MARINE BIOLOGICAL LABORATORY.

Received November 8, 1934

44195
Accession No.

Given by Dr. J. C. Waller
Place, ^.^^'^^^^^■'^y 0^ J^i ve^r

%*flo book Of pampiilet is to be removed from the liab-
Ofatoi^ «iitbout the permission of the Trustees.

I

LECTURES ON PHYSIOLOGY

FIRST SERIES

ON ANIMAL ELECTRICITY

UJ LIBRARY J

BY

AUGUSTUS D. WALLER, M.D., F.R.S.

Fullerian Professor of Physiology at the Royal Instihttion of Great Britain

Lecturer on Physiology at St. Mary's Hospital Medical School,

London

L O N G AI A N S , GREEN, AND CO.

39 PATERNOSTER ROW, LONDON

NEW YORK AND BOMBAY

1897

PRE FA CB.

The folloii'iiig ''First Scries" of lectures, as noiv printed,
contain part of the material of a conrse of tivelve lectnres
on '^ Animal Electricity," delivered at the Royal Institntion
(in ring the spring of iSgy.

The six printed lectnres are by no means co-extensive
with the tivelve spoken lectnres. The former, more especially
the fifth and sixth, inclnde matter that I sJiould have felt
it impossible to consider at length in the face of a non-tech-
nical andience, bnt that I nevertheless regard as essential
to the fnrther study of the snbject. The latter icere of necessity
largely diluted ivith elementary explanations, and included
three lectnres on the electromotive action of the heart, and
on the action of nitrons oxide, the pnbtication of which is
reserved for a '^ second series"

In Physical Science the Royal Institntion of Great
Britain has played a iisefnl as well as a brilliant part
as an organ of pnblic instrnction ; and the great physicists,
who fashioned the fntnre destinies of the Institntion, did

iv. Preface.

not neglect to cnltivate tliat portion of pliysicat science icJiicJi
is tlie iionuiin of tlie p/iysiologist — tJie physics of living
matter.

Davy, by his close physiological stndv of nitrons oxide,
pointed out the ivay toivards the establisJinient of Ancvsthesia.
Faraday took part in tlie foundation of onr knou'ledge of
Animal Electricity by his physiological investigation of the
electric eel. It is indeed throngJi its Fnllerian Professors
of Chemistry rather than through its Fnllerian Professors
of Physiology, that the Royal Institntion has fnrtJiered onr
knoivledge of living matter.

No clearer proof conld well be offered of the absolute
dependence of any branch of Science upon its laboratories
rather than upon its lecture-theatre. The Fnllerian professor-
ship of Chemistry has been fruitful, not only in its vivu
department, but also in the allied department of Physiology.
The Fnllerian professorship of Physiology has been com-
paratively sterile, even ivithin its own nominal province.
Both chairs have been held by men of the highest distinction ;
bid the former has rested upon a laboratory, while the
latter — so far from resting upon a laboratory — does not
possess even one small room in ivhich to keep itself alive.

A. D. WALLER.

Wcsiun Lodge, 16, Gvove End Rocuf N.IV.
August, J 897.

^iMi^L

CONTENTS.
LECTURE I.

I'AtiES

Currents of animal electricity are produced by animal
voltaic couples, in which injured or active proto-
plasm is electro-positive (" zincative "), resting
protoplasm electro-negative (" zincable ").

The utilisation of a nerve as a test-object representative
of living matter.

Experiments. — Current of a voltaic couple. Current of
injury of muscle — its negative variation. Current
of injury of nerve — its negative variation. Paral-
lelism between mechanical and electrical effects.
Electrical effects of non-electrical stimuli. Action
of ether and of chloroform upon isolated nerve ... 1-29

LECTURE n.

Description of method. Illustration of Ohm's law.
Dead-beat and oscillating magnet. Alcohol, soda
water, tobacco smoke. Carbonic acid. The func-
tion of respiration. Integration and disintegration.
Action of carbonic acid in further detail ... ... 30-54

LECTURE III.

On the production of COg by tetanised nerve.

Hypothesis and experiment. Three stages. Compari-
son between the effects of CO., and of tetanisation.

Direction of further inquiry. Significance of the stair-
case effect. Summation. " Bahnung."

Postscript ... ... ... ... ... ... ._ 55-75

44195

vi. Contents.

LECTURE IV.

PAGES

Polar effects. Pfluger's law. Illustrated by experi-
ments on Man.

Electrolytic dissociation. Electrolytic counter-current.

Internal polarisation.

Polarisable core-models. Extra-polar currents in core-
models.

Extra-polar currents in frog's nerve and in mammalian

nerve 76-100

LECTURE V.

ELECTROTO NUS.
" An." and " Kat." Influence of ether and chloro-
form. Physiological and physical effects. The
electro-mobility of living matter. Relation between
polarising and extra-polar currents in nerve.
Strength. Distance. Von Fleischl's deflection.
Action currents are counter-currents. Extra-polar
effects in mammalian nerve ... ... ... ... 101-123

LECTURE VI.

ELECT ROTON US (continued).

Influence of acids and alkalies. Influence of carbonic
acid and of tetanisation. Influence of variations
of temperature.

The action-currents of polarised nerve. Bernstein's
electrotonic decrement. Hermann's polarisation
increment ... ... ... ... ... ••• 124-144

\^\ ^^^^^^ /^/
ILLUSTRATIONS. '^^^^^*^^>''^

LECTURE I.

PAGF,

Fig. I. — A lump of protoplasm as a voltaic couple - - - 2

„ 2. — A simple voltaic couple ------- 4

„ 3. — Zinc is electro-positive ------- 5

„ 4. — Muscle currents -------- 8

„ 5. — Nerv^e currents -------- 10

„ 6. — Simultaneous record of the mechanical and electrical

responses of muscle - - - - - - - 13

„ 7.— Simultaneous record of the electrical response of nerve

and of the mechanical response of muscle - - - 18

„ 8. — Effect of ether on nerve ------- 23

,, 9. — Effect of chloroform on nerve ------ 23

LECTURE IL

,, 10. — Plan of apparatus -------- 33

„ II. — An application of Ohm's law. Compensation. - - ^<^

„ 12. — Dead-beat and ordinary galvanometers - - - - 39

„ 13. — Effect of soda water on nerve - ----- 43

„ 14. — Effect of alcohol on nerve ------ 43

„ 15. — Effect of tobacco smoke on nerve ----- 43

„ 16. — Excitant effect of carbon dioxide ----- 47

„ 17. — Anaesthetic effect of carbon dioxide - - - - 47

„ 18.— Excitant effect of expired air ------ 52

LECTURE IIL

„ 19. — Effect of COo on carbonised nerve ----- 56

„ 20. — Hypothesis --------- 58

„ 21. — Verification --------- -q

,, 22. — A typical " dead-beat "' series ------ 60

„ 23. — Three stages - - - - 61

„ 24 to 31. — Influence of carbon dioxide and of tetanisation upon

nerve in first, second and third stages - - 64-5

„ 32. — The staircase effect of the heart ----- 68

„ 32<:?. — The staircase effect in nerve ------ 68

„ 33. — Effect of tetanisation on " unfed ' nerve - - - - 74

„ 34. — Effect of tetanisation on '' fed '' nerve - - - - 74

viii. Ilhisfrnfioiis.

LECTURE IV.

PAGE.

Fig. 35.^ — Anodic and Kathodic alterations of excitability of human

nerve ---------- 82

36. — Excitability and zincability under the Anode and Kathode 84

^y. — A polarisation cell -------- 86

38. — Internal polarisation of the human subject - - - 90

39. — Anodic extra-polar currents of a core-model - - - 92

40. — Kathodic extra-polar currents of a core-model - - 93

41. — Electrolysis at four surfaces ------ 95

42. — Extra-polar currents of frog's nerve - - - - 96

43. — Extra-polar currents of mammalian nerve - - - 97

LECTURE V.

44. — Anelectrotonus and Katelectrotonus . . . . 102

45. — Influence of ether upon An. ------ 105

46.— Influence of chloroform upon An, ----- 105

47. — Schema of electrolysis in a medullated nerve fibre - - 109
48. — ^An. and Kat. of frog's nerve - - - - - -in

49. — Von Fleischl's deflection - - 115

50. — An. and Kat. of mammalian nerve ----- 120

LECTURE VI.

51. — Influence of CO., on K. ------ - 125

52. — Influence of COo on A. - - - - - - - '25

53.— Influence of COo on A. ------- 125

54.— Influence of alkali (KOH) on A. and K. - - - - 128

55. — Influence of acid (propionic) on A. and K. - - - 128

56. — Influence of ammonia on A. and K. - - - - 129

^7. — Influence of CO2 on A. and K. ----- 129

58. — Influence of tetanisation on A. and K. - - - - 129

59. — Influence of CO2 on A. ------- 130

60. — Influence of tetanisation on A. - - - . . i^o

61. — Influence of CO. on A. ------- 131

62, — Influence of tetanisation on A. - - - - - I3-

63. — Influence of rise of temperature on A. and K. - - 134

64. — Plan of connections for electrotonic decrements - - 136

65. — Anelectrotonus and Katelectrotonus - - - - ^37

66. — Flan of connections for polarisation increments - - 138

67. — Nerve currents summarised - ----- 143

ANIMAL ELECTRICITY

"Wonderful as are the laws and phenomena of
electricity when made evident to us in inorganic
or dead matter, their interest can bear scarcely
any comparison with thnt which attaches to the
same force when connected with the nervous sys-
tem and with life." — Faraday. '■'' Experimental
Researches in Electricity.'''' Eifteenth series, 1844.

LECTURE L

Currents of animal electricity are produced by animal voltaic
couples, in which injured or active protoplasm is electro-
positive ("zincative"), resting protoplasm electro-negative
(" zincable ").

The utilisation of a nerve as a test-object representative of living
matter.

Experiments. — Current of a voltaic couple. Current of injury of
muscle — its negative variation. Current of injury of nerve
— its negative variation. Parallelism between mechanical
and electrical effects. Electrical effects of non-electrical
stimuli. Action of ether and of chloroform upon isolated
nerve.

The master-key to many otherwise most intricate
and complex problems of animal electricity is a very-
simple idea. Active matter is electropositive^ to in-

^ This nomenclature, which is the opposite to the conven-
tional denotation, will perhaps be found justified by the context

2 ANIMAL ELECTRICITY. LECTURE I.

active matter ; more active matter is electropositive
to less active matter ; matter that is by any means
stirred up to greater activity is rendered electro-
positive towards undisturbed matter, matter whose
action is lowered is electronegative to matter whose
action is normal.

Picture to yourself a uniform mass or strand of
protoplasm, that is to say of living matter, inactive at

Fig. I. — A lump of protoplasm as a voltaic couple.

Any injured, i.e.^ chemically active spot B is zincative to any uninjured spot
A. Current in the lump is from B to A, in the galvanometer from A to B.

of these lectures. In the phraseology generally employed by
physiologists the active spot is said to be " negative," and the
term "negativity of action" is derived from this. But more
correctly speaking the active spot is positive, and we should
properly say " positivity of action." But to reverse these and
other derived terms in common use would lead to hopeless con-
fusion, which I desire to escape by employing the terms zincative,
zincativity. Moreover we shall soon experience the want of a
word to denote that a resting spot, capable of activity, is capable
of becoming positive, or has a capability for becoming positive ;
this will be met by the words zincable, zincability, which are by
no means to be taken as synonymous with the terms excitable,

ANIMAL ELFXTRICITV. LECTURE I. 3

all points, or what comes to the same thing, equally-
active at all points. Any two points being ex
hypothesi equally active, are equally electromotive —
" isoelectric,"— and if connected by wires to a galvan-
ometer, exhibit no current. But stir up B by pinching
or pricking or by a touch of a hot wire, and you
will at once obtain a current through the ralvan-
ometer that indicates the presence of current In the
rest of the circuit as shown by the arrows. In the
mass of protoplasm which Is no longer uniformly
active throughout, but more active at B than at
A, there Is current from B to A. In the galvan-
ometer the current Is from A to B.

These two unequally active regions B and A
form a w^eak voltaic couple, of which B, the more
active spot, where more chemical action Is going on
(we shall further on Inquire Into the possible character
of such chemical action), Is the generating or electro-

excitability. A spot of tissue under the influence of the anode
is less excitable and more zincable. I have not been willing to
use the less inelegant words electromotive and electromobile in
place of zincative, zincable, for fear of an ambiguity in the term
electromobile which has seriously impaired the precision of the
term excitable. A tissue may be more excitable (erregbar) inas-
much as it may be aroused to action by a weaker stimulus, or
more excitable (leistungsfahig) inasmuch as greater action is
aroused by a given stimulus. A more zincable spot, as the name
suggests, is capable of greater electropositive action than a less
zincable spot.

4 ANIMAL ELECTRICITY. LECTURE I.

positive plate, and A, the less active spot, where less
chemical action is going- on, the collecting or electro-
negative plate.

Let me try to fix this point in your memory by
two elementary experiments, the first to specify the
direction of current by a typical voltaic couple (zinc
and copper), the second to identify w^ith such a current
the current of animal electricity that passes from more
active to less active tissue.

ZINC

COPPER

jaVtwaterJ

I iiiiiii I ii.iiii
>

Fig. 2. — A simple voltaic couple.

The surface between zinc and fluid is the principal seat of chemical action.
Current in the cell is from zinc through fluid to copper. Through the galvan-
ometer it is from copper to zinc.

Preliminary Experiment. — A slip of zinc and a
slip of copper dipping into a glass of salt solution
and connected with a galvanometer will exhibit the
character and direction of action of a representative
voltaic couple. The current will indeed be so large
that with this delicate instrument arranged as it is for
the far smaller currents generated in living nerve, we
must "shunt" it, i.e., only let a small fraction of it
pass through the galvanometer.

ANIMAL ELECTRICITY. — -LECTURE I. 5

The direction of deflection is as you see such as
to indicate current in the voltaic cell from zinc to
copper. Whatever you may choose to remember or
forget, bear in mind that zinc is the active plate, at
which chemical change takes place, and electromotive
pressure takes origin. Later on when we come to
deal with the electrical response of living nerve, we
shall find it of the utmost convenience to make use
of language based upon this fundamental notion, to
speak of living nerve as being more or less zincative
or zincable, as having greater or smaller zincativity
and zincability.

Second Preliminaiy Experiment, — Let us in fact
simplify matters further ; omitting the copper plate

Fig. 3. —A bit of zinc wire held in the right hand and touching one terminal
of a galvanometer circuit (while the other hand rests on the other terminal) gives
current in the body from right to left, in the galvanometer from left to right.
The current is aroused at the contact between the zinc and the slightly moist skin,
and is directed from zinc to fluid. (If the galvanometer wire, instead of ending at
a metal terminal R, dips into a glass vessel of salt solution, and circuit is completed
by dipping the zinc into the same solution, current would run the other way round
— /.<?., anti-clockwise instead of clockwise — being as before from zinc to fluid.)

-6 ANIMAL ELECTRICITY. LECTURE I.

and substituting in the circuit our own body for the
vessel of salt water, by laying one hand upon one
terminal, and a zinc rod held in the other hand upon
the other terminal.

As before, you see that the current is from the zinc
through the body, and to the zinc through the galvan-
ometer, i.e., the zinc is electro-positive.

You will find in this simple observation not only
a stepping-stone towards the proper understanding
of an animal current, but a ready practical device for
ascertaining in a complicated circuit what direction of
current at any part of the circuit is indicated by a
given deflection of the galvanometer. If you put
your body into circuit by taking one end of a wire in
one hand L, and touch the other end with a bit of
zinc, you will get the deflection indicative of current
in your body from the zinc, i.e., from R to L in the
figure. If that deflection is of the same direction as
that of the deflection under question, you know that
the latter was produced by activity on the R side ;
if the deflection is reversed, activity has been on
the opposite side.

Our first representative experiment is a realisation
of the imaginary case that we took as our type, and
had best be shown to you at least twice, on the two
representative excitable, that is to say, living tissues —
on a muscle namely, and on a nerve.

We will begin with muscle, with which the experi-
ment is easier to make and easier to understand.

ANIMAL ELECTRICITY. LFXTURE I. 7

First Representative Experiment (on Muscle), —
This isolated muscle — it is the living muscle of a
dead frog — is connected with the galvanometer by
two electrodes touching it at two points T and L — its
tendinous end or transverse section, and its longitudinal
surface (fig. 4). As it stands, and though it has been
prepared as gently as possible, it is in all certainty
not absolutely uninjured and normal, therefore in all
certainty not homogeneous and electrically indifferent
at all points. It is living, that is to say it is dying —
for life is essentially slow death — and it is dying (or
if you prefer it living) in any case chemically changing,
more rapidly at its thin end T than at its thick part L.
If so — and for the purpose of making quite sure, I
may make it so by a touch of a hot wire — T will be
zincative to L, and we shall have current as shewn
by this diagram, illustrating on muscle that active
matter — in this instance stirred up by injury — is
zincative in relation to less active matter, crivinof
thereby a current of animal electricity.

This has been the first half of the experiment.
Its complementary half, illustrating the same principle,
will complete it and fix its meaning to you. The
nerve through which this muscle was controlled when
it was in its place in the body, has been carefully
dissected out and protected from drying so that it
is still alive. Its far end from the muscle is stirred
up by weak faradisation, and you see that the muscle
contracts — telling you by its contraction that it and

8

ANIMAL ELECTRICITY. LECTURE

its nerve are still alive — and at the same time you see
that the spot of light deflected one way by the current
of injury from T to L, moves the other way {i.e., under-
goes a negative variation) when the muscle contracts.
This negative movement of the spot means that the
chemico-physical change taking place in the con-

FiG. 4. — Muscle currents.

The "current of injury" is from T to L in the muscle. The "current of
action " (negative variation of the current of injury) is from L to T in the
muscle.

tracting muscle is greater at L than at T, or that L
has become zincative to T.

A little reflection will soon convince you that this
fact falls under our key principle. We started with
a current of injury due to a difference between T and
L ; T was active and zincative, therefore less capable
of further activity, i.e., less zincable than L. When
by exciting its nerve, we stirred up the whole muscle,
T and L included, we obtained a greater augmenta-

ANIMAL ELECTRICITY. LECTURE I. 9

tion of activity at L, the resting part, than at T, the
already active part. The current of injury generated
at T was due to a cHfference between T and L, its
negative variation generated at L was due to a
diminution of that difference. And there must be
a difference before there can be a diminution of
difference; there must be a current of injury for you
to get a negative variation of it. If the muscle had
been chemically homogeneous throughout, whether at
rest or in action, with therefore any two points T L
equally zincable or equally zincative, there could have
been no (or little) difference aroused between T and
L when both are equally (or nearly equally) altered.

Second Represent alive Experiment (on Nerve). —
In the first experiment (on muscle) the nerve was
used merely as an instrument to stir up the muscle,
and the muscle spoke in two ways — by an actual
movement of its substance, by a chemico-electrical
change revealed in the galvanometer.

In this second experiment (on nerve) the nerve
is to be used by itself, cut off from its natural organ
of expression, which is muscle, and connected by the
points T and L with a galvanometer that will serve
as an artificial organ of expression.

We shall begin by testing the nerve for current
of injury, expecting to find it directed in the nerve as
in the muscle from disturbed Transverse section to
undisturbed Lonoritudinal surface. And so it is.

Now, let us arouse the whole nerve — and for the

lO

ANIMAL ELECTRICITY. LECTURE

purpose of a distinct demonstration, I may hardly hope
to do so otherwise than by electrical stimulation — and
let us watch for a negative variation of our current
of injury. The variation is not large, but it is un-
mistakable ; (and while we are about it I will submit
it to two tests, the significance of which w^ll be
explained later — the test of direction and the test of

P^iG. 5. — Nerve currents.

The "current of injury" is from T to L in the nerve. The *' current of
action" (negative variation of the current of injury) is from L to T n the
nerve.

distance. I have now reversed the direction of the
electrical stimulation, and the variation has remained
negative and of unaltered magnitude. I have now
brought the exciting electrodes much nearer to the
leading out electrodes, from a distance of about 3 cm.
to one of about i cm, and I repeat the test with both
directions of stimulating current ; still the negative
variation remains nes^ative and of unaltered maoni-
tude. We are thereby entitled to conclude that the
effect was a ''true negative variation," and not due

ANIMAL ELECTRICITY. LECTURE I. 11

to current escape nor to du Bois-Reymond's electro-
tonic current.)

The value at which you will be disposed to
estimate the electrical signs of physiological activity
will be greatly enhanced by the closer consideration
of the first experiment (on muscle). Here you have
in the mechanical effects of muscular contraction, an
obvious measure of its physiological activity — ^the
muscle shortens much or little according as its phy-
siological activity is much or little, and one naturally
asks himself whether with this greater or smaller
mechanical effect there is a greater or smaller elec-
trical effect.

