ,\\ \ rH ( •( 1 into warmth during

letanu-; while during the raiding of a weight at tin;

THE MUSCLE-NOTE. 43

commencement of the tetanic condition, or during each
distinct pulsation, a portion of this force occurs in the
form of mechanical work.

There is yet another fact which shows that internal
motion must proceed within the muscle when con-
tracted in tetanus, notwithstanding the quiescent con-
dition in which externally it apparently is. A muscle
when in this condition produces a sound or note. On
placing an ear-trumpet on any muscle, for instance, on
that of the upper arm, and then causing the muscle to
contract, a deep buzzing noise is audible. This may
also be loudly and distinctly heard on stopping the
outer ear-passages with waxen plugs, and then contract-
ing the muscles of the face ; or by inserting the Little
ringer firmly in the outer ear-passage and then contract-
ing the muscles of the arm. In the latter case the
bones of the arm conduct the muscle-note to the ear.
This muscular note clearly shows that vibrations must
occur within the muscle, however apparently unchanged
the form of the latter may be. We found that teta-
nus thus apparently constant is induced by distinct
irritants applied in quick succession. Helmholtz has
shown that each of these irritations really corresponds
with a vibration ; for, if the number of the distinct
irritations is altered, the muscle-note is also changed,
the height of the muscle-note always corresponding
exactly with the number of irritants applied. Though,
therefore, no alteration in form can be perceived in the
tetanised muscle, this can only be due to the fact that
movements which occur among the particles within the
muscle effect the note, though the external form re-
mains unchanged. A somewhat similar phenomenon
is observable in rods when caused to vibrate longitu-

11 I'lIVSIoLtMiV OF MIX'l.KS AND M.KVES.

dinally ; for these al>o nnit a sound although n<> change
of form is externally percept ilile.

This raises a qiie-tion as to how many of these irri-
tations are really requisite in order t<> bring a muscle
into ;in enduring condition of contraction. By means of
Warner's hammer (fig. 12), just described, or by means
of an electric wheel (fig. 11), the number of the irrita-
tions may be regulated. It will be found that from 16 to
indistinct irritations in each second are quite sufficient to
• •aii>e a constant emit raction of t he muscle. In a living
body also, where the muscles are voluntarily contracted,
the i -olid it ion of tetanus appears to be produced by the

same number of irritations. It has been found that the

height <if the muscle-note heard during voluntary eon-
tract ion of the muscles is about equal to c1 or r/1, which
ivpre-.'iit- from :>2 to 3f> vihrat ions in the second. Hut
llelmholtx was able to show, with great probability.
that this is not the t rue niimln r of mnscle-\ ibrat ions,
but that the vibrations \\ithin the muscle are really
only half as many. As, however, notes of this pitch
are indistinguishable to our ears, we hear the next
higher tone instead, which represents twice the num-
ber of \ ibrat ions.1

(i. As yet we have noticed only the shortening of
mii-cles. This alone determines 1 he amount of labour
accomplished, which consists in raising weights. But
on looking at a contracted muscle, it is evident that
it ha- beiome, not only <hort<T. but thicker. This

1 Aci- Tiling t'> l'n-\rr, .-MIIII- ni' apable of distinguishing

• >f :is m:mv ;i< lit'irm tu t \vnit y-li vi- \ il.r:il ions per s.'CMUil ;
,-iinl. ;icc«iriliiiLr In llic s:uiic .-nil Imrit v, tin1 iiiii-,rlr-inil<> M.IIIH|S very

ihiit I'l-i'ilui'i'il l-y lYinii «-i.Lrlitii'-ii I" t\\i-nly vil«r;il inns
second, \'. ry \\>-l\ \\ith (!•<• \.i-\\>ni' Helmholtz

ALTERATION IN FORM DURING CONTRACTION. 45

raises the question whether the muscle in contracting
has undergone no change in the amount of space oc-
cupied by it, or if its mass has become more dense.
It is not easy to determine this accurately, for the
alteration in the volume of the muscle can only be
very slight. Experiments which have been made by
P. Erman, E. Weber, and others, agree in showing
that a very slight diminution in the muscle does cer-
tainly take place.

Kemembering, however, that muscle consists of a
moist substance, and that about three-fourths of its
whole weight is water, even this slight decrease in
volume must be the result of very considerable pressure
—for fluids are extremely difficult of compression— un-
less possibly a portion of the water is expressed through
the pores of the sarcolemma pouch.

More important than this structural change of the
whole. muscle is the change of form which each separate
muscle-fibre undergoes. This may be observed under
the microscope in thin and flat muscles, when it will
be found that each muscle-fibre also becomes both
shorter and thicker. On placing a muscle on a glass
plate under the microscope, in order to observe this,
the muscle, when the irritant ceases to act, is seen to
remain apparently in its shortened form. But the
separate muscle-fibres resume their former length as
soon as the irritant ceases, and they therefore lie in a
zigzag position until they are straightened by some /-
external force. I merely mention this here, because .
the phenomenon is of historic interest. Prevost and '
Dumas, who were the first to examine this condition, -
believed that the contraction of the whole muscle was
due to this zigzag bending of the muscle-fibres. With

•Ki P1IYS1OLOGY OF MUSCLES AM> NERVES,

the inruiiijilrtr apparatus which iln-y \\nv then a

alilr f.i cninmand, thry Wriv un;il>l«- t" induce an m-
(luriii!^ irritaliuii «•!' the iiiusclr ; and th«-y, llicnTorr,
confused tlir state of ivlaxatkm with that of contrac-
tion.

CHAPTER IV.

1. Alteration in elasticity during contraction ; 2. Duration of con-
traction ; the myograph ; 3. Determination of electric time ;
4. Application of this to muscular pulsation ; 5. Burden and
overburden— muscular force ; 6. Determination of muscular
force in man ; 7. Alteration in muscular force during contrac-
tion.

1 . We now approach one of the most remarkable of
the facts connected with the general physiology of the
muscles : this is the alteration in the elasticity of a
muscle during its contraction. Even E. Weber, who
first penetrated deeply in his researches into the sub-
ject of muscular contraction, showed that muscle is
further extended by the same weight when it is in a
state of activity than when it is quiescent. This is the
more striking because the muscle becomes shorter and
thicker during its activity, so that it should conse-
quently be less extended ; for, as we found, the exten-
sion by a definite weight is greater in proportion as the
body extended is longer, and is less in proportion as the
body extended is thicker. If, therefore, an active muscle
is further extended than one that is inactive by the same
weight, this can only be due to a change in its elasti-
city. It is hard to say how this occurs. The pheno-
mena of contraction may, however, be explained by
saying that muscle has two natural forms : one proper

is

I'lIYSItii.ouv OF MOSCLES AM> NERVES.

to it, \vlicii it, is in a quiescent state ; flic other, \\hen
it is active. When a quiescenl mu-de i- brought int.:
an active condition liy irritation, it assumes a form
which is no longer natural to it, it strives to attain the
latter, and shortens until it readies it- new form, which
i- then natural to it. It' the muscle is extended liy a
weight, and is then irritated, it immediately contracts;
but only to that length which represents the exten-
sion by the attached weight, proper to its ne\v form.
Let us imagine that A //, in ti<j. 16, is the length of

It "' I! //

I-'K,. Id. A i .1 1.1: A n.iN IN 1. 1.. \snci rv I

- JC

y

cnsTKAci I«,N.

the muscle when ijiiiescent and unburdened, and that
A I i- the length of the mn-de when active and un-
burdened. Then the inn-de. if it is irritated while
unweighted, will shorten to the extenl represented bv
J />' -- A 1> -.-. l> II; /> I! is. therefore, the height ,,f
e|e\ati«ui of the unweighted muscle. If a weight // is
attached to the nni-de, the latter in its inactive condi-
tion will lie extended to a certain degree (//'</'); so
that its length will now be J /,'-}- /,",/'= J ' /,". On
being now irritated, it contracts and assumes a length

ALTERATION IN FORM DURING CONTRACTION. 49

which must equal A B + c b' = A' b', in which A b is
the natural length of the active muscle when un-
weighted, and c b' is the extension which the active
muscle undergoes on the application of the same weight
p. A' B' — A'b'=b' B' is, therefore, the height of
e^ vat ion of the muscle when the weight p is applied.
Now, our former experiments have shown that the
height of elevation decreases as the weight increases.
The height of elevation b B, when the weight applied
= o, is, therefore, greater than the height of elevation
b' B', with the weight p. It therefore follows that the
extension c b' must be greater than the extension d' B' ;
or, in other words, the same weight, p, extends the
^muscle more when the latter is active than when it
is quiescent. Calculating on this principle the curves
of the extension of the active, as well as of the in-
active, muscle, for the first we find the curve b b' y ;
for the second the curve B B' x ; and these two con-
tinue gradually to approach each other, until they at
last cut each other at the point Biv. This point £iv,
which corresponds with the weight p, shows that when
this weight is applied, the length of the active and
the inactive muscles is equal. If, therefore, when the
weight p is applied, the muscle is irritated, the height
of elevation is nothing. The muscle is incapable of
raising this weight, a fact which we have already noticed
in previous experiments.1

Yet another point of great interest is observable in
studying this alteration in the elasticity. When a cer-
tain weight, />;, is applied, the extension of the active
muscle = c' b" : that is, the active muscle, when this
weight is applied, assumes exactly the length proper to
1 See Notes and Additions, No. I.

50 PHYSIOLOGY OF MUSCLES AND NERVES.

tin- quiescent muscle when unweighted. If an experi-
ment i> successfully arranged so that an inactive muscle

is not exlende.l by the Weight /,' by i';i-t eiiing t lie lat ter
t«i tlie mu-c]e, but ininie(li;ite]y supporting it, so that
it does not extend (lie muscle — and if the muscle is
then irritated, it is evident that the muscle is incapable
• •I' raising this weight from its support. Uy finding the
weight which is exactly sufficient i<> effect tliis, it is
evident that we shall find an expression for the magni-
tude of the energy with which the muscle strives to
pass from its natural into a contracted cnndilion. This
energy is called the force of the muscle. A method of
accurately determining this will presently lie explained.

2. As far as it is possible to examine the matter,
the condition of muscles during their distinct pulsations
is exactly as in tetanus. All that has been said of the
height of elevation, and of the accomplishment of la-
bour dependent on this, and of the alteration in the
elasticity, is as true of distinct pulsations as of the
tetanic condition. J'ut it is \.T\ hard to observe the
alteration in form during the very short time \\hieh is
occupied by one of these pulsat ions. Means of drawing
very accurate conclusions even on this point have, how-
ever, been found, especially since Helmholtz turned his
attent ion to the matter, in 1S,~>2.

Various methods are employed in experimental re-
search to measure very short period- of i imr accurately,
and to st i idy processes which occur even within tin-
shortest periods. ]S"ot only has the speed of the cannon-
ball during the various periods of its passage from the
mouth of the cannon to its arrival at its destination
been measured, but this has ;dso been done in (he, case
of the \e( shorter time occupied by the explosion of

DURATION OF PULSATION. 51

gunpowder. The duration of the electric spark alone
yet remains unmeasured. This may, therefore, be re-
garded as really instantaneous, or at least as occupying
a time shorter than any measurable period. Some
observers have estimated its duration as less than
__j__ of a second.

The most serviceable means of measuring very
short periods is by causing the process to be measured
to register itself on a rapidly moved surface, or by
using an electric current the action of which depends
on a magnet as regards its duration. Each of these
methods has been applied to muscle.

Supposing a smooth surface, such as a glass plate,
-moved with great rapidity in its own plane, then a
pointed wire turned at right angles to the plate will
mark a straight line on the latter. If the plate has
been smoked this line will be visible. Supposing the
wire is attached to an instrument vibrating, like a
tuning fork, upward and downward, then the line
drawn by the pencil when the plate is moved will be
not straight but waved. As the number of the vibra-
tions may be told from the note which the vibrating
instrument emits, it is known that the distance be-
tween each two waves of the waved line obtained
represents a certain period of time. Assuming that the
instrument makes 250 vibrations in each second, it
is evident that the plate must have moved the dis-
tance between each two waves in -^-^ of a second.
Now, if it is possible to cause a muscle-pulsation to
register itself on the same plate, then from the distance
of the separate parts of the line thus registered, when
compared with the waves drawn by the vibrating
instrument, the duration of time may be accurately

-s .\M> M-:K\I>.

determined.
this

The myograph «>f Helmholtz (li-jicmls on
< )rii,mi;dly it cnusistrd ..f ;i ylas.- i-ylin-

J-'it;. 17. Mvi>i:T:.\rir «T IT i I..MIIOLTZ.

.ii'r natiii'iil .-i.'c'.i

diT \\liicli rntntcd r.-ijiidly «>ii ils u\\n ;i\is. Tin- ;i]ij):i-

rat us lias, lm\\e\cr, since undergone m&ny alterations.

THE MYOGRAPH. 53

Fig. 17 represents it in the form given to it by du Bois-
Reymond. The clockwork enclosed in the case c sets
the cylinder A in rotation. A heavy disc B is fastened
on to the axis of the cylinder, on the lower surface of
which are certain brass wings arranged vertically and
immersed in oil. This oil is contained in the cylin-
drical vessel B'. By raising or lowering this vessel the
amount of resistance offered to the rotatory motion
may be graduated. This, together with the great
weight of the heavy plate B, causes the rate of rotation
of the cylinder A to increase but very slowly. As
soon as a proper speed has been attained, the muscle
is irritated ; and this, on contracting, raises the lever c
-so that the point e fastened to the latter traces a curve
on the cylinder.

To carry out the experiment, the muscle is fastened
in a vice within the glass case, so as to prevent its
drying up, and is then connected with the lever c ; the
cylinder A is covered with a coating of soot, and is then
firmly fastened on its axis ; the pointed indicator is
brought into contact with the cylinder by means of
the thread /. When this cylinder is slowly turned
round by the hand, a horizontal line is inscribed on it
by the indicator, and this represents the natural length
of the quiescent muscle. On the circumference of
the disc B is a projection called the ' nose.' When
the disc together with the cylinder connected with it
are in a certain position, this nose touches the bent
bayonet-shaped angled lever I. When the latter is
turned aside it raises the lever h by means of the arm
i, thus breaking the contact of a current between the
lever and the small column standing in front of it. The
current of an electric chain is conducted through this

54 PHYSIOLOGY OF MUS AND NKKVI

point of contact, and also through the ])riniarv coil of
an inductive apparatus The secondary foil is con-
nected with the muscle. When, therefore, the lever I
is turned aside, the muscle is irritated. Accordingly it
pulsates and raises the pencil of the index so that the
latter marks a vertical line, representing the height of
elevation of the muscle, on the cylinder A. ]>y press-
ing the finger on #, the bayonet -shaped point I may be
slightly raised, the index point c bring at the same time
slightly removed from the cylinder. The clockwork
is then sei in motion. The cylinder turns, at first
slowly, lint gradually more quickly ; but the mu>cle
remains inactive, and the point can make ho mark.
As soon as the cylinder has attained the desired speed
the linger is removed; / sinks, and is soon after caught
and turned aside by the nose, and the muscle, thus irri-
tated, pulsates, and this pulsation is recorded on the
cylinder during its rotation.

The irritation of the muscle being effected by the
apparatus itself, it occurs when the rotating cylinder
is in a definite position; that is to say, the evli'iid^r
is in that position in which the nose has ju>t touched
the end of the lever /. It is evident that this posi-
tion is the same as that at \\liich the muscle \vas at
t'n>t allowed to pulsate when the cylinder >t oo.l still.
The vertical line then drawn, therefore, indicates
exactly the position of the cylinder at the mom, nt at
which irritation, takes place. When- this vertical line
deviates from the hori/.oiital line first drawn is the
point at \\hirh the pencil \vas \\lien irritation \vas in-
duced in the muscle. The distance- from which the
periods are to be calculated must be me;i<ured from
this point .

THE MYOGRAPH. 55

In order to make the calculation, the rate of rota-
tion of the cylinder must be accurately known, as
uniformity in the time of registration of vibrations is
not effected by the apparatus. As we have already
seen, the rate of rotation of the cylinder is not uniform,
but increasing ; owing, however, to the weight of the
disc B and of the immersion in oil, the increase is very
gradual, and when a certain speed has been attained
the resistance offered by the oil is so great that no
further increase occurs and the speed remains constant.
By means of the hand on the face d this speed can be
determined ; and it is easy to cause the cylinder to
make exactly one revolution per second by adjusting
-the oil vessel of the apparatus.

The desired speed having been attained, it is only
necessary to know the circumference of the cylinder in
order to calculate the time value of that which is
marked on the cylinder. In order to facilitate the
measurement of the separate portions of the curve,
the cylinder, after being carefully removed from its
axis, must be fastened into a suitable forked handle
(such as is represented in the left-hand lower corner of
fig. 17, where it is marked -E"), and the cylinder must
then be rolled on a sheet of moistened gelatine paper.
The whole layer of soot adheres to the sticky gelatine ;
and the whole must then be fastened with the blackened
side downward on to a white ground. The described
curves will then appear in white on a black ground,
and will admit of easy measurement.

Fig. 18 is accurately copied from a curve described
in this way by the calf-muscle of a frog. The point at
which the irritation occurred is marked z. It will at
once strike the observer that the rising of the indicator

r.ivsioLiHiv or Mrsru> AM* NKKVKS.

did not hr-in :it tin- point :, l>u( :i< some lit 1 le di>tance
bevond ilii-. :it a. From this it is to he inferred that
the contraction of tin- mu>de did u«'t be^in at the
moment ,if irritation, for it i- evident thai the cylinder
of tin- mvoMTaph had time to turn from : to a before
tl,,. indicator was raised liy tin- contraction of the
muscle. A certain time, therefore, elapses before the
change produced in the mnsele by irritation re-nlts in
contraction. The duration of this tinu — \vhich can be
acc-nratelv calculated from the length of the >jiace exist-
ing Itetweeii ~ and a — is about one-hundredth of a

X a.

]•'!«;. IS. Tin: . URVES OF A MI M II-I-IM- \TloN.

second. Tliis stage is called that of lnt< at i i-
for dnriiiLf it the irritation has not yet bee.. me actively
eflicicnt in the muscle. From the point a the muscle
evidently contracts, as is shown by the rising of the
pencil from point a to point b, which is the highest
part of the curve described; from that point onward
the muscle again lengthens till it resnme< its original
length at the point c. The time which elapses bet ween
the beu-innin^ or the contraction and its maximum
is called the sta^e of incr.'asin^ energy ; tin' time from
this maximum to that of the full re-extension of the
mu-elr i- that of the stage of d. Tr. 'a si Hi,'- energy. The
whole duration of the muscular pul-at ion from the
commencenient of the contraction at « till complete
ext.-nsioii is a^-ain readied at C, i> from about one-tenth

to one-sixth of a second.

DETERMINATION OF TIME BY ELECTRICITY.

57

3. In a similar way the different periods in muscular
pulsation may be measured by means of an electric I
current. In order to understand this process, let us
suppose a sudden push to be given to a heavy pendulum.
The pendulum is thus caused to deflect from the
vertical position proper to it when
quiescent, the angle formed by its de-
rlection depending on the force of the
push which operated on it. Heavy
pendulums of this sort, called ballistic
pendulums, are used for measuring
the speed of gun-shots. A magnetic
needle which when suspended from a
thread assumes a direction from north
to south, may be regarded as a pen-
dulum in which, in place of the force
of gravitation, the magnetic attraction
of the earth determines its position
in a certain direction. If a sudden
push is given to a pendulum of this
sort, the force of the propulsion may
be calculated in this case also from
the degree of deflection. If a con- FlG 19_ MEASUI:E-
tinuous electric current be conducted WKNT OF
to a magnetic needle, the current

O '

being parallel to the needle, the latter
deflects and assumes a position at an angle to the cur-
rent, the magnitude of this angle depending on the
strength of the current. The magnetic needle assumes
a new position, the repelling force of the current and the
magnetism of the earth counterbalancing each other.

O O

If, however, the current, instead of acting continuously,
acts only for a short time, the mngnetic needle suffers
4

ANGLES OF DEFLEC-
TION WITH MIUItOK
AND LENS.

58 rilYsIOLOGY OF MUSCLES AND NERVES.

a push of but short duration and makes mily a single
vibration, after which it returns to the position prop. r to
it when at rest. Tin- degree of deflect ion mii>t in this
case be pm port ionat e to the strength of the current and
to the brevity of its duration. If, therefore, the strength
is known and remains constant, the time occupied by tin-
deflection maybe calculated from its extent. Such de-
flections are generally very slight. In order, therefore,
to measure them with certainty, an apparatus which was
first applied by the celebrated mathematician (ianss
is used. A small mirror o being connected with the
magnet, a graduated scale s s, which is reflected in
the mirror, is read by means of a magnifying glass. If
the scale is placed parallel to the mirror when the
magnet is at rest, and the magnifying glass is arranged
at right angles to the direction of the mirror and of the
scale, it is evident that exactly the point a on tin-
scale which lies over the centre of the magnify ing
glass will be seen reflected in the mirror. As soon as
the magnet with the mirror attached to it turns, thi-
n-flection of a different point on the fixed scale, the
point c, is seen through the glass, and an observer
looking at the mirror through the lens sees the scale
apparently move in the same direction as that in
\\hii-h the mirror, together with the magnet, turns.
From the extent of this change of position the angle
which the magnet describes in its deflection may In-
calculated.

4. This method, by which the duration of electric
currents may be measured with the ^reate-t accuracy,
must now he applied to our task of examining the
duration of a muscle-pulsation. Kor this purpose we
must find sonic arrangement by which an electric

MEASUREMENT OF PULSATION BY ELECTRICITY. 59

current is closed at the instant at which the muscle is
irritated, and to interrupt this current at the instant at
which the contraction of the muscle begins.

This experiment also was first effected by Helmholtz.
The apparatus used for the purpose is shown in fig. 20,
in the altered form used by du Bois-Reymond. From
a fixed stage rises a column to which a strong vice for
the reception of one end of the muscle is attached in
such a way that it can be moved upward or downward.
The lower end of the muscle is fixed by means of a
connecting piece i h with a lever which can be turned
on the horizontal axis a a'. The lever is prolonged
below into a short rod which, passing through a hole
in the stage, supports at its foot a scale plate for
weighting the muscle. On the fore-end of the lever
are two screws p and q, the former of which ends below
in a platinum point resting upon a platinum plate,
while the latter is extended into a point of copper-
amalgam, immersed in a capsule of quicksilver. The
platinum plate and the capsule of quicksilver are iso-
lated from the stage and from each other, the latter
being conduc* ively connected with the vice fc, the former
with If.

If tb.e current which is to act on the swinging mag-
net is inserted between k and &', it passes through the
quicksilver capsule, through the portion of the lever be-
tween p and g, through the platinum plate, &c., as long
as the muscle does not contract. As soon, however, as
the muscle contracts, it interrupts the current between
p and the platinum plate. If the apparatus is so ar-
ranged that the current is closed at the moment at
which any irritant affects the muscle, then this current
will circulate until the muscle, in contracting, again

GO

PHYSIOLOGY OF MI'X'LKS AND NKUVKS.

F ic. L'II. APPARATUS I »i: MEASURING Till. DUKATTON <>l MUSCLB-

i c.N I l;.\i I |..\.

MEASUREMENT OF PULSATION BY ELECTRICITY. 61

interrupts the current. This period, which may be cal-
culated by the method described in the last paragraph,
represents exactly that which elapses from the moment
at which the irritant affects the muscle to that at which
contraction begins.

Yet another circumstance must be taken into con-
sideration, in order to render actual measurements pos-
sible. The muscle contracts on being irritated. This
contraction, however, lasts only a very few parts of a
second, and the muscle then resumes its former length.
In the experiment just
described, the current
interrupted by the con-
traction of the muscle
would soon be again
completed, and the mag-
net would undergo a new
deflection even before
the first vibration was
finished. In order to
obviate this, Helmholtz
employed means the na-
ture of which is made
intelligible in fig. 21. This figure represents the end
of the lever of the apparatus already described, together
with the two screws p and g, the platinum plate and the
quicksilver capsule ; at k are the wires connecting the
latter with the vices. The quicksilver in the capsule
Hfj can be raised or lowered by means of the screw s.
Jf the level of the quicksilver is raised so as to immerse
the point q, and if it is then again lowered, the quick-
silver, by adhesion, remnins hanging from the amalga-
mated point, and is by this means drawn out in the

21. TlIE END OF THE LEVER OF
THE APPARATUS FOR TIME MEASURE-
MENT, TOGETHER WITH THE QU1I K-
SILVEU CAPSULE.

62

PHYSIOLOGY OF MI X'LKS AN1> .\KI;\ I >.

form of a iln'n tin-cad, through which the current may
pass. When, however, tlir miiM-le shorten*, the- qnick-
silvrr i- torn a\vay, and roinncs its ordinary r«niv<-x
surface; and wlit-n, on thr extrusion of tin.- niusrU-,

-c,

I.XI'I IMMI M I MI; I in. I I I < I l;]< Ml AM III Ml N L
M| I I Ml.

the lever a<niiu sinks, though the point // a-jain rests on
the platinum plate, yet the point </ remains separated
from the quicksilver l>y ;m intermediate air-filled space,
and the current remains permanent ly interrupted.

It -till \\;\> to be explained lm\v the irritation of the
mu.-cle and the clo>in.r ,,(' t he time-determining current

MEASUREMENT OF PULSATION BY ELECTRICITY. 63

are affected exactly at the moment of irritation. A clear
idea of this will be gained by examining fig. 22, in which
the arrangement of the whole experiment is diagram-
matically represented. The muscle and the apparatus
represented in fig. 20 are again shown. The muscle
is connected with the secondary coil of the inductive
apparatus J' '. In the primary coil / circulates a current
from the chain K. This current passes through the
platinum plate a, and through the platinum point a',
a' is attached to a lever of hard wood, of &', and is
pressed by a spring against the platinum plate a. At
the other end of the lever is the platinum plate &',
which is connected with the battery B. The other pole
of the battery is in connection with the galvanometer
g, which latter is itself connected with the quicksilver
capsule of the apparatus represented in fig. 20. Over,
but not touching, the platinum plate b' is the platinum
point 6, and this is connected with the platinum plate of
the same apparatus by the conductive material of the
key s, and of the wire k'. On pressing down the key s
by the handle, the platinum point b comes in contact
with the platinum plate b', and the current by which
the time is to be measured is closed. At the same
time, however, the end a' of the lever a' b' is raised,
and the current of the chain K is interrupted. This
produces an inductive current in the coil */', and this
irritates the muscle. Irritation is, therefore, induced
exactly at the moment at which the time-determining
current is closed.

As soon as the muscle contracts, it interrupts the
time-determining current. This, therefore, lasts from
the moment of irritation to that at which the pulsation
commences. In this, therefore, we measure that which

64 PHYSIOLOGY OF Ml'SCLES AM) NFUVKS.

we called the stage of latent irritation. When, how-
ever, weights are placed on the scale of the apparatus
(fig. 20), tin- r. •suiting deflections of the magnetic needle
are different, and are greater in proportion as the weight-
applied is heavier. As the lever connected with the
muscle rests on, and is supported by, the plate below
it, the weights placed in the scale-plate cannot extend
the muscle ; they only increase the pressure of the
platinum point p on the underlying platinum plate.
Before the muscle can contract after irritation, the ten-
dency to contraction must be greater than this pressure,
or than the tension which is exercised from below bv
the weight on the lever. As the muscle strives to draw
up tin- lever, while the weight, on the other hand, draws
it downward, the greater force obtains the masterv. It
will be evident from what has been said that the muscle
acquires the force with which it strives to contract, not
suddenly, but very gradually. At the moment at which
this contracting force becomes slightly greater than the
weight applied, it is able to raise the lever, and in BO
doing to interrupt the current which determines the
time. If, in a serie< of consecutive experiments, hea\i.T
weights arc each time placed in the scale of the appa-
ratus, and if the deflections of the magnetic needle re-
sulting from this are measured, this determines the
periods in which tin- mu>cle attains a tendency to C"ii-
traetii.n equivalent to tl:c weight. \Ve \\ill call tin's
lon-e the energy of the muscle. So lon^ as the muscle
does not contract at all- that is, throughout the >ta^e
of latent irritation its energy = (). From the periods
which we find as the result of the application of in-

creasing weights, it appears that this energy increases,
at first rapidly and then more >lowly, reaching itsmaxi-

BURDEN AND OVER-BURDEN. 65

mum in about one-tenth of a second. The maximum
having1 been reached, the muscle is unable to contract

o ?

further. The energy diminishes, and finally disappears,
the muscle returning to its original condition.

5. In the experiments described above, weights were"
connected with the muscle which the latter necessarily
raised as soon as it strove to contract; but these weights
did not act upon the muscle as long as it remained
quiescent. It was, therefore, not weighted in the sense
which has already been described ; for the weights at-
tached were unable to extend the muscle. The com-
paratively slight weight of the lever alone extended the
muscle, and could be regarded as burden in the ordinary
N sense. In order to distinguish these weights, which
are without effect until the muscle strives to contract
from weight in the ordinary sense, we will apply the
term ' over-burden ' to them. The burden of a muscle
may be great or small. In the experiments described
above it was equal to the weight of the lever. Greater
weights may be selected, a weight being placed upon the
scale-plate and the muscle being then raised by means
of the screw at the top of the apparatus, so long as the
platinum point p still rests on the platinum plate. The
muscle is then extended by the weight applied. If
additional weight is added to that already on the scale-
plate, the former acts as burden, the latter as over-
burden. When a muscle thus circumstanced contracts,
it has to lift both weights. Let us return to our first
series of experiments, in which the weight = 0, or was
at least very small. If more and more over-burden
is gradually added, it is evident that a point will be
reached at which the muscle will no longer be able to
lift the weight. This point may be very accurately

66 PHYSIOLOGY OF M1M I.KS AND NERVES.

determined bv inserting a chain and an electro-magnet
between the vices /-and //. The electric currenl then
passes through llie platinum poiut, the convspond-
ing lever, the quicksilver capsule, and the coils of the
electro-magnet. The latter becomes magnetic, and at-
tracts an armature. As soon, however, as the current
is interrupted by the contraction of the muscle, the
electro-magnet sets the armature free, and the latter,
striking against a bell, gives a signal which shows that
the muscle has contracted. In this way even very
minute contractions of the muscle are recognised. If
the weights which act as over-burden, and counter-
balance the tendency tn contraction in the muscle, are
gradually increased, a limit is reached at which, in spite
of the irritation of the muscle, the current oft lie electro-
magnet is no longer interrupted. The muscle is indeed
irritated, and a tendency to contraction is generated
within it ; but this is not sufficiently great to overcome
the weight used ; and the muscle, therefore, remains
uncontracted. In this way the extent to which the
tendency of a muscle to contract — or its energy, as we
called it, can increase — maybe found. This extreme
limit of its energy is called the force of a muscle. It
is the same in amount as that which we theoretically
inferred (p. 4H) from the change in the elasticity of
a muscle during contract ion. Kaeh muscle has a definite
force dependent on the conditions of its nourishment
and on \\< form. On comparing the muscles of the same
animal, it appears thai the fore.- is dependent in noway
on the length of the mux-le-libivs, but on the number
of these libres, or, in other words, on (he diameter of
the muscle; and that the force increases in exact pro-
portion with the diameter of the muscle. So that a

MUSCLE-FORCE. 67

muscle of double thickness therefore possesses double
force. It is usual, therefore, to refer the force to units
of diameter of the muscle, by dividing the force by the
diameter of the muscle, and thus to calculate the force
of a muscle of 1 square centimetre diameter.1 It has
been found that in the muscles of the frog the force,
for a diameter of 1 centimetre, is about 2-8 to 3 kilo-
grammes ; that is to say, a muscle of 1 centimetre in
diameter can attain a maximum tendency to contraction
which a weight of 3 kilogrammes is capable of resist-
ing. This value of the force reduced to units of dia-
meter is called the absolute force of a muscle.

6. An attempt has been made to determine the ab-
solute muscular force in the case of man also. Edward
Weber first tried to do this by an ingenious method.
The muscles of the calf were chosen for the experiment.
On standing upright and contracting these, the heels,
and at the same time the whole body, are raised from
the ground. Gymnasts call this balancing. The whole
force of the calf-muscles of both legs is therefore greater
than the weight of the body. If the body is weighted,
a limit is reached at which it is no longer possible to
balance. The total weight of the body together with
that of all the weights applied, therefore, equals the
force of the muscles of the calf; but in calculating
this, however, attention must be paid to the fact that
the force and the burden do not act on the same lever,

1 The following method, adopted by Ed. Weber, is used to de-
termine the diameter. The weight of the muscle, which is found
by the use of scales, is multiplied together with the specific weight
of the muscle-substance, the result being the volume of the muscle.
The length of the muscle is then measured, and the volume is
divided by the length, which gives the diameter.

(IS IMlYMnl.uiJY OF MTSCLKS AND NF.KVIX

;ill(l that (lie force — (lie ten-ion exercised by (lie mu-cles
(pf the cult' — acts obliquely on the lever. It is of onir-e
impossible to del ermine the diamet i-r in a living man;
it must be observed in a dead body of about the same
>i/e as that of (he person e\i)erimented on.

Ib-nke aUo lias lately determined the valuo of t he-
absolute force of human muscle. He used the flexor
muscles of the forearm (of. tii(. °2'.}>) to del ermine \}\\<.
In the tigure, a represents the upper arm. l> the fore-
arm— (he former hein«j in a ver-
tical, the latter in a horixontal
position; c represents the muscles
which raise or bend the forearm.
(There are in reality two of these
muscles, .17. /mv//x and .17. l>rn-
rlinili* intemus). Supposing thai

the muscles are >( retched, and
weights are placed on (he hand
It till (he muscles are no longer ca-

I'n. .-_'::. DI.\I;I:AM <>r THK pable of raising the hand, then,

FLEXOB^IUSCLES UF THE jug1 as Jn t lu/ (,N , „ ,,-j , , ,e,,( S will,

the- miiM-les of fn>«;s, eipiipoise is

olitained be(ween (he ( endeiicv of the muscle (o con-
tract ami 1 he weight carried. Care mus(, however, be
taken tha( (he muscles act on a lon^ lexer arm, the
weight on a short one, and the weight of the forearm
itself mii-t also be taken inlo considera) ion. Due at-
tention, beinir ^iven to al! these circumstances, and to
the diameter of the musc!e< when drawn into action,
Ib-nke calculated that the absolute force in human

mii-cle j- eijiial to from >i\ to ei^ht kilogrammes. 1*A-

pei inieiil in^- in a similar \\ay on the feet, he found
somewhat louer figures in that case. \Veher, lio\\e\cr,

MEASUREMENT OF MUSCLE-FORCE IN MEN.

G9

FIG. 24. DYNAMOMETER.

in his results as regards the calf-muscles, found much
lower figures. But in this case, errors in calculation
evidently occurred, and explain the difference.

To determine the muscles of the forearm which
bend the ringers, a dynamometer, as represented in fig.
24, may be used. The strong spring handle of steel, A,
being grasped with both
hands, is pressed together
with the whole strength.
The alteration in the
curves which is effected
in the instrument at the
points d and d', is trans-
mitted by the lever a b a'
to the index c, which indi-
cates in kilogrammes the amount of force exercised on
the graduated scale B. A somewhat elaborate calcu-
lation would be necessary to find from this the absolute
force of the muscles employed. If, however, the force
which men are generally able to exercise with their
hands is known, t'he apparatus may be conveniently used
to detect occasional variations, such as occur, for in-
stance, at the commencement of lameness and other
diseases of the locomotive apparatus. The dynamo-
meter has, therefore, become of importance in the in-
vestigation of diseases.

7. We have already observed that a muscle during
a single pulsation attains its full force, not at once, but
only gradually, and we have seen the way in which the
periods necessary for attaining the different values of
the energy may be determined by means of the electric
method of measuring time. If the muscle contracts
freely, little or no weight being attached, it exhibits

70 PHYSIOLOGY OF MlsCU:- ,\M> NERVES,

this energy during each in>tant in flu- f'«>nn of increase
in speed \\hich it imparts to its lower end and to the
slight weight attached to tin- latter. \Ve niav now
raisc tlic quest ion as to tin- amount of force which the
muscle \vhcn it has already accomplished part, sav one
half, of its contraction, can still evolve. Schwann, who
first raided tin- ([iiestion, fastened a muscle to one end
of the beam of a scale and attached \\einhts to the
other end, but supported this end in such a wav that
the muscle was not extended. He was ilius able to
determine the force of the muscle in the same way as
was described above with the apparatus shown in ti.uf. 20,
which depends on exactly the same principle. L. Her-
mann repeated SchwannV experiment with this appa-
ratus, which is more convenient for the purpose now
under discussion. The unweighted, or, at least, \ cry
slightly weighted, muscle having been inserted in the
apparatus as accurately as possible, so that the platinum
point j, just rots on the plate, the muscular force is
determined in the way described above (see pp. 65, G7).
The vice which carries the urn-de is then lowered to ;i
certain definite extent, say 1 mm. If the muscle is
then irritated it can become shorter by 1 mm. befoir

it pulls the lever k ; if it bee es yet shorter it mu.-t

raise the lever with the weights attach -d to it. The

weight which it can still lift after it has become shorter
by 1 mm. may thus be found. The muscle-A ice is then
a^ain lowered and \l\\~- is a^ain and a^ain repeated.
A ,-eries of weights-values is thus obtained \\hidi corre-
spond with the fon-e of the miiM-le during the different
Stages of it- contraction. The roiill .if the e\prriment

is to show thai the force of t he milx-lr di 'creases, slowlv

at the commencement . •(' contraction, but afterwards

ALTERATION IN MUSCLE-FORCE DURING CONTRACTION. 7 1

more rapidly. The muscle having contracted as far as
possible without any weight, it can naturally no longer
raise any weight — its whole energy is expended.

The interest of this experiment lies in the fact that
it shows in a different way that which we have already
said (p. 48) as to change in elasticity during contraction.
For these experiments determine the weight proper to
each length of the active muscle, so that we can also
directly deduce from these the curves of extension of
an active muscle, which we had previously constructed
only theoretically. The agreement of this deduction
with the theory, found in a different way, is an impor-
tant confirmation of the views which we have developed
as to the bearing of the conditions of elasticity on the
labour accomplished by the muscle.

72 ruvtiioLouv OF MI^CLES AND M:I;\J;S.

CHAPTER V.

1. Chemical jiioo -M -s \villiin t lie muscle ; 2. (Jem-nil i"n of warmth
daring contraction ; :>. Kxliaiislimi ami HTKWTV ; 4. SMUIVC of
musde-i'iin -c : .".. l>r;itli <>f the muscle; C. Death-stiffening

( /lii/i'l-

1. Tlie relations just described between the elasticitv
and tlie work accomplished Ity the muscle have led us
to suppose that a inusdi- has. as it were, two natural
I'. TIMS, one convsj>ondin<r to its condition of rest, tin-
other — a shorter form —corresponding to its active con-
dition. Irritation induces the muscle to pass from one
form into the other, and in so doin^ it contracts. This
is, however, rather a description than an explanation
of the fact of contraction, AH the muscle on contraction
is capable of raising weight, and thus of accomplishing
work, it is necessary to inquire how this labour is
etl'eeted. According to the law of the con>er\ation of
energy, the labour so accomplished can only come into
existence at the expense of some other energy. Now,
it can be proved that chemical processes proeeed \\itliin
the muscle (luring muscular contraction, while others,
\\hich pro.-ecd e\eii in the < | uie.-.ceiil muscle, are in-
creased in degree during this same contraction. The
tin chanical \\..rk must, therefore, be accomplished at
the cxpeii-e , ,f these chemical pr»ee>st-s ; and it could

CUEMICAL rilOCESSES IN MUSCLE. 73

be proved that the amount of work accomplished corre-
sponds exactly with these chemical changes.

It is easy to show that chemical processes occur
within the muscle ; but it is not so easy to determine
these quantitatively, so that we are as yet unable to
solve the question raised. Helmholtz long ago pointed
out the fact that during muscular contraction such con-
stituents of the muscle as are soluble in water decrease,
while such as are soluble in alcohol increase. E. du Bois-
Keymond showed that an acid — probably a lactic acid
(Fleischmilchsaure) — is generated in the muscle during
its activity. Quiescent muscles also contain a certain
amount of a starch-like matter called glycogen ; and, as
Nasse and Weiss have shown, part of the glycogen is used
up during the activity of the muscle, and is transformed
into sugar and lactic acid. Finally, it can be shown
that carbonic acid is generated in the muscle during its
contraction. All these chemical changes are capable of
producing warmth and work. In determining whether
the whole amount of work accomplished is referable to
this source, yet another special difficulty exists in the
fact that, as in other machines, warmth is also produced
as well as mechanical work. A muscle certainly grows
warmer during its contraction, as Beclard and, with yet
greater certainty, Helmholtz have shown. With suitable
apparatus it is possible to indicate an increase in the
warmth of a muscle even during a single contraction.

Our knowledge of the chemical constituents of
muscle is yet very incomplete. Not only is chemistry
as yet unprovided with adequate means of examining
albuminous bodies, which are the chief constituents of
muscles, but a special difficulty also exists in the great
tendency to change in the constituent matter of living

74 PHYSIOLOGY OF Mrsri.Ks AND NKKVES.

muscle. '1'ln' methods usually employed in chemistry
tor the separation and isolation of different substances
arc of no avail in this case, since they essentially alter
the nature of the muscle. We must, therefore, be sati —
tied to assume as certain only that various albuminous
liodi.-s occur in the muscle, one of which, called myosin,
appears to lie peculiar to muscle, and of which others
are the inm-nitrogenous bodies glycogen ;md inosit.
together with a certain amount of fat and a number <•!
salts. It a])pears somewhat doubtful whether lactic
aciil, which is always present in the muscle, if but in
small (plant it ics, is to be regarded as a normal c<m-
.-I it uent of muscle substance, or if it is nut rather a
product of decomposition. The same may be said of
the gaseous carbonic acid which, like the lactic acid, is
probably only formed during the activity of the muscle,
and also of the nitrogenous bodieSj such as creatin, which
an- present in small quantities in muscle, and which
must probably also be regarded only as the product.- of
the dissolution of the albuminous bodies.

2. The only conclusion to be drawn from tin's frag-
mentary information is that part of t he muscle-substance
unites during the activity of the muscle with oxygen,
forming, part ly carbonic acid, part ly less highly oxidised
products. That warmth is generated during these pm-
368868 of oxidation, as we have above stated, is not sur-
prising. To show this general ion of warmth, 1 1 elm holt/
employed the thermo-electric method. An electric cur-
rent rises in a circle composed of t w<> ditVercnt metals, e.g.
copper and iron, a> SOMH as both points ,.f contact the
points \\here the metals meet or are soldered together

acquire mieipial temperatures. The strength of this
current is proportionate to t he difference in temperature,

GENERATION OF WARMTH DURING CONTRACTION. 75

and thus, from the strength of the current, it is possible
to determine the temperature of one point of contact
if that of the other is known. In our case, in which it
is not necessary to determine absolute temperatures,
but only to show an increase in warmth, the method is
more simple. It is only necessary to provide that the
two points of contact have the same temperature at
first, a condition which can be recognised by the absence
of any current, and the additional degree of warmth ac-
quired can then be directly calculated from the strength
of the current which is afterwards generated.

Helinholtz performed the experiment by placing
the two thighs of a frog which had been recently killed
in a closed case, after he had so arranged the metals
which were to determine the warmth that one point of
contact was inserted in the muscles of one thigh, the
other in those of the other He then waited till the
temperatures of both thighs became equal, so that,
though the metals were connected with a sensitive mul-
tiplier, no current was apparent. The muscles of one
thigh were thrown into strong tetanus by introducing
a suitable inductive current, while those of the other
thigh remained at rest. The contracted muscles then
became warmer and imparted their warmth to the
soldered metals embedded in them ; the result was an
electric current the strength of which was measured.
The increase in the warmth of the muscle, thus de-
termined, was about '15 of a degree. This warmth
may seem slight, but it must be remembered that but
a small mass of muscle was treated, and that this
necessarily lost a considerable part of the warmth gene-
rated within it by radiation and by imparting it to the
surrounding substances.

76 PHYSIOLOGY UF MUSCLES AND NKKYI-.

•

In order In form some conception i>f tin- amount of
\vanntli thus generated, we will assume that the specific
warmth of muscle is the same as that of water. As the
greater part of muscle consists of water,1 this assumption
cannot be far wrong. ]>v the specific warmth of a sub-
stance is meant that amount of warmth which is neces-
sary to warm one gramme of the substance exactly one
degree, the amount nece<-ary in the case of water being
regarded as the unit. Therefore about one unit of
warmth is requisite to warm one gramme of muscle
substance one decree. According to our assumption, in
each gramme of muscle substance at least '15 of a unit
of warmth is generated. Now it is known that each
unit of warmth is equivalent to 424 units of work, that
is to say, when warmth is transformed into mechanical
work, .JU4 grammes can be raised one metre by one
unit of warmth. If, therefore, no warmth were set free
from the muscle during tetanus, but if it were tran--
formed into work, each gramme of muscle substance
would be able to raise 424-^-0-15 gramme to the height
of one metre. This amount, therefore, represents the
minimum of that which is accomplished as 'internal
work' in the muscle during tetanus.

By soldering rods or strips of t wo metals alternately
on to each other so that all the points soldered an-
arranged in two planes, differences in temperature much
more minute than those which occur during tetanus
may be measured. Such an apparat u- is called a thermo-
pile. Heidenh: in had one of the.-e made of rods of

1 ACCI rc'.'.ML' tn u ivo-nt M:itrinrnt nf I»r. Adamkiewicz, the spe-
cific \v:irintli I'!' musrV is even u-rratrr I li:ui I kit uf water, tliuu^li it

bad previously been assumed that tin- sprriiic wurmtli •>!' wain- is
greater tlian tlmi nf any otlii'r kimwn siili.st:nn-i', with tlio excep
nf liylr'

GENERATION OF WARMTH DURING CONTRACTION. 77

antimony and bismuth, and having covered the surface
of each of the ends with a muscle from the lower leg
of a frog, he waited until both had assumed an equal
temperature. He then by irritation induced activity
in one muscle, and owing to the sensitiveness of the
apparatus he was not only able to determine the warmth
arising during a single pulsation, but even to indicate
differences in this according to the circumstances
(burden, &c) under which the pulsation occurred.

The law of the conservation of energy would lead
us to expect that in cases in which the muscle ac-
complished a greater amount of mechanical work, the
production of warmth would be less, and vice versa.
When weights are applied, as burden, to the muscle,
the labour performed increases, as we found, up to a
certain point with every increase in weight. The
generation of warmth should accordingly decrease in
this case. This was not, however, the case in the
experiments made by Heidenhain. As we cannot sup-
pose that the law of the conservation of energy,1 which
is elsewhere throughout nature universally valid, is
invalid as regards muscle, we can only suppose that
the number of chemical modifications occurring at each
muscular pulsation is not always the same, but that
when greater weight is applied a larger amount of
substances are consumed in the muscle, so that both
the production of warmth and the work accomplished
may, though the irritant remains the same, differ
according to the degree of tension of the muscle. On
the other hand, it is quite in accordance with the law
of the conservation of energy that the muscle generates

1 On this law see the admirable work of Balfour Stewart (Inter-
national Scientific Series, vol. vi.).

78 PHYSIOLOGY (.)!• Mrsri.Ks AND NERVES,

the greatest amount of waiinth during tetanus, during
which no nj.jK'n nl labour i~ accomplished. The whole
intern;,! w..il< «•!' the miivle is in \}\\> case transformed
into warmth, thus rai>ing the t emperat are of the muscle-
substance ; and (lie amount of this warmth may, as we
liiive seen, be at least approximately measured and
calculated.

3. One result of the chemical changes which occur
within the muscle during its activity, is naturally
tint part of the constituent matter of the muscle is
expended, other matter being dep,,>ited in its place.
As long as the muscle remains uninjured within the
body of the animal, part of the matter thus formed is
carried away, and fresh nutritive matter is brought to
replace the expended material. The products which
arise by decomposition during the activity of the
muscle may therefore be indicated in the blood of the
animal, and from the blood they are removed from out
of the body by special excretory organs. Accordingly
we find that the amount of carbonic acid excreted is
considerably increased by muscular labour, and that
the other products of muscular decomposition, such as
creatiu and the urea arising from the latter, lactic acid,
\e., reappear in the urine. The more abundant Iv
the blood-current flows through the mu-cles. the more
quickly are the products of decomposition removed
from the muscle. This is of course possible onlv in a
very inferior degree when the mii>cle has been cut out
from the body. Tlii-i-the rea>oii \\liy ;m extracted
muscle retains its power of activity I'm- but a very short
time. If, for instance, such a muscle is eont inuoiisl v
tetanised, it will be found that the contraction, though
it is at first very considerable, \ery soon decreases and

EXHAUSTION AND EECOVERY. 79

finally entirely ceases. The muscle is then said to be
exhausted. But if it is allowed to rest it recovers
itself so that it can again be induced to contract. This
recovery is, however, never complete, and with each
repetition of the experiment it becomes more defec-
tive, the intervals requisite for recovery becoming
continually longer, and the muscle finally remaining
incapable of further contraction. If the muscle is not
tetanised, but distinct pulsations are induced in it by
separate irritants, it retains its power of activity for a
very long time. From this it may be inferred that a
portion of the products of decomposition perhaps re-
form ; or it may be assumed that the muscle contains a
large amount of matter capable of disintegration, but
that this is capable of only gradual decomposition. So
long as the blood continues to flow through the muscle,
the products of decomposition are, as we have seen,
soon carried away ; but as exhaustion occurs in this case
also, we must draw the same conclusion, that the de-
composable matter present can undergo decomposition
only gradually, and that therefore in this case also
intervals must necessarily occur between the separate
exercises of activity. A muscle while undisturbed within
the organism essentially differs from one that has been
extracted in that in the former the expended material
can be fully replaced. Accordingly, it is not only capable
of again becoming active after an interval of rest, but,
provided that the matter added exceeds that which was
expended, it is afterward capable of performing more
work than it was previously. To this is due the fact
that the strength of muscle is increased by a proper
alternation of rest and activity.

