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ELECTRO-PHYSIOLOGY

Al. HEADY PUBLISHED.

VOLUME I.

ELECTRO -PHYSIOLOGY. By W. BIEDEIIMANN, Professor of
Physiology at Jena. Translated by FRANCES A. WE LEY.
With 136 Illustrations. Svo. 17s. net.

MACMILLAN AND CO., LTD., LONDON.

4"

ELECTRO-PHYSIOLOGY

BY

W. BIEDERMANN

PROFESSOR OF PHYSIOLOGY IN JENA

TRANSLATED BY FRANCES A. WELBY

WITH ONE HUNDRED AND FORTY-NINE FIGURES

VOL. II

HonHon
MACMILLAN AND CO., LIMITED

NEW YORK : THE MACMILLAN COMPANY
1898

All t'if/ht* rest I'rui

CONTENTS

CHAPTER VI

PAGE

ELECTROMOTIVE ACTION IN VEGETABLE CELLS 1

BIBLIOGRAPHY . . 31

CHAPTER VII

STRUCTURE AND ORGANISATION OF NERVE . . 33

THE AXIS-CYLINDER . . . .46

CHAPTER VIII
CONDUCTIVITY AND EXCITABILITY OF NERVE . 52

1. PHENOMENA IN NERVE-FIBRES . . . . .52

•2. PHENOMENA IN FIBRES ASSOCIATED WITH NERVE -CELLS (REFLEX

ACTIVITY) ........ 66

3. INFLUENCE OF VARIOUS CONDITIONS UPON EXCITABILITY OF NERVE . 76

4. EXCITABILITY IN DIFFERENT NERVES . . 96

5. CHANGES PRODUCED IN NERVE BY ACTIVITY . 109

BIBLIOGRAPHY . .112

CHAPTER IX

ELECTRICAL EXCITATION OF NERVE llii

1. LAW OF EXCITATION BY ELECTRICAL CURRENTS (DU BOIS-REYMOND) . 116

2. INFLUENCE OF DIRECTION UPON THE EXCITING EFFICIENCY OF CURRENTS . 132

3. CHANGES IN EXCITABILITY AND CONDUCTIVITY PRODUCED P.Y THE

PASSAGE OF A GALVANIC CURRENT (ELECTROTONUS) . . 140

vi ELECTRO-PHYSIOLOGY

PAGE

4. EXCITING EFFICIENCY OF ELECTRICAL CURRENTS .... 155

5. CLOSING AND OPENING TETANUS THROUGH ELECTRICAL EXCITATION . 165

i. Conditions of Production by Excitation of Frog 's Nerve . . . 165
ii. Excitation of Nrrves in Crayfish . . . . . .185

6. POLAR EXCITATION OF OTHER NERVES AND SPECIFIC NERVE-ENDINGS . 194

7. POLAR EXCITATION BY CURRENTS OF SHORT DURATION (INDUCTION

CURRENTS) ... ... 207

8. EFFECT OF REPETITION OF STIMULUS . .215

9. UNIPOLAR EXCITATION . . ... 219

BIBLIOGRAPHY . . . . 223

CHAPTER X

ELECTROMOTIVE ACTION IN NERVE . 227

1. CURRENT OF "RESTING" NERVE ...... 227

2. ELECTROMOTIVE CHANGES PRODUCED BY ELECTRICAL EXCITATION

(CURRENT OF ACTION) . - . . . . . 242

3. ELECTROMOTIVE CHANGES PRODUCED BY STIMULATION OTHER THAN

ELECTRICAL ........ 251

4. TIME-RELATIONS OF ACTION CURRENT AS DETERMINED BY RHEOTOME . 259 •

5. ELECTROMOTIVE CHANGES (ELECTROTONUS) . 266

i. In Medullated Nerve ... . . 266

ii. In Non-mcdullated Nerve ...... 281

iii. In Cooled and Etherised Medullated Nerve . . . 286

iv. In PolariscMe Schemata ...... 298

6. SECONDARY ELECTROMOTIVE CHANGES IN NERVE FOLLOWING THE

PASSAGE OF A CURRENT . ... 309

7. THEORETICAL . . 315

The Action of Nerve upon Muscle . . . 337

BIBLIOGRAPHY . . . 353

CHAPTER XI

ELECTRICAL FISHES . 357

1. STRUCTURE AND CONSTITUTION OF ELECTRICAL ORGANS . . . 357

2. GENERAL ACTION OF DISCHARGE FROM ELECTRICAL FISHES . . 407

3. DISCHARGE FROM ARTIFICIAL EXCITATION OF THE ELECTRICAL NERVES

AND CENTRAL ORGANS 423

CONTENTS vn

PAGE

4. TiME-DlSTRIBUTION OF DISCHARGE FROM ELECTRICAL FlSHES . . 431

5. IMMUNITY OF ELECTRICAL FISHF.S TO THEIR OWN DISCHARGE . . 440

6. THE SUPPOSED "CURRENT OF REST" IN THE ELECTRICAL ORGAN . 443

7. SECONDARY ELECTROMOTIVE PHENOMENA IN ELECTRICAL ORGANS . 447

8. THEORY OF DISCHARGE FROM ELECTRICAL FISHES . . 461

BIBLIOGRAPHY . . . 467

CHAPTER XII

ELECTROMOTIVE ACTION IN THE EYE . 470

BIBLIOGRAPHY 480

SUPPLEMENTARY PAPERS . . 481

INDEX ...... ,483

SECONDARY ELECTROMOTIVE ACTION IN MUSCLE. Chapter IV., Section IV.

(Revised) . .... 4 IT.

CHAPTEE VI

ELECTKOMOTIVE ACTION IN VEGETABLE CELLS

IT has long been known that electrical currents can be led off
from certain parts of plants, under given conditions. Becquerel,
Wartmann, and Buff all made important contributions to this
subject. The last author concluded from his experiments (carried
out with comparatively imperfect technical accessories) that " the
roots and all internal parts of the plant filled with air are in a
state of permanent negativity, while the moist or wetted outer
surfaces of fresh twigs, leaves, flowers, and fruits are positively
electrical" (1). He explained this to mean that the epidermis
of the plant forms a dividing line between the external water of
moisture and the salts, acids, and other constituents of the sap.
Electrical excitation occurs at this boundary, and current flows
in the direction observed in the leading-off circuit. Jiirgenseii
(2), again, found the uninjured surface positive to the transverse
section, in the divided leaves of Vallisneria spiralis, in conse-
quence, as he believed, of chemical differences between the
exposed fluid of the cell and the surface of the leaf. The same
negativity of injured points (artificial transverse or longitudinal
sections) obtains, according to Hermann (3), in living stalks of
different species of plants. The cross-section, or artificial long
section, is plainly negative to the uninjured surface. The intensity
of these currents, " generally speaking, varies in a marked degree
with the charge of moisture in the plant, and the resulting
conductivity. The deflections range from 20 degrees of the
scale to its disappearance from the field of vision. The
stalks of fungi yield the strongest currents." The E.M.F. varies
between O'Ol and O'OS Dan., i.e. is of approximately the same
order as in the muscle current, although the deflections are often

VOL. II B

ELECTRO-PHYSIOLOGY CHAP.

small, owing to the high resistance. In the majority of cases the
" longitudinal- transverse " current in divided plant-stalks dimin-
ishes rapidly, and may even be reversed. Hermann (who refers
these currents, by analogy with the currents of muscle and nerve,
to the immediate contact of chemically altered dying and normal
plasma in the injured cells) explains this by the individual death
of the latter, as Engelmann has said of smooth muscle-cells. " If
the opened, or otherwise injured, protoplasmic tubes were con-
tinuous throughout the length of the tissue, like the fibres of
nerve and muscle, the process of death would creep forward, and
the cross-section be permanently negative to the surface of the
plant. Most of the cells which contain the protoplasm are,
however, short, albeit drawn out longitudinally, and thus the
negativity of a cross-section is transitory, although a further
section exhibits fresh activity " (I.e.).

Much greater interest attaches to the electrical reactions
which may appear in certain organs of plants that are perfectly
uninjured. The name of Burdon- Sanderson is foremost in the.se
researches. His admirable observations on the excitable leaf of
Dioncca muscipula are by far the best contribution to the
subject. Later on we shall have to study these in detail ; here
it need only be said that differences of potential are also found in
the totally uninjured leaf, particularly between upper and under
surface, and exhibit perfectly regular variations during the ex-
citatory movements of the plant.

A. J. Kunkel (4), working under Sachs' direction, concluded,
from the green foliage-leaves of different kinds of plants, that (on
leading off with unpolarisable electrodes, under uniform conditions)
the veins of the leaf were positive to its green surface. " The
stout mid-rib is weakly positive to the finer lateral veins ; in the
latter the junction of two veins is a highly positive point."
According to Kunkel, the sign of this P.D. depends essentially
upon the state of imbibition at the leading-off contacts at the
moment, since every point that has been moistened for some
time is at first positive to points that have been more recently
wetted.

And if these experiments indicate i;he great significance of
the distribution, or movement, of water in vegetable organs, with
reference to their electromotive activity, the same appears still
more plainly from Kimkel's experiments as to the effects of injury

vi ELECTROMOTIVE ACTION IX VEGETABLE CELLS

and tiexion on the development of differences of potential. On
leading oft' from two points of a green stern which is in itself
isoelectric, a P.D. always appears when the vicinity of one
electrode is injured (by cutting or squeezing), that electrode
being invariably negative to the other. The same occurs on
bending the stalk, if this is effected by a sudden jerk. Slow,
regular liexion, on the contrary, produces no effect on the
galvanometer. The electrodes were prevented, by threads, from
shifting along the stalk.

The theoretical conclusion from these experiments (which were
subsequently confirmed by 0. Haake, 5) was, like Griinhagen's
theory of the manifestations of animal electricity, referred to the
so-called diaphragmatic currents, nor did it obtain longer than the
former — once more proving that it is not sufficient, in explana-
tion of a physiological phenomenon, to bring forward a single,
purely physical, symptom, but that we are in presence of a vital
manifestation, the intrinsic character of which is determined by
a complex interaction of physical and chemical forces.

In the " migration of water " Kunkel believed that he had
discovered an infallible, and universally applicable, key to the
electrical phenomena which may at times be observed in vegetable
organs. In the case of his fundamental experiment with green
leaves, he ascribes the observed differences in potential to the
differing resistance presented by the tissues, at the leading-off
contacts, to the water, which diffuses inwards from the moist
electrodes, thus bringing about the requisite movement of water.
And indeed the unequal moisture of the ribs and mesophyll is
an easily-verified fact in many leaves. But, as Haake points
out, the leaf may be sponged over, or covered permanently with
water, without alteration of the electromotive reaction. Even
more convincing is the reaction of permanently submerged
leaves ( Vallisneria, Nitella), " from -which regular currents can
be led off even when they lie under water (to the depth of -|— 1
mm.)." Haake further remarks " that a normal electrical reaction
is exhibited only in the living leaf. A leaf killed by momentary
immersion in boiling water gives no more reaction if left one to
two days in the moist chamber, than a leaf that has died
naturally, and yet the conditions for quantitative differences in
the migration of water are still present."

And against the validity of the " drop experiment " Haake

ELECTRO-PHYSIOLOGY CHAP.

urges that it succeeds even when applied to a leaf of which the
tissues are fully saturated by long immersion in water, " so that
there can be no further absorption of water from the electrodes."

The chief point insisted on by Kunkel is the fact that
electromotive action appears only with rapid, and not with slow,
flexion of a green stalk. But without denying that electrical
effects might be caused in dead or living parts of plants by rapid
and adequate movements of water (due to purely mechanical
causes), it is equally certain that they are not under all condi-
tions solely due to the migration of water. This is sufficiently
plain from the experiments on excitable leaves, to which we shall
return later. Above all, an explanation is needed of the differ-
ences in potential (often permanent and very considerable) which
frequently make their appearance in certain vegetable organs, and
which, from the point of view we have been discussing, would
present insuperable difficulties to Kunkel ; for it is hardly a
satisfactory or probable explanation that derives the strong
" current of rest," amounting to O'l Dan. (which Kunkel found
in the leaf of Mimosa, on leading off from the upper border
of the excitable pulvinus at the base of the common [primary]
leaf-stalk, and from one of the two strong thorns near the inser-
tion of the leaf), from " the diffusion currents obtained, even in
the resting state, 011 moistening certain portions of tissues that
are peculiarly adapted to rapid alteration in their charge of
water, taking it up and giving it out quickly in large quantity."
Kunkel, however, concerned himself little with the electromotive
reactions of excitable parts of plants (which are theoretically of
fundamental importance), and his researches in this direction are
superseded by the later investigations of Burdon- Sanderson.

The intrinsically smaller differences of potential which Kunkel
observed in different species of green leaves must equally, ac-
cording to Haake, be referred to vital physiological processes. In
the first place, there is an obvious relation between the electro-
motive manifestations and respiration. "When suitable leaves or
stalks were enclosed in a glass tube, with the electrodes inserted
into one end, while gases were led through the other (Fig. 137), there
was invariably a rapid diminution of the original P.D. between
mid-rib (close to its entrance into the stalk) and mesophyll (near
the centre of the leaf), if the oxygen was completely driven off
by moist hydrogen. With the readmission of air the current

VI

ELECTROMOTIVE ACTION IN VEGETABLE CELLS

approximately recovered its former strength. The same reaction
occurred in seedlings of Pisxm sativum on leading off from the
collar of the root and the stem, where Hermann (3) had pre-
viously found a normal strong current, the root being negative to
the body (i.e. the cotyledons). The E.M.F. often exceeded ^
Dan. Johannes Miiller-Hettlingen (3), who studied this effect
more closely at Hermann's request, formulated the law as follows :
When one of the leading-off electrodes is persistently applied to
the cotyledons, while the other leads off successively from points
of the seedling above or below the cotyledon, there is always a
current directed from the electro-positive seed husk, or cotyledon,

FIG. 138.

to all other electro -negative parts of the seedling, its E.M.F.
being less in proportion as the exploring electrode is nearer the
cotyledon, above or below it. Fig. 138 gives a schema of this
reaction.

Haake occasionally found reversal, or augmentation, instead of
diminution, of the original current when respiration was inter-
rupted. " Such parts of plants as naturally exhibit marked
differences in respiration yield excessively strong currents, e.g.
the reproductive organs of flowers, on leading off from pistil or
anther, and flower-stalk." In such cases Haake obtained deflec-
tions of 50—80 degrees on the capillary electrometer, while in
green leaves the total effect is only 15-20 degrees.

The F.D. is also, comparatively speaking, very marked when
the respiration of a plant is checked at one electrode only, by
cutting off' the supply of oxygen, which Haake effected by en-
closing seedlings of Pisum or Faba in a double tube, and replacing
the air by hydrogen on one side only (Fig. 137). In one speci-

ELECTRO-PHYSIOLOGY CHAP.

men (a seedling of P-isum 14 days old), the initial deflection of
+ 5 degrees rose on leading off from collar of root and tip of stalk
to + 57 degrees, after driving off the oxygen from the root and
lower part of the stem, falling again with a fresh supply of air to
+ 14 degrees. With uninterrupted supply of air, the same effect
results from local changes in respiratory activity due to rise or
fall of temperature in the plant, near one or the other electrode.

The assimilatory process seems, from Haake's experiments,
also to contribute to the differences of potential exhibited by
green leaves. The arrest by darkness of the decomposition of
C02 regularly produces a diminution of the initial current. " If
the normal conditions are restored (by illumination), the former
potential reasserts itself ; but its magnitude is permanently
affected, and becomes either less or greater." Leaves that contain
no chlorophyll (petals of flowers) show no change of electrical
response when they are deprived of light. The most important
fact in these observations is the existence of an electrical P.D.
between the cells, or, strictly speaking, tracts of cells, in a
vegetable organ or entire plant, which differ in their chemical
constitution.

The electromotive reactions of vegetable organs (for the most
part very inconspicuous as compared with the corresponding
manifestations in animal tissues) have attracted much more
attention since the discovery of the striking manifestation in
excitable plants, as first pointed out by Burdon-Sanderson, when he
showed that the excitatory movements of the leaf of Dionoca musci-
pula are accompanied by highly characteristic alterations of the
original P.D. between upper and under surface (6).

The subject is best introduced by describing the organisation
and structure of the parts of plants involved, as well as the nature
and causes of their excitatory movements.

The general habit of growth in Dnnnm niiix<'ij>ula is shown in
Fig. 139, which at the same time gives the method employed by
Munk (to whom we owe an admirable work on the electm-
inotive action and excitatory movements of this plant, 7) for
setting up the specimens he investigated, so as to lead oft' from
the leaves as conveniently as possible.

The leaf, which is from 2 to l"2 cm. long in the full-grown

o o

plant, is divided externally into three sections — the winged leaf-
stalk, its unwinged part, and the Limi'im of the leaf. This last

VI

ELECTROMOTIVE ACTION IN VEGETABLE CELLS

consists of two distinct lobes, which, like the wings of the petiole,
are attached to the highly convex mid-rib. At its margin the
leaf is prolonged at tolerably regular intervals into bristle-like
processes, which hook together alternately when the lobes are
folded up. On the surface of each lobe are three small hairs, one

FIG. 139.

near the mid-rib, the other two somewhat external to it, and
these are essentially the seat of excitability. The inner surface
of the leaf is further provided with a number of small discoid
glands. The wings of the petiole consist of a soft unstable
tissue, while the lobes are lumpy, sappy, and highly resistant.
Lateral veins run out at approximately equal distances from the
fibro-vascular bundle which passes up the centre of the mid-
rib, and form an elegant system of arches at the margin of the

ELECTRO-PHYSIOLOGY

CHAP.

leaf (Fig. 140). The parenchyma of the lobe is entirely com-
posed of elongated or oblong
cells, their long axis being
parallel with the main bundles
of the lateral veins, and ver-
tical to the mid-rib (Fig. 141),
while they are circular (in
the long section of the leaf)
in cross-section. Large in-
tercellular lacunre appear be-
tween the single cells.

Below the epidermis of
the upper surface of the leaf,
the oblong hexagonal cells of
which are rich in starch, lies
a layer of somewhat shorter
thin-walled cells, succeeded
by 2—3 layers of larger, longer,

Fio.i4o.-Lateraiasi.ect of a cylindrical cells, with hardly
leaf of Dion«a, showing the any organised contents (Fig.

141). " The innermost layer
of these cells impinges on the
long slender cells which ac-
company the fibro- vascular
bundles in the petiole. Below the vascular bundle there are

venous system. (F. Kurtz

FIG. 141.— T.S. of lamina of Dininrn lr,-ii', parallel with the lateral nerves. (F. Kurt/.)

2-3 rows of cells resembling those described above, then 3-4 layers

vi ELECTROMOTIVE ACTION IX VEGETABLE CELLS 9

of much smaller, less conspicuous cells, rich in chlorophyll, and
finally, the epidermis of the under surface of the leaf" (F.
Kurtz).

The parenchyma of the leaf breaks through the epidermis of
the inner surface at the point where a sensory hair takes
origin. The parenchymatous cells lying immediately below
the epidermis are smaller at this point, and form a cylinder
(circular in cross -section) consisting of 4-5 layers of polygonal
cells, which rise above the surface of the leaf, and constitute about
T\jth of the total length of the hair. From this cylinder the
true hair rises as a slender cone ; it contains no vascular bundle,
and consists of long small cells (F. Kurtz, 8).

If unpolarisable electrodes are applied to opposite ends of a
fresh uninjured leaf of Dioncea, a regular current (as first pointed
out by Burden-Sanderson) is indicated on a galvanometer included
in the circuit, flowing in the leaf from the end proximal to the
stalk (according to Munk, the anterior end) to the distal (posterior)
end — Sanderson's " normal leaf current." On leading off from
symmetrical points of the external (under) surface of the lamina,
Munk either found no current, or a weak, irregular effect. If
lines are conceived on the surface of a lobe, at right angles to
the mid-rib (Munk's " transverse-lines "), each point of the same
will be negative to the corresponding point of the mid-rib, the
more so within a certain range in proportion as the point upon the
transverse line is nearer the margin of the leaf. The line con-
necting the most negative points of all the cross-lines running
approximately parallel with the mid-rib is called by Munk the
" principal longitudinal line " of the lamina ; as the most positive
point of the leaf he opposes the anterior end of the posterior third
of the mid-rib. The distribution and magnitude of potential at the
upper (inner) surface of the leaf corresponds, according to Munk,
with that of the lower (outer) surface ; so that on leading off from
two corresponding points of both surfaces there should be no
current ; this, as Burdon- Sanderson found later, is not the case.
The electromotive reactions of the leaf of Dioncea are associated
with its vitality, and at death decline to zero. The absolute
magnitude of E.M.F. is of considerable proportions. ' The P.D.
between a point in the proximity of the principal longitudinal
line, and one in the posterior half (distal to the stalk) of the
mid-rib, is not infrequently 0'04-0'05 Dan."

10 ELECTRO-PHYSIOLOGY CHAP.

Iii order to explain these electromotive effects in the
" resting " leaf, Munk formulated a " molecular theory," in which
the parenchyma cells function as cylindrical molecules, giving such
an electrical reaction that " the positive electricity is directed
from the middle of the cell towards either pole, the latter being
therefore positive towards the centre." Dioncea (in common with
a few other plants) has the power of making visible movements
under special conditions, consisting in this case of a rapid
closing of the two lobes, which enables it to capture the in-
sects that have alighted on it. This kind of excitatory move-
ment is distinguished by its rapid energetic character from the
slow " movements of absorption " which commonly succeed the
first, and only appear alone when absorbable substances (meat,
albumen, etc.) are applied cautiously, and without touching the sen-
sitive hairs, to the inner surface of the leaf. The excited leaf of
Dioncea closes with extreme rapidity (in a minute at the longest),
while the reopening may extend over many hours (24-3G). If
the leaf has closed on an absorbable substance it may not reopen
for several days.

The whole inner (upper) surface of the leaf is sensitive, yet, as
was said above, it is chiefly the six hairs (three sessile on each lobe)
which are so strikingly excitable that they were long held to be
the only sensitive part. Amputation of the petiole, or division
of the joint between leaf and stalk, does not act as a stimulus
unless the incision reaches the lower border of the mid-rib of
the leaf, where the vertical rows of excitable parenchyma cells
are situated beneath the epidermis of the upper surface. Am-
putation of the marginal bristles is equally ineffective. On the
other hand, incision of the lobe at any point induces closure.

Slight pressure has no effect upon the upper surface of the
lamina, while stronger pressure, as well as stroking with a pointed
needle, discharges an excitatory movement. The lower surface
is totally insensible to all these stimuli. Only the upper layer of
the parenchyma of the lobe and mid-rib is therefore excitable
and conductive, agreeing with the fact that the hairs (which are
not intrinsically excitable) are sessile upon the cones of excitable
parenchyma cells that break through the epidermis, and act upon
these something after the nianin-r of a lever (cf. taste-hairs of
rrrlaiii animals). Kadi hair can be shorn away from apex t<> base
with sharp scissors without evoking any excitatory movement,

vi ELECTROMOTIVE ACTION IN VEGETABLE CELLS 11

till the cone-like protuberance of the parenchyma of the lohe is
reached, when the contact at once causes the leaf to fold together.

Along with these mechanical irritants we must include the
abstraction of water, as a stimulus to the excitable parenchyma
at the base of the hair. Darwin (9) found, on placing the leaves
of Dioncea in concentrated solution of sugar, or even on applying
a single drop to an excitable hair, that the laminae closed up
immediately. Munk observed the same effect with alcohol
and concentrated salt solution, and again when the plants were
exposed to rapid evaporation in dry air.

The movements of the leaf of Dioncea, like all movements of
plants, are due to processes that cannot be compared with the
contraction phenomena of muscle, or with any true contractile
tissue. They are much rather special instances of cell co-ordina-
tion, depending on quite different mechanical principles. The most
characteristic type of plant-movement is the well-known Mimosa
pudica. Each leaf -stalk of the "sensitive plant" bears four
secondary petioles, provided in their turn with two rows of
leaflets. During the day the principal stalk is erect, the second-
ary petioles being spread out like the fingers of a hand. The
single leaflets are expanded into a smooth surface. At night the
leaves sink down, the secondary petioles are folded together, and
the leaflets stand up, so that the inverted surfaces are in contact.
This change of position in all the leaves can be induced in the
day-time also by violently shaking the plant, or bringing it into
an atmosphere of chloroform or ether vapour. Locally, howrever,
or within a limited tract, the same effects occur on mechanically
exciting the single leaflets (by touching, pricking, cutting), par-
ticularly at the point where the principal leaf-stalk is attached
to the stem. Here there is a cushion (pulvinus), which is simi-
larly developed at the base of the second and third petioles. In
every case an excitatory movement is discharged only on touching
the under side of the swelling at the joint, while the upper surface
is almost entirely non-excitable.

Anatomical investigation of one of these swellings shows it to
be traversed by a vascular bundle with a layer of very succulent
cells between the bundle and the green cortex ; these cells are
tolerably thick-walled upon the upper (insensitive) side of the
joint, while on the lower side the walls are comparatively slender.
On bisecting the swelling transversely, a funnel appears on

12 ELECTRO-PHYSIOLOGY CHAP.

either side (as was pointed out by Briicke, 10); this is due to an
initial tension in the living plant between the succulent cells of
the pulvinus and the vascular bundle, " so that on cutting through
it the cellular portion tries to expand in the direction of the long-
axis, while the central vascular bundle cannot lengthen beyond
its original proportions. It may be compared with an inexten-
sible wire drawn through a piece of gutta-percha, and screwed
against the end of it with a nut " (Briicke). This may occur
when a leaf-stalk changes its position, tension being raised in
the upper half of the swelling, or diminished in the lower.

It is easy to prove that the second alternative invariably
occurs in excitation. On comparing the colour of the excitable
under surface of a pulvinus before and after stimulation, a strik-
ing difference is apparent. Before excitation it is light green,
aftenvards it is a darker colour. There can be no doubt that
this change is due solely to the discharge of fluid from the cells
into the large intercellular spaces previously filled with air, and
obviously there must be extension and relaxation of the layers
of tissue involved in the process. The fact that any excitation
of the under side of the motor organ (cushion) of Mimosa, how-
ever scrupulously localised, discharges water from all cells of the
parenchyma, testifies to the propagation in all other cells of the
under surface, of certain alterations of protoplasm in the cells
directly excited, which result in the discharge of water. Pfeffer,
indeed, saw the darker colour spreading " like lightning " from the
point excited. Thus within the pulvinus itself there is con-
ductivity of excitation from cell to cell.

Still more striking, however, is the fact that the stimulus can
be transmitted over large tracts, and even to the most remote
parts of the plant. The external features of this phenomenon
are so well known that it is superfluous to dilate on them, but
the correlative internal processes must be briefly referred to.
The account given by Haberlandt (11) in his treatise on the
" sensitive plant " will be followed substantially.

Dutrochet (12) endeavoured to determine which parts of the
plant served to transmit the excitation. He showed that the
cortex was not involved, by paring away a ring of it, when the
conductivity of the twig remained unaffected. So, too, on re-
moving the pith. The wood alone was involved, without excep-
tion, or more correctly the fibre-vascular system (bast and vessels).

vi ELECTROMOTIVE ACTION IX YWJKTABLE CELLS 13

Dutrochet also pointed out that the transmission of excitation
depended on the movement of fluid contained in the conducting
elements. This view was subsequently confirmed by the experi-
ments of Meyen (13), Sachs (14), and Pfeffer (15). Meyen
observed that a drop of fluid was exuded on cutting the stalk of
3fiiiiosc(, immediately before the excitatory movement of the leaf.
This drop of fluid, which starts out instantaneously if the leaf or
stalk of Mimosa is wounded, has been an important factor in
nearly all the proposed explanations of conductivity, and formed
the basis of the "physical" theory. Sachs (I.e. p. 482) concludes,
from the rapid exudation of a drop of water from the incised
wood, that the fluid in the fibre-vascular bundles stands at very
high pressure in a sensitive mimosa, the excitable parenchyma
cells of the lower half of the pulvinus being also -in the highest
degree turgescent. " The water thus tends on the one hand to
exude from the endosmotically over-filled cells of the pulvinus,
and on the other, to penetrate them, on account of its high
pressure in the woody bundle." In the unexcited plant these
pressures are at equilibrium. Incisiug the stalk disturbs the
balance, the water in the wood migrates towards the wound,
pressure diminishes, and the water filters out of the highly
turgescent excitable parenchyma of the pulvinus into the walls
of the cells. Here it follows the direction of diminishing tension,
and flows towards the woody bundle of the axial cord. The
excitatory movement appears along with the diminished turgor of
the lower portion of the pulvinus.

From this point of view the true excitable cells are found in
the parenchyma of the lower side of the pulvinus only, where
any stimulus renders the plasma permeable to water, which then
filters through the cell-membrane into the intercellular spaces.
The relation between distant pidvini would thus be purely physical,
caused by the tension of a constant mass of water in the woody
parts of the plant. There is, however, another alternative, which
may seem a priori the more probable. Excitable cells may be
present in the vascular bundles also, and propagate the stimulus
from joint to joint. This theory finds substantial confirmation
in the discoveries of Tangl, Eussow, and Gardiner (Art. d. bot.
Inst. zu Wurzbury, iii. 1884) in reference to the connection of
adjacent cell-bodies by fine protoplasmic threads. Such a con-
nection was actually found to exist between the cells of the

14 ELECTRO-PHYSIOLOGY CHAP.

excitable parenchyma of the pulvinus, and it was natural to
assume similar bridges between the latter and the cells of the
conducting vascular bundles. The effect of local narcosis (ether
or chloroform) offered a simple means of deciding the question.
Claude Bernard pointed out that the excitability of Mimosa, can
be temporarily abolished by etherisation. If this is true of the
excitable parenchyma of the cushion, it may be conjectured that
the excitable cells of the vascular bundles will exhibit the same
reaction. The transmission of excitation should be abolished by
local narcosis. But the experiments undertaken by Pfeffer (15)
pointed to the contrary result. When the central portion of a
secondary petiole was treated with chloroform or ether, an injury-
stimulus was alwavs — a mechanical stimulus sometimes — trans-

f

mittecl over the narcotised area, Pfeffer therefore concluded "that
migration of water is the sole cause of the propagation of a stimulus.
This movement of water takes place in the vascular bundles. If
excitation is produced by incision of a vascular bundle, so that
fluid exudes from the wound, the disturbance of equilibrium in
the water distributed in the bundle depends upon abstraction of
water. If, on the other hand, excitation is by a mechanical
stimulus, a certain, albeit inconsiderable, quantity of fluid passes
out of the excited parenchyma of the joint into the vascular
bundle ; migration is due to the addition of water " (Pfeffer,
I.e. p. 315). In either case Pfeffer refers the propagation of
the stimulus from vascular bundle to excitable parenchyma of
pulviuus, and vice versa, to the migration of water. The dis-
turbance of equilibrium is transmitted to the innermost layers
of the parenchyma, immediately adjacent to the bundle,
where it acts " as a mechanical stimulus," and discharges the
movement.

Further confirmation of this theory appears in the observa-
tions of Haberlandt. He finds that excitation in Mimosa is pro-
pagated even over dead tracts of the petiole, destroyed by scalding.
If this were entirely the case, it would be conclusive evidence
that the conductivity of Mimosa depends not upon a connected
system of excitable, or conductive, cells in the vascular
bundle, but upon a disturbance of hydrostatic equilibrium due to
the injury, and transmitted indifferently over the dead zone of
the petiole. Migration of sap would in the same sense lead to
conductivity of excitation.

vi ELECTROMOTIVE ACTIOX IX VEGETABLE OEI.L1 If.

Haberlandt localises this process in certain funnel-shaped cells,
situated in the leptoma of the vascular bundle (soft bast) ; the
structure of these cells is so far remarkable that each transverse
wall bears a single large pit, closed by a porous membrane, and
traversed by plasma threads from the adjacent cells. Although
these "conducting" cells are in juxtaposition with the ring of
collenchyma which surrounds the central bundle of the pulvinus
(the cells of which are again connected by plasma bridges with
those of the conducting parenchyma), Haberlandt refuses to
admit any direct connection between the conducting cells and
the collenchyma. There must thus be two systems of cells,
functionally co-ordinated, but not in direct conducting, i.e. plas-
matic, connection.

Haberlandt's theory assumes a very high hydrostatic pressure
of sap in the intact conducting cells of the leptoma, which gives
elastic tension to the longitudinal walls of the conducting cells ;
the resulting wall tension represents the immediate source of
pressure which, on injury to the conducting system, causes a
movement of the sap towards the seat of the sudden diminution
of pressure. Clearly this can only be possible on the supposition
of a filtration of sap from within the cell, through the intact
cross-walls of the adjacent cells. And this entails the further
and somewhat improbable assumption that the plasmatic layer
covering the pit must invariably be permeable, in a high degree ;
for thus only is it possible that the conducting cells should
act as a system of fused and communicating hollow spaces.

The next point is the mode in which, under the above
presumptions, the flow of water within these funnel-cells can act
as a stimulus upon the excitable parenchyma of the pulvinus.

Haberlandt refers the propagation of the stimulus entirely to
alterations of form and volume in the conducting tissue or excitable
parenchyma, correlative with variations of pressure. " When, in
consequence of injury to stem or petiole, there is a sudden fall of
turgor from the adjustment of differences of pressure in the con-
ducting cells bordering on the collenchyma ring of a joint, the
contracting walls of these cells (which are diminishing in diameter)
exert a powerful traction on the adjacent collenchyma. Owing
to the pliability of the latter this tug is easily transmitted through
the ring (which is 2-3 layers deep) to the most internal
layer of the excitable parenchyma. If the mechanical force of

16 ELECTRO-PHYSIOLOGY

the traction corresponding with a single impact is sufficient,' an
excitatory movement will be discharged, and the cells contract-
ing from loss of water stimulate all the other excitable cells of
the joint by means of the pull they exert " (Habeiiandt, I.e.
p. 53). It is still harder to explain the mechanism by which
a stimulus is propagated from the relaxed parenchyma of the
curving pulviuus to the excitable parenchyma of an adjacent
joint, after a single mechanical stimulus, or with chemical or
thermic excitation. In this case the pressure associated with
the relaxation of the excitable half of the joint, and resulting
curvature, could alone effect a possible disturbance of hydrostatic
equilibrium in the conducting system, adequate for the trans-
mission of a stimulus. And when Haberlandt compares the re-
sulting movement of the sap " to that within an india-rubber tube
containing water at a given hydrostatic pressure, in which increase
of pressure at any point is propagated in the form of an undulatory
wave from one end of the tube to the other," the anatomical
relations of the conducting cells hardly seem to justify such a
presumption. The experiments on the conductivity of Mimosa
would have to be scrupulously repeated before forming any final
judgment, and the galvanic effects of excitation might prove a
convenient instrument for further investigation.

However this may be, it is in other cases certain that con-
ductivity depends upon excitation of the plasma of the connected
cells : and this must be true of Dioncea.

As in Mimosa, the visible excitatory movements are effected
by migration of water, and the normal position of the non-
excited leaf is the result of equilibrium between two forces,
one of which tends to close the leaf, the other to open it. The
cells of the upper surface of the resting (open) leaf are highly
turgescent, like those of the under side of the pulviuus in
Mimosa. If, as was observed by Munk, we picture the cushion
of the primary leaf-stalk of Mimosa as flattened out superficially,
with the characteristic veins in place of the wood-mass, we have
physiologically a lobe of Dioncea, save that the excitable side is
turned downwards ; while if two such altered pulvini are imagined,
so connected at a right angle that the excitable parenchyma of
the swellings is uninterrupted at the point of junction, the entire
leaf is practically before us.

The upper layer of cells exerts pressure upon the lower, so

vi ELECTROMOTIVE ACTIOX IN VEGETABLE CELLS 17

that the equilibrium is balanced as follows : on the lower side the
compressed tissue endeavours to extend itself and to increase its
length ; on the upper there is a marked turgescence, counteracted
by the elasticity of the cell-membranes which tend to contract
upon themselves. When, in consequence of excitation, water is
discharged from the cells of the upper surface, the equilibrium is
disturbed (Batalin, 1 6), and a new state induced, characterised by
an actual relaxation and shortening of the upper layers. This
cannot, even in the closed leaf, amount to perfect equilibrium,
since it is hindered by the contact of the lobes in juxtaposition.

This is plainly seen from the fact that, after cutting off one
lobe near the mid-rib, the other, in its excitatory movements,
is jerked far beyond the position it occupied in the closed and
uninjured leaf. Hand in hand with the shortening of the upper
layers at closure, there is a corresponding lengthening of the
lower, so that each lobe passes from downward to upward con-
cavity. On opening the leaf, the reverse processes occur. The
previously relaxed and diminished cells of the upper parenchyma
swell out as turgor increases, and recover their former tension.
According to Darwin's measurements, the shortening of the upper
layers in a lobe 10 mm. broad reduces it to 0-6 mm. only.
This is most obvious when, after taking away one half of a leaf,
two points are marked on both upper and lower surface of the
other half, and a movement excited ; the distance of the marks
alters in an opposite direction.

Along with these excitatory movements of the leaf of Dionwa
(as also of Mimosa) there are very striking .electromotive effects,
which, as was said above, were first recognised by Burdon-
Sandersou to be a " negative variation." As the result of his
first observations he communicated the following propositions :

(a) If the leaf is laid on the electrodes, so that the normal
current is manifested on leading off from both ends of the leaf
by a deflection of the magnet to the left, and a fly is then made
to creep on to it, the needle will swing to the right at the
moment when the fly reaches the interior of the leaf, and touches
the sensitive hairs of the upper surface, the leaf closing over
the fly at the same moment.

(&) After the fly has been captured, the needle swings to the
right each time that it makes a movement.

(c) The same series of manifestations occurs if the sensitive

c

18 ELECTRO-PHYSIOLOGY CHAP.

hairs are touched with a fine brush, or if two platinum electrodes
are plunged downwards into the leaf, and lead in the current from
an induction coil. The phenomena vary according as the leaf
is stimulated at different parts of its upper surface. Excitation
of the centre appears to be the most effective, being followed by
a negative variation after an interval of 4—^ sec.

Muuk, on leading off from the two ends of the mid-rib on
the lower surface of the leaf, without, or even with, compensation
of the current flowing from base to apex, invariably observed a
diphasic variation, i.e. a positive preceded by an initial negative
variation, and this is equally the case when all visible excitatory
movement of the leaf is wanting. Sometimes Munk even saw a
positive effect before the initial negative phase, resulting in a
complicated triphasic variation ; this only appeared when the
excited leaf exhibited an actual movement. When there was
at first no difference of potential between the two leading -off
points, the diphasic variation still appeared with excitation, the
mirror moving rapidly in the direction of an ascending current,
and then giving a much weaker deflection in the opposite direc-
tion. On leading off from two points of the under surface of
the leaf, taken on the same " transverse line," median to the
"principal longitudinal line," the excitation either produced a
pure positive variation, or at most gave a trace of initial nega-
tivity. All these electrical processes fall mainly within the
mechanical, and easily detected, latent period, i.e. the interval
between the moment of excitation and beginning of the final
movement of the leaf. From the standpoint of Munk's theoretical
construction of the leaf of Dioncea out of electromotive elements
(" peripolar " cells), there are three alternative explanations of the
two successive and opposite phases of which each variation
consists ; and these are so closely interwoven with the facts
actually observed by Munk, that, as Burdon- Sanderson has
pointed out, it is exceedingly difficult to separate observation
from theory.

(1) In the diphasic variation, as in the diphasic action current
of nerve and muscle, the electromotive elements at the two
contacts may not be simultaneously affected by the excitatory
change (negative variation of E.M.F.) ; (2) the elements may
all be affected simultaneously, and in the same direction—
which would be opposite in the two phases ; or (3), as Munk

vi ELECTROMOTIVE ACTION IN VEGETABLE CELLS 19

proposes to the exclusion of the first two alternatives, there may
be two different kinds of electromotive elements, which are
affected in opposite directions by excitation, the variation
reaching its maximum in one set later than in the other.
" In. consequence of excitation," says Munk, " the cells of
the upper parenchymatous layer of the leaf and upper mid-
rib undergo a negative, those of the under layer and under
mid-rib a positive, variation ; i.e. the negativity of the middle
of the cells to their poles diminishes, in consequence of excitation,
in the first-named cells, and increases in the second. These
changes must be propagated from the seat of excitation through
the entire cell-mass with great rapidity, in a period that is small
in comparison with the duration of the process in the single cells,
since otherwise differences in electrical manifestations could not
fail to appear according to the seat of the stimulus." Munk
therefore believes the electrical process to be for practical purposes
simultaneous in all the cells affected, which — in so far as the
transmission is plasmatic — is, in view of the very low rate at
which excitation is propagated in vegetable protoplasm, in itself
highly improbable. But as a matter of fact, Munk's fundamental
theory of the peripolar activity of the cells of the leaf-parenchyma
hardly calls for contradiction, since it is modelled upon Du Bois's
molecular theory, applying it to visible elements, of which the
structure and function are a priori exclusive of any such con-
ception. It is a purely arbitrary presumption to regard the
centre of the cells involved as permanently negative to the two
ends, and is indeed impossible where the plasma exhibits any
streaming movements.

The later investigations of Burdon- Sanderson (17) have
rendered these phenomena more intelligible.

In order, from the outset, to exclude the excitatory move-
ments of the leaf, the two lobes were fixed in plaster of Paris
attached to the ends of the mid-rib, while a strip of dry wood
was further fastened with gypsum between the two edges of
the lamina to the marginal bristles (Fig. 142). A favourable
temperature (32°— 35° C.) was maintained, and the plant kept in
a moist chamber.

As regards electromotive action during rest, the important
fact appears in contradiction to the earlier conclusions of Munk,
that in an overwhelming majority of cases the two opposite

20 ELECTRO-PHYSIOLOGY CHAP.

surfaces of each lobe of the leaf, external and internal (or upper
and lower), give a different electrical reaction, so that 011 leading
off from opposite points of the upper and lower surface, there is
found to be current, either so that the latter is positive to the
former (which Burdon- Sanderson at first held to be normal) or
vice versa. The degree of positivity, and corresponding magnitude
of P.D. and of the leaf-current, in the first case, depend, as soon
appears, essentially upon the physiological state of the leaf, and
above all upon the previous excitation.

If, after compensating the current of rest, mechanical or
other stimuli are sent in moderately rapid succession into a leaf
of which the under surface is already positive, there is without

FIG. 142.

exception a marked rise of positivity in the excited surface. It
is only by degrees, during the subsequent period of rest, that the
current diminishes, until with the same lead-off there is complete
isoelectricity, and finally, as has been said, a current in the
opposite direction, corresponding with negativity of the under
(external), and positivity of the upper (internal), surface of the
leaf — a state which, according to Burdon-Sanderson's later observa-
tions, must be regarded as normal in the leaf which has remained
a long time unexcited. In this instance the leaf-current must, in
regard to the internal surface, be regarded as outgoing.

Excitation in such a case is naturally followed by the
opposite alterations, as in an initially ingoing leaf-current : the
positive upper surface becomes suddenly negative to the lower
surface, so that the leaf-current is once more ingoing. It should
also be remarked that the lower surface of the leaf is the less
positive and more negative, in proportion with the time that has
elapsed since the last excitation. The current of rest, on the
contrary, is at all times dependent on the previous excitation of

VI

ELECTROMOTIVE ACTION IN VEGETABLE CELLS

21

the leaf, and must with an ingoing direction be regarded in a
certain sense as its after-effect.

Under these conditions it is clear that the manifestations of
excitation must be studied before the
state of rest. In leading off from the
upper and lower surface of a lobe, one
unpolarisable electrode being situated
between the three sensitive hairs, the
other directly opposite on the lower
(external) surface, and then exciting
the other lobe of the leaf mechanically
or electrically (as in Fig. 143), a diphasic variation appears
each time, as can easily be photographed with the capillary
electrometer (Fig. 144).

In the case of a leaf " modified " by previous excitation,
where the lower surface is already positive to the upper, the
current is in the first place reversed shortly after stimulating,
the lower surface becoming rapidly negative. After about half

FIG. 143.

PIG. 144. — Photographic record of the variations of an ingoing leaf-current, when one lobe is
electrically excited. The interruptions of the black line correspond with breaks in the
primary circuit of the induction-apparatus. Interval between the excitations about 5 sees.
Rapidity of plate about 1 cm. in 2 sees. (Burden-Sanderson.)

a second this phase will have reached its maximum, and a
second (somewhat slower) and opposite phase sets in, which is,
however, less marked, and reaches its maximum in about
1^ sec. after excitation. This, as shown by the photogram,
decreases very gradually, and loses itself in the after-effect
described above, which is characterised by increased positivity
of the lower surface of the leaf ; it follows that the second phase
is distinct in the first excitation only, those immediately subsequent
producing merely a simple, monophasic variation. A long interval

22

ELECTRO-PHYSIOLOGY

CHAP.

is required, in which the positivity of the lower surface diminishes
slowly, before the second phase again appears distinctly. The
stronger the positivity of the lower surface ab initio, the less
can it be increased by excitation of the leaf, and conversely,
the plainer will be the primary opposite variation.

In an unmodified leaf with outgoing leaf-current (Burdon-
Sanderson's "descending" current), the variation consequent on
excitation is again found, on leading off from opposite points of
the respective surfaces, to be diphasic. The first "entering" phase
(ascending in the leading-off circuit), which lasts about a second,
and in which the upper and previously positive leaf-surface

PIG. 145. — Photogram of the variations of an outgoing leaf-current, on exciting one lobe and
leading oft' from the other (cf. Fig. 143). 10 divisions of the time-marking correspond to 1 sec.
(Burdon-Sanderson.)

suddenly becomes negative, is often preceded by a momentary
alteration in the opposite direction, as shown in Fig. 145.
Here again the opposite (outgoing or descending) " after-effect "
(second phase) only appears plainly in the first excitation, and
owing to its very slow decline is wanting in those that immediately
succeed it.

The most important conclusion from these observations is
that the leaf of Dioncca is excitable in both the unmodified and
the modified condition, independent of the direction of the rest
current, save that the galvanic effects of excitation are reversed
pari passu with the reversal of the current of rest.

It is evident that the " modifications " of the leaf-current
consequent on repeated excitation are only the after-effect of the
slowly declining second phase of the excitatory variation. For
exact measurements of time, as well as of the E.M.F. of the varia-
tion, Burdon-Sanderson employed a pendulum myograph arranged
as a rheotome, which in swinging past opened three keys in suc-
cession (Fig. 146). Opening Kl caused a "break" induction

VI

ELECTROMOTIVE ACTION IN VEGETABLE CELLS

Fio. 14(5.

shock (O'l sec. after liberating the pendulum); opening K2 un-
bridged the galvanometer circuit, which was broken, finally, by
opening K3. The distance between Kl and K2, as also between
K2 and K3, is variable. We shall return later to the results of
these experiments ; here it is sufficient to note that Burdon-
Sanderson, with the
help of the compensat-
ing method, determined
the E.M.F. of the first
phase at about O'OS
Dan., while that of the
second did not exceed
0-82 Dan.

If one or other half
of the leaf is excited
by break induction
shocks (the electrodes
being usually applied,
as in Fig. 143, to opposite and approximately central points of the
two leaf-surfaces), the coils of the induction apparatus must be
pushed tolerably close (about 10 cm.) before an effect is produced.
The direction of the induced current is by no means immaterial, since
the effect appears much sooner when the current flows from upper
to under surface than in the opposite case. The same applies to
battery currents also. If a current, of moderate strength, adequate
for excitation, is sent transversely through one half of the leaf
in the direction of upper to lower (ingoing), it will be found on
leading off from the other half that an excitatory variation of the
leaf-current occurs, as a rule, at closure only. Stronger currents
(1 Dan. to 2 Groves), on the contrary, excite on opening also,
and with a long closure (30 sec.) produce as the visible sign of
persistent excitation a whole series of oscillations of the leaf-current,
which occur at irregular intervals during the passage of the current.

Summation of stimuli may also be demonstrated in the
Dioncca leaf, if stimuli (break induction shocks) are used of such
low intensity that a single shock is inadequate to produce an
effect, the interval between the stimuli being less than 0'4 sec.
At 0'5 sec. the result becomes uncertain. This applies both to
mechanical and to galvanic effects of excitation.

The " modified " state of the leaf in which, as we have stated,

24 ELECTRO-PHYSIOLOGY CHAP.

the under surface is positive to the upper, appears not only in
consequence of quickly repeated mechanical or electrical excita-
tions, but also as the after-effect of the prolonged passage of a
constant current. If such a current is led through a leaf by
means of non-polarisable electrodes at right angles to its surface,
the electrodes, as in certain polarisation experiments in muscle,
serving simultaneously to lead off to the galvanometer, there is
always, if the galvanometer circuit is closed immediately after
opening the exciting circuit, an ingoing after-current in the leaf,
directed from above downwards, whatever the direction of the
polarising current. An exciting current homodromous with the
after-current is, however, much more effective, other conditions
being uniform.

Burdon - Sanderson used a specially constructed rheotome
for these experiments, which made only three revolutions
in the minute, and thus closed the polarising current once in
2 0 sec. for -^ to ^ sec. ; after an interval of ^ sec. the
galvanometer circuit was closed for -^ sec. and the effect was
noted.

" If the polarising current is comparatively weak, the after-
effect gradually diminishes, and disappears in a few seconds.
But if somewhat stronger currents are employed, the after-effect
will only partially disappear, leaving a permanent alteration
{modification) in the electromotive response of the leaf." With
repeated closure of the polarising current at regular intervals of
about 20 sec., the modified state is very quickly developed, and
reaches considerable proportions. " In one leaf, e.g., the lower
surface was negative to the upper (P.D. = 140 degrees of com-
pensator) before the passage of the current ; four excitations
reduced the P.D. to zero, after which the lower surface subse-
quently became positive to the upper, and each excitation by the
current increased the effect, until it reached 320 degrees of the
compensator."

As in muscle, secondary electromotive manifestations appear
as galvanic indications of the action of the polarising current, in-
dependent of visible signs of activity, so here Burdon-Sanderson
observed a modification, with currents so weak that their
" make " produced no trace of excitatory reaction after closure.
The " modification " then remained local, and was not transmitted
further, so that a lobe or part of the same can be affected

vi ELECTROMOTIVE ACTION IN VEGETABLE CELLS 25

without involving the surrounding tissue. In this respect again
we are reminded of the polar after-currents in muscle.

It thus becomes intelligible that, according to the situation of
the leading-off points on the opposite surfaces of a partially
" modified " leaf, the excitatory variations discharged by a trans-
mitted excitation may be directly opposite in character, the
diphasic variation in the modified tract presenting different signs
from that in the tract that is unmodified (normal).

Munk, as we have seen, assumed the precise seat of the
excitation on the leaf of Dioncea to be without significance to
the character of the electrical variation discharged, and concluded
that the propagation of the changes which underlie the excitatory
effect (movement) must be so rapid that they begin, as it were,
simultaneously at all points. Burdon- Sanderson's investiga-
tions show that this theory (which is a priori improbable
if the excitatory movements of plants correspond with the
excitation of protoplasmic parts) is as a fact inadequate. It is
evident that if the view advanced by
Munk were correct, there should be no
galvanic effect of excitation with a sym-
metrical lead-off from upper or under
surface of both lobes, even when one
side only was stimulated (Fig. 147). A
variation under these conditions is only

. . FIG. 147.

to be expected when the activity of the

two lobes differs either in degree, or in the moment of its com-
mencement ; much as an electrical P.D. can only occur between
two points of a muscle when the physiological state of the two
points is different, or when the same state is developed in them
at different times.

And we find experimentally that this method of leading off is
invariably followed by galvanic effects of excitation, as appears at
once from the curves, Fig. 148, a, l>.

Fig. 147 represents a leaf led off symmetrically from the
under surface, and excited with opening shocks. The galvano-
meter is replaced by a capillary electrometer, the effects being
photographically recorded. The directly excited lobe is invariably
at first negative, and subsequently positive to the other, giving
rise to a diphasic variation similar in character to that which
results on leading off two points from the normally isoelectric

ELECTRO-PHYSIOLOGY

CHAP.

surface of the ventricle. The galvanometer, of course, shows the
same thing with the rheotome method.

In order rightly to interpret this " diphasic action current,"
it is essential to determine the rate at which the excitation
(? the effect of stimulus) spreads in the parenchyma of the
leaf.

Burden-Sanderson used a pendulum rheotome for this purpose,
with which it is easy to determine the time between the moment
of excitation and commencement of the consequent electrical
variation of the leaf-current. This current was, as before, led off
from the middle of the opposite surfaces of a lamina. In a
preliminary series of experiments, the exciting electrodes were
placed on either side of a leading- off electrode on the upper

FIG. 148.

surface of a leaf, so that a straight line connecting the two passed
through the leading-off contact. The first perceptible trace of phase
I. of the excitatory variation generally appeared 0'041 sec. after
the moment of excitation. If time is required for the spread
of the excitatory activity, it is evident that the " latent period "
must be very much longer (with unaltered position of the leading-
off electrodes) when the stimulus is applied to the lobe that is
not led off. That this is so appears from Burdou- Sanderson's
experiments, where the interval between excitation and beginning
of the variation as a rule exceeds 0'073 sec. Accordingly, if we
estimate the distance between the two points excited in succession
at 6 rnm., the transmission of excitation must occur at about 200
mm. per sec. (at a temperature of 30°— 32° C. in air saturated with
aqueous vapour). An even greater disparity between the latent
periods in the two cases might have been expected, supposing
that, as in muscle, there were no perceptible latent period in the

vi ELECTROMOTIVE ACTION IX VEGETABLE CELLS 27

galvanic effects of excitation at the actual point excited. Yet an
experiment, in which excitation and leading-off are absolutely
simultaneous, would encounter almost insuperable difficulties, not
the least being to determine exactly the real commencement of
the variation.

Burdon-Sanderson's assumption that the electrical variation
does not coincide with the beginning of excitation, may be met
with the same arguments that were brought forward above, in
discussing the relations between excitation and contraction in
muscle. If the galvanic alteration is really the expression of
the chemical change induced by the stimulus, it must commence
simultaneously with it, i.e. at the moment when the stimulus
takes effect.

The preceding observations show beyond doubt that the
primary phase of the excitatory variation accompanies and is the
direct consequence of excitation of the protoplasm of the excitable
parenchyma cells of the leaf — comparable throughout its manifest-
ation with the galvanic effects of excitation in excitable animal
tissues, i.e. the negative variation of muscle, nerve, or gland
currents. It is therefore to be expected that the time-relations
between the galvanic and mechanical effects in the leaf of Dioncea
would be similar to those exhibited in muscle — always remember-
ing the different causes of movement in the two cases.

In the first place it is evident that the excitatory variations
of the " current of rest " are quite independent of the coarsely
perceptible movements of the lobe, and are demonstrable
both on the fixed and open leaf, and on that which is entirely
closed. The next point, as Burdon - Sanderson has correctly
pointed out, is to ascertain " whether the interstitial movement
of the fluid discharged from the cells on excitation (which in
all excitable plant-organs is the active cause of the change of
form) may not occur without any perceptible change in the
curving of the lobe, no matter how fine the means of observation
employed." This entails the presumption that every excitation
implying an electrical alteration must also cause a perceptible
discharge of water from the excited cells. That there is further
a perceptible interval between the moment of excitation and the
consequent closure of the leaf of Dioncea may as a rule be verified
from direct observation, since, when the temperature is not too
high, the mechanical latent period is actually macroscopic, e.g. at

ELECTRO-PHYSIOLOGY CHAP.

20° C., about 1 sec. Under all circumstances the electrical
variation long precedes the excitatory movement.

For more exact investigation two methods were employed by
Burdon-Sandersou. In the first " a light straw lever was cemented
to two of the marginal bristles of a lobe, the opposite lobe being
fixed to a support. The lobe thus attached was mechanically
excited in such a way that the time of the exciting impact was
recorded on a horizontally-moving smoked plate below the curve
drawn by the lever."

In the second method the leaf was fixed in the same way,
but a small mirror was cemented to the lower surface of the free
lobe, by means of which the image of a horizontal slit was
thrown on to a vertical scale, so arranged that the movement of
the lobe could be exactly measured.

The result showed that with a temperature of 15°— 20° C. the
closing movement of a lobe, consequent on a single adequate ex-
citation, lasted 5-6 sec., occurring rapidly at first, and then with
diminishing speed.

With a succession .of very weak mechanical stimuli (gentle
impact on one of the sensitive hairs), inadequate singly to
produce complete closure of the leaf, Burdon-Sanderson observed
an effect which to some extent recalled the " staircase " of direct
muscular excitation, the mechanical effect of the movement in
each successive stimulation being greater than in those that
preceded it. This reaction must, however, be referred to the
fact that the resistance of the cells of the upper surface of the
leaf to the closing movement, due to turgor, diminishes with each
new excitation. " The magnitude of each diminution of resistance
produced by excitation grows with each repetition of the stimulus,
until the leaf finally closes together " (Burdou-Sanderson).

It may be assumed as certain that galvanic excitatory
manifestations, similar to those of Dioncea, are to be observed in
the pulvini of the no less sensitive leaves of Mimosa. Un-
fortunately there are, so far, few observations on this point.
Kuukel, who, as we have seen, found a strong " current of rest "
in the cushion of the primary leaf-stalk, the bristle being positive
to the upper surface of the joint, observed, with the capillary
electrometer, a variation of this current (consisting of a number
of alternating oscillations) at the moment when contact with the
most excitable point of the lower circumference of the pulvinus

vi ELECTROMOTIVE ACTION IN VEGETABLE CELLS 29

begins to produce a downward movement of the petiole. There
is a rapid preliminary variation, which is soon exhausted, and is
followed immediately by a much more pronounced deflection in
the opposite direction. The mercury slowly returns from the
extreme point of this last, and either reaches its resting-point
or exhibits a variety of smaller and slower oscillations.

Kunkel was quite aware of the difficulties of interpreting
these complicated excitatory variations from his own theory,
and was " not disinclined to refer them to single phases of the
active displacement of water." He derived the first rapid
negative swing from " alterations " of the protoplasm, which
disturb the diffusion-processes caused by the contact of the
moist electrodes, and fundamental to the current of rest. The
large positive deflection, 011 the contrary, " expresses the main
displacement of water which results in the movement of the
entire leaf; the (negative) return corresponds with the restitution
of the organ to its earlier state." Yet, as Kunkel himself
noticed, it must not be forgotten that in Mimosa, as in Dioncea,
electrical variations can still be observed when, after repeated
excitation, there is no longer any perceptible movement of the leaf,
so that there can hardly be any considerable displacement of water.

If we endeavour, on the basis of these experiments on
Dioncea, to form any picture of the possible causes of the difference
in potential in the " resting " state and during artificial excitation,
it is in the first place clear that the same principles which we
have already accepted as determining the appearance of " cell
currents " must hold good for vegetable as for animal cells. The
only question is whether we are here justified, as in the uni-
aud multicellular animal glands, in regarding the single cells as
individually electromotive, or whether this property is not rather
attached to them solely in connection with other dissimilar
elements, whether, i.e., we are dealing with electromotive cells
or cell -complexes. Munk notably tried to develop a theory
from the first standpoint — albeit in a very different sense from
electromotive activity of the isolated mucous cell. He held, as
was stated above, that the poles of each cell were positive to its
centre, and that after excitation the P.D. between the poles and
the negative equatorial zone either declined (as in the upper
layer of the parenchyma), or was augmented (cells of the lower
surface). Seeing, however, that the structure of these cells

30 ELECTRO-PHYSIOLOGY CHAI-.

does not give the smallest support to such a purely gratuitous
hypothesis, and that it fails, moreover, to account for the differences
of potential which Burdon- Sanderson has shown to exist regularly
between upper and under surface, we are thrown back on the
scarcely less arbitrary assumption of a constant (chemical)
difference, and resulting electrical P.D., between the upper and
lower halves of each parenchyma cell on the upper surface
of the leaf, comparable in some measure with the difference in
potential between free end and base of the mucous cells. But
it is obvious that neither structure nor arrangement of the single
cells agrees with even this presumption. Burdon - Sanderson's
view is undoubtedly the more probable, that the surface of a
single cell is individually, and under all conditions, isoelectric.
It is hardly necessary to add that no current can result from
the mere contiguity of two cell-bodies surrounded with cellulose
walls, and thus completely separated, when the one is altered
equally in all its parts with respect to the other ; any more than
a muscle-current appears when a fibre that is equally active at
all points is brought into contact with another fibre in the
resting state. But whenever the bodies of adjacent cells are
directly united by processes, and so form a physiological whole
(i.e. continuity of substance), any chemical differences arising
within the plasma of the cell-aggregate must produce current that
can be led off externally.

Many investigations in recent years concur to show that the
bodies of vegetable cells are frequently, and perhaps always, con-
nected directly through their cellulose sheaths by means of fine
processes, as also occurs in many animal tissues. If this may be
assumed of the cells in the Dioncca leaf (it has been directly
proved for the cells of the excitable cushion of Mimosa by
Gardiner and Haberlandt), and if the same continuity exists
between the excitable plasma of the upper and the non-excitable
plasma of the lower parenchyma cells, then all the electrical
manifestations so far described may be referred to differences of
potential between upper and lower cells, which are not merely
contiguous, but are in direct protoplasmic connection, and happen
to be in unlike and varying physiological states.

From this point of view it would not be without interest to
test the electromotive reactions of vegetable organs in other cases
where chemical differences between different layers of cells might

vi ELECTROMOTIVE ACTIOX IX VEGETABLE CELLS :',l

be expected, e.g. in the numerous examples of permanent differ-
ences in turgor (growing fruits, motor organs of bean, etc.).

The glandular parts of plants should also be suitable objects.
Biedermann found in various species of Drosera that on leading
off from the stalk on one side, and the surface of the leaf, which
is thickly set with little glands, on the other, there were con-
siderable differences of potential.

The intrinsic nature of the physiological changes of state
which underlie the galvanic effects of excitation in the excitable
leaf of Dioncca, or pulvinus of Mimosa, cannot with our present
knowledge be pronounced upon, any more than in the correspond-
ing electromotive activities of animal mucous cells. The wide-
reaching analogies in the two cases can hardly be overlooked,
as emphasised by Prof. Burdon-Sanderson, who has been good
enough to make especial communications on tin's subject. As
in the tongue of the frog, so in the leaf of Dioncca, we find a
" current of rest," of which the sign may alter with circumstances,
its internal relations with the galvanic excitatory effects being
invariable and unmistakable. In both cases, moreover, the effect
of excitation is a frequently diphasic variation, the sign of which
depends throughout on the state of the organ at the moment.
Burdon-Sanderson therefore holds it to be not improbable that
in the leaf of Dioncea, as in animal mucosne, the current led off
may be the result of two antagonistic chemical processes which
occur in the plasma of the cells, and are always simultaneously
present. These imply the development of an opposite potential,
while to one of them is due the permeability of the cell-wall
to water.

BIBLIOGRAPHY

1. H. BUFF. Anualen d. Chemie n. Pharmacie. LXXXIX. 1854. p. 76 if.

2. TH. JURGENSEN. Stud. d. physiolog. Inst. zu Breslau. Part I. 1861.

3 / L. HERMANN. Pfl. Arch. IV. p. 155. XXVII. 1882, p. 288, Note.
\J. MULLER-HETTLINGEN. Pfl. Arch. XXXI. 1881. p. 193.

4. A. J. IU-NKKL. Pfl. Arch. XXV. p. 342. Arb. d. bot. Inst. zu Wiirzburg,

II. p. 1.

5. OTTO HAAKE. Flora. 1892. p. 454 ff.

6. BURDON-SANDERSON-.

(a) Report of XLIII. Meeting of Brit. Assoc. Bradford 1873. London 1874.

Tr. of the Section, p. 133.

(b) Proceedings of Roy. Soc. XXI. No. 147. 1873. p. 495.

(c) Centralbl. f. med. Wiss. 1873. No. 53. p. 833.

32 ELECTRO-PHYSIOLOGY CHAP, vi

(d) Nature. X. Nos. 241 and 242. pp. 105 and 127. 1874.
/ Phil. Trans. 1882. CLXXIII. p. 8.
I Phil. Trans. 1888. CLXXIX.
J Biol. Centralbl. II. 1882-3. p. 481.
[Biol. Centralbl. IX. 1889-90. p. 1.

7. H. MUNK. Arch. f. An at. u. Physiol. 1876. p. 30 ff.

8. F. KURTZ. Arch. f. Anat. u. Physiol. 1876. p. 1 ft'.

9. DARWIN. Insectivorous Plants.

10. E. BRUCKE. Vorlesungen liber Physiologic.

11. HABERLANDT. Das reizleitende Gewebessj'stem der Sinnpflanzc. Leipzig, 1890.

12. DUTROCHET. Recherches anatom. et physiol. sur la structure intime des

animaux et des vegetaux. 1824.

13. MEYEN. Neues System d. Pflanzenphysiologie. 1839. III. p. 316.

14. SACHS. Experimental Physiologic d. Pflanzen. 1865. p. 482.

15. PFEFFER. Pringsheim's Jahrb. f. wiss. Botanik. IX. 1873. p. 308.

16. BATALIN. Flora. 1877.

CHAPTEE VII

STEUCTUEE AND ORGANISATION OF NERVE

IN nerve, as in muscle, function and all essentially physiological
properties are so bound up with the finer structure of the in-
dividual elements that it is desirable to give some account of
the latter. We need only consider the conductors, the nerve -
fibres, since all existing observations on electrical excitation
and electromotive action relate almost entirely to these. The
nervous system belongs exclusively to the animal organisa-
tion, and indeed to the more highly developed Metazoa only.
Plants, unicellular animals, and the lower Metazoa have no
nerves, and if in exceptional cases (as in the excitatory move-
ments of many plants) there are forms of activity which resemble
the vital manifestations of the animal organisation as effected by
nerves, it is easy to prove that the resemblance is merely
superficial.

In the animal organism, communication between distant organs
or groups of organs is generally effected in two ways : first, by the
circulation of the nutritive fluids ; second, by the nervous system.
The former may be said to act as the more sluggish transport ;
materials prepared or taken up in the organ are carried farther,
to be profitably assimilated, or excreted. In opposition to this
sluggish medium we have the marvellously rapid communication
between remotest parts, which is brought about by the nervous
system. The mode of action within the nerves has often been
compared to that of the telegraph system, and so long as we bear
in mind that what is transmitted in the nerve is not electricity,
the comparison is a very fair one. With regard to this last point
the most extravagant conceptions prevailed, long before the dis-
covery of the fundamental phenomena of electro-physiology, and

VOL. II I>

34 ELECTRO-PHYSIOLOGY CHAP.

the key to nervous activity was always looked for in electrical
manifestations. But as in muscle, so in nerve, these hopes were not
to be realised in their original sense, and although Albrecht (1) has
recently attempted to revive the old doctrine of the identity of
the " nervous principle " with current electricity, there can be no
serious discussion on these lines. In nerve, as in muscle, electro-
motive action must be viewed as the concomitant of chemical
processes, while — again as in muscle — its proper significance is
not yet adequately established. The nervous system invariably
consists of cellular elements (ganglion- or nerve-cells) and of
fibres, which must be reckoned as processes of the former, so
that the cell with its fibre forms an anatomical and physiological
unit (" Neuron" Waldeyer ; " Neurodendron," Kolliker). At
their first appearance, both phylogenetically and ontogenetically,
the nerve-fibres are pale fibrous structures, greater or less in
length, which always spring from special cell-bodies (ganglion-
cells), and either pass branched or unbranched into the peripheral
end-organs, or establish mutual communication between different
ganglion-cells. While in the lower forms of animals this condition
is permanent, it is only a temporary phase of development in the
higher species, since various sheaths are added later (in parts at
least) to the originally naked fibres, so that the structure of the
individual nerve-fibre may become very complicated. The fibres
may be classified into different groups according to the very
different properties of these sheaths or investments, the most
characteristic being those termed medullatcd and non-medidliitnl
fibres. The nervous system of vertebrates is composed almost
exclusively of the former, while the latter predominate among
invertebrates and the lowest vertebrata.

Hence we may conclude that the one essential constituent of a
nerve-fibre is, functionally speaking, the substance of the cdl process—
or " axis-cylinder" as it is termed from the sheath which usually
envelops it, and serves mainly as a protective covering. We
shall, therefore, understand by " nerve-fibre " the single axis-
cylinder, whether as the process of a central or peripheral
ganglion-cell, or as the branch of such a process ; irrespective of
its being per se naked, or enclosed in a sheath, or if the
same sheath encloses few or many axis-cylinders. The last case
occurs most frequently in invertebrates. The nerves of the pro-
boscis of many Nemertines, e.g., contain within a tolerably thick

VII

STRUCTURE AND ORGANISATION OF NERVE

35

nucleated sheath of connective tissue a whole bundle of the finest

axis-cylinders, each springing from one nerve-cell (2). On

hastily examining preparations stained intra vitam 'with methylene

blue, such a bundle of fibres might easily be taken for a single

nerve-fibre with one axis-cylinder and a thick sheath ; closer

inspection, however, shows the central filament to be composed of

excessively fine fibres, deeply

stained, and all doubt as to

their nature is removed by the

connection in every case with

a separate nerve-cell (Fig. 149).

The term " nerve-fibre " must,

therefore, only be applied to

the minute fibrils which branch

off from the central bundle of

the nerve-trunk to supply the

peripheral end-organs.

While in this case the rela-
tions of calibre between the

single fibres which constitute

FIG. 149. — Section of a nerve from the proboscis
of Amphiporus marmoratus with paired cells.
(Methylene-blue preparation from O. Burger.)

the bundle are tolerably uni-
form, we elsewhere find marked differences. In insects and crus-
tacea, e.g., broad band-shaped axis-cylinders frequently run alongside
very small and fibril-like filaments in the same sheath, and this
not merely in the coarser nerve-trunks, but in the finest terminal
branches also, where the calibre would justify us in reckoning them
individually as nerve-fibres. But it is in these muscular nerves
of Arthropoda with their copious ramifications (e.g. in the familiar
instance of the crayfish), that it is most easy to show that no
essential difference in structure exists between the coarser and finer
branches of the nerve, apart from the number of axis-cylinders
contained within one sheath of connective tissue. Neither the one
nor the other must be designated as nerve-fibres, but must be
treated simply as bundles. Notwithstanding therefore that,
even in the minutest ramifications, and actual terminal branches,
there may be several axis-cylinders in a common sheath, the
morphological definition of a nerve-fibre must be strictly con-
fined to one such axis-cylinder. It follows that the richly
developed connective-tissue sheath of the finest nerve-branches
in invertebrates must not be regarded as analogous to the

36

ELECTRO-PHYSIOLOGY

CHAP.

" sheath of Schwann," but is rather comparable with the con-
nective tissue (" endoperiueurium ") which, in vertebrates, unites
the axis-cylinders, along with their special sheaths, into primitive
bundles of fibres, or nerve-trunks. Only that fine, homogeneous,
nucleated sheath which partially invests the peripheral axis-
cylinders (medullated and non-medullated) of vertebrates and
some invertebrates is to be termed the sheath of Schwann.

In the muscular nerve of crayfish, the neural sheath, both in
the larger trunks and in parts where the axis-cylinders run singly,
exhibits, even in the fresh state, and still more after treatment
with the gold method, an obvious stratification, resembling in
places the highly developed and richly nucleated connective-
tissue sheath on the capsule of the Pacinian corpuscle (Fig. 150).
A similar concentric layering appears in the neural sheath of several
Orthoptera (locusts). In other cases, on the contrary (e.g. many

FIG. 150. — Isolated muscular nerve from the abductor muscle of crayfish. (Gold and formic acid.)

insects), the substance in which the axis-cylinder is embedded is
finely granulated, like protoplasm (3).

These relations between the nerve-fibres (axis-cylinders) of
invertebrates and their sheaths only appear fully on staining the
former by proper methods. The gold method, which was so much
employed, after Cohnheim, has been superseded by the methylene-
blue method of Ehrlich, more particularly for invertebrate animals.
Biedermann has failed to determine a special and individual sheath
within the common integument of the finer axis-cylinders of in-
vertebrate nerves, unless the compacter layers of connective tissue
immediately surrounding each axis-cylinder in the muscular nerve-
trunk of the crayfish be recognised as such. As a rule, invertebrate
nerves present a naked axis-cylinder within a common sheath, or
substratum of connective tissue, which is histologically distinct
from the specific sheaths of the nerve-fibres of higher animals,
even when it invests a single axis-cylinder. In vertebrates, similar

VII

STRUCTURE AXI) ORGANISATION OF XERYK

37

true sheath of
appears in the

r

but coarser sheaths of connective tissue surrounding a single axis-
cylinder appear exceptionally.

Thus the nerve - fibres of the electrical organ of Torpedo
exhibit a tolerably thick sheath, and an extreme development of
the same, consisting of many concentric layers closely packed
together, is also characteristic of the two giant nerve-fibres which
supply the electrical organ of Malapterurus. These nerves are as
thick as a sewing-needle, and yet contain only a single medullated
primitive fibre.

The sheath of Schwann and the medullary sheath are the
only " specific " sheaths of nerve-fibres. As we have stated, a

Schwann rarely /// /•'

in the nerve - fibres of
invertebrates, and then only in
cases where there is a compara- ! ,|
tively broad axis - cylinder. In
nearly all crayfish nerves, if not
excessively fine, there are, along
with a number of very delicate
axis-cylinders which never exhibit
a special sheath, others of much
greater diameter ; these, on treat-
ment with methylene blue, for the
most part become paler in colour,
and exhibit, in Remak's words, a
visible " tubular " structure, i.e. a
delicate, apparently structureless,
nucleated sheath with its content,
the axis -cylinder proper, to the
finer structure of which we shall
return later.

These structural relations of
invertebrate nerves have much in
common with the fine nerve-trunks found in the sympathetic
system of vertebrates, which contain a bundle of non-medullated
fibres (axis -cylinders) — the gray fibres of Eeniak — within a
strong sheath of connective tissue (epineural sheath), Fig. 151.
Each of these fibres appears when isolated as a transparent flattish
band — homogeneous, or with delicate longitudinal striations, in the
fresh state, with here and there a long oval nucleus. M. Schultze

FIG. 151. — A peripheral bundle of the human
sympathetic nerve, fixed with osmicacid.
T\vn medullated fibres (wF)lie in a bundle
of Remak's fibres. Epineural sheath be-
yond. (Schiefferdecker.)

38 ELECTRO-PHYSIOLOGY CHAP.

described Eemak's fibres as axis -cylinders with a sheath of
Schwann, and they have since been very variously interpreted.
It was even questioned whether they were nerves at all, but
later on Schultze's opinion was very generally adopted. Eemak
observed that the fibres, which he described as naked, " and
nearly always longitudinally striated on the surface," were readily
decomposed into the " finest threads," and in fact nothing could
be easier than to demonstrate this in suitable preparations, e.g.
the splenic nerves of ruminants. Kolliker and Schiefferdecker
(4), on the other hand, regarded each Eemak's fibre as " a bundle
of fine axis-cylinders, surrounded by a more or less complete sheath
of Schwann." The question again can only be determined by
reference to the origin of the fibres involved. If it can be shown
that a " Eemak's fibre " originates as a simple fibre, and that its
individual " elementary fibrils " are not independent cell processes,
there can then be no doubt that it represents a single axis-
cylinder (nerve-fibre), and not a bundle of such fibres. It has
long been known that broad prolongations spring from the sym-
pathetic ganglion-cells, which are invested with a complete sheath
of Schwann ; and these, in their turn clothed with a process
of the cell sheath, correspond throughout with Eemak's fibres.
These last, in continuing their course (notwithstanding the in-
equalities of the cellular sheath as first remarked by Eanvier),
make good their existence as special structural elements, which
are easily isolated — like the medullated nerve-fibres ; while the
elementary fibrils (" Eemak's fibrils," Kolliker) cling together much
more closely, and can only be isolated in places. It is, however,
easy to demonstrate their existence, both in teased preparations,
and at the cross-sections of large nerve-trunks containing Eemak's
fibres (splenic nerves of the ox).

The elements of the olfactory nerve are similar in structure
t<> Eemak's fibres. As shown by M. Schultze, the peripheral
expansion of this nerve consists in all vertebrates of non-medullated
dements, which, e.g. in the pike, are clearly defined, and sur-
rounded by a tolerably thick structureless sheath, regarded by
Schultze as the sheath of Schwann. The single fibres, some
10-40 p, in diameter, are round, or polygonal from pressure in
cross-section. The content of the sheath exhibits a somewhat
faint longitudinal striation even in the fresh state. After pro-
longed maceration in 0'04 chromic acid, or 0-4-0'6

*f^ v w iiivvvy w.*. i« w A \st-t. * ± M. v v -i- /__

vii STRUCTURE AND ORGANISATION OF NERVE 39

solution of potassium chromate, Schultze succeeded in isolating
two kinds of elements from the nerve-fibres, i.e. countless minute
fibrils, and a finely-granulated mass, " of which it is hard to say
whether it forms part of the little fibres or lies between them."
This is the characteristic structure of the olfactory fibres ; and
here we have the first mention of a fibrillated structure of nerve-
fibre, which became the starting-point for the further investigations
by which Schultze established the doctrine of fibrillated structure
for all nerve-fibres. Eegarding the axis-cylinder of medullated
nerves as a bundle of the finest fibrils with granulated iuterfibrillar
substance, he compared it with the fibrous elements of the olfac-
tory nerves, and defined the latter as " axis-cylinders with a sheath
of Schwann."

Babuchin objected to Schultze's theory, and declined to recog-
nise the sheathed " nerve-fibres " which Schultze isolated from the
olfactorius as comparable with the fibres of Eemak. Even if the
comparison is legitimate in many animals, it may be shown in other
cases that the supposed sheath of Schwann corresponds better
morphologically with the perineurium of the nerve-trunks. Fine
transverse sections of the olfactorius (of pike) show that secondary
septa run out from the external sheath of the large nerve " fibres "
(in Schultze's sense), and divide the fibre into two or more com-
partments. In the higher vertebrates, on the contrary, there is
no such marking out of single " fibres " by special sheaths. Boveri,
at any rate, has failed to find nucleated membranes, either by
isolation or in cross-section. "An arrangement of larger or
smaller irregular groups is indeed easily identified at the trans-
verse section, but they are not separated by sharp double lines,
as would be the case with membranes investing distinct parti-
tions. The dividing line is single, often obscure, and dotted in
appearance, in no way comparable with the secondary sheaths of
the pike's fibres." Boveri, therefore, assumes correctly that these
partition walls are " a superficial expansion of connective tissue,
such as are also found between the fibres of the white matter of
the spinal cord." This is borne out by the position of the nuclei.
" It is clear from the ' fibres ' of vertebrates higher than fishes that
the nuclei lie not only between but also inside them."

The spaces within these septa are seen in cross-section to be
filled with a gray reticulum (the interfibrillar substance of Schultze),
in the meshes of which dotted sections of minute fibrils appear,

40 ELECTRO-PHYSIOLOGY CHAP.

with a proper stain, as in the transverse sections of Kemak's
fibres. But while, from their origin, each of the latter must be
regarded as a single axis-cylinder, we are from the same reason
compelled to accept each of the fine elementary fibres, or fibrils,
within the common sheath of the olfactorius as being in itself
a nerve -fibre or axis -cylinder. The peculiar relations of the
olfactory fibres to certain spherical structures of the olfactory bulb
have long been known, but it is only with the help of recent
methods of staining that an explanation of them has become
possible.

It is now known that two processes run out from the spindle-
shaped body of each " olfactory cell " —one short and directed
towards the mucous surface, interpolated between the remaining
epithelial cells ; the other, long, fine, and filiform, extending as an
olfactory fibre towards the bulb, to end there in a " glomerulus."
A number of these extremely fine nerve-fibres are gathered up
into coarser bundles (olfactory bundles), which, after a shorter or
longer course, pass out of the olfactory mucosa into the olfactory
bulb, through the cribriform plate of the ethmoid, and enter the
layer of glomeruli. The individual fibres, which are undivided
and often varicose, remain of the same breadth throughout their
passage from olfactory cell to glomerulus. The fibres begin to
branch shortly before entering the glomerulus ; they divide
dichotomously several times, and traverse the glomerulus by
a somewhat complicated path, until they end freely (5). Often,
as described by Eamon y Cajal, Van Gehuchten, and Martin, as
well as by Kolliker, " not merely one, but two, three, or several
fibres, enter one glomerulus. They all pursue the same course,
branching freely (dichotomously) in the glomerulus, and inter-
lacing without anastomosis." These terminal ramifications of
the olfactory fibres in the glomerulus therefore represent the
central endings of the fibres, and in spite of their fine structure
they cannot be regarded otherwise than as independent nerve-
fibres (axis-cylinders). Each olfactory fibre, or more correctly
fibril, thus corresponds with the centripetal process of an " olfactory
cell " in the epithelium of the olfactory mucous membrane. The
branches of these fibres in the glomerulus interlace, without
anastomosing, with other fibres that arise from bifurcation of the
processes from the ganglion-cells (prolongations of the so-called
"mitral cells").

VII

STRUCTURE AND ORGANISATION OF NERVE

41

S—

If these excessively fine elements of the olfactory nerve, which
resemble the "fibrils" of Eemak's fibres in structure and appear-
ance, are thus independent and non-medullated fibres, they represent
in some degree the lowest and least developed form of nervous tissue.
Eemak's fibres are higher in the scale, since they present bundles
of fibrils, which possess (even if incompletely) a sheath of Schwann :
while the most developed non-medullated fibres again appear
as an axis -cylinder completely surrounded with AX

a sheath of Schwann, as, typically, in the peri-
pheral nerves of the lower, and even, at a certain
developmental stage, of the higher vertebrates
(Petromyzon, Amphioxus, Cydostoma). The axis-
cylinder, to the finer structure of which we shall
return later, is here immediately surrounded on
all sides by the sheath of Schwann. This is tubular
and transparent, and betrays its cellular formation
only in the presence of long nuclei upon the inner
surface ; the upper surface is often invested with a
delicate membrane of fibrillated connective tissue
(" Henle's sheath "), which may be regarded as part
of the connective tissue (perineurium) that binds a
number of fibres into a nerve-trunk (Fig. 152).

All nerves consisting of these kinds of elements
differ essentially, even to the unaided eye, from
those composed exclusively, or in great part, of
medullated fibres, the complicated structure of
which will be described below. Non-medullated
nerves, in consequence of the transparency of the
single fibres and their investment, are always clear,
and grayish in colour, and often, especially in
invertebrates, of an almost gelatinous consistency.
Medullated nerves, on the other hand, are much
more compact and resistant, and are characterised

. . „, . .

by their ivory whiteness and opaqueness. This is

due to the optical properties of the medullary

sheath, the finer structure of which has long occupied the

attention of histologists.

If a medullated nerve-fibre is examined in the living tissue,
or immediately after isolation in an indifferent fluid, it appears
as a highly refractive, transparent, and perfectly homogeneous

in. 152. — Fibre
from
nerve
myzon
treated with
Mull e r's fl u i d.

42

ELECTRO-PHYSIOLOGY

CHAP.

thread, with a simple contour, which is constricted here
and there at irregular intervals, known after their dis-
coverer as nodes of Ranvier (" dtranglements annulaires ") (Figs.
152, 153). The length of segment between the nodes is con-
siderably greater in the inferior vertebrates (fish, amphibia)
than in the higher, so that in the former there are fewer
nodes in the same tract ; corresponding per-
haps with varying consumption of materials,
if, as Ranvier believes, the nodes are to be
regarded as points of entrance for the nutritive
fluids. It may also be remarked that the
electrical nerves of Torpedo, as well as embryonic
nerves, have invariably shorter and more numer-
ous segments than fully-developed fibres. Ran-
vier's nodes, again, are found at all dividing
points of peripheral medullated nerve - fibres,
while in the central elements their existence
is doubtful. Near the constrictions, in fresh,
peripheral, medullated fibres, are the long nuclei
of the sheath of Schwann, which lie at the side
of the fibres, and seem to be embedded in the
medullary sheath. The fact that (in higher
vertebrates) one nucleus is placed centrally be-
tween each pair of nodes has, along with other
facts (infra), given rise to the view that eacli
nerve - fibre is due to the fusion of several
cells, a theory which can hardly be maintained
in the face of embryological researches. In the
FIG. las. — Nerve - ceii lower vertebrates (fishes) there are several nuclei
"r£enSSIE (5-18, according to Key and Retzius) in each
ganglion of rabbit, segment. In their finer structure the nuclei of
Schwann correspond essentially with other cell-
nuclei. While the sheath of Schwaun forms a complete tube,
investing the fibre closely on all sides, and surrounding the axis-
cylinder even at the nodes of Ranvier, where the medullary sheath
is interrupted (infra), the latter exhibits segmentation apart from
the constrictions of Ranvier. After death, the double contour of
the medullary sheath is interrupted by oblique lines on either side
of the nodes of Ranvier, which give the appearance of longer or
shorter segments of medulla, fitting together with funnel-shaped

vii STRUCTURE AND ORGANISATION OF NERVE 43

ends : the internal relations of these were specially investigated
by Schiefferdecker. These secondary breaks in the continuity of
the medullary sheath are known, after their discoverer, Lantermann,
as " Lantermann' s indentations" (Fig. 157). On treating fresh
medullated nerve-fibres with silver nitrate, characteristic black
crosses appear at the constrictions ; the solution of silver enters
most rapidly at this point, and not only colours the ground-
substance of the constriction (Schiefferdecker's Zwischenschcibe—
intermediary discs), but also penetrates a certain distance along the
axis-cylinder, spreading on either side between the latter and the
medullary sheath (" periaxial clefts") (Fig. 159). The long arms
of the cross are often discontinuous, and appear as a more or less
prolonged series of transverse stria?, the so-called " silver lines of
Frommann," the origin of which has not yet been adequately
determined.

During the death of the fibre many striking phenomena make
their appearance. We have said that the medullary sheath in
living nerve-fibre is smooth and homogeneous : in moribund nerve
it alters conspicuously. Even with the most favourable conditions,
in fluids that are as far as possible indifferent, the excessive
instability of the substance of the medullary sheath causes rapid
alterations, which are generally described as coagulation-phenomena,
or formation of " myelin figures." These are chiefly characterised
by a kind of folding and wrinkling of the medullary sheath, so
that the lateral border of the fibres, which was at first rectilinear,
becomes much undulated, while 'irregular lumps and knotty lines
and networks appear 011 the surface, and soon conceal the notches,
although the constrictions still remain visible.

These changes are intimately associated with the chemical
constitution of the medullary sheath, lecithin and cholesterin
being among its chief constituents. It is owing to the former
that the medulla of the nerve, when treated with osmic acid,
stains a more or less deep black, so that even the finest medullary
sheaths can be detected by this reaction. Water, dilute acids,
and solutions of salts cause a swelling of the medulla, which occurs
most rapidly and distinctly in the central nerve-fibres, where the
sheath of Schwann is wanting. Here, as also in the peripheral
medullated fibres, there is often a characteristic blistering of the
medullary sheath, beginning at the free end of the medullary
segment, and extending right along it.

44

ELECTRO-PHYSIOLOGY

CHAP.

w

8-

ufl"l

1

This swelling of the medullary sheath is naturally most
obvious at points where, e.g. at a cross section, the myelin
is in immediate contact with the entering fluid. Here, along
with the formation of characteristic " myelin figures," there
is often a regular outflow of medulla from the sheath, which
may extend far beyond the cross - section.
Very singular figures are produced by treating
medullated nerve - fibres with hot alcohol and
ether, when a great part of the medullary sub-
stance goes into solution, leaving a delicate
network of a highly refractile substance, which
gives a chemical reaction analogous with that of
keratin, and therefore termed nenrokeratin by
Kiihne and Ewald (Fig. 154). It is not known
whether these reticulate " horny sheaths " are pre-
formed as such within the normal medullary
sheath. All changes produced in the aspect of
medullated nerve-fibres by different reagents must
be accepted with great caution as to structural
conclusions, owing to the extreme instability of
the medullary sheath.

We said that all medullated fibres of ver-
FIG. 154.— Nerve-fibre tebrates are at first destitute of a medullary
aLho? b°in'lthe sheath, which only appears at a given stage of
centre is the twisted development. How this occurs, and how the iierve-

axis -cylinder; , ,. ,. -.

between this and fibres themselves are developed, is a disputed
the sheath of matter. It is certain that nerve-fibres arise

Schwann the net- .

work of neuro- under all circumstances from special cells (nerve-

keratin. (KOlliker.) e rearded

PT

tjlejr prolongations J

this K< >lliker and His have established for the roots of the spinal
nerves also. Both anterior and posterior roots at first appear
as bundles of naked axis -cylinders, springing in the former
from the motor cells of the anterior horn, while in the pos-
terior roots some of the fibres run inwards from the cells of the
spinal ganglia to the cord, and some outwards to the periphery.
Later on, the cells which arise from the mesoblast form first a
sheath which invests the entire bundle of unmedullated fibres,
and subsequently a special sheath to each fibre (sheath of Schwann).
This secondary origin of the sheath of Schwann appears still
more plainly in the developing nerves of the tadpole's tail

vii STRUCTURE AND ORGANISATION OF NERVE 45

(Kolliker, Eouget, Heusen). Henseu found that these nerves at
first consisted of fine shining forked threads without nuclei ; later
on single nuclei appeared, at first near the body-axis, and subse-
quently in the terminal ramifications also. These cells undoubtedly
belong to the connective substance, from the fusion of which
arises the sheath of Schwanu. Neither medullary sheath nor
sheath of Schwann appears to develop continuously at all points
along a nerve-fibre.

It is known that in the central nervous system (brain and
cord) the fibres of the pyramidal tract become gradually invested
with medullary sheaths, in the direction from parent cells to
spinal cord, and the same is stated by Kolliker of peripheral
nerves, where the development of medulla is directed from trunk
to periphery. Kolliker disputes the assumption of Hensen that
the medulla originates in the form of single drops, since he
observed on the tadpole "that it appeared ab initio as a coherent

FIG. 155.— Two medullated nerve-fibres of Palaemon squilla. (Retzius.)

tube, which gradually acquired the dark contour, the transition
from pale to dark- walled fibres being thus imperceptible."
This seems to occur first near the nuclei of Schwann, so that
medullary segments are formed, separated by longer non-niedullated
tracts corresponding with the constrictions of Eauvier.

The presence of true medullary sheaths in certain nerves of
invertebrates has frequently been asserted, but is under all
circumstances a rare occurrence. Without entering into the older
researches, we may quote the investigations of Eetzius on Palaemon
squilla, and of Friedlunder in Annelids (Mastobranchus, Lumbricus),
as proving the existence of medullated nerve-fibres in invertebrates.

The nerve-fibres of Palaemon present the most exact structural
conformity with the medullated nerves of vertebrates. In these.
Eetzius was able by the silver method, and also by methylene
blue, to show characteristic figures corresponding with Eanvier's
crosses, as well as Frommann's lines, corresponding with the
constrictions, and appearing at definite and regularly recurring
intervals (Fig. 155). Between the nodes there is a long oval

46 ELECTRO-PHYSIOLOGY <-HAP.

nucleus, which obviously corresponds with Schwann's nuclei in
medullated vertebrate nerves, although Ketzius disputes the
existence of the sheath of Schwann, not merely in the splanchnic
cord, but also in peripheral nerves. The myelin sheath runs
uninterruptedly from one constriction to the next, exhibits double
contours, and a shining, fatty appearance ; after treatment with
osmic acid the sheath becomes first gray, then black, exactly
like the medullary sheath of vertebrate nerve-fibres (6).

THE AXIS-CYLINDER

The finer structure of this, the functionally most important
part of the nerve-fibre, is again much disputed. Apart from
the undoubted difficulties of investigation, there is no doubt
that the most appropriate objects have not in many cases been
selected for experiment. On the one hand large elements are
required, on the other absence of thick sheaths which may
obscure the field of the microscope. It is a priori obvious
that medullated fibres must be less favourable objects than the
non-medullated fibres of vertebrates and invertebrates. And,
in fact, that theory of the structure of the axis-cylinder which
is most widely current, and appears morphologically and physio-
logically the best - grounded, is fundamentally derived from
observations on the nerve - fibres of invertebrate, and non-
medullated fibres of vertebrate animals. As early as 1843 Eemak
noted a bundle of fine fibrils in certain giant nerve-fibres of the
ventral cord of the crayfish, in place of the axis-cylinder, and
M. Schultze subsequently embraced the view of a uniform
fibrillated structure of the axis-cylinder in all nerve-fibres. He
pointed out that (more especially in the thick medullated fibres
from the lateral columns of the spinal cord, " in which, since
there is no sheath of Schwann, the axis-cylinder can be readily
isolated, either in the fresh state, or still better after maceration
in iodised serum ") a parallel striation and a finely-granulated
substance between the stria: may be distinguished with a high
power, which can only indicate " a composition of fibrils and
interfibrillar substance." Even within the medullary sheath,
Schultze was able to detect the same structure of axis-cylinder
in the thick fibres from the brain of the torpedo. Very significant
again for the fibrillated structure of the axis-cylinder are the

vii STRUCTURE AND ORGANISATION OF NERVE 47

various observations on its origin from the corresponding cells,
made by M. Schultze on the large nerve-cells of the spinal cord
and brain in vertebrates, and by Hans Schulze with even greater
success on invertebrates. In both cases the bodies of the
ganglion -cells also showed a more or less definite fibrillated
structure, which was most obvious in the cortex. This was the
more easy to recognise since adjacent fibrils were separated by
comparatively thick layers of plasmatic ground-substance. The
complicated course of the single small fibres within the cell
appeared, according to M. Schultze, with special clearness in
certain conspicuous multipolar ganglion-cells in the brain of the
torpedo, where it is easy to recognise that the fibrils partly
radiate in different directions from each process into the body
of the cell, and partly describe concentric circles round the
central nucleus. Any doubt as to the pre- existence of a
fibrillated structure of the axis-cylinder was finally removed by
the investigation of the broad non-medullated nerve-fibres of
Petromyzon, which are even better adapted than certain fibres
of invertebrates (e.g. crayfish) to demonstrate these structural
relations in the living preparation (Schiefferdecker, 7). Within
the sheath of Schwann two substances may usually be recognised :
(a) a bundle of the finest fibres situated in the axis (nerve-fibrils,
axis-fibrils), which often exhibit an undulating course, and are
closely invested with (&) a homogeneous substance, which no
doubt penetrates into the interior of the " axial filament," as
Schiefferdecker named the bundle of fibrils — and there separates
the single fibrils, some 0'4 ^ thick (Fig. 152). There is .between
the latter and the homogeneous ground - substance (Kolliker's
neuroplasm, " axoplasma ") a similar relation to that in smooth
and striated muscle-fibres between contractile fibrils and sarco-
plasm. The layer of axoplasm is best developed in the thickest
nerve-fibres, and forms a smaller constituent of the entire axis-
cylinder in proportion as the fibres are more slender. This is
plainly seen in transverse sections of hardened nerve-fibres (Fig.
156). The central bundle of fibrils seems to be almost equally
developed in large and in small fibres, while the extent of the
axoplasma varies considerably. " With decreasing diameter of
axis-cylinder, the mass of axoplasm diminishes more rapidly in
Petromyzon than the number of fibrils. Since these last are
probably the true conducting substance, it is impossible in

48 ELECTRO-PHYSIOLOGY CHAP.

Petromyzon to draw any direct conclusion at first hand from the

diameter of the axis-cylinder as to bulk of conducting substance.

The distance between two fibrils is always greater than the

diameter of the fibrils ; which are there-
fore separated by a comparatively large
mass of axoplasm. The fibrils of Petro-
myzon are excessively unstable, and are
visible only during life ; as soon as they
begin to die they break up, even when

FIG. 156.— T.S. of axis-cylinders examined in the serum of the same

from trigeminal nerve of . , . „ , . , P , .,

fluvtatiiis. animal, into fine granules of high retractile

power, which at first lie in rows, corres-
ponding with the fibrils of which they are the disintegration product.
With advancing dissolution the axial bundle flows away in a viscid
mass, along with the firmer substance of the axoplasma." The
fibrils appear less capable of resistance than the axoplasm.
" Shortly after death nothing remains of the fibrils ; in their place
there is a knotty string, which has often been figured." (Schieffer-
decker's words, thus quoted, are confirmed by the observations of
Biedermann.)

It is far more difficult to discover the structure of the axis-
cylinder in the nerve-fibres of the higher vertebrates, which are
surrounded with a thick medullary sheath ; and this no doubt
accounts for the current divergences of opinion. We should
a priori assume that the structural relations of the axis-cylinder
would coincide in all essential points throughout the animal
kingdom. When the existence of a fibrillated structure has been
determined in one case, it may almost be postulated that fibrils
are everywhere the proper constituents of the cylinder-axis. And
this presumption of Eemak and Max Schultze has in fact been
confirmed by the remarks of Engelmann, Kupffer, Maley, Boveri,
Kolliker, Jacobi, Joseph, and others — neither v. Fleischl's theory,
that the axis-cylinder is a column of fluid, nor that of Kuhnt,
that the axial space is filled with " a soft, somewhat elastic,
homogeneous mass, finely or coarsely granulated," and that the
fibrillar longitudinal strife are folds of the supposed " axis-
cylinder sheath," having any foundation.

As in the non-medullated fibres of Petromyzon and certain
invertebrates (crayfish), so in medullated fibres, the axis-cylinder
is composed of a soft ground-substance rich in water, and of

TII STRUCTURE AND ORGANISATION OF NERVE 49

apparently gelatinous consistency (the " axoplasma "), and the
fibrils embedded in the same. But while in the above examples
the fibrils constitute a central bundle, more or less thickly
invested with axoplasma, in medullated fibres they are distributed
equally over the entire section of the axis-cylinder, so that the
investing layer fails to appear, and forms an insignificant marginal
zone. With appropriate reagents (acid fuchsin, bismarck brown,
etc.) the fibrils are distinct upon the longitudinal aspect of the
fibres as well as at the cross-section. It then appears that the
fibrils lie closer together and are united by less cement-substance
at the constrictions, so that the axis-cylinder is most slender at
these points (Fig. 157). Engelmann (8) argues in favour of a pre-

FIG. 157. — L. and T.S. of medullatecl nerve-fibre from frog's sciatic nerve (osmic acid, acid fuchsin).
Nodes of Rauvier and two Lantermann's notches, fibrillar structure of axis-cylinder.

formed discontinuity of fibrils at the nodes, chiefly on the ground
that the axis-cylinder under certain conditions exhibits a break
in continuity at the point of constriction, " corresponding with
the black cross-lines of the silver reaction " (Engelmann's Quer-
schcibe). Engelmann's reasoning was subsequently rejected, and
cannot therefore be cited in support of the view that the medul-
lated nerve-fibre consists of single juxtaposed cells (cf. Jacobi,
Boveri) — an assumption that is disproved by recent embryo-
logical observations. It may be remarked that Ehrlich's
" intravital " methylene-blue method has never (in Biedermann's
experience) brought out distinct traces of fibrillar structure in the
axis-cylinder of fresh preparations, either in medullated or in
non-medullated fibres ; on the other hand, certain splanchnic
fibres of Hirudo medicinalis stained by this method show, after
treatment with picrate of ammonia, an unmistakable construction
from single fibrils. It is still uncertain whether the axis-cylinder
as a whole (fibrils + neuroplasm) may not, in addition to its

VOL. II E

•

50 ELECTRO-PHYSIOLOGY CHAP.

other investments (sheath of Schwann, medullary sheath), also
possess a special delicate sheath (" axis-cylinder sheath "). In
isolated cases this certainly appears to exist, always, however,
as an excessively fine layer, hardly to be counted as a membrane
proper.

The extreme instability of the substances of which the axis-
cylinder consists, leads, when it is treated with reagents, to the
appearance of many morphological changes which, without due
precautions, might easily lead to fallacies. Such is the marked
wrinkling induced even by physiological salt solution, and still
more by all strongly dehydrating methods of hardening, such as
alcohol, chromic acid and its salts, etc.

For the same reason, stained sections of nerves, hardened in
chromic acid solutions, or salts, usually fail to give a correct
picture of the ratio between size of axis-cylinder and medulla,
since the axis-cylinder shrinks up within the swollen medullary
sheath, and forms in cross-section the well-known " sun-figures."

The osmic acid method gives better, though still not un-
exceptionable, results. The ratio between axial space and
medulla was , estimated by M. Joseph in the electrical nerves of
Torpedo as 1 : 3—5. Within this great axial space the combined
osmic acid and alcohol method gives, both in longitudinal and in
transverse sections, a very delicate network (" axial reticulum " of
Joseph), which Joseph assumed to be preformed, and the meshes
of which should contain the axial fibrils, that do not appear in
preparations treated by this method. Joseph further asserted
that the " axial reticulum " is in direct connection with the
neurokeratin network of the medullary sheath; but this, as Kolliker
justly remarks, is rather evidence against preformation, since the
existence of the latter as a preformed constituent of the medullary
sheath is at least doubtful. The figures described by Joseph in
many respects resemble the structural relations predicated by
Btitschli of the axis-cylinder in its widest sense. The fibrillated
structure here — as in muscle — consists of a longitudinal series of
rods, the thicker lateral walls of which are united by very fine
cross-bridges. With a medium power this gives the appearance
of parallel longitudinal striation. It is uncertain whether this
rod-structure of Blitschli is really preformed, or is merely the
effect of reagents. In tissues of such excessive lability the last
hypothesis is always possible. Moreover, there are certain

vii STRUCTURE AND ORGANISATION OF NERVE 51

physiological indications in favour of isolated and separately
conducting fibrils (which would be out of place in this chapter),
rather than a conducting network.

The presence of varicose swellings along the single fibrils, or
finer bundles of fibrils (slender axis-cylinders), must also under all
circumstances be regarded as the effect of reagents. These
swellings appear freely, and in fact uniformly, both with the
gold method and with methylene blue, and are from the last fact
regarded by many authors as pre-existent. And the regular
appearance of varicosities in the end-plates of both motor and
sensory nerves in still living organs (muscles able to twritch, etc.)
is apparently in favour of this assumption. Nevertheless, Bieder-
mann, along with many others, is of -the opinion that varicosities,
under any conditions whatever, are abnormal manifestations, due
to commencing coagulation, or rigor — the first visible sign of
dissolution.

One important fact that has hitherto been overlooked is the
marked variation in calibre that occurs in both medullated and
non-medullated, central and peripheral, nerve -fibres. This is,
perhaps, most conspicuous in a large nerve-trunk stained with
methylene blue, or in the ventral cord of Crustacea and insects,
but the difference is also striking in the medullated nerves of
vertebrates. If, as we might expect, this is related with functional
dissimilarity, the mere anatomical differences (apart from physio-
logical reasons to be considered below) would be decidedly
against the homogeneity of all nerve-fibres so often insisted on,
according to which the differences of excitatory effect must
be referred solely to differences in the terminal organs. As
regards further histological details, it may be stated that large
ganglion -cells usually give rise to thicker nerve-fibres than the
small cells, and that all peripheral fibres become finer in pro-
portion as they approach their (peripheral) end ; this is seen
more especially at all bifurcating-points of motor and still more
of electrical nerves. Within the central system the contrary
often occurs, and the nerve-fibre enlarges in diameter from the
parent cell outwards.

CHAPTEE VIII

CONDUCTIVITY AND EXCITABILITY OF NERVE

I. PHENOMENA IN NERVE-FIBRES

CONDUCTIVITY is the chief and indeed exclusive function of the
nerve-fibre, and the principal facts relating to it have next to be
considered. There is absolutely no fundamental difference in
the conducting of an excitatory process within any kind of
excitable conductive protoplasm, e.g. muscle and nerve. In both
cases normal continuity of structure seems to be an indispensable
condition of conductivity, the excitation, at least in nerve-fibres,
being directly transmitted from point to point. Eecent conclu-
sions as to the finer anatomy of the central system, on the
other hand, render it highly probable that there is here an
exception to the rule, inasmuch as the transmission of excitation,
more especially from ganglion-cells to nerve-fibres, and vice versa,
is effected not by continuity but by contact — contiguity — only.

It has already been pointed out in muscle that excitation
under certain normal conditions remains localised to the directly
excited fibre, and does not cross over into adjacent fibres. The
same is true of nerve, whether medullated or non-medullated.
Kiihne (9) succeeded in exciting single fibres of the frog's sciatic
by the unipolar method, upon which only the correlated muscle-
fibres contract. The isolation and independence of the single; fibres
is confirmed by the effect of partially dividing a nerve-trunk ;
only a certain part of the tract supplied by the nerve will then
be paralysed. When a nerve-fibre bifurcates, the excitation of
the trunk is of course transmitted to all its branches. The
ramifications are most abundantly developed within the central
organs, but occur also in the peripheral terminations (muscles,
electrical organs, etc.), and even, though more rarely, along

CHAP, vin CONDUCTIVITY AXD EXCITABILITY OF NERVE

53

the nerve-trunk. As an instance of the first we need only recall
the wealth of ramifications of the single processes of monopolar

~" V r

m ! i -—

r- . •vO.iiU'-'.r >'/ '•^-' • •.•*'•.• vPv'o^x-.v-1-^ - .-iv- , >• ,'

-.

Pu-^i

i tp£*

FIG. 15S. — Ganglion-cell with richly-developed
nerve processes from ventral cord of cray-
fish. (Methyl blue and picric acid.)
(Biedermann.)

ganglion-cells in the ventral cord of crustaceans and worms (Fig.
158), as well as the " collaterals " from the vertebrate spinal cord.
Here the branching obviously forms connection between various

54 ELECTRO-PHYSIOLOGY CHAP.

more or less remote parts of the central nervous system. The
ramification of (peripheral) nerve-fibres is, however, most striking
in the electrical organs of certain fish (vide Electrical Fishes},
which must in the majority of cases be regarded as transformed
muscles. Thus in Malapterurus the whole of the paired organ,
consisting of thousands of separate plates, is supplied by a single
nerve - fibre, which must accordingly bifurcate an immense
number of times in order to subserve each electrical plate, and
the same is found in other electrical fishes. These are the
cases which throw most light on the functional significance of
the bifurcation of peripheral nerve-fibres. It is obvious that this
must occur most freely in cases where no isolated activity of
the end-organ is required, but where, on the contrary, the indi-
vidual elements are affected as far as possible simultaneously,
and for the same purpose. This also applies to muscles which
subserve movements of a low degree of complexity, e.g. the
rigidly-imprisoned muscles of Crustacea and insects, where the
nerves display a wealth of ramifications (Fig. 150).

The same relations exist, according to Stannius, in most
motor nerves of fish, and in those to certain muscles of Amphibia
(Fig. 159), where they are again explained by the low grade of
co-ordinated movement in these animals. The higher the latter,
the more a muscle is appointed, bundle by bundle, to engage in
co-ordinated movements — the more local will be the distribution,
and the less numerous must be the ramifications, of its motor
nerve-fibres (Fig. 159).

As regards the mode of division in the non-medullated fibres
of invertebrates, there is a great diversity, both in the central
organs and in the periphery. Every kind of transition exists,
from simple dichotomous branching to the richest arborisation.
As two main types we may take the ramifications of the axis-
cylinder processes from the central ganglion-cells in the ventral
cord of worms and Crustacea, and the muscular nerves of the latter.
Both these types occur along the same axis-cylinder, the central
and more or less richly branched portion being separated from the
peripheral expansion by an undivided or but little branched part.
Within the central organs the thick fibres give off numerous and
very fine lateral branches, which again arboresce freely, so that
the difference in calibre between stem and branches of the axis-
cylinder is often considerable, while in the peripheral expan-

VIII

CONDUCTIVITY AND EXCITABILITY OF NERVE

55

sions the type of strict dichotomous branching obtains. We
could hardly find a better example of this than the abductor
muscle of the crayfish claw with its nerves (3). Here the finer
trunks invariably contain, within a stratified sheath of connective
tissue, two axis-cylinders of very unequal diameter, and stain-

ill 'If

•.'•'iii1 .!':'&$fe.V

^ >S\

K-V, '4^\
^^.,. fy

lOi/H' '''.'M "r*? >' -.:^'.^.V -'"i.^v'K^^"

1 \--'f . '. \ . nEKv' ' \ ' .:' . ^t . '"Tm. *V-' V" "V-l "" •

,!

•riKs': Mft\\;w .'

|i»m4^

'liV-\'\W-^^ .'> w i '"'• '--^""

lite! ^r>

«• 4i m \\li? Jtx •:

I ;|I||1^,W;/" -:;-

\%fltPK ^^ft^^%^^-

FIG. 159.— Nerve-cords from the costo-cutaneous muscle of a frog injected with methylene blue,
showing numerous divisions and Ranvier's crosses. (Ko' Hiker.)

ing differently with methylene blue. If these are followed down
to the periphery, it will be found that both axis-cylinders divide
at exactly the same point ; this is repeated at each new bifur-
cation, even to the finest branches, so that the number of rami-
fications is conspicuously increased (Fig. 150). Both in the
central organ and at the periphery, the ratio of magnitude
between trunk and branches is remarkable. The dichotomous

56 ELECTRO-PHYSIOLOGY CHAP.

division rarely occurs so that both branches are equal in diameter ;
one twig is usually much finer than the other, and there is fre-
quently a marked disproportion, since a very thick axis-cylinder
may give off an excessively fine lateral branch.

We shall have more to say later as regards the mode of
division of vertebrate nerves, especially under the interesting
relations which obtain in the electrical organ of the torpedo.

The law of isolated conduction does not apply within the
central organs in the same sense as in the peripheral nerves
and their terminations. Here the conditions for irradiation of
excitation on all sides are obviously present, as appears more
particularly from the manifestations of strychnin tetanus, where
the stimulation of one or a few sensory nerve-fibres may, through
the spinal cord, throw nearly all the striated skeletal muscles into
active excitation. If, under normal conditions, the same localised
stimulus calls out one co-ordinated (reflex) movement only, con-
fined to one definite group of muscles, we may in a certain sense
speak of isolated conduction. But the reason why the excitation in
this case follows definite and invariably uniform paths, lies, not in
a sharply-defined anatomical connection of the nervous structures
involved (since these must on the contrary be connected on all
sides, as regards conductivity, within the central organ), but in
certain special conditions, excitatory or conducting, along certain
" canalised " paths " or lines of discharge " in the gray matter.

Wherever an excitable substance is endowed with highly-
developed conductivity, there is inevitably an equal irradiation of
the excitatory process on all sides, so that it almost appears inevit-
able that each nerve-fibre, like a muscle-fibre, must conduct in both
directions. At the same time, the fact that every nerve-fibre is
naturally connected with an organ of excitation and a peripheral
organ, renders it impossible that any direction of conductivity,
other than from the former to the latter, should produce a recog-
nisable effect. Many efforts have, however, been made to obtain
a direct experimental proof of the matter. Such are more par-
ticularly the attempted union of the central end of sensory, and
peripheral end of motor, nerve-fibres that have been divided.

Without going into the earlier and by no means unexcep-
tionable experiments of Bidder, Philipeaux, Vulpian, and others,
who endeavoured to unite the central stump of the sensory
ramus lingualis trigemini with the peripheral end of the hypo-

VIII

CONDUCTIVITY AXD EXCITABILITY OF XERVE

57

glossal nerve, we may refer to the recent repetition by Kochs (1 0) of
Paul Bert's experiment, in which the exposed tip of a rat's tail was
grafted on to the skin of the back, and then cut off at its original
attachment after the wound had healed up. After a short time
sensibility is restored in the transplanted tail, apparently indicat-
ing that the not yet degenerated nerves were able to conduct
excitation in a direction opposed to the normal. These experi-
ments were, however, shown by Kochs to be quite inconclusive.

On the other hand (apart from certain observations of du Bois-
Reymond on the transmission of the negative variation in both
directions), we must reckon as
genuine experimental evidence
for the double conductivity of
nerve, the experiments on
branching nerve -fibres, under-
. taken by Kiihne (11) in the
in tra- muscular nerve -branches
of different frog's muscles, es/.
sartorius and gracilis ; by Ba-
buchin in the still more suitable
organ of Malaptcrurus. The
delicate nerve, which enters the
middle of the sartorius by one
side, divides within the muscle,
so that the single fibres that

o

constitute the bifurcations branch many times dichotomously.
When Kiihne threw the broad upper end of the muscle
into heat-rigor by dipping it into warm oil (Fig. 160 a), the
half which remained normal twitched on cutting the rigored
portion with scissors, showing that excitable nerve-fibres could
still be mechanically excited between the rigored and dead
muscle - fibres, and thus carry the excitation centripetally
into branches which divide above the rigored portion of the
muscle. Still more convincing is the so-called " bifurcate experi-
ment," in which the broad end of the sartorius is split up length-
ways, when excitation of one fork nearly always produces an
accompanying twitch in the other (Fig. 160 &). Since auy propa-
gation by secondary excitation from fibre to fibre seems to be
excluded in normal muscles, fefre only possible interpretation is
that one twig of the branched nerve which supplies both forks

FIG. 160.

58 ELECTRO-PHYSIOLOGY CHAP.

is excited, and the excitation conducted in the first instance
centripetally. Later on, Kiihne attempted the same experi-
ment successfully on other muscles, e.g. in the frog's gracilis.
As is seen in Fig. 160 c, the entering nerve divides into two
branches a, b, one of which is cut round so as to form a lobe ;
and on exciting this (by incision) the whole muscle invariably
twitches. Since in this case also there are divisions of the fibres
at the point where the entire nerve divides, the experiment is
conclusive for centripetal conduction in the branch that supplies
the lobe. We shall return later on to Babuchin's experiment ;
in this there is a discharge of the entire organ when any twig of
the peripheral ramification of a single nerve-fibre is stimulated.
As in Klihne's experiment, the excitation in the centrifugal nerves
must at first travel centripetally, in order to spread to all the
other branches (12).

If the axis-cylinder were homogeneous, the bifurcate experi-
ment with sartorius, as well as the analogous experiments on
other muscles and on the electrical organ of Malapterurus, would
be clear and unimpeachable. On stimulating the lesser rami, the
excitation would take a backward course to the point of division,
and then presumably travel in the same centripetal direction along
the fibres of the trunk, taking the normal centrifugal path only in
the other peripheral ramifications. The axis-cylinder, however, is
not homogeneous, but is composed of fibrils, and there is much to
indicate that these are the true conducting elements. Hence we
cannot regard any tract of the nerve as a physiological unity,
but must recognise as many isolated paths of conduction as
there are fibrils. Then, however, the results of the bifurcate
experiment would, as Kiihne points out, be conclusive for double
conduction in the nerve under a succession of premises only. If
the law is admitted, it implies at the dividing point of a primitive
fibre a further division of axis - cylinder fibrils also (Kiihne).
When Max Schultze was elaborating Eemak's theory of the
fibrillar structure of the axis-cylinder he came to the opposite
conclusion. He believed the nerve-fibres to contain from the
outset all the fibrils destined for the peripheral expansions, so
that in the branching of the axis-cylinder there would only be
an unravelling, or bending aside, and no actual division of fibrils.
On the other hand, there are many facts against this conclusion.
Wherever nerve -division is present, the sum of the peripheral

vin CONDUCTIVITY AND EXCITABILITY OF NERVE 59

sections of the fibres is in striking disproportion with the cross-
section of the trunk. This is evident on comparing the incon-
siderable axis-cylinder of the single fibre in the electrical nerves of
Malapterurus with the area covered by the sections of its innumer-
able ramifications (Fritsch reckons the increase at 346,760
times) : examination of any muscle that is rich in bifurcating
nerve-fibres proves that the section of the trunk is far exceeded
by the sum of the sections in the branches nearest to it. This
is obviously not derived from increase of medullary sheath, and
must be due to the axis-cylinders, so that two possibilities only
remain in support of Schultze's hypothesis ; the fibrils must either
become thicker towards the periphery, or diminish in number at
the cost of the stroma — neither of which can be demonstrated
(Kiihne).

The study of nervous excitation is much complicated by the
fact that the excitatory process is not associated with any directly
perceptible alterations within the nerve. We are everywhere
thrown back upon the effects at its peripheral end, foremost
among which, as a delicate indicator of the changes taking place
in the nerve, is muscular contraction. Muscle — striated muscle in
particular — is the surest index of nerve-excitation, and we owe
nearly all our knowledge of the physiological properties of peri-
pheral nerve-fibres to experiments on motor nerves. On stimu-
lating any motor nerve there is a strikingly rapid reaction from
the muscle (whatever the distance of the excited point), without
any perceptible interval between moment of stimulation and
commencement of contraction, no matter what point of the nerve
is excited. This formerly led to very exaggerated statements of
the rate at which these alterations in the nerve were conducted,
and it was held to be incalculable.

Helmholtz (13) was the first who succeeded in measuring the
rate of conductivity in nerve, by means (in the first instance) of
Pouillet's method of time-measurement (Fig. 161), in which a
battery current is closed at P by a switch when C is opened, at
the moment of excitation, and broken again at B when the muscle
begins to contract. During the short interval between P and B

O O

the current passes through the galvanometer G, and causes a
perceptible deflection of the magnet proportional with the dura-
tion of closure. If two points of the nerve are stimulated, one
remote from the muscle (a), the other as near it as possible (&),

60

ELECTRO-PHYSIOLOGY

CHAP.

the deflection in the former case will be greater. The difference
gives the time in which the excitation travels from the distal

(central) to the proximal
(peripheral) point of exci-
tation. At a later period
Helmholtz arrived at the
same result by a simpler
method, i.e. the graphic
record of the muscle
twitches on stimulating
two points of the nerve,
as widely removed as
possible. The difference
in the latent period of the
two curves, which are

FIG. 161.— Rate of transmission of excitation in motor obviously nOll- Coincident,
nerve of frog (Pouillet's method). (Helmholtz.) n , ••

but otherwise congruent

{Fig. 162), corresponds to the rapidity with which the excitation
is transmitted in the intermediate tract of nerve. In the
motor nerves of the frog, at room temperature, this is about
27 m. per sec. Experiments on man by the same method
(muscles of ball of thumb) give a much higher result (34 m.).
Further observations of Chauveau on the nerves of smooth

Fio. 162. — Separation of curves of twitch on exciting the frog's sciatic close to the spinal cord,
and 5 mm. from the knee. (Engelinanii.)

muscles in mammals are interesting, as showing that the rate of
conductivity is much lower in these than in the nerves of striated
muscle. It hardly reached 8 m. per sec. The rate of conduc-
tivity in non-medullated nerves of many invertebrates appears to
be still lower, even when they are connected with striated
muscles. Fredericq and Vandervelde (15) found, according to
the temperature (10°-20° C.), 6-12 m. in the claw-nerves of the

vni CONDUCTIVITY AND EXCITABILITY OF NERVE 61

lobster, while Tick estimates the rate of transmission in the
commissural nerves of Anodonta at 1 cm. per sec. only. Aron
Uexkiill (16) has recently found values of 400 mm. to 1 in. in
the nerves of the mantle of Eledone.

