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Gift of
Dr. James Hopper, Jr.

AN INTRODUCTION TO BIOPHYSICS

PRINCIPLES OF HUMAN PHYSIOLOGY. By E. H.

Starling, C.M.G., F.R.S., M.D. Third Edition. 579
Illustrations. 25s. net.

TEXT-BOOK OF PHARMACOLOGY AND THERA-
PEUTICS. By A. R. Cushny, M.D., LL.D., F.R.S.
Seventh Edition. 71 Illustrations. 24s. net.

PRACTICAL PHYSIOLOGICAL CHEMISTRY. By

P. B. Hawk, M.S., Ph.D. Sixth Edition. 185 Illus-
trations. 21s. net.

SYNOPSIS OF PHYSIOLOGY. By Ffrangcon Roberts,
M.D. 73 Illustrations. 15s. net.

By EMIL HATSCHEK.

LABORATORY MANUAL OF ELEMENTARY COL-
LOID CHEMISTRY. 20 Illustrations. 7s. 61 net.

INTRODUCTION TO THE PHYSICS AND CHEM-
ISTRY OF COLLOIDS. Third Edition. 17 Illus-
trations. 5s. net.

J. & A. CHURCHILL.

AN INTRODUCTION

TO

BIOPHYSICS

DAVID BURNS, M.A., D.Sc.

GRIEVE LECTURER ON PHYSIOLOGICAL CHEMISTRY IN THE
UNIVERSITY OF GLASGOW

WITH A FOREWORD BY

D. NOEL PATON, M.D., LL.D., F.R.S.

REGIUS PROFESSOR OF PHYSIOLOGY AND DIRECTOR OF THE
PHYSIOLOGICAL INSTITUTE, UNIVERSITY OF GLASGOW

With Eighty-five Illustrations

LONDON

J. & A. CHURCHILL

7 GREAT MARLBOROUGH STREET
1921

TO
I. R. V. M.

PREFATORY NOTE

THIS book makes no pretensions to be a complete or even a
systematic survey of Biophysics. Its object is partly to be
explanatory. Current medical publications are full of terms
culled from physico-chemical and physical terminology ; the
clinician of to-day clothes his ideas in words unknown to his
brethren of yesterday ; his phraseology, at least, is physical.

Apart from and beyond a mere explanation of physico-chemical
terms, an attempt has been made in the following pages to present
physiological phenomena from a purely physical standpoint.
The problems of life, and vertebrate life in particular, have been
viewed through a physicist's eyes. This does not necessarily
imply that the matter of the book is permeated with mechanistic
philosophy. We are all, more or less, amateur philosophers, but
we would be poor scientists indeed if our " views " were permitted
to colour our facts. Phenomena, as they appear to-day, are set
out for the critical examination of the student. " He will have
all the facts and circumstances fully mobilised, standing up side
by side before him like an awkward squad, and there is nothing
more awkward than some facts that have to stand out squarely
in the daylight ! And he inquires into their ancestry, makes them
hold out their tongues, and pokes them once or twice in the ribs,
to make sure that they are lively and robust facts capable of
making a good fight for their lives. He never likes to see one
thing too large . . . lest he sees something else too small ; but
will have everything in true proportion." (David Grayson.)

It is a great pleasure to me, on reading over the final proofs,
to notice how generously my masters and colleagues have come to
my aid. Quite apart from the direct help given me by Professors
Noel Paton and E. P. Cathcart, who contribute the opening and
closing chapters of the theoretical part of the book, I have
received daily encouragement from them in my task, for which I
express my sincere gratitude. If this effort to make plain the

vi PREFATORY NOTE

essentials of Biophysics is in any way successful it is due to the
truly scientific atmosphere of the Institute of Physiology which
they govern and inspire.

I beg to record my obligation to Dr. Shanks for the care he has
devoted to the chapter on the eye ; to Dr. Morris for reading the
first three sections of the book in slip-proof ; to Dr. Watt, Lecturer
on Psychology in this Institute, for reading the chapters on
Receptors and for his suggestions thereon ; to Dr. Wishart,
because, by reading many of the proofs and by checking
mathematical matter, he has saved me from many a fault and
blunder.

My debts to previous authors are many and I cannot own
them all. Discerning readers will see, for example, the ideas of
my old teacher, Professor Soddy, mirrored in certain of the
earlier chapters ; Professor Thompson's Growth and Form is
the basis of part of Chapters XVI., XXIV. and XXXIV.;
McKendrick, Gray, Wrightson, Keith, and Watt are the sources
from which much of Chaps. XIX. and XXIX. have been drawn.
A book of this nature could not be written without constant
reference to the Principles of General Physiology. If my Intro-
duction but serves to turn some student to the great book of
Professor Bayliss, to meet the master mind, it will have succeeded.

I am under obligation to the authors and publishers of several
books from which illustrations have been borrowed.

To Professor Noel Paton and Messrs. Green for permission to
use eight figures from the Essentials of Human Physiology (viz.
Figs. 25, 27, 58, 59, 69, 72, 73 and 85) ; to Professor Starling and
Messrs. Churchill for the following figures from Principles of
Human Physiology : 1, 5, 8, 16, 35-41, 43, 45, 50, 70, 74, 75,
80 and 83 ; to Mr. Crowther for Fig. 21 from Molecular Physics,
and to Mr. Emil Hatschek for Figs. 7, 9 and 10 taken from
An Introduction to the Physics and Chemistry of Colloids, both
books from Messrs. Churchill.

To Professor Cushny for leave to reproduce the ideal diagram of
a Malpighian corpuscle (Fig. 28) from his monograph on The
Secretion of Urine (Messrs. Longmans, Green and Co.) ; to
Professor Soddy and " The Electrician " Publishing Co., for the
diagram of the gold-leaf electroscope (Fig. 22) from Radioactivity.

To Dr. Bradford for allowing me to reproduce, from the Bio-
chemical Journal, his photograph of adsorptive stratification
(Fig. 11) and to Professor Roaf for the pH-CH graph reproduced
from the Proceedings of the Physiological Society (Fig. 84).

PREFATORY NOTE vii

To Messrs, the Cambridge and Paul Scientific Instrument Co.
for the figures illustrating the electro-cardiograph (Figs. 64-67) ;
to Messrs. Hawksley for those of the viscosimeter (Figs. 77 and 82)
and to Messrs. Gallenkamp for Figs. 2 and 3 of the bomb calori-
meter.

The remaining forty illustrations were drawn by Dr. G. M.
Wishart, Assistant in the Department of Chemical Physiology, and
by Mr. John Waters, a student of medicine here. To their skill
and care I owe much.

I am greatly obliged to Mr. A. V. Steen, B.Sc., one of our
demonstrators, for reading all the proofs. The freedom of the
matter from certain errors is the result of his painstaking efforts.

Finally, I desire to record my gratitude to my publishers for
their patience and courtesy during the prolonged period of
publication and to the printers for the care they have taken and
the consideration shown when my ignorance made large demands
on their time and patience.

INSTITUTE OF PHYSIOLOGY,

UNIVERSITY OF GLASGOW.

CONTENTS

PAC1R

INTRODUCTION. By Professor D. Noel Paton, M.D., LL.D., F.R.S. - xi

PART I. SYSTEMATIC
SECTION I. ENERGETICS

CHAP.

I. LAWS OF ENEKGY 1

II. THE STORAGE OF ENERGY - - - - - - 13

III. LIBERATION OF ENERGY — (1) CALORIMETRY - - ... 21

IV. LIBERATION OF ENERGY — (2) THE ANIMAL AS A MACHINE - 32
V. LIBERATION OF ENERGY — (3) ENERGY OF SUBSTANCE IN

SOLUTION. OSMOTIC PRESSURE 36

VI. LIBERATION OF ENERGY — (4) SURFACE TENSION 46

SECTION II. CELLULAR MECHANICS

VII. IONS - 49

VIII. DISPERSE SYSTEMS - 65

IX. ENZYMES - - - 91

X. MEMBRANES ... 107

XI. RADIO-ACTIVITY - - - - 117

XII. THE CELL - 129

SECTION III. CELL COMMUNITIES

XIII. MUSCLE CELLS 135

XIV. MANUFACTURING CELLS 148

XV. ELIMINATING CELLS 155

XVI. CONNECTIVE TISSUE CELLS - - - . - - - - 166

XVII. INTELLIGENCE SERVICE — NERVE CELLS 182

XVIII. OUTPOSTS OF THE INTELLIGENCE SERVICE — GENERAL RECEPTORS 191

XIX. OUTPOSTS OF THE INTELLIGENCE SERVICE — EAR - - - 200

XX. OUTPOSTS OF THE INTELLIGENCE SERVICE — EYE ... 215

x CONTENTS

SECTION IV. TRANSPORT

CHAP. PAGE

XXI. INLAND TRANSPORT— THE BLOOD 229

XXII. INLAND TRANSPORT — RESPIRATORY FUNCTION OF BLOOD - 246

XXIII. INLAND TRANSPORT— LOADING UP - 258

XXIV. INLAND TRANSPORT — CIRCULATION - 274
XXV. INLAND TRANSPORT — ELECTROCARDIOGRAM .... 295

XXVI. OVERSEAS TRANSPORT — EXTERNAL RESPIRATION - - 301

XXVII. OVERSEAS TRANSPORT — ALIMENTARY CANAL - - - 313

XXVIII. OVERSEAS TRANSPORT — LOCOMOTION 320

XXIX. OVERSEAS TRANSPORT — VOICE .... . 325

SECTION V. THE ANIMAL AS A WHOLE

XXX. THE PRESERVATION OF NEUTRALITY - 331

XXXI. THE REGULATION OF TEMPERATURE - - - 336

XXXII. TROPISMS - - 354

XXXIII. ADAPTATION ..... 360

XXXIV. GROWTH 363

XXXV. DEVELOPMENT - - 377

XXXVI. DEATH AND DISSOLUTION - - - - - - - 388

XXXVII. EFFICIENCY - - - 391

PART II. ILLUSTRATIVE EXPERIMENTS - 398

INDEX 427

INTRODUCTION
BY PROFESSOR D. NOEL PATON, M.D., LL.D., F.R.S.

ON looking back over a forty years' association with physiology
nothing is more striking than the influence which the application
of physics has exercised upon the progress of the sciences.

I well remember that, as long ago as 1878, my first teacher
began his lectures on the Institutes of Medicine by defining
physiology as the application of physics and chemistry to the
study of the body in action.

But at that time the possibility of applying these sciences was
limited. In the first place, their development, and especially
the development of physics, was not sufficiently advanced. The
dissociation of atoms into ions was hardly recognised, the
significance of Graham's colloids was not appreciated, and
the phenomena of surface tension had hardly been applied to
molecular physics. In the second place, physiologists were then
generally men trained for medicine whose education in physics
and chemistry had been extremely limited. Of course, there
were notable exceptions — e.g. Helmholtz and du Bois Reymond.

These older physiologists had to be content with recording
phenomena rather than with explaining them, and they loved to
chronicle their observations in high-sounding Greek names.
Can one ever forget the sense of profound knowledge which one
enjoyed as a junior student in mastering such terms as " delo-
morphous " and " adelomorphous " as descriptive of the cells of
the stomach ? The so-called chemical physiologists were perhaps
the worst offenders. For, having isolated, or thought they had
isolated, some constituent of the body of quite unknown chemical
constitution, they promptly gave it a name with no connection
with its chemical nature, and these names have generally con-
tinued in use, to the confusion of generations of students. In the
present age of " hormones " and " vitamines " one wonders how
far the tendency has been eradicated.

xii INTRODUCTION

It was the " what happens ? " which interested these older
workers : " Why it happens ? " was generally beyond them, and
vague theories of some peculiar and special vital action took the
place of actual demonstration.

Undoubtedly the association of physiology with the more
exact science of physics, based as it is so largely upon mathe-
matics, has had an enormous effect in getting rid of this habit
of vague theorising and has materially helped to clarify minds
" debauched with the so-called science of biology " as Tait, in
the early eighties, was wont to describe our mental condition.

It has also stimulated the critical faculty, which insists upon a
clear proof and demonstration as a basis of conclusions.

It is much to be regretted that even at the present time the
importance of a mathematical training, so essential for the study
of physics, is not generally recognised, and that it is still possible
to take a higher degree in science without this necessary prepara-
tion.

It has been through the co-operation of physics and chemistry
that the solution of many of the problems of life have been
reached, and as the possibility of reaching these solutions has
become more generally recognised, the spirit of scientific curiosity
—the desire to know, which is the basis of all scientific work —
has been stimulated ; although probably in the future as in the
past, humanity will still be divided into the enormously large
class of those who have no real desire to understand the workings
of nature and the very small class of those who have the spirit of
curiosity, who do desire to know. These alone are the scientists,
although many science graduates belong to the major class.

With or without any wider diffusion of the spirit of curiosity,
the development of the critical faculty and the better training
of the younger workers in physics and chemistry has brought
physiology nearer to the position of an exact science, and with
this, its value as a training for students of medicine has greatly
increased. The doctor, in making a diagnosis, has not merely
to observe and record what has happened, but he must ascertain
why it has happened. His problems are the same in nature and
his methods are the same as those of the physiologist, and thus
physiology has regained its position as the Institutes of Medicine.

The doctor of the past considered that he had made a diagnosis
when he was able to give his patient's disease a name. The
physician of the future will care less and less for such names. He
will simply be concerned with the solution of the questions —

INTRODUCTION xiii

" What is abnormal ? " " Why is it abnormal ? " Perhaps it is
wiser not to enquire too curiously into the position of the physician
of the present.

The development of physiology on the lines indicated has also
made possible the growth of the sciences of experimental path-
ology, of experimental medicine and of pharmacology ; and the
knowledge of disease and of its treatment has thus been put
upon a sounder basis.

All this has followed the adoption of physics and chemistry
as the guides of the physiologists.

In the present volume, Dr. Burns attempts to show the part
which physics has come to play in the solution of the problems
of physiology. A science of bio-physics has evolved in the same
way as that of bio-chemistry. Perhaps some attempt should
have been made in the title to indicate that it is the problems of
the physiology of vertebrates rather than the basic problems of
life generally which are dealt with.

The book is intended for students of human physiology, although
it cannot fail to interest all workers in biology.

It demonstrates what a very large number of the characteristic
reactions of living matter may be explained in terms of ordinary
physical processes, and it thus shows the reduction which is
taking place in the number of phenomena which some are still
content to explain as due to a mysterious vital action instead of
simply confessing that they are yet not understood.

As the application of physics and chemistry to physiology is
extended, it is safe to predict that fewer and fewer of these vital
manifestations will remain unexplained.

The origin of living matter, its increase and dispersion all over
the globe, its marvellous and endless developments and evolutions,
and its reactions with its surroundings may all be explained in
terms of physics and chemistry. But consciousness and its
association with living things will ever remain the mystery it
has been and is.

BIOPHYSICS

PART I. SYSTEMATIC

SECTION I.: ENERGETICS

CHAPTER I
LAWS OF ENERGY

" The history of man is dominated by and reflects the amount of
available energy."

BIOPHYSICS deals with the application of physical and physico-
chemical laws to the actions of living things. It is neces-
sary at the outset to have a clear understanding of what
is meant by a natural law, or principle of nature. A law in
science is a different concept from a law in philology or in juris-
prudence. Repeated observation of a recurring phenomenon
leads to the conclusion that there is a natural and unalterable
sequence of events. This is summarised in a law. Newton's
Law, for instance, epitomises the conclusions of a large series of
observations, viz. that objects free to do so always fall towards
the earth. A natural law, then, is not a principle governing the
action of nature, but a generalisation drawn from observation of the
phenomena, stating, in short, how these phenomena have always
been known to act in the circumstances. If the observations
are correct, the law is true and, in like circumstances, will always
hold. If at any time a reliable observation were made that
seemingly went against the law, scientists would not doubt the
validity of the law, but would carefully examine the concomitant
circumstances to see in what point they differed from those
defined in the law. The problem before us is to determine
whether laws deduced from the study of non-living matter may
be applied to the elucidation of biological phenomena. Physical

2 LAWS OF ENERGY

science is the most fundamental of the experimental sciences
and, so far as is known, its laws are applicable to all non-living
matter. Biochemists have attempted to break down the wall
of partition which has been reared by common consent between
the chemical constitution of living and non-living. They have
been partially successful in that they have been able to build
up certain typical products of life from non-living material. No
one, however, has, as yet, either analysed or synihesised living
matter. The finest chemical technique available cannot be
employed without injury to the tissue studied. In spite of this
drawback, the science of nutrition may be classed as exact.
Mathematical formulae may be employed to express results, and
chemical response to a definite stimulus may be predicted.

Life has been compared to a flame. The Ancients looked on
fire as a living thing, and is their view not, to some extent, justi-
fiable ? The continual ringing of the changes — of form, of colour,
or of position — by the flickering flames of our house fires draws
the eye. Constantly, alterations are going on. No flame is still
for any length of time. All is seemingly unordered and uncon-
trolled change. Yet down to the most minute movement all is
governed by physico-chemical laws. Every flicker can be ac-
counted for, and could be recorded as due to pressure of liberated
gas, pressure and direction of draught, temperature of fire, etc.
Fire — mysterious and all-powerful gift of the gods — has yielded
to the prying endeavours of the scientist, and can be harnessed
and employed in the service of man.

Similarly, while nob committing oneself to a vitalistic or to a
mechanistic conception of life, one may study, with considerable
profit, the various physical phenomena exhibited by living matter.
Examination of even the simplest form of life is sufficient to
show that a characteristic phenomenon is change. No living
thing is absolutely still. It is undergoing change in one way or
another. It may alter its position relatively to its environment ;
it may alter in its parts ; it may grow ; it may undergo altera-
tions in internal (atomic or molecular) structure. The physico-
chemical processes indicated by these changes or initiated by
them are studied under the term metabolism (Gr. meta= change).
Metabolism may consist in a building up of matter, anabolism
(Gr. ana = up) or in the reverse process, a breaking down of
matter, catabolism (Gr. kata=down). If anabolism is greater
than catabolism, the organism grows ; if the two processes balance,
the organism exists. The predominance of catabolism leads to

FIRST LAW OF THERMODYNAMICS 3

disintegration. Complete immobility denotes death. Change
indicates the utilisation of energy, which obviously must have
come from some source outside the organism. '' The mechanistic
notion of life, the representation of the body as primarily and
fundamentally a machine, is often bitterly and not very intelli-
gently opposed. We are told that the machine — the scientists'
imitation of life — is not merely a purely inanimate mechanism.
In its cunning combination of valves and regulators it has a
brain, part of the brain of its designer. The partial likeness is
that of the machine to the man, of the limited imitation to the
original, not the other way about, which is true enough. But
let us bear in mind one essential and undeniable fact. Machine
or man, inanimate mechanism with the mechanical imitation of
a brain, or brain controlling an animate mechanism, what of the
power ? The power to live, the power to do work is not in the
brain nor in the body, not in the valves nor the moving parts.
The power, whether of life or of mechanism, is external. This is
the real ground of analogy " (Soddy). We must determine the
source of this energy, study its laws, see how it is made available
for living matter, and then see how it operates in living matter.

Energy is the underlying cause of all changes in matter. This
does not seem a very satisfactory definition but, so far, it is the
only one possible. It is a very striking fact that the two funda-
mentals of our external world, matter and energy, have for us
no existence apart from their effect on us. We cannot prove
that there are such things except in so far as they manifest them-
selves, matter by being changed, and energy by producing changes,
which in turn alter our sensation-complex.

There can be no change of any sort without free energy. Energy
exhibits itself in many forms — heat, light, movement of matter,
electricity, radio-activity, etc.

In 1798, Count Rumford, who was engaged in boring cannon,
showed that movement — or kinetic — energy could be transformed
into heat. Later, Joule demonstrated the equivalence of these
two forms of energy, 427 kilogrammetres of work always pro-
duce (under standard conditions) one Calorie of heat. Con-
versely, heat may be transformed into mechanical movement.
Indeed, any form of energy may be converted into any other
form of energy. (Radio-active matter evolves energy which
manifests itself in various forms, yet all attempts to change
other forms of energy into radio-active energy or even to influence
the rate of transformation have failed. Chap. XI.)

LAWS OF ENERGY

TABLE I.

MECHANICAL EQUIVALENT OP HEAT.

UNITS.

Tempera-
ture.

Time.

Mass.

Length.

Force.

Equiva-
lent.

1°C.

Second

Gram

Centimetre

Dyne at 15° C.

4-2 X 107

f

Wt. of a gram at

1

1°C.

55

55

„

15° C. at lat. of

142700

1

Greenwich

1°F.

5 »

Pound

Foot

Poundal at 59° F.

2504-7

f

Wt. of a pound at

1

1°F.

55

55

»

59° F. at lat. of

-778-1

I

Greenwich

J

1°C.

ii

»

55

Wt. of a pound at

1400-6

15° C.

To convert to ergs : Calories x 4-2 x 107 = ergs.

From observation it is found :

(1) That one form of energy may be transformed into any
other form.

(2) That when any quantity of energy in any one form dis-
appears, an exactly equal quantity of another form of energy
makes its appearance.

Energy like matter is therefore indestructible (Law I.).

Every substance possesses a certain amount of energy. This
is called its internal or intrinsic energy. Further, every group
of substances has associated with it a certain definite amount
of energy as long as it remains unchanged. When any change
takes place in the group, or in any member of the group, there
is usually a corresponding change in its total energy, either an
increase, due to the reception of energy from its environment,
or a decrease due to an evolution of energy. Put into other
words, each of the new substances will have its own charac-
teristic intrinsic energy, and the new group will, in general, have
a different total energy-content from that of the original group.

E.g. Cane sugar + O2^LCO2 + H2O + heat energy.

Corollaries of the First Law.

The following two deductions are of biological interest :

1. The total energy of a system in a given state is for the system

DEGRADED ENERGY 5

in question a definite characteristic of that state, and it is totally
independent of how the system reached that state.

The energy that would be liberated by the fall of a kilogram, e.g. of
lead, from a height of 300 metres would be the same no matter how the
kilogram was first elevated to the point from which it was dropped. For
instance :

(a) It might be lifted bodily and vertically.

(b) It might be lifted bodily and up an inclined plane.

(c) It might be lifted bodily and rapidly.

(d) It might be lifted bodily and with infinite slowness.

(e) Or it might be lifted in small pieces, say 1 milligram, at a time.

(/) It might be lifted as a series of chemical compounds weighing more
than 1 kilogram as salts of lead and reduced to metallic lead before dropping.

(g) Or it might be dug out from the top of a hill, 300 metres high, and
transported horizontally by aeroplane.

The essential conditions are that it weighs 1 kilo, and that it falls 300
metres, cosmic influences being constant.

Similarly, glucose has the same energy-content no matter how
it has been prepared provided the measurement is carried out
under similar conditions, e..g. glucose may be synthesised from
simple substances ; it may be prepared by the natural or artificial
hydrolysis of more complex carbohydrates, or it may be derived
from such .substances as proteins, fats, etc.

2. When a system changes from one state to another, the
alteration of total energy which accompanies that change is
altogether independent of the process by which the change is
brought about.

The examples given above, if reversed, will act as examples
of this corollary. The rate and angle of fall are not determining
factors in the liberation of energy, nor does the way in which
the energy of glucose is liberated have any effect on the total
amount set free.

These two corollaries, as we shall see later, make it possible to
construct a balance sheet of the energy intake and output of the
organism.

Degraded Energy (Law II.).

When a substance or group of substances is changed into a
substance or group of substances with a smaller energy-content,
the energy thus liberated is, in theory, available for work. In
practice, it is found that all this surplus energy cannot te
recovered as work. No system is absolutely isolated, and though
the total cosmical energy may be constant its distribution and
its state may alter. Some of the freed energy is always converted
into heat, part of which is diffused among surrounding objects

6 LAWS OF ENERGY

and is thus lost, as far as work is concerned. The quantity of
.energy is not decreased, but its dispersion is so great that in
quality it has not sufficient potential gradient to be of use. As
an example of dispersion of energy, consider a stone dropped
into an infinitely large lake. As the radius of the series of con-
centric ripples increases the wave-height decreases, till at infinite
radius the wave height will be infinitely small. The wave energy
has been so spread that it may be disregarded.

The second law is usually worded, " The entropy of an isolated
system tends to increase." Entropy is a function which, while
theoretically of great value as indicating the direction in which
chemical or other processes take place, cannot be directly measured.
Further, one never has, in Biology, to deal with an isolated
system. The difficulty as well as the great interest of our science
depends on the close interrelation and co-ordination of all the
systems in it. A simple expression of the law, and one suited
to our purpose would be, " Every change takes place at the cost
of a certain amount of available energy." The amount of energy
" degraded " during a transformation from one form of energy
to another may be taken as an inverse index of the efficiency of
the transforming mechanism.

States of Energy.

A substance may be endowed with kinetic energy, or with
potential energy, or with both. Kinetic energy is directly avail-
able for work, potential energy requires the use of some kinetic
energy to liberate it. The energy of a substance may be in the
motion of the substance itself or in the motion of the ultimate
particles composing it. This kinetic energy and its value depend
on the mass of the substance and the rate at which it moves or
at which its particles vibrate.

Potential energy, on the other hand, is said to be possible to
a substance in virtue of its configuration, i.e. position, composi-
tion, history, etc. A quantity of energy that may be measured
is stored up (or rendered passive in some way), and this same
quantity is theoretically recoverable in a measurable form. It
may not be apparent how energy is stored up, but it may be demon-
strated that it is stored and is recoverable. The simplest example
is the application of force to a perfectly elastic system. On
removal of the force the system will return of itself to its original
configuration, and an amount of work will be done by it, in
returning, exactly equivalent to the amount of the force of

POTENTIAL ENERGY 7

distortion. The hackneyed example of energy storage is, of
course, our coal supply.

Energy in the potential state, as long as it remains potential, is
useless. It cannot be transformed into any other form of energy
without altering its state, and its state cannot be altered without
the employment of kinetic energy. This point is biologically
important.

1. A weight hanging from a string has potential energy accord-
ing to its mass and its distance from the centre of the earth, etc.

2. An explosive has potential energy depending on its chemical
composition and physical state.

3. Petrol, coal, or any other fuel has similar energy bound in it.

4. A sleeping man may be said to have potential energy.
Now, in order to get work out of these quiescent bodies, all
that is necessary is the application of a suitable stimulus, i.e.
a small quantity of free kinetic energy. E.g.

(1) The resistance that prevents the weight from falling must
be overcome, i.e. the string severed.

(2) The explosive must be fired or detonated.

(3) The fuel must reach ignition temperature.

(4) The sleeper must be awaked.

In 1882 Helmholtz introduced the terms " free " and " bound "
to denote respectively that part of the kinetic energy of a system
free or available for conversion to work, and that part not free
or not available for this purpose. Later writers, realising that
potential energy as such was not available for work, widened the
connotation of " bound " to include this dormant energy. As
a matter of logical definition, only potential energy is really
bound. That which is bound can be freed by cutting the bonds,
i.e. by doing an amount of work which bears no relation to the
amount of energy bound, but depends on the nature of the bonds.
Dissipated or degraded energy is not in any true sense bound.
It is not free to do work, i.e. it is not available. To render it
available an amount of energy would have to be expended on
its environment at least equal to the amount of energy rendered
available.

A weight resting on the ground may be considered as representing a
body having degraded energy. Its energy potential is the same as its
environment. No work could be got from it without the previous ex-
penditure of work on it. If a certain amount of work were done in raising
it from the ground, then the same amount of work would be recovered on
letting it fall to the ground (taking into account the mechanical equivalent
of the degraded heat). On the other hand, a weight resting on a ledge

8

LAWS OF ENERGY

above the ground may perform work in falling if sufficient free energy
be applied to tip it over. The quantity of work done in tipping over the
weight bears no relation whatever to the amount of energy liberated in
falling.

The following scheme may help to make the matter clear :

Total Energy of the Universe

.(i)

.

Available for work,
i.e. Free Kinetic Energy

4- (2)

Not directly available for work

(4)

Potential Energy
Add trigger Energy from (1)

Free Energy
Total Available Energy

I (3)

Degraded Heat

(Entropy)
Totally unavailable

Total Unavailable
Energy

(3) Called " bound " energy by Helmholtz in 1882.
(3 + 4) Called " bound " energy by later workers.

(4) Called " bound " energy by Physicists.

One of the most important problems in biology is the means
by which potential energy is translated into work and the
mechanism by which this translation is controlled.

" The struggle for existence is the struggle for free energy " (Boltzmann).
Of potential energy there is an abundant supply. Some of
it, e.g. coal, requires the employment of only small quantities
of free energy to render it immediately available for work, while
other varieties, e.g. radio-active minerals, have their energy bound
in such a way that it is evolved with excessive slowness. Uranium
contains the same amount of energy as 250,000 times its weight

of coal (or more), but little more than 10 000 000 000 Part of

this is given out in a year (Chap. XI.). To enable mankind to
avail himself of this kind of energy, some means will have to
be devised for speeding up and controlling the output. As
Professor Soddy puts it : " Primitive man froze on the site of
what are now coal mines, and starved within sound of the water-
falls that are now working to provide our food. The energy
was there, the knowledge to utilise it was not. So while we are

INERTIA 9

leading cramped lives and fighting among ourselves, whether in
peace or war, for a modicum of the means of existence, science
tells us that, in the commonest materials that make up the
framework of the world, there is energy of a magnitude of which
we have no experience, and the means of livelihood of which we
have no standard. The energy is there. The knowledge that
can utilise it is not — not yet." In a similar way, the nations
had difficulty in procuring rations of sufficient energy-content
during the later days of the war, while all around them were
abundant supplies, but no method existed by which their energy
could be made available.

Physiological availability.

This introduces a further point. The energy- content of cellu-
lose is much the same as that of starch, yet as a source of energy
for man the former substance is useless, while the latter is perhaps
his main source of energy supply. An inorganic example may
make this clearer. Two lakes may be exactly similar except
that one has an outlet, while the other is surrounded by impass-
able mountains. The water power, i.e. the stored energy of the
former, is utilisable, while the latter could not be tapped with-
out arduous engineering labours. The energy-contents of the
radio-elements (atomic energy) of cellulose (as human food) and
of the undrained lake are said to be non-utilisable. Future
scientists may discover how to draw upon this surplus energy
supply.

Inertia.

The second law of energetics lends itself to the deduction that
the cause of all action (change) is the tendency of energy to attain
the same uniform degree of intensity as its environment. Further,
the degradation of energy follows the line of least resistance.
This is known as the " Law of Least Action " or the " Principle
of Le Chatelier." It is a law common to all sciences, and is
considered by some to be a universal principle. Physicists tell
us that bodies remain in a state of rest or of uniform motion in
a straight line unless energy be imparted to them to overcome
their inertia. Inertia is the resistance to change possessed by
everything, living and non-living.

One may take a step further and qualify the law by stating
that the nature of the change induced by an alteration in any
factor which influences the system will depend on what will, in

10 LAWS OF ENERGY

the circumstances, give relief from strain with the least possible
expenditure of energy. When a state of strain is made more
or less permanent, the organism readjusts itself to meet the
strain. That is, the easiest course is not to remove the cause
of strain, but to make such an alteration in itself as shall render
the external change innocuous. This is the principle underlying
the theory of adaptability. A tree arranges its branches so as to
offer least resistance to the prevailing wind. Other examples
might be drawn from the sciences of physiology, economics,
psychology and ethics.

Physiology. The introduction of an irritating substance into
the alimentary canal causes vomiting to remove the cause of
irritation, i.e. to relieve strain. Some less exhausting means of
relieving strain has to be taken to meet the more or less con-
tinuous administration of poison. The cells of the organism so
alter as to be immune from such irritation. Mithridates is said
to have qualified for the throne of Pontus by the ingestion of
all sorts of poisons in his youth.

Economics. The law of supply and demand, rates of ex-
change, etc., are merely restatements of this principle of least
action.

Psychology and Ethics. The unjust judge met the early appeals
of the widow with a firm refusal. His mind was relieved, his
case settled. Because of her very importunity, persistent strain
was set up which had to be relieved by reopening the case and
giving a just decision.

Enough has been said to show the possibilities of this deduc-
tion from the second law of energetics. The thorough-going
mechanist states that this law of least action is the principle
governing the action of living as well as dead matter.

All action, it is said, is a response to stimulus, and is such as
will most permanently and with " least action " relieve the state
of strain. The mechanist denies any cause of action but this.
What has been taken for the effect of will or instinct is in reality
the effect of light, of gravity, of friction, of chemical force, or of
some other known or knowable external force. In short, some
alteration in an external factor has brought about an instability
in the physico-chemical equilibrium of the object or of the
organism, and thus a shift in the equilibrium will take place in
such a direction as to decrease the magnitude of the alteration
which would otherwise occur. The animal, human or otherwise,
is but a machine, working according to physico-chemical principles,

PRINCIPLE OF LEAST ACTION 11

reacting blindly and quantitatively to every chance force which
plays on it. While, to a certain extent, we may regard this as
true, we must, nevertheless, draw a sharp distinction between
those actions which may be regarded as pertaining to organic
life and those which pertain to conscious life dominated by
personality. Plants and animals may be governed by this law
of equilibrium, and every one of their actions may be regarded
as a blind response to stimuli, just as the swing of a galvanometer
needle is. Man, in so far as he is an animal, may also be con-
sidered a blind agent. Is there not, however, something super-
added — not to interfere or even to govern, but to carry out a
function of its own ? For example, there are no grounds for deal-
ing with volition merely as a complex chemical equation or as a
problem in molecular physics, resulting merely from physical or
chemical changes in the body or environment. Suppose a man
meets another man in the street who suddenly strikes him. The
injured man has several courses open to him :

1. He may hit back.

2. He may run away.

3. He may fetch a policeman, and so on.

The action taken depends on several factors :

1. The previous history of the two men.

2. The relative sizes of the two men.

3. The nature of the spectators.

4. The nearness of the policeman.

5. The real business of the injured man, whether pressing, etc.

6. The personality of the injured man.

Knowing the man one may predict his action in a certain
case, and one may probably be right, but it is only a probability
—not a certainty. While the cause of volition is still unknown
and cannot but be regarded as mysterious, there is nothing to
hinder research into the mechanism whereby the Will causes
its dicta to become acta.

To summarise, the physical necessities of man have become
a problem of energy pure and simple. The fact that man is
living scarcely makes the problem more complicated than one
arising out of the fuel demands of an inorganic machine. So
much work has to be done, so much energy must be provided.

Energy is indestructible, and in itself is only valuable in its
conversion from what may be called higher to lower forms. This

12 LAWS OF ENERGY

transformation involves the loss of some available energy. A
certain amount finds its way into the great ocean (or " sink ")
of heat energy of nearly uniform temperature. The attainment
of this dead level is the final goal of all energy whether it is
utilised or not.

CHAPTER II
THE STORAGE OF ENERGY

" The energy available for each man is his income. Stored energy is a
legacy deposited in Nature's bank."

ALL life processes demand for their continuation and mainten-
ance a continuous supply of energy. In metabolism, as far as
matter is concerned, there is a closed cycle. Animals feed on
plants, and plants feed on the products of animal metabolism
and disintegration. The net result is practically nil. Energy,
however, must be supplied from outside. The one essential
physical factor that makes the process possible is the supply
of energy as sunlight to the plant.

The ultimate source of all the energy upon which existence
on this planet depends is the sun. (One need not here enter
on the interesting question of how the sun evolves energy ; see
Soddy, Matter and Energy, Chap. X.) As far as we know, the
higher forms of life are unable directly to use, either heat or
light as sources of bodily energy. Some of the lower forms of
animal life may have this power ; plants certainly have. As
we shall see later, light energy may act as the trigger, setting
free potential energy and causing work to be done.

All living matter may be divided into two distinct classes :
(a) that subsisting upon the materials which they take from
the earth and the air, and (6) that dependent upon other organisms
either living or dead. Examination shows that the main chemical
difference between these two classes is that the former contains
a green pigment called chlorophyll as a regular functioning con-
stituent, while the latter does not. It is evident that chlorophyll
is correlated with the state of independence that is typical of
plant life.

Chlorophyll.

(Revise : Physics of light, especially that of absorption spectra,
page 71 ; chemistry of chlorophyll and its relation to xantho-

13

14 THE STORAGE OF ENERGY

phyll, erythrophyll, etiolin and carotin ; botany of green plants,
distribution of chlorophyll in leaves ; variegation in leaves ; and
structure of chloroplasts) (see Fig. 1).

* \o\y\6

H£AT VISUAL ACTINIC

FIG. 1. — Curves showing relative energy and luminosity of different regions of the
spectrum. (Abney.) The wave-lengths are given in Angstrom units. An Angstrom
unit (A.U.)=one ten millionth of a millimetre = 0'1 n/j..

Absorption Spectrum of Chlorophyll.

An optical property of primary importance in a substance is
its differential absorption of light. The wave motion of the
ether, which constitutes white light, is very complex, consisting
not only of transverse vibrations in every plane, but of waves
of different lengths associated together. Now each wave length
produces a definite colour-sensation in the optical receiving
mechanism. The shortest wave length optically perceptible to
man is 4/10,000 mm. (violet), the longest 7/10,000 mm. (red).
Between these extremes there are blue rays 470 /x/x, green 510 /x/x,
and orange 620 yu/x. (These are average figures, e.g. the various
lengths classed under orange vary from 595 to 645 /x/x [u/x —
1/1,000,000 mm.].) Beyond these visible rays exist both shorter
(ultra-violet) and longer (infra-red) rays. From physics one learns
that the ultimate constituents of matter exist, not in a state of
rest, but in a state of ordered motion. That is, the electrons
(or other ultimate complex, see colloids, p. 75, and radiant
energy, p. 117) vibrate with a definite periodicity dependent on
the intrinsic energy of the system to which they belong. From
the study of the emission spectra of gases, a relationship may
be deduced between the period of vibration of a particle and the
position of the light bands emitted by the element in gaseous
form. Conversely, if one views the absorption spectra of that
gaseous element, black bands will be found in place of the light
emission bands. To take a concrete example, if a substance
when emitting light produced rays consisting for the most part
of waves 680 /xxx long, the colour of the light evolved would be

CHLOROPHYLL 15

red. The substance, if viewed through a spectroscope, either
when undergoing combustion or in the gaseous state, would
produce a dark band in the red section of the spectrum. Further,
light falling on a coloured substance is not completely absorbed.
A red substance reflects red light and absorbs the other rays.
Only light corresponding to the spectral bands is absorbed.
Grotthus proved that no effect could be produced by light unless
it was absorbed. He showed that red iron-thiocyanate was
bleached by exposure to green light, yellow chloride of gold and
blue starch-iodine complex by blue and yellow light respectively.

1. A mere glance at the absorption spectrum of the green leaf
is sufficient to show that the light best absorbed is that having
a wave length less than 500 /x^i, the amount absorbed becoming
greater as the wave length becomes shorter, i.e. the chloroplasts
absorb the actinic rays (violet and a small amount of the ultra-
violet rays). There is also a well-marked absorption band in
the red portion of the spectrum between 665 and 685 JJ./JL. The
figure for the maximal energy of solar radiation is given by
S. P. Langley as 650 to 666 /m/m. for high sun, so that the green
leaf is able to (a) utilise the actinic rays, and (b) absorb light of
that wave length (red) which is emitted by the sun in greatest
amount. The pigments of the chloroplast do not utilise green-
yellow light, nor do they absorb the heat (infra-red) rays at all.

2. Consider next the physical (and chemical) changes brought
about by the absorption of light. Although this is the primary
problem in Biology and has attracted many investigators, it
remains unsolved. Research has made it more apparent that
the mechanism for converting solar radiation into bound energy
is not so simple as was at first thought. Certain facts, however,
have been brought to light.

(1) Matter is assimilated. Elements taken from the environ-
ment are built into organic compounds. Boysen- Jensen has
shown that in July the accumulation of matter (dried) may reach
16-5 per cent, of the total dry weight of the plant. A large
proportion of this matter can be shown to be carbohydrate by
a very simple experiment. It is only necessary to screen a por-
tion of a leaf from the light, leaving a certain portion exposed,
and then observe any differences between the normal and the
darkened portions. If a leaf, like sunflower or fuchsia, is chosen
and previously kept overnight in the dark, exposure to light for
15 minutes is sufficient, and one hour is more than ample for our
purpose. The leaf is then bleached with warm alcohol, and

16 THE STORAGE OF ENERGY

iodine is applied. The part exposed to light will appear blue-
black — rich in starch, while the screened portion is starch free.
It has been shown that during the day the starch content of
leaves may rise to 6-44 per cent, of the dry leaf weight. At
night the starch value may drop as low as 0-38 per cent. Timi-
riazeff has devised a very neat experiment which demonstrates
that starch formation is greatest where there is greatest absorp-
tion of light. Living hydrangea leaves, previously deprived of
starch by retention in the dark, have then projected on them a
solar spectrum for 5 or 6 hours. The leaf is decolorised and
treated with iodine, and then the absorption bands of the chloro-
plast pigment complex are found mapped out in blue, showing
that starch has been formed only where light has been absorbed.
Other carbohydrates are also found. Cane sugar is formed and
can be detected before starch can be found, and it is generally
present in greater amounts, 7-63 per cent, to 2-63 per cent, of
the dried-leaf weight. Other sugars are present in small variable
quantities.

(2) It seems that CO2 is absorbed beyond the needs of respira-
tion, and that O2 is evolved. Engelmann has provided in a
striking manner a demonstration of the fact that the maximum
evolution of oxygen takes place where there is the maximum
absorption of light and, as stated above, the maximum formation
of starch. He placed a filament of cladophora in water, to which
he added some motile bacteria having an avidity for oxygen.
On the thread of alga he projected a minute solar spectrum and
kept it under the microscope. It was seen that the bacteria
gathered just at those places (red and violet) where light was
absorbed.

Kniep and Minder have determined the carbon assimilation,
and they find it directly proportional to the amount of energy
absorbed as light. Further, Willstatter and Stoll have estimated

(a) The CO2 taken up by a leaf area in the dark, i.e. respira-

tory CO2.

(b) The CO2 absorbed in light of a definite intensity.
(ft) _ (a) — assimilated CO 2.

(c) The O2 evolved in the dark - respiratory O2.

(d) The O2 evolved in the light -total O2.
(d) - (c)=non-respiratory O2.

TTT- -^ — -
(d)-(c) O2

(Cf. respiratory quotient, see Chap. III.).

(e) TTT- -^ — -^— assimilation coefficient.
' (d)-(c) O2

SYNTHESIS OF CARBOHYDRATE 17

They find that under all conditions of light the assimilation
coefficient is 1. From this it may be inferred that C not CO2 is
being built into the leaf. In short, the chloroplast acts as a
machine for converting CO2 into C and O2 which is evolved.
The carbon then unites with water to form some simple sugar,
which one is not known. The final product is starch. The
process may be represented by the equation :

#H2O +#CO2 +light energy =0^0^ +aO2.

It has been proved that the first step is the formation of
formaldehyde, i.e. a?=l.

(i) H2O +CO2 +112,090 gram cals (?)^O2 +CH2O

(formaldehyde).

Formaldehyde is injurious to plant tissues, and it is rapidly
transformed into other products.

If x=2 then the formaldehyde would condense to form gly collie
aldehyde — a diose.

(ii) CH2O +CH2O +energy-^C2H4O2.

Similarly, glucose could be formed.

(iii) C2H4O2 +C2H4O2 +C2H4O2 +energy^C 6H12O6.
Two molecules of glucose combine to form maltose.

(iv) CCH12O6 +C6H12O6 +3300 gram-calories

^C12H22OU +H2O.

(v) The gums or dextrins are composed of condensed mole-
cules of maltose, e.g.

C12H22On +C12H22On +H2O +energy^C24H46O23,

and so on.

(3) The energy value of CO2 is 2-1 cals. per gram, that of H2O
is 6-5, while starch has a value of 4191 gram cals. It is evident,
therefore, that in some way the plant has converted a certain
amount of kinetic energy into potential energy. Now, as the
formula for starch is uncertain, let us consider the amount of
energy required to form glucose from CO2 and H2O. Carbon
dioxide and water are fully oxidised. Theoretically, they may
be considered as undergoing a process of reduction before com-
bining to form the aldehyde, but as the energy evolved during
reduction would be balanced by the energy absorbed during
formation, we may limit our problem to the total energy change
according to the two equations given above, viz. (i) and (iii).

18 THE STORAGE OF ENERGY

From (i) we see that a gram-molecule of formaldehyde has an
energy-content approximating 112,300 gram calories. This store
of energy is derived from the constituents H2O (117 gram cals.),
CO2 (92-4 gram cals.), and from absorbed sunlight (112,090-6
gram cals.).

With the formation of formaldehyde, practically all the energy
necessary for the formation of carbohydrates has been absorbed.
As we shall learn later (Chap. V.), osmotic energy is a function
of concentration. Therefore, when six molecules of formalde-
hyde are condensed to one molecule of glucose, a corresponding
amount of osmotic energy is liberated, and this may be utilised
in part in endowing the glucose with the slightly higher content
of chemical energy which it possesses over that of the formalde-
hyde. Sunlight here acts as a catalyst (Chap. IX.).

As we have seen, all the light falling on the leaf is not utilised
— even all the light absorbed is not stored. Some energy is
required for direct domestic use, e.g. transpiration. It has been
calculated that about 10 per cent, of the incident light is absorbed
by the chloroplast pigments. In an experiment by Brown and
Escombe it was found that a total amount of incident light,
which, if converted into heat units would correspond to 0-041
cal. per sq.cm. per minute, caused the decomposition of 0-00034
c.cm. of CO2 per sq.cm. per minute. In the conversion of 1 c.cm.
of CO 2 into glucose 5-02 gram cals. are stored. Therefore, in
building 0-00034 c.cm. of CO2 into sugar the amount of energy
rendered potential would be

0-00034 x 5 -02 =0-0017 gram cals. per cm. per minute.

As that is about 4 per cent, of the total incident radiation,
the efficiency of the chloroplast under maximal conditions is
somewhere about 40 per cent. When the process is reversed
and carbohydrate split up with the assimilation of oxygen and
the evolution of carbon-dioxide, this energy is again set free.
It may be freed in such a way that a certain proportion of it
appears as light. This light has, according to Trautz, the same
wave length as the originally absorbed light. Of course, in
general, the energy will be evolved in a form more suitable for
utilisation than this (see Chaps, on Osmosis, Surface Tension, etc.).

Fats are stored up also in the plant. Very little research has
been done on the synthesis of fats in the plants. Whether the
plant can form these compounds directly or whether they are
only synthesised from carbohydrate is not known. That they

SYNTHESIS OF PROTEIN 19

can be formed from carbohydrates is known, and Leathes states
that this action is exothermic, several molecules of simple sugar
going to the formation of one (larger) molecule of fat, having, of
course, a higher caloric value. The fat is almost exclusively
found in the fruit.

Incidentally, energy is bound in the formation of proteins.
This energy comes indirectly from the sun. Atmospheric nitrogen
is fixed in a form available for plant use by certain bacteria.
Each gram of nitrogen so fixed carries with it a considerable
quantity of energy which is obtained from the oxidative decom-
position of 100 mg. mannitol, the parent alcohol of the carbo-
hydrate, mannose.

To conclude, the plant acts as a transformer of kinetic into potential
energy by the formation of carbohydrates, fats, proteins (the so-called
proximate principles of food) and a few other substances of minor
importance as storehouses of energy.

Having regard to the fact that free energy is of vital import-
ance, and that the potential energy of the foodstuffs is readily
rendered available, one would consider it a profitable study to
determine the exact mechanism of this conversion. So far, study
of pure chlorophyll has led to negative results. Kremann and
Schnidlerschitsch have recently shown that pure chlorophyll, in
alcohol, absorbed the same amount of CO2 as the alcohol itself,
and it made no difference whether the solution were exposed to
light or kept in the dark. The absorption spectrum of neither
chlorophyll a nor chlorophyll b nor chlorophyll a-\-b is similar
to the spectrum of the living green leaf. Knowledge is incom-
plete both of the chemical nature of the various constituents of
the chloroplast and of the distribution and physical state of the
components of this heterogeneous system. The pigments are
associated with a colloid complex and the absorption of CO2
with alterations in the electrical state.

To sum up, man obtains the energy necessary for his main-
tenance and for the performance of physical work from the
disruption of proteins, carbohydrates and fats, synthesised in
the first instance by green plants which trap and store solar
energy. Historically and until quite recently, the energy of sun-
light, apart from an insignificant amount drawn from the tides,
was the sole income of energy available for the world. Mankind
still maintains himself solely on the energy derived from the
sun through the intermediary of plant and animal metabolism,
but he derives his energy for work to an increasing extent from

20 THE STORAGE OF ENERGY

a legacy of potential energy laid by in former times. He has
devised detachable limbs (machines and tools) able to utilise the
energy of coal, petrol, etc., of which he could not avail himself
without their aid. This made possible an enormous increase in
the world's work — work done no longer by human beings and
beasts of burden, but by inanimate machines using the energy
of fire, electricity, etc. To-day, a single machine does the work
of an army of men. In this way he conserves present-day solar
energy and lives on the banked income of past ages. Some time
in the future he may learn how to synthesise food from inorganic
constituents by the use of any form of available energy. Then
and only then will he be able to dispense with plant life. Steps
in this direction have been made. Moore and Webster have
synthesised formaldehyde by exposing an aqueous solution of
CO2 to ultra-violet lignt (Chap. XI.) in the presence of inorganic
colloids (Chap. VIII.). They have also shown that dilute solutions
of nitrates exposed to ultra-violet rays are converted into nitrites
with an absorption of energy. One gram molecule of nitrite
formed from nitrate transforms about 10,000 gram-calories of
radiant energy into the potential state— a strong endothermic
reaction. This is similar to the change taking place in the plant
in the formation of nitrogen compounds — the first stage in protein
anabolism.

CHAPTER III
LIBERATION OF ENERGY

(1) CALORIMETRY

" From the use of materials arise physical results, such as work, heat and
electricity, which we can express in heat units. This is the power derived from
metabolism." VOIT.

THE next matter for consideration is the method of measuring
the potential energy of foodstuffs and comparing the value so
found with the actual amount of energy liberated in the organism.
It should then be apparent whether living matter in its various
energy-changes obeys the laws of energetics. For purposes of
measurement, it is customary in biology to convert all forms of
energy into that of heat. This is scientifically correct, as heat is
the " lowest grade " of energy, and all other forms of energy
(ordered motion) may be degraded to unordered motion (heat) ;
and it is not possible completely to convert any form of energy
into any other form of energy but heat. In any such conversion,
as we have seen, there is always a certain loss as heat. The
unit of heat adopted in biology is the large calorie — that is,
1000 times the amount of heat required to raise one gram of
pure water from 15° to 16° C. This value is almost the same as
that required to raise one kilogram of water 1° C.

Just as a country must have a standard coin of the realm —
pound or dollar — in which its assets may be computed, so must
there be a standard unit for the computation of energy. The
bank-teller totals up his day's transactions in £ s. d., no matter
how various are the forms in which he has received or parted with
the money. Cash, notes, cheques, deposit receipts, etc., all
appear on his final balance-sheet under one denomination. Simi-
larly, all energy transactions can be summed up and balanced
as so many calories received, so many calories expended. Further,
the fact that not a single sovereign may have crossed the counter

21

22 CALORIMETRY

does not hinder the banker from entering £ sterling in his books.
So calories may be the units employed, although heat may not
necessarily enter the reaction.

A. Measurement of energy -value (E.V.) of foods by ultimate analysis.

The energy of a pure chemical compound may be calculated
from its chemical formula. The amount of heat evolved when
C is oxidised to CO2 and when 2H is combined with O to form
water has been determined. The equations of these two reactions
could therefore be written :

C +O2= CO 2 + 94-31 cals.

2H2+O2=2H2O +117-4 cals.

(A horizontal line above the formula of a substance in a thermo-chemical
equation indicates that the substance is in the gaseous state, the absence
of any line indicates the liquid state, while a line below the formula indi-
cates the solid state. The suffix aq is intended to convey the idea that
the substance is in solution in such a large volume of water that the addition
of more water would not produce any appreciable effect — that is, the
substance is so dilute that its heat of dilution on the further addition of
water would be negligible.)

One must note that any alteration of gaseous volume or of
any other physical characteristic of any of the reacting units
would, by utilising some energy as positive or negative work,
produce an alteration in the amount of heat evolved. Welter
enunciated a rule whereby one might arrive at an approximate
value of the heat of oxidation of a compound containing oxygen
as well as carbon and hydrogen. According to this rule the
oxygen is subtracted from the molecular formula with as much
hydrogen as would serve to convert it completely into water,
the heat of oxidation of the carbon and hydrogen in the residue
then gives a rough value of the heat of oxidation in the whole
compound. For example :

A fat, tripalmitin, has the following formula C^HggOg
Deduct intramolecular water H12O6

Leaving for oxidation - - CsiHgg

C51H86 +145O2=51 CO2+43 H2O

=51 X 94 -31 +43X58 -7

=7333-9 cals.

That is, a gram molecule (806 grams) of tripalmitin in being
completely oxidised to CO2+H2O would liberate 7333-9 cals. of
heat. Similarly, the energy stored in the form of carbohydrate
may be calculated. A difficulty, however, occurs with proteins.

MEASUREMENT OF ENERGY VALUES

23

In the case of carbohydrates and fats the end-products are
those of complete oxidation, but in the case of proteins, the
final results of metabolism are not substances of the lowest

FlO. 2. — Berthelot-Mahler Bomb Calorimeter.
A. Bomb or autoclave (see Fig. 3).
H. Insulating vessel.

G. Manometer on stand with unions to fix to oxygen cylinder and to bomb (at S, Fig. 3).
D. A steel mould for making pellets from the material to be burned.

energy content, i.e. protein is not completely oxidised. Further,
these protein end-products are eliminated in solution, and this
requires some correction. Finally, to obtain the correct content

24

CALORIMETRY

-v*

of the foodstuff of C, H and O requires a complicated chemical
technique. This method of calculating energy-value is little used
in biology. Pure substances are seldom used as food material,
except in certain kinds of experiments.

B. Measurement of E.V. of foods by calorimetric combustion.

The principle underlying this method is the combustion of a
known amount of the material in an apparatus so devised that

practically all the heat evolved is ab-
sorbed by a known amount of water
and by the apparatus itself (which is
of known heat capacity). Some form
of bomb calorimeter is now universally
employed for this purpose. The in-
strument (Fig. 2) consists of three
main parts.

1. The bomb itself is constructed- of
steel, nickel-plated, with a cover to
be screwed on firmly against a lead
washer. Its capacity is about 300 c.cs.
Through the cover the entrance and
exit gas channels pass ; K2 with its
continuation platinum tube, R, is for
the introduction of oxygen, and Kl
for the withdrawal of the gaseous pro-
ducts of combustion. Both channels
are closed by means of the screw
spindles V\ and V2, running in stuffing
boxes. £1 and #2 are screws to stop
the lateral communication with Kl
and K2. Into these may be screwed
nickel - plated tubes. Through the
centre of the cover passes a strong
platinum wire, D, and this, as well
as R, is fitted with short pegs,
a1, a2, on which hangs the crucible

T. A short collar, just above these pegs, is for the attachment
of the ignition wire. Pi and P2 are two small screw-clamps for
attaching to the electric wires for ignition (Fig. 3).

2. The insulating chamber is a double- walled copper vessel
of about 11 litres capacity, and the space between the walls is
to be filled with water at room temperature. It is lined with

PIG. 3. — Section through a Kroeker
bomb (see text).

BOMB CALORIMETER 25

white enamel, and contains within it, but insulated from it by
a thin ebonite stand, 3. the bright nickel-plated water holder.

Besides this it is necessary to have a stirring device, a ther-
mometer to read to 1/100° C., and a means whereby oxygen at
15-20 atmospheres pressure can be put into the bomb.

Calibration.

Certain values have got to be determined before the apparatus
can be employed.

1. Calorie Value of Match.

In order to convert energy from the potential to the free state,
we have already seen that some free energy must be added —
the material must be ignited. Various forms of match are em-
ployed. Some workers prefer to suspend a dried cotton thread
of known weight from a platinum wire connecting D and R.
The thread dips into the crucible T, and touches or is embedded
in the material to be burned. On completion of an electric
circuit through Pi and P2 the platinum wire glows and sets off
the cellulose match, which in turn causes the foodstuff to ignite.
Others prefer to weigh out a piece of iron wire, 5-6 cms. long
and 0-1 mm. thick, and put it in place of both the platinum
wire and the cotton thread. In any case, the amount of heat
evolved in the ignition process has to be determined carefully,
and deducted from the heat evolved, in a complete estimation
or in the determination of the water equivalent.

2. Water Equivalent.

The apparatus itself — vessels, thermometer, stirrer — is heated
along with the water it contains. Its water equivalent, i.e.
the quantity of water which has the same heat capacity as the
apparatus, must be determined and added to the quantity of
water actually employed in the experiment. Several methods
exist for this determination. The most exact, and at the same
time the most convenient, is to burn in the calorimeter a weighed
quantity of a substance whose calorie value is known with
absolute certainty, and ascertain the resultant change in the
temperature of the water. The water equivalent is :

(Total heat generated (calculated) \ iri ... ,.

\ - (Quantity of water in
Observed increase in temperature of calorimeter water/ apparatus (in gins ) )

3. Calibration of Thermometer.

The thermometer has to be calibrated, and a correction
applied for this.

26 CALORIMETRY

4. Cooling Constant.

Another correction to be made in the final calculation is
that of the cooling constant of the apparatus. The chief source
of error in calorimetric. experiments lies in heat exchange with
external objects by conduction and radiation. To reduce this
error to a minimum (a) the chemical action must go on 'as fast
as possible, hence the use of oxygen under pressure ; (b) the
temperature of the calorimeter water is kept as nearly as possible
at the same value as the temperature of the room. We have
already stated how the grosser errors of conduction and radiation
are avoided by the structure of the insulating chamber. In spite
of this there is a certain loss, which is measured as part of the
regular routine of an experiment and is allowed for.

In order to calculate the energy of any material one must know
what the end-products of the combustion are. We have seen
that C and H are always under these circumstances completely
oxidised to CO2 and H2O, which undergo little or no further
energy changes. S and N, on the other hand, are converted into
sulphuric and nitric oxides, which in turn dissolve in and combine
with water forming H2SO4 and HNO3. A correction has to be
applied for their heats of solution and combination. For very
fine work, corrections may be applied for the latent heat of
evaporation of water and for the heat of solution of CO2.

Determinations of the energy- value of the proximate principles
of food have shown that only minute differences exist between
the various members of any class. For example, one gram of
each of the following carbohydrates has the accompanying value
in calories :

TABLE II.

Starch =4-191 large calories.

Cane Sugar =3-955 ,, „

Maltose =3-94 ,, „

Milk Sugar (Lactose) =3-95 „ „
Glucose =3-74 ,, ,,

Fruit Sugar (Fructose) =3 -75 ,, ,,

Average values have therefore been adopted and accepted as
standard. E.g.

Carbohydrate - 4-1 Calories.

Fat - " - 9-3

Protein - - - - - 5-3

PHYSIOLOGICAL CALORIE VALUE 27

Of course, the discerning student will understand that, except
in rare and restricted feeding experiments which have a special
end in view, pure carbohydrate, fat and protein are not exhibited.
Determinations are made of the energy-value of actual foods.
This gives opportunity for the display of some ingenuity on the
part of the investigator, since some of the commoner articles of
diet do not readily lend themselves to combustion and are not
easily dried. Nevertheless, extended experiments are being con-
ducted by physiologists, in which, as part of the routine, the
total energy- value of the daily diet is determined.

The energy-value of the diet does not represent the energy
used by the organism.

(a) Some energy-carrying substances cannot be digested, and
therefore are excreted unchanged in chemical composition and
energy content, e.g. cellulose.

(b) Other constituents of the diet may undergo some chemical
alteration, but may be excreted not fully deprived of their energy.

(i) Proteins are not completely oxidised in the body. Their
end-products are urea and allied substances.

Because of the difference in the end-products there is a physio-
logical calorie value for proteins different from their purely
physical value. Rubner determined this physiological value by
deducting from the absolute value, the heat value of nitrogenous
end-products in faeces and urine with their heats of solution.
He arrived at the figure 4-015. The accepted average value is
4-1 calories per gram of protein.

(ii) Certain substances are excreted in combination with protein
disintegration products, e.g. hippuric acid.

(c) Certain substances or their disintegration products seem to
be necessary constituents of faeces, e.g. fats (see Chap. XXVII.).

The energy-value of all excreta must therefore be deducted
from the energy intake before an energy balance can be struck.

C. Measurement of the E.V. of foods by animal calorimetry (a) direct,

(b) indirect.

It is obvious as a direct deduction from the first law of energetics
that if this law holds in living as well as in non-living matter-
energy transformations, the same amount of energy should be
evolved from the utilisation of food inside as well as outside the
body, provided always that the physical state and chemical
end-products are the same in each case. If an animal could be
put inside a calorimeter and given a definite amount of food,

28 CALORIMETRY

the heat evolved should, providing our hypothesis is true, be
exactly the same as would be evolved in direct food calorimetry.
Each gram of carbohydrate should produce 4-1 cals., and so on.
This can be put to the test in either of two ways. The first is
known as direct (animal) calorimetry, and consists in accurately
measuring the heat evolved by the animal under investigation.
The second or indirect method is based on a knowledge of the
amount of heat evolved per litre of the respiratory gases and per
gram of urinary nitrogen.

(a) The direct method was first employed by Crawford (1779).
His calorimeter, in principle, consisted of a double-walled box
with a known amount of water between the walls. The animal
was placed in the inner box for a definite time and the increase
in temperature of the water noted at the end of the experiment.
The method is, of course, primitive, and the veriest tyro in
physics could suggest quite a host of sources of error, but on this
crude instrument are based those finer implements of research
which, in the hands of Benedict and his colleagues, have con-
tributed so much to the knowledge of nutrition. Crawford found
that for every 100 ozs. of oxygen used during the combustion of
carbon in his calorimeter, the temperature of the water was
raised 1-93° F. A live guinea pig consuming the same amount
of oxygen produced an increase of 1-73° F. This seemed suffi-
cient evidence for him to conclude that, in each case, the heat
produced was due to the conversion of pure air into fixed, or, as
we should now say, to the combination of C and O2.

A year later, Lavoisier and Laplace published the result of
experiments which confirmed Crawford's results, and made firm
the principle of indirect calorimetry. They determined the
amount of ice melted by the combustion of a weighed amount of
carbon (a candle) and the volume of the CO2 evolved. A similar
experiment was then tried with a guinea pig. They found that
for equal volumes of CO2 formed, the candle yielded 25-4 cals.
as against the guinea pig's 31-8. The experiment is bristling
with errors, many of which the authors realised. For instance,
the respiratory and calorimetric determinations were not, as by
Crawford, made simultaneously, and obviously thermal con-
ditions were not the same. As we shall see' later, cold raises the
CO 2 output. If allowance is made for this and for other minor
errors, the figures for candle and animal come close enough to
justify the conclusion that the processes are similar, and that
the source of heat in both is the combination of C and O2.

ANIMAL CALORIMETRY 29

The various sources of error due to faulty technique have been
gradually eliminated, and the resultant calorimeters that bear
the names of Atwater, Rosa, and Benedict and that of Williams
produce results that are sufficient to convince even the most
sceptical of honest observers that the oxidation of assimilated
foodstuffs in the living body produces the same evolution of
energy as they would if burned in the bomb calorimeter, provided
the end-products are identical.

The direct method is not of such general use as the indirect.
Study of the papers from the Carnegie Institute of Washington
or of those from Cornell University makes clear the complexity
of the machine and the intricacy of its manipulation. The cost,
except for the smallest Williams' boxes, is prohibitive. The
apparatus can be much simplified if the direct estimation of the
energy-changes is omitted and the observer confines himself to
measuring the respiratory gases and the urinary output.

(b) Indirect. As we have seen, the basis of this method also
was laid by Crawford. It depends upon the following established
facts :

(I) The quantity of energy liberated depends on the chemical
composition of the food used.

(II) The quantity of oxygen absorbed depends also on the
chemical composition of the food used ; therefore,

(III) There must be some relation between the energy evolved
and the quantity of oxygen absorbed.

(IV) The three proximate principles of food differ markedly
in chemical composition, (a) Proteins contain nitrogen, which
is eliminated almost entirely in the urine, (b) Carbohydrates
and fats differ widely in their proportion of O to C.

(V) If a determination were made of the amount of heat and
the amount of C and O2 which corresponds to each gram of
urinary nitrogen, one could, from the nitrogen excreted, calculate
the heat liberated from the protein of the diet. (1 gram of
urinary nitrogen— 26-51 cals.) Having deducted the protein O2
from the total O2 absorbed and the protein CO2 from the total
CO 2 eliminated, one arrives at the figures corresponding to the
non-protein O2 and CO2 respectively.

(VI) Now, as we have said, carbohydrates differ from fats in
their respective contents of C and O2. Carbohydrates have the
general formula #(CH2O), while fats contain less O2 compared
with their content of oxidisable matter, e.g. #(C9H12O). There-
fore, when carbohydrates alone are used, the ratio of the volume

30 CALORIMETRY

of CO2 eliminated to the volume of O absorbed will be 1, as may
be deduced from the equation :

C(H20) +02=C02+H20

1 vol=l vol R-Q

Fats are compounds of the trihydric alcohol, glycerol, with organic
acids of the aliphatic (fatty) homologous series. The simplest
fatty acid is formic, H-COOH. The higher acids are built up
by successive additions of CH2.

TABLE III.
SATURATED SERIES. C^H-^Osj.

E.g. H-COOH -formic acid CH2O2

CH2-HCOOH— acetic acid C2H4O2

CH2 -CH, -HCOOH— propionic acid C3H6O 2

CH2-CH2-CH2-HCOOH— butyric acid C4H8O2

(CH2)15-HCOOH— palmitic acid C16H32O2
(CH2)16-HCOOH— margaric acid C17H34O2
(CH2)17 -HCOOH— stearic acid C18H36O2

UNSATURATED SERIES. CMH2M__2O2

oleic acid C18H34O2

A glance at this list will make it clear that the amount of
oxygen does not increase although the C and H are increased.
This paucity of oxygen content is more marked in the fats than
in the fatty acids.

Palmitic Acid Glycerol Palmitin

C15H31COOH HO,

C15H31CO OH H OC3H5=C51H9806 +3H2O

C15H31COOH

C51H98O6 +145O=51CO2 +49H2O.

Vol CO 2 51
Now ratio=^]re-=^r5=0.70.

That is, ratio for carbohydrates is 1.

„ „ fats ,, 0-7 (circa)

(Zuntz gives 0-707 as an average figure for fats.)

(VII) Values for a non-protein ratio lying between 0-7 and 1
denote the utilisation by the body of a mixture of fats and carbo-

INDIRECT CALORIMETRY 31

hydrates ; the closer the ratio comes to unity the more carbo-
hydrates are being oxidised, and vice versa.

(VIII) Now, knowing the proportion of carbohydrate and fat
in the diet, one may calculate the amount of energy set free
from the two following figures :

(a) If carbohydrate alone is used each litre of O2=5-047 cals.
(6) If fat „ „ „ „ „ -4-686 cals.

Intermediate values may be obtained by interpolation. The
results obtained by indirect calorimetry are within 2 per cent,
of results from the respiration calorimeter.

In a series of twenty-two different experiments with a dog,
Murlin and Lusk obtained the following results :

Indirect calorimetry - - 2244 cals.

Direct „ - 2230 „

Difference - 14 ,,

Percentage - 0-6 ,,

CHAPTER IV
LIBERATION OF ENERGY

(2) THE ANIMAL AS MACHINE

" The living and the dead, things animate and inanimate, we dwellers in this
world, and this world wherein we dwell, are bound alike by physical and mathe-
matical law." THOMPSON.

WE have just seen that :

(1) Some of the radiant energy of the sun is stored by plant
agency, and is ingested by the animal as food ; and (2) the sum
total of the energy taken in by the organism in this way can be
accounted for. There is neither gain nor loss of energy in the living
animal : the physical law of conservation of energy holds good.

We must consider the physics underlying the liberation of this
energy. Does it follow any of the methods well known to us ?
Can we compare the foodstuffs to fuel and the body to a heat
engine ? In other words, what intermediate stage, if any, does
the potential energy of, say, starch, reach before becoming
apparent as animal energy ? The physiological text -books are
so full of references to combustion, fuel value, burning of food-
stuffs, that it is natural for the student to look upon the life
processes as somewhat similar to those of a steam engine. In
spite of this it can be definitely said that the animal body bears
little resemblance to any form of heat engine. The intermediate
stage between potential and free energy is not the wasteful one
of heat. In order that heat may be converted into work there
must be a certain allowance for " spillage." There must also
be a certain gradient of potential. In other words, unless
there is a certain minimum difference in temperature between the
source of heat and the sink (or heat condenser), the machine will
not work. (Principle of Carnot.) In 1824 Carnot determined,
theoretically, the percentage of heat that any heat engine could
convert into work. A theoretically perfect engine, working

32

THERMAL EFFICIENCY 33

between the absolute temperatures T± and T2, takes up Q cals.
from a heat reservoir at the temperature Tl and transforms the
part W into work, then

T —T

W=Q -4^— * (Carnot's Equation).
•*- 1

T -T

Evidently the fraction — ^~ — - is that part of the Q units of heat

•* i
which represents the amount of energy made available for work.

That is, even under unattainably perfect conditions no more heat

T y

than — ~ — of the amount given can be converted into work.

•*• i
This equation gives the efficiency of the heat engine.

The most efficient steam engine yet constructed — a Nordbeg
air compressor of 1000 h.p. — converts 25 per cent, of the heat
energy it receives into work. Most steam engines are only 8 to
10 per cent, efficient, i.e. only 8 tons out of every 100 tons of
perfect fuel burned have their energy converted into work.

TABLE IV.

COMPARATIVE THERMAL EFFICIENCIES.

(Compound (non-condensing) - 8-12 per cent.
Steam - „ (condensing) - 10-16

^Parson's turbine - 15-18

(Petrol (motor) - 22-24

Internal I „ (aero)- - 26-28

Combustion -1 Coal gas (stationary) - 29-31

I Diesel - 33-35

Combined I.C. /Still engine - 41

and Steam -\Still-Diesel combination - 44

Combined steam and electric generator - 55

Animal body - 25-34

If one were to consider the animal as a heat engine, then it
must operate between two temperatures. One of these tem-
peratures we know, viz. body temperature, which is 38° C.
or 273+38=311° absolute. This is the condenser or "sink"
temperature. The other temperature, that of combustion,
must be higher. How much higher may be calculated from the

equation above.

ff y

Efficiency = — ™ — —E,
* i

or transposing

TI=TZ/I-E.

34 THE ANIMAL AS MACHINE

Suppose we take a low figure for animal efficiency, say 20 per
cent. Then, substituting, we find that

O1 1 O-| "I

T1=-—-— =— =389° absolute or 116° C.

1 — \}'£i O'O

That is to say, in order to have an efficiency of 20 per cent, with
a condenser temperature of 38°, the temperature of the heat
source would need to be 116° C. Experience teaches that the
production of any such temperature in any tissue would cause
death. Lethal temperature is somewhere about 47° C. How-
ever the animal may transform bound energy into free, it does
not do so by conversion to heat as one of the stages.

It is not definitely known how the living organism is able to
make use of the chemical energy of the foodstuffs. Analogy
with familiar non-living machines breaks down here. An electric
battery is able to transform chemical energy into kinetic energy
without the middleman heat, the go-between in this case being
certain unknown but ordered atomic movements. Observation
shows clearly that muscle at least is not similar to an electric
motor. Similarly, one can dispose of all other forms of energy-
transformation used in machines to get work from bound energy.

To attempt to gain an insight into the workings of the living
organism one must go back to elementary principles, and study
the machine itself. The history of the foodstuffs after ingestion
must be followed, and any changes they undergo must be noted.
The processes of digestion, absorption and assimilation will be
noted later. Meanwhile, we want to know what, in general,
happens to all foods used as sources of energy. Have they, in
the main, a common history ? Of one point at least we may be
sure, and that has been dealt with at some length in the preceding
chapter, namely, that liberation of energy in the animal and oxida-
tion are invariably concomitants. Thus the amount of oxidation
may be taken as a measure of the energy transformation.

Again, it has been definitely proved that all energy changes
and all vital oxidations take place in the living cell. Physiological
chemists, while unable to arrive at a definite conclusion as to the
composition of the cell, are at one with the histologists in stating
that the cell material is of the nature of a solution. Cell proto-
plasm consists of over 75 per cent, of water acting as the solvent
for certain crystalloids and as the dispersion medium for various
colloids. The cell comes into intimate contact with other cells,
and all cell contents are not of the same chemical composition

THE ANIMAL AS MACHINE 35

nor in the same physical state. There will, therefore, arise differ-
ences in surface tension and may be differences in osmotic pressure.
It will, therefore, be profitable for us to examine the energetics
of simple solutions ; then of colloid complexes ; and finally to
apply any relevant knowledge so gained to ascertained facts
regarding cell behaviour.

We must not forget that our aim in this digression (to solution-
dynamics) is to elucidate the processes by which the potential
energy of foods is rendered kinetic.

CHAPTER V
LIBERATION OF ENERGY

(3) ENERGY OF SUBSTANCE IN SOLUTION

" The problem of achieving perpetual motion contrary to the second law "
(of thermodynamics) " is that of bringing order and direction once more into
the chaotic rush of the molecules, to marshal and drill the mob so that once
more they can act together to produce a common effect." SODDY.

Osmotic Pressure.

The first process that affects food is that of digestion. Diges-
tion is merely the breaking down of the material supplied so that
it can pass through the absorbing medium in solution. It follows
(from this statement and from the physical state of the living
cell) that all energy manifested by an animal comes from sub-
stances in solution. No material is of any use for energy purposes
unless it is soluble, and until it is rendered soluble it cannot be
absorbed and utilised.

That is, the available energy of a cell may be divided into :

(1) The potential energy inherent in the various substances
that compose it.

(2) The kinetic energy these substances have because they are
in solution.

These two statements together imply that the mere solution
of a substance may so alter the state of that substance that
energy is set free. (Cf. heat evolved on diluting concentrated
H2SO4.) Further, it may be inferred from this that the physical
conditions which determine the character and behaviour of living
cells depend on the composition of the latter and on their environ-
ment.

Far-reaching dicta such as these cannot be accepted without
question. First of all, has the solution of a substance any effect
on its energy content ? Does sugar, for instance, lose some of
its energy-content when dissolved in tea ? Does the bound

36

VAN'T HOFF'S HYPOTHESIS 37

energy so liberated appear as kinetic energy without the inter-
mediation of heat, electricity, etc.?

When a solid goes into solution it at once loses the properties
characteristic of the solid state. Its particles become mobile,
and all the properties dependent on regular molecular arrange-
ment disappear. Thus the solid may be optically active
or doubly refracting, and the solution quite void of these
properties.

The passage of the substance into solution bears some resem-
blance to its passage into the liquid state. A doubly-refracting
crystal almost invariably loses its double refraction when it melts ;
and most substances which are optically active in the solid state
are inactive when fused.

The substance might conceivably have passed into the gaseous
state. Physical chemists are agreed that this is the most prob-
able course. They find that for dilute solutions, at any rate,
the simple gas laws hold good.

In order to explain and correlate these gas laws and the phe-
nomena of solution, evaporation, 'etc., the Kinetic Theory of the
structure of matter has been formulated. The views that have
been held regarding the constitution of solutions have been very
varied, and since Thermodynamics is too general in its method
of treatment to yield a complete answer to the problem, hypotheses,
guided and tested by experiment, are accepted. The following
theory was first propounded by van't Hoff in 1885, and it has
been improved by later physicists. It allows the Second Law of
Energetics to be applied with conspicuous ease and clearness
to the theoretical investigation of the quantitative relations
between the properties of solutions. Matter is regarded as an
aggregation of particles (molecules), each of which is perfectly
elastic and structurally independent. Between them there exist
spaces.

Two opposite forces are at work on molecules.

(1) A Cohesive Force. Newton's Law states that every portion
of matter attracts every other portion of matter. The stress
between them depends on the mass of the particles and the

m1 xra2
distance between them. Stress = ^—- where m± and w2 are

the masses of the particles and d the distance between them.

(2) A Repellent Force (Real Kinetic Energy =|rau2). Every
molecule is free to vibrate in a straight line within the limits of
the intermolecular spaces. In a solid these spaces are small,

38 ENERGY OF SUBSTANCE IN SOLUTION

and therefore the attractive forces are predominant. If a greater
kinetic energy be given to the molecules by means of heat, for
instance, their path will be increased at a rate corresponding to
the coefficient of expansion. At a point, the repellent force will

1 v2

exactly balance the attractive force, that is, ~rz==^- The sub-
stance then assumes the liquid state, gravity alone determining
the arrangement of the molecules.

If the temperature of the liquid be raised, some of the mole-
cules will have sufficient velocity to burst through the surface
layer and become free gas molecules. If these gas molecules
move away unhindered, other molecules from the liquid will
take their place, and the liquid will evaporate. If, however,
the liquid is kept in a closed space, the gas molecules which
leave its surface will be able to proceed no farther than the walls
of this space, and rebounding from these must eventually return
in the direction of the liquid. Some will strike the surface of
the liquid and will be retained by it. But the molecules still
continue as before to leave the surface of the liquid, so that, at
one and the same time, there are molecules entering and leaving
the liquid. When the pressure of the molecules leaving the
surface of the liquid balances the gaseous pressure above it, a
stationary state will be reached, i.e. the same number of molecules
will be freed from the liquid as are being absorbed by it. That
pressure is the Vapour Pressure of the substance. (Cf. tension
of gas in solution.)

In addition to the Kinetic Theory of gases, one must assume
the statement generally known as the Hypothesis of Avogadro :
" Equal volumes of different gases, at the same temperature and
pressure, contain the same number of molecules." This proposition
has been adopted as a working hypothesis, and as such has stood
the test of time. It is, in fact, a necessary supplement to the
Atomic Theory.

The laws governing the physical behaviour of gases are simple
statements correlating pressure, volume and temperature.

(1) Boyle's Law. The volume of a given mass of gas varies
inversely as the pressure on it, if the temperature of the gas
remains constant.

-P.

(2) Charles' or Gay Lussac's Law. The volume of a given mass

PRESSURE OF A GAS 39

of any gas varies directly as the absolute temperature if the
pressure remains constant.

VT=F0(l+aT).

(3) The pressure of a given mass of any gas varies directly
as the absolute temperature, provided the volume of the gas
remains constant.

PT=PQ(l+aT).

Any one of these laws may be deduced from the other two.
The whole may be summed up in the formula

PV=RT,

where R is a constant varying only with the unit of energy used.

TABLE V.

UNIT OF ENERGY. VALUE OF R.

Gram — Centimetre - - 84,760.

Joule (Volt— Coulomb) - - 8-315.

Volt— Faraday - 0-8613 xlO*.

Litre — atmosphere - - 0-08207.

Gram — calorie - 1-985.

The thermal equation with the gram calorie as unit is the one
most often employed in Biophysics, and is generally taken as 2.
That is, the gas equation assumes the approximate form

PF=2T.

What is the pressure of a gas ? The gas only manifests its
kinetic energy by alteration in its pressure or its volume. As
has already been stated, the molecules of a gas are free to move
in a straight line till they collide with another molecule or with
the walls of the containing vessel. The particle will then rebound
in its line of approach with a velocity equal to its orginal velocity,
but, of course, with the opposite sign.

The pressure of a gas is due to the bombardment of the walls of
the containing vessels by the molecules.

For unit volume, f of the total kinetic energy of the gas is
responsible for the pressure of that gas. Another conclusion
that may be drawn from the kinetic theory of gases is that the
velocity of a gaseous particle is inversely proportional to its mass.

40

ENERGY OF SUBSTANCE IN SOLUTION

This brings us to the study of gaseous diffusion. Before enter-
ing on this subject it is necessary to keep in mind Dalton's Law
of Partial Pressures, which may be stated as follows : In a mixture
of gases each gas exerts the same pressure as it would exert if
it were alone present in the volume occupied by the mixture.
The pressure of each gas is called its partial pressure. In other
words, if several gases are brought together, each of them will
be distributed through the whole space as if the other gases
were entirely absent.

Gaseous diffusion takes place, and as a result there ensues a
perfectly uniform mixture of the gases no matter what their
original proportions were, and irrespective of
the masses of their respective molecules. This
diffusion takes place independent of gravity.
A heavy gas will diffuse upwards into a lighter
one.

Now, suppose we separate the two gases, A
and B, by a thin porous septum such as a
plug of plaster of Paris. It was observed by
Graham that the pressure of the gases did not
remain the same on both sides of the mem-
brane. The pressure was greatest on the side
of the heavier gas. The molecules of lighter
gas B would bombard the septum far oftener
than those of the heavier gas A, and therefore
there would be a greater chance of some of
them hitting the pores and getting through
and so raising the pressure in A.

That this is so may be very easily demon-
strated by a simple piece of apparatus (Fig. 4).
"-"^i-tl ^~- C is an unglazed earthenware cell such as is
no. 4.— simple diffusio- usually employed to hold the zinc rod in a

meter. * f r

Leclanche battery. Into its mouth is fixed
a rubber stopper carrying a glass tube, the lower end of
which passes just through one of the holes in a similar rubber
stopper of the bottle B. The glass tube A passes right
through the other hole of this stopper and goes to the
foot of B, B is filled with coloured water. Both stoppers
must be thoroughly air-tight. If now a wide-mouthed bottle
containing coal gas is inverted so as to enclose C, the coloured
fluid will rise in A showing increase in pressure in C. If the gas
used were heavier than air, negative diffusion would take place,

OSMOTIC PRESSURE 41

and pressure in A would fall. This demonstrates the conversion
of unordered molecular motion into ordered hydraulic motion
capable of doing work.

The relative velocities of diffusion of any two gases even
through a thin porous septum are inversely proportional to the
square roots of their densities.

This does not hold if the septum is not very thin, for then the
velocity is decreased by the impact of the molecules on the inside
surface of the pores.

Graham further found that it was possible to procure semi-
permeable membranes — that is, a membrane which would allow
free passage to one gas but not to another. What will happen
in such a case ? Suppose B can pass freely through the septum
while A cannot. Both gases are at 1 atmos. pressure. Then
B will diffuse through the membrane, and fill up the next space
as if A were not there, i.e. there will finally be | atmos. of B on
both sides. The total pressure on A will be 1| atmos. The
excess of pressure is due to the gas A, which cannot pass through
the septum. So that by taking the difference of pressure on the
two sides of a semi-permeable membrane, we obtain the partial
pressure of the gas to which the membrane is impermeable. (See
Respiration, Chap. XXIII.)

An attempt may now be made to apply these laws (which are
only absolutely true for perfect gases) to solutions — in the first
instance to simple solutions only.

PV=RT=2I3 (Inmv*).

All these symbols seem applicable to a substance in solution
except P. What is the pressure of a solute ? This may be
determined in a way similar to the determination of gaseous
pressure. If an osmometer be fitted up (Part II. p. 398) with
a solution of sugar inside and water outside, in a short time
the fluid inside will increase in volume and will rise in the osmo-
meter tube developing a hydrostatic pressure. To what is this
pressure due ? Obviously water (and pressure) will be transferred
from a point where its pressure is high to a point where its pres-
sure is low. In some way or other the presence of sugar (or other
solute) has lowered the pressure of the water. Can this be
explained by reference to the kinetic energy ? Reasoning back-
wards, it may be argued that the sugar acts as a drag upon the
water molecules — that is, the bombardment of the membrane
becomes unbalanced. The pure solvent is able to exert a greater

42 ENERGY OF SUBSTANCE IN SOLUTION

pressure than the solution. When, then, will the pressure inside
become equal to the pressure outside — that is, when will the
hydrostatic pressure developed become great enough to balance
the reduction of pressure to the solute ? Experiment has shown
that the maximal rise of hydrostatic pressure is reached when its
value is equal to the difference in vapour pressures between the
solvent and the solution. Vapour pressure, as we have seen,
depends on the kinetic energy of the molecules in a liquid. Ex-
periment has further shown that for simple dilute solutions the
magnitude of the osmotic pressure depends on the molecular
weight of the substance dissolved, the amount of substance in
the solute per unit volume and on the temperature of the solution.
That is, osmotic pressure is controlled by just those factors which
control gaseous pressure. Suppose the gram-molecular weight
of the (undissociated) substance to be taken as m grams, dis-
solved in V litres of water, at the absolute temperature T. The

n
concentration, i.e. the number of mols. (n) per litre would be ^

Now, we may consider that dilute solutions obey the gas laws,
and therefore

We have seen that § of the kinetic energy of a gas is manifested
as gaseous pressure, and so we may state that

2 \nmvz
=3 ~F~-

That is, osmotic pressure is equivalent to f of the total kinetic
energy of the particles in solution. Put in another way, it might
be stated that in a simple solution the osmotic pressure of a sub-
stance would be numerically equal to the gaseous pressure which
the substance would exert were it a gas occupying the same volume
as the solution.

Now we have seen that the variables connected with gaseous
pressure are T and V . As, according to Avogadro's hypothesis,
equal volumes of gases under equal T and P contain the same
number of molecules, we may state that, if T is kept constant,
P varies as the number of molecules. De Vries (1884) found that
one gram-molecule of sugar dissolved in water to make up a
litre, has at 0° C. an osmotic pressure of 22-4 atmos. (Prac-
tically all gases at 0° C. and 760 mm. pressure have a gram

COLLIGATIVE PROPERTIES OF A SOLUTION 43

molecular volume of 22-4 litres, or conversely at 0° C. it would
require a pressure of 22-4 atmos. to reduce a gram molecular
volume to one litre.) De Vries, Pfeffer, and others have shown
that this is true not only for sugar, but for all simple (undis-
sociated) solutions. Van't Hoff (1887) pointed out that the
osmotic pressure of simple solutions is the same quantitatively
as gas pressure. We have already pointed out that vapour
pressure is a function of molecular activity, and may be taken
as an index of the kinetic energy of the liquid. The kinetic energy
again varies with the temperature of the liquid system. It
follows that vapour pressure varies directly with temperature. We
have seen that the putting of a substance into solution lowers
the vapour pressure of the solvent and, therefore, lowers its heat
content. This can be deduced from the second law of energetics.
From what has been said regarding the lowering of vapour
pressure, which always occurs when one substance is dissolved
in another, it may be inferred that the boiling point of a liquid
is always raised when a substance is dissolved in it. (These only
apply to instances where the V.P. of the solute is negligible.) A
very volatile substance, ether, for instance, would raise the V.P.
and lower the B.P.

Correlated with these two sequelae of solution is the lowering
of the freezing point. (Part II.)

The magnitudes of the osmotic pressure, lowering of the vapour
pressure and freezing point, and raising of the boiling point

n
depend in general on -^, the number of particles in solution per

unit volume. Because these magnitudes are all interrelated and
are interdependent they have been named the colligative properties
of a solution. They are definite physical quantities quite indepen-
dent of semi-permeable membranes, etc. The membranes make
osmotic pressure apparent.

Osmotic pressure is of considerable magnitude. We have seen
that a gram-molecular solution has an osmotic pressure of
22-4 atmos., i.e. 330 Ibs. per sq. inch. The ordinary dilute
laboratory reagents develop a pressure of about 50 atmos. In
a plant, root pressure has been estimated at about 60 feet of
water.

If, however, one were to tabulate the osmotic pressure of
gram-molecular solutions of all substances, one would find that
solutions could be divided into three great classes according to
pressure.

44 ENERGY OF SUBSTANCE IN SOLUTION

1. O.P. Approximately 22-4 atmos.

2. O.P. Decidedly greater than 22-4 „

3. O.P. „ less „ 22-4 „

The first class have been termed simple (undissociated) solu-
tions. According to the kinetic theory the second and third
classes have a larger or smaller number of particles in solution
than theory warrants.

Class 2. Where have the extra particles come from ? Has
the molecule divided ? If one compares the osmotic pressure
of cane sugar and sodium chloride in gram-molecular solution,
one finds them (roughly) as 1 : 2. How can this be explained ?
In 1887 Arhennius propounded his dissociation theory, which has
since been proved, amplified and universally accepted. Accord-
ing to this theory, some of the molecules of certain salts when
dissolved in water split up or dissociate into their constituent
ions. An ion is an atom or a sub-molecular group charged with
electricity and attached to certain water molecules.

For example,

NaCl ( solid) -faq= cat-ion +an-ion
=Na+Cl
=(Na(H20)*)+(Cl(H20)*/).

It is the presence of these ions which gives a solution the power
of conducting electricity, and so any substance which dissociates,
i.e. becomes ionised on going into solution, is said to be an elec-
trolyte.

All salts may therefore be classed as
Electrolytes, Class 2.
Non-Electrolytes, Class 1 and Class 3.

It is worthy of note that electrical conductivity is not a property
either of the solvent or of the solute, but of the solution.

Pure distilled water is a non-electrolyte.

Pure dry hydrochloric acid is a non-electrolyte.

But an aqueous solution of hydrochloric acid is a very good
electrolyte. All electrolytes are not dissociated to the same extent.
A salt of either a strong acid or a strong base requires the addition
of comparatively little water completely to convert all its molecules
into ions. On the other hand, a weak acid or base is difficult to
dissociate.

If the gram-molecular weight of an electrolyte be dissolved in
a litre of .water a certain fraction of the molecules will split into
ions. This fraction is the degree of ionisation of the electrolyte

CLASSIFICATION OF SOLUTIONS 45

at this concentration. The degree of ionisation may be deter-
mined by estimating the amount of resistance of the solution to
a small electric current (conductivity method), or it may be
approximately calculated from the lowering of the freezing point.
(For univalent strong electrolytes at concentrations not exceed-
ing 0-1 molar, Noyes and Falk consider that the percentage error
is in most cases between 1 and 4.)

One may note in passing that the ions of many electrolytes
possess the property of uniting with other ions, or even with-
non-electrolytes in solution, to form complex ions. For ex-
ample, ions cannot normally remain free in aqueous solution,
but become hydrated. A hydrated ion is sometimes termed an
ionic micelle.

In solutions of the third class, the O.P. and other colligative
properties point to a reduction in the number of particles in
solution. A clubbing of molecules has taken place. Because
the substances that compose this group have a somewhat gluey
consistency, Graham called them colloids (Gr. KoXXtj =glue). The
physics of colloidal complexes will be dealt with in a separate
chapter. Here we merely wish to draw attention to their low
osmotic pressure. Colloid substances may be converted into non-
colloid or crystalloid derivatives, and so liberate energy, e.g.
starch, a colloid having practically no O.P. may be readily hydro-
lysed to maltose, which is a crystalloid — non-electrolyte, having
a molal O.P. Glucose, which has a molal O.P., may be stored
in the liver as glycogen — a colloid, which again readily undergoes
hydrolysis to glucose. (See Chap. VIII., Colloids.)

CHAPTER VI
THE LIBERATION OF ENERGY

(4) SURFACE ENERGY

" This Phaenomenon proceeds from a propriety which belongs to all kinds of
fluid Bodies more or less, and is caused by the Incongruity of the Ambient and
included Fluid, which so acts and modulates each other, that they acquire, as
neer as is possible, a spherical or globular form." HOOKE, 1665.

(See also Chap. XIII. Muscular Contraction ; XIV. and XV.
Secretion and Excretion ; XVI. Nerve Conduction ; XXVI.
Respiration.)

A. Pure Liquids.

Two forces act on molecules :

(a) A repellent force — kinetic, revealed in osmotic pressure,
vapour tension, etc.

(b) A cohesion or attractive force — Newton's " Gravity."

" Every particle attracts every other particle with a force
inversely proportional to the square of the distance between
them." This gives rise within the liquid to intrinsic pressure,
whose magnitude we have no direct means of measuring, and
whose energy we cannot utilise. Why ? Because the various
tractative forces acting on each and every molecule within the
liquid neutralise one another. The attractions, except on the
surface layer, are uniform and cancel out. Consider a single
internal molecule. The tractative forces acting on it may be re-
solved into four components acting cyclically at right angles to
one another. It is obvious that these forces are paired. That
at twelve o'clock is equal to and opposite to that at six, and
therefore ineffective. Similarly, the eastwards pull at three
o'clock is neutralised by the westwards pull at nine. In the
surface layer, matters are different. One component, that is the
force pulling downward at 6 o'clock, has no opposing force at
12 to stabilise the molecule. There is, therefore, a state of strain

46

INTRINSIC PRESSURE OF A LIQUID 47

in the surface area. This state of strain is called the surface
tension of the fluid, and by release of this strain work may be
done. That there is apparently an elastic skin over fluids at
their junction with air is easily demonstrated. (Physicists call
the junction of a fluid with any other substance an interface.
They write of fluid-air, fluid-gas, fluid-fluid interfaces.) At a
water-air interface substances heavier than water can be sup-
ported. A clean needle floats on water. Water-beetles, etc., move
freely on the surface. Resistance to deformation is greater on the
surfacethan in the body of the liquid (cf. Searle's torsion balance).
How can this energy be utilised ? How can S.T. be either raised
or lowered ? Whatever alters intrinsic pressure will, of course, alter
surface tension. The magnitude of the intrinsic pressure depends
inversely on the kinetic energy of the molecules. The less the
kinetic energy the less the mean free path of the molecules, and
the less the distance between the molecules. Intrinsic pressure

varies as -=2. This variation of S.T. with K.E. does not concern

d

the biologist, as alterations in K.E. imply alterations of tempera-
ture, and we have seen that only slight alterations in temperature
are compatible with life.

It is possible to alter surface tension without altering intrinsic
pressure by altering the electric charge on the surface layer.
According to the Helmholtz-Lippmann theory, at any surface
there are two electrical layers equal in amount but opposite in sign.

1 . On the surface molecules of the fluid.

2. On the immediate external layer of the surrounding medium

— air, glass, etc.

Therefore, any alteration in the amount of the charge on the
liquid layer will produce an alteration in the surface tension.
If the charge on the surface is increased, the K.E. of the mole-
cules (i.e. repulsion of like signs) will be increased, " d " will be
increased and S.T. will be diminished. Conversely, an increase
in S.T. is brought about by decreasing the electrical charge.
The S.T. cannot, of course, be increased beyond that which the
superficial layer would have in the absence of any charge or
double layer. This alteration may be brought about directly or
indirectly;

I. Directly. Lippmann's capillary electrometer. If a capillary
tube be taken and a drop of mercury placed in it, the mercury
will run down and some will gather as a drop at the tip. If now
the tip of the capillary be immersed in dilute H2SO4, the Hg

48

will become + and the H2SO4 surface layer — . The S.T.
decreases and some Hg will drop out. Alteration in this charge
by connecting the Hg to a negative electrode will produce an
increase of S.T. and an upward movement of the mercury. The
amount of movement depends on the difference of potential
existing between the Hg and the H2SO4, and may be used as a
means of measuring small differences of potential (see Fig. 5).

ABC

FiO. 5. —Form assumed by mercury globules under different electrical states.
B is a mercury globule immersed in dilute H;jSO.|. It assumes a more spherical
form A when connected with the negative pole of a battery, while connection to the
positive pole reduces surface tension as shown at C.

II. Indirectly. Effect of solutes. Substances which when
fluid have a lower surface tension than water, lower surface ten-
sion when dissolved in water, and vice versa- Why this happens
is not known. A plausible explanation is that of ionisation ;
but if ionisation is the cause, why should weak organic acids-
only slightly dissociated — have great lowering power, while
strongly dissociated inorganic salts have very little effect ? Very
few substances raise S.T., and that only to a very slight extent.
Most organic substances lower S.T. markedly, e.g. addition of
butyric acid to water to make a 1 per cent, solution lowers S.T.
from 75 to 35 dynes.

A solid-liquid interface has always a lower S.T. than either
a liquid-liquid or a liquid-air interface. That is why water rises
in a capillary tube.

It is obvious, therefore, that means exist for readily lowering S.T.
and so setting free energy.

B. Solutions.

The addition of a solute makes some alteration in the intrinsic
pressure of a fluid and necessitates a redistribution of energy.
Solutes are not universally dispersed throughout a solution. " The
concentration throughout a fluid tends to be so adjusted as to
reduce the energy at every point in it to a minimum " (Gibbs-
Thomson Principle). Solutes that lower surface tension are more
concentrated at the surface, while those raising the surface tension
are found in smallest amounts at the surface. This may be
deduced from the second Law of Energetics. (See Part II. for
demonstration of S.T. and for methods of estimation : adsorption
will be treated in Chap. VIII., Colloids.)

SECTION II.: CELLULAR MECHANICS

CHAPTER VII

IONISATION

•

IONS — THE WORKMEN OF THE CELL

" Many things move me to suspect that everything [natural as well as
mechanical] depends upon certain forces, in virtue of Which the particles of
bodies, through forces not yet understood, are either impelled together . . . ,
or are repelled and recede from one another." NEWTON.

THIS subject has been alluded to in connection with abnormal
osmotic pressures (Chap. V. p. 44), where it was pointed out
that electrolytes, on going into solution, were more or less dis-
sociated into their constituent ions. The extent to which an
electrolyte is thus dissociated determines whether it is a strong
or a weak electrolyte. Inorganic acids and bases and their
salts are almost completely dissociated in solution, the dissociation
increasing with dilution until, of course, complete dissociation is
reached. Organic acids and bases, as a rule, are dissociated
with difficulty, complete dissociation being reached only at great
dilutions. There are exceptions, some organic bases are just as
well ionised as the strongest inorganic bases. Guanidin salts,
for instance, have dissociation values lying between sodium and
barium salts. Salts formed of a weakly dissociated acid and
a strongly dissociated base or of a weak base and a strong
acid have dissociation values intermediate to those of their
constituents.