A very simple variation of the experiment will
answer us in the affirmative, and the records of
more prolonged observations will confirm that affirm-
ative beyond all doubt.

Let us go back to the experiment on muscle, and
make the muscle contract much or little, watching by
the oralvanometer to see whether the size of the elec-
trical effect corresponds. It is difficult to watch two
things at once, so in place of the muscle itself I
show you the end of a lever acted upon by the
muscle and marking against a smoked plate that
runs past the lantern ; the lever is the contraction
indicator, and the galvanometer is the current indi-
cator. If now you will watch the galvanometer
spot while the muscle is stimulated more or less
strongly, you will see that the spot makes a greater

12 ANIMAL ELECTRICITY. LECTURE I.

or smaller movement, and turning to the muscle
you will see that the muscle has contracted more
or less strongly.

This is a very simple but very important fact,
as a link in the argument that electrical changes
are a measure of physiological activity. More and
less muscular action involve more and less chemical
change, a larger and smaller diminution of the
current of injury. And whereas by arousing the
quiescent muscle you get a negative variation of
the current of injury, you would get a positive varia-
tion of the same by "quelling" an active muscle.
To be fully assured of this correspondence between
the mechanical and electrical effects of this one
cause — chemical activity, pray look at this double
record, where the white line gives series of contrac-
tions and the black line the corresponding series
of electrical effects of one and the same muscle
(fig. 6).

Each of the two series exhibits a declining effect —
the expression of muscular fatigue — and the rate of
decline is nearly the same in both cases. Not quite
the same, however ; if you examine the twin record
at all critically, there are evident divergences ; the
two records do not tell precisely the same story ; and
although the point is not one upon which we need
dwell now, I may observe that of the two versions —
the mechanical and the galvanometric — the latter is
the more accurate. It gives a declining series of

ANIMAL ELECTRICITY. — LECTURE I.

^\^[\SMU^

Fig. 6 (2462). — Simultaneous record of the mechanical and electrical responses
of a gastrocnemius muscle (frog), excited by tetanising currents for 7| seconds (60
to 70 interruptions per sec.) at intervals of I minute.

The upper line (white on black) gives the series of lifts of a weight of 10 grms.

The lower line (black on white) gives the corresponding series of electrical
effects ; the large deflections at beginning and end of the series are standard
deflections made by ^^ volt. Dead-beat galvanometer (shunted).

In the first and second pairs of responses the strengths of stimulation were 4
and 5 units ; in the third and subsequent pairs the stimulation was at 10 units.

14 ANIMAL ELFXTRICITY. LECTURE I.

which the tops He In a curve convex towards the base
line ; and if I had adopted a rather better mechanical
method (the so-called "isometric" method by which
the muscle is made to record its tension against that
of a stiff spring which allows the muscle to shorten
but very little) you would have witnessed a declining
series of tension effects much more like the gal-
vanometer series. But we shall come back to this
point in dealing with the subject of fatigue ; for the
present I am only concerned to establish in your
opinion that the galvanometer is a good indicator of
physiological modifications ; later I shall hope to
convince you that it is in this respect the best
and most accurate indicator at our disposal.

To watch the alterations of physiological activity
taking place in fatigue or under other influences it
matters little as regards the muscle itself whether
you make use of a lever or of a galvanometer as
your indicator. Each record is almost a replica of
the other, and contrary to your expectation perhaps,
the less obvious method by galvanometer, once the
preliminary difficulties have been overcome, is easier
to work, as well as far more delicate and more
accurate than the mechanical method.

More than one very significant inference arises
from this simple observation, but 1 shall only com-
ment upon one at this stage — to wit that the
electrical effect is an exact measure of action in
muscle, and may therefore be appealed to as a
measure of action in nerve.

ANIMAL ELECTRICITY.— LECTURE I. I 5

There is, however, one preHmlnary objection to
the unHmited admission of this conclusion that must
be taken at once.

We arouse action in the nerve by artificial
"stimulation," and our artificial stimuli may be elec-
trical, chemical, mechanical, 8cc. As a matter of
convenience we most frequently employ electrical
stimulation from an induction coil. May we be sure
that the animal electric effects are not due to our
electrical apparatus ? An exhaustive examination at
this stage of the means by which the answer is
obtained would lead us too far afield ; and I shall
content myself with saying that while electrical
effects aroused in nerve may sometimes be coarse
fallacies, and are in general most pronounced when
electrical stimulation has been used, yet they can
certainly be produced by non-electrical stimuli, and
even when produced by electrical stimuli, are phe-
nomena proper to the living state of nerve. Reasons
for admitting this will be offered presently by means
of anaesthetics, as soon as we have clearly appreciated
the bearing of this variation of our first experi-
ment (on muscle), in which an electrical effect results
from non-electrical excitation. The muscle is con-
nected as usual with the galvanometer by points
L and T, giving as usual the current of injury
from T to L (in the muscle). I now excite the
nerve by pinching it, i.e., non-electrically ; the muscle
contracts and the current of injury is at the same
time diminished.

I 6 ANIMAL ELECTRICITY. LECTURE I.

That has been an electrical effect of a non-
electrical excitation, and I mieht with a little care
and a rather more sensitive oalvanometer demon-
strate a similar effect on the isolated nerve ; finally,
I might proceed a step further, and show that an
electrical effect accompanies a natural discharge of
nerve-impulses, as well as the impulses aroused by
all artificial stimuli, whether these be or be not of
electrical origin. But to do this would be super-
fluous to my present purpose, which is simply to
show^ that an electrical stimulus Is not indispensable
to an electrical effect. Electrical stimulation is
however so conveniently applied, can be so nicely
timed and graduated, that except in a few rare
cases w^e shall systematically make use of it, and
it was therefore essential that you should realise
at the outset that the electrical nature of the effect
is not determined by the electrical nature of the
stimulus. Later, when we shall examine the elec-
trical effects manifested by the heart and by the
retina, we shall see cause to be still more fully
convinced of this.

In recollection of the fact that as regards muscle
the mechanical and electrical response to stimukition
run a nearly parallel course, and utilising the fact
first ascertained by du Bois-Reymond that an im-
pulse aroused at any part of a nerve Is conducted
in both directions from the stimulated point, we
may establish a comparison between the changes

ANIMAL ELECTRICITY. LECTURE I. IJ

in a nerve and those in the attached muscle, stimu-
lating the nerve in the middle of its course, using
as indicator of the state of the muscle its me-
chanical contraction, and as indicator of the state
of the nerve its electrical response. This has been
done in the experiment of which fig. 7 is the
record. The muscle has been attached to a lever
carrying a small paper flag that threw its shadow
through a slit upon a photographic plate, which at
the same time received the impression of a galvano-
metric spot of light moving in obedience to the
electrical changes in the nerve itself. The nerve
is stimulated once a minute ; the muscle at one end
of the nerve contracts, the galvanometer at the
other end of the nerve exhibits a negative variation.
The pointed shadows of the flag moved by the
muscle, give on the developed plate a record of the
behaviour of the muscle ; the excursions of the bright
spot give a record of the behaviour of the nerve.
Now the obvious points are these. By excitation
of one and the same nerve there has been a declining
series of muscular contractions and a uniform series
of negative variations of the nerve-current. The
muscle, to all appearance,^ is fatigued, while the nerve
exhibits no sign of fatigue. It is thus very clear
that muscle does not faithfully express the state of

^ As will be shown in a future lecture, it is more the nerve-
terminal (end-plate) than the muscle that is fatigued ; but this
has nothing to do with the present argument.
2

i8

ANIMAL ELECTRICITY. LECTURE

the nerve itself, but only that of the combined
organ formed of the nerve, the nerve-terminal and the
muscle. It is equally clear that to follow the changes
taking place in the nerve, the galvanometer is prefer-
able to the muscle. And, finally, if once we are

ill I n

I n I

I lllilii miiniiiiiim

Fig. 7 (139). — Simultaneous record of the electrical response of nerve (upper
line), and of the mechanical response of muscle (lower line).

Stimulation at 10 units throughout. Ordinary galvanometer.

assured that the electrical indications are a true index
to the physiological state of nerve, regarded simply as
an excitable strand of protoplasm, it is evident that the
mathematical regularity of its electrical response to
regular electrical stimuli during long periods of time,
offers the best possible conditions and the best possible
object upon which to test the physiological modifica-

ANIMAL ELECTRICITY. LECTURE I. I9

tioiis, effected or not effected, by all kinds of chemical
and physical interference.

But this very regularity of response has a suspi-
ciously non-physiological appearance. The first thing
to do is to make sure whether or no it is physiological,
and the first step to take is to test it by anaesthetic
vapours. The best and most expeditious anaesthetic
to employ for this purpose is ether (diethyl oxide).

Experivient. — The nerve resting upon two pairs
of unpolarisable electrodes, one pair for the exciting-
current, the other serving to lead off the current of
Injury and Its negative variation to the galvanometer
(as shown In figs. 5 and 10), is enclosed in a glass
chamber into which air saturated with ether vapour
can be blown. The negative variation having been
provoked once or twice by completing the exciting
circuit, and having been found to be sufficiently large
and sufficiently regular, ether vapour is blown Into the
nerve chamber. The negative variation is tested for
at Intervals during the next two or three minutes ; it
is seen to diminish and to disappear. This abolition
of the negative variation by ether is not permanent ; at
the end of five or ten minutes the negative variation
reappears and gradually increases up to, and it may be,
beyond the normal.

This experiment (fig. 8), which represents the
regular and unfailing consequence of the etherisation
of a nerve, proves that the electrical effect we are
dealing with is a physiological phenomenon.

20 ANIMAL ELECTRICITY. LECTURE I.

The first thought that suggests itself when one
has seen by what a surprisingly regular series of
electrical effects the nerve responds if regularly
interrogated at regular intervals, and when one has
satisfied oneself further that such electrical response is
physiological, is that we are in possession of a most
excellent test by which to recognise the action of
chemical reagents upon the physiological properties
of nerve.

For the test is applied to nerve and to nerve only.
There is not, as when muscular contraction is used as
the indicator, any question as to the share borne by
muscle or by motor end plate. The experimental
isolation of the object of observation is complete. It
does not move. The excitation by which it is tested
does not exhaust its excitability. It is a subsidiary,
but by no means slight, advantage, that the photo-
graphic record of each and every observation can be
easily taken, and preserved for future reference, and
be as authoritative a century hence as it is to-day.
The nerve has recorded its own series of answers
during any treatment to which you may have chosen
to submit it ; it cannot give a false answer ; the worst
that may happen is that it may give some spurious
answer to a spurious question, or that we may for the
moment fail to correctly interpret the language in
which its answers are returned.

A good instance to take in illustration will be to
compare the action of different ana;sthetics, and I will

AM.MAL I'LKCTRICITV.- LECTURE I. 2 1

at once set i^oini^- a chloroform observation on nerve
in the manner now familiar to you, in order to
allow time for the observation to be sufficiently
cooent as regards one main fact in the subject,
viz., that chloroform is far more powerfully toxic
than ether, that its full effect is apt to be final,
not followed by recovery within any reasonable
lapse of time. Obviously this is a point of great
practical significance, that may at any moment be-
come a matter of urgent personal anxiety ; and in
what I shall have to say it will be impossible not
to make statements having immediate practical appli-
cations. My experiments were not, however, pri-
marily addressed to the practical issue ; they were
instituted solely for the purpose of testing the value
of nerve towards its further utilisation as a test-
object. And after all, anxious as I am not to
infringe upon medical matters in presence of a non-
medical audience, I shall prefer to explicitly formu-
late the inference as it presents itself to my mind,
thinking on the non-medical lines of a purely scien-
tific student, rather than to leave a perhaps hasty
and popular inference to be drawn less guardedly
and cautiouslv than mioht seem to be desirable.

This is the jubilee year — the jubilee day in fact—
of the first trial of chloroform as an anaesthetic. On
January 19, 1847, Sir James Simpson performed his
first operation under chloroform anaesthesia. The
manifestly beneficent effects of this powerful anaesthetic

2 2 ANIMAL ELECTRICITY. LECTURE I.

led to its widespread preference over all prior and
subsequent rivals, so that in this country at least,
the designation " chloroformist " has almost become
synonymous with ''anaesthetist," and many surgeons —
Lord Lister at their head — put all other anaesthetic
agents aside in favour of chloroform. Nevertheless,
like all potent drugs — potent because they are toxic —
perhaps above most potent drugs — chloroform, while
conferring quickly and effectually the great boon of
unconsciousness, exacts heavy toll. Not too heavy,
perhaps, if chloroform were the only anaesthetic in the
field, but far too heavy when we consider that there
are other, if less potent anesthetics to hand, amply
adequate to the needs of nine-tenths of the cases for
which chloroform has been used with fatal results. ^

It has been said that experimental physiology has
afforded no guidance in the use of anaesthetics — that
clinical experience is our only guide. I demur to this
statement, and shall ait once exhibit to you a contrast
experiment representing, as in a nutshell, the compara-
tive efficacy of these two principal re-agents.

^ Dr. Lauder-Brunton, although pleading emphatically in favour
of chloroform as against ether, expresses himself as follows in his
Text-Book of Pharmacology (3rd Ed., 1893, P- ^o^) •

"The operations in which death during chloroform chiefly
" occurs are short and comparatively slight, though painful, such
*' as extraction of teeth, and evulsion of the toe-nail — operations
'* in which the introduction of deep chloroform anaesthesia might
'* be regarded as superfluous, and involving a waste of time."

ANIMAL ELECTRICITY. LECTURE I.

!lthtlhl!itlli

Before. Ether.

After.

Fig. 8 (576). — Effect of ether (diethyl oxide, EtoO) upon the electrical
responses of isolated nerve. The electrical response is abolished for about five
minutes ; it then gradually recovers, and becomes somewhat larger than it was
before etherisation. The excitations and responses of the nerve are at intervals
of one minute.

Before. Chloroform. After.

Fig. 9 (552).— Effect of chloroform (Trichlormethane, CHCI3) upon the
electrical responses of isolated nerve. The electrical response is definitively
abolished ; there is no recovery during the period of observation.

24 ANIMAL ELECTRICITY. LECTURE I.

The action of ether you have just witnessed ; the
effect was quite typical — an aboHtion of excitability
consummated in about three minutes, and lasting
another five minutes.

But how about chloroform ? I applied it in strong
vapour for one minute nearly half-an-hour ago, and you
then saw that the "excitability" was promptly abol-
ished; on testing it now, you see that nothing happens;
the nerve has definitively lost its excitability — you have
witnessed its "death by chloroform."

Those are the facts in the rough — no slight differ-
ence of degree, but a striking contrast. There are
many accessory considerations to be weighed ; ob-
viously a question of this moment is not settled by a
single experiment. How about quantity? The nerve
has had in each case a maximum dose, i.e., for a period
of one minute, air saturated with the drug, i.e., with
about 50 per cent, of ether and about 1 2 per cent, of
chloroform. And to what extent may you argue from
a naked tag of nerve to the complex human organisa-
tion ? We shall not settle these matters offhand. We
have seen that there is a similarity between the
effects of anaesthetics on a living nerve and on a
living organism ; our next task will be to examine
some of the cases in which their effects differ.

ANIMAL ELKCTRICITV. LECTURE I. 25

HISTORICAL NOTE.

" Animal electricity " {i.e., the electrical phenomena mani-
fested by animals), is now a century old. In its bio^^raphy
the names of Galvani, Volta, Aldini, Matteucci, du Bois-
Reymond, Hermann, and Bernstein, stand out as the prin-
cipal marks, together with three somewhat bitter but fruitful
controversies between Galvani and Volta (about 1794), be-
tween Matteucci and du Bois-Reymond (about 1850), and
between du Bois-Reymond and Hermann (about 1867).

An admirable account of the Galvani v. Volta polemic is
given by du Bois-Reymond in his " Untersuchungen Uber
Thierische Elektricitat " (Berlin, 1848-49-84), but the un-
favourable verdict there passed upon the part played by
Aldini in "these troubled waters," is, in my opinion, not
borne out by the evidence.

"Animal electricity" may be considered as having taken
origin from the observation by Luigi Galvani (or, according
to some writers, by his wife Lucia), of spasms occurring, to
all appearance spontaneously, in the legs of frogs prepared
for the kitchen and suspended by copper ("copper" in 1791,
"iron" in 1786J hooks to an iron railing. Did the act of
discovery arise from Luigi or from Lucia ? Which of them
on noticing the frog twitch first said " ecco ! " might be
interesting to know, but is of little moment. There are,
however, certain points relating to the Galvani household
that call for mention. At this period, Aldini, a nephew of
Galvani, who was professor of Physics in 1793, was pursuing
his studies in the University of Bologna, and was living in
Galvani's house.

The memoirs bearing on the subject arc : —

1. Galvani. De viribus elcctricitatis in motu musculari

commentarius. Bologna, 1791.

2. Do., ristampate a Modena, 1792, con note e una dis-

sertatione del Prof. G. Aldini (De animalis electrical
theoriije).

26 ANIMAL ELECTRICITY. LECTURE I.

3. Deir uso e dell' attivita dell' arco conduttore nelle con-

trazioni dei muscoli. Anonymous. Bologna, 1794.

4. Do., Supplemento. Bologna? 1794.

The two representative experiments are : —

1. The contraction with metals.

2. The contraction without metals.

The principal difference between Galvani and Volta was
that according to the former the contraction with metals in
the circuit, was due to animal electricity conducted by the
metal, while according to the latter it was due to an excita-
tion by ordinary electricity aroused by contact of dissimilar
metals. The contraction with metals did not prove the
existence of animal electricity. This could only be done by
an experiment in which none but animal tissues were in
circuit. Thus the origin of "Animal Electricity" becomes
fixed at the " contraction without metals."

This experiment is first mentioned in the anonymous
Trattato of 1794, not in Galvani's Commentary of 1791.

Who was the author of the anonymous " Trattato," and
who therefore was the author of the " Contraction without
metals"? Aldini in his "Essai sur le Galvanisme " alludes to
the experiment as his own. But there is nothing to indicate
whether Aldini or Galvani was the author of the Trattato.

On the other hand, Gerhardi in his annotations to the
" Opere edite ed inedite del Professore Luigi Galvani,"
Bologna, 1841, and Du Bois-Reymond in his " Thierische
Elektricitat," unhesitatingly attribute the anonymous Trattato,
including the important experiment, to Galvani alone as the
" vero ed unico autore."

The manuscript of this Trattato, said by du Bois-
Reymond to be preserved at the University Library of
Bologna, and to be partly in Galvani's handwriting and
partly in another's handwriting, is not now to be found.
With regard to this, we are therefore thrown back upon
probabilities, and these in my opinion, indicate at least a joint
authorship of the Trattato, certainly not the exclusive author-
ship of Galvani, and certainly not a plagiarism by Aldini.

ANIMAL ELECTRICITY.— LFXTURE I. 2"]

In 1794 (the date of its publication) Galvani was 57 years
of age, professor of obstetrics and rector of the University —
having previously held the chair of Anatomy, and published
the following memoirs: de Ossibus 1762; de Rcnibus 1767;
de Manzoliniana Supellectili 1777; de Volatilium aure 1783 ;
and de Viribus Electricitatis in motu musculari Commentarius

1791.

While at the same date Aldini his nephew, who had long
been a member of his household, was 32 years of age, and
professor of physics in the University. In 1792 he published
his Dissertation " De animalis electrical theoria^ ortu atque
incrementis." In 1796 it is he who demonstrates the new
electrical experiments to Napoleon during his Italian cam-
paign, and it is to Aldini, not to Galvani, that all Volta's
controversial correspondence was addressed.

Matteucci's contributions to the subject are numerous and
scattered — in Italian, French and English literature of the
time, 1830-50. His " Essai sur les Phenomenes electriques
des Animaux," Paris, 1840, placed by Mliller in the hands of
du Bois-Reymond, was the starting-point of the latter's life-
long labours. This " Essai '' was expanded to a " Traite des
phenomenes electro - physiologiques des Animaux," Paris,
1844, and to his "Cours d'Electrophysiologie," Paris, 1858.
Matteucci's permanent legacy to the subject is " the Second-
ary Contraction " described by him in the Philosophical Trans-
actions of the R. S. for 1845, under the title of " The induced
contraction," and referred by du Bois-Reymond to an excita-
tion of the secondary nerve by the negative variation of the
primary muscle.

The differing points of view of the two men are thus given
by du Bois-Reymond in the Preface of his " Thierische Elek-
tricitat": "According to him [Matteucci] there are no elec-
" trical currents in the nerve. The muscle-current circulates
" in the muscle only after certain modifications due to pre-
" paration, and is in no relation with its contraction. The
" so-called nervous principle is to him from first to last a
" special hypothetical mode of motion, which he chooses to

28 ANIMAL ELECTRICITY. — LECTURE I.

" represent under the figure of the ether vibrations, holding it,
" under all conditions, absolutely distinct from electricity. I,
" on the contrary, am in favour of a diametrically opposite
" view. If I do not greatly deceive myself, I have succeeded
" in realising in full actuality (albeit under a slightly different
"aspect) the hundred years' dream of physicists and physio-
" logists, to wit, the identity of the nervous principle with
" electricity."

