MARINE BIOLOGICAL LABORATORY.

Received 8 No v1 34

Accession No. 44194

Given by Dr. j. c< B

Place, Univer sit y o f Liverpool

*£*r*o book or pamphlet is to be removed fpom the liab-
oratory muithout the pepmission of the Trustees.

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THE SIGNS OF LIFE

FROM THEIR ELECTRICAL ASPECT

LECTURES ON PHYSIOLOGY, PUBLISHED UNDER THE
AUTHORITY OF THE UNIVERSITY OF LONDON

VOL. I.— EIGHT LECTURES

ON

THE SIGNS OF LIFE

FROM THEIR ELECTEICAL ASPECT

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

X

i.F

LONDON
JOHN MURRAY, ALBEMARLE STREET

1903

PREFACE

THE following monograph embodies the first of a series of
lectures on Physiology, delivered by the Physiologists of
London in the Laboratory of their University.

The general object of the scheme of which these particular
lectures form part, is to present the results of recent investiga-
tion by the investigators themselves — orally and with experi-
mental demonstration in the lecture-room — outside the lecture-
room by monographs approved by the University.

With the modification considered suitable for the case of
University publications, the procedure of the Royal Society as
regards the printing of papers in the Philosophical Transactions
has been adopted by the Senate of the University of London,
the regulations in connection with the official publication of
lectures being as follows :—

" Manuscripts of Lectures delivered, or of the results of investiga-
" tions made in the Physiological Laboratory of the University, shall,
" in first instance, be submitted for consideration to the Physiology
" Committee, to be referred, if considered suitable, to two referees, who
" shall be requested to report to the Physiology Committee as to their
" fitness for publication.

" Manuscripts shall be accepted only if reported suitable for publi-

" cation —

" A. By reason of additions to knowledge in Physiology and
" Experimental Psychology.

" B. By reason of excellence of exposition of recent additions to
" knowledge and doctrine in Physiology and Experimental
" Psychology."

The present eight lectures embody in large measure the
recently published (and unpublished) results of my own current

vi PREFACE

work during the last five years. They are in continuation of a
First Series of Lectures on " Animal Electricity," published in
1897. They will no doubt be found to suffer from many of the
disadvantages inherent to the nascent state, I hope that they
may prove to possess also some of its advantages.

A. D. W.

October 1903.

CONTENTS

LECTURE I

PAOJ

Aim and Purpose of the Lectures — The Subject-matter of Physiology
-The Signs of Life ; The Sign of a Sign is a Sign of the Thing
itself — Two Familiar Instances ; on Muscle and on Nerve — A
Proof of Chemical Change in Seeds — An Experiment on Muscle
—Retinal Currents — Vegetable Currents — Terminology — Solu-
tion-pressure— Summary ...... i

LECTURE II

The Prospect — Demonstration of Retinal Currents — The Initial
Current — The Principal Fact ; Subordinate Features — Three
Types of Response — Two Opposed Processes — Effects of Com-
plementary Colours — Cause : Effect — Anaesthetics — Retino-motor
Effects 21

LECTURE III

Plan of this Lecture — Electrical Excitation of a Frog's Eyeball-
Modification of the Response to Light subsequent to Tetanisa-
tion, and during Tetanisation — Effects and After-effects of Single
Shocks — " Blaze-currents "- - Polarisation Currents — Electrocu-
tion— -Three Types of Blaze-currents — The Effect is greater than
its Cause — Influence of a Galvanic Current — Some Questions—
The Crystalline Lens . . . . . 41

LECTURE IV

Skin-currents (of the Frog) — The Normal Current is " Ingoing"- -The
Response to Indirect Excitation is Outgoing, Mixed, or Ingoing
—The Latent Period is Two Seconds — Fatigue — Atropine —
Mercuric Chloride — The Response to Direct Excitation is Out-
going— Summation — Effects of Tetanisation — Localisation of the
Response by the ABC Method — Terminology . . -59

44194

viii CONTENTS

LECTURE V

PAGE

The Discharge of an Electrical Organ in Response to Direct Excita-
tion— Du Bois-Reymond's Summary — Similarity between " Blaze-
currents" of the Skin and " Discharges" of an Electrical Organ-
Normal Direction of the Organ-current — A Speculation and some
Experiments — Further Investigation of these Currents by the
ABC Method — The Positive Polarisation of du Bois-Reymond
-The Polar After-currents of Hering and of Biedermann-
Ritter's Tetanus and the Post-anodic Action Current . . 76

LECTURE VI

A Representative Experiment — Effects of Indirect Excitation-
Effects of Direct Excitation immediately after Death, and
Later — How Long, after a Cat's Death, can a Cat's Foot con-
tinue to Exhibit Signs of Life ? — More A B C — A Vegetable
Surface — Surface against Surface — Anodic and Kathodic —
Biedermann and the Frog's Tongue — A Warning . . 97

LECTURE VII

Observations on the Human Skin — Du Bois-Reymond's Experi-
ments— Tarchanoff's Observations — Sweat-prints — Introduction
of Ions through the Skin . . . . . . 114

LECTURE VIII

The Fallacy of the Electrodes — Water Transport at Anode or Kathode

— Alteration of Resistance at Anode or Kathode . . .129

APPENDIX

The Normal Circuit — Galvanometer, Coil, Compensator, Electrodes,
and Keyboard — Photographic Recording — Lippmann's Capillary
Electrometer — Special Keys — Units of Resistance and of Con-
ductance . . . . . • • '51

INDEX . ..... 173

THE SIGNS OF LIFE

" The greatest thing a human soul does
in this world is to see something, and tell
what it saw." — RUSKIN.

LECTURE I

Aim and Purpose of the Lectures — The Subject-matter of Physiology — The
Signs of Life ; The Sign of a Sign is a Sign of the Thing itself — Two
Familiar Instances ; on Muscle and on Nerve— A Proof of Chemical
Change in Seeds — An Experiment on Muscle — Retinal Currents —
Vegetable Currents —Terminology — Solution-pressure — Summary.

§ I. Aim. — The aim and purpose of these lectures is
extremely simple. By the liberality of the Senate of the
University, seconded by the liberality of one of its distinguished
graduates, the teachers and students of physiology separately
working in the many scattered Colleges of the Metropolis, are
enabled to bring to its University, as to a focus, the best they
have to bring.

I shall not take upon myself to utter any forecast of the fate
of this effort towards concentration, nor attempt to justify our
undertaking by any high-flown anticipations. All that I venture
to say — on behalf of my colleagues as well as on my own behalf
— is that we believe that in Physiology as in other subjects, there
exist in this great metropolis, scattered — I had almost said lost
— in the several colleges that now form part of the University,
the elements which collectively constitute a university school of
learning.

And if I might venture to characterize by one word what
to my mind is the most essential mark of a teacher of university
rank, I should say that it is that such teacher should be an

A

THE SIGNS OF LIFE [LECT.

active student — not merely a learnt man, but a
man.

And that leads me to what we hope is to be the keynote
and dominant tone of these lectures — namely, that they are
especially to belong to what may be termed the growing surface
of our knowledge. Each one of us is to bring here the know-
ledge that he has himself gathered at first hand in the particular
garden that he has chosen to work in, and of such knowledge it
is an infallible characteristic that it is unsatisfied, incomplete —
an ever green surface, a surface of encroachment.

And so this, our talking-room, rests upon a foundation of
working-rooms, and these in turn ultimately rest upon our
working-rooms scattered throughout the colleges of the University
of London, at University College, at King's College, at the
London medical colleges, and at the colleges for women.

Another point : A critic, a friendly critic, in the days when
these lectures were first talked of, wanted to know to whom they
were to be given, urged indeed that in this great scattered
University of London there are not a dozen students requiring
or caring for advanced lectures in physiology ; he said that we
should have to lecture to each other. I hope we shall lecture to
each other and be each other's pupils. Looking to this list, I
think I may say that during the last twenty years I have been
the pupil of every one of my present colleagues, and I hope I
have not finished learning from them ; and I am very sure that
if this laboratory fulfils its true function, we, the professed
teachers, will receive as well as give instruction from and to the
students and frequenters of the laboratory.

§ 2. Subject. — The subject-matter of physiology is Life — or
more properly speaking — living things, vegetable as well as
animal. And although physiologists, in common with all man-
kind, must at times indulge themselves in speculations concerning
the origin of life, the existence of vital force, the immortality of
protoplasm and other insoluble philosophical problems, their real
daily work is the hardly less extensive task of learning how
plants and animals live, in what particulars their living organs
and tissues differ from the same organs and tissues when they

i.] NOTA NOTM 3

have ceased to live, how quickly they live, how much they live,
upon what they live, and how while they live, they absorb,
transform, distribute, and dispense the energy stored in food
and manifested in each act of life. In one word our task as
physiologists is to study the signs of life. To say that these
are lectures on the signs of Life is to say that they are lectures
on Physiology.

The Signs of Life.

The signs by which we can always recognise that living
matter is living are :—

r. Its reducing or deoxygenating power;

2. Its exhalation of carbon dioxide ;

3. Its excitability ; and

4. The electrical signs of its chemical activity.

The present series of lectures will be in chief measure drawn
from the fourth head — and I should have taken for their title
the electrical signs of life, were it not that the electrical signs by
themselves should not in my opinion be divorced from other
signs ; and are indeed, when so divorced, of comparatively small
general importance — matter of special and technical interest
rather than a chapter in General Physiology.

The point of view to be taken can be formally presented
in terms of the classical axiom of the logicians — nota notes est
nota rei ipsius — inasmuch as chemical change being a sign of
life, and electrical change a sign of chemical change, it follows
that electrical change is a sign of life — meaning by " sign "
an universal attribute of our subject rather than an occa-
sional or exceptional incident — a " propriuui " rather than an
" accidens."

From which formal position we may proceed a step further,
and recognise that in the study of electrical change we have the
most delicate and one of the most convenient means of approach
towards an answer to these two questions addressed to matter
that may be living or not-living :—

1. Are you alive?

And when this first qualitative question has been answered : — -

2. How much are you alive ?

4 THE SIGNS OF LIFE [LECT.

§ 3. Instances. — The two instances of electrical effects with
which you are no doubt familiar already, are :—

i. The negative variation of muscle; 2. The negative
variation of nerve : and I shall presently use the first of these
phenomena to illustrate the parallelism between the mechanical
sign of life (contraction) and the electrical sign of life (negative
variation).

Turning now to the syllabus of this first lecture, you find
there several headings that are more or less familiar to you, that
I shall nevertheless recall to your attention, for the sake of the
point of view I ask you to take.

Omitting any attempt to define " Life and the Living State,"
we shall in first resort seek to recognise what are the principal
differences between matter that is alive and matter that is not-
alive. And take note in passing that by this division into alive
and not-alive, or living and not-living, we include dead matter
as a sub-division of not-living matter, which we consider as falling
into the complementary sub-classes of matter that has previously
lived (but is now " dead ") and matter that has not previously
lived (and is called " inert ").

And although our physiological problems are in most cases
concerned with the comparisons and distinctions that we are
able to institute between living and dead matter, we shall find —
for the sake of logical discourse in dealing with matter in a state
of what has been called latent life or suspended animation — that
it is convenient to make a first division into living and not-living,
and a sub-division into dead and inert in accordance with this
dichotomous scheme : —

Matter.

f

Living.

Not-living.

}

Formerly
living.

Not formerly
living = Inert.

Capable of living
again = Dormant,
e.g., a dry seed.

Not capable
of living
again = Dead.

This scheme has been drawn up with the particular purpose
of showing how, in my opinion, we should logically deal

i.] ARE SEEDS LIVING OR DEAD? 5

the vexed question whether a seed (or a dry rotifer, or a hen's
egg, or a tissue completely " anaesthetised ") is alive or dead.

We shall have to recognise that the one general and all-
embracing sign of life, whether we consider a complete organism,
or a single organ, or an isolated part of an organ, is Movement-
movement of the whole mass, or that movement of its molecules
which we characterise as physical and chemical and physico-
chemical. All living matter is the seat of chemical change, or if
you prefer it, physical or physico-chemical change.

Now dry seeds, kept for long periods in hermetically closed
vessels, have not been found to manifest any evidence of the
most fundamental and general chemical change occurring in
living matter, viz., a production of CO.2. Their chemical reply
to the question, " Are you alive ? " has been " No."

But does this negative answer " not-alive " imply that such
seeds are dead ? Evidently not, as may be seen if under suitable
conditions of temperature, moisture, and so forth, they are found
to germinate and grow into plants. So that a seed, in so far as
it does not manifest chemical change, is not proved to be living ;
and, inasmuch as it germinates, is proved not to be dead.
Evidently, here is a dilemma ; in the absence of an objective
chemical sign of life, we have no right to say that a seed is alive ;
it is, as far as we can tell, not-alive ; in the presence of its
subsequent germination we are assured that it is living, and that
therefore it was not dead. And the usual manner of escape
from this dilemma of the seed which is neither living nor dead,
is to say that it is in a state of latent life, during which there is
a complete suspension of chemical changes characteristic of the
living state.

I will not, at this early stage, stop to comment upon the
contradiction involved in this form of words, nor upon the fact
that it involves contradiction of the fundamental axiom that the
essential attribute and objective sign of the living state is
chemical movement. But I will offer for your consideration a
different mode of escape from the dilemma.

It is possible — or rather certain — firstly, that our means of
chemical investigation are not refined enough to reveal to us
the smallest and most infinitesimal changes that may be going

6 THE SIGNS OF LIFE [LECT.

on in an apparently dry and perfectly dormant seed ; and
secondly, it is possible that chemical change may be completely
and absolutely arrested (e.g., by low temperature) without that
arrest being of necessity final and definitive.

I will place evidence before you of this first point, which I
have investigated at some length. As to the second, which I
have not myself investigated, I will only mention that it appears
to be established by the observations of Horace Brown,* who
found that dry seeds kept for no hours in closed vessels at a
temperature of -- 183° to — 192°, i.e., seeds in which the arrest of
chemical change must be considered to have been absolutely
complete, germinated quite normally when they were placed
under suitable conditions of temperature and moisture.

The inadequacy of our chemical methods to reveal small or
infinitesimal chemical changes taking place in seeds is, I think,
proved in two ways. We know, in the first place, that kept
seeds \vear out, that the percentage of seeds that germinate and
grow is smaller and smaller with the number of years they have
been kept. The deterioration is more or less rapid according
to the nature of the seed and the character of its protective
coats, but in every known instance there is deterioration sooner
or later, and I think you must admit such deterioration to be
sign and proof that chemical change has taken place. f

§ 4. Seeds. — A still closer and more manageable proof that
seeds may be the seat of chemical changes which chemical
methods are inadequate to reveal, is, as I shall develop in a
future lecture, afforded by an electrical method. As formally
laid clown above, electrical changes are the token of chemical
changes, which are the token of the living state. And these
electrical changes are manifested by seeds long before the

* Proc. Roy. Soc., vol. Ixii., p. 160, 1897. — Thiselton-Dyer has gone
further, viz., to - 250° to - 252°, Proc. Roy. Soc., vol. Ixv., p. 361.

+ The continued formation of aleurone granules in very old seeds is in
certain instances an objective sign of the occurrence of slow chemical
change. The germination of "mummy wheat" must be set down as
apocryphal, in spite of the wheat sheaf shown in a Paris museum grown
from Mariotte's mummy wheat. The wheat was given to Mariotte by
Arabs.

i.] HOW MUCH ARE YOU ALIVE? 7

manifestation of any microscopical or chemical signs that they
are the seat of a physiological activity. And yet we have not
reached a limit ; although our electrical test is more delicate
and closer-searching than either a morphological or a chemical
test, we may not flatter ourselves that it makes sensible to us
the real ultimate (or initial) chemical movements of infinitesimal
magnitude that herald (or attend upon) the awakening of the
dormant embryo— the birth of a renewed life.

And so, if driven to the foot of the wall by the question, " Is
this good seed living or dead ? " I should answer, " I can't tell by
looking at it, nor by chemically testing it, but come back in an
hour, and I will show you that this seed, since you say it is a
good seed, is an actually living seed ; and then, if you like, I
will kill it and show you how differently it behaves. At this
moment I do not know whether or no infinitesimal chemical
change is going on in the seed, but I believe that such infini-
tesimal change (if it exists) may be suppressed (by low tempera-
ture) without thereby making the seed dead"

Hence, in verbal physiological specification of a good seed, I
should say, in order of logical subordination : Matter — Not-living
— Formerly living — Capable of living again.

This has been a dialectical parenthesis. Before leaving the
topic let me, however, utilise it in illustration of the answers
desired (and in some cases obtained) to these two chief
questions: — Are you alive? How much are you alive?

To the qualitative question, " Are you alive ? " the seed
response is "Yes," "No," or " Doubtful"— " Yes " being an
electrical response of considerable magnitude, " Doubtful " or
" No" being little or no response.

To the quantitative question, " How much are you alive ? "
the affirmative response comes in the forms of units, which are
fractions of a volt, as in this instance, where seeds (Phaseolus)
of different years are submitted to the quantitative question.

It is of course impossible for me to carry out a long series
of trials like this on the lecture table ; it will be sufficient for the
purpose of illustration if I show you three trials — one on an
assuredly living seed, one on an assuredly dead seed (that has
been killed by heat), and a third on a very old seed of which I

8

THE SIGNS OF LIFE

[LECT.

VoLt

•0150

do not know beforehand whether it is alive or dead (but which
I believe to be dead as it dates from the year 1 860). And at
the end of this lecture, if you care to see the
trial, I will test some very old seeds indeed, that
were given to me by Mr Percy Newberry, who
combines the qualifications of botanist with those
of Egyptologist. They are seeds collected by
himself, and placed by him as dating from the
twelfth dynasty, z>., as being something like 4400
years old. I need hardly say that no such un-
doubtedly old seeds will give any electrical
response, nor will they germi-
nate. I have previously made
both tests.

•0100

•0050

/99 /9Q /97 /f)6 /95

[Experiment.]

the text, is taken as the index of
vitality.*

matters in a future lecture ;

_,

I he first seed gives, as you
FIG. i. — Average electrical response of see, a large electromotive re-

seeds of five successive years. The T-V ,1 j

ordinates represent the average vol- sP°nse- The other seeds give
tage of response, which, as stated in no response at all. The first

seed is alive, the others are
dead. We shall return to these
I wish in this first lecture to
exhibit to you two other experimental illustrations as typical
of the kind of problem and argument with which we have to
deal.

§ 5. Muscle. — Muscle is a favourite object of physiological
experiment ; it gives sign of life by contracting when it is
stimulated — either directly, by stimulation of the muscle itself,
or indirectly, by stimulation of the nerve that is its motor nerve.
And, roughly considered, its mechanical response or contraction
is measure of the degree of vitality that it possesses. No one
doubts that the contraction of a muscle is sign and proof of its
state of life, and that the degree of contraction and the work of
which that contraction is capable, are catcris paribus measure

* Proc. Roy. Soc., vol. Ixviii., p. 87.

MUSCLE CURRENTS

of the amount of vitality possessed by muscle. A weak muscle
can do less work than a strong muscle, and a given muscle in
the course of fatigue, or of that last act of life that we call
death, can give less and less extensive contraction, and effect
a smaller and smaller amount of work. Pari passu with declin-
ing contraction we witness declining electromotive response, and
we admit or assume that the common substratum of the decline,
whether mechanical or electrical, is decline of chemical activity.
An excised muscle has been set up to show this parallelism
between mechanical and electrical response. A lever attached
to the tendon indicates to you, by its excursion on a smoked
glass plate, the extent or height of the mechanical movements
(contraction). A galvanometer connected to the muscle by

Mechd.nicd.L Response.

ELectric&L Response,

FIG. 2. — Simultaneous records of a series of muscular contractions, and of the
corresponding series of negative variations. The method and apparatus for obtaining
such records is described in the Appendix, p. 160, Fig. 63.

wires and unpolarisable electrodes, indicates to you, by the
excursion of the reflected spot of light, the extent or voltage of
the accompanying electrical movements. The muscle is excited
indirectly, by excitation of its nerve, and, as you see, the two
sets of movements, mechanical and electrical, run an approxi-
mately parallel course — both are large together or small to-
gether, and if one is absent, so is the other. You would notice,
however, on closer comparison, that the parallelism is not perfect,
the mechanical and electrical responses are not an exact replica
of each other, and the defect of correspondence is particularly
apparent in simultaneous records of the two sets of responses.

I cannot at present enter further upon this difference, I think
it requires further study ; if you ask which of the two records is
the more faithful indicator of the chemical changes of which

10 THE SIGNS OF LIFE [LECT.

they are both the tokens, I shall answer that in my opinion the
electrical indications are the more faithful ; they are without
doubt the more sensitive since they are still of quite consider-
able magnitude when a muscle is so weak as to scarcely con-
tract at all, nor be competent to raise a lever to any measurable
height. In the pair of records you have just seen, the electrical
indications are reduced to manageable size by shunting the
galvanometer.

§ 6. Retinal currents. — The third object of experiment is a
frog's eyeball set up in a dark chamber between unpolarisable
electrodes which are connected with a galvanometer. By open-
ing a shutter the eyeball is illuminated at any desired time for
any desired period. When I do this, there is no mechanical
movement of the eyeball, at least no coarse mechanical move-
ment,* but you witness a large and obvious electrical change.
Holmgren, who first discovered this effect, found by a series of
experiments in which he made separate trial of the several
parts of the eyeball, that the electrical effect was of retinal
origin. Light acting upon the retina excites it ; in ourselves
the subjective token of that excitation is a sensation ; in the
isolated eyeball the objective token of excitation is an electri-
cal change. The detailed description of these changes will
form the subject of my next lecture, but I should be glad if
you would take note of what you have actually witnessed in
the present case. The eyeball has been set up on electrodes,
so that its fundus rests upon one electrode, while its cornea is
touched by the other electrode, the spot of light was deflected
to the left during the illumination, and returned to its original
position after illumination. I touch one terminal of the gal-
vanometer with a bit of zinc, and the other terminal with a
finger of the other hand ; the spot moves to the left, the ter-
minal I touched with the bit of zinc is that to which the
corneal electrode is connected : from which I conclude that
the current during illumination was from cornea to fundus. I
choose to call this direction " negative," and shall denote as

* On closer examination, there may be detected — (i) contraction of the
pupil, (2) protrusion of pigment, (3) retraction of cones.

i.] RETINAL CURRENTS 11

"positive" the opposite direction from fundus to cornea. And
I recognise in the deflection to the left that we have just
witnessed what I am accustomed to regard as a
reaction of the third stage, viz., a negative current,
directed from before backwards in the eyeball. And
I may just mention that a few hours ago, when I
put up this eyeball for ex-
periment (under difficulties
inseparable from the pres-
ence of belated workmen in

a new laboratory), it gave a -— -- -— -

_ . T NofmcLi response.

positive deflection, such as FlG

have learned to be typical of

a fresh and normal eyeball, and have chosen to characterise

as a reaction of the first stage.

These have been details of the laboratory, details that you
have hardly followed as I had to do, to make plain to myself
(and state to you) what was the direction of current in the
eyeball indicated by the direction of movement of the spot of
light. Those of you who are actual workers will appreciate
the importance of attention to such details, and the hopeless
confusion arising; from doubtful determinations of direction of

O

observed currents. Those of you who content themselves with
the literature of the subject, will find it almost impossible to
realise what writers mean by "positive" and "negative" effects.
But the response we have just seen is not of the type that
I wish to show in a first lecture ; it is of what will be
described later as a response of the third type, negative instead
of positive ; the eyeball may have been kept waiting too long,
or have been accidentally compressed in the course of pre-
paration. So I shall repeat the experiment on another eye-
ball that has just been carefully prepared and set up for me
by the assistant.

And now, as you see, the response to light is a normal
response of the first type, viz., positive, for the spot has moved
to your right during the illumination, indicating current through

12 THE SIGNS OF LIFE [LECT.

the eyeball from fundus to cornea — and I make sure of this
direction once more by touching the fundus electrode with a
bit of zinc, and seeing that the spot moves to your right.

Let me make one more pair of trials to assure you that
it has been luminous radiation in particular, and not thermal
radiation, that has excited the retina of this eyeball. I repeat
the exposure just as before, with the standard candle at un-
altered distance (5 feet), but with an alum cell interposed to
filter off most of the heat, and, as you see, the response is no
smaller than before. Finally, I take away the alum cell, and
expose the retina to the very sensible heat of a black hot
surface of metal, and, as you see, there is no response at all
to heat without light.

§ 7. TIic mechanical excitability of vegetable protoplasm. — The
fourth and last experiment that I wish to show is a very simple
one, but in my judgment a fundamental experiment in general
physiology. It relates to the mechanical excitability of vegetable
protoplasm, and is calculated to convince you of the essential
identity between the excitatory responses of vegetable and of
animal protoplasm. Those of you who are students of physi-
ology or of physiological botany, are no doubt acquainted with
various instances of movements in plants consequent upon
mechanical excitation ; and you probably know from the observa-
tion by Burdon-Sanderson on Dionxa, that these movements
are accompanied by electrical effects. You may take it that the
excited plant-stuff is the seat of chemical change, that this
change is of the nature of a disintegration from large complex
molecules to smaller, simpler molecules, that this disintegration
has involved an increased osmotic pressure, whence turgor of
certain cells, whence movement of petioles and leaves. And
with these chemical changes there are of course associated
electrical changes.

But these notions are to be extended, and we are to recognise
further that any and every living vegetable protoplasm, when
excited, undergoes chemical, and therefore electrical, change,
whether it actually moves or not.

I have used all kinds of vegetable protoplasm, usually during

'•1

PLANT CURRENTS

13

the months of March and May, and for the experiment now on
the table my favourite object has been the vigorously growing
shoots of a vine. But in this bleak month of May (1902) the
vine shoots have not yet appeared, and I have therefore taken
a less favourable object, viz., the petioles of ivy-leaves, which, in
comparison with young vine shoots, must be looked upon as
rather a sluggish variety of vegetable tissue. So I shall take a
stronger mechanical stimulus than usual.

The petiole of an ivy-leaf is fastened by modelling wax to a
glass plate ; to two points, 5 cm. distant from each other, un-
polarisable electrodes are connected, and attached, of course, by

FlG. 4. — "Plant-guillotine" for the demonstration of the mechanical
excitability of vegetable protoplasm. The shutter, visible only on one side
B, by which the twig or shoot is excited, is represented as having dropped.

v/ires to the galvanometer. Two slips of wood (weighing 5
grams each) running in vertical grooves, are suspended by catches
i cm. above the petiole close to the electrodes, which we will
call A and B. I let go the slip B, which strikes the petiole near
the B end with an energy of 5 c.g.m.m., the spot flies off scale to
your right. (I readjust the spot, and when it is steady, let go
the slip A, and now the spot flies off to your left.) I test for
direction as described above, by touching the galvanometer
terminals with a bit of zinc wire, and seeing that by touching B
the spot goes to right (and by touching A it goes to left). I
know that when the petiole was excited at B there was current

14 THE SIGNS OF LIFE [LECT.

through it from B to A (while when it was excited near A there
was current in it from A to B).

Is there any doubt in your mind whether these have been
physiological responses, for which the essential condition is that
the ivy petiole should be alive ? There should be such a doubt
in your mind, and you should set the doubt at rest by repeating,
or making me repeat, the experiment on a petiole of which the
molecular mobility has been abolished, i.e., on a petiole that has
been killed or otherwise immobilised. I might kill it at once by
plunging it into hot water, but to do this I should have to
remove it from the electrodes and replace it, which takes time ;
and even at best, when the petiole has been replaced as carefully
as possible as it was, you cannot be quite sure that I have
exactly replaced the petiole. So I shall otherwise immobilise
it, in a way that will allow me to leave petiole and electrodes in
statu quo, viz., by sending through it currents of such strength
that the living stuff will be completely stunned : which I now
do, and then repeat both trials as before, exciting at A and then
at B, without, as you see, any response in either case. The
previous effects you witnessed were therefore physiological.

§ 8. " Zincative." — So far so good, there is no doubt what-

O ^

ever about the facts, the excitatory currents are precisely such
as are aroused by excitation of animal protoplasm. But how
are we to label them ?

Following the best authorities — Faraday, Maxwell, du Bois-
Reymond — we should say, referring to the pole under our
observation, that B, the excited spot, is negative to A, the non-
excited spot (or A, the excited spot, negative to B, the non-
excited spot ; but since this confirmatory experiment is confusing
we will henceforth omit it, and consider only B excited, and A
non-excited).

And as a matter of fact, this has been the terminology
followed by physiological writers.

But in course of time, and especially in consequence of the
polemic that took place between du Bois-Reymond and
Hermann, the meaning of the term " negative " underwent a
curious twist. Du Bois-Reymond found that the " resting

PLANT CURRENTS

15

voLt -

O-O£>-

voLC
•010-

2

70

2O m.

FIG. 5. — Vine-shoot. Electrical Effects of Mechanical Excitation
(10 centigrammetres) before and after boiling.

The first four excitations (before boiling) give responses of 0.060, 0.045, 0.045,
0.040 volt. The 5th, 6th, and 7th excitations (after boiling) give no response.

The deflection preceding the ist excitation is by 0.04 volt, and the resistance of the
stem between leading-off electrodes was 500,000 ohms. The deflection preceding
the 5th excitation is by o.oi volt, and the resistance of the boiled stem was
60,000 ohms.

FIG. 6. Experiment (3023). — Bean-Radicle (Phaseolus) 3 inches

long and quite etiolated, incubated in the dark at 25° for five days. Led
off to recording galvanometer by two unpolarisable electrodes, A and
B. The radicle is struck transversely near A, then near B, by a bristle
fixed to the end of a revolving rod. In each case the deflection is such
as to indicate that the struck spot is rendered electropositive (galvano-
metrically negative) to the unstruck spot. The effects are completely
abolished by strong tetanisation.

16 THE SIGNS OF LIFE [LECT.

current " of quiescent muscle and of nerve is diminished when
the' muscle contracts or when the nerve is excited ; he called this
diminution "a negative variation of the previous current of
rest." Hermann then showed that this negative variation of a
current of rest (or current of injury) is only a special case of a
more general phenomenon, and that active tissue is, properly
speaking, negative to resting tissue, quite irrespective of any
previous " pre-existing " current. And from the fact that active
tissue is negative, and that the action is propagated in muscle
and in nerve, physiologists adopted the expression " negativity
of action," and spoke of propagation of a wave of negativity in
the excitable tissue. And little by little a confusion of thought
established itself; the origin of the expression " negativity" was
lost sight of, active tissue was spoken of as being " electrically
negative " and then " electro-negative " —which is clearly wrong
in the accepted physical sense of this term. In physical
language the negative pole of a voltaic couple is connected with
the electro-positive element, the positive pole with the electro-
negative element. And when a writer had escaped an actual
misnomer, an ambiguity that was even more mischievous to
clear thinking became effective ; a state of negativity of action,
propagated from active to non-active parts, arouses in the
reader's mind the picture of a current directed in the tissue
when connected by two points, active and non-active, from former
to latter, i.e., from " negative " to " positive." Now this direction
is correct, but it is disturbing to one's thought to regard current
as directed from negative to positive. And, in point of fact, the
language is actually wrong ; the adjectives " positive " and
" negative " as used by Faraday refer to the poles, current is of
course from positive to negative in an external circuit, positive
and negative refer to an external circuit, and should not be used
with reference to the internal circuit. It is a misuse of terms to
say that current in the tissue is directed from negative to positive
pole. The proper thing to say is that direction in the tissue is
from electro-positive to electro-negative, that active tissue is
electro-positive to resting tissue, that a wave of electro-positivity
travels in muscle (or in nerve) from an excited spot.

But, in the present state of our physiological literature, is it

"ZINCATIVE"

wise to attempt to use the proper expressions ? No doubt the
confusion is very great, no doubt the main bulk of our electro-
physiological literature is totally unintelligible to physicists and
to most physiologists. Shall we not, however, lay the foundation
of a further mass of worse-confounded confusion by any sudden
and unauthorised endeavour to call white white and black black,
when for the last twenty or thirty years our leaders have been
content to call white black and black white ?

I hardly like to hazard an opinion, but in presence, on the
one hand, of the impossibility of clear thought and speech, with
external adjectives for internal relations, and, on the other hand,
the mental impossibility of obtaining a sudden reversal of
language which is endeared to physiologists by its familiarity
and its obscurity, I have adopted a new and barbarous word
that avoids the pole name " negative " and the element name
" electro-positive," yet implies both names. And for the present,
at any rate, awaiting a. better word, or a clearer understanding,
I shall, whenever occasion seems to demand the word to make a
meaning clear, use the expression sincative, to imply " electro-

FIG. 7.

The current of a Daniel cell is A nerve current is from unin-

from copper to zinc through the jured to injured spot through the

galvanometer, and from zinc to galvanometer, and from injured

copper in the cell itself. to uninjured spot in the nerve

itself. The injured spot is "zinca-

tive."

motive like the zinc of a voltaic couple " ; zinc is, as we all
know, negative as to its external relation by its pole, and electro-
positive as to its internal relation in the cell. Current in the
cell is from zinc to copper, in the tissue from more active to less
active ; an active tissue-element is electro-positive to a resting
tissue element, or (under protest) an active tissue element is

u

18 THE SIGNS OP LIFE [LECT.

negative to a resting tissue element ; but whether we call it
electro-positive or negative, the active element is " zincative."

§ 9. " Solution-pressure"- -To those of you who are accus-
tomed to think about currents through electrolytes, in terms
of ions creeping through a solvent, this matter should present
itself in a very simple light. Active protoplasm takes on a
higher " solution-pressure " (in the sense with which Nernst
has made us familiar), and electro-positive ions migrate in
greater abundance from protoplasm to lymph. There is then
" current of action," and I do not think that we need at this
stage pause to object whether this increased pressure may
be — not of the protoplasm itself — but of paraplasm (? fat,
? carbohydrate) set in motion by protoplasm. Whatever the
nature of the ions may be, we must picture them as laden
with positive charges, and pressing into the lymph-bath from
spots where they have become congregated and accumulated,
i.e., in and around the meshvvork of living matter. Imagine
simple hydrogen kations, or if you like, more complex
hydrogen and carbon kations, as issuing forth from a solid
coast to a fluid atmosphere, where their oxidation is con-
summated--forming water, lactic acid, and carbon dioxide
as their typical end-products. These notions, in my way of
thinking, are the physiological connotations involved in the
brief statement that "active tissue is zincative" And if you
have gone so far, you will almost certainly go one step
further, and imagine that just as a zinc rod that has given off
zinc ions to its surrounding medium, is for the moment, nega-
tively charged, so a core or stem of living stuff, immediately
after a discharge of positively charged ions is relatively negative.
Current of action is thus followed by an opposite after-current ;
du Bois' " negative variation " is followed by Hering's " positive
after-variation." But I do not wish to pursue this point in detail
now, for there are no experiments in evidence before you. An
opportunity of demonstration may perhaps arise at a future
lecture.

5 10. Summary. — Will you think of these things? I will

i.] SUMMARY 19

try to place myself in the position of a listener, and offer some
criticism of what you have just listened to.

You would find, if you critically compared the lecture with
its syllabus, that many points mentioned in the syllabus have not
been fairly met by the lecture, that the order of the spoken (and
written) description differs from the order of items promised by
the syllabus, that points have been talked about of which there is
no mention in the syllabus. To which my defence is, that
memoranda of a printed paper cannot be placed in the same
logical order as the thoughts and comments that arise from
experiments in the act of demonstration. And so I have left
untouched (for the present) the headings " an excised nerve,"
" a piece of skin," " a green leaf," " a cut flower," " a stem," in
the hope that you may for yourselves realise how these things
associate themselves in the mind of any one planning a group of
considerations. The reason of such association may perhaps be
made plain in the course of these lectures.