There are' two outstanding points of interest about ions.

1. Ions are always electrically charged. The " metal " ion
having a positive and the " acid " ion a negative charge. (The
former, in Faraday's terminology, is called a cation and the latter
an anion.)

2. Ions are never free, but are always hydrated.

B.B. 49 4

50

IONISATION

1. Electrical Charge. It is obvious that if two electrodes from
a source of supply be dipped into a solution containing ions,
that in virtue of their charge the anions (negative ions) will be
attracted towards the anode (positive electrode) and the cations
(positive ions) will be drawn towards the cathode (negative
electrode). Such a solution will therefore conduct electricity,
and further, its efficiency as a conductor will depend on the
number of ions present, i.e. on the dissociation of the solute.

This provides the basis on which the method for estimating
the concentration of ions has been devised. In doing this the
electrical resistance, in ohms, is measured. Conductivity is the
reciprocal of resistance (Part II. p. 415).

Relative Speed. Another factor must be taken into account.
We have seen that ions do not all move at the same rate. The
rate depends on the atomic weight of the ions, the degree of
hydration and the influence of other ions. (Ions by their electric
charge influence one another.) Under similar conditions, each
ion moves at a constant rate.

That the rate is slow is shown by passing an electric current
through a solution containing coloured ions at one electrode and
noting the time they take to reach a similar concentration at the
other electrode. Kohlrausch determined the relative speed of
ions at 18° C. and for a constant potential gradient found as
follows :

TABLE VI.

CATIONS +

ANIONS -

Ion.

Atomic Wt.

Relative Speed.

Ion.

Atomic Wt.

Relative Speed.

H

1

318

OH

17

174

K

39

64-6

1S04

48

68

NH4

18

644

Br

80

67

IBa

68-5

55

I

127

66-5

iSr

43-7

51

Cl

35-5

65-5

|Ca

20

51

|C204

44

63

JMg

12

45

CH3COO

59

33-7

Na

23

43-5

Li

7

33-4

Bredig has pointed out that with organic ions the longer the
carbon chain, the less the speed. The decrease in speed is, how-
ever, comparatively slight.

2. Hydration. Consideration of the numerical values of the
relative ionic rates gives a means for calculating the hydration
of the various ions. It may be taken for granted that the speed

HYDRATION OF IONS 51

of ions apart from hydration is proportional to their mass, e.g.
potassium and chlorine have approximately similar atomic
weights and similar speeds. Any variation from this proportion
is usually attributed to the different hydration of the ions. It is
generally conceded that, as stated above, all ions are hydrated.
Therefore potassium and chlorine must be hydrated to almost
the same extent. Bousfield has shown that 9 water molecules
are attached to both ions of potassium chloride when completely

dissociated. Now, as the speed of K to Cl is as

39 35-5

i.e. as 16 : 19, almost as 4 : 5, it may be considered that K has 4
and Cl 5 water molecules per ion.

In the group of alkali metals tabulated above it will be seen
that the lightest metal, lithium, furnishes the most sluggish ion
of the three, and, conversely, the most mobile ion is that of the
heaviest metal, potassium, sodium being intermediate both in
atomic weight and in speed. This is supposed to mean that
lithium is more heavily hydrated than sodium, and sodium more
than potassium. The number of molecules of water combined
with their chlorides when completely dissociated is respectively,
21, 13 and 9. If the 5 molecules of water which form an envelope
for the chlor-ion, be subtracted from the total, lithium is found
to be hydrated to the extent of 16 and sodium to 8 molecules.

Effect of Temperature.

Increase in temperature according to the kinetic theory and
laws of energy will increase the speed of ions, provided of course
that dissociation is complete. Partially dissociated salts are more
completely ionised by increase in temperature. For equal
increment of temperature, different ions increase in speed accord-
ing to their degree of hydration. The more highly hydrated the
ion, the greater is its temperature co-efficient. This is explicable
on the hypothesis that a rise of temperature will favour the dis-
ruption of hydrate-complexes and decrease the size of the ion, and
so reduce the frictional resistance to its passage through the fluid.

When dealing with surface tension (p. 47), the Helmholtzian
double layer or surface electrical charge was mentioned. This
may now be attributed to the different ionic speeds. Whichever
of the two ions has the greater mobility will get into the surface
layer and of course will carry its charge with it. This will cause
the mobilisation on the immediately opposite " side " of the
surface of an equal and opposite charge. As has been said above,

52 IONISATION

this gives rise to a difference of electrical potential, which may
explain some of the anomalies of diffusion through living animal
membranes.

Of course there exists an enormous electrostatic attraction
between ions of opposite sign. The introduction of other electro-
lytes into a solution may therefore alter not only the rate of
migration of the original ions but the nature of the surface charge.
The addition of HC1 to a solution of KC1 would increase the
diffusion potential that would be produced at the boundary
between solutions of KC1 at different concentrations ; the more
HC1 present, the greater the diffusion potential.

This is due of course to the relatively greater speed of the
hydrogen ion. The K ions move at about the same speed as
the Cl ions, while the H ions move about five times as fast. The
boundary surface previously charged negatively with a low E.M.F.
would take on a positive charge with a higher E.M.F.

It is imperative to note that unless the electrostatic force
mutually exerted between anion and cation is overcome, these
ions though separated will never be far apart.

In ordinary solutions the " metal " ion, no matter what its
relative speed, cannot be separated from its " acid " ion by mere
diffusion. The disturbance of electrical equi-
librium caused by the introduction of elec-
trodes into the solution will produce a
separation of the salt into metal and acid.

Now, if there exist equal and opposite
charges on an- and cat-ions, tending to draw
them together, why, in the first instance, did
they separate, and what keeps them apart ?
This brings us to the discussion of the
dielectric constant. To put a name on a
CATION *NION thing or on a process does not explain it.

FIG. 6. — Model of anion "Neither is it siiffipipnt to sav that thf> rHpIpp

and cation. Two pith balls a

suspended by silk tiireads trie constant or specific inductive capacity

attract one another if carry- *

ing opposite charges when of any medium is a measure of the capacity

the charges are of the same • *

sign the bails diverge, i.e. of that medium to act as a dielectric (non-

repel one another. v

conducting) substance of an electric con-
denser. The higher the value of the constant, the greater is the
value of the condenser.

If two pith balls (Fig. 6) are hung by a dry silk thread and
given equal and opposite charges of electricity, they may be
regarded as representing ion-hydrates.

DIELECTRIC CONSTANTS 53

There is a constant relation between the charge of a body and
its electric potential. This ratio is called the capacity of the
body as a conductor, and depends on the nature of the medium
separating the two charged bodies. The tendency of two oppositely
charged bodies to come together is altered by altering the dielec-
tric or medium separating them. Air is taken as the standard
dielectric, and all other dielectric constants are referred to that
of air as unity. From the accompanying table it will be seen
that water has a high dielectric constant.

TABLE VII.

Air =1-0 Water =81-7

C02 =1-0004 Alcohol =25-0

H =0-9997 Formaldehyde =84-0

Acetic Acid =6-46

HCN (liquid) =95
Vaseline \
Turpentine „ ~

Benzine
Paraffin

Liquid Fat =3-3-2

(The determination of the dielectric constant of different
substances is of interest from its bearing on Maxwell's electro-
magnetic theory of light. The dielectric constant of a substance
in the case of light of long wave-length is the same as its refractive
index squared.)

According to the electron theory, an atom is composed of
electrons. Electrons are all similar, and are supposed to be not
sensible matter, but the smallest possible unit of negative elec-
tricity Atoms of different substances owe their different qualities
to the varying number of electrons they contain and to the
diversity of their combination. These electrons are supposed to
exercise an obstructing influence on the passage of an electric
charge due to their tendency to move in the direction opposite
to the direction of the current. The larger the number of the
electrons, therefore, the greater the obstruction and the greater
the value of the dielectric constant. Water has a high dielectric
constant, and so once the molecule has become dissociated, the
resultant ions may approach very near to one another without
combining. In short, the dielectric constant is a measure of the
insulating capacity of the substance. The addition of solutes
alters the value of the dielectric constant of the solvent.

The atoms in a molecule are held together by very strong

54 IONISATION

electrostatic forces. A very large amount of energy must there-
fore be expended in separating these atoms. Energy is also
expended in removing one of the valence electrons from each
cation. This energy is supplied by the energy of combination
of the electronegative molecules of the solvent (heats of dilution
and hydration) and by the heat of combination of the anions with
the freed valence electrons. It is thus that Sir J. J. Thomson
explains the charges of the ions. The ionising power of a solvent
seems to be some function of its dielectric constant. On the other
hand, the degree of ionisation of a salt seems to be due to the
electronic structure of its constituent atoms. The whole subject
is bristling with difficulties and so far explanations can only be
regarded as reasoned guesses.

Water.

The solutions dealt with above have all been aqueous. Solu-
tions in water as the solvent were early recognised as the most
important. According to the old Greek philosophers water was
" the beginning of all things." Thales said, " All things have
their origin in water and return unto the same." The importance
of water as a solvent was generally recognised early in the seven-
teenth century. Aqueous solutions are fundamental for all
biological phenomena. The physical properties of water are in
general extreme — their numerical expressions are either extremely
large or extremely small, and usually the former. Its specific
heat and its dielectric constant are the highest of any of the more
common liquids. Therefore, water should have a very high
ionising power as a solvent.

One has been accustomed to look upon water as a simple inert
substance, of the chemical formula H . OH and with a molecular
weight of 18. Physical chemists have proved that this conception
does not account for all the properties of water. Lewis and also
Langmuir, from thermodynamical principles and also from the
study of the colligative properties (see p. 43) of water, have
constructed diagrams of the molecule of water. Discussion of
this work is somewhat without the bounds of this book.

In recent years it has been amply demonstrated that a tri-
atomic molecule could not possess the properties of water. For
instance, it is composed of gases with extremely low freezing and
boiling points. Oxygen boils at —181°, while the figure for
hydrogen is — 253° C. From comparison with compounds of
known composition, ice should form at —150° and the tempera-

IONISATION CONSTANT 55

ture of steam should be —100° C. The inference from this is
that the molecule of water is bigger than H2O. Each simple
molecule or hydrol is supposed to combine with another hydrol
so as to form a dihydrol or three hydrols may polymerise to
trihydrol, and so on. Water, as we know it, consists of a mixture
of these various hydrols. The relative amount of each kind is
determined (a) by the temperature of the fluid, and (b) by the
substances present in solution or, in a less degree, in suspension.

(a) Temperature controls the kinetic energy of the molecules
and so the size of the intra-molecular spaces. Increase of tem-
perature, therefore, by increasing the kinetic energy will cause a
disruption of polyhydrol into its simpler constituents. Decrease
of temperature has the reverse effect. Theoretically, there is
the gas H2O and the solid (H2O)3, and between these extremes
the liquid (a(H2O)+&(H2O)2+c(H2O)3), a, b and c being
constants dependent on the temperature. At each temperature
there is equilibrium between the amounts of the various hydrols.
The temperature of water has thus an importance in deciding
its physical and chemical properties, and therefore, in all reactions
involving water, temperature should be stated.

(b) As has been pointed out above, there is a certain equilibrium
composition of water at each temperature. This equilibrium is
disturbed by the presence of a solute, especially if it is dissociated.
Hydrol is abstracted to hydrate the ions or molecules of the
solute and a rearrangement of equilibrium takes place.

lonisation Constant.

Absolutely pure water is almost, but not quite a non-electrolyte.
As absolutely pure water has not yet been prepared, this is a
deduction from the behaviour of water under certain circum-
stances.

Water is ionised according to the equation

According to Guldberg and Waage's Law of Mass Action (p. 61),
the product of the concentrations of the reacting substances,
H+ and OH~, bears a direct relationship to the mass of the
resultant substance H2O.
That is [H+]x[OH]-=constantg

[H20]

where [H+] =the fraction of the total water which is disso-
ciated into hydrogen ions.

56 IONISATION

[OH~] =the fraction of the total water which is disso-
ciated into hydroxyl ions

and [H2O] =the fraction of the total water which is left

undissociated.

Stated in words, the product of the concentration of hydrogen
ions and hydroxyl ions is always equal to a constant quantity Kw,
The value of Kw, the ionisation constant of water, depends only
on the temperature.

1

At o°r ~K = n^

w 10,000,000,000,000,000' 'k '
At 23 C. Kw =100;000;000;000;000 (2)

OQ

At 40° C. r

« ioo,ooO,000,000,000 ..................

At 100° C. Kw=- 4S ..(4)

100,000,000,000,000

To save writing those cumbrous fractions, the index notation
is used. Thus fraction

(1) is = 0-01 xlO-14 =CW at 0° C.

(2) is - 1 xlO~14 =CW at 23° C.

(3) is = 28 XlO-14 =CW at 40° C.

(4) is = 48 X10~14 =CW at 100° C.

Now, as the quantity of water dissociated is so very small
compared with the total quantity of water, it is clearly legitimate
to put [H2O] —1 in the mass action equation, which now becomes :

It is obvious that H+ and OH" are produced in equal amounts,
and therefore [H+] =[OH~] W^.

Between 22° and 23° C. water has a dissociation constant with
which it is convenient to work, and measurements of hydrogen
ion concentrations are usually made at this temperature or
referred to this temperature ;

i.e. at 23° C., Kw =10~14 ;
.'. [H+]x[OH-]=10-14.
[H+] is therefore equal to JlQ-1* =10~7,
and [OH-] „ „ „ VlO^-lO-7.

It is usual to write H* for H+ and OH' for OH~.

HYDROGEN ION CONCENTRATION

57

Still further to shorten the symbols, S^rensen suggested the
use of the logarithm to denote the hydrogen ion concentration.
Instead of writing 10 ~7 one may write merely the positive index 7,
keeping the rest of the formula in mind. This is called the pH,
p denoting the index to the base 10, and H, of course, showing that
hydrogen ions are under consideration. That is, in neutral water
at about 23° C.

or CH=COH=10-7.

In words, neutral water has a hydrogen ion concentration of 7.
Appended is a list of values of PH2o for various temperatures,
calculated thermodynamically.

TABLE VIII.

T.

PH.,0.

T.

PH.20.

0

16-04

31

13-70

18

14-14

32

13-67

19

14-11

33

13-64

20

14-07

34

13-61

21

14-04

35

13-58

22

14-01

36

13-56

23

13-96

37

13-53

24

13-93

38

13-51

25

13-89

39

15-47

26

13-86

40

13-45

27

13-83

50

13-34

28

13-80

75

12-77

29

13-76

100

12-31

30

13-73

Some people prefer a more cumbrous but nevertheless a more
comprehensible method of recording ionic concentrations. In
S^rensen's method it is rather difficult to see at a glance the
relative concentrations of ions at two temperatures. As the
temperature decreases, dissociation increases, but the negative
exponent or p^o decreases. At 18°, for example, the pH is 7-3,
and at 23° it is 7-0. Put in this way, one does not readily grasp
the fact that the pH at 23° is double the pH at 18°. If, however,
the negative exponent be kept a whole number and the fraction
be put as a multiplier, the relation is seen at once, e.g.

18°pH=7-3=0-5xlO-7=CH,
23° pH =7 -0-1 X10-7=CH.

58 IONISATION

The conversion of one expression into the other is simple.
For example : To convert pn 7 -6 to other notation

pR 7-6 =aO~7-6 =10-7-° xlO-°-6 -0-25 X10-7,

antilogof —0-6— 0-25.
Conversely we find the short expression for
CH 5xlO-6 = Iog5+logl0-6

-•6990 +(-6 -0000)
= 5 -3 = PH,
or 5 xlO-6 = 10- 6" X 10-6 = 10-5-3 =pH 5-3.

(Graph for conversion from one notation to other, Part II.
p. 424.)

Reaction.

It is very important to be able to ascertain with great exact-
ness, the true acidity or alkalinity of physiological media. It is
not sufficient to state that a certain fluid is acid to litmus, etc.
Litmus, for one thing, is not nearly sensitive enough to indicate
the minute changes in reaction which alone are of physiological
value. The whole activity, of the mammal at any rate, is regu-
lated by reaction. Alterations in acidity are the causative factor
in the regulation of respiration, the activity of muscle, the ex-
citability of nerve, and play an important part in regulating
secretion and excretion. Physical and chemical means are
employed to keep the healthy body within a narrow range of
reaction, about the neutral point. Any marked deviation from
this is pathological, and is the result of pathological (or experi-
mental) conditions. As we shall see later, the neutrality of the
organism is an equilibrium, any disturbance of which will produce
change, and, moreover, any change in the organism will tend to
disturb this equilibrium (Chap. XXX.).

Examination of a number of acids shows that when they
dissociate in water they disturb the balance existing between
the concentrations of H+ and OH~ ions.

For example :

HC1 =H++C1-

HN03 =H++NO3-
H2S04 =H++HS04-
CH3COOH =H+ +CH3COO-

REACTION 59

In each case the acid produces H+ ions. Now, as [H] x [OH] is
a constant, the result of this increase of H+ ions must cause a
decrease in the concentrations of OH~ ions.

In the same way, examination of the behaviour of alkalies
shows also a disturbance of the ratio of [H+] to [OH~].
For example :

NaOH =Na++OH-
NH3OH=NH3++OH-.

The concentration of OH~ ions is increased.

In water the concentrations of H and OH are equal. These
facts lead to the following definitions :

(a) Any substance which when dissolved in water yields H+
as one of the direct products of its ionisation is an acid.

(b) Any substance which when dissolved in water yields OH~
as one of the direct products of its ionisation is a base.

(c) Any substance which on ionisation yields at least one
positive ion other than H+ and at least one negative ion other
than OH~ is a salt.

(d) If, in addition to the positive and negative ions mentioned
in (c), the salt yields an H+ ion it is called an acid salt.

E.g. KHSO4 =K+ +SO4-

NaHPO4=2Na+ +PO4~
COOH

COONH4=NH4+ +(COO)2

(e) If, in addition to the positive and negative ions mentioned
in (c), the salt yields an OH-ion, it is called a basic salt.

E.g. Fe(OH)2Cl =Fe+++ +C1~ +20H-,

CH2-NH-OH-COOK=K++CH2NH3COO-+OH-.

(/) Substances which produce both H* and OH' ions on disso-
ciation are called amphoteric electrolytes or ampholytes. They
must evidently have two ionisation constants, jRTH and KOR.
It is obvious that acidity depends on the preponderance of hydrogen
ions over hydroxyl ions, and conversely, alkalinity is due to the
presence of hydroxyl ions in excess of hydrogen ions. Neutrality
is an equilibrium between H* and OH'.

This neutral point occurs in water at 23° C. when the concen-
tration of hydrogen ions is 1 xlO~7, i.e. pH=7. If the concen-
tration is greater than this, e.g. 1 XlO"5, or p^=5, then the

60 IONISATION

concentration of OH' must be correspondingly decreased according
to the equation,

[H+] [OH-] = 10-14

in -14

or [OH-] =-J=TC = 10-14 (-B) - 10-9.

(H+)

A y?H of 5 will be accompanied by a pOH of 9. This will be an
acid solution.

Conversely, if the concentration of hydroxyl ions is increased
there is a corresponding decrease in hydrogen ions. E.g.

IQ -14

if POH - 3> then (H+) = -^ = 10"11 = pH of 11,

an alkaline solution.

Reaction may, therefore, be expressed in terms of pH or of pOH.
Generally the former is used, and alkalinity is expressed as decrease
of acidity. The quality as well as the nature of the reaction is
expressed by the pH. The greater the concentration of hydrogen
ions, the greater is the degree of acidity and the smaller the degree
of alkalinity.

It is rather confusing for the beginner, but he must note :

(1) that as acidity increases, the exponent or p figure decreases ;

(2) that as the figures are logarithms, multiplication is done
by addition and division by subtraction ;

(3) that this does not give a measure of the amount of acid
present, but of its strength. The pR is not an index of quantity
but of intensity. It gives the number of H ions per litre, but of
course says nothing of how many litres or c.c. of acid are present.

The strength of an acid (or alkali) may be expressed as normal
or as a fraction of normal. A normal solution contains in one
litre, the gram-equivalent weight of the substance. A normal
solution of acid, for instance, has in each litre one gram of hydrogen
capable of forming hydrogen ions. If the acid is completely
dissociated, i.e. if it is a " strong " acid, it will contain one gram
of hydrogen as H+. The strength of acid commonly used for

N
laboratory purposes is 1/10 of normal = — . The hydrogen ion

concentration of such a solution would be 1/10 gram per
litre = (H+) of 1 x 10-1 or pH of 1 and pOH of 13.

Water of pH = pOH = 7 is thus, at 23° C., N/10,000,000 acid and
N/10,000,000 alkaline. If the acid added to water is not completely
dissociated (i.e. a weak acid), then, of course, the degree of disso-
ciation must be taken into account. A decinormal solution of

SALTS 61

acetic acid, for instance, at 23° is dissociated 1 -36 per cent. There-

1 ,O£»

fore its (H+) would be equal to - - x 10 -1 = 1 -36 x 10 ~3 or »w of

inn **»

2-86.

Normal solutions of acid are all equal as regards the amount
of alkali they can neutralise. 1 c.c. of any N/10 acid is exactly
neutralised by 1 c.c. of any N/10 alkali. That is, they have the
same titratable acidity. They differ in their concentration of
hydrogen ions.

As we have seen

N

— HC1 in water at 23° =pR I or CH =1 xlQ-1,

— CH3COOH „ =px 2 -86 or CH =1 -36 xlO~3.

That is, hydrochloric acid, under the above conditions, has
10 -1 -MO-2-86 = 73 -5

times the amount of hydrogen ions per litre that acetic acid has.
N/10 Hydrochloric acid at 23° C. is therefore 73-5 times as strong
as N/10 acetic acid.

Salts.

It is very seldom that acids, weak or strong, occur alone or
diluted with water in physiological fluids. Salts are always
present. In (d) and (e) are mentioned two classes of salts which
alter the [H] of water when dissolved in it. They do so directly
in virtue of their possession of an additional II* or OH' ion.

Other salts cause alterations in acidity by upsetting the balance
between H* and OH' in water. Their action is indirect.

(1) The salt of a strong acid and a strong base, e.g. NaCl, causes
little or no change in [H].

(2) If one of the constituents of a salt be weak, changes occur.
(a) If the salt BA of the strong base B . OH and the weak

acid HA~ be dissolved in water it forms BA=B+A~. But owing
to the ionisation of the solvent there are present H+ and OH" ions
and a second change takes place, H+ and A~ ions are present.
According to the law of mass action

HA or H' + A-HA.

As no HA is present to balance the reaction, H" will combine
with A' to form HA until the point of equilibrium for that dilution
has been reached. The removal of hydrogen ions from the

62

IONISATION

solution by this reaction, however, disturbs the equilibrium
between H* and OH' and some more water must ionise to maintain
the product [H] x[OH] constant.

Summarising these reactions as follows :
A'+H2O=HA+OH',

the net result is the liberation of OH ions. The addition of a salt
of a strong base and a weak acid is to make the solution alkaline,
i.e. to reduce the hydrogen ion concentration. This is a fact of
great physiological importance, as most of the salts of the body
are composed of organic acids combined with the strong bases
sodium and potassium.

KCN, a powerful poison, dissociates as follows :

KCN = K++CN-

H20 =H+ + OE

This causes an alkalinity equal to that of potassium hydrate.

The alkalinity of solutions of sodium carbonate is due to the

reactions,

Na2CO3 =2Na+ + CO3~

H20 =H+ + OH-

r*i~i — i TT c\ TIPO — _L nil—

l^vJ3 -f- Jtl.2U — XlL;U3 -f- UU

HC03-+H20 = H2C03 +OH-
H2CO3 ±^H2O -f- CO2

If the CO 2 is allowed to escape, the last reaction will only cease
when all the H2CO3 has been decomposed. The total result is
an increase in [OH] and, therefore, of alkalinity.

(b) In the case of a weak base combined with a strong acid,
the solutions become acid, as the following equations denote.

BA = B+

H,0 -

OH

and HA is a strong acid and BOH a weak base.
E.g. NH4C1 = NH4+

H2O = H+

HO-

=NH4OH+HC1.

EFFECT OF TEMPERATURE 63

(3) When both the constituents are weak the solution will
remain neutral, if acid and base are of equal strength, if the acid
be the stronger, the solution will be acid, and conversely an
alkaline solution will be produced if the base be stronger than
the acid. E.g.

CH3COONH4 + H2O « NH4OH + CH3COOH.

This solution will be almost neutral, because the degrees of
ionisation of ammonium hydrate and acetic acid are almost
identical.

Effect of Temperature.

The effect of temperature on the dissociation of water has been
dealt with above (p. 56 and Table VIII.). Increase in temperature
causes a very large increase in the amount of water ionised. An
increase in temperature of 1°C, say from 38° to 39°, causes the
[H] x[OH] to rise from 10~13-5 to 10~13'47, an increase of about
20 per cent. Strong electrolytes have a low temperature coeffi-
cient of dissociation. It is, therefore, obvious that increase of
temperature will affect salts according to the dissociation constant
of the acids and bases composing them.

(a) Both strong, temperature of little effect.

(b) Weak acid -f strong base. Increase of temperature causes
the degree of dissociation of acid to increase. Acid ions combine
with hydrogen ions from H2O and liberate OH~.

(c) Strong acid and weak base. Increase of temperature
causes the degree of dissociation of base to increase. Base ions
combine with hydroxyl ions from the H2O and liberate Hf.

(d) Both weak. The result of any increase in temperature is
to increase the dissociation of the weaker at a greater rate than
the stronger with correspondingly slight changes in [H] and [OH].

It will be seen that apart from the action of temperature on
the dissociation of water itself, in (b) increased alkalinity and in
(c) increased acidity result from increase in temperature. This
action is slight, however, compared to the action of temperature
on the weakest salt known, water.

The effect of alterations of temperature on a salt solution where
one of the constituents of the salt is weak is the combined effect of

I. the alteration in KH2O ;
II. the alteration in KSaJt.

In brief, the increased acidity or alkalinity produced by increase
of temperature is greater (theoretically) than could have been

64 IONISATION

produced from increased dissociation of the salt. The significance
of this will be seen later.

At present the point under consideration is the mechanism for
converting the potential energy of the food-stuffs into the kinetic
energy exhibited by protoplasm. Enough has been said to
indicate

(1) That slight alterations in hydrogen ion concentration may
produce large alterations in surface tension (Chap. VI.).

(2) That slight alterations in hydrogen ion concentration may
produce large alterations in the degree of dissociation of salts.

(3) That the degree of dissociation of salts, acids and bases
governs the value of surface tension and osmotic pressure. The
next chapter deals with the inactivation of these factors.

CHAPTER VIII

DISPERSE SYSTEMS

COLLOIDS — THE RESERVOIRS OF ENERGY

" The properties of colloidal solutions can be most efficiently inquired into
by application, as far as possible, of the same views and methods as those generally
applied to true solutions." S'/RENSEN.

IN Chapter V. colloids were mentioned as a series of substances
which when dissolved in water have a lower osmotic pressure
than would be expected from their molecular weight. The reason
for this, deduced from the colligative properties of their solutions,
is that in water they form aggregates or colloidal particles of extra-
molecular size.

The effect of this is enormously to increase the effective surface
of the solvent. Therefore the phenomena of surface tension and
surface adsorption will be marked.

The appended table makes clear the enormity of the increase
in effective surface that takes place when a sphere is divided into
a large number of small shot and these are, in turn, divided into
particles of colloidal size.

TABLE IX.

INCREASE IN SURFACE OF A, SPHERE WHEN ITS RADIUS is
DECIMALLY DIVIDED.

Lengtli of Radius.

Number of
Spheres.

Total Surface.

1 mm (Small Shot

1

103

12-6 sq. cm.
126

0-1 mm. ) •

106

1260

0-01 mm. Coarse
1 suspensions

109
1012

1-26 sq. metres
12-6

o-oiu lTypical

1015
1018

126
1260

j (Colloids

1021

12,600

0-1/j.fj. True Solution

1024

126,000

66 DISPERSE SYSTEMS

This table shows how a molecular solution of particles of
0-lyUyot radius which has no effective surface acquires an effective
surface of 12,600 square metres when the particles are increased
in size sufficiently to give them an effective surface, i.e. to bring
them into the colloidal realm. These figures demonstrate the
extraordinary adsorbing surface of a small amount of matter
highly dispersed. In connection with the theory of surface
tension Wo. Ostwald has introduced the term specific surface to
denote the ratio of surface to volume or SfV. In a sphere

O o

S = 4s-7rr2 and V = ±r3 : therefore — = -, It has been found in

V r

physical chemistry that adsorption to a surface becomes an im-
portant factor when the specific surface reaches a value of about
10,000. It has also been noticed that when the specific surface
becomes greater than 6 xlO7 or thereby, i.e. when the material is
so finely subdivided that it is in molecular solution, adsorption
phenomena cannot be detected.

Further, it has been demonstrated that colloids, as a rule, carry
a definite charge, some positive some negative. The sign of the
charge depends both on the nature of the colloid and on the
nature of the medium in which it is.

(1) As colloids have extremely low osmotic pressures they are a
suitable medium for the storage of potential energy. Carbohydrates
may be stored as starch or glycogen, both colloids, and changed
readily into maltose or glucose, which are crystalloids.

(2) The salts adsorbed by a colloid are so rendered osmotically
inactive, but may be set free again by alteration of the colloidal
electric charge.

(3) Some colloids imbibe water and compress it. A hydrated
gel (jelly) has therefore a store of hydraulic pressure within it.
Gels may thus be regarded as the great reservoirs of energy in
the body (Part II.).

A great deal has been done to elucidate the nature of colloids.
A full discussion of that work is out of place here, but a brief
account of the results may be acceptable.

Protoplasm maybe considered as a watery solution of crystalloids
and colloids. The division is due to Graham, the pioneer in
colloidal research. As the result of a large series of investigations
on the rates of diffusion of various substances in water, he was
led to divide all substances into two classes, e.g. Crystalloids,
which have a high rate of diffusion and which crystallise from

DIALYSIS 67

saturated solutions, and Colloids, which diffuse very slowly and in
general have a gluey consistency. " They appear," he writes,
" like different worlds of matter, and give occasion to a corre-
sponding division of chemical science." He noticed that crystal-
loids passed through animal membranes while colloids did not.

That is, if a mixture of colloids and crystalloids were put into
a simple dialysing drum (such as described in Part II. p. 406),
immersed in running water, after a time most of the crystalloidal
material would have been dialysed out of the mixture, while the
colloidal matter would still remain in the drum. The dlalyser
furnishes a method for the separation of crystalloids.

It has now been proved that matter may exist either in a
crystalloidal or in a colloidal state, and that by suitable means
a colloid may be crystallised and so pass through a membrane
previously impermeable to it. The converse process may also
take place.

The solvent is sometimes the factor on which depends the
state of the solute. The alkali salts of the higher fatty acids —
stearic, palmitic, oleic — form a true molecular solution in alcohol,
but with water they act as colloids. On the other hand, sodium
chloride, a typical water-soluble crystalloid, assumes the colloidal
state in benzol.

Von Weimarn and others have prepared colloidal solutions of
over two hundred substances usually considered as crystalloids.
By proper manipulation, almost any solid can be dispersed through
a liquid either as a crystalloid or as a colloid. Consequently, one
now speaks of the colloidal state rather than of certain substances
as being colloids.

The difference between a crystalloidal and a colloidal solution
depends, in the main, on the size of the particle in the fluid.

There is some difficulty in expressing the relationship between
the colloid and the fluid in which it is. It is not in true solution,
but is suspended and dispersed throughout the medium. The
colloid may, therefore, be called the dispersed substance or
dispersate and the fluid the dispersing medium or dispersant.

The application of the'" Phase Rule " (of W. Gibbs) has helped
to clear up several difficulties in physiological physics, and some
writers have adopted terminology suitable for use when this rule
is discussed. It is sufficient here to say that the dispersed phase
is the substance which is suspended or distributed throughout
the continuous phase. In nearly every case the former is the
colloid and the latter the fluid.

68

DISPERSE SYSTEMS

As an illustration, attention may be drawn to a disperse system
having two phases and only one component, e.g. A fine mist of
liquid water suspended in water vapour.

The dispersed, internal or non-continuous phase is composed
of the droplets of water ; the continuous or external phase, or
dispersion medium, is the water vapour. The stability of this
dispersion depends on two factors, (a) the temperature of and
(6) the diameter of the droplets*, (Such a system is called
divariant.) The smaller the droplets, the greater is the ratio of
surface to mass and the higher is the vapour pressure. All the
droplets will not be of the same size, and therefore the larger
droplets will tend to become larger still at the expense of the
smaller ones. The system is, on this account, said to be meta-
stable.

Disperse systems may be classified according to the nature of
the contact surface between the phases. Taking the three states
of matter, solid, liquid and gaseous, five different kinds of contact
surface can be produced, as is indicated in the following table, in
which are also given examples of the various disperse systems.

TABLE X.

Class.

Contact Surface.

Dispersed
Phase.

Continuous
Phase.

Examples.

I.

Gas — Liquid

Gas
Liquid

Liquid
Gas

Foam, Suds, Lather.

Mist, Spray.

II.

Gas — Solid

Gas
Solid

Solid
Gas

Hydrogen in platinum, lava,
meringues.
Smoke, dust and some fumes.

III.

Liquid — Liquid
(Emulsoids)

Liquid

Liquid

Milk (fat in water),
Lymph, egg white (raw).

IV.

Liquid — Solid
Suspensoids

Liquid
Solid

Solid
Liquid

Hock inclusions.
Colloidal metals, etc.

V.

Solid— Solid

Solid

Solid

Ruby Glass (Gold in Glass).

Class III. (Emulsoid) is of the most importance in biology,
but Class IV. (Suspensoid) has been most studied and is of con-
siderable industrial value. Colloids met with in nature are all
dispersed in water, having salts in solution. They might therefore
be classified according to their degree of dispersion. The degree
of dispersion of a phase is the ratio of total surface to volume, or

69

the surface exposed to each c.c. of the dispersed phase. There
would be a continuous series of systems ranging from a non-
dispersed two-phase system on the one hand to a homogeneous
mixture of an ionised salt in water, i.e. a true solution. Colloids
may thus be regarded as intermediate in this series, e.g. Gold coin
in water, gold dust suspended in water, very fine gold dust sus-
pended in water, range of colloidal gold in water ((Zsigmondy),
solution of gold salt (undissociated) and, finally, completely
dissociated gold salt in aqueous solution.

Physiological colloids differ from this metallic series in one
respect at least. They dissolve in water and they also imbibe
water. A solution of albumin, for instance, cannot be regarded
as a solid dispersed throughout a liquid, but is a strong solution
of albumin dispersed throughout a weaker solution.

This state is not peculiar to natural organic colloids, but, as
has been amply demonstrated by Von Weimarn, can be obtained
from such materials as NaCl, A1(OH)3 and silver salts. He has
enunciated a postulate called the law of corresponding states,
which is as follows : " The degree of dispersion and the general
physical appearance of precipitates are always the same irre-
spective of the chemical nature of the precipitates provided that
the precipitation takes place under corresponding conditions."
Working with substances as widely apart in their chemical nature
as the various salts of aluminium, barium, silver, sodium and
many others, Von Weimarn has prepared precipitates with almost
any desired degree of dispersion ranging in each instance, all the
way from coarse and obviously crystalline precipitates, to gela-
tinous precipitates and thick transparent jellies.

Colloidal matter may be further divided into two groups.
White of egg is an emulsoid colloid. In its ordinary state, as
obtained from the egg, it can be dissolved in water to form a clear
solution. Boiling the solution causes coagulation of the egg
white. It comes out of solution in the form of a white solid,
insoluble in water. Those colloids which form solutions like egg
white are called sols. According to the medium in which they
were dispersed they were termed by Graham, hydrosols, alcosols,
glycerosols, etc.. These colloids which assume a semi-solid form
like coagulated egg white are called gels. In a gel the more
liquid phase is dispersed through the less liquid phase.

An examination of the optical properties of these various disperse
systems makes it clear that there is a regular gradation in the
size of the particles dispersed, which passes from the easily visible

70 DISPERSE SYSTEMS

suspension to the invisible solute. If the size of a particle is
decreased below 200/u/z, it cannot be seen even by the most
powerful microscope made, or that could ever be made. The
particle is ultra-microscopic because its diameter is less than
half the wave-length of light. But, just as a beam of sunlight
renders visible innumerable specks of dust floating in the air, so
light may be diffracted by ultra-microscopic particles above a
certain diameter.

Faraday- Tyndall Phenomenon.

When a strong beam of light is sent through a rectangular cell
containing pure water, the beam may be rendered visible before
and after its passage through the water, but no cone of light is
seen in the water itself when viewed at right angles to the direction
of the light and against a dark background. If now a colloid be
dispersed through the water, light will be diffracted from the
particles in the water and the beam will appear in the solution
as a diffuse cone of light. This diffracted light is plane polarised
(p. 102), and is always produced when light passes through any
medium containing particles whose diameter is small in comparison
with the wave-length of light.

White light is composed of waves of different lengths varying
from 760 /*/* to 450/u/«. When white light is scattered from a
surface instead of being reflected as in a mirror, it gives rise to
the sensation of white. Ice, in mass, does not appear white
because light is not scattered from its surface. If the ice is
powdered, light is scattered from the powdered surfaces and the
whole appears white. Crystallised copper sulphate appears blue,
but the light scattered from the surfaces, of the finely powdered
crystals is white. The white colour of the lily or of white hair is
not due to the presence of a white pigment, but to the scattering
of light from the surfaces of innumerable minute air bubbles
embedded in the tissue. From this it follows that particles of
different sizes will scatter light of different wave-lengths. In
short, the colour of the scattered light may serve as an indication
of the size of the particle, provided the difference in the index of
diffraction between the dispersoid and the dispersant be kept
constant.

The blue colour of the sky is explained by considering that the
fine particles of dust, globules of water, etc., suspended in the
atmosphere cause lateral diffusion of light of short wave-length
giving a blue colour, while the red rays are transmitted direct,

FARADAY-TYNDALL PHENOMENON 71

producing the gorgeous sunset colours (see Spectroscope, Chap. II.).
In one ,of TyndalPs experimental verifications of this theory he
passed light through a tube containing a mixture of gases (butyl
nitrate in air and hydrochloric acid in air), which gradually
combined to form a dust -like suspended precipitate. At first the
particles were exceedingly small and the colour seen from the side
of the tube was a delicate tint of blue. As the particles increased
in size the blue became more intense, " until at length a whitish
tinge mingled with the pure azure, announcing that the particles
were now no longer of that infinitesimal size which scatters only
the shortest waves."

The colour of some samples of stained glass is caused not by an
even distribution of the pigment or stain throughout the glass, but
by the dispersion of fine metallic particles. Water of sufficient
depth appears blue due to the presence of tiny suspended particles.
If larger particles* are present, some light of longer wave-length,
e.g. yellow, is diffracted and the colour becomes green. The water
of the Rhone as it leaves Lake Geneva is intensely blue, while the
Rhine at Strassburg is green. The Rhine contains about 70 per
cent, more calcium carbonate in suspension than the Rhone.

Tyndall observed that the blue of the eye has a similar origin
to the blue of the sky, the sea, and the Rhone, viz. scattering of
light from small suspended particles. The uvea, the dark pig-
mented layer at the back of the iris, prevents the reflection of
light and prevents the colour of the blood in the vessels behind
it from becoming apparent. In an albino this pigment is absent
and the eye appears pink. The colour of blue eyes is due to finely
suspended unpigmented colloid particles in the iris. The various
colour stages between the blue and the grey eye arise from differ-
ences in the mean size of the dispersoid particles — the finer the
particles, the more intense the blue. Except with people who have
very black eyes, the pigment on the posterior surface of the iris
does not develop at birth. That is, most babies are born with
deep blue eyes. As they become older the colloidal particles
become larger and the blue becomes less intense. Further, the
uveal pigment may develop and the colour change from blue to
hazel, brown or black. The reverse change never takes place
(Bancroft).

Colour may be due, as we saw in Chapter II., to the reflection
of non-absorbed light. Complete absorption of light gives rise
to the sensation of black. A perfect reflecting surface would be,
of course, invisible. If follows that particles of different sizes

72

DISPERSE SYSTEMS

will " select " light of certain wave-length for absorption, and,
as a consequence, colour may result from " selective " absorption,
reflection or diffraction.

In the following table, from Ostwald, is given the relationship
between size of particle and colour (a) from light absorbed, and
(b) from light transmitted.

TABLE XI.
CORRESPONDING ABSORBED AND SUBJECTIVE COLOURS.

(a) Wave-length in p.
Absorbed Colour

•70
Purple

•65
Eed

•60
Orange

•55
Yellow

•53
Green-
Yellow

(6) Transmitted Colour

Green

Green-
Blue

Blue

Indigo

Violet

Wave-length in p.

•50

•48

•45

•

•43

•40

(a) Wave-length in p.
Absorbed Colour

•50
Green

•48
Green-
Blue

•45
Blue

•43
Indigo

•40
Violet

(b) Transmitted Colour

Purple

Red

Orange

Yellow

Green-
Yellow

Wave-length in p.

•70

•65

•60

•55

•53

One must, however, take into account the other optical com-
ponents, e.g. refractive index of medium. The absorbed colour
given above does not necessarily indicate the colour of light
scattered by the particles.

As the particle becomes smaller, the colour alters to light of
longer wave-length, e.g. from blue or green, through various
shades of yellow and orange to red. If the suspended particles
are very fine, blue light is, as we have noted above, scattered
laterally, while red light is transmitted. Such a system will
appear red by transmitted light and blue by reflected light (e.g.
skim-milk, tobacco smoke and colloidal gold). A very interesting
series of coloured plates to illustrate this will be found at the
end of Zsigmondy's monograph. It has also been shown that,
as the particles decrease in size, the absorption bands in the
spectrum of the solution shift towards the ultraviolet (Ostwald).

The amplitude of vibration of a particle is a function of its
mass, temperature being kept constant. As the mass alters so
will the period of vibration. According to Wood, metallic
particles, if highly dispersed, owe their colour not to ordinary

COLOUR OF DISPERSOIDS 73

reflection, diffraction, interference, etc., but to optical resonance.
Resonance is the production of vibrations in a body by the
periodic application of a stimulus which has the same period as
the natural period of the body. The vibrations of a tuning fork
may be transmitted through the air and cause to vibrate another
tuning fork of the same pitch. Since the resonator owes the energy
necessary to set it into vibration to the stimulating body it follows
that the stimulating body must lose energy to the resonator.
The particles in colloidal solution are supposed to be vibrating
with the same frequency as light of a certain wave-length. Con-
sequently, they will receive energy from the light which will tend
to increase their amplitude of vibration. The kinetic energy
of the solution will tend to increase, but any increase in kinetic
energy would mean increase in temperature and a slight alteration
in frequency. This opens up the possibility of considerable
energy changes in comparatively short times.

What effect will be produced when the rates of vibration are nearly
but not quite the same ? If two pendulum-controlled clocks which are
keeping nearly the same time when on separate stands are placed on the
same stand they will keep time exactly. Both pendulums transmit
vibrations to the stand, and so to one another. The faster pendulum
exerts a periodic force on the slower pendulum and is itself slowed by the
loss of energy. In the same way the slower pendulum tends to cause forced
vibrations in the stand and so influence the faster pendulum. Finally the
two pendulums (and stand) vibrate at periods exactly the same. Is it
possible that light may cause forced vibrations of colloidal particles ?

Certain investigators have claimed that the Brownian move-
ment may attain an increased velocity because of incident light.
Exner found that exposure to light of a suitable wave-length had
a positive accelerating effect. Compared with the movement as
a whole the alteration brought about by incident light is negligible.

One effect of optical resonance is the production of surface
colours. When light of a certain wave-length is strongly absorbed
by particles, they may also reflect that light " selectively." For
instance, magenta crystals (aniline colour) transmit red but reflect
green. If the particle is made small enough it will scatter the
light that it previously transmitted, and will transmit, of course,
the light that is not scattered. This is readily carried out with
indigo. In mass, this colloidal dye absorbs red and transmits
blue. It reflects red. If a fine suspension is made it scatters
blue, i.e. appears blue when observed laterally to the plane of
incidence of light. By transmitted light it is red, i.e. appears
red when looked at against the light.

74

DISPERSE SYSTEMS

The ultra- microscope is, in principle, just a means of viewing
the Tyndall cone through a microscope. A powerful beam of
light is thrown horizontally through a small body of fluid placed
under a microscope set vertically. The only light entering the
* t objective is that diffracted from the

particles present in and optically dif-
ferent from the fluid (Fig. 7). The
apparent image bears no relation to the
actual size of the particle, but depends
on the intensity of the light, and on
the indices of refraction of the par-
ticle and the dispersant. Neverthe-
less, by making certain assumptions,

FIG. 7. — Diagrammatic section the size of the particles may be cal-
culated.

Particles visible under the ordinary
microscope are called microns. Smaller particles are termed
sub-microns, if they are rendered apparent by the ultra-
microscope ; if not, they are amicrons. The smallest particle
of gold observed by Zsigmondy, using bright sunlight illumina-
tion, was 1 -0/uijUL in diameter. Bearing in mind the large difference
in index of refraction between gold and water, this may be
considered as the smallest particle ever observed. The follow-
ing table (from Zsigmondy) shows the limits of size of the
various classes of particles :

through a paraboloid condenser to
show the direction taken by the rays
of light. (Hatschek.)

TABLE XII.

LOWER LIMITS OF DIAMETERS OF SMALL PARTICLES.

Visible under
Microscope

MICRONS
O-25/i or
2-5 x 10~5 cm.

Not visible under microscope

SUB-MICRONS

AMICRONS

Visible by ultra-microscope Not visible by U.M.

under 1'0/x/z

Electric arc Strongest

Sunlight

15/x/x or 1'0/x/ji or

15xlO-7cm. l-OxlO-7cm.

equals 10~3 mm. = 10~4 cm., yu/x = 10 7 cm.

ULTRA-FILTRATION 75

Evidence tending in the same direction and towards the same
limits of size is afforded by experiments initiated by the classical
series of ultrafiltrations of Bechhold. Membranes of known
permeability are prepared, i.e. the diameter of the pores is known,
and the colloidal solution is filtered through these by pressure.
A series of filters is tried till one is obtained which has the smallest
pores which will allow the colloid to pass through. Obviously
the particles must be smaller than the pores, and probably, though
not necessarily, they are larger than the next filter in the series.
The sizes of particles obtained in this way are in reasonable
agreement with the values obtained from ultramicroscopic
calculations.

The little dots of light seen under the ultramicroscope are not
at rest. They dart about hither and thither in a seemingly
inexplicable way. According to the kinetic theory of matter, a
fluid was assumed to be made up of molecules in a state of very
rapid motion and having a mean free path intermediate between
that of a solid and that of a gas. The colloidal particles in the
liquid are hustled into motion by continuous collision with the
rapidly moving molecules of the liquid. If the particles have a
natural period of vibration which is a multiple of that of the water
molecules their amplitude of vibration will be increased (e.g. by
suitably timing blows on a pendulum its excursion can be increased
to a considerable extent. Each blow need be very slight).

This motion of the particles, while a very striking feature in
the field of vision of the ultramicroscope, is not characteristic of
colloidal solutions. Particles sufficiently small to be influenced
by the high velocity bombardment of the molecules or ions of the
solvent may still be well within the limits of visibility under an
ordinary microscope. This movement owes its name to its
discoverer Brown, a botanist, who described the peculiar oscilla-
tion of pollen grains suspended in water in 1827. This Brownian
movement may be seen by means of an ordinary microscope in a
solution of the water-colour gamboge especially when the dia-
phragm of the microscope is almost closed. The rate of move-
ment is independent of the chemical nature of the particles, but
depends on three factors, viz. (a) the size of the particle, (b) the
temperature, and (c) the viscosity of the dispersion medium. The
rate is increased by decrease in the mass of the particle, by increase
in temperature or by decrease in the viscosity of the medium.
The movement persists, never changing, once equilibrium has
set in, for all time. It has been observed in granite and in other

76

DISPERSE SYSTEMS

rocks in small pockets of liquid, which they must have occluded
for millions of years. But equilibrium must first be reached.

Direct observation of the absolute motion of the particles is
very difficult, although differences in motion are easily perceptible.
This difficulty has been overcome by the application of the
cinematograph to the microscope. A glance at Fig. 8, obtained
in this way, shows that a particle oscillates apparently in a
haphazard fashion about a certain mean position during a short
interval of time. Any alteration in the kinetic energy of the
dispersing medium, of course, produces alterations in the mean
velocity of the particles — e.g. increase of temperature increases

FIG. 8. — Movements of two particles of india-rubber latex in colloidal solution,
recorded by cinematograph and ultra-microscope. (Henri.)

velocity. The velocity may also be modified by alterations in
the hydration of the particles. Ramsay considers that the
particles in pure water do not touch one another at any time, each
particle being surrounded by a liquid layer. This layer is de-
stroyed by the addition of salts, which thus cause negative
acceleration.

To use a somewhat homely illustration, the colloidal particle
may be likened to a morsel of bait dropped into the water of a
river estuary. The moment that it reaches the water it is pushed
to and fro by a multitude of hungry small fish. The velocity
and amplitude of the oscillatory movements of the bait depend
principally on the size of the bait and on the energy with which
it is attacked.

BROWNIAN MOVEMENT

77

If a colloidal solution or a fine suspension of gamboge or mastic
be kept undisturbed at constant temperature for some time,
Perrin found that there was a distribution of the colloidal particles
under the influence of gravity. At the bottom of the container
will be found a denser distribution than at the higher levels.
This is exactly similar to the decrease in the density of the atmos-
phere with height above sea level, and Einstein argued that the

1

FIG. 9. — Apparatus for demonstrating cata-
phoresis. The deeply shaded lower portion
of the U-tube is filled with a colloidal sol, the
upper part with ordinary distilled water. On
the passage of an electric current the colloid
rises towards the electrode of opposite sign to
the sol. (Hatschek.)

FIG. 10. — Apparatus for ultramicroscopic
observation of the movements of colloids in
an electric field (see Part II.). (Hatschek.)

distribution of suspended particles with height should follow the
law which governs the density of the atmosphere with height.
Perrin proved by experiment that this was true. In one experi-
ment with mastic at four different levels 12/u. apart he found 116,
146, 170 and 200 particles per unit. For the same levels the follow-

78

DISPERSE SYSTEMS

ing values were calculated : 119, 142, 169, 201. This and
numerous other experiments confirm quantitatively the theory
that the Brownian movement is the result of molecular impacts.
After this adjustment of concentration to level has been reached,
no other change seems to take place. To this cause may be
attributed a share at least of the responsibility for the stability
of colloidal solutions.

The electrical properties of a colloidal dis-
persion may have much to do with the
permanence of the suspension. Each
colloidal particle carries a definite charge
seemingly dependent on the hydrogen ion
concentration of the dispersing medium.
The colloid generally has a greater con-
ductance than the intermicellar liquid itself.
This is due to the unequal adsorption of
ions of electrolytes present in the disper-
sion medium and in some instances by
ionisation of the colloid itself. By virtue
of this charge the particles of the disperse
phase will act like ions and will migrate
through the solution to any point of op-
posite charge. This electrical migration is
called cataphoresis (Figs. 9 and 10).

Diffusion of Electrolytes.

Cataphoresis should not be confused with
the electrical diffusion of electrolytes into
gels. That dissolved substances diffuse into
or out of gels was a fact familiar to Graham.
The rate of diffusion may be altered by the
addition of certain substances to the gel.
A gel, after treatment with sodium
sulphate, glucose, alcohol, glycerol, etc.
(dehydrating agents), offers considerable
resistance to the diffusion of electrolytes.
Urea, iodides, and chlorides, on the
other hand, cause acceleration of the rate of diffusion. These
added substances cause alteration in the relative amounts of
water held by dispersoid and dispersant and so produce alterations
in the more liquid phase. The degree of continuity of liquidity
is a causative factor in the velocitv of diffusion.

FIG. 11. — Adsorptive stratifi-
cation of silver bichromate in
an agar gel. (Bradford, Bio-
chemical Journal.)

COAGULATION 79

Liesegang Phenomenon.

If a gel contains a substance in solution and a second substance
capable of reacting with the first is allowed to diffuse into the gel,
the product of the reaction is deposited in strata separated by
clear intervals (Part II.). In Fig. 11 is illustrated a test tube
filled with 1 per cent, agar gel containing potassium bichromate.
On top of this was placed a solution of silver nitrate. It is
obvious that the silver bichromate formed is deposited in strata
separated by clear agar. No satisfactory explanation of this
phenomenon has been offered (Part II. p. 413).

Electrical Diffusion.

The rate at which electrolytes diffuse into gels may be increased
by the passage of an electric current. This method is sometimes
employed in the administration of drugs, — so called ionic medica-
tion. " Metal "-ions (cations) are carried into the tissues from the
positive electrode of any current-supply device, while " acid "-ions
(anions) are driven in from the negative electrode (see Chap. X.
and Part II. p. 413).

Coagulation of Gels and Precipitation of Sols.

If a colloid has a positive charge when in a liquid of high H+
concentration and has a negative charge when the H+ is low, an
intermediate point (isoelectric point] can be reached when the
colloidal particles has either no charge or, which comes to the
same thing, half of them with + and the rest — . In such a case
the colloid would lose its electrical stability. Positive and negative
particles would coalesce to form aggregates too large to exhibit
Brownian movement and the colloid would separate into discrete
phases.

This coagulation may be brought about by adding (a) acids or
alkalies, (b) suitable electrolytes or (c) colloids of opposite sign.
The coagulation of suspensoids (Class IV. colloids) by the above
means is easily carried out and is a reversible process. On washing
out the adsorbed precipitant the dispersoid is re-established.
Emulsoids (Class III.), on the other hand, are more stable than
suspensoids. They usually need the addition of a large quantity
of the coagulating substance and the resulting coagulum is
frequently irreversible. This may be due to alteration in the
continuous phase. We have seen that an emulsoid is a diphasic
system where the continuous phase is more or less a continuation
of the disperse phase. If a substance A is dispersed in water to

80 . DISPERSE SYSTEMS

form an emulsoid what really results is a dispersion of a solution
of water in A, throughout a solution of A in water. The stability
of such a system will depend in great measure on the viscosity of
the intermicellar liquid. The viscosity depends on the concen-
tration of the more viscous A in the less viscous water. The
range of viscosity making for stability will be bounded on the one
hand by a certain minimum and on the other hand by a certain
maximum concentration of water in the continuous phase.

Protective action of Emulsoids.

Many emulsoids when added in comparatively minute quantities
to suspensoids prevent the coagulation of the suspensoids by
electrolytes. As a matter of fact, each emulsoid which exhibits
this property has a characteristic protective power which may
be used as a definite factor for the identification of the colloid.
The suspensoid generally used in the test is colloidal gold. Zsig-
mondy, who devised the method, defines the " gold number "
as the number of milligrams of an emulsoid which are just suffi-
cient to prevent 10 c.c. of a bright red gold sol (prepared under
certain specified conditions) from changing into violet or shades
of violet after the addition of 1 c.c. of 10 per cent, sodium
chloride solution (Part II.).

He divides colloids into four classes according to their " gold
number," viz. :

TABLE XIII.

Class.

Gold Number.

Examples.

I.
II.
III.

IV.

0-005-0-1 mg.
0-1 -lOmg.
10 - 500 mg.
Inactive -

Gelatin, caseinogen, animal glue.
Crystalline egg albumin, gum acacia.
Dextrin, starch.
Mucin, silicic acid.

The general opinion seems to be that the emulsoid forms a
pellicle round each suspensoid particle and prevents coagulation,
either (1) because, as we have seen, emulsoids are less sensitive
to the precipitating action of electrolytes and the compound
particle is endowed with an emulsoid coat ; (2) because the
electrolyte does not come in contact with the suspensoid particle
and does not neutralise its electric charge, or (3) merely by offering
a material obstacle to the coalescence of the particles.

The fluids of the body contain two colloidal substances of
peculiar interest. Albumin and globulin are both emulsoids,

81

but they differ physically in at least three respects summarised
below.

TABLE XIV.

Albumin.

Globulin.

Sol in water.
(Sol in 5 per cent. NaCl.)
Not ppt. by £ sat. (NH4)2S04.
Protects suspensoids.

Insol in water.
(Sol in 5 per cent. NaCl.)
Ppt. by \ sat. (NH4)2S04.
Ppts. suspensoids.

Albumin has a protective action on gold sol while globulin
acts almost as if it were a suspensoid. The proportions of albumin
and globulin in the various body fluids is practically invariable
in health, but during the course of various diseases the balance
is upset. If the globulin content is increased relatively to the
albumin, then the body fluid will lose a portion of its protective
power. In some cases the globulin is not increased, but carries
an increased positive electric charge. This increases its precipi-
tating action. (Method given in Part II.)

Evaporation or dehydration, if it reduces the water content
below the minimum, will cause coagulation. Conversely, dilution
causes a disperse system to break up.

Heating and Cooling, which alter viscosity directly and also
indirectly by altering the amount of water distributed between
the two phases, also cause coagulation. Heating certain sols
changes them into the more rigid gels. Various native proteins,
for instance those of egg white, serum, muscle, coagulate to a
gel on heating to a temperature specific for each protein. This
process is irreversible and takes place in the presence of electro-
lytes. On the other hand, gelatin forms a sol on heating and a
gel on cooling — a reversible reaction which is profoundly modified
by the presence of electrolytes.

Action of Radium. (See also Chap. XI.)

The intimate connection between coagulation and the charge
carried by the particles is shown by the action of the /? rays of
radium. As these rays are negative charges of electricity, they
should stabilise negative colloids by increasing their charge, and
precipitate positive colloids by neutralising their charge. Hardy
found that positively charged acid-globulin was reduced to a
state of jelly in three minutes, while the particles of negatively
charged alkaline-globulin were rendered more mobile by exposure
to (3 radiation.

82 DISPERSE SYSTEMS

The behaviour of most organic gels is complicated not only by
the presence of electrolytes, and by the fact that the content of
the intermicellar fluid in electrolytes may be rapidly altered, but
also by the fact that the dispersed substance is a mixture of
closely related substances. Thus agar-agar, a carbohydrate
superficially similar to the protein-hydrate gelatin, consists of at
least two substances a and /? agar-agar which are mutually con-
vertible under certain conditions. Purified, a agar-agar is
practically insoluble in water. The (3 form is very soluble in water.
On warming some of the former with water it gradually passes
into the soluble form and thus goes into solution. Insoluble
a particles may be dispersed in larger particles of /?+ water.
They in turn form a true sol with water. Alteration of physical
or chemical conditions will therefore alter the relative concen-
tration of a and fi. The /3 colloid protects its a relative from
coagulation by thus forming a pellicle round it. Starch — a
pseudo-colloid — is a mixture of several carbohydrates of high
molecular weight, each of which is capable of taking up a different
quantity of water. (See under Emulsions.)

Of great physiological interest are soaps, the alkali salts of the
fatty acids. These soaps are found in the body wherever fats
are found — -in bile, blood, faeces, ear wax, sebum, etc., as well as
in some pathological fatty secretions. The soaps furnish a series
in which the molecular weight regularly increases. Step by step
with this increase in molecular weight there is a regular gradation
of the properties of the dispersoid from the true solution of the
soaps of the lower fatty acids to the colloidal gels of the higher
homologues. Still more important physiologically is the effect
of altering the anion. Sodium, potassium, ammonium, calcium
and magnesium soaps are found in physiological analyses and these
differ from one another, especially in their power to hold water.
Ammonium and potassium soaps are so hydrophilic that they do
not solidify but form jellies (soft soap). Sodium soaps also hold
a considerable amount of water, but only about | of that held by
" soft " soaps. So little water is held by the soaps of calcium
and magnesium that they do not form a sol to any appreciable
extent. The addition of alkali to a sodium soap greatly increases
its hydrophilic properties. Soap solutions may be broken up
in various ways.

(a) The addition of an acid stronger than the fatty acid frees
the fatty acids, e.g. H2SO4+2NaA=Na2SO4+2HA.

(b) On adding a powdered neutral salt to a soap solution the

EMULSIONS 83

soap is " salted out " as a curdy mass. The salt reduces the
hydrophilic powers of the soap and so reduces the stability of
the dispersoid. This is a different phenomenon from the precipi-
tation of a colloid by electrolytes.

(c) On adding a soluble salt of calcium or magnesium to a soap
of ammonium, sodium or potassium a curdy precipitate is produced.
This curd is a calcium or magnesium soap, which, as we have seen,
has little or no affinity for water.

(d) Solvents of soaps added to a water-soap dispersoid lead to
a partition of the soap between solvent and dispersion medium.
The effect of the anaesthetics on soap sols is interesting. Alcohol
brings about a rapid separation of soap and water, practically all
the soap dissolving in the alcohol. Chloroform has much the
same effect, but the partition is not so complete. To get anything
like a complete extraction large amounts of chloroform must be
used. Ether has hardly any effect.

Soaps have a powerful effect in lowering surface tension, which
effect is greatly increased by the addition of small quantities of
alkali (Shorter and Ellingworth). A stalagmometer reading
of oil dropping into water was 65 drops. When 1 per cent, soap
was added to the water the drops increased to 260 (Hatschek).

Emulsions.

Although, as far as is at present known, emulsions do not take
a direct part in the energy exchanges of the body, and should
therefore not be treated in this section ; yet as they are so closely
allied to the colloids, and are really never found unless mixed
with colloidal or semi-colloidal matter, it is convenient to deal
with them now.

An emulsion may be regarded as an emulsoid with somewhat
larger dispersed particles (microns). The term, as usually
employed, has, however, a narrower connotation, the disperse
phase being considered as a fat or fat-like substance distributed
throughout water in such a way as to remain stable for an in-
definite period. Oil and water are two immiscible liquids and
no amount of mechanical mixing will induce them to form a
permanent emulsion. It is true that after a prolonged beating
of the two together a maximum of 2 per cent, of the oil may be
taken up by the water, forming a stable dispersoid. Measurement
of the particles, however, demonstrates that they are of the order
of sub-microns, and thus a true colloidal system has been formed.
An example of this is the condensed water of steam engines, which
contains lubricating oil in suspension.

DISPERSE SYSTEMS

Analyses of natural and artificial emulsions, like milk, bile,
rubber, cod-liver-oil emulsion, etc., demonstrate the presence of
more than merely oil and water. A colloid or semi-colloid must
be present.

TABLE XV.

Emulsion.

Disperse Phase.

Continuous Phase.

Colloids.

Crystalloids.

Milk

Oil
3-8 per cent.

Water
87 per cent.

Caseinogen

Albumin
Globulin
3-2 per cent.

Lactose and
Salts
Na2C03, etc.

Bile

Fats and
Lipoids
5-9

Water

77-5

Soap 3-2
Mucin 0-45

Egg yolk

Fat
35-3

Water
47-2

Protein
15-6

Ear-wax

Fat
26

Water
10

Potas. Soap
52

Mostly organic,
little ash.

Butternut

Water
4-4

Fat
55-1

Protein
23-7

Human fatty
tissue.

Water
15

Fat

82-5

Protein
2-5

Rubber latex

Rubber 20
and
Resin 2

Water
76-2

Protein

20
•o

Sugars,
K and Ca, etc.

Pharmaceu-
tical
Emulsions

Oil
50

Water
50

Egg white
Gum arabic
Saponin

Sugar
Phosphates
Carbonates

Lubricating
Emulsion

Water
1

Oil
99

Soap
1

If the generic term oil is used to denote any liquid that is not
miscible with water, we may note that there are two entirely
different types of emulsions, the one being drops of oil suspended
in water and the other being drops of water suspended in oil
(cf. emulsoid sol and gel). For example, milk belongs to the
former and butter to the latter class. It is important to know

STABILISATION 85

under what conditions each of these types is formed. One
might at first imagine that the governing factor would be the
relative amounts of oil in water, much water and little oil producing
the oil-in-water type and excess of oil over water producing the
water-in-oil emulsion. This is not so. The nature of the emulsoid-
colloid determines the type of the emulsion absolutely. The relative
amounts of oil and water have nothing to do with it. To under-
stand the significance of this, one must examine the function of
the colloid.

Some means must be adopted once the oil has been dispersed
to (a) decrease the interfacial tension between the droplets and
the dispersion medium so that the dispersed particles will not
coalesce, (b) confer on the droplets an electrical charge so as to
cause mutual repulsion, and (c) mechanically keep the droplets
separate. The presence of an emulsoid seems to confer stability
on an oil-water emulsion. Two theories to account for this are
of sufficient importance to warrant attention.

1. Most physical chemists prefer the theory which postulates
a third phase, namely, a thin layer of colloid or semi-colloid
separating the disperse from the continuous phase. This inter-
facial film reduces the surface tension on the film-water interface,
confers a charge on the droplets by adsorption, and, by having
the remainder of the colloid as an outer phase, provides a medium
sufficiently viscous to keep the droplets in suspension.

2. Recently Fischer and Hooker have promulgated their theory
of the action of the protective colloid. They consider that an
emulsion may be triphasic but need not necessarily be so. Their
idea is that a diphasic system is all that is required for stability,
e.g. oil and an emulsoid in water.

The nature of the emulsoid determines the type of emulsion
produced. If the colloid is one which is " wetted " by water
(hydrosol or hydrogel), and is adsorbed by oil, it (or its solution)
will form a film round the oil droplets and give an emulsion of
oil in water. On the other hand, if the colloid is dispersed through
oil and is adsorbed by water it will emulsify water in oil. Most
emulsions are of the first type, oil-in-water.

The oil cannot be dispersed throughout a hydrated colloid
until a certain lower limit of water content has been exceeded,
nor can it be divided permanently into a hydrated colloid after
an upper limit has been passed.

Emulsions are broken through the institution of conditions
that are the reverse of those that make for their stabilisation.

86 DISPERSE SYSTEMS

In other words, a colloid is a suitable emulsifying agent only when
it holds a certain amount of water. That amount may vary
between an upper and a lower limit. If at any time the water in
the system oversteps either of the limits the emulsion will lose
its stability and will separate out. The emulsions hardest to
break are those where the emulsifying agent is a carbohydrate
like gum acacia, starch or dextrin. They hold their water of
hydration with avidity. Salts, acids, or alkalies in moderate
concentrations, alcohol, chloroform and ether have very little
action on them. Milk, an oil in protein emulsion, is very difficult
to break. Dilution has little effect and fat solvents do not readily
extract the fat. This is probably due to an adsorption effect in
which the carbohydrate plays a part as yet unknown. The
colloidal material comes to be concentrated on the surface between
the oil and the aqueous phase. These protecting films drawn
over the oil globules keep them from coalescing even when brought
close together and also form a membrane impermeable to fat
solvents.

At this point the two theories seem to be on common ground.
Neither of them can, however, give a satisfactory explanation of
the stabilising effect of the presence of a small quantity of carbo-
hydrate on oil-protein or oil-soap emulsion. The carbohydrate
need not be a hydrophilic colloid itself. Cane sugar is an excellent
stabiliser. Why are tissues less easily poisoned by anaesthetics
and other poisons when glycogen is in the cells ?

Similarly the colloid in a water-in-oil emulsion must be hydrated.
Using soap as his stabiliser, Pickering emulsified 99 per cent, oil
by volume in one volume of water. The resulting emulsion was
a stiff jelly which could be cut with a knife and the cube so prepared
would stand alone. These solid cubes when left standing in dry
air seem to liquefy. The reason for this is that the soap film loses
moisture by evaporation, cracks, and sets free the oil. The mass
does not become liquid because of the adsorption of water but
because of the loss of water. Several of the heavy lubricating
oils contain a considerable quantity of calcium soap. Now,
calcium soaps are very insoluble in water but form colloidal
solutions in oil, therefore, in these lubricants the water is emulsi-
fied into the oil and a thick grease is formed. Rosin acts similarly
to calcium soap and is used in the preparation of cheap brands
of ready-made paints as an instrument for the emulsification of
water in the linseed oil. As much as 80 per cent, water may be
absorbed in this way.

RIGIDITY OF TISSUES 87

The hydrophilic properties of sodium and calcium soaps have
already been mentioned. Their behaviour in emulsion-making
throws light on some peculiar problems in physiology. Loeb and
his co-workers found that certain marine organisms died when
put into fresh water. This will not appear surprising to the
student who remembers the phenomena of endosmosis, e.g. plasmo-
lysis, haemolysis, etc. That this explanation is not correct is
shown by putting the organisms into solutions of sodium chloride
or of calcium chloride having the same osmotic pressure as sea
water. If, however, the organisms which would have been
killed by immersion in these isotonic solutions were placed in a
solution having a definite ratio between the amount of sodium
and calcium present, life was maintained quite normally. All
protoplasm may be considered as an emulsion of lipoid material
in a colloidal-crystalloidal complex. The presence of the sodium
soap formed by interaction with the lipoids causes the formation
of a lipoid-in-water emulsion while the calcium soaps emulsify
water-in-lipoid. The two types of emulsion thus formed are in
equilibrium with an environment containing a definite Na/Ca
ratio, that of sea water. Alteration in this ratio upsets the balance
between the two types of emulsion and causes the cessation of
growth and subsequently of life (see Nerve, Chap. XVII.).

The rigidity of tissue is to a large extent due to their emulsion
character. We have up till now considered protoplasm as a
liquid, arguing that it is so because it shows the phenomena of
surface tension, because it allows the ready diffusion of crystal-
loids into and through it, and because it reacts chemically as a
liquid. On the other hand, tissues, as we handle them, are more
or less rigid, having elasticity and definiteness of form. Do
Pickering's solid emulsions and the Na/Ca ratio not suggest a
fairly plausible explanation of this double nature of protoplasm ?
The " softening " of tissues observed in various pathological
states may be due to the breaking of the protoplasm-emulsion
from any cause (Part II.).

Our food materials as well as our tissues are colloidal complexes.
They are derived in part from the animal, in part from the vege-
table kingdoms.
A. Animal foods may be classified as :

(1) Milk and its products — cream, butter, and cheese.

(2) Flesh.

(3) Eggs.

(1) Milk is a fine emulsion of fat in a protein-colloidal solution.

88 DISPERSE SYSTEMS

(a) The fat globules each seem to be enveloped by a covering
of adsorbed protein.

(b) The chief protein in milk is caseinogen, a phospho-protein
which exists in milk as a soluble calcium compound. This
compound is broken by the action of acid, and protein separates
as a curd.

(c) The carbohydrate of milk, lactose, is split by various micro-
organisms, forming lactic acid, thus souring the milk and causing
curdling.

Butter is simply the fat of the milk more or less completely
separated from the other constituents and forming a water-in-oil
emulsion. Whole, unchanged milk shows no tendency to form
butter. To form butter the fat particles are concentrated at the
surface by centrifugal action (or merely by allowing the cream
to rise), and then by causing the cream to sour, the fat is freed
from its emulsion with the colloidal matter. Since the hydrated
colloids tend to collect in the surface layer between the fat globules
and the dispersant aqueous phase of the cream, churning is
performed to break these layers and hasten the coalescence of
the fat. " The combined efforts therefore bring about a pro-
gressive increase in the concentration of the oil with a decrease
in the concentration of the hydrated colloid until the instability
of the oil in hydrated colloid becomes so great as to ' break ' and
yield the hydrated colloid-in-fat emulsion which we call butter "
(Fischer and Hooker). That milk and cream are oil-in-water
emulsions can be proved microscopically. They wet paper and
are not greasy to the touch. Butter is a water-in-oil emulsion,
feels greasy, oils paper, and microscopically appears as a finely
divided aqueous colloid phase in a continuous oil phase.

(2) Flesh. Under this head is included, not only the muscles
of various animals, but such cellular organs as the liver, kidneys,
thymus, etc. The colloidal nature of such tissues has already
been dealt with (see effect of cooking, below).

(3) Eggs. The white of eggs is practically an albumin hydrosol
containing some crystalloids, while the yolk is an emulsion of
lipins (lecithin, etc.), in a hydrosol of protein (ordinary proteins,
and vitellin, a phospho-protein).

B. Vegetable Foods.

In the food of man, vegetable foods play as important a part
as animal products. Generally, their make up is that of a mixed
hydrogel of protein, higher carbohydrates (and in the case of

COLLOIDAL NATURE OF FOODS 89

oatmeal, maize, nuts, certain legumes and vegetables), a fair
proportion of fat. This gel is enclosed in a capsule of cellulose —
a higher carbohydrate which is very resistant to the action of the
human digestive juices. The capsule must be destroyed by
previous treatment, e.g. milling, cooking, chewing, etc., before
the contents can be utilised. Far and away the most important
of our foodstuffs are derived from cereals. From 30 to 50 per
cent, of the energy of an ordinary diet comes from them. They
are generally used as flour, baked into bread, or as meal made into
porridge. Wheat flour is a complex gel powder consisting of
about 10 per cent, protein, about 75 per cent, carbohydrate
(starch and cellulose), and about 2 per cent, fat in the colloidal
state. The individual particles contain molecularly dispersed
salts, sugar, water, and adsorbed gases such as air and carbon-
dioxide. Of the 10 per cent, of protein, gliadin forms about
4 per cent, and glutelin about 4 per cent. There is less than
1 per cent, of globulin (0-6 per cent.) and albumin (0-3) present.
The mixture of glutelin and gliadin is known as gluten. Gluten
is insoluble in water or in dilute salt solutions, and therefore readily
forms a disperse system with water called dough. Dough is a
polydispersoid composed of the glutelin (and other proteins)
carbohydrates and crystalloids mentioned above bound together
by colloidal gliadin. It is a viscous semi-liquid mass which,
however, may be cut like a solid, and when torn exhibits a fibrous
surface. The elastic properties of dough depend upon the pro-
portion of electrolytes present, especially on the phosphates.
When it is dried it changes into a gel and later becomes brittle
like glue. There is doubtless a close connection between the
viscosity of flour-water mixtures, and the stickiness, rising
property, power of absorbing CO2 of the dough, hydration of the
starch and the porosity and volume of the resultant loaf.

The viscosity is found to increase with the concentration of
the flour and also to become greater for some time after mixing.
This is doubtless due to the slow swelling of the starch and albumin.
If concentrated solutions are suddenly diluted the viscosity is
too great at first, but gradually approaches a normal value. This
is probably caused by a slow increase in the dispersion, because
when the larger particles are removed by means of filter paper
normal results are obtained.

Cooking. While many reactions occur in cooking, the changes
that are of paramount importance are of a colloidal nature.
Dough, for instance, undergoes a marked alteration in its physical

90 DISPERSE SYSTEMS

characters during the baking process. The proteins are coagu-
lated (gel formation) and the degree of dispersion of the starch
is increased. Adsorbed gases are set free and the bread " rises."
Further alterations take place in the loaf after it is removed from
the oven.

The physical nature of flesh is profoundly altered by subjection
to cooking. In roasting, grilling, boiling, or frying, the meat is
exposed directly to heat. The proteins in the outer layers are
immediately coagulated, thus forming a more or less impermeable
covering which prevents the escape of the meat juices, leaving the
centre portion of the flesh only slightly altered chemically, but with
all sols converted into hydrogels. On the other hand, if the meat is
immersed in cold water and boiled much of the protein-sol and
practically all the salts and extractives are dissolved out and form
soup. In this soup the protein-sol is coagulated as the tempera-
ture rises, and on cooling it is adsorbed to the surface and often
is removed with the fats as a scum. The remaining meat under-
goes coagulation, but is flavourless. Stewing is a modification of
boiling, but the extractives, salts and soluble proteins, are served
as gravy.

CHAPTER IX
ENZYMES

THE TOOLS OF THE CELL

" Instances of Magic ; .... By which I mean those wherein the material
or efficient cause is scanty and small as compared with the work or effect pro-
duced ; so that even when they are common, they seem like miracles, some at
first sight, others even after attentive consideration." BACON.

THE living cell is a factory where, without any great display of
energy, work is carried on which, outside the body, could only be
done by the use of strenuous processes. In the cell are prepared
secretions which act on insoluble raw material, rendering it
soluble and so fit for transit to the cell and passage into it. Within
the cell, these prepared materials undergo further change ; some
are used as sources of energy ; from others, the cell builds up
complex tissue ; others again are altered somewhat and stored
for future use. The cell manufactures from the material supplied,
various substances such as are required, it may be by distant
cells which are so occupied by some special process that they are
unable to perform the particular synthesis. The by-products of
manufacture are rendered harmless by processes possible, as yet,
only in the cell. Some cells, as indicated above, have a specialised
function. To a certain extent, all the cells of a multicellular
organism are specialised. They are divided into communities,
each engaged on some special work and requiring special raw
material. Some of these communities, however, engage to a
certain extent in general manufacture. They are almost, though
not quite, self-supporting. The white cells of blood, for instance,
are really unicellular organisms. Other communities are almost
entirely dependent on imports for their sustenance. Nerve cells,
for example, form the means for intercommunication between
cell-communities. Their general metabolism is peculiar.

Contrast the quiet, economical, and neat living-factories with
the places where things are made outside the body. Our manu-

91

92 ENZYMES

facturing cities are not spotless nor are our processes there eco-
nomical. Smoke, sound, and slag-heaps are universal accompani-
ments of a manufacturing community. Most of the processes
carried on in the cell have not been reproduced in the laboratory.
Fischer, the finest physiological chemist of this or any century,
has failed to synthesise the simplest protein. Fat and carbo-
hydrates are interconvertible in vivo but not in vitro. True,
steps have been taken towards the building up of a protein.
Polypeptides — compounds containing eighteen amino acids —
have been the crown of Fischer's efforts, but at what a cost of
material, time, and energy. It has been well said that laboratory
processes are just a roundabout way to the sink.

How does nature accomplish her work ? What tools does she
use ? How does she harness her power ?

Nature employs catalytic methods. A catalyst is defined as a
substance which, while not entering into the final product of the
reaction, alters its rate and in some cases alters the point of
equilibrium. A model may make this clearer. A sheet of glass
may be inclined at such an angle that a body placed at its upper
end just slips slowly to the foot. The momentum of the sliding
body may be insufficient to carry it to the foot of the glass plate,
and motion may thus stop mid1way down the plane. If a small
quantity of oil be placed either on the glass or on the bottom of
the weight, it will slide rapidly to the foot of the plane. The oil
remains unchanged. No energy has passed from the oil to the
weight, and yet the rate of falling and the point of equilibrium
have been altered. The lubricant may be taken as representing
a catalyst. Some one has said that a catalyst, like a tip to a waiter,
accelerates a reaction that otherwise would proceed with infinite
slowness. It takes no part in the main reaction, is adsorbed to
the reacting body, and may be recovered intact at the end of the
reaction by destruction of the substrate.

Catalysts are of very many kinds, and the mechanism of their
action is so varied and so little understood that few, if any,
general principles can be enunciated. They may be classified
according to the means they adopt to influence a reaction.

1. Contact agents. Many reactions seem to be accelerated by
the adsorption of the reacting substance on the surface of the
catalyst, e.g. effect of colloidal catalysts.

Colloids, as we have seen, are characterised by the development
of surface. If we take a sphere of metal which just fits into a
cubical box, and divide that sphere into smaller spheres of uniform

CATALYSTS 93

size, the same mass of metal may be packed into the box regardless
of the size of the spheres, provided they are uniform in size. Mass
and total effective volume are not altered, but surface is increased.
The surface of a sphere is 4-Trr2. If the original sphere be divided
into 100 small shot, then the new surface would be 100 x47rr12
where r^radius of small shot. Now r1=v/T^1) =4-64, i.e. the
surface would be increased over four and a half times. If the
subdivision were carried still further till there were 1030 small
shot, then the total adsorbing surface would be increased
10,000,000,000 times. The intensity of adsorption is chiefly
dependent on the area of adsorbing surface (cf. Table, p. IX.). In
other words, contact catalysis is indicated where the specific
surface of the catalyst comes within the colloidal range. Charcoal
is used as an adsorbent in the clarification of sugar. A cubic
metre of charcoal consisting of particles 1 mm. in diameter has a
surface of about 600 sq. metres. If the particles are reduced to
colloidal dimensions, say to 0-1 //. diameter, then the adsorbing
surface becomes 60,000,000 square metres.

2. Carriers. In some cases the catalytic agent combines
chemically with one of the reacting substances to form an un-
stable intermediate compound. This, in turn, breaks up, regener-
ates the catalyst, and liberates the reagent in the active atomic
state — so called nascent. Many oxidations and reductions are
brought about in this way.

3. Ionic Catalysts. Hydrogen and hydroxyl ions act as cata-
lysts for many reactions which occur in aqueous solution. The
velocity of such a reaction in dilute solution is proportional to
the concentration of the ions in question, provided the thermo-
dynamic environment remains constant. The ion probably
acts as a carrier, forming an unstable perhydrate as intermediate
product.

The great majority of vital catalytic reactions have, as catalyst,
an enzyme. Enzymes themselves cannot be detected or estimated.
Their presence is made apparent by their action. By estimating
the amount of the products of enzyme activity an idea of the rate
of reaction may be gained. Many attempts have been made to
isolate and purify certain enzymes and, though complete success
has not been granted to any investigator, much has been learned
of their nature and of the conditions necessary for enzyme action.

(a) Enzymes are colloidal. They can readily be separated from
crystalloids by dialysis or ultrafiltration. Chemically, they
resemble their substrate or are so closely associated with their

94 ENZYMES

substrate that existence apart is impossible. It may be that the
colloidal character of enzymes is the secret of their action. At
any rate an artificial oxidising enzyme has been prepared by
mixing a suspensoid — finely divided manganese, with an emulsoid
— gum acacia. The adsorption complex so formed, if suitable
crystalloids were present, reacted as an artificial " laccase."

(6) Enzymes retain their activity only over a very well-defined
range of temperature. It is common knowledge that physio-
logical processes take place most readily at body temperature.
Every biological laboratory is equipped with devices for keeping
incubators at a constant temperature — say, 37°-40° C. Before
these appliances had been perfected, investigators in this realm
had to keep their experimental material on their person. The
Abbe Spallanzani (1729-1799), in his classical work on digestion,
carried his digest-tubes in small pockets in his armpits for several
days. During the Great War, when scientific work had to be
carried out in all sorts of places, at least one physiologist, bereft
of gas regulators, had to resort to this simple but efficient method
of maintaining a fairly uniform temperature. In this way,
reactions in which they play a part differ from those usually
styled chemical. The rate of most chemical processes is doubled
or trebled when the temperature is raised 10° C. The enzymes
follow this rule only from 0° C. to a temperature called their
optimum temperature, above which the rate decreases rapidly.
The optimum temperature of most enzymes lies between 30° and
40° C. The decrease in rate of reaction when the temperature
is allowed to go over 40° C. is probably due to coagulation of the
enzyme. Increase in temperature causes alterations in the
physical state of colloidal matter. These alterations, in viscosity,
in colour, and in conductivity, all indicate an increase in the size
of the colloidal particles, and consequently a decrease in their
specific surface. The effective adsorbing surface is diminished.
At the optimum temperature the increased chemical action due
to temperature more than balances the decreased adsorbing
surface. Beyond this temperature, the loss of surface becomes
relatively important. If the temperature is raised till the specific
surface is reduced, by coagulation, to a value below 10,000,
adsorbing power is totally lost, chemical action is stopped, and
the enzyme is said to be dead.

In the appended figure (Fig. 12) curve 1 (dotted line) shows
how, as the temperature increases, a pure chemical action is
accelerated. Curve 2 (dash line) represents the rate at which the

FACTORS INFLUENCING ENZYME ACTION 95

effective surface is decreased by rising temperature. The process,
it will be noticed, is not an instantaneous one, but proceeds with
a definite velocity which increases very markedly somewhere
about 30° C. Curve 3 (firm line) is the graph of the rate of the
same chemical reaction as shown in (1), but carried out by enzyme
action. fcThis curve may be drawn by plotting the differences of
the ordinates of (1) and (2) on the same scale of temperatures.

(c) The hydrogen ion concentration of the medium in which
the enzyme acts has much to do with its activity. Each enzyme
is active only when the bathing fluid has a pH of a certain range
with an optimum pa at which the action proceeds at its best.

TEMPER.ATUFLE:

FIG. 12. — Graph to show how the effect of increase of temperature on the rate of
enzyme action is the result of the interaction of two factors, (1) increased chemical
action and (2) increased destruction of enzyme.

The extraordinary sensitiveness of colloids to the pu has been
mentioned.

(d) The crystalloid content of the substrate solution is peculiar
for each enzyme. Certain salts are, of course, destructive. All
salts which break up colloidal complexes, inhibit or destroy
enzyme action. Enzymes are " salted out " by the neutral salts
that precipitate colloids and may thus be separated.

(e) Anaesthetics have no effect on enzyme action.
Chloroform, thymol, etc., may therefore be used to keep experi-
mental enzyme solutions free from bacteria.

To sum up, — the ranges of temperature, pH, salt content, etc.,
all point to the colloidal nature of enzymes.

The material on which an enzyme acts is called its substrate,
and each enzyme acts on a specific substrate and on no other. In

96 ENZYMES

many cases the name applied to the enzyme is derived from that
of its substrate by altering the terminal syllable to — ase. Thus
maltase acts on maltose.

Lactase acts on lactose

protease „ protein

aldehydase ,, aldehyde i

lipase ,, lipin

peroxidase ,, peroxide.

Sometimes the function of the enzyme may be indicated by
its name, viz. :

oxidase oxidises ( =peroxide +peroxidase)

catalase breaks down peroxides
invertase inverts cane sugar.

The majority of enzymes of physiological importance, however,
have no accepted systematic name. They are the ones first
known and they were named to suit the fancy of their discoverer.
Ptyalin (Gr. Pteuin — to spit) acts on starch and should be called
salivary amylase. Several others are in a similar position, e.g.
Pepsin (Gr. Pepsis — digestion) =acid or gastric protease. Trypsin
(Gr. Tribein — to rub — prepared by rubbing pancreas with sand
and glycerol) =alkaline or pancreatic protease.

Some writers prefer to use names which point to the splitting
power of the enzymes, e.g.

proteolytic or proteoclastic enzymes act on proteins
amylolytic or amyloclastic ,, ,, starches

lipolytic or lipoclastic ,, ,, fats.

On the other hand, hydrolytic enzymes produce their effect by
adding or subtracting water.

Some enzymes act in the cells while others are secreted by the
cells and act on a substrate outside the cell. The former, endo-
enzymes, have been little studied. An active suspension of them
may be prepared by grinding up tissue with sand and extracting
with watery glycerol. It is probable that all muscle cells contain
enzymes which act on protein — disintegration products, either
rebuilding proteins from amino acids or breaking down these
amino acids. Similarly ; the regeneration and the disintegration
of carbohydrates and fats have been attributed to endo-enzymes.
There are also special enzymes to carry out oxidations and re-
ductions in the cell. The various stages in the production of
uric acid from nucleoprotein have been studied exhaustively, and
each stage has been shown to have its enzyme or series of enzymes.

ACTIVATION 97

The ecto- enzymes are secreted in the various digestive juices
and act on their substrates in some portion of the alimentary
canal. They really act outside the body and have one function
only — to break down the food into a state in which it can pass
through the gut wall into the body.

Zymase Secretion. Some of these enzymes seem to be secreted
ready for action. They themselves are in the active state, and
the juice of which they form a part contains the necessary salts
and has a suitable PH. The moment that the juice comes in
contact with the substrate, digestion begins.

Zymogen Secretion.

Pseudo- activation. Others, however, enter the alimentary canal
in an inactive state. Their inactivity is not due to the lack of
a suitable medium, but to the form in which the enzyme appears,
i.e. as a pro-enzyme or precursor of the enzyme. An activator
is required. For example, the active principle of gastric juice is
secreted as pepsinogen which becomes active pepsin on coming
into contact with a fluid of a certain PH. This is not a true
activation. Acid does not so much activate pepsinogen as form
a necessary concomitant for pepsin. That this is so may be
demonstrated by neutralisation of the acid, with consequent loss
of activity in the enzyme. On reacidifying digestive activity
restarts. Acid and pepsin have been termed co-enzymes — a
misleading term. True activation is irreversible. Once an
enzyme has been rendered active its activity cannot be withdrawn
or restored at will. As an example of true activation, the pan-
creatic enzyme trypsin may be taken. Pancreatic juice drawn
from the duct contains trypsinogen. This precursor gives birth
to active trypsin on coming into contact with enterokinase of the
succus entericus. The mechanism of the change is unknown.
Enterokinase is an enzyme whose sole function is to act on the
zymogen form of trypsin. No other protease can be substituted.
The rate of activation is peculiar and suggests autocatalysis —
i.e. it starts slowly at first and the rate rapidly increases with time.
Vernon suggests that a third enzyme, deuterase, acts as a middle-
man.

A simpler explanation might be found in the adjustment of
equilibrium between two hydrophilic colloids with different
crystalloid contents.

In order to explain the immunity from digestion of the living
cells, anti-enzymes have been postulated. The stomach wall, for

98

ENZYMES

instance, contains protein which is not digested by gastric protease
as long as the blood supply is intact. Occlusion of the blood
supply to any part leads to the formation of a gastric ulcer.
Parasitic worms live in contact with enzymes that would cause
rapid digestion in the event of their death. Neither Cohnheim
nor Bayliss is inclined to accept the anti-enzyme idea as correct.
(1) The latter has shown that the phenomenon can be explained
without any such hypothesis — e.g. by the adsorption of the enzyme
by another colloid. Agitation of a suspension of trypsin with
charcoal results in a loss of digestive activity due to the adsorption
of the enzyme by the charcoal. The charcoal here acts as an
anti-enzyme. (2) Enzymes as colloids are sensitive to any altera-
tion in their environment. A slight alteration in salt content,
colloid or water concentration, or Pn leads to alteration in their
power of adsorbing or being adsorbed by their substrate.

Specificity.

Each enzyme acts on a specific substrate, and if the substrate
is a mixture of optical isomers, one of these (and always the same
one) will be selected for preferential treatment. Examples may
make this clearer. If maltase be added under suitable conditions
to the following disaccharides it will be found to act on one only
— maltose.

TABLE XVI.

Sugar.

Components.

Split by.

Maltose

Glucose a glucoside

Maltase.

Isomaltose

Glucose (3 glucoside

Emulsin.

Centiobiose

Glucose (3 glucoside

Emulsin.

Cellobiose

Glucose /3 glucoside

Emulsin.

Lactose

Glucose {3 galactoside

Lactase (crude emulsin).

Isolactose -

Glucose galactoside

?

Melibiose -

Glucose galactoside

Melibiase (crude emulsin).

Trehalose

Glucose + glucose -

Trehalase.

Cane Sugar

Glucose + fructose -

Invertase.

Turanose -

Glucose + fructose -

? (not invertase).

BALANCED REACTIONS 99

Similarly, lactose and melibiose are both glucose galactosides
differing only in the hydroxyl of the glucose molecule united to
the galactoside. As galactosides, both are slowly hydrolysed by
crude emulsin (known to be a mixture of at least three enzymes).
Lactase is, however, without action on melibiose, and melibiase
does not split milk sugar. Till further experimental work has
been done attempted explanation of these facts is mere guesswork.
Fischer has suggested that the enzyme is to its substrate as a key
is to its own particular lock. The evidence at present available
does not altogether lend itself to this explanation. It looks as
if a careful study of the alterations brought about in the con-
figuration of colloids by slight modifications of the surrounding
conditions might lead towards an acceptable explanation of
specificity. (See also Optical Activity, p. 101.)

Weight is given to this suggestion by examination of the
synthesising power of enzymes. Since enzymes accelerate re-
actions that would take place without them and all reactions are
theoretically reversible, the synthesis of complex bodies from their
constituents might be expected by the aid of the same enzyme as
brought about the splitting of the complex to simple. That is,
a lipase should not only split a fat into fatty acid +glycerol, but
should regenerate fat from fatty acid -fglycerol.

A reversible or balanced reaction is one in which, under definite
conditions, there is a certain equilibrium point at which the
amount of material being broken down is exactly balanced by the
amount being built up. For example, take a stoppered bottle
half full of water. Two processes are going on simultaneously.
(a) Liquid water is undergoing vaporisation and the gaseous
hydrol is passing into the air, (b) Gaseous water particles are
passing from the air into the water to form, say, dihydrol. When
the air is saturated with humidity for that particular temperature,
exactly the same number of water molecules will leave the water
as enter it. Now alter the conditions, (1) open the bottle to a dry
atmosphere, i.e. to unlimited air containing infinitely little
moisture. The reaction will proceed entirely in one direction-
evaporation. (2) If the bottle be opened to an air super-
saturated with moisture, the reverse process, condensation, will
predominate.

The effect of the removal of the maltose in increasing the speed
of digestion of starch is shown very clearly in the following
experiment by Lea, in which the course of the digestion of the
starch was followed by the iodine reaction. In one case, the

100

ENZYMES

digestion was carried on in a beaker, and in the other in a
dialysing tube immersed in running water so that the maltose
dialysed out.

TABLE XVII.

Time (in mins.).

Dialjsed Starch Solution.

Not Dialysed.

0

Pure blue

Pure blue

20

20
20

Trace of violet
Red with violet tinge
Colourless

5J >J

Violet
Red with violet

15
60

5J
»

Very faint red
Colourless

Ecto-enzymes generally have a catalytic function. The by-
products of their activity are removed as rapidly as they are
formed. Many endo-enzymes have for the most part an anabolic
activity. They are brought into contact with simple compounds
and proceed to build them into more complex substances. All
enzymes have both breaking - down and building - up func-
tions. The conditions under which they work determine their
function.

A peculiar phenomenon has been noted in this connection,
namely, that the substance built up by an enzyme may not be
quite the same as the complex substance originally broken down
by it. Maltase, for example, splits maltose into molecules of
glucose, but the substance formed by the action of maltase on
glucose is not maltose but its /? form, isomaltose. On the other
hand, isomaltose is split by emulsin into glucose, while emulsin
causes two glucose molecules to unite to form maltose. This is
explained by supposing that the nature of the enzyme-substrate
complex influences the rate of the reaction. If HC1 is used as
catalyst, the equilibrium point is reached with glucose, maltose,
and isomaltose present in the same proportions, irrespective of
the original proportions present in the substrate. The point of
equilibrium is changed by the enzyme. If maltase is used, the
proportion of maltose is diminished, but if emulsin is the enzyme
employed the point of equilibrium is shifted towards isomaltose.
The whole subject requires re-examination from the point of
view of colloid chemistry, especially with regard to the influence
of PH on activity. The following table gives the optimum PH for
certain enzymes :

OPTICAL ACTIVITY 101

TABLE XVIII.

Ptyalin - 6-7

Invertase - 4-5

Maltase acting on maltose 6-6

„ „ methyl-glucoside - 6-2

Pancreatic lipase 8-0

Pepsin on proteins 1-5-2 -5

,, (plastein formation) - 1-0

Rennin - 5-7

Trypsin on peptone - 7-7

,, gelatin - 9-7

Erepsin - 7-8

Urease (Decomp. of urea) - - 8-7

„ (Synth. )- - 7-0

Much has been made of the fact that enzymes seem to be
rather finical as to what compounds they will attack. Two
compounds may exist side by side similar except in one respect.
They may differ in structure as the right hand differs from the
left. That is, the one compound is structurally a mirror image
of the other. The enzyme selects one for attention and hardly
looks at the other. If the enzyme is engaged in synthesis, it
invariably builds right-handed sugars and left-handed leucine
(an amino acid). If engaged on demolition the enzyme will
hydrolyse all or nearly all of the right-handed sugar before
touching its mirror image, and similarly with leucine. How can
.this be explained ?

Optical Activity.

It is obvious that a paper-cutter or strip of metal can pass
through a book only in the plane of the pages, and may pass
through a second book when both books are similarly placed or
when one has been placed upside down, i.e. rotated on its central
axis AC by 180°. If, after passing through book one, the strip
of metal is given a twist, then book two will have to be turned
through a corresponding angle before the metal will slip through
its pages. The rotation of book two may be taken as an index
of the twisting of the plane of the metal strip. Various factors
may modify this twisting :

(a) The nature of the metal. The same twisting force would
produce very different results in, say, copper and steel.

(b) The length of the strip exposed to the twisting force. The
longer the strip between Bl and B2 the greater will be the
twisting, other conditions being equal.

102 ENZYMES

(c) Temperature. Increase in temperature will increase the
twisting.

(d) Obviously the nature and strength of the distorting force
will modify the angle of rotation of the strip.

A polarimeter is a device in which these basal facts are applied
to light. If a beam of light (at^4) is made to take the place of
the metal strip and for the books we substitute some optical
arrangement which will allow light vibrating in one plane only
to pass, then the eye (at C) would see a lighted field when Bl
and B2 were in the same plane and only then. As we shall see
presently, the plane in which polarised light vibrates may be
twisted by the action of various crystals and of several substances

FIG. 13. — Model of polarimeter. A -source of light, -Bi = polariser, D = point at
which twisting force is applied, 7?2 analyser, the amount of twisting at I) can be
estimated from the angle through which Ji.2 has to be rotated to allow of the passage
of the metal strip AC, C = eyepiece.

in solution and when fused. The amount of the rotation depends
on the factors enumerated above, viz. :

(a) The nature of the light. The angle of rotation depends
on the wave length of the light ; the shorter the wave length the
greater the rotation.