Yet du Bois-Reymond was no vitalist ; his animating
thought was to analyse the "vital forces" and to find their
physical and chemical components. His endeavours con-
centrated themselves upon the study of living nerve and
muscle, of their electrical manifestations in particular. He
laid, perhaps, undue stress upon these manifestations by
presenting them as evidence of an identity between the
nervous principle and electricity. In his view a filament of
nerve was a string of dipolar electromotive molecules, posi-
tive at their middle and negative at their two ends; between
longitudinal surface and transverse end a current exists
(current o{ rest) which undergoes a diminution (negative
variation) during excitation of the nerve or of the muscle.
In the electrotonic state (Lecture V.) the molecules are re-
adjusted with negative poles towards the anode and positive
poles towards the kathode.

Hermann's presentation of matters differs from the above
in several particulars. Electrical differences of potential do
not pre-exist in normal nerve or muscle, but are the con-
sequence of injury and of physiological activity. Injured
points are electronegative to normal points. Physiologically
active points are electronegative to resting points. Du Bois'
negative variation is an action-current. Du Bois' electro-
tonic currents are the effect of electrolysis.

ANIMAL 1:LECTRICITV. — LECTURE I

REFERENCES.

The controversy between du Bois-Reymond and Hcrinann
is scattered through several memoirs. Du Hois-Rey-
mond's case is given in his Gesamuielte Abliandliingeii,
vol. ii., Leipzig, 1877, p. 319 (reprint of paper of 1867).
Hermann's case is given in his Handbiick der Physiologie,
vol. i., p. 235 (Leipzig, 1879).

A compromise between the two theories is proposed by
Bernstein in U ntei^siiclmngen aiis dein PhysiologiscJien
Institute Halle, 1888, reproduced in Bernstein's LehrbncJi
der Physiologie (1894), pp. 359, 449. The newer litera-
ture of the whole subject is given in Biedermann's
ElektropJiysiologie^ Jena, 1895, English translation by
F. A. Welby : Macmillan & Co. The theory of the
"current of injury," or ''demarcation current," was first
given by Hermann in 1867, and is very fully described
in his HaiidbucJi der Physiologie, vol. i., p. 235.

The negative variation of the currents of muscle and of nerve
was discovered by du Bois-Reymond in 1843 {^TJiierische
Elel^tricitdt, vol. i., p. 425). It is now frequently referred
to as the " current of action."

The literature of anaesthetics is a very extensive one.
Among the best general accounts of the subject may
be named Claude Bernard's Leqons sur les AncEsthetiqiies
et sur I'Asphyxie, Paris, 1875, and Snow's " CJdorofonn "
(edited by Richardson), London, 1858.

30

LECTURE U,

CONTENTS.

Description of method. Illustration of Ohm's law. Dead-beat
and oscillating magnet. Alcohol, soda water, tobacco
smoke. Carbonic acid. The function of respiration. In-
tegration and disintegration. Action of carbonic acid in
further detail.

The value of experimental results depends above
all upon the method by which they may have been
obtained, and the great end of any method is that it
shall stringently insulate from amid a crowd of pos-
sibilities the particular phenomenon to be qualitatively
observed, and if practicable, quantitatively measured.
It is of the first importance that the method of inquiry
should be precisely given, for that method gives
measure of the degree of simplicity and therefore of
cogency to which experimental analysis and criticism
have been carried.

And short of this, even for the simple interchange
of information, such as students of particular branches
of science might desire from each other, it is necessary
that the instrumental means by which each expert
reads his little bit of natural knowledge should be
clearly understood. Each province of knowledge has

ANIMAL ELECTRICITV. LECTURE H. 31

indeed its own language, instrumental as well as
verbal, and it only happens too often that students of
closely allied phenomena fail to exchange lights for no
other reason than that they do not understand each
other's jargon.

The first steps in a language are generally the
dullest and most repulsive, but only by reason of
those steps taken does any language bear its message
to us. Where can be the interest of black marks on
paper if we cannot read them, or of a spot of light
wandering along a scale if we do not know what it is
saying.

''Current," "Pressure," "Resistance," "Galvano-
meter," are some of the ABC labels that must have
some meaning for us before we may be permitted to
proceed a step further otherwise than as sham
students.

Well, these labels having a meaning for us — I do
not say their full and complete meaning — ^I should
next ask you to make sure that we understand what is
meant by saying that "current varies with pressure
and inversely as resistance," and then being sure of
my ground, I should invite you to follow me in the
not very complicated details of the special case here
figured.

The central object is the nerve, lying upon two
pairs of electrodes, inside a glass chamber, through
which gases and vapours can be driven. The nerve
must not dry, therefore gases are made to pass in

32 ANIMAL ELECTRICITY. LECTURE II.

through a wash-bottle half full of water. Through
the electrodes T and L the current of injury of
the otherwise undisturbed nerve passes to the key-
board. The other pair of electrodes {Exc.) are
connected with an induction coil ; a circular com-
mutator revolving once a minute sets up excitation
at minute intervals, and each time this happens there
is a negative variation of the current of injury. A
reverser enables the direction of the exciting currents
to be changed at will.

The keyboard is made up of four keys, K, con-
nected with the nerve, K. with a galvanometer, K^
with a compensator, K^ with a second galvanometer.

When all four keys are closed, the board is simply
a square of metal. When K, is opened, a mouth is
made by which the nerve currents are let into the
square. When in addition K3 is opened, a mouth is
made by which the nerve currents are let out of the
square to the galvanometer. On the same principle
when K^ is opened, a standardising current is let into
the square, and thence through the nerve and the
galvanometer, and if need be the fourth key, K^, is
connected with a second galvanometer ; if there is no
such galvanometer in use, K^ is left closed.

The galvanometer, by which your nerve currents
are measured, consists essentially of a suspended
system of litde magnets fixed to the back of a light
mirror, which reflects a beam of light on to a scale.
The nerve currents traverse a coil of fine wire sur-

ANIMAL ELECTRICITY. LECTURE U.

33

^^e;:i^4^

Sec:C.

Fig io.

Plan of Apparatus.
(This figure is repeated on a fly-leaf at the end of the volume.)

34 ANIMAL ELKCTRICITV. LECTURE II.

rounding the magnets, deflect them, and with them
the mirror and beam of Ho^ht which moves rieht
and left on the scale, serving as a pointer to the
amount of deflection, which is an indicator of the
amount of current. The light moves right and
left on the scale ; replace the scale by a screen
with a horizontal slit, arrange a photographic plate
to descend vertically behind the screen, darken the
galvanometer room, and your pointer of light makes
its mark, and all its movements come out on the
developed plate as black lines on a clear background ;
you have a recording galvanometer.

It is a orreat convenience to have such an in-
strument by itself in a dark room well away from
coils and keys and moving people, and it is well
to leave the recorder severely to itself once adjusted
and started. But it is also very convenient to know
what is going on. This is effected by a second
galvanometer attached to K^, upon which all that
is happening in the dark room can be watched on
a scale in the usual way. , The resistance in circuit
added by the second galvanometer is of no moment^
that of the bit of nerve between T and L is already
100,000 ohms, that of the second galvanometer is
perhaps 10,000.

In the figure the galvanometer (and mirror) are
as if viewed from the back, the sensitive plate faces
you. Imagine K, and K3 open, so that the nerve
current passes through the galvanometer, and trace

ANIMAL ELECTRICITY. — LECTURE II. 35

the current from T to L, you will find that it will
be from S to N through the galvanometer, like-
wise that the negative variation from L to T will
he from N to S, and when we see the record that
1 am about to take during the next half hour, you
will realise as convenient and natural that the plate
should be turned to show deflections up and down
instead of right and left. The negative variation
then reads downwards, the current to which it is
negative reads upwards.

I have not yet noticed the apparatus connected
with K, for ''Graduation or Compensation," but
you will readily appreciate its use if you know that
current increases as pressure and inversely as resist-
ance.

Take a case like this : you have made an experi-
ment with carbon dioxide, let us say, and on measur-
ing out the record you have a negative deflection of
10 before and 20 after carbon dioxide. The current
has doubled, but this might be by doubled pressure
or by halved resistance, or from a mixture of the
two changes. You do not know where you are, but
you would do so at once if you had as terms of com-
parison the deflections made by a convenient standard
pressure before and after carbon dioxide. If they
were found equal, then the resistance is known to be
unaltered, and the augmented deflection was due to
pressure only. And from any inequality you would
be able to correct for resistance. If the standard

36 ANIMAL ELECTRICITY. — LECTURE 11.

deflection had fallen from lo to 9 then your deflection
20 indicates a pressure of 20 x ^, if it had risen
from 10 to 12, then the deflection 20 indicates pres-
sure of 20 X j|.

For nerve, it is convenient to take as a standard
the deflection by —^ volt (for muscle we shall take it
by ,^„- volt, for the retina by ~^ volt). Say that the
pressure of the cell is i volt, this will be done by
taking two resistances in the proportion of i and 999
(large enough at any rate to let us neglect the internal
resistance of the cell), connecting the cell with the two
extremes, and the key K^ with the two ends of the
smaller resistance. This is because the difference of
pressure at the two extremes being i volt, and falling
progressively from beginning to end in proportion with
resistance, if we take a given resistance between any
two points (say i ohm), we shall have a difference of
pressure between those two points equal to ^r^g or
^ of the total between the two extremes

For all our purposes it will be sufficient to take a
Leclanche cell (assumed as 1-45 volt) and fixed re-
sistances (i and 1450 ohms) to deliver -^ volt. And
as a matter of practical convenience, which will be
found a convenient ear-mark for reading our plates,
we shall put up connections so as always to take this
standard deflection in one direction, viz., towards the
left or S or negative side of the scale, i.e., downwards
on the completed record.

The usual way of measuring pressure or potential is.

ANIMAL ELECTRICITY. LECTURE II. 2)1

however, by compensation, and you may, if desired,
use the resistance boxes r R for this purpose. You
have only to see that the current from r opposes the
nerve current at the keyboard, and by successive trials
find that value of r + u. ^.t w^hich there is no current
through the galvanometer. The nerve current is then
compensated or balanced just as a given mass in one
scale-pan is balanced by an equal weight in another
scale-pan. Say, e.g., that the nerve current is balanced
when -fi^^ is J°^^ then — taking the pressure of the
Leclanche cell at i -5 volt — the pressure of your nerve
current is 0*015 volt.

It has been customary to take observations of the
excitatory changes (negative variation, &c.) of nerve,
with such compensation in force, and for rheotome
observations this is necessary. But for observations
such as these it is a mistake to use a compensating
current ; in its presence we have opposing each other
in the nerve {a) the injury current from T to L ; {b)
the compensator current from L to T. and the latter
current has its anode at L. We shall find later that
a foreign (polarising) current increases the zincability
of living nerve at its point of entrance or anode. ^
The negative deflection due to excitation and zinca-
tivity aroused at L is therefore unduly exaggerated —
reinforced by what we shall recognise as the polarisa-
tion increment of the compensating current.

^ See below, the polarisation increment, p. 135.

38

ANIMAL ELECTRICITY. LECTURE II.

We shall therefore neglect compensation, and if
the nerve current is so large as to send the spot " off
scale" or ''off plate," readjust the deflection by means
of a controlling magnet such as that fixed above the
case of Thomson (Kelvin) galvanometers.

We shall have yet another use to make of the re~
sistances r R when we come to study the polarisa-
tion increment. We shall then require to deliver to
the nerve, pressures of, say, o"i, 0*2, 0*3, &c., volt, and
shall do this without altering the connections, by ad-
justment'of the resistances.

I will illustrate the use of these resistances, and at
the same time give an example of the principle that
deflection (by current) varies directly as pressure, and
inversely as resistance, by the following pair of
experiments. This is the circuit (fig. 11); it need

V5L

Fig. II. — A Compensator.

not be separately put up ; it is sufficient to close the
superfluous keys K, and K^ of the circuit as given in
fig. 10, leaving only K3 and K^ open.

ANIMAL ELKCTRICITV. — LKCTURK !!. 39

I will take r small and R large, so as to take R
as a sufficiently accurate denominator of the fraction
iT^j^. Taking R at, say, 100,000 ohms., and r
successively at i, 2, 3, 4 ohms, you see that the
deflections are i, 2, 3, 4, i.e., current varies directly
as pressure. Taking r at, say, 4 ohms, and R at
100,000, 200,000, 300,000, 400,000, the deflections
are 4, 2, i^, i, i.e., as i, \, \, \, i.e., current varies
inversely as resistance, which you may recognise as
an instance of the fundamental principle known as
Ohm's Law.

Fig. 12. — Records of deflections by the dead-beat and by the ordinary
(partially damped) galvanometer.

The time-records are in quarter-minutes; the "falling time" of the dead-
beat magnet is about 15 seconds; the partially-damped magnet has 7 com-
plete oscillations in I minute, i.e., an oscillation period of %\ seconds.

In the galvanometer now at work before you the
movements of the magnet are partially damped ; you
see that at each deflection the spot swings to and fro,
above and below its position of rest, by a series of
diminishing oscillations. Many of the records you

40 ANIMAL ELECTRICITY. LECTURE II.

have seen have been taken with a galvanometer of
this character ; others have been taken with a fully-
damped or dead-beat instrument, in which the magnet
comes slowly to its position of rest without overshoot
or oscillations.

Each instrument has its advantages and dis-
advantages. The former is more sensitive, and
best adapted to show effects of short duration,
the latter to show more prolonged effects uncom-
plicated by oscillation ; and for after-effects in the
nerve they supplement each other. The time of
an oscillation to and fro, or " oeriod " of the partially-
damped magnet Is, say, eight seconds, and the range
of a swing is, say, double that of the next swing, i.e.y
the ''decrement" is 2. A swing, caused by an
electrical change lasting four seconds and ending
abruptly, will be followed by an instrumental after-
deflection In the opposite direction of, say, ^,
or about 07 of the original swing. And if the
change, Instead of ending abruptly, either goes on
of the same character, or gives way to an opposed
after-change, we shall have the after-oscillation either
checked and reduced, or helped on and augmented.
If this reduction or augmentation is very pronounced,
we shall be justified In saying that within the four
seconds Immediately after an excitation has ceased,
the after-state of the nerve has been like or unlike
Its state during the excitation. It would not do to
lay too much stress on slight alter^itions, but coarse

ANIMAL ELECTRICITY. LECTURE If. 4 1

alterations such as those exemplified in fios. 26 and
27 are not ambiguous.

With a dead-beat magnet, which moves sluggishly,
as if plunged in a sticky fluid, matters are quite
different. The time it takes to pass from one posi-
tion of rest to another is its " risincr " or " fallincr " time.
Any brief impulse that it may receive is lost ; and
while it is falling back to a position of rest at the
termination of an effect, it will not show whether
the after-state is positive or negative to the previous
state. It is only if the after-state is very prolonged,
in comparison with the falling time, fifteen seconds,
that the magnet will indicate its presence, and then
we practically only get signs of the after-state from
the end of the falling time onw^ards.

Thus, however, the two kinds of magnet supple-
ment each other as witnesses ; both indicate the state
durino- excitation, the swino^ino- mao-net indicates the
state immediately after excitation, the dead-beat
magnet the state during a later period after excitation.

Let us now turn to perhaps more familiar matters,
and make use of this apparatus to test the effects upon
nerve, of alcohol, soda water and tobacco smoke.

A nerve is lying upon its electrodes in the moist
chamber (fig. 10). The wash-bottle is half full of fresh
soda water, all the keys are closed, the galvanometer
spot is at zero. I open K, (from the nerve) and K3 (to
the galvanometer) and the spot moves half across the

42 ANIMAL ELECTRICITY. LECTURE II.

scale by reason of the current of injury from T to L
in the nerve. What is the value of the pressure
difference between T and L a-ivine that current ?
I open K2 from the graduation coils, and find that
the ,-^ volt oives i degree deflection, therefore the
current of injury that gives 8 degrees, is by a pres-
sure of ,^„ volt. Now let us start the excitation by
which the nerve is questioned, and watch the negative
deflection that is its answ^er. It is a fairly good one —
about I i degree, i.e., 0*0015 volt. Now for the soda
water. I am passing air through it into the nerve-
chamber for one minute. The first deflection after
this is not much altered, but a minute later it is
distinctly larger, and at the third minute it is about
doubled. Is this greater deflection due to raised
pressure or lowered resistance .^ The standard pres-
sure of j^ volt let into the circuit by opening K, is
unaltered ; therefore the augmented deflection is due
to augmented pressure, not to diminished resistance.

We go through the same steps with tobacco smoke
on a fresh nerve, and the result is precisely similar —
even more marked than in the previous experiment.
Like soda water, tobacco smoke is a stimulant.

And now to bring these trivial experiments to a
close, we will try the effect of strong alcohol, driving-
its vapour as before into the nerve-chamber. The
response of the nerve is promptly abolished. The
nerve seems to be dead, but is in reality no more
than •' dead-drunk " ; I have little doubt of its

ANIMAL ELKCTRICITV. LECTURE II.

43

'.^}^^^^vv^J

M

Fig. 13 (2466). — Effect of " soda water " upon the electrical responses of
isolated nerve.

The vertical dark bar indicates when the "soda water" acts on the nerve.

The deflections at beginning and end of the series are standard deflections
by ToW volt.

,^^^^\^\v,

Fig. 14 (2464). — Effect of alcohol vapour (ethylic alcohol, EtOH).

^-^-r.r,^'

h

'ji

i t

i i

,'!i?fIHTrrrr

Fig. 15 (2468). — Effect of tobacco smoke on the same nerve (2464) twelve
hours later.

44 ANIMAL ELECTRICITY. LECTURE II.

recovery within a few hours, ahiiost certainly by to-
morrow morning.

Let us pause now to consider the effects of these
three experiments, which are chosen on purpose to
enforce the principle insisted upon at my last lecture,
that living matter in the shape of a nerve, may give
us some clue to the action of drugs on the living body.
The soda w^ater has acted evidently by reason of its
dissolved gas, which is carbon dioxide. The tobacco
smoke has very likely acted by reason of the same
constituent, carbon dioxide ; still I am not prepared
to say that no other constituent of tobacco smoke is
active, since I have not yet tried the effect of tobacco
smoke deprived of its CO^.

Alcohol (that Is to say ethylic alcohol, EtOH ; we
shall on some future occasion have something to say
about other alcohols) has, in the way we used it, acted
as a profound depressant. If we had been very
careful, we might have witnessed on the nerve its
preliminary exhilarant effect. As to how it acts, I
do not wish to be positive, but may remark that it
not improbably acts by depriving the nerve of water
— the effects of alcohol vapour and of drying are very
much alike, and so indeed is that of prussic acid-^a
point that might perhaps be very effectively made u^e
of by a temperance advocate. But such a person
would probably omit to comment upon the effect lof
pure water, which very promptly puts an end to the
nerve. Here, however, we come to a point of diverg-

ANIMAL ELl'XTRICITY. — LECTURK H.

ence between the bit of nerve and the entire organism ;
pure water has certainly no such toxic effect on man as
it has when directly applied to one of his tissues.

Of the several materials just alluded to, by far
the most interesting and important is the gas, carbon
dioxide. It has perhaps been a little unfortunate that
I fell into the hands of carbon dioxide so early
in the investigation, for its allurements have been so
great, the hints it has vouchsafed have been so
significant yet so mysterious, that it has crushed out
nearly all other claimants upon my time, and pre-
vented me from pursuing as extensively as I could
wish that superficial survey of a large number of
chemical reagents which in the infancy period of
an inquiry is the necessary preliminary to further
and deeper analysis of the mode of action of a
few chosen substances.

Nevertheless, considering that carbonic acid is
one of the two principal disintegration products of
all living matter — the vehicle of the respiratory
export of carbon from the organism — that it produces
with unmistakeable clearness effects that might have
been predicted a priori were we only endowed with
sufficient imaginative wit ; considering further, that
from these data we shall be able to draw inferences
as to the existence and nature of physical changes
effected within the nerve itself, and put those infer-
ences to the test of clear-cut experiment, I cannot

46 ANIMAL ELECTRICITY. LECTURE II.

reoard it as matter for reoret that so much time
should have been necessary to investigate carbonic
acid at all thoroughly. And after all two years is
not so very long, but the investigation is not near

its end.

Let me at once, before entering upon any close
analysis, exhibit to you two observations that represent
the regular and typical action of carbonic acid upon
nerve. The first of these two figures shows that
carbonic acid in small quantity acts as a "stimulant."
The next figure shows that carbonic acid in large
quantity acts as a narcotic. It is in fact a typical
anaesthetic — excitant when its action is slight (fig. 16),
depressant when its action is complete (fig. 17).