4. We have now to discover which of the substances

80 PHYSIOLOGY OF MUSCLES AND NF.HYES.

within the muscle are expended during its activity.
A- mu-cle consists principally of albuminous bodies, it
lias been a— 'timed th:it it is to tin- d, •<-. imp, >-it i. m . if
these that the labour accomplished is dur. \\Y have,
however, seen that non-nitrogenous bodies, such as
glycogen and muscle-sugar, are also contained in the
nTuscle, and that lactic acid which must ori»-inate

7 ' C>

from the latter, is formed during the active state.
Although it is impossible to determine the products of
decomposition within a single muscle, yet this may be
done in the case of the whole mass of the muscles of
the body during an activity of long continuance; for
the products of decomposition finally pa>s into the ex-
cretions, and it is evident that the whole amount of
addition to the excretions may be regarded as a
measure of the decomposition in the active muscles.
The nitrogenous constituents of muscle are almost
without exception excreted in the form of urea with
the urine. At least the amount of nitrogen contained
in the other excretory products is so very small that it
may safely be disregarded. Now, the amount of urea
contained in the urine may be determined with very
great accuracy. Even when the body is in a state of
complete rest— though even then a considerable amount
of work is performed in the body, iu the action of the
heart and of the respiratory muscles- the excretion ()f
urea depends entirely on the amount of nitrogen intro-
duced in food. If entirely non-nitrogenous food is
taken, then 1 he e\cret ion of uren decreases to a definite
point, at which it remains constant for some time. Jf
a larger amount of \\ork is performed, a slight increase
in the excretion of urea in fai-t usually occurs. The
amount of albuminous matter \\hich mii^t be modified

SOu'RCE OF MUSCLE-FORCE. 81

within the body in order to afford this increase in the
amount of urea excreted may be calculated. Now, the
equivalent in warmth of albuminous bodies is known ;
that is, the amount of warmth produced by the com-
bustion of a definite weight of albuminous matter is
known. And, as the mechanical equivalent of warmth
is also known, the amount of work which could be
produced by these albuminous bodies under favourable
circumstances may, therefore, also be calculated. When
this value in work is compared with the amount of
work really accomplished, the figures found are always
far too low. From this it may safely be inferred that
the albuminous matter which undergoes combustion
within the body is not capable of affording the work
which is performed, and we must rather assume that
other substances also undergo combustion, and con-
tribute to the labour performed, contribute indeed even
the greater part of such labour. If, on the other hand,
the amount of carbonic acid excreted by a man during
rest is compared with that excreted during greater
labour, the increase is found to be very great indeed,
and on calculating the amount of labour which should
result from the combustion of a corresponding mass of
carbon, the amount found corresponds nearly enough
with that of the work really performed.

This experiment, therefore, shows that the muscles
generate their work not so much at the expense of
albuminous bodies as by the combustion of non-nitro-
genous matter. The addition of matter required by the
body if it is to remain in a condition capable of labour
must, therefore, be regulated accordingly. Hence fol-
lows the conclusion, of the greatest importance with
reference to the question of diet, that men who have
5

£2 PHYSIOLOGY OF MUSCLES AND NERVES.

to perform a great amount of labour require food
abounding in carbon. The oppose \\a> f..nnrrly as-
sumed, the view being founded on the fact that K.nglish
labourers, who arc, as a rule, more capable of work
than French peasants, eat more meat, which is a highly
nitrogenous substance. It used also to be pointed nut.
that the larger beasts of prey, which feed exclusively
on flesh, are remarkable for their great muscular pouer.
Neither instance really proves the conclusion which it
was intended should be drawn from it. In the lir>t
place, as regards English labourers, more accurate ob-
servation of the food usually consumed by them has
shown that, in addition to meat, very considerable
quantities of food abounding in carbon, such as bread,
potatoes, rice, and so on, are taken. As regards the
beasts of prey, it is impossible to deny that they are
capable of very great labour; but in this case, also,
closer observation shows that the whole amount of
work accomplished by them is, at any rate, very small
\\hen compared with the constant work of a draught
horse or ox.

The relation of the fond to the work performed by
the muscles must evidently be regarded as similar to
the relation borne by the fuel consumed by an engine
boiler to the work performed by a steam-engine. Every-
one knows that coal is burned under the boiler, and
that this is finally transformed into work by the me-
chani>m of the machine. The same work might be
produced bv the combustion of nitrogenous matter:

lint it would lie necessary to use considerably greater
quantities. But the machine called muscle cannot be
driven bv pun- carbon ; under the conditions presented
bv tli'1 organism pure carbon caniml be applied t > the

SOURCE OF MUSCLE-FORCE. 83

production of work, as it cannot be digested, and, owing
to the low temperature of the body, cannot be oxidised.
But combinations abounding in carbon, such as are at
hand in the carbon hydrates (starch, sugar, &c.) and in
fats, are fitted for the purpose, and a given weight of
these affords a considerably greater amount of work
than can an equal weight of nitrogenous albumens.
If, therefore, the muscle is capable, by the combustion
of the non-nitrogenous bodies which it contains, of ac-
complishing labour, it is evident that this relation is
similar to that in the case of the steam-engine, in which
the work is accomplished by the combustion of carbon.
It has been objected that the amount of non-nitro-
genous substance within the muscle is very small, but
the objection is scarcely tenable. If a whole steam-
engine with its boiler and the coal in the furnace could
be subjected to a chemical analysis, the percentage of
coal in the whole mass would of course be found to be
very small. But it is not by the amount of coal present
at any given moment that the work is performed, but by
the whole amount which in the course of a considerable
time is added little by little by the stoker. In the
case of muscle the blood acts the part of the stoker.
It continually adds matter to the muscle, and the
products of combustion resulting from labour escape
from the muscle, just as the carbonic acid does from
the chimney of the steam-engine. It is evident that
the amount of carbon consumed by a steam-engine
might be accurately determined by collecting and
analysing the carbonic acid which escapes from the
chimney. We proceed in exactly the same way in the
case of the muscle. The lungs represent the chimney ;
the carbonic acid escaping from these may be collected,

84 PHYSIOLOGY OF MUSCLES AND .NERVES.

and from this the amount of carbon which must be con-
sumed may be calculated. Whatever does not escape
in the form of gas during combustion remains behind
as ash. The ash of the fire of the steam-engine is
represented by the urea and other matter which passes
from the muscles into the urine. The whole amount of
both must correspond exactly with the whole amount
of the products resulting from combustion within the
muscle.

Although the small amount of the non-nitrogenous
substances present in the muscle does not, therefore,
prevent us from regarding them as the main source of
muscular labour, yet in one point the machine called
muscle differs from the steam-engine, which it other-
wise so strikingly resembles. We found that the ex-
cretion of urea undergoes an increase, though this may
not be very great, when the muscular labour is in-
creased. It is, therefore, evident that there must be a
greater destruction of the chief constituents of muscle-
substance, of the tissue of which muscle is mainlv

\J

formed, and which may be compared to the metallic
parts of the steam-engine. Even in the latter a waste
of the metallic parts occurs; but this is comparatively

very small in degree. The muscular machine is ii"l
constructed of such durable material; during its ac-
tivity it, therefore, continually wastes a comparatively

considerable Amount of its own substance. As the
matter lra\es the body in a more highly oxidised form
than it had \vheii it was |>n-ent in the muscle, warmth
and work mu-t al-o be freed during this partial com-
bustion of the material of the machine. The muscle-
niachine works, therefor.-, partly at the expense of its
own form-element ; and, if it is to work continuously, not

SOURCE OF MUSCLE-FOKCE. 85

only must the main fuel, but also matter to replace the
form-element must be constantly added. The more
closely the composition of the food consumed corre-
sponds with the material expended, the more complete
will be the replacement which can occur. The expen-
diture of non-nitrogenous substance is, as we found,
comparatively great, so that it would be entirely wrong
to try to supply the loss merely with nitrogenous matter.
All experience in the nourishment of labouring men
,and animals fully confirms this. The addition of nitro-
genous matter is necessary, to keep the muscles in good
condition ; but a yet more abundant addition of carbon
compounds, such as are afforded by the non-nitrogenous
^food materials, is required, in order to supply the neces-
sary amount of the chief producer of labour. The
wood-cutters of the Tyrol, who work exceedingly hard
and with great expenditure of strength, accordingly con-
sume an immense amount of food abounding in carbon
in addition to a certain quantity of nitrogenous matter.
They live almost exclusively on flour and butter. Only
on one day in the week, Sunday, do they eat meat and
drink beer. For six days they are limited to whatever
they carry into the forests with them. The nature of
the food may, therefore, be very accurately regulated
in this case. Their power of enduring very great toil
is principally due to the large amount of fat contained
in their daily food. Chamois hunters and other moun-
taineers take chiefly bacon and eugar by way of pro-
vision on their laborious expeditions. Experience has
taught them that these highly carboniferous com-
pounds are especially suited to enable them to accom-
plish great labour. Sugar is especially suitable for
the purpose, because, being very readily soluble, it

8(5 rilYSIUl.oiiY OF MUSCLES AND NERVES.

pusses rapidly into the blond, and is, therefore, espe-
cially capable of rapidly replacing the expended forces.
Ii i> not suit, ill].' for ;i sole or main food material duriii"-

&

long periods, because when, a great quantity of sugar
i- introduced into tin- stoiuaeli it is transformed into
laetie arid and the digestion is injured.

5. When muscles have lain by for some time after
their extraction from the body, a change occurs in them
which deprives them of their capacity for contracting
when irritated. This change intervenes yet more
rapidly when they are induced to pass into a state of
activity by many repeated irritations. The time neces-
sary for the intervention of this change varies much,
and depends chiefly on the nature of the animal and on
the temperature. The muscles of mammals in a tem-
pi-rature such as that of an ordinary room lose their
power of contraction in as little as from twenty to
thirty minutes; the muscles of frogs do not lose this
power for several hours, and some from the calf-muscle of
a frog have been observed to pulsate even for forty-eight
hours in the temperature of an ordinary room. At a
temperature of from 0° to 1° C. the same muscle may
retain its power of contraction even for eight days. On
the other hand, in a temperature of, or above, -4,1 . the
contractile power is lo.-t in a Jew minutes. Kxact ly
the same happen.- in mu.-eles yet remaining within the
liodv »f the animal if the blood-current ceases to pa>s
through the body, either because of the death of the
animal, or in e<Mi><-i|uence of the local application of
ligatures to the vessels. This loss of contractile po\\er
is spoken of as the <//•(//// of the muscle. ^Muscular
death does not, therefore, correspond jn time with the
general death of the \\ hole animal, but it follows this

DEATH OF THE MUSCLE. 87

general death at a period varying from thirty minutes
to several hours.

6. On looking at the dead muscle of a frog it will be
noticed that its appearance differs essentially from that
of a fresh muscle. It does not appear so transparent, is
much duller and whiter in colour ; at the same time it
feels harder, less elastic, but is capable of greater ex-
tension, and, finally, it is tender and easily torn apart,
the more so the further the change has proceeded. Ex-
actly similar changes affect the muscles of a dead body.
This is called the death-stiffening (rigor mortis). E. du
Bois-Reymond showed that on the occurrence of this
death-stiffening the original alkaline or neutral reaction
gives place to an acid reaction. This is probably due to
the transformation of the neutral -glycogen and inosit
into lactic acid, which with the alkalis present forms
acid-reacting salts. This change is the cause of the
fact that butcher's meat, which remains hard and tough
if it is cooked directly after death, becomes gradually
more tender. If the meat is allowed to lie for a time
after death, the death-stiffening again relaxes, the sepa-
rate bundles of fibres no longer adhere so firmly to
each other ; and when in this condition the meat is
better adapted for preparation as food, because it is
tender and may be more easily chewed, and because
it offers less resistance to the digestive juices.

The death-stiffening in its chemical nature, there-
fore, bears a certain resemblance to the changes which
occur during the activity of the muscle. In the latter
case also an acid is formed, which is, however, again
eliminated and carried away by the blood. In the death-
stiffening this elimination cannot occur, the circulation
of the blood having ceased. For this reason death-

N-i rilYSIOLOCY 01- MUSCLKS AND NKKVES.

stiffening int» rveues much more quickly in muscles
which have been strongly irritated before death, as for
instance iu those of hunted animals. But while the
formation of acid must always be very slight in active
muse].-, it increases greatly in muscles which have un-
dergone death-stiffening, and the acid acts as a relax-
i;ig agent on the connective tissue which holds the
fibres together, so that the laiier separate more readily.
At the same time, however, another distinct change
occurs within the muscle-fibre. If a fresh living muscle-
tiluv ;nid one that has undergone death-stiffening are
examined under the microscope, the latter appears dull
and opaque ; the transverse striations are narrower and
approach more nearly together, and the contents are
not active and fluid, as in the living fibre, but are fixed
and broken into fragments. When unext ended muscles
undergo death-stiffening, they usually become shorter
and thicker. In the mobile facial muscles of a dead
body the result of this is that the lines, which imme-
diately after death were relaxed, again acquire a certain
expression. The death-stiffening of the muscles is the
cause <if a certain rigidity in the limbs of corpses, so
that, the limbs are retained in the same relative posi-
tion in which they were at death; and it is to this
circumstance that the name s death-stiffening ' (rigror
mortis) is principally due. .Moreover, this change does
not occur simultaneously in the muscles of all parts of
the dead body; it usually begins in the muscles of the
lace and neck and passes gradually downward, so thai
the muscles of the legs are the last to lie a Heeled by
it. The relaxation of the rigidity takes place in the
game <>rd<T.

On account of the slioriening undergone by muscles

DEATH-STIFFENING. 89

during death-stiffness it was formerly believed that the
latter was to be regarded as a true contraction, as a last
exertion of muscular force in which the muscle took
leave of its peculiar capacity. There is, however, nothing
to show that this shortening which takes place at death,
and which may moreover be hindered by the application
of even a slight weight, corresponds in any way with
the real state of activity. All the phenomena of mus-
cular rigidity are, indeed, more fully explained by the
assumption that some constituent part of the muscle
which is liquid in the living muscle becomes fixed or
coagulates. Death-stiffening would accordingly be a
process analogous to the coagulation of the blood, which
after death or after it has been allowed to escape from
the blood-vessels becomes firm, in consequence of the
fact that one of its constituents, the blood fibrous matter,
or fibrine, secretes itself as a solid. This view of death-
stiffness was first expressed by E. Briicke and was after-
ward confirmed by Kiihne. If the muscles of a frog are
freed from all blood by injection with an innocuous
fluid, such as a weak solution of common salt, and are
then pressed, a fluid is obtained which represents part
of the liquid contents of the muscle-fibres. If this fluid
is allowed to stand for some hours in the ordinary tem-
perature of a room, a flaky clot forms in it at the same
period at which other muscles of the same animal
undergo death-stiffening. The expressed muscle-fluid
is originally quite neutral ; but while the clot is forming
it becomes continually more acid. The resemblance of
the process in this muscle-fluid to that in the muscle
itself is, therefore, such as to justify the assumption
that at the same time a coagulation, simultaneously
with an acid-formation, takes place within the muscle

90 PHYSIOLOGY OF MUSCLES AM) NERVES,

itself, mid that this cna^ulal ion repiv-eiit- the e-seutiaJ
'act in ilcath-st itVening.

Death-stiffening intervenes. as \\v found, earlier
in ]ii-oj)orlion a- tin- tcmj). -rat ure is higher. Kxactly
the same is the case in expressed muscle-thud. If it
is heated to a temperature of 45° C. it coagulates
in a fe\v minutes, becoming acid at the same time.
Muscles also, if they are heated to a temperature of

45° C., undergo death-stiffening in a few minutes. If

they are still further heated, up to or above a temj e-
rature of 73° C., they contract into shapeless lump-,
become quite hard and white, and exhibit a firm solid
tissue re-emblin^ the white of eggs when cooked.
lY'iin this it may be inferred that, besides the matter
which coagulates during the death-stiffening, other
soluble albuminous bodies are also present in muscle,
ami that these act as ordinary albumen as it occurs in
blood and in e^gs ; for the latter also coagulates when
heated to 73° C. It therefore appears t hat various kinds
of albumen occur in muscle. That which coagulates
at 45°, or, though somewhat more slowly, in the or-
dinary temperature of a room, is called myo.-in. It
mav be assumed that this albuminous body is natu-
rally soluble, but that it is rendered in>oluhle by tin-
acids occurring \\ithin the mu-cle. Death-stiffening
would accordingly be the result of the formation of
acid. Our knowledge on this point K however, yet

very incomplete, and mu>t remain so until chemistry

ha- afforded more full explanation of the nature of
albuminous boilies.

CHAPTER VI.

1. Forms of muscle ; 2, Attachment of muscles to the bones; 3.
Elastic tension ; 4. Smooth muscle-fibres ; 5. Peristaltic mot ion;
6. Voluntary and involuntary motion.

1. Tn examining the action of muscle in the previous
chapters we have invariably dealt with an imaginary
muscle the fibres of which were of equal length and
parallel to each other. Such muscles do really exist.
but they are rare. When such a muscle shortens, each
of its fibres acts exactly as do all the others, and the
whole action of the muscle is simply the sum of the
separate actions of all the fibres. As a rule, however,
the structure of muscles is not so simple. According
to the form and the arrangement of the fibres, anatomists
distinguish short, long, and flat muscles. The last-
mentioned generally exhibit deviations from the ordinary
parallel arrangement of the fibres. Either the fibres
proceed at one end from a broad tendon, and are directed
towards one point from which a short round tendon
then effects their attachment to the bones (fan-shaped
muscles) ; or the fibres are attached at an angle to a
long tendon, from which they all branch off in one
direction (semi-pennate muscles), or in two directions
like the plumes of a feather (pennate muscles). In the
radiate or fan-shaped muscles the pull of the separate
parts takes effect in different directions. Each of these

02 PHYSIOLOGY OF MUSCLES AND MIKVKS.

p:iris may act separately, or all may work together; and
in the latter case they combine their forces, as is inva-
riably the casewith forces act in- in different directions,
in accordance with tlie so-called parallelogram of forces.
As an example of tins sort of muscle the elevator of the
upper arm — which was before alluded to in the second
chapter, and which on account of its triangular shape is
called the deltoid muscle — may be examined. Contrac-
tions of the separate parts really occur in this. When
only the front section of the muscle contracts, the arm is
rai-cd and advanced m the shoulder socket; when only
the posterior part of the muscle contracts, the arm is
raised backward. When, however, all the fibres of the
miiM-le act iii unison, the action of all the separable forces
of tension constitute a diagonal which results in the
lifting of the arm in the plane of its usual position.

In some semi- pen nate and pennate muscles the line of
union of the two points of attachment does not coincide
with the direction of the fibres. When the muscle con-
tracts each fibre exerts a force of tension in the direct i< >n
of its contraction. All these numerous forces, however,
produce a single force which acts in the direction in
which the movement is really accomplished, and the
whole action of the muscle is the sum of these separate
components, each derived from a single fibre. In
order to calculate the force which one of these muscles
can exert, as well as the height of elevation proper to
it, ii would be necessary to determine the number of
the fibres, the an*_dc \\hidi each of these makes, with
the direction finally taken by the compound action. EU9
\\ell a> t he length of the filuvs these not being alwavs
equal. This task if only carried oul in the case of a single
muscle would be a very greal te.-t of patience Fortu-

ATTACHMENT OF MUSCLES TO BONES. 93

nately no such tedious calculations are requisite for our
purpose. The force may be directly determined by ex-
periment in the case of many muscles, by the method
already described in Chapter IV. § 6 ; the height of
elevation possible under the conditions present in the
body may be yet more easily found ; and as regards the
work which the muscle is able to perform, it makes no
difference whether the fibres are all parallel and act in
their own direction, or if they form any angle with the
direction of work.1

2. The direction in which the action takes effect
does not, however, depend only on the structure of the
muscle, but chiefly on the nature of its attachment to
the bone. Owing to the form of the bones and their
sockets, the points of connection by which the bones
are held together, the bones are capable of moving only
within certain limits, and usually only in certain direc-
tions. For instance, let us watch a true hinge-socket,
such as that of the elbow, which admits only of bending
and stretching (cf. ch. ii. § 4). As in this case, the
nature of the socket is such that motion is only possible
in one plane, the muscles which do not lie in this plane
can only bring into action a portion of their power of
tension, and this may be found if the tension exercised
by the muscle is analysed in accordance with the law
of the parallelogram of forces, so as to find such of the
component forces as lie within the plane.

It is different in the case of the more free ball-
sockets, which permit movement of the bone in any
direction within certain limits. When a socket of this
sort is surrounded by many muscles, each of the latter,
if it acts alone, sets the bone in motion in the direction
1 See Notes and Additions, No 2.

94 PHYSIOLOGY OF MUSCL1> AM' NKKVES.

of its own action. If two or more of tin- muscles as-
sume a >tate nf act is it y at the same time, then the action

Will be the roultant <»f the separate tensions of cadi,
and this may also be found by the law of the parallelo-
gram of forces.

There is yet another way in which the work per-
formed by the muscles is conditioned by their attach-
ment to the bones. The latter must be regarded as
levers which turn on axes, afford id by the sockets.
They usually represent one-armed, but sometimes two-
armed levers. Now, the direction of the tension of
the muscles is seldom at right angles to that of the
nioveable bone lever, but is u-iially at an acute angle.
In this case, again, the whole tension, of the muscle
does not take effect, but only a component, \\hicli is at
ri^ht angles to tin- arm of the lever. Now, it H notice-
able that in many cases the bones ha\e projections
or protrusions at the point of the attachment of the
muscles, over which the muscle tendon passes, as over
a reel, thus grasping the bone at a favourable angle;
or, in other cases, it is found that cartilaginous or bony
thickenings exist in the tendon itself (so-called sesam-
oid bones), which act in the same way. The large>t of
these sesamoid bones is that in the knee, which, in-
serted iu the powerful tendon of the front muscle of
the upper thigh, gives a more favourable direction to
the attachment of this tendon than there \\oiild other-
\\ ise be.

Sometimes the tendon of a mux-le passes over an
actual reel, -o that the direction in \\ hich t he muscle-
tibres contract i- cut iivly diffei cut from that in which
their force of ten-ion acts.

3. The last important ( "ii-i ijnence of the attach-

ELASTIC TENSION. 95

ment of the muscles to the bones is the extension thus
effected. If the limb of a dead body is placed in the
position which it ordinarily occupied during life, and if
one end of a muscle is then separated from its point
of attachment, it draws itself back and becomes shorter.
The same thing happens during life, as is observable in
the operation of cutting the tendons, as practised by
surgeons to cure curvatures. The result being the same
during life and after death, this phenomenon is evi-
dently due to the action of elasticity. It thus appears
that the muscles are stretched by reason of their attach-
ment to the skeleton, and that, on account of their elas-
ticity, they are continually striving to shorten. Now,
when several muscles are attached to one bone in such
a way that they pull in opposite directions, the bone
must assume a position in which the tension of all the
muscles is balanced, and all these tensions must com-
bine to press together the socketed parts with a certain
force, thus evidently contributing to the strength of the
socket connection. When one of these muscles con--
tracts, it moves the bone in the direction of its own
tension, but in so doing it extends the muscle which
acts in an opposite direction, and the latter, because of
its elasticity, offers resistance to the tension exerted by
the first muscle, so that as soon as the contraction of
the latter is relaxed the limb falls back again into its
original position. This balanced position of all the
limbs, which thus depends on the elasticity of the
muscles, may be observed during sleep, for then all ac-
tive muscular action ceases. It will be observed that
the limbs are then generally slightly bent, so that they
form very obtuse angles to each other.

Not all muscles are, however, extended between

9G PHYSIOLOGY OF Ml >n.ES AND NERVES.

bones. The tendons of some pass into soft structures,
such as the muscles of the face. In this case also the
different muscles exercise a mutual power of extension,
though it is but slight, and they thus effect a definite
balanced position of the soft parts, as may be observed
in the position of the mouth-opening in the face. If
the tension of the muscles ranged on both sides is not
equal, the mouth opening assumes a crooked position.
This happens, for example, when the muscles of one
half of the face are injured ; and it thus appears that in
this case the elastic tension is too weak to allow of the
retention of the normal position of the mouth.

In muscles attached to bones the elastic tension is,
however, much greater, a circumstance which natural 1 v
exercises an influence on their action during contrac-

O

tion.

4. As yet attention has only been paid to OIK; kind
of muscle-fibre, that which from the very first we dis-
tinguished as striated fibre. There is, however, as ue
have seen, another kind, the so-called smooth muscle-
fibre. These are long spindle-shaped cells, the ends of
which are frequently spirally twisted, and in the centre
of which exists a long rod-shaped kernel or nucleus.
Unlike striated muscle, they do not form separate mus-
cular masses, but occur scattered, <>r arranged in more
or less dense layers or strata, in almost all organs.1
Arranged in regular order, they very frequently form
widely extending membranes, especially in such tube-
shaped structures as the blood-vessels, the intestine,

1 An instance of a C"nsidi-rahl«: accumulation of Miionth musi-lc-
til.n a i> atli'nli-d by the muscle-pouch of birds, which, with the ex-
ception of the outer and inner skin coverings, consists solely of
fibres collected in extensive layers.

SMOOTH MUSCLE-FIBRES.

97

£<?., the walls of which are composed of these smooth
muscle-fibres. In such cases they are usually arranged
in two payers, one of which consists of ring-shaped fibres
surrounding the tube, while the other consists of fibres
arranged parallel to the tube. When, therefore, these
muscle-fibres contract, they are able both to reduce

Fro. 25. SMOOTH MUSCL.E-FIBIJKS (300 TIMES ENLARGED).

the circumference, and to shorten the length of the
walls of the tube in which they occur. This is of great
importance in the case of the smaller arteries, in which
the smooth muscle-fibres, arranged in the form of a
ring, are able greatly to contract, or even entirely to
close the vessels, thus regulating the current of blood
through the capillaries. In other cases, as in the in-
testine, they serve to set the contents of the tubes in
motion. In the latter cases the contraction does net

98 PHYSIOLOGY OF MUSCLES AM) NKRVKS.

take place simultaneously throughout the length of the
tube; but, commencing at one point, it continually
propagates itsdf' along fivsh lengths of the tube, so thai
the contents an- slowly driven forward. The principal
agents in this are the circularly arranged fibres, which
atone point completely close the tube, while, bv the

< traction of the longitudinal fibres, the wall of the

tube is drawn back over its contents, thus providing for
the propulsion of the contents. This is called peri-
sf, i/t',c Hill/inn. It takes place along the whole of the
digestive canal, from the throat to the other end, and
in this ca-e affects the forward motion of the food, as
aUo, finally, the expulsion of the undigested re-idue.

5. Peristaltic motion may be very well observed by
laying bare the throat of a dog, and then placing water
in the mouth of the animal, so that the motion of swal-
lowing takes place. It may also be seen in the intes-
tines when laid bare, as also in the urinary duct, in
which each drop of urine leaving the kidneys produces
a wave which propagates itself from the kidneys to ihj
urinary bladder. Such movements may also be artifi-
cially elicited by mechanically or electrically irritating
some one point of the intestine, urinary duct, or other
>uch part, or by irritating the nerves appropriate to
these parts. The most striking feature is the slowness
with which these motions take place. No| only does a
Long time, observable without any artificial aid, elapse
after the application of (he irritant be lore the motion
begins, bui, even if tin- irritation is sudden and in-
stantancoii-, the motion excited ;it one point passes
along very gradually, idowly increa-ing up to a definite
point, and then again gradually decreasing. This slow-
ii' ss of motion es>entially distinguishes sniooih from

PERISTALTIC MOTION. 99

striated muscle-fibres. But, as we know, this is not a
distinction of kind, but only one of degree; for we
found that in the case of striated muscle also there is
a stage of latent irritation, then a gradually increas-
ing, and then again a gradually decreasing contraction.
But that which in striated muscle occupies but a few
parts of a second, in smooth muscle-fibres occupies a
period of several seconds. No artificial aid is, there-
fore, required in this case to distinguish the separate
stages. At present, research into the nature of smooth
muscle-fibre has not resulted in the acquirement of more
than this somewhat superficial knowledge. Owing e^p?-
dally to the difficulty of isolating the fibres, and to the
rapidity with which they lose their irritability when
separated from the body, it is very difficult to experi-
ment with them. It is especially not yet clear by what
means the transference of the irritation arising at one
point to the other part is effected. The transference
never occurs in the case of striated muscle. If a long,
thin, parallel-fibred muscle is separated out on a glass
plate, and a very small part of it is then irritated, the
irritation immediately propagates itself in a longitudinal
direction in the muscle-fibre immediately touched. It
is impossible to produce contraction in a striated muscle-
fibre only at one point in its length, at least while the
muscle-fibre is fresh. In dying muscle-fibres such local
contractions do indeed occur. Each separate muscle-
fibre, therefore, forms a closed whole in which the con-
traction excited at one point spreads over the whole
fibre. The speed with which it spreads within the
fibre has even been measured. As the striated muscle-
fibre in contracting becomes also thicker, a small light
lever, if attached to the fibre, is somewhat raised.

100 HIYSIOLOGY OF Ml'SCLES AND NERVES.

and this, rise can be indicated on a rapidly-moving

mvograph plate. If two of these small levers are
placed near the ends of a long muscle, and one of the
ends is then irritated, the nearer lever is first raised,
the more remote not till later. This •litter, aee may be
read off the plate of the myograph, and thus the
>|tecd of the propagation from one lever to the other
may be calculated. Aeby, who first tried this experi-
ment, found that the speed was from one to two metres
in the second, or, in other words, that a contraction
excited at one point of a muscle-fibre requires a period
of from about TT^ to -fo of a second to advance one
centimetre. More recent measurements by Bernstein
and Hermann show the higher value of from three to four
metres in the second, ^n the death of the muscle,
t he rate of propagat ion becomes r,,nt inually less, finally
ceasing entirely in muscles which are just about to pa —
into a state of death-si iff ue->. so that on irritation only
a slight thickening is seen at the point directly irritated,
and this does not propagate it.-elf. Under all circum-
stances, however, the excited contraction is confined to
the fibres which are themselves actually irritated, the
neighbouring fibres remaining perfectly quiescent. In
smooth miiscle-Jibres, however, it is found that tin-
contractions excited at one p"int propagate themseho
in (he adjacent fibres also. The marked distinction
which thus appears to exist between smooth and striated
nm-cles \\ould, it is true, di-appear if the views of
Kngelmann, resulting fr»m his >t udy of the urinary
dift, are continued. According to that writer, the
mu-cular ma-s of the urinary duct does not COnsisj
during life of separate mu-de-libre cells, but forms
a homogeneous connected mass \\hidi only separate-

VOLUNTARY AND INVOLUNTARY MOTION. 101

into spindle-shaped cells at death. If this view could
also be extended to the smooth muscle masses of other
parts, a real connection would exist throughout the
muscle-membranes, and the phenomena of the propaga-
tion of irritation would admit of a physiological explana-
tion.

6. As a rule, such parts as are provided only with
smooth muscle-fibres are not voluntarily movable, while
striated muscle-fibres are subject to the will. The latter
have, therefore, been also distinguished as voluntary,
the former as involuntary muscles. The heart, however,
exhibits an exception, for, though it is provided with
striated muscle-fibres, the will has no direct influence
upon it, its motions being exerted and regulated inde-
pendently of the will.1 Moreover, the muscle-fibres of
the heart are peculiar in that they are destitute of sar-
colemma, the naked muscle-fibres directly touching each
other. This is so far interesting that direct irritations,
if applied to some point of the heart, are transferred
to all the other muscle-fibres. In addition to this,
the muscle-fibres of the heart are branched, but such
branched fibres occur also in other places, for example,
in the tongue of the frog, where they are branched like
a tree. Smooth muscle-fibres being, therefore, not sub-
ject to the will, are caused to contract, either by local
irritation, such as the pressure of the matter contained
within the tubes, or by the nervous system. The con-
tractions of striated muscle-fibres are effected, in the
natural course of organic life, only by the influence of

1 Striated muscles also occur in the intestine of the tench
(Tinea vulgaris), which in this differs from all other vertebrate ani-
mals. It is doubtful whether this tissue ?s capable of voluntary
motion, but it is very improbable.

lit.! PHYSIOLOGY OF MtX'LKS AND NERVES,

tin- nerves. We must now, therefore, examine the
characters of nerves, after which we shall try to explain
the nature of their influence on muscles.

It must also be observed that the distinction between
striated and smooth muscle-fibres is not absolute; for
there are I ransitionary forms, such as the muscles of
molluscs. The latter consist of fibres, exhibiting to
some extent a striated character, and, in addition to
this, the character of double refraction. At these points
the disdiaclasts are probably arranged regularly and in
large groups, while at other points (as in true smooth
muscle-fibres) they are irregularly scattered and are
therefore not noticeable.

CHAPTER VII.

1. Nerve-fibres and nerve-cells; 2. Irritability of nerve-fibre;
3. Transmission of the irritation ; 4. Isolated transmission ;
5. Irritability ; G. The curve of irritability ; 7. Exhaustion and
recovery, death.

1. In the body of an animal nerves occur in two forms :
either as separate delicate cords which divide into many
parts and distribute themselves throughout the body,
or collected in more considerable masses. The latter,
at least in the higher animals, are enclosed in the bony
cases of the skull and vertebral column, and are called
nerve-centres, or central organs of the nervous system ;
the nerve-cords pass from these centres to the most
distant parts, and are spoken of as the peripheric nerve-
system. When examined. under the microscope these
peripheric nerves are seen to be bundles of extremely
delicate fibres united into thicker bands within a mem-
brane of connective tissue. Each of these nerve-fibres
when examined in a fresh state, and enlarged 250 or
309 times, is exhibited as a pale yellow transparent
fibre in which no further differentiation is visible. The
appearance of the fibre soon, however, changes ; it be-
comes less transparent, and a part lying along the axis
becomes marked off from the circumference. This inner
part is usually flat and band-like, and when seen under
a higher power exhibits a very minute longitudinal

104

PHYSIOLOGY OF Ml'SCLKS AND M'.KVKS.

striation, as though it were formed of very delicate
fibrillnp, or small tilnvs. It is called the a.i-is-lxi n<L < <r
(/o'x-rv// /»/'•'•. The outer part li;is a crumpled appear-
ance, and oo/es at the cut ends of the nerve in drops
which soon coagulate; it is called the medullary, or
marrow-she ith. The medullary sheath entirely sur-
rounds the axis-cylinder; as, however, when in a fresh,

nncoagnlated condition, it re-
fracts light in exactly the same
way as the axis-cylinder, it
is undistinguishable from the
latter, nor do the two become
really separately visible till
after the conn- Ration of the
marrow. The medullary-
sheath and the axis-cylinder
are further enclosed in a
tough elastic tube, which is
called the neurilemma or
nerve-sheath.

These three parts are not
present in all peripheric

Q . , ,

Some of the latt.'l

metjul];iry <!,,.;,,],,

and are, therefore, avi>-cylinders immediately sur-
rounded by the nerve-sheaths. When many nerve-
liln-es are united into a bundle, these marrowless fibres
are ^r rev and more t ransjiarent, and ;,re therefore some-
times called grev ner\c-libres. Those nerve-tibres which
have medtillarv sheaths appear more yellowish white. If
the nerves are traced to the periphery, more and more
nerve-fibres are continually found to branch off from
the common stem, so that the branches ami brailchlets

FIG. -2.;. NKI:VI:

a a «,, axte-cylinder, still parly

Bnirounded by the medullary flheath.

NERVE-FIBRES AND NERVE-CELLS. 105

gradually become thinner. At last only separate fibres
are to be seen, these being, however, still in appearance
exactly like those constituting the main stem. Such
fibres as up to this point have had medullary sheaths
now frequently lose them, and therefore become exactly
like grey fibres. The axis-cylinder itself then some-
times separates into smaller parts ; so that a nerve-fibre,
thin as it is, embraces a very large surface. The ends of
the nerve-fibres are connected sometimes with muscles,
sometimes with glands, and sometimes, again, with
peculiar terminal organs.

In the central organs of the nervous system many
nerve-fibres are found which are in appearance in-
distinguishable from those of the peripheric system.
There are fibres with axis-cylinder, medullary sheath,
and neurilemma, others without medullary sheath, and,
finally, others in which no neurilemma can be detected,
and which may therefore be described as naked axis-
cylinders. But,, besides these, very delicate fibres, far
finer than the axis-cylinders, occur. The central organs
of the nervous system are however especially marked
by the abundant occurrence of a second element, which,
though it is not altogether unrepresented in peripheric
nerves, yet is only found in the latter distributed in a
few places, whilst in the central organs it constitutes
an important portion of the whole mass. This consists
of certain cell-like structures called nerve-cells, or gan*-
glion-cells. In each ganglion-cell it is possible to dis-
tinguish the cell body, and a large kernel (nucleus')
within this ; within the kernel, a smaller kernel (nu-
deolus) may also frequently be distinguished. Some
ganglion-cells are also surrounded by a membrane
which occasionally passes into the neurilemma of
G

106

OF MI'SCI.I- AM> M-:i;\ KS.

nerve-fibres, which are connected \\itli tin- cell. The

kernel is finely Lrranulated and is composed of a pn>-

topla-mie mass, \vliicli, uhen
heated, or subjected to certain

other influences, becomes dull

nnd opaque, but which iii a fiv-h
condition is usually somewhat
transparent. The form of the
ganglion-cells is very variable.
Sometimes they appear almost
globular; in other cases they
are elliptic; others, a^ain, an-
irregular, ])i-o\ided with numer-
ous offshoots. Mo- 1 M-;I 11 o'l ion-
cells have one -,r more project-
ing pp C( SSi : -OIMC are. indeed,
found without processes, but it
is certain that this condition is
merely artificially produced, tin-
processes having been torn oft'
during the preparation of the
ganglion -cell. ( ranglion- cells
are oeea>ioiially insert efl in the

cour.-e of the lier\f-tibre-, SO
that the ])roce>-es dit't'er in no
wav from other ner\ e-fibres, as
Is shown in fig. 27. In the^au-
glion-cells of the dorsal marrow,
\\hich ha\e manv iiroee-- .

IM... 27. <: VNOLION-l ELL8

WITH SKRVB-PHOCKS8E8. some OI these a|)pear exactly

like the l'e>t of tll<' Cell body -

that is to say, they are finely u-ranulated; these are
called protopla>mic processes. On the other hand, in

NERVE-FIBRES AND NERVE-CELLS. 107

almost every cell a process may be distinguished which
is altogether distinct in appearance from the rest. The
protoplasmic processes become gradually finer and sepa-
rate into more parts, and the processes of neighbouring
cells are partly connected together. But the one pro-
cess which is distinguishable from the rest passes along
for a certain distance as a cylindrical cord, and then,
suddenly becoming thicker, it encases itself in a me-
dullary sheath, and in appearance entirely resembles
the medullary fibres of the peripheric system. It is
extremely probable, although it is hard to prove it with
certainty, that a fibre of this sort passing out of the
dorsal marrow is directly transformed into a peripheric
"nerve-fibre, while the protoplasmic processes continu-
ing on their course within the central organ serve to
connect the ganglion-cells.

The nerve-system, the main parts of which we have
thus roughly examined, effects the motions and sensa-
tions of the body. These qualities belong, however,
mainly to the central parts, in which ganglion-cells
occur. The peripheric nerve-fibres act merely as con-
ducting or transmitting apparatus to or from the
central organs. Before examining the peculiar action
of the central nervous system, it is desirable to devote
some attention to this conducting apparatus and to dis-
cover its nature.

2. On exposing one of the peripheric nerves of a
living animal and allowing irritants to act upon this,
in the way which was described in the case of muscles,
two effects are usually observable. The animal suffers
pain, which it expresses by violent motion or cries, and,
at the same time, individual muscles contract. On
tracing the irritated nerve to the periphery, it will be

108 PHYSIOLOGY OF MUSCLES AND NEKVF-.

found tliat certain of its fibres unite with those muscles
which pulsated. We already know that the other end

of the lierve is connected with tile nerve-cent l'c. If

the nerve is cut at a point between the irritat.-d
spot and the nerve-centre, the niusoular pulsation
occurs as before on the re-application of the irritant,
but the sensation of pain is al»eiit. If, on the other
hand, the nerve is cut at a point nearer the periphery,
no muscular pulsation results from irritation, but pain
is felt. It thus appears that the peripherie nerves,
when irritated at any point in their course, are able to
e.iuse etVe.-ts both at their central and peripherie ends,
provided that the conductive power of the nerves re-
mains uninjured in both directions. This enables us
to study more closely the action of the nerves on the
muscles, bv extracting and preparing a portion of the
nerve with its mu<c|e. in an uninjured condit ion. and
then subjecting this nerve to further research.

That a nerve is irritable, in the same sense as we
found that the muscle was, is already shown by these
preliminary experiments. But while it was possible
to observe the effects of the irritation on the muscle
directly, the nerve does not exhibit any immediate
change, either in form or appearance. Kven under the
strongest microscopic power nothing is discernible, and
it would be impossible to know if a nerve is in any way
irritable if the muscle which occurs at one end of it
did not show by its pulsation that some change must
have occurred within the ner\c. The muscle is there-
fore used as a re-agent to test the changes in the nerve
itself. The requisite experiments may be either \\ith
warm-blooded or \\ith cold-bl.ioded animals. As. how-
ever, the muscles of warm-blooded animals, \\hen with-

IRRITABILITY OF NERVE-FIBRES. 109

drawn from the influence of the circulation of the blood,
soon lose their power of activity, the nerves and muscles
of frogs are preferable for these experiments. The
lower part of the thigh of a frog, with a long portion of
the sciatic nerve, which is very easily separable up to
the point where it emerges from the vertebral column,
is best suited for this purpose. In some cases it is
better to use only the calf-muscle with the sciatic
nerve ; the muscle must be fastened in the same way
as in the former experiments, and its contractions must
be made evident by use of a lever.

If the muscle, thus fastened, is pinched at any point
in its course it pulsates. The same result follows if a
thread is passed round the nerve, and the latter is thus
constricted, or if a small piece is cut from the nerve
with a pair of scissors. These are mechanical irrit-
ants which act on the nerve. Pulsation will, however,
also be seen if the nerve is smeared with alkaline
matter, or acid — these are chemical irritants. A por-
tion of the nerve may be heated ; that is, it may be
thermicallv irritated. In all these cases, the nerve at

tf

the point irritated, immediately, or, at least very soon,
loses its capacity for receiving irritation. But if the
nerve is placed on two wires, by means of which an
electric current is passed through one point in the
nerve, it may, in this way, be repeatedly electrically
irritated without its irritability being immediately de-
stroyed. It therefore appears that, in this respect, a
nerve acts exactly as does a muscle. If a constant
electric current is applied, the result is usually a pul-
sation on the closing and the opening of the current,
but sometimes a lasting contraction ensues while the
current flows through the portion of the nerve. If

110 PHYSIOLOGY OF MU.-C'LKS AM» MiKYKS.

inductive shocks an- applied, each separate >l.ock \>\-«-
duces a muscular pulsation, and if many separate in-
ductive shocks are applied to the nerve, the muscle
passes into a state of tetanus. These inductive shocks
must be applied to the nerve at some distance from
the muscle. Each inductive shock induces a muscu-
lar pulsation. On cutting the nerve with a pair of
scissors, between the point irritated and the muscle.
all influence upon the muscle ceases. It is useless to
place two cut surfaces together, even with the greatest
care; they may adhere, and the nerve, when super-
ficially examined, may appear uninjured, but irritants
applied above the point of section cannot act through
the nerve upon the muscle. The same thing occurs if
a thread, passed round the nerve, is drawn ti^ht be-
tween the point irritated and the muscle. The thread
may be removed, but the crushed spot proves an im-
passable barrier to all influence on the muscle. ]f,
however, the wires are moved and the inductive cur-
rents are applied to another point below the cut or the
constriction, the action at once recommences.

3. The conclusion to be drawn from these experi-
ments is, either that the nerve, even if only a small
portion of it is irritated, passes at once into an active
condition throughout its entire length as far as the
muscle, or that the irritant acts direct ly only on the
spot immediately irritated, and that the activity which
is excited in the nerve at this point propagates itself
alon^r the tihn-s until it reaches the muscle in which it
causes a contraction. It' the latter view is correct, it
must also he inferred that any injury to the nerve-fibre
prevents the propagation of the activity in the latter;
ami it may also be deduced from the experiments with

TRANSMISSION OF THE EXCITEMENT. Ill

the constricted nerves, that even if the nerve-sheath is
in no way injured, the crushing of the contents of the
nerve is in itself sufficient to prevent propagation of
the activity. It can be shown that this latter view
of the nature of the case is actually correct. For it is
possible to determine the time which elapses between
the irritation of the nerve and the commencement
of muscular pulsation. For this purpose the same
methods are applicable as we employed in the case
of muscles. Electric measurement of time, or the
myograph represented in fig. 17, may be used for this
purpose. As however in the present case the point to
be determined is, not the form of the muscle-curve,
but the moment of its commencement, duBois-Keymond
simplified the apparatus so that the curve is drawn on
a flat plate, which is pushed forward by spring power.
Fig. 28 represents the apparatus. It stands on a strong
cast-iron stand from which rise the two massive brass
standards A and B. A light brass frame carries the
indicating plate, which is of polished looking-glass,
1 60 mm. in length by 50 mm. in breadth. The frame runs
with the least possible amount of friction on two parallel
steel wires stretched between the standards. The dis-
tance between the standards is equal to twice the length
of the frame, so that the whole length of the plate passes
across the indicating pencil when the frame is pushed
from standard to standard. Bound steel rods are fastened
to the short sides of the frame ; and these rods in length
somewhat exceed the path along which the frame passes,
and they then pass, with as little friction as possible,
through holes in the standards A and B. The end b of
one of these rods is surrounded by a steel spring. By
compressing this between the standard B and a knob on

.11'

PHYSIOLOGY "!•' MCSCI.KS AND NKK\ I s.

t h< i Mil i >f the nx|, mid thus driving" the frame \\ it h the
rods from // to J. iu a direct j.m oppusitt1 to that, of the
arrow on the indicating jilate, a point is reached at
which the • trigger ' which is seen on the standard A ,
and which ;:cts upward, tits into a corresponding notch
in the rod at a, thus preventing the re-ext elision of the
spring. It therefore remains compressed till pressure

A

I I'.. -J>. Sl'lil.NO MvncKAril. AS I'SKD BY DC IJolS H I V M. >N i '.

Oil the trigger frees the frame, which then traverses the
whole length of the wires at a speed depending on the
strength of the spring, A.V.. in the direct i.m from .-1 to />',
that indicated by th<' arrow.

In order to dc>eril>e the muscle-pulsation on this
plate, side liy side uilh ,t t he;-e is a lever \\ith an
indicating pein-il, such as was u>ed iii the former ex-
periment , t« indicate the height of miix-iilar elevation

TRANSMISSION OF THE EXCITEMENT. 113

and the elastic extension (see fig. 8, p. 26). This part
is omitted in fig. 28, in. order to make the indicating
plate more visible. The rate at which the plate flies
from A to B at first increases up to the point at which
the spring exceeds the position in which it was when at
rest. When the frame is in the position corresponding
with this point, a projection d, which is situated on the
lower edge of the frame, strikes the lever h and thus
opens the main current of an inductorium, by which an
inductive current is caused in the secondary coil of the
inductorium ; and this traverses and irritates the muscle.
The result of this is that the muscle is irritated exactly
at the moment at which the glass plate assumes a
definite position relatively to the indicating pencil of
the lever. If the glass plate is first pushed toward A, and
is then slowly pushed toward 5, until the projection d
just touches the lever, and if the muscle is then caused
to pulsate, the indicating pencil, being raised by the
pulsation, describes a vertical line, the height of which
represents the height of elevation of the muscle. If
the glass plate is again brought back to A, and, by
pressing the trigger, is then caused to fly suddenly and
with great speed toward B, then the irritation of the
muscle will occur when the glass plate is in exactly the
same position, the indicating pencil standing exactly
at the vertical stroke before described. The muscular
pulsation thus produced will, however, in this case be
indicated on the rapidly moving glass plate, with the
result of giving, not a simple vertical stroke, but a
curved line. The distance of the point of commence-
ment from the vertical stroke expresses the latent
irritation.

If, instead of irritating the muscle itself, a point

114 PHYSIOLOGY (>F Ml SCLF.S AND .NKKV1-.

in tin' nerve i- exposed to the irritation. (I,,- muscle in
thi< case also describes tin- curve of its pukition ,,n

tin- rajiidly mo\ ed plate of tin- myograph. Arranging
matters BO thai two curves of pulsation arc allowed
to describe thenisi'lve- in immediate sequence, hut with
the dil'i'ereiice that the nerve is irritated in one case at
a point near the muscle, but in the other case at a
point far from the muscle, two curves will lie obtained
on the plate of the myograph, which will appear ex-
actly alike but yet will not cover each other. On the
contrary, they are everywhere somewhat separated
from each oti;"r, as is shown in figure 29. l In this

0 ll "

I 10. •_".'. PROPAGATION or THE Kxrm.MF.XT WITHIN M i:\ I:R.

figure, a b c is the curve lirst described, on irritation
of the nearer portion of the nerve; in order to dis-
tinguish it from the other it is marked by small nicks;
a' b' c' represent s t he curve indicated immediately after
the former, but obtained as the result of the irritation
of a port ion of the nerve remote from the muscle. The
ond curve is seen to lie somewhat separated from the
other; it does not commence so soon after the moment
of irritat ion ( \\hich i> indicated by the vertical stroke o r.
that i<. a longer time elap-ed bet \\ ecu t lie moment of

1 Tin- curves in \\'-r. '-".' \\ • 'liin •<} \\lim tlic glass \

mn\ri| niori- r;i|ii«lly. so lli:il ll.ry :\\-\ i'.ir ninrc rxicmlrd than Ihi'.-t:
in li'j ni'i- 1 s.