(b) The length of beam exposed to the optically active material.

(c) Temperature as above.

(d) I. Nature of the optically active material : each such has
a specific rotatory power.

II. Strength of solution ; double the concentration produces
double the rotation.

The modification of a prism for producing light vibrating in one
plane was devised by Nicol and so bears his name. He made use
of a property of Iceland spar (calcium carbonate), namely, its
double refraction. Iceland spar crystallises in many forms, but
they are all split most readily along certain planes which are all
inclined to each other at fixed angles, and by cleavage the crystals
can always be reduced to the rhombohedral form. If such a
crystal of Iceland spar be placed on a piece of paper in the centre
of which a black dot has been made, on looking down through the
crystal, two black dots will be seen. If now the crystal be rotated
without lifting it from the paper, one dark spot will remain station-

POLARIMETRY 103

ary while the other will rotate round it as a centre. This pheno-
menon of double refraction may be demonstrated in another way.
If a strong beam of light be allowed to fall on one of the faces
of a crystal of Iceland spar and the transmitted light be received
on a screen, two spots of light will be seen, and if the crystal be
rotated as before one spot will circle round the other. That is,
the beam of light has been split into two rays of equal intensity.
One ray, the stationary one, has travelled through the crystal
just as it would pass through glass — obeying the ordinary laws of

FIG. 14.-Diagram of the paths of the ordinary and extraordinary rays of light through
a rhombohedron of Iceland spar. The light, falling on the face AC divides into
two rays, both of which are polarised. The extraordinary ray (E) is the lesser refracted
ray : the ordinary ray (O) is the more refracted ray.

refraction (Snell's Law). It is called the ordinary ray. The other
ray is called the extraordinary ray, and it docs not obey the
ordinary law of refraction. It is this ray which gives the movable
image when the crystal is rotated. (Snell's Law states that the
ratio of the sine of the angle of incidence to the sine of the angle

of refraction is constant, •- — - =«.

sin p

Both rays are plane polarised, but in planes at right angles to
one another. Nicol's problem was to get rid of one of these rays

c

FIG. 15. — Diagram of refraction in a Nicol's prism.

so as to get light vibrating in one plane. The method he adopted
is very ingenious. The angular separation between the ordinary
and. extraordinary rays is not very great, so that it is not possible
to screen off one of the rays unless a very thick crystal be employed.
A rhomb of Iceland spar was cut in two by a plane BC (Fig. 15)
perpendicular to the principal plane for the face AB. The cut
surfaces were carefully polished and then cemented in their
original position by a thin film of Canada balsam. The index
of refraction of balsam (1 -55) is intermediate between the minimum

104 ENZYMES

values for the ordinary ray (1-66) and the extraordinary ray
(1-48). Therefore the ordinary ray falling on the surface AC at
an angle greater than the critical angle will be totally reflected,
while the extraordinary ray will pass through the prism. This
ray, as we have stated above, is plane polarised. To the unaided
eye it differs in no way from ordinary light, -but, when viewed
through a second Nicol's prism, its condition is recognised by the
fact that on rotating the prism the beam of light from the first
prism alters in colour, passing through the various colours
of the spectrum and returning again to white when the
rotation has been carried through 180°. If monochromatic
light has been used the field will be illuminated when the
principal planes of the two prisms are parallel. On rotating the
second prism through an angle of 90° the ray is extinguished and

0

FIG. 16. — Diagram of Laurent Polarimeter. Monochromatic light from the source L
passes through the lens A which renders the rays of light parallel, and then through
the polariser B. O is the observation tube containing the fluid under examination,
while D is the analysing Nicol prism. The field of view is observed through the
telescope EF. At C, the circular opening of the tube carrying the polarising prism is half
covered by a thin quartz plate (shown at C'), the thickness of which is such that the
light in passing through the plate is altered in phase by half a wave-length.

the prisms are said to be crossed. If the rotation be carried on
to 180° the planes are again parallel and again the field is bright,
and so on. In two positions the planes are parallel and in two
at right angles. The first prism is called the polariser, the second,
by which alone we can recognise the polarisation of the light from
1, is called the analyser (Fig. 16). If now a plate of quartz cut
with the faces perpendicular to the optic axis be placed between
crossed Nicols, it will be found that some light passes through the
analyser. That is, the quartz has rotated the plane of the light
polarised by the first prism. By rotating the analyser a position
can be found when all light is stopped. The amount of rotation
of the analysing Nicol is a measure of the rotation of the plane
of polarised light by quartz. A body which has this property of
rotating the plane of polarised light is said to be optically active.

Some samples of quartz rotate the plane of polarisation in a
clockwise or right-handed (or +) direction, other samples have a
reverse (or — ) direction of rotation. (The direction is taken as
from the direction in which the light is travelling, not from the
analysing eye.) A dextrorotatory piece of quartz superimposed

ASYMMETRIC CRYSTALS

105

on a similar laevorotatory piece would be optically inactive.
Physical examination of quartz crystals shows that d-crystals
differ from Z-crystals in one respect only, viz. : the position of
their secondary facets. The ordinary form of a quartz crystal
is a six-sided prism topped by a six-sided pyramid. The alternate
solid angles where two prism faces meet two pyramid faces is
generally levelled off to form a small secondary face or facet.
When the crystal is viewed with the pyramid upmost and these
facets slope to the right, the specimen will rotate the plane of
polarisation to the right, and vice versa when the facets incline
to the left. The one crystal is a mirror image of the other, and
is called its optical isomer.

If the crystal is symmetrical with no secondary facets then
optical activity is impossible. Any perfect cube is an exact

ABC

FIG. 17. — Crystals of Ammonium Hydrogen Malate. (a) Symmetrical crystal, optically
inactive ; (b) Asymmetrical crystal, dextrorotatory ; (c) Asymmetrical crystal,
laevorotatory. (After van 't Hotf.)

duplicate of any other perfect cube. Such holohedral crystals
can be prepared. In Fig. 17, A represents a holohedral crystal
of inactive ammonium hydrogen malate ; B represents a dextro-
rotatory crystal, while C represents its mirror image, a laevo-
rotatory crystal of this salt.

Of amorphous bodies which are optically active, with the
exception of one or two little known compounds of nitrogen, all
are compounds of carbon in which one or more of the carbon
atoms has its valencies satisfied by four different atoms or radicles.
Such a carbon atom is termed asymmetric (Fig. 18).

Compounds containing asymmetric carbon atoms are a geo-
metrical necessity and exist in proteins, carbohydrates and fats.
Each member of a pair of optical isomers is identically equal in
every respect but one. As stated at the beginning of this section,
enzymes preferentially act on one isomer. For example, those

106

ENZYMES

sugars which are dextrorotatory are more readily hydrolysed
than their laevorotatory isomers. The mould penicillium glaucum
destroys Z-leucine and d-glutamic acid without having any ex-
tensive action on d-leucine or Z-glutamic acid.

Fischer showed that the proteoclastic enzyme, trypsin, acted
asymmetrically on synthetic polypeptides, e.g. inactive d.L-
alanyl-leucine was digested in such a way that only the compound
of d-alanine and Meucine was hydrolysed, whereas the compound
of d-alanine and d-leucine was undigested. That is, the natural

FIG. 18. — Diagram of a carbon atom (A) having its valencies- supplied with four
different atoms B, C, D, E. The mirror image of this structure would be its optical
isomer.

isomers were destroyed by the enzyme before the isomers not
occurring in nature were manifestly attacked.

Much research has been done to elucidate the reason for this
preferential treatment, and some fanciful explanations have
been put forward. The problem is a difficult one and the bias
of the enzyme at present inexplicable. One fact, however, may
be of importance for future development, viz. : if inactive reagents
are used to destroy or produce compounds having an asymmetric
C atom, then both isomers will be produced or destroyed equally ;
if, on the other hand, optically active agents are employed, one
isomer has preferential treatment.

CHAPTER X

MEMBRANES (PLASMAHAUT)

THE HOUSE OF THE CELL.

" The retention of an individuality by the cell must be determined by chemical
and physical differences between this layer and the surrounding fluid."

STARLING.

THE unit of life is the cell. It follows that all changes that
affect life take place in the cell. The metabolism of a complex
organism is the sum of the changes of the cells that compose it.
It is therefore logical to study unicellular animals with a view
to the application of the knowledge so gained to the elucidation
of the more intricate problems of multicellular organisms.

We have seen that the cell consists of protoplasm, which may
be regarded as a watery solution, containing all three classes of
solutes (i.e. colloids, dissociated and non-dissociated crystalloids)
and also substances in suspension. Now it is clear, that as amoeba,
for instance, lives in water, some skin or pellicle is necessary to
prevent the protoplasm from suffering infinite dilution. Further,
if osmotic pressure is to be converted into hydraulic pressure,
a membrane is necessary, as we have seen. In plants, growth
is, in part, due to osmotic energy, and therefore plant cells must
be bounded by a cell wall which will allow the passage of water,
but not of, say, sugars. Nageli, Pfcffer, De Vries and others have
demonstrated the existence of such a cell wall. If plant cells are
immersed in a hypertonic salt solution, i.e. in a salt solution having
a greater osmotic pressure than the osmotic pressure of the cell
contents, then exosmosis will take place. Water will pass from
the cell, causing the cell substance to shrink. But the cell wall
does not shrink and a space is left between the contents and the
container, so rendering the latter apparent. This process is
termed plasmolysis.

The cell wall differs considerably from the cell contents in
chemical composition as well as in physical state. It is a secretion

107

108 MEMBRANES (PLASMAHAUT)

or excretion from the cell. In plants, it generally consists of
cellulose. Certain animals develop an exoskeleton of the excreted
salt of lime, of silica or of chitin. These excreted membranes
should not be confounded with the true cell membrane or plas-
mahaut, which term connotes the layer of cell protoplasm which,
in animal and plant cells alike, lies between cell and environment.
Only through this layer or membrane can the cell be influenced
by changes in the surrounding medium.

The presence of a covering for animal cells cannot be proved
in quite the same way. Animal cell membranes are more elastic
than those of plants. Microscopic examination shows generally
a difference in refractive index (page 103) round the border of
cells. Free cells like red blood corpuscles may be submitted to
experiments similar to the plasmolytic one detailed above. If
corpuscles are put into a solution of lower osmotic pressure
(hypotonic solution) than their contents, they will swell up because
of the passage inwards of water, i.e. endosmosis, and will probably
burst. This is called haemolysis, and may be brought about in
other ways, which are, however, all obviously methods for de-
stroying a membrane (page 243). Artificial membranes may be
made which act in a similar way to animal cell coverings. These
experiments, together with the fact that it is quite impossible to
conceive of energy changes taking place in naked protoplasm, are
sufficient evidence of the need for cell membranes.

Much research and much speculation has been published on the
nature of these membranes. What conditions have they to
fulfil ? At least four qualities are essential :

(1) The membrane must prevent the outward passage of cell

substance while allowing water to pass freely in and
out.

(2) The membrane must permit of the intake of nutrient

material and of the output of undigested and non-
utilised material.

(3) The waste products of metabolism, gaseous and liquid, must

find a way out, while oxygen must find a way in.

(4) Finally, the membrane must be of such a nature as to allow

of expansion. Mere elasticity will not answer this end.

The membrane must be capable of almost instantaneous

growth.

The animal cell membrane must not be considered as a box
or container in which the cell protoplasm has been placed. It is
not something apart from the cell like an eggshell. It is not even

FORMATION OF MEMBRANES 109

something made by the cell and deposited outside like the crus-
tacean shell. It is just as much part of the cell as the protoplasm
itself. Unless this point is understood, difficulties will be found
in the study of alterations in permeability. The animal cell
membrane must be considered as a part of the cell, having a
similar metabolism to the interior of the cell and dying when the
rest of the cell dies.

The exact chemical composition of animal cell membranes
is not known, but modern research tends to show that it is similar
to that of the cell as a whole. We are meantime more concerned
with their formation and structure. The fourth essential quality
of a cell membrane mentioned above gives a clue as to the mode
of its origin.

Formation.

The only membrane that could answer to this test, i.e. as
capable of instantaneous formation and expansion, is one formed
by a Gibbs-Thomson deposition of solutes on the surfaces (see p. 48).
That such a membrane can be formed is readily demonstrable.

1. Brailsford Robertson's artificial amoeba (Part II. p. 403)
shows mobility and keeps intact for some time.

2. Egg albumin solution forms a pellicle or coat of great tough-
ness, cf. meringues.

3. Traube's membranes, especially in the hands of Leduc (Part
II. p. 399), yield life-like growths.

Strictly speaking, a substance which is adsorbed under certain
circumstances will be set free when the circumstances are reversed.
Many substances, however, undergo alteration in physical state
on adsorption. For example, in the formation of meringues, the
egg white becomes coagulated and so becomes incapable of re-
entering the liquid state. Such an irreversible reaction is termed
pseud o- adsorption.

Adsorption (including pseudo-adsorption) is, as we have seen
in the last chapter, dependent on the ability of the adsorbed
substance to lower surface tension. Now, from its very nature,
surface tension has a negative temperature coefficient. Increase
of temperature lowers surface tension. It follows that increase
of temperature will diminish the amount of material adsorbed,
and, conversely, a decrease in temperature will increase the ad-
sorbability of substances in solution. Can we associate with this
fact the varying thickness of membranes according to their
degree of exposure to cold ?

110 MEMBRANES (PLASMAHAUT)

Structure.

In spite of many attempts to overthrow it, the most satisfactory
explanation of the structure of a cell membrane is the pore theory.
The question as to whether the pores are like those of a sponge
or like those of a honeycomb is not of importance, for the membrane
is of extreme thinness. It has been proved that the rate of passage
of a fluid through an artificial membrane is the same as the rate
of flow through capillary tubes. For our purpose, then, we may
consider that cell membranes are composed of some of the cell
material concentrated at the surface and admitting water, etc.,
through the spaces between the molecules or other complexes
which compose this layer.

Permeability.

Artificial membranes may be prepared of any desired permea-
bility (Part II. p. 405). A membrane which allows water to pass
through and no solute is said to be semipermeable. A perfect
semipermeable membrane has never been prepared, though
Traube's copper ferrocyanide membranes are very nearly so.

If an animal membrane, such as a pig's bladder, be stretched
across the end of a cylindrical tube so as to form a drum-head,
one has a simple dialysing membrane such as was employed by
Graham in his classical researches. When this membrane-
covered end is immersed in water, the liquid cannot rush into the
dialysing vessel all at once, but slowly oozes through. A solution
of sodium chloride passes in almost as rapidly as water alone.
Sugar passes through the membrane slowly, while a starch solution
fails to penetrate at all.

A list of hydrated ions could be drawn up in the order of their
magnitude or, which comes to the same thing, in the order of their
speed of migration. With certain apparent exceptions, which will
be mentioned immediately, the ability to pass through a membrane
is a function of the size (or speed) of a particle in solution. By
a careful selection of membranes a mixed solution may be separated
into its constituent solutes. In general, a membrane acts like
a filter-paper made infinitely fine — so that ultramicroscopic
particles may be retained on the filter. Indeed, the process of
separating substances in solution from one another has been
termed " ultra-filtration."

A living membrane, however, alters in its permeability. It may
at one time allow a solute to pass through and at another prevent
its passage : or at times allow a comparatively large particle to

ALTERATIONS IN PERMEABILITY 111

pass through while retaining smaller particles. It may also
appear to " select " certain constituents of the surrounding fluid
to pass in, seemingly quite^ irrespective of their size compared
with their fellows. Again, the' process of negative osmosis may
take place through an animal membrane. That is, water may
pass from the more concentrated side to the more dilute side.
This flow of water takes place against osmotic pressure. Of
course a cell is in close juxtaposition to several other cells, and
therefore the composition, structure, and permeability of any one
cell membrane may vary from place to place according to the
nature of the interface. One interface may he such as to allow
free passage of solutes to which other interfaces may be semi-
permeable.

Alterations in permeability may be due to (1) alterations in
the membrane or (2) alterations in the material presented to it.

(1) The membrane itself may undergo change in composition
and permeability as the cell contents or the environment change
in (a) composition, or in (6) physical state. The composition of
the surface layer depends on the substances present in solution
in the interior and on the nature of the interface. Any alteration
in the chemical state of either of these phases will produce such
an alteration at the surface as will alter permeability. The
electrical double layer on the surface plays a considerable part in
deciding the composition of the membrane. If a solute of opposite
electrical sign to the membrane come within the electrical sphere
of attraction it will be adsorbed and will either thicken the
membrane or may occlude, wholly or partially, some of the
interstices. In any case, adsorption will alter the permeability
of the adsorbing surface. It may have a further effect. The
adsorbed material may enter into combination, chemical or
physical, with the membrane, producing a second alteration in
permeability. It may even cause a third alteration, by ultimately
passing through the membrane and going into solution on the
other side.

If the adsorbed material be an amphoteric colloid, then the
electrical charge on the membrane may be modified and so
produce apparently abnormal osmosis. Collodion membranes,
for instance, are practically indifferent as regards electrical charge.
Water passes through these membranes into solutions of non-
electrolytes and of electrolytes more concentrated than -— at a
rate in accordance with the van t'Hoff theory of osmotic pressure,
i.e. a linear function of the concentration of the particles (colloidal

112 MEMBRANES (PLASMAHAUT)

aggregates, molecules or hydrated ions) in solution. Treatment
of the membrane with an amphoteric colloid like gelatine or
haemoglobin causes an anomalous osmotic pressure. These
colloids, as we have seen, form salts with either acids or bases.
One may prepare, for instance, gelatine hydrochloride or sodium
gelatinate. In the first instance, cationic gelatine has a + charge,
while in the second case it acts as an anion and so has a — charge.
The result of this is that when the membrane has a positive charge
it will attract water as if the water had a negative charge, and vice
versa. That is, the rate at which water will pass through the
membrane will depend on the intensity of the charge in the
membrane, not on the sign of the charge.

(2) The material presented to the membrane may undergo
changes :

(i) Its particles may be increased in size,

(a) by adsorption of other material,

(b) by combining with similar particles,

(c) by hydration.

An increase in size, if sufficiently great, will prevent passage
where previously passage was free.

(ii) The converse may take place, i.e. the particles may be
dissociated and so be able to pass through interstices previously
too narrow for them.

(iii) The electrical state of the material on either side of this
membrane may undergo alterations. This is a general statement
in which is included the effect of hydrogen ion concentration on
permeability. The diffusion of water through an indifferent
membrane depends on two forces, (a) pure osmosis, (b) electrical
osmosis caused by the presence of electrolytes. The intensity
of the electrical forces depends on the nature of the electrolytes.
Neutral salts of mono- or di-valent cations influence the rate of
diffusion as if they conferred a positive charge upon the water
molecules. In other words, the molecules of the pure solvent are
attracted by the charge on the anions and repelled by the charge
on the cations of the electrolyte, the attractive and repulsive
forces obviously increasing with the valency of the ion and
diminishing inversely with the radius of the ion. Alkalies act in
the same way. If, however, one considers neutral and acid salts
of tri- or tetra-valent cations then one finds the reverse to be the
case. The water molecules act as if they were negatively charged
and so are attracted by the cations and repelled by the anions
of the electrolyte. Acids act in this way and have a high electro-

NEGATIVE OSMOSIS 113

static effect on account of the small ionic radius of the hydrogen
ion. It is important to note that certain salts of biological
interest have a marked electrostatic value — very dilute solutions
of oxalates, phosphates, and citrates and of the tetra-valent ion
Fe(CN)2 attract water violently. On the other hand, the effect
of the anion may be masked by the opposite electrostatic effect
of the cation. As the valency of the cation increases, the attrac-
tive force of the anion decreases. Calcium chloride, for instance,
has little more action than distilled water, because the calcium
almost neutralises two positive charges on the two anionic charges
(cf. Hydrophilic property of Ca, Chap. VIII.).

The value of this electrical force has been determined by Loeb
in a very neat manner. Inside a collodion bag he placed an M/128
solution of KC1 and outside the bag an M/64> solution of sugar.
These solutions are approximately isotonic, i.e. movement of
water through the membrane by osmotic forces is thus eliminated.
He found that water did diffuse from the sugar solution to the
KC1 solution. This transport of water must be due to the
electrical pull of the KC1. He then raised the concentration of
the sugar outside the bag till its osmotic pressure just balanced
the attractive forces of the KC1. The sugar solution was now M/8.
Therefore the electrical forces which are at work correspond to
an osmotic pressure which is the difference between the osmotic

7M 7 x 22 '4

pressures of an M/8 and an M/64 solution of sugar = =

> 64 64

—2-4 atmos. (approx.).

These electrical forces also account for negative osmosis — the
passage of water from a more to a less concentrated solution.
As far back as 1835, Dutrochet observed that water diffused out
of a pig's bladder filled with a dilute solution of oxalic acid, into
pure water. Early investigators tried to explain this on the
assumption that there was a greater imbibition of water on the
acid side of the membrane and a lesser on the side in contact with
the pure water. In 1914 negative osmosis was observed taking
place through a porcelain filter and, therefore, the imbibition
theory becomes untenable. Loeb has shown that negative
osmosis occurs when neutral salts as well as acids and alkalies
in certain well-defined concentrations are separated from water
by a membrane capable of taking up either a positive or a negative
charge. At these concentrations the repelling action of the ion
with the same sign of charge as that of water becomes greater
than the attractive action of the ion with the opposite charge.

114

MEMBRANES (PLASMAHAUT)

The appended curve (from Loeb) shows the effect of concentration
on the attractive force of Na2HPO4 on water. Various concen-
trations of this salt from Af/8192 to M/S were put into collodion
bags fitted with a manometer. The ordinates are the values for
the rise in the level of the solution in the glass tube (after the first
twenty minutes) which occurred when the collodion bags filled
with different concentrations of disodium phosphate were dipped

s: 160

120

REGION OF PREVAILING ELECTRICAL EFFECT
OF ELECTROLYTES

PREVALENCE OF ATTRACTIVE ACTION OF ANION INCREASING
UPON THE POSITIVELY CHARGED PARTICLES OF WATER PREVALENCE

Or REPELLING
ACTION OF
CATION UPON
THE POSITIVE-
-LY CHARGED

PARTICLES
OF WATER.

REGION OF PREVAILING GAS
PRESSURE, EFFECT OF

ELECTROLYTES
(TRUE OSMOTIC PRESSURE)

M M M
8I3Z 4096 2048

M M M M M M M

IOZ4- 512 Z56 128 64- 32 16

CONCENTRATIONS
FIG. 19.

into beakers of distilled water. The abscissae are the logarithms
of the concentrations of the phosphate solutions. This curve
shows clearly that at a very low concentration of the salt the rate
of diffusion of water from pure solvent into the solution through
the collodion membrane increases rapidly with increasing con-
centration, and that it reaches a maximum at a comparatively
low concentration of the salt, viz. : M/128. This increase in rate
has been shown to be due to the predominance of the attractive
action of the anion upon the positively charged hydrols. With
an increase in concentration beyond M/128 the rate of diffusion

ELECTRICAL OSMOSIS

115

ELECTRICAL

OSMOSIS

CATHODE

falls abruptly to reach a minimum at a concentration of M/IQ.
This fall is caused by the increasing prevalence of the repelling
action of the cation on the positively charged particles of water.
Further increase in concentration causes an increase of rate of
diffusion. This final passage of water into the solution is due to
true osmotic pressure. At the concentrations where the rate of
diffusion is decreased, i.e. where the curve falls (M/256 —M/IQ in
the case of Na2HPO4) water passes from the solution through the
collodion membrane to the pure solvent. That is, negative osmosis
takes place.

Negative osmosis is a particular
instance of electrical osmosis.

In Part II. p. 399 will be found ANODE
details of an experiment which shows
that water can be drawn through
certain colloidal membranes by
direct electrical means. If the pH
of the water is greater than 7 (i.e.
acidulated water) the attraction is
towards the anode, but if the pH is
less than 7, the water rises in the
tube containing the cathode. To
obtain this result, the membrane
used must be of material capable
of combining either with anions
or with cations — e.g. proteins.
Collodion does not form such

j j /• FIG. 20. — Diagrammatic section through

Compounds and SO Cannot torm a a gelatine- collodion membrane showing a

membrane suitable for experiments SS£4T P°re * demonstrate
on electrical osmosis until it has

adsorbed an amphoteric colloid. In Fig. 20 is represented
a gelatine-collodion membrane in acidulated water — i.e. in
water with a slight excess of hydrogen ions. The mem-
brane adsorbs some of these excess ions, interacts chemically
with them to form gelatine hydrochloride and so acquires a
positive electrical charge. The passage of a current through
the membrane and water depends on the carriage of the
charge by ions — in this case H> and OH~. The negative ions
are attracted to the positively charged membrane till the charge
on it is equalised. The positive ions attracted by the negative
potential pressure at the cathode, pass through the membrane,
and raise the hydrostatic pressure on the cathodal side. It is

116 MEMBRANES (PLASMAHAUT)

obvious that the hydrogen ion concentration must increase at the
cathode and decrease at the anode. (Pole finding paper is blotting
paper soaked in phenolphthalein — an indicator which while
colourless in neutral solutions becomes red in distinctly alkaline
solutions).

Water passes through the membrane in the reverse way when
the solution on both sides of the membrane is alkaline. A dilute
acid solution separated from a dilute alkaline solution of the same
relative strength by an amphoteric membrane will produce a
passage of water from the anodal to the cathodal side due to the
greater speed of the positive ion.

Polarisation. When a current is passed between two electrodes
immersed in an aqueous solution, the potential difference between
the electrodes tends to decrease and will in time fall off altogether
on account of the deposition of ions of the opposite sign on the
surface of the electrode. This polarisation of the electrode may
be prevented by physical or chemical means (cf. various types of
concentration cells). A similar ionic layer forms on membranes
when a current is passed through them for some time (see also
Chap. XII., Polarisation Current).

Selective permeability of membranes has often been noticed in
electrical transference experiments. The classical experiments
of Hittorff are now known to be, in some cases, vitiated by his
use of ox-gut membranes to prevent connection currents. For
instance, such membranes are much more permeable to SO4 ions
than to Cu ions. A large error is thus introduced into electrical
diffusion experiments with CuSO4 due to the adsorption of the
copper ions on the substance of the membrane.

Till more is known of the physical state of the cell and its
environment, definite statements cannot be made concerning the
causes of alterations in permeability of membranes. Phrases
like " selective " adsorption should meanwhile be avoided, as they
postulate intelligence in the cell to " select." Although the
unknown must be explained in terms of the known, the day is
surely past when it is necessary to assume a Maxwellian " demon "
or a cellular intelligence. It is certainly not unscientific to admit
the possibility that the unknown is similar to the known or may
be explainedjlby analogy to known physical processes.

CHAPTER XI
RADIO-ACTIVITY

THE ATOM IN DISSOLUTION

" From harmony, from heavenly harmony

This universal frame began ;
When nature underneath a heap

Of jarring atoms lay." DRYDEN.

THE various manifestations of energy already dealt with have
all been associated with matter in the form of small aggregates
(colloids), atoms, or ions (charged hydrated atoms). Chemists
once defined the atom as the smallest non-divisible portion of
matter. Needless to say, many scientists were content to be
decry ed as old fashioned and refused to accept this ; opinion of
the atom. My old teacher, Prof. John Ferguson, would allow no
one to refe,r to atoms. He ^referred the mote cumbrous but
exact term?'" Combining Proportions." Modern work has con-
firmed these opinions of the atom. Physicists are how interested
in the structure of the atom. No longer is it considered as non-
divisible. No longer does it remain as fundamental. Of what
then does the atom consist ? Many and varied are the present-
day theories of its structure, but in general most schemes are
similar. It is supposed to consist of a number of smaller units,
negative electrons, all moving rapidly and irregularly round a
central positive charge. A negative electron is nothing more
than a unit charge of electricity. The number of electrons in
each ring is definite and may undergo alteration in definite
quanta only.

(1) Not more than a certain number of electrons can continue
in stable motion in one ring. If more are added the system breaks
up into two or more rings.

(2) If the orbital velocity of the rings exceeds or falls below a
certain critical value, the electrons are rearranged to ensure
stability for that speed.

117

118 RADIO-ACTIVITY

A model may make this clearer. The outer particles may be
represented by a number of exactly similar sewing-needles,
magnetised simultaneously in a solenoid. They are floated
vertically in a small trough (Fig. 21), by having, say, their N
poles inserted each to the same depth in exactly similarly pieces
of cork. The place of the positive core is taken by a bar magnet
set vertically, N pole upwards, below the trough. It will be
noticed that the needles arrange themselves in two rings. If ten

FIG. 21. — A " Model " Atom. (From Crowther's Molecular Physics.)

needles are floated, seven will be in the outer ring and three in
the inner.

It has been found that the greatest number of magnets which
we can have in an empty ring is five. If a sixth is added, two rings
are formed with five needles on the outside and one in the middle.
The number which must be placed in the middle rapidly increases
with the number in the outer ring. The removal of one needle
from the outer ring may cause a complete rearrangement of the
needles, i.e. a new series of concentric circles may be formed
differing from the first series in the number of the component
needles in each ring.

As we have mentioned, the electrons forming an atom are
supposed to be in constant rapid and irregular motion. If for

ROENTGEN RAYS

119

some reason the motion of an electron becomes centrifugal, then,
if sufficient speed be developed, it will tend to fly off. The
atom will be ruptured and a new atom will be formed.

TABLE XIX.

Total number
of needles.

Number in each ring.

Outer.

Concentric inner rings.

(1)

(2)

(3)

(4)

5

5

. .

6

5

1

—

'

10

7

3

—

15

10

5

—

30

15

10

5

45

17

14

10

4

51

18

15

11

6

1

In 1878, Crookes found that the passage of an intermittent
high-tension current of electricity through a tube from which air
had been so thoroughly withdrawn that only about 10 ~7 of atmo-
spheric pressure was present, produced the so-called Kathode Rays.
These rays originate at the kathode at right angles to its surface
and proceed in straight lines like light independent of the position
of the anode. Whatever comes in the path of the rays is caused
to fluoresce, e.g. the walls of the tube. They heat the object
struck. By using a concave kathode, they may be focussed on
a piece of platinum which soon becomes red hot, and may even
be fused. Mechanical pressure is exerted by the rays. If directed
on to light vanes attached to an axle they may be made to turn
little mills, or in the " railway tube " they drive a wheel along
glass rails. The stream of rays is deflected by a magnet as if it
were a stream of negatively charged particles. In 1893, Lenard,
following up Hertz's discovery that metal was transparent to the
kathode rays, made a small window of aluminium foil in the end
of the vacuum tube and so brought the kathode rays through the
foil into the open air.

In 1895, Roentgen, repeating Lenard's work, accidentally dis-
covered the X-rays. He had covered the vacuum tube with a
black paper case to shield the eyes from the kathode fluorescence,
so that the effect of the rays outside the tube might be more easily
observed. He thus noticed that a barium-platinocyanide screen
which happened to be near became fluorescent whenever the tube
was working though no visible rays could reach it. On placing

120 RADIO-ACTIVITY

his hand between the screen and the tube, he saw, for the first
time, the now familiar sciagraph of the bones of the hand. The
X- or Roentgen rays originate from the place where a kathode
ray strikes, from the walls of the tube, in the first instance, or in a
focus tube from the piece of platinum (anti-kathode) upon which
the kathode rays are focussed. They issue equally in all directions
and travel in straight lines. For any tube, the power of pene-
tration of the X-rays is inversely proportional to the density of.
the substance penetrated. The higher the degree of exhaustion
of the tube the greater the penetrating power of the rays produced.
In a " hard " tube the vacuum is so good that a very great differ-
ence in potential between the electrodes is necessary to force the
discharge through. The kathode rays therefore attain a high
velocity and the X-rays they produce on impact with the anti-
kathode have a high penetrating power. On the other hand, if
the tube is not well " exhausted," the X-rays evolved are easily
absorbed. Such a tube is termed " soft." Unlike the kathode
rays they are not affected by the most powerful magnetic field.
Like the kathode rays they excite fluorescence, act on sensitised
photographic plates and ionise gases, i.e. they 'make air, or other
gas through which they pass and which under ordinary circum-
stances are practically insulators, capable of conducting limited
quantities of either positive or negative electricity.

Poincare suggested that the production of X-rays might be an
effect common to all fluorescence. In 1896, Becquerel, acting
on this idea, examined some fluorescent salts of uranium. He
found that the double sulphate of uranium and potassium exposed
to sunlight could affect a sensitised plate even when the plate was
protected by a layer of copper or aluminium foil. This metallic
layer excluded the possibility of action by ultra-violet light or by
chemical vapours emitted by the salt. Further investigation
showed that the phenomenon was exhibited by uranous salts
which are not fluorescent as well as by the fluorescing uramc
salts. Both are active in proportion to the amount of uranium
they contain. That is, the continuous emission of these rays is
a specific property of uranium now generally termed Radio-
activity.

The characteristics of the radiation from uranium are very
similar to those of the X-rays. They are found to consist of three
very distinct types of rays, differentiated in the first instance by
their power of penetrating matter. They have been termed by
Rutherford a, {3 and y rays. The a rays are particles of the gas

a, /3 AND 7 RAYS

helium expelled radially from the uranium with the colossal
speed of 20,000 miles a second. They have so feeble a penetrating
power that they are completely stopped by a single sheet of note-
paper or by a few centimetres of air. The a rays carry a positive
charge, but are only slightly deviable by an intense magnetic field.
The /? rays resemble the X-rays in penetrating power, and pass
with ease through thin metal, glass, etc., but are nearly all stopped
by a single coin. Becquerel proved that the /? rays are identical
with the kathode rays, i.e. negative charges of electricity. Their
superior penetrating power is due to their enormously greater
velocity. The y rays are not deflected by magnetic fields. They
resemble in all respects the X-rays, but are far more penetrating
than rays even from the hardest vacuum F _

tube. They will readily pass through a
pile of twelve coins. Their nature is
probably the same as that of X-rays, i.e.
thin pulses in the ether.

The power of ionising a gas which is a
common characteristic of the radiations
from radio - active matter is used as a
means for measuring the intensity of
radiation. The simplest apparatus for
this purpose is a gold-leaf electroscope.
Fig. 22 represents the type of electroscope
used by Soddy. It consists of a tin can
with a movable bottom E for the inser-
tion of the substance to be tested. A
paraffined rubber cork H, is pierced in
the centre by the metal wire G which
carries at its end a rod of fused quartz, A.
A thin brass strip, B, to which a single gold leaf, C, is attached is
fastened to the lower end of the quartz rod. F is a vulcanite
handle by means of which the charging rod D can be brought into
contact with B. The rate of collapse of the gold leaf may be
observed by means of a reading microscope through a window in
the can (dotted line).

In 1903, the Curies, who were examining the minerals containing
uranium, discovered a new element, radium, in pitchblende.
This very radio-active material was obtained pure in 1911. From
a ton of pitchblende may be extracted about 200 mgrms. of
radium chloride, which was responsible for over 80 per cent, of
the radio-activity of the raw material.

FIG. 22.— section through gold-

122 RADIO-ACTIVITY

Subsequent investigations by the above workers, and principally
by Rutherford, Soddy, and their collaborators, have shown that
there are three series of radio-active elements. The appended
chart from Soddy shows the relationship between the members
of the series and between two of the series themselves. This chart
demonstrates to us the remarkable fact that the atom of the
heavy elements at the head of each series are continuously and
regularly undergoing disintegration. Matter and energy are being
lost at a rate which, so far, cannot be modified in any way.

Lately Campbell and Wood have discovered that certain of the
elements of low atomic weight are also radio-active. One of
these, potassium, is found universally and in abundant quantities
in animal and vegetable cells. Potassium is a necessary per-
manent constituent of every living cell. Of the 12-15 elements
essential to life, it is the only one possessing distinct if minute
radio-activity. The activity of potassium may readily be demon-
strated by means of the gold-leaf electroscope. It is shown that
P rays are emitted. Potassium is 1000 times weaker than uranium
and 1,000,000,000 times weaker than radium in the emission of
/3 rays.

As is well known, potassium is an absolutely necessary con-
stituent of the fluid used for the perfusion of an organ. If a
potassium-free Ringer's fluid is passed through a frog's heart, the
heart will come to a standstill in about half an hour. The frog's
peripheral vessels may be perfused with Ringer's fluid for hours
without any sign of oedema. As soon as a potassium-free fluid
is used, marked oedema begins, causing the frog to swell and
increase in weight. Further, the frog's kidneys when perfused
with Tyrode's fluid or similar fluid containing glucose allows no
glucose to pass out into the urine. If the potassium is omitted
in making up the fluid, glucose at once escapes into the urine.
Ringer demonstrated, long before its radio-active nature was
discovered, that rubidium may be substituted for potassium in
equimolecular amounts. He explained this by its similar chemical
nature. Similarly, caesium, another of the lighter radio-active
elements, may take the place of potassium in the perfusion fluid.
No non-radio-active element has been found which is capable of
acting as a substitute for potassium. Further, Zwaardemaker
was able to perform normal perfusions provided a substance
emitting /5 rays was within effective distance of the frog.

The last named worker and his collaborators then set out to
determine the amounts of the heavy radio-active elements necessary

RADIO-ACTIVE ELEMENTS

123

TABLE XX.
TABLE OF RADIO-ACTIVE DISINTEGRATION.*

I. MAIN SERIES.
A. URANIUM, RADIUM AND ACTINIUM SERIES.

Element.

Atomic
Weight.

Radiation.

Period of Average Life.

Chemical Character
(Isotopic with).

Uranium— I.

238

a

8,000,000,000 years

Uranium.

Uranium-X1

234

P

35-5 days

Thorium.

Uranium— X*

234

p

1-65 minutes

Eka-tantalum.

Uranium-II.

234

a

3,000,000 years (?)

Uranium.

Ionium

230

a

100,000 years

Thorium.

Radium

226

a

2440 years -

Radium.

Ra. Emanation -

222

a

5-55 days ...

Emanation.

Radium-A -

218

a

4-3 minutes -

Polonium.

Radium-B -

214

P

38-5 minutes

Lead.

Radium— C -

214

B

28-1 minutes

Bismuth.

(99-97%)

Radium-C' -

214

a

1/1, 000,000th sec. (?) -

Polonium.

Radium-D -

210

P

24 years

Lead.

Radium-E -

210

P

7-2 days

Bismuth.

Radium-F

210

a

196 days

Polonium.

(Polonium)

End Product

206

—

Infinitely long

Lead.

End Product

206

—

Infinitely long

Lead.

B. THORIUM SERIES.

Thorium

232

a

25,000,000,000 years -

Thorium.

Mesothorium-I. -

228

p

9-67 years ...

Radium.

Mesothorium-II. -

228

p

8-9 hours

Actinium.

Radiothorium

228

a

2-75 years

Thorium.

Thorium-X

224

a

5-25 days ...

Radium.

Th. Emanation -

220

a

78 seconds -

Emanation.

Thorium-A -

216

a

0-2 second -

Polonium.

Thorium-B -

212

p

15-4 hours - -

I^ead.

Thorium-C -

212

P(65%)

87 minutes -

Bismuth.

Thorium-C'

212

1 /100,000,000,000th

Polonium.

sec. (?)

End Product

208

—

Infinitely long

Lead.

II. BRANCH SERIES. (A.)

(At either Uranium-I. or Uranium-II. the series branches, and 8 per cent, of the total

number of atoms disintegrating, follow the branch Actinium Series.)

Uranium-Y

—

P

2-2 days.

Thorium.

Eka-tantalum

—

a

1000 to 10,000 years (?).

Eka-tantalum.

Actinium

—

P(t)

(?) . . ' .

Actinium.

Radioactinium

—

a

28-1 days

Thorium.

Actinium-X

—

a

16-4 days -

Radium.

Ac. Emanation -

—

a

5-6 seconds -

Emanation.

Actinium-A

—

a

0-003 second

Polonium.

Actinium-B

—

B

52-1 minutes

Lead.

Actinium-C

—

a

3-1 minutes -

Bismuth.

Actinium-D

—

P

6-83 minutes

Thalium.

End Product

Either 208

Infinitely long

Lead.

or 210

(At Radium-C, 0-03 per cent, of the atoms follow the branch series.)

Radium-C -

214

a

28-1 minutes

Bismuth.

Radium-C2

210

P

1-9 minute ...

Thallium.

End Product

210

Infinitely long

Lead.

(B.)

(At Thorium-C/35 per cent, of the atoms follow the branch series.)

Thorium-C -

212

a

87 minutes -

Lead.

Thorium-D -

208

P

4-5 minutes ...

Thallium.

End Product

208

_

Infinitely long

Lead.

* (From Soddy.)

124 RADIO-ACTIVITY

to replace potassium. These radio-elements; as we have seen,
emit a rays in marked excess of the /? rays necessary for physio-
logical purposes. They found that, as was to be expected, the
a radiation completely masked the ft radiation. If means were
taken to exclude the ft rays these a+/? radiating salts acted as
excellent substitutes for potassium. Radio-active substances
may thus be classified for biological purposes into two groups.

TABLE XXL

I.

(3 Radiating (negative).

Potassium.
Rubidium.
Caesium.

II.

a Radiating (positive).

Uranium.

Thorium.

Radium.

Ionium.

Lanthanum.

Cerium.

Niton (Emanation).

A heart beating with a fluid containing the appropriate quantity
of any of Group I. may be switched on to any other group I.
element in aequi-radio- active amounts. Similarly, the group II.
elements are interchangeable. But direct transference from a I.
fluid to a II. I or vice versa at once produces complete stoppage.
The two groups are antagonistic. If, however, the heart is washed
completely free from one group with radio-active-free fluid it may
without harm be perfused with a fluid containing one of the
elements of the antagonistic group.

Fluorescein and eosin adsorb the a and ft rays unequally. If
one of these dyes be added to the perfusion fluid the amount of
radio-active material present may be reduced appreciably and
still produce normal action. In summer, smaller quantities of
radioactive salts are needed than in winter. This is related to
the lowered calcium content in the frog's blood in winter.

To summarise, potassium is a necessary constituent of all
living matter because of its property of emitting negative electrons
(/? rays). It may be replaced by other radio-active substances
in aequi-radio-active proportions provided these substances are
not otherwise toxic. How potassium acts in the living cell can
as yet be only a matter of surmise. Presumably the freed electron
passing with great velocity through crowds of ions, molecules and
colloidal aggregates will have some effect on them. It is known
to have at least two effects :

THE HYDROGEN ION 125

(1) Because of its velocity, the /? ray accelerates the rate of
migration of gaseous ions in a similar way to ultra-violet light
of extremely short wave-length (below 2000 Angstrom units), i.e.
the ionised gas becomes an electrical conductor.

(2) On account of its unit negative charge, it has a disturbing
effect on all systems in electrical equilibrium through which it
passes.

Rutherford has recently shown that a particles (positively
charged atoms of helium, atomic weight =4) may cause trivalent
nitrogen (14) to disintegrate with the formation of monovalent
hydrogen (1). He considers that the hydrogen ion is nothing
more or less than a unit positive charge. Other atoms are spheres,
composed as we have seen of a positive core (probably an atom
of hydrogen) surrounded by negative electrons. The negative
electric charge is evenly distributed over the surface.

The modern tendency is thus to postulate the sameness of all
elementary matter. What we have been accustomed to look
upon as elements may merely be stages in the disintegration of
more complex substances into their positive and negative units.
When the disintegration takes place explosively and continuously
the substance is considered as radioactive.

In the preceding portion of this chapter, ultra-violet rays,
kathode rays, X-rays and the a, /?, and y rays of radioactive matter
have been mentioned as types of radiation. These various
radiations differ from one another in their effects on living matter
in degree rather than in kind. In general, the lower the velocity
of the ray, the greater its physiological action, provided always
that its velocity is sufficiently great to produce any physiological
effect. (A high velocity bullet cuts a clean hole in a piece of
glass, while a spent bullet shatters the glass). The effect seems to
depend more on the velocity of the ray than on its nature, e.g.
a rays are material while the others are not, yet similar actions
may be produced under proper conditions (Zwaardemaker's
expts., I.e.). (A soft candle may be fired through a wooden
target, cutting a hole just as if it were a hard-nosed bullet). The
physiological effect of any ray is proportional to its power to ionise
air. /? rays have 60 times the ionising power of y rays, and
experiment has shown that y rays require to operate for 60 mins.
on living matter to have the same effect as one minute's exposure
to /? rays. That is, by varying the length of exposure, similar
results may be obtained from radiations having different ionising
powers. If rays are classed according to their power to ionise

126 RADIO-ACTIVITY

air, then those having the greatest ionising effect will have a toxic
rather than a beneficial effect on living organisms, while, con-
versely, the weaker rays will promote the function of the organism.
The power of ionisation being equal, then generally a long exposure
produces toxic effects and a brief exposure beneficial.

This latter effect has induced experimentalists to study the
effect of radium on plant growth. They have found that up to
a certain optimum point the rays of radium act as a positive
stimulus. In early stages, root growth is stimulated, from which
there is, as result, an increased growth of shoot. Inflorescence
is generally fuller and is better coloured. Ultra-violet rays
acting for a brief period on sugar cane not only produce growth
but produce an increase in the percentage of sugar. If, however,
this optimum amount of radiation be overstepped, that is, if the
plant is submitted to a longer exposure or to a greater concen-
tration of rays, depression, culminating in complete arrest of
physiological function, is produced. Further exposure to the rays
causes death of tissue. The beneficial effects of short exposures
are not considered sufficiently great to justify the employment
of radio-active matter in horticulture or agriculture.

Similar results have been obtained by those who studied the
effect of radiation on eggs and cells. For example, exposure of
the fertilised eggs of arbacia to rays of radium, if short, causes
stimulation of the cell function. If the radium is applied during
the approach of the germ nuclei, then cell division is accelerated.
If the exposure is long, cell division is retarded. The effect of
radium is more marked during the metaphase than during either
the prophase or the telophase. Eggs are not so easily influenced
by radium emanations after the dividing stage is passed. In order
to produce any effect on the rate of growth of ascaris eggs about
ten times the intensity of radium has to be applied as was effective
during the dividing stage, or the length of exposure has to be
increased tenfold. The ft and 7 rays seem to act on different
parts of the egg. The nucleus, especially if it is undergoing
mitosis, is influenced by the 7 rays, while the /5 radiation has most
effect on cytoplasm. The fertilisation membrane of nereis is
thickened as a result of exposure to radium. The length of
exposure being, in this case at least, more efficacious than the
intensity.

The physician is interested in radiant energy of this type because
of its lethal influence on pathological growths and on bacteria.
Ultra-violet rays, or lights like the Simpson Light, which emit a

MEDICAL APPLICATION 127

large proportion of ultra-violet rays, have been employed as
germicides in surface wounds. The penetrating power of these
rays is slight, and, therefore, they can have little effect on deep-
lying structures. Nevertheless their action on certain bacilli have
been somewhat extensively studied. Typhoid bacilli are killed
by exposure to rays of wave-length 2100 —2800 Angstrom units.
Bacilli vary in vulnerability, e.g. on exposure to light from a
Cooper-Hewit (mercury vapour) lamp placed 12 cm. above them,
b mucosus capsulatus was killed in 20 sees., staphylococcus aureus
in 90 sees., while 150 sees, elapsed before the death of b subtilis.
Lupus (tubercular ulceration), carcinoma and other morbid
growths are occasionally treated with ultra-violet light. It is
worth while noting that normal cells equally may suffer through
exposure to rays over 2800 Au. Digestive enzymes are killed.
Protection may be provided by passing the light through 1 per
cent, solutions of gelatine-peptone, amino-benzoic acid, cystine,
tyrosine and leucine. Tyrosine has especially good detoxifying
action in alkaline solution. These solutions absorb rays of wave-
length 2480 —2710 A. and so reduce the toxicity and bactericidal
action of ultra-violet light.

Similarly, X-rays have a strong lethal action. Pioneers in
radiography suffered from this action. There is no doubt as to
the power of the X-rays to kill ft-typhosus suspended in water,
or to inhibit the growth of tumours. But care has to be exercised
in their application. For instance, a number of mice were arti-
ficially immunised against a transplantable carcinoma. Half of
them were then exposed to the X-rays. It was found that the
mice so exposed had lost their immunity and had been rendered
susceptible to carcinoma while the controls were still immune.
Animals which have been X-rayed repeatedly are generally more
susceptible to certain diseases than unexposed animals, e.g.
monkeys more readily develop poliomyelitis after being exposed
to the X-rays.

The rays emitted by radio-active elements, especially radium,
have been employed more extensively in the treatment of morbid
cell growths than either ultra-violet light or X-rays. The cells
are not killed outright but division of the nuclei is inhibited,
eventually leading to death of the cell. The successful treatment
of cancer patients by radium is well known. The rays of radium
are capable of causing definite regressive changes in deep seated
tumours such as mediastinal lympho-sarcoma, carcinoma of the
lungs, and abdominal metastases of carcinoma of the testis.

128 RADIO-ACTIVITY

Several investigators have reported results to show that the
growth-promoting substance in yeast may be partially inactivated
by exposure to radium emanation. It is probable that the
therapeutic effect of radium treatment may be due to this de-
struction of the growth-promoting substance. It has been known
for long that radium rays have a destructive effect on colloidal
solutions, due probably to a disturbance of their electrical state.
Globulin and vitellin are coagulated and lecithin suspensions are
decomposed on exposure to the emanation from radium. That
the action is electrical is borne out by the antagonism between
a radiation and /? radiation. Either of them prevent bacterial
growth in agar cultures, but the simultaneous application of both
kinds of rays is ineffective (cf. antagonism of colloids, etc., p. 81).
Of course, normal as well as pathological tissue may be damaged
by exposure to radium. Especially sensitive are the sexual cells.
Spermatozoids of sea urchins are enfeebled and killed, as are also
the gametes of the grasshopper by exposure to radium sufficiently
weak to have no action on other cellular units of the testicles. The
action is similar to exposure to cold. Radium causes an immediate
decrease in the total number of white cells in the blood (Chap. XV.).
This result is probably due to inhibition of the formation of the
leucocytes rather than to the destruction of already formed cells.
The greatest decrease occurs from |- to 6 hours after application
of the radium. Within 24 hours a normal concentration of white
cells may be observed.

By the operation of Le Chatelier's principle (p. 9), matter
exposed to radio-active elements should develop some protective
mechanism against the action of the rays. Becquerel noticed
that /? rays changed yellow phosphorus into its red form, which is
not acted on by the rays. We have already mentioned that the
fertilisation membrane of nereis is thickened where exposed to
radium. Some observers find that the presence of chlorophyll
is protective. Others deny this.

CHAPTER XII
THE CELL

" Citizens of the state which the entire multicellular organism seems to be."

WE have seen that foodstuffs are broken down into units suffi-
ciently small to pass through the intestinal wall. Logically,
we ought next to study the system by which these absorbed
substances are conveyed to the cell. It is important to realise
that until they are inside the cell they are useless. All energy
changes take place in the living cell. It will, however, be convenient
first to examine a cell, note its imports and exports and study the
various activities by virtue of which it is said to be alive.

In 1893, Schwann put forward the theory that animal tissues
were an aggregation of large numbers of cells. Later work has
justified this assumption. It is now generally held by biologists
(1) that the earliest form of living matter was undifferentiated
protoplasm, and that from this simple form of life there has been
evolved, first the unicellular and then the polycellular organism ;
and (2) that each individual life follows this evolutionary course,
originating as a single cell and gradually gaining in complexity
•with age. In view of these two beliefs, the evolutionary hypo-
thesis (phylogeny) and the developmental history (ontogeny), it
is logical to subject a unicellular organism to close examination
in order that the various manifestations of life may be, at least,
catalogued.

Amoeba is a unicellular animalcule which may be found in the
stagnant water of almost any ditch. It is made of material
differing so slightly from the medium in which it lives that it can
only be seen under the microscope after patient search. When
seen it is found to be non-homogeneous. Apparently it consists
of a greyish mass in which there are occasional granular aggregates,
spaces containing water, spaces containing extraneous matter and
a darker more compact mass, the nucleus. If the amoeba were

B.B. 129 9

130 THE CELL

cut in two the part which did not contain the nucleus would only
live for a short time, while the other part would functionate
normally. The nucleus is, therefore, necessary for life. Ultrami-
croscopic examination shows that the grey mass is a colloidal
(emulsoid) solution in water. Chemical analysis of dead amoeba
confirms the ultramicroscopic examination. Water to the extent
of about 75 per cent, acts as dispersion medium for a colloidal
complex and as a solvent for certain crystalloids. The colloid is
an aggregate containing protein, fat and carbohydrate. The
crystalloids are to some extent adsorbed on the surfaces of the
colloidal mass and to some extent are in free solution. The
elementary chemical composition conveys little information as
to the properties of the complex. To say that protoplasm contains
a certain percentage of carbon, hydrogen, oxygen, nitrogen,
sulphur and phosphorus in a colloidal state, and potassium, calcium,
sodium, chlorine and phosphorus in solution is not of much use
as a contribution to the study of life. It is just as preposterous
to appraise the value of great pictures in terms of the chemical
composition of the paints and pigments employed as to attach
any great significance to the chemical elements of a dead cell.
What is of great importance is the physical state of the matter,
just as the value of a painting lies in the physical juxtaposition
of pigments, an artistic blending of colour, light and shade,
whereby the eye is pleased, so the life of a cell depends on the size,
consistency, etc., of the colloid- crystalloid complex forming its
protoplasm. " When," says Schafer, " the chemist succeeds in
building up this complex it will, without doubt, be found to
exhibit the phenomena which we are in the habit of associating
with the term ' life '." What are the phenomena commonly
associated with the term " life," especially as manifested by a •
unicellular animal ?

(a) Movement is the commonest phenomenon indicative of life.
Amoeba moves. It extrudes footlike processes, pseudopodia
(Gr. pseudio, false ( =similar to), podes, foot), at one part and
retracts them at another and so moves along. Similar amoeboid
movements are characteristic of the white cells or leucocytes
(Gr. leukos, white) of the blood. Recently, Goodrich has carefully
studied these movements of the leucocytes. He produces camera
lucida drawings to show that the pseudopodia usually take up
the form of expanded motile membranous folds when the living
leucocytes are examined suspended freely in the normal fluid
which is their habitat. One of his drawings is reproduced in

IRRITABILITY

131

Fig. 23. Movements of a precisely similar character may be
produced in substances which are certainly not alive, such as
Brailsford Robertson's model amoeba made of camphor, benzene
and water (Pt. II.). These purely physico-chemical reactions
are produced by alterations of the surface tension of the fluids
under observation. Macallum has shown (pp. 140 and 151), that
alterations in surface tension occur in living tissue during motion.
Movement can, therefore, not be considered as a specifically vital
phenomenon. Certain parts of the cell, e.g. the vacuoles, show a
rhythm in their movements. In polycellular organisms, certain
organs, e.g. the heart, pulsate. It is comparatively easy to produce
rhythmical movement in material which is not living. A globule

FIG. 23. — Leucocyte of invertebrate, (lledrawn after Goodrich.)

of mercury more than an inch in diameter may be made to pulsate
with perfect regularity for hours. (See Ostwald's " Physical
Heart," Pt. II.).

(b) Irritability is a general property of living matter. When
amoeba is touched, it withdraws its pseudopodia (barotaxis).
It moves towards and over suitable food and moves away from
quinine or from a hypertonic solution of crystalloids (negative
chemiotaxis). Hydrogen ions if not too concentrated exert
positive chemiotaxis, while hydroxyl ions have a repellent effect.
This may explain galvanotaxis. Strong light repels while a
moderate illumination attracts many lower organisms. Further,
the more refrangible rays of light exert a negative phototaxis,
while the less refrangible rays are positively attractive. If the
swarm spores of certain algae are placed in a tank with a cover,
half of which is blue glass and half is red, and exposed to light, they
will stream away from the blue and towards the red end of the

132 , THE CELL

box. Ultra-violet rays have a marked effect on living organisms.
They kill, e.g. the tubercle bacillus is killed by ultra-violet light
and lupus is cured by projection of the Finsen arc on the growth.
Change of temperature may exert either a positive or a negative
effect, the animalcule avoiding the abnormal. That is, too high
or too low a temperature exerts negative thermotaxis. Non-
living matter shows irritability. We have seen how sensitive
colloids are to slight alterations in their environment. They
exhibit chemiotaxis and galvanotaxis very markedly. Even
inorganic matter may respond to stimulation. Lillie has demon-
strated this in the case of iron. A piano wire which has been
dipped in concentrated nitric acid and then suspended in dilute
nitric acid will show changes if " stimulated " mechanically,
chemically, or electrically. The irritability of living matter is,
according to Verworn, of a specific type and is thus indicative
of life.

(c) Ingestion and excretion are phenomena exhibited by all
living cells. Nutrient material is taken from the environment,
prepared, used, and the non-utilisable rest is forced out. Amoeba
engulfs food and forms a vacuole in which will be found food and
water. Into this vacuole are secreted digestive enzymes which
reduce the ingested material if possible from the colloidal to the
crystalloidal state. It then passes into the protoplasm and
the undigested residue is forcibly excreted by contraction of the
vacuole. These processes all have their physico-chemical counter-
parts. A drop of chloroform will reject a piece of capillary glass
tubing forced into it. If the glass be coated with shellac it will
be drawn into the chloroform, the shellac dissolved from it and
then the clean glass is expelled from the interior of the chloroform
to the surface.

(d) Growth is not a property characteristic of living matter.
Leduc has taught us that by osmosis life-like forms may be
produced which grow.

(e) Electric Phenomena. The electrical power generated by
living matter has always been a subject of interest and of amaze-
ment. Quite apart from such animals as possess electrical organs,
e.g. the electric eel which can generate an E.M.F. of several
hundred volts, every living animal, in fact every living cell, pro-
duces electromotive forces. The ordinary potential differences
observed in living matter may seldom reach 0 -1 volt, but everyone
knows that if n small units are connected in series, the resultant
voltage is n times the voltage of the single unit. Dissection of an

BIO-ELECTRIC PHENOMENA 133

electric organ shows that it is built up serially of large numbers
of units. The cause of the potential differences in cells must be
sought for in the " selective " permeability of the cell membranes,
or in alterations of the content of the protoplasm in electrolytes.

(i) Differential permeability. Bayliss separated a concen-
trated from a dilute solution of the sodium salt, congo red, by a
membrane of parchment paper which is permeable to the sodium
ion but not to the anion. He found that the dilute side became
electro-positive on account of the preponderance of cations on
that side.

(ii) Differential permeability does not afford a sufficient ex-
planation for all bioelectric phenomena. Even when the membrane
is freely permeable to both ions of the salt and when the anion is
the faster of the two, the dilute side of the parchment becomes
electropositive. This brings us again to the charge on the
membrane. Parchment has a negative charge in water, and in
dilute solutions of neutral salts — so has baked clay, wood, bone,
charcoal, natural gelatine, etc., and all these cause a positive
charge to develop on the dilute side. That is, the generation of
a potential difference is just the reverse of electrical endosmose
(Chap. X.). This may be confirmed by altering the charge on
the membrane. Gelatine may be induced to take up a positive

charge. Mines found that when a dilute solution \™/ was

separated by a gelatine membrane from a more concentrated

/N\

y— ) solution of sodium chloride, the dilute solution became electro-

positive. Gelatine is made positive by treatment with the ions
of polyvalent metals. When an electropositive gelatine membrane
was used, the dilute solution became negative.

(iii) A slight alteration in hydrogen ion concentration occurring
on one side of a membrane will cause the development of E.M.F.
If two solutions, one of pH 7 and the other of pH 8 are separated
by a membrane more permeable to //+ ions, an E.M.F. of about
30 millivolts may be obtained. The living cell has a pH of about
7-4 and its E.M.F. is not usually greater than 30 millivolts.
Polarisation current.

In all chemical processes, alterations in potential difference take
place. The living complex, known as a cell, is a system in which
chemical transformations proceed continually and, therefore,
electromotive force is being generated continuously. These
currents may be demonstrated if special arrangements are made

134 THE CELL

to prevent polarisation of the electrodes (Part II.). The electrodes
which are used to lead the current from the cell (or group of cells)
to the galvanometer are subject to polarisation as explained in
Chap. X. The products of electrolytic decomposition of the cell
substance are transported to the electrodes and accumulated there.
The deposition of these products at the two poles, in course of
time, alters the nature of the electrodes. The cathode, for instance,
because of the accumulation of positive ions on it, becomes more
and more anodal. This produces an electric tension that causes
a current, the so-called polarisation-current, to flow in the opposite
direction to the original one. As this current grows in strength
it reduces the value of the tissue-current and after a short time
completely obliterates it. (See also Muscle, Chap. XIII., and
Nerve, Chap. XVII.)

(/') Electrical effects are produced in living cells by suitable
stimulation. If a cell is injured the injured part becomes electro-
positive to the rest. This phenomenon, apart from any other
conditions, would be quite sufficient to justify the postulation of a
cell membrane. Consider the cell as a mass of protoplasm in an
envelope of matter which is permeable to the negative ion but
not to the positive ion of a dissociated electrolyte. This will
cause a difference of potential on the twro sides of the membrane.
Inside will be a preponderance of negative ions while outside will
be an equal preponderance of positive ions. Current of Injury. —
If now we could connect the inside of the membrane with the
outside, there would be a flow of current till the difference of
potential had been equalised. Current would flow to the pierced,
injured (or inside) part from the outside. That is, the injured
part would be similar to the zinc pole of a zinc-copper galvanic
couple. There the flow of current is from the zinc to the copper
inside the battery. The zinc is therefore said to be electro-
positive. The current, however, flows from the copper to the
zinc, outside the battery. The zinc is, therefore, said to form the
negative pole. Current of action. — When alterations of tension
or stress take place in a cell they are accompanied by alterations
in electric potential. The part under stress becomes as if injured,
i.e. electropositive or zincy to the normal or unstressed part.
This may be due to an increase in the permeability of the membrane
at the stressed part, so that the positive ion gains access to the
cell. The seat of stress does not, however, remain at its point of
origin but passes as a wave of increased stress over the whole cell,
followed immediately by an electropositive wave.

SECTION III: CELL COMMUNITIES

CHAPTER XIII

THE ARMY WHEREWITH THE BODY WAGES WAR
WITH NATURE— THE MUSCLE CELLS

" Tho' born to fight,
Yet, mix'd and soften'd, in his work unite ; "

POPE.

IN the animal body there are various kinds of cell communities.
There seems to be no doubt that originally each cell was self-
supporting, and a small cell-community, like a small village in a
remote corner of civilisation, was able to perform all necessary
activities without the help of other communities. In a big
complex concern like the mammalian body, however, each cell
community has specialised in some form of activity, and it has
therefore to depend on other communities for certain necessities.
No such cell is absolutely self-supporting. For the same reason
we cannot validly consider any cell as typical of all others. Each
has its own particular duty to perform and is adapted to perform
that particular duty most economically. It could, if circum-
stances compelling it arose, do other things usually left to other
cells, but would perform these unaccustomed duties clumsily and
uneconomically.

The dominant cell communities in the somatic body are those
forming the muscles. Their activity, to a great extent, regulates
all other changes taking place in the body. They demand for
their use the lion's share of the energy intake of the body. The
bulk of the repair material in the food is earmarked for their use.
They keep a firm hand on the transport system and soon cause a
" speeding up " if supplies fall short of their needs, or if the bye-
products of their activity are not removed with sufficient rapidity.
The system of inter-communication between cell-communities

135

136 THE MUSCLE CELLS

(the nervous system) exists in large measure to suit the muscles.
In short, the muscles are the master-tissues of the soma. They
are not a manufacturing community but are power users. In
another sense the muscles are the servants of the body. By
means of them the body fights a war not merely of defence but
of aggression against its environment. As civilisation has
advanced, man has found it convenient by means of tools and
machines to add to his muscle power. In this way, he has been
able to harness and utilise power from sources that could not have
been tapped without the use of these machines. Tools and
machines are thus as it were extended and detachable limbs.

Muscle is a transformer of potential energy into kinetic energy,
and of course into heat. The source of the energy is, as we have
seen, the foodstuffs as broken down by enzymes, i.e. glucose, fat
and deaminised amino acids. There seems to be no doubt as to
the means by which the energy is ultimately liberated from these
food units. In Chapter III. we saw that the intake of oxygen
and the output of carbon dioxide was so intimately connected
with the process of energy liberation that we could calculate the
amount of energy set free in an organ by measuring these gases.
That is, the basis of muscular activity is oxidation, just as the
basis of the activity of a steam, engine is the oxidation of coal.
In Chapter IV. there was a discussion of this, and evidence was
produced proving that in all other details the oxidative process
in muscle differs from that of coal. What then happens in muscle ?
There seems to be three stages in the translation of potential
energy of food into muscular work.

(1) Contraction. The muscle shortens and thickens. During
this phase oxygen is not necessary. An excised frog muscle in
nitrogen will give a maximal contraction once every five minutes
for over two hours before showing signs of fatigue. The output
of carbon dioxide is not increased over the amount evolved during
rest. The heat evolved is negligible if the muscle is allowed to
shorten under certain conditions. If it is made to contract
isometrically i.e. against a spring that does not permit of its
shortening, the energy developed, that would in ordinary course
produce contraction, appears as heat. This heat is directly pro-
portional to the length of the muscle fibres. Further, increase
of temperature causes a decrease in the tension developed on
stimulation, i.e. contraction has a negative temperature co-
efficient. A muscle at 0° C. in an experiment of Bernstein's
developed a tension of 375 grams. On raising the temperature

SURFACE TENSION

137

to 18° C. the maximal tension was found to be 205 g. Surface
energy is the only possible form of energy that could be associated
with muscular contraction which has a negative temperature
coefficient.

In dealing with surface tension (Chap VI.) it was pointed out
that most physical and chemical actions are accelerated by increase
of temperature, while surface energy is diminished as tempera-
ture rises.

A glance at Fig. 24 may make it clear how surface energy may
be made to do work.

A wire frame is made, to one side of which is attached a silk
thread. Over the whole area is a film of soap. The thread M

A B

FIG. 24. — Frame of wire enclosing a Soap Film.
In A there is a loop of fine silk floating in the film.
In B, the film enclosed by the loop has been broken. (After Van der Mensbrugghe.)

takes up an indifferent position as shown in (A) as the surface
tension at the interface between F and S is exactly balanced by
the internal energy of F ^internal energy of S. If now the film
is broken inside F, say by pricking with a needle, M tends to
become a circle. That is, the internal energy of S is increased
relatively to that of F. However it is brought about, the result
is an increase in the surface tension at the interface F —S, i.e. the
thread. It is of value to note that it is not necessary for the film
to be broken. Theoretically, all that is necessary is a difference
in internal energies on the two effective sides of the thread, the
lower internal energy being inside the loop. Further, no matter
how slight the difference on the two sides of the thread the movement
would be maximal.

Muscle consists of a number of long fibrillae immersed in
sarcoplasm. The membranes of the fibrillae may be represented
by the thread mentioned above, the protoplasm of fibril and
sarcoplasm as the soap film. Anything which causes a difference

138

THE MUSCLE CELLS

of surface tension at the interface between fibril and sarcoplasm
will cause the fibril to contract to its fullest extent. Of course
the student will understand that the subject bristles with diffi-
culties, and the above explanation can only be taken as a very
crude and incomplete basis for further elaboration.

The only metabolite of muscular contraction that stands on a
very firm experimental foundation is lactic acid. In the absence
of oxygen muscle becomes acid. If contraction takes place in
the presence of oxygen, lactic acid does not appear. Lactic acid
formation in muscle has been a veritable red herring drawn
across the track. The problem looks so simple with lactic acid
as an intermediate step in the oxidation of carbohydrates. The
careful investigations of Prof. A. V. Hill of Manchester have made
it clear that no such simple process is possible. First, the lactic
acid is not a step in the oxidation of carbohydrates, and secondly
it is not oxidised itself to CO2 and H2O as was thought. It is
not part of the fuel but is a necessary part of the machine, moving
to and fro like the piston of a gas engine. The arrival of the
stimulus (free kinetic energy) is the trigger setting free lactic acid
from some physico-chemical combination and so causing an
increase in H ion concentration and consequently an increase in
tension at the surface of the fibril and sarcoplasm. If this tension
is not allowed to cause contraction, the energy of tension can be
converted, as we have seen, into heat. The amount of heat so
obtained has been shown by Hill to be quantitatively equal to
the amount of work derivable from the tension. That is, the
efficiency of contraction is 100 per cent.

(Mean maximum value =91 per cent.)

(2) Restitution. This extraordinarily efficient first stage of
muscular activity where stored energy is converted into work

TABLE XXII.

GASEOUS EXCHANGE IN M. Levator Labii Superioris OF THE HOR;-;E PER

GRAM OF MUSCLE PER MINUTE (CllAUVEAU AND KAUFMANN).

1

2
3

REST.

ACTIVITY.

Oxygen absorbed.

CO-2 given out.

Oxygen absorbed.

CO2 given out.

0-0032 c.c.
0-0079
0-0028

0-0019 c.c.
0-0058
0-0026

0-054 c.c.
0-014
0-010

0-063 c.c.
0018
0-013

RESTITUTION PHASE 139

must be followed by a stage in which energy is again stored for
work. During this phase four things are evident, viz. :

I. Oxygen is necessary.

II. Carbon-dioxide is evolved.

III. Lactic acid disappears.

IV. Heat is evolved.

Examination of table XXII. given above will make it clear to
the student that I. and II. are different parts of the same reaction.
Oxygen is used to oxidise some carbon compound which is excreted
as CO2( +H2O). If oxygen is not present we learn from the work
of Fletcher and Hopkins that the lactic acid set free during the
contraction phase is not removed. The amount of heat evolved
has been very carefully estimated by Hill and others. They
find that it is almost exactly equivalent to the tension developed
in contraction. If the tension be estimated in heat units and found
to be 5 xlO~6 cals. per gram- weight of tension per centimetre of
muscle length, the heat evolved during the restitution phase
would also be 5 xlO~6 cals. per gram-weight. The work done in
putting the muscle back into its precontraction state is equal to
the tension developed during contraction.

Two views are held regarding the mechanism of . restitution.
The commoner idea is that lactic acid is in muscle as elsewhere
an intermediate compound in the oxidation of glucose. Glucose,
we know, is stored in muscle and this store is decreased during
contraction. The amount of heat liberated from glucose in the
formation of lactic acid is very small, while the amount liberated
when lactic acid is itself oxidised to CO2+H2O is considerable.
1 gram of lactic acid in oxidation sets free 3700 cals. These
facts seem to fit in well to the following scheme. During
contraction lactic acid is formed from glucose. For this, very
little oxygen is required and very little CO2 is evolved. Practi-
cally no heat appears. During restitution the lactic acid is
removed by oxidation and heat is evolved.

Neat though this theory is, it has been rendered untenable by
the brilliant researches of A. V. Hill and V. Weizsacker with their
ingenious myothermic apparatus, and by Fletcher and Hopkins
who devised a delicate means of estimating lactic acid. When
1 gram of lactic acid disappears from muscle, only 450 cals.
instead of 3700 are produced. Obviously, only a small fraction
of the lactic acid is oxidised if any. Fletcher and Hopkins could
not detect any oxidation of lactic acid.

140 THE MUSCLE CELLS

The lactic acid set free in the contraction phase is, in the
restitution phase, once more built up into the physico-chemical
compound of which it was a part before the arrival of the stimulus
provoked a contraction. As A. V. Hill has said, " The lactic
acid is part of the machine and not part of the fuel." During
contraction it is set free, during restitution it is built up again.
To provide energy to build the lactic acid into its old place,
i.e. to restore equivalence of internal energies between sarcoplasm
and fibril, glucose has to be oxidised to CO2 and H2O.

There seems to be little doubt about the experimental evidence
regarding the utilisation of glucose during restitution. The
glucose stored in the muscle furnishes the main reservoir of
energy on which the muscles draw for carrying out this work.
There is some evidence, not very clear it is true, suggesting that
stored fat may also be called on to supply energy for muscle
restitution. Either because carbohydrate is more readily
mobilised or because it requires a lower tension of oxygen for
disintegrative oxidation than fat or for both reasons, muscle
utilises carbohydrate in preference to fat.

The liberation of lactic acid in the first phase of muscular
movement produces not only contraction but a whole series. of
physico-chemical changes which have got to be reversed during
restitution. I. As a dissociable acid (Chap. VII.) it will produce
an increase in H ions. II. This increase in pH reacts on the
colloids in suspension in the muscle, causing them to alter in
electrical charge (Chap. VIII.). III. This in turn sets free salts
adsorbed to the colloidal surfaces and so produces an increase in
osmotic pressure. IV. Further, the membranes will become
polarised. V. From III. and IV. will result endosmosis and the
water content of muscle will increase.

Roaf has shown that there are definite alterations in H ion
concentration associated with different stages of muscle con-
traction. Macallum proved that activity caused an alteration
in the concentration of salts in muscle, and Fletcher has demon-
strated the increase in water content after exercise.

What is the effect of temperature on the restitution phase ? We
have seen that the contraction phase has a negative temperature
coefficient. Theoretically, each of the five sequelae to the libera-
tion of lactic acid as mentioned in the preceding paragraph has
a positive temperature coefficient. The building up of lactic acid
into a complex would be accelerated by temperature just like any
other chemical reaction.

TEMPERATURE AND EFFICIENCY 141

That is

(I.) The dissociation of lactic acid, the setting free of H ions,
is increased in rate and extent by increase in temperature (Chap.

VII.).

(II.) No change known.

(III.) Temperature increase causes increase of salt de-adsorption.

(IV.) No change known.

(V.) Because of the increased dissociation of salts by the
increase in temperature and because of the increased kinetic
energy of water seeking admission the rate of endosmosis will
increase with increase in temperature.

These have all to be restored to precontraction state, and there-
fore do not materially contribute to this part of the discussion.
But the temperature coefficient of contraction is negative, there-
fore all these reactions must fall within the phase of restitution.
Experimentally it has been found that this phase increases in rate
with temperature. (The other effects of temperature on muscular
contraction will be dealt with later. Just now we are concerned
with isolated muscle.) A moderate increase of temperature
thus increases the removal of lactic acid and the restoration of
potential energy to the muscles, while not appreciably lessening
their power to transform potential into kinetic energy, i.e. to
contract. Further, it has been shown by Lagrange that an in-
crease in temperature increases the efficiency of muscle. Lately,
workers have ascribed this increased efficiency to the more rapid
removal of lactic acid.

Now we have seen that :

(a) The restitution phase is accompanied by an increase in the
temperature of muscle.

(b) The rate and efficiency of contraction is reduced by increase
in temperature, and

(c) The rate and efficiency of restitution is increased by increase
in temperature.

It therefore follows that there will be a temperature at which
muscle work (contraction and restitution) will be performed most
efficiently. Further there will be an optimum speed at which
work will be carried out. This speed will be regulated

(1) By the natural rhythm of contraction of the muscle —
depending on the length of the contractile body (Fig. 25).

(2) By the optimum temperature, and

(3) By the amount of resistance that has to be overcome in
shortening. (See also Chap. XXVIII.)

142

THE MUSCLE CELLS

The efficiency of this second phase of muscle work is less than
that of the contraction phase, which we saw was 91 per cent.
Taken together they give a gross efficiency
for a complete muscle twitch as 50 per cent.
But to this one might apply a correction to
take into account the energy expended
during muscle rest.

(3) Rest. During complete inactivity,
energy is used for maintaining the muscle
FIG. 25.— influence of the in a state of preparedness for action, just

length of a muscle upon the •_• . i i • *_ •

work done. A muscle one as a nation has to spend money maintam-

inch long (left-hand figure)
in contracting to half its
length lifts a weight to half
an inch. A muscle of two
Inches, on the other hand, is
capable of lifting the weight
to one inch.

(Noel Paton's Essentials of erroneously termed rest. As we shall see in
the sequel, this phase is anything but restful.
Again, just as in peace time, the coordinating and integrating
machine of empire, the Cabinet, keeps our standing army in a
high state of efficiency, so the nervous system constantly sends
impulses to the muscles, keeping them ready for instant action.
This state of resting readiness may be called the tone of muscle,
and is, as indicated above, regulated in part by the nervous
system (q.v.). During rest, energy is expended which if sub-
tracted from the total energy expended during restitution would
raise the efficiency of that phase by about four per cent.

ing an army in peace time, so the muscle
cell must always be ready for action. This
is the third phase of muscular life —

TABLE XXIII.

OXYGEN USED BY CAT'S Gastrocnemius M. (VERzAR, 1912).

c.c. Oxygen used by muscle.

per minute.

per gram
per minute.

Rest (Normal)

0-050

0-003

Contraction

0-178

0-010

Restitution 15 sees, later

11 „ „
11 „ „

0-336

0-208
0-154

0-020
0-012
0-009

Rest (Normal) 146 „

0-059

0-0035

ELECTRICAL PHENOMENA 143

The efficiency of muscular contraction is found from the formula

where a =actual work done (in cals.) per unit of time.

b =total energy used (in cals.) ,, ,, ,,

This gives the gross efficiency. The net efficiency is obtained
by correcting for the energy expended during complete inactivity
during a similar unit of time.

Net efficiency E= T - xlOO,

b — c

where c=energy expended during inactivity (in cals.) per unit
of time.

As no external work is done during inactivity it is difficult to
assess the value of the efficiency of this phase.

The temperature co-efficient for a complete muscle cycle is
1 -8, which means that the rate of the physico-chemical reactions
involved is almost doubled by an increase of 10° C. As we have
seen this rate is a compromise between the decrease in the rate
of the physical reactions of the contraction phases and the increases
in the physical and chemical reactions of the restitution phase.

Character o! the Electrical Variations in Muscle.

The existence of electrical currents in tissues did not find
direct proof until the year 1824, when Nobili devised the galvano-
meter and showed that " natural currents " occur in the frog.
Other investigators examined this current of rest and found that
in a muscle removed from the body the current in the muscle
passed from the ends to the middle and in the external (galvano-
meter] circuit from the middle to the ends. It has been con-
clusively proved that these " natural " currents are not natural
at all but are an indication of injury to the muscle. Slight injury
is unavoidable in the process of removing the muscle from the
body — the less the preparation is injured the smaller is the current
obtained from it. In other words, normal resting muscle is iso-
electric and therefore currentless.

Current of Injury or Demarcation Current.

The injured part of a muscle is like the injured part of any
cell (p. 134), " zincative " or electropositive to the uninjured part.
That is, if non-polarisable electrodes are led off from injured and
non-injured parts to a current-detecting device, it will indicate

144 THE MUSCLE CELLS

a passage of current from the uninjured to the injured parts of
the preparation through the galvanometer. Within the tissue, of
course, the circuit will be completed by the passage of the current
from injured to uninjured. This difference of electromotive
force may be demonstrated without a galvanometer. If the
nerve from an uninjured muscle be laid over an injured muscle
in such a way that at one point it touches a cut portion, then, the
undamaged muscle will contract every time the circuit is com-
pleted by laying a second point of the nerve on an uninjured
portion of the injured muscle.

This difference in E.M.F. persists as long as the injury. In a
degenerating muscle its degenerating portion is electropositive,
galvanometrically negative or " zincative " to its normal portion.
Naturally, the difference ceases when degeneration is complete.
The whole mass is then isoelectric. The current is due, as has
previously been explained (p. 133), to physico-chemical differences
at the junction of living and dying tissue. Dead tissue gives no
current.

Current of Action.

Similar physico-chemical changes are answerable for the wave
of " negativity " which precedes the mechanical change in a
contracting muscle. The part which is just about to contract
is electropositive, or " zincative," to the rest. Consider for a
moment a muscle, say 5 cm. long. The preparation is supposed
to be perfect and, therefore, there will be no demarcation current.
If such a muscle be stimulated by a single induction shock at one
end and two points A 3 cm. and B 5 cm. from the point of stimu-
lation be led to an electrometer, then each stimulus will cause
a wave of contraction to pass along the muscle, preceded by a
wave of " negativity." That is, A will become " zincative " to
the rest of the muscle — so that current would pass through a
galvanometer from B to A. A fraction of a second later, the
disturbance will have passed on to B which will now be " zincative "
to the rest, causing a current to pass through the galvanometer
from A to B. That is, A has first been electropositive and then
electronegative to B. Such a current is termed diphasic and is
an indication of a propagated change.

A muscle nerve preparation may be used to demonstrate the
presence of the current of action. If the sciatic nerve of a frog's
gastrocnemius be placed on another gastrocnemius, the former
muscle may be made to contract by stimulating the nerve of

HEAT PRODUCTION 145

the latter. The essential point about this preparation which is
called the rheoscopic frog is that it actually proves the occurrence
of a diphasic current in muscle in consequence of its activity.
If the free nerve is stimulated by a tetanising current both muscles
go into tetanus. This secondary tetanus demonstrates that
although the stimuli are being applied so rapidly that the con-
tractions of the " battery " muscle are fused, the diphasic nature
of the excitatory process is still quite distinct and is indicated by
the contraction of the " galvanometer " muscle.

The current of action may be considered as inclusive of the
current of injury. Injury is stimulation. Therefore, the current
produced by an injury confined to a small area should be weaker
than that obtained by the excitation of the whole muscle. The
E.M.F. of the current of action of a sartorius is about 0-085 volts,
while the demarcation current may be about 0-053 volts.

An important piece of research work by A. V. Hill and W. Hartree has
just been published. They devised instruments and methods enabling
them to record photographically, not only the mechanical response of a
muscle to a stimulus, but the heat produced at each phase of the mechanical
response. Their apparatus was sensitive to 0-000001° C. One may
summarise their main findings as follows :

(1) " The time relations of the heat production in the first few seconds
after excitation are independent of the presence of oxygen." It has been
stated above that the magnitude of the heat production was independent
of the presence of oxygen. One may therefore consider that the energy
required for the initial chemical changes caused by excitation does not
arise from oxidation.

(2) A complete muscle twitch may be resolved into four phases.

HEAT PRODUCTION.

(a) Contraction - Initial rapid production diminishing

gradually jn rate as the stimulus
proceeds.

(6) Maintenance of Con- Small constant value ending shortly
traction after stimulus ceases.

(c) Relaxation Relatively large evolution of heat,

occurring rather suddenly during the
later stages of relaxation.

(d) Recovery - A large but slow production of heat

occurring in the presence of oxygen
for some minutes after the contraction
is over.

B.B. 10

146 THE MUSCLE CELLS

(3) " The absolute amount of heat liberated in relaxation increases as
the duration of the stimulus increases, up to a certain limit, after which it
remains more or less constant."

(4) The heat developed during relaxation is derived from the mechanical
potential energy liberated on excitation.

A close analogy is drawn by these workers, between the energy changes
of muscle and of an accumulator.

(a) The energy of an accumulator- — stored electrical energy — is liberated
by the application of a " trigger," i.e. by completing the circuit between
positive and negative poles. In the same way, the potential energy of
muscle is liberated by the application of a stimulus. The chemical changes
that accompany the evolution of energy from an accumulator do not
involve oxidations — just as the initial processes of contraction in muscle
do not.

(&) The amount of energy used in making electrical contact, e.g. de-
pressing key, is very small and bears no relation to the amount of energy
so liberated from the accumulator, as is the amount of energy required to
stimulate a muscle fibre.

(c) If a suitable machine is in circuit, the energy set free from the accumu-
lator will manifest itself as " work " ; if not, it will be converted into heat.

(d) The moment the key is pressed the current starts in the electrical
machine — say an electric motor. It passes round the coils of the arma-
tures, and their soft iron cores develop attractive powers. The current,
however, does not immediately rise to its full value owing to the self
induction of the coils, nor do the soft iron cores become magnetised in-
stantaneously under the influence of the magnetic field of the coil. Hence,
the attraction exerted by the fixed poles on the armatures increases gradually
up to a certain limit and then remains constant. These phenomena are
similar to the development of mechanical response in a muscle.

(e) As long as the circulation is complete and the accumulator inex-
hausted, the motor will rotate. Roughly speaking, the mechanical response
and the length of stimulation are synchronous.

(/) If the current is left on too long, the accumulator becomes polarised,
the current falls off and the magnetic field consequently decreases. After
a period of rest, the electromotive force of the storage element rises to its
full value and the magnetic field is restored. This may be compared to
muscular fatigue.

(g) On breaking the electrical circuit the magnetic field of the armature
diminishes rapidly, though not instantaneously, to zero, and the motor
slows down and stops. This process is analogous to relaxation. .

(h) The current passing through the coils of the armatures and trans-
forming them into magnets, endows them with (magnetic) potential
energy which, as we have just seen, is, after a brief latent period converted
into the kinetic energy of rotation. If the load on the motor is so great
that revolution is prevented, then although tension is developed, no work
is done. In the same way, muscle develops elastic potential energy on
excitation which may result in the performance of external mechanical
work if the muscle be allowed to shorten, but in an isometric contraction,
shortening is prevented and no " work " is done. " The work actually
performed depends in both cases on the conditions of loading."

(i) Heat production.

(i) Developmental. The electrical energy sent through the armature

ELECTRICAL ANALOGY 147

coils is converted partly into magnetic potential energy and partly into
heat energy (Joule's heat) which is dissipated. The magnetic potential
energy is converted partly into the kinetic form (rotation) and is partly
dissipated as heat. The proportion of the incident energy which manifests
itself as " free " and as " bound " depends on the length of time during
which the current passes. A short excitation leads to the development
of power in preference to heat while the reverse is the result of a prolonged
excitation. Similarly, with muscle — a single twitch develops very little
initial heat while an increasing fraction of the potential energy appears as
heat as the mechanical response is prolonged.

(ii) Maintenance. In order to maintain a constant magnetic field a
constant current has to be maintained in the coils of the armatures. The
coils heat up. This is analogous to a tetanic contraction.

(iii) Relaxation. The induced currents, set up in the coils and in the
neighbouring conductors by breaking the circuit, are converted into heat,
i.e. the evolution of heat continues until the whole of the magnetic energy
of the field has been dissipated as heat. Similarly in the muscle when the
stimulus ends, the heat production does not stop at once ; it continues
until all the elastic potential energy of the muscle has disappeared.

(iv) Recovery. None of the above processes require the immediate
presence of oxygen. In order to restore the electrical system to its former
level, i.e. to recharge the accumulator, some mechanism has to be employed
to convert kinetic into electrical energy. The normal process implies
oxidation — an engine is started, oxygen and fuel are consumed, a dynamo
is driven and current produced. Similarly oxygen is necessary during the
recovery phase of muscular contraction.

(v) Rest. Accumulators " run down " when not in use, and liberate
a certain small amount of heat. To keep them in condition they must
have periodical additions to their material and energy contents. This
recharging involves heat production and oxidation. In the same way,
muscle at rest (in the absence of oxygen) liberates heat (and lactic acid).
In the presence of oxygen this liberation is made good by oxidation. That
is, muscle normally is prevented from " running down " by " continuous
recharging " with, of course, a steady evolution of heat.

The foregoing notes are taken materially and almost verbally from an
article by Prof. A. V. Hill and W. Hartree in the Journal of Physiology,
Vol. LIV., p. 84. The student will, of course, bear in mind that no theory
of muscular contraction is implied. A physical phenomenon which bears
a very close resemblance to certain phases of the mechanical response
of muscle to stimulation is given as suggestive of a type of mechanism.
But, as has been said, " Resemblance is no proof — analogies can never
replace analysis."

CHAPTER XIV
MANUFACTURING CELLS

" For know, whatever was created needs
To be sustained and fed ; of elements
The grosser feeds the purer."

MILTON.

IN the preceding chapter attention has been drawn to the
muscles as cell communities which consume power but do not
produce commodities for the use of the body as a whole. Other
cell groups, the glands, may be regarded as the industrial com-
munities manufacturing goods for use elsewhere. Others again
are mere handlers of goods. These latter, the organs of absorption
or excretion (negative absorption), do not as a rule alter the
chemical state of the material, raw or manufactured, that they
handle. They accept delivery, repack in suitable containers it
may be, and forward for transport.

The glands may be divided for convenience into two classes.
First, those which by means of a duct, opening outside the body,
secrete manufactured material. The glands of the alimentary
tract and the skin glands (sweat and milk) belong to this class.
The other class prepares material which itself is used by the
body cells. They secrete into the blood stream. The former
may be termed organs of external secretion, the latter organs of
internal secretion, ductless glands or endocrine organs.
*- As^far as is known the principle underlying the activities of
air*glands is the same. Each manufactures some material which
is stored up, and when wanted this material is washed out by a
stream of water. That is, they all consist of a workshop and a
dispatch department. These two functions are seemingly under
different control and have to be studied separately.

The work done by a gland may be divided into three phases —
just as we saw that muscle work could be so treated — viz. :
(a) Activity,' (b) Restitution, (c) Rest or Maintenance.

148

RATE OF OUTPUT 149

(a) Activity. The outsider may gauge the activity of a factory
by studying its output, and so, much may be learned of a gland
by noting how much it secretes and when. Some glands secrete
continuously, others in spurts. With the former should be
placed the endocrine organs, with the latter the digestive glands.
Of course those which maintain a steady output may, under
stress, greatly accelerate their rate of secretion, and of the latter
class the salivary glands at least maintain normally a level of
secretion which under a suitable stimulus is enormously increased.

There seems no doubt but that the industrial cell-group consists
of four different parts or activities. (I.) The factory itself
where the secretion is prepared. (II.) The store room where it is
packed and kept in bulk. (III.) The dispatch department where
it is first packed small and ready for delivery and then (IV.) is
sent out. Now when we speak of the activity of a gland we
refer exclusively to this, last function, viz., active secretion.
What then regulates the rate of secretion ? Just those factors
come into play which operate in our industrial world.

1. Stock on hand and rate of output from workshop.

2. Efficiency of the dispatchers.

3. Demand for goods.

Normally, the store of goods on hand and the rate of manu-
facture do not materially influence the output. Of course, if the
operatives are poorly nourished or badly supplied with raw
material, then output will fall. Similarly, insufficiently fed or
overworked dispatchers will perform their duties half-heartedly
and output will be decreased, but as a rule this factor does not
come into play.

The decisive element controlling, rate of output is the demand for
goods. The store of goods is drawn upon and the factory speeds
up to replenish the store. If the stored material is sent out more
rapidly than it can be replaced, then overtime has to be worked
in the factory, and if persisted in, industrial fatigue is caused and
total cessation of work is the final result.

These various conditions may be studied conveniently by
studying the intake of oxygen or output of CO2. In some instances
the intake of potential energy may be measured. From these
it is found, as in muscle, that a very small proportion of the
total O2 intake goes to the dispatch department. That is, the
actual setting free of the secretion does not require much energy
(cf. muscle contraction).

150

MANUFACTURING CELLS

(b) Restitution. Just as in muscular, so in glandular activity
the great proportion of the oxygen used is associated with the
phase of restitution. Energy is required for the building up of
material to replace that lost during secretion.

(c) Then, as in muscle, the gland requires a certain amount
of energy for domestic use. To keep its parts in repair and to
preserve its identity, it requires a maintenance allowance. The
following figure from Barcroft will help the student to realise the
energy expended during these three phases in the activity of the
salivary gland in the cat.

From the figure it will be seen that the maximal rate of secretion
occurs sometime before the maximal consumption of oxygen, and

Ml MS.

a "b c d.

FIG. 2C. — Oxygen used by the salivary gland during rest, activity and restitution.
From a to b, the gland was not secreting, but was using a fairly constant amount of
oxygen. From b to c, the gland was active — secreting saliva at the rate denoted by the
dotted line. From c to d, the gland was being restored to its pre-secretory state.
0-0= oxygen base line. The area, ooss, represents the basal or resting metabolism
of the gland. Dark continuous line = oxygen consumption. s-s=base line for
saliva. Dotted line = saliva formed in c.c. per minute. (After Barcroft.)

that the increased consumption of oxygen lasts for some time
after the saliva has ceased to flow. Barcroft and his colleagues
found that the length of this period of increased oxygen con-
sumption depended upon the previous degree of activity of the
gland as well as on its functional capacity. In other words, if a
previous inroad upon the store of material had not been made
up, the factory cells would have to work at high pressure to keep
pace with the demand. Work at high pressure is not economical.
Each gram of secreted material is formed at an increased cost in
oxygen and energy.

The energy required for secretion comes from the oxidation of
glucose. (Again compare with muscle.) For the dispatch of
the material, little extra oxygen and little extra glucose is required.
Asher and Karalov found that the restitution phase required the
most energy. That is, the glucose content of the blood was
markedly diminished in the post-secretory period. The amount

MECHANISM OF SECRETION 151

of glucose used runs, as one would expect, parallel to the oxygen
consumption.

The mechanism of secretion has been provocative of much
controversy. A regular pitched battle results when vitalists,
neovitalists and mechanists discuss the problem. What are the
facts ?

1. Microscopical examination of the gland shows that during
inactivity the lumen (storehouse) becomes filled with granules
and the gland increases in volume. When the gland is excited
to secretion, these granules disappear with the secreted fluid and
the gland decreases in volume.

2. Water passes from the blood into the gland and out with
the secretion.

There seems to be no difficulty in giving a plausible explanation
of the second of these phenomena. The postulation of a semi-
permeable membrane is sufficient. The first fact presents diffi-
culties.

(a) The osmotic pressure of the secretion is often greater than
the osmotic pressure of the blood.

(b) The pressure in the duct against which the saliva may be
secreted was found by Ludwig, in 1851, to be greater than that
of the artery supplying the gland. Hill and Flack recently
estimated this difference in pressure. They found that the
pressure of secretion was as high as 240 mm. Hg. and the arterial
pressure 130 mm.

3. Macallum demonstrated alterations in surface tension during
secretory activity.

As mentioned in Chap. VI. this worker made use of the Gibbs-
Thompson distribution of salts to determine the relative values
of surface tension in cells which had been killed and fixed almost
instantaneously. He found, in the pancreas for instance, that
during rest there was an unequal distribution of potassium, but
when the gland was stimulated to activity potassium salts were
found equally distributed throughout it.

Theoretically, in an active gland there must be at least three
different values for surface tension, viz. :

(1) Cell-lymph interface, i.e. on the outer face through which
raw material and power enter.

(2) Cell-cell interface where the cell wall is in contact with some
of the other cells of the gland.

(3) Cell-lumen interface through which the secretion and the
leaching out water pass.

152 MANUFACTURING CELLS

Now during activity he found that there was the densest con-
densation of potassium at (3), the cell-lumen interface, less
potassium was found at the cell-cell interface and least at (1), the
cell-lymph interface. According to the Gibbs-Thompson principle
these results may be taken as an indication.

(a) That during rest there is no marked difference of surface
tension at the gland interfaces, and

(b) That during activity a high tension develops at the surface
between cell and lymph, a low tension between cell and lumen
and that the cell-cell interface has a value intermediate.

4. It is well known that during glandular activity there is an
increase in the rate at which blood enters the gland. In other
words raw material and power are taken into the factory at an
increased rate. The view was at one time held that the secretion
was due to this increased flow of blood. Barcroft's experiments
have shown that this cannot be true, because

(a) The increase in the blood flow through the organ is initiated
after the secretion begins and is continued for some time after
secretion has ceased ; and

(b) Vaso-dilatation may take place without secretion.

The increase in blood flow or vasodilatation is a consequence
of secretion and not the secretion a result of the vasodilatation.
The actively secreting gland, as it were, sends out a call for
oxygen, for power and for material. This call is in part met
by this increase in the transport service (see Chap. XXIV.).

5. Alterations take place in electrical potential of one part of
the gland to another. These have. been studied principally by
Bayliss and Bradford on the salivary gland and by Orbelli on
the skin glands of the frog. The results vary somewhat with
the means of investigation, but may be taken as indicating two
things.

(a) The secretion of water, i.e. dispatch of secretion, is a different
function of the gland or a function of a different mechanism in
the gland from the elaboration of the true secretory material.
That is, we have to consider two phenomena, the preparation of
material and its flooding out of the cell by water. The former is
accompanied by

(6) A large difference of potential between the cell-lymph
interface and the cell-lumen interface, the latter by a small
potential difference of the opposite sign from the former.

The cause of the former difference may be sought in the in-
creased permeability (lowered surface tension) of the cell-lumen

ELECTRIC PHENOMENA 153

interface ; allowing free passage to cat-ion and an-ion. That
is, at this surface the electrical potential recorded will be that
of the interior of the cell (cf. muscle-current of injury).

An explanation of the current which flows during the elaboration
of secretion is more difficult. There seems no doubt that just
before being carried out through the duct, the granules undergo
some change. The large colloidal particles either break down
into smaller particles or go into solution. Either of these actions
is accompanied by the setting free of adsorbed salts and altera-
tions in the electrical charge.

6. These two processes, water secretion and the elaboration of
the organic secretory material, seem to be controlled by different
sets of nerves. Secretory nerves when stimulated cause the
gland to be flooded with water, while " trophic " nerve fibres
have to do with the elaboration of the granular material of the
secretion. (Heidenhain, 1868, and Babkin, 1913.) Both sets of
fibres may go to the gland in the same nerve. It is interesting
to note that acid and other irritants excite secretory fibres only,
while normal excitants stimulate both secretory and trophic
fibres.

Can we from these facts construct a picture of the mechanism
of secretion ?

(1) The formation of granules in the cell may be similar to the
formation of starch in the plant. Substances are thus put out
of action. The colloidal granules not only have a low osmotic
pressure but they adsorb crystalloids and so prevent endosmosis.