It will not be amiss if at this stage I invite you
to make a brief digression in order to recognise
the relations of carbon dioxide in the economy of
living matter, and perhaps broaden the view you
may have formed of the respiratory function. It
happened to me a few years ago to overhear a con-
versation in a conservatory between a young gentle-
man and a young lady. They were discussing the
plants, and the two disputants (they were of quite
tender years, nine and eight respectively) took up
what struck me as very typical standpoints. The
man-child said "of course plants breathe, how
could they live if they didn't breathe " ; the woman-
child said "of course plants don't breathe, how
can they breathe without lungs." Well, of course —

ANIMAL ELECTRICITV.— LKCTURE II. 47

Before. CO.. A Tier.

Fig. 16 (674).— Effect of " little " CO.,. Primary Excitation.

Aftei

Fig. 17 (627).— Effect of " much " C0._,. Complete An^vsthesia followed by
Secondary Excitation.

4d ANIMAL ELECTRICITY.- — LECTURE II.

the woman crot the best of the arorument, but the
man was right, and gave evidence, I think, of
superior imaginative power. We breathe by lungs,
so do all our personal friends among animals ; but
fishes breathe by gills, plants breathe by leaves,
and protoplasm, devoid though it be of diverse parts
or organs, breathes by direct take and give between
itself and the atmosphere. And in an organism
where the living units are buried away from the
atmosphere, lungs or gills, heart vessels and blood
are the intermediate instruments of this take and
give between protoplasm and air. Protoplasm, then,
directly or indirectly, takes from the air oxygen, and
gives to the air carbon dioxide, and such respira-
tion is the primitive essential function to which the
instrumental means — organs of respiration, organs
of circulation — are secondary and accessory compli-
cations.

It has been said that "respiration is a slow com-
bustion," and Black, a century and a half ago, fifty
years before the discovery of oxygen by Priestley, and
the closer identification by the Lavoisier school of
respiration with combustion, showed that the end-
product of respiration is identical with that of com-
bustion. And even to-day, if we bear in mind that
the carbon dioxide produced by respiration (as indeed
that produced by combustion) is not a product of
direct 6xidation — that carbon and oxygen do not, so to
speak, meet and join hands directly, either in the lungs,

ANIMAL ELECTRICITY. LECTURE II. 49

or in the blood, or in the tissues, and straightway run
down hill together — I think the phrase " respiration
is a slow combustion " is permissible. Oxygen, the
incoming "food" — for oxygen is even a more imme-
diately necessary " food " than water, bread and meat —
first climbs a mountain where it is lost to view, as a
member of that mysterious company of atoms we call
''proteid,"^ which have power to act, which by acting
are expended, yielding to the body movements that
are the expression of its life, heat which is a sine qua
lion of its action, and carbon dioxide which is the
token and measure of its activity.

The immediate antecedent of physiological activity
is chemical change — a disintegration of "inogen," of
which at least one end-product is carbon dioxide.
Living tissue is deoxydative or reducing towards the
oxygen-yielding blood by which it is traversed ; it is
at the same time oxydative and synthetic as regards
the formation of its own working balance of inogen,
deoxydative and analytic as regards expenditure of
that balance. It is a maxim of political economy that
imports equal exports ; a similar maxim applies to the
organism and to any portion of the organism that is to
maintain itself in the physiological economy. If a

^ Perhaps it would be better to say '' inogen," in order not
to seem to prejudge the vexed question whether the force-
producing compound that disintegrates is proteid or carbo-
hydrate.

4

50 ANIMAL ELECTRICITY. LECTURE IL

muscle works and does not diminish, carbon and oxy-
gen must come to it, as carbon with oxygen leave it.
There must be integration reparative of disintegra-
tion. And although no doubt during heightened
action the disintegrative movement is hastened, and
during subsequent repose reintegration, yet we must
not too absolutely imagine as independent and disso-
ciated these two opposite movements — they are rather
the concomitant aspects of one complex process of
metabolism, although, no doubt, action gives promi-
nence to the negative movement of expenditure, and
rest favours the positive movement of recuperation.

Turninor back to the electrical sigfns of nerve
action, we find this opposition of movements mirrored
as it were by the currents during and after action.
During action we have a negative effect, after action
we have a positive after-effect. To which double
statement I may add that in certain states of nerve
we may witness even during action a positive effect
that may possibly signify that even during action
integration may predominate over disintegration.
But however that may be, we shall find in the
empirical study of reagents that this positive varia-
tion contributes some very significant items to the
series of arguments upon which we are about to
enter.

To sum up, we shall have as elements of study
three principal effects upon a nerve set up for experi-
ment as shewn in ^^. lo.

ANIMAL ELECTRICITY. LECTURE IL 5 I

(i) The negative variation of du Bois-Reymond,
due to disintegrative activity at L.

(2) The positive after- variation of Hering, due
to reintegrative chemical movement at L.

(3) The positive variation to which I have alluded
above, present only in certain states of nerve, attri-
butable to integrative chemical movement during
augmented activity at L.^

In the first case zincativity at L, deoxidation of
inogen, rejection of CO^, acidificatory effect.

In the second, and possibly third cases anti-
zincativity at L, oxidation of inogen, deacidification.

But I cannot interpret matters at this stage with
any degree of assurance, and shall therefore refrain
from the attempt. Let me rather emphasise the bare
fact that nerve is an extraordinarily sensitive reagent
to the presence of CO^. Here is a fresh nerve, giving
a by no means impressive response, but I breathe
through the little vessel that contains it, and there will
be a perfectly obvious improvement of the response
within one or two minutes, due to the carbonic acid
contained in expired air. The nerve is by far the
most sensitive reagent I know of to carbonic acid ; left
for a minute or two in a tube of one cubic centimetre

^ The conceivable changes at T are left out of count ; there
is, however, evidence to support the view that the negative

variation is often the sum of two homodromous activities

zincativity at L and anti- zincativity at T.

52

ANIMAL ELECTRICITY. LECTURE II.

capacity containing i per cent, of carbonic acid, it is
unmistakeably altered. Thus it has reacted to a
hundredth of a cubic centimetre (or about one fiftieth
of a milHgramme) of CO,, and no doubt this has not
been a minimum Hmit.

Fig. i8 (598).— Effect of expired air (Excitation by "little " CO.,).

In conclusion let me place before you the record
of a complete experiment such as that of which you
have just witnessed an initial stage. Plate 589 is
an instance of the effect of expired air in an obser-
vation lasting about forty minutes. The series of re-

ANIMAL ELECTRICITY. LECTURE II. 53

sponses to the left of the Hght bar gives the normal
of this particular nerve — the light bar shows when
expired air was blown in — and the next twenty or
thirty responses give token of the altered state of
the nerve during the next twenty or thirty minutes.
The expired air contained 3 per cent, of CO^ and was
blown throuo'h the nerve chamber for two minutes.

By other experiments it was ascertained that the
alteration was neither due to altered temperature nor
to anything else in the expired air but CO^. It is
then evident that nerve is extraordinarily sensitive
to CO,, and this clear fact will form the point of
departure of our further study.

REFERENCES.

The general notion of " internal respiration," the functional
attribute of all protoplasm, as distinguished from " ex-
ternal respiration," the accessory means, alluded to on
p. 48, is developed by Claude Bernard, in his Leqons
siir les PJienoinenes de la Vie couiniiuis aiix aniniaux et
aux vegetaux, vol. ii., Paris, 1879. The notion of the
double aspect of functional changes in living matter,
expressed in the terms — analysis and synthesis, breaking-
down and building-up, dissimilation and assimilation,

54 ANIMAL ELECTRICITY. LECTURE II.

katabolism and anabolism, disintegration and reintegra-
tion— is developed at length by Claude Bernard in Pheno-
menesdela Vie, vol. ii., by Hering in ''Lotos!' ix., 1888,
Zzir Theorie der Vorgdngein der lebendigen Sttbstaiiz, and
from the particular standpoint of electrical phenomena by
Hering's pupil Biedermann,in several papers summarised
in his Elektrophysiologie. Hering's paper of 1888 is
translated in the current volume (1897) of ''Brain:'

55

LECTURE III.

CONTENTS.

On the production of CO„ by tetanised nerve.

Hypothesis and experiment. Three stages. Comparison between

the effects of CO2 and of tetanisation.
Direction of further inquiry. Significance of the staircase effect.

Summation. " Bahnung."
Postscript.

It was comparatively early in these experiments —
during the month of October, 1895 — that the nerves
under study presented some puzzling- features in their
mode of response, that for some time were a grievance
and a stumbling-block. The nerves said "check,"
just as this month (February) they are again saying
" check." My disgust at their enigmatical conduct
came to its climax on October 27 with plate 672, and
vanished in the evening of the same day with the
appearance of plate 675.

I will venture to tell the story of these two plates,
for I think that it illustrates what so often happens in
the course of an inquiry as almost to be the rule, viz.,
that "check" in the course of some otherwise smooth
and glib interrogation, although at first disliked as a
stumbling-block, ought in reality to be welcomed as a
stepping-stone in disguise, a sign that some unexpected
bit of truth has cropped up.

I had undertaken to show a friend the stimulant
action of carbon dioxide, and had announced it as an

56 ANIMAL ELECTRICITY. LECTURE III.

unfailing experiment. I had previously noticed that if
a frog is killed and its two sciatic nerves used in suc-
cession, the second nerve always gave larger varia-
tions than the first. I had also noticed that in the
case of a nerve that had been left lying for twelve
hours in the killed animal, the variation was extra-
ordinarily large — four or five times its usual value.
But I had never tried the effect of carbonic acid
upon such a variation.

Fig. 19 (672). — Effect of C02upon a "carbonised " nerve, i.e., a nerve left for
24 hours subject to the reducing action of the surrounding muscles.

Wanting to make the demonstration as clear as
possible with a good variation to start with, I took a
nerve that had been left for twelve hours in the frog
and got the result recorded on plate 672 (fig. 19),
to my considerable disgust. The stimulant action of
carbon dioxide was conspicuously poor, and I don't
think my friend watched the experiment out, in fact,

ANIMAL ELECTRICITY. LECTURF: IIL 57

I recollect that the experiment of which you saw the
record last week (fig. i6, plate 674) was made upon a
fresh nerve immediately after his departure.

Later in the day the failure (which was the first I
had met with) came under discussion. Clearly this
nerve had been very much altered in its disposition
towards carbonic acid. A reducing action of the sur-
rounding muscles must have been at work ; CO. of
course. But has this been only muscle CO^ or also
nerve CO^ ? Who shall decide and how ? That
question must wait, but the obvious question w^hether
exaggerated activity of nerve is or is not attended with
an increased production of CO^ can be tested at once,
since the nerve itself is such a delicate reagent to its
presence from outside. A little expired air, acting on
the nerve by reason of a quantity of CO^ much below
what can be detected by orthodox chemical tests, pro-
duces a great change of the galvanometric response
(see fig. 18) ; surely if any change takes place within
tetanised nerve, if one single molecule of CO, is pro-
duced within it, we shall have the characteristic altera-
tion of response. Let us do this : take say five
normal responses, then tetanise the nerve continuously
for five minutes, then take some more responses. If
one single molecule of CO^ is evolved within the nerve,
we shall have an augmented response, diminishing
minute by minute with the disappearance of CO2.

A blackboard sketch (fig. 20) accompanied this
rather extravagantly expressed argument, and the slope

58 ANIMAL ELECTRICITY. LECTURE III.

of the chalk line, indicating the state of things during
the proposed five minutes' tetanus, was dictated by the
thought that with the imagined progressive evolution of
CO3 there should be a gradually increasing negative
variation, giving a gradually increasing departure from
the general base line. Such was the forecast — yet,

Fig. 20. — Hypothesis.

when half an hour later, I watched the lines of plate
^75 (fig- 21) appearing in the developing dish, it was
with something of astonishment that I found the greater
regularity of the series to be the sole difference
between the autographic record of the nerve itself,
and my rough blackboard drawing.

Well, this is not proof, but it is very remarkable
evidence. And considering that we have no previous

ANIMAL ELECTRICITY. LECTURE III. 59

evidence of any chemical or physical change in
tetanised nerve, it seems to me not worth while
pausing to deal with the criticism that it is not CO^
but ''something else" that has given the result.

Moreover, the evidence is corroborated in a very
remarkable manner under a considerable variety of
conditions.

Fig. 21 (675). — Verification.

But before we are in a position to properly
appreciate this further evidence, it will be necessary to
enter into a digression, speculative from one point of
view, empirical, however, as regards our experimental
survey of the effects of carbonic acid acting from
without and presumably acting from within.

The typical electrical effect of excitation of a
freshly excised nerve is the negative variation of du

6o

ANIMAL ELECTRICITY. LECTURE III.

Bois-Reymond, and the hardly less typical after-effect
is the positive after - variation of Hering. The
electrical state of nerve after excitation is for a short
period the reverse of that obtaining during excitation ;
and if we call the latter " negative," v^e must call the
former ''positive." Here, for example, recorded by a
quite dead-beat galvanometer, is a typical series of
negative followed by positive after-effects, the former

Fig. 22 (2177).

undiminishing, the latter progressively diminishing.
That progressive diminution of the positive after-effect
will presently be clear to us as a characteristic change
produced by carbonic acid — but I anticipate.

The positive after-effect presents itself more or less
obviously — more so as a rule in nerve that is becoming
a little stale, or that has been trifled with by previous
experiments. Sometimes the positive after-effect is so
pronounced as greatly to exceed the negative effect
that precedes it. As a matter of convenience I
distinguish such nerve as beint/ in the second stage,

ANIMAL ELECTRICITY. LECTURE III.

6l

neither undoubtedly fresh nor unmistakeably stpile —
transitional in short.

Finally it is not uncommon — nor yet common — to
witness, even during excitation, what I have been led
to regard as characteristic of stale or experimentally
maltreated nerve, viz., a positive electrical effect, which
has generally prolonged itself in more or less pro-
nounced degree as a positive after-effect subsequent to
excitation, and has rarely given place to a negative
state durino- the first few seconds after excitation. I
lay, however, no stress upon this last point ; indeed, it
is chiefly for convenience of description that I make
this, for the moment empirical, division into three
stages — fresh, transitional, and stale, of which the three
characteristic features are respectively — (i) a negative
effect, (2) a positive after-effect, (3) a positive effect.^

^%

II.

Fig. 23.

III.

^ I have argued elsewhere what cannot be argued here, viz.,
that the positive effect above referred to has not been produced
by an ordinary Anelectrotonic current.

62 ANIMAL ELECTRICITY. LECTURE III.

Let US now take nerves of these three stages,
giving respectively the three types of electrical
response just enumerated, and examine upon them the
alterations of response brought about by carbonic acid.

The alterations produced in fresh nerve you have
already witnessed. The negative variation was aug-
mented. Those produced in transitional and stale
nerve, especially the latter, are under all circumstances
more uncertain ; we cannot unfailingly obtain a varia-
tion of the desired type, and even when we have
obtained it — we cannot confidently predict the altera-
tion that may result from our interference. And this
is the worst month (February) in which to attempt to
make such delicate demonstrations.

But the records of past experiments are of equal
value with the experiments themselves, and the
examples already alluded to in my second lecture,
and to which I now return, are representative of
the regular results of several hundred experiments,
all the records of which are indexed and open to
your inspection.

Here, then, is the effect of carbonic acid upon
nerve of the second stage (fig. 26). The negative
effect is increased, the positive after-effect is dimin-
ished.

Here is the effect *of carbonic acid upon nerve of the
third stage (fig. 28). The positive effect is abolished
and replaced by a negative effect.

ANIMAL ELECTRICITY. LECTURE III. 63

Here is another and less pronounced effect of
carbonic acid upon nerve of the third stage (fig. 30).
The positive effect is diminished.

Compare now with these three typical and charac-
teristic effects of carbon dioxide, the effects produced
upon nerve — either upon the same nerve, or at least
upon nerve in a similar state — by prolonged artificial
activity. You will recognise that in each separate
case the effect of activity is similar to the effect of
carbon dioxide. Considering the conditions of the
case — that the a /r/6>r/ probable product of activity is
carbon dioxide, we are, I think, entitled to conclude
that the similar series of effects has been due to a
common cause — to known CO^ introduced from with-
out in one series ; to the hitherto unknown CO^
evolved from within in the second series. The nerve
itself has served as the reagent indicative of the
presence of the latter.

Here is the nerve giving a small negative deflec-
tion followed by a large after-deflection, altered as
you have seen by CO^ from without, and similarly
altered in consequence of tetanisation. (Compare
figs. 26 & 27).

Here is the nerve giving a positive deflection,
reversed to a negative deflection by CO^ from without,
and here is the same nerve exhibitino- a similar
reversal in consequence of tetanisation. (Compare
figs. 28 & 29).

Here, finally, is the nerve of which the positive

64

ANIMAL ELECTRICITY. LECTURE III.

First Stage.

Fig. 24 (869). — Augmented negative effect.

Second Stage.

Fig. 26 (710). — Augmented negative effect. Dimin-
ished positive after-effect.

Third Stage.

vuithouf-. ■ ' I 1

fe

11 '

lafter

Fig. 28 (859). — Positive converted into negative effect.

Third Stage.

.'■M'ltlLilLllli .Mllininiii

f CO 2 from,

r without

Fig. 30 (985). — Positive effect diminished.

Influence of Carbon Dioxide on the Electrical Response of Nerve

in its three stages.

ANIMAL ELECTRICITY. LECTURE III,

65

First Stage.

FiCx. 25 (675). — Augmented negative effect.

Second Stage.

,^;^''-:

jM ' llllUllUiUllt.'

ERRATUM.

p. 65. Description of Fig. 29 (858), for negative after-
effect read negative effect.

i i ! f f !

z/ter

Fig. 29 (858). — Positive converted into negative after-effect.
Third Stage. '! '! ! ' I

M t I

Fig. 31 (984). — Positive effect diminished.

Influence of Tetanisation on the Electrical Response of Nerve

IN ITS Three Stages.

66 ANIMAL ELECTRICITY. LECTURE III.

deflection is only diminished by CO^ from without, and
here is the same nerve o^ivinor a similar diminution as
the consequence of tetanisation. (Compare figs.
30 & 31). Indeed, if this last plate had been first
brought to your notice, and without reference to the
group of considerations just traversed, you would
very likely have taken the diminution to be a
common fatigue effect.

Provisionally admitting as an established datum
that carbon dioxide is one of the products of nerve
activity, our next question is : what becomes of it ?

I can venture upon no positive answer to this
question. For the moment it seems to me that
there are two possible answers open to our further
investigation.

It is possible that the CO^ may be dissipated by
diffusion from the nerve, but it is also possible that it
may be reintegrated within the nerve itself.

I have not yet found means of deciding between
these two alternatives, which I have nevertheless not
felt it unprofitable to state and briefly consider.

Obviously the first alternative presents itself first ;
what more natural fate can we imaoine for CO,, if
produced within a nerve, than its dissipation by dif-
fusion into the surrounding atmosphere or into the
lymph and l)lo(3d, as in the case of the CO^ evolved
within a muscle ? I have nothing to say against this
obvious probability, and can only point out as a

ANIMAL KLECTRICITV. --LECTURE IIL 67

remote possibility, suogested indeed by one or two
peculiar features in the behaviour of isolated nerve,
that CO2 evolved in the process of disintegration may
conceivably be reinvolved in a process of reintegra-
tion ; that, in short, baseless as the idea may seem at
present, there may be in an animal tissue an assimila-
tion of CO2 analogous with the assimilation of CO^
taking place in vegetable protoplasm. We have rea-
son to associate the negative effect with a dissimilatory
evolution of CO^, we may some day find reason to
associate the positive after-effect with an assimilatory
reinvolution of CO^. But at present this is a mere
fiying conjecture for which I have no positive base.

Putting this conjecture aside, let us turn to another
less imaginary, yet still distinctly conjectural point.

Contractile tissue — that of the heart in particular,
but also the contractile tissue of jelly-fish, as well as
voluntary muscular tissue — exhibits a peculiarity
known to physiologists as the "staircase phenome-
non." Stimulated at regular intervals, not too long nor
too short, by strong induction shocks, such contrac-
tile tissue gives a series of responses, each of which
is the greatest effort of which the muscle is capable at
the time, but each of which is a little orreater than its
predecessor. Such an increasing series is called a
staircase, and we have seen that a series of electrica
responses of nerve exhibits a similar staircase — in-
creasing in the case of a series of negative effects,
decreasing in the case of a series of positive effects or

68

ANIMAL ELECTRICITY. LECTURE III.

after-effects. Remembering that the characteristic
effect of CO2 from without, and presumably from
within, Is an augmentation of negative response and
a diminution of positive response, we have no diffi-
culty in admitting that the electrical staircase of nerve,
whether ascending or descending. Is brought about by
carbonic acid evolved at each step in a series. It is
pretty obviously a CO^ phenomenon.