W. A. Boekelmann (17) has recently made some interesting
attempts to estimate the rapidity of conduction in the non-
medullated fibrils of the frog's cornea, by determining the interval
at which a reflex movement (retractio bulli) appears after me-
chanical or electrical excitation of the centre and periphery of
the cornea respectively. The same ratio of values was obtained
as for the medullated fibres of the trunk, a fact not without sig-
nificance to the question whether the peristaltic movements of
smooth muscular organs depend upon nervous conductivity, or
upon direct propagation of the stimulus from cell to cell.

From all these calculations we arrive at the important con-
clusion that the excitatory process in nerve is transmitted at a
comparatively low rate — incomparably less, at all events, than the
velocity of light or electricity. If, as cannot be doubted, there
is propagation of a material, chemical alteration of the sub-
strate (substance of axis-cylinder), the qualitative constitution
of the latter cannot fail to affect the process of conduction.
And, in fact, the dependence of rate of conductivity upon different
physiological conditions in the nerve is well known. Helmholtz,
in his investigations on the motor nerves of frogs, observed a
marked retardation of conductivity in the nerve, as the effect of
cold. Fre'de'ricq and Vandervelde again found that the rapidity
of nervous conduction in the lobster depended, to a great extent,
upon season and temperature. Nerve in this respect behaves
analogously to muscle and all other excitable protoplasm. This
correspondence is another proof that the process transmitted in
the nerve is really a similar alteration to that in all excitable
conducting plasma, i.e. a chemical process associated with metabol-
ism. These observations are not unnecessary, in view of certain
facts and hypotheses to be considered later.

Sustained pressure and compression of the nerve may seriously
injure conductivity, and it is to be remarked that this seems to
occur in a different degree in motor and in sensory fibres—
Liideritz (18) and some others finding the pressure-effect earlier
in the former, Zederbaum (19) and others in the latter.

The action of anaesthetics upon the conductivity of nerve is

62 ELECTRO-PHYSIOLOGY CHAP.

very remarkable, and of great theoretical interest. We found
(vol. i. pp. 359, 450), in considering the effect of ether on muscle,
that conductivity is first abolished, next contractility, and last of
all local excitability. This last is still expressed in certain
secondary electromotive phenomena (including the positive
polarisation current), and in the demarcation current, at a time
when contractility is already abolished. In nerve also, conduc-
tivity appears to surfer in first degree from the action of ether,
chloroform, alcohol, etc., as appears directly from the persistence of
the nerve-current with abolished conductivity (if this be accepted
in the sense laid down above as the expression of persistent
local excitation). By using a method first applied by Griinhagen
(20), the conductivity of nerve may easily be abolished locally
if the narcosis is confined to the lower end of an exposed frog's
sciatic, by drawing the nerve through a glass tube which leaves
the central end free, and is itself closed at both ends save for a
small opening for the passage of the nerve. Three other glass tubes
are fused into the wall of this tube ; two serve to lead in the
gases or vapours, the third is for the electrodes ; the middle
portion of the nerve rests upon the electrodes. There will then
invariably be a stage of narcosis, in which the strongest excitation
above the narcotised tract is ineffective, while a much weaker
stimulus still excites below (i.e. in the tube). Eventually, of
course, this part is also anaesthetised. If air is passed through
the tube the normal condition will be reinstated. Under these
circumstances, therefore, the conductivity of the nerve is ex-
tinguished, while local excitability is maintained, and even at
first augmented, in the narcotised tract — a state which we found
to be the rule in muscle under similar conditions (supra). In
these experiments again, as pointed out by Pereles and Sachs
(21), there are perceptible differences between the centripetal and
centrifugal fibres of a mixed nerve (sciatic). If the minimal
stimulus, which discharges a movement of the foot, is first deter-
mined above the central tract that is to be narcotised, along with
the strength of stimulus necessary to produce a reflex movement
of the leg from the web of the foot, the inevitable consequence
of narcosis is the earlier disappearance of reflex than of direct
movements. The same result follows even more infallibly
from analogous experiments in which the nerve-trunk is excited
by tetanising, now above and now below the etherised tract.

viii CONDUCTIVITY AND EXCITABILITY OF NERVE . 63

Here, too, the disturbance of the body caused by the centripetal
conduction of a sensory excitation, on stimulating the lower point,
is the first to die away, while movements of the foot can still be
excited from above, although the stimulus which produces them
is weaker than the other. " In local narcosis of the frog's sciatic,
conductivity is first abolished in the sensory, and later in the
motor nerve-fibres. On recovery from narcosis, the motor fibres
sooner become capable of conducting than the sensory fibres."

More exact investigation shows that the ratio between con-
ductivity and excitation in nerve may alter in quite another sense.
Grunhagen (I.e.) observed, at a certain stage of C02 narcosis, that
the local excitability of a (peripheral) tract of nerve may be
considerably depressed, while the effect of stimulating the un-
poisoned part of the nerve is unaltered, although the excitation
process there discharged must be transmitted through the
narcotised area. Similar experiments were carried out later by
Szpilmann and Luchsinger, Hirschberg, Efron, Gad and Sawyer,
Goldscheider, and lately in detail by Piotrowsky (22). From
these the very significant fact appeared, that with local application
of alcohol vapour, ether, or chloroform, conductivity was as a rule
first and most fundamentally affected at such parts of the nerve, before
excitability underwent any perceptible diminution. With C02,
on the contrary, as well as CO, conductivity is quite unaffected,
while local excitability is quickly abolished. These observations
are the more striking because they seem to contradict the current
opinion that excitability and conductivity are in the same ratio,
i.e. that when one declines the other sinks, and vice versa. Yet
we must admit the double capacity of nerve-fibres, on the one
hand to conduct excitation, on the other to be thrown into
excitation at any point of their course by external factors
(stimuli), to be but different expressions of the same fundamental
property of nerve-substance, and consequently inseparable. The
most natural conclusion from this is, in the language of Hermann,
that the excitatory process repeats itself constantly during con-
duction— that each particle of the nerve falls into the same state,
whether it is affected by the impulse running along the nerve,
or is directly excited by an external stimulus, so that the process
of conductivity is first initiated in it.

From this point of view conductivity in nerve is, like every
conductive process within an excitable substance, no more than

64 ELECTRO-PHYSIOLOGY CHAP.

transmission of excitation from particle to particle, and might
thus be designated as the propagation of the excitatory process.

On the other hand, there are several indications which make
it probable that excitability (expectancy) and conductivity are dis-
tinct properties in nerve, and not in causal inter-relation. The first
exact physiological observation of this was made by Mimk (23),
who noticed, in following out the changes in excitability associated
with the dying of the nerve in a frog's nerve-muscle preparation,
that the principal bifurcating points of the sciatic nerve could be
insensitive to the strongest electrical stimuli, at a time when the
muscle still responded by vigorous twitches to a much weaker
excitation applied to more central parts of the nerve. A better
known instance is that of Erb (24), who found that when, after
crushing the sciatic nerve of frog or rabbit, regeneration had set
in, and the lamed extremities were again moved normally by the
animal, the part of the nerve that had been crushed, and was now
regenerated, was still insensitive to electrical stimuli. Here, too,
we must include the more complete experiments on the spinal
cord (infra) by which Schiff was led to his doctrine of " aesthe-
sodic " and " kinesodic " nerve-substance, capable, i.e., of con-
ducting, but not directly excitable. Above all, however, the
experiments already quoted of Griinhagen, Efron, Gad-Sawyer,
Goldscheider, and Piotrowsky, on the effect of local narcosis on
motor nerve, have contributed to bring forward the view that the
two processes of response to stimulus and conduction of stimulus
are distinct from one another. Indeed, the fact that a peripheral
tract of nerve under C02 narcosis is inexcitable, and yet transmits
an excitation coming from a more central point, hardly admits of
any other interpretation, save that excitability and conductivity
may alter independently of each other.

If we are justified in regarding the process concomitant with
the excitatory condition of a nerve element, as a stimulus by
which the element longitudinally next to it is excited, conduc-
tivity must be a permeability of the nerve to certain in-
fluences which affect it in the longitudinal direction. We may,

\j '

with Gad, denote this sensitiveness as " longitudinal lability." It
is conceivable, and even probable, that the stimulus which one
nerve-molecule exerts upon the next molecule may, although closely
related to an external stimulus, or identical with it, find even
more favourable conditions than the latter. This assumption (cf:

vin CONDUCTIVITY AND EXCITABILITY OF NERVE 65

Hermann's Ha-ndbuch, ii. 1, p. 187) makes it possible that at a
certain stage of localised narcosis local capacity of response
may have sunk considerably, while conductivity, in consequence
of the predominance of " longitudinal lability," is still intact
(Griinhagen's C02 experiment). Under other conditions, on the
contrary (as in treatment with alcohol), direct excitability declines
much more slowly than conductivity, as normally occurs in
muscle. In view of this fact, we shall hardly, with Szpilmann
and Luchsinger, interpret the reaction as signifying that the exci-
tation, starting from a distant normal point, has to pass through a
longer and injured tract, losing thereby in intensity. But even
Gad's view of a difference in the longitudinal and transverse
excitability of nerve would appear to be fundamentally impossible,
since the inexcitability of nerve to pure transverse passage of cur-
rent is as well established for nerve as for muscle (Biedermann).
A true grasp and right interpretation of these facts will only be
possible when we know more about the manner in which one
excited section of the nerve acts as a stimulus upon that section
next to it. Innumerable examples show us that the excitatory
condition per se does not necessarily imply conduction of the im-
pulse to the contiguous sections. Localisation of persistent closing
and opening contraction, the " positive anodic polarisation " (due
to purely local alterations) of the narcotised muscle, the gradual
introduction (cinsckleichen) of even strong currents into nerve and
muscle, all prove sufficiently that the conditions of development,
particularly as regards time, of the excitatory process are of funda-
mental importance to its propagation. It is conceivable that
different substances might so affect the time-relations of the trans-
mission of excitation from section to section, that the effects in
question could be interpreted.

Helmholtz, in his experiments on the motor nerves of frogs,
employed maximal stimuli, or else reduced the strength of stimulus
at one point of excitation only so far that the twitches were equal in
magnitude. The experiments which he undertook later with Baxt
(14) on man, in which the muscles of the ball of the thumb were
excited by stimulating the median nerve at two different places,
appeared to show that the latent period on exciting the distal point
of the nerve was regularly less with stronger excitation while
at the proximal point no effect from altered strength of excita-
tion is perceptible. Hence wre may conclude that strong excitation

VOL. II F

66 ELECTRO-PHYSIOLOGY CHAP.

is more rapidly transmitted in nerve than a weak stimulus.
This view finds support in the later investigations of Valentin,
Troitzsky, and Wundt, while Rosenthal and Lautenbach affirm
that conductivity is independent of strength of excitation. From
a recent and detailed research of v. Vintschgau (25), it appears
that "when a frog's nerve is initially excited at two different
points with that strength of stimulus (induction shocks) which
causes the first, or approximately the first, maximal twitch, and
the stimuli are subsequently increased from that point, there is a
certain range within which the rate of transmission of the
nervous excitation undergoes no essential alteration." So soon,
however, as this has been exceeded, the rapidity with which the
excitation is transmitted increases with the further augmentation
of the stimulus, till it becomes impossible to measure it. A. Tick
(26) found in the non-medullated commissural nerves of Ano-
donta that a strong stimulus was more rapidly transmitted in the
nerve-fibre than a weaker excitation, and S. Fuchs (27) has
recently arrived at the same result in determining the rate at
which the negative variation is transmitted in the nou-medullated
nerves of the mantle of Elcdone.

II. PHENOMENA IN FIBRES ASSOCIATED WITH NERVE-CELLS

(IiKFLEX ACTIVITY)

At this point it is desirable to discuss the question whether
the interpolation of ganglionic elements upon the course of the nerve-
fibre has any, and if any, how much, effect upon the transmission of
excitation.

In stimulating motor fibres outside the central organ, this
question has of course but little application ; the most that can
be ascertained is whether the transmission of excitation from nerve
to muscle produces any perceptible delay in conduction or no.
Certain experiments of Bernstein (infra} seem to indicate that
such is the case.

Far greater importance attaches to the interpolation of
ganglion -cells, in all excitatory experiments where parts of a
central organ are excited directly, or by means of centripetal
nerves. Exner (28) examined into the seemingly simple case
in which the only question is whether the interpolation of a
single ganglion -cell effects any marked alteration in rate of

viii CONDUCTIVITY AND EXCITABILITY OF NERVE 67

conductivity. It is plain that if the time occupied by the
passage of excitation through the ganglion is perceptibly longer
than the known time of conductivity through an equal tract
of normal nerve-fibre, there must be an interruption of some
kind. The only histological elements in the ganglia which can
present such an interruption are, however, the nerve-cells. The
relations are far simpler here than in the central nervous
system, where also the time occupied by the transmission of exci-
tation has been taken as a proof of the existence of special elements
interpolated along the course of the simple conducting paths; there,
however, the delay in transmission must be referred not merely to
nerve-cells, but also to the nervous network which is possibly
present. Exner, who undertook to determine the time in
which the centripetal wave of excitation traverses the frog's
spinal ganglia, employed Bernstein's rheotome to measure (on
the sciatic, ganglion, and posterior root) the interval between the
excitation of the sciatic and the arrival of the negative variation
in the fibres of the posterior root, as led off to the galvanometer.
He obtained figures below those quoted by Bernstein for the
rapidity in normal peripheral nerve, and concluded that con-
ductivity was not blocked at the ganglion. The rheotome method
is, however, open to many objections. Wundt (29) had pre-
viously tried to determine the point by testing the influence of
the spinal ganglia upon reflex excitability. Curves of twitches
from the muscles of one leg (in the frog), obtained by alternately
exciting the opposite sciatic trunk and a posterior root on the
central side of the ganglion (between the ganglion and the spinal
cord), invariably gave a marked difference of latent period, corre-
sponding with a delay in conductivity at the ganglion. Gad (30)
repeated the same experiments on the jugular ganglion of the
rabbit's vagus. The reaction to be determined was in this case
the reflex modification of respiratory movements, by excitation of
the vagus. The sole variable was the point, alternately central
and peripheral to the ganglion, at which the stimulus was
applied. The respiratory movements were graphically recorded
by the usual method, and in order to ensure uniformity of
external conditions at the centre during the respective tests,
apncea was induced, or the stimuli were carefully regulated for
the same phase of respiration. The reaction-time yielded by
these experiments was—

68 ELECTRO-PHYSIOLOGY CHAP.

"With excitation peripheral to the ganglion 0'123 sec. (average of 148 experiments)
,, central „ 0'OS7 sec. ( „ 97 „ )

Difference . . 0'036

V. Uexkiill's recent experiments on the function of the stellate
ganglion in Eledone moschata (16) bear on the same question. A
large number of nerves (stellar nerves) radiate laterally from
this ganglion, and supply the muscles of the skin and mantle.
" On exciting the stellar nerves the near muscles first come
into action, and then the more distant, in ratio with the con-
ductivity of the nerves. With excitation above the ganglion
the contraction of the near muscles is delayed, as is expressed in
the gentler rise of the curve. The apex is, however, steeper,
thus showing that the total effect on all the muscles is com-
pressed into a shorter time. The ganglion stellatum would thus
appear to correct the slower conductivity, since it enables the
muscles of the mantle to perform more syuchronic and therefore
more effective movements."

If the difference in reflex time, on stimulating at different points,
thus affords a gauge of the influence exerted by the ganglion-
cells interpolated along the nerve-fibre, upon the time-relations
of the excitatory process, the same is no less evident from the
character of the reflex period itself. A reflex movement (i.e. a
motor impulse in the muscular apparatus in consequence of a
centripetal stimulus) can only occur when the centripetal path,
which is first traversed by the stimulus, is connected with the
efferent path by means of the central nervous system. The
solitary ganglia of invertebrates, the spinal cord and bulb in
vertebrates, are more especially the seat of these nervous pro-
cesses. In 1855 Helmholtz first pointed out that the time
between the impact of a stimulus and the corresponding reflex
movement of a striated muscle was 10—12 times longer than the
time required to conduct an impulse in a peripheral nerve of the
same length. This assumes the rate of conductivity to be approxi-
mately equal in motor and in sensory nerves, as does in the
above experiments appear to be the case.

The duration of an entire reflex process may be summed up
in three factors: (1) the time occupied by conduction in a
centripetal nerve, from the point of stimulation to the central
end ; (2) the time which elapses between the arrival of the
excitation at the centre, and its transmission to the central end

vin CONDUCTIVITY AXD EXCITABILITY OF XERVE 69

of the centrifugal (motor) nerve ; this is the " reflex time " proper
(Exner's "reduced reflex period"); (3) the time required by
the excitation to traverse the motor nerve and evoke a contrac-
tion in the muscle.

The rate of conductivity usually accepted for frog's nerve, i.e.
27 in. per sec., is by no means an invariable figure. Helmholtz
indeed assumes that the excitation is transmitted at constant
rapidity, but this is neither certain nor even probable. These
figures must therefore stand for an upper limit of the reflex period,
and in longer nerves than those employed there would presumably
be a lower rate of transmission. Even with these reservations,
however, Helmholtz's facts are incontestable. The excitatory pro-
cess undergoes a considerable retardation during its passage
through the spinal cord from sensory to motor fibres. This delay
must be attributed to the structure of the nerve-cells, in virtue of
which they are distinct from their processes, the nerve-fibres. The
difference of constitution is best expressed by saying that the
central nervous organ presents greater resistance to the transmis-
sion of excitation than the sensory or motor peripheral paths.

Like rapidity of conduction in peripheral nerve, only in a
much higher degree, the reflex time, as the expression of the rate
at which excitation is transmitted within the central organs, is
conditioned by several factors, and is itself very variable.

The length of tract within the central organ, or, as it may
perhaps be expressed, the number of ganglion -cells to be
traversed, is of great importance. One fact must be mentioned by
which central is distinguished from peripheral conductivity,
and is rendered very complex. Each central organ consists
of course of a multitude of nerve-cells, with centripetal and centri-
fugal fibres. If the la\v of isolated conduction obtained strictly
within the centres also, so that each conducting path was isolated
as in the peripheral nerves, each impulse from an afferent nerve-
fibre could have but one definite localised effect, that would never
vary under any circumstances. If, on the other hand, we recog-
nise that the connection of different fibres by ganglion -cells
(which finally establish a closer or more remote relation between
all departments of the central organ) admits of conduction in
all directions with equal facility, then impulses arriving at any
part of the central organ would radiate diffusely without pro-
ducing any definite and localised action. Neither the one nor

70 ELECTRO-PHYSIOLOGY CHAP.

the other hypothesis, however, covers the case of reflex move-
ments, the peculiarities of which are remarkable even in the
lower vertebrates. The movements involved are always co-
ordinated, i.e. they originate in the activity of a definite number
of definitely grouped muscles. This is most obvious in reflex
movements in the narrower sense, i.e. in those movements pro-
duced in striated skeletal muscle, after exciting a sensory nerve
through a central organ.

If the end of a toe is pinched in a decapitated frog, the
leg is withdrawn, and then remains quiescent. This is a typical
reflex, via the spinal cord. The excitation, acting on the sensory
nerves of the skin, travels centripetally from the periphery to
the spinal cord, and gives rise to an impulse in the contrary
direction — from cord to certain muscles of the leg. In this, and
all similar cases, we must assume a definite irradiation of
the excitation in the central organ, for the number of motor
fibres excited is obviously in considerable excess of the number
of primarily excited sensory fibres. Any touch, or least contact
of the skin, with the fine point of a needle, suffices to throw a
great number of muscles into simultaneous contraction, and as in
the sensitive mimosa we concluded from the diffuse reaction con-
sequent on local excitation, for the propagation of the stimulus
along certain paths, so in this case we must assume that each
sensory fibre is functionally connected with many motor fibres
within the central organ — all possibility of transmission ceasing
as soon as the latter is destroyed. The law of isolated conduction,
which is universally valid in the region of the peripheral nervous
system, does not therefore hold good for reflex processes. From
the facts already discussed we may affirm that if it were possible
to excite a single primitive fibre of a motor nerve, the muscle-
fibres which are supplied by this fibre would alone contract, and
the same is true of sensory nerve-fibres until they enter the
central organ. In reflex movements it is otherwise ; the excita-
tion is here conveyed by one or a few sensory fibres via the
central organ to a plurality of motor elements. It may be
objected that a rigid anatomical relation between certain centri-
petal and certain centrifugal fibres still underlies this irradiation
of excitation. This view is, however, unfounded. The strength
of the peripheral stimulus is the most important factor in the
diffusion of irradiation. In a headless frog, if the sensory

vni CONDUCTIVITY AND EXCITABILITY OF XERVK 71

stimulus is strengthened, reflex movements occur in both legs, and
subsequently in the arms and trunk. This implies diffusion of
excitation over nearly the whole spinal cord, and almost all the
motor nerves which originate in this part of the central organ
are reflexly excited. The movements, however, are still co-
ordinated throughout, i.e. the groups of simultaneously excited
motor fibres are always in physiological correlation.

The transmission of excitation to remote muscles must
obviously take a longer time under these conditions. If the
reflex period is estimated for a muscle of the same, and for one
of the opposite side (on stimulating a given point of the skin), the
reflex time of the latter exceeds that of the former. The amount
of this difference is the time of cross -conduction. There is
apparently less resistance in the longitudinal direction of the
spinal cord (Wuudt, 29).

The specific characteristics of conductivity within the central
nervous organs are least ambiguous in the striking changes
which result from the action of certain poisons. It has long
been known that in most vertebrates, after intoxication with
strychnin, the slightest stimulation of any sensitive part evokes
exaggerated uncoordinated muscular movements (spasms), which
in warm-blooded animals soon end in death. Both earlier and
later experiments concur to show that the spinal cord is an indis-
pensable factor in strychnin-spasm, as in the initiation of reflex
movements. Neither in peripheral motor nor in sensory nerves is
excitability perceptibly modified by the poison. Strychnin must,
therefore, be reckoned as a specific poison of the spinal medulla.

The introduction of minute doses (0'02-0'0-t mgr.) at first
produces no change in the frog, beyond a marked increase of
reflex excitability. The reflex twitches appear with weaker
stimuli, and with greater precision at eacli successive stimulus ;
neither in the duration of the latent period nor in the subse-
quent course of the twitch is there any perceptible divergence
from ordinary reflex twitches. After somewhat larger doses
(while, according to Eosenthal, the length of the latent period
steadily decreases — Wundt states the contrary) the twitch changes
gradually into a sustained tetanus, which appears with even the
weakest stimuli, and is little increased with stronger excitation.
At the climax of the strychnin effect, any stimulus capable of
discharging the reflex at once produces maximal excitation. As

72 ELECTRO-PHYSIOLOGY CHAP.

regards the dependence of a reflex twitch upon strength of excita-
tion, it should be remarked that it is only within a very narrow
range of stimuli that magnitude of contraction increases with that
of stimulation. Directly the stimulus is capable of discharging
any reflex it provokes a fairly strong twitch of the muscle, which
cannot be much increased by further augmentation of stimulus :
the reflex time, on the other hand, is diminished. Accord-
ing to Eosenthal (31), the reflex time may be so reduced with
strong excitation that nothing remains of Helmholtz's phenomenon,
and if the time which the excitation takes to travel from the
point stimulated to the spinal cord, and thence to the muscle, is
calculated, the sum of botli will be approximately equal to the
latent period as measured. The limited range within which
increment of stimulus produces perceptible increase of reflex
action diminishes with stronger doses of the poison, and finally
vanishes (Eosenthal).

The phenomena exhibited by strychninised frogs are very
characteristic. In normal reflexes the least stimulus applied to
the hind foot induces flexion of the corresponding leg, while the
extensor muscles remain quiescent. The action after strychnin
poisoning is quite different; there is always pronounced contrac-
tion of all the muscles of the leg, and the extensors being the
most powerful, the limb is stretched out convulsively. It is a
question how the normal co-ordinated flexor reflex is converted
after strychnin poisoning into the uncoordinated reflex of exten-
sion. If the normal dose is much reduced ( = 0*0001 gr.) it
will be found insufficient to transform the flexor into the extensor
reflex, though there is still some effect on the spinal medulla,
since a weaker stimulus provokes the reflex, and the reflexes
appear more promptly and inevitably. As soon as these minute
doses are exceeded, the spasmodic extension reflex sets in. While
in the co-ordinated flexor reflex certain definite paths are alone
excited, in the uncoordinated reflexes of extension all are
excited simultaneously, and the extensors, as the more active,
determine the movement of the limb. If the spinal cord is
sufficiently strychninised there is a simultaneous contraction of
all the skeletal muscles, discharged from every possible point of
active sensory excitation — as though all the corresponding nerves
were caught into a bundle and excited at the same moment. But
if it is possible, under the action of strychnin, thus to excite all

vin CONDUCTIVITY AXD EXCITABILITY OF XERVE 73

the motor nerves from any sensory nerve of the skin, it is obvious
that all the prolongations of the same within the reflex centre
(spinal cord) must be similarly associated. Clearly the poison
cannot alter the structure and direction of the central paths, along
which the excitation travels in the spinal medulla. We must
rather assume that the new relations into which the central
nervous elements have reciprocally entered are due to a chemical
alteration of their substance. The action of strychnin proves
that the path taken by the excitation in the normal central
organ is circumscribed, not by any definite arrangement of fibres,
but by the mobility in a definite direction which characterises
the mass through which the excitation is transmitted. If we
picture the whole of the gray matter as a coherent network of
homogeneous, excitable, and conducting plasma, in direct con-
nection with the sensory and motor nerve-fibres (a conception
that is not indeed borne out by recent histological discoveries),
then the only possible explanation of the organised reflex move-
ments which regularly follow on a given stimulus must be that
there are certain " lines of discharge," along which excitation is
normally transmitted, because there is here less resistance — the
protoplasm is more excitable. The path along which a sensory
excitation, calling out a definite reflex movement, travels in the
spinal cord, has often been compared to a canalised track, and
from a certain point of view the crude illustration suffices. But
there is the further question of how this perfectly co-ordinated
network of lines of discharge originated, and of whether it is pos-
sible during the life of the individual to form new combinations,
and new excitatory paths to reflex movements. The question is
too wide to be entered upon here ; we can only say that there
is some ground for assuming that every impulse traversing the
central nervous system, along any path, leaves its traces behind it,
inasmuch as it causes certain molecular alterations, which,
as they become sharpened by repetition, facilitate the subsequent
discharge of action along the same lines (Exner's " Balmuny ").
This hypothesis not only accounts for the fact that new reflex
combinations of movements may be formed during the life of
the individual, but it also gives us the key to an understanding
of those co-ordinated reflexes which the individual acquires as an
" inheritance " from his ancestors.

If these facts show that the law of isolated conduction does

74 ELECTRO-PHYSIOLOGY CHAP.

not hold in a strict sense within the central organ as in the
peripheral nerves, the same is true of another great law, viz.
that of " conductivity in both directions." The efferent (especi-
ally motor) and afferent nerves are known to enter the spinal
cord of vertebrates by different roots. Central excitation of a
divided anterior root never (even after strychnin poisoning)
discharges any reflex movement or spasm. With regard to the
structure of the cord we should, therefore, conclude that the
protoplasmic processes of the cells of the anterior horn, in so far
as they serve to transmit excitation, do so in one direction only.
It would thus be characteristic of these cells that they confined
the conductivity, which in ordinary nerve-fibres is in both direc-
tions, to one direction only (Gad). Recent conclusions as to the
constitution of the gray matter, and more particularly the ana-
tomical structure of the reflex arc, place the matter in another
aspect. For if instead of continuity of substance we have merely
contact between the end-branches of the conducting nerve-fibre
(" terminal arborisations ") and the " reflecting " (motor) cells of
the ganglion, conduction in one direction becomes intelligible,
and is no more surprising than the fact that excitation of a muscle
does not simultaneously excite its motor nerve.

There is a striking dissimilarity in the action of strychnin
upon different animals, pointing to corresponding and quite un-
known differences in the chemical composition of the central
nerve-cells. Among vertebrates, guinea-pigs and fowls are char-
acterised by a special insensibility to strychnin (Leube, 32).
And in most invertebrates the characteristic spasms are wanting,
even with large doses of the poison. Claude Bernard first made
the (often-confirmed) observation that the reflex excitability of
invertebrates (crayfish, leech) is not altered by strychnin. Both in
leech and crayfish the stages of excitation characteristic of verte-
brates were entirely wanting, and he found only a rapid and primary
(central) paralysis. Krukenberg (33) confirmed Bernard's con-
clusions, while Yung (34), on the contrary, witnessed sharp
tetanic spasms in the crayfish which soon gave way to paralysis.
Luchsiuger (35), too, pointed out in invertebrates (leech, crayfish)
that had been poisoned with strychnin, phenomena which he
regarded as reflex spasms. In any case these only appear under
certain conditions. Luchsinger, like Krukenberg, employed the
ingenious method, first devised by C. Bernard for the frog, of

viii CONDUCTIVITY AND EXCITABILITY OF NERVE 75

partial intoxication. A leech was divided into three parts by two
ligatures; the ligatures stopped the circulation without crushing
the ventral cord. Strychnin (O'OOOo gm.) was then injected
into the middle section, the effect, according to Luchsinger,
depending wholly upon temperature. If the leech had been
left for some time in water of about 8° C. it showed no sign
of excitation, whereas the strychninised section of an animal that
had previously been exposed to 25°— 30° gave lively manifesta-
tions of excitation. " Waves of excitation ran from segment to
segment, and if these quieted down, the least stimulus to the skin
of the animal evoked disorganised movements." The unpoisoned
ends throughout remained quiet. After a certain time the centre
was paralysed. From this it would appear that there is no radical
difference in the reaction of the spinal ganglia to strychnin in
vertebrates and invertebrates, though gradations of sensibility
are undeniable. The striking effect of temperature upon the
action of strychnin, as exhibited in the leech, appears to some
extent in the frog also, where it was first observed by Kiihne,
and subsequently worked out by Wundt.

Stronger doses of strychnin produce both in vertebrates, and
even more rapidly in invertebrates, a condition similar to par-
alysis, the cause of which — as of the antecedent rise of excita-
bility— is central in origin. The behaviour of the animal in this
stage of strychninisation is highly suggestive of narcosis from
anaesthetics (ether, chloroform, alcohol). We have already studied
the peculiar effect produced by these reagents on all contractile
substances, as also on nerve-fibres. The ganglion - cells must,
however, be ranked first in order of sensibility, in all animals.

The depressing effect of anaesthesia upon the reflex move-
ments of vertebrates has long been known, and it may reasonably
be concluded that the ganglion -cells of the centres are first

o o

and most profoundly affected in their normal vital properties by
the substances in question — as shown by the final and complete
loss of excitability and conductivity. It was Claude Bernard who
first pointed out that the action of anaesthetics is universal, and
takes effect upon all excitable protoplasm. All experiments,
however, show that the different tissues in an organism are
affected in very different degrees. On submitting man, or any
vertebrate, to the action of chloroform or ether, it is the sensitive
protoplasm of the cells of the cerebral cortex that is pre-eminently

76 ELECTRO-PHYSIOLOGY CHAP.

affected by the narcotic. Consciousness, conscious sensation, and
voluntary movement — in short, all psychical activities in the
narrower sense — are extinguished, while reflexes still continue.
Reflex function is next abolished, nerve, muscle, glands, etc.,
remaining still unaltered. This explains why the vital functions
survive, and why at its early stages narcosis is not directly
dangerous to common vitality. The anaesthesia of the surgeon is
really incomplete ; it affects only the most susceptible elements
of the central nervous system, while the other excitable parts
(muscle, nerve, glands, etc.), although equally accessible to
narcosis, are attacked later, long after the functions of the nervous
centres have been abolished. Under all circumstances, however,
excitability and conductivity are indubitably functions of the proto-
plasm of the axis-cylinder in nerve-fibres also, a conclusion that
is significant in regard to certain theories to be discussed below.

III. INFLUENCE OF VARIOUS CONDITIONS UPON EXCITABILITY

OF NERVE

If the effect of certain poisons thus leaves no doubt that the
central and conducting parts (cells and fibres) of the nervous
system differ essentially in their physiological properties, the same
conclusion is no less obvious from the consideration of many other
circumstances which influence the excitability and conductivity of
the nervous centres. Temperature is of the first importance ; its
marked action on the functions of all living matter is well
known. The fact that frogs exhibit differences of reflex excitability
at different temperatures, preserving it generally longer at low
temperature than at high, has long been familiar, but accurate
observations on the point are wanting, which is the more to be
regretted since the existing data are very contradictory. On the one
hand, it is affirmed that warming of the spinal cord to 24°— 27° C.
increases reflex excitability — the more transiently in propor-
tion as the temperature is higher ; on the other hand, Tarchanow
and Fretisberg find that when the trunk is packed with ice, the
reflexes discharged from the hind limbs are considerably augmented
— a fact which, if true, recalls the effect of cooling on striated
muscle (supra), as discovered by Gad and Hey mans. The point,
in any case, requires further investigation. In the ganglion-cells,

viii CONDUCTIVITY AND EXCITABILITY OF NERVE 77

too, the dissimilatory and assimilatory processes may be affected
in different degree by cooling.

However this may be, it is certain that within a given range
(which is lower for cold-blooded and higher for warm-blooded
animals), increase of temperature produces increase of reflex
excitability. The next point is to determine this range experi-
mentally. Excessive rise and fall of temperature are alike
injurious to all excitable tissues. At high temperatures heat-
rigor (paralysis) overtakes the protoplasm ; excitability is of course
affected at a somewhat lower limit. If a frog is kept for some
time at a temperature of 30°— 38° C., it falls into a state of
apparent death. The heart still beats, but the animal gives no
reaction — even the strongest stimuli have no perceptible effect,
and localised muscular contractions are alone discharged. If the
frog is then placed in cold water for a short time, it soon recovers
all its central functions. Eeflex movements of the throat-
muscles appear first, then spontaneous respiratory movements, and
finally the reflex excitability of the spinal cord is also restored.
Later still the other centres of the medulla oblongata, and last
of all the cerebrum, resume their activity, along with the power
of voluntary movement. This sequence recalls the effects of
increasing venosity of the blood. That the gases contained in
the blood must be quantitatively and qualitatively normal,
has long been recognised in warm-blooded animals as a neces-
sary condition for the normal functioning of certain parts of
the central nervous system, more especially the " respiratory
centre," and if the gas exchanges of the blood are interrupted, i.e.
if an animal is suffocated, a succession of striking excitatory
effects arising in the central organs makes its appearance. These
involve not merely the respiratory centre, vaso-motor centre, etc.,
but the whole of the central nervous system, which falls into a state
of exaggerated excitation. The same occurs (in warm-blooded
animals) when the blood-supply is entirely cut off. Blood — and
blood of normal composition, more especially with regard to its
contained gases — is absolutely indispensable to the preservation
of the functions of the nervous centres ; but it is indispensable in
very different degrees to warm and cold-blooded animals. If we
ligature the heart of a frog, or place the animal in a medium devoid
of oxygen, it long retains the power of voluntary movement-
leaps, swims, feels, etc, Interruption of the circulation does not at

78 ELECTRO-PHYSIOLOGY CHAP.

once abolish the functions of the central nervous system. The
entire blood-supply of a frog may even, as Cohnheim pointed out,
be replaced by physiological salt solution, and the normal functions
of the nerve-centres will none the less continue unchecked for
hours at a moderate temperature. If the experiment is inordi-
nately prolonged, the reflex functions are gradually extinguished.
But even when the aorta has been obstructed for hours, or after
prolonged exposure to a deoxygenated atmosphere, the frog will
recover completely. The functions of the great nerve-centres are
first attacked, and much later, the peripheral excitable parts (nerve
and muscle). The different elementary constituents — tissue-ele-
ments— again are variously sensitive to the cutting-off of the blood-
supply, and resulting changes in metabolism. Some die quickly,
as the gray matter of brain and cord ; others more slowly, as the
peripheral nerve-trunks and muscles. In warm-blooded animals
the phenomena are essentially the same, but they occur much more
rapidly; here, too, the central system is first to die, and then the
peripheral nerves and muscles. This is true, both of amemia, and
of the asphyxia due to poverty of oxygen in the blood. Stenson's
experiment is a good illustration of the first of these. If the
abdominal aorta is ligatured in a warm-blooded animal, paralysis
of the hind limbs occurs in a few minutes, although excitability
and conductivity of nerve-trunks and muscles remain perfectly
normal.

The dependence of the central nerve-cells upon the blood is
indicated in the anatomical distribution of vessels within the
white and gray matter of the central organs, as well as by
the vascular poverty of the peripheral nerves. It is known,
moreover, that a protracted interruption of the blood -supply
induces more or less definite histological changes in the ganglion-
cells of the gray matter of the spinal cord in warm-blooded
animals : these may even disappear altogether (degenerate), while
the fibres of the white matter are still intact (36).

The facts thus briefly summed up show that the organ of
reflexes, the automatic central structure of the brain and spinal
cord, differs in a marked degree (and that by a whole series of
characteristic peculiarities in excitability and conductivity), if not
fundamentally, from other excitable parts of the nervous system.
The central nerve-cells are peculiarly susceptible to certain poisons.
Strychnin specifically affects the excitability of the ganglion-cells

vin CONDUCTIVITY AND EXCITABILITY OF XERVE 79

of the spinal cord, while it has little appreciable action on nerve
and muscle ; anaesthesia notably attacks the central structures
first, and the heart, peripheral nerves, and muscles at a later
period only. The same facts are met with when the temperature
is raised above a certain limit. Finally (and this is perhaps the
most characteristic), the amount of gas contained in the blood is
of the utmost importance to the excitability of the nervous centres,
which, more especially in warm-blooded animals, are so extra-
ordinarily sensitive to changes in their normal metabolism
(whether from aiuemia or from dyspnoeic condition of the blood)
that they can, in this respect, hardly be compared with the peri-
pheral nerves and muscles.

Accepting the highly probable assumption that the central
and peripheral nerve-fibres are, in the main, alike in physiological
properties, as also in structure and origin, it is easy to understand
why the motor consequences of direct excitation of the central
organs, and more especially of the spinal cord, should differ
in many respects from those of direct excitation of the peri-
pheral motor nerves, and should appear to depend essentially
upon the same conditions as reflexly-provoked movements. This
is the immediate outcome of the fact that each motor nerve-fibre
(of the anterior root) is the process of a nerve-cell, and that the
spinal cord can only affect it indirectly through the cell. Dis-
regard of this fact can alone account for the acceptance of the
singular theory that the central nerve-fibres conduct, but are not
excitable.

The contrast is the more striking, since, on the one hand,
the central nervous organs, brain and spinal cord, seem to react in
such an extraordinary degree to the weakest natural " organic "
stimuli, and to propagate the excitation, while, on the other, the
nerve-fibres which participate in the structure of the nervous
centres are scarcely to be distinguished anatomically from those
in the peripheral nerves.

On reviewing the experiments in point, we find that they
all aim at establishing that movements consequent on excitation
of the central organ are not reflexes, and ascertaining safe
objective criteria of sensibility in the animal. Thus Van Deen
tried to exclude the objection just made (re interpretation of
motor effects of excitation from the spinal cord) by a special
method which has since been frequently repeated. He exposed

80 ELECTRO-PHYSIOLOGY CHAP,

the spinal cord of the frog from about the 3rd to the 5th verte-
brae, divided the roots of all the spinal nerves except those of the
sciatic, arid pushed in a small knife horizontally above the lumbar
swelling, so that it divided the dorsal and ventral halves of the
cord. If the knife were then drawn forward in the same
position to the upper boundary of the cord, there would be a free
lobe, composed of the posterior columns, a greater or less propor-
tion of the lateral columns, and gray matter ; which, after
dividing its anterior and posterior ends, could be removed
altogether. In this way the whole posterior (dorsal) half of the
spinal cord, along writh the entering sensory roots, was eliminated,
and the possibility of discharging reflex movements at the seat of
excitation excluded. If the isolated ventral part of the cord was
then mechanically excited, Van Deen sometimes obtained move-
ments of the hind-foot, which he at first believed to be due to
direct excitation of the anterior column. Meantime Stilling drew
attention to the possibility that the highly sensitive anterior roots
of the sciatic plexus might be excited in these experiments by
slight traction of the cord, and Van Deen himself, before the
publication of Stilling's work, had been led by new experiments
to the remarkable conclusion that neither the anterior column
nor the other parts of the spinal cord were excitable — thus first
formulating a dogma destined to prevail in physiology for many a
decade.

In subsequent demonstrations Van Deen did not even consider
it necessary to remove the upper dorsal half of the spinal cord,
but employed the uninjured medulla which protruded from the
vertebral canal. Mechanical, chemical, or electrical excitation of
the cephalic end failed, it was said, even with strong currents, to
produce any symptoms of activity in the muscles of the posterior
extremities.

Schiff (37) meantime, without knowing of Van Deen's earlier
publications, arrived at the same conclusions, as the result of
a series of experiments on the spinal cord of different warm-
blooded animals. Total insensibility of the paths which con-
duct painful influences (" sesthesodic "), and inexcitability of the
paths along which motor impulses travel (" kinesodic "), seem
here, too, to be the general rule. Schiff' s experiments were in
the main analogous to the first of Afan Deen's, since he removed
the posterior columns in the partially exposed cord for a distance

vin CONDUCTIVITY AXD EXCITABILITY OF NERVE 81

of 5—6 cm., when the careful application of electrical, as well as
chemical, or mechanical stimuli (pricking, squeezing with forceps)
to the segment of cord under observation failed to produce any
muscular movement, or sign of painful sensation.

The conclusion drawn by Schiff from this experiment, to
the effect that "in such an animal the (painful) sensations
conducted through the spinal cord which has been deprived of
its posterior columns cannot be excited by artificial stimulation
of the cord itself, and that motor excitability is also wanting in the
latter, although it is fully able to transmit a motor impulse," was
under these conditions very natural. It proved, however, im-
possible to excite the entire uninjured spinal cord of a warm-
blooded animal without effect, even after the most careful
removal of the posterior roots, since (according to Schiff's view)
the irradiating fibres of the sensory roots " still invest the
posterior column with a marked degree of sensibility, which
is transmitted farther, and results partly in painful sensations,
partly in reflexes of various kinds, at different levels of the
spinal medulla." Schiff, moreover, differs from Van Deen in
ascribing excitability to the nerve-fibres which run ceutripetally
along the posterior columns. Excitation of these never produces
pain, but causes exclusively tactile sensations, or "kindred sensa-
tions of less intensity," betrayed chiefly by alterations in the size
of the pupil on electrical or mechanical stimulation of the mostly
isolated posterior columns.

Without entering into details of the numerous attempts to
decide the pros and cons of the Van Deen-Schiff theory, we may
state that on the one hand Fick (37), followed by Luchsinger,
brought forward experiments which determined the existence
of directly excitable motor elements in the anterior (ventral)
section of the frog's spinal cord, while on the other a series of
communications from Ludwig's laboratory asserted the excita-
bility of centripetal fibres running in the lateral columns.
It is known that the excitation of sensory nerves frequently
produces a considerable rise of blood -pressure, owing to in-
creased resistance in the arteries from the reflex constriction
of numerous vessels. Dittmar (o7) showed that both electrical
and weak mechanical excitation of the central end of the rabbit's
spinal cord, that has been deprived of its posterior columns for
some considerable distance, produces the same marked rise of

VOL. II G

82 ELECTRO-PHYSIOLOGY CHAP.

blood-pressure. From this he inferred the direct excitability
of the " sesthesodic " elements of the cord, which, according to
Miescher's experiments, are situated chiefly in the lateral columns.

Schiff disputes the validity of this experiment, and more
particularly denies that the centripetal fibres of the lateral columns,
from which the reflex is discharged, can be termed " sensory " in
the true meaning of the word. This, however, is a by-point in the
present connection, where the main object is the determination of
direct excitability. How far Schiff's later objections (in which he
refers the results of Dittmar's experiments entirely to spread
of current to the posterior columns, that are alone excitable) can
be justified, must provisionally be left undecided.

The direct excitability of the motor elements of the spinal
cord has, on the other hand, been firmly established. Pick's early
experiments above referred to, which were essentially founded on
the first of Van Deen's, are open to the objection that the move-
ments of the posterior limbs that appear when the ventral half
of the frog's spinal cord deprived of its posterior columns
is electrically excited, may be due to reflex or direct excita-
tion of the fibres of the motor root — since there might be
spread of current to the uninjured inferior portion of the spinal
medulla. Nor is this objection completely removed by the
fact that on dividing the ventral half of the cord immediately
above the lumbar swelling, and laying the edges together again
as closely as possible, the excitatory effect in question fails to
make its appearance. On the other hand, the experiment of Van
Deen and Fick is fully convincing, under the presumption that
motor fibres run longitudinally -in the ventral portion of the
spinal medulla, and that their physiological properties coincide in
all essential points with those of the peripheral nerve-fibres. And
since there is no doubt (infra) that the excitability of peripheral
nerves is considerably greater in the immediate proximity of a
fresh section than along the continuity of the nerve, it is to be
expected, if the motor fibres of the cord give a similar reac-
tion, that electrical excitation will take effect at the cut end of
the isolated ventral half of the cord sooner, i.e. with less in-
tensity of current, than at a lower point, where — seeing the
closer proximity of the roots of the sciatic — the danger of
direct excitation by current diffusion is proportionately greater.
Biedermaim (37) found, as regards excitability to tetanising in-

vni CONDUCTIVITY AXD EXCITABILITY OF NERYK 83

duction currents, that the divided anterior columns of the frog's
spinal cord gave — apart from quantitative differences — a reaction
precisely similar to that of any peripheral motor nerve. If, with
descending direction of the " break " shock, the electrodes con-
nected with the secondary coil are (at not too great a distance)
so placed that one is at first actually applied to the section,
and are then moved farther and farther away, the initially
marked effect of excitation diminishes rapidly, and soon dis-
appears altogether. The first effect of stimulating with currents
which, if directly applied to the free surface of the muscle,
produce no visible excitation, and which are not felt by the
tongue, invariably consists in a more or less pronounced tetanic
disturbance of the muscles of the two posterior extremities, often
amounting to regular tetanus. Stronger excitation often evokes
co-ordinated movements. When the just effective stimulus at
the transverse section of the anterior column has been determined,
the electrodes (with descending direction of break shock, which
alone acts at first) can usually be shifted into the im-
mediate proximity of the lumbar enlargement — thereby greatly
increasing the danger of direct or reflex excitation of the anterior
roots — without producing any trace of excitatory phenomena in
the muscles of the hind limbs. This, however, is only the case
if the electrodes are shifted along the ventral surface of the
anterior column. If they are applied to the inner surface, i.e.
the cut section of the ventral half of the medulla, in direct
contact with the exposed gray matter, there is never a perceptible
difference of excitability at points near the cross-section, as com-
pared with the deeper parts. It is doubtful whether this experi-
ment by itself justifies the conclusion that in the last case the
gray matter is directly excited, while in the former there is cer-
tainly excitation of the longitudinal nerve-fibres (in the anterior
columns).

By using proper precautions we can thus excite the spinal
cord of the frog (divided below the medulla oblongata, but
not otherwise injured), without fear of complication by reflexes.
It is sufficient to shift the exciting electrodes along the ventral
surface of the cord, after determining that distance of coil at
which the descending break shock takes effect in the immediate
proximity of an artificial cross-section, at any point. The ex-
citation of any other point along the cord, even close to the

84 ELECTRO-PHYSIOLOGY CHAP.

lumbar swelling, is then absolutely ineffective. If these experi-
ments establish the presence of directly excitable motor elements
in the ventral half of the frog's spinal cord, it is on the other
hand undeniable that there are important differences as regards
both excitatory conditions and the natiire and mode of the
reaction, according as the muscle is stimulated by excitation of its
motor nerve, or through the spinal cord. The comparative in-
efficacy of mechanical and of single electrical stimuli, as well
as the total failure of chemical excitation, must be remembered.
Nor is this surprising, since the motor fibres of the cord
are not, like the peripheral motor nerves, in direct connection
with the muscle, but are interrrupted by ganglion -cells (as
proved, more especially by the observations of Birge, for the frog).
This view is supported by the far-reaching analogies which 'exist
with regard not merely to time - relations, and distribution,
in direct (i.e. with excitation of the motor elements of the cord)
and in reflex muscular movements, but also to the conditions of
discharge in the two cases.

With reference, first, to time -relations, we have already
seen that the transmission of the excitatory process from sensory
to motor fibres, via nerve-cells, takes up a considerably longer
period than the simple conduction of excitation through a corre-
sponding length of nerve. Mendelssohn (37) has recently found
that the reaction-time of the ventral half of the frog's spinal cord,
i.e. the interval between the moment of excitation and the appear-
ance of the gastrocnemius twitch on one side, is shorter than the
reaction-time of the dorsal half. In other words, excitation of the
ventral half of the spinal cord produces movement of the limbs
more rapidly than when the same stimulus is sent into the corre-
sponding point of the dorsal segment. The difference, according
to Mendelssohn, amounts to Q'01-0'025 sec. This reaction
indicates that (in accordance with theoretical presumptions) the
muscular contraction due to direct excitation of the anterior
column makes its appearance earlier than the reflex contraction
discharged from the posterior column, the cause of the delay in
the last case being the larger mass of interpolated gray matter.

The most significant factor in judging of the differences that
result from stimulation of the spinal cord, and direct excitation of
the peripheral motor nerves, is the fundamental difference in the
physiological properties of nerve-cells and nerve-fibres, the former

vm CONDUCTIVITY AND EXCITABILITY OF NERVE 85

being much more sensitive to changes in their normal metabolism,
as well as to any kind of injury, than the latter. This is, how-
ever, most conspicuous on comparing the excitability of different
parts of a motor organ (consisting of nerve-cells and fibres, along
with their peripheral terminations in the muscle), solely with
reference to the excitatory effects which each exhibits. It must
obviously depend upon the momentary state of excitability, or
conductivity, of the cellular elements interposed along the fibres,
whether an excitation on the distal side of the same will produce
any excitatory movement or no. And in fact \ve see that the
reflex functions of the spinal cord may suffer, or be entirely
abolished, under certain conditions, while excitability and con-
ductivity in the motor and sensory portions of the reflex arc are
not perceptibly affected. Luchsinger applied this unequal capacity
of resistance in central nerve-cells and fibres to prove the direct
excitability of the cord after local destruction of the reflex
functions. Various cold-blooded animals with a long spinal
column (snakes, blind-worms, tritons, etc.) were decapitated, the
fore-part of the body being then plunged into salt water heated
to 40°-45°, while the rest of the body was kept at normal
temperature. The warmth soon destroyed the reflex properties
of the cervical and dorsal medulla, while excitability and con-
ductivity were still presumably intact in the long medullated
fibres. If (as usually occurs) electrical excitation of that part of
the medulla which no longer discharges reflexes can cause move-
ments of the tail, these can only (according to Luchsinger) be
due to direct excitation of the longitudinal motor fibres of the
spinal cord. Schiff objected that the testing of reflex capacity
in this part of the body by stimuli applied to the skin is no sure
guarantee of the total destruction of the reflex functions of the
spinal medulla. He pointed out the possibility of "mtra-medullary "
reflexes, which only fail to appear within the warmed segment,
because its muscles are rigored by the previous exposure to heat.
Schiff adduces experiments on bombinators and toads, in which,
after warming the entire cord exclusive of the peripheral end of
the can da eqtdna till the trunk-muscles were completely rigored,
the reflex excitability of the hind limbs still persisted.

Nevertheless the low resistance in the gray matter of the
cord, as compared with that of the white mass of the fibres, is
indisputable. By this, inter alia, we may explain the fact that

86 ELECTRO-PHYSIOLOGY CHAP.

the motor effect of direct excitation of the spinal cord appears the
more plainly in the muscles of the posterior extremities, in
proportion as the reflex excitability of the preparation is greater,
while it fails altogether when the latter is extinguished. Accord-
ing to Birge's experiments (supra), the same elements of the gray
matter .of the lumbar cord (nerve-cells of the anterior horns) must
convey the excitation in the one case from centripetal, in the
other from centrifugal fibres, to .the same fibres of the anterior
root. The reflex centre of the posterior extremities would there-
fore not merely be thrown into excitation from periphery to
afferent nerve-path, but also, as it were, possess two poles, one cen-
tral (the motor paths in the cord), the other peripheral (the sensory
fibres). All injuries that involve central conductivity are equally
prejudicial to the effects of reflex and of direct excitation of the
spinal cord.

The extraordinary sensitiveness of the central nerve -cells
of warm-blooded animals to all disturbance of normal nutrition
indicates a priori (as is confirmed by Stenson's experiment) that
conductivity in the spinal cord will diminish and be abolished
much more rapidly in all paths interrupted by ganglion -cells,
under certain influences (especially anaemia or asphyxia), than
it is in cold-blooded animals, so that experiments on the
direct excitation of the cord involve much greater difficulties,
and fail much more easily, than in the latter. Moreover, it
is clear that the rapid and total interruption of the blood -
supply to the spinal cord (taking precaution to avoid the
cerebral circulation, and with artificial respiration), affords a
working method of ascertaining the uninterrupted conducting
paths in the medulla after exclusion of the others. For con-
ducting paths which are blocked in a few minutes by anaemia
cannot be regarded as the direct continuation of peripheral
nerve-fibres. It is far less probable that a medullated fibre of
the white columns of the cord should react differently to
amernia from the like fibre of a peripheral nerve, than that tin-
functional disturbances that are induced by an;emia so much
earlier in the cord than in the peripheral nerves should be located
in the interpolated cells of the gray matter. And S. Mayer's
experiments on the effect of antenna produced on the rabbit's
spinal cord by ligaturing the aorta high up, do in fact show that
vuso- motor fibres originate in the medulla oblongata, and

viii CONDUCTIVITY AXD EXCITABILITY OF XKltVE S7

traverse the spinal cord without interruption from ganglionic
elements.

These facts respecting conductivity of excitation within the
nervous centres suggest important conclusions as to the ana-
tomical arrangement and reciprocal relations of the conducting
paths. Starting with the fact that every nerve-fibre is connected
inside or outside the central organ with at least one ganglion-cell
(its parent -cell), it may be assumed that every reflex arc is
built up of nerve -cells, and that these (especially the motor
cells) are under the most favourable conditions for mutual
conduction.

Histological investigation has so far contributed very in-
adequate support to this physiological postulate. It was indeed
natural to regard the great multipolar ganglion -cells of the
anterior horn, along with their numerous ramified " protoplasmic
processes," and Deiter's axis -cylinder process passing directly
into an anterior root - fibre, as the elements through which
the functionally distinct nerve -fibres from the periphery are
anatomically related at the centre. This view is expressed in
Gerlach's theory, which represents the protoplasmic processes
of the ganglion -cells as forming a rich network of the finest
nerve-fibrils, connecting the cells of the anterior horn not merely
with one another, but also with the posterior root-fibres, which
also, according to Gerlach, terminate in a fine fibrous network
after their entrance into the gray matter. Eecent researches into
the finer structure of the nervous centres (Golgi, Ramon y Cajal,
Kolliker, Retzius, and others) have substantially modified the
earlier doctrine of Gerlach in certain important physiological
particulars. There is no proof of a central nervous network, as
the anatomical substrate of irradiation of excitation. The cell-
processes (nerve-fibres) which arboresce within the gray matter
seem all to terminate freely, without anastomosing with the
processes of other nerve-cells. Certainly it can only be said at
present that no anastomosis has yet been detected ; its non-
existence may be questioned, in view of the wealth of ramifications
exhibited by the protoplasmic processes. Golgi indeed denied
the " nervous " nature of these processes, but his opinion must be
disallowed, since in many cases all the processes are of the same
character, and the nerve-fibre may even (as in the giant electrical
ganglion-cells of Malaptci-urm} spring, not from the body of the

88 ELECTRO-PHYSIOLOGY CHAP.

cell, lint from the protoplasmic processes that interlace in a close
network.

The physiological connection of the central motor elements is
still, therefore, an open question, while the nature of their relations
with the afferent (sensory) fibres may be regarded as histologically
established.

The posterior root-fibres, which must be regarded as processes
from the cells of the spinal ganglia, bifurcate (according to Ramon
y Cajal and Kolliker), as they enter the cord, into two branches,
running respectively upwards and downwards in the mass of the
posterior column. These longitudinal fibres give off ("collateral")
branches — mostly at a right angle — which enter the gray matter,
and terminate in free dendritic ramifications (Kdlliker's " arborisa-
tions"). The similarity of these bouquets to the terminal expansion
of the axis-cylinder in the striated muscles of vertebrates at once
suggests a similar relation with the motor cells of the spinal cord.
Kolliker, indeed, maintains that the twigs of an arborisation (which
usually carry a small swelling) are closely interlaced with the
ganglion-cells, but never really anastomose with these or their
processes. Contiguity is, however, indispensable to transmission
of excitation. " Radiation " (Anstralilung} from a free nerve-
ending to another that merely lies near it (as in the olfactory
giomeruli), or to a cell (as in the simple reflex arc), is an assump-
tion the less justifiable since there is no sufficient histological
•evidence for a hypothesis so divergent from all prevailing views on
conductivity of excitation.

Since each nerve-fibre represents the process of a cell, and
forms with the same a physiological unit (neuron, neurodendron),
it is intelligible that a nerve-fibre separated from its parent-cell
should sooner or later undergo degeneration. Each nerve-cell is
thus the " trophic " centre of the outgoing nerve-fibre, and the
normal connection between them is one of the most essential
conditions of the permanent preservation of conductivity and
excitability in the nerve-fibre. In view of the facts above cited,
we can hardly doubt that this trophic influence is largely due to
the action of the nucleus, as follows, indeed, by analogy with other
cells.

Seeing the extraordinary instability of the central ganglion-
cells, the resistance which in peripheral mednUntc<l nerve-fibres
preserves the fundamental vital properties (provided the nerves are

vin CONDUCTIVITY AND EXCITABILITY OF XERVE 89

protected from drying, and other injurious circumstances) is very
striking, and emphasises the radical physiological differences
between the two. Excitability and conductivity will, in a nerve-
trunk which is isolated for a considerable length, and connected
only at one end with its terminal organ (in which the circulation
is wholly abolished), persist for hours, even in warm-blooded
animals.

Non-mcdulliiti'd nerves, on the other hand, are far more
perishable. The nerves of crayfish and lobster, at least, do not
maintain their excitability for even approximately so long a time
as frog's nerves, when isolated and stimulated. Piotrowsky found
the experiment quite impossible in summer, while excitability
disappeared in winter after 8—10 min. Kiihne also found the
iion-medullated olfactory nerve of the pike to be excitable for a
very short time only.

It is evident that we can estimate the true duration of survival
in an excised nerve only when the nerve alone, and not the
terminal organ (which is the sole indicator of activity in the
former), is withdrawn from normal conditions of nutrition. No
certain conclusion as to survival in an excised warm or cold-
blooded nerve can therefore, as a rule, be formulated from
observations on a perfectly isolated nerve-muscle preparation : the
muscle obviously becomes inexcitable long before the nerve.

The fact that nerves, when removed from their natural situa-
tion and laid across the electrodes, remain excitable for hours even
in warm-blooded animals, points to an enormous power of resistance,
and it follows that the medullary sheath is an effective means of
protection.

If any excitation, best an exactly measurable electrical stimulus,
be employed to test the excitability of a nerve which has been
separated from its centre, by observing the gradual alterations in
the reaction of the terminal organ (e.g. muscle), the alterations of
excitability at any one point of the nerve, as well as at different
points along its course, will be of a very involved character. The
simplest hypothesis, as regards the former, is that the excita-
bility of every particle of the nerve sinks in time by regular
gradations to zero. Certain observations of Rosenthal (38)
appear to contradict this theory, as showing that a considerable
increase of excitability precedes its diminution, at every point.
Biedermann, however, like Mommsen and more recently Werigo

90 ELECTRO-PHYSIOLOGY CHAP.

(39), was not convinced of the accuracy of this last statement,
and invariably found (if desiccation and all injurious influences
were as far as possible excluded) a slow and regular fall of
excitability at any point of the nerve, so far as could be
determined on an excised frog's nerve -muscle preparation by
comparing the heights of twitch, on stimulating with single sub-
maximal induction shocks of uniform strength. Another fact,
on the contrary, is easily confirmed. Valli, Pfaff, and Bitter
observed that any (motor) nerve, after the death of the
animal, or simply after separation from the central organ,
invariably lost its capacity to produce twitches in the correlated
muscle, on stimulation, first in its central parts, next in the
brandies, last of all in the ramifications by which it terminates in
the muscle. This centrifugal march of death in the nerve (Valli
and Bitter) might be expected' at a very different rate in different
animals, i.e. it is quickest in warm-blooded, slowest in cold-
blooded creatures, the nerves of the latter retaining their excit-
ability for days when protected from evaporation at low
temperature. The interpretation of these observations is less
simple than might be concluded at first sight. Du Bois-Beymond
pointed out the possibility that the dying nerve might not be able
to transmit excitation over as extended tracts as the normal
living nerve, and Mommsen (I.e.}, as well as Szpilmann and
Luchsinger (22), afterwards subscribed to the same opinion. And,
in fact, all phenomena corresponding with the Bitter- Valli law
may be interpreted without difficulty under the presumption of
an equal fall of excitability at all points, assuming only that
conductivity sinks more quickly than the power of direct
response.

At a further stage of dissolution, visible anatomical changes,
known as fatty degeneration, occur in the nerve (more especially
when medullated) that has been separated from its centre. If a
mixed nerve is divided at any point, and the peripheral trunk
examined after some days or weeks, the fibres will throughout be
found uniformly altered, and the medullary sheath broken up or
whollv disintegrated. The remains of the sheath will be visible

\j O

as spindle-shaped lumps upon the fibre, in which, along with flakes
of medulla, there are drops of fat of different sizes. Eventually,
the connective tissue alone remains, all nervous structures having
vanished. If the alterations in the central end of the divided

vin CONDUCTIVITY AXD EXCITABILITY OF XERVE 91

nerve are simultaneously investigated, they will be found only in
the immediate neighbourhood of the cut surface, and are but little
developed ; further on, the fibres show hardly any perceptible
changes, and the nerve also remains permanently excitable.

"Waller's investigation of the roots of the spinal nerves threw
much light on the subject, showing plainly that the ganglion-cells
exert a "trophic" influence on the nerve-fibres connected with them,
as indeed does every nucleated cell upon its non-nucleated pro-
longations. Degeneration of the peripheral end invariably follows
the division of the anterior root of a spinal nerve, while the
central end, which is still connected with the cord, remains normal.
After dividing a posterior root the consequences vary according
as the section is between spinal cord and ganglion, or is peripheral
to the latter. In the first case the central end, which is connected
with the cord, degenerates, and the degenerated fibres may be
followed a long way into the cord itself (in the posterior columns) ;
the end connected with the ganglion, on the contrary, like the
ganglion itself, is unaltered.

After dividing the nerve on the peripheral side of the ganglion,
the end connected with the latter is not affected, while the
peripheral end degenerates. From repeated experiments, there-
fore, we must conclude that the cells of the spinal ganglion are
the parent-cells (or trophic centres) of the posterior root-fibres,
while the cord, and its large multipolar cells in the anterior horn,
are the trophic centres of the anterior root-fibres. This agrees
with the development of the fibres, since the spinal ganglia
comprise the true parent -cells of the posterior roots. The
degeneration of divided nerve -trunks has been successfully
employed in vertebrates to discover the course of certain bundles
of fibres within the central organ (spinal cord), by means of the
easily -recognised alterations of the medullary sheath. The
arrangement of the posterior columns of the cord has been very
accurately determined by this method.

We have thus far assumed that a nerve-fibre must be perfectly
homogeneous under normal conditions from its origin to its end,
at all points of its course, i.e. that it presents no essential
differences in regard to excitability and conductivity. This pre-
sumption is indeed not justified. We have long been in
possession of certain facts which show that different parts of the
nerve are anything but homogeneous. The sole gauge of

92 ELECTRO-PHYSIOLOGY ''HAP.

excitability is, of course, the reaction of the terminal organ as
discharged by a stimulus of definite magnitude, and nearly all
experiments bearing on this point relate to electrical excitation of
motor nerves — the electrical stimulus being the sole test that is
sufficiently accurate. The relations to be determined at any
point of the nerve between magnitude of stimulus and magnitude
of effect coincide in the main with those shown above to obtain
in direct excitation of the muscle. If a tract of nerve is stimulated
by gradually increasing single induction currents, it will be found
that currents of which the intensity lies below a given limit
(" limiual " value) do not excite, while with increasing current
intensity the height of twitch is also augmented — the rise, according
to Tick (40), being proportional within a certain range, while, accord-
ing to Hermann (40), it is at first rapid and then more gradual.
The connecting line between the summits of the single twitches
would thus, according to Tick, rise obliquely to its maximum,
according to Hermann it would form a curve concave to the
abscissa.

Seeing that there is a discharge of potential energy in excita-
tion of nerve, as in direct excitation of muscle, and indeed in any
excitation of living matter, it is a priori evident that there can
be no constant relation between strength of stimulus and
effect. The excitability of a nerve can only be compared with
other organs, or nerves, or -different points of the same nerve,
by employing the " liminal value" of the electrical stimulus as
the (reciprocal) measure of excitability. Eosenthal (41) was
thus able to establish the fact that the specific excitability of
nerve-substance is greater than that of striated muscle, or, as it may
be expressed, that the indirect is greater than the direct excitability
of muscle. Eosenthal applied the sciatic nerve longitudinally to
a curarised gastrocnemius. Induction currents were then led
through both nerve and muscle, which, as the resistances of the two
were approximately equal, were proportionately distributed between
both sections, i.e. current flowed in both tissues at equal density.
The indirectly excited muscle first began to twitch as the
current was gradually strengthened by pushing up the coil, i.e.
nerve responds to weaker electrical excitation. The results
obtained by this method at different points of the same nerve are
also of interest.

Budge (42) observed that "the sciatic nerves are more

VIM CONDUCTIVITY AND EXCITABILITY OF NERVE 93

excitable near the point where they leave the spinal cord than
lower down, and at this last point again than at a still lower place,
etc." He concluded that "greater force must be employed to
evoke a twitch, in proportion as the seat of excitation is further
from the spinal origin of the nerve, or (which is the same thing)
nearer to its insertion in the muscle." He found, moreover, in the
course of his experiments that certain points in the nerve " are
much more excitable than others lying both above and below
them, while others again are characterised by great inexcitability."
These last he termed " nodal points." The excitation of one point
of a nerve at a given strength of current will often discharge a
perceptible twitch, while a point 1 mm. off, with the same strength
of current, gives no sign of contraction. One point especially

FIG. 163.

noticeable in this connection lies in the middle third of the thigh,
where the nerve gives off a large branch. Another such is
commonly found near the starting-point of the motor roots.
Pf! tiger (43) subsequently summed up all these facts in the dictum
that " the same stimulus, applied in succession to two different
points of the nerve, does not excite the muscle in the same degree ;
that excitation is the more effective which is applied at the point
most distal to the muscle." The highest tract alone, next to the
section, was relatively less excitable. According to Pfliiger, the
curve of excitability drawn from the nerve as abscissa would,
therefore, resemble Tig. 163. There is a depression at the point
where the branch is given off to the thigh. It is questionable
whether the ordiuates of this curve can really be regarded
as a direct measure of excitability. It is evident that they
express only relative magnitudes of stimulation -effects at the
different points of the nerve, two explanations of the diminution
towards the periphery being conceivable. Either the excitability
of the nerve is greater in proportion as the point stimulated
lies nearer the central organ, or the same stimulus calls out

94 ELECTRO-PHYSIOLOGY CHAP.

the same strength of excitation at all points of the nerve,
while the excitation itself increases with the distance from the
motor organ (muscle). Pfl tiger decided for the last alternative, and
concluded from the above facts that the excitation gathers strength
in its passage down the nerve (" avalanche theory "), although the
contrary would a priori be expected. The avalanche-like increment
would, as Hermann pointed out (Handbuch, ii. 1, p. 113), justify
the important conclusion " that conduction depends not simply
upon an undulatory movement propagating itself from particle to
particle, but upon the independent discharge of potential energy in
the nerve, from which it follows that the transformed energy in
each consecutive element of the nerve is slightly greater than in
the preceding element." The wide bearing of this conclusion
makes it essential that the underlying facts should be thoroughly
sifted. Heidenhain (44) referred the cause of the greater activity
of the higher tracts of divided nerves to the proximity of the
artificial section. " The lower end of the nerve at once exhibits
the same marked activity as the upper end, if a section is made
lower down ; excitability is raised near the section. The distance
from the divided end is not, therefore, the determining factor in the
magnitude of effect," and this applies to each stage of the survival
of rnedullated nerve. The cause of this marked action from the
cross-section will be discussed below, in considering the effect of
electrical stimulation upon the excitability of the nerve.

Given that the unequal excitability of different points of the
divided nerve is conditioned by the cross-section, there is on the
other hand evidence to show that regular, local differences of
excitability exist in the undivided nerve as well, the points at
which branches are given off being in particular characterised
by irregular excitability. According to Heidenhain (/.c.), excit-
ability in the frog's sciatic is, as a rule, higher in the upper
two -thirds than in the lower third. The curve shows a
turning-point somewhat above the bifurcation of the sciatic into
peroneal and tibial branches. It is lowest at this point, highest near
the point of departure of the branches to the thigh (Fig. 164).
Still more complicated, according to Hermann and v. Fleischl (45),
is the curve of excitability of uninjured nerve, since the direction
of the exciting currents is also of extreme importance to the
magnitude of the effect. Descending induction currents are
particularly effective at upper points of the sciatic, ascending

vin CONDUCTIVITY AND EXCITABILITY OF NERVE '.if,

currents at lower points. V. Fleischl, indeed, makes the matter
still more complicated by dividing the entire nerve into a number
of segments, each of which is more susceptible to the descending
current in its upper half, to the ascending current in its lower, and
to both currents equally at the centre ("equator").

In view of these several experiments it seems a priori most
probable that excitability in the
normal nerve of the living animal
is equal at all points of its course.
Electrical excitation is really less FIG. 104.— curve of excitability along the

. . . ' sciatic nerve. (Hriilenhain.)

fitted tor determining this than

chemical or mechanical stimuli. With the last, Tigerstedt (46)
has actually ascertained the equal excitability of all points of the
uninjured nerve. There is therefore no " avalanche " increment
of excitation, or, at least, no fact is known which compels us to
assume its existence.

Certain differences (which seem, however, to be caused less by
local disparity of the true excitable substance of the axis-cylinder
than by local irregularity of development in the investing
medullary sheath) do nevertheless exist between the central and
peripheral tracts of nerve. These are indicated not merely by
histological evidence (Clara Halperson, 47), but also by the fact
that the upper end of the frog's sciatic is more susceptible to the
action of poisons (alcohol, etc.), than the deeper segments.

The observations of Clara Halperson show for electrical, and
those of Efron (48) for other (chemical, thermal, mechanical)
stimuli, that the responsive capacity in the upper segments of
the nerve is greater in itself, and is raised more rapidly, and to a
higher degree, by reagents which augment excitability, as well as
by heat, than is the case in the lower segments.

The application of toxic substances, or of cold, again takes
effect sooner in the upper segments. Efron found, e.g., with
two frog's nerves (of equal length and equal excitability), one of
which was treated above, and the other below, with dilute amyl
alcohol, that the excitability of the upper tract of the nerve dis-
appeared completely, while that of the lower was still uninjured.
In view of the intimate connection between excitability and
conductivity, it is not remarkable that conductivity should be
differently affected in the upper and lower parts, like excitability.
According to Efron, who depressed the excitability of the middle

96 ELECTRO-PHYSIOLOGY (HAP.

tract of the nerve by treatment with amyl alcohol, and compared
its local capacity of response with excitability at two other points
of the nerve, above and below, excitability diminishes in the first
place more rapidly than conductivity, since (as in Griinhagen's
experiment with local C02 narcosis) the excitability of the injured
point is considerably reduced, at a time when it still appears to
be unaltered at the upper point. At a later stage, on the other
hand, there is an opposite reaction : conductivity is totally
abolished, while local excitability persists in a low degree.

IV. EXCITABILITY IN DIFFERENT NERVES

All these facts regarding excitability of nerve-fibre relate to
the usual frog's nerve-muscle preparation, i.e. gastrocnemius muscle
and sciatic nerve. If we take the whole limb, and test the
reaction of the other muscles supplied by the same nerve, with
different strengths of current, the same intensity of stimulus does
not throw all the muscles simultaneously into excitation ; on the
contrary, weak stimuli applied in the leg of the frog to the
common nerve -trunk produce movement in one functionally
co-ordinated group of muscles, i.e. the more excitable, while
stronger excitation causes movement of another functionally com-
bined, but less excitable, group of muscles. The first set comprise
the flexors, as was pointed out by Bitter at the beginning of the
century, the second the extensors. His often confused remarks,
wThich are interwoven with the mystical speculations of the natural
philosopher, culminate in the notion of an excitability "limited,
conditioned, and finite " of the flexors, " unlimited, unconditioned,
absolute " of the extensors. Bitter's conclusions have been
frequently contradicted, amongst others by du Bois-Beymond, who
refers to them in his great work as highly improbable, urging that
they should be rejected until fresh and unimpeachable experiments
should be forthcoming.

This task was undertaken in 1874 by Bollett (49), who
rescued the investigations of Bitter from oblivion, and confirmed
them by numerous experiments. He did not, like Bitter, employ
the constant current, but a rapid succession of tetanising induction
currents. With these it is easy to ascertain that minimal stimuli
first send those muscles into tetanus which move the foot
and tendon forwards and upwards, and also abduct the toes

vni CONDUCTIVITY AXD EXCITABILITY OF NERVE 97

(M. tibialis antic., perouseus, flexor tarsi anterior and posterior, M.
exteusores, abductores digit, and iuterossei) ; with stronger excita-
tion of the common nerve, on the other hand, the extensors of the
foot move backwards and downwards along with the adductors
of the toes. The first group (" flexors ") are mainly, if not
exclusively, supplied by the peroneal nerve, the second by the
tibial nerve, so that in this preparation (frog's leg) all, or at any
rate nearly all, the fibres which subserve the antagonistic groups
of muscles are found in the two primary branches of the
common nerve. In subsequent experiments Kollett recorded
the isolated contractions of the antagonistic groups of muscles,
showing that only the flexors really contract at first, and not the
extensors ; increase of stimulus iuduces weak extension along
with more pronounced flexion, and finally the extensor exceeds
the flexor contraction. By making the antagonist muscles
work against each other on the same lever (antagonistograph),
and record the effects of this opposite action, Eollett finally con-
vinced himself that when the nerve is excited, the flexors respond
to weak stimuli with a greater yield of work than the extensors.
The flexor movements increase with augmentation of stimulus up
to a certain point, at which they are overtaken by the extensors ;
there is an intermediate stage of " struggle " between the anta-
gonistic reactions. The same differences in excitability of flexors
and extensors obtain in the rabbit ((/. Frl. Volklin, Hermann's
Handb. i. 1, p. 113). Mechanical and chemical stimuli produce
the same effect as electrical excitation (Osswald, 50). Osswald,
by careful graduation of the shocks from an apparatus modelled
upon Heideuhain's tetano-motor, succeeded (with minimal excita-
tion of the nerve) in evoking flexor movements from frogs
as well as toads, which changed to extensor movements on
gradually increasing the stimulus. The extensors ultimately got
the upper hand, and tetanus in extension made its appearance.
The same effect was produced by chemical stimulation with sodium
chloride and other salts.

Similar differences in the excitability of the nerve -muscle
organ appear with other antagonistically working muscles.
Griitzner (51) found that during weak excitation of the vagus
the constrictors of the glottis, during stronger excitation the
dilatators, contracted. Frankel and Gad (52) showed that the
effect of gradually cooling the recurrent nerve was to cut out the

VOL. n H

98 ELECTRO-PHYSIOLOGY CHAP.

crico-arytaenoideus posticus muscle earlier than the constrictor of
the glottis, and Semon and Horsley (53) determined a peripheral,
differentiating action of ether upon the laryngeal muscles in the
same sense.

The differences of excitability in functionally differing nerve-
muscle organs are, however, most striking iu certain invertebrates,
and most of all in the claw of the crayfish. Eichet and Luch-
singer (54) first observed that weak excitation of the claw-nerve
opened, and stronger excitation closed, the claw. Tick (55), who
had made objections (subsequently shown to be unfounded)
to Eollett's first experiments on the frog's leg, tried to explain
the observations of Eichet and Luchsinger on purely mechanical
grounds, as due to the anatomical relations of the excited muscles.
This, however, was easily disproved (Biedermann, 56). If the
claw-nerve is excited with the alternating current of an induction
coil, by inserting two platinum points through the second or
third joint (after arranging for the simultaneous graphic record of
the changes of form in both antagonist muscles, by means of
separate levers for each muscle) the same fact appears as in the
normal uninjured claw, i.e. as a rule the abductor muscle con-
tracts with weaker, the adductor with stronger excitation of the
nerve.

When the current is strengthened by gradually pushing up the
coil, the response to excitation being read off each time, it is found
in a muscle free of tomis that the abductors alone react at a given
distance of coil. With further strengthening of stimulus, the
effects increase up to a certain limit, and then decrease and finally
disappear, without any simultaneous change of form in the
adductor muscle. The coils may then be brought much closer
together without producing any perceptible excitatory effects in
either muscle. The adductor muscle first comes into play at a
given strength of stimulus, and responds to each subsequent
excitation up to the maximum of current intensity, while the
abductors give no perceptible reaction. The abductor, however,
frequently contracts at the close of excitation, with the coil
pushed home (Figs. 165, 166).

In every such case there is a certain interval of current
intensity, during which neither of the antagonist muscles reacts
to excitation from the nerve. The magnitude of this " neutral
zone" varies in different cases. Moreover, it should be noted that

VIII

CONDUCTIVITY AND EXCITABILITY OF NERVE

99

a neutral period, in the strict sense of the word, is not always
demonstrable, and does not usually exist, as meaning an
interval of current intensity at which neither muscle gives

FIG. 165.— Contraction curves of adductor muscle (upper) and abductor muscle (lower) in the cray-
fish claw, excited from the common nerve with increasing strength of tetanising induction
currents. The figures mark the distance of coil in centimetres.

any sign of response. There is always a given strength of
excitation at which the contraction of both abductors and
adductors is very feeble, but the stimulation is never wholly
ineffective. In such a case a slight alteration of the secondary
coil in one or the other direction suffices to elicit maximal
contractions from either adductors or abductors.

In order to ascertain the presence or absence of a " neutral

FIG. 166. — Contraction curves with indirect, tetanising excitation of adductor (upper) and abductor
(lower) muscles of crayfish claw, with gradual approximation of secondary coil.

zone," it is convenient to excite the nerve continuously, while
steadily pushing up the coil. The abductor muscle is first to

100 ELECTRO-PHYSIOLOGY CHAP.

contract and relax again, after which follows the neutral period,
or else the relaxation of the abductor is immediately followed by
the contraction of the adductor (Fig. 166).

Although the alternation between the antagonist muscles is thus
by no means such that the excitation of the one must inevitably
exclude that of the other, this frequently is the case. And with-
out exception, during maximal excitation of the adductor muscle,
the abductor is quiescent, and vice versa.

The analogous effect of mechanical and chemical stimulation
may be demonstrated here, as in the ordinary Bitter- Eollett
phenomenon. It is always plain that the action of the abductor
muscle preponderates immediately after cutting off the claw,
while at the moment of amputation there is a rapid and transi-
tory adduction.

Obviously there is here a complicated action of the mechanical
stimulus upon the nerves of both muscles, which could only be
analysed after further investigation ; no less striking is the fact
that, in the majority of cases, chemical excitation of the claw-
nerve (by dipping a fresh section of the limb into concentrated
NaCl solution) causes the action of the abductor to preponderate,
although the adductor may be thrown into violent contraction by
the same stimulant, as appears more especially when the abductor
has previously been divided.

The innervation of the antagonist muscles of the crayfish
claw is further complicated by the fact that each of the two
muscles is undoubtedly supplied by inhibitory as well as by
motor nerve-fibres, and these — as regards relations of excitability-
behave in a diametrically opposite manner to the motor nerves.
Both adductors and abductors usually exhibit a kind of tonus,
which appears most plainly after dividing the antagonist muscle.
If in such a case (after cutting through the abductor) the nerve
of the limb is excited with alternating tetanising currents, while
the secondary coil is gradually pushed up to the primary, the first
effect of exciting the nerve will invariably be abduction of the
claw, which under the circumstances can only be caused by the
relaxation and consequent elongation of the adductor muscle. If
the excitation is strengthened by gradual approximation of the
coils, the same effect increases at first, until, at a certain and
generally considerable intensity of current, each excitation causes
a vigorous adduction of the claw which lasts throughout the

vin CONDUCTIVITY AND EXCITABILITY OF XERVE 101

tetanus. If the excitation is weakened again, the opposite effect
occurs, /.c. the muscle relaxes. With the gradual disappearance
of the tonic contraction, the visible excitation effects appear in
one direction only, namely, closure of the claw, i.e. contraction of
the muscle. The same thing of course follows in preparations
where the adductor muscle from the first manifests no perceptible
tonus. In correspondence with the
characteristics of this muscle as cross-
striated, the changes of form described
take place with considerable rapidity.
If they are graphically recorded on a
slowly-moving surface (Fig. 167), the 1 1 , . , I , . , . I , . , . I , ,
curve sinks nearly at right angles at Flo. w.-Tetanising excitation of ad-
the beginning of the tetanus, when the dllctor muscle of crayfish claw in

0 persistent tonic contraction ; suc-

niUSCle Undergoes SUdden and Often cession of brief inhibitions (relaxa-

maximal relaxation. At that strength tion) at eac1' excitation of the nerve"
of current with which the inhibitory excitation passes into its
contrary, the effects are not seldom in both directions, and many
irregularities are manifested.

In cases where the natural tonus is wanting, the inhibitory
effect of stimulating the nerve may sometimes be demonstrated if
the relaxed and resting muscle is artificially thrown into persistent
or rhythmically interrupted excitation. This is easily effected by
including a metronome in the secondary circuit, as well as the
vibrating hammer of the coil, so that groups of induction shocks at
any required rhythm may be sent into the adductor muscle by
means of two platinum points thrust through the chitinous sheath
of the claw. Eegular rhythmical contractions are thus produced,
which can be affected by simultaneous excitation of the nerve in
the same way as the natural heart-beat, by excitation of the vagus.
If, in the preparation in question, the adductor muscle is thrown
into moderate persistent contraction by direct rhythmical excita-
tion, and only oscillates, as it were, about its new position of
equilibrium, in the rhythm of the metronome, a more or less rapid
relaxation occurs at the commencement of inhibitory excitation of
the nerve by tetanising induction currents (as in natural tonus).
This is graphically expressed as a shallow inflection, or as a rapid
fall of the curve, corresponding with complete relaxation of the
muscle. In the first case (as nearly always happens with minimal
excitation of the nerve), the magnitude of the rhythmical variations

102

ELECTRO-PHYSIOLOGY

CHAP.

usually remains unaltered, or at most undergoes some insignificant
changes. With stronger excitation the result is otherwise. There
will then be, along with the relaxation of the muscle and conse-
quent fall of the curve, a perceptible and often considerable
diminution in the height of the individual contractions, which
does not necessarily entail an alteration in rhythm. This may be
carried so far as to render the changes of form in the muscle quite
imperceptible at the time of greatest relaxation, or at most in-
dicated as slight undulations in the curve (Fig. 168). The tracings
obtained from such inhibitory effects not infrequently exhibit a
superficial resemblance to kymographic curves, which show the
inhibitory action of the excited vagus upon cardiac movements.

FIG. 168. — Inhibition of artificial contractions of adductor muscle
of crayfish claw owing to stimulation of the nerve. The
contractions were evoked by direct, rhythmic tetanisatious
of the muscle.

FIG. 169.— As in Fig. 168.
Predominant diminution
of single contractions.

From these observations we learn that diminution of the
artificial rhythmical contractions proceeds pari passu with the
relaxation of the muscle, and the same fact is even more evident
in cases where the muscle has time to relax completely between
two consecutive stimuli. The active inhibitory action then
betrays itself only by a more or less considerable diminution
of the single twitches, or (more correctly) short tetani (Fig. 169).
Such a series of curves reminds us directly of the demonstrations
of Heidenhain and Lowit, on the effect of minimal vagus-excitation
on the rhythmical contractions of the frog's heart, where the
first effect of inhibition is a diminution of the single beats.

The reaction thus described in the muscles of the crayfish
claw (which can hardly be explained otherwise than by the
antagonistic working of two opposite kinds of fibres passing by
the same nerve-trunk into the adductor muscle) is by no means

viu CONDUCTIVITY AND EXCITABILITY OF NERVE 103

without analogy. Pawlow (57) long ago communicated observa-
tions on the adductor muscles of the shell of Antx/mifa, from
which it appeared that these are supplied by two kinds of nerve-
fibres, one motor, subserving shortening of the muscle, the other
inhibitory, running parallel with the first, and counteracting the
shortened state of the muscle, so as to induce relaxation. By
appropriate excitation, first one and then the other effect can be
brought prominently forward. The crayfish claw is, however,
better suited for this demonstration, since its muscles are striated,
and the reaction follows incomparably quicker than in the smooth
and sluggish molluscan muscles, in which, moreover, ganglion-cells
are interpolated between the nerve and muscle, and are not easily
excluded from interference.

Cardiac muscle is also subserved by nerve-fibres of opposite
function and antagonistic action, which in many vertebrates run
in a common trunk, in others again are separate, and bring out
differences of excitability comparable in many respects with the
above. Heidenhain (58), and later on Lb'wit, showed that
minimal excitation of the vagus always resulted in inhibition,
never (under these conditions) in acceleration, of cardiac activity.
The latter only appears with greater strength of current, so that,
under the presumption of two kinds of fibres, it may be said that
the inhibitory nerves are more excitable than the accelerators.
(Similar relations exist in warm-blooded animals — vagus, accclerans
—cf. Meltzer, 58.) On the other hand, Lowit finds, I.e., that the
former are more easily injured by certain chemical reagents
than the latter. If the vagus-trunk in the frog is treated with
KN03 (^ °/Q}, there is a stage at which excitation of the nerve
produces acceleration of cardiac activity only, while the same
excitation below the part treated with potash is inhibitory. On
washing the nerve with 0'6 NaCl the potash -effect in-

variably disappears again, and this transformation of the vagus
from accelerator to depressor may be repeated several times on
the same preparation. Other substances (I.e. p. 493) have a
similar action to KN03, as also vigorous cooling (ice). Alterations
farther seem to occur in the immediate vicinity of an artificial
section, as expressed by a different ratio of loss of excitability
in the antagonistic kinds of fibres. When Lowit placed the
electrodes close together (1 mm.) upon the divided vagus, so that
one was applied directly to the cross-section, there was invariably,

104 ELECTRO-PHYSIOLOGY CHAP.

with given intensity and ascending direction of the single
induction currents, a visible acceleration of cardiac activity, while
reversal of the current was sufficient to produce inhibition. This
is no doubt due to the fact that, as will be seen later, the
excitation in the two cases actually occurs at different points of
the nerve (in the first instance nearer the cross-section), where
the different degrees of excitability thus give rise to different
excitatory effects.

As the vagus-nerve of the frog contains distinct accelerating
and inhibitory fibres, there are no less certainly differences of
excitability in the same. It may further be concluded that the
accelerating (augmentor) fibres are less excitable than the de-
pressors, but more resistant to all processes that threaten to
destroy the excitability of both kinds of fibres. This recalls the
analogous relations of excitability in the vase-constrictor fibres of
a nerve-trunk that conducts both vaso-constrictor and vaso-dilator
impulses.

At the same time it is not the functionally analogous fibres
that agree in regard to excitability and resistance, since the cardiac
inhibitory fibres agree with the vaso- constrictors, the cardiac
accelerators with the vaso -dilators respectively. This contrast
finds its most pronounced expression in the relations of excitability
between the motor and inhibitory fibres of the antagonist muscles
of the crayfish claw. From the above evidence we are forced
to conclude that each of these muscles is supplied by two
kinds of fibres (motor and inhibitory) which are functionally
distinct, and differ in regard to excitability, not merely quantitatively,
since the one effect invariably occurs before the other, in regular
proportion with the strength of excitation, but also qualitatively,
seeing that the inhibitory fibres of the one muscle correspond in
their excitatory conditions with the motor fibres of the antagonist
muscle.

Similar differences of excitability to those described above for
centrifugal nerve-fibres seem to obtain in centripetal fibres also,
as shown by the varying effects of excitation of the central end
of the vagus, in proportion with the strength of stimulation.
Two kinds of fibres have been determined in the vagus, which
have an opposite action upon the respiratory centre ; the one
favouring inspiration, the other expiration, when stimulated. On
exciting with induction currents, the intensity of which has been

vnr CONDUCTIVITY AXD EXCITABILITY OF XERVE 105

graduated as carefully as possible, the first effect observed (in the
rabbit) will in the majority of cases be the appearance of longer
or shorter extpiratwy pauses, or arrest of respiration in the
expiratory position, while stronger excitation always has an
inspiratory effect. The marked expiratory action of chemical
stimuli may depend upon their lower intensity. According to
Meltzer (I.e. p. 385), there is ground for assuming in the vagus-
trunk, as in the claw-nerve of the crayfish, four different kinds
of fibres : a, inspiratory ; l>, inhibitory of inspiration ; c, expiratory ;
d, inhibitory of expiration. Here, again, it is remarkable that
there seems to be a gradation of excitability, resembling that in
the claw-muscles, since the fibres inhibitory of expiration are
most excited at a strength of stimulus which simultaneously ex-
cites the inspiratory fibres. At approximately the same strength
of stimulus the inspiratory fibres are excited and their antagonists
inhibited.

In all these cases (where with different intensities of stimulus
there are obviously different effects in the peripheral and central
•organs supplied by the same nerve-trunk) it is a question whether
the differences of reaction observed are due to corresponding
differences in the excitability of the correlated nerve-fibres, or
in that of the end-organ itself, or in both together.

o O

In the cases observed by Bollett, he inclines to the view (since
no such difference appears with direct excitation of the muscle)
that the cause of the Ritter-Eollett phenomenon lies solely in the
properties of the nerve, leaving undecided whether it derives only
from the different excitability of the fibres destined for different
muscles. Grutzner (59), on the other hand, regards it as probable
that these phenomena arise from actual physiological differences
in the groups of flexor and extensor muscles, as well as in the
entire nerve-muscle apparatus. He bases this upon a series of
observations already referred to, which show a real physiological
disparity between these groups of muscles, and further prove that
the Kitter- Eollett phenomenon comes off after the exclusion of the
nerves and nerve-endings by curare (I.e. p. 231).

The preceding discussion shows that there are great and almost
insuperable obstacles to the comparison of the specific excitability
of different nerves, since we are thrown back solely upon the
reactions from the peripheral or central end-organs, which differ
intrinsically in regard to excitability. And if this is apparent

106 ELECTRO-PHYSIOLOCV CHAP.

even in functionally analogous end -organs, e.g. striated and
smooth muscle, any comparison of the excitability of nerves con-
nected with dissimilar terminal organs is fundamentally impossible.
This is most plainly seen when the conditions for the discharge
of refle-x muscular contractions are compared with those for the
direct excitation of motor nerves. The great differences apparent
in the two cases can hardly be referred to specific differences in
the nerve-fibres, but derive much rather from the inherent pro-
perties of the nerve-cells, as described above.

The most striking among many facts is that a single short
stimulus, whether mechanical or electrical, inevitably discharges
a twitch when the motor nerve of a striated muscle is stimulated
directly, but by no means as certainly in the case of reflex
excitation. Here, indeed, it is the rule that a single brief stimulus
acts only (if at all) at very high intensities. That the cause for
this lies not so much in special properties of the centripetal
nerve-fibres as in dissimilar relations of excitability in the central
reflex organs (nerve-cells) may be presumed from the above
observations on conductivity of excitation in cells and fibres.
We have seen that nerve-cells present a certain resistance to the
conduction of the excitatory process, and thus to excitation itself,—
expressed on the one hand by a more or less conspicuous delay in
transmission, on the other by the greater susceptibility of the sub-
stance of the ganglion to short impacts of stimulation. At the
same time, while the great sensitiveness of the nerve-cells to any
kind of injury is very striking, it must be observed that in regard
to excitability they resemble the less excitable, sluggish, smooth
muscles rather than the quickly-reacting striated muscles. We
shall see later how much the excitation of the more sluggish
excitable tissues depends upon duration of stimulus, the most
striking proof of which is perhaps the fact that the same induc-
tion shock which inevitably produces a twitch of the striated
muscle when applied to its nerve, evokes no perceptible con-
traction of smooth muscles when sent into their nerve-fibres, and
is as little able to excite a reflex twitch from the former. As
regards the first, Langendorff (60) has shown that on exciting
the cervical sympathetic with single induction shocks there is no
perceptible change in the width of the pupil, whereas repeated
shocks become effective by " summation." With increasing
strength, however, Muhlert (61) was frequently able, even with

vin CONDUCTIVITY AND EXCITABILITY OF NERVE 107

single shocks, to perceive a marked dilatation of the pupil, and
Piotrowsky (62) also found this kind of excitation effective as
regards constriction of the vessels of the ear. Still, the action

O

of single shocks is extremely small, while tetanising excitation in
both cases produces marked effects.

If the stimulation-frequency is altered, with constant strength
of current, it is easy to show that the excitatory action (dilatation
of pupil) is augmented, within a wide range, with increasing-
frequency. At an excitation interval of about two seconds Muhlert
could not find any summation of stimulation - frequency, at a
strength of 85*19 E, with even sixty-two consecutive stimuli.
Where number and interval of stimuli are so arranged that an
effect may be anticipated, the influence of strength of current may
easily be determined, in the sense that niydriasis first begins above
a certain range, and then with growing intensity rises to its
maximum, at first rapidly, and afterwards more slowly. In this
case the smooth muscle-fibres in which the summation occurs
give a precisely similar reaction to that of the reflex centres of
the spinal cord with excitation of the centripetal nerves. The
more sluggish of the striated muscles seem to give a similar
response. Thus Piotrowsky (56), on exciting the claw-nerves of
the crayfish with single and intrinsically ineffective induction
shocks, sent in at an interval of half a second, observed a weak
contraction after every seven stimuli.

The striking insusceptibility of centripetal (sensory) nerves,
or more correctly of their central end-organs, to single induction
shocks has long been known.

Munk (63) pointed out that no reflex twitches were elicited
from the frog by single induction shocks, impinging on a sensory
nerve, unless it had previously been weakly strychninised.

Setschenow (64) also showed that induction currents with
the vibrating hammer that were quite perceptible to the tongue
discharged no reflex from the central end of the sciatic. In

O

determining the upper limit of current intensity at which the
animal remained undisturbed by single shocks, and the lowest
intensity at which it was first excited with the vibrating hammer,
he invariably found a great difference between the two, " because
the sensory nerves (especially the central apparatus of transmission),
which are so unsusceptible to single induction shocks, exhibit
almost the same activity to a succession of shocks as the motor

108 ELECTRO-PHYSIOLOGY CHAP.

nerves (or striated muscle)." The same fact appears also in the
slender cutaneous (sensory) nerves of the frog's back, as shown by
Pick (65). "When, instead of giving single shocks, the spring of
the induction apparatus is set vibrating, no such enormous strength
of current is required to evoke (reflex) muscular contractions."
The same phenomena of summation have recently been investi-
gated by A. Ward (66), who found in the brainless frog that the
.application of electrical stimuli, as nearly as possible uniform in
quality and intensity, but not capable intrinsically of producing a
reflex twitch, did after a certain number of stimuli evoke the same,
if the excitation was repeated at intervals of about 0'5 sec. The
required stimulation -frequency was about the same on raising the
interval to 0'4 sec.

These, like all similar phenomena, can obviously be explained
only on the presumption that a stimulus that is in itself in-
effective produces a certain alteration in the nerve-cell (as in
other cases in muscle, gland-cells, etc.), which is favourable to the
production of an effective excitation, or rather is itself a weak
excitation, and summates along with similar changes from
succeeding stimuli, until an effective discharge is produced.
Within the limits cited by Ward the time-interval is immaterial,
as appears from the fact that the alteration caused by excitation
is perceptibly of the same magnitude after 0'4 sec. In principle,
these central summations are in no way dissimilar from those
induced under certain conditions in the peripheral organs, and the
nerve-cells only differ in degree from muscle, gland-cells, etc.

The same is sometimes expressed in a striking after-effect of
tetanisation. After prolonged tetanisation of the divided spinal
cord in the frog (near the cross-section), the same (descending)
opening current that was formerly quite ineffective is often found
to produce vigorous twitches, and this effect only dies out slowly
after an interval of several seconds (Fig. 170). This phenomenon
apparently stands in close relation with that termed by Exner
" canalisation " (" Balmunrj "), as opposed to " inhibition," in the
antagonistic action of excitation within the central nervous system.
If — as can hardly be doubted — we are here dealing essentially
with alterations of excitability in the conducting elements of the
gray matter of the lumbar region, an effect analogous to that of
canalisation might also be expected in cases where the modifying
and testing stimuli act in succession upon the two opposite poles

VIII

CONDUCTIVITY AND EXCITABILITY OF NERVE

109-

of the reflex centre, so that in the one case the direct excitability
of the motor fibres of the spinal cord appears to be heightened,
in consequence of a previous excitation of the central end of the
sciatic, while in the other the reflex functions of the lumbar
enlargement are favoured by previous tetanisation of the spinal
cord. And it has, in fact, been found that single descending
induction currents, which, when applied directly to a fresh section
on the ventral surface of the frog's spinal cord, are per se
ineffective, do produce marked excitatory effects after a pro-
longed reflex tetanus has been induced by excitation of the central
end of the sciatic. Conversely, reflex stimuli that were formerly

FIG. 170. — a, b, Incomplete tetanus of frog's gastrocnemius on excitation of the cord (divided above)
with a rapid succession of induction shocks. Single and previously ineffective opening shocks
then excite strongly, if led iu at the part of the cord that has just been tetanised, by the
same electrodes.

ineffective can be made to act by protracted and immediately
antecedent tetanisation (Biedermann, 37).

A7". CHANGES PEODUCED IN NERVE BY ACTIVITY

No less difficult than the establishment of the specific
excitability of the nerve is the Question whether (as seems a priori
the more probable) the course of the excitatory process in the nerve
is associated with metabolism, and in what degree. Two methods
are here conceivable. It might be possible to demonstrate altera-
tions in the chemical composition of the nervous substance either
directly by means of prolonged excitation, or indirectly by
investigating the laws of fatigue, and recovery, in the nerve. As
regards the first question, it is even harder to decide this point in
nerve than in muscle, owing partly to its smaller bulk, and partly

110 ELECTRO-PHYSIOLOGY CHAP.

to the structure of the nerve -fibres. The sole functional,
chemical alteration of nerve which, if not undisputed, is still
maintained on experimental grounds, is its reaction. Immediately
after du Bois-Beymond had established the functional alteration
of the reaction in muscle, Funke (67) made a corresponding
statement for medullated nerve, finding the cross-section both of
peripheral nerve-trunks and of the more easily tested spinal cord
of the curarised rabbit and frog to be neutral, while at a certain
time after death, or in strychnin poisoning, they gave an acid
reaction. Both assertions were disputed by Heidenhain (67), and
confirmed by Eanke (67). According to Gescheidlen and Edinger
(67), the gray matter of cord and brain is acid even in the fresh
state, the white matter being neutral : Moleschott and Battistini
invariably find the former more strongly acid than the latter, both
during rest and during strong excitation. In direct contradiction
of this, Langendorff (67) affirms that the central nervous system
of the frog as a whole gives an alkaline reaction, and that the
same is true of the living cerebral cortex of the rabbit or guinea-
pig. Both in asphyxia and in ansemia, however, the reaction
quickly becomes acid. The obvious contrariety of these statements
is in large measure owing to the fact that the chief subject of
experiment has been the excessively unstable ganglionic substance
of the nerve-centres, the reaction of which alters with extreme
rapidity. Pfliiger, in fact, after even the most rapid washing-out
of the brain with ice-cold physiological saline, observed an
immediate post-mortem acidity of the gray matter. In view of the
complete similarity of vital conditions in nerve-cells and fibres, it
can hardly be found surprising that the metabolism of these two
most essential structural elements of the nervous system should
differ completely. In no case can the conclusions as to ganglionic
parts be taken to gauge the reaction of nerve-fibres. Moreover,
it is hardly to the purpose to take (as has usually been the case)
a medullated nerve as the test of a final reactionary alteration,
since only the substance of the axis-cylinder in these fibres can
be counted as the essential physiological constituent. It is quite
possible that the medullary sheath (which bears little direct part
in the excitatory and conducting processes) may mask a real
alteration of reaction at the cross-section.

As little as chemical alterations of the nerve-fibre have been
established during, and in consequence of, excitation, can the ther-

vni CONDUCTIVITY AND EXCITABILITY OF NKKVK 111

inal processes be taken as proven. Neither Heideuhain nor Helin-
holtz, in spite of the great delicacy of their methods, was able to
determine a reaction in peripheral nerve-trunks analogous to that
of muscle; Schiff (69), however, recorded positive results. Here
again it is necessary to distinguish between the ganglionic
substance of the central organs and the nerve-fibres proper, and
differences of thermal reaction must be expected in correspondence
with the established differences of chemical reaction.

In view of the total lack of facts as to metabolism in the nerve-
fibres, we are thrown back upon probabilities. The functional
metabolism must under all circumstances (save in the gray matter
of the centres) be very insignificant, as is proved inter alia by the
poor supply of blood, as well as by the extraordinary tenacity of life,
at least in medullated nerve-fibres. The same conclusion appears
from the investigations into fatigue and recovery of nerve. The
main difficulty here lies in the comparatively great fatiguability
of the terminal organs (muscles, ganglion-cells) in which alone the
capacity of reaction, or alteration, can be demonstrated. The
existence of fatigue in nerve was for a long time assumed on quite
insufficient analogies, since experiments on fatigue of brain, retina,
etc., prove nothing as to the reaction in nerve-fibres. Bernstein
(70) was the first who endeavoured to demonstrate fatigue of the
persistently excited nerve in a nerve-muscle preparation.

In studying the effect of long -continued excitation of any
point of the nerve upon its excitability, it is evidently essential
to block off the stimulus, during the greater part of the excitation,
from the terminal organ (muscle). Bernstein succeeded in doing
this by sending a constant current through a part of the nerve
between the point of excitation and the muscle. As we shall
see, conductivity may be locally abolished without suffering
permanent injury. From the reaction of the muscle after
opening the insulating current, Bernstein formed conclusions as
to the state of the muscle excited by the induction current. If
the muscle no longer reacted to the constant stimulus at the free
end of the nerve, Bernstein assumed a local fatigue, and computed
its appearance at 5-15 min. Wedenski tried to obviate the
injurious effect of the long closure of the battery current by send-
ing in a strong ascending or descending constant current at the
outset for a short time, so that the tract of nerve involved became
incapable of conducting (70). Very weak currents then sufficed

112 ELECTRO-PHYSIOLOGY CHAP.

to keep up this state. On breaking the current, the nerve almost
immediately recovered its conductibility. Under these conditions
Wedenski was unable to detect any fatigue in nerve at the point
of stimulation, even after six hours' excitation. Maschek (70),
who confirmed the experiments of Wedenski, succeeded in pro-
longing the experiment for twelve hours, without any perceptible
fatigue of the point of stimulation. Maschek further showed by
means of local ether-narcosis, which of course implies rapid
recovery, that an excitation lasting many hours produces no
visible fatigue at the point excited. Bowditch (70) arrived at
the same conclusion in warm-blooded animals (cats) by means of
curare, the effects of which are soon dissipated (cf. also Szana, 7'0).
" When the action of curare has quite worn off after persisting
three to four hours, the induction current, which has been passed
uninterruptedly through the peripheral end of the muscle during
the action of the poison, resumes its full effect."

The fact that nerve may be excited for many hours without
perceptible fatigue suggests, as remarked by Bowditch, the idea
that excitation may be transmitted without consumption of mote rial.
In view of certain facts to be considered later, it is, however,
more accurate to say that a certain expenditure of nervous
energy is consumed (even if it cannot be measured experi-
mentally) in the mere propagation of the excitation.

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VOL. II I

114 ELECTRO-PHYSIOLOGY CHAP

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p. 275. Arch. Italiennes. VIII. p. 90.
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vin CONDUCTIVITY AND EXCITABILITY OF NERVE 115

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et pathol. 1869, pp. 157, 330 ; and 1870.
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BOWDITCH. Du Bois' Arch. 1890. p. 505.
. Du Bois' Arch. 1891. p. 315.

CHAPTEE IX

ELECTRICAL EXCITATION OF NERVE

I. LAW OF EXCITATION BY ELECTRICAL CURRENTS
(DU BOIS-REYMOND)

THE electrical current again ranks first among all the artificial
means of nerve-excitation. A succession of experiments in this
direction dates from very early days, and forms one of the most
interesting chapters in physiology.

Du Bois - Key mond (1) has given an admirable historical
survey of this part of the subject. At its outset we encounter
the fact that a, motor nerve — like the corresponding striated muscle,
but in a still higher degree — is apparently excited only at the
moment of closing, or opening, a IxMcry current. In fact, du Bois'
" general law of electrical excitation of nerve " was at first laid
down for indirect excitation of the muscle, and was only extended
at a later period to direct muscular stimulation. The law in
its original form ran as follows :—

" It is not the absolute value of current-density in the nerve,
at any given moment, that determines the response of the muscle,
but the variations of this value from moment to moment : the
stimulus to movement consequent on these changes being the
more considerable according as they are (in a given interval)
greater in magnitude, or more rapid in their onset."

If a motor nerve, still attached to the muscle, is laid across
unpolarisable electrodes, and excited by the closure or opening of
a sufficiently strong battery current, a single rapid twitch of the
muscle appears at make and often at break also, after which it
returns to the normal resting position. The most careful observa-
tion fails to detect any permanent shortening during closure, or

« IIAI-. ix ELECTRICAL EXCITATION OF NERVE 117

wheii the current is opened. The directly excited muscle of
course gives a different reaction, inasmuch as it remains shortened,
under certain conditions, during the passage of the current, and
even for some time after it has been opened, though the contrac-
tion may be only local (persistent closing, or opening contraction).
A visible persistent effect of current may also (infra) appear with
indirect excitation of the muscle, both during closure and after
opening the current. This is expressed in a more or less prolonged
contraction of the muscle excited through the nerve, which may
be continuous, or interrupted by single twitches, and which, from
its resemblance to the tetanic form of contraction due to inter-
rupted rhythmical excitation, is known as closure, or openiny, tetanus.

Bitter (1798) was the first to point out that an indirectly
excited muscle may, after prolonged closure of a powerful battery-
current, fall, on breaking the circuit, into a state of persistent
tetanic excitation — a manifestation named, after its discoverer,
Hitter's opening tetanus. With this we shall have to deal later :
for the moment it is sufficient to point out that nerve1, like
muscle, may, when a constant current is opened, fall into a pro-
tracted state of excitation, so that the opening tetanus and the
persistent opening contraction are practically equivalent pheno-
mena. A similar persistent excitation (as first remarked by
Pfliiger, 2) appears sometimes during closure of the current,
and may be perfectly regular. Pfliiger obtained this " tetanic '*
effect with quite weak currents ; it increased up to a certain point
with increasing intensity of stimulation, and then declined again.
Under the most favourable conditions, i.e. with maximal excit-
ability of nerve, closure tetanus makes its appearance at any
effective strength of current. This is more especially the case
with frogs kept in a low temperature for some time before making
the preparation (" cooled frogs ").

The excessive excitability of such preparations is a well-known
physiological fact, and we shall frequently have to refer to it. It
may be said, as a general rule, that the nerves of all frogs kept
at a temperature below 10° C. will sooner or later acquire the
property of being tetanically excited by constant currents (v.
Frey, 3, Fig. 171).

Similar excitability is exhibited by nerves at a high temperature
(Engelmann, 4), provided they are in a certain stage of dehydration
(from evaporation, or treatment with NaCl). In both cases there

118 ELECTRO-PHYSIOLOGY CHAP.

is sooner or later a spontaneous excitation of the nerve-fibres, as
shown first in twitches of the fibrils and then in tetanic con-
traction of the entire muscle (desiccation- and salt-tetanus). If
the excitability of such a nerve is tested from time to time with
a current of uniform strength, it is found to increase, until, just
before the commencement of desiccatory spasm, each closure, or
opening, discharges powerful but irregular tetani. The closure-
tetanus of " cooled " nerves, on the contrary, is usually quiet and
regular, the curve showing no marked divergence from the
tetanus-curve of intermittent excitation. The conjecture that
closing and opening tetani are due to abnormal activity in the
nerve, is completely contradicted by the fact that the motor

FIG. 171. — Tetanus curve of gastrocnemius on closure of a battery current (closure tetauus).
Preparation from a cooled frog. (Von Frey.)

nerves of other animals invariably react by tetanus, under all cir-
cumstances. This applies, according to Eckhardt's observations
(5), especially to nerves of warm-blooded animals, when excited
with descending currents of average strength, as well as to the
non-medullated motor nerves of many invertebrates (claw nerve
of crayfish, etc., Biedermaim). In both cases closure-tetanus is
the rule and not the exception, and thus du Bois' "universal
law " has as little application to indirect as to direct excitation of
the muscle. We must rather hold that, although the visible
effects of the transmitted excitation are fundamentally due to
variations of density in the current flowing through the nerve,
the excitatory process is locally initiated throughout its cnfir*
•jtassage, and that other circumstances determine whether this
continuous excitation is expressed at the peripheral organ (muscle)
or no. The same applies to the state of activity at break of the

ix ELECTRICAL EXCITATION OF NERVE 119

current. " Ritter's tetanus " is a direct proof of its persistence
under certain conditions.

The similarity of effect in closing or opening tetanus, and in
the true tetanus produced by discontinuous excitation, raises the
question whether here too there may not be fusion of single,
rapidly succeeding impacts of stimulation. In other words, does
the steady constant stimulus during closure, or after opening,
produce under the above conditions a discontinuous rhythmical
excitation of the nerve ; is the tetanus of closure and opening a
genuine tetanus or not ? We are familiar with the same difficulty
(supra) in the previous question of whether the tetanic contraction
of the muscle stimulated directly, or from its nerve, is really an
unbroken process, or whether discontinuous invisible changes are
masked by the apparent continuity. Ocular evidence is here
inconclusive. We may indeed reason with apparent probability
from the fact that every conceivable transition exists between
irregular tetani broken by single twitches (clonic) and a perfectly
steady (smooth) tetanus, and that these transitions must obviously
consist of so many more single twitches in the time-unit, in pro-
portion as they approximate to uninterrupted tetanus, that the
latter, too, consists of fused twitches : and the trembling which
concludes a long voluntary tetanus may equally be cited as
evidence of its discontinuity. This, however, is insufficient proof.
In addition to the form of the muscle-curve, the muscle-sound
and the electrical reaction of active muscle throw some light on
the nature of a persistent contraction. As regards the first, the
investigation of such a minute mass as a frog's muscle is obviously
very difficult (the experiment has not yet been tried for warm-
blooded muscle). And there has in fact been no result from the
various attempts at transmitting to the plate of a microphone,
or (according to Helmholtz's method) to consonant reeds, the
vibrations during the period in which a frog's muscle is in
closure-tetanus.

On the other hand, experiments with the capillary electro-
meter upon the electrical reaction of muscle have yielded more
definite conclusions (v. Frey, 3), showing that closure-tetanus is
in fact derived from a succession of discontinuous rhythmical
impacts (10-15 per sec.) ; cnjo nerve like muscle is thrown, during
certain conditions, into persistent rhythmical excitation under the
action of current flowing at constant density. (The inadequacy

120 ELECTRO-PHYSIOLOGY CHAP.

of closure and opening tetanus to throw a second nerve-muscle
preparation into secondary tetanus, as discussed iu vol. i., has
obviously no application as a counter-argument). Inasmuch as
cardiac muscle and the ureter exhibit a similar reaction, this
would seem to be a general law, applicable to all excitable
substances. The time -distribution, i.e. succession of single
excitatory impulses, differs of course in different cases, and
exhibits a regular gradation. As a rule, therefore, and contrary
to du Bois-Eeymond's " universal law of excitation," it must be
affirmed that the electrical current flowing at constant density
gives rise (locally, at least) to continuous excitation, and the
problem is rather why such excitation is not invariably trans-
mitted ; or, if transmitted, is not uninterruptedly expressed at
the peripheral organ. The nature of the terminal organs is here
undoubtedly of the first importance, as appears plainly from the
afferent nerves.

The earlier electricians knew that centripetal impulses excited
by the action of a constant current produce, in addition to a
sharp make and break twinge, constant sensations, which may
become insupportable with sufficient strength of current. It is
true that the peripheral, sensible end-organs are nearly always
coexcited, while there have only been solitary experiments upon
the continuous excitation of sensory nerve-trunks by the direct
action of the constant current. The fact (already known to Volta)
of an excentric irradiation of pain so long as the electrodes are
applied below the joint of the elbow, comes under this category.
Griitzner (6) further showed that both ascending and descending
currents were effective throughout their passage, when the central
end of the dog's sciatic was excited after previous curarisation,
and division of the vagus on one side. A considerable rise of
blood-pressure occurred at and during closure, with a simultaneous
acceleration of pulse, which changed after opening the circuit, or
at the end of excitation, into its contrary, i.e. slowing down of
the pulse. Griitzner found the same results on stimulating the
central end of the vagus, with additional respiratory modifications,
consisting in arrest of the diaphragm in expiration, or retarded
respiration with expiratory pauses. The same observations have
recently been confirmed and extended by Langendorff and E.
Oldag (7). By gradually shunting the current into the nerve,
they were enabled to observe its continuous action, and obtained,

ix ELECTRICAL EXCITATION OF NERVE

121

with ascending direction, an expiratory slowing, or arrest, of
respiration, — although a frog's leg included iu the circuit was
not once made to contract (Fig. 172).

The persistent excitation of secretory nerves by the constant
current has been established on the frog's tongue, by the changes

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111111

! -•> i—

fill!

\

1

1

1

1

\
U

f!

^/-

W

Vj U

\ II

1

J1

J

« &

Fio. 172. — Respiratory curves (rabbit). Gradual shunting of ascending current into vagus. 1 Dan.
(S) Closure, (Oe) opening of current. The rheochord slider was shifted from a to b. (LangendorfT
and Oldag.)

of the mucosa current during excitation of the glosso-pharyngeal
(Biedermann, 8). In the cardiac vagus Griitzner confirms the
earlier conclusions of v. Bezold (Unters. ilber die Innerv. des
Hcrzens, Leipzig, 1863, p. 72), since with a current of twelve
pincus-cells the make and break only are effective, as shown by
the following curve (Fig. 173).

Another proof that current excites not merely at the moment
when it begins (or ceases), or during variations of density, but
throughout its entire passage, is seen in the fact that at a given
uniform strength of cur-

f\ I c. 1

rent a closure twitch only *'

appears when the duration
of current has outlasted
a certain time (A. Fick).
This fact is already familiar to us in muscle — more particularly
when non-striated — where it is easily determined. Its proof is
more difficult in nerve, because the time -values involved are
exceedingly small. While, e.g., in smooth molluscan adductor-
muscle the maximum effect of a given strength of current is not
reached even with a duration of ^—^ sec., the same, according
to Konig (10), is obtained in excitation of the nerve after
0'017 -O'0 18 sec. Under all conditions, therefore, we must
allow for the fact that very brief closures of current produce no

FlG-

122 ELECTRO-PHYSIOLOGY CHAP.

muscular twitch during their action upon medullated, motor
nerves. With increased duration of current beyond a certain
point the twitches increase also, and reach their maximum with a
relatively short closure, after which they cannot be augmented by
any further prolongation of current or increase of intensity (pro-
vided an adequate strength of current is employed at the outset).

If we compare the susceptibility of different excitable sub-
stances to currents of brief duration, it will be found lowest in the
non-fibrillated plasma of protozoa and in smooth muscle-fibrils,
highest in medullated nerve-fibres ; midway are cardiac muscle
and striated skeletal muscle. This is well shown in experiments
with single induction shocks, the effect of which agrees in the
main with that of excessively brief constant currents. The
medullated nerve of striated vertebrate muscle is peculiarly
sensitive to this method of stimulation, the latter itself less so
(especially when curarised), and smooth muscle still less, where in
order to excite by single induction shocks an enormous intensity
is often required. It is remarkable that the same graduated
difference appears to exist between medullated and non-medullated
nerve-fibres in regard to their susceptibility to single, brief currents
(more particularly to induced currents), as between striated and
smooth muscle. It is far less easy to elicit twitches from the
claw -nerves of the crayfish with single induction shocks than
with the constant current.

We must now consider the second postulate in du Bois'
" universal law of excitation," by which he affirms that a positive or
negative variation of current must always be of a certain abruptness
in order to excite, and that (with otherwise uniform conditions)
the excitation appears more certainly, and within a certain range
more strongly, in proportion as the variations of intensity are
more sudden in their onset.