(2) On stimulation, these granules are broken down into smaller
particles and water rushes in. It may be that stimulation of the
gland follows the same course as in muscle and produces acid.
This acid would interfere (a) with the colloids present, especially
with their power to hold water (imbibition) and salts (adsorption)
and so bring about alterations in their size, electrical charge and
the osmotic pressure of their dispersion medium, (b) Acid has
a direct action on the electrical charge of any solution and, there-
fore, acts on its surface tension, lowering it. The only surface
where this can take place is between the cell and the lumen. The
alkaline reserve of the blood is sufficient to keep the cell-lymph
interface normal ; or rather supernormal, while the cell- interfaces
obviously need not be considered.

(For a neat model of Mucoid secretion due to M. Fischer, see
Part II. p. 415.)

In short, the arrival of the appropriate stimulus causes the

154 MANUFACTURING CELLS

cell to draw on its store of material, alter the packing of the
material and launch it into the duct on a current of water. The
stimulus may be nervous or it may be a hormone (chemical
messenger) formed in another organ and transported to the gland
by the blood.

Of the mechanism of these glands which secrete directly into
the blood stream little is known. Seemingly the secretion is
extruded from the cell and washed away by the blood itself.
Their oxygen consumption has never been measured nor yet their
utilisation of glucose.

Bayliss and Hill have shown that the salivary gland does not
become heated during activity. From this we may deduce that
all the additional energy set free during the course of activity is
used in doing work (in elaborating the secretion and in setting it
free, etc.), and in maintaining to some extent the normal tempera-
ture of the body (cf. Muscle). Thus leaving alone the latter sink
of energy we may consider a gland as 100 per cent, efficient and
calculate the work done from the oxygen intake or carbon dioxide
output or from the diminution of sugar in the blood passing
through it.

A considerable amount of work has been done in connection
with the electrical changes which take place when a gland secretes.
Bayliss and Bradford found that two kinds of changes occurred
in the salivary gland. That associated with the secretion of
water produced changes in the opposite direction from that
associated with the output of the colloidal matter. The causes of
this phenomenon are not yet certain but two " pointers " may be
indicated. (1) The work of Loeb and his colleagues has shown
how the presence of colloidal matter may alter the sign of electrifi-
cation of water (p. 111). (2) In accordance with the accepted
theory of secretion, the onset of true secretion leads to an increase
in the permeability of the cell membrane at one end. It is obvious
that, at the more permeable end, we are in electrical contact
with the interior of the cell and so obtain the potential difference
of the Helmholtz double layer between permeable and imper-
meable parts of the surface. During a mere secretion of water
permeability is not supposed to undergo alteration.

CHAPTER XV
THE ARMY FOR HOME DEFENCE

" Whatever uncertainty and variety may appear in the world, we remark,
nevertheless, a certain secret concatenation and regular order at all times carried
on by Providence, which causes everything to proceed in its course, and to follow
the law of its destiny." LA ROCHEFOUCAULD.

THERE are certain cells and certain cell-communities whose
function it is to guard the organism from the invasion of its cells
by noxious substances and by predatory parasites.

1. Cells. The leucocytes or white cells of the blood are amoeboid
in character and act as scavengers and dust cart combined.
They absorb, kill and digest micro-organisms which have invaded
the organism. They also ingest and digest effete tissues, such
as the tail of the tadpole when the frog stage is reached. This
is termed phagocytosis. Certain drugs, e.g. iodoform, are supposed
to increase the amoeboid movements of leucocytes and so increase
their phagocytic power. This takes for granted that the bacteria,
etc., are enclosed by the pseudopodial processes of the leucocyte.
In the blood vessels it is very rare for leucocytes to be seen with
extruded processes. They are found as spherical cells, and
Ledingham has shown that when a leucocyte collides with a
bacterium, ingestion, death, and digestion of the bacterium
follows as a matter of course. They act just as we saw that
amoeba acted, and phagocytosis is just the same as any amoeboid
organism feeding. There seems no doubt but that they are
subject to chemiotaxis like other amoebae — chemical lowering
of surface tension applied unilaterally. Exposure to an electric
field causes the leucocytes to move towards the cathode. Certain
substances, so called opsonins, cause leucocytes to take up bacilli
more readily. This is due, as Ledingham has pointed out, to the
agglutination of the bacteria so that more are ingested at each
encounter. The clumping of the bacteria by an opsonin follows
the law of colloidal adsorption. It was once thought that the

155

156 THE ARMY FOR HOME DEFENCE

opsonin either stimulated the leucocyte or sensitised the bacterium,
making it more chemio-attractive to the destroyer (Fig. 23).

2. The kidneys are the great eliminating organs of the body.
Each of them is built up of a number of long unbranched tubes
closed at one end and, at the other, opening, along with several
other similar tubules, into a common collecting tubule. This
in turn opens into the pelvis of the kidney. The production of
urine goes on in these unbranched tubules, the collecting tubule
serving apparently only as a conduit to the pelvis. The closed
end of each tubule is invaginated within itself to form a Bowman's
capsule, where its epithelium lies in close contact with the capillary
tuft of blood vessels — the whole end- structure being called a
Malpighian corpuscle (see over, Fig. 28).

The kidney does not manufacture any of the constituents of
its secretion except hippuric agid, but merely eliminates unchanged
certain of the bodies brought to it by the blood.

It is not a mere filter, as the concentration of the constituents
of. the urine are vastly different from the concentrations of the
same substances in the blood. There seems to be a threshold
value for each and every substance in the blood which when
exceeded is at once reduced to its normal value by the elimination
of the excess by the kidney. It keeps the salt content of the blood
steady ; therefore, abnormal constituents will be eliminated in
their entirety. Not only is there an alteration in the relative
concentration of the various substances eliminated, but there is
in general a concentration of solutes. This concentration of
solutes necessitates the expenditure of energy.

The total energy used may be estimated, as in other glands,
by the consumption of oxygen. When the kidney is at rest, that
is, when little or no urine is being formed, very little oxygen is
consumed. During activity the amount of oxygen used increases
greatly. The following table taken from Barcroft and Brodie
shows this :

TABLE XXIV.

BESTING KIDNEY. ACTIVE KIDNEY.

Urine. Oxygen. Urine. Oxygen.

0 c.c. 0-57 c.c. 0-85 c.c. 2-95 c.c

0-07 0-64 0-34 1-14

0 1-66 1-53 5-58

0-05 0-04 2-1 0-09

0-04 0-03 2-8 0-09

Average— 0-03 0-4 1-52 1-97

Work per minute = 320 gram centimetres = 1650 gram centimetres.

WORK OF KIDNEY 157

During rest, the bulk of the oxygen consumed goes to the
maintenance of the kidney cells. On the average, the kidney
cells use about 0-04 c.c. of oxygen per gram per minute and
secrete about 0-003 c.c. of urine. During a period of increased
activity, the oxygen absorbed may rise to 0-28 c.c. per gram of
kidney per minute. Each c.c. of normal urine costs about 1 -05 c.c.
of oxygen over and above what is required for cellular use.

The CO 2 output varies very much even during rest and does
not always increase in proportion to the oxygen absorbed. It
may be that this metabolite is excreted by some other channel
than the blood stream.

Attempts have been made to correlate the total energy exchange
in the kidney with the work done, calculated from the alteration
in the 'osmotic concentration in the various urinary constituents.
The minimum work done in the formation of a litre of urine may
be calculated from the Hill-Donnan formula.

Work =R.T.[z (Cu log.5?) + SC6 - 2CM]

where R =the gas constant, T ^absolute temperature,

Cb =concentration in the blood of any constituent

a, b, c, etc.
and CM =its concentration in the urine.

This, of course, would only give the minimum work of the
kidney, even if we knew the concentration and degree of dissoci-
ation of each and every urinary constituent. It may be advisable
to call the student's attention to the fact that the energy used in
effecting any change is independent of the means by which that
change is effected. The work done, calculated from the Hill-
Donnan formula, is simply the minimum necessary to cause the
necessary change in the molecular concentration. It is independent
of any process and commits one to no theory (see Chap. III.).
Attention to this point will prevent many a ludicrous mistake.

Rhorer has calculated the work done by the kidney in concen-
trating urea and sodium chloride, and from his figures Cushny
considers that as the concentration of urea causes the consumption
of about 0 -7 cals., and similarly about 0 -05 cals. are used in con-
centrating sodium chloride (per litre of urine), it would not be an
overestimate to state that the production of a litre of urine entails
the expenditure of at least 1 -2 cals. This value, however, is but
a fraction of the chemical energy used as determined by the
oxygen consumption. We have seen above that for each volume

158 THE ARMY FOR HOME DEFENCE

of urine secreted, the kidney consumes about an equal volume
of oxygen. Assuming that the oxygen all goes to the oxidation of
glucose, then each cubic centimetre of oxygen will cause the
liberation of 0-05 cals. of energy from 0-015 grams of glucose.
That is, the intake of energy for the output of about a litre of
urine will be about 50 cals. There is thus a discrepancy between
the total energy absorbed and the apparent work done. Meltzer
and others account for this on the principle of the " factor of
safety."

Macallum dissents from this explanation. He adduces evidence
of a permanent low surface tension on the lumen-cell interface
and ascribes the excess of energy used to the continuous main-
tenance of this surface energy gradient. On the other hand the
difficulties to be overcome in measuring the fall in oxygen potential
in the blood passing through the renal vessels are very great, and
it may be that although the results are relatively accurate their
absolute values may be somewhat high. Barcroft and Brodie
estimate that about ^ of the total oxygen intake goes to the
kidney.

These workers have attempted, by means of estimations of
the oxygen intake of the renal cells, to tell when the kidney acts
as a passive filter and when the renal cells take an active part in
secretion. During filtration, they say, no osmotic work is done,
and therefore no energy is required and no oxygen used. Actual
renal activity will entail expenditure of energy and consumption
of oxygen.

A solution made up so that in composition it approximated to
blood minus the colloids was injected into a blood vessel of a cat.
Immediately there was an increase in the amount of urine secreted
but no increase in the amount of oxygen consumed — proof
positive of the non-participation of the renal cells. Now let us
see what has happened. The introduction of the saline fluid causes :

(1) A temporary increase in the volume of blood corresponding
to the amount of the fluid injected.

(2) An increase in general blood pressure and therefore an
increased pressure in the renal arterioles.

(3) An increase in the rate of the blood flow through the kidney
vessels.

(4) A decrease in the concentration of the corpuscles of the
blood. This results in a decreased oxygen carrying power and a
decreased viscosity.

(5) A dilution of the colloids of the blood.

OXYGEN CONSUMPTION OF KIDNEY 159

The saline diuresis may have been caused by all or any of these
concomitants. They may be eliminated one by one.

(1, 2, and 3) Increased blood volume, pressure and flow may
be considered together. Increase in pressure, etc., produced
mechanically without altering the concentration of corpuscles or of
colloids, certainly does produce an increased flow of urine, the
constituents of which have a concentration approximating to
that produced after injection of Ringer's solution. Barcroft and
Straube overcame this difficulty very ingeniously.

They previously removed a quantity of blood equal in volume
to the Ringer they were about to inject, thus keeping the blood
volume, etc., normal. The diuresis was produced as before,
entailing no extra oxygen consumption.

(4) The addition of blood corpuscles to make up the deficient
concentration made no appreciable difference in the flow of
urine.

(5) Knowlton introduced a colloid, gum acacia or gelatine into
the perfusion fluid so that the colloidal osmotic pressure of the
injected fluid was equal to that of the blood (25-30 mm. of Hg.).
This prevented the onset of marked diuresis, gelatine being more
efficient in this respect than gum acacia. Two causes may be
ascribed to the lower efficiency of gum : (a) its lower osmotic
pressure (5 per cent, gum has an osmotic pressure of about 12 mm.
compared with 5 per cent, gelatine whose O.P. is 23 mm. of Hg.
Bayliss recommends a 7 per cent, solution), (b) Gelatine has a
certain water holding power which is altered by treatment with
salts (see Imbibition, Chap. VIII.).

The conclusion that one would draw from this series of experi-
ments is that the passage of fluid and salts through the kidney by
filtration is controlled by the concentration of colloids in the
blood plasma.

Let us consider now a case where oxygen is consumed and,
presumably, work done. Sodium sulphate is a diuretic. It is
less diffusible than sodium chloride. A collodion membrane can
be prepared which will allow the chloride and not the sulphate to
pass through. Yet in the kidney the very reverse seems to take
place. Sodium chloride' acts very much like Ringer's solution,
and though after a large injection of NaCl the chloride content
of the urine rises, it does not materially alter the concentration
of the other solutes. On the other hand, the injection of Na2SO4
is followed by the secretion of a urine almost entirely a water
solution of the sulphate. Cushny has shown that, after the

160

THE ARMY FOR HOME DEFENCE

injection of a mixture of equal amounts of chloride and sulphate
of sodium, more sulphate than chloride is excreted, and while the
chloride elimination falls to normal in about an hour, at the end
of three hours the sulphate content of the urine is above the
normal. These results point to the sulphate as having a direct
action on the renal cells. It is known to be a cell irritant. The
question now is, does the kidney use up more oxygen during a
sulphate diuresis than during a Ringer diuresis ? Fig. 27, from
Barcroft and Straube, shows that the oxygen used increases as
the amount of urine increases. Therefore, one may say that the
sulphate diuresis entails energy expenditure.

The various factors dealt with above as concomitants of saline
diuresis may now be dealt with.

FIG. 27. — To show the relationship between the production of urine and the con-
sumption of oxygen by the kidney under the influence of Ringer-Solution and of
Sodium Sulphate. The black area indicates the amount of urine secreted, the thin line
the consumption of oxygen. (Barcroft.)

1, 2, and 3. Increase in flow of blood, etc., do not play a part.
Bainbridge and Evans showed that in a perfused living kidney,
sulphate diuresis may occur without any increase in volume.
Gottlieb and Magnus are inclined to think from a study of kidney
volume that circulatory conditions are less favourable for sulphates
than for chlorides.

4. The corpuscular concentration of the blood has as little effect
under sulphate as under chloride injection.

5. The introduction of a colloid after a sulphate made little
difference in the flow of urine, while it diminished it markedly
after a chloride injection (Knowlton).

In short, filtration plays but a small part here. No doubt
sulphates have a certain salt action but this is masked by their
strong secretory effect.

DIURESIS 161

Next, one wants to consider what cells the sulphate stimulates.
Cushny caused one kidney to secrete against a pressure of 30 mm.
Hg., leaving the other kidney free. During the height of a
NaCl -f Na2SO4 diuresis he found that for equal weights of urine
the obstructed kidney produced a fluid containing less chloride
and more sulphate than the kidney with unobstructed ureter.
The result of one experiment is appended.

Urine Gins. Cl. Gms. SO< Gms.

- (a) Unobstructed side - 24 O081 (H08

(b) Obstructed side 8 OOH O067

He supposed that the filtrate from Bowman's capsule must be
of identical composition in both kidneys, as both had the same
blood supply. Therefore, some change must have taken place
during the passage along the tubules. In one case (obstruction)
the fluid remained in contact with the lining cells for a prolonged
period, while on the other side free passage was allowed. Either
sulphate must have been added to the fluid during its stay in the
tubule or chloride and water absorbed. The two main modern
theories of renal action differ on this point. The experiment is
quoted at this stage to demonstrate that it is probable that
sulphate stimulates the cells lining the tubule, and that their
activity entails the consumption of oxygen and the expenditure
of energy.

It is very difficult to get reliable experimental results from the
kidney. Its nature, blood supply and position do not lend them-
selves to surgical interference, and the student ought to be keenly
critical of results which are produced under uncontrolled abnormal
conditions. Some facts, however, are obtainable and may be
detailed here shortly.

1. Function. No one doubts that the kidney as a cell-com-
munity has specialised in excretion. Every cell in the body has
the power of eliminating waste products. Most of these substances
find their way into the blood and those that are non-volatile are
voided by the kidney cells.

2. Structure.

The functioning parts seem to be structurally, two, (a) the
capsules, and (b) the tubules. Each capsule is lined by flattened
pavement cells supported by a delicate basement membrane.
The tubules are formed of columnar cells containing rows of
granules running radially towards the lumen and becoming finer
as they reach the striated border of the cell-lumen interface.

B.B. 11

162

THE ARMY FOR HOME DEFENCE

3. Blood Supply. The artery supplying the kidney breaks up in
the cortex into a large number of capillaries, each of which forms
a nodule or glomerulus invaginated in Bowman's capsule. The
capillaries again coalesce to form the efferent vessel, and this
again breaks into a number of capillaries entwining round the
tubules. After this the blood leaves the kidney by way of the
renal vein. That is, the blood is first supplied to the glomeruli
and then to the tubules.

4. Blood Pressure and Secretion. If the blood pressure is
lowered to between 40 and 30 mm. Hg. secretion stops. Starling

Afferent
vessel

Efferent
vessel

Glomerular
capsule

Capillary
tuft

Capsule

Tubule

FIG. 28.— Diagram of Malpighian corpuscle. (From Cushny's Secretion of Urine.)

measured the osmotic pressure of plasma and found it to be about
30 mm. Hg. It is generally inferred from this that unless the
blood pressure be greater than the osmotic pressure of the plasma
colloids no secretion will take place. Starling confirmed this by
obstructing the ureter so that the Hydrostatic pressure therein
was equal to 92 mm. Hg. when secretion stopped. The blood
pressure was 133. That gives a filtration pressure of 133 minus
the osmotic pull back of the colloids (30), i.e. 103, approximately
equal to the pressure in the ureter.

It is only fair to point out that, though modern theorists are
at one regarding the forced filtration of colloid free blood through
the capsule by means of glomerular pressure, i.e. heart work,

FUNCTION OF TUBULE 163

arguments against the supposition may be found. For instance,
the thin layer of epithelial cells is not strengthened in any way
to stand a large filtration pressure. Again it is doubtful whether
any such pressure exists in the glomeruli. Measurements are
given of general arterial pressure, say in the carotid artery. The
capillary pressure may be under ^th of this.

Simple diffusion through a membrane impermeable to colloids
will answer as well. Increase in blood flow instead of pressure
regulates the amount of dialysate. Furthermore, it is generally
stated that capsular fluid has the same composition as blood, less
the colloids. No direct evidence of this has been produced.
Theoretically, it is not probable. Colloids have not only the
power of holding salts by adsorption, but globulin especially holds
water and sodium chloride in solution. This was proved by
Milroy and Donegan, who showed that even when 250 c.c. of water
per hour passed the outside of the collodion membrane, a solution
of globulin (containing 0-15 per cent, nitrogen) in 0-15 per cent,
sodium chloride, lost practically no salt in six hours. Any salt
over the amount mentioned rapidly passes through the mem-
brane.

5. The bone of contention between the two modern schools is
the function of the tubule. One group holds that the tubular
epithelium absorbs water and threshold salts (i.e. salts of use to
the organism) from the fluid passing down the lumen. The other
group holds that salts are excreted into the lumen by its lining
epithelium. Much of the evidence produced is of equal value to
both sets of thinkers. Macallum's work, already mentioned,
showing that a constant low surface tension was maintained at
the cell-lumen interface rather weights the scales in favour of the
second view. There is also no doubt that experiments where
dyes, etc., are injected show that matter does pass, under these
conditions, from tubular capillary through the tubular cells to
the lumen of the convoluted tubule. On the other hand, there is
nothing to hinder the reverse process from taking place if need
arises. Consider the cell as middleman between blood and
secretion. Any abnormality in the blood would produce an
alteration in the cell, which, if it could, would pass on the change
to the secretion. Let us take a concrete example. Say there is
a deficit in NaCl in the tubular capillary. As a result, because
the cell Nad-tension must be equal to the blood NaCl-fe/mow,
salt will pass from the cell to the blood. Similarly, if the dialysate
or filtrate in the lumen has any NaCl at all, some of it will pass

164 THE ARMY FOR HOME DEFENCE

into the cell to make up the deficit. The experiments of Milroy
and Donnegan, already referred to, contain a series demonstrating
the passing of NaCl from a watery solution to one containing a
globulin.

Cushny's obstructed ureter experiment referred to above may
be interpreted in this light. Assuming, as he does, that the fluids
coming from both capsules are identical in both kidneys, then on
the obstructed side there is a fluid in prolonged contact with the
tubular epithelium, while on the other this fluid passes away more
or less rapidly. Take for granted, for the sake of a standard,
that the freely passed urine remains unaltered, that is, it is equal
to the glomerular filtrate on the obstructed side — e.g. 24 gms.
water, 0-08 gms. NaCl and 0-11 gms. Na2SO4. Sodium chloride
is more diffusible than sulphate and readily penetrates cells, there-
fore the positive tension of NaCl in the tubule will cause some
NaCl and water to enter the lining cells and so into the blood
stream. The sulphate, not being so diffusible, will not so enter
the cell. Thus the result would be a concentration of the urine
with a decrease in chloride, i.e. with sulphate steady ; chloride
would drop to a quarter =0-02 and water to a half =12 gms.
But no great energy need be expended here, only sufficient to
evaporate urine to half its bulk. The water and salt so secreted
into the blood stream would cause a further diuresis and so on.
On the other hypothesis, viz. that the sulphate is to a great extent
secreted by the tubule epithelium into the lumen, this difficulty
does not to the same extent arise.

In short, two factors may come into play in the secretion of
urine, (a) the adjustment of the cell to alterations in its environ-
ment, and (b) a mechanical dialysis of water and crystalloids in
solution through the capsule under sufficient pressure to wash
the actively secreted material through the collecting tubule and
on towards the pelvis of the kidney.

Other Glands of Elimination.

Of the physics of the other detoxifying glands, little or nothing
is known. The largest of these is the liver, but beyond the
isolation of enzymes, the physico-chemical mechanism has not
been to any great extent investigated.

The spleen is the burying-place of dead erythrocytes. It is a
modified lymph gland where the blood comes into intimate
contact with the spleen cells or " pulp." In structure it is a
spongework of fibrous tissue, in a capsule of the same material

EXCRETION 165

containing muscle fibres. These fibres contract and relax con-
tinuously, causing the whole organ to beat, like the heart, only
much more slowly. The spleen contracts slowly about once a
minute.

The intestine. Much waste matter is excreted by the large
intestine and here the physico-chemical mechanism is more
clearly indicated (see Chap. XXVII.).

Skin glands — sweat excretion will be considered under regula-
tion of temperature (Chap. XXXI.), and elimination by the lungs
under Transport (Chap. XXIII.).

CHAPTER XVI
THE CIVIL ENGINEERS OF THE BODY

CONNECTIVE TISSUE CELLS

" Which doth neatly declare how nature Geometrizeth and observeth order
in all things." SIR THOMAS BROWNE.

WE have just seen how increase in the size of an organism necessi-
tates increase in its complexity. Groups of simple naked cells
held together only by a pellicle resulting from surface adsorption,
would at the best form unwieldy organisms which would easily
be distorted beyond their elastic limit and so destroyed. Some
means of binding the component cells together to form a body
sufficiently rigid to withstand shock and yet possessing sufficient
mobility to seek its prey and avoid its enemies, is a logical outcome
of growth in size and in complexity. ' Moreover, if the animal is
to have an efficient muscular system under complete control and
able to be employed under all environmental conditions, some
absolutely rigid systems of portable levers and fulcrums must be
presupposed.

The Vegetative Tissues are those which support, bind together
and mechanically protect the other tissues of the body. They
may be divided into two groups — the epithelial tissues which
protect surfaces, and the connective tissues which bind together
.and support the various organs of the body.

I. Epithelium.

The shape of the cells forming a protective layer or series of
protective layers depends entirely on the resultant of the forces
acting on them. We may take it for granted that here as well
as with the single cell the agency of surface energy is obviously
of first importance.

The theory underlying the phenomena associated with the manifestations
of surface energy depends on the principle of Le Chatelier. Surface tension
is proportional to the area of the surface of contact. It is also proportional

166

EPITHELIUM 167

to a coefficient which is specific for each pair of substances provided tem-
perature is kept constant. It may be profoundly modified by the slightest
alteration in one or more of the physical or chemical conditions of one or
both of the phases forming the contact surface.

The form of a cell depends in great part on the magnitude of
the surface forces brought to bear on it. If it is surrounded by
exactly similar cells then it will tend to assume a more or less
spherical form. This is exactly what one finds in the centre of a
mass of soap bubbles or in the middle layers of stratified squamous
epithelium. The cells are not absolutely spherical in shape, not
only because the cells in mass are not absolutely similar but because
the cells have to fit the space. No vacant spaces occur. Now,
according to the principle of Le Chatelier, the surface energy will
manifest itself by tending to reduce the area of contact. Mathe-
matical proof has been given that the least possible area of contact
surface is attained when the partition walls meet together in
groups of three, at equal angles, i.e. at angles of 120°.

The outer and inner layers differ markedly in shape from one
another and from the middle layers. The outer layer is exposed
to air (skin) or to the free external fluids of the body (mouth and
gullet) on the one side, but is in contact, with cells on all other
sides. In addition, the outer surface is liable to undergo chemical
changes — oxidations, etc., and physical changes — adsorption, etc.
These again affect tension. The result is that the outer layers
are flattened and scale-like.

The inmost layer of cells is in contact on one side with the
structure on which the epithelium is laid and from which it
takes its origin and its nourishment. These younger cells are
more or less elongated in shape. Their form is governed by
certain forces in addition to those acting on the more central
cells, (a) It is obvious that the surface tension will be different
at that surface where the cell is in contact with a cell differing
from itself in structure and condition. These cells are in contact
on either side with similar cells, but above, they press against
fully grown spherical cells, while below they form interfaces with
the structure on which they lie and from which they derive
their nourishment, (b) These deeper cells are in process of division,
and, therefore, one must take into account the pressures of seg-
mentation and of growth (cf. Plant Cells), (c) The outmost
layer, away from the nourishing fluids of the body, undergo
keratinisation and resist the outwards push of young cells which
are thus put under stress. These various factors modify the shape
of the deeper layers.

168 THE CIVIL ENGINEERS OF THE BODY

II. Connective Tissues.

To appreciate the significance of the structure of the vegetative
tissues, due attention must be directed to their function. These
tissues are cell communities with an important but little studied
industry. They are the civil engineers of the body. The structures
they build are designed to stand stress and strain. Before
critically examining their handiwork let us study some elementary
engineering problems, so that we may the better understand the
phenomena of cell structures.

All the tissues of the body are more or less elastic. This
property includes (a) change of form under the action of some
force and (b) the return of the body to its original form when the
deforming force ceases to act.

The elasticity of connective tissues plays an important part in
the body. (1) It is a permanent resistance to permanent distorting
forces such as muscular tension and gravity. The elasticity of
the intervertebral discs, and of the ligamenta subflava, assists in
maintaining the erect posture of the body. (2) The form of
tissues is preserved against distortion by temporary forces
(Buffer action) and by intermittent forces. The elasticity of the
costal cartilages and of the ribs restores the chest wall to its
original position when the inspiratory muscles relax. (3) Inter-
mittent movement is transformed into a continuous movement
by transmission through an elastic medium (see circulation).
(4) Elasticity economises muscular work by coming into play
in the intervals between successive shocks (Marey).

The amount of elasticity is determined by ascertaining the force
necessary to change the form of the object to which the force
is applied, and the perfection of the elastic action, by the quickness
and accuracy with which the object returns to its former condition
on release from the mechanical force. Thus, when a strong force
is required to produce deformation of a body, that body is said
to be highly elastic. On the other hand feeble elasticity is over-
come by the application of a feeble force.

The force which is applied to a body is termed by engineers
the strain. The resistance to strain by a body necessitates the
postulation of a stress within the body. Hooke (1660) stated
that stress was directly proportional to strain. As a formula
this is known as Young's Modulus,

stress _T7 / .-, load on specimen 4- area of cross-section

strain alteration in length 4- original length

ELASTICITY 169

Let P be the pull, a the cross-sectional area, I the length of the
fibre, and e the elongation produced ; then :

stress P/a PI PI

—^=Y= -LJT=— or 6=-=^.
strain e/l ea Ya

Wertheim gives the moduli of the following substances in
grams weight per sq. cm.

TABLE XXV.

Bone - - 2304-1 x 106

Tendon 16341 x 106

Nerve 18-89 x 106

Muscle (resting) 0-95 x 106

Vein 0-87 x 106

Artery - 0-052 xlO6

The above values are given in order of increasing " perfection "
and decreasing " strength " of elasticity. The figure last given,
that of arterial walls, may be taken as substantially that of
elastic fibrous tissue.

Now strains may be applied in two ways. They may press
or they may pull. A pressing or crushing force is called a thrust
and a pulling or tearing force is called a stretch.

The stress set up in- the tissues is a function of the colloidal matter
which we have seen gives rigidity to the tissues. Water and
aqueous solutions of crystalloids are practically incompressible,
i.e. their volume elasticity is negligible. It is obvious that they
cannot have any elasticity of shape. The dispersion of less than
a gram of gelatine in a hundred cubic centimetres of water endows
the solution with rigidity.

The emulsoid gel has elasticity of shape, i.e. it returns to its
original shape after the application of a strain by thrusting,
stretching or bending provided it has not been strained beyond
the elastic limit.

A moment's thought will convince one that a quite different
structure is required to meet strains of the stretching and of
the thrusting varieties, (a) The material used in the building
of struts to withstand thrust must have a high crushing limit,
while that going to form ties requires high resistance to tearing.
In the following table drawn up by Sir Donald MacAlister, are
given the approximate values of the crushing and tearing limits
of some building materials.

170 THE CIVIL ENGINEERS OF THE BODY

TABLE XXVI.

AVERAGE STRENGTH OF MATERIALS

(in kga. per sq. mm.).
Material. Crushing Strength. Tensile Strength.

Steel - 145 100

Wrought Iron 20 40

Cast Iron 72 12

Wood (fibrous tissue) 2 4

Bone - - 1,3-16 9-12

A glance at this table is sufficient to show that a material
which may make a very good strut may make a very poor tie,
e.g. cast iron. A further factor has to be taken into account,
viz. elasticity. In the following table, borrowed from " Growth
and Form " by Prof. D'Arcy Thompson, are given the loads
which various fibres and various wires were found capable sus-
taining just at their elastic limit.

TABLE XXVII.

Stress at Elastic Limit , t o^t'etchm*
(grams per sq. mm.). per mille)

Secale cereale - 15-20 4-4

Lilium auratwn 19 .7-6

Phormium tenax 20 13-0

Papyrus antiquorum - 20 15-2

Molina coerulea 22 11-0

Pincenectia recurvata - 25 14-5

Stress at Elastic Limit , . o
(grams per sq. mm.). mt°

Copper Wire 12-1 1-0

Brass „ 13-3 1-35

Iron „ 21-9 1-0

Steel „ 24-6 1-2

Comparison of these figures with those of the previous table
will demonstrate the suitability of fibrous tissue to withstand a
stretching strain and yet retain a very high degree of elasticity.

The engineer plans his structures to give the maximum strength
with the minimum weight. Nature is equally economical.
Examination of the girders holding a roof will show that they are
of two shapes. Those running from wall to wall having a cross-
section like the capital letter "I." This girder is a tie and has
to withstand a stretching force. How has the engineer arrived
at this form ? Figure 29 represents a beam of square section.
When such a beam is loaded midway between its supports it
is slightly bent to give a concave upper surface. The upper

FIBROUS TISSUE

171

surface is compressed while the lower is stretched. There-
fore midway between the upper and lower surface lies a neutral
zone or line of no stress and in its neighbourhood the material
needs to have little strength. The girder maker can therefore
quite safely cut away the centre of his beam, leaving only the upper
and the lower surfaces, and of course some connection between
them which may be almost as thin as he likes without destroying

BEAM UNLOADED

BEAM LOADED

FIG. 29. — To show lines of compression (dark) and lines of tension (dotted) in a
loaded rectangular beam. The clear space between the strut-lines and the tie lines
indicates the neutral zone.

the strength. In other words, if the engineer can map out the
lines of stress or directions of compression and tension in the
loaded structure, all the manufacturer has to do is to see that these
lines lie in his material ; all the rest may be cut away.

By means of the truss (Fig. 30) the simple girder becomes a tie
between two struts. The horizontal member of the truss
undergoes tension only, while the sloping beams are compressed.

LOAD

FIG. 30. — A simple triangular roof truss.

Such a structure permits of the use of two kinds of material —
matter with a high tensile strength for the tie and matter able to
bear up under compression for the struts.

The two principal connective tissues are fibrous tissue and
cartilage and their modifications. Fibrous tissue is the main
binding medium of the body. It is derived from the mesoblast
of the embryo. The cells of the mesoblast, which are typical
spherical bodies lying close together, are gradually pushed apart
by a clear transparent jelly-like exudant from the cells. They

172 THE CIVIL ENGINEERS OF THE BODY

retain connection with one another by elongated processes giving
the whole tissue the appearance of an attenuated sponge filled
with a gel. The cells apparently secrete a colloid in a non-
hydrated form which then swells up to form a gel by the imbibition
of water. A model of this process may be made by adding water
to a mixture of gum and oil (Part II.).

As development advances the cells of this mucoid tissue become
longer and more spindle shaped (fibroblasts). The fibres are of
two classes, differing from one another in chemical constitution
as well as in physical properties.

(a) The white fibres are delicate transparent non-elastic fibres
arranged in bundles which do not branch.

(b) The yellow fibres are highly refractile elastic fibres which
branch and anastomose with one another. (Feebly but perfectly
elastic.)

The difference in their physical properties may be explained
by their different chemical constitution. The former are composed
mainly of a non-elastic protein collagen which readily takes up
water to form gelatine. The latter have in place of collagen
another sclero-protein elastin. Though difference in chemical
constitution may explain difference in physical properties, it does
not make any clearer how such a difference is brought about. If
elastic and non-elastic fibres existed side by side in definite
proportions one could easily mimic the formation by the separation
of two colloids from a colloidal matrix. But there is no such
definite proportion. Some tissues, e.g. tendons, are almost
entirely composed of white fibres, while elastic fibres predominate
in ligaments. In short, white fibrous tissue is found where
binding power alone is required, and where elasticity as well as
strength is desirable, there one finds elastic fibrous tissue. The
function of the tissue governs its form.

Just exactly how function governs form, one cannot at present
say. There is no doubt that external physical forces do affect
chemical actions and internal physical properties. Material
under strain acts quite differently from the same matter unacted
on by any force. An almost non-elastic block of rubber may be
endowed with considerable extensibility by being worked with.
The optical properties of glass can be altered by submitting it to
pressure. The electrical conductivity of selenium depends on
the amount of light falling on it. When more is known of the
laws governing matter in the colloidal state, then one may be
able to give a clear answer to this problem.

ADIPOSE TISSUE 173

In certain situations peculiar modifications of fibrous tissue are
found :

(1) Endothelium consists of flattened cells forming a membrane.
It differs from pavement epithelium by having the formed material
(colloidal exudate) between and not in the cells. Such endothelial
layers line all the serous cavities of the body and the lymphatics,
blood vessels and heart. A structure similar to endothelium may
be produced when an aqueous solution of, say, fatty acid is added
to a mixture of hydrated colloids of high concentration. Under
such circumstances the pressure of separation deforms the
originally spherical globules to form a beaded flattened honey-
comb.

(2) Fat cells. The experiments upon emulsoids detailed in
Chapter VIII. throw light upon the appearance of fat in the
cells. There is scarcely a tissue or fluid in the body that does
not contain fat in amounts in excess of the quantities that can be
dispersed in colloid-free water. Finely divided fat in cell proto-
plasm is comparable to an emulsion. It depends for its perma-
nence on the same factors as maintain fat in a finely divided form
in an aqueous dispersant, i,e. mainly on the presence, in the
tissues, of hydrophilic colloids. While the fat in the cells is not
ordinarily visible or even demonstrable by microchemical methods,
when an excessive amount of fat is present it may be seen in the
network of areolar fibrous tissue, especially round the smaller
blood vessels. Little droplets of oil at first appear and these
become larger, run together and coalesce, forming a single large
globule, distending the cell and pushing to the sides the proto-
plasm as a sort of capsule. Reference to the chapter on emulsions
will show that when the fat in an oil-in-colloid emulsion is increased
beyond a certain amount, the nature of the emulsion is changed
to colloid-in-oil. This latter emulsion differs from the former not
only in the visibility of the fat, but in this respect that the fat may
be stained (black) by osmic acid or (orange) by sudan III.

In starvation the fat gradually disappears from the cell leaving
the hydrated colloid, which also in time disappears and the cell
resumes its shape.

Apart from acting as a storehouse of energy, fatty tissue has
important mechanical functions. As we shall see later the layer
of subcutaneous fat serves as an extra garment protecting the
wearer from the too rapid loss of heat (Chap. XXXI. ). Then too,
fatty fibrous tissue has a considerable amount of resilience, acting
as a buffer protecting organs from external violence.

174 THE CIVIL ENGINEERS OF THE BODY

(3) Pigment cells. Fibrous tissue cells (and other cells) in
certain parts of the body (e.g. eye) may contain a pigment —
melanin. How this pigment is formed and what exactly are its
functions remain matters of conjecture. Chemically, melanin
is closely related with the melanoidins — dark pigments resulting
from digestion of proteins with hot mineral acids. They serve
(a) as light niters — preventing the passage of light through the
pigment cell. That is, the pigment absorbs energy. These
pigmented areas are nearly always found in places exposed to
light, and one may suppose that the incidence of strong light on
fibrous tissue may cause the formation of melanin from the cell
protein. Inorganic examples of the formation of light-absorbing
chemical compounds by the absorption of light will occur to the
student (cf. Silver Salts), (b) Their function is not only to
protect the underlying tissue from the harmful action of radiant
energy, but in many cases the pigment cells act as a transmitting
station— receiving the light stimulus and transmitting it to the
effectors. This dermatoptic function has been studied and
described by R. Dubois. Light falling on the pigment cells of the
epithelium of the siphon of Pholas, a mollusc, causes a reflex
retraction of the siphon. Observation under the microscope
has shown that the pigment cells in the skin of the frog contract
when light falls on them. The pigments of the eye and their
action in transmitting light stimuli will be dealt with in another
chapter.

Two modifications of fibrous tissue warrant separate treatment,
i.e. cartilage and bone. In lower animals and during the foetal
life of higher animals (as well as in certain situations in adult life)
rigidity is given to the body by cartilage. The function of
cartilage cells will be dealt with later under bone and lubrication.
Here it is sufficient to note that the peculiarity of this tissue is the
secretion of a homogeneous translucent gel which is tough and
elastic. This chondro-mucoid material is a mixture of at least
three colloids : ordinary protein, collagen and chondroitin. On
decomposition this latter substance yields substances of a carbo-
hydrate nature, glucosamine and glycuronic acid (cf. emulsions).

(4) The great supporting tissue of the body is calcified fibrous
tissue or bone.

(i) Development. Bone is formed by a deposition of calcium
salts in white fibrous tissue. Some bones which are more or
less flat, e.g. vault of the skull and the scapula, are formed
directly in fibrous tissue. This is the so-called intra-membranous

BONE

175

bone formation. The long bones are preformed in cartilage into
which processes of fibrous tissue find their way and they in turn
undergo calcification. All bone is developed from fibrous tissue.
The cartilage merely plays the part of scaffolding and is all
replaced by fibrous tissue before ossification takes place.

TABLE XXVIII.

RELATIVE STRENGTH OF THE LONG BONES.
(MAN AGED 31.)

Bone

Crushing Strength
(in kg. per sq. mm.)

Bending
Strength
(in kg.)

Shearing
Strength

Place of Rupture

Torsion*
(in kg.)

1st appear-

Complete

breakdown

crushing

Max.

Min.

Max.

Min.

Humerus

8-5

300

120

505

250

At ends

40

Radius

5-3

140

55

334

105

In middle

12

Ulna

5-5

— -

140

70

235

90

Anywhere

8

Femur

13

29

475

230

810

400

At the neck

89

Tibia

6-0

42

500

135

1060

450

At the lower

48

end

Fibula

3

—

55

21

61

20

In the middle

6

* Torsion applied to the extremity of the bone with a leverage of 16 cm. produced
a spiral fracture with the forces given above. (Amar.)

Practically nothing is known of the physical chemistry of bone
formation. Microscopic investigation suggests to our mind a
process similar to the formation of a honeycomb. The cells of
fibrous tissue detailed to build bone, i.e. osteoblasts, secrete
material containing a fair proportion of the phosphate and car-
bonate of calcium. It is known that the presence of a small
quantity of a colloidal complex alters the solubility of inorganic
matter. For example, calcium phosphate is more soluble in an
albuminous hydrogel than in water. This effect is even more
marked with calcium carbonate. If we presume the presence
of the salts of lime in the fibrous tissue cells, then, by the principle
of Willard Gibbs, they will be found in greatest concentration
where the surface tension is lowest, that is at the cell borders.
Another factor may be brought into play, viz., alterations in the
colloidal matrix. Albumin is broken down in the body to
proteoses and peptones. Now, experiment has shown that calcium
salts dispersed in an albuminous hydrogel are thrown out of
solution when proteoses and peptones appear in the gel. Further,
calcium phosphate is much more insoluble in proteose-peptone
solution than the carbonate, which is only slightly affected by the

176 THE CIVIL ENGINEERS OF THE BODY

change. It is significant that bone ash contains about 84 per cent,
of the former and only 7-6 per cent, of the latter salt.

One cannot say why cells in certain situations should have this
property of ossification. How far stresses and strains affect
the process is unknown. This we do know, however, that the
internal structure of the bones undergoes alterations to suit alter-
ations in the application of external forces.

(ii) Internal structure. In the earlier part of this chapter
mention was made of lines of stress, and it was there stated that as
long as sufficient strong material was present to include the course
of these lines it was an obvious economy to cut away as much as
possible of the matter in which there were no stress lines. If
these lines lie wholly in the structural material, then the danger
of rupture under shearing stress is eliminated. A shearing stress
is a force which tends to cause one part of a structure to slide over
another part. For example, a pile of coins compressed by a
force acting at right angles to the face of the coins effectively
resists the compression. If, however, the force were to act
obliquely to the face of the topmost coin, it would immediately
cause the pile to slip asunder. In other words, a shearing stress
is ineffective along the lines of maximum compression. The same
can be demonstrated for lines of maximum tension. For all other
lines, shearing stress has a definite value which is obviously at
maximum at 45°, i.e. half way between the lines of tension and
compression. Prof. Culmann, an engineer from Zurich, happened
to see some drawings by Prof. H. Meyer of the cancellous tissue
of the femur and at once noticed how the trabeculae of the bone
coincided with the lines of stress. He gave his class of engineering
students an outline of the femur and told them where the stresses
fell. He asked them to draw the internal structure which would
be necessary to meet these stresses. Fig. 31 shows the result.
Alongside this figure is given a diagram of the Fairbairn crane —
one of the best weight-lifting mechanisms known. The similarity
between the natural and the artificial structures is obvious. It
will be noticed that the lines of the trabeculae of the femur run
in two systems of curves. One system runs along the outer
convex side of the shaft, curves downwards as it opens out with
concavities downwards. The other system starts from the inner
side of the shaft and rises spreading outwards with the concavities
upwards. ' These systems correspond to the two kinds of lines
of stress present, e.g. tension and compression. The convex or
outer side has to resist tension, while the inner convex side,

STRESS LINES

177

overhung by the loaded head, is the compression member. The
head of the femur is a little more complicated than Fairbairn's
crane, in that the load is applied on two points, i.e. on the head of
the bone and on the great trochanter. This entails a division in
the distribution of the stress lines corresponding to the incidence
of the loads. In the compact tissue of the shaft the tension and
compression lines run parallel. The lines of stress are closest
together at the point of greatest strain, i.e. in midshaft. This
place has to be thickened to prevent the bone from snapping
(a walking stick pressed vertically against the floor breaks half-

INCIDENCE OF LOAD

FIG. 31. — To show the stress lines in the head of the Femur, A, in section, andjU,
on the surface. The central diaaram gives an idea of the location of the lines of
stress in the head of a crane. (After Culmann, Meyer and Dixon.)

way up). The central portion of the shaft has to bear no strain,
and therefore is hollow. It may be considered as a large mesh
between the tension and compression lines. In the cancellous
tissue the tension lines cross the compression lines at right
angles.

The same phenomenon may be seen in any bone which undergoes
tension and compression. It is very noticeable in the human foot,
especially in the heel bone (calcaneus). It is roughly triangular,
having three bearing surfaces. The upper surface is compressed
by the weight of the body applied from the ankle bone. There-
fore, compression lines start from it and run downwards. The
lower surface rests on the ground, i.e. has to bear an upward

B.B. 12

178 THE CIVIL ENGINEERS OF THE BODY

thrust, and so compression lines run upwards from this surface
to meet the compression lines from the upper surface. The third
or anterior surface is in contact with the bones of the arch of the
foot and transmits the ankle pressure forwards to them. This
gives rise to a second system of compression lines running obliquely
forwards. These two systems correspond to the two beams in
Fig. 30. Now the application of a load at the apex would
cause the beams to diverge at their lower ends if they were
not tied together by the girder. So tension lines must exist
to prevent the fracture of the bone between the two systems
of compression lines. These tension lines will be seen in Fig. 32

•TIBIA

CAPSULE

FIG. 32. — Diagram showing some of the stress lines in the arch of the foot. (After
Hermann Meyer.)
(The diagram is not strictly a section, and the stress lines are not all in one plane.)

forming curves with their concavities upwards and orthogonal
to the compression lines. It will be noticed that these ties are
closer together at the arch of the bone between the two struts,
i.e. at the point where fracture is most likely to take place. Just
above this point no stress lines can be .seen, i.e. there is a neutral
region. Examination of the bone makes clear the fact that in
this neutral zone trabeculae are almost entirely absent. Where
there are no stress lines it would be a waste of material to build
struts or ties. As Sir Donald MacAlister puts it, " any mass
of bone put there would not ' row its weight,' and it has been
' turned out '."

LUBRICATION 179

This internal structure is altered to meet alterations in the
incidence of stress. For example, during the first twenty years
of life when the body is growing and the bone lengthening, constant
alterations in internal and external structure have to be made.
The unnecessary parts are decalcified and the fibrous tissue under-
goes alteration. During this process some of the fibrous tissue
cells become enlarged and multinucleated. Histologists call
these cells osteoclasts. The remaining fibrous cells afterwards
become bone marrow. An adjustment to meet altered conditions
may be seen when a bone is broken and allowed to set badly, so
that its parts lie somewhat out of their former positions. Tension
and compression lines do not now coincide with the trabecular
structure. It has been shown by Wolff and others that in a few
weeks, not only has an alteration taken place at the seat of fracture
but the entire trabecular system, right to the ends of the bone, has
undergone remodelling to suit the new incidence of forces. More
recent work on bone grafting has amply demonstrated the
astonishing rapidity with which reconstruction of the trabecular
meshwork takes place. One must remember that in spite of its
rigidity, bone is plastic. Physical chemists have proved that
when an inorganic constituent separates as a definite phase from
a colloidal matrix, the new phase is at first liquid. We may,
therefore, infer that the new trabeculae are more or less liquid
when formed. The action of force upon them will tend to set
them along the lines of that force, e.g. straws set along the direction
of the wind. They are practically " carded " into position.
There they are in equilibrium and will tend to " solidify " in
that position.

(5) Lubrication. Certain cartilage cells have a peculiar function,
that of acting as a lubricant between rubbing surfaces. One of
the most worrying problems of the engineer is to prevent " heating
up " of moving surfaces. This he attempts to do by interposing
a fine uniform film of oil between surfaces where friction is apt
to take place. The particles of the oil film act as microscopic ball
bearings over which the moving surfaces slide with the minimum
of friction. The motor cyclist knows how essential it is to have
the right amount of the right grade of oil in the right place. In
spite of all precautions however, " seizing " does take place. The
film of oil is rubbed away just at the point where it is most required.
Only one machine has, as yet, been designed which has a perfect
lubricating system, and that is the animal body. In the body
there are many rubbing surfaces. At joints, bone works against

180 THE CIVIL ENGINEERS OF THE BODY

bone : tendons run like Bowden wires in sheaths, and yet the
healthy animal body moves noiselessly and without " heating up "
or " seizing " at any speed.

(a) Joints. There are, counting great and small, 230 joints
in the human body varying in degrees of magnitude and import-
ance. The ends of the two opposed bones in a joint are coated
with a thin layer of cartilage. This cartilage, in the adult, is
what is left of the scaffolding of bone. As we have seen, it is
elastic and acts as a resilient buffer. The surface is always
covered, in health, with a film of synovial fluid.

This synovia is kept in place by being enclosed with the joint
in a flaccid membrane or joint capsule (Fig. 32). The synovial
fluid results from the destruction of the cartilage cells on the
rubbing surface of the joint. In this way the supply of lubricant
is absolutely automatic. The more the joint surfaces move on
each other, the greater is the destruction of the cartilage cells and
the more plentiful is the supply of synovia.

Two other points require our attention, (i) How is the supply
of synovia kept up and (ii) what happens to the waste fluid,
(i) The cartilage is constantly, like epithelium, growing. The
young cells take their origin in the layer next to the bone and push
their way up towards the outer surface of the articular cartilage.
Every cell destroyed to form synovia has its place taken by a cell .
from the layer below and so on. Growth and destruction exactly
balance one another, (ii) The waste synovia is drained into the
blood stream through certain warty structures which project into
the crevices of the joints.

In chronic rheumatism the cartilage cells fail to form synovia.
The articular cartilages become dry and leathery and the joints
may be heard creaking as they move. The underlying bone,
stimulated by the unaccustomed friction, thickens and throws out
gnarled processes. The supply of lubricant has failed, and until
someone discovers just how cartilage can be converted into
synovia and what controls the process nothing can be done to
prevent " seizing " of the joints.

(b) Tendon sheaths. Muscles are attached to bone by sinews
or tendons and these cordy structures work in sheaths. The
inner surface of the protecting sheath as well as the outer surface
of the tendon is endowed with a lubricating substance similar to
that of the joints.

There is one outstanding point of interest about the lubrication
system of the body and that is its nourishment. As far as is

TENDON SHEATHS 181

known all other cell communities draw the material they require
for maintenance and growth from the blood stream. As we shall
see in the sequel the red blood corpuscle performs the duty of
oxygen carrier. No red corpuscles enter articular cartilage — the
gristle in joints is pearly white. One can only suppose that the
plasma which reaches the cells from the rich vascular network
on the surface of the underlying bone, carries dissolved in it
sufficient oxygen to meet the needs of these lubricant-formers,
as it carries sufficient protein, carbohydrate, etc., for their use.

The formation of cartilage and of synovia and of the relation
of these two substances to bone and to fibrous tissue is a rich
field for investigation. Certain colloidal phenomena will occur
to the student as suggestive of an explanation, but absolutely no
definite physico-chemical facts can be brought forward as accept-
able evidence.

CHAPTER XVII
THE INTELLIGENCE SERVICE

NERVE CELLS

" The messengers that preserved a communication between the soul and the
outward members." BERKELEY.

IT is obvious that in an organised conglomeration of cell bodies
like the animal body some means of rapid communication must
exist between one organ and another. Without it, rapid co-
ordinated movement by the body as a whole would be impossible.
This work is accomplished by the nervous system. Two entirely
different systems of rapid communication exist in the body. One
runs to and from the body wall and has to do with the relation
of the body to its environment. It belongs to the army of defence
and defiance. The other system of rapid communication conveys
messages to and from the industrial communities.

Embryologically, communication between an inland cell and
the outer world is effected, in the first instance, by an ingrowth
of the external epithelial covering. That is, messages are passed
on to the inmpst cell by a file of cells, detailed for this service.
These cells are, to begin with, all structurally and functionally
alike (neuroblasts). Later, some few of them send out long
processes towards the surface and towards the organ. These
processes end in branching twig-like structures called dendrites
(Gr., a tree), through which they seem to be able to pass on
stimuli to one another. The name synapse (Gr., a junction), is
given to the juxtaposition of the dendrites from the processes of
two nerve cells. The cell with its processes is called a neuron.
(See Fig. 33.)

The second system of nerves, that of the viscera, is formed of
neuroblasts which have migrated towards the organ from the
neural canal. They all pass through at least one ganglion or a
plexus which acts like a local headquarters or exchange.

182

NATURE OF STIMULUS 183

Some nerves have a sheath or coat composed of un saturated
fatty acids and lecithin (and allied lipoids). The function of
this medullary sheath has not been discovered. It is formed
from separate cells, but it must retain some connection with the
nerve cell, as it dies and disintegrates when dissociated from it.

1. Structure. The neuron, like any other cell, is a colloidal
fluid mass. This may be demonstrated by examination of the
living nerve by means of the ultra-microscope, when particles in
Brownian movement will readily be seen. Some of these particles,
at times, clump together to form local large aggregates which
again dissociate. Further, Carlson has shown that nerves may
be stretched without altering their efficiency, judged by rate of
conduction of an impulse. Macallum states that alterations in
surface tension can be detected especially in the growing nerve.
It has been urged by Gothlin that, as a nerve is doubly
refracting to a slight extent just like muscle it must have a
similar composition. These facts all go to prove that nerve is
of a liquid nature.

2. Its function is to conduct. One cannot lay too much stress
on the fact that it does not conduct an impulse originating outside,
as a telephone wire conducts current from a battery. The battery
is an integral part of the neuron.

3. The nature of the stimulus seems immaterial. Mechanical,
electrical or chemical stimuli all cause the nerve to propagate the
same kind of impulse. Furthermore, the excitatory result of the
propagated impulse depends not on the nature of the " trigger "
stimulus but on the nature of the effector mechanism to which
the nerve goes. That is, stimulation of the sciatic nerve by
electrical, mechanical, thermal or chemical means always causes
contraction of the gastrocnemius muscle ; stimulation of the
vagus nerve by any means always slows the heart, stimulation
of the chorda tympani causes the salivary glands to secrete, no
matter how the stimulation is effected. Miiller's law of the
specific energies of the senses states that, by whatever manner
a sensory nerve is stimulated, the resulting sensation is always
that produced by this nerve when stimulated by its specific
" trigger." That is, the receptor organ of a sensation-carrying
nerve controls the sensation received. To be concrete, stimulation
of a taste nerve (chorda tympani), by pinching, sudden heating
or cooling, electrical shock or chemical reagents, produces the
sensation of taste and nothing else. Similarly, stimulation of
the eye nerves by any means makes one see light. Keith Lucas

184 THE INTELLIGENCE SERVICE

states that there is no evidence to show that the nerve impulse
is in any way modified by the nature of the stimulation. Each
nerve has however a rhythm of its own — an optimal rate of
stimulation known as Waller's " characteristic," which is similar
to the natural rate of incidence of energy.

No difficulty should be experienced in grasping this idea,
especially if an electrical model be kept in mind.

Consider an electrical circuit such as shown in Fig. 33s. C is
a galvanic cell or electrical unit where chemical energy is converted
into electrical energy. Fl and F2 are wires connecting C to M, an
electric machine, and a key closes the circuit, (a) It does not
matter how the key is closed, the current passing along F will be
the same, and (b) the manifestation of the current will depend

NERVE CELL

^ DENDRiTES IN

A

// CONDUCTING AXON RZCEIVING AXON Y

v RECEPTOR, ORGAN

CONTACT KEY

FIG. 33. — A. Diagram of a unit of the nervous system compared with B.
B. Electrical Model to illustrate Miiller's Law and the " All or Nothing " hypothesis
as explained in the text.

on the nature of M. If M is a telephone receiver, the closing
of the key will cause a sound to be heard, if M is an incandescent
globe, light will be seen, if M is a motor, motion will result, and
so on. The electrical energy of C can thus be converted into any
form of energy by an appropriate M. Further, the magnitude
of the force applied to the key makes no difference to the
magnitude of the resulting manifestation at M. That depends on
the energy set free by the cell and on the resistance of the circuit.
Of course the receptor must be modified to suit different kinds
of stimuli. A telegraph key or a bell push is a convenient kind of
mechanism for closing a circuit mechanically, but it would not
answer for electrical, thermal, sound or light vibrations. Special
means for closing the circuit have to be devised to suit different
kinds of stimuli. For example, sound waves may be caused to
close an electrical circuit by microphone, e.g. telephone trans-
mitter.

ALL OR NOTHING

185

The neuron may be likened to this electrical model (Fig. 33A).
C is then the nerve cell, F the process or nerve fibre, the key the
receptor mechanism and M the effector mechanism. A second
circuit of the nature of a telephone relay could be added to the
first, S being an electro-magnet which closes the second circuit
when the key of the first is depressed (Fig. 34).

S may be termed the synapse joining an effector and receptor
neuron. The student will notice that there is no material con-
tinuity between the two neurons and that no energy passes from
one to the other.

4. " All or nothing." It is obvious in the electrical model that
connection is either made or not made. The energy available

.REACTING OR. EFFECTOR. UNIT

RECEIVING OR RECEPTOR UNIT

£

KEY

ELECTROMAGNET

FIG. 34. — A. Diagram showing a receiving (JVi) and a reacting Neuron (NJ, each
with dendrites at its extremities, and their connection to one another through a
Synapsis (S).

B. Electrical Model to illustrate the functional continuity of two neurons.
See text.

from Cj is a fixed quantity independent of the energy used to
close the circuit, and similarly the energy in the system of which
C2 is the cell is independent of the energy used in the electro-
magnet S.

It is true also for the nervous system that the maximum motor
effect is produced, if any effect is produced at all. It is a case of
" all or nothing." Nerves are, however, made up of several more
or less parallel neurons, and some of these may be stimulated
and some may not. As each nerve fibre activates one muscle
fibre and as each muscle fibre responds to the activation by a
maximal contraction, the result is that the extent of contraction
depends on the number of muscle fibres which shorten and which,
in turn, depends on the number of nerve fibres implicated.

5. Temperature coefficient of the nervous impulse. When a
length of nerve is cooled its power to conduct an impulse is

186 THE INTELLIGENCE SERVICE

decreased ; that is, nerve-conduction has a positive temperature
coefficient. It was pointed out by Van't Hoff that the velocity
of chemical reactions is increased twofold or more for each ten
degrees in temperature, i.e. the temperature coefficient for chemical
reactions is greater than 2. On the other hand, the temperature
coefficient for physical processes is less than 2. The temperature
coefficient (i.e. ratio of velocity of propagation of nervous impulse

at (T+10)° to its rate at T° = — -=-0 — ^ has been estimated

v at T )

by Lucas as approximately 1 -8. This value has been proved to
be right by later workers. Therefore, physical factors are involved
in the propagation of a nervous impulse. This does not exclude
chemical reactions but tends to show that the process is not
purely chemical.

6. Decrement of the nervous impulse. If a length of nerve is
cooled, not only does the velocity of the propagation of the
impulse suffer diminution but there seems to be a diminution in
the intensity of the impulse as well. If the degree of cold is
sufficient, or if the length cooled is extensive, the impulse may be
stopped entirely. If, however, any of the impulse is propagated
through the cooled region into a normal piece of nerve it seems to
recover its full intensity and velocity. Lucas compares this
phenomenon to the transmission of fire along a fuse of gunpowder.
If a section of the fuse is slightly damp, the rate of burning as
well as the heat evolved will be decreased but will recover as
soon as combustion starts on a dry section. Narcotisation of a
nerve by ether, alcohol, cocaine or other drug has a similar effect
to cooling.

7. Refractory period. The passage of a nervous impulse
produces some change in the physico-chemical state of the nerve,
so that it is followed by a state during which its function is de-
pressed. A certain time must elapse between each nervous
impulse. This spare time is called the refractory period, during
which a stimulus will not receive normal treatment. The length
of the period varies inversely as the temperature. The refractory
period may be divided into three stages : (a) The absolutely
refractory period when no strength of stimulus is effective.
(b) During the relative refractory period the nerve is recovering
and will respond to stimulus stronger than usual, (c) The
supernormal stage follows during which subnormal stimuli are
effective. Two factors at least come into play to cause the
refractory period, viz. alterations in excitability and alterations

REFRACTORY PERIOD 187

in conductivity. These two factors go hand-in-hand, i.e. the
nerve is non-irritable and offers a resistance to the passage of the
impulse sufficient to swamp it during the absolute refractory
period ; during the relative refractory period the nerve steadily
recovers its irritability and its conducting power ; while the last
period is one of supernormal irritability and conductivity.

8. Summation. If a second stimulus be applied to the nerve
during the third refractory period, it will give rise to an impulse
which will meet with less resistance in its passage along the nerve.
Now, if the first impulse be subminimal, i.e. insufficient to cause a
manifestation of energy in the motor mechanism which the nerve
supplies, then the second impulse if it be propagated along a
nerve during the supernormal period may cause the motor end-
organ to act. Such a phenomenon is called summation.

9. Fatigue. Nerve fibres can apparently act as conductors of
the nervous impulses for very long periods without showing any
signs of fatigue. It is generally said that nerves cannot be
fatigued. While this is true of the conducting power of the fibre
it is not applicable to the neuron as a whole. (1) The nerve cell
loses something in the process. Granules which are apparent while
the cell is at rest diminish slowly during activity. Then (2)
changes take place at the synapses, the junction between neuron
and neuron, and also at the " end plate " or junction between
nerve fibre and organ. These potential junctions lose their power
to cause the impulse of one neuron to act as stimulus to the next
neuron or to the end organ. They become fatigued.

10. Metabolism. This leads one to infer that the energy
exchanges during the conduction of impulses are small. The
amount of oxygen used is negligible and it is doubtful whether
a measurable amount of CO2 is produced. There is no doubt of
the need for oxygen for the metabolic changes of the nerve cell,
but the extra amount necessitated by the passage of a nervous
impulse has not been estimated. It must be very small indeed.
Ingenious methods have been devised by Waller and by Tashiro
for the measurement of the CO2 evolved during activity, but so
many uncontrolled sources of error enter into the experiment
that many physiologists hesitate to accept their figures as repre-
senting the actual amount of oxidation undergone. One must
bear in mind that an increased output of CO2 does not necessarily
mean a simultaneous absorption of oxygen or a corresponding
liberation of energy. The CO2 may be due to liberation of CO2
from solution in the surrounding tissue by the heat of the stimulus

188 THE INTELLIGENCE SERVICE

or from carbonates from the action of acids set free electrolytically
by either the impulse or the stimulus.

Hill has found that when a nerve is placed in a carefully shielded
thermopile, the registering galvanometer shows unaccountable
fluctuations corresponding to temperature changes of the order
of 7 xlO ~6 of a degree C. The passage of some 600 impulses does
not produce any larger variation. Therefore, the amount of
heat produced must be less than this figure.

11. Electrical changes during conduction. Just as in muscle,
so in nerve, an electrical wave accompanies the nervous impulse.
The part excited becomes electro-negative to the rest (see Muscle,
p. 143), and this negative wave passes along the nerve in the
direction of and at the same rate as the nervous impulse. It is
followed by an electro-positive wave of greater potential. The
combined electrical changes are thus said to be diphasic. The
electrical wave complex must not be confused with the nervous
impulse. In other words the nervous impulse is not electrical
in nature but produces localised differences of potential in nerve
as it passes. The rate of conduction of an electrical impulse along
frog's nerve is about 300 metres per second, while the nervous
impulse travels at about 30 metres per second.

12. Electrical changes during stimulation. This wave of
negativity is the current of action (or of injury) of the nerve.
It may be made manifest as indicated in Fig. 35, by rapidly

s*^ p\ Polarising

ft\ \

a/ -* k

/
* Positive polarisation

FIG. 35. — Diagram to show direction of the positive polarisation current, due
to a break excitation at the anode.

connecting anodal and cathodal parts of a nerve through a gal-
vanometer. If a .stimulating current is passed through a section
of a nerve so that a is the positive electrode and k is the negative
electrode, then on breaking the circuit and connecting a and k
through a galvanometer (circuit 2), it will be obvious that a
current flows momentarily along the nerve from a to k, i.e. in
the same direction as the previous stimulating current. This is
sometimes termed a positive polarisation current.

Under certain conditions it is possible to observe an electrical
change in the opposite direction after cessation of the stimulus

POLARISATION CURRENTS

189

(Fig. 36). Nerve consists of a conducting core of electrolytes
and colloids surrounded by a sheath enclosing electrolytes and
colloids. The passage of a constant current through this mass
gives rise to certain physico-chemical changes in core and in

">, Polarising

v
VV^,^ Negative polarisation.

Fia 36. — Diagram to show direction of the negative polarisation current.

sheath. These electrolytic and polarisation changes set up a
current which tends to restore equilibrium (back E.M.F.). This
is negative polarisation.

The changes that take place may be studied conveniently by
means of a model (Fig. 37). A platinum wire, forming a con-

Glass tube

containing 0-6% Na Cl.

Pt.wire

1 — j

c d a b e

FIG. 37. — Apparatus for imitating the polarisation phenomena in medullated nerve.

ducting core, runs inside a glass tube filled with cotton wool
soaked in 0-6 per cent, sodium chloride solution.

The points a and b are connected to a battery and the extra-
polar points c and d, e and / are led off to galvanometers. On
the passage of a current from a to b it is found that an extra-polar

FIG. 38. — Diagram to show polarisation at the surface between conducting core
and electrolyte sheath.

current is flowing from c to d and from e to / (cf. Fig. 40). The
cause of these extra-polar or, as Du Bois-Reymond called them,
electrotonic currents, is to be. sought in the movements of the
dissociated salts in the sheath. Opposite the anode (Fig. 38),
the positive ions are concentrated on the surface of the core.
This causes opposition to the passage of the primary current and

190

THE INTELLIGENCE SERVICE

also sets up currents in the electrolytic fluid (Fig. 39) from a to b,
b to c, etc. These currents are indicated by the galvanometers.

FIG. 39. — Diagram^tolshow polarisation currents in a medullated nerve or in a
polarisation model.

Emphasis must be placed on the fact that these electrotonic
currents are absolutely distinct from the nerve impulse as well
as from the wave of negativity or current of action and the
current of injury, (a) The former have a much greater velocity
than the nerve impulse, as indicated by the wave of negativity

$ 1

a 6 j

!>-*(!

[ c d

— *•

x y

— ».

f 1

, s~2\ >

f \

„ /T\ j

6' 6*

FIG. 40. — Diagram showing electrotonic currents. P, polarising circuit ; Ol, G1,
galvanometers.

(see 11 above). (/3) Their E.M.F. may attain a value twenty-five
times that of the current of injury. (7) The direction in which
electrotonic currents flow depends entirely on the direction in
which the primary current is flowing, reversion of the latter
leading to reversion of the former. Action and injury currents
always maintain a flow in the nerve from a stimulated or injured
part to a resting or uninjured portion of the nerve.

CHAPTER XVIII
OUTPOSTS OF THE INTELLIGENCE SERVICE

(a) GENERAL AND INTRA-COMMUNAL RECEPTORS

" By mine eye, I do not know that I see, or by mine ear that I hear, but by
my common sense who judgeth of sound and colours." BURTON.

THE Cabinet which controls a nation has to set up machinery
to provide itself with two different kinds of intelligence. First
it needs to know how its orders are being carried out by the
civilian population as well as by the military. The internal or
interoceptive intelligence staff is distributed among the factory
workers, along lines of transport and in the various effective units
of the army. Their duty is to report on the conditions in their
sector. Before a shortage of raw material has become so marked
as to cause an outcry from, or mayhap, a strike of some part of
the population, the outposts of the intelligence staff should have
their report " on the wires." Very little is known of how this
work is carried out. It is mere guesswork to say that slight
alterations in the physico-chemical condition of the material
surrounding a nerve-ending is sufficient to cause stimulation of
the nerve. The other intelligence staff operates on matters
outside the organism. They are exteroceptors.

Sherrington divides interoceptors into two groups :

1. General, which have to do with sensations of hunger or
thirst, nausea, respiratory and circulatory sensations, sexual
sensations, visceral pain, etc.

2. Special consists of end organs for taste and smell. These
are distinctly chemical in their actions and are the chief extero-
ceptors in many animals (see later).

To these fall to be added a group with a double function :

3. The somatic proprioceptors, which are situated in the muscles,
tendons and joints, and are concerned with the production of
the muscle sense. To this group also belong the organs which
have to do with the sensations of equilibrium. Not only have

191

192 RECEPTORS

the proprioceptors to report on work done but it is obvious that
they have to form some opinion of the relation of the organ to
its environment. They thus have a function closely allied to
that of the true exteroceptors which are stimulated under ordinary
conditions by forces outside the organism.

It is a good thing to bring in the aid of comparative physiology
when about to study a fresh group of organs. One may then see
how various modifications arise and how the simple undifferentiated
cell becomes specialised and fitted to act as a receptor for one
particular form of external energy. Time and space do not permit
such a digression here, but the student would do well before
reading further to revise his knowledge of the comparative zoology
of the sense organs.

The sense organs or receptors may be considered as points of
least resistance, gateways through which the manifestations of
external forces may reach the internal structures. They are
much more than that. They are specialised outposts of an
intelligence service which pick up minute alterations in the energy-
complex of the environment, make a rapid but incomplete analysis
of these changes, and send in a report to departmental head-
quarters for complete analysis and transmission to headquarters.

Only by specialisation can efficiency be obtained. The
organism is subject to stimulation from various forms of energy
which may be classified into vibratory and chemical.

A. Vibratory Energy.

1. Mechanical impacts received by the tactile corpuscles of the
skin. They may be perceived as separate stimuli even when
they arrive as rapidly as 1552 per second.

2. Slow vibrations especially in air are received by the ear. The
human ear may be stimulated by vibrations ranging from 16 to
40,000 per second. Practice may extend this range.

3. Rapid vibrations in ether.

(a) Radiant heat. Vibrations with a frequency of between
3 billions and 400 billions per second stimulate the temperature
receptors of the skin.

(b) Light. The retina is capable of receiving as light, ether
waves, the frequency of which varies between about 400 billions
and 800 billions per second.

B. Chemical Energy.

The various chemical stimuli to which the organ is exposed,
have receptors in the skin, giving rise to sensations of pain or

MULLER'S LAW 193

discomfort, and in the special end organs to those of taste and
smell.

The function of the receptors is to receive that form of energy
for which they are fitted and to transform that energy into nervous
energy. We have previously shown that any one form of energy
can be transformed into any other form. It has been found
convenient, for instance, to calculate all forms of energy mani-
festations found in the body in heat units — calories. Nervous
energy may be electrical energy. It can readily be demonstrated
that any form of energy can be converted into the electrical form.

As receptors for these various manifestations of energy we have
the so-called five senses. That is, five different means are
employed for the purpose of orientation, viz. touch, hearing,
sight, smell and taste. These senses come into contact with the
external forces through the skin, ear, eye, nose and tongue.
But some of these are composite end-organs. The skin, for
instance, includes not only touch corpuscles but the end-organs
for pain and temperature. The ear not only analyses sounds but
contains organs for the static and dynamic senses. In all there
are over twenty different kinds of receptors and sense-organs in
the body.

Specific irritability. In the preceding chapter we have alluded
to Miiller's law of specific irritability, and an electrical model
was discussed as illustrative of this idea. A very little con-
sideration suffices to show (a) that the same physical stimulus
applied to various receptors will give rise to absolutely different
sensations and (/3) that different physical stimuli applied to the
same end-organ, if they arouse any response at all, give rise to
the specific sensation of that organ or to pain.

Stimulus and Sensation. Each receptor has a certain functional
inertia and will not respond to stimulation until the energy of
the stimulus has reached a minimal value which is specific for
each receptor and for each form of stimulus. This threshold
value is lowest, as has been said above, for the form of stimulation
specific for that organ. Once this value is gained, the resulting
sensation bears a definite relationship to the incident stimulus
until an upper limiting value has been reached, after which
increase of stimulation is of no avail. In fact, fatigue rapidly
sets in, and the resulting sensation is sub-maximal (Fig. 41).

Touch is the sense by which mechanical force is appreciated
Mere contact is gentle pressure, a greater amount of applied force
causes a feeling of resistance referred to the skin, a still greater

B.I!. 13

194

RECEPTORS

amount evokes a response from receptors in the muscle, while
pain results from great pressure. The total number of tactile
corpuscles (excluding those on the head) has been estimated as
500,000. These are not evenly distributed over the skin but are
more numerous and more sensitive on certain of the more mobile
parts of the body, e.g. tongue and fingers. The degree of sensitive-
ness of the skin may be determined by some form of aesthesiometer

ST/MULUS

SENSATION

LATENT PEKJOD
OR. THRESHOLD

FIG. 41. — Diagram to show relationship between stimulus and sensation.

(say a pair of compasses) by means of which one may measure
the smallest distance at which impress of the two points may be
perceived as two distinct sensations. The following table gives
the activity of the discriminating sense for different parts of the
skin :

TABLE XXIX.

Tip of the tongue

Third phalanx of finger, volar surface -
Red part of the lip

Second phalanx of finger, volar surface
First phalanx of finger, volar surface -
Third phalanx of finger, dorsal surface
Tip of nose

Head of metacarpal bone, volar surface
Ball of thumb -
Ball of little finger
Centre of palm -
Dorsum and side of tongue ; white of lips ; meta-
carpal part of the thumb

Third phalanx of the great toe, plantar surface -
Second phalanx of the fingers, dorsal surface
Back -
Eyelid
Centre of hard palate -

Millimetres.
M

- 2-2-3

4-5

- 4-4-5

- 5-5-5

6-8
6-8

5-6-8

- 6-5-7
5-5-6

- 8-9

9

11-3
11-3
11-3
11-3
13-5

SENSITIVENESS 195

Millimetres.

Lower third of the forearm, volar surface 15

Tn front of the zygoma 15-8

Plantar surface of the great toe 15-8

Inner surface of the lip 20-3

Behind the zygoma 22-6

Forehead, - 22-6

Occiput 27-1

Back of the hand 29-8

Under the chin - 33-8

Vertex 33-8

Knee - 36-1

Sacrum, gluteal region 44-6

Forearm and leg 45-1

Neck - - 54-1

Back of the fifth dorsal vertebra ; lower dorsal

and lumbar region 54-1

Upper arm ; thigh ; centre of back 67-7

.Middle of the neck 67-7

The intensity of the contact sensation is increased in a mechani-
cal way by the presence of hairs, because they act as levers on the
tactile corpuscles. The whiskers of the cat render the touch
points of the jaw very sensitive in this way, being able to detect
even slight air currents.

Absolute sensitiveness as indicated by a sense of pressure is
generally determined by finding a minimum pressure necessary
to evoke a minimal sensation. Below is given the weight in
grams which could just be detected when placed on various parts
of the skin. The values given are normal values (Table XXX.).
Practice may increase the discriminating point. Every one
knows how a blind man " sees " with his fingers.

TABLE XXX.

Tongue and nose 2

Lips - 2-5

Finger-tip and forehead - 3

Back of the finger 5

Palm of the hand, arm and thigh 7

Forearm 8

Back of the hand - 12

Back of the leg and shoulder - 16

Abdomen • 26

Sole of the feet 28

Back of the forearm 33

Gluteal region 48

In a similar way one could map out the hot and cold spots and
the pain spots in the skin. They vary in distribution but not in

196 RECEPTORS

the same order as the pressure spots. For example, the minimum
perceptible difference of temperature in degrees centigrade is given
in the succeeding list for various regions :

TABLE XXXI.

Back - 0-9

Leg - 0-6-0-2

Thigh 0-5

Back of foot 0-4

Cheek 0-4

Temple - 0-3

Palm of hand - 0-4

Back of hand - - 0-3

Arm - - 0-2

Taste and smell are the chemical senses (partly chemical and
partly physical) and are closely allied to touch. To stimulate the
end organs of chemical sense, the substance must be in a fine state
of division and capable of going into solution in the fluid on the
superficies of the sense organ. In spite of much research, little
more can be added to this brief statement. Of the two senses,
taste is the more limited as well as the less useful. Four kinds
of taste may be discriminated, viz. sweet, salt, acid and bitter.
Flavours are odours and really give rise to an olfactory sensation.
Smell is the ancestral chemical sense and may be classed, especially
in the lower animals, as a distance receptor. In civilised man,
this sense, unless rendered acute by training, is merely vestigial.

The areas of nasal mucosa associated with this perceptive
mechanism, are small rectangular strips in the upper part of each
nasal cavity, just above the superior turbinate bone. In ordinary
respiration, air does not pass directly over the olfactory mucous
membrane, but some air diffuses backways through the posterior
nares (Fig. 42). This is important for the preservation of the
sense. The receptor neurons have retained their primitive con-
dition of cell body in the epithelium itself (Parker). They are
rapidly fatigued and readily destroyed. Now, by their situation
in a backwater they do not come directly into contact with high
concentrations of odoriferous substances and, furthermore, air
attains body temperature and moisture and is freed from suspended
particles (dust, bacteria, etc.) before reaching the sensory surface.
The physical details of the mechanism for the perception of smell,
that is, for the conversion of chemical into nervous energy, have
not yet been brought to light. The sense is extraordinarily
delicate. Mercaptan, in as low a concentration as 0*0000000004

SMELL

197

gram per litre of air, can be detected. Training renders the sense
more acute. The working chemist relies on his sense of smell to
a great extent to help him in the identification of compounds.
The tea blender and the wine expert can detect very slight differ-
ences in " flavour.'*

It is worth while noticing that receptors all depend for stimu-
lation on the existence of an alteration in external energy. This

OLFACTORY BULB

OLFACTOR.Y EPITHELIUM

OPENING OF

EU5TACHIAN

TUBE

HYOID

THYREOID CARTILAGE-'^,.
EPIGLOTTIS-'"

VOCAL CORD''

ARYTENOID

CESOPHAGUS

TRACHEA •'

FlO. 42. — Antero-posterior section through nasal fossae, mouth and neck. The
arrows show the direction of the air currents during inspiration.

is specially marked in the case of this ancestral chemical sense.
Our accustomed environment presents no stimulus. Air has no
smell and water no taste. The introduction of a trace of foreign
body alters the energy content of the environment and stimulation
follows. It is a common experience to find that people do not
experience sensations that have, for the time being, become
permanent in their environment. A room may be stuffy to an
incomer but quite comfortable to the tenants. The physiological

198 RECEPTORS

chemist works in an atmosphere which causes his visitor to choke
and splutter, but the introduction of a new odour, say ammonia,
is at once perceived and produces instant action.

Hunger is a sensation which must be regarded as primitive and
basal. It is not our business to analyse the feelings of hunger,
but to consider the mechanism by which the lack of nourishment
is signalled to consciousness. The evolution of knowledge of this
sensation is largely due to Prof. Cannon, whose book on the subject
should be read by every student. There can be no doubt that the
feeling of hunger is closely allied to pain.

" The sensation of hunger is difficult to describe, but almost
everyone from childhood has felt that dull ache or gnawing
referred to the lower mid-chest region or epigastrium, which takes
imperious control of human actions. As Sternberg has pointed
out, hunger may be sufficiently insistent to force the taking of
food which is so distasteful that it not only fails to rouse appetite
but may even produce nausea. The hungry being gulps his
food with a rush. The pleasures of appetite are not for him — he
wants quantity rather than quality, and he wants it at once

Hunger may be described as having a central core and certain
more or less variable accessories. The peculiar dull ache of
hungriness referred to the epigastrium is usually the organism's
first strong demand for food ; and when the initial order is not
obeyed, the sensation is likely to grow into a highly uncomfortable
pain or gnawing, less definitely localised as it becomes more
intense. This may be regarded as the essential feature of hunger.
Besides the dull ache, however, lassitude and drowsiness may
appear, or faintness, or violent headache, or irritability and rest-
lessness such that continuous effort in ordinary affairs becomes
increasingly difficult. That these states differ much with
individuals — headache in one and faintness in another, for,
example — indicates that they do not indicate the central fact of
hunger, but are more or Jess inconstant accompaniments. The
' feeling of emptiness,' which has been mentioned as an important
element of the experience, is an inference rather than a distinct
datum of consciousness and can likewise be eliminated from
further consideration. The dull pressing sensation is left, there-
fore, as the constant characteristic, the centra] fact to be examined
in detail " (Cannon).

Cannon and his colleagues have definitely proved that the
sensation of hunger is caused by strong contractions of parts of
the alimentary canal. As we shall see later when dealing with

HUNGER 199

transport (Chap. XXVII. ), there are certain definite movements of
the alimentary canal designated as peristaltic associated with the
forward transference of the contents of the canal. In the absence
of any content other than gaseous, the cavities of the stomach,
lower oesophagus and upper intestinal region, at least, are almost
obliterated. This wave of contraction precedes the sensation of
hunger and may be regarded as the cause of it. Carlson and his
students, who were fortunate in having a subject with a per-
manent gastric fistula, have confirmed Cannon's work and carried
it further. They have shown that the local contraction is a sign
of a general state. According to Carlson and Luckhardt the
blood of a fasting animal, if injected into the vein of a normal
animal, is capable of producing in the latter, contraction of the
gastric muscles, an effect which does not occur when the blood
of a well-fed animal is injected.

The significance of this phenomenon is plain. In Cannon's
words :

" The very condition which causes hunger and leads to the
taking of food is the condition, when the swallowed food stretches
the shortened muscles, for immediate starting of gastric peri-
stalsis. In this connection, the observations of Haudek and
Stigler are probably significant. They found that the stomach
discharges its contents more rapidly if food is eaten in hunger
'than if not so eaten. Hunger, in other words, is normally the
signal that the stomach is contracted for action ; the unpleasant-
ness of hunger leads to eating, eating starts gastric digestion and
abolishes the sensation. Meanwhile the pancreatic and intestinal
juices as well as bile have been prepared in the duodenum to
receive the oncoming chyme. The periodic activity of the
alimentary canal in fasting, therefore, is not solely the source of
hunger pangs, but is at the same time an exhibition in the digestive
organs of readiness for prompt attack on the food swallowed by
the hungry animal."

CHAPTER XIX
OUTPOSTS OF THE INTELLIGENCE SERVICE

(6) DISTANCE RECEPTOR FOR SOUND
THE EAR

" A clue to the structure of a machine lies in the discovery of the purpose
for which it was designed and the manner in which its various parts are co-ordinated
to secure that end. That is eminently true of the ear." KEITH.

THE ear is a modified touch receptor. In the lower invertebrates
it consists of hair-like appendages, either on the free surface or
in a depression, more or less protected. In the higher vertebrates
it is a much more complicated structure. The human ear may
be considered as composed of three structural elements, viz. :

External ear — collector and conductor of sound to the middle ear.

Middle ear — converter of air vibrations to a to-and-fro moveT
ment of a piston-like lever and the accentuation of these
movements.

Part of internal ear — transformer of mechanical pressure, via
hydraulic pressure, into nervous energy.

1. External ear. The structure of this presents no outstanding
points of physical interest. It consists of the pinna and the
external acoustic meatus at the end of which is the membrana
tympani or eardrum (Fig. 43).

(a) The pinna is a flattened horn presenting irregularities of
surface. If these undulations are filled in with wax or if the pinna
is awanting, the quality of sounds is altered and difficulty in
localising sound is increased. This may be due to a differential
reflection of tones by the pinna, e.g. it may reflect a fundamental
tone more strongly than the partial or vice-versa.

(b) The external acoustic meatus is a curved tube about 21-26
mm. long. Its function is two-fold, (i) On account of its shape,
secretion, and hairs (at orifice) it protects the delicate tympanic
membrane from draughts and dust, and from the incursion of

200

MIDDLE EAR

201

insects. This is its main function, (ii) The sound waves are
conducted by reflection from the walls without loss of intensity,
and directed almost perpendicularly on to the drum which lies
at an angle of 150° to the axis of the canal.

2. Middle ear. The mechanism found in the middle ear con-
verts vibrations in air into vibrations in fluid by means of mem-
branes and a series of levers. It consists of an air-filled cavity
hollowed out of the petrous part of the temporal bone. It is
separated from the external ear by the tympanic membrane, and

11

FIG. 43. — Diagrammatic view of auditory organ. (After Schafer.)
1, Acoustic nerve ; 2, internal acoustic meatus ; 6, canalis media of cochlea ;
9, vestibule containing lymph ; 12, stapes ; 13, fenestra cochleae (rotunda) ; 19,
incus ; 18, malleus ; 17, membrana tympani ; 16, external acoustic meatus ; 14,
auricle or pinna ; 23, Eustachian or auditory tube.

from the internal ear by the membrane closing the round window
and by a disc of bone — the foot of the stapes, which along with the
membranous collar surrounding this bone makes a fluid-tight
packing or gland filling the fenestra ovalis, the oval opening into
the internal ear. Between the drum and the stapes lie two bony
levers — the malleus and the incus. «.

(a) Membrana tympani. This structure is fixed in a frame
of bone which is almost circular (vertical diameter 10 mm. ; hori-
zontal diameter 8-5 mm.). Although it is not more than 0-1 mm.

202 THE EAR

thick, it is constructed of three layers. On the outer surface
there is a layer of epithelium protecting the membrane proper
which is of fibrous tissue and is covered on the inner side by a
layer of mucous membrane. The fibres of the fibrous layer are
arranged partly circularly and partly radially — the circular fibres
being most marked near the rim. To the inner surface is attached
the handle of the malleus, the first of the chain of three auditory
ossicles. This attachment to the malleus, which is pulled inwards
by the tensor tympani muscle, gives the tympanic membrane the
form of an eccentric funnel opening outwards. The membrane
is highly elastic and responds very readily to very slight variations
in the pressure of the air waves entering the external ear. The
peculiar form of the membrane contributes to its value as a sound
transmitter. In the first place, it acts synkinetically, i.e. moves
passively with the vibrations of the sound-waves. It begins and
ends its vibrations synchronously with the impact of the sound
vibrations. There is no latent period, no waiting for a summation
of impulses before it can get into its swing, having no swing to get
into. It does not continue to vibrate after the sound vibrations
have ceased. It is dead-beat. Further, it does not vibrate
sympathetically to any special overtone present in a compound
tone reaching the ear. This is brought about by (i) the damping
effect of attachment to the ossicles and (ii) by the dragging inwards
at the point of attachment (umbilicus). On this account the
fibres vary in tension as well as in length, so endowing each bit
of the membrane with a different period of vibration resulting, in
toto, in an aperiodic membrane. It is obvious that such a property
is valuable in rendering hearing distinct. In the second place
the arched sides of the membrane act as a lever of the 1st class.

" As the outward curvature of the radial fibres is slight, each
fibre may be regarded as the long arm of a lever, while the handle
of the hammer is the short arm. This mechanism secures that a
slight pressure of the air corresponding to a sound wave, exerts
a considerable force upon the malleus. To aid in understanding
the mechanism, it will be easier to consider, first, the effect of
pressure upon a single radial fibre. The fibre may be regarded as
inextensible and slightly curved outwards ; hence variations in
pressure on the convexity of the curve will cause the degree of
curvature to change, while the length of the arc will remain the
same.

In other words, the radius of the arc and the chord of the arc
will change, while the length of the arc remains constant. But

EFFICIENCY OF MEMBRANE 203

the length of the arc may be regarded as the length of a radial

fibre ; hence , / X

/=2r siirV —

where I = length of fibre, r = radius of the circle of curvature, and

X chord of the arc Z, because - is the sine of half the angle at

2r

the centre belonging to the arc /. This equation may also be

written / Z

X = 2r si

Now, if we subtract the (each side) from /, we have

I . (I

— sm( -

2r \2r

which gives the difference between the chord of the arc and the
curve. But as the curve is very slight, r is large in comparison
with I and the divisions become rapidly very small as the sine
in the formula is developed by the involution of its arc. Hence

I I 1

sm — —

2r 2r 6

and from this the preceding equation becomes

Again, let s be the distance of the centre of the arc from the
centre of the chord. Then the degree of curvature is found by
the equation

r - s I

r 2r

so that s = r - r cos —

2r

=r (1 -cos — ).

2r/

C°2r2

r ( i / 1

we have s=r\l- 11- - (

2 \2

1 /2
that is s=-~ (2)

8 r

204 THE EAR

Now, eliminate r from equations (1) and (2), and we obtain

This equation gives the amount of shortening of the chord
which occurs when the curve of the arc is increased ; that is to
say, it gives the extent to which the two ends of the fibre are
drawn together. Now, if s, the displacement of the middle of the
fibre, be very small in comparison with I, then I - X obviously
becomes very small in comparison with s. Conversely, the very
small increase in the magnitude of Z-A must cause a relatively
great increase of s ; that is to say, it must cause a relatively great
displacement of the centre of the fibre.

Again, if t = the tension of the fibre, p = the pressure on each
unit of its length, and r = the radius of curvature, then

t=pr,

and the forces which act upon both ends of the fibre must be
equal to the pressure which acts upon the diameter of the semi-
circle through a width equal to that of the fibre (Helmholtz).
Therefore

2t = 2pr.

Hence the greater the radius of curvature, the greater will be
the alterations in tension of the fibre caused by alterations in
the pressure of the air. Further, as the radial fibres are those
which are attached to the malleus, it is evident that the variations
in the tension of the fibres cause movements of the bones when
sound-waves strike the drum-head. Thus a very small change
of pressure in the air causes a considerable change in the tension
of the fibres ; and further, in accordance with the laws regulating
the action of the lever, as the force which fibres exert upon the
handle of the malleus increases, amplitude of movement of that
bone diminishes. In this way, the special form of the drum-head
secures a maximum of efficiency for tones of the feeblest intensity"
(M'Kendrick).

Briefly, energy applied to the membrane is passed on to the
handle of the malleus diminished in amplitude but with increased
intensity.

(b) Ossicles. The three bones of the middle ear, — the malleus,
the incus and the stapes, — stretch across the tympanic cavity
forming an articulated chain of levers, so that every normal move-
ment of the tympanic membrane is transmitted by the stapes to

TYMPANIC OSSICLES

205

the fluid of the internal ear. The Malleus, or hammer, is about
18-19 mm. long, and has an average weight of 23 mgms. It
consists of a thickened rounded head and a long handle — the
manubrium, which is attached to the tympanic membrane, the tip
of the handle reaching the umbilicus. Near the insertion of the
head and handle rises a bony process — the processus gradlis or
processus Folianus, which projects forward and is continued by a
ligament, the anterior ligament by means of which the hammer is
anchored to the wall of the tympanum. There is also a shorter
protuberance, the processus brevis, which presses against the edge
of the upper surface of the drum. Three other ligaments are
attached to the malleus, the external ligament, binding it to the

SUPERIOR. LIGAMENT OF MALLEUS

BODV OF INCUS

SHORT PROCESS e,
POSTERIOR LIGAME
OF INCUS

= -r=M. TENSOR.

LONS PROCESS OF INCUS — '

EMtNLtfTIA PYRAMIDALI5
TO WHICH THE TENDON OF
M. SMPtDIUS 15 ATTACHED

FIG. 44. — Diagram of the left Membrana Tympani and Chain of Tympanic Ossicles
seen from the medial aspect. _.

The line A— B is the axis of rotation of the malleus and incus. The dotted line
represents the line of leverage applied from the handle of the malleus to the posterior
ligament of the incus. The stapes lies almost at right angles to the plane of the
paper.

external face of the tympanic cavity, the superior or suspensory
ligament, attaching the top of the head to the roof of the cavity,
and the posterior ligament. These ligaments prevent the malleus
from rotating in any other axis than a horizontal one whose line
passes through the head of the malleus and the anterior ligament
(Fig. 44). The posterior surface of the head of the hammer fits
into the saddle-like hollow in the anterior surface of the body of the
anvil-bone or incus. This is a larger bone than the malleus, weigh-
ing on the average 25 mgms. The body of the incus is drawn
out on its posterior side to a process — the short process, which
is attached by a ligament to the posterior wall of the tympanic
cavity, forming one end of the malleo-incal axis mentioned above.
Almost at right angles to the short process, the inferior surface of

206 THE EAR

the incus tapers down to the knob-like os orbiculare, forming the
long process.

The os orbiculare articulates with the knob on the top of the
stirrup bone or stapes. This bone, a flattened stirrup arch,
weighing only about 3 mgs., is set almost at right angles to the
long process of the incus. Its oval footplate is attached to the
margin of ihefenestra ovalis by a short stiff membrane, the annular
ligament.

Muscles of middle ear.

Two slender muscles are attached to the ossicles :

(i) The stapedius is inserted into the knob at the head of the

stapes and is attached to the posterior wall of the tympanic cavity,
(ii) The tensor tympani arises from the inner wall of the cavity,

passes outwards and upwards above the Eustachian tube, to be

inserted in the upper part of the handle of the malleus.

Function of the muscles.

The tensor, on contraction, draws the handle of the malleus
inwards, and so, as its name implies, increases the tension on the
tympanic membrane. This decreases the natural period of
vibration of the drum, and this makes it more sensitive to high
tones, and better fitted to adjust its vibrations to rapid changes
of phase. Paralysis of this muscle impairs hearing.

The stapedius prevents the footplate of the stapes from having
purely a piston-like action in the fenestra ovalis. Its line of
traction (Fig. 44), which is almost parallel to the long axis of the
oval window, causes the footplate to move on the posterior annular
ligament as on a hinge. Contraction of this muscle thus draws
the anterior end of the footplate outwards.

These two muscles are therefore antagonistic ; simultaneous
contraction balances the ossicles and regulates the degree to
which the perilymph of the internal ear is displaced. Further,
the tension of the two muscles prevents a slack engagement
between the ossicles. If the bearings were not kept together with
sufficient force, slipping, knocking and loss of power would ensue.
This state of equilibrium is absolutely necessary if the system of
membranes and ossicles is to move in immediate response to the
slightest alteration in air pressure.

Before going into the mode of action of the ear bones, a pressure
equalising device comes up for consideration. As has just been
said, perfect equilibrium of vibrating parts is necessary for perfect

207

transmission of energy. One can therefore realise how important
it is for there to be some open communication between the tym-
panic cavity and the atmosphere. By means of the Eustachian
tube, communication is established between the middle ear and
the pharynx and through the latter with the exterior, and so both
sides of the tympanic membrane are kept at atmospheric pressure.
Normally, it is closed by an arch of cartilage which surrounds the
lower end. The tensor palati muscle is inserted in one side of this
arch, and when this muscle contracts during the act of swallowing
(Chap. XXVII.), it draws down and flattens the cartilage and so
opens the tube. Occlusion of the tube by mucus or by inflam-
mation of the throat, isolates the air in the middle ear. The air is
gradually absorbed by the tissues, pressure is thus reduced and the
drum is sucked inwards. This increased tension in the membrane
makes it less responsive to sound. Temporary deafness caused
by a rapid alteration in external air pressure (e.g. rising in an
aeroplane ; descending in a submarine, or diving in a bell or suit,
entering a caisson, etc.) is immediately relieved by movements of
swallowing. The Eustachian tube is also the drainage tube to the
middle ear, preventing the accumulation of mucus (Figs. 42 and 43).

Mechanism of the middle ear.

The function of the mechanism is to transform the alternate
condensations and rarefactions of air, which we call sound, into
a series of hydraulic movements of the fluid in the internal ear.
Direct observation has shown that the ear-bones form a chain
of levers which together conduct the vibrations incident on the
drum to the foot of the stapes.

A. Let us look first at the mechanism of the levers. In Fig. 44
is given a schematic sketch of the ossicles illustrating their lever
action. The axis on which the malleus and incus together turn
is represented by the line A-B passing from the tip of the short
process of the malleus to the tip of the short process of the incus.
A movement inwards of the manubrium will cause the head of
the malleus to swing outwards, carrying with it the upper part
of the incus and so moving the long process of the incus in the same
direction as the manubrium. This movement is directly trans-
mitted to the stapes. The chain of bones, therefore, acts as a bent
lever whose fulcrum is at a,* the power arm being represented by
the dotted line and the load arm by the line i- a. According to

* a = junction of dotted line with A - B ; i = tip of long process of incus ; p = point
of application of power, i.e. tip of manubrium mallei.

208 THE EAR

Helmholtz, the distance p-a is 9-5 mms., and i-a is 6-3 mm.
The movement at i therefore will be only f of the movement at p,
but will have 1| times the intensity. We have now to consider
the transmission of this power to the foot of the stapes. If x - y
represents the range of the tip of the incus, c-d the distance from
c, the hinge (lower annular ligament) to d the centre of the foot
of the stapes, and c - r, the distance from the tip of the incus to
the lower end of the stapes, then the range of motion of the centre

i np _ fit \ y/ If* /7\

of the foot of the stapes will be - ^-— - which, according

to the scale of a drawing given by Helmholtz, would give a leverage
of about 2-1.

So that, on the whole system of bones there is a leverage of
about 3-1. This theoretical value is, however, reduced by the
friction of the levers and by the damping effect of the air filling
the internal ear. It has been estimated that half the force is thus
dissipated.

Three further points about the chain of ossicles claim our
attention. Firstly, by the position of the axis, a - b, the mass of
the heads of the hammer- and anvil-bones are above the line,
while the lever arms are below the line on which the bones rotate.
This keeps these two bones suspended in equilibrium. Secondly,
there are tooth-like processes on the surface of the hammer which
engage with the body of the anvil, enabling each to move the other
in the to-and-fro movements of the drum. In the case of unusually
sudden alterations in air-pressure, e.g. a blow on the ear, these
processes slip over each other and prevent damage to the internal
ear. Thirdly, by the way in which they are hung on opposing
ligaments, and controlled by opposing muscles, they form a kind
of balance wheel which is very sensitive to the transmission of
power in small vibrations. Its efficiency in this respect is derived
from the fact that the elastic forces balance one another in the
mechanical centre of the system, and so practically the whole
power applied to the drum is transmitted to the foot of the stapes.