TRANSMISSION OF THE EXCITEMENT. 115

irritation and the pulsation of the muscle in the latter
case than in the former ; and this difference evidently
depends only on the fact that in the latter case the
excitement within the nerve had to traverse a longer
distance, and therefore reached the muscle later, so
that the pulsation did not begin till later.

This 'time may be measured, if the rate at which
the plate moved is known ; or if simultaneously with
the muscle-pulsation the vibrations of a tuning-fork
are allowed to indicate themselves on the plate. From
the time thus found and from the known distance
between the two irritated points of the nerve, the rate
at which the excitement propagates itself along the
nerve may be calculated. Helmholtz, on the ground
of his experiments with the nerves of frogs, found it to
be about 24 m. per second. It is not, however, quite
constant, but varies with the temperature, being greater
in higher and less in lower temperatures. It has also
been determined in the case of man. If the wires of
the inductive apparatus are placed on the uninjured
human skin, it is possible, as the skin is not an isolator,
to excite the underlying nerves, especially where they
are superficially situated. On thus irritating two points
in the course of the same nerve, the resulting pheno-
mena are exactly the same as those just observed in the
case of the nerves of frogs. In order to determine the
commencement of the muscle pulsation in the un-
injured human muscle, a light lever is placed on the
muscle in such a way that it is raised by the thickening
of the latter. Experiments of this kind were made by
Helmholtz with the muscles of the thumb. The appro-
priate nerve (n. medianus} may be irritated near the
wrist and near the elbow. From the resulting difference

JIG PHYSIOLOGY OF ML'SCLKS AND NERVES.

in time and from the distance between the two irritated

{'••hits the rate of propagation of tlie excitement was
found to be 30 in. per second. The high figure ;is com-
pared \vith that found with the nerves of frogs i>

A O

plained l)y the higher temperature of human ner\es.
The rate of propagation would indeed be much lowered
if the temperature of the arm were considerably de-
creased by the use of ice.

The above calculation of the rate of propagation is
made OH the assumption that this rate is constant,
throughout its duration. There is, however, nothing
to show that this is the case. On the contrary, it is
more probable, that the propagation proceeds at first at
a greater and afterwards at a less speed. This may be
infern-d from an experiment arranged by H. IMunk. If
three pairs of wires are applied to a long nerve, one
close to the, muscle, another at the centre, and the
third considerably above, and then causing three con-
secutive curves to describe themselves on the mvo-
graph plate by irritating these three points, it will
be found that the three curves are not equally removed
from each other; on the contrary, the first and second
stand very near together, while the third is far from
the two former. More than double the time was re-
quired for the excitement to traverse the full distance
from the upper to the lower end than it took to traverse
the half-distance from the middle of the nerve to its
louer end. The simplest explanation which can be

given of this phenomenon is that t he excitement during

its propagation is gradual ly retarded, just as a billiard ball
moves al tirst very quickly bill afterward at a gradually
decreasing speed. The retardation of the billiard ball
is due to the friction of (he undcrl \ ing surface. From

ISOLATED TRANSMISSION. 117

this it may be inferred that a resistance to the trans-
mission exists within the nerve, and that this gradually
retards the rate of propagation. Such a resistance to
transmission is also probable on certain other grounds,
to which subject we shall presently revert.

4. If the main stem of a nerve is irritated by elec-
tric shocks, all the fibres are invariably simultaneously
irritated. On tracing the sciatic nerve to its point of
escape from the vertebral column, it appears that it is
there composed of four distinct branches, the so-called
roots of the sciatic plexus. These rootlets may be
separately irritated, and when this is done contractions
result, which do not, however, affect the whole leg but
only separate muscles, and different muscles according
to which of the roots is irritated. Now as the fibres
contained in the root afterward coalesce in the sciatic
nerve within a membrane, it follows from the experi-
ment just described that the irritation yet remains
isolated in the separate fibres and is not imparted to
the neighbouring fibres. This statement holds good of
all peripheric nerves. Wherever it is possible to irri-
tate separate fibres the irritation is always confined to
these fibres and is not transmitted to those adja-
cent. We shall afterwards find that such transmis-
sions from one fibre to another occur within the cen-
tral organs of the nervous system.' But in these cases
it can be shown with great probability that the fibres
not only lie side by side, but that they are in some
way interconnected by their processes. In peripheric
nerve-fibres the irritation always remains isolated.
Their action is like that of electric wires enclosed in
insulating sheaths. One of these nerves may indeed
be compared to a bundle of telegraph wires, which are

118 PHYSIOLOGY OF MUSCLES AM> NKRVES.

protected fnun direct contact with each other by gutta-
]>ereh;i or by some other substance. The comparison
i-. h«i\vever, but superficial. No electrically-isolating
membrane can really be discovered in any part of the
nerve-fibre, but all their parts conduct electricity.
When, as we shall presently find, electric processes
occur within the nerve, these standing in definite re-
lat ion to the activity of the nerves, we must assume that
isolation as it occurs in the nerves is not the same as
in telegraph wires. We cannot here trace the matter
further, but must accept the fact of isolated conduction
as such, reserving its explanation for a future occasion.
5. On irritating the nerves by means of currents
from an inductive apparatus, it is found that the pulsa-
tions which occur are sometimes strong, sometime>
weak. All nerves are not alike in this respect, and
even the parts of one and the same nerve are often
very different. We must accordingly suppose that
nrncs are variable in the degree in which they receive
irritation. This is spoken of as the excitability of the
nerve, to express the greater or less ease with which
they may be put in action by external irritation. T\\<>
ways may be adopted to measure the excitability of a
nerve or of a certain point in a nerve. Either the
same irritant may always be used, and the excitability
may be determined- by the strength of the muscular
pulsation evoked by this irritant; or the irritant mo.y
be altered until it just suffices to evoke a muscular
pulsation of a definite strength. In the former case
it is evident that the excitability must lie estimated
as higher in proportion as the muscular pulsation pro-
duced I iy the irritant is stronger; in the latter case
the exeitabilily is said to be greater in proportion

EXCITABILITY. 119

as the irritant which is able to evoke a pulsation of
definite strength is weaker. Each of these methods
when practically applied has advantages and disad-
vantages. The former is capable of detecting very
minute differences in the excitability, but it can only
do this within certain narrow limits ; for when the
excitability sinks, the limit for a definite irritant is
soon reached, after which no further pulsation at all
results ; and when the excitability rises, the muscle
attains its maximum contraction, above which it is
incapable of further contraction. Changes above or
below either of these limits are, therefore, beyond
observation so long as the irritant remains the same.
The best way to apply the second method practically is
to find that strength of irritant which exactly suffices
to produce a just observable contraction of the muscle.
This assumes the power of graduating the strength of
the irritant at pleasure. If inductive currents are used
to effect irritation, this graduation may be made with
the greatest precision by altering the distance between
the primary and secondary coils of the apparatus. In
du Bois-Reymond's sliding inductive apparatus, repre-
sented in fig. 13, p. 35, the secondary coil is, there-
fore, attached to a slide which may be moved forward
in a long groove. This arrangement is used in order
to find the particular distance of the secondary coil
from the primary which results in a just observable
contraction of the muscle ; and this distance, which
can be measured by means of a scale divided into
millimetres, is regarded as the measure of excitability.1
6. If a recently prepared nerve, as fresh as possible,
is placed on a series of pairs of wires, and the excita-
1 See Notes and Additions, No. 3.

120 PlIY.SlMl.'H.y OF MUSCLI> AM> NEBVES.

bility at the \ari. -us points of t he nerve is cou.-eciit i\ , 1 v
determined in tin- way described above, it is generally
found tliat tlir r\ritaliility of the upper j art of the
nerve is greater tliaii that of the lower. Ihnv is. how-
ever, no great ivniilant y in this charact <T. Sometime- a
point is found in the centre of the nerve which is Irss
irritalilr. than those immediately above and below it.
Vn-y fVr(|iirntly the most excitable point occurs, not
immediately at the cut end, but at some little distance
from this; so that, on proceeding downward, it is found
to increase at tirst, and then, at a yet ]o\\n- point, to
decrease again. If such a nerve is observed for some
little Him-, its excitability at the various points being
tested every five min ut es. it is found that the excita-
bility alters especially soon at the upper end : it de-
creases, and in a short time is entirely extinguished, so
that no muscular pulsations can afterwards he elicited
from the, upper parts even by the most powerful
currents. The nerve is then said to be dead in its
upper parts, and this death proceeds gradually down-
ward in the nerve, so that pulsations can only be
obtained by irritating tin- p.-m >itna!rd nr.-n-est the
muscle, and at a little later period even this part,
lircoino dead. After the \\holr nn-\r is drad, pul-
sations may yet always be olitained ibr a timr bv
direct irritation of thr muscle. The mnscU- dors not,
usually die until much later than the nervo Yet in a
(|iiite fresh preparation of the nerve and mn>i-|r. t he
Latter i- always less ex«-italile than the former, and
a much stiMii^er irritant is required to excite the
mii-elr diri'ctly, than indirectly through the n.-rve.

In all these experiments the oerve must lie ca re-
full \ protected from drying up, a> oilurwise ilsexcita-

CURVE OF EXCITABILITY. 121

bility is very soon destroyed, and in a very irregular
manner.

We have seen that the nerve dies gradually from
the top downward. This death does not, however,
consist in a simple falling off in the excitability from
its original degree till it completely dies out. If the
excitability is tested from time to time at a point some
distance from the cut end, it is found to increase at
first until it reaches a maximum, at which it remains
for some time stationary, and it is not till after this
that it gradually decreases and finally expires. The
further the point experimented on is from the point
which has been cut, the more slowly do all these
changes occur ; but their sequence is in all cases essen-
tially alike. The explanation of this may be that the
upper parts of the nerve, which directly after the pre-
paration is made usually exhibit the highest degree
of excitability, are really already changed. It must be
assumed that these changes intervene very quickly at a
point close to the section, so that it is impossible to
submit these points to observation until they are al-
ready in the condition which does not intervene till
later at the lower points — in the condition, that is, of
increased excitability. This view is confirmed by the
following experiment : if the excitability is determined
at a lower point of the nerve, and the latter is then cut
through above this point, the excitability increases at
the point tested, and this takes place more quickly in
proportion as the cut was made nearer to the tested
spot. Each of the lower points may, therefore, be
artificially brought under the same conditions under
which only the upper parts of the nerve usually lie,
that is, it may be arranged that they are near the

122 PHYSIOLOGY OK MUSCLES AM) NKKYF.S.

point of section. These changes in the excitability
may, then-fore, be thus conceived: tliat when the
nerve is cut smne influence makes itself felt from this
cut, and that this first increases the excitability of the
nerve, then decreases, and then extinguishes it. If
this view is right, we must assume that the high
degree of excitability of a freshly cut nerve is also
only the result of the incision which is made. This is
not, however, exactly the case. The nerve with the
muscle of a living frog may be freed and prepared up
I-, the vertebral column without separating it from the
dorsal marrow. On irritating the various points in such
a nerve, differences, slight indeed but yet observable,
are noticed in the excitability, the upper parts being
always more excitable than the lower. Uninjured
human nerves may also, as we have seen, be irritated
at various points in their course, and in this case also
it is found that irritation is invariably more ea-ily effec-
tive in the upper than in the lower parts.

rtliiger, who first called attention to the differences
of excitability at the various points of the nerve, thought
that the explanation of this is that the irritation evoked
atone point in the nerve, in propagating itself along
the nerve, gradually increases in strength; he spoke
of it as an <ir<tl<ni< /,<-/;/,•< i/ncreaae in tin- <•./•<•/'/< ,,,ent
WttJtiii //" iii'i'i'<>x. This explanation appears to contra-
diet the above-meiit ioiied fact as to the effect of cutting
on the nerve, for in such eases it appears that the irri-
tation is strengthened by the cutting away of the
higher portion of the nerve, even though the length of
that portion <>f (he n.Tve which is traversed by the.
irritation remains unaltered. It must at any rate be
admitted that at one and the same point in the nerve

DEATH OF THE NERVE. 123

the excitability may vary in degree, and it is therefore
simpler to assume that the difference in the results of
irritating the nerve at various points depends directly
on differences in the excitability at those points, instead
of being in the first place dependent on changes caused
by transmission ; it can even be shown to be probable
on various grounds, as indicated above, that the excite-
ment in propagating itself through the nerve meets
with resistance, and is therefore rather weakened than
strengthened. Why the excitability differs in different
parts of the same nerve we cannot explain. As long
as we are ignorant of the inner mechanism of nerve-
excitement, we must be satisfied to collect facts and to
draw attention as far as may be to the connection of
details, but we must decline to offer a full explanation
of these.1

7. The phenomena of exhaustion and recovery may
be exhibited in nerves as in muscles. If a single
point in a nerve is frequently irritated, the actions
become weaker after a time, and finally cease entirely.
If the nerve is then allowed to rest for a time, new
pulsations may again be elicited from the same point.
It is not known whether this exhaustion and recovery
corresponds with chemical changes in the nerve. We
are almost entirely ignorant of the whole subject of
chemical changes within the nerve. Some observers
maintain that in the nerve, as in the muscle, an acid
is set free during the active condition, but this is
denied by others. The generation of warmth in the
nerve during its activity has also been asserted, but
this is also doubtful. If any chemical changes do take
place within the nerve, they are extremely weak and
1 See Notes and Additions, No. 4.

v or MI .-ru-:s AM» M:I;\I

cannot lie shown with mil' present appliances. As

motions of the smallest particles (molecules) probably
take plaee iu the nerve, though the external form
remains unaltered, mid therefore no work worthy of
consideration is accomplished, it is ea>ilv intelligible
that the>e processes may be accompanied only by ex-
tremely slight changes in the constituent parts.

The speed with which death and the changes in
excitability connected with death take place mainly
depends, apart from the length of the nerve, on the
temperature. The higher the temperature the more
quickly does the nerve die. At a temperature of 44° C.
death occurs in from ten to fifteen minutes; at 75° C.
in a few -eeonds; and in the ayerage temperature of a
room the lower ends of a long sciatic nerve may re-
tain their excitability for twenty-four hours or longer
after extraction and preparation. Drying at lir.-t in-
creases the excitability, but a fterwards. rapidly deciva.-es
it. Chemical agents, such as acids, alkalis and salts,
destroy the excitability the more rapidly the more
concentrated they are. In distilled water the nerve
swells and rapidly becomes incapable of excitement.
There are, therefore, certain densities of salt solutions
in \\hich the nerve remains excitable longer than in
thinner or in more dense solutions. A solnt ion of com-
mon salt of 0-6 to 1 per Cent., for instance, has almost

llo effect on ;i l|er\e submerged ill it, and preserves the

excitability of this nerve about a- long as damp air.
I'ui'e olive oil, if not acid, may al-o be reganled as
innocuous. These are, therefore, u-, d when the in-
Iliiciiee of different temperatures on the nerve is to he-
studied.

CHAPTER VIII.

1 Electrotonus ; 2, Modifications of excitability : 3. Law of pulsa-
tions ; 4. Connection of electrotonus with excitability; 5. Trans-
mission of excitability in electrotonus; 6. Explanation of the
law of pulsations ; 7. General law of nerve-excitement.

1. It has already been observed that a constant elec-
tric current, if transmitted through the nerve, is able
to excite the latter; but that this exciting influence
takes effect especially at the moment at which the cur-
rent is closed and opened, and that it is less effective
during the course of the current's duration. As yet it
has been desirable for our purpose, that of studying the
process of excitement in nerves, to make use of induc-
tive currents, which are of such short duration that the
closing and the opening, the beginning and the end,
immediately follow each other in quick succession.
Without now entering into the question, to be dis-
cussed later, as to why the exciting action of the cur-
rent is less during the steady flow of the latter than at
the moments of closing and opening, we will now ex-
amine whether the electric currents which traverse the
nerves do not act on the nerves in some other way,
distinct from their exciting influence.

Let us suppose that the current traverses either the
whole or a portion of a nerve. At the instant at which
the current in the nerve is closed, the appropriate muscle

126 -PHYSIOLOGY OF MOCM- AM> NKi;\ i

pulsates, thus indicating that something, which AVI- have
called excitement, has occurred within the nerve. "While.

however, tho current flows steadily through the nerve,
the muscle remains perfectly quiescent, nor is any
change apparent in the nerve itself. Yet it may easily
be proved that the electric current has effected a com-
plete change in the nerve, not only iu that part traversed
by the cunvni , but also in the neighbouring parts above
and bel»w the portion of the nerve subjected to the
electric current. The great importance of this lies in
the fact that it reveals relations between Ihe forces
prevailing in the nerves and the processes of the elec-
tric currents, which relations are of great importance in
the explanation of the activity of nerve-.

Our knowledge of nerves has not as yet reached
a point at which it is possible to understand all the
changes which occur within them under the influence
of elect ric currents. Indeed, but one set of these changes
can as yet be described: these are the changes in the
excitability. Of all the vital phenomena of nerves, their
capacity of being brought into an active condition by
irritants has at present alone been studied by us. This,
as has been said in the previous chapter, may be quan-
titativdy determined. Experiment shows that the ex-
citability may be altered by electric currents It' a
small pMi-tion of a nerve is placed on two \\ires in such
a way that an electric current may be caused to traverse
this port i<>n. jt appeal's that not only the portion actually
traversed by the current, but the nerve bevoiul this
also suiters changes in its excitability. In order to
study these, let us imagine several piirs of wires ap-
plied to the nerve; n n' (fig. 30). Through one of
these pairs of wires, c d, let a constant current be

ELECTROTONUS.

127

conducted ; by means of proper apparatus the current
may be strengthened or weakened, and may be closed
and interrupted by means of a key at s. Let a current
from a sliding inductive apparatus pass through another
portion of the nerve, e.g. a 6, and let us find that posi-
tion of the secondary coil at which the muscle exhibits
marked pulsations of medium strength. The changes
which occur in these pulsations when the current in
the portion c d is alternately closed and interrupted

FIG. 30. ELECTROTOXUS.

must now be observed. It is found that these changes
depend on the direction of the current within the nerve.
If the current passes in the direction from c to d, then
the action of the same irritant is weakened in the por-
tion a b as soon as the current is closed, but regains its
former strength as soon as the current is' interrupted.
In this case, therefore, the excitability in the contiguous
portion a b was lowered or hindered by the influence
of the constant current traversing the portion c d. If,
however, the constant current is reversed, so that it

128 PHYSIOLOGY OF MCSCLES AND NERVES.

passes from d to c, the influence of the irritant seems,
on the contrary. to increase, in a 1> when the current is
closed, and to roiiine its original strength uhni the
current is interrupted. In this case, therefore, it ap-
pears that 1 1n- act i- m of the current tends to increa>e
the excitability. If the wires e f are next connected
with the secondary coil of the inductive apparatus, and
if the irritants are again applied in such a way that
weak but noticeable pulsations occur, these latter arc
strengthened when the current in the portion c d passes
from do d; and are, on the contrary, weakened when
the current is in the opposite direction. In these two
series of experiments the irritant was applied in one
case above, in the other case below, the constant cur-
rent. Both cases showed consistent results. As soon,
that is, as the irritant acted on the side of the po«'tt'ir>>
electrode or the anode, through which the current
entered the nerve, the excitability was in both cases
lowered. But when the irritant was applied on the
side of the negative electrode or the kathode, through
which the current emerged from the nerve, the irritant
1 icing1 strengthened, the excitability increased.

These changes in the excitability may be shown
throughout the whole length of the nerve; but they
are strongest in the immediate neighbourhood of the
portion traversed by the constant current, gradually
decreasing upward and do\\ uward from the electrodes.
In order to find whether a change in the excitability
aUo occurs within the .electrodes, the current must be
made to traver-c a long,-]- p,.rt i,,n (,f (he nerve, and the
irritant must then be applied (o a point \\itliiu the
electrodes. Accordingto the point at which the elec-
trode is applied, VarioUfl changes maybe sho\\u to occur

ELECTROTONUS 129

here also. If the irritant is near the positive electrode,
the excitability is lowered ; near the negative electrode
it is increased ; and between the two occurs a point at
which no noticeable change in the excitability takes
place under the influence of the constant current.

From all these experiments we may infer that a
nerve, one part of the length of which is traversed by a
constant current, passes throughout its whole length
into an altered condition, and that this is expressed in
the excitability. One part of the nerve, that on the
side of the positive electrode, exhibits decreased excita-
bility; the part of the nerve corresponding with the
negative electrode exhibits increased excitability. This
altered condition is spoken of as the electrotonus of the
nerve, the condition which exists on the side of the
anode being distinguished as anelectrotonus ; that on
the side of the kathode as katelectrotonus. Where the
anelectrotonus approaches the katelectrotonus, a point
occurs between the electrodes at which the excitabilitv
remains unchanged ; this is called the neutral point.
The neutral point does not, however, always lie exactly
between the electrodes ; but its position depends on
the strength of the applied currents. When the cur-
rents are weak, it lies nearer the anode ; when they
are stronger, it is situated nearer the kathode ; and
when the currents are of a certain medium strength,
the neutral point is exactly midway between the two
electrodes.

This electrotonic condition of the nerve may be ex-
hibited as in fig. 31. In this n nf indicates the nerve,
a and k the electrodes, a signifying the anode, k the
kathode. The direction of the current within the nerve
is, therefore, that indicated by the arrow. In order to
7

130

PHYSIOLOGY OF MrsfLER AXU NERVES.

indicate the change \\hich the excitabilit y undergoes at
any definite p >int in the nerve, let us suppose a straight
line drawn at this point at ri^ht angles to the longitn-
dinal direction ,>f the n«-r\e. and let this line he made
longer in prop .rtioii as the change i> greater. In order.
inoreo\er, to show that the changes which occur toward
the anode are of an opposite tendency to those toward
the kathode, let the line on the anode side be drawn
downward, that on the kathode upward. ]'>y connect ing
together the heads of these lines a curve is obtained
which diagrammatical]? represents the changes at each

rr

X

X

ixrs rxni-:u TIIK IXFI.IKM i. OF
VAKVIM. yn:i:.\<:Tii.

])oint. Of the three CUrVCS, the middle represents the
condition under the influence of a current of medium
strength; (he other (wo curves, indicated, the one by
short lines, the other by a dotted line, represent ihe
conditions under the influence of a >trong and of a
weak current respectively. These curves show thai tin
changes are more marked in proportion as the cur-
rent is stronger ; that they are most strongly developed
exactly at the electrode poinl>; and, finally, that the
neutral point, under the influence of currents of dif-
ferent degrees of strength, assumes a \ariable portion

betWeell th'- electrodes.

MODIFICATION OF THE EXCITABILITY. 131

2. Apart from these changes in the excitability
which are thus observable while a continuous current
passes through the nerve, others can also be shown to
occur immediately after the opening of the current.
Indeed, the excitability altered in electrotonus does not
immediately revert to its normal value when the cur-
rent is interrupted, but only regains this after the lapse
of a short time. The duration of the changes in the
excitability observable after the opening of the current
is greater in proportion as the current is stronger and
its duration is longer. These changes, which, to dis-
tinguish them from the electrotonic changes, are called
modifications of the excitability, are not merely the
continuance of an electrotonic condition, but are some-
times completely different from the latter. If, for in-
stance, the experiment is tried at a point near the
anode, at which the excitability is decreased during the
continuance of the current, the excitability is found
to be increased immediately after the opening of the
current, and it is not till after this that the original
normal excitability is regained. Similarly, in the neigh-
bourhood of the kathode, the excitability decreases for
a short time after the opening of the current, after
which it again increases, and only gradually regains its
normal condition. As a rule, these modifications do not
last more than a few parts of a second. If, however,
the constant current has been long present in the nerve,
these modifications may endure for a somewhat longer
period. On account of their transient nature it is diffi-
cult to observe and test them. The change of condi-
tion which follows the opening of the current within the
nerve may, moreover, lead to excitement in the latter ;
so that, on the opening of a current which has been

132 niYSIoUHJY OF MI-n.KS AND NKKYKS.

present in tin- ner\e for -Mine time, a scrips of pulsa-
tions or :in apparent tetanus is occasionally observed.
Thi.- phenomenon lias long been known as an opening
t claim.-, "i- as // /'//••/•"* /»•/»/// /fx. Tin- comic. 1 ion existing
between these changes in the excitability, and the fact
that the nerve may be' excited by electric current-, ha-
led to the adoption of a \ ie\v of t he elect ric excitement
in nerves which we shall not be able to develop until we
have more closely studied electric excitement itself.

3. If a continuous current is passed through a nerve,
and is alternately closed and opened, the excitement
appears to occur irregularly, sometimes at the closing,
-"met imes at the opening of the current, and occasion-
ally even at both. Closer observation has, however,
shown that very definite laws control this. pro\ ided that
attention is paid to the strength of the current and its
direction within the nerve. Let us tir.-t examine these
phenomena as they occur in fresh nerve, and, as we found
that the conditions in the nerve change very rapidly
in the neighbourhood of the cut end, let us commence
onr observations at a low point in a fresh nerve, of
which as great a length as possible has been extracted.
For this purpose it is especially neces-ary to possess a
convenient mean- of graduating at will the strength of
the applied currents. Various methods have been used
for this purpose. The best is that which is based on
the distribution of the currents in branching conduc-
tors. The electric current, on being made to traverse
a conductor which sepaiates at any point into two
branches, divides, the stiviiv.th of the currents distri-
buted into these two branche- no) being ahvav- eipial,

but being in each branch in Inverse ratio to the resis-
tance offered in that branch. Supposing thai the nerve

LAW OF PULSATIONS.

133

is inserted in one branch, and that the resistance of the
other branch is altered, then the strength of the cur-
rent passing through the nerve will change, although
the conductor which contains the nerve remains un-
altered ; the current -within the nerve will increase
in strength when the resistance in the other branch is
increased, and it will decrease when the resistance in
this branch is decreased.

The resistance of a wire being proportionate to its
length, it is only necessary to arrange, as the conductor

FIG. 32. EiiEociioitn.

A S, a wire the length of which can be in some way
altered. The simplest way of doing this is by extend-
ing the wire in a straight line and moving a sliding-
piece along it, so that any required length of the wire
may be brought into the conductor. Such an apparatus
is called a rheochord, from psos, a current, and ^opEy,
a chord — because the current is conducted along a wire
extended like a chord. A rheochord of the simplest kind
is represented in fig. 32. The current of the chain
P Z traverses the wire A B. From J. a branch con-

134 PHYSIOLOGY OF MUSCLES AND NKKVI 3.

diu-t MI- passes to the nerve, aud returns from there
to tli^ >lide S, which slips along the wire A B. The
branch-current traversing the nerve is strengthened or
weakened according as this slide is placed further from
or nearer to J .

r.y niraus of a rheochord of this sort there is no
difficulty in making the currents within the nerve so
weak that they exercise no influence at all. If their
strength is then gradually increased, a pulsation is
always first seen to occur in the fresh nerve when the
current is closed, whatever the direction of the current
within the nerve. In order to be able to indicate the
direction, it has become customary to speak of such a
current, when it passes within the nerve from a central
to the inure peripheric parts, as <l<.«-< mling, and when
it passes in the opposite direction, as ascending.

Ascending and descending currents, then-fore, when
they are weak, afford pulsations only on the closing
of the current. If the strength of the current is in-
creased, pulsations gradually begin to occur also on
the opening of the current, at first usually with the
descending current, though, when the -tivngth is in-
creased yet more, they occur in connection with the
ascending current, al.-o. Finally, the pulsations in all
four eases are of eijual strength. If, ho\\e\er, the
strength of the current is yet further increased, two
of the-e f..ur pulsations again become weaker — the
closing pulsation with the ascending current., and the
opening pulsation with the descending current. A
strength of current is at last reached at which these
two pulsation-, ent irely cease, so that pulsations OCCUT
only on the closing of the defending, and on the
opening of the a-eeiiding currents. Tlwse phenomena,

LAW OF PULSATIONS. 135

which represent the dependence of the excitement of
the nerve on the strength and direction of the current,
are spoken of as the law of pulsations. This law is
represented in the following table, in which S signifies
closing, 0 opening, Z pulsation, and R rest — i.e. no
pulsation — the duration of the currents being indicated
by the arrows.

LAW OP PULSATIONS IN THE CASE OF FRESH NERVE.

Ctirrent Weak

Current of Medium
Strength

Current Strong

1

S, Z

0, R

S, Z 0, Z

S, Z 0, R

t

s, z

0, R

S, Z 0, Z

S, R 0, Z

As soon as the nerve dies, the phenomena under
the law of pulsations change. If weak currents are
applied to a fresh nerve, which in either direction
produce pulsations only on the closing of the current,
and if then, the currents remaining entirely unaltered,
their influence on the nerve is tested from time to
time, it will be found that pulsations gradually begin
to occur on the opening of the current; these are at
first weak, but they continually become stronger till
they are fully equal in strength to the pulsations
resulting on the closing of the current. This condi-
tion is retained for some time, after which the closing
pulsations of the ascending current and the opening
pulsations of the descending current become weaker,
and finally entirely disappear, so that the descending
current produces only closing pulsations, and the
ascending current only opening pulsations ; and this
condition endures until the excitability at the points
examined is entirely expended, the pulsations be-

136 PHYSIOLOGY OF MUSCLES AND NKKVKS.

coming gradually weaker, and finally disappearing en-

liivly. The law of j)iilsations in the case of dying
nerve may also In- represented in tabular form, three
>tages of excitability being distinguished; the signs
remain the same as in the former table.

L.\\v OF PULSATIONS IN THE CASE OF DYIM; NI:UVK.
(Under the Application of Weak Cum-nts.)

1

1'irst Stage

Second S:

Third SUige

S, 7. 0, 11

S, Z 0, Z

S, / O, U

t

8, 7. 0, R

S, V. 0, Z

S, 11 0, Z

It is at once apparent that these two eases of the
law of pulsation, occurring in different circumstances,
• lit irely agree. The sequence of the phenomena which
occur at the death of the nerve on the applicat ion of cur-
rents of little power is exactly the same as that which
may be elicited from a fresh nerve by gradually increas-
ing the strength <->f the current. In other words, if the
nerve is irritated with weak, unvaried currents, these
aet on a f re>li nerve, after a time, in exactly the same
way as currents of medium .strength, and, after a
somewhat longer time, as powerful currents would have
aei,-d. In order to understand this, it is accessary to
recall our pre\ioiis experiences of the changes in the
excitability at the death of the nerve. We found thai
iu that case tlie excitability at first rises and attains a
maximum before it again falls. Supposing, therefore,
a I're.-h in-r\ e is irritated by means of current s of detinil e

but weak strength, and supposing that this nerve is ex-
amined after the lapse of a .-hort time, during which its
excitability has risen, it is evident that these weak cur-

LAW OF PULSATIONS. 137

rents must already act as would stronger, and that, when
the excitability has risen yet further, that they will act as
very strong currents. The expressions weak, strong, and
medium currents bear no absolute meaning, the same
in the case of all nerves, but must always be under-
stood relatively to the excitability of the nerve. That
which in the case of one nerve is a weak current may
evidently act as much stronger in the case of another
nerve the excitability of which is much greater; and,
moreover, one single nerve, at different times, may be
conditioned in this respect as though it were two diffe-
rent nerves, if its excitability has in the interval under-
gone considerable changes. There can, therefore, be
no difficulty in understanding how, as the excitability
gradually rises, the action of weak currents gradually
becomes equal to that of medium and strong currents.
One striking fact must, however, be observed. As the
excitability after it has reached its highest point begins
to fall again before it entirely disappears, it might be
supposed that the same currents which at the extreme
height of the excitability acted as strong currents,
would now act again as currents of medium strength,
and then as weak currents, before they entirely lose
their power. According to this, the third stage of
excitability, in which a closing pulsation is observable
in the case of the descending current, an opening pul-
sation in the case of the ascending current, should
be succeeded by a fourth and a fifth stage, of which
the fourth should resemble the second, and the fifth
the first. This has indeed been said to occur by some
observers, but it does not appear as a rule. In explana-
tion of this, it has been assumed that no real, but only
an apparent decrease of the excitability takes place after

138 PHYSIOLOGY OF Mt\SCLES AND NERVES.

it lias reached its highest point. It must, moreover, be
remembered that it is nev.er merely a single cross-section
of ;i inTVe which is irritated, but always a portion of
greater extent, and that the excitability measured by us
is in reality only the average excitability of the various
point.- within the irritated portion. It may further be
a—iimed that the excitability at each point, when it
has reached its height, is very rapidly, if not instan-
taneously, destroyed. As this, however, occurs sooner
at the higher than at the lower points, it follows
also that the excited portion, beginning from the top,
gradually becomes a powerless thread, which is, how-
ever, still capable of transmitting electricity. The ex-
citement occurs in reality only in the lower division of
the portion irritated, and this, as long as it retains an\
power of action, must remain at the highest point of
excitability.1

4. In studying the law of pulsations we attended
• •nly to the closing- and opening of the current, entirely
disregarding the period during which the continuous
current flowed through the nerve. In reality, tin-
nerve, as a rule, remains unexcited during this period.
Sometimes, however, especially on the application .,f
but moderately powerful currents, an enduring excite-
ment expressing itself as a tetanus in the muscle is
ob-er\able while the current lasts. Ascending and
descending cm-rents do not behave quite alike in this
matter. The latter are followed by tetanus, even in the

case of currents of Somewhat high power, while the

ascending currents are only followed by tetanus when

they are weak. In all cases this tetanus is, however.

but slight, and cammt lie compared \\Jth t]ia| which

1 Sec NI.V- .-in 1 \<Miti"!i>. Nil. .",.

RELATION OF ELECTKOTONUS TO EXCITEMENT. 139

may be induced by repeated separate irritations, for
instance, by inductive shocks, or by frequently and
repeatedly closing and opening a current. It thus
appears that variable currents are better adapted
for effecting the excitement of a nerve than are con-
stant currents. Inductive currents, though their dura-
tion is extremely short, may be regarded as similar to
constant currents which are re-opened immediately
after being closed. True pulsations may indeed be un-
failingly elicited, even with constant currents, if, by
using suitable apparatus, they are but momentarily
closed, and are then again reopened. But experience
of the law of pulsations shows that either the closing
or the opening are under certain circumstances alone
sufficient to elicit pulsations. As we know that the
altered condition called electrotonus is produced in the
nerve by closing the current, and that on the opening
of the current this condition gives place, if not im-
mediately, yet after a short time, to the natural con-
dition, we may, therefore, assume that the excitement
of the nerve is actually due to the fact that the nerve
passes from a natural into an electrotonic condition, or
back again from this into its natural state. We may
suppose that the smallest particles of the nerve are
transferred, on the intervention of electrotonus, from
their normal into changed positions, and that this mo-
tion of the particles is under certain circumstances con-
nected with excitement. We have, however, found
that a nerve, when electrotonus intervenes, is distin-
guishable into two parts, the conditions of which evi-
dently differ ; for in the one, that of kat electrotonus,
the excitement is increased, while in the other, that
of anelectrotonus, it is decreased. It might, therefore,

uu

PHYSIOLOGY OF MIX 1.1 > AM) M-iK\ I >.

lie posnlile that these t\\o conditions differ 111 the IV-

lilt inn uhich they bear to the excitt ment. Indeed,
1'lliiger suppo.-ed that excitement occurs only at the
commencement of katelectrotonus and at the cessation
of anelectrotonus. ( )n the basis of this hypothesis the
phenomena of the law of pulsations may be explained;
and it becomes intelligible why on the eliding and
npeiiing of the current pulsations sometimes occur and
MX- sometimes absent. In order, however, fully to

FlO. ">'•>. F.I.I'-' TI:i>Tii\TS.

understand this hypothe-is and the law of j)iilsations
lia-ed upon it, we lilll>» study the phenomena of elri-
trotonus more closely than we have yet <loue.

.">. We have already seen that the excitabilit v is in-
creased mi the side of the kathode during the closing
of the current, ami is decreased en the side of the
anode. Kasy as it i> to prove this law under the appli-
cation of \\eak, or medium currents, it is sometime.-*
very hard to do ,-o \\ hen t he current causing the eh-c-
trotoiuis is strong. Lei us a-ain iiiiiigine thai I he

TRANSMISSION OF EXCITEMENT DURING ELECTROTONUS. 141

nerve, nn' (fig. 33) is traversed between c and d by an
ascending current, and that it is irritated between the
points e and/, above the portion traversed by the current.
The muscle is accordingly at 71', as in our previous ob-
servations. Irritation takes place on the side of the
kathode. An increase in the excitability should there-
fore occur. This may easily be shown when the cur-
rents used for effecting electrotonus are weak. Tf,
however, the current used for this purpose is somewhat
strengthened, no increase in the excitability is ob-
servable ; and, indeed, if the currents are sufficiently
strong, it becomes quite impossible to effect contrac-
tion in the muscle by irritation at ef. This may seem
to afford an exception to the law of the electrotonic
changes in the excitability. But from the previous
experiments it is evident that this must not be in-
ferred. Possibly the excitability is in reality increased
at e f in entire accordance with the law ; but in order
that the action of the excitement at this point should
become visible, the excitement must pass through the
portion under the influence of electrotonus, as well
as through the an electrotonic portion lying below the
latter, and it may be supposed that this propagation of
the excitement meets with an insuperable obstacle in
the condition of strong anelectrotonus which prevails
there. It can indeed be shown that this is the case.
If the current is reversed, so that it flows in a descend-
ing direction through the nerve, then irritation at
the portion a b will invariably show the existence of
heightened excitement, however strong the current
may be. But the portion a b is now under exactly the
same conditions as was the portion e f previously. It is
in itself very improbable that the nerve acts differently

142 PHYSIOLOGY (•!•• MUSCLES AND M'.KVFS.

ill two sndi entirely similar cases. The difference
between the two cases consists solely in the fact that
in the latter the katelectrotonic point examined is
situated immediately next to the muscle, so that its
condition of excitability can be indicated directly by
the muscle;, while in the case first observed, the con-
dition <>f excitability at the point e /, before it can find
expression in the muscle, must find means of passing
through, the otherwise altered portions c d and a 6. Now
it may, on the other hand, lie shown that transmission
in a nerve under the influence of electrotonus really
takes place at an altered speed. In the katelectrotonic
portion the rate of propagation is but little altered-
is, perhaps, slightly increased; but in the anelectro-
tonic portion it is markedly decreased. From this it,
may be inferred that anelect rotonus not only decrea-. -
the excitability, but also hinders the propa^at i<m of the
excitement ; and that where the anelectrotonua is -tmng,
propagation is even entirely prevented.

6. This not only explains the apparent exception to
the laws of electrotonus, but also affords explanation of
the fact that strong ascending currents, when closed,
are followed by no pulsations. We know that a strong
electric current induces katelectrotonua in the upper
half, anelect rotonii- in the lower. According to Plliiger's
hypothesis, excitement occurs in the nerve only at the
point ;it which kat elect rotonus intervenes; that is, on
the closing of the ascending current, in the upper por-
tion of the nerve. In order to reach the muscle, this
excitement must pa-- through the lo\\er portion of the
nerve, and as this is stron-l\ an. 1< •••( rotonic, it pre.-eiits
an <>l»tacle to the further pa->age of t he excit eiiient .
The excitement \\hich occurs in ' lie upper half is, there-

EXPLANATION OF THE LAW OF PULSATIONS. 143

fore, unable to reach the muscle, so that pulsation is
necessarily absent on the closing of the current.

In order to apply the corresponding case to the
opening of a descending current, the help of another
hypothesis is required, according to which the great
modification which follows the disappearance of katelec-
trotonus, and which so greatly decreases the excitability,
also involves a hindrance to transmission. This assump-
tion has not yet been experimentally proved ; proof is
indeed difficult, on account of the ephemeral charac-
ter of the modifications. The similarity of negative
modification to anelectrotonus, both decreasing the
excitability, favours the hypothesis that in negative
modification also an obstacle is afforded to transmission.
According to this view, the case is the same on the

O 7

opening of a descending current as on the closing of an
ascending current. According to Pfliigers hypothesis
excitement occurs on the opening of a current only in
that portion of the nerve at which anelectrotonus dis-
appears. This, in the case of a descending current,
is the upper portion of the nerve. In order to reach
the muscle thence, the excitement would have to tra-
verse the lower portion, which is at the same time taken
possession of by a strong negative modification, and this
prevents propagation of the excitement; no opening
pulsations, therefore, occur in the case of the descend-
ing current.

Pfliiger supported his hypothesis by the following
experiment. Mention has already been made of the
so-called Ritter's tetanus, which intervenes when a
current which has traversed a nerve for some time is
interrupted. According to Pfliiger's hypothesis, this
excitement should also be located on the side of the

144 rilYSIoLOiiY OF MUSCLES AND NKUVKS.

anode. If an a-cending current is passed through a
nerve, the anode side is situated in its lower portion j

but it' lli«' ciirrcnt is descending, then it i- situated in
the upper portion. If Hitter's tetanus is induced by
mean- <if a descending current, and if the nerve is bi-
sected between the electrodes immediately after the
opening of the current, the tetanus at once ceases. If
the same experiment 'is tried with an ascending current,
then the cutting of the nerve in no wav influences the
tetanus.

Yet another proof of the truth of this hypothesis is
afforded by Prluger's study of the excitement of the
seiiM»ry nerves by an electric current. As the terminal
apparatus of sensory nerves, by the action of which the
irritation is recognised, is situated at the opposite cud
of the nerve, it seems that the law of pulsations should
prevail in an opposite way to that in which it pre-
vails in the ca-e of the motor nerves. Prliiger as-
certained that in reality strong ascending currents
induce sensation only when closed, strong descending
currents only when opened. The explanation is the
same in this case as in that of the motor nencs. On
the closing of the descending current, excitement oc-
curs in the lower portion of the nerve. In order to
effect -eii.-ation the excitement must pass to the spinal
marrow and the brain ; it would have, therefore, to pa-s
through the upper parts .if the nerve, \\here it would he
checked by the strong anelectrotonus which prevails
there. The opening ,,f the a-ceiiding current ha- a
similar irritating effect on the l»\\er parts < if the nerve.
In order in reach the spinal mai row and brain, this
excitement \\.nild ha\eto pass through the upper parts.
\\here, in this ca-e, it \\oiil.l be checked by the strong

t i\e modification*

GENERAL LAW OF NERVE EXCITEMENT. 145

The only explanation of the fact that weak currents,
whatever their direction, act only on being closed, is
that the changes in the nerve probably begin more
quickly than they disappear on the closing of the cur-
rent. The differences are, however, very slight; and
a very slight strengthening of the current suffices to
elicit opening pulsations of the nerve also. This is
especially true of the descending current ; if the nerve
is not quite fresh, opening pulsations may occasionally
be observed even in the case of very weak currents
which do not as yet afford any closing pulsations.
This is connected with the circumstance that the ex-
citability is somewhat greater in the upper than in the
lower portions of the nerve. The natural superiority
of the closing pulsation is thus cancelled in the case of
the descending current, and opening pulsation is con-
sequently rendered more easy.

7. From what has been said it seems very probable
that every excitement in the nerve is due to a change
in its condition, which might be directly shown in the
case of the electric current by the electrotonic change
in the excitability. The more quickly these changes
occur, the more easily are they able to excite the
nerve. This law is exhibited even in the case of
non-electric excitement. It is, for instance, possible
by gradually increasing pressure on the nerve entirely
to crush the latter without producing any excitement,
though every sudden pressure is, as we have seen,
inseparable from excitement. A similar fact may be
observed in the case of thermic and chemical irrita-
tion. From this it may be inferred that the excitement
in the nerve is due to a certain form of motion of its
smallest particles, and that a sudden blow is better

146 PHYSIOLOGY OF MI.H'LES AND NERVES.

adapted for exciting tin's motion than is slow action.
That even slight mechanical disturbances are capable
of producing excitement, although the nerve is not
• rushed, has been proved by Heidenhain. lie attached
a small ivory hammer to the instrument which we have
already described under the name of Wagner's hammer,
and, having laid the nerve on a small ivory anvil,
placed the latter under the hammer in such a way
that the latter tapped gently on the nerve. The result
of this was strong tetanus lasting for several seconds.
To obtain a more accurate conception of the mechanism
of nervous excitement, it would be necessary first to
learn accurately the arrangement of the smallest par-
ticles in the quiescent nerve. Now we shall later on
examine certain behaviour of the quiescent nerve from
which conclusions may be drawn as to the regular
arrangement of the smallest particles. While postpon-
ing the closer examination of these details, we may at
present try to explain the facts of excitement as clearly
as circumstances permit. For this end we will assume
that the particles of the nerve are retained in an en-
tirely definite relative position by molecular forces.
Kxcitcment can, accordingly, only intervene when the
particles are displaced from this position and are set in
motion. The more powerful are the forces which retain
the particles in their balanced position, the greater
must be the forees which move them, and, therefore.
I he smaller is the excitability. It 7nust also be ex-
plained that the separate particles of the nerve mutu-
ally influence each other, each particle influencing the
other and helping to retain it in its relative position.
A comparison drawn by du Bois-Reymond may be used
to make; this somewhat involved explanation more

GENERAL LAW OF NERVE EXCITEMENT. 147

intelligible. It is a well-known fact that a magnetic
needle suspended by a thread assumes such a position,
in consequence of the magnetic attraction of the earth,
that one of its ends points to the north, the other to
the south. Now, supposing a series of many magnetic
needles, all suspended one behind the other in the same
meridian line, as in fig. 34, then each of these needles

NS NS NS NS NS

12345
FIG. 34. A SEKIES OF MAGNETIC NEEDLES ARKANGED AS A DIAGRAM

OF THE PARTICLES OF A NERVE.

will be yet more firmly retained in its position by its
neighbours, for the adjacent north and south poles of
the needles mutually attract each other. If, for ex-
ample, we wish to move the middle needle, No. 3, more
force must be used to do this than would be necessary
if the needle were alone. But when the centre needle
is turned, the immediately adjacent needles cannot re-
main at rest, but are similarly deflected ; these exercise
a similar deviating influence on their neighbours ; and
so on. So that the disturbance created at one point
in this series of magnetic needles passes like a wave
through the whole series.

This evidently bears much resemblance to that
which takes place in nerves. It explains not only
how a disturbance commencing at any point in the
nerve propagates itself, but also how each separate part
of the nerve is able to influence the other parts. We
have already found that the excitability of any point of
the nerve increases if the immediately superior portion
of the nerve is cut away. The magnetic needles show
that just in the same way each is more readily move-

PIIYSlnLocJY OF Ml'SCLES AM> .NF.KYI-.

able when some of its neighbours have been removed.
NYithoiit, therefore, a-suming other resemblances be-
tween tin: foive.s which act on the magnetic needles
and those present ill the nerve, -we may arcept the
comparison so far that we may imagine the nerve to
consist of -eparate ininiite particles, arranged one behind
the other in the longitudinal direct ion of the nerve,
and mutually retaining each other in their position.
Now, if there are forces which retain the particles in
this relative position yet more firmly, it is evident that
thev nm-t lesM-u the excitability; while, on the other
hand, such forces as tend to move the nerve-part id
from their relative positions must at the same time
decrease the strength of their connection, and rai^t
therefore render the nerve more excitable. As regards
the elect rie current, we have seen that the two poles
act on the nerve in opposite ways. \Ye may, therefore,
as<ume that by one pole, the positive, the nerve pa,--
ti.-K-s are retained in their quiescent position, while by
the negative pole, on the other hand, they are disturbed
from this position. If this is the case, it explains tin-
fact that excitement occurs only at the negative pole
when the current is closed. The excitability is in-
creased at the positive pole on the opening of the cur-
rent ; here, therefore, there occurs a mo\einent of the
particles such as follows the closing in the negatise
pole, so thai in this case the excitement can occur on
the op'-ning of the' current.

'The fact that the nerve ivnnins niiexcited by
change- in Its condition, although these same changes
if they occur suddenly do induce excitements, bears so
-i^ni Meant! von the explanation of the nervous process* 3,
that we must study it in yet greater detail. The fact

GENERAL LAW OF NERVE EXCITEMENT.

149

may be most easily and surely shown in the case of
electric excitement, as there is no difficulty in allowing
the strength of the currents to increase or decrease

O

more or less gradually. Let the apparatus be arranged
as in fig. 35 in which the nerve is traversed by a

FIG. 35. RHEOCIIORD.

current, the strength of which may be altered by moving
the slide S. Let a key be inserted in the circle, and let
the slide be so placed that pulsations occur on the
closing and the opening of the current. On placing the
slide S close to A (in which position the resistance in
the branch A S is nil, so that no current passes through
the nerve), and pushing it slowly forward to its former
position at S, the current within the nerve slowly in-
creases from zero to its former strength : on again push-
ing the slide slowly back till it touches A, the strength
of the current again slowly decreases to 0. In neither
of these cases is the nerve excited. As soon, however,
as the movement of the slide is in any way effected

1 E. du Bois-Reymond has described apparatus of this sort ur.der
the name of Schn-ankitnr/srhc'oehurd.

150 PHYSIOLOGY OF MtX'LKS AM> NKKVKS.

with great speed,1 the ner\e is excited and the muscle
pulsates. When, therefore, the current being closed
or opened by means of the key, the nerve is excited,
tliis is due to the fact that, the strength of the current
increases with great rapidity from zero to its full
strength, or sinks from the latter to zero.