Whatever application this may have to medullated nerves in
connection with twitching, striated, vertebrate muscles, it is by
no means a universal law, appropriate to all excitable tissues.
Nothing is easier than to show in the usual frog's nerve-muscle
preparation (the " physiological rheoscope ") that even the weakest
electrical currents may excite, provided they are adjusted
sufficiently sharply, i.e. that the intensity of variation is as steep
as possible. The peculiar susceptibility of these nerves towards
even a trace of frictional electricity is due to the presence of

IX

ELECTRICAL EXCITATION OF NERVE

123

currents of exceedingly rapid onset, and induced currents have a
powerful excitatory action, even at low intensity, from the same
reason. This tendency of the ordinary nerve-muscle preparation
to react to the weakest currents, provided they are adjusted with
sufficient rapidity, renders it a valuable indication of the presence
of weak currents of brief duration (action currents in the muscle).

An interesting fact in this connection, and one that also
depends mainly upon the influence which the onset of any
current exerts upon its excitatory action, is the unequal effect of
the make and break shock from an induction apparatus. The
excitatory action of the make shock is without exception much
lower than that of the break. This is plainly seen when the
secondary coil is a long way off from the primary. There is
always a point at which the break shock is effective, when the
make shock fails to excite ; on approximating the coils, the latter
also takes effect.

Since, as is easily shown on the galvanometer, the quantities
of electricity in the make and in
the break shock are equal, the
dissimilarity of physiological effect
must be fundamentally due to the
differences in time-distribution of
the two induction currents, caused
by the appearance of the extra cur-
rent on closure of the primary
circuit. Since the primary current

,11 -i FIG. 174. — Schema of induction currents.

in the last case does not _ at once Pj> Abscissa of primary current; s>
reach its full strength, but increases
gradually, while it suddenly dis-
appears on opening the circuit,
the induced current must rise more
abruptly at break than at make of
the primary circuit (Fig. 174). Accordingly, the break shock
gives a sharp " crack " in the telephone, the make shock, on the
contrary, yields a dull, weak sound (Griitzner).

This inequality of physiological action in the make and break
shocks, as due to inequality of time-distribution, is very inadequately
compensated by the contrivance of " Helmholtz's side wire," which
is attached to most induction coils, and there have been later
attempts at producing induction cu.rreuts by other means, better

S

abscissa of secondary current; A,
initial; E, terminal currents. 1,
Curve of rise of primary current (de-
layed by extra current) ; 3, opening of
the same ; 2 and 4, corresponding
secondary currents. (Hermann, Hutulb.
ii. 1.)

1-24

ELECTRO-PHYSIOLOGY

CHAP.

suited to experimental requirements. Hering (11) made the
secondary coil rotate round a vertical axis in front of the primary,
which was traversed by a constant current, giving rise to uniform
induced currents — since, with the coils at right angles, induction
is at zero, and with other definite inclinations of the coils
corresponding definite induction currents make their appearance.

Griitzner (12) subsequently investigated the physiological
action of currents from a Stohrer's machine, in which two
wire-coils with iron axes revolve in front of a powerful horse-
shoe magnet. Each revolution yields four currents, correspond-
ing as two pairs in respect of time-distribution. If 8 and N
(Fig. 175) are the poles of the magnet, and I and // the coils

FIG. 176. (After Griitzner.)

FIG. 175.

rotating round the axis A, then when they have shifted ^
revolution clockwise from this position, so that / is opposite N,
the first current rises gradually from 0. If / is then moved
away from N, the falling current alters instantaneously in the
reverse direction. Rising suddenly, it gradually falls to zero,
and then rises again equally gradually to its former height, as
the coil / travelling through all three quadrants approaches S, the
south pole. This is succeeded by an abrupt rise of current in the
reverse direction, so that (as shown by the accompanying curves,
Fig. 176) two gradually and two abruptly rising currents appear
with each revolution. This can be elegantly demonstrated (after
Griitzner) if the platinum-point electrodes are drawn at uniform
speed over paper moistened with iodide of potassium during the
revolution of the apparatus. The resulting electrolytic curves
appear as lines which are correspondingly thicker at the apexes
of the curves than in the rest of the tracing. The gradually
rising currents are represented by lines, small at first, and after-

ix ELECTRICAL EXCITATION OF NERVE 125

wards broader, while the abruptly rising currents give the reverse,
the decomposition being marked at first and subsequently
diminishing (Fig. 177). While investigating this electroly to-
graphic method Griitzner also found that the steeply rising break
induction current of an ordinary du Bois' sliding apparatus had
a far more marked electrolytic action than the gradually rising-
make induction current.

In the frog's nerve-muscle preparation, with low intensity of
current, abruptly rising currents are always the most effective
(now one and now the other, according as the electrodes are
situated on the nerve). On increasing the current, a second
smaller twitch appears, corresponding with the other steeply rising

FIG. 177.

(and opposite) current. Further increase of current intensity
complicates the excitatory effects still further, since with an
ascending direction of current the anodic inhibition becomes
apparent. In rare cases, all four induction currents may excite,
and there are then at each revolution two strong and two weak
twitches, alternating as one strong and one weak twitch. The
most significant result of Griitzner's investigation is the pre-
dominant action of the abruptly rising currents, where the direction
is again of importance, inasmuch as (according to the observations
of Hermann and Fleischl, supra] the upper portion of the nerve
is first excited by descending, the lower portion by ascending
currents, while they both take effect at the " equator " only. It
is with much higher intensities of current that the gradually
rising currents also become effective.

The beneficial influence of great abruptness of oscillation is
shown inter alia by the fact that even very strong currents may
be shunted into the nerve without perceptible signs of excitation,

126

ELECTRO-PHYSIOLOGY

('•HAP.

provided only that the increment accrues gradually and evenly.
The same thing is, as we have said, still more easily established
in muscle.

If the action of make and break induction currents is
investigated in the nerve-muscle preparations of other animals,
very different results are arrived at (as recently pointed out by
Schott, 13), showing once more how unjustifiable it is to lay too
much stress on facts derived from experiments with one kind of
animal.

In the nerve-muscle preparation of toads Schott (13) found
the steeper break induction shocks relatively less effective than in

FIG. 178. — Toad's gastrocnemius. a, Make induction twitch ; b, break induction twitch.

(J. Schott.)

the frog ; there is hardly any difference in the distance of coil at
which the make and break shocks take effect. While the in-
directly excited frog's muscle always describes much higher
twitches (of medium size) if break shocks are employed, this is
not the case with the toad, and the make shocks may even be
the more effective (Fig. 178). According to Griitzner (14), single
induction shocks of different time-distribution can also be produced
as follows. A ring of sheet-iron is fastened to a brass disc in
the form of Fig. 179. This consists of two parts, M and N, of
which the latter (on rotating the disc to the right) rises gradually
from its base H upon the brass-plate to its greatest height, while
M is cut off in the direction of the radius of the disc. If the
ringed iron piece MN is then rotated between the poles of a
horse -shoe magnet, surrounded with wire -coils, there will (on
turning the disc to the right) be a constantly increasing part of

IX

ELECTRICAL EXCITATION OF XERYE

127

the iron ring from the point H between the poles of the magnet,

the magnetic force of which is correspondingly diminished.

This slow decline in the magnetism corresponds to a magnetic

induction current in the coil,

which rises the more slowly as

the iron ring increases more

gradually in thickness, and as the

disc is the more slowly rotated.

On the other side the part M

of the ring induces, under similar

conditions, by its sharp edge, an

almost instantaneous ascending

current. In the frog-preparation

the current from the sharp tooth

(like the break shock) is always

more effective than that from the

obtuse tooth, while this is reversed in the toad, where the slowly

ascending current invariably excites more effectually than the

sharp rise (Fig. 180).

It is a question whether this is due merely to the known

FIG. 179.

FIG. ISO. — Gastrocnemius of toad. Twitches on excitation with a, obtuse tooth ; b, sharp tooth.

sluggishness of toad-muscle as compared with that of the frog,
or whether there are actual differences in the nerve-fibres im-
plicated. In any case du Bois-Eeymond's dictum, that current
excites not in virtue of its actual density, but from the rapidity
of its variations, is not applicable to all locomotor apparatus.
The rapidly twitching muscles of the frog correspond with the

128 ELECTRO-PHYSIOLOGY CHAP.

» .

law, the muscles of the toad do not, arid it applies even less to
the more sluggish contractile tissues (smooth muscle, many
Protozoa, etc.). " Since in these, from their sluggishness, a given
physiological state is more than usually prolonged, they are
especially adapted for stimuli of long duration and gradual onset."
To borrow a comparison from Griitzner (14, p. 384), it is with
these as with the movement of heavy sluggish masses impelled
by external momentum. " If we shoot a bullet against a large
heavy wooden door, turning easily on its hinges, the ball passes
through, without pushing the door on the hinge. But if the
same amount of energy as is contained in the moving bullet is
directed against the door by increasing the mass of the ball while
its velocity is diminished, then such a ball will readily turn the
door on its hinges. Thus an induction shock of abrupt onset
injures a sluggish (smooth) muscle without causing contraction,
while the same quantity of electricity distributed over a longer
period may excite a vigorous twitch, without injury." Slow
moving stimuli are thus, according to Griitzner, the adequate
incitation for slowly developing processes.

The different physiological action of the make and break
induction shock again appears to rest, not solely upon differences
of time-distribution, but also upon the still obscure dissimilarity
of electrolytic effects. Griitzner (14) found that currents of
abrupt onset, including break induction currents, have a much
stronger electrolytic action than those which commence more
gradually. This would account for the fact that, in direct excita-
tion of homogeneous striated or even smooth muscle (e.g. the
adductor muscle of the shell of Anodonta), the contraction dis-
charged by a break shock is usually the most conspicuous, i.e.
makes its appearance earlier.

These facts lead us to anticipate that the form of the curve
of oscillation of an electrical current is not without effect upon
the excitatory action ; and the first essential for determining this
point is that we should be able at will to modify and vary the
nature of the increase of intensity (or density) in a battery
current. The problem of raising a galvanic current in a circuit
from zero, by different degrees, to a certain final value, was first
attacked by v. Fleischl (15).

He succeeded by means of his " orthorheonome " in producing
increment and decrement of the exciting current at any uniform

IX

ELECTRICAL EXCITATION OF NERVE

129

desired rate — within a certain range, and in exact proportion
with the time-interval. The apparatus, which is constructed on
the principle of Wheatstone's Bridge, consists essentially of a
homogeneous circular conductor (trough filled with ZuS04 solution).
The current is led in at a b, the opposite ends of a diameter. _ A

PIG. 181.— Schema of v. Fleischl's orthorheonome. (Ellenberger, Physiologic, ii.)

metal conductor turning on its centre runs across diametrically
(Fig. 181, zz), its two points with amalgamated zinc terminals
dipping into the trough E. The nerve is included in the circuit
of this rotating diameter (between c d). As often as it is in the
direction of the entrance points of the current AB, a certain
fraction of the current will pass through it; while at an angle of
90° (at CD} this fraction = 0. The current through the nerve
diminishes regularly with the magnitude of the angle («), provided

FIG. 182.

the resistance of the circuit is otherwise vanishing. Von Fleischl
showed that, with regular rotation of the rheonome, the oscillations
of current might be expressed in a broken line similar to
Fig. 182. Equal sections of the abscissa correspond with equal
times, while the ordinates are proportional with strength of

VOL. II K

130 ELECTRO-PHYSIOLOGY < HAP.

current. The ordiuates above the abscissa correspond with
descending currents in the nerve, those below the abscissa with
ascending currents. The curve (abcdc) corresponds to an entire
revolution of the bridge.

It is obviously easy to determine by this method the
amplitude, duration, and abruptness of the oscillation within wide
limits ; it is also possible to lead a current into the nerve which
shall correspond only with the tract (abc). The action of a
single linear oscillation of current was investigated by Fuhr
(15), using a similar apparatus to that of v. Fleischl. No special
differences from the ordinary method (in which current intensity
rises, as it were, with infinite steepness) could be detected in the
indirectly excited muscle-twitch. Von Fleischl always saw the
twitches first at a certain rate of rotation of the rheonome, i.e. at
a given pitch of current oscillation. They do not last throughout
the entire period of increase of intensity, but commence at a
certain pitch, and soon terminate, while the curve of oscillation
increases still further, and finally sinks abruptly. The sharp
turning-points (kinks) of the curve are not excitatory. The re-
action of the muscle during the entire period of current oscillation
is thus comprised in a single contraction.

Von Kries subsequently constructed a " spring rheonome " on
an entirely different principle, by which he obtained linear

variations of current of different steep-
nesses, while the resulting intensity re-
mained constant, producing oscillations of

the form / . If ab (Fig. 183)

is a solid or fluid conductor traversed
by a constant current, there will at any
two points be a difference of potential
proportional to the distance between them. If c and d are
then joined by a conductor, the resistance of which as compared
with the resistance of cd is very high (nerve, e.g.], it will be
traversed by a current of which the intensity can easily
be raised lineally as required, if — as is the case in v. Kries'
apparatus — one leading -off electrode is firmly attached to the
point c while the other slides with constant rapidity along
the wire ab, and is finally brought up at a certain point of the
conductor (Kries, like Fleischl, employed a trough of fluid) tra-
versed by the current.

ix ELECTRICAL EXCITATION OF NERVE 131

Von Kries agreed with v. Fleischl that the twitches discharged
by " time -stimuli" (i.e. linear variations of current) are not
usually distinguishable from those due to " instantaneous stimuli."
In single cases, however, we meet with notable exceptions, the
twitches from time-stimuli being much more extended. Yet it
must be remembered that the mechanical changes of form in the
indirectly excited muscle-twitch give a very incomplete repre-
sentation of the true time-distribution of the excitation at the
point where the nerve is directly excited. So that when v.
Kries concludes from his experiments that a linear variation of
current in one direction excites the nerve for a brief period only,
this would seem to be as little justified as the postulate of a
universal law of excitation, based upon observation of the make
and break twitch.

As a rule, in order that a time-stimulus may evoke as high
a twitch as an instantaneous stimulus, the intensity (is} finally
reached at a given pitch (D) must exceed the intensity of the

momentary stimulation (im) for the same effect. This different

(• \
- ) for each value (D) is termed by v. Kries the stimula-
m/

tion quotient. It increases of course with increasing values of
(D), and affords a direct gauge of the diminution of excitatory
effect caused by the extension in time of the oscillation. In the
frog's nerve-muscle preparation v. Kries found it almost invariably
greater than 1. In other cases, however, strong time-stimuli
yielded larger twitches than were usually produced by momentary
closures. This seems to be the rule in sluggishly reacting
excitable substances. A stimulation quotient is naturally not to
be obtained in such cases. The integral dependence of the nerve
upon the nature or mobility of its constitution is clear from the
observation of v. Kries, that cooled nerve reacts better to lower,
warmed nerve to higher oscillation-pitch.

It is noteworthy, as first pointed out by v. Fleischl, and con-
firmed by v. Kries, that rheonome twitches do not readily evoke
secondary contractions. Secondary action only appears with very
strong supramaximal stimuli. V. Kries also observed stronger
effects in the capillary electrometer with time-stimuli, along with
simultaneous failure to excite the secondary preparation. It is
plain that the wave of oscillation is differently distributed in
instantaneous and in linear excitation, the latter being characterised

132

ELECTRO-PHYSIOLOGY

CHAP.

by less steepness of pitch and more extended time-distribution.
We may affirm without hesitation that nerve and muscle are
thrown into a much more protracted state of excitation by linear
variations of current of a finite pitch than by momentary stimuli.
The same may be true of physiological innervation. The
strikingly low rate of oscillations of the muscle-current, as noted
by Loven, both in strychnin-tetanus and in voluntary innervation,
on the capillary electrometer, makes it probable that a complete
tetanus may none the less occur in the frog's muscle, while
induction shocks must act at considerably greater frequency to
produce the same effect.

II. INFLUENCE OF DIRECTION UPON THE EXCITING

EFFICIENCY OF CURRENTS

In addition to pitch, density, and duration, as well as kind
of increase, of the exciting current, the effect of electrical excita-

FIG. 184.— Schema for the transverse excitation of nerve. (Hermann.)

tion of the nerve depends, as in muscle, upon direction of current,
with reference both to arrangement of fibres and to peripheral organ
at the working end of the nerve. As regards the former, it was
known to Galvani that transverse passage of current through a
motor nerve at — as nearly as possible — right angles to the axis of
the fibres produced no effect. Galvani bridged the nerve across
a moist and not very thick thread (Fig. 184 a\ through which he
led a constant current. In consequence of the narrow path of
the current through the nerve, there are comparatively few
opportunities for the formation of longitudinal components,
though these are by no means entirely excluded. On the other
hand, it is doubtful whether any considerable fraction of the
current traverses the nerve, unless very strong currents are made

ix ELECTRICAL EXCITATION OF NERVE 133

use of. Since, however, these do produce vigorous twitches, the
conclusion for transverse inexcitability of nerve, based upon
observations with weaker currents, seems to be insufficiently
established. Hitzig (16) ancI_.Filehne (16) employed two strips
of clay, mixed with 1 ' ^ salt solution, for leading in the current.
The broad thin edges of the clay strips were applied on both
sides to the nerve, and the strength of current appropriately
graduated. Here again there was inexcitability to transverse
passage.

As in muscle, the best method is to lay the nerve in an
" exciting chamber " filled with indifferent conducting fluid
(physiological saline), through which the current is sent from two
opposite points or surfaces (Fig. 184). The results and con-
clusions of the several experimenters are, notwithstanding simi-
larity of method, very divergent. A. Fick, jun., (16) affirms the
complete inexcitability of nerve to pure transverse passage of
current, confirming du Bois-Beymoud's conjecture (16), that with
approximately equal conditions the influence of the angle at
which the current passes must be about equal to its cosinus.
Tschirjew (16), on the contrary, denies the influence of the
current angle, and regards the excitability of the nerve to trans-
verse and longitudinal passage of current as equal. It is
important to remember that (as was first pointed out by
Hermann, 17) the resistance of nerve is very different in the
longitudinal and transverse directions, being much higher in the
latter than in the former. If a layer of parallel frogs' nerves
between two square glass plates is traversed by current, first
lengthways and then across, the transverse resistance, as measured
by Wheatstone's method, is found to be about five times as great
as the longitudinal resistance (according to Hermann, the first
exceeds the resistance of the mercury by 12^- million times, the
second by only 2^- million). Similar differences exist in striated
muscle, and appear in both cases to be bound up with the normal
vital properties of the tissue, since they diminish considerably
after mortification has set in. (According to Hermann, the ratio
in nerve sinks, even with heating to 50° C., from 1:5 to 1 : 2 -• 4.)

With regard to these facts, it is clear that when the nerve
enclosed in the exciting chamber is longitudinally traversed, a
greater fraction of the current must pass through it than when
the lines of current are in the transverse direction, and it only

134 ELECTRO-PHYSIOLOGY CHAP.

remains to be seen whether this fact is sufficient to justify
Tschirjew's assumption. On purely theoretical grounds this is
a priori improbable, while experiments carried out under Her-
mann's direction by Albrecht and A. Meyer (16) are distinctly
against it. From the first point of view we have the fact that
both in the pseudopodia of Ehizopods (Actinosphaerium^), and also
in striated muscle, iiiexcitability to currents directed vertically
to the long axis of the cells is indubitably established. Since
there is general conformity between nerve and muscle in their
reaction to current, it would be surprising if there was any
exception in this particular. Albrecht and A. Meyer showed,
moreover, that with pure transverse passage of current through
the nerve, the strongest battery and induction currents had no
effect, although the least displacement of the nerve caused a
twitch. Starting with certain experiments already described on
locally alcoholised nerve (which indicate that excitability rises
within the tract involved, while conductivity is simultaneously
diminished), Gad and Piotrowsky (16) have recently reaffirmed
the transverse excitability of nerve, urging as proof that the local
increase of excitability from alcohol is more conspicuous in a
prepoiideratingly transverse passage of current (through a trough
between two clay strips connected with unpolarisable electrodes)
than with the longitudinal direction. Without entering into
detailed criticism it may be said that this experiment hardly
suffices to throw over the older conclusions as to transverse in-
excitability of nerve.

The differences of excitatory effect, according as the current
flowing longitudinally through the nerve is directed to or from
the terminal organ, belong to a department which has been
explored from every point of view since the first days of
galvanism. A solution and a legitimate interpretation have, how-
ever, only recently been attempted. We know as a general law
that a constant electrical current flowing through a motor nerve
excites mainly at closure or opening of the circuit, although the
passage of current at constant density may also have an excita-
tory effect upon the muscle. Along with this fact we know that
the magnitude of make and break twitch, and even the appear-
ance of one or the other, is also conditioned by direction of
current in the nerve, i.e. whether it flows from a point proximal
to the muscle to a more distal point, or vice versa in a descend-

IX

ELECTRICAL EXCITATION OF NERVE

135

ing direction. We cannot linger over the earlier discussions
of the matter, which for the rest have been admirably and
exhaustively summed up by du Bois-Keymond. It is sufficient
to state that (after Pfaff had pointed out certain regular differ-
ences in the action of ascending and descending currents) Bitter
was the first to formulate a " law of contraction " — as subse-
quently confirmed by Nobili. It will be seen from the following
table that, apart from direction of current, the temporary
excitability of the preparation plays a great part in the effects of
stimulation.

BlTTER-NOBILl'S LAW OF CONTRACTION

Stages of Excitability.

Ascending Current.

Descending Current.

I. (Ritter)

M. contraction
B. 0

M. 0
B. contraction

II. (Hitter)

M. contraction
B. weak contraction

M. weak contraction
B. contraction

III. (Ritter)
I. CXobili)

M. contraction
B. contraction

M. contraction
B. contraction

IV. (Ritter)
II. (Nobili)

M. weak contraction (0)
B. contraction

M. contraction
B. weak contraction

V. (Ritter)
III. (Nobili)

M. 0
B. contraction

M. contraction
B. 0

VI. (Ritter)
IV. f Nobili)

M. 0
B. 0

M . weak contraction
B. 0

Hitter distinguishes six, Nobili four, stages of excitability. The
completely contrary effect of homodromous currents at the first
(highest), and later (Eitter's fifth), stages of excitability is very
striking. Nobili denies it and asserts that there is only one
marked twitch for each direction of current, the opening twitch of
ascending, the closure twitch of descending currents. More
recently there have been various attempts to determine the facts
which underlie the law of contraction, as well as a theoretical
explanation of them. An important step was taken almost

136

ELECTRO-PHYSIOLOGY

CHAP.

simultaneously by Heidenhain and by Pfliiger, who pointed out
that the " law of contraction " was a function not merely of direc-
tion of current and of excitability, but also of current intensity.
Beginning with the weakest currents, Heidenhain (18) obtained
the following table of effects from freshly-prepared nerve : —

Strength of Current.

Descending Current.

Ascending Current.

I.

Make.

Break.

Make.

Break.

0

0

C

0

II.

0

C

C

0

III.

(rarely contraction)
C

(rarely 0)
C

C

0

IV.

C

C

C

C

Heidenhain does not seem to have exceeded a certain average
strength of current, for Ritter's fifth stage (and Nobili's third),
(i.e. closure twitch only with descending, opening twitch with
ascending direction of current, in the fresh nerve), do not appear.
All later observers state that at a given medium strength of
current both closure and opening are effective, with both descend-
ing and ascending directions. It is only with stronger currents
that the contrary effect of opposite direction of current becomes
apparent. In regard to minimal currents, on the other hand,
there are considerable differences of opinion. Heidenhain noted
as the first contraction the closure twitch of the ascending, as
the second the opening twitch of the descending current, while
most later observers give the closure twitch with both directions
of current as the first effect of minimal currents (Bibliography to
Herm. Hamlb. ii. 1, p. 61), the only difference being whether the
descending or ascending current was the first to act. The
formula given .by Pfliiger (2) must undoubtedly be accepted as
the most correct expression of the law of contraction—

St rei

gth of Current.

Ascending Current.

Mrscendinj; Current.

Make.

Break.

Make. Break.

Weak

C 0

C

0

Medium

C <'

C

C

Strong

0 C

C

0

(weak contraction)

ix ELECTRICAL EXCITATION OF XERVE 1---7

In fresh, vigorous, motor frog's nerves the closure of weak
currents therefore effects a twitch with both ascending and
descending direction of current, while the opening of the current
remains without effect in both cases (first stage of the law of
contraction). The opening contraction then makes its appearance
gradually with growing intensity of current, so that the second
stage is characterised throughout by twitches from the muscle,
which accompany the closure and opening of both ascending and
descending currents. The opposite effect of a contrary direction
of current first appears when the intensity has exceeded a certain
limit, the rule being then universal that only the closure of
descending and opening of ascending currents elicit any contraction,
while closure of ascending and opening of descending currents
invariably fail in effect. These consequences are so regular that
they can be employed as a means of determining the direction of
current physiologically, upon a rheoscopic preparation. In order
to demonstrate the law of contraction it is essential whenever
possible to test upon the same preparation the effect of different
strengths of current in one direction only, without changing the
position of the nerve upon the electrodes, the most convenient
method being to excite two nerve-muscle preparations from the
same frog simultaneously, by laying the two nerves in opposite
directions across the same unpolarisable electrodes. It is then
possible to observe at the same time all the changes in the reaction
of the muscle which follow upon increased intensity of current, as
when, in the third stage, one preparation twitches only on closing
the current, the other on opening it.

Pfl tiger was the first to give any satisfactory explanation of the
facts (at first sight very striking) which underlie the law of con-
traction. There is first of all the marked contrast between make
and break effects in the third stage. It is obvious that the mere
alteration in direction of the electrical current is not per se a
sufficient explanation, and if, as can hardly be doubted, the nerve
is also excited at closure of the ascending and opening of the
descending current, the failure of the excitation can only be
explained by the fact that it is in some way hindered from
expressing itself in the muscle. In other words, there must at
some part of the tract of nerve traversed be an alteration which
blocks the excitatory process on its way to the muscle, at closure
in the one case, on breaking the circuit in the other.

138 ELECTRO-PHYSIOLOGY CHAP.

Iii view of the experiments on striated and smooth muscle as
discussed above, it is natural to conjecture for nerve also that we
are in presence of antagonistic polar effects of current, in the seuse
that the excitation is from the kathode only at closure, from the
anode on opening the current. When, therefore, at closure of a
strong descending current, or on opening a strong ascending
current, there is a twitch, it is evident that there is nothing in
either case to block the transmission of the excitation from the
corresponding electrode to the muscle. When, on the contrary, the
break twitch fails to appear in the first instance, the make
twitch in the second, it may be assumed with probability that
the kathodic excitation discharged above the anode with ascending-
direction of current is blocked there, and never reaches the muscle.
And conversely the break excitation, discharged with a descending
current above the kathode, appears to die out at the previously
kathodic point of the nerve. Thus, in the precise analysis of the
phenomena consequent upon the electrical stimulation of motor
nerves, we reach the same ultimate conclusion as for contractile
substances, viz. that the current does not discharge the process of
excitation equally, at all points of the area traversed, but produces
" polar " alterations, manifested partly as excitatory and partly as
antagonistic inhibitory phenomena, as expressed in the third
stage of the law of contraction. We are indeed less favourably
situated here than in the direct excitation of contractile substances,
where the polar action of the current is immediately translated
into corresponding changes of form at the physiological pole, since
we are thrown back in nerve upon the reactions of the terminal
organ (more or less remote from the seat of stimulation), in proof
that the change usually takes place in one direction only.

The fundamental importance of the postulate of polar
excitation by current, which Prliiger at first deduced simply as
an inductive consequence of the law of contraction, rendered it
desirable to obtain further direct evidence of its accuracy. V.
Bezold (19) attempted to confirm the law by time-measurements
for motor nerve, as he had for striated muscle. The method,
which in both cases consisted in measuring the latent period of
the muscle-twitch, proved to be even simpler for indirect than for
direct excitation of the muscle. If an ascending current of
medium density is led through a sufficiently extended part of
the nerve in a nerve-muscle preparation, the latent period of the

ix ELECTRICAL EXCITATION OF NERVE 139

make twitch must obviously be much longer (if the excitation is
discharged at closure of the current from the kathode, distal to
the muscle, thus having a longer course than the anodic opening
excitation) than the latent period of the break twitch under
otherwise similar conditions. The contrary must occur with a
descending current. The difference corresponds in either case
with the time required by the excitation to propagate itself
through the intrapolar portion. These presumptions are con-
firmed by the results of v. Bezold. The interval between the
moment of excitation and commencement of the muscle-twitch is
greater at closure of the ascending, and opening of the descending,
current than it is conversely.

Further evidence, at least for the localisation of the changes
in the nerve that underlie the break excitation, was brought forward
by Pfltiger himself, when he showed that a Eitter's opening tetanus
manifested under favourable circumstances with descending direc-
tion of current disappeared as soon as the nerve was divided in
the middle of the intrapolar tract, the muscle being thus removed
from the influence of the anode. This experiment does not of
course come off in a Eitter's tetanus with ascending direction of
current.

In order to explain the phenomena comprised under Pfliiger's
law of contraction, we are experimentally forced to assume that
the electrical current, along with the excitatory action proceed-
ing at make from the kathode, at break from the anode, elicits
simultaneous inhibitory action, the localisation of which can only
be conjectured. If by analogy with the excitatory process we
regard the inhibitory effect also as polar, we should a priori,
on the analogy of the muscle, presume that changes take place
in the substance of the nerve — at the anode at closure, at the
kathode on opening the current --as expressed in a more or
less pronounced depression of excitability and also of conduc-
tivity. All the phenomena of the law of contraction are
satisfactorily explained on this hypothesis, with the aid of the
further postulate that the development of excitation arid of
inhibition are not perfectly parallel, since weaker currents suffice,
as a rule, to produce the former, than are required to elicit the
latter. We can thus understand why currents of medium
strength should evoke both closing and opening twitches, with
either direction of current. The inhibition which they discharge

140 ELECTRO-PHYSIOLOGY CHAP.

at the anode or kathode respectively is manifestly insufficient
to neutralise the excitation approaching the muscle, from the
kathode at make of the ascending current, from the anode at
break of a descending current. While, lastly, the single
reaction on stimulating with weak ascending or descending-
currents is readily explained on the assumption that the magnitude
of the two impulses excited by current is unequal— the fall of
the current in particular being the weaker stimulus. With
gradually rising current intensity, the more active kathodic
stimulus at make is first to take effect, and the weaker anodic
opening stimulus only comes into play when the current is still
further strengthened.

III. CHANGES IN EXCITABILITY AND CONDUCTIVITY PRODUCED

BY THE PASSAGE OF A GALVANIC CURRENT (ELECTROTONUS)

We have next to consider the facts from which it is con-
cluded that an inhibitory impulse arises at the anode on closing,
at the kathode on opening, a constant current. It is again to
Pfliiger that we are indebted for decisive evidence. While in the
muscle, polar inhibition finds double expression in change of form,
along with simultaneous depression of excitability, we are in
nerve thrown back solely upon the latter, and should therefore
(according to the previous observations) expect, with sufficiently
strong currents, to find depression of nervous excitability at the
anode during closure, at the kathode after breaking the circuit.
Here we are at once confronted by a marked dissimilarity from
striated muscle. While in the latter, " electrotonic " changes of
excitability are essentially local and confined to the physiological
poles, in medullated nerve (under similar conditions) not merely
the whole intrapolar, but considerable sections of the extrapolar
region also, exhibit alterations of excitability during and after
the passage of current, these alterations being unlike and opposite
in the vicinity of the two poles. Even the earlier electricians
observed indications of such a reaction on sending current through
an entire limb, but Eckhardt was the first to show by unex-
ceptionable experiments that a nerve of which a portion was
traversed permanently by a constant current, underwent substantial
modifications as expressed by increased or diminished excitability
to artificial stimuli at points of the intra- and extra-polar regions.

IX ELECTRICAL EXCITATION OF NERVE 141

The former is universally the case on the side of the kathode,
the latter on that of the anode. In a typical series of experi-
ments (the results and theoretical conclusions from which form
the contents of the classical work on " Electrotonus " so frequently
alluded to), Pfliiger has exhaustively investigated all the facts
which relate to this subject.

If a constant current is led, by means of unpolarisable elec-
trodes, into the middle portion of a nerve that is still united at
one end with the muscle, the resulting alterations of excitability
are easily demonstrated in the tract of nerve that lies between
muscle and polarising current. As " test - stimulus " we may
employ either an easily graduated electrical, or a chemical, or
mechanical excitation, the height of the muscular contraction
being of course the gauge of excitability. If increase of
response is to be demonstrated, the twitch discharged by the
test-stimulus before the polarising current is made must obviously
be submaximal. When the latter is ascending, and the stimulus is
applied at a point of the nerve not too remote from the anode, in
the direction of the muscle, a more or less definite depression of
excitability inevitably appears, which increases in magnitude with
increasing strength of the polarising current. Under these condi-
tions a current that previously discharged a maximal twitch may
become totally ineffective, and in the same way a vigorous tetanus
produced by electrical or chemical excitation (concentrated salt-
solution) may be momentarily interrupted if a strong ascending
current is closed above the part excited. If different points of
the " myopolar " portion of the nerve (between muscle and polar-
ising current) are excited as equally as possible, it can easily be
determined that, on the one hand, the depression of excitability
spreads with increased intensity of current over an increasing
portion of the myopolar region, while, on the other, the degree of
alteration from the anode diminishes rapidly. With a descending
polarising current, the relations of excitability within the myopolar
region are precisely opposite in character. The response is now
augmented under all circumstances, in a greater degree in propor-
tion as the test-stimulus is nearer the kathode, and the polarising
current (other conditions being equal) stronger. Tetanising
stimuli, which previously elicited little or no trace of excitation,
evoke a vigorous tetanus, when a descending current of sufficient
strength is made above the point at which the nerve is excited.

142 ELECTRO-PHYSIOLOGY CHAP.

The relations of excitability in the extrapolar ("centropolar")
tract of nerve above the ascending or descending polarising current
are much more complicated, particularly in the first case. The
augmentation of excitability still appears indeed (as pointed out by
Pfliiger) with weak currents, but quickly passes into its contrary
with stronger excitation, since at a certain strength of polarising
current a stimulus of given intensity discharges a weaker contrac-
tion than was previously the case, while at last the strongest
stimuli (which excited maximal twitches before the closure) fail
to give any effect. This, however, is due less to declining
excitability above the kathode, i.e. centropolar diminution of ex-
citability, than to decreased excitability and conductivity below,
at the anode, which becomes more and more prominent with
increasing strength of polarising current, and modifies in a greater
or less degree the action of every excitation discharged from
above upon the muscle. This is the principal reason why
Valentin and Eckhardt failed to detect the extrapolar increase
of excitability above the kathode. We must accordingly assume
a constant increase of excitability, proportionate with strength of
current, above the ascending as well as below the descending
current : as in the latter, it is the more pronounced the nearer the
point tested lies to the polarised tract of nerve ; at a definite
distance from the kathode (according to the intensity of the
current) it is 0. The extrapolar excitability above the anode of
the descending current is again in complete conformity with the
anodic alterations of excitability which appear below the ascending-
current. There remains only the excitability within the intra-
polar tract that is actually traversed by the ascending or descend-
ing current. Obviously, whatever has been stated above of muscle
under the same conditions, both as regards difficulties of investiga-
tion and method adopted, must hold good of nerve also.

Starting with the erroneous presumption that an induction-
current excites the entire tract of nerve through which current is
passing, Pfiiiger attempted in the first place to determine the
" total excitability " of the intrapolar tract, as dependent upon the
strength of the polarising current, — leading in the induction current
employed as test-stimulus by the polarising electrodes (according
to a method previously employed by Eckhardt), as was described
above for muscle. But since polar action has now been determined
for induced currents also, it is clear that the results of these

ix ELECTRICAL EXCITATION OF NERVE 143

experiments cannot be accepted in the original sense. Pfliiger
himself has made certain experiments with chemical excitation of
single points of the intrapolar tract of the nerve which show it
to be divided into two sections, separated by an " indifferent
point " —in one of which excitability is depressed, while it appears
to be raised in the other — -the former occurring in the vicinity of
the anode, the latter in that of the kathode. With increasing
strength of current the indifferent point shifts from the region
of the anode to that of the kathode (independently of the direc-
tion of the current) in a higher degree in proportion with the
strength of the polarising current. The anodic depression of
excitability spreads in this way with increasing strength of
current over a constantly enlarging area of the tract of nerve
traversed. These facts, as to alterations of excitability in the
intrapolar tract, have been recently confirmed by Tigerstedt (20)
with mechanical single stimuli, since his observations coincide
entirely with all the other results of Pfliiger.

The after-effects of the constant current upon the excitability of
nerve (among the immediate consequences of which must be
reckoned the break excitation itself) are no less important than
the alterations of excitability which appear during the closure of
the polarising current. Here again certain isolated researches
date from the first days of galvanism, and have been carefully
summarised by Pfliiger (Electrotojius, p. 72 ff.) : these refer
mainly to the conditions of appearance, and to the interpretation
of the opening excitation. But, as Pfliiger pointed out, the after-
effects of the passage of current are expressed not merely in visible
excitatory phenomena, but also in regular alterations in response
at all those parts of the nerve which manifested changes of
excitability during the passage of the polarising current. This
may be briefly expressed by saying that there is, generally
speaking, at all points where a rise of excitability is apparent
during the passage of the current, a diminution of response
immediately after the opening of the circuit, and vice versa. It
should be added that the positive modification (increase of excita-
bility) on both sides of the kathode of the polarising current is
only temporarily reversed at break, and finally terminates in a new
increment of excitability, while the negative modification (depres-
sion of excitability) in the region of the anode undergoes a
permanent positive modification, and subsides as such. The

144 ELECTRO-PHYSIOLOGY CHAP.

duration of the first phase of decline of the kathodic alteration
of excitability (negative modification) is shorter, other conditions
being equal, in proportion as the polarising current is strengthened,
so that it is sometimes difficult to demonstrate (Obernier, 21),
and can only be shown when the test-stimulus acts simultaneously
with or immediately after the opening of the polarising current.
Otherwise the intensity and duration of the after-effects depend
entirely upon the intensity of the original changes, including of
course strength of the modifying current.

From these facts, therefore, we learn that, when a tract of
medullated nerve is continuously traversed by a constant current,
the nerve falls not merely at and between the electrodes, but also
beyond the poles, into an altered state (elcdrotonus), as manifested,
apart from other phenomena to be described below, in alterations
of excitability towards given stimuli, in the sense that there is,
while the current is passing, an increase of excitability in the
region of the kathode, a depression of excitability in the region
of the anode. The term katelectrotonus is commonly applied to
the former state, the term amlectrotonus to the latter, though it
should be remarked of both expressions that they cover not
merely the alterations of excitability, but also the modification of
the nervous substance produced by an electrical current in the
region of the two poles, — which, as we shall see, may find other
modes of expression.

The electrotonic alterations of excitability may be clearly shown
in a graphic representation. If the excitability of each point is
drawn as ordinate upon the nerve as abscissa, the line which
unites the tops of the individual ordinates usually (apart from the
increase of excitability near the cross-section) forms a line parallel
with the abscissa. If current is then led through the middle
portion, there will be increased excitability on the side of the
kathode, diminished excitability on that of the anode. If the
former is represented by an ordinate drawn upwards (positive), the
latter may be similarly drawn as a downward line (negative).
The excitability declines from either point, both between and
beyond the poles, and spreads over a larger tract of the nerve as
the polarising current becomes stronger. Let gi (Fig. 185) be
the nerve, to which are applied the electrodes ^4 and B ; the
excitability of single points during closure to weak, medium, and
strong currents may be expressed by the three curves abc, dcf,

ix ELECTRICAL EXCITATION OF NERVE 145

and yhi. Here again the true form of the curve is uncertain, and
this merely represents the general relations. The curve abc
shows that nearly the whole of the intrapolar tract is thrown
with minimal currents into a state of augmented excitability
(katelectrotonus), while the indifferent point in this case is near the
anode. Excitability increases gradually from this point on the
one side, while on the other it is correspondingly diminished.
The alteration reaches its maximum in the immediate proximity
of the two electrodes, whence it declines again to 0. The curve
(clef} from currents of medium strength is essentially the same,
but is distinguished by the larger tract of nerve which it embraces,
and by higher ordinates, while the indifferent point lies about
midway in the intrapolar region. These differences correspond

FIG. 185.

with the fact that the electrotonic alterations of excitability
increase in intensity and extent of diffusion with the strength of
the polarising current. The same applies to the curve (glii} of
strong currents, which contrasts with abc, inasmuch as the
indifferent point lies near the kathode, so that almost the whole
intrapolar tract is in a state of anelectrotonus. It would also
be easy to record the after-effects of an- and katelectrotonus, since
the excitability of every point, at all events immediately after
breaking the current, is exactly opposite to the effect at closure.

We have up to this point considered only the effect of
strength of polarising current upon magnitude and diffusion of
electrotonic alterations of excitability, yet, as Pniiger has shown,
the length of tract traversed, as well as the time-relations of the
passage of the current, are not unimportant factors. The first of
these two (besides the older experiments of Humboldt, Eitter,
and others) was investigated by du Bois-Eeyrnond. According
to Ohm's law, the intensity of an electrical current is directly
proportional with its E.M.F. and inversely proportional with the

VOL. II L

146 ELECTRO-PHYSIOLOGY CHAP.

resistance of the circuit. If the effect of length of tract upon
excitation, or upon electromotive alterations of excitability, is to
be studied, care must be taken, in view of the great resistance
of nerve, that the total resistance is not unduly altered with the
enlargement of area traversed. Du Bois-Beymond accomplished
this by introducing an alcohol rheostat as resistance, against
which the resistance of the nerve-tract is practically minimal.
He then found that the extrapolar electrotonus (i.e. its galvanic
manifestation), and the negative variation as the expression of
excitation, were more strongly developed when the intrapolar
tract was lengthened. Pfliiger subsequently reached the same
conclusions.

Willy (22) then tested the different magnitudes of twitch
under uniform conditions. He employed two nerves, traversed
one in longer, the other in shorter portions by current.
Stronger excitation of the longer portion was found to be
effective with the closure of descending currents only, while
closure of ascending currents gave the contrary effect. Willy
formulated his observations as follows : " Excitability is cceteris
paribus the stronger, in proportion as the muscle is nearer the
kathode, and farther from the anode."

Marcuse (22) investigated the same problem under Eick's
direction, the nerve being placed in a small parallel-epipedic
glass trough filled with physiological saline. Its opposite walls
were made of amalgamated zinc, through which an induced
current was led in. As a longer or shorter portion of the nerve
was bathed, it was traversed by the current at constant density ;
with increasing length the minimal, just effective strength of
current diminished, at first rapidly and then more slowly,
" appearing to approach a limit asymptotically, or after passing
a minimum to increase again." With the constant current also,
Marcuse found a beneficial effect from a longer intrapolar tract,
with both ascending and descending direction of current, since
the first perceptible twitch made its appearance earlier than in
a shorter tract. Tschirjew (16) and Clara Halperson (23)
arrived at much the same results.

The time-development of all the modifications in the nervous
substance which are characteristic of electrotouus, including the
above alterations of excitability, will be discussed at a later period.
Pfliiger places the katelectrotonic increase of excitability im-

ix ELECTRICAL EXCITATION OF NERVE 117

mediately after the closure of the battery current, from which
point it declines slowly, while anelectrotonus is relatively slow to
develop and to diffuse ; the maximum invariably occurs some time
after closure. We shall see that this agrees perfectly with the
galvanic alterations of the nerve in electrotonus.

If conductivity is, in the words of Gad, only the expression
of " longitudinal excitability " in the nerve, i.e. capacity of trans-
mitting a local excitation longitudinally from section to section,
it seems a priori highly probable that it should undergo alterations
of conductivity coextensive with the electrotonic alterations of
excitability. The law of contraction indeed indicates directly
that the persistent anelectrotonus (with ascending direction of
current), as well as the diminishing katelectrotonus (with descend-
ing direction of current), do cause an inhibition of conductivity
as regards the excitation approaching in the first case from the
kathode, in the last from the anode. It must further be assumed,
in view of the first and second stages of the law of contraction,
that the depression of conductivity effects an active inhibition only
with relatively high strengths of polarising current. Von Bezold's
admirable investigation (19) of conductivity in electrotonised
nerve only corresponds partially with these presumptions. It
has been stated that every excitation discharged above a tract
of nerve traversed by an ascending or descending current
remains without effect at a certain strength of polarising
current, because the diminution of excitability (and conduc-
tivity) is presumably so considerable in the entire anelectrotonic
tract, that it offers an actual hindrance to the propagation
of the stimulus to the muscle. Before this point is reached,
however, this betrays itself in a more or less considerable
delay in the entrance of the muscle-twitch, which is greater in
proportion with the strength and duration of passage of the polaris-
ing current. In order to determine exactly the share taken by
the polarised tract, the two poles, and also the extrapolar tract of
nerve, v. Bezold in the first place stimulated the muscle directly,
and then the nerve at three different points (a, l>, c) of its course, by
a single induction shock (Fig. 186). It was then possible from
the differences of latent period to calculate the rate of conduc-
tivity of the excitation from a to the muscle, from & to «,
and from c to 5. An ascending battery current was then led
uninterruptedly through the tract c, the secondary coil of an

148

ELECTRO-PHYSIOLO* ;Y

CHAP.

induction apparatus being included in the circuit, when the finally
retarding influence of the extrapolar anelectrotonus upon the rate
of conductivity appeared on repeating the four twitches. This
occurred in fact without exception : apart from the influence of
duration of closure (as already mentioned), the value of this
retardation at each cross-section of the nerve was creator in

O

proportion with its proximity to the positive pole of the polarising
current. If this result can hardly be regarded as surprising

o>

FIG. 186. — Influence of electrotonus upon conductivity in nerve, (v. Bezold.)

since it agrees perfectly with the reaction of excitability at the
single points of the extrapolar tract of the nerve as described
above, v. Bezold's further observations are at first sight very
remarkable. He finds a similar reaction of conductivity when
the polarising current at c is descending, the myopolar tract of
the nerve being therefore in katelectrotonus. In view of the
contrast expressed in all other relations between anelectrotonic
and katelectrotonic alterations of the nerve, we should a priori
expect the contrary, i.e. acceleration of conductivity, or no
alteration. The fact is, however, less surprising when it is
remembered that v. Bezold employed very strong constant
currents, and prolonged the closure for thirteen minutes. Under
these circumstances the polar katelectrotonus of the muscle is
also expressed as a pronounced depression of excitability and of

ix ELECTRICAL EXCITATION OF NERVE 149

conductivity, which long outlasts the opening of the polarising
circuit (local fatigue). Eutherford (24) indeed has shown, with
weaker polarising currents and shorter closures, that conductivity
is retarded in anelectrotonus only, while it is accelerated in kat-
electrotonus ; it is only with strong currents or longer closure
that such acceleration passes into its contrary. It had previously
been pointed out by Hermann (25) and Grlinhagen (25), and also
by Werigo (25), that with longer closure of strong currents the
initially augmented excitability of the kathodic points of the nerve
gave way to a gradually developing inexcitability, which may
amount to complete impenetrability to excitation with even the
strongest induction shocks. This state develops in the muscle
proportionately with the strength of the polarising current,
and may make such a rapid intra- and extra -polar entrance
that it is hardly possible to demonstrate the transitory rise
of excitability. With weak currents, on the other hand, it is
hours before this secondary alteration in excitability makes
its appearance. If the polarising current is opened at the
moment at which the kathode becomes impenetrable, excitability
(conductivity) returns almost instantaneously — to disappear again
with renewed closure of the current. V. Bezold attempted to
draw conclusions as to conductivity within the intrapolar tract
itself, and assumed an indifferent point, halving the area traversed
by the current (its position being independent of strength of
current), from either side of which conductivity diminished
regularly towards both poles.

In immediate connection with these changes in the excitability
of nerve during the electrotonic state, and its direct after-effects,
there is a whole series of excitatory and inhibitory phenomena
which must be briefly considered. The opening excitation was
referred to above as an after-effect of the passage of current,
in Putter's sense, i.e. a reaction of the nerve to certain alterations
produced by the current. Eitter expresses himself character-
istically as follows (Bcitraye zur ndheren Kenntniss dcs Galvanismus,
i. p. 78 ff., 1802): "We have stated that the phenomena which
accompany the removal of battery -currents are of peculiar
significance. In justification of this assumption we need only
emphasise the fact that they appear at the instant in which
the organic body and its constituents are withdrawn from the
influence of the battery. Hence they are in no way the im-

150 ELECTRO-PHYSIOLOGY THAI'.

mediate product of the battery, for how could this engender them,
seeing that it is no longer present ? The organism which has
been in circuit must yield them itself, and can only yield them
because it lias been in the circuit, since otherwise it would not
have done so."

It would, as Pflliger remarks, be hard to find a more correct
description of the peculiarities of the opening excitation ; and the
recent attempts at giving another interpretation of this original
theory of the break excitation (by which it depends upon the dis-
appearance of a peculiar state engendered by the current) can only
partially be endorsed.

The later observations of Pfliiger and others state that : as
the closure excitation is caused by the appearance of katelectro-
tonus (i.e. the sum of alterations in the nervous substance
produced at the kathode by current), so the opening excita-
tion is the immediate consequence of the disappearance of the
anelectrotonic changes. The alterations of excitability which
accompany electrotonus, or its disappearance, seem however to
authorise a further step in the explanation of these phenomena.
It must always be remembered that (as has been repeatedly
expressed from other points of view) no sharp dividing-line
between increase of excitability and excitation can be predicated.
Rise of excitability beyond a certain point may pass directly
into excitation, while, on the other hand, a weak persistent latent
excitation, which has not produced any visible consequences, may
only be expressed in a heightened capacity for response. Both
appearance of katelectrotonus and disappearance of anelectrotonus
are accompanied by a marked and easily demonstrated, increase
of excitability, which reaches its greatest intensity at the poles,
and in fact discharges an effective excitation there, provided other
conditions are favourable. From this point of view the altera-
tions of excitability in nerve as well as in muscle (which are
only the partial manifestation of electrotonus) fall into immediate
relation with the excitatory phenomena characteristic of the two
moments of appearance and disappearance, closure and opening
of the current. There is no special alteration of the living-
matter fundamental to excitation, and distinct in nature from
the alterations expressed in rise of excitability, but both together
are different manifestations of one and the same change of state
which the excitable substance sutlers under the influence of

ix ELECTRICAL EXCITATION OF NERVE 151

the electrical current, in the one case at the kathode, in the
other at the anode.

A law which appears to . hold for all excitable substances
depends upon the fact that, after prolonged or repeated closure
of a battery current, with unaltered position of electrodes and
direction of current, the effect of the closure excitation declines
more and more, and finally fails altogether. We have already
pointed out for muscle that this depends not upon a gradually
developing inexorability of the entire tract traversed by current,
but upon a local alteration of that point (or points) at which the
excitatory process was discharged primarily, and indeed during
the entire closure of the current, i.e. the physiological kathode.
The simplest proof of this is given in the fact that the muscle
reacts vigorously on reversing the current, as a rule even
more vigorously than before. The same is true of indirect
excitation of the muscle from the nerve. Volta, and after him
Marianini, came to the conclusion that each direction of current
diminished excitability toivards itself, and raised it for the opposite,
direction. " For if current is led through a galvanic prepara-
tion so that one leg is traversed in the ascending, the other
in the descending direction, the twitches will gradually die out
in both legs according to the duration of closure of the current.
On reversing the current, lively contractions reappear in both
muscles." This phenomenon is termed " the Voltaic Alternative "
(supra). Eosenthal (26) has recently made the facts relating to
it the subject of a thorough investigation, the results of which
are summed up in the observation, " Every constant current tliat
f ' i'n 'verses a motor nerve for any length of time throivs it into a
state of increased excitability to the opening of the same, and
closure of the opposite, current, of diminished excitability to the
closure of the former and open in// of the latter" Ritter pointed
out that the opening tetanus disappeared, and the muscle
became relaxed instantaneously, when the battery current was
closed in the same direction as before, just as in direct excita-
tion of the muscles the anodic persistent opening contraction is
suppressed by closure of the homodromous current. Eosenthal
adds that closure of the current in the opposite direction not
merely fails to abolish Eitter's tetanus, but even increases it con-
siderably ; while opening of the circuit acts like closure of the
homodromous current, i.e. neutralises the tetanus. An extinguished

152 ELECTRO-PHYSIOLOGY CHAP.

opening tetanus may even be reinstated by closure in the oppo-
site direction, if closure and rapid reopening of the homodromous
current fail to do so. If the tetanus which derives from the
opening of an ascending or descending current is strengthened
by closure in the opposite direction, and if this last is persistent,
the tetanus which was at first reinforced will disappear gradu-
ally. But if the current remains closed after its disappearance,
tetanus reappears when it is opened, and the preparation reacts
to this current, as previously to its opposite, i.e. as if this current
had acted from the first upon the nerve. The new current,
therefore, in the first instance abolishes the original modification,
and then begins to reinstate it.

All these facts find a direct explanation in the polar altera-
tions of excitability, or excitatory and inhibitory phenomena in
nerve, as described above, and might indeed have been predicted
from this standpoint. In this sense Eosenthal's law is no more
than a consequence of the polar law of excitation as set forth
above — a necessary effect of the simultaneous and antagonistic
changes produced at the two poles by current, and the suc-
cessive changes at one and the same pole during closure and after
opening of the current. It thus appears almost self-explanatory
that renewed closure of the homodromous current should at once
break off a persistent opening excitation, since at that moment
anelectrotonus would again prevail at every point of the nerve
at which the excitability had been heightened. Closure of
current in the opposite direction would of course have the con-
trary effect, since excitation resulting from the vanishing anelec-
trotonus would be supported by the katelectrotonus appearing at
the same point.

Seeing the importance which has accrued to the application
of the electrical current in practical medicine, the many attempts
to determine electrotonic alterations of excitability, and the law
of contraction on man, become intelligible. Yet it is a priori
obvious that the difficulties of investigation are incomparably
greater, since the complicated and in part intangible relations of
current distribution and conduction render any direct comparison
of results with those obtained from the stimulation of isolated
nerve difficult, and often quite impossible. Under any circum-
stances the greatest caution is required in accepting the conclu-
sions obtained from experiments on man.

ix ELECTRICAL EXCITATION OF NERVE 153

In the older literature of galvanism there is only one often-
quoted communication by Patter (1802), with reference to altera-
tions of excitability in human nerve under the influence of the
electrical current. On dipping both hands into two vessels of
water connected with the poles of a strong battery, Flitter found
after a certain time (he remained half an hour in connection with
the battery) that mobility was perceptibly increased in the arm
through which current was ascending, while it was correspond-
ingly diminished in the arm traversed in the descending direc-
tion. These modifications continued for a short time after
opening the circuit. Ffliiger saw in this experiment an entire
confirmation of his conclusions from the frog-preparation. If a
battery is closed through both arms, " the nerves of the arm are
traversed by currents of different density from the brachial
plexus, or the spinal cord with its motor-nerve roots, because
the cross-section of the path of the current is here so large that
current density may, generally speaking, be regarded as minimal.
For this reason the arm traversed in a descending direction may
be pictured as if the positive electrode was applied to the
shoulder, the negative to the hand. That traversed in the
descending sense must correspond with the opposite distribu-
tion." Now since stimuli above a descending current discharge
twitches weaker than the normal, those above an ascending cur-
rent on the contrary being stronger, the conformity with the
laws of electrotonus would seem to be complete, when it is
remembered that " the sensorium itself here takes on the business
of excitation above, in the one case, the positive, and, in the other,
the negative electrode." At a much later period Fick (27) again
endeavoured to estimate the electrotonic alterations of excitability
in man. He tried to polarise the ulnar nerve at the posterior
side of the internal coudyle, in order to test the anelectrotonus,
but without success. " At an almost unbearable strength of
current (10—14 Bunsen) no trace of inhibition was visible in the
muscles supplied by the ulnar nerve." Fick ascribed his failure
to the impossibility of applying sufficiently strong currents, which
is the more improbable, since electrotonic alterations of excitability
appear with extremely weak currents.

This was followed by the investigations of Eulenburg (27),
Erb (27), Samt (27), and others, which partly confirmed and
partly contradicted the conclusions of Pfluger. Euleuburg agreed

154 ELECTRO-PHYSIOLOGY CHAP.

with him on the ground of his own experiments, finding invari-
ably a diminution of excitability in the region of the anode, an
augmentation in that of the kathode. Erb, on the contrary, ob-
served on his own ulnar nerve an initial decrease of excitability
near the kathode, and increase near the anode, which, as was sub-
sequently pointed out by Helmholtz and admitted by Erb, is
essentially due to the formation of secondary electrode points pro-
duced by relations of conductivity within the arm. Samt again
obtained contradictory results in different cases, and referred this
apparent inconstancy of reaction to an inconstancy of the nerve itself.

No one who is unprejudiced can doubt (in spite of these
contradictions) that if it were possible to test human motor
nerves in the same unexceptionable manner as the nerve of a
frog's leg, there would be essentially the same reaction of excit-
ability under the influence of a battery current — this effect being
only masked in man and other intact animals by the masses of
tissue which surround the nerve, and the complications that arise
in applying the electrodes. De Watteville (27) in fact finds,
with due precaution against every possible source of error, that
there is complete conformity between the electrotonic alterations
of excitability in the nerves of man and in frogs' nerves, both
as regards the effects during closure of the modifying constant
current and the after-effects of opening the circuit.

These considerations, which apply more especially to the
difficulties and fallacies attending the investigation of electro-
tonus in man, are no less apparent in all experiments brought
forward in proof of the law of contraction 011 other intact living-
animals. There is again great uncertainty among the different
authors, both as to results and in method. It appears to be
quite impossible to speak of airy definite (lir<rf/<»i of current
in the nerve, as long as it is still in situ, since, as Hermann
points out, " the current necessarily divides so that it flows
through both apparently extrapolar tracts, and that in a direction
contrary to the intrapolar current" (H. Handl. ii. 1, p. 62,
Fig. 187). For this reason it lias been usual to fall back
upon the so-called " unipolar " (more correctly monopolar) method
of stimulation, the application of which is (xiipm) sometimes of
value in direct excitation of the muscle, in testing the local
visible action of current at the point of greatest density. For
nerve, however, it must be regarded as illusory to test, at any

ix ELECTRICAL EXCITATION OF NERVE 155

strength of current, the action of a single isolated pole. It is
clear that if one pole be applied as close to the nerve as possible,
while the broad surface of the other rests upon any distant
(indifferent) part of the
body, the density of the
current must be unequal
at the physiological anode
and kathode of the nerve,
but by no means to such

an extent that the One FIQ.IST.— Schema of current distribution!

in a nerve in

Dole lloiie is involved in S!'" * ''^' '• v'r';ua' kathodes ; ««, virtual anodes.

(Bernstein.)

respect of physiological

action. This might occasionally be the case with minimal
currents, but with even a low increase of current intensity
the action of the other pole must come into play. Every
nerve that has an anode must have a kathode also, even
if only one electrode is directly connected with it, and it
depends on the ratio of density between the two poles
whether one or the other acts alone or preponderatingly.
This agrees with the fact that the make twitch (" anodic closure
twitch " of the pathologist) is observed in monopolar excitation
of a motor nerve with the anode as well as with the kathode.
The widespread opinion among pathologists (c.y. Brenner, 27) that
the results of monopolar excitation of nerve may, theoretically,
be set side by side with the facts of ordinary bipolar excitation,
and the recent acceptance of this view by some physiologists
(Jofe, 28), cannot be admitted for the study of electrical excita-
tion of nerve, although the monopolar method may legitimately
be applied in single cases. The above theory would undoubtedly
lead, as in the case of Jofe, to false conclusions, — con-
tradicted by the many facts and experiments underlying the
established principles of electro-physiology, which must be the
substrate of all future discoveries. We must therefore set aside
all attempts to demonstrate the law of contraction in man and in
intact animals, since no new points of view can be elicited from
them.

IV. EXCITING EFFICIENCY OF ELECTRICAL CUREENTS

It is evident that the phenomena underlying Pfliiger's law of
contraction must be more or less altered by local or general

156 ELECTRO-PHYSIOLOGY CHAP.

alterations of excitability in the nerve, so that it is no wonder
if, under certain conditions, there are apparent exceptions from
the rule. Apart from the well-known tendency of " cooled frogs "
to sustained tetanic excitation, which renders them almost en-
tirely unsuitable to the demonstration of the law of contraction,
we have to remember the influence exercised by the proximity of
an artificial cross-section, not merely upon general excitability,
but also upon the mode of action of the battery current.

As regards the former, the raised excitability at the cross-
section of a medullated nerve must be regarded essentially as
a consequence of katelectrotonus, produced within a certain
tract from the cross-section, by internal short-circuiting of the
nerve-current, — a fact to which we shall return later. We must
first consider the influence, of the transverse section upon the polar
action of current.

If unpolarisable electrodes are applied to the cut end of a
motor nerve of a frog, so that the lower electrode in contact with
the " long section," and the upper resting on the cross-section,
are sufficiently approximated, the intrapolar tract being very short,
the effect, even with minimal currents, invariably corresponds
with the third stage of the law of contraction. At a some-
what greater distance of the peripheral electrode (intrapolar
tract = 1—2 cm.) the effect of excitation with weak currents
is, on the other hand, a closure twitch with ascending, a closure
and an opening twitch with descending direction of current. In
this connection we have also the experiment of Heidenhain (29),
who divided the nerve between the electrodes and closed up the
cut ends again ; whereupon, if the incision was made sufficiently
near the myopolar electrode, the activity of the latter alone
persisted. The zone of depressed excitability in the region of the
cut surface in nerve appears to be considerably greater in warm-
than in cold-blooded animals. At least the experiment comes off
with a greater distance of electrodes in the first case than in the
last. If the sciatic nerve of a mammal or bird is exposed in its
full extent, and then divided (after previously determining the
exclusive effect of closure with not excessively strong ascending or
descending currents, at the electrode proximal to the centre),
there will, with the electrodes close together (about 1 cm.),
under the same conditions as before, be a closure twitch only witli
descending direction of current, an opening twitch with ascending

ix KLKCTRICAL EXCITATION OF NKHVK 157

direction. Similar effects may be observed in frog's nerve on
warming the cut end to 40—00° C., or by freezing for an extent
of about 1 cm. By gradually moving the electrodes along a
distance of 1-2 cm. it is easy to find the place at which, begin-
ning with minimal currents, there is with ascending direction of
current a break twitch, with descending direction a make
twitch, only. This is obviously another proof of the law of polar
excitation.

We have seen that the closure and opening of a current sent
through a regular parallel-fibred muscle will only excite normally
when the active electrode is at the uninjured end of the muscle.
The explanation of this phenomenon as given above leads us to
conjecture, from the wide-reaching conformity of reaction to the
electrical current in nerve and muscle, that analogous effects
would appear in the partially injured nerve also. But we have
seen that it is not sufficient to apply one electrode to the cross-
section of an otherwise normal nerve, while the other rests/
upon any point of the longitudinal surface, in order to obtain
the effects corresponding with the third stage of Pflliger's law :!
it is necessary to destroy a considerable portion of the nerve from
the transverse section, while as far as possible preserving its finer
histological structure. This, as we shall presently see, is due to
the fact that there are in medullated nerve (in consequence of a
peculiar diffusion of the exciting current on either side of both
kathode and anode) innumerable points where the current leaves
or enters, so that the " physiological kathode " or anode extends
over a comparatively large portion of the nerve, according to the
strength of current at the moment. The intrapolar tract of nerve
thus falls into two parts, differing according to its length and the
intensity of the current, and termed respectively anodic and
kathodic, while each of these also embraces a larger or smaller
portion of the extrapolar region. These two segments, in one of
which (the kathodic) activity is set up simultaneously at many
points at closure, in the other at opening of the current, are
separated by a spot known as the " indifferent point."

If the nerve is destroyed as locally as possible, without
essential alteration of structure at the point corresponding
with the electrode distal to the muscle, the extrapolar interference
from the kathodic or (according to direction of current) anodic
section is eliminated ; but the excitatory action of the intrapolar

158 ELECTRO-PHYSIOLOGY CHAP.

portion is in no way abolished, so long as excitability is not
materially depressed at the points adjacent to the indifferent
point. For these must obviously play the same part in relation
to the effectuation or failure of the excitation proceeding from
the upper electrode as the fibre-ends in the parallel-fibred muscle
traversed by current, and injured at one end (Biedermann, 30).

Certain chemical substances may also be employed for the
partial killing of medullated nerve, and Harless (31) has com-
municated observations on the effect of ammonia upon the
nerve-trunk, which agree essentially with the above results from
local death of the nerve. Ammonia, when applied in a con-
centrated solution, destroys the vital properties of the nerve at the
point of application without exciting it, or (at least at an early
stage) essentially altering its structural relations. Thus by
applying ammonia with a little brush (Harless) to points of the
intrapolar tract, the kathodic or anodic section of the nerve
traversed by current (i.e. the sum of all points which at given
strength of current and position of electrodes must be regarded
as exit- or entry-points of the current) may be functionally cut off,
and the intrapolar tract divided at the indifferent point, without
alteration of structure ; so that in the case before us only those
excitatory effects can come into play which correspond with the
peripheral electrode, i.e. with descending direction of current the
closing, with ascending direction the opening excitation. Since
the effect of ammonia (and to a lesser degree of other chemical
substances in solution) spreads in time with even carefully
localised application beyond the original point of contact, becoming
weaker in proportion with the distance from the seat of direct
action, it is clear that after applying ammonia in the region of the
central electrode, the modifications of excitability in successive
sections of the nerve must be very gradual. It is consequently
unnecessary to apply the ammonia to the intrapolar tract itself;
it is sufficient (especially if the electrodes are not too far apart) to
apply it to the points of the nerve which lie beneath the
central electrode, or even, if the excitation is in the continuity
of the nerve, on the far side of this, within the " centropolar "
region. When the advancing ammonia-effect has penetrated to
the region of the lower electrode, it is of course desirable to
shift the electrodes (at their original distance) farther along the
nerve. If, however, the electrodes are placed so that the distribu-

IX ELECTRICAL EXCITATION OF NERVE 159

tion of current corresponds with the above conditions, the
exclusive effect of excitation will be the appearance of the
closure twitch with descending direction of current. In regard
to the action of weak ascending currents, there is a perceptible
difference from the cases of partial death of the nerve as previously
described. For while in these last even weak ascending
currents (and an arrangement of the electrodes at which the same
currents when descending produce only a closure twitch) elicit
unmistakable opening twitches hardly less in size than the latter,
these fail altogether with local application of ammonia, or appeal-
merely as a trace when the drug begins to act, or with marked
strengthening of the current.

When PnuQ-er formulated his law of contraction in 1859, it

O

seemed hardly doubtful that the effectuation of the opening
stimulus in the motor nerve depended in first degree upon
the momentary intensity of current. This view was confirmed
by the majority of later workers in this department. Yet
Bitter, and subsequently Nobili, had already pointed out as a
second factor the differing " states of excitability " in the nerve.
Bosenthal and v. Bezold (32) accordingly drew up a law of con-
traction for moribund nerve, which conforms perfectly with
Pfliiger's law, and by which, with unaltered (low) strength of
current at the same point of nerve in three successive stages of
dying, the same alternating effects of excitation are observed as
appear in fresh nerve (according to Pfiiiger's law) with weak,
medium, and strong currents. These changes may be simply
explained on Pfiuger's theory from the course of the alterations
of excitability, which (according to prevailing views) characterise
the single points of nerve that is in process of dying, and which
appear at the more central points before the peripheral.

Pfliiger in the first instance deduced his law from observations
taken almost exclusively from the isolated nerve-muscle prepara-
tion of the frog, where the conditions of excitability are not
essentially different from the normal. For this preparation,
therefore, his law is practically uncontested.

Yet there have been objections even here to its validity in
the case in which the excited nerve is still connected with the
central organs of the living animal.

Bernard, Schiff, and Valentin (33) all agree that the electrical
excitation of undivided nerve "produces contraction of the muscle

160 ELECTRO-PHYSIOLOGY CHAP.

V at closure only and not at opening of the circuit, whatever the
' direction of the current," provided only that it is not too strong.
Valentin, who characterises this reaction as " the true law of con-
traction in vigorous, unaltered, living nerve," certainly carried out
his experiments under conditions that did not admit of a fail-
estimate of current distribution, since he introduced (metal) elec-
trodes into the thigh of the intact animal. This, however,
matters the less, since Claude Bernard and Schiff had already
arrived at the same results on stimulating the exposed nerves
(connected with the central organs) of vertebrates, of different
classes. Bernard already inclined to the view that the nervous
centres exert a special influence upon the efferent nerve-trunks,
thus keeping up the normal excitability, and enabling them to
fall into excitation at the entrance only of (not unduly strong)
currents. The following remark seems at all events to bear such
an interpretation : " Le nerf moteur tire ainsi ses proprietes de la
nioelle. II les perd a 1'air ; mais il peut les reprendre, pourvu
qu'il communique encore avec le centre nerveux." At the same
time, the experiment adduced as evidence hardly justifies the
conclusion. It is merely that a partially isolated frog's sciatic
regains its normal excitability, when the part is moistened, after
previous alteration from drying.

The idea that the failure of the opening twitch, on exciting
undivided nerves with even strong currents, is due to an inhibitory
impulse from the central organ, finds definite exposition in a recent
work by T. Eumpf (33). The experiments were mostly carried out
on the same preparation as was employed by Bernard. The
sciatic nerve forms the only connection between one of the legs
and the otherwise intact body of the frog. From the fact that
here, " in the nerve connected with the central organ, the
opening twitch of the ascending current occurs much later
(i.e. with stronger currents) than in that separated from the
central organ " —as appears still more plainly when the spinal
cord is cooled by external application of some freezing mixture,—
Rurnpf concludes that " constant effects are visible in the motor
nerve connected with the central organ (as expressed in altera-
tions of electrical excitability) which cannot be demonstrated in
a nerve separated from its centre, since in this case the opening-
twitch either appears simultaneously with, or shortly after, the
closure twitch." The latter is "not modified" by the section.

IX ELECTRICAL EXCITATION OF NERVE 161

Hermann (34), finally, points out the possibility "that the
opening excitation, which is dependent on the disappearance of
some change in the nerve, may be influenced by a certain resist-
ance of the nerve to deeper effects of the current (at an earlier
stage of excitability)."

It is remarkable that the different accounts of the initial
appearance of the opening excitation, on stimulating with weak
currents, i.e. at the first stage of Pfliiger's law of contraction, should
again vary in the case of nerve separated from its centre. Pfliiger
himself lays down that the make twitch is the primary consequence
of stimulation with either direction of current, agreeing with the
observations of Bernard, Schiff, v. Bezold, and Eosenthal. Heiden-
hain (18), on the contrary, finds in most cases that the closure
twitch with ascending, the opening twitch with descending direc-
tion, is the first effect of stimulation with minimal currents.
Sometimes, however, he obtained only a closure twitch with both
directions of current, Wundt (35) made similar observations.

The perfectly regular effects of excitation, with a given arrange-
ment and distance of electrodes in divided or partially killed nerve,
gives rise to the conjecture that the differences cited may perhaps\
be explained by differences in the position of the electrodes upon|
a nerve divided from its centre.

We have already seen that in exciting the cut end of a freshly
exposed nerve (one electrode being applied to the cross -section
itself, or to a point of the nerve close to it) the immediate effect
of closure of a minimal descending current is a twitch of the
muscle. A slight increase of current elicits a closure twitch with
ascending, as well as an opening twitch with descending direction
of current. These are approximately equal, and weaker than the
descending closure twitch at the same strength of current. The
ascending opening twitch only makes its appearance with much
greater strength of current. The effects of stimulation are very
different, under otherwise uniform conditions, with weak and even
with medium currents, if both electrodes are applied to a section]
of the same nerve lying a little deeper. For then, without excep- ,
tiou, only the closure twitch occurs with both directions of current,
as was pointed out by Eosenthal and v. Bezold.

The electrodes may be shifted to the immediate vicinity of
the muscle, or middle portions of the nerve may be excited ; so
long as the most central contact is sufficiently distant (about 1 cm.)

VOL. II M

162 ELECTRO-PHYSIOLOGY CHAP.

from the cross-section', the described reaction undergoes no change,
or such only that the closure twitches discharged at different
points of the nerve, with uniform distance of electrodes and
strength of current, are of different magnitudes — corresponding
with the fact that the excitability of a divided nerve is, as a rule,
not merely greater in the vicinity of the cross-section than at
the periphery, but also that certain special points in its continuity
are characterised by a higher excitability.

If with descending direction of current the central electrode
is placed quite close to the cross-section, there is invariably an
opening twitch along with the closure twitch, at any given posi-
tion of the other electrode, and that at very low intensity of the
exciting current, hardly exceeding the threshold of activity.
With ascending direction of current, on the other hand, the
peripheral electrode must be brought to within a few millimetres
of the kathode at the cross-section, in order to demonstrate the
opening twitch, as well as that at closure. The closure twitch is
then, with low intensity of current, very small, and often entirely
absent ; the same applies, after reversing the current, to the
opening twitch.

The dependence of the opening excitation upon the proximity
of the cross-section of a nerve to the anode stands out with
especial clearness when (as was first shown by Heidenhain, 29)
the electrodes are applied anywhere along the continuity of a
nerve, and the " centropolar " tract so shortened by amputation
that the cross-section is brought into the immediate vicinity of
the upper electrode. The opening twitch is at first seen only
with descending direction of current, and it is not till
the intrapolar region is shortened, whether by bringing the
lower electrode close to the upper, or, as was said before, by
making the cross-section within the intrapolar tract itself, and
applying the cut ends together again, that the opening twitch
appears with ascending direction also, while the closure twitch
becomes less, or fails altogether.

The most obvious interpretation of the efficacy of even very
weak opening stimuli in the immediate proximity of the cross-
section of a nerve is that derived from the well-known observa-
tions of Heidenhain (29), to the effect that on applying a cross-
section either to a fresh nerve or to one in which excitability
is already declining, the response of each point not unduly remote

ix ELECTRICAL EXCITATION OF NERVE 163

is considerably increased towards the electrical stimulus. This is
caused by the fact that both ascending and descending currents,
which produce only minimal effects of excitation upon closure,
will, when led in by unpolarisable electrodes to the lower portion
of the nerve, produce almost maximal closure twitches, provided
the nerve is divided at not too great a distance from the central
electrode. The appearance of the break twitch seems, at first
sight, to indicate the same thing, since it is hardly perceptible
with low intensity of current, if the anode falls within the region
which is obviously the most strongly affected by the cross-section.
Although it is indisputable that the opening excitation
takes effect at a very low intensity of current if the anode is
placed in the immediate vicinity of a section (mechanical,
chemical, or thermal) applied to the nerve, the preceding,
and till now generally accepted, interpretation ought not to
pass muster. We need not dwell on the fact (as frequently con-
firmed by experiment) that the opening twitch, in those very
nerve-muscle preparations which are taken from animals brought
fresh from a cold chamber into the laboratory, and in which
excitability is very high, appears plainly for the first time with
relatively strong currents, while in preparations from less excitable
frogs there is sometimes (if rarely) an opening excitation without
the application of any transverse section, at a low strength of
current — because the inevitable closure tetanus masks the weaker
opening effects, which are thus detected only by a delay in the
muscular relaxation.

On the other hand, decisive evidence against the exclusive
agency of rise of excitability in the production of the opening
twitch is afforded by the fact that division of a nerve in the
vicinity of the anode is at once followed by the appearance of
the opening twitch ; even when excitability has from any reason
been much reduced during the experiment, so that (as far as can
be judged from the height of the closure twitches then discharged)
it is not, even near a fresh cross-section, as great as it was at the
same point in the uninjured nerve. Nevertheless the opening-
twitch fails completely with the same strength of current at the
commencement of the experiment, while it appears immediately
after making the cross-section, in spite of the absolutely lower
excitability.

In this connection there are certain very instructive experi-

164 ELECTRO-PHYSIOLOGY CHAP.

ments on nerve, relating to preparations enclosed for several
hours in a moist chamber at the temperature of the room ;
excitability being in consequence much diminished. Immediately
after dividing such a nerve near the electrode distal to the muscle,
a weak descending current will discharge a break twitch, along
with the make twitches, which are not essentially altered in magni-
tude by the incision. The ascending closure twitch may indeed
appear rather larger than before, but is nothing like its original
height. It thus appears that other factors come into play near
a point of section, which favour the appearance of the opening
twitch independently of augmentation of excitability.

At this point we must ask whether the opening excitation
of the nerve is conditioned to the same extent as the closing
excitation by its state of excitability at the moment. Whether,
in other words, it is possible to produce opening twitches with
weak currents, by artificially increasing the excitability to closure
stimuli.

This question might seem to be already decided by the experi-
ments of Eosenthal and v. Bezold (32) to which we have fre-
quently alluded, since in these observations the opening twitch
appears even with weak currents, owing to the alleged rise of
excitability during the spontaneous dying of the nerve. But
this appears to occur only under certain conditions. At all events,
Biedermaun has been unable, on repeating the experiment, to dis-
cover the regular succession of the three stages of the so-called
law of contraction in moribund nerve, on exciting any point with
uniformly weak currents — provided the preparation was enclosed
in a moist chamber, and carefully preserved from injury, and
especially from evaporation. As was pointed out above, even
the primary stage of increased excitability described by Rosen-
thai in the moribund nerve was not apparent under these
circumstances ; there was rather for the most part a gradual
sinking of excitability. It should also be noted that, with un-
altered position of electrodes, the closure of the ascending
current is first to become ineffective, so that at a certain stage
of dying the descending closure twitch is the sole effect of weak
currents. This fact agrees with the so-called Bitter- Valli law,
by which excitability is more quickly extinguished at points
nearer the centre than at the periphery. It would seem, how-
ever, as already pointed out, that the facts which support this

ix ELECTRICAL EXCITATION OF XERVE 165

law relate nut so much to unequal diminution of excitability at
different points of the nerve, as to impaired conductivity.

On the other hand, it is a well-known and easily confirmed
fact that the response of a nerve to weak electrical stimuli is
considerably heightened by loss of water ; and that indeed — as
was pointed out more especially by Harless and Birkner (36)—
at a time when the spontaneous twitches which induce the so-
called desiccation-tetanus are still completely absent. Griin-
hagen and Mommsen (36) have recently shown that " a nerve is
the more sensitive to the effect of the electrical current in pro-
portion with its loss of water, especially when the characteristic
spontaneous twitches make their appearance." Hence it is of
interest to see whether the opening of a battery current of low
intensity acts in this case as sufficient stimulus. Harless dis-
covered that after partial loss of water in the nerve, the opening
twitch was discharged by weak ascending, as well as descending,
currents, and it is easy to confirm the truth of this fact by the
simple experiment of exposing a frog's nerve, laid over unpolar-
i sable electrodes at not too high (room) temperature, to gradual
evaporation, a.nd exciting it from time to time with ascending or
descending currents, the intervals not being excessive. It is
advisable in these experiments to use a nerve-muscle preparation
still connected with the spinal cord,1 in order completely to
exclude the action of the cross -section, although precisely the
same results are obtained on exciting the peripheral tracts of
divided nerves. Moreover, in the last case the preparations with
divided nerves may be left for several hours (Mommsen's process)
in 0'6 ' \ NaCl, in order to equalise the alterations of excitability
caused by section.

V. CLOSING AND OPENING TETANUS THROUGH ELECTRICAL

EXCITATION

1. Conditions of Production by Excitation of Frog's Nerve

The first effect of commencing desiccation appears in the
graphic record of the muscle - contraction, as a more or less

1 Allusion to a nerve still connected with its centre always implies a preparation
taken from a chloralised frog, consisting of the isolated vertebral column (after
destroying the brain), sciatic nerve, and corresponding gastrocnemius muscle, on the
same side.

166 ELECTRO-PHYSIOLOGY CHAP.

considerable augmentation in the height of the closure twitches.
At a later stage the closure of even weak currents causes tetanic
shortening of the muscle. The opening twitcli then appears along
with the closing contraction. The direction in which this first
occurs depends less upon direction of current than upon what
point of the tract of nerve between the two electrodes is sub-
mitted first, and in a higher degree, to the influence of dehydration.
If the electrodes are applied to an undivided nerve, so that the
sacral plexus falls for the greater part within the region of the
upper electrode, the opening excitation will be seen, on account
of the slow drying of this the thickest portion of the nerve, to
appear first with ascending direction of current ; while, if the elec-
trodes are placed in the middle of the nerve, the break twitch follows
almost simultaneously upon the strengthened make twitch, with
both directions of current, unless one or the other part of the nerve
is protected from loss of water by frequent moistening with 0'6 °/Q
NaCl. If the excitation is limited to weak currents, the closure
lasting only so long as to produce a visible opening excitation
(a few seconds is, as a rule, sufficient), there will regularly be a
more or less delayed appearance of the opening twitch, the
magnitude of which depends to a high degree upon the duration
of closure of the current. If this is very brief, the break twitch
may fail altogether, even when the excitability of the nerve is
considerably increased, while a vigorous twitch never fails to
appear when the current remains closed a little longer. It is
remarkable that the form of the curve also depends essentially
upon the duration of current, every transition existing between
a simple muscular contraction, which cannot be distinguished
from the closure twitch, and a long-sustained tetanic shortening
(Ritter's opening tetanus).

That this opening tetanus, which readily appears at an
advanced stage of desiccation, after a brief closure of weak
currents, must be regarded as homologous with the opening
twitch of earlier stages, inasmuch as both are due to the same
causes (to be described below), is evident both from the presence
of the above-described transitional forms, and from the fact that
the opening tetanus makes the same retarded entrance as the
opening twitch.

Prliiger (2, p. 75) was the first to draw attention to this
significant fact in relation to the opening twitcli. He observed

i\ ELECTRICAL EXCITATION OF NERVE 167

repeatedly, oil stimulating the deeper portions of the sciatic of
Ju/tm esculenta with weak descending currents, that "the opening
twitch responded to the moment of opening the descending
current at a very long interval, often lasting for several seconds."

Such a striking delay has been observed by Biedermami in
rare cases only, and never on nerves in which excitability had
been raised by loss of water ; and notwithstanding the compara-
tively small number of experiments, and the possibility of indi-
vidual variations, it is impossible not to suspect that Pfliiger
had before him in these cases preparations which were in the
first stage of desiccation. We have never observed the pheno-
mena in question, save when the excitability of the nerve
was artificially raised above the normal by certain influences to
be described below. Eckhardt (37), e.g., explained the excita-
tory manifestations observed with the action of neutral salts of
alkalies (more especially NaCl, as a solid, or in strong solutions),
as caused by abstraction of water — comparing them directly
with the excitatory phenomena concomitant with the drying of
the nerve. And there is in fact a great similarity of action in
both cases — as regards alterations of excitability in general, and
also the appearance and character of the opening excitation.

The use of concentrated solution of ISTaCl is so far advan-
tageous that it is more easy to localise the effect to a definite
tract of nerve therewith, than in desiccation ; but, on the other
hand, there is the objection that in electrical excitation of a nerve-
section treated with NaCl the tendency to tetanic contraction of
the muscle is far more pronounced with even the weakest closure
or opening stimuli than it is in desiccation, so that this method
nearly always results in opening tetanus, and rarely in opening
twitches.

Since in treating a nerve with ISTaCl in its entire length the
closure tetanus (which at once appears, independently of direction
of current, provided that, as always, weak currents are employed)
would considerably interfere with the recognition of excitatory
phenomena at break of the current, it is well to confine the
action of the NaCl as far as possible to the region of the anode.

It is convenient in these experiments to employ the
form of unpolarisable tube electrode first described by Eugel-
mann (38). A little pad of cotton wool soaked in saline
is then placed upon one of the electrodes, so that a length

168 ELECTRO-PHYSIOLOGY , HAP.

of nerve, the breadth of the glass tube, is covered by it.
It is advisable to bring the whole preparation, with the electrodes,
into a moist chamber, to preserve the free end of the nerve from
drying in prolonged experiments. The muscle is connected with
a writing-point outside the chamber by means of a thread wound
round a cylinder, by which the changes of form are recorded on
the cylinder of a kymograph rotating at varying rapidity. On
exciting with weak currents a plain increase of effect from
closure will be observed after a few minutes, if the current leaves
at a part of the nerve treated with NaCl. The twitches, how-
ever, soon become tetanic, and after a short time there is a marked

FIG. 188. — Effect upon excitability, of local treatment with salt at the kathode. Transition from
descending closure twitch to closure tetanus.

tetanus (Fig. 188) at every closure of the current in the direc-
tion indicated, which at first disappears again completely on
opening the circuit, but is persistent at later stages of the NaCl
effect, when of course further observations are impossible. At a
time when, after application of NaCl to the electrode proximal to
the muscle, a weak descending current already discharges a
vigorous closure tetanus, the closure of the same current in the
opposite direction yields, as a rule, only a simple twitch, which
cannot in time-relations or magnitude be distinguished from
the closure twitches discharged under the same experimental con-
ditions by local application of NaCl. This fact is by no means
without interest, since it shows that, as regards the magnitude of
final result from the excitation of any point of the nerve, it is a
matter of indifference whether the " excitatory wave " discharged
passes through a tract of nerve already in a condition of heightened
excitability, or no.

The opening of weak ascending currents has, as a rule, no
effect after local application of NaCl at the anode, although on

ix

ELECTRICAL EXCITATION OF NERVE

reversing the current the closure produces a vigorous tetanus.
It is necessary either to strengthen the ascending current, or to
prolong the closure in the same proportion, in order to obtain
effective (usually tetanic) opening excitation. Neither of these
is required at a later stage of local salt treatment. The muscle
then becomes disturbed very quickly, and goes into the familiar
salt tetanus, which makes further experiment impossible, unless
the affected part of the nerve is washed with 0'5 °/Q NaCl (after
taking away the pad), when it returns to the state in which it
shows increased excitability without discharging any spontaneous
excitatory phenomena.

In other respects the character of the opening effects after

n

J\

FIG. 189. — Frog's nerve-muscle preparation. Stimulation in the middle of the .-strip of nerve.
Ascending current. After applying a pad of cotton wool soaked in concentrated Nad to the
anode for three minutes, opening of a weak battery current produces tetanus after a brief
closure, which makes a delayed entrance (II). After single closure of a stronger current, the
opening twitch (I) appears between the. moment of opening a current of equal intensity with
the former, and the commencement of tetanus.

treatment with NaCl corresponds almost completely with the
analogous phenomena described above for drying nerve ; the de-
layed entrance of the break contraction, and its dependence upon
the duration of closure, being in most cases very obvious (Fig.
189). It is therefore unnecessary to go into further details in
respect of these curves, and we may pass on to the interesting
effects of treatment with very dilute alcohol.

Mommsen (supra) showed that the excitability of motor
nerves was considerably increased by the application of a weakly
alcoholised (1—2 vols. '/) NaCl solution, the augmentation only
giving way after prolonged treatment to diminution, and subse-
quent inexcitability. Even then it is possible to restore excita-
bility by washing with 0'6 ' NaOl.

When the sciatic of a frog's nerve -muscle preparation is
treated in its entire length with alcoholic saline, and excited every
minute with a weak ascending or descending battery current, the

170

ELECTRO-PHYSIOLOGY

CHAP.

first effect is invariably a considerable increase in height of the
closure twitches, without actual tetanus. Almost at the same
time (usually after 2—4 minutes) a twitch, which is usually
delayed, appears with the opening of the current also, provided
the duration of closure is not too brief (Fig. 190).

The duration of closure required, under the given conditions,
to produce an excitation on opening the circuit, depends of course,
apart from its intensity, upon the degree of alcohol effect, i.e.
strength of solution and length of application. The rise of excita-
bility in the nerve usually occurs fairly soon, when it is treated
with not excessively weak alcoholic saline, and the break twitch

-7"

JL

JL

JL

JL

JL

FIG. 190. — Frog's nerve-muscle preparation. Excitation in the middle of the strip of nerve.
Ascending direction of current. After the nerve has been bathed for thirty seconds in alcohol-
ised saline (10 vols. %) the current discharges delayed opening twitches (II) along with the
closure twitch, preceded 'after long treatment with alcohol by the opening twitch (I), which
appears (according to duration of closure) alone, or partially or wholly fused with the opening
twitch (II).

also appears quickly, even with weak currents and brief closure.
Here again it may be remarked that the opening of ascending-
currents excites, as a rule, a little sooner than descending currents
—which is no doubt related to the appearance of the so-called
" negative modification " of katelectrotonus in the last case.

The alcoholised nerve never sets up spontaneous tetanus, and
isolated twitches of the muscle only appear occasionally with
strongly alcoholised saline — up to 20 vols. c/o (Mommsen) — so that
the dependence of the opening excitation upon the state of excita-
bility of the nerve, as well as upon its special characteristics,
may be studied here as in no other case — the raised excitability
remaining for a long time constant.

Two characteristics of the break excitation as it appears
with artificially raised excitability of a nerve in consequence of
weak battery currents are, as we have noted («), the more or

IX

ELECTRICAL EXCITATION OF NERVE

171

less pronounced but always perceptible delay in the entrance of
the twitch ; (b) the dependence of the magnitude and form of
the curve of the twitch upon duration of closure. Both are
clearly seen in the graphic tracing of the opening twitch, as
discharged with weak currents from the alcoholised nerve.

The extent of the delay varies within a considerable range.
At times it is hardly perceptible ; in other cases the shortening
of the muscle is much retarded. The determining factors
are here duration and intensity of current — the " latent period "
being usually reduced as these increase.

The " latent period of the opening excitation " is also

affected, in alcoholised nerve, by the

degree

of increase of

JL.

FIG. 191.— Alcohol treatment of nerve. Method of experiment as in Fig. 190. Effect of duration
of closure upon height of break twitch (II). Break twitch (I) appears quite independent of
the same.

excitability, so that it usually appears much greater at the
beginning of a series of experiments than during their course, even
if in this case the influence of the single stimuli following at short
pauses (with constant duration of closure) is of more importance.
As Pfliiger pointed out, " the phenomenon (of delay) alters after
repeated closures, since the break twitch follows more and
more closely upon opening, until finally no perceptible interval
remains."

A glance at the opening twitches marked II in Fig. 191
shows the striking dependence of the break excitation upon
duration of exciting current under the given conditions
of experiment — comparatively slight modifications of current
sufficing, on the one hand, to suppress the twitches altogether,
on the other to discharge maximal contractions. So far the effect
of electrical stimulation upon alcoholised nerve, and upon nerves
of which the excitability has been heightened by partial loss of

17-2

ELECTRO-PHYSIOLOGY

CHAP.

water, or treatment with NaCl, correspond almost exactly. Yet
the main features of the curve of contraction (Fig. 192, II) differ
—albeit inessentially. In the drying nerve the discharge of
simple opening twitches (at a certain stage which immediately
precedes the appearance of spontaneous excitatory effects) fails
even with very weak currents, so that there is only tetanic
contraction of the muscle (Hitter's opening tetanus') as appears in
an even higher degree in nerves treated with NaCI ; the alcohol-
ised nerve, on the other hand, requires a tolerably protracted
passage of current, along with moderate intensity of stimulation,
to produce a definite opening tetanus. At most there will only
be extended twitches — even with prolonged closure, — which

FIG. 192.— Frog's nerve-muscle preparation. Ascending direction of current, otherwise the same
experimental conditions as in the previous Figs. Effect of commencing desiccation on the
result of breaking a battery current of medium strength. The opening twitch (I) appears
as the initial phase of the delayed opening tetanus (II).

must be regarded as transitional forms between the simple opening-
twitch and persistent tetanic shortening of the muscle.

This agrees with the fact that the appearance of closure
tetanus in weak electrical excitation of alcoholised nerve must
be regarded as exceptional, although the curves of both closing
and opening twitches are distinguished by their rounded tops
from such as are obtained on exciting normal nerve by
instantaneous stimuli (single induction shocks), or by the closure
of a battery current.

These experiments show conclusively that while in normal,
uninjured nerve it is never possible to obtain an opening
excitation from weak currents, this may result when excitability
is artificially raised : thus seeming to justify the view that the
appearance of the break twitch on applying a cross-section to the
nerve is due to the consequent rise of excitability.

Yet (in addition to the objections already cited) the bare
comparison of the opening effects of excitation in the two cases

ix KLKCTHK'AL EXCITATION OF NERVE 173

proves, not merely that there is no correspondence of fundamental
characteristics (as would necessarily occur if the same cause
underlay the opening excitation in both instances), but that
- as becomes more and more evident on investigating the
phenomena — there are here two perfectly different effects of
current, distinct not merely in regard to appearance, but also in
their mode of expression in the muscle.

The characteristics of the opening twitch discharged by the
action of weak currents, upon nerves of which the excitability
is considerably heightened, are, in first degree (according to
the above experiments), its delayed entrance, as also its dependence
upon duration of closure ; and these distinguish it fundamentally
from the opening twitches which appear (under otherwise uniform
conditions of experiment) at the transverse section of an otherwise
normal nerve. In the curve of the latter there is never, unless
finer methods of time-measurement are resorted to, any perceptible
interval between the moment of opening the current and the
commencement of muscular contraction ; the curve is also much
steeper, and invariably exhibits a pointed apex, while it never
reaches the height of the opening twitches discharged in conse-
quence of artificially raised excitability in the nerve. It is,
however, remarkable that the duration of the exciting current
affects the magnitude only within a very narrow range, and in
no case the character, of the opening twitches from the transverse
section ; for the curve of the latter never acquires a more extended
form, or becomes tetanic, even when a tolerably strong ciirrent
traverses the cut end of a nerve protected from evaporation for
a considerable time, in the descending direction. These facts
alone would justify the assumption of a double opening excitation,
distinct in origin and in mode of manifestation ; there are, how-
ever, further and still more convincing proofs.

In the first place, the uninjured nerve may, under certain
conditions, with even weak currents, exhibit opening twitches of
precisely the same character as those deriving from the transverse
section — independent of action from any incision. Here, how-
ever, it is not so much a raised as a considerably diminished
excitability of the nerve which seems to favour their appearance.

If the sciatic nerve of a frog is treated, as described, with a
moderately strong solution of alcoholic saline (about 10 vols. 0/Q\
and excited once a minute by an ascending or descending battery

174

ELECTRO-PHYSIOLOGY

CHAR.

current of low intensity (the ascending direction is, on the whole,
to be recommended, because the anodic effect is there developed
without interference) — there will soon be seen along with the
retarded opening twitch, which is alone visible at first, a second,
which commences at the moment of breaking the circuit, filling
up the interval before the delayed muscle twitch begins, and thus
being in some sort introductory to it (Figs. 190, 191,1). Whether
this effect appears as a perfectly distinct twitch, the muscle relaxing
again completely before the retarded twitch (opening twitch II)
begins, or whether it fuses with the latter partially or completely,
depends of course upon the time that elapses between the moment
of opening and the commencement of break twitch II, and thus
upon the duration of the current also.

The excitability of the nerve sinks gradually as the alcohol

A.

Ji

FIG. 193. — Bud of series, Fig. 191. Decrease of break twitch II to zero, with persistence (and sub-
sequent increase) of break twitch I.

treatment takes effect, the height of the closure twitch, as well as
of the opening twitch II, being proportionately diminished, and
it is remarkable that the first opening twitch (break twitch I)
reaches its greatest height when the excitability is already much
diminished. The second opening twitch fails altogether at a
somewhat later period, and does not reappear even with pro-
longed passage of current ; break twitch I, however, persists
along with the reduced closure twitch, with which it is for the
most part equal, if it does not exceed it (Fig. 193). If the whole
preparation is freely moistened at this time with a 0*6 °/Q solution
of NaGl, it is easy to restore the normal relations of excitability
in the nerve, so that a closure twitch is the only effect of excita-
tion at any point, with moderately strong ascending or descending
currents. Upon renewed application of dilute alcohol the former
series of effects may be repeated a second and sometimes even a
third time.

The treatment of a nerve with alcoholic saline has the ad van-

ix ELECTRICAL EXCITATION OF NERVK 175

tage of enabling us — without otherwise altering the experimental
conditions — to follow exactly, on one preparation, the nature and
course of the gradual changes developed at break of the current
during the chemical action. We thus learn directly that the two
forms of twitch may exist simultaneously, and must, therefore, be
regarded as distinct effects of current. This cannot be determined

^

with equal certainty from the opening effects of excitation in
drying or in " salt " nerves, since the prompt appearance of spon-
taneous tetanus prevents any prolonged observations ; nor would
those cases be decisive in which break twitch I alone makes its
appearance, since the initial increase of excitability is either want-
ing altogether, or finds insufficient expression.

Ranke (39) states that "the excitability of the nerve is in
the first instance raised by the action of potash salts. It is only
later, and with very strong potash, that excitability is depressed,
and the nerve dies." He reckons neutral salts of potash among
the " fatigue products " of the nerve, giving as characteristic of
" nerve fatigue " that " it presents two different stages : the
primary stage is a heightening, the secondary a depression of
excitability," passing finally into the death of the nerve. The
order of alterations of excitability in the different stages of
potash effect is therefore the same as in treatment with alcohol-
ised saline ; and a similar reaction towards weak opening stimuli
might be expected. Experimentally, however, these anticipations
are only partially realised.

If the nerve of a nerve-muscle preparation, separated from
the central organ, is thoroughly bathed in a very dilute solution
(1 %) of KN03, a highly characteristic alteration in the reaction
from the muscle to excitation of the nerve by weak battery
currents will shortly (5—10 minutes) be observed. An opening
twitch (of the character of break twitch I) now appears not
merely, as before, with the descending direction of current only,
so soon as the anode is applied to the cross -section — but is
discharged, independently of position and distance of electrodes,
with both descending and ascending direction of exciting
current, without any apparent increase of response to closure
stimuli. In most cases indeed the height of the closure twitches
is less than at the beginning of the potash treatment. The same
results appear with undivided nerves, still in connection with the
spinal cord, and treated with 1 °/Q KNOS solution (Fig. 194).

176

ELECTRO-PHYSIOLOGY

CHAP.

If different points of the nerve are excited from time to
time with constant distance of electrodes (about 1-2 cm.) by weak
currents, it is usually found that the opening stimulus acts sooner
in the part of the nerve corresponding with the plexus, than in
deeper parts. It is evident that the saline will take effect more
quickly at points where the bulk of fibres in the nerve are still
distributed into single bundles, than at a lower part where they
are joined into a single trunk, and this — along with the greater
sensibility of central tracts of the nerve to injuries (Efron, Clara
Halperson) — explains the above reaction. If only the part of
the nerve below the plexus is treated with KNOg near the lower
point of bifurcation, by placing it between two pads soaked in

FIG. 194.— Frog's nerve-muscle preparation. A weak ascending or descending current only dis-
charges a closure twitch (b) with any position of electrodes. After 5 min. bath of 1 % KNOg,
the excitability of the nerve is lowered. The same current now discharges opening twitches nf
equal height with the closure twitches (c, d) from all points of the altered tractjof nerve. After
washing with physiological saline (15 min.) the opening twitch disappears again (g, h).

saline, the same strength of current will produce uniform break
twitches at all points of that part of the nerve. But if in such
a preparation the electrodes are laid closely together upon the
plexus, there will either be a closure twitch alone, with both
directions of current, if the connection with the spinal cord is
still intact, or else, from the proximity of the cross-section, there
will be closing and opening twitches, with descending direction
of current.

If the action of the potash saltpetre does not affect the
immediate proximity of the muscle, but is arrested at about 2 cm.
off it, it may be demonstrated that by gradually shifting the
electrodes at uniform distance (1 cm.) from the centre to the
periphery, the break twitch becomes less and less as the normal
portion of the nerve is approached, and an increasing part of it
included under the anode — and finally disappears altogether—

ix ELECTRICAL EXCITATION OF NERVE 177

while the height of the closure twitch is unaltered, or even
increases perceptibly. The same occurs with descending currents,
only in this case the electrodes must be brought nearer the
muscle in order to abolish the opening twitch, since here the
kathode first, and only later the anode, falls within the normal
region. The height of the closure twitch then increases con-
spicuously, showing once more that excitability to closure stimuli
is more vigorous at normal points of the nerve than at those
which are altered by the action of the potash — although opening-
twitches are not discharged in the normal nerve, and never fail to
appear in the other.

If, at a not too advanced stage of KN03 action, the nerve-
while giving approximately equal make and break twitches at all
points when excited with weak constant currents — is moistened
sufficiently with 0'6 °/o NaCl, it soon appears that while the
make twitches are at first unaltered, the height of the break
twitches decreases more and more the longer the bath is con-
tinued. Finally, after 10—15 minutes, they disappear altogether,
with uniform or even much stronger currents, leaving the closure
twitch, as at the beginning of the experiment, the sole effect of
excitation in either direction (Fig. 194, g, li).

It was stated above that the break twitches discharged by
weak currents in consequence of potash treatment are identical
in character with those observed under the action of alcohol to
precede the delayed break twitch II, which at first makes a
solitary appearance. Twitches analogous to these latter are
altogether wanting in " potash nerves."

It is a priori not improbable that treatment of a more
restricted area with KN03 might locally induce the conditions
favourable to the appearance of " primary opening twitches "
(break twitch I), thus enabling weak ascending or descending
currents, with given position of electrodes, to produce an effective
opening excitation.

If the same method be employed as in the above-described
local treatment of nerve with concentrated saline, currents of low
intensity being used for excitation, a different reaction follows
in the nerve according as (after applying a pad of cotton-wool
soaked in 1 °/Q KN03 to one or the other electrode) the solution
of potash acts upon the electrode proximal to the muscle or to
the centre. In both cases the size of the make twitch during

VOL. II X

178 ELECTRO-PHYSIOLOGY CHAP.

the first minutes remains unaltered, as can easily be seen from
its graphic record. Later on, there is nearly always a difference
in the height of the make twitch, according as the current is
ascending or descending, and always in favour of that direction
of current with which the kathode is at the normal point of
the nerve. Sometimes, however, after local treatment of the
nerve for ten minutes or more with a 1 °/0 solution of KISTOS,
the excitability to closure stimuli of the point affected is hardly
diminished perceptibly. On the other hand, there is invariably
during this period a much increased susceptibility in the part of
the nerve treated with KNOS to -opening stimuli, however weak,
whether the nerve be separated from the central organ or still
connected with it.

According as the cotton- wool pad on the electrode is proximal
or distal to the muscle, the opening twitch appears, with either
ascending or descending direction of current, in addition to the
already existing closure twitch, and usually reaches the same
magnitude.

Obviously these local alterations of excitability in nerve to
opening stimuli also, may be neutralised by washing out with
0'6 % saline.

" Primary opening twitches " do not appear merely in con-
sequence of certain artificial, chemical alterations in the sub-
stance of the nerve, which may imply a considerable depression
of excitability, and are notably produced by the action of potas-
sium salts : the same alterations are apparently brought about
by the electrical current, at its points of entrance into the nerve.

The dictum that electrical excitation of normal and un-
injured nerve gives rise to closure twitches alone, independent
of direction of current, applies, as we have said, in general to
weak and medium currents only. Biedermann has almost with-
out exception obtained effective break excitation with a Daniell
cell, after introducing resistance from a du Bois' rheochord, both
before and after separation from the central organ (in the latter
case at a point of nerve sufficiently removed from the cross-
section).

Then, however, we are met by the remarkable fact that
immediately after the expiration of an opening twitch dis-
charged by a strong current, the fall of other weaker currents,
that had previously acted at closure only, will produce excita-

ix ELECTRICAL EXCITATION OF NERVE 179

tion, and that in almost the same degree as the opening of the
strong current. This effect, however, soon diminishes, and dis-
appears completely after a few minutes if the nerve is sufficiently
vigorous. With otherwise uniform conditions this characteristic
after-effect is the more persistent, in proportion with the previous
passage of the strong current, and defective vitality in the nerve.

Any point along the nerve may thus (as in local treatment
with potash) he rendered sensible to weak and, under normal
conditions, non-effective opening stimuli, by making it for a short
time the entrance point of a stronger constant current. And as
in the previous case the raised disposition to the opening excita-
tion may be neutralised by washing off the toxic substance with
an indifferent fluid, so in the excised nerve the continuous process
of restitution suffices to neutralise the anodic alterations pro-
duced by the current, and to restore the normal insensibility to
opening stimuli.

The break excitation which may be discharged at the anodic
points of the iier\7es after brief closure of a stronger current, by
currents of lower intensity, is always expressed, as we have seen,
in twitches of the muscle, which correspond throughout with
those that appear on treatment with potash salts, or in the
immediate proximity of a fresh transverse section. This, apart
from the absence of any perceptible interval between the break
of the current and the beginning of contraction, is more par-
ticularly expressed in the uniformity between the curves of the
two twitches, and in the slight effect of intensity and duration of
exciting current upon the magnitude of the twitches.

A further proof of the correspondence between the break
twitches discharged after treating a nerve with potassium salts
(these again being identical with the " primary opening twitches "
of the alcohol effect), and those discharged by strong currents
in normal, uninjured nerve, appears in the fact that the latter
are discharged simultaneously with " secondary " delayed opening
twitches (break twitch II) in the same preparation. Since
Patter's tetanus is equivalent with break twitch II (.s^ra), and
since this is sometimes delayed (as pointed out by Wundt), the
effect of the opening excitation in such cases either consists in
a completely or incompletely separated double twitch, or else
break twitch I is introductory to Patter's tetanus (Figs. 189,
192).

ISO ELECTRO-PHYSIOLOGY CHAP.

The curves in question were obtained by closing a strong
current for some seconds (after heightening the excitability of
the nerve in a marked degree by abstraction of water, treatment
with saline, or alcohol, which set up a tendency to secondary
opening excitation), to predispose the anodic points of fibres
for the discharge of primary opening twitches (by currents of
lower intensity). So long as the after-effect of the single closure
of a strong current persists, the double excitatory action may be
seen with the opening of the weaker currents, being indeed very
distinct, while with stronger currents the two twitches readily
fuse into one, on account of the shortened " latent - period "
of break twitch II — as is also the case in Eitter's tetanus.
This last fact explains how it has been possible till now to over-
look the existence of two quite distinct opening effects of current.

We are here met by the further question, whether the two
effects of the break excitation (as disclosed under certain experi-
mental conditions) may, notwithstanding their dissimilarity, be
referred to a common origin ; or if not, from what cause they are
derived.

As regards the first point, a fair and unprejudiced con-
sideration of the facts ought to convince us of the im-
probability of a single origin for excitatory effects, as unlike in
conditions of appearance and general characteristics as the break
twitches I and II. While the appearance of the latter seems
1 to imply a considerable rise of excitability in the nerve, the
former, on the contrary, enters with depressed excitability ; and
while with weaker currents there is, as a rule, delayed entrance of
1 >reak twitch II and of the equivalent Patter's tetanus (dependence
upon duration of current being also very evident), there is never
any perceptible interval between the moment of opening and the
appearance of break twitch I ; moreover, when the conditions of
its entrance are once present, the latter is almost independent of
the duration and intensity of the exciting current.

The undoubted equivalence of break twitcli II and Patter's
tetanus points to a common origin. Pfiiiger, who regarded
every opening twitch as a consequence of excitation of the nerve,
by the disappearance of anelectrotonus, gave the same explana-
tion of Patter's tetanus, and actually demonstrated, by the well-
known experiment of cutting off a previously anelectrotonised
portion of the nerve, that the opening tetanus originates at that

ix ELECTRICAL EXCITATION OF NERVE 181

part. According to Engelmann (4, p. 411), however, it arises
here from pre-existing spontaneous stimuli, which were at first
inadequate, and now become effective from the positive modifica-
tion in excitability at the previously anelectrotoiiic tract of the
nerve, on opening the current --thus producing a change of
form in the muscle. Engelmann makes special reference to
the fact (as is easily confirmed) that " a simple twitch,
which cannot be distinguished from the closure twitch, or the
twitch from a single induction -shock, appears in fresh nerve-
muscle preparations of normal frogs (when preserved from
evaporation) on breaking the current." " On the other hand, the
opening tetanus (as also the analogous closure tetanus) makes its
appearance with the greatest regularity in cooled preparations,"
the nerves of which are characterised by peculiar excitability-
referred by Engelmann to the presence of internal stimuli, that
are often so powerful as to induce spontaneous twitches, or even
tetanus, when every precaution is taken against evaporation.
Further support of Engelmann's views, as to the nature of
Bitter's tetanus, is found in an experiment of Griinhagen (40),
which shows that " weak tetanising excitation that produced no
visible effect before the closure of the polarising current, calls
out an unmistakable tetanus when the latter is opened, lasting
the longer in proportion with the strength of the polarising
current and susceptibility of the nerve." Griinhagen hence
deduces the following proposition : " The raised excitability of
the nerve at the previously anelectrotonised region, summating
with the increased disintegration stimuli, normal to the nerve,
results in the opening tetanus of constant currents. These
chemical stimuli may be counterfeited by a sub-liminal tetanis-
ing excitation."

We should thus expect the secondary opening twitch only
when the nerve is, so to speak, in a state of latent excitation.
And the above facts relating to the appearance of break twitch II
are in complete agreement with this anticipation. For with loss
of water from evaporation, or in treatment with concentrated
saline, the nerve falls directly into that state of excitation which,
though at first too weak to express itself in twitches of the
muscle, appears later on as a vigorous tetanus. Just at the
moment at which the 'excitation is latent, break twitch II, or
Eitter's tetanus, may be produced even by weak currents. The

ELECTRO-PHYSIOLOGY , HAP.

highly favourable action of dilute alcohol to the appearance of
break twitch II must surely bear a similar interpretation,
although Eckhardt and Kiihne limited its excitatory action to
80 °/Q. Mommsen, however, has not infrequently observed
twitches of the muscle on treating the nerve with comparatively
dilute alcoholic saline (20 vol. °/o}, and the same is confirmed
by Biedermann's observations.

The statement that the discharge of break twitch II, as well
as the appearance of Bitter's tetanus, is associated with the
presence of latent excitation in the nerve, finds striking con-
firmation in the fact that break twitch II, with all its character-
istic properties as above described, may be elicited in nerves
which have been thrown by weak tetanisatiou into a state of
latent excitation (Griinhagen's process).

To this end it is only necessary to tetanise the central
end of a sciatic nerve, divided from the spinal cord, or still con-
nected with it, at a distance of coil which is only just able to
excite. If a lower point of the nerve is simultaneously excited
with weak descending constant currents, opening twitches will
not fail to appear at a moderate duration of closure ; and these
twitches are, in every respect, equivalent to break twitch II,
since, like the latter, they make a delayed entrance, and are in a
marked degree dependent 011 duration of closure. If current
intensity is strengthened, the break twitches become more ex-
tended, and finally pass into tetanus, which, like the twitches, is
delayed in its entrance. The identity of this opening effect with
that described above as secondary is indisputable, seeing that
here too the opening of weak currents is followed by a double
effect, if the disposition to primary opening twitches is previously
induced by brief closure of a stronger current. This effect either
consists in double twitches, or else break twitch I appears as
introductory to Hitter's tetanus.

If the nerves are excited during weak and intrinsically in-
effective tetanisation by an ascending constant current, there
will, in proportion with the intensity of the latter, be either a
reinforcement of the closure twitch or closure tetanus, never, how-
ever, an opening excitation.

The application of a fairly strong chemical excitant has
substantially the same effect as weak tetanisation above the
point of nerve excited by the constant current. Glycerin is

IX ELECTRICAL EXCITATION OF NERVE 183

especially appropriate. In favourable cases a weak descending
current discharges break twitch II shortly before the explosion
into tetanus. A similar experiment was made by Griinhagen
(36). But if this proves that break twitch II and Patter's
tetanus (as well as the closure tetanus) are in many cases due, not,
as Pfliiger thought, to disappearance of anelectrotonus (or entrance
of katelectrotonus), but to latent stimuli, which, in themselves
inadequate to excite the muscle, first become effective when the
excitability of the nerve is raised after the disappearance of
anelectrotonus (or during an existing katelectrotonus) — it must be
admitted that in many cases an adequate opening excitation of
the same character appears without any previous state of latent
excitation (cooled nerves). Nor is this surprising in view of the
relations between rise of excitability and excitation, as described
above. On the other hand, the nature of break twitch I is still
unexplained, although the conditions of its appearance are known
more precisely than before.

Arguing from experiments in which break twitch I appears
immediately after making a (mechanical, chemical, or thermal)
cross-section in the close proximity of the anode, it follows that
the demarcation current developed by this injury must be in
causal connection with the appearance of break twitch I. Yet
this cannot be in the sense that the raised excitability in the
vicinity of the cross-section (the cause of which will be discussed
below) renders weak opening stimuli effective ; for this hypothesis
seems to be sufficiently contradicted by the foregoing data. Griin-
hagen's view that the appearance of the make twitch, when a
fresh section is applied to the nerve near the anode, is to be
regarded primarily as a " product of summation " (" on the one
hand, of the intrinsically inadequate excitation, consequent on the
opening of the descending current," i.e. the anodic stimulus ; " on
the other, of the continuous, weak, mechanical stimulus of the
incision/'), must be regarded as disproven. For — apart from the
fact that an after-effect of simple division, lasting for hours
(and the disposition to the discharge of break twitch I does
last that time in the vicinity of the cross -section), is highly
improbable — it may further be urged against Griinhagen that the
effects of the make excitation would then have to be propor-
tionately strengthened, with uniform position of electrodes, and
ascending direction of current, which is not the case. We have

184 ELECTRO-PHYSIOLOGY . n.vr.

already seen that the same effect appears in striated muscle.
There we had direct proof of " false " break twitches caused
by internal short-circuiting of the demarcation current, compen-
sated during closure of the battery current in the leading-off
circuit. It is natural to apply the same explanation to the
primary break twitch from the transverse section, in nerve-
excitation. This was actually done by Griitzner (41) and
Tigerstedt (41), who only go too far, inasmuch as they deny
any real break excitation due to fall of the current, and assume
that every so-called opening excitation is constitutionally an
effect of closure, deriving from an interference between exciting
current and nerve current, which last may be either a demarca-
tion or a polarisation current.

As against this view it must be maintained that in nerve, as
in muscle, there is a true opening excitation, viz. a reaction of the
excitable substance towards the changes produced by current
(at the anode). The interference effects between exciting current,
and pre-existing differences of potential, which underlie the
" false " opening twitches, can only be dealt with later, in
discussing the electromotive action of nerve.

Since (as appears directly from the above) the effects of
exciting motor nerves with the constant current depend essen-
tially upon the relations of excitability in the nerve, we should
anticipate a fairly complicated reaction from a nerve -muscle
preparation, inasmuch as it presents a multiplicity of functional
elements, differing in excitability — as was shown, e.g., for the
rheoscopic frog's leg with flexors and extensors supplied by a
common nerve-trunk, and in a far higher degree in the crayfish
claw. As regards the first case, it may be remarked that, accord-
ing to Griitzner (42), the excitation of the frog's sciatic with
currents of increasing intensity excites quite different muscles
at closure, and at a later period. If there is eventually an
adequate break excitation, those muscles alone twitch which first
became active at closure. The opening stimulus thus acts here
(with stronger currents) like a weak closing excitation. The
same may be observed on man when the electrodes of a sufficiently
strong battery are applied to the sulcus bicipitalis interims. At
a certain strength of current, the muscles that twitch at make
and at break are different (flexion of lumd at make, pronation at
break).

ix JSLECTRICAL EXCITATION OF NERVE 185

2. Excitation of Nerves in Crayfish

On the crayfish claw, under certain conditions, the excita-
tory effects of the constant current may be remarkably developed
(Biedermann, 43). It has already been stated that with tetanising
excitation of the claw -nerve, the tonically contracted adductor
muscle relaxes at about the same comparatively low strength of
current at which the abductor contracts vigorously ; while strong
currents, again, throw the former into tetanic contraction, the
abductor either suffering no visible change of form, or, if there is
any tonus, becoming relaxed. Hence there would appear to be
a complete antagonism of excitatory conditions in the nerves
corresponding with the two muscles.

The results of excitation with the constant current, on the
other hand, are much more complicated. In the first place, there
is never a " neutral zone " of current strength as denned above,
although striking and perfectly regular differences of action
between currents of different strength are by no means want-
ing. In agreement with the excitatory reaction on tetanising
the nerve by means of alternating currents, e.g., we find with
closure of a battery current that the excitatory effects pre-
dominate or appear alone in the abductor, the inhibitory effects
at the adductor, with low intensity of current, while with stronger
currents the contrary effect appears. In detail, however, the
effects are far harder to analyse, because at each adequate ex-
citation both impulses (excitation and inhibition) usually appear,
so that in tracing the changes of form in one of the two tonically
contracted muscles, highly complicated curves may arise, which
are only intelligible on the ground of the previous data.

The effects of excitation are best seen in the atonic adductor
muscle, where the results agree throughout with experiments on
other nerve-muscle preparations, and correspond perfectly with
Pfliiger's law of contraction. Medium currents here work in-
dependent of the direction in which they are passed through
the nerve, exciting both at make and at break, while a strong
descending current excites at make, a strong ascending current
on the contrary at break only. It is to be remarked for these
experiments that every stronger excitation gives rise to a more
or less prolonged tetanic contraction of the muscle, so that per-
sistent excitation by the constant current is here the rule (supra).

186 ELECTRO-PHYSIOLOGY CHAP.

Similar experiments on the atonic abductor muscle show
that, apart from other differences to be discussed below, it is,
as a rule, excited by much weaker currents than the adductor
muscle, while strong currents under some conditions prove wholly
ineffective, at other times discharging contractions considerably
weaker than those from currents of lower intensity. This last
paradox, however, is not invariable, and cannot even be termed
a frequent occurrence.

Direction of current seems to be of importance in all experi-
ments on the muscles of the claw, inasmuch as the closing excita-
tion appears in the majority of cases with ascending, rather than
with descending currents, while the contrary is true of the
opening stimulation. The cause of this reaction must be sought
less in any special property of the nerve-fibres than in the fact
that with the above conditions of experiment, current density at
the two electrodes is not equal, but is less at the contact that
lies towards the periphery than at the central contact. This is
due to the form of the joint to which the (thread) electrodes
are applied, since the diameter of the joints increases considerably
towards the claw. The above difference may be neutralised, or
even reversed, by merely passing the threads as near as possible
to the nerve, which runs along the inner surface of the limb, or
by using a more basal joint for excitation.