B. The pressure in the internal ear is reinforced not only by
the system of lever transmission but by the relative sizes of the
membranes at either end of the chain of ossicles. The area of
the tympanic membrane is about twenty times the area of the
fenestra ovalis. This means that, keeping the total power constant,
the power per unit area is increased twenty times. This is
augmented by the intermediate leverage (correcting for air-
damping, friction, etc.), which we have seen has been estimated

INTERNAL EAR 209

as not less than l£ - 1. This would give a total increase of effective
pressure of at least 30 - 1 . ( Wrightson puts the value as high as
60-1 on the assumption that no slip occurs at the malleo-incal
joint, etc.)

3. Internal ear. The internal ear is a somewhat complex
cavity in the petrous part of the temporal bone. Two separate
organs are housed in this cavity, viz. the labyrinth by which
equilibrium is maintained, and the cochlea.

The Cochlea is a tube, 20-30 mm. long, which takes two and a
half spiral turns round a conical bone, the modiolus through the
centre of which the auditory nerve passes. The cochlea is divided
into three portions by means of (a) a spiral lamina of bone ex-
tending from the modiolus about f across the tube, and (b)
joined to the walls of the tube by two membranes, Reissner's
and the basilar membrane. The former is a thin layer of cells
and separates the vestibular duct from the intramembranous
middle duct. The part below the basilar membrane is called the
tympanic duct. The fenestra ovalis closes the vestibule — the
swelling at the wide end of the scala vestibuli — while the membrane
of the fenestra rotunda does similar service to the lower duct, the
scala tympani. The two ducts are united at the apex of the
cochlea by an irregular crescentic aperture called the helicotrema.
This opening has an average area of 0-15 sq. mm.— markedly less
than the sectional area of the terminal part of either scala. These
scalae are filled with a fluid, perilymph, which obviously, because
of the fenestra rotunda, is normally under atmospheric pressure.

Chief interest in the internal ear lies in the structure of the
scala media and its contents (Fig. 45). It is triangular in section,
having for base the basilar membrane which separates it from the
tympanic duct ; the long side is composed of Reissner's membrane,
which divides it from the vestibular duct. The short side is
separated from the outer wall of the ojsseous cochlea by a vascular
layer (stria vascularis], laid on and in a continuation of Reissner's
membrane, which in turn is placed on the spiral ligament, or pad.
Roughly, the cubic capacity of this duct is about a quarter of
that of the scala tympani and about a third of that of the scala
vestibuli. It is filled with endolymph, a fluid similar to the peri-
lymph of the rest of the cochlea. No communication exists
between the scala media and any other part of the cochlea. There
is a narrow tube, the canalis reuniens, which runs from this duct
to the saccule — part of the organ for maintaining equilibrium.

The reason for the attention that has been directed to the scala

B.B. 14

210

THE EAR

media is that the auditory nerve, which runs down the modiolus,
enters only this scala, passing along the basilar membrane and
ending in dendrites among the hair-cells of the organ of Corti.
This structure is a development of the epithelium lining the tube.
It is set on the basilar membrane at its junction with the limbus
laminae spiralis, and consists of four essential elements. (1)
Certain columnar cells with short stiff hair-like processes pro-
jecting from their free border, the hair cells, to which pass, as we

FIG. 45. — Vertical section of the first turn of the human cochlea ((?, Retzius).

s.v, scala vestibuli ; s.t, scala tympani ; D.C, scala media ; sp.l, spiral lamina ;
n, nerve fibres ; l.sp, spiral ligament ; str.v, stria vascularis ; m.t, membrana tectoria ;
b.m., busilar membrane ; h.i, and h.e, internal and external hair cells ; R, section of
Reissner's membrane ; t.C, tunnel of Cortl ; I, limbus laminae spiralis.

have just said, branches of the cochlear nerve ; (2) elongated
strengthening cells between the hair cells, cells of Deiters, the
peripheral processes of which join together to form a network
through which the hair-cells project (membrana reticularis) ; (3)
stiff short fibres set one against another in the form of an arch ;
and (4) an exceedingly delicate membrane attached to the upper
surface of the spiral lamina, and lying over or fixed to both the
outer and the inner walls of Corti's organ.

The arch of Corti, which lies just outside the single row of inner
hair cells, is composed of a row of inner " rods," shaped like ulnar
bones, attached by their terminal end to the basilar membrane, and

RESONANCE THEORY 211

iitting on to the heads of the outer " rods." The latter resemble
swans' heads and necks, the backs of the heads fitting into the
hollows of the inner " rods."

The mechanism of the internal ear.

It is obvious that every movement of the stapes is communi-
cated by the perilymph to the membranes of the scala media, from
them to the endolymph, and so to the organ of Corti. There is
also no doubt about the hair cells as being the final instruments
for the transmission of the impulses to the nerve. Two main
theories are held as to the mechanism of the cochlea, viz. the
resonance theory and the displacement theory.

Resonance Theory.

Helmholtz considered that the only mechanism capable of
analysing compound vibrations was a system of resonators. In
his own words, " Suppose we were able to connect every string of
a piano with a nerve fibre in such a way that this fibre would be
excited and experience a sensation every time the string vibrated.
Then every musical tone which impinged on the instrument would
excite in the ear, as we know to be really the case, a series of
sensations corresponding to the pendular vibrations into which
the original motion of the air had to be resolved. By this means,
then, the existence of each tone would be exactly so perceived, as
it is really perceived by the ear. The sensations excited by the
higher particles under the supposed conditions, would fall to the
lot of different nerve fibres, and hence be produced perfectly,
separately and independently. Now, as a matter of fact, later
microscopic discoveries respecting the internal construction of
the car, lead to the hypothesis that arrangements exist in the ear
similar to those which we have imagined. The end of every
fibre of the auditory nerve is connected with small elastic parts
which we cannot but assume to be set in sympathetic vibration
of the waves of sound."

He considered that the fibres of the basilar membrane consti-
tuted this system of resonators. This membrane increases its
width (about three times) as it passes from its beginning in the
base of the cochlea to its termination in the apex and contains
somewhere about 10,000 of these fibres within its substance.
He considers that " damping arrangements exist in the ear
so as to quickly extinguish movements of the vibrators"
(M'Kendrick).

212 THE EAR

This theory receives confirmation from the following facts :

(1) Birds and other animals whose calls have a short range of
pitch have short basilar membranes.

(2) Prolonged subjection to a definite note produces degenera-
tion in a definite part of the membrane — e.g. in boiler makers'
disease there is inability to hear high notes with degeneration of
the short fibres ; animals give evidence of deafness to low notes
when the long fibres of the membrane have been destroyed.

Against this theory are arrayed most psychologists and not a
few physiologists and anatomists. They find in it no adequate
explanation of certain phenomena.

(1) The parrot has only half a whorl of cochlea, but is able to
imitate speech and to whistle musical notes over a fair range, while
the guinea pig, with one and a half whorls more than man, produces
only squeaks and grunts.

(2) The bird has a short basilar membrane, about ^ that of
the mammal, but has numerous hair cells. These cells are set in
the bird in rows of 30 or 40, and in the mammal in rows of 4.
If equal lengths of membrane vibrate sympathetically to the
same note, then as the bird has ten times the number of hair
cells stimulated as the mammal, it ought to hear the sound
correspondingly louder. This does not appear to be so.

(3) It is rather difficult to see how, even taking differences
in tension into account, sufficient resonators could be obtained
to receive the wide range of notes that it is known we do receive.
Displacement Theory.

The latest form of this theory is put forward by Sir Thomas
Wrightson, an engineer. He is supported by Professor Arthur
Keith, the eminent anatomist. He considers that the ear is not
a physiological piano played upon by the sound waves, but a
delicate spring weighing every phase of a sound wave, simple
or compound, and transmitting to the brain a record of every
fluctuation of pressure in the endolymph of the scala media.
Every variation of pressure transmitted by the stapes to the
perilymph is in turn transmitted to the membrane closing the
fenestra rotunda. The cochlear system is a closed one, in shape
rather like a long drawn out, doubled over hour glass, with the
stapes operating at one end. The only relief for the motion of
displacement is at the fenestra rotunda, at the opposite end,
whose membrane moves to and fro simultaneously with the
stapes. These movements are transmitted to the endolymph
enclosed in the tube, the scala media, which ends blindly at the

DISPLACEMENT THEORY 213

helicotrema. He believes that the hair cells and not the basilar
membrane are the sensitive organ. They pass through the meshes
of the reticulate membrane, and, according to Wright son and
Keith, have their upper ends fixed in the tectoria. The tectorial
membrane, it will be remembered, is attached to the spiral lamina,
as a nail grows out of the finger. Now, displacement of the
fluid causes movement of the whole reticulate membrane. This
latter produces a to-and-f ro movement of the base of all the hairs,
and as these hairs are fixed in the tectorial membrane, they will
bend. " It would only be the simple pure tones which would give
to the hairlet a pure symmetrical harmonic motion, but by the
displacement of liquid under pressure, every conceivable succes-
sion of bendings of the innumerable hairlets can be obtained
to convey to the auditory nerve every impulse required to pro-
duce the pitch of each resultant and component tone" (Wrightson).

Thus, the cubic displacement of fluid is converted, by means
of the arch of Corti, into a linear movement of the reticulate
membrane, etc. By means of the resistance of the tectoria,
the linear movement is converted into the bending of the hairlets.

Such an explanation fails to account for the ability of the
trained musical ear to perceive as separate entities the different
sounds from an orchestra reaching it simultaneously, and it
does not give a very clear explanation of " tone-gaps."

To conclude in the words of Helmholtz : " On reviewing
the whole arrangement there can be no doubt that Corti's organ
is an apparatus for receiving the vibrations of the basilar mem-
brane and for vibrating of itself, but our present knowledge is
not sufficient to determine with accuracy the manner in which
these vibrations take place."

There remains one very important matter which should be
considered because of its diagnostic value to the physician, viz.
conduction of sound waves by the bones of the head. It is common
knowledge that sound vibrations travel more readily through
a solid than through a liquid or a gaseous medium. A watch,
placed sufficiently far away to be inaudible, can be heard ticking
if touched by a lath held between the teeth. If something goes
wrong with the mechanism of the ear, one wants in the first
place to locate the fault. Is the external ear, the middle ear or
the internal ear the seat of the trouble ? The test is usually made
by placing a vibrating body, such as a tuning fork, on one of the
cranial bones. If the sound is not appreciated, then the fault
lies within the internal ear. Either the organ of Corti (or

214 THE EAR

its nervous attachments) have broken down or the membrane
of the fenestra rotunda is not normal. Provided the organ of
Corti and its nervous attachments are intact and the round mem-
brane is flaccid, sounds may be heard by bone conduction, and
ordinary hearing is not impossible. The vibrations are trans-
mitted directly through the thick, exceedingly dense but elastic
bony walls of the aural cavity, and produce a movement of the
basilar membrane, etc. This can only take place if the membrane
of the round window is functioning properly, or if the stapes
moves normally in its oval window. If the openings were to
lose their elastic windows and not move to and fro with every
condensation and rarefaction, then the cochlea would be, to all
intents, a sealed cavity filled with fluid. Such fluid could not
oscillate ; it could be alternately compressed and released from
this extra pressure, but this slight molecular movement could
not stimulate the hairlets.

Further, if both the stapes and round membrane were free to
move, hearing in the case of a diseased middle ear would not be
so good as when only one of the pair were free. This is because
part of the displacement of the cochlear fluid caused by the
vibrations of the surrounding bone is dissipated by moving the
stapes outwards. People may hear fairly well after the stapes has
become immovably fixed in the fenestra ovalis. In cases where the
drum of the ear has been punctured, hearing may be improved by
fixation of the stapes, e.g. by application of a plug of cotton wool.

When sounds are conducted to the inner ear by means of the
bones of the skull, in people with normal hearing, the intensity
of the sound is markedly increased if the movement of the stapes
is hindered. For example, on p. 423 of Part II. is given an experi-
ment where a vibrating tuning-fork is placed on the region of
the interparietal suture. When both ears are unobstructed and
normal, sound is heard equally by both. If the drum of one ear
and appended ossicles are hindered from taking a full excursion
by blocking the meatus with a finger, the sound appears most
distinctly at this ear. WThen both ears are treated in this way,
localisation is again median. A common entotic phenomenon is
the audibility of the pulse in an obstructed ear. It may be due
to the transmission of the pulse-wave oscillation to the air of the
middle ear — which acts as a resonator — reinforcing the vibrations
and then transmitting them to the internal ear. It is more
probable, however, that the beat of the carotid artery is trans-
mitted through the parietal bone direct to the fluid of the cochlea.

(c) DISTANCE RECEPTOR FOR LIGHT
THE EYE

By W. F. SHANKS, B.Sc., M.B., Lecturer on Experimental Physiology in the
University of Glasgow.

THE following points in connection with light are recalled to
the student's memory.

(1) Refraction.

When a ray of light passes from a rare to a dense medium
(or vice versa) it undergoes refraction, i.e. it is bent towards

Fia. 46. — Refraction of incident ray PO at interface AB.

(or away from) the perpendicular to the surface at the point of
incidence. This perpendicular is called the normal. Snell's Law

215

216

THE EYE

states that for any two media, the sine of the angle of incidence
bears a constant ratio to the sine of the angle of refraction.

In Fig. 46 PO is the incident ray, OQ the refracted ray, NOM the
normal to the interface AB between the media (the upper being

A

the less dense). Then — - - — = constant. This constant is

sin QOM

called the refractive index, and is usually denoted by the letter /*.
The refractive index of air is taken as unity, and other refractive
indices are expressed as numerical values compared with it.

FIG. 47.

If we are given the angle of incidence and JUL, we can easily
find the direction of the refracted ray. Let PO be the incident
ray. Measure 0V = unity and OP=v- (stated in the same units).
With centre O and radius OP describe a circle. Draw VS, PR
perpendicular to normal NOM. Draw VT parallel to ON. Join
TO and produce it to cut circle at Q. Then OQ is the refracted
ray.

Proof : Sin PON =

PO'

sin TOW (or QOM) =

TO

that is,

SinPOJV PR TO PR PR

Sin QQM

PO TW TW~VS

DIOPTRICS 217

PR PO

But in the similar AS POR, VOS, ==-_ =T^V

r a VU

, p°

and vr = yu by construction.

Sin POZV

A = w. Hence OQ is the refracted ray.
Sin QOM

A A

If PO is perpendicular to AB, sin PON =O. Hence sin QQM =O,
i.e. the ray is unrefracted in its passage.

But, in addition to this refraction, a part of the incident light
is reflected. The amount reflected varies with (i) the obliquity
of incidence, (ii) the difference in refractive index.

When a source of light, e.g. a candle, is placed near a biconvex
lens, we see very clearly two images produced by reflection.
The first is formed by the anterior convex surface and is upright,
the second is formed at the posterior surface, which is concave
in respect of rays passing out of the lens into the atmosphere,
and is inverted. The size of the image decreases as the convexity
of the lens increases. Its brightness increases, the more obliquely
the rays from the candle strike the surface and also with increase
of the refractive index of the medium composing the lens.

(2) Images formed by a Convex Lens, (a) When the object is
between GO and 2/ (/ being the focal length), the image lies
between -/ and - 2/, and is real, inverted and diminished.

(b) When the object is between 2/and/, the image lies between
— 2/and -co , and is real, inverted and magnified.

(c) When the object is between / and the optical centre of the
lens, the image lies between +00 and the optical centre of the
lens, and is virtual, erect and magnified.

(3) Chromatic Aberration. When white light passes through a
lens its component rays are unequally refracted, the violet being

FIG. 48. — Chromatic Aberration.

brought to a focus nearer the lens than the red. If the image
is received on a screen midway between these points it will
appear to be surrounded by a red and violet halo.

218

THE EYE

(4) Spherical Aberration. Rays of light passing through the
peripheral part of a lens are refracted more than those passing
through the central part. This tends to produce distortion of
the image at the periphery.

We will point out the application of these facts to the eye
in due course.

Anatomy.

To understand the mechanism of the eye even from the purely
physical standpoint, i.e. as an optical instrument, it is necessary
to have a clear conception of Restructure.

FILTRATION

CONJUNCTIVA

.SCLEROTIC.

OPTIC NEKVE1

FIG. 49. — Diagrammatic section of eye.

The eyeball is a hollow sphere of dense fibrous tissue — the
sclerotic. In front there is a window, the cornea, formed also of
fibrous tissue, but so modified as to be transparent. Its radius
of curvature is much smaller than that of the sclerotic. Inside
the eyeball is a second layer, the choroid, constituting the vascular
portion of the eye, and loaded with pigment. This last performs
the function of the black lining of optical instruments, preventing
the reflection of rays in the interior. At the corneo-sclerotic
junction the choroid ceases to be in contact with the wall of the
eyeball, and hangs free as a curtain — the iris. In this curtain
there is a central aperture, the pupil, which in the human subject
is circular. In the iris are muscular fibres, a well-marked circular
set serving to diminish, and a feebly marked radial set serving

REFRACTION 219

to enlarge the pupillary opening. Thus the amount of light
entering the eye can be regulated. At the back of the eyeball,
slightly internal to and just below the antero-posterior axis,
the optic nerve pierces the sclerotic and choroid, and its fibres
spread out on the inner surface of the latter to form the retina
which extends forward almost to the ciliary body (see below).
Where the antero-posterior axis meets the retina is a small yellow
area, the macula lutea, in the centre of which is a depression,
the fovea centralis. The macula constitutes the area of distinct
vision. The retina is a sensitive screen, on which a picture of
external objects is brought to a focus, and corresponds to the
plate of a photographic camera. Along with the optic nerve the
arteria centralis retinae enters, and its branches radiate outwards
on the inner surface of the retina. Internal to the retina is a
delicate layer, the hyaloid membrane, which, like the choroid,
becomes free near the corneo-sclerotic junction and splits to
enclose the crystalline lens. The latter is a laminated biconvex
structure placed just behind the iris, and centred with the pupil.
Between the wall of the eyeball and the lens the hyaloid membrane
is considerably thickened, and forms the suspensory ligament or
Zonule of Zinn. Close to the corneo-sclerotic junction the choroid
is thickened and raised in radiating ridges, the ciliary processes.
To these the hyaloid membrane is firmly attached, and into them
are inserted fibres of the ciliary muscle. The ciliary muscle arises
from the corneo-sclerotic junction and its fibres are arranged in
two sets — a radial passing back into the ciliary processes and a
circular. The ciliary processes, plus the ciliary muscle fibres,
constitute the ciliary body. The lens, with its attachments,
separates the eyeball into an anterior chamber filled with clear
fluid, the aqueous humour, and a posterior containing a rather
more jelly-like substance, the vitreous humour. The anterior
chamber is divided into two compartments by the iris, but there
is free communication between them through the pupil.

Refraction in the Eye.

Let us now consider the passage of a ray of light through the
instrument we have described. We must first know the indices
of refraction of the various media. They have been determined
experimentally, and may be given approximately as follows :

Cornea 1-33

Aqueous - 1-33

Lens - - 1-43

Vitreous -------- 1-33

220 THE EYE

Remembering that refraction takes place only at the plane
of junction of media of different densities, we see that it will occur
at (i) the anterior surface of the cornea, (ii) the anterior surface
of the lens, (iii) the posterior surface of the lens. At each of these
surfaces the incident ray will be bent towards the central axis,
and in the normal eye the result is to bring all incident rays
to a focus exactly on the retina. Thus a picture is produced.

We have seen that refraction is always accompanied by a
certain amount of reflection, and this is the cause of the pheno-
menon known as Sanson's Images. If a candle is held at a short
distance from one side of the eye, the observer can distinguish
the images formed by each of the refracting surfaces. The image
produced by the cornea where the change in refractive index is
from 1 to 1-33 is much brighter than the images from the lens,
where the change is from 1 -33 to 1 -43 and from 1 -43 to 1 -33.
In the case of the two latter also there is a certain amount of
absorption of light by the media. The images from the cornea
and the anterior surface of lens are upright, that from the posterior
surface of lens is inverted. The radii of curvature of the refract-
ing surfaces are respectively, 8, 10 and 6 mm. Consequently the
images differ correspondingly in size.

The combination of the three refracting surfaces constitutes
the physiological lens of the eye.

Accommodation.

Every one knows that in a photographic camera it is necessary
to adjust the distance between plate and lens in order to focus
sharply objects at varying distances. The eye, regarded as an
optical instrument, must suffer from this disadvantage, and it
is a matter of daily experience with us that near and far objects
cannot be seen clearly at the same time. How does the eye over-
come this difficulty ? The eyeball is rigid and the lens practically
fixed. No change in the relative positions of the latter and the
retina is possible. The adjustment, called accommodation, is
brought about by changes in the lens, so that the eyeball har
virtually a series of lenses of varying strength, from which it
selects the one most suited to the requirements of the moment.

The lens suspended in the resting eye has not its natural
shape ; it is kept somewhat flattened by the tension of the
capsule. If this tension can be relaxed, the lens will become
more convex on account of its inherent elasticity. A mechanism
for bringing this about is present. The ciliary muscle is fixed

ACCOMMODATION

221

at the corneo-sclerotic junction, when its radial fibres contract
they drag the ciliary processes, with the adherent hyaloid mem-
brane, forward, simultaneously the circular fibres by their con-
traction constrict the circle round which the suspensory ligament
is attached. The result is to relax the ligament and lens capsule,
and the elasticity of the lens comes into play. The maximum
alteration in radial curvature, which affects the anterior surface
almost exclusively, is from 10 mm. resting to 6 mm. fully accom-

Cornea

Sinus venosus

Conjunctiva

Retina

FIG. 50. — Section of anterior part of eyeball, showing structures concerned in
accommodation. (After Merkel and Kallius.)

modated. The normal adult is thus enabled to see objects dis-
tinctly to within 10 or 15 cms. distance. (Note. This is the
theory of accommodation at present almost universally accepted.)

The Abnormal Eye.

In the normal or emmetropic eye, parallel rays, which in
practice are those coming from a distance greater than 6 metres,
are focused in the resting state. Within 6 metres accommodation
begins, and it increases as the object approaches, reaching its
maximum at about 10 or 15 cms. This is called the near point
of vision, and the point at which accommodation begins is called
the far point.

222 THE EYE

The eyes of a considerable proportion of persons do not produce
sharply focused pictures within normal limits. The defect
consists most commonly in the screen being (i) too far from the
lens, or (ii) too near the lens. In the first case the picture in the
resting eye falls in front of the retina. This is the condition of
Myopia or short sight. Divergent rays from near objects are
focussed with little or no accommodation, and images are sharply
defined when objects are well within the normal near point.
But parallel rays cannot be focused unless they are artificially
rendered divergent before entering the eye. This is effected by
the use of concave lenses. In the second case, parallel rays are
focussed behind the retina in the resting eye. This is Hyper-
metropia or long sight. Such rays can be converged and brought
to a focus by using accommodation, but the near point is reached
while the object is still comparatively distant. To enable the eye
to focus objects near at hand we strengthen its converging powers
by interposing a convex lens.

Presbyopia is the result of a gradual diminution of the power
of accommodation through loss of elasticity of the lens as age
advances, the retina retaining its normal position relative to
the lens.

Astigmatism is the variation of the radius of curvature of the
cornea in different planes.

The Dioptre.

The measurement of the refraction of the eye is made in terms
of lenses which have their focal lengths expressed in metres.
A lens of 1 metre focal length is a lens of 1 dioptre, of -5 metre,
2 dioptres, etc. Errors of refraction are thus measured by the
clinician, e.g. a hypermetropic patient who requires a lens of -3
metre focal length in order to render his eye emmetropic is said
to have 3 dioptres of hypermetropia.

Movements of the Eyeball.

The eyeball lies at the front of the bony orbit, a cone-shaped
canal with its apex directed backwards and pierced by the
optic foramen. The antero-posterior or visual axis of the eye,
i.e. the line passing through the centre of the cornea and the
fovea makes an angle of about 20° with the long axis of the orbit.
The movements of the eyeball are carried out by the extrinsic
muscles, which are six in number. Of these, four (called the
recti) originate in a common tendon surrounding the optic foramen,

MOVEMENTS OF EYEBALL

223

TRAN3VER5E

and pass forward to be inserted a short distance in front of the
equator of the eyeball. One is placed above (R. superior), one
below (R. inferior), one on the outside (R. externus) and one on
the inside (R. internus). The remaining two muscles are the
superior and the inferior oblique. The former arises from the
same tendon as the recti, and follows a course similar to but above
the internal rectus. At the front of the orbit its tendon passes
through a fibrous loop or
pulley, and bends sharply
back to be inserted in the
eyeball about the equator.
Its line of action makes an
angle of about 60° with
the visual axis. The in-
ferior oblique arises from
the inner anterior part of
the orbital floor, and passes
outwards and backwards
to its insertion rather be-
yond the equator. It acts
on the same line as the
superior oblique.

All the movements of
the eyeball are rotations
round axes passing prac-
tically through the centre
of the sphere, but it can
be proved experimentally
that rotation never occurs
round the visual axis.

The internal and exter-
nal recti rotate the eye
round a vertical axis, and
their action is unaffected by the relative obliquity of the visual
and orbital axes.

The rectus superior acts along the line of the orbital axis,
and its force can be resolved into two components, the one tend-
ing to rotation round a horizontal axis at right angles to the
visual axis, the other tending to rotation round the visual axis
itself in a counterclockwise direction (viewed from the front).
In order to overcome the latter tendency, the inferior oblique
acts simultaneously. Its force can likewise be resolved, one

FIG. 51. — Diagram of extrinsic muscles of eye.

224 THE EYE

component tending to rotation round the horizontal axis at right
angles to the visual axis, the second component tending to rota-
tion round the visual axis, clockwise. The two rotations round
the visual axis counteract each other, the remaining two act as a
couple, and reinforce each other. The result of the combined
action is to move the cornea vertically upwards. For movement
upwards and inwards, for instance, the co-operation of a third
muscle, the internal rectus, is required. The rectus inferior
and the obliquus superior combine in an exactly similar manner
to move the eyeball downwards.

Ophthalmoscopy.

When we look at a person's eye the pupil appears perfectly
black. Nothing can be seen of the interior because it is feebly
illuminated compared with the outside world. If we could light
up the interior it would become visible, just as we can see into
a lighted room at night if the window is not covered with a blind.
When we try to illuminate the interior of the eye, we find that
we must always interpose our head between it and the source of
light in our attempts to peer into it. This difficulty is overcome
by reflecting light from a mirror provided with a small central
aperture, through which the observer can look. This instrument
is called an ophthalmoscope. It may be used in two ways :

A. In direct ophthalmoscopy, the mirror and the observer's
eye are brought close to the observed eye, and the refracting
media of the latter produce a virtual image, erect and magnified,
of the retina. The lens, etc., of the observed eye act in exactly
the same way as a magnifying glass, the object being just inside
the focus.

B. In indirect ophthalmoscopy the observer holds a convex
lens in front of the observed eye, and places himself farther
away. The interposed lens brings the rays leaving the observed
eye to a focus between itself and the observer, who consequently
sees an inverted image of the retina. This is real and magnified,
the magnification depending on the lens used.

Defects of the normal eye as an optical instrument.

(i) The eye is not perfectly centred, i.e. the axis of the lens
does not coincide with the axis of the cornea.

(ii) The optical axis passing through the centre of the cornea
and the centre of the lens does not coincide exactly with the
visual axis passing through the centre of the cornea and the
fovea centralis.

BINOCULAR VISION 225

Neither of these defects interferes appreciably with the accuracy
of vision.

(iii) Slight degrees of astigmatism are almost always present.

(iv) Chromatic aberration is uncompensated optically. The
retina, however, is less sensitive to the extremes of the spectrum,
consequently the slight halo of red rays focussed behind and of
violet focused in front produces no sensation.

(v) Spherical aberration is provided for by the iris which cuts
off the peripheral rays. This is particularly noticeable in accom-
modation where in order to exclude the more divergent rays the
pupil contracts.

Binocular Vision.

1. The Visual Field. When one eye is closed and the other fixed
on a certain point the whole range of objects which can be seen
without moving the eye or the head is called the visual field.
The angle subtended by these objects is called the visual angle.
With both eyes open and fixed we command a greater range.
(For the mapping out of the visual field and measurement of the
visual angle see pages 425 and 426.)

2. Focusing of objects within the far point. We have seen that
in order to focus near objects we employ accommodation.
This is always accompanied by a movement of the eyeballs,
causing the visual axes to converge from their parallel resting
position towards the middle line. Such a movement is necessary
in order that the images in both eyes may fall on the fovea centralis
(Fig. 52). If this mechanism is defective, strabismus or squint
results.1^ The amount of convergence varies inversely as the
distance of the object. This may be proved as follows (Fig. 52) :

OP A O'P' OP

Sin OEP OP O'E O'E

Sin '' OP OE'

Since OEP and O'EP' are small, sin OEP =OEP and sin O'EP'

OEP O'E

Hence — — — = — — .

O'EP' OE

The power of convergence is rather less than that of accommoda-
tion, for we can focus an object with one eye at a slightly shorter
distance than when we use both eyes.

B.B. 15

226

THE EYE

It is only in the emmetropic eye that convergence and accom-
modation correspond exactly in amount. A hypermetropic
person viewing a near object may require to use, say 4 dioptres
of accommodation, whereas an emmetropic person uses only
2 dioptres, but both employ the same amount of convergence.
Similarly an emmetrope may focus a near object, and if concave
lenses are placed in front of his eyes he can continue to see the
object plainly by increasing his accommodation sufficiently to
neutralise their effect. The object still remains at the same dis-
tance, i.e. the convergence does not alter. Hence we see that
accommodation and convergence are to some extent independent.

FIG. 52. — Convergence.

FIG. 53. — Artificial divergence of visual axes.

3. Divergence. In normal circumstances the visual axes never
diverge, for they are in parallel adjustment for objects at infinity.
Divergence can however be brought about artificially. Thus if
we interpose prisms to render the rays divergent we can produce
a corresponding divergence of the visual axes.

4. Visual Judgments. On account of the distance between the
eyes, objects are viewed from a slightly different angle by each
eye. This is readily demonstrated by looking at an object first
with one eye and then with the other. It is particularly well
brought out by two objects almost or completely in alignment,
and the phenomenon persists at long distances. Each retina thus

VISUAL JUDGMENTS 227

receives a slightly different picture, and we are furnished with a
most important means of judging solidity and distance. Objects
seen with one eye only have a very flat appearance. Shadows
help materially in conveying impressions of solidity, and their
significance may be illustrated in the interpretation of aeroplane
photographs. In such photographs taken during the War there
were numerous marks which might have either a positive or a
negative solidity, i.e. they might have been either projections
above the ground, such as machine-gun emplacements, or depres-
sions, such as shell holes. This could only be determined by the
shadows cast, and the direction of the sun's rays was always marked
on such photographs. Thus A is a projection and B a depression.

In judging very short distances, two ^

eyes are an enormous advantage. Try
to thread a needle with one eye closed. ^— ^
At rather longer distances this may 0. ]
be demonstrated by looking at a wall ^%^
between which and the observer an A B

object, such as the wire of an electric Fl°- 54~ Shadows-

lamp, is suspended. Using one eye only and avoiding looking
at the point of attachment to the ceiling we will judge its distance
from the wall very imperfectly, but with both eyes we can make
an accurate estimation.

At long distances numerous external factors come into play.
Perspective, light and shade and atmospheric conditions are of
importance. Thus " visibility " may be good or bad, and will
influence our judgments. At sea, where the surface is perfectly
flat and the gradations of illumination change uniformly with
distance, the untrained eye commits the grossest errors. The
proximity of an object of known size frequently supplies a scale
against which to measure the size and consequently the distance
of unknown distant objects. The faculty of judging distances is
poorly developed in the average man. A trained soldier or a
big game shot can make incomparably more accurate estimations
of distances for rifle fire than the novice. The same thing occurs
with the expert golfer for certain distances.

5. The Stereoscope. The combination of two slightly dissimilar
pictures to form an apparently solid object is illustrated by the
stereoscope. This instrument consists of two prisms or half
lenses placed, with the thin edge inwards, about the same dis-
tance apart as the eyes. The dissimilar pictures P1 and Pz are
fixed one in front of each lens, and a median screen cuts off each

228

THE EYE

opposite picture. By means of this apparatus we obtain a single
picture in the most pronounced relief, and situated apparently
at P.

-I n

FIG. 55. — Diagram of stereoscope.

We may summarise the advantages of binocular vision as
follows :

(i) The visual field is increased,
(ii) We receive impressions of solidity,
(iii) We have a most important means of judging distances
(iv) The loss of one eye does not reduce us to blindness

SECTION IV. : TRANSPORT.

CHAPTER XXI
THE BLOOD

INLAND TRANSPORT SERVICE

" If they flourish not, a kingdom may have good limmes, but will have empty
veines and nourish little." BACON.

WE have seen reason to consider the animal body as a country
containing numerous towns or cell-communities, each busily
engaged on its specific staple industry and connected with one
another and with the seat of government by an extremely efficient
means of communication — the nervous system. Such a country,
on account of its complex nature, must have a system of transport.
Raw materials from outside must be brought into the country and
some means must exist for sorting out the imports and forwarding
the suitable ones to the appropriate cell-communities, etc. It
is convenient to carry still further this simile of a country.

It is obvious that some imports may arrive from overseas
ready for use and have only to be handed to the distributors for
transmission to the consumer. Others again have to undergo
some change before they can be transported inland. That is,
there are two classes of raw material arriving at the same port,
viz. : gas and liquid-solid food. These are handled by different
gangs of labourers. The oxygen is sent directly to the inland
transport service, while the food material is sent to a series of
factories where it undergoes partial manufacture and is repacked
in smaller containers, before being handed to the same inland
transport service as the oxygen. Just so, iron ore may be shipped
to the Clyde, from which it passes through a series of factories,
in which it is partially purified, smelted, etc., and then sent as
pig-iron, say to Sheffield, for final treatment, before being distri-

229

230 THE BLOOD

buted in a useful form over the country. There are, therefore,
two forms of transport which we may term external and internal.
As all material has finally to be carried by the inland transport
service and as the amount of traffic on this system to some extent
controls the rate of importation, it will be convenient to direct
attention to it in the first place.

Inland Transport — The Blood.

The blood has been called the liquid tissue of the body. On
two counts this is a misnomer. Firstly, it tends to detract from
the liquidity of the tissues in general. Further, blood cannot
rightly be considered a tissue at all. No doubt a very pretty
picture could be drawn of blood and its containing membranes
as a tissue, clotting, as other tissues clot, on death, but when the
facts are examined they do not bear out such an idea. The evid-
ence too, culled from comparative studies of the development of
a circulatory system, is all at variance with the liquid tissue theory.

1. Development.

Much may be learned from a study of the evolution of
any system. Material exists for such a study in Comparative
Physiology.

(a) Unicellular organisms require no circulatory system. Their
imports go direct to the sole factory of the place. They may be
landed at any part of the coast and are at once acted on. What
is suitable is accepted, the residue is rejected or left untouched.
Examination of a unicellular animal leads to the conclusion that
the cell contents are in a state of constant motion. Water, every
now and then, is engulfed, passes more or less directly through
the organism, and is excreted, carrying with it the by-products
of cell activity.

(b) Some invertebrates have an open coelomic system. Their
more complex structure necessitates the production of a current
of fluid so that material may reach the inner cells. That is, some
of the water in which the animal lives is passed by means of canals
to the different parts of the body. The fluid is kept in circulation
by the rhythmic contractions of whip-like processes called cilia.
The ciliary waves force the water through the tubes into the
lacunae of the tissues. Such a system is difficult to control. It
is dependent on the nature of the bathing medium. It carries the
possibility of constant changes in the salt content of the cells of
the animal. Any change in the environment will be passed on

FUNCTION OF BLOOD 231

to the coelomic fluid and at once reflected in the cell. It demands
constant adaptation on the part of the organism, and thus it is not
economical (cf. our system of canals).

(c) Higher invertebrates and the vertebrate amphioxus have
a closed system in which the fluid passes through tubes capable
of rhythmic contractions.

(d) The vertebrates have a closed vascular system with the
advantages of ease of control and freedom from constant adapta-
tion. It is the most economic system of transport known.

When the sea animals crawled on to land and became breathers
of air, they included a certain proportion of the sea- water in their
vessels. By the alteration in surface tension caused by the
exchange of a protoplasm-water interface for a protoplasm-air
interface their open coelomic system automatically closed (cf.
camels' hair brush experiment, p. 403).

The vertebrate has, therefore, a fluid in its vessels having a
composition similar to that of the sea from which originally it
came (see salts of plasma, p. 239). Some arose from a tropical
sea and therefore this included fluid was warm. Others again
did not attain to this. We have, therefore, warm and cold
blooded animals (Regulation of temperature, Chap. XXXI.).
This is a very pretty theory. It cannot be considered as proved
any more than the hypothesis of evolution, but in the same sense
both fit in with certain facts.

2. Function.

(a) The blood-stream conveys food including oxygen to all
parts of the organism.

(b) It removes the waste products of activity including carbon-
dioxide, which would paralyse function if allowed to accumulate.

(c) The carriage of chemical substances (hormones) from the
organs in which they are produced in order to influence the
activity of other organs may be considered as the co-ordinative
action of the circulation.

(d) The movement of blood aids in the regulation of the tem-
perature of the body (Chap. XXXI.).

(e) It plays a very important part in the defence of the
organism against parasites, etc.

(/) The preservation of the H-ion concentration of the body
is principally a function of the circulating fluid (Chap. XXX.).

(g) It maintains the water and salt content of the body at a
certain level.

232 THE BLOOD

3. Composition.

Since the function of the blood is to act as common nutritive
medium to all the parts of the body, it has to convey food material
from the digestive organs and oxygen from the lungs to the tissues.
From these, it receives in exchange their waste products, viz.,
results of nitrogenous metabolism, CO2 and H2O, and carries them
away to the excretory organs, kidneys, lungs, skin, etc., by which
they are eliminated. It is therefore evident that the composition
of the blood must vary from time to time and from place to place,
according to the activity and the function of the organ which it is
traversing. The cells of the body are adjusted to respond to
very minute changes in the composition of the blood and,
therefore, changes are kept within infinitesimal limits.

The term blood or whole blood is usually applied to the fluid
content of the vascular system, i.e. to the fluid plus formed
elements.

I. Fluid or Plasma.
(a) Physical Characters,
(i) Colour, light straw.

(ii) Opacity, practically transparent.

(iii) Specific Gravity, about 1030. The specific gravity is
lowered after a meal because of the dilution of the plasma by
ingested water. Conversely, exercise and profuse perspiration
cause a slight increase in the specific gravity on account of the loss
of water (see specific gravity of blood, p. 277). Variation in
activity will therefore produce a diurnal variation — a decrease
during the day and an increase during rest at night. The night
worker, of course, has this reversed. It varies greatly in individuals
so that a figure which is normal for one person may be pathological
for another.

(iv) Viscosity. At body temperature (37° C.) plasma has a
viscosity about twice that of distilled water, i.e. 1-7-2-09. Salt
solutions have almost the same viscosity as water. This factor
is due to the emulsoid colloids present (q.v.), one of which by
forming a gel under certain conditions may produce so great an
increase in viscosity that the flow of plasma may be entirely
stopped. The plasma is then said to clot (see fibrinogen and also
viscosity of blood).

(v) Reaction. Plasma turns red litmus blue and therefore has
an H-ion concentration under 10 ~7. It is acid to phenolphthalein
and therefore has anH-ion concentration greater than 10~8. Exact

COLLOIDS OF BLOOD 233

determinations have shown that the pH of plasma is 7-4, i.e. just
on the alkaline side of neutral. This alkalinity is due to the
presence of sodium bicarbonate (see below).

(vi) Osmotic Pressure. The osmotic pressure of plasma as taken
by an ordinary osmometer with a semi-permeable membrane or
by the depression of the freezing point is almost the same as that
exhibited by a 0-9 per cent, solution of sodium chloride. It
varies with the diet and with the amount of fluid ingested. If
the kidneys are not functioning properly so that the products of
metabolism are not eliminated with sufficient rapidity the osmotic
pressure will rise.

The student cannot guard too carefully against the errors of
considering that (a) the osmotic pressure of plasma is due to the
presence of 0-9 per cent. NaCl in it and (b) that the figure given
even approximates to the proper value of the osmotic pressure
in the blood vessels. These vessels are permeable to salts in
solution, and, therefore, the true osmotic pressure of plasma must
be due not to electrolytes but to colloids (see below).

(vii) Refractive Index (see p. 216). The refractive index of
plasma depends primarily on the amount and nature of the
proteins present. Its variations are governed by practically the
same factors as are responsible for the variations in specific
gravity.

(b) Components, (i) Colloids.

The major colloidal constituents of plasma are protein in
chemical nature. These proteins are :

(a). Albumin - 2-5% circa.

(/5). Globulin - 3-8% „

(y). Fibrinogen - - O15-0-6%.

(a) Albumin, probably a mixture of three albumins. At least
it is possible by careful heating to discover three separate coagula-
tion temperatures.

(/3) Globulin is similarly a mixture of two or more globulins.
Globulins are insoluble in distilled water but soluble in dilute salt
solutions. They therefore require to have a certain concentration
of electrolytes present if they are to remain in solution. They
may be partially separated from albumin by dialysis. When the
salt contents of plasma is forced below a concentration of about
0-2 per cent., the globulins are almost completely precipitated.
In the blood stream they function to a great extent as regulators
of the amount of NaCl present. It is of importance that this fact

234 THE BLOOD

be thoroughly grasped. Where the amount of globulin in the
blood is increased, the chloride content increases, e.g. in pneumonia.
In patients with this infection, as well as in cases of chronic
nephritis and syphilis, the total protein content of plasma is
decreased and the globulin content increased both absolutely and
relatively. In mild infections and in chronic septic conditions
the total amount of protein present remains normal while the
amount of globulin and of chlorides shows a marked increase.
NaCl held by globulin acts as if adsorbed, i.e. exerts no osmotic
pressure. Globulin is precipitated by an increase in hydrogen
ions. It is specially sensitive to CO2.

(7) Fibrinogen, a globulin.

The osmotic pressure in the vessels is due to proteins. They
are also responsible for the viscosity of blood. The defibrina-
tion of blood lowers its viscosity to very little greater than that
of water. After extensive bleeding, water pours into the vessels
from the tissues through the lymph, and the specific gravity,
viscosity, etc., drop. The blood ceases to be an efficient carrier.
Bayliss found that the injection of a non-toxic emulsoid colloid
would restore normal conditions for sufficiently long a time as
would enable the cell-factories, especially the liver, to manu-
facture new blood proteins from the amino acids in the blood.
The most efficient sol, he found, was a solution of gum arabic in
Ringer's solution. The story of this discovery as told in his
monograph is one of the most interesting side-lights on the medico-
scientific work of the War.

Clotting.

The main use of fibrinogen lies, not in its viscosity or in its
osmotic pressure, but in its property of changing from a sol into
a gel. The clotting of plasma prevents the loss of blood and keeps
the blood channel free from any angularities. The evolution of
the knowledge of the process of clot formation has been very
slow and even now the physico-chemical reactions involved are
anything but well understood.

Mammalian plasma, if left standing in a tube exposed to the air,
clots to a jelly in two to ten minutes. The gel has the same
volume as the sol, and no heat is evolved in the process. This
is a process common to most emulsoid colloids. In about half an
hour the clot contracts and expresses a clear straw-yellow liquid,
the serum.

i.e. Plasma = Clot +Serum.

CLOTTING OF BLOOD 235

This process whereby the fluid content of the gel is decreased
is common to gels and is called syneresis.

Historical.

Observers at first thought that living tissue had a restraining
influence. They noticed that in the living tissue the blood did
not clot. Lister formed a living test-tube by ligature of the
aorta and showed that the blood did not clot until a foreign body
such as glass was introduced.

This demonstrated that clotting was not due to (1) removal
from living vessels, (2) stoppage of the circulation, (3) cooling or
(4) to contact with air. This latter fact has been confirmed by
the observation that blood clots as readily in a vacuum as in air.
Further, air embolism and caisson disease do not lead to intra-
vascular clotting. Nor is clot formation due to cooling. As a
matter of fact reduction of temperature lengthens the time taken
to produce a clot and, if the plasma is cooled sufficiently, may
prevent it altogether.

The classical work on blood clotting was performed by Andrew
Buchanan, Professor of Physiology at Glasgow, who gave ex-
planations of the process to the Glasgow Philosophical Society,
in March, 1844, and February, 1845. Using hydrocele fluid from
the tunica vaginalis of a horse he showed that it would clot if to it
were added a drop or two of blood, of clot washings, of serum or of
tissue juice. He compared the process to the curdling of milk
by rennin and considered that the white corpuscles or leucocytes
were the active agent.

In 1861, Schmidt, who had devoted some thirty years to the
work, proved that :

(i) Fibrinogen, the precursor of the clot, was a globulin in the
plasma.

(ii) There was a fibrin-former in plasma, in serum and in clot
washings.

He also showed that this fibrin-former (now called thrombin)
did not exist as such in the blood but only appeared after treatment
with a fibrin-ferment or -kinase. That is, the clotting scheme as
he left it appears as follows (modern names) :

Fibrinogen + Thrombin = Fibrin (or Clot)
Pro-thrombin + " Thrombokinase."

Arthus and Pages in 1890 showed the need of calcium in the
clotting process.

236 THE BLOOD

Hammersten confirmed this, and found that the calcium ions
act on the pro-thrombin producing active thrombin. Later work
explains the action of calcium ions here and in milk curdling as
being due to the non-hydrophilic property of calcium compounds.

This still does not explain why blood does not clot in the vessels,
so physiologists had to postulate the presence of some substance
in the blood which would prevent the calcium ions from activating
the pro-thrombin. This hypothetical substance they called anti-
pro-thrombin. In all cells there is a large or small quantity of
thrombokinase, which is the trigger setting off the whole clotting
process. When a vessel is ruptured and blood comes into contact
with the tissues or into contact with disintegrating blood-cells,
it takes from them thrombokinase which neutralises the inhibitory
action of the anti-pro-thrombin and so allows the calcium to act.
It is now known that this substance from the tissues is not a
ferment or kinase. Some people, therefore, prefer to call it
thromboplastin.

The scheme now stands as follows :

(2) (Clot) Fibrin (synerised gel) + Serum

t
.(Clot) Fibrin enmeshing serum

t
Fibrinogen (sol) + Thrombin (a proteose).

(a globulin)' t

(1) Calcium -*• anti-pro-thrombin •«- prothrombin
(in blood) (in blood) (in blood)

*
I

thromboplastin
(from tissues, etc.).

Free calcium ions are necessary for the first step, but apparently
not for the second.

It has been known for long that thromboplastin is a phosphatide,
a body like lecithin, containing nitrogen, phosphorus and a fatty
acid. That this substance is kephalin has been proved by Howell.
Pure kephalin has not been prepared in sufficient quantity to
allow of complete analysis but its molecule probably consists of :

m r . -j (Stearic (saturated)
Two fatty acids '

unsaturated)>

+
an amino alcohol, NH2-CH2-CH2-OH

(amino ethyl alcohol),

+
a glycero-phosphoric acid.

KEPHALIN 237

It is optically active, rotating the plane of polarised light to
the right.

The main point of interest for us apart from its presence in all
tissues is its colloidal character. It is an extremely hydrophilic
emulsoid with a strong negative charge. On exposure to air it
readily absorbs oxygen (a property dependent on its unsaturated
fatty acid) and undergoes partial decomposition.

The addition of calcium ions to a solution of kephalin causes it
to form a calcium soap with very little water-holding power
(see p. 82). Calcium seems also to combine readily with the
products of decomposition mentioned above.

One must not consider for a moment that the last word on
clotting has been spoken. The subject has recently been investi-
gated from the standpoint of colloidal physics. The scheme
given above does not account for the experiment of Lord Lister
already quoted. Kephalin does not seem to be necessary.
Freund noted that blood would not clot if it came into contact
with a vaselined surface. Placed with due precautions on a
nasturtium leaf, which is not wetted by water, blood does not
clot. Clotting is induced by contact with a water- (i.e. plasma)
wettable surface. This is normally afforded by colloidal kephalin,
but may be produced artificially by the introduction of powdered
glass, etc., or even by bubbling CO2 gas through the plasma.

Tait and his colleagues have shown that the precursors of
thrombin are the thigmocytes of the blood. These thigmocytes
or platelets are spindle-shaped cells which have a strong phago-
cytic action. In place of prothrombin we may write thigmocyte.
Now in calcium-free plasma the thigmocytes may come in contact
with a surface, but will not stick. The introduction of an ionisable
calcium salt causes them to adhere to the surface, and, on account
of the extreme lowering of surface tension, the covering membrane
of the thigmocyte is ruptured, i.e. it undergoes cytolysis and the
cytoplasm is sent into the blood stream. Thrombin comes from
this cytoplasm.

To summarise : (a) Shedding of blood sets free kephalin from
the cells of the blood or of the tissues, (b) this forms a surface on
which, in the presence of ionised calcium, the thigmocytes may
spread themselves and rupture, setting free thrombin, which
causes the formation of fibrin-gel from fibrinogen sol.

It is worthy of note that kephalin particles of a size just visible
under an oil-immersion microscope are capable of producing
intra vascular clotting when injected into the blood stream, while

238 THE BLOOD

powdered glass or quartz particles of apparently the same size
are without effect. Coarser glass suspensions are necessary to
produce the effect. Some other factor in addition to surface must
come into play or kephalin particles must have a wrinkled surface.

Birds' blood is peculiar in that, if drawn with due care to prevent
contact with the tissues it may be kept liquid for a long time. The
avian thigmocytes even under normal conditions will not adhere
to glass surfaces. The addition of the slightest trace of tissue
extract (kephalin) causes immediate and extensive clotting.

This gel formation has been studied ultramicroscopically. The
first sign of clotting is the appearance of blood platelets or thigmo-
cytes, and from them as centres liquid crystals of fibrin crystallise
out, forming a feltwork of long elastic threads.

Anti-coagulants. Certain substances by preventing the calcium
from acting on the thigmocytes, i.e. on pro-thrombin, prevent
clotting. One of these, called heparin by Howell, arises in the
liver. Other substances are really anti-thrombins. Hirudin, a
proteose prepared from the buccal glands of the medicinal leech
belongs to this class and is injected in blood-pressure and similar
experiments to prevent the formation of clots in the cannulae.
Certain salts act on the calcium. For example, oxalates, fluorides,
etc., form insoluble calcium salts, citrates form a double salt in
which Ca is not a free ion. Differing from all the above anti-
coagulants which act whether injected into the blood stream or
added to shed blood, are those which prevent clotting only when
injected. Snake venom in amounts as small as 0 -00001 gram per
Kg. suffices. Commercial peptone (mixture of proteoses and
peptones) injected into the circulation in the proportion of 0-3
gram per kg. produces a non-coagulable blood for an hour or so.
This class of coagulant seems to act by stimulating the liver to
manufacture heparin. Peptonisation and the injection of venom
may cause some alteration in the state of the thigmocytes. This
has not been investigated. Of course, plasma or blood from
which the fibrinogen or fibrin has been removed will not clot.

Coagulants. Extracts of organs rich in kephalin, e.g. thymus,
testes, lymph glands, produce intravascular clotting.

Similarly, certain snake venoms which contain large quantities of
thrombin cause clotting of the blood in the vessels and rapid death.

Components, (ii) Crystalloids.

There is nothing more remarkable than the maintenance of
a fairly constant concentration of crystalloids in plasma, under

CRYSTALLOIDS OF BLOOD

239

the most varied conditions. As we have seen, this is due in great
part to the salt- and water-holding power of the colloidal con-
stituents, especially of the globulins. Bunge, in his handbook of
physiological and pathological chemistry (1889), suggested that
as the notochord and branchial clefts were legacies from fore-
bears who had lived in the sea, the high sodium chloride content
of mammalian blood might also be an heirloom from marine
ancestors. No doubt the circulation fluid of marine animals
with an open coelomic system is sea water. It is held by many
observers, that when the ancestral form of vertebrates acquired
a closed form of circulatory system, the fluid shut in was sea water.
Analysis shows that while the concentrations of crystalloids in
plasma and in sea water are not similar, yet there is a remarkable
resemblance in the proportions of the main salts present in both.

Na K Ca Mg

Serum (defibrinated plasma) 100 6-69 2-58 0-8

Ocean - - - - 100 3-66 3-84 11-99

TABLE XXXII.
Non- clotting Blood.

Nature of Plasma.

Whipped
(Defibrinated)

Salted.
| sat. with
(NH)2S04.
Cooled to 0° C.

Oxalated.
Addition of
soluble oxalate.

Citrated.

Hirudinised.

Peptonised.

Reason.

Fibrin removed as soon as
formed by whipping with
a bunch of twigs.

Fibrinogen precipitated.

Cooling slows the physico-
chemical changes which
are optimum at about
40° C.

Ppts. calcium.

De-ionises Ca.
Combines with thrombin.
Stimulates production of
anti-prothrombin.

To cause Clotting.

Add fibrinogen to whip-
ped plasma (or
blood).

Dilute with water and
so reduce concentra-
tion of electrolytes.

Warm.

Add soluble calcium
salt.

Add soluble calcium salt.

Add thrombin.

Dilute to decrease con-
centration of anti-pro-
thrombin, or add tis-
sue extract or kephalin
or pass in C02 gas.

The similarity in proportion is not very striking because the
figures given are from analysis of the ocean as it is to-day. What

240 THE BLOOD

we should have is the analysis of the ocean in prevertebrate days.
Not only has the concentration of the salts of the sea undergone
change, but alterations have taken place in the proportion of its
constituents. Sodium and magnesium have increased in concen-
tration and are still increasing. Material lixiviated from river
beds, etc., is rich in those salts.

On the other hand, potassium and calcium have decreased.
The formation of soil leads to the abstraction of potassium from
the river water. Water evaporated from the ocean contains
potassium in not inconsiderable amounts. The rain falling in the
region of Caen is responsible for an annual increment to the land
of 1 -23 tons of potassium per square mile. Rivers discharge more
calcium into the ocean than they do of sodium, magnesium or
potassium and yet the concentration of this element appears to be
fairly steady. The cause for this lies in the formation of rock-beds
of gypsum (CaSO4) and limestone (CaCO3) and in the formation
of calcareous skeleta (CaHPO4). From the study of fossil seas
and of lakes surrounded by pre-Cambrian formations as well as
from other geological considerations it has been decided that the
ocean of Cambrian days had a ratio of salts somewhat as follows.

Na K Ca Mg

Present day - 100 3-6 3-9 11-9

Cambrian - 100 6-0 3-0 2-0

Serum - 100 6-6 2-5 0-8

The following table (from Macallum) shows the evolution of
plasma through a series of animals.

TABLE XXXIII.
A. MARINE INVERTEBRATES.

Na K Ca Mg

Ocean - 100. 3-61 3-84 11-99

Limulus polyphemus - 100 5-30 3-83 11-67

Aurelia flairdula - 100 5-18 4-13 11-43

B. ELASMOBRANCHS, TELEOSTS, MAMMALS.

Dog-fish - 100 4-61 2-71 2-46

Pollock - 100 4-33 3-10 1-46

Dog- - 100 6-86 2-52 0-81

Man 100 9-22 3-37 0-76

The salt content of the plasma is regulated by the kidneys. It
is interesting to note that while the blood is Cambrian the tissues
are decidedly pre-Cambrian in their salt content, e.g. Muscle.
Na=100, K=400, Ca=9-3, Mg=26-4, This may t>e in part

FORMED ELEMENTS 241

accounted for by the adsorption of salts by the protoplasmic
colloids. Of these salts one of the most important is sodium
bicarbonate on account of its power of neutralising acid. This
has been termed its " buffer " value — a term which, although
faulty, has crept into the writings of physiologists and clinicians
and seems firmly ensconced there because it is handy. As Prof.
Bayliss points out, a railway buffer absorbs shock but not the
engine, while NaHCO3 absorbs the acid.

The amount of NaHCO3 present in plasma has been called the
alkali reserve of the body. How does it act ? The addition of
acid to bicarbonate may be represented by the equation

NaHCO3 +HA=NaA +H2O +CO2.

Until nearly all the bicarbonate has been acted on by the acid,
no increase in acidity can be detected. This is a mechanism of
great value to the organism. Acids are constantly being produced
in the tissues, especially in muscle. Unless the organism had an
alkali reserve, the concentration of hydrogen ions would so increase
after muscular exercise, for instance, that a serious derangement
of metabolism would ensue (see Preservation of Neutrality,
Chap. XXX.).

II. Formed Elements.

The formed elements borne by the plasma have a volume of
half the plasma and weigh about the same amount.

Plasma. Corpuscles.

Volume 2 1

Weight 3 2

This may be determined by the haematocrite (see p. 422) or by
an ingenious method due to Stewart. He made use of the fact
that the presence of corpuscles reduces the electrical conductivity
of plasma in proportion to their number.

They are of two kinds, viz. : the leucocytes and erythrocytes.
The former have been discussed in Chaps. XII. and XV. They
play a further part in stopping bleeding from a wound. As we
saw (p. 237) the thigmocytes (altered leucocytes) on undergoing
cytolysis set free thrombin. The blood contributes in a second
way towards the arrest of haemorrhage, viz. : by the agglutination
of certain cells to form a plug closing the opening. The primary
event is the local adhesion of the thigmocytes to the edge of the
wound. These altered cells acquire stickiness and any other
formed element coming into contact with them adheres. In this
way a plug is formed.

B.B. 16

242 THE BLOOD

The erythrocytes are the carriers, submerged barges into which
are packed the oxygen for the tissues and the carbon dioxide from
the tissues.

Number. In health, a man has about 5,000,000 of these
corpuscles per cubic millimetre of blood.

Shape. Mammals (except Camelidae) have circular biconcave
discoids. The camels have elliptical biconvex corpuscles.

Size. Human corpuscles have a fairly constant diameter of
about 7 to 8 micro -millimetres.

Colour. Individual corpuscles appear pale yellow, but in bulk
they appear red.

Structure. The pigment is enclosed in a fine sponge-work of
lipoid nature which also forms the covering membrane of the
corpuscle. This membrane is elastic, allowing the corpuscles to
elongate in passing along capillary vessels.

History. Erythrocytes are born in the red bone marrow. The
young corpuscle is called an erythroblast and has a nucleus. It
may live and die in its place of origin. In that case the valuable
constituent of the pigment, the iron, is retained by the marrow
and used in the construction of other cells. Most of the cells,
however, do not remain in the bone marrow. Their nuclei
atrophy and the enucleated corpuscles are shot into the blood
stream on their way to the liver, the crematorium of the body,
where they are alleged to be destroyed after 10 to 14 days. Those
which die by the way are taken out of the circulation by the
spleen. Economical Nature in this way makes use of the dying
erythrocyte as a beast of burden.

Viscosity of whole blood.

The presence of corpuscles prolongs the time taken by whole
blood to traverse a viscosimeter as compared with plasma. The
following figures show this. Serum was used instead of plasma,
to prevent complications by clot formation.

TABLE XXXIV.

Viscosity at 32° C.

Serum + 0 Corpuscles 1-9

„ + 3-2 xlO6 „ 3-3

„ + 6-3 xlO6 „ 4-9

„ +12-6xl06 „ - 15-6

The last high value was due to the mechanical blocking of the
capillary tube by the corpuscles which tend to agglutinate when
so concentrated.

VISCOSITY 243

The stroma (and capsule) are colloidal in character. The
enmeshed fluid is also colloidal and, therefore, the corpuscle as
a whole will act as a colloid. Acids increase the power of colloids
to imbibe water and, therefore, one would expect that CO2 would
cause an increased imbibition of water by the corpuscles and,
consequently, increase the viscosity of blood, due (a) principally
to the absorption of water from the plasma rendering it more
viscous and (6) the swelling of the corpuscle itself. The experi-
mental proof of this has not been very satisfactory, but some
workers have observed increased viscosity in venous blood,
especially in cases where the unsaturation of haemoglobin is low
(pneumonia, gas poisoning).

Viscosimetric measurements afford a means of determining the
volume of blood corpuscles. Viscosity depends principally on
the total volume of corpuscles per unit volume of fluid. Having
determined (i) the viscosity of whole blood =pc, and (ii) that of
the plasma —p, the total corpuscular volume K may be derived
from the formula

1 -K=".

pc

If the total number of corpuscles per unit volume be N, then
the average volume of each will be K/N.

The results obtained from such an indirect method are fairly
regular but cannot be considered as absolutely accurate, as
viscosity does not depend, in principle, on either the number or
the volume of corpuscles, but on the effective surface, i.e. on the
area liable to friction (see relation between viscosity and blood-
pressure).

The sponge-work, which is a colloidal complex of protein,
lecithin, kephalin, cholesterol, etc., with adsorbed electrolytes,
encloses water and electrolytes in solution and the pigment
haemoglobin. This pigment is an electropositive protein con-
taining 0-399 per cent. iron. It is not in true solution in the
corpuscles. The corpuscle contains 32 per cent. Hb in 63 per cent,
water, while the solubility in water is 18 per cent. It may be
set free by rupturing the corpuscle. This is known as haemolysis
and haemolysed blood, because it is similar in colour to crimson-
lac-resin (a gum extruded from tropical trees after puncture by
the lac insect), is said to be laked.

Blood may be laked by various methods :

1. Mechanical, grinding corpuscles with sand or powdered glass
and taking up with salt solution.

244 THE BLOOD

2. Physical, freezing and thawing, heat, condenser discharges, etc.

3. Endosmosis, dropping blood into water or into a hypo-tonic
solution.

4. Exosmosis (see crenation), dropping blood into a hypertonic
solution.

5. Action on Lipoid constituents of capsule.

i. Anaesthetics are lipoid solvents,
ii. Bile salts and pigments affect permeability of lipoid

membranes.

iii. Glucosides, e.g. saponin are adsorbed by the membrane
(Willard Gibbs' Law), because they lower surface
tension. They then insert themselves into the texture
of the membrane and increase its permeability (see
p. HI).

6. Biological Agents.

i. Toxins of certain bacteria produce haemolysis, e.g.

tetanolysin of B. Tetani ; megatheris lysin of B.

Megatherium ; toxic lysins of staphylococcus and

B. pyocyaneus.
ii. Cobra and rattlesnake venom cause laking both in vivo

and in vitro.
iii. The serum of one animal is often haemolytic for the

blood of a different species,
iv. Certain phyto-albumins, e.g. abrin, ricin, and robin

produce haemolysis.

7. Chemical Agents.

Haemolysis may be caused by the ingestion or injection of
certain drugs, e.g. chlorates, nitrites, nitrobenzene, aniline deriva-
tives (e.g. acetanilide and phenacetin) quinine. These, generally,
partially convert the haemoglobin into methaemoglobin (q.v.).

The laking of blood thus depends on altering the permeability
of the stroma or capsule of the erythrocyte. Normally this
membrane is impermeable to colloids and to most crystalloids.
This has been determined by estimating the electrical conduc-
tivity of blood before and after laking. The corpuscles hinder
the passage of small electrical charges because their walls are
impermeable to ions carrying the charge. On rupturing the
membranes these ions get a free passage and the conductivity of
the blood increases. That this increase is not due to the liberation
of haemoglobin may b,e shown by fixing the corpuscles with for-
malin which prevents the egress of the pigment but not of the salts.

HAEMOLYSIS 245

Laked blood has a lower viscosity than whole blood due to the
pseudo-viscosity caused by the corpuscles.

Haemolysis by freezing and thawing.

It has been noticed that blood could be repeatedly frozen and
thawed as in the determination of the osmotic pressure (freezing
point method) with little or no laking. If, however, the blood
was suddenly cooled to below the freezing point of water, was kept
at that temperature for a long time, or was rapidly thawed, pro-
nounced haemolysis was produced. Burton-Opitz prepared com-
pletely laked blood by eight times freezing it solid, and thawing
it rapidly. The mechanism of this laking is not clearly under-
stood. Possibly the withdrawal of water from the membrane to
form ice might be adduced as sufficient reason (Guthrie). (Cf.
Test for frozen meat.)

Endosmotic laking.

Normally, the corpuscle has within it a concentration of colloids
and of crystalloids isotonic with 0-9 per cent, sodium chloride.
A similar state prevails, as we have seen, in the plasma in which
the corpuscle is immersed. The corpuscular membrane is almost
semipermeable. That is, water may pass through it but not
certain salts in solution and not colloids. If the concentration of
salts and colloids inside and out of the membrane were not exactly
balanced, water would pass from the place of low concentration
to that of high concentration (see Osmotic pressure, Chap. V.).
That means that blood dropped into water or into a solution of
lower concentration than 0-9 NaCl would gain water. Water
would pass into the corpuscle, cause it to swell, and when the limit
of elasticity had been passed, the corpuscle would burst and
scatter its contents into the fluid.

Crenation.

Loss of water by evaporation or by immersion in a solution more
concentrated than 0-9 per cent. NaCl causes the corpuscles to
shrink and shrivel. They then break up into fragments, due to
inequalities in the tensile strength of the corpuscle. Most peculiarly
the first stage in exosmotic laking is a swelling of the corpuscle.
Some change in the physico-chemical state of the protein moiety
in the envelope is indicated. It has been shown that the power
of colloids to imbibe water may be altered by alterations in their
crystalloid content.

CHAPTER XXII
RESPIRATORY FUNCTION OF THE BLOOD

" There is no instance in which it can be proved that an organ increases
its activity under physiological conditions without also increasing its demand
for oxygen." BARCROFT.

THE erythrocyte assumes importance as the carrier of the
respiratory gases, oxygen and carbon dioxide. Air has an
average composition of about 79 volumes per cent, of nitrogen
and 21 of oxygen. The amount of carbon dioxide present is so
small (0-03 per cent.), that it may for the present be neglected.
The partial pressure of oxygen, therefore, at normal pressure would
be y2^ x 760— 159-6 mm. of mercury. The partial pressure of
oxygen in the lung is, on account of the carbon dioxide and
aqueous vapour present, much less than this. Alveolar air
contains in 100 c.c. about 5-5 vols. of CO2, 13 vols. of O2 and 79-5
vols. of N. Their partial pressures will be (at normal barometric
pressure) o2== ^3. X760= 98-8 mm. Hg.

CO2 = 1fV'irx760 = 41 -8 mm. Hg.
N=TT>! X 760 =604 -2 mm. Hg.

The partial pressure of the oxygen in the lung is thus about 2/3
of its partial pressure in the atmosphere. The percentage of
nitrogen shows an apparent increase because the total air is
decreased in the ratio |-^{} by the absorption of oxygen without
a corresponding production of carbon-dioxide. Then, too, the
tension of aqueous vapour at body temperature is by no means
negligible. It amounts to about 50 mm. of Hg. That is, dry
air at 760 mm. Hg. when taken into the body has its pressure
reduced to 760 —50 —710 mm. Hg. This causes the actual oxygen
pressure to fall to 92 -3, and carbon-dioxide to 39 mm. Hg.

The quantity of gas by weight (or by volume reduced to N.T.P.)
dissolved in a liquid is proportional to its partial pressure provided
chemical and physical conditions remain constant. If, for

246

HENRY'S LAW 247

instance, the pressure of the gas be doubled, twice as much of it
will go into solution. The appended table contains experimental
verifications of this Law of Henry.

TABLE XXXV.

SOLUBILITY OF CO, IN WATER AT 15° C.
p. v. V./P.

69-8 0-94 0-0135

128-9 1-86 0-0144

200-2 2-90 0-0145

311-0 4-5 0-0145

where P = pressure in mm. of Hg. of C02,

v = volume of C02 (measured at N.T.P.) absorbed by 1 c.c. of water
at 15° C.

(The same volume of gas at constant temperature is absorbed
by the fluid, no matter what the pressure is. Increase of pressure
proportionally increases the weight of unit volume. Thus, if one
volume of water dissolves one volume of gas weighing 1 gram at
1 atmosphere pressure, then, if the pressure be raised to two
atmospheres, 1 volume of water would dissolve 1 volume of the
gas weighing 2 grams, or if reduced to normal pressure, 1 volume
of water would dissolve 2 volumes of the gas weighing 2 grams.)

Absorption coefficient (usually denoted by the Greek letter a).

Different gases, just like different solids, vary in their solu-
bilities. The volume of gas (at N.T.P.) which dissolves in 1 c.c.
of water under a pressure of one atmosphere is termed its absorp-
tion coefficient, e.g. 1 c.c. of water will dissolve at N.T.P. 0-0489 c.c.
of oxygen, 0-0239 c.c. of nitrogen, and 1 -713 c.c. of carbon dioxide.
The volume of gas absorbed by 1 c.c. of water under any pressure
may be found by the following equation :

L=ap,

where L=amount of gas dissolved,
a = absorption coefficient,
p=pressure in atmospheres.
Increase of temperature causes the solubility of gases to decrease.

TABLE XXXVI.

ABSORPTION COEFFICIENTS AT VARIOUS TEMPERATURES.

Temperature. Oxygen. Nitrogen. Carbon-dioxide.

0°C. 0-0489 0-0239 1-713

10° C. 0-0380 0-0196 1-194

20° C. 0-0310 0-0164 0-878

30° C. 0-0262 0-0138 0-665

40° C. 0-0231 0-0118 0-530

248 RESPIRATORY FUNCTION OF THE BLOOD

Effect of solutes.

Plasma contains crystalloids and colloids. The crystalloids are
all more or less hydrated. They combine loosely with a certain
amount of water and, therefore, reduce the effective absorption
volume. Similarly, the emulsoid colloids present reduce the
effective concentration of water by imbibition. They, however,
are able to adsorb a quantity of gas (see p. 66).

It has been found that at the pressure of about 90 mm. Hg.,
which we saw oxygen had in the lung, 100 c.c. of plasma will
dissolve 0-273 c.c. of oxygen (measured at N.T.P.). The tension
of oxygen in the tissues cannot be less than zero, and, therefore,
one has as a maximum amount 0-273 c.c. of oxygen for every
100 c.c. of plasma passing through the tissue. A cat's gastro-
cnemius muscle weighing 20 grams uses about 0-24 c.c. of oxygen
per minute and, therefore, would need to have at least 100 c.c.
of plasma passing through it per minute. A warm-blooded animal
would need to have about twice as much plasma by volume as the
present volume of its body. The body would be unable to cope
with the wieght of its own circulating fluid. For example, the
average man weighing 66 kg. would have to carry, in addition,
at least 140 kgs. of plasma, thus increasing his total weight to
206 kilos. As Barcroft puts it, " man would never have attained
any activity which the lobster does not possess, or had he done
so it would have been with a body as minute as the fly's." In
the experiment quoted above the actual amount of blood passing
through the cat's muscle was 4-5 c.c. per min. — just under a
twentieth of the amount necessary when plasma alone was
considered. This is due to the specific oxygen capacity of the
haemoglobin in the blood.

The following table gives the volume (in c.c. at N.T.P.) of
oxygen, nitrogen and carbon dioxide which will dissolve in 100 c.c.
of fluid at 38° C. and 760 mm. pressure.

TABLE XXXVII.

Oxygen. Nitrogen Carbon-dioxide.

Water - 2-37 1-2 5-55

Plasma - 2-3 1-2 541

Blood - 2-2 1-1 5-11

In addition to the amount dissolved one has to consider the
amount held by the haemoglobin. The table given below contains
the results of a series of experiments on the blood of a horse,

DISSOCIATION OF OXY-HAEMOGLOBIN

249

where the amount of oxygen in the blood was determined at
various pressures.

TABLE XXXVIII.

Oxygen tension
in mm. of Hg.

(1)

Oxygen in c.c. (at N.T.P.)
per 100 c.c. of blood.

Degree of
Saturation
ofHb. %.

(4)

Degree of
Dissociation %
(unsaturation).

[100-(4)]

Bound by
Haemoglobin.
(2)

Dissolved in
Plasma.
(3)

10

6-0

0-020

30-0

70-0

20

12-9

0-041

64-7

35-3

30

16-3

0-061

81-6

18-4

40

18-1

0-081 •

90-4

9-6

50

19-1

0-101

95-4

4-6

60

19-5

0-121

97-6

2-4

70

19-8

0-141

98-8

1-2

80

19-9

0-162

99-5

0-5

90

19-95

0-182

99-8

0-2

150

20

0-303

100

0-0

If the tensions (1) are taken as abscissae and the degree of
saturation (4) as ordinates, a curve (Fig. 56, heavy line) is
obtained called the dissociation curve of blood. This curve is
compound and may be resolved into its component factors :

(a) Pure Haemoglobin. The dissociation curve for pure haemo-
globin will be found in Fig. 56, dotted line. It differs from that
of whole blood in that its contour is that of a rectangular hyperbola.

(b) Solutes. The materials in solution in the blood corpuscles
and in the plasma are the cause of the difference between the
dissociation curve of pure haemoglobin and haemoglobin in blood.
If the pure haemoglobin is dissolved in the actual salts which are
present in the red blood corpuscles, the curve of the haemoglobin-
salt solution will be found to lie, point for point, on that of whole
blood. Examination of such curves will demonstrate the value
of these salts in the unloading of oxygen from the corpuscle.

From the curves it will be seen that at the pressure of oxygen in the
lung — i.e. 90 mm. Hg. — both whole blood and pure haemoglobin solution
are saturated to about the same extent with oxygen. (To say that they
are 92 per cent, saturated is equivalent to saying that 92 per cent, of the
haemoglobin has got its full cargo of oxygen, and 8 per cent, has no oxygen
at all. This must not be considered as admitting the correctness of such
a supposition. It may be that each molecule of haemoglobin has got
92 per cent, of its maximum load.) That is, the presence of solutes does
not materially modify the oxygen capacity of the blood at high tensions of
oxygen. In the tissues, the tension of oxygen is low, say 15 mm. Hg.

250 RESPIRATORY FUNCTION OF THE BLOOD

At this tension, whole blood can only be 15 per cent, saturated. Therefore
the oxygen carried by 77 per cent. (92 - 15) of the haemoglobin, is discharged.
On the other hand, pure haemoglobin is still 65 per cent, saturated at
15 mm. Hg. It will only be able to discharge the oxygen borne by 27 per
cent, of its haemoglobin. In other words, because of the presence of
solutes, whole blood is able to set free in the tissues the full amount of
oxygen that could be obtained from pure haemoglobin, with, in addition,
the amount that would be carried by the haemoglobin represented by the
space between the heavy curve and the dotted curve in Fig. 56. That
is, salts so aid in the unloading of oxygen that 50 per cent, of the haemoglobin

DISSOCIATION CURVE. OF H/EMOGLOBIN AT 37 C.

z
o

L

I

10 20

TENSION

JO <*O SO

OF OXYGEN IN

60

MM

80

90 JOO

7O

OF Hg

FIG. 56. — Dissociation curve representing the equilibrium between oxygen tension,
oxy-haemoglobin and reduced haemoglobin :

=Curve from pure 14% haemoglobin solution.

— = „ „ 14% haemoglobin in plasma.
- = , „ „ „ ,, with increased

tension of carbon-dioxide.

The hatched portion represents the amount of haemoglobin which gives up its
oxygen when the oxygen tension is reduced from 100 to 15 mm. Hg.

that would otherwise have retained its oxygen, is induced to give it up to the
tissues. Because of the solutes, whole blood becomes an effective carrier
of oxygen, and the total volume of fluid (and mass of haemoglobin) is
kept within reasonable limits.

Nature of union.

The average normal man has about 5 litres of blood, 2 -5 litres
of this is occupied by 25 xlO12 red corpuscles with a total surface
of about 3000 sq. metres. When fully saturated with oxygen at

UNION OF HAEMOGLOBIN AND OXYGEN 251

atmospheric pressure (160 mm. Hg.) each litre of blood will take
up 200 c.c. of oxygen. Leaving out of account the relatively
small amounts of oxygen carried in solution in the plasma and
adsorbed by the plasma proteins, we may calculate that each
corpuscle will carry oxygen to the extent of

Total oxygen capacity of blood 1000

J& J ._ __ _ =4 xlO~u c.c.

Total number of corpuscles 25 xlO12

Each cubic centimetre of oxygen will need 25 XlO9 corpuscles
to carry it.

Further, the total iron content of human blood is about 2-5
grams (Schmidt).

That is, each gram of iron is associated with 1000/2-5=400 c.c.
of oxygen — a figure closely approximating to Barcroft's experi-
mental finding of 401 c.c. Normal blood contains 14 grams per
cent, of haemoglobin. It follows that each corpuscle carries

140 x5

=28 xlO~12 grams of haemoglobin. In other words, each

^o X

cubic centimetre of oxygen postulates the presence of

28X25X109

=0-7 gram, of Hb.

1012
The iron content of Hb. must therefore be - — T~7—~~ gram

/

per gram of Hb. Putting this in molecular terms, one molecular
proportion of iron (56 grams) enters into the composition of
15,680 grams of Hb. The molecular weight generally given for
Hb is 16,660.

Evidence has been produced which shows that when haemo-
globin is fully saturated with oxygen there are 401 c.c. of oxygen
for every gram of iron. That is, each combining proportion
of iron (56 grams) co-exists with two combining proportions
(32 grams) of oxygen. From this, some deduce the presence of a
compound FeO2 in haemoglobin. That may be. On the other
hand, the idea of a chemical combination between haemoglobin
and oxygen raises hosts of difficulties which would not arise on
the hypothesis of adsorption of gas on a colloidal surface. How-
ever, no reliable direct experimental evidence bearing on this has
come to hand. If analogies could be taken as a proof instead
of analysis, the adsorption theory would hold the field un-
disputed.

252 RESPIRATORY FUNCTION OF THE BLOOD

How the tissues unload the oxygen.

These little barges 7-6/x in diameter squeeze along the capillary
vessels in the tissues. During their passage along a tube with a
diameter less than their own the corpuscles naturally undergo
distortion. This distortion has at least one effect on the loading
and unloading of the oxygen from the corpuscles. It puts on the
brake, slows down the corpuscles and gives the dock-labourers
and others opportunity to carry out their work.

Another physical factor comes into play, viz. : alterations of
temperature, and that has a profound effect on both the amount
of gas liberated and the speed at which it is handled. The
temperature in the lung where oxygen is taken on board is usually
less than 37° C. while the temperature of active tissue may be
greater (see Chap. XXXI.).

Increase in temperature increases the desaturation of haemo-
globin. The amount of desaturation brought about by an
increase in temperature may be calculated from the laws of van't
Hoff and Arrhenius. The process of saturation and desaturation
may be represented by the reaction formula

The velocity of this reaction depends, other things being equal,
on the active masses of oxygen — C0 and of haemoglobin CR,
i.e. v=k(C0 xCR).

Now kv the velocity constant of the saturation process, and &2,
the corresponding constant for desaturation, vary with the
temperature. We have seen (p. 247) that a, the absorption
coefficient of oxygen in blood, varies inversely with the tempera-
ture.

where Cu— concent ration of oxyhaemoglobin and p= oxygen
pressure.

This value, K, is constant for each temperature, and by the law
of van't Hoff the values of K for any two temperatures 7\ and Tz
are related by the equation

(e=base of Napierian logs, g=heat evolved when 1 gram molecule
of Hb unites with 1 gram molecule of oxygen).

CH AND DISSOCIATION 253

For example, let us try to determine what desaturation would
arise from raising the temperature from 36° C. to 39° C.

Here 2^=273 + 36 =309 absolute,

T2=273 +39=312

and 2=28,000 cals.,

- 28000 _3

K39=K36 € 2 ' 800X818 = J^.e-O-4856.

If KS6 be 30 per cent., then K39 is equal to 30e-°'4356=19-4,
we find that haemoglobin which was 30 per cent, saturated at
36° becomes only 19-4 per cent, saturated at 39°.

An increase in 3° C. between the values of 36 and 39 causes the
HbO2 to lose oxygen to the extent of about 10 per cent, of full
saturation.

A physico-chemical factor, however, is much more potent than
temperature in producing desaturation. Active tissues tend to
become acid. In dealing with muscle, we have seen how lactic
acid is set free as the result of activity and how oxygen is required
before it can be replaced in the muscle complex. This free lactic
acid performs another service. Either directly by partially
diffusing into the surrounding lymph or indirectly by producing
alterations in the Helmholtz (polarising) electric charge, it causes
a potential alteration in the hydrogen ion concentration of the
tissue fluid. By a series of changes which we have already briefly
considered, and to which we shall return, the net effect is to
increase the tension of CO2 in the capillaries. The molecules of
CO2 are to be the new passengers on the erythrocytes, and because
of their acidity they cause an aggregation of the colloidal particles
of haemoglobin and a marked desaturation. Carbon-dioxide
acts as if the tension of oxygen in the tissues were reduced to
10/24ths of its real value. That is, haemoglobin parts with as
much oxygen at a tissue tension of oxygen of 24 mm. Hg. as if
the tension of oxygen were only 10 mm. For example, blood
which, in the absence of CO2 would be 30 per cent, desaturated is
actually desaturated to the extent of 78 per cent, by the presence
of a CO 2 tension of 40 mm. Hg. The blood becomes now a carrier
of CO 2 from the tissues to the lungs (Fig. 56, dash line curve).

Handling of Oxygen. Consider an inland village supplied by
a canal coming as close as possible to the community. Internal
communication is effected by waterways fed from the canal. The
by-products of manufacture (sent elsewhere for elaboration) are
transported along these waterways to the canal and the same

254 RESPIRATORY FUNCTION OF THE BLOOD

gangs of labourers unload the raw material from the barges and
float it up to the factories.

To take a specific instance, muscle, as a result of its activity,
produces carbon dioxide. This weak acid acts on the sodium
hydrogen phosphate of the tissue fluid according to the following
equation :

H2CO3+Na2HPO4 ^ NaH2PO4+NaHCO3.

The sodium bicarbonate so formed finds its way into the blood
stream. Now in plasma, bicarbonate is in equilibrium with free
dissolved carbon dioxide when the volume of CO2 in solution is
1/20 of the volume of CO2 combined

The result of the influx of NaHCO3 is to increase the volume of

CO free 1

f ree CO o in order to preserve the ratio ^.r— — =-r-. Briefly,

CO 2 combined 20

the CO2 tension in the muscle capillaries tends to increase. As
stated above, increase of CO2 tension causes increased unloading
of oxygen from haemoglobin.

That is to say — increased activity postulates increased energy
usage, which renders necessary an immediately increased supply
of oxygen. The amount of oxygen required is liberated by the
desaturating action of CO2 — the main chemical product of
the activity.

The amount of oxygen in the blood does not control oxidation
in the tissues, but the call for oxygen by the tissues controls the
rate of unloading of oxygen.

Transport of carbon dioxide.

The principle underlying the transport of carbon dioxide is
identical with that enunciated for oxygen. In the tissues, the
tension of carbon dioxide is relatively high and the gas passes to
the blood, is carried to the lungs and is there eliminated. Haemo-
globin, once freed from its load of oxygen, takes on a cargo of
carbon dioxide. But haemoglobin is not the sole means of trans-
port. Carbon dioxide is about twenty-five times as soluble as
oxygen under similar conditions. Relatively more CO2 will,
therefore, be carried in true solution in the plasma. In addition
to this amount (which we have just seen is carefully regulated) a
considerable quantity of the gas is adsorbed to the various colloids
of the plasma, (i) Each gram of fibrinogen can carry 1/30 gram
of CO2. (ii) Serum proteins may adsorb a measurable quantity of
carbon dioxide — at the lowest estimate, over 5 per cent. It is

TRANSPORT OF CARBON-DIOXIDE

255

obvious that while these factors may almost be neglected in the
consideration of the transport of oxygen, they have to be reckoned
with in the case of carbon dioxide.

TABLE XXXIX.

PARTITION OF C02 IN 100 c.c. OF DEFIBRINATED BLOOD

Oxygenated
Reduced -

Vol. of CO2
in corpuscles.

19-1
224

(HAEMATOCRITE VALUE = 51).

Vol. of C02 Vol. of C02

CO2 tension. in blood. in serum.

40 45-0 25-9

40 50-4 28-0

That is, in arterial (whole) blood, there is about 50 c.c. of CO2,
of which amount the fibrinogen carries about 5 c.c., the serum
(proteins, water and crystalloid bases) about 26 c.c. and the
corpuscles about 19 c.c.

TABLE XL.
100 c.c. OF ARTERIAL BLOOD (C02 tension 40 mm., 02 tension 100 mm.).

CORPUSCLES \ f in solution - 0-85 c.c.

51% by volume L carry -| of total C02 j bound (e.g. NaHC03) 8-45 c.c.

J ' adsorbed by Hb, etc. 9-7 c.c.

PLASMA

49% by volume

carries 5 of total CO,

19 c.c.

in solution - 1-2 c.c.

bound (NaHC03) 23-8 c.c.

adsorbed by fibrino-
gen - 5 c.c.

adsorbed by serum

proteins - 1 c.c.

31 c.c.

100 c.c. OF VENOUS BLOOD (C02 tension = 45 mm., 02 tension = 40 mm.).
CORPUSCLES carry - 22 c.c. = + 3 c.c.
PLASMA carries - 34 c.c. = +3 c.c.
56 c.c +6 c.c.

For all practical purposes there is very little difference between
the corpuscles and plasma as transporters of carbon dioxide.
But, in times of stress when the CO2 tension tends to be abnor-
mally high or when the desaturation of oxyhaemoglobin becomes
abnormally great (e.g. over 40 per cent.) the corpuscles will play
the major part in the transport of CO2.

Plasma must be considered as a fluid separated from other
fluids (with which it is in equilibrium) by membranes permeable
to certain solutes. The whole transport system is a multi-phase
fluid in equilibrium. Alterations in any phase produce regulatory

256 RESPIRATORY FUNCTION OF THE BLOOD

changes in every other phase. Briefly, blood has an integrative
action.

To come back to the simile of a community : suppose Cotton-
opolis failed to function normally. This could be manifested by the
scarcity of cotton goods in the hands of the distributors. The
cause of the failure might be found by a process of elimination.
In general, (1) either the supply of raw material was inadequate
(bad harvest or transport strike), (2) or the supply of fuel was
restricted (coal strike), (3) or the workers were on strike, or (4) the
means of distributing the finished product had broken down
(transport strike). It might even happen that (5) over-production
had " drugged " the market, producing the invariable reaction on
the factory. Similar mishaps might overtake that collection of
cell-communities called the animal organism. (1) If the various
raw materials are not available even when ample fuel supplies
exist, cell life becomes narrowed and inefficient. Certain matter
must be imported — it cannot be manufactured. If the raw
material is imported but does not reach the cell, then the transport
system is at fault. (2) A similar statement could be made about
the supply of energy. (3) The cell itself may be at fault — e.g. after
HCN poisoning, in spite of adequate supplies of energy and material,
metabolism is at a low ebb. (4) The transport trouble might be
due to the scarcity of barges, e.g. anaemia, or to want of force in
the driving mechanism, e.g. heart failure. (5) In certain patho-
logical conditions a cell-community may take the bit between its
teeth and overproduce. The immediate result is to hamper its
own activities by the presence of the products of its activity.

To take a specific instance — suppose we find that an organ
seems to suffer from a lack of oxygen. This may be due (i) to
a scarcity of oxygen in the air breathed — analysis will show
that, (ii) The lung mechanism may be out of order (Chap.
XXVI.). (iii) The membrane separating lung-air from blood
may have lost its permeability. Comparison of the oxygen
capacity of arterial blood with its actual oxygen content will
indicate whether or not this is the fault, (iv) This will also
show if the erythrocytes are taking on their full load, (v) If
the blood suffers little or no desaturation on passing through the
organ, then one may presume either that the haemoglobin has
lost its power of unloading oxygen (methaemoglobin) or that the
organ has lost the power of using oxygen. Examination of the
blood pigment by means of the spectroscope may help us to choose
which of these alternatives is correct.

DYNAMIC EQUILIBRIUM 257

No matter what organ or tissue it is that fails to function
normally — it must remain in dynamic equilibrium with the blood,
and through the blood with every other tissue and organ in the
body. Every change occurring anywhere in the body sets in
motion a series of far-reaching alterations tending to restore
equilibrium. It is this constant adjustment of physical and
chemical force and matter brought about mainly via the inland
transport system that goes to make up the metabolism of the
organism.

Other materials are carried by the plasma, viz. :

I. SUBSTANCES TO BE USED BY THE TISSUES.

AmiCnoeAcids - - I FrOm Chouses ^^ "^ ^

Accessory substances and Salts I

Hormone ' I From thoracic duct and from depots.

II. SUBSTANCES EXCRETED BY THE TISSUES.

Urea - - \

Ammonia - - - - ( ,-,,. . , , , ,, , .,

Creatin and Creatinin ( Eliminated by the kidneys. (q.v.).

Purins -----

B.B. 17

CHAPTER XXIII
LOADING UP

" I send it through the rivers of your blood
Even to the court, the heart, the seat o' the brain,
And through the cranks and offices of man,
The strongest nerves and small inferior veins
From me receive that natural competency
Whereby they live." SHAKESPEARE.

WE have now come to one of the most interesting parts of our
study, namely the handling of the imports in their course between
the external and the internal transport systems. As we have
seen, the material brought to the body may be divided into two
classes. One of these consists of the gas, oxygen, which comes
to the port of arrival almost ready for use, and which is passed
directly to the inland transport system for transmission to the
various cell-communities.

The foodstuffs form the other class. They are " raw material "
and have, as a rule, to undergo some process of manufacture
before they can be distributed to the consumer. They are
handled by a special mechanical transport service and are taken
through the various factories and then handed to the inland
transport.

In this chapter, we are to deal with the importation of oxygen
and the mechanism by which it is received at the port, carried
overland and loaded on the submersed barges on their way inland.
Indissolubly associated with any system of importation is the
provision of exports. Any barge travelling empty on the blood
stream as on any external industrial canal is a distinct loss to the
whole community. Every ship that leaves our shores without a
full cargo tells a tale of industrial inefficiency. In the body the
output of carbon-dioxide and the intake of oxygen are nicely
balanced. As a matter of fact, the regulation of the rate of
importation by the rate of exportation is as much a law here as
in the realm of Political Economy.

258

VITAL CAPACITY

259

A separate chapter has been devoted to the mechanism whereby
the oxygen is brought from outside into the port. Briefly, by
muscular movements air is drawn through filtering and warming
appliances into the harbour, and after a very short interval is
expelled from the harbour into the outer air.

In the average resting man, somewhat over 500 c.c. of air come
into the respiratory chambers at each ordinary quiet inspiration
and somewhat less than this amount is expelled at each expiration.
One may say, in round numbers, that the tidal air of the average
adult is about 500 c.c. The tidal air at various ages and weights
has been determined and is given below :

TABLE XLI.

Age.

Weight in Kilos.

Tidal air in c.c.s

0- 6 months.

3-77

48

6-12 months.

7-7-12

85-129

3- 7 years.
8-14 years.
Adult.

14-3-19
22-29
60-70

124-221
221-395
440-550

If a very deep inspiration is taken, more than 500 c.c. can be
sucked into the lungs. This extra quantity, which varies with
the " build " and expertness of the subject but which usually is
about three times the tidal volume, is called the comple mental air.
By a forced expiration after a normal inspiration the reserve air
may be expelled from the lungs. The volume so expelled varies
very much with practice. Some people can only breathe out an
additional 500 to 700 c.c., while singers, physical training experts
and others who practise abdomino-thoracic breathing,' may
register a volume of 1500 to 2500 c.c. These three quantities
together give the vital capacity of an individual, i.e. the amount
of air that a person can expire after a deep inspiration. It is not
possible completely to empty the lungs. As we shall see later,
a mechanism exists in the air vesicles which prevents their total
collapse. They retain about a litre of air — the residual air.

To summarise, taking average figures :

j Tidal air • 500 c.c.

Vital capacity • Complemental air 1500 c.c.

( Reserve air 1500 c.c.

Residual air

Volume of fully distended respiratory apparatus

3500

- 1000 c.c.

- 4500 c.c.

260 LOADING UP

This volume of 4500 c.c. includes not only the volume of the
lungs but of the approaches to the lungs — the nasal cavity,
the trachea, the bronchi and the bronchioles. These constitute the
outer harbour or " dead space," which has a capacity of about
140 c.c. That is, in ordinary quiet breathing each respiration
brings about 360 c.c. of air into the inner harbours (air sacs,
alveolar sacs, or infundibula). These funnel-like chambers to
which the air passages lead are the most expansile structures in
the lung, and they are largest where the expansion of the lung is
greatest. All round their walls open myriads of small thin-walled
air-cells or alveoli — the true wharves of the port. There and
there alone takes place the interchange of exported CO2 and
imported O2.

Let us look first at the area of wharfage. The interior of the
air sacs and their alveoli is lined by a thin transparent layer of
endothelium. If the lining could be stripped from all the sacs
of both lungs and inflated, it would form a spherical balloon about
17 feet in diameter. If it were spread as a continuous flat sheet
it would cover a square floor of 30 feet by 30 feet. In other words,
the area of wharfage is, at least, over fifty times the surface area
of the body. The average diameter of an air cell is 0-2 mm.,
with a volume of 0-004 cub. mm., and an area of 0-125 sq. mm.
Suppose these air cells to be spherical and closely packed together,
then the maximum number contained in a cubic millimetre of lung
substance would be 250 cells of total surface 31'2 sq. mm. Now
the average value for the total volumeof lung substance is 1'617 c.c.
This provides for the possible presence of 404,500,000 air cells
with a surface of 50-56 square metres. Of course this is a
maxintum value for the number. From the volume of lung
substance has to be deducted the volume of the supporting cells
of the lung and of the air passages. On the other hand a minimal
value is given for area, since no account is taken of the increase of
surface caused by the projection of the blood capillaries into the
lumen of the alveoli. Various estimates have been made of the
surface area of the alveoli ranging from that of von Huschke of
2000 sq. metres to that of Aeby given above. Hufner's value
is generally taken as a mean, viz. 140 sq. metres. Of this area,
about three-fourths consists of thin-walled capillary blood vessels.
That is, the effective absorptive surface is about 100 sq. metres.

Over a surface of about 100 sq. metres, interchange between
alveolar air and blood is possible. Just behind this surface-
epithelium lie capillary blood vessels of such small bore that the

EFFECTIVE ABSORPTIVE SURFACE 261

red blood corpuscles are distorted in their passage through them.
This naturally produces a decrease in the rate of blood flow. The
rate is further decreased by the increase in the total sectional area
of this capillary system which is at least seven times greater than
that of the aorta (Chap. XXIV.). The sudden increase in the
area over which the blood has to spread itself in a layer less than
one corpuscle thick causes a marked decrease in the velocity of
the stream. These two conditions, (a) narrow bore and (6) in-
creased area of distribution, of course facilitate the processes of
unloading and reloading the erythrocytes. The structure is, in
principle, just the same as that of the kidney.

The next problem before us is that of the transference of carbon
dioxide from the blood to the air and of the oxygen from the
alveolar air to the blood. About the first process there seems to
be no difficulty. Everyone is agreed that, as the tension of
carbon dioxide in the blood of the pulmonary artery just as it
enters the capillary system is greater than its tension in expired
air, a simple process of diffusion through a wet membrane is all
that is required. The tension of CO2 in alveolar air and in the
blood is 40 and 46 mm. Hg. respectively. There is, therefore, a
difference of 6 mm. Hg. in the CO2 pressure tending to cause a
flow of CO 2 from blood to air. Is this gradient of pressure
sufficient to account for the 250 c.c. of gas normally expired per
minute ?

The passage of gas through a membrane depends (a) on the
nature of the membrane, (6) on the structure of the membrane,
(c) on the physical state of the membrane, (d) on the nature of the
gas, and (e) on the gradient of pressure.

(a) The layer of flattened cells separating blood from alveolar
airdiffers little in chemical nature from any other similar structure.
One may note, however, its richness in lipoids. (b) It is constructed
of large irregular flattened cells forming an extremely delicate
layer as thin as the film of a soap bubble. The average thickness
of this membranous layer is 0 -004 mm. (c) Not only does the
protoplasm forming the membrane contain about 90 per cent,
of water, but it is kept moist on both sides, (d) Carbon dioxide
is very soluble in water. Water at body temperature and atmos-
pheric pressure will absorb over half its volume of carbon dioxide.
(e) Experiments by Krogh and others seem to have proved beyond
question that the differences in tension existing on the two sides
of the lung tissue are quite sufficient to account for the passage of
the necessary volume of gas.

262 LOADING UP

It is worth while to look a little more closely at this problem.
In Chap. XXII., p. 247, is given a table of absorption coefficients
of the respiratory gases. These values of a' indicate the volumes
of gas at N.T.P. which will dissolve in 1 c.c. of water. Later in
the same chapter, figures which hardly differ from a were given
for the solubility of these gases in plasma, etc. The velocity of
diffusion depends not merely on the pressure gradient and on the
absorption coefficient of the gas, but also on a factor k — the
diffusion coefficient, k is a constant for each gas and each
temperature. The appended table (from Loewy) will amplify this.

TABLE XLII.

DIFFUSION COEFFICIENTS.

Temperature 16° C. 37° C.

Oxygen - 1-62 1-68

Carbon dioxide - 1-38 143

Nitrogen - 1-73 1-79

The product of a and k gives the diffusion rate in cm. per
24 hours through a layer of water, 1 cm. xl sq. cm. with a pressure
gradient of 1 atmos. For example, at 37° C. carbon dioxide has
a diffusion rate of 1-43 X 0-57 =0-81 5 cm. .per 24 hours.