The facts thus observed explain why inductive
shocks, which are of but very short duration, and in
which closing and opening follow each other in such
rapid succession, are so especially capable of exciting
the nerve. All inductive shocks are not, however,
equally adapted for this purpose. When, making use
of the inductive apparatus already described, the current
in the primary coil is closed and then interrupted, the
result is the creation of two currents differing in their
direction in the secondary coil, these being the closing
inductive current and the opening induetive current.
If these are made to pass through a nerve, the exciting
influence of the latter is always much greater than that
of the former. This can be very plainly shown In-
placing the secondary coil at a distance from the pri-
mary. By this means, a distance may always be found
at which the opening inductive current i> active, while
the closing inductive current as yet exercises no in-
fluenee ; if the coils are then brought nearer to each
other, the latter al-o becomes active. If, howe\.r.
when the c.,iU of the inductive apparatus are in any
portion, the secondary coil is connected with a mult i-
plier, then the deflections of the magnetic nt edle are
ahvavs of eijiial strength in the case of both inductive
currents. The nerve, therefore, exhibits a difference
which the multiplier is incapable of indicating. It ha-.
however, been sho\\ n that the two inductive currents

GENERAL LAW OF NERVE EXCITEMENT. 151

differ entirely in duration. The closing inductive cur-
rent increases slowly, and decreases just as slowly,
while, on the other hand, the opening inductive current
very rapidly attains its full strength and ends just as
quickly. It is to this difference that the latter evi-
dently owes its greater physiological effect.1

Let us return to the experiment as first arranged
with the rheochord. Instead of pushing along the
slide between A and S} it may be moved backward or
forward between any two points. The current in the
nerve, in this case, never ceases, but is either strength-
ened or weakened according to the direction in which
the slide is moved. If the latter is moved suddenly
and with great speed, it may produce excitement ; bi\t
the nerve always remains unexcited when the move-
ment is gradual. It therefore appears that it is not
the actual closing and opening of a current which is
required to excite the nerve, but that any change,
whether it strengthens or weakens the current, is suffi-
cient to effect this, provided that the alteration is
sufficiently great and sufficiently rapid. Closing and
opening are but special cases of alteration of the cur-
rent in which one of the limits to the strength of the
current = 0. The following law regarding the electric
excitement of nerve may therefore be stated: any
change in a current traversing a nerve may excite the
latter if it is sufficiently strong, and if it occurs with
sufficient speed. We have however seen that this law
has very many exceptions. For under certain circum-
stances a greater alteration (the closing of a strong
ascending current) may appear to be without effect, al-
though one less strong takes effect. If, however, it is
1 See Notes and Additions, No 6.

]52 rilYMMl.oiiY OF MUSCLES AM> NKKYl -.

admitted that in sneh cases <A<-if <'iii<'iit dors in reality
take place. Imt thai it is not observable on account of
external circumstanc ss i hindrance to tin- propa^at ion to
the muscle), tl'i-n t! :ceptions may be said t<» be

7n:Tely apparent. MoR-oYi-r, assuming that "the changes
in tin1 strm^tli <•(' the currents within the ii'-rvc mily
i-xrite in conseiiiii'iici' of the fact that they bring about
changes in the mnltrular cmiilil ion of tin- IKTVC, and
combining with this all that \\c km»\\- of the i-tVrot of
other forms of nerve irritation, the following l;«\v regard-
ing nervous excitement may he regarded as the tinal
result:—

Excitement of flu' nerve <!'•]» n</* on a c//"//;/'1 ///•
its molecular coiu/il !<>//. It occurs as soon «* such a

flnl il</<' /'N f'ft'l'ctl'tl H'illi xiljjif'irnt *jit>ed.

It may be added that this law is in all essential
points true also of muscle. Hut it appears that, the
molecules of muscle are more sluggish than are those
of nerve, so that in the former very transient- influences
may more easily be without effect.1

1 Sec Notes and Additions, Xos. 7 and 8.

CHAPTEE IX.

/. Electric phenomena; 2. Electric fishes; 3. Electric organs;
4. Multiplier and tangent galvanometer ; 5. Difficulty of the
study; 6. Homogeneous diverting vessels; 7. Electromotive
force ; 8. Electric fall ; 9. Tension in the closing arch.

1. As yet in examining the essential qualities of
muscles and nerves we have disregarded a series of
important phenomena common to both, in order that
we may now treat them as a whole. We refer to the
electric actions which proceed from these tissues.
Muscles and nerves are especially distinguished among
all other tissues of the animal body by the fact that
they exercise very regular and comparatively powerful
electric action ; and from the relation existing between
electric currents and the excitability of muscles and
nerves it may be inferred that these independent elec-
tric actions bear some relation to the essential qualities
of muscles and nerves.

It is true that electric action is exhibited in other
animal, as well as vegetable tissues ; but these are very
slight, and are apparently insignificant.1 Electric cur-
rents are so easily generated under all circumstances
that it is not very surprising that traces of them are

1 An exception is perhaps afforded by the electric phenomena
of the leaves of Diuncea miiscijmla which will presently be men-
tioned.

8

154 niYSlOl.iHiY OF MUSCLES AND NERVES.

everywhere to lie found. In the researches in which
\\c are about t<> engage, we must always endeavour as
far as possible to exclude these accidental currents, or
at least to distinguish them from those currents which
it is our task to examine. ;ind the causes of which lie
in the animal tissues themselves. Apart from muscles
and nerves, but one tissue seems endowed with some-*
what strong elect lie action ; this is that of the glands.
This has, indeed, not as yet been fully proved, but it
ha- lieen shown to be in a very high degree probable.
In connection with this it is a very interesting fact that
the glands are in some physiological respects very similar
to the muscles, and that they bear the same relations
to nerves as do muscles.

2. There is, on the other hand, a tissue in which
electric action is exhibited in far greater strength, so
that its nature was known long before it was recog-
nised that muscles and nerves possess the same capa-
city. This tissue does not, however, occur in all
animals, but only in a few fishes, which on this account
are called electric tishes. In these animals special
organs of peculiar structure occur, in which, as in an
electric battery, currents of very considerable strength
arise, the discharge of which is caused by the influence
of t lie will, the animal using t his power to frighten its
enemies, or to benumb and kill its prey. Long before
the world knew anything accurately as to the phvsical
nature of elect ric phenomena, such powerful influences
a- are exhibited in elei-trie li.-hes did not fail to attract
the attention of chance observers. Notices of these
remarkable phenomena are actually found in ancient
writers; and the h'.imaii pod Claudius Claudianus1

1 He lived in Alexandria toward ti.rcnrl nf tbe fourth century.

ELECTRIC FISHES. 155

has given a very vivid description of these actions in
the following lines :—

1 Who has not heard of the power of the dreadful
ray, of the benumbing force to which it owes its name.1
Formed only of gristle, it swims slowly against the
waves or creeps sluggishly on the waterwashed sand.
Nature has armed it with an icy poison, has poured
into its marrow coldness to freeze and stiffen all living
things, and has filled it with everlasting winter. To
these gifts of nature it adds craft, and, conscious of
power, it remains quietly stretched among the sea-
grasses ; yet when some animal, swimming upward to
the sea-top, passes near, unpunished it fearlessly feeds
on the living limbs. Nor when, having carelessly bitten
at some bait, it feels the line, the bent hook in its mouth,
does it attempt flight, biting itself free, but craftily
creeping yet nearer to the dark hair-line, conscious of
its power, it pours the electric breath from its poison-
ous veins far and wide over the water. The electric
fluid flashes along hook and line, harming even the
fisherman where he stands above the water ; from the
lowest depth the dreadful lightning flashes, and passing
along the hanging line, by the magic of its power
carries cold as of ice through the rod, woundino- the

o

strong arm and curdling the blood of the fisherman,
who, terror-struck, throws away the baneful prey, and,
careless of his line, hurries homeward with dismay.'

After the theory of electricity had received a new
development in consequence of the discoveries of
Cralvani and Volta, these fishes were frequently studied

Older notices of the Torpedo occur in Pliny, ^Elian, Oppian (whose
poem on fishing Claudianus appears to have known), and in Aristotle.
1 Torpedo, from torpor = numbness.

1.5G PHYSIOLOGY OF Mf.-n.KS AND MlltVI 3.

by various observers, and the electric character of their
innate force was incontrovertibly shown. Faraday's
study of tlie electric eel, and du liois-Keymond's of
another clcciric ti>h, an- especially important.

'I'h. -re are three fishes, especially, which have been
proved to possess this capacity for giving electric shocks.
These are, the electric ray of the Adriatic and Medi-
terranean (Torpedo eli-<-tr'i<-n and T. m<ir,i,(ir<it<i'}; the
electric eel (Gymnolus dectricus), wliich occurs in the
fresh waters of South America : and lastly, another elec-
tric fish (Malapterurua rli-rh-icus or M. lenim //>.•/.$),
which has but recently been carefully stydied, and
which occurs in the rivers of the Bay of Benin on the
east coast of Africa. "SYe cannot omit this opportunity
of inserting Alexander von Ilumboldt's description of
the electric eel and its action ' : — •

'The crocodile and the jaguar are not. however, the
only enemies that threaten the South American h< ree :
tor even among the fishes it has a dim 14 emus toe. The
marshy waters of Bern ;md Kastro are filled with innu-
merable electric eels, which at pleasure are a Me to
discharge a deadening shock from every part of their
slimy, yellow-speckled bodies. This species of ^\ mnof us
is about five or six feet in length. It is powerful enough
to kill the largest animals when it discharges its ner-
vous organs at one shock in a favourable direction. It
was once found neces-ary to change the line of road
from trritncii across the >-i\annah o\\in^' to the number
of horses which, in fording a certain ri\ uli-t. annually
fell a sacritice to the-e electric t-els, which had accu-
mulated there in -41-1 -at niiml>er<. All other species of
fish shun the vicinity of these formidable creatures.

1 I7/-//-.S- a/ \utnri'.

ELECTRIC EELS. 157

Even the angler, when fishing from the high bank, is
in dread lest an electric shock should be conveyed to.
him along the moistened line. Thus, in these regions,
the electric fire breaks forth from the lowest depths of
the waters.

' The mode of capturing the gymnotus affords a pic-
turesque spectacle. A number of mules and horses are
driven into a swamp, which is closely surrounded by
Indians, until the unusual noise excites the daring fish
to venture on an attack. Serpent-like, they are seen
swimming along the surface of the water, striving
cunningly to glide under the bellies of the horses.
By the force of their invisible blows numbers of the
poor animals are suddenly prostrated ; others, snorting
and panting, their manes erect, their eyes wildly flash-
ing with terror, rush madly from the raging storm ;
but the Indians, armed with long bamboo poles, drive
them back into the midst of the pool.

' By degrees the fury of this unequal contest begins
to slacken. Like clouds that have discharged their
electricity, the wearied eels disperse. They require
long rest and nourishing food to recover the galvanic
force which they have so freely expended. Their
thocks become weaker and weaker. Terrified by the
noise of the trampling horses, they timidly approach
the brink of the swamp, where they are wounded by
harpoons, and drawn on shore by non-conducting poles
of dry wood.

' Such is the remarkable contest between horses and
fish. That which constitutes the invisible but living-

O

weapon of these inhabitants of the water — that which,
awakened by the contact of moist and dissimilar par-
ticles, circulates through all the organs of animals and

158 I'livsioi.ociY OF Mi.-t i.i> AMI M:I;VI:S.

plants thai which, Hashing amid the roar of thunder,
illuminates the wide canopy «i' heaven \\hich liinils
in>n to iron, and directs the silent recurring cour>e ot
the magnetic needle .-ill, like die varied hues of the
refracted ray of light, rld\v from one common source,
and all lilen 1 together into one eternal all-pervading
power.'

3. All electric fishes are distinguished by the pos-
session of peculiar organs in which the el.-et rie discharge
originates. These resemble jiowerfnl batteries, Avhich
can be put in action by the will of the animal, and
Avliich then generate currents which, pas-ing through
the A\aler, meet and act upon other animals which
happen to be near, so that the latter may even be
thus killed. These electric «/y/,//,x. as they are called,
are formed on the same plan in all the three above-in en-
tioned genera of fishes. They consist of a large number
of minute and delicate plates which, arranged .-ide by
side and enclosed in coverings of coiinei-iive tissue,
form the whole organ. In the Torpedo these organs
lie flat on either side of the. vertebral column. In the
(i't/iiin<>(tiH and the Malopterurus they are arranged
longitudinally; and in the latter they form a closed
lube, in which the animal is concealed, its head and
tail, as it were, alone projecting. The separate plates
of which the organ consists are arranged, therefore,
horizontally in the 7'«/'/" 'In, vert ically in t lie '///'" ""/"*
and Mnln/'/i'i-itriix. Kadi of the-e plates consists of

an extremely delicate membrane which, when the organ
isinastateof activity, exhibits positive elecl nVity on the

one side, negative on the other. The currents of the
numerous plates combine as in a bat t cry, and (hus all
together atl'onl a very j owerful current. With each

THE MULTIPLIER. 159

plate is connected a nerve-fibre, by means of which
the animal is capable of voluntarily effecting the elec-
tric discharge, just as voluntary muscular contractions
can be effected by means of the nerve. These nerves
may also be artificially irritated, with the result of pro-
ducing one or more electric shocks, just as irritation of
a motor nerve elicits one or more muscular contraction.
The analogy of electric organs and of muscle is, in fact,
from a physiological point of viewT, complete.

Mention must yet be made of the fact that forms
nearly allied to these fishes— for instance, the various
forms of Mormyrus, which in structure resemble rays-
possess similar organs, though these have not as yet
been shown with any certainty to be capable of any
electric action. It has, moreover, been assumed that,
the luminous organs of certain insects are to be referred
to electric forces ; but this has not, been in any way
proved.

4. Before entering further into the statement of the
electric phenomena in animal structures it will be neces-
sary to say something of electric phenomena in general,
and of the means of exhibiting them.

It is well known that an electric current results
when two different metals are in contact
with each other, or with a fluid. Elec-
tricity occurs" in this case as a current,
that is, in a state of motion ; while in
other c.ises it exists in a quiescent con-
dition. On immersing a piece of copper
and a piece of zinc, as in fig. 36, in a glass
containing diluted sulphuric acid, and then AN ELECTRIC
uniting these above the fluid by a wire,
the positive electricity passes through the wire from the

16'0 rilYS'loLOC.Y OF MfSCLES AND NKUVKS.

ii tin- x.iuc and through the liquid from the zinc
to the copper. A magnetic needle is used to indicate
tin- prex-nce of such M current. Aii elect ric current, if
made t<» pa>s parallel 1o a magnetic needle, deflects

the latter from its normal position, and tends to place

it at right angles to its original position. According
to the direction in which the positive electricity rl<>\\-,
and according <<> the position of the conducting -wire
relatively to the magnetic needle, the north pole of
the needle is deflected either to the east or to the west ;
so that not only the actual presence of an electric cur-
rent may he shown by means of a magnetic needle, but
its direction in the wire may also be determined. This
simple means, however, only serves the purpose \\hen
the current is comparatively strong, for the magnetic
needle is retained in its position by the attracti..n of
the earth, and the magnetic current must overcome
this before il can deflect the needle. In order to d« t. . t
weak currents, the wire through which the current flow-
is wound in several coils round the needle. As cadi
coil exercises a force tending to cause the deflect i,,n
of the needle, the deflect ing force is increased ; and an
instrument of this sort is, therefore, called a /// ttt/lj>lii /•.'
In order to increase the sen sit i\ vness of t his st ill further,
the attract ion of the earth must be annihilated as far
as possible, so that e\eii \\cak currents are able to cause
deflection. This is accomplished, for instance, by ar-
ran-ing a li\ed magnet above or below the magnetic
needle, so that it acts on the latter in a direction

1 If :it trnl ion is | a :•! to crrtnin circumstances, \\ 1 1 idi c:iniii'l !'••
in ill-tail lii-iv. iln- Miuir i i ist ni inriit can also \n- usc-d to
nirasiirr tin- stivnyth of ciirn-nts ; it is, tlu-rrforc, also callnl a <jnl-
rniioini ti-r.

THE MULTIPLIER OR GALVANOMETER.

161

trary to that of the attraction of the earth, and by
carefully bringing this magnet nearer until the action
of the earth is almost entirely cancelled. Or two mag-

FIG. 37. A MULTIPLIER.

netic needles, as similar as possible, are connected by a
fixed intermediate piece in such a way that the corre-
sponding poles are turned in opposite directions. As
the force of gravitation now tends to turn the two

lf>2 PHYSIOLOGY OF MrsCI.KS AND NKKVI 3.

needles iu opposite direct inns, the force of :it tract ion
of the earth-magnetism is entirely, or almosi entirely
removed, ><> that even very weak electric currents, if
cause, 1 to jnss round the needle in a suitable way. can
cause a noticeable deflection of the needle.

Fig. :>7 represents a sensitive multiplier of a form
well suited for physiological experiments. The t\vo
needle- are connected together, and are suspended by
means of a thread of silk from the frame k' h; the screw
i serves to raise the needles to a proper height, so that
one of them can move- freely within the coils of the wire,
the other above the latter and over a graduated circle, by
which the deflection effected by the current can be mea-
Mired. The very thin wire, enclosed in silk, is wound
on to the frame C ; the hindm-' screws f f serve to

I/ •/

transmit the current.

The use of the multiplier for physiological pnrpo.-es
has recently considerably decreased, owing to the more
perfect adaptation of another form of apparatus, called
the tangent galvanometer, for such purposes. The ad-
vantage of this consists in the fact that it is not only
very sensitive, but it also allows the strength of the
current to be measured. If, for example, the deflec-
tions of the magnetic needle are very slight, t he strength
of the currents may be regarded as proportionate to the
trigonometrical tangents of the angle of deflect ion.1 In
order to measure slight deflect ions of this sort, our
former method of observation hv means of the mirror
and lens may be used (chap, iv., § 3, p. 57). Kither
the magnel [a in it.-e|f reflecting, or it is connected
with a mirror, and is suspended by a silk thread in a
copper sheath, J. which is closed by plates of looking-
1 Sec N'»f i-s aii'l .\<l<lit ions, N.I. It.

THE REFLECTING GALVANOMETER.

163

glass. The electric current can be transmitted through
the coils B' B, which move on slides, in order that by
their greater or lesser distance from the magnet, the

sensitiveness of the instrument may be graduated at
will. In order to measure the deflections, a graduated
scale is placed parallel to the mirror when in its qui-

104. PHYSIOLOGY OF Ml- LES .\M> NKKVF.S.

escenl portion, ami Its reflection is observed through
the leu- afl de-erlbed in Chap. IV., § 3. This m:iy :ilso
he used to render the deflection visible to a large audi-
ence, l>y allowing tin- light of a sufficiently powerful
l.-inij) io full on the mirror and throwing tlic reflection
on to a screen by means of a l-'iis. In order to in-
crease t In- sensit i\ eness of the inst riiiin-iit, the influence
of gravitation on the deflecting magnet is decreased, as
already de>cribed, by means of a properly arranged
magnet.

5. Having, in one or other of these ways, provided
as sensitive a multiplier as may be, all that is necessary
is to connect (lie animal substances which are to l>e ex-
amined with this, and then to observe whether deflec-
tion occurs or not. ; whether, that is, with the arrange-
ment selected a current is proent or not. ]>ut the
more sensitive is the multiplier, the harder is it to
connect any part of an animal with it in such a uay
that no current occurs, and it would be a mistake to
suppose that all these currents are elicited by the ani-
mal substances themselves. If, for example, the ends
of the wires of the multiplier are connected with two
wires of the same metal— for example, copper; and if
these wires are immersed in a conducting fluid— for
example, diluted sulphuric acid — considerable deflect ion
of the needle a 1 \\ays occurs, o\\ing to the fact that the
copper \\ ires are never so homogeneous that they do
not themselves generate a slight current. If platinum
wires are used instead of copper, these can, it is true,
be rendered homogeneous by careful denning; but this
homogeneity soon di-app--ar<. >o that even with this
metal cnrn nt- result \shidi depend solely on the dis-
similar nal lire of the metallic surfaces. Fortunately,

HOMOGENEOUS DIVERTING VESSELS. 165

there are combinations of metals with fluids which are
free from these faults. Two pieces of zinc, the surfaces
of which have been amalgamated by smearing with
quicksilver — which have, therefore, been equally covered
with a coating of zinc-amalgam, a combination of zinc
and quicksilver — act as though entirely homogeneous if
they are immersed in a solution of sulphate of zinc; and
these metals retain their homogeneity even when elec-
tric currents traverse the metals and the fluids. The
wire of the multiplier may be connected with strips of
amalgamated zinc of this sort, and these may be im-
mersed in a solution of sulphate of zinc without any
deflection being indicated even by a very sensitive mul-
tiplier. While, therefore, it might lead to serious error
if the wires of the multiplier were brought into imme-
diate contact with the animal substances to be ex-
amined— as electricity would, in such case, be generated
at the point of contact itself — it is possible, by using
this amalgamated zinc and solution of sulphate of zinc,
to exclude any foreign source of electricity, and, pro-
vided that the animal tissue is properly inserted, to
be sure that the observed deflections of the magnetic
needle are really due to electric forces situated in the
animal substances themselves. The point to be aimed
at in this experiment is, therefore, to place the animal
substances in such a position that any currents gene-
rated in them can only pass to the wire of the multi-
plier through the zinc solution and the plates of amal-
gamated zinc.

6. In order to attain this object, du Bois-Eeymond,
to whom is chiefly due our knowledge of the electric
phenomena of animal tissues, arranged the apparatus
in the following way (fig. 39). The ends of the wires

1GG

PHYSIOLOGY OF MUSCLES AND NERVES.

of the multiplier were connected with two troughs or

Vessels »\' ra-t /.inc. the mild- Hirfarrs uf which had
been Lacquered, while tin- inner cavity had hern care-
fully amalgamated. A Dilution of sulpliatc of zinc- wa>
poured into this cavity, and pads. formed of many folds
of blotting-paper saturated with the same solution, were
folded over the edge of the vessels in such a \vav that

FII;. ."!». H.IMIICI \rors t>ivr.nTi\o VFSSKI.. AS [tgED nv E. nu

KKYMOND.

part \va- inini(>rsed in the x.lntion, part protruded over
tlie edges, and these ).ad> end in a >harply rut cross
section. Small discs of an isoktmg substance (vulca-
nised india-rnl.lier), \\itli the- help of caoutchouc hands,
rrlaiurd tlie p;i,l< in tln-ir places. The vessels hein^

|)U>hed tOWard each other til! the pads touched, or the

intermediate space l><t\\een the pads being bridged 1»\ a

third pad, al-o >alurated \\ith a >o|ntioii of sulphate of

zinc, the needle <>t' the multiplier continued unmoved,

ELECTROMOTIVE FORCE. 167

thus affording proof that no cause of the generation of
currents is present in any part of the apparatus. If the
body to be examined is then substituted for the third
pad, with the result of deflecting the needle, proof is
afforded that some cause effecting the generation of a
current exists in the body. The only disadvantage
of the arrangement is that the animal substances thus

O

examined, being in contact with the concentrated solu-

* O

tion of sulphate of zinc, are corroded, and their vital
qualities are injured. To avoid this, so-called protec-
tive shields, i.e. thin plates of plastic clay (porcelain)
which has been mixed with a diluted solution of com-
mon salt (i to 1 per cent.), are used. These are placed
on the pads of blotting-paper, where the tissue to be
examined touches the latter. The clay protects the
tissue from direct contact with the solution of sulphate
of zinc, though, clay being a conductor, the electric
action present in the tissues can reach the zinc and the
wires of the multiplier.

7. In examining muscles or nerves by this method,
according to the way in which the animal substance is
applied, sometimes no deflection of the magnetic needle
is observable, sometimes slight, and sometimes stronger
deflections appear. The same body, for example a piece
of muscle, may in one position afford a very strong cur-
rent, while in another position it affords none at all.
In order to understand this, we must examine the way
in which the electric currents present within the tissue
examined are able to impart themselves to the wire of
the multiplier, in the case of the method of experiment,
selected.

Let us revert to the simple apparatus (fig. 36, p. 159)?
in which we first studied the action of electric currents

168 PHYSIOLOGY OF MUSCLES AND NERVES.

• in ;( magnetic needle. Apiece of zinc and a piece of
nipper are immer.-ed in diluted sulphuric acid, their
projecting edges being connected by a piece of wire.
\VLen in this condition the apparat us is said to be closed.
Within it circulates a current which passes within the
wire from the copper to the zinc, and within the fluid
from the zinc to the copper. If the closing wire is
oh.-erved by itself, no current arises in it until it is
joined to the apparatus. And if the apparatus is ob-
served by itself, that is, without the closing wire, there
is no current present in it. It is only in a closed circle
that a current can be generated. It is, however, in the
apparatus that the cause which under favourable cir-
cuin.-tances gives rise to the electric current, lies ; for if
the \\ire by itself is bent into a circle no current is
generated within it. Even the cause of the generation
of currents within the apparat us may be shown. If when
the apparatus is open, that is, when the circuit is not
completed by the addition of the connecting wire, the
projecting edges of the copper and zinc are connected
with an electrometer, the gold leaflets are seen to di-
verge, thus showing that an electric tension prevails
at these metallic ends projecting from the fluid. This
tension is po.-,iti\e at the copper end, negative ;(t
the /inc end. On connecting the two metals by a

closing \\ ire, tl ppo>ed electric currents unite, and

this is the cause of (he current in the wire. The force
\\hichwithin the wire exhibited electric tension con-
tinues to act, and causes the current to continue to
tra\erse the \\ire. This is called the electrOTTlOtive force

of the apparatus It e\pre--;e- itself, when the apparatus
i- not dosed, in the electric tension at the projecting
metallic ends or pol,- of the apparatus; and \\hen the

ELECTROMOTIVE FORCE. 169

poles are connected together by a closing arch, it finds
expression in the current which it generates in this
arch.

Supposing that the two metals contained in the
fluid did not protrude from the latter, but were in
contact with each other within the fluid, then it is
evident that the apparatus would be closed in this case
also, but the closing arch would then lie within the
fluid. Through this the current must pass from the
copper to the zinc, and from the zinc to the copper
through the fluid. That this is really the case can
easily be shown, for on the immersed metallic surfaces
globules are seen to be generated, due to the gases
generated by the electric current by the separation of
the water into its constituent parts, hydrogen being
found at the copper, oxygen at the zinc point. In this
case, therefore, the apparatus is in itself closed. No
external closing-arch is present, the existence of a mag-
netic current at which can be indicated by means of a
magnetic needle. Yet with a multiplier it is possible
to show the currents circulating in the fluid, and in
the immersed metals ; this may be done by a principle
spoken of as the distribution of electric currents.

Let us assume that an apparatus k is not directly
closed by a closing-arch, but that from each pole passes
a wire which touches the conductor, the form of which
does not matter, shown in fig. 40 at two points, A B.
It can be shown that the electric currents pass in this
case through the body, but distribute themselves, not
merely in straight lines connecting A and 5, but
throughout the body, so that they represent a number
of lines of conduction, all of which meet together at
the points A and B, where the electric currents enter

170 rilVSIoI.OCY OF MUSCLES AM) NKUV! -.

and leave the body. If the body which is insert e.l is of
.-imple form, the separate lines of transmission mav easily
be calculated from the form; in bodies of invirular
shape this i> s-inieuhat hard to do, but even in such
cases it i.- pos-ihle to determine experimentally, not only
that the electricity distributes it>elf throughout the
b"dy, hut even the lint > along which the separate cur-
rents pass.

Taking a simple example, for instance, a thick cyl-
indrical rod, in which the electricity passes in at the

FIG. -10. DISTRIBUTION «r THI. < IT.IIKXTS IN IKKI:<.I I.AI; IONM CI.IKS.

surface <.f one end and out at theother.it is ///•///,// /',<
probable that the lilies -imply traverse the length of
the rod purallel to its ;i\is. \\'e may in imagination
repine.- tin- r-id hy a bundle of wires, each of which will
in this case be traversed by a portion of the whole
current, [f one of these wires is cut, and it- ends are
connected with the multiplier, it is evident that that
part of the current \\hich traver-es this \\ire mn>t
pass to the multiplier and cause a defleei i >u of the
needle. Jiut even if the wire is not cut. but is con-

ELECTRIC 'FALL.' 171

nected with the multiplier at two points in its length,
in this case also a part of the current must, in ac-
cordance with the law of the distribution of currents,
branch off through the multiplier.

8. This may be made intelligible in another way.
We saw that a certain electric tension exists at the poles
of an open apparatus, and that the opposed tensions
of the two poles are the causes of the current in the
closing wire. If the poles were but once charged with
proper quantities of electricity, these would unite in
the wire, with the result of producing an instantaneous
current. But as, in consequence of the electromotive
force of the apparatus, the tension at the poles is con-
tinually renewed, the current is continuous. So that at
both ends of a closing wire opposed tensions prevail con-
stantly, and these act on the natural electricity present
in the wire, as in every other body, and set it in motion.
Consequently, while the current flows through the wire,
different tensions must prevail at the various points of
the wire. At the point of contact with the positive
pole there is a definite positive tension ; at the point
of contact with the negative pole there is a similar
negative tension, and in the middle of the wire there
must be a point at which the tension = 0. This may
be diagrammatically shown by representing the tension
which prevails at each point of the wire by a line de-
scribed at right angles to the wire, the length of which
represents the tension proper to the point in case. Let
a b (fig. 41) be the wire ; then the line a c is the ex-
pression of the tension existing at one of its ends,
which is connected with the positive pole. In order
to indicate that the tension at the other end, 6, is
negative, i e. of an opposite kind, let the line b d be

172 PHYSIOLOGY or MCSCI.I:- AND M:I;\ i:s.

dr:i\vii downward from <i It. In tin- centre there is no
tension. At any ]><>int between the middle and the
end ", :-ay at <-, a positive tension must prevail which is
less than that at <i, but greater thanO. It is expressed
Ity the line e f. Similarly at any point between the
middle an 1 the end 6, say at //, there is a definite
negative tension which may be expressed by the line
// It. The same thing may be done for each of the
other points in the wire. If the wire is quite uniform,
the positive tension decreases quite regularly from tin-
end a to the middle, and in the same way the nega-
tive tension decreases quite regularly from the end b
to the middle. Uniting the ends of the lines which

FIG. -11. Tin-: FAI.I, IN TIIK KI.KCI UK 1 1\ .

thus express the tensions, the result is an oblique
straight line which cuts the wire in the centre, and
the distance of which from the wire at any point re-
presents the tension at that point.

This regular decrease in the tensions prevailing in
the wire may be shown by means of an electrometer, if
the latter is brought into contact \\Jth each point in
the wire. The gradual decrease of the tensions in the
wire is e\idently also the essential cau-e of the move-
in. -nt of the electricity through the \\ire, for nt each
point in the wire there are adjacent portions in which
tin- ten-ion- gradually become less from left to right,
so that the elect ricity is enabled to How from left to
right. The case i- evidently like that of a tube through

ELECTRIC 'FALL.'

173

which water flows, for in that case also the pressure of
the water gradually and regularly decreases from one
end to the other. To express this similarity we will
apply to electric currents a term borrowed from flowing
liquids, and will call the gradual decrease in the tension
the fall in the electricity.

Let us compare two wires of the same thickness,
but of unequal length, a b and c d (fig. 42). If a b
is inserted between the poles of a chain, the fall is
represented by the oblique line e /. Supposing a b

FIG. 42. THE ELECTRIC FALL IN DIFFERENT WIRES.

removed, and c d inserted between the poles of the
same chain, the tensions at the ends would be the same,
so that the fall in the case of the wire c d may be
represented by the oblique line g h. It wrill be ob-
served that in the case of the shorter wire the line runs
much more abruptly, the fall is greater, and the cur-
rent of electricity advances much more rapidly in this
wire. Assuming now that the two wires a b and c d
are simultaneously attached to the poles of the chain,
in this case also the tensions at the two ends must be
equal, but the fall must be different. Supposing that

171 PHYSIOLOGY OF Ml'SCLKS AND NKKVKS.

in-t.-ad of the-e two \\ir.-s ;i number of separate wires
are u-ed. then tin- same thin^ happen- : and if the wires
are w.-lded together i lit . . a cm 1 1 n i. >n conducting bodv,
this does not esseni ially alter the t-onditions of the fall,
80 that we may imagine the whole liodv to consist of
these separate -wires, in each of which a definite fall,
the steepness of which depends on the length of the
particular wire, prevails. Tlic.se wires are, however,
merely paths alon<.- which the electric currents pass,
and of which we have already spoken. In tin- case
of these paths also definite falls mii.-t prevail, and these
must be more steep in proportion as the points at
which the elect ric current s enter and make their exit
are nearer together.

9. Let us return to the case of a simple wire
through which a current passes. On uniting two
points in this with two electrometers these exhil.it
varying tensions, and the difference is greater the fur-
ther the two points are separated" from each other. If
the points are then connected by a bent wire, it is
evident that the different tensions at the points of
contact nuist effect a disturbance in the natural elec-
tricity within the applied wires, and consequent Iv iiiu-t
generate an electric current from the point :it which
the tension is -rreater to t-hat at which it is le-s. If a
multiplier is inserted in the applied \\iiv, the needle
will be deflected. This is a> t rue of a n^'iilar as of an
irregular conductor. If in the 1 o ly .1 // (ti^. -I.".),
electricity moves along \arions paths, and if, as we
have seen, different ten-ions pre\ail at t\\o points in
such a path, a current mii.-t ari-e if (he ends of a Lent
wire are applied to these point-, and if the bent wire
i- Hipplied with a multiplier the needle \\ill be de-

TENSION IN THE ARCH. 175

fleeted. On the other hand, in two different paths of
conduction there must always be points at which the
tension is the same. For in each path the tension
begins at a certain positive value (at A}, and passes
through a value = 0 to a certain negative value (at £).
The needle of the multiplier must, therefore, remain at
rest if the two ends of the wire of the multiplier are

FIG. 43. PATHS OF ELECTIUCITY IN A CONDUCTOR.

applied, not to two points of different tension, but to
two points of equal tension. This enables us to ob-
serve whether in any body in which electric currents
move in any form, two points have similar or dissimilar
tension, and by systematic experiments of this kind we
shall evidently gradually obtain an insight into the
form and relative position of the paths of conduction
within the body examined.

176 1'llYSIOLOGY 01-' SEKVKsf AND MUSCLES.

CHAPTER X.

1. Diverting arches j 2. Current-curves and tension-curves ; 3. Di-

verting cylindi-rs; 4. Method of measuring tension diflVivi

liV

1. If the two ends of a bent wire urc applied, in
tin- way described in the last chapter, to any conductor
\vhich is traversed by currents, then part of the currents
present in the conductor may flow through this win-.
Part of the curr.ent is, as it were, conducted out of tin-
body in order to facilitate its examination. I'nder
certain circumstances this may cause an alteration in
the conditions of the currents within the conductor.
\\'e will, however, assume that tin's is not the case,
but that the tensions at the point > at which the wire
is applied to the conductor are not altered.1 The
direction and strength of the current which arises in
the conductor will then depend only on the differences
in tension at the point of contact , and mi the resistance
ofVcivd by the wire.

A wire of this sort applied to a conductor liaversed
by currents is called a <// mi i n</ <i rcjt ; the end-; of the
\\ire with which it touches the body to be examined
are called \\n-firf uf tin- nrrli; and the distance be-
tween these feet is called ih • dixfit IH'I' of tension.

1 I';, i ririMiiii-i'ainvs umli-r wlfii-h tin- i-xc •]>( imx nc.'iir

• >l:iiin -i I IICTI- ; \ d ma1 t'-rs may In- BO aMMii^fl I !iat such

ti. n- rl

CURRENT-CURVES AND TENSION-CURVES. 177

The further nature of the arch does not matter.
It may consist of one or more wires, and it may or
may not include moist conductors. Only one condition
must be fulfilled : no electric actions must be caused
by the contact of the diverting arch with the conductor
which is to be examined. Now, we have already seen
that this is unavoidable when metallic wires are ap-
plied to moist animal substances. The ends of the
wire of the arch must, therefore, be connected with the
zinc diverting-vessels described above (fig. 88). In
this arrangement the clay shields, saturated with a
salt-solution, represent the feet of the diverting arch.
Such an arch, which neither in itself nor by its appli-
cation to the conductor under examination affords any
cause for the generation of currents, is an homogeneous
arch.

In order to attain a thorough knowledge of the
distribution of tensions in a conductor, it would ap-
parently be necessary to touch all points of the latter
in turn with the feet of the diverting arch. • This is
easily done in the case of the surface of the body, but
as regards the inner parts it is hard and often imprac-
ticable. . We must therefore rest satisfied with an
examination of the surface ; but it may be shown that
trustworthy conclusions as to the character of the inner
parts may be drawn from this study of the surface.

2. Two cases must be distinguished. Either the
body to be examined is in itself incapable of electric
action, and the electric currents, the internal distri-
bution of which is to be examined, are imparted to
it from external sources ; or electromotive forces are
situated within the body itself, and it is the currents
generated by these which form the object of research'.

178

I'UVSKC.o iV OF M!>d.I-:s AM> MCKVKS.

The case «>f organic tissues, with which we are con-
cerned, is of the latter sort ; for we have seen that
when (hrse an- iliserteil liel \veen ( he ends of a honio-

<;eneo;i-. arch, electric action takes place under certain
circumstances. The f^ct that in other cases no such
action occurs will be intelligible after the account just
given, for we may assume that in such cases the two
points which are touched by the ends of the arch are
similar in tension.

Let BODE (fig. 44) represent a section through

E

-b

JJ

D

FIG. II. Ci UUI-;NT-< i uvi - \M> 1 1 N-K>N-< TI:\ i -.

a body in which an electromotive force is present. For
the sake of simplicity we will assume that the body

is a regular cylinder, and that the elect ro;n«t i\c force
i- nt nated in its axis; then that which we show in

the case "f I!('l>h' \\ill be e(|iially true of every

ot her .-ect ion. Let the point .1 represent the seat, of

elect roniot i\e force l which >et>the po>it i \ e elect ricit V

in motion to\\ard the ri^ht. the negative electricity
toward the left. The \\hole body is t hen .icciipied by

1 In (.rili-r ti. l,avf a pliv^iral l.asis fur tlii> elecl nuimi ivr t'on-c \\c
may iinaL'im- tin- cylinder tu cuiisisl nf a lluiil, and I liat at the i>niiit

.1 is situated a body consisting 1ml f uf -/\].f, lalt' nf CM].] « r.

CURRENT-CURVES AND TENSION-CURVES. 179

current-paths. We naturally think of these paths
•within the cylinder as planes, so that we obtain current-
planes, which enclose each other like the scales of an
onion, and which in the section which we figure form
closed curves all of which pass through the point A.
They are represented on the figure by unbroken lines.
On each of these paths a definite fall prevails, as we
know — that is, in each of these the point immediately
on the right nearest to A is the most positive, the ten-
sion gradually decreasing toward and up to the middle,
where it = 0, then becomes negative, the greatest
negative tension being immediately next to A on the
left. This is true of all paths or lines of conduction.
In each there is a point at which the tension = 0 ; on
the right of this the tension = -f 1 ; yet further to the
right it = +2, and so on up to the greatest tension at
A ; and similarly in each curve, to the left of the zero
point there are points at which the tension = — 1,
— 2, and so on. If all the points of equal tension are
united, the result is a second system of curves, which
are at right angles to the current curves, and which are
represented in our figure by dotted lines. There is a
curve which unites all points at which the tension = 0,
another which unites those points at which the tension
= + 1, and so on. These may be called tension-curves
or iso-electric curves. In the cylinder the section of
which is here drawn, these curves evidently represent
planes which cut the planes of the currents already
mentioned, and which may be called tension-planes or
iso-electric surfaces. On the outside of the cylinder
these iso-electric surfaces are exposed, and meet the
surface in bent lines, which in the simple figure
which lies before us are all parallel, that i?, surfaces

180 rilYSloLOGY OF MUSCLES AND NKltVI 3,

which cut the surfaces of the cylinder parallel to the
surfaces of its mils. The iso-electric surface repre-
senting a tension = 0, cuts the cylinder near its centre,
and dhides it into two unequal halves, of which the
riijht is positive, and the left negative. The other iso-
'•lectric curves cut the surfaces of the cylinder in par-
allel curved lines; -and the iso-electric curves repre-
senting the greatest positive and the greatest negative
tensions meet the surfaces at the central points of the
end surfaces of the cylinder which, in the figure given,
are marked + 6 and — b.

The conditions are not always as simple as in this
case. If the body under examination is not a re-
gular cylinder, and if the electromotive force is not
situated exactly in its axis, then the arrangement of
the iso-electric surfaces is more complex. The body
under examination is, however, always occupied by a
system of current-planes inserted one within the other,
and a system of iso-electric surfaces can be constructed
which cut the outer surfaces of the body in curves of
one fofm or another. Along each curve of the outer
surface corresponding with an iso-electric surface the
same tension always prevails ; on two of these curves if
adjacent the tensions always differ. Regarding therefore
only the Mirfaro, it may be said that if an electro-
motive force is present within the body, this must cor-
respond with a (1. -finite arrangement of tensions on
the surface of the body. By studying this superficial
arrangement of the tensions we may therefore draw
conclusions from this as to the situation of (he electro-
motive force within the body,

3. The diverting vessels (fig. 38) above described
are not always sufficient for the purposes of research.

DIVERTING CYLINDERS.

181

Apart from the fact that the insertion of the animal
substances between the pads cannot always be con-
veniently managed, it is impossible to bring individual
points of the substance into contact with the pads. This
does not matter at all when the iso-electric curves run
parallel to each other, as in the case described in § 2,
on the outer surface of the cylinder. In such cases it
is always sufficient to apply the sharp edges of the clay
discs to the surface in such a way that all the points
which come in contact with these edges belong to the
same iso-electric curve. But even in observations on

FIG. 45. DIVERTING CYLINDERS AS USED BY E. t>u Bois REYMOXP.

the surfaces of the ends of the cylinder the case is dif-
ferent. Here the iso-electric curves form concentric
circles. In such cases it is absolutely necessary to
carry out with somewhat greater accuracy the theoretic
condition that the diverting arch should touch the
conductor which is to be examined at two points. An-
other form of diverting apparatus, invented by du
Bois-Reymond, is used both for this purpose and for
conducting currents to the body under examination in
cases wThere it is important to avoid electrical polari-
sation. These, which are usually called unpolaris-
able electrodes, are represented in fig. 45. The glass

182 PHYSIOLOGY OK Ml'SCLES AND NKKVES.

cylinder ". somewhat flattened, is attached to the stand
A. The Mu-ket i' :ind the motor apparatus on the
column // allow the glass cylinder to be placed in any
desired position. Within the cylinder i< a strip of
amalgamated sheet zinc b, which can lie connected
with the multiplier by means of a wire. The glass
cylinder is closed below with a stopper of plastic clay
inoi>tened with a solution of common salt, the project-
ing ends of which can be moulded into a point which
touches the suialle-i possible point on the conductor
to lie examined. The space within the glass cylinder
is filled with a concentrated solution of sulphate of
zinc, and thus forms an unpolarisable and homogene-
ous conductor between the strip of zinc and the clay
point. A second and exactly similar apparatus, which
is only partly represented in the figure, provides for
the divei>iou from the other point of the conductor.

Whatever form of diverting apparat us i- employed,
the determination of the fact whether the two points
touched bv the feet of the diverting arch have like or
unlike tension will be more accurate the more sensi-
tive is the multiplier which is inserted in the diverting
arch. By placing the body to be examined in such a
\\-.\\ that the various points in its surface successively

lie on the pads of the above-descril ied diverting vessel
(see ch. ix. § ,r>), or liy touching them with the ends of
the diverting cylinder ju-t mentioned, it may be dis-
covered which points have equal tension (for in such
cases the multiplier will indicate no deflect ion), or, if the
points touched are unequal in tension, it may lie dis-
covered at which the positive ten-ion i> great e>t. For,
from this latter point a current must pass through the
multiplier to the point at which Hie positive tension is

MEASUREMENT OF DIFFERENCES OF TENSION. 183

less (or, in other words, the negative tension is greater),
a fact which can be recognised by the direction of the
deflection exhibited by the multiplier. In order, how-
ever, thoroughly to understand the position of the iso-
electric curves, it would also be necessary to know the
absolute amount of the iso-electric tension at each
point. Instead of this, however, it is sufficient to de-
termine the difference between the tensions at each
two points, which may be found by very accurate and
trustworthy methods.1

4. To calculate these differences from the extent of
the deflection of the multiplier would, for reasons which
cannot here be further explained, be very inconvenient
and would afford very inaccurate results. But these
differences may be measured with quite sufficient pre-
cision by a method invented by Poggendorff and after-
wards improved by du Bois-Keymond.

If it is required to determine the weight of any
body, the latter is placed in one of a pair of scales,
and weights are placed in the other until the two are
again in equilibrium. As in this case the action of
the two weights on the beam of the scales is to raise
each other up, they must be equal. This well-known
principle is, however, capable of an important generali-
sation. It is, for example, required to determine the
attraction exercised by a magnet on a piece of iron.
The iron is attached to one end of the beam of the
scales, weights to the other, till the beam is again
balanced. The magnet being then placed under the
iron, the balance of the beam is again disturbed by the
magnetic attraction, and weight must be added to the
other scale before it is restored. It is evident that the
1 See Notes and Additions, No. 10.

.Y OF MUSCLES AM> NKKYKS.

184

amount of weight required for this latter purpose affords
a measure of the force of attraction between the iron
and the magnet.

In the present case a certain deflection in the multi-
plier results from the difference in tension at the feet
of the diverting arch. It is required to measure the
difference. If it is in any way possible to influence the
deflect ion of the multiplier in an opposite direct ion, and
exactly to such a decree that the multiplier no longer
indicates any deflection, then the two influences must

I'K.. If,. Ml. AM KI.MKNT T.Y COMI'KXSATloX «>!•• Till-: IHFKKia.Nt 1. (>K

TENSION.

he equal, and the one may serve as a measure for the
other. The experiment indicated in these instances

i- called measurement by compensation. In order to

applv it to the case in point, the action of one dif-
ference of tension is cancelled by that of another \\liich
ma\ lie altered at will. The rheochord. v, hich has al-
n.;idv lieen described, affords a COnvenienl means of
doiu<_;- I hi-.

Let /.' /.'' (li^r. -Hi) 1'c^i wire extended in a straight

Line (the line of the rheo< hordj thro-.-^h \\hich a current is

MEASUREMENT OF DIFFERENCES OF TENSION. 185

passed from the apparatus K. W indicates an arrange-
ment by which the current of this apparatus may be
made to pass as desired either from R to R' or in the
opposite direction. T is a multiplier by the deflection
of which proof may be obtained that the current of this
apparatus remains constant in its strength. The other
parts given in the figure we will for the present dis-
regard. According to what we have already seen (ch.
ix. § 7) a definite electric fall must be present in the
rheoehord. Let us assume that the current passes from
R' to jR, that the tension at R = 0, and that it in-
creases toward R'. As the rheoehord line is entirely
homogeneous, this increase must take place quite regu-
larly; i.e. the tension at every point of the chord must
be proportionate to the distance of that point from R.
Now let us imagine that a body, A .5, within which
an electromotive force is present, is to be examined.
Naturally two points on its surface, a and 6, have dif-
ferent tensions, and it is this difference which is to be
measured. The point a must be united by means of a
wire (in which is inserted as sensitive a multiplier as
possible) with R ; the point b must be connected by a
wire with a sliding-piece S which moves on the rheo-
ehord line. Two differences of tension now act on the
multiplier. Firstly, the differences of tension between
the points R and S of the rheoehord; and, secondly,
that between the points a and 6. If at 6 there is a
greater positive tension than at a, then the two dif-
ferences of tension are opposed in action.1 As the

1 If the positive tension were greater at a than at b, then it
would be necessary to reverse the direction of the current within
the rhecohord. The commutator W is therefore inserted to effect
this reversal of the current.

186

rilVSlOl.oiiV <•!• MrSCI-KS AM> NKKVES.

difference in ten-ion between /.' ;md S can be nil ered
liy chanLMiiM; tin- ]>n>ition of ,S', tlio slide X m:iy he
placed in such a ]>o-it inn tliat the t w<> inflm -n- •< - rxnctly
halanci' facli ntluT, <>r, in ntli.T ^-i>nl>. in >u<-li ;i |msition
tliat tin- multiplier indicates no di-lli-ctinn. Thus it is
evident tliat

S - I!

l>iflVri-ur<- in tr-n-inn nt
'.Mi jioints i if tin- I

li — a

= 0

the two
doctor.

or S — R = b -- n ;

in trnsinn at
-: of the con-

flu- difference, that is, of the tension l>et\\» en 1> and a
is equal to the difference of tension between S and R.

111.. 17. lM );c>l~-Kl.YM<>M>'> KOI'M) ( . M !•[ \> \ mi;.

The Litter i> e\]ires-ed in i nill line) r< >, each nf \\hich
intlieiite- a certain cnii-t;mt anmunt \\hen a delinite
vhenclmrd \\ire is u>cd. and when the current which is

cd tlimn^li the lulter is of a delinitr >1n-n^th.
'J'o facilitate lie a-iii-riin nts of this kind, du Hois-

MEASUREMENT OF DIFFERENCES OF TENSION. 187

Reymond invented a ' round compensator ' (fig. 47), in
which the wire of the rheochord r r' is placed on the cir-
cumference of a circular disc of vulcanised india-rubber.
The beginning and the end of the wire are connected

FIG. 48. DIAGRAM OF ELECTRIC MEASUREMENT BY MEANS OF A UOUNP

COMPENSATOR.

with the clamps I and II ; from the beginning a wire
also passes to the clamp IV. The clamp III is con-
nected with the small reel r, which is pressed by

188 PHYSIOLOGY OF MUSCLES AMi M-RVKS.

a spring against the wire, and replaces the slide. P>y
turning tlir disc the length 01 the inserted port ion of
rheorhoi-o! i.- altered.