All doubt as to the validity of Pfliiger's law of excitation for
the nerves of the adductor as well as the abductor muscle is
removed by simply excluding the central electrode, as will be
shown below.

While in atonic muscles treated by the above method the
effects of excitation by the constant current are tolerably uniform,
there is, along with conformity of detail, a surprising variety of
effect, on exciting preparations from either of the two claw
muscles, when there is a more or less well -developed tonus.
This is intelligible since each single stimulation affects the
muscle in an exactly contrary direction, and thus, as will be
shown, produces opposite changes of form. Excitatory or inhibi-
tory effects preponderate according to the state of the prepara-
tion, and the strength and direction of the exciting currents.

The preparations of the adductor muscle which most con-
veniently show the dependence of inhibitory and excitatory
action from the constant current, upon its direction and in-

IX

ELECTEICAL EXCITATION OF NERVE

187

tensity, are such as are in a state of moderate tonic contraction,
and therefore react by corresponding changes of form to both
effects of excitation.

If with increasing intensity of current the preparation is
excited with alternately ascending or descending currents, or
with uniform direction of current, there are, as a rule, certain
obvious characteristics of the mode of reaction which — given the

I 110

FIG. 195.— Adductor of crayfish claw. Excitation of nerve with constant currents. The exi.stin.u'
tonus is little if at all increased by closure of weaker currents (a, &), which essentially inhibit
it. Closure of a strong current on the other hand = c.

previous data re tetanisation of the nerve — distinguish the
adductor muscle sharply from the abductor.

In the first place, it is evident that in preparations of the
former muscle weak currents and medium currents have a
predominantly inhibitory action, while with stronger currents
the effects of excitation preponderate, or alone appear (Fig.
195, a, It}. This is expressed, on the one hand, in the fact
that the augmentation of tonus that invariably corresponds with
the moment of closure, i.e. shortening of the muscle, increases
with increasing intensity of current to a certain upper limit,
which (from the mechanical conditions of the experiment) is

188 ELECTRO-PHYSIOLOGY CHAP.

not necessarily the maximum of contraction ; while, on the other
hand, the duration of closure tetanus increases also, thus account-
ing for the fact that the obvious inhibition (relaxation) at each
single stimulus begins so much later after the beginning of
excitation (closure) in proportion as the current is strengthened.

If the successive alterations which occur in contraction are
considered synthetically, there appears to be a gradual transition
from increasing and more or less extended twitches to definite
and prolonged closure tetanus ; which recalls the similar reaction
of the relaxed atonic muscle under the same conditions. Make
twitches of characteristic brevity occur not infrequently at a
certain strength of current, their curves being distinguished by
a very sharp apex : these presumably represent the effects of
inhibition following rapidly upon closure, since the curve of make
twitches under normal conditions is extended.

The beginning and end of a series of experiments on atonic
adductor muscle are usually characterised by single (and oppo-
site) signs of excitation, with many intermediate transitions of
action, which, according to the strength of current, exhibit a
regular antagonism between excitation and inhibition, contraction
and relaxation.

As shown by all previous experiments, inhibitory action
appears singly (in indirect excitation of the adductor muscle by
constant currents) at comparatively low intensity of current only ;
while very strong currents have an exclusively exciting action-
at all events, this is the rule immediately after closure.

It should be further observed with regard to the abductor
muscle of the crayfish claw, that when once the exciting current
is sufficient to produce a perceptible reinforcement of the existing
tonus at closure, this effect under all circumstances precedes the
subsequent diminution of tonus due to inhibition.

In the curve this only appears at first as a slight rise,
previous to the deep depression described by the lever in
consequence of the sinking (from inhibition of tonus) of the
free, and downward directed, arm of the claw. With each
stronger stimulus, the consequences of excitation are seen more
plainly, while those of inhibition are at first equal, and then,
owing to the increasing closure tetanus, make a more and more
delayed entrance.

The curve at first rises steeply from the initial abscissa (which

ix ELECTRICAL EXCITATION OF XERVF, 189

corresponds with the existing tonus), and then, sooner or later,
makes a sudden drop below it (Fig. 196), either rising again
immediately, or more slowly, after a certain interval, so that the
lever often recovers its initial position
during closure, in other cases, however,
only when the circuit is opened. It
not infrequently happens, at a given
strength of current, that the shortening
of the tonic muscle, 011 closing the circuit,
corresponds both in magnitude and dura-
tion with the subsequent relaxation, so
that the first section of the curve above
the abscissa is almost equal with that of
the lower half (Fig. 196). In current-
intensities below this limit, the second

half of the curve seems generally to preponderate, while beyond
it the effects of excitation come more and more into play at the
expense of the inhibiting action — so that the first section of the
curve is highly characteristic.

The inhibitory effects are often so indefinite, that their
existence as independent signs of stimulation might easily
be overlooked, without some knowledge of the action of
weaker currents ; and they might be viewed merely as fatigue-
effects from the immediately preceding persistent excitation.
This is indeed contradicted by the fact (as insisted on above) that
re-entry of the more or less strongly inhibited tonus usually
occurs during the passage of the current ; while, moreover, the
break of a stronger current not unusually inhibits to the same
extent as the closure of a weak current. On opening the exciting
circuit a fall of the curve similar to that previously obtained
during closure (Fig. 195,c) is apparent.

We thus learn that the reaction of the tonically contracted
adductor muscle, on exciting its nerve with the constant
current, is characterised throughout (with increasing strength of
current) by depression of inhibitory effects in favour of excitatory
action, until the inhibition becomes imperceptible. In the abductor
muscle the contrary occurs, owing to its much stronger and
more persistent tonus. This is evident from comparison of the
curves (Figs. 19-5, 197), which, though recorded as far as possible
under uniform conditions, are in many respects exactly opposite.

190

ELECTRO-PHYSIOLOGY

t.'HAP.

While the tonus of the adductor muscle is, as a rule, inhibited
by minimal effective currents, without any perceptible excitation,
either previously or during prolonged closure, the first effect
of weak stimuli upon the abductor muscle is pre-eminently a
strengthening of the existing tonus ; and there is, in this par-
ticular, complete agreement between the effects of stimulation
with tetanising alternating currents and with the battery-current.
Even slight augmentation of the latter, however, in the one as

FIG. 197. — Abductor muscle of the crayfish claw (tonic) ; stimulation with constant currents of
increasing intensity ; augmented inhibition as primary effect of excitation. Time-marking
in seconds.

in the other, brings out the striking dissimilarity, that each
single stimulus now produces double action. But while in the
adductor muscle excitation invariably precedes inhibition, the
contrary occurs in the abductor. At the moment of closing the
exciting circuit, excitation (contraction) in the one case, inhibition
(relaxation) in the other, makes a delayed entrance, and must in
each case be regarded as the primary effect of the current.

As in the adductor muscle the consequent excitation seems,
at its first appearance, to be merely indicated, as an independent
constituent of the curve, so the same holds good of the effects
of inhibition, with indirect excitation of the abductor muscle.

IX ELECTRICAL EXCITATIOX OF XERVE

Fig. 197, a, shows, after an insignificant fall of the curve
beginning at the moment of closure, a marked rise, in consequence
of the now developing make excitation, leading at b and c to
a permanent reinforcement of the initial tonns. AVith the less
favourable descending direction, the same weak current produces
excitation only at closure, without previous inhibition, i.e. acts
as a weaker stimulus. The same gradation of effect with the
two directions of current is in most cases more or less plainly
visible on stimulating with alternately ascending and descending
currents. With increasing strength of excitation, the primary
inhibition becomes more and more conspicuous, the curve falling-
deeper on the one hand at closure of the current, and on the
other rising again the more slowly to the abscissa, or passing
beyond it, in proportion with the intensity of the current.

Seeing that with indirect stimulation of the adductor muscle

O

by not unduly weak constant currents, inhibition — with stimula-
tion of the abductor muscle by strong currents, on the other
hand, excitation — makes a more or less delayed entrance after
closure (as expressed in the corresponding changes of form in
the muscle), insufficient duration of closure in either case will
give the impression of single, or negative, effects of excitation.
This is more especially the case in preparations of the abductor
muscle, where, owing to want of tonus, the inhibitory effect,
as expressed directly in changes of form in the muscle, is
absent.

Such inhibitory action is then apparent only in a retardation
of the latent period, which may, under certain conditions, last for
several seconds — a fact which gives a characteristic form to these
curves, and indicates their origin from the abductor muscle (Fig.
198, a, b). That this is really no more than the effect of an
inhibition, antecedent to the excitatory action of the current, is
most plainly seen in cases in which the muscle is excited once
with uniform strength of current, while there is still a perceptible
tonus, and again later in the relaxed condition.

In both cases the make contraction is retarded in about the
same degree, but while in the one, closure of the circuit produces
a visible diminution of tonus, inhibition is expressed in the other
solely by the lengthening of the latent period.

It follows that the inhibitory action of the constant current
antecedent to excitation may be demonstrated in almost every

192

ELECTRO-PHYSIOLOGY

CHAP.

single case, even with comparatively weak currents, since a
perceptible delay in the appearance of contraction (visible even
at a slow rate of the recording surface) is wanting, as a rule,
only in the weakest, minimal currents. The time-value of the
delay differs much in different preparations, and, as a rule,
diminishes in the same preparation with frequent repetition of
stimulus, even when the excitatory action of the current shows no
sign of diminution.

Just as the inhibitory effect of stimulation is sometimes very
apparent in preparations of the adductor muscle (according to its
state), while in other cases it is merely indicated, or quite imper-
ceptible, notwithstanding an equal development of tonus — a
variation that may essentially be due to altered conditions in
the muscle: so in the abductor, we find similar differences,

I tno

J

FIG. liiS. — Abductor muscle of crayfish claw (atonic) ; excitation with (o) weak and (1>) strung
battery currents ; in the last case there is a pronounced delay in the make contraction.

although the inhibitory action here takes effect, as a rule, far
more certainly than in the antagonist muscles.

The excitatory action of strong constant currents in the
adductor muscle (supra) so far preponderates over its inhibitory
effect that the latter only appears very exceptionally with strong-
excitation, when a transitory relaxation may sooner or later
interrupt the closure tetanus. This is not equally true of the
abductor, where, even with strong currents, the inhibition (which,
as regards dependence on strength of stimulation, corresponds
with excitation in the antagonist muscles) is almost regularly
interrupted by the succeeding excitation in the course of a long
closure ; which excitation — like the inhibition of the adductors
—first effects entrance when the strength of the stimulus begins
to decline during the passage of the current. This last fact may
well cause the differences of effect on exciting with constant or
with tetanising alternating currents.

ix ELECTRICAL EXCITATION OF NERVE 19:1

As regards the break excitation, it should be observed that
it requires stronger currents (here as everywhere) than the make
effect, and may, like this last, produce opposite changes of form
in the muscle under certain conditions. In consequence of the
inferior strength of the opening stimu-
lus, however, it only excites the muscle
in the majority of cases, and seldom
reaches sufficient proportions to inhibit
a pre-existing tonus. But if in such
a case the exciting action of the
current fails to find expression, the
effects of stimulation both at make
and at break of the circuit may

consist in a transitory relaxation of the tonically contracted
muscle : the curve then presents two depressions, one beginning
at closure, and disappearing only during the passage of the
current, the other less considerable — corresponding with the
break of the exciting circuit (Fig. 199).

In view of the double, partly inhibitory, partly exciting
effect of stimulating the two muscles of the crayfish claw with
the constant current, the important question arises whether —
under the presumption of pure polar action of current — the two
effects, at make on the one hand, at break on the other,
proceed from the same electrode, or whether there is an
antagonism between the respective discharges of excitation and
inhibition.

It has already been stated of the atonic adductor muscle that
the order of excitatory effects corresponds throughout with
Pfliiger's law ; i.e. both on applying very strong currents, and after
excluding the influence of the central electrode by partially
killing the nerve, the descending current takes effect at make,
the ascending current at break only of the circuit.

Since in the first case — owing to the enormous resistance in
the exciting circuit, and low density within the part traversed—
the current must be of very considerable intensity in order to
obtain the third stage of Pfliiger's law (with unpolarisable elec-
trodes), the second of the methods given above seems the most
appropriate.

By this it is easy to ascertain, with given intensity of
current for both adductor and abductor muscle, that inhibition

VOL. II 0

194 ELECTRO-PHYSIOLOGY CHAP.

\ as well as excitation proceeds at make from the kathode, at break
from the anode.

It suffices to divide the claw-nerves in the proximity of the
central electrode, or to kill a certain portion of them ab initio
by warming (dipping the limb of the claw in hot water almost
to the point of excitation). This is obviously liable to affect the
tonus of the muscle, so that it does not always yield satisfactory
results ; in other cases, however, the experiment is perfectly
successful.

VI. POLAR EXCITATION OF OTHER NERVES AND SPECIFIC

NERVE-ENDINGS

Bonders (44) has established polar action in the inhibitory
fibres of the cardiac vagus according to Pnuger's law, by graphically
recording the heart-beats. With adequate closure or opening of a
constant current there is plainly seen, after a short latent period,
to be lengthening of the succeeding, and especially of the next two
pulsations ; and with increasing strength of current the order is
as follows — ascending make, descending make, descending break,
ascending break. The effects of ascending make and descending
break soon reach a maximum, after which they decline, and fail
even with strong currents, thus corresponding exactly with the
law of contraction.

In view of the sluggishness of most smooth muscles, and their
consequent inability to react to a single brief stimulus, we should
a priori expect the manifestations of the law of polar excitation to
fail altogether, or at most to appear exceptionally, with indirect
excitation. Thus a single closure or opening of the constant
current produces no effect on the cervical sympathetic, while
repeated closure and opening result in unmistakable constriction of
the vessels of the ear (in rabbit). On the other hand, Pfliiger's
law is easily demonstrated on the comparatively quickly reacting
muscles of the sphincter iridis (of cat). So, too, on the mantle-
nerves of Eledone (v. Uexkiill, 45). The closure and opening of
medium currents cause contractions with both ascending and
descending direction. Closure of a strong descending current
gives tetanus throughout the period of closure, but has no effect
with ascending direction ; opening of the circuit in this case pro-
duces prolonged opening tetanus. The descending closure tetanus
is often rhythmical.

ix ELECTRICAL EXCITATION OF NERVE 195

Pfliiger's law can also be demonstrated on secretory nerves, if
the galvanic alterations in gland-cells be taken as the index of
excitation. This is easily shown on the frog's tongue if the
glosso-pharyngeal nerve is excited (Biederraann, 8). Here again
we see that constant currents are much more appropriate for the
excitation of secretory nerves than single induction shocks, which
with even powerful intensities produce hardly any modification of
the lingual current, while the single closure of a medium battery
current invariably produces visible consequences. This striking
disparity of action is undoubtedly, in either case, caused solely by
dissimilar duration of the currents — thus not merely testifying
against the infallibility of clu Bois' " universal law of excitation,"
but proving the accuracy of the view of Griitzner and Schott,
viz. that rapid stimuli excite the quickly reacting, slow stimuli
the more sluggish end-organs. If, with a strong ingoing lingual
current, 3—6 Dan. are closed in the descending direction, after
previous compensation of the current, there will regularly be-
after a short latent period (1—2 sec.) — a monophasic negative
variation, which is often of considerable strength, persisting for
some time during closure, and vanishing rapidly when the circuit
is broken ; whereupon, if the current is not too strong, the break
excitation appears as a delay, or even as a brief arrest of the
backward impulse. This is usually still more plain on exciting
with ascending currents, closure of which produces the same
monophasic, albeit essentially weaker, negative variation as the
descending direction. If very strong currents are employed, the
effects may correspond throughout with the third stage of the " law
of contraction " ; since with the descending direction a " closure
variation," with the ascending direction an " opening variation,"
alone appears. As we should anticipate, the alternate closure of
opposite currents by means of a Pohl's reverser invariably
results in an excessively strong variation of the current of rest.

Pfluger (46) was again the first to investigate the action of
currents of different direction and intensity upon centripetal
(sensory) -nerves, using the reflexes discharged as indications of
excitation. The frogs were weakly strychniuised, and current
then led through the isolated sciatic — the unskinned leg remain-
ing attached to the nerve, to avoid artificial cross-sections. The
presumptions of Marianini and Matteucci for strong currents
were entirely realised. Eeflexes were excited only by closure

196 ELECTRO-PHYSIOLOGY CHAP.

of ascending and opening of descending currents, because in
the first case the katelectrotonic, in the second the anelectrotonic
part of the nerve communicated directly with the spinal column ;
the leg connected with the nerve, on the other hand, twitched
according to the law of contraction only with the two opposite
stimuli. With medium currents, all four stimuli were renexly
responded to, as previously pointed out by Matteucci. Setscheuow
and Hallsten (46) have since investigated the same question,
arriving at essentially the same results.

The consequences of exciting minced centripetal nerves, which
consist of antagonistically working fibres, e.g. the vagus, are
much more complicated. Griitzner discovered that the closure
and passage of constant ascending currents, and in a less degree
the opening of descending currents, had an inhibitory, expiratory
effect upon respiration, while opening of ascending and closure
of descending currents remained ineffective. Langendorff and
Oldag (7) have recently submitted these facts to more accurate
investigation, finding that an ascending constant current, sent
into the central end of the vagus, " in all cases influences
respiration in the expiratory direction ; i.e. it either induces a
longer expiratory arrest, or retards the breathing by inducing
expiratory pauses." And this is the case not merely at the
moment of closure, but throughout prolonged passage of current.
Breaking the current in most cases induces a visible inspiratory
effect, expressed either in a deepening of inspiration, or in a short
inspiratory stoppage. The closure and passage of the descend-
ing constant current were always found by Langendorff and
Oldag to be less effective than those of the ascending current,
and that in an antagonistic sense, i.e. inspiratory ; while opening
the circuit again produces an inspiratory standstill.

" Inhibition of respiration (expiratory") is therefore produced by
closure of the ascending and opening of the descending constant
current ; excitation of respiration (inspiratory) l>y opening of the
ascending and closure of the descending current."

The same (expiratory) action as with ascending constant
currents may also be produced on thoroughly narcotised animals
by interrupted constant currents of uniform direction, especially
where the frequency of interruption is small, and the closure of
prolonged duration. Inspiratory effects, on the other hand, not only
appear with closure of descending persistent currents, but still

ix ELECTRICAL EXCITATION OF XKRVK 197

more with rhythmical excitation at uniform direction of current.
A positive interpretation of these data is hardly possible without
further investigation ; in any case, Langendorff s assumption that
"simple galvanic variations of current, and the passage of
the current, are merely inhibitory, while oscillatory variations
are excitatory in action " —and that " the excitation which pro-
ceeds from the lower, distal electrode implies a tetanising
element" — needs further corroboration.

Great theoretical interest attaches to experiments on the
•polar excitation of the higher sensory nerves by the constant current,
sensation here serving as the excitatory reagent. The earlier
electricians collected a fund of experimental data in this depart-
ment, although the interpretation of their facts is very dubious.
Those relating to the taste-sense are the most obvious. Here, as in
all other cases, it must be noted that excitation of the isolated
sensory nerve involved is not possible, the peripheral end-organ
(sensory epithelium} being under all circumstances excited with it.

The first and weightiest conclusion from the older experiments
is as follows : When an electrical current is passed through the
tongue, an acid taste is perceived at the point where current
enters (anode), and a different taste, usually described as alkaline,
at the point where it leaves (kathode). Volta, however, described
the latter as being merely somewhat alkaline, sharp, and rough,
approaching to bitter. These two sensations, one of which
(kathodic) is always much weaker than the other (anodic),
continue as long as the current is passing, and are perceptibly
reversed (as observed by Kitter) when the circuit is opened.
Eosenthal (47) was unable to discover this, finding merely that
the acid taste continued for a short time after breaking the

o

current, while the alkaline trace quickly disappeared. At the
same time v. Vintschgau (47) confirmed the observations of
Patter — the predominant acid being converted into a faintly
metallic taste at the moment of opening the current, when the
kathode was applied to the root of the tongue.

As early as 1793 Pfaff discovered the relation between the
difference in electrical taste according to the disposition of the
metals on the tongue, and the difference in contraction according to
their distribution in nerve and muscle ; and the possibility at once
presents itself of direct comparison between the qualitatively
different, and in a certain sense antagonistic, polar effects, on excita-

198 ELECTRO-PHYSIOLOGY CHAP.

tion of the sensitive lingual rnucosa, and those exhibited by so
many other excitable substances — the more so since the contrast
between closing and opening effects finds complete analogy in the
law of polar current action.

Further details of electrical sensations of taste are subjoined
from the recent investigations of Laserstein (47). Just as there
are individual differences in the sense of taste, so there are individual
variations in sensibility to the current, varying in the same person
at different times, and in different individuals. As might be ex-
pected from the greater intensity of the anodic acid taste, the
liminal value for the ingoing (acid) current lies considerably
lower than that for the outgoing current. With non-polarisable
electrodes, the liminal value of current for the acid taste was
about Tl^ milli-ampere. This very low figure is undoubtedly
due to the high specific excitability of the organ of taste towards
constant currents, in which respect it far exceeds all other sense-
organs. Oscillations of current produce no visible augmentation
of gustatory sensations.

The electrical taste has been very differently interpreted.
One question is of primary importance : Do the sensations of taste
arise from the direct stimulation of the taste-nerves 'by the current, or
are they caused indirectly by electrolytic decomposition of the fluids
in the mouth ? We know that when an electrical current passes
through a fluid containing salts of alkalies — instance the fluids of
the mouth which are moistened by the lingual mucosa — the salts
are decomposed ; the acids coming off freely at the anode, the
alkalies (which are immediately oxidised) at the kathode. The
presence of free acids at the positive, of free alkalies at the
negative pole, would thus very simply account for the acid taste
at the latter. Against this explanation it may be urged that the
sensations of electrical taste are also present when the current
does not enter and leave by metallic electrodes (in which case
electrolysis is inevitable), but is led through the tongue by other
electrolytes, or by non-polarisable electrodes ; this experiment
has been tried by Monro, Volta, and, more recently, by
Eosenthal (47).

" Eosenthal brought two persons into contact by the tip of
their tongue, the one holding the positive, the other the negative
pole of a battery, with moist hands : the first person has an alka-
line, the second an acid taste. Here the two persons are under

ix ELECTRICAL EXCITATION OF NERVE 199

identical conditions, except as to the direction of the current in
the tongue. This is opposite in the two subjects, so that they
have opposite sensations, although their tongues are in contact,
and the same capillary layer of fluid covers the one as well as
the other. Eosenthal, moreover, sent the current of 1—4 Dan.
through the body and tip of the tongue, both poles consisting of
zinc plates dipping into two vessels of zinc sulphate : these were
connected by siphon-shaped tubes with two other vessels, one
filled with saturated salt solution, the other with distilled water.
A pad of filter-paper, also soaked with distilled water, projected
from the latter. On dipping one hand into the saline and
touching the pad of filter-paper with the tip of the tongue, the
current either passed from tongue to pad, or vice versa — as regulated
by a reverser in the circuit. A strip of red litmus-paper was
laid on the pad so that both were in contact with the tongue.
The red paper turned faintly blue when touched by the alkaline
fluid of the mouth — blue remained unaltered. On closing the
current there was a distinct sensation of taste, but the colour
of the two papers remained unchanged with either direction of
the current " (v. Vintschgau, I.e.).

Against the cogency of these experiments there is good
evidence to indicate that the electrical taste depends not upon
electrolysis of the fluids in the mouth, but upon direct excitation
of the taste-nerves. It must in the first place be remembered,
as pointed out by du Bois-Eeymoud, that polarisation occurs at
the interface of dissimilar electrolytes (Gfes. Abh. I. p. 1), so that
under given conditions there may be a separation into acids and
alkalies (Hermann, 48). There is no reason why the electrical
taste should not be derived from electrolytic processes within
the lingual tissues, the direction of current being indifferent.
From this point of view, Volta's experiment with a tin beaker
filled with lime (34, iii. 2, p. 185) loses all point; as also,
according to Hermann (I.e.), the second of Eosenthal's experiments,
as cited above. Neither, however, is the electrolytic theory
tenable, as appears from electrically exciting other sense-organs,
and also from the opposite after-sensations on breaking the
current when the tongue is stimulated. Hermann pointed to this
last difficulty (I.e. p. 538) when he remarked that an ingoing
depolarising current was discharged in the polarised organ at
the moment of breaking an outgoing current ; this current is

200 ELECTRO-PHYSIOLOGY CHAP.

only capable of neutralising the alkali present, and not of
forming acid, so that there should be no acid after-taste at the
kathode — which does, notwithstanding, make its appearance.

If we attempt to determine the phenomena in question as
the consequences of direct polar excitation of nervous organs, we
meet with an initial difficulty in deciding which portion is
primarily excited by the current flowing in alternate directions.
Laserstein has contributed to the solution of the question in the
communication above quoted. It is known that cocaine has the
property of abolishing the excitability of most peripheral sensory
nerve-endings, the sense of taste not excepted. In Laserstein
himself this was not fully abolished by cocaine — disappearing
first for bitter and sweet, then for salts, but not entirely for
acids, though enormously reduced for these also. A trace of
acid electrical taste remained with an ingoing current, but the
full strength of a Dan. was then required, whereas previous to
the application a current with 5000 ohms principal, and 210
deriving, resistance was sufficient. For Hermann, cocaine abolished
all taste, including the electrical. This experiment proves
essentially that the structures, upon alteration of which by
current depends the sensation of taste, are situated in the extreme
periphery. The strength of current that produces these sensations,
as compared with other physiological persistent effects of stimula-
tion, is so low that its density can only be adequate immediately
beneath the electrode.

If the trunk of the nerve also were traversed, there would
each time be other sensations in the region of the cervical nerves.
Moreover, there can only be a question of orientated passage of
current through nerve-fibres or end-organs immediately under
the electrode, and it thus becomes intelligible that when
both electrodes are applied to the tongue there should be an
acid taste under the one, an alkaline taste under the other.
The electrical taste therefore depends exclusively upon passage of
current through the end-organs, or the ultimate nerve-endings
radiating in the mucosa. According to the law of specific energy,
by which each sensory nerve, wherever and however excited,
produces but one and the same specific sensation, the results
from electrical excitation of the tongue seem to coincide with and
witness to this principle. But if the law is strictly adhered to,
all nerve-fibres being regarded merely as indifferent conductors

ix ELECTRICAL EXCITATION OF NERVK 201

of excitation, the difference in effect being occasioned by the
central or peripheral end-organ, the fact that the two directions
of current call out different sensations by their excitatory action
011 the nerve, or its end-organs in the tongue, is contradictory.

Whether we assume, e.g., that the ascending current excites the
acid-reacting fibres only, or mainly (which is highly improbable),
or that the action of the ascending current in each fibre differs
from that of the descending, the law of specific energy is
inevitably contravened if it is construed in the preceding sense.
On the other hand, there is little difficulty in bringing facts into
line with theory, to which indeed they appear the inevitable
corollary, if the effects of polar excitation of the taste-nerves are
viewed as parallel with the antagonistic polar action of the
electrical current in other excitable substances (muscle, nerve).
There is only one point in which the consequences of the
electrical excitation of centrifugal nerves and muscles differ from
those in sensory nerves, viz. that in the last case the end-organs
(central ganglion-cells) react by qualitatively different (antagon-
istic) sensations to the changes produced at the kathode, as well as
at the anode, whence it follows that centripetal nerve-fibres must
transmit the two opposite kinds of alterations.

According to the view developed by Hering it may be
presumed that a sensory nerve gives rise to opposite sensations,
according as the dissimilatory or assimilatory process predominates
(Hermann, Pfluyer's Arch. xlix. p. 536). If we add that the
former is always developed persistently at the kathode, the
latter at the anode, the phenomena of electrical taste find a
simple explanation without prejudice to the law of specific energy.
Moreover, the phenomena consequent on the electrical stimulation
of other sense-organs will then be satisfactorily accounted for, since,
as Hermann pointed out (I.e. p. 537), there is no difficulty in
deriving opposite sensations from opposite directions of current.
In most cases the peripheral end-organs must be understood, since
these alone, as a rule, are perceptibly polarised under experimental
conditions. The ingoing current causes the assimilatory, the
outgoing current the dissimilatory change to preponderate ; but
it must always be assumed that the electropolar sensations
are mutually complementary, or (which amounts to the same
thing) stand in relation of contrast (Hermann, I.e.).

This is even more plainly seen in the electrical excitation of

202 ELECTRO-PHYSIOLOGY CHAP.

the ci/c than in the taste-sense. The following facts are taken
from Helmholtz's latest communication (49).

If the eye is excited by variations of current of adequate
intensity, one electrode being applied to the forehead or closed
eyelids and the other to the neck, more or less pronounced
flashes of light appear across the entire field of vision, while
if galvanic currents are employed they occur both on closing and
on opening the current.

Stronger currents are usually required to produce a persistent
effect from a steady constant current, than for make and break
flashes. In order to avoid these, as also twitches of the muscles
on making and breaking the current, Helmholtz found it advisable
to place two metal cylinders, surrounded with paste saturated
with salt solution, and connected with the two poles of a Daniell
battery of 12-24 cells, at the edge of the table where the subject
was sitting. The forehead is firmly applied to one cylinder,
while the hand touches the other, and if this is clone gradually
the effects of alternating the currents are quite inconsiderable.
The direction of current varies according as the forehead touches
now one and now the other of the cylinders. " If a weak
ascending current is led through the optic nerve, the dark field of
vision of the closed eye becomes brighter than before, and takes
on a greyish-violet hue. The point at which the nerve enters
looks at first like a dark circular disc in the bright field. The
illumination soon diminishes in intensity, and disappears altogether
on breaking the current. As the field of vision becomes
obscured, the previous blue tinge is replaced by a contrasting
reddish yellow from the subjective light of the retina." " On
closure of the opposite, descending direction of current there is a
marked effect, i.e. the field of vision (which is illuminated only
from the intrinsic light of the retina) usually becomes darker
than before, and appears to be reddish yellow ; the entrance point
of the optic nerve alone stands out as a bright blue disc upon the
dark fundus. On breaking this direction of current the field of
vision becomes bright again, and bluish white in colour, while
the optic disc is obscure." Other observers have described the
phenomena somewhat differently ; the views of Bitter, Purkinje,
Helmholtz, and Brenner are summarised (after Bossbach) in the
following table.

IX

ELECTRICAL EXCITATION OF NERVE

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Ix ELECTRICAL EXCITATION OF NERVE 205

With very strong currents Helmholtz found " a confusion of
colours," in which no rule could be discovered.

" The electrical excitation may also be confined to individual
parts of the retina, although it cannot be sharply localised.
The essentials of these manifestations have already been de-
scribed by Ptirkinje. Helmholtz made one conductor out of a
thin cylinder of sponge fully saturated with saline and tightly
bound to a copper rod with an insulating handle. The other
electrode was placed on the neck or grasped in the left hand,
while the sponge made contact with the skin near the
external or internal angle of the eye, which can be moved to
and fro under the closed eyelids. When the sponge is positive
electrode, the current passes on the proximal side of the eye
into and through the retina, leaving it again on the distal
side ; the reverse occurs when the sponge is negative.

" The side of the retina at which current enters will then
appear more obscure than the half by which the current leaves
it, which is relatively brighter. It is to be remembered that
these sensations are always referred by the subject to the
opposite half of the field of vision, as if the electrical brightness
were due to external illumination. The same rules hold good
for the phenomena that occur when the electrode is placed
anteriorly upon the cornea, covered by the eyelid. The positive
electrode then gives current from within outwards, through the
entire retina, producing the sensation of brightness." Helmholtz
invariably found that the optic disc exhibited a contrary effect
from that of the surrounding field.

" If positive electricity enters at the temporal side of the
eye, the current passes from without into the peripheral portion
of the retina, i.e. from cones to ganglion-cells, producing obscurity.
But in the fibres of the yellow spot that are directed towards
the temporal side, the current passes from ganglion-cells to cones,
and 'produces brightness. The several effects may be summed
up as follows : A constant electrical current through the retina
from cones to corresponding ganglion -cells gives a sensation of
darkness, the opposite direction of current a sensation of light"

This, even more plainly than in the organ of taste, shows
the antagonism of sensations with opposite directions of current
in the same end-organ of the optic nerve. Any interpretation
other than dissimilar action at the two poles is hardly conceivable.

206 ELECTRO-PHYSIOLOGY ,-HAP.

It is obvious that we cannot speak of any regular passage
of current in a given direction in the terminal apparatus of the
auditory nerve. Brenner (27), to whom we owe the most
extensive researches in this subject, placed one (the indifferent)
electrode at any part as far removed as possible from the ear
(back of head, chest, hand), while the other, with which he
experimented, was introduced as a fine wire into the auditory
meatus, after filling this with water, or applied as a small knob
covered with moist flannel to the skin near the meatus.

If the kathode is used for the exploring electrode, a sound
will be heard on closing a constant current of medium strength,
which gradually dies away during closure ; opening the circuit
gives no auditory sensation. On the other hand, if the anode
is applied to the ear there is no effect at closure, while the
opening is accompanied by a sensation of sound, which is usually
weaker than that at closure of the opposite current. On reversal
from anode to kathode, auditory sensations are produced with
an intensity of current at which a simple kathodic closure
gives no reaction (voltaic alternative). Oscillations of current,
starting not from zero, but from any finite value, produce the
same auditory sensations.

In character the galvanic auditory sensation is for the most
part in successful experiments, with not too strong currents, a
true musical sound. Kiesselbach (49) determined its pitch as
that of the intrinsic tone of his ear. Since this is also the
pitch of the subjective sound heard with the so-called singing
in the ear, Eosenthal (I.e.} assumes that " on simultaneously
exciting all the auditory fibres with a weak stimulus, the
resulting tone is always that to which the subject is, as it were,
most accustomed."

As regards electrical stimulation of cutaneous sensory nerves
many opinions have prevailed from the time of Ritter, the most
prominent fact being that an ascending current produces warmth
during its closure, while a descending current gives a cold
sensation. With a zinc -copper pile of 150 couples, the poles
of which terminated in beakers of salt solution into which the
hands dipped, du Bois-Reymoud experienced " waves of heat, and
cold shudders, alternately, running up the arms to the shoulders."
He was unable to convince himself that one arm felt heat and
the other cold. Goldscheicler (49), on the other hand, with even

ix ELECTRICAL EXCITATION OF XERVE 207

twelve cells, experienced a feeling of warmth in the arm con-
nected with the anode, but could not detect cold in the other
arm.

VII. POLAR EXCITATION BY CURRENTS OF VERY SHORT DURATION

(INDUCTION CURRENTS)

It has already been repeatedly pointed out that it is necessary,
in order that current should produce electrical activity in excitable
substances, that it should pass for a certain period, varying in
absolute value within a wide range, according to the nature
of the excitable tissue. This is especially true of the break
excitation by the constant current, which implies, besides ade-
quate intensity, a due period of closure, since the anelectrotonic
state (i.e. the anodic alterations of current with the disappearance
of which it is connected) can only develop fully under these
conditions. Here, with indirect stimulation of the muscle, there
can be no doubt that the development of an adequate an-
electrotonus in the nerve itself requires such an interval : on the
other hand, there are cases in which it may be asked whether the
inefficacy of a make stimulus with brief currents is due to some
property of the nerve, or of its peripheral end -organ (muscle).
If, e.g., a single impact of current, or induction shock, is effective
when applied to the nerve of a cross -striated muscle, and in-
effective when it acts upon the motor fibres of smooth muscle,
it may be conjectured that the absence of contraction in the
last case derives solely from the muscle, i.e. that the excitation
passing along the nerve may be of the same nature and magnitude
as in the first case, but that it is inadequate, or in some way
inept, to stimulate the more sluggish tissues. Internal variations
in the nerve must also be reckoned as factors.

However this may be, the manifestations of the law of
contraction undergo considerable modifications with brief currents,
even where the most rapidly reacting preparations are employed.
Pfluger's law of contraction would lead us to anticipate that
very brief currents effect no opening twitch, and this is supported
by experiment. We have already seen that induction currents
(which should theoretically produce a double excitation, since
they are equal at make and break) act in striated muscle,
at moderate intensity, from the kathode only ; and within a

208 ELECTRO-PHYSIOLOGY CHAP.

certain range of strength of current the same is undoubtedly
true of indirect excitation of the muscle also. On the other
hand, we know that stronger induction currents, acting upon
curarised muscle, produce changes at the point of entrance
(anode) also, which, if not invariably expressed in visible changes
of form, cannot be interpreted otherwise than as the consequences
of a break excitation. To this category belong more especially
the positive anodic polarisation currents which appear as the
after-effect of excitation by single induction shocks. In nerve,
as in muscle, it may be shown by any of the above methods
for proving the polar action of the constant current, that
both impacts of current and single induction shocks excite within
a certain range of intensity at the kathode only, i.e. that
the twitches thus discharged must be defined as closure
twitches. At Tick's suggestion, Lamansky (50) undertook ex-
periments to determine (by v. Bezold's method, as applied to the
constant current) the difference of latent period, with ascending
and descending induction currents, at the seat of stimulation.
The latent period was found longer for the ascending than for
the descending direction of current. V. Vintschgau (51) next
ascertained that with maximal, or nearly maximal, induction
currents this difference of latent period is considerably greater
than on exciting with weak currents. He is inclined to refer this
to differences of spatial extension, and relative intensity of the
electrotonic changes in the nerve produced by current.

The polar action of induced currents is also manifested in
the different effects of excitation, according to the direction of
current, in medullated nerve, — excitability being depressed in
the region of the central electrode (Biedermann, 30). The
facts relating to this point were already known to Hai'less, who
found, on applying ammonia to a portion of tire intrapolar
region of the nerve, "that even the intrinsically stronger break
shock had no effect after the action of ammonia, if applied to
the nerve, at its former strength, in the ascending direction,"
while the make shock sent through the nerve in the opposite
direction is effective. With uniform distance of coil there is
never excitation when, with ascending direction of current, the
kathodic section ?.- is rendered inexcitable by ammonia or any
similar reagent, i.e. the excitatory process can only proceed from
the kathode. We learn from the same fact that kathodic

IX ELECTRICAL EXCITATION OF NERVE 209

excitation aloue is discharged by induced currents of a certain
intensity. Analogous experiments to those with frogs' nerves
can easily be demonstrated on warm-blooded nerves, immediately
after division without previous injury.

If two unpolarisable electrodes are applied respectively to the
fresh cross-section, and to a point lying about 1 cm. below on
the rabbit's sciatic, it will be found on exciting with single
induction shocks of moderate strength that a twitch is discharged
only when the current is descending in the nerve. Under certain
conditions this striking reaction has a methodic value also, for it
is clear that when any section of the nerve, within which approxi-
mately equal excitability may be predicated at every point, is
excited with alternating currents, each single make as well as
break shock must take effect at a certain distance of coil. This
is no longer the case on stimulating the cut end of a warm-
blooded nerve. Only the descending direction of current will
then discharge an excitation, i.e. according to the direction of the
primary current, the break shock or make shock only. With
greater distance of coil, however, when the break induction
current is eventually alone effective, excitatory action can only
be expected when the current traverses the nerve in a descending-
direction. With uniform position of electrodes and distance of
coil there will thus in the one case be a visible effect of excitation,
in the other complete absence of effect, according to the direction
of the primary current. And when Tick (52) observed that the
action of an induction shock can only be augmented when its
kathode, and not when its anode falls in the katelectrotonic
region of a polarising constant current, this must be viewed as
direct evidence of the polar kathodic action of induced currents.
It was formerly supposed by Pfliiger that the total excitability of
the intrapolar tract could be measured by sending an induction
shock through it during the passage of the constant current ; but
this could only be correct under the presumption that the induction
current excited the whole tract simultaneously. Pfliiger always
made the induction current in the same direction as the polarising
current, and therefore tested excitability each time at the kathode
(which coincided with the kathode of the induced current) ; his
conclusion, that weak polarising currents strengthen the effect of
the (homodrornous) induction current, while stronger currents
diminish or abolish it, must therefore be interpreted like the

VOL. II P

210 ELECTRO-PHYSIOLOGY CHAP.

analogous data for direct excitation of the muscle. These ex-
periments also show that mere variations of current density in
the nerve (as also in the muscle) may excite equally with the rise
or fall of the current from or to zero (make or break of the circuit).
Later on, 0. Nasse (53), Hermann (53), du Bois-Eeymond (53),
and others attacked the question of how far the absolute height
of previously existing polar alterations affects the discharge of
a twitch from the muscle, in sudden variations of intensity in the
(" electrotonic ") changes of the nerve that occur during closure at
the kathode, after opening at the anode. Nasse showed (by a fall
apparatus which closed or opened an incremental current, derived
through a rheochord) a positive or negative variation of intensity
superposed upon the existing battery current. The positive
variation of descending currents was found to be increased with
weak constant currents, to be diminished with stronger currents,
while the negative variation of ascending currents was depressed
at all strengths of the constant current. Hermann sums up the
result of his investigations, on the Eckhardt-Pfluger method, in
the dictum that the effect of a given induction current is raised
(as in muscle) by homodromous constant currents (provided these
do not exceed a certain range of intensity), and depressed (to
abolition) by opposite currents. Since, as Hermann concludes,
increase of a homodromous current is equivalent to closure of a
homodromous or opening of a heterodromous current, while its
sudden diminution corresponds with closure of an opposite or
opening of a homodromous current (so that in the former case
the seat of excitation coincides with a pre-existing katelectrotonus,
but otherwise with previous anelectrotonus), the experimental
results of indirect, as of direct, excitation of the muscle seem to
be intelligible from the same standpoint.

If the exclusively kathodic excitation is thus to be regarded
as ascertained for weak induced currents, we must, on the other
hand, concede the probability that with strong currents even brief
duration may develop an electrotonus adequate to produce ex-
citation in the descending portion also. This is indicated in
certain observations of Fick, Lamansky, and others. These
refer, in the first place, to a characteristic feature of the height of
twitch, in indirect excitation of the muscle with very brief
constant currents (current impacts), on changing the intensity,
duration, and direction of the latter. Tick determined (supra)

ix ELECTRICAL EXCITATION OF NERVE 211

that there is at every intensity of current a minimum direction
below which it cannot fall without abolishing the contraction ;
while, if the duration of the current increases beyond this limit,
the twitch rises steadily from zero, and gradually reaches
the maximum possible at that strength of current. The
time-values involved are very low in excitation of the nerve.
A duration of O002 sec. is the maximum. Tick finds that the
increase of twitch does not proceed constantly with increasing
duration of a current of uniform strength descending in the nerve,
lint- that the rise is intermittent : the twitches increase again after
an initial maximum, if the passage of the current is prolonged.

If, e.g., a descending current of given strength discharges a
maximal twitch with a closure of 0-003-O004 sec., this will not
increase with further increase of current intensity, provided the
current continues to pass for a very short time only. But if the
same current is persistently closed, a twitch results which is con-
siderably in excess of the ultimate maximum from the momentary
action of current, i.e. is in a certain sense a supramaximal con-
traction. This can only mean that the kathodic make excitation
exhibits the greatest possible maximum, in consequence of the
prolonged passage of the current, as is expressed in both direct
and indirect excitation of the muscle by the fact that no in-
duction shock, however energetic, can effect the same degree of
contraction as the closure of even a moderate constant current.
Single induction shocks never elicit more than the relative maxi-
mum, that is not exceeded in brief constant currents also (Fick,
I.e. p. 25). Between these extremes of brief impact of cm'rent,
and persistent closure, it is quite possible that the irregular increase
in height of twitch with increasing closure depends partly upon
an anodic break excitation, since the effects of the closure and
immediately succeeding opening excitation are summated in the
muscle. In favour of this interpretation we have in the first
place the fact that (as Tick discovered later) the same phenomena
appear with descending induction currents, of increasing intensity,
since after reaching a first maximum the twitches rise again to a
second.

Along with these data we have the still more weighty
observations of Fick (54). He found that with ascending
impacts of constant currents the twitches declined after the
first maximum to zero (the so-called " breach," Liickc}, so soon as

21'2 ELECTRO-PHYSIOLOGY CHAP.

the passage of the current, which remained at uniform strength
throughout the experiment, exceeded a certain value. If the
experiment was then continued with increasing" duration of
current, the twitches reappeared and rose to a second maximum,
from which point they remained constant with further extension
of stimulation. The same effect appears when the strength of
the shock is varied with unaltered duration of current ; further,
with diminishing values of current duration the diminution
and disappearance of the twitches implies increasing strength
of current (Tigerstedt, 54, p. 4). Tick subsequently deter-
mined the same effect with ascending induction currents, since
here too, with increasing intensity, there is a " breach " after
the first maximum, followed by renewed twitches with further
increase of current intensity, which soon become " supramaximal."
The existence of the breach was confirmed by Tiegel (55),
and again by Griitzner (55). Tiegel claims to have seen it
with both ascending and descending currents. Griitzner, like
Tigerstedt, on the other hand, failed to discover it with descend-
ing induction currents. The effect is quite regular with ascending
induction currents. The twitches — beginning at a given, and
under uniform conditions of experiment fairly constant, strength
of current (distance of coil) — diminish rapidly, and then
gradually rise again. The diminution in height with increasing
strength of current occasionally fails to reach the zero, so that
here the breach is, as it were, imperfect. As regards its interpre-
tation, the breach must, according to Tick, be viewed as a result
of inhibition at the positive pole, which at a certain strength
(duration) of current is sufficient to neutralise the excitation
proceeding from the negative pole. The character of the twitches
appearing after the breach will be discussed later. The diminution
and abolition of the twitches with an ascending shock, or
induction current, would thus be perfectly analogous with the
corresponding phenomena of the ascending constant current
(Fick, 55). Griitzner's theory, according to which the breach is to
be referred to a sort of interference between pre-existing differ-
ences of potential between nerve current and exciting current,
was finally disproved by Tigerstedt. The strongest evidence in
favour of Fick's view is the fact that the breach only appears
with ascending direction of current ; if the inhibition at the
kathode is not strong enough to neutralise the kathodic excita-

ix ELECTRICAL EXCITATION OF NERVE 21 :j

tion completely, there is merely a diminution in height of the
twitches. In currents of brief duration the inhibition has not
time to develop adequately and produce a breach ; unless, at all
events, the currents employed are excessively strong. This is
doubtless the reason that the breach is not produced as readily
with break as with make induction currents (Tigerstedt, 54), at
least in cases in which the primary circuit is fully opened.

If we accept Pick's explanation of the cause of the breach,
the reappearance of the twitches, and their rise above the initial
maximum (" supramaximal contractions "), demand a special
interpretation, more particularly when the effects of ascending
excitation with the constant current is compared with that of
single induction shocks, from the point of view of Pfliiger's law of
contraction. In the former, the make twitch never reappears
after the third stage, whatever the augmentation of current
intensity, the break excitation alone being effective. Presumably
the twitches which appear beyond the breach on stimulating with
ascending impacts, or with single ascending induction currents,
may be viewed as break twitches. These, as we have said, begin to
increase again after the breach, and with protracted rise of stimulus
may gradually reach the same height as before. In some cases,
but not always, the twitches rise with increased strength of
current beyond the first maximum, and reach a considerably
greater height (i.e. are "supramaximal"); Tigerstedt (I.e. p. 22)
has shown that when supramaximal twitches do not appear even
with the coils pushed home, it. is quite easy to call them out if
the nerve is further excited with uniform, direction of current at
the same rhythm. Whether this is due to a kind of summation
of effects, or to other changes in the nerve produced by current,
must for the moment be left undetermined. It is easy to see
that the appearance of supramaximal twitches with brief
descending currents, as described above, can be interpreted
on the same principle. On the theory of Fick we have here
only summation of the excitations produced by the rise and
fall of current. With descending currents we know that ex-
citation proceeds from the pole proximal to the muscle. On
its passage to the muscle it therefore encounters no inhibition,
and arrives with undiminished strength. But when a (break)
excitation starts from the positive pole of the induction current,
it has a longer course than the make excitation, and reaches

214 ELECTRO-PHYSIOLOGY CHAI-.

the muscle perceptibly later. Let the make excitation be
maximal ; if the twitch which it induces begins in the
muscle before the terminal excitation arrives there, summation
of the two twitches must ensue — there is " supramaximal "
contraction. The time-relations of the two curves harmonise
with this conclusion.

Pick found, in the course of an experiment on the latent
period of twitches with increasing intensity of current, that the
first (considerably reduced) contraction after the breach showed " an
enormous prolongation of latent excitation." This cannot be due
to diminished strength of stimulation immediately after the breach,
for, even when the twitches after considerably exceed those
antecedent to it, the latency in the former is measurably greater
than in the latter. This sharp distinction between the twitches
before and after the breach determines them not to be perfectly
homogeneous. It has been pointed out by Waller (56) that the
latency of break twitches with the constant current is much
greater than that of the make twitches, and Biedermann confirms
this fact. If the twitches after the breach, as well as those
which bridge it with falling strength of current, really correspond
with the break twitches of the constant current, we should a
priori expect them to exhibit the same characteristics in regard
to the latent period.

Summing up the previous data, it may be stated with great
probability that — " The twitches before the breach are discharged
by the impact of an induction current (shock) ; these have a brief
latent period ; the twitches after the breach, as well as the twitches
which Bridge it with diminishing intensity of stimulus, are
caused by the disappearance of the brief current. These, like
all opening twitches, have a long latent period in comparison
with the closure contraction. When, with falling strength of
current, the point is reached at which the inhibition at the
positive pole can no longer hinder the transmission of the
excitation to the muscle, the short latency (suddenly) reasserts
itself " (Tigerstedt).

If certain " supramaximal " twitches thus depend upon sum-
mation of the anodic and kathodic excitation, we may expect to
demonstrate the same by separating the two stimuli so far in time
that the interval should be at least as great as the latent period
of the contraction. This, according to Tick and Lamansky, could

ix ELECTRICAL EXCITATION OF NERVE 215

be accomplished by lengthening the intrapolar region. In order
to obtain the necessary interval between kathodic and anodic
stimulation, the intrapolar tract must, however, be at least 150
mm., conductivity being reckoned at 30 m., and the latent
period at O'OOS sec. It is not possible to produce summation
of muscular contraction by this means with induction currents in
frog-preparations (Mares, 57). On the other hand, the method of
time-measurements still further supports the assumed bipolar
excitation from strong induction currents. If, i.e., the excitation
occurs at one pole only — the kathode — the latent period of the
muscle-twitch must (as is indeed well established) be longer with
ascending than with descending direction of current, and that
proportionately with the time occupied by rate of transmission
in the intrapolar region. If, on the contrary, excitation takes
place at both poles, the latency with both directions of current is
equal, and corresponds with the excitation from the pole proximal
to the muscle. This presumption was experimentally verified by
Mares' (I.e.).

VIII. EFFECT OF REPETITION OF STIMULUS

No matter what conception we adopt of the nature of the
excitatory process, it is always interesting to see in any appropriate
terminal organ the effect of several simultaneous or successive
stimuli at different points of the nerve. We have already referred
to the case of bipolar excitation by induced or constant currents,
but still greater interest attaches to the action of simultaneous
stimuli. A priori it is, as Hermann points out, most probable
that the two independent processes of excitation travel undisturbed
over the nerve, at an interval corresponding with the distance
between the two points of stimulation, and arrive successively at
the terminal organ. The resulting effects must depend solely
upon the nature of the end-organ. In muscle, e.g., the second
stimulus would, according to the interval, be ineffective, or would
cause a superposed twitch, or a second independent twitch.
Even when two excitations meet in the same fibre, an undisturbed
passage in either direction is conceivable ; and such an encounter
must, in fact, take place in every simultaneous stimulation of two
points of a nerve, since the upper excitation cannot reach the
muscle without crossing the lower impulse, which, of course,

216

ELECTRO-PHYSIOLOGY

CHAP.

travels up as well as downwards (Hermann, 34, p. 109). All
observations hitherto made on this point refer exclusively to
experiments with two electrical stimuli. The results of this
method, which have been variously diagnosed as summation, or
as interference effects, are by no means free from ambiguity. In
using electrical stimuli, i.e., we must take into consideration not
merely the combination of two independent processes of excitation,

FIG. 200. — Schema for simultaneous excitation of a nerve by induction shocks at different

points. (Werigo.)

but also (owing to the nature of the electrical stimulus) alterations
in the conductivity of the nerve, which are unfavourable to the
integrity of the experiment.

Grii.nb.agen (58), in order to obtain the absolutely simultaneous
action of two or more distinct currents upon different points of
a nerve, devised the method of leading the current from a
sufficiently strong battery through two or more primary induction
coils, with as many corresponding secondary coils. Every closure

ix ELECTRICAL EXCITATION OF NERVE 217

or opening of the battery circuit will then discharge absolutely
simultaneous induction currents in all the secondary coils,
and these can be led off to points of the nerve by means of un-
polarisable electrodes. The method is shown in the accompanying
diagram (Fig. 200) from Werigo (58).

Four combinations are possible, relatively to the direction of
the two exciting currents. These may either be homodromous
(ascending or descending), or, with opposite direction, may flow
to or from each other, so that with the first the kathodes, with the
second the anodes, are in juxtaposition. If current intensity
is so adjusted that one current in itself gives minimal, the other
no contraction, both shocks being in the ascending direction, a
reciprocal effect appears ; i.e., with not too great a distance
between the exciting electrodes, the ascending stimulus directed
towards the muscle (peripheral), and of itself inadequate (infra-
minimal), perceptibly augments the action of the central,
ascending current, while conversely a central, ascending, infra-
minimal stimulus inhibits the already minimal effect of an
ascending, peripheral current. If both induction currents are
descending, the same effects as in peripheral, inframinimal
excitation hold good of the central, and vice versa. If the
currents flow towards each other, the final effect is that of
mutual augmentation, until a maximal twitch may arise from
two stimuli, each per se ineffective; while with not undue distance
between the excited parts an antagonistic inhibition may be
detected.

These results coincide with those of Sewall (58), and are
easily reduced to the polar action of the current. " Augmentation
will invariably be found on applying the exciting current in the
vicinity of the kathode of the modifying current, with the
converse diminution when it is sent in near the anode." Always,
however, the increase of excitability in the katelectrotonic region
is more strongly marked than its diminution in that of auelectro-
tonus. If both shocks are effective, even if unequally, the
distance between the two excited parts being such that electro-
tonic effects are absolutely excluded, the muscle reacts to
the stronger excitation only — and that as if this alone were
present. There would thus seem to be no real interference in /
the sense of addition or subtraction of stimuli. If the distance 1
between the excited parts is reduced, the effects become much

218 ELECTRO-PHYSIOLOGY CHAP.

more complicated (owing to the interference of electrotonic
alterations of excitability) than when one shock only is acting ;
since both the modification of the central current by the
peripheral and that of the peripheral by the central then come
into play. In such cases, all the resulting phenomena are in
line with the laws of electrotonus.

Kaiser (59) has recently described a special case of interference
between two excitations discharged at different points of a nerve.
He found, i.e. with simultaneous excitation of the frog's sciatic
at two points as far apart as possible, on the one hand by 'tetauising
alternating currents, on the other by glycerin, that the glycerin
tetanus was sometimes inhibited at the beginning of and during
the electrical stimulation. Since the same effect appears in the
simultaneous action of two different chemical stimuli (glycerin
and NaCl, or glycerin at both points), explanation by electrotonic
alterations of excitability is ab initio excluded. When the same
chemical stimulus acts upon two distinct points of the nerve,
there is at most a very moderate tetanus, the sudden strengthening
of which after amputating the upper seat of excitation is very
striking. It seems tolerably certain that the inhibition that
occurs in nerve-fibres, subjected simultaneously at two distinct
points to tetanising stimuli, is due to processes which run
their course in the nerve itself. Since the negative varia-
tion (as shown by the capillary electrometer) is invariably
augmented under these conditions, instead of diminishing, as
might a priori be expected, there cannot be merely an inter-
ference effect of the electrical waves of variation in the nerve, in
the physical sense that they are neutralised by the coincidence
of unequal phases. According to Kaiser, there must, whenever
an excitatory wave is overtaken and submerged by the following
wave, be " summation of negativity in the coincident points," so
that in the given case " the waves of excitation resulting from
the two stimuli are more or less fused together, and the amplitude
of the variation sinks below the liinen required to evoke action
from the muscle."

We already know from innumerable examples that simple
summation of excitatory conditions may occur at any point of
the nerve, inasmuch as the excitability of any part of the
nerve appears to be heightened when it is the seat of a weak
and intrinsically inadequate (latent) excitation.

ix ELECTRICAL EXCITATION OF XKRYE 219

IX. UNIPOLAR EXCITATION

Under certain conditions, excitation with induced currents
brings to light phenomena which are not merely of theoretical
interest, but have great practical value in all experimental observa-
tions. Among these is the so-called unipolar excitation by in-
duction, first noted and worked out by clu Bois-Eeymond (I.e. p.
423). The facts underlying the entire subject are as follows : " If
the nerve of a rheoscopic leg is connected with one end of an open
induction circuit, either the leg or the other terminal of the circuit
being led off to earth, a twitch occurs each time that an excitatory
process is set up near the circuit, sufficient to have produced a
secondary current in the circuit if it had been closed " (I.e. p.
429). This occurs even with complete insulation of the prepara-
tion, and also, at a given (short) distance of the coils, when there is
no lead-off to earth (by touching the preparation, or connecting the
other free pole with the ground). The excitation fails when
the metallic end of the induction circuit is led off by contact above
or below the point on which the nerve rests, or when, with the
nerve hanging freely, contact is made with the preparation, and
the muscles are led off by touching them. In the first case,
ligaturing or crushing the nerve does not inhibit the excitation,
seeing that the nerve is traversed by electricity in its entire length,
inclusive of the crushed part. Pfh'iger (2, pp. 57, 121, 410) found
that break shocks were markedly the most effective — explained by
clu Bois-Eeymond as due to delay in charging the secondary coil,
by the development of the extra current.

In order to produce unipolar excitation, it is not necessary to
lead off from one pole to an infinite conductor (such as the earth).
The effect on the contrary appears, as first pointed out by Pfliiger
(/.'•. p. 128 f.), even when the led-off pole is in contact with a
comparatively small surface, the more so in proportion as the
P.D. arising from the E.M.F. due to induction is higher. " The
degree of unipolar action increases rapidly with the magnitude
of the lead-off, unipolar stimulation being greater at any given
point, with a restricted leading-off surface, in proportion as this
point lies nearer the seat of unipolar action at the metal pole."
Pfliiger placed a row of frogs' legs (4-6) upon a glass plate, after
insulating all the apparatus as carefully as possible, so that only
the nerve of the first touched the (single) metal pole, that of the

220 ELECTRO-PHYSIOLOGY CHAP.

second the foot of the first, that of the third the foot of the
second, and so on. Gradual approximation of the coils of the
induction apparatus caused each leg to twitch in succession. This
shows that " unipolar action in the vicinity of the metal pole is a
fallacy likely to occur even with scrupulous insulation."

Under certain conditions the effect of "induction" is very bene-
ficial to unipolar excitation. Du Bois-Reymond had occasionally
observed, when the finger was brought closer to a nerve-muscle
preparation attached only to one pole, that twitches appeared
which were not otherwise present at the same strength of current.
This — as found by F. W. Zahn (60) — is the case not merely
when the free end of the circuit is led off by contact with the
other hand, but even without this. Zahn modified this experiment
in many ways. He placed the preparation upon a round glass
plate, the under surface of which was covered with tinfoil to
within 10 cm. from the edge. On connecting one pole with the
leg, the other with the sheet of tin, tetanus appeared even with
weak currents. The same thing occurs with rather stronger
currents when the limb is disconnected from the secondary coil,
at the moment of leading off by contact, or when the free metal
pole is grasped in one hand while the other is brought near the
preparation. The experiment is still more successful if the
glass plate is evenly covered on both sides with metal, turning it
into a Franklin's Board. If one sheet is then connected with
one pole, the other with the nerve of the preparation, while the
leg hangs over the non-metallic glass edge and makes contact
with the other free pole, so that the circuit is interrupted only
by the glass disc between the two sheets of tinfoil, twitching
and tetanus are set up with even weak currents. The result is
the same on connecting one end of the induction circuit with
the lower sheet, while the other terminates in a plate of tinfoil
brought close to the leg. With the coils pushed home, there is
also stimulation when one end of the circuit is left free and
isolated, on bringing a plate of tinfoil sufficiently near to the
limb.

Tiegel (60) connected one pole of an induction apparatus with
a gas-pipe, while the other terminated in an isolated metal plate
which could be moved towards a corresponding plate standing
opposite to it. The latter was in circuit with a glass plate
covered with tinfoil, on which the preparation was lying. Each

ix ELECTRICAL EXCITATION OF XERVE 221

time the muscle-nerve was touched there was excitation, varying
in strength with the distance between the plates, and susceptible
with a suitable lead-off (by a fine metal point) of very exact
localisation. In this case also, the break shocks only took effect.
Schiff and Fuchs (60) also obtained unipolar action -iritlinut
iinlni'tioii, with the exclusive action of static electricity. They
carried the charges from the ends of an open circuit into a large
conductor, or the plates of a condenser, and then led them
through an excitable nerve. The following experiment by
lloseuthal (60) is also suggestive. A nerve-muscle preparation
insulated on a glass plate, upon which the nerve and muscle lie
in a trough, is suddenly brought near a charged conductor, held
by an insulated glass handle, on which a small twitch may occur
when the end of the nerve is proximal to the conductor, — never,
on the other hand, when the conductor is brought near the
muscle end. But if in the last case the nerve is led off by
contact, or even connected with an insulated conductor of any
size, there is always marked excitation.

The theory of unipolar excitation, of which we have thus
been considering some instructive instances, was essentially
developed by du Bois-Eeymond, who showed that it depended
upon the electrical potential at the two free ends of an induction
coil. At the moment of opening or closing the primary circuit,
an open secondary circuit represents, as it were, an open battery,
with free electricity at its two ends. If each pole of the secondary
coil is connected respectively with the nerve of a frog's leg, both
preparations twitch if one of them is led off to earth — because
both nerves are traversed by the flowing electricity, in opposite
directions. The same thing of course takes place when only
one metal pole is connected with the nerve of a preparation, the
lead-off being either from the leg or from the other free pole.
The electricity necessary to charge the leg always flows through
the nerve, and thus excites it. Obviously, the intensity of
the excitation depends in first degree upon the amount of
electricity flowing through the nerve — increasing accordingly
with difference of potential, approximation of coils, and lead-off
from free pole. Augmentation of the electrical capacity of the
leg produces the same result. To this is due the favourable
effect of connecting up a unipolar preparation with conductors
of a larger surface (human body, etc.), as well as the approxima-

222 ELECTRO-PHYSIOLOGY CHAP.

tion of a neutral body, or better, of a conductor containing the
opposite charge, from the other end of the coil ( = induction}.

When, as in the above experiment from Tiegel, one pole of
the secondary coil is led off to earth, there must at the moment
of induction be a certain (positive or negative) charge (potential)
at the metal plate connected with the other pole, which must be
twice as great as it would be if the other pole were not led off.
The effect of induction upon the second insulated metal plate,
parallel to the first, is to set up a potential of the opposite sign
which varies with the distance. At the next moment, the negative
electricity (let us say) of the charged pole flows through the
secondary coil to the other pole, and the positive electricity of
the plate charged by induction flows through the nerve-muscle
preparation to earth, whereby excitation is produced.

The unipolar effects that occasionally appear (as was again
pointed out by clu Bois-Eeymond) with incomplete closure of the
circuit are of great practical importance in all electrical experi-
ments with induced currents. If the nerve of a frog's leg is laid
across two electrodes connected with the poles of a secondary
coil, so as to close the induction circuit, a ligature being then
applied to the myopolar tract, tetanus may still be observed in
the isolated leg, on making the lead-off from it at a certain
distance of coil. It is evident that the same would occur if the
nerve were cut away above the crushed and no longer conducting
point, and replaced by any moist conductor. Here, as in all the
previous experiments with an open circuit, the direction of the
unipolar passage of the current makes itself apparent, in accordance
with the law of contraction. Excitation occurs only with charges
in which positive electricity leaves, or negative electricity enters,
the nerve. These unipolar effects may obviously be very dis-
turbing, and are indeed productive of fallacies in vivisection, and
also in experiments with the galvanometer, if not avoided by due
precautions. Hering (61) has pointed out that in experiments
such as the investigation of the negative variation of nerve
currents, in which galvanometers and exciting circuits are
separated by a long tract of nerve, the most complete insulation
of the two circuits is no guarantee against the overflow of
induced electricity through the interpolar part of the nerve into
the galvanometer circuit.

There must always be, along with the short-circuiting through

ix ELECTRICAL EXCITATION OF XERVK 223

the interpolar tract, a flowing off in the complex of conductors
which forms the galvanometer circuit, and which must (however
well insulated) be connected through the nerve with the secondary
coil. Hering further showed by special experiments that the
sudden charges and discharges in the galvanometer circuit, caused
under all conditions by the interpolar flow of electricity, do
not as a rule produce any deflection of the magnet.

The following experiment demonstrates plainly in what
degree the connection of the nerve with the galvanometer circuit
is responsible for unipolar excitation. " A sciatic nerve, still in con-
nection with the leg, was laid across the exciting and galvanometer
electrodes just as in the determination of the negative variation
(exciting tract = 5 mm., intermediate tract =2 5-30 mm., gal-
vanometer tract = 6-8 mm.). The stump of the thigh-bone was
fixed in a paraffin clamp with a corresponding bore, so that the
leg is as far as possible insulated. After repeated crushing of
the intermediate tract, the preparation was stimulated, and the
secondary coil gradually pushed up. Unipolar action began at
20—25 cm. distance of coil, and the muscle went into tetanus
even if one galvanometer electrode only was in contact with the
nerve. On taking both galvanometer electrodes off the nerve,
the muscle remained quiescent " (Hering). The difference
between this and ordinary unipolar excitation is that electricity
here does not flow over to the muscle, but passes through the
galvanometer electrodes into the galvanometer circuit, and thereby
excites the nerve, partly below the crushed point, partly at the
seat of the galvanometer electrodes (more particularly at the long
section).

This kind of unipolar stimulation is an obvious danger in
all experiments on action currents and negative variation in
nerve, while it shows what narrow bounds restrict the intensities
of current that may be safely used in these experiments.

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VOL. II ci

226

ELECTRO-PHYSIOLOGY

CHAP, ix

1

A. FICK.

W. S.-B.

2.

Abth.

XLV

I.

p. 350,

XLVII. p. 79,

und

XLVII I

54.

p. 220.

1862-63.

1

Ti<;r.RSTE!

DT. Arbeiteu

aus deni

phys

110

1. Labor.

•/AI Stockholm.

3.

Heft.

56.
57.

58.
59.

60.

61.
62.

(TiEGEL. P. A. XIII. p. 280.
GKUTZNER. P. A. XXVIII. pp. 174, 177.
I f Wiirzburger Yerhaiullungen. N.F.

(Ueber das Pliiinomen der Liicke.
WALLER. Archives de Physiologie. 1882. I.
MARES. Berichte der k. bb'hm. Ges. der Wiss.

II. 1871. p. 150 ff'.
Inaug.-Diss. Bern, 1883.
p. 383.
1891.

J-GRUNHAGEN. P. A. XXXIV. p. 301. XXXVI. p. 518.
\ WERIGO. P. A. XXXVI.

UEWALL. Journ. of Physiol. 1880-81. Vol. III. p. 347.
K. KAISER. Zeitschr. fiir Biol. XXVIII. N.F. X.
"F. W. ZAHN. P. A. I. p. 256.

TIEGEL. P. A. XIV. p. 330.

M. SCHIFF. Zeitschr. fiir Biol. VIII. 1872. p. 71.

FUCHS. Zeitschr. fiir Biol. VIII. 1872. p. 100.

J. ROSENTHAL. Du Bois' Arch. 1881. p. 63.
E. HERING. W. S.-B. LXXXIX. 1884. 3. Abth. p. 219.
G. E. MULLER. <: Ueber die galvanischeu Gesichtsempfindungen," Ebbingliaus'
Zeitschrift fiir Psych, u. Physiol. d. Sinnesorgane. XIV. 5.

CHAPTEK X

ELECTROMOTIVE ACTION IN NERVE

I. CURRENT OF " EESTING " NERVE

Du Bois-PtEYMOND communicated his first observations on galvanic
action in the divided nerve in 1843, after many vain attempts
on the part of Matteucci and others to demonstrate its existence.
A complete historical account of all the preliminary researches
may be had in the second volume of du Bois-Eeymond's classical
work. Modern methods have facilitated the recognition of the
" law of the nerve current " in each excised particle of cold- or
warm-blooded nerve — which law, apart from differences of in-
tensity in the resulting effects, coincides in every particular with
that of the muscle current. In both cases, each point of the
natural, uninjured surface (the "natural longitudinal section ") is
positive to all points of an " artificial transverse section " ; in
both the difference of potential is greatest when the " equator "
is connected with the cross-section by the leading-off circuit, such
P.D. being greater or less according as the points of the long
section are less positive to the cross-section, i.e. are more closely
approximated to it; each point nearer the equator being also
positive to each more distant point (weak longitudinal current).
As in muscle, we must assume each single nerve-fibre to be
equally electromotive with the entire nerve-trunk.

Du Bois-Eeymond determined the absolute E.M.F. of the nerve
current as 0'022 Dan. in frog, 0'026 Dan. in rabbit. The follow-
ing table from Fredericq (1) shows the E.M.F. of medullated nerve
in the frog to be much the same as in various warm-blooded
animals, while the nerves that are composed of non-inedullated
fibres in both vertebrates and invertebrates are characterised

228 ELECTRO-PHYSIOLOGY CHAI-.

by a striking preponderance of electromotive force (Kiihne and
Steiner, 2) : —

Cat

Dog

Eabbit

Duck

Lobster

0-018 Dan.
0-018-0-021 Dan.
0-020-0-028 Dan.
0-024 Dan.
0-048 Dan.

In the non-medullated olfactory nerve of the pike, which is
of approximate diameter with the frog's sciatic, Kiihne and
Steiner found an E.M.F. of 0'0215-0'0105 Dan., while in the
frog's sciatic it was only 0-002-0'006 Dan. In any case these
figures show the E.M.F. of the non-medullated olfactory nerve of
pike to be greatly in excess of that in medullated frog's nerves.
The difference is more than half. The medullated optic nerve
of the pike, which has a far larger diameter than the olfactorius,
alone approaches the lowest figure (O'OIOO Dan.) given for the
latter. The cause of this striking difference between medullated
and non-medullated nerve is, according to Kiihne, " either that
the specific E.M.F. is greater in non-medullated than in medullated
nerve, or that the medulla of medullated nerve is per se electric-
ally inactive, electromotive force being confined to the axis-
cylinder; so that similar cross-sections of medullated and non-
inedullated nerve would not correspond in electromotive condition,
and medullated nerve would only exhibit the same electromotive
force as non-medullated nerve, when its anatomical cross- section
exceeded that of the latter to the extent occupied by the medulla
in the section" (Kiihne and Steiner, I.e. p. 160).

The electrical reaction of the slender, non-medullated con-
nective nerves of Anodonta (3) also points to the conclusion
that the electromotive activity of medullated nerve-fibre derives
from the axis - cylinder only, without participation of the
medulla. These nerves, under favourable conditions, yield very
strong currents — as also the mantle nerves of Eledone, in which
the E.M.F. amounts, according to S. Fuchs (4), to 0'0259 Dan.,
though they are frequently of smaller diameter than the sciatic
nerves of large Transylvanian frogs. Gotch and Horsley (5)
find a striking difference of potential between longitudinal and
artificial transverse sections in the spinal roots of mammals.
While the E.M.F. of the demarcation current of mixed mammalian
nerve is O'Ol Dan. in cat, 0-005 Dan. only in monkey, it amounts
in the posterior spinal roots of the cat to 0'025 Dan., and even

x ELECTROMOTIVE ACTION IN NERVE 229

ill the spinal cord to 0'046 Dan., and 0'029 Dan. in monkey.
Comparison of the spinal cord of young full-grown animals with
the large nerve of adults proves that this is not due solely to the
greater sectional area.

In all experiments upon the so-called current of rest in the
nerve (Hermann's " demarcation current "), it is essential that the
lead-off from the cross-section should be as clean as possible. It is,
of course, more difficult to lead off from the transverse section of
finer nerves than from coarse trunks. Hence it becomes advisable
to destroy a certain tract near the transverse section, and to
lead off from the dead end. Under conditions in which the
demarcation current of the frog's sciatic yields at most a galvano-
meter deflection of about 70 degrees, Biedermaun obtained
deflections of 60-200 degrees from the two juxtaposed nerves
of mollusca, the diameter being still considerably below that of
a single frog's nerve. In non-medullated nerve also there is
a zone of rapidly diminishing negativity near the demarcation
surface, which again produces " weak longitudinal currents "
(Biedermann. supra, also Kuhne and Steiner).

The reaction of nerves that are different in function is very
striking on leading off from two cross-sections, when the current
should be zero, if the negativity on both sides were equal. This
is not, however, the case (du Bois-Eeymond, 6) : a difference of
potential occurs not merely in the frog's sciatic, but also in the
nerves of warm-blooded animals (Fredericq, 1, p. 68, note).

Mendelssohn (6) subsequently found regular and apparently
constant differences of negativity between any two cross-sections
in pure centripetal or centrifugal nerves. Du Bois-Eeymond
had already in electrical nerves shown greater negativity of the
peripheral cross-section as compared with the " equator," so that
the current from section to section, the so-called " axial current,"
is always in an ascending direction. The same is true, according
to Mendelssohn, of the (purely centrifugal) muscular branches of
the rabbit's sciatic ; while in the posterior roots of frog and rabbit,
as also in the optic and olfactory nerves of the fish, the axial
current is descending. In the mixed trunk of the sciatic, again,
the direction is alternating. If any law could be formulated
from these observations, it would be that the axial nerve current
is opposed in direction to the physiological action of the nerve
fibres. These observations may conceivably be brought into line

230 ELECTRO-PHYSIOLOGY CHAP.

with the data cited above for differences of excitability, and
susceptibility to injury, at different points of the uninjured
nerve. Mendelssohn convinced himself that the E.M.F. of the
axial current was greater in proportion with the rate at which
the excitatory impulses traversed the nerve in one or the other
direction, i.e. the more the nerve was excited within the organism.

The great regularity of electromotive action in divided or
otherwise injured nerve obviously goes no further towards
establishing the pre-existence of an electrical potential within
such tissues than in the parallel case of muscle. Here, as there,
on the contrary, it must be affirmed that the perfectly uninjured
nerve is electrically inactive. It is obvious, in view of the mode
in which the nerve-fibres end in the peripheral organs, or central
system, that we cannot speak of leading off from a " natural
cross-section " (in the same sense as in muscle), especially as
not merely the motor end-organs (muscle), but others (e.g. gland-
cells) also, are proved to be, actually or potentially, the seat of
electromotive action. This applies, inter alia, to the organ which
seems at first sight best adapted to decide this question, viz. the
eye, as investigated by du Bois-Eeymond and others. Some
account of its electromotive activity will be given below.

Electromotive action in nerve, as in muscle, is a vital property
of the living tissues. The nerves of a corpse gradually (albeit in
most vertebrata very slowly) cease to exhibit any difference of
potential between a fresh demarcation surface and points on the
uninjured superficies. It is intelligible that this should occur
sooner in warm- than in cold-blooded animals, as also that nerves
left in the body should preserve their normal properties longer
than excised nerves ; and that excitability should decline most
rapidly in the central tracts that are, generally speaking, the
least capable of resistance. Steiner (7) finds that the E.M.F. of
the nerve current increases within a certain range with rising
temperature, reaching its maximum between 14° and 25° C. At
boiling-point the current is reversed, according to du Bois-Bey-
moiid, as Harless also finds at a certain stage of drying. Electro-
motive activity may persist for a long time during the process
of degeneration suffered by nerves that have been separated from
their centres, which is also natural, seeing that the medullary
sheath is first to be disintegrated in medullated fibres. Schiff
and Valentin (8) found that nerves of birds and mammals,

x ELECTROMOTIVE ACTION IN NERVE 231

when divided in the living animal, exhibited a normal current
weeks and months afterwards, although excitability disappeared
8-14 days after the operation. Schiff asserts that the axis-
cylinder was still present, in spite of advanced disintegration of
the medullary sheath, — a further proof of the physiological signifi-
cance of this portion of the fibre.

The alterations in time suffered by the demarcation current
in medullatecl nerve are of extreme interest, since they are
analogous with those of cardiac and smooth muscle. Engelmann
(9) found that the E.M.F. of the cross-section fell with extreme
rapidity, and appeared again in undiminished vigour when a
new section was made. This he explained from the fact that
the individual cells die separately, notwithstanding their physio-
logical coherence — the process of death is confined to the cells
that are directly injured. Similar relations appear in medullated
nerve-fibres, although these cannot be regarded as consisting of
separate cells fused together. After only 1-2 hours Engelmann
noted that the E.M.F. of the artificial cross-section fell from
60 to 25 per cent of the initial value, in 20—24 hours to at least
35'5 per cent, more often to 0 ; frequently, as pointed out above,
there was a weak reversed current. Eenewal of the cross-section
in every case restored the full value of the original current.

Head (10) found, on repeating Engelmann's experiment, that
the diminution of the demarcation current was especially marked
in the nerves of summer frogs, so that the increase of E.M.F. in
consequence of the new cross-section is here particularly striking.
After 14 minutes the very pronounced current of rest was
observed by Head to fall to 1 of its original value. Twenty-eight
minutes after beginning the experiment a new section was made,
upon which the nerve current at once reappeared in its former
vigour. As a rule, there was even a marked rise of E.M.F.

O

beyond the original magnitude. In one special case the current
of rest in a frog's sciatic gave a deflection of 155 degrees, which
fell 20 minutes later to 32 degrees of the scale. After making
a new section, the current at once increased to 120 degrees, and,
after a second rapid fall, gave a deflection of 232 (!) degrees, on
applying another (fourth) cross-section, 33 minutes after beginning
the experiment. Engelmann explains this striking reaction from
the fact that the process of mortification in the injured fibres is
arrested at the nearest node of Eanvier. The same effect appears,

232

ELECTRO-PHYSIOLOGY

CHAP.

however, in the optic nerve of the fish (Ktihne, 9), where the fibres
have no constrictions, and also in non-mednllated nerve (Bieder-
inann, 3), although in a less marked degree, so that there is no
adequate reason for assuming definite anatomical boundaries within
the continuity of the axis -cylinder, at which the process of
mortification shall be arrested. If the fact that the separate
cell-individuals in cardiac and smooth muscle are directly united
by plasma-bridges is of universal application, the consequences of
renewing the section can only indicate that the death-process is
arrested at some distance from the cut surface, without confining
it within preordained anatomical barriers.

Nerve, like muscle, can be excited by its own demarcation current.
The facts relating to this subject have been familiar since the days

FIG. 201. — Excitation of nerve by its own current.

of Galvani, and have more especially been investigated by Kiihne
and Hering (11). Galvani introduced the nerve of a rheoscopic
leg into an open circuit, and allowed the nerve of another leg,
completely isolated from the first, to fall upon the circuit, in such
a way that the cross-section of the first nerve formed one of the
two points of contact. Both legs twitch in a successful experi-
ment. Du Bois-Reymond laid the central end (transverse and
longitudinal sections) of a sciatic nerve, still connected with the leg,
across the pads of his zinc trough-electrodes, making and breaking
the nerve current by means of a mercury key. " The leg twitched
at closure and at opening, in some cases on breaking the circuit
only." Du Bois-Reymond subsequently simplified this experi-
ment by placing two long pads of filter-paper saturated witli salt
solution close together upon an insulating stage, and laying acr< iss
them the long and transverse sections of the rheoscopic nerve.

x ELECTROMOTIVE ACTION IN NERVE -233

The circuit was closed by applying a third pad quickly, where-
upon the muscle contracted (Fig. 201). The point here being
adequate rapidity of closure and opening, the two pads on which
the nerve is resting may hang freely over the edge of a glass
plate, a vessel of salt solution being rapidly raised or lowered
below them (Hering, I.e.), or two blocks of salt clay can be employed,
which are readily moulded into any form (Kiihne, I.e.). The
twitches resulting from this last method are, as Kiihne showed,
most energetic. In excitable preparations Hering obtained
vigorous make and break twitches, when the tract of nerve
between the clay blocks was lengthened to 1 cm. This gave
reason to anticipate that a nerve may be tetanised by its
own current as well as by the interruptions of a battery
current. AYith this object, Kiihne employed a vibrating mercury
key ; Hering, on the other hand, constructed a special apparatus,
by which he obtained a " tetanus without metals." "The rapid
raising and dropping of the closure pad (supra) was effected by
the teeth of a rotating cog-wheel, which lifted the one-armed
lever, and the closure-pad attached to its free end, while a spring
fastened to the lever drew it down again after each rise." ' The
simplest means of exciting a nerve by its own current is, as
remarked by Hering (I.e. p. 241), to let its end fall upon a second
isodectric moist conductor." Metals (platinum, amalgamated
zinc) are less suitable for this purpose, because they very shortly
set up polarising currents. " If the end of the nerve falls upon a
drop of lymph, blood-serum, or weak salt solution, the effect usually
occurs once only, because the fluid that clings to the nerve when
it is lifted out again short-circuits it permanently and effectively.
But if the nerve falls upon a coagulated drop of blood, or a block
of clay saturated with 0-6 per cent NaCl, the experiment may
be freely repeated." An isoelectric muscle will obviously be a
convenient sub-stage for the same purpose. " If a nerve still
connected with the leg is allowed to fall upon the gastrocnemius
muscle, the resulting twitch is no proof that the nerve is excited
by a muscle current, although this may generally be the case."
Czermak pointed out that frogs' legs of great excitability will
contract when their nerves fall upon portions of the intestine,
kidneys, or liver of a rabbit, which no more proves the pre-
existence of a P.D. in those parts than the observation of Bonders
that frogs' legs may twitch under certain conditions, when the

234 ELECTRO-PHYSIOLOGY CHAP.

cut end of the nerve drops upon the pericardium during diastole
(cf. Kuhne, I.e. p. 85).

A twitch is often produced, as in muscle, by merely bringing
the cross-section of the nerve into contact with a drop of con-
ducting fluid. Eckhardt (12) employed this last method to
investigate chemical stimulation of nerve, as Kiihne had done
for muscle. For both we must distinguish between the electrical
excitation caused by short-circuiting of the demarcation current,
and the resulting chemical action — a difficult if not impossible
task in many cases. The electrical origin of the twitch which
(as Hering noted) makes its appearance on touching a fresh cross-
section with a drop of 0'6 per cent salt solution, or of the con-
centrated solution of zinc and copper sulphate, said by Eckhardt
to be chemically inactive, can hardly be disputed. With the
very active solutions of fixed alkalies, on the other hand, where
we must take into consideration that the magnitude of the twitch
may be due solely to the fact " that they moisten the nerve more
rapidly and efficaciously than other fluids, and thus produce a
quicker electrical variation in the nerve," the same cannot be
asserted with equal certainty. In all experiments on excitation
of nerve and muscle by their intrinsic currents, great excitability
of the preparation is, as has been stated, indispensable ; hence
they come off best in the cold season. In experimenting on
frogs' nerves that have been kept in a cold room (at about 0° C.),
Hering has again pointed out the extraordinary tendency to
tetanic excitation exhibited under these circumstances — particu-
larly by H. esculenta, in a less degree by E. temporaria. The
simple division or constriction of the sciatic is, as a rule, sufficient
to induce a protracted, unbroken spasm of the leg, which is on an
average the more marked as the nerve is divided higher up, and
may be called out again after it has expired, by making a fresh
cross-section.

Since these very excitable preparations fall, under the action
of the weakest battery currents, into a "closure tetanus" that
lasts during the entire passage of the current, it is not surprising
that, under such conditions, the mere short-circuiting of the
demarcation current will cause tetanic excitation — as was
frequently observed by Hering. Vigorous closure twitches, with
or without subsequent clonic disturbance, occur not merely on
bringing a fresh cross-section of the sciatic nerve into contact

x ELECTROMOTIVE ACTIOX IX XERYK 235

with the nearest accessible point of the longitudinal surface,
but also when the cut end drops upon that of a second
nerve. In the last case, however, contraction occurs only when
the two cut ends are not in the same line, but the one nerve
falls longways upon the other, so that the two ends come
together. There is thus mutual reaction of the two demarca-
tion currents, since they flow in the same direction through the
circuit formed by the two cut ends. (Hering previously per-
formed the same experiments successfully with two curarised
frogs' muscles — sartorius). " The fact that sufficiently vigorous
nerves fall into persistent excitation when their own current is
short-circuited externally, leads us to conjecture that the above-
mentioned tetanic excitation, as seen in cooled frogs after dividing
the nerve of the leg, or the sciatic plexus, may also be caused
solely by the current incident upon such division " ; since the
sheaths of the single fibres, and the common neural integu-
ment, alike provide an internal path for the individual currents
of the fibres.

The above facts refer to motor frogs' nerves only. It was,
however, shown by Knoll (13) that centripetal nerves of warm-
blooded animals can also, under certain conditions, be excited by
their own currents. These experiments refer exclusively to the
cervical vagus of dog and rabbit, and more particularly again to
the central portion, which is in connection with the respiratory
centre. The mere exposure of these nerves, especially where
they are injured, causes protracted expiration, or even a brief
expiratory pause in respiration, in the rabbit ; while similar
effects of longer duration appear with great regularity on raising
a cervical vagus, ligatured at the thoracic end and isolated, from
the wound, or lifting it out of an indifferent conducting fluid,
especially when the nerve has previously been divided peripher-
ally to the ligature (cf. Langendorff, 13). A more or less pro-
longed expiratory pause is again produced on dropping the
vagus on the wound, or moistening it with a conducting fluid
(0'6 NaCl). Since it can be shown in all these cases
that neither mechanical, thermal, nor chemical stimuli come into
play, and since " all the factors known to produce a nerve current
react favourably upon the experiment as described above,"-
respiration further remaining unaltered " when uniformity of
other conditions has prevented the setting-up or reinforcement of

236 ELECTRO-PHYvSIOLOGY CHAP.

a short-circuit,"- —it cannot be doubted that these expiratory effects
are due to excitation of the expiratory fibres of the cervical
vagus, by some variation in the intrinsic nerve current. Obviously,
when the nerve is raised from, or dropped on to, the wound in the
neck, there must be complication from the currents of the injured
muscles. Knoll also refers the brief expiratory effect which
usually appears after simple division or constriction of the vagi
in situ, to excitation of the nerve by its own current, and this
effect must certainly be regarded as the analogue of tetanus from
division of the sciatic nerve in a cooled frog. It should be
noticed that the peripheral end of the vagus cannot be stimulated
to action, i.e. retardation of the cardiac beat, by its own current.

The marked E.M.F. of the non-medullated olfactory nerve of
the pike explains the fact that its current readily and invariably
excites frog nerves. If looped over the end of a glass rod, it
may be dropped on to any point of a frog's nerve, forming a fine
pair of electrodes, and never fails to produce vigorous twitches
in the leg if contact is made at the transverse and longitudinal
sections (Kuhne, 11, p. 97). Kiihne even succeeded in exciting
curarised frogs' sartorii by the demarcation current of the pike's
olfactorius.

Much interest, especially in regard to the theory of the
break twitch, attaches to the phenomena of interference
between the nerve current and an artificial current, when the
exciting electrodes are applied to the proximity of a cross-section,
or to any point along the nerve that happens to be electrically
active. Pfliiger pointed out that the excitability of a tract of
nerve must be positively affected by its own current when a
transverse section is made, or a lateral branch of the nerve
amputated above the tract, since the demarcation current throws
that part of the nerve into katelectrotonus. If a leading -off
circuit connects the transverse section, or a proximal point on the
longitudinal surface, with any other point of the latter, current
passes through the part of the nerve between the contacts from
transverse to longitudinal section. Seeing that the separate axis
cylinders are, like the entire nerve -trunk, surrounded by in-
different conducting sheaths, there must (apart from the special
conditions in inedullated nerve) be lines of current within the
sheaths in the same direction, making their exit at different
points of the surface of the single fibres, as of the entire nerve,

x ELECTROMOTIVE ACTION IK KERVK 237

in the part near the transverse section (as was pointed out
more particularly by Hermann). If the leading-off electrodes
serve at the same time for excitation, i.e. if they lead an artificial
current into the nerve, this will either be homoclromous or hetero-
dromous with the current already present in the entire system,
—the former when the anode is proximal to the cross-section.
Other conditions being uniform, the closure of a current homo-
dromous with the intrinsic current increases the excitation, so
that it is intelligible that a descending current in the vicinity of
the cross-section should prove more effective than an ascending-
current. In view of the previous argument, it is clear that the
interference effects between exciting current and nerve current
are due, strictly speaking, not to addition and subtraction of
these currents (Griinhagen remarks that an exciting current
increased or diminished by the sum of the nerve current exhibits
no appreciable alteration of its physiological action), but to
polarisation effects discharged at points at which the disposition
to response has been altered in one direction or the other by
the internal neutralisation of the nerve current.

If actively electromotive (negative) points occur in the con-
tinuity of the undivided nerve, the same considerations of course
apply to them. Griitzner (14), indeed, inclines to refer all
changes of excitability in the continuity of the otherwise un-
injured nerve (in particular the dissimilarity of action with equal
but opposite currents in different parts of the same nerve, as
described by Hermann and Fleischl) to differences of potential
induced by preparation.

If a frog's sciatic is tested with unpolarisable electrodes
5—8 mm. apart, there is regularly, according to Griitzner, a
descending current below the point at which the branch to the
thigh is given off, an ascending current, on the contrary, above the
gastrocnemius. About midway between pelvis and knee there is
a point at which no current can be led off to the galvanometer
(Fleischl's " equator "). There is no doubt that the P.D. is caused
by the side branches given oft1 from the main stem. When these
are as far as possible uninjured, the currents are very weak.
Each point of bifurcation in the nerve is thus, as it were, pre-
destined for the appearance of a P.D., since it presents a suitable
point of attack to injuries of all kinds.

" Wherever the intrinsic currents of the nerve are descending,

238 ELECTRO-PHYSIOLOGY CHAR

excitation is best effected by a descending current, and vice versa.
If, on the contrary, the nerve current and exciting currents are
heterodromous, the action of the exciting current will be dimin-
ished or abolished " (Griitzner, I.e.). Meischl (15) subsequently
tried to overthrow this interpretation on the ground that effects
corresponding to his " law of contraction " might also be ob-
served in nerves of which the P.D. was compensated by an
artificial current. This, however, was answered by Griitzner and
Hermann, who pointed out that compensation can only neutralise
the branch of the current that flows in the applied circuit, and
not the internal P.D. of the nerve (or muscle), with its corre-
sponding currents.

A remarkable case of interference between nerve and muscle
currents is that cited by Heriug (11), in which the tetanus
consequent on division (supra) is absent, even in preparations
from highly susceptible cooled frogs, on dividing the thigh with
a single cut, when the current from the divided muscle, ascending
in the nerve, acts upon the latter so as to neutralise its current.

As in striated muscle (sartorius) denervated by curare, "spurious
break twitches " may result from interference between demarcation
current and artificial exciting current, — so likewise in nerve. The
striking dependence of the opening excitation upon the proximity
of the anode to an artificial section of the nerve has already been
insisted on. It is highly probable, if not proven, that these
opening twitches from the cross -section are not true opening
twitches, but closure contractions from the nerve current previ-
ously compensated in the leading-off circuit — i.e. that this effect
is wholly analogous with the " false opening twitches of injured
muscle" (Hering, Griitzner, 11).

If a rheochord is employed to send a branch of the current
from a battery through a nerve resting by its transverse and
longitudinal sections upon unpolarisable .electrodes, the closure or
opening of the circuit being effected by a key introduced between
rheochord and electrodes, there may in favourable cases (Hering,
11) be a contraction, both on closing and on opening the "nerve
circuit " (which short-circuits the demarcation current externally),
even when the rheochord is not in the circuit. If this is effected,
and a key introduced, together with a reverser, into the same
(" battery ") circuit, the excitatory effects must differ (when the
deriving current from the battery is ascending in the nerve, and

ELECTROMOTIVE ACTION IX XKRVK 239

therefore compensates the demarcation current at a sufficient
intensity) according as, with previous closure of the nerve circuit,
the battery circuit is made, or with closed battery current the nerve
circuit is completed. The " apparent " closure twitch that appears
in the former case alone must, properly speaking, be an opening
effect of the nerve current, as, on the other hand, the " false "
break twitch discharged after previous closure of both circuits, by
the opening of the key in the battery circuit, must be a closing
effect of the nerve current, as indicated by its absence when the
nerve circuit alone is opened. " If the branch current from the
battery is too weak to compensate the nerve current in the nerve
circuit, it will still have some effect in the same direction, though
not in the same degree. If, on the other hand, it is stronger
than is necessary for compensation, the current in the nerve, after
closure of both circuits, will actually be ascending, although it is
only, as it were, traversed by the remainder of the branch from
the battery current. If the nerve circuit therefore be closed,
with previous closure of the battery circuit, there will be no con-
traction, provided the branch current from the battery be not too
strong. If, on the other hand, the battery circuit be made with
previous closure of the nerve circuit, the opening effect of the
nerve current is superposed upon the weak and intrinsically
inadequate closing effect of the battery current, and a contraction
is obtained."

' If the nerve circuit is opened with previous closure of
the battery circuit, there is no twitch, provided always that
the ascending battery current in the nerve is not so powerful
as to excite opening twitches — notwithstanding its partial
compensation by the nerve current. If, on the other hand, the
battery circuit is opened with closed nerve circuit, the nerve
current simultaneously finds a new short-circuit, and contraction
follows, which is here still further augmented by the action of the
voltaic alternative " (Hering, 11).

Accordingly, "on commencing operations with the weakest
outgoing branches of the battery current, as they find exit at the
transverse section of the nerve, the break twitch makes its first
appearance on opening the battery circuit, and only with much
stronger currents at break of the nerve circuit also. The ' make
twitch,' again, is first seen on closing the battery circuit, and only
with stronger deriving currents at closure of the nerve circuit also."

240 ELECTRO-PHYSIOLOGY CHAI-.

If the battery current enters at the transverse section of tli3
nerve, i.e. is descending, the effect, as pointed out by Hering, is
again dissimilar, according as the battery circuit is closed with
previous closure of the nerve circuit, or vice versa. " For in the
former case a current, viz. that of the nerve, is already entering at
the longitudinal electrode, so that the superposition of the branch
from the battery current will only increase it. But if the nerve
circuit is closed subsequent to closure of the battery circuit, the
nerve current and battery current will summate at the moment of
closure, and the effect of the latter is thus augmented. At break
of the nerve circuit, again, the two currents disappear simul-
taneously." " On commencing with minimal ingoing currents at
the cross-section of the nerve, the make twitch appears first at
closure of the nerve circuit, and only with stronger currents on
closing the battery circuit also. An analogous reaction may be
determined for the opening twitches" (Hering, 11).

Du Bois-Eeymond (Ges. AbhandL i. p. 196) pointed out that,
under certain conditions, the effect is fundamentally different
according as the current is made or broken in the principal or
deriving circuit (battery or nerve circuit). But as metal electrodes
were exclusively employed in these experiments, there must have
been extensive external polarisation at the interface of the animal
tissues and the electrodes.

A characteristic effect of interference between exciting and
nerve current is the " breach " in the series of opening twitches,
first pointed out by Griitzner (1-i). It may be observed when
any part of the nerve, in which there is a descending current (as,
e.g., at the cross -section), is excited with ascending battery
currents of increasing strength. Opening twitches then appear
even with very low intensities of current, increasing at first with
its augmentation, and then diminishing to zero, after which they
again increase in magnitude.

The magnitude, i.e. E.M.F., of the current in a leading-oft
circuit, in which one contact is applied to the transverse
section of a nerve, while the other rests upon a point of the
longitudinal surface, of course depends to a large extent upon the
distance between the electrodes. The deriving current is experi-
mentally found to be greatest when this =5 — 7 mm., when com-
pensation by an artificial heterodromous current will accordingly
be most adequate. The conditions are much less favourable with

ELECTROMOTIVE ACTION IN NERVE 241

a loss distance between the exciting (or leading-off; electrodes.
Accordingly the breach in the series of opening twitches is much
plainer in the first case than in the second (Ludinilla Nemer-
owsky, 16). Griitzner (I.e.) proposes to explain the phenomenon
as follows : — " The exciting current may be less than, equal to, or
greater than the nerve current. In the first case the nerve
current will diminish at closure of the exciting current, and when
the latter is opened will return to its original height. When the
exciting current is equal to the nerve current, the nerve current
(in the deriving circuit) sinks to zero at closure of the exciting
current. On opening the latter the nerye current returns from
zero to its original height. Lastly, where the exciting current is
stronger than the nerve current, its closure sends into the
nerve a current less than, and opposite in direction to, the nerve
current. At break, on the contrary, this reduced exciting cur-
rent disappears, and the nerve current rises again from zero in
the momentarily isoelectric nerve." According to Griitzner,
an exciting current weaker than the nerve current — as well
as one that is stronger — excites when the circuit is opened. In
tlie first case the excitation is discharged at a point which has
been rendered considerably more excitable by the kathode of the
intrinsic current ; in the second, on the other hand, the action of
the voltaic alternative comes into play, since a current traverses
the nerve shortly after the passage of a heterodromous current.
The disappearance of a current just sufficient to compensate does
not excite, because the current which rises from zero does not
find exit at any especially excitable point. This coincides with
the fact that the " breach " in the opening twitches never appears
at isoelectric points of the nerve, unless these have been polarised
by the previous passage of stronger currents. In such cases the
breach reappears, if exciting currents are employed which are
heterodromous to the polarising current passing through the
nerve.

Lastly, we must reckon among the phenomena of interference
between nerve current and artificial exciting current the charac-
teristic reaction which (as first investigated by Hering, 11) appears
in nerves that are stimulated with induction currents in the
proximity of the cross-section. " If the electrodes from the
secondary coil of an induction apparatus are placed at a distance
of only 2—3 mm. upon the freshly divided or ligatured nerve, in

VOL. II R

242 ELECTRO-PHYSIOLOGY CHAP.

such a manner that one rests upon the transverse section, or point
of ligature, even minimal currents will produce a very marked effect,
when the opening current in the nerve is abterminal (i.e. parallel
with the nerve current). With atterminal direction of current,
on the contrary, the effect — albeit with uniform position of elec-
trodes and strength of current — is very much weaker, or fails
altogether. If with an abterminal opening current the electrodes
are removed farther and farther from the cross-section, the effect
of the current declines quickly, and finally vanishes altogether.
If, on the other hand, the opening current is atterminal, its
action on moving the electrodes away from the cross-section
increases rapidly, attains its maximum, and then subsides with
further shifting, until it disappears entirely."

11. ELECTROMOTIVE CHANGES PRODUCED BY ELECTRICAL
EXCITATION (CURRENT OF ACTION)

The state of activity in nerve-fibres is not characterised by
any directly visible alterations in the nerve, so that in order to
recognise it the nerve must be left connected with its muscle or
other peripheral organ. This acts as indicator for the nerve,
since neither optic, nor chemical, nor any other demonstrable
alterations can be recognised in the nerve itself. In its electro-
motive reaction, however, du Bois-Eeymond perceived a means of
detecting the state of activity by means of the nerve itself.
Immediately after discovering the nerve current, du Bois-
Eeymond found in the year 1843 that it ilinnnixlit'il dui-in;/
tetanus — i.e. underwent a " ne<ji<1irc variation" the signs of which
agree essentially with those of the negative variation of the
muscle current. Du Bois-Eeymond showed that, as in the latter,
the effect is the expression of an altered state of the nerve, and
not of any experimental errors whatsoever. Apart from other
facts to be mentioned below, this is more particularly seen in the
circumstance that the negative variation can be observed with
even very weak alternating induction currents, quite independent
of the length of tract between the leading-off and exciting
electrodes in the nerve; so that it essentially depends upon a
diminution of E.M.F., concomitant with the state of tetanic excita-
tion in the divided nerve. The extent of the negative variation,

x ELECTROMOTIVE ACTION IX XERVE 243

measured by the resulting swing of the galvanometer magnet, is pro-
portional at all points of the nerve to the strength of the original
demarcation current, and is therefore maximal on leading off from
the cross-section and most positive point of the longitudinal
surface, nil on leading off from two isoelectric points. Even with
a maximal negative variation, it can be seen directly with
an aperiodic galvanometer that the diminution of the nerve
current during tetanic excitation never amounts to complete
abolition, so that a greater or less fraction of E.M.F. remains con-
stant. The negative variation of the demarcation current is, as
we should a priori anticipate, the same in non-medullated as in
medullated nerve.

In the olfactory nerve of the pike it was found by Kiihne and
Steiner to be very vigorous, which agrees with the high E.M.F.
of the " current of rest." Since non-medullated nerve, like
muscle, reacts better to stimuli of prolonged duration than to
short induction shocks, the negative variation is perceptibly
stronger when the tetanising excitation is effected by the rapid
make and break of a constant current. This is more especially
the case (as tested on molluscan nerve — Biedermanu, 3) when
the unfavourable effects of a current flowing in one direction are
eliminated by introducing a rotating reverser, or by quickly turning
a Pohl's commutator. At the close of the rhythmical excita-
tion the magnet usually returns with decreasing rapidity to its
position of rest, or there may in stale preparations be a negative
remainder of the deflection. On attempting to tetanise molluscan
nerve in the ordinary way by means of a du Bois' sliding inductorium,
and thus to obtain a negative variation of the demarcation current,
there is usually complete absence of effect, under the most favour-
able relations of excitability, even when the coils are pushed close
together. This minimal activity of brief currents is also very
marked with interrupted constant currents, where the magnitude
of the negative variation does not usually increase (as in
medullated nerve under similar conditions) with increasing
frequency of stimulation, but on the contrary undergoes a
diminution, which is the more considerable in proportion as the
interruptions of the current are more rapid, i.e. as each single
stimulus is shorter. Since a similar reaction may be observed in
the electrical excitation of the non-medullated claw-nerves of
crayfish, this must be a widespread property of non-medullated

244 ELECTRO-PHYSIOLOGY THAI'.

nerve, which thus stands in the same relation to medullated
fibres as smooth to striated muscle. In agreement with this,
the single closure (eventually the opening also) of a constant
current produces as a rule a marked negative variation of the
demarcation current, an effect that occurs in medullated frog's
nerve only under special conditions (Biedermann, 3).

Let the two connective nerves of Anodonta be prepared
together, with leading-off electrodes at the cross-section (after kill-
ing one end), and at a point of the longitudinal surface some 6
mm. higher up, while unpolarisable electrodes are simultaneously
applied to the other end of the pair of nerves (which are
moderately stretched between two supports), these electrodes being
connected by means of a reverser with 1—2 Dan. cells. There will,
then, at each closure of the exciting circuit, after compensation of
the demarcation current, be a more or less marked deflection of
the magnet in the direction of decrease, or negative variation, of
the nerve current, the magnitude of which is essentially dependent
upon the direction of the exciting current. If the latter flows
towards the end led off (which may be termed descending), the
action is invariably much stronger than with the opposite
direction. Careful investigation of this phenomenon leaves no
doubt that it arises from the consequences of exciting the nerve
by the constant current, i.e. is a negative variation in the true
sense of the word. This is shown not merely by the independ-
ence of the direction of the deflection from that of the current,
but also by the time-distribution of the effect, and the relations
exhibited between strength and direction of exciting current on
the one hand, and magnitude of effect on the galvanometer upon
the other.

As regards, first, the distribution of the negative variation.
With descending direction of current this usually occurs so that
the deflection seems to begin at the moment of closure, or
imperceptibly later, reaches its maximum with tolerable rapidity,
and then, the current being still closed, declines rapidly at first
and afterwards more slowly. If the circuit is opened during this
period there is sometimes a marked delay in the backward pro-
cess, or even a reinforcement of the negative deflection. In most
cases, however, the opening has no effect, or there may even be
a positive after-variation, which with prolonged closure of the
exciting current may develop while the current is passing. This

x ELECTROMOTIVE ACTION IN NERVE 245

deflection — i.e. increase of the nerve current, to which we shall
return below — is either (as in the majority of cases) smaller than, or
equal to, or even larger than the previous negative variation. Its
appearance seems to accompany the most favourable conditions of
excitability in the nerve, from which we can understand how
there comes often to lie a distinct positive after-effect with the
first excitations, that subsequently fails altogether. As regards
dependence of these excitation effects upon strength of current, it
must be stated that visible effects upon the galvanometer appear
first at a comparatively marked intensity of the exciting current,
and always in the first place with the descending direction. These
rapidly increase in magnitude, and attain a maximum that
is not exceeded with any subsequent increase • of the descending
current, while the negative variation at closure of the ascending
direction, on the contrary, declines, and even fails altogether when
the current is increased beyond a certain point. And as ascend-
ing closure inevitably produces a weaker negative variation of the
demarcation current, its subsidence is invariably more rapid than
after the closure of a descending current. If the exciting tract
is remote from the led-off galvanometer tract, the magnet usually
returns to its position of rest even while the current is passing.
With less distance between the two, there are, on the contrary,
very striking effects (infra], which have nothing to do with the
excitatory manifestations we are here discussing.

The dissimilar action of descending or ascending currents is
again characteristic at break of the exciting circuit. While a
negative " opening variation " rarely appears distinctly with
descending direction of current, it may with the ascending
direction be equal to, or larger than, the initial deflection
at closure of the exciting circuit, which then, as a rule, recedes
considerably, or even fails altogether. With tolerably strong
ascending currents, and a longer distance between leading-off
and exciting tracts, the negative opening variation is, as a rule,
the sole effect of stimulation.

It is evident from these data that there are simple and
regular relations between the magnitude of negative variation
induced by closing or opening an adequate battery current, and
the intensity, direction, and duration of the latter, proving
immediately that we are in presence of the consequences of
make and break excitation.

246 ELECTRO-PHYSIOLOGY CHAV.

At closure of both descending and ascending currents there is
often a considerable diminution of E.M.F. between the longitudinal
and transverse sections in the nerve, which is, however, much less,
and continues for a shorter time, with the ascending direction.
If the current remains closed for a sufficiently long period, the
negative variation will either be entirely abolished in the course
of a few seconds, or (with descending direction) there may be a
remainder of negative variation, which only disappears — if at all

—on opening the exciting circuit.

The magnitude of the negative variation is therefore almost
independent of the distance between leading-off and exciting
electrodes. It does not increase perceptibly when the intermediate
tract is shortened, nor will it exceed a certain (easily attained)
maximum on strengthening the descending exciting current.
If the current, on the other hand, is ascending, the negative
variation declines with its increasing intensity, and is finally
abolished, exhibiting therefore, in this respect, a reaction precisely
similar to that of the closing excitation with ascending direction
of current. With respect, lastly, to the sequels of the break-
effect, there is again complete uniformity between the reaction of
the opening excitation (in so far as it is expressed on exciting
the motor nerve by changes of form in the muscle) and the
alterations of the demarcation current, as above. This is more
especially true of the dependence of the negative opening variation
upon the strength and duration of the ascending exciting-
current. It invariably appears first with a much higher
intensity of current than that demanded by the closing effect,
and increases in proportion with the duration of closure in the
exciting circuit. Hence it is possible, with sufficiently pro-
longed closure, to produce a distinct negative opening variation,
even with comparatively weak ascending currents. With
descending battery currents there is seldom a pronounced negative
variation at break ; in most cases it is merely indicated by a
transitory delay in the return of the scale. The most striking
coincidence is that exhibited between the galvanic effects of
excitation in non-medullated molluscan nerve, and the mechanical
effects in an ordinary nerve-muscle preparation, on employing an
electrical stimulus corresponding with the first or third stage of
1 'ringer's law of contraction. In the first of these two cases a

negative variation (closing excitation) is apparent at closure of

x ELECTROMOTIVE ACTIOX IX XERVE 247

both ascending and descending currents, while the opening of
the exciting circuit has no visible effect. In the second the
consequences are exactly opposite with the two directions of
current, since a negative variation then appears only with closure
of the descending and opening of the ascending current, while
closure of ascending and opening of descending currents has no
effect.

Further evidence of the causal relation between the galvanic-
effects in question, and the excitation of the nerve by current, is
afforded in the fact that both are equally affected by killing the
terminal portion of the exciting tract. We have already seen
that in medullated and non-medullated nerve, as in striated and
smooth muscle, the excitatory process is hindered, or altogether
obstructed, when the current enters or leaves at a point that has
been injured. And in fact, after killing a portion of the exciting
tract (2—4 mm.), the negative variation at closure of the ascend-
ing current disappears almost as completely in molluscan nerve
as does, in the other case, the closing excitation in the muscle.
On the other hand, the negative variation is as little affected by
the same injury at make of the descending current as by
break in the ascending direction, thus showing that the first
effect is caused by an alteration of the nerve deriving from the
kathode, the second by alteration from the anode.

In medullated frog's nerve an analogous effect is apparently
hindered only by the suppressed inclination to persistent excita-
tion from the current flowing at constant density. Engelmann
(17) long ago observed on nerves that were in the peculiar state
in which every closure, or opening, of a battery current induces
more or less sustained excitation (expressed in the muscle by
closing or opening tetanus), that the galvanometer showed a corre-
sponding negative variation of the demarcation current, on
leading off from the transverse section.

In order to obtain this effect in its integrity on medullated
nerve, i.e. undisturbed by other galvanic manifestations to be
discussed below, it is advisable to take very sensitive preparations
of cooled frogs, and to test at maximal distance between
leading-off and exciting tracts, with the weakest possible currents.
A distinct negative variation will then regularly appear below
the kathode of a descending current, reaching its maximum at a
low intensity of current, and being invariably more pronounced

•248 ELECTRO-PHYSIOLOGY CHAP.

than at closure of au ascending current. On the other hand,
there is usually in this last case (as the galvanic expression of
opening tetanus) a negative deflection, conditioned essentially by
the duration of the previous passage of current, which declines
very slowly.

We have already seen that the negative variation in nou-
medullated molluscan nerve is followed, under given circumstances,
by a distinct 'positive after-variation — i.e. increase of the demarca-
tion current. Hering (18) had previously observed the same
effect in inedullated frog's nerve during tetanus, where also the
negative variation of the nerve current is generally followed by a
positive variation that makes its appearance at the close of
excitation, immediately subsequent to the negative variation. Thus
<lu Bois-Reymond's statement that " the needle of the multiplier
in variably returns to rest more or less imperfectly after tetanisation"
(which he attributes to loss of E.M.F. in the nerve in consequence
of the previous excitation) is, as Hering points out, inadequate.

The effect is most distinct when the nerve current has been
previously compensated. " The negative variation is then
expressed in the deflection of the magnet from its point of rest,
in an opposite direction, by the now predominant compensation
current. At close of excitation, however, the magnet does not
merely return to its zero-point, but passes beyond it, and is then
immediately, or shortly after, reversed, and slowly settles down at
zero. This is the positive after-variation." Owing to its rapid
subsidence, and to the sluggishness of the magnet, the effects are
generally still stronger when the galvanometer circuit remains
open during excitation, and is only closed immediately afterwards.
' The positive after-effect increases up to a certain point with the
duration of excitation. It is already visible when the stimulus
lasts only a fraction of a second, and reaches considerable pro-
portions after excitation for one second. The increment, as pro-
duced by duration of excitation, is only conspicuous in very
brief periods of stimulation. It subsequently grows lint
little with an increased duration of stimulation, declines again
when the excitation exceeds a certain limit, and disappears
altogether with further prolongation" (Hering). Head (10),
who studied the positive after-variation more closely under
Hering's guidance, found that it increased within certain limits
with intensity and duration of stimulation. Under favourable

KLKCTROMOTIVE AOTIOX IN XKRVE

conditions (more especially in preparations of cooled Tem/poraria)
the positive deflection not infrequently exceeded the previous
negative variation. In jR. cscidenta, according to Head, the average of
maximal positive variations was something over 50 per cent that of
the largest negative effects ; in R. tcmpomria it was over 8 1 per cent.
In " warm " frogs kept for several days in a room where the temper-
ature did not fall below 15° C. even at night, the positive after-
variation invariably failed, in spite of a marked negative variation.
This seems to be due to some alteration at the longitudinal lead-
off, developed at the close of the stimulation, and opposed in its
electrical relations to the effect of excitation. It may perhaps be
regarded as the galvanic expression of some reaction of the
excitable substance from the previous excitation (as negative
variation upon the galvanometer), a process of restitution that
only appears fully under favourable conditions.

From this point of view it is intelligible that the positive
after-variation should increase within certain limits with the
duration of the previous excitation, as also that with repeated
stimulation the positive should decline before the negative effect.
For the potential reaction in the nerve must be essentially reduced
by persistent activity, supposing this to be accompanied by definite,
even if minimal, metabolism. The " non-fatiguability " of inedullated
nerve proves this to occur only in the lowest possible, and not
directly demonstrable, degree. The positive after-effect (or, more
correctly, its absence) would accordingly be the only certain
criterion of fatigue in nerve -substance. "The more or less
exhausted nerve is characterised less by weakened response to
excitation, than by failure to give the opposite reaction at the
cessation of the stimulus, as energetically as the fresh nerve. The
vigour of this reaction, as expressed in the positive (after) varia-
tion, is the measure of energy in the nerve " (Head).

In view of the extraordinary resistance of medullated nerve,
whether cold- or warm-blooded, to the total interruption of its
normal nutritive relations (siqyra), it is scarcely surprising that
the negative variation should appear on the galvanometer as the
expression of excitation (like the excitation itself in .the nor-
mally-nourished and natural end-organ), long after the nerve has
been isolated. Hermann (19) often observed galvanic manifesta-
tions of excitation in rabbit's nerves for several hours after
the muscle had ceased to respond, and had indeed lost its

250 ELECTRO-PHYSIOLOGY CHAP.

direct excitability. Fredericq (1) observed a negative variation
in the nerves of rabbit, dog, and horse, with electrical stimulation,
up to 24 hours after death, and Boruttau (20) claims to have
kept frogs' nerves for 7 to 12 days at low temperature without
impairing their faculty of giving a distinct, though weak, negative
variation when electrically excited. Lastly, Steinach (21) has
observations to the effect that (recently) dried frogs' nerves
yield a genuine negative variation again, if they are bathed in
O'G NaCl. Starting from certain purely physical effects on
the so-called core-model (infra}, Boruttau thence concludes that
" the persistence of those properties in the nerve, by virtue of
which its galvanic manifestations when at rest (demarcation
current), and during electrical action (negative variation), are to
be observed, must be referred less to the survival of that by
which the nerve is still capable of discharging muscular activity,
than to the conservation of its normal structure." In other
words, " the galvanic effect known as the negative variation of
current appears in the nerves of dead preparations also, when
these are submitted to the same electrical stimulus that calls out
muscular activity in fresh preparations." " Both mechanical
stimuli (cutting, crushing) and chemical excitation " produce,
according to Boruttau, a negative variation from " dead " frogs'
nerves, 8 days old, on the capillary electrometer, and he finds
the same result from the vago-sympathetic of the dog, on
tetanising it mechanically 2 to 3 days after excision.

Granting the facts as stated in these observations, the con-
clusions can hardly be accepted. Unless absolute reason can be
shown to the contrary, we are presumably justified under all
circumstances in maintaining that the negative variation in nerve,
as in muscle, is the rjalvanic c.'t'p)rxxi»n <>f <'.>r//a_fion in living nerve
—a vital physiological manifestation— and not merely an "undu-
lating (physical) katelectrotonus." No one accustomed to consider
the excitatory manifestations of living matter from a general point
of view can for an instant doubt that the negative variation is
to be regarded as a special case of the action current, not merely
iu medullated, but also in non-medullated nerve, in smooth and
in striated muscle ; probably indeed in many other kinds of
excitable protoplasm as the concomitant, and effect, of those
chemical alterations which, properly speaking, constitute the pro-
cess of excitation. Clearly we ought not to revive in "nerve

x ELECTROMOTIVE ACTION IX NERVE -j:i

and muscle physics " (where it long- enough blocked the way)
the one-sided physical conception of vital phenomena so recently
disproved in all departments of physiological investigation. There
is, on the other hand, no sufficient reason for regarding the nerves
on which Boruttau experimented as really dead, with no re-
mainder of physiological excitability ; as will be admitted by every
one who has seen how even warm-blooded nerves (e.g. vagus),
when divided, and completely isolated by lifting them out of the
wound, so that they cannot be normally nourished, may be suc-
cessfully excited many hours afterwards, provided only that the
peripheral organ (heart, respiratory centre) be in good condition.
Under all circumstances, the failure of indirect and even of direct
muscular excitability in no way establishes the complete death of
the nerve belonging to it, and, notwithstanding Boruttau's protest,
we may still legitimately classify the action current, as well
as the negative variation of all excitable tissues, under one
category.

III. ELECTEOMOTIVE CHANGES PRODUCED BY STIMULATION

OTHER THAN ELECTRICAL

The galvanometer, by recording the negative variation of
the nerve, is thus (supra) a reliable indicator of the state of
its excitability, without further reference to the alterations
of the peripheral end-organ. It must be admitted to afford
indubitable evidence of conductivity in both directions. If
the peripheral end of a motor nerve is stimulated, a negative
variation appears on leading off from the central cut end, and
vice versa. Again, on exciting a purely centripetal (sensory)
nerve, the negative variation may be demonstrated at any point
peripheral to the seat of excitation. From this point of view it
becomes essential to test the negative variation with excitation
other than electrical. We are already familiar with the fact that
nerves which are dissimilar in function do not react alike to
identical stimuli, but exhibit marked differences. Griitzner (22),
e.g., showed that centrifugal and centripetal nerves react quite
differently to thermal excitation, the latter becoming, with few
exceptions, highly excitable at a temperature of 40° to 50° (J.,
while the former (with the exception of the vaso- dilators) do
not seem to be excited. Strictly speaking, however, these

•2»-2 ELECTRO-PHYSIOLOGY THAI-.

experiments prove nothing as to the processes that are
taking place within the nerve, the conclusion being only formed
retrospectively, from the reaction of the peripheral organ. If the
motor apparatus exhibits activity when the nerve is stimulated
by any means, there can of course be no doubt as to its
excitation. Otherwise, however, there are two possible alter-
natives : either the nerve is not really excited, or at least the
excitatory process is not transmitted ; or the terminal apparatus
may not react to the conducted stimulus (Griitzner, I.e.).