You may have found it rather perplexing to be told at some
length that positive means negative, and that negative means
positive. Some of you have hitherto been quite satisfied to
talk about the negative variation of contracting muscle or of
excited nerve. I believe that these expressions are nearly
always empty to utterers and hearers alike, and I have deliber-
ately tried to disturb your easy acceptance and use of paper
language, and put you to the trouble of mentally imaging the
facts denoted by the words. The points to be definitely
registered from what you have witnessed, are :—

(1) From the muscle experiment : that pari passu with its
contraction, its ordinary and indubitable sign of life, an electrical
change is proof and measure of its state of life.

(2) From the eyeball experiment : that we have witnessed
an electrical response to luminous stimulation.

(3) From the ivy leaf: that vegetable as well as animal proto-
plasm, while alive, gives an electrical response to mechanical
excitation.

(4) From the seed experiments : that the electrical response
to electrical excitation can be utilised as a measure of "vitality."

20 THE SIGNS OF LIFE [LECT. i.

REFERENCES

BURDON-SANDERSON. — "On the Electro-motive Properties of the Leaf of
Dionoea," Proc. Roy. Soc., p. 495, 1873 ; Phil. Trans. Roy. Soc., 1882 ;
Phil. Trans. Roy. Sac., p. 417, 1888.

HORACE BROWN AND F. ESCOMBE. — " Note on the Influence of very Low
Temperatures on the Germinative Power of Seeds," Proc. Roy. Soc., Ixii.,
1897, p. 1 60.

THISELTON-DYER. — " On the Influence of the Temperature of Liquid Hydro-
gen on the Germinative Power of Seeds," Proc. Roy. Soc., Ixv., 1899, p.

361.
WALLER. — " An Attempt to estimate the Vitality of Seeds by an Electrical

Method," Proc. Roy. Soc., vol. Ixviii., 1901, p. 79.
WALLER. — Lectures on Animal Electricity, 1897.
WALLER. — " Researches in Vegetable Electricity," International Congress

of Physiologists, Turin, September 1901.
WALLER. — "Electrical Response of Vegetable Protoplasm to Mechanical

Excitation," Proc. Physiol. Soc., November 1901.
BURCH.— " On the Interpretation of Photographic Records of the Response

of Nerve" [Terminology], Proc. Roy. Soc., vol. Ixx., 1902, p. 194.

Note.— The misuse of the terms "ELECTRO-POSITIVE" and "ELECTRO-NEGA-
TIVE," to which I called attention six years ago in the first paragraph of Lectures on
Animal Electricity, is now very generally recognised. In the Oxford Laboratory
the remedy proposed is to simply transpose the words ; but until a general agreement
is arrived at that " POSITIVE " (new style} is to be the equivalent of " NEGATIVE " (old
style), and vice versa, I think the remedy will be even more prejudicial to clear think-
ing than the disease. I do not think the word " zincative " has yet fully served its
purpose, and shall therefore continue to use it when it appears to me to be required.

LECTURE II

The Prospect — Demonstration of Retinal Currents — The Initial Current—
The Principal Fact ; Subordinate Features — Three Types of Response
— Two Opposed Processes — Effects of Complementary Colours-
Cause : Effect — Anaesthetics — Retino-motor Effects.

§n. Prospective. — It is my intention — in the eight days'
laboratory excursion which I hope some at least of my present
hearers will complete — to visit several apparently disconnected
points of physiology. And while I shall not attempt to show
you at once that these points are in fact intimately connected,
I will name them to you now, and promise that their uniting
bonds shall become evident to you in due season — by your
own thinking, rather than by my talking. " The Excitability
of the Retina "— " The Excitability of Vegetable Protoplasm "
— "Skin Currents "—" The Development of a Hen's Egg"
" Secreto-motor Action " — " The Action of Anaesthetics." These
are some of the topics that are at present linked together in my
mind, as on a thread of intention, towards the next few lectures.

And before I commence to tell the first bead of my chaplet,
let me make further confession of faith, and outline to you the
sort of purpose and intention by which scientific research may
be animated. There are two chief moments in the life of every
explorer — the moment of discovery, and the moment of dis-
closure, when the first pleasure is shared with others. But before
this second moment may be enjoyed, a language — not necessarily
of words alone — must be common to talker and to hearer. The
talker must in a measure generalise his language, the hearer
must in a measure specialise his understanding, and learn the
meaning of terms and formulae and labour-saving symbols that

are current coin in the daily dealings of every specialist,
21

00

THE SIGNS OF LIFE [LECT.

I shall do my best to talk in simple language, but I know
that we shall often be forced to fall back upon technical terms.
The ideal way would be, in first place, to have written a mono-
graph in the dry and freely technical language of a Philoso-
phical Transactions paper ; in second place, to retell the same
story here in the simple words and homely metaphors by which
we ordinarily attempt to tell each other what we are thinking
about. It will not be possible to me to strictly follow this ideal
way, but I shall do my best to justify narrative by reference to
duly accredited publications ; and as to technicalities, well, perhaps
some degree of physiological technicality may be excused in the
Physiological Laboratory of the University of London.

Every one here is no doubt acquainted with the physiology
of vision, in so far as it is given in the text-books. You have
studied the eyeball as an optical instrument, containing a living
sensitive surface that receives the focussed (or unfocussed) radi-
ations of light. You have studied the course and the central
cortical terminus of the nerve fibres leading from retina to
brain. You know that the thing as seen by you is your
subjective picture, aroused by the objective retinal pattern of
the objective field of vision. You have proceeded to the closer
study of the objective retinal change from which the subjective
visual sensation takes origin, and have learned that the objective
effects of light acting upon the retina of an excised but sur-
viving eyeball are : — a bleaching of its visual purple, a movement
of expansion of its pigment cells, a movement of contraction of
its cones, and, as in every case of physico-chemical change, an
accompanying electrical change.

One more preliminary consideration. Our own retina, that
arouses in our own brain the detailed images of complicated
objects when detailed images are focussed upon it, gives rise
to diffuse sensations of light and to the fantastic appearances
called phosphenes when it is stirred into action by direct
mechanical or electrical stimuli. Mechanical pressure of the
eyeball, or an accidental blow upon it, or an electrical current
traversing it, anything, in short, that suddenly disturbs the retina,
elicits in consciousness the specific subjective symptoms of a
suddenly disturbed retina, formless or fantastic, a blaze of

II.]

EYEBALL CURRENTS

23

flashing lights, or a succession of colours, in accordance with
the accidents and irregularities of such coarse artificial disturb-
ance. And no doubt — could we only detect it — the physico-
chemical disturbance is attended by an electrical disturbance
The latter will, however, be most easily demonstrated to you
with an excised eyeball.

§ 12. Demonstration. — Such an eyeball has been removed

Light.

FlG. 8. — Frog's eyeball between unpolarisable electrodes for demonstration oi
the electrical effects of light and of electrical excitation. The circuit from the eye is
completed through a compensator, secondary coil, and a galvanometer. The arrows
through the eyeball and the galvanometer indicate the direction of the initial current
and of the normal response. Arrows near the compensator wires indicate the direction
of a compensating counter-current.

as carefully as possible a few moments ago from a pithed frog.
" Carefully " in this connection means with as little compression
of the eyeball as possible, and in point of fact such compression

24

THE SIGNS OF LIFE

[LECT.

has been nearly quite avoided by cutting the frog's head in half,
taking up the fragment with forceps, and trimming away the
orbit from the eyeball with scissors. The eyeball is now resting
upon the clay pad of an unpolarisable electrode, the pointed pad
of the second electrode touches the cornea, the actual contact
being by a droplet of salt solution. The electrodes are con-
nected to a galvanometer. The eyeball and electrodes are
enclosed in a black box with a hole, tube, and shutter opposite
the eye, so that when desired the latter can be exposed for any
required time to light of any required strength.

The connections are such that the fundus of the eyeball is
attached to the south terminal, and the cornea to the north
terminal, of the galvanometer as in Fig. 3 or in Fig. 8, with the
keyboard unplugged. (The circuit includes a compensator and
a secondary coil, to be used in our next Lecture.)

§ 13. The initial cur-

«) **

rent. --Notice as a first
point that the natural cur-
rent of the eyeball has
given current through the
galvanometer from N to
S terminal, i.e., that within
the eyeball it has been
from fundus to cornea.
Notice further the fact that
this current is rapidly de-
clining. The spot deflec-
ted to your right is sink-
ing to your left towards
its zero point.* If we
could afford to wait, we should see the spot reach the zero and
continue its journey to the opposite end of the scale, indicating
to us that the eyeball current, at first directed from fundus to

* The lecture- room is east and west, the former being the lecturer's end.
The galvanometer is on a bracket fixed to the east wall of the room, and the
movements of its suspended magnet are shown by a vertical spot of light
reflected to a transparent scale placed on the lecture-table. The audience

u-u/u

y

+0-0

084

omm.

>52
-0-0053

0-006

\

\

0-002
0

o-ooa

0-004

\

-$~O'0

\

925

l\

1

) \2

O -3
^0-0

0 4
3/3

J £>

0 6

\

-O-0(

L33

£4 —
-0-0(

^•^

U Ou

FIG. 9. — Normal declining current of a frog's
eyeball. The rate and shape of decline resemble
those of a blaze current.

ii.] "BLAZE-CURRENT' 25

cornea (positive), is ultimately directed from cornea to fundus
(negative). We shall get a better general view of this gradual
change by plotting a curve of readings taken at regular intervals
(Fig. 9). I think you will agree with me that the entire curve,
falling with diminishing rapidity towards and beyond the zero
value, is badly named when it is called a current of rest, and
that it cannot possibly be only a subsiding current of injury at
the transverse section of the optic nerve. I think and speak of
it as a declining manipulation blaze caused by the unavoidable
mechanical disturbance that occurs in the most careful possible
preparation of the eyeball, for the effect can be at once
reproduced by slightly compressing the eyeball, and the current
aroused by such intentional manipulation declines just like the
current unavoidably aroused in the preparation of the eyeball.
So much for the normal or accidental current, which is de-
creasingly positive and increasingly negative, at least during
the first hour or two of observation.

§ 14. The principal fact. — We may now proceed to the
principal part of the experiment as first made by Holmgren,
and subsequently repeated by Dewar and MacKendrick, Kuhne
and Steiner, Fuchs, and many others.

The eyeball current is steady, the galvanometer spot is
sinking with imperceptible slowness to your left, and I expose
the eyeball to a brief flash of light by means of an ordinary
photographic shutter timed at about -^ second. The galvano-
metric spot makes a small excursion to your right (positive),
indicative of a current through the eyeball from fundus to
cornea in response to the flash of light. The direction and
character of this response, which are perfectly normal, are
nearly sufficient to assure me that we have under our observation
a normal and well-prepared eyeball, but I shall not be quite
sure of this until I have seen how the galvanometer spot

faces east, so that the N terminal of the galvanometer is to the left and the
S terminal to the right. As far as possible the connections are arranged so
that currents in a "positive" or "outgoing" or "ascending" direction shall
give deflections to the right, " negative " or "ingoing" or "descending"
currents deflections to the left.

26

THE SIGNS OF LIFE

[l.ECT.

behaves itself with a more prolonged exposure of the eye. So
I adjust the shutter for such prolonged exposure to light
—a minute will be a convenient time — expecting to obtain,
if the eyeball is quite normal, a larger and increasing posi-
tive deflection during exposure. And now watch the spot
rather closely for what will happen when I cut off the light by
closing the shutter ; as you hear the click of closure, you see
that the spot makes a short positive excursion to your right
before falling back to its original starting position. All these
features will be best realised from a photographic record of the
travelling spot ; here is such a record, on which you readily
distinguish the large positive and increasing response to a
prolonged exposure, ending by the small positive response er-
as we familiarly call it in the laboratory — the " parting bow "

o mins.

!0

FlG. 10. — Frog's eyeball. Galvanometric record of five successive
normal responses to light ; each illumination lasts for one minute.

at the cessation of illumination, after which the current
gradually falls to its original level. This has been no excep-
tional result, but the typical and regular mode of response of a
normal carefully prepared eyeball ; the photographic record of
five such responses taken on a more slowly travelling plate will
be sufficient evidence of this. In each case there is deflection
in the positive direction at " make " of light, during light, and
at " break " of light.

1 5. Further points. — There are several subordinate points

II.J

RETINAL DELAY

27

relating to the above described typical positive response to light
that demand consideration. I will deal with them as briefly as
possible. In the first place, it is of no moment as regards the
response, whether the accidental current described in paragraph
13 happens to be positive or negative. Kiihne and Steiner,
who paid particular attention to the point, refer to the fact
under the heading, Law of Constant Alteration of Tension, and
describe it thus : —

" Reversed direction of the current of darkness (our accidental
current) is without influence upon the magnitude and character
of the photo-electrical variations, which reverse their signs." That
is to say, according to the German designation, that the response
of a positive current of darkness is in the same direction as that

FlG. II. — Frog's eyeball. Galvunometric record of the normal
response at beginning (a) and end (w) of illumination. '1 he delay in
each case is about i sec. ; that of the galvanometer is ^ sec. ; the net
retinal delay is therefore about ^ sec.

current, or "positive," while the response of a negative current of
darkness is in the opposite direction to that current, or " negative."
I have preferred to this correct, but rather confusing mode of
description, to say that the response is normally from fundus to
cornea or positive^ whether it starts above or below the line of

28

THE SIGNS OF LIFE

[LECT.

zero current, i.e., whether the accidental current upon which it
is superposed be positive or negative. Or to use a familiar
laboratory mnemonic — the normal excited eyeball always " looks
through its own galvanometer." (See Fig. 3).

There is always a considerable interval of time between the
incidence of light and the electrical response ; sometimes the
delay at " make " of light may be so great as to be measurable
by a stop-watch, but in such cases the delay at " break " is much
less considerable, and I have considered the interval at make
as a period of hesitation (vide infra) rather than as a true
physiological lost-time. But even under the most favourable
conditions, with fresh and typically reacting eyeballs, I have

FlG. 12. — Frog's eyeball. Electrometric record of the normal response at
beginning (a) and end (u>) of illumination. The retinal delay is in each case about
£ sec., i.e., approximately the same as that of cortical grey matter.

never seen the latency as short as given by Dewar and
MacKendrick, and more recently by Fuchs — viz., " less than
T^th of a second." The shortest intervals I have measured
have been of about i second, no difference being detectable
between the make and the break deflections in this respect.
These values have been obtained from galvanometer records, of
which Fig. 1 1 is an example, and are subject to a correction, by

ii.J THREE TYPES OF RESPONSE 29

reason of the physical lost-time of the suspended magnets and
mirror. With the capillary electrometer, which has no appreci-
able lost-time, the latency comes out at about 0.15 second — still
a very considerable delay, and indicative of a rather surprising
physiological inertia of the retinal organ.* (See Fig. 12.)

I had the curiosity to repeat the experiment under precisely
similar conditions on an oxidised copper plate, which, as is well
known, is acted upon by light, and gives, therefore, electrical
currents in response to illumination (Fig. 61, p. 159). There
was no detectable lost-time, either by galvanometer or by
electrometer — a fact which is of interest in the present con-
nection merely in that it bears witness to the correctness of the
retinal data taken by the same apparatus.

When it has been clearly recognised that the regular and
typical response of the fresh uninjured eyeball is of positive
direction, i.e., directed from fundus to cornea, we may proceed to
consider, without losing our way amid a tangle of abnormalities,
the varieties of character that present themselves, not merely in
the response to light, but in the response to mechanical and to
electrical stimulation. And when we have considered such
varieties, we shall return to the consideration of the above
described typical positive response, and recognise that this posi-
tive response is in all probability the algebraic sum of two
opposite and not perfectly congruent electrical changes. The
terminal positive effect at the closure of illumination, which
must have been to us at first sight a somewhat puzzling feature,
will then become intelligible to us.

§ 1 6. Three types. — For the sake of distinct description, I
have classified the response to light as falling into one or other
of three types : —

I. Positive response of the first type, characteristic of the
normal fresh uninjured eyeball.

II. Mixed responses, characteristic of transitional states
between types I. and III.

III. Negative response of the third type, characteristic of the
compressed or partially injured eyeball.

* Gotch has recently and independently made similar observations (see
References).

30

First or normal type.

Second or transitional
type.

Third or reversed type.

THE SIGNS OF LIFE

Dark. Light.

LLECT.

•OOO3t

O

D&rk.

I mm.

am ins

FIG. 13. — Frog's eyeball. The three types of its response to light,
as described in the text.

INFLUENCE OF MASSAGE

31

I have formed the opinion, from a large number of observa-
tions and trials, that the principal factor in bringing about that

O i a mins.

FlG. 14. — Positive — before massage.

O I 2. mins.

FlG. 14. — Negative — after massage.

Response to light (25 units). The horizontal lines in both
these records denote a scale in TTriinTths of a volt ; the resistance
of the eyeball has been much diminished by massage.

state of eyeball in which the response to light is purely negative,
is a moderate compression, or shrinking by drying of its retinal

32

THE SIGNS OF LIFE

[LECT.

coats. A fresh eyeball prepared with such care as to give the
typical positive response of the first type can at once be made

r\

\\

•0

FlG. 15. — Diagram to illustrate the effect upon a galvanometer
(broken line) of a simultaneous larger positive current and smaller
negative current, the latter commencing and ending more rapidly.

FlG. 15. — Retinal response of the second stage, illustrating
the double effect.

to give the negative response of the third type by gentle massage
by steady moderate compression, and in the latter case it is

or

I'.]

PERIOD OF HESITATION

33

possible with very gradual compression to obtain response of
the transitional type.

The conversion of type I. into type III. by means of gentle
massage forms a simple and almost an unfailing lecture demon-
stration. Fig. 14 is the record of a case in point.

§ 17. A double process. — I think that any one who has wit-
nessed a great number of experiments of this character, and
who has carefully inspected a large number of records such as
those figured above, will be forced to the conclusion that the
normal positive response is the algebraic sum of two opposite

FlG. 16. — Frog's eyeball. False latent period or period of hesitation
in this instance = 5 sees.

and almost synchronous electromotive phenomena, one giving
a positive current that over-compensates the other giving
negative current ; the first more labile than the second, so that
by gentle compression it may, so to say, be wiped out, and
the second be thus unmasked.

A careful scrutiny of the manner in which the normal positive
response begins and ends confirms this view, and at the same
time offers to us a plausible explanation of what has been referred

C

34 THE SIGNS OF LIFE [LECT.

to above as the "parting bow." If during the exposure to light
there is a tug-of-war between positive and negative current,
with predominance of the former, and if at the end of exposure
both currents should cease, but the negative cease more rapidly
than the positive, then we should witness what actually does
happen, viz., a short movement in the positive direction preceding
the return to a state of rest. And finally, on turning back to the
nicer examination of the rising effect at the outset of exposure,
we find another sign of an opposition between two contrary and
all but synchronously developing currents. There is often at this
point a false latent period, or period of hesitation, perceptible on
simple observation, or, better still, by means of records where
the beginning of an exposure has been mechanically signalled,
amounting to several seconds, and intelligible only on the sup-
position that our galvanometric magnet is, so to say, trembling
in the balance between two opposite and almost perfectly con-
gruent forces. And generally, indeed, on the record of such a
false latent period, we may detect signs of such a preliminary
struggle, as if an initial positive movement had been forthwith
interfered with for a brief period by a contrary negative move-
ment. On some records the magnet remains almost perfectly at
rest during several seconds of hesitation ; on others it is caught
back by a sharp negative jerk ; on others still the curve of positive
movement is only slightly hitched or notched in its progressive
development. All these facts — viz., the transitional responses
from positive to negative, the immediate conversion from positive
to negative by compression, the initial period of hesitation, the
terminal "parting bow" —point to one and the same conclusion,
viz., that the retina, when exposed to light, is the seat of two
contrary electro-motive changes. And it matters little whether
you imagine two single processes or one double process behind
the movements of the machinery.

Thus, following a path step by step as it happens to lead us,
we find ourselves quite unexpectedly at a place where theory
and doctrine seem to be quite familiar to us. We are all of us
more or less intimately acquainted with Hering's theory of
colour-vision setting forth that contrary processes of dissimila-
tion and assimilation are aroused by complementary colours,

ii.] COLOURED LIGHT 35

white and black, red and green, yellow and blue. And whether
or no we happen to believe that, e.g., a red light is katabolic and
a green light anabolic, we assuredly do believe in what has been
termed by Bernard the axiom of general physiology — that
katabolic analysis and anabolic synthesis are inconceivable apart
from each other. I think that we should not hastily admit that
our double electrical change is presenting us to another aspect
of a familiar if somewhat nebulous colour theory ; I think we
have no ground for assuming that our conclusion means any-
thing more than the old axiom behind a new face. A process
necessitates the anti-process, and if the process is attended
by an electrical change of given sign, we may expect that
the anti-process will entail an electrical change of opposite
sign. The chemical changes taking place in living matter are
in general reversible changes.

§ 18. Complementary colours. — One question we may indeed
put to the test before passing on. We may see whether or
no complementary colours have opposite electrical effects, and
whether the excessive action of a given colour favours or dis-
favours the action of its complementary. I have tried both
these points ; I had no real expectation that red and green
light, e.g., should have electrical effects of opposite signs, nor
that the excessive action of a given monochromatic light would
promote the subsequent action of its complementary. And in
point of fact, neither of these things happened. The effects
of all sorts of colours were of the same sign. The joint effect
of two complementary colours was practically the sum of their
separate effects. And the prolonged excessive action of a
given colour fatigued the retina to that colour just as much o/
as little as to the complementary colour. All colours, in fact,
as regards the electrical response they elicit from the retina,
give that response of the same sign, and seem to act in the same
direction, more or less powerfully according as they are more
or less luminous. Thus, e.g., in a given series of trials, the
responses came out of the following relative magnitudes : —

Red . . . +4
Yellow . . . + 16
(White). . . +33

Green . . . + 1 2
Blue , , , +9

36 THE SIGNS OF LIFE

In other trials the responses were : —

[LECT.

To Red alone . + 5

To Green alone . + 10

To Red and Green conjoined + 14
(To White) . . . +40

§ 19. Cause: effect. — I have upon more than one occasion
taken records of the series of electrical effects elicited by a
series of illuminations of arithmetically increasing and de-
creasing strengths. The general question to which this special
question belongs is in my opinion one of fundamental elemen-
tary importance, coming under our notice in almost every pro-
vince of study, sometimes in simple and accessible shape,
sometimes disguised or hidden by the manifold circumstances
and accessories of organic life.

The question is : What quantities of physiological effect, Y,
are elicited by given quantities of physical cause, X ? And the
answers to that question in its various forms will be most
conveniently and symmetrically expressed by a curve to the
co-ordinates OX, OY, with the physical cause or stimulus or
excitation plotted along OX, and the physiological effect
along OY.

Generally speaking, we cannot hope to reach in physiological
matters an accuracy such as is possible in physical matters.
Our data are too rough, perturbed by too many uncontrollable
variables, and may not as a rule be formulated in mathemati-
cally correct curves characterised by simple equations. The
well-known logarithmic law of sensation is at best of very
limited application, and a sensation curve actually plotted from
experimental data exhibits great divergences from any loga-
rithmic curve that can be fitted to it. Without, however, making
any attempt to trim or strain experimental results and fit them
with orthodox mathematical curves, we may with advantage
plot them out to scale on a simple system of co-ordinates OX,
OY, and thus recognise at a glance whether, within the range of
the observations made, a given physiological effect has varied
(i) as its cause, or (2) more rapidly than its cause, or (3) less
rapidly than its cause. I mean of course exciting or proximal
efficient cause or stimulus, and not the whole previous chain of
principiants resulting in the particular event

n. I CAUSE : EFFECT

Let us consider the three cases : —

y y y

37

FlG. 17. — Straight.

The effect Y varies as its '
cause X.

Equal increments of cause
produce equal increments of
effect. The cause /effect curve
is a straight line.

Concave.

The effect Y varies more
rapidly than its cause X.

Equal increments of cause
produce increasing incre-
ment of effect. The cause /
effect curve is convex to its
abscissa OX.

Convex.

The effect Y varies less
rapidly than its cause X.

Equal increments of cause
produce diminishing increments
of effect. The cause / effect
curve is concave to its abscissa
OX.

And now turn to the case in point, where the cause X is the
intensity of a light, and the effect Y the magnitude of a galvano-
metric deflection (which we shall assume to measure magnitude
of electrical change, and therefore magnitude of retinal change).
With a light of suitable strength, varied on an arithmetic
scale constructed in conformity with the law that luminosity
varies inversely as the distance squared, we find the following
series of results from the given series of stimuli :—

Stimulation by light . 2 4 6 8 loX
Retinal change . . 208 248 274 296 326 Y

which, plotted as described above, gives the curve figured below
as that of the retinal effects of medium illumination.

•0002
•OOOI

Unk

(
I

3 ;

(

h

5 s

14 c

5 C

5 t

i

•OO02

•OOOI

» £

|

> ^

^

•

X

•)

5
(

! i

! '

^

^^

r^ ^J *^ ^t ^

;^^/7. H'ed/r.

3 2 ^* 6 3 l(

Medium.

_^^-

•OQQ3

q
c

> a

) c

1 q

i i

i

\ c

? ^

3 «

i

:> c

j

> <

i ^

> '

.77

^O 4O

fa eo 100

Strong.

FlG. 1 8. — Frog. Retinal response to illumination of constant duration and of
varying strength. The unit of light is a standard candle at a distance of lo feet from
the eyeball.

Now this curve, concave to its abscissa OX, with the effect
Y increasing less rapidly than its excitant cause X, is in

38 THE SIGNS OF LIFE [LECT.

conformity with almost every series of observations we are able
to carry out on living matter. The familiar logarithmic curve
of sensation is concave to its abscissa, sensation Y increases by
diminishing increments for equal increments of stimulation X.
Muscular contraction, the negative variation of a nerve-current
(as I have shown previously), give the same type of curve within
at least a certain range of observation. And other cases might
be quoted illustrating the general law, that the response of living
matter to the excitation of its environment increases by dimish-
ing increments, giving a cause/effect curve that is concave towards
its abscissa. And we need not attempt to see whether or no
this curve can be neatly fitted with a logarithmic formula, for
the fit or the misfit of a curve, constructed from such a formula,
would not afford much information beyond what is to be learned
from inspection of the empirical curve, and comparison with
other curves.

Moreover, one may convince himself at once by somewhat
closer observation, that the entire range of any given cause/
effect curve cannot be fitted by a logarithmic formula. Above
the range of moderate stimulation, we have no further increment
of effect, but, on the contrary, a decrement, attributable to fatigue
or to shock, or to actual injury by excessive stimulation. And
below the range of moderate stimulation, the curve does not
spring suddenly from its abscissa and rise by increments diminish-
ing from the very outset, but it rises gradually from zero by
increments smallest at first then increasing, so that a first part
of the curve instead of concave is convex to the abscissa, and the
whole curve S-shaped, convex at first, concave at a higher range.
I have urged elsewhere that this S-shaped character of the
cause/effect curve is general, and that any well-studied case,
where we can plot physical cause along an abscissa and physio-
logical effect along ordinates, will probably be found to yield
such an S-shaped curve.*

§ 20. Ancesthetics. — In conclusion of this chapter I will
briefly remark on the two last headings of the syllabus in

* WALLER.—" On the Excitability of Nervous Matter." Presidential
Address to the Neurological Society, 1900. Brain, 1900.

ii.] ANESTHETICS 39

your hands ; one of these — the action of anaesthetics — I took
the opportunity of examining with some care a few years ago
in connection with a methodical study of the action of anaes-
thetics on isolated nerve ; * the other— retino-motor effects — I
have not worked at myself; it rests upon the authority of
Engelmann, who discovered and worked the point with his
pupil Grijns.

The ordinary anaesthetics — carbon dioxide, ether, and chloro-
form— influence the electrical response of the retina to light as
might be expected from a consideration of the physiological
character and conditions of the response and the relative power
of the anaesthetics used. With an enucleated eyeball as the
object of experiment, the layer to be anaesthetised is compara-
tively well protected by the sclerotic coat, and the effects of an
anaesthetic vapour are obstructed if only because its access to
the retina is obstructed. Still the characteristic effects of the
three anaesthetics are produced, although more slowly and im-
perfectly than in the case of an isolated nerve. Carbon dioxide
gives diminution followed by augmentation of the response.
Ether gives temporary diminution or abolition of the response,
followed (usually) by perfect recovery. Chloroform gives aboli-
tion of the response, and the abolition, once it is produced, is apt
to be final.

§ 21. Rctino-nwtor effects. — The effects studied by Engel-
mann and Grijns are interesting in two chief particulars : they
indicate the possible existence of efferent fibres in that most
typical afferent nerve, the optic nerve (retino-motor) ; and they
afford some answer to a question that has no doubt occurred
to you, whether, namely, the electrical change occurring in an
illuminated retina, belongs to altered pigment or to retracted
cones or to both phenomena. The chief points in Engelmann's
observations are, that retraction of the cones and an electrical
effect can be produced in one eye by electrical excitation of
the peripheral end of its optic nerve, or of the central end of

* WALLER.—" The Action of Anaesthetics on Nerve." Presidential
Address to the Section of Anatomy and Physiology of the British Medical
Association. Montreal, 1897. British Medical Journal, 1897.

40 THE SIGNS OF LIFE [LECT. 11.

the other optic nerve, or by luminous stimulation of any part of
the skin. I think we are bound to accept as correct the results
vouched for by an observer of Engelmann's experience, yet, I
must confess, that I cannot defend myself from a lingering
doubt when I remember how sensitive the retina may be to
the weakest trace of light (I have seen distinct reaction to
a flash of moonlight lasting y^o-th second, and quite recently, by
courtesy of Sir W. Crookes, to the luminosity of radium), and
when I consider how difficult it must be to absolutely protect
an eye from all trace of direct illumination, while sunlight is
reflected on to the other eye or on to the skin.

REFERENCES

HOLMGREN. — "Ueber die Retinastrome, Cbt. f. d. med. Wissensch." 1871,

P- 423-
DEWAR AND MACKENDRICK. — "On the Physiological Action of Light,"

Trans. Roy. Soc., Edinburgh, 1873, p. 141; and, Journ. of Anat. and

Physiol., vii., 1873, p. 275.
KUHNE AND STEINER. — I. " Ueber das Electromotorische Verhalten der

Netzhaut," II. "Ueber Electrische Vorgange," Unters. a. d. Physiol. Inst.

Heidelberg, iii. and iv., 1880-1881.
BECK. — "Ueber die bei Belichtung der Netzhaut von Elodone moschata

entstehenden Actionstrome," Pfliiger's Archiv. Ixxviii., 1899, p. 129.
FUCHS. — " Untersuchungen u'ber die im Gefolgeder Belichtung auftretenden

galvanischen Vorgange in der Netzhaut und ihren zeitlichen Ver-

lauf," P finger's Archiv., Ivi., 1894, p. 408.
WALLER. — •" On the Retinal Currents of the Frog's Eye, excited by Light, and

excited Electrically," Phil. Trans. Roy. Soc., B vol. 193, 1900, p. 123.
WALLER. — "On the Blaze-Currents of the Frog's Eyeball," Phil. Trans.

Roy. Soc., B vol. 194, 1901, p. 183.
WALLER.— "The Eyeball as an Electrical Organ," Proc. Physiol. Soc.,

10 November 1900.

ENGELMANN AND GRIJNS. — Helmholtz* Festschrift, 1891.
GOTCH.— "The Time-Relations of the Photo-Electric Changes of the Eye-
ball of the Frog," Journ. of Physiol., vol. xxix., 1903, p. 388.

LECTURE III

Plan of this Lecture — Electrical Excitation of a Frog's Eyeball — Modifica-
tion of the Response to Light subsequent to Tetanisation, and during
Tetanisation — Effects and After-effects of Single Shocks — "Blaze-
currents" -Polarisation Currents- — Electrocution — Three Types of
Blaze-currents — The Effect is greater than its Cause — Influence of a
Galvanic Current — Some Questions — The Crystalline Lens.

§ 22. I propose to consider to-day, and as much as possible
demonstrate : —

1. The effects and after-effects of tetanisation upon the
eyeball.

2. The influence of tetanisation upon its electrical response
to light.

3. The influence of light upon the electrical effects of elec-
trical shocks.

4. The effects and after-effects of single induction shocks
(and of condenser discharges) upon the eyeball ; and

5. The influence of galvanic currents on the effects of
induction shocks.

No small undertaking indeed for a single day's work,
nevertheless one that we shall hope to meet by aid of a series
of simple experiments. Of course I well know that a string
of experiments, perfectly successful it may be, but imperfectly
explained and understood, has equal value with a string of con-
juring tricks, but I take it that by this time you see your way
through the apparatus set out on the lecture table and the
diagrams hung at your elbow. Moreover, I can refer you to a
paper published last year, on the Blaze-currents of the Frog's
Eyeball, that contains at greater length than would be suitable
for a lecture the results and considerations that we are about to
review. I venture to think that the reading of the paper would

41

42

THE SIGNS OF LIFE

[LECT.

help you to understand the lecture, and that the hearing of the
lecture may help you to understand the paper.

§ 23. The effects of tetanisation. Experiment I. — When one
has seen that the stimulation of an eyeball by light arouses

, Light.

InducCorium.

FlG. 19.— Frog's eyeball between unpolarisable electrodes for demonstration of
the electrical effects of light and of electrical excitation. The circuit from the eye is
completed through a compensator, secondary coil, and galvanometer. The arrows
through the eyeball and the galvanometer indicate the direction of the initial current
and of the normal response. Arrows near the compensator wires indicate the direction
of compensating counter-current.

a positive electrical response (and that any mechanical dis-
turbance arouses current in the same direction), he naturally
thinks of electrical excitation, and expects to find that
if the retina is stirred up to activity by such means, it will
manifest current in that same positive direction. The ex-

in.] TETANISATION 43

pectation is realised by the following experiment, in which,
as you will readily see from the diagram, a weak tetanising
current is to be passed through a secondary coil, an eyeball,
and a galvanometer, all the plugs being removed. The
tetanising current is so weak that its constituent single shocks,
alternating in direction, do not of themselves affect the gal-
vanometer, but do stimulate the eyeball, which gives current
in the circuit, current which, as you see from the deflec-
tion of the spot to your right, is in the expected (positive)
direction.

I repeat the experiment, having turned over a reverser in
the secondary (or it might have been in the primary) circuit,
in order to reverse the directions of the constituent shocks,
and the spot is again deflected to your right. I take it that
this experiment needs no comment ; it says that induction
currents of both pairs of directions arouse a positive electrical
response of the eyeball.