The whole arrangement is shown more clearly in
. 18, \\hieh may at t In-same time serve as a diagram
of tin- rxpiTinit-nts with muscles and nerves, to which
we arc now about to turn our attention. N r' r S is the
circular rheochord wire, through which the current of
the measuring apparatus passes in the direction of the
arrow ; /j, is a muscle, two of the points on the outer
surface of which, being connected with the multiplier,
afford a current, which is exactly compensated by that
portion of the current which branches off from the
rheochord at the points r and o. The particular length
o r of the rheochord wire at which this exact compen-
?ation is accomplished, indicates according to the fixed
standard (the degree of compensation) the difference in
tension at the particular points on the muscle which are
t e.-t ed. This length may be found by turning the round
disc, together with the platinum wire, until the mul-
tiplier no longer indicates any deflection. By means
of a magnifying glass, the length of the inserted wire,
from its commencement at o to the reel at r, can be
read off on a graduated scale.

CHAPTER XL

1. A regular muscle-prism ; 2. Currents and tensions in a muscle-
prism j 3. Muscle-rhombus ; 4. Irregular muscle- rhornbi ; 5. Cur-
rent of m. gastrocncmius.

1 . Beginning1 the study of the electric phenomena
exhibited in animal tissues with muscles, we will at first
experiment only with single, extracted muscles. Even
these, however, exhibit phenomena so complex in some
respects, that it will be better to take first a compara-
tively simple case. In taking one not exactly under
natural conditions— if, that is, we use a muscle artifi-
cially prepared for the purpose of experiment — this pro-
ceeding will find ample justification in the greater ease
with which we shall thus be enabled to understand the
more complex examples which we must afterwards
examine.

Taking a regularly shaped muscle, in which the
fibres are parallel, we will cut out a part of this by
making two even cuts at right angles to the direction
of the fibres. A piece of this sort may be called a
regular muscle-prism. It is, according to the shape of
the muscle used, either circular or more oval, or flat
and band-like ; its shape makes no difference, and the
length and diameter are of equally little account. The
only essential point is that all the muscle-fibres are

190 rilYHDl.MiiY OF MfSCLFS AND NKKVF>.

parallel to cadi other, and that the l\vo ruts are made
at right angles to the direction of the fibres. Yig. 4!»
diagrammatically represents a regular muscle-prism of
this sort. Tin- horizontal stripes represent the separate
bundles of the fibres. The outer surface of the prism,
\vhich therefore corresponds with the upper surface of

the fibres, is c;dle<l the liHij/itiK/iinll xi'i-tiuii of the

p/ism ; and the terminal surfaces, at right angles to
the Longitudinal section, are the < /v>.sN-.svr//'o//x of the
muscle-prism. The lines running at right angles to
the direction of the fibres are, as \ve >hall presently
find, tension-curves.

A regular muscle-prism such as this exhibits a very

«'«' a' n' a' ,i n' a' a' a' a'

IM<; -10. A i:i:<a I..M: Mrst I.I:-PI:I>.V,

simple distribution of tension. All the lines of tension,
or the iso-eleetric curves, run on the surface and are
parallel to the cross-sections. Kound the middle of the
muscle-prism passes a line separating it into two sym-
metrical halves; this \\ e will call the equator. The
•jri'iiti-xt jiox'it'ii-i' li'usinii to be found anywhere on the
surface prevails at this point. Kvery point on the
equator has a greater positive tension than any other
point on the longitudinal, or the cross-section. On
either side from the equator, the posit i\e tension gra-
duallv decreases along the longitudinal section quite
r-gularly in both direction-, until, at the point \\hen-
the longitudinal meets the cro eetion, i! =().

D

On the cross-sections themselves the tension is

CURRENTS AND TENSION IN A MUSCLE-PRISM. 191

everywhere negative, and the greatest negative tension
prevails at the centre of these, and decreases from these
points up to where the cross-sections meet the longitu-
dinal section.

2. From this distribution of the tensions it is easy
to infer the phenomena which the muscle shows when
it is inserted between the pads of the diverting vessels
above described, or between the diverting cylinders
which represent the feet of the diverting arch. It is
evident that no current will result when two points on
the equator, or two points on any one of the tension-
curves are tested. Nor will any current result when
two different points, on either side of the equator, are
connected, if these points are equidistant from the
equator. Nor will any current result when the two
cross-sections are applied to the pads; but, on the con-
trary, a current will be observed as soon as any point
on the longitudinal section and any one on either of
the cross- sections are connected, or when two points
on the longitudinal section, situated at unequal dis-
tances from the equator, touch the pads ; or. finally,
when two points on the same cross-section, or two
points, one on each of the two cross-sections, situated
at unequal distances from the central point, are con-
nected. The strongest current will result when a point
on the equator is connected with the central point on
one of the cross-sections ; weaker currents are gene-
rated when two unsymmetrical points on the longi-
tudinal section, or two unsymmetrical points on the
cross-section are connected. All these cases are re-
presented in fig. 50. The rectangular figure abed
represents a section through the muscle-prism ; a b
and c d are transverse sections through the longitu-

192

OF Mrsn.r.s AND NF.RVKS.

dinal section, and <i rand J> >/ arc transverse
through tin- cross-section. The curved lines represent
the divert ing arches, and the arrows show the direction
of the currents which arc generated in these. No
currents are generated in arches 0, 7, or 8, for these
unite symmetrical points.

Moreover, the rate at which the tension decreases
in the longitudinal section is, not regular, Imt at a
gradually increasing speed from the equator to the
en-Is. If, therefore, we find these iso-e!ectric curves, the

l-'i<;. fill. Ci IIUKNTS IN A Mix u; ritis.M.

tensions of which differ by a definite amount, these, in
the centre of the muscle-prism, are at some distance
from each other, but gradually approach more closely
together toward the edge of the cross-section. If the
ten-ion prevailing at each point in one side of a longi-
t ndiinl sec! ion is represent ed by the height of a >< raight
line drawn at right angles to that side of the longitu-
dinal section, then the ciirxe \\hieh unite.- the heads of
thc-e lines is level at the centre of < he longitudinal
sect ion, but sinks rapidly do\\n to\\ard 1 he edges of the
cross-.-ection. Asome\\hat similar fact is observable on

THE MUSCLE-RHOMBUS.

193

the cross-sections, where the tension-curves, correspond-
ing with equal differences of tension, are nearer to-
gether toward the edge of the longitudinal section
than in the middle. If the feet of the diverting arch
are equidistant, the currents, both from the longitu-
dinal section and from the cross-sections, are therefore
stronger the nearer is the point under examination to
the limit between the longitudinal and cross-sections.
Fig. 51 shows this circumstance: A in the figure re-
presents the tensions on one of the longitudinal sections

FIG. 51. TENSION ox THE LONGITUDINAL AND CROSS SECTIONS OF A

MUSCLE-PRISM.

and on one of the cross-sections of the transverse section
represented in fig. 50 ; while at B the tension-curves in
a cross-section itself are represented. The latter, if the
muscle-prism is perfectly round, are concentric circles.
In order to judge of the direction and strength of the
current resulting when a conducting arch is applied to
any two points of a muscle-prism, it is only necessary
to determine the difference of tensions at the feet of
the arch, and, in so doing, to notice that when positive
tension prevails at one of these points, negative tension
at the other, the current through the arch is always in

li)-i PHYSIOLOGY OP MfSCLl-S .\M> NERVES.

the direction from the positive to the negative point ;
hut that, if the feet are both positive, or both negative,
the current, passes lY'>in tin- more to the less positive
point, or from the less to the more negative point.
From the curves in A and B, fig. 51, which show the
tensions, the currents indicated in fig. 50 may therefore
easily be discovered.

3. Once more let ns take a muscle, the fibres of
which are parallel, and cut a piece out of this, but in
such a way that the cross-section, instead of being at
right angles to the direction of the fibres, is obliquely
directed toward the latter. A piece of this sort may be
called a muscle-rhombus ; if the cross-sections are
parallel to each other, it is a regular muscle-rhombus ;
if otherwise, an !>•>•> yilar muscle-rhombus. In such a
muscle-rhombus, the distribution of the tensions, and,
consequently, the form of the iso-electric curves, is
much more complex than in a muscle-prism. In this
case the curves are not, as in a muscle-prism, parallel,
but are sometimes of very complex form.

It is true that in this case also there is the main
distinction between the longitudinal section, or outer
surface of the muscle-rhombus, and the cross-sections.
The former arc always positive, the latter negative.
But both in the longitudinal and cross-sections a
difference is noticeable between the nlituse and the
acute angles. The positive tension is greater at the
obtuse than at the acute angles of the longitudinal
section; and, similarly, the negative tension is greater
at the acute than at the obtuse angles of the cross-
sections. Consequent ly, a peculiar displacement of the
tension-curves, of which tig. -~>2 is intended as a re-
presentation, takes place in a regular muscle-rhombus,

THE MUSCLE RHOMBUS.

195

Let us suppose that the muscle from which the rhombus
was cut was cylindrical. The two cross -sections will
then form ellipses ; in the case of a regular muscle-
rhombus, equal ellipses. A section through the longi-
tudinal axes of both these ellipses will therefore give
an asymmetrical parallelogram with two obtuse, and
two acute angles (a rhomboid). Such a section is re-
pre3ented in the figure. In it, a b and c d correspond
with the longitudinal section, a c and b d the cross-
sections. The latter are identical with the longitudinal
axis of the actual cross-sections. On the side corre-

FIG. 52. TENSIONS ON A REGULAR MUSCLE-RHOMBUS.

spending with the longitudinal section, the greatest
positive tension is no longer found in the middle, but
is removed toward the obtuse angles, at e and e'. The
tensions fall very rapidly from here toward the obtuse
angle, gradually toward the acute angle. In the cross-
sections the greatest negative tension occurs near the
acute angles ; and the fall toward the acute angles is
very abrupt, that toward the obtuse angles is gradual.

The iso-electric curves on such a regular muscle-
rhombus in the cross -sections form ellipses, one pole
of which corresponds with a focus on the edge of the

OF Mr>ci.i's AND .Ni:i;\ i:>.

,-,-,, ,.t j,,1K !,,.;,,- t]l(, acute .-HIM],.. jn the lon^itn linal

section they form spiral lines, which run ohliqudv n.iind
the outer surface of the cylinder. The electromotive
equator, which unites the points ;it which the «,Mv;it.-t
positive tension prevails, forms a line round the circum-

n

''"•• 53. Tin; < i I;I;I:\TS ix A i:i:«,n..\i: MIX 1,1: I:IK«MI:I a.

Cerence, which separates the rhombus into two equal
halves.

Supposing that a plane is drawn in such a iv-ular
muscle-rhombus, throu-h th,. small axis of the elliptic
cross-sections, a rectangular tin-lire will lie obtaine.l.
The niiiscl.-filiivs lyi]i_.r in siK'li a secti,»n are all cut
in a Hinilar \\ay, and their c.,nilit i.>n is exact ly alike,
i,, this section also the ^reat.'st tension on

JRREGULAE MUSCLE-RHOMB1. 197

the longitudinal, as on the cross-sections, is situated in
the centre, and an arrangement of the tensions exactly
similar to that in a muscle-prism is observable.

From -what has been said, the direction and strength
of the currents which are generated on the intercon-
nection of any points in a muscle-prism by the appli-
cation of an arch may easily be inferred. They are
represented in fig. 53. The direction of the currents
in the applied arches is in every case indicated by
arrows ; where there are no arrows the arch connects
two points of equal tension, so that there is no current
(e.g. arches 4 and 9). The currents all pass from the
obtuse to the acute angle, through the applied arches,
except in the fifth and tenth, in which the direction is
reversed.

4. The phenomena in irregular muscle-rhombi do
not differ essentially from those just described, but the
arrangement of the tensions is asymmetrical. Passing
to muscles in which the arrangement of the fibres is
irregular, it is apparent that each cut made must always
meet a part of the fibres obliquely, and that, therefore,
the matter just explained must always be borne in mind
in explanation of the phenomena, which are sometimes
very complex. Not to enter too far into details, we
need only say that the same fundamental principle
asserts itself in all muscles ; everywhere the longi-
tudinal section, as distinguished from the cross-section,
is positive ; and in all cases there is a point or line in
the longitudinal section which is the most positive,
and a point in the cross-section which is most negative ;
so that, if an arch is applied, currents pass through this
from the longitudinal to the cross-section, weaker cur-
rents between points in the longitudinal section, and

198 PHYSIOLOGY OF MUSCLES AND NKRVES.

betvreen points in the cross-section respectively. The
position of these most strongly positive and most
strongly negative p >iuts depends on tin- angles -which
the fibres form wilh the cross-sect inn-, and may be
found by the rules given in tin- la. -4 paragraph as to the
influence of oblique section.

Of all the many muscles of the animal body one
claims special attention, because, for purely practical
reasons, it is most frequently used in physiological ex-
periments : this is the calf-muscle (in.yaxlrui-itt'nti
It is easily prepared, even without severing its connec-
tion with its nerve, a fact which, for reasons presently
to be stated, is of great importance. It affords, as we
shall see. a powerful current ; it long retains its capacity
for action; and, in short, it has many advantages by
which we were induced, when studying the activity of
muscle and the excitability of nerves, to make use of it
almost exclusively. As, however, the structure of the
muscle is very complex, the nature of its electric action
is by no means easily understood. We mu-t, h.>\\e\vr,
describe at least its main outlines, as we must employ
the muscle in further important experiments.

In order to understand this action we must pre-
viously observe that it is not absolutely necessary to
cut a piece out of a muscle, but that entire muscles are
also capable of affording currents. In dealing wilh the
nniM-le-|ii-ism and muscle-rhombus, \\e assumed that
the pieces were cut from parallel-fibred muscles. The
longitudinal sections of these pieces retained their
covering of muscle-sheath ( /» /•/'//* //xmm) and, in fact,
corresponded with the natural surface of the muscle.
The cross-cuts were, ho\\e\er, made into the actual
substance of the mu>ele. BO that part of the interior

THE CURRENT OF M. GASTROCNEMIUS. 199

was laid bare. Such cross-sections may be termed
artificial, while the longitudinal sections of these prisms
or rhombi may be called natural. Longitudinal sections
may also be formed artificially, by splitting the muscle
in the direction of its fibres ; and we may speak of
natural cross-sections, by which we understand the
natural ends of the muscle-fibres while still closed with
the tendonous substance. Now the action both of longi-
tudinal and of cross-sections is the same whether they
are natural or artificial.1 It is, therefore, always pos-
sible to obtain currents from an uninjured muscle
exactly as from artificially prepared muscle-prisms and
rhombi.

5. To the circumstance that it can, while still un-
injured, afford powerful currents, is due the special
importance of the gastrocnemius. This muscle may
in all essential points be classed among the penniform
muscles ; though in reality it is thus conditioned only
towards its upper tendon, the part toward the lower
tendon being rather of the character of a semipenniform
muscle. In order to understand its structure, let us
imagine two tendonous plates, an upper and a lower,
connected by muscle-fibres stretched obliquely between
them, so as to form a semipenniform muscle. Now let
us suppose the upper tendonous plate to be folded in the
middle, as a sheet of paper might be, and that the two
folded halves are in apposition. We now have an
upper tendon plate, situated within the muscle, from
which muscle-fibres pass obliquely in both directions ;
the lower tendon has, however, been so bent by the
folding of the upper so that the whole muscle is shaped
like a turnip split in a longitudinal direction, the flat
1 Exceptions to this rule will presently be mentioned.

200

PHYSIOLOGY OF MI'SCLKS AND NERVES.

surface , ,f which (turned toward tlir hone of tin- lower
le^-jis torn i "d solely of muscle-fibres, exhibiting a delicate
longit udinal streak a< the only indicat inn of tin- tendon
buried within it; th' .-irclifd dorsal surface is, on the
contrary, clothed, as regards the lower 1 \vo-t hinls of its
length, with tendonous sul»t:uicc wliich passes below
into the so-i-iilh.'d ti-,t<l<> JrA/7//s.

It is evident that such a muscle has naturally an
oblique cross-section, represented by this tendonons
covering, and a longitudinal section which includes the
whole of the flat, and a little of the curved portion.
This muscle can, therefore, without any further p;v-

!•';<;. ," I. Tin: cruuKSTs <u A i..\>Ti;orNi:.\iii s.

paration afford currents; for \\hich reason it maybe
mos' advantageously used in a large number of experi-
ments.

lien'ardiiig once more the structure of t he </«/>•//•«-
<'ii' mius, as it has just been doeribed.a natural loii^itu-
din;d section i- reco^nisMbli- in the whole Hut part and
a litt le of the upper portion of the curved surface : and
a nat unil cross-sect imi is to be recognised in the ^re.-iti'i-
and lower ]iart of the <-iirved tipper surface. No second
cro8S-S( ct ion exi>ts in (hi- muscle, i'or the upper tendon
is buried \\ it hin the muscle. The currents which the
-:'iid< through an ardi applied so as to connect

THE CURRENT OF M. GASTROCNEMIUS. 201

different points on its outer surface will now easily be
understood, and are as represented in fig. 54. It is
most especially necessary to notice that a strong current
must be generated on the interconnection of the upper
with the lower end of this muscle, and that the current
within the arch is directed from the upper to the lower
end of the muscle. The upper end must be strongly
positive ; for it represents the middle of the longitu-
dinal section. The lower end must be strongly negative ;
for it is the acute angle of an oblique cross-section.
There are very few points so alike in the matter of ten-
sion that no current results from their connection. A
case of this kind is, however, shown in the fourth
arch.

10

L'O'J PHYSIOLOGY OF Ml'SCLKS AND NKKVES.

CHAPTER XII.

1. Negative variation <>f tin- mnscle-cnrrenl : L'. Living muscle is

alont" elrrlrically active ; 3. 1'aivli •<•' niiminy : t. Srr, .ndavy ]>ul-
and M'cn Hilary tetanus; 5. (ilands and tlu-ir currents.

1. Tin- p iwerful current alVorded by an entire ni. ;/as-

trni-iiniiiii* enables US to answer the iin])ort:int ijllest ioll

as to the character of dectric phenomena during con-

traction, All that is necessary is to pivp'V.v this muscle,
together with its nerve, and to in.-ert its upper and
lower ends liet \\een (he pads of the diverting \ •< ssel
already described, and then to place the nerve mi two
wires so that ^t ean lie irritated In inductive currents;
it, must then liecome evident whether the activity of
the muscle has any influence on its electric action or
not.

In order to carry out the experiment, lei us snppo-r
the muscle, as shown in ti^. 5,1, placed between the
pad< of a diverting vessel, these pads bein^ brought
somewhat near each other, so that the contact of the
muscle with the pads is not di>t;irbed by the con-
(raetion of (he former. The nerve, which has been
f racted with the muscle, is laid on t wo wires which
are connected \vilh the >. <-oiidary spiral of the induct he
apparatus. A key, iiiM-rted between the nerve and (he
-piral. r- filial es the inductive ciirreiils so that the ner\e

i- not excited. \Vhen all i- arranged, and the multi-

NEGATIVE VARIATION OF THE MUSCLE-CURRENT. 203

plier has assumed a fixed deflection, the extent of which
depends on the strength of the muscle-current, the key
at S is opened. Inductive currents pass through the
nerve, and the muscle contracts. At the same instant
the deflection of the multiplier is observed to decrease.
If the irritation of the nerve is interrupted, the deflec-
tion of the multiplier again increases ; and when the
irritation is again commenced, it again decreases, and
this process continues as long as the muscle continues
to afford powerful contractions.

FIG. 55. THE MUSCLE-CURRENT DURING CONTRACTION.

This experiment, therefore, shows that the current
of the gastrocnemius is weakened during contraction.
This may be most strikingly shown by a variation of
the experiment just described. After the muscle has
been placed in position and a deflection of the multi-
plier has been caused, the muscle- current may be com-
pensated, as described in Chapter X. § 4. Two currents,
equal but in opposite directions — the current of the
muscle and that of the compensator — now, therefore,
pass through the muscle and cancel each other. As
long as these two currents are equal, no deflection can
occur in the multiplier. When the nerve is then irri-

204 riiYsioLoiiY or MTSCLKS ANI> NKKYI-.

tated and tin- muscle contracts, the current becomes
ker; the cum n( afforded l>y the compensator thus
preponderance, and effects a deflection which is,
of course, in exactly the opposite direction to that which
was originally effected l>y the muscle.

Tlu-re i- -troug reason to believe that this alteration
in (he strength of the muscle-current really depends on
the activity of the muscle and is not occasioned by any
accidental circumstances. Any form of irritant may be
used indifferently to effect this activity. Chemical,
thrrmieal, or other irritants maybe used in place of
electricity to irritate the nerve ; or the experiment may
be made on a muscle which is still in connection with
the whole nervous system, and the contraction may
be effected by influences acting through the spinal
marrow and the brain. But the result is always the
same. Even when external circumstances entirely pre-
vent contraction, the irritated muscle, without changing
its form, exhibits this decrease in its current as soon as
it is brought into the condition of activity by irritation.
If, for example, care is taken that the muscle retains
its form unaltered, by fastening it in a suitable clamp,
and if this muscle is then irritated into activity, the
current decreases in exactly the same way as when the
experiment is carried out as before described.

It is an especially interesting fact that this >ame
phenomenon may al-o be observed in the muscles of
living and uninjured men. It is very hard to prove
that the electric action of muscles of living animals
in their natural position is exactly the same as that of
muscles when extracted; but the fact that on contrac-
tion exactly the same electric processes occur in muscle^
whether they are in their natural position or have been

NEGATIVE VARIATION OF THE MUSCLE-CURRENT. 205

extracted is quite certain. E. du Bois-Keymond showed
this in the human subject in the following way. The
ends of the wire of the multiplier are connected with
two vessels filled with liquid, and the index finger of
both hands is dipped in these vessels, as in fig. 56.

FIG. 56. DEFLECTION OK THE MAGNETIC NEEDLE BY THE WILL.

A rod arranged in front of the vessel serves to steady
the position of the hands. Currents are then present
in the muscles of both arms and of the breast, which,
since the groups of muscles are symmetrically arranged,
cancel each other, acting one on the other. If for any
reason any current remains uncancelled, it may be
compensated in the way before described. When all
is thus arranged, and the man strongly contracts the

200 niYSIoI.oi.Y OF MIX'US AM) .NKKYKS.

of one arm, tin- ivsulf is an immediate deflec-
tion of tin- multiplier, which indicates the presence of

a ciinvnl ascending in the contracted arm from the

o

hand to the shoulder. If the muscles of tin- other arm
are contracted, a deflection occurs in the opposite direc-
tion. \Ye are, then-fore, ;il»le by the mere power of tin-
will to generate an electric current and to set the mag-
netic needle in motion.

Summing np all that has been said, it appears that,
during muscular contraction, the electric forces acting
in the muscle undergo a change which is independent
of the alteration of form in the muscle, and is con-
nected \vilh the fact of activity itself. As. during this
alteration, the current which may be exhibited in an
•applied arch becomes weaker, the term negative-variar
tinii of Un' muscle-current has been applied to it.

2. The negative variation of the muscle-current on
contraction, as described in the last paragraph, is a
proof of the fact that in the electric action of muscle
we have to do, not with an accidental physical pheno-
menon, but with an action very closely connected with
the essential physiological activities of muscle. It is
therefore worth while to trace an action of this sort
more accurately, as it may possibly aid in the explana-
tion of the act ivity of the muscle.

It may. in the tirst place, be safely asserted that all
niUM-le.s of all animals, as far as they have at present
IK -eii examined, exhibit the same electric action. K\en
-moolh muscles art electrically in the same way;
though in that case the phenomena are less regular,
o\\ing to the lad that the fibres are not so regularly

arrayed a- in striated muscle. Moreover, the electric

activity of smooth muscles seems to be somewhat

weaker.

LIVING MUSCLE ALONE ELECTRICALLY ACTIVE. 207

Further, it is to be observed that the electric activity
of muscles is connected with their physiological power
of accomplishing work. When muscles die, the electric
phenomena also become weaker, and finally cease en-
tirely when death-stiffness intervenes. Muscles which
can no longer be induced to contract even by very
strong irritants may indeed still show traces of electric
action ; but this power soon disappears. Nor does the
electric activity, when it has once disappeared from a
rigid and dead muscle, ever, under any circumstances,
return.

Although it may be assumed as proved that the
electric activity of muscle is connected with the living
condition of the muscular tissue, it must not, however,
be inferred from this that this activity is necessarily
always present during life. It is conceivable that the
preparation necessary for the study of electric action
(the exposure of the muscle, its connection with the
arch, &c.) might produce changes in the living muscle
which are themselves the cause of electric activity.
To satisfy this doubt it would be necessary to show the
previous existence of electric activity, wherever it is
possible, in uninjured men and animals. The great
difficulty which lies in the way of such proof has already
been mentioned. The more complex is the arrange-
ment of the fibres and the position of the separate
muscles present in any part of the body, the harder is it
to say, a priori, how the separate currents of the various
muscles combine. It must also be added, that the skin,
through which the electric action is necessarily observed,
is in itself somewhat electrically active,1 and that, in
other ways also, it increases the difficulty of proving the
1 Theso skin-currents will be again mentioned.

208 PHYSIOLOGY OF MUSCLES AND NKRVES.

of muscle-currents. Due regard being l::ul
tn all these circumstances, the conclusion mav vet be

drawn ihal entirely uninjured muscles situated in their
natural position are in themselves electrical! v aetive.
It is true that this has been repeatedly denied by many
observers. Our reason for reasserting it is that the ex-
planation of the phenomena on the assumption of the
absence of electromotive opposition in uninjured muscle
necessitates very forced and complicated assumptions,
while our view is able to explain all the known facts
very simply and in a thoroughly satisfactory manner.

3. The electric action of muscles which, though ex-
tracted, are otherwise uninjured, is often verv weak,
and is sometimes even reversed; that is to say, the
natural cross-section is not negative, but positive, in
opposition to the longitudinal section. This condition
is found chiefly in the muscles of frogs which have
been exposed during life to severe cold. It is, however.
only necessary to remove, in any way, the natural cross-
section with its tendonous covering, in order to elicit
action of normal character and strength. In parallel-
fibred muscles it is often necessary to remove a short
piece, of from 1 to 2 mm. in length, from the end
of the muscle-fibres, before meeting with an artilieial
cross-section in which the aeti.ni is powerful.

This phenomenon, which was called ]></,•< /«•/ roiio/,, >/
by K. du r.oi.-K'eymoud, l>ee;nise it differs from the
ii-ual electric action of muscles, gave rise to that e\-
planat ion of the electric phenomena, according to which

t lie elect I ic opposit ion | let \\eell different portions of the

muscle is not. present in the normal muscle, but . onlv

intervenes OH the exposure of the mu-ele. The (litli-

eully in. ntioned above, of showing the mu>c|e-currents

SECONDARY PULSATION AND TETANUS. 209

in uninjured animals, lent force to this explanation.
Yet no sufficiently strong proof of this view has been
brought forward to cause us to doubt the existence of
electric action in uninjured and living muscles.

The question does not, however, essentially affect
the physiological conception of the relation of this ac-
tivity to the other vital qualities. It is unimportant
whether the separate portions of the outer surface of
a muscle are similar or dissimilar in the matter of ten-
sion. The only essential point is, as to whether electro-
motive forces are present within the muscle, and whether
these are in any way related to the physiological work
of the muscle. Negative variation has a deeply impor-
tant bearing on this question, so that we will, after this
digression, return to a more detailed study of this
phenomenon.

4. It is unnecessary to tetanise the muscle in order
to exhibit negative variation. If a sufficiently sensitive
multiplier is used, a single pulsation suffices. Even
without a multiplier, negative variation may be very
well shown in the following way.

Onagastrocnemius prepared with its nerve (fig. 57),
or on an entire thigh (5, fig. 58), the nerve of a second
gastrocnemius, or thigh, A, is placed in such a way
that one part of the nerve touches the tendon, another
part touches the surface of the muscle-fibres. The nerve
then represents a sort of applied arch, uniting the nega-
tive cross- section and the positive longitudinal section,
and a current, corresponding with the difference of ten-
sion at these points of contact, passes through the nerve.1

1 This current may at the moment of ils generation, i.e. OD the
sudden application of the nerve, exercise an irritating effect on
the nerve and may elicit a pulsation of the muscle. This is the

210

rilYSIiM.ni.Y <>!• MUSCLES AND NKKViS.

If (lie nerve «•{' the mii-ele /> is tin 'ii irritated, cither liy
closing or by opening ;i current , by an inductive shock, by
x-i.-sion, by pressure, or in any other way, the muscle A
\> oh<er\ed In j»ul>ate also. 'J'liis is called .svr, >//,/-
ary pulsation. The explanation is easy. The muscle-
ctirren! from />' during its pulsation suffered a ne^ati\e
variation. This variation took place also in that por-
tion of the current which passed through the applied
nerve; and, as every nerve is, irritated by sudden change

C

Jf

FlO. .">7 \ 58. S-l -• i«M)AKY

in the strength of the current, the re-ult was a secon-
dary pulsation.

A variation of this experiment is very interesting.
The heart of a fn>Lr continues to bent for some time
after it has been extracted from the bodv. If the nerve
of a nniM-lr i- placed on this heart so as to touch its
base and point, the muscle pulsates at every beat of
tile heart. In this case, the heart-muscle affords the
muscle-current, the negative variat ion of which irritates
the applied nerve and cau-e- >rcondary pulsation.

']m]s;ill<m uilhiiut in. 'tills' (/tirl;ini<i nlun- Mitnllf) \\hich l::is
-allied .•cl.'l.riiy I'l'-ni the \\ritin-.s ..!' Vnlta, HuiiilMil.lt, uiul

SECONDARY PULSATION AND TETANUS. 211

If the nerve of one muscle is placed on a second
muscle in such a way that no observable part of the
current passes through the former (as shown in the
nerve of the muscle (7, in fig. 58), no secondary pul-
sation takes place in the muscle.

If the nerve of the first muscle is repeatedly irri-
tated in such a way that the muscle B passes into a
state of tetanus, then the muscle A assumes the con-
dition of secondary tetanus. This important experi-
ment shows that variations of electric activity take
place in rapid succession in tetanised muscle. For it
is only owing to such rapidly succeeding variations in
the strength of the current that a persistent, tetanising
irritation can occur in the second nerve. Just as the
phenomenon of muscular tone led us to the conclusion
that muscle-tetanus, though the similarity in external
form is apparently complete, is not a state of rest, but
that the molecules of the muscle must be in constant
internal motion during tetanus, so we now find from
the phenomenon of secondary tetanus that throughout
its duration a continual variation occurs in its elec-
tric condition ; and from this we may infer that elec-
tric variation is connected with the motion of the
molecules which causes contraction.

More detailed study of negative variation has also
shown that it occurs even in the stage of latent irri-
tation, that is, at a time at which the muscle has not
yet altered its external form in any way. It has also
been, found that the electric change which occurs on
irritation propagates itself when the muscle-fibre is
partially irritated at a rate equal to that of the propa-
gation of the contraction (from 3 to 4 m. per second :
cf. ch. vi. § 5, p. 100). When, therefore, a muscle-

212 PHYSIOLOGY OF MTSCI.KS AM> NERVES.

fibre of some length i> irritated at one point, an electric
change at first occurs only at this point; this continues
an extremely brief time, and then runs wave-like along
the muscle-fibre ; and this electric change is then fol-
lowed by the mechanical change of contraction and
thickening, which is called contraction, and which then
propagates itself in a similar wave-like manner. If,
however, the whole fibre is irritated at once, the elec-
trie change occurs simultaneously throughout the fibre,
and this is then followed by the mechanical change.

."i. The glands are in many points very similar to
the muscles, though their structure is so different. A
gland of the simplest form is a cavity lined with cells,
opening by a longer or shorter passage through the
outer surface of the mucous membrane, or the miter skin
(comtm), which lies above it. The cavity maybe hemi-
spherical, flask-shaped, or tubular. In the latter case t he
1 ube is often very long, and is either wound like a thread,
or is coiled, and is sometimes expanded at its closed
end in the form of a knob. Tln-se are all *////y//< i/lm/ds.
Compound glands are found when several tubular or
knoli-shaped glands open with a common mouth. Sub-
stances, oft en of a very peculiar character, arc found
within the glands, and are secreted on to the outer
surface through the mouth. These are the sweat and
fat of the skin, which are prepared in the sweat or fat
glands of the skin, the saliva and the gastric juice,
which, o\\ing to their power of fermentation, play an
important part in digestion, the gall, which is formed
within the liver, and other substances. The similaritv

alluded to bet\\ee|| the Ulll-ele- ;md the glands cnllH-t-

iii the dependence of both on the nerves. 11' a nerve
\vhicli is connected with a muscle is irritated, the muscle

GLANDS AND THEIR CURRENTS. 213

becomes active, that is, it contracts; and if a nerve which
is connected with a gland is irritated, the gland be-
comes active, that is, it secretes. If, for example, the
nerves which pass into a salivary gland are irritated, the
saliva may be made to ooze in a stream from the mouth
of the gland. It is certainly an important fact that,
except muscles (and disregarding the nerves, which will
be spoken of in the following chapter), the glands are
the only tissue which has been shown to possess regular
electric activity. This is not, indeed, true of all glands,
but only of the simple forms, the bottle-shaped or skin
glands. Wherever a large number of these occur regu-
larly arranged, side by side, it is found that the lower
surface, that which forms the base of the gland, is posi-
tively electric, while the upper surface, that which forms
the exit duct of the gland, is negatively electric. This is
best shown in the skin of the naked amphibia, in which
glands abound, and in the mucous membrane of the
mouth, stomach, and intestinal canal of all animals.
In these tissues all the glands are arranged in the same
order, side by side, and all act electrically in the same
direction.1 In compound glands, on the contrary, the
separate gland elements are arranged in all possible di-
rections, so that the actions are irregular and cannot be
calculated.

In the skin-glands of the frog, as in the glands of

1 These currents of the skin-glands afford one of the reasons to
which allusion has already been made (§ 2) why the indication of
niuscle-curren'ls in living and uninjured animals is beset with diffi-
culties. As the cairrents of the skin-glands at two points of the
skin from which the muscle-current is to be diverted are not
always of equal strength, therefore the action of the skin mingles
with, and affects that of the underlying muscles, so as to hinder the
detection of the latter.

214 I'llYM'M.iHiY "I' MUSCLES AM) NERVES.

thr mucous membrane nf the stomach and intestinal
c;,nal, it may be clearly ,-hown that the electric force
is really situated in the glands. On irritation of the
ner\es which ]):i.ss into the skin by which the glands
are excited into activity, the ^land-current decreases in
strength, and exhibits a ne-at ive variation, just as the
muscle-current decreases -when the muscle is excited
into activity. In this case, also, a relation therefore
exists between the act ivify and thr elect ric fond it ion ;
and this adds to ihe similarity between muscles and
glands.

Kngelmann tried to explain the secretion of the
glands physically, by the electric currents present
within them. This must, however, be regarded as not
yet sufficiently confirmed to claim further attention in
this place.

CHAPTER XIII.

1. The nerve-current ; 2. Negative variation of the nerve-current ;
3. Duplex transmission in the nerve ; 4. Rate of propagation
of negative variation; 5. Electrotonus ; 6. Electric tissue of
electric fishes ; 7. Electric action in plants.

1. In addition to the many points of similarity
between muscles and nerves exhibited in their be-
haviour when irritated, it cannot escape notice that
the nerves also exhibit electric phenomena, and that
they do this in exactly the same way as does muscle.
Nerves being formed of separate parallel fibres, these
phenomena are exactly analogous to those in a regular
muscle-prism ; only that in a cross-section of a nerve,
on account of its small extent, differences of tension
cannot be shown at the various points, and the cross -
section must be regarded as a single point.

In an extracted piece of nerve all the points on
the upper surface, that is, on the longitudinal section,
are as a fact positive, in distinction from those on the
cross-section, which are all of one kind. On the longi-
tudinal section the greatest positive tension is always
in the centre, and the tension decreases toward the
cross-sections, just as in the muscle-prism, at first
slowly, afterwards more abruptly, as shown in fig. 59.

Because of the small diameter of the nerve-trunks,
distinction cannot, of course, be drawn between straight

216 PHYSIOLOGY OF Mt'SCLES AND NERVES.

and oblique cross-sections, such as we made in the ea-e
of muscle ; nor can phenomena due to the oblique course
of the fibres be detected, as in muscle. Where lann-r
masses of nerve-substance occur, as in the dorsal nun-
row and brain, the course of the fibres is so complex
that nothing can be affirmed except that tin- en.ss-
• lions are always negative in distinction fn.m the
natural upper surface or longitudinal section.

2. If a current is conducted from any two points en
the longitudinal section of a nerve, or from one point
on the longitudinal section or one on the cross-section,
and if the nerve is then irritated, the nerve-current
evidently becomes weaker. It does not matter what
form of irritation is used, provided that it is sufficiently
strong to cause powerful action in the nerve. It thus
appears that in the nerve, as in the muscle, a change
in the electric condition is connected with its activity,
and that this change is a decrease, or negative variation
of the nerve-current. We must now go back to the
statement already made (chap. vii. § 2), that the ac-
tive condition of the nerve is not shown by any change
in the nerve itself. We then found it necessary, in
order to observe the action of the nerve, to leave it in
undisturbed connection with its muscle. The muscle
was used as a reagent, as it were, for the nerve, because
in (lie latter neither optical, chemical, nor any other in-
diealile changes could be observed. In its electric quali-
ties we have, however, now found a means of testing
the condition of the nerve itself. Whatever \ie\v is
taken as to the causes of electric action in nerves, it
is at lea>t certain that every change in the electric con-
dition must be founded »\\ a change in the nature or
arrangement of the nerve substance; and that there-

DUPLEX TRANSMISSION IN THE NERVE.

217

fore the evident negative variation of the nerve-current
is a sign — as yet the only known sign — of the processes
which occur within the nerve during activity. This sign,
therefore, affords an opportunity of studying the ac-
tivity of the nerve itself independently of the muscle.
3. E. du Bois-Reymond made an important use of
this fact in order to determine the significant question,
whether the excitement in the nerve-fibre is propagated
only in one, or in both directions. If an uninjured
nerve trunk is irritated at any point in its course, two

FK;. 59. TENSION IN NEUVES.

actions are usually observable ; the muscles connected
with the nerve pulsate, and, at the same time, pain is
caused. The excitement has therefore been transmitted
from the irritated point both to the periphery and to
the centre, and it exercises an influence in both places.
Now, it may be shown that in such cases two differ-
ent kinds of nerves are present in the nerve-trunk
— motor nerves, the irritation of which acts on the
muscle; and sensory nerves, the irritation of which
causes pain. In some places each of these kinds of
fibre occurs separately; and where this is the case, irri-
tation of the one results only in motion, irritation of
the other only in sensation. It is evident, therefore,
that the experiment in no way determines whether when
a motor nerve alone is irritated, the excitement is trans-

218 PHYSIOLOGY OF Mt'SCLES AND NERVES.

milled only toward the periphery or also toward tin-
centre; or as to whether, when a sensory nerve alone is
irritated, the excitement is transmitted only toward the
centre or also toward the periphery. For as the sensory
nerves do not pass at the periphery into muscles, by
means of which their actions could be expressed, there
is no means of telling whether the excitement in them
is transmitted to the periphery. But our knowledge of
the electric changes which occur during activity affords
a means of determining this question. For these
changes are observable in the nerve itself, independently
of the muscles and other terminal apparatu.-. If a
purely motor nerve is irritated, and is then tested at a
central point, negative \ariatiou is found to occur in
this also; and similarly, if a purely sensory nerve is
irritated, negative variation may he shown in a part of
the nerve lying between the irritated point and the
peripherv. This, therefore, shows that the excitement
in all nerve-fibres is capable of propagation in both
directions; and that if action occurs only at one end,
this is due to the fact that a terminal apparatus capable
of expressing the action is present only at that end.1

4. If negative variation in the nerve current is
really a neces.-ary and inseparable -i^n of that condition
within the nerves which is called the 'activity of the
nerves,' it must, like the cxeilement. propagate itself
\\illiin the ner\e at a measurable speed. lierustein
succeeded in proving this, and measured the .-p.-ed at
which the preparation occurs. If one end of a Ion-,'

nerve is irritated, tl (her end bein^ connected with

a multiplier, a certain time must elapse before the
irritation, and consequent 1\ also the negative variation,

1 Sn- Null-sand Addition-, N.I. 11.

RATE OF PROPAGATION OF NEGATIVE VARIATION. 219

reaches the latter end. In ordinary experiments the
irritation occurs continuously, and the connection of
the other end of the nerve with the multiplier is also
continuous. But the time which elapses between the
commencement of irritation and the commencement of
negative variation is, even in the ca.se of the longest
nerves with which experiments can be tried, far too short
to allow of observation of this retardation. Bernstein
proceeded as follows : two projecting wires were fastened
to a wheel which turned at a constant speed. One of
these wires, at each revolution, closed an electric current
for a very brief time, and at regular intervals of time
repeatedly effected the irritation of one end of the
nerve. The second wire, on the other hand, for a very
brief time connected the other end of the nerve with a
multiplier. When irritation and connection with the
multiplier occurred simultaneously, no trace of negative
variation was observable; for, before the latter could pass
from the irritated point to the other end of the nerve, the
connection of the latter with the multiplier was again
interrupted. By altering the position of the wires it
was, however, possible to cause the connection of the
nerve with the multiplier to occur somewhat later than
the irritation. When this difference in time reached a
certain amount, negative variation intervened. From
the amount of this time, together with the length of the
passage between the point irritated and that at which
the current is diverted, it is evidently possible to calcu-
late the rate of propagation of the negative variation
within the nerve. Bernstein in this way determined
the rate at 25 m. per second. This value corresponds
as nearly with that found for the propagation of the
excitement in the nerves (24*8 m. ; see ch. vii. § 3) as

220

OF Mrsri.F.s AND M:I;YF.S.

ic expeeted iii experiments of this nature ; and it
may In- uueoiidit ionally inferred fromtlii< c. >rrespond-
ence that i icgat Lve variation and excitement in thener\es
are two intimately connected and inseparable processes,
««r rather t \vo a>peets of the same process observed by
dit't'erent means.1

5. The negative variation of the nerve current is
not the only electric change known to occur .in nerves.
l'nder the name ' Elect rot onus ' we have already (ch.
viii. § 1, p. 125) mentioned certain changes in the ex-
citability which occur in the nerve fibre as soon as an

n

ci

n

V\<;. 60. Tnii CIIAN<.I.S IN

nri;iN(; I.I.KI i \;< • I«M -.

electric current is transmit led through a part of it.
These changes in the excitability corropond with
changes in the electric condition of ner\es, \\hich \\ e
called electrotonic. In tig. <><>, " n" represents a nerve,
a and /,• two wires applied to the ner\c through \\hich an
elect ri" current is transmitted from *' toward fc; " i-
Iherefore the aipule, /,• the kathode of the current em-
])loved for the generation nf , Ird rolonns. As soon as
this current i- closed, "// ///' i»>inl« <>/ tin' //- /•/•, on I In'
x't,lt> uf tin- <iiin,/, ( from /» bo a) became more positive^
a// ,,,i ihr *i'l<- i >f /In- hiilxi.lr (from /,- to // ) more

' gee N 1 Aildili.uis, N". 1L'.

ELECTROTONUS. 221

negative than they were. These changes are not, how-
ever, the same in degree at all points ; the change is
greatest in the immediate neighbourhood of the elec-
trode, and decreases proportionately with the distance
from this. If the degree of positive increase from a
to n is indicated by lines, the height of which expresses
the increase, and if the tops of these lines are con-
nected, the result is the curve n p, the. form of which
shows the changes in tension occurring at each point.
The changes on the kathode side may be represented
in the same way, but that in this case, in order to
show that the tension on that side becomes more nega-
tive, the lines may be drawn downward from the nerve.
The curved line q n', is the result. The two portions
of the curve n p and q n' then show the condition of
the extrapolar parts of the nerve. Nothing is really
known of the condition of the intrapolar portion of the
nerve, for, for external technical reasons, it is im-
possible to examine this.1 We can only suppose that
changes in tension such as those indicated by the
dotted curve p q occur there.

If the curve in fig. 60 is compared with the dia-
gram of the changes in excitability during electro-
tonus (as given in fig. 31, page 130), the analogy
between the two phenomena is very striking. The
two really represent but different aspects of the same
process — of the changes, that is, which are induced in
the nerve by a constant electric current. Comparison
of the two curves shows, however, that when the
tension becomes more positive the excitability is de-
creased, and that when the tension becomes more
negative the excitability is increased. The change
1 See Notes and Additions, No. 13.

I'l'l PHYSIOLOGY OF MUSCLES AM> NKIIY! -.

in tension and the dinner in excitability both probably
depend on molecular changes within the nerve, as to
the nature of which we are not yet in a portion to say
anything further, but the simultaneous appearance of
which, under the influence of externally applied electric
currents, is nevertheless \ery interesting and will per-
haps in future afford a key to the nervous processes
which occur during- excitement.

In examining- the changes in tension which take
place during electrotonus, the differences in tension
already existing at the various points must of course
be taken into consideration. ]f the diverting arch is
applied to two symmetrical points of the nerve, thev
are homogeneous. If it is applied to any other points.
the existing differences in tension can be cancelled l>v
the method of compensation above described (chap. x.
§ 4). The differences in tension due to electrotonns
are then seen unmixed. In all other cases these dif-
ferences express themselves in the form of an increase
or decrease in the strength of the nerve-current which
happens to be present. Yet the law of the changes
in tension is the same in all cases.

6. As we found certain points of resemblance be-
tween nerves and glands, so the ner\e< of the tissue of
the electric organs, in which in the cases of the tishes
already mentioned such powerful electric action takes
place, may he classed with these. Without entering
deeply into the researches, as yet very incomplete,
which have Keen made into the structure of tlioe
electric organs, we may yet accept as already pr»\ ,-d
that the so-called cln-lrir jil<ite — a delicate membran-
ous structure. \ery many of \\hich, arranged side bv
>ide and under one another in regular order, constitute

ELECTRIC TISSUE OF FISHES. 223

the whole organ — is to be regarded as the basis of the
organ. A nerve-fibre passes to each electric plate ;
and under the influence of irritation, whether this is
due to the will of the animal or to artificial irritation
of the nerve, one side of this plate always becomes
more positive, the other more negative. As this occurs
in the same way in all the plates, the electric tensions
combine, as in a voltaic battery, and this explains the
very powerful action of such organs as compared with
that exercised by muscles, glands and nerves.

There is, indeed, a great difference between the
last-mentioned tissues and the electric tissues of elec-
tric fish. Muscles, nerves and glands when quiescent
generate electric forces, which undergo a change during
activity. Electric tissue, on the other hand, is en-
tirely inoperative when quiescent, and becomes elec-
trically active only when it is in an active condition.
Though unable to explain this difference, we must re-
mark that it affords no ground for the inference that
the actions of these tissues are fundamentally dif-
ferent. Whether a tissue exercises externally apparent
electric action, depends on the arrangement of its ac-
tive elements. But the changes which occur during
their activity in muscles, glands and nerves, and also
in electric tissue, are evidently so similar that they
must be regarded as related. An attempt will be made
in the next chapter to obtain a common explanation of
all these phenomena.

7. It has already been stated that electric phenomena
have been observed in plants also, though we found no
sufficient reason to attribute any great physiological
importance to these. It therefore created much sur-
prise when the physiologist Burdon-Sanderson a few

224 riiysioi.ot.v <>F Mrsn.r.s AND NKKYF.S.

years ago stated as tin- result of his observations,
that in tin- lea\es of Venus' Flytrap (Dtcnitra musci-
/<"/«), regular electric currents occur, which, during
the movement of these leaves, exhibit negative \aria-
ation exactly as do nerve-current-. He was induced
to make his observations by Charles I)ar\vin, who, in
the course of his study of insectivorous plants, at-
tempted to show an analogy between the leaf-move-
ments of the Dloncea and the muscular movements of
animals. Darwin's observations have since been pub-
lished in detail.1 They show the interesting fact that
in various plants glandular organs occur which secrete
juices capable of digesting albuminous bodies. The
plant above mentioned, DioncBrt mztscipuZa, i> provided
with these glands; and in addition to this it is irri-
table, as is the Mimosa pudica described in the first-
chapter. When an insect touches the leaf, the hah.-
of the leaf close on each other, and the imprisoned
insect is digested and absorbed by the secreted juice.
In judging of the nature of these leaf-movements, it is
necessary to decide whether they are really analogous
to muscle-movements, and whether the identity extends
even to the electric phenomena, as Burdon-Sanderson
would have us believe. Recent researches by Professor
Munk of Berlin have not confirmed this. The move-
ments of the leaf of the Dioncra must be regarded as
entirely similar to those of the Mimosa pudica. These
movements are dependent, not on contractions, as are
those of muscle, but on curvatures which occur in the
leaf in consequence of an alteration in the supply of
moisture in the ditiereu' cell-strata. The leaf does
indeed exercise electric action, though not in the simple
1 OH Tngectlrorout Plants. Lnnd'ui, is;.-,.