Fig. 32. — "Staircase" of contractions
of a frog's heart.

iifflfflii^

Fig. 32 A. — "Staircase" of electrical responses of nerve.

Staircase effect, then, is not confined to contractile
tissue, it clearly applies to nerve where it is equally
clearly produced by CO^. To my mind this precise
notion is a welcome addition to ouf somewhat less
definite psychological notions concerning staircase
effects obtaining In central nervous action.

Summation of stimuli — i.e., the gradual accumu-
lation of a series of individually Insufficient stimuli
into an effective excitant — is itself conceivable as the
expression of augmenting excitability by augmenting
evolution of CO^. The establishment of paths of less

ANIMAL ELECTRICITY. LECTURE III. 69

resistance in this or that direction of the central
nervous system — the " Bahnung " of German psycho-
logists — is conceivably due to a facilitation of
transmission along some line previously traversed by
nerve-impulses, and therefore with its excitability
sharpened by CO^. We may even be tempted to
cast our imagination much further back — to the
very origin of specially conductile tissue within a
mass of homogeneous protoplasm. Picture to your-
self a first linear discharge of action within such
mass ; carbonic acid is evolved along this line, and
the subsequent discharge of action will be in this
rather than in other lines. That will have been a
primitive form of " Bahnung " in the sense with
which Spencer's writings have made us so familiar,
and to my mind a knowledge of the relations be-
tween carbonic acid and nerve makes this idea more
concrete and tangible by suggesting a possible^ I had
almost said probable — physico-chemical mechanism of
the result. And if there has been a disintegration,
there follows along the same line a reintegration of
matter, by which the nerve-path becomes organically
as well as functionally constituted. We know that
wear is followed, and more than made good, by repair ;
we also know that one of the products of wear is
carbonic acid. I wonder does this carbonic acid
become altogether dissipated ; may it not perhaps be
relnvolved in some storage combination, as the nerve-
fat perhaps, that is so prominent a constituent of fully

JO ANIMAL ELFXTRICITV.^ — LECTURE IIL

evolved nerve. Such nerve consists of proteld axis
and fatty sheath ; the axis — which is the offshoot of a
nerve-cell — is the specially conductile part, the sheath
is a developmental appendix, not directly connected
with any nerve-cell. Yet, cut the nerve, and sheath
as well as axis undergo Wallerian degeneration,
which is evident proof of a functional commerce
between sheath and axis. You have seen further,
that such nerve is inexhaustible, yet that it exhibits
very clear symptoms of chemical change after action.
All these things, to my mind, reconcile themselves
with the notion that the active grey axis both lays
down and uses up its own fatty sheath, and that it is
inexhaustible, not because there is little or no expendi-
ture, but because there is an ample re-supply.

This is wild hypothesis — an unbridled excess of
the imagination — and I shall be the first to admit
this, nor claim for it any value other than as a possible
motive for further trial.

Still, leaving aside the imaginary reinvolution of
CO2 and the imaginary origin of specially conductile
strands, let me at least urge that the staircase effect as
a general phenomenon gains value in a definite and
concrete sense, both as a physiological and as a psycho-
logical idea, when we have admitted that carbonic acid
is a product of nerve activity and that carbonic acid
facilitates nerve activity. From a physiological stand-
point it seems to me preferable to admit as an effective
factor of ''summation " and of " staircase effect " and

ANIMAL ELECTRICITY. LECTURE III. 7 I

of " Bcihnung," that augmented mobility of protoplasm
which is a characteristic effect of carbonic acid, the
principal product of previous activity, than to say
"that excitation arouses a tissue to a state of greater
expectancy as well as of greater activit)."

And in this connection one is tempted to at least
ask oneself whether the converse phenomena known to
us as "fatigue," the "refractory state," "inhibition,"
may not also be connected with the evolution of car-
bonic acid — whether its anaesthetic action, which is its
full effect, may not come into play with exaggerated
or with culminating activity. But upon the considera-
tion of this negative aspect of nerve activity I do not
feel able to enter at present.

In conclusion, let me briefly answer two questions
that have been very frequently put me with regard to
these records. I will answer them briefly, and by no
means to my own satisfaction, for the answers are
little more than counter-questions.

What interpretation do you place upon these nega-
tive and positive effects ?

What is the meanino- of that remarkable alteration
of base-line caused by carbonic acid ?

As to the first question, 1 ask myself whether the
negative and positive effects are to be regarded as
signs of opposite chemical movements, whether the
neo-ative is to be taken as a sio-n of disintegration and
the positive as a sign of integration, in the sense of
Hering's dissimilation and assimilation — or whether

']2 ANIMAL ELECTRICITY. LECTURE III.

they are to be considered as algebraic sums of
kathodic and anodic effects respectively — resultant
from the predominance of one or other factor in
the series of alternating currents used to stimulate
the nerve. Further investigation will, perhaps, decide
this point.

As regards the second question, I am very tired of
it indeed, for no one fails to put it to me, and I do not
know what the remarkable alteration of base-line
means. Sometimes I get away from the question by
saying that it means an alteration of the galvanometer
zero, which is a pretty obvious "answer." If that
does not answer, I have to apologise for the remarkable
alteration, and to say that it has only been by reason of
this uncompromising method of recording that it has
been made so prominent, and that in ordinary galvano-
metric observations one does not attend to it. But
that does not get me out of trouble, and I am told
it ought to be attended to, that the rise or fall, as the
case may be, are very significant. Yes, they are
significant, but I don't know what they are significant
of. I am quite aware of the fact that carbonic acid
from without always drives the zero up at first, while
carbonic acid from within (by tetanisation) always
drives the zero^ downwards, but I do not know what
that means.

^ By zero, I mean the position of rest of the permanently
deflected magnet, not its position of rest when no current is
passing.

ANIMAL KLKCTRIdT\. LKCTURE III. "] ^iy

Postscript, — The dubious tone of the remarks
made on p. 62, arose from the fact that the rehearsal
experiments carried out during the week preceding-
the lecture were so unsatisfactory that I abandoned
all hope of obtaining any clear demonstration of the
principal experiment. The nerves persistently said
*' check," giving only a very small augmentation of
response in consequence of prolonged tetanisation,
so small indeed as to be liable to escape detection
on the demonstrating galvanometer, except to very
close scrutiny. For this reason a recording galvano-
meter was put up in a dark room behind the lecture
theatre, in circuit with the demonstrating galvano-
meter (as shown in fig. 10), so as to have a record
of the experiment actually made, to be put into the
witness-box at the end of the lecture.

As it turned out, however, the lecture experiment
came out with remarkable distinctness ; the response,
after prolonged tetanisation (ten minutes), appeared
to be about three times as great as before, and the
photographic record was subsequently brought in as
a somewhat superfluous piece of evidence.

This result, which was more surprising to the
lecturer than to any of his audience, had been secured
by Miss Sowton, who acted as lecture-assistant, and
arose as follows : —

From previous experiments made in order to test
the possible nutritive action upon nerve of proteids
and of carbohydrates, we had found that lactose, among

74

ANIMAL ELECTRICITY. — LECTURE IH.

Others, appeared to have a considerable, if not abso-
lutely certain, "nutritive" action. Miss Sowton had,
therefore, without my knowledge, made tetanisation
experiments the day before lecture upon nerves
allowed to soak in saline solution of lactose, and

fic, 33. (2478.) EH ect of 5 minutes' tetanisation on an ''unfed"' nerve.

Fig. 34. (2501.) Effect of 10 minutes' tetanisation on a " fed " nerve.

had found that the typical effects in such nerves
were considerably augmented. The lecture experi-
ment had been made upon a lactosed nerve, and,
like the experiments of the previous day, contrasts
very markedly with the other rehearsal experiments
made at this period on "unfed" nerves.

ANIMAL ELECTRICITY.— LIXTUKK III.

75

REFERENCES.

A full account of the subject of this lecture is given in PJnl.
Trans, of the Royal Society for 1897 (Observations on
Isolated Nerve ; with Particular Reference to Carbon
Dioxide. Croonian Lecture for 1896).

The " Staircase " phenomenon, first pointed out by Bowditch
as being characteristic of heart-muscle, and by Romanes
as occurring in the contractile tissue of Medusa, is con-
sidered by Romanes at some length from a general
standpoint in Jelly-FisJi and Star-Fish, International
Scientific Series, p. 54.

The notion of " canalisation " or " Bahnung " is developed
by Herbert Spencer in the Principles of Psychology, and
alluded to by Romanes (loc. cit., p. 87), who gives
references to earlier statements in a similar sense by
Lamarck

i_> r^ ^. /

LECTURE IV.

CONTENTS.

Polar effects. Pfliiger's law. Illustrated by experiments on

Man.
Electrolytic dissociation. Electrolytic counter-current.
Internal polarisation.

Polarisable core-models. Extra-polar currents in core-models.
Extra-polar currents in frog's nerve and in mammalian nerve.

Polar effects. — In studying the electrical effects
manifested by living matter, we shall repeatedly have
occasion to employ electrical stimuli. It is important
at the outset to avoid a perhaps natural confusion of
ideas, and to expressly distinguish between electricity
applied from without by way of what we shall desig-
nate as leading-in or exciting electrodes, and elec-
tricity arising within ox aroused within the living
animal or tissue, and conducted to the galvanometer
or other electrical indicator by way of what we shall
designate as leading-out electrodes. The latter alone
is animal electricity, the former is not, although it is
often used to arouse within living matter that chemico-
physical action of which the deflection of a galv^ano-
meter is an outward and visible sign.

ANIMAL ELECTRICITY. ^LECTURE IV. "]"]

This is, to some extent, a preliminary dioression —
inasmuch as the title of these lectures is Animal Elec-
tricity, not Electro-physiology. Strictly speaking, the
former title covers only the electrical effects derived
froui animals, not the effects of electricit)- applied to
animals. But seeing that we shall very shortly have
to deal with polarisation phenomena which belong to
both categories — being electrical responses to elec-
trical currents; and that we shall have to examine
the relation between such electrical responses and
the ordinary mechanical responses significant of
physiological excitation, the digression is not merely
convenient and necessary, but logically defensible,
even if we are to be restricted to animal electricity.
The polar reactions of living matter are, as regards
their physico-chemical mechanism, of the same
nature as those of inert matter, but in many respects
the former exhibit features that are peculiar, and
characteristic of the living state. And while we
must recognise that electrolytic disruption, whether of
living, or of dead, or of inert matter, is of one nature
in its essentials, we must also recognise that, in
correspondence with varying conditions of greatly
diminished chemical stability, varying degrees of
greatly increased polarisability will be found in living
as compared with dead matter. In the course of these
lectures I shall show that the electrolytic polarisation
of living matter is extraordinarily sensitive to chemical
modifications that may certainly be termed slight, that,

78 ANIMAL ELECTRICITY. LECTURE IV.

e.g., the electrolytic changes within a nerve are modi-
fied by irritant and by sedative drugs, and that a
poison that kills protoplasm is, from our present
standpoint, a reagent that immobilises the living-
electrolyte.

The questions arising in the consideration of the
polar reactions of nerve are partly electro-physical,
partly physiological, partly electro-physiological, and
in this last respect distinctly overlap the narrower
province of purely animal electricity.

Without, then, entering into details such as would
be required under the heading of electro-physiology,
and considering merely the general features of elec-
trical excitation in so far as they involve electrical
reactions and their relations to physiological re-
actions, these are the main points to be insisted
upon.

It has been laid down by du Bois-Reymond that
nerve is excited by a constant current, when that
current begins and ends, i.e., at "make " and " break "
— but not while it flows, i.e., between the make and
break effects.

It was thereupcMi further proved by Pfluger- —

(i) That the "make" excitation arises at the
kathode.

(2) That the " break " excitation arises at the
anode.

(3) That during the passage of the constant current
excitability is raised at and near the kathode.

ANIMAL ELIX'TRICITV. — LKCTURE IV. 79

(4) That during the passao-e of the constant current
excitabiHty is depressed at and near the anode.

These four propositions, specially applicable to
nerve, express a very general law, and cover more
particularly the case of muscle — of heart-muscle as
well as of ordinary muscle. Subject to a possible
exception in the case of non-fibrillated protoplasm,
they express the law of response of living matter to
electrical currents.

I have been at some loss how most briefly to
present to you an experimental illustration of these
two pairs of principles. The obvious and orthodox
object of experiment, a nerve-muscle preparation of a
frog, will not serve the whole purpose — for, while it
would do well enough to exhibit augmented kathodic
and diminished anodic excitability, it would afford no
direct and evident proof of kathodic make excitation
and of anodic break excitation.

I shall, therefore, have recourse to a less orthodox,
and, in one particular, more complicated object, viz., a
nerve-muscle preparation of a man, selecting for the
purpose the ulnar nerve of my own forearm and the
muscles to which it is distributed — these are, among
others, several of the Hexor muscles of the wrist and
fingers.

ExperiiJieiit. — I have connected myself with a bat-
tery by means of a large flat electrode at the back of
the neck ; with the knob of the other electrode held by
its insulating handle in my right hand, I feel about for

8o ANIMAL ELECTRICITY. LECTURE IV.

the ulnar nerve at the back of the elbow ; when the
knob is felt to be comfortably applied, the current,
directed so as to have its kathode at that spot, is
gradually increased, the effect of its make and break
being tested for occasionally. A strength is reached
at which each make of the current gives a sharp flexor
movement of wrist and fingers — i.e., the kathode ex-
cites at make, or, otherwise, the make excitation is
kathodic. Now the current is reversed, so that the
kathode pressed down on the nerve is changed to an
anode, and the current is made as before at the key, as
you hear — but, as you see, without producing any effect ;
the anode does not excite at make. But neither does
it excite at break — at least at this rather low current-
strength. The current must be increased before any
break effect appears with the anode over the nerve,
and then there is also a make effect — which apparently
contradicts the statement that the anode does not excite
at make — that on the contrary it quells excitation.
The contradiction is apparent and not real, yet, as
regards the course of our main channel of thouoht,
any full consideration of the point would lead us
astray. Let me then say rapidly that in this em-
bedded nerve, current, having a fairly narrow way in
(= anode), just under the electrode, has also a com-
paratively broad way out (= kathode) into the sur-
rounding tissues, at some little distance from the actual
electrode. The make effect is due to this extra-polar
kathode — please do not regard it further ; it is a com-

ANIMAL KLECTRICITV. LECTURE IV. 8 I

plication due to the fact that the nerve is not isolated,
but embedded. Notice only that there is a contraction
at break, which contraction is due to excitation of the
nerve just under the anode, and let that signify for you
that the anode excites at break, i.e., that the break
contraction is anodic.

These two statements — that the kathode excites
at make and the anode at break — will be supple-
mented by the double statement that during the
passage of a constant current, excitability is increased
at the kathode, decreased at the anode — which is easily
to be demonstrated. And the clearest and least ob-
jectionable way to do this will be by an apparently
very clumsy proceeding, viz., by light blows to the
nerve, through the medium of the electrode itself,
which is made anodic or kathodic at pleasure. Pressing
the electrode somewhat carefully upon the nerve, it is
regularly tapped by a light mallet, just hard enough to
give distinct twitches of the hand and fingers. While
the taps and twitches are proceeding regularly, a key
is closed, rendering the electrode kathodic, and the
twitches are evidently more pronounced, whereas with
reversed current and an anodic electrode they are
abolished. This double experiment — of which the
principal virtues are that it is simple, and that me-
chanical, i.e., non-electrical, stimulation of perfectly
normal nerve is employed — is good and sufficient
evidence of the double statement that excitability is
increased under kathodic influence and diminished

6

82 ANIMAL ELECTRICITY. LFXTURE IV.

under anodic influence. Here is the record of an
experiment {hg. 35) that will serve as a memor-
andum of the fact. Anyone who may desire further
acquaintance with the doubts and complications of
which this very domestic-looking experiment is the

Before. During A. After.

Anodic diminution of excitability.

Before. During K. After.

Kathodic augmentation of excitability.

Fig. 35. — Influence of a polarising current upon the electrical excitability of
human nerve. (From Waller and de Watteville, P/u7. Trans. R. S., 1882).

settlement, may refer to the literature of the subject,
from which it may be gathered that a verifica-
tion on human nerve of Pfluger's universally-admitted
principles r^ isolated frog's nerves was by no means a
matter of course, but had to be cleared before it was
clearly visible.

ANIMAL ELECTRICITY. LECTURE IV. 83

It is not my present purpose to enter into any-
detailed examination of this law of response ; that
will form part of a future course of lectures. But it
is necessary, in order to make clear to you the relation
between the excitability and the electro-mobility of
living- matter, that I should allude to them now, if
only to warn you that "excitability" and "electro-
mobility " are not parallel attributes — that the term
excitability is, in English, subject to an ambiguity
that is avoided in the richer German by the terms
Erregbarkeit and Leistungsfahigkeit, and that one
of the several reasons leading me to adopt " zinc " as
a new root word has been that its substantive "zinc-
ability " {i.e., capability of being aroused to action
analogous with that of the zinc of a voltaic couple)
does not naturally lie wide open to ambiguity, as do
the terms excitability and electromobility. By the
terms "greater excitability," "more excitable," there
may be implied "more easily excited," or "capable of
greater reaction." By the terms " greater electromo-
bility," "more electromobile " might be implied "more
easily aroused to electromotive action," or capable
of beine aroused to oreater electromotive action.

By the terms "greater zincability," "more zinc-
able " it is most natural to understand — and at any
rate it is the sense in which the expression will be
used in these lectures — capability of being aroused to
greater electromotive action, analogous with that of
the zinc in a voltaic couple. That is the sense in

84 ANIMAL ELECTRICITY. LECTURE IV.

which the term " zincable " is to be understood in
the legend of this diagram (fig. 36), which is
intended to serve as a memorandum to the polar
alterations of excitability and of electromobility effected
by the action of the galvanic current.

hmiL Katholc

Fig. 36.
' ' Excitability " and ' * Zincability. "

Less excitable. More excitable.

Less zincative. More zincative.

More zincable. Less zincable.

We may tentatively proceed a step further in the
direction of general expression, and — admitting that
the grey axis is the essential part of a nerve-fibre —
recognise as a possible series of associated facts : —
(i) the kathodic excitation of the grey axis; (2)
the liberation of electro-positive elements ; (3) the
reduction of deoxydisable ''Inogen " (? carbohydrate) ;
(4) the evolution of carbonic acid.

The point mentioned on p. 74, is in some measure
confirmatory of this view. The sugar appears in this
case to have played the part of an oxygen-giving food,

ANIMAL ELKCTRICITY.— LECTURE ■ IV. '85

and it is conceivable that by the reducing action of
living matter upon sugar, a deposit of fat might be
effected.

There would at first thought seem to be very little
continuity of ideas between the experiments we have
just witnessed and those to which I am now turning.
In [)oint of fact there is a close relation between them ;
the electrolytic disruption of simple chemical mole-
cules, which we are about to touch upon, is in all
probability the key phenomenon that will one day
admit us to the deeper comprehension of the manifold
disruptions and reunions of the complex chemical
molecules that compose living matter.

It is a first step in that direction to make clear to
ourselves that the phenomena of electrical excitation
and inhibition are above all of polar and electrolytic
(that is, of chemical) mechanism. It will be a further
step in the same direction to recognise that electro-
lytic movements, which stand out with comparative
clearness from amid the unexplained jungle of
excitatory phenomena — with such clearness indeed
that we are at first sight tempted to deny their physio-
logical character — are nevertheless subject to physio-
loo-ical conditions, and at the same time accessible to
chemical modifications.

But I shall not apply myself to the building of a
visionary castle — it is my purpose rather to diligently
grovel among phenomena that are elementary and
fundamental ; I allude more especially to electrotonic

86

ANIMAL ELECTRICITY. LECTURE IV.

currents, which underlie the electrotonic alterations of
excitability touched upon in the previous paragraph,
and which are undoubtedly the effects of electrolytic
polarisation.

Preliminary Experiment. — The two platinum
electrodes of a battery of two or three volts dip into
a rectangular glass vessel containing a mixed solution

Fig. 37.

of dextrine and potassium iodide. The molecule of
the potassium iodide is composed of a basic moiety
potassium, and an acidic moiety iodine, and the latter
as soon as it is set free by the electrolytic disruption
of the molecule, will signify its presence by striking
a red colour with dextrine. [I have taken dextrine
in preference to starch because iodine strikes blue
with starch, and to most of us there is an association
of thought between redness and acid, blueness and
base.] The circuit is now completed, and at once
you see that the anode is becoming surrounded by a
red halo, indicative of the presence of free iodine, the

ANIMAL ELECTRICITY. LECTURE IV. ^J

acidic moiety of the molecule K I. We may take
this as our memorandum experiment signifying to us
that with passage of current and consequent electro-
lysis there appear :

at the Anode at the Kathode

acid base

oxygen hydrogen

chlorine sodium

electro-negative ions electro-positive ions.

