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Full text of "General physiology of muscles and nerves"

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THE IKTERNATIONAL SCIENTIFIC SERIES. 

VOLUME XXXII. 



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D. APPLET ON & CO., Publishers, 1, 3, & 5 Bond Street, New York. 



THE INTERNATIONAL SCIENTIFIC SEKIES. 



GENERAL PHYSIOLOGY 



OF 



MUSCLES AND NERVES. 



BY 

Dr. I. ROSENTHAL, 

PEOIESSOR OF PHYSIOLOGY IN THE UNIVEKSITY OF EKLANGEN. 



WITH SEVENTY-FIVE WOODCUTS. 



NEW YORK: 
D. APPLETO:^" AND COMPANY, 

1, 3, AND 5 BOND STREET. 
1881. 



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THIS BOOK IS DEDICATED 



TO 



HIS VENERATED MASTER 
EMIL DU BOIS-KEYMOND 



BY 



THE AUTHOR 



PEE FACE. 



-•o»- 



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 siib- 
iect, I have been obliged to dpend 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 



Vlll PREFACE. 

is presented. From the experience gained by teach- 
ing during more than fifteen years, I believe that I 
have acquired sufficient clearness of expression, even in 
treating of more difficult matters, to be intelligible 
when studied carefully even by those who are not 
specialists. In certain cases it has been impossible to 
avoid somew^hat 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 
Elektricitdtslehre fur Mediciner (Berlin, Hirschwald). 
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, &c. 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 right to omit occasional mention of the 
names of the chief founders of this branch of know- 
ledge — Ed. Weber, E. du Bois-Eeymond, and H. Helm- 
holtz. 

Eexanoen: April 15, 1877. 



CONTENTS. 



PACK 

PREFACE vii 

CHAPTER I. 

1. 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 

CKAPTEE II. 

1. Muscles, their form and structure; 2. Minute structure of 
striated muscle-fibres; 3.' Connection of miiscles 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 IT. 

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



CONTENTS. 



I'AGE 



time; 4. Applicatic>n of this to muscular pulsation: 5. 
Burden and over-burden, musctilar force ; 6. Determina- 
tion of muscular force in man ; 7. Alteration in muscular 
force durinof contraction ....... 47 



o 



CHAPTER Y. 

1. Chemical processes within the muscle ; 2. Generation of 
warmth during contraction ; 3. Exhaustion and recovery ; 
4. Source of muscle-force ; 5. Death of the muscle ; 6. 
Death-stiffening {Iligor mortis) ...... 72 

CHAPTER VI. 

J, Forms of muscle ; 2. Attachment of muscles to the bones ; B. 
Elastic tension; 4. Smooth muscle-fibres; 5. Peristaltic 
motion ; 6. Voluntary and involuntary motion ... 91 

CHAPTER VII. 

r 

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

3. Transmission of the irritation ; 4. Isolated transmis- 
sion ; 5. Irritability ; 6. The curve of irritation ; 7. Ex- 
haustion and recovery, death ...... 103 

CHAPTER VIII. 

1. Elcclrotonus ; 2, Modifications of excitability; 3. Law of 
pulsations; 4. Connection of electrotonus with excita- 
bility; 5. Condition of excitability in electrotonus; 6. 
Explanation of the law of pulsations; 7. General law of 
nerve-excitement 125 

CHAPTER IX. 

1. Electric phenomena; 2. Electric fishes ; 3. Electric organs ; 

4. ]\Iultiplicr and tangent galvanometer; 5. Difficulty of 
the study ; 6. Homogeneous diverting vessels; 7. Electro- 
motive force ; 8. Electric fall ; 9. Tension in the closing 
arch 163 



CONTENTS. XI 



CHAPTEK X. 



PAGE 



1. Diverting arches; 2. Current-curves and tension-curves; 
3. Diverting cylinders; 4. Method of measuring tension 
differences by compensation . . . . . .170 

CHAPTER XI. 

1. A regular muscle-prism; 2. Currents and tensions in a 
muscle-prism ; 3. Muscle-rhombus ; 4. Irregular muscle- 
rhombi ; 5. Current of m. gastrocnemiua . . . .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. Kate of 
propagation of negative variation ; 5, Electrotonus ; 6, 
Electric tissue of electric fishes; 7. Electric action in plants 215 

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; 3, Discharge-hypothesis; 4. Prin- 



XU CONTENTS. 

PAGE 

ciple of the dispersion of forces; 5. Independent irrita- 
bility of muscle-substance; 6. Curare; 7. Chemical irri- 
tants ; 8. Theory of the activity of the nerves . , . 244 

CHAPTER XVI. 

]. 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. Re- 
flex motion and co-relative sensation ; 7. Sensation and 
consciousness ; 8, Retardation ; 9. Specific energies of 
nerve-cells; 10. Conclusion 261 



NOTES AND ADDITIONS. 

1. Graphical Representation. Mathematical Function . . 293 

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

formance of Work . 297 

3. Excitability and Strength of Irritant. Combination of 

Irritants 299 

4. Curve of Excitability. Resistance to Transmission . . 800 
6. Influence of the Length of Irritated Portion of Nerve . 303 

6. Difference between closing and opening Inductive Cur- 

rents. Helmholtz's Arrangement 304 

7. Effect of Currents of Short Duration 307 

8. Unipolar Irritation 309 

9. Tangent Galvanometer 310 

10. Tensions in Conductors ....... 311 

11. Duplex Transmission. Degeneration, Regeneration, and 

Healing of P>isected Nerves 312 

12. Negative Variation and Excitement 313 

13. Electrotonus. Secondary Pulsations effected by Nerves. 

Paradoxical Pulsation 314 

14. Parelcctronomy 315 

15. Discharge Hypothesis and Isolated Transmission inNerve- 

Fibro 31G 



LIST OF WOODCUTS. 

PIG. PAGR 

1. AmoebjB .......... 6 

2. White Blood- Corpuscles from a Guinea'Pig .... 7 
3rt. Ciliate Cells situated with the other Cells on a Mem- 
brane .......... 10 

^b. A single Ciliate Cell, greatly magnified, of somewhat 

abnormal form ........; 10 

4. Striated Muscle-Fibres 13 

5. The Double-headed Calf-Muscle (»?. gasti'ocncmhis) with 

its Tendons 17 

6. The Bones of the Arm 19 

7. Du Bois-Reymond"s Apparatus for studying tlie 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 ..." 60 

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 Apparatus of the Forearm . . 68 

24. Dynamometer 69 



XIV 



LIST OF WOODCUTS. 



25. Smooth Muscle-Fibres 

26. Nerve-Fibres 

27. Ganglion-Cells with Nerve-Processes 

28. Spring Myograph of E. du Bois-Keymond , 

29. Propagation of the Excitement in the Nerve 

30. Electrotoniia 

31. Electrotonus under the influence of Currents of varying 

Strength ......... 

il2. Pheochord 

.S3. Electrotonus 

34. Series of Magnetic Needles representing Nerve-Particles 

35. Rheochord 

36. Electric Current 

37. Multiplier 

38. Reflecting Galvanometer 

39. Du Bois-Rcymond*s homogeneous Diverting Vessel 

40. Distribution of Currents in Irregular Conductors . 

41. Electric Fall 

42. Fall in different Wires 

43. Current-Paths in a Conductor .... 

44. Current- Curves and Tension-Curves 

45. Dn Bois-Reymond's Diverting Cylinders 

46. Measurement by Compensation of Differences in Tension 

47. Du Bois-Reymond's Round Compensator 

48. Diagram of Electric Measurement by Round Compensator 

49. A Regular Muscle-Prism 

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

51. Tensions on the Longitudinal and Cross Sections of a 

Regular Muscle-Prism 

52. Tensions in a Regular Muscle-Rhombus 
63. Currents in a Regular Muscle- Rhombus 
54. Currents in the Gastrocnemius 
65. Muscle-Current during Pulsation 
56. Deflection of the Magnetic Needle by the Will 
57 and 58. Secondary Pulsation .... 

59. Tension in Nerves 

60. Changes in Tension during Electrotonus . 

61. Theory of Magnetism 

62. Diagram of a Piece of Muscle-Fibre . 

63. Diagram of the Electric Action in an Aggregation of 

Muscle-Elements . . . . 

64. Diagram of an oblique Cross- Sect ion . 



TACIC 

97 
104 
106 
112 
114 
127 

130 
133 
140 
147 
149 
159 
161 
163 
166 
170 
172 
173 
175 
178 
181 
184 
186 
187 
190 
192 

193 
195 
196 
200 
203 
205 
210 
217 
220 
230 
231 

233 
234 



LIST OF WOODCUTS. 



XV 



Go. Magnetic Induction 

66. Magnetic Induction 

67. Nerve-Terminations in the Miiscles of a Guinea-Pig 

68. GangHon-Cells from the Human Brain 

69. Graphical Representation of Muscle-Extension 

70. Representations of Positive and Negative Values 

71. Action of Oblique Muscle-Fibres .... 

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

73. Duration of Inductive Currents .... 

74. Helmholtz's Arrangement with a Sliding Inductive Appara 

tus 

75 J , B, C. Secondary Pulsation from the Nerves 



PAGE 

242 
243 
245 
266 
295 
296 
297 
302 
305 



307 



oio 



GENEEAL PHYSIOLOGY 

OP 

MUSCLES AND NEEVES. 

a-o'^^oo 



CHAPTEE 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 
ditferentiation 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 PHYSIOLOGY OF MUSCLES AND NERVES. 

of a different kind. The contraction of a polyp when 
touched and the voluntary movement of the 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 lind that special organs are formed to 
serve principally for movement. Such are the muscles, 
which form what is ordinarily called 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 motion occur 
in exactly the same way in the plant as in the animal 
organism. 

These movements are most evident, and are most 
easily explained in the sensitive plant {M imosa pudica). 
The stem and branches of the sensitive plant bear leaf- 
stalks, each of which again bears secondary leaf-stalks, 
to which latter the individual leaflets are attached. If 
the plant is shaken, the leaf-stalks suddenly bend and 
sink, the upper surfaces of the two halves of each leaflet 



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 iibres 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 that the 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 w^hen the under 
side of the node becomes slack. Before, however, w^e 
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 AND NERVES. 

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 
by the fact that perfectly inanimate bodies, for instance, 
the carbon particles of finely rubbed Indian ink, exhibit 
the same movement. The effect is, in fact, due merely 
to currents in the fluid, by which the light particles 
suspended in the fluid are carried away. Such currents 
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 activities 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 bodies. 

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 bodies, moving tremulously about 
with greater or less rapidity. It is often hard to 
distinguish whether the motion seen in these latter is 
independent or molecular. It must be observed whether 
of these bodies two contiguous individuals always pass 
along in the same direction, or whether their move- 
ments 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 jproto'plasr^i} 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 Imnp 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- 

* 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. 



b rilYSIOLOGY OF MUSCLES AND NERVES. 

tion in this case occurs in two ways. Sometimes single 
processes are seen to protrude from the whole mass ; 
these 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 way 
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 processes. ^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. 






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Fi(i. 1. A.M(i;r..K. 
a. Amoeba verrucosa, b. Amceba poiTccta. 

5. Movements entirely similar to those in these 
independent living animals, called Amoehw^ occur in 



PROTOPLASMIC AND AMCEBOID MOVEMENTS. 7 

more higlilv 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 Aonoeha3. 
jNIost 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 
Amoebce, and which move like the latter. It is a well- 
known fact, that when a drop of blood is placed under 

^>U' ^•'-' 

a 

w 

Fig. 2. White blood-corpuscles from a guinea-pig. 
a, b, c, Vai'ious foiius assumed by one 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 Amcxbce, and which have, there- 
fore, been called Artioehoid miovements. The corpuscles 
send out processes and again retract them ; they creep 
about on the glass ; and, in short, they behave exactly 




8 PHYSIOLOGY OF MUSCLES AND NERVES. 

like Amoehcc, and like the latter they even absorb matter, 
such as granules of any colouring substance which may 
have been added, from the blood-fluid — they eat, 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, may 
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 closed 
sac or pouch, over the inner surface of which protoplasm 
is spread in a thin layer. Even this represents a much 
more advanced modification of the protoplasmic mass, but 
yet the protoplasm still retains its power of indepen- 
dent motion. Wave-like movements are seen to pass 
over the mass of the protoplasm, and by this, just as in 
the Amwbce, 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 cur- 
rent separates itself into two, others unite, and so on. 
If the protoplasm dies — and this may be artificially 
caused by the application of heat — all motion ceases. 
It is inseparably bound up with the vital powers of the 
cells. 

6. The free protoplasmic mass, as seen in the 
Amoeba, is one of the simplest of organic forms. Such 
masses sometimes occur in groups, which thus repre- 
sent colonies of organisms, each of the components 
of which, however, retains complete independence, 
and is exactly like every other. Sometimes, however, 
modification takes place amongst these ; and when 
these modifications advance at an unequal rate in 
the separate members of the colony, a composite or- 



ELEMENTARY ORGANISMS : DIFFERENTIATION OF TISSUES. [) 



> 



ganism witli 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 ; 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, w^hen 
occurring in fixed bodies, to move foreign matter — that 
is, for the drawing in of food. 
2 



10 



PHYSIOLOGY OF MUSCLES A^'D ^'ERYES. 



7. If a light powder — such, for instance, as finely 
powdered charcoal — is spread over the skin of the 
palate of a living or a recently killed frog, the powder 
is seen to advance with some speed towards the gullet. 
Microscopic examination shows that this skin is studded 
with a dense layer of cylindrical cells standing, palisade- 
like, side by side. The free surface of each of these 
cells is studded with a large number of delicate hairs 





Fig. 3. 
a. Ciliated cells, pointed be- 
low, and, with other cells, 
attaclied to the mem- 
brane. 



b. A single ciliated cell, more 
enlarged ajid of some- 
what more modified form. 



or cilige, which are in continual motion in a definite 
direction in such a way that they propel all such liquid, 
together with the particles contained in this, as adheres 
to their upper surface in that direction. This is calle(f 
ciliary motion. It occurs very frequently in the animal 
body, e.g. in the windpipe and its branches, where the 
motion is upward, serving to propel the phlegm to the 
larynx, from which it can be thrown out by coughing. 



CILIARY MOVEMENT. 1 1 

lu many fixed animals of low order a crown of cilije 
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 cilige, 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. 

None 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 MUSCLES A?s"D NEKVES. 



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. Elas- 
ticity of the muscles. 

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 pro- 
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 thus 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 the 
space within these cavities, so that the contents of the 
latter are thus forced onward. In any case, muscles 
always serve to produce movement — either of the limbs 
in opposition to each other, or of the whole animal, or 
of the substances contained within the cavities. 

We must first confine our attention to those muscles 
which are attached to bones, and which are therefore 



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, 




a 



^33.33C!.^XXX3 




d 



Fig. 4. Stkiatkd musclk-fibrks. 

fl. Two fibres cut tlirough in tlio middle, and passing, on the left, into tendons, b. A 
single muscle-fibre deprived of its discs, and separating into fibrilliE. c Two 
single fibrilljB. 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 microscoj)e, it appears as a pouch, 
consisting of a firm, solid wall, with certain contents ; 
and this contained matter exhibits alternate lighter and 



/ 



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-ag^nts which split up the fibre in a longitudinal 
direction, so that it separates into extremely delicate 
smaller ^6?'es or fibrillce 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- 
loid structure actually exist in the muscle-fibre itself; 
it must rather be assumed that both forms of structure 
are 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 we may also call it, the living muscle-fibre 
really is. Eecent 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.^ 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 

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



16 rHYSIOLOGY OF MUSCLES AND NERVES. 

each other. Briicke, therefore, supposes that the muscle 
substance is in itself homogeneous or uniform, but that 
in it are inserted small particles which are of double- 
refracting power. When these particles are massed in 
large numbers, and are regularly arranged, they refract 
the light doubly, so that the whole of that particular 
part seems to refract doubly, while the intermediate 
parts, since they contain few or none of the particles 
in question, continue to refract simply. These latter 
parts, however, when seen under ordinary unpolarised 
light, so that it is impossible to judge of their powers 
of double refraction, appear lighter, while the former 
appear darker ; and so together they cause the striated 
appearance of the muscle. 

3. In one of these muscle-fibres it is necessary to 
distinguish the contained matter and the containing 
pouch. The latter is called the muscle-fibre pouch, or 
sarcolemvia. In it, especially after the addition of 
acetic acid, which causes the whole fibre to swell and 
become more transparent, a number of longish pointed 
kernels (jiiiiclei) 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 long closed sac, the white cords mentioned 
above attach themselves, and these are completely 
coalescent with the sarcolemma. 

They consist of strong slender threads of the nature 
of the so-called connective tissue. As a considerable 
number of muscle- fibres constitute the trunk of the 
muscle, these threads also unite into cords which are 
called the muscle-tendons. They are sometimes short, 
sometimes long, 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 



.,111^'f 



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 nmscle is 
capable of two different movements : it can either 



/.' 



Fig. 5. The double-iikaded 
CALF :mus(;lk (M. gastiome- 

mhis), WITH ITS TWO TEN- 
DONS. 

a, a. The two lieals. c. The com- 
nri'^ncement of the tendon which at 
k is attached to tlie heel-boue. 



18 PHYSIOLOGY OF MDSCLES AND NERVES. 

stretch the knee, previously bent, so that the upper 
and the lower thigh-bones are in a straight line ; or it 
can raise the whole extended leg yet higher and bring 
it nearer to the pelvis. But the points of origin and 
of attachment of muscles may exchange offices. 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. Fiat bones, as their name indicates, 
are expanded chiefly in two directions ; they form thin 
plates. Short bones are expanded almost equally and 
but slightly in all three directions. In long bones, 
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 elbow bone and 
the radius), which together form the fore-arm ; and 
secondly, by means of several shorter bones, wdiich con- 
stitute the WTist, the hand itself; this latter consists of 
the five bones of the palm and the five fingers, of which 
the first has two, the others each have three divisions. 
In all these bones, with the exception of those of the 
wrist, a l^ng middle part, or shaft, with two thickened 
ends, are noticeable. As this shaft is hollow, these 
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 forw^ard in any 
direction. The socket in this 
ease 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. g. The boxes of the 
where it ends in a ball-shaped 

surface which is applied to a "■ ^^S.lLT TbIZT ,t 
corresponding socket surface in ll%lTeT^^L:lS::^r'' ""' 
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 U23per and fore arms. These are called 
hinge-sockets. They serve to increase or decrease the 




20 PHYSIOLOGY OF MUSCLES AND NERVES. 

angle between the two parts. To mention all the 
various forms of sockets and the movements which they 
allow would lead us too far ; it is sufficient to have 
shown that the action of the muscles is affected by the 
bones between which they are extended. In order, how- 
ever, to examine the contractile power of muscles, the 
latter may be detached from the bones and examined 
b^ themselves. 

The muscles of warm-blooded animals are but ill- 
adapted for this purpose ; fortunately, however, those of 
cold-blooded animals not only possess the same qualities, 
but retain the power of contraction long after their re- 
moval from the animal, a circumstance which renders 
them very valuable for purposes of study. The frog is 
most frequently used in such experiments, both on 
account of its common occurrence and of the power of 
its muscles. If a frog is beheaded and an entire 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- 
presenting as it were the bone, by the motion of which 
the contraction of the muscle may be studied.^ Weights 
may also be attached to this lever in such a way that 
the burden which the muscle is capable of lifting may 
be studied. It will at once be observed that the muscle 
is extended when such weights are attached, and is 
extended more in proportion as the weight attached 
is heavier. This results from the elastic qualities of 
muscle ; and before examining the contraction of muscles 
it will be necessary carefully to study their elasticity. 

' In order to fasten tlic muscle more securely, it is generally 
well to leave a small piece of the bone at either end attached to the 
tendons, and to fasten 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 Ipnger. 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 OF MUSCLES AND NERVES. 

one square centimetre, we may assume that this con- 
sists of a hundred rodlets of equal length, lying side by 
side, the cross-section of each of which measures ex- 
actly one square millimetre. On attaching a weight of 
one kilogramme ( = 1000 gr.) to this rod, each one of the 
hundred thin rodlets would have to bear a weight of 
but ten grammes. Comparing with this the tension of 
another steel rod of the same length, but of which the 
cross-section measures twice as much, we may assume 
that this second rod is composed of two hundred minute 
rodlets, the cross-section of each of which measures one 
millimetre. The weight being now distributed between 
two hundred of these rodlets, each has to support a 
weight of only five grammes. This explains why the 
tension by the same weight 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 views 
of modern physicists every body consists of a number 
of small molecules or particles 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 
by these means slightly separated from each other. 
The sum of all these small separations represents that 
whole extension measurable at the end. The long-er 
any given body is, the greater is the number of these 
small particles which occur in its whole length, and 
consequently the greater must its extension be, pro- 
vided all other circumstances are equal. 

P'rom these observations may be deduced a law as 
to elastic tension, which is further confirmed by accurate 
researches, and this law is that the tension is directly 



ELASTICITY OF MUSCLES. 23 

proportionate to the length of the body extended, and 
to the amount of the extending lueights ; 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 sc^uare 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 



24 PHYSIOLOGY OF MUSCLES AND NERVES. 

former also exhibit another peculiarity. If a weight ig 
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 the weight 
is removed the steel resumes its original length. It is 
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 gradual extension of organic 
bodies. It takes place in very considerable degree in 
muscle, and natm*ally 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 muscular extension. The latter can be most 
accuratel}' read by means of the apparatus invented by 
du Bois-Reymond, represented in fig. 7. The muscle 
is firmly fastened to a fixed bearer, its upper tendon 
being fixed in a vice. A small, finely graduated rod is 
fastened to the lower tendon by means of a small hook. 



ELASTICITY OF MUSCLES. 



20 



Below the graduations the rod branches into two 
arms, which again re -unite at a lower pointy 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 tw^o 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 obser\^ed. Of 
course, in calculating the ex- 
tensibility from the figures thus 
obtained, the weight of the ap- 
paratus attached to the muscle must be taken into 
consideration. 




Fig. 7. Du Bois-KKYMOxn's 

APPARATUS FOR THE 

STUDY OF ELASTIC EX- 
TENSION IN MUSCLE. 



26 



PHYSIOLOGY OF MUSCLES AND N'ERVES. 



Experiments in muscular elasticity may also be made 
with the apparatus briefly described above, by measuring 
the extensions of the muscle by the variations of a lever 
attached to it. The easiest way to do this is by fasten- 
ing an indicating apparatus to the lever in such a way 




Fig. 8. Simple myogi£Aph, 



that it traces the movements of the lever on a plate of 
smoked glass placed in front of it. This apparatus is 
called a myograph, or muscle-writer. Fig, 8 represents 
it in the simplihed form adopted by Pflliger. The body, 
the elasticity of which is to be examined, is firmly fixed 



ELASTICITY OF MUSCLES. 27 

in the vice (7, and is connected witli 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 MUSCLES A:SD NERVES. 



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. 



o 



1. If a muscle is cut from the body of a frog, and 
is fastened into the myograph just described, it never 
shortens spontaneously. If this does seem to happen, it 
may safely be assumed that some accidental and un- 
perceived external cause has influenced it. A muscle 
may, however, always be induced to shorten by 
pinching it with tweezers, by smearing it with strong 
acid, or by bringing certain other external influences, 
the nature of which we shall presently learn, to bear 
upon it. Muscle, therefore, never shortens sponta- 
neously, but it can always be induced to do so. This 
quality of muscle enables us to produce the state 
of contraction at pleasure^ and to examine accurately 
the nature and method of the conditions which give 
rise to it and the phenomena by which it is accom- 
panied. 

The myograph which, by means of the indicator 
attached to it, marks the contraction of the muscle on 
the smoked glass plate, and at the same time affords 
opportunity for measuring the extent of the contraction, 
will presently prove of yet greater service. But for 




29 



Q 
O 



I 

CO 

o 

Q 

D 
m 



Hi 

O 
I-] 

O 

CO 

S 

1^ 

a 



d 



30 niYSIOLOGY OF MUSCLES AND NERVES. 

our present purpose — which is to discover whether or 
not contraction takes place under certain circumstances 
— it is hardly adapted. It may, therefore, be replaced 
by another apparatus, arranged by du Bois-Eeymond 
especially for 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 with a 
thread running over a reel. The reel supports a long 
indicating- hand to which a coloured disc is attached. 
The muscle in shortening turns the wheel and lifts the 
disc ; and this is easily seen even 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 cause the contraction of the 
muscle, such as pinching or smearing with acid, are 
called irritants^ and the muscle is said to be irritable, 
because contraction can be 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 disadvantao^e. If the vice which holds 
the upper end of the muscle and the hook to which the 
lower end is attached are fastened to the two coatings 
of a charged Kleistian or Leyden jar, the charge acts at 
the moment at which the connection is formed, and 
an electric shock 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 Kleistian 
jar. But similar electric shocks may be more con- 



IRRITABILITY OF MUSCLES 31 

veniently 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 B, 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 batterj' by means of the \\ires 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 thinof occurs when the current in the coil A 
is again closed ; so that this electric irritant affords an 
easy and simple means of causing this sudden con- 
traction of the muscle at pleasure. This contraction 
may be called a 'pulsation i 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. 