ELECTRIC ACTION IN PLANTS. 225

way claimed by Burdon-Sanderson. Changes in the
electric action also occur during the curvature, but
these changes do not correspond with negative varia-
tion in the nerve-current ; they are probably connected
with the circulation of the sap within the leaf. From
my own study of Mimosa pudica I had already adopted
similar views. In this plant I was unable to detect
regular electric action during quiescence ; but on the
falling of the leaf-stalk, I observed electric currents
which might be explained as the result of the circu-
lation of the sap. We must, therefore, be content to
accept the fact that electric phenomena in plants are
not to be classed with those observed in muscles,
glands, nerves, and in the electric organs of certain
fishes.

11

22(5 TIJYSIOLOGY OF MUSCLES AND NERVES.

CHAPTER XIV.

1. General summary; 2. Fundamental explanatory principles; 3.
Comparison of muscle-prism and magnet ; 4. Explanation of I he
tension in muscle-prisms and muscle-rhomM ; 5. Explanation
of negative variation and parelectronomy ; f>. Application to
nerves; 7. Application to electric organs and glands.

1 . Summing up the most important facts given in
the foregoing chapters, we may make the following
statements :—

(1) EI->JI'I/ muscle, and ever// jmrt of a muscle, win n
quiescent, is positive on its lungitudiruil section ;
n <<</<i five on its cross-section. In a regular muscle-
prism, the positive tension decreases regularly

the centre of the loiuj'ttndinal section toward the
and the )t<'</<iti>-e tension does the same in ///«' cross-
sections. In a muscle-rhombus the <//'*Y/-/7,, <//,»>/. of
the tension is someivhat different, for in it the
greatest positive tension is removed toward the obtn*<:
<nifjle of the lon</i(n<linal section, the greatest nei/nt'fi'.
ti'itxion toward the acute angle of the cross-section.

(2) During the activity of the muscle the difh ,-, ,,,-. g
in tension decrease.

(3) Entire muscles often exhibit l>ut x!/:/ht </iii'i ,-
ences in tension, or even none at all; but ive must
nevertheless assume th<' *'.i-ixl< nee of electric ojijmxitioit

in tli- ''ill.

(4) Nerves arepoaitice on the longitudinal section,

SUMMARY. 227

negative on the, cross-section. The greatest positive
tension is in the centre of the longitudinal section.
During activity the differences in tension decrease.

(5) The electric plate of electric fish is, when qui-
escent, electrically inactive ; influenced by the nerves,
the one side becomes electrically positive, the other
negative.

(6) In the glands the base is positive, the opening
or inner surface negative ; during activity the dif-
ferences in tension decrease.

These propositions state only the most important of
the conditions which have been shown by experiment.
On the outer surfaces of the tissues examined we found
differences in electric tension ; and we found reason
to believe that the causes of these differences in tension,
which occur with great regularity, must be situated
within the tissues themselves. We now have to dis-
cover these causes, and this is not so easy to do as
it perhaps appears at first sight. Difficult as it may be
to calculate the tensions which must prevail at each
point on the outer surface of a given body, within
which an electromotive force is situated, yet the diffi-
culties in this case may be overcome by skill. It is
different, however, when the problem is reversed, when,
the distribution of the tension having been experi-
mentally found, it is required to discover the seat of
the electromotive force. The difficulty in this case
consists in the fact that the task is undefined, and
that many very various solutions may be found. More-
over the task is rendered yet more difficult by the
fact that we do not know whether one or many elec-
tromotive forces are present, situated in different parts
of the body.

228 PIIYMOLOGY OF MUSCLES AND NI-RVJ >.

2. Let us suppose, for example, that in the body
described in Chapter X. § 2, the distribution of the
tension \\hich prevails on the surface as the result of
tin- electromotive forces then assumed, has been pro\eol.
Let us now imagine that this particular electromotive
force is removed, and is replaced by another, situ-
ated at any other point in the body. Accordingly, the
body will be occupied by current-curves of different
form, corresponding with different iso-clectric curves.
Consequently, the distribution of tension on the sur-
face is also quite different. A third electromotive
force situated at any other point would again involve
an entirely different distribution of the tension, and >o
on. Ilelmholtz has shown that when many siu-li
electric forces are present at one time in a bodv, the
tension which actually prevails at each point of the
surface is equal to the sum of all the tensions which
would be generated at this point by each of the electro-
motive forces by itself. If, therefore, a certain distri-
bution of tension has been experimentally found, it is
possible to conceive many combinations of electromotive
forces which might afford such a distribution of tension.

The rules of scientific logic afford a standard by
which to choose to which of all these possible c<>m-
lii nations the preference shall be given. The theory
Delected must, in the first place, be able to explain, not
only one, but all the circumstances experimentally
found. If new facts are discovered by new experi-
ments, then it must be able to explain these also, or it
must be relinquished in favour of a better theory.
Secondly, if several theories seem equally to satisfy tin-
required conditions, then preference must be given to
the simplest rather than to the more complex theories.

A MUSCLE-PRISM AND A MAGNET. 229

But in all cases it must be borne in mind that these
are only theories, the value of which consists in the
very fact that they afford a common point from which
all the known facts may be regarded, and that they
must in no case contradict the value of scientifically
established facts. We require such hypotheses, partly
because they point the way to further research, and
thus greatly aid the advance of science ; and partly
because the human understanding finds no satisfaction
in the simple collection of separate facts, but rather
strives, wherever it has discovered a series of such
facts, to bring these, if only provisionally, into reason-
able connection, and to gain a common point of view
from which to regard them.

3. Turning now to our task provided with these
preconceptions, we will at first confine our attention to
muscle. A regular muscle- prism exhibits a definite
distribution of tensions. But every smaller prism
which may be cut from the larger exhibits the same
distribution of tensions. No limits to this are as yet
known, for even the smallest piece of a single muscle-
fibre susceptible of examination is conditioned in this
respect just as a large bundle of long fibres. Two
possible explanations may be given of this. It may
be assumed that the electric tensions are due merely
to the arrangement of the muscle-prism, or such an
arrangement of electromotive forces already present
in the muscle may be conceived as explains all the
phenomena found to occur in the muscle. Mateucci
and others tried the first of these ways. But when
du Bois-Eeymond undertook the study of this subject,
and, with a degree of patience and perseverance un-
equalled in the history of science, discovered very many

230 IMIYSIOLCM1Y <>F MfSCLES AND NKRYI -.

facts, for but a few of which we have been able to find
place in tin- foregoing chapters, lie was dissatisfied with
tliis wav, and, therefore, tried the second. And thus he
was enabled t > form an hypothesis which afforded an
explanation of all the previously-known facts, of all
those which have come to light since the hypothesis
was first formed, and even of some which were first
indicated by the hypothesis itself and were then con-
finned by experiment. It is true that attempts on
the other side have since been again made to restore
credit to the older hypothesis, but the attempts have
been in vain. We shall, therefore, fully accept the
hypothesis constructed by du Bois-Keymond as being
alone capable of including and combining all electro-
physiological facts.

CCCC€CC€€)CCCD€Cf)€CC€t €€)C

6

Fi<;. 01. TMI:OKY <>K MAC.M.TISM.

The phenomenon, that when a muscle-prism is cut
into two halves, each part exhibits an arrangement of
the electric tensions exactly analogous to that which
before prevailed in the entire prism, recalls a corre-
sponding phenomenon observed in the magm-lic rod.
It is a well-known fact that every magnetic rod has two
po]e<, a north pole and a south pole. The magnetic
tension is greatest at these two poles, and decreases
towards the centre; and at the actual centre it = 0.
If the magnet is then cut through in the cent re, each
half becomes a complete magnet, uith a north and a

A MUSCLE-PRISM AND A MAGNET.

231

south pole, and exhibits a regular decrease of the mag-
netic tensions from the poles to the centre. However
often the magnet is subdivided, each fragment is always
a complete magnet with two poles, and a regularly
decreasing tension. To explain this, it is assumed that
the whole magnet consists entirely of small particles
(molecules), each of which is a small magnet with a

FIG. G2. DIAGRAM OF A PIECE OF MUSCLE-FIBKE.

north and a south pole. These small molecular mag-
nets being all arranged in the same order, somewhat
as is shown in figure 61, they act in combination in
the whole magnet ; but each separate part also acts in
the same way.

The muscle may be similarly conceived. A stri-
ated muscle consists of fibres, all of which in the case
of a regular muscle-prism run parallel to each other,
and are of equal length. Each fibre must be regarded,
according to that which was said in Chapter I. § 2, as

232 PHYSIOLOGY OF MUSCLES AND NERVES.

composed of regularly arranged particles, each of which
consists of a small portion of the simply refracting
elementary substance, in which is embedded a group
of tlic double-refracting disdiaclasts. Such a particle
may lie called a muscle-dement. The muscle-fibre
would accordingly consist of regularly arranged muscle-
elements, the sequence of which, in the longitudinal
direction, forms the fibrilla3 of which mention has been
made; in the lateral direction forms the discs into
which the muscle-fibre may separate under certain
circumstances. A diagram of a piece of muscle-fibre
would, therefore, present an appearance somewhat a>
in fig. 62, in which each of the small rectangular
figures represents a muscle-element. Each such muscle-
element is, therefore, in all essential points an entire
muscle, for the fibre is but an accumulation of such
muscle-elements, each exactly like the other ; and the
whole muscle is but a bundle of homogeneous muscle-
fibres. Iri each muscle-element we must, therefore,
recognise the presence of all the qualities which belong
to the whole muscle. It possesses the capacity of
becoming shorter, and at the same time thicker; and
finally — and this is the gist of the question here under
discussion — it has the same eleetric characters as are
observable in the entire muscle.

4. We therefore assume that every inu>c!e- •l.-nn-iit.
i- the seat of an electromotive force, in \irtue <>f \\hich
it is positive on the longitudinal section, negative »\\
the cross-section. If a single muscle-element of this
sort were surrounded by a conducting substance, sys-
tems of current-curves from t lie side of the lon^it udinal
M-ction to that <>f the cross-section would be present
within it. If many such muscle-elements are arranged

TENSIONS IN MUSCLE-PBISMS AND RHOMBI.

233

side by side and one behind the other in the regular
arrangement which we have assumed, then the whole
must, as has been shown by calculation, be positive
throughout its longitudinal section, negative through-
out its cross-sections. Now, supposing that this whole
aggregation of muscle-elements is surrounded by a
thin layer of a conducting substance, then currents
such as are represented in fig. 63 must be present
within it. These current-curves then accurately corre-
spond with that distribution of the tensions which was
experimentally shown. The greatest positive tension

FlG. Co. DlAGUAM OF THE ELECTRIC ACTION IX AX AGGP.EGATIOX OF

MUSCLE-ELEMENTS.

must prevail in the centre of the longitudinal section ;
the greatest negative tension in the centre of the
cross section ; and both must decrease in a regular wav
toward the edges.

We now take a bundle of muscle-fib] e 3, the ends
of which are formed by two artificial straight cross-
sections, in other words, a regular muscle-prism. The
separate muscle-fibres, which constitute the bundle,
are surrounded by sarcolemma, held together and en-
veloped by connective tissue. Moreover, the outer-
most strata must obviously become subject sooner than
the inner to the unfavourable influences of mortifica-
tion, which, as we have seen, finally lead to the entire
loss of electric qualities ; these outermost strata there-

234

IMIYSIOLOUY OK MI'H'I.KS AND NKKVFS.

f<>re become quite inoperative, or less operative than
(lie inner. This injurious influence must be yet more
strongly developed on the cross-section, where a layer
of crushed, that is, deal muscle-substance, overlies
the ]):irts which yet remain operative, Owin^ to all
these circumstances, a coating of inoperative but con-
ducting substance envelopes the operative muscle-
elements, and the distribution of the tensions on the
regular muscle-prism is fully explained. And when
such a muscle-prism is divided, the conditions al \vavs
remain unaltered. Karh part of a miisele-prism mu>t
act as would the whole.

I'l<. . <!l. Dl.Uii: AM i IK AX oill. Kill: t K(»S sl-;< HON.

Our hypothesis is therefore quite able to explain
the electric phenomena of a regular muscle-prism.
We must now see how it stands in relation to the other
facts which we have learned. If the artificial cross-
section is made obliquely to the axis of the musde-
tibivs, as in a .regular or irregular mnscle-rh unbus, then
our a-simied muscle-elements, at the cross-section, will

be arrane-ed one over tl ther like steps, and are

clothed by a ];i\er of crushed, and therefore inopera-
tive tissue, as is represented in fi-r. (H. ou sncli a
cross-section it is evident that separate currents must
circulate from the positive 1 m-it udinal section to
the ne..-;, in,, cross-section of each individual muscle-
clement, and tlie->e combine with (l,e current elicu-

NEGATIVE VARIATION AND PARELECTRONOMY. 235

lating from the longitudinal to the cross-section of
the entire prism, to make the obtuse angle more
positive than negative.

5. We must next inquire how the negative varia-
tion of the muscle-current during activity can be ex-
plained in accordance with our hypothesis. We have
already found reason to believe, from the phenomena
of muscle-tone, that the contraction of the muscle
depends on a movement of its smallest particles. Mi-
croscopic observation of muscular contraction shows
that the movement takes place within each muscle-
element, for the change in form may be detected in
each muscle-element just as in the whole muscle-fibre.
It is therefore not difficult to conceive that, in con-
nection with these movements of the smallest particles
within each muscle-element, the electromotive opposi-
tion between the longitudinal and cross-sections of that
element undergo a change. It is of little importance
whether we conceive the matter as though the mo-
lecules of the muscle undergo vibratory motion during
contraction, or whether we give the preference to some
other theory. Where facts are wanting to support or
contradict certain assumptions, the imagination may
have free play, and may picture any process by which
changes of the kind under consideration might pos-
sibly be brought about. But the discreet man of
science, while allowing himself this liberty, ever re-
members that such free play of the imagination is of
no real scientific value, either didactically, as explain-
ing known facts, or temporarily as leading and inciting
to new researches. Grood hypotheses are always avail-
able in both these ways, and the scientific man uses
only such. He may perhaps amuse himself in a leisure

riIYSIOLO(.\ OF MUSCLES AM- NKRVKS.

quarter of an hour by allowing his imagination to
-•any the hypotheses further than tin- point up to
which they are based on known facts; but he docs not
presume to urge the results on others.

Filially, we have to examine how far t he hypothesis
to which we have given the preference is confirmed by
the phenomena observable in entire muscles. The
tendonous covering on the ends of muscle-til ires may
be regarded as a layer of non-active conducting sub-

-tance. In so far as the same phenomena are ex-

•

hibited in the uninjured muscle, as in the muscle-
prism or muscle-rhombus with its artificial cross
section, nothing need be added to the previous ex-
planations. But this is, as we have s -en, though
nerally. yet not always the case. The natural CTO8E
section of a muscle is generally very slightly negatixe.
sometimes not at all, as compared with the longi-
tudinal section; but the negative character becomes
marked as soon as the natural cross-section has been
destroyed in any way, either mechanically, chemically,
or thermieally. In explanation of this condition of
the natural ends of muscle-fibres, we may assume that
the arrangement of the molecules in the latter or in
the, terminal mu>c|e-element s in each mii-cle-fibiv may
sometimes be dit'f'eren! from that at all other points.
If, for example, the cro-- sect ion in the terminal
muscle-element were not negative, the miiM-le-libre
could afford no current, though such a current would
arise as soon as this terminal muscle-'lemeii! wa- re-
mo\ed or was traii-forim d into a non-active conductor.
I1], du I'>oi--h'eymond has lately succeeded in discover-
ing a verv probable iva-on for this abnormal condition

of the ends of muscle-fibres j but without entering too

THE NERVES. 237

deeply into details we should not be able to explain
this here.1

6. We will now turn our attention to nerves. The
resemblance of the phenomena in the case of muscles
and of nerves is so great that it is natural at once to
transfer the hypotheses assumed for the former to the
latter. It is true that in nerves there are not the
microscopically visible particles (the so-called muscle-
elements) on which we based our theory in the case
of muscles, and in which we recognised the presence of
electromotive forces. But from what we have already
seen of the processes of excitement in the nerve, it is
at least evident that in the nerve also separate par-
ticles, with independent power of movement and inde-
pendent forces, must be arranged in sequence in the
longitudinal direction of the nerve. If, without beingf

O 3 O

able to say anything further of their nature, but be-
cause of the analogy, we call these particles nerve-
elements, and if we assume that each of these nerve-
elements is the seat of an electromotive force, in
consequence of which the longitudinal section exhibits
positive tension, the cross-section exhibits negative
tension, then the phenomena in the quiescent nerve
and the negative variation of the nerve-current during
activity are explicable exactly as were the correspond-
ing phenomena in muscles. The entirely similar be-
haviour of nerves and muscles when irritated is alone
sufficient to show satisfactorily that the two must be
very much alike in their physical structure ; and the
similarity of their behaviour in point of electromotive
activit}r is such as to lend weight to our assumption of

1 See Notes and Additions No. 14.

23S PHYSIOLOGY OF MUSCLES AND NERVES.

the similarity in tin- arrmirem -at of their small^t
particles.

But together with many points of resemblance.
iK-rve aad muscle exhibit some points of difference.
The muscle during activity changes its form and is
able to accomplish work; the nerve is incapable of
this. The nerve, on the other hand, under the in-
tl IK 'iice of continuous electric currents, exhibits tho»-
elianges in excitability which we observed under the
name electrotonus, and which, as we have seen, corre-
spond with elianges in the distribution of the tensions
on the outer surface of the nerve. No correspond-
ing phenomena have been shown in muscle. Other
changes which effect, these changes in tension must,
therefore, occur within the nerve-element.

It is a well-known fact that all substances occupy-
ing space are regarded as composed of small partido,
to which the name molecules is given. In a simple
chemical body, such as hydrogen, oxygen, sulphur, iron,
and so on, all these molecules consist of homogeneous
atoms ; in a chemically compound body, such as wat.-r.
carbonic acid, and so on, each molecule is composed of
several atoms of different kinds. A molecule of water,
for instance, consists of an atom of oxygen and two
atoms of hydrogen; a molecule of carbonic acid con-
sists of an atom of carbon and t\\o atoms of oxygen ;
a molecule of common salt consists of an atom of
natron and an atom of chlorine, and so on.1 A piece
of salt contains a very large number of such atoms
of ehlovinc and natron, but each of these

1 Details of tin mid molecular theory will IT found in

'Tlic ]S'(j\v Chi -niistry.' Coukc (lull-mat i-«!i:il ScicuLi::- Si
vul. ix.).

THE NERVES. 239

(in pure cooking salt) is like every other. But a
muscle, a nerve, or any other organic tissue, is much
more complex in structure. Molecules of albumen,
of fats, of various salts, of water, and so on, are
mingled in it. A very small piece of such a tissue
must be regarded from a chemical point of view as a
compound of very many different substances. To avoid
confusion, the name ' muscle-element ' or ' nerve-
element ' has been given to these particles, in which
we assume the existence of all the qualities of muscle
or nerve, but this name expresses nothing further than
a fragment of a muscle or nerve. Even such a frag-

•J CJ

ment must be regarded as of very complex structure.
Very complex physical and chemical processes may
take place within it ; and the processes of muscle and
nerve activity, the actual nature of which is as yet
quite unknown to us, are certainly connected with such
chemical tlnd physical processes. If electric forces also
occur in such a nerve- or muscle-element, it is not sur-
prising that these also undergo various changes. Of
this sort must be the changes which occur during ac-
tivity and during electrotonus.

In speaking, as we have occasionally done, of nerve-
and muscle-molecules, we have, therefore, not used the
term molecule quite in the clear and fixed sense in
which the term is used in chemistry. Our conception
was rather of something which, itself composed of va-
rious chemical substances, forms a unit of another
order. For the sake of brevity we shall still sometimes
use the expression in this sense, as, after the explana-
tion which has now been given, we may do this without
fear of being misunderstood. A muscle- or a nerve-
molecule accordingly means a group of chemical mo-

240 PHYSIOLOGY OF MUSCLES AND NERVES.

lecules combined in a particular way, many of which,
in combination, form a muscle-molecule or a nerve-
elemeiit respect ively.

Wu have learned to regard the negative variation of
the muscle- or nerve-current as a movement of these
muscle- or nerve-molecules respectively, in consequence
of which the differences in tension between the longi-
t ud i mil and cross-sections become less. In explanation
of the electric phenomena of electrotonus, we may now
assume that under the influence of continuous electric
currents the nerve-molecules assume a different relative
position by reason of which the distribution of the
tensions on the outer surface of the nerve is (limited.
This changed position is retained as long as the electric
current flows through the nerve, and disappears more
or less rapidly after the opening <>f the current. At
first it takes effect only within the electrodes, but it
propagates itself through the extrapolar portions, be-
coming gradually weaker the further it is from the
electrodes. In illustration of this conception, we may
avail ourselves of the comparison which we have already
made of the nerve-molecules with a series of magnetic
needles. When the position of some of the needles in
the centre of such a series is changed, owing to some
external influence}, those needles which lie more on the
outside of the series must be turned to an extent de-
creasing ^ it h their distance from the centre. Or we
may al-o refer to the conception which physicists have
formed of the so-called elect r. .lysis, the analysis of a
Huid bv an electric current. All these analogies can
only explain the process in so far that \ve ivoignise how
an electric current is capable of causing a change in the
relative po<iti,,n of the muscle- and nerve-molecules,

GLANDS AND ELECTRIC ORGANS. 241

at first only between the electrodes, but afterward
beyond these, which change then corresponds with a
change in the distribution of tension on the surface.

7. We have yet to consider how far the hypothesis
under discussion explains the electric phenomena in
electric fishes and in the glands. The electric shock
of the torpedo must evidently be regarded as analo-
gous to negative variation in muscle- and nerve-
currents. The apparently great difference that in the
latter a current present during a state of quiescence
becomes weaker during activity, while in electric fishes
an organ which is entirely inoperative during the state
of quiescence generates a current when it becomes
active, appears, when closely examined from the point
of view afforded by our hypothesis, to be of no account.
For, from the fact that no current in an organ can be
externally shown, it by no means follows that no elec-
tromotive forces are present within the organ. A piece
of soft iron is in itself entirely non-magnetic ; but as
this may at any time be transformed into a magnet by
bringing a magnet into its neighbourhood, or by the
influence of an electric current, we suppose that mole-
cular magnets are present even in the soft iron, though
these are not regularly arranged as in a regular magnet,
such as that represented in fig. Gl, p. 230. The action
of the magnet which is brought near, or of the electric
current, therefore consists solely in the fact that it ar-
ranges the irregularly placed molecular magnets within
the soft iron, and thus allows their action to appear
externally. If no magnetic action were known in soft
iron, no one would ever have had an idea that magnetic
forces were present within it. But comparison with the
permanent magnet, and the possibility that thoroughly

242 PHYSIOLOGY ov MUSCLK- AND .VEUVES.

non-magnetic iron may at any time be transformed into
a magnet, maki s the involved conception quite natural.
It i< exactly the same in the case of the electric organs
of the torpedo. The fact that they, though in them-
selves electrically inoperative, become electrically oper-
ative under the influence of the nerves, when c- >ml lined
with what we know of nerves and muscle, naturally
leads us to suppose that electromotive forces are pre-
sent in the electric plates, but that they are so ar-
raiM'ed as to cause no observable differences of tension

D

on the outer surface. Under the influence of the ac-
tive nerves, the particles endowed with electric forces
undergo a change in their relative position, differenco
of tension between the two surfaces of the electric plates
inter\ene, 'ind, as all the electric plates in an organ act
in (lie same way, the result is a powerful electric shock,
which, in spite of its powerful effect, differs from the
negat ive variation of the muscle- and nerve-currents only
as does the powerful current of a many-celled galvanic
batterv from the weak current of a small apparatu-.

In order to make the similarity between the electric
organ on the one hand, and muscles and nerves on the
oih.-r. yet more prominent, we will carry the compari-
son with magnetic phenomena yet further. In fig. 65,

IS \

I'll;. (')."). M Ai.M I 1C 1MMC Tl<>\.

.1 // isa piece nf M>|'I iron. .V N ;i magnet which we bring
from some distance toward the in.u rod .1 />'. The result
is to evoke magnetism in J II. A becoming a north pole,

and />' a .-oitth pole. Now, let i;< snppo>e that the non-
magnetic iron rod .1 I! i> replaced by an entirely similar,

GLANDS AND ELECTRIC ORGANS. 243

but magnetic rod Nl Sl (fig. 66). At the moment at
which the magnet NS is brought near, the magnetism
of Nl Si becomes weaker, ceases entirely, or is even

FIG. G6. MAGNETIC INDUCTION.

reversed. The same process of magnetic induction is
concerned in both cases. The only difference is that in
one case the induction seizes on an iron rod the mole-
cular magnets of which are irregularly arranged, and
which therefore appears non-magnetic; while in the
second case the iron rod is in itself magnetic. So that
in one case magnetism is evoked by induction, in the
other, magnetism which was already present is weak-
ened ; but the induction is the same in both cases. In
just the same way electric tensions are induced in the
electric plate by the influence of the nerves, while the
tensions present in the muscle are weakened ; but the
process in the electric plate and in the muscle is the
same.

We have now only to say a few words about the
glands. The phenomena in these are, so far as we can
infer from the few known facts, so entirely like those in
muscles, that it is only necessary to transfer the expla-
nation which we have given in the case of the muscles
to the glands. In each gland-element electric forces
are present which make the base of the gland positive,
the mouth-opening negative. When the gland becomes
active, these differences in tension become less. There
is no occasion to speculate as to how far this affects the
process of secretion, as it could not further explain the
process.

244 I'HYSIOLOGY OF MIM I.i'..S AND NF.KVKS.

CHAPTER XV.

1. Connection of IHTVC and muscle; 2. Isolated excitement of
individual muscle-fibres; I!. Discharge-hypothesis; 4. Principle
of the dispersion of forces; 5. Ind<-| cndrnt irritability of muscle-
Mil'Stancr ; <'.. Curare; 7. Clu-mira! irri'ants ; S. Theory of tlie
activity • >!' the n< r\« s,

1. Ill till' foregoing chapters We have examined the

characters of muscles and nerves separately. Tin-
muscle is distiiiiMiislird l>y its jiowcr of shortening ami
thereby accomplishing work. The nerve 1ms imt this
power: it is only able t<> incite the nmscle to activity.
We must now inquire how this incitement, this trans-
fnvnct' of activity from the nerves <,> tli,. mu c1 -.
occurs.

To understand tin act j.ni of a machine, of any piece
of mechanism, it is necessary to learn its structure and
the relative positions of ite separate parts. In our ca-. .
microscopic observation can alone aH'«>rd the explana-
tion. If we (rare the course of the nerve within the
mu-cle, we tind that the separate til >re<, which enter
the inii-i-le in a c.iniieeted luiiidle, separate, run among
the muscle-fibres, and sjiread throughout the muscle.
It then appear- t hat the single nerve-fibres divide, and

this explains the fact that each mn>«-h-iil>re is eventu-
ally pro\ id. d wit h ;' ner\e-lilire IMH- ne,-\-e-til.res . ven
\\ilh two— although the numlier of nerve-libres which
tin muscle is generally much less than the

CONNECTION OF NERVE AND MUSCLE.

245

number of the muscle-fibres which compose the muscle.
Till the nerve approaches the muscle-fibre, it retains its
three characteristic marks — the neurilemma, medullary
sheath, and axis-cylinder. When near the muscle-fibre,
the nerve suddenly becomes thinner, loses the medul-
lary sheath, then again thickens, the neurilemma co-

FIG. 67. TERMINATIONS OF NERVES IN THE MUSCLES OF A GUINEA-PIG.

alesces with the sarcolemma of the muscle-fibre, and
the axis-cylinder passes directly into a structure which
lies within the sarcolemma pouch, in immediate con-
tact with the actual muscle-substance, and is called the
terminal nerve-plate. Fig. 67 represents this passing
of the nsrve into the muscle as it occurs in mammals.
In other animals the form of the terminal plate is some-

240 PHYSIOLOGY OF Mrsri.KS AM> NKIJVES.

what differ* >nt ; hut tin- relation between the nerve and
the muscle is the same. The essential fact is the same
in all cases: ////>, m-rre _/"'•-'*'* ''"/" direct contact
n-ltli tlf muscle-substance. All observers are now
a -Teed on this point. Uncertainty prevails only as to
the further )iature of the terminal plate. In the frog,
for instance, there is no real terminal plate, but the
nerve separates within the sarcoleinma into a net-like
series of branches, which can be traced for a short dis-
tance from the point of entrance in both directions.
Professor Gerlach has recently declared that this net,
as well as the terminal nerve-plate, are not really the
ends of the nerves, but that the nerve penetrates
throughout the muscle-substance, and that throughout
the whole muscle-fibre there is an intimate union of
nerve and muscle.

2. However -this may be, the fact that the nerve-
substance and the muscle-substance are in immediate
contact must serve as the starting-point from which to
attempt an explanation. "When it was thought that
the nerve remained on the outer surface of the muscle-
fibre, there was difficulty in explaining how a pulsation
of individual muscle-fibres within a muscle could bo
elicited by irritation of individual fibres of a nerve.
Kor the nerve-fibres, in their course within the nm-< le.
touch externally many muscle-fibres, over which they
pass before they finally end at another mnsde-liltre.
In the case of flat, thin muscles, it may be shown con-
clusively that such a nerve-fibre may be irritated in
such a way that those muscle-fibres over which it,
passes remain quiescent, and only those pulsate at
which the nerve-fibre ends. As soon, however, as it is
understood that the excite nt present in tl e nerve-

THE DISCHARGE HYPOTHESIS. 247

fibre cannot penetrate through the sheaths, it is clear
that the excitement can only act on the muscle-
substance where the nerve-substance and the muscle-
substance are really in immediate contact — that is, only
within the sarcolemma pouch. The nerve-sheath is, as
we already know, a real isolator as regards the process
of excitement within the fibre ; for an excitement within
a nerve-fibre remains isolated in this, and is not trans-
ferred to any neighbouring fibre. It is quite impos-
sible, therefore, that it can transfer itself to the muscle-
substance, since it is separated from the latter not only
by the nerve-sheath, but also by the sarcolemma.

But if the nerve-fibre penetrates the sarcolemma, as
appears from the microscopic observations above de-
scribed, and if nerve-substance and muscle-substance
are in immediate contact, then the transference of the
excitement present in the nerve to the muscle substance
is intelligible. The argument holds good whether we
assume that the nerve, directly after its entrance within
the sarcolemma, ends in a nerve -plate or a short nerve-
net, or whether, as Gerlach says, it spreads further. All
that is needed to make the process of transference in-
telligible is that the two substances should be in imme-
diate contact, and so much is granted, whichever view
is preferred. But the process, if intelligible, is yet not
explained. An attempt at explanation must be based
on, and have regard to, all the established facts.

3. It is natural to think of the electric characters
of nerves and muscles, and to seek the explanation in
these. In nerves electric tensions prevail which dur-
ing the activity of the nerve undergo a sudden decrease,
a so-called negative variation. Such sudden variations
of electric currents are, we know, able to excite the

248 rnvsiOLOGY OF MUSCLES AND NEKYI

muscle. We may, therefore, conceive the process some-
what as follows. Tin- excitement in the nerve, however
caused, propagates itself along the nerve-fibre until it
reaches the end of tin- latter. Connected \\ith it is :in
electric process, by which a sudden electric variation
18 caused in the terminal apparatus of the nerve-
h'bre, and this excites the nerve-substance, just as a
shock acting externally immediately on the muscle
would excite it.

Following du Bois Ixeymond, the above conception
may be called the discharge-hypothesis (Entladwnga-
hypothese). According to it, the muscle end of a nerve-
fibre must be regarded as similar to an electric pla'e
in the peculiar organs of electric fish. Indeed, in the
latter, an electric discharge is effected by the influence
of nerve-excitement, which is able to cause other excit-
able structures, such as muscles and glands, to contract.
We do not attach any weight to the accidental external
resemblance of the terminal nerve-plate to the electric
plate. In frogs and many other animals there are no
terminal plates, and yet the conditions are the same in
their case also. And even if the view upheld by Gerladi
is confirmed, and it is shown that nerve-substance comes
into more intimate contact with muscle-substance than
merely at the point at which it enters the muscle-
pouch, our explanation will be unaffected. All that we
claim is that an electric discharge, by which themuscle-
sub.-faiice is irritated, takes place in the terminal expan-
sions of the nerves, of \\hatever form these expansions
may be.

Against the acceptance of this \ie\va ditlicnlty at
first seems to present itself in the fact that such an
electric shock, taking place in the end of a nerve, would

THE FREEING OF FORCES. 249

excite not only the muscle-fibre in which the nerve
ends, but the adjacent fibres also. For in the muscle
and its envelopes no electric isolators are present, and
an electric shock, occurring at any point, can and must
spread throughout the whole muscle mass. But from
the law of the distribution of currents in irregular con-
ductors, the essential outlines of which are given in the
twelfth chapter, it appears that the strength of the cur-
rent in the immediate neighbourhood of the spot at
which the discharge actually takes place may be con-
siderable, though it decreases so rapidly with increasing
distance, that it is easy to believe that it may be quite
unnoticeable, even in a muscle-fibre which stands side
by side with the fibre directly irritated. It is this
very circumstance which lends especial weight to the
fact that the nerve penetrates within the muscle-fibre,
and there comes into immediate contact with the muscle-
substance. Only in this way is it intelligible that a
discharge occurring in the nerve can irritate the muscle.
When the excitement has once arisen at any point
within the muscle-substance, it can, as we have seen,
spread within the muscle-fibre. It is possible that this
may result without any co-operation of the nerve-sub-
stance ; so that the spreading of the nerve within the
muscle-substance, as claimed by Gerlach, is not required
to explain the processes within the muscle.1

4. We therefore assume that the excitement aris-
ing in the nerve itself becomes an irritant, which
then irritates the muscle. The forces which are gene-
rated, in consequence of this, in the muscle are, as we
know, able to accomplish considerable labour, which
bears no relation to the insignificant forces which act

1 See Notes and Additions, No. 15.
12

250 PHYSIOLOGY OF MUSCLES AND NERVES.

on the nerve and which are active in the nerve itself
vJiile tin- latter transmits the excitement. To use a
common but appropriate simile, the nt-rve is but the
-park which causes the explosion in the powder-mine;
or. to carrv the simile further, the sul])hur train which,
being tireil av one end, carries the fire- to the mine, and
there causes the explosion. The forces which are set
free within the muscle are chemical, due to the oxida-
tion of its substances ; the irritant originating from tin-
nerve is only the incitement in consequence of which
the chemical forces inherent in the miiM-le come into
play. Physicists call such processes the freeing of
forces. The nerve-irritant, therefore, frees the rauscle-
forces, and these translate themselves into warmth and
mechanical work. In every such freeing, the freeing
force is generally very small when compared with tin-
forces set free, and which may be dormant for incalcu-
lable periods ; though when they are once set free, they
are, capable of enormous effects. A huge block of stone
may for years hang in unstable equipoise on the edge
of a precipice till some insignificant disturbance makes
it fall, carrying destruction to all in the way of its de-
scent. It is even supposed that the slight disturbance
caused in the air by the sound <>f a mule-bell is suf-
ficient to start the ball of snow which at last thunders
down into the valley in the form of a mighty, all-
destroying avalanche, This freeing by small forces is

only possible in the case »f unstable equipoise. But
there is also a chemical unstable equipoise. Carbon
and oxygen may lie for thousands of years side by side
without combining. C|o>ely mingled, as in gunpowder,
<>r still more closely, as in nitro-glycerine, they are in

unstable equipoise; the sli^hte-t blow suffices to cause

INDEPENDENT IRRITABILITY OF MUSCLES. 251

their combination, which by their expansion is able to
accomplish such gigantic work.1 In muscle, too, carbon
and oxygen lie side by side in chemical unstable equi-
poise; and it is the irritation of the nerves which effects
the solution which destroys the equilibrium. An arrange-
ment such as that just described is called sen-sitir<\
because even an insignificant disturbance is sufficient to
disturb the unstable equipoise and to develop force. The
muscle is therefore a sensitive machine. But the nerve
is in a yet higher degree sensitive, for the smallest dis-
turbance of its equipoise gives play to the forces within
it. But these forces are in themselves incapable of any
great effects. They would hardly be iudicable, were
not this sensitive machine, which we call the nerve,
connected with the machine, also sensitive, which we
call muscle, in such a way that the activity of the one
sets free the forces within the other.

5. A sensitive machine is not equally sensitive to
ail possible disturbances. Dynamite 2 may be placed
on an anvil and hammered without exploding ; or, if
lighted with a cigar, it burns quietly out like a fire-
work. But when it comes in contact with the spark of
a percussion cap, it explodes, and develops its gigantic
forces. A nerve is sensitive to electric shocks, and to
certain mechanical, chemical, and thermic influences.
It is not sensitive to many other influences. The in-
fluences to which the nerve is sensitive we have called
irritants. A muscle is sensitive to electric shocks, to
certain mechanical, chemical, and thermic influences ;

1 On these processes see Balfour Stewart ' On the Conservation
of Energy' (International Scientific Series, vol. vi.) ; and Cooke
on ' The New Chemistry ' (same series, vol. ix.).

2 Dynamite is a mixture of nitro-glycerine wi'.h 'kieselguhr,' an
earth consisting of the shells of infusoria.

252 PHYSIOLOGY OF MUSCLES AND NKKVI-.

above all, to the influence of the active nerve.
The latter niav perhaps, as \ve have explained in the
foregoing paragraphs, be referred back to electric irri-
tation. It is thus apparent that muscle and ner\e
beha\e essentially in the same way towards irritants.
F>ut, remembering that nerves run for part of their
course within the muscle, between its fibres, and even
penetrate within the very niuscle-tibres, the thought
now suggests itself, that perhaps the muscle is in no
wav electrically, chemically, thermically, or mechani-
cally irritable ; perhaps, when these irritants are allowed
to act on the mu-ele. it is only t he hit ra-musciilar nep,
which are irritated, and which then in turn act on the
muscle-fibres. In other words, we have to determine
whether the muscle is only irritable mediately through
the nerves, or whether it is also immediately irritable,
independently of the nerves, by any irritants.

The question is not a new one. Albert von Haller,
pr.et and physiologist (170S-77), asked it, and even he
was not the first, to do so. Haller declared himself in
favour of the second of the two above-mentioned possi-
bilities. He called this capacity of the muscles to re-
ceive independent irritation (Irritabilitat ). and the name
has been retained. Haller met with much Opposition
from his contemporaries : and a dispute arese which has
lasted to the present time. In llaller's days, «.f course,
onlv the larger nerve-branchings \\ere known. The
further the nerves can be traced by means of the micro-
M-ope, t he harder does it evidently become to determine

I he qlle-t i.i]| Ullder di-cllSMoli.

(i. [n the year 1856, the French physiologisl Claude
I'ernard made experiments with a poison brought from
(iuiana, which the Indians of that region use to poi.-mi

CURARE. 253

their arrows. It is called curare, ourari, or wurali, and
is a brown, condensed plant juice, which is brought over
in hollowed, gourd-like fruits called calabashes. He
found that animals poisoned with this curare are dis-
abled, and that in animals thus disabled, irritation of
the nerve- trunks, even with the strongest electric or
other irritants, is entirely ineffective, though the
muscles are yet easily irritable. This was indeed no
new phenomenon. Harless, at Munich, had already
observed something similar in strongly etherised ani-
mals. But soon afterwards, Koelliker, at Wiirzburg,
and, simultaneously, Bernard himself, in extending
the experiments of the latter, found something new.
If ligatures are applied to the hough of a frog, and
the animal is then poisoned with curare, the lower leg
is not disabled. By irritation of the sciatic nerve the
muscles of the lower leg may be induced to contract
where the poison could not penetrate, the appropriate
vessels being tightly constricted. Curare, therefore,
does not disable the muscles, for these always and
everywhere remain irritable ; nor does it disable the
nerve-trunks, for these remain irritable if the poison
cannot reach the muscles. There is but one other thing
possible : the poison disables something which is be-
tween the nerve-trunk and the muscle-fibre, so that the
nerve-trunk can no longer act on the muscle. If that
which is disabled is the end of the nerve, then the im-
mediate irritability of the muscle-substance, without
the participation of the nerves, about which there has
been so much strife, is proved.

This striking phenomenon is not solitary. The
action of some other poisons, such as nicotine and
conine, is entirely like that of curare. These also dis-

'2.') I rilYSIOLOGY OF MUSCLES AND NERVES.

aide, not the nerve-trunks or the muscle-substance, but
some par! Intermediate between these two. The diffi-
culty is I.i prove that this partis exactly the final termi-
nation of the nerves. Assuming that these poisons
disable some pirf which lies bstween the nerve-trunk
and the muscle, but not the very end of the nerve, then,
though all the phenomena explained above are quite
intelligible, yet no answer has been gained to the ques-
tion of irritability, which we are discussing.

Considering now the characters of the nerve, and of
its passage into the nerve-fibre, it is easy to understand
why the poison does not take effect on the nerve-trunks.
The ncrve-tibres receive but few blood-vessels, so that
the poison in solution in the blood can only reach them
slowly, and in very small quantity. Moreover, the
fatty medullary-sheath probably forms a sort of protec-
tive envelope round the axis-cylinder. But where the
nerve enters the muscle-fibre it loses the inedullarv
sheath : and just at this same point a very complex net
of blood-vessels is present. Probably, therefore, it is
exactly the terminal nerve-plate (or the corresponding
nerve-branchings in the naked amphibia) which is most
exposed to the attack of the poison. So long, however,
as it is impossible to prove that this is really (he actual
end of the nerve-fibre, a chance is left open to the op-
ponents of the theory of irritabilit v.

Great pains have heeii taken to settle this point
with certainty. If a muscle poisoned with curare is
compared with a similar but imprisoned muscle, it ap-
pears thai Ihe former is less excitable; that is, that
stronger irritants are needed to cause it to pulsate.
The explanation of this maybe that the imisch'-suh-
sfance is excitable, hut not so much so as the infra-

CHEMICAL IRRITANTS. 255

muscular nerves. The following reasons may also be
given for the probability of the independent irritability
of muscle-substance. A nerve is, as is known, strongly
excited by short, sudden variations of a current, and an
unpoisoned muscle behaves in the same way; but a
muscle poisoned with curare is less sensitive to current
shocks of short duration than to such as take place
more slowly. If we ascribe independent irritability
to muscle-substance, then greater sluggishness prevails
in muscle-substance than in nerve-substance, so that
the irritating influences require longer time to take
effect in the former. In the case of nerves it has,
moreover, been shown that currents which pass at right
angles to the longitudinal direction of the nerve-fibre
are entirely ineffective. In muscles under the influence
of curare no difference in this point can be shown. If
the independent irritability of muscle-substance is de-
nied in spite of this, it must be assumed that in these
experiments the point lies in differences between the
nerve-fibres and their real ends. But nerves and muscles
are evidently very similar, and it might evidently be
possible to assume considerable difference between
nerve-fibres and nerve-ends, and that these nerve-ends
differ from the muscle-substance in nothing but that
the power of being irritated is ascribed to the former,
while it is denied to the latter. It appears then, that
the whole dispute resolves itself into an empty word-
strife as to whether this thing which lies between the
nerve-fibres and the muscle-substance is to be reckoned
as part of the nerve or as part of the muscle.

7. The much-discussed question of the independent
irritability of muscle-substance is, as appears from what
has now been said, due principally to the fact that the

256 PHYSIOLOGY OF MlX'l.r.s .\M> M:i;VES.

same irritants which act on tin- nerve are also able to
act on a muscle, and even on a muscle poisoned with
curare. We have, however, found slight difference-,
and, if it were possible to show the existence of yreat. r
differences, especially if irritants were found which act
<>n muscle-substance but not on nerve-substance, a new
point of departure would be gained for this theory of
independent irritability. Chemical irritants are beyond
all others capable of variation. From the endless num-
ber of chemical bodies we may choose such as irritate
the nerve or muscle in general, and we may try each of
these in every degree of concentration. If differences
between nerve-substance and muscle-substance really
exist, it is probable that we shall find them by these
means. Starting from these premisses, Kiihne experi-
mented on the condition of nerves and muscles; and
he was so far successful that he discovered some dif-
ferences.

In studying the character of nerves and muscles
relatively to chemical irritants, it is best to make a
cross-section, and to apply the substance which is to
be tested to this section. It is best to apply the te-t
toa thin parallel-fibred muscle, usually to the /// //NC/////X
sn i-tm-i "x of the upper leg. It is Mi-|>euded upside
down from a vice, which holds fast its lower pointed
tendon; and its upper end, which now hangs down-
ward, is then cut. The liipiid which is to be tested is
fheii brought in contact with the cross-section thus
made, and care is taken to observe whether a pulsa-
tion takes place or not. The short, used portion having
tlieii been cut off, the experiment can be repeated,
and so on till the whole length of the muscle has been
u-'-d. The nerve is treated similarly; the sciatic nerve

CHEMICAL IRRITANTS. 257

is, as in all experiments by irritation, used for the pur-
pose, either in connection with the whole lower leg, or
only with the calf-muscle. If the effect of volatile
bodies — vapours or gases — is to be tested, the muscle
must be shut off from the nerve in an adequate manner.

The muscle is extraordinarily sensitive to certain
substances. One part of hydrochloric acid in from one
thousand to two thousand parts of water affords strong
pulsations. The smallest trace of ammonia is enough
to cause strong contraction. The observer must there-
fore abstain from smoking whilst experimenting, for
the slight amount of ammonia in tobacco-smoke is suf-
ficient to elicit continued pulsations. The nerve, on
the contrary, is much less sensitive towards hydro-
chloric acid, and is not at all sensitive towards am-
monia. If the nerve is immersed in the strongest
solution of ammonia it very soon dies, but is not at
all irritated. These are the most marked differences.
But it must also be mentioned that glycerine and lactic
acid in concentration exercise an irritating effect on the
nerve, but not on the muscle ; and that when many
other substances (alkalies, salts) are applied, small dif-
ferences are exhibited, in that sometimes the nerves,
sometimes the muscles, contract in response to a some-
what thinner concentration.

It thus appears that the differences are extremely
slight. Kiihne, however, attaches weight to these, and
interprets them as favourable to the theory of the in-
dependent irritability of muscle-substance. He sup-
ports this conclusion by the following observations. In
the case of specific muscle-irritants (ammonia, greatly
diluted hydrochloric acid) the result is the skme whether
the experiment is tried on an ordinary muscle, or on

2,58 PHYSIOLOGY OF MUSCLES AND NERVES.

one poisoned with curare. Nor does it make any dif-
ference whether a strong ascending current is passed
through the nerve of a sartorius thus conditioned, thus
inducing strong anelectrotonus in the intra-muscular
nerve-branchings, so as to disable it. He sees in this
a proof that the nerves which spread through the muscle
do not share in this form of irritation. He has, more-
• iver, discovered that the nerves are not equally dis-
tributed throughout the sartorius. They enter at a
point somewhat below the middle of the muscle, and
distribute themselves upward and downward between
the muscle-fibres; but they cannot be traced to the
ends of the muscle, and there are at these ends retnons

7 O

of from 2 to 3 m. in length, in which at least tin-
larger muscle-fibres are wanting. (Whether the nerve-
in-t which, according to Gerlach, lies within the sarco-
h '1111110, extends to these regions, is another question
with which we have nothing here to do.) The specific
muscle-irritants affect these regions exact !v as they do
the rest of the muscle ; while the specific nerve-irritants
(concentrated lactic acid and glycerine) are never able
to affect these ends, though they elicit single pulsa-
tions in the parts containing nerve-. These nerve-
containing parts are also more electrically excitable than
are the ends; by curare and by anelectrotonus their
excitability is decreased, though that of the nervel- -
ends remains unaltered.

Many objections have been lironid.it forward again* t
the-e conclusions. For my part, ill the very insiniilti-
eaiice of the differences between nerve and miir-de in
this point a l-o. I am inclined to sec new reason to
lu-lieve that these t wo organ s. -,, similar in all points
(:\- vet \\c know only two important differences, which

THEORY OF NERVE-ACTIVITY. 259

are, that the muscle is contractile, which the nerve is
not, and that electrotonus, which intervenes in nerve,
cannot be shown in muscle), may also be entirely simi-
lar in the matter of irritability, and that those who dis-
pute this quality are forced to assume the existence of
a substance intermediate between that of the nerve
and of the muscle, and which differs almost more from
the nerve than from the muscle.

8. Summing up, it appears that the independent
irritability of muscle-substance has not been proved ;
nor has it been disproved. To understand how the
nerve acts on the muscle one must assume that the
latter is irritated by the former, and therefore there is
no sufficient reason, remembering the similarity in all
other points between nerve and muscle, to dispute that
it may also be irritated by other irritants (electric,
chemical, mechanical, or thermic). In the theory above
explained as to the nature of the influence on the
muscle, we have assumed that this irritation takes
place electrically. We have therefore tacitly presup-
posed that the muscle is electrically excitable. Except
on this assumption, all that can be said is that the
molecular process originating in the nerve is trans-
ferred to the muscle : which explains nothing, but rather
renounces all explanation. Our hypothesis, on the other
hand, has the undeniable advantage that it is based
on the well-known process of the negative variation of
the nerve during its activity. That the negative varia-
tion, when it has once originated in the nerve, propa-
gates itself to the nerve-ends, can only be regarded as
natural, and, provided that it is of sufficient strength,
it can then act as an irritant on the muscle.