These electrolytic products at the two poles respec-
tively are themselves, so long as they are in stattt
nascendi, electromotive against the current that pro-
duces them ; thus oxygen, produced at the anode, and
hydrogen, produced at the kathode, constitute a voltaic
couple of which the current obstructs the original
current by which they are generated, giving a
secondary or polarisation counter-current that amounts
virtually to a resistance against the original current.
A voltaic cell in action, like living matter in action,
surrounds itself with products of its own activity,
obstructive of that activity. And the analogy that
might be drawn up between the polarisation and
depolarisation of a voltaic cell, and the disintegration
and reintegration of living matter, would perhaps be
not very far-fetched nor much more inaccurate than
are all analogies.

But let me formally exhibit to you this fundamental
fact of the polarisation counter-current. [It has in-
deed already exhibited itself informally in a way that

88

ANIMAL ELECTRICITY.— LECTURE IV.

is rather instructive. During the passage of the
original current the reddening of the fluid occurred
only at the anode ; but now — i.e. a few moments after
the original current has been cut out, and only the
counter-current has been in play — there is also a slight
reddening of the fluid round the other wire ; this
wire, which was kathode or way-out from liquid as
regards the original current, is now anode or way-in
to liquid as regards the counter-current.]

Experiment. — Beginning with K^ closed (to cut out
the battery ©) and K^ open, I first open and shut
the galvanometer key K3, to see that there Is no

Fig. n

current from the as yet unpolarised wires In the
polarisation cell. Leaving K3 closed (to protect the
galvanometer from the comparatively large battery
current about to be used, and which will be
through the cell and would be through the galvano-
meter as shown by the arrows) I polarise the
electrodes for a moment by opening K,. FInall)\
I switch off the battery by closing K„ and switch

ANIMAL ELECTRICITY. LECTURE IV. 89

In the galvanometer by opening" K3 ; the galvano-
meter indicates current against the direction of the
arrows, arising from the now polarised electrodes.
The key K^ with which these are connected has
remained open throughout the experiment. The
electrodes have been so to say charged at K^ from the
battery, and discharged at K. through the galvano-
meter, and, as you may have noticed, the magnitude
of the deflection has increased with the duration of
polarisation, and has diminished with the interval
between closure of K^ and opening of K^—i.e., with
the time during which depolarisation has proceeded.

We seem to be a long way off from the case of a
living nerve, yet the distance between this case and
that of the polarisation cell is not so great as it seems.
Two more experiments will, I think, suffice to bridge
the gap — or at least to serve as stepping-stones
between the two orders of phenomena — from the
electrolysis that is purely physical to the electrolysis
that is at the same time physiological — from the dis-
ruption of inert matter to the disruption of living
matter : —

Of these two experiments one is intended to illus-
trate the fact — first established by du Bois-Reymond —
that the interface between different moist electrolytes
may be the seat of electrolytic polarisation ; the other
to illustrate the physical mechanism of the electrotonic
or extrapolar currents to which such polarisation gives
rise.

90

ANIMAL ELECTRICITY. LECTURE IV.

In illustration of the first of these two points I
cannot do better than show you an extremely simple
experiment that suggested itself only two or three
days ago as a possible lecture demonstration, and
of which nevertheless I already venture to say that
it does not fail. I only wonder how it is that I
never tried it before, for I have frequently wanted
an illustration of the kind, and wondered whether
the living tissues of the human body traversed by a

Current
>

Counter' Current
<

Fig. 38. — Plan of apparatus for the demonstration of " internal polarisation
of the human subject.

galvanic current give rise to any demonstrable internal
polarisation, or whether they are so to speak kept
too well washed by the alkaline blood traversing their
capillaries.

Experiment, — Here are two vessels of salt solution
R and L connected with the two poles of a battery.
Here are two other vessels R' and L' of salt solution
connected with a galvanometer, which is shunted to
such an extent that on completing circuit through my

ANIMAL ELECTRICITY. LECTURE IV. 9 I

body by dipping a finger into each vessel, any acci-
dental inequality on the two sides does not affect the
instrument. Such being the case I polarise myself for
an instant by dipping a pair of fingers into the battery
vessels R L, and quickly transfer the same pair of
fingers to the galvanometer vessels, R' L' and as
you see, the spot is sharply deflected to the left. That
is a mixed effect of polarisation that may be wholly
external, at the way-in and way-out of current between
skin and fluid ; it merely serves to show the direction
in which to expect the effect of internal polarisation if
it exists. To this end — and this is the experiment
proper — I polarise myself again In the same way
through the same fingers dipped Into R and L, but
for a little longer to make sure of the effect ; then I
put my possibly polarised tissues Into the galvano-
meter circuit by dipping another pair of fingers Into
the vessels R' L', thus avoiding the external polari-
sation of the first pair of fingers. There is now a
considerable deflection, not quite so sharp as before,
but in the same direction, independent of external
polarisation at the skin, and significant of internal
polarisation in the tissues below the skin. Finally
repeating the experiment with reversed direction of
current, a reversed effect Is obtained. But to show
this without fail it Is necessary to let the current flow
for a rather longer time In order to wipe out the effect
of the previous polarisation.

I shall not now enter Into any details as to the

92 ANIMAL ELECTRICITY. LECTURE IV.

possible seat of this effect, which may obviously arise
at many sorts of interfaces between the various tissues
traversed by the current, but give the experiment as it
stands, in evidence of an internal polarisability of living-
tissues taken en bloc. Obviously it gives no specific
information as regards the polarisability of any one
particular tissue.

The second of our two stepping-stones towards
the case of nerve is a purely physical experiment —
indirectly demonstrative of a peculiar distribution of

i

ULOJUt

4 .3-.^-*/ A— 'K

Fig. 39. — " Anelectrotonic " current from a core-model.

current, effected by polarisation, and characteristic of
nerve, which is just the one tissue among all other
tissues in which polarisation is most easily produced,
yet most difficult to directly demonstrate by reason of
its extreme evanescence. I know of no direct means
by which to demonstrate an internal polarisation of
living nerve. The chief evidence of polarisation is in
fact the peculiar extrapolar distribution of current
along a nerve, termed an electrotonic current, and it is
a similar extrapolar current that we are about to wit-
ness upon a polarisable core-model consisting of a
platinum wire surrounded by a fiuid sheath of zinc
sulphate.

ANIMAL ELECTRICITY. LECTURE IV. 93

Experiment. — The original or polarising current
[fig. 39] is from A to K. In consequence of electrolysis
at the surfaces of entrance and exit between liquid
sheath and metal core, counter-current is aroused, acting
as a resistance, causing the surfaces of entrance and exit
to spread along the model. In the figure you must
imagine that the anodic or electropositive state shades
off to the left from a maximum to a minimum value, so
that if you connect a galvanometer with extrapolar
points I and 2, then 2 and 3, then 3 and 4, you will

b^

r%)

EiG. 40. — " Katelectrotonic " current from a core model.

get three diminishing values for current in the gal-
vanometer from I to 2, 2 to 3, 3 to 4 (in the wire core
from 2 to I, 3 to 2, 4 to 3).

Precisely similar effects would be observed on
connecting the galvanometer with a series of points
on the side of the kathode to the right of the polar-
ising current in ^g. 40. But it will obviously be
simpler to reverse the poles of the polarising battery,
giving all currents with arrows pointing to the left
instead of to the right.

94 ANIMAL ELECTRICITY. LECTURE IV.

These extrapolar currents, on the side of the
anode in fig. 39, on the side of the kathode in
fig. 40, precisely imitate what are known to phy-
siologists as the Anelectrotonic and Katelectrotonic
currents of nerve. And it is highly probable that
the latter like the former are of electrolytic origin.^

But now as regards any possible future identifica-
tion of ionic products in nerve, we must be on our
guard. At the anode the current enters the fiuid,
then leaves it to enter the metal core ; the ions arising
at the interface between sheath and core are thus
kathodic or basic. Similarly the ions of the fiuid
sheath round the core under the battery kathode, are
not kathodic, but anodic or acidic.

This point will come up again in the case of
medullated nerve-fibres, where core as well as sheath
is a moist non-metallic electrolyte. Meanwhile, to-
wards the avoidance of a confusion not seldom made
here between anode and kathode, way-in and way-out,
I give a formal experiment on a core-model, in which

^ Similar experiments can be made on core-models without
any central wire, on e.g. a clay pipe soaked in salt solution and
filled with a solution of copper sulphate; du Bois-Reymond in-
deed showed long since that the surface of separation between
two different electrolytes traversed by a current, gives birth to
electrolysis (hydrogen and base in the electrolyte behind the
current, oxygen and acid at the electrolyte in front). Monatshev.
d.Beyl. Akad.,ij. ]\i\i,i^$6. Gesammelte Abhandlungen. Ueber
Polarisation an der Grenze ungleichartiger Elektrolyte, vol. i.,
p. I.

ANIMAL ELl^XTRICITV. — LECTURE IV. 95

the anodic surfaces will be made visible to us by their
acidic character. In the experiment illustrated by
%. 41, the battery electrodes (of platinum) are
at I and 4, the electrodes between fluid sheath and
platinum core are at 2 and 3. Taken in order we
have anode to fluid at i, kathode from fluid at 2,
anode to fluid at 3, kathode from fluid at 4. The
fluid is a mixture of dextrine and potassium iodide,
soon after closure of the battery current the effect of
anodic electrolysis is apparent as a reddening at the
two surfaces 1 and 3, and you will not fail to remark

— 2

4 - ___7- -V^

iiilililiiillliilliliilliliiiiiiim

Fig. 41. — Experiment illustrating the entrance and exit of current to and from
the sheath and axis of a core-model. The current in the direction i, 2, 3, 4,
enters the fluid at i and 3, leaves the fluid at 2 and 4, i and 3 are thus "anodic,"
2 and 4 are " kathodic " as regards the fluid.

that at the latter of these the effect is most pro-
nounced immediately under the battery kathode, but
shades off in diminishing degree to a considerable
distance along the wire in an extrapolar direction.

The core-model used in the experiment of p. 92,

96

ANIMAL ELPXTRICITV.— LECTURE IV.

consisted of a platinum wire in a solution of zinc
sulphate, and in that case there was no marked
difference of magnitude between the anodic and the
kathodic extrapolar currents.

Here is another core-model, composed of a zinc
wire in a solution of sodium chloride ; in this case
the effects are unequal. On closure of the polarisinor

OT volt

o'3

0-4

0-5
0-6

Fig. 42 (2369). — Extra-polar ( = "electrotonic") currents of frog's nerve,
produced by polarising currents of increasing strength, from 0"i to 0"6 volt. At
each strength the A. and K. currents are taken twice. Their magnitude may be
approximately estimated by reference to the standard deflection of O"00i volt re-
corded at the commencement of the observation.

current in one direction (to the right), there is a well
marked anodic extrapolar current (to the right). On
closure of the polarising current in the opposite
direction (to the left), there is a much smaller kathodic
extrapolar current to the left.

These two core-models reproduce to us what we
shall find to be the rule in the case of the nerves of

ANIMAL ELECTRICITY. LECTURE IV.

97

cold-blooded and warm-blooded animals respectively,
and I will bring this group of introductory considera-
tions to their conclusion by a cursory demonstration
of this contrast— upon the nerves of a frog and of a
kitten respectively — laying them in turn upon two pairs
of electrodes by which polarising current is led into
the nerve and extrapolar current is led out to the
galvanometer.

With the frog's nerves the anodic extrapolar effect
(to the right) is comparatively large, the kathodic

0*5 volt

Fig. 43 (2383). — Extra-polar ( = " electrotonic ") currents of kitten's nerve.
produced by polarising currents of increasing strength from 0*5 to 2*0 volts. (The
standard deflection by O'ooi volt had a value of 40 mm., so that e,g: the A. and
K. currents at 2 volts have an E.M.F. of about 0*0007 volt).

extrapolar effect (to the left) is comparatively small.
These extrapolar effects are not due to current-escape,
for they are, as you see, completely abolished by
pinching the nerve between the two pairs of elec-
trodes.

With the kitten's nerve the anodic and kathodic

7

98 ANIMAL ELECTRICITY. LECTURE IV.

extrapolar effects are well-marked and of equal
mag-nitude. They are completely abolished by
pinching the nerve between the two pairs of
electrodes.

These last experiments — that relating to frog's
nerve in particular— will form the point of departure
of my next lecture. We shall then become fully
convinced of the "physiological" nature of these
extrapolar currents — at least in the case of frog's
nerve. Of mammalian nerve I have little know-
ledge, and therefore, little to say. Isolated mam-
malian nerve gives no " negative variation," and I
was thereby deterred from taking It as an object of
systematic study. At present it is to me a rather
mysterious stranger.

hote. — Electrotonic currents, according to Biedermann,
are much less marked on non-medullated than on medullated
nerves, the katelectrotonic current in particular being absent.
This however is denied by Boruttau (Pfliiger's Arcliiv, Ixvi.,
p. 285, 1897).

The presence of electrotonic currents on non-niedullated
nerves is in apparent contradiction with the view taken in
these lectures, that the interface between grey axis and fattv
sheath is the surface at which electrolytic polarisation takes
place. But the non-medullated state is not absolute, many
non-medullated nerves are more or less distinctly and
continuously myelinated, and in any case electrotonic
diffusion appears to be much less pronounced than on fully
myelinated nerves. There may prove to be some signili-
cance in the relation that apparently obtains in the com-

ANIMAL ELECTRICITY. LECTURE IV. 99

parativc magnitudes of anelectrotonic and katelectrotonic
effects in tlie different classes of nerves, viz., A. much greater
than K. in non-medullated nerves, A. greater than K. in
mechillated nerves of cold-blooded animals, A. equal to K. in
medullated nerves of warm-blooded animals.

But I am still in doubt concerning the " physiological "
nature of the extrapolar A. and K. currents of isolated
mammalian nerve, nor do I yet know whether the absence
of '* negative variation " on such nerves is in any way con-
nected with the equality of these currents.

REFERENCES.

" Polar effects " were first fully described by Pfluger in his
" Untersuchungen uber die Physiologie des Electrotonus."
Berlin, 1859.

The polar effects on Man are described by Waller and de
Watteville in the Phil. Trans. R. S. for 1882. (Influence
of Galvanic Current on the Excitability of Motor Nerves
of Man.)

Polarisable core-models were first systematically investi-
gated by Hermann {Pfliiger's Archiv, vols, v., vi., vii.,
1872-3. Handbuch, vol. ii., p. 174). They have recently
been still more closely studied by Boruttau. Pfliiger's
Archiv, 1894-6.

These three topics are briefly summarised in my " Intro-
duction to Human Physiology," 3rd Ed., pp. 364, 2>^6, 370.

Internal polarisation first alluded to by du Bois-Reymond in
the " Thierische Elektricitat " in 1849, and again in 1883

lOO ANIMAL ELECTRICITV. LECTURE IV.

in his monograph '' iiber seciuiddr-elektroniotoriscJie Ers-
cheimmgen am Muskeln, Nerven und elektriscJien Organen.
Berliner Sitztingsberichte ^ 1883.

In connection with the italicised words on p. 91, the following
sentence is of particular interest : " Ich begreife aber
heute nicht, warum ich nicht den Versuch so abanderte,
dass beispielsweise mit den Zeigefingern der Schlag
genommen, von den Mittelfingern die secundar-elektro-
motorische Wirkung abgeleitet wurde." (Loc. cit., p. 371).

OI

LECTURE V.

E L E c: T R O T O N U S .

**■ An." and *' Kat." Influence of ether and chloroform.
Physiological and physical effects. The electro-mobility
of living matter. Relation between polarising and extra-
polar currents in nerve. Strength. Distance. Von
Fleischl's deflection. Action currents are counter - cur-
rents. Extrapolar effects in mammalian nerve.

To-DA\'s chief experiment presents to you a demon-
stration of du Bois-Reymond's electrotonic currents,
commonly referred to by physiologists as Anelectro-
tonus and Katelectrotonus, but which I shall often
take the liberty of calling by the shorter and more
familiar workshop names of An. and Kat., and by
the still shorter pen-names A. and K.

Experiment. (Fig. 44.) The nerve is resting
upon two pairs of unpolarisable electrodes, to receive
through p p' the polarising cicrrent from a battery (in
the present instance at the pressure of i '5 volt), and
to give off through e e' the electrotonic current which
will be indicated by the galvanometer. The polaris-
ing circuit is completed at will by the key, and it is
made to pass in one or the other direction in the
nerve by means of a reverser, rev.^ parallel with the
transparent scale of the galvanometer.

^ For prolonged experiments a revolving key is used, by
which the polarising current is made through the nerve at
regular intervals in opposite directions.

102

ANIMAL ELECTRICITV. LECTURK V

The nerve Is facino- you ; and the connections are
such that the direction in which the spot moves
represents the direction of current through the
nerve. Closing- the key, I make a polarising- cur-,
rent In the direction p p' ; there Is a considerable
deflection to your right, indicating the presence of
an extrapolar current in the nerve in the same direc-
tion from e to e', or towards the polarised region of

EiG. 44. — Diagram of experiment to demonstrate A. and K.

the nerve. This Is an Anelectrotonic current, so-
called because it Is on the Anodic side of p p'.

Turning over the reverser to the left, and again
closing the key, I make the polarising current In the
opposite direction p' p ; there is now a rather less
pronounced deflection to your left, that indicates the
presence of an extrapolar current in the nerve to your

ANIMAL ELECTRICITY. LECTURE V. [ 03

left, from e' to e, or from the polarised region p' p.
This is a Katelectrotonic current, so called because
it is <_)n the Kathodic side of p' p.

\ OLi have now seen — and I will repeat the two
trials in rapid succession — that in each case the
extrapolar or electrotonic current, whether A. or K.,
passes in the nerve in the same direction as the polar-
ising current by which it is aroused.

Your first thought, perhaps — as was mine when
I first repeated the experiment — is one of disappoint-
ment. Is that all ? Yes, that is the gist of the whole
story, which you will find set forth at great length in
a long series of memoirs extending over the last
fifty years — at such length indeed that without some
definite assurance of the simplicity of the facts, even
a careful reader might pass it by, either missing the
point altogether, or as was the case in every English
text-book a few years ago, confusing it quite unneces-
sarily with the current of injury. Indeed, this con-
fusion was made by du Bois himself at the very out-
set of his work, but the confusion that remained in
his mind for at most a few months, was scrupulously
preserved in the text-books for upwards of fifty
years.

Your next thought is one of suspicion. Why this
is mere current-diffusion along a conductor, just like
what would happen along a hank of wet wool. That
is a perfectly reasonable thought ; ordinary current-
diffusion might well take place ; it is indeed a common

I04 ANIMAL ELECTRICITY. — LECTURE V.

fallacy ; we must In the first place observe all care to
exclude It, and then we must take means of assuring
ourselves that it has been excluded.

But even before this is done you will have noticed
a point that hints at something in the nerve other than
ordinary current-diffusion. The A. deflection and the
K. deflection are unequal — A. is greater than K. If
the two deflections had been by current-escape they
would have been equal.

This does not indeed exclude all thought of
current-escape, for the latter may be present with
the peculiar something else that is becoming apparent
to us. So we shall use further means to try the
point.

Let us anaesthetise the nerve by a little ether or
chloroform vapour, that will presumably distinguish
between a "physiological" and a "purely physical"
factor in the phenomenon, which in toto is, of course,
physical. That which is "physiological "?>., depen-
dent on the physico-chemical conditions peculiar to
the living state will be suppressed ; that which is
purely physical, i.e., dependent on the physical
properties of the dead nerve will persist.

Ether, Chlorofoj^m. — Here, then, are a couple of
experiments In which this test has been applied, and
from which you may recognise the propriety of dis-
tinguishing two factors In the entire phenomenon — a
physiological factor, true An. and Kat., subject to
anaesthetic Influence — a purely physical factor, the

ANIMAL ELECTRICITY. LECTURE V. lO'

Fig. 45. — Effect of ether on the anelectrotonic current.

Fig. 46. — Effect of chloroform on the anelectrotonic curieni.

I06 ANIMAL ELECTRICITY.-- LECTURE V.

" physIcaP electrotonus " of German monogTaphs, not
suppressed by anaesthetics, which we shall designate
by the colourless and non-committal expression "resi-
dual deflection."

This residual deflection — particularly well marked
in tig. 46 — ^itself gradually declines in course of time,
mainly I think, by reason of the drying, and therefore
increasing resistance, that you recollect to be one of
the effects produced by anai^sthetics. But this is a
detail upon which we need not dwell, and in this
connection it is hardly necessary to insist upon the
obvious fact that in this case, as in that of the neoa-

o

tive variation, chloroform exercises a permanent effect
and ether a temporary effect.