In ordinary language, the "effect" of a modifying cause is
subsequent to that cause, and is therefore, properly speaking, an
" after-effect." But it is in some instances necessary to distinguish
between the effect during its cause, and the after-effect subse-
quent to that cause. You have just witnessed the effect during
tetanisation — necessarily during weak tetanisation. I cannot
show you an effect during strong tetanisation, since strong
induction currents traversing the galvanometer would mask the
physiological current of the eyeball. If you should wish to
observe the effects of strong tetanisation, you must be content
with what are properly speaking after-effects, since I must put
the galvanometer out of circuit during tetanisation, and unplug
it to receive the eyeball current that may be present as the effect
or after-effect of strong tetanisation. And I will do this now, to
show that the effect (or after-effect) of tetanisation may be very
great indeed. The eye current is exactly compensated so that
I can plug and unplug the galvanometer without disturbing the
spot. I plug the galvanometer and tetanise the eyeball. Then
I unplug and the spot flies off scale to your right, indicating
positive current in the eyeball as an effect (or after-effect) of the
tetanisation.

44

THE SIGNS OF LIFE

[LECT.

| 24. The effects of tetanisation upon the effects of light.
Experiment II. — Our next experiment is to show that the
electrical response to light is modified by tetanising cur-
rents. I had to use very weak currents for the first ex-
periment, I shall use much stronger currents for this one,
because I want to show an unmistakable modification of the
electrical response to light, and I may use strong currents if
while they are passing they are short-circuited from the gal-
vanometer. First notice the response to light, it is about + 14
degrees of scale. Now, I plug out the galvanometer and tetanise
the eyeball for half a minute. I then unplug, and the spot has
flown off scale to your right. That has been what on first
witnessing it I called a blaze-current ; it has been provoked by
the tetanisation to which the eyeball has just been subjected.
But for the present it is not our principal concern. I bring the
spot back on to scale by means of a compensating current,
and as soon as the spot has come to comparative rest — it has
been gradually falling off to the left by reason of the gradual
subsidence of the blaze-current — we again take a reading of the
electrical response to light ; it is now 30 as compared with 14,
its value before tetanisation, i.e., the normal response to light
has been more than doubled in consequence of tetanisation.

1] (5,000)

O 5 iomins.0 |_ L5 L \L° L /5L \_20mins.

Before bebc3.nisa.bion. Afber bebc3.nisc3.bion.

FlG. 20. — Frog's eyeball. Influence of tetanisation upon the normal retinal
response to light. Ordinary arrangement of induction coil, fed by two Leclanche cells.
Secondary coil at 9 centims. (5000 units on Berne scale). After tetanisation the
positive response is considerably augmented, and falls during illumination. The
terminal positive deflection at break of light is almost completely abolished.

This marked augmentation of response as to current may be
due to augmentation ^{voltage or of conductivity,®? to both factors ;

iii.J SINGLE INDUCTION SHOCKS 45

as a matter of fact it is due to both factors, the electro-motive
force of the response is increased, and the resistance of the eye-
ball is diminished. You will recognise both these points on the
accompanying record, where the tetanisation has raised the
voltage of the response from about TjoVo to nearly T<yVo- 5 y°u
notice also that the standard deflection by rITVcr v°lt has been
evidently increased — indicating increased conductivity, i.e.,
diminished resistance.

§ 25. In the experiment just made you have witnessed a
marked effect subsequent to tetanisation ; a similar effect is
witnessed during tetanisation, but it is rather more troublesome
to demonstrate properly, and I have not therefore included it in
to-day's list. I will content myself with quoting the results of
a former experiment in which the deflections in response to
light were :—

Before tetanisation 12 degrees of scale.
During tetanisation 36 degrees of scale.
After tetanisation 27 degrees of scale.

| 26. The effects of single shocks. Experiment III. — The
very strong currents that you have just witnessed as after-
effects of strong tetanisation are — as I hope to prove to
you in a future lecture — in chief part of physiological origin,
but in minor degree merely the physical effects of ordinary
polarisation. Their experimental analysis is a complicated
matter that cannot profitably be dealt with before we have
become familiar with the less complicated results of excita-
tion by single induction shocks and by condenser discharges.
And since for the purpose of our third experiment it is indifferent
which of these two forms of electrical excitation we may choose
to take, I will use the more familiar apparatus, to show the effects
and after-effects of a single break induction shock, first in one
and then in the other direction. You understand, of course, that
the expressions " effect " and " after-effect " are simply used to
distinguish between the two experimental cases, where (i) the
induction shock and the response are allowed to pass through
the galvanometer ; and (2) only the respon.se is allowed to pass,,

46 THE SIGNS OF LIFE [LECT.

the induction shock (and first part of the response) occurring
while the galvanometer is plugged.

It will be most convenient if we make a first pair of trials to
witness the after-effects of two single break induction shocks in +
and — directions.

It is necessary, in first place, to get rid of the make induction
shock. You will readily see by reference to the diagram how
this is done. The primary circuit of the inductorium is closed
by a spring key, and while this is done, the secondary coil is
short-circuited at the keyboard (see Fig. 19, p. 42). Then this
plug is removed and the spring-key released so that a break
induction shock is passed through the eyeball. And finally the
galvanometer plug is removed, so that the current (if any)
aroused in the eyeball, traverses the galvanometer and deflects
its spot. These steps are quite automatically made after a little
practise, and at a quite sufficiently uniform rate ; the electro-
motive response of the eyeball is so prolonged that it is not
necessary to hurry ; although obviously for comparative trial it
is preferable, as well as more convenient, to use a special key
that breaks short-circuit of the galvanometer at a regular interval
(?•£-•> iVth sec.) after breaking the primary circuit.* It is evident
that in order to plug and unplug the galvanometer without dis-
turbing its spot, all current in circuit must be compensated.
This compensation has been adjusted at the outset, and must
be exactly re-adjusted before each trial. Then we shall be
assured that a given deflection is in reality due to current
aroused by excitation, and not to any accidental current in
circuit.

I may now proceed with the experiment. I begin by testing
the compensation, and, if necessary, adjusting it. I then send a
break induction shock through the eyeball in the negative
direction, and afterwards unplug the galvanometer. The spot
flies off scale to your right. That has been a blaze-current, of
positive direction in response to an induction shock of negative
direction ; it is not a polarisation current ; although at first
sight by reason of its direction it might have been set down as

* See Appendix, Fig. 68, p. 166.

III.]

BLAZE-CURRENTS

47

such ; I characterise it, in distinction from the next variety of
current that you will witness, as equivocal or antidrome. The
current is subsiding, rapidly at first, now more gradually, and
more and more so as the spot approaches its zero position, some-
times, indeed, we may witness a permanent positive deflection, a
current-remainder reminding one of the contraction-remainder
of muscle.

I will now test the eyeball by an induction current in the

VoLb

J_

mms. IO

/? - zooo

o mins.

10

20

FlG. 21. — Normal blaze-currents of a frog's eyeball in response to excitation by
a single break induction current in the negative or antidrome direction (B - 2000),
and in the positive or homodrome direction (B + aooo).

positive direction ; so I adjust the compensation and turn a
reverser in the induction circuit, send a break induction shock
through the eyeball in the positive direction, and unplug the
galvanometer. The spot flies off to your right as before. That
also has been a blaze-current, of positive direction in response to
an induction shock of positive direction ; it is evidently not a
polarisation current ; I characterise it in distinction from the
first variety as unequivocal or homodrome.

This, in my opinion, is a cardinal experiment, and when it
was deciphered, became sign-post as well as hinge of further and
more general investigation.

But let us complete the experiment. The eyeball — upon
which you saw a moment ago that two very large responses in
one and the same direction followed excitation by single break
shocks first in one and then in the opposite direction — has been
plunged into hot water, i.e., killed and replaced between the
electrodes. I repeat the test of a right and left induction shock
and no movement whatever of the galvanometer spot is to be
detected. The dead eyeball gives no blaze-current.

48 THE SIGNS OF LIFE [LECT.

§ 27. Polarisation. — But I have been using the galvanometer
" at low power," much shunted, in the knowledge that the blaze-
currents in the main experiment would be very strong. And to
see whether or not there is any trace of response, a " high power "
of the galvanometer must be taken by unshunting it. Which
has now been done (and you notice by the way that an exact
compensation is a little more troublesome to effect), and I repeat
the test, right and left. There is just a trace of after-effect — to
your left ( — ) after excitation to your right ( + ), to your right
( + ) after excitation to your left ( — ) — and this is not a physio-
logical response, it is only the ordinary polarisation counter-
current exhibited by any electrolyte. I will show it you in
more pronounced form with a couple of wires dipping in salt
solution, but not now — after lecture, when I shall also test
these unpolarisable electrodes.

§ 28. Experiment IV. — You have just witnessed the third
experiment in one form, demonstrating to you physiological
after-effects, and you will have no difficulty now in following
the steps by which I am about to make it in another form, to
demonstrate to you these same after-effects inclusive of their
earliest visible manifestations, which I have referred to as the
effects. I do not think that the distinctive words are justified
by any distinction of phenomena ; their use has, however, been
pressed upon me by the necessity of distinguishing between
the results of two methods.

A fresh eyeball (that has just been tested by the assistant
and found to respond normally to light) is set up between elec-
trodes, and I intend to send through it and through the gal-
vanometer a break induction shock of suitable strength, first in
one, then in the other direction. The strength taken as suitable
is one that gives through a circuit of resistance equal to that
formed by eyeball electrodes and galvanometer, a distinct and
equal swing of the spot to the right and to the left, and that if
sent through the eyeball is fully adequate to arouse a normal
(positive) blaze.

I now send a break shock through the eyeball (and galvano-
meter) in the positive direction, and you see the galvanometer

in.] ELECTROCUTION 49

spot sharply deflected to your right. " Naturally," you say,
" since it has been traversed by an induction shock in a positive
direction, and ' positive ' is to our right." But notice the magni-
tude of the deflection, notice also, how slowly it is subsiding ;
that has not been any short kick by an induction shock, but
something more, it has been a positive kick heralding our now
familiar friend, the positive blaze. And you will be quite sure
that this has been so, when you see the effect of sending a break
shock through the eyeball (and galvanometer) in the negative
direction. Now, you have a short, sharp kick of the spot to the
left by the induction shock, and a -prolonged large deflection to
the right, slowly subsiding, evidently the electrical expression
of what by this time we are tempted to call the retinal blaze
(but vide infra as regards the justification of "retinal").

§ 29. Electrocution. — The proof has to be completed by
showing that these blaze effects do not occur on a dead eye-
ball. I killed the last eyeball by putting it into hot water. I
will kill * this one by electrocution, a method that has the
advantage of leaving the eyeball undisturbed between the elec-
trodes, and then apply the test of an induction shock right and
left through eyeball and galvanometer. I strengthen the cur-
rent, sliding the secondary quite home over the primary, and
tetanise for half a minute or so with these strong currents
(taking care, of course, to plug out the galvanometer to preserve
it from such currents). Finally, 1 unplug the galvanometer and
apply the double test. The positive break shock gives a sharp
deflection to the right, the negative break shock gives a sharp

* It has been objected to me that I cannot tell whether the eyeball has
really been killed, may not be merely shocked, would not in time recover.
In point of fact I do not think it has been finally killed, but the discussion
need not be entered upon further, our sufficient point is, that blaze-currents
are not manifested by an electrocuted eyeball, and it does not matter to us
whether this inert state is that of death or of shock. A similar objection has
been made with reference to capital punishment by electrocution, and in this
case accidental recovery is guarded against by a prompt " post-mortem " ex-
amination. For the conditions of recovery or non-recovery of electrocuted
animals, cf. Prevost and Batelli, Journal de Physiologic et de Pathologic
Generate, 1899, pp. 399, 427, 1085, 1128 ; 1900, pp. 40, 422, 443, 755-

D

50

THE SIGNS OF LIFE

[LECT.

and equal deflection to the left. There is no blaze. The eye-
ball is dead, or in that state of latent life, or temporary non-
living state to which we give the name of " shock." Evidently,

10 m.

FlG. 22. — Frog's eyeball, induction coil and galvanometer in series. Effects of
single break induction shocks in positive and negative directions before and after
" electrocution " by strong tetanisation.

as regards the retina, or the eyeball, the blaze reaction is a
very nice and convenient '•'sign of life"

§ 30. The three types. — So far, the several experiments that
have been grouped together under the head of the third experi-
ment (| 26), have come off perfectly well, and, in accordance,
with expectation and prediction.

It might have been otherwise. I took care to be provided
with fresh, normal, uncompressed eyeballs, because I did not
wish, in introducing the subject, to have to confuse your first im-
pression of it by interpolated explanation of unexpected results
of experiment. And I was careful to be provided with the
lively Rana Tcinporaria, as the sluggish R. csculenta would pro-
bably not have answered as well. Nevertheless, I felt it neces-
sary to have at my elbow a diagram, in which are schematically
summarised the various cases that I have met with in various
states of the eyeball. I have divided them into three types : —

in.]

THREE TYPES

51

(i) Both reactions positive; (2) Both reactions homodrome ;
and (3) Both reactions negative ; and although I do not find any

Direction of exciting current

Negative

Positive

TVI-E I.

The response to excitation in both direc-
tions is positive,
response.

This is the normal

TYPE II.

The response to excitation in the negative
direction is negative, and in the positive
direction positive.

TYPE III.

The response to excitation in both direc-
tions is negative.

DEAD EYEBALL.

The response to negative excitation is
positive and to positive excitation
negative.

FIG. 23. — Frog's eyeball. The three types of response to excitation by single
induction shocks in positive and negative directions.

strict parallelism between these three types of electrical response
to electrical stimuli, and the three types described above of
electrical response to luminous stimuli, I do find correspondence
to this extent that a perfectly normal eye gives positive response
of the first type in both series, while a considerably compressed
or massaged eye gives negative response of the third type in
both series. The extremes in the two series correspond, but I
fail to trace correspondence in the intermediate and transitional
forms of the two series. It is hardly necessary to point out that
the very existence of such a series of responses graded from
positive to negative, is confirmatory evidence of the coexistence
of two contrary electro-motive changes, a conclusion which we
saw reason to infer from the effects of light already described.

5$ THE SIGNS OF LIFE [LECT.

§31. Cause < Effect. — I have thought it hardly necessary to
repeat to you a series of experiments similar to the preceding,
but with condenser discharges in place of break induction
shocks. Moreover, time forbids that I should do so, with the
explanation necessary to bring out the particular advantages
of this method. We may find time for this at a future
lecture, meanwhile I will again refer you to the paper already
quoted,* where you will find experimental justification for the
statement that the electrical energy of excitation is greatly
exceeded by the electrical energy of the blaze-current that it
arouses.

§ 32. Galvanisation. Experiment V. — The fifth and last
experiment on our list is to show how the direction of a
blaze - current aroused by an induction shock, can be modi-
fied by the passage of a galvanic current through the eye-
ball.

An eyeball is put up as before, the compensator is arranged
to give a current of comparatively high E.M.F. (o.i volt) through
the eyeball and galvanometer. I first take this galvanic current
in the positive direction, when, of course, the galvanometer spot
is driven off scale to your right. I bring the spot back in scale
by means of a controlling magnet, and as soon as it is steady,
send a break induction shock through the circuit (comprising
the eyeball, compensator, and galvanometer in series) first in the
positive, then in the negative direction. In both cases the
positive deflections are greatly augmented.

Then I reverse the galvanic current to the negative direction,
readjust the spot on scale by means of the controlling magnet,
and repeat the test. Both the induction shocks, positive and
negative alike, now give negative deflections, i.e., blaze-currents
in the same direction as the galvanic current. Nothing of the
sort happens, I should add, in the case of a dead or " electrocuted "
eyeball. If I had made the experiments upon an eyeball giving
negative blaze-currents of the third type described above, you
would have witnessed an augmentation of these currents during

* Phil. Trans. Roy. Soc., vol. 194 B., p. 183. 1901.

m.]

EXPERIMENT V

53

negative galvanisation, and their reversal to positive currents
during positive galvanisation.

I think these points will be best illustrated by the values
obtained in some previous experiments of the kind. The values
are approximate only, as I did not correct for kick due to the
induction shock itself.

Direction of Excitation
by Break Shock of Berne
Coil at 1000 units, with
two Leclauchi's in prim-
ary circuit.

VOLTAGE OP RESPONSE.

During
Galvanisation by
- l/10th volt.

Without
Galvanisation.

During
Galvanisation by
+ l/10th volt.

+

- O.o6o
-0.040

+ O.OIO
+ O.OIO

+ 0.050
+ 0.030

+

-0.024
-0.033

-O.Oig
-0.029

+ 0.024
+ 0.019

§33. Some questions. — Our experiments are at an end, and
so is the lecturer's hour. But I will tax your patience for five
minutes longer and attempt to answer two questions that must
have occurred to you as they have to me. How much of this
blaze-reaction is due to the retina, and how much to other
tissues of the eyeball ? Is the retinal stuff that reacts to light
the same as, or different from, the stuff that reacts to an
induction shock ?

I cannot fully or confidently answer either of these
questions. I can only give partial and tentative answers, and I
do so far less on account of any value that I place on the answers
in themselves, than because I believe you will see how the chief
value of a question — somewhere, somehow — we cannot at the
outset foresee either where or how — may be wrapped up in our
very failure to obtain a neat answer.

At first I thought that the blaze-current was retinal, like the
current excited by light. The expression " retinal blaze "
obtained currency in the laboratory, and the title of my first
paper runs, " On retinal currents excited by light and excited
electrically," and the title of my second paper was intended to
be " On the ' blaze-currents ' of the Retina," but it soon became

54 THE SIGNS OF LIFE [LECT.

" On the blaze-currents of the Eyeball." That the electrical
response of the eyeball to light has its exclusive seat in the
retina, is proved by the fact that of the two halves of an eyeball
bisected into an anterior and a posterior half, only the latter
responds to light, and if further — as recommended by Kiihne,
the retina itself be separated from the remaining coats, electrical
response to light persists of the isolated retina, but is absent
from the remaining tissues. But a similar procedure in the case
of electrical response to electrical excitation taught me that the
reaction is not confined to the retina, that it is manifested by
the anterior as well as by the posterior half of the eyeball, that
the isolated cornea and the isolated lens give blaze-currents. I
therefore concluded that tissues other than retinal are coeffective
in the electrical response to electrical stimulation of the entire
eyeball, and accepted the fact as a hint to examine other living
tissues for this presumably common sign of life. Meanwhile,
from the retinal sheet in animals excitable by light, my attention
naturally turned to the chlorophyl sheet in vegetables presum-
ably excitable by light, and a demonstration of the electrical
response to light in green leaves was the immediate result* I
tried petals of flowers in the same way, as one among other
control tests of the reality of the leaf response. Petals proved
to be absolutely inert in this respect. Yet petals are obviously
" alive," so I tested petals by the blaze-test, and found that to
this test petals are at once found to be alive. The idea by this
time had fully generalised itself in my mind, and I placed all
sorts of living things, animal and vegetable, on the unpolarisable
electrodes, leaves, stems, seeds, fruits, etc., muscle, nerve, lung,
liver, pancreas, skin, hen's eggs, etc., and found that some things
reacted well, and others not at all, or irregularly. But these
were digressions — digressions, however, that have in my opinion
become far more interesting than the original questions.

§ 34. To return to the second of these. To get an indica-
tion whether the same or two different substances react to
light and to induction shocks, I looked for modifications of the

* WALLER. — " The Electrical Effect of Light upon Green Leaves,"
. Roy. Soc., vol. 67, p. 129, 1900,

III.

TETANISATION AND ILLUMINATION

55

response to light by strong tetanisation, and vice versa for modi-
fications of the response to induction shocks by strong illumina-
tion, I also took series of positive responses to light and to
weak tetanisation alternated, to see whether or no they would
decline pari passu. An example of such a series has been

voit

•00/0

•0005

\

FlG. 24. — Frog's eyeball. Series of normal responses to light and to tetanisation
alternated ; each excitation lasts for one minute. The response to tetanisation falls
more rapidly than that to light.

figured above. The series of responses to tetanisation appears
to decline more obviously than does the series of responses to
light. But the difference is not very striking, and in other
records it is even less so. In fact, when I took the records, I
thought they justified me in saying that the two kinds of response
wear out in a parallel manner. Clearly, however, the parallelism
has not always if ever been absolute ; the instance figured above
exhibits more rapid decline of the tetanisation responses than
of the light responses. The point clearly needs to be tested
again. As regards modification of the response to induction
shocks by strong illumination, we have seen that no appreciable
effect occurs. As regards modification of the response to light
by strong tetanisation, we have seen that the regular effect has
been an increased response during and after tetanisation. Indeed,
the resistance of the retina as regards its excitability by light
has been a constant yet surprising feature. The strongest tetani-
sation at my disposal (Berne coil, 2 Leclanches, secondary over
primary coil, current unbearable by wetted fingers) has failed
to abolish its response to light. And strong tetanisation (10,000
units) that has completely abolished all blaze-reaction (as e.g.,

56 THE SIGNS OF LIFE [LECT.

in the experiment of Fig. 22) has left the response to light
unaltered.

On review of all these facts, I am inclined to think that, as
regards their action upon the retina, the two forms of excita-
tion act upon two distinct but closely related substances holding
to each other the relation of pro-substance and substance, the
former acted upon by electrical currents and not by light, the
latter acted upon by light and not by electrical currents.

Among the tissues that give most dubious results in a first
rapid survey of blaze-currents, the skin was one of the most
notable. I therefore studied it the more closely. The next two
lectures will be given to the consideration of " Skin-currents."

§35. The crystalline lens. — Further investigation of the blaze-
currents manifested by the anterior parts of the eyeball led
to very definite, constant, and, I may add, quite unexpected,
results. The observations relating to this matter were made at
the sea coast during the months of August and September
of last year — principally on the crystalline lens of freshly
caught fish — and may be most briefly described by the following
quotation : — *

" In the course of investigation of the effects of light and of
electrical excitation on the frog's eyeball, I came to the con-
clusion that tissues other than retinal are coeffective in the
response to strong induction shocks, and proceeded therefore
to look for blaze-currents in other living tissues.

" The particular point that aroused my attention in the case
of the eyeball was the fact that the anterior half of the eyeball
was sometimes found to give a larger response than the posterior
half, and the present observations proceed from an attempt to
determine the principally effective part in such reaction. And
I may state at once, as my chief conclusion, that it is the
crystalline lens.

"The eyes upon which the determination was made, in the
first instance, were those of fish — whiting and mackerel — by
reason of the fact that these were for a season at my disposal

* " On the Blaze-currents of the Crystalline Lens," Proc, Roy. Soc.,
4th December 1902,

LENS CURRENTS

57

quite fresh from the sea. I subsequently made similar observa-
tions on the eyes of octopus, on sheep's eyes fresh from the
slaughter-house, and on the eyes of recently killed cats and
rabbits.

" The point that was most striking in these first observations
was the great endurance of the reaction in the crystalline lens
as compared with its rapid disappearance from the remaining
tissues of the eyeball and from the skin, and with the rapid
disappearance of the direct electrical excitability of muscle. I
should, as an outcome of these observations, look for the last
sign of life of a fish by testing the crystalline lens, whereas in
the case of man I should test a piece of skin. The reaction — as
far as I have yet seen — has been completely absent from frozen
fish (salmon) as received from London fishmongers. Its normal
direction in the lens is ' negative,' i.e., from external to internal
pole. It is abolished by heat (70°) and by pressure. A typical
pair of responses is illustrated by the following record :—

FlG. 25. — Codfish. Antidrome and homodrome responses of the isolated lens,
from anterior to posterior pole, of - 0.0009 and - 0.0022 volt respectively.

58 THE SIGNS OF LIFE [LECT. in.

" I conclude from this and similar experiments —

" i. That a crystalline lens of suitable size is a good object
upon which to study the nature of blaze-currents.

" 2. That a ' blaze-current ' is a physical sign of the ' living '
state.

" 3. That a blaze-current may be post-kathodic as well as
post-anodic, antidrome as well as homodrome.

" 4. That the normal direction of blaze-currents in the crystal-
line lens is negative or ingoing, i.e., from the external or anterior
to the internal or posterior pole."

REFERENCES

WALLER.—" On the Retinal Currents of the Frog's Eye, excited by Light

and excited Electrically," Proc. Roy. Soc., Ixvi., p. 327 ; Phil. Trans.

Roy. Soc., B vol. 193, p. 123.
WALLER.— "The Eyeball as an Electrical Organ," Proc. Physiol. Soc.,

loth November 1900.
WALLER.— "On the 'Blaze-currents' of the Frog's Eyeball," Proc. Roy.

Soc., Ixvii., p. 440 ; Phil. Trans. Roy. Soc., B vol. 194, p. 183.
WALLER. — "Le Dernier Sigrie de Vie," Comptes Rendus de P Academic des

Sciences, 3rd September 1900.
WALLER.—" On the Blaze-currents of the Crystalline Lens," Proc. Physiol.

Soc., November 1902 ; Proc. Roy. Soc., 4th December 1902 ; Engel-

manris Archiv f. Physiologie.
DURIG. — "A contribution to the action of Blaze-currents," Proc. Roy. Soc.,

4th December 1902.

LECTURE IV

Skin-currents (of the Frog) — The Normal Current is " Ingoing "--The Re-
sponse to Indirect Excitation is Outgoing, Mixed, or Ingoing — The Latent
Period is Two Seconds — Fatigue — Atropine — Mercuric Chloride — The
Response to Direct Excitation is Outgoing — Summation — Effects of
Tetanisation — Localisation of the Response by the ABC Method-
Terminology.

§ 36. From the preliminary observations alluded to in my
last lecture (§ 33), I formulated the following working rule for
the experimental distinction between the living and the dead
states of matter : —

" If the object of examination exhibits blaze in one or in
both directions, it is living." *

One of the earliest objects of examination upon which I
tested this rule was the human body, living and dead. I thought
that it might be possible to place, e.g., a finger between a pair of
electrodes, and to learn from the presence or absence of blaze
reaction whether the finger was living or dead. But by reason
of the fact that a finger is covered by skin, and that it is im-
possible to send current by unpolarisable electrodes into the
intact human body otherwise than through skin (or mucous
membrane), the question has proved to be much less simple than
it appeared. It has involved me in an investigation of skin-
currents that has taken the best part of two years, and the
results, instructive though they are as regards the original
question, are, I think, of still greater interest from another point
of view. It will be well, therefore, to consider ourselves as
entering upon a fresh field, albeit an already much trodden field,
in undertaking an exploration of " Skin-Currents."

* I do not commit myself to the obverse, that if an object exhibits no

blaze it is not alive. Vide infra, § 82,
59

60

THE SIGNS OF LIFE

LECT.

We shall study the skin-currents of the frog, of the cat,
and of man, also the currents of mucous membranes and the
currents of vegetable " skins." To-day we shall confine our-
selves to the case of the frog, examining : (a) the normal
current, (ff) the effects of indirect excitation, (V) the effects of
direct excitation.

§ 37. TJie normal current. — A piece of skin of the back, or
indeed of any part of the body, carefully excised and placed
between impolarisable electrodes, gives current, directed from
outer to inner surface (through the skin). This "ingoing"
" negative " or centripetal current increases during observation.
A piece of skin spread upon a glass plate with a central hole,

and placed between the elec-
trodes as figured, gives current
that reflects the galvanometer
spot to your left. And, as you
notice, the spot is creeping
further to the left. Two re-
flections arise from this obser-
vation : clearly the current
cannot be due to injury of the
internal surface, since in that
case it would be outgoing ;
probably the increasing nega-
tive current is due to the sub-
sidence of what in the case of
the eyeball we referred to as
the manipulation blaze. It
looks as if resting skin were
the seat of an ingoing current
of rest, and as if the increasing
negative deflection occurring on the galvanometer scale were in
reality a decreasing positive effect caused by the previous
disturbance by manipulation. We shall find confirmation of this
view later on, when we have learned that direct mechanical and
electrical excitation of the skin gives almost invariably a positive
or outgoing electrical effect

FlG. 26. — Frog's skin on a perforated
glass or ebonite plate, between unpolar-
isable electrodes. The external surface
of the skin is uppermost. The arrows
signify the direction of " normal cur-
rent " — " ingoing," from external to
internal surface.

IV

.] SKIN CURRENTS 61

§ 38. Indirect excitation. — The effects on the skin of excita-
tion of its nerves are particularly interesting ; it is easy to
demonstrate them, but by no means easy to interpret them in
detail. I do not think that any interpretation yet offered has
properly embraced all the facts, and I shall not pretend to mend
matters much in this respect. But I will lay the facts before you,
more completely and more briefly than you will find them hitherto
described, by means of graphic records that exhibit better than
any narrative the character and dimensions of the phenomena.

The experiment I am about to show you is one that was
first made by Roeber (on the suggestion of Rosenthal) more
than thirty years ago, and that has since been repeated with varia-
tions by Engelmann and by Hermann. The preparation is as
follows :— A frog's sciatic nerve is dissected out in the usual way,
the foot is cut off, the skin of the leg is longitudinally divided on
the anterior aspect and peeled off the leg up to the knee-joint,
the leg is cut off just below the knee-joint, the femur and thigh
muscles are divided just above the joint. We now have a sciatic
nerve in connection with the skin of the leg, and the ends of the
femur and tibia serving as a handle. The skin is now laid over
one leading-off electrode, and the other electrode is brought into
contact with the other surface of the skin, the sciatic nerve is
laid across a pair of exciting electrodes that are connected to a
coil. We now have a nerve-skin preparation, the analogue of a
nerve-muscle preparation, quite as easy to make, and affording,
when made, an unfailing demonstration of a current of animal
electricity and of the action of nerve on skin. It ought long ago
to have become a regular lecture experiment and student's
exercise, yet somehow or other it has almost dropped out of
notice. Every student of physiology makes nerve-muscle pre-
parations by the score. I wonder how many students or teachers
have ever made a nerve-skin preparation, and what would be
said if, as a change from the regular round of about six practical
experiments (that cannot be properly done in the time allowed)
an examiner were to ask an honours candidate to show some-
thing by means of a nerve-skin preparation.

Well, our experiment is waiting, and the spot has come to
rest. The normal skin current is ingoing and increasing, the

62 THE SIGNS OF LIFE [LECT.

spot has crept to the left of the scale, therefore to the left signi-
fies ingoing, to the right outgoing ; but we shall verify this
presently with a bit of zinc.

I tetanise the nerve for a second or two, and after a distinct
interval, long enough to allow the thought that there is no
effect, the spot sweeps across the scale to the right, signifying
that the skin, aroused by excitation of the sciatic nerve, has given
an outgoing current. And knowing what to expect, I took care
to shunt the galvanometer, for the resistance of the skin is so
low, and the voltage of response so great, that the spot would
assuredly have flown off scale if the galvanometer had not been
shunted. I wanted, however, to have a measurable effect, such
as should allow us to make further trials. Five minutes have
elapsed, and I repeat the excitation ; deflection to the right occurs
again, but is much smaller. It looks as if the nerve-skin pre-
paration were becoming fatigued. And while we wait for a
second five minutes to elapse, let us consider matters. How
has the nerve acted upon the skin ? What is the meaning of
the declining effect we are looking for? Is the response always
in this positive or outgoing direction ?

All authorities who have worked at the subject are agreed
that it is upon the skin-glands that the nerve acts, and that the
skin effect is the sign of a glandulo-motor or secreto-motor
phenomenon. I share this view, and do not think it probable
that nerve has any connection with the general epithelial invest-
ment of the skin ; but, in remembrance of the fact that cutaneous
pigment cells are demonstrably influenced through nerves, I
make some mental reservation to the assumption that the effect
is exclusively glandular. The wearing-out of the response in
repetition is not due to wearing-out of the nerve, nor even
wholly, I think, to wearing-out of the discharging gland, but
more probably to a wearing-out of the junction between nerve-
fibre and gland-cell.

The second five minutes is at an end, and now you see that
excitation gives a negative instead of a positive response, and
thus answers the last of the three questions we put a few
minutes ago. Clearly, the response is not always positive or
outgoing ; you have just seen that it may be negative or

THREE TYPES OF RESPONSE

63

ingoing, and I may add, to complete the account, that it may
also be " mixed " — negative then positive, or positive then nega-
tive, or positive negative positive.*

And now that you have witnessed a representative experi-
ment, I will project on the screen the records of some previous
experiments.

voit
0-01

Second.

•OO3J

FlG. 27. — Frog. Nerve-skin response,
(l) Positive or outgoing. (2) Mixed. (3) Negative or ingoing.

| 39. Latent period. — Here are a couple of photographic
records, taken on a more rapidly travelling plate, in order to
bring out more distinctly what was already obvious to simple

* The accounts given by previous observers — by Engelmann and by
Hermann in particular — are not quite easy to reconcile with each other, and
with the description given in the text of these lectures. Thus Engelmann, in
1872, concluded that the usual effect of indirect excitation is a " negative varia-
tion " of the normal (ingoing) current. Hermann, in 1878, gives the usual
and principal effect as being a "positive variation" of the normal current.

The two accounts are summarised in the following diagram, and their

THE SIGNS OF LIFE

[LECT.

inspection — viz., the great delay between excitation and response
—about two seconds with a fresh preparation, about three

Voit..

•005-

•OO4-
•OO3-

•ooa-

•001 -

o

10

30 sees.

.
•002 —

•OOI -

[ I 1 t I

o

10

20

jo sees.

FlG. 28. — Frog. Nerve-skin preparation. Galvanometric records of the lost
time of the response to indirect excitation by tetanisation of the sciatic nerve. Lost
time — 2 to 3 sees. Lost time of the galvanometer itself = I sec.

relation to that given in the text will be easily traced if it be remembered
that there all outgoing effects read upwards and all ingoing effects down-
wards.

Outgoing-

*

I "Exceptional;1

Hermann..

Ingoing

FIG. 29.

iv.] ATROPHINE ; MERCURIC CHLORIDE 65

seconds as the response becomes more sluggish. And this
has been a true physiological latency ; it is of the same order
as the similar effect that will be demonstrated to you on a
mammal, which a priori you might have expected to react
more quickly (infra, p. 105). With the capillary electrometer,
and excitation by a single strong induction shock, the latency
came out at 0.9 sec.

§ 40. In connection with the action of nerve upon skin, one
naturally thinks of atropin — the drug which so promptly abolishes
the action of secreto-motor nerve — and remembering how small
a dose of atropin dries the mouth and dries the skin in the case
of man, you have reason to anticipate that atropin, if it produces
an effect at all, will do so when it has been administered to the
animal by subcutaneous injection. I have not found this to be
the case in two experiments ; the nerves of atropinised frogs acted
perfectly well upon the skin, but after the drug had been applied
to the skin itself, the nerves ceased to be effective. So, in order
to demonstrate that atropin acts, it will be preferable to test it by
local application ; and to show this quickly, it will be best to apply
the drug to the external surface of the skin.

A second nerve-skin preparation is set up, for an experiment
to consist of three steps. These will be : firstly, to see that indirect
excitation (from the nerve) is effective ; secondly, to apply atropin
to the skin, and see that the indirect effect is abolished, but that
an effect can still be produced by direct excitation ; finally, to
show that this direct effect is abolished by mercuric chloride.

With indirect excitation you see that the large deflection before
application of atropin has been completely abolished by atropin.
The nerve no longer acts upon the skin. But the response to
direct excitation is quite well marked ; (and note in passing that
it is to your right — in the positive or outgoing direction). I now
apply some mercuric chloride solution to the external surface, and
you see that direct excitation gives no response. The skin is dead.

§ 41. The effects of direct excitation deserve and will repay
closer study. The first and only allusion to these effects that I
am acquainted with, occurs in Engelmann's paper of 1872, sub-

E

66 THE SIGNS OF LIFE [LECT.

sequent observers having principally studied the effects of direct
excitation on the mucous membranes (Biedermann), and on the
skin of the eel (Reid). Engelmann seems to have obtained a
negative variation of the current of rest — i.e., presumably an out-
going effect — but he took no account of direction of excitation.
Biedermann, in the mucous membranes of the tongue and of the
stomach, observed positive and negative variations of the current
of rest ; but in the case of the tongue two layers of mucosa are
under experiment, and in any case a mucosa is not the same
thing as the skin.