32 PHYSIOLOGY OF MUSCLES AND NERVES. 

An electric current from the battery itself is also 
capable of acting as an irritant on muscle. If the poles 
of the battery are connected with the muscle, a constant 
current passes through it. If one of the connecting 
wires consists of two parts, a capsule filled with quick- 
silver may be 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 
of a hook so as to allow it to be easily immersed in, and 
again withdrawn from, the quicksilver. This makes 
it easy to close the current within the muscle, and 
to interrupt it again at pleasure. At the moment 
at which the current is closed, a pulsation is observed 
entirely similar to that which would be produced by 
an electric shock. The muscle contracts, and the disc 
is jerked upward and then falls again. But it does 
not return quite to its original position ; it remains 
somewhat raised, thus showing that the muscle is now 
continuously contracted ; and this contraction lasts as 
long as the current passes iminterruptedly through the 
muscle. 

If the current is interrupted, a pulsation which 
jerks the lever upward is sometimes but not always 
observable ; the muscle then, however, resumes its 
original length, which it retains until it is irritated 
anew. 

2. These experiments show that muscle exhibits 
two forms of contraction : the one, which we called pul- 
sation, is of short duration ; the other, which is produced 
by a constant electric current, endures longer. This 
more enduring form of contraction may, moreover, be 
yet more conveniently produced by allowing an irritant 
such as in itself would only produce a single pulsation 



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 -iT Fig. 11. Electric Wheel. 

Wire 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 




34 



PflYSIOLOGY OF MUSCLES AND NERVES. 



traction of this sort is called tetanus of the muscle to 
distinguish it from a series of distinct pulsations. 

Another method of frequently and repeatedly clo- 
sing and opening the current is by means of a self- 
acting apparatus which is put in motion by the current 
itself. This, which is called Wagner's hammer, is re- 
presented in fig. 12. The current of the chain is con- 
ducted through the column 
represented on the right to 
the German silver spring o o. 
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 current 
passes from this to the coils 
of a small electro-magnet, 
and, after passing through 
this, back to the chain 
through the clamp connected with it on the left. An 
armature of soft iron, n, fastened on to the spring 
o o, is suspended over the j)oles of the electro-magnet. 
This iron being attracted by the electro-magnet, the 
small plate c is forced away from the point and the cur- 
rent is thus interrupted. In so doing, however, the 
electro-magnet parts w^ith its magnetism, and conse- 
quently relinquishes its hold upon the armature ; the 
plate is thus again pressed by the action of the 
spring against the point. The current being thus again 
closed, the electro-magnet recovers its force, again at- 
tracts the armature, and again interrupts the current ; 
and these processes are continued as long as the chain 
remains inserted between the column on the right and 




Fig. 12. Wagner's Hammer. 



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. ^ 

Wagner's hammer in a more simple form may be 
permanently connected with coil xi. In this case it is 
best to place the second coil 5 on a sliding-piece which 
is so arranged that it can be moved along a groove to a 




Fig. 18. Thk sl.lDl^G inductive apparatus. 

(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 ; 6 is the 
electro-magnet ; h the armature of the hammer ; / is 
a small screw, at the point of contact of which with the 

' In order to set Wagner's hammer itself in motion, these clamps 
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 OF MUSCLES AND NERVES. 



small plate soldered on to the surface of the German 
silver sj)ring the current is closed and interrupted. An 
apparatus of this kind is called a sliding inductorium. 
It is only necessary to attach the ends of the coil i to 
the muscle, and to insert the chain between the columns 
a and g. The action of the hammer then at once 

commences ; the inductive cur- 
rents generated in c pass through 
the muscle, which contracts te- 
tanically. 

Instead of connectinor coil c 
immediately with the muscle, it 
is better to carry the wires from 
the coil to the two clamps h and 
c in the apparatus shown in fig. 
14, which is called a tetaiiising 
key. Two other wires pass from 
these same clamps h and c to the 
muscle. When the inductive ap- 
paratus is in action the muscle is 
put into a tetanic condition. But 
as soon as the lever d is pressed 
down, so as to connect h and c 
together, the current of coil i is 
Fio. 14. Tktanising key of enabled to pass through this le- 

DU lioiS RliYiMOND. rrii 1 7 1- i n 

ver. Ine lever a bemo- made of 
a short and thick piece of brass, which offers hardly any 
resistance to the current, while the muscle on the con- 
trary offers great resistance, very little of the current 
passes through the muscle, but nearly all through the 
lever cL The muscle, therefore, remains at rest. As 
soon, however, as the lever d is again raised, the in- 
ductive currents must again pass through the muscle. 




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 



38 



PHYSIOLOGY OF MUSCLES AND NERVES. 



key so as to allow the inductive 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 
weight is small the height to which it is raised is great. 
As a rule, as the weight increases, the height to which 
it is raised becomes less, and finally, when a certain 
weight is reached, it becomes unnoticeable. Fig. 15 







50 



100 



150 



200 



250 



Fig. 15. Height of elevation consequent on the application of 

varying weights. 

shows the result of a series of experiments of this sort. 
The figures under each of the vertical strokes represent 
in grammes the amount of the weight raised ; the height 
of the strokes is double the real height of elevation, 
the apparatus employed in the experiment representing 
them twice their natural size. Between each two of 
the experiments the glass plate was pushed on a little 
further in order that the separate experiments might 
be indicated side by side. In finding the first of 
these heights of elevation, under which stands an 0, no 
weight was applied, and even the weight of the indi- 
cating lever was neutralised by an equivalent weight. 
It appears, therefore, that the heiglit of 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 
case, 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. . 
Height of elevation . 14 
AVork accomplished . 

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 ; w^hen 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 



50 


100 


150 


200 


250 gr. 


9 


7 


5 


2 


mm 


450 


700 


750 


400 


mm 



40 THYSIOLOGY OF MUSCLES AND NERVES. 

not always the same in the case of different muscles. On 
comparing thick with thin muscles, it appears, in the first 
place, that the extension in the case of thick muscles be- 
comes less in proportion as the weight applied increases ; 
and that the decrease in the height of elevation corre- 
sponding to the increase in the weight applied proceeds 
less rapidly ; so that much greater weights can be raised 
by thick than by thin muscles. On the other hand, it 
appears that in the case of muscles of equal thickness 
the height of elevation is greater in proportion as 
the muscle-fibres are longer. Under an equal weight 
the height of elevation increases proportionately with 
the length of the muscle-fibres. 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 
by a muscle, 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 back after each pulsation to its former 
height. The muscular work accomplished at each pul- 
sation is, therefore, cancelled. It is probably converted 
into warmth. It is, however, possible to retain the 
weight at the height to which it was raised by the muscle. 
A. Fick' accomplished this very ingeniously by causing 
the muscle to act on a light lever, which moves a wheel 
each time it rises, but leaves the same wheel undis- 
turbed when it again sinks. A thread, on which the 
weight hangs, passes over the axis of the wheel. The 
effect of this arrangement is that the muscle at each 
pulsation turns the wheel slightly, and thus slowly 
raises the weight. If the muscle is made to pulsate 
frequently, the weight is raised 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, 



42 PHYSIOLOGY OF MUSCLES AND NERVES. 

they accomplisli no work in a mechanical sense. Yet 
everyone knows the difficulty of holding a weight long 
in this position ; the sense of weariness which very 
soon makes itself felt shows that work in a physiological 
sense is really done. The kind of work thus accom- 
plished may be spoken of as the internal work of the 
muscle, 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 durirtg its active con- 
dition, we find that chemical processes occur witLin 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 acts 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 active state, 
and the energy released by this chemical process is 
the source of the work accomplished by the muscle. 
The production of warmth in a muscle can be shown 
even during a single pulsation; but this production 
of warmth is far more noticeable during tetanus ; 
and as warmth is but another form of motion, we may 
infer from this that the whole force resulting from 
the chemicnl process is converted into warmth during 
tetanus ; while during the raising of a weight at the 



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 df the fate ; or by inserting the little 
finger 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, 
tlie 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 eiTect the note, though the external form re- 
mains unchanged. A somewhat similar phenomenon 
is observable in rods when caused to vibrate longitu- 



44 PHYSIOLOGY OF MUSCLES AND NERVES. 

dinally ; for these also emit a sound although no change 
of form is externally perceptible. 

This raises a question as to how many of these irri- 
tations are really requisite in order to bring a muscle 
into an enduring condition of contraction. By means of 
Wagner'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 
18 distinct irritations in each second are quite sufficient to 
cause a constant contraction of the muscle. In a living 
body also, where the muscles are voluntarily contracted, 
the condition of tetanus appears to be produced by the 
same number of irritations. It has been found that the 
height of the muscle-note heard during voluntary con- 
traction of the muscles is about equal to c* or d^, which 
represents from 32 to 36 vibrations in the second. But 
Helmholtz was able to show, with great probability, 
that this is not the true number of muscle-vibrations, 
but that the vibrations within 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 vibrations.^ 

6. As yet we have noticed only the shortening of 
muscles. This alone determines the amount of labour 
accomplished, which consists in raising weights. Bat 
on looking at a contracted muscle, it is evident that 
it has become, not only shorter, but thicker. This 

• According to Preyer, some men are capable of distinguishing 
notes of as many as fifteen to twenty-five vibrations per second ; 
and, according to tlie same authority, the muscle-note sounds very 
like that produced by from eighteen to twenty vibrations per 
second, which corresponds very well with the views of Helmholtz 



ALTERATION IN FORM DURING CONTRACTION. 45 

raises the question whether the muscle in contracting 
has undergone no cliange 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 
v^er}'^ 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. 

Remembering, 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. 

^lore 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 



46 PHYSIOLOGY OF MUSCLES AND NEEVES. 

the incomplete apparatus which they were then alone 
able to command, they were unable to induce an en- 
during irritation of the muscle ; and they, therefore, 
confused the state of relaxation with that of contrac- 
tion. 



CHAPTER lY. 

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 must 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 



48 



PHYSIOLOGY OF MUSCLES AND NERVES. 



to it, when it is in a quiescent state ; the other, when 
it is active. AVhen a quiescent muscle is brought into 
an active condition by irritation, it assumes a form 
which is no longer natural to it, it strives to attain the 
latter, and shortens until it reaches its new form, which 
is then natural to it. If the muscle is extended by 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 new form. 
Let us imagine that A B, in fig. 16, is the length of 



./' 



A 



y, 



/' 



Z^ 





c 


I 


r' 


r" 


C" 






, ' . 


x^ 


I" 


d" 


,1'" 






(/ 




\^^ 


/// 










^"^-v^ 


(, 






/i^ 


~-~~- 


.^_____^^ 


^"-^.^^^ 










/y 


''*"*"^-- 


- — ^""'~^--~ 


 


— 



Fio. 16. Alteration' in Elasticity during contraction. 



3 



the muscle when quiescent and unburdened, and that 
^ 6 is the length of the muscle when active and un- 
burdened. Then the muscle, if it is irritated while 
unweighted, will shorten to the extent represented by 
AB— Ah = hB; b B is, therefore, the height of 
elevation of the unweighted muscle. If a weight p is 
attached to the muscle, the latter in its inactive condi- 
tion will be extended to a certain degree {B^ d') ; so 
that its length will now be A B + B' d'= A' B\ On 
being now irritated, it contracts and assumes a length 



ALTERATION IN FORM DURING CONTliACTION. 49 

which must equal A ^ -h 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 
elevation of the muscle when the weight id 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 apph'ed 
= o, is, therefore, greater than the height of elevation 
b' B\ with the weight id. It therefore follows that the 
extension cb' must be gi'eaterthan 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 5^^. This point 5^% 
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.^ 

Yet another point of gi'eat interest is observable in 
studying this alteration in the elasticity. When a cer- 
tain weight, k, 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 
* See Xotes and Ad'litions, No. 1. 



50 PHYSIOLOGY OF MUSCLES AND NERVES. 

the quiescent muscle when unweighted. If an experi- 
ment is successfully arranged so that an inactive muscle 
is not extended by the weight h — by fastening the latter 
to the muscle, but immediately supporting it, so that 
it does not extend the muscle — and if the muscle is 
then irritated, it is evident that the muscle is incapable 
of raising this weight from its support. By finding the 
weight which is exactly sufficient to effect this, 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 condition. This 
energy is called the force, of the muscle. A method of 
accurately determining this will presently be 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. But it is very hard to observe the 
alteration in form during the very short time which is 
occupied by one of these pulsations. Means of drawing 
very accurate conclusions even on this point have, how- 
ever, been found, especially since Helmholtz turned his 
attention to the matter, in 1852. 

Various methods are employed in experimental re- 
search to measure very short periods of. time acciuately, 
and to study processes which occur even within the 
shortest periods. Not 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 also been done in the case 
of the yet 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 

w^-oWo ^^ ^ 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 -^p^ 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 
comjDared with the waves drawn by the vibrating 
instrument, the duration of time may be accurately 



52 



niYSIOLOGY OF MUSCLES AND NERVES. 



determined. The myograph of Helmholtz depends on 
this principle. Originally it consisted of a glass cylin- 




FiG. 17. Myograpit of Helmholtz. 

(Oue quai'tLT natural size.) 

4 

der which rotated rapidly on its own axis. The appa- 
ratus has, however, since undergone many alterations. 



THE MYOGRAPH. 53 

¥ig. 17 represents it in the form given to it by du Bois- 
Eeymond. 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 sl 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 bv 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 MUSCLES AND NERVES. 

point of contact, and also throug-li the primary coil of 
an inductive apparatus. The secondary coil 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, By press- 
ing the finger on g, the bayonet- shaped point I rday be 
slightly raised, the index point e being at the same time 
slightly removed from the cylinder. The clockwork 
is then set in motion. The cvlinder turns, at first 
slowly, but gradually more quickly ; but the muscle 
remains inactive, and the point can make no mark. 
As soon as the cylinder has attained the desired speed 
the finger is removed ; I 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 
cvlinder durinof 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 cylinder 
is in that position in which the nose has just touched 
the end of the lever I. It is evident that this posi- 
tion is the same as that at which the muscle was at 
first allowed to pulsate when the cylinder stood still. 
The vertical line then drawn, therefore, indicates 
exactly the position of the cylinder at the moment at 
which irritation takes place. Where this vertical line 
deviates from the horizontal line first drawn is the 
point at which the pencil was when irritation was in- 
duced in the muscle. The distances from which the 
periods are to be calculated must be measured 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 reofistration 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 w^ay 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 



5Q THYSIOLOGY OF MUSCLES AND NERVESo 

did not begin at the point z, but at some little distance 
beyond this, at a. From this it is to be inferred that 
the contraction of the muscle did not begin at the 
moment of irritation, for it is evident that the cylinder 
of the myograph had time to turn from z to a before 
the indicator was raised by the contraction of the 
muscle. A certain time, therefore, elapses before the 
change produced in the muscle by irritation results -in 
contraction. The duration of this time — which can be 
accurately calculated from the length of the space exist- 
ing between z and a — is about one-hundredth of a 



/T a C 

Fig. 18. The curvks of a muscle-pui.satiox. 

second. This stage is called that of latent irritation, 
for during it the irritation has not yet become actively 
efficient 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 6, which is the highest 
part of the curve described ; from that point onward 
the muscle again lengthens till it resumes its original 
length at the point c. The time which elapses between 
the beginning of the contraction and its maximum 
is called the stage of increasing energy ; the time from 
this maximum to that of the full re-extension of the 
muscle is that of the stage of decreasing energy. The 
whole duration of the muscular pulsation from the 
commencement of the contraction at a till complete 
extension is again reached at c, is 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 
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- | ^ 

flection 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 w^hich 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 orravitation, the mao-netic 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- 
tinuous electric current be conducted 
to a magnetic needle, the current 
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 
maofnetism of the earth counterbalancino- each other. 
If, however, the current, instead of acting continuously, 

acts only for a short time, the magnetic needle suffers 
4 




Fig. 19. Mkasure- 
imknt of smalt, 
angles of deflec- 
tion with mirkor 

AND LENS. 



58 PHYSIOLOGY OF MUSCLES AND NERVES. 

a push of but short duration and makes only a single 
vibration, after which it retiurns to the position proper to 
it when at rest. The degree of deflection must in this 
case be proportionate 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 the 
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 Gauss 
is used. A small mirror o being connected with the 
magnet, a graduated scale 8 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 aj'ranged 
at right angles to the direction of the mirror and of the 
scale, it is evident that exactly the point a on the 
scale which lies over the centre of the magnifying 
glass will be seen reflected in the mirror. As soon as 
the magnet with the mirror attached to it turns, the 
reflection 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 
which 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 be 
calculated. 

4. This method, by which the duration of electric 
currents may be measured with the greatest accuracy, 
must now be applied to our task of examining the 
duration of a muscle-pulsation. For this purpose we 
must find some 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 Jc^ the former 
with Jv, 

If the current which is to act on the swingfino- mas*- 
net is inserted between k and Jc\ 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 



60 



PHYSIOLOaY OF MUSCLES AND NERVES. 




Fig. 20. ArpAUATus for mkasurtng the duiiation of jiuscle- 

COXTR ACTION. 



MEASUREMENT OF TULSATION 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 jp 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 
Hg can be raised or lowered by means of the screw s. 
If the level of the quicksilver is raised so as to immerse 
the point g, and if it is then again lowered, the quick- 
silver, by adhesion, remains hanging from the amalga- 
mated point, and is by this means drawn out in the 




Fro. 21. The kxd of the lever of 

THE APPAIIATUS FOR TIME MEASURE- 
31ENT, TOGETHER WITH THE Qt'KK- 
SILVEU CAPSULE. 



62 



PHYSIOLOGY OF MUSCLES AND NER\ES. 



form of a thin thread, through which the current may 
pass. When, however, the muscle shortens the quick- 
silver is torn away, and resumes its ordinary convex 
sm'face ; and when, on the extension of the muscle, 




Fig. 22. Diagram of experiment for the electric measuremlni' 

OF time. 

the lever again sinks, though the point p again rests on 
the platinum plate, yet the point q remains separated 
from the quicksilver by an intermediate air-filled space, 
and the current remains permanently interrupted. 

It still has to be explained how the irritation of the 
nuiscle and the closing of the 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 J 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, a' b% and is 
pressed by a spring against the platinum plate a. At 
the other end of the lever is the platinum plate b\ 
which is connected with the battery^. 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 j^latinum 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^ V is raised, 
and the current of the chain K is interrupced. This 
produces an inductive current in the coil J"', 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 MUSCLES AND NERVES. 

we called the stage of latent irritation. When, how- 
ever, weights are placed on the scale of the apparatus 
(fig. 20), the resulting 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 jp 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 by 
the weiofht on the lever. As the muscle strives to draw 
up the lever, while the weight, on the other hand, draws 
it downward, the greater force obtains the mastery. 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 so 
doing to interrupt the current which determines the 
time. If, in a series of consecutive experiments, heavier 
weights are 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 the muscle attains a tendency to con- 
traction equivalent to the weight. We will call this 
force the energy of the muscle. So long as the muscle 
does not contract at all — that is, throughout the stage 
of latent irritation — its energy = 0. 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 slowly, reaching its maxi- 



BURDEN AND OVER-BURDEN. 65 

mum in about one-tenth of a second. The maximum 
having been reached, the muscle is unable to contract 
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 v»hich the latter necessarily 
raised as soon as it strove to contract; but these weights 
did not act upon the muscle aa 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 
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 niYSlOLOGY OF MUSCLES AND NERVES. 

determined by inserting a chain and an electro-magnet 
between the vices k and h\ The electric cmTcnt then 
passes through the platinum point, the correspond- 
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 
niinute contractions of the muscle are recognised. If 
the weights which act as over-bm*den, and counter- 
balance the tendency to contraction in the muscle, are 
gradually increased, a limit is reached at which, in spite 
of the irritation of the muscle, the current of the 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 — may be found. This extreme 
limit of its energy is called the force of a muscle. It 
is the same in amount as that Avhich we theoretically 
inferred (p. 48) from the change in the elasticity of 
a muscle during contraction. Each muscle has a definite 
force dependent on the conditions of its nourishment 
and on its form. On comparing the muscles of the same 
animal, it appears that the force is dependent in no way 
on the length of the muscle-fibres, but on the number 
of these fibres, or, in other words, on the diameter of 
the muscle ; and that the force increases in exact pro- 
port ion 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.^ It has 
been found that in the muscles of the frog the force, 
for a diameter of I 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 kilogTammes 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, 



* The following method, adopted by Ed. Woher, 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. 



68 



PHYSIOLOGY OF MUSCLES AND NERVES. 



and that the force — the tension exercised bj the muscles 
of the calf — acts obliquely on the lever. It is of course 
impossible to determine the diameter in a living man ; 
it must be observed in a dead body of about the same 
size as that of the person experimented on. 

Henke also has lately determined the value of the 
absolute force of human muscle. He used the flexor 
muscles of the forearm (cf. fig. 23) to determine this. 
In the figure, a represents the upper arm, b the fore- 
arm — the former being in a ver- 
tical, the latter in a horizontal 
position ; c represents the muscles 
which raise or bend the forearm. 
(There are in reality two of these 
muscles, 31, biceps and M, bra- 
chialis internus). Supposing that 
the muscles are stretched, and 
weights are placed on the hand 
till the muscles are no longer ca- 
FiG. 28, DiAGHAM OF THK pable of raislug the hand, then, 

FLEXOU MISCLES OF THE : x „ • j.1 • j 'i.! 

FOREAUM. .1^^^^ ^^ ^^^ ^'^^ experiments with 

the muscles of frogs, equipoise is 
obtained between the tendency of the muscle to con- 
tract and the weight carried. Care must, however, be 
taken that the muscles act on a long lever arm, the 
weight on a short one, and the weight of the forearm 
itself must also be taken into consideration. Due at- 
tention being given to all these circumstances, and to 
the diameter of the muscles when drawn into action, 
Henke calculated that the absolute force in human 
muscle is equal to from six to eight kilogrammes. Ex- 
perimenting in a similar way on the feet, he found 
somewhat lower figures in that case. Weber, however. 




MEASUREMENT OF MUSCLE-FORCE IN MEN. 



69 




Fig. 24. Dyxamo.mkter. 



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

To determine the muscles of the forearm which 
bend the lingers, 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, tlie 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- 
vestiofation 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 
freelv, little or no weight being attached, it exhibits 



70 PHYSIOLOGY OF MUSCLES AND NERVES. 

this energy during each instant in the form of increase 
in speed which it imparts to its lower end and to the 
slight weight attached to the latter. "We may now 
raise the question as to the amount of force which the 
muscle when it has already accomplished part, say one 
half, of its contraction, can still evolve. Schwann, who 
first raised the question, fastened a muscle to one end 
of the beam of a scale and attached weights to the 
other end, but supported this end in such a way that 
the muscle was not extended. He was thus able to 
determine the force of the muscle in the same way as 
was described above with the apparatus shown in fig. 20, 
which depends on exactly the same principle. L. Her- • 
mann repeated Schwann's experiment with this appa- 
ratus, which is more convenient for the purpose now 
under discussion. The unweighted, or, at least, \ery 
slightly weighted, muscle having been inserted in the 
apparatus as accurately as possible, so that the platinum 
point jp just rests on the plate, the muscular force is 
determined in the way described above (^see pp. 65, 67). 
The vice which carries the muscle is then lowered to a 
certain definite extent, say 1 mm. If the muscle is 
then irritated it can become shorter by 1 mm. before 
it pulls the lever /i ; if it becomes yet shorter it must 
raise the lever with the weights attached to it. The 
weififht which it can still lift after it has become shorter 
by 1 mm. may thus be found. The muscle-vice is then 
again lowered — and this is again and again repeated. 
A series of weight-values is thus obtained which corre- 
spond with the force of the muscle during the different 
stages of its contraction. The result of the experiment 
is to show that the force of the muscle decreases, slowly 
at the commencement of 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 rilYSlOLOGY OF MUSCLES AND 2sEllVES. 