It has been found that k bears a definite inverse relationship
to the square root of the molecular weight of the gas. The result
of multiplying the diffusion coefficient by the square root of the
molecular weight of the gas is thus a constant for all gases. This
diffusion factor kjm has a value, for water, of 0 -0649.

The diffusion rate through lung substance, because of its large
content of lipoids and lipins must be greater than that through
water. Experiments with soap bubbles and with frogs' lungs
have confirmed this deduction. It has also been found that the
velocity of diffusion is absolutely unaltered by slight alterations
in the pH of the lung tissue. Loewy maintains that the rate of
diffusion is the same in dead and in living lung tissue. The
diffusion factor through lung has been estimated as 0-139. Ex-
periment has shown definitely that CO2 passes just as readily in
either direction through the lung wall. This has been amply
confirmed by Krogh, who found that the direction of diffusion
depended entirely on the direction of the gradient of pressure, and
the rate of diffusion was regulated by the steepness of this gradient.

The volume of gas diffusing per minute through one sq. cm.
of alveolar wall may be calculated from this formula :

_
~

760 — x/ra • d

DIFFUSION 263

Dealing with carbon dioxide we may evaluate as follows :

a at 37° =0-57,

px=CO2 tension in the blood of the pulmonary artery

=about 46 mm. Hg,

p2=CO2 tension in alveolar air=about 40 mm. Hg,
p1—p2=,46— 40=^6 mm. Hg.

This difference of pressure, of course, only exists at the beginning of
the experiment. The blood loses carbon dioxide, i.e. pt decreases ; C02
passes into the alveolar air, i.e. pz increases, and p1 — p2 tends towards
zero. It is, therefore, necessary to take a mean value between 6 and 0,
i.e. 3 mm. Hg.

C=diffusion factor=0-139,

d=thickness of alveolar wall=0-004 mm.,

0-57X3XO-139
~760X6-63XO-004
=0-01 c.cm. per minute.

As the effective absorptive surface of the lung is about 100 sq.
metres, there can pass through it each minute

100 x 10,000 xO -01 =10,000 c.cm.

of carbon dioxide by simple diffusion.

One may consider the problem from another aspect and deter-
mine the gradient of pressure necessary to furnish the 250 c.c. of
carbon dioxide normally expired per minute. Transposing the
formula one gets

v X760— »Jm xd
P'-p2= axe • •

Evaluating this,

250x760x6-63x0-004
Pi ~P*—Q.57 xO-139 XlOO X 10,000

=0 -063 mm. Hg.

That is, a difference of CO2 tension between blood and alveolar
air of only 2 xO -063=0 -12 mm. Hg. would be quite sufficient to
cause 250 c.c. of CO2 to pass through the lung wall per minute.
During work the amount of carbon dioxide eliminated by the
lungs may be increased tenfold. The above figures show that there
is ample wharf-space for this exportation.

The transference of oxygen from alveolar air to blood has been
the cause of much controversy. Two conflicting views both
backed by experimental facts are held.

264 LOADING UP

(1) The lungs may be considered as secretory glands. Fish
have a swim bladder which is, like the lungs, an outgrowth from
the alimentary canal. Oxygen is secreted by it so as to equalise
the specific gravities of fish and water. The fish may secrete
oxygen against the pressure produced in the bladder by immersion
to a great depth, e.g. against the pressure of hundreds of atmo-
spheres. Against this view may be opposed the histological fact
that cells composing the walls of the swim-bladder structurally do
not resemble those of the lung. The former are deep granular
cells typical of secretory tissue, while the latter, like the capsule
of Bowman in the kidney, are thin and flat. Moreover birds,
which have of all animals the most rapid and efficient respiratory
exchange and so should have a lung epithelium exhibiting marked
secretory qualities, have no epithelial covering at all, so that the
capillaries appear to be almost completely free and surrounded
by alveolar air.

(2) Most modern workers maintain that just as CO2 diffuses
outwards so does oxygen diffuse from air to blood. The whole
controversy turns on the existence of a pressure gradient for
oxygen. The earlier investigators got results which indicated
that the oxygen tension of the blood frequently exceeded that of
the alveolar air. Later workers like Douglas and Haldane
disagree with the earlier findings, and by the employment of finer
technique have proved definitely that normally the tension of
oxygen is always less in the blood than in the alveolar air. They
still maintain, however, that under certain more or less abnormal
conditions — say, acclimatisation to high altitudes — there is an
active absorption and transference of oxygen to the blood on the
part of the pulmonary epithelium.

A man at rest requires about 300 c.c. of oxygen per kilo of
body weight per hour. The average man weighs about 66 kilos,
i.e. 330 c.c. of oxygen must pass into his blood every minute.
During violent exercise the necessary intake of oxygen may be
as great as 3000 c.c. per minute. In order to produce this
transference from air to blood a certain pressure difference is
necessary.

Krogh has shown by an ingenious tonometric method, that
the oxygen tension of the blood is always lower than the alveolar
oxygen tension, and the difference is generally 1 to 2 — even 3 to 4
— per cent, of an atmosphere. One must now consider whether
1 per cent., i.e. 7-6 mm. Hg, is a sufficient pressure gradient for
respiratory purposes.

SECRETORY HYPOTHESIS 265

Employing the same formula as for CO2 one finds with a differ-
ence of pressure of 7 -6 mm. Hg that

0-0239 X3-8XO-139
v=— — =0-0006c.cm.

760x5-66x0-004

per minute per sq. cm. This gives a value of

100 x 10,000 xO -0006 =600 c.cm.

passing through the total effective absorptive surface of the lung.
Thus we see that the physical conditions allow for an ample supply
of oxygen for ordinary purposes. As a matter of fact a difference
in pressure of less than four millimetres would be quite sufficient
to ensure the supply of the 330 c.c. per minute required by the
average man resting but awake.

How is the rate of transference increased to meet the needs of
the man doing hard muscular work who uses up 3000 c.c. of oxygen
per minute ? One very obvious point of difference between a
resting and a working man lies in the volume of air passing into
the lungs per unit of time. The following table shows that the
ventilation of the lungs is markedly increased by the performance
of work.

TABLE XLIII.
VENTILATION OF LUNGS.

Litres per min. Kespir. per min.

Resting 6-7 13-14

Walking 24 14

Running - 60 15

Swimming in cold water - 90

Running up and down stairs

(Greatest possible effort of a

noted swimmer) - 190 over 60

That is, by the constant addition of fresh air to the lungs the
tension of oxygen in the alveoli is kept from falling. A tenfold
increase in ventilation provides an ample margin for even the
most strenuous work.

Those who hold to the secretory hypothesis maintain that
while diffusion is capable of providing a sufficient oxygen supply
for a normal existence even with hard muscular work, yet when
the pressure of oxygen in the lung is brought much below normal,
active secretion by the lung epithelium must be brought into
play. Aviators, for instance, rise to great heights, and so come
under a low barometric pressure.

266 LOADING UP

It is well known that ballooning, for instance, causes respiratory
distress ; so, too, does mountaineering. Mountain sickness fre-
quently begins at altitudes of 2000 to 3000 metres, particularly if
the ascent has been fairly rapid by railway. Airmen usually suffer
after ascending 5000 to 6000 metres. The partial pressure of
oxygen in the blood as determined by the carbon monoxide method
has been found to be 35 mm. Hg above the oxygen pressure of
alveolar air. Considerable doubt exists, however, as to the validity
of this method. It depends on the careful matching of a carboxy-
lated blood with a blood-carmine mixture, and minute quantities
of blood are used.

TABLE XLIV.

EFFECT OF HEIGHT

ON BAROMETRIC

PRESSURE.

Height above sea level
in metres.

Barometer,
mm. Hg.

Per cent, of an
atmosphere.

0

760

100

1000

670

88

2000

593

78

3000

524

69

4000

463

61

5000

410

54

6000

357

47

7000

320

42

TABLE XLV.

EFFECT OF ATMOSPHERIC PRESSURE ON ALVEOLAR OXYGEN
TENSION.

Height above sea O2 tension of Alveolar O2 tension,
level in metres. air. mm. Hg. mm. Hg.

Berlin 54 157 105

Brienz 500 148 88

Brienzer Rothorn - 2130 121 62

Cold'Olen 2900 110 60

Monte Rosa 4560 89 61

One fact in the data given by those investigators is a little
strange although it may have no significance. Notwithstanding
that the arterial oxygen tension was always higher than that
given for the alveolar air, it was never higher than that of the
atmosphere at the time, although occasionally not much below it.
Why should the secretory power fail just at this level and not
raise the oxygen tension above that of the atmosphere ? Is
it possible that the blood had come into equilibrium with an
oxygen tension which was not given correctly by the measurement
of that of the alveolar air ? Might it not also be possible that
the carbon monoxide method gives different values when the

EFFECT OF ALTERED AIR PRESSURE 267

haemoglobin content of the blood is increased, as in the case of
acclimatisation to high altitudes ?

TABLE XLVI.
ATMOSPHERIC PRESSURE AND NUMBER OF ERYTHROCYTES.

Height above sea Red

level in metres. corpuscles.

Christiania 0 4,970,000

Zurich 412 5,752,000

Davos 1560 6,551,000

Arosa 1800 7,000,000

Cordilleras - 4392 8,000,000

Hasselbalch shows that the hydrogen ion concentration is
increased under those circumstances.

" This question of secretion by the lungs is instructive from the point
of view of ' vitalism.' When first proposed, it was held to apply to
the ordinary state of affairs ; but as improvements were made in experi-
mental methods, the absorption was shown to follow physical lines ;
it was then held to apply to cases of muscular exercise, and now only
to acclimatisation to high altitudes. One might venture to say that the
more accurate the methods of investigation the better is it found that
chemical and physical laws are capable of explaining physiological pheno-
mena."— Bayliss, Principles of General Physiology.

Let us now consider what happens to the inland transport
service when the port becomes congested with incoming traffic.
Compressed air is used in all the great sub-aqueous works of to-day,
in diving, in preparing foundations for bridges, in pier building, and
in the construction of tunnels or shafts through water-bearing
strata. It is well known that a large percentage of the men
working under those conditions suffer illness and many die. In
the construction of the Adour bridge 90 per cent, of the workers
suffered from " compressed air " disease, and in the boring of the
Hudson Tunnel 2 per cent, of the caisson workers died each month.
Compressed air sickness is characterised by its protean symptoms
— loss of speech, blindness, deafness, transitory madness, vertigo,
loss of consciousness, emphysema, spinal paralysis", etc. None
of the symptoms, with the exception of some slight ear trouble,
ever occurs while the men are under pressure. " Mules lived about
a year in the Hudson tunnel and were healthy enough to kick and
bite at all comers." The illness seemed to come on during or
after decompression and is now known to be due to the appearance
of bubbles of nitrogen in the tissues. Boyle, in the seventeenth
century, showed that bubbles of gas appeared in the humours of a
viper's eye when submitted to rapid decrease of air pressure under

268 LOADING UP

an air pump. Paul Bert in a remarkable series of experiments
(1870-1880) proved that these bubbles were nitrogen and that
they might block up the capillaries in some part of the body and,
by cutting off that part from the blood supply, produce one or
other of the symptoms mentioned above.

If merely the pressure of the surrounding air is increased, why
should nitrogen alone be set free on decompression ? When a
person is placed in compressed air, the blood passing through the
lungs dissolves the same volume of the atmospheric gases as it
does under normal conditions, but the weight of gas absorbed
will be increased above normal in proportion to the increase in
partial pressure of each gas in the alveolar air. Now we have seen
that the partial pressure of carbon dioxide in alveolar air is a
constant, hence there can be no increase in the amount of carbon
dioxide present in the blood during exposure to compressed air.
Oxygen is carried in two ways, (a) by haemoglobin, and (b) in
simple solution in the plasma, (a) At atmospheric pressure the
haemoglobin is almost saturated with oxygen, — the little erythro-
cyte barges are comfortably filled. Increase of alveolar tension
may produce a slightly better oxygenation of the haemoglobin,
but it requires a very marked increase of pressure to make an
appreciable increase in the amount of oxygen carried by this
means (Fig. 56). (b) According to Dalton's Law, the amount of
gas dissolved is directly proportional to its partial pressure.

At body temperature and normal pressure, arterial blood holds
3 c.c. of oxygen in solution in every litre of fluid. If the pressure
is increased x times, then each litre will still dissolve 3 c.c. of
oxygen, but this oxygen will weigh x times as much as normally.
On being carried to the tissues, the blood will share its dissolved
oxygen with them in proportion to its partial pressure and to its
solubility in the various tissues. These tissues will use up the
dissolved oxygen in preference to that carried by the corpuscles,
and as the amount in solution, except after exposure to enormous
pressures, is only a small percentage of the total available oxygen
in the arterial blood, it will soon be used up. We again draw
attention to the fact that increase in the available oxygen does not
cause increase in its utilisation by the cell. A candle burns more
brightly in oxygen and soon ends its light-giving career. The
cell " ca's canny " — holds on the even tenor of its way, takes up the
oxygen it requires for its immediate needs and keeps no store but
the tiny quantity dissolved in its protoplasm.

To take a concrete example. At 38° C. and atmospheric

CAISSON DISEASE 269

pressure 1 litre of blood contains 200 c.c. of oxygen carried by
haemoglobin and only 3 c.c. in simple solution (measuredat N.T.P.).
Sixfold increase of pressure makes no appreciable difference to the
value of the corpuscular • oxygen but increases the dissolved
oxygen to about 18 c.c. That is, the ratio of dissolved to " bound "
oxygen is increased from about 1/70 to 6/70. The entire result
would be that as there are about 3| litres of blood in the average
man the venous blood would carry not more than 20 per cent, more
oxygen than normally. In other words, the desaturation of
haemoglobin would take place to quite the same extent as under
atmospheric pressure. This eliminates oxygen as the gas causing
" compression illness " and leaves nitrogen alone to be dealt with.
Let us first consider how the nitrogen taken up by the blood
from the alveolar air is distributed to the various tissues of the
body. In view of what we have seen as to the ease and complete-
ness with which the blood becomes saturated with oxygen in its
passage through the pulmonary capillaries, we may take for
granted that saturation with nitrogen under the same conditions
is just as complete. It is also reasonable to suppose that Dalton's
Law of partial pressures is just as applicable to blood exposed to
compressed air as to any ordinary solution. This supposition is
supported by experimental facts. When blood is exposed to
compressed air it will absorb a volume of nitrogen commensurate
with the absorption coefficient of this gas in blood. During its
passage through the tissues it will share its load of nitrogen with
them in proportion (a) to the absorption coefficient of the gas in
blood and tissues and (b) to the partial pressure of the gas in
blood and tissues, (a) With regard to the first point, the solu-
bility of nitrogen per unit mass of tissue varies greatly. For
example, fat can absorb about six times as much nitrogen gas as
blood, while the earthy constituents of bone probably absorb only
an infinitesimal amount. With these two tissues excepted we
may consider that, as the others differ but slightly in chemical
and physical constitution from plasma, they also take up approxi-
mately the same quantities of gas. (b) Normally the tissues are
saturated with nitrogen at its partial pressure in the atmosphere —
every -gram of tissue contains approximately 0-0145 c.c. of
nitrogen. If the external pressure is increased, this volume will
immediately be diminished correspondingly, and the deficit will
be made good at the expense of the circulating blood. Take for
example the sudden increase in pressure to three atmospheres
brought about by a rapid descent through 60 ft. of water to the

270

LOADING UP

bed of the sea. The volume of gas in solution in the body is at
once reduced to 1/3, viz.: 0-005 c.c. per gram. At the same time
the blood in the lungs has its content of nitrogen reduced from its
normal value of 0-87 c.c. per 100 c.c. of blood to 0-29 with almost
immediate restoration to the normal figure. The litre of blood
in the capillaries of the lungs would now have in solution three
times the weight of nitrogen as under normal pressure. When
the blood arrives at the tissues, partition of its load will take
place. Each gram of tissue has a deficit of 0-01 c.c. of nitrogen,
and nitrogen will pass from blood to tissue till each gram of tissue
contains the normal value of 0-015 c.c. per gram. This value
will not be reached at once, because the very acquisition of
nitrogen by the tissue implies the loss of nitrogen by the blood.
The blood then returns to the lungs for a fresh charge, which it
again shares with the tissues, and so on. Haldane calculates
that somewhere about five hours are required before the body is
completely saturated with nitrogen after any change of pressure,
i.e. till the partial pressure of nitrogen in the tissues corresponds
with its partial pressure in the blood and so to its partial pressure
in the alveolar air.

If we consider the amounts taken up by the various tissues we
may arrive at some conclusion as to the mechanics of the processes
of saturation and desaturation. The average working man
weighs 70 kg., of this amount 15 per cent, or 10-5 kg. is fat or
fatty material ; 5 per cent, or 3-5 kg. represents the amount of
blood ; while the earthy constituents of bone (about 3 per cent.)
may be neglected.

TABLE XLVIL

DISTRIBUTION OF NITROGEN IN THE TISSUES OF MEN WEIGHING 70 KG.

Tissue.

Per cent, of
body wt.

Wt. of tissue.

Vol. of nitrogen.

Blood -
Fat-

5
15

3-5 kg.
10-5 „

30 C.C.

530 „

Bone

3

2-1 „

0 „

Residue -

77

53-9 „

435 „

100

70 kg.

995 c.c.

Blood, as we have seen, can take up in simple solution about
0-87 c.c. of nitrogen for every 100 c.c. Taking the specific
gravity of blood as 1 -06 we may consider that about 30 c.c. of

DESATURATION RATE 271

nitrogen are constantly in solution in the blood. Fat is capable
of absorbing six times as much nitrogen as an equal weight of
blood, i.e. we may write down 500 c.c. as the volume of the gas
held by the fatty matter of the body. Leaving out the earthy
part of bone the remaining tissues account for about 435 c.c.

Taking round figures we see that the average man has, dissolved
in his blood, about a litre of nitrogen. The weight of this litre
is a function of the pressure under which it has been absorbed.
Looked at from another point of view, the weight of nitrogen held
in solution by the tissues is 32 times as great as that present in the
blood. If, therefore, the blood is, for the purpose of this calcu-
lation, considered as spread uniformly and at a uniform rate
throughout the body, the tissues would receive at the end of one
complete circuit of the blood after exposure to a sudden increase
in air pressure, 1/32 of the excess of nitrogen corresponding to
complete saturation at the new pressure. The second round of
the circulation would add 1/32 of the remaining deficit in satura-
tion, and so on. Haldane finds that it takes 23 rounds of the
circulation to half saturate the tissues at the new partial pressure
of nitrogen. The progress of the saturation of the body with
nitrogen may be represented by a logarithmic curve (Fig. 57).
As about 3 -5 litres of blood pass through the lungs every minute
and as the total blood volume is also 3 -5 litres, we may substitute
minutes for rounds of the circulation and state that it requires
23 minutes to render the tissues half saturated to a new pressure
of nitrogen.

The process of desaturation, provided physiological conditions
are kept constant, follows the same curve. If the tissues are
exposed to blood carrying nitrogen in excess of the normal amount,
for sufficiently long to be in gaseous equilibrium with that blood —
i.e. to be saturated — then in order to prevent the formation of
bubbles, the process of desaturation would need to be carried out
at the same rate as the saturation. If the desaturation rate were
too rapid, then gas would be released from the tissues more
rapidly than it was being passed from blood to alveolar air.
This would entail a very slow and uniform rate of decompression.
A diver's ascent from the sea bed might have to be spread over
hours. Paul Bert, from his experiments on animals, concluded
that the decompression period should be 30 minutes for under
3 atmospheres, and 60 minutes for 3 to 4 atmospheres. This
ruling of the famous French scientist has never been carried out
in industrial practice, the usual period for " leaking out " being

272

LOADING UP

about 15 minutes altogether. As a result of this haste to get into
" free air," constructional engineers are afraid to put their men
under more than +3-5 atmospheres. Bullion has been salved
from ships lying 171 feet below the surface. The divers in this case
stayed below for only 20 minutes at a time and took 20 minutes
to ascend. Even then some of them were stricken with paralysis.
Greenwood endured compression to 7 atmospheres (=210 feet of
sea water), but took over 2 hours to decompress. These long

too
so

70
60

(30)

(60)

(90)

(120)

MINUTES

(JSO)

20

1C

01 231-5

MULTIPLES OF THE TIME REQUIRED TO PRODUCE HALF-SATURATION

FIG. 57. — Curve showing the progress of saturation of any part of the body
with nitrogen after any given sudden rise of air pressure (after Haldane).

periods of decompression which seem necessary for safety, put
the men in charge in an awkward dilemma when, on account of
some mishap, it is necessary to bring men at once to the surface.
From table XL VIII. it will be seen that the diver is brought to
the surface from the bottom in stages. These stages are three
metres apart and the time spent at each one depends on the
duration of his stay on the bottom. This method of decom-
pression by stages depends on the empirical fact that no
untoward results arise from even a rapid decompression of one
atmosphere or less.

DECOMPRESSION RATE

273

An atmosphere or 760 mm. of mercury is equal to a pressure
of 1 kg. per sq. cm. or to about 3 metres of sea water. Even with
this more rapid means of attaining normal pressure, the diver is
limited either to a very short stay under water or to a tedious
waiting at various levels.

TABLE XLVIII,

A PORTION OF A DIVING TABLE USED BY NAVAL DIVERS.

Depth.

Depth and duration

Total

Time from surface

in minutes of stop-

Time for

pressure in

to beginning of

pages during ascent.

total ascent

Fathoms.

Metres.

atmospheres

ascent.

METRES.

in minutes.

12 9 6 3

•

Up to 15 min.

- 2 3 7

15

15-25 ,

- 5 5 10

25

18-20

33-36|

4-6 I

25-35 ,

- 5 10 15

33

35-60 ,

5 10 15 25

57

60-120 ,

10 20 30 35

97

>

Over 120 ,

30 35 35 40

192

Haldane and his collaborators have very fully investigated
this question. They argue that, as the volume of gas in solution
is constant no matter what is the pressure, and as it has been
proved to be perfectly safe to decompress rapidly from a plus
pressure of one atmosphere (1-25 atmospheres to be exact) to
normal, then it must be equally safe to decompress rapidly to half
pressure for any value. For example, if the total pressure were
eight atmospheres, these workers advise a rapid decompression
to four atmospheres, and after a pause to two atmospheres, and,
after a pause, more slowly to normal pressure. The principle
underlying this plan is that the discharge of nitrogen from the
start of decompression is at the maximum rate consistent with
safety. The rate of discharge, of course, depends on the gradient
of pressure between venous blood and alveolar air. This gradient
is kept as steep as possible, and there is, therefore, a maximum
elimination by the lungs.

18

CHAPTER XXIV
CIRCULATION

" The circling streams, once thought but pools of blood,
(Whether life's fuel or the body's food)
From dark oblivion Harvey's name shall save."

DRYDEN.

THE inland transport system that we have had under consideration
differs materially from our canal system. Not only are the barges
submersed in the plasma but the force which carries them along
is the force which causes the plasma itself to move. The water-
ways are a series of elastic-walled tubes forming a closed circuit.
In this circuit is a central pumping station, the heart which keeps
the bloofl in motion. The accompanying figure (Fig. 58) is a
diagrammatical view of a vertical-mesial section through the
heart. From it we learn that the heart is not a simple structure.
In the diagram four distinct cavities can be seen, viz. : right and
left ventricles, left auricle and aortic space — the right auricle is
not shown. The heart is really a double pump consisting of a
main pump or systemic heart (left auricle and ventricle) and
a subsidiary pump or pulmonary heart. In Fig. 59 is given
a scheme of the circulation. By contraction of the left ventricle
the blood is forced along a series of conducting tubes or arteries
(Art.) which lead to every part of the body and end in the substance
of the tissues in a network of innumerable hair-like canals, the
capillaries (Cap). These capillary vessels are the wharves of the
tissues. Through their walls takes place the exchange of imports
and exports by which we measure the metabolism of the tissues.
Consequently it is found when the capillaries join together to
form the wider conducting canals, venules and veins, that the
blood has lost some of its cargo of oxygen and nutrient matter,
and has gained a certain amount of waste matter. This with-
drawal of nutrient material is made good by the diversion of
some of the blood from an arterial canal to the capillaries in the

274

GENERAL SCHEME

275

walls of the intestine (ALC.). The waste matter is eliminated,
as we have seen, by a capillary mechanism in the kidney. Chemical

FIG. 58. — Vertical Mesial Section through Heart to show Aortic and Mitral Valves.
P.V ., right ventricle ; L.V., left ventricle with papillary muscle ; L.A., left auricle
with the mitral valve extending into the left ventricle ; Ao., aorta with anterior cusp
on top of septum.

(Noel Paton's Essentials of Human Physiology.)

CAP

ART.

FIG. 59. — Scheme of the Circulation. S.H., systemic heart sending blood
to the capillaries in the tissues, Cap. The blood brought back by veins, and the
exuded lymph by lymphatics, Ly., passing through glands ; blood sent to the ali-
mentary canal, ALC., and from that to the liver, Liv . ; blood also sent to the kidneys,
Kid. ; the blood before again being sent to the body is passed through the lungs by
the pulmonic heart, P.H.

(Noel Paton's Essentials of Human Physiology.)

changes occur on the passage of the blood through the capillaries
of certain factories, e.g. liver and spleen. The loss of oxygen is

276 CIRCULATION

not made good until the blood has been carried by the veins into
the right auricle, passed from this reception house into the body
of the pump, the right ventricle (P.H.) and forced by the action
of this subsidiary pump into the lung capillaries. There, as we
saw in the last chapter, it gets rid of the excess of carbon dioxide
and makes up its deficit of oxygen. Finally the blood, with its
fresh supply of nourishing substances from the alimentary canal
and of oxygen from the lungs, is poured into the receiving chamber
of the main pump — again to pass into the left ventricle and so
to the tissues.

From the capillaries some of the constituents of the plasma
are forced into the spaces between the cells as lymph. From
these spaces the fluid either passes back into the capillaries or
flows away in a series of lymph vessels which carry it through
lymph glands (Ly.) from which it gains certain necessary consti-
tuents and finally bring it back to the central pump.

This, in brief, is the circulation as we know it to-day, and this
knowledge is due in great part to the labours of Harvey. Before
his time little was known of how the blood was distributed in
the body. Of one point the old physiologists were sure, and that
was that there was no circulation of the blood, only an ebb and
flow. Harvey's work is a perfect example of how scientific work
should be carried out. First of all, he cleared his mind of all
preconceived ideas and got down to bedrock. Then he stated
his method. The method employed was that now made famous
by the author of Sherlock Holmes, viz., induction, based on careful
investigation. He examined the valves of the veins, and using
them as sign posts, traced the course of the blood. Similarly,
the valves of the heart permit a current to flow in one direction
only. There never was a more complete argument than the one
that Harvey pressed for the circulation of the blood. There
could be no ebb and flow where all the valves were " one way."
No scientific work is complete without a reference to quantities.
The test of truth must rest with the balance or measuring
mechanism. Harvey found that the left ventricle of a man's
heart held two ozs. of blood without being distended. If only
half the load were discharged at each systole and the heart beat
70 times per minute, then 700 ozs. or 44 pints of blood would be
discharged into the aorta every 10 minutes. The total blood
volume is under 9 pints. From this he urged the necessity of
some communication between the arteries and veins. That is,
after experiment, observation, analysis and argument come

HARVEY'S WORK 277

reasoned hypotheses. Four years after Harvey's death the great
Italian anatomist Malpighi saw under the microscope these
capillaries which the physician had seen with the eye of faith.
The demonstration of the actual passage of blood from arteries
to veins through capillary channels was given in 1688 by Leeuwen-
hoek, the illiterate janitor of the aldermen of Delft.

Dynamically considered, the blood acts in much the same way
as any other equally viscous fluid driven through a series of tubes.
In order to understand many of the problems which one meets
in the study of physiological phenomena, it is necessary to obtain
some insight into the movement of fluid under an external driving
force. As Servetus says, '; In order to learn how the blood is
formed it is necessary to ascertain how it moves." First of all,
let us consider the flow of liquid from a reservoir through a series
of tubes. In a liquid the molecular forces are in equilibrium ;
the kinetic forces characteristic of matter in the gaseous state are
exactly balanced by the Newtonian forces predominant in solids.
As Soddy would put it, the processes of pellation and tractation
would not be manifest. Gravitation alone has to be reckoned
with. In common parlance, liquids seek their own level and so
always tend to flow to the lowest possible position. It is a well-
known fact that the speed attained by a body falling in vacuo
through the distance (h) equals \/2gh, g being the acceleration
produced by gravity. This formula cannot be used to estimate
the velocity of fluid escaping from a reservoir. As every boy
knows, when the waste water is being run out from the bottom
of a wash-hand basin, the fluid tends to rotate round the orifice
and to assume a conical form. This is due to the attempt of the
water particles to rush the exit (so to speak). Only a limited
number of them lie in the column vertically above the opening.
The majority, occupying more lateral positions, tend to escape
along with the minority in the queue and so exert a force applied
at an angle to the line of exit. Consequently, the total energy
cannot be used to produce velocity. Some of it has to be spent
in overcoming the resistance at the outlet.

Still further modification of the formula is required if the
orifice is fitted with an exit tube. It must be evident that the
presence of this passage imposes a greater resistance to outflow
and materially reduces the rate. Let us consider the effect
produced on rate of flow by attaching a rigid cylindrical tube of
uniform bore to the lower orifice of the reservoir. In order to
simplify matters, we will place this pipe horizontally. Two causes

278 CIRCULATION

tend to reduce the kinetic energy of fluid flowing through a tube,
viscosity or internal friction and external friction on the walls of
the tube. On account of the latter, the outermost layers of the
fluid adhere to the walls of the tube and become more or less
stationary. The molecules of the layers of fluid next to the outer-
most tend to cohere to the stationary layer on one hand and are
pulled along by their cohesion to the next inner layer. As a
result, their velocity is decreased. The net result is that a whole
series of cylindrical layers is produced each with a different rate
of flow — ranging from the almost stationary outer layer to the
central axial column, which is retarded least of all and, therefore,
possesses the greatest kinetic energy. In a straight tube of uni-
form bore, such as is under consideration, this retarding influence
reduces the average rate of flow to half that of the axial stream.
It is obvious, therefore, that a considerable amount of the potential
energy of the liquid in the reservoir is absorbed in overcoming the
peripheral resistance caused by cohesion and adhesion. Resist-
ance to flow also depends on the area of cross-section of the tube —
the wider the tube the larger the number of cylindrical layers
over which the adhesive resistance spends itself and, therefore,
the less the resistance met by the axial stream. A tube so narrow
that only an outer layer and a central column could pass along
would move with infinite slowness. Except in instances in which
the conducting tube has a very large or a very small diameter,
the rate of flow is proportional to the area of cross-section.
Furthermore, since the resistance in a tube of uniform diameter
is proportional to its length, the energy of the fluid must decrease
gradually from the reservoir to the outlet of the tube. The energy
of the fluid is shown by the pressure it exerts. Pressure may be
measured by some form of manometer. It is sufficient to insert a
number of vertical glass tubes, of uniform bore and open to the air,
at various points of the conducting tube to see the fall of pressure
with distance from the source of power. The fluid rises in these
collateral tubes or piezometers to a height proportional to the
pressure in the main conduit. In other words, the level of
the liquid in those pressure-gauges is accurately adjusted to the
peripheral resistance encountered by the liquid as it passes their
points of insertion. Such a system is represented in Fig. 60.
The power furnished by the liquid, in the constant-level reservoir
(R), is the downward pressure of gravity. The pressure at
various points is manifested by the height of the fluid in the
branch tubes (A) 1, 2, 3, etc. If the levels of the column of

HAEMODYNAMICS

279

liquid in each of these piezometers be joined by a straight line
which is produced to the reservoir wall at (y) the mass of liquid
will be divided into two portions. The lower portion (r) represents
the portion of the energy of the total spent in overcoming the
resistance and is consequently known as resistance-pressure. Of
the remainder, a certain amount (o) is spent in forcing the fluid
through the orifice into the tube. The actual driving force or
velocity pressure comes from the mass (v).

FALL OF PRESSURE.

<NpO TUBE OF UNIFORM DIAMETER IN(B) TUBE OF VARYING DIAMETER.

765432 I t RESERVOIR. I 23456789 IO

R,

FIG. 60.'

If the main tube is not of uniform bore — suppose (B) it increases
in sectional area, at first gradually (a to b) and then somewhat
suddenly (at b) — corresponding alterations in pressure may be seen
in the manometers. Increase in width means smaller resistance,
and therefore a smaller resistance-pressure is required to drive
the fluid along the tube. As the total mass in the reservoir is
kept constant, the amount not required in r goes to increase v.
There being relatively a greater head of pressure, the levels shown
by the manometers will tend to decrease progressively at a slower
rate than before. If, on the contrary, the bore of the tube is
diminished as at c, the fall of pressure will become more rapid.
Further, if at b a constriction is produced, resistance to flow is
augmented, and therefore there is a heaping up of the fluid in the
earlier tubes 1, 2 and 3, a rapid fall to tube 4, and thereafter a
fall of pressure at the same rate as in the earlier part of the system.
All the above is stated in terms of pressure. Putting the same
matter in terms of velocity of flow, one may say that if a tube be
used, the second segment of which is wider than the first and
third, the speed of flow will be decreased in the central one.

In the preceding experiment, the head pressure has always
been kept constant by making provision for a steady influx of

280 CIRCULATION

water to the reservoir to compensate for the outflow. If, how-
ever, the head of pressure is produced by the action of a piston
in a cylinder, it will not cause a continuous but an intermittent
flow in the main conduit. The pressures shown in the piezo-
meters will vary from a maximum to a minimum as the wave of
pressure passes down the system after each stroke. Such con-
ditions entail great loss of power. In order to reduce this loss
to a minimum, it is necessary to replace the rigid conduit by an
elastic tube. Such a tube would, of course, if rigid, permit a
certain flow of fluid per unit of time per unit of pressure, say with
a constant velocity of ( v). Now on the descent of the piston more
water tends to be forced into the conduit than can be passed out
with this velocity (v). The elastic walls distend till their elastic
power exactly counterbalances the extra energy, and the fluid
has an outflow velocity of (v). The influx of water having
ceased, the steady pressure of the distended walls of the tube as
they recoil keeps the fluid flowing at the constant velocity (v).
In this way the fluid is held under a continuous pressure and,
provided the pump has the proper frequency, the outflow remains
practically constant. That is, the elastic tube really converts an
intermittent inflow into a constant outflow, the property of elasticity
preserving normal conditions of flow even during periods when the
piston is not descending.

Such a system of single stroke pump and elastic regulator does
not differ in essentials from the one contrived by nature to provide
a perfect transport service to every unit of a complex organism
like the human body. In Fig. 61 a simple force pump and its
circulating system is compared with the left ventricle, aorta, etc.

The manner in which the contents are forced out from the
ventricle differs in some details from that obtaining in the water
pump. In the latter, a rigid piston descends within a rigid
cylinder and thus obliterates the space of the main chamber and
forces the water through the outflow pipe. The power necessary
to drive the plunger home is derived from an engine of some sort,
external to and independent of the pump itself. In the heart,
the elastic muscular walls of the ventricles contract as a whole,
deriving their force just as any other muscular structure does,
from the potential energy of materials brought to them by the
blood and liberated in their protoplasm.

The value of the work done by a pump may be calculated approxi-
mately by the formula w—OR wv*

WORK OF HEART

281

where W (gram-metres) is the work done at each stroke, w is the
weight in grams and Q the quantity of fluid in c.c. expelled at
each stroke ; R is the average resistance of the circuit, v (metres
per sec.) is the velocity of expulsion, and g is the acceleration
due to gravity =9-8 metres per sec. per sec. That is, QR repre-

wvz
sents the resistance pressure (r in Fig. 60) and — (v in Fig. 60)

the velocity pressure while 0 is the energy expended in overcoming
the resistance to outflow at the orifice of the pump.

FIG. 61. — Diagram of a simple force pump (outer circuit) to compare with diagram
of circulation from left side of heart (inner circuit).

If we take average figures for the left heart as follows :
Q=60 c.c.,

12=100 mm. Hg pressure in aorta
=0-1 X13-6 gram-metres (1 c.c. of Hg weighs

13-6 grams),
the expression QR may be evaluated as

60 xO-1 m. x 13 -6 =81 -6 gram-metres.

282 CIRCULATION

That is, about 80 gram-metres of work is done in overcoming the
resistance of the conducting tubes. This value is only approxi-
mate, as the work done in forcing a fluid along an elastic tube in
which the pressure falls steadily, say from 150 mm. Hg to 50 mm.
Hg is not strictly proportional to the average pressure, but would
need to be determined by integration. The error is, however,
less than 10 per cent. If the blood is expelled at a velocity of
0-5 metre per second, the velocity pressure will have a value

wv* 60 x(0-5)2

— = — — =0 -7 gram-metre.

2g 2 X9-8

This quantity is so small compared with the former that for all
practical purposes the work of the heart may be taken as pro-
portional to the output multiplied by the average arterial pressure,
i.e. W=Q . R.

Similarly the work of the right heart may be estimated from
the average pressure of the pulmonary artery (20 mm. Hg) as
60 xO-02 xl3-6=16-l say, 16 gram-metres per beat. The average
heart beats seventy times per minute and, therefore, in 24 hours
the work done by the heart (of a man at rest) will be about 10,000
kilogram-metres.

Muscular work, of course, augments this figure not only by
increasing the volume of blood per beat and increasing the number
of beats but by raising the value of the velocity factor. During
a short sprint, an athlete may have a pulse rate of 180 per minute
with an output of 180 c.c. at each beat and an average arterial
pressure of 120 mm. Hg. Then for the systemic heart :

QR=180 xO-12 x!3-6=294 gram-metres,
and QR (pulmonary) =180 xO-025 X13-6— 61 gram-metres.

If the time of outflow is considered as 3/8 of each cardiac cycle,
of which there are 180 per minute, then the contents of the
ventricle, 180 c.c., are shot into the aorta at the rate of 1440 c.c.
per second (say 1500 c.c.). If the cross-section of the root of the
aorta be taken as 625 sq. mm., then the velocity of expulsion will

be - —=2-48 metres per sec. (say 2-5 metres). Therefore :
625

wvz 1 80 X (2 -5)2
— = — — = 57 gram-metres .

2g 2 X9-8

The total work on both sides of the heart will be :

I-+-I*. . , V=462 gram-metres per beat

Left side] (Right sidej

=83-2 kilogram-metres per minute.

MUSCULAR WORK AND CARDIAC OUTPUT 283

The main fault to be found with this calculation is that the
various quantities required are almost impossible to obtain. For
instance, the only methods by which the output of the heart in
situ can be determined are indirect. Zuntz, by finding the
percentage amount of oxygen which the blood gains per unit of
time in passing through the lungs, and the actual amount of
oxygen taken from the lungs per unit of time, calculated the
amount of blood that had passed through the lungs during that
period. For example, if the blood gains 5 per cent, of oxygen
and the lungs part with 30 c.c. of oxygen to the blood, then, in
order to have a 5 per cent, mixture, 600 c.c. of blood must have
passed through the lung in unit time. Now if the heart beats
70 times per minute, and the unit of time chosen was 1/5 of a
minute, then the volume of the right ventricle would be

5 X 600/70 —almost 43 c.c.

Since, of course, the left and right ventricle must discharge equal
amounts of blood, the output of the left ventricle is found.

Muscular work causes an increase in the output per beat.
Under resting conditions, it is probable that the amount of blood
entering the heart during the diastole is not sufficient to fill the
ventricle up to the limits set by the fibrous inextensible bag
surrounding the organ (pericardium). The first effect of the call
for more oxygen set up by the muscles is to increase the output
of the heart per beat. The power of the heart to thus increase its
capacity is limited. By a reflex mechanism the heart rate is
increased and so the output per minute is augmented. The
following table shows approximately the share of the burden
of increasing the output borne by increased distension of the
ventricular walls and by increased pulse rate.

TABLE XLIX.

EFFECT OF WORK ON CARDIAC OUTPUT.

Muscular work per min.
in Kgms.

Pulse rate
per min.

Output per
beat in c.c.

Output per
min. in c.c.

At rest - 0

70

45

3,150

Moderate exercise 270

100

75

7,500

110

120

13,200

Light labour - 735

130

115

14,950

Very hard work - 1000

180

117

21,060

It will be seen that at first the pulse rate is practically unaltered
although the amount of work done has been increased from 270 to

284

CIRCULATION

735 kilogram-metres while the output per beat has increased from
75 to 120 c.c. After this, the output per beat is not materially
changed, if anything it tends to decrease while there is a marked
increase in the pulse rate. It is interesting to note the increase
in the rhythm of the heart when work has just been started, viz.
from 70 to 100. This is associated with the initial changes
originated by the acts of volition and attention. The mere
caution, " Are you ready ? " is sufficient to cause a rise in the
pulse rate due, in part, to the increase of muscular tone in the
act of attention, and, in part, to psychological causes.

A fair day's muscular work may be taken at 100,000 kilo-
gram-metres. We have seen that the work done by the heart is,
at least, 10,000 kilogram-metres per day. Hence the work done
by the heart is always more than 1/10 of that done by the skeletal
muscles.

The efficiency of the heart may be taken as the percentage
amount of the energy taken in as fuel that is converted into work.
Workers in this field are agreed that it is extremely probable that
the sole normal source of cardiac energy is the glucose taken to
the heart by the blood and in part stored as glycogen in the
heart substance. This storage of glycogen renders difficult the
interpretation of the results of estimations of the amount of
glucose in the blood before and after passing through the coronary
vessels. More accurate calculations of the energy generated
during the cardiac cycle can be made from the oxygen consump-
tion and carbon dioxide production during bodily rest and during
measured work. The appended table from a paper by Evans
and Matsuoka demonstrates this method for obtaining a value
for the efficiency of the heart The total output of blood from
the ventricle is fairly constant — averaging about 16 litres per

TABLE L.
EFFICIENCY OF THE HEART UNDER VARIOUS CONDITIONS.

1

Pulse-
rate.

Arterial
pressure in
mm. Hg.

Total
output per
hr. Litres.

02 used
per hour
in c.c.

Energy
generated
in Kg.
metres.

Work of
heart in
Kgs. perhr.

Per cent.
Efficiency.

Venous
pressure,
mm. H2O.

134

80

17-4

139

288

21-1

7-3

38

. —

120

16-3

175

362

30-7

8-5

50

150

160

14-7

249

518

40-8

7-9

80-103

143

80

27-8

217

448

34-1

7-6

—

80

52

277

572

65-6

11-5

146

80

92

649

1343

126-3

9-4

B

EFFICIENCY OF THE HEART 285

hour. The resistance to outflow was increased by steps of 40 mm.
Hg from 80 to 160 mm. Hg, corresponding to an increase in
cardiac work of about 10 kilogram-metres a time.

To free the energy necessary for this increased work the heart
uses up more oxygen. The amount of oxygen (in c.c.) so used
multiplied by 2-07 gives, in kilogram-metres, the energy developed.
It is clear that, with a moderate increase in arterial resistance, the
mechanical efficiency of the heart improves but tends to decrease
when the resistance is doubled. In other words, when the arterial
pressure is raised, the oxygen intake is increased, and more tension
developed in the cardiac muscle. The mechanical efficiency is
raised to a certain limit, beyond which it again diminishes. The
venous pressure in the experiment quoted, and in most others,
runs parallel with the oxygen usage. In the series of observations
tabulated as B, the arterial pressure was kept constant at about
80 mm. Hg, while the output per hour was increased roughly
as 1 : 2 : 3. This was done by varying the inflow of blood to the
heart. The increase in oxygen usage is not quite proportional
to the increase in work done, but is if anything, less. The efficiency
values therefore tend to increase with increasing outputs up to a
certain limit. Beyond this point, the amount of oxygen used
increases very suddenly. In the example given, for a little less
than double the output, almost two and a half times as much
oxygen is required. As this involves the liberation of enough
energy to lift 1343 kilograms to the height of a metre, and as only
126-3 kilogram-metres of work are done, the increased work is not
done so economically and therefore the efficiency value falls.
How can this primary increase in efficiency and subsequent
decrease be explained and what factors are brought into play to
settle the critical point at which maximal efficiency will be found ?
If output is to be increased, intake must first be increased and the
ventricle must be distended to hold the extra amount of blood.
That is, the muscle fibres of the ventricular wall will be stretched.
We have already mentioned, in connection with skeletal muscle,
that a stretched muscle develops more tension during the iso-
metric phase. The heart responds to increased work by such a
lengthening of its fibres. If the lengthening process is carried too
far. the muscle fibres per unit of area will become fewer, so that
the larger the ventricular volume, the more strongly will each
fibre have to contract in order to produce a given tension. At
this greater length they also use up more potential energy just
as skeletal muscle does.

286 CIRCULATION

The maximal mechanical efficiency was obtained by moderate
increase of both pressure and output and reached 26 per cent.

It has been suggested that a term Energy Index should be used
to denote the total force developed by the heart per minute. If
the systolic blood pressure be 120 mm. Hg and the diastolic 80 mm.,
then the force of each beat would be 120 +80 =200 mm. Hg. This
figure multiplied by the number of beats indicates the total force
per minute. From an examination of about 26,500 recruits for
the American army the normal index was found to be about
20,000 mm. Hg. per minute. This Systolic-Diastolic-Rate index
designates the amount of effort which the heart is putting forth.
A high S.D.R. index indicates increased cardiac effort due
either to inability of the heart to carry on its normal work at a
normal rate or to the presence of some resistance to flow in the
circulation.

For example, adrenalin causes an increased blood pressure by con-
stricting the peripheral vessels. A man who had S.P. = 108, D.P. = 70,
P.R. =84, giving an index of 19,852, had a small injection of adrenalin.
His S.D.E. index then rose to 23,520, made up from S.P. = 140, D.P. = 70,
P.R. = 112.

The diagrammatic section of the heart (Fig. 58) demonstrates
that the walls of the left ventricle are much thicker than those
of the right. The mean of a large number of determinations
furnishes the ratio of 6-8:1. This may be interpreted as indi-
cating that the left ventricle develops about seven times as much
pressure as the right ventricle. Proof confirmatory of this
deduction is obtained by determining the hydrostatic pressures
necessary completely and symmetrically to fill these two chambers.
The right ventricle is dilated by a seventh of the pressure employed
in equally dilating the other ventricle.

A dog weighing 10 kilos with an average aortic pressure of 100 mm. Hg,
and an output of 2,000 c.c. of, blood per minute, develops pressure in
right and left ventricles of 25 and 150 mm. Hg respectively — a ratio of
25 : 150 = 1 :6.

The pressure developed in a distended hollow elastic vessel
depends on (i) the elasticity of the walls, (ii) the degree of dis-
tension and (iii) inversely, the radius of curvature of the walls.
The volume output from both ventricles is the same and their
radii of curvature are similar. There remains only a marked
difference in elasticity. As both are formed from the same
material, alteration in elasticity must be brought about by
alteration in wall thickness.

THICKNESS OF WALLS 287

Sections of the ventricles at different points show that the
ventricular walls vary in thickness at different parts. For
instance in the left ventricle the apex, in the fully dilated ventricle,
has, by far, the thinnest wall. As presumably the pressure in the
chamber is constant over the whole wall area at any moment, some
other factor must be found to account for this diminution in
thickness. From the purely physical study of the shape assumed
by elastic-walled cavities the conclusion has been drawn that
where an elastic membrane is subjected to internal pressure, its
shape will be determined by the law of distribution of radial
pressure. With a given shape and size of body, equilibrium is
maintained by altering the thickness (resistance to pressure) of
the wall so that where curvature is least the wall is thickest and vice
versa. The apex of the heart is the portion with the greatest
curvature.

To take a very simple example : if an elastic band is stretched between
two points on a flat surface it will exert no pressure on any part of the
underlying surface. But if it is stretched over a curved surface, e.g. a
cylinder, it will exercise a downward pressure depending on the radius of
the cylinder. A flat surface may be considered as equivalent to a curved
surface of infinite radius. As the numerical value of the radius is decreased,
i.e. as the curvature is increased, the pressure exerted by the band will
increase. In mathematical form p = T/R, i.e. Pressure per unit of surface
= Tension of band divided by Radius of curvature.

Where there are curvatures in two dimensions, e.g. a sphere,

2T

the two pressure effects are additive, i.e. p=-^>

K

The ventricles are roughly egg-shaped, i.e. they have radii in
two dimensions and of unequal length. The pressure will there-
fore be equal to the sum of these, i.e. p=T/R-\-T/R1.

We have seen reason to correlate thickness with pressure.

We may therefore say that thickness of wall varies inversely
with the radius of curvature. This gives the formula

where £— thickness of the walls and C a constant.

The wall of the apex of the heart has the largest mean curvature
(R is least and, therefore, t is least).

Similar reasoning may be applied to the consideration of the
thickness of the walls of the blood vessels. The pressure (P)
within the vessel is balanced by (1) the elastic tension of the wall
(T) divided by the radius of curvature (R), and (2) by the pressure

288

CIRCULATION

brought to bear on the external surface of the wall by the resist-
ance to distortion of the surrounding tissues (p).

Thus T=R(P-p),

or putting £=thickness and C=a constant, we may write

t=CR(P-p).

That is, if (P —p) be kept constant the thickness of the walls will
vary as the radius of curvature.

TABLE LI.

THICKNESS OF WALLS AND DIAMETER OF LUMEN OF ARTERIES IN MM.

Artery.

Intima.

Media.

Adventitia.

Total.

Lumen.

Brachial (human)

0-03

0-5

0-25

0-78

4-17

Carotid (ox)

0-84

1-176

0-484

1-744

6-0

„ (sheep)

0-028

0420

0-168

0-616

3-0

Metacarpal (horse)

0-03

0-513

0-31

0-853

2-7

• (Mac William and Kesson.)

According to measurements made on excised vessels the carotid
artery of the ox has a lumen of 6 mm. while that of the sheep
is 3 mm. The maximal pressure developed in these vessels at
body temperature amounted to 60 and 40 mm. Hg respectively.

That is R/R1=2/l and pfpl=3/2.
Now tlil—RJBl and as p/p1=6/2=3/l.

The actual thickness of the carotids as measured by Mac-
William and Kesson are 1-74 and 0-61 mm. respectively. Of
course, the main elastic resistance to distortion is met with in the
muscular tunica media which in the ox is 1-12 mm. and in the
sheep 0-42 wide. Either pair of figures gives a close approxima-
tion to the ratio 3 to 1.

The valves of the heart and veins are interesting mechanical
structures. During the two years that Harvey studied at the
University of Padua, Fabricius, the renowned Professor of Anatomy
there, was investigating the valves of the veins. He demonstrated
their presence in the veins of the arms and legs and also in the
vessels at the root of the neck. These sluice-gates are very
simple contrivances — just little pockets set in pairs opposite each
other in the vein. ' Fabricius noted that the openings of the pockets
were always directed toward the central part of the body. He
interpreted this as indicating a mechanism to prevent the blood

VALVES OF HEART 289

from gathering, under the influence of gravity, in the lower parts
of the body. Harvey saw that this explanation did not account
for the setting of the valves in the veins of the neck, and we saw
how, by noting the direction in which the valves would allow
fluid to pass, he discovered the circulation of the blood.

It is clear that the pockets offer practically no resistance to the
passage of blood towards the heart. If, however, the pressure
on the heart (or central) side of a valve becomes greater than the
pressure in the preceding segment, the pockets will fill with blood,
become distended and effectively prevent a back-flow. That
this is so can be proved by repeating one of Harvey's experiments.
He tied a ligature round the upper part of his arm and so dammed
up the blood in the lower part of the arm. When he milked these
swollen veins towards the hand he noticed that the blood could
not pass certain points where he knew valves were placed. No
valves are necessary in the arteries as there is always a positive
driving pressure. The type of two of the valves of the heart is
indicated in Figs. 58 and 61.

(1) The auriculo- ventricular valves are triangular sheets of
fibrous tissue — tough but flexible — fixed by one side to the
auriclo-ventricular ring and hanging apex downwards into the
ventricular cavity. The pointed part of each flap or cusp is tied
to the ventricular wall by a number of cords, chordae tendineae.
The main cords are, however, not inserted directly into the
ventricular wall but are attached to the finger-like papillary
muscles. These muscles regulate the tension of the valve-flaps.
When the ventricles contract so do the papillary muscles —
pulling on the chordae and thus bringing the cusps closer together.
The increasing pressure of the blood in the ventricle causes the
flaps to bellow out and block the passage-way so that the blood
cannot pass back into the auricles. The greater the pressure
developed in the ventricle, the more tightly is the valve shut.
The cusps may even bulge up into the auricles. Valves con-
structed on this principle are obviously fitted to occlude openings
which vary in size and shape during the various phases of the
cardiac cycle.

The right and left sides of the heart differ in the number of
cusps in their valves and in the details of their movements.
The mitral valve on the left side of the heart has only two triangular
flaps like a bishop's mitre, while on the other hand the passage
way from right auricle to right ventricle is guarded by the three
cusps of the tricuspid valve.

K B. x 19

290

CIRCULATION

During systole, the strong anterior cusp of the mitral valve
does not materially shift its position. The other cusp is pulled
forward against it.

On the right side, one of the cusps hangs down on the septum
and is practically immovable. The other two cusps by the action
of their papillary muscles are pulled over towards the septal cusp.
The mass of blood pressing on the sides of the cusps completes
the closing of the orifice.

When this mass of blood, under the pressure induced by the
contraction of the ventricles, stretches the auriculo-ventricular
valves it causes them to emit a sound which is a component of

rrTU'S ARrtNTII

FIG. 62. — Semilunar valves. .4, in longitudinal-mesial section. B, Artery laid
open and exposed, and C, closed valves from the arterial aspect.

the first sound of the heart. The other component is the sound
produced at the same time by the contraction of the ventricular
walls. It is said that a trained ear can pick out the notes due to
closure of the valves from those due to stretching of the muscular
walls.

(2) The valves situated at the openings of the ventricles into the
arteries are similar in shape and in action to the pocket valves of
the veins (Fig. 62). Each is composed of three pockets or half
cups attached along their curved margins to the walls of the
artery and upper part of the ventricle and with their openings
set away from the ventricle.

The cusps are not placed all exactly on the same plane. One
cusp lies somewhat deeper in the heart than the others. This
cusp is mounted on a muscular septum which acts as a cushion,

SOUNDS OF THE HEART 291

absorbing the shock when the pressure falls on the valve and the
other two cusps shut down on it.

The sudden stretching of these semilunar valves by the impact
of the high arterial pressure sets the valves in vibration like the
blow of a drum-stick on a drum-head. It produces a clear
sharp high-pitched sound, the so-called second sound oJ the
heart.

A third sound has been described. It has been attributed to
the rebound of the semilunar valves when the ventricle relaxes
and the ventricular exit again becomes patent.

When the valves are diseased certain more or less continuous
sounds or murmurs are heard. They are in the main due to
either of two causes.

(1) Stenosis. When a fluid flows along a tube of uniform bore
or a tube where the bore alters gradually no vibrations are set up.
On the other hand, if the cross-section is altered suddenly and
appreciably, the fluid is set into vibrations. These vibrations
are transmitted to the solid tube and to the material in which it
is set and a sound is produced. Most people have heard the
rather irritating purr emitted by the domestic water supply when
there is " air in the pipe." The vibrations may not only be heard
but they may be felt at the tap and seen in the water issuing.
Something similar takes place when, by disease, the opening from
auricle to ventricle is narrowed. During the whole period when
the ventricle is filling up from its auricular reservoir, the blood
flowing through the narrowed opening is set into vibrations which
are transmitted through the more solid tissues to the inner ear—
this is the murmur of mitral or of tricuspid stenosis, according
to whether the fault lies on the systemic or pulmonary side
respectively. The narrowing does not need to be absolute. If
the previous part is dilated, the orifice will become relatively
narrower and will produce the result.

Similarly the murmur caused by stenosis of the aortic or of the
pulmonary valves will be heard during the expulsion of blood
from the ventricles.

(2) Incompetence. The failure of any of the valves to close
completely, allows blood to trickle back into the empty expelling
chamber. This regurgitation throws the tightly stretched cusps
into vibration and produces a murmur. If this sound is heard
during ventricular systole it may be ascribed to incompetence of
either of the auriculo-ventricular valves — if during ventricular
diastole, the aortic or pulmonary valves are at fault.

292 CIRCULATION

In aortic incompetence the sound will be best heard where the
aorta comes nearest to the surface, viz. at the second right costal
cartilage ; in pulmonary incompetence the stethoscope will be
placed over the second left interspace just external to the margin
of the sternum.

The sound of the mitral valve is heard at its best just over the
apex of the heart ; that of the tricuspid valve at the junction of
the fourth right costal cartilage with the sternum.

By means of a recording microphone, a tracing may be obtained
representing the values of these sound waves. Such a phono-
cardiogram (Figs. 66 and 67), if taken simultaneously with a
tracing of the mechanical or electrical changes of the heart, is of
great use to the physician as an indication of cardiac efficiency.

If any of the large arteries be compressed, say by the imposition
on the overlying skin of the stethoscope, murmurs will be heard.
These sounds are caused by the sudden narrowing of the lumen
of the artery by the pressure of the instrument. The blood rushes
through the narrowed part into the comparatively wide part of
the vessel beyond the point of pressure and so sets up eddies.
The vibratory movement of the fluid is transmitted to the arterial
walls and passed on to the internal ear (Part II.).

Considering the circulatory mechanism as a whole one is struck
by the extraordinary efficiency of this method of transport.
Comparatively little energy is wasted. Fluid leaves the ventricle
under a pressure of over 100 mm. Hg, passes through a system of
large and small tubes and returns to the reservoir of the central
pump with no surplus pressure. Just enough blood is provided to
carry the fluid within range of the auricular suction and no more.
It has been stated that by the rhythmic contractions (peristaltic
waves) of the muscular coat of the vessels, the blood is helped
along its course. The mechanics of peristalsis will be considered
shortly (Chap. XXVII.).

One further point making for the economical working of the
inland transport service, owes its enunciation to John Hunter.
He wrote, " To keep up a circulation sufficient for the part and
no more, Nature has varied the angle of the origin of the arteries
accordingly." Suppose a point C is h units vertically distant
from an artery AB, the problem is to find out the route by which
the blood could be conveyed from A to C with the least possible
loss of energy. This is not necessarily by the shortest route or
by the route using the shortest piece of branch tubing. The
shortest route would be h units long and would arise from AB at

ANGLE OF ORIGIN OF VESSELS 293

right angles (say at D). For the purposes of this calculation
let us consider that the least loss of power occurs when the branch
originates at X which is x units from Z), making an angle of 6
with the main trunk. Then the distance from X to C would be
N/#2+/i2 (hypotenuse of right-angled triangle).

Assuming that loss of pressure is due to friction on the walls
of the vessels, then it will be directly proportional to their lengths
and indirectly proportional to their radii (e.g. main trunk=.R,
branch =r) ;

XCAX

i.e. loss is proportional to — 4— vr-

r R

If the whole distance from A to D be put =6, then AX=b —x.

- i_ i.-4. 4.- \/#2+/&2 b— x

Substituting, we have - +— ^- »

/ JL\T

multiplying by Rr gives us the value

Differentiating and equating to zero we obtain a value for x
which makes S a minimum.

d.S

Thus - =- — r=0 ;

d.x

r x XD

That is, the angle of origin required is such that its cosine is
numerically equal to the radius of the branch divided by the radius
of the main trunk.

The size of the angle of origin is governed neither by the radius
of the branch vessel nor by the radius of the main vessel but by
the ratio of these two quantities. For any particular value of the
ratio r/R, we have therefore a constant value of 0 ; that is, all
branches of equal radius will be equally inclined to the main
artery.

(1) In particular, if the artery bifurcates into two equal
branches, the angles of bifurcation will be equal.

(2) If r is so small compared with R that the amount of blood

r

going to the branch is almost negligible, then cos 6 — — tends to

R

be infinitely small, i.e. angle 9 will be close to 90°.

294 CIRCULATION

(3) If r differs but slightly from R it is obvious that cos 6
tends towards the limiting value—-!, i.e. 6 will be very small.

While these statements are true as they stand they are not the
whole truth. Other factors come to bear on the angle of origin
and produce modifications not comprehended in Hess's Law.

CHAPTER XXV
THE ELECTROCARDIOGRAM

" Providence . . . can make a harmony
In things that are most strange to human reason."

MIDDL.ETON.

THE electrical changes that occur during each cardiac cycle have,
of late, become rather important to the clinician, as a rapid and
reliable indication of the state of the heart. Cardiac muscle,
just like any other muscle, or, in fact, like any other living tissue,
is the seat of electrical differences in potential. Ordinary skeletal
muscle on contracting develops potential in such a way that the
contracting part becomes electro-negative or zincative to the rest.
This causes a current to pass through the external or galvano-
metric circuit to the contracting part, from the rest of the muscle.
Heart muscle acts in a similar way. It has been found that the
wave of contraction starts in the auricles. Therefore the auricles
will become electro-negative to the rest of the heart. The auricles
contract as a whole, passing on the excitation through a piece of
primitive tissue (Bundle of His) to the ventricle. This will then
become negative to the rest of the heart and so on.

(1) The existence of this change in the sign of the potential
developed may be demonstrated, as it was in muscle, by the use
of a fresh nerve-muscle preparation. The nerve is laid across the
beating ventricle and produces two muscle twitches per beat.

(2) Earlier experimenters used the capillary electrometer
(p. 404) as the instrument wherewith to measure the potential
differences. They found (Fig. 63), on leading one electrode from
the auricular sinus and one from the ventricular apex, that on the
initiation of the contraction of the auricle, the mercury^an up the
capillary away from the tip, indicating the presence of a negative
difference of potential. This was followed immediately by a tiny
positive movement constituting the second part of the auricular
diphasic response. Similarly, a large upward excursion of the

295

296 THE ELECTROCARDIOGRAM

mercury followed by a smaller downward movement demon-
strated a similar but greater ventricular diphasic response. It
is not necessary to expose the heart and lay non-polarisable
electrodes on it in order to see this diphasic response by the electro-
meter. The right arm may be considered as electrically con-
tinuous with the base and the left leg (or arm) with the apex of
the heart. Connection of the arms by non-polarisable electrodes
to the electrometer gives results similar to those obtained from
animals by direct " leading."

Clinicians seem to prefer the more sensitive string galvanometer
as an instrument for electrocardiographic work, in spite of its
great expense and the difficulty of analysing its records. The

AURICLE

VENTRICLE

FIG. 63. — Record of the electrical variations in the beating heart of a tortoise,
taken by a capillary electrometer (after Gotch).

instrument at present generally employed is substantially that
invented by Ader and modified by Einthoven. The earlier forms
of string galvanometer were almost useless as a means of registering
the rapid alterations in the electrical state of the heart. Any
recording apparatus for such work must be as " dead beat " as
possible — moving in exact accordance with the exact potential
difference developed and having no period of vibration of its own.
As its name implies the moving part of the string galvanometer is
a string or fibre. The string (C, Fig. 64) which is an extremely
light fibre of silvered glass, quartz, or platinum is stretched
between the poles (N, S) of a powerful electromagnet. When a
current passes along a fibre, the fibre is deflected at right angles
to the magnetic field, the amplitude of the excursion depending
on the magnitude of the potential difference causing the current ;
and the direction of the deflection (observer's left or right) depend-
ing on the direction in which the current is passing. If the current

STRING GALVANOMETER

297

passes in the direction of the arrow, from top to bottom of the
diagram, the fibre will bend outwards, i.e. in the direction of the
arrow a. Reversal of the direction of the current of course causes
reversal of the movement of the fibre. The excursions of the
string can be observed by means of the reading microscope AE,
which passes through a hole in the magnet, or records may be
made by placing an arc lamp at G, concentrating the light on the

c s i

613

FIG. 64. — Diagram of the essential parts of the string galvanometer. N and S
are the poles of a powerful electromagnet, between which is stretched the fibre C.

fibre by a lens F and throwing the shadow on to a moving photo-
sensitive surface. Fig. 65 shows diagrammatically the arrange-
ments of galvanometer and accessories for photographing the
fibre movements. The distances are given in millimetres.

The optical mechanism for producing the electrocardiograms
needs some mention. The camera is a light-tight box fitted with
a cylindrical lens and an arrangement whereby a sensitive photo-
graphic plate or film (or bromide paper) is made to travel at a
uniform speed past the narrow lens. The field of the objective
is projected by an eyepiece on to the lens which focuses it as a
spot of light on the part of the sensitive surface exposed by the
slit. The shadow of the fibre appears as a dark spot in this band
of light. Thus if the plate or paper be moved downwards normal
to the cylindrical lens, the whole surface will be exposed to the
action of the light except that portion protected by the shadow

298

THE ELECTROCARDIOGRAM

of the fibre. The movements of the fibre are, as we have seen,
parallel to the plane in which the lens is set, and therefore when
the fibre moves towards the reader (in the diagram) the result

will be a corresponding alteration in
the position of the shadow spot. A
continuous record of these positions
is formed on the moving sensitised
surface.

The records (Figs. 66 and 67) show
vertical and horizontal markings as
well as the electrocardiogram itself.
The horizontal markings enable one
to find by inspection the potential dif-
ference generated at different phases
of the cardiac cycle. The space be-
tween each line is generally 1 mm.=
1/10,000 volt (Einthoven's standard).
The lines are engraved across the
width of the cylindrical lens. When
illuminated they produce shadows
forming lines along the length of the
record. The vertical lines, shortened
to ticks at the foot of the records
illustrated, are a measure of time-
in the cases given =1/30 of a second.
They are produced by the inter-
ruption of the focused beam of light
by a serrated wheel (Fig. 65) so
that for a short interval no light falls
on the whole (or on part of the sensi-
tised surface) "as it is travelling past
the slit. In consequence, a sharp line
falls on the record.

Before a record can be taken, it is
necessary to know the resistance of
the subject's body and the magnitude
of the "skin-current." The latter
factor is a relatively large and fairly
constant potential difference caused
by the glandular activities of the skin. It has to be counter-
balanced by sending an equal current through the fibre in the
opposite direction. The resistance of the body to the passage of

ANALYSIS OF TRACES

299

a current is very rarely considered in routine clinical electro-
cardiography.

The analysis of electrocardiograms is by no means simple.

FIG. 66. — Electrocardiogram from lead II. and Phono-cardiogram taken simul-
taneously from a normal subject.

Considerable uncertainty exists as to the exact interpretation of
certain units in the trace. If Einthoven's symbols PQRST are

FIG. 67. — Similar records to above, but taken from a subject suffering from mitral
stenosis. The space between the first and second sound is filled by a coarse, loud,
diastolic murmur (M).

used it is generally agreed that P is pre-systolic and that Q (positive
E.M.F.) indicates that the wave of contraction does not start at
the base of the ventricle but a short distance from it. R is no

300 THE ELECTROCARDIOGRAM

doubt the wave of negativity produced by the contraction of the
ventricles and S is the second phase or positive reaction. The
space between S and T represents the time during which the whole
ventricle is excited, and T probably indicates the arrival of the
wave of negativity at the apex. Other interpretations have been
given.

It has been suggested for ease in analysis, that it is advisable to
compound the records from all three leads into one diagram. This
so-called monocardiogram represents the algebraic sum of all the
potential differences at every point of the cardiac cycle.

CHAPTER XXVI
EXTERNAL RESPIRATION

" The body is sustained by three kinds of nutriment, food, drink, air (irvevfj.a.Ta),
of which the last is by far the most important."

HIPPOCRATES.

FEW of the mechanical arrangements of the body lend themselves
better to popular descriptive writing than the lungs, and fewer
still have given rise to more misconception of the actual means
employed in the performance of their function. From the
earliest times of which written records exist, one of the most
important and yet most mysterious problems of physiology has
been the part played by the lungs. The regular inhalation of air
and its regular exhalation was recognised by all as essential to life.
Prolonged stoppage of either caused death, and death was accom-
panied by cessation of breathing. Hippocrates, following Hindu
philosophers, maintained that " aerial nutriment " was " the chief
support of animal life " (Cicero). Aristotle denied this and
considered that the function of respiration was to cool the heart.
The followers of Hippocrates, noticing that the arteries and veins
differed in structure, suggested that they might differ also in
function. It was further observed that the arteries of a dead man
were empty although the veins were full. Hence they argued that
the arteries were channels for air and not for blood (Erasistratus,
circa 294 B.C.). That these philosophers had a glimmering of the
truth may be adduced from Galen's writings, e.g. "The air which is
drawn outwards from the rough arteries (trachea and bronchial
tubes) receives its first elaboration in the flesh of the lungs but
afterwards in the heart and arteries." It is our business at
present to consider the first step in this sequence, viz., the passage
of the respiratory gases between lungs and atmosphere.

Principle of Mechanism.

The lung mechanism may be considered as an elastic bag with
one opening, the whole suspended in an air-tight box with movable

301

302

EXTERNAL RESPIRATION

sides. When the sides are pulled outwards the box increases in
capacity and the air is sucked into the bag to keep the pressure
constant. When, however, the force which drew the sides out-
wards is released, the box and bag re-
sume their former volumes, and air is
expelled. In short the lungs are a form
of suction pump or bellows (Fig. 68).

Structure of Mechanism.

While the foregoing account of the
principle underlying the respiratory
mechanism may be taken as substan-
tially correct, it is apt to convey a
wrong impression of the details of the
mechanism.

(a) The lungs are not simple elastic
bags but are composed of thousands of
little distensible air sacs — a sponge-
work.

(b) These complex bags are suspended
in and almost fill the thoracic cavity.
Each organ is enclosed in a membranous
sac — the pleura, which bends back from
the bronchi and lines the entire internal
surface of the chest wall. That is, the
pleura consists of two layers — an outer,
parietal or chest wall layer, and an

inner, visceral or lung layer. These surfaces are kept moist
with lymph. It is important to note that as long as the chest wall
is kept intact the pleural cavity is only a cavity in name. The
layers of the pleura are always normally in close contact with one
another and with the underlying and overlying surfaces. In
otJier words, the chest wall, the two layers of the pleura and the
outer surface of the lungs move almost as one structure. The
elasticity of the lungs has been determined as about 30 mm. Hg.
If this inwards pull of the pulmonary tissue be subtracted from the
atmospheric pressure (760 mm.) in the lung, the resulting figure
(730 mm.) represents the force tending to keep the lungs expanded.
If, now, communication be established between the outer air and
the intra-pleural cavity, there will be a pressure of 760 mm.
tending to cause the lungs to collapse. As these outwards and
inwards pressures (760 as against 730 mm.) do not balance, one

FIG. 68. — Model to demonstrate
action of diaphragm. On pulling
the rubber sheet downwards, air
enters the lungs and they expand.

STRUCTURE OF DIAPHRAGM 303

would expect to find that the lungs collapse. This is not always
so. A further force comes into play. Moistening the various
surfaces is the lymphatic secretion already referred to and, by the
force of surface tension, the lungs are held to the chest wall, just
as firmly as a boy's leather " sucker " is held to the pavement
and for the same reason.

Mechanics of Respiration.

During inspiration the capacity of the thorax is increased in all
directions. That expansion occurs laterally and in an antero-
posterior direction may be made manifest by measurement or by
moulding strips of lead (cyrtometers) to the circumference of the
chest. The movements in a vertical plane have been studied by
means of the X-rays and by percussion. If the intercostal spaces
are tapped with the finger, a clear resonant note will be emitted
when the percussion has been performed on a part overlying
inflated lung. Otherwise a dull sound will be produced. Hori-
zontal expansion is obtained by movements of the ribs while the
vertical movements are caused by contraction of the diaphragm.

I. Structure of the diaphragm. This is a vaulted musculo-
fibrous sheet separating the thorax from the abdomen. It
consists of a central tendon like a double-arched cupola which is
attached on its thoracic surface to the pericardium and marginally
to the thoracic walls by muscles. These diaphragmatic muscles
may be divided into two sets, (i) crural and (ii) costal. The
former have their origin in the three or four lumbar vertebrae and
in the arcuate ligaments and are inserted into the posterior margin
of the central tendon, while the latter arise from the cartilages and
lower six ribs and from the back of the ensiform process. Such
a division of the muscle into crural and sterno-costal portions is
supported not only (1) by their different origins, but (2) by their
development from different muscular sheets in the embryo ;
(3) by their different blood supply — the former directly from the
aorta and the latter from the intercostal and internal mammary
arteries ; and (4) by their different nerve supply, the crus being
served by the posterior branch of the phrenic nerve and the costal
by the anterior branch. Moreover, the two portions act some-
what differently, and further, people may be classed as having
respiration of a crural or of a parietal type depending on whether
the crural or the costal portions of the diaphragm are employed
during quiet breathing. The majority of individuals employ
both parts of the muscle in varying degrees.

304 EXTERNAL RESPIRATION

II. Mechanics of diaphragm. The crural portion, when it
contracts, acts as power to a lever of the third class. That is,
the fixed point or fulcrum is the point of origin of the sheet of
muscle in the posterior wall of the thorax — on the vertebral
column. The resistance to be overcome is mainly the pressure
of the contents of the abdomen, the pericardial fixture and the
point of insertion of the vena cava and other vessels. They may,
on the whole, be considered as a weight applied at the central
tendon. The power is thus between weight and fulcrum — giving
speed at the expense of strength. The sterno-costal part of the
muscle connects the lower ribs with the central dome and acts as a
lever of the same class as the crura. In this case, however, the
fulcrum is movable and is moved outwards by other muscles.
This results in a forward as well as a downward movement of the
dome.

On the whole, the final result of the contraction of the dia-
phragm is similar to the descent of a piston — increasing the
capacity of the thorax vertically. The average descent is
" equivalent to a drop of about half an inch all over. For ease in
calculation, say that the distance through which the diaphragm
moved in an ordinary quiet respiration were 10 mm. and that
the mean area of the piston were 250 sq. cm., then the volume of
air sucked in would be 250 c.c. (complemental pleura). Now as
the tidal air in quiet breathing is under 400 c.c., it will be clear
that the part played by the diaphragm in ordinary respiration
is of major importance.

Acting along with the diaphragm there are those muscles which
abduct the lower ribs, viz. : the quadratus lumborum and the deep
costal muscles. These are synergic — contracting synchronously
with the diaphragm, and preventing the lower ribs from being
pulled inwards. In children where the musculature is poorly
——developed one sometimes observes a distinct depression of the
lower chest wall at every inspiration.

The antagonistic muscles together with the viscera form the
resistance against which the diaphragm moves. These are the
muscles of the abdominal wall, viz. : external oblique, internal
oblique, tranversalis and rectus abdominis on each side.

(a) External Oblique (Descendens). This is the outermost and
largest of the paired abdominal muscles. It is muscular laterally
and tendinous in front. Above, it is attached to the lower eight
ribs by eight fleshy digitations from which the muscular fibres
pass obliquely downwards and forwards. The muscle fibres of

ABDOMINAL MUSCLES 305

the lower rib are attached dorsally to the anterior half of the crest
of the ileum. The middle and upper parts of each muscle termi-
nate in aponeuroses which, covering the whole of the front of the
abdomen, are joined together at the mid line (linea alba).

(b) Internal Oblique (Ascendens). This pair of muscles lies
between the external oblique and the transversalis and is attached
below to the outer half of Poupart's ligament and to the anterior
two-thirds of the crest of the ileum. Dorsally it is attached to
the lumbar fascia. From this origin, the fibres spread in a fan-
shape passing behind to the lower three ribs and in front forming
an aponeurosis.

(c) Transversalis. A pair of flat muscles lying behind the other
pairs. The fibres arise from the outer third of Poupart's ligament
and from the anterior two-thirds of the iliac crest. They are
attached behind to the lumbar fascia and above to the inner sur-
faces of the cartilages of the lower six ribs. The fibres run
transversely and horizontally, being inserted into the aponeurosis
of the linea alba.

(d) Rectus. This muscle extends along the front of the abdomen
on each side of the linea alba from the sternum to the pubes.

The floating ribs (and in 40 per cent, of people, the tenth rib
also) are functionally part of the abdominal wall. Their move-
ments are controlled by the quadratus lumborum and erector
spinae muscles. The twelfth rib, in addition, is anchored to the
transverse processes of the first and second lumbar vertebrae by
a strong ligamentous membrane, an extension of the middle layer
of the lumbar fascia. In this way the upward movement of the
rib especially in its spiral segment is restricted. The anterior
and lateral segments have a freer movement, so permitting of a
movement of the floating ribs (and the tenth) round an axis corre-
sponding to their spinal segments. It has been noticed that
during inspiration, the spaces between those ribs widen and that
during expiration the reverse takes place.

Function of Abdominal Muscles. The four pairs of abdominal
muscles and their fibrous attachments act antagonistically to
the diaphragm. When the latter contracts the former have to
yield to accommodate the displaced viscera. That is, during
diaphragmatic breathing, inspiration is accompanied by a relaxa-
tion of the abdominal wall which will move forwards. Corre-
spondingly, expiration will be aided by the tendency of the
viscera to return to their normal positions and by the return of
the abdominal muscles to the position of rest.

B.B. 20

306

This musculature has also an important part to play in the
maintenance of an adequate circulation. There is no doubt
that the diaphragm, with its synergic and antagonistic muscles,
was evolved not in connection with respiration but with circula-
tion. Amphibians, for instance, carry on their interchanges of
air between lungs and atmosphere by the action of muscles under
the jaw. Without the constant tension of the abdominal muscles
applied to the abdominal viscera, the larger veins would become
distended with blood. These veins are capable of holding the
entire amount of blood in the body. If for any reason the muscles
of the abdominal wall lose tone, considerable fall in arterial blood
pressure is the result. It may even fall to zero and death ensue.
This may be determined experimentally, either by dividing the
spinal cord at the level of the first dorsal vertebra, or by using
an animal with poorly developed abdominal muscles such as the
tame rabbit. In the first case, the influence of the bulbar centres
on the part below the section is removed, and the tone of the
abdominal wall is abolished. If the animal is now placed verti-
cally erect, the abdominal veins distend under the haemostatic
pressure. In them the whole of the blood collects and there is
no blood to fill the heart.

III. Thoracic Respiration. The upper and lower regions of the
thorax should be considered separately. The muscles and move-
ments of the upper series of ribs are quite different from the lower
series.

(a) Lower costal series (6th to 9th or 10th rib).

This segment moves along with the diaphragm and leads to
the expansion downwards of the lower lobes of the lungs. The
ribs are articulated to the spinal column so that during inspira-
tion the lateral and anterior part of each moves outward more
than the one above it. Two movements may be noted :
**' (i) The 50 to 7 mm. of each rib next the spine to which is
attached the erector spinae muscle moves forward at each respira-
tion. The tubercle of the rib slides forward on the flat upper
facet of the transverse process.

(ii) The non-spinal portion of a pair of ribs moves with a bucket-
handle action, rising and coming forward with each inspiration.
At the centre of each pair is the sternum-cartilage complex which
is raised and forced forwards during inspiration. The muscles
concerned in this increase of the volume of the lower thorax,
transversely and antero-posteriorly, are the external intercostals.

(b) Upper costal series (2nd-5th rib).

THORACIC RESPIRATION

307

These ribs differ from the lower series in shape, articulation,
ligamentation, musculature and, consequently, in their move-
ments.

(i) Shape. The upper ribs have a concave upper margin and
do not have such a marked twist as those in the lower costaJ
series. The second rib as a matter of fact may be laid flat on a
table.

(ii) Articulation. The spinal articulation differs from the lower
series mainly in that the convex ovoid facet of the tubercle fits
into a corresponding cavity in the transverse process instead of
gliding on a flat facet. Each transverse
process from above downwards is tilted a
little more backwards so that the angle of
articulation becomes more oblique as one
passes down the series (Fig. 69).

Further, the upper ribs not only articu-
late with the vertebral column by their
tubercles but also the facets on the head of
each rib work against the corresponding
facets on the head of the vertebra.

(iii) Ligamentation. Each of the upper
series of ribs is joined directly to the sternum
by a band of cartilage. The following are
the lengths of these attachments in a well-
built man : second, 37 mm. ; third, 50 mm. ;
fourth, 62 mm. ; fifth, 75 mm. The angle
of attachment increases as the length in
creases, e.g. the second costal cartilage joins
the sternum at right angles while the third
ascends to the sternum.

(iv) IduSCulatUTe The musculature of en^e 'n the obliquity of articu-

these ribs is the intercostal interchondral. S"1 the exPansion of the

(v) Movements. Because of the double (From Noel Paton's Essent ials
.,. „ i-u j-u 4-Ui of Human Physiology.)

articulation of each rib to the vertebral

column by tubercle and head, rotation round a spino-sternal axis
is limited. Very little bucket-handle action can take place. As
the articulations are practically transverse, movement must occur
at the manubrio-sternal articulation, i.e. chiefly forwards.

(c) The first rib provides the necessary fulcrum for the inter-
costal muscles. Along with the manubrium sterni, to which they
are firmly bound by their broad but short costal cartilages, the
first pair of ribs form the operculum or lid of the thorax. This

FIG. 69. — Bib and vertebral
column in upper and in lower
costal series to show the differ-

308 EXTERNAL RESPIRATION

lid is articulated anteriorly with the thoracic wall, at the manubrio-
sternal joint, forming a synchondrosis. That is, the opposing
surfaces of bone covered with a layer of hyaline cartilage and
united by fibre-cartilage are bound together firmly by longitudinal
fibres developed from the strong and thick periosteum. The
cartilages of the first ribs are implanted upon the side of the
mamibrium forming a synchondrosis with the sterno-manubrial
joint and there is no synovial cavity.

Great importance has been attached to the movements of this
joint. Its amplitude varies, of course, with the type of respiration,
being greatest with those who make least use of the muscles of the
abdominal wall and vice versa. In other words, if the sternum
moves freely then the excursions of the sterno-manubrial joint
will be small. On the other hand, in cases where the lower part
of the sternum moves but little during inspiration (thoracic
breathing), there will be a correspondingly large rotation of the
upper end of the sternum on the end of the manubrium. Some
physicians declare that in phthisical subjects this joint does not
move freely. Whether phthisis causes an anchylosis or whether
want of free movement leading to incomplete expansion of the
apices of the lungs is a factor favouring the development of the
disease, is as yet an unsolved problem. On the whole the evidence
tends to show that ossification of the costal cartilages in question
is a consequence rather than a cause of a limited expansion of the
apices of the lungs.

Posteriorly the lid is articulated to the vertebral column by a
joint which is set more transversely and is wider in the extent of
its attachment than any other of the costal arcs.

IV. Mechanics of Thorax. The ribs are a series of bent levers.

(1) The fulcra or hinges on which the levers work have been
inentioned when dealing with the ribs of the various thoracic

' segments.

(2) The power differs according to whether inspiration or
expiration is being performed (p. 320).

(a) Inspiration.

(i) The lid or operculum is raised by the action of a flat triangular
muscle (scaleni). The scalenus anticus is inserted in the upper
surface of the first rib just dorsal to the cartilage and passes almost
vertically to the transverse processes of the third, fourth, fifth and
sixth cervical vertebrae. The scalenus medius lies dorsally to the
anticus and passes to the transverse processes of the lower six
cervical vertebrae.

MECHANICS OF THORAX 309

(ii) The external intercostal muscles may be regarded as a
triangular sheet of muscle having its origin in the dorsal part of
the lid and being inserted into the upper surfaces of the ribs.
It pulls upwards.

(b) Expiration.

(i) The power causing collapse of the chest wall is mainly the
elastic recoil of the lungs together with the weight and elasticity
of the chest wall.

(ii) The abdominal muscles, especially the external oblique, play
a part in expiration in pulling down the ribs. The fixed basis
from which they act is the pelvis, and they act as if attached
to the lower margin of the ribs exactly opposite the external
intercostals.

(3) Load. This too is different in inspiration and expiration.
' (a) Inspiration.

The resistance to be overcome is :

(i) The elasticity of the lungs — a variable load, as the greater
the expansion of an elastic body, the greater is the resistance
that it offers to further expansion. This factor, therefore, is
numerically greater towards the end of inspiration than at the
beginning.

(ii) The elasticity of the chest wall — the costal cartilages have
to be twisted and the muscles overlying the chest wall have to be
stretched.

(iii) The elasticity of the abdominal wall.

(iv) The elasticity of the vertebral column. During inspiration
the spinal column is lengthened by a stretching of the ligaments,
cartilages and articular processes.

(v) Gravity — weight of chest wall, etc.

These loads may be resolved into one applied to the upper
surface of the ribs at their frontal tips. That is, we are dealing
with levers of the third order where power is applied between
load and fulcrum — giving speed at the expense of strength.

(b) Expiration.

The main resistance to expiration is the resistance to the outflow
of air from the lungs. We have seen that the principal force
causing expiration is the inspiratory load. Here then we have
a lever of the second class with the load between the power and
the fulcrum. During forced expiration, when every muscle that
can reduce the size of the thorax is brought into play, we have a
simple bellows action. The front of the thorax acts like the
movable side of a pair of bellows and is depressed towards the

310 EXTERNAL RESPIRATION

other side by the abdominal muscles. This is also a lever action
of the second order.

V. Elasticity of the lungs. The work done by the respiratory
musculature cannot be treated as a simple problem in hydraulics.
The dynamics of the ordinary force pump cannot be applied to
this question. Not only are the walls of the pump elastic and
complex but (a) they are not equally extensible throughout and

(b) their elastic force varies with the degree of extension. Further,

(c) the fluid enmeshed in the pulmonary capillaries has to change
its position to be accommodated at every alteration in the exten-
sion of the lungs.

(a) Examination of the structure of the lungs shows that they
cannot be equally extensile throughout. Anatomists divide each
lung into three zones.

(1) Root zone containing bronchus, artery, vein, lymphatic
vessels, etc. This apical part contains much fibrous tissue and,
therefore, offers considerable resistance to distortion. Using
physical terms one may say that its elasticity is strong but far
from perfect (p. 168).

(2) Outer zone, estimated as extending for about 30 mm. from
the pleura containing very little fibrous tissue and made up mostly
of small capillaries and pulmonary tissue. Of these the pulmonary
tissue is perfectly but feebly elastic and the capillaries (empty) have
a modulus of about 0-04 xlO6 — not quite so perfect as the lung
substance but offering a greater resistance to distortion. Even
within this zone extensibility is not uniform. The stratum lying
immediately below the pleura is much more extensible than the
inner stratum. Inflation of a lung recently removed from the
body clearly demonstrates that certain parts of the surface are
inflated first and that the inflation of certain parts of the sub-
pleural stratum spreads from these points.

(3) The middle zone, lying between the apical and surface
zones, is intermediate to them in its elastic properties, containing
as it does highly elastic pulmonary tissue interspersed between
the rays of the bronchial and vascular systems.

(b) That the elastic force of a material alters with the degree of
distension is a physical fact that has already been considered in
dealing with the force of the heart. Since the pressure of a gas
acts equally in all directions, the pressure caused by any given
tension of the walls of the hollow (spherical) vessel containing air
will increase with the diameter of the vessel. If we consider that
the diameter of each air sac is doubled during inspiration, then the

EFFICIENCY OF LUNG MECHANISM 311

total pressure exerted by the walls will be increased four times,
i.e. distending force— resistance to distension —pressure of gas
multiplied by area of vessel. Moreover with increasing distension,
the lung substance will become more attenuated.

(c) The blood and lymph enmeshed in the pulmonary system
has to adjust its position to suit every alteration in the shape of
the lungs. These fluids are highly viscous and as such resist
distortion roughly in proportion to their pressure and to the area
of the cross-section of their vessels. Further, the capillary
vessels are so narrow that the corpuscular component of the blood
viscosity becomes predominant.

(d) In addition to these factors which may be deduced from
a study of lungs removed from t-he thorax one must take into
consideration the position of the lungs in the thorax. Certain
parts of the thoracic wall are stationary and the surfaces of the
lungs in contact with these parts cannot directly expand.

(i) The mediastinal surface is in contact with the pericardium
and with the structures of the mediastinum, (ii) The dorsal
surface lies close against the vertebral column and spinal portions
of the ribs, (iii) The dorsal part of the apical surface is bounded
by Sibson's fascia at the root of the neck.

On the other hand the parts of the lungs in contact with (iv) the
diaphragm, (v) the lower ribs (ventro-lateral aspect) and (vi) upper
ribs (sternal aspect) undergo direct expansion at each inspiration.

VI. The efficiency of the lung mechanism. If figures could be
obtained denoting the work done by the respiratory mechanism
and its efficiency, they would be invaluable. One may arrive at
an approximate value by measuring the oxygen consumed by an
animal under standard conditions with normal and with increased
respiration. With man, it was found that during muscular rest,
1 to 3 per cent, of the total basal oxygen intake is utilised by the
respiratory mechanism. This amounts to from 0-3 to 0-7 c.c. of
oxygen per litre of ventilation. Assuming that all the energy
used is obtained from glucose, these figures indicate that from
0-0017 to 0-005 calories are expended for each litre of air breathed.
This amount of energy is liberated from 0-004—0-0012 grams of
glucose. During quiet breathing each breath (400 c.c.) costs at
most 0-002 calorie obtained from just about 0-0007 of a gram of
glucose and 0-28 of a cubic centimetre of oxygen. If it is assumed
that the lung mechanism is at least 20 per cent, efficient, then
at each quiet complete respiration, 0-00016—0-0004 calories are
converted into work =1/3 to 1/2 kilogram-metre.

312 EXTERNAL RESPIRATION

This work is almost entirely performed by the diaphragm.
The other muscles concerned, whether synergic or antagonistic,
seem to play an almost passive part. This may be inferred from
the fact that although they are skeletal in structure yet they
undergo constant slow contraction without showing fatigue.
When the respirations are forced the subsidiary musculature has
to perform work and the CO2 output increases. The effort
sooner or later brings on fatigue. Forced respirations are carried
out uneconomically, i.e. at a relatively higher cost per litre than
ordinary quiet ventilation.

Regulation of Respiratory Rate. The activity of the respiratory
centre, which lies in the medulla near the root of the vagus, is
normally governed by the tension of the CO2 in the blood going
to it. The rate of breathing is increased by any increase in
the CO2 tension ; and, conversely, diminution of the CO2 tension
leads to a decreased respiratory rhythm.

The CO2 tension of the blood and the partial pressure of the
CO2 in the alveolar air are, as we have explained (Chap. XXIII.),
always in dynamic equilibrium, and, therefore, any change in the
one will lead to corresponding changes in the other. It has been
found that an increase of 0'2 per cent, in the CO2 of the alveolar
air, i.e. a rise of tension of from 40 to 41' 6 mm. Hg, is sufficient
to double the rate of respirations. The increased ventilation
leads to a " washing out " of CO2 from the blood and from the
lung, thus rapidly restoring a normal condition. The power
of adjustment is so extraordinarily effective that under wide
variations of metabolic and atmospheric conditions, the tension
of CO2 in alveolar air is maintained at an almost constant level
of about 40 mm. Hg (see p. 334).

Regulation oJ Depth. Impulses are constantly passing from
the lungs, through the vagi, to the respiratory centre and, by a
reflex act, inspiration is checked when a certain tension is set
up in the lung substance, i.e. the respiratory mechanism carries
out the inspiratory phase of its function till this stretch-reflex
inhibits it. In cases where the vagi are hyper-irritable, the stop
mechanism acts too soon and breathing becomes shallow and
rapid.

ALIMENTARY CANAL

" I receive the general food at first,
Which you do live upon ; and fit it is,
Because I am the store-house, and the shop
Of the whole body :

Though all at once cannot

See what I deliver out to each :
Yet I can make my audit up, that all
From me do back receive the flour of all,
And leave me but the bran."

SHAKESPEARE.

As has been indicated (Chap. XXI.) the non-gaseous imports
are submitted to a certain amount of manufacture before being
handed over to the inland transport service for transportation
to the cells of the body. For instance, proteins have to be split
into their constituent amino-acids, carbohydrates are broken
down into monosaccharides and fats undergo some change.
In addition to these changes in molecular complexity and pre-
ceding them come, in many cases, changes of physical state.
Most of our foodstuffs are solid or semi-solid and in such a state
are useless to the organism. Before they can be split into their
constituent units they must be rendered soluble.

General. In brief, the function of the alimentary canal is to
provide (1) a series of mills and factories where food may be
comminuted and dissolved in water, (2) a series of factories for
breaking down the dissolved foods into units which the organism
is capable of absorbing, (3) a mechanism for absorbing these units,
(4) a mechanism for eliminating the waste material, (5) a means
of transport from one factory to another and (6) an adequate
control over these various processes so that all maybe co-ordinated.

In structure, the alimentary canal is a tube passing longi-
tudinally through the body having anteriorly a voluntary mechan-
ism for receiving and grinding food ; intermediately, stations,
not controlled by the will, for completely breaking down the food

313

314 ALIMENTARY CANAL

mass to convenient units and for absorbing the same, and
posteriorly, a semi-voluntary mechanism for ejection of waste.

I. The mouth is the port of the alimentary transport system.
First, by nose and eye the cargo is sighted and its nature estimated.
Messages are sent inland, factories get busy and all is ready when
the ship reaches port. By means of the taste buds on the tongue,
the nature of the cargo is further ascertained and appropriate
secretions from the salivary glands take place. Bitter or saline
substances provoke a profuse secretion of watery saliva. Flesh
is met by a secretion containing a large proportion of the lubri-
cating material — mucin. Dry matter causes the flow of a thinner
and more watery saliva than moist matter.

(a) The functions of saliva in the mouth are purely mechanical.
It acts as a lubricant : moistening the surfaces of the mouth and
the passage from it : infiltering the food mass and so necessitating
the expenditure of less energy in milling the food ; and finally
covering the outside of the bolus with mucin, thus rendering
deglutition easy. Normally, saliva has no chemical action in the
mouth. It contains a diastatic enzyme, ptyalin, which, however,
carries out its action on polysaccharides during the earlier period
of gastric digestion (q.v.).

(b) The tongue is a mobile organ lying on the floor of the mouth.
It consists mainly of a mass of muscles which are paired. Some
of these muscles lie wholly within the tongue (intrinsic), and for
the most part, by their contraction, give rise only to alterations
in shape. The extrinsic muscles have their point of attachment
outside the organ, and so are capable of causing alterations in
position as well as in form.

Intrinsic Muscles.

1. Superior longitudinal, pulls tip upwards and decreases length of

dorsum.

2. Inferior longitudinal, pulls tip downwards and inwards, i.e. curves

dorsum.

3. Vertical, working in conjunction with the transverse they produce

a concave surface on the dorsum. Acting alone a convex surface
is produced.

4. Transverse.

Extrinsic Muscles.

1 . Genio-glossus — downwards.

2. Hyo-glossus — backwards.

3. Chondro-glossus (not always present) — backwards and downwards.

4. Stylo-glossus — backwards and towards palate.

5. Palato-glossus — side to side — continuous with intrinsic transverse.

MECHANICS OF MASTICATION 315

The tongue has a threefold duty to perform as a unit of this
transport system — («) working in conjunction with the lip-
sphincter— orbicularis oris, and with the triangular and other
muscles it acts as a suction-plunger ; (/3) during deglutition it
functions as a force plunger and (y) it forms with the cheeks an
effective hopper during the mastication of food.

(c) The lower jaw is a horse-shoe shaped lever of the third
order. The load is placed on the teeth, the fulcra are at the
ends of the horse-shoe, where they articulate with the fixed upper
jaw while the power is applied at a point on either side between
the teeth and the fulcrum. The jaw is pressed against the upper
jaw by the action of the temporal, masseter and internal pterygoid
muscles which act antagonistically to the mylo- and genio-hyoids,
to the platysma and to the anterior belly of the digastric muscle.
Nuts having a crushing point of about 400 kilograms may be
crushed by a direct thrust of the front teeth. The molars, lying
as they do nearer the fulcra and further from the application of
the power, may exert a direct pressure of about 550 kg. The
employment of such pressures is rarely necessary on account of
the previous treatment of the food (milling, cooking, etc.), and
of the influence of saliva. Soft bread, for instance, is merely
compressed by a pressure of 100 kgs. but, after moistening with
saliva, only a twentieth of this pressure is necessary to obtain
a clean bite through.

The grinding operations of the molars (and of the incisors at
times) are a compound motion made up of a side-to-side and a
forwards-backwards motion. The former is produced by the
action of the external pterygoids working in conjunction with the
posterior fibres of the corresponding temporal muscle. The
latter movement may be ascribed to the forwards pull of the
external pterygoids and the backwards pull of the posterior fibres
of the temporals.

This mill-like motion tears the food with a smaller exhibition
of pressure than direct crushing. Cooked meat which could be
crushed by the application of from 30 to 100 kg. pressure can be
torn by a grinding movement when the pressure is only 2 to 5 kg.

In Chap. XVI., we saw how bone was formed in accordance
with the stresses and strains upon it. It is, therefore, interesting
to note that in proportion as the food is prepared by factory
milling and cooking, in proportion in fact, to the avoidance of the
stimuli to growth furnished by incident stresses and strains, so
the jaws of civilised men tend to become weak. In consequence

316 ALIMENTARY CANAL

faces are elongated and narrow instead of short and round like
those of primitive men.

II. The act of swallowing. The food, after being chewed, is
collected on the surface of the tongue by the action of the bucci-
nator and other voluntary muscles. The tip and sides of the tongue
are pressed against the hard palate and teeth. A rapid contrac-
tion of the mylo-hyoid muscles, which form a floor for the front
portion of the mouth (diaphragma oris), pushes the tongue up
against the hard palate. At the same time the hyoglossus pulls
the tongue backwards and the bolus is shot towards the gullet.
This closes the voluntary stage of deglutition.