Reid found that direct excitation of the eel's skin by induc-
tion shocks of either direction caused ingoing effects, sometimes
preceded by outgoing effects. I have made a large number of
experiments on this point with the same disposition of apparatus
as that described in a previous lecture in the case of the eyeball,
with results that have practically been invariable, i.e., with only
one or two exceptions in several hundred experiments. So that
I am practically certain that in the experiment you are about to
witness, direct excitation of the frog's skin by an outgoing or by
an ingoing induction shock will cause an outgoing skin response.

{Experiment^

A piece of skin is set up between unpolarisable electrodes,
as in Fig. 26, and connected with a keyboard, galvanometer,
coil, and compensator, as in Fig. 19. We are, in fact, about to
test the skin for blaze-currents, just as we previously tested an
eyeball or a seed. Compensation is established (the galvano-
meter is shunted because a large effect is expected). With
the galvanometer plugged out of circuit, a break induction
shock is sent through the skin in the positive (outgoing)
direction (spot to your right), and immediately afterwards the
galvanometer plug is removed. A large deflection to your
right occurs ; and to show you what this large deflection with
the shunted galvanometer means as regards electro-motive
force of the excited skin, I will send current through the circuit
from T^-Q of a volt ; the skin response has been two or three
times as great, i.e., its voltage has been 0.02 to 0.03 ; and this
is by no means a maximum value, I have seen it as much as

IV.]

DIRECT EFFECTS

67

0. 10 volt. The positive response is declining, rapidly at first,
then more slowly, and as soon as the spot is fairly steady, I
compensate and repeat the excitation in the reverse (ingoing)
direction, and, as before, you witness a large positive (outgoing)

voit

•oa

30 mms.

FlG. 30. — Frog's skin. Response to direct electrical excitation. The first
deflection is by a standard voltage. The next two small deflections are in response
to + and - break induced shocks with the coil at 1000 units. The last two large
deflections are with the coil at 5000. (The principal "outgoing" effect is preceded
by a brief ingoing effect in the case of ingoing excitation.)

deflection, which, although in the direction of a polarisation
counter-current, is a blaze-current, like the antidrome blaze-
current of the eyeball (p. 47). Indeed, these skin effects are
precisely similar to the effects you have already seen in the
case of the eyeball. The positive response to positive excita-
tion is the unequivocal blaze, the positive response to negative
excitation is the equivocal blaze.

And to complete the proof, I will kill the skin either with
a few drops of mercuric chloride solution, or by plunging it
into hot water, and now the skin gives no response at all
to either direction of excitation. The spot does not stir. If I
unshunted the galvanometer we might see the small polarisa-
tion effects that occur with any electrolyte. But this is an
unessential point, and we will leave the galvanometer as it is

68

THE SIGNS OF LIFE

[LECT.

for our further experiments, i.e., with its scale to take in a
range of about 0.05 volt.

§ 42. Summation. — The positive response of the skin is ordi-
narily of considerable duration ; in general, the stronger the
stimulus, the longer the response ; five minutes has been a very
ordinary duration in these experiments. If, then, a second
stimulus is applied at the end of one or two minutes, before
the first response has fully subsided, we shall obtain a second
response superposed on the first, and so on for a third and
fourth and nth response, which give a summation of effects by
successive deflection remainders. Here is a record that will
make this point clear.

vott

o

mins.

FlG. 31. — Frog's skin. Summating effect of excitation at intervals of 2 mins.
(The first response is to a weaker excitation.)

With stimuli at shorter intervals, the summation is steeper,
and the individual effects of which it is composed may be
indistinguishable. There is a fusion of deflections analogous
with the tetanic fusion of muscular contractions with which we
are all familiar.

By reason of this summation, and of the fact that both
directions of induction shock arouse response in one and
the same (positive) direction, the rapidly alternating currents
of an induction coil as ordinarily used for tetanisation give
rise to a much larger (positive) response than does a single

iv.] ABC 69

shock at the same strength of coil. This is a summation of
effects. Moreover, if a strength of coil be taken so small as
to produce no response with single shocks, tetanisation at the
same strength will bring out an evident or even large positive
response. Notice that, in making this experiment with tetanisa-
tion, I have taken the response immediately after and not
during tetanisation. A similar effect can be brought out during
tetanisation, and 'in cases (like the present) where there is a
clear and manifest effect in one direction, we may without
fear of fallacy demonstrate that effect during as well as after
tetanisation. But in doubtful cases (p. 131) there is con-
siderable difficulty in distinguishing a true blaze-current from
the disturbance of the galvanometer by the necessarily strong
currents i^sed, and from the relatively large polarisation currents
manifested during strong tetanisation. For this reason I have
deliberately abstained from laying any stress upon the effects
produced during tetanisation, and have limited myself to the
information obtainable with and after single shocks, and after
tetanisation.

| 43. The ABC plan. — With a piece of skin arranged as
shown in Fig. 32, an induction current passed through the
skin in the positive direc-
tion from B to A has its
anode at the lower surface
B and its kathode at the
upper surface A. A blaze-
current is aroused in that
same direction from B to
A, and we put to ourselves
the question whether that

current depends upon an electro-positive state at B, or upon an
electro-negative state at A, or upon both states. Or more
familiarly put : is the B to A current by push of B, or by pull
of A, or by both?

The question will be answered by the following plan of
experiment, which will enable us to examine separately the two
surfaces B and A by connecting first one, then the other, with an

70 THE SIGNS OF LIFE [LECT.

indifferent point C through the galvanometer. And having
done this by a first pair of trials with excitation from B to A,
we shall complete the experiment by a second pair of trials
with excitation in the opposite direction from A to B, i.e., A
having been anodic, and B having been kathodic, and the
blaze-current being as before in the outgoing direction from
B to A.

Try to forecast the result a priori, as I did ; I think you will
probably guess wrong, as I did. I imagined at this stage that
we had to do with something of the nature of so-called positive
polarisation, which Hermann and Hering have shown to be in
reality (in the cases of nerve and muscle) post-anodic action
current. On this view, the positive effect in the first case was
presumably due to a post-anodic "push" at B, and we should
therefore expect current through the galvanometer from C to B
(in the skin from B to C). But the positive effect in the second
case could not be explained, post-anodic " push " should be in
the negative direction, and the effect observed was evidently
either by post-anodic "pull" or by post-kathodic "push"
(through the skin).

So I gave up forecasting and proceeded to experiments, of
which I hope you now see the interest.

We shall begin by a first pair of trials to localise the seat of
electro-motive change in the case of the unequivocal blaze-
current, positive response to positive shock. We shall examine
the anodic surface B. Therefore, we have to compensate B with
C (the indifferent point) through the galvanometer, then to send
an induction shock through B A, then to reconnect B C with the
galvanometer to observe the altered electrical state of B. All
which we have now done, and find somewhat to our surprise that
the spot does not stir, i.e., that the electrical state at B has not
been altered. You suspect, perhaps, as I did, that there is a
break in the galvanometer circuit, so I throw a ^oV^y v°lt mto
circuit, and you see by the movement of the spot that the circuit
is all right.

We next examine the kathodic surface A, so I balance A
with C (the indifferent point) through the galvanometer, send
then an induction shock through B A, and finally reconnect A C

ABC

with the galvanometer. There is a large deflection to your
right, indicating current in the skin from C to A, i.e., that A has
been rendered electro-negative to C, an unaltered point, and to
other unaltered points inclusive of B, which by the previous
trial you saw to be unaltered. We infer from this first pair of
trials that the outgoing (unequivocal) blaze B A depends upon
post-kathodic " pull " under A at or near the outer surface.

Now reverse the direction of excitation, passing the induction
shock through the skin in the negative direction from A
to B.

First test the altered state of B, in the same way as before
(balance B with C, excite through A B, connect B C with the
galvanometer), there is no effect. Then test the altered state of
A (balance A C, excite A B, connect A C), there is a large deflec-
tion to your right, i.e., current in the skin from C to A, i.e., A is
electro-negative to unaltered points C and B, etc. We infer
from this second pair of trials, that the outgoing (equivocal)
blaze B A depends upon post-anodic " pull " under A at or near
the external surface. And from both pairs of trials we infer the
simple conclusion that the blaze-currents B A — unequivocal by
excitation B A and equivocal by excitation A B — depend upon
an electro-motive action aroused at or near the external surface.
We must further infer, against all our preconceptions of the
matter, that this electro-motive action is aroused by the kathode
as well as by the anode of an exciting current (i.e., is post-
kathodic as well as post-anodic) and that in both cases it
consists in an electro-negative state of the active part, i.e., that
this part is galvanometri-
cally positive to inactive
parts — the seat of an in-
creased anionic solution-
pressure.

§ 44. Intact external
surface. — We shall find in
this ABC plan a ready means of testing an intact external
surface, and of thereby learning what are the separate contri-
butions of A and of B in any total reaction between A and B ;

72 THE SIGNS OF LIFE [LECT.

we shall do so by observing the separate partial reactions A C
and B C. Both these reactions will be found to be outgoing at
A and at B, being directed (in the skin) from C to A and from
C to B.

§ 45. There has been one very striking feature in the fore-
going experiments that must at once have attracted your
attention, namely, the surprisingly strict and limited localisation
of the reaction. With a layer of skin only a fraction of a
millimetre thick between our exciting electrode A and B, we
saw a great reaction when the external electrode A and an
indifferent electrode C were connected with the galvanometer,
but no reaction at all when the connection was with B and C ;
yet in this case also we had quite close above B an active
area A that might have been expected to alter the potential
of B.

J. S. MacDonald, to whom I had the pleasure of showing
this experiment, said, " Oh, there must be a membrane." I
think he is quite right, but I am unable to analyse the mode of
action of this membrane.

This strictly local character of the response— which in the
present case of electrodes A and B in close juxtaposition is as
difficult to understand as it is easy to demonstrate — is a singularly
favourable condition as regards the experimental application of
the blaze test to skin and to other animal and vegetable tissues,
in which there is little or no diffusion of the local polar effect
of excitation. In the cases of muscle and of nerve these local
effects are to some extent masked by the propagated distal
effects of excitation, and require for their manifestation current
strengths greatly in excess of those sufficient to give maximal
propagated effects. In a piece of skin, or in a leaf or petal-
provided they are alive, the excited and therefore blazing spot is
limited as to depth and breadth, and the exhaustion of that spot
by excessive stimulation does not sensibly modify the vitality of
parts in its close proximity. Of course the result is a question
of degree ; the entire interpolar length of a tender shoot traversed
longitudinally by violent currents is stunned (or killed) and may
shrivel up and be obviously dead in a day or two / a flat leaf

iv.J WHY "BLAZE-CURRENTS?" 73

traversed by violent currents will exhibit changes outside the
polar area in general accordance with ordinary current-diffusion.
But for all moderate strengths the blaze reaction of a living skin
or of a living leaf is strictly local.

These experiments have been troublesome to follow, as they
have been troublesome to demonstrate, and we may perhaps find
it a relief from a somewhat absorbing effort of attention, to turn
to an academic discussion, touching the nomenclature of these
phenomena, and their relation to other known phenomena, and
their conceivable biological significance.

§ 46. I have been asked why I chose to designate the effects
by the name of " blaze-currents " rather than " positive polarisa-
tion currents," or "post-anodic action currents." I think you
will readily understand the answer to the negative parts of this
question. Apart from the fact that the name " positive polarisa-
tion," as first used by du Bois-Reymond to designate certain homo-
drome effects observed by him in muscle, nerve, and electrical
organs, has been adversely criticised by Hermann and Hering—
shown by them, indeed, to be a misnomer inasmuch as the
effects to which it was applied are demonstrably due to post-
anodic action current — I think it is sufficient to refer to the
equivocal or antidrome blaze as forbidding the use of the term
" positive polarisation." The use of the term " post-anodic
action currents " you have just seen to be altogether unjustified
for these skin-currents ; in one case the current is not post-anodic
at all, and in the other it is post-anodic, but of opposite elec-
trical sign to that of a post-anodic state. In muscle and in nerve
a post-anodic spot is galvanometrically negative ; in the skin it
is galvanometrically positive. So that both these cumbersome
expressions are happily inapplicable, and a new term is required.
I have been led to adopt the term blaze-current, and I think
you may now understand how it arose in the study of retinal
effects, and how it serves to clearly earmark a natural group of
phenomena of very definite physiological meaning.

A blaze-current is literally and strictly a " current of action " ;
but it is a particular kind of action current, and requires a dis-
tinctive name. The known phenomenon to which it bears most

74 THE SIGNS OF LIFE [LECT.

resemblance is the discharge of an electrical organ, and we shall
not infrequently find the term " discharge " a convenient indica-
tive word. But as a distinctive and specific name, the word
" discharge " is insufficient, all the more so from the inconvenience
that would arise when we have to refer to the blaze-currents
aroused by the condenser discharge.

I have had another reason in my mind that has helped to
make me use the expression blaze-current. The great mass of
living things, whatever else they may give and take from their
surroundings, take oxygen and give carbonic acid ; they may live
slowly or they may live quickly — sluggishly smoulder or suddenly
blaze. A muscle at rest is smouldering, a muscle in its contrac-
tion is blazing ; the consumption of carbohydrate and the produc-
tion of C(X, never absolutely in abeyance, even in the most pro-
found state of rest, are sharply intensified when the living machine
puts forth its full power ; and there is then a sudden burst of
heat, and an electrical discharge, by reason of an electro-positive
state of the active muscle giving birth to a current of action
which in effect you may, without great stretch of thought, regard
as of the family of blaze-currents. So that in last resort we find
that these striking electrical effects in living matter that we had
hardly considered as electro-motive at all — in the eyeball, in its
crystalline lens, in a bean or pea or leaf or flower — are, after all,
intense local changes, significant of intense local action, that may
be imagined and characterised as a blaze amid the smouldering
state of living matter.

There is a certain similarity between a blaze-current and
the discharge of an electrical organ — no very close and detailed
resemblance indeed, yet one that cannot be ignored, and that
may be of service to us towards a further comprehension of the
electrical signs of life. But it will not be an easy matter to
appreciate the connection, and in preparation for the attempt,
I should advise you to read two papers by du Bois-Reymond,
the first on " Secondary Electromotive Phenomena in Nerve,
Muscle, and Electrical Organ," the second on " The Polarisation
Phenomena caused by Constant Currents in the Electrical Organ
of Torpedo."

And let me say in conclusion that I have not named these

iv.] ELECTRICAL ORGANS 75

papers to you because either nerve or muscle or electrical tissue
are favourable objects upon which to demonstrate blaze-currents
—they are, in fact, among the least favourable objects for this
purpose — but because their secondary electromotive action or
response, as described by du Bois-Reymond, presents points of
similarity with the currents that are now engrossing our
attention.

Those of you who do not read German may refer to the
Translations of Foreign Biological Memoirs (Oxford, 1887),
edited by J. Burdon-Sanderson. And any one who is specially
interested in the phenomena of electrical fishes should also
read in the original the two memoirs by Gotch, published
fifteen years ago in the Philosophical Transactions. For a
student preparing for examination, the general summary by
Gotch in Schafer's Text-book of Physiology will be more than
sufficient.

REFERENCES

Du BoiS-REYMOND. — " Ueber secundarelektromotorische Erscheinungen

am Muskeln, Nerven, und Elektrischen Organen," du Bois-Reymond 's

Archiv, p. i, 1884.

Du BoiS-REYMOND.—" Lebende Zitterochen zu Berlin." Ibid., p. 86, 1885.
GOTCH. — " The Electromotive Properties of the Electrical Organ of Torpedo

Marmorata," Phil. Trans. Roy. Soc., p. 487, 1887, and p. 329, 1888.
GOTCH.— "The Physiology of Electrical Organs," Schafer's Text-book of

Physiology, vol. ii., p. 561, 1900.

LECTURE V

The Discharge of an Electrical Organ in Response to Direct Excitation — Du
Bois-Reymond's Summary — Similarity between " Blaze-currents " of the
Skin and " Discharges " of an Electrical Organ — Normal Direction
of the Organ-current — A Speculation and some Experiments — Further
Investigation of these Currents by the ABC Method — The Positive
Polarisation of du Bois-Reymond — The Polar After-currents of Hering
and of Biedermann — Ritter's Tetanus and the Post-anodic Action
Currents.

§ 47. Electrical organs. — We shall take a point of departure
from the diagram on p. 121 of the second paper by du Bois-
Reymond,* where he gives a summary of the effects of direct
electrical excitation of an excised portion of the electrical organ
of torpedo marmorata.

The prefix "absolutely" in du Bois' terminology is used
with reference to the organ discharge, the response being
denoted as " absolutely positive " or " absolutely negative,"
according as it is in the same direction as the normal discharge,
or of opposite direction.

The prefix " relatively " refers to the direction of response
with reference to the exciting current, " relatively positive " and
" relatively negative " signifying that the response is in the same
and in the opposite direction to that of the exciting current.
If you are puzzled by these expressions, or doubt my
rendering of them, you should refer to the original paper.
Negative polarisation is of contrary direction to that of the

* Archiv, 1885.
76

LECT. V.]

ELECTRICAL ORGANS

77

exciting current ; positive polarisation is in the same direction
as the exciting current.

These four stages are reducible to two, by omission of
Type II. (variety below Type I.) and of Type III. (variety

Tlic response is absolutely The response is absolutely
and relatively positive. and relatively negative.

!° a t

aS I

O-4J

•-

The response is absolutely positive and relatively
negative.

FlG. 34. — Du Bois-Reymond's diagram (_Archh\ 1885, p. 121) to illustrate the
electrical response to electrical excitation of a strip of the electrical organ of Torpedo.
The direction of the normal organ-discharge is supposed to be upwards, so that the
first two responses of the upper line are homodrome in relation to the exciting
current ; the next two responses and all four responses of the lower line are
antidrome.

above Type IV.). We thus have Type I. as the characteristic
response of the living organ, and Type IV. as that of the dead
organ. This — if you will carefully read du Bois' description,
and clearly appreciate the significance of his terminology-
is the essential pair of features that respectively characterise
the living and dead states of an electrical organ — it discharges
in a direction of its own while it is alive ; after death, it exhibits
the ordinary polarisation of a non-living electrolyte.

78

THE SIGNS OF LIFE

[LECT.

The response of skin is on a precisely similar schema,
thus : —

Electrical organ
of Torpedo.

Dorsum
Venter

Frog's Skin.

Eoct. surfd.ce

Inb. surface

Response of
living organ.

Polarisation
currents of-
dead organ.

FlG. 35. — Diagram exhibiting the similarity between an electrical organ and the
skin as regards their normal electrical responses during life (and the polarisation
effects after death).

And as you see from the diagram (or from the experiment that
is set up to reproduce it), we are justified in saying of the skin
that it discharges in a direction of its own while it is alive, and
exhibits after death the ordinary polarisation of a non-living
electrolyte. It responds better, as you may notice, to an anti-
than to a homodrome excitation, agreeing in this respect with
the organ of Malapterurus (Gotch), but disagreeing, I may add,
from that of Torpedo (du Bois-Reymond).

§ 48. The organ-discharge. — The essential component of an
electrical organ is a disc, upon one surface of which a nerve
twig ramifies, while the other surface is vascular. The electrical
organ consists of piles of such discs, surface to surface, like the
elements of an old-fashioned voltaic pile ; its structure, as well
as the great electro-motive force of the discharge, suggest that

v.] THE ORGAN-DISCHARGE 79

it actually is a battery of which the elements (discs) are dis-
posed in series. Further, the direction of discharge, excepting
in the somewhat doubtful case of Malapterurus, is always such
that current passes (in the animal) from the nervous to the
vascular surfaces of the discs. Thus, in Torpedo, where the
nervous surface is ventral and the vascular surface dorsal,
the discharge is from venter to dorsum. In Gymnotus the
nervous surface is posterior, and the discharge is from tail to
head. In Raia (the skate, which possesses a well-formed, if
attenuated, pair of electrical organs) the nervous surface is
anterior, and the discharge is from head to tail. This relation
between position of nervous plate and direction of discharge
is called after its discoverer " Pacini's law." The discharge is
attributable to a sudden action of the nervous surfaces, which,
while active, play the part of a series of zinc plates in a
voltaic pile. The electro-motive force in the discharge of a
single disc has been estimated to be 0.03 to 0.05 volt,* and
it is by reason of their columnar arrangement and large
number, that the high electro-motive values of the organ-
discharge are reached — 200 volts from a column of 500 plates
is an E.M.F. estimated by Gotch and Burch in the case of
Malapterurus.

The discharge can be brought about experimentally by
indirect (reflex) and by direct excitation. If, as was first done
by du Bois-Reymond, a longitudinal strip of organ be excised,
placed between unpolarisable electrodes, and directly excited,
it will respond to both directions of excitation by a discharge in
one given direction, that namely of the normal discharge. This
photographic record (Fig. 36) gives the responses (both in head
to tail direction) to induction shocks in positive and negative
directions, in the case of a portion of the rudimentary (or
vestigial) organ of the skate. The similarity between these
effects and the effects above described in the case of the eyeball
and the skin, are sufficiently obvious, and you will readily under-
stand how it has come about that I have compared the " blaze-
currents " of the eyeball, and of the skin, and of other organs

* Gotch, ScJiafetJs Text-Book of Pliysiology, vol ii., p. 584.

80

THE SIGNS OF LIFE

[LECT.

with the discharges of an electrical organ. I do not mean to say
that eyeball or skin are specifically " electrical organs," for there
are no structural features in common ; but I think that the

voit

•QIO \—

•OO5

o

A

m.b.

\ i i

m. b.

n. l,OOO

, 1

b b
Singie shocks iflpoo

\ \ \

o

10

15

2.0 mins.

FlG. 36. — Normal (head to tail) discharges of a strip of the electrical organ of a
skate {Raia clavata) in response to tetanisation and to strong single break induction
shocks.

comparison goes some way towards generalising our notion
of the electrical signs of life. It is at least remarkable that the
electro-motive values of the discharge in the cases of the eye-
ball and of the skin are of the same order of magnitude as that
calculated for a single plate of the electrical organ (0.03 to 0.05).
According to a recent estimate by Gotch,* the E.M.F. of nerve
in response to a single induction shock reaches a value not far
short of this — -viz., 0.03 volt. And the very points where
the comparison is defective should serve to instigate further
study. Thus the organs of Torpedo, Gymnotus and Raia are

Gotch and Burch, Proc. Roy. Sac., vol. 63, p. 300, 1898.

v.] DIRECT RESPONSE 81

modifications of muscle.* The organ of Malapterurus (which
does not follow Pacini's law) is a modification of cutaneous
gland ; we therefore want to examine that organ by the light of
what we have learned of skin. Does the electrical case of
Malapterurus give an outgoing current ? Perhaps one of these
days we shall have an opportunity of finding out.

Meanwhile let me warn you that our knowledge of even
the most carefully studied of electrical organs — that of Torpedo,
namely — is by no means exhaustive. Its discharge is of very
short duration ; one may feel an intense thrill from a discharge
giving by no means an excessive effect upon a galvanometer ;
the organ itself while reacting perfectly well to indirect excita-
tion, is peculiarly refractory to direct electrical excitation. This
same peculiarity is exhibited by the excised organ or by strips
of organ from even the most lively fish, and I have failed to
obtain from such strips any well-marked response to single
induction shocks ; I had to use tetanising currents to bring out
any regular venter-to-dorsum response ; the organ was easily
exhausted, and easily injured, by e.g., removal of the skin,
which is closely attached to it ; obviously an effect obtained
only in the presence of skin, and not obtained after its removal,
might not straightway be set down as "organ-response"; I
have indeed seen similar responses, of a value of +0.005 volt,
with strips of fish that contained no electrical organ at all, but
only muscle between two layers of skin.

So that on the whole the case of the electrical organ is a
good deal less satisfactory than that of the skin, and in com-
paring the skin and the eyeball with an " electrical organ," we
use the expression in a general rather than in a special sense. As
regards blaze-currents, the skin of a frog is a far more efficient
electrical organ than is the electrical organ of a Torpedo. And
perhaps this is not so very unfortunate ; you may easily control
statements concerning the frog's skin, you would have to take

* Developmental!)', inasmuch as muscle and electrical organ come from
the same muscle plates ; and, in the skate, muscle shades into organ by
gradual transition. Gotch considers the electrical organ to be a nerve-
ending. But, in a sense, muscle itself is a nerve-ending.

F

82 THE SIGNS OF LIFE [LECT.

a good deal of trouble if you wanted to control statements
concerning the Torpedo.

§ 49. Its direction. — The direction of response to stimuli of
both directions is an indication of the natural direction of
organ response. The strip of organ discharges in the way
determined by its structural and functional disposition. Can we
trace any analogous disposition in the case of the analagous
response of eye or skin ? May we consider that the direction of
a blaze-current is in any measure determined by structural and
functional disposition of organ ; or, otherwise expressed, have we
any right to attribute an organ-current to such structures ? I
think there are reasons for and reasons against an affirmative
answer. As regards the eye, we have positive response to light
and positive response to both directions of electrical excitation.
We also have negative response to light and negative response
to both directions of electrical excitation. But here is no
definite and fixed direction of organ-discharge, only a pre-
dominance, fluctuating with state of organ and kind of animal.

§ 50. The skin-discharge. — As regards the skin, we have
positive response and negative response to indirect excitation,
and almost exclusively positive (outgoing) response to direct
electrical excitation of whatever direction. Here, again, is no
definite and fixed direction of organ-discharge by the natural
mode of action through nervous channels, but a marked pre-
dominance in one (the outgoing) direction in response to both
directions of electrical excitation.

With direct excitation of the skin, we must suppose that all
its living parts are aroused to action, gland cells and general
epithelium alike, and we may not attribute the effect to any one
kind of tissue element to the exclusion of others. We know by
experiment, however, that the action proceeds from elements
at or near the external surface ; and we find further that with
shavings of skin, including Malphigian layer and excluding the
deeper situated glands, the direct response is obtained as before,
while with shavings of cuticle only, no response whatever is
obtained. Mercuric chloride, which, as you saw, abolished the

V-]

THE SKIN DISCHARGE

83

direct response, is said by Bach and Oehler not to abolish the
indirect excitability, which presumably depends on deeper parts.
We therefore conclude that the main factor of the response is
the general epithelial investment — its Malpighian layer in
particular. Indirect excitation of the skin through nervous
channels presumably arouses the cutaneous glands alone ; the
general epithelium is, as far as we know, as much outside the
control of nerve fibres as are blood-corpuscles.

We cannot, therefore, in comparing the effects of direct and
of indirect excitation, regard the comparison as a simple one,
like that of direct and indirect excitation of muscle.

Thus, in frog's skin, the effect of indirect excitation is often
negative (ingoing) when that of direct excitation is positive
(outgoing). In cat's skin the effect of indirect excitation is
always ingoing, that of direct excitation is at first ingoing, at
last outgoing.

It would be interesting to see what effect, if any, the two
forms of excitation exercise upon each other. I have not found
time to do this, although obviously it would be an easy matter
to take a regular series of indirect effects, interpolating in the
series one or more direct excitations of some convenient duration
and strength ; or a regular series of direct effects, interpolating
in the series one or more indirect excitations. Of course, it
would be necessary to photograph the effects ; I wonder what
they would be ? *

* I have since tested this point, as regards the effect of direct upon
indirect excitation, in the case of frog's skin, also in the case of the cat
(vide infra, Lecture VI.), with the following results :—

VoU
•OO6-1

•003-
•003-
•OOI -
•OOO-

Before

After.

FlG. 37. — Indirect responses of frog's skin to tetanisation of the sciatic nerve
before and after direct excitation of the skin itself by a single strong induction

shock D.

[For continuation of Note, see next page.

84

THE SIGNS OF LIFE

[LECT.

So that, in sum, while pointing to the conclusion that
there is, as regards the external cover of an animal body,
an outgoing organ-current of action, the facts forbid us to
rest content in an exclusive conclusion of such simplicity, and
we are obliged to admit that a cutaneous organ-current, even if
it really exists by reason of a general functional and structural
organisation of the integument, is twisted and obscured by other
accessory and complicating conditions.

Let us, however, imagine how things might have been. The
fancy will, if nothing else, remind us of facts, and make us
curious for further facts. The facts — let me reiterate them once
more — are that the skin, when first placed on the electrodes,
gives an ingoing current which increases, and that excitation of
either direction gives an outgoing response which diminishes.
The former is " current of rest," the latter " current of action."

§ 51. A speculation. — A lump 9f protoplasm, at rest and
homogeneous throughout, is iso-electric throughout ; let it be

VoLb

•OOOO-i
•OO25-
•OOSO-
•0075-

ir

/I

f

T

r

r

TIT

TIT

TYir

TTV

•o/oo-

•O/25-

1

n

n.

77.

7X

FlG. 38. — Indirect responses of a pad of a cat's paw to single induction shocks
exciting the sciatic nerve, before and after : —

D, = direct excitation of the pad by one strong break shock.
D0 = „ ,, by two strong break shocks.

Da : „ ,, by tetanisation for 5 seconds.

D4 = „ ,, by tetanisation for 15 seconds.

It is somewhat surprising that direct excitation should have produced a
greater diminution of the indirect response in the frog than in the cat. But
in the former case the indirect response was elicited by tetanisation of the
'nerve, while in the case of the cat, the nerve was excited by single strong
shocks. The regular effects (on the skin glands) of such stimulation are in
themselves sufficiently remarkable ; their true physiological character was
proved by the long interval between each excitation and response — about
3 seconds.

'.J

EXTERNAL AND INTERNAL

85

" Current of rest " from E to I.
" Current of action " from I to E.

acted upon by its environment, any point of its surface E is
chemically more active than any point of its mass I ; E becomes
electro-positive to I ; there is therefore current from E to I, an
ingoing current, the so-called " current of rest." Let the lump

become active, any point I is
chemically more active than any
point E ; there is current from
I to E, outgoing current, the
" normal organ-current of action."
Now, the currents that we call
" electrical " and actual currents of
matter, streaming through a porous
substance, generally occur in the
same direction, so that there is an association of phenomena
— (i) in the case of ingoing electrical current and centripetal
current of matter (and of energy) from environment to living
substance, and (2) in the case of outgoing electrical current
and centrifugal current of matter (and of energy) from living
substance to environment. A priori, therefore, we should
expect the " skin " of living substance to be the channel of a
double current, material and electrical — (i) of a current of rest
or reception, ingoing and centripetal, subserving the synthetic
accumulation of energy ; (2) of a current of action or emission,
outgoing and centrifugal, subserving the analytic expenditure
of energy. If you are accustomed to think in terms of charged
ions, you will imagine the kation as travelling from without
inwards with a receipt of energy, from within outwards with a
discharge of energy.

And now consider further what kind of modifications we may
expect and look for with the differentiations of function and
of structure that have occurred in the external surface of plants
and animals.

Consider, in first place, the principal difference of chemical
direction in the main drift of vegetable and of animal metabolism.
Vegetable protoplasm is in major degree an instrument of syn-
thesis and accumulation, in minor degree the seat of analysis
and emission. Animal protoplasm is in major degree an instru-
ment of analysis and emission, in minor degree the seat of

86 THE SIGNS OF LIFE [LECT.

synthesis and accumulation. The vegetable, in most immediate
contact with inert things, combines, organises, and accumulates.
The animal, in less immediate contact with inert matter, disrupts,
utilises, and dissipates in their fragments organic compounds
that it has received ready-made from other animals and from
plants. And quite early in its development the external surface
of the animal is distinguishable into two parts: (i) a surface
principally receptive of incoming matter, the digestive and
absorbent surface ; (2) a principally emissive surface, the ex-
ternal skin, through which the greater moiety of animal energy
is dissipated. An " organ-current of action," if aroused in these
surfaces, should, according to their several physiological habits
and dispositions, be :—

Principally ingoing for the vegetable " skin."
Principally outgoing for the animal skin.
Principally ingoing for the animal mucosa.

§ 52. Some experiments. — And whatever the fate of our
theoretical motive, it will have served to instigate a search for
facts ; but we must take due care to emancipate observation
from expectation, and not merely see that which we expect
or hope to see. Here is a piece of orange peel, chosen for our
purpose not merely because it is a handy object, but because the
" skin," presumably living, is easily separated from the " body "
of the fruit by breaking through "subcutaneous tissue," pre-
sumably not-living. And in point of fact, you notice that the
bit of orange peel, placed between unpolarisable electrodes,
exhibits little or no current, unlike a paring of an apple or a
potato that necessarily has an injured inner surface, and ex-
hibits, therefore, a strong outgoing current of injury. I com-
pensate precisely and then test in the way now familiar to you
(plug the galvanometer, send an induction shock through skin,
unplug the galvanometer), and you see that to both + and —
directions of excitation the orange peel responds by a deflection
to your left, signifying current of negative or ingoing direction,

§ 53. Human skin. - -I next take a piece of human skin,
twenty-four hours after excision, and test it in the same way

v.] MUCOUS MEMBRANES 87

by + and — break induction shocks. You see that to both
directions of excitation the response has been a deflection
to your right, signifying current of positive or outgoing direc-
tion.

§ 54. Mucous membranes. — These two experiments are in
accord with our theoretical forecast, but that they prove that
forecast to be a .true guess, or even bear it out to any serious
extent, I shall be the last to urge. The two facts (both of
which are representative results based upon a sufficient number
of trials) are, however, interesting in themselves, whether this
or any other explanation be the true one. With regard to the
digestive mucosa, I prefer, for lack of sufficient experience, not
to show you any experiment at all, for I am at present by no
means sure what is to be considered as a typical and what as
an exceptional result. I have seen ingoing response * more
frequently than outgoing response, but I desire to study the
conditions and magnitude of the response before coming to
any conclusion as to which is the typical one.*

I would rather show you another pair of experiments,
illustrating in a different way the apparent opposition of
direction in the blaze-currents of vegetable and of animal
" skins."

§ 55. Intact surfaces. --We want to test, e.g., the skin of
an animal, or of a vegetable, without previous injury of the
surface. A very little reflection will convince us that this can
only be done by applying what has already been alluded to
above as the ABC method, viz., stimulating through A B, and
leading off through either A or B and a third indifferent
point C (p. 69).

The three electrodes, ABC, are applied to three separate
external spots of a piece of frog's skin. I intend to test the

* From further observations made subsequently to the delivery of these
lectures, I think the above statements may be considerably hardened.
In the great majority of cases — so great that we may reckon an opposite
result as exceptional — the mucosas manifest ingoing response to both
directions of excitation.

88 THE SIGNS OF LIFE [LECT.

point B, so I compensate B C, then excite through A B, and then
lead off B C to the galvanometer, as shown in Fig. 33. You
note the deflection. I repeat the experiment with excitation
in the reverse direction ; again you note the deflection. I
repeat a similar pair of trials upon another point A, merely
to get a further pair of observations — compensating A C, ex-
citing through A B, and leading off through
A C. You have noted the deflections,
both the B C deflections to your left, and
the A C deflections to your right, thus :—
signifying — as you will easily verify — in
all four instances that the after-effect at
A or at B, whether anode or kathode of
the exciting current, has been outgoing.