CHAPTER . V. 

1. Chemical procesaes within the muscle ; 2. Generation of warmth 
during contraction ; 3. Exhaustion and recovery; 4. Source of 
muscle-force ; 5. Death of the muscle ; G. Death-stiffening 
{Rigor mortis). 

1. The relations just described between the ekisticity 
and the work accomplished by the muscle have led xis 
to suppose that a muscle has, as it were, two natural 
forms, one corresponding to its condition of rest, the 
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 doing it contracts. This 
is, however, rather a description than an explanation 
of the fact of contraction. As the muscle on contraction 
is capable of raising weight, and thus of accomplishing 
work, it is necessary to inquire how this labour is 
effected. According to the law of the conservation 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 proceed within 
the muscle during muscular contraction, while others, 
which proceed even in the quiescent muscle, are in- 
creased in degree during this same contraction. The 
mechanical work must, therefore, be accomplished at 
the expense of these chemical processes ; and it could 



CHEMICAL PROCESSES 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 imable 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- 
Reymond showed that an acid — probably a lactic acid 
(^Fleischmilchsdure) — 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 MUSCLES AND NERVES. 

muscle. The methods usually employed in chemistry 
for the separation and isolation of ditferent substances 
are of no avail in this case, since they essentially alter 
the nature of the muscle. AVe must, therefore, be satis- 
fied to assume as certain only that various albuminous 
bodies occur in the muscle, one of which, called myosin, 
appears to be peculiar to muscle, and of which others 
are the non-nitrogenous bodies glycogen and inosit, 
toofether with a certain amount of fat and a number of 
salts. It appears somewhat doubtful whether lactic 
a,cid, which is always present in the muscle, if but in 
small quantities, is to be regarded as a normal con- 
stituent of muscle substance, or if it is not 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 bodies, such as creatin, which 
are present in small quantities in muscle, and which 
must probably also be regarded only as the products of 
the dissolution of the albuminous bodies. 

2. The only conclusion to be drawn from this frag- 
mentary information is that part of the muscle-substance 
unites during the activity of the muscle with oxygen, 
forming, partly carbonic acid, partly less highly oxidised 
products. That warmth is generated during these pro- 
jesses of oxidation, as we have above stated, is not sur- 
prising. To show this generation of warmth, Helmholtz 
employed the thermo-electric method. An electric cur- 
rent rises in a circle composed of two different metals, e.g. 
copper and iron, as soon as both points of contact — the 
points where the metals meet or are soldered together 
— acquire unequal temperatures. The strength of this 
current is proportionate to the ditfereuce in temperature, 



GE^'ERATION 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 temperatiu'e at 
lirst, 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. 

Helmholtz 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 
w^hich 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 'lo 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 rHYSIOLOGY UF MUSCLES AND NERVES. 

In order to form some conception of the amount of 
warmth 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,' this assumption 
cannot be far wrong. By 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 necessary 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 degree. 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, 424 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 trans- 
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 two metals alternately 
on to each other so that all the points soldered are 
arranged in two planes, differences in temperature much 
more minute than those which occur during tetanus 
may be measured. Such an apparatus is called a thermo- 
pile. Heidenhain had one of these made of rods of 

' According to a recent statement of Dr. Adamkiewicz, the spe- 
cific warmth of muscle is even greater than that of water, though it 
had previously been sssumed that the specific warmth of water is 
greater than that of any other known substance, with the excep- 
tion of hydrogen. 



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,' 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 
wiien 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 

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



78 THYSIOLOGY OF MUSCLES AND NERVES. 

the greatest amount of warmth during tetanus, during 
wliich no apparent labour is accomplished. The whole 
internal work of the muscle is in this case transformed 
into warmth, thus raising the temperature of the muscle- 
substance ; and the amount of this warmth may, as we 
have 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 
that part of the constituent matter of the muscle is 
expended, other matter being deposited 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 
creatin and the urea arising from the latter, lactic acid, 
&c., reappear in the urine. The more abundantly 
the blood-current flows through the muscles, the more 
quickly are the products of decomposition removed 
from the muscle. This is of course possible only in a 
very inferior degree when the muscle has been cut out 
from the body. This is the reason why an extracted 
muscle retains its power of activity for but a very short 
time. If, for instance, such a muscle is continuously 
tetanised, it will be found that the contraction, though 
it is at first very considerable, very soon decreases and 



EXHAUSTIOJ^ 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 NERVES. 

within the muscle are expended during its activity. 
As muscle consists principally of albuminous bodies, it 
has been assumed that it is to the decomposition of 
these that the labour accomplished is due. We have, 
however, seen that non-nitrogenous bodies, such as 
glycogen and muscle-sugar, are also contained in the 
muscle, and that lactic acid Avhich must orioinate 
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 pass 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, in the action of the 
heart and of the respiratory muscles — the excretion of 
urea depends entirely on the amount of nitrogen intro- 
duced in food. If entirely non-nitrogenous food is 
taken, then the excretion of urea decreases to a definite 
point, at which it remains constant for some time. If 
a larger amount of work is performed, a slight increase 
in the excretion of urea in fact usually occurs. The 
amount of albuminous matter which must 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 nearl}^ 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 



82 PHYSIOLOGY OF MUSCLES AND NERVES. 

to perform a great amount of labour require food 
aboundiug in carbon. The opposite was formerly as- 
sumed, the view being founded on the fact that English 
labourers, who are, 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 out 
that the larger beasts of prey, which feed exclusively 
on flesh, are remarkable for their great muscular power. 
Neither instance really proves the conclusion which it 
was intended should be drawn from it. In the first 
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 
when compared with the constant work of a draught 
horse or ox. 

The relation of the food 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- 
chanism of the machine. The same work might be 
produced by the combustion of nitrogenous matter ; 
but it would be necessary to use considerably greater 
quantities. But the machine called muscle cannot be 
driven by pure carbon ; under the conditions presented 
by the organism pure carbon cannot be applied to 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 wdiole steam- 
engine with its boiler and the coal in the furnace could 
be subjected to a chemical analysis, the percentage of 
coaJ 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 A^D 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. 

AlthouGfh the small amount of the non-nitros^enous 
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 mainly 
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 not 
constructed of such durable material ; during its ac- 
tivity-it, therefore, continually wastes a comparatively 
considerable amount of its ow^n substance. As the 
matter leaves the body in a more highly oxidised form 
than it had when it was present in the muscle, warmth 
and work must also be freed during this partial com- 
bustion of the material of the machine. The muscle- 
machine works, therefore, partly at the expense of its 
own form-element; and, if it is to work continuously, not 



SOURCE OF MUSCLE-rOKCE. 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 occiu'. 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 labom\ 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 sugar 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 



86 PHYSIOLOGY OF MUSCLES AND NERVES. 

passes rapidly into the blood, and is, therefore, espe- 
cially capable of rapidly replacing the expended forces. 
It is not suitable for a sole or main food material durino- 
long periods, because when a great quantity of sugar 
is introduced into the stomach it is transformed into 
lactic acid 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- 
perature 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, 45°, the 
contractile power is lost in a few minutes. Exactly 
the same happens in muscles yet remaining within the 
body of the animal if the blood-current ceases to pass 
through the body, either because of the death of the 
animal, or in consequence of the local application of 
ligatures to the vessels. This loss of contractile power 
is spoken of as the death of the muscle. Muscular 
death does not, therefore, correspond in time with the 
general death of the whole 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 colom- ; 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 Qnortis). E. du 
Bois-Eeymond 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- 



88 niYSioLOGY OF ml'sci.p:s and nerves. 

stiffening intervenes mucli more quickly in muscles 
which have been strongly irritated before death, as for 
instance in those of hunted animals. But while the 
formation of acid must always be very slight in active 
muscle, it increases greatly in muscles which have un- 
dergone death-stiffening, and the acid acts as a relax- 
ing agent on the connective tissue which holds the 
fibres together, so that the latter separate more readily. 
At the same time, however, another distinct change 
occurs within the muscle-fibre. If a fresh living muscle- 
fibre and 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 unextended 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 of 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 ' death-stiffening ' [rigor 
mortis) is principally due. Moreover, this change docs 
not occur simultaneously in the muscles of all parts of 
the dead body ; it usually begins in the muscles of the 
face and neck and passes gradually downward, so that 
the muscles of the legs are the last to be affected by 
it. The relaxation of the rigidity takes place in the 
same order. 

On account of the shortening 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-stift'ening. 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 THYSIOLOGY OF MUSCLES AND NERVES. 

itself, and that this coagulation represents the essential 
fact in death-stififening. 

Death-stiffening intervenes, as we found, earlier 
in proportion as the temperature is higher. Exactly 
the same is the case in expressed muscle-fluid. If it 
is heated to a temperature of 45° C. it coagulates 
in a few 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 tempe- 
rature of 73° C, they contract into shapeless lumps, 
become quite hard and white, and exhibit a firm solid 
tissue resembling the white of eggs when cooked. 
From this it may be inferred that, besides the matter 
which coagulates during the death-stiffening, other 
soluble albuminous bodies are also present in muscle, 
and that these act as ordinary albumen as it occurs in 
blood and in eggs ; for the latter also coagulates when 
heated to 73° C. It therefore appears that 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 myosin. It 
may be assumed that this albuminous body is natu- 
rally soluble, but that it is rendered insoluble by the 
acids occurring within the muscle. Death-stiffening 
would accordingly be the result of the formation of 
acid. Our knowledge on this point is, however, yet 
very incomplete, and must remain so until chemistry 
has afforded more fidl explanation of the nature of 
albuminous bodies. 



CHAPTER YI. 

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

1. In 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 



92 PHYSIOLOGY OF MUSCLES AND NERYES. 

parts may act separately, or all may work together ; and 
in the latter case they combine their forces, as is inva- 
riably the case with forces acting in different directions, 
in accordance with the so-called parallelogram of forces. 
As an example of this 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 
raised and advanced in the shoulder socket ; when only 
the posterior part of the muscle contracts, the arm is 
raised backward. When, however, all the fibres of the 
muscle act in unison, th-e 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-pennate 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 direction 
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, it would be necessary to determine the number of 
the fibres, the angle which each of these makes, with 
the direction finally taken by the compound action, as 
well as the length of the fibres — these not being always 
equal. This task if only carried out in the case of a single 
muscle would be a very great test of patience Foriu- 



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 
^elev^ation 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 
ditference whether the fibres are all parallel and act in 
their own direction, or if they form any angle with the 
direction of work.^ 

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 (c/. 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 
* * See Notes and Additions, No 2. 



94 PHYSIOLOGY OF MUSCLES AND NERVES. 

of its own action. If two or more of the muscles as- 
sume a state of activity at the same time, then the action 
will be the resultant of the separate tensions of each, 
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, afforded 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 
moveable bone lever, but is usually at an acute angle. 
In this case, again, the whole tension of the muscle 
does not take effect, but only a component, which is at 
right angles to the arm of the lever. Now, it is notice- 
able that in many cases the bones have 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 largest of 
these sesamoid bones is that in the knee, which, in- 
serted in the powerful tendon of the front muscle of 
the upper thigh, gives a more favourable direction to 
the attachment of this tendon than there would other- 
wise be. 

Sometimes the tendon of a muscle passes over an 
actual reel, so that the direction in which the muscle- 
fibres contract is entirely different from that in which 
their force of tension acts. 

3. The last important consequence of the attach- 



ELASTIC TENSION. 95 

ment of the muscles to the bones is the extension thus 
effected. If the Hmb 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 



96 PHYSIOLOGY OF MUSCLES AND NERVES. 

bones. The tendons of some pass into soft structures, 
such as the muscles of the face. In this case also the 
dift'erent 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 naturally 
exercises an influence on their action durinor contrac- 
tion. 

4. As yet attention has only been paid to one kind 
of muscle-fibre, that which from the very first we dis- 
tinguished as striated fibre. There is, however, as we 
have seen, another kind, the so-called sviooth 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. 
Unhke striated muscle, they do not form separate mus- 
cular masses, but occur scattered, or arranged in more 
or less dense layers or strata, in almost all organs.* 
Arranged in regular order, they very frequently form 
widely extending membranes, especially in such tube- 
shaped structures as the blood-vessels, the intestine, 

' An instance of a considerable accumulation of }-'mooth muscle- 
fibres is afforded by the muscle-pouch of birds, which, with the ex- 
ception of the outer and inner skin coverings, consists solely of these 
fibres collected in extensive layers. 



SMOOTH MUSCLE-FIBRES. 



97 



&c., the walls of ^Yhicll 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 





Fig. 25. -Smooth MuscLE-FiBitiis (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 blocd 
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 AND NERVES. 

take place simultaneously throughout the length of the 
tube ; but, commencing at one point, it continually 
propagates itself along fresh lengths of the tube, so that 
the contents are slowly driven forward. The principal 
agents in this are the circularly arranged fibres, which 
at one point completely close the tube, while, by the 
contraction 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- 
staltic motion. It takes place along the whole of the 
digestive canal, from the throat to the other end, and 
in this case affects the forward motion of the food, as 
also, finally, the expulsion of the undigested residue. 

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 w^hen 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 tlu 
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 
such part, or by irritating the nerves appropriate to 
these parts. The most striking feature is the slowness 
with which these motions take place. Not only does a 
long time, observable without any artificial aid, elapse 
after the application of the irritant before the motion 
begins, but, even if the irritation is sudden and in- 
stantaneous, the motion excited at one point passes 
along very gradually, slowly increasing up to a definite 
point, and then again gradually decreasing. This slow- 
ness of motion essentially distinguishes smooth 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. JSTo 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 espe- 
cially 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 longitudiiial 
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 PHYSIOLOGY OF MUSCLES AND NERVES. 

and this rise can be indicated on a rapidly-mo\'ing 
myograph 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 difference may be 
read off the plate of the myograph, and thus the 
speed 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 ^ot ^^ To~o ^^ ^ 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. On the death of the muscle, 
the rate of propagation becomes continually less, finally 
ceasing entirely in muscles which are just about to pass 
into a state of death-stiffness, so that on irritation only 
a slight thickening is seen at the point directly irritated, 
and this does not propagate itself. 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 muscle-fibres, however, it is found that the 
coutractions excited at one point propagate themselves 
in the adjacent fibres also. The marked distinction 
which thus appears to exist between smooth and striated 
muscles would, it is true, disappear if the views of 
Engelmann, resulting from his study of the urinary 
duct, are confirmed. According to that writer, the 
muscular mass of the urinary duct does not consist 
during life of separate muscle-fibre cells, but forms 
a homogeneous connected mass which only separates 



VOLUNTARY AND INVOLUNTARY MOTION. 101 

into spindle-shaped cells at death. If this view could 
also be extended to the smooth muscle masses ot 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 ride, 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.^ 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 tliis, 
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 

• Striated muscles also occur in the intestine of the tench 
(^Tiiica vulgaHs), which in this differs from all other vertebrate ani- 
mals. It is doubtful whether this tissue is capable of voluntary 
motion, but it is very improbable. 



102 PHYSIOLOGY OF MUSCLES AND NERVES. 

the 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 transitionary 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 ; 6. 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 
300 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 MUSCLES AND NERVES. 



striation, as though it were formed of very delicate 
fibrillse, or small fibres. It is called the axis-band, or 
axis-cylinder . The outer part has a crumpled aj^pear- 
ance, and oozes at the cut ends of the nerve in drops 
which soon coagulate ; it is called the Qnedullary, or 
Ttiarroiu-sheith. The medullary sheath entirely sur- 
rounds the axis-cylinder ; as, however, when in a fresh, 

uncoagulated 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 coagulation 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 
Fig. 2j. Xkkve-Fibiies. ^ r i i 

a a, the axis-cylinder, still partially UerVCS. boUlC of the latter 
suri'ouuded by tbe medullary sheath, v in i ii 

nave no medullary sheath, 
and are, therefore, axis-cylinders immediately sur- 
rounded by the nerve-sheaths. When many nerve- 
fibres are united into a bundle, these marrowless fibres 
are grey and more transparent, and are therefore some- 
times called grey nerve-fibres. Those nerve-fibres which 
have medullary 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 and branchlets 




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 how^ever 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- 
glioii-cells. In each ganglion-cell it is possible to dis- 
tinguish the cell body, and a large kernel (nucleus) 
within this ; wdthin the kernel, a smaller kernel {nu- 
cleolus) may also frequently be distinguished. Some 
ganglion-cells are also surrounded by a membrane 
which occasionally passes into the neurilemma of 
6 



106 



PHYSIOLOGY OF MUSCLES AND NER\ES. 



nerve-fibres, which are connected with the cell. The 
kernel is finely granulated and is composed of a pro- 
toplasmic mass, which, when 
heated, or subjected to certain 
other influences, becomes dull 
and opaque, but which in a fresh 
condition is usually somewhat 
transparent. The form of the 
paneflion-cells is very variable. 
Sometimes they appear almost 
globular ; in other cases they 
are elliptic ; others, again, are 
irregular, provided with numer- 
ous offshoots. ]Most ganglion- 
cells have one or more project- 
ing processes ; some are, indeed, 
found without processes, but it 
is certain that this condition is 
merely artificially produced, the 
processes having been torn off 
during the preparation of the 
ganglion - cell. G anglion - cells 
are occasionally inserted in the 
course of the nerve-fibres, so 
that the processes differ in no 
way from other nerve-fibres, as 
is shown in fig. 27. In the gan- 
glion-cells of the dorsal marrow, 
which have many processes, 
some of these appear exactly 
like the rest of the cell body — 
that is to say, they are finely granulated ; these are 
called protoplasmic processes. On the other hand, in 




Fio. 27. Gangmox-ceij-.s 

>V nil X EK V E-rUOCESSES. 



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 deskable 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 NERVES. 

found that certain of its fibres unite with those muscles 
^yhich pulsated. We already know that the other end 
of the nerve is connected with the nerve-centre. If 
the nerve is cut at a point between the irritated 
spot and the nerve-centre, the muscular pulsation 
occurs as before on the re-application of the irritant, 
but the sensation of pain is absent. 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 peripheric nerves, 
when irritated at any point in their course, are able to 
cause effects both at their central and peripheric 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, by extracting and preparing a portion of the 
nerve with its muscle, in an uninjured condition, 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. Even 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 nerve. The muscle is there- 
fore used as a re-agent to test the changes in the nerve 
itself. The requisite experiments may be either with 
warm-blooded or with cold-blooded animals. As, how- 
ever, the muscles of warm-blooded animals, when 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 
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 MUSCLES AND NERVES. 

inductive sliocks are applied, each separate shock pro- 
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 tight 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. If, 
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 directly only on the 
spot immediately irritated, and that the activity which 
is excited in the nerve at this point propagates itself 
alonof the fibres until it reaches the muscle in which it 
causes a contraction. If the latter view is correct, it 
must also be inferred that any injury to the nerve-fibre 
prevents the propagation of the activity in the latter ; 
and 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 activitv. It can be shown that this latter view 
of the natiu'e 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 j&g. 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-Reymond 
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. Eound 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, 
throuo^h 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 



112 



PHYSIOLOGY OF MUSCLES AND NERVES. 



the end of the rod, and thus driving' the frame with the 
rods from B to J., in a direction opposite to that of the 
arrow on the indicating pkxte, a point is reached at 
which the 'trigger' which is seen on the standard A, 
and which acts upward, fits into a corresponding notcli 
in the rod at a, thus preventing the re-extension of the 
spring. It therefore remains compressed till pressure 




Fig. 28. Spuing Myograph, as used by du Bois-Eeymond. 

on the trigger frees the frame, which then traverses the 
whole length of the wires at a speed depending on the 
strength of the spring, &c., in the direction from A to B, 
that indicated by the arrow. 

In order to describe the muscle-pulsation on this 
plate, side by side with it there is a lever with an 
indicating pencil, such as wjis used in the former ex- 
periment, to indicate the height of muscular 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 
phxte 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 induct orium, by which an 
inductive ciu-rent 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 B, 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 wiien 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 OF MUSCLES AND NERVES. 



in the nerve is exposed to the irritation, the muscle in 
this case also describes the curve of its pulsation on 
the rapidly moved plate of the myograph. Arranging 
matters so that two curves of pulsation are allowed 
to describe themselves in immediate sequence, but with 
the difference 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 be 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 other, as is shown in figure 29.^ In this 




u (f 

Fig. 29. Pcopagatiox of the kxcitemext witiiix nehves. 



figure, a 6 c is the curve first 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' y d represents the curve indicated immediately after 
the former, but obtained as the result of the irritation 
of a portion of the nerve remote from the muscle. The 
second curve is seen to be somewhat separated from the 
other ; it does not commence so soon after the moment 
of irritation (which is indicated by the vertical stroke o); 
that is, a longer time elapsed between the moment of 

' The curves in fig. 21) were describerl when the glass plate 
moved more rapidh% so that they appear more extended than those 
represented in figure 18. 



TRA^■SMISSION 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 ftict 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 (}i. medianus) may be irritated near the 
wrist and near the elbow. From the result inq- difference 



J 16 niYSIOLOGY OF MUSCLES AND NERVES. 

in time and from the distance between the two irritated 
points the rate of propagation of the excitement was 
found to be 30 m. per second. The high figure as com- 
pared with that found with the nerves of frogs is ex- 
plained by the higher tem2:)erature of human nerves. 
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 on 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 
inferred from an experiment arranged by H. JMunk. 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 myo- 
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 
lower end. The simplest explanation which can be 
given of this phenomenon is that the excitement during 
its propagation is gradually retarded, just as a billiard ball 
moves at first very quickly but afterward at a gradually 
decreasing speed. The retardation of the billiard ball 
is due to the friction of the underlj^ing surface. From 



ISOLATED TKANSMISSION. 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 neighbom'ing 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 AND NERVES. 

protected from direct contact with each other by gutta- 
percha or by some other substance. The comparison 
is, however, 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- 
lation 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, sometimes 
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 
nerves 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. Two 
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 may 
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 be estimated 
as higher in proportion as the muscular pulsation pro- 
duced by the irritant is stronger; in the latter case 
the excitability is said to be greater in proportion 



EXCITABILITY. 119 

as the irritant wliicli 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-Eeymond'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.^ 
6. If a recently prepared nerve, as fresh as possible, 
is placed on a series of pairs of wires, and the excita- 
• See Notes and Additions, No. 3. 



120 PHYSIOLOGY OF MUSCLES AND NERVES. 

bility at the various points of the nerve is consecutively 
determined in the way described above, it is generally 
found that the excitability of the upper part of the 
nerve is greater than that of the lower. There is, how- 
ever, no great regularity in this character. Sometimes a 
point is found in the centre of the nerve which is less 
irritable than those immediately above and below it. 
Very frequently 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 first, and then, at a yet lower point, to 
decrease again. If such a nerve is observed for some 
little time, its excitability at the various points being 
tested every five minutes, 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 be 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- 
Avard in the nerve, so that pulsations can only be 
obtained by irritating the part situated nearest the 
muscle, and at a little later period even this part 
becomes dead. After the whole nerve is dead, pul- 
sations may yet always be obtained for a time by 
direct irritation of the muscle. The muscle does not 
usually die until much later than the nerve Yet in a 
quite fresh preparation of the nerve and muscle, the 
latter is always less excitable than the former, and 
a much stronger irritant is required to excite the 
muscle directly, than indirectly through the nerve. 
In all these experiments the nerve must be care- 
fully protected from drying up, as otherwise its excita- 



CUKVE 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 t)f the nerve usually lie, 
that is, it may be arranged that they are near the 



122 PHYSIOLOGY OF MUSCLES AND KERVES. 

point of section. These changes in the excitability 
may, therefore, be thus conceived : that when the 
nerve is cut some 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 
to 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 easily effec- 
tive in the upper than in the lower parts. 

Pfliiger, 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 
at one point in the nerve, in propagating itself along 
the nerve, gradually increases in strength; he spoke 
of it as an avalanche-like increase in the excitement 
within the nerves. This explanation appears to contra- 
dict the above-mentioned fact as to the effect of cutting 
on the nerve, for in such cases 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 of the nerve 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 dej)endent 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.^ 

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. AYe 
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 
' See Notes and Additions, No. 4. 