If, then, the negative variation is a true expression of excita-
tion in the nerve, it affords a simple and convenient means of
testing the excitability of different nerves, independent of the end-
organ, towards various stimuli. Here, again, there are two alter-
natives: (1) homogeneous stimuli, acting upon different nerves, may
produce the same negative variation, and in this case the dis-
parity of effect must be referred to the end-organ ; (2) the
negative variation itself may differ, in correspondence with the
dissimilar effects of excitation in the end-organ. The cause of
the heterogeneous effects must then lie within the nerve itself.
From this point of view Griitzner (22) in the first place investi-
gated the effect of thermal excitation upon the negative variation
in different nerves. A similar experiment, but one that is open
to criticism, had been made by du Bois-Reymond (23). He
placed the nerve (frog's sciatic) upon a layer of moist gunpowder,
which, when lighted, charred the nerve from one end onwards.
Notwithstanding the indisputably drastic stimulus to the succes-
sive sections of the nerve (which, by the way, can hardly be
termed " thermal "), the galvanic consequences were very incon-
spicuous, and not to be compared with the marked effects of
electrical excitation. Obviously," as was pointed out by Griitzner,
the negative variation may here be checked ab initio by the un-
avoidable shortening of the excitable portions of the nerve.

Yet, with a more perfect method, Griitzner failed in obtain-
ing any effective results. At temperatures of 40°-50° C. the
demarcation current of frog nerves did indeed decline perceptibly,
but only to an inconspicuous degree, and very slowly ; there was,
moreover, as a rule, a persistent diminution of the current, so
that the effect was hardly comparable with that from electrical
stimulation. Experiments on the anterior and posterior roots
gave still less certain results, so that the question whether

ELECTROMOTIVE ACTION IX XERVE •_'.-,:;

thermal stimuli affect centripetal move than centrifugal nerves
must therefore, as concerns the magnitude of the negative varia-
tion, remain undecided. Nor did Griitzner elicit negative
variation from mechanical stimuli (c./j. scissors-cut) at any distance
from the seat of excitation. Only when the incision came
within 10 mm. of the longitudinal electrode was there a slight,
and that a permanent diminutiaii of the current. On the
other hand, in dividing the non-medullated olfactory nerve of
the pike, Hering (24) found not merely a strong negative varia-
tion, but a distinct positive after-effect also, and analogous results
are exhibited by non-medullated molluscan nerve (Bieclermann).
Steinach (21) has recently succeeded in proving that in suitable
frogs' nerves (e.g. from cooled animals) each single cut will, under-
certain conditions, produce a marked negative variation, the time-
distribution of which corresponds as a rule with that found in
electrical stimulation. The mirror swings back rapidly, and reaches
the point of rest again more slowly. This is obviously in line
with the slow subsidence of the persistent excitation, as expressed
in the inclination of a muscle to tetanus, wThen its nerve is excited
by the constant current, or by short-circuiting of its own current.
Boruttau (p. 31) also noted positive results in frog nerve
with mechanical excitation, both with simple division and in
mechanical tetanus.

With chemical excitation by NaCl, Griitzner observed a
gradual diminution of current, while Kiihne and Steiner (2)
obtained a negative variation of the demarcation current on the
pike's non-medullated olfactory nerve, under the same conditions.
"Whether the poverty of effect is due solely to asynchronous
excitation of the separate fibres of the nerve-trunk (Griitzner),
or to other factors also, is uncertain.

After cutting off the part of the nerve that had been excited,
or bathing it in physiological saline, Steinach found that the
diminution of the demarcation current due to chemical stimula-
tion was completely neutralised. Alcohol proved the most
effective excitant, and here again there was a marked difference
between cooled and warmed frogs. With the former, immersion
of the central end of the nerve produced tetanus of the flexors,
succeeded by a vigorous extensor-tetanus, wThile, under similar
conditions, a nerve-muscle preparation from a warmed frog gave
only a few twitches, and was then quiescent.

ELECTRO-PHYSIOLOGY rH.u>.

The negative variation of the nerve current is under all cir-
cumstances a far less sensitive excitatory reagent than the
reaction from the natural end-organ. Even in electrical excitation
the visible reaction from the muscle appears earlier, i.e. at a
greater distance of coil, than the negative deflection on the gal-
vanometer. The requisite interval of current intensity is invari-
ably much greater in warmed than in preparations of cooled
frogs. Steinach excited both sciatic nerves simultaneously with
induction currents, one nerve being connected with the leg, while
he led off from the other to the galvanometer. In a warmed
frog, tetanus first appeared with the coils 43 cm. apart, the
negative variation at 2 7 cm. : in a cooled frog the distances were
respectively 39 and 38 cm. Granting that these experiments
are inconclusive as regards the presence of qualitative differences
in the nerve-fibres, the fact that the negative variation is some-
times very weak, or altogether absent, in electrical stimulation,
where all the fibres are simultaneously and equally excited, at
least suggests this inference. Frede'ricq (1) remarked upon the
insignificance of the negative variation in electrical excitation of
mammalian nerve, and Grtitzner has recently notified the same
effect. ISTo trace of negative variation can be obtained from an
artificially-cooled rabbit, although the same excitation of the sciatic
nerve causes a pronounced tetanus of the muscle. Apparently
the alterations fundamental to the negative variation are in this
case not transmitted, although the nerve as a whole is still
excitable, and able to conduct, at all points. The negative
variation may be observed in normal, uncooled, mammalian nerve,
always, however, in a strikingly inferior degree from that of frogs'
nerve. In this case a negative variation of 10 per cent of the
nerve current is readily obtained with maximal currents, while
the same stimulus only elicits a variation of 4 per cent in
mammalian nerve.

In all these cases we have been concerned with excitation of
the nerve in its continuity. IT/ntf, in tin' m-.d place, is ///<'
/n'!/f(fitr variation on, */ i//t ///<// /'//// tin- ,n// ///•>// cnd-ori/nn (<•/'////•///
or pc f I i>l in-iil] of the nerve-fibre ? We are again indebted to
du Bois-Reymond for the first observations on this point. In
strychnia-spasm he observed a distinct diminution of the longi-
tudinal-transverse current, on the frog's sciatic nerve still in con-
nection with the spinal column. In the conviction that the

x KL1-XTROMOT1YE ACTION IX XERVK

negative variation was to be regarded as the galvanic expression
of excitation, du Bois-Reymond poisoned a conveniently arranged
frog with strychnia, and then, after ligaturing the iliac artery on
one side, divided the sciatic nerve of the same side at the knee,
and exposed it as far as the vertebral column. He then led off
to the multiplier from the peripheral end. If the strychnia-
spasm happened to coincide witli the moment at which the needle,
after deflection by the nerve current, had returned to rest, it
swung back several degrees at the commencement of the spasm.
The experiment is, however, most uncertain, and depends upon
various irregular conditions. On the other hand, there is regu-
larly, on exciting the motor zone of the cerebral cortex, a
negative variation of the longitudinal-transverse current in the
spinal medulla, expressed on the capillary electrometer as a suc-
cession of rhythmical oscillations, occurring simultaneously with
epileptic spasms in the muscles.

In opposition to the marked effects on leading off from longi-
tudinal and transverse sections of the spinal cord, there is, as was
shown by Gotch and Horsley (5), very little result from leading
off at the cut end of the sciatic nerve, during excitation of the
motor zone. According to Horsley's observations the excitation
diminishes on its way from the cord to the mixed nerve, by more
than 80 per cent. The same difference appears when the fibres
of the corona radiata, instead of the cortex, are directly excited.

If it is thus established that efferent impulses from the
centres, however excited, produce a negative variation of the
nerve current, more recent observations seem to establish the
same for sensory impulses also. Du Bois-Eeyinond made experi-
ments to see whether excitation of the natural ending of a
sensory nerve by an adequate stimulus might not result in
movement of the multiplier-needle, instead of in sensation (just as
the motor nerve in the above experiment with strychnine had
displaced the magnet, and not the muscle). He obtained a
negative variation on the frog's sciatic when the leg, with the
skin in situ, was progressively scalded with boiling salt solution
from tendon to knee, or corroded and burned with concentrated
sulphuric acid (23). Yet, as du Bois-Beyinond himself pointed
out, this was rather " tetanising of the sciatic through its
cutaneous branches," than excitation of the sensory end-organs
of the skin. Kiihne (9) in fact found that the negative variation

ELECTRO-PHYSIOLOGY CHAP.

persisted when the skin was stripped oft' before scalding to a
ligature at the foot, and then lifted back as far as the knee, after
dividing the cutaneous nerves, or removing them completely.
On the other hand, he succeeded (9) in demonstrating the negative
r/t/'iation of the optic nerve on stimulating the retina with light,
in the eye of the pike, as, later on, in that of the perch, and still
more perfectly in the frog's eye. It is therefore certain that
the current of the sensory nerves reacts in this case to the
highly-specialised excitation of the epithelial end-apparatus by
light, exactly as that of the mixed or motor nerve reacts to
excitations of all kinds, it being immaterial whether the stimula-
tion proceeds from the central ganglion - cells, or whether it
impinges upon the continuity of the nerve itself, as a mechanical,
chemical, thermal, or electrical stimulus. In every case it is the
same negative variation of current in the nerve that appears
as the concomitant of excitation, and this is one of the main
supports of the prevailing theory of the physiological homo-
geneity of all nerve-fibres, and of the identity of the excitatory
process within them. It is a striking fact " that the optic nerve,
during the continuous stimulation of its terminal organ by light,
gives no different reaction from that of a tetanised nerve, under
discontinuous electrical stimulation. If in the last case we have
reason to believe the galvanometer inadequate to show the pre-
sumptive discontinuity of the variation, we must in the former
instance accept its evidence, since there is no reason to suppose
that the immediate effects of sustained illumination are, like most
other tetani, discontinuous " (Kiihne).

This persistent diminution of current in the optic nerve
may be termed phototonius (Kiihne). It is a striking fact
that the close of the illumination, i.e. cessation of excitation
by light- " or, more properly, the resumption of certain retinal
processes interrupted by light — is also marked by a final negative
variation of the optic nerve, which cannot be interpreted other-
wise than as a repeated excitation traversing the nerve." If
" phototonus " is thus a sign of activity in the optic fibres, we
may justly conclude with Kiihne (I.e.) " that the cutting-off of light
is able to produce a greater effect upon the central organ, and to
discharge a more intense sensation (excitation), than the prolonged
action of the same light upon the eye."

At the same time we cannot overlook the fact that the

ELECTROMOTIVE ACTIOX IN XERVE

similarity of electromotive reaction in the two cases proves
nothing as to qualitative equality of chemical process. Hering
points out that " we must hesitate, in view of the endless
variety of the different chemical processes by which electrical
currents are engendered, to affirm an equality of internal process
in the nerve from the similarity of electromotive reaction in
two nerve -fibres (more especially in those of which the excita-
tion produces very dissimilar central and peripheral reactions),
or in one and the same fibre under different conditions : or
to exclude the possibility that different kinds of internal altera-
tion may be transmitted within certain nerves, or even to
assume the same process for all nerves (with the single possible
exception of certain sensory nerves)." "Muscle, gland -cells,
plant cells, perhaps indeed all living substances, exhibit under
certain conditions an electrical reaction, which from its very
commencement presents a striking analogy with the electrical
reaction of nerve. Should we therefore " (continues Hering)
" conclude that the internal chemical processes which are the
cause of these manifestations are alike in all parts of the living
substance, or that when the same electrical effects occur in two
cases within the same substance the underlying chemical altera-
tions must necessarily be the same?" (Hering, 24, p. 19 ff.)
From this point of view it is, if surprising, at least intelligible
that the presumably assimilatory, cardiac inhibitory, vagus fibres,
the excitation of which produces a positive variation of the
muscle current, should, even as regards their galvanic reaction
to excitation, differ in no respect from other nerve-fibres.

S. Fuchs (25) has recently communicated some interesting
observations upon the negative variation of centripetal nerves
during adequate excitation of their peripheral end-organs. The
Selachians, and notably the Torpedinidce, possess a special system
of canals beneath the skin, which partly open under the skin
(Lorenzinian ampullae and pectic tubes), and partly form blind
sacculffi (Savian bladders), but are always intimately connected
with the nervous system, and are undoubtedly sense-organs. In
Torpedo, the Lorenzinian ampullae are globular sacs divided into
four compartments by partition walls. These sacs are enclosed in
a special capsule, of which there are two pairs in Torpedo ; one
pair lies in the nose exactly in front of the eyes, and contains,
according to Leydig, about 100 ampulla? in the two capsules, the

VOL. II S

258 ELECTRO-PHYSJOLOGY CHAP.

canals for the most part opening against the wall of the body.
The second pair of capsules lies farther back, at the external wall
of the electrical organ. The system of Savian bladders consists
of saccules 2—3 mm. in diameter, which in life are perfectly
transparent. These occupy the four-sided space between the
anterior ends of the electrical organ as far as the upper lip, and
extend still farther backward. " Each sac consists of a homo-
geneous membrane of connective tissue, and is filled with a clear
gelatinous mass. The ingoing nerve forces its way through a
peculiar felted tissue, which lies like a cushion at the lower part
of the bladder ; it then divides into three branches, of which the
central is the strongest. Each of these forms a kind of expan-
sion, which supports the true sensory epithelium (hair -cells
resembling the auditory cells of the organ of Corti). In the
cervical region this structure is supplied by the trigeminal nerve,
in the region of the trunk by the vagus.

After extirpation of brain and cord, the trigeminus (which
supplies the lateral ampullae and Savian vesicles) was dissected
out, the central end of the nerve, which is 2—3 cm. long, being
laid by its long and transverse sections across unpolarisable elec-
trodes; there was then a distinct, if small, deflection on the
galvanometer, in the direction of a negative variation, each time
the skin was lightly compressed above the lateral packet of
Lorenzinian ampulLe and Savian vesicles. It was subsequently
found that the last alone are responsible for the effect.

This is, therefore, the second authenticated case in which
excitation of the peripheral end of a sensory nerve l>ij adequate
stimuli produces negative variation of the demarcation current in
the divided trunk of the nerve. Obviously there is here a wide
and still unexplored field.

The electromotive changes in the central endings of the
superior sensory nerves — i.e. the sensory cortical regions — in
consequence of adequate excitation of the peripheral sense-organ
(eye, ear), are of the greatest interest, although theoretically still
obscure : this is not, however, the place to discuss them. We
must now return to the negative variation of peripheral nerves
under artificial excitation.

x ELECTROMOTIVE ACTIOX IX NERVE -2.r,9

IV. TlME-EELATIONS OF ACTION CURRENT AS DETERMINED

BY KHEOTOME

If a single brief stimulus, e.g. an induction shock, is sent into
the nerve, the existence, much less the time-relations of the
negative variation, will hardly be recorded by the galvanometer,
owino- to the slussishness of its magnet. We are therefore driven

O OO Q

back upon the repeating method, with the rheotome, for the
solution of the questions already familiar to us in muscle. The
method and instrument have already been described (vol. i. p. 367).

Bernstein (26) found, in investigating the course of the
negative variation of the nerve current with tetanising, electrical
stimulation, that there was a measurable period between the
excitation of any point of the nerve and the commencement of a
negative variation (i.e. negativity) at a more distant lead-off,
corresponding with the rapidity of transmission of the negative
variation in the nerve, and the distance between the point of
excitation and the first longitudinal contact. The distance
between excited point and transverse section, on the other hand,
is immaterial. From this we may conclude, as in muscle, that
the process of negative variation in the part led off begins at the
precise moment in which the excitatory process transmitted in
the nerve arrives at the longitudinal electrode. It is further
evident that there is no perceptible interval between the moment
of stimulation by induction currents and the commencment of
negativity at the excited point. The negative variation lias no
latent period. Both in medullated and non-medullated nerve
the negative variation is transmitted at a rate corresponding with
that of excitation, so that the negativity of any point of the
nerve may, as in muscle, be accepted as the galvanic expression
of excitation. Fuchs (4) determined the transmission rate of
the negative variation in cephalopod nerves as something between
less than 1 in. and 3 "5 m.; according to temperature. With in a
ll'n-m range it increases with sfrr/u/fh of stimulus.

The process of negative variation within a tract of nerve is
further found, on leading off from longitudinal and transverse sec-
tions, not to be instantaneous, but to last for a measurable period.
It does not at once attain its full strength, nor does it disappear
immediately. Experiment rather shows that negativity rises (at

260 ELECTEO-PHYSIOLOGY CHAP.

the longitudinal lead-off) after a single stimulus, within a certain
limited period, to its maximum, and slowly disappears again.

According to Bernstein's method (in which that arrangement
of the slider is determined on the rheotome, which gives the
beginning and ending of the variation, the time occupied by the
galvanometer closure being then subtracted from the total period
of difference between these two positions) the duration of the
negative variation does not exceed 0'0007 (j^Vo) sec- *n mec^ul"
lated frog nerve. This very low, and theoretically improbable,
figure is as a matter of fact incorrect. Hermann (27) claimed a
much longer period for the negative variation ( = 0'0056 sec.),
while Head (10), by means of Bering's specially-constructed
rheotome, estimated it at 0'024 sec. — i.e. a value more than
thirty times as great as that of Bernstein.

The duration of the negative phase varies with the state of
the frog from 0-0079 to 0'0239 sec. Hermann at first referred
this extension to his system of cooling the nerve, as retarding the
transmitted excitation, and corresponding negativity, of each
element of the nerve. Further experiments, however, showed
that even at normal temperature the variation takes longer than
was stated by Bernstein. Hermann then concluded that his use
of a highly-sensitive galvanometer, and packet of six nerves, were
responsible for the more complete expression of the last part of
the declining variation. The far larger figure given by Head
implies that his rheotome followed the descending portion of the
curve in each single negative phase, beyond that employed by
Bernstein : the longer closure of the galvanometer circuit magni-
fies the effect of the variational, or action, current upon the
magnets, and multiplies it much more with increased stimulation-
frequencies than was possible to Bernstein and Hermann (Fuchs, 4).

Head's experiments show that the magnitude of the negative
variation is chiefly conditioned by the magnitude of the nerve
current. On the other hand, it is to a remarkable degree
independent of fatigue in the nerve (according to Fuchs, there
is some relation between the two in non-rnedullated nerve), in
which respect it behaves quite differently from the positive after-
variation. Lastly, the duration of the single negative phase is
shown to be affected in a marked degree by the condition of the
frog. In winter frogs there is a comparatively prolonged single
negative phase, although the total negative variation is, relatively

x ELECTROMOTIVE ACTION IN NERVE 261

speaking, small ; in spring frogs the single variations are short,
with comparatively large total effects.

In the non-medullated nerves of Cephalopoda, Fuchs (I.e.}
estimates the average duration of the negative variation with
stronger stimuli at O'Ollo sec., with weaker excitations at 0'OOS2
sec., i.e. a value intermediate to those given by Bernstein and
Head. With a method corresponding to that of Hering and
Head, the duration of the negative variation would no doubt
be found even greater than Head's estimate of it in frog nerves.

Fuchs further investigated the significance of the retarded
variation of non-medullated nerve, and indicated a possible
relation with the slow rate at which the excitatory process is
transmitted. If (as cannot be doubted) the transmission of
excitation does really depend upon some sort of propagation from
section to section, the prolonged duration of the process must be
advantageous, and we know experimentally that non-medullated
is far less sensitive to very brief stimuli than medullated
nerve.

These facts show that the tetanic negative variation is
rhythmically discontinuous, and (notwithstanding its apparent
steadiness) of an oscillatory character in nerve as in muscle,
We have next to ask what magnitude can be reached by the
single negative swing on strengthening the stimulus ? Will the
demarcation current corresponding with the maximum of the
variation fall each time to zero, or even reverse itself (as
Bernstein found in medullated frog's nerve) ; or will there merely
be (as in muscle) greater or less diminution of the existing P.D.,
in the rhythm of the stimulation ? The question in both cases
can be decided by the rheotome method, on making the galvano-
meter closure as short as possible, and then finding that position
of the slider which corresponds with the maximum of the varia-
tion. If compensation is then cut out. and that fraction of
current measured which is sent by the rotating rheotome into the
galvanometer circuit, and the tetanising key opened, it can be
seen at once whether the variation is less than, equal to, or
greater than the current of rest. By such experiments Bernstein
determined the negative variation with an augmented stimulus to
be much in excess of the current of rest, in frog's nerve. On
repeating the experiment Hermann (27, p. 385) at first found
the variation to be much less than the current of rest, and

262 ELECTRO-PHYSIOLOGY CHAP.

Bernstein (28) himself doubted the accuracy of his observations.
In the end, however, Hermann confirmed Bernstein's original state-
ment, on leading off from a mechanical cross-section (made by
crushing), and not from a thermal section, in which the fine nerves
may be injured by the steam from the hot water. He then
repeatedly observed cases in which the negative variation was
nearly double the current of rest. But, as Head (I.e. p. 241 f.)
showed in theory, if we start from the low value quoted by
Bernstein for the duration of the single negative phase (0-0007
sec.), the variational current (i.e. current through the galvanometer
in consequence of negative variation) must at the moment of
maximal intensity be 4|--9 times as strong as the nerve
current : which is highly improbable, " so long as the intensity of
the exciting induction currents is kept within the (narrow) range
in which direct excitation of the* nerve by unipolar action in the
part led off (galvanometer tract) is absolutely excluded." His
own experiments (which, owing to the method employed, failed
to determine the intensity of the variational current directly,
and only gave the minimal indispensable height of the negative
variation, not— as in Bernstein's experiment — its actual height)
afforded no indication of variational currents of such magnitude
as was assumed by Bernstein and Hermann.

In the non-medullated nerves of Cephalopoda, Fuchs invari-
ably found that, " at that position of the rheotome slider which
corresponds with the maximum of the negative variation, the
latter only induced a more or less considerable diminution of the
current of rest — never its abolition, or even reversal."

It is far harder to demonstrate a phasic action current
between two longitudinal points of the uninjured nerve, than
on leading off from long and (artificial) transverse sections. As
we have stated, Bernstein was the first to show on striated
muscle that during the passage of a directly-stimulated wave of
excitation the points over which the wave was passing were
invariably negative to all other (unexcited) points. Hermann
extended this law to the natural ends of the uninjured muscle,
as well as to the case of indirect excitation, and proved the
•imircrsal presence of a diphasic action current in all uninjured
muscles, those of man included. It is plain that a similar
reaction might be anticipated for nerve : the difficulties of
experiment are equally apparent. Owing to the extreme rapidity

x ELECTROMOTIVE ACTION IN XERATE 203

of conduction in nerve, the interval at which the wave passes
the two leading-off contacts is too small to be analysed by the
rheotome, even when the electrodes are far apart ; while on
extending the tract led off, the resistance, which is already con-
siderable, increases so much that the effect becomes imperceptible.
Hermann, however, overcame these obstacles ; he depressed
the rate of conductivity by cold, and employed bundles of 4-6
sciatics. He was then able to obtain a distinct separation of the
two opposite currents with the rheotome, and thus established
the undulatory character of that alteration in the nervous sub-
stance, which in the galvanic expression of excitation is charac-
terised by negativity.

FIG. 202.

If one lead-off is at the artificial transverse section, the corre-
sponding phase fails, as in muscle, or is at any rate "rendered uncer-
tain." Hermann found, without exception, that the second phase
was less conspicuous and more prolonged than the first ; this is not,
however, due, as in muscle, to decrement of excitation, but
refers strictly to the fact that the first phase has not nearly
expired when the second is at its maximum. This is clear from the
accompanying diagram (Fig. 2 02, from Hermann). "The abscissa
of represents the times, positive ordinates the homodromous,
negative ordinates the heterodromous direction of current. The
curve Aaa gives the temporal relations of the action current from
the first lead-off, Bbb that of the action current from the second.
AB is the time required for transmitting the excitation between
the two leading-off contacts. Accc is therefore the curve of the
resulting diphasic current of action, the second phase (2) of

264 ELECTRO-PHYSIOLOGY CHAP.

which is lower and more extended than the first phase (1), and,
moreover, reaches its maximum at a different point from the
maximum of excitation at the second lead-off. The superficies of
the parts of the curve corresponding with the two phases must
he equal ; hence their action upon the galvanometer ceases
simultaneously in tetanus."

In muscle, we have in the physiological rheoscope and its
secondary excitation an exceedingly convenient indicator of the
discontinuous nature of the negative variation of the demarcation
current, as well as of the action current in the uninjured and
intrinsically isoelectric muscle. Du Bois-Eeymond tried in vain
to obtain secondary excitation from one nerve to another, and
later experimenters were no more fortunate, so that it seemed
impossible to decide from one excitable nerve whether another
was or was not excited. This is contrary to what we should
have expected a priori ; for the electrical variation in nerve is,
absolutely and relatively, a more vigorous process than that in
the muscle, and there is no sufficient reason why (to all appear-
ance) no nerve has an excitatory action upon another superposed
upon it. Hering (11) has now, indeed, established the possibility
of true secondary excitation from nerve to nerve, by availing
himself of every advantage, the increased excitability in the
vicinity of an artificial transverse section included. If the
peripheral end of an excitable sciatic (exposed from, vertebral
column to knee, and cut at both ends) of a cooled frog is applied
to the central end of a second nerve still connected with the leg,
so that the two nerves lie together for 5—0 mm., and their
cross -sections are in the same place, then the demarcation
current of the one nerve will, as it were, compensate that of
the second. " Supposing the longitudinal - transverse current
suddenly to disappear from the peripheral end of the primary
nerve (through negative variation to zero) in consequence of an
instantaneous excitation, the compensation of current in the
second nerve will be abruptly abolished. The end of the
primary nerve that in consequence becomes isoelectric, now
functions solely as a shunt to the current of the secondary nerve,
and the latter will be weakly excited by the sudden short-
circuiting of its own current. But if the direction of current in
the exciting nerve is reversed, it will after reversal act upon the
second nerve like a weak descending current, and summates with

x ELECTROMOTIVE ACTIOX IX XERYK

the intrinsic and suddenly short-circuited current of this nerve "
(Hering).

If under these conditions excitability is heightened as much
as possible by making a new transverse section simultaneously
at the peripheral end of the primary and central end of the
juxtaposed secondary nerve with a scissors-cut, and then weakly
tetanising the central end of the primary nerve, Hering invariably
noted a weak tetanic disturbance of the secondary preparation.
Current escape and unipolar stimulation were excluded, since the
weak exciting currents only took effect when the electrodes were
placed near the transverse section, all secondary action failing
when they were applied to other points of the primary nerve
nearer the second preparation. Electrotonic action is excluded
by the great distance between the point of stimulation and the
position of the secondary nerve, so that the possibility of true
secondary excitation from nerve to nerve was no longer doubtful.
Obviously, the result would be even less ambiguous if the tedious
process of applying the two nerves together could be replaced by
a preparation in which the bundles of nerve-fibres serving as
primary and secondary nerves should lie naturally in a common
sheath. Hering accordingly, in a cooled frog, exposed the sciatic
nerve above the knee, ligatured its two branches together, divided
them below the ligature, dissected out the nerve to the place
where the branch is given off to the thigh, and then divided the
sciatic plexus, and (when the muscles \vere quiet, again) stimulated
the knee-end of the nerve with weak currents. The muscles — of
which the nerves were still in connection with the plexus — fell at
once into strong secondary tetanus. The experiment never fails,
provided the preparation be so excitable that the division of the
sciatic plexus produces a slight muscular disturbance in the leg,
in addition to the twitch, and that there is a fresh transverse
section. The proof that this is not due to current-escape,
electrotonus, or unipolar excitation, again lies in the fact that there
is regularly no effect so soon as the electrodes are moved slightly
away from the cross-section, and approximated to the muscle.
In three preparations, moreover (and in two cases, twice or three
times consecutively), a weak partial twitch of one of the muscles
of the thigh was observed by Hering on crushing the primary
nerve. This, together with the inevitable failure of other kinds
of stimuli, is hardly surprising, in view of the difficulties (supra)

266

ELECTRO-PHYSIOLOGY

CHAP.

of eliciting any considerable negative variation of the nerve
current by other than electrical stimulation. V. Uexkiill (29)
has recently obtained positive results from his mechanical tetano-
motor, and has, moreover, proved the justice of Bering's pre-
sumption, that the whole effect will fail, or die out, even under
electrical stimulation, if the long and transverse sections of the
plexus are brought into circuit by dipping them into physiological
saline before, or during, the appearance of the current of action.

V. ELECTROMOTIVE CHANGES (ELECTROTONUS)
1. In Medullated Nerve

It has already been stated that polar alterations of excita-
bility appear under the action -of a battery current, flowing

FIG. 203.

steadily at uniform density through any portion of a medullated
nerve. These changes are not (as in muscle) confined to the
points of contact with the electrodes, i.e. the visible entrance and
exit of the current, but extend beyond them, not merely into the
intrapolar tract, but to a greater or less extent over the extra-
polar region also. As early as 1843 du Bois-Eeymond showed
that there were corresponding changes of galvanic reaction which,
like those of excitability, must be diagnosed as one of the manifesta-
tions of electrotonus, representing in some degree two different
sides of one process. Let nnf (Fig. 203) be a nerve, A and K
the two electrodes through which a battery current is led in the
direction A—K; A is therefore the anode, K the kathode, of the
current that produces electrotonus. On making this current, all

ELECTROMOTIVE ACTION IX XERVE

267

points of the nerve lying on the kathodic side (k—e) become more
negative, all points on the anodic side (A—e) more positive than
before. These alterations are, however, unequal in degree at different
points, being greater in the vicinity of the electrodes, and less at
a distance from them. If the positive increment from A-c is
represented by lines, the height of which expresses the increase,
and if the heads of these lines are joined together, the resulting
curve represents the alterations of potential occurring at the
respective points. The alterations on the kathodic side may be
similarly expressed, only here the ordinates must be drawn down-
wards from the nerve as abscissa, to show that the potential on
this side is negative. The two parts of the curve represent the
state of the extrapolar regions. As a matter of fact we do not

know the reaction of the intrapolar tract, because it is impossible
(on technical grounds) to investigate this area. We can only
presume that the alterations of potential there are such as are
expressed by the connecting line i. These curves do not of
course represent actual magnitudes of potential at given extra-
polar points, they merely express the general fact that there is a
diminution from the poles outwards.

Since the nerve to be examined is usually bounded by two
cross-sections, and is thus a~b iniiio electromotive, there must,
with a suitable lead-off, be interference between the demarca-
tion current and the electrotonic increment, which is of course
always in the same direction as the polarising current. This pro-
duces at one end of the nerve a negative, at the other a positive
variation of the longitudinal-transverse current, lasting as long as
the closure of the polarising battery current (Fig. 204). If
the electrodes are shifted from the cut end towards the centre,
there will obviously be deflections in the galvanometer, on either
side of the tract traversed by the current, in the direction of the
polarising current. And this will equally be the case when the

268 ELECTRO-PHYSIOLOGY CHAP.

nerve, with both ends cut, is isoelectrically disposed, i.e. is in contact
with the galvanometer electrodes at points symmetrical with the
equator, laterally to which it is traversed by the polarising cur-
rent. The situation may then be expressed as follows : — If a con-
stant electrical current is led through a portion of a medullated nerve,
the entire nerve (while preserving its original electromotive activity]
becomes electrically active in the direction of the polarising current
at all points, each point of the nerve being negative to every other
that is anterior to it in the direction of the current.

The magnitude of the electrotonic deflections diminishes (as
is prima facie obvious from the distribution of potential) with the
distance of the leading-off tract from the poles, as appears plainly
in the vicinity of the latter ; it is further in ratio with the
strength of the polarising current. Moreover, the electrotonic
effect increases constantly with increased intensity of current,
and never seems to find a limit. Certain experiments of du
Bois-Eeymond (23), which were intended to determine the
eventual maximal value of electrotonus, were unsuccessful, although
they showed that the E.M.F. of the incremental current on the
side of the anode and kathode (Griinhagen's anodic and kathodic
current) may exceed that of the normal longitudinal-transverse
current by more than twenty-two times, without finding a limit.
As expressed in units of a Daniell, the E.M.F. of the anodic
current = 0'5 Dan., that of the kathodic current 0'05 Dan. This
difference of E.M.F. in the an- and katelectrotonic incremental
currents, which finds similar expression in regard to intensity, is
distinct in every case, and is the reason that in a graphic represent-
ation the curves of potential are shorter upon the side of the
kathode, and the corresponding ordinates lower, than on the
anodic side (Fig. 203). Under all conditions the maximum of
anelectrotonus exceeds that of Jcatelectrotonus.

A further factor in the magnitude of electrotonus is ///<•
length of tract traversed l>// the polarising current. If the
electrodes are gradually shifted so as to lengthen the tract of
nerve excited, the incremental currents diminish part paxsn with
the extension of the tract through which current is passing ;
this diminution is, however, obviously due to the weakening of
the polarising current, from the increased resistance of the
conductor. If (as was first effected by du Bois-Eeymond) the
intensity of the polarising current is kept constant by introducing

x ELECTROMOTIVE ACTIOX IX NERVE -jt;«t

a high resistance (tube of alcohol) into the polarising circuit,
or ligaturing the intrapolar tract with a moist thread, the
magnitude of electrotonic increment increases with the extension
of the electromotive tract traversed by the current, or vice versa
diminishes with its restriction. The direction of the polari*in</
i'n I'i'cnt in relation to the low/ axis of the nerve has, moreover, a
great effect upon the intensity of electrotonic action, and the
increment, like the excitation, is found to be greatest when the
polarising current flows longitudinally through the nerve — nil
with transverse passage of current.

As regards the theory of electrotonic action, its dependence
upon the constitution and state of the nerve is of the first im-
portance. The conjecture that it is due to ordinary current-
escape in the galvanometer circuit is at first sight plausible, in
view of the entire reaction, but is at once refuted by the fact
that dividing, or crushing of the nerve, between the polarised
and leading-off tracts, abolishes all sign of excitation. This proves
that the diffusion of electrotonus, as of excitation, is correlated
with uninterrupted continuity in medullated nerve. And it is
not merely the complete interruption of conductivity, but every
modification of it, or of excitability (Leistungsfahigkeif) in the
nerve, that affects the magnitude of electrotonus in a greater
or less degree. No electrotonic action, or at most only a trace
of the ordinary effects, can be detected on dead nerve, or nerve
that is fundamentally altered in its physical and chemical
properties. The entire manifestation is indisputably bound up
with certain structural peculiarities that arc present only in living,
nni iijui'td medullated nerve. The utmost importance attaches to
the fact (to be discussed below) that — under uniform conditions
—the electrotonic incremental current, in the above sense, does
not appear either in non- medullated nerve, or in muscle, or
other moist conductors (wet threads), so that the presence of a
niiiJullated sheath seems to rank first among the necessary structural
requirements.

The fact that division of the nerve between polarised and
led -off tracts prevents the development of electrotonus, even
when the cut surfaces are replaced as carefully as possible, leads
on to the question whether the underlying alterations are,
like excitation, transmitted at measurable velocity in the nerve.
After du Bois-Eeymond had shown that the development of

•270 ELECTRO-PHYSIOLOGY CHAP.

electrotonus takes no appreciable time, since it appears at full
strength immediately after closing the polarising current, and can
be demonstrated with even the most fugitive induction currents,
Helmholtz was the first to prove the same fact by means of the
physiological rheoscope (31).

In view of the known sensibility of the latter to much weaker
currents than are here under consideration, it is quite intelligible
that the electrotonic incremental current should be adequate to
excite the nerves of a rheoscopic frog's leg, if properly led through
it. It is even possible (as du Bois-Eeymond showed) to throw a
superposed nerve into secondary electrotonus, by the electrotonic
incremental current of the first nerve. If one end B (Fig. 205)

of a medullated nerve pol-
arised at A is applied to
a second nerve CD by
part of its length, the
second nerve at once falls
into a state of electrotonus ; the end D is, however, at the
opposite phase to B, since the incremental current at B flows
through the end C of the applied nerve, which forms a shunt
circuit in the opposite direction. If this nerve is still connected
with its muscles, then both at make and, under favourable cir-
cumstances, at break of the polarising current there will be a
secondary contraction, which is not to be confused with the true
secondary twitch from nerve to nerve caused by the current of
action, as first demonstrated by Hering. Du Bois-Reymond's
" paradoxical twitch " is a very interesting form of this secondary
contraction depending on electrotonus. The conditions for the
discharge of this secondary twitch by the electrotonic incremental
current are especially favourable when the fibres of the two
nerves, in so far as they are in juxtaposition, are as it were
coherent, i.e. fused into a single stem. This is the case in the
frog's sciatic with the two branches into which it divides at the
knee (peronceus and tibialis, Fig. 206). If one or the other
is non- electrically excited, the muscles innervated from that
branch alone become active, never those from the other. If,
however, an electrical current is passed through the tibial branch
at a point not too remote from the bifurcation, contraction occurs
at make and break not merely in the muscle A but also in B,
which is supplied by the peronreal branch, because the primary

x ELECTROMOTIVE ACTION IX XERVE 271

electrotonic nerve throws the other nerve forming with it a com-
mon trunk into secondary electrotonus. Since even brief impacts
of current, or induction shocks, have an electrotonic
effect, it is clear that secondary tetanus may readily be
induced by tetanising the primary nerve. The excita-
tory action of both primary and secondary electrotonus
increases rapidly with approximation of polarised to
led-off tract (as might be anticipated from the marked
rise in potential near the polarised tract). In this we
have apparently (supra} a means of distinguishing
between the true secondary excitation from nerve to
nerve, and the paradoxical contraction (Hering, 11).

Helmholtz made use of the latter as follows, in order
to determine the time occupied in establishing the gal-
vanic changes in electrotoiius. A second, isolated nerve was applied
to a sciatic still in connection with the gastrocnemius, in such a way
that the half of the nerve proximal to the recording muscle was
brought into contact with the corresponding half of the other
nerve (Fig. 207). Electrotonic stimulation of corresponding
points at the central end of the two nerves yielded two twitches
in succession, one produced by direct excitation of the nerve to
the muscle, the other by secondary electrotonus. The secondary
contraction from the nerve was not found to enter perceptibly
later than the primary twitch, whence Helmholtz concludes that
" the electrotonic state does not make its appearance demonstrably
later than the electrotonic current which excites it," and does
not therefore, like excitation, require a measurable period in
which to diffuse over the extrapolar region. I)u Bois-Reymond
(6, p. 258) had already pointed out that Helmholtz's experiment,
strictly speaking, can only mean that the changes fundamental to
electrotonus, and the process of excitation, are transmitted at
egiial rapidity in the nerve. This follows directly from Hermann's
words (19, p. 1G2). "If the interval between excitation and
contraction of the muscle [M, Fig. 207] is the same, whether a
or b be excited, this proves that the electrotonus, in order to
spread in the first nerve from a to c, requires as much time as is
taken by the excitation to spread in the second nerve from b to
c'. But if the electrotonus at c is strong enough to excite the
second nerve, it will certainly produce direct excitation at c', at
least as strongly, when it is directly produced by excitation of b

272 ELECTRO-PHYSIOLOGY CHAP.

in the second nerve ; in other words, at the strength of current
employed, the second nerve is directly excited as far as cf, as soon
as the current is applied at & : thus the experiment only shows
that the electrotonus spreads in both nerves with equal rapidity,
and gives no conclusions as to the rate of this transmission.

Another series of experiments refers to the time-development
of the electrotonic changes of excitability, which — as was pointed
out by Pfliiger — are in close relation with the galvanic effects,
and, as it were, merely represent another symptom, or another side
of the same underlying process in the nerve. It is therefore
legitimate to draw conclusions from the temporal distributions of
the one alteration to that of the other. Pfliiger (32) has, more-
over, demonstrated by direct experiment, at least for anelectrotonus,

l<? 1 kj— 1 _/=S^_^

I

a

b c

d ^

^_— *=

— -. -

^ /

— ,

e

a B

FIG. 20V. FIB. 208.

that the alterations of excitability appear simultaneously with
the galvanic alterations.

If (Fig. 208) a strong ascending current («&) is passed steadily
through the central end of the nerve of an ordinary nerve-muscle
preparation, the myopolar portion of the nerve falls into anelectro-
tonus ; the corresponding incremental current can be led off by
a second pair of electrodes (cd) situated within the same region,
to the nerve B of a second preparation, so that this is traversed
at the same distance from the muscle, but in the opposite, i.e.
(in the respective position of both preparations) ascending direc-
tion. As soon as the primary nerve (cd) becomes electromotive,
under the presumption of a transmission of electrotonic alteration
at given rapidity from the polarised region cd), a branch current
passes at the same moment through ef, and produces secondary
excitation in this nerve. From the fact that it is invariably the
muscle (B}, and never that of the primary preparation (A), that
twitches, Pfliiger concludes that at the time when the electro-
tonic incremental current traverses the tract (cd) of the first
nerve - muscle preparation, and excites the second muscle to
secondary (paradoxical) contraction, the same incremental current
which excites the second muscle leaves the first at rest ; i.e. in

x ELECTROMOTIVE ACTION IN XERYE 273

other words, the alteration of excitability is present simultaneously
with the corresponding galvanic alteration.

Subsequent experiments undertaken by different workers in
the hope of deciding this question (i.e. the absolute time occupied
by development of the electrotonic alterations in the nerve after
closure of the polarising current) have not so far produced any
congruous results. According to Wundt (33), who undertook a
comprehensive inquiry into the time-distribution of the electrotonic
alterations of excitability in the frog's nerve-muscle preparation,
these changes are not developed simultaneously with the closure
of the polarising current at all points of the nerve, but spread
from the poles with comparatively low and easily measurable
rapidity from section to section by an undulatory process analogous
with that of excitation. In this sense Wundt speaks of an
" anodic wave of inhibition " (i.e. an altered state of the nerve-sub-
stance, characterised by diminished capacity for response), trans-
mitted from the anode at a rate that varies with the strength of
the polarising current from 80 to 1 7 0 0 mm. per sec. ; and a
l-atlwdic wave, of excitation (i.e. katelectrotonic rise of excitability),
of which the rate of transmission appears to correspond with that
of active excitation. In regard to method, it is sufficient to state
that it consisted essentially in exciting different points of the
myopolar part of the nerve, at different periods after the closure
of an ascending, or descending, polarising constant current, with
single induction shocks, and then recording the discharged con-
traction graphically. The differences which then appear in regard
to time-distribution, the magnitude (height), and duration of
twitches, before and after closure of the polarising current, form
the basis of conclusions as to the state of excitability at any point
of the nerve at a given moment. Wundt's observations, into which
we cannot here enter in detail, seem to have been little regarded ;
they are in direct contradiction with Pfliiger's experiment, as described
above, and also with certain experimental results of Griinhagen
(34), in which the commencement of the electrotonic alteration of
excitability coincides, at all points of the nerve, with the moment
of closing the polarising current. If (Fig. 209) a rheochord (rrl)
and the primary coil of an induction apparatus are included in the
polarising circuit (K}, a branch of the primary current may be
led into the nerve of a nerve-muscle preparation (cd) in an
ascending direction. Although in itself inadequate to excite

VOL. II T

274 ELECTRO-PHYSIOLOGY CHAP.

the muscle, it is sufficient to cause a demonstrable anelectrotonic
depression of excitability within the myopolar part of the nerve.
With sensitive preparations, the height of the twitch discharged at

ab by the ascending make induc-
tion shock was then regularly less
1 when the region cd was simul-
taneously polarised by a branch of
the primary current. To Griin-
hagen's conclusion that the anelec-
trotonic depression of excitability at ab existed previous
to the induction closure, i.e. coincided with the entry of the
polarising current, Tschirjew (35) objected that with the
combined action of the two currents, the induced exciting current
must necessarily be weaker than in the other case, because a part
of the inducing current would now be led into the nerve by the
rheochord. But this objection is, as Hermann (35) subsequently
pointed out, of no weight in view of the relations of resistance ;
since it can hardly be of consequence to the current in the
primary coil of low resistance (1-2 Siemens' units), whether a
branch current, sent into the nerve with its 40,000 to 70,000
units, is made or broken, as was also demonstrated experimentally
by Baranowsky and Garre" (35, p. 449).

Tschirjew's experiments on the rate of transmission of galvanic
as well as excitatory charges in medullated nerve during electro-
tonus led him to conclusions fundamentally different from those
of his predecessors, and his views were subsequently confirmed
by Bernstein in an investigation which we have not yet referred
to. He stated that the electrotonic alterations in nerve are
transmitted at a. rate approximating to that of excitation, Imt,
generally speaking, somewhat lower.

In order to determine the rate at which the anelectrotonic
decrease of excitability in the nerve is transmitted, Tschirjew
employed a method analogous to that of Wunclt.

" The minimal stimulus which will discharge a twitch is deter-
mined at any point of the nerve inafrog's gastrocnemius preparation.
A strong ascending current is then made in the part of the nerve
proximal to the central end, at a certain distance from the point
of excitation. Closure of this current of course evokes no twitch
under these conditions. After a certain brief period the excita-
bility of the nerve is tested again at the former point. If the

x ELECTROMOTIVE ACTION IN NERVE 275

earlier minimal strength of excitation still produces a perceptible
twitch, the interval between this excitation and the closure of
the polarising current is lengthened, and the experiment repeated.
This is continued until the minimal excitation remains without
effect." " The interval between the two closures gives the time
occupied by transmission of the decreased excitability from
the intrapolar tract to the excited point. If this distance were
taken, the required rate of transmission could be deduced from it."
In order to determine the appearance of the galvanic alterations
of electrotonus at a point of the nerve beyond the polarised part,
two points symmetrical to the electromotive equator are in the
first place uninterruptedly led off, and existing differences of
potential compensated. This circuit, which included a sensitive
galvanometer, could be opened by means of a spring myograph,
at different times after brief closures of a battery current, that
traversed the nerve in an ascending or descending direction at a
given distance from the leading-off tract. The interval between
closure of the polarising current in the nerve, and the opening of
the galvanometer circuit, could thus be varied at pleasure. It
is clear that the determination of the time required between this
last and the closure of the polarising current, in order to detect
the first trace of electrotonic variation of current on the galvano-
meter, must also determine the time required by the latter in
every case, for its transmission from the polarised to the led-
off tract. Both series of Tschir Jew's experiments were severely
criticised by Hermann (36), who emphasised the fact (as regards
Tschirjew's galvanic measurements) that, as will presently be
shown, the electrotonus at any given point of nerve does not reach
its full intensity at the first minute, but increases gradually. " And
if the electrotonus immediately after its origin is weaker by
only a quarter of its total amount, the results of Tschirjew
are quite compatible (as Hermann points out) with an instan-
taneous appearance." The same of course holds good of the
experiments in which the time to be determined is that which
must elapse after closure of the polarising current, in order to
produce anelectrotonus at a distant point of the nerve sufficient
to suppress the twitch called out here by a test stimulus.
" This interval is not, however, identical with that which must
elapse before the commencement of auelectrotonus at that point
of the nerve," but probably shorter. Consequently, as Hermann

276

ELECTRO-PHYSIOLOGY

CHAP.

pointed out, the electrotonic alterations (unlike excitation)
diminish rapidly in intensity with increasing distance from the
polarised tract, and finally become imperceptible. So that, when
immediately after closure of the polarising current the electro-
tonus is still undeveloped, the region in which it can be
demonstrated is necessarily even smaller than that in which it
appears definitely.

Tschirjew subsequently repeated his experiments with the same
results, using the capillary electrometer (which is peculiarly
sensitive to rapid oscillations of current), and Bernstein's rheotome,

FIG. 210.

which of course are open to the same objections. Bearing in
mind the theory of this last ingenious instrument, it is evident
that it affords an easy means of leading a polarising current at
any given moment into the nerve, and interrupting it again
directly, at the same time leading off the electrotonic currents from
a distant tract of the nerve at different intervals after closure.
Bernstein's own method of experiment (as referred to above) is
explained by the following schema (Fig. 210). During the
rotation of the rheotome the polarising current is periodically
closed whenever the contacts dip into the mercury pools (qq),
the galvanometer circuit as often as the contact (^j1) dips into
(ql). The period of closure of the polarising current varies
between - and sec. : the direction of the led-off current

x ELECTROMOTIVE ACTION IN NERVE 277

(which is closed by altering the position of the slider on the
rheotome at any given moment between the closure and opening,
or after the opening of the polarising current) at most occupies
10100 sec. Under these circumstances the electrotonic incre-
mental current does not make a clean entrance, either when the
galvanometer electrodes are applied to the nerve under isoelectric
conditions, or on leading off from longitudinal and transverse
sections; the contacts always interfere with either the phasic
current of action or the negative variation. The diminution of
the nerve current observed in the last case, even without the
rheotome, on tetanising with descending currents, must always—
with adequate approximation of the leading-off and exciting tract
—be due to the negative variation and the katelectrotonic
incremental current. The rheotome, as it were, analyses this total
effect into its single components, and determines the time-relations
between the arrival of the excitatory wave, and of the electrotonic
current, in each single stimulation. If the latter is already present
at its full strength at the moment of closing the polarising
current, the galvanometer deflection must obviously begin from
that point, and increase steadily in proportion with the shifting of
the rheotome from zero (i.e. the position at which the opening of
the galvanometer circuit occurs simultaneously with the closure
of the constant current) to that position at which closure of the
polarising current coincides with that of the nerve circuit. This
never occurred in Bernstein's experiment ; on the contrary, after
closure of the polarising current, there was a definite and
measurable period before any effects appeared on the galvanometer.
Let SO (Fig. 211) be the time-abscissa, S the closure, 0 the
opening of the battery current, Sy the height of the " resting
nerve current," then the entire process of katelectrotonic alteration
that accompanies each single stimulus in the tract led off, is
expressed by the curve ngskte. The galvanic expression of
the excitation, which would otherwise produce a closure twitch,
is first a fugitive negative variation, temporarily of the opposite
sign (absolutely negative) to the nerve current in the given case.
It is only much later, at Jc, that the negative variation due to
the slowly rising katelectrotonic current commences. It occasion-
ally outlasts the opening of the polarising current, and then
disappears rapidly. The end of the kathodic closure wave (as
Bernstein terms the initial negative variation due to the closing

278

ELECTRO-PHYSIOLOGY

CHAP.

excitation) usually coincides with the beginning of the katelectro-
tonic variation, and is inseparable from it.

From these experiments, as well as from the earlier observa-
tions of Tschirjew, it would appear that the entrance of the
katelectrotonic current at the point of leading off docs not coincide
in time with the closure of the polarising current, and that the
underlying alteration of the nerve diffuses more slowly than the
wave, of excitation which precedes it. This separation of the
two apices is only seen distinctly when the tract of nerve led
off is sufficiently remote from the polarised tract, since both

FIG. 211.

processes appear to begin simultaneously at the kathode, i.e. at
the moment of closure, and, according to Bernstein's view, can
only be separated after further propagation. The absolute rate
at which the katelectrotonic alteration is transmitted can there-
fore hardly be determined exactly from such experiments.
Bernstein estimates it at about 9—10 in. per sec. The develop-
ment and diffusion of galvanic anelectrotonus is shown by the
same method to be essentially similar, when the excitation by
the rheotome is effected (by reason of the led -off transverse -
section of the nerve) with ascending currents. Even with strong
currents there is invariably a much smaller negative initial varia-
tion (excitatory wave) than with descending excitation, along
with which there is a positive anelectrotonic deflection increasing

x ELECTROMOTIVE ACTION IX XERVE 279

in proportion with the time (Fig. 211, ng'at'e). Once
more, then, we find propagation of a certain alteration in the
nerve, the absolute rapidity of which is best determined by
leading off isoelectrically from two longitudinal points, since the
negative variation then causes hardly any interference. Bern-
stein reckons this transmission at 6—13 m. per sec. In both
phases of galvanic electrotonus, therefore, certain alterations
are i>f<>i>f<g<iti'd in the nerve from section to section, at a rate which,
viiJcr all conditions, is considerably lelow that of the excitatory
process. This fact is obviously of great importance to the theory
of electrotouic alterations.

None of these experiments, however, seem to have taken
sufficient account of the time-distribution of an- and katelectrotonic
changes at any one point of the nerve, with a single closure. The
earlier experiments of du Bois-Reymond and Pfltiger showed
that with prolonged closure of the polarising current, both
the state of depressed excitability, and the corresponding altera-
tions in anelectrotonus at every point of the nerve, reach
their maximum gradually, and then slowly decline again.
Pfliiger (32, p. 319) frequently found no trace of altered
excitability, on rapidly exciting after a make twitch, the depres-
sion only setting in after 30 sec.— 1 min.

" As the anelectrotonus swells up at any point, and reaches
its maximum, so it declines again subsequently, and ebbs back
towards the intrapolar tract, if the closure is protracted."

" The period of flow is less in proportion as the same current
is more frequently closed, or is initially stronger, so that with
very strong currents the anelectrotonus appears to break in
suddenly."

According to du Bois-Eeymond (30, p. 446, and 6, p. 255),
this reaction is expressed, with reference to the apparently
corresponding galvanic effects of anelectrotonus, by a curve of
the form a^a, (Fig. 212); S being the moment of closure,
t1 the first reading of the galvanometer. The time-distribution
of the katelectrotonic alterations during the passage of current
is very different. The katelectrotonus at any point of the nerve
invariably reaches its maximum (which is always lower than
that of anelectrotonus under the same conditions) much earlier
than the latter, and appears, at least as regards galvanic
changes, to decline steadily from the commencement of the

k.

280 ELECTRO-PHYSIOLOGY CHAP.

observation (curve Jcjc^). In regard to excitability, Pniiger
(I.e. p. 349) determined a brief increase immediately after
closure of the polarising current. It is clear, as was pointed
out above, that the comparatively slow process of electro-
tonic alterations at any
given point of the nerve,
as well as the rapid diminu-
tion of intensity with in-

P \^ creasing distance from the

polarised part, must present
great obstacles to an experi-
v mental determination of the

FIG. L'1-J.

rate of transmission. Gal-

vanometric time-measurements more particularly break down (as
Hermann pointed out, 35, p. 453) in this department, owing to our
ignorance of the time-distribution of the initial stages of electro-
tonus. Even the foregoing experiments of Bernstein cannot
therefore be regarded as decisive in this question of the trans-
mission of the electrotonic state, the more so since they are
opposed by other experiments which have not yet been contra-
dicted. Valerius von Baranowsky and Carl Garre* worked out
a series of experiments under Hermann's direction upon the rate
of diffusion of anelectrotonic alterations of excitability, partly on
Griinhagen's principle as described above, and partly by a method
of Hermann. A strong ascending current is led into the central
end of a nerve connected with its muscle, while (with a Helm-
holtz's switch) another weaker constant current, also in an
ascending direction, is closed as a test stimulus. Then, after
ascertaining that the polarising current per se gives only opening
and no closure twitches, while the weaker test current infallibly
excites at closure, and on comparing the magnitude of this closing
twitch with and without simultaneous closure of the polarising
current, it will be found that in the last case, even where the
two tracts of nerve are at a long distance from each other,
the test stimulus will be ineffective, or will discharge a weaker
make twitch than before. The fact that the interval between
the closure of the two currents was in these experiments some-
thing under O'OOOl sec., wives a value for the diffusion of

O O

anelectrotonus, which at a distance of 16 '5 mm. between the
two tracts of nerve is in any case greater than 10,000 x 16 '5,

x ELECTROMOTIVE ACTION IN XEKYK -jsi

i.e. more than 165 in. Further experiments undertaken with
Hermann's fall rheotome on Tschirjew's principle showed beyond
doubt that the anelectrotonic depression of excitability is present
at a point of the nerve 1 0 mm. distant, at the moment of closing
the polarising current. The same must be assumed for the
katelectrotonic rise of excitability, as well as for the galvanic
expression of electrotonus. These experiments imply that the
alterations are not propagated, like excitation, as a wave from
section to section, but begin simultaneously at all points, at
closure of the polarising current. These diametrically opposite
opinions have not yet been reconciled, but it must be admitted
that the last experiments of Hermann and his pupils are open
to no well-founded objection, while the results of Bernstein's
rheotome experiment are not, for reasons stated above, perfectly
free from ambiguity.

2. In Non-medullated Nerve

A series of facts which are of great importance for the recog-
nition of the true nature and characteristics of the electrotonic
alterations in medullated nerve may be observed on certain non-
living (dead) conductors of a particular kind, and also upon
at i /i -medullated nerve. As regards the latter, it has already been
pointed out that the appearance of the true, typical, extrapolar
electrotonus is correlated with certain structural peculiarities of
medullated nerve - fibres, more particularly the presence and
integrity of the medullary sheath. This point must now be
examined in detail. Among the few suitable objects of experi-
ment we have — in addition to the olfactory nerve of the pike, as
first employed by Kiihne, and the unfortunately over-susceptible
nerves of the crayfish (lobster) claw — in the larger examples of
our native species of Anodonta, long unbranched non-medullated
nerves, which extend from the two anterior to the posterior
ganglia, and present a high capacity of resistance (Biedermann).
As regards the electromotive properties of these fine nerve-fibres
(which, if taken together, are not nearly as thick as the frog's
sciatic), it has already been stated that the demarcation current
is unusually vigorous, as in the pike's olfactorius.

If it is led off with unpolarisable electrodes to a sensitive
galvanometer, while a battery current of 1—2 Dan. is passed into

282 ELECTRO-PHYSIOLOGY CHAP.

the other end of a horizontally-stretched pair of nerves, there
will, after compensation of the demarcation current, be (as
described above) a more or less considerable deflection of the
magnet at each closure of the exciting circuit, in the direction of
a diminution (negative variation) of the nerve current, the
magnitude of which depends essentially upon the direction of
the polarising current. It is invariably greater when the current
is flowing towards the leading-off end (3). We shall term this
the descending, and its contrary the ascending direction of
current.

The fact that the deflection in the two cases is homodromous,
but unequal in magnitude, as well as its independence of distance
between the led-off and polarised tracts, leaves no doubt that
these are not pure electrotonic manifestations, but are compli-
cated by the sequelae of excitation of the nerve by current. The
time-relations of the negative variation are remarkably different,
according as the exciting current is ascending or descending. In
the latter case it declines slowly during closure, in the former
with great rapidity. If the polarised part of the nerve is at
maximal distance from the leading-off tract, the negative varia-
tion at closure is, as a rule, the sole effect of excitation with
either direction of current. If the intermediate tract is reduced,
a positive deflection regularly succeeds the initial negative varia-
tion with ascending direction of current, its development and
character being essentially conditioned by the ratio of its magni-
tude to that of the previous negative variation. Where this
is large, the entrance of the positive after-effect is delayed after
closure, and it increases more slowly during the passage of the
current. An increasing acceleration of the deflection, or distinct
swelling of the positive effect to its maximum, may often be
observed, after which the magnet rests at its new position of equi-
librium as long as the current is passing. The maximum of the
positive variation invariably corresponds with a higher intensity
of current than is required by the initial negative variation.
Regarding the latter as an effect of closing excitation, it is .signi-
ficant that it becomes weaker in proportion as the intensity of
the current increases, and finally disappears altogether (according
to the third stage of the law of contraction). Under these con-
ditions closure either produces no visible effect, where the
distance between the exciting tract and the end led off is too

x ELECTROMOTIVE ACTION IN NERVE 283

great to allow of a genuine positive variation, or (in other cases)
the latter alone may appear, when the initial negative effect is
often indicated by a distinct delay in the commencement of the
positive variation. The different mode of action of ascending
and descending currents also appears characteristically on
breaking the circuit. With the descending break there is rarely
any distinct augmentation of the negative deflection that is
present during closure (in consequence of the opening excitation
from the anode) ; for the most part there is no clear effect, or
merely a slight delay in the return swing of the magnet. With
ascending direction of current the negative " opening variation "
is much more frequent and regular.

If these facts are compared with Bernstein's rheotome experi-
ments on medullated frog's nerve, as above, a certain analogy can
hardly be disputed.

Setting aside, in the first instance, the phenomena relating to
" electrotonus," there is in the two cases a marked negative deflec-
tion immediately after closure of the descending polarising current,
which from its whole character must undoubtedly be regarded as
the galvanic expression of the make excitation. It is not surprising
that this should be a rapid variation in frog preparations, a persistent
modification in non-medullated molluscan nerve, seeing that in-
direct excitation of crayfish muscle by the constant current is,
as a rule, sufficient to produce closure tetanus (supra). The
closure of a not immoderate ascending current further produces in
both cases a weaker but equally negative variation, which must,
like the former, be referred to the closing excitation, and only
fails with strong currents (third stage of the law of contraction).
At a certain medium distance from the polarised tract there is in
this case in molluscan nerve a positive deflection, immediately
after the initial negative effect, which slowly increases during
closure, exactly as was determined by Bernstein under similar
conditions for frog's nerve. The graphic representation of this
reaction (Fig. 211) may, with slight modifications, serve to express
the consequences of ascending current in molluscan nerve on
leading off from transverse and longitudinal sections, at not too
great a distance from the polarising current. Owing, however, to
the time- differences in the respective excitatory manifestations, the
effects which in the former case require the application of the
repeating-method for their analysis, are here directly obvious with

284 ELECTRO-PHYSIOLOGY

a single closure of the polarising current. From this it appears
that non-medullated nerve also exhibits an alteration initiated at
the anode of a polarising current, and connected with a develop-
ment of positive potential, which spreads with diminishing intensity
over a certain region beyond the poles, and is more widely diffused
in proportion with the strength of the polarising current.

We cannot hesitate to compare this alteration (which is only
expressed galvanically) with the " anelectrotonus " of medullated
nerve, seeing that there is a fundamental conformity between
them. It is therefore the more remarkable that there should be
no sign of alteration in non-medullated molluscan nerve compar-
able with the (galvanic) katelectrotonus of mcdullated nerve. This
is most apparent in experiments in which the galvanometer
electrodes are isoelectrically arranged upon the nerve. With
a descending polarising current there is then, as a rule, no
effect ; the magnet remains absolutely at rest at and during the
closure of the exciting circuit, even when the galvanometer tract
is only a few millimetres distant from the part excited. This
shows that there is no spread of the polarising current by
current-escape of any kind, in the preparation in cp:iestion, beyond
the region immediately traversed. The effects at and during
closure of an ascending current, under similar conditions, are
therefore the more striking. If the galvanometer electrodes
(at uniform distance) are brought gradually nearer to the anode
of the polarising current, there is invariably an increasing
deflection in the sense of a rapidly augmenting anelectrotonus,
which may reach considerable proportions while still comparatively
remote from the anode.

The magnitude of these positive effects of the ascending
current is determined not merely by its intensity, but also most
essentially by the excitability of the preparation. The effects are
always more distinct and more vigorous in proportion with the
vitality of the nerve.

At a given position of the galvanometer electrodes, the
magnitude of the positive deflection increases with augmentation
of the ascending current only within a comparatively narrow
range, and there is no approximate proportion between the two.
The effect is generally maximal with the full current from two
Daniell cells, while further rise of current intensity produces only
an inconspicuous increase of deflection (Biedermann). This is true

x ELECTROMOTIVE ACTION" IN NERVE 285

both of the pronounced effects that obtain near the exciting tract,
and also of the weaker and weakest effects at more remote
parts. Seeing that the alterations of the nerve, fundamental
to the homodromous incremental current below the ascending
exciting current, require an incomparably longer period for their
development than the initiation and transmission of excitation,
the duration of closure of the constant current is an indispensable
factor in the positive effect in question. Immediately after
making the ascending current, or at the close of the negative
variation, the scale passes beyond the zero-point in the positive
direction, and moves towards the acme of the deflection, at first
slowly and then more rapidly, until it reaches its limits
after a closure of 5—6 sec. The nearer the galvanometer
electrodes are brought to the exciting tract, the greater will be
the positive effects, and the more marked this gradual swelling of
the incremental current (homodromous with the exciting current),
its strength remaining constant during further extension of
closure. When — as is usual on leading off from the transverse
end of the nerve — the variation is diphasic, i.e. first negative and
then positive, the first phase nearly always predominates where
the intermediate tract is of any length, and a moderate ascending
current is employed. In this case, owing to the slow decline of
the negative phase, a much longer closure is required before the
gradually appearing and weak positive effect can be detected, than
in a nerve with less distance between the o-alvanometer and

O

exciting tracts, where the positive effect, as a rule, far outweighs
the negative, or alone makes its appearance. In order to deter-
mine with certainty to what distance from the anode the effect
extends, it is advisable to exclude the interference of the negative
deflection, either by using very strong currents ab initio, or by
killing the upper part of the exciting tract, and thus making
closure excitation from the kathode impossible. In such a case,
both with transverse leading off, and along the continuity of the
nerve, there will only be a monophasic positive deflection, while,
if the limit to which the alteration from the anode extends be
exceeded, all perceptible effects upon the galvanometer will fail, at
and during the closure of an ascending current. The rapid
increment of effect on bringing the galvanometer electrodes
nearer the exciting tract may thus be demonstrated with great
distinctness.

286 ELECTRO-PHYSIOLOGY CHAP.

As regards the interpretation of these electromotive effects
beneath the anode of the ascending current, there cannot well —
since 110 diffusion of the polarising current can be demonstrated
on the side of the kathode — be any such in the vicinity of the
anode either : the differences of potential developing along the
nerve under the influence of current must therefore be referred
to a physiological alteration of its state, transmitted apart from
any presumable di (fusion of current from the anode. This
modification must undergo a marked decrement, otherwise it
would be difficult to explain why there should sometimes be a
mere trace of positive action at a distance from the anode, while
vigorous deflections appear in the course of the nerve under
uniform conditions. Nor is this the only point in which the
positive alteration starting from the anode differs from the
excitation discharged at the kathode, which is transmitted with
a smaller decrement and apparently at much greater velocity ;
it further persists during the passage of the current at almost
undiminished strength, or even increases, and only subsides
rapidly on opening the exciting circuit.

Eecent experiments of v. Uexkiill (37) show that cephalopod
nerves (Eledone moschata) react like those of Anodonta, in so far,
at least, as regards failure of any conspicuous electrotonus.

3. In Cooled and Etherised Medullated Nerve

Biedermann (38) subsequently obtained effects from medul-
lated frog nerve, under certain conditions, analogous with those
described above for iion-medullated nerve. These chiefly refer to
alterations of electromotivity under the influence of the constant
current, at maximal distance from the exciting tract, and with
minimal currents. Usually, under these conditions, the single
closure of an ascending or descending current, with transverse
lead-off, gives at most a trace of effect as a negative variation
of the demarcation current. But if, with preparations of cooled
frogs (where the nerves frecpiiently react tetanically to the weakest
excitation), the galvanometer contacts are applied,at a small distance
apart, to one end of the nerve, and the exciting electrodes (as far
off as possible) to the other end, a very weak descending battery
current being used as stimulus, — then the conditions for the

x ELECTROMOTIVE ACTION IN NERVE i>s7

appearance of electrotonic action in the ordinary sense are most
unfavourable, and any negative variation of the nerve current
observed under such conditions may presumably be referred to
persistent excitation from the kathode. Other data are also of
great importance, theoretically, to this point.

In the first place, the magnitude of the initial deflection is
independent both of intensity of exciting current, and also, within
certain limits, of length of intermediate tract. The maximum
effect usually appears with very weak currents, and it is
immaterial whether a fraction of the current from a single cell or
the full current of several cells is employed as excitant — the
effect may indeed be less in the last case than with weaker
currents. Nor, with uniform intensity of current, can the effect
be increased by bringing the exciting electrodes nearer to the
galvanometer tract (up to a certain limit). If, on the other
hand, the intermediate tract is shortened by gradually shifting
the galvanometer electrodes away from the transverse end of the
nerve, with unaltered position of the exciting electrodes, a
diminution of the negative variation is regularly observed at first
with descending direction of current, amounting under some con-
ditions to its complete disappearance (cf. Table I. infra}.

If the galvanometer electrodes are approximated to the kathode
beyond a certain point, a new series of homodromous (negative)
deflections will appear, which, both as regards character during
passage of current, and intensity, are quite distinct from the first
series, and in all respects exhibit the same characteristics as those
generally accepted as the signs of the electrotonic incremental
current. These are, in first degree, dependence on strength of
exciting current, and strikingly rapid increase of effect with
approximation to the exciting tract. During the closure of the
excitatory circuit these deflections either remain constant, or
exhibit a gradual diminution, never amounting to disappearance.

The following tables illustrate this reaction. Both sciatic
nerves of a very sensitive (cold) frog (R. esculenta) were simultane-
ously excited at their central end. NS= magnitude of deflection
produced by the demarcation current ; R W, the rheochord
resistance ; ZS, the length of the intermediate tract ; SR, the
direction of current. The sign > indicates the diminution of the
deflection during passage of the current.

Much stronger negative deflections have frequently been

2SS

ELECTRO-PHYSIOLOGY

CHAP.

observed, under similar conditions, with both descending and
ascending closure, in the nerves of cooled frogs, on keeping
them for 12—24 hours before the experiment, with the skinned
legs to which they are connected, in 0'6 °/0 NaCl at room
temperature.

TABLE I.

NS.

1 Daniell.

zs.

SR.

8ize of Deflection.

Remarks.

Make.

Break.

130 degrees

12Hr=lQ cm.

40 mm.

4-

-9>-2

+ 2

The longitudinal and
transverse sections

A

-1+ 6

-3

of the nerve were

i

laid across the

55 ,,

30 „

4

- 6>-2

+ 4
_ 2

galvanometer elec-
trodes. Length of

T"

T x* i

galvanometer and

20 „

22

*

-1

+ 3

exciting tracts = 10
mm. in each case.

? I

/*K

+ 16

-3

20 „

...

19 „

^V

0

+ 25

+ 2
-4

Z,s' was gradually
shortened by bring-

1

ing the galvano-

v'

.. _

i O

meter electrodes

• Jo j,

11 ,,

•*••

+ O

nearer the excited

yTv

+ 40

- 7

tract.

100 „

40 ,,

*"

_ 2

+ 2

/TV

+ 21

-2

The gradually increasing concentration of the saline, from
evaporation, seems here to increase the previous inclination of the
nerve to tetanus, on exciting it with the constant current, as
appears directly from observation of the muscle connected with
it, which falls at closure of both descending and ascending-
currents into prolonged and vigorous tetanus. The galvanometer
effects under the same conditions as before are proportionately
stronger, and negative deflections of 15-20 degrees with de-
scending, 4—7 degrees with ascending closure, are not infrequent,
on leading off from the lower (transverse) end of such a pair of
nerves. The diminution of effect on shortening the intermediate
tract, by moving the galvanometer contacts away from the cross-
section, is therefore all the more striking.

If deflections in the direction of katelectrotonic variations
are accordingly perceptible at a greater distance from the
kathode, only in the case of an initial P.D. between the contacts,
then in uninjured, isoelectric frogs' nerve, at maximal distance

x ELECTROMOTIVE ACTION IN NERVE 289

from the exciting tract, there will be absence of an- and katelectro-
tonic reaction, corresponding essentially with the electrotonic
manifestations throughout the entire extrapolar tract of non-
medullated molluscan nerve, and characterised above all by failure
of genuine katelectrotonus.

If the sciatic nerve of a cold frog is prepared, together
with the leg connected with it, and led off from two points as
near as possible to the muscle (the exciting electrodes being as
before — at the central end), then if there is no marked difference of
potential the closure of a descending current will have no percep-
tible effect, even when it is of considerable intensity. This is
also the case when the intermediate tract is shortened by shifting
the galvanometer electrodes up to the bifurcation of the branch
to the muscles of the thigh.

These statements imply that there is no considerable difference
of potential within the unbranched part of the nerve. If the
distance between the galvanometer and exciting tracts is reduced
beyond a certain point, there will of course be katelectrotouic
action here as in all medullated nerve, which will increase rapidly
on shortening the intermediate tract, and essentially depends
upon the intensity of the current. We shall return later to the
character of the anelectrotonic manifestations in uninjured nerve,
and need only state here that they can be demonstrated at
maximal distance from the exciting tract (with ascending currents),
and increase steadily on shortening the intermediate portion.

This is illustrated by Tables II. and III., which relate to highly
excitable preparations of R. esculenta. The indications are the
same as in the previous series.

If we first consider the electromotive alterations on the side
of the kathode only, the extrapolar tract of the nerve is
seen to fall, with sufficient length, into two sections, in which
the electromotive effects that appear at and during the closure
of a constant current originate (notwithstanding their similarity
of direction) in fundamentally different causes. At maximal
distance from the effective pole, distinct effects of katelectrotonus
appear only when a current of rest is present, and occur more
especially in nerves that are predisposed to tetanus. These effects
diminish — irrespective of the shortening of the intermediate
tract — with the diminution of P.D., when the galvanometer
electrodes are shifted back from the cross-section, while much

VOL. II U

290 ELECTRO-PHYSIOLOGY CHAP.

more pronounced, but homodromous, electromotive alterations
appear — under all circumstances, and independent of the excita-
bility of the preparation, or of the pre- existence of a rest
current — in the vicinity of the exciting tract, under the influence
of the current. These increase rapidly with further shortening of
the intermediate tract. The striking independence of the first-
named, weaker effects in regard to current intensity (they may
even decline in magnitude as the intensity of the current increases),
and length of intermediate tract, makes it hardly doubtful that
this is not ordinary electrotonus, but an effect of excitation.

The reaction of non-medullated molluscan nerve, in which true
katelectrotonus seems to be altogether absent, is therefore comparable
—under similar conditions — only with that tract of medullatcd
nerve which is most remote from the part excited.

The electromotive alterations in medullated nerve below an
ascending current exhibit several marked differences from the
corresponding effects on the kathodic side, irrespective of the
opposite direction of the deflections on the galvanometer.

On leading off from the peripheral end of a sensitive cooled
nerve with an artificial section (it is usual to take two juxtaposed
sciatics), and passing a weak ascending current through the
central cut-end (1 Dan. RW ' = 10—20 cm.), there is invariably
a positive variation of the (compensated) current of rest on
closing the exciting circuit (cf. Table I.) ; this variation averages
5—15 degrees of the scale, and in most cases exceeds the corre-
sponding effect of the descending current under similar conditions
(Biedermann). It is altogether independent of the presence or
absence of a demarcation current (an important point), and is
present at almost equal strength in the perfectly uninjured and
isoelectric nerve also (Tables II. and III.).

ELECTROMOTIVE ACTION IN NERVE

•291

TABLE II.
Ram esculenta (cooled frog). Nerve with dependent leg.

Size of Deflection.

Strength of

*Xw'

C7?

Remarks

NS.

Current.

Z.S.

<s /i .

Make.

Break.

i

The first lead-off was effected

0

1 Dan.

28 mm.

Y
T

0
+ 6>2

close to the point where the
nerve enters the muscle.

»

2 „

28 „

i

0

+ 4>2

0
_ i Length of galvanometer tract
and exciting tract = 10 mm.

3 ,,

28

Y

0

0

respectively.

"

^u ) >

i

+ 3>0

0

„

1 „

19 „

T

Trace -
+ 12>3

~ Z8 was shortened by bringing
the galvanometer electrodes
nearer the exciting tract.

Y

- l

0 Each descending closure

»

2 „

19 „

A

+ 12

_ 2 produced vigorous tetanus

I
i

of the leg.

2

15

Y

- 2

0

T

+ 21

2

TABLE III.
B. temporaria (cooled frog). Sciatic with connected leg.

Size of Deflection.

NS.

Strength of
Current.

ZS.

si,:

Remarks.

.Make.

Break.

0 degrees

2 Dan.

32

T

0

+ 6>2

0

Method of experiment as
above.

1

i

0

4 „

25

T

"

T

+ 11>3

- 1

17

^

_ 2

0

,,

"

t

+ 20>8

_ 2

10

"

11

Y
T

-13

+ 34

0

-4

The only difference is the appearance in the first case of a more
or less definite negative initial swing, often indicated only by the
somewhat retarded entrance of the positive variation.

It is only in rare cases (when the ascending current produces

292 ELECTRO-PHYSIOLOGY CHAP.

a strong closure tetanus) that there is a deliection of more than
1-2 degrees of the scale for the negative fore-swing. The
positive effect quickly reaches its maximum, and at once declines
again (sometimes even to zero).

On opening the exciting circuit there is usually a negative
deflection, the magnitude of which depends essentially upon the
duration of the previous passage of current ; this declines slowly.

If the galvanometer electrodes are approximated (at unaltered
distance) to the exciting tract, the intermediate portion of nerve
being thereby shortened, the deflections caused by closure of the
ascending current are rapidly augmented, independent of any pre-
existing P.D., and soon exceed the negative variation produced
with the same position of the leading-off electrodes by closure of
the descending current.

The negative fore-swing which is generally present, or at
least indicated, in the transverse lead-off is nearly always absent
in leading off from the continuity of the nerve, so that mono-
phasic, positive variations alone ensue, the magnitude of which
diminishes the less during closure, in proportion as the distance
between galvanometer and exciting tract is reduced. There iis
even a perceptible increase in the vicinity of the anode during
closure. On opening the exciting circuit, there is usually a more
or less pronounced heterodromous (negative) effect, with longi-
tudinal as with transverse lead-off. This is at all events the rule
in the vicinity of the exciting tract. At more distant points the
appearance or failure of a negative opening variation seems, like
the negative closure effect, to be conditioned essentially by the
existence of a P.D. between the two contacts. The experimental
tables quoted above contain evidence for all that has been said
with regard to the galvanic alterations of the extrapolar region
of the nerve, 011 the side of the anode.

The interpretation of these facts — relative to manifesta-
tions of negativity at make and break of the ascending current-
can hardly be doubtful. The agreement with the corresponding
phenomena in non-medullated molluscan nerve is here so striking
that the same explanation, as the consequence of closing or opening
excitation, is obvious. The frequent absence of the negative
initial swing with ascending stimulation of medullated nerve,
and its insignificance when present, is hardly surprising, when
we remember that the effect depends, on the one hand, upon a

x ELECTROMOTIVE ACTION IN NERVE 293

definite state of excitability (not always present in the same
degree) in the cooled nerve, while on the other a pro-
nounced closure tetanus with ascending direction of current is
usually under these conditions of experiment exceptional ; and
further, the subsequent and much stronger positive effect soon
defeats the initial heterodrornous action. It is thus intelligible
that the latter should disappear, or be present as a trace
only, on shifting the galvanometer electrodes away from the
transverse end of the nerve, and thereby rendering the essential
conditions of its appearance still more unfavourable. Lastly,
it can hardly be necessary to state that the application of
strong ascending constant currents may obstruct the negative
fore-swing, as well as the transmission of the closure excita-
tion ; it is, moreover, absent in isoelectric leads from the un-
injured nerve, as, under all conditions, in preparations of warmed
frogs.

We have already noted that Engelmann found a marked
negative variation in the demarcation current of medullated
frog's nerve on opening the battery current, provided the excita-
tion took place under conditions in which a tetanic opening
excitation might be expected.

As such, for instance, must be reckoned adequate strength
and duration of the ascending exciting current, but most of all
the disposition of the nerve to persistent excitation so frequently
alluded to. Under favourable circumstances the negative opening
effect on leading off from the transverse end of the nerve is not
inferior in magnitude to the negative closure effect with descending
excitation.

No definite conclusion as to the nature of the positive
anelectrotonic closure effects can be deduced from the above
experiments, since these exhibit along the whole extrapolar anodic
portion of the nerve, a reaction essentially similar to that of non-
medullated molluscan nerve, unless it be reckoned as a distinction
that they appear in the former with weaker currents, and at a
much greater distance from the part of the nerve traversed by
the current. Since, as has been shown, the anelectrotonic altera-
tions in non-medullated nerve can scarcely be explained otherwise
than by a physiological change of state transmitted from the anode,
it seems highly probable that a similar process occurs likewise
when medullated nerve is traversed by current on the side of the

294 ELECTRO-PHYSIOLOGY CHAP.

anode. On the other hand, the presence of an extrapolar kat-
electrotonus, homodromous with the alterations undoubtedly trans-
mitted by conduction, leads us in the last case to conjecture that
the galvanic anelectrotonus of medullated nerve may also, as it
were, arise from two components — one, a physiological change of
state transmitted, as in non-medullated nerve, from the anode,
the other, a galvanic alteration, peculiar to medullated nerve, and
corresponding with katelectrotonus proper, the purely physical
origin of which has still to be discussed. We should thus
anticipate that " physiological anelectrotonus " would appear in
greatest integrity at maximal distance from the exciting tract,
while in the vicinity of the anode it is complicated by other
homodromous local alterations of the nerve, due to specific
diffusion of the polarising current. This is also indicated in the
fact, as above stated, that anelectrotonic effects far exceed the
katelectrotonic in intensity and range, which is easily explained
in view of the relations obtaining in non-medullated nerve. It
is, however, desirable to bring forward further arguments, and, if
possible, evidence, for such a separation between physical and
physiological clectrotonus. In one direction such evidence is offered
by experiments on medullated nerve, in ether or chloroform nar-
cosis, where all changes transmitted ly conduction would seem to ~be
definitely excluded.

From these experiments (for method cf. Biedermann, 38) it
appears that all electromotive alterations of the nerve, that may
othenoise lie observed at points remote from the tract through-
which current is flowing, disappear shortly after the commence-
ment of etherisation (5—10 min.). This applies both to the
negative variation on closing the descending constant current,
and to the positive effects with an ascending current. The
ordinary negative variation, moreover, fails when the nerve is
tetanised, showing that conductivity is really abolished (thus
giving additional evidence contra Boruttau's theory of the negative
variation, as above). Seeing that treatment with ether cannot
fundamentally alter the physical and chemical properties of a
nerve (as shown on the one hand by the constancy of P.D. between
transverse and longitudinal sections, on the other by the rapid
restoration of all normal vital properties of the nerve at the
close of narcosis), the presumed double character of electrotonus
becomes highly probable. It is proved, i.e., to depend not merely

x ELECTROMOTIVE ACTION IN NERVE 295

on the preservation of normal structural conditions in the nerve,
but also, fundamentally, upon its conductivity.

Moreover, it can be shown that at a time when no trace of
electrotonic action is demonstrable during ether narcosis at a
distance from the exciting tract, there are strong and regular
electrotonic currents in its immediate vicinity, and the reaction
of these under prolonged etherisation is of great interest.

Normally there is without exception a marked difference in
the strength of electromotive action on the side of the anode and
of the kathode respectively, which is most distinct under the
action of weak and medium battery currents. It follows that
katelectrotonic deflections often fail altogether, or appear only as
a trace at a distance from the exciting tract, while on reversing
the current auelectrotoiius may appear in its full strength, other
conditions being uniform. Even in the vicinity of the exciting
tract the difference between kat- and anelectrotonic deflections is
considerable, the latter being often more than double.

This reaction is completely altered with progressive etherisation,
i.e. the anelectrotonic deflections rapidly diminish at uniform excita-
tion, while the katelectrotonic effect remains at first unaltered, or may
even increase slightly. Subsequently there is always a point at which
the kat- and anelectrotonic defiections are completely equalised, in
respect of magnitude as well as of time-distribution, and this persists
whatever the strength of current. It should also be remarked that
with increasing current intensity the increment of deflection is
approximately proportional in the later stages of ether narcosis.
If the narcosis is sufficiently protracted, the katelectrotonic effect
will also be modified in course of time (as would be anticipated),
but the increasing diminution of the deflections will then keep
pace with the simultaneous diminution of arielectrotonus.

If the narcosis is interrupted only when all trace of electro-
tonic action has disappeared, there is no recovery of the normal
vital properties of the nerve ; it is then, anatomically and
physiologically, dead — the medullary sheath of the single fibres
exhibiting the familiar clefts by which dead nerve is characterised.
But if the preparation is removed earlier — directly after the
heterodromous electrotonic deflections have been equalised — from
the action of the ether, and placed in a moist chamber, recovery
will at once set in, as evidenced by a rapid increase in f/ir
magnitude of the anelectrotonic deflections, with constancy of

296

ELECTRO-PHYSIOLOGY

CHAP.

Jcatelectrotonic effect. Under favourable circumstances, vigorous
preparations that have been cautiously narcotised will completely
recover their normal properties, including that of conductivity in
the nerve ; in other cases there is, on the contrary, a perceptible
loss (as expressed, e.g. in preparations of cooled frogs, by the
frequent suppression of the negative variation of the nerve current
described above as the galvanic expression of the make or break
persistent excitation, at the close of narcosis — so that the nerve
reacts precisely like a preparation from a warmed frog). With
tetanising induction currents also there is frequently a visible and
permanent diminution of the negative variation.

The figures contained in the following table will illustrate
these facts : they refer to deflections observed under the same
experimental conditions as the former series. NS = strength of
the nerve current ; E, number of (Daniell) cells ; ZS, length of
the intermediate tract ; SR, direction of current.

jVS.

£.

ZS.

,S'JZ.

Deflection.

Remarks.

Make.

Break.

be

0

1

10 mm.

i

+ 46

+ 3
-5

-\

Before commencement of narcosis ;
length of galvanometer, exciting,
and intermediate tracts, all 10

c

2

4

-48

+ 2

mm. The galvanometer elec-

( ,

"

r j

t

+ 73

-6

trodes are placed along the

O>

\

continuity of the nerve, and

"o

o

4

-60

+ 2

the exciting electrodes at the

• — •

"

"

r1

+ 96

- 7

'

central end.

e

V

-30

0

5-

|

"

1

"

TV

+ 30

0

s

V

-53

0

1

»»

2

» »

t

+ 54

0

Alter 12 minutes' action of ether.

JS

1

^

"v

-66

0

3
o
.^*

1 )

3

"

l"

+ 68

0

*

V

-24

0

.

75

> I

1

"

/TV

+ 24

0

o

2

J}

2

,,

4

A,

-40
+ 41

0
0

Alter 10 more min.

!K

'

09

M

"v

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ELECTROMOTIVE ACTION IN NERVE

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If the above facts prove the existence of physiological changes
of state, i.e. such as are transmitted from the poles — comparable
throughout with electrotonus — they would seem to indicate a
satisfactory explanation of the hitherto irreconcilable experiments
of Bernstein, as well as of Hermann and his pupils. We have
already pointed out that with regard to anelectrotonus the
galvanometric effects in non-medullated nerve agree in every
particular with the results of Bernstein's rheotome method on
medullated frog's nerve. This is intelligible if it be admitted
that, at the given distance between galvanometer and exciting
tracts, the galvanic manifestations of excitation and of transmitted
physiological electrotonus alone take effect ; while the experiments

298

ELECTRO-PHYSIOLOGY

CHAP.

of Griinhagen and Hermann relate essentially to the consequences
of physical anelectrotonus, the development of which, at different
points of the nerve, is governed by quite a different law. Wuudt's
communications may possibly find an explanation from the same
point of view. Under any circumstances, however, further
investigation is required, in order to make a decisive judgment
possible. Above all, it is legitimate to ask whether the katelectro-
tonus of medullated fibres (which appears to fail altogether in
non-medullated nerve) may not also mask a " physiological com-
ponent," as is certainly implied by Bernstein's experiments.

4. In Polarisable Schemata

We must now enter more particularly into the nature of
jihysical electrotonus," as exhibited in medullated nerve, during

A

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Fio. 213.

ether narcosis. Du Bois-Keymond attempted, from the stand-
point of his molecular theory, to explain the whole of the galvanic
manifestations of electrotonus by a directive influence of the
polarising current upon the electromotive molecules of the nerve,
which is not confined to the tract directly traversed, but extends
more or less widely beyond it. If the nerve is conceived as con-
structed of peripolar molecules, each consisting of two dipolar
halves (Fig. 213), the exciting (polarising) current, which is passed
through one portion of the nerve, induces a homodromous incre-
mental current in the entire nerve, — the electrically heterogeneous
particles being arranged after the pattern of Volta's pile, the
positive zones directed to the side towards which the current
is flowing in the nerve, the negative zones, on the contrary,

x ELECTROMOTIVE ACTION IN NERVE 299

to that from which it is coming — as in Grottlmss' theory of
electrolysis. Du Bois-Eeymond further assumes that this dis-
position in the direction of the current is not confined to the
intrapolar tract, but extends in a diminishing degree to the extra-
polar regions also, by which he explains the electrotonic incre-
mental current. Since this interpretation stands and falls with the
theory of pre-existing electromotive force in the nerve, which may
now be regarded as disproven, we need not enter upon it in
detail ; and may turn to those experiments by which Matteucci, in
1863, indicated the true physical explanation of galvanic electro-
tonus (39). He found regular differences of potential in stretched
metal wires (platinum) soaked in a conducting fluid, when any
part of the wire was traversed by a constant current. At
every point of the extrapolar region there was between each pair
of points led off to the galvanometer a current homodromous with

FIG. 214.

the primary (polarising) current, which was weaker in proportion
as the point tested was more remote from the polarising tract.

Later on, the same phenomenon was thoroughly investigated
by Hermann (39), who gave a complete theoretical explanation of it;
showing it to be due, not — as Matteucci at first thought — to the
consequences of spread (by diffusion) of the electrolysis occurring
at the electrodes, but to a special case of polarisation (" secondary
polarisation"}. If a current is led into the moist sheath of a wire
(Fig. 214) at two points, it depends, as Hermann showed, essentially
upon the polarisability or unpolarisability of the combination how
far the current will diffuse in the sheath of the metallic core.
Matteucci stated that an amalgamated zinc wire, of which the
sheath is moistened with zinc sulphate, gives no extrapolar
differences of potential ; and this was confirmed by Hermann. It
is, in fact, easy to see that the current, under these conditions, will
enter or leave the metal core at the actual electrodes and their
immediate vicinity only, since the lines of current rapidly
diminish in intensity, with increasing length, owing to the

300

ELECTRO-PHYSIOLOGY

CHAP

augmented resistance. But if polarisation occurs at the point at
which the lines of current pass from the fluid into the metal,
and if there is in consequence such a marked " resistance "
that the resistance due to unequal length of the lines of current
is practically out of consideration, there is evidently nothing
to prevent a wider diffusion of the current in the moist sheath
along the core (Hermann).

As is obvious from the accompanying schema, a branch
current must flow in every extrapolar leacling-off circuit, at what-
ever point it is applied, in the direction of the polarising current
(Fig. 214). The following observations of Hermann (39, v. p.

A

270) point to the same result. " In Fig. 215 the lines Ah and Cg
show the path that would inevitably be taken by the current if
there were no polarisation, in view of the thinness of the moist
sheath and good conductivity of the metal core, in order to pass
from the electrode points A and C to the core. If polarisa-
tion occurs at h and g, the metal (e.g. platinum in dilute
sulphuric acid) would be charged with hydrogen at h, with oxygen
at g. The platinum point h, which is charged with hydrogen,
would then be electrically active towards the uncharged points
near it h-Ji^, and currents would be generated in the moist sheath
in the direction shown in the figure. These currents give off
hydrogen at h-Ji^ oxygen at h, but in a quantity insufficient to
neutralise the fresh hydrogen which is constantly being deposited
by the current. The charged points 7^ are now electromotive to
their uncharged neighbours /to, fresh currents /t^t., arise which

ELECTROMOTIVE ACTION IN NERVE 301

again charge h.2 with hydrogen, and so on. The whole region
round A is, however — so soon as a stationary condition has been
established — charged (in a degree that diminishes with the distance)
with hydrogen, that round C with oxygen. The currents that
arise from these charges, and at the same time maintain them, can
be detected in a leading-off circuit," as indicated above (Hermann).
For the more exact investigation of these phenomena, which
are important to the theory of electrotonus, Hermann subse-
quently employed a model, in which the moist sheath was
replaced by a free fluid (saturated zinc sulphate). This circulated
in a glass tube (Fig. 216) with lateral openings, through which
he passed a platinum wire. Amalgamated zinc wires served as
the leading-in and leading-off electrodes. Apart from the facts
quoted above, this experiment showed that every interruption of
the wire (core-conductor), or of the liquid sheath, between the
polarised and led-off parts, hindered the production of the extra-
polar currents, which, for the rest, are proportional with the
polarising current. They coincide with the electrotonic incre-
mental current of medullated nerve, in so far that, with a given
distance between the two tracts, their intensity increases with the
length of area traversed (with uniform intensity of polarising
current). The currents are further present at the moment of
closure, and where the combination employed (e.g. platinum in
zinc sulphate or sulphuric acid) is polarisable on both sides, are of
equal strength at anode and kathode. On the other hand, the
extrapolar currents on the kathodic side fail altogether, or appear
only in the immediate vicinity of the pole, when the combination
polarises on one side (the anode) only — e.g. zinc wire in H2S04 or
Nad, copper wire in H.2S04 or ZnS04. Lastly, as in nerve,
so in the core-model, the extrapolar incremental current fails
altogether with transverse direction of current.

In the year 1883 Hermann discovered on a core-model
(platinum in zinc sulphate), 2 metres long, — on passing in frequent,
brief, constant currents of uniform direction, with Bernstein's
rheotome — that, with a great distance between the polarised and
led-off parts, the electrotonic currents sometimes began, or at any
rate attained their maximum, only after the polarising current
had been opened, which obviously points to an undulatory character
of the corresponding galvanic processes. With a shorter distance
between exciting and galvanometer tracts, the maximum of homo-

302 ELECTRO-PHYSIOLOGY CHAP.

dromons, electromotive activity occurs at the end of the closure of
the polarising current. Between the two leading-off electrodes,
again (as in the phasic currents of action), there are two
successive, opposite, and unequal phases of current, the first and
stronger of which is homodromous with, the second on the other
hand heterodromous to, the polarising current. This last phase
does not here imply that the undulatory process moving forward
with a rapidity of 20-65 metres per sec. — which on reaching the
first leading-off electrode produces the first phase — gives rise to an
opposite phase at the second contact (when it is simultaneously
extinguished or greatly diminished at the first) ; hut it is due to a
heterodromous current arising at break of the polarising current, in
the intrapolar tract of the core-conductor. " Shortly expressed,
the second phase is nothing else than the comparatively retarded
state into which the core-conductor is thrown by polarisation, in
consequence of the rapid succession of momentary closures of the
polarising current. The first phase, however, is the undulatory
action of each single momentary closure, superposed upon this con-
dition. It appears in complete integrity, when the two opposite
polarisations of the wire core do not neutralise each other, or
when one polarisation only is present, so that a bipolar current is
impossible " (Hermann).

While Hermann is very cautious in accepting the possible
bearings of these remarkable but theoretically insufficiently - ex-
plained phenomena upon the transmission of excitation in the
nerve, and admits that there may be only plausible analogies,
Boruttau (20) has recently adopted the extreme physical stand-
point. He finds that, on leading in the alternating currents of an
induction apparatus to a core composed of platinum or palladium
wire in 0'6 per cent saline, by means of a rheotome, galvanic un-
dulations are manifested, due to the rapid transmission (over 100
metres per sec.) of a negative phase to a considerable distance, and
corresponding throughout with the phasic currents of action
(inter alia, as regards effect of temperature upon rate of trans-
mission). As we have stated, he views the negative variation
also as no more than an undulatory katelectrotonus. By employ-
ing very long core-models, consisting of many glass tubes placed
together, by which the distance between traversed and led-off
tracts could be increased to 4 metres, Boruttau observed the
undulatory transmission of negativity, and this alone, with great

x ELECTROMOTIVE ACTION IN NERVE 303

distinctness. On passing a constant current there is at the
kathode only, on closing the current, at the anode on breaking it,
" an effect, albeit brief and inconspicuous, in the direction of
negativity of the proximal electrode." " This momentary negative
effect is much more visible when single induction shocks are sent
into the ' exciting tract ' by a key. A brief negative effect
corresponds with each such shock, independent of its direction."
Alternating currents produce negativity of the proximal electrode,
which lasts as long as the " tetanisation." " Analysis by the
differential rheotome also shows that a wave of negativity (i.e.
katelectrotonus) is transmitted at these distances," it being a
matter of indifference whether short, frequent battery currents,
or induction shocks, are led through the exciting tract by the
rheotome. " Both cases exhibit the wave of negativity spreading
over the tract led off, in two phases, so that the proximal
electrode is first negative and then positive to the distal contact."
Such complete identification of the negativity which is the
concomitant of excitation, with the katelectrotonic wave, must be
protested against, in spite of the many striking analogies between
these phenomena in the core-model, and the galvanic reaction of
niedullated nerve traversed by the current. The objections which
we hold to be conclusive against such a point of view are, in the
first place, the appearance of analogous galvanic manifestations in
electrical excitation of the most diverse " irritable " tissues, the
structure of which in no way justifies us in assuming that they
are core-conductors in the same sense as niedullated nerve ; further,
the fact that etherised niedullated nerves, in which physical
" fixed polarisation " appears after, as well as previously, exhibit
no trace of transmitted activity ; and lastly, and above all, the fact
that the galvanic manifestations of excitation appear equally in
all appropriate objects with other than electrical stimulation.
Boruttau, indeed, does not hesitate to refer once more to the
properties of the core-conductor. He sees an analogue to the
mechanical excitation of nerve and its galvanic consequences in
the sudden rupture of the wire inside the moist sheath, after
previously filing it at a given point, since he then observed in
every case " with great precision," on leading off from a remote
tract, " a comparatively conspicuous momentary appearance of
current, or charge, followed by an immediate return to the previous
state of rest." Without disputing these experimental data, no

304 ELECTRO-PHYSIOLOGY CHAP.

one who has accepted the point of view that living animal or
vegetable cells are alone excitable, could subscribe to the con-
clusions deduced from them. This is another example of the
danger of generalising from observations on any one object, and of
criticising vital manifestations from a one-sided physical point of
view, without regard to differences of structure.

Without denying that further investigation may perhaps
bring to light other analogies between the conduction of excita-
tion on the one hand, and that of the undulatory electrotonus in
the core-model on the other, it must be borne in mind that
excitation and conductivity of excitation may be observed in
objects, and under conditions, where Boruttau's physical assump-
tions are certainly not present.

Even for "fixed polarisation" however, it is questionable
whether the persistent electrotonic currents that appear in the
immediate vicinity of the area traversed in medullated nerve can
be explained entirely on Hermann's principle of interpretation,
although they are no doubt partly physical in origin. That
structural constitution of the medullated fibres which here comes
more especially (and perhaps solely) under consideration, i.e. the
investment of the axis-cylinder with the medullary sheath, exhibits
prima facie few characteristics integral to the original core-model
of metal and fluid. In the first place, there is the enormous
difference of conductivity between moist sheath and metal core.
Any such marked disparity in conductivity between axis-cylinder
and medullary sheath is obviously excluded ab initio ; it may,
indeed, be asked whether any perceptible difference exists. A
second question is, whether any polarisation at all is present at
the interface of these two elementary constituents of medullated
nerve, and if so, whether such a polarisation at the surface of two
electrolytes can, as regards its effect upon current diffusion, be
compared with that taking place at the junction between metal
and fluid ?

With regard to the first point, Hermann long ago gave ex-
perimental proof that the very considerable difference between
longitudinal and transverse resistance in the nerve is essentially
to be referred to an E.M.F., heterodromous to the current and clue
to polarisation. With transverse passage of current this seenis
to occur mainly at the boundary between neurilemma (sheath of
Schwann) and medullary sheath, so that with Hermann we must

x ELECTROMOTIVE ACTION IN NERVE 305

regard as core-substance, not merely the axis-cylinder, but the
" entire protoplasmic contents of the tube " ; as sheath, not
merely the medullary sheath, but also " the neurilemma, and the
interstitial connective tissue."

Hermann brought parallel frogs' nerves, placed together,
between two quadratic glass plates, and determined the resistance
by Wheatstone's method, passing the current once longitudinally,
and once transversely, to the direction of the fibres. " The trans-
verse resistance was five times as great as the longitudinal resist-
ance ; the former is about twelve and a half million, the latter
only two and a half million times as great as that of mercury."

If the existence of surface polarisation is accepted 011
the analogy of the core-model for medullated nerve, it must
further be asked whether the intensity of such polarisation
at the interface of the two electrolytes is sufficient to account
for the observed diffusion of current in the nerve. From
a purely theoretical standpoint this cannot be disputed.
In view, however, of the intensity of the electrotonic effects,
we should practically be compelled, with Hermann (40),
to recognise in the nerve an " unparalleled " force of surface
polarisation, since " the polarisation at the interface of normal
fluids (which is very weak as compared with the metal-fluid
combinations) could only, in consequence of the resistance,
induce a very feeble diffusion, which would be altogether masked
by the experimental errors."

Nevertheless, experimental combinations of moist conductors
have been found to give exceptionally strong effects in the sense
of a pronounced and regular electrotonus ; this reaction, however,
must be referred less to surface polarisation in Hermann's sense
than to a peculiar mode of current diffusion, according to a
theory advanced by Griinhagen (41) and .Hering (24). Hering
employs a simple model for " physical electrotonus," which is
admirably suited to all demonstrations, i.e. the long stem of the
pipe-grass, without internodes, which is first soaked in water,
and then filled just before the experiment with concentrated
saline. The feelers and bones of the crayfish, preserved in
alcohol, and saturated before the experiment with 0'6 per cent
saline, are no less convenient.

The striking similarity of the resulting electrotonic manifesta-
tions with those observed under the same conditions in etherised

VOL. II X

306

ELECTRO-PHYSIOLOGY

CHAP.

nerve, extends not merely to equality of an- and katelectrotonic
deflections, but also to the more or less approximate proportion
which exists at a given position of leading-in and galvanometer
electrodes, between the magnitude of effect produced and intensity
of the polarising current (38). An essential characteristic of
" electrotonic " currents, as opposed to ordinary current escape, is
presented by the fact that the direction of the extrapolar
current led off is determined by the position of the galvanometer

(t

772

+

•I- !

FIG. 217.— Schema of current diffusion in an ordinary conductor partially traversed by current.

FIG. 21S. — Schema of current diffusion in a "core-model." (Griinhagen.)

current. This is shown by the accompanying schema (Fig. 217),
where it is seen that the extrapolar branches of current led off
from opposite sides of the conductor must necessarily be hetero-
dromous. On the other hand, this does not occur either in the
nerve or in any of the models described above. Whatever the
position of the galvanometer electrodes, the current led off is invari-
ably homodromous with the polarising current. The sole essential
condition is that the axis of a moist conductor should contain a core of
letter conductivity than the sheath. It is immaterial whether, as in

x ELECTROMOTIVE ACTION IN NERVE 307

Matteucci's core-model, this is a metal, or, as in Hering's experi-
ments, as well as in an analogous method of Griinhagen (42), and
in certain combinations recently employed by Boruttau, & fluid
conductor. According to Griinhagen (Fig. 218), we should
imagine that in every combination of conductors on the plan of
the accompanying schema (Fig. 218), "the branch currents
running in the sheath take only one direction towards the better-
conducting core, while the recurrent branches, on the contrary,
are included within the better-conducting axis." " In consequence
of this absorption of all recurrent diffusion-currents by the core-
conductor, the sheath is free of them, and wherever the leading-
off contacts of the galvanometer circuits are applied, whether at
the side near, or opposite to, the leading-in electrodes, there will
only be branch currents in the one direction, identical with that
of the diverging lines of current as described above " (Griinhagen).
If this view is accepted, the axis-cylinder should be a much better
conductor than the medullary sheath, which, indeed, from the
histo-chemical point of view, seems not improbable. The com-
plete failure of any definite physical electrotonus in non-medullated
nerve, and in muscle, would accordingly be determined by the
absence of badly-conducting sheaths to the single elements ; to
which it must further be added that (as has been recently con-
firmed— Biedermann) electrotonic effects are also absent in cases
where, as in many crustacean nerves, the solitary axis-cylinder is
surrounded by well -developed stratified sheaths of connective
tissue. The physico-chemical constitution of the medullary
sheath appears, therefore, to be indispensable to current diffusion.
In this connection there are some interesting experiments on the
nerves of Palcemo7i, which, according to Eetzius, contain meclul-
lated fibres, and thus differ completely from those of most other
Crustacea.

As the outcome of the preceding discussion, it must be
admitted that there is in medullated nerve a diffusion, whether
produced by " secondary polarisation " or by direct current escape,
of the external current over the tract directly traversed, i.e. an
electrotonus of physical origin, which is however complicated, as
a rule, by homodromous physiological alterations of the nerve.
From the physiological standpoint the chief interest lies in the
alterations of the nerve, i.e. of its excitability, produced by the
diffusion of the exciting current. In muscle, where the entrance

308 ELECTRO-PHYSIOLOGY CHAP.

and exit of the current are confined essentially to the actual
contacts and their immediate vicinity, the polar action of the
current finds localised expression 011 the one hand as excitation,
on the other as inhibition, only at the points at which it is
initiated. But where, as in medullated nerve, the physiological
anode or kathode (i.e. the region within which lines of current
pass in and out of the excitable substance of the axis-cylinder)
has any considerable extension, the same must of course hold
good of all the consequences of excitation and inhibition. The
spatial extension of physical electrotonus as the sum of all the
changes directly produced by the electrical current is, in other
words, masked by the spatial diffusion of anodic and kathodic
points in the tissue traversed by the current. If it is thus a law
for muscle as well as nerve that, within certain limits of current
intensity and passage at the physiological kathode (i.e. at every
point by which current leaves the excitable substance), there is
during closure a condition of augmented " expectancy " - the
contrary being the case at the physiological anode — we have in
this a direct interpretation of the facts of intra- and extrapolar

alterations of excitability, as diffused
antagonistically from the poles in a
polarised medullated nerve. This
further explains the striking rise of

^~"^577"[ O t/

excitability in the vicinity of each

FIG. 2i9.-Eiectrotonic diffusion of the artificial cross - section. As in the

demarcation current along the nerve

(weak longitudinal currents). (Her- case of an external current, the

demarcation current of each medul-
lated nerve-fibre will not merely equalise itself in the immediate
proximity of the demarcation surface, but (again for the same
reasons) will give off lines of current to a long distance from
the cross -section, as indicated in the accompanying schema
(Fig. 219); and these, escaping in all directions from the
axis-cylinder, throw the latter into katelectrotonus with all its
sequela?, the intensity of the same of course declining rapidly
with distance from the cross-section. The so-called weak longi-
tudinal currents may therefore, as was first pointed out by
Hermann (cf. Fig. 219), be regarded simply as the electrotonic
spread of the demarcation current.

Lastly, there is the fact already alluded to that, in electrical
excitation of a medullated nerve that has undergone local morti-

x ELECTROMOTIVE ACTION IN NERVE 309

ficatiou, the physiological action of one pole may, as in muscle, be
excluded, if a greater or less part of the iutrapolar tract is killed,
•with as little injury as possible to histological structure. This,
again, is simply explained by the spatial distribution of the points
by which current leaves and enters, as well as the difference
already pointed out between abterminal and atterminal induction
currents, sent into the transverse end of a medullated nerve. The
E.M.F. at the boundary of " altered " and non-altered nerve-sub-
stance is presumably very high, since there is a marked action
from the deriving currents led off externally ; so that the intensity
of the branches of current, which are short-circuited in the
proximity of an artificial transverse section of medullated nerve,
by the substance of the sheath, must undoubtedly be very great,
owing to the low resistance of their microscopic longitudinal path
(Hermann).

VI. SECONDARY ELECTROMOTIVE CHANGES IN NERVE FOLLOWING
THE PASSAGE OF A CURRENT

As in muscle, so in medullated nerve, it was shown by du
Bois-lieymond that every part traversed by a current of adequate
strength exhibited regular electromotive action in a given direction
when the circuit was broken. He referred the phenomena in
both cases to " internal polarisation," since it appeared that an
opposite (eventually hoinodromous) after -current could also be
observed when the two leading-off electrodes to the galvanometer
were situated between the exciting electrodes, within the intra-
polar region. It has already been shown (I. p. 444) that this view
is erroneous, at least as regards muscle. In the case of nerve
the investigation is much more difficult, owing to the smaller
intensity of effect, and still more from the electrotonic diffusion
of the (polarising) exciting current. Nevertheless, it may be
affirmed from all the observations made up to the present time
that no real difference exists in regard to secondary electromotive
phenomena, between nerve and muscle. Du Bois-Eeymond
obtained maximal negative effects after prolonged passage of com-
paratively weak currents, while maximal " positive polarisation "
occurred after a brief closure of a strong battery (25—30 Groves !),
(43). Hermann, who at first found no fundamental difference in
the deflections, on sending current through a tract of nerve 40

310 ELECTRO-PHYSIOLOGY CHAP.

mm. long (two frog's sciatics with the opposite ends in contact),
when the leading -off tract was successively as near as possible to
the anode, and then to the kathode, finally determined that " the
homodromous after-phase of the current was regularly absent in
nerve, as in muscle, when the physiological anode coincided with
the artificial transverse section and was led off from there." Hence
there is no doubt that the homodromous after-current (" positive
polarisation ") is to be viewed exclusively as the galvanic expres-
sion of the opening excitation.

The wide extrapolar diffusion of the polarising current in
medullated nerve makes it desirable to test the reaction of the
extrapolar after -current on breaking the circuit. The first
investigation was made by Tick (44), who found that a hetero-
dromous after-current appeared on both sides of the polarising
current, and quickly vanished again. A little later on Hermann
(45), followed by Fick, asserted that this occurred only on the
side of the anode, while a current, homodromous with the polar-
ising current, appeared beyond the kathode, its strength being
always less than that of the anodic after-current. In regard to
the latter, moreover, Hermann subsequently ascertained (46) that
it was preceded by a brief variation, homodromous with the polar-
ising current.

Hermann explained all these manifestations by the " polar-
isation " after-currents (which he carefully investigated on the
" core-model "), in combination with the " irritative " after-currents
due to polar manifestations of excitation, and especially to the
opening excitation. We have already seen that these last are
alone sufficient to account for all secondary electromotive effects
in muscle, and the same is a priori probable for nerve also.
Further investigation is, however, desirable before coming to a
final decision. In any case, the extrapolar, anodic after-current
(heterodromous to the polarising current) depends upon the
negativity, which gradually diminishes from the pole outwards,
and is the galvanic consequence of the opening excitation ; while
the homodromous, extrapolar, kathodic after-current may equally
be defined as " irritative," if the negativity, which — as in muscle
—again declines from the pole outwards, is viewed as the after-
effect of the previous excitation, extending, of course, in a
medullated nerve as far as there are points of exit for the lines of
current.

x ELECTROMOTIVE ACTION IN NERVE 311

We have farther to examine the reasons brought forward by
Griitzner and Tigerstedt (48) for their contention that certain
forms, perhaps indeed all opening twitches, produced by negative
polarisation currents are really closing twitches. In view of the
above, it is evident that this current, when of adequate strength,
may play the same part along the continuity of the nerve as the
demarcation current at the transverse end, i.e. that it can eventu-
ally set up " false " opening twitches.

And, in fact, Peltier (who in 1836 was the first to observe
negative polarisation in the limbs of frogs through which current
was passing, and whose investigations formed the starting-point
of du Bois-Eeymond's labours in this direction) had already
interpreted the opening twitch by the polarisation current. Du
Bois-Keymond, however, stated against this view that " these
charges, in order to induce a current through the nerve, required
to all appearance a closed circuit, which condition was cancelled
by opening it" (23, i. p. 381). Matteucci was also of Peltier's
opinion, that the opening twitch could be explained by the
(negative) polarisability of the nerve, without, however, adducing
any cogent evidence (4V).

As regards du Bois-Eeymond's objections, their importance
is lessened, since it has been established experimentally that
the internal short-circuiting of a demarcation current that occurs
both in muscle and in nerve is sufficient to discharge an " apparent "
break twitch. Under the presumption of adequate intensity, the
same phenomenon may be anticipated for the negative polarisa-
tion current produced by the exciting current, and it only remains
to show experimentally that certain opening twitches may really
come about as described above.

Griitzner (7.c.) set up experiments with the view of determining
whether there might not be different modes of appearance of the
opening twitch, with indirect excitation of the muscle, according
as the polarising heterodromous current is short-circuited at the
moment of opening the exciting current by a good external shunt
circuit, or, in the absence of such a shunt, short-circuits itself
internally in the nerve. And there does actually seem, more
particularly with metal electrodes, always to be a difference
agreeing with the theory. The opening twitch, i.e., appears much
earlier (viz. with weaker exciting currents), or is more pronounced,
in the presence of an external shunt for the polarisation current,

312 ELECTRO-PHYSIOLOGY CHAP.

than when it is absent. Hermann has communicated similar
experiments which he carried out in 1875-76, with the same
result, but did not publish.

From these facts it appears that the polarising heterodromous
current is, under the given conditions, implicated in the discharge
of the opening twitch, although we must by no means conclude
that it is invariably the sole factor. This conclusion seems, how-
ever, to Griitzner and Tigerstedt to be justified, mainly by the fact
that all those circumstances which are favourable to the appear-
ance, or increase, of a negative polarisation current are also con-
ducive to the appearance of the break twitch.

The normal, vigorous, and uninjured nerve is characterised (as
was remarked above) by a certain resistance to excitation from the
break of an electrical current, so that tolerably strong battery
currents are required to discharge opening twitches after a brief
closure. When, however, a break twitch has once been dis-
charged by an adequate current, then even weak currents (that
previously took effect at make only) will excite directly after-
wards, provided that in both cases the same tract of nerve
is traversed by the current. After a brief period of rest this
excitatory effect disappears again completely. Griitzner and
Tigerstedt interpret this reaction to mean that the negative polar-
isation current, set up by the stronger current in the tract
traversed, and gradually subsidiug at break of the exciting
current, disposes this tract during its passage to the discharge
of "false" opening twitches, in which case the short-circuiting
of the polarisation current can only (with the normal method of
opening the exciting current) be internal, occurring within the
nerve itself.

Tigerstedt arrived at the following results from his investiga-
tion of the time-relations of negative polarisation in frog's nerve,
as well as its dependence upon intensity and duration of the
exciting current :—

(i.) Within certain limits of current intensity the (negative)
polarisation of the nerve is directly proportional to the strength
of the exciting current.

(ii.) If the polarising current acts upon the nerve during an
indefinite period, polarisation increases ; it rises quickly at the
beginning, then more slowly, reaching its maximum with extreme
sluggishness.

x ELECTROMOTIVE ACTION IN NERVE 313

(iii.) When the polarising current is opened, the polarisation
rapidly reaches its climax, and then sinks again continuously ;
this fall occurs quickly at first, and afterwards more slowly, so
that polarisation lasts for a long time after the opening of the
polarising current, and only reaches its zero asymptotically.

The opening twitch agrees in all three points with the nega-
tive polarisation current. We have already referred to the fact
that motor frogs' nerves are so altered by the action of dilute
solutions of alkaline salts, or alcoholic salt solution, that at a
given stage the weakest constant currents will discharge opening
twitches, after quite brief closures, of the same character as the
break twitch from a transverse section, — which alteration may be
completely neutralised by washing out the foreign substances.

Tigerstedt finds that " the (negative) polarisability of the
nerve also rises on treatment with alcoholic saline to 1'5 times
its original height," and sees in this fact a further confirmation
of the view that the opening twitch is the closure twitch of the
negative polarisation current. Finally, Tigerstedt refers the
earlier appearance of the break twitch 011 exciting the divided
sciatic plexus, as compared with the excitation of peripheral
points of the nerve (Biedermann and Grutzner), to a more ready
polarisability of those sections of the nerve. The demarcation
current must, however, play the principal part.

In summing up these facts, it can hardly be doubtful
that certain forms of opening twitch are to be interpreted as closure
twitches from the negative polarisation current. Such sweeping
generalisations as those formulated by Tigerstedt, and more
recently by Hoorweg (49), which " refer the opening excitation
and all phenomena that occur on opening the polarising current "
to " the (negative) polarisation current, and in certain exceptional
cases to the nerve-(rnuscle) current," are, however, quite unjustifi-
able. They are more especially contradicted by the fact that, as
was pointed out by Hermann, break twitches also appear on
merely diminishing the current (in negative variations of intensity),
in which case there is usually 110 polarisation current, since the
anode can never become kathode if the diminution is less than
half.

There is yet another point of view from which it appears
possible to approach the question of whether the electrotonic
incremental current is due solely to physical current escape, or to

314 ELECTRO-PHYSIOLOGY CHAP.

physiological alterations of the nervous substance. Something
may be learned from the reaction of electrotonic currents on
exciting the nerve, i.e. the current of action in electrotonised nerve.
The first of these points was investigated by Bernstein (50).

He began by examining into the alterations of the negative
variation of the demarcation current, when a tract of nerve is
simultaneously traversed above or below the exciting tract by a
constant current. If the latter is, in the first place, very weak,
the polarising electrodes being also so remote from the trans-
verse lead-off that any perceptible interference of electrotonic
currents must be excluded, there will, when the exciting elec-
trodes in connection with the secondary coil of an induction
apparatus are placed between the polarised and led-off tracts of
the nerve (are, i.e., " infrapolar "), regularly be an augmentation of
the negative variation with the descending, a diminution of it
with the ascending, direction. The contrary effect occurs on
exciting above the polarised region of the nerve.

These results obviously agree in the main with the electro-
tonic alterations of excitability as determined by Pfliiger, since
the galvanometer merely takes the place of the normal index
of muscular excitation. But if the polarising electrodes are
brought nearer to the led-off transverse section, so that the
electrotonic differences of potential are at first weak, and sub-
sequently augmented, — the demarcation current either diminish-
ing (in the negative phase) or growing stronger (positive phase),
according to the direction of the polarising current,— there will
then, with infrapolar tetanising excitation, be a distinct decrement
of the negative variation in the negative phase of electrotonus,
produced by descending current ; an increment, on the other hand,
in the positive phase, with ascending current. In the first case
the negative variation may, if the strength of the polarising
current exceeds a certain limit, be reduced to 0, or even reversed
in sign. The former invariably occurs when the demarcation
current vanishes altogether in the negative phase. If, on the
other hand, the current is reversed, the P.D. increases during
excitation in the same direction. There is thus " a distinct de-
pendence of the negative variation upon the strength and direction
of the entering electrotonic phase. If the latter augments the
nerve current, the' negative variation increases also ; when it
diminishes it, the negative variation is also diminished, and

ELECTROMOTIVE ACTION IN NERVE

falls to zero, so soon as the led-off current disappears entirely
in the negative phase. The variation consequent on excitation
is therefore invariably negative to the initial sign of
the nerve current." As Bernstein remarks, these results are
easily explained on the assumption " that the current led off from
the nerve in a state of electrotonus reacts like an ordinary nerve
(demarcation) current. The weaker it is, the weaker is its
negative variation, and vice versa. The two disappear together,
just as the negative variation disappears on leading off from
two symmetrical points of an unpolarised nerve, and reversal of
the current reverses the sign of its variation also" (I.e. p. 622).