Repeating a similar series of four trials with an apple — a
living apple of course — and noting the deflections as before,
you find that they are in every case

the other way round, viz., both B C deflec- EOCC-. B C A
tions to your right, both A C deflections Resp:
to your left, like this :—
signifying in all four instances that the after-
effect at A or at B, whether anode or kathode
of the exciting current, has been ingoing.

Now, is not this an interesting result,
and does it not come out very clearly on this system of
notation? In my first attempts to examine one of two stimu-
lated points by conjoining it through the galvanometer with a
third indifferent point, I found it very troublesome to take
notes correctly, very difficult to read notes when taken, and
quite impossible to realise during an observation, what was
the meaning of each individual deflection. But since I have
followed and become familiar with this system of notation, all
these drawbacks have disappeared, and we may read and
compare at a glance " formulae of response " of a great variety
of living things.

I shall not enter into further explanations now ; the method
will be used again, and more fully explained in a future lecture,
and then appreciated by you as a simplification, if meanwhile

v.] « POSITIVE POLARISATION " 89

you will puzzle the thing out for yourselves. To save space, the
formulas, which to show order of individual trials have been set
out as above, will sometimes be given thus :—

Frog's skin. Fruit skin.
-« > ~* *"

§ 56. Positive polarisation. — Let us now turn our attention
to another related subject, that of positive polarisation, and of
post-anodic (and post-kathodic) action-currents.

Du Bois-Reymond obtained his first inkling of " positive
polarisation" in 1843, but it was not till 1883 that he published
a full account of the subject. He introduces that account in
the following terms, which clearly indicate the place held by the
matter in his thoughts :—

" I consider that the time has come to break the silence which I have
preserved till now concerning certain electro-physiological experiments that
have engaged my attention for nearly forty years, and to which I attribute
very great importance."

Taking the case of muscle, he studies the secondary polari-
sation effects produced by strong constant currents, tabulating
his results in relation to current-strength and time of closure ;
and how laborious a task this was du Bois' own words will most
vividly bring before you.

"The preparation of such a table of data is a very wearisome under-
taking. The secondary effects of currents that are at all strong or long, are
for the most part so enduring that a fresh preparation is required for nearly
each single experiment . . . each fresh preparation requires a fresh frog
. . . to permit of comparison, the frogs must be as uniform as possible in
size and health. ... So that the completion of a table of data is the
work of many weeks, and it will therefore hardly be matter for surprise that
I have only twice accomplished the task, once in the autumn of 1855, once
in the summer of 1882."

Each such table comprised 2OO successful observations,
with currents of I Daniel to 40 Groves, and closure times of
0.006 sec. to 25 minutes. The polarisation currents were of two
kinds : — negative, first visible after a current of I Daniel passed
for a period of I sec. ; positive, requiring at least 2 Groves

90

THE SIGNS OF LIFE

[LECT.

strongest

negative

with a closure time of 0.3 sec. The
polarisation occurred after a current of i Daniel passed for 10
minutes ; the strongest positive polarisation after a current of
20 Groves passed for 0.0/5 sec- '•> m tne latter case the E.M.F.
appeared to be rather less than that of a muscle-current.

FlG. 39. — T is the time of closure, A the density of the polarising current,
+ S the strength of the secondary electromotive effect, so that the plane viewed in
perspective is the T A Plane. The individual ordinates S are not represented,
but only the curves joining the ordinates belonging to given current density and given
time (from du Bois-Reymond, Archiv, 1884, p. 15).

§ 57. Two criticisms. — Hermann — du Bois' former pupil and
untiring critic — pounced at once — showing and saying in a
paper of upwards of sixty closely printed pages of Pfluger's
Archiv (vol. xxxiii.), that du Bois' positive polarisation current
was in reality a post-anodic action-current. Hering also inter-
vened, and said the same thing in two successive papers of the
Wiener SitzungsbericJite (i2th and I3th communications, 1883).

Both du Bois' critics confined themselves to a discussion of
the interpretation to be placed upon du Bois' phenomenon, and
proved that it was of post-anodic nature, and that the designa-
tion of positive polarisation was a very unhappy one. But the
critics did not demur to or subtract from the fact itself, nor

v.'J THE FOUR AFTER-CURRENTS 91

indeed did they add to or extend it. Indirectly, however, by
the effect produced in the mind of his pupil Biedermann,
Hering has " authorised " a very considerable extension of
fact and still more of doctrine. Biedermann finds evidence
of the existence not only of a positive anodic, but also of a
negative kathodic after-current, and further of the counterpart
of this first pair, viz., a negative anodic and a positive kathodic.
The last pair of currents are, however, asked for by theory
rather than offered by simple observation ; Biedermann him-
self admits that of his four currents the positive kathodic is
very doubtful, and it is clear that the negative anodic, being
in the direction of ordinary polarisation, is also on a doubtful
footing of fact. Nevertheless he considers theoretically the first
pair as being of irritative origin, and the second pair as being
of inhibitory origin. His quadrille of after-currents may be
put together in the following schema :—

Exciting or primary
Anode 4- - Current:.

> _

Irritative or (positive anodic > "the most certain"

dissimilatory. {negative kathodic < [PpoU3.n3d.Cion]

Inhibitory or WafrVe anodic < [PpoiarisaCion]

assimilatory. \oositive kathodic > the most uncertain

§ 58. A demonstration. — I should be sorry to attempt to
demonstrate to you the existence of these four currents upon
muscle or upon nerve, which are the tissues upon which Bieder-
mann claims to have observed them ; you must refer to Bieder-
mann's own account for what in his opinion constitutes the
evidence of their existence.

At most, I shall be able to show you the first and " most
certain " of them, viz., the positive anodic or post-anodic action-
current, and that only in a form that does not exclude a partici-
pation in the total effect of a positive kathodic factor. And I
will show the experiment in a form intended to associate in
your mind this post-anodic action-current with an irritative
phenomenon long known to physiologists under the name of
Ritter's tetanus.

THE SIGNS OF LIFE

[LECT.

Here is a nerve-muscle preparation, the nerve of which is
laid across electrodes that are connected with the keyboard
and galvanometer. There can also be led into the keyboard,

Anode Kathode

FlG. 40. — Nerve-muscle preparation ; to demonstrate the muscular contractions
associated with the positive anodic after-current in nerve.

by means of a double key, a strong battery-current which is to
traverse the nerve in an ascending direction as figured (the
galvanometer meanwhile being plugged). During the passage
of the constant current, the muscle remains quiescent, but when
I break the current, the muscle, as you see, contracts, and will
contract for a longer or shorter period. Immediately after
breaking the battery current, I unplug the galvanometer, when
you witness a strong and permanent positive deflection, signifi-
cant of an action-current in the nerve of the same direction
as that of the previous battery-current. The deflection is not
absolutely permanent, it is gradually falling, the muscle will not
remain indefinitely contracted, it will relax sooner or later ; the
positive current in the nerve, and the contraction of the muscle,
are associated effects of a state of local irritation or action in the
previously anodic region of the nerve. You know that the
current from an active to an inactive spot of nerve runs in the
nerve from active to inactive (in the galvanometer from
inactive to active, the latter pole being therefore called nega-
tive), and that the active spot acts like the zinc of a voltaic
couple — is in brief a zincative spot. Therefore you know from
the direction of this after-current that the active spot from
which the irritation to the muscle proceeds is post-anodic as
to its source in the nerve itself.

§ 59. Locality of reaction. — Polar inequalities of effect have

v.] BOTH POLES ARE EFFECTIVE 93

been alluded to above, and now demand our somewhat closer
scrutiny. Is a blaze-current exclusively post-anodic or post-
kathodic, or both, and if both, which is the more effective pole ?

The question can be experimentally tested in three ways —
the exciting current can be sent through the skin by two
electrodes in contact with its two surfaces (Fig. 26), or through
electrodes both of which are applied to the external surface, or
with three electrodes A B C on the external surface (Fig. 33).

By the first of these three plans we have already seen that
with both directions of excitation an outgoing response is pro-
voked ; we have seen farther (§ 43) that both these responses
depend on an electro-negative state at or close to the external
surface. Both poles produce this change, and the fact (illustrated
by Fig. 30) that the antidrome is sometimes greater than the
homodrome response, signifies at first sight that the anode is
more efficacious than the kathode. But this conclusion is not
confirmed by our next two experiments, and the inequality of
response, which, indeed, I find on reference to my notes, is by
no means invariable, may have been due to other causes, e.g.,
to ordinary polarisation currents against homodrome and with
the antidrome response, the true physiological response being
greater in the homodrome sense.

The second plan of experiment, by two external electrodes,
gives a result that can hardly consist with superiority of a post-
anodic effect. The response in this case is always homodrome,
and since it is the algebraic sum of two opposed outgoing currents
at the two poles, this signifies that the kathode has been more
efficacious than the anode. A homodrome post-anodic response
would have been ingoing, but as we have seen, and shall see
again, it is the post-anodic response which is antidrome and
outgoing. This experiment exhibiting homodrome response
with two external electrodes is easily repeated ; the result is
very constant and contrasts sharply with that obtained when
the two electrodes are applied to the internal surface ; this
surface is ineffective, and gives only small antidrome deflections
attributable to ordinary polarisation, whereas the external sur-
face gave large homodrome deflections of which the physiological

94

THE SIGNS OF LIFE

[LECT.

integrity of the skin is a necessary condition. With killed skin,
both surfaces give only the small counter currents of ordinary

Eocc
Poi. •«-

Eocc. «f-
PoL. -

SKIN OF FROG.

Excited and led off by its
external surface.

Excited and led off by its
internal surface.

polarisation. With three external electrodes, and proceeding
on the ABC plan, to test the separate unipolar effects at A
and at B (p. 69), the antidrome-anodic effect has sometimes
exceeded and sometimes fallen short of the homodrome-
kathodic effect. The first inequality proves nothing, as it
might be an effect of ordinary polarisation ; the second
inequality proves, that under certain conditions, and in spite
of ordinary polarisation, the kathode is the more effective pole.

So that, in sum, we may conclude with certainty that both
poles are effective, and with less certainty that the kathode

PA B C A

//•?£.

— >• E.OCC.
• i Resp.

1

2

FROG'S' SKIN.

All responses are outgoing.
The homodrome kathodic cur-
rents I and 4 exceed the anti-
drome anodic currents 2 and $•

VEGETABLE SKIN.
All responses are ingoing.
The homodrome anodic currents
2 and 3 exceed the antidrome
kathodic currents I and 4.

is more effective than the anode. It is somewhat surprising

v.] UNFINISHED WORK 95

to have to admit that we have to do with a homodrome post-
kathodic current. A homodrome post-anodic current would
have seemed more familiar to us.

In all these experiments, it is remarkable how strictly the
effects of excitation are limited to the directly excited spot.
Outside the area of direct excitation, the excitability of the
skin remains unaffected ; we can locally exhaust the skin by
strong excitation, and obtain good response from other spots
of the same piece of skin.

This local independence of parts, characteristic of vegetable
tissues as well as of the skin, is in marked contrast with the
spread of disturbance that is peculiar to muscle and nerve
where propagated effects are the salient feature. It is one
of the reasons why a piece of skin or of a plant is a more
favourable object than a muscle or a nerve for the demonstra-
tion of blaze-currents.

Plants, excited and led off by two points of their external
surface, give, like the frog's skin, homodrome responses to both
directions of excitation. But whereas in the case of frog's
skin, the total .homodrome effect between A B is the alge-
braic sum of the partial outgoing effects at A and B, in that of
a vegetable skin it is the sum of two ingoing effects. The pre-
potent pole, in the case of the frog's skin, was the kathode, in
that of the vegetable skin, it is the anode, as will be evident to
you on careful consideration of the figure. It is not difficult in
the case of vegetables to obtain measurements of the total and
partial blaze-currents, showing quite clearly that the anode has
been the prepotent pole, thus :—

Excitation from B to A

Total response from B to A + 0.012 volt.

Partial response from B...to...C + 0.035 »

Partial response to C from A - 0.021 „

Cut surfaces of fruits — e.g., of apples and pears — have given
ingoing currents at both poles after excitation, but smaller than
the currents aroused at intact surfaces. Ripe orange peel has
given ingoing effects at its external surface, and only small
polarisation counter-currents at its internal surface, the former
is " alive," the latter is " dead."

96 THE SIGNS OF LIFE [LECT. v.

§ 60. Exposed muscle has given precisely the same formula
as that of vegetables, i.e., ingoing effects at both poles ; while
dead muscle gave only the small antidrome deflections due to
ordinary polarisation.

A frog's sciatic nerve gave responses homodrome with ex-
citation, larger on the anodic than on the kathodic side. But a
detailed examination of blaze-currents in nerve and in muscle
still remains to be made.

REFERENCES

Du BoiS-REYMOND. — " Ueber secundar-elektromotorische Erscheinungen
an Muskeln Nerven und elektrischen Organen," Sitzungsberichte Berlin,
5th April 1883, p. 343 ; and du Bois-Reymond's Archiv, p. i, 1884.

Du BOIS-REYMOND. — " Lebende Zitterochen zu Berlin," du Bois-Reymond's
Archiv, p. 86, 1885.

HERING. — " Ueber du Bois-Reymond's Untersuchung der secundar-
elektromotorischen Erscheinungen am Muskel," Wiener Sitzungs-
bericlite, 22nd November 1884, p. 445 (and p. 415).

HERMANN. — " Ueber Sogenannte secundar-elektromotorische Erscheinun-
gen an Muskeln und Nerven," Pfliiger's Archiv, xxxiii., p. 103, 1884.

GOTCH. — " The Electromotive Properties of the Electrical Organ of Torpedo
Marmorata," Phil. Trans. Roy. Soc., p. 487, 1887, and p. 329, 1888.

BURDON-SANDERSON AND GOTCH. — " On the Electrical Organ of the
Skate," Journal of Physiology, vol. 9, p. 137, 1888 ; vol. 10, p. 259, 1889.

ROEBER. — " Ueber das Elektromotorische Verhalten der Froschhant bei
Reizung ihrer Nerven," du Bois-Reymond's Archiv, p. 633, 1869.

ENGELMANN.— " Die Hautdrusen des Frosches," Pfliiger's Archiv, vi., p. 97,
1872 (also vols. iv., p. i, 321, and vol. v., p. 498).

HERMANN. — "Ueber die Secretionsstrome und die Secretreaction der Haut
bei Froschen," Pfliiger's Archiv, xvii., p. 291, 1878.

BACH u. OEHLER [HERMANN]. — Pfliiger's Archiv, xxii., p. 30, 1880.

BAYLISS AND BRADFORD. — " On the Electrical Phenomena accompanying
Secretion in the Skin of the Frog," Jottrnal of Physiology, vol. 7, p. 217,
1886.

REID.— "The Electro-motive Properties of the Skin of the Common Eel,"
Phil. Trans. Roy. Soc., p. 335, 1893.

REID AND TOLPUT. — " Further Observations on the Electromotive Proper-
ties of the Skin of the Common Eel," Journal of Physiology, vol. 16,
p. 203, 1894.

WALLER.—" On Skin-currents : The Frog's Skin," Proc. Roy. Soc., vol. 68,
p. 480, 1901.

LECTURE VI

A Representative Experiment — Effects of Indirect Excitation— Effects of
Direct Excitation immediately after Death, and Later— How Long,
after a Cat's Death, can a Cat's Foot continue to Exhibit Signs of
Life? — More A B C— A Vegetable Surface — Surface against Surface
— Anodic and Kathodic — Biedermann and the Frog's Tongue — A
Warning.

§ 61. Demonstration. — This cat is dead, but its tissues are
still alive. It was decapitated at 4.45 ; it is now 5.5, and I shall
talk with my eye on the clock, as I wish to show you an experi-
ment just half an hour after the death of the cat.

FlG. 41. — Diagram of experiment described in the text.

The story of the cat's skin, or, more properly speaking, of its
foot-pad, commences from the observations of Hermann and
Luchsinger, who showed that on the skin, as on glands, secreto-
motor can be disentangled from vasomotor reactions. The
experiment of Hermann and Luchsinger cannot be shown here.
It is a vivisection of which preliminary No. I is the abolition of
97 G

98 THE SIGNS OF LIFE [LECT.

muscular movement by curare, and therefore preliminary No. 2
is artificial respiration.

It is now 5.10 P.M.; the cat has been dead twenty-five
minutes. I have therefore five minutes time to further explain
my meaning. The surviving tissues are dying ; the junction
between motor nerve fibre and muscular fibre is dying ; the
junction between secretomotor fibre and gland cell is also
dying ; but, according to my experience, the first will die in
thirty, the second will die in sixty minutes. I have therefore
a margin of thirty minutes during which excitation of that
packet of nerve fibres called the sciatic nerve will not cause any
movement of the limb (nor, therefore, any possible shifting of
contacts or other disturbance), but will cause an activity of the
cutaneous glands.*

You will find as a book datum (and as a printed datum it is
a very satisfying datum) that the independence of secretomotor
nerves is proved by the fact that after death (of the cat), when
the circulation, and therefore vasomotor, effects are out of count,
beads of sweat are made to appear on the carefully wiped pad
by excitation of the sciatic nerve.

I have never succeeded in witnessing these beads of sweat,
and will not therefore make the attempt to demonstrate them
to you ; but I shall show you by means of the galvanometer,
within this margin between the thirtieth and sixtieth minute
post-mortem, that the excitation of the sciatic nerve on one side
(and on the other), causes a marked physical alteration in the
skin of the pad, first on one side and then on the other. Cats
differ, and I will not answer for my times to a minute, but it
is now thirty-five minutes post mortem felis, and I am well within
the margin. The two hind pads are connected with the two
terminals of the galvanometer. I don't know which is which, so
I test my connections with a bit of zinc, by touching the
two terminals on the operation table with which the two
galvanometer terminals are connected. Touching the terminal
of the left pad with the bit of zinc, while my finger is on the

* The longest period recorded in my notes has been 2 hrs. 15 mins., in
the case of a particularly well-nourished cat.

VI

.] SECRETO-MOTOR EFFECTS 99

terminal connected with the right pad, sends the spot off to
your right ; I know, therefore, that on excitation of the left sciatic,
the spot will go to your right. I know that the skin under its
control is rendered zincative (galvanometrically negative accord-
ing to physiologists, electro-positive according to physicists — but
in any case in the direction of the arrow on the black board —
from outer to inner surface of that skin, i.e., in an ingoing
direction).

The spot has " flown off scale " —as Biedermann so often
expresses it — to your right (I am giving a demonstration, and
not making a measurement). In order to save time to make
the converse experiment without undue delay, I bring the spot
back by the counter current of a compensator. I have used
.015 volt; that therefore has been the approximate electro-
motive value of the response — by no means an inconsider-
able value.

I now apply similar excitation to the sciatic nerve of the
right side. You think nothing happens, but before you have
made up your mind that nothing happens, the spot flies off to
the left. Opposite side — opposite direction of course. Ingoing
current in the right side gives deflection to the left, just as
ingoing current in the left side gave deflection to the right ; and
the pause perceptible to most of you at the second observation,
but not at the first, was the latent period between cause and
effect, between excitation of the sciatic nerve and response of
the cutaneous gland-cell. I guess it to be about three seconds,
but we will measure it presently.

This obvious delay between excitation and response should
make its mark upon your memory. It is a sure and reassuring
sign that we are dealing with a true physiological response,
outside all possibility of coarse physical fallacy. The response
— I mean the indirect response of the skin to excitation of the
nerve — can be elicited by a single induction shock. This in
itself is rather curious ; we should have expected a visceral
(sudo-motor) nerve to need prolonged or summating stimuli
for its effective excitation ; you see for yourselves, however,
that a single shock causes an unmistakably delayed, well-
marked and somewhat prolonged response.

100 THE SIGNS OF LIFE [LECT.

The nerve-skin response, now before your eyes, is a very
good case to use for familiarising you with some of our
apparatus.

We guessed the lost time at three seconds, we will now make
a rather more accurate measurement by photographing a galvano-
metric deflection, and finally we will control our measurement
by taking an electrometer photograph. ( Vide infra, p. 105.)

Two galvanometers are in circuit in series (as described
in the Appendix, p. 1 56) ; the recording galvanometer or galvano-
graph will take on the sensitive plate a replica of the indica-
tion witnessed by you on the demonstrating galvanometer, and
it will be rather interesting to you, perhaps, to see whether
the impression on your mind is borne out by the impression
on the photographic plate. The plate is set to fall at the
rate of about 2.5 mm. per second (or an inch in 10 seconds),
and the instant of stimulation is signalled on the plate by
a device that you can examine afterwards. I start the clock-
work, and 2 or 3 seconds after you have heard the commence-
ment of excitation (of the nerve), you see the deflection
caused by the electrical change that has taken place in the
skin. When the plate has got to the end — i.e., after 40 seconds
— it is shut up in its carrier and sent to the developing-room,
from which it will be brought back in a few minutes, and
placed in the projecting lantern (Fig. 43).

Meanwhile let us examine the response by means of another
instrument — the capillary electrometer — put into the circuit
instead of the galvanometers (Appendix, p. 162). The
magnified image (x about 1500 diameters) of the mercury
column, projected on the transparent screen, looks to you like
a large manometer — and, in point of fact, it is an electrical
manometer, as you see at once if I raise or lower the elec-
trical pressure in circuit by, e.g., thousandths of a volt.
Having verified that the connections are such that movement
of the mercury upwards on the screen signifies outgoing
current, and downwards the reverse, we may proceed to excite
the sciatic nerve as before and watch the electrometer image
on the screen. It reacts perfectly well — by a downward move-
ment each time I excite the sciatic nerve — and my impulse

vi.] DIRECT EXCITATION 101

is to exclaim on seeing these responses on the screen — " What a
splendid cat ! " For they are, as you may have noticed, responses
to single break induction shocks. And notice also the delay,
about 2 seconds — with an electrometer this time.* But we must
photograph this, which will be easily and expeditiously done on
the lecture-table by slipping in a recording instrument, so as to
receive the image of the mercury column. This is now done ;
the plate travels horizontally at a rate of about 3 mm. per
second ; the record is completed in 40 seconds; and in a few
minutes you will be able to compare it with that previously
taken by the recording galvanometer, and with your own
memory-image (Fig. 44).

I repeat the two experiments to make sure that the effects
of indirect excitation are clear to you, and turn to the results
of direct excitation. I have no history to give you in this
connection, nor list of German names. You must be satisfied
with the story of the thing as given by the thing itself — not a
complete story indeed, but a fragment, a word or two.

§ 62. Direct excitation.--^ pad of the cat's foot is cut off
and placed between electrodes on a bit of ebonite with a
central perforation, to ensure normal passage of the excita-
tion current. Excitation, compensation, etc., are applied as
you now well understand from previous lectures, in accordance
with the diagram now fully familiar to you (p. 152). I compensate
exactly, so that the galvanometer may be plugged and un-
plugged without disturbance (notice in passing that the current
to be compensated has been from surface to section, i.e., ingoing
through the skin ; it cannot therefore be current of injury, for
such current should be from section to surface, i.e., outgoing
through the skin) ; I excite the pad by a break induc-
tion shock in the ingoing direction, and on unplugging the

* In another case a series of electrometer records came out :—
Time post mortem . . 30 40 48 55 65 minutes.
Voltage of response . . 12 10 8 5 2 millivolts.
Period of latency . . 1.4 1.6 1.7 1.8 2.0 seconds.
There was no appreciable lost time with direct excitation, nor exces-
sive delay of transmission in the nerve itself; the delay was exclusively
" junctional,"

102 THE SIGNS OF LIFE [I.ECT.

galvanometer you see an effect (or after-effect) in that same
direction. I turn over the reverser of the exciting current, I
apply a similar induction shock in the outgoing direction ; the
response (or after-affect) as you see, is again to your left, in the
ingoing direction, and it is larger than the previous one ; there
is perhaps a polarisation factor (ingoing after outgoing) that
makes this ingoing response larger than in the previous case,
where the polarisation factor (outgoing after ingoing) was
opposite to the main physiological ingoing effect — but that is a
detail. The principal point is, that the effects of electrical
excitation of whatever direction have been ingoing, or as I
choose to call it — " negative."

The effects of excitation in either direction being ingoing, it
is clear that a series of currents of alternating directions will
produce an ingoing effect. Tetanisation, i.e., a series of make-
and-break current in rapid succession, will therefore produce an
ingoing effect ; and as you now see, that ingoing effect is off
scale to your left ; there has been a summation of separate
stimuli forming the tetanising series.

I reverse the direction of the tetanising currents, and as
before, you see the spot flying off scale to your left, indicating
response (or more precisely after-effect) through the directly
excited pad in the ingoing direction.

This has been a single experiment. I do not remember
having ever seen better marked ingoing effects of excitation ;
but the pad was very fresh, and I did not use very strong
tetanisation, which two conditions have been shown by previous
experiments to be favourable as regards the demonstration of
ingoing effects of direct excitation. In previous experiments I
have indeed observed precisely the reverse effects, viz., outgoing
effects by direct excitation ; but I was then following out the
effects day by day, and using excitation of full strength, in
order to learn how long after the death of a cat this sign of life
was observable on one of its feet.

Such a pad has now been set up, taken from a cat twenty-
four hours after death, and you see as a matter of fact that it
gives large outgoing effects (deflections to your right) after both
directions of strong tetanisation,

VI.]

OUTGOING EFFECTS

103

It is an easy matter in the case of an animal like the cat,
to test the skin in situ. Two or three hours after death, when
the muscles are no longer inconveniently excitable, a pad is
cut off, and one electrode is applied to the wounded surface ;
the other electrode is applied to an intact pad. The accidental

•oo

' FlG. 42. (4219.) — Outgoing responses of the pad of a cat's foot, directly excited
by single break induction shocks in both directions, and by tetanising currents in
both pairs of directions.

current (which is not an " injury current," since its direction in the
cat is from intact to injured spot, but the normal and accidental
ingoing current at the uninjured spot) is compensated, and the
blaze test applied in the usual way. Both responses are in
the same direction as that of the accidental current, from intact
to wounded spot, ingoing through the intact skin. These
are evidently not negative variations of any injury current.

We may provisionally infer from the absence of obvious
injury current that the subcutaneous connective tissue is of
very inert character, and that an unpolarisable electrode

104 THE SIGNS OF LIFE [LECT.

applied to subcutaneous tissue will serve us as an indifferent
electrode, under which little or no local response to excita-
tion need be expected. But we must take care that the
wound does not involve injured or exposed muscle, we need
only transfer our " indifferent " electrode to an injured muscle
(or to an injured nerve) to be convinced that the latter is
strongly electromotive in the usual (zincative) sense. The
hint may, perhaps, prove of some service to us ; we may one
day want to make use of an indifferent electrode for the
further investigation of the electrical reactions of undisturbed
skin or mucous membrane. Reflect for an instant — we must
always get a resultant of two factors, if our circuit includes
two active surfaces, whether both be of skin, or both mucous
or one skin and one mucous. So that to get at the reaction
of one spot of skin in situ or of mucosa in situ, it will greatly
simplify our task if the subcutaneous tissue may be treated
as electrically indifferent and non-responsive.

§ 63. Review. — We have gone over the whole ground, and
rather more rapidly than I expected. These three experi-
ments— exhibiting, first, the ingoing current aroused by in-
direct excitation ; second, the ingoing current aroused by not
too strong direct excitation of a fresh pad ; third, the outgoing
current aroused by strong direct excitation of a twenty-four
hour pad — very fairly summarise all I have learned about these
currents during the last few months. Some few details may,
indeed, be added — the lost time of indirect excitation for instance,
and the rapid exhaustion of the indirect effect by repeated
stimuli ; but these will be best shown to you by projecting on
the screen the actual records of these phenomena. And I may
mention that in one experiment directed to the point, it was
found that no effect was produced by excitation post-mortem
of the sciatic nerve of a previously atropinised cat, and that in
another experiment the same state was found on a cat killed
by chloroform * ; in both these experiments the effects of direct
excitation were found to be normal. One other point — in both

* In other cats, chloroformed and killed, the indirect effects have always
been normal j the instance quoted in the text was exceptional.

VI.

THE LATENT PERIOD

105

excised pads that we tested by direct excitation, the " normal
current " was ingoing — in precisely the opposite direction to
what might have been expected in a piece of living tissue with
an artificial section — in one pad the effects of excitation were
ingoing, increments of the normal current ; in the other they
were outgoing, decrements of the " normal current."

Seconds.

FlG 43. — Cat. Ingoing response of pad of foot aroused by excitation of the
sciatic nerve. Berne coil at 1000 units. The latent period is 3 seconds. (Galvano-
meter record.)

Here are the records you saw taken a few minutes ago
(p. 100), showing the lost time and the course of the indirect
effect, on the galvanometer and on the electrometer. Compar-

Seconds.

FlG. 44. — Electrometer-record. Indirect response (ingoing) of cat's foot-pad to
single break induction shock through sciatic nerve. Lost time — 3 seconds.

ing the two curves, you see that they have very similar time-
relations, and there does not seem to be much to choose between
the two instruments. This, however, is merely due to the fact

106

THE SIGNS OF LIFE

[LECT.

that the phenomenon is comparatively slow and prolonged, so
that it can be followed and observed by galvanometer almost
as well as by electrometer ; the former instrument has indeed
inertia and " lost time," but these are not considerable in com-
parison with the physiological inertia and lost time of the change
observed ; this particular galvanometer has a lost time of about
0.3 second, i.e., only one-tenth that of the physiological lost time
under observation ; the electrometer has no appreciable lost
time, which of course, is an advantage.

The voltage of the response is greater in the galvano-
metric than in the electrometric curve, but that is only
incidental to the fact that in the former case the response
was taken to tetanisation, and in the latter to a single
induction shock ; perhaps also the nerve-skin was becoming
fatigued. Such fatigue, in consequence of repeated action,
does in fact always appear in more or less pronounced degree.
Here is an instance in which it is very well marked.

The direct (blaze) effects
that persist for hours or
days after the indirect ex-
citability of the skin and
the indirect and direct ex-
citability of muscle have dis-
appeared. I am here refer-
ring to the direct and indirect
excitability of muscle in the
usual acceptation of these
terms ; I have not yet
studied in detail the direct
(blaze) effects in either

FlG. 4o. — Cat. Response of skin to , u i

tetanisation of the sciatic nerve, repeated at muscle Or nerve, but only

I minute intervals, and lasting for about 5 jn the skin. The question,

seconds. The deflections at the beginning and u TT , , ,, r

at the end of the record are standardising^ de- How long does a Cat S foot

flections by T^th volt. live ? " is, I believe, to be

answered by reference to the blaze-currents of the skin, which
I have found in a favourable case as long as a week post-
mortem, when no other sign of life on any other tissue could
be detected. And by a favourable case I mean that of a

5 mins.

VF.

ABC

107

strong, well-nourished cat — the half-starved derelicts that some-
times find their way into a physiological laboratory have a dead
skin two or three days post-mortem.

§ 64. More A B C.— Our second half-hour will have been
well employed if the application of what in the last lecture was
entitled the ABC method can be made absolutely plain. We
shall follow the system of notation that I then recommended to
your attention, and work through the four tests on a cat's foot in
accordance with the following diagram, which gives the ABC
switch in its several positions and the manner of its connection

Co Che
keyboard.

\\

Skin

C A

C A

Excitation from B to A (B is anodic)

Response outgoing at B
Excitation from A to B (B is kathodic)

Response outgoing at B
Excitation from B to A (A is kathodic)

Response outgoing at A
Excitation from A to B (A is anodic)

Response outgoing at A

FlG. 46. — Cat's paw (24 hours post-mortem), A, B, C, as indicated above. Ex-
citation by tetanising currents. Berne coil. Two Leclanches. 10,000 units. The
response is always of the nature of an outgoing current at A, and at B for both direc-
tions of excitation.

with the keyboard and galvanometer. You will see, if you trace
out the connections, that, with the switch in the first position,
deflection to your right means current from B to A, that in the
position IIB it means current from B to C, and that in the posi-
tion IIA it means current from C to A. By a glance at the
swatch and reverser, you can therefore recognise the direction of
excitation and the direction of response at B or at A ; and it
will be a perfectly simple matter to work through the four tests

108 THE SIGNS OF LIFE [LECT.

to verify the following formula, which previous experiments have
shown to be that of the responses of a cat's paw twenty-four
hours after death :—

B C A

Excitation from B to A (B is anodic)

Response outgoing at B
Excitation from A to B (B is kathodic)

Response outgoing at B
Excitation from B to A (A is kathodic)

Response outgoing at A
Excitation from A to B (A is anodic)

Response outgoing at A

And now, if I have succeeded in making clear to you that the
deflections seen on the scale indicate current in the object
towards B (i.e., out at B), or towards A (out at A), or from B (in
at B), or from A (in at A) — the results of the experiment will be
clear to you as it progresses.

I intend to examine B ; I therefore compensate the points
B C with the switch in the position II . Then I plug the
galvanometer at the keyboard, move the switch to the first
position, and send a break induction shock through the paw
from B to A. I turn back the switch to the old position, IIB,
and unplug the galvanometer. The deflection is to your left
as figured, signifying that there is now current from C to B (the
previous anode), which is outgoing at B. It is what in Bieder-
mann's terminology is called a negative anodic current — i.e.,
" negative " to the original current.

I repeat a second trial in precisely the same way, but with a
reversed direction of excitation, so that B is now its kathode.
The deflection is again to your left, outgoing at B ; it is a posi-
tive, kathodic current — i.e., " positive " to the original current.

And in precisely the same way, as a confirmatory pair of
trials, I repeat on the A C side ; only, perhaps, especially if the
previous trials have been made with strong currents, it may
be prudent to shift the electrode A to a fresh pad. Both the
trials give deflection to your right, outgoing at A, positive
kathodic after excitation from B to A, negative anodic after
excitation from A to B. So that the formula previously
sketched has been precisely fulfilled ; all the responses have
been outgoing.

vi.] VEGETABLE "SKIN' 109

§ 65. A vegetable surface. — In contrast with the preceding,
let me now show you another group of four trials — on a vegetable
surface — of which the formula has been drawn up beforehand, to
be verified presently. I have chosen a geranium leaf.

But let us pause a moment to reflect upon the conditions of
experiment if we were limited to the use of two electrodes, and
had no previous knowledge of the direction in which the re-
sponse takes place. We should be obliged to apply our elec-
trodes to two external points of the leaf, the deflection would be
the sum or the difference between two opposed responses, and
we could not tell which was the greater of the two. Suppose,
e.g., that we applied the two electrodes to opposite points on
the upper and lower surfaces, and observed a response directed
from upper to lower surface ; this might result either from

two outgoing currents A
that at B exceeding — 1

or from two ingoing
currents, that at A —

1

that at A : B + exceeding that at B : B

and until we know whether the effects are ingoing or outgoing,
we could not decide between the two alternatives. We are
obliged to use three electrodes to enable us to test separately
the point A and the point B, by connecting first one and then
the other point through the galvanometer with an indifferent
point C.

We proceed then with the experiment, B C A
having clearly realised the simplicity and
necessity of its apparent complication.
The results, as you see, come out precisely
as figured in the diagram before you :

All four reactions are ingoing ; Nos.
i and 4 are homodrome post-anodic ;
IN' os. 2 and 3 are antidrome post-kathodic.