124 PHYSIOLOGY OF MUSCLES AND KERVES. 

cannot be shown with our present apphances. As 
motions of the smallest particles (molecules) probably 
take place in the nerve, though the external form 
remains unaltered, and therefore no work worthy of 
consideration is accomplished, it is easily intelligible 
that these 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 tempei*ature of 44° C. 
death occurs in from ten to fifteen minutes ; at 75° C. 
in a few seconds ; and in the average 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 first in- 
creases the excitability, but afterwards rapidly decreases 
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 which the nerve remains excitable longer than in 
thinner or in more dense solutions. A solution of com- 
mon salt of 0'6 to 1 per cent., for instance, has almost 
no effect on 'a nerve submerged in it, and preserves the 
excitability of this nerve about as long as damp air. 
Pure olive oil, if not acid, may also be regarded as 
innocuous. These are, therefore, used when the in- 
fluence of different temperatures on the nerve is to be 
studied. 



CHAPTER VIII. 

I Electrotonus ; 2, Modifications of excitability ; 3. Law of pulsa- 
tions ; 4. Connection of electrotonas 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 MUSCLES AND NERVES. 

pulsates, tlius indicating that something, which we have 
called excitement, has occurred within the nerve. While, 
however, the 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 in that part traversed 
by the current, but also in the neighbouring parts above 
and below the portion of the nerve subjected to the 
electric current. The great importance of this lies in 
the fact that it reveals relations between the 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 nerves. 

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 electric 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- 
titatively determined. Experiment shows that the ex- 
citability may be altered by electric currents. If a 
small portion of a nerve is placed on two wires in such 
a way that an electric current may be caused to traverse 
this portion, it appears that not only the portion actually 
traversed by the current, but the nerve beyond this, 
also suffers changes in its excitability. In order to 
study these, let us imagine several pairs 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 



ELECTROTOXUS. 



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 




ft-' 



Fig. 30. Electrotoxus. 

must now be observed. It is found that theee 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 6 as soon as the current is closed, but reo-ains its 
former strength as soon as the current is interrupted. 
In this case, therefore, the excitability in the contiguous 
portion a h 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 MUSCLES AND NERVES. 

passes from d to c, the influence of the irritant seems, 
on the contrary, to increase in a h when the current is 
closed, and to resume its original strength when the 
current is interrupted. In this case, therefore, it ap- 
pears that the action of the current tends to increase 
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 are 
strengthened when the current in the portion c d passes 
from c to 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 positive 
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 
being 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 downward from the electrodes. 
In order to find whether a change in the excitability 
also occurs within the electrodes, the current must be 
made to traverse a longer portion of the nerve, and the 
irritant must then be applied to a point within the 
electrodes. According to the point at which the elec- 
trode is applied, various changes maybe shown 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 aneledrotonus ; that on 
the side of the kathode as hatelectrotoniis. Where the 
anelectrotonus approaches the katelectrotonus, a point 
occurs between the electrodes at which the excitability 
remains unchanged ; this is called the neutral jpoint. 
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 fiof. 31. In this n n' indicates the nerve. 
a and li the electrodes, a signifying the anode, Iz the 
kathode. The direction of the current within the nerve 
is, therefore, that indicated by the arrow. In order to 
7 



130 



PHYSIOLOGY OF MUSCLES AND NERVES. 



indicate the change which the excitability undergoes at 
any definite point in the nerve, let us suppose a straight 
line drawn at this point at right angles to the longitu- 
dinal direction of the nerve, and let this line be made 
longer in proportion as the change is greater. In order, 
moreover, 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 
downw^ard, that on the kathode upward. By connecting 
together the heads of these lines a curve is obtained 
which diagrammatically represents the changes at each 




Fig. 31. Electrotonus under the influence of currents of 

varying strength. 

point. Of the three curves, the middle represents the 
condition under the influence of a current of medium 
strength ; the other two curves, indicated, the one by 
short lines, the other by a dotted line, represent the 
conditions under the influence of a strong and of a 
weak current respectively. These curves show that the 
changes are more marked in proportion as the cur- 
rent is stronger ; that they are most strongly developed 
exactly at the electrode points ; and, finally, that the 
neutral point, under the influence of currents of dif- 
ferent degrees of strength, assumes a variable position 
between the 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 
immediatelv 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 chano-es in the 
excitability observable after the opening of the current 
is greater ir 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 PHYSIOLOGY OF MUSCLES AND NERVES. 

present in the nerve for some time, a series of pulsa- 
tions or an apj^arent tetanus is occasionally observed. 
This phenomenon has long been known as an opening 
tetanus, or as Rittefs tetanus. The connection existing 
between these changes in the excitability, and the fact 
that the nerve may be excited by electric currents, has 
led to the adoption of a view of the electric 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, somel imes at the closing, 
sometimes at the opening of the current, and occasion- 
ally even at both. Closer observation has, however, 
shown that very definite laws control this, provided that 
attention is paid to the strength of the current and its 
direction within the nerve. Let us first 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 
our 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 necessary to possess a 
convenient means 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 separates at any point into two 
liranches, divides, the strength of the currents distri- 
Inited into these two branches not being always equal, 
but beinof in each branch in inverse ratio to the resis- 
tance offered in that branch. Supposing that 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 strenofth 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 j)roportionate to its 
length, it is only necessary to arrange, as the conductor 




Fig. 32. EiiEociionD. 



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 pFos, a current, and x^P^V^ 
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 A a branch con- 



134 THYSIOLOGY OF MUSCLES AND NERVES. 

ductor passes to 'the nerve, and returns from there 
to the slide aS', which slips along the wire A B, The 
branch-current traversing the nerve is strengthened or 
weakened accprding as this slide is placed further from 
or nearer to A. 

By means 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 more peripheric parts, as descending, and when 
it passes in the opposite direction, as ccscending. 

Ascending and descending currents, therefore, 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 strength is in- 
creased yet more, they occur in connection with the 
ascending current also. Finally, the pulsations in all 
four cases are of equal strength. If, however, the 
strength of the current is yet further increased, two 
of these four pulsations again become weaker — the 
closing pulsation with the ascending current, and the 
opening pulsation with the descending current. A 
strenofth of current is at last reached at which these 
two pulsations entirely cease, so that pulsations occur 
only on the closing of the descending, and on the 
opening of the ascending currents. These phenomena, 



LAW OF PULSATIONS. 



135 



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



Law of Pulsations in the case of Fresh Nerve. 




Current Weak 


Current of Mediam 
strength 


Current Strong 


i 


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 KERVES. 



coming gradually weaker, and finally disappearing en- 
tirely. The law of pulsations in the case of dying 
nerve may also be represented in tabular form, three 
stages of excitability being distinguished ; the signs 
remain the same as in the former table. 



Law of Pulsations in the case of Dying Nerve. 
(Under the Application of Weak Currents.) 





First Stage 


Second Stage 


Third Stage 


; 


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 



It is at once apparent that these two cases of the 
law of pulsation, occurring in different circumstances, 
entirely agree. The sequence of the phenomena which 
occur at the death of the nerve on the application 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 of the current. In other words, if the 
nerve is irritated with weak, unvaried currents, these 
act on a fresh 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 
acted. In order to understand this, it is necessary to 
recall our previous experiences of the changes in the 
excitability at the death of the nerve. We found that 
in that case the excitability at first rises and attains a 
maxinuun before it again falls. Supposing, therefore, 
a fresh nerve is irritatcid by means of currents of definite 
but weak strength, and supposing that this nerve is ex- 
amined after the lapse of a short 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 excitabilit J 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 MUSCLES A^'D NERVES. 

it has readied its highest point. It must, moreover, be 
remembered that it is never merely a single cross-section 
of a nerve 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 
points within the irritated portion. It may further be 
assumed 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 any 
power of action, must remain at the highest point of 
excitability.^ 

4. In studying the law of pulsations we attended 
only to the closing and opening of the current, entirely 
disregarding the period during which the continuous 
current flowed through the nerve. In reality, the 
nerve, as a rule, remains unexcited during this period. 
Sometimes, however, especially on the application of 
but moderately powerful currents, an enduring excite- 
ment expressing itself as a tetanus in the muscle is 
observable while the current lasts. Ascending and 
descending currents do not behave quite alike in this 
matter. The latter are followed by tetanus, even in th6 
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 cannot be compared with that which 

' Sec Noles and Additions, No. 5. 



RELATION OF ELECTROTOiS'US 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 dm'a- 
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 cinrrents, 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 katelectrotonus, 
the excitement is increased, while in the other, that 
of anelectrotonus, it is decreased. It might, therefore, 



140 



PHYSIOLOGY OF MUSCLES AND NERVES. 



be possible that these two conditions differ in the re- 
lation which they bear to the excitement. Indeed, 
Pfliiger supposed that excitement occm's only at the 
commencement of katelectrotonus and at the cessation 
of anelectrotonus. On the basis of this hypothesis the 
phenomena of the law of pulsations may be explained ; 
and it becomes intelligible why on the closing and 
opening of the current pulsations sometimes occur and 
are sometimes absent. In order, however, fully to 




Fig. 33. Electuotonus. 

understand this hypothesis and the law of pulsations 
based upon it, we must study the phenomena of elec- 
trotonus more closely than we have yet done. 

5. AVe have already seen that the excitability is in- 
creased on the side of the kathode during the closing 
of the current, and is decreased on the side of the 
anode. Easy as it is to prove this law under the appli- 
cation of weak, or medium currents, it is sometimes 
very hard to do so when the current causing the elec- 
trotonus is strong. Let us again imagine that the 



TRANSMISSION OF EXCITEMENT DURING ELECTROTONUS. 141 

nerve, n n' (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 n\ 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. If, 
however, the current used for this purpose is somewhat 
strengthened, no increase in the excitability is ob- 
servable ; and, indee'd, if the currents are sufficiently 
strong, it becomes quite impossible to effect contrac- 
tion in the muscle by irritation at e/. 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 / 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 h will invariably show the existence of 
heightened excitement, however strong the current 
may be. But the portion a h 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 OF MUSCLES AIs'D KERVES. 

in two such 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 of 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 h. Now 
it may, on the other hand, be 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 anelectrotonus not only decreases 
the excitability, but also hinders the propagation of the 
excitement; and that where the anelectrotonus is strong, 
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 katelectrotonas in the upper 
half, anelectrotonus in the lower. According to Pfliiger's 
hypothesis, excitement occurs in the nerve only at the 
point at which katelectrotonus 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 pass through the lower portion of the 
nerve, and as this is strongly anelectrotonic, it presents 
an obstacle to the further passage of the excitement. 
The excitement which occurs in the upper half is, there- 



EXPLANATION OF THE LAW OF PULSATIONS. 143 

fore, unable to reach tlie 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 
opening of a descending current as on the closing of an 
ascending current. According to Pfliiger's 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 Eitter'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 niYSIOLOGY OF MUSCLES AND NERVES. 

anode. If an ascendiog current is passed through a 
nerve, the anode side is situated in its lower portion ; 
but if the current is descending, then it is situated in 
the upper portion. If Kitter's tetanus is induced by 
means of 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 way influences the 
tetanus. 

Yet another proof of the truth of this hypothesis is 
afforded by Pfluger's study of the excitement of the 
sensory 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 end 
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 case of the motor nerves. Pfliiger as- 
certained that in reality strong ascending cm'rents 
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 nerves. On 
the closing of the descending current, excitement oc- 
curs in the lower portion of the nerve. In order to 
effect sensation the excitement must pass to the spinal 
marrow and the brain ; it would have, therefore, to pass 
through the upper parts of the nerve, where it would be 
checked by the strong anelectrotonus which prevails 
there. The opening of the ascending current has a 
similar irritating effect on the lower parts of the nerve. 
In order to reach the spinal marrow and brain, this 
excitement would have to pass through the upper parts, 
where, in this case, it would be checked by the strong 
negative 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 gTadually 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 MUSCLES AND NERVES. 

adapted for exciting this motion than is slow action. 
That even slight mechanical distiu'bances are capable 
of producing excitement, although the nerve is not 
crushed, has been proved by Heidenhain. He 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 flicts 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 po>ition by molecidar forces. 
P'xcitement 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 forces which move tliem, and, therefore, 
the smaller is the excitability. It must also be ex- 
})lained that the separate particles of the nerve mutu- 
ally influence each other, each particle influencing the 
olher 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 tliread 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 



12 3 4 5 

Fig. 34. A seuies of jMagxeiic needles ahranged as a diagkaji 

OF THE PAUTICLES 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- 



148 PHYSIOLOGY OF MUSCLES AND NERVES. 

able when some of its neiglibours liave been removed. 
AVitbout, therefore, assuming other resemblances be- 
tween the forces w^hich act on the magnetic needles 
and those present in the nerve, we may accept the 
comparison so far that we may imagine the nerve to 
consist of separate minute particles, arranged one behind 
the other in the longitudinal direction 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 
they must lessen the excitability ; while, on the other 
hand, such forces as tend to move the nerve-j^articles 
from their relative positions must at the same time 
decrease the strength of their connection, and must 
therefore render the nerve more excitable. As regards 
the electric current, we have seen that the two poles 
act on the nerve in opposite w^ays. We may, therefore, 
assume that by one pole, the positive, the nerve par- 
ticles are retained in their quiescent position, wliile by 
the negative pole, on the other hand, they are disturbed 
from this position. If this is the case, it explains the 
fact that excitement occurs only at the negative pole 
w^hen 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 movement of the 
particles such as follows the closing in the negative 
pole, so that in this case the excitement can occur on 
the opening of the current. 

The fact that the nerve remains luiexcited by 
changes in its condition, although these same changes 
if they occur suddenly do induce excitements, bears so 
significantly on the explanation of the nervous processes, 
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 strenofth of the currents to increase or decrease 
more or less gradually. Let the apparatus be arranged 

in which the nerve is traversed by a 



as in fig. 



35 




Fig. 35. Rheochoud. 

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 J. /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 

* E. da Bois-Eeymond has described apparatus of this sort iir.der 
the name of Scliivankungsrhcochord. 



150 PHYSIOLOGY OF MUSCLES AND NERVES. 

with great speed,' the nerve is excited and the muscle 
pulsates. When, therefore, the current being closed 
or opened bj means of the key, the nerve is excited, 
this 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 inductive 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 by 
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 is active, while 
the closing inductive current as yet exercises no in- 
fluence ; if the coils are then brought nearer to each 
other, the latter also becomes active. If, however, 
when the coils of the inductive apparatus are in any 
position, the secondary coil is connected with a multi- 
plier, then the deflections of the magnetic needle are 
always of equal strength in the case of both inductive 
currents. The nerve, therefore, exhibits a difference 
which the multiplier is incapable of indicating. It has, 
however, been shown 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.^ 

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 ; but 
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 luith 
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 
* See Notes and Additions, Xo 6. 



152 rnYsiOLOGY of muscles and nerves. 

admitted that in such cases excitement does in reality 
take place, but that it is not observable on account of 
external circumstances (hindrance to the propagation to 
the muscle), then these exceptions may be said to be 
merely apparent. Moreover, assuming that the changes 
in the strength of the currents within the nerve only 
excite in consequence of the fact that they bring about 
changes in the molecular condition of the nerve, and 
combining with this all that we know of the effect of 
other forms of nerve irritation, the following law regard- 
ing nervous excitement may be regarded as the final 
result : — 

Excitement of the nerve depends on a change in 
its molecidar condition. It occurs as soon as such a 
change is effected ivith sufficient speed. 

It may be added that this law is in all essential 
points true also of muscle. But 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.* 

> See Notes and Additions, Nos. 7 and 8. 



CHAPTEE IX. 

i. Electric phenomena; 2. Electric iishes ; 3. Electric organs; 
■i. 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.^ Electric cur- 
rents are so easily generated under all circumstances 
that it is not very surprising that traces of them are 

' An exception is perhaps afforded by the electric phenomena 
of the leaves of Dioncra vncscijmla which will presently be men- 
tioned. 

8 



154 PHYSIOLOGY OF MUSCLES AND NERVES. 

everywhere to be found. In the researches in which 
we are about to 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, and the causes of which lie 
in the animal tissues themselves. Apart from muscles 
and nerves, but one tissue seems endowed with some- 
what strong electric action ; this is that of the glands. 
This has, indeed, not as yet been fully proved, but it 
has been 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 ph3^siological 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 fishes. 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 the will, the animal using this power to frighten its 
enemies, or to benumb and kill its prey. Long before 
the world knew anything accurately as to the physical 
nature of electric plienomena, such powerful influences 
as are exhibited in electric fishes did not fail to attract 
the attention of chance observers. Notices of these 
remarkable phenomena are actually found in ancient 
writers ; and the Roman poet Claudius Claudianus ' 

' Ho lived in Alexandiia toward the end of the fourth century. 



ELECTRIC FISHES. 155 

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

' Who has not heard of the power of the dreadful 
ray, of the benumbing force to which it owes its name.* 
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, wounding the 
strong arm and curdling the blood of the fisherman, 
who, terror-struckjCthrows 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 
Galvani and Volta, these fishes were frequently studied 

Older notices of the Torpedo occur in Pliny, iElian, Opj.ian (whose 
poem on fishing Claudianus appears to have known), and in Aristotle. 
' Torj)edo, from /y7yor = numbness. 



156 PHYSIOLOGY OF MUSCLES AJsD NERVES. 

by various observers, and the electric character of their 
innate force was incontrovertibly shown. Faraday's 
study of the electric eel, and du Bois-Eeymond's of 
another electric fish, are especially important. 

There are three fishes, especially, wdiich have been 
proved to possessthis capacity for giving electric shocks. 
These are, the electric ray of the Adriatic and Medi- 
terranean {Torpedo electrica and T. marmorata) ; the 
electric eel (Gymnotus electricus), which occurs in the 
fresh waters of South America ; and lastly, another elec- 
tric fish (^Malapterurus electricus or M. benioiensis), 
which has but recently been carefully studied, and 
which occurs in the rivers of the Bay of Benin on the 
east coast of Africa. We cannot omit this opportunity 
of inserting Alexander von Humboldt'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 horse ; 
for even among the fishes it has a dangerous foe." The 
marshy waters of Bera and Eastro are filled with innu- 
merable electric eels, which at pleasure are able to 
discharge a deadening shock from every part of their 
slimy, yellow-speckled bodies. This species of gymnotus 
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 necessary to change the line of road 
from Uritucu across the savannah owing to the number 
of horses which, in fording a certain rivulet, annually 
fell a sacrifice to these electric eels, which had accu- 
mulated there in great numbers. All other species of 
fish shim the vicinity of these formidable creatures. 

' Vietvs of Nattire. 



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 pi»ostrated ; 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 livino- 
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 PHYSIOLOGY OF MUSCLES AND NERVES. 

plants — that which, flashing amid the roar of thunder, 
illuminates the wide canopy of heaven — which binds 
iron to iron, and directs the silent recurring course of 
the magnetic needle all, like the varied hues of the 
refracted ray of light, flow from one common source, 
and all blend together into one eternal all-pervading 
power/ 

3. All electric fishes are distinguished by 'the pos- 
session of peculiar organs in which the electric discharge 
originates. These resemble powerful batteries, which 
can be put in action by the will of the animal, and 
which then generate currents which, passing through 
the water, meet and act upon other animals which 
happen to be near, so that the latter may even be 
thus killed. These electric organs, as they are called, 
are formed on the same plan in all the three above-men- 
tioned genera of fishes. They consist of a large number 
of minute and delicate plates which, arranged side by 
side and enclosed in coverings of connective tissue, 
form the whole organ. In the Torpedo these organs 
lie flat on either side of the vertebral column. In the 
Gymnotus and the Malajjterurus they are arranged 
longitudinally ; and in the latter they form a closed 
tube, 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 Torpedo, vertically in the G'^/wnofi^s 
and Malapterurus. Each of these plates consists of 
an extremelv delicate membrane which, when the organ 
is in a state of activity, exhibits positive electricity on the 
one side, negative on the other. The currents of the 
numerous plates combine as in a battery, and thus all 
together afford a very powerful current. With each 



THE MULTIPLIER. 159 

plate is connected a nerve-fibre, by means of which 
the animal is caj^able 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 view, complete. 

Mention must yet be made of the fact that forms 
nearly allied to these fishes — for instance, the various 
forms of J/orm2/rt('§, which in structure resemble rays — 
possess similar organs, though these have not as jet 
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 residts 
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 cAses 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 j,^ .,^ 
containing diluted sulphuric acid, and then Ax klec tric 
uniting these above the fluid by a wire, clkre>t. 
the positive electricity passes through the wire from the 




lOO PHYSIOLOGY OF MUSCLES AND NERVES. 

copper to the zinc, and through the liqnid from the zinc 
to the copper. A magnetic needle is used to indicate 
the presence of such a current. An electric current, if 
made to pass parallel to 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 flows, 
and according to 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 be 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 when 
the current is comparatively strong, for the magnetic 
needle is retained in its position by the attraction of 
the earth, and the magnetic current must overcome 
this before it can deflect the needle. In order to detect 
weak currents, the wire through which the current flows 
is wound in several coils round the needle. As each 
coil exercises a force tending to cause the deflection 
of the needle, the deflecting force is increased ; and an 
instrument of this sort is, therefore, called a multiplier? 
In order to increase the sensitiveness of this still further, 
the attraction of the earth must be annihilated as far 
as possible, so that even weak currents are al)le to cause 
deflection. This is accomplished, for instance, by ar- 
ranging a fixed magnet above or below the magnetic 
needle, so that it acts on the' latter in a direction con- 

' If attention is paid to certain circumstances, which cannot be 
mentioned in detail here, the same instrument can also be used to 
measure the strength of currents ; it is, therefore, also called a gaU 
vauometer. 



THE MULTIPLIER OR GALVANOMETER. 



161 



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




FlG. 37. A i\IULTIPLIER. 



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 



162 PHYSIOLOGY OF MUSCLES AND NERVES. 

needles in opposite directions, the foi'ce of attraction 
of the earth-magnetism is entirely, or almost entirely 
removed, so that even very weak electric currents, if 
caused to pass round the needle in a suitable way, can 
cause a noticeable deflection of the needle. 

Fig. 37 represents a sensitive multiplier of a form 
well suited for physiological experiments. The two 
needles are connected together, and are suspended by 
means of a thread of silk from the frame h' 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- 
sured. The very thin wire, enclosed in silk, is wound 
on to the frame (7; the binding screws /' / serve to 
transmit the current. 

The use of tlie multiplier for physiological purposes 
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, the strength 
of the currents may be regarded as proportionate to the 
trigonometrical tangents of the angle of deflection.^ In 
order to measure slight deflections of this sort, our 
former method of observation by means of the mirror 
and lens may be used (chap, iv., § 3, p, 57). Either 
the magnet is in itself reflecting, or it is connected 
with a mirror^ and is suspended by a silk thread in a 
copper sheath, A, which is closed by plates of looking- 

' See Notes and Additions, No. 9. 



THE REFLECTING GALVANOMETER. 