We have already seen that the nerve must be

200 PHYSIOLOGY OF MUSCLES AND NKUY1-S.

regard -d a- composed of many particles arranged one
behind the other, each of •which is retained in a defi-
nite position by its own forces and by the influence
of tin- neighbouring particles. Whatever acts as an
irritant on the nerves must displace these particles
from this position, and must cause a disturbance, which
then propagates itself, owing to the fact that. a change
in the position of one particle causes a disturbance in
the equilibrium of the adjacent particles, in consequence
of which the latter are set in motion. ^Negative Yaria-
tion must lie regarded as a result of this movement of
the nerve-particles, in that the electrically acting parts
are arranged in different order by the movement, and
therefore must exercise a different external influence.
Pmt just as thi< change in the portion of the nerve-
part ides is able to set the needle of a mult iplier, if it
i- properly connected with the nerve, in motion, so the
electric process originating in the nerve must act on
the imiM-le, if the latter is sensitive to electric varia-
tions. This was the assumption from which we started,
and which, after the above explanaf ions, will be regarded
as thoroughly trustworthy. To enter further into the
details of the activity of nerves and muscles, and to
substitute more definite conceptions for such as are at
present often indefinite, is impossible in the present
:-tate of knowledge.

CHAPTER XVI.

1. Various kinds of nerves ; 2. Absence of indicable differences
in the fibres ; 3. Characters of nerve-cells ; 4. Various kinds of
nerve-cells ; 5. Voluntary and automatic motion ; 6. Reflex
motion and co-relative sensation ; 7. Sensation and conscious-
ness ;, 8. Eetardation ; 9. Specific energies of nerve-cells ; 10.
Conclusion.

1. At present we have paid attention only to such
nerve-cells as are in connection with muscles, and by
the activity of which the appropriate muscles are ren-
dered active. We have referred only incidentally to
other kinds of nerves. The difficulty due to the cir-
cumstance that a suitable reagent is necessary for the
study of such nerve-activity as does not express itself
in any visible change in the nerve, compelled us to con-
fine our studies in the first place to muscle-nerves or
'motor nerves, in which the muscle itself acts as the
required reagent. We now have to discover how far
the experiences which we have gained of motor-nerves,
and the views which we have based on these experiences,
are applicable to other nerves.

Besides the real motor nerves, we may distinguish
those which act oil the smooth muscle-fibres of the
blood-vessels, through these effecting a decrease in the
diameter of the smaller vessels, and thus regulating the
circulation of the blood. These are called vaso-motor
nerves. They are, however, in no way different from

262 PHYSIOLOGY OF MUSCLES AM. M'RVI P.

other motor nerves. But a difference is observable
even iu (lie case of the secretory newes or gland-nerves,
of \vhieh we have already had occasion to make mention.
When these nerves are irritated the appropriate nerves
begin to secrete. The connection of these nerves with
the glands must from a physiological point of view be
entirely similar to that of the motor nerves with the
muscles. When the latter are irritated the muscles
connected with them at once pass into a state of net ivity.
Just in the same way the gland-nerves, when they are
irritated, cause the glands connected with them to pass
into a state of activity. That this activity is quite
different from that of the muscles, is obviously due to
the entirely different structure of the glands and the
muscles. A gland, unlike a muscle, cannot contract ;
\\heu it becomes active, it secretes a liquid, this being
its activity. There is therefore no reason to assume
any difference in any of these nerves, the difference in
tin' terminal apparatus, in which the nerves end, being
sufficient fully to explain the difference in the pheno-
mena.

But there arc other nerves the action of which is
much harder to understand. Among these are the
sensory nerves. When these are irritated, they effect
sensations of different kinds, some being of light, others
of sound, and so on. Moreover these nerves are capable
of rec.-i\ in<_r irritation in a peculiar way, some by waves
of light, others by sound vibrations, and others again
by heat-rays; but in all cases, only when these influ-
ences aet on the ends of the, respective nerves. It is
ii"t .self-evident that these nerves are homogeneous
in themselves or with the previously mentioned kinds.
Finally, it is yet harder to understand the art ion of

SIMILARITY OF NERVE-FIBRES. 263

another, and the last class of nerves, which are called
retardatory nerves (Hemmungs-nerven). It is com-
mon knowledge that the heart beats ceaselessly during
life. Now, if a certain nerve which enters the heart
is irritated the heart ceases to beat, recommencing
when the irritation of the nerve is discontinued. This
remarkable fact was discovered by Edward Weber, who
spoke of the phenomenon as retardation. It is curious
that a nerve can by its activity still a muscle which
is in motion.

2. Before we endeavour to determine this and the
other points raised, we must note whether any differ-
ences can be shown in these various nerves, which act
in such entirely different ways. In the previous chap-
ters we have observed so many peculiarities in nerves,
and among these, qualities which can be examined
without the intervention of the muscle, that it seems
not altogether unjustifiable to hope that we may be
able to observe differences also in nerves if any such
occur. But if this is impossible, if all nerve-fibres,
though examined in every possible way, seem to be
quite homogeneous, then we shall be justified in con-
sidering them really homogeneous, and must look for
an explanation of the variety in their actions in other
circumstances.

It may at once be said that it is quite impossible
to show differences in the different kinds of nerves.
Microscopic observation shows no differences; for the
difference, to which allusion has already been made,
between medullary and medulla-less fibres does not
affect the point in question. We are obliged to infer
that the medullary sheath is of entirely subordinate
significance in the activity of the nerve. At any rate,

2(14 PHYSIOLOGY OF MUSCLES AND NERVES.

the presence or ab-ence of this medullary sheath does
not correspond with differences in tin- physiological
actions of nerves. Nor are the small differences in
diameter of the separate nerve-fibres of greater import-
ance. Nor do experimental tests bring any differen. •< -s
to light. The bearing of nerves to irritants does not
vary: the electromotive effects are the same in all. Jn
all these points we need simplv refer to the previous
chapter, for the explanations there given are equally
true of all kinds of nerve-fibres.

If, therefore, all kinds of nerve-fibres are alike, we
can only explain the difference in their action as due
to their connection with terminal organs of various
form. We have already made use of this principle
in explanation of the difference between motor and
secretory nerves, and \ve must now endeavour to ex-
tend it to all other nerves.

3. While the motor and secretory nerves have their
terminal organs in the periphery of the body, the sensi-
tive or sensory nerves act on apparatus which are situ-
ated in the central organs of the nervous svstem. An
irritant which affects a motor nerve, to become appa-
rent, must propagate itself toward the peripherv, till it
reaches the muscle situated there; an irritant, on tin-
other hand, which affects a sensory nerve, must be pro-
pagated toward the centre before it seta tree anvaction.
Nerves of tin' former kind are therefore called n'ntrif'n-

ifill, tho>e of the latter <•> III I' I IK till. We have, l|o\V(.\er.

already found that this does not depend «n a difference
in the nerve itself, but that each ner\ e-libre, when it is
alfeded at any point in its course, transmits the e.\-
ci ten lent in both directions ; and we therefore presumed
that the faet that action takes place only at one end

CAPACITIES OF JVERVE-CELLS. 2()5

must be due to the nature of the attachment of the
fibres to the terminal apparatus. (Cf. chap. xiii. § 3,
p. 217.)

After we had carefully examined the peripheric ter-
minal apparatus of the motor nerves, that is to say, the
muscles, we were in a position to study the processes
in motor fibre. In order now to understand the action
of sensory fibres, it will be therefore necessary first
to obtain further knowledge of the central nervous
organs.

The central organs of the nervous system, in ad-
dition to nerve-fibres, include, as we have seen (chap,
vii. § 1, p. 105 et seq.\ also cellular structures, called
ganglion-cells, nerve-cells, or ganglion-balls. They
are not always globular, but are generally irregular in
form. Beside the forms represented in fig. 27 (p.' 106),
which occur scattered here and there in the course of
the peripheric nerves, forms such as those represented in
fig. 68 occur much more abundantly in the central or-
gans. They generally have many processes (four, six and
even up to twenty), which branch and unite together
like network. Many cells exhibit one process, differ-
ing from the others, which passes into a nerve-fibre
(nerve-process : cf. fig. 68, la and 3c). These nerve-
processes pass out from the central organ and form
the peripheric nerves. Within the central organ the
processes of the ganglion-cells form a very involved
network of fibres ; between these there are, however,
other fibres which completely resemble the peripheric
nerve-fibres. There is no reason for ascribing to these
fibres of the central organ qualities other than those of
the peripheric fibres. When in the central organ phe-
nomena are observed which never occur in the peri-

266

I'lIVSlDl.MiiV OF MI-SCI.KS AND NKKVF.S.

pherie nerve-filires, it is natural to refer these to the
proence of the ganglion-cells.

As a mailer of fact, all organs which contain ner\ i -
cells, tin- central organs as well as tin- peripheric

TITI. IIIMVN r.i:ux.

1. A U'.ill'-li.HI I'dl. of wllioll one |iripi'r~-. ((. (M.-..III.- ih. ;i\i- r\lilliliT of :i in 1 \v.

iihri'. //. •-'. 'J'un i-i-ii-i. it :ui'i /«. iiiic-M-iiiinrcti'd. :\. Diagnuumatic representa-

tion "I Iliri'i- fii|]|M-i-t,-.| CCllS, r:i.-ll nf \\llirll |i:i--r- ilit.i :i niTVr- lihlf. ''. I.
Ill n 11 |i:ll'll\ lilli-cl with hlark I'i^lllrllt.

-. in \\hieli they are promt, though not so almn-
daiitly, exhiliit certain peculiarities, \\hich \\ e nni>t re-
gard as caused l.y the iier\ e-c.-ils. And as we are in no

Case aide to examine tlu- ller\e-ce]| 1 iy itself, hilt llllist

always examine ii in connection witH, and mingled with
t he oerve-fibres, we can Imt carefully determine the dif-

*

CAPACITIES OF NERVE-CELLS. 267

ference in the behaviour of these organs from that of
ordinary nerve-fibres, and then regard all not appertain-
ing to the nerve-fibres as peculiar to the nerve-cells.

We know that the nerve-cells are irritable, that
they transmit the excitement which arises in them, and
transfer it at the terminal organ. The excitement can

O

never occur of itself in a nerve-fibre, but it always re-
sults from an irritant acting externally, and can never
pass from one nerve-fibre to another, but always remains
isolated in the excited fibre.

But where nerve-cells • occur, the case is different.
As long as a nerve-fibre passes uninjured from the brain
and spinal-marrow, or from one of the accumulations of
nerve-cells situated in the periphery, to a muscle, ex-
citement arises without externally visible cause, and
this acts through the nerve on the muscle, sometimes at
regular intervals independently of the will, sometimes
from time to time at the instigation of the will. Again,
where nerve-cells occur, we find that excitements which
are transmitted to the central organ by a nerve-fibre
may there be imparted to other nerve-fibres. Thirdly,
we find that excitements which are transmitted to the
central organ by nerve-fibres there elicit a peculiar
process, which is called sensation and consciousness.
Fourthly and finally, the remarkable phenomenon,
mentioned above, of retardation, only occurs where
nerve-cells are present. The four following qualities,
which are entirely absent in nerv.e-fibres, must there-
fore be attributed to nerve-cells :—

(1) Excitement may arise in them independently,
i.e. ^vithout any visible external irritant.

(2) They are 'able to transfer the excitement from
one fibre to another.

2G8 riivsioi.oiiY OF Mrscu.s AND NF.IIVI s.

(3) Tln-fi fin receivt an '.'•'•il'mcnt transmitted to
ini'1 truiixiitiiti' if info conscious sensation.

(4) Tin1;/ are "/'/<• t<> muse the mi^in-i-^lon (retar-

,1 ill, m ) nj ,i a I.I-'IKI'I IKJ <:r<-!/< I,H nt.

4. From t he above it must not be supposed that all
gangli< ni-cflls ])nssess all these qualities. On the con-
trary, it is to he supposed that each nerve-coll per-
forms but one of these functions, and even that there
arc more minute differences in them, so that, for in-
stance, the nerve-cells which accomplish sensation are
of various kinds, each of which accomplishes but one
distinct kind of sensation. This is no mere hypo-
thesis, for there are established facts which confirm
the view. Conscious sensations occur only in the brain,
and the various parts of the hraiii may be separately
remo\e. 1 or disabled, in which case individual forms
of sensation fail, while others remain undisturbed.
If the whole lirain is removed, the nerve-cells of the
dorsal marrow suffice fully to act ..... iplish the pheno-
mena of the transference of excitement I'mm one nerve-
fibre to another. Attain, there an- certain regions of
the brain which separately are able to give rise to inde-
pendent excifenienf. in themselves ; and certain accumu-
lations of nerve-cells which lie outside the actual central
nervous organs have the same power. The forms which
nerve-cells assume being very varied, it often happens
that the cells of certain regions, where only certain capa-
bilities can be shown, are alike in form, and differ in this
respect from the cells of other regions, where the capa-
bilities are different. As vvt. however, it has not been
found possible to distinguish differences in form sufti-
dentlycharacterisl Lc, and relations bel ween the form and
the function of nerve-cells sufficiently characf eri-t ic to

FORMS OF NERVE-CELLS. 269

make it possible definitely to infer the function of a cell
from its form. On the contrary, it is better, by experi-
ments with animals and experiences with invalids, to
determine step by step what functions belong to the
cells of a given region. Considering the complex and
yet very imperfectly known structure of the central
nervous organs, it is not surprising that this task has
by no means yet been fully accomplished. As in the
present work we are not treating of the physiology of
the separate parts of the nervous system, but are only
concerned with the general characters of the elements
which constitute the nervous system, we must not
enter into details ; but we must be satisfied to show
what the nerve-cells in general are able to accomplish
and to give due prominence to the fact that each
separate nerve-cell is probably always able to accom-
plish only one definite thing. We will now run
through these capacities and show the facts which
serve as proof of these.

5. The natural rise of excitement takes place
either voluntarily or involuntarily. We are always
able voluntarily to contract our muscles, though not
all of these, for many, especially the smooth forms,
are not subject to the will, but contract only as the
result of other causes. Sometimes, moreover, the want
of power to contract certain muscles is to be ascribed
only to want of use, as is shown by the fact that
some men are able voluntarily to contract the skin
of their scalps or their ear-muscles, though this is
impossible to most men, or is possible only in a
very restricted degree. Similarly, it is a matter of
use how far the will is able to effect a limited con-
traction of separate muscles or parts of a muscle.

270 rnYsmi.oiiv OF MTSCLKS AM> NERVES..

Those In •Binning to play the piano find it difficult to
move individual lingers apart ['mm the others, though

by practice they soon learn to do this. \Vhene\er
:ui intended contraction of a muscle i- accompmied
by another unintended and simultaneous, the latter
is called a co-relative movement. Such co-relative
movements sometimes accompany illness. Stammerer-.
for instance, when they speak, twitch the face muscles
or even those of the arm. It has also been observe I
that in the case of injuries, after blood has lieeii lost
from the brain, movements of the injured limbs not
voluntarily possible occur involuntarily as co-relative
motions. Some co-relative movements are natural in
the organism; for instance, when the eye is turned
inward, the pupil simultaneously decreases in size, and
a contraction of the adjusting muscle occurs, l>y which
the eye is enabled to see at a short distance. This
co-relative motion has been regarded as a case of the
transmission of the excitement from one nerve-fibre to
another; but it seems to me that this is incorrect.
For there is nothing to show that the excitement
originated in one fibre and was then <ran>ferred to
other fibres, and it is more simple to assume that the
various fibres were excited simultaneously by the will,
either because isolated excitement of these fibres sepa-
rately i.- really impossible on account of the anatomical
structure of the nerve, or because of an insufficient
specialisation of the influence of the will, resulting
from want of e\eivi>e that is, it is due to un>kilful-

oti the part of t he will.

If it is asked how the \obmtary excitement of the
nerve-fibres is caused in the nerve-cells, an answer
is yet to be sought in physiology. Into the quest ion

VOLUNTARY AND AUTOMATIC MOVEMENTS. 271

whether there is actually a purely voluntary excite-
ment, that is, that no incitement acted externally
on the brain but that the excitement originated quite
spontaneously, we will not enter further here. All
that is certain is that in many cases an action appears
to be voluntary which, if the process is more closely
analysed, is found to result from external influences.
But the physiological process by which (whether
externally influenced or not) excitement arises in
the nerve-cells, which excitement is then transmitted
through the nerve-fibre to the muscle, is as yet ex-
tremely obscure ; and if it is said that it is a molecular
motion of the constituent particles of the nerve-cell,
this explains nothing, but merely expresses the convic-
tion that it is not a supernatural phenomenon, but
merely a physical process analogous to the process of
excitement in the peripheric nerves.

Involuntary movements occur sometimes irregularly,
as twitchings, spasms ; sometimes regularly, as in the
case of respiratory movements, the movements of the
heart, the contractions of the vascular muscles, of the
intestinal muscles, and so on. The latter, which occur
with more or less regularity while life lasts, and are
for the most part of deep significance as regards the
normal condition of the vital phenomena, have natu-
rally been especially subjected to thorough research.
They are called automatic movements, that is, they
occur independently of the co-operation of the will,
and apparently without any incentive. But notwith-
standing this, it is chiefly in such cases that the causes
which effect the excitement of the nerves concerned
have been to a certain extent established.

Automatic movements may be distinguished into

272 PHYSIOLOGY OF MCSCLES AND NERVES.

sucli as are rhythmic, in which contraction and relaxa-
tion <>f tli-' muscles concerned take place in regular
alternation, as in respiration and in the movements of
the In-art : such as are tonic, in which the contractions
are more constantly enduring, even if the decree of
contraction varies, as in the contraction of the vascular
muscles, and of the rainbow membrane of the eye; and
such as are //•/•» ;//(7«r, i.e. the peristaltic movements of
the intestine. Our knowledge of automatic movements
is based principally on those connected with respira-
tion; but the conceptions gained in this case may be
directly applied to the other cases. It will be suffi-
cient therefore to speak of respiratory motion only.

Kespiration begins immediately after birth, and
it- movements continue from that time throughout life.

C7

In the higher animals (mammals and birds) they are
unconditionally necessary for the preservation of life,
for only by their means is sufficient oxygen conveyed
to the blood to provide for all the vital processes. On
the other hand, when the organ from which the ex-
citement of the respiratory muscles proceeds is in
any way insufficiently nourished or is otherwise in-
jured in condition, respiratory action ceases and life is
tlireatened. This organ is a limited point ill the
medulla, oblongata, formed of a mass of nerve-cells, in

which (lie excitements originate, and from which they
are conveyed by the nerves to the respiratory muscles.

This is called the /vxy, ,'/-,//,,/•_// <;>,</,•<> (LrtH'nxkmm it
of the (iermans, mi ml r/fn/ of the I'Vendi), because
of its importance to life. It is the spot \\hich the
matador in bull-tights inn<( reach by a skilful blow
with his knife, to bring the enraged animal to the
ground; it is the spot which, if crushed between the

VOLUNTARY AND AUTOMATIC MOVEMENTS. 273

first and second vertebrae, the result is instant death
by the so-called dislocation of the neck. It has been
shown that the cause which induces this ceaseless
activity in the nerve-cells of the respiratory centre
lies in the character of the blood. When the blood
is quite saturated with oxygen, then the activity of
the respiratory centre commences.1 When the blood
becomes freer from oxygen, the respiratory motions
become stronger.

Far from being necessarily active, independently and
without external incentive, the nerve-cells of the respi-
ratory centre are also rendered active by external cir-
cumstances. But they are much more sensitive than the
nerve-fibres, so that they are influenced even by slight
changes in the gaseous contents of the blood which
plays over them. And the other automatic nerve-cells
behave exactly as do the cells of the respiratory centre.
Yet small differences in sensitiveness occur among
them, so that some are excited even when only the
average amount of oxygen is contained in the blood,
others when a point lower than this average has been
reached, as happens only occasionally during life.

It would take too long to apply this theory, now

1 Experimental proof of this may always be tried by anyone
on himself. Attention must be given for a time to the respiratory
movements, their depth and number being noted. From eight
to ten inspirations and expirations are then drawn slowly one
after the other. By this means much more air is introduced into
the lungs than by ordinary respiration, and the blood can therefore
thoroughly saturate itself with oxygen. If, after this, voluntary
respiration i§ ceased, it will be found that twenty seconds or more
elapse before a respiration again occurs, long enough that is for the
consumption of the introduced oxygen. Only after this do respira-
tions begin, at first weakly, but always increasing in strength, until
the former regular respiration again prevails.
13

274 1'IIYSIOLOGY OF MUSCLES AND NERVES.

briefly explained, <•> each of the other processes of
automatic motion. We must content ourselves -with
the remark that an analogous conception of the nature
of the movements of the heart i.- probable, though DO
experimental proof of its correctness has yet been
aehieved. The cause of movements of the intestine is
not quite so difficult to understand ; at any rate, the
main principles found in the case of the nerve-cells of
the respiratory centre are valid in the case of all other
automatic centres.1 Mention must still be made of
the fact that in the heart and intestine the nerve-cells
from which the automatic action proceeds are situated
within the respective organs themselves. For this
reason these organs can yet. exhibit movements after
the nerve-centres have been destroyed, or the organs
have been cut from the body.

G. The tran-fen IK-', by means of the nerve-cells,
of an excitement from one nerve-fibre to another is
most clearly shown in that which is called reflec-
tion. By this term is meant the passage of an excite-
ment, which having acted on a sensory fibre has been
transmitted by it to the nerve-cells, to a centrifugal
fibre, by which it is conducted back from the centre
(as a ray of light is reflected from a mirror) and
makes Its appearance ;(t another point. The reflection
can occur either in a motor fibre, in which case it is
called a rell'-x action, or in a >eeivlory or relarda-
tory fibre. The former case is more common and
better known. As examples (.f >urli reflex actions, I
may mention t he do-in;,' of the eyelids on the irrita-

1 Tlmsc \vli<> \vi>h t<> ni it. -i in furthrr information as to these cir-
i-umst;ni<vs may ]tt- ri-frnvd to my work ]><'mirl\i»<jcn iilirr die
Tliiil'njlu-it ili'r init<>nniti*i-/ii n .Y/vvr/f-iv////1//, \o. KrlaiiLTdi, 1875.

REFLEX MOTIONS. 275

tion of the sensory nerves of the eye, sneezing on
irritation of the mucous membrane of the nose, cough-
ing on the irritation of the mucous membrane of the
respiratory organ. Wherever sensory nerves are con-
nected by nerve-cells with motor nerves, these reflex
actions may occur. If an animal is decapitated and
its toe is pinched, the leg is drawn up and contractions
occur in it. The reflex actions are here accomplished
through the nerve-cells of the spinal marrow, and the
removal of the brain favours the action, while it at the
same time excludes the possibility of the intervention
of voluntary movements.

There is no doubt that in this process the nerve-
cells play a part, and that the process does not depend
solely on the direct transference of the excitement from
a sensory nerve-fibre to an adjacent motor nerve-fibre.
Apart from the fact that the transference never takes
place except where nerve-cells can be shown to be pre-
sent, this is confirmed by the fact that the process of
reflex transference occupies a very noticeable time,
much longer than that required for transmission
through the nerve-fibres. With the knowledge which
we have now gained of the structure of the central
nervous organs, it may be considered established, that
nowhere is there immediate connection between sen-
sory and motor nerve-fibres, but a mediate connection
through the nerve-cells. This allows the possibility of
the propagation of an excitement from a sensory nerve-
fibre, through a nerve-cell, to a motor nerve-fibre. It
is thus intelligible how, owing to the interconnec-
tion of the nerve-cells, the passage of the excitement
from any sensory nerve-fibre to any or every motor
nerve-fibre is possible, for the excitement advances

276 PHYSIOLOGY OF MUSCLES AM> NT.KYES.

from nerve-cell t<> nerve-cell, from each of which it
can ivpass into a motor fibre. From the length of
the time occupied by the reflex irritant, it is to be
iiit'i-iTrtl that the transmission of th<' excitement has
to meet considerable resistance in the nerve-cells.
This resistance naturally increases with the number of
nerve-cells to be traversed, so that the transference of
a rellex action from a definite sensory fibre to different
motor nerve-fibres is not always equally difficult,. and
is the more difficult the greater is the number of
the cells which lie between the two. All this agrees
with the facts found by experiment. It also explains
why, by certain influences, not only is the reHex trans-
ference rendered easier, but the passage of the excite-
ment to the most remote motor fibres is also rendered
peculiarly possible. The be-t known case of this is
poisoning by strychnine. This so greatly facilitates the
reflex transference that the slightest touch on any point
of the skin, or even the disturbance caused by a breath,
is sufficient to throw all the muscles of the body into
violent reflex tetanus.

As each excitement of a senary jibre which reaches
the nerve-centre can give riVe to a conscious sensation,
the spread of the excitement vithin the centre must
have the same effect as would be the case if u larger
number of excitements of several sensory fibres readied
the centre simultaneously. This proce^, »vhich, IK>\\-
c^vr. only occurs in the case of strong excitements,
is called ni-i'i'l'ilifi' BenfHtt'uni. Sensation is caused
not only by the exeitement of the ner\e-cell directly

concerned, ),,,£ also ],y the .-ju'ead of tile excitement

to the other nerve-cells. It may also be spoken of as
t lie radiat ion of (he sen-ory irritant, because (he excite-

SENSATION AND CONSCIOUSNESS. 277

ment seems to spread within certain limits from the
point directly touched.

7. These phenomena will become more evident
when we have more accurately learned the origin of
conscious sensations in general, and the conceptions
which depend on this. In order that such conscious
sensations should result it seems absolutely necessary
that the excitement should reach the main brain
(cerebrum). Whether other parts of the brain, or even
the spinal marrow, are able to give rise to conscious
sensations is at least very doubtful, and is at any rate
not proved.1 But when the excitement reaches the
brain, it gives rise not only to feelings, but also to
very definite conceptions as to the nature of the excite-
ment, its cause, and the locality at which it acts. It
is true that sometimes this effect fails and the irritant
does not reach consciousness, as, for example, when the
attention is strongly attracted in some other direction,

1 The dispute about the so-called ' mind in the spinal marrow '
(Ruc1tenmarksscele),t'he question, that is, whether more or less clear
conscious conceptions can occur in the nerve-cells of the spinal cord,
was long and hotly debated, but is now at rest. It appears to me
that the whole form of the question is unscientific, for the question
can simply not be solved with the means for research which we can
command. Our own consciousness informs us as to our own sensa-
tions and conceptions, and we learn those of others from their lips.
Where this fails, opinion is always untrustworthy, as, for example,
where we try to infer the feelings of men from their behaviour.
It is, however, yet more hazardous to attach importance to the
movements of a brainless animal, and it is therefore not surprising
that two observers should draw quite different conclusions from the
same facts, one explaining them as simple reflections, the other being
of opinion that such behaviour under such circumstances is only ex-
plicable as the result of conscious sensations and conceptions. The
lower the animal is in the scale, the more untrustworthy, naturally,
is the decision.

278 PHYSIOLOGY OF MUSCLES AND NERVES.

or as in sleep. The irritant can then elicit a reflex
action, though there is no consciousness of this. That
the origin of conscious conceptions is also an acthity
of the nerves is certain, and it is the cells of the
grey matti-r of the brain which possess this activity.
On the other hand, we are entirely unable even to
indicate ln>\v this consciousness comes into being. It
may be due to molecular processes in the nerve-cells
which result from the received excitement ; but mole-
cular processes are but movements of the molecules,
and though we can understand how such movements
cause other movements, we are entirely unaware how
these can be translated into consciousness.1

The excitements transmitted by the various sensory
Jibres do not all art in the same way on the brain, and
the sensations to which they give rise differ. Accord-
ingly, we may distinguish the various sensations of
the various senses, and even within one and the same
sense various sub-species, as the colours in the sphere
of optical sensations, the various pitches in the sphere
of auditory sensations. But as all the nerve-til MVS
which accomplish the various sensations differ in no
\vay from each other, we are forced to look in the
ner \e-cel Is for the reason of the difference in sensations.
.lust as we as-nmed th;it motor nerve-cells differ from
sensory, so we must further assume that among
sensory nerve-cells, ihe excitement of which always
elicits the conception of light, others again the excite-

1 E. dii BOIE li> \ iii'ind bag entered further into this question in

his addivs-; In the' a>srinb]y of nalurali-ts ;il I,rii>/.iir ( I < hi r die
firm:t'ii il<x ^'utiii-i'f/.'i'iiiiciin, Lcip/iir, is;-.'). Some of tbr \.<ui
natural philosophers srrin inclined to avoid the dillk-ully by a.-c'.rib-
in;.', as does Si-ln'i culiaucr, sensation and ronscimisno-; to all mole-
ruk-s, but tliis does not seem to nit- to be any real t,rain.

SENSATION AND CONSCIOUSNESS. 279

ment of which always elicits the conception of sound,
others again the excitement of which always results in
the conception of taste, and so on. In entire accord-
ance with this assumption is the fact that it does not
matter what external cause effects the excitement of
any one nerve-fibre, but that every excitement of a given
nerve-fibre is always followed by a given sensation.
Thus, the nerve of sight may be mechanically or elec-
trically irritated, with the result of producing a sensa-
tion of light ; mechanical or electric irritation of the
auditory nerve effects a sound sensation ; electric irri-
tation of the nerve of taste effects just such a sensa-
tion of taste as does the influence of a tasted substance.
It even happens that the exciting cause is situated
in the brain itself and directly excites the nerve-cells,
and the sensations which are thus elicited are indis-
tinguishable from those which are effected through
the nerves. To this are due the subjective, sensations,
hallucinations and so on, which depend on an altera-
tion in the character of the blood, or on an increase
in the sensitiveness in the nerve-cells.

Wherever the excitement occurs, whether in the
nerve-cells themselves or anywhere in the course of the
nerves leading to the cells, consciousness always refers
the sensation to the presence of some external cause of
excitement. If the nerve of sight is pressed, the
patient believes that he sees a light external to his
body ; if a nerve of touch is irritated at any point in
its course (e.g. the elbow-nerve at the furcation of the
elbow-bones), the patient feels something in the
nerves distributed in the skin (in our example in the
two last fingers, and in the outer edge of the palm of
the hand). Our power of conception therefore always

280 niYSiOLOiiV m Mtsn.Ks AND M:I;\ i .-.

projects every sensit ion which readies the conscious-
ness "lit ward, that is, to where the cause of the excite-
ment is normal! v. This so-called Id in of ec<'< -ulr'n-
Sensations finds an easy explanation in the supposi-
(inn that the conception of the locality of the efficient
cause i> gained from experience.1 It will easily be
understood that this necessarily follows from the cha-
racters which we have ascribed to the nerve-cells.
\Vlien the nerve-cell is irritated, the same sensation
and the same conception must always result. Just a> it
makes no difference in the case of a muscle whether the
excitement conveyed to it by a motor nerve starts from
a higher or from a lower point on the nerve, or whether
the nerve has been irritated mechanically, electrically.
or by the will, so the process in the nerve-cell docs not
depend on the locality or the natiire of the excite-
ment. When the circumstances \\hich MJ\C rise to
the irritation are abnormal, the result is an illusion
of the senses, that is, a false cause is assigned to a
perfectly clear and true sensation.

8. The nature of the last of the capabilities which
we have attributed to the nerve-cells, t he retardation
of a motion, is still very obscure. The faet of retarda-
tion is as yet principally known in the ca<e of auto-
matic motion, though retardation of reflex action ;dso

ocnirs. as may be inferred even from the fact thai the
rise of reflex actions is hindered by the activity of the
nerves, especially when this originates from the brain.
The n-spiratorv movements being of all automatic mo\e-

1 l>.-t;iils (.r tlii> iintirr, into which \\ c c immt ruler furtlnr
v.iil !.,• fnund in InTiist. -iii's '/'//c I-'irf Si'iisi-ii iff Mnn (Intcr-
n.-il i"ii:il Srii'iil ilic Srrii-s, vul. xxi.). :>IH] in Huxli-y's l'.l< nn'n tanj
Physiology,

RETARDATION. 281

ments the best known, it is on these that the current
views as to the retardatory nerves are based. It has
been explained in § 5 that the respiratory movements
result from the excitement of the nerve-cells of the re-
spiratory centre. These movements may be accelerated
or retarded, though all the other conditions remain
unchanged, if certain nerve-fibres which pass from the
mucous membrane of the air-passage to this respira-
tory centre are irritated. These retardatory nerves
are distinguished from those which pass to the heart
by the fact that it is not known whether the latter pass
to the muscles of the heart or to the nerve-cells
situated in the heart, a doubt which is satisfied in
the case of the former by their anatomical arrange-
ment. Of the retardatory fibres of the heart it might
be supposed that they in some way incapacitate the
muscle from contracting ; in the case of the retar-
datory nerves of the respiratory system such supposi-
tion may be at once rejected, for they are in no way in
contact with the respiratory muscles. The only pos-
sible explanation is therefore, that the retardatory
nerves act on the nerve-cells in which the excitement
is generated, thus either preventing the excitement from
even coming into existence, or preventing the excite-
ment from passing from the nerve-cells in which it is
generated to the appropriate motor nerve-cells. For
various reasons the latter view has been preferred. It
is supposed that the automatically acting ganglion-cells
are not directly connected with the appropriate nerve-
fibres, but that conducting intermediate apparatus are
present between the two, and that these offer a great
resistance. This explains both the occurrence of the
rhythmic motions and the retardation. The latter,

282 PHYSIOLOGY OF Mr.sfLKS AM> NERVES.

that is, is due to an inen-a.-e in the resistance by
which the motion is temporarily suspended.1

Retarda tory nerves have been recognised in almost
all automatic apparatus, and all are accounted for by
the above explanation. The same explanation may also
1) - applied at once to the retardation of refiYx action ;
for even in the passage of the excitement from the
sensory to the motor nerves very great resistance lias
to be overcome, and an increase in this resistance
must prevent the passage of the excitement and thus
hinder reflex action. Our acquaintance with this sub-
ject is, however, not yet by any means complete, and
a final opinion on the matter is therefore for the time
impossible.

I will only mention further that the opposite ell- ct,
the facilitation of the passage of the e\i-iteinent from
the nerve-cells in which it originates, to the peripheric
nerve-coiir-i'-, appears to occur.

Finally, it is sometimes observable that when those
portions of the nerves which contain nerve-cells are
continual! v and regularly irritated, a. rhythmic or even
an irregular movement results, instead of a regular
tetanic contraction of the muscles concerned, — a cir-
cumstance \vhichis evidently to be explained in the
same way as rhythmic automatic activity. The regu-
lar excitement having to pass through nerve-cells is
modified liythe "Teat resistance present in these, and
i- transformed into a rhythmic motion, while when the
nerve and the muscle are directly connected, the latter
re-pond- to a continuous excitement of the nerve with
a regular and continuous contraction.

my account of theautumat ir nerve-centres, to which refer-
ence lias already been made.

SPECIFIC ENERGIES OF NERVE-CELLS. 283

9. From all these details it is very evident that
the nerve-fibres are homogeneous the one with the
other, and that the difference in their effects is to be
referred to their connection with nerve-cells of varied
form. This seems, however, to be opposed to the fact
that the different sense-nerves are irritable by quite
different influences, and each of them only by quite
definite influences — the nerve of sight by light, the
nerve of hearing by sound, and so on. It would, how-
ever, be a mistake to infer from this that the nerve of
sight is really different from the nerve of hearing. If
the matter is examined more closely, it appears that
the nerve of sight cannot be excited by light. The
strongest sunlight may be allowed to fall on the nerve
of sight without producing excitement. It is not the
nerve, but a peculiar terminal apparatus in the retina
of the eye with which the nerve of sight is connected,
which is sensitive to light. The case of the other
sense-nerves is similar; each is provided at its peri-
pheric end with a peculiar receptive apparatus, which
can be excited by definite influences, and which then
transmits these influences to the nerves. On the
difference in the structure of these terminal apparatus
depend which influences have the power of exciting
them. When the excitement has once entered the
nerve it is always the same. That it afterward elicits
different sensations in us, depends again on the character
of the nerve-cells in which the nerve-fibres end. Sup-
posing that the nerves of hearing and of sight of a
man were cut, and the peripheric end of the former
were perfectly united with the central end of the
latter, and contrariwise that the peripheric end of the
nerve of sight were perfectly united with the centra]

284 I'ilYMOLiMiY OF MTSCLES AND NKItVKS.

end of the nerve of hearing, then the sound of an
orchestra would elicit in us the sensation of light and
colour, ami the sight of a highly coloured picture
\v. mid elicit in us impressions of sound. The sensa-
tions which we receive from outward impressions arc
therefore not dependent on the nature of these im-
pres.-ions, but on the nature of our nerve-cells. We
feel not that which acts on our bodies, but only that
which goes on in our brain.

Under these circumstances it may appear strange
that our sensations and the outward processes by
which they are evoked are so entirely in agreement ;
that light elicits seii.-ati<>ns of 'light, sound sensations
of sound, and so on. But this agreement does not really
exist ; its apparent existence is only due to the use of
the same name to express two processes which have
nothing in common. The process of the sensation of
light bears no likeness to the physical process of the
ether vibrations which elicit it; and this is evident
even iii the fact that the same vibrations of ether
meet ing the skin elicit an entirely different sensation,
namely, that of warmth. The vibrations of a tuning-fork
are capable of exciting the nerves of the human skin,

and then they are felt ; they may excite our auditory
n. r\.--. and then they are heard: and under certain
eirctim-lances they may lie seen. The vibrations of
the tuning-fork are always the same, and they have
nothing in common with tin- sensations which th<\
elicit. Though the phy>ical processes of the \iliration-
of ether are called. ~, unet inies li^ht. and at another time
heat, a more accurate study of phy-ic- sho\\< that the

is the same. The usual classification of physical

into t ho-e of sound, 1 igli t , warmth, and so on.

SPECIFIC ENERGIES OF NERVE-CELLS. 285

is irrational, because in these processes it gives pro-
minence to an accidental circumstance, that is, to the
way in which they affect human beings, who are endowed
with various sensations, while in other, such as mag-
netic and electric processes, it is based on quite different
marks of classification. Scientific study of the phy-
sical processes on the one hand, and of the physio-
logical processes of sensation on the other, exposes this
error, which penetrates further owing to the fact that
language uses the same words for the different pro-
cesses, thus making their distinction harder.

Language is, however, but the expression of the
human conception of things, and the conception of
the innate identity of light and the sensations of light,
of sound and of the sensation of sound, and so on, was
regarded till quite recently as incontrovertibly true.
Goethe ' gave expression to this in the lines—

War' nicht das Auge sonnenhaft,
Die Sonne konnt' es nie erblicken ;
Liig' nicht in uns des Gottes eigne Kraft,
Wie konnt' uns Gottliches entziicken !

Plato expresses himself in the same way in the
* Timaeus.' On the other hand, Aristotle held correct
conceptions on the subject. But it is only since the
researches of Johannes Miiller laid new ways open to
science that these conceptions have gained a scientific
foundation, and have been brought in all points into
harmony with the facts, so that they have now become
the basis of the physiology of the senses and the
psychology of the present day.

One expression of the erroneous views once pre-
valent is to be found in the theory of so-called ade-
1 Zahme Xenien, iii. 70.

286 PHYSIOLOGY OF MUSCLES AM) NKRVES.

qiKtte irrilnitfx, according to which there is such a
sufficient irritant for each sense-nerve, that is, an
irritant in its nature adapted to the nature of the
sense-nerve, and that this was alone able to excite it.
We kii'i\\- now that this is not true. Yet the expres-
sion maybe used to indicate the irritants which are
especially able to act on the terminal organs of the
nerves.

In the same way we may look upon the idea of
so-called specific energies of the sense-nerves, if by
this it is intended to express any character of tin-
nerves, as disproved. But we must ascribe specific
energies to the individual nerve-cells in which the sen-
sations are originated. It is these alone vJiich ar-
able to produce in us different kinds of sensation. If
all the nerve-cells of the sensations were alike, sensa-
tions could indeed be elicited in us by the influence
of the outer world on our sense organs ; but these
would only be of one and the same kind, or at most it
could only be in the strength of (his one undefined
.-.•nsation that differences would be perceptible. There
may be animals which are only capable of >uch a >in^le
undefined sensation, their nerve-cells hein^ all alike
ami not yet differentiated. Such animals would be
able to form a conception of the outer world as
distinguished from their o\\n bodies, that is, they

Would be ;ible to c\,i|ve self-rolisciollslle-- : but the\

would not be able to attain a knowledge of the ]>r»-

in the outer \\orld. The development of -ndi

knowledge in us i- great ly a-si>i ed by a comparison
of the different impressions brought about by the
different or^m- of the senses. A body presents itself
to our eye as occupying a certain .-pace, being of a

CONCLUSION. 287

certain colour, and so on. By tasting1 we may gain
further conceptions of this body. If it is out of reach
of our hands, by approaching it we may observe how
the apparent size of the body, as the eye shows it
to us, increases as we approach. These and many
thousand other experiences which we have gained
since our earliest youth have gradually put us in a
position to form conceptions as to the nature of a body
merely from a few sensations. In this act many com-
plete inferences are unconsciously involved, so that
that which we believe to have been directly perceived
is really known by inference from many sensations
and from a combination of former experiences. For
instance, we think that we see a man at a certain dis-
tance ; really, however, we only feel a picture of a
certain size of the man on our retina. We know the
average size of a man, and we know that the apparent
size decreases with the distance ; moreover, we feel
the degree of contraction of the muscles of our eye
which is necessary to direct the axis of our eye to the
object and for the adjustment of our eye to the neces-
sary distance. From all these circumstances, the
opinion, which we erroneously regard as a direct sensa-
tion, is formed.

10. We have already (chap. iv. § 2 ; chap. vii.
§ 3) made acquaintance with the methods by which
Helmholtz measured the details of the time occupied
by the contraction of the muscle and the propagation
of the excitement in the motor nerves. By the same,
or very similar methods, Helmholtz, and others after
him, determined the propagation of the excitement in
sensory nerves, and found that it was about 30 m. per
second, and therefore, at nearly the same rate as in the

288 riivsioLouY OF MTSCLES AND NKRVKS.

motor nerves of men. More than this has been done:
the time has been measured which is requisite for an
irritant conducted to the brain to be transmuted into
cous-cioii<ne.— . Such determinations, in addition to
their theoretical value, are of practical interest to
observing astronomers. In observing the passage of
stars on the meridian and comparing the passage seen
through the telescope with the audible beats of a
second-pendulum, the observer always admits a slight
error, dependent on the time which the impressions on
the two senses require to reach the state of conscious-
ness. In two different observers this error is not of
exactly the same value; and in order to render the
observations of different astronomers comparable witli
each other, it is necessary to know the difference

bet ween the t Wo e:ises, the SO-Called p<> i-xu mil i'i/ n,it iu/i .

In order to refer the observations made by each indi-
vidual to the correct time, it is necessary to determine
the error which is made by each individual.

Let us suppose that an observer sitting in complete
darkness suddenly sees a spark, and thereupon give-;
a signal. By a suitable apparatus, both the time at
which the spark really appeared and that at which the
signal was given are recorded. The difference between
the two can be measured, and it is called the )>hi/sio-
Ini/irnJ t'niic. for the sense of sight; the physiological
time for the sense of hearing and for that of touch
may be determined in the same way. Tims Profes-or

Ilirsch, of Neiifchatel, (bund

111 the case of the Sense of sight O'lDTl to 0'1>OS3 sec.
„ „ hearing 0-194 „

„ „ tollrli 0-1733 „

When I he impression which was to be recorded was

CONCLUSION. 289

not unexpected, but was known beforehand, the physio-
logical time proved to be much shorter ; in the case
of the sense of sight it was only from 0-07 to 0*11 of
a second. From this it follows that, in the case of
excitement the advent of which is expected, the brain
fulfils its work much more quickly.

Certain experiments made by Bonders are yet more
interesting. A person was instructed to make a signal,
sometimes with the right hand, sometimes with the
left, according as a gentle irritant applied to the skin
was felt in one place or the other. If the place was
known, the signal succeeded the irritant after an in-
terval of 0-205 of a second, but if the place was not
known, only after an interval of 0-272 of a second. The
psychological act of reflection, as to where the irritant
occurred, and that of the corresponding choice of the
hand occupied, therefore, a period of 0-067 of a second.

The physiological time in the case of the sense of
sight was somewhat dependent on colour ; white light
was always noticed somewhat sooner than red. If the
observer knew the colour which he was to see, he gave
the signal sooner than when this was not the case and
he had first to reflect as to what he had seen before he
gave the signal. In such experiments, the observer
always forms a preconception of the colour which he
expects to see. If the colour when it becomes obser-
vable corresponds with that which he expected, the
reaction in. the observer takes place sooner than when
this is not the case.

Similar observations were made in the case of the
sense of hearing : the recognition of any sound heard
follows sooner when it is known beforehand what sound
is to be heard than when this is not the case.

290 PHY.SIOLOiiY OF MCSCLKS AM" NERVES.

This sluggishness of the consciousness, if we inav so
call it, is exhibited in another way in certain experi-
ments instituted by Helmhol£z. The eve sees a figure,
\vhieli is immediately followed by a bright li.^'ht : the
more powerful the latter i<. the longer must the first
have been seen, if it is t«> lie recognised at all; more-
over, complex figures require m..re time than simpler.
If letters are seen lighted up on a bright ground for a
very short time, no other light following, a shorter time
is necessary for the recognit ion, the larger are t he letters
and the brighter the illumination.

It i> true that it is only very simple brain activities
the origin of which can be in any wav made dearer bv
such experiments as these; but yet these are the rudi-
ments of all mental activity -sensation, conception, re-
flect ion, and will; and even the most elaborate deduct ion
of a speculative philosopher can only be a chain of such
simple processes as those which we have been observ-
ing. These measurements, therefore, represent the
beginnings of an experimental physiological p>ycholo^\,
the de\elopment of which is to be expected in the
future. It seems to me that remunerative study of
the processes in nerve-cells must start from the very
simplest phenomena. Results are, then-lore, to be fir>(
looked for in the study of the processes of reflection :
possibly these will prepare the ground on which at some
future time a mechanism of the nervous pmco-es m;iV
be built. 'In truth; say- I ). !•'. Strains, in 'The Old
and the Ne\v Faith/ ' lie who shall explain the gra-p
of the polyp after the prey which it has perceived, or
the Contraction of the insect lar\a \\heii pierced, will
indeed be yet far from having in this comprehended
human thought, but he will be on the way to do so, and

CONCLUSION. 291

may attain his end without requiring the help of a
single new principle.' Whether this end will ever be
attained is another matter. But we can always gain
fuller knowledge of the conditions under which it may

O v

come to pass, and of the mechanical processes which
form its first principles. Such is the lofty aim after
which the science of the General Physiology of Muscles
and Nerves strives — an aim worthy of the labour of the
noblest.

NOTES AND ADDITIONS

1. GRAPHICAL REPRESENTATION. IDEA OF MATHEMATICAL

FUNCTION (p. 49).

The method employed in fig. 16 of representing by a
sign the dimensions of the expansion relatively to the amount
of the expanding weights, admits of such a variety of appli-
cations, and will be used so frequently, that a brief explana-
tion of it may not be out of place here.

When two series of values bear such a relation the one
to the other that each value of one series corresponds with a
definite value in the other, mathematicians speak of the one
value as the function of the other. This relation may
always be exhibited in tabular form, as in the following
example : —

1234 5 6 7 8 9 10
2 4 6 8 10 .12 14 16 18 20

The relation which prevails in this case is very simple.
Each number in the upper series corresponds with a number
in the lower, and the latter is always double the value of
the former. Representing the numbers in the upper series
by x, those in the lower by y, the relation between the two
series of numbers may be expressed in the formula :

y=1x
This formula expresses the same and even more than the

294 rilY.-Iol..ic;Y ('I- .MtX'l.KS AND NKRVES.

table. Substituting tor tin- unknown a:, which may repiv-
sent any number, the number 1, then thr table expresses
that tin- value of the corresponding?/ is 8. If x=5, thru tin-
table expresses that y=10. But when the value of x is
intermediate between 4 and 5, e.g. 4 2371, the table does not
help us; but by the use of the formula the value of tin-
corresponding y may easily be found ; it is = 8-4742.
The formula may he reversed, and written thus :

that is to say, for any given value of y we may calculate the
corresponding value of a;. It is exactly the same in the case
of tin- similar formula :

V = 3#,
which may also hi: written thus :

<*<• = :!//•

fn tin- case, tin -ret'., re. \\ith each Driven value of x corresponds
a certain value of ?/, the latter being three times the value
of the funnel1. In the two corresponding formulae

y = ux and x=-y,
a

is a somewhat wider expression to this kind of relation; in
this case x and y are again the signs of the two correspond-
ing series of numbers, a expresses a definite figure which is to
be regarded as unchangeable within each particular case. In
our first example f — 'l. in our second example ,/ = :',. and
similarly 'in any other instance « may have any other value.
Looking now at the following table :

1 •_' :: I 5 <; etc.
1 4 -.» hi L'.-I 36 etc.

we see that any number in the lower series is found by
multiplying the corresponding number in tin- upper series by
itself, as may be exiuessed in the formula

y-=.<- ./• i.r // =

NOTES AND ADDITIONS.
This formula when reversed appears thus :

295

Provided with a formula of this sort, which expresses the
mutual relation of two corresponding series of values, it is
always possible to draw out a table, though, on the contrary,
the relation laid down in the table cannot always be ex-
pressed in a formula, for the relations are not always as
simple as in our examples. Generally the values which are
treated in the table are such as have been found by observa-
tions, as for instance in our case, the expansion of the muscle
caused by various weights. With each weight an expansion
corresponds, and this is found by experiment and may be
expressed in tabular form, thus :

Weight: 50 100 150 200 250 300 grm.
Expansion : 3'2 6 8 9'5 10 10'5 mmt.

A A' A" A" JIV

FIG. C9. GRAPHICAL REPRESENTATION OF MUSCLE-EXPANSION.