§ 66. Surface against surface. — And now, having learned
that the reactions of the external surface of a leaf are ingoing,
we may make use of the resultant effect when only two elec-
trodes are used, to learn whether one of two points or of two
surfaces acts more powerfully than the other. Is, e.g., the
ingoing blaze of the upper or of the lower surface predominant

110 THE SIGNS OF LIFE [LECT.

when points of both surfaces act against each other through the
galvanometer? If to both directions of excitation, the resultant
is in one, say, a descending direction, we may be pretty sure
that the upper surface reacts more powerfully than the lower
surface ; but to make quite sure, it is better to take two pairs of
tests, reversing the order of direction in each pair, i.e., to take
the responses after excitations B to A, A to B, and after excita-
tions A to B then B to A, because it may well happen with
excitations of any considerable strength that the first is greater
than a second excitation, and we are not assured that a differ-
ence thus caused might not disturb a comparison.

Homodrome post-anodic of upper surface greater than
Antidrome post-kathodic of lower surface ; therefore A | ^

Homodrome descending response A to B. [ ~Y\

B~pt
Antidrome post-kathodic of upper surface greater than

Homodrome post-anodic of lower surface ; therefore
Antidrome descending response A to B.

A result of this character clearly proves that the blaze of
the upper surface of a leaf (beside geranium I have also tested
lilac and violet leaves) predominates over the blaze of its lower
surface. The ingoing current of the upper surface, whether
anodic or kathodic, has exceeded the ingoing current of the
lower surface, whether kathodic or anodic. We must be careful,
however, to secure equal areae of the two exciting electrodes (see

§ 69>

§ 67. Anodic versus Kathodic blaze. — You ask again, whether,
cceteris paribus, an anodic or a kathodic blaze is the greater.

To answer this question, you only
require to make a sufficient number

, of trials in which the two currents

x * are opposed to each other from points

Eacc. >• on one surface. You apply, e.g., your

'sp' two electrodes to the upper surface

(or to the lower surface), and find

that the after-effect is homodrome with the exciting current.
You conclude that normally the post-anodic ingoing homodrome
blaze exceeds the post-kathodic ingoing antidrome blaze.

B

vi.] THE FROG'S TONGUE 111

The frog's skin gives — with two electrodes applied to its
external surface — a similar positive effect ; but in this instance
we found, by analysing its polar factors, that the after-effect is
homodrome with the exciting current by reason of an excess
of post-kathodic outgoing homodrome over post-anodic out-
going antidrome blaze. The complete formulae in the two cases
run as follows : —

/ Eocc

Fruit skin\ 0 ,„ „ /
T f \ Resp. (tot<a.L)
or Leaf . r

I Resp. t 'pcLrU&i) • (

( E.3CC.

Frog skln\ Resp
( ffesp.

| 68. Tongue surfaces. — The frog's tongue, examined in
the usual way by the electrodes applied to the upper and
lower surfaces, presents an analogous case to that of a leaf;
its response, when stimulated, is the resultant of two effects
at the two opposite poles. The tongue, as it lies on the floor
of the mouth, gives an ascending resultant, which, if we might
be sure that the effects were outgoing at the two surfaces,
indicates that the upper surface of the tongue acts more power-
fully than the lower surface. The current of rest is descending,
and if we may admit as proved that the upper is the more effec-
tive surface, this descending resultant indicates an ingoing
current of rest.

But the detailed study of the frog's tongue belongs to the
intricate and theoretically important subject of mucous currents,
which has been treated of at a considerable length by Bieder-
mann. I hope to discuss the whole question of mucous currents
in a more complete manner than is possible to-day. Any one
who is curious in the matter should refer to Biedermann's papers
or to the full account in his Electro-pJiysiology. You will find
there that he attributes great importance to the positive and
negative responses of the tongue in connection with the theory
of assimilatory and dissimilatory phenomena. You may very

112

THE SIGNS OF LIFE

[LECT.

probably think, as I do, that an organ with two effective
epithelial layers, even if one of these layers is greatly more
effective than the other, is not the most suitable object to
afford contrary electrical effects significant of contrary chemical
changes. It would have been preferable if Biedermann had
based his case upon contrary electrical effects of a single
mucous surface. And I think that when you have reflected
upon the conditions of the problem, you will realise as a
clear economy of labour and an escape from much perplexity,
to methodically follow the ABC plan for the separate examina-
tion of the single points A and B of a simple mucous surface.
I have done so to some extent, but by no means sufficiently.
As far as I have gone, I find that the electrical response of a
mucous surface may be ingoing or outgoing, but that it is
usually the former. Here, e.g., is the record of a series of
ingoing responses of a frog's stomach :—

a L IOOCQ br. —

Serosa.

FlG. 47. — Frog. Stomach. Two series of ingoing responses to ingoing single
break induction shocks at one minute intervals. Interval of one hour between the
first and second series.

| 69. A warning. — Let me here put you on your guard
against a fallacy to which I was myself hardly alive in the
first comparisons of anode versus kathode, and surface against
surface. It is important that the area of contact between
surface and electrode shall, as far as possible, be equal on
both sides and not accidentally extended by excess of clay or
by fluid used to moisten the electrodes. As a matter of fact, it

VI.]

CURRENT-DENSITY

113

A

generally happened that this necessary condition obtained in

my earliest experiments, for the tubes of both electrodes were

of equal bore, and any excess of fluid around them was removed

by filter paper. But failing

this precaution, we should be

liable to have unequal effects,

due to unequal current densi-

ties at the two poles. If the

inequality is very marked, we

shall obtain greater response

from the pole of smaller area

(i.e.. where current density is

J

greater), whether that pole be

anode or kathode. The fact

deserves to be illustrated by an

experiment ad hoc. Here then

is a living surface — it happens to be a vegetable surface — to

which two electrodes of different area are applied ; the exci-

tation is applied first in one then in the other direction, and

as you see, both the responses are in the same direction,

ingoing at the pointed electrode, whether that electrode has

been anodic or kathodic.

Will some one be good enough to repeat this experiment
on a piece of frog's skin ? I should expect him to find both
responses to be outgoing at the pointed electrode, instead of
ingoing as in the vegetable surface.*

* This has since been verified by Dr Alcock.

FlG>

REFERENCES

HERMANN u. LUCHSINGER. — " Ueber die Secretionsstrome der Haut bei

der Katze," Pfliiger's Archiv, xvii., p. 310, 1878.
WALLER. — " On Skin-currents. Observations on Cats," Proc. Roy. Soc.,

vol. 69, p. 171, 1901.
BIEDERMANN.— "Ueber Zellstrome" (Frog's Tongue), Pfliiger's Archiv,

liv., p. 209, 1893.
BOHLEN (BlEDERMANN). — "Ueber die elektromotorischen Wirkungen rde

Magenschleimhaut," Pfliiger's Archiv, Ivii., p. 97, 1894.
BIEDERMANN.— "Elektrophysiologie," Jena, 1895 (translated by Miss F. A.

Welby. Macmillan & Co., 1896-98).

H

LECTURE VII

Observations on the Human Skin — Du Bois-Reymond's Experiments —
Tarchanoffs Observations — Sweat-prints — Introduction of Ions through
the Skin.

EXPERIMENTS by which electro-motive reactions are sought to
be demonstrated on the human subject are full of pitfalls, and
beset with fallacies. I do not consider that any one of the three
principal experiments I am about to show you ought to be re-
garded as convincing or conclusive, and it is mainly as an exercise
in criticism that they have been prepared for demonstration.

A monotonous series of successful experiments is against all
nature ; lecture-table discoveries are never as easy as they are
made to appear ; there is often more real instruction in " failure "
than in " success."

§ 70. A fruit/ess "experiment." — More than one person,
on learning that a blaze-current is a characteristic sign of life,
has said this : " Will my finger give a blaze-current if I place
it between those electrodes : it is alive I suppose ? " To which
question the obvious reply is, " Try it." In some cases the
"student "has said, "Oh, I don't like electric shocks," and his
research has terminated at this point. But if of a more inquir-
ing type, he has perhaps placed a finger between the electrodes,
and thereby experienced a first difficulty in this simple-looking
experiment. He cannot keep his finger absolutely still between
the electrodes, and the galvanometer spot wanders aimlessly
to and fro on the scale. The " research " may stop here ; the
"student" has to catch a train; his scientific curiosity is satis-
fied. A third student having cleared the first (imaginary) and
second very real and most obstructive fence, keeps his finger fairly
quiet between the electrodes, so that it is possible to neutral-
ise the accidental effects occurring between electrodes and skin,
and get the galvanometer spot fairly steady at or near its zero
point. An induction shock may now be passed through the

114

LECT. vii.] THE HUMAN SKIN 115

finger. This is the third fence ; for take the shock as weak as
you like, and you may be sure that the patient will jump, shift
contact, disturb compensation, and have to begin over again
many times, before he is able to keep his finger quiet while a
sufficiently strong shock is passed through it. But let us say
that he has reached this point, and that his finger is in circuit,
steady and currentless, and unmoved when a shock is passed.
You would find, even now, that the response is uncertain,
irregular, and capricious, always open to the objection that
contact between skin and electrodes has been altered during
experiment. And if you reflect upon the conditions of
experiment, I think you may fairly abandon it at this point.
For you have at best the resultant of two opposite effects at
the two electrodes, which resultant will depend upon at least two
or three unknown variables. You do not know what is the normal
direction of skin response, nor whether one or other portion of
skin is physiologically more or less effective, nor whether there are
polar differences when one or other portion is anodic or kathodic.
The original question cannot be answered by this apparently simple,
but in reality most objectionable and complicated experiment.

I am not sure yet, in spite of several trials of the point,
whether or no a conclusive answer is to be obtained as to the
nature and direction of excitatory currents in the intact human
skin. I am, however, quite sure that no such answer is to be
got with a single pair of electrodes, and that we must first study
the separate polar effects by the ABC method, B C A
exciting through A B, leading off through A C
or B C after previous compensation.

I did this two years ago, obtaining what

then appeared to me to be sufficiently constant — — »•

and regular effects ; the formula of skin response

was thus — > ~4

The responses Nos. i and 4, being antidrome to the exciting
current, I regarded as equivocal ; Nos. 2 and 3, being homodrome
to the exciting current, as unequivocal. All the responses
were " ingoing " at the excited spot, a direction that is gener-
ally assumed to be the normal direction of skin-current in the
cat and in man. But there was the principal and unavoid-

116 THE SIGNS OF LIFE [LECT.

able defect in these trials, that they have not and cannot be
repeated on the same skin after death ; so that we cannot feel
certain that the so-called unequivocal responses have not been
due to anomalous polarisation, which with the form of elec-
trodes employed was found liable to occur. Amalgamated zinc
plates covered with chamois leather soaked in zinc sulphate
are rarely free of polarisation currents, ordinary kathodic
antidrome as well as anomalous anodic homodrome, and with
tetanisation they give a formula in all points similar to that
given above. I do not therefore regard the results as being
conclusive until repeated with more perfect electrodes.

The fallacy caused by anomalous
B C A polarisation of imperfect electrodes — so
"<-— far from being avoided by the use of

^ """} tetanising currents — is favoured, for we
j- — > then have to do with antidrome katho-

( ^ die polarisation by one current plus

« / homodrome anodic polarisation by the

opposite current.

§ 71. A fruitful experiment. — Allusion has been made above
to the "blaze-currents" of excised human skin (§ 53, p. 86), and
I should like to bring the point once more under your notice, as
it has been for the last few weeks under my close observation.
I wanted to know how long after death this sign of life can be
detected in the skin itself, and whether the duration of survival
is found to vary after various modes of death. The skin is a
tissue of quite remarkable vitality ; it seems as if it had learned
to resist injury from its surroundings, and to have become tough
and hardy of habit. You may have noticed in your rambles logs
by the wayside from which young shoots have sprung from
surviving subcortical tissues ; perhaps you have heard that on
Napoleon I.'s removal from St Helena to the Invalides, his toe-
nails were found to have grown through his boots — a sign of the
extraordinary vitality of the cells of the nail-matrix, or of the
perishable quality of boot-leather — nearly twenty years had
elapsed between burial and exhumation. There is no doubt
whatever that the hair grows after death.

VII.]

DIRECT EFFECTS

117

In surgical practice it is a very common proceeding to
accelerate the recovering of a raw surface by "skin-grafting."
It is essential that such grafts should include cells of the
malpighian layer.

All these things point to an exceptional vitality of cutan-
eous or rather subcutaneous malpighian elements.

I find that in the skin of persons dying suddenly in other-
wise good health, .the cutaneous blaze-currents persist for several
days, whereas the skin taken from ordinary post-mortem room
subjects, having died gradually and completely, exhibits little
or none of this sign of life twenty-four and forty-eight hours
post mortem.

Let me remind you of the nature of this sign, for the
questions to which it may serve as an indicator are by no means
exhausted. A piece of living skin set up between electrodes,
and tested in the usual way by induction currents of both
directions, responds by blaze-current in one — the outgoing
direction. A piece of dead skin does nothing of the kind, but
gives, if anything, small polarisation counter-currents. And
since living skin responds in one direction to both directions
of excitation, you may (observing due reservation and pre-
caution) obtain outgoing blaze-currents after tetanisation by
alternating currents in both pairs of directions. Here are
galvanometric records of the electrical responses of surviving
human skin, and of the same skin, killed by heat.

0-0010,

voit.

Time

TTTTTTT

Dead.

•Living:

FlG. 49 (4201). — Skin of breast 8 hours after amputation. Living. — Two +
responses to single break induction shocks in + and -- directions. 8 L. 10,000.
Dead. — Several - and + effects to + and - shocks, i.e., polarisation. Resistance
diminished.

118

THP: SIGNS OF LIFE

[LECT.

A

JOO

B -

(M +
\B -

10

20 /T7//75.

B _

/- !&-

500\B +

{B-

IX-

\B +

{B-

7<500

1

i

I

o

o /o 20 mm.

FlG. 50 (Nos. 4199-4200). — Skin of breast 5 hours after amputation. Tested by
tetanising currents for periods of 5 seconds each from a Berne coil at 5000 units,
supplied by 8 Leclanche cells. Conductance at outset of experiment = 5, and
calculated resistance = 520,000 ohms. After tetanisation the conductance was
raised to 12.5 (= 196,000 ohms); after further tetanisation it rose further to 25
( = 88,000 ohms), when the record commenced. The resistance of the galvanometer
and electrodes = 20,000 ohms. The deflection by -j^th volt through i megohm = 27.

A , living. — Conductance

1st response t

2nd „

3rd

4th

Conductance
£\ boiled. — Conductance

ist response t

2nd

3rd

4th

Conductance

it outset

.

.

=

25

i tetan.,

m. -,

br.

+ , =

+ O.OI2O Volt.

) i

m. +,

br.

- , =

+ O.OO92 „

,,

m. -,

br.

+ , =

+ O.OIOO ,,

,,

m. + ,

br.

- , =

+ 0.0076 „

,t end

. . .

=

35

i tetan.,

m. -,

br.

+ , =

+ 0.0004 volt.

,,

m. + ,

br.

- , =

-0.0004 11

fl

m. -,

br.

+ , =

+ 0.0004 .1

„

m. +,

br.

-, =

- O.OOO4 !!

=

us

VII.]

THE CONGELATION BLAZE

119

voit

One more point to conclude this matter of the surviving
human skin. If a piece of living skin, placed between electrodes
and connected with a galvanometer in the usual way, is
gradually cooled in a freezing-
box, we shall notice, at a
given temperature of about
- 5°, a sudden deflection of the
galvanometric spot indicative
of a sudden electromotive
change. The effect is due to
the sudden congelation of the
under-cooled tissue. This
" congelation blaze," which is
manifested by vegetable as
well as by animal tissues, is in
general their last sign of life ;
if the frozen tissue is thawed,
and then cooled a second
time, there is little or no
second blaze according as the
tissue has been more or less
completely killed by the first
proceeding. In the present

10 m ins.

case, that of the human skin,
the congelation blaze-current
is of outgoing direction.

FlG. 51 (4209). — Skin of man. 2nd
day after excision. Skin gradually cooled
by surrounding the skin-chamber with a
freezing mixture. Sudden electromotive
discharge (ouigo:ng current) at a tempera-
ture of - 6° inside the skin-chamber. Be-
fore freezing the + responses to + and -
single induction shocks were +0.004 ar>d
+ 0.008 volt. After freezing, the + responses
were absent, being replaced by small
and + polarisation effects. On recongela-
tion no second discharge was observed.

Alterations of electrical resistance occur in marked degree in
connection with the electromotive effects that first attract our
attention. Surviving skin as it dies exhibits a fall of resistance.
There is a well-marked diminution of resistance as the im-
mediate consequence of electrical excitation ; Fig. 50 incident-
ally shows this. And in the course of cooling, there is first a
gradually increasing resistance, then at the point of congelation
a sudden increase of resistance, which in some instances is
preceded by a small and evanescent diminution, not unlike a
congelation blaze, which, however, I have reason to attribute to a
slight rise of temperature and of conductivity occurring when
the under-cooled tissue juices pass from the liquid to the solid

120 THE SIGNS OF LIFE [LECT.

state. But the details of this effect require closer investigation
than I have yet found time to give to them. Thawed skin,
subsequent to congelation, has a greatly diminished resistance
— e.g., a diminution to 50,000 ohms from an original resistance
of 1 50,000 ohms.

Vegetable tissues likewise exhibit a very marked diminution
of resistance in consequence of excitation, and the diminution
is not solely a diminution of "contact resistance" at the elec-
trodes. It is internal or interpolar as well, owing probably
to a multiplication of electrolytes, possibly also to an actual
rupture of cell membranes. A very simple experiment will
serve to show you that the augmented conductivity is inter-
polar as well as polar. A flower stalk is laid across four
unpolarisable electrodes, E I I E, at 5 cm. intervals ; a tenth
of a volt is allowed to act upon the galvanometer through the
entire length of stalk E E, and through an intermediate portion
I I. The deflections indicate the current strength, and there-
fore the conductance of the corresponding lengths of stem.
Noting their values before and after tetanisation of the whole
stem through the terminal electrodes E E, you will find that
the conductance is augmented in the intermediate part I I,
showing that the alteration is not restricted to the contacts E E.
The conductance of I I, which was 0.8 y before the excitation
through E E, is raised to 2.0 y ; in E E itself, it has been raised
from 0.4 y to 1.6 y.*

§ 72. Du Bois experiment. - - The galvanometer is in its
usual position, with its magnets pointing N and S, and the
scale correspondingly arranged N and S ; you may consider that
the two ends of the scale represent the two terminals of the
galvanometer. I am seated facing you below the scale, with my

* The symbol y denotes our unit of conductivity. (See Appendix, p. 169.)
The conductance and resistance in the above experiment are :—

of I I before 0.87 1.25 V.

after 2.0 „ 0.5 „

E E before 0.4 „ 2.5 „

after 1.6 „ 0.625 »

VII.

DU BOIS' EXPERIMENT

121

left hand connected with the S terminal, and my right hand
with the N. The forefinger of each hand dips in salt solution,
there is little or no difference of potential between my two
hands, and the spot is at rest.

FlG. 52. — Du Bois-Reymond's " Willkurversuch," to demonstrate a negative
variation during voluntary muscular contraction. The current is ascending in
the active arm. (From du Bois-Reymond's Thierische Elektncitaf).

I now firmly contract the muscles of my right forearm ;
the spot moves to my right (your left), or clockwise in the
circuit, or in my body from right to left. The spot is " pulled."

Now I contract the muscles of my left forearm, and every-
thing is reversed. You have witnessed du Bois-Reymond's

122 THE SIGNS OF LIFE [LECT.

celebrated " willkiirversuch," by which he considered that he
had demonstrated on the normal human subject the electrical
effects of voluntary muscular contraction, and I think you may
be interested to see the actual figure by which he illustrated
the experiment (Fig. 52).

The usual criticism quoted of this experiment is that of
Hermann, who explains the deflection observed in du Bois-
Reymond's experiment as being the effect of a secretion current
provoked in the skin of the contracting side. He says that
in the skin of that side such current will be directed from
without inwards, giving current ascending in the active arm.

This criticism is based upon observations by Hermann
and Luchsinger concerning the effects of atropine on the
sweat currents of cats, and he expresses himself as follows : —
" A curarised man could give the du Bois current in the
absence of muscular contraction. In the case of an atropinised
man it would be absent, in spite of the presence of muscular
contraction." *

I do not myself think that the alternative explanation is
necessary. To my mind, du Bois-Reymond's experiment does
not demonstrate the existence of contraction currents on man ;
nor do Hermann's experiments on cats show that du Bois'
currents on man are secretion currents. Neither the contraction
current nor the secretion current has been separately obtained
on man ; the currents that we have witnessed are susceptible
of a far simpler explanation.

I think they are simply capillary currents arising at the
surface of separation between salt solution and skin. Let me
show you a couple of experiments in point.

Instead of dipping the two fingers simultaneously, I will dip
them successively, so that the skin of one finger may be pretty
completely soaked when the skin of the second finger com-
mences to be moistened. There is no deflection so long as
only one finger is introduced, but on introduction of the second
finger there is current through the galvanometer from the first
to the second finger, therefore through the body from the second

* Hermann, Handbuch, vol. i., p. 225.

VII

.] TARCHANOFF'S EXPERIMENT 123

to the first. The spot is " pulled by the ingoing capillary
soakage."

Here, now, is a counter experiment : —

Both fingers are resting against the bottom of the vessels, as
indeed was recommended by du Bois-Reymond in order to
avoid the fallacy that I have just mentioned, and when the spot
is at rest I squeeze one of my fingers, say, of the left hand,
against the bottom of the vessel. The current through the
galvanometer is now from the compressed skin. The spot is
" pushed." In case you should object to the possible muscular
or secretory origin of the current by reason of the voluntary
action on that side used to effect the compression, I will remain
perfectly passive, and have the compression effected by a second
person without any act of mine. The effect follows as
before.

While I am on this subject, let me show you one more
surface experiment. You have seen that contraction pulls the
spot, that soaking skin pulls the spot, that squeezed skin pushes.
I want to dry a wet finger in order to dip it in dry, I naturally
rub it, and then proceed to show that on soaking it again the
spot is pulled. But now, as you see, the effect is reversed, the
spot is pushed ; dry rubbed skin pushes the spot.

And so we may use for our memorandum, that if zinc

pulls the spot, last-dipped and therefore soaking skin pulls,

that squeezed skin pushes, and that recently rubbed skin

pushes. Neither du Bois-Reymond's contraction current, nor

Hermann's secretion current are above suspicion in presence

of those unavoidable capillary currents. And for my part I

find it quite impossible to contract the muscles of my forearm

without moving a finger or pressing it against something.

§ 73. TarcJianoff's experiment. — Over ten years ago, Tar-
chanoff published an account of observations on the skin-
currents of the human subject, in which he considered that he
had obtained evidence of their reflex causation by all kinds
of peripheral stimuli — by tickling, by induction shocks, by
pricking with a pin, by hot and cold water, by sudden sound,
sight, taste, and smell. He assures us, further, that imaginary

124 THE SIGNS OF LIFE [LECT.

sensations, intellectual effort, or strained attention bring about
similar effects — "always, of course, during complete immobility
of the subject." Voluntary movement of any part of the body,
during absolute quiescence of the part connected with the
galvanometer, gives a skin current the strength of which is
dependent on the strength of the voluntary effort. He says
that parts in which sweat-glands are most abundant (palm of
hand, toes, axilla, etc.) become negative to parts containing few
glands (back, nates, external surface of thigh and arm), and
considers, therefore, that the active state of the nervous system
gives rise to an ingoing secretion current similar to that shown
by Hermann in the case of the frog's skin, by excitation of its
cutaneous nerves.

Tarchanoff further assures us that he used a sensitive, almost
completely aperiodic, galvanometer, giving with the nerve cur-
rent of a frog's sciatic a deflection " off scale " (i.e., greater than
50 divisions) ; the skin effects he observed also gave deflections
" off scale," had a latent period of one to three seconds, outlasted
the stimulus by several minutes, and returned gradually but
irregularly to rest. Connection with the skin was made from
unpolarisable electrodes of the usual type by strips of hygro-
scopic wool (10 to 15 cm. long) soaked in normal saline, brought
in contact with pads of the same material previously applied to
the skin. These pads were of an area of 10 to 15 cm. The
currents of rest were previously compensated. In the case of
the hand, the effect of gentle tickling was generally such
that "die Basis der Finger in der Mehrzahl der Falle nega-
tive, der Thenar dagegen positive elektrische Spannung
besitzt." Imaginary sensation gave deflections of 10 to 15
divisions.

Now these things are clearly of considerable interest, if a
true physiological effect regularly coincident with nervous
activity can be demonstrated ; and I have somewhat minutely
described to you the conditions of observation, in case any one
should be inclined to make fair and patient test of the state-
ments. I must confess, however, that for my own part I am not
convinced that the deflections have been anything more than
rather unduly pronounced galvanometric vagaries occurring

vii.] IMPORTATION OF IONS 125

with shifting contacts. We all know how difficult it is to pre-
serve a limb absolutely quiet, and that even when we think that
our muscles are completely at rest, a "thought-reader" can
obtain information from our unconscious movements. It is no
easy matter to have a loose pad immobile against the skin, and
if it be fixed by a band, the least swelling or movement will alter
its pressure against the skin ; and I cannot say that I have suc-
ceeded in satisfying myself that the irregular deflections that
certainly do occur with a subject keeping as quiet as possible,
and more markedly when the subject is anywise startled or
stimulated, have been anything else than the effects of accidents
of surface contact. I am willing to admit that they might be
accidents of nervous tension giving true alterations of skin-
currents, but I cannot admit that this possibility has been
proved to the exclusion of the coarser fallacy. Will any one
undertake to clear up this point? If so, perhaps it may be
worth while to mention that the skin can be locally atropinised *
by means of a belladonna plaster, and that obviously a locally
atropinised skin should show no effect of glandular action, but
the usual effects of accidents of contact.

I do not think that these observations on the human sub-
ject are particularly satisfactory, and shall not dwell upon them
any longer. I will use the remainder of the hour to place
before you certain facts relating to the transport of medica-
ments into the human body under the influence of the galvanic
current.

§ 74. Importation of ions. — All such facts are illustrations of
the principles of electrolytic conduction. If a sufficiently strong
current is passed through a saline solution, or, as I am about to
show you, through a porous electrode soaked in a saline solution,
the electro-positive kations of the salt travel with the current
from the anode to the kathode, while the electro-negative
an ions travel against the current from the kathode to the anode.
Taking, e.g., the case of NaCl, the Na travels with the current,
the Cl against the current. You may for the present purpose

* Aubert, "Sweat-prints," Ann. de Dermatologie, 1877-8; Article
" Sueur," (by Frangois Franc) in Diet. Encycl. des Sciences Medicales, xiii.

126

THE SIGNS OF LIFE

[LECT

regard the tissues as represented by a sponge of such NaCl
solution ; if you pass the current into the body by porous
electrodes soaked in some other salt — and for this purpose we
shall take permanganate of potash — you will, after a few minutes,
observe a visible sign of the transfer of the anion from electrode
to body in the form of a discoloration of the skin at the spot
where the anions have travelled against the direction of current
from kathode to anode. I chose permanganate of potash

K MnOa

FIG. 53- — Circular areas of skin of the forearm that have served as electrodes to a
constant current for a few minutes. In the upper pair of circles the two electrodes in
contact with the skin were a solution of permanganate of potash ; the coloured ion was
the anion MnO4, which travels up stream and enters the body at the kathode. In the
lower pair of circles, the two electrodes in contact with the skin were a solution of
copper sulphate ; the coloured ion was the kation Cu, which travels down stream and
enters the body at the anode.

because it has a coloured ion, in this case the anion. If I had
taken copper sulphate, where it is the kation copper that is
coloured, I should have made the anodic spot the more apparent
since the metal travels with the current and is carried into the
body at the anode.

Two electrodes — one-inch glass tubes half full of perman-
ganate of potash — are strapped to the front of my forearm,

vii.] AN OBITER FACTUM 127

and perpendicular to it. The electrodes are connected with
the house current, which is at 1 10 volts. Out of caution for my
own comfort, I have means of taking any desired fraction of the
whole current ; and to tell what current I am taking, there is a
milliamperemeter in circuit with my arm. The electrodes have
are?e of about seven square centimetres, and a current of between
two and three milliamperes should produce a distinct result in
about five minutes.. The kathode is, I believe, nearer to the
wrist, the anode above it ; but we shall soon see, for it is at the
kathode that we shall find evidence of penetration of the coloured
anion, MnO4.

The trial is over ; and after washing the forearm under the
tap, you see a number of indelible brown spots over the pre-
viously kathodic area of the skin, which are due to its penetra-
tion by the coloured anion, which you remember travels against
the current, and therefore gets into the body where the current
leaves it. Notice their clearly defined punctiform appearance ;
this signifies that the path of current has been chiefly, if not
entirely, by way of the sweat-ducts, hardly or not at all through
the general epidermic investment.

A similar principle of transport holds good in the case
of other electrolytes, and it is interesting to note, in the
case of poisonous salts, whether it is the anode or the
kathode that acts as the channel of introduction. In most
cases, e.g., in that of strychnine sulphate, the poisonous
property belongs to the base, the kation, which penetrates at
the anode ; in others, e.g., in that of cyanide of potassium, it
belongs to the acidic moiety, the anion, which penetrates by the
kathode. In the first case the anode is the poison carrier, the
kathode being innocuous ; in the second case it is the kathode
that kills. If, following the example of Leduc, I should place
two rabbits side by side, connecting them by a couple of elec-
trodes of indifferent nature, i.e., soaked in NaCl, and then
run a current through both rabbits in series, by means of elec-
trodes moistened with strychnine sulphate, I should put the
anodic rabbit into strychnine convulsions by reason of pene-
tration of the kation, while the kathodic rabbit, taking in only
the non-toxic anion, would remain quite unaffected.

128 THE SIGNS OF LIFE [LECT. vn.

§ 75. A supplementary experiment. — Let us take advantage,
of the altered area of skin of our KMnO4 experiment to make
a further trial. Its sweat-ducts are choked with MnO4 — i.e., with
a non-living electrolyte that may serve us as a conductor to
the inner aspect of the skin. I should like to take this altered
area of skin and an unaltered area of intact skin into circuit
with an induction coil and a galvanometer, to be tested in the
usual way. This is now done by tubes of zinc sulphate, and the
first point you notice is that there is a considerable current
directed in the body from the irritated to the intact spot, or
ingoing through the former and outgoing through the latter.
This current being compensated and the galvanometer plugged
out, I apply excitation in the usual way by induction shocks and
by tetanisation, and look for the after-currents that may be
aroused. In accordance with your expectation, they are in
every case opposed to the current of injury — i.e., ingoing at the
intact skin and outgoing at the manganised skin. This result,
as far as it goes, agrees with the conclusion that the normal
irritated skin of man is the seat of an ingoing current ; but I
should be sorry to lay much stress on the result of an isolated
experiment, the point deserves further investigation.

REFERENCES

Du BoiS-REYMOND. — " Willkiirversuch," Untersuchungen iieber thierische

Elektricitaf, vol. ii., p. 289, 1849.
HERMANN. — "Ueber den Actionsstrom der Muskeln im lebenden Men-

schen," Pfliiger's Archiv, xvi., p. 410, 1878.
TARCHANOFF. — " Ueber die Galvanischen Erscheinungen in der Haut des

Menschen," u.s.w., Pfliiger's Archiv, xlvi., p. 46, 1890.
LEDUC. — "Action des Courants Continus sur 1'Organisme Vivant," Annales

d'Electrobiologie, 1901, p. 261.
WALLER. — "On Skin-currents. Part III. — The Human Skin," Proc.

Roy. Soc., vol. 70, p. 374, 1902.

LECTURE VIII

The Fallacy of the Electrodes — Water Transport at Anode or Kathode —
Alteration of Resistance at Anode or Kathode.

§ 76. Review. — This lecture is to be partly retrospective,
partly prospective. We shall pass under a rapid review the
principal steps of our investigation, inspecting with most care
what may appear to us to be weak points, rinding perhaps in
those very weak points, points of attraction to further investiga-
tion.

The main principle and "motif" running through the in-
vestigation has been that the electrical responses to electrical
stimulation are a token and measure of vitality in the objects
selected for examination — in the retina, in the entire eyeball, in
its crystalline lens, in the skin of animals, in the " skin " of
plants, in all the living tissues of plants, in living tissues of
animals ; and in my last lecture, when I tried to show you how
slowly and gradually the vitality of human skin is lost, I
ventured to touch upon a fallacy that becomes specially
apparent when one undertakes to follow the sign to its last
discernible trace. It was lost to sight among accessory
physical reactions, fortunately small as compared with the
physiological reactions of full vigour, but quite unavoidable,
since they are inherent to the apparatus we have to use, I
mean the electrodes. And although I call your special atten-
tion to the " Fallacy of the Electrodes " at this last stage, I
should like to assure you that it has been carefully excluded
in all the experiments you have witnessed, and that from the
very outset of the investigation the possible simulation of a
blaze-current by a polarisation at the electrodes has been con-
sidered and excluded. You remember, no doubt, that we hardly

100

I

130 THE SIGNS OF LIFE [LECT.

ever omitted to control the result observed on the living thing
by the identical test applied to the same thing killed.

§ 77. Fallacies. — Fallacy of the electrodes arises from
polarisation ; our " unpolarisable " electrodes are not abso-
lutely unpolarisable, and may accidentally be quite sensibly
polarisable. Their polarisation currents, anomalous or positive,
as well as normal or negative, are most manifest with a constant
current, much less so, but still sensibly so, with induced currents.
We have made use of induced currents only, and shall therefore
restrict our attention to these.

With single shocks I do not think there is any liability to
fallacy ; an unequivocal or homodrome blaze-current cannot be
simulated by anomalous polarisation, which is a rare and feeble
effect manifested by a defective electrode, and quite absent
from a properly prepared electrode. An equivocal or anti-
drome blaze-current might at first sight be taken as being due
to ordinary polarisation, since it is of the same direction ; but the
magnitude of the response, its absence from the electrodes
themselves when joined, and from the tissue itself when killed,
will leave us in no doubt as to the physiological character of the
reaction. It is only in the cases where single shocks having
proved to be ineffective, we have recourse to the further test
of tetanisation by alternating currents, in order to bring out a
summated effect (p. 68), that there is any real possibility of
deception. Distinguish between the two cases: (i) that in
which the alternating currents are passed through the galvano-
meter and test-object ; (2) that in which they are passed through
the test object only while the galvanometer is short-circuited.
The first of these two dispositions reproduces an arrangement
that was first adopted by V. Fleischl in the case of nerve, and
that I have already considered at some length in that connec-
tion. The opposed make-and-break currents are supposed to
neutralise each other through the galvanometer, and such deflec-
tion as occurs is attributed to an electro-motive action of the
test-object. This deflection occurs in the direction of the break
current, i.e., is such as would be produced by a physiological
reaction in that direction, or as a physical reaction — the sum

VIII

.] FALLACY OF THE ELECTRODES 131

of counter-currents at make exceeding the sum of counter-
currents at break. A closer scrutiny of the conditions of the
reaction shows that both factors are, or may be, effective, i.e., a
physiological reaction in the direction of break can occur by
reason of post-anodic action-current, and a physical reaction in
that same direction can be due to an algebraic sum of ordinary
polarisation currents.*

It is not quite, easy to clearly demonstrate the physiological
factor even in a favourable case, and practically impossible to
do so in an unfavourable case ; I have therefore not made
systematic use of this first disposition of test

The second disposition, by which only the after-effect of
tetanisation is observed on the galvanometer, is, in my experi-
ence, less liable to be misleading than the first. But the
case to which I systematically applied it, viz., the human skin,
has been a somewhat favourable one to follow out, since by

SKIN Living- Decid

Response

break *• >

Response > >

reason of its physiological disposition the skin gives sign of
life by an outgoing response to all directions of induction
currents. Tetanisation by such alternating currents provokes,
first, a summation of physiological (outgoing) effects ; second,
a resultant of alternated polarisation effects which is in the

* Von Fleischl's deflection is discussed at some length in Animal
Electricity, pp. 115-119, 1897. The superior polarisation by make there
alluded to is shown in a paper to the Physiological Society (i2th Nov.
1898), on the "Influence of Polarisation on the Electrical Resistance of
Nerve." A deflection in the direction of break, during the* passage of alter-
nating induction shocks, might also be due to an irreciprocal resistance,
smaller to the break than to the make shock, as occurs in the passage of
alternating currents through a vacuum tube. I have not undertaken the
physical analysis of these possible factors, and have simply abstained from
using von Fleischl's deflection as a sign of life.