163 



glass. The electric ciirrent 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 iristrtimeiit may be graduated at 
will. In order to measure the deflections, a graduated 
scale is placed parallel to the mirror when in its qui- 



164 PHYSIOLOGY OF MUSCLES AND NERVES. 

escent position, and its reflection is observed through 
the lens as described in Chap. IV., § 3. This may also 
be nsed to render the deflection visible to a large audi- 
ence,- by allowing the light of a sufficiently powerful 
lamp to fall on the mirror and throwing the reflection 
on to a screen by means of a lens. In order to in- 
crease the sensitiveness of the instrument, the influence 
of gravitation on the deflecting magnet is decreased, as 
already described, 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 the animal substances which are to be 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 present or not. But the 
more sensitive is the multiplier, the harder is it to 
connect any part of an animal with it in such a way 
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 coniiected 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 deflection 
of the needle always occurs, owing to the fact that the 
copper wires 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 cleaning; but this 
homogeneity soon disappears, so that even with this 
metal currents result which depend solely on the dis- 
similar nature 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 
amalofamated zinc of this sort, and these mav 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-Reymond, 
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 



166 



PHYSIOLOGY OF MUSCLES AND NERVES. 



of the multiplier were connected with two trou^^hs or 
vessels of cast zinc, the outer surfiices of which had 
been lacquered, while the inner cavity had been care- 
fully amalgamated. A solution of sulphate of zinc was 
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 way that 




Fig. 39. Homogeneous diverttxg vessel, as ised by E. du Bois- 

Keymond. 

part was immersed in the solution, part protruded over 
the edges, and these pads end in a sharply cut cross 
section. Small discs of an isolating substance (vulca- 
nised india-rubber), with the help of caoutchouc bands, 
retained the pads in their places. The vessels being 
pushed toward each other till the pads touched, or the 
intermediate space between the pads being bridged by a 
third pad, also saturated with a solution of sulphate of 
zinc, the needle of the multiplier continued unmoved, 



ELECTROMOTIVE FORCE. 167 

thus affordiug 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 arrang-ement is that the animal substances thus 
examined, being in contact with the concentrated solu- 
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 (^ 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 rUYSIOLOGY OF MUSCLES AND NERVES. 

on a magnetic needle. A piece of zinc and a piece of 
copper are immersed in diluted sulphuric acid, their 
projecting edges being connected by a piece of wire. 
When in this condition the apparatus 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 
observed 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- 
cumstances gives rise to the electric current, lies ; for if 
the wire by itself is bent into a circle no current is 
generated within it. Even the cause of the generation 
of currents within the apparatus 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 positive at the copper end, negative at 
the zinc end. On connecting the two metals by a 
closing wire, the opposed electric currents unite, and 
this is the cause of the current in the wire. The force 
which within the wire exhibited electric tension con- 
tinues to act, and causes the current to continue to 
traverse the wire. This is called the electromotive force 
of the apparatus. It expresses itself, when the apparatus 
is not closed, in the electric tension at the projecting 
metallic ends or poles of the apparatus ; and when 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 b}^ 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 B, 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 



PHYSIOLOGY OF MUSCLES AND NEKVES. 



and leave the body. If the body which is inserted is of 
simple form, the separate lines of transmission may easily 
be calculated from the form; in bodies of irrecrular 
shape this is somewhat hard to do, but even in such 
cavses it is possible to determine experimentally, not only 
that the electricity distributes itself throughout the 
body, but even the lines along which the separate cur- 
rents pass. 

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




Fig. 40. Distribution of the currents in irregular conductors. 

surface of one end and out at the other, it is prhiia facie 
probable that the lines simply traverse the length of 
the rod parallel to its axis. We may in imagination 
replace the rod by a bundle of wires, each of which will 
in this case be . traversed by a portion of the whole 
current. If one of these wires is cut, and its ends are 
connected with the multiplier, it is evident that that 
part of the current which traverses this wire must 
pass to the multiplier and cause a deflection of the 
needle. But even if the wire is not cut, but is con- 



ELECTKIC '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 tha,t 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 tendon 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 h (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 h d be 



172 PHYSIOLOGY OF MUSCLES AND NERVES. 

drawn downward from a h. In the centre there is no 
tension. At any point between the middle and the 
end a, say at e, a positive tension must prevail which is 
less than that at a, but greater than 0. It is expressed 
by the line e f. Similarly at any point between the 
middle and the end h, say at g, there is a definite 
negative tension which may be expressed by the line 
g h. 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 the 
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. 4L The fall ix the electricity. 

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 with each point in 
the wire. The gradual decrease of the tensions in the 
wire is evidently also the essential cause of the move- 
ment of the electricity through the wire, for at each 
point in the wire there are adjacent portions in which 
the tensions gradually become less from left to right, 
Bo that the electricity is enabled to flow from left to 
right. The case is 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 hi the electricity. 

Let us compare two wires of the same thickness, 
but of unequal length, a h and c cl (fig. 42). If « h 
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 ix diffeuext 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 cl may be 
represented by the oblique line g h. It will 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. Assuminsf now that the two wires a b and c cl 
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 



174 PHYSIOLOGY OF MUSCLES AND NERVES. 

instead of these two wires a number of separate wires 
are used, then the same thing happens ; and if the wires 
are welded together into a common conducting body, 
this does not essentially alter the conditions of the fall, 
so that we may imagine the whole body to consist of 
these separate wires, in each of which a definite flill, 
the steepness of which depends on the length of the 
particular wire, prevails. These wires are, however, 
merely paths along which the electric currents pass, 
and of which we have already spoken. In the case 
of these paths also definite falls must prevail, and these 
must be more steep in proportion as the points at 
which the electric currents 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 exhibit 
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 must effect a disturbance in the natural elec- 
tricity wdthin the applied wires, and consequently must 
generate an electric current from the point at which 
the tension is greater to that at which it is less. If a 
multiplier is inserted in the applied wire, the needle 
will be deflected. This is as true of a regular as of an 
irregular conductor. If in the body A B (fig. 43), 
electricity moves along various paths, and if, as we 
have seen, different tensions prevail at two points in 
such a path, a current must arise if the ends of a bent 
wire are applied to these points, and if the bent wire 
is supplied with a multiplier the needle will 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 = to a certain negative value (at B). 
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 ellctkicity ix 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 w^hich 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 rHYSIOLOGY OF xNEKVES ASD MUSCLES. 



CHAPTEE X. 

1. Diverting arclics ; 2. Current-curves and tension-curves ; 3. Di- 
verting cylinders; 4. Method of measuring tension differences 
by compensation. 

1. If the two ends of a bent wire are applied, in 
the way described in the last chapter, to any conductor 
which is traversed by currents, then part of the currents 
present in the conductor may flow through this wire. 
Part of the current is, as it were, conducted out of the 
body in order to facilitate its examination. Under 
certain circumstances this may cause an alteration in 
the conditions of the currents within the conductor. 
We will, however, assume that this is not the case, 
but that the tensions at the points at which the wire 
is applied to the conductor are not altered.' 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 on the resistance 
offered by the wire. 

A wire of this sort applied to a conductor tiaversed 
by currents is called a diverting arch ; the ends of the 
wire with w^hich it touches the body to be examined 
are called the feet of the arch; and the distance be- 
tween these feet is called tlu distance of tension, 

' The circumstances under wliich the excoptions occur cannot 
be explained here ; yet matters may be so arranged that such excep- 
tions do occur. 



CUERENT-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. »^8). In 
this arrangement the clay shields, saturated with a 
salt-solution, represent the feet of the divertiug 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 sm'face. 

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. 
9 



178 



PHYSIOLOGY OF MUSCLES AND NERVES. 



The case of organic tissues, with which we are con- 
cerned, is of the latter sort ; for we have seen that 
when these are inserted between the ends of a homo- 
geneous arch, electric action takes place under certain 
circumstances. The fact 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 —^ — ^~ — I D 




+ 



/" 



I'lG. 44. CURRENT-CUKVES AND TENSION-( U IIVES. 



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 electromotive force 
is situated in its axis ; then that which we show in 
the case of B G D E will be equally true of every 
other section. Let the point A represent the seat of 
electromotive force ^ which sets the positive electricity 
in motion toward the right, the negative electricity 
toward the left. The whole body is then occupied by 

* In order to have a phj-sical basis for this electromotive force we 
may imagine the cylinder to consist of a fluid, and that at the point 
A is situated a body consisting half of zinc, half of copper. 



CURRENT-CURVES AND TEXSION-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 J. 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 = ; 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 oiitside of the cylinder 
these iso-electric surfaces are exposed, and meet the 
surface in bent lines, which in the simjile figure 
which lies before us are all parallel, that is, surfaces 



180 THYSIOLOGY OF MUSCLES AND NERVES. 

wb-ich cut the surfaces of the cylinder parallel to the 
surfaces of its ends. The iso-electric surface repre- 
senting a tension = 0, cuts the cylinder near its centre, 
and divides it into two unequal halves, of which the 
right is positive, and the left negative. The other iso- 
electric 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 — h. 

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 form 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 surface, it may be said that if an electro- 
motive force is present within the body, this must cor- 
respond with a definite 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 the 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 foct 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. Diveuting cylinders as used by E. du Bois Reymond- 

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 divertins^ arch should touch the 
conductor which is to be examined at two points. An- 
other form of diverting apparatus, invented by du 
Bois-Eeymond, is used both for this purpose and for 
conducting currents to the body under examination in 
cases where 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 OF MUSCLES AND NERVES. 

cylinder a, somewhat flattened, is attached to the stand 
A, The socket e and the motor apparatus on the 
column h allow the glass cylinder to be placed in any 
desired position. Within the cylinder is a strip of 
amalgamated sheet zinc h, which can he connected 
with the multiplier by means of a wire. The glass 
cylinder is closed below . w ith a stopper of plastic clay 
moistened with a solution of common salt, the project- 
ing ends of which can be moulded into a point which 
touches the smallest possible point on the conductor 
to be examined. The space within the glass cylinder 
is filled with a concentrated solution of sulphate of 
zinc, and thus forms an unj)olari sable 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 diversion from the other point of the conductor. 

Whatever form of diverting apparatus is employed, 
the determination of the fact whether the two points 
touched by 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 
way that the various points in its surface successively 
lie on the pads of the above-described diverting vessel 
(see ch. ix. § 5), or by touching them with the ends of 
the diverting cylinder just mentioned, it may be dis- 
covered which points have equal tension (for in such 
cases the multiplier will indicate no deflection), or, if the 
points touched are unequal in tension, it may be dis- 
covered at which the positive tension is greatest. For, 
from this latter point a current must pass through the 
multiplier to the point at which the 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.^ 

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 measm'ed with quite sufficient pre- 
cision by a method invented by Poggendorff and after- 
wards improved by du Bois-Eeymond. 

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 
• See Notes and Additions, No. 10. 



184 



PHYSIOLOGY OF MUSCLES AND NERVES. 



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 
deflection of the multiplier in an opposite direction, and 
exactly to such a degree that the multiplier no longer 
indicates any deflection, then the two influences must 




Fig. 46. Measurement by compensation of the difference of 

TENSION. 

be equal, and the one may serve as a measure for the 
other. The experiment indicated in these instances 
is called ineasurement by compensation. In order to 
apply it to the case in point, the action of one dif- 
ference of tension is cancelled by that of another which 
may be altered at will. The rheochord, vrhich has al- 
ready been described, affords a convenient means of 
doing this. 

Let R R (fig. 46) be a wire extended in a straight 
line (the line of the rheochord) through which a current is 



MEASUREMENT OF DIFFERENCES OF TENSION. 185 

passed from the apparatus A". 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 
rheochord. Let us assume that the current passes from 
R' to R, that the tension at jR = 0, and that it in- 
creases toward R\ As the rheochord 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 B, within which 
an electromotive force is present, is to be examined. 
Naturally two points on its surface, a and b, have dif- 
ferent tensions, and it is this difierence 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- 
chord line. Two differences of tension now act on the 
multiplier. Firstly, the differences of tension between 
the points R and S of the rheochord; and, secondly, 
that between the points a and b. If at b there is a 
greater positive tension than at a, then the two dif- 
ferences of tension are opposed in action.^ As the 

• 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 



PHYSIOLOGY OF MUSCLES AXD ^'ERVES. 



difference in tension between R and S can be altered 
by changing the position of S, the slide S may be 
placed in such a position that the two influences exactly 
balance each other, or, in other words, in such a position 
that the multiplier indicates no deflection. Thus it is 
evident that 



S - B 

Difference in tension at tlie 
two points of tlie rlieochord. 



b - 



a 



= 



Difference in tension at 
the two points of the con- 
ductor. 



m ^ - R = h - 



a 



the difference, that is, of the tension between 6 and a 
is equal to the difference of tension between B and K. 




Fig. 47. Du Bois-Rkymond's round cumim^nsator. 

The latter is expressed in millimetres, each of which 
indicates a certain constant amoiint when a definite 
rheochord wire is used, and when the current which is 
conducted through the latter is of a definite strength. 
To facilitate measurements of this kind, du Bois- 



MEASUREMENT OF DIFFERENCES OF TENSION. 187 

Eeymond 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 kouni> 

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 7% which is pressed by 



188 PHYSIOLOGY OF MUSCLES AND NERVES. 

a spring against the wire, and replaces the slide. By 
turning the disc the length of the inserted portion of 
the rheochord is altered. 

The whole arrangement is shown more clearly in 
tig. 48, which may at the- same time serve as a diagram 
of the experiments with muscles and nerves, to which 
we are 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 ; yu, 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- 
sation 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 
tested. 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 XI. 

1. A regular muscle-prism ; 2. Currents and tensions in a musele- 
prism ; 3. Musole-rhombus ; 4. Irregular muscle- rhombi ; 5. Cur- 
rent of VI. gastrocncviiKS. 

1. Beginning 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 T^iuscle-jprisin. 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 PHYSIOLOGY OF MUSCLES AND NERVES. 

parallel to each other, and that the two cuts are made 
at right angles to the direction of the fibres. Fig. 49 
diagrammatically represents a regular muscle-prism of 
this sort. The horizontal stripes represent the separate 
bundles of the fibres. The outer surface of the prism, 
which therefore corresponds with the upper surface of 
the fibres, is called the loiujitudiiial section of the 
prism ; and the terminal surfiices, at right angles to 
the longitudinal section, are the cross-sections of the 
muscle-prism. The lines running at right angles to 
the direction of the fibres are, as we shall presently 
find, tension-curves. 

A regular muscle-prism such as this exhibits a very 



n, a' a/ n' a' a n.' a' a' a' a' 

Fig 49. A regilau mlscle-prism, 

simple distribution of tension. All the lines of tension, 
or the iso-electric curves, run on the surface and are 
parallel to the cross-sections. Ivound the middle of the 
muscle-prism passes a line separating it into two sym- 
metrical halves ; this we will call the equator. The 
greatest 'positive tension to be found anywhere on the 
surface prevails at this point. Every 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 positive tension gra- 
dually decreases along the longitudinal section quite 
regularly in both directions, until, at the point where 
the longitudinal meets the cross-section, it = 0. 

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 shoAvs 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. Xor 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 ah c d 
represents a section through the muscle-prism; a h 
and c d are transverse sections through the longitu- 



192 



PHYSIOLOGY OF MUSCLES AND NERVES, 



dinal section, and a c and b d are transverse sections 
through the cross-section. The curved lines represent 
the divertinof arches, and the arrows show the direction 
of the currents ^Yhich are generated in these. No 
currents are generated in arches 6, 7, or 8, for these 
unite symmetrical points. 

Moreover, the rate at which the tension decreases 
ill the longitudinal section is, not regular, but at a 
gradually increasing speed from the equator to the 
ends. If, therefore, we find these iso-electric curves, the 




Fig. 50. Curuents in a muscle-pkism. 

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 
too-ether toward the edge of the cross-section. If the 
tension prevailing at each point in one side of a longi- 
tudinal section is represented by the height of a straight 
line drawn at right angles to that side of the longitu- 
dinal section, then the curve which unites the heads of 
these lines is level at the centre of the longitudinal 
section, but sinks rapidly down toward the edges of the 
cross-section. A somewhat 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. Texsiox 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 concentiic 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 



194 PHYSIOLOGY OP MUSCLES AND NERVES. 

the direction from the positive to the negative point ; 
but that, if the feet are both positive, or both negative, 
the current passes from the more to the less positive 
point, or from the less to the more negative point. 
From the curves in A and 5, fig. 51, which show the 
tensions, the currents indicated in fig. 50 may therefore 
easily be discovered. 

3. Once more let us 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 onuscle-rhomhus ; if the cross-sections are 
parallel to each other, it is a regular muscle-rJiombus ; 
if otherwise, an irregidar niiiscle-rlioinhus. 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 cm'ves 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 lonsfitudinal section, or outer 
surface of the muscle-rhombus, and the cross-sections. 
The former are always positive, the latter negative. 
But both in the lonijitudinal and cross-sections a 
difference is noticeable between the obtuse 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. Consequently, a peculiar displacement of the 
tension-curves, of which fig. 52 is intended as a re- 
presentation, takes place in a regular muscle-rhombus. 



THE MrSCLE RHOMBUS. 



195 



Let us suppose that the muscle from which the rhombus 
was cut was cyhndrical. 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- 
f resented in the figure. In it, a h and c d correspond 
with the longitudinal section, a c and h d the cross- 
sections. The latter are identical with the longitudinal 
axis of the actual cross-sections. On the side corre- 




TeNSIOXS ox a llEGUr.AIi MUSCLE-EHOMBL'S. 



sponding 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 



196 



PHYSIOLOGY OF MUSCLES AND NERVES. 



cross-section, near the acute angle. In the longitudinal 
section they form spiral lines, which run obliquely round 
the outer surface of the cylinder. The electromotive 
equator, which unites the points at which the greatest 
positive tension prevails, forms a line round the circum- 




FiG. 53. The curkexts in a regular muscle-rhombus. 



ference, which separates the rhombus into two equal 
halves. 

Supposing tliat a plane is drawn in such a regular 
muscle-rhombus, through the small axis of the elliptic 
cross-sections, a rectangular figure will be obtained. 
The muscle-fibres l3"ing in such a section are all cut 
in a similar way, and their condition is exactly alike. 
Therefore in this section also the greatest tension on 



IRREGULAR MUSCLE-RHOMBl. 197 

the lono-itadinal, 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 w^hich 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 NERVES. 

between points in the cross-section respectively. The 
position of these most strongly positive and most 
strongly negative points depends on the angles which 
the fibres form with the cross-sections, and may be 
found by the rules given in the last 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 (m. gastrocnemius). 
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 wc 
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 excitabihty 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 must, however, 
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 with the 
muscle-prism and muscle-rhombus, we assumed that 
the pieces were cut from parallel-fibred muscles. The 
longitudinal sections of these pieces retained their 
covering of muscle-sheath (j^erimysium) and, in fact, 
corresponded with the natural surface of the muscle. 
The cross-cuts were, however, made into the actual 
substance of the muscle, so 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. Kow the action both of lonofi- 
tudinal and of cross-sections is the same whether they 
are natural or artificial.^ It is, therefore, always pos- 
sible to obtain currents from an uninjm-ed 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. ^Ye now have an 
upper tendon plate, situated within the muscle, from 
which muscle-fibres pass obhquely 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 
' Exceptions to this rule will presently be mentioned. 



200 



PHYSIOLOGY OF MUSCLES AND NERVES. 



surface of which (turned toward the bone of the lower 
leg) is formed solely of muscle-fibres, exhibiting a delicate 
longitudinal streak as the only indication of the tendon 
buried within it ; the arched dorsal surface is, on the 
contrary, clothed, as regards the lower two-thirds of its 
length, with tendonous substance which passes below 
into the so-called tendo Achillis. 

It is evident that such a muscle has naturally an' 
oblique cross-section, represented by this tendonous 
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 pre- 




FiG. 54. The cuuhents of a gastrocnemius. 

paration afford currents ; for which reason it may be 
most advantageously used in a large number of experi- 
ments. 

Eegarding once more the structure of the gastro- 
cnemiiis, as it has just been described, a natural longitu- 
dinal section is recognisable in the whole flat part and 
a little of the upper portion of the curved surface ; and 
a natural cross- section is to be recognised in the greater 
and lower part of the curved upper surface. No second 
cross-section exists in this muscle, for the upper tendon 
is buried within the muscle. The currents which the 
muscle sends through an arch 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 



202 PHYSIOLOGY OF MUSCLES AND NERVES. 



CHAPTEK XII. 

1. Negative variation of the m uscle- current ; 2. Living muscle is 
alone electrically active ; 3. Parelectronomy ; 4. Secondary pul- 
sation and secondary tetanus; 5. Glands and their currents. 

1. The powerful current afforded by an entire m. gas- 
trocnemius enables us to answer the important question 
as to the character of electric phenomena during con- 
traction. All that is necessary is to prepare this muscle, 
together with its nerve, and to insert its upper and 
lower ends between the pads of the diverting vessel 
already described, and then to place the nerve on two 
wires so that it can be irritated by inductive currents ; 
it must then become evident whether the activity of 
the muscle has any influence on its electric action or 
not. 

In order to carry out the experiment, let us suppose 
the muscle, as shown in fig. o5, placed between the 
pads of a diverting vessel, these pads being brought 
somewhat near each other, so that the contact of the 
muscle with the pads is not disturbed by the con- 
traction of the former. The nerve, which has been 
extracted with the muscle, is laid on two wires which 
are connected with the secondary spiral of the induct ive 
apparatus. A key, inserted between the nerve and the 
spiral, regulates the inductive currents so that the nerve 
is not excited. When all is 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 powerfu. contractions. 




Fig. 55. The muscle-current during contractiox. 

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 niYSIOLOGY OF MUSCLES AND NERVES. 

tated and the muscle contracts, the current becomes 
weaker ; the current afforded by the compensator thus 
gains preponderance, and effects a deflection which is, 
of course, in exactly the opposite direction to that which 
was originally effected by the muscle. 

There is stronsf reason to believe that this alteration 
in the 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, 
thermical, or other irritants may be 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 same 
phenomenon may also 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 muscles 
whether they are in their natural position or have been 



NEGATIVE VARIATION OF THE MUSCLE-CUKRENT. 205 

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




Fig. 66. Deflection ov the magnetic needle by the avill. 

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 



206 PHYSIOLOGY OF MUSCLES AND NERVES. 

muscle of one arm, the result is an immediate deflec- 
tion of the multiplier, which indicates the presence of 
a current ascending in the contracted arm from the 
hand to the shoulder. If the muscles of the other arm 
are contracted, a deflection occurs in the opposite direc- 
tion. We are, therefore, able by the mere power of the 
will to generate an electric current and to set the mag- 
netic needle in motion. 

Summing up 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 with the fact of activity itself. As, during this 
alteration, the current which may be exhibited in an 
applied arch becomes weaker, the term negative-varia- 
tion of the 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 activity of the muscle. 

It may, in the first place, be safely asserted that all 
muscles of all animals, as far as they have at present 
been examined, exhibit the same electric action. Even 
smooth muscles act electrically in the same way ; 
though in that case the phenomena are less regular, 
owing to the fact that the fibres are not so regularly 
arranged as in striated muscle. Moreover, the electric 
activity of smooth muscles seems to be somewhat 
weaker. 



LIVING MUSCLE ALONE ELECTRICx\LLY 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. I*for 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, 
throuofh which the electric action is necessarilv observed, 
is in itself somewhat electrically active,' and that, in 
other ways also, it increases the difficulty of proving the 
* Tlies3 skin-currents will be again mentioned. 



208 THYSIOLOGY OF MUSCLES AND NERVES. 

presence of muscle-currents. Due regard being had 
to all these circumstances, the conclusion may yet be 
drawn that entirely uninjured muscles situated in their 
natural position are in themselves electrically active. 
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 very 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 artificial 
cross-section in which the action is powerful. 

This phenomenon, which was called parelectronomy 
by E. du Bois-Keymond, because it differs from the 
usual electric action of muscles, gave rise to that ex- 
planation of the electric phenomena according to which 
the electric opposition between different portions of the 
muscle is not present in the normal muscle, but only 
intervenes on the exposure of the muscle. The difii- 
culty mentioned above, of showing the muscle-currents 



SECONDARY PULSATION AND TETANUS. 209 

in uninjured animals, lent force to this explanation. 
Yet no sufficiently strong proof of this view has been 
brouofht 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 
w^hether 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. 

On a gastrocnemius 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.* 

' This current may at the moment of i'.s generation, i.e. on Vne 
sudden appli< nation of the nerve, exercise an irritating effect on 
the nerve and may elicit a pulsation of the muscle. This is tV.e 



210 



PHYSIOLOGY OF MUSCLES AND NERVLS. 



If the nerve of the muscle B is then irritated, either by 
closing or by opening a current, by an inductive shock, by 
scission, by pressure, or in any other way, the muscle A 
is observed to pulsate also. This is called second- 
ary pttlsation. The explanation is easy. The muscle- 
current from B during its pulsation suffered a negative 
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 





FiQ. 57 & 58. Secondahy PULSATrON. 

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

A variation of this experiment is very interesting. 
The heart of a frog continues to beat for some time 
after it has been extracted from the body. If the nerve 
of a muscle is placed on this heart so as to touch its 
base and point, the muscle pulsates at every beat of 
the heart. In this case, the heart-muscle affords the 
muscle-current, the negative variation of which irritates 
the applied nerve and causes secondary pulsation. 



' pulsation without metals ' (^ZucliUfffi oJn/e Mehdlc) which lias 
gained celebrity from the writings of Volta, Humboldt, and others. 



SECONDARY PULSATION A^D 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 MUSCLES AND NERVES. 

fibre of some length is 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 w^hole fibre is irritated at once, the elec- 
tric change occurs simultaneously throughout the fibre, 
and this is then followed by the mechanical change. 