Several other muscles come into play at this point. As will
be seen from Fig. 42, just above the larynx is a busy crossing
common to two routes. Gaseous food and gaseous excreta pass
to and fro right across the track of the descending bolus. At
the moment of swallowing, the nose-to-lung and lung-to-nose
traffic is reflexly held up. Further, the escape of the food mass
by either of these incorrect routes is prevented as follows :

(a) The naso-pharynx is closed by the action of the pharyngo-
palatini muscles, which form the posterior pillars of the fauces.
The pharynx is thus drawn to a narrow cleft. Against this narrow
opening the soft palate is pressed by the action of the levator and
tensor veli palatini muscles, (b) The laryngeal aperture is kept
closed by the action of the crico-arytaenoideus lateralis, arytae-
noidei, and the thyreoarytaenoidei muscles, which pull the
arytaenoid cartilages forwards against the back of the epiglottis.
Accompanied by a quick downward motion of the tip of the
epiglottis, the bolus is pushed over the back of this structure
and is impelled into the gullet.

III. The stomach. By the impulse imparted to it at its entry
into the gullet, aided generally by gravity and to a questionable
extent by peristalsis, the bolus is forced down to the gateway to
the stomach. This aperture, in common with the exit from the
stomach, is guarded by a thick ring of visceral muscle. When
contracted, i.e. during the normal state of tonus, these sphincters
prevent the too hurried passage of material along the alimentary
canal and also prevent its regurgitation. They are not controlled
by the will but by local nerve centres. By its weight, the bolus
usually exerts sufficient pressure to cause the opening of the
cardiac sphincter and gain admission to the stomach, in which
it is locked by the operation of a local automatic arrangement.

The processes of digestion or splitting of the foodstuffs by

PERISTALSIS 317

enzymes now commence (Chap. IX.). Polysaccharides are
broken down to maltose by ptyalin and the native proteins first
converted to metaprotein by the action of the hydrochloric acid
of the gastric juice and reduced in size and complexity to the
proteose stage by the action of pepsin.

Even a casual examination of the stomach will show that it
is divided into two parts, each with a distinct function. The
upper or cardiac portion is a reservoir or hopper where the food
pulp is stored for a short time without mixing. % It is during its
stay here that salivary digestion reaches its maximum. By
the steady pressure of the walls in the cardia, the mushy mass
is fed little by little through the throat of the hopper (prepyloric
sphincter) into the lower or pyloric part of the stomach. By
peristaltic contractions of its walls, this pyloric section of the
stomach mixes food and gastric juice most thoroughly. The
acid of the juice aids peptic while inhibiting diastatic action.
Cathcart showed that the prepyloric sphincter was controlled
by the hydrogen ion concentration of the duodenum and of the
pyloric part of the stomach. Acid entering the intestine un-
doubtedly causes constriction of the sphincter. While the CH
of the pyloric portion of the stomach does not seem to effect the
closure of the sphincter, the above worker demonstrated that a
sufficient reduction of the CH brought about a rapid opening of
the sphincter. The introduction of an extra alkaline juice, e.g.
by regurgitation from the intestine, leads to a smart flow of acid
chyme into the antrum pylori.

The rate of exit from the antrum is controlled by the hydrogen
ion concentration of the duodenum. As long as the duodenal
contents are markedly acid, the pyloric sphincter remains firmly
closed and only opens to admit more acid chyme when its receptors
are no longer stimulated by acid.

IV. The intestines have three functions to perform : (a) trans-
porting, (b) mixing and digesting, (c) absorbing.

(a) Transporting. This is carried on by means of a series of
peristaltic waves, i.e. a section of the muscular wall adjacent
to the anterior end of the food-mass undergoes relaxation
while a corresponding posterior section contracts. This double
wave of relaxation and contraction passes along the tube and
acts as a piston with a central orifice. In this way, the chyme
is passed along at the rate of about 1 inch a minute, and churned
meanwhile.

(b) These driving peristaltic waves are not the only movements

318 ALIMENTARY CANAL

of the intestinal musculature. The chyme is kneaded and its
surface broken by the rhythmic segmented contractions of the
circular muscles of the bowel. By this means (i) the various
digestive juices of the intestine are thoroughly mixed with the
chyme, (ii) fresh surfaces are exposed to the absorbing surfaces
of the wall and (iii) the capillary blood-vessels of the lining
membrane are compressed rhythmically, so helping to drive the
blood laden with the products of digestive activity on to the
liver, etc.

The work of digestion, begun in the mouth and stomach,
is completed in the intestine. Carbohydrates are reduced
to single sugars and proteins are broken down to amino acids,
etc. In addition to this, the fats are attacked by lipase, which
resolves them into their component fatty acids and glycerol
(or other alcohol). In this process, the bile salts, by lowering
the surface tension at the fat-lipase interface, play an important
part.

(c) Absorption seems to be a case of passage of material through
a membrane (q.v.).

V. Faeces. The materials not absorbed by the intestine are
eliminated by the rectum as the faeces. One suggestive physico-
chemical fact about these excreta is the proportion of soap to
mass in their make up. It has been found that, normally, fat
forms approximately ^ of the faecal mass (dry). About 10 per
cent, of this fat is in the form of soap. This may be correlated
with the water-holding power of soaps and with their lubricating
properties. Somewhere about 80 per cent, of their contents is
water. This is somewhat remarkable, as both water, fatty acids
and soaps are readily absorbed from the gut. If one desires to
reduce the water content, calcium is exhibited. As we have
already seen (p. 82) calcium soaps are hard " dry " soaps. On
the other hand, the addition of easily dissociated sodium and
potassium salts leads to the formation of " softer " soaps and a
marked increase in the water content of the faeces. It is note-
worthy that the fat content (as soap) remains constant. That
unabsorbed fat is an excellent faecal lubricant is an axiom in
present-day prescribing when mineral oil (liquid paraffin), which
cannot be absorbed, is given to produce easy defaecation.

For the final discharge of the waste alimentary contents a
simple kind of " touch button " mechanism is provided. The
act is initiated by a voluntary response (removal of inhibition)
to the stimulus produced by the stretching of the muscular wall

DEFECATION 319

of the rectum by the faeces. When the pressure of the fasces in
the rectum reaches a value of about 30-40 mm. Hg, there is a
call to defsecate. If no response be made, the call is not repeated
immediately, as the rectal walls relax and so lose their irritability
to pressure. While the initiation is voluntary the act itself is
purely reflex like the other movements of the intestine. The
reflex contractions and relaxations are generally aided by Voluntary
contraction of all the muscles, which will increase abdominal
pressure.

From a physico-chemical standpoint practically nothing can
be said of the mechanism of alimentary transport. While the
movements, etc., are apparent the underlying causes are com-
pletely hidden. No help so far is given by attempting to trace
the development of the highly complex system of the vertebrate
from the apparently simple physico-chemical response of the
amoeba to contact with food.

CHAPTER XXVIII
MOVEMENTS OF THE LIMBS

" If the mountain will not come to Mohammed,
Mohammed must go to the mountain."

IN order to get food, prepare food, and preserve its life and that
of its race, the higher animal makes use of a series of levers to
move its body in whole or in part. These levers are generally,
but not always, made of bone, and generally but not always they
work against a bony fulcrum.

In general, a lever is a rigid bar either straight or curved which
is capable of a rotatory motion round a fixed point — the fulcrum.
It is usual to divide levers into three classes depending on the
relative positions of power, fulcrum and load.

Class I. The fulcrum lies between the power and the load.
In this class of lever, if the power arm is equal to the load arm, we
have a balance. The application of one kg. of power will lift one
kg. of load. If the power arm is lengthened by shifting the
fulcrum nearer to the load, then power will be increased propor-
tionally as speed is decreased. For example, dealing with a
straight lever and putting P=point of application of power,
jF=fulcrum and L=point of application of load, then PF
represents the length of the power arm, and LF=length of
the load arm of the lever. If PF=10 times LF, then 1 kg.
at P would balance 10 kg. at L, i.e. the load of 10 kg. would be
lifted by the exertion of a little over 1 kg. weight. This is the
crowbar lever and is very little employed in the body. The
most notable example of it is the forwards and downwards move-
ment of the head when one is overtaken by unconsciousness, e.g.
sleep. The fulcrum on which the head moves is the atlas, and
the weight of the prefulcral part of the head (long power-arm)
outbalances the postfulcral portion (short load-arm).

Generally, speed is the desideratum. The fulcrum is placed

320

LEVERS 321

near the power. The power-arm PF is short and the load-arm
LF is long. The relative speeds of the points will be as LF/PF.
The catapults employed by the ancients to cast stones are examples
of this kind of lever. The arm is used as a lever of the first class
with a short power member when a cricket ball is thrown.

Normally, the head is a lever of this order, the power being
applied very close to the fulcrum. The quick nod of assent is
caused by the contraction of the anterior straight muscles which
are yoked close to the fulcrum, while the slower backward move-
ment is due to the placing of the effective muscles (splenii and
complexi) somewhat further away from the occipito-atlantal
joint. The feature of this arrangement is stability. Another
good example is when the foot is lifted off the ground and the
ground pressed on by the toes on contraction of the gastrocnemius.

Class II. The fulcrum is at one end of the lever and the load
lies between it and the power. That is, the power-arm is always
of the same length while the load-arm may vary in length with the
position of the load, e.g. nut crackers. The outstanding example
of this lever in the body is the foot. On rising on the toes, the
base of the metatarsals is the fulcrum, the body-weight, borne by
the tibia to the ankle, is the load, while the power is applied to
the os calcis by the gastrocnemius. A foot with a long load-arm,
i.e. with the load near the power, is designed for speed not power, —
well adapted for running. On the other hand, the further the
load is from the point of application of power, in this case, the
longer the heel, the smaller will be the force necessary to lift
the body. That this is so, may be inferred from a study of the
development of the gastrocnemius muscle compared with the
length of the heel bone. Europeans have short heel-bones and
well-developed, bulky calves, while Africans have long heels
and ill-developed calf muscles.

Class III. The point of application of the power is between
fulcrum and load. This power must always be greater than the
load. It is the commonest class of lever in the body, and this is
to be expected as its use results in the most rapid action possible.
Speed is obtained, as before, by shortening the power-arm. In
the arm, the brachial muscle is inserted about one centimetre
beyond the fulcrum (elbow) while the total length of the load-arm
(forearm) is about 30 cms. The result of this arrangement is
that the load (hand) moves with about 30 times the speed of the
bone at the point of the application of the power. " Speed is
gained at the expense of power." It follows that while a long-

B.B. 21

322 MOVEMENTS OF THE LIMBS

armed man may be able to give a quick blow he will be quite
unable, unless his brachial muscles are abnormally developed, to
give a heavy one.

This introduces a point to which the author of the " Tarzan "
stories paid little attention. Tarzan was able to hold his own
among the tree tops. Now, man has a fore-arm considerably
shorter than the upper arm while the anthropoid ape has a fore-
arm only a little short of twice as long as its humerus. This gives
it a long and quick reach. In swinging and climbing, the upper
arm is the lever employed to lift the body, mainly by the con-
traction of the anterior brachial muscle, and the insertion of
the brachial over half-way up the humerus from the elbow
(fulcrum) gives a power-arm with rather more power than speed.
That is, a short humerus is a necessity for climbing animals —
to furnish strength, just as the long forearm is necessary to give
agility. To have equal climbing power, man would need to have
extraordinarily bulky biceps, etc., and this would not aid him
when he desired to swing and seize distant branches surely and
rapidly.

So far, we have dealt with the levers of the body in a general
sense, as if they were straight bars. As a matter of fact, none of
the bones of the body can be considered as straight levers, and none
of the muscles act absolutely at right angles to the length of the
bone. The lengths of the effective power and load arms may be
obtained by dropping perpendiculars from the fulcrum to the lines
of application of power and load. The ratio of these perpen-
diculars gives the ratio of the distribution of power and speed by
the lever.

The value of the bone-muscle mechanism depends on the mass
of active muscular fibres, their degree of contraction and the angle
which they make with the bone to be moved. The very movement
of the bone will alter the angle of pull of the muscle. For each
of its positions, the lever will have a moment of rotation determined
by the size of the angle made by the line of traction (axis) of the
muscle and the axis of the bone. By resolving the force of the
muscle into two components, one of which acts along the axis
of the bone and the other at right angles to it, one can readily
perceive that the latter, the effective component, varies in value
directly with the sine of the angle of pull. The ineffective or
parallel component varies as the cosine of the angle of pull and
represents the pressure exerted by the muscle on the fulcrum.
As the moment of rotation is equal to the tension developed (F),

PULLEYS 323

and the perpendicular distance (d) of the axis of the muscle from
the fulcrum, one may write M=Fd. Then the effective com-
ponent is equal to F sin a where a is the angle of pull, and the
parallel component to F cos a. Hence, as the bony lever gets
pulled up, the effective component will become greater and the
parallel component will become less. In other words, the more
parallel the axis of a muscle is to the axis of the bone which it is
to move, the weaker will be its action — the maximum value is
obtained when the line of action is at right angles to the bone.

Pulleys. By means of a single fixed pulley the direction of a
force is altered, but not its magnitude. In the body, instead of
reducing friction by means of a rotating pulley the tendon operates
in a synovial sheath (q.v.). Good examples of the pulley may be
found in the cartilaginous loop (trochlea) for the superior oblique
on its way to the eyeball : and the peroneus longus looping
round the outer malleolus on its passage to the inner side of the
foot.

Opponents. All the muscles attached to levers in the body
are set in opposing pairs or antagonistic groups. As one group
contracts, the opposing group will relax to exactly the same
degree. The ulna, for instance, is pulled up towards the humerus
by the action of the anterior brachial and it is pulled downwards
by gravity and the action of the posterior brachial muscle. Both
sets of muscles act together and harmoniously, so that in any
position of the ulna relative to the humerus, the opposing (muscular
and gravity) forces exactly balance one another. That is, the
arm may come to any position and remain there without the
expenditure of any extra energy (not taking into account gravity).

Syner gists. Movement does not usually take place merely by
the contraction of a muscle and the relaxation of its opponent.
There are numerous other muscles brought into play, synergists —
whose action, though secondary, helps the primary movements,
generally by altering the pose of the body as a whole, but some-
times by immobilising the bone to which the muscle is fixed. As
an example of the former, may be cited the action of the trunk
muscles holding the body erect while a weight is being held above
the head. The latter synergetical complex may be illustrated
by the various muscles brought into action in opening a table
drawer. " One hooks his fingers into the handle of the drawer
and if it opens easily enough, the contraction of the flexors of the
fingers is sufficient. If it works a little harder the flexors at
the elbow contract to hold the bones of the forearm up so that the

324 MOVEMENTS OF THE

flexors of the fingers may have a firm origin. If still more force
be needed the latissimus and teres major spring into action to
support the humerus and rhomboid to hold the scapula. To
make a strong pull one pushes against the table with the other
arm and brings the extensors of the trunk into action, and finally
if this does not suffice, the legs are braced and the whole body is
converted by muscular action into a single solid piece in order
that the flexors of the fingers may exert all their power to open
the drawer." This description by Bowen shows clearly the
complexity of an apparently simple action. The student will
note too that as more muscles are called upon, the lever is length-
ened and the position of the fulcrum altered.

CHAPTER^XXIX
THE VOICE

" As the power of the vital soul is situated in the substance of the heart, and
the power of the natural soul in the proper substance of the liver, ... so also
does the brain, in appropriate structures and in organs properly subserving its
work, manufacture the animal spirit, which is by far the brightest and most
delicate, and indeed is a quality rather than an actual thing. And while on
the one hand it employs this spirit for the operations of the chief soul, on the
other hand it is continually distributing it to the instruments of the senses and
of movement. . . ." (1543) VESALIUS quoted by FOSTER.

ARTICULATE speech may be considered as the resultant of
essentially two component factors, (a) the production of sound,
and (6) the modification of the sound to produce speech.

I. The latter factor is the simpler and may be dealt with first.
Speech sound-units may be classed as vowels and consonants.

The vowels, U, 0, A, E and I are produced by the continuous
issue of a blast of air through the mouth. U, 0 and A, pro-
nounced 66 (cook), oh and ah, respectively, are simple tones.
They are produced by a regular series of vibrations emitted by
a single cavity formed by lips, cheeks, palate and tongue (Fig. 42).

A (0/4) U(oo) l(ee)

Fia. 70. — Changes in the Shape of the Mouth in Sounding the Vowels, A, U, and I.
(Griitzner.)

This cavity is widest and shortest with A, longest and narrowest
with U, while 0 is intermediate. On the other hand, E (as in

325

326

THE VOICE

pet) and I ( =ee) are double-toned. The back of the tongue is
brought up against the front part of the soft palate so that the
mouth is divided into two resonating cavities each with a charac-
teristic note (Fig. 70).

By whispering the vowels one may readily determine the
resonance-pitch characteristic of each. U has the lowest pitch,
followed by 0 and A. It is thus easier to sing U and 0 on low
than on high notes. An attempt to go up the scale by sounding
" oos " will cause a tendency to clip the full vowel and sound a
short " ee." The characteristic notes of each of these vowels
(by percussion, Expt. 51, p. 422) is given by Helmholtz as follows
(Fig. 71) :

U = F

0 = Bl
A = Bn

E =Fl;BUL

1 = F, Dlv

U

E

FIG. 71 (Starling). — Values obtained by percussing mouth cavity while shaped for the
pronunciation of the vowels.

The English I is really a diphthong and is pronounced by
rapidly uttering the component unit sounds, e.g. I (as in fight)
= AI =ah-ee.

Consonants are not continuous but are sharply interrupted
sounds. The issuing air is suddenly shut off by the lips to give
the labials ; by the teeth to produce dentals ; by the tongue to
give rise to gutturals. If the check occurs before the sound is
produced, and the air is suddenly released, explosives are the
result. The characteristic sounds of some consonants, e.g. M
and N (which are mechanically the same as B and D), are produced
by keeping patent the posterior opening of the nares. In this
way some of the air comes continuously through the resonant
nasal passages.

TABLE LII.
CONSONANTS.

Class.

Labial.

Dental.

Guttural.

Explosives

P. B. V.

T. D.

K. G.

Aspirates

F.

S. L. Th.

Ch. (Scots)

Vibratives

—

—

K. (Scots)

Nasals

M.

N.

Ng.

PHONATION 327

All these with the exception of the hard consonants (e.g. B
and D) can be pronounced quite well without the use of the
larynx. The hard consonants are accompanied by phonation.
Thus, although in pronouncing D there is a check at the teeth,
the production of the laryngeal sound goes on.

II. Phonation, or the production of sound, is not so simple as
articulation. At least two essential factors are concerned. The
mechanism for producing sounds consists of a bellows or blower —
the lungs ; a vibrating structure — the vocal chords ; a cyclone
chamber — the ventricle or space between true and false vocal
cords ; the wind pipe or trachea ; and resonating chambers —
the cavities of pharynx, mouth and nose. Musical notes can be
produced without the intermediation of the vocal cords. It has
been shown that the sudden expansion in bore of the windpipe
at the ventricle is quite sufficient to produce a cyclonic distur-
bance of the air, and sound is the result. Most people are of
opinion, however, that the vocal cords play the major part in
sound production.

Loudness is due to amplitude of vibration and depends, in part,
on the force and volume of the blast of air emitted.

In part, it depends on the size of the larynx and of the resonating
chambers, and on the tension of the vocal cords. A true cres-
cendo is obtained by relaxing the tension of the vocal cords.

Pitch, or tone-height, is a function of the rate of vibrations.
This may be proved by running a gramophone record at various
speeds. When running at its slowest the plate of the sound-box
is receiving and transmitting vibrations at the rate of about
100 per sec., and one hears a bass voice. As the speed is increased
the voice rises in pitch till it may be a distinctly light tenor with
500 vibrations per second.

The limits for the human voice are given in Table LIII.

TABLE LIII.

Bass • - Fj to D3 85 to 288 vibrations per second.

Baritone - Al to F3 106 to 340
Tenor - C2 to A3 128 to 424

Alto -E"2toC4 160 to 512

Soprano - B, to G4 240 to 768

(M'Kendrick.)

We derive the musical notion of high and low pitch from the
rise and fall of the larynx in the production of sounds — an entirely
subjective phenomenon. The pitch of a tone, from a physical

328 THE VOICE

point of view, is absolutely defined by its vibration number. High
pitched notes have a higher rate of vibration than low pitched
notes. Alterations in the pitch of a note are probably brought
about in the larynx by altering the tension of the vocal cords,
by the action of the crico-thyreoid muscle — the greater the
tension of the vibrating membrane, the higher the pitch of the
note produced. The part of the cords free to vibrate may be
varied by the approximation of the arytenoid cartilages to one
another. A long cord vibrates more slowly than a short one.
This accounts for the high pitched voices of children.

In addition to this, it is common knowledge that when the force
of the blast of air is increased, .the pitch of the voice rises. There
is thus a tendency to sing sharp when forcing the voice, say in a
large badly built hall.

In one and the same larynx, different parts or regions of the
scale are produced in different ways. Those notes of the scale
which are produced by the same means are said to be produced
in the same register. Thus, we produce deep notes in the chest-,
or thick-register, while high notes come from the high-, head-,
or small-register. The thin or middle register is used normally
by tenors and when the male voice sings falsetto.

Laryngoscopical investigation has shown that, when producing
notes from the chest register, the glottis forms an elongated slit
and the vocal cords, stretched as tightly as possible, are vibrating
as thick masses over their whole extent. In taking the lowest
notes the posterior portion of the arytenoid cartilages are close
together with a wide elliptical chink between the cords. As the
pitch of the note rises the arytenoid cartilages are brought closer
together and so shortening of the vibrating portion of the cords
is produced. The thyreoid cartilage approximates to the cricoid
and the vocal cords are stretched and brought close. The
epiglottis rises as the pitch rises.

When the upper limit of this register has been reached the
tension on the various parts is extreme and one passes with relief
to the middle register — the normal mechanism in the female
(and tenors) for the production of notes between F3 and P4.
The thyreoid cartilage returns to its normal position, the tension
on the cords is decreased and they vibrate at their thin mem-
branous edges only. As the pitch rises the thyreoid and the
cricoid cartilages are again pulled together by the action of the
crico-thyreoid muscle, and this state of tension lasts in tenors,
sopranos and contraltos alike from F3 to C4. Higher notes than

ENERGETICS OF SPEECH 329

this are attained by a shortening of the vocal chink. In the small
or head register the notes are produced by vibrations of only the
inner margins of the cords, and the vocal chink is reduced to a
small anterior aperture which becomes smaller as the pitch rises.
These different mechanisms produce tones of perceptibly different
quality.

Timbre or quality of the voice depends largely on the accessory
resonating chambers. These cavities pick out and accentuate
the overtones produced by the vibrations of the segments of the
cords. Trained singers consciously or instinctively adapt the
shape of the mouth so as to secure for each tone the most suitable
overtones.

The work done in speaking and in singing is complex. Many
muscles are brought into play and the energy expended by them
varies with the rate of speech and the intensity of the sound
produced. The pressure of air employed in ordinary quiet con-
versation amounts to between 140 and 240 mm. of H2O, while
nearly 1000 mm. are required when shouting is indulged in.

If work (phonation only) is taken as equal to the product of
the pressure and volume of air expelled, i.e. W =VH, we may
make a rough assessment of the amount of work done. During
ordinary conversation, a man with a tracheal cannula developed
an air pressure of 100 mm. (H2O) and expired 300 litres of air
per hour i.e.

300 xlOO
VH =- =3° kgm. per hour.

Speaking in a large hall the same man expired 1440 litres of air
per hour and developed a mean pressure of 150 mm. (H2O),

W =1440 xO-15 =216 kilogrammetres.

One may arrive at an estimate of the work of speaking by
measuring the oxygen used during rest and during speech.
Delivering an oration at the rate of 150 syllables a minute
caused the consumption of 28-78 litres of oxygen. Subtracting
from this the amount used during a similar period of rest, viz.
16-96 litres, we find that 11-82 litres were used by the orator. In
large Calories this amounts to 11-82x4-9=57-9 Cals. per hr.

57 -92

In kgm. this gives - - x 425 =6154 kilogrammetres.
4

The value just obtained is about 15 times as great as that
of mere phonation. We must remember that the orator, and
the subject of the experiment was a Frenchman too, uses many

330

THE VOICE

additional muscles in gesticulation, etc. A speech of an hour's
duration may tax his entire powers. To add to his troubles
he has to make himself heard in a large hall. Table LIV. gives
the relative values of the expenditure of energy in the utter-
ance of a single perceptible note in various sizes of halls. The
notes were produced by an artificial larynx (syren).

TABLE LIV.

Nature of Hall.

Tenor.

Baritone.

Bass.

Theatre

1-0

3

7

Church

4

• 6

42

Lecture room -

14

4

12

Dining hall (bad acoustics)

4

6

66

These figures, multiplied by 2 x 10 5, give, in kgms. per sec., the minimum
expenditure of energy necessary to make the sound perceptible in ten
different parts of the hall.

In every case the possessor of a bass voice has to expend more
energy than the baritone or tenor. Generally speaking, the tenor
has least trouble in making himself audible, but instances may occur
where on account of its resonating qualities, a building may prove
more suitable for a baritone than for the former.

SECTION V.: THE ANIMAL AS A WHOLE

CHAPTER XXX
THE PRESERVATION OF NEUTRALITY

" To test a principle by its consequences is allowed by good logic and enjoined
by sound reason." JOUBERT.

FROM a physico-chemical standpoint, the animal body may be
considered as a polyphase liquid, the various phases being separated
from one another by a series of membranes of varying and variable
permeability. From the moment of origin of the organism as an
entity, that is, from the time when the conjugation of spermato-
zoon and ovum produced a mass of protoplasm which was not
in equilibrium with its environment, the various external forces
brought to bear on the organism still further accentuate this
disturbance. The sum of the changes termed life may be looked
on as the response of this polyphase-multimembrane-enclosed
liquid to these impacts. Briefly, all changes tend to restore
balance — which, when attained, is death. It is difficult to make
statements on this subject without using terms implying purpose,
for example we speak of water reaching its own level — cell adjust-
ing itself to its environment, etc. To use other terminology
would be cumbrous if correct.

We dealt (Chap. XVI.) with the effect produced, on the internal
and external structure of bone, of altering the incidence of a load.
Not only are the nearby bones altered but even distant and
apparently unaffected bones undergo changes. In our study of
the transport system we saw how an alteration produced in one
part of an organism spread throughout the whole animal.

One of the main functions of blood is to maintain constant the
concentration of hydrogen ions throughout the organism. A
slight potential increase in the acidity or alkalinity of the system

331

332

PRESERVATION OF NEUTRALITY

acts as a trigger, setting off a series of reactions resulting, finally,
in the restoration of neutrality. Acid is set free, say in muscle,
and before it can be rebuilt into the muscle complex, oxidation
of glucose has to take place. The introduction of this acid in a
minute amount has three profound effects. Firstly, it increases
the dissociation of oxyhaemoglobin (p. 253) setting free the needed
quota of oxygen, secondly, by stimulating the respiratory centre
(Chap. XXVI.), it speeds up the intake of o-xygen, and lastly, the
blood flow is increased, both locally by vasodilatation, and generally
by increased cardiac action.

In the work of preserving the neutrality of the organism, the
blood is aided by the eliminating organs, — the lungs and the
kidneys.

Factors tending to preserve neutrality.

I. In the plasma we have (a) colloids, and (b) crystalloids.

(a) The colloids of blood plasma are mainly serum albumin and
serum globulin and they are amphoteric in character, i.e. they may
act either as acids or as bases. Experiments carried out in the
laboratory show definitely that, although the proteins of the
plasma readily combine with mineral acids, they are unable to
react with the weakly dissociated acids found in the body. Both
albumin and globulin form hydrochlorides for instance, but
protein lactates or carbonates are unknown. Apart from the
amount of CO2 adsorbed by the colloidal particles, the blood
colloids can play but a small part in reducing the carbonic acid,
etc., produced in the organism.

(b) Of the crystalloids in solution in the plasma, sodium
bicarbonate has a marked " buffer " effect. In this salt a strong
base is united with a weak acid and, therefore, any acid stronger
than H2CO3 will take the place of the HCO3 ion in its combination
with Na.

For instance,

= Sodium bicarbonate.
= Acetic acid.

CH3COONa H2CO3

(Sodium acetate) (Carbonic acid).

This reaction appears just to postpone matters because carbonic
acid is set free and, although this acid is only slightly dissociated,
yet, as an acid, it must be reckoned with. But the equation

ALKALI RESERVE 333

of the dissociation of NaHCO3 shows that it is a reversible
reaction :

e.g, NaHCO3 •* ™~ +

H20

Na

OH

Strong. Weak.

This means that the direction of the reaction will, in the main,
depend on the relative amount of CO2(H2O) present compared
with the amount of NaHCO3. This ratio has been determined
experimentally. To give the normal pH. of 7-4, plasma must have
3-75 grams of CO2 bound in NaHCO3 present for every gram of
uncombined CO2 : or, by volume, one volume of CO2 remains
constant when associated with 20 volumes combined as carbonate.
In tabular form this reads :

Free CO, 1 1

by weight, — by volume.

Bound C02 3-75 .& ' 20

If excess of NaHCO3 over this ratio is present, some will dissociate
to balance the dissociation pressure. If too much CO2 is present
it will in the first instance combine with any free base to form a
bicarbonate ; if no free base offers, the excess CO2 will be elimi-
nated by the lungs.

The bicarbonate of the plasma represents the excess of base which
is left over after all the non-volatile acids have been neutralised. It
is the alkali reserve of the body which can be drawn upon to
neutralise any free acid stronger than CO2 which may find its
way into the blood stream (Demonstration, Part II.). Not until
practically all the alkali reserve has been used up, will the blood
show any change in hydrogen ion concentration. Long before
that point can be reached, other mechanisms will be brought into
action to preserve neutrality. The bicarbonate is a nest egg of
potential base which may be drawn upon when required, but the
inroad must be made good at the first opportunity. It is really
an emergency measure useful to tide one over the difficulties that
occur suddenly and frequently. It is not a widow's cruse of oil —
always magically replete. If the ratio of H2CO3 to NaHCO3 is
kept within normal limits even though the reserve is permanently
lowered, the acidosis necessitating the draft on the reserve is
called compensated. If on the other hand, the amount of H2CO3
increases to a value greater than 1/20 of the alkali reserve in
arterial blood, the acidosis is said to be uncompensated.

334 PRESERVATION OF NEUTRALITY

II. The lungs eliminate CO2. The amount eliminated per unit
of time is a function of the capacity of the lungs and the rhythm
of respiration. The rate and depth of respiration are controlled
by the amount of CO2 in the blood perfusing the respiratory
centre in the medulla oblongata. Any increase in the CO2 of the
blood causes an increase in the rate of respiration. Similarly, the
process of respiration may be slowed down, till it stops, by de-
creasing the amount of CO2 in the blood. It has been stated that
this regulatory action of the medulla is caused not by CO2 but by
the hydrogen ion concentration of the blood, i.e. any acid perfusate
will quicken respiration. But, as is obvious from the context,
no free acid but CO2 can occur in the blood of a living animal.
Further, careful research has shown that the pH. of blood does
not alter, the regulation is so nice.

III. Excess of base, and acids in combination with bases are
eliminated by the kidney. The cells of this organ have a low
threshold for such salts.

IV. The red corpuscles of the blood play an ill-defined part
in the preservation of neutrality. In common with other tissue
elements, the erthrocytes have a phosphate buffer system. Sodium
dihydrogen phosphate, NaH2PO4, is an acid salt and reacts with
bicarbonate, for instance, to form the basic salt Na2HPO4,

viz. : NaH2PO4 + Na2HCO3-Na2HPO4 + H2O + CO2

acid phosphate. basic phosphate.

A mixture of these two phosphates such as is found in all tissues
obviously will not increase in acidity till nearly all the disodium
phosphate has been converted into dihydrogen phosphate, nor
will the [H]* markedly decrease till all the dihydrogen phosphate
has been converted into the basic salt.

In addition to this it seems as if the pigment, haemoglobin, took
some part in the reaction. Some evidence has been produced
which indicates that Hb adsorbs or combines with CO2 at high
CO2 tensions and parts with it at low tensions, i.e. in the lungs.
Be that as it may, the haemoglobin acts as a buffer to a degree of
which the plasma proteins are incapable, and promotes the dis-
sociation of bicarbonate during diminishing tensions of CO2.
This property is due to the electrical charge of haemoglobin.
In an alkaline medium, haemoglobin carries a positive charge ;
the more alkaline the medium, the more acidic is haemoglobin,
and conversely, when the blood is taking up CO2 from the tissues,
haemoglobin is least acidic.

" BUFFERS " 335

V. The tissues themselves exert a neutralising effect on the
blood. As mentioned above they are endowed with a phosphate
buffer system.

To summarise :

Blood and tissue fluids normally neutral pH. =7-4.

Alterations caused.

1. Tending towards alkalinity — Alkaline tide after digestion.

2. Tending towards acidity.

A. Normal. (1) Muscular activity. CO2.

Lactic acid.

(2) Protein disintegration. food \ H2SO4

muscle J P2O5

B. Abnormal. Mai-oxidation acidosis.
Alterations checked.

1. Tissue compensation — Phosphates.

2. f Alkali reserve — NaHCO3.

R -|TJ .• f CO 2 stimulates respiratory centre.

( Lack of free CO2 depresses centre.

(a) increased elimination of <C ,. ras salts.
4. Kidney -I v ^alkali }

[_ (b) NH3 salts. (Liver action.)

An apology is necessary for the use of the word " buffer "to denote the
power of phosphates and bicarbonates to maintain a steady pR in spite
of additions of acid or alkali. Prof. Bayliss has pointed out the misleading
nature of this expression and has shown how it crept into use. Non-
descriptive as the word undoubtedly is, it has found a place in current
physiological and physico-chemical literature, dislodgment from which
will be a difficult task.

CHAPTER XXXI
THE REGULATION OF TEMPERATURE

" Where hot and cold, and dry and wet
Strive each the other's place to get." PRIOR.

ONE of the most striking phenomena in the life of man and of
the hot-blooded animals generally is the remarkable constancy
of the temperature maintained in spite of the variations of tem-
perature to which they may be subjected. This is a fact which
did not escape the attention of the ancients,* who thought out
many weird and wonderful explanations. Even well on in the
nineteenth century, text-books echoed the idea of Haller (1757)
that animal heat arose mainly from the friction of the blood in
the vessels.

The mammal or the bird may travel from the arctic regions
where the external temperature may be at - 53° C. to the tropics
at 53° C. without much increase in body temperature. Contrast
this freedom from variation with the continuously changing
temperature of the cold-blooded animal as the temperature of its
environment changes.

TABLE LV.

Temp, of Water.

Temp, of Frog's Stomach.

2-8° C.
20-6° C.
41° C.

5-8° C.
20-7° C.
38° C.

Within natural limits, the temperature of the cold-blooded animal
is usually about 1° C. above that of its environment. It is
interesting to note that those animals which hibernate become
for the time as if cold-blooded. The evolutionists postulate that,
as all animals were once marine cold-blooded organisms, the
ancestors of the warm-blooded animals must have crawled out

336

THE THERMOMETER 337

of a tropical sea and ever since have had to maintain this initial
high temperature. The advantages that they possess by reason
of their higher temperature are due (a) to the well-known fact
that most chemical and some physical reactions are increased
in rate by heat, and (b) to their freedom from constant fluctuations
of temperature. Against this must be placed the fact that they
have to maintain a temperature greater than their environment
by about 20° C.

Of all animals, birds have the highest temperature. For
example, that of the chicken is about 43-8° C.: of mammals, the
rabbit and the fox have a temperature as high as 40° C., while
the horse and the elephant come low on the scale with 37-6° C.

In health, the temperature of the human body varies so little
from the normal value of 37° C. (98-4° F.) that temperature is
regularly taken as a clinical indicator and any fluctuation from
the normal points to the employment of remedial measures.

Homoiothermic Animals maintain a constant temperature.
Mammals and Birds - Birds - about 42° C.

Adult and not during hiber- /Mammals (except man) „ 39° C.
nation or activity - - \Man - "„ 37° C.

Heter other mic or Poikilothermic Animals.

(a) Lethal temperature, New born Homoiothermes.

about 20° C.

(b) Hibernation starts when Hibernating animals.

temperature falls to
about 20° C.

(c) Still active below 20° C. Keptiles, Batracia, Fish, Molluscs,

Insects, etc.

Instruments used.

(a) Mercury thermometer.

(b) Electrical resistance thermometers.

(c) Thermo-electric couple (Thermopile).

(a) The thermometer was probably invented by Galileo (1603), and was
first used clinically by Sanctorius (1626), who reported the temperature
of a fevered man.

The clinical thermometer is an adapted form of the common mercurial
thermometer having, (1) a long cylindrical reservoir to admit of rapid
attainment of equilibrium between body and mercury. (2) A small
bulbous part just above the mercury reservoir to catch the mercury driven
out of the reservoir by the expansion due to the increase in temperature
to 34° C. (3) A small bore capillary graduated from 35° C. to 45° C. to
admit of reading to a tenth of a degree, and finally, (4) another bulbous
part to catch any mercury that might be driven over by accidental heating
beyond 46° C. Usually the thermometer is made self-registering by having
a small detached thread of mercury which is pushed up by the expanding
fluid and remains at the highest temperature reached.

B.B. 22

338 REGULATION OF TEMPERATURE

Where a continuous record has to be made, or where great accuracy is
desired, one of the electrical methods is employed.

(6) This method depends on the alteration of the electrical resistance
of a platinum (or other metal) wire caused by a slight increase in its tem-
perature. The alteration in conductivity may be measured by a Wheat-
stone's bridge or may be recorded photographically as in the study of the
electrical changes in tissues (p. 297). This is by far the more sensitive
of the two electrical methods, but great care must be exercised in its use.
It has, however, some disadvantages. For example, the current flowing
through the thermometer tends to heat the fine coil of wire. The heating
is proportional to the square of the current, and to the resistance of the
wire.

(c) The thermopile is based on the principle that, if the junction of two
dissimilar metals (e.g. constantan and iron) be warmed, a difference of
potential between the two will be produced. In order that small fluctua-
tions of temperature may be measured, a second thermopile is arranged
in the circuit in series with but opposed to the first. This second thermo-
electric junction is kept at a certain known temperature differing but
little from the temperature to be measured. By this means the bulk of
the electromotive force resulting from thermopile 1 will, be neutralised by
the E.M.F. produced by thermopile 2, and thus the E.M.F. produced by a
small change of temperature becomes a relatively large proportion of the
net E.M.F. The current changes are read from a potentiometer.

Location of Thermometer.

(a) Natural Cavities.

(i) Mouth. The cavity underneath the tongue is generally chosen by
the physician as suitable for the taking of temperature. The thermometer
should remain at least 7 mins. in situ. If the mouth is kept open, low
readings will be obtained due to the inrush of cold air and the vaporisation
of moisture.

(ii) Rectum. Practically all physiologists are agreed that the most
favourable position for the thermometer for the indication of the true
temperature of the interior of the body is the rectum (or vagina in females).
The instrument should be inserted sufficiently deeply (7 cm.), to make
sure of the maximum temperature, and, in the case of the rectum, it
should not be imbedded in faecal matter.

(b) Artificial Cavities.

(iii) Axilla. In the private practice of a physician, temperatures are
generally taken from the armpit. Care has to be taken to free the skin from
moisture and sweat and to close the cavity on the thermometer for a time
sufficiently long to enable the surface of the skin to attain the temperature
of the interior of the body.

(iv) Groin. In young children the thermometer is usually placed in
the fold of the groin.

While the temperature of the body is so constant that it is
taken as a clinical sign, yet it does vary regularly during the
24 hour day. From the chart (Fig. 72), it will be seen that
between 3 and 4 in the morning body temperature is at its lowest

VARIATIONS OF TEMPERATURE

339

and between 3 and 4 in the afternoon it is at its highest. This
rhythm or periodicity is shown by night workers as well as by
those who live a normal average life. Benedict tells of a night

FIG. 72. — Chart of the Daily Variation of Temperature in the Normal Human Subject,
in degrees Centigrade. The hours are marked" from midnight. (Richet.)

watchman who for seven years had been working during the night
and sleeping during the day, and had his maximum temperature
about 4 o'clock in the afternoon when sound asleep and his
minimum about 4 o'clock in the morning when he was awake and
active.

It is common knowledge that certain means may be taken to bring
about alterations in the body temperature :

1. Muscular exercise causes heat.

2. Want of muscular exercise is followed by cooling, e.g. cold has to be
guarded against during sleep.

3. Heat or work causes sweating.

4. Heat produces lassitude. Compare the day's work of a man in
Spain with that of a man in Scotland.

5. Still air has the same effect as that of heat on the feeling of lassitude.
The production of a movement of the air removes the tired feeling.

6. A higher temperature can be endured in a Turkish than in a plunge
bath. Further, a hot dry climate is comfortably endured, while air at
the same temperature, but saturated with moisture, oppresses.

7. Cold air does not chill one to the same extent as water at the same
temperature. Cold much more severe than is experienced in Britain may
be enjoyed in the dry, Canadian climate.

For example, a temperature of - 40° may be borne if the air be dry and
still, while a much warmer but damp and windy atmosphere may " cut
to the bone."

8. Ingestion of hot or cold food or of heat-producing food normally
produces an almost negligible increase in rectal temperature.

340

REGULATION OF TEMPERATURE

What we want to get at is the mechanism whereby the body
temperature of the higher mammal is kept fairly constant despite
variations of outside and " inside " temperature. In this re-
spect, they obey the ordinary laws of cooling — surface phenomena.
Heat may be lost by :

I. Conduction and convection.

la. Ingestion and excretion. Inspiration and expiration.
II. Radiation.
III. Evaporation of moisture.

I. Conduction.

By conduction is meant the loss of heat from a body at a higher
temperature to one at a lower temperature by passage from
particle to particle, for example, the passing of heat along a poker,
one end of which is in the fire. The amount of heat lost by the
body in this way depends on several factors.

(i) Surface exposed, (a) The loss of heat varies directly with
the area of the surface exposed. For example, the flow across
two square metres is double that across one square metre. The
area of surface of a child of 2 years weighing 10 kg. is 5120 sq. cm.,
and of a man of 60 kg. is 14,079 sq. cm. That is, the area per
kg. for a child of 2 years is 512 sq. cm., and for a man is 234 sq. cm.
It is obvious that weight for weight the child will lose more heat
than the man.

(b) The loss of heat depends on the moistness of the surface.
The thermal conductivity of all liquids except mercury is very
low. Water may be boiled in the top portion of a test tube without
affecting a piece of ice at the bottom.

TABLE LVI.

THERMAL CONDUCTIVITY.

Substance.

Conductivity (c).

Substance.

Conductivity (c).

Silver

1-52

Cotton flock -

4 x 10~5

Platinum -

1-HxlO-1

Water at 37° C.

135 x 10-5

Marble

180 x 10-5

Sea water

108 x 10-5

Wood

10 x 10-5

Olive oil -

39 x 10-5

Paper
Vulcanised rubber

30 x 10~5
8-9 x 10~5

Human skin -
Lard

60 x 10-5
48 x 10~5

Wool

5 x 10-5

Leather -

42 x 10-5

Compressed cotton

3 x 10~5

Air (dry)

5 x 10-5

(c) The loss of heat depends on the nature of the surface and
of the subcutaneous tissue. A good layer of subcutaneous fat

CONDUCTION OF HEAT 341

which has a low thermal conductivity will decrease the rate at
which heat arrives at the surface and retard heat loss.

Every one knows that certain substances do not readily conduct heat.
In the hot room of a Turkish bath, where all the objects are at the same
temperature, metallic objects feel much hotter than those of wood, bone,
rubber, etc. A familiar example of the retention of heat by a body sur-
rounded by some bad conductor is found in the hay box or Norwegian
cooker, which consists of a wooden box having a thick lining of felt. The
partially cooked meal while still hot is placed in the box and the inter-
vening space firmly packed with hay or paper. The felt-lined lid is closed
and the meal left to cook itself. After several hours the temperature will
have fallen only a few degrees. The Dewar or thermos flask depends on
a vacuum as non-conductor.

Animals which have a good layer of subcutaneous fat lose
heat much more slowly than lean ones.

Fat acts as a heat insulator and retards loss by conduction.
On a moderately warm day, the obese person becomes uncomfort-
ably warm. He is unable to eliminate heat with sufficient
rapidity, and, as a consequence, his temperature rises, and may
cause an increase in general metabolism amounting to 50 per cent,
over that of a thin person. Aquatic mammals rely on their
adipose tissue to protect them from a too rapid loss of
heat.

Several measurements of the temperature inside the body have
been made. The natural cavities, e.g. the rectum, and vagina,
are generally used, both being deep cavities into which the ther-
mometer or thermal elements can be inserted for a considerable
distance. Measurements have been made of the temperature in
the inside of the stomach in patients with gastric fistulae. The
temperature of freshly voided urine was suggested by Stephen
Hales in 1731 as representing that of the interior of the body.
It has been found that, while the temperature of the surface of
the body is about 32° C., as the depth from the surface increases,
the temperature rapidly rises till the depth of about 5 cm. is
reached. It continues to rise much more slowly for the next two
cm. or so. Apparently the temperature after this is fairly uniform,
i.e. 37° C. That is, the subcutaneous tissues cause a temperature
lag or thermal gradient of about 5° C. This is due to the large
proportion of water which enters into the composition of the
tissues, giving the body the high specific heat of about 0-83.
A man weighing 60 kg. would consequently have a water equiva-
lent of 50-4 kg. of water, so that a rise of 0-1° C. would only be
registered after 5-04 cals. of heat had been rendered latent.

342 REGULATION OF TEMPERATURE

(d) The loss of heat varies directly with the time of exposure
of the surface. In actual practice, this can be determined for non-
living systems only, because, as we shall see, in the living body
secondary reactions take place ; alterations in the state of the
surface and also of the deep-lying tissues are produced, rendering
difficult the application of this law to living beings. If the
student uses his common sense, however, he will readily see that,
if all conditions are kept constant except time, the amount of
heat lost by conduction must vary directly with the time of
exposure.

(ii) Temperature gradient. Newton's law states that the amount
of heat lost by a body in unit time is proportional to the difference
in its temperature from that of the surrounding medium. The
warm body loses heat and becomes colder, while the environment
becomes warmer. This loss and gain goes on till the body and
its environment are at the same temperature. Inspired air or
cold food is warmed to body temperature at the expense of body
heat. The drinking of cold water may cause a temporary
reduction of rectal temperature. Conversely, hot food and drink
tend to increase the temperature of the body.

The heat lost by excretion depends not so much on this factor
as on the amount and nature of the excreta. Compared with
the total heat lost, the amount lost by the heating of inspired air,
cold ingesta, and by the excreta is trivial.

(iii) Force of wind. In still air, the loss by conduction is very
slight. Air is not a very good thermal conductor. A layer of
warmed air soon forms an envelope round the cooling body and
prevents rapid conduction. A very slight movement of the air
may produce a very appreciable effect by driving off the warm
particles and bringing cool ones into contact with the body.
This may arise naturally by the formation of convection currents.
The heated air expands and becomes lighter and so rises and
allows the colder air to flow in.

An air current may be felt when it moves at the rate of about
0-4 to 0-5 metre per second. A non-perceptible draught with a
velocity of 0-2 metre per second playing on the naked arm may
increase the heat loss over that experienced in still air by 19 to
75 per cent, depending on the temperature of the air. A moderate
breeze at 8 metres per second (15 miles per hour) with a tempera-
ture of 20° C. causes more rapid chilling of a naked man than
exposure to still air at 2° C. (see also p. 346).

(iv) Humidity of atmosphere. Water is a better conductor

RADIATION OF HEAT 343

of heat than air. A moment's consideration of the feeling of cold
before entering cold water and during the process will convince
one of this. We have already mentioned the difference in the
cold sensation caused by a dry cold wind compared with that pro-
duced by a wind of even a much higher temperature but laden
with moisture.

II. Radiation.

The transmission of heat by radiation differs essentially from
conduction and convection. The particles of a body have a
vibratory movement depending on their kinetic energy. Increase
of temperature will therefore cause increase in the velocity of
these movements. In conduction some portion of another body
is heated by contact with the warm body. This second body
passes the heat on. There is molecular continuity. By radiation,
on the other hand, one body can affect the thermal state of another
body not in contact with it without sensibly affecting that of the
intervening medium. Radiation is not dependent upon the
presence of air. It takes place quite readily in a vacuum. This
is manifest when we consider how we derive heat from the sun
whose radiant heat is transmitted through the ether at a very
high velocity (about 186,000 miles per second) by means of
transverse wave motion.

Radiant heat may be detected and measured by means of a
suitable thermopile provided with a collecting horn or by means
of Leslie's differential air thermometer. The amount of heat lost
by radiation depends on :

(i) The area and colour of the surface. It has been proved
experimentally as well as deduced mathematically that the
emissive and absorptive powers of a body are equal. A perfectly
black body absorbs all the heat energy that falls on it, and therefore,
since a body cannot absorb more than is incident on it, the
absorptive power of such a body is unity. The emissive power
of a body is the ratio of the quantity of heat radiated per sq. cm.
of surface to the quantity radiated per cm2, of a "perfectly "
black body under the same conditions. (Expt. 53, p. 424.)

TABLE LVII.

RADIATING AND ABSORBING POWERS OF BODIES.

Lamp black - - 1-0

Cinnabar - 0-28

White paper - - 0-9

White lead - - 0-21

Polished silver ------ Q-03

344 REGULATION OF TEMPERATURE

(ii) There is a connection between the amount of radiation
from, and the temperature of, a body. The total heat-loss by
radiation is proportional to the difference between the fourth
powers of the absolute temperatures of the body and its environ-
ment as well as to the area and nature of the surface. If body
and environment differ little in temperature, the heat lost by
radiation will thus be comparatively small. For example, if the
temperature of the air were 17° C., the heat radiated from a
" perfectly " black man at 37° C. would be (273 +37)4-(273 +17)4
=3104-2904=216 xlO6 per unit surface.

Of course a perfectly black man does not exist nor yet a perfectly
white man. If black skin has a radiation-coefficient of 0-98 and
white skin of 0-7, then the difference in radiating power would be

expressed by =1-4, a trivial advantage to black-skinned

animals. This has been confirmed experimentally by Leslie, who
used a differential air thermometer as a very delicate method for
the detection of very small differences in temperature.

III. Evaporation of Moisture.

As the temperature of the air and of the body approach the same
value, the heat lost by the body by radiation and conduction will
be exactly balanced by the heat absorbed from the environment
by the body. If the atmosphere attain a higher temperature
than the body, then these means of heat elimination will become
inadequate, and the body temperature should increase synchron-
ously with that of its surroundings. That this is normally not
so is common knowledge. Many interesting instances have been
known of persons submitted to high temperatures, and an examina-
tion of some of these cases may lead us to a knowledge of the

TABLE LVIII.

TIME TO KILL SPORES or HAY BACILLI AT VARIOUS
TEMPERATURES.

Temperature.

Time.

100° C.

over 16 hours

105-110°

2-4 hours

115°

30-60 minutes

125-130°

5-6 minutes

135°

1-5 minutes

140°

about 1 minute

LATENT HEAT OF EVAPORATION 345

mechanism called into play to prevent untoward results. On one
point preliminary emphasis must be laid, viz. the times during
which these extreme temperatures were endured were of very
short duration. That the time factor is of immense importance
may be adduced from the preceding experiment (Table LVIII.)
by Christen.

In warm-blooded animals, 45° C. is generally considered a
lethal temperature, but death may occur at a lower temperature
(42°), provided the time of exposure is sufficiently prolonged.

Bakers' assistants are known regularly to have entered ovens heated
to over 126° C. When the temperature approached 160°, they experienced
extreme superficial vasodilatation. Young girl labourers are said to ex-
perience no inconvenience from a stay of 5-10 minutes in a kiln heated to
about 130° C. Chaubert, the " Fire King," is reported as having with-
stood a temperature of between 226° and 315-5° C. Yet immersion in a
bath of water at 45° C. is unbearable. It is a matter of common knowledge
that those who habitually work in abnormally overheated places consume
large quantities of fluid, and sweat profusely. The latent heat of water
is the greatest of all substances known. Every gram of water which is
vaporised entails the use of 536 calories. This is in accordance with the
principle of energetics laid down by Le Chatelier (p. 9). In general, if
any change is brought about by the incidence of energy, then alteration
will take place in the substance acted on to nullify these changes, i.e. a
reaction of opposite direction occurs.

Substances which expand on heating will be cooled by mechanical
expansion. Water increases its volume in passing from the liquid to the
gaseous state, and therefore, as the result of such an expansion, the parent
fluid is cooled. The evaporation of moisture from the surface thus causes
cooling of the body (see also clothes, p. 351).

The quantity of heat lost by the evaporation of moisture (a) in
the bronchial passages, etc., (b) in the form of sensible and in-
sensible perspiration, depends mainly on five factors, viz. :

1. Area of moist surface exposed.

2. Colour . „ „

3. Gradient of temperature between body and environment.

4. Force of wind (partial pressure equilibrium).

5. Humidity of the air.

(1) The effective area of surface exposed to cooling depends
in great measure on the state of the superficial blood vessels.
Dilatation of these enormously increases the area.

(2) The effect of colour is merely a matter of the differential
absorption of radiant energy producing local heating in proportion
to the amount of energy absorbed and so causing a more or less
rapid evaporation. The black moist muzzle of the bull-dog is
much cooler than its white, comparatively dry skin.

346 REGULATION OF TEMPERATURE

(3) The gradient of temperature has much to do with the
amount of heat lost by evaporation. This is an indirect effect.
It has been suggested that the pigmented skin of tropical races,
by absorbing radiant energy and so becoming unduly warm, stimu-
lates epidermal nerve-endings and produces vasodilatation and
profuse sweating. The evaporation of this water then cools the
body in a similar way to the Indian chatti or water cooler. Accord-
ing to G. F. Hearne, exhaustion of the sweat mechanism always
preceded heat-stroke in Mesopotamia.

(4) The presence of a current of dry air removes the gaseous
water from the surface, and so brings dry air in contact with the
body. In other words, the partial pressure of the gaseous water
in the layer next to the body is kept at a minimum. This drying
effect of wind is operative irrespective of the temperature of the
wind, as witness the drying of shallow pools of water and of wet
clothes by cold and by warm breezes.

(5) Humidity of Air. The presence of moisture in the air affects
its cooling powers in two ways, (a) Obviously, if the air is
already saturated with moisture it is unable to absorb more, and
evaporation from the body even when played upon by a draught
will be at a minimum. (/3) On the other hand, as we have already
mentioned, moist air is a much better conductor of heat than dry
air, and therefore, the heat lost by conduction tends towards a
maximum in a humid atmosphere. The former of these factors
plays a major part when the surroundings are warm, the latter
operates maximally in cold climates.

In the assessment of the conditions of the atmosphere making for ideal
heat-loss, two instruments are in common use, viz., the wet and dry
bulb thermometer and Hill's " Kata " thermometer (or its popular modifi-
cation— the Comfimeter). The first of these instruments consists of two
similar mercury thermometers fastened side by side on a stand. The
reservoir of one is covered by a close fitting muslin bag which is kept
moist by connection to a wick dipping in water. The water evaporates
from the bulb at a rate depending principally on the degree of saturation
of the atmosphere with aqueous vapour. It is obvious that, if the air is
already saturated with moisture and no evaporation is taking place from
the wet bulb, both thermometers will register the same temperature. On
the other hand, if the difference in the temperatures recorded is great, one
may consider that the air is dry.

Example. The degree of humidity of the air may be calculated from the
formulae,

degree of humidity = i- and /= F - AH (t - 6),

KATA-THERMOMETER 347

where A = the constant of the instrument,

F = ihe tension corresponding to 6°, the reading on the wet
bulb thermometer,

H — atmospheric pressure,

t = reading on dry bulb thermometer,
and m = maximal vapour tension at t° C.

If ^=0-00082, « = 20°C., 0 = 16° C., H = 758 mm. Hg.,

F (from a table of vapour tensions) = 13-63 mm. Hg.
Then /= 13-63- 0-00082 x 758 x 4 -11 -16 mm. Hg.
The maximal vapour tension at 20° C. (from a table) = 17-52 mm. Hg.

Therefore, the degree of humidity= - = ^^-=0-637.

*¥Yl 1 / *OZi

The " Kata " thermometer is a large bulbed spirit thermometer. It may
be warmed to say 38° C. The time is then taken while it cools to 35° C.
It may be surrounded by wet muslin and the experiment repeated. The
dry bulb instrument gives an indication of the possibilities of heat-loss
by radiation and conduction, while the wet bulb indicates, in addition,
the possibility of heat-loss by evaporation of moisture.

The Comfimeter is a form of kata-thermometer designed to give an
immediate indication of the cooling property of the air in rooms. It
consists of a cylindrical metal box in which is inserted an electric incan-
descent lamp.

On the top of the box is fixed an inverted metal funnel having a long
stem. An ordinary thermometer is hung from inside the upper part of
this stem so that about 2/3 of its length remains outside the instrument.
When the lamp is lit, air enters the comfimeter by means of holes in the
cylindrical box and the heated air rises and leaves by the orifice in which
the thermometer is hung. The whole apparatus is cooled by radiation,
convection and by conduction. When the comfimeter gives a reading of
30° C., this indicates a cooling power of about 7 millicalories per square
centimetre of effective cooling surface per second — an ideal condition.
If, now, the box be screened from draughts, the comfimeter thermometer
will rise to 45° or maybe 50° C. On permitting free ventilation, the instru-
ment will again record a temperature of about 30° C. A lower temperature
than this is a sign of too rapid cooling. The designer, Prof. L. Hill, says
that as long as schools, factories, etc., are kept with the comfimeter indi-
cating somewhere about 30° C., conditions suitable for work will be main-
tained.

Work of itself, as is well known, causes production of heat in
the body. Some 75 per cent, of the energy generated in muscular
contraction is dissipated as heat. In spite of the large quantity
of heat thus liberated, the body temperature does not increase to
any great extent. It may rise by about 2° C., depending on the
cooling value of the environment as well as on the severity of the
work. The following figures from Pembrey (Table LIX.) illus-

348

REGULATION OF TEMPERATURE

trate the influence of the rate of cooling on the body temperature
after severe work :

TABLE LIX.

SOLDIERS ON COMPLETING A MARCH OF SEVEN MILES.

External Temp.

Increase of pulse rate.

Increase of temp.

Dry bulb.

Wet bulb.

79

45

67 -5° F.

38° F.

62
14

1-4°F.

0-8° F.

On the cold day with a percentage difference of about 15
between dry and wet bulb temperatures, i.e. under good cooling
conditions, the temperature and heart rate of the soldiers showed
only a slight increase, while on the hot day with almost the same
humidity, the men became uncomfortably hot, and the heart rate
was increased. Under these conditions work is inefficiently done.

The effect of the temperature and the humidity of the external
air on the loss of heat from the body is very well marked in those
people endowed with a good layer of adipose tissue. As has
already been mentioned, this dense non-conducting material is a
very effective heat insulator, thus preventing rapid heat loss.
In hot weather and during exercise, fat subjects become unduly
heated. If, in addition, they have poorly functioning sweat
glands, then severe or prolonged work becomes impossible.

The following table gives a rough indication of the amount of
heat lost per day through the various channels :

TABLE LX.

Per cent.

Calories per day.

1. Eadiation and conduction

73

1792

2. Evaporation (a) lungs, etc.

7-2

182

(6) skin

14-5

364

3. Excreta (a) C02

3-5

84

(6) urine and faeces -

1-8

48

Total heat loss per day

-

2470

The question now under consideration is, provided some 2500
calories of heat are lost per day, (a) how is excessive heat loss
prevented and (b) how is the amount lost made good ?

PREVENTION OF HEAT LOSS 349

A. Physical Regulation — Preventative. (Usually effective be-

tween 40° and 20° C.)

This is obtained by decreasing the effective cooling surface, a
result which may be produced in three ways :

1. By wearing clothes (or fur), a layer of still air is established
between the body and the outer air. Heat will then be lost from
the covered area by radiation only (see clothes).

2. A good layer of subcutaneous fat prevents a rapid diffusion
of heat from the interior to the exterior of the body.

3. Constriction of the cutaneous blood vessels, a reflex act,
results (a) in a decrease in the amount of blood carried to the
surface, i.e. decrease in cooling surface and (b) in a decreased
output from the sweat glands.

Paralysis of the vasomotor nerves leads to vasodilatation.
This is given as the reason for the death of animals whose skins
have been covered with a layer of impenetrable varnish. It is
alleged that, at the enthronement of Pope Leo X., a boy was
gilded to represent an angel. Before the ceremony was finished
the boy, despite the efforts of Leonardo da Vinci and other
physicians, had died. That excessive heat loss was the cause of
this accident is proved by the experiments of Valentin. He
showed that, under similar circumstances, the carbon-dioxide
output of the subject was reduced to about 1/6 of the normal,
i.e. metabolism was at a low ebb. If the animal were kept
normally warm, the carbon-dioxide output returned to a normal
figure. On the other hand, Senator states that the human body
can be covered for 8-10 days with an impenetrable layer without
producing any disturbance of metabolism. He avers that, in
those cases where vasodilatation occurred, some toxic substance
must be i absorbed from the varnish.

m

Alcohol produces vasodilatation — an increased cooling surface. That
is, this drug, because it causes more warm blood to come to the surface,
gives rise to a sensation of cutaneous warmth while at the same time
materially aiding in the depletion of the body's store of heat.

B. Chemical Regulation — Curative. (Usually predominant below

20° C.)

These mechanisms come into play to replace heat which has
been lost.

(a) Voluntary or involuntary work. We have already seen
that work causes the liberation of heat and we have discussed
the reason for this. Shivering, or involuntary work is a reflex
act which occurs in any person of normal muscular tone when the

350 REGULATION OF TEMPERATURE

skin temperature is allowed to drop below a certain value. Any-
thing which will prevent muscle from responding to this stimulus
will do away with this curative heat production, e.g. curari,
alcohol, etc. Young animals which have little muscular develop-
ment are, obviously, unable to keep themselves warm by exercise
and have to be carefully protected against undue heat loss.

(6) Increased muscular work ultimately leads to increased
catabolism of food material and so, indirectly, to an increase in the
quantity of heat liberated. Over and above this amount, however,
the result of exposure to excessive cold may be combated by the
ingestion of foods having a high energy value. Natives of the
colder climates introduce much fatty matter into their diets.

One may just glance at a problem connected with the above.
If the action of any tissue-complex, muscle, liver, etc., results in
the liberation of " waste " heat, is heat then liberated during
cerebral activity ? At present, careful investigation has failed to
show the production of heat by the brain. It is admittedly true
that the head becomes heated during prolonged mental work, but
this is accounted for by the increased cranial blood supply — blood
flowing away from the extremities and from the viscera to the brain.

Centre. Since the means adopted for the maintenance of an
unfluctuating temperature involve the bringing into play of so
many structures and of such a variety of nerves, — vasomotor,
muscular, secretory and so on, — it is plain that a co-ordinating
centre is a necessity. Experimental evidence leads one to the
conclusion that such a centre exists in the corpus slriatum. Vaso-
constriction, shivering, and a rise in rectal temperature result
from the stimulation of this structure with a cold object. On
the other hand, the application of a warm stimulating point leads
to vasodilatation, muscular relaxation, and a fall in body tem-
perature. Such results are generally interpreted as indications
of the sensitiveness of the corpus striatum to alterations of the
temperature of the blood flowing through its capillary system.

Clothes. The question of the maintenance of the human body
in comfort is so closely associated with the nature of clothing that
a few physical facts bearing on the nature and value of artificial
protective and decorative coverings are not out of place here.
Liebig made clear one aspect of the function of clothing, saying,
" Our clothing is, in reference to the temperature of the body,
merely an equivalent for a certain amount of food." In other
words, if we were to do without the protection afforded by clothing
we would have to make good the heat thus lost by eating more food.

CLOTHES

351

The protective value of clothing mainly depends (1) inversely
on the thermal conductivity of the material, (2) on its power of
absorbing water, and (3) on the arrangement of the fibres of the
material in the cloth. The conductivity of various materials is
given in Tables LVI. and LXI.

TABLE LXI. (FROM RUBNER).

Substance.

Coefficient of Conductivity.

Air -

53 x 10-6

Brown human hair -

76 x 10-6

Grey human hair

74 x 10~6

Feathers (eiderdown)

57 x 10-6

Horse hair

57 x 10-6

Cotton cloth (smooth)

81 x 10-6

Woollens -

68 x 10-6

Silk

68 x 10-6

Cashmere wool-

68 x ICH5

Cambric -

81 x 10-6

Flannel -

72 x 10~6

Flannelette

75 x 10-6

In order to calculate the coefficient of protection of clothing
one must know the thickness of the material. Table LXII.
compiled by Rubner gives further information regarding the
density of the material and of the amount of air enmeshed in the
structure. This layer of imprisoned air, as we have already
mentioned, has a greater protective value than mere thickness of
material.

TABLE LXII.

Substance.

Thickness in mm.

Mean Density.

Percentage
volume of
air
euineshed.

Total.

Of the Skin.

Black cat fur -

12-6

0-6

0-0429

96-7

Black lamb's wool -

13-0

0-3

0-0484

96-4

(Astrakan)
Rabbit skin -

13-0

0-5

0-0304

97-7

Musk rat skin

14-0

0-6

0-0576

95-6

Otter skin

17-0

0-9

0-0638

"95-1

White bear skin

21-5

0-9

0-0582

95-5

Beaver skin -

22-0

0-8

0-0514

96-1

Skunk -

26-0

0-5

0-0410

96-8

Sheepskin
Cashmere wool

40-0
0-37

0-7

0-0461
0-364

96-4
72-0

Cambric

0-29

—

0-179

86-7

Silk

0-25

—

0-329

74-7

352 REGULATION OF TEMPERATURE

A man entirely clothed in a garment of a total surface (s) of
19 xlO3 sq. cm., of a thickness (t) of 75 xlO~2 cm. and having a
difference of temperature (d) on the two sides of 10° C., loses
heat (Q) as shown by the following formula :

c x s x d .
Q = calories per minute,

v

where c = coefficient of conductivity,

c xs xd x3600 x24
i.e. Q= "7x1000 calories per day.

If the garment were of wool, c = 68 x 10 ~6, we have
68 x!9 x36 x24 xlO"6 xlO3 xlO2 xlO

75 xlO~2 xlO3
= 1888-3 calories per day.

The coefficient of utility of clothing materials may be determined
by covering with them a number of similar copper spheres filled
with warm water and finding how long they take to cool through
10° C. If the time taken to cool 10° C. by an unclothed sphere
with an external temperature of 12° C. be taken as 0, and the
time necessary for the same sphere (clothed) to cool to the same
extent be t, then t/0 = U (Coefficient of utility).

TABLE LXIII. (FROM BERGONI£).

Clothing.

Values of U.

Cycling vest (tight fitting)
Woollen shirt -

1-1

1-5

Black leather waistcoat -

1-6

Flannel shirt -

1-75

Rough tweed coat -
Weatherproof cloak -
Woollen undervest -

1-9
2-1
2-5

Heavy greatcoat

4-5

The efficiency of clothing depends in great measure on the
arrangement of the fibres of the cloth so as to enmesh air and thus
form a stationary layer between the body surface and the outer
air. The following table (Table LXIV.) from Lefevre gives an
idea of the protective value of clothing. His subjects were placed
in a rectangular box through which a measured amount of air was
passed. The temperature of the air just before it reached the
body and immediately after leaving the body was taken. If M,

COEFFICIENCY OF UTILITY OF CLOTHING 353

the mass of air passing in t mins., is heated by 6°, then the heat

0-237 x0xM . w .

lost per minute --=— calories, where 0-237 is the specific

t

heat of air.

TABLE LXIV.

Rate of
wind.
Metres per
sec.

Tempera-
ture of air
entering.

Loss per hour in calories.

Ratios.

Naked.

Clothed.

Fast/slow.

Naked/clothed.

1-2
3-8
1-5
3-8
4-0

9°C.
9° C.
5°C.
5°C.
4°C

134
201
185
277-5
313

98

130
143

172
170

201
134 =1<5

130 1-32

134
-98 =1'36

201 1-45

98
277-5

130 ~
lb5 1-3

185 "

148 -
277-5

™ =1-2
143

172 -

1 -«

It will be noticed that heat production increases with the
lowering of the temperature of the wind and also with increasing
the speed of the wind. It is obvious that, under similar conditions,
the heat lost (and the heat produced) by the clothed is less than
that of the naked subject.

The colour of clothes has also something to do with their pro-
tective action. Quite apart from psychological effects, certain
colours conduce to warmth and others to coolness. This is a
problem that exercised the minds of those responsible for the health
of white troops in tropical countries. The final result of one
series of investigations was to recommend the wearing of white
clothes with a black lining. The student may find it an interesting
exercise to furnish a reason for this.

23

CHAPTER XXXII
TROPISMS— THE SLAVES OF THE LAMP

" Behold the child, by Nature's kindly law,
Pleased with a rattle, tickled with a straw :
Some livelier plaything gives his youth delight,
A little louder but as empty quite ;
Scarfs, garters, gold, amuse his riper stage,
And beads and prayer-books are the toys of age,
Pleas'd with this bauble still, as that before,
Till tir'd he sleeps, and life's poor play is o'er." POPE.

IT may be laid down as axiomatic that once an object has come
into equilibrium with its environment, it will remain so until some
change in the environment disturbs the harmony. In other
words, matter has inertia — moves when it is moved, stops when
it is stopped, and alters only in so far as it is altered. All in-
organic substances are not in equilibrium with their environment.
Radioactive minerals, as we have seen, are characterised by
undergoing considerable change — seemingly independent of the
nature of their surroundings. It is a moot point whether living
things may be brought under this general statement. That they
have inertia both in the ordinary physical sense and functionally
is undoubted. Moreover, that alterations in the distribution of
energy in the environment do lead to apparently corresponding
alterations in the organism will be granted by most workers in
this field, but all are not agreed as to how far the interpretation
can be applied to animals high in the scale.

I. One of the best investigated phenomena in this line of study
is that of heliotropism or phototaxis. It is well known that
radiant energy is capable of influencing the rate of some chemical
reactions — in proportion to the intensity of the light. This is
known as the Bunsen-Roscoe Law, which may be formulated as :

it = constant,

where i is the intensity of the light and t the time of exposure.

354

HELIOTROPISM 355

(1) Certain animals and free-swimming plant-organisms move
towards or away from the source of light. These are said to be
positively or negatively heliotropic respectively. Caterpillars of
Porthesia chrysorrhoea are of the former class. They move towards
the light and may starve, with abundance of food just behind
them.

(2) If positively and negatively heliotropic animals are placed
in a trough covered half with red and half with blue glass, those
that are positively heliotropic collect at the blue end and the
others at the red end of the trough. Red glass is practically
opaque, as every photographer knows, to the photo-chemical rays
of light. The most efficient rays for heliotropic reactions are
(a) the blue between 460 and 490//M and (b) the yellow-green
between 520 and 530/m/u.. Now, most blue glass permits not only
the passage of the blue rays but of the yellow-green rays also
(cf. Fig. 1).

(3) That the heliotropic animal is oriented in relation to the
source of light is shown by a simple experiment due to Loeb.
Direct sunlight is allowed to fall from the upper half of a window
on to a table and diffused daylight from the lower half on to the
same table on which is placed a test-tube in such a way that it
lies at right angles to the window and is illuminated over one-half
of its length (room half) by direct sunlight and over the remainder
by diffused daylight. Positively heliotropic animals are intro-
duced into the sunny end of the tube. They promptly and invari-
ably move towards the window, i.e. out of the sunlight into the
shade towards the source of light.

(4) To explain these facts (and others) Loeb has put forward
an interesting theory. " Animals possess photosensitive elements
on the surface of their bodies, in the eyes or occasionally also in
the epithelial cells of their skin. These photosensitive elements
are arranged symmetrically in the body and through nerves are
connected with symmetrical groups of muscles. The light causes
photochemical changes in the eyes (or photosensitive elements of
the skin). The mass of photochemical reaction products " so
formed " influences the central nervous system and through this the
tension or energy production of the muscles. If the rate of photo-
chemical reaction is equal in both eyes, this effect on the sym-
metrical muscles is equal and the muscles on both sides of the
body work with equal energy ; as a consequence the animal will
not be deviated from the direction in which it is moving. This
happens when the axis or plane of symmetry of the animal goes

356

TROPISMS— THE SLAVES OF THE LAMP

through the source of light, provided only one source of light be
present. If, however, the light falls sideways on the animal the
rate of photochemical reaction will be unequal in both eyes and
the rate at which the symmetrical muscles on both sides of the
body work will no longer be equal ; as a consequence, the direction
in which the animal moves will change. This change will take
place in one of two ways, according as the animal is either posi-
tively or negatively heliotropic."

(5) If this is true, it follows that the animal will obey the Bunsen-
Roscoe Law. This is rather troublesome to prove for free-moving
animals. The following table shows the applicability of the law
to regenerating polyps of Eudendrium. The intensity of the light
was altered by varying the distance between the source of light
and the polyps.

TABLE LXV.

Distance between Polyps
and source of light
(metres).

Time in minutes required to cause 50 per cent, of Polyps to
bend towards the source of light.

Observed.

Calculated.

0-25
0-50
1-00
1-50

10
35-40
150
360-420

40
160
360

The calculated values'of t tend to be somewhat larger than the
observed results. Schwarzschild observed that when develop-
ment followed exposure to light the formula should be modified to

itp = constant.

For silver bromide gelatine plates, the value of the exponent p
varies between 0-8 and 1 according to the brand of the plate.

Talbot's Law is the Bunsen-Roscoe Law modified to make it
applicable to intermittent light. Intermittent light is as effective
as constant light of the same intensity provided that the total
duration of the intermittent light is equal to that of the constant
light.

(6) What is going to be the result when the organism is sub-
jected to two sources of light ? One might predict that, if Loeb's
hypothesis is correct, the organism will be oriented so that it comes
to rest in a position where it is symmetrically stimulated, (a) If
the two sources of light are of equal intensity and duration and

BUNSEN-ROSCOE LAW

357

are set at an equal distance from the organism it should be oriented
with its plane of symmetry at right angles to the line joining the
sources of light, (b) If the lights are of unequal intensity, the
animal should move so that its photosensitive elements are in a
position to absorb equal amounts of light energy. Further, the
absolute intensities of light should have no effect on the deviation
of the path of the organism from the perpendicular path outlined
at first. The relative intensities should be the governing factor.
These three predictions have been amply proved experimentally.
The following results (Table LXVI.) from Patten's investigations
illustrate the nature of the findings.

TABLE LXVI.

No. of lamps
used.

Difference of intensity between the two lights in
percentages.

0 25 50

1

Deflection in degrees.

0-55

9-04

19-46

2

0-1

8-55

22-28

3

0-45

8-73

20-52

4

0-025

9-66

19-88

5

0-225

8-30

19-28

This table shows clearly that (col. 1) when the intensity of the
two lights was equal, the animal varied on the average only 0-09
degree from the perpendicular. It also demonstrates that when
the one light was reduced to three-quarters (col. 2) the intensity
of the other, the angle of deviation was about 8-86, and that when
a further reduction to a half was made, the angle of deviation was
more than doubled. Finally, the figures show that the angle of
deviation depends on the relative differences of light intensity and
is independent of absolute intensity (provided sufficient light is
present to overcome inertia (cf. stimulation, p. 193).

(7) A model with a heliotropic mechanism has been constructed
by Hays Hammond, the inventor of the dirigible torpedo. The
principle on which the machine depends is the alteration in the
electrical resistance of metallic selenium when exposed to light.
The " eyes " are lenses separated from each other by a projecting
" nose " which permits the shading of one eye while the other is
illuminated. The lenses are each focused on separate selenium

358 TROPISMS— THE SLAVES OF THE LAMP

cells. The heliotropic machine consists of a rectangular box
about 3 ft. long, 1 1 ft. wide and 1 ft. high mounted on three wheels,
two of which are geared to a driving motor. The third wheel,
mounted at the rear-end, controls the steering. It may be turned
right or left by the differential action of two solenoid electro-
magnets. The selenium cells are in circuit both with the driving
motors and with the steering magnets. In the former case, the
selenium cells control a series of very sensitive relays (cf. nervous
system) in such a way that the amount of energy sent through the
driving motors and hence their speed is determined by the intensity
of the light falling on the lenses. The steering magnets are opposed,
i.e. if both selenium cells are illuminated equally, both magnets
will receive the same current and the steering wheel will lie parallel
to the driving wheels. If more light falls on one selenium " retina"
than on the other, the former has its power to conduct electricity
increased in proportion to the relative increase in intensity ;
consequently the magnets controlling the position of the rear
wheel are activated asymmetrically. The wheel is pulled over
to make an angle with the previous line of traction of the " dog."
The mechanism is so arranged that this steering movement turns
the machine towards the light. It will continue to turn till both
lenses are equally illuminated. As soon and as long as both
" eyes " are equally illuminated in sufficient intensity, the machine
moves in a straight line towards the source of the light. The
apparatus is fitted with a reversing switch which will convert it
from a positively to a negatively heliotropic machine.

If, say, a portable electric light be turned on in front of the
machine it will immediately start to follow (or run from) the light
at a speed which may attain to 100 yds. per min. On reducing
the intensity of the light, the " dog " will slow down, and on
switching off, it will stop. In this way, the machine follows a
lantern in a dark room just like a positively heliotropic animal.
By reversing the direction of the current one may make the
machine negatively heliotropic.

II. Stereotropism is the term applied to the tendency of certain
organisms to bring their bodies as much as possible on all sides
in contact with solid bodies. " The butterfly Amphipyra, which
is a fast runner, will come to rest under a glass plate when the
plate is put high enough above the ground so that it touches the
back of the butterfly." Man orients himself partly by apprecia-
tion of the tactile influences on the soles of the feet. When these
are weakened as in locomotor ataxia, and when the orienting

ORIENTATION IN SPACE 359

influence of the eyes is removed, the patient finds difficulty in
standing and in walking (Romberg's sign).

III. Chemotropism plays an important part in the life of the
lower organisms. By it, the animal is drawn towards or draws
away from certain chemical substances. The organ stimulated
asymmetrically is oriented so that the stimulating impacts on it
are symmetrical.

IV. Orientation in space is determined mainly by three factors,
light, tactile sense and gravitation. Normal equilibrium or normal
geotropic orientation is denned as that position in which the plane
of symmetry of the animal passes through the centre of the earth.
Any deviation from that position causes unilateral stimulation
and corrective movements are instituted. The tight-rope walker
perceives that his centre of gravity is tending towards unstable
equilibrium and voluntary (though generally sub-consciously)
corrects his balance. In the labyrinths, we have a delicate
mechanism for detecting alterations in our orientation in space.

Sufficient has been said to show the nature and indicate the
mechanism of those actions termed tropisms. In principle they
depend on unilateral stimulation of a symmetrical animal. How
far they can be accepted as explanations of all the instinctive
actions of the lower organisms or of any of the actions of the
higher animals remains an open and debatable question.

CHAPTER XXXIII

" The free use of final causes to explain what seems obscure was temptingly
easy .... Hence the finalist was often the man who made a liberal use of the
ignava ratio, or lazy argument : when you failed to explain a thing by the ordinary
process of causality, you could ' explain ' it by reference to some purpose of
nature or of its Creator."

PRINCIPAL GALLOWAY quoted by D'ARCY THOMPSON.

IF the environment exerts such an all-powerful effect on the
organism, can the organism alter itself according to the principle
of Le Chatelier so that it may live with the least possible expendi-
ture of energy ? That is, has the animal the power of adaptation?
There is no doubt whatever as to the adaptation of growing bone
or growing tissue of any sort to the stresses and strains incident
upon it. Various organs are known to adapt themselves to meet
alterations in the conditions under which they work.

When one comes to consider the organism as a whole, the
evidence for adaptation is not so conclusive. The arctic fox and
the polar bear are not white because they have adapted themselves
to a white background, but because their coloured relatives, not
having their invisibility, have paid the penalty. It has been said
that trypanosomes may be obtained which are almost unaffected
by treatment with arsenic. The process for producing them is
to give their host a high but non-lethal dose of arsenic, infect
another host with the survivors and so on. This is clearly a case
of the survival and propagation of the most resistant strains.

Animals which live in dark or semi-dark places have generally
defective eyesight. Is this due to atrophy from want of use or
might one not argue that the environment of the cave was the
fittest for the blind or semi-blind animal ? Not only would they
be at a manifest disadvantage in the struggle for existence outside,
but they have a distinct advantage in the cave over any seeing
animal that may stray in.

360

EFFECT OF INTENSITY OF TEMPERATURE 861

.To be brief, one must consider that, as anything but a rapid
response to the distribution of forces in the environment is incom-
patible with life, the animal capable of adapting itself to circum-
stances will live and propagate. Man, because of his highly
organised nervous and muscular systems, is able to adapt himself
readily and, therefore, reigns supreme.

No case is known where acquired characters have been trans-
mitted to offspring.

On the other hand the environment may have profound effects,
not in the nature of adaptation, but on the development of the
organism.

Temperature. In Chap. XXXI. the effect of alterations in
temperature on physical, chemical and physiological phenomena
was considered. Temperature influences all life phenomena.

(a) Development. One of the simplest experiments of this
nature is to determine the temperature coefficient of the develop-
ment of an egg. Usually the egg of the sea-urchin is chosen for
this purpose. Table LXVIL (Loeb and Chamberlain) gives the
time in minutes required from insemination to the first cell-
division for various temperatures.

TABLE LXVIL

EFFECT OF INCREASE OF TEMPERATURE ON CELL-DIVISION.

Temperature (°C.)

8

10

15

20

25

Time (minutes)

411

208

100

56

39-5

Increase of temperature thus causes a more rapid development
of the egg.

(b) Rate of Metabolism. Increase of temperature, within
limits, as we have seen, causes an increase in general metabolism.
More oxygen is used, more carbon dioxide is excreted, etc. Organs
work at a greater rate, e.g. the heart beats more rapidly. The
alterations of the rate of the heart of Fundulus (embryo) keeps
such regular pace with alterations in external temperature that
it could form the basis for a rough thermometer as Table LXVIII.
shows. From the figures we are also justified in inferring that the
influence of temperature in this reaction is a function of this
particular temperature and does not depend on whether the
organism is gaining or losing heat.

362

ADAPTATION

TABLE LXVIII.

RELATION BETWEEN TEMPERATURE AND RATE OF HEART
BEAT IN FUNDULUS EMBRYO.

Temperature (° C.)

20

15

10

5
61

10

15

20

Time for 19 beats (minutes) -

11-5

19-0

32-5

33-5

18-8

12

(c) The time necessary to reach sexual maturity is decreased
by increase of temperature. Stefansson reports that the Eskimo
girl usually has offspring by her twelfth year. This early maturity,
he states, may be attributed to the fact that the Eskimo keeps his
body at a temperature as high if not higher than that of dwellers
in Southern Europe. Be that as it may, other observers have
noticed that growth in height and in weight is increased during
periods of increased temperature, e.g. summer (see Growth).

CHAPTER XXXIV

«

GROWTH

" The living organism is so constituted that each disturbing influence stimu-
lates it to put in action a compensatory mechanism which will neutralise and
render innocuous the disturbing agency." FREDERICQ.

GROWTH may be considered as an attempt of a system to get
into equilibrium with its environment. Generally, but not
invariably, increase in size is accompanied by changes in external
form and in internal structure. Development is, in most cases,
a necessary result of growth. This chapter will deal with increase
in size quite apart from any concomitant alterations in complexity.

I. Nature of the Phenomenon.

At first sight it seems easy to distinguish between a mere
accretion of material like crystal growth, snowball increase or
accumulation of interest on capital, and organic growth. A
more careful examination of the cause and resultant velocity of
growth shows that in both inorganic and organic worlds similar
principles are involved, and that similar factors operate towards
similar ends.

A series of interesting and illuminating experiments emanating
from Leduc's laboratory are suggestive. If a little seed com-
pounded of copper sulphate and glucose be planted in a gelatine
(1-5 per cent.) gel, through which a little potassium ferrocyanide
has been dispersed, growth will take place. In the first place, by
the interaction of copper- and ferrocyanide-ions, a membrane of
copper ferrocyanide will be formed round the seed. This membrane
is semi-permeable, allowing free passage of water but preventing
the egress of the crystalloid ions. As a result, the seed, thus
gaining water by endosmosis, will swell up and, when the elastic
limit of the membrane has been reached, will burst. Immediately
this happens, a new membrane will form round the copper-glucose

363

364

GROWTH

solution and the process will be repeated. By this means re-
markable life-like growths are obtained. (Details of preparation
are given in Part II., p. 399.)

Botanists are agreed that osmosis plays an important part in
plant growth. An experiment is given in Part II., p. 399, to
illustrate the production of turgescence and consequent rigidity
as the result of endosmosis. Plant growth is conspicuously
associated with turgor, and depends in great measure on the amount
of water taken up. Another and more plausible explanation may
be given of the swefling of plant tissues. In Chap. VIII., p. 66 (3),
we mentioned the power of colloids to imbibe and compress water.
It is extremely probable that plant turgor may be due to this
imbibition, initiated by some alteration in the hydrogen ion con-
centration of the tissue.

It has been definitely proved that animal growth is accompanied
by increase in water content as shown in Tables LXIX. and LXX.

TABLE LXIX.

WATER CONTENT OP HUMAN EMBRYO. (FEELING.)

Age (weeks).

Weight (grams).

Increment.

Increment
per week.

Water per cent.

6

0-975

97-5

17

36-5

35-525

3-23

91-8

22

100-0

63-5

12-7

92-0

24

242-0

142-0

71-0

89-9

26

569-0

327-0

163-5

86-4

30

942-0

355-0

88-75

83-7

39

1640-0

716-0

79-56

74-2

TABLE LXX.

WATER CONTENT OP FROG EMBRYO. (DAVENPORT.)

Age (weeks) -

1

2

5

7

9

14

41

84

Water per cent.

56-3

58-5

76-7

89-3

93-1

95-0

90-2

87-5

In the later stages of growth and especially in the higher
mammals the ratio of water to solids tends to diminish. In-
hibition of growth occurs when means are taken to prevent the
entrance of water. For example, Loeb put Tubularia and Ceri-
anthus, which live and grow in sea- water having about 3-3-5 per
cent, salts, into a more concentrated mixture. He found, when
the concentration of salts in the water was 5-4 per cent., that

NORMAL RATE OF GROWTH 365

these organisms ceased to grow. The water-holding power of
the salt solution, i.e. the exosmotic property of the artificial sea-
water, balanced the inwards pull of the protoplasm.

II. Normal Bate of Growth.

(a) Weight. Brailsford Robertson has shown that the rate of
increase in weight follows a curve characteristic of autocatalytic
reactions, i.e. of reactions in which one of the resultant products
acts as a catalyst for the whole reaction. A simple example of a
reaction of this type may be found in the inversion of an aqueous
solution of cane sugar at 100° C. Part of the product of the
reaction (glucose and fructose) appears to undergo further decom-
position, giving rise to an unknown acid which accelerates the rate
of inversion.

If a? denote the amount of invert sugar formed during hydrolysis,
x will also be proportional to the amount of acid produced. Now,
by the ordinary compound interest law in which a function varies at
a rate proportional to itself — an exponential function — we have :

.... 1 .ax

or, on integrating, k = — log

at a-x
where k is a constant.

As the result of a series of experiments on auto- in version at
100° C., the value of k for this reaction has been put =122 x 10-6.
With this value we can tell at any time after the inception of the
reaction just how much sugar has been inverted. Further, it
is obvious, that as the action proceeds, the velocity due to the
concentration of the original substance gradually decreases
(i.e. the ordinary mass action without the catalyst), while that due
to the concentration of the newly formed substance keeps steadily
increasing. Hence, there must, at a certain time, be a maximum
velocity due to definite concentrations of a and x. In an auto-
catalytic reaction this maximum velocity is reached when the
concentration of the newly formed substance is half the concen-
tration of the original substance, i.e. when x =a/2-

Do statistical results bear out the statement that growth is an
autocatalytic reaction ? In the following table (LXXI.) is given
for comparison, the weight of the human body at various ages,
as found and as calculated from the assumption that the rate
of growth is autocatalytic.

366

GROWTH

TABLE LXXI.

Age (years).

Body weight (Kg.).

Number of cases.

Found.

Calculated.

0-5

34

34

100

5-5

22-7

16-5

176

6-5

24-6

20-1

327

7-5

25-9

234

631

8-5

27-0

26-2

1038

9-5

28-3

284

1262

10-5

304

304

1200

11-5

32-3

32-2

1129

12-5

35-0

34-0

863

15-5

47-1

44-8

1451

20-5

66-1

654

459

From these results we see that the agreement between observed
and calculated results is excellent in all cases where a sufficiently
large number of subjects have been weighed, except at age 15|,
where weight increases more rapidly than theory demands.

A simple but empirical formula for obtaining " expected "

A

weight is , where A = conceptional age in years and m is a

4 -75m

constant for each age (see Table LXXII. for values of m and for
results).

(b) Length. It was at first believed that the length curve was
of parabolic form of the equation y* = a (x+b), but later and more
complete investigation has shown that this is untenable. There
is for each type of body a definite relationship between length and
weight, viz. : 1= ^Jmw, where I — length in metres, w = weight in
kilograms, and m is a constant for each age (and each type). As
A

, therefore A =4>-75l3 or 1 =

(Pfaundler.)

4-75m V 4-75

Pfaundler gives the following examples :

(i) A boy aged 1 year has a conceptional age ^4 = 1-75 yr.

Hence length = A/ j-== = VO-36 = 0-72 metre, which compares favourably
with the value given in Table LXXII.
(ii) A boy aged 8 yrs. has A = 8-75.

3/8-75

Hence length = * T-=^ =Vl -74= 1-23 metres.
\ 4-75

(Average length of boy of 8 yrs. = 1-20 metres.)

SACK'S RULE

367

TABLE LXXI1.

Age from
birth.

Concep-
tional
age A
(yrs.).

Length (metres).

Constant
m.

Weight (Kg.).

Weight,

Found.

Calc.

Found.

Calc.

Height " '

3 months^

0-225

0-08

25-6

20 x 10-3

0-025

e „ h

0-450

0-31

0-45

46-91

635 x 10-3

—

2

8 ,, (Ǥ

0-600

0-42

0-50

36-1

2100 x 10-3

—

5

10 „ J

0-750

0-50

0-53

39-73

3300 x 10-3

3975 x 10-3

6

1 month

0-833

0-54

0-55

38-72

4-25

4-53

8

2 months

0-916

0-58

0-58

40-24

4-95

4-79

8-5

3 „

1-008

0-61

0-60

41-33

5-6

5-09

9

6 „

1-25

0-66

0-64

40-56

7-2

6-50

10

9 „

1-50

0-70

0-69

40-74

8-6

7-75

12

1 year
2 years

1-75

2-75

0-74
0-84

0-72
0-83

42-88
48-98

94
12-1

8-59
11-82

12-6
14

3 „

3-75

0-90

0-92

55-06

13-2

14-34

14-6

6 „

6-75

1-11

1-12

68-17

18-1

17-76

16-3

9 „

9-75

1-24

1-27

7841

24-9

26-15

20

12 „

12-75

1-38

1-39

84-94

30-9

31-60

22

Table LXXII. is from Pfaundler's data. It gives the calculated
and observed weights for each age as well as his values for m and
the centimetre index.

The ratio, weight in Kg. /length in cm., is called the centimetre index.
Sometimes the ratio is modified as in Levi's ratio, which is

100 f/wt. in grams
length in cm.

This ratio diminishes as age increases up to puberty.
Dreyer suggests that instead of the total length of the body it would be
better to deal with the sitting height.
He has established the following ratios :

Males, W= 0-38025 °'3^/l;

Females, W = 0-36093 ° '31f/l ;

where W = weight of the body in grams

and I — length of trunk in cm.

Some organisms when their size reaches a certain limiting
value tend to divide into two equal portions (Sach's Rule). There-
fore, one has to deal with an increase in number quite apart from
increase in individual size or weight. It has been proved by
numerous experiments that the increase in the number of cells
follows the compound interest law, i.e. is an autocatalytic reaction.

To summarise : When it is said that growth is an autocatalytic
reaction it is inferred that (i) superimposed on the velocity of

368 GROWTH

reaction, which may be classed as chemical and is governed by
the law of mass action, (ii) there is a variation in rate due to the
presence of a catalyst in one of the products of the main action.
The phases of such a reaction are, at least, four :

(1) Ordinary velocity, proportional to the mass of the reacting
bodies.

(2) After a short period the catalyst makes its appearance, and
the total rate gradually and steadily increases.

(3) Certain limiting factors probably caused by the presence
in the blood (or in the sap of plants) of endocrinetes inhibit too
rapid a growth.

(4) The accumulation of the products of the reaction produces
a tendency to cause a reaction in the reverse direction. That is,
arrest of growth and even negative growth may be produced.

Quetelet, who was the pioneer of the statistical study of growth,
found that the rate of growth alters with age in a definite orderly
way, and the velocity curve may be divided into fairly well-defined
regions, each having a definite and characteristic slope, e.g.

(1) From conception to about 3 lunar months the velocity is
low, about 2 cm. per month.

(2) Period of rapid growth from 3-9 lunar months =9 cm.
per month.

(3) Rate almost equal to (1), i.e. 2 cm. per month from birth
to 3 years or so.

(4) Slower but still rapid growth in early boyhood. (Marked
quickening in teens (growing age).)

(5) Period of arrest — full stature has been reached.

(6) Somewhere about fifty years of age the period of negative
growth sets in. That is, the curve of growth and picture of velocity
follows point by point the velocity curve of a typical autocatalytic
reaction.

III. Factors modifying Growth.

Chemical reactions may be profoundly altered by alterations
in external conditions, and therefore, we may expect to find
certain variations in the rate of growth which may be correlated
with alterations in the conditions to which the subjects are
subjected.

1. Phase Differences.

(a) Individual. Quetelet found that under normal conditions
the variations in the rate of growth of man were just what might

FACTORS MODIFYING GROWTH

369

be predicted from the application of the mathematical law of
probability. This law is represented by the equation

h

where so and y are rectangular coordinates and h — parameter
of the curve. Riedel tabulated the heights of nearly 4000 school-
boys of various ages, and found that the variations in height
observed for each age were, for all intents and purposes, just what
the mathematician predicted. Other investigators have con-
firmed this and have extended the scope of the equation, applying
it to variations in weight, chest measurement, etc.

The index of variability, or standard deviation denoted by the
letter <r, is equivalent to a determination of the point on the actual
frequency curve, where it changes its curvature on either side of
the mean. For example, if the curve showing the number of
individuals of a certain age having a certain height, for instance,
be plotted it will cut the theoretical curve at various points.
or is a measure of this divergence.

The coefficient of variability is obtained by dividing a- by the
mean and, for convenience, multiplying by 100,

i.e.

cr

M

TABLE LXXIII.

COEFFICIENT OF VARIABILITY IN MAN AT VARIOUS AGES.

Age (yrs.).

Height C.

Weight C.

0

6-5

15-66

5

4-1

11-5

10

4-3

11-6

15

5-5

15-3

20

3-6

10-8

From this, we see that the coefficient of variability tends to
decrease when the rate of growth decreases and tends to increase
again when rapid growth restarts in the " teens."

(b) Sex introduces a phase difference in the rate of growth.
Girls run through the various phenomena of growth at a more
rapid rate than boys.

(c) Difference in race, even under similar climatic conditions,
has a profound effect on the final result of growth— i.e. on total
stature, weight, form, etc. — but seems to have little or no effect

24

370 GROWTH

on the rate of growth. The little Jap increases in size year by
year at the same rate as the tall Norwegian. The rate of growth
is a specific phenomenon governed by factors deep rooted in the
composition of the organism.

2. External Factors.

Quite apart from these more or less normal variations due
mainly to hereditary influences, there are various external factors
which have a modifying effect on the rate and amount of growth.

(d) Temperature. As we have seen previously, all chemical
and physical reactions respond to alterations in temperature by
an alteration in velocity. In the terminology of van't Hoff, it
may be said that if x is the temperature coefficient of a reaction,
and the temperature of the reacting mass is raised n degrees, the
consequent alteration in velocity will be as xn. Usually the
interval taken (i.e. n) is 10° C. and x is written as Q10. For most
chemical reactions Q10 is = 2. This may be taken to mean that
for an increase of temperature of 10° C. the velocity of the re-
action will be doubled. Van't Hoff noticed that, at low tempera-
tures, very high temperature coefficients were obtained — in
some cases Q10 reached the value of 5 or 6. Most physical re-
actions, as we have seen, differ from most chemical reactions in
having a negative temperature coefficient, i.e. their rate is decreased
by an increase of temperature. The various reactions which are
manifested as growth are some chemical and some physical, and
it is, therefore, somewhat difficult to apply the van't Hoff law to
this phenomenon. Moreover, as pointed out in the earlier pages,
Errera extended the principle of Le Chatelier by stating that —
every physiological process causing change, by its very action, set
in being other reactions to inhibit change. It is, therefore, a difficult
matter to interpret the figures obtained for the influence of
temperature on the velocity of growth in animals.