There are other signs by which we can recognise
that the extrapolar currents, An. and Kat., although

^ How much sometimes turns upon a word ! Hering, and
his chief lieutenant, Biedermann, speak of " physiological" and
"physical" electrotonus, and by physical electrotonus I for a
long time supposed that they meant to designate a phenomenon
intermediate between the physiological effect proper to living
nerve and physical current-diffusion — an electrotonus in fact
proper to dead, but otherwise anatomically perfect nerve. And
in this [relief, although explicitly stating that in my hands
anaesthetics had served to distinguish between electrotonus and
current-escape, I nearly succeeded in persuading myself of the
existence of a physical electrotonus distinct from current-escape.
Hering, however, has since informed me that " physical electro-
tonus " arose as a laboratory term meaning neither more nor
less than current-escape.

ANIMAL ELECTkI(IT\. LK<:TUkK V. TO7

in last resort physical, and, as we shall see, of electro-
lytic origin, are, nevertheless, entitled to the rather
indefinite qualification "physiological."

Interrupt the physiological continuity of the nerve
between the leading-in and leading-out electrodes, by
crushing it in the interpolar region e' p (fig. 44), or
better by touching it with a drop of strong acid. The
physiological conductivity is abolished, the physical
conductivity is intact (or enhanced if acid has been
used), but the extrapolar effects A. and K. are com-
pletely abolished.

Raise the temperature of the nerve above 40°, or
lower it to sav — S°, and al though — in the first case at
least — the physical conductivity has been enhanced,
the extrapolar currents, A. and K. are abolished, either
temporarily or permanently.

There is no time to-day for me to show you a
properly made temperature observation, as given in
fig. 6^) (and it is only as I am speaking that it occurs
to me that we might have made a rough and expedi-
tious trial by merely dropping the nerve into some
hot salt solution), but I can at once show proof that
the A. and K. effects you have just witnessed did not
depend upon current-escape. Pinching the nerve
with forceps, and then testing as before, we find
that they are completely abolished. There is no
deflection whatever, i.c ., no current-escape.

These currents depend therefore upon the physio-
logical state of the nerve —upon its "vitality" — and I

I08 ANIMAL ELECTRICITY. — LECTURE V.

may add, vary with variations in that state. Bad
nerves give bad currents, and that is specially the
case at this season of the year (February) when
nerves are at their worst.

There can be, I think, little doubt that these
extrapolar currents are an effect of electrolytic
polarisation. This interpretation, which was origin-
ated by Matteucci, elaborated by Hermann, and
more recently by Boruttau, has completely displaced
the original interpretation of du Bois-Reymond, who
discovered the facts — so completely indeed that I think
its consideration could only complicate the question
to us ; if you are curious in the matter, you will find
it argued at length in the '' Thierische Elektricitat,"
vol. ii., p. 289 to 389.

Nerve, made up of medullated fibres, is an
electrolyte, or rather a pair of electrolytes. Each
fibre consists essentially of a central grey core sur-
rounded by a sheath of white matter. And from
the fact that nerve composed of such fibres is the
only^ tissue of the body that exhibits the extrapolar
currents just described, we may conclude that the
electrolytic interface is the surface of separation be-
tween grey axis and white sheath.

The electrolytic effects are as follows : current
entering the nerve by the anode, traverses the w^hite
sheath to the grey core ; at the interface between

' Subject however to some reservation, as indicated in the note to Lecture IV.,
p. 98.

ANIMAL ELECTRIdTV,

LECTURE V.

109

sheath and core It has its exit from sheath where it
Hberates the positive ions (base, hydrogen), and its
entrance into core where it Hberates the negative
ions (acid, oxygen, &c.). Leaving the nerve by the
kathode, the current passing from grey core to white
sheath has its exit from the core and its entrance
to the sheath, and consequently positive ions are

Fig. 47. — Diagram illustrating the theory that extra-polar currents of medull-
ated nerve are due to electrolysis at the interface between sheath and axis.
Following the direction of the polarising current from copper to zinc through the
nerve fibre we have :

(i) Anode to sheath Acidic electrolysis.

(2) Kathode from sheath

(3) Anode to axis
5 (4) Kathode from axis
t (5) Anode to sheath.

(6) Kathode to sheath

Basic

»'

horizontal shading

Acidic

15

vertical ,,

Basic

>>

horizontal ,,

Acidic

»>

vertical ,,

liberated in the former, negative ions in the latter.
The counter-current from these liberated ions
weakens the original current, is in fact tantamount

IIO ANIMAL ELECTRICITY. LECTURE Y.

to added resistance at the interface, by reason of
which a loniritudinal spreading- of current takes place
on each side of each electrode. The extrapolar anodic
and kathodic currents witnessed at the commence-
ment of the lecture are thus accounted for.

Again you say perhaps "but this is physical, not
physiological " ; to which I should reply : " yes cer-
tainly it is physical, but that does not mean that it
is not physiological." It is physiological in so far
as it depends upon physiological conditions, upon the
state of nerve that we call living, a state of peculiar
physico-chemical lability, subject to all kinds of
modifying influences — temperature, moisture, drugs,
all the influences in short that we are accustomed
to consider in terms of their unanalysed effect on
living matter.

Yes, the phenomena are physical ; but they are
also physiological ; the two terms are not mutually
exclusive, unless we reserve the term physiological
for phenomena of which we are unable to detect
the physico-chemical mechanism. The chief aim of
physiological study is to express physiological pheno-
mena in terms of physics and chemistry. And I
venture to hope that we shall be able to push this
enterprise a good deal further in this direction ; I
shall not be disappointed or surprised if much of our
study of living nerve should turn out to be a study
of the simple phenomena of electrolytic mobility, and
if the depressant action u])on nerve of anaesthetics

ANIMAL l•:L^:(■TRI(:^^^

■LFX'TURE V.

1 1 1

and narcotics, and alkaloids, 8:c., should ultimately
prove to be a chemical immobilisation of normallv
electro-mobile prot(^plasm. I do not, however, wish
at this sta^e to pursue the aroument further than
may be necessary to convince you that it is the dis-
tinct aim of ])hysiolo^ical endeavour to express the
"physiological" in terms of the ''physical" and
" chemical."

L. o'ooi volt. R.

o"i volt

Fig. 48(2369). — Extra-polar (= "electrotonic") currents of frog's nerve, pro-
duced by polarising currents of increasing strength, from o*i to 0'6 volt. At each
strength the A. and K. currents are taken twice. Their magnitude may be
approximately estimated by reference to the standard deflection of o'ooi volt
recorded at the commencement of the observation.

And it will be part of our immediate task to
examine all the accessible electro-physiological phe-
nomena of nerve with a view to determine whether
or no they are reducible to the somewhat less myste-
rious form of electro-physical and chemical phenomena.

112 ANIMAL ELECTRICITY. LECTURE V.

In this connection the next effects to be analysed
will be those first discovered by Bernstein and by
Hermann, viz., the electrotonic decrement and the
polarisation increment.

But before doing this I should like to take up two
or three further points relating- to the electrotonic
currents themselves.

I shall recapitulate these points by means of a few
simple experiments, showing how the magnitude of
the extrapolar current varies (i°) with the magnitude
of the polarising current and (2°) with the distance
between leading-In and leading-out electrodes.

(1°) The nerve is resting upon two pairs of elec-
trodes p p' and e e' as shown in fig. 44. A polar-
ising current of 0*1 volt grives rise to an electrotonic
deflection of 1*5; with the polarising current at 0*2
and 0*3 volt, the deflection is 3 and 4*5. From which
(and perhaps still better from the record reproduced
in fig. 48), we learn that the magnitude of the extra-
polar current led off at e e' varies directly as the
magnitude of the polarising current led in at p p'.
This is quite in harmony with the view that the
extrapolar current Is an electrolytic effect, and with
the fact that electrolysis varies directly with current
density.

Now for the effect of distance between leading-in
and leadlng-out electrodes.

(2°) A nerve is resting upon six electrodes ; i and
2 are to remain throughout electrodes of the polar-

ANIMAL ELECTRICITY. — LECTURE V.

I I

isinof current, which is to be at the constant value
of about I "5 volt ; we shall lead off the extrapolar
current by 6 and 5, then by 5 and 4, then by 4 and 3,
that is to say, with distances between leading-in and
leadino--out electrodes at 3, 2 and i centimetres.

654321

We begin with e e' at 6 and 5, and complete
the polarising- current through i and 2 ; the electro-
tonic deflection is just visible to you, being about
5 cm. of scale. We make a second trial with e e/ at
5 and 4 ; the electrotonlc deflection is larger, about
30 cm. of scale. We make a third trial with e e' at 4
and 3, the electrotonic deflection is much larger still,
right off scale, and to get a measurement of this deflec-
tion the galvanometer would have to be shunted.

From these data, and still more clearly from this
table, we see that the magnitude of an electrotonic

Distance between leading-in electrodes = i cm.
Distance between leading-out electrodes = i cm.
Polarising current by i leclanche cell (= i"4 to 1*5 volt).

Length of nerve between leading-
-in and leading-out electrodes.

Anelectrotonic
current.

Katelectrotonic
current.

{Negative variation
by teta7iisation.)

3 cm.

2 „

-f I -5 mm.

+ 7'5 ,,

+ I20-0

— 0"5 mm.

— 2-5 „

— 90-0 „

{— 4'o mm.)
( — 4-0 mm.)

current diminishes very rapidly with increasing dis-
tance between leading-in and leading-out electrodes.

114 ANIMAL ELECTRICITY. — LECTURE V.

This is, in fact, the one obvious distinction between
an electrotonic current proper and a negative varia-
tion ; the latter is independent of the distance between
leading-in and leading-out electrodes. No doubt both
phenomena are an expression of polarisation, the
former of a stable polarisation, the latter of an un-
stable and fugitive polarisation that propagates itself
as a wave along the compound electrolyte^ ; but at the
present juncture it is not necessary that we should
study this rather complicated question, and I shall
reserve it for a future occasion.

I wish rather to exhibit some further definite data
concerning the polarisation phenomena of nerve — data
of which I cannot at present propose any final ex-
planation, but which are evidently pieces of that
particular puzzle.

One is a fact first pointed out by v. Fleischl, that
has figured in physiological literature for several years
past as a sterile item. The other is a little bunch of
facts that have tantalised me for the last ten years
by their paradoxical bearing. I have not hitherto
ventured to call attention to them, and I do so now
in a very dissatisfied frame of mind. They are frag-
ments, evidently significant, but I do not know what
they signify, I cannot even imagine what they signify.

^ Boruttau has placed the finishing touch upon the identiti-
cation between the phenomena in nerve and in core-models by
showing that in the latter as in the former a diphasic negative
wave is aroused by a single induction shock whatever the
direction of the latter.

ANIMAL ELECTRICITY. LECTURE V.

Here is von FleischTs experiment.

Fig. 49.

Nerve, galvanometer, and secondary coil are in one
circuit. Without the nerve in circuit {i.e., with a short
circuiting- key down) I test for the direction of the make
and the break induction currents in the secondary coil
and galvanometer. The make deflection is to your
right, the break deflection is to your left, and, as you
see, the two deflections are equal and opposite, so that
if a series of rapidly alternating make and break
currents is passed through the galvanometer there is
no deflection. But when I open the nerve-key so as
to put the nerve in circuit, keeping up the alternating
currents, there is a deflection to your left, i.e., in the
direction of the break current.

To what is this deflection due } Is it physical or
is it physiological ? It is in any case due to a polari-
sation counter current ; a few years ago I should have
answered that it is physical, not physiological, and I
might have illustrated the answer by reproducing^- the
experiment on a polarisation cell without any nerve at
all. But I should have had to take stronger currents,

Il6 ANIMAL ELECTRICITY. LECTURE V.

and with various electrolytes I might have shown
deflection, now in the direction of the make, now in
the direction of the break. But now I answer that
it is physiological, and shall illustrate this statement
by killing the nerve (dipping it into hot water and
replacing it on the electrodes), and showing that on
the dead nerve there is no longer any deflection in
the direction of the break when the nerve is traversed
by the same series of alternating currents. As you
see, the galvanometer spot remains unmoved, even
when I considerably strengthen the induced currents ;
it is not till these are raised to an excessive strength
that the spot begins to shift. This is a physical
effect which I do not understand, and shall there-
fore make no attempt to explain. It is however
easy to distinguish from the deflection afforded by
living nerve.

Well then, admitted that the deflection in the
direction of the break is "physiological," present with
the living nerve but absent from the dead nerve, and
dependent upon the polarisability of living nerve —
are we able to proceed further in our explanatory
analysis ?

Not much further, with any legitimate assurance;
v. Fleischl gives a highly complex explanation which
I shall not reproduce to you.^ Hermann regards it

^ V. Fleischl's experiment and his interpretation of it are
given in the "Wiener Sitzungsberichte, 1878.

ANIMAL KLIXTRICITV. LECTURE V. II7

as a polarisation increment.^ I am not satisfied with
either of these explanations, but think it more probable
that the v. Fleischl's deflection which you have just
witnessed is a case of what du Bois-Reymond
designated as " positive polarisation," and Hering
and Hermann subsequently showed to be an after-
anodic action-current." These are the several currents,
of which on this view only the after-anodic action-
current is apparent to you as a deflection in the
direction of the break. Seeing that the nerve and
galvanometer scale are facing you, and that the
connections are such as to make deflections on the
scale signify directions of current in the nerve (you

^ Hermann, Handbuch, vol. ii., p. 167.

- There is still a fourth possibility, i.e., that the effect in the
direction of the break may be due to a superiority of the
polarisation current after make over the polarisation current
after break. Although under the ordinary conditions of
physical experiment, the electrolysis by a break-current
exceeds that by the corresponding make-current, it is con-
ceivable that the polarisability of living matter may be such
that the longer make-current may produce a greater electrolysis
than the shorter break-current.

The so-called " positive polarisation" or post-anodic action-
current, which is in the same direction as the exciting current,
is very readily intelligible as the effect of a post-anodic zinca-
tivity. It is easy to demonstrate. Its theoretical counter-
part during the passage of an exciting current, and opposed
to that current, is equally readily intelligible as the effect of
kathodic zincativity. It is, as far as I can see, insusceptible
of dived demonstration.

Il8 ANIMAL ELECTRICITY. LECTURE V.

may Indeed for the moment Imagine that the scale
is an enormous nerve) we have : —

1. The make-current to the rioht + — ^ —

2. Its counter-current to the left ^ —

3. The break-current to the left - <-€ +

4. Its counter-current to the right — ^

5. V. Fleischl's current to the left ^ —

i.e., as an after-anodic action-current of current No. 3,
which alone is exciting, and which gives rise to
" zincativity " on the side where the arrow-tail has
been figured. But for this arrow-tail representing a
post-anodic zincativity the four currents i, 2, 3, 4
would neutralise each other, or if any difference
occurred it should be to the right by reason of an
excess of 4 over 2.

I am sorry to dwell so long upon this apparently
small and dubious point, still let me state in a few
sentences the reasoning that brought me up against
it. Considerino- that make excitation is kathodic
(p. 78), that excited tissue is zincative (p. 84), that
the make and break induced currents being equal
in quantity and unequal in potential, will therefore
be unequally excitant, while neutralising each other
on the galvanometer, I argued that with the nerve
and galvanometer In one circuit, it might be possible
to obtain a deflection in the direction of the make
owing to an action-current opposed to the break.
In the event I obtained just the opposite effect,
and reproduced what I recognised to be the effect

ANIMAL P:LI:CTRICITV. LECTURE V. I I9

in the direction of the break previously observed by
V. Fieischl. My reasoning had evidently been im-
perfect ; starting from the no doubt theoretically
correct assumption that any exciting current should
arouse an action-current of the nature of a polarisa-
tion counter-current, I sought to obtain evidence of
it upon nerve, and failed to do so, partly by reason
of the fact that the excited state in nerve does not
remain localised but spreads rapidly, partly by reason
of the then unknown after-anodic action-current,
which on the contrary appears to be a prolonged and
localised state. Direct evidence during the passage
of an exciting current of an opposite action current
did not and does not exist, yet from a theoretical
standpoint, it was and is a rather crucial point, and
I intend as soon as possible to try the point upon
more slowly reacting tissue. Meanwhile as regards
nerve, the nearest approach to direct evidence is
afforded by the '' polarisation increment " to be
considered next ; this in my view is the negative
variation of a latent action-current opposed to the
polarising current. Indirect evidence is also afforded
by the abterminal and atterminal or abmortal and
admortal effects of Encrelmann and of Hermann, as
will be developed in a future lecture.

Let me now ask your attention to another curious
and puzzling fact, concerning which I have no
glimrnering of an explanation to offer.

I20

ANIMAL ELECTRICITY

LECTURE V.

Instead of a frog's nerve there is now a kitten's
nerve upon the two pairs of electrodes p p' e e' (fig.
44, p. 102) ; It Is thicker than the frog's nerve, so
that our standard deflection by ~^ volt is large, but
this is a detail. There Is nothing remarkable about
the current of injury. I now test for the negative
variation in the usual way, and none is to be seen, al-
though the resistance In the exciting as well as in
the galvanometer circuit Is small, and although the

0-5 volt
i-o „
1-5 .,

2-0 „

Fig. 50 (2383). — Extrapolar (=" electrotonic ") currents of kitten's nerve,
produced by polarising currents of increasing strength from o"5 to 2*0 volts. (The
standard deflection by O'ooi volt, not here reproduced, had a value of 40 mm.,
so that e.£. the A. and K. currents at 2 volts have an E.^NI.F. of about 0*0007 volt.)

strenofth of excitation be still further increased. This
has been no exceptional result ; I have never yet wit-
nessed a true action-current from isolated mam-
malian nerve, placed upon the electrodes within a
few minutes after the death of the animal, whereas
frog's nerve under similar conditions has continued
to exhibit the action-current for hours and days
after excision. The contrast is glaring, and out of

ANIMAL 1:L1-:CTRRITV. LECTURE V. 12 1

all measure with the more enduring vitality of cold-
blooded as compared with that of warm-blooded
animals.

Turning our attention to the extrapolar or electro-
tonic effects, which are, as you have just seen, the
most obvious evidence of electrolytic polarisation
within the nerve, we shall speedily find ourselves
confronted by some paradoxical results. We obtain,
as you see, extrapolar currents that are equal and
opposite on the side of the Anode and of the Kathode
respectively, instead of greater on the side of the
Anode than on that of the Kathode as in the case of
frog's nerve. Of course you think of ordinary current
diffusion, but the extrapolar effects are not due to
ordinary current diffusion, for they are abolished by
crushing the nerve betw^een the leading-in and leading-
out electrodes, or by dipping into hot water either the
end of the nerve that lies on the leading-in electrodes,
or the end that lies on the leading-out electrodes. wSo
we put the effects down in the category of physio-
logical phenomena, and proceed to test them by
anaesthetic vapours, which as you remember produced
unmistakeable modifications of the extrapolar currents
of frog's nerves. The result is a little surprising and
by no means satisfactory ; the anaesthetics with which
we are most familiar — ether, chloroform, carbonic acid
—do not modify the extrapolar effects in the least.

And there the matter must stand for the present
as regards isolated mammalian nerve. No negative

122 ANIxMAL ELECTRICIT\'. LECTURE V.

variation. Equal extrapolar currents. Anodic and
Kathodic, physiological as judged by the tests of
crushing and of hot water, not physiological as judged
by the test of anaesthetic vapours. In short a
thoroughly unsatisfactory position of matters ; from
which, althouo'h I see no issue at this moment, an
issue must be found. All that I feel entitled to say
at this perplexed stage is that you will at least realise
how it has happened that my experiments on nerves
that answered by "yes" and "no" have been many,
while on nerves that give no clear answer at all my
experiments have been few. And perhaps at this
juncture the negative results afforded by mammalian
nerve may serve to throw into clearer relief the
positive results obtained on frog's nerve.

REFERENCES.

(i) Electrotonic currents discovered and named by du Bois-
Reymond in 1843 (" Thierische Elektricitat," vol. ii., p.
289) ; explained as being polarisation effects by Hermann
(" Pfluger's Archiv," v., p. 264 ; vi., p. 312 ; vii., p. 301 ;
1872-3; Summary in " Hermann's Handbuch," vol. ii.,
P- 174).

(2) ''Positive polarisation'' first mentioned by du Bois-
Reymond in the '* Thierische Electricitiit," vol. i., p. 240.
and more fully described in the " Berliner Sitzungs-

ANIMAL KLKCTRICITV.- LIXTUkl-. W I 23

berichte," 1883, p. 343 ; explained as beiiif^ after-anodic
action-currents by Hcring in the "Wiener Sitzungs-
berichte," 1883, p. 445, and by Hermann in " Pfliiger's
Archiv," vol. xxxiii., p. 103, 1884.