5. 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 outer skin 
(corium), which lies above it. The cavity maybe hemi- 
spherical, flask-shaped, or tubular. In the latter case the 
tube 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. These are all simjple glands. 
Compound glands are found when several tubular or 
knob-shaped glands open with a common mouth. Sub- 
stances, often of a very peculiar character, are 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, owing to their power of fermentation, play an 
important part in digestion, the gall, which is formed 
within the liver, and other substances. The similarity 
alluded to between the muscles and the glands consists 
in the dependence of both on the nerves. If a nerve 
which 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 month 
of the gland. It is certainly an important fact that, 
except mnscles (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.^ 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 

^ These currents of the skin-glands afford one of the reasons to 
which allusion has already been made (§ 2) why the indication of 
muscle-currents in living and uninjured animals is beset with diffi- 
culties. As the currents of the skin-giands 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 PHYSIOLOGY OF MUSCLES AND NERVES. 

the mucous membrane of the stomach and intestinal 
canal, it may be clearly shown that the electric force 
is really situated in the glands. On irritation of the 
nerves which pass into the skin by which the glands 
are excited into activity, the gland-current decreases in 
strength, and exhibits a negative variation, just as the 
muscle-current decreases w^ien the muscle is excited 
into activity. In this case, also, a relation therefore 
exists between the activity and the electric condition ; 
and this adds to the similarity between muscles and 
glands. 

Engelmann 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 MUSCLES AND NERVES. 

aud oblique cross-sections, such as we made in the case 
of muscle ; nor can phenomena due to the oblique course 
of the fibres be detected, as in muscle. Where hu-ger 
masses of nerve-substance occur, as in the dorsal mar- 
row and brain, the course of the fibres is so complex 
that nothing can be affirmed except that the cross- 
sections are always negative in distinction from 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 actiorf 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 the latter neither optical, chemical, nor any other in- 
dicable 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 view is 
taken as to the causes of electric action in nerves, it 
is at least certain that every change in the electric con- 
dition must be founded on 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-Eeymond 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 




+ 



+ - 4- 

FiG. 69. Tension in neuvks. 



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 exercise's 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 MUSCLES AND NERVES. 

mitted only toward the periphery or also toward the 
centre ; or as to whether, when a sensory nerve alone is 
irritated, the excitement is transraitted 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 apparatus. If a 
purely motor nerve is irritated, and is then tested at a 
central point, negative \ariation is found to occur in 
this also; and similarly, if a purely sensory nerve is 
irritated, negative variation may be shown in a part of 
the nerve lying between the irritated point and the 
periphery. This, therefore, shows that the excitement 
in all nerve-fibres is capable of propagation in l^oth 
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.^ 

4. If negative variation in the nerve current is 
really a necessary and inseparable sign of that condition 
within the nerves which is called the ' activity of the 
nerves,' it must, like the excitement, propagate itself 
within the nerve at a measurable speed. Bernstein 
succeeded in proving this, and measured the speed at 
which the propagation occurs. If one end of a long 
nerve is irritated, the other end being connected with 
a midtiplier, a certain time must elapse before the 
irritation, and consequently also the negative variation, 
' See Notes and Additions, No. IL 



RATE OF TEOrAGATION OF NE(jAT1VE 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 
ne«-ative variation is, even in the case of the longest 
nerv^es 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 multi23lier to occur somewhat later than 
the irritation. When this difference in time reached a 
certain amount, negative variation intervened. From 
the amount of rhis 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 wav 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 



niYSIOLOGY OF MUSCLES AND NERVES. 



can be expected in experiments of this nature ; and it 
may be unconditionally inferred from this correspond- 
ence that negative variation and excitement in the nerves 
are two intimately connected and inseparable processes, 
or rather two aspects of the same process observed by 
different means.^ 

5. The negative variation of the nerve current is 
not the only electric change known to occur in nerves. 
Under the name ' Electrotonus ' 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 




Fig. 60. The changes in texsiox during electrotoxls. 

electric current is transmitted through a part of it. 
These changes in the excitability correspond with 
changes in the electric condition of nerves, which we 
called electrotonic. In fig. 60, oi n' represents a nerve, 
a and k two wires applied to the nerve through which an 
electric current is transmitted from a toward Z-; a is 
therefore the anode, h the kathode of the current em- 
ployed for the generation of electrotonus. As soon as 
this current is closed, all the points of the nerve on the 
side of the anode (from n to a) became more positive, 
all on the side of the kathode (from h to n) more 

' See Notes and Additions, No. 12. 



ELECTROTONUS. 221 

negative than they %uere. 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 Hnes, 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.^ 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 
^ See Notes and Additions, No. 13. 



222 PHYSIOLOGY OF MUSCLES AND NERVES. 

in tension and the change in excitability both probably 
depend on molecular changes within the nerve, as to 
the nature of which we are not yet in a position to say 
anything further, but the simultaneous appearance of 
which, under the influence of externally applied electric 
currents, is nevertheless very 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. If the diverting arch is 
applied to two symmetrical points of the nerve, they 
are homogeneous. If it is applied to any other points, 
the existing differences in tension can be cancelled by 
the method of compensation above described (chap. x. 
§ 4). The differences in tension due to electrotonus 
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 nerves of the tissue of 
the electric organs, in which in the cases of the fishes 
already mentioned such powerful electric action takes 
place, may be classed with these. Without entering 
deeply into the researches, as yet very incomplete, 
which have been made into the structure of these 
electric organs, we may yet accept as already proved 
that the so-called electric plate — a delicate membran- 
ous structure, very many of which, arranged side by 
side 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 nnder 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 diflference 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 tl e 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 PHYSIOLOGY OF MUSCLES AND NERVES. 

years ago stated as the result of his observations, 
that in the leaves of Venus' Flytrap {Dioncea musci- 
pida), regular electric currents occur, which, during 
the movement of these leaves, exhibit negative varia- 
ation exactly as do nerve-currents. He was induced 
to make his observations by Charles Darwin, who, in 
the course of his study of insectivorous plants, at- 
tempted to show an analogy between the leaf-move- 
ments of the Dioncea and the muscular movements of 
animals. Darwin's observations have since been pub- 
lished in detail.! They show the interesting fact that 
in various plants glandular organs occur which secrete 
juices capable of digesting albuminous bodies. The 
plant above mentioned, Dioncea muscipula, is 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 halves 
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 analogotis 
to muscle-movements, and whether the identity extends 
even to the electric phenomena, as Bm-don-Sanderson 
w^ould have us beheve. Eecent researches by Professor 
Munk of Berlin have not confirmed this. The move- 
ments of the leaf of the Diono'a 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 different cell-strata. The leaf does 
indeed exercise electric action, though not in the simple 

' Oil Tnsecth'07'ou8 Plants. London, 1875. 



ELECTRIC ACTION IN PLANTS. 225 

way claimed by Biirdon-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 



226 PHYSIOLOGY OF MUSCLES AND NERVES. 



CHAPTER XIV. 

1. General summary; 2. Fundamental explanatory principles; 3. 
Comparison of muscle-prism and magnet ; 4. Explanation of the 
tension in miLScle-prisras and muscle-rhombi ; 5. Explanation 
of negative variation and parelectronomy ; 6. Application to 
nerves ; 7. Application to electric organs and glands. 

1. Summing up the most important flicts given in 
the foregoing chapters, we may make the following 
statements : — 

(1) Every muscle, and every part of a muscle, luhen 
quiescent, is positive on its longitudinal section; 
negative on its ci^oss-section. In a regular muscle- 
prism, the p)0sitive tension decreases regularly from 
the centre of the longitudinal section toiuard the ends; 
and the negative tension does the same in the cross- 
sections. In a muscle-rhomhus the distribution of 
the tension is someiuhat different, for in it the 
greatest positive tension is removed toward the obtuse 
angle of the longitudinal section, the greatest negative 
tension totvard the acute angle of the cross-section. 

(2) During the activity of the muscle the diff^erences 
in tension decrease. 

(3) Entire muscles often exhibit but slight differ- 
ences in tension, or even none at all; but vje must 
nevertheless assume the existence of electric opposition 
in them. 

(4) Nerves are positive 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, ivhen 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 onter 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. AYe 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. INIore- 
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 PHYSIOLOGY OF MUSCLES AND NERVES. 

2. Let us suppose, for example, that in the body 
described in Chapter X. § 2, the distribution of the 
tension which prevails on the surface as the result of 
the electromotive forces then assumed, has been proved. 
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-electric 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 so 
on. Helmholtz has shown that when many such 
electric forces are present at one time in a body, 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 com- 
binations- the preference shall be given. The theory 
selected 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 the 
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 tliese 
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 PHVSIOLOGY OF MUSCLES AND NERVES. 

fiicts, for but a few of winch we have been able to find 
place in the foregoing chapters, he was dissatisfied with 
this way, and, therefore, tried the second. And thus he 
was enabled to form an hypothesis which afforded an 
explanation of all the previously-hnow^n flicts, 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- 
firmed 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-Reymond as being 
alone capable of including and combining all electro- 
physiological facts. 

€€€€€C)€l)€€€)f|€C€€C)€€€e)€€C ' 
C€€€C€€€C€C€B)€CC€€€€)C)€€0 
€Ce€€C€€€€€€KC€«)€C)€€€€€C) 
C€€€€€€€€€©C|€€€€€€€«)C€€C> 

Fig. GJ. Theory of magnetism. 

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 magnetic rod. 
It is a well-known fact that every magnetic rod has two 
poles, 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 centre, each 
half becomes a complete magnet, with 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 




EMfi 



Fig. 02. Diagkam of a piece of muscle-fibue. 



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 j^art 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 rnYSiOLOGY 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 the double-refracting disdiaclasts. Such a particle 
may be called a onuscle-element. The muscle-fibre 
would accordingly consist of regularly arranged muscle- 
elements, the sequence of which, in the longitudinal 
direction, forms the fibrillae 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 as 
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. In 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 electric characters as are 
observable in the entire muscle. 

4. We therefore assume that every muscle-element 
is the seat of an electromotive force, in virtue of which 
it is positive on the longitudinal section, negative on 
the cross-section. If a single muscle-element of this 
sort were surrounded by a conducting substance, sys- 
tems of current-curves from the side of the longitudinal 
section to that of the cross-section would be present 
within it. If many such muscle-elements are arranged 



TENSIONS IN MUSCLf>rRISMS AND RHOMBI. 



233 



side by side and one behind the other in the regular 
arrangement which we have assumed, then the Avhole 
must, as has been shown by calculation, be positive 
throughout its longitudinal section, negative through- 
out its cross-sections. Now, sipposing that this whole 
ao-ofreofation 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 




Fig. 63. Diagham of the electric action in an aggregation 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 way 
toward the edges. 

We now take a bundle of muscle-fibies, 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 



niYSIOLOGY OF MUSCLES AND NERVES. 



fore become quite inoperative, or less operative than 
the inner. This injurious influence must be yet more 
strongly developed on the cross-section, where a layer 
of crushed, that is, dead muscle-substance, overlies 
the parts which yet remain operative. Owing 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 always 
remain unaltered. Each part of a muscle-prism must 
act as would the whole. 




Fig. G-i. Diagram of an oblique cross-sectiox. 

Oar 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 muscle- 
fibres, as in a regular or irregular muscle-rhombus, then 
our assumed muscle-elements, at the cross-section, will 
be arranged one over the other like steps, and are 
clothed by a* layer of crushed, and therefore inopera- 
tive tissue, as is represented in fig. 64. On such a 
cross-section it is evident that separate currents must 
circulate from the positive longitudinal section to 
the negative cross-section of each individual muscle- 
element, and these combine with the current circu- 



NEGATIVE VARIATION AND PARELECTRONOMY. 235 

latiiig from the longitudinal to the cross-section of 
the entire prism, to make the obtuse angle more 
positive than negative. 

5. AVe 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. Good hypotheses are always avail- 
able in both these ways, and the scientific man uses 
only such. He may perhaps amuse himself in a leisure 



236 PHYSIOLOGY OF MUSCLES AND NERVES. 

quarter of au hour by allowing his imagination to 
carry the hypotheses further than the point up to 
which they are based on known facts ; but he does not 
presume to urge the results on others. 

Finally, we have to examine how far the 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-fibres may 
be regarded as a layer of non-active conducting sub- 
stance. 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 seen, though 
generally, yet not always the case. The natural cross- 
section of a muscle is generally very slight Ij^ negative, 
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 thermically. 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 muscle-elements in each muscle-fibre may 
sometimes be different from that at all other points. 
If, for example, the cross-section in the terminal 
muscle-element were not negative, the muscle-fibre 
could afford no current, though such a current would 
arise as soon as this terminal muscle-element was re- 
moved or was transformed into a non-active conductor. 
E. du Bois-Reymond has lately succeeded in discover- 
ing a very probable reason for this abnormal condition 
of the ends of muscle-fibres ; but without entering too 



THE NERVES. 237 

deeply into details we should not be able to explain 
this here.^ 

. 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 being 
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 dui'ing 
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 
activity is such as to lend weight to our assumption of 

' See Notes and Additions No. H. 



238 PHYSIOLOGY OF MUSCLES AND NERVES. 

the similarity in the arrangement of their smallest 
particles. 

But together with many points of resemblance, 
nerve and 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- 
fluence of continuous electric currents, exhibits those 
changes in excitability which we observed under the 
name electrotonus, and which, as we have seen, corre- 
spond with changes 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 particles, 
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 water, 
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 two atoms of oxygen ; 
a molecule of common salt consists of an atom of 
natron and an atom of chlorine, and so on.' A piece 
of salt contains a very large number of such atoms 
composed of chlorine and natron, but each of these 

* Dotails of tlie atomic and molecular theory will be found in 
* The New Chemistry.' Cooke (Litcrnational Scientific Series, 
voL ix.). 



THE NERVES. 239 

(in 2^^^^'^' 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- 
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 and 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- 



24:0 PPIYSIOLOGY OF MUSCLES AND NERVES. 

lecules combined in a particular way, many of which, 
in combination, form a muscle-molecule or a nerve- 
element respectively. 

We 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- 
tudinal 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 changed. 
This changed position is retained as long as the electric 
current flows through the nerve, and disappears more 
or less rapidly after the opening of the current. At 
flrst 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 with their distance from the centre. Or we 
may also refer to the conception which physicists have 
formed of the so-called electrolysis, the analysis of a 
fluid by an electric current. All these analogies can 
only explain the process in so far that we recognise how 
an electric current is capable of causing a change in the 
relative position 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 hj^pothesis 
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 bo 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 a,re 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 magrnetic 
forces were present within it. But comparison with the 
permanent magnet, and the possibility that thoroughly 



242 PHYSIOLOGY OF MUSCLES AND NERVES. 

non-magnetic iron may at any time be transformed into 
a magnet, makes the involved conception quite natural. 
It is 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 combined 
with what we know of nerves and m.uscle, naturally 
leads us to suppose that electromotive forces are pre- 
sent in the electric plates, but that they are so ar- 
ranofed as to cause no observable differences of tension 
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, differences 
of tension between the two surfaces of the electric plates 
intervene, and, as all the electric plates in an organ act 
in the same way, the result is a powerful electric shock, 
which, in spite of its powerfid effect, differs from the 
negative variation of the m.uscle- and nerve-currents only 
as does the powerful current of a many-celled galvanic 
battery from the weak current of a small apparatus. 

In order to make the similarity between the electric 
organ on the one hand, and muscles and nerves on the 
other, yet more prominent, we w^ill carry the compari- 
son with magnetic phenomena yet further. In fig. 65, 



B N s 

Fig. Go. IVLvgxktio im)L'<ti(»x. 



J. j5 is a piece of soft iron, N S a magnet which we bring 
from some distance toward the iron rod A B. The result 
is to evoke magnetism in J. J5, J. becoming a north pole, 
and B a south pole. Now^, let us suppose that the non- 
magnetic iron rod AB i?> replaced by an entirely similar, 



GLANDS AND ELECTRIC ORGANS. 243 

but magnetic rod JS\ S^ (fig. 66), At the moment at 
which the magnet NS is brought near, the magnetism 
of i\^i S^ becomes weaker, ceases entirely, or is even 



Fig. 66. Magnetic inductiox. 

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 PHYSIOLOGY OF MUSCLES AND NERVES. 



CHAPTER XV. 

1. Connection of nerve and muscle; 2. Isolated excitement of 
individual muscle-fibres; 3. Discharge-hypothesis; 4. Principle 
of the dispersion of forces ; 5. Independent irritability of muscle- 
substance ; G. Curare; 7. Chemical irri'ants; 8. Theory of the 
activity of the nerves. 

1. In the foregoing chapters we have examined the 
characters of muscles and nerves separately. The 
muscle is distinguished by its power of shortening and 
thereby accomplishing work. The nerve has not this 
power : it is only able to incite the muscle to activity. 
We must now inquire how this incitement, this trans- 
ference of activity from the nerves to the muscles, 
occurs. 

To understand the action of a machine, of any piece 
of mechanism, it is necessary to learn its structure and 
the relative positions of its separate parts. In our case, 
microscopic observation can alone afford the explana- 
tion. If we trace the course of the nerve within the 
muscle, we iind that the separate fibres, which enter 
the muscle in a connected bundle, separate, run among 
the muscle-fibres, and spread throughout the muscle. 
It then appears that the single nerve-fibres divide, and 
this explains the fact that each muscle-fibre is eventu- 
ally provided with a nerve-fibre — long nerve-fibres even 
with two— although the number of nerve-fibres which 
enter the 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-cvlinder. 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 nekves 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- 



246 PHYSIOLOGY or muscles axd xekves. 

what different ; but the relation between the nerve and 
the muscle is the same. The essential fact is the same 
in all cases : the nerve ^^a-s'ses into direct contact 
ivith the muscle-suhstance. All observers are now 
agreed on this point. Uncertainty prevails only as to 
the further nature of the terminal plate. In the frog, 
for instance, there is no real terminal plate, but the 
nerve separates within the sarcolemma 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 be 
elicited by irritation of individual fibres of a nerve. 
For the nerve-fibres, in their course within the muscle, 
touch externally many muscle-fibres, over which they 
pass before they finally end at another muscle-fibre. 
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 excitement present in the 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- 
telUofible 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 PHYSIOLOGY OF MUSCLES AND NERVES 

muscle. We may, therefore, conceive the process some- 
what as follows. The excitement in the nerve, however 
caused, propagates itself along the nerve-fibre until it 
reaches the end of the latter. Connected with it is an 
electric process, by which a sudden electric variation 
is caused in the terminal apparatus of the nerve- 
fibre, and this excites the nerve-substance, just as a 
shock acting externally immediately on the muscle 
would excite it. 

Following du Bois Keymond, the above conception 
may be called the discharge-hypothesis {Entladiings- 
hypothese). According to it, the muscle end of a nerve- 
fibre must be regarded as similar to an electric plate 
in the pecuhar 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 Gerlach 
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 v/ill be unaffected. All that we 
claim is that an electric discharge, by which the muscle- 
substance is irritated, takes place in the terminal expan- 
sions of the nerves, of whatever form these expansions 
may be. 

Against the acceptance of this view a difficulty 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 irreo^ular 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.^ 

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 

' See Notes and Additions, No. 15. 
12 



250 PHYSIOLOGY OF MUSCLES AND NERVES. 

on tlie nerve and which are active in the nerve itself 
while the latter transmits the excitement. To use a 
common but aj)propriate simile, the nerve is but the 
spark which causes the explosion in the powder-mine ; 
or, to carry the simile further, the sulphur train which, 
being fired at 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 the 
nerve is only the incitement in consequence of which 
the chemical forces inherent in the muscle come into 
play. Physicists call such processes the freeing of 
forces. The nerve-irritant, therefore, frees the muscle- 
forces, and these translate themselves into warmth and 
mechanical work. In every such freeing, the fireeing 
force is generally very small when compared with the 
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 of 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 of unstable equipoise. But 
there is also a chemical unstable equipoise. Carbon 
and oxygen may lie for thousands of years side by side 
without combining. Closely mingled, as in gunpowder, 
or still more closely, as in nitro-glycerine, they are in 
unstable equipoise ; the slightest blow suffices to cause 



IXDErENDENT IRRITABILITi' OF MUSCLES. 251 

their combination, which by their expansion is able to 
accompHsh such gigantic work.^ 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 sensitive, 
because even an insiornificant 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 indicable, 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. 

o. A sensitive machine is not equally sensitive to 
all possible disturbances. Dynamite ^ 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 ; 

' 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.). 

- Dynamite is a mixture of nitro-glycerine with 'kieselguhr,' an 
earth consisting of the shells of infusoiia. 



252 THYSIOLOGY OF MUSCLES AND NERVES. 

and, above all, to the influence of the active nerve. 
The latter may perhaps, as we have explained in the 
foregoing paragraphs, be referred back to electric irri- 
tation. It is thus apparent that muscle and nerve 
behave essentially in the same way towards irritants. 
But, remembering that nerves run for part of their 
course within the muscle, between its fibres, and even 
penetrate within the very muscle-fibres, the thought 
now suggests itself, that perhaps the muscle is in no 
way electrically, chemically, thermically, or mechani- 
cally irritable ; perhaps, when these irritants are allowed 
to act on the muscle, it is only the intra-muscular nerves 
which are irritated, and Avhich 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, 
poet and physiologist (1708-77), 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 arose which has 
lasted to the present time. In Haller's days, of courscj 
only the larger nerve-branchings were known. The 
further the nerv^es can be traced by means of the micro- 
scope, the harder does it evidently become to determine 
the question under discussion. 

6. In the year 1856, the French physiologist Claude 
Bernard made experiments with a poison brought from 
Guiana, whicli the Indians of that region use to poison 



CUEARE. 253 

their arrows. It is called curare, oiirari, 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, 
do6s 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 thins" 
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 solitriry. The 
action of some other poisons, such as nicotine and 
conine, is entirely like that of curare. These also dis- 



254 PHYSIOLOGY OF MUSCLES AND NERVES. 

able, not the nerve-trunks or the muscle-substance, but 
some part intermediate between these two. The diffi- 
culty is to prove that this part is exactly the final termi- 
nation of the nerves. Assuming that these poisons 
disable some part which lies between 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 nerve-fibres 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 medullary 
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 the actual 
end of the nerve-fibre, a chance is left open to the op- 
ponents of the theory of irritability. 

Great pains have been taken to settle this point 
with certainty. If a muscle poisoned with curare is 
compared with a similar but un poisoned muscle, it ap- 
pears that the former is less excitable ; that is, that 
stronger irritants are needed to cause it to pulsate. 
The explanation of this may be that the muscle-sub- 
stance is excitable, but not so much so as the intra- 



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 
anorles to the lono^itudinal 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 MUSCLES AND NERVES. 

same irritants whicli act on the nerve are also able to 
act on a muscle, and even on a muscle poisoned with 
curare. We have, however, found slight differences, 
and, if it were possible to show the existence of greater 
differences, especially if irritants were found which act 
on muscle-substance but not on nerve-sabstance, 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 test 
to a thin parallel-fibred muscle, usually to the musculits 
sartoriiis of the upper leg. It is suspended 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 liquid which is to be tested is 
then 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 
then been cut off, the experiment can be repeated, 
and so on till the whole length of the muscle has been 
used. The nerve is treated similarly ; the sciatic nerve 



CHEMICxVL 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-m-itants (ammonia, greatly 
diluted hydrochloric acid) the result is the same whether 
the experiment is tried on an ordinary muscle, or on. 



258 PHYSIOLOGY OF MUSCLES AND XERVES. 

one poisoned with cm-are. Nor does it make any dif- 
ference whether a strong* ascending cun'ent is passed 
through the nerve of a sar^o/'iits thus conditioned, thus 
inducing strong anelectrotonus in the intra-muscular 
nerve-branchings, so as to disable it. He sees ip this 
a proof that the nerves which spread through the muscle 
do not share in this form of irritation. He has, more- 
over, 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 regions 
of from 2 to 3 m. in length, in which at least the 
larger muscle-fibres are wanting. ( ^yhether the nerve- 
net which, according to Gerlach, lies within the sarco- 
lemma, extends ta these regions, is another question 
with which we have nothing here to do.) The specific 
muscle-irritants affect these regions exactly as they do 
the rest of the muscle ; while the specific nerve-m-itants 
(concentrated lactic acid and glycerine) are never able 
to affect these ends, though they elicit single pulsa- 
tions in the parts containing nerves. 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 nerveless 
ends remains unaltered. 

Many objections have been brought forward against 
these conclusions. For my part, in the very insignifi- 
cance of the differences between nerve and muscle in 
this point also, I am inclined to see new reason to 
believe that these two organs, so similar in all points 
(as yet we 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, ^vhich 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 ii'ritated 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. \Ye 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 exj)lanation. 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 nritant on the muscle. 