132 THE SIGNS OF LIFE [LECT.

direction of the break current. Therefore, if to both pairs of
directions of tetanisation the after-effect is in one (positive or
outgoing) direction, we have proof that the skin is alive ; if to
both pairs of directions it is in the direction of the break, we
have proof that it is dead.

I found it at first not a little confusing that a deflection in
the direction of the break current — which in V. Fleischl's
experiment on nerve is generally considered as a sign of life —
should on skin (and on other killed tissues) be a sign of death.
But evidently the deflection in question is, by reason of the
physical factor mentioned above, a balance of ordinary polari-
sation in the direction of break. Here is the analysis of this
physical resultant for the two pairs of tetanisation directions :—

/. Mcike current >• •«

a.lCs poLcs.ri3a.Cion < >

3. Bre<a.k current •* >-

the resultant in each case being due to the summated effects,
No. 2 being greater than the summated effects No. 4.* You
ask, perhaps — if you have followed the argument so far — why
it should be preferable to observe an after-effect of tetanisation
rather than an effect during tetanisation. Ought not a positive
outgoing effect to manifest itself during as well as after tetani-
sation ? So it does, with a lively skin, that will respond to
strengths of tetanisation that can be passed through the
galvanometer ; such a skin will, however, also respond to the
simpler question of single induction shocks ; a skin so little

* This result maybe observed ; with strong tetanisation the resultant may
be in the direction of make, the after-effect of the summated effects No. 4 being
greater than that of the summated effects No. i. Yet even in this case the
effect during tetanisation is in the direction of the break. I am not certain
whether the after-deflection in the direction of the make is physiological or
purely physical. I place no reliance whatever upon the deflections obtained
during strong tetanisation. They can happen by alterations of the gal-
vanometer magnets by the opposed long and short currents, or by reason
of asymmetry of the magnetic field in the absence of any electrolyte at all
in circuit, or by reason of irreciprocal resistance.

viu. j QUINKE CURRENTS 133

alive as to require a series of shocks to bring about summation
of effects, must be tested by tetanisation that cannot be passed
through the galvanometer, which, therefore, must be short cir-
cuited during the process.

There is one more shape in which the fallacy of the elec-
trodes may appear, which, under certain conditions, may be
very deceptive indeed. The state of the electrodes, especially
if they have been long put up, may be such that anomalous
polarisation of one electrode may be present, with ordinary
polarisation of the other electrode. The seat of such polarisa-
tion may be between zinc and zinc sulphate, or between zinc
sulphate and saline clay. The deflection may be in one and
the same direction for both pairs of directions of tetanisation,
thus simulating the formula given above as characterising the
living state. Electrodes of this nature must not be used.
Electrodes prepared with ordinary care do not exhibit the fallacy.

§ 78. A future preliminary. — A methodical examination by
the ABC method, of the polarisation effects produced by con-
stant and by induced currents passed through various electrodes
and electrolytes, would form a very useful preliminary exercise
introductory to the study of physiological polarisation. You
would find that some combinations are polarisable at both
poles, that others give only anodic or only kathodic polarisa-
tion, and prominent among these purely physical effects you
would find that by reason of anomalous polarisation the chief
physiological after-current — the positive post-anodic action
current — is exactly imitated, which things should not lead you
to imagine that the physiological effects are " merely physical,"
but invite you rather to the further physical analysis of physio-
logical phenomena.

§ 79- Quinke currents. — Currents of liquid through a porous
partition, e.g., a membrane through which osmose is taking
place, arouse electrical currents in the direction of the water
movement. Conversely, an electrical current passed through a
porous partition between two electrolytes causes a flow of water
in its own direction. This water transport, from anode towards

134 THE SIGNS OF LIFE [LECT.

kathode — kataphoresis — is a chief factor in the electrical osmose
first made known to us by the investigations of Ouinke.

Our attention is naturally directed to the question of such
water transport through porous bodies by a very remarkable
diminution of resistance that occurs — in skin, in leaves, etc. — as
a consequence of the passage of induction shocks. This diminu-
tion of resistance, or augmentation of conductivity, is far more
pronounced in living than in dead matter, and a diminution of
resistance in consequence of molecular dissociation of active
stuff must therefore be thought of.

I think it probable that both factors contribute to the result ;
their experimental distinction and separate examination appears
very desirable, but very difficult.

It is indeed easy enough to witness what must be an effect
of kataphoric water movement on an inert object, such as an
eggshell ; it is the distinction between effects of kataphoresis
and a dissociation on a living object that is difficult. The best
thing that can be hoped for, is to find cases where one factor is
predominant and the other insignificant. In a muscle, e.g., we
may expect to get most distinct evidence of dissociation ; Loeb*
has, in fact, shown that the osmotic pressure of muscle is con-
siderably augmented by tetanisation, resting muscle being
isotonic with a 0.6 per cent. NaCl solution, tetanised muscle
with a i.o per cent, solution. We should accordingly expect to
find 'an increased conductivity in active muscle, perhaps also in
active nerve — as was supposed to be the case by Griinhagen. I
have not yet found time to carry out such experiments ; perhaps
someone among my present hearers will take them in hand.

The following experiment has been put up to show this
purely physical effect of kataphoresis ; it will at the same time
serve to illustrate another of the fallacies that might deceive an
inexperienced observer.

An eggshell (with its membrane) has been set up between
the exploring electrodes to be examined in the usual way.
From a compensator I pass T^ volt through the shell and
galvanometer ; the deflection is \ degree of scale. I pass

* Loeb, " Physiologische Untersuchungen iiber lonenwirkungen (I Ver-
suche am Muskel)," Pflitge^s Archiv, Ixix., p. i, 1898, and Ixxi., p. 457.

vni.] EVAPORATION CURRENTS 135

strong alternating induction currents through the eggshell
(plugging out the galvanometer meanwhile), and then again
pass yi^ volt through the eggshell and galvanometer. The
deflection is now 20 degrees of scale, i.e., the conductivity, by
reason of water transport from electrodes to shell, has been
increased more than fortyfold.

A propulsion of water, through capillary pores, by an
electrical current,- might conceivably outlast its original cause.
And since a capillary current can give rise to an electrical
current in its own direction, it is conceivable that a homodrome
after-current might be thus brought about. I have at various
times made a good many trials of this point, with porous septa
of various kinds between saline solutions of various strengths,
without ever observing anything at all comparable with an
unequivocal blaze-current of a living object. Here is an
ordinary dialysing tube containing a strong solution of zinc
sulphate, and surrounded by a weaker solution ; two amalga-
mated zinc rods dipping in the fluid on each side of the septum,
serve as electrodes ; the dialysing cell, compensator, induction
coil and galvanometer are connected to the keyboard in the
usual way. Notice, in the first place, the normal current — from
less concentrated to more concentrated solution in the dialysing
cell, i.e., " with " the water current, and from more to less through
the galvanometer. And now, with this concentration current
compensated, I send a strong break shock through the dialyser
first from B to A, when you see a polarisation deflection from A
to B ; then from A to B, when you see a polarisation deflection
from B to A. And I do not stop to inquire whether these
polarisation counter-currents are at the electrodes or at the
interface of the two solutions ; for they are antidrome effects,
and we are now looking for homodrome effects.

So we find that although no doubt water transport through
pores occurs in living as well as in dead matter, and contributes
no doubt to augmented conductivity caused by electrical currents,
it cannot be made responsible for the currents now familiar to
us as blaze-currents ; the sine qua non of these currents, what-
ever their chemico-physical mechanism may ultimately prove to
be, is the living state.

136

THE SIGNS OF LIFE

[LECT.

And yet, while we find reason to reject an appeal to water
currents (or " concentration currents "), as being the original
source of electrical effects that arise or are provoked in living
matter, we should be careful to remember that water currents
must actually play an important, if secondary part, in the com-
plicated molecular play of physiological action. Local action
implies local disintegration, raised osmotic pressure, attraction
of water, and electrical current. The water current is towards
the active spot ; the electrical current is from that spot ; we
must imagine it as a kationic current.

§ 80. Evaporation current. — This first experiment should
serve as reminder to you that gradual shiftings of the galvano-

FlG. 5-4- — To illustrate evaporation currents.

meter spot may, among other causes, be due to evaporation of
water, and to capillary currents thereby produced. The circuit
contains nothing but the galvanometer, and a pair of unpolaris-

viii.] CONCENTRATION CURRENTS 137

able electrodes, the clay of which has been so shaped as to give
dissimilar surfaces of evaporation. The clay is moist, the air of
the room is dry, B is giving off water more quickly than A,
and is sucking water from A, so the electrode current is to your
left, as figured. I now bring down over the electrodes a bell-
jar with a bit of wet blotting paper sticking inside it, i.e., con-
taining wet air. The galvanometer spot is sharply deflected to
your right (by the checked or reversed water current). On
removal of the bell-jar the spot is sharply deflected to the
left (evaporation current to room air), and finally, when the
evaporation and deflection have become steady, I cover the
electrodes with a dry heated bell-jar, which at once, by accelerat-
ing the evaporation, causes a sharp deflection to the left. And
for the present I am not concerned to know whether or no the
concentration of saline solution plays a part in these evaporation
effects ; all I want to do is to show you that trifling altera-
tions of evaporation can give quite considerable electrical
effects.

§ Si. Concentration current. — The next experiment is intended
to remind you of the usual direction of a concentration current
— a point which in most text-books and monographs appears to
be considered as too self-evident to be worth specifying. Two
amalgamated zinc rods dip into a 25 per cent, solution of zinc
sulphate, and are connected with the galvanometer.

A drop of distilled water allowed to run down B into the
solution gives deflection to your right (current from B to A).
A drop of saturated zinc sulphate to B gives deflection to your
left (current from A to B).

And of course dilution at A gives deflection to the left, con-
centration at A gives deflection to the right. In terms of the
ionic movements, this happens by reason of greater velocity
of the anion (which travels from the more concentrated to the
less concentrated solution, giving therefore current in the reverse
direction). With acids, e.g., HC1, and complex organic salts,
e.g., CHgCOOK, in which the kation travels faster than the
anion, the current is from more to less concentrated solution.
But with all our ordinary neutral salts, and with alkalies, the

138 THE SIGNS OF LIFE [LECT.

current is from dilute to concentrated, i.e., with the water
current.

The direction of electrical current between two unequally
concentrated solutions of any electrolyte depends upon the
relative velocities of the two ions, both of which are of course
travelling from concentrated to dilute solution. If the anion is
of higher velocity, as is the case with alkalies and most salts, the
current is from dilute to concentrated ; if the kation is of higher
velocity, as is the case with acids and some salts, the current is
from concentrated to dilute. (See Fig. 55.) You may be dis-
posed to admit provisionally, as I do, that the latter condition
obtains in the case of the complex organic compounds that take
part in the dance of life ; current of action proceeding from the
spot of greatest " livingness," where solution pressure is in-
creased--and dissociation — and ionic concentration — and
osmotic pressure.

SOME RELATIVE IONIC VELOCITIES.

Kation + Anion -

NaCl Sodium 37 Chloride 63

HC1 Hydrogen 80 Chloride 20

NaOH Sodium 20 Hydrate 80

CH3COOK Potassium 68 Acetate 32

SOME ABSOLUTE IONIC VELOCITIES.

(At P.D. of i volt per i cm., and Temp, of 18° C.)

In cm. per sec. In mm. per hour.

Hydrogen H + 0.00320 115

Hydroxyl OH - 0.00182 65

Sodium Na + 0.00045 Io

Chlorine Cl - 0.00069 25

Potassium K + 0.00066 24

Acetyl CH3COO - 0.00036 13

Engelmann in the course of his investigation of skin
currents, and Biedermann in his examination of mucous
currents, paid particular attention to the effects of water, and
of saline solutions on the normal current. Neither of these
authors explicitly distinguishes the physical imbibition current,
which must evidently have been a considerable, if not the chief

VIII.]

CONCENTRATION CURRENTS

139

or sole efficient cause of the effects. If you refer to the detailed
accounts given by Engelmann,* and by Biedermann,f you will

Concentrate
A

t

DiUube
B

Zn

.'.Current

Cl> '

..'.Current

»- 69

.-66

OH"

..'.Current

A/ci+
CL ~

..'.Current

K +

CH^.CO.O.
.'.Current >

FlG. 55. — To illustrate concentration currents. The thin arrows indicate direction
of ions from concentrated to dilute side of an electrolyte. The thick arrow in each
case indicates the resultant current — from dilute to concentrated where the anionic
is higher than the kationic velocity ; from concentrated to dilute where the kationic
is higher than the anionic velocity. (The relative ionic velocities are indicated by
the numbers at the arrow-heads.)

N.B. — With the kation travelling from left to right, there is current from
left to right, and vice versa.

With the anion travelling from left to right, there is current from right to
left, and vice versa.

find that a large ingoing effect was generally produced by water
or weak saline, a large outgoing effect by strong saline. The

* Engelmann, P. A., vi., p. 1 10.

t Biedermann, ElektropJiysiologic, p. 401.

140 THE SIGNS OF LIFE [LECT.

former is such as would be produced by an ingoing current of
water through the skin, the latter by an outgoing current of
water. The effects appear to be similar in character to those
more recently pointed out by MacDonald, as regards the
injury current of nerve — which he considers as being essentially
a concentration current — viz., augmentation by water or by
dilute salt solution, diminution or abolition by strong salt
solution.

§ 82. A limitation. — While it is perfectly true that blaze is
a sign of life, it is equally true that many assuredly living things
do not blaze. But at this stage, without a fuller and more
exhaustive examination of all sorts and conditions of living
matter, it would be hazardous to propound any absolute and
unrestricted negation. In the more familiar case of the evolution
of CO2, we know that the phenomenon is a sign of life ; but we
also know that many assuredly living things do not demonstrably
discharge CO2, and that the same living things may comport
themselves very differently under different conditions. The low
resistance of organs like the liver and kidney, the absence of a
definite membrane between our electrodes enabling living cells
to exercise the osmotic pressure that underlies ionic transfer,
are conditions obviously unfavourable to the delivery of blaze-
currents into an external circuit.

Many assuredly living things have not, to such examination
as we have as yet made, manifested the clear and typical effects
familiar to us in the case of the eye, and the skin and vegetable
tissues. Muscle and nerves give comparatively small effects,
and I have even failed to obtain any trace of response — under
similar conditions of experiment — from the recently excised
organ of torpedo which a few moments before, in the animal
itself, gave me the well-known thrill characteristic of the dis-
charge. I have witnessed well-marked effects in frog's spawn
at one time, and have failed to obtain any effect at all in other
spawn at a different stage of development. I do not conclude
from this that blaze is not a sign of life ; indeed, I should be
reluctant, without further and closer examination — by the ABC
method, and with shortest possible transfer time — to state abso-

viii.] A LIMITATION 141

lutely that any given object exhibits no blaze at all. The
internal organs certainly do not blaze like the skin, or even like
nerve, the failure is in itself of interest, and the cause of differ-
ence matter for investigation, and we shall have to learn what is
the determinant factor between a living tissue that manifests
blaze, and another living tissue that does not. Durig thinks
that the effect is peculiar to epithelial tissues, and it is certainly
the case that epithelial tissues do give it better than other
tissues — witness the case of the crystalline lens. But I do
not think it is confined to epithelia, for it occurs in muscle,
and in vegetable tissues which can scarcely be classed as
epithelial.

I am unwilling to express any opinion at all. I have
witnessed it in muscle ; witnessed it in some frog's spawn,
and failed to witness it in other frog's spawn. Does it depend
upon some regular orientation of cells? Is their regular
arrangement on a basement membrane a favouring condition
of things? What part do membranes play in the effect?
These are questions all of which I must leave unanswered
now.

In two successive years I took occasion to examine seaweeds,
with the object of comparing their reactions with those of land
plants. To my considerable surprise, they gave little or no
reaction, and I left the seaside on the first occasion without
having been able to satisfy myself of the physiological nature of
such small reactions as were occasionally witnessed. The " weeds "
— obtained in the Channel Islands in an obviously living state
during the month of August — always gave small antidrome
after-currents at both poles to single shocks as if by ordinary
polarisation. But the effects were abolished by boiling. This
was a puzzle, and I cannot yet explain it. The elements of
the problem are : deflections antidrome throughout, therefore
apparently ordinary polarisation ; but abolished by boiling,
therefore apparently of a physiological character.

Pieces of apple gave a similar puzzle, viz., antidrome effects
abolished by boiling, and it is possible in such cases that we
have to do with a mere physical effect of altered structure or
altered composition, possessing no physiological significance.

142 THE SIGNS OF LIFE [LECT.

On the second occasion after several trials with negative
results, I excited the cupidity of my children by the offer of
a reward for a blazing seaweed, and was myself rewarded by
their discovery of a long, narrow seaweed, called " boot laces "
by the fishermen — chorda filuin by its museum name — that
gave typical homodrome effects of more than 0.02 volt to both
directions of excitation, and therefore saved me from saying
that sea-plants unlike land-plants do not blaze. The difference
between the two kinds of vegetable is indeed very marked, but
it is one of degree rather than of kind, and one of the chief
conditions of the difference is that the former are bad and the
latter good conductors. Evidently, if the resistance of the
inactive stuff between our electrodes is so low as to afford
great internal shunting, an electromotive change, unless very
large, will not give much current to a high resistance galvano-
meter.

The common animals of the sea shore — limpets, anemones,
jelly-fish, etc. — afforded little or no response to the usual test of
single and of tetanising induction shocks. The eyes and the
muscles of crabs and lobsters, the eyes and the skin of fishes
(whiting, sand eel), gave very well-marked effects.

But we should not hastily conclude that the absence or
smallness of blaze-currents depends on conductivity alone.
Absence of blaze depends, also, I think, upon the relatively
small amount of active living electromotive stuff in the mass
of indifferent stuff that is its habitation. Low-class living
matter, pervaded and diluted by the medium in which it
lives, cannot be expected to exhibit any very intense sign
of life ; we do not expect it to blaze much. The mass of a
jelly-fish or of a seaweed is in chief part sea-water ; its living
stuff has not the power to emancipate itself from the external
medium, nor to create an internal medium, different and distinct
from the general environment. It is practically isotonic with
sea-water ; its freezing point, and that of sea-water, are both
about —2°. Like sea- water, it contains over 3 per cent, of salts,
and its conductivity is at least fifty-fold that of land-plants.
This no doubt is an unfavourable condition to the production
as well as to the manifestation of a local alteration of potential.

vm.J INJURY CURRENT AND BLAZE-CURRENT 143

But we may hardly proceed further on these lines of
argument without further information concerning the exact
freezing points and the relative conductivities of various animal
and vegetable tissues, and to obtain such information means
engaging in a new investigation, for which new methods have to
be elaborated.

§ 83. A question. — It has probably occurred to some of us to
ask what relation, if any, exists between the normal current and
a blaze-current. Is not the normal current itself a sign of life,
and in certain cases of obviously identical nature with a blaze ?

To some extent these questions have been incidentally
answered in previous lectures, but not formally and explicitly.

Indeed it is difficult to frame a formal and explicit answer,
and I should prefer to avoid giving such an answer otherwise
than with much reservation. For the facts of the case are by
no means as clear as they seem to be at first sight. As regards
the first question, we can make, with about equal probability,
the two apparently contradictory statements that in some cases
there is an evident relation between normal and blaze-currents,
in other cases there is evidently no relation at all between the
two currents. And on reflection it will appear that our first
question should logically be preceded by our second as to
whether normal current is or is not a sign of life, which amounts
to asking what view we take of the nature of normal currents.

Now, I think you may take as granted that normal current
is always injury current or excitation current ; but I do not
think you may take as granted that injury current is always
excitation current.

The question of the nature of injury current has largely
turned of late years upon the demarcation current of medul-
lated nerve ; in opposition to the view of Gotch, who assumes
that this current is wholly an excitation current, MacDonald
urges that it is a concentration current dependent upon the
electrolytes of nerve. He regards nerve as a concentration cell
in which the sheath is the dilute solution (= 0.9 per cent. KC1),
the axis-cylinder the concentrated solution (== 10 per cent. KC1),
and the current determined by the physico-physiological state

144 THE SIGNS OF LIFE [LECT.

of a membrane between sheath and axis. It would lead us too
far to discuss this theory in all its details. My own opinion of
the matter is that MacDonald has sufficiently proved the reality
of the concentration currents of nerve by the annulling effects of
strong salt solutions and by the recuperative effects of weak
salt solutions, but that he has not disproved the irritative factor.
I think both factors are concerned in the current, and if called
upon to put a figure upon their value, should guess that in a
fresh demarcation current of say 0.05 volt something like 0.04
is by concentration, and o.oi, or less, by irritation.

To return to the first question, stated at the outset of this
paragraph, I should tentatively answer that, in so far as an
" injury current " is irritation current, blaze-current bears relation
to it, but that in the absence of irritation current, or in so far
as " injury current " is of mere physical origin, blaze-current is
quite an independent phenomenon.

I think that, on this view, we may now reconcile with each
other these several facts, of which the first three are affirmative
as regards a relation between blaze-current and injury current,
the last negative.

1st. That a blaze-current is in general antidrome to an
injury current.

2nd. That it is always antidrome to a previous (maximal)
blaze-current.

3rd. That a (polarising) constant current favours homodrome
and disfavours antidrome blaze-current.

4th. That in some cases blaze-current may be homodrome
with injury current.

5th. That in many cases — eyeball, skin, and electrical organ —
there is no discernible relation between the direction and mag-
nitude of normal current and of blaze-current.

The fact that a blaze-current, antidrome to an injury current,
is aroused by both directions of excitation, proves of itself, what
is more clearly proved by the ABC method, viz., that the
response may be post-kathodic as well as post-anodic, or, in
Biedermann's phrase, negative-kathodic as well as positive-
anodic. In either case it is the analogue of the " negative
variation " of a demarcation current of muscle or of nerve, where

viii.] INJURY CURRENT AND BLAZE-CURRENT 145

it is known to us as a transmitted excitatory effect, whereas
the " blaze " is a direct excitatory effect.

The fact that a blaze-current homodrome with its exciting
current, is obtained between two uninjured and iso-electric points,
signifies that in general the post-anodic homodrome is greater
than the post-kathodic antidrome current. There is an ex-
citatory state at both poles, greater at anode than at kathode,
and if the excitation be reversed, there is as before a homodrome
effect, but reversed with the reversal of excitation. If, before
applying the second stimulus, we shift one of the electrodes
that have served for the first stimulus and blaze, to a fresh spot
(or, better, if by the ABC plan we transfer the A or B con-
nections to a third indifferent point C), we shall find (on muscle,
on vegetables) that both A and B — i.e., post-kathodic and post-
anodic points — are zincative (electro-positive) to C. And if, now,
having compensated, we stimulate in either direction through
these points A C or B C, i.e., through one active point A or B,
and one passive point C, we shall arouse blaze in the tissue from
C to A or B. The first excitation has given blaze of A and B,
which are zincative (electro-positive) to C. The second excita-
tion has given a second blaze of either A or B, which is opposed
and greatly exceeded by the first blaze of the previously un-
touched C. We may regard the first current from A or B to C
as an injury current, and the second current from C to A or B
as its negative variation.

So that in sum total we assimilate, as belonging to one class,
what has been variously designated blaze-current, injury current
(in so far as it is an irritation current), and action current. The
fact that a blaze-current is augmented where it occurs in the
same direction as a polarising current, is essentially similar with
the phenomenon known to you in nerve-physiology as the
polarisation increment. In the latter case, an active state sweep-
ing wave-like along a nerve undergoes a sudden increment on
reaching an anodic region, and the polarising current is in-
creased ; the anodic region, in which action is lowered, is
capable of great increase of action when it is aroused by the
transmitted excitation. It is more " zincable." In our case,
also, the anodic region of a polarising current is more " zincable,"

K

146 THE SIGNS OF LIFE [LEct.

i.e., more capable of that electro-positive change which is the
essential factor of a blaze-current, and is aroused to action by
the direct stimulus of an induction shock whatever its direction.

§ 84. Solution-pressure. — I will bring these lectures to a
conclusion with certain theoretical views to which slight allusion
was made in the first lecture (p. 16).

I there attempted to account in some measure for the use of
the term " zincative," and promised, when an opportunity should
present itself, to formulate on similar lines a view of the
mechanism of excitatory phenomena in general.

You are familiar with the idea that active tissue gives off
electro-positive ions to its lymph bath, that in the tissue itself
there is current of action from active to resting spot, that active
tissue is zincative. You also know that in the electrical excita-
tion of nerve and of muscle, the effective pole is the kathode,
when current is made, the anode when current is broken. And
you know that while a constant current is passing there is
augmented excitability by the kathode, diminished excitability
by the anode.

I take the case of medullated nerve, since the results are
typical. Moreover, its coarse structure of central core as the
essential part and surrounding sheath as the accessory part,
which is a familiar image in everyone's mind, will help us to
form a clear picture of what can be imagined as the actual
movements of ions between any core of living stuff and any
surrounding medium. (A word of warning, however — this is only
a coarse picture, there is no doubt a peculiar commerce of ions
between axis-cylinder and medullary sheath of a nerve-fibre,
but there is probably a further and more refined commerce
of ions between fibrils and fluid within the axis-cylinder
itself.)

Consider then a core of living stuff, bring it in contact with
an electrode, and let the latter be suddenly made kathodic by
closure of a contact key in the circuit. The core of living stuff
has been aroused to action. What have been the movements of
ions when the electrode was made kathodic ?

Clearly, there must have been movement of kations towards

viii.] SOLUTION-PRESSURE 147

the kathode, of anions from the kathode — viz., attraction of the
former, repulsion of the latter, as regards the surface of separa-
tion between core and bath.

The attraction of the kation to the surface of the core is in
this view of the matter to be regarded as the essential factor of
excitation (and of increased excitability), inasmuch as such
attraction is equivalent to an increased " solution-pressure " of
kations. The living core, under the influence of the kathode, is
rendered more active and discharges into the surrounding
solution a greater number of electro-positive ions since the
pressure-difference of such ions in the core and in the solution is
increased. As mentioned in a previous lecture, this is the state
of things that I conceive to exist when I make use of the
expression that active (or excited) living matter is " zincative "
to resting living matter. I imagine " current of action " as
being conditioned by the discharge from active stuff of free
kations, and I choose zinc by name as the representative kation.
But, you say perhaps, why have you specified the kation
rather than the anion as the effective agent in the produc-
tion of an action current ? Is not current from an excited to
an unexcited spot accounted for by a transport of negative
electricity by anions towards an excited spot, as well as by
a transport of positive electricity by kations away from an
excited spot ?

Or again, you definitely object that it is wrong to think
of kations as travelling against current, or anions with current.
To the second of these possible objections in your mind, I
answer at once that we are not considering simple passage of
the exciting current through the electrolyte, but the excited
current arising at the exciting pole of the former — viz., at the
kathode. And, if you are in any doubt about this kathodic
action current produced during the passage of the exciting
current, perhaps you had better consider on similar lines the
post-anodic action current that is witnessed after an exciting
current has been stopped. In this case we clearly have to do
with a sudden release of kationic pressure, as the repellant
influence of the anode terminates.

To the first point — I have to offer you at least two consider-

148 THE SIGNS OF LIFE [LECT.

ations in support of my choice of the kation rather than the
anion as the principal carrier in the case of an action current.

We have regarded the tension and solution-pressure of
metallic, basic, positive sign as increased at the surface of the
living core under the influence of the negative pole.

Under this same influence we should also have a decreased
tension and solution pressure of non-metallic, acidic, negative

sign.

This second mode of transport seems to me to imply neces-
sarily the diminution of a pre-existing state of difference ;
whereas the kationic nature of an action current does not
necessarily imply any pre-existing state of difference. No
doubt, as a rule, all living matter is at least sub-active at low
pressure within its internal medium, the lymph. But that is
" pre-existing difference " of very different order to a pre-
existing difference great enough to permit of the great diminu-
tions of difference that should be caused by great augmentation
of activity and of pressure.

On these general grounds, therefore, without wholly dis-
regarding the possibilities of anionic transport, I have chosen
to consider action currents as effected by kationic transport from
the seat of action rather than by anionic transport towards the
seat of action. And I say again on these grounds, as well as
for reasons given in a previous lecture, that active living matter
is zincative.

One further reason for this preference of the kationic to the
anionic view of action currents (vegetable as well as animal, I
may remark) may be briefly mentioned now, in anticipation of
evidence that I hope to more fully place before you at some
future occasion.

You know that, according to modern theory, the molecules of
a neutral salt, such as, e.g., NaCl in aqueous solution, exist not
solely as non-electrical molecules of NaCl, but also (and in dilute
solutions chiefly) as charged ions Na+ and Cl - . In, e.g., what
we ordinarily call " normal saline " in the laboratory, made up
to contain TV grammolecule per litre of water, i.e., 5.84 grammes
per litre, ^j- of the amount of salt is present in the dissociated or
ionised state as Na+ and Cl - , and the only uniting force

VIII

.] SOLUTION-PRESSURE 149

between these dissociated ions is the mutual attraction of their
-f- and charges. Chlorides, bromides, and iodides, etc., of
sodium, potassium, and ammonium, etc., in dilute solution — and
decimolecular solutions such as we find it convenient to use in
the physiological laboratory are in this connection " dilute "
exist in this active state of ionisation as positively charged
kations and negatively charged anions. I said this active state
of ionisation, since it is to this state of ionisation that their chief
chemical and physical actions are due, and among these actions
no doubt we must reckon their action upon living matter.

Now, if we take a number of salts, such as those just named,
in dilute equimolecular (or, better, in isosmotic) solution,
and systematically compare their respective effects upon some
convenient physiological reaction of living matter, we shall find
that differences of the kation produce far greater differences of
reaction than do differences of the anion.

I do not pretend that this is in itself any proof that action
and action currents are essentially characterised by increased
solution-pressure and actual discharge into solution of electro-
positive ions. But I think we may provisionally conclude that
in the action of dilute saline solutions upon living matter, it is
the electro-positive kation that takes the lead, acting presum-
ably in the sense that we should anticipate, viz., increasing the
kationic pressure of the lymph bath, and decreasing, therefore,
the difference between that pressure and the kationic solution-
pressure of the living matter.

The state of things under the influence of the anode must be
regarded as the converse to that just pictured as obtaining under
that of the kathode. Anions are attracted, kations are repelled ;
the solution-pressure of the latter must be lowered, and the sur-
face of living matter must be rendered less zincative, less easily
made to discharge kations ; and, if forced to such discharge by
adequate excitation, manifesting greater effect than when the
initial pressure was higher.

The post-anodic action current, which makes its appearance
at the moment of cessation of an exciting (or polarising)
current, is very easily accounted for. The kationic solution-
pressure, depressed under the influence of the anode, is suddenly

150 THE SIGNS OF LIFE [LECT. vin.

released when that influence is removed, and manifests itself in
a kationic discharge from the previously anodic surface. Thus
we have a post-anodic action current which is of the same direc-
tion as that of the previous (polarising) current.

Blaze-currents — of which such frequent mention has been
made in these lectures — are an effect of local intensifications of
electrolytic solution-pressure — of kationic pressure when their
direction is from the excited spot ; of anionic pressure when
their direction is towards the excited spot.

This is hypothesis which, whether or no it " explains " all
the known facts, at least neither contradicts nor obscures them ;
it seems to me to bring them under a common denomination,
and to invite us to their further investigation. Hypothesis is
the mother of experiment.

REFERENCES

ENGELMANN. — "Ueber das Vorkommen und die Innervation von con-
tractilen Driisenzellen in der Froschhaut," P finger's Archiv, iv., p. i,
1871.

ENGELMANN. — "Ueber die electromotorischen Krafte der Froschhaut,
ihren Sitz und ihre Bedentung fiir die Secretion," PfliigeSs Archiv,
iv., p. 321, 1871.

ENGELMANN. — "Die Hautdriisen des Frosches," Pfliiger's Archiv, v.,
p. 498, 1872, and vi., p. 97, 1872.

MACDONALD. — "The Injury Current of Nerve," Thompson Yates Labora-
tories Report, vol. iv., part ii., 1902.

BIEDERMANN. — Elektrophysiologie, Jena, 1895 ("Action of Water and of
Saline Solutions on Mucosa Currents," p. 401.)

LOEB. — " Physiologische Untersuchungen tieber lonenwirkungen," PfliigeSs
Archiv, Ixix., p. i, 1898, and Ixxi., p. 457.

APPENDIX

The Normal Circuit — Galvanometer, Coil, Compensator, Electrodes, and Keyboard —
Photographic Recording — Lippmann's Capillary Electrometer — Special Keys —
Units of Resistance and of Conductance.

IN a physiological laboratory the galvanometer may be used either
for special electro-physiological research, or in the course of research
work where electro-physiology is of secondary interest — the galvano-
meter playing the part of a balance, to indicate physico-chemical
differences between any two different points.

The following remarks are more especially directed to meet this
latter case. The galvanometer may be looked upon either as a
manometer, measuring electrical pressures just as one measures
blood-pressure, or as a chemical balance, by means of which one
can compare numerically the energy values of physiological pheno-
mena capable of an electrical expression. In many cases it will be
found convenient, or even necessary, to record the indications of
the galvanometer photographically.

The requisite apparatus consist of: (I) the galvanometer; (II)
the compensator ; to these must be added various accessories ; (III)
the exciting apparatus ; (IV) the electrodes ; and (V) the keyboard,
by means of which the constituent pieces of apparatus will be con-
nected together to form what may be termed the normal circuit.
(The arrangement for taking photographic records is a further
accessory described below, p. 156.)

The galvanometer. — The style of instrument matters very little
so long as its sensibility can easily be ascertained and adjusted.

The delicacy of the galvanometer should be such that o.ooi volt
through a megohm gives a deflection of 10 cms. at a distance of
2 metres. Thus a deflection of i cm. corresponds in such a circuit
to a current of xo"10 ampere,

152

THE SIGNS OF LIFE

It is advisable to fit up a galvanometer once and for all in one
particular place. The best position for the instrument, and one
in which it will always be ready to work, is either a recess or small
cupboard built in the thickness of a perfectly firm wall. Failing
this, a firm bracket or shelf, not connected with the floor, is sufficient.