Bernstein established by further experiments (in which the
excitation, whether suprapolar or otherwise, along the continuity
of the nerve, was led off from two longitudinal contacts) that the
electrotonic incremental currents give a precisely similar reaction
on exciting medullated nerve to that of the ordinary demar-
cation current. This appears most plainly when the polarising
and exciting electrodes are applied to either end of the longest
nerve available, the lead-off being from two points of the inter-
mediate tract. Since in this case the electrotonic alterations
are not obliged to pass the point of excitation, nor the excitation
the polarised tract, in order to reach the leading-off circuit, the
effect of excitation on electrotonic currents may be investigated
in its integrity. While Bernstein explains these observations by
a diminution, consequent upon excitation, of the energy or activity
of the supposed electromotive molecules, Hermann is led, by his
interpretation of the galvanic manifestations in electrotonus, to
refer these facts to alterations of intensity in the negative wave
of excitation, during its passage through the nerve, when the latter
is polarised. " It is indeed more pronounced at any point of
the nerve, the more strongly positive and weakly negative the
polarisation of the latter, i.e. it increases when it is becoming
algebraically more positive, and diminishes when it advances
upon more negative points " (Hermann's law of the " polarisation
increment " of excitation).

VII. THEORETICAL

Although it is hardly possible at the present time to formu-
late any theory of electrical excitation that shall cover all its

316 ELECTRO-PHYSIOLOGY CHAP.

manifestations, it still seems advisable, in view of the previous
data, which are based upon a great number of single observations,
to attempt to reach certain general standpoints whence a
survey of the whole department shall become possible. In the
present state of our knowledge it is obvious that this can only be
the most general orientation, and we may perhaps say with justice
that here, as in other departments of physiology, the final explana-
tion is more remote than seemed probable at no very distant
period. Du Bois-Eeymond's brilliant discoveries roused a hope,
amounting even to conviction in many minds, that the molecular
theory — so acutely conceived and fraught with such weighty
consequences — pointed to a real physical comprehension of all
phenomena of nerve and muscle activity, although it was clear
from the beginning that chemical processes played a no less
important part. So strongly, however, had the first view obtained
the ascendant, in consequence of the overpowering effect of the
data arrived at in experimental physiology by purely physical
methods, that there was no hesitation in finding a parallel between
muscle and nerve, and dead, inorganic bodies. As against this
there has of late been notable progress, most workers now insist-
ing on the chemical aspects of vital function, or at least regarding
these as equal with the physical processes. Du Bois-Beymond,
indeed, subsequently defined the electromotive molecules, which
he regarded as the constituents of nerve and muscle, as a definitely
orientated crowd, with pronounced chemical activity, and Bern-
stein, to whom we shall return, took the same view. Neverthe-
less, in judging of the significance of this hypothetical molecular
structure to vital processes, and more particularly to electromotive
changes in the activity of nerve and muscle, stress was laid, not
on the concomitant alterations of intra-molecular constitution, 1 >ut
on the physical change of place of each molecule. Du Bois-Bey-
mond himself never attempted to apply his theory to the explana-
tion of excitation per se, or its propagation from the seat of direct
stimulation. He was contented to derive the correlative galvanic
manifestations from it, and expressly warns us against considering
the " pile-like" polarisation of the nerve, by which he accounts for
electrotonus, to be identical with " the process which conditions
movement and sensation" (23, p. 385). Notwithstanding this,
there is no lack of conjectures which in this respect far outstrip
those of the founder of the molecular theory ; and it is interesting

x ELECTROMOTIVE ACTION IN NERVE 317

(as well as characteristic of the physical considerations which till
recently prevailed in physiology) to study the theories which
were subsequently expressed as to the nature of electrical ex-
citation in particular, from the starting-point of the molecular
hypothesis. In vol. i. of Funke's excellent text-book (2nd ed.
IS (3 3) the following characteristic statement occurs on p. 859 :
" The exciting electrical current disposes the molecules of the
nerve between the electrodes in a dipolar arrangement, on the
system of the voltaic pile ; the molecules which lie at the edge of
the dipolar layer first produced by the electrical current attract
those which lie beyond the electrodes, and are directed contrary
to the exciting current. These again act upon the next inverted
series, and so on, until all the molecules are arranged down to the
end of the nerve like a pile. It follows that at the moment
when electrotonus is produced in the tube of the nerve, a process
of transmission takes place, analogous with the course of a wave
along a trough filled with water. In this last case we learn from
physics that there is a progressive displacement of the single
particles of fluid, at a given rate, from the point at which the wave
is excited to the end of the trough : in nerve there is a progres-
sive displacement of the molecules from the excited spot to the
two ends in succession, in consequence of the electrical action at
a distance of each molecule upon its neighbours. The propaga-
tion of this molecular movement occurs like that of the wave of
water, with comparatively low and measured velocity. A process
of transmission corresponding in some degree with the negative
wave occurs in the nerve-tube at the moment when electrotonus
ceases. When the exciting current is interrupted, the molecules
between the electrodes return by virtue of an unknown directive
force to the peripolar arrangement; their directive action upon
those external to them consequently disappears — the latter also
return to the peripolar disposition, along with those succeeding to
them, and so on to the end of the nerve. The attraction of the
molecules at the close of electrotonus (opening of the current) is
opposite in direction to that at its commencement ; the direction
of transmission is the same, analogously with the relations of the
positive and negative wave of water. We have already seen that
the beginning and end of electrotonus, the closure and opening of
the exciting current, are accompanied by a twitch of the muscle
connected with the nerve, i.e. that the muscle twitch due to the

318 ELECTRO-PHYSIOLOGY CHAP.

arrival of excitation at the muscular end of the nerve occurs
at the two moments in which the progressive change of position
in the molecules of the nerve reaches the molecules of that end of
the muscle. We have seen that a twitch of the muscle accom-
panies every sudden alteration of density in the exciting current ;
here too, as may easily be shown, the twitch which notifies the
state of excitation coincides with a motion propagated in the
nerve from molecule to molecule in succession till it reaches the
muscle. The pile-like arrangement in electrotonus is not quite
perfect, i.e. the molecules directed contrary to the direction of
the pile are turned not quite at an angle of 180°, but only at
fractions of the half-circle, of different magnitudes. The size of
this revolution depends, apart from other conditions, upon the
density of the exciting current. If this density is suddenly
increased to a certain degree, then each molecule in order turns
a fraction farther, as directed by its neighbour ; conversely each
molecule turns back a fraction on the momentary diminution
of the current density. This progressive and partial revolution
of the molecules already deflected out of the peripolar disposi-
tion is, like the original rotation at the beginning of electro-
tonus, accompanied by a twitch of the muscle ; while no twitch
occurs so long as the molecules are at rest, no matter whether
they are peripolar or more or less dipolar in arrangement, or
whether the rotation of the single molecules follows gradually at
greater intervals, as is the case in gradual increase or decrease
of current density. The more considerable the instantaneous
rotation communicated from neighbour to neighbour, the greater
will be the state of excitation expressed by the degree of the
muscle twitch."

"A persistent and apparently constant state of excitation in the
nerve is produced by a current interrupted at short intervals (either
by homodromous or by alternating and heterodromous shocks) :
here we must picture each of these short currents as accompanied
at its commencement and termination by movements of the mole-
cules of the nerve, so that during electrical tetanisation the mole-
cules undergo a rapid series of rotations in different directions.
Under these circumstances, therefore, the transmitted movements
of the electromotive molecules, and the excitatory condition, co-
incide in the electrically-excited nerve ; neither is seen without
the other, neither outlasts the other. The two must therefore be

x ELECTROMOTIVE ACTION IN NERVE 319

intimately related, if they are not identical; i.e. the transmitted
state of excitation is constituted by the transmitted movement of the
electromotive molecules"

The difficulties in the way of such a schematic and one-sided
point of view, under even the most favourable instances of excita-
tion by the electrical current (e.g. the fact of the rapid diminution
of intensity of electrotonic action with distance from the point of
excitation), have not prevented attempts to explain the mode of
action of other stimuli on the same principle. Eckhardt, for
instance, thought it possible to refer the effect of chemical excita-
tion of the nerve to a transmitted change of position of the
supposed molecules, starting from the erroneous presumption that
the necessary condition of every non-electrical excitation is the
momentary death of the excited part of the nerve. The
destruction of the electromotive molecules in the part that has
been killed, and consequent loss of their directive influence on
their uninjured neighbours, causes these to take up new positions,
and thus progressively alters the position of all the following
molecules.

But even the simple molecular theory of electrical excitation,
as set forth above, is shown to be wholly untenable, so soon as the
law of the exclusively polar excitation of " excitable " substances
is recognised as universally valid. In particular, the evidence
brought forward by Pfliiger to show that there are antagonistic
changes of state, expressed in opposite alterations of excitabilty
in the vicinity of the two poles of a constant current led through
the nerve, as well as the further proof that excitation starts at
closure from one electrode only (the kathode), at opening from
the other (the anode), cannot, as is evident even from the
standpoint of the molecular theory, be reconciled with the
idea of complete identity between the progressive " pile-like "
polarisation and excitation. For it is not conceivable that
the molecule should change its position at closure at the kathode
only, on opening, on the contrary, at the anode ; much rather
would every point of the whole tract traversed participate equally
in the discharge of the excitatory process, since the primary
changes of position of the molecules, according to du Bois' theory
of electrotonus, occur equally between the two poles throughout
the intrapolar area.

Without directly subscribing to du Bois-Reymond's molecular

320 ELECTRO-PHYSIOLOGY CHAP.

theory, Pfliiger (32) has very acutely tried to establish a view
associated, on the one hand, with the idea of a molecular structure
of the nervous substance, and illustrating its essential phenomena
under the figure of physical alterations within the system, while,
on the other, it is in line with all the experimental data known
up to the present. We shall mainly refer to the lucid
account which Funke (Physiol. 4th ed. i. p. 865 ff.) gives of
Pfliiger's theory. Pfliiger starts with the presumption that there
is in nerve — as, indeed, in all " excitable " substances — a combina-
tion of molecules " which constantly strives to enter into motion,
but cannot, because there is an obstacle, a molecular inhibition.
Since the molecular combinations of the system have a constant
tendency to movement, there must be a constant force which
drives them. But inasmuch as the molecules remain at rest, the
force of inhibition must be equal and opposite to the former "
(Pfiiiger, I.e. p. 478). In the resting condition of the nerve, the
two forces of molecular energy and molecular inhibition are in
equilibrium, the latter being maintained by given forces at a given
position, which it instantly recovers when other forces working
upon it have produced a temporary disturbance. Displacement
of the elastic molecular inhibition in a double and opposite direction
must further be possible, the conditions for discharge of energy
being induced by the displacement in one of these directions, in
such a way that more potential is converted into dynamic energy
in proportion as inhibition is displaced in one direction, while
displacement in the opposite direction, on the contrary, produces
accumulation of potential energy.

Pfliiger gives a graphic figure of the mechanism of discharge in
any cross-section of the nerve. A cylinder bent at right angles
(ABC, Fig. 220) carries on its horizontal limb AB a water-tight
piston D, which is movable in the direction of the arrows ab and
cd. A compressed spring fastened to the piston presses against it
on one side, and impels it with a certain force in the direction
ab. On the other side, the fluid poured into the vertical arm of
the cylinder pushes against the piston, with the hydrostatic
pressure corresponding with the height of the column of fluid
in the vertical limb BC, and tends to push the piston in the
direction cd. The piston will obviously come to rest in
that position at which the tension of the spring, and the pressure
of the column of fluid, are in equilibrium. Behind the piston

ELECTROMOTIVE ACTION IN NERVE

321

FIG. 2-20.

there is an opening g in the horizontal arm of the cylinder,
which Pfliiger conceives to be spiriform, its highest point lying next
the piston. If the elasticity of
the spring is increased, it presses
more strongly upon the piston,
pushes it farther from the opening
g, and displaces the fluid in front
of it, which then rises higher in
the vertical limb, and there is in-
creased hydrostatic pressure. If,
on the other hand, the elasticity
of the spring is diminished, the
fluid displaces the piston in the
opposite direction cd, and pushes
it more or less away from the
opening g, which is then reached
by the fluid, which, on streaming out, acquires vital energy deriving
from the height of fall. With this streaming out, the hydrostatic
pressure diminishes, so that the force of the spring gradually
pushes the piston back again over the opening and ends the
discharge.

We have next to see how this schematic mechanism explains
the reaction of the living transverse section of the nerve with
respect to excitation, conductivity, and excitability, and, in the first
place, the phenomena and laws of electrotonus. This explanation
follows simply from the following hypothetical premiss as set out
by Pfliiger. The electrical current flowing through a portion of
the nerve alters the force of molecular inhibition, and this alone, in
a direct sense, with no immediate modification of potential energy.
The effect of current on the inhibitory force is to increase it in
the region of anelectrotonus, and diminish it in that of katelectro-
tonus, i.e. the elastic force of the piston-spring increases in all
sections of the cylinder, which represent anelectrotonised sections
of the nerve, and decreases in those that are katelectro-
tonised. Further, in the anelectrotonic region the inhibitory force,
i.e. the piston D, is displaced in the direction of the arrow ab,
whereby the potential energy, i.e. the height of the column of fluid
at BO, increases, while in the katelectrotonic region, on the con-
trary, the piston is displaced in the direction cd, so that potential
energy is indirectly diminished. A positive increment of inhibi-
VOL. n Y

322 ELECTRO-PHYSIOLOGY CHAP.

tory force is therefore the indirect cause of a positive increment of
potential, and, conversely, a negative increment of the one tends
to negative increase of the other. On this assumption the de-
pression of excitability in the anelectrotonised parts, and its rise
in such as are katelectrotonised, is quite intelligible : the greater
elastic force of the inhibitory spring in the anelectrotonic region
involves a greater expenditure of force in order to push back the
piston to the opening of the cylinder-sections, than in the normal
state ; the diminished energy of inhibition in the region of kat-
electrotonus involves less force. It is harder to explain, first,
how with low intensity of polarising current an excitation
generated at any transverse section can be transmitted through
katelectrotonised as well as anelectrotonised tracts in the
same way as through the nerve in the natural state (and, strictly
speaking, this is not the case), — so that the stronger excita-
tion discharged above an ascending current produces a more
vigorous twitch than in the natural state, although it must be
transmitted through the anelectrotonised parts, which, with direct
excitation, give less response : secondly, how it is that at a consider-
able strength of polarising current the anelectrotonised parts lose
their conductivity also. These difficulties were, however, surmounted
by Ptiiiger. The conduction of excitation set up at any transverse
section is effected by the expenditure of the dynamic energy
discharged at the seat of stimulation upon the displacement of
molecular inhibition in the next section, the energy thereby
released in the second section displaces the molecular inhibition
in the next, and so on. The molecular inhibitions are less easily
displaced in the anelectrotonised parts in consequence of the
increased elasticity of the spring, more easily displaced in the
katelectrotonised parts, than under natural conditions. The fact
of unaltered conductivity in weak electrotonus therefore indicates
that in all conducting sections of the nerve, the magnitude of dis-
placement of the molecular inhibitions depends entirely upon the
amount of dynamic energy set free at the directly-excited trans-
verse section, and is proportional with the same in every section,
irrespective of whether the displacement of inhibitions is facilitated
or hindered. This is only possible if, when excitation is trans-
mitted from one section to the next, the total sum of dynamic
energy released is not consumed in the displacement of molecular
inhibition : such a proportional aliquot part only being required as

x ELECTROMOTIVE ACTION IN NERA^E 323

suffices for the extent of displacement involved by the strength uf
stimulus, viz. a larger proportion in the region of anelectrotonus,
where displacement is less easy ; a smaller amount in that of
katelectrotonus, where it is facile. Pfl tiger illustrates this
hypothesis by the figure of a wheel turning on a horizontal
axis, its revolutions being aided or hindered by the greater or
less pressure of a sliding spring. This wheel carries, at the
peripheral end of a horizontal spoke, a laterally -projecting,
horizontal paddle. A thin stream of water falls on this from
above, and thus presses down the wheel, until the paddle is pushed
out of reach of the stream of water. The proportion of the falling
stream of water, i.e. of the dynamic energy available, required by
this constant revolution of the wheel, is greater in proportion as
the spring presses more heavily upon the wheel, and the latter
therefore revolves less easily. The reason that the anelectro-
tonised parts lose their conductivity in pronounced electrotonus
would accordingly be that, in consequence of the excessive rise of
inhibitory energy, the total sum of active energy discharged by the
stimulus is no longer adequate to bring about the corresponding
displacement of molecular inhibition, just as, with undue pressure
of a spring against the wheel, the whole column of water is
inadequate to move the paddle, with the wheel, beyond its reach.
The fundamental law of electrical excitation at the poles, as laid
down by Pfliiger, whereby the commencement of katelectrotonus
produces the closure twitch, the disappearance of anelectrotonus
the opening twitch, is explained by himself as follows, upon this
theory. The commencing anelectrotonus reinforces the inhibitory
energy, and therefore displaces the piston D of the schema in the
direction of the arrow cib, driving it away from the opening of the
sluice ; obviously no fluid can then escape from the opening g. On
the contrary, the streaming out, i.e. the conversion of potential into
active energy, is now even less possible than in the previous rest-
ing state of inhibition ; it is therefore impossible that excitation
should ensue from the entry of anelectrotonus. The opposite occurs
at the region of the kathode. The commencing katelectrotonus
diminishes inhibitory energy, weakens the elastic force of the
piston spring, the piston is pushed by the overwhelming hydro-
static pressure in the direction of the arrow ccl, the mouth by
which the fluid escapes is freed, — in other words, there is a dis-
charge of potential energy. If the energy lost in the discharge

324 ELECTRO-PHYSIOLOGY CHAP.

is not replaced, the latter can only be instantaneous ; for the outflow
of fluid reduces the hydrostatic pressure in BG, the spring once
more pushes the piston D over the opening ; there could only be
a momentary closure twitch. But if the potential energy given off
is replaced, the discharge will also continue, like the outflow of
fluid, provided always that fluid is poured into the vertical limb
of the cylinder in the same quantity that flows out, i.e. there is
closure tetanus. The opposite relations obtain on opening the
current. At the moment of opening, the previous rise of inhibitory
energy in the region of anelectrotonus returns to the normal ;
potential energy then, of course, predominates, displacing the
inhibition in its own direction, i.e. in the line of the arrow cd.
The retreating inhibitions, however, come to rest as little as a
pendulum, on again reaching the equilibrium from which they were
driven by the anelectrotonus. They go slightly beyond it, so that
the mouth g is opened for a moment for the discharge of the fluid ;
this produces the opening twitch. It is obvious that no potential
energy can be set in the katelectrotonised region, when, at the
moment of opening the current, the reinforced elasticity of the spring
displaces the inhibitions in the direction of the arrow ab, i.e. there
can be no excitation. The hypothesis based on the phenomena
of the law of contraction, to the effect that the closure of a given
current excites more strongly than its opening, follows as the
naturally corollary from Pfliiger's theory of discharge ; for, if at
the closure of the current the inhibitions at the anode are as much
displaced in the direction ab as they are at the kathode in the
direction cd, then, at opening, the inhibitions in the anelectro-
tonised region are not displaced as far from the normal, in the
direction cd, as the inhibitions in the region of katelectrotonus at
closure, i.e. there cannot be the same discharge of potential energy.
If a rapid succession of brief electrical currents is sent into the
nerve, the apparently continuous tetanic excitation is due to the
continuous alternating discharge of energy at anode and kathode,
which persists as long as metabolism continues adequate between
every shock to replace the energy dissipated in the last shock.
The mechanics of the law of contraction are thus simply explained
on Pfliiger's hypothesis.

We have next to see whether it can account for the after-effects
of the constant current, the so-called modifications of the nerve as
above described. We have seen that a state of heightened

x ELECTROMOTIVE ACTION IN NERVE 325

excitability (positive modification) appears, and slowly subsides, in
the previously anelectrotonic portion of the nerve, on opening the
current. Pfliiger takes this to mean that the action of the
constant current weakens the energy of molecular inhibition,
which is highly probable, seeing that, according to his theory,
the current acts during its passage upon the inhibitory forces, but
not directly upon potential energy. The weakened inhibitory
force left over at break must obviously present less resistance to
the transformation of potential into active energy than it would
on resuming the proportions normal to it before closure of the
current ; and this explains how the nerve that is depressed by
current comes to be more excitable, i.e. apparently invigorated.
The restitution of the normal inhibitory forces, as gradually
brought about by metabolism, explains the subsidence of the positive
modification. The brief negative modification that appears in the
region of katelectrotonus after opening the current is explained by
Pfliiger as a momentary deficit of potential energy, and this again
by the fact that katelectrotonus (sv^ra) keeps the sluice permanently
open, i.e. causes a continuous outflow of potential energy.

Lastly, with regard to the after-effects of the polarising current,
manifested in a more or less prolonged discharge of potential
energy, Pfliiger has shown that the opening tetanus starts from
the region of anelectrotonus; this indicates that there is, on opening
the more sustained currents within the previously anelectrotonised
tract, a persistent discharge of potential energy. If we represent
this as the displacement of the piston by the reinforced spring, and
assume that the column rises so much under the action of the water
in A, that the piston is pushed back again to the spiral opening,
there will be then a considerable accumulation of water at A.
If the elasticity of the spring is suddenly depressed, the column of
water will push the piston far back, and a greater quantity of
water will flow for a longer time, until equilibrium is restored
again. This process corresponds with the opening tetanus.

Pfliiger's theory thus succeeds in presenting the main phenomena
of electrical excitation of nerve under the figure of a complicated
mechanical schema : it gives no real explanation of them. It
seemed, however, advisable to give the theory in detail, seeing
that it found wide acceptance. While Pfliiger himself developed
his hypothesis independently of du Bois-Keymond's molecular
theory, Bernstein attempted later to establish a direct relation

326 ELECTRO-PHYSIOLOGY CHAP.

between them (28, p. 52). The "molecular tension," i.e. the
potential force inherent in each molecule, which "accumulates
persistently in the process of nutrition," is identified by Bernstein
with the electrical E.M.F. of du Bois-Reymond's peripolar mole-
cules, as neutralised in excitation, with correlative movements of
the molecules. " The tendency in the latter to neutralise their
electrical E.M.F. is opposed by an inhibitory force (unknown to
us in its intrinsic nature), which prevents any movement of the
molecules in the resting state " (Pfliiger's " molecular inhibition ").
Whether this is the result of friction, of elasticity, or of both is
uncertain ; there is a play of forces " which tends to maintain
the components of the molecules (i.e. the peripolar molecules
formed of two dipolar bodies) in their natural position, and re-
stores them to the same after each alteration." Any stimulus,
of whatever kind, " disturbs the natural position of the molecules,"
whereby molecular inhibition is interrupted, and there is neutral-
isation of the electric potential. As regards electrical excitation
in particular. Bernstein accounts for the reinforcement of mole-
cular inhibition at the positive pole, and consequent decreased
mobility of the molecules (diminished excitability), as well as the
lowered inhibition and raised mobility (increased excitability) at
the negative pole, by the attraction or repulsion exerted by the
polarising electrodes upon the peripheral molecules next to them.
The positive electrode fixes these, as it were, in their place, the
negative zones being turned towards the pole, while the kathode,
by repulsion of the same zone, renders them more mobile. This is
why, at closure of the current, excitation proceeds from the kathode
only. The molecules at the positive pole remain in their normal
position ; " at the negative pole, on the other hand, inhibition is
weakened, the exciting energy preponderates and causes excita-
tion." On opening the circuit, inhibition falls suddenly at the
positive pole, and the increased potential energy of the molecules
is now discharged, and induces excitation. Electrotonic altera-
tions of excitability, and other phenomena, receive a similar
interpretation.

The dictum long since expressed by du Bois-Eeymond
(Untersuchungen, II. i. p. 387), to the effect that yalciniir
excitation is nothing more tlian the first stage of electrolysis in
excitable tissues, may still (though in a somewhat different
sense) be accepted as the most apt theoretical definition of the

x ELECTROMOTIVE ACTION IN NERVK 327

physiological action of current. It is singular that it should
date from a time at which the law of polar excitation was still
unknown, since the evidence of the latter again turns our
thoughts, almost involuntarily, in the same direction. Von
Bezold expresses himself directly in this sense at the close of
his detailed investigation into the electrical excitation of nerve
and muscle. In the fact that " the molecular process of excitation
arises with such regularity at and during closure, and on opening
the current, at a definite pole, and not in the whole extension of
the tract through which the current is passing," he sees evidence
that " the excitatory action of the galvanic current is to be sought in
the chemical effects produced ~by the current in the moist conductor
n-hich it traverses" (I.e. p. 237). He recalls the antagonism of
the polar alterations, and Kiihne's remark that a tract of muscle
traversed by current shows coagulation in the region of the anode,
and corrosion at the kathode, as well as Jtirgensen's experiments
upon the cataphoric action of the current, and concludes from
all these data that the excitatory process is nothing more than
an effect of electrolysis due to current. "Electrical excitation
would, accordingly, be nothing else than a definite form of chemical
stimulation — the process, like that of the generation of hydrogen,
occurring exclusively at the negative pole, during closure of the
current" (I.e. p. 328). The arguments adduced (by von Bezold
in particular) to show that the process of excitation is dis-
charged at the kathode during the entire passage of the current,
are obviously quite in line with this theory.

The greatest advances in the direction indicated came, how-
ever, from Hermann's electro-physiological researches, which most
of all contributed to bringing forward the chemical side of function
in all these vital phenomena, while the resolution with which he
attacked du Bois-Eeymond's molecular theory helped to remove
one of the greatest hindrances to the fruitful development
of general nerve and muscle physics. Hermann's law of the
current of action (to the effect that each excited part is negative
to parts that are less excited, or unexcited) forms, indeed, with
the law of the exclusively polar action of electrotonic currents in
excitable tissues, the basis of all modern opinion on the subject,
and gives the key to the interpretation of a vast number of
experimental data. Hering, again, like Hermann, has steadily
maintained that all the processes in excitable living matter are, in

ELECTRO-PHYSIOLOGY CHAP.

first degree, to be regarded as chemical, and that " the true
chemical nature of vital processes must not be overlooked in
their physical symptoms" (24, p. 59). Hering has developed
upon the most general grounds, and, as it were, in final
consequence of his physiology of the senses, a theory of the
functions of living matter (more particularly under electrical
excitation), which, though as yet little recognised, is really the
most comprehensive expression of all the data relating to this
department. By it he is able to derive and to explain all facts
quite simply from a few fundamental postulates of metabolism.
Hering starts with the proposition that, when a muscle or nerve
is longitudinally traversed by current, the excitable substance is
altered in an opposite sense at the physiological anode and kathode :
more correctly, antagonistic alterations in the chemical state of
the substance are set up at the two poles — since at all points by
which current enters the uninjured living matter, the assimilatory
process preponderates, and (to use Hering's expression, cf. p. 71 f.)
effects an " allonomous ascending" alteration, while dissimilation
(disintegration) prevails at the collective points of exit, inducing
" allonomous descending " alteration. Every excitation, in the
ordinary sense of the word, is undoubtedly characterised by the
predominance of the dissimilatory process, it being immaterial
whether this process is confined to its seat of origin, or propagated
further by conduction. Under all circumstances, therefore, the
physiological kathode is the seat of excitation lasting throughout
the closure of the current, the closing excitation. Hering's
account of the processes at the anode, developed as the corollary
to his theory of visual sensation, is less obvious.

" Just as we may conceive of external stimuli which compel
the living substance to vigorous dissimilation, so others are
conceivable which enforce greater activity of assimilation. This
increase of assimilation, which is no longer purely autonomous,
and is not balanced by corresponding activity of dissimilation,
modifies the living matter in a direction contrary to that
described above as ' below par', and therefore to be denoted ' above
par.' At the close of such excitation the living matter is over-
nourished ; its disposition to assimilation is less than before, in
ratio with the intensity and duration of stimulus, and the
corresponding preponderance of allonomous assimilation over
autonomous dissimilation — the disposition to dissimilation is pro-

x ELECTROMOTIVE ACTION IN NERVE 329

portionately greater. Hence, at close of excitation, autonomous
dissimilation preponderates over autonomous assimilation, and
the living matter, owing to its gradual depreciation, returns to
par" (I.e. p. 39). The effect of the anode upon muscle and nerve
is, according to Hering, to be regarded as a similar assimilatory
stimulus. If, e.g., the living matter had previously been at par,
and, therefore, in autonomous equilibrium between D and A, it
rises above par at the point where the current enters. When
the current ceases to flow, there is a corresponding autonomous
down change at the point of entrance, which is the more rapid in
proportion as the substance has risen above par during the
previous " up " change. Thus, the point of entrance may become
the starting-point of a second excitation (" opening excitation ")
spreading over the fibre. At the point of exit, on the contrary,
there is an autonomous up change on breaking the current,
provided this point has not been seriously injured by the previous
action of the current, or, generally speaking, disturbed in its
assimilatory conditions.

" Since a rapid allonomous ' down ' change occurs during the
passage of current, at the point of exit, this point is negative to
the rest of the fibre (in so far as the latter is not in transmitted
' excitation ') ; while the point of entrance, in consequence of
localised allonomous ' up ' change, gives the opposite reaction.
This causes an internal current in the fibre, opposed in direction
to the led-in, foreign current. This internal current weakens the
foreign current. It has been termed a ' polarisation current.'
But inasmuch as it is a physiological keterodromous current, an
intrinsic vital manifestation, it must be rigorously distinguished
from those polarisation currents which are not properly physio-
logical, since they do not arise from the up or down changes in
the living substance that occur at the points where current enters
or leaves it; for heterodromous currents may also appear, with
artificial excitation, in dead tissues, or parts that are no longer
intrinsically excitable in the still living organ.

" Given normal activity of living matter, an autonomous down
change may, as we have seen, appear at the anode, on opening
the foreign current — this point being now negative to the rest of
the fibre, in so far as the latter is not undergoing progressive
descending alteration ; while the kathode becomes positive to the
rest of the fibre, in virtue of an autonomous ' up ' change. A

330 ELECTRO-PHYSIOLOGY CHAP.

physiological current is thus developed in the fibre, in the same
direction as the opened foreign current. This physiological
current may be termed homodromous, in contradistinction to
that previously denned as heterodromous. It appears the more
certainly in proportion as the substance is more energetic ; and the
less the vital processes are affected by the foreign current, the
more rapidly will the allonomous alterations, induced by the latter
(after-effect of excitation), disappear, and the opposite autonomous
changes develop, when it is broken. The homodromous physio-
logical current is more or less likely to be disturbed by complica-
tion with physical polarisation currents, heterodromous to the
foreign current.

" If a foreign current is led through the central portion of a
medullated nerve, the points by which it enters and leaves the
excitable matter spread far beyond the contacts of the physical
electrodes. So far as these points of entrance and exit extend,
there is correlatively with the distribution of the lines of current
a purely physical ' an- and katelectrotonus,' as may be de-
monstrated, e.g. on a dry hollow stalk of grass without internodes,
or on a bundle of the same stalks that have been lying for some
time in distilled water, or weak alcohol, and are then moistened
externally, and saturated internally, with salt solution. From
this wide distribution in the excitable substance (axis-cylinder) of
the nerve, of the collective points at which the foreign current
enters and leaves it — i.e. the physiological anode and kathode
proper — those ' up ' and ' down ' changes develop respectively in
the nerve, which are fundamental to physiological clcctrotonus
(Pfluger). Both down and up change may, after closure of the
foreign current, be transmitted along the nerve beyond the tracts
altered in a kathodic (negative) or anodic (positive) sense by the
direct action of the current, so that fugitive alterations may occur
even at very remote parts of the fibre, as expressed in its electro-
motive reactions. On breaking the foreign current, an opposite
alteration takes place at the points of entrance and exit, with
corresponding changes in the living matter, i.e. autonomous
descending or ascending alterations respective!}". The two points
have interchanged their parts ; the ascending alteration, character-
istic of physiological anelectrotonus, now appears at the former
kathode, the descending alteration, significant of physiological
katelectrotonus, at the former anode.

x ELECTROMOTIVE ACTION IN NERVE 331

" 111 non-medullatecl nerve, e.g. olfactorius, and in muscle,
where the excitable substance, unlike medullated nerve, has no
imperfectly -conducting sheath, the characteristic diffusion of
entrance and exit points is wanting. The electrical phenomena
which depend upon this diffusion (due, in the first place, to rela-
tions of conductivity), together with the physiological local con-
sequences of the same, are accordingly absent. On the other
hand, the phenomena caused by transmission of the ascending or
descending alteration induced at the anode or kathode of the
foreign current are more or less plainly exhibited both in non-
niedullated nerve and in muscle-fibre.

" If a tract of nerve has been traversed for some time by a
foreign current, and the current is then reversed, the excitable
matter at the point of exit (i.e. former point of entrance) will be
absolutely, or relatively, above par, and thus has a greater dis-
position to ' clown ' change ; the current accordingly produces a
more rapid descending alteration than would otherwise be the
case (Yolta's alternative).

" Muscle-fibre, as compared with nerve-fibre, has the great
advantage of expressing the excitation due to descending altera-
tion, by change of form of the part affected ; while a foreign current
can, moreover, enter and leave at the natural ends of the fibres.
In the latter case, the allonomous change which occurs on closure
at the point of exit is, in the first instance, transmitted along the
fibre, but when the closure twitch has expired, it persists only
near the point of exit daring closure (persistent kathodic con-
traction), and steadily decreases. Meantime, the autonomous up
change continues at the point of entrance, and may raise the
living matter considerably above par, given adequate strength and
duration of current. At break there will accordingly be an
autonomous down change, which, if sufficiently rapid, may pro-
duce an opening twitch, or persistent opening contraction, near the
point of entrance. Even when this autonomous down change is
so weak that no visible alteration of form can be detected in the
muscle, it may express itself in the physiological homodromous
current (supra], which appears on connecting the anodic end with,
e.g., the centre of the muscle.

" Autonomous ascending alteration cannot always be demon-
strated at the point of exit, on breaking the internal current,
because the autonomous assimilation of the living matter in excised

332 ELECTRO-PHYSIOLOGY CHAP.

muscle is too slow and inadequate a process — as was pointed out
above. Yet in favourable cases the autonomous up change is
exhibited in a physiological homodromous current, that makes its
appearance at break, if the now kathodic end of the muscle is put
in circuit with the centre of the muscle.

" The fact that muscle-, like nerve-fibre, fails to react to trans-
verse passage of current, obviously signifies that living matter is
not intrinsically the same living continuum in the transverse as in
the longitudinal direction ; as appears from optical polarisation
phenomena, and from the relations of elasticity. The failure in
reaction is perhaps clue to the fact that the antagonistic points at
which the current leaves and enters are too closely approximated
in the structural elements traversed at right angles by the current.

" When a strong foreign current has been flowing longitu-
dinally through an uninjured muscle for so long that the
persistent kathodic contraction has already expired, the persistent
anodic contraction (supra) will appear when the current is broken,
and may extend over a large tract of the muscle, and last for a
considerable period. If the current is then closed again, it will
act as an inhibitory stimulus on the contracted muscle, which at
once relaxes completely. The anodic stimulus of the foreign
current, which tends to upward alteration in the substance, now
works against the rapid autonomous down change that prevailed
after break at the point of entrance, and substitutes an up change.
Owing, however, to the previous exhaustive allonomous descending
alteration, there is not inevitably a new closure contraction at
the point of exit.

" Just as the persistent opening contraction of a muscle may
be inhibited by renewed closure of the current, another contraction
depending on autonomous down change may be inhibited by the
action of an anodic current. If, just at the beginning of systole,
a stronger current is sent in through one brush-electrode, the
point of which rests upon the frog's heart (exposed with uninter-
rupted circulation), while the other electrode forms contact with,
e.g., the skin of the throat, a more or less extended diastole of the
heart-wall, starting from the point where the current enters, will
make its appearance. The commencing autonomous down change
is immediately converted, by the anodic action of the current,
into an allonomous up change, and the relaxed part of the cardiac
wall swells out freely in consequence of blood -pressure. The

x ELECTROMOTIVE ACTION IN NERVE 333

contrary effect appears when current leaves the heart by the
brush-electrode. If closure occurs at the beginning of the general
diastole, a new systole will at once appear at the point of exit
(Jcufhodic closure contraction}.

" If the current is left undisturbed for some time in this
last direction, and is then opened during a general diastole, the
wall of the heart near the brush-electrode will not take part in
the ensuing systole, owing to the marked autonomous up change ;
it remains diastolically relaxed, and the systolic pressure of the
blood causes the relaxed point to swell out considerably. This
is the kathodic opening inhibition, which thus expresses itself in
precisely the same way as the anodic closure inhibition above
described, and cannot be viewed as a mere fatigue effect. If, on
the contrary, current enters the wall of the heart for a prolonged
period by the brush-electrode, a contraction appears immediately
after it is broken, in the proximity of its point of exit. This
contraction may even be more pronounced than the natural sys-
tolic contraction, as appears externally from the paler colouring
of the heart-wall. This is the anodic opening contraction derived
from autonomous descending alteration, the analogue of the
kathodic closure contraction described above, which depends upon
allonomous descending alteration.

" The anodic opening contraction and kathodic opening
relaxation are fundamentally analogous with the phenomena of
successive contrast, as observed in other living substances, and
are as little as these to be referred to a mere fatigue effect."

In contrast with this straightforward exposition, the " modified "
molecular theory recently (in 1888) advanced by Bernstein (52)
is unsatisfactory, in spite of its elaborate detail. It starts, more-
over, with certain postulates that are, at least, doubtful. In
the first place, it is held necessary to conceive the living fibres (in
muscle and nerve) as consisting of longitudinal series of mole-
cules, looped together at the natural transverse section of the
muscle (tendon-end), and " polarisable in the fluid which contains
them," although, on account of their close juxtaposition longitudin-
ally, such polarisation can only take place " at the free surface "
of the row of molecules. By this hypothesis (which he believes
to be confirmed by the inexcitability of the artificial cross-section
of a muscle to current), Bernstein explains the inexcitability of
the tissues in question to transverse passage of current, since it

334 ELECTRO-PHYSIOLOGY CHAP.

is inconceivable that there should be reciprocal neutralisation of
anodic and kathodic polarisation, unless the two ions are, so to
speak, in immediate juxtaposition. Is it, however, so impossible
that the two polarisations should neutralise their respective
action upon the living matter, when they merely arise at either
border of a visible fibril ? Bernstein further supposes that his
series of molecules behave in regard to spatial distribution of
polarisation exactly like Hermann's core-model, or the equivalent
medullated nerve-fibre, and he refers the excitation at closure
and opening of the current solely to the appearance of negative
and disappearance of positive ions within the collective molecules
of the living matter under the electrode — a view that recalls the
electrolytic theory of v. Bezold, where electrical excitation is
explained by (or at any rate referred to) chemical stimulation
from the separated ions.

It is, however, under any circumstances difficult to explain
the opening excitation, as also the alterations of excitability
that occur during the passage of current, by a purely chemical
theory of electrical stimulation, and Bernstein was compelled to
lay down further postulates as to the nature and behaviour of
the liberated ions. These are :—

(i.) The negative ion at the kathode (oxygen, or an oxygenated
element) is the cause of the closing excitation.

(ii.) This ion is constantly reduced by a chemical process, in
ratio with the mass in which it is developed.

(iii.) The positive ion at the kathode produces no excitation ;
it is not therefore reduced, but accumulates.

(iv.) The internal polarisation, more particularly at the anode,
neutralises the current in the excitable, polarisable conductor,
save for a proportionate remainder — provided the polarisation
is not maximal.

The active oxygen separated off from the excitable molecules
at the region of the kathode tears apart the labile molecules by
its oxidising action, whereupon the intramolecular oxygen also
cornes into play and induces excitation. The alterations of
excitability during polarisation are taken by Bernstein to mean
that the molecule charged with negative ions (oxygen) is more
easily split up, that charged with positive ions less easily ruptured
than the unaltered molecules. More particularly in the kathodic
region, throughout the closure of the current, there is a slow 1 »ut

x ELECTROMOTIVE ACTION IN NERVE 335

constant development of oxygen, along with its steady reduction
by the oxidisable groups of atoms of the excitable molecules.
" With weaker currents this process is not intensive enough to
liberate the intramolecular oxygen to any appreciable extent,
and thus transmit it as excitation. In principle, however, it is
co-significant with excitation, since there is a constant discharge
of potential energy. The molecule is thereby thrown into a state
of more labile equilibrium, since the freed oxygen slackens
its constitution, i.e. increases its excitability ; the intramolecular
oxygen is thereby more readily liberated by any stimulus." With
the exception of these special views in re the chemical process at
the kathode, and its localisation in definitely arranged and pre-
formed " molecules," Bering's theory conforms to that of Bernstein
in so far as both assume a constant discharge of energy,
or broadly speaking, in other words, a predominance of the
dissimilatory process over simultaneous assimilation throughout
the kathodic region ; i.e. both theories fall within the range of
the preceding experiments.

Bernstein also has detailed views with regard to the processes
at the anode. " The positive ion liberated from the series of
molecules has, of course, opposite chemical properties to those of
the active oxygen at the kathode." Accordingly, there is no
excitation at closure of the current. Bernstein assumes, with
regard to the simultaneous depression of excitability, that " the
positive ion enters into molecular relations with the excitable
molecules of the fibre, and thereby renders the constitution of the
molecule more solid." We may thereby conceive " the positive ion
as an oxidisable component of the groups of atoms in the mole-
cule, the intramolecular oxygen being in consequence more
firmly linked with them as an electro-negative element." Here,
again, it is interesting to note the similarity of views between
Bernstein and Hering, as to the cause of the discharge of an
opening excitation. According to Pfliiger's theory as given
above, anelectrotonus is a state in which there is accumulation of
potential energy corresponding with the increased molecular
inhibition. This is interpreted by Bernstein to mean that " not
merelv is there a firmer combination of the intramolecular

t/

oxygen, but that a greater quantity of it can be assimilated by
the molecule. Anelectrotonus therefore implies a -process of con-
stant assimilation, while the opposite process occurs in katclcctrotonus."

336 ELECTRO-PHYSIOLOGY CHAP.

At break " there is a sudden depolarisation, whereupon the positive
ion at the kathode disappears. The firmer combination of intra-
molecular oxygen suddenly breaks down, and as the molecule
had during the passage of the current collected an over-charge
of the same, which it is no longer able to hold, this portion is
liberated, and causes a rupture of the molecule, co-significant with
excitation." Without going more closely into details of the
explanation of opening tetanus, and the modifications of excita-
bility at break, it may be stated that on this theory the in-
efficacy of transverse passage of current is explained as meaning
" that the positive ion locks each excitable molecule in the same
degree in which the negative ion slackens it. The liberated
negative ion is therefore unable to combine with the oxidisable
groups of atoms of the molecule, and remains stationary." This is
not the place to enter further into Bernstein's elaborate account of
the possible constitution of his hypothetical molecules. He sup-
poses them to consist of N-containing nuclei, longitudinally linked
with atoms of 0, while the free superficies is set with oxidisable
groups of atoms that are rich in C and free of 1ST. These last
react towards the nucleus as electro-positive charges, while the
" assimilated " combining 0 appears at the artificial cross-section
as the electro-negative charge of the nucleus (cf. Fig. 111). The
ions of molecules are not therefore polarisable in the previous
sense, " but are already, in their normal state, charged with certain
ions, as though polarised by a foreign current." We have else-
where shown that Bernstein tries to explain all galvanic mani-
festations in nerve and muscle by this " electro-chemical molecular
theory." Yet it may be doubted whether these profound specula-
tions as to the structure of the molecules, and the constitution of
living matter, are a better foundation for a comprehensive theory
of the correlative manifestations than the straightforward
propositions which Hering derives solely from facts, and from
the fundamental laws of metabolism. And as Bernstein
remarked of du Bois-Eeymond's molecular theory, that it gave
no further outlook on the mechanical and electrical sides, unless
a very one-sided view of the constitution of living matter were
adopted, so many will not fail to say the same of his own " electro-
chemical molecular theory."

In conclusion, a word must be said as to the prevailing
theories of the nature of conductivity of excitation, in which, as

ELECTROMOTIArE ACTION IN NERVE 337

Hermann showed, the electromotive action of the conducting
tissues is perhaps of the first importance. In view of the fact
that muscle as well as nerve can be excited by its own demar-
cation current, as well as by the current of action of a second
preparation, provided the conditions of short-circuiting are other-
wise favourable, it is prima facie not improbable that the internal
short-circuiting of the action current may be an essential factor
in the wave of negative excitation (or contraction) also.

If with Hermann (Handb. d. Physiol. i. 1, p. 256, and ii. 1,
p. 194) we consider the galvanic action of any excited point with
reference to its environment, this is found (as shown by Fig.
'2 '21, E} to consist in the "initiation
of minor currents in its immediate
vicinity," which are short-circuited
within the indifferently conducting
sheath of the electromotive tract.
As in the immediate proximity of

an artificial cross-section, numerous point of fibre. (Hermann.)
lines of current find exit on both sides of the excited segment
at the non-excited surface, and eventually effect an excitation
there, while at the excited point itself there is, on account of the
ingoing lines of current, a tendency to alteration in the opposite
sense. Hermann makes express reference to the presumably
high intensity of these minute currents, in which the short-
circuiting lines are microscopic, so that the resistance is practically
negligible. It is evident that a progressive wave of excitation
may well be produced in this way.

The Action of Nerve upon Muscle

opens out a further question, which has as yet found no solution.

Notwithstanding the fact that muscle possesses the same
independent excitability as nerve, and as living protoplasm in
general, the excitation of striated and smooth muscle occurs, in
the majority of cases, indirectly from the nerve. The actual
process of transmission is thus unknown to us, seeing that muscle
cannot forthwith be regarded as a prolongation of the nerve,
surrounded with contractile substance, although this view has
been advanced on several sides. Here, as elsewhere, it is seen
how the physiological conception of a process may, according to

VOL. n z

338 ELECTRO-PHYSIOLOGY CHAP.

circumstances, be affected by the prevailing knowledge of the
morphology of the substrate. Appreciation of the intimate rela-
tion between structure and function of an element has not always
been as apt as could be desired, and as is indispensable to the
fruitful development of knowledge. The strong physical bias
obtaining in many minds has obscured the perception that it
profits little to substitute general theory and hypothesis for the
certain facts of histological investigation. Now, indeed, it is
universally accepted that histology and physiology are not two
independent departments of science, but are, on the contrary,
intimately correlated, each inspiring and attracting the other.
Physiology is as much concerned with histological data as with
those deriving from physics and chemistry. It is almost super-
fluous to refer to the recent developments of the cell theory, or
to the importance attaching to microscopic methods in general
muscle and nerve physiology, and in the theory of secretion.
The fundamental significance of an anatomical knowledge of
structure to the right interpretation of function has always been
recognised for the motor nerve - endings, and for the electrical
organs to be described below.

Doyere, in 1840, was the first to observe on a micro-
scopic arthropod, the much -discussed Milncsium tardigradu m ,
that the five filaments of nerve entered the muscle -fibres,
and apparently terminated in a conical swelling. The motor
nerve -en dings in striated, skeletal vertebrate muscle subse-
quently attracted most attention, on the one hand from purely
technical reasons, because it was easier to follow the more
coarsely-grained medullated fibres to their extreme termination,
on the other from the possibility of here approaching the
question from its physiological aspect. Frog -muscle, with its
nerves, has thus been the prominent if not the sole object of
all experiments in nerve and muscle physiology. Without
entering into the history of the question, we need only remark
that at the present time, thanks to innumerable researches, more
particularly those of Kiihne (53), it must be regarded as certain
that every striated muscle of a vertebrate possesses one or more
distinct nerve-endings, the structure of which is essentially similar.
When the medullated fibre, usually after frequent bifurcation,
penetrates into the muscle-fibre, its sheath of Schwann coalesces
with the sarcolemma, the axis-cylinder alone passing through to

X

ELECTROMOTIVE ACTION IN NERVE

339

reach the contractile substance ; the medullary sheath, as a rule,
terminates shortly before the definite ending. Stress must be
laid upon the much-disputed fact of the passage of the axis-
cylinder, since, admitting certain premises as to the nature of the
propagation of a stimulus, the sarcolemma would offer no absolute
hindrance. The axis-cylinder seldom remains entire, but exhibits
a more or less copious arborisation (Kiihne's terminal arborisation],
" hypolemmal " in situation, and occurring according to two types,
(a) in amphibia (Fig. 222), (6) in reptiles, birds, and mammals.
The former presents tolerably straight, rounded, or flattened
terminal branches, running parallel with the axis of the muscular
fibre ; these extend widely for some little distance close under

FIG. 222.— Arborisation from frog's gastrocuemius. (Kiihne.)

the sarcolemma, and always end distinctly in a blunt point.
Here and there they bear long, oval nuclei, which Kiihne termed
" end-buds." In contrast with these " branches " are the " plates "
of other vertebrates, where the rarni take a bending and intricate
course, or form laminal, lobed expansions within a small circular
or oval " field of innervation," that rarely comprises the whole
muscle-fibre (Figs. 223-225). It is characteristic of these "end-
plates " that they nearly always present a more or less conspicuous
accumulation of finely -granulated substance set with nuclei
(sarcoplasm), within which are embedded the ramifications of the
axis-cylinder (Kiihne's " end -plate" Fig. 224). In the branched
form this " granulosa " is seldom perceptible, while in the plates it
is frequently well-developed and appears in profile as a projecting
expansion, corresponding with Doyere's expansion in insect-muscle
(Fig. 225).

340

ELECTRO-PHYSIOLOGY

CHAP.

The motor nerve-endings in fishes differ in several respects.
Along with such as correspond completely with the " end-plates "
of the higher vertebrates (Myxine, Raja ; cf. Eetzius, 53), there are
in the same species a proportion of much simpler forms, in which
the axis-cylinder is little if at all bifurcated, after losing the

t;

FIG. 223. — End-plates from muscle-fibre of rabbit (a), guinea-pig (c), rat (&). Gold preparations.

(Kiihne.)

medullary sheath, and lies simply along the muscle-fibre, where
it is visible as a very large number of knotty varicosities (" end-
discs" of Eetzius). Certain amphibians and the higher vertebrates
also present innumerable transitions from the simplest forms of
ending to the most complicated " branches " and " plates." It is
remarkable that a particular type of nerve-ending is sometimes
confined to one muscle, or group of muscles, in the same animal.

X

ELECTROMOTIVE ACTION IN NERVE

341

Iii the eye-muscles of the frog, the predominating nerve-endings
recall the simpler types of low amphibians (Proteus} and tishes
(Eetzius, I.e.). The contrast between eye-muscles and skeletal
muscles in mammals is in this respect even more striking (cf.

1

, Ifc/illlsrt
FIG. 224.— End-plates (fresh) of Laccrta agilis—in 0'6 % NaCl. Expansion with nuclei.

Eetzius, I.e. p. 48). While the former invariably exhibit charac-
teristic end-plates, the latter present terminal arborisations which
vary in a marked degree from the ordinary type, and again re-

FIG. 225. — End-plates from muscle-fibre of mouse. Expansion of the nerve in profile.

semble the forms that obtain in the lower animals. The rami
that extend longitudinally in the muscle are but little branched,
and bear a varying number of " terminal discs." Of interest, too,
are the " simplest forms of end-branches " observed by Eetzius
(I.e. p. 48) in the same object (and confirmed by Biedermann),
which consist of an unbranched non-medullated lateral fork of a

342 ELECTRO-PHYSIOLOGY CHAP.

medullated nerve-fibre, " bearing only a single end-disc." In other
cases the twig runs on without branching, and bears two, three,
or more end-discs, which may be of a considerable size. Every
possible transition exists between these simple forms and the
most complicated ramifications of the axis-cylinder. But what-
ever the mode of ending of the motor nerve-fibres, there is never
with either gold method or methylene blue an " intravaginal
nervous reticulum " in Gerlach's sense (53); the contact between
nerve- and muscle-substance is always distinct and confined to the
immediate vicinity of the point of entrance. It is obvious that
this point is of crucial importance to physiological theory, for our
views of the relations between nerve and muscle would have to
be considerably modified if it were true, as Gerlach says, " that
the presence of nervous elements is implied wherever there is con-
tractile substance, and that no sharp separation between nervous
and muscular tissue can be accepted." Long before any good
results had been obtained with vertebrate muscle (where, owing
to erroneous interpretation of gold preparations, Gerlach's con-
ceptions had been accepted), valuable work was done by means
of methylene blue, with the muscles of certain arthropods.

In the crayfish it is easy to stain the nerves of the trunk- and
tail-muscles so clearly that no doubt can exist as to the finest
endings of the rami of the axis - cylinder. Under such condi-
tions, both the wide band-shaped muscles which run along the
ventral surface of the thorax, and the superficial layers of the
muscles of the tail, exhibit an extraordinary wealth of nerves.
The smallest particle from the surface of a nerve thus stained is
seen under the microscope to be interwoven, and studded with
a more or less dense tissue of the finest axis-cylinders, stained
blue, and characterised by richly varicose swellings. These arise
from the branching of the larger trunks (containing several axis-
cylinders of unequal size, and depth of stain), which traverse the
muscle throughout its volume. Ehrlich, who was first to observe
the effect, is of opinion that this really is an " intramuscular
plexus " (corresponding with Gerlach's " intravaginal nervous reti-
culum "), and that there is a fundamental distinction between the
mode of nerve-ending in these muscles and in those of the ex-
tremities, where (in his words) " the nerves run an isolated course
and form superficial ramifications, which rarely stain with methy-
lene blue."

x ELECTROMOTIVE ACTION IN NERVE 343

It is undeniable that these marked differences exist. Unless
we assume (and in Biedermann's opinion there is no ground for
doing so) that the methylene-blue staining of the nerves in the
claw-muscles of the crayfish is in all cases very imperfect, the
most superficial comparison of two preparations of trunk- and
claw-muscles from the same animals, and similarly treated, is suf-
ficient to show the striking difference in the number of nerve encl-
branches. This expresses itself, on the one hand, in that the
terminal rarni traverse the whole interior of a muscle-bundle,
consisting of numerous larger and smaller groups of striated fibrils,
separated by sarcoglia, on the other by a far more copious branch-
ing of the several axis-cylinders. In contradistinction from these,
the motor endings in the muscles of the claw (as of the extremi-
ties) resemble those which are found in the lowest vertebrates.
In many respects the mode of arborisation and termination of the
nerves in the adductor muscle of the crayfish-claw is of especial
interest. It was stated above that the axis-cylinders, of which
there are always two of different size within the common sheath
of connective tissue, divide dichotomously and very freely, in such
a way that loth axis - cylinders invariably branch at the same
point, at each new bifurcation of the nerve-trunk, down to the
final endings (cf. Fig. 150). In the coarser branches the small
fibres are generally stained as a darker blue, while in the finest
terminal rami there is no apparent difference. These contain,
within a very thin sheath, two fine fibres of equal diameter, and
mostly highly varicose, which cross the direction of the muscle-
fibres, and at different points give off the true terminal branches.
These are also paired, and seem to end freely within the sarco-
plasmic mantle of the muscle-fibre. In rare cases these terminal
twigs also exhibit a scanty bifurcation. But there is never here,
or in the muscles of the extremities, any such rich plexus of
nerves as in the trunk-muscles. A similar type of muscular
nerve-endings is met with in insects also, the thorax-muscles of
the larger species of locust in particular giving with the same
method clear and elegant figures, which, in their abundance of
nervous ramifications, frequently recall the trunk -muscles of
Crustacea. But wherever there are well-marked Doyere's expan-
sions, the bifurcation of the ingoing axis-cylinders is markedly
localised, as in the end-plates of vertebrates. Thus in Hydro-
pliilus Biedermann found at most two knotty terminal branches

344

ELECTRO-PHYSIOLOGY

CHAT,

of the axis-cylinder, running in opposite directions, within the
substance of the expansion. These are for a short distance
parallel with the long axis of the muscle-fibre, and then appear
to end freely. In other cases they send out a few short side-
branches, the presence of which is sometimes indicated only by

isolated dark - blue droplets.
Finally, the nerve -endings (in
consequence of the great in-
stability of the intrinsically
delicate, naked axis - cylinder)
often appear merely as an ac-
cumulation of greater and smaller,
and no longer coherent, drops
(stained blue) within the expan-
sion - - their real nature being-
apparent only on comparison
with other parts of the same
preparation. Similar observa-
tions have recently been com-
municated by Eina Monti (53)
upon different insects.

Foettinger (53) gives a differ-
ent account of the motor nerve-

FIG. 226. -Nerve-ending in a muscle- endings ill illSGCtS, pointing tO a

''"'""' fundamental difference between
vertebrates and insects. In the
beetles investigated by him
( Chri/somela coerulea, Lina tremula,
Hi/t!r<>t>lt //us piceus, Passali'*
glaberrimus) there were, as a
rule, several, often many, nerve-
endings to one primitive fibre,
and these — as may be verified on

hardened preparations — are frequently (? always) the starting-
point of waves of contraction. After treatment with osmic acid
and alcohol, delicate fibrils or filaments may sometimes be dis-
tinguished in the side-view of a Doyere's expansion ; these start
from the junction of the ingoing nerve-fibres, and pass to the
intermediate discs (Fig. 226). If this be a real irradiation of
the axis -cylinder, there must be direct continuity between

x ELECTROMOTIVE ACTION IN NERVE 345

certain layers of the striated muscle-fibres and the nerve : thus
verifying a conjecture long since hazarded by Engelmann (54),
when he defined the isotropous ground-substance of the muscle as
"a somewhat modified continuation of the axis-cylinder of the motor
nerve-fibres/' and distinguished it as " nervous " from the " con-
tractile " tissue. Biedermann's own (methylene-blue) experiments
are little favourable to the assumption of any such intimate
relation between the final endings of the ingoing axis-cylinder
and the intermediate discs, although he has recently devoted
special attention to this point. The most favourable preparations
of Crustacea (crayfish), and of several kinds of locusts (Locusta and
Acridium), failed to show any such relation. Farther investigation
of the point is indispensable.

Comparison at once suggests itself between the marked
difference in the motor nerve-endings of different animals (and in
different muscles of the same species), and the differences of
function in the same muscles — such, e.g., as the sluggishness of the
claw- and agility of the tail-muscles in crayfish. The experi-
mental data in this direction do not, however, justify any con-
clusion. Nor must it be taken for granted that the characteristic
morphological differences seen in the parallel axis-cylinders down
to their final ending (e.g. in the abductor muscle of the crayfish-
claw) actually correspond with the double innervatioii here ex-
hibited from the motor and inhibitory nerves, although such a
conjecture is by no means unfounded.

Information as to the motor nerve-endings in uninuclear
striated and smooth muscle cells of vertebrates and invertebrates
is still very imperfect. The absence of characteristic end-platen in
cardiac, muscle, even in the higher vertebrates, is however estab-
lished, the character and ending of the finest non-medullated
rami being usually such that they branch many times dichoto-
mously, and then wind round the muscle-bundles, after which
they penetrate into these last, and terminate at the individual
cells in very fine, varicose end-branches (Eetzius). The same
mode of ending seems to prevail in smooth muscular parts, where
again there is remarkable similarity with certain very simple
forms of nerve-ending in the striated muscles of low vertebrates
and invertebrates.

I)u Bois-Eeymond affirmed that the major part in the
doctrine of muscular iimervation devolved upon histology, and if

346 ELECTRO-PHYSIOLOGY CHAP.

this be true, it is essential to review the known facts of the
morphology of motor nerve-endings in vertebrates and inverte-
brates in order rightly to appreciate the several theories. With
this object we have briefly summarised all the relevant data.
Starting with the striking anatomical resemblance (which can be
histogenetically accounted for) between the motor " end-plates "
of striated skeletal muscle in the higher vertebrates and the
nerve-endings in the " electrical plates " of the electric organ
of Torpedo (to be described below), W. Krause (55), followed
shortly after by Kiihne (56), was the first to express the opinion
that the action of nerve upon muscle might depend upon the
passing of an electric shock into the latter by means of the end-
plates, thereby producing a contraction. From this point of view
it must be assumed that the excitation conducted by the nerve
to the end-plates induces a brief electrical P.D., as in the electric
plates. " One surface of the nerve end-plates, no matter which,
becomes positive, the other negative. The resulting electrical
shock excites the contractile substance on which it impinges at
sufficient density," and a twitch immediately ensues. " Tetanus
arises from a more or less compressed series of such shocks."
Tliis hypothesis (the so-called " theory of discharge " -Entladungs-
liypotliese — of du Bois-Eeymond) gained acceptance, leading inter
alia to the conjecture that the secondary twitch from muscle to
nerve, discovered by Matteucci, is due less to the production of
electricity on the part of the former than to discharges of the
intramuscular nerves, or end-plates. Becquerel, without know-
ledge of the histological relations, had in fact placed Matteucci's
secondary contraction in direct parallel with the physiological
shock of the torpedo, referring it to an electric discharge in the
muscle (cf. du Bois-Eeymond, 23, p. 15). Kiihne's recent
investigations have, however, invalidated the suggestion that there
may be discharges from the end-plates. For neither does the
region by which the nerve enters, which is especially rich
in end-organs, exhibit any greater secondary activity than other
poorly-innervated or nerve-free tracts of muscle ; nor did Kiihne,
in carrying out a method of du Bois-Eeymond, succeed in
obtaining secondary twitch from muscles in which excitability
had been abolished, with careful preservation of the intramuscular
nerves (Kiihne, 2, p. 42). This does not, however, contradict
the " theory of discharge," which refers primarily to the relation

ELECTROMOTIVE ACTION IN NERVE

347

between motor end-plates and corresponding muscle-fibres, and
we must therefore cite it in detail. Du Bois - Reymond gives
the whole argument in his well-known treatise, Experimented
Critique of the Theory of Discharge (57). If each end-plate is

FIG. 227.

conceived as developing opposite potentials when excited at the
dorsal- and under-surfaces, like an electrical plate, then — the two
surfaces of the plate being presumably isoelectric — the resulting
lines of current will be according to du Bois-Reymoud's schema
(Fig. 227, a, b).

348

ELECTRO-PHYSIOLOGY

CHAP.

It is evident that not merely the muscle-fibres corresponding
with the plate, but those surrounding it also, would be similarly
excited ; under normal conditions, however, this is experimentally
found not to be the case. Moreover, the lines of current traverse
the adjacent fibres at right angles to the long axis, i.e. in the
ineffective direction. There are certain artificial, and therefore
a priori improbable, conditions under which such a distribution of
potential might come about in the plate, " that the resulting current
through the corresponding fibres should be perceptibly denser
than in the adjacent fibres," but these commend themselves the
less in that they at once destroy analogy with the electrical plate.
It is, e.g., conceivable that a P.D. should arise at the under-surface
only of the end-plate, on excitation (Fig. 228); this would then

t

at the moment of discharge form " a mosaic of positive and nega-
tive points, between which only molecular currents circle, and
these, at a distance equal to the least diameter of the plate, would
be of imperceptible density." Considering further that the facts
of comparative histology of the motor nerve-endings are in direct
contradiction with the theory of discharge, since the presence of
true typical end-plates appears to be confined to the muscles of
the higher vertebrates, a few fishes, and insects, the theory in its
original form is hardly tenable. Du Bois-Eeymond accordingly
proposed a " modified theory of discharge " ; but this is scarcely
more acceptable than the first, since its postulates are equally
inadequate.

" Definite anatomical relations are required to account for
the inefficacy of the process towards adjacent muscle-fibres, and
should consist in a slight, hook-shaped curvature of the extreme
end of each hypolemmal nerve-fibre on to the surface of the con-

ELECTROMOTIVE ACTION IN NERVE

349

tractile cylinder, its direction being towards the axis of the rami "
(du Bois-Eeymond, I.e. p. 555). To the end-surface of each hypo-
lemmal nerve-hook, du Bois-Eeymond ascribes the properties of an
artificial cross-section, pre-eminently that of negative potential in
relation to the " natural long section " of the terminal fibre
(Fig. 229). The negative variation of this pre-existing current
is the stimulus for the muscle- substance with which it is in
contact, and this implies the further, and highly improbable,
supposition that the muscle-substance is sensitive to such a weak
stimulus as the negative variation of the nerve current. Kiihne
(11, p. 90 ff.) instituted many experiments, as varied as possible,
with the view of discovering practical evidence for the modified
theory of discharge, or any parallel hypothesis, but with no

result. What du Bois-Eeymond claims for a single primitive fibre
was not to be elicited on applying a vigorous frog's nerve, contain-
ing many hundred fibres, to a muscle under the most favourable
conditions, and then exciting it ; nor did the artificial transmission
of excitation from nerve to muscle come off any better with the
non-niedullated olfactorius of pike, in which the E.M.F. is much
higher (Kiihne's method).

Kiihne himself, on the strength of his comprehensive re-
searches into the morphology of motor nerve- endings of verte-
brates, attempted subsequently to refer the innervation of the
muscle to electrical processes within the excited nerve ; but this
hypothesis went the way of all its predecessors, when confronted
with the growing knowledge of the motor nerve-endings in
invertebrates. Kiihne tried, by comparison of innumerable single
cases, to reduce the two main types of hypolemmal nerve-endings
in vertebrates, i.e. rpl&tzs (reptiles, birds, mammals, fishes), and
terminal fibres (arborisation of amphibia), to the simplest possible

350 ELECTRO-PHYSIOLOGY CHAP.

schema, in order " to arrive at what was common to all, or to the
last reduction that still preserves the type of the ending."

In Salamandra, where the motor nerve-endings consist entirely
of non-medullated, non-nucleated terminal fibres, embedded directly,
with no intermediate element, between the sarcolemma and the
contractile tissue, the simplest form = j - , where the stronger
stem represents the last epilemmal, medullated nerve, the lines at
right angles being the intramuscular end-fibres, approximately
parallel with the fibres of the muscle. Asymmetrical forms =
.-J— , ^=L-, frequently appear, never the simple |~ form. As
against these, the " plates " of the higher vertebrates are chiefly
characterised by the bulging walls of the branches, studded with
small lobes, or humps. Here too, however, a closer inspection de-
tects the asymmetrical branching of the end-rami (characteristic of
arborisation), "with sharp angles like a bayonet " ("never in the form
of a tuning-fork "). " This discloses another feature, to be interpreted
in the same sense, i.e. the arched and recurrent curvature of the
branches, their lateral or terminal prominences lying so close
together that they only embrace very small bridges of muscle."
" This arrangement presents every transition, from the simplest,
consisting of a single loop, curved on the surface and humped, to
the more circumscribed and labyrinthine plates, which form ex-
pansions with circular, elliptical, and oblong bases. The simplest

schema therefore — ^W , the more complex °| ." To this
character of the terminal fibres Klihne refers a peculiarity
in the excitatory waves impinging on them, " which is of some
importance to muscular excitation," since " in the never-failing
homodromous fibres no waves can advance in a parallel course
without exhibiting phasic differences." " In view of Bernstein's
remarkably steep, almost vertical decline of the wave of electrical
variation in nerve, the distances between the terminal fibres
running parallel with each other and the nearest root must be
sufficient to initiate a considerable P.D. between each pair of
points connected by a perpendicular." " Between these points,
which have diametrically opposite signs, if the wave of variation
is, in Bernstein's sense, heterodromous to the nerve current, there
is, however, muscle-substance, which must complete the circuit of
the potential." Kuhne thus imagines that a current completes
itself between opposite points of the terminal branches of ingoing

x ELECTROMOTIVE ACTION IN NERVE 351

nerves, in consequence of the phasic differences in the wave of
excitation, which current excites the intermediate muscle-substance.
This, hypothesis, too is open to objection, not merely from the
theoretical point of view (du Bois-Eeymond, 58, and Bernstein,
59), but still more (supra} on anatomical grounds, more particularly
the character of the motor nerve-endings in all invertebrates.

To sum up all that has been said in relation to these various
" discharge theories," their justification seems more than doubtful,
and we must rather subscribe to Bernstein's opinion (I.e. p. 33V),
that every hypothesis whereby the muscle is to be excited by
an electrical shock irradiating outwards from the nerve-ending is
excessively improbable. Apart from the preceding objections, the
time-relations of muscular excitation are decidedly against such a
view. The point is whether a measurable time is required for the
propagation of the excitatory process from the nerve-ending to the
muscle. Yeo and Cash pointed out that the latent period, with
indirect stimulation of the gastrocnemius muscle, is considerably
greater in the immediate vicinity of the entrance of the nerve
than it is with direct excitation of the muscle, and Bernstein (59)
subsequently examined the same fact more closely.

" The marked extension of the time-difference (0'0032-0-Q049
sec. on an average) leads us to infer that it depends not merely on
transmission of the excitation in the nerve down to its entrance
into the muscle-fibres, but also upon the retardation of the excita-
tory process in the end-organ of the nerve-fibre, as compared with
its duration in any parallel tract of the same." Subtraction of
the period of conductivity in the nerve from the interval deter-
mined experimentally between the two curves of contraction
gives the presumptive "period of excitation in the nerve-ending."
If, in view of the structure of the gastrocnemius muscle, we
take the central point of the whole muscle as the central
point of entrance for the nerve, estimating the rate of
nervous conductivity at 27 m. per sec., then, according to Bern-
stein, the period of excitation of the motor end-organs will on an
average be 0'0032 = 3^- sec. The same value appears, as Bern-
stein pointed out, from the latent period of the negative variation
with indirect excitation of the muscle. "We must assume that
the negative variation begins at the point of excitation at the
moment of stimulation (i.e. with no perceptible latent period), in
natural excitation from the nerve-ending, as in artificial electrical

352 ELECTRO-PHYSIOLOGY CHAP.

stimulation of the muscle. Then, on subtracting the period of
nervous conductivity from the latent period of the negative
variation, as observed with indirect excitation of the muscle, the
remainder will again be the excitation period of the nerve end-
organ. Certain observations of Tigerstedt may be interpreted in
the same sense, showing that in direct excitation of non-curarised
muscle, maximal twitches may sometimes appear with sub-
maximal strength of stimulus, in which the latent period is to a
marked degree more extended than it would be in maximal
stimulation. Again, twitches of medium and minimal height are
distinguished in non-curarised muscles by a longer latency than
the corresponding twitches of curarised muscles.

Hoisholt (60) subsequently disputed the justice of Bernstein's
conclusions, on the strength of experiments performed under
Kuhne's direction. He equally observed (on sartorius and gracilis)
a much shorter latent period on stimulating the richly innervated
muscle-substance near the hilus, than with excitation of the
ingoing nerve-trunk at the same point ; but found, on the other
hand, with direct stimulation of the non-innervated terminal
sections of the muscle, that there was not merely an equal but
even a far more prolonged latent period than with indirect
excitation of the nerve. Hoisholt believed himself able to explain
these facts by summation of stimuli in the muscle and intramuscular
nerves; against w7hich Boruttau (60), on the strength of his
experiments, urged the validity of the first view, confirming with
supramaximal excitation the difference, as found by Bernstein,
for parallel-fibred muscle also, on stimulating it first indirectly,
and then from the nerve-free end. The latent period was
invariably shorter in the latter case. L. Asher (60) objected
to this, that a supramaximal stimulus cannot be sufficiently
localised to the non-innervated end of the muscle. At Kuhne's
instigation, Asher employed a new method in which parts of the
muscle, free from, and containing, nerves, should twitch separately,
and describe a curve under absolutely parallel conditions. In the
successful experiments, which were not numerous owing to the
shortness of the bits of muscle employed (these being hung parallel
with, and close to, one another), and consequent difficulties of
experimenting, the two curves fully correspond at the initial
point, and exhibit the same latent period. In spite of this, the
protracted latency on stimulating the nerve-trunk demands farther

x ELECTROMOTIVE ACTION IN NERVE 353

investigation. Should this eventually establish the conclusions
of Bernstein's hypothesis, a " theory of discharge " would still be
possible only under the assumption " that, after the wave of
excitation had reached the end-organ, the electrical charge would
at first develop slowly, and only after about -3^ sec. reach the
climax at which excitation of the muscle would be effected."

Since it has been established by Kiihne that the final expan-
sion of the axis- cylinder is liypolemmal in striated muscle-fibres
invested with a sarcolemma, a theory of discharge, in the original
sense, no longer seems to be necessary to the explanation of
innervation. On the other hand, we cannot overlook the
possibility that there may be direct transference of the molecular
processes fundamental to excitation, from nerve to muscle ; just
as, in both tissues, transmission of excitation occurs from section
to section. This in no way excludes essential participation of
Hermann's galvanic processes (as set forth above), but, on the
contrary, renders it highly probable. No real objection exists in
the fact that, since actual continuity of substance between nerve
and muscle has not thus far been proven, the conductivity
of excitation must occur per contiguitatem. Eecent evidence,
moreover, tends to show that transmission of excitation may
occur by contiguity alone in the central nerve-endings also.

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3. W. BIEDEKMANN. W. S.-B. XCIII. 3. Abtli.

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ITH. W. ENGELMANN. P. A. XV. 1877. p. 138.
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[p. GRUTZNER. P. A. XXXII. p. 357.
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VOL. II 2 A

r

20.

354 ELECTRO-PHYSIOLOGY CHAP.

| PH. KNOLL. W. S.-B. LXXXV. 1882.

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Bern, 1883.

17. ENGELMANN. P. A. IV. 1871.

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•BORUTTAU. P. A. LVIII. 1894. p. 1.
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LXIII. 1896. p. 145.

LXIII. 158.

LXV. 145.

LXVI. 285. LXVIII. 1897, p. 337.

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39 P- 5S°-

1 M. SCHIFF. Zeitschrift fiir Biologie. VIII. p. 91. 1872.

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p. 343.

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x ELECTROMOTIVE ACTION IN NERVE 355

45. L. UKKMAXN. Untersnchungen zur Physiol. der Muskeln und Nerven. 3. Hel't.

p. 71. Berlin, 1868.

46. - — . P. A. XXXIII. 1884. p. 135.

47. MATTEVCUI. Compt. rend. 1S67. p. 65.

(GRUTZNER. P. A. XXVIII. und XXXII.

^TIGERSTEDT. Arbeiteu aus dem physiol. Labor, zu Stockholm. 2. Heft.

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vLehrbuch der Physiologic. 1894.

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W. KUHNE. 1862.

IzeitschriftfurBiologie. 19 und 23. 1887.
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Wirbelthiere. Leipzig, 1S74.

EHRLICH. Deutsche med. Wochenschrift. 1886. Nr. 4.
W. BIEDERMANN. W. S.-B. XCVI. 3. Abth. 1887.
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.RlNA MONTI. Reudiconti del r. instituto Lornbardo. 1891. Ser. 2. Vol.25.

54. ENGELMANN. P. A. XI. 1874. p. 463.

55. W. KRAUSE. Zeitschrift fiir rat. Med. (3). XVIII. p. 152. 1868.

56. W. KUHNE. Arch, fur patholog. Anat. XXIX. p. 446. 1864.

( Monatsberichte der Berliner Acad. 1874. p. 519.

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58. Du BOIS-REYMOND. C. Sachs' Untersuch. am Zitteraal (Gymnotus electr.). 1881.

p. 417.

59. BERNSTEIN. Du Bois' Arch. 1882. p. 329 ff.

/ HOISHOLT. Journ. of Physiol. VI. p. 1.

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IL. ASHER. Zeitschr. fiir Biol. XXXI. N.F. 13.

61. E. STEINACH. Ueb. d. electromot. Erscheinungen am Hautsinnesnerven.

P. A. LXIII. 1896. p. 495.

62. F. SCHENCK. "Spannung u. negative Schwankung. P. A. LXIII. 1896.

317.

63. HERMANN. Eine physikalische Erscheinung am Nerven. P. A. LXVII. p.

240. 1897.

64. HERMANN. Ueb. Keruleiter mit Quecksilberkern. P. A. LXVII. 257. 1897.

65. BERNSTEIN. Theorie d. negativen Schwankung. P. A. LXVII. 349. 1897.

(The Action of Anesthetics upon Isolated Nerve. Proc.

Physiol. Soc. Nov. 1895.
Observations upon Isolated Nerve. Croonian Lecture. March

1896.
Action of Reagents on Isolated Nerve. Brain. 1896. p. 43.

66. A. D. AVALLER. X ,, ,, ,, ,, ,, p-277.

„ 1897. p.569.
Action of C02 on Nerve, and Production of C02 by Nerve.

Proc. Physiol. Soc. Jan. 1896.
Action of C02 and Et20 on Electrotouic Currents. Proc.

Physiol. Soc. Feb. 1896.

356

ELECTRO-PHYSIOLOGY

CHAP. X

^Action of Temperature on Electrotonic Currents. Proc.

Physiol. Soc. Proc. Roy. Soc.
66. A. D. WALLER. _/ Action of Acids and Alkalies on Electrotonic Currents. Proc.

Physiol. Soc.
^Lectures on Animal Electricity. 1897.

CHAPTER XI

ELECTKICAL FISHES

I. STRUCTURE AND CONSTITUTION OF ELECTRICAL ORGANS

THE wonderful physiological properties of certain fishes, e.g. more
particularly the TorpedinidcB of the Mediterranean, and the
Siluroids (Malapterurus electricus) of the Nile and other African
rivers, have been known and dreaded from the earliest times.
The most superficial acquaintance with any representative of
this small and highly specialised group of fishes at once reveals
their power, when touched, of exhibiting activities, which were
first shown to be similar to electrical discharges by Adanson
(1751). Francesco Eedi (1666) had long since pointed out, in
his masterly anatomical investigation of the electric ray (Tor-
pedo], that the mysterious power of the electrical fishes was, in
all likelihood, associated with special organs, situated symmetric-
ally on both sides of the head. These he described from their
shape as " sickle-shaped bodies, or perhaps muscles." " It appeared
to me," writes Eedi, in describing his experiments, " as if the
painful action of the electric ray was located in these two sickle-
shaped bodies, or muscles, more than in any other part." From this
may be dated the first scientific treatment of the problem. For
centuries it had sufficed to describe the striking and unpleasant
sensations resulting from unwary contact with electrical fishes.
The Latin name torpedo, the French torpille, the Italian
tremola, the old Greek narke for the ray, the Arabic radd or
radscli for the cat-fish, and the Spanish templador for the South
American eel, all point to the stunning and shattering effect
of the shock from an electric fish, without hazarding anything
as to the cause of the manifestation.

358 ELECTRO-PHYSIOLOGY CHAP.

Eedi's predictive designation of the electrical organs of
Torpedo as " muscles " led, in the first instance, to a purely
mechanical theory of their action, which was most clearly set
forth by Borelli (1685). He assumed that the organs contracted
rapidly several times in succession, thus giving to the limbs in
contact with them a series of vigorous shocks, which produced a
cramp similar to that due to a blow on the elbow. This theory
was universally accepted, — the most famous scientists, Reaumur,
Linnaeus, Haller, sanctioned it, — and it may be said by 1750 to
have reigned supreme as the sole possible, and at the same time
adequate, explanation. Soon after the discovery of the Leyden
jar (1*745), a French botanist, Michael Adansoii (1751), travelling
on the Senegal, became acquainted with the far more energetic
action of Malapterurus, the shocks from which at once impressed
him (as previously noted by Gravesaiide ; du Bois-Eeymond,
4 e, p. 127) by their similarity to discharges from a Leyden
jar, more especially as it was found possible to lead them off
by long wires. The same was reported by Dutch explorers from
Surinam, of Gymnotus, the first account of which reached Europe
in 1672. It was found that the shock would pass through a
circuit of several persons, and, like the electric current, could
only be conveyed by conductors, and not by insulators (William-
son, 1773). Walsh had discovered the same in the previous
year at La Eochelle for Torpedo, and thus for the first time
established the electrical nature of the discharge (du Bois-
Eeymond, 4 c, p. 418). He showed at the same time that the
back and belly of the fish give a different electrical reaction at
the moment of the shock, and therefore held the " sickle-shaped
muscles " of Eedi to be an electrical apparatus, which the animal
could throw into voluntary activity. In a gymnotus sent in
1775 from Guiana to London, Walsh saw sparks leaping over a
gap in the discharging circuit, and was able to show the experi-
ment ten or twelve times consecutively to the Fellows of the
Eoyal Society (3, p. 158). From this time the attention of ex-
plorers in this department was mainly directed to establishing
the complete identity of the discharge from the fish with the
electrical current. Cavendish (1776) — whose investigations on
Torpedo were so extensive that (as du Bois-Eeymond pointed out)
Faraday was the first to recover the same standpoint — attempted
to imitate the action of the shock by ordinary electricity. On a

ELECTRICAL FISHES 359

leather model of the tish, saturated with sea-water, he covered the
organs corresponding to the poles with tinfoil, connecting them
by insulated wires to a Leyden battery. In this way he made a
true picture of the distribution of potential (lines of current) out-
side the fish in the surrounding water, and then showed how a
hand dipping into the water must feel the electric shock without
actually coming into contact with the fish, the intensity being
greater in proportion as the hand is nearer the fish. This agrees
with the observations of van der Lotts (4 e, p. 128) in 1762, to
the effect that a shock can be given through the air, which the
electric eel projects through its air-holes ; as well as the later
observations of C. Sachs that the jet of water from the bung-hole
of a vessel containing a gymnotus may conduct the shock.

The discovery of galvanic electricity, and subsequent dispute
between Galvani and Volta, could not fail to be of great import-
ance to the theory of electrical activity in these fishes, as the
most pronounced manifestation of animal electricity ; while here,
as so often elsewhere in physiology, the mechanism of the electrical
organs was referred directly to the dominant physical theories.
Volta himself detected the analogy between the pile which he
discovered, and the organ of the torpedo, which is built up of
prismatic columns (Collezione dell' Opere, etc., Florence, 1816, t. ii.
pt. ii. p. 99) ; and even defined the pile as an artificial electrical
organ. Such a theory, according to which electricity is developed
from the contact of three dissimilar elements, had to encounter
great difficulties, foremost among which is the constant action
of the pile ; while the activity of the electrical organ is obviously
under the control of the animal. These objections were got
over by conceiving the fish to execute certain movements in the
act of discharging, by which the supposed electromotive elements
of its batteries, the nature of which was quite unknown, were
first brought into contact (Volta) ; or by conjecturing the
outfiow of a defective constituent at the will of the animal (A.
von Humboldt). One great difficulty was the impossibility of
insulating the organ, which led Valentin (34) at the beginning
of the forties to ascribe to the tendinous septa that surround
the columns (prisms) of the organs the function of insulators.
Schonlein, at the same time, held that the gymnotus could
voluntarily insulate itself from the surrounding water.

The uncertainty (notwithstanding the apparent proof of the

360 ELECTRO-PHYSIOLOGY CHAP.

electrical character of the discharge) of all these more or less
hardy speculations is best seen in the fact that, even in 1829,
Humphry Davy (whose brother, John Davy, at his instigation,
made extensive researches on Torpedo at Malta), expressed doubts
as to whether the electricity of the electrical fishes were really
identical with ordinary electricity ; while Faraday (who had the
good fortune to be one of the first who investigated that most
powerful of all electrical fishes, the South American eel, with the
best physical aids that Europe could supply) was unable a few
years later to procure from the discharge of the gymnotus the eight
effects which he laid down as essential to the identity of all
electricity (viz. sparking, thermic action, attraction and repulsion,
deflection of magnetic needle, magnetisation of steel rod, hydro-
lysis, conduction through hot air, physiological action). At a
later period, one blank only remained, failure of conductivity
through hot air.

It is to du Bois-Reymond that we owe the fundamentals of
a scientific physiology of electrical fishes, founded no less upon
theoretical considerations than upon sound experimental investiga-
tion. His data have been amplified by later workers, and the
main points, at least, may now be taken as established.

Since the more recent contributions to the subject are only
intelligible if the structure and finer relations of the organs have
been mastered, it is, in the first place, advisable to give some
detailed account of these, taking the Toi^cdinidce as the best
known representatives of the group; their structural relations being
the simplest and most obvious. Fig. 256 « represents half the
dorsal aspect of Torpedo marmorata, after removing the skin. On
either side of the head and branchial sacs lies a kidney-shaped
organ, running right through the highly- flattened, broad body,
from dorsal to ventral surface. From the superficial aspect these
resemble a honeycomb, consisting of irregular 5- to 6-sided
prismatic columns in juxtaposition. A section vertical to the
plane of the body shows that the columns decrease in height from
within outwards. They are separated by partition-walls of con-
nective tissue, and in fresh preparations resemble, both in
appearance and in consistency, a grayish-red, semi-transparent

jelly-

The finer structure can be examined both in longitudinal
sections, parallel with the axis of the columns, and from the super-

XI

ELECTRICAL FISHES

361

ricial aspect. The latter is easily obtained by a method first
employed by Savi ; this consists in cutting off the convex trans-
verse section of a column with scissors, and then separating out
the single thin plates of which it consists, in some indifferent
fluid. It is these fine discs, lying one upon the other like
the coins in a rouleau, or the plates in a voltaic pile (Fig. 230),
which (as du Bois-Eeymond was
the first to point out) become
electromotive under the influence
of the nervous system. " The
electromotive components of the
primitive batteries of the fish's
columns must not lie sought in
optically separable structures, in
heterogeneous, contiguous tissues,
or in animal fluids. The seat
of E.M.F. lies rather in the centre
of a morphologically homogeneous
tissue, the so - called ' electrical
plate ' " (du Bois-Eeymond 4 cl, II.).
In their normal position in
situ the plates are approximately
horizontal, curving only in the
middle towards the
animal.

back of the
On treatino; them with

FIG. 230. — Schema of a single prism in
Torpedo with ingoing nerve (Wagner's
< mi-brush). (Fritsch.)

reagents, however, various strata
appear in the longitudinal sections.
Each plate seems to be bent
backwards at the margin, where
it is attached to the connective-
tissue septa, the ventral half being more particularly involved
(Fig. 231). The single plates are somewhat further apart
in the larger than in the smaller columns. From the ventral
aspect, each plate exhibits a rich plexus of nerve-fibres, with a
sprinkling of capillaries, embedded in a gelatinous tissue studded
with star-cells, which fills the intermediate spaces of the plates,
and gives the appearance of a quivering jelly to the fresh sub-
stance of the prisms. When we remember the number of nerve-
fibres in each single plate, the wealth of nerves in the entire
organ is surprising, and witnesses to its intimate relations with

362

ELECTRO-PHYSIOLOGY

CHAP.

the central nervous system. This is no less strongly marked at
the origin of the " electrical nerves," which arise from two special

lobes of the brain, that are wanting in
all other fishes. Lorenzini, 1677 (as
was pointed out by Boll, 5 d), described
these parts as a posterior pair of
tubercles, without divining their function,
while A. v. Humboldt was the first to
recognise them more exactly for the
centres of the electrical nerves of
Torpedo. After exposing the central
organ, they are perceived as two long
grayish-yellow bodies lying close to-
gether, from which four nerve -trunks
run out right and left, on either side,
and supply the organs. According to
Fritsch (whose view was also adopted
by Schenk on developmental grounds),
the dorsally protruding electrical lobes
arise from branches of the motor nuclei

Fi,;.231.-Marginal portion of three of the VRgUS, ill the medulla obloilgata,

electrical plates: longitudinal wnich froni the excessive proliferation

aspect of the column. (Ranvier.)

ol the ganglion-cells that subserve a

special function, appear to be pressed upwards from their original
seat on the floor of the fourth ventricle. Transverse sections
reveal a dense layer of large ganglion-cells, the axis-cylinder pro-
cesses of which pass directly into the fibres of the electrical nerves.

The character and distribution of the nerves that enter the
organ within each single column, or prism, is highly characteristic.
As Eudolf Wagner (35) first showed, the fibres all divide up
suddenly into many branches before they enter the plates,—
forming the characteristic bundle (Wagner's brush — Figs. 230
and 232), of which the spatial distribution, and relations to the
single plates, were determined more exactly at a later period by
A. Ewald and Fritsch (9).

They found th*t the fibres of a brush, about eighteen in
number, are superposed upon one another in regular arrangement,
entering by the corners of the hexagonal plates ; so that each plate
is supplied by six fibres, which again present a rich dichotonious
ramification (Fig. 230).

XI

ELECTRICAL FISHES

363

So soon as a medullated twig of Wagner's end-brush reaches
the plate with which it is correlated, and one part of which

it is to innervate, it gives off branches on either side, at 'an
approximately right angle. These are still medullated, and in

364

ELECTRO-PHYSIOLOGY

CHAP.

their turn divide repeatedly (dichotomously), or give off lateral
branches ; and finally, after losing the medullary sheath, form two
horned bundles of non-medullated, pale fibres, the final ending of
which in the substance of the plate can hardly be detected (Fig.
233). Not only the dichotomous branches of the medullated,
but in part those of the non-medullated terminal arborisations
also, are invested with a sheath of connective tissue with em-
bedded nuclei, which is more particularly developed in the former.

FIG. 233.— Arborisation jf nerves on the ventral surface, of an electrical plate o Torpedo.

(Ranyier.)

According to Eanvier, this sheath ends suddenly at a given point
of the non-medullated terminal expansion.

Remak, 1856 (27), was the first to observe that the fine
non-medullated terminal branches can be followed much farther
than is described by Wagner. In good preparations the whole
of the apparently empty intermediate spaces proved to be filled
with pale and visibly anastomosing nerve-branches. Kolliker,
1857 (16 b), and later on M. Schultze, described a true nervous
network, which Schultze represents as a very fine reticulum

•

XI

ELECTRICAL FISHES

365

with nearly quadratic meshes (31 V). The majority of later
workers have determined by the help of modern methods (in
particular with metallic impregnation, e.g. gold, silver), as also
on fresh electrical plates of Torpedo, that the nerve -endings
are in all respects homologous with the motor end-plates of
striated muscle in the higher vertebrates. If we examine
Uanvier's picture of a small portion from the terminal arborisation
of the nerves of the plate, treated with silver (Fig. 234)—
or such figures as are given by Ciaccio (6), Boll (5), Krause

FIG. 234. — Small portion of the terminal
nervous arborisation in electrical
plate of Torpedo (silver preparation).
(Ranvier.)

y 'J\9 ^~^*{m (*

<X) *§'

Fi<:. 235.— Portion of nervous ramitication in a
plate of Torpedo, showing Boll's punctua-
tion. (Ciaccio.)

(17), and recently Ballowitz (2) and Iwanzoff (15), after treat-
ment with osmic acid, gold chloride, hasmatoxylin, Golgi's method,
etc. — the exactness of the comparison is at once obvious,
and it is difficult to understand how Fritsch (12) could entirely
deny the existence of such a terminal nervous arborisation.
Biedermann has invariably been able to recognise it in fresh
preparations, where it covers the whole ventral surface of each
disc like a gigantic end-plate. And, indeed, when we consider
the development of the electrical plates from- metamorphosed,
striated muscle-fibres, the homology between the terminal nervous
arborisations on the ventral surface and the motor end-plates can
hardly be disputed. Schonlein even states that he is now

366 ELECTRO-PHYSIOLOGY CHAP.

inclined to regard the whole of the developed plate as the
homologue of the motor end -plate only. Eeniak (I.e.) drew
attention to a peculiar and regularly arranged punctuation upon
the ventral surface of each electrical plate (as observed by all
later workers), which Boll (5) described many years later as a
new structural relation. This consists of a remarkably fine,
regular, and homogeneous punctuation, immediately subjacent
to the terminal network, viewed from below (Fig. 235). The
arrangement of dots corresponds perfectly with the configuration
of the terminal network, so that the little points follow the
reticulation of the net, and to some extent mark its distribution.
Several (2—3) irregular rows of clots correspond, for the most
part, to the single threads of the net, the number of points in
1 sq. mm. amounting, according to Krause and Iwanzoff, to about
a million.

In optical cross-sections of the plate (at the bending-points)
the punctuation is seen to be the expression of a fine and regular
striation, vertical to the surface (cf. Fig. 231, ce), which extends
from the ventral side to the border of the first sixth of the
diameter of the plate (palisade border, Eanvier's cils elcctriques),
and was known to Eemak, who regarded the dots of the super-
ficial aspect as the bending-points of small cylinders arranged in
a palisade upon the surface. Krause in the main subscribed to
the same opinion, regarding the dots as " the optical expression
of small cylindrical rods, viewed from above, which belong to the
neurilemma, and form as it were ' nails,' riveting the flattened
terminal fibres." Boll, Eanvier, Ciaccio, and Trinchese viewed
them as the true, terminal nerve-endings. According to Iwanzoff1
the palisade merely represents the processes of the structureless
membrane which clothes the lower surface of the electric plates,
corresponding with the sarcolemrna of the muscle-fibre.

Fritsch, on the contrary, holds the dots (which look black
when treated with osmic acid, and examined under the highest
dry power, or a weaker immersion lens) to be " the optical ex-
pression of strongly refracting and closely approximated granules,
embedded in a less refractile, semi-fluid substance, which covers
the lower surface of the plate." Fritsch proposes to call this
layer, which has nothing to do with the true nerve-ending, the
xtrntmn yranulosii m. Its relation to the other layers of the
electric plate is most plainly seen in transverse section (Fig. 236).

XI

ELECTRICAL FISHES

367

According to Fritsch (who is again contradicted by Iwanzotf),
" it is possible, in speciall}7 favourable parts of the cross-sections
of a plate, to discover fine threads of nerve at right angles to the
direction of the plates, entering at the granular layer and dis-
appearing between the granules." Beyond these again, in the
palisade border, they are plainly visible, and form the direct
boundary of the palisade (Fig. 236). Their proper ending seems
to be at the dorsal border of this layer, in " soft protoplasmic
bodies, which in the preparation cohere in spherical (berry-like)
masses." Beyond the border of the palisade comes the dorsal
(" muscular," Fritsch ; " metasarcoblastic," Babuchin) part of the
plate (Eanvier's couche intermddiaire). This layer, which is

Fio. 236.— Torpedo ocdlata. T.S. of electrical plate with dependent nerve. ? = dorsal border, or
layer, of connective tissue; m = stratnm moleoihu-c ; p = palisade-border with nerve-endings;

(G. Fritsch.)

developed by the transformation of embryonic muscle-substance,
exhibits nothing further of the characteristic structure of striated
fibres. Krause, indeed, describes " striated, bowed fibres " as a
residue of muscle-fibrils, but other observers have not detected
them. According to Fritsch, this layer, like the stratum
granulosum, " is composed of minute particles, set in rows parallel
with the axis of the prisms, and little more refractile than the
intermediate substance" (Fig. 236, m}.

Fritsch inclines to regard the regular structure (as observed
by him) as a confirmation of clu Bois-Eeymond's molecular
theory, though he does not go so far as to affirm that the rows
of particles are actually " the required electromotive molecules."
Iwanzoff, on the contrary, views them merely as a kind of honey-
comb or foam-like structure of the plasma of which the "inter-
mediate layer" consists.

368

ELECTRO-PHYSIOLOGY

CHAP.

To summarise the main points relating to structure, and more
particularly to innervation, of the organ of Torpedo, this much is
certain. Each ganglion-cell of the electric lobe in the brain gives
off an axis-cylinder process (analogous to Deiter's process in the
ganglion - cells of the spinal cord), which continues as an un-
branched constituent of the electric nerve, down to one of the
columns that compose the organ. Here the medullated fibre
'suddenly breaks up into a number (12— 20) of small ramifications
(Wagner's brush), which are arranged regularly, one over the
other, and each partially supply a plate. On entering the mucous
tissue that fills up the space between every pair of plates, each

Fn;. 'J3~. — Hijiiiiirjtus <'lci.'ti'ii'ii*.

terminal fibre divides many times dichotomously, and finally ends,
after losing its medullated sheath, at the ventral surface of the
plate, in a manner analogous with the terminal ramification of
the axis-cylinder in the motor end-plates of striated muscle-fibres.
The nature of the true ending and whether it is free, or, as
Fritsch says, lies within the palisade layer, is still undecided, and
awaits further investigation.

The uniformity of structure and internal relations in the
electrical organ is of great moment to the theory of the discharge
of these fishes. In <_li/nniotus, as in Torpedo, the organs exhibit
a bilateral symmetry, and are so powerfully developed that the
fish might be said to consist principally of electric organs. Fig.
237 is a good representation of the form of the fish. Notwith-

XI

ELECTRICAL FISHES

369

standing its eel-like shape, the body-cavity occupies but a small
part (not quite one-fifth, including the head) of the total length,
while the four electrical organs fill up the space that would other-
wise be devoted to the abdomen (C. Sachs). As seen from above,
the trunk of the fish appears to taper off behind like the blade of
a knife. The gymnotus, in comparison with other electrical
fishes, reaches a considerable size (according to Sachs the length
may be 155 cm., or 170 cm. according to v. Humboldt), while
the species of torpedo most common
in Europe measures, at most, 20—30
cm., rarely 70 cm. The electric ray
peculiar to the coast of Eastern
America (T. occidcntalis, Storer) is
the sole species that becomes double
this size under certain conditions,
and may be defined as the largest
and heaviest, if not the longest, of
all the electrical fishes (Fritsch).

As seen in a transverse section
of Gymnotus (Eig. 238), the body
consists mainly on the( farther side
of the head and body-cavity, of a
gelatinous, transparent mass, which
forms on each side a large, and a
second much smaller accumulation,
situated below. These are separated
by a layer traversed by muscle-fibres, FIG. ass.-T.s. through trunk of

. , notus. 00 = great organ; fcO = s

termed by du Bois - Keymond the organ; Zm= intermediate muscular
" intermediate muscular layer," and

viewed by Fritsch as a vestige of the muscles whose transforma-
tion gave rise to the greater organs (Fig. 238).

Closer inspection proves the substance of the organ to be
penetrated by parallel walls of connective tissue, lying one
above the other, and running, in transverse section, from a
middle, vertical septum to the external circumference of the
body. These " longitudinal partition walls," which (as shown
by the lateral aspect, Fig. 239) extend throughout the entire
length of the organ, including the intermediate muscular layer,
serve to bound shallow spaces lying in horizontal strata, each of
which, with its content, corresponds to a column of the Torpedo

VOL. II 2 B

370 ELECTRO-PHYSIOLOGY CHAP.

organ. Fine septa, parallel with the plane of the cross-section
(" transverse partition walls "), produce from the lateral aspect a
delicate cross-striation of the single prisms, and divide them into
closely-compressed narrow compartments, in each of which an
" electrical plate " is supported at right angles. The form of this
compartment, and of the plate within it, may in general be
described as rectangular, with greater or less diminution towards
the centre.

The average width of the compartments in the organ of
Gymnotus is about T^ mm., agreeing with the older observations
of Hunter, who reckoned about 240 transverse septa to the
English inch, i.e. about O'lOoS mm. width of compartment. In
Torpedo it is about -^ mm. The distance between the two
longitudinal septa (height of compartment) is of course much
greater. It is about 0'64 mm. in Gymnotus (Hunter). The total

FIG. 230.

number of compartments lying between two longitudinal partition
walls, with the band-shaped plates which they contain, may again
be described as " columns," analogous with the prismatic columns
standing at right angles to the body superficies in the organ
of Torpedo. The columns of the large organ spring collectively
(as shown by the lateral schema, Fig. 239) from behind and
below the intermediate muscular layer, and ascend at a sharp
angle above and in front. Only the foremost run approximately
parallel with the axis of the fish.

Even to the unaided eye a certain part of the two large
organs exhibits peculiar characteristics ; i.e. it is darker, more
transparent, and of a yellow-gray or pinkish colour, instead of
being white like alabaster. This is because (as Paciui, 25, showed,
Fig. 240, a, b) there are, along with the ordinary columns with
small compartments, others in which the spaces are very wide.
Sachs confirmed these observations. The " Sachs' bundle of
columns," which he was inclined to regard as a new electrical
organ in Gymnotus, lies as a rule above the posterior half
of the large organ. It begins anteriorly in a fine point

XI

ELECTRICAL FISHES

371

(Fig. 239), increasing posteriorly, so that it soon occupies the
upper half of the total diameter of the organ, and finally pushes
its way completely behind the large organ. A section parallel
with the long axis of the fish shows a general fusion of the
longitudinal septa between the wide-spaced columns, which end
before and behind in sharp wedges (Fig. 240, b) ; the cross-
section is spindle-shaped, or rhomboidal.

If a longitudinal section of the electrical organ (parallel
with the axis of the organ, and vertical to the long partition walls)
is examined under a high power, it is easy to see the cross-sections
of the. transverse septa of connective tissue, extended between
each pair of longitudinal partition walls, together with the com-
partments which they enclose, each containing a transversely

FIG. 240. — a, Portion of several superposed prisms of Gymnotus (two wide compartments below).
(Pacini.) b, L.S. through prisms of Gynmotus, wide and narrow compartments. (Du Bois-
Reymond.)

bisected electrical plate (Fig. 241). With regard to the position
and mode of attachment of the latter, there is a fundamental
difference between Pacini and M. Schultze (31), as appears from
the two figures (241, a, b). While Pacini holds that the plates
depend freely in the compartment, and are attached only at the lon-
gitudinal septa, Schultze maintains that each transverse partition
wall (Q) coheres with the posterior surface of the corresponding
plate, so that there is a space only in front of, and not behind it.
Both anterior and posterior surfaces of the plate are thickly set
with papilla; (" villi," M. Schultze), behind which there are
posteriorly, thorn-like processes (prolungamenti spiniformi, Pacini),
which extend to the posterior partition wall, and are attached there.
Schultze failed to discover the latter, while Sachs confirmed the
observations of Pacini, as also for the cleavage of the plates (as
observed by the latter), into an anterior and a posterior half. He
regarded the papilla with their so-called " nuclei " (known later

372

ELECTRO-PHYSIOLOGY

CHAP.

on as star-cells) as ' cells," distributed over the anterior and

Fio. 241.— Two electrical plates of Gymnotus ; L.S. of the organ (as in Fig. 240).
(", 1 'acini ; b, M. Schultze.)

posterior surfaces of a ground -membrane (parte fondamentale,

XI

ELECTRICAL FISHES

373

Fig. 241, a). According to Sachs, the transverse section of
the electrical plate exhibits the following layers from the front,
posteriorly (Fig. 242). Next to the anterior papillar layer
(stratum papillare anterius) comes a clear and perfectly structure-
less stratum, termed by Sachs the intermediate layer (stratum
intermedium), corresponding essentially with Pacini's parte fonda-
mentale. This is succeeded by the nervous layer (stratum
ncrveuni), which, apart from the processes of the posterior star-
cells which traverse it, is of a homogeneous gray colour. It
gives off the posterior
papillae, and the thorn-like
papillae, forming collect-
ively the stratum papillare
posterius. The electrical
nerves end at the nervous
layer, as will be described
below. Transparently
homogeneous in the fresh
state, the papilla? become
granulated within even 1—2
minutes after removal from
the living animal, while a
sharp boundary line (PL)
appears inside the inter-
mediate layer, dividing it
into two tolerably equal
halves. Cleavage of the

plate USUally OCCUrS at FIG. 242.— X.S. of electrical plate of Gymnotus; L.S. of
.. -T-, . . •, . „ organ. (Sachs.)

these raciman lines,

which appear in osmic preparations as a sharp dark streak in a
broad, light zone. Sachs found " a substance resembling spider-
web " between the anterior papilla?, " consisting of meshes of fine
threads with small nuclear -like structures." Pacini detected
nerves upon the transverse septa only, where Sachs also noted
them plentifully, but in addition discovered their terminal branches
between the thorn papilla?, and traversing the posterior cavity
of the compartment, to end finally, after loss of the medullated
sheath, in the plate itself.

The posterior surface of the plate exhibits in transverse
section (with osniic preparations) the striation (or punctuation as

374

ELECTRO-PHYSIOLOGY

CHAP.

seen from the surface) first described in detail by Boll for
Torpedo. The nerve-ending itself presents, according to Sachs,
a varying aspect "resembling now Kuhne's end-plate, and now
Schultze's net." According to Fritsch, the thorn-like papillae are
to be viewed as the real bearers of the nerve -endings in the

Gymnotus plates. " Upon these
there are comparatively coarse
prolongations of the axis-cylinder,"
so that they are "allied to the
stalk of the Malapterurus plate."
As regards the indisputable genetic
relation between the electrical
organs and striated muscle, it may
be conjectured that the mode of
ending of the nerve in the sub-
stance of the plate is analogous
to that of Torpedo, although the
observations made up to this time
afford no positive evidence of it.
The plates in the wide compart-
ments of Sachs' columns are dis-
tinguished from the others mainly
the greater lensth of the

p p

FIG. 243. — One wide and two narrow compart- by

ments of Gymnotus, seen in cross-section • M1 /T-,. 0 . 0.

(as in Fig. 241) under a high power, with anterior papillae (Fig. 243), 111

enclosed plates (P). (DU Bois-Reymond.) which, moreover, in the fresh state,
Sachs observed a broad, dim cross-striation and traces of double
refraction, in the axis or at the margin.

If the final distribution of the nerve in the peripheral organ
(electrical plates) is thus uncertain, no such doubt exists as to
the central origin and coarser anatomical structure of the electrical
nerves.

Valentin, reasoning from a likeness (afterwards proved to be
inadequate) between the brain of Gymnotus and that of the eel,
assumed a certain section of it (by analogy with Torpedo} to
be the electrical lobe, and centre whence spring the electrical
nerves. Later investigations, however, showed the part of the
brain in question to be identical with the cerebellum so markedly
developed in the allied cat-fish (Silurus glanis), the spinal cord
being the immediate seat of origin for the electrical nerves. Max
Schultze first pointed out the very numerous and large ganglion-

xt ELECTRICAL FISHES 375

cells in the spinal cord of Gymnotus, and showed that there were
twice as many as in other fishes, indicating a probable relation
with the electrical nerves that pass out from this region. Du
Bois-Beymond also concludes " that there must be a similar
structure in the cord of the electrical eel to the lobus electricus of
the electric ray." This is the more probable since the electrical
organ of Gymnotus is supplied by intercostal nerves, which are so
numerous as to have excited attention from the time of Hunter.
Fritsch's thorough investigation of the materials brought by C.
Sachs from Calabozo showed in point of fact that at a certain
level of the cord, which is differently localised according to
individual variations (12—23 vertebra?), large ganglion-cells, highly
characteristic in their entire habit, appear at first singly, and
later on as a closed column, in the form of a cylinder, surrounding
the central canal, and open anteriorly ; these must undoubtedly
be denoted " electrical cells." " They exhibit the usual multi-
polar characteristics of well-nourished finely-granulated protoplasm,
drawn out into several broad processes and bladder-like nuclei,
with conspicuous, strongly-refracting nucleolus." The size of the
rounded cell-body, which is invariably drawn out into a well-
marked axis-cylinder process, is on an average O'OSl mm. The
ordinary motor cells exhibit a more polygonal form, with better
developed protoplasmic processes. No sharp division can, how-
ever, be predicated, since, according to Fritsch, there are transitional
forms at the level of the 6—16 cervical vertebra. At about
the 30th vertebra the quantity of electrical cells has increased so
much " that the entire cavity of the anterior horns, and central
mass of the gray matter, seems to be filled with them, and they
even cause a thickening of the spinal cord in the sagittal direction.
It is only in front of the central canal that the cells do not meet,
on either side, so that the cell-group in cross-section resembles a
wide half-moon" (Fig. 244). "Here, where the seat of origin of
the electrical nerves appears most fully developed, the axis-
cylinder given off from the cells forms at each cross- section a
distinct group of fibres, which run very obliquely. These coincide
in arrangement and mode of origin with the ordinary anterior
roots of other bony fishes. There are no special motor roots in
the cord of Gymnotus alongside of the electrical, but the fibres
from which the muscular nerves originate, succeed immediately
upon the electrical nerves (Fritsch). Corresponding with the

376

ELECTRO-PHYSIOLOGY

CHAP.

fact that the electrical organs of Gymnotus extend to the tip of
the tail, we find ganglion-cells of the electrical type as far as the
end of the spinal cord, but they gradually diminish in number
and size, and more nearly resemble in form the ordinary motor
cells of the anterior horn.

While in these cases we have in Torpedo and Gymnotus
electrical organs of such high differentiation that even the most

powerful effects seem tib
initio to be accounted for,
there are in the tail of the
common Skate (Rajct), as well
as in the species of Mor-
myrus, organs that in struc-
ture and arrangement are
unmistakably allied with the
electrical, but of which the
effects are so slight that they
have only recently been de-
termined. These du Bois-
Keymond named " pseudo-
electric " organs. This dis-
tinction is, however, obsolete,
•seeing that both Mormyrus and the various species of Raja belong
to the true electrical fishes, so that, as Babuchin expresses it,
" there are no pseudo- electrical fishes, but only large and strong,
or small and weak, electrical fishes, severally."

As James Stark was first to discover, the electrical organs in
the tail of Raja lie on either side, near the vertebral column, as
two cylindrical, grayish, transparent bodies, pointed anteriorly and
posteriorly. "They begin at the centre of the sacro-lumbalis
muscle, near the junction of the anterior and second thirds of the
tail, become gradually thicker, and, after completely displacing
the muscle, lie close under the skin, where they are as thick as
the muscle itself, and extend as far as the extreme end of the
tail" (Fig. 245, a, I). Their position is shown even better in
transverse than in longitudinal section (Fig. 246). Here the corn-
position out of single, concentric " columns," running parallel with
the axis of the tail, and separated, as in Torpedo or Gymnotus, by
septa of connective tissue (M. Schultze's "primary partition
walls," 3 1 «)) is ver7 obvious. Each column again breaks up by

FIG. 244.— T.S. through the spinal cord of Gymnotus
electricus. (Fritsch.)

XI

ELECTRICAL FISHES

377

numerous (" secondary ") transverse partitions, set vertically to the
long axis, into single, flat, quadrilateral chambers or compartments,
lying one behind the other, and enclosing the true electromotive
elements of the " plates " (Kolliker's " spongy bodies "). It appears
from even superficial consideration of a long section that the
single longitudinal columns of the electrical organ have in some
degree replaced the involuted, cone-shaped muscle-segments, so
that the primary septa are in part only a restoration of the
tendinous partition walls of the sacro-lumbar muscles, and, like

Fie;. -45. — Eaja davata ; L.S. of electrical organ in the^tail. «-, Anterior end, lying between the
layers of M. socroium&aZis (magnified three times) ; &, from the centre of the organ ; the electrical
plate lies at the anterior wall of each compartment. (M. Schultze.)

these, form cones with pointed anterior ends, fitting parallel into
one another (Fig. 245). Fig. 247 gives a good representation of
the arrangement of the single compartments within the columns,
as well as the position of their contents.

These figures show that the comparatively thick plates, which
are irregularly bounded on the posterior side, are attached to the
anterior wall of each compartment, and occupy about one- third
of the available inner space. Under a higher power the plates
are seen (Fig. 248) to be surrounded by gelatinous connective
tissue, which fixes them within the cavity of the compartment.
The nerves to each compartment travel, as Kolliker (16) showed,
from the anterior wall to the anterior plane, or goblet-shaped
surface of the plate, forming by rapid division a rich plexus of
non-medullated fibres. The true mode of ending is of course

378

ELECTRO-PHYSIOLOGY

CHAP.

only to be found on the surfaces of the plate, i.e. at the cross-
section of the columns, but it has not yet been accurately
determined. M. Schultze (I.e. p. 201) describes a net with
narrow meshes, applied almost directly to the anterior surface
of each plate. It is set with numerous nuclei, and is further

• o .

FIG. 246.— T.S. of Raja latis. 0=T.S. of
the organ. (Burdon-Sanderson and
Gotch.)

PIG. 247. — L.S. through electrical organ
of Raja batis. K = compartment ;
P = electrical plate. (Burdon-
Sanderson and Gotch.)

n m

m
IF

•mm*

FIG. 248. — Rajabatis. Part of a compartment with cross-section of enclosed plate (L.S. of the
organ). ?i= nervous layer; m = meandering layer ; p= papillary layer (alveolar layer). (Burdon-
Sanderson and Gotch.)

continued posteriorly into a much finer network, exhibiting
as a whole the same characteristics as the net described by
Schultze and Kolliker in the Torpedo plate, and fuses directly with
the substance of the plate. Babuchin failed to assure himself of
the existence of this net, and Burdon-Sanderson and Gotch (13 c,
p. 142) were uncertain as to the exact mode' of ending. Beyond
the nucleated zone into which the nerve expands, there is at the
cross-section of the plate a tolerably thick layer without laminse
(meandering layer), the single strata of which lie parallel with

ELECTRICAL FISHES 379

and horizontally over each other (.ft. bat is), or are much bent
and undulating (E. circularis). In immediate contact with
this is a stratum that is frequently drawn out into papilli-
forni processes, similar in character to the nucleated zone which
invests the anterior surface of the entire plate, and forming the
posterior border of the plate ; this consists of a finely-granulated
mass of protoplasm richly set with nuclei.

Eecent investigations of Fritsch (12 i} have contributed to
our knowledge of the structure and innervation of the Mormyrus
organ. Here, again, there are compartments of connective
tissue filled with gelatinous substance, and containing plates ; but
the finer structure seems to differ in many points. The nerve
enters by means of special prolongations of the plates, which are
club-shaped, and terminate in a conical, pointed form (" cones "),
which Fritsch compares with the expanded motor end-plate of
muscles.

In Mormyridce, as in Torpedo, the fibres of the electrical
nerves (corresponding with the situation of the organ in the tail)
"are broad, unbranched axis -cylinder processes from large
ganglion-cells, which at given parts completely fill up the gray
matter of the spinal cord, and then leave the central organ as the
anterior roots. Fritsch makes the important observation that
the huge protoplasmic processes of these parent cells form a
number of short, broad anastomoses, so that the electrical ganglion -
cells, which form by actual continuity a narrowly circumscribed
complex, are, as it were, bound up by a common function.
Fritsch rightly lays stress on this observation, since on the one
hand it shows the undoubtedly nervous character of these proto-
plasmic processes, while on the other it indicates the possibility,
and, indeed, probability, of a similar course for the finest arborisa-
tions of motor nerve cells of the spinal cord in other vertebrates.

Even from a more anatomical investigation of these " pseudo-
electric organs," it cannot be doubted that they are homologous
with striated muscles, and formed by the gradual transformation
of the latter. A glance at the tail of Mormyrus cyprino'ides,
when skinned, will reveal this, even to an unpractised eye. At a
certain point, i.e. near the end of the anal fin, the regularly-
arranged and flattened tendons of the caudal muscles suddenly
lose their solid, fleshy attachment, as described by Fritsch, and
stretch superficially across a transparent gelatinous mass, the

380 ELECTRO-PHYSIOLOGY CHAP.

discoid structure of which at once betrays it as an electrical organ
(Fritsch). It is more difficult to prove the muscular origin of
the electrical organ in the Torpedinidce and in Gymnotus. The
evidence must be sought in the developmental history, and in
comparative anatomy.

Torpedo is peculiarly adapted for the study of ontogenetical
development. "This viviparous fish bears its young within itself
to an advanced stage of growth, so that the newly-born fishes are
already 6-8 cm. long, and able to give distinct electric shocks "
(Fritsch).

The best observations in this department of anatomy, with its
important physiological bearings, are those of Babuchin (1), and
more recently Fritsch (12) ; de Sanctis having previously given an
erroneous description of the development of Torpedo. Ewart
(10) and Engelmann (8) have contributed further data of import-
ance to the " pseudo-electrical " organ of Raja.

With regard to the development of the external form of the
body in Torpedo, de Sanctis distinguishes three main stages,
squaliform, rayiform, and torpediniform. At the end of the
first stage the position of the electrical organ can already be
recognised externally ; swellings — which soon fuse together-
make their appearance upon the visceral arches at the point where
these bend to the ventral side. As soon as the trunk widens,
the embryo assumes the form of the common ray (stadium rayi-
forme), and the continuous forward progression of the discs at
last completes the characteristic rounded form of the electrical
ray. At this stage the electrical organ of the then developed,
but still unborn, fishes exhibits under the lens a delicate
punctuation — the indications of the already perfected column
(Fritsch).

At a very early stage in the development of the gill-arches,
as described above, these appear to consist of bundles of elon-
gated cells, invested by others of a rounded, embryonic character,
and in all respects similar to embryonic muscle-fibres. The deli-
cate cross-striation may be recognised in situ, still better on the
isolated fibre (Fig. 249, a). The fibres, which are at first small,
containing only one or two nuclei, bear many nuclei later on, and
swell up at the ventral end, where a multitude of nuclei are
formed by rapid division, and lie all together, while the plasma
surrounding the terminal part increases in bulk, and exhibits a

XI

ELECTRICAL FISHES

381

kind of swelling (Fig. 249, b, c, rf). The whole is suggestive
" of a tassel, hanging from a loop set with knots (muscle-nuclei) "
(Babuchin). Striated fibrils from the fibres of the trunk extend
into the bladder-like swelling, described by Babuchin, on account
of its being the initial stage of an electrical plate, as the plate-
rudiment (" plattenbildner "). Fritsch defines them as "young

FIG. 249. — Development of the electrical plates of Torpedo from embryonic muscle-fibres. (Babuchin.)

plates," since with continued growth they are transformed directly
into the final structure, and he believes that the characteristic
pear-shaped form of Babuchin's figures must be referred to the
swelling effect of the macerating methods employed. He him-
self, like Krause (17), finds them more loaf-shaped. The
unequal length of the single muscle -fibres, which form the
foundation substrate of a column, causes the plates to be of
different heights in longitudinal section (Fig. 250).