\Ve have already seen that the nerve must be 



260 PHYSIOLOGY OF xMUSCLES AND NERVES. 

regardid as composed of many particles arranged one 
behind tlie other, each of which is retained in a defi- 
nite position by its own forces and by the influence 
of the 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 particle s, in consequence 
of which the latter are set in motion. Negative varia- 
tion must be 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. 
But just as this change in the position of the nerve- 
particles is able to set the needle of a multiplier, if it 
is properly connected with the nerve, in motion, so the 
electric process originating in the nerve must act on 
the muscle, if the latter is sensitive to electric varia- 
tions. This was the assumption from which we started, 
and which, after the above explanations, 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 
state of knowledge. 



CHAPTER XYI. 

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. Retardation ; 9. Specific energies of nerve-cells ; 10. 
Conclusion. 

1. At present we Lave 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. ^Ye 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 on 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 AND NERVES. 

other motor nerves. But a difference is observable 
even in the case of the secretory nerves or gland-nerves, 
of which we have akeady had occasion to make mention. 
When these nerves are irritated the appropriate nerves 
beffin 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. AYhen the latter are irritated the muscles 
connected with them at once pass into a state of activity. 
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 glaud, unlike a muscle, cannot contract ; 
when 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 
the terminal apparatus, in which the nerves end, being 
sufficient fully to explain the difference in the pheno- 
mena. 

But there are 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 receiving 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 act on the ends of the respective nerves. It is 
not self-evident that these nerves are homofifeneous 
in themselves or with the previously mentioned kinds. 
Finally, it is yet harder to understand the action of 



SIMILARITY OF NERVE-FIBRES. 263 

another, and the last class of nerv^es, which are called 
7'etardatory 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. 



264 niYSlOLOGY OF MUSCLES AND NERVES. 

the presence or absence of this medullary sheath does 
not correspond with differences in the 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 differences 
to light. The bearing of nerves to irritants does not 
vary: the electromotive effects are the same in all. In 
all these points we need simply 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 we 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 system. An 
irritant which affects a motor nerve, to become appa- 
rent, must propagate itself toward the periphery, till it 
reaches the muscle situated there ; an irritant, on the 
other hand, which affects a sensory nerve, must be pro- 
pagated toward the centre before it sets free any action. 
Nerves of the former kind are therefore called centrifu- 
gal, those of the latter centripetal. We have, however, 
already found that this does not depend on a difference 
in the nerve itself, but that each nerve-fibre, when it is 
affected at any point in its course, transmits the ex- 
citement in both directions ; and we therefore presumed 
that the fact that action takes place only at one end 



CArACITIES OF J\EKVE-CELLS. 2fi5 

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 knowledg-e of the central nervous 



'O' 



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-halls. 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, lot 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 



PHYSIOLOGY OF MUSCLES AND NERVES. 



pheric nerve-fibres, it is natural to refer these to the 
presence of the ganglion-cells. 

As a matter of fact, all organs which contain nerve- 
cells, the central organs as well as the peripheric 




Fig. 68, Gaxgliox-cells from the ihiman brain. 
1. A paiiglioncell, of which one process, a, becomes the axis-cylimler of a nerve- 
fibre, b. 2. Two cells, n and b, interconnected. 3. Diagi-uniniatic rei)resenta- 
tibn of three connected cells, each of which passes into a nerve-fibre, c. 4. 
Ganglion-cell partly filled with black i)ignient. 

organs, in which they are present, though not so abun- 
dantly, exhibit certain peculiarities, which we must re- 
gard as caused by the nerve-ceils. And as we are in no 
case able to examine the nerve-cell by itself, but must 
always examine it in connection with, and mingled with 
the nerve-fibres, w^e can but 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 
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 nerve-fibres, must there- 
fore be attributed to nerve-cells : — 

(1) Excitement may arise in them independently, 
i.e. ivithout any visible external irritant, 

(2) They are able to transfer the excitement from 
one fibre to another. 



268 niYsioLOGY of muscles a>d nerves. 

(3) They can receive an excitement transmitted to 
them and transmute it into conscious sensation. 

(4) They are able to cause the suppression (retar- 
dation) of an existing excitement, 

4. From the above it must not be supposed that all 
ganglion-cells possess all these qualities. On the con- 
trary, it is to be supposed that each nerve-cell per- 
forms but one of these functions, and even that there 
are 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 brain may be separately 
removed or disabled, in which case individual forms 
of sensation fail, while others remain undisturbed. 
If the whole brain is removed, the nerve-cells of the 
dorsal marrow suffice fully to accomplish the pheno- 
mena of the transference of excitement from one nerve- 
fibre to another. Again, there are certain regions of 
the brain which separately are able to give rise to inde- 
pendent excitement 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 yet^ however, it has not been 
found possible to distinguish differences in form suffi- 
ciently characteristic, and relations between the form and 
the function of nerve-cells sufficiently characteristic 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 . niYSIOLOGY OF MUSCLES AND KERVES. 

Those beginning to play the piano find it difficult to 
move individual fingers apart from the others, though 
by practice they soon learn to do this. Whenever 
an intended contraction of a muscle is accompanied 
by another unintended and simultaneous, the latter 
is called a co-relative movement. Such co-relative 
movements sometimes accompany illness. Stammerers, 
for instance, when they speak, twitch the face muscles 
or even those of the arm. It has also been observed 
that in the case of injuries, after blood has been 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, by 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 transferred 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 is 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 exercise — that is, it is due to unskilful- 
ness on the part of the will. 

If it is asked how the voluntary excitement of the 
nerve-fibres is caused in the nerve-cells, an answer 
is yet to be sought in physiology. Into the question 



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 twit chin gs, 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 THYSIOLOGY OF MUSCLES AND NERVES. 

such as are rhythmic, in wliicli contraction and relaxa- 
tion of the muscles concerned take place in regular 
alternation, as in respiration and in the movements of 
the heart ; such as are tonic, in which the contractions 
are more constantly enduring, even if the degree of 
contraction varies, as in the contraction of the vascular 
muscles, and of the rainbow membrane of the eye ; and 
such as are irregular, 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. 

Eespiration begins immediately after birth, and 
its movements continue from that time throughout life. 
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, resj)iratory action ceases and life is 
threatened. This organ is a limited point in the 
onedulla oblongata, formed of a mass of nerve-cells, in 
which the excitements originate, and from which they 
are conveyed by the nerves to the respiratory muscles. 
This is called the respiratory centre {Lehenshnoten 
of the Germans, noeud vital of the French), because 
of its importance to life. It is the spot which the 
matador in bull-fights must 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 AUTOiMATIC 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.^ 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 

' 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 is 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 PHYSIOLOGY OF MUSCLES AND NERVES. 

briefly explained, to 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 is probable, though no 
experimental proof of its correctness has yet been 
achieved. 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.^ 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. 

6. The transference, 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 at another point. The reflection 
can occur either in a onotor fibre, in which case it is 
called a reflex action, or in a secretory or retard a- 
tory fibre. The former case is more common and 
better known. As examples of such reflex actions, I 
may mention the closing of the eyelids on the irrita- 

• Those who wish to obtain further information as to these cir- 
curastances may be referred to my work Bemcrhnngcn iiher die 
Thdtiglicit der autoinatischeti Ne?'ven- centra, &c. Erlangen, 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. AYith 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 AND NERVES. 

from nerve-cell to nerve-cell, from each of which it 
can repass into a motor fibre. From the length of 
the time occiipied by the reflex irritant, it is to be 
inferred that the transmission of the 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 reflex 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 reflex trans- 
ference rendered easier, but the passage of the excite- 
ment to the most remote motor fibres is also rendered 
peculiarly possible. The best 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 sensory fibre which reaches 
the nerve-centre can give rise to a conscious sensation, 
the spread of the excitement within the centre must 
have the same efi'ect as would be the case if a larger 
number of excitements of several sensory fibres reached 
the centre simultaneously. This process, \vhich, how- 
ever, only occurs in the case of strong excitements, 
is called co-relative sensation. Sensation is caused 
not only by the excitement of the nerve-cell directly 
concerned, but also by the spread of the excitement 
to the other nerve-cells. It may also be spoken of as 
the radiation of the sensory irritant, because the excite- 



SENSATION AND CONSCIOUSNESS. 277 

ment seems to spread within certain limits from the 
point directly touched. 

7. These j)henomena 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.' 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, 

* The dispute about the so-called ' mind in the spinal marrow ' 
(^RilckeiunafJcsseele), the 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 activity 
of the nerves is certain, and it is the cells of the 
grey matter of the brain which possess this activity. 
On the other hand, we are entirely unable even to 
indicate how this consciousness comes into being. It 
may be due to molecular processes in the nerve-cells 
w^hich 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.^ 

The excitements transmitted by the various sensory 
fibres do not all act 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-fibres 
which accomplish the various sensations differ in no 
way from each other, we are forced to look in the 
nerve-cells for the reason of the difference in sensations. 
Just as we assumed that motor nerve-cells differ from 
sensory, so we must further assume that among 
sensory nerve-cells, the excitement of which always 
elicits the conception of light, others again the excite- 

• E. du Bois-Reymond has entered further into this question in 
his address to the assembly of naturalists at Leipzig ( Uchcr die 
Grenzen des Kaiurei'liennens, Leipzig, 1872). Some of the younger 
natural philosophers seem inclined to avoid the difficulty by ascrib- 
ing, as does Schopenhauer, sensation and consciousness to all mole- 
cules, but this does not seem to me to be any real gaift. 



' 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 PHYSIOLOGY OF MUSCLES AND NERVES. 

projects every sensation wliich reaches the conscious- 
ness outward, that is, to where the cause of the excite- 
ment is normally. This so-called laiu of eccentric 
sensations finds an easy explanation in the supposi- 
tion that the conception of the locality of the efficient 
cause is gained from experience.^ It will easily be 
understood that this necessarily follows from the cha- 
racters which we have ascribed to the nerve-cells. 
When the nerve-cell is irritated, the same sensation 
and the same conception must always result. Just as 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 does not 
depend on the locality or the nature of the excite- 
ment. AYhen the circumstances which give 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, the retardation 
of a motion, is still very obscure. The fact of retarda- 
tion is as yet principally known in the case of auto- 
matic motion, though retardation of reflex action also 
occurs, as may be inferred even from the fact that the 
rise of reflex actions is hindered by the activity of the 
nerves, especially when this originates from the brain. 
The respiratory movements being of all automatic move- 

' Details of this matter, into which we cannot enter further 
here, will be found in Bernstein's The Fice Senses of Man (Inter- 
national Scientific Series, vol. xxi.), and in Huxley's Elementally 
Physiologrj. 



EETARDATION. 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 § o 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 MUSCLES AND NERVES. 

that is, is due to an increase in the resistance by 
which the motion is temporarily suspended.^ 

Retardatory nerves have been recognised in ahnost 
all automatic apparatus, and all are accounted for by 
the above explanation. The same explanation may also 
be applied at once to the retardation of reflex action ; 
for even in the passage of the excitement from the 
sensory to the motor nerves very great resistance has 
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 sul)- 
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 effect, 
the facilitation of the passage of the excitement from 
the nerve-cells in which it originates, to the peripheric 
nerve-courses, appears to occur. 

Finally, it is sometimes observable that when those 
portions of the nerves which contain nerve-cells are 
continually and regularly irritated, a rhythmic or even 
an irregular movement results, instead of a regular 
tetanic contraction of the muscles concerned, — a cir- 
cumstance which is evidently to be explained in the 
same way as rhythmic automatic activity. The regu- 
lar excitement having to pass through nerve-cells is 
modified by the great resistance present in these, and 
is transformed into a rhythmic motion, while when the 
nerve and the muscle are directly connected, the latter 
responds to a continuous excitement of the nerve with 
a regular and continuous contraction. 

' See my account of theautomatic nerve-centres, to which refer- 
ence has already been made. 



SPECIFIC ENERGIES OF I«;ERVE-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 central 



284 PQYSIOLOGY OF MUSCLES AND NERVES. 

end of the nerve of hearing, then the sound of an 
orchestra would elicit in us the sensation of light and 
colour, and the sight of a highly coloured picture 
would elicit in us impressions of sound. The sensa- 
tions which we receive from outward impressions are 
therefore not dependent on the nature of these im- 
pressions, 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 sensations 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 in the fact that the same vibrations of ether 
meeting 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 
nerves, and then they are heard ; and under certain 
circumstances they may be seen. The vibrations of 
the tuning-fork are always the same, and they have 
nothing in common with the sensations which they 
elicit. Though the physical processes of the vibrations 
of ether are called, sometimes light, and at another time 
heat, a more accurate study of physics shows that the 
process is the same. The usual classification of physical 
processes into those of sound, light, warmth, and so on. 



SPECIFIC ENERGIES OF NERVE-CELLS. 285 

is irrational, because in these processes it gives pro- 
minence to an accidental circumstance, tliat 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 sonnenliaft, 
Die Sonne konnt' es nie erblicken ; 
Liig' nicht in was 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- 

' Zahne Xenien, iii. 70. 



286 PHYSIOLOGY OF MUSCLES AND NERVES. 

quale irritants^ 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 know now that this is not true. Yet the expres- 
sion may be 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 sjpecific energies of the sense-nerves, if by 
this it is intended to express any character of the 
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 which are 
able to produce in us dififerent 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 this one undefined 
sensation that differences would be perceptible. There 
may be animals which are only capable of such a single 
undefined sensation, their nerve-cells being all alike 
and not yet differentiated. Such animals would be 
able to form a conception of the outer world as 
distinguished from their own bodies, that is, they 
would be able to evolve self-consciousness ; but they 
would not be able to attain a knowledge of the pro- 
cesses in the outer world. The development of such 
knowledge in us is greatly assisted by a comparison 
of the different impressions brought about by the 
different organs of the senses. A body presents itself 
to our eye as occupying a certain space, being of a 



CONCLUSION. 287 

certain colour, and so on. By tasting 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 PHYSIOLOGY OF MUSCLES AND NERVES. 

motor nerves of men. INfore tlian this Las been done: 
the time has been measured which is requisite for an 
irritant conducted to the brain to be transmuted into 
consciousness. 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 stat e 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 with 
each other, it is necessary to know the difference 
between the two cases, the so-called personal equation. 
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 gives 
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 physio- 
logical time 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. Thus Professor 
Hirsch, of Neufchatel, found — 

In the case of the sense of sight 0*1974 to 0-2083 sec. 
„ „ hearing 0*194 „ 

„ „ touch 0*1733 - „ 

When the impression which was to be recorded was 



CONCLUkSION. 280 

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 Donders are yet more 
mteresting. 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 w^hich 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 PHYSIOLOGY OF MUSCLES AND NERVES. 

This sluggishness of the consciousness, if we may so 
call it, is exhibited in another way in certain experi- 
ments instituted by Helmholtz. ^ The eye sees a iigure, 
which is immediately followed by a bright light : the 
more powerful the latter is, the longer must the first 
have been seen, if it is to be recognised at all ; more- 
over, complex figures require more 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 recognition, the larger are the letters 
and the brighter the illumination. 

It is true that it is only very simple brain activities 
the origin of which can be in any way made clearer by 
such experiments as these ; but yet these are the rudi- 
ments of all mental activity — sensation, conception, re- 
flection, and will; and even the most elaborate deduction 
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 psychology, 
the development 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. Eesults are, therefore, to be first 
looked for in the study of the processes of reflection ; 
possibly these Avill prepare the ground on which at some 
future time a mechanism of the nervous processes may 
be built. ' In truth,' says D. F. Strauss, in ' The Old 
and the New Faith,' ' he who shall explain the grasp 
of the polyp after the prey which it has perceived, or 
the contraction of the insect larva when 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. 29 L 

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 
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 

JFUNCTION (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 : — 

123456789 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. Kepresenting 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=2x 
This formula expresses the same and even more than the 



294 PHYSIOLOGY OF MUSCLES AND NERVES. 

table. Substituting for the unknown x, which may repre- 
sent any number, the number 4, then the table expresses 
that the value of the corresponding y is 8. If a;=:5, then the 
table expresses that ?/=10. But when the value of x is 
intermediate between 4 and 5, e.g. 42371, the table does not 
help us; but by the use of the formula the value of the 
corresj^onding y may easily be found ; it is = 8'4742. 
The formula may be reversed, and written thus : 

x^\y, 

that is to say, for any given value of y we may calculate the 
corresponding value of x. It is exactly the same in the case 
of the similar formula : 

y = 3aj, 

which may also be written thus : 

x-=-^y. 

In this case, therefore, with each given value of x corresponds 
a certain value of ?/, the latter being three times the value 
of the former. In the two corresponding formulae 

y = a x 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 wdthin each particular case. In 
our first example a=2, in our second example a=.3, and 
similarly in any other instance a may have any other value. 
Lookinnr now at the following: table : 



1 


2 3 


4 


5 


6 etc. 


1 


4 9 


16 


25 


36 etc. 



we see that any number in the lower series is found by 
multiplying the corresponding number in the upper series by 
itse^.f, as may be expressed in the formula 



y=^x X or y=X' 



NOTES AND ADDITIONS. 



295 



This formula when reversed appears thus : 

Piovided 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 alw^ays 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'" A'' 




Fig. 69. Graphical representation of muscle-expansion. 



3 



All that is showm 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 or in a table drawn 
up on the basis of observations, may be diagrammatically 



296 PHYSIOLOGY OF MUSCLES AND NERVES. 

shown by a metliod first employed by Descartes, -vvhicli it is 
our present object to explain. 

The amounts treated may be of the most varied kinds : 
numbers, weights, degrees of warmth, the number of births 
or deaths, and so on. In all cases the amount may be diagram- 
matically shown by 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 ; 
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 case, 
the weights attached to the muscle) are measured off on the 
e 
^ f 




Jx 

Fig. 70. Diagram of positive and negative values. 

horizontal line. From each of the points thus obtained, cZ', h" , 
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 d' B\ 
h" B", d" B'", d'" j5^^'. By connecting these points we 
obtain the curve BB' B" B'" B''' x" , which at a glance 
shows the relation between the weight and the expansion. 
In exactly the same way the curve h h' h" h'" B'" y is pro- 
jected, and this represents the expansion of the active muscle 
by the corresponding weights. 

In many cases it is required to represent values of oppo- 
site kinds. If, for example (fig. 70), the wire a 6 is tra- 
versed by an electric current, then one half assumes positive 
tension, the other negative tension. To express this, the 



NOTES AND ADDITIONS. 



297 



lines Avliicli 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- 
vailinsr. 



2. Direction of the Muscle-Fibres, Height of Elevatiox, 
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, ^\^hen 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 6, but that motion 
of the point B, 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 ; vn that case the muscle- of oblique mus- 
fibre, in contracting, undergoes a change in ci.e-fibues. 
direction from its fixed point of origin -4, and thus assumes 
the position A h' ; the elevation which is really effected is, 
14 




298 PHYSIOLOGY OF MUSCLES AND KEKVES. 

therefore, B h'. The small triangle Bhh' may he regarded 
as a right-angled triangle. This gives 

Bh 



Bh' = 



sin i'/ 



The force with which the muscle-fibre strives to contract 
in the direction A B being called k, only part of this force, 
the component k^ lying in the direction B C, finds expression. 
According to the law of the parallelogram of forces, this com- 
ponent is 

k'=-k sin /3. 

This force may be regarded as proportionate to the 
weight which the mnscle-fibre is able to raise to the given 
height of elevation. If we then calculate the work which 
the muscle can accomplisli, we find, if the motion can take 
place in the direction A B, 

A=Bbk', 
but if motion can only occur in the direction B C, 

A = B¥ k'= ^^ ^ k sini3=Bb k. 
sm [j 

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, consequently, 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 irie- 
gular. The possible height of elevation is always greal:er 
the longer the fibres are, and^ the force proj^orlionatc to the 
diameter or to the number of the fibres. In oblique-fibred 
muscles the fibres are generally very short, but very nume- 
rous ; these must, therefore, whatever their accidental form, 
be regarded as short and thick muscles, possessed of small 
elevation and great force. 



NOTES AND ADDITIONS. 299 



3. Excitability and Strength of Irritant. Combination 

OF Irritants (p. 119). 

"When the coils of a sliding inductive apj^aratus aro 
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 ea^h 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 le^;s 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 very brief current, in w^hich 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 efiective : this gives two 
irritations following each other in rapid succession, and these 



300 PHYSIOLOGY OF 2ICSCLES AND NERVES. 

together effect a greater pulsation tlian 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 
can 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 not mutually disturb 
each other, but are transmitted one after the other, in the 
sequence in w^hich they originate, to the muscle on which 
they act. But when the number of the irritants becomes 
too great, the nerve-molecules are no longer able to keep 
pace -with the rapidly succeeding shocks, and the nerve is 
unexcited. 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. Eesistaxce to Transmission 

(p. 123). 

The increased excitability at the upper parts of the un- 
injured sciatic nerve, when not severed from the body, 
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 increase 
in the irritation merely from this higher excitability 'of the 
upper parts. Beside the experiments of Munk alluded to 
on page 116, there are other experiments from which a 
resistance to transmission 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 mutually exclude each 



NOTES AND ADDITIONS. 301 

otlier. 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 anelectrotonns it is even rendered 
altogether impossible. It is natural to regard this greater 
difliculty 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 {cf. p. 274). This transference always occupies 
a considerable time, which I call reflex-time. If a sensoiy 
nerve is irritated sufficiently to cause a pow^erfiil 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 aflfected; 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 



PHYSIOLOGY OF MUSCLES AND N^ERVES. 



probable that in one nerve-fibre a resistance to transmission 
exists, and in another an avalanche-like increase. All the 
facts are more easily and simjily exjDlained by assuming that 
there is a resistance to transmission in all nerves, allowance 
being at the same time made for the difference in the ex- 
citability of different points in the nerve. 

Moreover the curve of excitability in the case of the 
sciatic nerve is not a simple ascending line from the muscle 
to the dorsal marrow. This nerve is found, as is shown in 
fig. 72, by the union of several roots ; it then, at various 




Fig. 72. The sciatic xerve and calf-muscle of a frog. 

points, gives off branches which enter the muscles of the 
upper leg, and then separate into two branches, one of which 
provides for the calf-muscle {gastrocnemius), the other for the 
flexor muscle of the lower leg. If various points of this 
nerve are irritated in the living animal, the nerve having 
been merely exposed and isolated from the surrounding parts, 
but not sepai-ated from the dorsal marrow, it is very evident 
that the excitability at the upper points is generally greater 
than at the lower ; but points are also found in the course 
of the nerve at which a greater excitabilitv exists than at the 
points above and below, as also, on the contrary, a less ex- 
citability than at the adjacent ])oints. Such irregulaiities 
are most abundantly exhibited at the points where nerve- 
branches separate from the main trunk, especially when these 
branches have been cut away. This is partly due to elec- 
trotonic infiuences {cf. p. 125 et scq. ; p. 215 et seq., Note 13). 
The nerve- fibres which are cut generate a current which 



NOTES AND ADDITIONS. 303 

passes tlirougli tliose whicli 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 ^ivintr rise to irremilarities the further nature of which 
we need not trace. 



5. Influence of 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 degi^ees 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 he 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 arsumed, 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 thu^d 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 



304 PHYSIOLOGY OF MUSCLES AND NERVES. 

uiiclianged, but tlie pulsations must gradually decrease in 
strength, and all effect must finally disappear, just when 
the maximum of excitability, and the deatli which follows 
this, pass the lower limit of the excited port'on. 



6. Difference between Closing and Opening Induc- 
tive Currents. Helmholtz's Arrangement (p. 151). 

When an electric current is suddenly closed in a spiral, 
tins not only acts inductively on a neighbouring spiral, but 
the individual coils of the ])rimary spiral act inductively on 
each other ; an analogous effect would occur on the opening, 
but that the sudden interruption of transmission prevents the 
development of this opening inductive current in the primary 
coil. The inductive current which orisjinates on the closing 
of the current being in an opposite direction to the closed 
i current itself, the former must weaken the latter ; the cur- 
rent can therefore attain full strength, not at once, but only 
gradually ; but on the opening the current suddenly ceases. 
This difference in the duration of the closing and opening 
of the primary current corres[)onds with differences in the 
currents induced by them in the secondary spiral, which are 
used for the irritation of the nerve. Figure 73 exhibits these 
characters. The upper part of the figure represents the tem- 
poral course of the main current in the primary spiral of an 
inductive apparatus ; the lower part represents the temj)oral 
course of the induced currents in the secondary spiral. The 
line . . .0 . . .t represents the duiation. The primary current 
is closed at the moment o. Were the retardatory influence 
which has been mentioned not present in the piimary spiral, 
the current w^ould at once attain its full strength J ; but 
owin^ to that influence it attains this strength onlv firraduallv, 
somewhat as shown by the crooked line 3. With this gradu- 
ally occurring cuiTent corresponds a closing inductive curi-ent 
in the secondary spiral, as is represented by the curve 4 ; 



NOTES AND ADDITIONS. 