Whether the instrument is being used for purposes of demonstra-
tion or for actual measurement, the objective method must be used.
This consists in the projection of a beam of light either on to a trans-
parent and graduated scale or upon a photographic plate. The most

FlG. 56. — Normal circuit described in the text. (The secondary coil is
figured as if for direct excitation of a given object, IV. Obviously, if we
have to apply indirect excitation, the wires are removed from the keyboard,
and the plug hole is filled to complete the keyboard circuit.)

convenient light for either purpose is the image of the filament of an
incandescent lamp. When photographic records are required, it is
very desirable, indeed almost indispensable, to work with two galvano-
meters in series, one for purposes of observation, the other as record-
ing instrument.

Calibration of the galvanometer, and choice of a convenient scale.

-The deviations of the same galvanometer have not always a

constant value, seeing that the resistance of the circuit varies

according to the resistance of the object under examination and

of the unpolarisable electrodes.

The quickest way to calibrate a galvanometer is to observe or
photograph the deflection of the spot when a current of known

APPENDIX

153

voltage from the compensator is allowed to flow in the circuit, which
must be of known resistance (Fig. 59)- It is convenient to use a
carbon megohm for calibration (vide infra p. 169).

In those cases where an alteration of resistance actually occurs
during the course of the experiment, the value of the standard voltage
must be taken before and after.

Note, — In early trial experiments the deflections obtained will
probably be too large to be kept well within the scale limits. The
best way to obtain a readable deflection is to shunt the galvano-
meter, thus sending only a convenient fraction of the total current
through the instrument.

The compensator or potentiometer is a means (i) of supplying a
standard voltage, and (2) of compensating and so measuring P.D.
currents derived from the object under examination. Further, the
compensating current affords the quickest means of verifying the
integrity of the general circuit and of the galvanometer.

In its simplest, and for all ordinary purposes, sufficiently accurate
form, the compensating arrangement consists of a Leclanche cell,

FlG. 57. — To illustrate the principle on which a compensator
is constructed ; with a battery of I volt, R — 1000 ohms and ;• — I
ohm, the P.D. at the ends + and - would be approximately -5-^7;
volt; the same P.D. would obtain with a battery of 1.4 volt and
R = 1400 ohms. Compensation is established by varying r.

joined up with two resistance-boxes, which act as numerator and
denominator of any convenient fraction of a volt.

Taking the voltage of the cell as 1.4, and the resistance (R) of
the denominator to be 14,000 ohms, than the resistance (r) of the
numerator reckoned in ohms will give a voltage in ten-thousandths
at the electrodes — e.g., if r—io ohms, the voltage obtained — .001 ;
if r — i oo, voltage = .o i ,

154

THE SIGNS OF LIFE

Note. — Obviously this yields only approximate results, since the
voltage of a Leclanche is never quite 1.4 volt, and the fraction

of the voltage taken is not - but

Further, the internal

R + r.

resistance of the cell is not taken into account. The method is,
however, sufficiently accurate, seeing that the principal error is
a constant one and the variable error is negligible.

In actual experiments it is advisable to have a standard com-
pensator which will give values of .01, .001, .0001 volt, independently
of the compensator proper.

90 14100

FlG. 57 A. Compensator to deliver nrihnrth, nsVijth, or
volt from a Leclanche cell (of 1.42 volt).

oth of a

The comparison between experimental deflections and the
standard deflection of known external voltage is not calculated
to give the absolute value of internal E.M.F. of active tissue. The
external circuit and galvanometer receive only a fraction of the
total internal electromotive difference, which produces current
partly through the internal conducting tissues, partly through the
external (galvanometric) arc. Moreover, the time- relations of
physiological action are generally such that internal effects of
brief duration produce small external effects that cannot be
standardised by a prolonged external voltage.

Thus, e.g., a nervous impulse with a duration of say 0.005 sec.
might, on a given instrument, produce the same deflection as a
constant current from an E.M.F. of o.ooi volt, but this would
not indicate electromotive value of the nervous impulse. A closer
approximation would be arrived at by making the comparison with

APPENDIX 155

an external voltage effective for only 0.005 sec. ; in this manner
Gotch and Burch have assigned 0.03 volt as the electromotive value
of a single nervous impulse. And this is not yet a true value, by
reason of the internal derivation alluded to above.

The principal object of a standard voltage at the commence-
ment and termination of experiment is (i) to indicate that the
resistance has or has not sensibly altered during experiment ; and
(2) to indicate the sensibility of instruments employed. It does
not afford in itself satisfactory data for a comparison between
electromotive values of response of different tissues, and it is only
with reservation (i.e., after control of altered resistance and altered
duration of action) that it can be utilised for the detection and
estimation of altered electromotive values during any one obser-
vation.

Bearing these reservations in mind, we may, however, be
allowed to speak of the " voltage " of an injury current as
"measured" by that of a compensation current,* and to indicate
by reference to standard deflections the scale of voltage in which
blaze-currents are externally manifested.

The exciting apparatus. — In the great proportion of experiments
the du Bois-Reymond induction coil (Berne model) is used. This
coil has its graduation in arithmetical progression.

In those experiments where it is necessary to estimate the
quantity or energy of the discharge, a condenser must be used.
In either case there are two possible methods of excitation : —
(i) the excitation is sent through object and galvanometer in
series, and (2) the galvanometer is short-circuited during excita-
tion, and put into circuit after a given short interval of time.

Electrodes. — It is absolutely essential that the electrodes should
be unpolarisable. Du Bois - Reymond's combination (zinc and
sulphate of zinc) has, in my experience, given better electrodes
than those recently introduced — e.g., silver and silver chloride,
or mercury and calomel.

Keyboard. — In the constant use of a galvanometer as a measuring
instrument, the circuit should be set up in such a manner that the
direction of exciting and reaction currents may be quickly determined.

' The instrument by which this is done 5s a compensator ; it is not strictly speaking
a potentiometer \

156 THE SIGNS OF LIFE

The simplest way of obtaining this arrangement is to have a
keyboard with several pairs of terminals, to which are connected
the various parts of apparatus, making up what has already been
called the normal circuit. Each particular piece of apparatus is
controlled by a plug, opening or closing the interval between the
two terminals to which each pair of wires is connected. Two
commutators, one in the exciting circuit and the other in the
compensator circuit, allow the current to be sent in the direction
desired. An ordinary key interrupts the principal circuit of the
compensator.

Note. — It much simplifies matters to arrange the circuit
permanently, or at least at the beginning of each experiment, so
that a positive or negative current may be in conventional
directions, i.e., positive to the right and negative to the left.
The quickest way of determining the direction of a current is
to touch ,one of the terminals with a piece of metal (e.g., zinc)
held in one hand, while a finger of the other hand makes contact
with the other terminal. The terminal touched by the zinc " pulls "
through the galvanometer, and if the previous deflection has been
in the same or in the opposite direction, we know that the spot
in connection with the same terminal was then zincative or counter-
zincative, i.e., electro-positive or electro-negative.

Photogaphic recording.— If necessary, it is possible to photograph
and to take readings at one and the same time. To this end the
transparent scale must be replaced by a vertical opaque screen,
with a narrow horizontal slit, behind which a photographic plate
is let down by clockwork.

The use of two galvanometers in series so simplifies matters,
however, that it is preferable to use a second instrument for taking
graphic records. One of the galvanometers stands in the laboratory,
with its transparent scale in front of the observer, while the second
is some distance away in a dark (and non-vibrating) room. The
former exhibits and the latter registers the currents under obser-
vation.

The graduation of the recording galvanometer should be to a
smaller scale than that of the indicating galvanometer. A con-
venient relation between the two scales is I to 10, so that each
centimetre deflection of the indicator is represented by a millimetre
on the recorder, The relation is, if necessary, adjusted by shunting

APPENDIX

157

one or other of the two galvanometers ; and once established, we
may, if desired further, shunt both galvanometers, so as to reduce
both deflections in the same proportion. For this reduction, the
common shunt is to be connected with the terminals on each side
of plug No. i.

,SL

FlG. 58. — Galvanograph.

The most convenient arrangement of the two galvanometers is
shown in Fig. 58, in which Gx is the indicator and G2 the recorder,
The two galvanometers are controlled simultaneously by plug No. i,
separately and individually by plugs No. 5 and 6 of a secondary key-
board. We are therefore able to adjust compensation and make
any necessary preliminary adjustments with the photographing
galvanometer short-circuited at No. 6, and therefore undisturbed
by manipulations in the remainder of circuit, where we are guided
by the indicating galvanometer. For an observation of any duration,
both galvanometers are in circuit and simultaneously controlled by
plug No. i, and the general progress of a record on G2 in the dark
room, can be followed on the scale of G: placed in front of the work-
table.

The accessory apparatus, containing the sensitive plate, consists
in a box, -| metre in height, which carries the scale, and the horizontal
slit, \ mm. in width, upon its anterior surface. The plate, which is

158

THE SIGNS OF LIFE

FIG. 59. — Photographic record of the galvanometric deflections
in + and - directions, caused by (approximate) voltages of o.oi,
0.02, 0.03, 0.04, and again 0.03, through a circuit of (approximately)
one Megohm ( = 1000000 ohms).

. -

LL

^

„

ww

u-iai

tat

mMa

••

•m

cm

L4u

•JU

i-4-H

n^

O
0
Q

2,OOO

0

o

0

"J

o
o
o
T

o
o
o
ff

o
o
o
>o"

o

I

O
O

§

o

o
o
of

o
o
o

Cf

FlG. 60. — Photographic record of the deflections caused by
break induction shocks of a Berne coil. Two trials at each strength.

APPENDIX

159

in a photographic carrier suspended by a thread from a wheel revolv-
ing by clockwork, descends vertically. The deflections of the
galvanometer spot are recorded laterally upon the line of the
horizontal slit. An electric bell gives warning when the plate has
completed its descent. If necessary, a chronograph, and a signal
to mark the beginning and close of excitation, are easily added
when required.

Before. During. After.

•looo voit.

FiG. 61. — Response of an oxydised copper plate, illuminated
for seven seconds at one minute intervals. A prolonged illumination
was made in the middle of the series to see whether any sign of ex-
penditure would be elicited. (The first deflection by T^ volt
turned into circuit exhibits signs of ordinary polarisation.)

Before. ILLumln.

After.

FiG. 62. — Similar observation on a chlorinated silver plate. In
consequence of prolonged illumination there is well-marked evidence
of alteration.

Speed of registration. — By reason of the inertia of the suspended
magnets and mirror of the galvanometer, we must content ourselves
with registering phenomena that are, comparatively speaking, pro-
longed, or repeated at regular intervals. The method is not adapted
to record phenomena that require a speed of recording surface
greater than 5 mm. per second. It is best adapted to the recording
of phenomena of long duration, or to reactions that are repeated

160

THE SIGNS OF LIFE

at regular intervals. In this class of observations, a speed of 2^ to
5 mm. per minute is usually sufficient. The " lost time " of nerve-
skin reaction is a good instance of a phenomenon fitted for the
galvanometric record, e.g., Figs. 28 and 43.

It is convenient to adopt a standard size of recording plate ; the
"quarter plate" in England, and the 9 by 12 on the Continent,
answer all ordinary purposes. These dimensions enable us to
record a series of deflections with an amplitude varying from
i to 5 cm., and a length of at least 10 cm. The speeds named

FlG. 63. — Galvanograph and Railway Myograph.

give records lasting 40 and 20 minutes ; 5 mm. per second gives
a 20 seconds record. For speeds above 5 mm. per second a record-
ing electrometer should be used.

Simultaneous records. — In certain cases it is desirable to obtain
the simultaneous record of a series of electrical reactions and of the
corresponding series of muscular contractions.

For this purpose, a truck carrying a smoked plate, and con-
nected with the suspended carrier that holds the photographic
plate, is added to the apparatus. The thread by which the carrier
is suspended passes round the axis of the motor and over two small
pulleys, and is fastened to the carrier of the smoked plate,

APPENDIX

161

which accordingly moves in a horizontal direction, corresponding
with the vertical descent of the sensitive plate. In this manner a
simultaneous record may be obtained, e.g., of a series of muscular
contractions along with the negative variations of the muscle -
current ; or, again, of contraction and heat (by means of a thermo-
galvanometer) ; or of the contractions of a muscle and the negative
variations of its nerve ; etc., etc.

LARGE DARK ROOM

W/////////S

FIG. 64.

In the Physiological Laboratory of the University of London
the apparatus described above is disposed according to the following
plan, so as to afford two complete working tables with two pairs of
galvanometers and accessory apparatus : —

The galvanometers Gl to G5 are placed on brackets along one

162 THE SIGNS OF LIFE

side of the general laboratory as figured. (The extra galvanometer,
G3 is a separate low-resistance instrument, for use with either table,
to give thermo-electric readings of temperature ; it is worked by a
constantan-iron junction, the varying E.M.F. of which is balanced
by compensation ; the compensator is graduated so that a known
length has a known temperature value.)

Each pair of galvanometers, Gl and G2, G4 and G5 is intended to
be used as described above ; for ordinary work, only the observation
galvanometer G2, or G4, is used ; when a phenomenon deserving to
be recorded presents itself, the recording galvanometer Gp or G5, is
unplugged, and the recording surface is set in motion.

The apparatus is thus utilised in the general laboratory without
suffering any disturbance from other work in progress in the same
room.

Lippmami's Capillary Electrometer, like the galvanometer, can
be used (i) as a refined instrument of research for the special
purposes of electro-physiology, in which case its photographed
indications must be mathematically analysed ; or (2) as an ordinary
laboratory instrument for the summary inspection and the con-
venient demonstration of electrical changes that are too brief or
in too rapid succession to be readable by galvanometer — e.g., the
electrical changes accompanying the beat of the heart. By means
of very simple recording apparatus, the value of the electrometer
as an ordinary instrument of inspection and demonstration is greatly
enhanced. In this laboratory a capillary electrometer is currently
xised in place of a demonstrating galvanometer. The image of
the capillary in the projection microscope, with J to ^ objective,
is first thrown upon a transparent screen, where the movements
of the column of mercury are shown. An opaque screen with a
narrow vertical slit, behind which a vertical photographic plate
travels horizontally, is then placed on the lecture-table, so as to
receive the image of the moving column of mercury, which is thus
photographed. And lastly, the developed photograph is exhibited
in the ordinary projection-lantern. Thus the record of move-
ments that have just been seen, is exhibited and examined. In
this manner there is no difficulty in demonstrating in the course
of a quarter of an hour ist, the electroscopic indications of, e.g.,
a frog's heart ; 2nd, the photographed records of such indications.

The diameter of the capillary column of mercury is, e.g., 25 ft.

APPENDIX

163

b *•£«> 3 o °^S °^

S»«agflo« r.* ^s

-
CD p

- '"*3

<D £ WJ3

c3 So-+-*55_5

^S^^^O^; ^^"o

b^Ii^i^

^^^ °-S • r-'P <»E , CT1® *

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u^ .2-2S5'2"lo.S=« M **

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& o is s i,* <D a ^ 3 !

^•^ S-z ., a^ S'x'S'

164

THE SIGNS OF LIFE

On the screen, at a distance of 8 to 12 feet the magnification of
the image given by the -^Q inch objective is 1000 to 1500 diameters,
z'.£., the column has an apparent diameter of 25 to 37.5 mm. — an
inch to an inch and a half. On the photographic plate, at a
distance of 2 feet, the apparent diameter is upwards of 6 mm.—
far more than is sufficient to certainly cover the vertical slit, the
breadth of which is less than | mm. For the frog's heart, a lower
magnification is generally sufficient. For the human heart, as
high a magnification as practicable should be employed.

o Sec. -I -z --5 -4- -5 -6 -7

miiiivoit
0-5

i

rl —

i

i

i

Left hand

1

Co H^SO^

i

i

X

1

C-5\

\ I

\ I

\ I

S/

kb ha.nd
to H\

I-O\

/•51

FlG. 66. — An electrometer-curve of the electrical variation of the human heart ;
the values calculated from the record of the mercury level are given as a dotted line.
(From Einthoven, Pfliiger's Archni, vol. 60, 1895.)

The principle upon which electrometer values are obtained from
such electroscopic records is readily illustrated by demonstrating the

APPENDIX

105

excursions and records caused by different voltages acting for equal
times, and by a given voltage acting for different times.

The voltage actually indicated by any given curve or portion of
a curve is most readily ascertained by superposing the record upon
the record of a "normal curve," z>., of the curve described by a
known constant P.D. taken under similar conditions. The two
plates are slipped over each other, with abscissae kept parallel until
portions of the curve under examination coincide with portions of
the normal curve' at known voltage. Such coinciding parts are
equipotential, so that the value on the normal curve gives the value
on the curve under inspection.

For the more minute analysis of electrometric curves, the student
should consult the papers of Burch, Einthoven, and Garten. In
many instances the calculated curve appears very different from the
original record of the curve described by the mercury column, e.g.,
Fig. 66.

FlG. 67. — The primary circuit of the inductorium is completed through the pools
pp. The galvanometer is short-circuited through the other pair of pools G G. The
level of mercury in the lateral pool, and the length of the semicircular wirep, are
adjusted so that circuit is completed at G G (i.e., the galvanometer is short-circuited)
before circuit is completed at pp. On releasing the commutator cradle the weight, W,
lifts the two wires from the mercury, breaking first the primary circuit, and subse-
quently the galvanometer short-circuit. The time of transfer is thus kept constant.

Keys. — For the study of blaze-currents, occasional use has been
made of two special keys, modified from the well-known model of
the Pohl's commutator, for the purpose of automatically (i) breaking

166

THE SIGNS OF LIFE

the primary circuit, and (2) opening the galvanometer circuit, in
quick and regular succession.

This is very simply effected in the first of these keys by making

B C A

Object, '

FlG. 68. — A B C Key. The primary circuit of the inductorium is completed
through the pools / /. Connection between G G short-circuits the galvanometer.
Of the three pools in the centre of the key, the middle is connected to A, via the
keyboard and galvanometer, the pool under W to C, and the remaining pool to B.
The three arms of the rocker are of unequal length, that connecting G G being a
little longer than the centre arm, and this again longer than the connection between
p p. On rocking the arms to the left, and then letting go the weight, the following
events take place in order :—

(a] The circuit// is broken, and an induction current passes through B A.
(K) „ ,, B A is broken.
(c) ,, „ A C is made.

(r/) ,, ,, G G is broken, and any potential difference between A and C
acts upon the galvanometer.

Thus the in luction shock caused by breaking p p passes through A B, A is then
connected to C, and not till then is the galvanometer short-circuit G G broken, and
the current from A C allowed to pass. To take the current from B C, the connections
A and B are transposed.

the curved wire in the galvanometer short-circuit a little longer
than that in the primary circuit, so that the hreak shock takes

APPENDIX

167

place a little before the galvanometer is un-short-circuited. The
removal of the two curved wires from their respective mercury
pools is maintained at a regular interval by the use of a weight.
This key is used to demonstrate the total effect between two points,
A B, after excitation of these same points.

The second key is a little more complicated, and serves to
demonstrate a partial effect A C or B C after excitation of two
points A B.

Units of Resistance and of Conductance* — The units of resistance
are the ohm and the megohm (=1,000,000 ohms). The corres-
ponding units of conductance are the mho and the gemmho, which
are the reciprocals of the ohm and megohm.

A substance having a resistance of one megohm (0) has a con-
ductance of I gemmho or i 7.

The conductances of, e.g., the skin in the experiment illustrated
by Fig. 50 are accordingly :—

Deflection by
0-01 volt

Resistance
-20,000 ohms

Conductance

At outset ....
After 1st tetanisation
„ 2nd
„ 3rd
After boiling .
,, 4th tetanisation

5
12.5
25
35
H5
H5

520,000 ohms
196,000 ,,
88,000 „

57,143 „
3,478 „
3.473 „

1.92 7.
5.67 „
"•35 ,,
17-5° ,,
288.90 „
288.90 „

Standard deflection through
I megohm, or I y.

2-7

1,0:0,000 ohms

i.oo 7.

* I am indebted to Professor Ayrton for the suggestion of the reciprocal megohm
as a convenient unit of conductance, and for the further suggestion of " gemmho " or
7 as its convenient name and symbol, thus utilising Lord Kelvin's proposal to take
resistance names written backwards to denote their conductance reciprocals. Kohl-
rausch's unit of conductivity i K is the same as Kelvin's " mho," and is equal to
1,000,000 7. I have also to acknowledge the kind assistance of Dr T. .Martin
Lovvry in connection with conductivity measurements.

168

THE SIGNS OF LIFE

From which it is evident that where the resistance of the object
examined is great as compared with the resistance of the galvano-
meter and electrodes (20,000 ohms in this instance), we may regard
alterations of deflection as indicating alterations of conductance.
Whereas, if the resistance of the object be relatively small, we must
calculate the conductance after subtracting from the total resistance
in circuit the resistance of the galvanometer and electrodes.

For many purposes — e.g., for comparing the resistance (or con-
ductance) of various objects — it will evidently be necessary to reduce
our results to a common denomination, i.e., to the resistance (or
conductance) of a cube of i centimetre. Thus, e.g., a stem 10 cm.
long with a sectional area of 10 square millimetres, having a
resistance of say 200,000 ohms ( = a conductance of 57) has a

resistivity = - and a conductivity = 5 x 10 x 10. The reduction

to the cube of i cm. is in conformity with the practice of modern
physical chemistry. The conductivity of I megohm, or i y, = i.io~15
C.G.S. unit, that of i ohm, or io°y being i.io~!).

Electrolytes in general are increased in conductivity by rise of
temperature, the co-efficient of increase being approximately 2 per
cent, per degree.

Resistivity
(in ohms)

Conductivity
(in reciprocal
megohms)

Mercury ......

0.000,094

10,630,000,000

Sulphuric acid, 30 % at 40° .

I

I,OOO,OOO

Sodium chloride, sat. sol. at 18°, 26.4 °,

4.627

2l6,IOO

„ „ mol. sol. at 18°, 5.62 %

1345

74,400

nt

— sol. at 1 8°, 0.58 %

1 08

9,250

Sea-water, at 15° .

20

5O,OOO

Seaweeds ......

80

12,500

Urine

50

20,OOO

Blood serum .....

125

8,000

Defibrinated blood ....

250

4,000

Muscle and Nerve (longitudinally)

2OO

5,000

Grape-juice

500

2,000

Vegetables and Fruits ....

2,OOO

500

Ordinary tap-water ....

2,5OO

400

Ordinary distilled water

IOO,OOO

10

Good „ „ . .

I ,OOO,OOO

r

Kohlrausch ,, ,, ...

25,OOO,OOO

0.04

APPENDIX 1G9

Measurements of resistance (and of conductance) are best taken
by means of a Wheatstone bridge, preferably by Kohlrausch's method,
but for many purposes where polarisation of electrodes and of tissue
may be disregarded, it is convenient and sufficient to estimate con-
ductance directly from the galvanometric deflection. In the case
of plants the resistance is generally so great that it is allowable to
disregard that of the galvanometer and electrodes, and to at once
express deflections in terms of conductance. A carbon megohm
(=1,000,000 ohms) attached to the keyboard is a convenient
standard of reference, giving at once on the scale or photograph
the value of our unit of conductance, i y.

Correction for the resistance of the galvanometer and electrodes
is to be made, when required, as follows : —

Let rl and d^ be the resistance of the galvanometer + megohm,
and the deflection by any convenient voltage.

;'o and d.2 the resistance of the galvanometer + electrodes, and
the deflection by the same voltage (practically we must take y^th
or Yjjoth that voltage and multiply by 10 or 100).

7'3 and dz the resistance of the galvanometer + electrodes + object
of experiment, and the deflection by the same voltage.

The required resistance, rv of the object examined = r3 - r.2,

j • r-i d., ?', d<,

and since —± , and -± = -?

r.2 ^ r.A dl

r-2 4-1, and 7-3 Li

the required resistance r, = -i—1 - -V1

and the corresponding conductance = • , ,'\ 3 , N-

If the galvanometer resistance is known, it is, although convenient,
not necessary to take a megohm into circuit.

Kohlrauscli1 s method is used in this laboratory for the rapid
testing of distilled water, of dilute saline solutions, and of blood,
serum, urine, etc.

The electrodes (of platinised platinum) are adjusted to a suitable
"resistance capacity" (about -^ for water, i for dilute saline, serum,

170 THE SIGNS OF LIFE

and blood, and 10 for solutions of higher conductivity) so that the
resistance under observation shall fall between the limits of 100 and
1000 ohms. The electrodes, forming the A: arm of aWheatstone bridge,
are plunged into the fluid under examination ; a telephone is in the
bridge in place of a galvanometer ; the testing currents come from a
small induction coil, and the silence point (or its equal " to much "
and " too little ") is sought for by alteration of the variable resistance.
Readings of resistance are thus easily obtained within an error of
± I per 100, with the normal temperature = 18°. A correction of
± 2 per 100 of the reading is to be made per ± i°.

rr,, . ,- 7 , . ., Resistance Capacity

1 he specific conanctivitv =

Observed Resistance

The resistance capacity of a given pair of electrodes in a given
vessel is ascertained by taking a measurement of resistance through
a standard solution of known conductivity. E.g., a pair of electrodes
in decinormal KC1 at 18° is found to have a resistance = 200 ohms.
The resistance capacity == 200 x 0.01119 = 2.238 (Resistance x
Conductivity = Capacity).

With the same pair of electrodes the resistance of a specimen
of serum is found to be 320 ohms. Its specific conductivity

•^ = 0.006994 mho or 6994 7.
320

The necessary data are given in Kohlrausch and Holborn's
tables, from which the following useful empirical rule is taken :—

For weak saline solutions | — and under ) the specific conduc-

\io /

tivity (in mhos) x 10 == the number of gramequivalents per litre,
and -- the specific conductivity x molecular weight == the percentage
of salt in solution.

REFERENCES

LIPPMANN. — " Capillary Electrometer," Comptes Rendus de P Academic des

Sciences, p. 1407, 1873.
MAREV AND LIPPMANN. — " Electrometer Records," Comptes Rendus, p. 278,

1876.
BURDON-SANDERSON AND PAGE. — " On the Electrical Phenomena of the

Excitatory Process in the Heart of the Frog and of the Tortoise, as

investigated Photographically," Journal of Physiology, vol. iv. p 327,

1883.

APPENDIX 171

BURCH. — " On the Time Relation of the Excursions of the Capillary Electro-
meter," Phil. Trans. Roy. Soc., vol. 183, p. Si, 1892 ; Proceedings Roy. Soc.,
vol. 60, p. 329, 1896.

EINTHOVEN. — " Lippmann's Capillar-Electrometer zur Messung Schnell-
wechselnder Potentialunterschiede," Pfliiger's ArcJiiv, Bd. 56, p. 528,
1894 ; Bd. 60, p. 91, 1895 ; Bd. 79) P- r> JQ00-

HERMANN. — "Das Capillar-Electrometer und die Actionsstrome des
Muskels," P finger's Archiv, Bd. 63, p. 440, 1896.

GARTEN. — "Ueber ein einfaches Verfahren zur Ausmessung der Capil-
larelektrometer-Curven," P finger's Archtv, Bd. 89, p. 613, 1902.

KOHLRAUSCH UND HOLBORN. — Leitvermogen der Elektrolyte. Leipzig,
1898.

E. COHEN. — Vortrage fiir Artzte iiber Physikalisch Chemie. Leipzig, 1891.

WHETHAM. — Solution and Electrolysis. Cambridge, 1895. (New edition,
1902.)

R. HOBER. — Physikalische Chemie der Zelle und der Gewebe. Leipzig, 1902.

INDEX

ABC METHOD, 69, 87, 94, 95, 107,

112, 115, 133, US-
After effects in eyeball, 43, 45.
Aim of lectures, i.
Anaesthetics, action of, 38.
Anodic (post) action currents, 73.
Anomalous polarisation, 130.
Antidrome currents, 47.
Atropin on skin, 65.

Bach on action of mercuric chloride,

83-
Bean-radicle, mechanical excitation

(fig. 6), 15.

Bernard on analysis and synthesis, 35.

Biedermann on anodic and kathodic
currents, 91, 108 ; on mucous mem-
branes, 66, in, 138.

Blaze (manipulation-) in eyeball, 25; in
skin, 60 ; currents, 49, 53, 106, 143 ;
definition of, 73 ; similarity with
discharge, 74 ; anodic and kathodic,
no.

Blaze, partial and total, 95.

Brown, Horace, on seeds, 6.

Burdon- Sanderson on Dionaea, 12.

CARBON dioxide, action of, 39, 74.
Cause, its relation to effect, 35, 36, 52.
Chemical change, 3 ; methods, 6.
Chloroform, action of, 39.
Coil, induction, description of, 155.
173

Colours, complementary, 35.
Compensator, description of, 153.
Concentration currents, 135, 137, 139

(fig. 55), 143.
Conductance, 167, 169.
Conductivity, 168.
Conductivity in eyeball, 44.
Congelation blaze, 119.
Copperplate, effect of light on, 29,

159 (fig. 61).

Crystalline lens, blaze-currents of, 56.
Current in retina, 10 ; initial (in retina),

24 ; of darkness, 27; normal (in skin);

60, 104 ; of action, 73 ; plant, 94 ;

accidental, 103 ; Quinke's, 133 ;

concentration, 135, 137, 140 (fig. 55) ;

density, 113 ; evaporation, 136.

DARKNESS, current of, 27.

Dewar and MacKendrick on latency
in eyeball, 28.

Discharge of electrical organ, 73, 76)
78 ; skin, 82.

Du Bois-Reymond, negative varia-
tion, 14, 1 8 ; on positive polarisa-
tion, 73, 89 ; on electromotive pheno-
mena, 74, 76 ; on torpedo, 78, 79 ;
" Willkiirversuch," 121 (fig. 52); in-
duction coil, 154.

Dung on surviving skins, 141.

EFFECT, its relation to cause, 35, 36, 37.

174

INDEX

Electrical fishes, 75 ; organs, 76 ; organs

of torpedo, 78.
Electrocution of eyeball, 49.
Electrodes, 155 ; fallacy of, 129, 130,

133.
Electrometer, capillary, 29, 100, 162.

Rngelinann and Grijns on action of
anaesthetics, 39 ; Engelmann on
nerve-skin, 61, 63 (fig. 29), 65 ; on
skin, 138.

Ether, action of, 39.

Evaporation current, 136.

Excitability of vegetable protoplasm,
12, 19.

Excitation, indirect (of skin), 60, 65 ;
direct (of skin), 65 ; of cat's pad, 101 ;
summating effect of, 68 (fig. 31) ;
effect of, direct or indirect, 83.

Eyeball, currents in, 10, 11, 12, 19, 25 ;
as an optical instrument, 22 ; electri-
cal effects of light and of electrical
excitation, 23 (fig. 8), 55 ; normal
response in, 27 ; three types (fig. 13),
30, 50; massage of, 31 ; tetanisation
of, 42; electrocution of, 49; galvanic
current through, 52.

FALLACY, of electrodes, 113, 130.
Fishes, electrical, 75.
Fleischl, Von, on nerve, 130, 132.
Frog's tongue, 11 1.

GALVANISATION through eyeball, 52.
Galvanometer, description of, 151.
Geranium leaf, 109.
Gotch on electrical fishes, 75 ; on

malapterurus, 78, 81, 142.
Gymnotus, 79, 80.

Hering on colour-vision, 34 ; on
positive polarisation, 73, 90.

Hermann, polemic with du Bois-Rey-
mond, 14, 90, 121 ; on nerve-skin
preparation, 61, 63 (fig. 29) ; on
positive polarisation, 73 ; on cat's
skin, 97 ; on effects of atropin, 122.

Hesitation, period of, in eye, 28, 33.
Holmgren, photoretinal currents, 10,

25-

Homodrome currents, 47.
Human skin, 86, 115, 116, 117, 119.

IVY-LEAF, electrical response in, 13,

19.

Ionic velocities, 138.
Ions, importation of, 125, 147.

KATAPHORESIS, 133.

Keyboard, description of, 155.

Kiihne and Steiner on accidental

current in retina, 27 ; Kiihne, light

on retina, 54.

LATENCY in eyeball, 28 ; in skin, 61
(fig. 28), 99, 105.

Lens currents, 56.

Life, signs of, 3 ; latent, 5.

Light, action of, on eyeball, 55.

Lippmanifs capillary electrometer,
162.

Living matter, properties of, 3.

Loeb, osmotic pressure of muscle, 134.

Lost-time, physical, 29 ; in oxidised
copper plate, 29 ; in cat's nerve ex-
citation, 105.

Litchsinger, on cat's skin, 97, 122.

MacDonald, 72, 140, 144.

MacKendrick and Dewar on latency
in eyeball, 28.

Malapterurus, 78, 79, 81.

Malpighian layer, 82, 83.

Man, skin of, 119 (fig. 51).

Matter, properties of living, 3 ; divisons
of, 4 ; currents of, 85.

Mercuric chloride on skin, 65, 83.

Mucous membranes, 87.

Muscle, negative of variation, 4 ; con-
traction of, 8, 19 ; modification of,
8 1 ; (nerve-) preparation, 92 ; by
A C B plan, 94.

INDEX

175

NEGATIVE variation, 4, 16 ; (abso-
lutely), 76.

Nerve-skin preparation, 61 ; response,
100 ; muscle preparation, 92 ; by
ABC method, 95.

Neivberry, Percy, on seeds, 8.

Oehler on action of mercuric

chloride, 83.

Orange peel, current in, 86.
Osmotic pressure, 12, 134, 138.

Pacini's law, 79.
Permanganate of potash, 125.
Photographic record, description of,
156; of current in retina, 26 (figs.

10, II).

Physiology, subject of, 2.
Plant currents by A B C plan, 94.
Plant-guillotine, 13 (fig. 4).
Polarisation currents, 48 ; positive, 73,

89 ; in electrodes, 130.
Positive, absolutely, 76 ; polarisation,

89.

Properties of living matter, 3.
Protoplasm, mechanical excitability of

vegetable, 12, 84, 85.

Quinke currents, 133.

RADIUM, luminosity of, 40.

Raia, 79, 80.

Reid, on eel's skin, 66.

Resistance, 119, 133, 142, 167.

Resistance of eyeball, 45.

Resistance of seaweed, 141.

Resistivity table, 168.

Retina, currents of, 10 ; action of light

on, 10, 11,37 ; action of anaesthetics

on, 38 ; Engelmann on, 39.

Roeberon. nerve-skin preparations, 61.

S-SHAPED curve, 38.

Sea- water, 168.

Seaweeds, 141.

Secreto-motor nerves, 99.

Seeds, 5, 6 ; experiments on, 8, 19.

Shocks, single, on eyeball, 45, 48.

Signs of Life, 3.

Skin currents, 60 ; by A B C plan, 94 ;
normal currents of, 60 ; (nerve) pre-
paration, 6 1 ; Roeber, Engelmann,
and Hermann on, 61 ; discharge, 82 ;
human, 86, 116, 117 (figs. 49, 50),
119.

Solution-pressure, 18, 145, 146.

Steiner (and Kiihne], on accidental
current of retina, 27.

Stomach, frog's, 112.

Strychnine sulphate, 127.

Subcutaneous tissue, 86, 104.

Subject of physiology, 2.

Tarchanoj? 'on skin currents of human

subject, 123.
Tetanisation of eyeball, 42 ; on effect

of light, 44 (fig. 20).
Tongue, on frog's, in.
Torpedo, 78, 79, 80.
Types of response to light in case of

retina, 29, 51.

VEGETABLE protoplasm, mechanical
excitability of, 12 ; surface, 109.

Vine-shoot, electrical effects of
mechanical excitation (fig. 5), 15.

ZINCATIVE, use of term, 14, 17, 104.

PRINTED BY OLIVER AND BOYD, EDINBURGH.