[These three memoirs are given in Burdon-
Sanderson's " Translations of Foreign Biological Me-
moirs." Oxford, 1887].
Von FleiscJir s deflection described in the " Wiener Sitzungs-
berichte," 1878 ; considered by Hermann to be a polari-
sation increment (" Handbuch," vol. ii., p. 167).

(3) EiJier as a means of distinguishing between "physical"
and " physiological " electrotonus, described by Bieder-
mann in the "Wiener Sitzungsberichte," 1888, p. 84;
and in his " Elektrophysiologie, p. 693, Jena, 1895.

124

LECTURE VI.

ELECT ROTON US {Cotitinned),

Influence of acids and alkalies. Influence of carbonic acid and
of tetanisation. Influence of variations of temperature.

The action-currents of polarised nerve. Bernstein's electro-tonic
decrement. Hermann's polarisation increment.

InfltLence of Acids and Alkalies. — Turning back to
the kind of nerve upon which we have found that
experimental comparisons can be made systematically,
let me next direct your attention to some experiments
that at once suggest themselves when we have ad-
mitted that the extrapolar currents of nerve are
caused by electrolytic polarisation.

Looking back to the series of effects represented
and summarised In ^<g. 47, p. 109, we naturally ask our-
selves what will be the effects of acids and bases upon
An. and Kat.

Reviewing any considerable number of experi-
mental records in which A. and K. have been taken
before and after the nerve has been submitted to the
action of a weak acid or of a weak base, we shall
find :—

ANIMAL ELECTRICITY. LECTURE VI. I 25

.r^^!

h

in

Fig. 51. — Efl'ect of COgOn K, primary augmentation.

n

ff !(

i M

i

D

Fig. 52. — Effect of COg on A, primary diminution, secondary augmentation.

If II I

( ! 1

h

^y li iin,

! (

^'^^^'^^^^^^^

Fig. 53. — Effect of COo on A, primary augmentation.

126 ANIMAL ELECTRICITY. LECTURE VI.

(i) That the most prominent and unmistakable
modifications have been : an augmentation of Kat. by
sHght acidification ; a diminution of Kat. by slight
basification.

(2) That An. has been sometimes augmented,
usually diminished, but sometimes augmented by weak
acidification, and

(3) That An. has been but little affected by weak
basification.

These results do not sound particularly har-
monious intei'- se, nor seem to be held together under
any very obvious law. That depends, I think, upon
the somewhat narrow range of concentration within
which an acid or alkaline reagent effects what we
may be entitled to designate as characteristic acid
or alkaline changes. Still we may even at this
stage pick out as characteristic the augmentation and
diminution of Kat. by acidification and basification
respectively ; and we may remark that the augmenta-
tion of An. has always been effected by weaker
acidification than the diminution of An.

A distinct step forward will be taken by the
examination of records in which both An. and Kat.
have been observed on the same nerve before and
after its treatment with acid or with alkali. Within
a certain range these reagents will have acted in
opposite directions upon the two effects, or in the
same direction but unequally, so that the ratio
between their magnitudes is altered. We shall now

ANIMAL KLECTKRITV. LFXTURE VI. 12/

find it convenient to adopt some conventional ex-
pression for that ratio. The number expressing the
value of the magnitude of A. divided by the magnitude
of K. presents itself as a natural formula, and we shall
hereafter refer to it as the quotient ^/k-

We are now able to say from examination of
records in which both A. and K. have been modified,
that the characteristic effect of acidification is a
diminution of the quotient ^/k, and the characteristic
effect of basification an augmentation of the quotient

We are entitled further to make the statement

that acidification affects first Anodic then Kathodic

polarisation, causing first increased then decreased
effects, their order of appearance being :

1. Increased A. as the first effect.

f Diminished A. ) .u . • i /r .

2. -, T T jr -as the typical enect.
( Increased K. ) ^^

3. Diminished K. as the last effect.

The first effect is frequently missed, even with
a weak acid, such as COo. The second effect is not
often obtained pure ; more frequently we find a large
diminution of A. together with a relatively smaller
diminution of K., i.e. an absolute diminution of the
quotient -^ k.

These are dry statements ; it was, however, in-
cumbent upon me to make them, in order to lay open
the grounds upon which I have concluded that //ic

128

ANIMAL ELECTRICITY. LECTURE VI.

characteristic effect of acidification is a diminution of
the quotient ^Jk, cind the characteristic effect of basi-
fication an augmentation of the quotient ^/a-.

^^4444^^^^}^^

v\V

Fig. 54.— Effect of a weak alkaline bath (KOH. N .„ or 0-285 per 100) upon

A. and K.

1 «

'][Yt/A\j

y

Fig. 55. — Effect of a weak acid bath (propionic acid N/,„) upon A. and K.

The influence of carbonic acid and of tetanisat ion. —
We have seen in a previous lecture that the nerve is
altered by tetanisation precisely as it is altered by

ANIMAL ELECTRICITY. LECTURE VI. I 29

Fig. 56. — Action of COg on A. and K.

Fig. 57. — Action of ammonia vapour on A. and K

AlMfWfwVW

Fig. 58. — Effect of Tetanisation on A. and K.

130 ANIMAL ELECTRICITY. LECTURE VI.

carbonic acid, and we concluded therefrom that
tetanisation gives rise to an evolution of carbonic
acid within the nerve.

Fig. 59. — Effect of COo on A. (primary augmentation).

Fig. 60. —Effect of Tetanisation on A. (augmentation).

We are naturally led to test the effects of car-
bonic acid upon these extrapolar currents A. and K.,
which we have just found to be subject to modifica-

ANIMAL ELECTRICITY. — LECTURE VI.

131

tion by ether and chloroform ; and as soon as we
have witnessed the effects of carbonic acid upon
these currents, our next obvious step is to test upon
them the effects of prolonged tetanlsation.

Fig. 61. — Effect of CO^ on A. (primary diminution, secondary augmentation).

Fig. 62. — Effect of Tetanisation on A. (diminution).

The effects produced by carbonic acid — and I may
add, by tetanisation — are very characteristic. Their
description may best be given by the exhibition
of a series of representative experiments. Here, for
example, is a group of four such experiments, in

132 ANIMAL ELECTRICITY. LECTURE VI.

which the effects of carbonic acid and of tetanisa-
tion upon anodic currents have been recorded. Car-
bonic acid produces either an augmentation or a
diminution of these currents. Tetanisation also pro-
duces either an augmentation or a diminution.

On reviewing a considerable number of records,
we should find that In the case of carbonic acid, a
diminution of A. Is the rule, an augmentation of A. the
somewhat rare exception ; whereas in the case of
tetanisation, although a diminution of A. has usually
been produced, an augmentation of A. has occurred
frequently enough not to deserve the qualification
of exceptional.

I think we may admit these results to rank as
confirmatory evidence of the conclusion that tetanisa-
tion gives rise to carbonic acid ; an augmented A. Is
a slighter effect than a diminished A., and it is not
surprising perhaps to find the slighter effect more
frequent by tetanisation than by carbonic acid freely
supplied.

But whether this be admitted as evidence or not
— in Chapter III. the point is Indeed already based
on evidence which Is, In my opinion, sufficient and
conclusive — these experiments clearly show that
the electro-mobility of nerve Is modified by carbonic
acid and by prolonged tetanisation.

The modifications of the Kathodic current effected
by carbonic acid are more regular than are those of
the anodic current. The former appears to be less

ANIMAL ELECTRICITY. LECTURE VL I 33

sensitive than the latter, and in all the experiments
I have made up to this time, an augmentation of K.
has been produced by carbonic acid and by tetanisa-
tion. This is illustrated in figs. 57 and 58, where
both A. and K. alternately produced have been
placed under observation. In both cases the K. cur-
rent has been obviously increased by carbonic acid
and by tetanisation respectively, but the A. current
diminished by carbonic acid in fig. 57, exhibits no
marked alteration in consequence of tetanisation in
fig. 58. Presumably in this last case a mean hap-
pens to have been struck between augmentation and
diminution.

The Influence of Temperature. — It is a very
simple matter to examine the effect of a raised or
lowered temperature upon the extrapolar currents,
and the results — in the case of raised temperature
at least — are very constant and very characteristic.
All we have to do is to place the nerve-chamber in
a receptacle that is packed round with ice and salt,
or gradually warmed by a spirit-lamp, and then take a
continuous observation in the usual way. I shall not
tax your patience by asking you to witness such an
observation ; to be of any value it would have to be
slowly made w^ith the temperature raised or lowered
through a range of 20 degrees at a rate of a degree
a minute. Moreover, the photographic record gives
a better general view of matters than the observation
itself, and although less interesting perhaps, is cer-

134

ANIMAL ELECTRICITY. LECTURE VI.

tainly more trustworthy. Here is such a record
(fig. 62,), of a series of alternating A.'s and K. 's at
one minute Intervals, with the temperature gradually
raised from 1 8° to 40*^ and then allowed to fall. There
are two principal points exhibited In this record,
which is a typical one ; firstly the fact that at about
40° the extrapolar currents are somewhat suddenly
diminished almost and sometimes quite to extinction —

Fig. 63. — Influence of rise of temperature upon A. and K.

which is evidence of their physiological character ;
secondly, the fact that in consequence of the rise of
temperature A. has diminished and K. has increased.
This last is, I think, a very characteristic and note-
worthy point. For referring back to the last two sets
of experiments, relating to the effects of acidification
and of tetanisation, we find that all three of these

ANIMAL ELECTRICITY. LECTURE VI. I 35

agents — acid, heat, and action — which presumably
provoke a chemical disruption of living- matter —
have as their common effect an augmented kathodic
polarlsability.

And please notice with reference to this record,
that there can be no question here of any fallacy by
alteration of resistance. This point has of course
been carefully examined by other experiments into
which it is not necessary to enter now ; but in the
present case, with a raised temperature (40°), i.e.,
with increased conductivity, there are diminished
currents, and the inc7'eased K. is with a falling
temperature, and cotemporary with a diminished A.
Comparing the relation between A. and K. before
and after the rise of temperature, there is a very
evident diminution of the ^/k quotient ; as was the
case in consequence of acidification, and in conse-
quence of tetanisation.

The Eledrotonic decrement. The Polarisation
increment. — There are two more cardinal experiments
belonging to our subject that I am anxious to demon-
strate and to explain as clearly as I am able, and that
will bring to its conclusion this preliminary exposition
of the principal data concerning the electromotive
reactions of nerve.

The first experiment is to show that an electro-
tonic current, like a current of injury, is diminished
during excitation — undergoes a negative variation.

'36

ANIMAL ELECTRICITY. LECTURE VI.

(Bernstein.) We shall see that this is true for both
directions of current — that both An. and Kat. are
diminished during excitation.

Let us begin with An., the connections being as
in fig. 64, with exciting and polarising circuits con-
joined as shown, so that both these currents pass into
the nerve by the same pair of electrodes.

/C./V 1 /

AnelecCroConas.
Decrement,

icm. 1 1

K&telecCroConu^.
Decrement

u-v:^

Fig. 64.

I first make the polarising current, which provokes
an anodic extrapolar current to the right in the nerve
and in the galvanometer ; now that the deflection is
steady I excite the nerve, and during the excitation
the spot moves to the left, indicating a diminution of
the extrapolar anodic current.

How shall we best interpret these facts. Let us
first formulate them in terms of the usual signs + and
— , positive and negative. During polarisation /' is

ANIMAL ELECTRICITY

-LECTURE VI.

^2>7

— , / is -\- y e' is less +, ^ is least +. In relation to
each other e is 4- and e is — . Write these signs down
then against e' and e of the figure (fig. 65) and trace
the current through. You probably first give it as
being from e' to e, i.e., the reverse of what it is, until a
little reflection makes clear to you that as regards ex-
trapolar current, e is kathode and e is anode. So you
change the signs to + at ^ and — at e'. If from this
point you follow the change produced during excita-

FiG. 65.

tion, you would not go wrong whether you take +
and — potentials at 3 and 4 respectively, or their
— and + poles at the galvanometer. Still mistakes
are often made, and it is necessary to be carefully on
one's guard, for it to come out evidently that excita-
tion must give an effect negative to the electrotonic
current.

The way in which I prefer to express it is this : e
is more anodic than e, i.e., less zincative, and current in

138

ANIMAL ELECTRICITY

-LECTURE VI.

the nerve Is from e to e' . e' is more anodic than e^
i.e., more zincable, and the excitatory change gives
current in the nerve from e to e.

Our second experiment is to show that a polarising
current is increased during excitation — undergoes a
positive variation. (Hermann).

The connections are as in fig. 66, as being perhaps
a Htde more obvious than would have been the case
with polarising current, galvanometer and secondary

icm i-s

v5

N PolansdCion

Increment.

ic.m 1-5

•J

S.Poldr/saCion

ffS^

Increment

Fig. 66.

coil in one circuit connected with the nerve by a
single pair of electrodes. [The resistance boxes r. R.,
used as shewn in figs. lo and ii on pages :^'^ and i"^,
enable us to take a convenient voltage (o'l to 0*5) for
the polarising current.]

Using a Leclanche cell and having set the resist-
ances at 1000 and 14000 ohms respectively to get a
voltage of about o'l, I close the key in the polaris-
ing circuit giving current from e to e' in the nerve.

ANIMAL ELECTRICITY. LECTURE \T. I 39

The Spot flies off scale to the rioht. I brino- it back
on scale by a considerable movement of the controlling
magnet, and when it' is steady, excite the nerve by
closing the key of the induction coil. The deflection
during excitation is to the right, i.e., the polarising
current is increased.

This is precisely as you might have foretold, never
having seen the experiment before. The nerve
at e is anodic, zincable, and during excitation it gives
current from e to e\ i.e., with the polarising current.
You may perhaps express this in terms of positive and
negative, but by no means so clearly ; in fact this
simple matter under the title of " polarisation incre-
ment " is one of the well known posers of honours
examinations in physiology. But I should not advise
any candidate to say "zincable" to his examiner, I
only advise him to think '' zincable " in order to under-
stand the subject.

Let us fix the matter by repeating the two experi-
ments with a reversed polarising current.

In the first experiment (of the electrotonlc decre-
ment) p Is Kathodic ; the electrotonlc deflection
(Kat.) Is from right to left; during polarisation the
nerve is less Kathodic at e than at e\ i.e., less zincative
and more zincable at e, and during excitation there is
current in the nerve from e to e\ i.e., the electrotonlc
current is diminished.

The second experiment (of the polarisation incre-
ment) is obviously the same whichever way you take it.

140 ANIMAL ELECTRICITY. LECTURE VI.

Here is the experiment of the polarisation incre-
ment with a sHghtly different circuit. The polarising
current, galvanometer, secondary coil and nerve are
in one circuit. The nerve receives the polarising
and exciting currents, and gives its electrical response
through a single pair of unpolarisable electrodes.

The first thinor to do is to see that there is little
or no current from the electrodes and portion of nerve
between— if the nerve happened to be injured near
one or other of the electrodes, we should have a
current of injury and on subsequent excitation a
negative variation of that current that might confuse
or mislead us.

The next step is to set the alternator in movement
and see that the induction shocks rapidly pulsating
to and fro through the nerve and galvanometer, do
not of themselves give any deflection. If the induc-
tion currents were taken too strong, we should be
confused by an initial and terminal kick by the first
make and last break shock of the exciting series, and
by a permanent deflection during the series in the
direction of the break current, to which allusion was
made above (p. 114).

These two preliminary sources of error having
been excluded, we may proceed with the experiment
proper.

I close a key in the polarising circuit. The spot
flies off to the right. I bring it back to scale by
means of the controllinijf maonet. And now that it

ANIMAL ELECTRICITY. LECTURE VI. I4I

is at rest, I excite the nerve. There is a deflection
to the right, i.e., an increment of the polarising
current.

Repeating the experiment with the reversed
direction of polarising current, everything is re-
versed, viz., this current is to the left, and its
excitatory variation Is also to the left.

Trace out the rationale of the polarisation Incre-
ment in this form, and you will recognise that in both
cases the anodic portion of nerve, or "way in" of
current, being the more zincable spot, becomes more
zincatlve during the superadded state of excitation.
There is thus "current of action" in the same direc-
tion as polarising current.

These varieties of effect in accordance with various
combinations of circuits, might readily be extended.
We might, e.g., test for the decrements of An. and
Kat. with the coil In the electrotonic and oalva-
nometer circuit, instead of in the polarising circuit.
Or going back to our second fundamental experi-
ment, as described In the first lecture — the negative
variation of nerve current (p. lo) — we might combine
Into one the leading-in and leading-out circuits.

The results of such experiments would come out
precisely as might be anticipated. Wherever current
enters a nerve from an electrode, the nerve is anodic
and zincable, whether such current be a polarising
current sent into the nerve, or an electrotonic current,
or a current of injury drawn o^ from the nerve.

J 42 ANIMAL ELECTRICITY. LECTURE VI.

But I have thought that the possible confusion
of ideas resulting from such experimental complica-
tion might overbalance the advantage of the exten-
sion of data, and even the distinct practical advantage
in certain cases, of being able to ■ test short bits of
living tissue through a single pair of electrodes.

Besides, if the principle has been mastered, its
manifold applications can present no further difficulty ;
an allusion to them will have been sufficient, their
detailed description would be superfluous and there-
fore tedious.

An action-current, however excited, and under
whatever circumstances, whether as a negative varia-
tion of an injury current, or as a positive variation of a
polarising current, or as a negative variation of an elec-
trotonic current, is due to a physiological (= physico-
chemical) inequality between two points. Active tissue
is "zincative," resting tissue is " zincable."

Look at this last diagram. Is it not forbidding.^
It summarises all the currents experimentally detected
in nerve ; I shall not undertake to wade through their
redescription in cold blood. To anyone who has not
mastered their key, they must remain unintelligible ;
to anyone who has mastered their key, they will be a
legible and symmetrical page in the story of living
matter.

AxMMAL ELKCTKICIT v.— LECTURE VI.

H3

T ' '^■'"L '.^ J

Demd red tion

m >

•* m

Poi.Vdr.

I cm IS J

N PolariidCion

ic-m IS -J

5 Po/dr/saCion

Ane/ecCroConus.
Decremenc

I cm. I I

Ka. CelecCroCon u6.
< a(((C

Fig. 67.

144 ANIMAL ELECTRICITY. LECTURE VI.

REFERENCES.

Electi^otonic decreme7it first described by Bernstein in du Bois-
Reymond's Archiv., 1866, p. 614.

Polarisation increment first described by Hermann in Pfluger's
Archiv., vol. vi., p. 560, 1872; and further explained in
Pfliiger's Archiv., vol. vii., p. 349, 1873.

[Previously noticed by Griinhagen, but by him
attributed to a diminution of resistance. (Zeitschrift
fiir rationelle Medicin, 1869.)]

Experiments illustrating the action of anaesthetic and other
reagents on electrotonic decrements and polarisation incre-
ments are given in the Croonian Lecture for 1896. (Phil.
Trans. R.S., 1897).

General plan of apparatus employed to investigate the influence of
reagents upon the electrical response of isolated nerve.

The iierveeliaiiiher cmita
cirodes connected wiih K,,

IS I lie nerve resiing upon a pair of iiiipolarisahle
. ;iri>l a pair of platinum elcctioiles, through which
the nerve is excited. The w.ashliollle serves to prevent drying of the nerve, an.l
in certain cases is used to slop acid vapour.

'K\\e exciling apl>aratiis is represented above; the circular interrupter in the
primary circuit revolves once a minute, and makes contact at a mercury pool for
; of each revolution. The vibrating interrupter of the coil starts as the circuit is
completed, an<l the nerve is thus letanised each minute for 7J seconds, at a fre-
ipiency of 70-75 interruptions per second.

The keyboard is composed of four bridging keys : K, in connection with the
nerve at T and L, !-:„ with the compensator, K, with the recording galvanometer,
and K, on occasion with a demonstrating galvanometer. When all the keys are
closeil everything is short-circuited through Ihem ; the keyboard is then simply
a metallic ring. Opening K, and K, puts the nerve into connection with the
galvanometer : opening K, lets into the nerve-circuit any suitable fraction of a
volt from the cell and rheostats r R. To take 0001 volt from a Leclanche
cell, r is taken - 10 ohms, and R ^ 14,690 ohms : to take a polarisation current
ol o-oi voir, r is inken - too ohms, and R 14,600 .ihms, Xr.

N.B.-The galvanometer records its movements to Right and Left of
some arbitrary position of rest. The connections and disposition of the
apparatus are such that deflections to the Right or Northwards represent
positive effects, and deflections to the Left or Southwards represent
negative eff^ects.

The completed records (with the exception of Figs. 42 and 43) are
turned so that positive deflections to the Right or North read upwards,
and negative deflections to the Left or South read downwards.

Thus ;/. the negative variation reads downwards, anodic deflections
read upwards, kathodic effects read downwards.