" The non-swollen section of the muscle-fibres always remains
at the same stage of embryonic development, and finally forms a

382

ELECTRO-PHYSIOLOGY

CHAP.

long, narrow, still plainly striated stalk to the plate-rudiment,
which has meantime increased considerably in breadth owing to
proliferation of nuclei. Its ventral half consists of an almost
transparent plasma traversed by little fibres (muscle-fibrils?),
while the characteristic rounded nuclei lie in a finely granulated
dorsal stratum (Babuchin, Fig. 249, e). An isolated column at
this stage consists of thick loaf-shaped bodies, not perfectly regular,
and separated by embryonic cells. These do not take up the entire
width of the column, but lie near and over each other." The
stalks (remains of primitive muscle-fibres) are often attached
laterally to the plate-rudiment, and become steadily thinner,

subserviently disappearing altogether,
while the latter now finally assume the
shape of very thin plates, and fill up the
entire cross - section of the column.
Isolation of the plates is very difficult at
this stage, seeing that the external border
cells gradually coalesce into a firm sheath
of connective tissue round the electrical
prisms. Little as the structure of a
complete column of Torpedo recalls a
striated muscle structure, there cannot, in
view of the above facts, be the slightest
doubt as to the genetic relations between
the two tissues, and one of the most
significant advances, not merely in the

FIG. 250. — L.S. of embryonic column . , . ., 1-1 n

of Toledo. P = rudiment of anatomy, but also in the physiology ot
plate. (Babuchin.) t]ie eiectrical organ, was the discovery

by Babuchin of this connection. As Engelmann remarks (8, p.
149), " oSTo where else in nature have we, side by side, and so
completely accessible to research, the anatomical and physiological
factors for the vital production of mechanical and electrical
energy."

Unfortunately all attempts made by C. Sachs to determine
the embryonic development of the organ of Gymnotus were
fruitless, and we can only conjecture that it occurs in the same
way, generally speaking, as in Torpedo.

In the Bay, on the other hand, there is no doubt as to the
very interesting development of the less highly differentiated
pseudo-electric organs.

XI

ELECTRICAL FISHES

383

Here we no longer have undeveloped embryonic muscle-fibres,
but such as are completely differentiated, striated, and capable of
functioning, from which, " at a late moment of post -embryonic
life," a special modification gives rise to the elements of the
electrical organs.

It can be demonstrated in all certainty that the meandering
layer of the plate, as described above, is directly derived from the
striated substance, more especially in Raja radiata, where, as
Ewart shows, it has the appearance of normal striated muscle

FIG. 251.— Raja batis. Section through a compartment with developed electrical plates. n =
nervous layer; fc=nucleated layer; «i= layer; a = alveolar layer; m/= remains of muscle-
fibre (stalk of plate). (Ewart.)

substance, even in the fully-developed animal. Between this, the
phylogenetically lowest, to the highest forms, which are dis-
tinguished by a complicated meandering course (R. circularis, latis),
there is every possible transition.

As has been said, each single plate of Raja latis consists,
apart from the surrounding connective tissue and ingoing nerves
and vessels, of an anterior stratum of plasma with embedded
nuclei, which is very probably homologous with the motor end-
plates of striated muscle, and in which the numerous and at first
dichotoniously branching nerves terminate.

Then follows the non-lamellated layer, of parallel striation in

384 ELECTRO-PHYSIOLOGY CHAP.

cross-section ; and finally the " alveolar " layer, once more richly
set with nuclei, which Ewart (10) aptly compares with the bayed
inner wall of the frog's lung. From this layer there is, moreover,
a long stalk-like process which extends backwards through the
mucous tissue of the compartment, and ends in the connective
tissue wall of the chamber (Fig. 251).

In very young embryos of R. batis there is no trace of any
electrical organ as such. It is only at a length of about
7 cm. that a horizontal longitudinal section through the tail
exhibits, between the ordinary normal fibres, others which must
be regarded as in the first stage of transformation into electrical
plates (Fig. 252, a). This is at first shown only by a club-like
swelling of the anterior end (where a nerve enters with copious
bifurcation), and a striking proliferation of nuclei, resulting
finally in a sort of end-plate or cap, with which the head of the
club is invested. The further stages of transformation are intelli-
gible without more description from the figures (Fig. 252, 5, c, d},
drawn from preparations from an older embryo 10 cm. long.
Here it is easy to recognise all the essential parts of the developed
electrical plate — the nucleated nerve end-plate at the top, the
non-nucleated, striated meandering layer, with its undoubted rela-
tion to the original cross-striation of the muscle-fibre, and lastly
the alveolar stratum (e,f} derived from an exuberance of the sarco-
plasm and (muscle-) nuclei at the base of the club, with the tail-
like appendage of the atrophied stalk of the plate as the remains
of the original fibre. This long exhibits indications of cross-
striation, and -may under certain conditions be detected even in
the perfectly developed plate.

The electrical organ of R. circular-is is longer, but much
smaller. It consists of curved goblet-shaped plates, correspond-
ing essentially with those in R. batis, where there are already
indications of a goblet-like pitting of the initially club-shaped
and swollen ends of the muscle-fibres.

The approximately parallel lamella? of the meandering stratum
in R. batis are much curved in R. circularis, and the alveolar
layer also exhibits a different structure, and presents a fine
radial striation at its base (Fig. 253). The first trace of a
transformation of muscles into electrical tissue is, however,
ascribed by Ewart to Raja radiata, as shown on the one
hand by the much later commencement of the process, on

ELECTRICAL FISHES

385

the other by the obvious cross-striation of the fully-developed

plates.

The important question of homologies between the lamellae of

I-'i'.. L' :••_'. —L'lijrt batis. a, Portion of a longitudinal section through an embryo.' Club-shaped muscle-
fibres developing into electrical plates, b-f, Further stages of development. (Ewart.)

the matured laminated layer, and the transverse strias of muscular
fibres, was till recently quite undecided. The careful investiga-
tions of Engelmann have thrown some light on the subject.

VOL. II

2 c

386

ELECTRO-PHYSIOLOGY

CHAP.

Exact comparative observation of the different stages in the
development of the organ in Raja clavata in the same embryo,

d

f

7 IT cm. in length (Fig. 254, a-c), leaves no doubt that both the
small, dark, and the broad, clear, transverse stria? of the original

ELECTRICAL FISHES

387

muscle-fibres correspond with the similar cross-bands in the
lamellar stratum of the fully - developed plate. Not merely
preparations at different stages, but the same individual fibre
will present every transition from the " typical striated muscle
substance, to the typical meandering stratum of the perfect
electrical organ." Still plainer is the homology between the
thin, strongly -refractile lamellae of the electrical organ and the
arimetabolous (isotropous) layers, and that of the thick, weakly-

FIG. 253.— Raja circvlaris. Portion of L.S. through an electrical goblet. w = nervous and
nucleated layer ; m=meandering layer ; a=alveolar stratum. (Ewart.)

refractile lamellae, with the metabolous (anisotropous) layers of
striated muscle, under a very high power. In this process of
transformation, the superficial growth of the lamellae increases
vertically to the fibre-axis on the one hand in a marked degree,
while on the other the height of the layers also increases doubly
and trebly. Along with this there are fundamental alterations in
the morphological and physico-chemical reaction of the two layers,
expressed above all in polarised light by the marked diminution
in double refractability, which " in the metabolous layers becomes

388

ELECTRO-PHYSIOLOGY

CHAP.

almost imperceptible, before any other alteration due to the trans-
formation can be discovered." The strong surface -growth of
lamellae depends (as Engelmann showed), previous to the forma-
tion of loculi, essentially upon multiplication of the fibrils at the
periphery of the lamellie, not upon the thickening of those which

FIG. 254.— Raja clamta. Successive stages in the development of an electrical plate from a cross-
striated muscle-fibre. (Engelmann.)

already exist, or upon the widening of the inter-fibrillar spaces.
Later on, in the perfected organ, no fibrillated structure of the
lamelUe can be detected.

If the optical alterations in the series of strata during the
development of the electrical are compared with those seen in
vigorous, physiological contraction, there are striking coincidences,
as pointed out by Engelmann. On the one hand, the arimetabolous

xr ELECTRICAL FISHES 389

(isotropous) lamelke become " optically more homogeneous, more
strongly refracting on the whole, and therefore firmer (less watery),"
while on the other the metabolous strata (particularly those
of the transverse discs) lose in refractability, which simultaneously
diminishes their power of double refraction. The amount of this
diminution is, however, " nil in contraction, as compared with that
in the transformation of muscle-fibres into the meandering layer of
the electrical compartments." It is, moreover, apparent at such an
early stage of development (previous to the club-shaped swelling
of the proximal end of the muscle-fibre) that no other sign of
approaching transformation can yet be detected. At this point,
again, the phylogenetically younger status of the organs of Raja
radiata is apparent, since the double refractility here dis-
appears much more slowly and incompletely than in other kinds
of the same species (R. ~batis, clavata, circularis). This reaction
during the transformation into electrical organs gives substantial
confirmation to Engelmann's conjecture that " only the doubly-
refracting metabolous elements of the muscle-fibrils are the seat
and source of the contractility of the muscle."

The development of the " pseudo-electric " organ in Mormyrus
is much less certain than that of Raja. Yet here, too, Babuchin
(1) was able, on investigating six varieties of the species, to state
definitely that " the electrical organs are again developed from
muscles, and retain their muscular characteristics even when the
formation is perfect." Each " plate '" of Mormyrus consists of
three laminae that can be separated from one another, the two
outer being " structureless, invested from the inner side with a
layer of granulated substance, and set with numerous rounded
nuclei." One of these laminae is the immediate prolongation of
the sheath of the pale (ingoing) nerve-fibres. The middle layer
consists exclusively of very thin flattened muscle-fibres or bands,
lying irregularly near each other. Each single fibre is sharply
striated, while collectively they form a muscular lamina of
firmer consistency towards the border of the electrical plate than
in the centre, with no meandering markings. According to
Babuchin, therefore, the electrical plate of Mormyrus does not
correspond outogenetically with a single metamorphosed nerve-
fibre, as in Torpedo or Raja, but with " an entire bundle of short
muscle-fibres, as found in the lateral trunk-muscles of fishes."

Fritsch (12), too, affirms that a tissue of varying density is

390 ELECTRO-PHYSIOLOGY CHAP.

visible in fine transverse sections of Mormyrus plates, " which
preserves the complicated cross-striation of the muscle in an
extraordinary degree." This forms the middle stratum of each
plate ; the anterior exhibits a delicate longitudinal striation
(analogous to the palisade border of the Torpedo plate), beneath
a fine cuticular border.

If it is thus certain that the electrical organs so far described
are to be viewed collectively as transformed, and specially
differentiated, striated muscles, the most superficial anatomical
comparison serves on the other hand to show that quite different
groups of muscles are in each several case the starting-point of
this marvellous process of differentiation. Thus in Torpedo the
external layer of the small muscles of the bronchial apparatus,
and the external muscles of the jaw which are so marked in the
allied ray, are wanting ; in Gymnotus the deepest part of the
ventral trunk-muscles, save the small remnant known above as
the " intermediate muscular layer," is transformed into the large
electrical organs, while the small organs are derived from the upper
part of the inner muscles of the fins. In Gymnarchus, again, the
electrical organ corresponds with the central portion of the
lateral muscles, while in Mormyrus and Raja the parts of the
caudal muscles adjacent to the lateral lines afford the material of
the " imperfect " organ. The appearance of the electrical organ
is not therefore confined topographically to any definite region,
but every group of muscles, the normal functioning of which is not
indispensable to the existence of the individual, may be held as an
adequate substrate for the development of an electrical organ (G.
Fritsch, 12).

If a transverse section through the trunk of Malapterurus,
which, as regards its muscles, is nearest to Gymnotus, is com-
pared with a similar section of the latter, it is easy on either side
to detect the transverse sections of the four lateral trunk-muscles
so characteristic of the bony fishes (M. latcralcs proprii inferiores
et superior -es, Fig. 255, a, b [Ms] and [Mi], and M. laterales dorsales
et ventrales, [m.d] and [mv] of the figures). These, as shown more
particularly from the lateral aspect, are divided segmentally in
the long axis of the fish by the zigzag ligamcnta intcrmuscularia,
the single discs, each corresponding with a segment, being trans-
formed into hollow cones, which are, as it were, inserted into
each other. Malapterurus is distinguished from other bony fishes

xr

ELECTRICAL FISHES

391

by the appearance of a group of muscles, given off from the flat
abdominal muscles, and beginning behind the shoulder -girdle.
These diminish rapidly in size, and run as a clearly marked band
of muscles below the lateral muscles proper, to the caudal end
( M. lateralis imus [me], Fritsch). The lateral aspect further shows
this strip to be distinctly curved towards the horizontal behind
the ligamenta inter muscularia, so that the short bundles of
primitive muscle-fibres stretched between them are presented as
low, narrow compartments. It is easy, especially in cross-
section, to see that the position of the large electrical organs

FIG. 255. — a, T.S. from tail of Silurus glanis ; I, T.S. from the fourth i of Gymnotus. (Fritsch.)

of Gymnotus corresponds throughout with that of the band of
muscle just described in Malapterurus, which is here wanting,
and has by its transformation given rise to the organ. There is
no less certain proof that the so-called small organ of Gymnotus
has been formed by the transformation of a part of the lower
muscles of the fins. In correspondence with the very scanty
development of the dorsal fin, two small triangular sections
of muscles only are left in the cross -sections of both Malap-
terurus and Gymnotus, beneath the skin of the back (Fig. 255,
a, b, mp). On the other hand, there are, on the ventral aspect
of the cross-section, on both sides from the median plane, two

392

ELECTRO-PHYSIOLOGY

CHAP.

systems of transversely - divided fin muscles (external and
internal, Fig. 255 [mp]), which are especially numerous and
well developed in Gymnotus, and increase posteriorly in number
and extension. The small organ increases similarly in height,
while the number of prisms in the large organ, on the other
hand, decreases towards the caudal end, " since they become
rolled up underneath, and leave the lateral surface of the
body." In the region where the small organs are fully developed,
the upper bundles of the deep fin muscles are wanting, so that
the genetic relation between the two is unmistakable. So,

a

Fir;. 250.— Homology between the electrical organs (0) of Torpedo, and the muscle of the

common Ray (KM). (Pritsch.)

too, in the Torpedinidce, where the powerful jaw muscles of
the common ray (Fig. 256, I [-Of]), which are balled into a
clump, fail almost entirely, and are reduced to an insignificant
vestige. This chiefly involves the external or ventrally-
developed muscles of the gill chamber, representing the system
of the adductores arcnum and the so-called constrictor corn-
munis supcrftcialis (Fritsch), which here correspond functionally
with the masseter, pterygoid, and temporal muscles. The con-
strictor seems more especially to have yielded the elements for
the posterior part of the organ, while the broad, anterior
portion seems to derive more particularly from the modification

xi ELECTRICAL FISHES 393

of the adductor (Vetter, "Kiemen- u. Kiefer-muskulatur der Fische,"
Jcnaische Zeitschr. VIII.).

As regards the developmental processes of the electrical
organs, it is a priori improbable that the number of separate
elements (plates or columns) should increase with the growth of
the individual. Even in 1839 it was affirmed by Delle Chiaje
" that the columns of the electric ray grow by intussusception
(the same number being developed as exists in miniature in the
embryo), merely by gradual increase in mass and size." K.
Wagner in 1847 defended this statement against Valentin and
Babuchin, extending it to the number of plates in the columns,
and tracing it back to its embryological origin. This dictum of
the preformation of the electrical elements makes the number of
columns (and plates) in different individuals of the same species
of electrical fishes to be approximately the same, whether the
animals are examined young and small, or when fully developed.

Du Bois-Ileymoncl (4 e, p. 403) put together in the following
table (Table I.) all the estimates then made of the columns in the
electrical organs of Torpcdinidce.

In these the calculation from the foetus of Torpedo ocellata
speaks very decidedly in favour of the above conclusion. The
anomalous and divergent results of Valentin and Girardi, however,
leave an uncertainty which at first drove du Bois-Reymond
also to the conclusion " that the deposit of columns in different
individuals of the same species was initially different, and did not
alter subsequently." Marked deviations in number of columns,
exceeding the range of individual variations (such as the cases
cited by Hunter and Henle in the above tables), would of course,
on the preformation theory, be ascribed to difference of species.
Fritsch took the trouble to review the family of Torpedinidce
from this standpoint, and the following data (Table II.) give
some examples from his numerous calculations (Fritsch, 12).

[TABLE

394

ELECTRO- PHYSIOLOGY

CHAP.

TABLE I. NUMBER OF COLUMNS IN THE ELECTRICAL ORGANS

OF DIFFERENT TORPEDINID^E

Species.

Length.

Number of Columns in Organ.

Experimenter.

Left.

Single.

Right.

mm.

r

1219

457

1182
470

...

-Hunter

490

^

Raja torpedo . . -J

4Qf)

...

i

|

520

514

}• Girardi

290

265

j

T. Galvanii .
(foetus).

273

82

...

410

298

-Valentin

t

262

...

420

R. "Wagner

T. marmorata . -{

I

393
230

449

420

J-Leukart

Fi i-tns of T . ocellata

81

410

Leukart

With yolk-sack .

400

R. Wagner

Narcine dipterygia

61

130

...

Henle

TABLE II. NUMBER OF COLUMNS IN ONE ELECTRICAL ORGAN

OF TORPEDINID.E

Species.

Length of

Number of Columns.

Difference.

Pish.

( >rgan.

Dorsal.

Ventral.

iniii.

mm.

Torpedo ocellata

121

37

487

491

• 4

,, marmorata

216

66

469

536

-67

, ocellata

161

68

406 .

? ? ) •

335

98

379

404

-25

; ! j

373

114

396

426

-30

, marmorata

357

123

446

484 -38

, ocellata

405

128

404

436 - 32

From this it appears that the number of columns is not the
same on the dorsal and ventral surfaces, but varies to a consider-
able extent. It is questionable whether this is due to a free
ending of the columns within the organ (as is the case in Gym-
notus also). In the sense of the preformation theory, on the
other hand, the number of columns remains approximately equal,
with variations in the length of the organ of 37-128 mm. The
same appears from Babuchin's later calculations from a mother-
fish 42 cm. long, and 3 embryos of 10^- cm. long, with a gut

xi ELECTRICAL FISHES 395

still tilled with yolk. The number of prisms in these was 478,
4G7, 443, while in the former it was 471.

Species of Torpcdinidce (T. marmorata, occllata, panHiera)
which are otherwise quite characteristic, exhibit only small and
inessential differences in the number of columns. On the other
hand, Fritsch confirms the strikingly small estimate (146) in
Astrape dipt&rygia, already given by Henle, finding equally low
numbers of columns in other species of Narcine, cf. N. tas-
iiinniensis, New Zealand, 278; .A7, linyula, China, 274; N. timid,
230 ; N. indica, 145 ; Astrape capcnsis, 147 ; and Tenter a Hard-
wickii, 139. On the other hand, there is an unusually large
number of columns in a speckled degenerate type of Torpedo
nmnnorata (var. annulata). Fritsch was able in Vienna to
investigate two examples of the giant (152 cm. long) American
T. (Gymnotorpcdo} occidental-is, in which he found over 1000
columns (1037), so that it is natural to regard the example
quoted above from Hunter as one of the same species brought to
the English shores by the Gulf Stream. To this, the largest species
extant, must be added, in view of the number of its prisms, T.
(Gymnotorpcdo) hebetans (Lowe), the only specimen of which, in the
British Museum, contains 1025 prisms, although it is no larger
than a medium-sized T. marmorata. The rare T. (Gymnotorpedo)
californica, from the west coast of Africa, is equally distinguished
by its small size and large number of columns.

It is much more difficult to determine the number of columns
in Gymnotus, more particularly, according to Fritsch, in the pos-
terior section of the body, which presents the greatest structural
irregularities. The total sum of all the columns in the large organ
seems, from Fritsch's investigations, to vary within a wide range,
since it falls below 50 in some instances, while in others it is
nearly 100. The greatest number is always found in the smaller
individuals of Gymnotus. Whether this is due to arrested develop-
ment, or to differences of sex, race, or species, cannot be decided.

The exact determination of the number of plates in the
columns of the organ would be theoretically of great value ; un-
fortunately the data are not satisfactory. " There are, on an
average, 10 plates to the millimetre in the electric eel, and since
the organs are about 80 cm. long in a medium-sized animal, 1
metre in length, this would give 8000 plates one behind the
other, without reckoning the wide compartments of Sachs' bundle

396 ELECTRO-PHYSIOLOGY CHAP.

of columns" (clu Bois-Iieyinond). Valentin gives only 5150,
Pacini only 4000. Hunter reckons 150 plates in a column 2 5 '4
mm. long of a medium-sized ray ; Leukart, 180; Pacini, reckon-
ing the height of column at 40 mm., counted 2000 plates, while
Valentin only finds about 300 plates in medium columns (of 11 '3
mm.). The figures thus vary considerably, as is not surprising
when one reflects on the difficulties of enumeration, even with
the most favourable conditions' of preservation. Fritsch (12 g, ii.
p. 1105) estimates the number of plates in a column of Torpedo
(Fimbriotorpedd) marmorata (length of body, 265 mm.) 13 "5 mm.
high, at about 375; since the organ contains 479 columns, the
total number of plates would be 179,625 ; in T. ocellata, with an
average column number of 433 (height of column usually 6 '2 5
mm.) and a content of 380 plates, the sum total would be
164,540 plates. These measurements also bring out the further
and striking point that " the plates are closer together in the lower
than in the higher columns of the same organ," so that the
growth of the latter is in this respect also " a process of swelling,
leading to the divergence of the plates," which on growing increase
in diameter, as found by Boll.

There is another method of determining the number of plates
in the organ of Torpedo. If, as cannot be doubted, each fibre
of the electrical nerve is to be regarded as the axis-cylinder
process of a ganglion-cell of the electric lobe, it is evident that
definite and regular relations must exist between the number of
cells and the number of plates in the entire organ. If the total
number of cells = 1ST, these will, by means of the correlative 1ST
axis-cylinders, which each divide into 18 branches, and supply

1 S

the 6 corners of each plate, innervate N x - - = 3 N plates. From

6

this point of view the enumeration of ganglion-cells in the lobe
is of great interest. After Boll had undertaken a research in
this direction, estimating a number of 53,760 cells, which is far
too low, Fritsch adopted the much safer method of counting the
axis-cylinders in the electrical nerves by photographing sections
of the four nerve-trunks. He obtained a total of 58,318 nerve-
fibres, which on multiplying by 3 gives the number of plates as
174,964. This agrees with the number as given above at
179,625 sufficiently to justify the method.

XI

ELECTRICAL FISHES

397

The Electrical Cat-fish (Malapterurus electricus), the liaasch of
the Arabs, which inhabits many of the rivers of Central Africa, is
an exception to the other electrical fishes, inasmuch as its powerful
batteries are not due to the transformation of striated skeletal
muscle-fibres, but are localised in the skin, which is in conse-
quence transformed into a thick, transparent, speckled rind, which
loosely invests the greater part of the trunk, and causes the
animal to look bulky and shapeless. This peculiarity expresses
itself internally in parallel folds of the skin, during sideway

ir ntHtsiti^-

fc§tJtfit

FIG. L'.JS. — Particle of skin of

terztrus.seen I'roin above ; jnagidfied.
(G. Fritsch.)

!''iu. 257. — T.S. through trunk of Mn{i<iiti I'IU-HZ.
HI = muscles; 0 = organs. (G. Fritsch.)

movements of the body. In cross-section it is evident that this
rind invests the body proper like a sack, and is separated from
the muscular surface by an excessively loose tissue (the so-
called integument of Eudolph), so that it is easily drawn off
(Fig. 257). Between the epidermis proper and the internal,
tendinous boundary of the rind there is in the fresh state a
transparent, gelatinous mass of a clear yellow-gray colour, which
is unequal in consistency, but entirely absent in a few places
only. In the older specimens two longitudinal partition walls
running dorsally and ventrally in the middle line divide the
brawn -like intermediate mass symmetrically into two hemi-

398 ELECTRO-PHYSIOLOGY CHAP.

cylinders surrounding the trunk on either side, and these
represent the single, albeit bilaterally symmetrical, electrical
organ, the weight of which, according to Fritsch, is more than
one -third of the total body -weight. "Anteriorly it extends
laterally as far as the pectoral fin, superiorly in a lobe-like
prolongation to the region between the eyes, inferiorly to the
anterior wall of the shoulder-girdle. Posteriorly ; above to the
origin of the dorsal fin, below to the origin of the anal fin." The
diameter is greatest in the centre of the trunk, and a little in
front of this, and gradually diminishes towards the anterior and
posterior ends of the body.

The complete integrity of the system of skeletal muscles, both
anatomically and as compared with all other electrical fishes, is
very remarkable, and causes Fritsch to assume that the electrical
organ has not in this case been differentiated from the muscles.
Since it here arises wholly from elements of the skin, its struc-
ture must be described in detail.

Under the lens (Fritsch, 1 '2 f) the wealth of small conical
villi is especially remarkable, between the bases of which there
are rounded openings leading into tubular pits in the epithelium.
Around these there is a crowd of binuclear " club-cells " (Fig.
259), which function as unicellular glands, and are well developed
from below, like those found in the skin of other fishes ; these
finally empty their contents into the adjacent epidermoid tubes.
But in this case a special interest attaches to the club-cells, since
Fritsch ascribes to them conjecturally " the same embryonic
arrangement as the elements of the electrical organ." As we
are completely ignorant of the ontogenesis of the latter, this is
only a hypothesis, and must be left over for future investigation.
It should be no matter of surprise if the elements (unicellular
glands) next in electromotive activity to muscle were to prove
capable of forming true electrical organs. For the rest, the epi-
dermis of Malapterurus consists of ordinary epithelial cells (bristle
or prickle cells) and a few goblet cells, i.e. on the side of the villi.
As regards the finer structure of the organ, the first point that
strikes one is the lack of any regular arrangement of the plates
into " columns," as in Grymnotus and Torpedo. Nor can the
brawn-like mass deposited from the skin of Malapterurus, and
similar in consistency, when fresh, to the vitreous body, or to
Wharton's salts, be compared with the imperfect electrical

xi ELECTRICAL FISHES 399

organ of Raja, with its distinct series of cases. Closer inspection
reveals in sections parallel with the surface of the skin, or
with the axis of the fish, a delicate lattice-work of fibres, which
cross at an acute angle, the intermediate spaces appearing grayish
and semi-transparent. After treatment with a hardening reagent
(alcohol, chromic acid) these structural relations are seen still
more plainly. The lattice-work (" sieve," Bilharz) is then found
to correspond with the cross-sections of innumerable fine mem-
branes of connective tissue, which run vertical to the axis of the

• '-

• \ - '^L LJ "

C
-

FIG. 259.— Portion of T.S. through epidermis of Main pic i -itnis. (Fritsch.).

fish, separated by small intermediate spaces. These pass externally
into the mass of fibres of the corium, while they unite internally
into the so-called tendinous integument. In this way the organ
is composed of innumerable partition-walls, running parallel with
each other, but at right angles, collectively, to the axis of the fish,
and divided into a number of small, hollow spaces, of approxi-
mately the same size, with no internal communication (Fig. 260).
The axes of these compartments, which are mostly lens-shaped, or
double pyramidal, all lie parallel with the axis of the fish. Their
equatorial planes are thus vertical to the same, so that the one
wall is turned to the head-, the other to the tail-end. Within

400

ELECTRO-PHYSIOLOGY

CHAP.

this compartment there is " a special, disc-shaped, integumental
expansion," which Bilharz (3) was the first to recognise for the
electromotive element proper, the terminal expansion of a twig of

p x P

FIG. 260. — Mulapternrus electriciis. Portion of L.S. through the organ, showing the spar. •*_(/•') buumli'il
by septa of connective tissue ; an electrical plate is attached to each posterior wall (P) ; NP1 =
plate with nerve-stalk. (Fritsch.)

nerve, the electrical plate, analogous in all respects with the many
tissues of similar structure and composition in the other electrical
organs. Each of these is attached to the posterior wall of its

ELECTRICAL FISHES

401

compartment, while the anterior surface, presenting many in-
equalities, is free, and turned towards the head-end of the fish ;
it is separated by a small fissure filled with gelatinous substance
from the anterior wall of the next compartment (Fig. 260).
From the front aspect, each plate appears as a fairly circular
disc, its central point being marked by a shallow prominence,
giving origin to several high radial folds, while there is a corre-
sponding depression on the posterior surface, from the founda-
tion of which springs a kind of stalk connected with the ingoing
nerve-fibre (Fig. 260, N Pl).

n

yaaaD

igSfc*^^ f ^,— :%,:.

FJQ. 2(jl.—Malaptcrurus. Medium portion of a plate (PI) with nerve-stalk (ne), under high

power. (Fritsch.)

The substance of the plates, which increases in diameter with
the size of the animal, is homogeneous and transparent in the
fresh condition (Fig. 261). Bounded nuclei are embedded at
regular and tolerably wide intervals, and were taken by Babuchin
for star-shaped cells, with fine, hair-like processes. According to
Fritsch, on the other hand, each electrical disc must be regarded
as a multinuclear protoplasmic body, a kind of " giant electrical
cell."

The marginal striation first observed by Eemak on the plates
of Torpedo occurs also on the discs of Malapterurus, and is
ascribed by Fritsch to a peculiar porosity of the most external
layer of the plate-substance (Fig. 261). The "rods" enclosed

VOL. II 2 D

402 ELECTRO-PHYSIOLOGY CHAP.

between each pair of porous canals appear under a high power to
consist of cemented lumps. Each disc is surrounded externally
by a cuticular membrane which here and there may stand free
of the anterior surface.

According to Fritsch, the construction of the electrical organ
out of round discoid plates, which hang " like grapes on their
stalks " from the stems of the finest nerve-branches, is seen most
plainly in young animals, if a section is spread out in a hardening
fluid (1 per cent osmic acid), the intermediate tissue being still
relatively undeveloped. From this we may conclude that, in the
embryo, " the elements destined to form electrical discs appear
as a dense accumulation of cells, between which there is an in-
definite intercellular substance, somewhat resembling the strata
of unicellular glands, as found in the body-wall of many insects,
even in the fully - developed state " (Fritsch). The regular
arrangement so essential to function is developed later, and not
at all in the peripheral parts of the organ. This is so constant
that plates have been found at the posterior end of the organ, in
the same or nearly the same plane as the body-superficies, i.e. at
a right angle with those lying normally, or even in contact with
their posterior surfaces. The inferior activity of the posterior
half of the organ, as determined by du Bois-Keymond, is partly
due to these irregularities of arrangement.

Fritsch also endeavoured to count the electrical plates in the
organ of Malapterurus by calculations from sections of known
length, multiplied into the total extension of the organ. He
found " the number of the electrical discs contained in a longi-
tudinal unit of the organ, as compared with those of another
specimen of Malapterurus, to be in inverse ratio with the length
of the organ in both cases," while in the same individual they
are 2 0 per cent less numerous in the posterior than in the anterior
sections. Fritsch estimates the total number of discs in the
organ at about 2,000,000. " About 1600 lie in series from head-
to tail-end, while a cross-section from the middle of the organ
contains about 3000. One cubic centimetre of organ contains
about 14,000 in a medium-sized specimen."

The whole innervating system of Malapterurus exhibits the
same anomalies as the minute structure of its electrical organ, in
an even higher degree. At the commencement of the spinal cord in
the region where the first vertebra is connected with the os

XI

ELECTRICAL FISHES

403

re, a seemingly unpaired grayish bundle of nerves (Fig. 262,
ne) appears from below, apparently from the lower (anterior)
median cleft. This bundle at once divides right and left, and
consists of three pairs of nerves, closely invested with connective
tissue, the roots of the second and third spinal nerves, and the elec-
trical nerve. Bilharz regarded the last as a new element, inserted
between the others, while Fritsch (12) has
determined its connection with the so - called
lateral nervous system, derived in all fishes from
the trit'/i: in Inn s and vagus. The physiological
function of this system is to supply the skin-
organ, which is so highly developed in fishes,
with secretory and sensory nerve-fibres. The
superficial portion of the lateral nervous system
of the vagus in Mcdapterurus, as shown by
Fritsch, runs over the electrical nerve just beneath
the shoulder-girdle, and then posteriorly into the I
muscles. Comparative observations on the
lateral nervous system of the closely allied, lion- jy/,
electrical, common cat-fish (Silurus) shows that
the truncus lateralis vagi emerges after interlacing
with the lateralis trigcmini " in two fasciculi
behind the shoulder-girdle. Immediately after
its passage it sends a slender branch to the skin
for the shoulder region, and a stronger descend-
ing branch to the anterior extremities, and their
vicinity, and to the skin of the ventral region.
A superficial branch is then given off, which
passes downwards from the lateral canal in the antero-posterior
direction, and sends 5—6 long descending branches to the ventral
region just below the skin." All these branches of the truncus
lateralis are wanting in Malapterurus, being replaced (in Fritsch's
opinion) by the electrical nerve, ivhich here represents a branch of the
nerve that in other fishes subserves secretory and sensory functions.

And, in fact, like the lateralis vagi in the cat-fish, this nerve
does, immediately after its exit from the vertebral column, send
out a fine ramus to the shoulder region, and pectoral fin, which
reappears at the inner border of the head of the lateral
muscle to the shoulder -girdle, along with the artery of the
electrical organ. It then passes backwards between this and the

404

ELECTRO-PHYSIOLOGY

CHAP.

straight muscle to the belly, running in the loose connective
tissue between muscles and integument, in company with the
artery and vein, along the side-line towards the posterior border of
the organ. Branches are given off repeatedly on either side,

FIG. 263. — Rind of Mulu^/i TCC/IV, from the inner aspect, showing the two electrical '
nerves (ne), and their immediate ramifications. (Fritsch.)

which, after running a short distance and dividing once or twice,
pierce suddenly through the inner tendinous integument of the
organ (Fig. 263).

The electrical nerve is of considerable diameter at the middle
of its course, this being the more remarkable since — as Bilharz first
pointed out — it is a single, giant, medullated primitive fibre, which

XI

ELECTRICAL FISHES

405

rises integrally from the spinal medulla, and subsequently bifurcates,
by repeated branching, into as many branches and rarni as there
are nerves in the electrical organ, i.e. as are contained within its
plates and chambers. The total diameter of the entire nerve,
characterised in the fresh state by its peculiar silvery colour, is in
no way due to extraordinary size of the original primitive fibre,
but much more to the vigorous development of the connective-
tissue sheaths, with which the nerve is invested down to its finest
terminal ramifications. The disposition of these sheaths is best

FIG. 264. — Portion of T.S. from electrical nerve-fibre of Main ptcr tints. (Fritsch.)

understood from transverse sections, such as Fig. 264, after Fritsch,
from the nerve-trunk. In the centre is the round section of the
axis-cylinder, O'OOS mm. in diameter, surrounded with a medullated
sheath from about 0'03 to 0'012 mm. in breadth. Externally to
this there is first a broad zone of reticulated connective tissue,
regarded by Fritsch as the analogue of the Henle-Schwaiin
sheath (the " inner sheath " of Bilharz). This occupies ^ of the
total diameter of the trunk, which is about 1/1 mm., and may,
with the nerve-fibre, easily be shelled out from the next, concentric
layers of connective tissue, which are richly vasculated. Seeing
that at every division of a nerve-fibre the total cross-section of

406 ELECTRO-PHYSIOLOGY CHAP.

the branches considerably exceeds that of the trunk, the same, of
course, occurs in the electrical nerve also, and Fritsch computes
that after giving off twenty-five branches only, the diameter of
the nerve is more than doubled. Although the cross-section of the
axis-cylinder in the medullated terminal branches is of scarcely
measurable proportions, the sum of the cross-sections of the collective
nervous processes in the plates (which swell enormously after losing

ne

FIG. 265. — J\Inlii]iti i'ii /-H.S. One of the two yiunt ganglion-cells ; nt = axis-cyliinler process. (Fritsch.)

the medullary sheath) must be reckoned at about 14'113 sq. mm.,
so that if the superficies of the trunk were only 40'7l51 p the
total cross-section might increase (by ramifications and terminal
swelling) 346,760 times during its course from centre to organ.
This is mainly due to the increase of interfibrillar intermediate-
substance, although a fibrillated structure of the axis-cylinder,
apart from the stalk of the discs, has not been demonstrated.

A small rounded spot may be detected, even with the unaided
eye, upon the long section of the spinal cord, near the origin of

xi ELECTRICAL FISHES 407

the two electrical nerve-fibres (Bilharz). This spot is distinguished
from the surrounding matter of the cord by its darker colour, and
is found under the microscope to be a multipolar ganglionic body
of giant dimensions, its axis-cylinder process forming an electrical
nerve. The two ganglionic bodies (Fig. 265) are lenticular in
form, the equatorial diameter being as much as 0'21 mm., the
axial about one-half this. Internally there is a large blistered
nucleus, which, like the cell itself, is ellipsoid. ' " The body of the
cell is never rounded towards its neighbours, but lengthens gradu-
ally into large protoplasmic processes, which subsequently curve
distinctly, and form a loose tissue at about the middle diameter of
the cell." This becomes more dense after the axis-cylinder process
has been given off, and forms a kind of sieve (base of the electrical
nerve), from which the nerve emerges, and becomes invested on the
other side with the medulla. This structure is the more remark-
able since the protoplasmic processes, as well as the axis-cylinder
developed from them, are certainly of nervous 'origin.

II. GENERAL ACTION OF DISCHARGE FROM ELECTRICAL FISHES

The physiological action of the shock is, of course, of first
interest, in so far, at least, as concerns the powerful discharges
from the highly differentiated electrical organs of Torpedo,
Gijmnotus, and Malapterurus. The subjective physiological action
of the shock of the fish may, as was pointed out by du Bois-
Eeymond, take effect under different conditions. It is, however,
indispensable (since all action of an animal or vegetable electro-
motor is produced by short-circuiting) that the curves of current
should impinge upon the human body at sufficient density, either
directly, or by means of a conductor of resistance parallel with
that of the organic tissues, e.g. water, moist non-conductors,
etc. Metal, employed as the intermediate layer — seeing that its
resistance vanishes against that of the moist parts — is a protection
against current-diffusion, according to Kirchhoff's law of refrac-
tion for electrical currents ; so that it is possible- — as shown by
Humboldt and Gay Lussac — to carry an electrical fish between
two movable electrical plates that are in contact, without dis-
turbance from shocks. This fact was compared by the elder
Becquerel to the well-known experiment in which the secondary
twitch from muscle to nerve (Matteucci's contraction) may be

408 ELECTRO-PHYSIOLOGY CHAP.

blocked by the introduction of gold-leaf or tinfoil, between the
primary contracting muscle and the nerve of the secondary pre-
paration (cf. I. p. 361).

The effects of shock from Torpedo are most apparent when the
subject is in circuit with the whole battery (which is vertical in
this case), i.e. when the lead-off is from upper and under surface
of the fish. In Gymnotus, too, and in Malapterurus, the shock is
more powerful in proportion as the contacts are further apart, and
the conductivity of the leading-off circuit more perfect, i.e. it is
strongest when the animal is held in the air by head and tail.
Some idea of the force of the electrical discharges from G-ymnotus
is conveyed in the fact that Sachs obtained very marked shocks
on grasping an electrical eel 123 cm. long with rubber gloves.
On one occasion he received the full effect of the shock. He
relates that " he had fallen into the water, and emerged with wet
clothes clinging to him, while endeavouring (guarded with the
rubber gloves) to throw a lively, fresh-caught eel, over five feet
in length, into a trough. The animal escaped and fell on to both
his feet, so that its head made contact with one leg, its tail with
the other, remaining thus for several seconds. In this position,
when Dr. Sachs' legs completed the circuit between the poles of
the fish's battery, he received a rapid series of shocks which,
since they were not weakened by any deriving circuit, and were
easily conducted through the wet clothes, took effect with in-
describable intensity. Uttering loud cries of pain he stood as
though petrified by the shock, and was quite unable to rid himself
of the animal" (du Bois-Eeymoncl, 4 c, p. 131).

This was the effect of direct contact with the fish outside
the water, but the action is hardly less strong in the case of
immersion in the electrical current, where the lines of current which
traverse the water impinge upon the human body. In this mode
of action, to which, as Faraday points out, the electrical organs
are peculiarly adapted, each point in contact (or animal body)
receives a part of the discharge approximately proportionate to its
size. Even the early observations frequently refer to falling
under these conditions (du Bois-Eeymond, 4 e, p. 132). Sachs
affirms that horses invariably drop when struck by gymnoti, so
that in traversing the cafios it is necessary to seek out shallow
places, and the foremost rider pushes a stick into the w;it»ir.
" The water becomes filled for a considerable distance with lines of

ELECTRICAL FISHES 409

current from the disturbed eels, and dead fish and frogs then appear
at the surface."

As regards the nature of the effect produced by a not im-
moderately strong discharge, it was remarked by Sachs that it
exhibited a strong resemblance to the brief action of the sliding
inductorium with so-called vagus electrodes (hook -shaped metal
wires). " There is an unmistakable sensation of persistence, of
oscillatory character in the shock." In the Gi/mnotus the
shock, according to du Bois-Eeymond (4 d, ii. p. 619) is "less
sharp than that from a Ley den jar, and rises more gradually ;
it is often possible to distinguish several maxima,"

" The discharge of Malapterurus is surprisingly powerful in com-
parison witli its size. If the head and tail of a vigorous fish are
touched in water with the fore-finger, the shock does not indeed reach
beyond the middle-finger joint, but if the animal is grasped with
well-moistened hands a sharp shock is perceived as far as the elbow.
AVith the secondary coil pushed right up, and a Grove's cell in the
primary circuit, a break shock taken through the hand is about
equal to a " strong " shock from a fish. Babuchin received such
a powerful discharge from one-half of the electrical organ of
Malaptcrurus, on exciting the oblongata, that " he remained uncon-
scious for several minutes." He points out the difference in
sensation between the shocks of Torpedo and of Malapterurus.
The shocks from the former are, as it were, blunter and duller,
those from Malapterurus are sharper, more stinging and penetrat-
ing ; briefly, the difference is the same as that between the currents
of the primary and the secondary coils — between the extra-current
of the principal, and the break shock of the secondary circuit.
Mere contact with the point of a barbel of Malapterurus is enough
to cause a sharp prick in the finger. This is never the case with
Torpedo. Du Bois-Eeymond suggests that the difference may be
due to the different mode of innervation of the organ in the two
cases. " At the half of the Malapterurus organ (which is inner-
vated by a single ganglion-cell) the shock of the most distant plate
is separated from that of the nearer ones only by a minute fraction
of a second, as required for the wave of induction to travel the
length of the organ. In the organ of Torpedo, on the other hand,
the duration of the discharge is determined by the time required
for the excitation of the entire electrical lobe. And this period,
judging by what we know of the transmission of any stimulus

410 ELECTRO-PHYSIOLOGY CHAP.

through a ganglionic complex, e.g. spinal cord, may be comparatively
protracted. It is obvious that the shock will be sharper, more
stinging, and more acute, in proportion as the discharge from the
plates occurs more simultaneously." The effect, moreover, differs
according to the part at which the Torpedo shock takes action.
Schonlein experienced pain on receiving it on the back of the
fingers and hand, while in the palm of the hand it is a mere
" pricking " sensation. In artificial excitation with induction
currents the feeling of contraction in the muscles of the hand
may always be distinguished from the cutaneous sensations.
According to Schonlein this never occurs in the shock of
Torpedo; the discharge must therefore be inadequate to excite
the muscles beneath the skin. Faraday compared a medium
shock from the electric eel 101'G cm. long, on which he experi-
mented in 1838, with the discharge of a Leyden battery, charged
to the maximum with fifteen jars, and a double-glazed glass
surface of 2 '2 5 8 sq. m. The physiological action of the Torpedo
discharge is disproportionately weaker, with the exception of the
large species (T. occidentalis), by the shock of which Captain Atwood
was repeatedly thrown to the ground, " as if felled by an axe."

In order more exactly to investigate the action, strength, and
direction of the discharge from a fish still in water, Faraday
employed a pair of saddle-shaped, curved electrodes (Fig. 266) for
Gymnotus, invested internally with metallic, externally with in-
sulating substances. These were applied to two points, correspond-
ing with the poles of the organ, of the fish, lying upon an insulating-
stage (glass plate), which again was gripped by the gutta-percha
rim of the saddle. The segments of the fish are then almost as well
insulated as if they were in the air. It is best only to leave as
much water as just covers the animal when lying upon the glass floor
of a shallow trough. In order as perfectly as possible to insulate
the part of the body gripped by the saddle in the smaller and
weaker Malapterurus, du Bois-Keymond made use of a cover for
leading off, shaped like the lid of a mummy-case (Fig. 26V). This
was moulded in gutta-percha to the shape of the animal, the ends
being lined with tinfoil (4 r/, ii. p. (>70).

The insulation from the surrounding water was in this
instance so complete that even the very delicate method of
testing for current escape in water (to be described below) failed
to detect any at the time of the discharge. Du Bois-Eeymond

XI

ELECTRICAL FISHES

411

(4 g, h) finally decided on the arrangement shown in Fig. 268, as
the most convenient for leading off from the torpedo in water.
A circular zinc-plate, covered with flannel, about the same size
as the body (v vj, was placed at the bottom of a glass vessel
30 cm. wide and 10 cm. deep. A portion of the zinc was bent
outwards for leading off. The fish lay upon the flannel. The
dorsal shield, for leading off from the back, is again a zinc-plate
shaped to the fish with the edge turned up ; the upper surface is
lacquered, and a wooden knob in the middle carries the second
wire for leading off.

By this method it is easy to lead off the shock, and to
experiment without injuring the animal. A valuable instru-
ment, with many applications, is the nerve-muscle preparation

FIG. it>i ;.

Fit;. -T'7.

of a frog, employed as early as 1797 by Galvani, and later again
by Matteucci, in experiments on Torpedo. Du Bois-Eeymond
constructed the so-called "frog-alarum" (Fig. 268, FW), by lead-
ing off part of the discharge that was passing through the water
containing the fish, by means of a pair of submerged electrodes,
to the nerve of a rheoscopic leg, the muscle of which rang a bell
when it contracted, and thus indicated the successive dis-
charges of the organ. In this way the electrical activity of a
fish under water can be observed with little trouble and absolute
certainty for hours at a time.

Schonlein (30) has recently employed the telephone for the
same purpose, with very good results. He connected one end of
it with a lead plate lying 011 the floor of the fish-trough, while
the wire from the other pole ended in a smaller lead plate, that
dipped into the water. Even in weak animals (Torpedo}

412

ELECTRO-PHYSIOLOGY

CHAP.

Schonlein found that the discharges were sufficiently vigorous to
fill the entire basin, measuring 1 x 0'4 x 0'3, with lines of
current audible in the telephone. He thus detected that the
animals sometimes give spontaneous discharges without apparently
any direct stimulus, e.g. on the approach of other animals, or of the
collecting plate. But as a rule 'a true discharge follows only from

FIG. 268.— Schema for leading off the shock of Torjialn. ] .Ff7=frog-alaruin. (Du Bois-Reymoml.)

contact, or some other excitation. In G-ym/notus, and according
to du Bois-Beymond in Malapterurus also, the seat of stimulation
is by no means immaterial. The barbels of the last fish seem
to be peculiarly insensitive, since their stimulation never pro-
duces a discharge. As regards requisite strength of stimulus,
again, great differences are apparent. G-ymnotus at times reacts
to the faintest impression, at others a discharge can only be
provoked by determined "picking" with a pointed body. In

ELECTRICAL FISHES 413

making preparations from the organ of Torpedo, Schonlein
usually observed a discharge on cutting through the skin, as
well as on removing the cranium, especially if the canals and
utriculus were broken into. Division of the medulla oblongata
was also accompanied by a discharge.

The relatively considerable duration of all spontaneous or
reflex discharges is apparent not merely in subjective sensations,
but also objectively with the above modes of investigation.
With strong excitation, the hammer of the frog -alarum is
.•(intinuously pressed against the bell in both Gymnotus and
Malaptcrunis. When Malaptcrii.rus is excited, it seldom discharges
once only. The bell usually rings 2-3 times, either in quick

\

\

i i i \ ^inm iwiid j

\\\V-~^fnWj:// /

x<— ^r^-' '

x^_^x / \ -v ,x

/ X
__ -" x.

FIG. 269.— Schema of current distribution outside the body of 7'<« pedo. (Cavendish.)

succession or at longer intervals. In telephone observations
Schonlein found that both pitch and character of sound, from the
natural discharge of Torpedo, varied considerably. " If the sound
were expressed in letters, the vowels a\ e, or i must be selected,
never o or u." Brief shocks seem to be best expressed by R,
sung at different pitches. Longer discharges seem as a rule to
correspond with a higher pitch than brief shocks.

The endurance of the fish is considerable. Du Bois-Eeymond
tested his-malapterurus every ten minutes, for two hours. "In-
cluding the removal of the fish to the experimental trough and
back again, it was excited 11-14 times; it yielded at least
twice or three times that number of shocks. During the series
of experiments the fish became visibly fatigued. It grew pale,
and at last responded only by a single shock when the cover

414 ELECTRO-PHYSIOLOGY CHAP.

was put on" (4 d, ii. 618). Of Torpedo, too, we know that "it
keeps up a series of discharges at more than seconds speed, for
over a minute." Schonlein states that the living organ, with
intact circulation, cannot give more than 1000 shocks, either
when the discharges follow spontaneously upon strong protracted
stimulation of the animal, or when they are artificially discharged
from preparations of the organ. In the first case the animal
requires a longer recovery (at least a quarter of an hour) for
the restoration of its power of discharge. The excited organ, on
the other hand (unlike muscle), shows no recovery after con-
tinuous excitation of only 10 sec. with tetanising induction
currents. Sachs' gymnotus was electrically non-fatiguable.
200—300 shocks could be elicited from it without perceptible
diminution; an animal which had presumably discharged 150
times in an hour could still send a powerful shock through a
chain of eight persons, if those at the ends were in contact with
its head and tail (du Bois-Eeymond, 4 e, p. 256).

We have seen that Cavendish (1776) arrived, by means of a
submerged model of Torpedo, connected with a Leyden jar, at a
substantially correct idea of the distribution of potential on the
surface, and in the surrounding water - - as shown by the
accompanying schema, Fig. 269. The improvement in physical
technique, more particularly the introduction of the galvano-
meter, enabled Colladon, and still more du Bois-Keyrnond, to
confirm and enlarge the results of Cavendish in all essential
points (4 g, k, p. 193). Colladon formulated the three following
propositions in 1 8 3 1 re distribution of potential upon the surface
of a torpedo in air, during discharge :—

1. "All points of the back are positive towards any point of
the ventral surface. Intensity of current diminishes in pro-
portion to the distance of these points from the organ ; at the tail
it is almost at zero.

2. 'Two asymmetrical points of the back, or two similar
points of the belly, almost always give current through the
galvanometer ; the point proximal to the organ is positive on
the dorsal, negative on the ventral surface.

3. "There is no deflection in the galvanometer from two
symmetrical points of the back or belly."

Since the columns, of which the E.M.F. increases with the
number of plates, diminish about 0'6 mm. in height from the

xr

ELECTRICAL FISHES

•115

medial to the lateral wall of the organ of Torpedo, it is quite
clear why there should, in the fish in air, he a current as
stated by Colladon and Matteucci between median and lateral
points, from former to latter on the back, and vice versa on the
belly. If all the columns were of equal height in both organs,
the organs being, moreover, brought together in the median plane,
and there united, the centre of the median line would be most
positive on the dorsal aspect, most negative on the ventral. :' On
separating the organs again, the most positive and most negative
points in each organ would — -as du Bois-Eeymond pointed out—

FIG. 270.— Schema of current distribution outside the body of Torpedo. (Du Bois-Reyraoml.)

(in correspondence with the distance between the organs) lie mid-
way between the median edge and the centre." There would
thus — at equal height of all the columns — be a P.D. between
back and belly in the same direction, although weaker. Reduced
height of columns towards the sides, on the contrary, sends the
points of greater positivity and negativity to the median border
of the organ. There are thus, as du Bois-Reyrnond pointed out,
currents in the back of Torpedo from these borders also to the
median line, and vice versa in the belly. The accompanying
Fig. 270 shows the direction of the lines of currents in a diagram
of the fish, after du Bois-Reyniond. Here we see that the curves
" not merely radiate from the so-called polar surfaces, but also cut

416 ELECTRO- PHYSIOLOGY CHAP.

the lateral surfaces of the organ. They are directed inwards as
well as outwards through the body of the fish, and further fill up
the cavity."

With regard to the immunity of Torpedo to its own shocks,
it is to be noted that " the currents which flow along the back,
from the median walls of the organ to the middle line, and con-
versely on the ventral surface from this line to the border,
necessarily find their path through brain and cord ; and, since
this is the shortest path between the most active parts of the
two organs, there can be no stronger current through the torpedo "
(du Bois-Eeymond).

Du Bois-Eeymond was able to reproduce all these effects
upon artificial models, by grouping zinc -platinum elements
together in series like electrical plates, and dipping them sud-
denly into water, upon which the current spread itself as in a
discharge, and was led off in a similar manner.

On leading off from symmetrical points of the dorsal or
ventral surface, du Bois-Eeymond obtained deflections from his
fish during the shock, which might be due to unequal innervation
of the two organs.

In Malapterurus du Bois-Eeymond established that " during
the discharge each point of the organ proximal to the tail is
positive to those nearer the head, and that it is unimportant
whether the point lies at the circumference of a given cross-section
of the fish, or at its back, side, or belly," so that the polar surfaces
of the organ lie, as in Gfymnotus, towards the head and tail.

It follows that the direction of the normal discharge in
electrical fishes is invariably at right angles to the plane of the
plates. In Torpedo, where the plates are horizontal, with normal
position of the animal, the discharge therefore occurs between
back and belly ; in Gymnotus, on the contrary, where the plates
are, as a rule, vertical to the long axis of the organ, i.e. in the
transverse plane of the animal, the discharge passes longitudinally
from head to tail. The same is the case in Malapterurus, where
the plates exhibit a similar arrangement.

A very remarkable rule at first appeared to be indicated in the
fact, as pointed out by Pacini, that the distribution of the nerves in
Torpedo and Gymnotus occurs always upon that surface of the plate
which is negative in the discharge, i.e. the lower surface in Torpedo,
the posterior surface in Gymnotus. In this last animal Faraday

xi ELECTRICAL FISHES 417

had already proved by potassium-iodide electrolysis that " every
point of the fish in water, or of its immediate vicinity, is negative
to every point anterior to it on the fish, and positive to every
posterior point, the effect being stronger in proportion as the
points with which contact is made are farther apart, while it
disappears on leading off symmetrically to the sagittal plane."
This is intelligible if, at the moment of discharge, the anterior
surfaces of all the electrical plates are positive, the posterior
negative, as du Bois showed upon a submerged model of prisms
made of zinc and platinum elements soldered together (4 d, ii.
p. 683). The current is accordingly ascending ("positive" in
direction) in the columns of the organ, i.e. directed from tail to
head.

Bilharz, having convinced himself that the nerve entered by
the posterior surface of each plate in Malapterurus, also concluded
forthwith that the direction of discharge would correspond with
that of Grymnotus, without actually being able to perform the
experiment. Du Bois-Eeymond showed, on the contrary, that
the .discharge in the Malapterurus organ is invariably directed
from head to tail, i.e. the opposite of Pacini's rule. This is also
true of Raja.

It was stated at the beginning of the chapter that Faraday
had succeeded in demonstrating all the signs of a true electrical
discharge (as laid down by him) with one exception, in the shock
of electrical fishes (Grymnotus). He obtained physiological action,
deflection of magnetic needle, magnetisation, production of heat,
spark, electrolysis, attraction and repulsion ; conduction through
hot air (flame) alone seemed impossible, a fact already observed by
Cavendish, and of which he had failed to find any explanation.
Du Bois-Eeymond subsequently pointed out that this is only a
special instance of the general fact that, notwithstanding the
frequently enormous power of the discharge from electrical fishes,
it is unable to overcome even slight hindrances to its passage.
This is expressed inter alia in the fact that it is seldom
possible in Torpedo and Malapterurus to elicit so-called discharg-
ing and closing sparks from the shock ; while, on the other hand,
it is easy to get separation sparks. In the first case there is a
gap between the stationary or approximating metal points, which
the current bridges over at closure ; in the second case a circuit
in which current is flowing is interrupted. Du Bois-Eeyniond

VOL. II 2 E

418 ELECTRO-PHYSIOLOGY CHAP.

when experimenting on Malapterurus, employed a spark micro-
meter, with which two platinum points could be brought as close
together as O'Ol mm.; he also made slits in strips of tinfoil,
which were not wider than 0'0033-0-0050 mm. Yet he never
succeeded in getting a discharging spark during his investigations
with the microscope in a dark room, although an induced current,
imperceptible to the tongue, leapt over the same gap with produc-
tion of sparks, at 90 mm. distance of secondary coil.

On the other hand, Santi-Linari and Matteucci on Torpedo,
Faraday on Gymnotus, and du Bois-Reymond on Malapterurus
saw separation sparks, when the fish was stimulated by the con-
tact of mercury with a platinum point, or by rubbing two files
together, or by drawing a spring along a cogged wheel. By
means of the frog-interrupter it was possible to open the circuit
each time by the twitch of the muscle at the acme of the
discharge, when the separation spark always appeared. Dis-
charging sparks have been several times observed on Gymnotus
only. As early as 1773, Hugh Williamson, in Philadelphia,
received a shock through a gap in the circuit, the diameter of
which he compared to the thickness of "double post paper"; but he
saw no spark. Walsh, on the other hand (as communicated by
du Bois-Reymond, 4 c, p. 158), succeeded in discharging a spark
at a slit in tinfoil with a gymnotus brought to London from
Guiana in 1775, so infallibly that he was able to demonstrate it
10—12 times in succession to more than forty members of the
Royal Society. Sachs again failed conspicuously to produce
closing (discharging) sparks in a tinfoil gap of O'l mm. Under
these conditions it is not to be wondered at that the shock from
Gymnotus fails to pass through rarefied air and to light up a
Geissler tube.

The explanation of all these facts, which are at first sight so
remarkable, is simply, as du Bois-Reymond (I.e. p. 161) showed,
that the current of electrical fishes, like all other animal electro-
motivity, is due solely to derivation. " In the case of two equal
currents A and B, flowing in two conductors of equal resistance,
A, however, being in an undivided circuit, while B is completed
by derivation, the addition of an equal resistance to both
conductors will diminish B more than A, the more so in propor-
tion as the resistance of the rest of the circuit is greater."

" If the fish is connected with a metallic circuit forming a

xi ELECTRICAL FISHES 419

good conductor, an intense current is developed in this, and by
opening the circuit at the appropriate moment, a gap is produced
at the instant of opening, which is smaller than can be attained
by placing two fixed metals in close proximity. Across such a
gap, the current, augmented by induction effects, will readily
pass as a spark.

" If, on the other hand, there is a previous gap in the experi-
mental circuit, no matter how small, there will be no deriving
branch of current in the circuit, capable of sparking across it.
It is thus a delusion to suppose that the powerful discharge of
the electrical fish is incapable of bridging over the gap, for in
reality the gap prevents the development of the derived current,
which results in a powerful shock when well conducted. The
powerful shock that is expected to spark across the gap is
actually non-existent when the gap is present " (within certain
limits of extension for the gap).

Accordingly, in all experiments on electrical fishes where
strength of effort is required, it is a rule to reduce the external
resistance in the leading -off circuit as much as possible. Du
Bois-Eeymoud first pointed out the adaptation of the different
electrical organs to the media in which they have to act. " The
organs of Torpedo require no great internal resistance in sea-
water, and can do with less E.M.F. ; they are short, with a wide
cross-section. The fresh- water organs of Malapterurus and G-ym-
notus 'require great internal resistance, ergo greater E.M.F. ; these
are long with a small section."

Du Bois-Eeyniond first drew attention to the ease with which
a discharging spark can be elicited by the shock from a fish, with
the help of induction, by leading it through the primary coil of a
Euhmkorff 's inductorium. If a spark-micrometer is introduced into
the secondary circuit, two sparks will regularly appear, one larger
immediately followed by a smaller. Armand Moreau (du Bois-
Eeymond, 4 d, p. 628) even succeeded in showing the electroscopic
attraction and repulsion by the shock, on replacing the platinum
points of the spark-micrometer by two bent copper wires, to the
ends of which two gold leaves were attached. " At a distance of
3 mm. the movement of the leaves at the moment of the dis-
charge was doubtful, at 2 mm. they obviously attracted each
other, and at a less distance they flew together, with a magnificent
green flash, which left the leaves in cohesion."

420 ELECTRO-PHYSIOLOGY CHAP.

Electrolysis of potassium iodide was often used instead of
the multiplier to determine the direction of shock in the fish and
the distribution of surface-tension. The discharge was then led in
by two annealed platinum points to a strip of filter-paper saturated
with solution of potassium iodide. Du Bois-Eeymond (4 c, p. 163
and 7) then encountered the paradoxical phenomenon that in the
discharge from both Malapterurus and, as he found later, Torpedo,
an iodine spot appeared under loth electrodes, but was as a rule
more distinct in the former beneath the point corresponding with
the tail. John Davy and Matteucci had not remarked this effect
on Torpedo, nor Faraday, Schonlein, and others on Gymnotus,
and Sachs also failed to obtain it in the latter.

Since the alternation of the discharge thus seemed possible,
a closer examination was required. It then appeared that the
" secondary " iodine spot under the negative electrode can be
produced by single induction -shocks also, if, as is usually the
case, the circuit is left closed after the current has ceased to flow.
Here it is undoubtedly due to the " current from the opposite
discharges received by the platinum points dipping into the
iodide of potassium solution, under the action of the induction
current." " The process in the fish is quite similar to that in
the induction circuit. The circuit remains closed for some
moments after the shock has been given, however quickly the
saddle be lifted out of the water, there being, moreover, no especial
reason for haste. During this time a secondary current must
cross the current of the fish in the opposite direction. This is
derived not merely from the charges of the platinum points
which dip into the iodide of potassium solution, but from those
of the platinum saddle also. This secondary current must in-
evitably produce a corresponding spot of iodine under the previous
kathode and present anode" (4 d, p. 651 f.). Du Bois-Eeymond
proved by experiment that demonstrable polarisation of the
electrodes does occur from the discharge of the fish. The current
from the shock was conveniently kept away from the galvanometer
(by the frog -interrupter) through a derivation circuit, and in
order to make the polarisation visible, it was only necessary to
open this as soon as possible after the shock.

The electrical manifestations in those species which were
termed above " pseudo-electric " (Raja, Mormyrus) are much less
conspicuous than in the electrical fishes proper, as described

xi ELECTRICAL FISHES 421

above. Here, as in muscle, galvanometric evidence alone is
reliable. James Stark (cf. 32) was led to the discovery of the
electrical organ of the ray on hearing a fisherman say that a
shock resulted from touching the tail of the living animal. It is,
in fact, easy with the galvanometer to determine the fairly
energetic action of the organ. If a living ray is stretched, with
its ventral side downwards, upon a board (shaped like a draw-
net), the body being then immersed in sea- water, so that only the
tail projects beyond the handles of the board, it is easy to apply
two unpolarisable electrodes corresponding with the ends of the
organ. During rest there is, as a rule, little or no difference of
potential. Mechanical stimulation of the skin, on the other hand,
always produces a discharge of such intensity that even a small
fraction (YOTF) °f the current is sufficient to drive the scale out of
the field (Burdon-Sanderson and Gotch, 13 c). In the leading-off
circuit the current passes from posterior to anterior electrode in
the organ itself, therefore it is antero- posterior. In the Mor-
myridcv, as pointed out by Fritsch (12 i), the electrical current
flows in the body from tail to head, i.e. in the same direction as
in Torpedo and (rymnotus. Specimens 15 and 20 cm. long
produce, as Babuchin remarks, " hardly perceptible twitches in
the rheoscopic frog's leg, while fish of 40 and 50 cm. evoke
sharp, maximal twitches, and can be felt by man, although
not more distinct than from a torpedo 10 cm. in length." In
vigorous and selected animals Fritsch was able to detect dis-
charges with the frog-alarum, when the electrodes, dipping into
the water of the holder, were brought as near as 20-30 cm.
without actually touching it.

A. v. Humboldt had already pointed to the possibility of
a partial discharge of the electrical organ : he noted that
only one of two metal rods at 10—12 mm. distance from the
gymnotus received the shock ; the other not. C. Sachs placed
four toads' legs on four different points of a gymnotus taken
from the water. All four twitched with strong discharges, but
if weak shocks were provoked by picking at the skin of the
tail, the hindmost preparation alone contracted. In view of the
innervation of the organ of Gi/mnotus, its " local discharges "
(du Bois-Eeymond) are easily interpreted, while it seems equally
clear that the Mcdapterurus organ can only function as a whole.
C. Sachs found a striking difference in regard to the strength

422 ELECTRO-PHYSIOLOGY CHAP.

of the discharge from the anterior and posterior half of Gym-
notus, in the same sense as that previously noted by du Bois-
Eeymond in Malaptcrurus (4 d, p. 630), where the anterior
half gave much stronger deflections of the galvanometer than
the posterior (in the ratio of about 11:6). Since this differ-
ence, as shown by du Bois-Eeymond, disappears with increasing
resistance of the experimental circuit, there is no reason, in
Malapterurus at any rate, to assume a different E.M.F. in the
two halves. The diminishing diameter of the fish (or of the
organ) in the antero- posterior direction, with the consequent
diminution of resistance in the same direction, sufficiently explains
the reaction. In Gi/mnotus there is the further possibility that
the posterior prisms of Sachs' bundles (with wide compartments)
may give a different electromotive reaction from those with
small chambers.

Under all circumstances the shock increases here with the
length of the fish, and the question then presents itself whether this
is due to diminution of resistance, or to increase of E.M.F., or both.
As appears from comparison of the length and weight in different
animals, Gi/mnotus grows more in length than in diameter, so
that its cross-sections are relatively smaller in proportion as their
length increases ; and since we may assume that the reaction of
the electrical organ will be the same, its resistance also will
diminish more slowly than if the organs remained parallel in
their growth, or it may even be augmented. In any case the
greater intensity of shock in longer fishes must be referred to
increase of E.M.F. , and not to diminution of resistance (du Bois-
Eeymond).

The anatomical relations of innervation in the electrical organs
of the several electrical fishes show considerable differences as
regards the initiation of spontaneous (voluntary) and reflex dis-
charges. In Torpedo it might be predicated that the discharge
after destruction of the electrical lobe or sensory nerves leading to
it could only occur from excitation of the electrical nerves, or
of the electric lobe itself. In Malapterurus, too, the property of
spontaneous and reflex discharges must be associated with the
integrity of the two giant ganglion-cells. In Gymnotus, on the
other hand, the innervation of the organ is evidently more analo-
gous to the muscular innervation of the fish. Humboldt found
no shock from the decapitated gymnotus, so that when an animal

xi ELECTRICAL FISHES 42*

was bisected, the anterior half alone twitched, and the experiments
of Sachs confirm this. He also, in individual cases, obtained
" powerful reflex discharges " from the headless trunk, which can
be sensibly felt, as well as expressing themselves by marked
deflections on the galvanometer. He explains the absence of
effect in the majority of cases as follows : " Smaller and smaller
sections of the organ are thrown into simultaneous activity by
the reflex, just as, on decapitating the common eel, localised
excitation of the skin is followed by more local contractions of
the muscles." A more exact investigation of these partial dis-
charges, by means of a superposed frog's leg, is very desirable.

The effect of strychnine poisoning, on the other hand (the
action of which was proved by Matteucci and Boll on the torpedo),
is highly characteristic, and corresponds with what might be
expected. Marey, too, employed strychnine to produce reflex dis-
charges easily and certainly upon Torpedo, and he made graphic
records of the time-distribution of electrical strychnine-tetanus.
In order to poison the animal, he dissolved the poison in the
sea- water of its trough. Sachs observed convulsive spasms in
Gymnotus after the injection of strychnine, accompanied by re-
peated single discharges. Reflex excitability was much exag-
gerated. " The slightest tap on the wall of the thick wooden
trough produced reflex twitches and discharge."

III. DISCHARGE FROM ARTIFICIAL EXCITATION OF THE
ELECTRICAL NERVES AND CENTRAL ORGANS

Anatomical considerations at once make it clear that
Gymnotus, Raja, and Mormyrus are, among the electrical fishes,
the least suitable for indirect excitation of the organ, since the
anatomical arrangement of the very short electrical nerves
presents great difficulties to the dissection of a nerve-organ pre-
paration. " In Malapterurus, a cut which hardly draws a drop
of blood will expose a long tract of both the nerves, as if pre-
pared by nature. Regular strips may be cut out of the organ
with scissors, of any length and breadth, and these, bounded ex-
ternally by skin, internally by fascia, preserve their form well."
In Torpedo also, though with more difficulty, it is possible to
prepare and excite the four nerves that run from brain to organ.
In Gymnotus, on the other hand, about 250 nerves enter the elec-

424 ELECTRO-PHYSIOLOGY CHAP.

trical organ on either side of the spinal cord. " These are too
short to admit of a number of them being collected into a bundle,
while each governs too small a part of the organ to be sufficient
in itself" (du Bois-Beymond, 4 e, p. 187).

In order to make the necessary preparations from Torpedo, with
simultaneous control of the activities of the organ, Schoiilein (30)
placed the animal upon a flat dish of zinc, and covered the skin of
the back above the organ with a second zinc plate of the same
shape ; a telephone in circuit with the two contacts signalled the
discharges. After dividing the medulla oblongata, and extirpating
the spinal cord, there is no difficulty in exposing the electrical .
nerves. Preparations consisting of the two organs and their cor-
responding nerves alone are somewhat more difficult.

We have already discussed the character of the pitch, and
intensity of the natural discharge of Torpedo as observed in the
telephone. It is essentially characterised, not merely to touch
but also to the ear, by the same manifestations as a rapid series
of induction currents, so that with electrical stimulation of the
animal it is not always easy to separate the discharging and in-
variably audible currents from the shocks discharged. This, how-
ever, becomes possible, owing to a striking difference in pitch, if
with uniform distance of coil the electrodes are placed first upon
one of the electrical nerves, and then upon the exposed lobe. In
the latter case the tone swells suddenly to " the pitch of a trumpet
blast." With weaker stimulation, and the introduction of the
acoustic current-interrupter, it is often possible to hear a tone of
the same pitch, but different intensity. The pitch may vary with
repeated stimulation, and indeed during stimulation, in constant
oscillations. Electrical excitation of the part of the brain anterior
to the lobe again as a rule provokes a shock, corresponding in
intensity with that of the spontaneous discharges, i.e. not as a rule
coinciding with the stimulation frequency. As was pointed out by
F. Piolmiann (29), there seems in the electrical lobe of Torpedo
to be, as it were, a kind of localisation, i.e. a definite grouping
and arrangement of ganglion-cells, since only a limited portion of
the organ can be excited from any given point of the lobe.

It is characteristic of every spontaneous (voluntary) or reflex
discharge of an electrical organ, that it is discontinuous like
voluntary muscular contraction, and consists of a closely-packed
series of short impacts of current (Marey's "flux dcctrique "), each

xi ELECTRICAL FISHES 425

of which corresponds to an elementary motor impulse, producing
tetanic contraction of the muscle. Du Bois-Reymond proposes to
call each such elementary shock a " partial discharge " (" Theil-
< /tf ladling "), not to be confounded with the earlier local
(" Strcckcu-"} discharges of the organ. The rate of the incomplete
discharges, which — as Marey showed with the Marcel-Desprez
signal, as also with the capillary electrometer and telephone — make
up a shock, depends much upon the greater or less energy with
which the animal reacts, and it falls with increasing fatigue or
cooling. There are usually some 25 shocks at a rate of 100—
200, on an average 150 per sec. This gives a duration of the

24
total discharge of -^-r + O'OV" = 0'23 sec., assuming for the

-L O U

duration of an incomplete discharge the figure cited by Marey for
the shock from the organ produced by a single impulse from the
nerve, i.e. TV = 0'07".

The buzzing sensation often noted in the shock of electrical
fishes is not, in the opinion of du Bois-Eeymond, to be referred to
the tetanic character of the discharge, since the partial dis-
charges follow too quickly, and a total discharge is too soon over.
He rather holds " this sensation to be due to a succession of total
discharges, which may become half fused, so as to form maxima
and minima of the curve uniting the maxima of the incomplete
discharges : hence there arises a double tetanising ctenoid " (4 c,
p. 239).

Among artificial stimuli the electrical current is really the
only suitable means of studying the indirect excitation of the
organ exactly — for the same reasons as in the nerve-muscle
preparation. In mechanical excitation (pinching, cutting) of the
electrical nerve of Torpedo, Schonlein (30) heard a "very slight
scratching noise " in the telephone, which could only be detected
when the room was quiet. Crushing the nerve between two glass
plates gave the same result. On the other hand, Babuchin found
the electrical nerve of Malaptcrurus to be sensible at all points to
mechanical stimulation. " The bisection of the trunk, and also of
its branches, with sharp scissors, pressure, stabbing with a thorn
or pointed glass needle, never failed in effect." Chemical stimu-
lation (bathing in saturated solutions of sodium or potassium salts)
was practically inactive. In electrical excitation, single induction
shocks acted, if at all, only at high intensities. Sachs was unable

426 ELECTRO-PHYSIOLOGY CHAP.

to detect " any appreciable response " in a nerve-organ preparation
of Gymiiotus with the strongest single induction shocks obtained
from a sliding inductorium by means of the thermo-electric
battery (4 c, p. 192), and he also failed to get response from
the make and break of the current of four Groves in either
direction. Sachs apparently refers this to a special property
of the electrical nerves, and not to the organ, ascribing to
the former a " more solid molecular constitution " and " more
stable equilibrium " than to the nerves of other animals. Du
Bois-Eeymond, on the other hand, points with justice to the
part played by the electrical plates of the organ, the
similarity of conditions under which the electrical excitation
of sensory nerves will discharge reflex movements, and an
analogous stimulation showing the electrical organs. " Gentle
tetanisation of the sensory nerves produces marked reflex
twitches of certain groups of muscles from the cord ; strong
single shocks elicit no response. Strong single shocks sent
into the electrical nerves discharge no shock from the organ,
while it responds by tetanus to the gentle tetanisation of the
electrical nerves. The electrical plates of the organ therefore
react to the two forms of excitation of the electrical nerves,
as the ganglion-cells of the cord respond to the same kinds of
stimulation of the sensory nerves" (4 e, p. 272). Eckhardt
(11) repeatedly and successfully excited the electrical nerves of
Torpedo with single induction shocks, as well as with the constant
current. In the last instance Schonlein (I.e.) again observed a
peculiar response of the nerve-organ preparation of Torpedo.
< hi leading off from a bit of the organ, with a current of 1 6 Dan.
and 6 Bunsen passing through the nerve, he found, "according to
the direction of current at closure or opening of the exciting
circuit, or even at both, a single movement of the scale ; during
closure, there was in addition a permanent deflection," the direc-
tion of which appeared to be independent of that of the current.
The possibility of current escape seemed excluded, since on cutting
through the nerve and laying the ends together again, as well as on
ligaturing it, the deflections were entirely abolished. There is
no adequate explanation of this effect, which Sachs apparently
noted on Gymnotus also (4 e, p. 189).

After this discussion it is unnecessary to state that the much
more effective tetanising excitation from the nerve produces, as in

xt ELECTRICAL FISHES 427

muscle, a discontinuous change of state in the organ. That is to
say, it causes repeated discharges at the rhythm of the excitation,
which summate into a true electrical tetanus, as may be proved
each time by the secondary tetanus of a rheoscopic frog's leg lying
on the organ, or otherwise brought into the discharging circuit.
From observations with galvanometer and telescope Sachs describes
the phenomenon of electrical tetanus (at great distance of coil) in
the Gfymnotus organ as follows : " The thread moves slowly up-
wards in an absolute, positive direction (i.e. according to that of the
direction of the discharge), pauses there with twitching up-and-
down movements, and then falls again after a short time, although
not to the zero-point. Sometimes the thread will suddenly rise
again from the initial height at which it rests. When tetanus
ceases, the thread drops quickly as though released (4 e, p. 193).
Rapid succession of the single induction currents is essential on
tetanising the organ from the nerve, since even the most rapid hand
make and break of the current from 4 Groves proves ineffective.

In Malaptcrurus also, according to Babuchin, the tetanisation
of the electrical nerves is followed by discontinuous discharges,
which last for a longer or shorter time according to the vitality
of the organ -preparation. "The shocks can be felt with the
fingers, and make the same impression as when the fingers actually
touched the inductorium."

The trunk-fibres of the electrical nerves of Malaptcrurus were
found by Babuchin to be little sensitive to tetanising currents.
This seems partly due to the thick perineurium, since currents
that failed to excite the thick fibres of the trunk excited the
thinner branches effectively. Schonlein (30), too, on tetanising
the nerves to the organ of Torpedo with the rheotome (in order
to determine the time-distribution of the discharge), found the
threshold of stimulation to be very high in comparison with the
stimulus required by frog-preparations, and he is inclined to refer
this solely to the large size of the electrical nerves. The diameter
in large specimens is over 4 mm., and the cross-section is fifty
times as great as in an average frog's sciatic. And, in fact, on
splitting up the fibres of an electrical nerve " until the bundles
were as fine as in the frog's sciatic," Schonlein found that " the
distance of coil for minimal stimulation lay within the same
range as for the frog," a fact that is of great importance in the
question of immunity, which we shall presently discuss.

428 ELECTKO-PHYSIOLOGY CHAP.

Seeing the extraordinary wealth of nerves in the electrical
organ, and the comparative inefficacy of curare (infra), direct
excitation, more particularly electrical, does not give safe evidence
for the independent excitability of the substance of the electrical
plates. At the same time certain results undoubtedly point to
such a reaction. Matteucci made some successful experiments
with direct mechanical stimulation (pricking, cutting, etc.) upon
the excised prisms of Torpedo. He then observed twitches in
the rheoscopic frog's leg, when its nerve was applied to the
preparation. Du Bois-Eeymond, it is true, points out that
Matteucci seems " always to have hit upon a visible branch of
the nerve."

Babuchin (1) elicited "fairly strong shocks" from Mcdapterurus,
on cutting the organ, even at parts where the unaided eye failed
to discover any fibres of nerve upon the inner surface, and Sachs
also succeeded, by striking an organ-preparation placed between
unpolarisable electrodes in the galvanometer circuit lightly with
the flat part of a ruler, in obtaining frequent deflections, the size
of which depended unmistakably upon the strength of the
mechanical stimulation. The same occurred on touching the
preparation with a hot soldering-iron. The action of chemical
stimulants is especially interesting, since it is here that we should
expect excitation of the plates, independent of the ingoing nerves
that ramify in them. Sachs found on placing a strip of filter-
paper upon the skinned lateral surface of the long section of a
strip of organ 3-4 cm. in length (of which all the sections were
artificial, the lead-off being from the two cross-sections), that the
galvanometer magnet was at once deflected in the direction of
the discharge when ammonia was dropped on the paper with a
pipette. Ammonia is, of course, a strong stimulus to muscle,
while it does not appreciably excite the nerve. Moistening of
the cross-section, on the other hand, gives no perceptible effect
on the same preparation (4 c, p. 178), which may be due to the
fact that the ammonia here can only penetrate slowly through
the transverse partitions, while it easily gets " into the upper and
lower spaces opened by longitudinal section in all the compart-
ments that are beneath the wetted part of the filter-paper."

In order to test the action of .direct electrical excitation,
Sachs led single induction shocks, through unpolarisable electrodes,
into a prismatic organ-preparation lying on the pads of du Bois-

ELECTRICAL FISHES

429

Raymond's zinc trough, as in Fig. 271. It is evident that there
must under these conditions be cur-
rent escape into the galvanometer
circuit, which must be investigated,
and allowed for at the end of the
experiment. There is in the first
place the not very striking fact that
make shocks do not excite the organ-
preparation, while break induction
currents elicit effective discharges.
The electrical organ therefore reacts
like most excitable substances. It is
further remarkable that (according to
Sachs' experiments) break shocks
heterodromous to the discharge from
the organ excite more strongly than
homodromous currents. Schonlein
was unable to confirm this for Tor-
pedo. Induction shocks passed trans-
versely to the organ appear to have
the least effect. A rapid series of
induced (alternating) currents (tetanus)
gives large deflections in the direction
of the discharge, with a distance of
coil at which single break shocks,
under the most favourable conditions,
give little or no effect. This is again
the same reaction as on stimulating
ganglion- and gland-cells, as well as
all sluggishly reacting contractile
substances.

The simple method of curarising,
by which it is so easy to exclude the
nerves in the muscles of most ver-
tebrates, breaks down almost entirely
for the electrical organs, since electrical
fishes, and more especially Torpedo,
are, like all other fish, comparatively
immune to curare. This is evident
in the nerves to the muscles, but still more in the electrical organs

FIG. 271.

430 ELECTRO-PHYSIOLOGY CHAP.

and their nerves, which take much longer in becoming paralysed.
With very strong doses of curare, Steiner (33), and later on Eanvier
and Boll (4 c, p. 194), as previously Marey, succeeded in
paralysing not merely the motor but also the electrical nerves
in Torpedo. The poison, of course, took effect more quickly when
injected directly into the blood, than when it was given subcutane-
ously or through the abdominal cavity. According to Babuchin, 1
cc. of a 2 °/Q solution is sufficient, in the first case, to induce com-
plete motor paralysis in a full-grown torpedo in 15—20 min., while
the electrical organ is still reflexly excitable ; in subcutaneous
application three times the dose was required. Malapterurus was
found to give the same reaction. Schonlein states that in order
to obtain a complete effect, in which case the direct excitability
of the organ also disappears completely, it is necessary to give
enormous doses (15 cc. of a 4 °/Q solution = 6 decigr. curare), even
when the poison is injected directly into the blood (anterior gill
artery). Immediately after injection of the first 5 cc., one or
two sharp discharges occur with commencement of an opistho-
tonus, followed by a rapidly -decreasing tetanus of the organ.
"Weak reflex discharges, however, continue for some time on
touching the animal, unless a second and even third injection is
given, after which it is still necessary to wait some 20 miu.
Schonlein inclines to make the slow circulation responsible for
this pronounced immunity to curare. Armand Moreau (23)
could not discover any action of curare upon the electrical nerves
of Torpedo. It is easy to paralyse small torpedoes so completely
by subcutaneous injections of about ^ cc. of 1 ^ solution, that
there is no sign of movement on stimulating the cord or motor
nerves ; whereupon mechanical excitation of the skin will still effect
reflex discharges of the same strength as before the intoxication.

Sachs made two curare experiments on Gymnotus, showing
complete paralysis of the electrical nerves with very strong doses.
Tetanisation with normal distance of coil then gave hardly any
perceptible effect on the galvanometer, while direct stimulation
still called out very marked deflections, as also the application of
ammonia to the long section of the organ -preparation. We
cannot, however, regard these observations as proof of the
independent excitability of the electrical plates, which Schonlein
regards, on the strength of the curare experiment, solely as
" nerve-endings."

XI

ELECTRICAL FISHES 431

IV. TIME-DISTRIBUTION OF DISCHARGE FROM ELECTRICAL

FISHES

Seeing the close relation between most, if not all, electrical
organs, and striated muscle, it is interesting to compare the time-
distribution of the twitch, or accompanying current of action,
with that of the discharge. In the first place it must be asked
whether, with a single momentary stimulus, there is any latent
period of the elementary discharge which it elicits from the
organ. Marey at first decided in the affirmative for Torpedo.
By means of a pendulum-myograph the circuit (in which there was
a rheoscopic frog's leg, as well as the organ which was excited
from its nerve by single induction shocks) could be closed for a
moment at any given time after the excitation, so that a fraction
= ^Ly" was cut out of the discharge. This fraction, expressed
on the leg as a twitch, might therefore be shifted along the dis-
charge, so that on one hand the total duration (TV')' on ^ie
other the presence of a perceptible latency, could be determined,
since a certain interval between the fraction cut out and the
moment of stimulation was required in order to produce con-
traction. The time occupied by the conduction of excitation
from nerve to organ was thought by Marey to be negligible on
account of the shortness of the nerve.

Another of Marey's methods was founded on the earlier
experiment of v. Helmholtz, by which the fraction of the negative
variation of the muscle current that discharges a secondary
twitch was determined. Two twitches of a frog's nerve-muscle
preparation were graphically recorded, one being discharged
directly by an induction shock, the other through the discharge
of the organ, generated by the induction current at the same
position of the indicator (Fig. 272). The displacement of the
curves corresponds with the latent period of the discharge, and
less with the time lost in nervous conductivity, which is again
neglected, although Marey had already remarked that excitation
travels more slowly in electrical than in frogs' nerves, as was
subsequently confirmed by Jolyet and Gotch. Gotch determined
the commencement of the galvanometer effect on a nerve-organ
preparation by stimulating the nerve at points farthest from and
nearer to the organ. If the distance amounted' to 13 mm. the
galvanometer effect began YO%O" earlier on stimulating the

432

ELECTRO-PHYSIOLOGY

CHAP.

proximal point ; this gives a rate of propagation of 6 '5 m. per
sec. (at 12° C.), or in another case 7'3 m. Schonlein has
recently given much higher values (12—27 m.), and reckons
them in the same order as those of frogs' nerves.

Marey's experiments seem to give a latent period of O'Ol" for
the discharge of Torpedo, i.e. the value originally given by von
Helmholtz for twitch in the frog's muscle. But as here, so in
the electrical organ it was subsequently found that if there is
any latent period of discharge — in the sense that the causative
alterations in the substance of the plates are initiated later than

Fir:. 272. — p = twitch from the muscle, as marking moment of stimulation; c<7 = latent period of
muscle twitch discharged directly by an induction shock';~ef = latent period of twitch from the
organ discharge; t;< = latent period of electrical organ.

the commencement of excitation (which from analogy with the
electrical phenomena of muscle is not very probable) — such
latency must be much smaller than the original determination.

Sachs, who experimented on Gymiwtus by a method corre-
sponding on the whole with Marey's, employed direct stimulation
with opening shocks, because it was found impossible to excite
organ-preparations from the nerve by single induction shocks.
He also adopted Pouillet's method of time-measurement. The
arrangement is according to Fig. 273.

The strip of organ ( VH) lies between the clay shields of the
leading-in electrodes, from which wires lead to the double reverser
(D W). Other wires come from the uupolarisable electrodes
applied to the organ, that lead in the break shock from the
secondary coil (£ft); the latter is discharged by Helmholtz's switch

ELECTRICAL FISHES

433

(WW ), W being opened at the same moment in which the time-
measuring circuit is closed at W, With the double reverser, as in
B, the organ-preparation is not excited, and the break shock directly

excites the nerve of the frog's muscle.

The time-measuring cir-

FIG. 273.

cuit is therefore closed only during the period occupied by the
transmission and latency of excitation in the nerve and muscle,
since the contracting muscle opens the galvanometer circuit at H.
In A, on the other hand, the frog-preparation is stimulated by
the discharge from the organ-preparation, and the closure of the

VOL. II 2 F

434 ELECTRO- PHYSIOLOGY CHAP.

galvanometer circuit is accordingly longer than the latent period
of the shock. This may be calculated on du Bois-Eeymond's

formula for the a-periodic magnet T = --^—-.x, F being the

deflection from the constant current ; e, the basis of the natural
logarithms ; as, the effect due to current impact ; t m a x, the
duration of this or any other effect under the same conditions.

Sachs accordingly gives a value of 0'00350", which ap-
proximately coincides with the latency of the muscle element
as given by Gad. Gotch determines it for Torpedo at 5° C.,
as 0-012"-0-014" ; at 20° C., on the other hand, it is only 0'005".
He invariably finds the latent period less in large specimens
than in small, and this cannot be altogether referred to the
greater intensity of discharge in the first case. Schonlein, on
exciting Torpedo indirectly with descending constant currents,
found, with Bernstein's rheotome, a latent period of only 0-0002—
0'00025 sees. Since (as was said above) it cannot be sup-
posed that any appreciable time elapses in a plate of the electrical
organ, between the impact of a stimulus and the initiation of the
chemical process that underlies the electromotive action, the
apparent latency of the discharge in electrical organs must lie
referred solely to the imperfection of experimental technique.

The duration of discharge from the electrical organ seems, like
its latency, to be, generally speaking, of the same order of magni-
tude as that of the muscle twitch. Du Bois-Eeymond pointed
this out as early as 1857 with the frog-interrupter. He led a
branch of the current discharged by Gymnotus into the nerve of
the frog's gastrocnemius muscle, which in twitching opened the
galvanometer circuit. With increased after-loading of the muscle
the initial deflections became steadily larger, while if the twitch did
away with a shunt to the galvanometer circuit the terminal de-
flections became smaller and smaller. " With sufficient loading a
point is reached at which — in the first case — the deflection of
the mirror due to the discharge shows no further increase, while in
the second, with unpolarisable (leading-off) saddles, there is only a
weak and inconstant remainder of the discharge." Marey sub-
sequently determined the period of the discharge of Torpedo (supra}
with the pendulum-myograph at about T^". Sachs experimented
on Gymnotus by du Bois-Eeymond's method. His apparatus is
given in Fig. 274.

Leading-off saddles are applied to the fish in water, the current

XI

ELECTRICAL FISHES

435

being led through wires to the galvanometer circuit, which includes

O O G3

the frog-interrupter (Gu). Two copper electrodes (EE^) are
further placed in the frog-trough, their wires being connected with
the muscle (GJ of the frog-alarum and (Gn) of the frog-interrupter.
The first was directly excited, owing
to the force of the shock from the
gymnotus, the last indirectly, from
the nerve, by means of the exciting
reed. " With the reverser placed as
in the figure, the lever of the inter-
rupter forms part of the experimental
circuit. The arrows show the direc-
tion of current. With the reverser
turned over, the lever makes the shunt
circuit ; this distribution of current
corresponds with the dotted arrows."
Gotch has recently employed
another and widely applicable method
in his numerous experiments in time-
measurement on the torpedo. The
apparatus is essentially modelled after
du Bois-Reymond's spring-myograph.
Three contacts (Kl K^ K^, which are
opened in succession by the trigger,
were connected as in Fig. 275. K^
opens the primary circuit of an in-
duction coil, the break shock being
passed into the nerve of an organ -
preparation. A corresponding part
of the discharge that follows acts
upon the galvanometer when the
opening of K abolishes a shunt to
the galvanometer circuit. Lastly,
the latter is permanently opened
(by JT3), so that the discharge from the organ only acts upon the
galvanometer for the period between the opening of K.2 and K.,.
The trigger shoots past so rapidly that this interval may be
reduced to O'OOl". Hence if K, is opened O'Ol" after Kv
while KZ is gradually withdrawn from K^ the effect on the
galvanometer will be perceptible Ttj{jV' after tne stimulation

FIG. 274.

436

ELECTRO-PHYSIOLOGY

CHAP.

of the nerve, and reaches its full development at j^§^". For the
rest, the rapidity of reaction is obviously modified by temperature.

FIR. 275. — Schema of apparatus for determining the duration of the Torpedo discharge. (Gotch.)

FIG. 270.

Fig. 270 (a schema by Gotch, in which the ordinates are
the galvanometer deflections, the figures (10, 20, 30, etc.) on
the abscissa Y<y\)<y", find their commencement the moment of

XI

ELECTRICAL FISHES

437

stimulation) shows that the discharge from the organ quickly
reaches its maximum after the period of latency, which maximum,
unlike the latent period, is higher in large vigorous specimens
(curve a} than in small animals (curve b). It declines much
more slowly, passing gradually into an after-effect in the
direction of the discharge, which may last for minutes after a
single brief stimulus. The duration of shock is, in round numbers,
0'0-i— O'OG" on exciting a lively fish with break induction shocks
at room temperature. Schonlein determined the period of
discharge at O'OOS" or less, a value that agrees with Gotch's
figures for the direct total excitation of a bundle of prisms.

Jolyet, in his time-measurements, occasionally observed a rise
and fall of the discharge in the organ, on stimulating the nerve
with a single induction shock, which he referred to temporal
differences in the commencement of discharge in different parts
of the organ. Gotch obtained the same effect subjectively on
dividing the nerve of an organ - preparation held between the
fingers, with a rapid scissors' cut. The oscillatory form of the
curve of discharge, with several (even 4) apices, can then be
detected unmistakably with the spring rheotome after each single
stimulus, both on larger strips of organ, and on bundles of a few
prisms only. The following table gives the results of such a

series of experiments, and shows that at about

after the

first maximum of the discharge there is a second weaker and

(after another

Too

') even a third still weaker maximum : —

K2-K3

Ko — K.;

K2— K3

Ko — K.,

K.,— K,

K2— K3

Ko— K3

Galvano-

O'OOl"

0-0125"

0-015"

0-0175"

0-02"

0-0225"

0-025"

meter.

to

to

to

to

to

to

to

0-0125"

0-015"

0-0175"

0-0-2"

0 -0225"

0-025"

0-0275"

TTTU"

0

+ 48

+ 367

+ 316

+ 75

+ 120

+ 225

I. Max.

II. Max.

K,-K:!

K2— K:i

K2— K,

K2— K3

K., — K3

Ko— K3

Iv2 — K.j

Galvano-

0-0275"

0-03"

0.0325"

0-035"

0-0375"

0-04"

0-0425"

meter.

to

t

to

to

to

to

to

0-03"

0-03-25"

0-035"

0-0375"

0-04"

0-0425"

0-045"

TITO"

+ 212

+ 89

+ 64

+ 98

+ 130

+ 30

+ 24

III. Max.

These results are even more apparent from the schema in Fig. 277,

438

ELECTRO-PHYSIOLOGY

CHAP.

Schonlein noted the same effect in the discharge of Torpedo
from a single induction-current with Bernstein's rheotome, i.e. rise
and fall of the climax two or three times in succession. " Usually,
but not always, the first apex is higher than the second, and if
the latter is greatest the differences of apex height are generally
less than in the opposite case. The intermediate section is very
deep, often reaching to the abscissa without, however, crossing it
on the other side." The duration of the single partial discharges
varies little. It is remarkable that the same form of curve with

'•:;,

Temp°15'C

Fio. 27T.

several apices is exhibited with similar excitation of the electric
lobe, so that it is questionable whether in the last case the
ganglion-cells or only the nerve-fibres are excited.

Schonlein obtained true simple curves of discharge with one
apex, corresponding with a single, non-oscillating discharge of the
Torpedo organ, only on stimulating the nerve with single descending
impacts of current, as shown by the rheotome with 5 0 Dan. in
the exciting circuit. On stimulating with ascending constant
currents it is seen that the discharge usually begins much later,
and increases more slowly, than with the descending direction.

The character of the effects further depends upon the

XI

ELECTRICAL FISHES

439

length of intrapolar tract, and the latent period may, with
40-50 mm., be prolonged 0'0055-0'004 sec. With shorter
interpolar tracts there is usually an " introductory apex," its
latency of discharge with descending currents being sometimes
0, sometimes, however, of measurable proportions. This Schon-
lein refers to the diminution, not merely of rate of conductivity,
but also of intensity of excitation, due to anelectrotonic inhibition
at the anode during each single impact of current (O'OOl" dura-

Fir,. 278.— Excitation of one organ-preparation by discharge from another, through the nerve.

(Gotch.)

tion). We should anticipate that the discharge of an organ-
preparation provoked by excitation of the nerve would be sufficient
to excite directly a second preparation in the same circuit.
The accompanying schemata (Fig. 278) show that there must
then be either summation or subtraction of the galvanometer
effect. That this is actually the case has been proved by Gotch
with the spring -rheotorne. The alteration (augmentation or
diminution) of the galvanometer effect caused by the discharge
of the nerve-organ preparation appears regularly about O'Ol"
after the maximum of the discharge. One then asks whether

440 ELECTRO-PHYSIOLOGY CHAP.

self-excitation of the organ, by its own discharge, is not merely
possible but the rule. Gotch refers the multiple apices of the
curve of discharge (supra), 011 stimulating with single induction
shocks, principally to a second set of discharges excited from
other prisms by the current of those first discharged by the
impulse from the nerve, so that the later discharges are in a
sense analogous with secondary contraction. Schonlein urges
against this view that oscillating discharges might then be
expected with brief closures of the battery current, which is not
the case.

V. IMMUNITY OF ELECTKICAL FISHES TO THEIK OWN

DISCHARGE

It is in the last degree surprising, in view of the intensity
of physiological action in the discharge of electrical fishes, that
the most powerful shocks, which at once kill fish or other animals
within reach, should apparently not have the smallest effect upon
the generators of these electrical batteries, although " the body
of an electrical fish is better fitted to receive the shock of its own
organs than the body of any other animal " (du Bois-Reymond).

Humboldt made experiments on Gymnolus which show the
insensibility of the animal to the most powerful shocks from its
own kind. He chose out one strong and two very weak gymnoti,
placing them so that the weak fish led the discharge from the
vigorous animal into his own body. The two weak fish were
totally unaffected. He suggested that the skin might be a pro-
tection against the electrical current, and this opinion was widely
held before the publication of du Bois-Eeymond's " preliminary
sketch." Du Bois showed first in Malapterurus that two wires
insulated down to the ends, and introduced into mouth and gut,
received the discharge in any position, and led it off externally
in accordance with the received theories, thus proving that the
shock really passes through the body of the fish, though, strangely
enough, the point was again disputed by de Sanctis in 187-J.
Mcdapterurus, moreover, proves to be as insensible to other electrical
shocks as to its own. " The alternating currents of an induc-
torium, which soon killed the fresh-water fish in the trough, were
hardly detected by Malapterurus. It only pointed its barbels
backwards, and placed itself with its body vertical to the least

xi ELECTRICAL FISHES 441

density of the lines of current. It occasionally showed disturb-
ance by discharging its own batteries." A dying malapterurus
was placed in a small parallelepipedic glass trough, which it
nearly filled, and was excited by du Bois-Eeymond (4 d, ii. 640)
with the sliding inductorium, the coils being pushed up, and two
Groves in the primary circuit. Its breathing was not disturbed,
nor did any discharge follow. It was equally insensible to the
constant current from a battery consisting of thirty Groves, which
is noteworthy inasmuch as the relative immunity might have been
conjecturally referred to the time-distribution of the current (as
in smooth muscle). Schonlein. further communicated to the
author that he was unable in Cephalopoda, Crayfish, and different
fishes, with an induction-apparatus double the usual size, having
four Bunsen cells in the primary circuit, to excite any sign of
action when the wire from one pole (insulated right down to the
end) was brought as close as 1 cm. to the animal, the other
pole being connected with a small plate on the floor of the
holder.

Gymnotus was found by Sachs to be equally immune to its
own shocks. He relates that "10 gynmoti were quietly extended
in the middle of the canoe, nearly all close together. I dipped
my finger in the water at a distance of three feet, and tickled the
back of the largest animal with a stick. Several capable persons
were told off to watch the animals, one to each. In spite of the
distance, I received an appreciable shock. Not one of the
animals gave the faintest sign of movement" (4 d, p. 267).

At the same time, this immunity (as follows from the previous
discussion) is far from absolute. Babuchin saw a small malapte-
rurus that had bitten the flanks of a larger animal draw back to
a distance, while he received a shock at the same moment through
his immersed fingers, and Steiner, whose observations were con-
firmed by Fritsch, has seen small torpedoes twitch from shock on
coming into contact with larger ones. Schonlein (I.e.) states that
if pregnant female torpedoes from which the embryos have been
removed are laid, still living, upon each other, no single animal
will move. " They all lie in relaxed condition, or all become
suddenly rigid, like a frog from which the spinal medulla has
been extirpated. When this last occurs, a shower of electrical
shocks passing through the entire heap of animals is plainly felt
011 the hand. They contract collectively without exception." The

442 ELECTRO-PHYSIOLOGY CHAP.

fresher and more healthy the animal (Torpedo) — the signs being
arched back and slight protuberance of the contours of the
organs — the more certainly, according to Schonlein, will it react
to every discharge.

Since the electrical nerves may be excited by the discharge
of the animal itself as well as by artificial currents, the compara-
tive immunity of the electrical fishes might depend principally upon
quantitative differences in the threshold of excitation for their
nerves as compared with the nerves of other animals, and many
facts seem at first sight to support this view. Boll made com-
parative observations on the nerves of a frog's leg and the first
spinal nerves of Torpedo, tetanising them with the sliding induc-
torium according to Eosenthal's method for determining the differ-
ence of excitability in nerve and muscle. Contraction always
occurred in the frog's muscle at a greater, often far greater, dis-
tance of coil than in the Torpedo muscles. Humboldt has a
corresponding observation. To his surprise he failed to elicit
twitches from the exposed muscles and muscle-nerves of Gym-
notus with a simple circuit (silver-zinc), although he succeeded in
doing so under the same circumstances in other animals.
Schonlein has recently made legitimate objections to Boll's ex-
periment, protesting against the application, to the doctrine of
immunity, of his own experiments on the apparently sluggish
excitability of electrical nerves (supra). In any case,
further comparative observations in this direction are much
wanted before any sufficient explanation of the apparently deep-
seated immunity of electrical fishes to electrical discharges of
any kind can be given. That such really does exist appears to
Biedermann evident from the reaction of the most powerful
electrical fishes (Gymnotus and Malapterurus), the shocks of
which may be fatal to other animals. Partial attempts at ex-
planation are not wanting. Pfluger suggested that the animals
might be thrown at the moment of the discharge of their own
nerves, from the central organ, into a state of depressed excita-
bility parallel \vith anelectrotonus, and thus be steeled against the
shock. But, apart from other reasons, it would then be difficult
to see why electrical fishes should be " steeled " against the dis-
charges of other individuals, as also against artificial electrical
currents. The results of other experiments of du Bois-Pteymond
and Boll, in proof of the same idea, have been equally negative.

xr ELECTRICAL FISHES 443

VI. THE SUPPOSED "CURRENT OF BEST" IN THE ELECTRICAL

ORGAN

The question of whether the electrical organ is normally
electromotive during rest, or in the state of excitation only,
is obviously of great significance to the theory of its mode
of action. This is another aspect of the same problem which
-with reference to muscle — formed the subject of the long
and animated controversy between du Bois-Eeymond and
Hermann (supra), that ended finally in favour of the latter. If,
as has been determined, certain electrical organs are to be re-
garded as transformed muscles, adapted to a special function, it
would seem a priori very probable that the discharge of the
organ is no more than the " action current " of the " specialised
muscle," which would give as little external reaction in the resting
state as a true muscle. As a matter of fact, all previous investi-
gations have shown the " rest current " of the electrical organ,
when present, to be exceedingly feeble. Du Bois-Eeymond him-
self found the organ of Malapterurus totally inactive during rest
(4 d, ii. pp. 672, 718). "It neither exhibited any similarity
with the muscle current, nor did it work, like a battery, in the
direction of a discharge." Eckhardt (I.e.) gives a precisely similar
reaction for the organ of Torpedo, in which Zantedeschi and
Matteucci had observed weak constant action in the direction
of the discharge. These effects, again, were comparatively
weak and insignificant. Eckhardt found all points of the dorsal
surface permanently positive to all points of the ventral surface,
and all points nearer the brain positive in the former, and
negative in the latter, to all more distant points. Matteucci
measured frogs' gastrocnemii against a bit of organ in the
multiplier circuit, proving one to be weaker, two, arranged like a
pile, stronger than the organ. He, moreover, observed that the
permanent P.D. between dorsal and ventral surface " is temporarily
removed after each discharge provoked in the preparation by
electrical or mechanical stimulation of the still attached nerve,"
as could be demonstrated at a low temperature for days after-
wards.

C. Sachs, one of whose chief distinctions it was (as du Bois-
Eeymond said) to have tested the reaction of the resting organ in
Crt/itinofus, invariably observed on leading oft' from the two polar

444 ELECTRO-PHYSIOLOGY CHAP.

surfaces — i.e. the cross-sections at the head and tail ends of the
prisms — a current in the direction of the discharge (du Bois-
Beymond's " organ current "), which, however, was again remark-
able for its low E.M.F. It usually corresponds with that of a
stronger nerve, or weaker muscle (0'15— 0'03 Dan.) applied by
long and transverse sections, although the strips were about 4 cm.
in length and 6—7 sq. cm. diameter. Since there are about 400
chambers in 4 cm. of organ, the organ current of each compartment

can only have an E.M.F. of ° — = 0-0000375-0 "000075

400

Dan. There is also a weak current, in the direction of the dis-
charge, between two points of the natural long section (i.e. the
natural, lateral boundary of the organ). Du Bois-Beymond, after
punching out the electrical lobe in Torpedo, either led off from the
skin of the dorsal and ventral surfaces of the vertically dependent
fish, or with scissors and scalpel prepared four-sided prisms of the
organ, containing a fair number of columns, and bordered by a
square piece of skin of 5-6 mm. on the dorsal and ventral surfaces.
In the first case there is always a current in the direction of the
discharge. " It was most pronounced when the highest prisms
were at the medial border of the organ between the leading-off
parts, and became weaker in proportion as the parts were brought
nearer the thinner, lateral edges of the organ " (4 g). In the
excised pieces there was also a P.D. in the same direction on
leading off from two points of the lateral surface of the prism, the
magnitude of which increased with the distance of the leading-off
points. The deflections were, however, very small in the one case
as in the other (between 3 and 2 3 degrees of the scale) ; the
E.M.F. was also considerably less than that of the nerve current
in fish (0-005-0-013 Eaoult). For the single plates, du Bois-
Eeymond estimated a medium E.M.F. of 0'00001l7 Dan., i.e. three
times smaller than that determined for the single plates of
Gymnotus.

Like Eckhardt (11), Gotch (13) ascribes no great importance
to this weak electromotive action during " rest," the more so
since he failed to discover it in freshly -caught and perfectly
uninjured animals. Upon ten fishes he obtained on leading off
from two points corresponding with the centre of an organ, and
lying opposite to each other on the skin of back and belly, very weak
and fluctuating effects, which occurred six times in the direction

xr

ELECTRICAL FISHES 445

of the discharge, four times in the reverse, and which in his
estimation are clue solely to inequalities of the skin.

Little as the possible, and even probable, interference of skin
currents — the presence of which was demonstrated by du Bois-Eey-
mond in Torpedo — can be denied, it must, on the other hand, be
admitted that regular differences of potential might, and indeed do,
make their appearance under certain conditions (though not in the
true physiological state of rest of the organ) even in the wholly un-
injured animal. Du Bois-Eeymond ascribes these " to the same,
though far less active, order of electromotive force as that which
produces a discharge via the nerve, or with direct excitation."
Under these conditions it is an obvious conjecture that the " organ
current " may be " an after-effect of the discharge, which passes
into it imperceptibly." And du Bois-Eeymond elsewhere remarks
that the E.M.F. of the organ current may in all probability be
regarded as " the remainder of the discharge," while " the fall
which always characterises it represents the slow progress of the
far quicker but still not quite sudden diminution of the discharge."
Finally, du Bois-Eeymond explains the negative experiments of
Gotch on the organ current of .uninjured and resting torpedoes as
signifying that the animals " not having discharged for a long-
time, showed no perceptible after-effect of the last shock, and thus
save no organ current."

O o

By this it is easy to see that the pre-existence of E.M.F. in
the resting state of the organ is practically contradicted, and the
effects can be altogether explained according to the views of Gotch
and Eckhardt.

Since an organ-preparation cannot, of course, be made without
stimulating it, it is natural that the E.M.F. of such a preparation
should sometimes be considerable. A section through the organ
in the vicinity of the electrodes that lead off from back and belly
may, as Gotch stated, convert a weak and previously hetero-
dromous current into a somewhat stronger effect, homodromous
with the discharge. " Further incisions, that bounded the part
led off, so that it only remained in its natural connection
on the median side, increased the E.M.F. in the same
direction, till it finally amounted to 0-0015 Eaoult. If by
subsequent transverse sections the resulting wedge-shaped
disc of organ was still more reduced, until by sagittal cuts
it became a bundle with only a few prisms, the E.M.F. of the

446 ELECTRO-PHYSIOLOGY CHAP.

organ will be a little increased after each cut, but falls deeply
after a few minutes." Gotch obtained the strongest effect on
immersing the mixed bundles of prisms for a short time in hot
water, leading off two minutes later from ventral and dorsal
surfaces. The E.M.F. (in the direction of the discharge) then
rose to 0'0226 or even 0'0336 Raoult, but fell within a quarter
of an hour to its normal magnitude. That this was not a case of
hydrotherrnal action follows from the fact that even superficial
scalding of the dorsal and ventral halves of the prisms increased
the E.M.F. in the direction of the discharge.

On the tail of the ray, Burdon-Sanderson and Gotch (13 c)
again occasionally determined a " current of rest " in the direction
of the discharge, on leading off from the anterior and posterior
ends. In organ-preparations this is usually much more developed,
especially after the momentary action of high temperatures
(immersion in hot water). Every natural or artificial stimulation
of the organ causes a more or less pronounced " after-effect " in
the direction of the discharge, and this only declines gradually.

After these experiments there can be no doubt that we are
here in presence of a slowly-declining excitation of the prisms of
the electrical organ (due to mechanical or thermal stimulus), in
which the process in each plate may be compared to the gradually
disappearing negativity of a strip of muscle modified by veratria,
and excited by a brief stimulus. This seems to Biedermann an
even more cogent example than that which Gotch selected, of the
normal demarcation current in muscle, although both phenomena
are fundamentally due to the same cause, the preponderance of
the dissimilatory process over simultaneous assimilation. As the
persistent excitation in the muscle is expressed by negativity of
the affected parts, so in the electrical organ it is expressed by
weak electromotive activity in the same direction as that of the
strong electromotive action during its natural function. Du Bois-
Reymond calls this comparison of Gotch a logical error, but it
would not be difficult to invalidate the objections adduced against
it. In the present connection, however, this is unnecessary, since
we are really dealing only with the question of whether under
the above conditions any permanent excitation of the electrical
organ in the direction of the discharge can be affirmed or not,
and du Bois-Eeymond himself admits the former. For how other-
wise can the dictum be interpreted that the organ current is only

xi ELECTRICAL FISHES 447

" an after-effect of the discharge that passes into it imperceptibly,"
and that it is due to the same, albeit much weaker disposition of
electromotive force, as that which provokes discharge via the
nerve or in direct excitation. Then, however, as was pointed out
by Hermann, there remains no more tangible difficulty from the
standpoint of his theory (in so far as this can be applied to the
electrical organ) than from that of du Bois-Eeymond's molecular
hypothesis. For the rest it appears to Biedermann that the differ-
ence insisted on by du Bois-Reymond between his own and Gotch's
view of the organ current is non-existent, since the " persistent
excitation " can only be interpreted as the after-effect of a previous
effective stimulation.

VII. SECONDAKY ELECTROMOTIVE PHENOMENA IN ELECTRICAL

ORGANS

Du Bois-Reymond lays special weight upon the study of that
group of electromotive activities which — as they appear in muscle
and nerve from the after-effects of artificial currents — were first
investigated by him. While their great significance to the theory
of current-action cannot be doubted in the case of nerves and
muscles, the far more complicated structure of the electrical
organs renders them at first sight less appropriate to the experi-
mental determination of further conclusions, if we are to assume,
as in nerve and muscle, that every after-effect is a phenomenon,
partly of excitation and partly of physical polarisation. If the
current passing through any part of the organ has — as we can
hardly doubt — a polar action, and this in each individual plate
per se, and if the connective-tissue walls of partition are the seat
of true (negative) polarisation, it is easy to see that the prism-
like arrangement of these elements within any given area may,
and indeed must, give rise to complex positive and negative
effects which would be hard to unravel in any single case.

Du Bois-Reymond thought it remarkable that the electrical
organ (of Malapterums) should exhibit " positive polarisation,"
along with negative after -currents produced by true internal
polarisation ; the same effect was subsequently interpreted in
muscle as the consequence of (opening) excitation. A similar
relation with the physiological process of excitation was naturally
conjectured to exist in the electrical organ also. Before entering

448 ELECTRO-PHYSIOLOGY CHAP.

upon this point it is advisable to cite the essential data in re
polarisation phenomena.

Let a still-living piece of Malapterurus organ, which, as we
have seen, is usually isoelectric, be laid across unpolarisable
electrodes, serving simultaneously to lead in and lead off; a
special contrivance sends in a battery current of definite intensity
and duration, and immediately after (when the polarising circuit
is opened) closes the galvanometer circuit, as has already been
described for muscle. The organ-preparation will then, as a rule,
have become temporarily electromotive (polarised), and this — at
low current-density — invariably in the direction of a negative
after -current heterodromous to the exciting current. This
negative polarisation occurs in Malapterurus in loth directions
(homodromous and heterodromous with the discharge) in equal
strength, and grows in density and duration, with the product, to
still undetermined proportions. Positive polarisation invariably
occurs first, as in nerve and muscle, at high densities of current,
and is most apparent (du Bois-Eeymond) with brief currents, its
intensity increasing with the duration of the exciting current less
rapidly than that of negative polarisation. The greater intensity
of positive polarisation in the direction of the discharge (also
observed by du Bois-Eeymond) is very striking. " The current
from head to tail exhibits strong positive polarisation under the
same conditions in which that from tail to head gives negative
polarisation" (4 d, p. 206). Obviously wherever there is simul-
taneous appearance of both polarisations, the actual after- current
is the algebraic sum of the two opposite actions, and it is easy to
understand that there might also, under certain conditions, be
diphasic (first negative, then positive) deflections, or oscillations
of the magnet.

Sachs made analogous observations on strips of Gymnotus
organ, with the inessential difference that polarisation is, in
this case, invariably negative at first, while du Bois-Eeymond
occasionally obtained pure positive effects on the Malapterurus
organ under certain conditions, which must, however, be re-
ferred solely to the lesser density of the currents employed by
Sachs. (Du Bois-Eeymond sent current from 20-30 Groves
through strips of Malapterurus that were hardly -g- sq. cm. in
diameter.)

Du Bois-Eeymond subsequently found occasion in Berlin to

xi ELECTRICAL FISHES 449

carry on the same experiments on Torpedo, without having to
stint himself in materials (4 g-i).

In order to understand what follows, it must be kept in mind
that current in the direction of the discharge is termed homo-
dromous, in the opposite direction heterodromous ; an after-current
opposed to the polarising current is relatively negative, its contrary
relatively positive ; an after-current in the direction of the discharge
(homodromous) is absolutely positive, its converse absolutely negative.

Du Bois-Reymond employed prismatic pieces of organ, the
polarising current being led in at the end-surfaces covered with
skin, while a second pair of impolarisable electrodes led off the
polarisation current, the clay tips being applied to the preparation
between the clay shields that led in the polarising current.
Here, again, under certain conditions, i.e. with brief closure of
stronger currents, there may be positive polarisation, otherwise a
diphasic effect is seen — first a negative, then a positive variation.
As in muscle, the positive polarisation is more dependent on vitality,
on the normal physiological state of the preparation. " With de-
pressed excitability (Leistungsfahigkeit) only negative polarisation
at last survives, but it is a long time before the positive effect
dies away completely. The relation between polarisation and
direction of polarising current is conspicuous." Sachs found in
G-ymnotus that " the negative polarisation current is invariably more
marked in the direction of the discharge," and du Bdis-Eeymond
also determined in Torpedo that both homodromous (in direction of
discharge) and heteroclromous currents, after longer closure, or with
less excitable preparations, yield (with reference to direction of
polarising current) relatively negative polarisation, but that this is
invariably stronger with a homodromous current. The apparent
contradiction between this discovery and the original observations
of du Bois-Eeymond, according to which negative polarisation in
the organ of Malapterurus is independent of direction of current,
is explained by the fact that the heterodromous current never
produces any relatively positive polarisation either in Malapterurus
or Torpedo. Diphasic polarisation — first relatively negative and
then positive — appears with homodromous currents only. If it
be admitted that " both currents yield relatively negative polarisa-
tion in the same degree, but that the homodromous current is very
much stronger than the heterodromous, or alone polarises positively,
so that heterodromous, relatively positive polarisation (when pre-

VOL. II 2 G

450

ELECTRO-PHYSIOLOGY

CHAP.

sent) is invariably masked by relatively negative polarisation,"
the reaction of all three electrical fishes will be found to coincide.
The augmentation of relatively negative polarisation, as observed
by Sachs and du Bois-Eeymond with homodromous currents —
as also in du Bois-Eeyrnond's observations on Qymnotus — are thus
intelligible, since the resulting polarisation current through the
galvanometer may assume different values at different stages of
any experiment. The accompanying curves (Fig. 279) will

FIG. -279.

elucidate these complicated interference effects of the two simul-
taneous directions of polarisation, which from obvious reasons
cannot be separated as they are in muscle (du Bois-Eeymond,
4 fj, p. 06). Fig. 279 (after du Bois-Eeymond) gives a summary
of the process in a series of experiments, the two currents being
sent alternately through a strip of organ. The abscissae = time.
The ordinates in each cut (i. ii. iii. iv. corresponding with different
stages of the experiment) express the moment of closure of the
galvanometer after the battery circuit has been opened.

Absolute positive polarisation (in. direction of discharge, i.e.
from ventral to dorsal surface) is drawn above, absolute nega-

XI

ELECTRICAL FISHES 451

tive below, the abscissa. With homodromous currents (upper
series, with ascending arrow) the course of the curve above the
abscissa is absolutely and relatively positive ; below, it is absolutely
and relatively negative. With heterodromous currents (lower
series and descending arrow) the upper portion of the curve is
absolutely positive (relatively negative), the lower portion absolutely
negative (relatively positive). The resulting polarisation current
through the galvanometer is in each cut represented by the
shaded surfaces which comprise the curves resulting from algebraic
summation of the two polarisations with the axis of the co-
ordinates. It is obvious that the relatively negative polarisation
is equal in both currents, while the relatively positive polarisation,
on the other hand, is widely different (and with heterodromous
currents may fail altogether). Consequently the absolute posi-
tive polarisation (which with heterodromous currents is also
relatively negative) is unequal in fresh, excitable preparations
(i.) at the beginning of the experiment in the two cases. At a
subsequent stage this ratio of magnitude may be reversed (ii.) ;
the resulting homodromous polarisation finally becomes absolutely
(and relatively) negative, but is always smaller than the relatively
negative heterodromous polarisation (iii.) ; until finally there is
equal, relatively negative polarisation with both directions of
current (iv.). Sachs also saw stage iii. and du Bois-Eeymond iv.
on Malapterurus.