All that is shown by the table is that the expansion does
not increase proportionately with the weight (as would be
the case in inorganic bodies), but increase in a continually
decreasing proportion. But any required function-character,
whether it is expressed by a comparison er in a table drawn
up on the basis of observations, mny le diagrammatically

29G PHYSIOLOGY OF MUSCLES AND NERVES.

shown by a method first employe. 1 l>y 1 >escartes, which it is
our present object to explain.

The amounts treated may be of the most varied kinds :
numbers, weights, decrees of \vunnth, the number of births
or deaths, and soon. In all rases the amount may bediai;ram-
matically sho\vn )>y the length of a line. If a line of a cer-
tain length represents any given amount, then double this
amount is represented by a line twice the length of the
former. It does not matter what is the standard selected j
but when once selected it must not be varied in the same
representation. Two lines are drawn at right angles to
each other ; from the point of section B (fig. 69) the lengths
which are to represent the values of one series (in our CMS-,
the weights attached to the muscle) are measured off on the
c

•^^

A

TlG. 70. DlAGHA.M 01'- POSITIVE AM) .NKGATIVI. VAI.1I.S.

horizontal line. From each of the points thus obtained, tl', b",
d", d'", a line is drawn at right angles to the first, care being
taken to make its length express the expansion corresponding
with each weight respectively. This gives the lines </ /.''.
I" B", d" B'", d"1 7;iv. I'.y connect in- those points we
obtain tho curve Jill' It" B'" Jf* x", which at a glance
shows the relation h. 'tween the weight and the expansion.
In exactly the same \\ay the curve b b' b" b'" J>v // is pro
jecied, and this repn sents the expansion of the active muscle
by the corresponding weights.

In many caSOB it is reijuired to represent values of oppo-
site kinds. Jf, for example (tig. 7<M, the wire a b is bra-
\er-rd by an electric current, then one half assumes jnjsitive
tension, the other negative tension. To express this, the

NOTES AND ADDITIONS.

297

Hues which are to represent positive tension are drawn
upward, those which are to represent negative tension down-
ward, from the basal line. The figure then shows that
the tension in the middle of the wire = 0, and that toward
the left the positive, toward the right the negative, tensions
increase regularly. In order to find the amount of the
tension, prevailing at any particular point, e.g. at e, a per-
pendicular line is erected at that point; and the length
of this, e f, accurately represents the tension there pre-
vailing.

2. DIRECTION OF THE MUSCLE-FIBRES, HEIGHT OF ELEVATION,
AND THE ACCOMPLISHMENT OF WORK (p. 93).

Because of the extreme rarity of long parallel-fibred
muscles, it is interesting to examine more closely the in-
fluence which oblique arrangement of the
fibres exercises on their force, height of ele-
vation, and on the work which they accom-
plish. When a muscle-fibre is so arranged
that it is incapable of effecting a movement
in the direction of its own contraction, only a
part of the force of tension which is generated
in it by its contraction comes into play, and
this part may be easily found by the law of
the parallelogram of forces. This is the case
in all simply and doubly penniform muscles.
Supposing that the muscle-fibre A B (fig. 71)
contracts to the extent B b, but that motion
of the point £, on account of the attachment
of the muscle to the bone, and of the nature
of the sockets of the latter, can only occur in
the direction B C ; in that case the muscle-
fibre, in contracting, undergoes a change in
direction from its fixed point of origin A, and thus assumes
the position A b' ; the elevation which is really effected is,
14

B

IMG. 71. ACTION

OFOBtlQUEML'S-
CLE-FIBKES.

298 PHYSIOLOGY OF MUSCLES AND NEKVES.

therefore, B I'. The small triangle J! I !>' may l>e regarded
as a right-angled triangle. Tliis gives

BV = --^

817]

The force with which the mu<e!e-libre strives to contract
in tin- direction A B being called /.•, only part of this force.
the component k' lying in the direction B (.'. finds expression.
According to the law of the parallelogram of forces, this com-
ponent is

k '= k sin p.

This force may be regarded ns proportionate to tin-
weight which the muscle-fibre is aide to raise to the given
height of elevation. If we then c.-dciilate the work which
the muscle can accomplish, we find, if th • motion can take
place in the direction A B,

A—£bk;

but if motion can only occur in the direction B C,

The value in the two cases is therefore exactly the same,
or, in other words, the amount of work accomplished by the
muscle is quite independent of the direction in which its
action takes place. This is, naturally, true of every other
muscle -fibre, and, ci >iise<jueiit 1 y, of the whole muscle. The
statements which we have made of parallel-fibred muscles
are therefore also true of those of which the fibres are irre-
gular. The possible height of elevation is always grea'ei-
the longer the fibres are, and the force proportionate to the
diameter or to the number of the fibres. In oblique fibred
muscles the fibres are generally very short, but very nume-
rous ; the>e must, therefore, whatever tln-ir accidental form.
lie regarded as short and thick muscles, possessed of small
ele\atinii and great f.-ive.

NOTES AND ADDITIONS. 299

3. EXCITABILITY AND STRENGTH OF IRRITANT. COMBINATION
OF IRRITANTS (p. 119).

When the coils of a sliding inductive apparatus are,
brought nearer together, the strength of the inductive current
does not increase in exact proportion with the decreasing
distance betweeen the two, but in a complex way, which
must ba provided for in each apparatus separately. Fick,
Kronecker, and others have shown methods by which this
calibration of the apparatus may be accomplished. If the
real strength of the irritating current is compared with
the height of the pulsation which it elicits, it appears that
when the current is very weak no action is observable;
action first appears, in the form of a slight, just visible pulsa-
tion, when the current has reached a certain strength, greater
or less according to the condition of excitability of the
nerve. As the currents increase further in strength, the
heights of elevation increase in exact proportion to the
strength of the currents, till a certain maximum has been
reached. If the strength of the current becomes yet greater,
the pulsations remain constant for a time ; but then they
again increase and reach a second maximum, above which
they do not pass.

These so-called ' over maximum ' pulsations are due to
a combination of two irritants. An inductive shock is, as
we have seen, a veiy brief current, in which the commence-
ment and the end succeed each other very rapidly. For
reasons which will be further explained in Note 7, the com-
mencement of an inductive current is a more powerful
irritant than its end. As long, therefore, as the current
does not pass a certain strength, only the commencement of
the current irritates ; but in the case of very powerful cur-
rents the end may be sufficiently effective : this gives two
irritations following each other in rapid succession, and these

300 riivsini.oiiY or Mr.-n.rs AM> NF.KVES.

together effect a gre.iter pulsation than does a single irrita-
tion.

If more than two irritants follow each other in rapid
succession, tetanus results, as we know. In this case also
the height of elevation is always greater than that which
ran be attained by a single pulsation. For the muscle has
the power of being again irritated even when it is already in
the act of contraction, a more powerful contraction being
thus induced in it. The bearing of these facts on the case
of nerve is that the separate excitements effected in it by
these rapidly successive irritations do nob mutually disturb
each other, but are transmitted one after the other, iu the
sequence in which they originate, to the muscle on vJiich
they act. But when the number of the irritants becomes
too great, the nerve-molecules are no longer able to k< ep
pace with the rapidly succeeding shocks, and the nerve is
uncxciti-d. The limit at which this intervenes has, how-
ever, not yet been determined with any certainty. It
appears to lie at between SOO to 1000 irritants per second.

4. CURVE OF EXCITABILITY. RESISTANCE TO TRANSMISSION

(p. 123).

The increased excitability at the upper parts of the un-
injured sciatic nerve, when not se\en,l from the hod\ .
which, on the strength of our earlier experiments, we have
assumed in the text, has recently been again defended by
Tiegel against various objections. For reasons explained in
the text, it is inadmissible to infer an avalanche like incn a^-
in the irritation merely from this higher excitability of the
upper parts. 1'vside the experiments of Munk alluded to
on page 11G, there are other experiments from which a
tance to tran>nnVsion in the nerve may be inferred.
Such a resistance, weakening the irritant during its propa-
gation, and an avalanche like increase in the irritant, are

irreconcilable contradictions which mutuallv exclude each

NOTES AND ADDITIONS. 301

other. If resistance to transmission can be shown, then the
irritation cannot increase in strength during its propagation
through the nerve. I will, therefore, here briefly mention
the reasons which induce me to declare in favour of one, and
against the other, of these assumptions.

As is mentioned on p. 141, transmission becomes con-
siderably harder when the nerve is in an anelectrotonic
condition, and in strong anelectrotonus it is even rendered
altogether impossible. It is natural to regard this greater
difficulty as an increase of a resistance already present. A
more important reason is however to be found in the phe-
nomena which occur in reflex actions. If a sensory nerve
is irritated, the excitement can be transmitted to the dorsal
marrow and the brain, where it may be transferred to a
motor nerve (of. p. 274). This transference always occupies
a considerable time, which I call reflex-time. If a sensory
nerve is irritated sufficiently to cause a powerful reflex action
(called a 'sufficient irritant'), if the reflex-time in this case is
determined, and if irritants of continually increasing strength
are then allowed to act on the same point in the nerve,
then the reflex-time is found to become continually shorter.
If, however, a point in the nerve lying very near the dorsal
marrow is irritated, then even in the case of a 'sufficient
irritant ' the reflex-time is short. It is evident that the
duration of the reflex-time depends on the strength of the
irritant when it reaches the dorsal marrow. The irritant
which comes from the point in the nerve adjacent to the
dorsal marrow is but slightly affected; but that coming
from a more remote point is weakened ; so that a much
stronger irritant must be applied to these more remote points,
if an equally short reflex- time is to be attained.

It is true that these observations have been made with
sensory nerves. But owing to the entirely similar character
exhibited by all kinds of nerve-fibres in all points, where
comparison is possible, we are justified in applying the views
thus gained to the motor-nerves. It is, at all events, im-

302 1'IIYSIoU.XiY "!• MUSCLES AM> NKKYKS.

probable that in OIK- nerve-fibre .1 resistance (o transmiwion
exists, and in another an avalanche-like increase. All the
facts arc more easily and simply explained liy assuming that
there is a resistance to transmission in all nervi s, allowance
beiiiLjat tlie same time made tor the difference in the ex-
citability of dili' rent points in the nerve.

.Moreover the curve of excitability in the case <,f the
sei.-Uic nerve is not a simple ascending line from the muscle
to the dorsal marrow. Thi> nerve is found, as is shown in
fig. 1'2, liy the union of several roots J it then, at variou.s

Fn.. 7 1'. Tin: -< IATII- M:I:VI. AM> < AI.K-MIX 1.1: or A

points, »i\-es oil' ln-anches which enter the muscles of tie
upper h% and then separate into two branches, one of which
provides for the calf-muscle (f///.s7/-«cV' IHIHH), the other for the
(lexor muscle of the lower ]e^. If various points of this
iicrxe are irritated ill the living animal, the net ve havin;,'
been merely exposed and isolated from the surrounding parts,
but not s-parated from the dorsal marrow, it i^ ver\ e\ iilcnt.
th;it the excitability at the upper points is generally Create!'
than at the lower; but p'int>are also found in the com se
of the nerve at which a greater excitaliility exists than at the
p lints above and below, as also, on the c. nti-ary. a lev-; i \
citaliility than at the adjacent jioints. Such irregularities
are m.i-t abiindiintly exhibited at th- points \\here nerve-
brancln - separate from t he main trunk, especially when tl>
branches bave been cut a\\ay. This is partly due to clec-
t rot 01 iic iiillu -nci's (.•/'. p. 1 L'"> <l 8tq. \ |>. - 1 •"> ' / >-'/•• ^"tr ' :^)-
The nerve libres which ai'e cut generate a i-urreiit which

NOTES AND ADDITIONS. 303

passes through those which are not cut off, those the excita-
bility of which is tested, and alters their excitability. This
influence changes in the whole mass, as the cut nerves die,
thus giving rise to irregularities the further nature of which
we need not trace.

5. INFLUENCE OP THE LENGTH OF THE PORTION OF THE
NERVE EXCITED (p. 138).

If the irritant remains the same, the longer is the portion
of the nerve irritated, the stronger is the action on the
muscle. If the excitability of a portion of the nerve is found
by the method of minimum irritants, that is, if the weakest
irritant capable of effecting an observable pulsation is looked
for, and if various degrees of excitability prevail in the por-
tions of the nerve simultaneously exposed to the irritant,
action may result, even if only a part of the portion of nerve
is really excited ; in reality, therefore, it is but the excita-
bility of the most excitable part of the whole nerve-portion
which is tested. In a fresh nerve this is generally the upper
part of the nerve-portion. But when there is no great dif-
ference in excitability within the nerve-portion, then every
part of the portion will be excited by an irritant of a certain
strength in an approximately like manner, and the action
observed in the muscle will therefore be the combined effect
of the excitement of the separate parts of the nerve-portion.
But if, as we have assumed, the loss of excitability in each
part follows the highest excitability very suddenly, the effect
must be that the portion actually irritated continually be-
comes shorter ; the parts which are irritated are however
still in the highest state of excitability, and therefore exhibit
the third stage of pulsation (the testing current having been
so chosen that, in the fresh nerve, it originally produced the
first stage). The form in which the third stage exhibits itself
— pulsation on the closing of a descending current and on the
opening of an ascending current— must therefore remain

:>04 rnvsioLociY OF MUSCLES AM> NEEVES,

unchanged, bui tin- pulsations must gradually decrease in
strength, anil all effect must finally disappear, just \\h-Mi
tin' maximum «[' excitability, and tin- death which follows
this. pas> tin' lower limit of the excite 1 jmrt'on.

G. DiiTi:i:r.NCE BET\VI:I:N CLOSING AND OPENING IMX r-
TIVE CURRENTS. HKI.MIIHITZ'S ARRANGEMENT (p. 151).

When an electric current is suddenly closed in a spiral,
this not only acts inductively on a neighbouring spiral, but
the individual coils of the primary spiral act inductively on
each other; an analogous died would occur on the opening.
but that the sudden interruption of transmission prevents the
development of this opening inductive current in the primar\
coil. The inductive current which originates on the clo>ing
of the current being in an opposite direction to the closed
i current itself, the former must -weaken '.he latter; th" cnr-
i-ent can therefore attain full strength, not at once, but only
irradually : but on the opening the current suddenly ceases,
Tliis difference in the duration of the closing and opening
of the primary current corresponds with differences in the
currents induced by them in the secondary spiral, -which are
used for the irritation of the nerve. Fi-u.v 7;! exhibits these
characters. The ujiper part of tbc fig!ii-e represents the tem-
poral course of the main current in the primary spiral of an
inductive apparatus; the lower part repn-s -nts the temporal
course of the induced currents in the .secondary spiral. The
line o ... o ... / represents the duration. The primary current,
is dosed at til- moment o. Were the retardatory influence
which lias been mentioned not present in the primary spiral,
the current would at once attain its full Strength < > .1 \ Imf
uuing <«' tbat i nil uence it at tains this st ren-t li only gradually,
somewhat as shown by the crooked line .">. With ihis-radu-
allv occurring current corresponds a closing induct ivr current
in the secondary spiral, as is i-eprcseuted by the cu:-ve -1 ;

NOTES AND ADDITIONS.

305

the curve is drawn downward from the time-line o . . . o . . . t,
to indicate that the direction of this induced current is
opposed to the direction of the primary current. If the
primary current is interrupted, it suddenly falls from the

fv,

strength /, as indicated by the straight line 1. With this
fall corresponds an inductive current, which suddenly rises
very abruptly and again falls somewhat le^s abruptly, as
shown in curve 2. From this it is evident that the latter
must be physiologically much more effective than the former.

306 PHYSIOLOGY OF MUSCLES AND NKI;\ I -.

Occasion. illy i' is de-iral'le to remove this difference, and
to provide two inductive currents which flow and act nearly
in the same way. This may L- inanagi d. if, instead of
rlo-ing and interrupting the current of the primary coil, an
additional closing wire offering small resistance is provided,
ami tlit- interruption is effected in this. If this additional
apparatus is present, only a very small part of the current
passe.> through the primary coil. The strength of this part is
indicated by «7, i/,. "When the closing in the additional ap-
paratus i.s inten upied, the primary curr. nt slowly incre.-i-
in strength from J ' , to J as shown by the dotted curve ."• ;
with this incivas • corresponds an inductive current in the

'iidary coil, as represented by curve 6. If the closing of
the additional apparatus is once more effect d. the current in
the primary coil sinks in strength from J to J -, but tbe so-
calle 1 >:.<-tr<i cttrr-'nf, that, which originates in consi-tpn-nce of
the sinking in the primary coil, is now able, the coil being
closed, to take riled, and, as its direction is the same as that
of the main current, it retards the sinking of the litter, so
that this now takes place as indicated l>y curve 1 ( and with
this slow sinking of the miin current c.irre-pnnds an induc-
tive current in the s r'jnd-iry coil, siu-h as is shown )>y
curve 8.

Helmholu mule an alteration in du I'.oi- lleyniond's
sliding inductive apparatus by means of which this ad-
ditional closing and opening is automatically arc-implNied.
lie adapted Wagner's hammer for this purpose, as shown in
Jig. 71. The current of the apparatus A' pa-i-rs through tin-
wire arranged ln-tween ;i and /' to the jirimary coil c. from
this to the Coils round the small electromagnet /', and fi-om
the latter through the column n. Lack to its original starting
piint. The electro magnet attracts the hammer //, in con-
si'ijuence ut' which a small platinum plate fastened Lelow
the < leriirm silver spring is Lrought into contact with the
platinum ]niint of (lie screw/, thus ci.mplrting a Lrief and

flljcirnt additi"l'a! cl. ..-,11 re // / u. Tlir curisi •( jlli 'lice . .f this

NOTES AND ADDITIONS.

307

is that the current in the coil c, and at the same time in the
electro-magnet, is much weakened ; the latter can no longer
attract the hammer, which springs upward, so that the plate
is removed from the point ft and the additional closure is
interrupted. The current once more passes in full strength
through the coil c and the electro-magnet b, the hammer is
again attracted, and the whole process is repeated as long as
the circuit K endures. If it is required to restore the appa-

K

^J

FIG. 74. HELMIIOLTZ'S APPARATUS.

ratus to its original condition, it is only necessary to remove
the wire gn and to lower the point/.

7. ACTION OF CURRENTS OF SHORT DURATION (p. 152).

Either the closing or opening of a continuous current
or an inductive current is used to excite the nerve. In the
latter case, however, as has already been indicated in Note

m- MUSCLES AM> M:K\ :

", we have really to ilo with a closing imme ti it -ly sttC-
c vded liy an opening, for the inductive current ai i~e., mil
a,' mi disappear:- as SOOD as it lias r.-aeh-d si c.-rt tin strength.
Th> may lie imitat -d with suitable apparatus, l.y closing a
cm-taut current for a very l>rkf time. Such a ; cm rent
sho,-k ' may exhih'.t exactly the same phenomena as does an
inductive current. If its duration remains unaltered, hut
the strength of the current is giadually increased, the height
i.t' elevation at first increases, remains for a time at a first
maximum, after which it again increases and reaches a second
maximum. Tho explanation is the same as was given in
Note :; I'm- inluctive currents. At first only the beginning
of the current (the closing) acts excitingly; but when the
current H stronger, the cessation of the current (the o|ienin^ )
c.ni also act in the snne way. and a comliination of the two
irritant* cm l,c t'onued.

If the duration of such a current shock i-> very >hort. I he
current mu>t he M rongi-r, if it is to exercise any exciting
elVect at all, than would he in n -.sary if the duration were
longer. It is evident that a current, if it lasts too short a
time, cannot effect a sufficient chang,- in t!ie molecular con-
dition of the nerve, and weaker currents require a longer
time t:> do this than st rongor.

From the curves in fig. ~'.'> \\!;ic'i ivpreseiit the duration
of inductive Currents, it apjicars that without exception the
commencement of the current results more abruptly than its
disappearance. The coniinenc'-ment of every inductive cm-
rent must th>-re!'ore inure easily excite than dues its end,
esp 'cially as this isalwavs the case «'Vcii in the ordii arv
closing and opening of e\ ery coiislant cm rent, in which such
e.-n-ideralilc diflerenci-s in the duration do not occur. In
the case of weak inductive cunents il is always only the
• uiiimencement which is active, in other words mi 'nuliicttr ••
i-in-i-i ni HI-IK a* :lu s tl/' i-JiiKiinj (if a continuous c///-r< uf.

Now let US suppose that all inductive current is pas>ed
through a nervein an a-c-'iidiug direction. So long :is the

NOTES AND ADDITIONS. 309

current does not exceed a certain strength, it can excite;
but when it is strong it is ineffective, since the closing of
strong ascending currents is always ineffective. If, however,
the current is made yet stronger, it may again become effec-
tive, because the opening portion of the current can now, in
spite of its retarded course, cause an irritation. This gap
(Liicke) in the action was observed by Tick, and afterwards
by Tiegel. How far other causes besides those here ex-
plained combine to produce this peculiar phenomenon, we
cannot examine further here.

8. ACTION OF TRANSVERSE CURRENTS. UNIPOLAR IRRITATION

(p. 152).

If a current is passed transversely through a nerve, that
is, in a direction at right angles to the long a,xis of the nerve
fibres, it has no effect. To effect the alteration in the posi-
tion of the nerve molecules which we regard as the cause
of the process of excitement, the current must, therefore,
pass in the longitudinal direction of the nerve. This is pro-
bably due to the peculiar electric forces of the nerve-par-
ticles, which are treated of in detail on page 215 et scq. Just
as an electric current if it flows parallel to a magnetic needle
deflects the latter, but has no such effect when it flows in a
direction at right angles to that of the needle, so the nerve
particles can only be disturbed from their quiescent position
by currents which run parallel to the axis of the nerve. If
the current is directed oblique!}' to the nerve fibre, it acts
but not so strongly as when it is parallel, and the degree of
the action decreases proportionately as the angle which the
current makes with the nerve-fibre approaches more nearly
to a right angle.

The connection between the phenomena of electrotonus
and excitement of the nerve led us to believe that the excite-
ment takes place, not throughout the whole portion of the
nerve traversed by the current, but only in a part which on

310 riivsiol.ut.v OF MUSCLES AND NKUVI

closing is near the kathode, on opening is near tli • anode.
'I'liis Drives ri.se to the question, whether it is possible to
expos*' the nerve to the action of one electrode :iluiie. This
may lie done, in the case of men or other animal-. by placing
one electrode on tlie nerve, the other on a remote part of
the body. If the kathode is situated on the nerve, only
closing pul.-at ions are obtained; if the anode is situated on
the nerve, opening pulsations are alone observed. If the
currents are very powerful, excitement may certainly occur
at the point where the nerve meets the adjacent tissues.
This form of nerve irritation maybe called ii,ii/«i['tr, though
in a different sense from that in which the name is usually
used in cases where only one wire is laid on the nerve, and
vet currents may flow through the nerve. Such cases, how-
.-. are physiologically of no speci.-il interest.

9. T\M:::.NT CALVANO.MI;TI:I; (p. Kii').

In the ordinary tangent-galvanometer a small magnetic
needle is placed in the centre of a, comparatively, very lar-e
circle, through the periphery of which the current is ma le to
pass. When the needle is deflected, the position of its poles
does not alter essentially us regards the cm-lent, the action of
which may therefore I e re-aided as directly proportionate to
its strength: and from the opposed action of the current,
and of the force of attraction which the earth c\erci.-es on
the needle, \\hich must also be regarded as constant, it is
evident that the two forces must be in equilibrium, if the
trigonometric tangent of the aii^le of deflection is propor-
tional, i to 1 lie si ren^lli of the current.

Such tangent-galvanometers are. however, only adapted
f -r measuring powerful currents. The ^ih aiiom. t r which
we have described, adapted for very \\eak currents, i- dill'er-
enl. Hut if, as wa> a ..-limed, all the deilrrtinns which are
to 1 e measured are Iml very small, we may still assume that
the mode of the influence «,(' i|M. current on the magnet is

NOTES AND ADDITIONS. 311

not altered by the deflection. Then, in the case of this ap-
paratus also, the strength of the currents may be regarded
as proportionate to the tangent of the angle of deflection.
A glance at fig. 19, on p. 57, shows that the displacement
of the scale is equal to the tangent of the double angle of
deflection. For so small an angle we may put

tc, (2 «) = 2ty «,

that is to say, the tangent of the double angle is equal to
double the tangent of the single angle. And from this it
follows that the strength of the currents is proportionate to
the displacement of the scale directly observed.

10. TENSIONS IN CONDUCTORS (p. 133).

To determine the absolute amount of tension at any
point in a conductor, it would be necessary electrically to
isolate the conductor, and to connect the point in question
with a sensitive electrometer. But if any point of the iso-
lated conductor is brought into conducting connection with
the surface of the earth, this point would assume a tension
equal toO, without any alteration in the differences of tension
at the various points. Other points of the conductor may
now be brought successively into connection with the earth,
thus altering the absolute values of the tensions at the
separate points, though the difference between the tensions at
the various points remains the same. From this it follows
that these differences are alone of importance for us. In our
later explanations we have therefore represented the matter
as though certain points (the boundaries between the longi-
tudinal and cross section) had a tension =0 ; that is, we always
thought of them as connected with the earth. All tensions
that are greater than this we call positive, all that are less
negative.

312 rilYHOI.OGY 01- MUSCLES AM' M-.KVK*.

11. l>riM.i:x TRANSMISSION. |M-:..I;\I:I;ATION,

\-.n I COALESCENCE OF A ]>lsi;( Ti;i> Xi:i;\ i: (l». L'lS).

Duplex transmission has been shown in another way,

but the proof is not 8O trustworthy ami cleir as tlial gained
by the ai<l of negative variation. If nerves of the living
animal arr bisected, a striking change ocours in a very short
time in the parts of the nerve -Jil>re below the point of scission.
The nit'diillary sheath becomes crinkled, and* the excitability
is lost. If, however, the cut surfaces are not too far sepa-
rated, the nerv, '-fibres r;,u coalesce, the lower cuds again
become exciialile, and the excitement can be transmitted
through the cicatiix thus formed in the nerve. ( >n these
facts Kidder based an experiment, in which he tried to cause
a sensory nerve to coalesce with a motor nerve. The sen-
sory ner\c of the tongue (.V. i< in/inilix}, a branch of the fifth
brain nerve, and the motor nerve of tin- tongue (.V. Itjpo-
i/li'ssus) cross each other below the tongue before they enter
the latter. If the two nerves are cut at the point where
they cross, and if the upper eud of the sensory nerve, which
conies from the brain, is connected with the lower end of the
mot )r nerve, \\hich enters the tongue, as much as possible
of the two other ends of the nerves being cut out, then the
two dilleivnt nerves coalesce, SO that after a time pulsations
may be caused in the muscles of the tongue by in Station
above the cicatrix, and indications of pain may be elicited
by irritation below the cicatiix. The proof that in this ca-e
the excitement is transmitted downward in the upper .sensoi y
i.erve, up\\ard in the lower motor nerve, would lie unassail-
able if it could be sho\\ ii that nerve fibres of the one nerve
lave not grown through the cicatiix and entered into the
other nerve. This possibility, improbable as it is. cannot
be di <pro\ed.

A recently published experiment of 1'aul Mert is founded

NOTES AND ADDITIONS. 313

on a similar idea. Bert made a wound in. the back of a rat,
cut off a small piece of the end of the tail, and fixed the tail
firmly in the wound on the back. The tail of the rat coa-
lescing with the flesh of the back, it TV as attached at two points
like the handle of a pot. The original root of the tail was
then cut through, so that the attachment to the back alone
remained. If the free end of the tail, which was originally
the tail-root of the rat so treated, is pinched, the animal
feels it ; so that the irritation is evidently transmitted in
the sensory nerves in a direction opposite to that which is
usual in the tail of a rat under normal conditions, and it is
accordingly evident that the sensory nerves of the tail have
the power of transmitting the excitement in both directions.

12. NEGATIVE VARIATION AND EXCITEMENT (p. 220).

That negative variation is a constant and inseparable
accompaniment of nerve-excitement has been shown by
du Bois-Reymond by a large number of careful and varied
experiments, which have been confirmed and extended in
various directions by many observers. It makes no difference
by what irritant the nerve is excited ; and both motor and
sensory nerves are conditioned exactly alike in this matter.
From a large number of experiments to select but one of
peculiar interest, I may allude to the experiment recently
made with the nerve of sight. If the eye is extracted and
prepared in connection with a portion of the nerve of sight,
and if the latter is suitably tested as to its nerve-current,
and light is then allowed to fall on the eye, previously shaded,
then the current of this nerve exhibits negative variation.

If ligatures are applied to a nerve so that the excitement
can no longer propagate itself from one side to the other,
irritation of one side causes no negative variation in the
other side. This experiment is of importance because it
affords a means of proving with sufficient certainty that no

314 riiysioLotiY or MTSCLES AND NKKYJ .-.

branch-Currents of tin- electric current used for irritation,
which miijit e.-isily 1 -ml to errors, are pre ent ill the mul-

tiplier.

13. ELE:TUOTONUS. SECONDARY PULSATION EFFECTED BY
NERVES. PARADOXICAL PULSATION (p. 221).

The reason why it is impo-sible to examine the electro-
tunus of the intrapolar portions is purely physical. It' the
constant current is trausmitt d through the portion a k
(fig. GO, p. 220), and two points of this portion are o>n-
neeted with the multiplier, then a part of this current p.
through the multiplier itself, so that the portion of the
in rve which is situated between these points is travei>ei|
I >y a weaker current than are the adjacent portions. The
condition- ore thus rendered so complex that it becomes
very hard t;> explain the phenomena. Other attempts to
study the character of the intrapolar regum have as yet
aUbrde-d no clear results.

If a nerve a is laid on a nerve //. in the way sh<,\\n in
liir. ".">, A,B, 6', so that the nerve // forms a diverting arch for
a portion of the nerve a, and if electrotonus is generated in
the lutt.T liy a coiistant current, 1 lien the electrotonic cnr-
r.-nt passes through tlie nerve J, and can at its commence-
ment and cessation (closing and opening) excite the in rjc !>,
:ind cause pulsation in the muscle of the nei ve. Tliis is
spoki-n of as .s- condary pulsation from tin nerv . l'-\ rapidly
re|iOateil closings and openings of the circuit, tetanus may lie
elicited. I'.ut this secondary ]iulsation is caused only by
eVetrotoniis and not. by ne-.iii\e variation, so that it can
!.• more easily brought almiit by constant currents than by
inductive current^. h i ihus distin^ni>lied from the xx-mi-
• fm-i/ inilantiiin ,j/', <•/•:/ I,,/ /////.s-.-/ , -which was di'sciibed on
p. _"!•. The negative variation of the nerve eiirivnt i
\\<:.k to Cause any not ic 'able etl'i cl in a second nerve.

NOTES AND ADDITIONS.

315

A special form of secondary pulsation effected through the
nerve has been described bydu Bois-Reymondas paradoxical
pulsation. If a constant current is passed through the branch
of the sciatic nerve to which allusion is made in Note 4,
which passes to the flexor muscle of the lower leg, then the
calf-muscle may also pulsate when the current is closed and

FIG. 75. SECONDARY PULSATION EFFECTED BY NERVE.

opened. This is an apparent exception to the law of the
isolated transmission of the excitement (cf. p. 117); but
actually the excitement has not passed from the irritated
fibres to the adjacent fibres, but the electrotonic current of
the one fibre has flowed through the neighbouring fibres and
lias independently irritated them.

14. PARELECTRONOMY (p. 237).

The real causes of parelectronomy and the conditions
tinder which it is more or less strongly developed, are as yet

3LG rilYsloU'i.Y 01 MUSCLES AM> NERVES.

far from being understood. I'.ut at any rate it is impossible
to conceive tin- matter, as though the currentleB8 condition of
the muscle--- tliat is to say, the same tension on the longi-
tiulinal and traiisver.se sections — wen- iidiinal, and as if every
negati veness on the transverse section were the result of
injury. For all possible degrees of parelectronomy are to be
found e%e:i the reversed order, in which the cross-section is
more positive than the longitudinal section — in uninjun d
niuseles ; \\hile in other cases the ordinary muscle-current
is found powerfully developed in quite uninjured muscles.
Mon -over, as we have stated in the text, the question whether
ditl'eremvs of electric tension occur in uninjured muscle has
110 bearing on the question whether electromotive forces are
present within the muscle. "We declare ourselves ill favour
of this hypothesis, because it most simph and easily explains
nil the phenomena. Wo also apply it to structures on
the outer surface of which it can be proved with certainty
that 1:0 dill'erences of tension are present, as in the electric
plat' s of iishes. For this assumption ^e have the same
grounds on which physicists rely in claiming the existence of
molecular magnets in every, even quite uniuagnetie piece of
iron. Whatever, therefore, may be the true explanation of
parelectronoiny, it cannot essentially affect our well-founded
conception of the electric forces of muscles. If, however,
dn Bois-Reymond's supposition is confirmed, thai the puUi
tioiis which occur during life leave behind them an after
etleet on the muscle- ends, which niaki s the latter less neira
live, some approach wou'd be made to an ex[)lanation of the
phenomenon.

l.'i. |)isi iiAia.r. lhro-|iii>|S ANP [SOLATED TKANS.MISSK.N
IN TIM N i i > I:-|MI:KI: (p. L' I'.t).

'The explanation of the fact that the processes of r\
citeinent remain i>olattd iii a nerve lihie without passing
into adjacent liel ve libres. appears tlie more inexplicalile. if

NOTES AND ADDITIONS. 317

we regard these processes as electric, in that the separate
fibres are not electrically isolated from each other. But
the explanation which we gave of the isolated excitement of
but one muscle-fibre by a variation of the electric current in
the appropriate nerve, also explains isolated transmission in
the nerve-fibres. For if the electrically active parts are
very small, comparatively powerful electric action can take
place in them, and yet the current may be quite unobserv-
able at a little distance. This is a consequence of the law
of the distribution of currents in irregular conductors,
explained in chapter x. § 2. We must, therefore, assume
that the electrically active particles situated in the axis of
a nerve-fibre are small in comparison with the diameter of
the fibre, and that therefore their effect at the outer surface
of the fibre is already so weak that it cannot act and cause
irritation in an adjacent fibre. In Note 13 we have seen
that no action takes place by negative variation from one
fibre on an adjacent fibre. Our multipliers are much more
sensitive than nerve-fibres, so that the separate negative
variations during the tetanisation of the nerve can combine
their action on the multiplier ; but this is impossible in the
case of the excitement of nerve-fibres.

INDEX.

ABS

A BSOLUTE force of muscles,
A 67, 68

Acid, formation of, in muscle,

7H, 87
Activity of muscle, 37, 202,

235 ; of nerve, 107, 216
ADAMKICIEWICZ, 76
Adequate irritants, 285 •
AEBY, 100

Albuminous bodies, 73, 80
Ammonia, 257
Amoeba?, 6

Amoeboid movements, 7
Anelectrotonus, 129, HI
Animal, 5
Anode, 128, 220
Arches, diverting homogeneous,

177, 181

ARISTOTLE, 155, 285
Ascending currents, 134
Attachment of muscles, 17
Automatic movement, 271
Avalanches, 250
Avalanche-like increase in the

excitement of nerves, 122,

300

Axis-band, 104
Axis-cylinder, 104

"UACOX as food, 85

Ball-sockets, 19, 93
BECLARD, 73
BERNARD, 253

CITE

BERNSTEIN, 100, 219

BERT, 312

Blood, 78, 273

Blood-corpuscles, 7

Blood-vessels, 96, 272

DU Bois EEYMOND, 25, 30, 35,
36, 53, 59, 73, 87, 111, 150,
156, 165, 181, 183, 186, 205,
208, 217, 230, 248, 278, 313,
315, 316

Bones, 17, 18, 93

Branched muscle fibres, 101

Branching of electric currents,
132, 150

Brownian movements, 3

BRUCKE, 89

Burden, 23, 39, 64

BURDON- SANDERSON, 223

HALF-MUSCLE. Sec Cas'.ro-
cnemius

Carbonic acid, formation of, in
muscle, 42, 73, 81

Carrying-height (Traghche) 41

Cells, 9. St'C also Nerve-cells

Central-organ of the nervous
system, 103, 117, 265

Centrifugal and centripetal
nerves, 266

Cerebrum, 277

Chamois-hunters, 85

Chemical composition of mus-
cles, 73

320

1NDKV.

CUE

mical irritants, :$0, 109, 267
Chemical processes in mus

II', 7:5

Ciliary cells, 10
Ciliary-movements, 10
Circuit, electric, 153, 103
CLAUDIUS CLAUDIANIS, i.v>
Closing of a current, :;L', 1 :;.',:'.(' I
iuductive current, 151,
'

Comhination of tensions, 228;

of irritants, L'-.c.t
Compensation, 1*:;
Compensator, round, 186
Concept inn, L'7'.', L'sn
Conine, 2.~>:!

Conscious sensation, L'77
Conservation of energy. 77
Cuns'ant currents, 31, K>:>, ll'f,,

131

Correlative action. 1'7»>
Correlative -ensatimi, i'7tj
Creal in, l\
Cross-section of the muscle, fif.,

!!»(), I'.IS, "JOS. L'lir,, L>.-,f,; of the

nerves, 1 •_'(). 1'K',. 256
Curare, L'.Vi
Current -curvet, 1 7S
Current-planes. 1 7'.»
Curve of excitability, IL'1, noO

FJAEWIN, 224

Death of the. muscle, 86,
207 ; <>r the. nerve, li'o, H'l
Death-ytiiVness, 87
I i.-j-eiic'i-ation of a ciit nerve, :!!•_'
Jie-;.-.. n,lin^ currents, I:: I
Lioncea mvioipvla, 1 I1.', --I
I lischarge-hypothesis, -is, :il n

l»ises of musclc-lilires, H
Disdiaclasls, IT,, H»L'

Dislocation of the neck, i'7:!

I liverl iliLT arelies, 177
I »i\ert iii'j" cylinders, 181

l>i\crtiii.ir vessels, 1 ''>•'•

J)i\i-inll (if elect! ieclirrelll-, \'.''~2,

170

r.i:s. 289
marrow, Kid, L'77

FIB

Double refractii.u, 1,"
lUiplex traiismU.-ii>ii, '_'1
Dynamite, I'.M

, 69

J;I,\>TICITV. L-l ; alteration of,
-^ on contraction. II. 7<>: CO-ef-

lieient. of, L':;; l;i\\ of, i'L'
Electric current, l.V."
Electric eel,

Electric ashes, I.'!. 222, 227, I'll
Electric irritation, :;L', Km, 1 I'.i
151

• -trie organs, l.'s, l_'L"J
Electric plate-, 158, L'l".', L'L'7. '-Ml
' lie ray. l."i)i

lie wheel, :i::

Electrodes, 128; unpi»lari>ahlc,
181

Kh'.'tr ....... ti\e fore,'. ]i\<. '.'I'.!' ; of

tin; muscles and ner\e<, l.".:i.
it an/.

BL ctromotive surface, 17'.i, L'L'7
Electrotonus, iL'7, 1 :!-.», L'L'II, L':IS,
301), 311

Klemelit. X/Y- ^Ilisclc-clelliclit,

//in/ Norve-eleiiient
Elementary organisms. S
Energy, IK 50, ii|, 7i'. 77 ; -

cilic, L'M;
I;\(;I:I.MANX. inn

;. 2HO,

r, electromoi i\e,

I'iUMANN. t.".

Excitahility, 11 :i, IL'L'.

300
Excitement, ILV,, i 1 1, i.-.n, i:,l,

313

Exhaustion, 7'.', 1 '_' I

ension, IM. :>:'. i".1:. : -radual,
24
Kxtra| nlar regions, '-"JO

I;AI:AI>\Y.

1 Teel Of

176

the divcrtinir arch,

Fibres. >',,- Musele-lihrcs and

Nerve-fibres
Fibre-cells, '.>«;

INDEX.

321

FIB

Fibrillse, 1-1

FICK, 41, 299, 309

Fish, electric, 154, 222, 227, 241

Flat-bones, 18

Flesh, 2, 11, 86

Force, electromotive, 168, 232

Force, muscular, 50, 67

Forms of muscles, 91

Form, changes of, in muscle

during contraction, 45
Freeing of forces, 249
Function, 293

riALVANOMETER, 160

Ganglion-cells. See Nerve-
cells

Ganglion-balls. See Nerve-cells

Gastrocnemius, 17, 67, 109, 199.
200, 203, 209, 302

GAUSS, 58

GERLACH, 246, 247, 259

Gizzard, 96

Glands, 212, 227, 262

Glycerine, 257

Glycogen, 73, 80, 87

GOETHE, 285

Graphical representation, 293

S'GRAVESANDE, 23

Grey nerve-fibres, 104

Gunpowder, 250

Gymnotus, 156 .

IJALLER, 252

Hallucination, 279
HARLESS, 253
Head of muscle, 1 3
Heart, the, 101, 210
HEIDENHATN, 76, 146
Height of elevation, 37, 2D7
HELMHOLTZ, 50, 52, 59, 73, 75,

115, 228, 287, 290, 306
HERMANN, 70, 100
Hinge-socket, 19, 93
HIRSCH, 288
Homogeneity of all nerve-fibres,

263

HOOK, 23
HUMBOLDT, 156
Hypotheses, 229, 234

15

MAG

INCREASE in thickness of
muscle on contraction, 41

Induction, magnetic, 243

Inductive currents, 31, 110, 139,
304, 308

Induction coil, 31, 35, 119, 306

Inertia of consciousness, 290

Inosit, 74, 87

Internal work during tetanus, 41,
76,77

Intestine, 96, 272 ; of the tench,
101

Intrapolar regions, 129, 221

Involuntary movements, 271

Irregular movements, 272

Irritants, 30, 109

Irritability, 30, 108 ; independent,
255

Isolated transmission in the
nerve-fibre, 117, 315

Isoelectric curves. See Tension-
lines

T7ATELECTROTONU8,129,141

1V Kathode, 1 28, 220

Kernel (nucleus) 5,7, II, 16, 96,

105

Key, tetanising, 36
Kleistian jar, 30
KOLLIKER, 253
KRONECKER, 299
KUHNE, 89, 256, 257

T ABOUR accumulator, 41

-^ Lactic acids, 73, 80, 87, 258

Latent irritation, 56, 64

Law of eccentric sensation, 280

Law of pulsations, 135, 142

Leverage of bones, 93

Leyden jar, 30

Life centres, 272

Light, 15, 284

Long bones, 18

"MAGNET, compared to muscle
^- and nerve, 147, 230, 200

322

INDKX.

MAI.
ti rnni.f, 1 ."iti

M A 'I I.I "I •••!. 22'.l

M'-fhani.-al irritants ::»i. inn, i it;
Meduiiarv .-heath, lol, 21.1, 2M,

263

.Viiiio.tu pinl ifii, 2, 224
Mirror, rea.ling uf small angles

liv means tit', .17. 1 i'iL'
Miidiiie.itinii til' excitability, 131,

1 1:;

Molecular hypothesis, 238

Molecular iini\ ement, :!

Moling, li>2

Monti i/rtts, 1.1'.'.

.Mnliir nerves, 2C,1

Mcivciucnt, 1 ; in plants, 2, 8,
224 ; of the smallest organisms,
4; molecular, 3; ]>rotnp!u>-
inic, G ; amoeboid, 6 ; ciliary,
!i; muscular, 9 ct scq.\ peri-
staltic, 98, 272 ; voluntary
and involuntary, '.is. 27.1 ; au-
tomat if., 1'::; ; rhytlunic, L'72 ;
i- Hi if, L'7:.'

.Mulii|ilicr, Kit

MI-NK, lie,, 224, 300

Muscle, 2, 11, 12 ct scq., 180 ct

srq., L'i'il // AW/.
^lu-.-lr-cunvnt, I'.M, 202, 22G
Muscle-element, '.':'.'_', 2:;:»
Jlusclc-librc, striatfd, 14, 4.1, 9(1,

245 ; smooth, 9G, 101 ; zig/.ag

arrai!ir''nirnt of, 14
Muscle-tibrc poiifh. >'»(• Sarco-

Lemma
Muscle-fluid,

Musci(-]iri.-ui, is1.', •_•::(), -J:M
Muscle-rhombus, ];•::, \ '.<:>, •-'::<•
.Musf!.!-ni.tc, 4:5, 211
Muscle-telegraph, 30
Mvu-raiih, I'll. :!7, 62, !<»», Ill
Blyosin, 71, '.'<•

MASSE, 73

11 Nfjativf variation, 2<>::, 2 in,

21 I, 2 ic,, 22H, 2:11, :;i:;
ells, lu:;, 2i;c,, 2i'.'.i

POL

>Sr rv-ntral Or-
gans.
\rivt-furivnt, 21.1, 22G, 236

. l':i7 (t KI ij.

' -, 1":: it teq.\ termi-
nation of, in musclt ~, L'1.1
Nerve-net, 2ir,
Nrrvu-pn ><• esses, 107, 2C..1

Nerve-sheath, lot, ill

Nerve, terminal plates of, 21.1

Nt rvous system, 103

N ft lie, stinging, movements in

hairs of, 8

-V< ii rllciuin/i. Sn Nfrvi-->lieatli
\< utral jdiint, ll'U
Nicotin, 2.1.",
Ni;roglycerine, 250, 251

Nuiriiiifiit of labourers, 82
Nut-socket, I'.i, :'.'{

Of a current, 32, 131,

308

Opening induction-current, l.io,
304

0].fi;in.u'-tetanus, 132, 1 I:1.
ori'lAN, 155

i ns. Sec Cent ral Oru a 1 1 .- and

Electric Organs
( >\ I'l'-liurdfii, (i.1
Oxidatinn, process "f, in muscle,

12

])Ai;Ai)<)XK'AL pulsation, :;i i
1'ai-flfctr. ..... my, 208, 236,316

Pi-nnil'tirm muscles, '.H, I'.'H
l'fri|iherie. nerves, I(i3. Iu7
I't-ristali ie. miivi-iiiciit, W, 272
l'i i,i Cr.H, 122, 1 M

Physiological tin

Plants, movements of, 2, '.', 221 ;

eli-ei i to at- tit,ii nf, 1.13, 223 it
teq.
Hates, electric, 168,222,227,241

I'M NY. 1.1.1

POOOBNDORP,

I'.il.ll i-e,l light, 1.1

INDEX.

323

PRE

PREVOST and DUMAS, 45
Prism. See Muscle Prism
Propagation, of the pulsation
within the muscle-fibre, 99;
of the irritation within the
nerve-fibre, 110, 114, 287; of
the negative variation in the
nerve-fibre, 129
Protoplasm, 5
Protoplasmic movement, 6
Protoplasmic processes, 106
Pulsation, 31, 56, 210 ; secondary,
210, 314 ; law of, 135, 142,299

of sensations, 276
Rate of excitement in the
nerve-fibre, 98 ; of transmission
within the nerve-fibre, 1 10, 1 ] 4,
129, 287

Reaction in muscles, 87
Receptive apparatus of sensory-
nerves, 283
Reflection, 290
Reflex actions, 274, 290, 301
Respiratory movements, 272
Respiratory centre, 272
Rest of muscles, 37
Retardation (He>nmv>iy\ 80
Retardatory nerves, 263
Rheochord, 133, 149. 184
Rhombus. See Muscle-rhombus
Rhythmic movements, 272, 281
Ritter's tetanus, 132, 143

VARCOLEMMA, 16, 101, 233

SCHWANN, 70
Secretory nerves, 213, 2(52
Secondary pulsation, 210, 314
Secondary tetanus, 211
Semi-penniform muscles, 91
Sensation, 1, 262
Sensitive machines, 251
Sensitive plant, 2
Shaft of a bone, 19
Short bones, 1 8
Shortening of muscles. 12, 28

TRU

Skeleton, muscles of, 13
Skin-currents, 207, 213
Sliding inductive apparatus, 35,

119'

Smooth muscle-fibres, 12, 96, 206
Sockets, 19, 93
Source of muscle-force, 42
Specific energies, 286
Specific warmth, 76
Steam engine, comparison of,

with muscle, 82
Stinging-nettles, movements in

hairs of, 8
STRAUSS, 290
Striated muscle, 1 1 et seq.
Sugar, 73, 80, 85
Surface, electromotive, 179, 227

TAIL of muscle, 13

Tangent galvanometer, 162,

310
Temperature, influence of, on

muscles and nerves, 86, 124
Tench, 101
Tension, electric, 168, 171, 229,

311

Tension-curves, 179, 190
Tension, differences of, 182, 311
Tension-lines, 179, 190
Tension-surfaces, 179
Terminal apparatus of nerves,

262, 267
Tetanus, 34", 37, 41, 109, 300;

secondary, 211, 314
Thermic irritants, 109
Thermo-electricity, 74
TIEGEL, 300, 309
Time, measurement of, 51, 61, 98,

111, 115, 131, 288
Tonic contraction, 272
Torpedo, 155, 158
Transmission, in the nerve-fibre,

110, 141, 287 ; isolated, 117,

316 : duplex, 217, 312
Transverse currents through the

nerves, 309
Trunk of a muscle, 13

324

I.NHKX.

VM

j'NIl'ol.Ai; irritatinn. ::o'.)

UiipdlarNalili' rln-t r< «lr<, 181
Urinary ilu.-t, loo
Urea, 80, M

VASI>-MOT<>!; nerves, 261
Volume ol' iiiiix-li', !."», GG

WAiiNKK'S kmmior, 34, ?>(><>
Wiinntli t'(|iiivak'iit, 7G, 81

WOB

Warmth, generation of, in muscle,
»•_', 7:i, 71; in IKTVC, 1-.'::

Wi;i;i:i;, i:,, IT,:;

WKISS, 73

AVIiip-ccll movrniont, 11

Will, 270, 200 ; dcllcclinn ,,f
]]iaurnctir iiccilli- liy, 205

Woodcutters, Tyrolcse, 85

Work acc(ini|ilislicil l>y tlic
muscle, 37, 38, 72, K\,

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