305 



the curve is drawn dovv-nward from the time-line o . . . o . . . f, 
to indicate that the direction of this induced current i.s 
opposed to the direction of the primary current. If the 
primary current is interrupted, it suddenly falls from the 




strength /, as indicated by the straight line 1. With this 
fall corresponds an inductive current, which suddenly rises 
very abruptly and again falls somewhat less abruj^tly, as 
shown in curve 2. From this it is evident that the latter 
must be physiologically much more effective than the former. 



306 FHYSIOLOGY OF MUSCLES AND NERVES. 

Occasionally it is desirable to remove this difference, and 
to provide two inductive currents which flow and act nearly 
in the same way. This may ba managed, if, instead of 
closing and interrupting the current of the primary coil, an 
additional closing wire offering small resistance is provided, 
and the interruption is effected in this. If this additional 
apparatus is present, only a very small part of the current 
passes through the primary coil. The strength of this part is 
indicated by J^ J ,. When the closing in the additional ap- 
paratus is interrupted, the primary current slowly increases 
in strengt^h from J , to J as shown by the dotted curve 5 ; 
wdth this increase corresponds an inductive current in the 
secondary coil, as represented by curve 6. If the closing of 
the additional apparatus is once more effected, the current in 
the primary coil sinks in strength from J to J •, but the so- 
called extra current, that which originates in consequence of 
the sinking in the primary coil, is now able, the coil being 
closed, to take effect, and, as its direction is the same as that 
of the main current, it retards the sinking of the latter, so 
that this now takes place as indicated by curve 7 ; and with 
this slow sinking of the main current corresponds an induc- 
tive current in the secondary coil, such as is shown by 
curve 8. 

Helmholtz made an alteration in du Bois-Reymond's 
sliding inductive apparatus by means of which this ad- 
ditional closing and opening is automatically accomplished. 
He adapted Wagner's hammer for this purpose, as sliown in 
fig. 74. The current of the apparatus A" passes through the 
wire arranged between g and f to the primary coil c, from 
this to the coils round the small electro-magnet 6, and from 
the latter through the column ct, back to its original starting 
point. The electro-magnet attracts the hammer A, in con- 
sequence of which a small platinum plate fastened below 
the German silver spring is brought into contact with the 
platinum point of the screw/, thus completing a brief and 
efficient additional closure g^f, a. The consequence of 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 /^ and the additional closure is 
interrupted. The current once more passes in full strength 
through the coil c and the electro-magnet h, 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- 



/* I!!L1_.22UD 




Fig. 74. Helmholtz's apparatus 



ratus to its original condition, it is only necessary to remove 
the wire g^ 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 



308 PHYSIOLOGY OF MUSCLES AND NERVES. 

3, we have really to do with a closing immediately suc- 
cgeded by an opening, for the inductive current aiises and 
a^^ain disappears as soon as it has reached a certain strength. 
This may be imitated with suitable apparatus, by closing a 
constant current for a very brief time. Such a ' current 
shock ' may exhibit exactly the same phenomena as does an 
inductive current. If its duration remains unaltered, but 
the strength of the cuiTent is gradually increased, the height 
of elevation at first increases, remains for a time at a fii-st 
maximum, after which it again increases and reaches a second 
maximum. The explanation is the same as was given in 
Note 3 for inductive currents. At first only the beginning 
of the current (the closing) acts excitingly; but when the 
current is stronger, the cessation of the current (the opening) 
can also act in the same way, and a combination of the two 
irritants can be formed. 

If the duration of such a current-shock is very short, the 
current must be stronger, if it is to exercise any exciting 
effect at all, than would be necessary if the duration were 
lonijer. It is evident that a current, if it lasts too short a 
time, cannot effect a sufficient change in the molecular con- 
dition of the nerve, and weaker currents require a longer 
time to do this than stronger. 

From the curves in fig. 73 which represent the duration 
of inductive currents, it appears that without exception the 
commencement of the current results more abruptly than its 
disappearance. The commencement of every inductive cur- 
rent must therefore more easily excite than does its end, 
especially as this is always the case even in the ordinary 
closing and opening of every constant current, in which such 
considerable differences in the duration do not occur. In 
the case of weak inductive currents it is always only the 
commencement which is active, in other words an inductive 
current acts as does the closing of a continuous current. 
Now let us suppose that an inductive current is passed 
through a nerve in an ascending direction. So long as the 



NOTES AND ADDITIONS. 309 

current does not exceed a certain strength, it can excite; 
but wlien 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 ii-ritation. This gap 
(Liicke) in the action was observed by Fick, and afterwards 
by Tiegel. How far other causes besides those here ex- 
plained combine to produce this peculiar phenomenon, Ave 
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 axis of the nerve 
fibres, it has no effect. To effect the alteration in the posi- 
tion of the nerve molecules which we reijard 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 obliquely 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 ancjle. 

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 PHYSIOLOGY OF MUSCLES AND NErxVES. 

closing is near the katbode, on opening is near tho anode. 
This gives rise to the question, whether it is possible to 
expose the nerve to the action of one electrode alone. This 
may be done, in the case of men or other animals, by placing 
one electrode on the nerve, the other on a remote part of 
the body. If the kathode is situated on the nerve, only 
closing pukations 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 may be called unipolar, 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 
yet currents may flow through, the nerve. Such, cases, how- 
ever, are physiologically of no special interest. 

9. Tangent GalvanoiMeter (p. 162). 

In the ordinary tangent-galvanometer a small magnetic 
needle is placed in the centre of a, comparatively, very large 
circle, thi'ough the periphery of which the current is made to 
pass. When the needle is deflected, the position of its poles 
does not alter essentiall}^ as regards the current, the action of 
which may therefore be regarded as directly proportionate to 
its strength ; and from the oj^posed action of the current, 
and. of the force of attraction which the earth exercises on 
the needle, which must also be regarded as constant, it is 
evident that the two forces must be in equilibrium, if the 
trigonometric tangent of the angle of deflection is propor- 
tionate to the strength of the current. 

Such tangent-galvanometers are, however, only adapted 
for measuring powerful currents. The galvanometer which 
we have described, adapted for very Aveak currents, is differ- 
ent. But if, as was assumed, all the deflections which are 
to be measured are but very small, we may still assume tliat 
the mode of the influence of the current on the magnet is 



NOTES AND ADDITIONS. 311 

not altered bj 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 

tg (2 a) r=2tg a, 

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 to 0, without any alteration in the difl'erences 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 difierence between the tensions at 
the various points remains the same. From this it follows 
that these difierences 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 
thoufrht of them as connected with the earth. All tensions 
that are greater than this we call positive, all that are less 
negative. 



312 niYSIOLOGY OF MUSCLES A^^D NERVES. 



11. Duplex Thansmissiox. Degeneration, Regeneration 
AND Coalescence of a Bisected Nerve (p. 218). 

Duplex transmission has been shown in another way, 
but the proof is not so trustworthy and clear as that gained 
by the aid of negative variation. If nerves of the living 
animal are bisected, a striking change occurs in a very short 
time in the parts of the nerve-fibre below the point of scission. 
The medullary sheath becomes crinkled, and the excitability 
is lost. If, however, the cut surfaces are not too fur sepa- 
rated, the nerve-fibres can coalesce, the lower ends again 
become excitable, and the excitement can be ti-ansmitted 
through the cicatrix thus formed in the nerve. On these 
facts Bidder based an experiment, in which he tried to cause 
a sensory nerve to coalesce with a motor nerve. The sen- 
sory nerve of the tongue [JV. lingualis), a branch of the fifth 
brain nerve, and the motor nerve of the tongue {N. hypo- 
ylossus) 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 end of the sensory nerve, which 
comes from the brain, is connected with the lower end of the 
motor nerve, which enters the tongue, as much as possible 
of the two other ends of the nerves being cut out, then the 
two difierent nerves coalesce, so that after a time pulsations 
may be caused in the muscles of the tongue by irritation 
above the cicatrix, and indications of pain may be elicited 
by irritation below the cicatrix. The proof that in this case 
tlie excitement is transmitted downward in the upper sensory 
nerve, upward in the lower motor nerve, would be unassail- 
able if it could be shown that nerve-fibres of the one nerve 
1 ave not grown through the cicatrix and entered into the 
other nerve. This possibility, improbable as it is, cannot 
be disproved. 

A recently published experiment of Paul Bert is founded 



NOTES AND ADDITIONS. 313 

on a similar idea. Berfc 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 Avith the flesh of the back, it was 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 Yariation 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 caieful 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 



o 



14 PHYSIOLOGY OF MUSCLES AND NERVES. 



branch-currents of tlie electric current used for irritation, 
which might easily lead to errors, are pre ent in the mul- 
tiplier. 



13. Electrotonus. Secondary Pulsation effected by 
Neryes. Paradoxical Pulsation (p, 221). 

The reason why it is impossible to examine the electro- 
tonus of the intrapolar portions is purely physical. If the 
constant current is transmitted through .the portion a k 
(fig. 60, p. 220), and two points of this portion are con- 
nected with the multiplier, then a part of this current passes 
thi-ough the multiplier itself, so that the portion of the 
nerve which is situated between these points is traversed 
by a weaker current than are the adjacent portions. The 
conditions are thus rendered so complex that it becomes 
very hard to explain the phenomena. Other attempts to 
study the character of the intrapolar region have as yet 
afforded no clear results. 

If a nerve a is laid on a nerve h, in the way shown in 
fig. 75, A, B, 6', so that the nerve b forms a diverting arch for 
a portion of the nerve a, and if electrotonus is generated in 
the latter by a constant current, then the electrotonic cur- 
rent passes through the nerve 5, and can at its commence- 
ment and cessation (closing and opening) excite the nerve b, 
and cause pulsation in the muscle of the nerve. This is 
spoken of as secondary 2^ulsation from the nerve. By rapidly 
repeated closings and openings of the circuit, tetanus may be 
elicited. But this secondary pulsation is caused only by 
electrotonus and not by negative variation, so that it can 
be more easily brought about by constant currents than by 
inductive currents. It is thus distinguished from the secon- 
dary 2ndsatio7i effected by muscle, which was described on 
p. 209. Tlie negative variation of the nerve-current is too 
weak to cause any noticeable effect in a second nerve. 



NOTES AND ADDITIONS. 



315 



A special form of secondary pulsation effected tlircugb the 
nerve lias been described bydu Bois-Heymond as paradoxical 
jndsation. 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 
has independt ntly irritated them. 



14. Paeelectronomy (p. 237). 

The real causes of parelectronomy and the conditions 
under which it is more or less strongly developed, are as yet 



316 THYSIOLOGY OF MUSCLES AND NERVES. 

far from being understood. But at any rate it is impossible 
to conceive the matter, as though the currentless condition of 
the muscles — that is to say, the same tension on the longi- 
tudinal and transverse sections — were normal, and as if every 
negativeness on the transverse section were the result of 
injury. For all possible degrees of parelectronomy are to be 
found- even the reversed order, in which the cross-section is 
more positive than the longitudinal section — in uninjured 
muscles ; while in other cases the ordinary muscle-current 
is found powerfully developed in quite uninjured muscles. 
Moreover, as we have stated in the text, the question whether 
differences of electric tension occur in uninjured muscle has 
no bearing on the question whether electromotive forces are 
present within the muscle. We declare ourselves in favour 
of this hypothesis, because it most simply and easily explains 
all the phenomena. We also apply it to structures on 
the outer surface of which it can be proved with certainty 
that no differences of tension are present, as in the electric 
plates of fishes. For this assumption we have the same 
grounds on which physicists rely in claiming the existence of 
molecular magnets in every, even quite unmagnetic piece of 
iron. Whatever, therefore, may be the true explanation of 
parelectronomy, it cannot essentially affect our well-founded 
conception of the electric forces of muscles. If, however, 
du Bois-Keymond's supposition is confirmed, that the pulsa- 
tions which occur during life leave behind them an after- 
effect on the muscle-ends, which makes the latter less nega- 
tive, some approach wou\l be made to an explanation of the 
phenomenon. 



15. DisciiAUGE Hypothesis and Isolated Teansmissiox 
IN THE Nerve-Fibre (p. 249). 

The explanation of the fact that the processes of ex- 
citement remain isolated in a nerve-fibre without passing 
into adjacent nerve-fibres, ajipears the more inexplicable, if 



NOTES AND ADDITIONS. 317 

we regard tliese 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 ajipropriate 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 activ^e particles situated in the axis of 
a nerve-fibre are small in comparison with the diametor of 
the fibre, and that therefore their efiect 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. 



-»o*- 



ABS 

A BSOLUTE force of muscles, 
^ G7, G8 
Acid, formation of, in muscle, 

73,87 
Activity of muscle, 37, 202, 

235 ; of nerve, 107, 216 
Adamkiciewicz, 76 
Adequate irritants, 285 
Aeby, 100 

Albuminous bodies, 73, 80 
Amraonia, 257 
Amoehcs, 6 

Amoeboid movements, 7 
Anelectrotonus, 129, J 11 
Animal, 5 
Anode, 128, 220 
Arches, diverting homogeneous, 

177, 181 
Aristotle, 155, 285 
Ascending currents, 131 
Attachment of muscles, 17 
Automatic movement, 271 
Ava]anche3, 250 
Avalanche-like increase in the 

excitement of nerves, 122, 

300 
Axis-band, 101 
Axis-cylinder, 101 



T)ACOX as food, 85 
•*^ Ball-sockets, I'J, 93 
Beclard, 73 
Bernard, 253 



CHE 

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. 218, 278, 313, 
315, 316 

Bones, 17, 18, 93 

Branched muscle fibres, 101 

Branching of elec'.ric currents, 
132,. 150 

Brownian movements, 3 

Brucke, 89 

Burden, 23, 39, 61 

BuRDON- Sanderson, 223 



pALF-MUSCLE. See Gas!ro- 

^ cnemius 

Carbonic acid, formation of, in 

muscle, 42, 73, 81 
Carrying-height (Traghohe) 11 
Cells, 9. See also Nerve-cells 
Central-organ of the nervous 

system, 103, 117, 265 
Centrifugal and centripetal 

nerves, 266 
Cerehrum, 211 
Chamois-hunters, 85 
i Chemical composition of mus- 
i cles, 73 



320 



INDEX. 



CUE 

Chemical irritants, 30, 109, 257 
Chemical processes in muscle, 

42, 73 
Ciliary cells, 10 
Ciliary-movements, 10 
CiAjuit, electric, 159, 165 
Claudius Claudtanus, 155 
Closing of a current, 32, 132, 304: 
Closing inductive current, 151, 

299 
Combination of tensions, 228 ; 

of irritants, 299 
Compensation, 183 
Compensator, round, 186 
Conception, 279, 286 
Conine, 253 

Conscious sensation, 277 
Conservation of energy, 77 
Constant currents, 34,' 109, 126, 

131 
Correlative action. 270 
Correlative sensation, 276 
Creatin, 74 
Cross-section of the muscle, 66, 

190, 198, 208, 236, 256 ; of the 

nerves, 120, 216, 256 
Curare, 253 
Current-curves, 178 
Current-planes, 179 
Curve of excitability, 121, 300 

TjARWIX, 224 

^ Death of the muscle, 86, 

207 ; of the nerve, 120, 124 
Death-stiffness, 87 
Degeneration of a cut nerve, 312 
Descending currents, 134 
Dioneea mvscijn/la, 149, 224 
Discharge-hypothesis, 248, 316 
Discs of muscle-Mbres, 14 
Disdiaclasts, 15, 102 
Dislocation of the neck, 273 
Diverting arches, 177 
Diverting cylinders, 181 
Diverting vessels, 166 
Division of electric currents, 132, 

170 
DONDERS, 289 
Dorsal marrow, 106, 277 



FIB 

Double refraction, 1 5 
Duplex transmission, 217, 312 
Dynamite, 251 
Dynamometer, 69 

■ELASTICITY, 21 ; alteration of, 
•^ on contraction, 44, 70 ; co-ef- 
ficient of, 23 ; law of, 22 
Electric current, 159 
Elecrric eel, 156 
Electric fishes, 154, 222, 227, 241 
Electric irritation, 32, 109, 149 

151 
Electric organs, 158, 222 
Electric plates, 158, 222, 227, 241 
Electric ray, 156 
Electric wheel, 33 
Electrodes, 128 ; unpolarisable, 

181 
Electromotive force, 168, 232 ; of 

the muscles and nerves, 153, 

et seq. 
Electromotive surface, 179, 227 
Electrotonus, 127, 139, 220, 238, 

309, 314 
Element. See Muscle-element 

avd Nerve -element 
Elementar}'- organisms, 8 
Energ}', il, 50, 64, 72, 77 ; spe- 

citic, 286 
Engelmanx, 100 
EquiiDoise, unstable, 250 
Equator, electromotive, 190 
Ermann, 45 
Excitability, 119, 122, 126, 299, 

300 
Excitement, 126, 141, 150, 151, 

313 
Exhaustion, 79, 121 
Extension, 21, 92, 295 ; gradual, 

24 
Extrapolar regions, 220 

"PARADAY, 156 

Feet of the diverting arch, 

176 
Fibres, See Muscle-fibres a}id 

Nerve-fibres 
Fibre-cells, 96 



INDEX. 



321 



FIB 

Fibrillie, U 

Tick, 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 

rjALVANOMETEPt, 160 

^ Ganglion-cells. See Kerve- 

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"Geavesanue, 23 
Grey nerve-fibres, 104 
Gunpowder, 250 
Gi/mnotus, 156 

XTALLER, 252 

Hallucination, 279 
Haeless, 253 
Head of muscle, 1 3 
Heart, the, 101, 210 
Heidenhatn, 76, 146 
Height of elevation, 37, 2^17 
Helmholtz, 50, 52, 59, 73, 75, 

115, 228, 287, 290, 306 
Hermanx, 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, 44 
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 
IiTitability, 30, 108 ; independent, 

255 
Isolated transmission in the 

nerve-fibre, 117, 315 
Isoelectric curves. Sec Tension- 
lines 



17ATELECTROTONUS,129,141 

-'^ Kathode, 128, 220 

Kernel (nucleus) 5, 7, 11, 16, 96, 

105 
Key, tetanising, 36 
Kleistian jar, 30 
Kollikee, 253 
Keoneckee, 299 
KtJHNE, 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 

Ley den jar, 30 

Life centres, 272 

Light, 15, 284 

Long bones, 18 



]VrAGXET, compared to muscle 
-^ and nerve, 147, 230, 260 



322 



INDEX. 



MAL 

3falaj)tcriirus, 156 

Mateucci, 229 

Mechanical irritants, 30, 109, liG 

Medullary sheath, 101, 245, 251, 
263 

Mimosa pudiea, 2, 224 

Mirror, reading of small angles 
by means of, 57, 162 

Moditication of excitability, 131, 
143 

Molecular hypothesis, 238 

Molecular movement, 3 

Mollusca, 102 

J\fo)'myrus, 159. 

Motor nerves, 261 

Movement, 1 ; in plants, 2, 8, 
224 ; of the smallest organisms, 
4 ; molecular, 3 ; protoplas- 
mic, 6 ; amoeboid, 6 ; ciliary, 
9; muscular, 9 et seq.; peri- 
staltic, 98, 272 ; voluntary 
and involuntary, 98, 275 ; au- 
tomatic, 273; rhythmic, 272; 
tonic, 272 

MiJLLER, 285 

Multiplier, 161 

MUNK, 116, 224, 300 

Muscle, 2, 11, 12 et seq., 189 ct 
seq., 226 et seq. 

Muscle-current, 191, 202, 226 

Muscle-element, 232, 239 

Muscle-fibre, striated, 14, 45, 96, 
245 ; smooth, 96, 101 ; zigzag 
arrangement of, 14 

Muscle-fibre pouch. See Sarco- 
lemma 

Muscle-fluid, 88 

Muscle-prism, 189, 230, 234 

Muscle-rhombus, 193, 195, 230 

Muscle-note, 43, 211 

Muscle-telegi'aph, 30 

INIyograph, 26, 37, 52, 100, 111 

Myosin, 74, 90 



^ASSE, 73 

^^ Negative variation, 203, 210, 

214,216,226, 235, 313 
Nerve-cells, 103, 266, 269 



POL 

Nerve-centres. See Central Or- 
gans. 

Nerve-current, 215, 226, 236 

Nerve-element, 237 et seq. 

Nerve-fibres, 103 et seq. ; termi- 
nation of, in muscles, 245 

Nerve-net, 246 

Nerve -processes, 107, 265 

Nerve-sheath, 104, 111 

Nerve, terminal plates of, 245 

Nervous system, 103 

Nettle, stinging, movements in 
hairs of, 8 

Neurilemma. See Nerve-sheath 

Neutral point, 129 

Nicotin, 253 

Nitroglycerine, 250, 251 

Nucleolus, 105 

Nutriment of labourers, 82 

Nut-socket, 19, 93 



f OPENING of a current, 32, 131, 
^ 308 

Opening induction-current, 150, 

304 
Opening-tetanus, 132, 143 
Oppian, 155 
Organs. See Central Organs and 

Electric Organs 
Over-burden, 65 
Oxidation, process of, in muscle, 

42 



PARADOXICAL pulsation, 314 
J- rarelectronomy,208,236,315 
Penniform muscles, 91, 199 
Peripheric nerves, 103, 107 
Peristaltic movement, 98, 272 
Pfluger, 122, 140 
Physiological time, 288 
Plants, movements of, 2, 9, 224 ; 

electric action of, 153, 223 et 

seq. 
Plates, electric, 158, 222, 227, 241 
Pliny, 155 
poggendorf, 183 
Polarised light, 15 



INDEX. 



323 



PEE 

Prevost and Dctmar, 45 
Prism. See Muscle Prism 
Propagation, of the pulsation 
within the muscle-fihre, 99; 
of the irritation within the 
nerve-fibre, 110, 114, 287 ; of 
the negative variation in the 
nerve-tibre, 129 
Protoplasm, 5 
Protoplasmic movement, 6 
Protoplasmic processes, 106 
Pulsation, 31. 56, 210 ; secondary, 
210, 314 ; law of, 135, 142,299 



pADIATION of sensations, 276 
^^ Eate of excitement in the 
nerve-fibre, 98 ; of transmission 
within the nerve-tibre, 110, 1 1 4, 
129, 287 
Reaction in muscles, 87 
Receptive apparatus of sensory- 
nerves, 283 
Reflection, 290 
Reflex actions, 274, 290, 301 
Respiratory movements, 272 
Resj)iratory centre, 272 
Rest of muscles, 37 
Retardation {Hemmunfi^j, 80 
Eetardatory nerves, 263 
Rheochord, 133, 149, 184 
Rhombus. See Muscle-rhombus 
Rhythmic movements, 272, 281 
Ritter's tetanus, 132, 143 



OARCOLEMMA, 16, 101, 233 
^ Schwann, 70 
Secretory nerves, 213, 262 
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 ct 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, 220, 

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 



INDEX. 



UNI 

T]NIPOLAIl irritation, B09 
^ Unpolarisable electrodes, 181 
Urinary duct, 100 
Urea, 80, 8-t 

IfASO-MOTOR nerves, 261 
' Volume of muscle, 45, 66 

WAGNER'S hammer, Si, 306 
* ' Warmth equivalent, 76, 81 



WOR 

Warmth, generation of, in muscle, 
42, 73, 74 ; in nerve, 123 

Weber, 45, 263 

Weiss, 73 

Whip-cell movement, 11 

Will, 270, 290 ; deflection of 
magnetic needle by, 205 

Woodcutters, Tj^rolese, 85 

Work accomplished by the 
muscle, 37, 38, 72, 76, 296 



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though it deals with many subtle subjects, it expounds them in a style 
which iS admirable for its clearness and simplicity." 

From the London " Athenipum." 

" The fullest scientific exposition yet published of the views held on 
the subject of psychology by the advanced physiological school. It 
teems with new and susGfestive ideas." 



FOR SALE BY ALL BOOKSELLERS. 

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