The results of these experiments, as well as of those subse-
quently undertaken by Gotch (I.e.}, may be summarised by saying
that constant currents, of whatever strength and direction, if led
for a considerable time through an organ-preparation, invariably
yield relatively negative after-currents which are much stronger
with a homodromous than with a heterodromous direction of
the polarising current. Stronger homodromous currents, be-
ginning at a certain limen and lasting only a short time, yield
strong, absolutely and relatively positive after-currents, that sink
very gradually (du Bois-Eeymond's positive internal polarisation).
Heterodromous currents of equal strength and duration generally
yield weaker after-currents, relatively negative, absolutely positive
(du Bois-Eeymond's internal polarisation).

As the strength of the relatively negative after -currents
(negative polarisation), which must be partly caused by physical
internal polarisation, depends in first degree upon the duration

452 ELECTRO-PHYSIOLOGY CHAP.

of closure of the current, we should anticipate that induced
currents (which are of such brief duration) would be peculiarly
appropriate to the production (with homodromous stimulation) of
a positive after-effect in the same direction.

The part played by duration of closure with the constant
currents also, is shown by the following table from Gotch :—

Instantaneous closure (7 Groves) homodromous ; galvanometer deflection

+ 50 (homodromous).
1 second closure (7 Groves) homodromous ; galvanometer deflection

-52 (heterodromous).
Instantaneous closure (7 Groves) homodromous ; galvanometer deflection

+ 30 (homodromous).

1 second closure (7 Groves) homodromous ; galvanometer deflection
- 40 (heterodromous).

By means of a contrivance to be described below, Gotch sent
a break induction-shock, first in one and then in the other direc-
tion, through an organ -preparation, in a galvanometer circuit
which also included the secondary coil and a resistance of 10,000
ohms. On opening the primary circuit, the full after-current in
the preparation due to the induced current went through the
galvanometer. With a strip of organ 1 6 mm. long, 7 mm. broad,
and 2 mm. in diameter, the deflection (with three Groves in
primary circuit and 5 cm. distance of coil) =

Break shock— heterodromous — 150 (homodromous)
,, homodromous 650 „

„ heterodromous 180 ,,

,, homodromous 780 „

The excitation effect of the homodromous current is thus
much stronger than that in the heterodromous direction. Yet,
as Gotch pointed out. this is not invariably the case. At times
no difference can be detected in the (exciting) action of the two
currents, or the heterodromous current may even be stronger than
the homodromous. Gotch is inclined to bring this into relation
with the facts observed by Eckhardt, to the effect that descending
induction-currents via the nerve excite more strongly, since the
homodromous current passes through the majority of the finer
branches of the nerve in a descending direction. The exceptions
are no doubt due to the fact that the larger nerve-trunks some-
times lie in the organ-preparation, so that they are traversed by
descending heterodromous currents, and produce an effective
excitation.

XI

ELECTRICAL FISHES 453

The galvanic effects of the homodromous current usually
increase with the strength of the exciting current, and it can be
demonstrated many hours after the preparation has been excised,
although it disappears completely after scalding. Here, as in
indirect excitation, there is a very slow decline of electromotive
effect, lasting for several minutes, its development and time-
distribution corresponding throughout with the discharges induced
by indirect excitation.

An important fact, as observed by Gotch, is that partial
longitudinal passage of current in an organ-preparation discharges
an excitation effect (after - current) within the part that is
traversed only, and not beyond the poles. It follows that ex-
citation in the, longitudinal direction of the prisms is not transmitted
from one plate to the next. Each plate appears to be physiologi-
cally insulated from all the rest, and total discharge of a whole
prism can only occur either when all the nerves which supply
them are excited, or when an electrical current traverses all the
compartments in series.

As regards the interpretation of the absolute, and relatively,
positive after-effect from homodromous exciting currents, du
Bois-Eeymond reminds us of two possibilities :

(i.) Like the current of rest in the organ, it may be viewed
as the after-effect of a discharge caused by electrical excitation.

(ii.) It may be interpreted on the molecular theory "as the
consequence of a prismatic arrangement of the electromotive
molecules in direct consequence of the homodromous current."

In reference to the last view, it may be stated that du Bois-
Eeymond, in order to explain the discharge from the plates, i.e.
the electromotive action of each single plate of the organ,
assumed its construction from dipolar molecules, similar to that
said to underlie the electrical manifestations of nerve and muscle.
In the resting state the molecules turn their poles either
towards all possible, or in two opposite directions, so that the
effect disappears externally. In discharging, on the contrary,
they " collectively turn their positive poles towards the surface
of the organ, whence proceeds the positive current." Du Bois-
Eeymond pictures the molecules as " a free crowd revolving round
their centre of gravity, in the direction of the axis, by a chemical
force comparable to some extent with the respiration of the
organ." " Several molecules may lie behind one another in the

454 ELECTRO-PHYSIOLOGY THAI-.

cross-section of the plate, so that the organs thus form prisms
with a much larger number of constituents than follows from the
number of the plates."

If in the discharge of the organ we assume a sudden transi-
tion of the dipolar molecules from the " peripolar " to the
" pile-like " arrangement, the process that takes place obviously
coincides with that which du Bois-Keymond postulated in order
to explain the (galvanic) electrotouus of medullated nerve.

But if the molecular hypothesis has already been proved
inadequate for nerve and muscle (to say nothing of gland-
currents and plant-currents), save on the boldest hypotheses to
account for the phenomena, we have the more reason to reject
it for the electrical organs, since all known reactions of these
structures can be explained from the " Alteration Theory "
without difficulty, starting only from the fundamental notion
that chemical differences are initiated in each plate in consequence
of excitation from the nerve, which produces a P.D. between the
interfaces in the given direction.

Hence we must fall back upon the view, supported as
du Bois-Eeymond himself admits (4 g, p. 46) by the strongest
reasons, that the absolutely and relatively positive polarisation of the
electrical organ by the homodromous current is nothing more than
the after-effect of the discharge produced ly the latter.

It therefore becomes very difficult not to regard the homo-
dromous positive after-current as the remainder of a previous
excitation, even from the standpoint of the molecular hypothesis.
.Since this explains the discharge " from a pile-like arrangement
of the electromotive molecules," it is necessary to ask (as du Bois-
Eeymond himself pointed out) " in what particulars this arrange-
ment and that produced directly by the homodromous current
differ ? why the latter does not always complete itself in a
discharge ? " Du Bois-Eeymond imagines that " there may be
two states which, although both associated with a pile-like arrange-
ment of the molecules, and identical in their external action, are
yet distinct within the electrical plate " (since one corresponds with
discharge, the other with absolute positive, homodromous polar-
isation). Yet this seems to present far more difficulties than
the conception that, — just as there are at the seat of direct
excitation, at the close of a muscle-twitch, prolonged galvanic
alterations (negativity), recognisable as the after-effect, or more

xi ELECTRICAL FISHES 455

properly continuation, of the excitation — so in the electrical
organ also the true discharge (shock) may pass off in a honio-
dromous current.

We may admit, with du Bois-Eeymond, that " every absolute
positive effect is not a discharge" just as every excitation of the
muscle, even if demonstrable on the galvanometer, does not
produce a visible contraction (twitch) ; in the fresher preparations
du Bois-Eeymond often observed a very pronounced effect, which
drove the scale out of the field of vision, and in which we must
undoubtedly admit the after-effect of a discharge, if not the last
phase of it. " This phenomenon," he continues, " is, however,
quite distinct from ordinary absolute positive polarisation
(obtained after frequent repetition of the experiment on the
same preparation under identical circumstances), since it exhibits
no duration proportional with the original intensity." Yet this
is just as little the case in the mechanical and galvanic conse-
quences of excitation of the muscle.

If the absolute positive (homodromous) after-current in these
experiments is to be viewed as the after-effect of exciting the
organ-preparation by the homodromous current, we may expect it
to be very marked after brief tetanisation with alternating currents.
In order to avoid the disturbances caused by the inequality of
time-distribution in the make and break shocks of the ordinary
sliding coil, du Bois-Eeymond used a Sexton's machine, which pro-
duces series of quite congruent alternating currents. The results
were uniform ; no matter how the ends of the rotating coils
were connected up with the dorsal and ventral surfaces of the
preparation (Torpedo], or what was the duration of the tetanus,
there was always an absolute positive after-current, " in fresh
preparations of such magnitude that the scale disappeared from
the field, the effect becoming gradually weaker."

The striking difference in the relative strength of homo-
dromous and heterodromous exciting currents in the electrical
organ, seems to depend intimately upon positive homodromous
polarisation, as du Bois-Eeymond observed in his earliest polar-
isation experiments 011 the Malapterurus organ. " The descend-
ing homodromous current in Malapterurus was always stronger
in fresh strips than with the ascending (heterodromous) direction,
in the ratio of 100:112, 116, even 125. In boiled and in
moribund strips the difference vanished." The same fact was

456 ELECTRO-PHYSIOLOGY CHAP.

even more apparent later on in preparations of Torpedo, in which
the homodromous current (of 30 Groves) was more than double
as strong as the heterodromous. A similar effect was seen still
more plainly on stimulating with induced currents, when the de-
pendence of the seeming irreciprocity of conduction upon current
density in the electrical organ was apparent. Du Bois-
Reymond " sent opening shocks from the sliding inductorium
(the primary coil being filled with rods), from surface to
surface of the skin in a preparation of Torpedo, which rested
between the clay shields of the leading-in vessels. The galvano-
meter was included in the same circuit." Each shock sent in by
opening the mercury key traversed the preparation alternately
in the homodromous and heterodromous directions. In the
following table RA stands for distance of coil, the figures
correspond with the deflections, reduced from 5000 turns at
2 0 mm. distance from the galvanometer mirror :—

RA= 0 -^501 -|215 -f5°l i21^ ^453 ^215 ^477
RA = 10cm. ^25 ^28 ^27 -^28 -f 27 -f 27

KA = 15cm. ^7^7^7^7

RA= 0 ^453 ^227

Above a certain limit of current density the homodromous
current is thus much stronger than the heterodromous (^).

It should not be unnoticed that, as has been said, " positive
polarisation " exhibits the same dependence upon the density of
the polarising (homodromous) current. Since it further shows
augmentation in proportion with the length of prismatic tract
between the leading-off clay points, and therewith the number
of polarised plates, the difference in intensity between homo-
dromous and heterodromous current is the more distinct accord-
ing as the distance between the leading-in electrodes on the
lateral surface of the organ-preparation is greater, so that we
may say that the apparent irreciprocity of conduction grows, like
positive polarisation, with the length of the prismatic tract
traversed. In this respect also it has been proved that the
ascendency of the homodromous current is much more pro-
nounced with induction shocks, or brief constant currents,
than with longer closures. Both manifestations are further
associated with vitality, and do not appear with sodden or
spontaneously defunct preparations, or with transverse passage

ELECTRICAL FISHES 457

of current. This notwithstanding, du Bois-Eeymond refers the
difference of current-intensity in the homodromous and hetero-
dromous directions, not to inequality of E.M.F. in either case,—
since the relative and absolute positive after-current follows on
the homodromous polarising current, — but to a real irreciprocity,
i.e. to unequal resistance in the two directions, the organ con-
ducting better in the direction of the discharge than in the other.
It is evident that such a mode of conduction, " which is thus
far without any counterpart," can hardly be accepted without
stringent justification. When all attempts at deciding the point
showed only that, " contrary to all appearance, it is not necessary
to invoke irreciprocal resistance to explain the facts," du Bois-
Eeymond finally believed that he had found such justification in
his determinations of the resistance to conductivity in the elec-
trical organ (Torpedo}. He compared the resistance in prisms
of the electrical organ of uniform length and diameter, of
frog's muscle (parallel with the fibres), and of salt solution (sea
water). "With this object the different bodies were enclosed in
glass tubes of uniform dimensions, and traversed longitudinally
by current. The resistance of the circuit, which included a
galvanometer as well as the tubes, was measured by the
reciprocal magnitude of the galvanometer deflections, as caused
by the opening current of a sliding inductorium. He found that
an organ -preparation drawn through the glass tube was a far
worse conductor, even with homodromous passage of current in
the long directions of the prisms, than frog's muscle parallel
with the fibres, or salt water, under the same conditions.

Du Bois-Eeymond thence concluded that if the ascendency
of homodromous currents depended upon positive polarisation
-i.e. an additional E.M.F., amounting even to 40 Groves — the
organ -preparation would, in comparison with muscle, or with
physiological salt solution, conduct better, and its resistance would
therefore " seem to be enormously increased," when it loses
positive polarisability, along with its vital properties. Neither con-
sequence, however, occurs in du Bois-Eeyrnond's experiments, but
rather the contrary. Without referring to this fact, which it is
hard to judge without personal investigation, Gotch, with whom
Schonlein is now in full agreement, endeavoured by direct experi-
ment to disprove the theory of irreciprocal conduction. He em-
ployed apparatus modelled on the " spring myograph," in which the

458

ELECTRO-PHYSIOLOGY

CHAT.

shooting trigger successively opens three contacts. The first of
these (Fig. 280, $,_) opens the circuit of the primary coil of a
sliding apparatus, the second, $„, abolishes the shunt to the galvano-
meter, which can only then be affected by the current from the organ-
preparation; and, finally, the third, S.A, opens the galvanometer circuit
again, so that the effect in the galvanometer can only last for the
interval between the opening of S2 and that of S3. This interval, in
Gotch's first experiments, was 0'02 sec. If $2 is shifted close to Sly
so that the shunt to the galvanometer is opened almost simul-
taneously with the inducing circuit, the former will exhibit the

FIG. 280.

same intensity with both homodromous and heterodromous direc-
tion. This result can obviously be referred only to the fact that
the galvanometer circuit was closed in Gotch's experiments for a
very short time after the moment of stimulation, while in du
Bois-Eeymond's method, not merely the exciting current, but also
the whole after-current of the preparation, passes through the
galvanometer. In the first case, therefore, the homodromous
after-current (positive polarisation, in du Bois-Eeymond's sense)
can add nothing to the homodromous induction -shock which
produces it, since, according to Gotch, it is not developed for
0-05 sec.

Gotch subsequently extended his operations (I.e.), making the

xi ELECTRICAL FISHES 459

interval between closure of galvanometer circuit and moment .of
stimulation still finer, by means of the same apparatus. He
found, in accordance with his previous observations, that when
the closure of the galvanometer was shortened so much that
the induction -current alone could affect the galvanometer
(S.-, — Ss= 0" — 0'0025") there was no difference in the deflec-
tions produced by the homo- and heterodromous currents ; at the
next moment the electromotive action of the organ-preparation
discharged by the shock makes its appearance ($0 — S3 =
0'0025// — O'OOS") as the homodromous after - current, and
increases rapidly with further augmentation of closure. The
apparent irreciprocal conduction thus arises only when the action
upon the galvanometer of the exciting induction-shock is com-
bined with that discharged from the organ-preparation (du Bois-
Reymond's positive polarisation).

In further confirmation of this view we have the results of
experiments on the influence of varying temperature upon the con-
sequences of direct excitation of organ-preparations. Gotch was able
to show easily, by means of his spring rheotome, that the intensity,
and more particularly the time -distribution of the excitation
effects, on applying single homo- and heterodromous induction-
currents, are essentially influenced by temperature, and that in
the direction we should a priori expect in the matter of dis-
charging an excitation. As appears from comparison with the
curves in Fig. 281, which give a graphic representation of the
experimental results (the ordinates corresponding with the gal-
vanometer deflections, the abscissae with the interval after the
moment of excitation, at o), the intrinsically less important
effects of excitation in the cooled preparation are considerably
retarded, and only become appreciable on the galvanometer long
after the induction- current has been made, so that there is a
long " latent period " during which the closure of the galvano-
meter circuit has no effect. It must thus be relatively easy to
separate the effect of the induction-current upon the galvano-
meter from that of the excitation (supposed positive polarisation),
and hence to determine whether irreciprocity of conduction
really exists or no. Gotch succeeded in demonstrating that
apparent irreciprocity does appear at higher temperature (22° C.)
with the same closure of the galvanometer, while the same pre-
paration cooled, under otherwise uniform conditions, conducts

15° C.

3°C.

400 —

300

FIG. 281.— Graphic representation of the distribution of the discharge in direct excitation of an organ-preparation (Torpedo), witl
homodromous (+) and heterodromous (-) induction-shocks at 15° and 3° C. The shaded part of the curves.correspondi
with the exciting induction-currents. (Gotch.)

CHAT. XI

ELECTRICAL FISHES

461

the induction-current equally well in both directions, as appears
from the following table : —

Temperature.

Direction of Current.

Duration of Closure.

Sa-Sa

0"- 0-005"

S-2 - 83

0"-0'01"

22° C.

f Homodromous
\ Heterodromous

+ 338
-290

+ 475
12

8°C.

f Homodromous
\ Heterodromous

+ 270
-270

+ 380
-174

There is as little reason for assuming irreciprocal conduction
in the less differentiated electrical organ of Raja. With direct
excitation of an excised strip of organ, by single induction-shocks,
there will be a single discharge after an interval of about
0'005 sec., the direction of the exciting current being quite
immaterial. It is only when the closure of the galvanometer
circuit occurs at a time when the discharge of the organ has
already taken place that the apparent irreciprocity is again
visible in consequence of the algebraic summation between the
discharge and the exciting current. When the direction of the
induction-current coincides with that of the discharge, the deflec-
tion increases with the duration of closure, while in other cases
it declines, and is eventually reversed (Gotch, 1 3 c). This is not
the place to enter more in detail into clu Bois-Eeymond's treat-
ment of the teleological significance of " irreciprocal conduc-
tion " of the electrical organ.

VIII. THEOKY OF DISCHARGE FROM ELECTRICAL FISHES

Without entering further into the older and in part very
naive views that were briefly alluded to at the beginning of this
chapter, and which do not at the present level of knowledge call
for serious discussion, we will only consider certain newer theories,
in re the discharge of electrical fishes, which have indeed been
contradicted, but which still claim our interest, because they
show how the theories predominating in nerve- and muscle-
physiology were adapted to the electrical organ also.

462 ELECTRO-PHYSIOLOGY CHAP.

In 1873 Boll discussed the possibility of "explaining the
discharge of the electrical organ solely by the negative variation
of the nerve current, concomitant with inuervation. In this
arrangement the dorsal surface of the electrical plate (of Torpedo}
would at the moment of innervation become positive, the ventral
surface negative, as actually occurs." The free ending of the
nerve-fibres within the plates suggests the question, " What, under
these conditions, must finally become of the negative variation of
the nerve current, since it accompanies the excitatory process
within the nerve-fibre in every case to the extreme periphery :
and whether the more than million-fold multiplication of this
variation of the current as engendered in the electrical plates of
Torpedo (not Malapterurus) by the anatomical relations of the
nervous ramification may not be a sufficient explanation of the
discharge of the Torpedo ? "

But, as du Bois-Eeymond pointed out (4 e, p. 276), this
hypothesis in the first place predicates the existence of a current
of rest, caused by the " natural " cross-sections (acting like arti-
ficial sections) of the nerves in the plates, and accordingly hetero-
dromous to that of the discharge. Instead of this permanent
current — which must correspond in E.M.F. with the discharge if
the nerve current is to disappear in the negative variation —
there is only an inessential P.D. during rest, and the resulting
" organ current " is always homodromous with the discharge, as
the after-effect of which we have learned to characterise it. Du
Bois-Eeymond declared it to be " no bad hypothesis " which, in
order to explain this, assumes " the cross-section of the nerve to
be covered over by a parelectronomic layer, the electromotive
activity of which does not merely neutralise that of the former,
but even to some extent outweighs it, and which has no part in
the negative variation. At the moment of the discharge, the
E.M.F. of the nerve current disappears in the negative variation,
and the discharge is brought about through the release of E.M.F.
in the parelectronomic layer."

In the meantime, however, such an assumption became
illegitimate, even from the standpoint of the molecular theory,
owing to the indubitably powerful E.M.F. of the Torpedo dis-
charge,— apart from the fact that Boll's hypothesis does not apply
to Malapterurus. As we are about to show, there are even in
Torpedo, not to mention the other more powerful electrical

XI

ELECTRICAL FISHES 463

fishes, considerable magnitudes of E.M.F. which, as du Bois-
Eeymond himself pointed out, cannot be explained on Boll's
hypothesis, owing to the very marked short-circuiting that exists
under all circumstances between the individual nerve-endings.
In Malaptcrurus, however, where one axis -cylinder is alone
correlated with each plate, each axis-cylinder would, as du Bois-
Eeymond remarks, under even the most favourable conditions
(such as " that the point of junction 'should contain a cross-section
of the nerve with the parelectronomic layer, and that, as appears
hardly possible, this cross-section should be a superficial element
at right angles to the direction of activity in the organ), be
embedded separately in the mass of the plates, whereby such a
diminution of its external action would result, that there could
no longer be any question of explaining the discharge of Malapte-
ri/.rus by the variation of the electrical nerve-endings. Du
Bois-Eeymond further points out that on Boll's theory the
existence of the electrical plates (often of such a complex structure)
would have no significance in the electrical organ, and would be
inexplicable.

As we have said, it was du Bois-Eeymond who first, in 1843,
expressed his conviction that it was the latter (the so-called
" gelatinous discs ") which " at the moment of discharge become
electromotive in a given direction, under the influence of a nervous
agency stimulated by whatever means," and which multiply
their action after the manner of the voltaic pile. It would thus
not be the negative variation of the nerve current that pro-
duced the discharge, but a process in the electrical plates trans-
formed from muscles, comparable with the negative variation of the
muscle current, as set forth from the standpoint of the pre-existence
theory. Du Bois-Eeymond (supra) would accordingly represent
each plate as containing countless dipolar electromotive mole-
cules, " able during rest to turn their poles either in all possible
•or in two opposite directions, so that the external action
neutralises itself, while during discharge the poles are turned
rapidly and collectively toward the surface of the organ, whence
proceeds the positive current." Du Bois-Eeymond reckons as
one of the main supports of this theory the dictum derived from
Delle Chiaje's and Babuchin's doctrine of the preformatiou of the
electrical elements, that the E.M.F. of the discharge must increase
proportionately ivith the diameter of the plates. Since the E.M.F.

464 ELECTRO-PHYSIOLOGY CHAP.

increases with the size of the fish (whether proportionately re-
mains, as Hermann pointed out, 14, p. 486, an open question),
while the number of the prisms (or plates) is unaltered, a direct
relation between the diameter of the plates (i.e. number of mole-
cular layers in du Bois-Keymond's sense) and the E.M.F. may
be assumed as proven, although Schonlein disputes this on the
ground of his experiments (30, p. 503). This, moreover, co-
incides with the small diameter of the plates of the Torpedo organ
9 '6 /A, as compared with those of G-ymnotus 8*2 //,, and Malapte-
rurus 4' 8 fju. As stated above, the Torpedo organ, adapted to
sea-water, can suffice with less E.M.F., while those of the two
fresh-water fishes require much greater E.M.F. to meet their
higher internal resistance (greater length, smaller cross-section).
Given the surface mass, and under the presumption that the E.M.F.
of the plates is proportional to their diameter, du Bois-Eeymond
(4 c, p. 286) finds the ratio of E.M.F. in the entire organ of
G-ymnotus, as compared with that of Torpedo, to be 128 : 1.

Du Bois-Eeymond brought forward the following conclusions
as evidence that the molecular hypothesis, in the same form in
which it was drawn up for muscle and nerve, accounts for the
E.M.F. of the electrical organ also (I.e. p. 288 f.) : "The E.M.F.
of a dipolar molecule from a regularly constructed test-muscle, as
diminished by short-circuiting, = the double P.D. between equator
and poles of the muscle, about 0'15 D. Let it be taken for
security sake as = O'lO D. The diameter of the Gymnotus plate,
inclusive of the papillie (which are also regarded as electromotive),
as compared with the diameter of the Torpedo plate = 8 '2 : 9 '6 =
S'5 : 1 ; the first contains 8 '5 times as many molecules as the
second. Two molecules alone, one behind the other, of the Torpedo
plate yield a total E.M.F. of400x2x010D = 80D, which is
sufficient. In Gymnotits we reach the formidable value of
6000x17x0-10 D = 10,200 D." According to Schonlein
(I.e.), the highest E.M.F. that has yet been calculated for the
discharge of Torpedo = between 3 0 and 3 1 D. The calculation
was made " either by comparing the deflection from the discharge
of the organ with that from a number of Daniell cells, introduced,
with the addition of a resistance approximately equal to that of
the organ, into the circuit in place of the organ, or by com-
pensation " (Schonlein). If with Fritsch we reckon the number
of plates in Torpedo ocellata at 370, in T. marmorata at 380

XI

ELECTRICAL FISHES 465

per prism, this gives us for each single plate an E.M.F. of

These values are undoubtedly of quite a different order
from those given for the E.M.F. of cold-blooded nerves, which
is always below 0'025 D. On the other hand, it is a striking
and hardly adventitious fact that the figures for the E.M.F.
of the discharge from the plate, and the maximal negative varia-
tion of the muscle, are not merely of the same order, but are
identical, whence Schonlein (I.e. p. 501) concludes that "the
substratum at which the discharge of the electrical organ of
Torpedo is completed may be identified exclusively with the
substratum in which the negative variation of the muscle
completes itself." 1 The hypothesis that there is any change
of position of preformed electromotive molecules in the dis-
charge, seems, however, under all conditions to be excluded, from
the fact that the majority of electrical organs are no more
than transformed muscles, and that the molecular theory has
been disproved in regard to the latter. This is obviously not
the place (since we are here concerned solely with the summary
of the data so far contributed to the physiology of electrical
fishes) to go beyond the intentions of the founder of the
alteration theory, and attempt from that standpoint to explain
the phenomena. It is, however, permissible to say that, in the
opinion of the author, Hermann's theory is as well adapted to
cover the new department (which merely, as it were, contains old
matter in a new garment) as it proved to be in regard to gland
and plant currents.

From this standpoint the principal interest attaches to
chemical processes within the active substance proper of the
electrical organ ; it is well, therefore, to subjoin a few remarks
on this subject, more particularly as comparing these with the
corresponding reaction of striated muscle, since this is the material
whence develops the electrical organs.

That the activity of muscle is correlated with chemical processes
is shown inter alia by the fact (first pointed out by du Bois-Eey-

1 More recently, on the other hand, Schoulein has adopted the view that the
electrical plate is a "nerve-ending" (analogous with the motor end-plate). The
electromotive substance of the muscle would then have entirely disappeared (which
is certainly not the case in Raja).

VOL. II 2 H

466 ELECTRO-PHYSIOLOGY CHAP.

mond) that the reaction differs in resting, and in excited as well as in
dead muscle. The acidity is in the latter case so striking that it is
easily demonstrated by less sensitive methods. In the electrical
organ (of Torpedo} it is quite otherwise, as proved by repeated
observations of many authors who have investigated this point.
Boll (5 a}, who, like du Bois-Reymond, tested the reaction with
litmus-paper, found it unmistakably alkaline in the non-excited
organ (Torpedo}, and all later investigators have agreed with him
(cf. Th. Weyl, 36 &; W. Marcuse, 20). As regards post-mortem
acidity there is not, however, the same consensus of opinion.
While Boll and Weyl convinced themselves of its appearance,
Marcuse emphatically denied it. M. Schultze, again, found that
the electrical organ of freshly-killed torpedoes was constantly
very acid, which from analogy with the muscle was referred both
by Fuuke and du Bois-Reymond to an exhaustive effort of the
muscle previous to death, resulting from its frequent discharges.
Experimental results are, again, in direct contradiction with this
statement, neither strychnine poisoning, nor direct stimulation of
the electrical lobe, nor cutting-off the blood-supply being successful
in producing any marked degree of fatigue. Boll found none ;
Marcuse, who determined the reaction of the alcohol extract by
titration, with litmus-paper, detected only the merest shade of
difference between excited and non-excited organ (isolated by
section of the nerve), the second state being slightly more acid
than the first.

Rohmann (29), who has recently repeated these investigations
at the zoological station at Naples, employed a method first
invented by Dreser (Cbl. f. Physiol. i. 1887, p. 195) for muscle.
This is based on the property possessed by acid-fuchsin, of
forming with the alkali of the tissue fluids a colourless combina-
tion, which breaks up again with quite weak acids (even CO.,),
and assumes a reddish colour. " If, after ligaturing the circula-
tion (in a frog), the sciatic nerve on one side is tetanised
intermittently (after previous injection of acid - fuchsin), there
will (in 10—15 minutes) be a pronounced reddening of the
excited limb, which on the ground of the chemical properties of
the acid-fuchsin is a proof of the production of acid by active
muscle " (Dreser). Rohmami was able to establish a similar
reaction in the electrical organ, since in a torpedo injected with
fuchsin, and strychninised, or persistently excited from the lobe,

ELECTRICAL FISHES 167

the resting organ (isolated by division of the nerve, the skin
having been removed) will be colourless or faintly pink, while
the excited organ varies from pale pink to peach blossom colour.
It must thus be taken as proven that " during the generation of
electricity within the electrical plates there are alterations of
metabolism which lead to the production of a small quantity of
acid substances." On the other hand, liohmann, like Marcuse,
finds no increase of the nitrogenous extractive, or substances
contained in the ether extract. Any participation of carbo-
hydrate (glycogen) in the generation of electricity seems excluded
by the fact that Marcuse finds neither glycogen nor any similar
carbohydrate in the electrical organ.

" It is far more probable that a substance closely related to
the albuminous bodies is the source of electromotive energy, and
liberates it in the formation of acids which are soluble in ether "
(Eohmann). It is above all remarkable that, according to the
foregoing experiments, " the production of the electrical discharge
of Torpedo seems to occur with the consumption of a minimal
quantity of potential energy," which for the rest holds good
equally of muscular work, though not in the same degree.

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6. F. BOLL.

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10.

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xi ELECTRICAL FISHES 469

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CHAPTEE XII

ELECTROMOTIVE ACTION IX THE EYE

ALTHOUGH subjective observation and the analysis of sensations
must under all conditions take first rank among the methods of
investigating the physiology of the senses, the objective signs of
sensory activity, though scanty, are no less deserving of con-
sideration. It is true that the great expectations associated at
first with the discovery of visual purple, and the bleaching of it
by light, have not hitherto been fulfilled, and the later endeavours
of Konig and v. Kries to attribute a predominant role to this
" visual substance " must be regarded as discredited.

Along with the " photo-chemistry " of the retina, its electro-
motive action and the alterations thereof by light stimuli claim
the chief share of attention.

As early as 1849 du Bois-Eeymond investigated the electrical
reaction of the optic nerve, at its peripheral expansion in the
eye, while he was engaged in proving the identity of the
"natural" and artificial cross -section in nerve --as already
established for muscle. On leading off from the artificial section,
or from some point near it of the natural long section, of the
optic nerve, and the external surface {e.g. cornea) of a fish's eye-
ball as free from muscle as possible, the nerve was invariably
negative to the eyeball. The natural ending of the nerve thus
seems no more positive than the tendon end of the muscle-fibres.

Sixteen years later, Holmgren (1) repeated these experiments,
using principally the frog's eye. He confirmed the observations
of du Bois-Eeymond in regard to the " current of rest," and
found, moreover, on leading off from the posterior portion of the
bulb and the optic nerve, that the former was weakly negative to
the latter. " If one electrode is applied to the optic nerve

CHAP, xii ELECTROMOTIVE ACTION IX THE EYE 171

while the other is moved, touching now the back of the bulb
and now the cornea, there results in the first case what Holmgren
calls the ' weak reaction,' where the optic nerve is positive to
the eyeball, in the second the ' strong reaction,' nerve negative
to cornea." Holmgren rightly observes that retina can no more
than muscle be termed the " natural cross-section " of the cor-
related nerve, since it forms both anatomically and physiologically
an end-organ distinct from the nerve, capable conceivably of
independent electromotive action, like muscle or glands, under
certain conditions. If, therefore, in agreement with du Bois-
Eeymond's view, we are still to speak of natural transverse and
longitudinal sections, the former must be defined as the entire,
external, mosaic surface of the retina, bordering on the choroid,
while the inner boundary (layer of optic fibres) facing the
vitreous body forms the natural long section. Holmgren
determined the distribution of potential upon the surface of
the bulb with great accuracy, and endeavoured to bring the
retinal current into line with du Bois-Eeymond's law of the
muscle current. Without entering into detail, it may be said
that, as we should anticipate from the electromotive action of
the entire eye, there are in the retina differences of potential in
the direction of an " ingoing " current (i.e. from without, inwards),
signifying, in du Bois-Eeymond's sense, that the natural cross-
section (rods and cones) is negative to the natural long section
(internal surface of the retina).

The inadmissibility of such an interpretation is, however,
obvious if we consider the structure of the retina, which, as
justly remarked by Kiihne and Steiner, " exhibits throughout,
and exclusively in the most external layer, objects that are quite
unlike free nerve -endings, while in no other layer is there
anything resembling such endings."

Kiihne and Steiner (3) principally employed the isolated
retina of the frog in their successful researches. This tissue
may be slipped out of the fundus as out of a shell, with or
without pigment epithelium, its vital properties being preserved
intact, after which it can be drawn over a rounded glass rod,
and brought into contact with the leading-off electrodes. If
the rod -surface is external, and different points of the same
are tested, there is invariably a strong current between the
entrance of the optic nerve and the periphery, the former being

472 ELECTRO-PHYSIOLOGY CHAP.

positive to all other points of the retina. In leading off, on the
other hand, from the fibrous layer (internal surface), the entrance
of the optic nerve is invariably negative to every peripheral
point. Like Holmgren, Kiihne and Steiner further observed, on
leading off simultaneously from internal and external surface of
the fresh retina, an " ingoing " current, the former being negative
to the latter. The retina was so arranged between the electrodes
" that the lower of the two supported the membrane on a clay
cap curving upwards, while the other made contact with the
opposite surface of the retina by a blunt point." The E.M.F. of
this current, which is at first considerable, diminishes rapidly,
and at times disappears completely, although in most cases it
remains for some time longer at a medium height.

The variations of the retinal current under the influence of
light are of far greater interest than its intrinsic behaviour.
Here, again, it is to Holmgren that we owe the fundamental
observations : he showed that the retinal current invariably
gives a positive deflection, if light falls on an eye that had
previously been in the dark, or when light is shut off from it.
This occurs in the frog without exception, while in reptiles
(snakes), birds, and mammals Holmgren finds 011 the contrary
a negative effect at the impact of light, a positive variation at
darkness. The mere alteration of intensity of illumination makes
an effective stimulus.

Dewar and M'Kendrick discovered, independent of Holmgren,
that a positive variation resulted from illumination of the eyes
of vertebrates (of all classes), as also of Crustacea, correspond-
ing to an increase of E.M.F. in the rest -current of 3-10 °/Q.
During part of the experiments the lead-off (frog) was not
merely from the bulb, but from this, and a portion of the brain
still connected with it by the optic nerve. Here, too, the impact
of light was followed by a strong positive variation. The same
occurs in the pigeon on leading off from optic lobe and cornea
of the opposite eye. The variation in this case is nearly doubled
if the two retinse are simultaneously illuminated, nor is it
altogether absent on leading off from lobe and cornea on the
same side. Of coloured lights, yellow was the most effective,
then came green, red, and blue. Lastly, Dewar and M'Kendrick
eventually believed that they had discovered relations between
stimulus and effect, corresponding witli Fechner's law.

xii ELECTROMOTIVE ACTION IX THE EYK 473

Kiihne and Steiner (/.c.) at first experimented in a dark room
divided into three parts. The two farthest contained the
galvanometer and telescope, while the eye was prepared in the
third room by a lamp. In the later experiments the galvano-
meter was placed in a light room, while the electrodes and
illuminating arrangements were in an adjacent and absolutely
dark chamber. The stimulus was made by an Argaud gas-
burner at a distance of 50-75 cm. from the preparation. The
lamp was turned up and down by an assistant at a signal, so
that the retina was suddenly illuminated or darkened. The
lead-off from the inner and outer surfaces of the retina was
effected by specially constructed clay electrodes, covered (Engel-
mann's method) with frog's lung. Each adequate and sudden
illumination with blue, green, yellow, red, or white light then
produced a considerable complex varia-
tion of the retinal current, with or
without the presence of visual purple.
The typical effect (Fig. 282) in a retina
containing the purple is a positive
variation at the moment of illumina-
tion (b c) rising rapidly to its maxi-
mum, and then passing quickly into the
negative variation. This phase reaches
its maximum (d e] during the impact

FIG. 282.

of light, is delayed some time at this

point, and then declines very gradually to zero, even during con-
stant illumination. At the moment of darkness there is again a
sudden positive effect (e /), which must be regarded as the result
of a second stimulus due to the disappearance of light. The
mode of excitation is therefore in a measure comparable with
that from an electrical stimulus. As in the latter, the impact
and duration of the current on the one hand, and its disappear-
ance on the other, act as a stimulus, so with the impact of light
upon the retina, where the effects are visible on the galvanometer
as an initial diphasic (positive then negative) and a second
simple (positive) variation of the rest-current. The presence or
absence of visual purple appears from Kiihne and Steiner to
be of essential importance to the intensity of the retinal " current
of action." Not merely does the magnitude of the variations
differ in the two cases, being greater in the unbleached retina

o

474 ELECTRO-PHYSIOLOGY CHAP.

for the same stimulus, but they are qualitatively different. In
" light " frogs — such, i.e., as have been exposed for hours to the
full effect of daylight — the positive fore-swing of the negative
variation concomitant with the impact of light is entirely
wanting, or appears as a trace only. The same reaction,
according to Kiihne and Steiner, is exhibited by the retinae of
winter-frogs even when confined for days in darkness in a warm
room.

If the current of rest in an unbleached " dark " retina is of
low E.M.F., and the negative variation in illumination only
moderately developed, there is usually a reversal of the current
at excitation, immediately after the positive fore-swing, which
lasts throughout the period of light (Fig. 283). In other cases

Fio. 283. Fir;. 284.

(with a strong current of rest), there is often no genuine
negative variation, merely a more or less considerable decrement
of the preliminary positive fore-swing (Fig. 284). The current
of rest often begins to sink rapidly from the moment of
preparation. It may not merely sink to zero, but be reversed.
The photo-electric variations are only thereby affected in so far
that the individual phases collectively exhibit the opposite signs,
while entry, order, course, and magnitude undergo no alteration.
The three variations accordingly present the indices — +
instead of the normal + — + .

The fact that the three phases of the retinal action current,
due to transitory illumination, appear in sensitive preparations
even when, as with the electric spark, the impact of light is
momentary, shows that the medium negative phase must not be
regarded merely as the consequence of pcri/xtnait illumination,

xii ELECTROMOTIVE ACTION IN THE EYE 475

since it is just this phase which alone appears in less excitable
preparations with instantaneous light stimuli.

It is further remarkable that, as was found by Fuchs (4),
" the first (positive) phase of the variation produced by the
electric spark occurs incomparably more rapidly than in non-
instantaneous illumination." This is a strong argument for
considering the (photo-electric) variations as the expression of
the excitatory process in the sensory matter " (S. Fuchs).

Every considerable variation- in intensity of illumination
produces, indifferently as to whether it occurs in the negative or
the positive direction, a positive variation of the rest-current ; as
expressed . on leading off from the isolated retina by twitching
movements, if the flame is made brighter or darker by turning
the gas up or down. " And since our eyes cannot perceive such
increments above a certain limen of intensity, the movements on
the galvanometer cease just before the highest luminosity is
attained " (Kiihne and Steiner).

The retina is extraordinarily sensitive towards even the
merest trace of light (glimmer of a cigarette, flash of phos-
phorescent powder), so that it may be said, on the ground of
Kiilme and Steiner's experiments, that the galvanometer reacts
to the same intensities of light " that produce a clear sensation
in the eye." If the illumination is confined to the smallest
possible point of the retina, there is none the less a photo-
electric variation at every other point, however distant, due
either to currents deriving from the tract that is directly
illuminated, or to the effect of diffusion of light in the retina.

The effect in the entire, uninjured eyeball differs essentially
from the course of the photo-electric variation in the isolated
retina as described above, since in preparations of maximal
excitability the second negative phase of the variation upon
the impact of light is wanting : so that even when the illumina-
tion is protracted for several minutes there is a uniform increase
between the first positive initial and second equally positive
terminal variation of the current. An effect analogous to that
in the isolated retina appears only with injured, fatigued, or
living bulbi (which may be compared with certain observations
of Dewar and M'Kendrick).

The variations of the eyeball current are further much
smaller, in consequence of the less favourable conditions of

476 ELECTRO-PHYSIOLOGY CHAP.

leading off, and may after previous, strong illumination fail
altogether, while the isolated retina would still yield a vigorous
current of action.

These differences in the photo-electrical variations of the
eyeball and isolated retina appear to derive solely from unavoid-
able alteration of the latter during preparation, since careful
division of the eye into anterior and posterior halves, with removal
of the lens, never produces the middle, negative phase, while this
never fails to appear on tearing the retina, or letting out the
vitreous humour. The same occurs in the uninjured eyeball,
when excitability diminishes gradually in a stale preparation
(accumulation of C09). The positive initial phase of the
diphasic variation becomes gradually smaller, and at last fails
altogether. Holmgren was the first to observe the differences
in the photo-electrical variations of the retinae of various animals.
In reptiles (Vipcm Berus\ birds (fowl), and mammals (rabbit,
dog), the uninjured eyeball in situ invariably exhibits first a
negative and then a positive variation of the current of rest,
instead of the diphasic — in both cases positive — variation of the
frog's eye at the commencement and end of illumination. Since
(supra) a similar reaction takes place in dying or fatigued frogs'
eyes, the effect might presumably be due to the lower resistance
of warm-blooded eyes, on the assumption that if investigated
under conditions as nearly as possible normal, they would exhibit
the same characteristics of photo-electrical variation as the frog's
eye. Against this, however, we have on the one hand the fact
that in certain cases, e.g. the pigeon (where the long rods and
cones are very enduring), the isolated retina lends itself readily
to experiment, and plainly shows at least the initial negative
phase (especially if the temperature of the chamber is raised
a little, Klihne and Steiner) : on the other hand, the reaction
of reptiles' and still more of fishes' eyes may be urged as a
plausible objection.

The results of illuminating the fish's eye were nil for
Holmgren, and very unsatisfactory to Dewar and M'Kendrick.
Kiihne and Steiner, on the contrary, obtained successful effects
from the uninjured eyeball, and still more from the isolated
retina of several species of fish (Ferca flnv., Esox lucius, Leuciscus
and Cyprinus barlus).

While the current of rest gives the same reaction as in the

XII

ELECTROMOTIVE ACTION IN THE EVE

17

Bulbus.

HoU-
schaale.

frog — i.e. greatest in the uninjured eyeball, least, and often
reversed, in the isolated retina — the photo-electrical variations are
essentially different in character and distribution (Fig. 285).
In the eyeball there is at the commencement of illumination a
positive and very slowly increasing variation, that only rises
abruptly at the end to its maximum. This is succeeded by an
increase of the current of rest which persists during the impact
of the light, and at the close of illumination is followed by an-
other, but much weaker, posi-
tive variation. On the other
hand, the posterior half of the
eye, as also the isolated retina,
yields an initial negative varia-
tion, followed immediately by
a positive phase, in which the
current of rest is more or less
augmented beyond its original
proportions. At cessation of
light there is, as in the frog,
another positive variation of
considerable magnitude. If
any alteration occurs in the
retina, the current of rest will
not, at the close of the first
negative phase, regain its ori-
ginal base - line during the
illumination — while finally, in
fatigued or dying preparations,
a decrement of the negative
variation fails altogether, so that this phase remains as the sole
effect of excitation.

Van Genderen-Stort (5) observed that the movements
(change of position) in the cones of the retina, as well as the
displacement of pigment in the retinal epithelium, were pro-
duced not merely by the direct illumination of that eye, but
also by illumination of the other ; whence it might be concluded
that the optic nerve contains not merely sensory but also centri-
fugal (retino-motor) fibres. Engelmann has shown (5) that this
might incite reflex alteration in the electromotivity of the eyeball.
Obvious variations were obtained in every instance, on leading off

Nctzhm't.

Nctzhaut.

478 ELECTRO-PHYSIOLOGY CHAP.

from the middle of the cornea and a point posterior to it or near
the equator, in the upper half of the eyeball of a " dark " frog,
when (with complete obscurity of this eye) the other eye was
illuminated. The same occurred after removal of the skin as
well as of the mucosa of the palate, although in a lesser degree.
In opposition to the photo -electrical variations with direct
illumination, absence of the second positive phase occurred
only with sudden obscurity. After dividing the optic nerve,
there was no galvanic effect from illumination of the opposite
side. Chemical stimulation (application of a crystal of salt to
the retina of the opened eyeball) produced considerable variations
of the rest-current in the other eye, first in the positive and
then in the negative direction.

Starting from the experiments of Kiihne and Steiner upon
instantaneous illumination of the retina, Sigm. Fuchs (4) has
recently been attempting to determine more exactly the time-
relations of the photo-electrical variations in the frog's eye,
and to discover whether (as might be anticipated) the excitation
of the apparatus of the optic nerve, and therewith of the ac-
companying light sensation, occurs subsequently to the stimulus
which discharges them. A series of opening sparks were
discharged by means of Bernstein's rheotome as adequate
stimuli for the retina, the galvanometer being closed, on the
other hand, at a variable interval after each impact of light.

The form and time-relations of the curve of variation could
thus be investigated by the same method as the negative
variation of the muscle or nerve current. The experiment was
of course performed after compensating the current of rest.
Kiilme and Steiner had previously made observations upon
the E.M.F. of the latter, which are approximately confirmed
by the valuable data obtained by S. Fuchs with the Poggendorff-
du Bois-Reymond method of compensation.

The E.M.F. of the current of rest during a single experiment
was sufficiently constant to give assurance that the conditions
underwent no substantial alteration during the period of investi-
gation. Each rheotome experiment started " from the appearance
of the spark at the moment of opening the retina circuit in the
rheotome. The characteristic position of the slider must be
regarded as the zero-point, from which the experiment starts
each time, or to which it returns." Under these conditions

xii ELECTROMOTIVE ACTION IX THE EYE 479

there was never an effect upon the galvanometer, since the
photo -electrical variation occurred during the period of ;m
entire revolution (0'25G4 sec.). It further appeared "that a
measurable period (0'0005-0'0060 sec.) elapsed between the
moment of stimulation and the perceptible commencement of
the positive part of the variation, after which the positive
preliminary phase rapidly attains its maximum, and then falls
quickly, passing into the negative portion of the photo-electrical
variation. If this latter makes its appearance alone, with no
positive fore-swing, a stage of latent excitation (from 0'0004 to
Q'0064 sec.) is still plainly visible, followed first by a weaker
phase (negative fore -swing) and then by the true negative
principal variation. The maximum duration of the positive
fore-swing lasts, according to Fuchs, O'OISI sec.; the minimum
= O'OOVO sec. The negative fore-swing lasts (with exclusive
appearance of the negative variation) between 0-0029 and
O'OIOS sec.; the period to the maximum of the negative varia-
tion = 0-0089-0-0352 sec.

The question may be raised as to what portions (layers)
of the retina are mainly or solely concerned in initiating
the electrical P.D. The exclusive appearance of the negative
variation at the trunk of the optic nerve on stimulating the
eye with light, permits us to conclude with tolerable certainty
that the anterior fibrous layer gives a similar reaction, whence
it follows that the processes underlying the complex photo-
electrical variations of the retina are situated in layers that
do not extend anteriorly beyond the ganglion layer. That
this layer is not itself directly implicated appears from the fact
that retinal preparations from warm-blooded animals are usually
very unstable, and quickly lose their photo-electrical reaction
even when the whole fuudus of the eye is examined. This
must be referred to the well-known sensibility of non-ganglionic
elements to all disturbances of their normal metabolism. The
///'//// resistance of the bird's retina is therefore the more
remarkable. Kiihue and Steiner obtained good results with
even the isolated retina (pigeon), which can only be referred to
the great vitality of the long rods and cones in the pigeon,
since it can scarcely be supposed that ganglion-cells or nerve-
fibres of the retina would be excitable 45-50 rnin. after making
the preparation. We are thus forced to conclude that the

480 ELECTRO-PHYSIOLOGY .-HAI-. xn

epithelial elements (the true sensory cells} are again the seat
of electromotivity , which is the more probable since it can
be shown that the changes produced by light are initiated in
these elements. According to Klihne and Steiner, however, this
is due less to primary photo-chemical processes occurring in the
external elements of the visual cells — the alteration of the
hypothetical visual substance by light — than to the con-
sequences of excitation of " the protoplasm contained in the
internal constituents of the visual cells, by the photo-chemical
products of disintegration."

BIBLIOGRAPHY

1. F. HOLMGKKN. Untersuchungen aus dem physiol. Inst. der Univ. Heidelberg.

III. p. 278.
•2. (a) DEVVAII and M'KENDRICK. Trans. Roy. Soc. of Edinburgh. XXVII. p.

141.
(b) DEWAR. The Physiological Action of Light. Pro. Roy. Inst. 1876.

3. KiJHNE and STEINER. Untersuchungen aus dem physiol. Inst. der Univ.

Heidelberg. III. and IV.

4. SIGM. FUCHS. Pfliiger's Arch. . LVI. 1894. p. 408.

5. ENGELMANN. Beitriige zur Psychol. u. Physiol. der Sinnesorgane. H. v.

Helmholtz zum 70. Geburtstag gewidmet. 1891.
ti. A. D. WALLER, (a) Points relating to the Weber-Fechner Law. (Retina,

Muscle, Nerve.) Brain. 1895.

(b) Action of Ether and Chloroform on Retinal Excitability.
Brain. 1896. p. 574.

SUPPLEMENTARY PAPERS

I. p. 113 (and II. p. 115), 74. GOTCH AND MACDONALD. Temperature and Excita-
bility. Journ. of rhysiol. XX. 1896.
I. p. 113. 75. SCHENCK. Ueber die Gipfelzeit bei summirten isotonisclien u.

isometrischeu Zuckungen. P. A. LXIV.
I. p. 319. 49. Rorx. Ueber die polare Erregung der lebendigen Substanz, etc.

P. A. LXIII.

VERWORN. Untersuchuugen liber die polare Erregung der leben-
digeu Substanz clurch den constauten Strom. P. A. LXII.

50. <, and LXV.

Roux. Berechtigungen zu M. Verworn's Mittheiluug IV. P. A.
LXVI.

51. SCHENCK. Kritische u. experimentelle Beitrage zur Lehre von

der Protoplasma Bewegung u. Contraction. P. A. LXVI.

52. LOEB. Zur Tlieorie des Galvanotropismus. P. A. LXVIII. ,

LXV., LXVII.

53. JENNINGS. Reactions to Stimuli in Unicellular Organisms.

Journ. of Physiol. XXI.

54. EXNER. Electrische Eigenschaften von Haaren u. Federn. P. A.

LXL, LXIII.
fENGELMANN. Einfluss der Reizstarke auf der Fortpflanzungs-

geschwindigkeit der Erregung, etc. P. A. LXVI.
>0' | BERNSTEIN. Bemerkung, etc. P. A. LXVIII.

(ENGELMANN. P. A. LXVIII.

I. p. 517. 91. HERMANN. Das Capillar-Elektrometer u. die Actions-strome des
Muskels. P. A. LXIII.

92. BERNSTEIN. Zur Tlieorie der Negative Schwankung. P. A.

LXVII.

93. SCHENCK. Ueber den Einfluss der Spannung auf die "negative

Schwankung " des Muskelstroms. P. A. LXIII.
[R. DU BOIS-REYMOND. Ueb. den Verlauf der negative Schwan-

kuug bei Isotonie u. Isometrie. Ceutralbl. f. Physiol. XI.

No. 2.
CHENCK. Die negative Schwankung, etc. Ib. XI. 4.

95. AMAGA. Ueb. die negative Schwankung bei isotonisclier u.

isometrischer Reizung. P. A. LXX.

96. SCHENCK. Zur Tlieorie der "negative Schwankung." P. A.

LXX.
II. p. 115. 70. SHERRINGTON. Croonian Lecture for 1897. (Double Conduction in

Nerve. )
VOL. II 2 I

482

ELECTRO-PHYSIOLOGY

II. p. 115. 71.

fHERZEN. Fatigue des Nerfs. L'Intermediaire des Biologistes.
| I. No. 5.

"1 BORUTTAI;. Fatigue des Nerfs. Ib. I. No. 7.
\ WALLER. Fatigue des Nerfs. Ib. I. No. 8.
II. p. 226. 63. DANILEWSKY. Kyniorheonomische Untersuclamgen. P. A. LXI.
oEE. Ueb. die angebliche erregende Wirkung elektrisehen
StrahlenaufdenNerven. Centralbl. f. Physiol. XL No. 13.

64. \

DANILEWSKY. Erwiderung. Ib. XI. No. 20.

LOEB.
P. A.

Wirkung

elektriseher Wcllen.

II. p. 356. 67. BORUTTATJ. <

68.

Ueb. die pliysiologische
LXIX.

1. Fortgesetzte Untersuchungen lib. die electrische

Erscheinungen am thatigenNerven. P. A. LIX.,
LXIII.

2. Graphische Rheotomvers\iche am Nerven, Kern-

leiter, u. Muskel. P. A. LXIII.

3. Beitrage zur allgem. Nervreu u. Muskel Pby-

siologie. P. A. LXY.

4. Der Elektrotonus u. die pluisischen Actions-strome

am markloseiiCeplialopodeu-nerven. P. A. LXVI.

5. Ueb. temporare Modificationen der elektroto-

nischen Strb'me des Nerven. P. A. LXYIII.
L. A.SHER. Beitrage zur Physiologic der motorischeu Endorgane.
Zeitschr. f. Biol. XXXII.

INDEX1

ABDUCTOR muscle, of crayfish claw, ii. 98,

185, 191

Abgleiclnin.L'. .Vr Short-circuiting
Aliruptiu-ss of current oscillation, i. 193

- effect on excitation of nerve, ii. 125 ff.
Ali.-tractiou of water, action on muscle,

i. 4-J1.'

— on nerve, ii. 165 ff.

— on the skin, i. 47:?. 479
Aetinospliaerium, electrical excitation, i.

299
Action current, in afferent nerves, ii. 257

— in cardiac muscle, i. 396 ft". ; time-rela-

tions, 397

— in electrical organ, ii. 407 ff., 443

— in electrotonised nerve, ii. 314

— in epithelial gland cells, i. 4b'l ff.

— in mammalian heart, i. 404

— in man, i. 391

— in muscle, i. 359 ff. ; methods of investi-

gation, 362, 399, 408, 410 ; phasic and
decremental, 380 ; ii. 262 ; theory,
388 ; time-relations, 376 ff. ; undula-
tory character, 384

— in nerve, ii. 242 ff. ; diphasic, 262 ; time-

relations, 259 ; with central excitation,
255 ; with various stimuli, 251
- in non-medullated nerve, ii. 243 ; time-
relations, 261
— in retina, ii. 472 ff.

— in skin and mucosa, i. 461 ff.

— in smooth muscle, i. 395

— in tortoise heart, i. 404

— telephone observations, i. 410

— tension, effect of, i. 413

Action of nerve upon muscle, ii. 337
Ailillllmi I at cute, i. 117
Adductor muscle, of crayfish claw, ii. 98,
185 ff.

— of mollusca, i. 68 ; contraction, 177, 187,

189 ; electromotive action, 345 ;
indirect excitation, ii. 103 ; polar ex-
citation, i. 233 ; secondary electro-
motive action, 456 ; tonus, 100

^Esthesodic substance, ii. SO
After-effects of current, in electrical h'shes,
ii. 447 If.

— in muscle, i. 443 ff. ; alterations of ex-

citability from, 287, 292 ; excitatory,
see opening excitation ; inhibitory,
258 ff.

— in medullated nerve, ii. 309 ff.
After-loading of muscle, i. 121 ff.

After - variation, positive in. excitation of
frog's nerve, ii. 248

— of inolluscan nerve, ii. 244
Alcoholised nerve, ii. 169

Alkalies, action on muscle, i. 104, 110, 220,

354 ; on nerve, ii. 167, 175
Alteration theory (Hermann, Heriug), i.

351, 388 ; ii. 327, 465
Alternative. See Voltaic
Ammonia, action on electrical nerves of

malapterurus, ii. 428

— on excitability of nerve, ii. 158, 208

— on muscle, ii. 428

— on secondary excitation from muscle to

nerve, i. 413

Amoeba, electrical excitation, i. 305
Anabolic and katabolic nerves (Gaskell),

i. 433
Anaesthetics, action on central organs, ii.

75
-5- on muscle, i. 358, 450 ; antagonist

laryugeal muscles, ii. 98

— on nerve, ii. 61, 75. 294
Auelectrotonus. See Electrotouus
Anode, definition, i. 210 ; inhibitory action,

i. 236, 257, 264 ; ii. 139, 140 ; physio-
logical, i. 212 ; relation to opening ex-
citation, 216 ; ii. 138

Anodic closing excitation, apparent, i. 236,

270 ; of protozoa, 305
- "closure twitch" (pathological), ii. 155

— excitability, i. 289

— excitation, unipolar, i. 237 ff.

— polarisation, in muscle, i. 445 ; in nerve,

ii. 310

The translator is responsible for the subdivision of chapters, and enlargement of index,

in this volume.

484

ELECTRO-PHYSIOLOGY

Auction ta, adductor muscle, towns, i. 100 ; ]

electrical excitation, 177, 187, 233 ; !

nerves, ii. 281
AnspruchsfaMgk&it (capacity of response).

See excitability
Antagonism, in cardiac innervation, i. 432 ;

ii. 103, 104

— nmsculnr, flexors and extensors, ii. 96 ;

constrictors and dilators of glottis,
97 ; crayfish claw, 98, 185

— in nerves to crayfish claw, i. 434 ; ii.

185 ff.

- polar, of current, i. 264, 270 ff. ; ii. 138,

144, 201 ff.

— in sensory nerves, ii. 201 ff. ; auditory,

206 ; cutaneous .sensory, 207 ; optic,

201, 205 ; taste, 201
— of vagus fibres in respiration, ii. 196
Apex-time anil -height, i. 11 "i
Arthropod muscles, i. 34
Assimilation (and dissimilation) in living

matter, i. 83, 433 ; ii. 201, 328
Auditory nerves, ii. 206
Avalanche increment of excitation, ii. 94

- theory (PHiiger), ii. 94

Axial current in nerve (du Bois-Reymond),
ii. 229

Axis-cylinder, definition, ii. 34 ; mortifica-
tion, 232 ; structure, 46, 58

— as polai isable core, 307

BAT, muscle-fibres, i. 32 ; twitch, character

of, 63
Beetle, muscle structure, i. 34 ; nature of

twitch, 63 ; tetauisation, 125
Bell's palsy, i. 181
Bernstein's experiment, on fatigue of nerve,

ii. Ill ; on muscle wave, i. 373
Bifurcate experiment (Kiihne), i. 430 ;

ii. 57
Breach (Liicke), ii. 211 ff. ; in opening

twitches, 240

Break and make induction shocks, in-
equality of physiological action, ii.

123 ff.
Brush, Wagner's, ii. 361

CANALISATION, ii. 56, 73

Capillary electrometer, i. 401 ff.

(Jar! ionic acid, effect on nerve (Griinhagen),

ii. 65
Cardiac innervation, i. 432 ; antagonism of

inhibitor and accelerator fibres, ii.

103
Cardiac muscle, chemical excitation, i. 106

— conductivity, i. 162, 397

— contraction, i. 58; time -relations, 58,

162 ; contraction wave, 163

— electromotivity, during action, i. 397,

432 ; during rest, 344 ; positive varia-
tion (Gaskell), 432 ; time-relations of
action current, 399

Cardiac muscle, excised mammalian, i. 94

— polar law of excitation, i. 257

— reaction to constant current, i. 194, 257

— refractory period, i. 129

— rhythmical response, i. 195
- "staircase," i. 70

— structure of invertebrate, i. 20 ; verte-

brate, 24 ff., 91

— summation of stimuli, i. 130

— temperature, effect of, i. 100

— tension, effect of, i. 79

— vitality, i. 91

Cat fish. See Malapterurus

Cell currents, in plants, ii. 29 ; theory of,

i. 462, 508

Central innervation, rhythm, i. 138 ff.
Central (and peripheral) nervous system, ii.

78, 84
Cephalopoda, muscle-cells, i. 15 ; nerves, ii.

259 ff., 286
Ciliated infusoria, i. 3
Circulation, action on nervous system, ii.

77, 86 ; on vitality of muscle, i. 92
Closure contraction (persistent), i. 183,

205

Closure of current, general effects, ii. 266 ff.
Closure tetanus, ii. 117 ; secondary in-

effieacy, i. 422

Cnidaria, epithelial muscles, i. 10, 11
CO., on nerve (Griinhageu), ii. 65
Cohnheim's Areas in muscle, i. 29
Cold, action on muscle, i. 97 ; oil muscle

current, 338

— on nervous conductivity, ii. 61 ; excita-

bility, 95, 117 ; reflex excitability, 76
Columns of electrical organ, ii. 359 ff. :

enumeration, i. 396 ,
Compensator, round, i. 336
Conduction, in both directions, ii. 56, 74,

251

— law of isolated, 56, 73
Conductivity, in cardiac muscle, i. 162,

397

— in electrical organs, ii. 431 ; irreciprocal,

456

— in muscle, i. 144 ff. ; red and pale-

muscle, 150 ; smooth muscle, 165 :
time^- relations, 373 ; of electrotonic
alterations in muscle, 295

— in nerve, ii. 52 ff. ; in nerve-cells, 66,

69 ; in nerve- fibres, 52, 63 ; in afferent
nerves, 120 ; in afferent and efferent
fibres, 62 ; in electrotonised nerve, 147 ;
time-relations, 59

— and excitability (Griinhagen), ii. 62 ff.,

95

- theory, ii. 336

Consonating springs (Helmholtz), i. 135
Constant current, action on cardiac muscle.

i. 194 ff, 2'J^

— on electrical fishes, ii. 425 ff.

— on muscle (smooth and striated), i. 174 fl'.,

IXDEX

485

197 : at make, 170 II'. ; at Ineak,
185 IV. : dosing and opening excita-
tion, 187 ; persistent, action, 185 11'. ;
polar excitation, 210 11'., ±28 11'., ii.
140 ; polarisation after-effects, i. 287,
289 ; tetanic character of excitation,
197

( 'onstant current, on fatigued and moribund
striated, as compared with smooth
muscle, i. 182 ; on partially injured
muscle, 21 7

— on nerve, ii. 116 fl'. ; closing and opening

excitation, 116; direction (Pfliiger's
law), 134 fi'. ; electrotouic phenomena,
140 : after-effects, 143 ; persistent
action, 118 ; polar action, 138 tf., 266 ;
rhythmical excitation, 119 ; tetanic
character of excitation, 1 19

— on afferent nerves, ii. 195 ; ou cardiac

vagus, 121, 194 tf. ; on cooled nerve,
117 ; on crayfish claw, 185 ; on optic
nerve, 202 If. ; on secretory nerves,
121, 195 ; on sensory nerves, 120,
197 ; on specific nerves, 194 ff.

— in pathological cases, i. 181
Continuity of muscle substance, i. 229
Contraction, alteration in optical properties

of muscle, i. 46 ft. ; effects of tempera-
ture, 99 ; rhythmical, with chemical
excitation, 106 ; with excitation In-
constant currents, 195

Contraction wave, i. 144 ff., 158, 163

Contraction without metals, i. 326

Contracture, i. 89

Core-model, ii. 29'J, 307

Crayfish, muscular nerves of, ii. 36, 342 ;
excitability, i. 98 : excitation with
constant current, 185 ff. ; inhibition
of muscular tonus by kathodic excita-
tion. 100 ; tetanus, 118

Cross-striation of muscle, during contrac-
tion, i. 46 ff. ; physiological signifi-
cance, 39

< 'm-rent distribution, in muscle, i. 346

— in nerve, ii. 266

— in polarisable schemata, ii. 298

— in discharge of torpedo, ii. 347. 414
Current intensity, effect on .height of

twitch, i. 69'
Current of rest, in electrical organ, ii. 443

— in man and other warm-blooded animals,

i. 391
-in muscle, i. 321 tf., 345

— in nerve, ii. 227 ff.

— in optic nerve, ii. 470

— in retina, ii. 470
See Injury current

Current oscillation, excitatory action on
muscle, i. 180. 286 ; on nerve, ii. 116
ff., 210

Cutaneous sensory nerves, excitation bv
cnrrent, ii. 207

DEATH, local, effect on polar excitation by
current, i. 218 ; ii. 157

Dciifli of muscle, i. 90; effect on conduc-
tivity, 151 ; on excitability, 182. :; 13 ;
on muscle current, 337, 343, 351 ; on
current of action, 382, 388

— of nerve (degeneration), ii. 90 ; effect

ou excitability, 89 ; on nerve-current,
230 ; on reaction, 1 1 7

— of terminal organ, ii. 89

Decline of excitability in moribund nerve,
ii. 89

Decrement of contraction wave in muscle,
i. 149 ; absence in living man, 395

Decremeutal action current (Hermann),
i. 382

Degeneration of medullated nerve, ii. 90 ;
relation to nerve current, 230

Dehydration of nerve, ii. 165 ; by alcohol,
69 ; by NaCl, 167

Demarcation current, i. 321, 352 ; ii. 227
ff. See Injury current

Demarcation surface, i. 337, 352

Derivation of animal electromotivity (du
Bois-Reymond), ii. 418

" Diminutional current " (du Bois-Rey-
mond), i. 362 ff.

Dionaja muscipula, ii. 6 ff. ; negative varia-
tion, 17

Diphasic current of action, in muscle, i.
381 ; in nerve, ii. 262

Direction of current, in muscle, i. 199 ; in
nerve, ii. 132 ff.

Discharge of torpedo, action of curare, ii.
429 ; of strychnin, 423 ; after-effects,
437 ; direction, 416 ; distribution of
potential, 414 ; electrolytic action,
420 ; E.M.F., 464 ; method of leading-
off, 410; oscillatory character, 409;
physiological action, 407 ; sparking,
417 ; telephone observations, 424 ;
time-relations, 431

— local, ii. 421

— partial, ii. 425
- reflex, ii. 423

— spontaneous character of, ii. 424

— theory of (du Bois-Reymond), ii. 346
Dissimilation (and assimilation) in living

matter, i. S3, 441 ; ii.*201, 328
Distilled water, action on muscle, i. 356
Double myograph, i. 175
Double refraction of muscle, i. 46
Doyere's expansion, i. 384 ; ii. 338 ff.
Duration of current, excitatory action, i.

177; ii. 121
Dytiscus muscle, i. 35, 63 ; tetanus, 125

ECHINUS, electrical excitation of muscles,

i. 238

AY//.sr///< I'rltfii. See Gradual entrance
Electric eel. See (-J-ymnotiis

486

ELECTRO-PHYSIOLOGY

Electrical columns (prisms), ii. 360, 370 ;
enumeration, 393 ff.

Electrical current, action on electrical organ,
i. 425 ff. ; on muscle, i. 174 ff. ; on
nerve, ii. 116 ff. ; on protozoa, i. 299 ;
resistance of muscle, i. 200 ; of nerve,
ii. 304. See Constant current

— cause of electrolysis in living matter, i.

317

Electrical fishes, discharge from, ii. 407 ff. ;
conduction by air (sparking), 417 ;
direction, 416 ; discontinuous nature,
424 ; distribution of potential, 414 ;
duration, 434 ; electrolytic action,

420 ; latent period, 432 ; partial,

421 ; reproducible on models, 416 ;
telephone observation's, 413, 424 ;
temperature effect of, 459 ; theory
of, 453, 461 ff. ; time-relations, 431 ;
voluntary and reflex (strychnin), 423

— derivation theory, ii. 418

— electromotivity, ii. 443 ff.

— immunity to curare, ii. 429

— pseudo-electrical manifestations, ii. 420
Electrical organ, excitation, ii. 425 ; chemical

(ammonia), i. 428 ; direct, 428 ; in-
direct, 423 ; mechanic.il, 425

- E.M.F., ii. 443 ; pre-existeuce of, 445 ;

"resting" current, 443

— homology with striated muscle, ii. 379,

385, 390, 431

— iunervation, ii. 422

— irreciprocity of conduction, ii. 456

— pseudo-electrical, ii. 376 ff.

— reaction, ii. 465

— reflex discharges and tetanus (strychnin),

ii. 423

— secondary action, ii. 431

— secondary electromotive action (polarisa-

tion), ii. 447 ff.

— structure, ii. 357 ff.

— tetanisation, ii. 426

Electrical plates, ii. 361, 377 ; Schunlein's

theory of "nerve-endings," 430
Electro-cardiogram, i. 408
Electrodes, vmpolarisable for muscle, i.

174 ; for leading off discharge of

electrical fishes, ii. 410
Electrolysis, i. 317 ; ii. 198, 326, 420
Electromotive action, in crayfish muscle,

i. 410

— in electrical fishes, ii. 407 ff.

- in epithelial and gland cells, i. 461 ;

theory of cell-currents, 462

— in the eye, ii. 470 ff.

- in lingual currents, i. 4<>4

— in man, i. 391

— in mammalian heart, i. 404

— in mammalian >\vcat glands, i. 513

- in muscle, i. 320 If.

— in nerve, ii. 227 ff. ; cooled, 247;

molluscan, 243 ; moribund, i. 230 ;

non-medullated, 281 ; non-medullated
olfactory of pike, 236, 243 ; sensory,
235 ; with chemical and thermal exci-
tation, 252
Electromotive action in plant cells, ii. 1 ff.

— in polarisable schemata, ii. 298

— secondary, in electrical organ, ii. 447 ; in

muscle, i. 442 ff. ; in nerve, ii. 309 ff.

— skin currents, i. 478 ff.

— strychnin spasm, i. 410

— in sub-maxillary glands, i. 510

— in throat and cloaca, i. 473
- theory, ii. 315

Electromotive cell-unit (Munk) or cell-com-
plex (Burden-Sanderson) in plants, ii.
29

Electrotonus, definition, ii. 144 ; dis-
similarity in muscle and nerve, 140

— anelectrotomisaiidkateletrotonus, defini-

tion, ii. 144, 335 ; difference between,
268, 279

— in anaesthesia, i. 450 ; ii. 294

— importance of medullated sheath, 269 ii.

— in man, ii. 152 ff.

— in muscle (polar alterations of excita-

bility), i. 280 ; ii. 140 ff., 307, 308

— in nerve, ii. 140 ff. ; cooled and etherised

medullated nerve, 286 ; medullated,
266 ff. ; non-medullated, 281

— physical and physiological, ii. 250, 294

— in polarisable schemata, ii. 298

— reaction during excitation (current of

action in electrotonised nerve), ii.
314

— secondary after-effects in muscle, i. 287

291, 442 ff. ; in nerve, ii. 309 ff.

— secondary electrotonus, ii. 270

— time-relations, ii. 272, 279

— undulatory character, ii. 301
-theory, ii. 298, 315

E.M.F., measurement of, i. 335 ; in electri-
cal organ, ii. 464

End-brush (Wagner), ii. 361

End-plates, i. 384 ; ii. 338 ff. ; electrical
(Scluinlein's theory), 430

Epithelial muscles, i. 10 ; muscle-cells, 10

Ether, action on laryngeal muscles, ii. 98 ;
on lingual current, i. 473 ; on muscle
current, 359 ; on nerve, ii. 61, 75,
294 ; on polarisation after-currents, i.
450

Excitability and conductivity, ii. 64 ; and
contractility, i. 452

Excitability, of central reflex organs (nerve-
cells), ii. 106

— of crayfish claw, ii. 98

— of electrical nerves, ii. 423 ff.

— of end-organs (peripheral and central), ii.

105

— of the eye, ii. 470

— of muscle, i. 54 ff. ; different muscles, 57

ff. ; dying muscle, 182, 343; in flexors

INDEX

487

and extensors, ii. 96, 105 ; effect of
chemical substances, i. 104; of circula-
tion, 19;") ; of desiccation, -l'Jl> ; of
fatigue. 83 ft'. ; of galvanic current,
-iTti fl'. : of glycerin, 432 ; of tempera-
ture, 97 ; of transverse section, 227
Excitability of nerve, ii. 59 ff. ; effect of
abstraction of water, 117, 165 ; of
current, sec Electrotonns ; of tempera-
ture, 117 ; local differences, 93 ; at
transverse section, 94

- - specific, of muscle and nerve (Rosenthal),

ii. !>2

— of spinal cord (direct), ii. 79 ; sensory

and motor elements, 81
Excitation, of electrical organ, ii. 423 ff.

— of eye, ii. 470

— of muscle, chemical, i. 104 ff. ; electrical,

174 ff. ; "general law," 191; by
intriusic current, 326 ; polar, 203 ff.
of nerve, chemical, ii. 165 ff., 253 ;
electrical, 116 ff. ; " general law," 116 ;
by intrinsic current, 232 ; mechani-
cal, 2.") 3 ; polar, 266 ; with sumniatcd
stimuli, 106 ff., 215 ff. ; thermal, 251 ;
unipolar, 219 ff. ; theory, 315 ff.

— of afferent nerves, ii. 120 ; of secretory

nerves, 121
X e Constant current

— secondary, from heart, i. 396, 420, 427 ;

muscle to muscle, 427 ; muscle to
nerve, 361, 396, 413 ; nerve to
nerve, ii. 264

Excitatory wave in muscle, i. 373 ; relation
to contraction wave, 376

FALL rheotome, i. 353, 3S5
Fatigue, in electrical organ, ii. 413

- in muscle, i. 66, 83 ff. ; chemical, 354 ;

local, from passage of current in one
direction, 223 ; from tetanus, as com-
pared with fatigue from polarisation,
224 ; of kathodic fibre-points, 287

— in nerve, ii. 109 ; Bernstein's experiment,

111

Fibrillated structure, i. 3

Fibrils, i. 3, 144, 160

Fixed polarisation, ii. 303

Fixed wave of contraction, i. 384

Flagellata, electrical excitation, i. 307

Flexor (and extensor) muscles, fatigue, i.
66 ; specific excitability, ii. 96, 105

Form of current oscillation, i. 194 ; in-
fluence on nerve-excitation, ii. 128 ff.

Freezing of muscle, i. 103, 218

Frog alarum, ii. 411

Frog interrupter, ii. 434

Frog's skin, electromotive action, i. 462 ff.

GALVANIC current. See Constant current
Galvanic wave, i. 273
Galvanotropi.sm in protozoa, i. 307

Ganglion-cells, conductivity of excitation,
ii. 66 ; effect of anaesthetics, 75 ; of
composition of the blood, 77 ; of
strychnin, 71 ; of sunimated stimuli,
108 ; of temperature, 76

— electrical, of gymuotus, ii. 375 ; of malap-

terurus, 407
Gastrocnemius, electromotive action, i. 325 ;

schematic structure (Rosenthal), 324 ;

telephone observations, 411 ; triphasic

wave, 387

Gerlach's theory of nerve-endings, i. 383
Glands, electromotive action, i. 461 ff.
Glycerin, action on nmscle, i. 432 ; on nerve

(Kaiser), ii. 218

Goblet cells, electromotive action, i. 474
Gradual entrance of current, i. 192 ; ii. 65,

120

Griinhagen's C02 experiment, ii. 65, 84
Gymnotns, ii. 368 ff.

HEAT, effect on nervous excitability, ii. 95,
117 ; thermal injury of muscle, i. 218

Heart, iimervation, i. 432 ; ii. 103 ; nutri-
tive, fluids, i. 96 ; secondary contraction
from, 396, 420, 427; "staircase con-
traction," 70

— snail's, i. 79. See under Cardiac muscle
Helmholtz's consonatiug springs, i. 135
Hippocampus float-muscles, structure, i. 30
Holothurian muscles, electrical excitation,

i. 234
Homology between electrical organs and

striated muscle, ii. 346, 385, 431
Hydra, nervo-muscular cells, i. 9
Hydrophilus muscle, i. 63 ; tetanus, 125

IDIO-MUSCULAR contraction, i. 152, 172,
205, 225 ; electromotive 7-eaction, 390

Immunity of torpedo to its own shock, ii.
416,.440 ff. ; to curare, 429

Inclination current (du Bois-Keymond),
i. 325, 386

Increment, law of polarisation (Hermann),
ii. 315

Indifferent point, ii. 143, 157

Induced currents, action on ganglion-cells,
ii. 106 ; on muscle (cardiac, smooth,
striated), i. 119, 177, 181, 218; ii.

122 ; kathodic action, i. 225 ; in
pathological cases, 181

-on nerve, ii. 121, 123 ff., 142, 207;
polar action, 1 42

— on plants, i. 177

-on protozoa, i. 177 ; ii. 122, 299, 305
Induction, effect on unipolar excitation, ii.
219

— inequality of make and break shock, ii.

123 ff.

Infusoria, myoid layer, i. 5
Inhibition, anodic in muscle, i. 243
— cardiac, ii. 257

488

ELECTKO-PHYSIOLOGY

Inhibition, in cardiac vagus, ii. 194

— from central organs, ii. 160

— in intestine, i. 247

— in striated muscle, i. 267

— in nerves of crayfish claw, ii. 100, 185
Jnitial twitch, i. 133, 315 ; cardiac muscle,

134
Injury current in cardiac muscle, i. 344

— in electrical organ, i. 443

— in muscle, i. 321 ff., 345 ; smooth muscle,

i. 344 ; theory, 345 ft'.

— in nerve, ii. 227

— in retina, ii. 470, 474

— persistence during anaesthesia, ii. 358

— with chemical stimulation, ii. 354 ft*.
Innervatiou, voluntary, i. 138 ft".

Insect muscle, contraction phenomena, i.
49 ; fatigue, 91 ; nature of twitch, 64 ;
quick and sluggish fibres, 67 ; struc-
ture, 33 ff. ; tetanus, 125, 132 ;
transmission of contraction, 155, 164

— nerves, ii. 36

Interference of excitation, in muscle, i. 425 ;
in nerve, ii. 215

- between exciting and muscle currents, i.

329

- between exciting and nerve currents,

ii. 236
Interpolation of ganglionic elements along

nerve-fibre, ii. 66
Internal polarisation, i. 442 ff.
Intersections, tendinous, i. 228
Interstitial granules in muscle, i. 30, 33
Intestine, conductivity, i. 170 ; electrical

excitation, 240, 248 ff.
Irradiation of excitation in central organs,

ii. 70
Irreciprocity of conduction (clu Bois-Rey-

mond), ii. 457
Irritative after-currents (Hermann), i. 448 ;

ii. 310

Isoelectricity of uninjured muscle, i. 341, 379
Isolated conduction, law, ii. 56, 73
Isotonic and isometric contraction, i. 77, 81,

99

KAISER'S glycerin experiment, ii. 218
Katelectrotonus. See Electrotonus
Kathode, definition, i. 210 ; inhibition of
conductivity, 293 ff. ; ii. 140 ff. ; in-
hibition of excitability, i. 279 ft'. ; ii.
140 ft'. ; physiological, i. 212
Kathodic closure twitch, i. 272
Kinesodic substance, ii. 80
Kiihne's bifurcate experiment, i. 430 ; ii. 57

- theory of muscular innervation, 349

LANTERM ANN'S notches, ii. 43

Latent period, i. 56, 72 ; of muscle elements,
73 ; of opening excitation in muscle,
190 ; dependence on current density,
216 ; on strength of stimulus, 72

Latent period, of negative variation, i. 375

— with indirect excitation of crayfish claw,

ii. 191

Law of contraction (Pfliiger), with indirect
excitation of smooth muscle, ii. 193

— with excitation of afferent nerves, ii. 195 ;

higher sensory nerves, 197 ; secretory
nerves, 195

Laws, general, of contraction, Ritter-Nobili,
ii. 135 ; Pfliiger, 136 ; Helmholtz, 136

— of excitation (du Bois-Reymoud), i. 191,

313

— of electrical excitation of nerve (du Bois-

Reymond), ii. 116, 122

— of isolated conduction in nerve-fibres, ii.

52 ; in nerve-centres, 56, 69

— of the current of action (Hermann), ii. 327

— of moribund nerve (Roseuthal), ii. 159 ;

Hitter- Valli, 90, 164

— of muscle current, i. 353

— of nerve currents, ii. 227

— of polar excitation, i. 277

— of polarisation increment (Hermann), ii.

315

— of preform ation of electrical currents, ii.

393

— of vital currents of nerve and -muscle,

i. 353

Leaves, electromotive reaction, ii. 2
Leech, electrical excitation of cutaneous

muscular integument, i. 245 ; electro-
motive action of skin, 477
Leistungsfah igkeit (capacity for work). See

Excitability
Length of iutrapolar nerve-tract, effect on

excitation, ii. 145
Light stimulation, negative variation of

optic nerve, ii. 256 ; of retinal current,

472 ff.
Liicke. See Breach

MALAPTERURUS, electrical nerves, ii. 37.
403 ff.

— electrical organ, ii. 398
Mammalian heart, i. 404

Man, electrotonic alterations of excitability,

ii. 152 ft'. ; phasic action current, i.

394 ; in heart, 405 ; skin current,

393, 513
Medullary sheath, ii. 41 ; function in

electrotonus, 269
Medusa muscle, i. 59
Metabolism, i. 83

— in the eye, ii. 480

-in nerve, ii. 201, 249, 328

Metazoa, structure of muscle, i. 9

Microphone (Roth), i. 133

Mimosa, excitatory movements, ii. 11 ;
negative variation, 17 ; theory of con-
ductivity, 12 11'.

Mobility of protoplasm (excitation), i. 177
ff., 192

INDEX

489

Molecular theory, of electrical discharge «{'
torpedo, ii. 453, -hi.!

— of electrotonus, ii. i".'>

ul' leaf currents (Munk), ii. 10
-of muscle (ilu Hoi--liVymoiid). i. 345,
389 ; (Bernstein), 350, 389

— (if nervous activity, ii. 316
.Molecules, peripolar. i. 348
Moribund nerve, ii. 159

Mormyrus, electrical organ, ii. 379 ; de-
velopment, 389

Motor and inhibitory nerves, ii. 104

Motor end-plates, ii. 340

Motor impulses, frequency, i. 138 if.

Mucosa currents, i. 464 ff.

Mucosa, electromotive action, in tongue, i.
464 ff. : throat, 473 ; stomach, 500 ff.

Multinuclear muscle fibres, i. 28

Muscle, alterations of excitability by in-
jury, i. 223

— contraction, i. 48, 54 ; effect of tension

on, 78 ; time-relations, 56

- death of, i. 90, 93

— effect of temperature, i. 97

— fatigue, i. 66, 83 ; chemical, 354 ; local.

223 ; of kathodic fibre-points, 287 ; of
ivrl and pale fibres, 66, 125 ; of smooth
muscle, 93 ; from tetanus, 224

— fibrillated structure, i. 3

— microscopic reaction, i. 46

— natural contraction, i. 139

- polymerous, i. 228

— quick and sluggish fibres, i. 57 ff., 65

— reaction, chemical, of active and resting

muscle, ii. 465; electrical, of partially-
injured muscle, i. 110, 217

- red and pale fibres, i. 30 ff., 90, 127

— resistance, i. 200

— respiration, i. 96

- smooth, i. 21. 92 ff.

— striated, i. 3 ff.

>'••»' Cardiac muscle, Muscle current,
Electromotive action, Excitation, Ex-
citability, etc.

Muscle columns, i. 20, 25, 32

Muscle current, decline, i. 343, 344 ;
E. M. F., 335 ; excitation from muscle.
326, 362, 427 ; negative variation,
362 ; positive variation, resting, 321 ff.,
344; weak longitudinal, 322

Muscle sound, i. 135 ff.

Muscular antagonism, ii. 96 ff.

Muscular innervation (Kiihne's theory), ii.
349

Muscular relaxation (and contraction), i. 99

Muscular tonus, i. 100, 235, 260, 265 ; ii.
100, 185 ff.

Myogram, i. 57

Myograph, principle of, i. 56 ; double
(Heriug), 175

Myonema of infusoria, i. 4

Myoplast, i. 9

-\E<i.lTI\'K AY/o •l.'ii-liii;il/l,-i-ii. N«' Single

negative phase
Negative variation of muscle current (du

Bnis- Reynmnd), i. 362 ff. ; of nerve

current, ii. 2 I 1
See Action current

,\V/'//';///.v//vi///. ,SVc Inclination current
Nerve, aiui'.-thetics, action of, ii. 61 ff., 294

— bifurcation of fibres, ii. 52 ff.

- cells, ii. 34, 66 ff. ; electrical, 37"), 407

— conductivity and excitability, ii. 52 If.
— degeneration, ii. 90, 117, 230

— development, ii. 44

-effect of cold, 61, 76, 117, 247: of
transverse section, 94, 156

— electrical, ii. 3, 422 ; chemical reaction,

446

- E.M.F., ii. 227 ft'. ; in moribund nerve.

230

- fatigue, ii. 109 ff.

- fibres, ii. 34 ff.

— invertebrate, ii. 36 ff.

— medullated, ii. 41

— molluscau, ii. 281 ff.

- non-medullated, ii. 37 : E.M.F., 242

- olfactory, of pike, ii. 38 ; E.M.F., 243, 336

— reaction, chemical, ii. 110

— resistance, longitudinal and transverse,

ii. 133, 304 ; structure, ii. 33 ff. ;
transverse, 304

Xi't' Conductivity, Constant current, Ex-
citation, Electromotive action, Electro-
tonus, etc.

Nerve currents, ii. 227 ff.

Nerve-endings, in muscle, i. 383 ; ii. 338 ;
Schoulein's theory of electrical, 430

Neurokeratin, ii. 44

Neuron, ii. 34

Non-fibrillated protoplasm, i. 299 ff.

Nutrition, indispensable to vitality of
muscle, i. 92

Nutritive fluids, i. 96

OBLIQUE striatiou of muscle, i. 15 If.

Olfactory nerves, ii. 38 ; E.M. F. (in pike),
236, 243

Opening contraction (persistent), i.186, 210,
233

Opening excitation, i. 185 ; in nerve, de-
pendence on cross-section, ii. lb'2

Opening inhibition, anodic and kathodic, in
heart, i. 263

Opening tetanus (Ritter), ii. 117, 139, 166,
179 ; theory, 180

Opening twitch, effect of alcohol, ii. 170 ;
of polarisation, 178 ; of potassium, 175

— retarded, ii. 166

— supposititious, on excitation of muscle,

i. 329, 333 ; of nerve, ii. 238, 311
Optical properties of muscle fibrils, i. 46
Optic nerve, ii. 201

490

ELECTRO-PHYSIOLOGY

Orthorheonome (von Fleischl), ii. 128
Ova, polarisation of (Roux), i. 310

PALAEMON squilla, nerve-fibres, ii. 45
Paradoxical contraction, ii. 270 ; tetanus,

271
Paramsecinm, galvanotropic manifestations,

i. 308
Parelectronomy in electrical organ, ii. 462 ;

in muscle, i. 338 ft'., 389
Pelomyxa, electrical excitation, i. 305
Peristaltic wave, i. 170
Petromyzon, nerve-fibres, ii. 47
Pfiuger's law of contraction, ii. 136 ; for

cardiac vagus, 194 ; secretory nerves,

195 ; sensory nerves, 195 ; smooth

muscle, 194

— avalanche theory, ii. 94
Phasic action current, ii. 262
Phototonus, ii. 256

Physical (and physiological) electrotonus,
ii. 250, 294

Plant currents, ii. 1 ff., 31

Plates, electrical, ii. 361, 373 ; enumera-
tion, 396 ; nerve-endings, 364, 374

Polar action of electrical current, in cardiac
muscle, i. 228 ff., 258 ; in muscle, 203
ff., 228 ; in nerve, ii. 138 ff. ; in ova,
310 ; in protozoa, i. 202

— of brief (induction) currents, ii. 207
Polarisation, of electrical organ, ii. 447 ff.

— of muscle, i. 276 ff. ; of smooth muscle

(ureter), 294 ; of uninjured muscle,
458 : during ether narcosis,' 451 ; in-
ternal (du Bois - Reymoud), 442 ;
positive, 443

- of nerve, ii. 309 ff. ; positive, 309

— of ova (morphological), i. 310

- utter-effects (on excitability) in muscle,

i. 287, 291 ; in nerve, ii. 143
Polarisation currents, in electrical organ,
ii. 447 ff.

- in muscle, i. 442 ff. ; anodic and kathodic

(Bering), 445 ; relation to polar action
of current, 444 ; theory, 445

— in nerve, ii. 309 ft'. ; anodic and kathodic,

310; theory, 315 ff.

— after-currents, in muscle, i. 442 ff. ; in

nerve, ii. 309 ff. ; in electrical organ,

447 IV.
Polarisation increment (Hermann's law), ii.

315

Pole, definition of physiological, i. 212
Polystomella, electrical excitation, i. 303
Porret's phenomenon in muscle, i. 273
Positive variation of muscle-current, i. 432

— after- variation, ii. 248

Potassium iodide electrolysis, ii. 417, 420
Potassium salts, action on muscle, i. 67, 172;
on E.M.F., 355, 356 ; on polar excita-
bility, 220

— on nerve, ii 175

Potassium salts, antagonism to sodium salts,
i. 221, 354

Pouillet's method of time-measurement, ii.
59, 432

Pre-existence of muscle current, i. 338

Preformation of electrical elements, ii.
339

Pressure of muscle, action on secondary ex-
citation from muscle to muscle, i. 427

Primary and secondary opening twitches,
ii. 178 ; comparison with Ritter's
tetanus, 180

Protozoa, structure of muscle, i. 3 ; electri-
cal excitation, 299

Pseudo-electric organs, ii. 379 ; activity, 420

Pseudopodia, reaction in electrical excita-
tion, i. 300

Pupillar dilatation, ii. 106

QUICK and sluggish muscle-fibres, i. 59 ft'.

RAJA, electrical organ, ii. 376 ; current of
rest, 446 ; development, 383 ; dis-
charge from organ, 420

Reaction of degeneration, i. 182, 273 ; of
partially injured muscle, i. 217

Reaction (chemical) of electrical organ, ii.
465

— of active and resting muscle, ii. 465

— of nerve, ii. 110

Recovery of muscular excitability, i. 354

Reflex arc, ii. 87
- time, ii. 67, 72

Reflexes, discharged by electrical excita-
tion, ii. 70, 108 ft'.

Refractory period of cardiac muscle, i. 288

Relaxation and assimilation, i. 99

Remak's fibres, ii. 37

Renewal of cross-section, effect on muscle
current, i. 344

Repeated stimuli, action on nerve, ii.
215 ff.

Resistance in muscle and nerve, i. 200 ; ii.
133, 304

Respiration, effect on electromotivity of
leaves, ii. 4

— of muscle, i. 96
lletinal currents, ii. 470 ff.
Rheonome (v. Fleischl), ii. 128
Rheotachygraphic method, i. 373, 386,395
Rheotome, Bernstein's differential, i. 367 :

fall, 353, 385

Rhizopoda, electrical excitation, i. 299
A' ///"/• i/ini-fia (and water rigor), i. 357
Ritter-Nobili law of. contraction, ii. 135
Ritter-Rollett phenomenon, ii. 105
Ritter's tetanus. See Opening tetanus
Ritter-Valli law, ii. 90, 164
Rosenthal's law of moribund nerve, ii.
159 ; schema of gastrocnemius struc-
ture, i. 324

INDEX

491

SALIVARY glands, electromotive action, i.

509, 510

Salpa muscles, i. 20
Salt, action on muscle, i. 104 ; on nerve, ii.

167

Sarcoplasm, i. 0, 2S tl'., 68, 90
Scheinbare Oeffnungszuckung. Sec, Sup-

]>osititious opening twitch
Schiff's trxtlti'soilic and kiix'xuiHc experi-
ments, ii. 80
Secondary contraction, i. 361, 413 ft'. ; effect

of tension, 413
Secondary electrode points, effect on polar

excitation, i. 255
Secondary electromotive action, in electrical

organ, ii. 417 : in muscle, i. 442 ft'. ;

in nerve, ii. 309
Secondary excitation from heart, i. 396,

420,~4L>7

— from muscle to muscle, i. 427

— from muscle to nerve, i. 361, 396, 413 ;

ii. 346 ; during life, 426 ; in strychnia
spasm, 423

— from nerve to nerve, ii. 264
"Secondary polarisation," ii. 299
Secondary tetanus, i. 421, 424 ; ii. 265
Secretion currents, i. 463, 485, 513

-in man, i. 391, 513
Secretory nerves, excitation by constant

current, ii. 195

Seedlings, electromotive action, ii. 5
Sensory nerves, excitation by constant

current, ii. 195

Sepia banding of muscle, i. 207, 232, 269
Sheath of Sehwann, ii. 36
Short-circuiting, of muscle current, i. 195,

327 ff. ; internal, of muscle current,

332

— of nerve current, ii. 311 ; of action

current in nerve, 337

Single negative phase, time -relations, i.
371 ; ii. 260

Skin current in frog, i. 462 tt'. ; with in-
direct excitation, 493
-in man, i. 391, 513

— in warm-blooded animals, i. 513
Sluggish muscles, excitation, i. 177
Smooth muscle, polar reaction, i. 247, 256 ff.
Snail's heart, i. 79

Sodium salts, action on muscle, i. 104, 221 ;
011 nerve, ii. 167 ft".

— antagonism to potassium, i. '221, 354
Specific excitability of nerve and muscle.

ii. 92

Spinal cord, action of poisons, ii. 71 ; direct
excitability, 79 ; electromotive re-
action, 228, 254 ; reaction, 110 ;
structure of conducting paths, 87

— of gymuotus, ii. 376

Spinal ganglia, rate of conductivity, ii. 66 ;

trophic function, 91
pring rheonome (v. Kries), ii. 130

Staircase contraction, i. 71, 121, li'.'i
Stentor, structure, i. 4
Stimulation-frequency, effect on contraction,

i. 142
Strength of current, effect on height of

twitch, i. 70 ; exciting elHcii-ncv, ii.

178 ff.

Striation of muscle, schema, i. 41
Stroboscopic method, for analysis of tetanus,

i. 409
Strychnin, dissimilar action in different

animals, ii. 74 ; eft'ect on central

conductivity, 71 ; tetanus, i. 143, ii.

423

— action on electrical fishes, ii. 423
Summation of stimuli, i. 113 ft., 189
Superposition of twitches, i. 11. ">
Supported muscle, effect on twitch, i.

121 ff.
Supposititious opening twitch, in muscle, i.

329, 333

-in nerve, i. 184, 238, 311
Supramaximal twitches, ii. 213
Sympathetic system, ii. 37

TASTE nerves, ii. 197 ; electrical, 197
Telephone as rheoscope, i. 410, 424 ; ii.

411, 424

Temperature, effect on muscle, i. 91, 97 ft'.,
151 ; on muscle current, 339 ; on con-
ductivity of nerve, ii. 61 ; on current
of action, 260 ft'. ; on excitability,
76, 117 ; on lingual currents, i. 468
Tendinous intersections, i. 228
Tension, effect on muscle twitch, i. 76 ft".
Tetanus, composition, i. 123 ff. ; galvanic
effects, 129 ; natural. 139 : nature of,
113 ; paradoxical, 271 ; rhythmical,
131, 135 ; strychnin, 143 ; ii. 423

— cardiac, i. 129

- electrical, ii. 423, 425

- in functionally dissimilar muscles, i.

125

— secondary, from muscle, i. 364 ; from

nerve, ii. 265
Theory of conductivity, ii. 336

— of discharge, ii. 357

— of electrical excitation, ii. 315 ; du Bois-

Reymond, 316 ; Funke, 317 ; Pfliiger,
320 ; Heriug, 327 ; Bernstein, 333
Time-relations, of action current in muscle,
i. 377 ; of excitation in different kinds
of protoplasm, 191 ; of excitatory
process in motor end-organs, ii. 351

— in electrical organ, ii. 431

— in the eye, ii. 478

Toad, excitability of nerve-muscle prepara-
tion, ii. 126 ; telephone sound in con-
traction, i. 424

Tonus, in cardiac muscle, i. 102, 260 ; in
smooth muscle, 100

492

ELECTRO-PHYSIOLOGY

Torpedo, electrical organ, ii. 360 ft'. ; inner-
vation, 362

— viviparous development, 380
Tortoise heart, i. 433 ; muscle, 59 ff., 124
Total excitability of muscle (v. Bezold),

i. 280

Transmission of excitation, in leaves of
diontea, ii. 26

— and contraction wave, in muscle, i. 147,

373, 374

— in nerve, ii. 59, 65

Transverse excitability of muscle, i. 199 ;

ii. 134 ; of nerve, 132 ; of protozoa,

134
Transverse resistance of muscle, i. 200 ; of

nerve, ii. 305
Transverse section (artificial), effect on

excitability, ii. 94, 156 ; on opening

excitation, i. 330 ; ii. 162 ; on polar

excitation by current, i. 217 ; ii. 156 ;

on total excitability, i. 227

— relation to muscle current, i. 322
Treppc. See Staircase contraction
Triphasic wave in gastrocneniius, i. 387
Twitch, cardiac, i. 58 ; composition of,

55 ; isotonic and isometric, 82 ; para-
doxical, ii. 271 ; summation of stimuli,
i. 421 if.

— secondary, i. 361 ; effect of tension in

primary muscle, 413 ; position of
secondary nerve, 417 ; with direct and
indirect excitation of primary muscle,
416

UEBERLEBEX. See Vitality
Under-propping, effect on twitch, i. 121
Unipolar excitation of cardiac muscle, i.
231 ; of nerve, ii. 154, 219

Unterstiitzung. See Under-propping, After-

loading

Ureter, electrical excitation, i. 180, 251 ;
mechanical excitation, 167 ; effect of
polarisation, 294 ; effect of tension
upon contraction, 80

VAGUS, action on heart, i. 433 ; antagonism
of respiratory fibres, ii. 104 ; excitation
by constant current, 120 ; polar inhibi-
tion, 194

Vascular nerves, antagonism of constrictors
and dilators, ii. 104 ; excitability, 104

Veratrin, action on polarisation, i. 454 ff. ;
on striated muscle, 107, 265

Verlanf (Contractions). See Time-relations

Visual stimulation, ii. 202

Vitality of cardiac muscle, i. 91 ; of smooth
muscle, 92 ; of nerve, ii. 89 ; of
retina, 479

Voltaic alternative, in muscle, i. 224, 292 ;
in nerve, ii. 151, 239

Von Fleischl's rheonome, ii. 128

Vorticella, stalk muscle, i. 4

WAGXEK'S brush, ii. Stil

Walleriau degeneration, ii. 91

Water rigor, i. 357 ; not true rigor mortis.

358
Worm muscles, i. 12 ; electrical excitation

of cutaneous muscular integument,

240 ff.

ZWEIGIPFEL VERSUCH.

periment

See Bifurcate ex-

THE END

l>y R. it R. CLARK, LIMITED, Edinburgh.

ERRATA IX VOL. I

l'i_;r xi., insert Cross-striated, Multinuclear Muscle Fibres, page 26, after The
Muscles of Metazoa.

Page xii. , insert The Electrical Excitation of Muscle, page 174, above The
Electrical Excitation of Unfibrillated Protoplasm.

Page 3, line 4 from bottom, for Acanthocystiden read Acanthocystidse.

Page 4, line 16, read Opalinidse.

Page 18, line 3, for bisected read when cut across (am! transpose to end of line).

Page 29, lines 11, 13, for arete read areas, passim.

Page 46, line 25, for refractibility read refracting power.

Ib. line 32, read refraction.

Page 47, lines 32, 40, page 48, line 14, for double refractibility read double
refraction.

Page 47, line 27, insert in after dark.

Page 49, lines 17, 18, for accept the penetrating conclusions read follow the
admirable researches.

Page 56, line 19, for abscissa read base-line ; ib. page 116, line 8 ; page 146, line
12 ; page 205, bottom line ; page 364, 5 from bottom ; page 366, 11 from bottom ;
page 375, 12 from bottom.

Page 58, line 16, delete elementary; line 27, ib., and for an elementary read a
simple.

Page 68, line 26, for muscles read mussels.

Page 70, Hue 24, insert only after cardiac muscle.

Page 80, lines 11, 14, and passim, for canula read cannula.

Page 81, line 28, for while at the same time read although.

Ib. lines, 36, 37, read and at the same time to give a graphic record of its
varying tension.

Ib. line 38, for the short read a very short.

Page 82, line 8, insert the before muscle.

Ib. lines 14 and 8 from bottom, insert quotation marks before The, and (Fick 39)
after tension.

Ib. lines 6 and 5 from bottom, read with the greatest possible tension the muscle
only shortens by a.

Ib. line 3, insert during before its contraction.

Page 97, line 24, insert in muscle after death.

Ib. line 25, for denoted read readily explained by the ; for products read processes.

Page 98, 4 from bottom, for at a moderate rate read by a suitable rate.

Page 99, line 6, for by read in.

Page 102, line 15, for i.e. read namely ; Hue 18, for or read of.

Page 103, Hue 17, read This tonus may be at once abolished.

Ib. line 19, for reduces read disappears.

Page 107, line 7, insert comma after fall.

494 ELECTRO-PHYSIOLOGY

Ib. line 14, for Na.2C02 read Na2C03.

Page 109, bottom line, insert the before sartorius.

Page 110, line 10, delete and, read so that the twitches, usually of very brief
duration, served up, etc. ; line 11, for abscissa read abscissae.

Page 114, line 22, for tetanus read tetanic ; line 28, for behind read near.

Page 115, line 3, read interval between the two stimuli is equal to the period of
rising energy of a single contraction.

Ib. line 11, for scheme read schema ; line 13. read vertically over.

Page 116, line 11, read according as the second twitch was superposed at a more
advanced stage of the first contraction.

Page 117, line 13, and passim, for crab read crayfish.

Ib. last line, for tetanus read tetanic.

Page 120, line 9. ib.

Ib. Fig. 54 should be reversed.

Page 121, line 24, for the read a loaded muscle.

Page 122, last line but one, for proportionately read suitably.

Page 128, line 27, for 250 read 280.

Page 130, line 7, read stimuli and contractions ; line 8, for working read
sent in.

Page 131, last line, read As regards strength of current, the rhythm was limited
between just effective distance of the coils, and 1-2 mm. ; in other words, to a very
small interval of difference.

Page 134, line 6, for over read by ; last line, insert only after systole.

Page 136, line 17, for since read and.

Page 137, line 14, insert to before which.

Page 139, line 9, delete comma after registered.

Page 144, No. 38 of Bibliography, tr. into Griffiths.

Page 148, last lines, for pseudopod read pseudopodium (passim).

Page 149, 3 from bottom, for sense read direction.

Page 152, line 6, for excitating read exciting.

Page 174, line 9, for momentary read instantaneous.

Page 182, line 3, for in read with ; 5 from bottom, for between read in.

Page 193, line 28, for steepness read abruptness.

Page 195, line 5, for in read within ; line 27, insert (Biedermann, 14).

Page 219, line 3, for less read more.

Page 221, line 9, for potash read potassium (passim).

Page 299, line 10, read Becquerel (passim).

Page 310, line 23, for arese read areas.

Page 320, line 3, comma after mass motion ; and line 4, insert in before electricity.

Page 333, line 9, for spurious read false or supposititious.

Page 338, last line, read albumin ; page 340, line 25, ib.

Page 358, line 9, for sense read direction ; line 26, for i.e. read e.g.

Page 371, line 4, for negative variation read single negative phase ; line 28, for
record read representation.

Page 372, 1 from bottom, for free read light.

Page 376, line 20, for was the precursor of read preceded the.

Page 384, line 24, for Doyer read Doyere.

Page 385, line 25, and page 386, lines 7, 27, 29, for achilk-s rea</ achillis.

Page 510, lines 4, 14, 36, a.nA passim, for hilus read hilum.

SECONDARY ELECTROMOTIVE ACTION IN MUSCLE
CHAPTER IV., SECTION IV. (REVISED)

I'cmJ, 111 muscle (as in nerve, electrical organs, and irritable protoplasm
in general) the passage of the electrical current is followed by certain
electromotive reactions, which are intimately related with the action current,
and are to a certain extent only a special manifestation of the same. As
early as 1834, Peltier discovered that the protracted passage of current in
frogs' limbs, in isolated muscles, and even in pieces of muscle, will develop
a current in the reverse direction. This he interpreted to mean that oxygen
and hydrogen are separated at the interface of animal tissue and conducting
fluid, as they would be at an intermediate metal surface.

Du Bois-Reymond (67), who took up the investigation later, came to the
conclusion that the secondary current (after - current) does not depend
exclusively, if at all, upon the ions separated at the poles, but is also
generated in the tract lying between them. He found, namely, that all
sections of the intrapolar tract of a longitudinally-traversed muscle will give
electromotive action in the same direction, after opening the polarising
current. Accordingly, he advanced the view that this effect mainly depended
on what he termed " internal polarisation."

Many inorganic and organic porous bodies, saturated with an electrolyte,
do, in fact, acquire the property of negative internal polarisation. The
polarising current then divides itself between the badly-conducting, saturat-
ing fluid, and the porous vessel, when the latter becomes polarised from the
separated ions. " Each of the many interfaces now gives electromotive
action in the reverse direction from that in which it was traversed by the
current." The superposition of all these partial currents results in a
current through the circuit. Each tract of equal length in any regularly
constructed (prismatic, or cylindrical) body will, as a rule, exhibit marked
secondary electromotive action after the passage of the current.

Soon, however, it was observed that living muscle, traversed by the
current, behaved in this respect quite differently from dead organic, or
inorganic, bodies ; as shown, above all, in the fact that positive, as veil n*
negative, after-currents make- their appearance under certain conditions. For
the investigation of polarisation effects in muscle, du Bois-Reymond generally
employed the r/racilis and semimembranosus muscles, at a convenient
tension. He used one pair of unpolarisable electrodes to lead in the polar-
ising current, and another to lead off the polarisation current. The
latter were usually placed between the first pair, within the intrapolar

496 ELECTRO-PHYSIOLOGY

tract. A special contrivance enabled him to alter the " period of closure "-
i.e. the time for which the polarising current was sent through the polaris-
able object — from 0 '00 1-20 sees. The same contrivance effected closure of
the galvanometer circuit, after breaking the battery circuit at a minimal and
constant interval.

The resulting secondary electromotive effects in the muscle are essentially
dependent on the density and duration of the primary current, and are very
confused, owing to the constant interference of negative and positive effects.
" With a current density below that of 2 Groves, and with a very brief
closure, no polarisation is, as a rule, perceptible on the galvanometer. The
first traces obtained with 1 Dan. and 1 sec. closure are negative. The first
positive traces appear with 2 Groves, and about 0'3 sec. closure."

With increasing period of closure, du Bois found that positive polarisation
quickly reaches its maximum, and then declines more slowly, and passes
over into negative polarisation, which again rises to a maximum. He fixes
the " critical point " of closure as that at which positive passes into negative
polarisation. The maximal positive polarisation in these experiments was
at a closure of 0-075 sec. with 20 Groves (!) ; the maximal negative
polarisation at ten minutes' closure of 1 Grove. Brief impacts of current
(induction shocks) invariably produce positive polarisation only.

Both positive and negative polarisation are very persistent, and some-
times outlast the opening of the polarising current for twenty minutes or
more. If the current is broken at the " critical point," du Bois not
infrequently observed a diphasic effect, usually in the direction of first
negative and then positive polarisation. This is due to the fact that, while
both polarisations are simultaneously present from the moment of closure,
they increase in a different degree, "negative polarisation rising more in
proportion with the time of closure, while positive polarisation rises quickly
at first, and then more slowly."

Du Bois-Reymond further concluded from experiments in which the
upper and lower half of regularly - constructed muscles were traversed
alternately by the current, and tested for polarisation, that " strong positive
polarisation is exhibited in the upper half with ascending, in the lower half
with descending direction of current."

Dead muscles still exhibit traces of negative internal polarisability, that
are completely abolished only by boiling ; positive polarisation, on the
contrary, is exclusively characteristic of living muscle.

Du Bois-Reymond concluded, " not that electromotive forces homodro-
mous with the primary current are generated by the positively polarisable
tissues, but that the carriers of pre-existing electromotive forces (electromotive
molecules) are homodromously adjusted with the primary current."

How little these results really support the molecular theory, is obviovis
from the later investigations of Hering and Hermann (68, 69).

In the first place, Hering proves conclusively that there can be no
question of internal positive or negative polarisation in da Bois-Reymond's
sense, since the actual seat of the electromotive changes induced by the
exciting current is at those points of the contractile substance by which
the current enters or leaves the muscle (the physiological poles) : so that the
close relation between these phenomena and the polar action of the current
is unmistakable.

SECONDARY ELECTROMOTIVE ACTION IX MUSCLE 497

If (as already set forth) each alteration of chemical activity in any part
of the muscle-fibre necessarily implies the appearance of electromotive .n linn,
we should anticipate that on sending current through a muscle with parallrl
fibres, the chemical alterations in the contractile substance at the physio-
logical kathode and anode would initiate differences of potential. And these
differences must be manifested when one or the other end, so altered, of the
muscle is led off in connection with a point on the otherwise uninjured
surface. The results which Hering obtained from experiments on the
frog's sartorius did, in fact, correspond in every particular with this
assumption.

If, namely, this muscle is fixed at moderate tension, the current being
passed through it from the stumps of bone on either side, then on leading off
from one or the other tendon-end, and from a point on the longitudinal
surface, the muscle current measured previous to the passage of the current
will, on breaking the latter, be found to be considerably altered. It is
increased, diminished, neutralised, or the reverse, according to the direction,
strength, and duration of the exciting current, and the strength and direction
of the original muscle current. When the muscle current has been pre-
viously compensated, " polarisation currents " make their appearance in
correspondence with the positive or negative modification of the muscle
current. These may be positive or negative, i.e. hotnodromous or hetero-
dromous to the exciting current. Since they are really initiated at the
anodic and kathodic points of the muscle-substance, Hering distinguishes
between anodic and btthodic polarisation. The former may be either positive
or negative, the latter is in most cases negative only.

With a brief closure, very weak currents invariably give a negative
polarisation current in fresh muscle, so long as only the anodic tendon-end,
and a point at about the middle of the muscle surface, are in the galvanometer
circuit. With stronger exciting currents, on the other hand, and not too
brief a closure, positive polarisation alone results, and increases with the
strength of current, until finally it far exceeds the strongest negative anodic
polarisation.

Very strong currents produce positive polarisation at once, even with
the shortest possible closure. Weaker currents, with brief closure, give
negative or diphasic (first negative, then positive) polarisation, and the pure
positive effect only appears after prolonged closure. Induction currents are
like strong constant currents, with minimal closure, and produce positive
anodic polarisation only.

All these polarisation effects (after-currents) an' mniti'ii;/, or at most «jv'""' "x
a trace, if both kading-o/ electrodes are ,ijtj>li\'<l to the lontiitntlinal surface of the
muscle, ami not too close to one or tin- other <:n<J nf it.

Since, according to Hermann's "alteration theory," excited muscle-
substance is negative to unexcited substance, there can, when we consider
the conditions and the character of the opening excitation in muscle, be no
doubt that positive anodic polarisation is the expression of the latter. '•' The
positive poln-;*«ti»n current produced by alteration of the anodic points of the
contractile substance is an action curn nt, tine to the bn-nJc excitation starting from
the anode" : albeit, an action current '//"> /»7i«m very differently from the action
current due to the make stimulus, that has so far exclusively concnm.l us.

The lono- persistence of negativity at the anodic points is remarkable in

1 T."

VOL. II

498 ELECTRO-PHYSIOLOGY

this connection. It is easily explained by the fact that the opening of a
constant current leads, under certain conditions, to the protracted excitation
(persistent opening contraction) of the muscle. This gradually declines,
becoming more and more restricted to the anodic points of the muscle. Even,
however, in cases where (as with weaker currents, or brief closure of strong-
currents) there is no visible persistent break contraction, nor even a break
twitch, we are free to regard the positive polarisation current as the ex-
pression of a break excitation lasting for a considerable period — inasmuch as
a low degree of contraction is difficult or impossible to demonstrate, especially
when it is confined to the immediate vicinity of the anodic or kathodic points
of the muscle, while negativity may be present as the expression of excitation,
without the slightest manifestation of contraction.

Hermann's view of the positive anodic after-current only differs from
that of Hering in that (starting with the assumption of an intrapolar
electrotonus) he locates the break action current in the entire anelectrotonic
tract of the muscle. But it has already been shown (supra) that, provided
we avoid an undue strength of polarising current, the alterations that are
termed collectively " electrotonus " are all strictly confined to the physio-
logical electrode points.

With respect to kathodic polarisation, we find that it is almost exclusively
negative in striated muscle. On leading off from a sartorius (through
which current is passing) by the kathodic end, and centre, of the muscle,
polarisation first appears, with very weak currents, after a closure of several
seconds, and is steadily augmented with increased strength of current and
longer closure. On comparing it with the positive anodic after- currents
observed at the same end of the muscle, at the same strength of current
and duration of closure, the latter soon exceed it very considerably. With
very strong currents and prolonged closure, negative kathodic polarisation
may become as strong as the equally abterminal muscle current seen on
killing the same end of the muscle, without shifting the galvanometer
electrodes. Induction currents also give negative kathodic polarisation, but
it is essentially weaker than the positive anodic polarisation produced by the
same strength of induction current in the same (sartorius) muscle. The
conclusion is therefore that, icith ///c/v^x///// stn'i/i/th «.ml ilnrntinn nf c^ritii,,/
i-i'rrcnt, the ItatlioiHr region i if the muscle (physiological kathode) IHWIH,* moreand
more negative in comparison n'itli tin' rr////v of the m-nscle. If this effect were
the equivalent of internal physical polarisation, the negative polarisation
current would, as has been shown, appear at approximately constant strength
on leading off from any point within the intrapolar tract ; and Hering has
shown that this never is the case. On the contrary, when the leading-off
electrodes are placed at the boundary between the upper and middle thirds
of the sartorius, while the polarising current is led in as before through the
bones, there is either no polarisation current, or it is so insignificant in com-
parison with the anodic and kathodic polarisation that it is practically
negligible. The relatively weak effects which may be observed in the
intrapolar tract with very strong polarising currents, and prolonged closure,
are to be explained by the fact that the polar points of the muscle are never
confined exclusively to its ends, e.rj. in the sartorius there are not infre-
quently short fibres which terminate, or begin, somewhere in the length of
the muM.-le. Again, the appearance of the make and break persistent con-

SKOONDARY ELECTROMOTIVE ACTION IN MUSCLE 499

traction necessarily produces inequalities in the individual parts of the inter-
polar tract. Hence, there is no adequate reason for assuming an internal
]H)larisation of the muscle-substance in du Bois-Reymond's sense. On the
ofhir 1/in/d, nil the iiiiti/ij'rxtiitioiix nf itn/nfirc knlliniHr fioln fixation i in; mjiiin

ri'iniilij explained Inj chemical alterations (excitation <>r Ini'al j'nt/ijnr) in tin-.
1,-ntliiiii !<• /loiiitti of (In film* collectively.

Nor are the later experiments of du Bois-Reymond more convincing, in
which the application of a current from 10 Groves produced, after 15-25
minutes' closure, " a secondary E.M.F. in the reverse direction to the polarising
current, in every part of the muscle" — its magnitude increasing with the
length of the tract led off. For the extent to which excitability and con-
ductivity in the muscle would be altered by such impossibly strong currents
is sufficiently attested by the appearance of the galvanic wave under similar
conditions, as also by the persistent excitation (often extremely marked, and
widely distributed over the intrapolar tract of the muscle) in the anodic
region, which depends, as was shown above, upon the effectuation of
secondary electrode points. Indeed there can hardly be a doubt, after the
preceding discussion, that experiments performed under such abnormal
conditions in no way contravene the clear and simple result of Hering's

investigations.

The most striking proof that secondary electromotive phenomena are
pure polar effects of the current is, however, the fact that both positive anodic
and negative kathodic polarisation are abolished by killing the anodic or
kathodic ends of the muscle, exactly as occurs with the opening and closing
excitation. Tlie ucijatirc, m/d xtill more the positive, polarisation < nrroit ?x
iii/ly d< ji, ,,:l> i/f ///in,/ tin /,/ti'i/r/ti/ of the kathodic or anodic points of the

Hermann points this out in reference to the positive anodic after-current
only in muscle, designating this alone as " irritative" in contradistinction to
the negative after-current " resulting from true polarisation." Like du Bois-
Reymond, he derives the latter from the entire intrapolar tract, and after
partial passage of the current from the extrapolar tracts also, in consequence
of a polarisation which he takes to be equivalent with certain polarisation
phenomena (to be discussed below ; see vol. ii. pp. 309 ff.) that occur in medul-
lated nerve — as also in a polarisable wire surrounded by air electrolyte,
through the sheath of which the current enters. He concludes that the
effects upon this core model coincide with the polarisation effects, both intra-
and extra-polar, of muscle (and nerve), the " polarisation after-current " being
in the first case heterodromous, in the second homodromous, with the
polarising current.

AVe shall enter more fully into these relations in discussing the electrical
excitation of nerve ; for the moment it may be said that little as the phenomena
can be disputed under some conditions, yet that in muscle (within a certain,
so to speak, physiological limit of current strength) the negative kathodic
must, equally with the positive anodic after-current, be designated as " irrita-
tive," and resulting altogether from pure jiolar action of the current.

I'.-iici' 449, line 16, for has recently read subsequently.
Hi. line '2\. fur antagonistic read heterodromous.
11. line 30, insert designated as after is.

500 ELECTRO-PHYSIOLOGY

Page 449, line 35, for proper read itself.
Page 450, line 26, for no trace read only a trace.

Page 451, line 28, after the read presence of the alterations fundamental to the
after-current.

Page 452, line 22, for exist read be manifested, insert quite before different.
Page 453, line 23, delete or after positive.
Page 459, line 19, for end read close.

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