Hertwig's classical work on the rate of growth of the tadpole
illustrates the type of result got in this line of research. He found,
for instance, that at 10° C. the tadpole took 6-5 days to reach
the same stage of development that at 20° would have taken two
days, i.e. the two rates are as 6-5/2 = 3-25. Using the equation
given above and putting n — 10,

x10 =3-25,
i.e. 10 logx = log 3-25 = 0-5119,

Therefore log x = 0-05119,

and x = 1-125.

TEMPERATURE COEFFICIENT OF GROWTH 371

The temperature coefficient for the development of the tadpole
is thus (Qi0) = 1-12. That is to say, if it takes t days at a certain
temperature 0° (between 10° and 20°), for a certain amount of
growth to take place, then it will take t x l-12n days when the
temperature has fallen to 0 - n° C.

(e) Climate. The various meteorological conditions — tem-
perature, relative humidity, nature of soil, etc., which are all
included under the term climate — undoubtedly exercise an
influence on animal and vegetable growth. The effect of relative
humidity on plant growth has been exhaustively studied and
conclusions have been drawn as to the concentration of moisture
at each temperature which best promotes the growth of specified
plants. It is more difficult to get statistics correlating animal
growth with the various climatic factors. In order to study
biological problems like this experimentally, one must have the
power of altering the component factors one at a time and
noting the results.

(/) Seasonal variation. Indubitable evidence is available to
show that the growth-rate of the lower animals is subject to
seasonal alterations. There are indications that positive and
negative variations occur in man in summer and winter respec-
tively.

TABLE LXXIV.

GROWTH IN HEIGHT OF GERMAN MILITARY CADETS IN HALF
YEARLY PERIODS. (DAFFNER.)

Number observed.

Age.

Increment in cm.

Winter, 6 months.

Summer, 6 months.

12

11-12

1-6

2-3

80

12 - 13

1-5

2-9

146

13-14

2-0

3-0

162

14-15

2-5

3-5

162

15-16

2-3

3-0

150

16-17

1-9

2-3

82

17-18

1-2

1-5

22

18-19

0-8

0-9

6

19-20

0-4

0-4

Other investigations (West Point, Sing-Sing, etc.) do not yield
such a marked seasonal variation.

(g) Diurnal variations. Both weight and height vary in the
course of 24 hours. The weight is lowest in the morning before

372

GROWTH

breakfast, and is highest after supper in the evening. This may
be accounted for by the fact that the weight of food eaten is greater
than the weight of excreta. On the other hand, stature decreases
during the day by from 1 to 3 cm. This trifling shortening is
attributed to compression of the intervertebral discs, curving of
the spine and depression of the arch of the foot. Measurements
for comparative purposes should, therefore, always be taken at
the same time of the day — e.g. before breakfast.

(h) Nutrition. It is obvious that, if the animal does not get
an adequate supply of the material to be built into tissue, and
of the energy necessary for these processes, the work will be
done slowly and badly. In man at least, this only applies to
increase in girth and weight. Growth in stature seems to be
specific and is almost independent of the quality and quantity
of the food available. In the lower animals, while decrease in
growth is conspicuous in underfed animals, one may also detect
a clear falling off in the rate of increase of length (cf. Table LXXV.).

TABLE LXXV.

COMPARATIVE WEIGHTS AND LENGTHS OP FULL FED AND
UNDERFED RATS.

Length of body.

Weight.

Full fed.

Underfed.

Full fed.

Underfed.

0

48 mm.

48

5-4 gm.

5-4 gm.

6

128

98

42

24

10

173

100

150

25

The underfed rats were given food of just sufficient energy content to
provide for their maintenance.

It is well known that quite apart from its energy content, food
for growing animals must have certain of the amino acids in its
make up. These are the building stones or units of which the
complete organism is constructed. It has been shown that if
animals are deprived, say, of the amino acid lysin, their growth is
inhibited. On the addition of this amino acid to their diet, not
only is growth restarted but leeway is made up and a normal
growth is produced.

Certain much studied but little known accessory factors are
absolutely essential constituents of the diet of the growing child.
Of their chemistry a little is known — of their physics or of the
mechanism of their action, nothing positive can be said.

ENERGETICS OF GROWTH 373

(i) Social position. The children of the well-to-do are generally
markedly heavier and slightly taller than those of the working
classes. Quite apart from any possible underfeeding of the
latter, one must take into account the more or less sheltered life
of the former and their freedom from those influences which tend
to put the burdens and responsibilities of the adult on the child
of the lower classes at a comparatively early age.

(/) Endocrinetes. Considering the factors which influence the
rate of growth, and keeping well in mind the unthinkable com-
plexity of the polyphase solution of colloids and crystalloids
composing the animal body, one can hardly be surprised that so
little is known of the mechanism of growth. In some way, the
various alterations in size and shape are interrelated and regulated
through the blood and through the nervous system, by various
secretions from endocrine organs. Growth in length is associated
with the secretion of the pituitary gland. Any alteration in this
gland causes alteration in the performance of other endocrine
organs, e.g. the gonads and thyreoid. The growth of cartilage and
bone are profoundly modified by alterations in the output of the
thyreoid gland, while the gonads, and in early life, the thymus,
control both growth and development, again by processes of which
the mechanism, from a physico-chemical standpoint, is quite
unknown.

IV. The Energy of Growth.

It is generally believed that young animals require much food
because they are growing. That this is not quite correct has been
shown in Chap. XXXI., where we saw that the young animal,
because of its large surface compared to its mass, lost heat most
rapidly. To prove this we need only examine the metabolic
balance sheet of the child. Camerer gives the following com-
position of a new born child (in grams) :

Total weight. Protein. Fat.

2820 320 348

Now, as we have seen, in 180 days the child doubles its weight.
It does not, however, do so by adding equal quantities of the
material already present. In a child 180 days old, weighing
5600 grams, there are 790 grams of protein and 733 grams of fat.
Thus 470 grams of protein and 385 grams of fat are added. In
calories that gives 470 x 5-3 =2491 cals. + 385 x 9-3 =3580-5 cals.
= a total of 6071 -5 calories for the period, or about 35 calories

374 GROWTH

per day. A child of that age has an intake on the average of
about 500 cals. per day. That is, the energy used for growth
amounts to about 7 per cent, of the total energy intake.

It has been calculated that each gram of infant's body sub-
stance has a value of 1-87 cals. Thus, if the child adds 20 grams
a day, it " fixes " 20 x 1-87 = 37-4 calories per day, a result closely
approximating to that just given.

Rubner has formulated the following law regarding the energy
of growth.

Law of constant energy consumption. " The number of
calories required to double the weight of a new born animal of all
species (except man) is practically the same in spite of the
enormous differences in time taken in attaining the double weight."
Analysis has shown that each kilogram of body substance contains
about 113 grams of protein and 120 grams of fat having an energy
value of 1726 calories. Experiment has shown that in building
this up the animal uses about 4800 calories. Man is an ex-
ception and requires six times the amount.

The growth quotient is the percentage of the energy intake

/1726\

which is " fixed " in the animal tissues. It is about 36 ( - - ) for

\ 48 /

all animals except man, who is able to " fix " only 6 per cent, of
his energy intake.

The question now arises as to why growth stops. If it is an
autocatalytic reaction, growth should stop when the process is
balanced, i.e. when anabolism and catabolism mathematically
cancel one another. According to Loeb, this happens when the
organism has reached a certain size, or a certain number of cells
have -been formed. Rubner's second law, that of length of life,
is suggestive rather of the cessation of positive growth after the
cell had expended a certain amount of energy. It is certain that
if growth is inhibited during a certain period, i.e. if energy which
would normally have been expended on building up tissue is not
used for this purpose, the whole " growing time " may be pro-
longed.

The healing of a wound, the regeneration of tissues and the
growth of tumours, etc., bear a close resemblance to animal
growth as a whole. They may be modified by the same factors,
and investigation of the various processes involved has shed
considerable light on the mechanics of growth.

Leo Loeb and his co-workers have made an extensive study of
the healing of a skin wound. They found that if the skin is

GROWTH AND FORM 375

removed from any spot, epidermal cells from the edge of the
wound creep upon the denuded spot and form a covering layer —
a surface-tension phenomenon. The stretching of the contents
of the surrounding cells so produced, causes a rapid series of cell
divisions, i.e. growth under stimulation of stress takes place
(Chap. XVI.). That the cause of the increased cell division is the
stretching of the cells is borne out by the fact that the larger the
area to be covered (within limits) the greater is the tension and
the more rapid the process of forming a new skin. When the skin
is formed and the internal pressure is altered from one of stretching
to one of compression due to the crowding of the proliferating
cells, growth slows down to normal. It is noteworthy that, before
this return to a normal rate of cell division can take place, distinct
pressure must be exerted by the epithelial cells on one another,
i.e. excessive formation of epithelial cells occurs. Is it possible,
from this and similar experiments, to consider that cell pressure is
one of the limiting factors in growth ?

There are, as we have seen, two main epochs of growth, each
followed by a slowing down of velocity. In the first case, in early
life, the slowing down is temporary, This may be correlated with
(a) the fact that the increase in weight during this period is due
in great part to a deposition of fat which is absorbed during the
subsequent period of slower growth, and (b) to the changes in
glandular functions, etc., which usher in the second period of very
rapid growth. This final period is followed by a complete arrest
of positive growth. The increased weight is due to muscle and
organ building — protein is laid on and the percentage of water
decreases. No further change resulting in increased metabolic
activity takes place after this. Cell pressure now developed is
not relieved.

The physical chemistry of negative growth will be considered in a later
chapter.

V. Growth and Form.

One cannot leave this subject without a brief reference to the
relationship existing between growth and form. Form is deter-
mined by the specific rate of growth in various directions, i.e. as
D'Arcy Thompson puts it, form is a function of time. If a spherical
organism grew symmetrically its form would not alter, but
because of its complexity, growth is not uniform in all directions.
There are structural differences in protoplasm which set up
unequal resistances to growth. One part may be more viscous

376 GROWTH

than another, or may have a higher surface tension and so on.
Although it has been pointed out that the presence of external
resistance acts as a stimulus to growth, it has also been said that
internal resistance arrests growth.

Bohn propounds the following four laws relating growth and
form in plants, and they may be applied to animals with some
measure of justification :

(1) Law of Vectors. A vector in distinction from a scalar
phenomenon is one representable graphically by a line of known
direction and definite length, i.e. a conception of a change of
magnitude with time. " The principal forces of growth are
directed along axes offering a geometrical disposition."

(2) Law of Depolarisation. " When growth becomes exag-
gerated in a certain direction, a force is developed in the living
organism which tends to oppose the growth, " i.e. Errera's Rule,
q.v., or the ordinary law of balanced reaction.

(3) Law of Axial Repulsions. " When secondary axes are
borne on the principal axis of a plant or animal, a reciprocal
repulsive force is developed between the principal axis and each
secondary axis."

(4) Law of Compensation. When an axis branches in one plane
there is a tendency for the re-establishment of the destroyed
bilateral symmetry."

To summarise :

1. Growth is a balanced reaction having the mature organism
for an end point.

2. The organism grows at a definite rate which is, at any
moment, proportional to the amount of growth yet to be made.

3. The rate of growth is not uniform throughout but is specific
for each epoch of life.

4. The growth in each epoch proceeds at a rate corresponding
to an autocatalytic reaction.

5. Various factors which influence chemical and physico-
chemical reactions, influence the rate of growth.

6. If the rate of growth is arrested in any epoch, the length of
time spent in that cycle is prolonged — so that the amount of
growth characteristic of that epoch is accomplished.

7. Form is a function of growth.

DEVELOPMENT

"... I compared the cell-growth, by which Nature builds up a plant or an
animal, to the glass-blower's similar mode of beginning, — always with a hollow
sphere, or vesicle, whatever he is going to make."

OLIVER WENDELL HOLMES.

OCCURRING simultaneously with increase in size, are changes
in external form and internal structure — the organism develops.
Mainly through the brilliant researches of J. Loeb and his school,
some light has been thrown on this seemingly mysterious and
apparently inexplicable process. The changes taking place are
most readily perceived when the transparent eggs of the echino-
derms are used as the material on which to experiment, and
consequently, our ideas of the processes involved in mammalian
development are largely derived from the study of processes in
the lower aquatic animals which may or may not be quite
analogous.

The unfertilised ovum is a moribund body which disintegrates
more or less rapidly. If, before disintegrative processes have
become apparent, the egg undergoes fertilisation, destruction is
stayed. The fertilised egg develops, grows and becomes differ-
entiated into various structures. This process of differentiation
of protoplasm is an orderly one, taking place always in the same
manner and being modified always by the same conditions.

On the entry of the spermatozoon, some change in the free
energy of the egg must take place. The egg is no longer static
but becomes endowed with dynamic force. In order to discover
the underlying physico-chemical change, Loeb attempted to induce
development of unfertilised eggs by alteration of the environ-
mental conditions. No change in a system in equilibrium can
take place unless the relative amount or incidence of the free
energy of the environment is first altered. The two series of

377

378 DEVELOPMENT

changes — external and internal — are cause and effect. This is
merely a restatement of the Law of Inertia. The entry of the
spermatozoon alters the balance of free energy between egg and
environment. Loeb attempted to bring about the same result
by altering the free energy balance between environment and egg.
He found that two separate and distinct changes took place after
fertilisation, viz., membrane formation and development. These
involve totally different physico-chemical reactions. Membrane
formation is not followed necessarily by development.

I. Membrane Formation.

Loeb found that all those substances or agencies which can
bring about haemolysis (Chap. XXI., p. 244) also induce membrane
formation. The best agent for this purpose is dilute butyric acid.
Immersion of sea-urchins' eggs (unfertilised) in sea-water con-
taining about 5 per cent, of 2V/10 butyric acid for two to four
minutes brings about typical membrane formation. This mem-
brane is tough and is separated from the egg-substance by a layer
of more fluid material.

Examination of the performance of the other cytolytic sub-
stances makes manifest the mechanism of the change brought
about by their agency, and its similarity to that caused by butyric
acid or other fatty acid. The former all lead to the abnormal
production of acids in living protoplasm, and these acids pro-
duce, as a secondary effect, the physico-chemical change now
under consideration. These cytolytic substances are, as we
saw in Chap. VIII., just those substances which break emulsions.
Egg protoplasm is an emulsion very rich in fat, and it is obvious
that the breaking of such an emulsion would lead to the setting
free of protein and would probably change the nature of the
complex from a water-(and protein)-in-oil type to an oil-in-water-
(and protein) type. The protein and lipoids carried to the surface
and coming in contact with sea-water would readily be adsorbed
and form a membrane (Chap. X.).

Eggs undergoing artificial parthenogenesis quickly show dis-
integrative changes unless means are taken to confine the cytolytic
effect to the surface. This is provided for in some cases (e.g.
starfish and certain annelids) by the specific nature of the proteins
in the cortical layer. The diffusion of the acid causes them to
alter in electrical state. They imbibe water, swell up and develop
normally.

PHASES OF DEVELOPMENT 379

II. Exosmosis.

In most cases, however, unless a second alteration is made in
the bathing medium, the egg will either not develop at all, or
will die at some intermediate stage. It is known that after
fertilisation, the electrical conductivity of the egg is increased
for fifteen minutes or so. This may be interpreted as a sign of
increased permeability of the membrane to surrounding salts, or
it may, with equal justice, be accounted for by a withdrawal of
water with a consequent increase in the concentration of electro-
lytes. During this period of increased electrical conductivity,
the eggs readily undergo plasmolysis if placed in a solution of cane
sugar. Unfertilised eggs, of course, do not show alterations at
this early stage in electrical conductivity nor are they easily
plasmolysed. This may be taken as a confirmation of the second
hypothesis, viz., that water is removed by exosmosis and, con-
sequently, the concentration of electrolytes in the egg is increased.
Whatever be the actual physico-chemical process brought about
by the entrance of the spermatozoon, the result has been imitated
by simple physico-chemical means.

If, after removal from the butyric acid bath (or other cytolytic
agency), the egg is placed in hypertonic sea-water for about half-
an-hour and then returned to its normal environment, it will,
in all likelihood, reach maturity. That is, not only does artificial
membrane formation initiate the processes of development but it
starts, at the same time, processes which ultimately lead to the dis-
solution of the organism.

These latter activities may be, for a time, suspended, by a short
exposure to a hypertonic solution.

Loeb has proved that the withdrawal of water is merely the
trigger setting off a series of chemical as well as physical changes.
Attention has been repeatedly drawn in previous pages to the fact
that while most physical processes have a low or even a negative
temperature coefficient, most chemical reactions have a high
(Qio = 2 or more) temperature coefficient. This worker found
that, at a temperature of 5° C., the eggs had to remain in the
hypertonic solution for at least 210 minutes. The time of ex-
posure was decreased to 40 minutes when the temperature of the
solution was raised to 15°. Therefore, the temperature coefficient
for this process is 2_i o i e Q =5

Hence, superimposed on the physical process of exosmosis are
secondary chemical reactions initiated by it.

380 DEVELOPMENT

Attempts have been made to determine what part the sperma-
tozoon plays in the process of fertilisation. Brailsford Robertson
has extracted a substance oocytin from the testicles of the sea-
urchin which produces membrane formation. The question then
arises — " Is this substance a catalyst speeding up some slow
change or does it counteract some obstacle to development ? "
To the first part of the question a negative answer can be given
The velocity of the process of development is not catalytic. It
does not follow Schiitz's law and vary in velocity with the square
root of the concentration. If two spermatozoa are caused to
enter an ovum, the rate of segmentation should increase by 1-4
(i.e. >/2) times, if the process were catalytic. The rate, as a
matter of fact, is unaltered by the introduction of additional
spermatozoa. Therefore, the spermatozoon does not contain a
catalyst for developmental processes.

Loeb is inclined to believe that the spermatozoon removes
from the egg a substance or condition which inhibits or prevents
the process of development.

On the other hand, it is conceivable that the entry of the
spermatozoon increases the free energy of the now fertilised ovum.
The potential energy of the system cannot be utilised without
the employment of a small quantity of free energy. This quantity
of free energy may be extraordinarily small as long as it is sufficient
to start the series of reactions which once started are autocatalytic.

One result of the entrance of an effective spermatozoon into
an ovum is an acceleration of the processes of oxidation, i.e.
metabolism begins, and the various phases of development can be
followed by the same calorimetric methods (direct and indirect)
adopted in the study of the energy exchanges of the mature
organism (see over, p. 386).

Differentiation.

Cell division is the most general of the specific functions of
living protoplasm and it is the basis underlying the differentiation
of the comparatively simple structure of the egg into a more
complex organism. The division of a cell is a necessary conse-
quence of its increase in volume. The metabolic activity of the
cell is a function of its effective surface, i.e. its surface must be
of such a size compared with its volume that an adequate supply
of oxygen can reach the centre of the cell and that all the by-
products of cellular activity can be eliminated with sufficient
rapidity. A freely suspended unicellular animal is spherical.

FIELDS OF FORCE 381

Its surface- volume ratio is 3/1. Doubling the radius increases
the surface four times while increasing the volume eight times,
i.e. S/V =%, i.e. the effective surface has been halved. The
immediate result of decreasing the specific surface to a value below the
minimal effective value is to decrease the supply of oxygen to the centre
of the cell and to cause a heaping up of carbon-dioxide and other
products of metabolic activity. This has, at least, two effects —
(a) The process of development is retarded (Law of balanced
reactions), (6) The protoplasm becomes acid. The effect of acid
on an alkaline gel-emulsion has already been considered and may
possibly be the cause of cell division. We have, however, to
inquire into the reason for the symmetrical division of the cell.

Some cells divide directly without showing mitotic figures.
After a change in the distribution of free energy manifested by a
division of the nucleolus into two separate nucleoli, the whole
nucleus is divided equally into two daughter nuclei. This
separation is followed by the formation of a cell membrane
between the two nuclei dividing the entire cell into two equal
and similar portions.

Usually, however, cell division is accompanied by a complex
but regular series of changes in the distribution of the nuclear
chromatin. These mitotic or karyokinetic changes are dependent
on the bipolarity of the cell. Morphologically the polarity of
a cell refers to a symmetry of visible structure about a
particular axis. For instance, a line, drawn through the centres
of nucleus and centrosome, symmetrically divides a typical resting
cell and may be considered as its axis of polarity. This symmetry
of form is an indication or expression of a symmetry of free energy.

In a bipolar cell there are two " poles " or centres of force,
and the axis of symmetry must divide the field of force equally
about these poles.

Typical fields of force may be plotted by scattering iron filings on a
sheet of glass resting on the pole (monopolar field) or poles (bipolar field)
of a magnet. The filings set themselves along the lines of force, each
little filing becoming polarised and exerting an influence on adjacent
filings. (This " carding out " under the influence of stress was dealt with
in Chap. XVI.) In addition to the strength of the field and the direction
of the force, the movement of particles under its influence depends on the
friction of the contiguous matter and on the chemical nature of the particles
themselves. Friction prevents the filings from collecting in mass round
the poles while the specific inductive capacity (p. 52) or " permeability "
of the particles is a measure of the influence exerted by the " force " on
the particle. In the case of magnetic force, the specific inductive capacity
of iron is high while that of bismuth is low. Iron filings will, therefore, be

382 DEVELOPMENT

attracted towards the poles and will tend to lie on the lines of stress. On
the other hand, bismuth filings are polarised in a sense opposite to that of
the adjacent field. They are forced by the incidence of stress to move (or
because of friction, to tend to move) from the stronger to the weaker parts
of the field and thus take up positions as far from the poles as possible.
In general, a body placed in a field of force will tend to move towards regions
of greater or less intensity of stress according as its " permeability " to the
particular form of energy in question is greater or less than that of the surround-
ing medium,

The introduction of an aggregate of high permeability into the field of
force makes considerable changes in its configuration. Suppose a small
heap of filings were placed in the magnetic field already referred to, so that
it lay somewhat out of the interpolar axis but on the equatorial axis, the
result would be to provide an " easier path " for the lines of force. It is
obvious that, within certain limits, a longer path through a more per-
meable mass would be more advantageous than a shorter path through a
less permeable medium, and so many of the lines of force would be " short-
circuited " through the heap of filings. If, moreover, the heap of filings
were free to move, they would be drawn en masse into the field of force until
a point of equilibrium was reached. This resting place would depend for
its position on the relative " permeability " of the filings in heap and the
filings distributed over the field.

We have dealt with a magnetic field of force because it is easy to demon-
strate and may be readily modified experimentally, but our remarks are
applicable to any field of force. A simple experiment, due to Leduc,
shows that the lines of stress set up by diffusion may be made manifest.
A layer of salt solution is spread over a flat sheet of clean smooth glass,
and on top of this is placed a small drop of indian ink or blood. A drop
of a hypertonic solution of common salt is placed on either side of this
central drop. In a short time the pigment seems drawn out into threads
(pros) stretching between the centres of the two salt drops, so making
a figure exactly the same as that formed by iron filings under bipolar
magnetic influence.

The Bjerknes phenomenon demonstrates the applicability of this treat-
ment to the stresses and strains set up in a fluid as the result of movement
in it. Bodies synchronously vibrating or pulsating in a liquid medium
attract or repel one another according as their oscillations are identical
or opposite in phase. That is, a bipolar field exists which may have, like
a magnetic field, similar or dissimilar poles. In such a field of force
currents are set up in the fluid (hydrodynamic lines of force) and any
particles in suspension, if lighter than the fluid, act like the iron filings, if
heavier like the bismuth filings above. Moreover, the lines of force set up
by identically pulsating (attractive) bodies are exactly similar to those
produced by similar (repulsive) magnetic poles, and vice versa.

The first stage in the development of a cell consists in the
division of the centrosome into two equal parts which draw
away from one another. A field of force is set up between the
two centrosomes and threads of those cell constituents which are
more " permeable " to the form of energy existing, are carded
by the incident stress into a figure closely resembling those

ENERGETICS OF KARYOKINESIS 383

mentioned above. On the " outer " side of the centrosomes
can be seen starlike radiations (astral rays) recognisable as indi-
cations of incomplete lines of force which run externally to those
stronger interpolar lines which constitute the spindle.

The nucleus is composed of material of fairly high " permea-
bility " and, therefore, may be expected to travel towards the
equatorial axis. This is found to be so. In some cases the
nucleus is wholly, and in other instances it is only partially drawn
into the field between the centrosomes. Differences, too, exist
in the relative development of asters and spindle which are
capable of explanation by analogy to the magnetic model. If,
in the experiment with iron filings, the field were surrounded by an
iron ring, the majority of the lines of force would pass round by
the ring. That is, the interpolar lines would be slight and the
extra-polar rays would be heavy. Similarly, we may correlate
a mitotic figure having good astral rays and a poor spindle with a
marked " permeability " of the surface of the cell.

One would be entering the realms of pure hypothesis if physico-
chemical interpretations were attempted of the various stages of
karyokinesis. The constitution of protoplasm — vaguely stated
as an emulsion of various lipoids in a complex protein-water
emulsoid with various crystalloids in solution or adsorbed, presents
excellent opportunities for the theorist to draw parallels between
certain manifestations of force in living things and in dead matter.
The mechanisms underlying these processes are as yet unknown.
The processes themselves, like all other changes in matter, are
accompanied by changes in electrical potential. These changes
are measurable and are not constant but fluctuate (even reversing
in direction) at epochs coinciding with phases of development.

We are now in a position to consider the actual cause of cell
division. To state why the cell must divide — to argue from a
surface-volume ratio — is to presuppose a cell consciousness or to
postulate an external directing force — both alternatives being
without the domain of physics. The use of the final cause or the
argument that division is of obvious advantage to the cell, sheds
no light on the mechanism involved. Consideration must be
given to the forces at work in the cell. Further, experiments
such as the much quoted one of Brailsford Robertson, where an
oil drop is divided by the imposition on it of a thread soaked in
alkali, are not very illuminating. The energy of cell division is
not external to the cell but depends entirely on a redistribution
of forces inside the cell.

384 DEVELOPMENT

We have seen that, as a result of the diminution of specific
surface with growth, metabolic processes are retarded and acid
by-products tend to accumulate. It is obvious that at the centre
of the cell, i.e. at the region most distant from the surface, these
changes due to maloxidation will be most marked. This decrease
in metabolism is accentuated by the fact that the nucleus which
is always in the centre of the field of energy of the cell and usually
near the centre of the cell material, is the seat of the most rapid
oxidation changes in the cell. It will, therefore, show the effects
of the lack of oxygen at a very early stage. It follows from this,
that the intrinsic energy of the fluid at the centre will either suffer
an increase or a decrease. Everything points to the latter as
occurring. Now, as surface tension is, as far as cell problems are
concerned, a relative magnitude, we may say that the tension
of the superficial layer of the cell which, on account of its proximity
to the surface, remains practically normal, increases in close corre-
spondence with the decrease of intrinsic energy of the central
portion. This increase is still further accentuated by the increase
in the relative " permeability " to energy of the surface of the cell,
which as we have seen causes the development of radial lines of
force. The high tension of the surface of the egg operating on the
central region of low intrinsic energy causes the material in the
centre to be dispersed into the cytoplasm of the cell. These
dispersed particles first set themselves in a neutral position,
i.e. on the plane of segmentation — cf. iron filings in a magnetic
field of force between two similar poles. The position of the nucleus
determines the first plane of segmentation, since apparently
nuclear division precedes the visible division of* the cytoplasm of
the egg. In other words, the plane of nuclear division becomes
the plane of segmentation of the whole cell. The nuclear matter
as manifested by the chromosomes, gradually sets in the lines of
force between the centrosomes and slowly separates into two equal
portions which ultimately form the two nuclei. Hence we have
a spherical cell which is capable of division into two exactly
similar portions. It is, therefore, manifest that each potential
segment, because of this similarity of structure and energy content,
will repel the other half and, according to the ordinary laws of
stresses and strains, will cause division in the plane of symmetry.
The high tension of the cell surfaces will ensure the continuity
of the surface-membrane of each of the daughter cells. These
daughter cells adhere to one another but do not coalesce. From
this it is inferred that the cell membrane is insoluble in. the

ORGANO-GENESIS 385

surrounding medium and in the cytoplasm as well. (It has been
proved experimentally that hanging drops coalesce if their surface
films are soluble in the drops themselves, while they separate if
the film is soluble in the surrounding medium.)

After the second segmentation we have four cells each a
diminutive whole egg of identical composition and each capable
of developing into an embryo.

The third division brings about an unequal division of the
cell material. Three zones can be recognised in all the cells up
to this stage. These three zones, viz. (A) a clear cap at one
pole ; (B) a zone with a pigmented surface ; and (C) a large
unpigmented zone, each give rise to a definite part of the deve-
loped egg. Thus up to the third division every constituent of
the original egg is present in the segments in the original pro-
portions. The third division is equatorial and cleaves the cell-
mass unequally. Four cells are formed containing little or no A,
and the other four cells contain only a trace of C. These latter
form at the next division four very small cells called micromeres
mostly of A, and four larger pigmented cells (intestinal cells).
Eight large cells (ectodermal cells) are formed from material which
is mostly C, but contains some B.

The cell division proceeds and the tiny cells all gather at the
surface of the egg — surface adsorption. Soon after the tenth
division, when the number of cells is theoretically 1024, the
processes of invagination and differentiation begin.

Organo-genesis. Various parts of the egg give rise to various
organs. Always the same organ is formed from the same part.
This means that the apparently homogeneous protoplasm is
heterogeneous, i.e. contains colloidal matter in different parts of
maybe a specific chemical nature — certainly in a specific physical
state. One cannot as yet say why certain cells grow in certain
directions or why certain organs should be evolved from certain
cells and only from these cells, but certain mathematical and
physical phenomena have been observed in this connection.

If one postulates, in the first instance, the presence in the egg
of regions denser than others, for example, one can imagine as
a result unequal growth in various parts. Unequal growth sets
up strain ; and strain, as we saw in Chap. XVI., influences the
external form and internal structure of organs. This can be
demonstrated experimentally by building an artificial blastula of
little pellets of dough containing different quantities of yeast.
The unequal growth of the various pellets will set up mutual

]-.. n. 25

386 DEVELOPMENT

strains and produce a considerable folding and distortion of the
whole (Roux).

Both the circulatory systems and the alimentary c; ual- are
evolved from tubular structures, and it is suggestive to iind that
certain phenomena of development are mirrored in inorganic tubes.
For instance, a thin test-tube very often cracks in a spiral way.
The more homogeneous and isotropic be the glass the more even
and regular will be the spiral. That is, the crack tends to follow
the shortest course on the surface of the tube between the point of
origin of the crack and a point diametrically opposite — a ring
formation. Generally, however, the ring winds into a helicoid
form and is continued. This helicoid geodetic is shown in the
coil which stiffens the tracheal tubes of an insect and is apparent
in the growth of the intestine. Carey plotted the positions of the
cells showing mitosis in the intestinal epithelium at various levels.
He found that they formed a left-handed helix (5 per cent, right
handed) having its base towards the rectum and its apex towards
the ileocaecal valve. Further, the mitotic figures were few near
the base and increased in number as the apex was approached.
From this he inferred that growth was from below upwards and
followed a helicoid path.

One must consider that a definite mechanical action is due to
incidence of stress and that similar results under similar con-
ditions are good evidence of the imposition of similar forces. The
homogeneous hollow glass tube splits spirally, which can only be
interpreted as the spiral path being the line of least resistance in
a hollow cylinder. We can apply this with justice to the growth
of intestinal epithelium.

A growth tension applied helically must lead to torsion in a
structure like the intestine where there are layers of material
growing at different rates, and one could present a very plausible
diagram of forces to explain the twisting and looping of the gut.
Similarly and inversely, dilatation, e.g. stomach formation, would
produce alterations in the direction of the lines of growth leading
to alteration in the arrangement, say, of the muscular fibres.

Energy of Development.

Interesting observations have been made of the amount of
energy used by a developing organism. Tangl determined the
energy content of fresh laid eggs and compared that amount with
the energy value of the embryo and yolk found in the shell at
the moment of hatching. He reported that each gram of chick

ENERGY OF DEVELOPMENT 387

had been formed at the cost of the energy represented by 658
small calories.

Further, 35 per cent. (32 calories) of the total chemical energy
of the fresh egg is deposited in the tissues of the young embryo ;
48 per cent. (44 calories) is found to a large extent in the abdomen
of the chick as a store of potential energy to be drawn upon during
early life ; while the balance — 17 per cent. (16 calories) — has been
spent in the development of the chick. That is, about one- sixth
of the total energy of a hen's egg is required for the work of
elaboration of the tissues of the chick, which tissues contain one-
third of the original energy of the egg.

CHAPTER XXXVI
DEATH AND DISSOLUTION

"It is easy to show that these differences in temperature which are required
to secure organic liquids from ultimate change depend exclusively upon the
state of the liquids, their nature and above all upon the conditions which affect
their neutrality whether towards acids or bases." PASTEUR.

IT has been said that death is a necessary stage in the process
of development. Rubner considers that death takes place
naturally after the organism has utilised a certain amount of
energy per kilo. His second law, that of " length of life," is as
follows, " The amount of energy consumed in a kilogram of living
protoplasm from maturity to death is constant for all animals (and
equals 191,600 cals.), except in the case of man, who uses up four times
as much." Be that as it may, and no adequate proof of its truth
is offered, it does not serve as a guide to any reasonable physico-
chemical explanation of the process. An inorganic piece of
machinery will last an indefinite time provided it is kept in repair
and parts are renewed before they have become too much worn.
As long as suitable energy, etc., is supplied the machine will run.
The human machine, with its large repair staff always " on the
spot " and with plentiful supplies of material and energy, begins
to show signs of failure after 35 or 40 years of life. The curve
of growth, development and efficiency each shows a maximum
and then decline sets in.

Length of life is specific for each species and seems to be related
to the time taken by the animal to reach sexual maturity. With
that consummation, changes take place in the whole organism
leading, according to Loeb following Metchnikoff, to the (unavoid-
able) formation in the body of some toxin or, as more modern
work suggests, to the inhibition of the formation of an endocrine
secretion.

Death is followed by a more or less rapid dissolution of the body,
a process whose mechanism is more easily followed. The lack

388

FATTY DEGENERATION 389

of oxygen in the tissues leads, as we have seen, to the accumulation
of acids. This, after death of the organism, occurs in every tissue,
but it may also be demonstrated in cases where a particular
organ or region of the body is deprived of its quota of oxygen.
By the administration of certain drugs, e.g. anaesthetics, heavy
metals, phosphorus, potassium cyanide, oxidation processes are
inhibited and acids accumulate. The first visible change after
the inhibition of oxidation — general or local — is a " softening "
of the tissues concerned. If water is available the involved cells
swell and become cloudy accompanied or followed by a " yellow-
ing " and the appearance of fat globules. The cells then tend to
shrink and liquefy. These changes can be mimicked by the
addition of a trace of acid to an oil-in-protein emulsion. The
emulsifying colloidal proteins, under the influence of acid, develop
an increased capacity for the imbibition of water. If water is
available, the proteins swell and become extremely dilute and the
emulsion is broken. The " graying " or cloudiness is due to the
presence of colloids (globulins ?) which become less hydrated in
an acid solution. The hydration of the one class of colloids and
the dehydration of the other class leads to " cloudy swelling.''''

The breaking of the emulsion sets free the fat which is present,
though normally invisible, in all cells. The tissue becomes yellow,
and as the pathologists say, " fatty degeneration " has become
apparent. It must be understood that the fat made manifest
by this process existed previously in the cell masked by its associa-
tion with proteins, etc., in the emulsion. Its appearance at this
stage of dissolution is not due to the conversion of protein or any
other cell-constituent into fat as the name " fatty degeneration "
might suggest. Careful analysis has shown that the total amount
of fat in the cell has not increased.

As an emulsion has a much higher viscosity than its consti-
tuents, one might expect that the breaking of the emulsion would
lead to a decrease in viscosity or softening of the tissue concerned.
Further changes take place which make this loss of rigidity more
marked and cause the ultimate dissolution of the protoplasm.

Almost co-incident with the cessation of respirations, the endo-
enzymes begin to accelerate the processes of hydrolysis of the
tissues (p. 96). Under sterile and anaerobic conditions, the tissues
may be converted into an almost odourless fluid — a process termed
autolysis. Proteins are broken down to their constituent amino
acids and, if autolysis is carried on sufficiently long, some of these
acids may be destroyed. Instead of fat, autolysed tissue contains

390 DEATH AND DISSOLUTION

fatty acids and soaps. This self -digestion is a consequence of the
lack of free oxygen in the tissues, which lack, as we have seen,
causes the accumulation of acids. It has been shown that a very
slight increase in hydrogen ion concentration so alters the tissue
constituents that they are readily acted on by cellular enzymes.

In Chap. IX. we mentioned the interesting fact that the enzyme
which hydrolyses maltose builds up another carbohydrate,
isomaltose, which it is incapable of breaking down. In general,
when a synthesis is brought about by an enzyme, the product is
immune from being broken down by its builder. But, by the
hydrating effect of acid these synthetic products are converted
into isomeric forms which can be destroyed by the enzymes which
originally formed them.

In addition to autolysis, micro-organisms present in the intes-
tinal tract or otherwise entering the body from outside, play a
large part in the dissolution of the organism. Putrefaction is
readily distinguished from autolysis by the odour of the products
of its action.

Just as the material composing the body returns to the earth
to begin anew the cycle of life — passing from soil bacteria to
plant, from plant to animal and from lower to higher animal —
so the energy of the constituents of the body pass into the great
cistern of unavailable energy, " waste heat," from which we are
unable to draw supplies, but which by raising the level of the total
cosmical heat energy ever so slightly, contributes to the well-
being of all living things by raising, in imperceptible amounts,
it is true, the level of metabolism.

CHAPTER XXXVII
THE EFFICIENCY OF THE ORGANISM

By E. P. CATHCART, M.D., D.Sc., F.R.S., Gardiner Professor of Chemical
Physiology, University of Glasgow.

THE consideration of the efficiency (i.e. the relation of the
consumption of energy in the form of fuel to the output of
energy in the form of effective work) of man in the production
of external work is a question not merely of great physiological
but of economic importance, as this factor plays an important
role in the assessment of an adequate diet. Physiologically we
are concerned with the abstract problem of the conversion of food
energy into work — that is, the problem is simply the relation of
the increased energy output during the actual performance of
muscle work to the energy expenditure of a similar period when
no work is being done. In the case of industry, armies, etc., the
question is plain enough, but there are many factors both psychic
and physical which qualify the answer, in other words, the types
of work, the conditions under which it is performed and the
personal qualifications of the performer all play an important part
in the degree of efficiency with which the work is carried out.
Hence it is very essential that the " net or physiological " efficiency
be differentiated from the " gross, crude, or industrial " efficiency.
The "net" efficiency may be defined as the value obtained by
dividing the heat equivalent of the external effective muscular
work by the increase in energy output of the body developed as
the result of the work done. The "gross" efficiency, on the
other hand, is the value obtained as the result of dividing the heat
equivalent of the external effective muscular work by the total
energy output of the individual during the period in which the
work was done. The following table will make the point
clear :

391

392

EFFICIENCY OF THE ORGANISM

TABLE LXXVI.

Heat output per min.

Heat equivalent of
external muscular
work per min.
(425Kgm. = lCal.).

(d).

Efficiency.

Work,
(a).

No Work.
(6).

Increase of
work over no
work=«-&.
(c).

Gross.
d x 100

Net.
d* 100

a

e

Cals.

9-50
5-71

Cals.

3-09
1-14

Cals.
641

4-57

Cals.

1-96
1-06

Per cent.

20-6
18-6

Per cent.

30-6
23-2

It is obvious that the two efficiencies may give very different
values. The gross efficiency, which is largely influenced by the
amount of work performed during the day and the amount of
time which is actually expended in doing work, as a physiological
measure gives little or no information regarding the capacity of
the human body for work, and certainly no conception of the
possibilities in the way of the efficiency of the organism as a
machine. The net efficiency, which is determined by the deduc-
tion of the maintenance quota from the work quota of the energy
output, does give the actual increase in cost necessitated by the
performance of the external muscular work and thus permits of the
determination of the actual physiological efficiency of the organism.

In view of the fact that engineers and others have found it a
comparatively simple matter to determine the efficiency of
ordinary thermo-dynamic machines by the use of a simple formula
E =(Tl-T2)/T1, where T1 is the absolute temperature at the
source of the heat (the steam in the boiler in the case of an engine)
and T2 the temperature at the sink (the condenser ol the engine),
there has been a great temptation to apply the apparently almost
universal rule of the Second Law of Thermodynamics to the living
organism (Chap. IV.). It is, however, obvious from a very brief
consideration of the above simple thermodynamic formula that
the efficiency is simply a function of the difference of potential,
the higher the temperature at the source and the lower the tem-
perature at the sink the greater is the efficiency. Now the
efficiency of the living organism has experimentally been shown
to be high, probably over 30 per cent., a result which would
necessitate an impossible difference of potential in the tissues.
It is perfectly true that this difficulty has been appreciated, but
it is not solved, except on paper, by positing minute points of
enormously high temperature alternating with points of low
temperature at intervals of a few /a. (10 ~3 mm.). The mechanism

ASSESSMENT OF EFFICIENCY

393

of muscular activity, it is true, is not yet clear, but it may be
stated with a considerable degree of certainty that, whatever the
type of change which takes place, all the experimental evidence
available points to the muscle not being a heat engine. The
majority of workers now look upon muscle as a chemical machine
which works at a relatively constant temperature."

On the purely experimental side much work has been done on
the determination of the efficiency both of isolated muscle and of
the body as a whole.

If the organism be considered as a whole and its efficiency
determined, it is found that, although it is high, it is never as
high as the results which have been obtained experimentally with
isolated muscle. This result is not to be wondered at when the
methods of attacking the problem are considered. In the case of
the isolated muscle, its position, the amount of work to be done
and the mode and time of stimulation can all be accurately
controlled, conditions which are, for the most part, lacking when
the whole organism has to be dealt with.

Modern work has shown very considerable agreement as regards
the degree of efficiency, as is shown by the following table :

TABLE LXXVII.

GROSS AND NET EFFICIENCY OF THE BODY AS A WHOLE.

Efficiency.

Gross.

Net.

Katzenstein (1891)

13-19%

254%

Sonden and Tigerstedt (1895)

17-3

274

Zuntz (1909) -

• —

28-0

Benedict and Carpenter (1909)

15-0

20-6

Amar (1910)

— •

32-5

Benedict and Cathcart (1913)

—

21-33

Lindhard (1915)

—

25-0

Douglas (1920)

• — •

23-26

The outstanding difficulty in the assessment of the net efficiency
is the selection of the proper base line for comparison. It is
immaterial whether the work done be that of marching or mountain
climbing, of turning an ergostat or a bicycle ergometer, the same
difficulty crops up. As the bicycle ergometer has been most fre-
quently used in the modern experiments it will be dealt with here.

In the determination of the mechanical efficiency with this
machine no less than five base lines may be used though they are

394 EFFICIENCY OF THE ORGANISM

not all of equal value. In this type of ergometer, where the work
to be done can be readily altered by increasing the resistance to
be overcome, it is a comparatively simple matter to devise a
wide range of experiments in which the effective muscular work
can be varied. The only difficulty lies in the selection of the base
line. If the work standard be taken as that of the subject sitting
on the bicycle performing a definite measured amount of work,
in order to find the increased cost in energy caused by the per-
formance of this work there may be subtracted :

(1) The energy expenditure during complete rest— the ordinary
basal or standard metabolism.

(2) The energy output when the subject is sitting at rest in
the saddle.

(3) The energy expended when the subject is sitting on the
saddle, feet on pedals and his legs are rotated by mechanical
means — internal or organic work.

(4) The energy expenditure when the subject is freewheeling,
i.e. overcoming the ordinary resistance of the unloaded wheel
with most or all of the concomitants of work, of this type, sitting
posture, internal friction of the legs, extraneous movements asso-
ciated with cycle riding, etc.

(5) The energy expenditure involved in (a) the performance of
light work compared with that of hard work or (b) the increased
cost of work done at slow and high speeds using the same load
in each case.

When these various base lines are utilised experimentally it is
found that there is a steady increase in the degree of efficiency.
The average results are as follows :

TABLE LXXVIII.

Base line.

Net efficiency.
Average value.

(1) At rest

21%

(2) Sitting

similar to (1)

(3) Internal friction

27%

(4) Free wheel

30%

(5) Low to high speed

30-33%

There is then a variation in the determined efficiency of approxi-
mately 10 per cent., and it is a moot question which base line
should be selected. Lindhard maintains that the most reliable
result is obtained when complete rest or rest in the riding position
is adopted as base line, but there is much to be said in favour of

FACTORS INFLUENCING EFFICIENCY 395

the adoption of other base lines in which movements which play
little or no part in the determination of the efficiency are elimi-
nated. As the main object is to determine the efficiency of the
body performing a definite act it has been suggested that the best
result will be obtained when the various activities associated with
the determination of the energy output both of the base line and
of work are more or less comparable, that is, where the extraneous
muscular motions incidental to riding with weight are common
to both determinations. Such a comparison is that obtained
when there is a change from a moderate to a heavy load. As
will be noted from the above summary of efficiencies the average
efficiency under these conditions is about 30 per cent.

There is a certain amount of evidence available which would
suggest that the degree of efficiency obtained varies with the
groups of muscles used in performing the work. The efficiency
of muscles less commonly in use than the leg muscles is some-
what lower, flexor groups may differ from extensor groups, etc.
The state of training, too, probably influences, although apparently
not very markedly, the degree of efficiency. And finally, some
workers maintain that the efficiency may also be, to some extent,
dependent on the nature of the diet. Macdonald maintains that
the efficiency of muscular work is a function of body mass.

Greenwood, who has carefully analysed the data obtained by
many of the workers, has come to the conclusion that although
as yet no law can be formulated connecting heat production
and work performance, within fairly wide ranges, simple formulae
of linear regression do describe the relations subsisting between
heat production, body mass and work performance, with an
accuracy sufficient for such purposes as roughly computing the
energetic needs of workers doing the kind of work studied.

In addition to the above-mentioned factors which influence
efficiency there are certain others connected with the performance
of the work itself which apparently play a determining part.
These are load and speed.

Although it might be presumed that load would exercise a
marked influence, such experimental work as exists tends to show
that increase of load within limits does not materially influence
the efficiency of the body. There is, however, a slight tendency
for the work to be done more efficiently when the load is changed
from a moderately heavy to a heavier one than when the change
is from a light to a heavy load.

The influence of speed, that is the rate at which the work is

396

EFFICIENCY OF THE ORGANISM

done in unit time, is of much greater moment. Experimentally
it has been found that the total energy expenditure per revolution
of the pedals is constant for all speeds, but that although there is
naturally an increase in the amount of the total work done, the
effective muscular work per revolution decreases as the speed

1

/

t

1

1

1

1

I

/

I

/

4"

\

1 •

d

1

A

LA

/>•

1

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* 70 80 90 ISO 110 13) UO 1

Fia. 73.

increases, and there is therefore a steady fall in efficiency (see Fig.
73). The same result is obtained when the speed is varied, with,
however, approximately the same production of effective muscular
work in the two experiments, as shown in Table LXXIX. :

TABLE LXXIX.

Revs, per min.

Heat equivalent of
external muscular work
per min. in Cals.

Net efficiency.*

90
124

1-94
1-96

22-6%
•15-7

80

1-77

22-1

105

1-83

17-7

71

1-57

24-5

108

1-58

15-6

71

1-34

23-1

94

1-29

20-4

105

1-35

17-0

72

T20

21-5

88

1-26

19-5

* Base line — complete rest, lying.

EFFICIENCY OF ISOLATED MUSCLE 397

As regards the work which has been carried out on isolated
muscle, the results which have been obtained are of great interest,
as they have led to fresh consideration of the nature of the
muscular machine. A. V. Hill, in a long series of ingenious and
striking experiments, using special methods of his own devising,
has shown that the solution of the problem is not quite so simple
as it was formerly imagined. Hill found the simple determination
of the mechanical efficiency, i.e. W/H, the heat equivalent of the
work done, divided by the energy output determined as heat,
was of no real importance. The true efficiency of the muscle is
the ratio between the " potential energy thrown into an active
muscle by excitation " and the " total chemical energy liberated
as heat." He found further, that the heat production varied
according to whether the muscle was, or was not, allowed to
shorten on stimulation. If shortening were permitted the heat
output might be 30 per cent, smaller than if the muscle was
prevented from shortening. On examination of the potential
energy developed by a stimulated muscle not allowed to shorten,
it was found to be approximately 1/6 Tl, where T =the maximum
tension and I =the length of the muscle. Hill maintains that the
true mechanical efficiency can be determined by comparing this
quantity with the heat production. This value 1/6 Tl when
expressed in heat units is 10~4/4-26 calories. (See Table LXXX.)
He found efficiencies approximating 90 per cent, in the initial
phases of contraction, and if the whole process, i.e. initial and
recovery phases taken together, were assessed, the efficiency,
under the conditions of his experiments, was in round figures
50 per cent.

TABLE LXXX.

EXPT. — Length of muscles, 3-3 cm. ; weight of muscles, 0-135 gin. ;

1 scale division of deflection = 8-32 x 10~6 cal. Sartorius and isometric

contractions.

Duration of excitation : sees. - 0-075 0-075 0-075

Initial tension : grm. wt. - 10-5 10-5 10-5

Heat production H : cal. x 10~6 - 574 740 757

Tension T : grms. wt 44-8 47 47

Tl/QH - - 1-01 0-82 0-80

Incidentally he found that different types of muscle (e.g. semi-
membranosous and sartorius) definitely differed in efficiency. He
also found that the maximum efficiency was only obtained under
very special conditions of initial tension, strength of stimulus and
the physiological state of the muscle.

PART II

ILLUSTRATIVE EXPERIMENTS

1. Gaseous Diffusion. Experiment on page 40. Try this first with
coal-gas and then with C02. Soak the porous pot in water and com-
pare the rate of diffusion inwards of carbon-dioxide with the outwards
diffusion of air. What part does solubility play in diffusion through a
membrane ?

2. Osmotic Pressure of Crystalloids. Preparation of a Semipermeable
Membrane. Take a clean porous pot such as is sold for Leclanche units.
Allow it to soak for a day in distilled water. Fill it with a 0-25 per cent,
solution of copper sulphate and immerse it in a 0-21 per cent, solution of
potassium ferrocyanide for a day or two. Wash thoroughly in distilled
water. The copper sulphate and potassium ferrocyanide meet in the porous
pot and a membrane of copper ferrocyanide is there formed (see Expt. 6).
The prepared pot may keep for years and be used many times.

A rubber stopper with two holes should be permanently fixed in its
mouth with wax. Through one hole should be passed a long glass tube
or a U-shaped glass manometer. The other hole carries a tap funnel for
filling the pot. The solution to be tested should be coloured with methylene
blue or other dye which is easily seen.

(1) What happens after 24 hours or so when a sugar solution is placed
in the pot and the pot immersed in water ?

(2) Now add sugar to the fluid outside the pot till its concentration is
the same as that inside the pot and leave for the same period as before.

(3) Increase the concentration of sugar outside and note the effect
on the level of fluid in the manometer.

3. Blood Corpuscles. (1) Take three test tubes and place in one about
5 c.c. of water and in another a similar amount of 0-9 per cent, sodium
chloride, and in the third 2 per cent, sodium chloride. Prick the finger
with a sterile needle and add the same number of drops of blood to each
tube. Shake and examine the tubes (a) as to opacity and (b) as to depth
of colour. Take a drop of the fluid from each and examine under the
microscope. Measure the diameter of a number of corpuscles and average
those from each tube.

(2) Add a drop of fresh blood to a drop of 0-5 per cent, sodium chloride
solution on a microscope slide. Place a card on the side of the microscope
stage and keeping both eyes open trace the projection of a corpuscle from
time to time or measure the diameter.

(See also Haematocrite, Expt. 47.)

398

OSMOTIC PRESSURE 399

4. Turgor (see Expt. 19, ii. for precautions). Take a length of sausage
skin parchment. Close one end tightly round a glass stopper. Fill with
treacle or a strong solution of sugar and then similarly close the other end.
Suspend horizontally in water from a loop round the middle. The ends,
which droop at first, giving the whole the appearance of an arch, soon begin
to assume a horizontal position. In a day or so the sausage skin will be
rigid and straight.

5. Chemical Gardens. (1) Place 50c.c. of potassium ferrocyanide in a
glass jar or beaker and add a small particle of ferric chloride (small pea).
A semipermeable membrance of ferric ferrocyanide (Prussian blue) is
formed round the solid. Endosmosis occurs and peculiar growths may be
formed.

(2) Add a drop of almost saturated potassium ferrocyanide from the
end of a glass rod to a solution of copper sulphate (bench reagent). A
semipermeable membrane of copper ferrocyanide is formed round the
drop and endosmosis takes place. This causes an increase in the concen-
tration of the copper sulphate immediately round the drop, and blue
" rootlets " may be seen descending from the drop. These are due to the
increased density of the sulphate.

(3) Leduc's Growths. A small flat-sided jar, e.g. a specimen jar, is filled
with a 1-2 per cent, solution of gelatine to which is added just enough
potassium ferrocyanide to give it a pale green colour. Just before the
gelatine has set, a little seed made from a mixture of glucose and copper
sulphate is planted on the bottom of the jar. Within an hour, growth will
be visible and may proceed for several days.

See Leduc, Etudes de Biophysique. I. Theorie Physico-Chimique de la
Vie (1910) ; II. La Biologic Synthetique (1912).

6. Electric Endosmose. (a) The passage of water through a membrane
by electrical means may be observed in the preparation of a semipermeable
copper ferrocyanide membrane when the solutions are forced into the pores
of the earthenware pot by an electrical current (Expt. 2).

(b) A clean porous pot, fitted with a manometer and a non-polarisable
electrode, is filled with and placed in a solution of K2S04 (0-05 per cent.).
A current of 2-4 volts is passed so that the electrode inside the pot is
cathode. Note the rise in level of the fluid inside the pot. Note also the
increase in the alkalinity of the fluid outside the pot.

(c) Make a collodion test tube to fit one limb of the U-tube
(Fig. 9).

(1) Fill both limbs with dilute K2S04 solution. Mark the level of the
fluid in both limbs and, using non-polarisable electrodes, pass a current of
4 volts for some time through the solution. Note that water passes towards
the cathode and that the cathodal fluid becomes acid.

(2) Repeat, using tartaric acid in the collodion sac and pure water
outside. Test for tartaric acid.

(3) Fill the sac with gelatine sol and leave overnight. Wash out the
sol and repeat the expts.

7. Determination of the Freezing Point of Urine. Principle. The freezing
point of water is depressed by the addition of salts which go into true
solution. The magnitude of the depression termed A bears a relation to
the molecular concentration of the solutes and therefore to their osmotic
pressure.

400

ILLUSTRATIVE EXPERIMENTS

Apparatus. Beckmann's (Fig. 74). It consists of a specially devised
test tube A with a side neck. Through the rubber stopper, closing the
main neck of this, pass a thermometer D and a short glass tubular
guide for a stirrer. The freezing point tube
is supported in the neck of a large test tube
B, by means of a cork or asbestos ring so
that the freezing-point tube is protected from
incoming heat by a mantle of still air. This
ensures that the cooling of the liquid in the
freezing-point tube is slow and fairly uniform.
The whole apparatus is inserted through a hole
in the middle of a brass sheet, to which it is
fixed by a ring of cork or of asbestos. The
sheet of brass acts as a lid to a glass jar C which
contains powdered ice and salt — the cooling
bath. Other holes in the lid permit of the
passage of a stirrer, a thermometer, and a test
tube containing pure water.

The Beckmann Thermometer. The thermo-
meter in the freezing point tube must be
graduated to, at least, hundredths of a degree.
Such a thermometer, if made in the ordinary
way, unless it were inconveniently long, would
have a very short range. To obviate the
necessity of having a series of thermometers
for use over various ranges of temperature,
Beckmann designed one which may be set to
indicate temperatures over any desired range.
This result is produced by a device permitting
of alterations being made in the amount of
mercury in the bulb. At the upper end of the
thermometer there is a small reservoir into
which the excess of .mercury may be driven, or
from which a larger supply of mercury may be
obtained.

Setting the Beckmann Thermometer. Hang
the thermometer in a beaker of water, the
temperature of which is 2-3 degrees higher than
the highest temperature to be met with in the
experiment and see whether or not the top of
the mercury comes within the scale.
A. If there is too much mercury in the bulb and the column rises beyond
the graduated part, the excess is removed by warming the mercury in the
bulb till the column of mercury unites with the mercury in the reservoir.
This is done, (a) by placing the bulb in water just a little warmer than
before. (6) When the mercury passes to the top of the capillary tube and
forms a small drop there, the thermometer should be carefully inverted
and tapped gently so as to cause the mercury in the reservoir to coalesce
with the mercury in the top of the capillary, (c) The thermometer is
returned to the upright position by a gentle steady movement and its
upper end is struck a sharp tap against the palm of the hand, causing

Fia. 74. — Freezing Point
Apparatus.

DETERMINATION OF FREEZING-POINT 401

the excess of mercury to break off from the end of the capillary. The
thermometer is again tested in the first bath.

B. If, on the other hand, the amount of mercury in the bulb is so small
that the top of the column does not rise to the bottom of the scale, more
mercury will have to be drawn from the reservoir. The procedure is similar
to that outlined above, but at (c) the thermometer is replaced in the first
bath before breaking the mercury column. That is, the mercury in the
bulb is allowed to contract and draw in more mercury from the reservoir
before the connection between column and reservoir is broken by tapping.

These operations are repeated till the proper level of mercury has been
attained. This is always tested by placing the thermometer in baths having
temperatures equal to the highest and lowest to be encountered in the experiment,
and noting that the top of the column of mercury remains on the scale.

Method. (1) Set up the apparatus completely so as to ensure all parts
fitting properly. See that the stirrer in the inner tube is working smoothly
and does not strike against the bulb of the thermometer.

(2) Remove the thermometer and stirrer from the tube. Clean and
dry the latter.

(3) Pipette in 25 c.c. of urine.

(4) Set the Beckmann thermometer so that, at 0° C., the mercury stands
not lower than the middle of the scale.

(5) Dry the thermometer and insert it along with the stirrer in the
freezing-point tube, so that the bulb of the thermometer is completely
immersed in the urine.

(6) Fill the outer cooling vessel with water, ice and salt. The freezing
point of urine can now be determined.

(7) First make an approximate determination by placing the freezing-
point tube directly in the cooling bath so that a rapid fall of temperature
occurs.

(8) As soon as the urine shows signs of freezing remove the tube from the
freezing mixture, dry it quickly and place it in the air jacket in the cooling
bath.

(9) Stir slowly and read the temperature when it becomes constant.

(10) Withdraw the tube and melt the ice by warming with the hand,
trying to avoid raising the temperature more than 1° C.

(11) Rapidly dry the tube and reinsert it in the air jacket and repeat the
freezing process, stirring slowly all the time.

(12) When the temperature has fallen to from 0-2° to 0-5° below the
approximate freezing point found in (9) stir more vigorously. This
generally is sufficient to induce solidification to commence and the tempera-
ture will now begin to rise.

(13) If so, stir slowly and take readings of the temperature every few
seconds — tapping the thermometer each time before reading. Note the
highest temperature reached.

(14) Again melt and repeat the determination. At least three deter-
minations of the freezing point should be made, the mean being taken.
The deviations of the chosen readings from the mean should be less than
0-002° C.

(15) The depression of the freezing point or, in this case, the thermo-
metric readings may be converted into osmotic pressure in metres of water
by multiplying by the factor 122-7.

B.B. 26

402 ILLUSTRATIVE EXPERIMENTS

Thus suppose that the A observed is -2-3°, the osmotic pressure of
this sample of urine would be 2-3 x 122-7 = 282-2 metres of water = 282-2/13-6
= 20-7 mm. of mercury.

Precautions, (a) The temperature of the cooling bath must not be
too low. It should not exceed 3° below the freezing point of the liquid.

(/3) Excessive supercooling should be avoided. It should not be greater
than half a degree.

(7) Stirring should not be too rapid — say 1 up-and-down movement
per second, and it should be as uniform as possible.

(8) If the liquid shows a tendency to give up heat without freezing and
that even vigorous stirring does not initiate solidification, the introduction
of a small crystal of ice through the side tube generally suffices to start
solidification.

8. Osmotic Pressure by Burger's Method (Fig. 75). Trans. Chem. Soc.
85, p. 286. Prepare a number of capillary tubes by drawing out soft glass
tubing of | inch bore into capillaries 1-2 feet long. These should be cut
into smaller pieces, having a smooth regular edge, in order that the tube
may be closed tightly with the finger while it is being filled. The internal
diameter of the capillaries should be between 1 and 2 mm., preferably
about 1-5 mm.

The filling of the tubes requires a little practice. The tube is taken
between the middle finger and thumb, and its upper end, which should be
rounded, is closed with the index finger. The other end is then dipped
below the surface of solution A. By lifting the index finger very slightly
enough liquid is admitted into the tube to make a column of about 5 mm.
long. The finger is replaced on the end of the tube, which is then lifted
from the fluid and inverted so that the open end is uppermost. It is held

/ 2 3 4 S 6 7 8 9

Fia. 75. — Barger's Method for determining Molecular Concentration.

Upper figure,'actual size. Lower figure, as seen under the microscope ; micrometer
scale in eyepiece. M

in a slanting position, and, by diminishing the pressure of the index finger
on the lower end, the globule of liquid is allowed to slide down the tube,
its progress being regulated by the slant of the tube. The process is repeated,
using solution B and so on, using solution A and B alternately and finishing
with A. When all the drops are in, the collection is moved so that the last

SURFACE TENSION 403

drop is about 1 cm. from the open end of the tube and this end is sealed
in a small bunsen flame. The other end of the tube may then be similarly
sealed. The upper diagram, in Fig. 75, shows the appearance (actual size)
of a filled and sealed tube. The dark drops are A. The first and last
drops, 1 and 9, are large and are not taken into account. The drops are
numbered in the order in which they were pub into the tube, i.e. the open
end of the tube is to the right of the diagram. The tubes are cemented
to a microscope slide and a coverslip fixed with Canada balsam. The
slide is placed in a Petri dish with enough water to cover the tubes.
(Constant temperature.) Under the microscope the tubes present an
appearance like that shown in Fig. 75. lower diagram. With an eyepiece
micrometer, measure the drops. After an interval whose length depends
on the solvent, the drops are remeasured.

In what direction, if any, does the alteration in size take place ? That
is, do the drops of B become larger or smaller ? If B drops increase in
size it shows that the vapour pressure of B is less than that of A, and,
consequently, the osmotic pressure of B is greater than that of A, and
vice versa. A = 2-5 per cent, glucose in water, B = 2-5 per cent. NaCl in
water. Time about 20 hours.

9. Camel-hair Brush Expts. Many illuminating experiments may be
made with a small camel-hair paint pencil. Under water the hairs diverge,
but when the surface tension of the water-hair surface is increased,
e.g. by removing the brush from the water, the hairs form a compact pencil.

10. Boy's Leather Sucker (p. 303). To show that surface tension is the
causative factor suspend a microscope slide horizontally in the receiver of
an air pump. By means of a drop of water between, cause a second slide
to adhere to the lower surface of the first slide in such a way that the second
slide may be loaded. Load with the maximum weight and exhaust the
receiver. Repeat the expt. under various conditions, e.g. trace of oil,
ester, bile salts, etc.

11. Work done by altering Surface Tension. In performing the experi-
ment mentioned in p. 137 (Fig. 24), it is necessary to have a good soap
solution. It may be made as follows from pure sodium oleate and glycerol.
To 500 c.c. of distilled water in a stoppered bottle of 1 litre capacity, add
200 c.c. of pure glycerol, shake and allow to stand in the dark for a week.
Siphon off the clear underlying fluid and add four drops of concentrated
ammonia. Keep well stoppered and away from light.

12. Experiments with Soap Bubbles. Make a film on the wide end of a
conical tube (filter funnel), closing the other end with the finger. What
happens when the finger is removed ? Where does the film come to rest
and why ?

13. Camphor " Water-beetle." Prepare a rectangular piece of camphor.
To one short side affix a short piece of stick and place the whole thing on
the surface of water in a large dish. How do you explain the direction of
the movements ? Remove the stick and replace the camphor in the water.

14. Camphor-Benzene " Amoeba." (Brailsford Robertson.) The amoeba
is made of a saturated solution of camphor in benzene to which a dye
(e.g. carmine) has been added to make the solution easily visible when
placed in water. Place a drop of the solution on the surface of clean water
in a clean Petri dish. The movements may be slowed down by the addition
of the faintest trace of oil. Generally the first " amoeba " disintegrates

404 ILLUSTRATIVE EXPERIMENTS

rapidly. Do not throw out the fluid in the dish, but add another drop of
the camphor solution. What effect has increase or decrease in temperature
on the movements ? What happens when a solid particle is suspended in
the water near the " amoeba ." ? What is the effect of putting two separate
drops on the surface of the water at the same time, (a) when the drops are
equal in size, (6) when they are unequal in size ? What is the effect of the
addition of a trace of fat, obtained, for example, by touching the surface
of the water with a glass rod which has been rubbed on the side of the nose ?

15. Mercury " Amoeba." Place a small globule of mercury in a large
Petri dish and cover it with potassium bichromate (sat. solution) to which
has been added some nitric acid (bench reagent). How do you explain
the movements ?

16. Electrical Alteration of Surface Tension. Carry out the experiment
detailed on p. 48. Place a small globule of mercury on an iron or enamelled
plate and cover with water. Note shape of globule. Add sulphuric acid
(bench reagent) drop by drop (to make about a 10 per cent, solution).
What happens to the globule ? Explain. Connect the plate and globule
to a single cell of a battery through a commutator. First pass the current
through the globule to the plate and note alterations in shape, then reverse
the commutator.

17. Ostwald's Physical " Heart." (Verworn's Physiologisches PraJc-
tikum.) The method of carrying out this demonstration of electrical
alterations in surface tension is indicated in the diagram (Fig. 76). A
globule of mercury about an inch in diameter is placed in a clock glass
almost rilled with 10-15 per cent, sulphuric acid. Potassium bichromate

.CORK.

SEWING NEEDLE

.-WATCH GLASS

GLOBULE Of I

FIG. 76.— Mercury " Heart."

solution (say N/10), is added drop by drop till the fluid becomes a light
yellow in colour. A clean sewing needle thrust through a cork is placed
in a diagonal position so that the point of the needle just touches the margin
of the mercury globule. At the moment of contact the globule becomes
more spherical. This breaks its contact with the needle and it loses its
semispherical form and so again makes contact. These rhythmic pulsa-
tions may go on for hours. When the action has stopped remove the
needle and note the odour of acetylene. How do you account for this ?
What is the reason for adding bichromate ?

18. The Capillary Electrometer. This instrument for measuring differ-
ences of electric potential depends for its action upon the alteration of surface
tension between mercury and sulphuric acid with alterations of the potential
difference of the interface (see p. 48, and Expts. 16 and 17). For class use
the simplest satisfactory form is that made by the Harvard Apparatus Co.
It consists of a capillary tube containing mercury which is continuous with
a reservoir in the form of a plunger pump. The position of the mercury
in the capillary may be altered by adjusting the plunger by means of a
micro-screw. The glass capillary dips into a small test tube containing
dilute sulphuric acid and a drop of mercury to make good contact with the

CAPILLARY ELECTROMETER 405

platinum wire sealed through the bottom of the tube. This platinum wire
and the one coming from the mercury in the capillary are short-circuited
through a spring key. The whole instrument is placed on a microscope
stage set vertically.

Details, (a) Mercury. Pure dry mercury must be used. To clean
mercury : shake for 10-20 minutes with a solution of mercurous nitrate
acidified with nitric acid. Wash thoroughly with distilled water and dry
with filter paper.

(6) Sulphuric acid. The pure (boiled) acid in six times its volume of
distilled water is skaken up with a little pure mercury and is best kept, in
contact with some mercury.

(c) The glass parts must be free from grease and the rubber connections
from French chalk.

Filling and Setting the Electrometer. Fill the pump-reservoir with
mercury, allowing free access to the capillary. Before inserting the plunger,
cover the mercury surface with a film of thin oil (balance oil). The
insertion of the plunger will cause mercury to be forced through the
capillary. Fix the capillary in position in the test tube, which should be
half full of acid. A slight turn of the plunger screw will force a little
mercury into the test tube to cover the platinum contact. Adjust by means
of the plunger screw till the Hg-H2S04 interface lies in the middle of the
microscopic field. The definition of the mercury meniscus may be im-
proved by cementing a cover glass to the test tube with Canada balsam.
An eyepiece micrometer provides a scale whereby the movements of the
mercury may be measured. (1) Connect the terminals by non-polarisable
electrodes, one to the cut and the other to the uncut surface of a muscle.
Depress the short-circuiting key and so bring the electrometer into circuit
with the muscle E.M.F. Note the movement of the mercury. (2) Similarly
attempt to demonstrate the diphasic electrical variation in the beating
heart (frog). (3) Take off leads (salt solution) from the human heart (arms,
see p. 296). (4) If the electrometer is used to find the point of balanced
E.M.F. on a Wheatstone bridge (Expt. 39), it is essential to arrange that
the direction of the positive current is such that the capillary mercury is
the cathode, otherwise mercurous sulphate might be formed in the
capillary tube on account of the passage of a rather large current. For the
same reason, the short-circuiting key should only be opened for as brief periods
as possible.

Fine instruments may be purchased filled, adjusted and sealed ready
for use. They are of a somewhat different type, and while of value for fine
measurements in the hands of a careful worker, are unsuited for class
work.

The current of injury, etc., of muscle (pp. 134 and 143) is usually measured
by compensation. A cell of constant known E.M.F. is put in the same circuit
as the tissue giving rise to the current but sending its current in the opposite
direction (Fig. 78 and Expt. 45). By moving the jockey along the slide
wire (/2j-JR2) till the E.M.F. from the cell exactly balances the demarcation
current, i.e. till the meniscus at the mercury-acid interface becomes steady,
one may determine what relationship the constant E.M.F. bears to the
muscle E.M.F. Non-polarisable electrodes must be used.

19. Preparation of Membranes. I. Collodion membranes are easily
made in any size or shape, and, as they are transparent, are very convenient

406 ILLUSTRATIVE EXPERIMENTS

for general use. They are, as ordinarily prepared, unsatisfactory for the
dialysis of whole blood or of bile.

Cellulose nitrate (gun-cotton or pyroxylin) is generally sold damped with
alcohol and, for very accurate work, should be dried before weighing. For
the following experiments this refinement is unnecessary.

Acetic Acid Collodion. Four grams of commercial gun-cotton are placed
in a wide-mouthed glass-stoppered bottle of 200 c.c. capacity ; 100 c.c.
glacial acetic acid are added. The mixture is shaken gently until the gun-
cotton has dissolved, leaving no residue. The resulting sol is transparent
and will keep for weeks.

Alcohol-Ether Collodion. (Bigelow and Gemberling.) 75 c.c. of ethyl
ether are poured on 3 gms. of gun-cotton in a wide-mouthed stoppered
bottle as above. After 10 to 15 minutes, 25 c.c. of ethyl alcohol are added
and the mixture agitated until a clear solution is obtained.

Either of these collodion solutions (after standing till free from bubbles)
may be used in the preparation of membranes.

(i) To cover a vessel similar to a Graham dialyser. Cleanse a piece of
plate glass thoroughly and polish it. Pour sufficient collodion sol on the
centre of the plate to give a large enough membrane. Avoid bubbles. By
tilting the plate, spread the sol evenly over the surface of the plate and,
if necessary, drain off any excess into the stock bottle, taking care to avoid
any unevenness in the distribution of the collodion. The diameter of the
sheet should be fully 2 inches larger than that of the dialysing glass. If an
acetate sol has been used, immediately plunge the glass and adherent gel
into cold water and leave it immersed for about half-an-hour to convert
the acetate gel into a hydrogel. After the minimum time of immersion
has elapsed, the collodion film may be readily detached from the glass,
placed centrally over the rim of a dialysing cup, and fixed in place by a
broad rubber band. The dialyser should now be tested for leaks by filling
it with water and observing that no fluid escapes round the junction. The
film must be kept moist or it will shrink and rupture.

The ether-alcohol gel is not placed in water at once like the above, but
is allowed to dry in air or in alcohol vapour for a period depending on the
permeability required. If a very permeable diaphragm is required, a glass
trough is inverted over the film so as to prolong the period of gelation.
Although the degree of drying is the crucial point of the whole process, no
definite rules can be laid down. Each " make " of collodion requires
treatment on its own merits and experience alone will tell when the film
is ready. If the sol has been made as directed, it should be dry enough
when it does not stick to the finger when touched lightly. The edges can
be loosened with a spatula or paper knife and the whole film slowly lifted
from the glass. When about three-fourths of the sheet has been raised
vertically from the plate the rim of the dialysing cylinder is placed below
it so that the edge of the rim comes in contact with the collodion surface
which has been next the glass plate, i.e. with the surface which has been
dried least. The edges of the membrane are carefully turned down over
the sides of the cup and will adhere quite firmly. If desired, a broad
rubber band may be placed round the rim to ensure tightness. Test, as
above, for leaks and leave immersed in water for 10-15 minutes to allow
the alcohol to be replaced by water.

(ii) To make a collodion sac. A small Erlenmeyer flask, clean and dry,

MEMBRANES 407

is filled with collodion sol, care being taken to pour the fluid slowly down
the side so as not to form air-bubbles. The sol is now poured back into the
stock. This should be done slowly and steadily with a constant rotatory
motion of the flask, leaving a thin film adherent to the glass. If this
operation is carried out too quickly, the layer of collodion at the bottom
of the flask will be too thin. It is convenient to allow a little collodion to
overflow all round the outside of the neck of the flask to enable one to get
a good grip in pulling out the film afterwards. The flask (acetate sols are
at this stage submersed in water) is inverted over the mouth. of a bottle
containing a little alcohol (or empty, see above), and allowed to dry as
before. When dry, the flask is filled with water or, better still, immersed
in water and allowed to stand for at least 15 minutes. The collodion sac
is loosened at the neck and carefully withdrawn. This is a slow process
and must not be hurried or grave risk will be run of tearing the thin film.
It is quite a good thing to remove the film in stages, letting it soak in water
between times. The complete bag is usually fitted with a glass mouth —
a piece of glass tubing of suitable size inserted in the neck and affixed
thereto by broad rubber bands, or by wrapping in oiled silk, gutta-percha
tissue, etc., and winding thin string over this, or by causing it to adhere
with a little fresh collodion.

(iii) To make collodion test tubes, (a) Collodion tubes may be formed
inside test tubes or boiling tubes in the same manner as has been described
for sacs.

(6) Sometimes it is desirable to make a dialysing tube which will fit on
the outside of a specified tube. A test tube of the required width is taken
and a small hole blown in the end. This hole is covered with a thin film
of collodion which is allowed to dry. The whole tube is then dipped in the
collodion solution. The excess collodion is allowed to drip into stock, the
test tube being held bottom upwards at an angle of less than 45° and
rotated steadily. The film is treated with water, or after drying as above,
depending on the nature of the solution. After soaking in water, the test
tube is filled with water and the film gently worked off like a tight glove.
It is eased a little at the bottom, water meanwhile passing into the collodion
tube through the hole in the test tube. Little by little a fine film of moisture
will creep up between film and glass and the transparent collodion tube
will slip off easily. This method yields tubes which are more uniform in
thickness and permeability than the former.

(iv) Thimbles. Strong dialysing vessels may be made by impregnating
Soxhlet extraction thimbles with collodion. The thimble, soaked in
alcohol, is immersed in alcohol-ether collodion, withdrawn, allowed to drip
and partially dried, and then the process of impregnation is repeated. It
is advisable to fix a short glass tube into the mouth of the thimble before
impregnation and to use a fairly thin collodion solution.

II. Parchment Paper is sold for this purpose in sheets, or made up in
long tubes (sausage skins) or in thimbles. When dry the paper becomes
very brittle, so that great care has to be observed in its storage to prevent
creases, etc.

(i) Sheet. Select a piece of the paper free from obvious defects (pin-
holes, etc.) and fully two inches larger in each direction than is required.
Soak in water till soft and pliable. Place it centrally over a dialysing glass
as is described above for collodion sheets. The folding of the free edges

408 ILLUSTRATIVE EXPERIMENTS

requires some care to ensure even lying against the side of the glass. Tie
with thin string. Test for leaks.

The sheet may be made into a bag as follows : " Cut a regular hexagon
and soak it thoroughly in water. Then place it centrally on the bottom
of an inverted beaker or jar, the diameter of which is about one-third of
that of the inscribed circle of the hexagon. Gently pinch radial folds
from the circumference of the beaker to the corners of the hexagon and
mould them so that the paper midway between the corners touches the
wall of the beaker, and then turn the folded portions over and smooth them
into cylindrical shape. The folds must not be sharp, as even wet parch-
ment may be damaged by too drastic treatment. When the bag has been
moulded as described, a string is loosely tied around it, or a fairly slack
rubber band slipped over it within about 2 inches of the edge, and the bag
is then drawn off the beaker. Its permanent shape is secured by threading
a clean thin string through the folds, which is gently drawn tight after
every completed stitch so that the circumference at the open end is roughly
the same as at the bottom. The bag is suspended in a jar of suitable size
by two or three strings tied at equal distances to the string which secures the
circumference." (From Hatschek's Laboratory Manual, Messrs. Churchill.)

(ii) Similar care must be taken when working with parchment tubes or
thimbles. The " sausage skin dialysers " are excellent for demonstration
purposes, as they offer a large effective surface. They are sold flab in lengths
of about a metre and are very easily damaged. They are best kept hanging
from one end. Thoroughly soak and test a piece. Cut it to a convenient
length and with a large cork- borer excise a circular piece from both ends
about \ inch from the opening. Bend the tube into U -shape and place
it in a tall cylinder. A glass rod longer than the diameter of the cylinder
thrust through the holes at the ends of the dialyser acts as support. The
tube may now be filled, by means of a funnel, with the fluid to be dialysed
while the cylinder is filled with water at the same time and at the same rate.
This is to prevent undue strain on the tube.

20. Dialysis. In using any dialyser it is advisable to look to the following
points.

1. Test for leaks.

2. See that neither the preservative nor the fluid to be dialysed act on
the substance of the membrane, e.g. bile pigment increases the permea-
bility of collodion. (Bile may be dialysed through a double dialyser, i.e. a
collodion tube suspended in a larger tube of the same material. Blood
pigment occasionally presents the same difficulty.)

3. If the dialysate is wanted as well as the dialysed fluid, dialysis must
be carried out by changing the external fluid from time to time.

4. If it is not necessary to keep the external fluid for examination, rapid
dialysis may be obtained by keeping up a continuous flow of water in the
outer vessel. This is most conveniently done by placing the dialyser or a
series of dialysers in a sink, the level of water in which may be adjusted
by means of a wide glass tube running through the waste plug. The water
supply is led to the bottom of the sink.

(1) Dialyse (a) Egg albumin + Sodium Chloride. (6) Starch + Iodine +
HC1. (c) Starch + Glucose. Test dialysate for both constituents.

(2) Using a glass dialyser with a collodion membrane dialyse a mixture
of either congo red, litmus or ali/arin and hydrochloric acid.

COLLOIDS 409

(3) Dialyse some blood serum. What is the precipitate ? How do
you explain this ?

21. Faraday-Tyndall Phenomenon (p. 70). Arrangement of apparatus.
The fluid to be examined is placed in a prismatic cell (small flat-sided
specimen jar, say, 5" x 5" x 2J"). One large face of the cell is covered with
a black velvet curtain. Light from any optical projector is passed through
the cell in a plane parallel to the long side. A lens is interposed so that the
focus falls about the middle of the cell forming a cone. A darkened room
is essential for any but individual demonstrations.

(1) Fill the cell with water and show that the beam is hardly shown.
(With conductivity water the beam is not seen.)

(2) Dust lycopodium or puff smoke into the beam outside the cell to
show how small particles in air affect the visibility of the light.

(3) Add about 1 c.c. of an egg albumin solution to the water in the cell.
Why is the cone bluish in tinge ?

(4) Eeplace the solution with another containing a red gold sol. Why
is the cone green ?

22. Brownian Movement (p. 75 and Fig. 8). (1) Clean slides and cover
glasses in hot potassium bichromate-sulphuric acid mixture, rinse in
distilled water and then in two changes of alcohol. Keep till required
in alcohol.

(2) When ready to examine a sol, withdraw a slide from alcohol (using
forceps) and evaporate dry over a clean flame. Cool. A large drop of
sol free from air bubbles is placed on the centre of the slide. The cover
glass, prepared like the slide, is gently placed on the drop. Use a good
electric light, such as the Ediswan " Point o' light " tungsten arc, and focus
on the central portion of the fluid. A 1 per cent, suspension of gamboge
shows the Brownian movement well.

23. Gelation. A. Heat a small quantity of 1 per cent, solution of
(1) gelatine, (2) serum, (3) dextrine. Cool. What is the result ? Has
reheating any effect ?

B. Effects of Solutes on Gelation. Into four boiling tubes put the same
quantity of 2| per cent, gelatine. In one tube dissolve about 5-7 per cent,
magnesium sulphate crystals. Potassium iodide crystals are added to the
second tube, while a few drops of 40 per cent, formalin are mixed with the
gelatine in the third tube. The fourth tube is left as a control. Allow all
tubes to stand overnight and examine by tilting and shaking. How do
you explain the varied viscosity ?

Sulphates, citrates and phosphates increase the viscosity of aqueous
emulsoid gels. Iodides, bromides cyanides and some chlorides similarly
decrease viscosity. Alcohol, formaldehyde, etc., in small amounts increase
viscosity.

24. Determination of the Relative Viscosity of a Liquid. Principle.
When a liquid flows through a narrow tube the velocity of flow depends
mainly (a) on the force producing the flow and (ft) on the resistance to flow
produced by the viscosity or internal friction of the liquid. In Chap.
XXIV. p. 278 we considered the shearing of the different layers of the
blood stream. The liquid, we saw, could be regarded as made up of a
number of concentric tubes sliding past one another. When the liquid
is moving through the narrow tube there will be, under constant conditions,
a constant difference in velocity between the different tubular layers. The

410

ILLUSTRATIVE EXPERIMENTS

force per unit area necessary to maintain this condition is proportional
to the difference of velocity, v, of two adjacent layers, and inversely pro-
portional to their difference apart x.

V

Briefly, Force = r; x -, where t] is the coefficient of viscosity, which is the

X

force per unit area when v = x. If, now, the quantity of fluid and the pressure
be kept constant and the time observed which the fluid takes to travel a
certain distance, the viscosity of two liquids with densities s' and s" with
times of flow t' and t" will be as

if jif = s't' js"t" .

Neglect of the difference of density introduces an error of less than 1 per
cent, and materially simplifies the operation, i.e.

V,v=f/r.

Apparatus (Denning- Watson Viscosimeter). The instrument is a modi-
fication of the Ostwald-Poiseuille viscosimeter. It consists of a U-tube
with a long and a short arm (Fig. 77). The long arm
(6 cm. in length) is blown out at its free end into a cup-
shaped receiver with a thin edge.

On the short arm (2 cm. in length) there is a small
elliptical bulb, the capacity of which is defined by the
two lines m' and m".

Method of Use. The receiving cup at the end of the
long arm is filled (and kept filled) with the fluid to be
tested, which passes down the capillary tube. A stop-
watch is started when the fluid reaches the point m'
and stopped when it reaches m". The time taken is
compared with the time reading of water, which is re-
corded on the back of the tube used. Denning and
Watson urge attention to the following points. (1) The
tubes should be scrupulously clean and perfectly dry.
(2) The viscosimeter and the fluid must be at the same
fixed temperature. (3) The receiver of the instrument
must be kept filled with the fluid, for pressure-height
must be kept constant, i.e. compared with water. (4)
The movement of very viscous fluids may be initiated by
slight suction applied to the short arm. (5) Clean the
tubes immediately after use. They are best cleaned by a strong reagent like
cone. HN03 (depending on the fluid last measured), followed in quick
succession by distilled water, alcohol and ether. Hot air is passed through
the tube to dry it.

25. Imbibition, (a) A strip of thin sheet rubber (dental or patching
rubber) about 12" x 1 1" is cut almost its whole length into two fingers of
equal width. One of the divisions is immersed in a boiling tube filled with
benzol, while the other half is left hanging outside. In a few minutes the
immersed division imbibes benzol and swells so that it is at least half again
as long and as broad as the unimmersed division.

(b) Allow a sheet of ordinary glue to lie overnight on a moist surface so
that the under portion of the glue alone is in contact with water. Note
the increase in volume of the immersed portion and also the alterations
in colour, opacity, elasticity, etc.

m

FIG. 77. — Viseosimeter
(Hawksley).

IMBIBITION AND ADSORPTION 411

(c) To show that imbibed fluid is held under compression. Tie a short
piece of surgical laminaria tanga to the stem of a hydrometer (near the
foot). Float in water and note the level. After some hours, again read
the hydrometer scale. If the water imbibed is not under compression both
readings should be the same.

(d) Effect of various electrolytes on imbibition. First of all, prepare a
number of standardised gelatine discs as follows. Make a concentrated
solution of gelatine, adding a trace of a colloidal dye (e.g. Congo red) to
render the gelatine easily visible. Pour the hot solution upon a glass plate
and allow to set. With a large cork-borer (diam. 10-15 cm.), cut into discs
which are dried, measured and weighed. Seven Petri dishes are required
and are almost filled with the following fluids : (i) water, (ii) N/10HC1 or
H2S04, (iii) N/lONaOH, (iv) N/2KI, (v) N/2NH4CNS, (vi) N/5CaCl2,
(vii) Sat. MgS04.

Put a few gelatine discs (not touching one another) into each dish,
immersing them quickly and completely to avoid the adherence of air
bubbles. After an hour's immersion some of the discs will have visibly
swelled. Leave for 24 hours and examine against a black background.
Measure and weigh. Which disc has swelled most ? Arrange the electro-
lytes in a descending order as they have favoured imbibition. This is the
so-called lytropic series. Instead of gelatine, 1 per cent, agar may be used.
The lytropic series will be in the same order.

(e) Effect of Acid on Imbibition. Stretch a piece of catgut vertically
between a weight and a weighted frog-heart lever so that weight and catgut
lie in a tall cylinder. The lever may be made to mark a smoked rotating
drum. Set the drum going very slowly and almost fill the cylinder with
water. Note the changes. Now add sufficient hydrochloric acid to make
the whole fluid 1-2 per cent, acid and note the result.

26. Shell Formation (Rhumbler). (1) Mix a little powdered glass with
chloroform and set a drop of the mixture in water. The glass particles
gather rapidly round the surface of the drop.

(2) Repeat the experiment, using fine silver sand dispersed through oil
and finally dropped into 70 per cent, alcohol. The movements take place
more slowly and the drop requires about three hours to attain equilibrium.

27. Adsorption. (1) Adsorption of Colloids to a Surface. Into a number
of flasks place a spoonful or two (2-3 gm.) of bone charcoal and pour into
each, one of the following fluids. Shake vigorously and then pour into a
large filter paper in a funnel.

Liquids to try : Berlin blue, congo red, acid fuchsin (2-3 mg. per 100 c.c.).

To show that lowering S.T. sets free the colloid, add methylated spirit
to funnel mixture and collect filtrate.

(2) Adsorption of Colloid to Colloid. Capillary Analysis. Cut a number
of strips 2 x 15 cm. from a good filter paper. (Do not take the slip from
too near the edge' of the sheet.) Hang two or three of these strips so that
each one dips its edge into a narrow-necked vessel (Erlenmeyer flask) con-
taining a fluid to be tested, taking care that the papers are immersed to the
same and to a sufficient depth (about 2 cm.), and that glass and paper do
not come in contact. Filter paper becomes negatively charged in contact
with water, and therefore positively charged colloids will become " fixed "
electrostatically at the liquid-paper interface, while negatively charged
colloids will ascend with their dispersion media, (i) Flask i. Water.

412 ILLUSTRATIVE EXPERIMENTS

ii. Aqueous night blue or Prussian blue. iii. Aqueous alkali blue. In
10 to 15 minutes examine the height of water and each dye on the strips.

(ii) Flask iv. Mixture of 20 c.c. 2 per cent, aqueous alizarin red and
0-5 c.c. sat. aqueous picric acid. Leave paper hanging in this mixture for
20-30 minutes. Remove and examine. Hold over strong ammonia for
a moment to make alkaline (i.e. to redden the alizarin). How do you
account for the extremely dark band at the junction of the stains of picric
acid and picric-alizarin mixture.

(3) Adsorption of Salts to Colloids. Cut a series of discs 3-4. mm. thick
from a fairly concentrated gelatine gel and place them in a Petri dish
containing a 2 per cent, aqueous solution of commercial aluminium sulphate
(contains iron) and leave for some days. In three days or so the gelatine
becomes tinged reddish brown (ferric salts). Now test the original solution,
the solution after standing with gelatine, and the gelatine itself for iron
by adding a few drops of ammonium thiocyanate to each. Note the depth
of colour.

28. An Acid Periusate from an Alkaline Solution. Prepare some
colloidal ferric hydrate either by dialysing 5 per cent, ferric chloride or
by gradually adding 1 c.c/of SO^per cent, ferric chloride to 25 c.c. of boiling
water. Put 10 to 15 c.c. of this sol into a dialysing thimble suspended in
an Erlenmeyer flask, containing distilled water and some indicator (litmus
or methyl red). Estimate the concentration of iron in the wash-water by
abstracting, at each change of water, 10 c.c. of the fluid and adding K4FeCy6
solution. When the iron content becomes very small (after 48 hours) add
some HC1 to the colloid. Note the increase in the diffusibility of the Fe.
How can you explain this ? Why does an acid perfusate come from an
electro-negative sol ?

29. Preparation of Colloidal Gold. (1) Protected Solution (Ostwald). To
100 c.c. of ordinary distilled water add a few drops of 1 per cent, neutral
gold chloride. Mix and add a few drops of 0-1 per cent, tannic acid sol.
Heat over a free flame till boiling, shaking it constantly. If the red colour
does not appear on boiling add a little more tannic acid and a little more
gold chloride alternately. Divide into two parts.

A. To one part, while still hot, add about an equal volume of water.

B. Cool the other part before diluting. A is violet in colour while B is
cherry red. Blue gold sol. may be prepared from neutral 0-05 gold chloride.
Take three portions of the gold chloride solution and add (i) 5-10 drops,
(ii) 10-15 drops, and (iii) 15-20 drops respectively of a hydrazine hydro-
chloride solution prepared by adding a tiny crystal to about 20 c.c. of water.
If (ii) does not turn blue add more hydrazine. If it is greenish, too much
hydrazine has been added.

(2) Gold Sol for Colloidal Gold Test (p. 80). Heat 150 c.c. of triply
distilled water (from a resistance glass still). Add 1 c.c. of 1 per cent, gold
chloride solution and then 2-5 to 3 c.c. N/5 pure K2C03. Bring to the boil,
stirring vigorously. Add gradually but not too slowly, 2-3 c.c. of 1 per
cent, commercial formaline (1 c.c. 40 per cent, formaline in 99 c.c. of water)
and remove the flame. See that the sol (which should be ruby red without
any purple tinge) is neutral to alizarin red and that a 5 c.c. sample of it is
completely reduced in one hour by adding 1'7 c.c. of 1 per cent. NaCl.

(3) Determination of the Cn of Colloidal Gold. Take a series of small test
tubes of equal bore, etc., and range them in two equal rows. Into each

LIESGANG PHENOMENON 413

tube put 1 c.c. of triply distilled water. To the first tube of one row add
1 c.c. of N/50HC1. Mix. Remove 1 c.c. of the mixture and add this to
the second tube, and so on down the row. This will give a series of acid
solutions as follows : N/100, N/200, etc. The other series of tubes is treated
in exactly the same way with N/50NaOH. The final 1 c.c. of each series
is discarded. Two drops of alizarin red and 1 c.c. of the gold sol are added
to each tube and the contents mixed. The tube showing the neutral alizarin
colour is picked out and its value determined. The whole gold sol is now
neutralised by the addition of the exact amount of NaOH or HC1 as the
case may be.

30. Protective Action of Emulsoids (p. 80). Two equal portions (9 c.c.)
of neutral gold sol are treated (1) with 1 c.c. of a 0-1 per cent, gelatine sol
and (2) with 1 c.c. of distilled water. To both are added 1 c.c. of N/lNaCl
solution. Examine by pure transmitted light, i.e. by looking through the
tubes at a uniformly illuminated screen of white paper.

31. Diffusion of Electrolytes and Colloids into Gels. Two-thirds fill four
test tubes with 3 per cent, gelatine and allow to gel. Add 1 per cent,
solution of (1) CuS04, (2) picric acid, (3) colloidal iron, (4) Congo red, one
to each tube, and put aside for some days.

32. Electrical Diffusion (p. 79). Fit up a U-tube with an electrode of
platinum- or silver-foil rolled cylindrically at the top of each tube. Fill the
tube two-thirds full with 3 per cent, gelatine containing a trace of citric acid,
and allow to stand overnight to form a gel. Fill one limb with coloured
electrolyte (e.g. CuS04), the other with acidulated water. Determine
roughly the rate of diffusion (2 hours). Then pass a current through the
tube (lighting supply with a lamp in circuit) and note rate of diffusion
(2 hours). Reverse the direction of the current for 2 hours or more and
note changes. Try various electrolytes and find which are forced into the
gel at the cathode and which at the anode.

33. Adsorptive Stratification. (Liesgang Phenomenon, p. 79). " 4 grams
of gelatine are dispersed in 100 c.c. of water and 2 c.c. sat. potassium
bichromate are added to the sol. The mixture is poured on clean glass
plates to form a thin layer, about 0-45 c.c. per sq. inch of surface being
allowed. The plate is supported on a horizontal surface and the sol allowed
to set ; 10-15 minutes will be required. A large drop of 20-30 per cent,
silver nitrate is placed in the centre of the plate, preferably by allowing five
successive drops of about 0-1 c.c. each to fall on the same spot from a
small pipette.

The drop should have a clean circular outline. The plate is kept in the
dark for 24-48 hours. At the end of this period any traces of the original
drop may be removed with a pointed strip of filter paper, and the gel is
then allowed to dry. (1) Use commercial gelatine. (2) Do not disturb
the plate after adding AgN03, till excess has been removed. (3) A trace
of citric acid (5-10 drops of 5 per cent, solution to 100 c.c. of sol.) gives
wider rings.

34. Electrophoresis (Fig. 10, p. 77, and letterpress, p. 78). The electrodes
(Fig. 10) are two strips of platinum- or silver-foil fastened parallel to one
another about 16 mm. apart (Chatterton's compound is an excellent fixative).
The slide is placed on a microscope with a paraboloid condenser (or with
a small stop) and the lighting, etc., arranged to suit the particular type of
condenser used. A large drop of the sol under examination is placed in

414 ILLUSTRATIVE EXPERIMENTS

the centre of the space between the electrodes, making contact with them
and covered with a | in. glass. After 10 minutes the microscope is focussed
on the central layer of liquid (particles not in contact with glass and free
to move) and a current of 4-5 volts (keep amperage low) passed between
the electrodes. Determine the sign of the electric charge on dialysed iron
sol, gold sol, night blue, alkali blue, etc. Fit an eyepiece micrometer and
with a stop-watch determine the velocity of the particles in cm. per volt
per sec.

35. Model to Illustrate some Phases of Urine Formation. (Fischer and
MacLaughlin.) Prepare some cups of sodium stearate by pouring the hot
stearate solution (1/10 molar) into a mould consisting of one beaker (120 c.c.)
suspended within another similarly shaped (350 c.c.). A cup is supported
on a nitration disc in a filter funnel whose stem enters the mouth of a
graduated cylinder. Another cylinder (gas jar) or bottle inverted may be
used as a constant level device. Fill the cup and the gas jar with the
solution. Invert the full jar and suspend it vertically so that its mouth
just dips below the surface of the fluid in the cup. From time to time
measure the fluid in the lower graduated cylinder, say every hour.

Try the following solutions : (a) water (3-6 hrs.), (b) molar sodium
oleate (24 hrs.), (c) NaCl 1/8 m., 1/4 m., and 1/1 m. (3-6 hrs.), (d) 1/8 m.
CaCl2 (1-4 hrs.), (e) 1/8 m. NH4C1 (7 hrs.).

Note increased flow with (c) and (d) ; initial increase and final decrease
of flow with (e) and total inhibition with (6). Test, in each case, the per-
fusion fluid, the perfusate and the cup, with phenolphthalein. How do
you account for your results ? Test the perfusates for fatty acids. Why
does pure water dissolve out more of the acid than do the salt solutions ?

36. Mimicry of Cell Structure (Herrera after Harting). A crystallising
dish 18 cm. in diameter is filled with colloidal silica. This may readily be
prepared by dissolving freshly precipitated gelatinous silica in a solution
of ammonia (density 26°). Silica is added till all the ammonia has been
driven off and the colloid has a density of over 1-032 (i.e. 3-5 per cent,
solid silica). (A solution of sodium silicate of a density of 1-020 may be
used instead of colloidal silica.) At one edge of the crystallising dish place
10-20 mgrms. of recrystallised potassium bifluoride. At the diametrically
opposite side of the dish place 5 gms. pure powdered anhydrous calcium
chloride. Cover and keep at 20° C. for 24 hours. Various structures which
may be stained by any of the dyes used by histologists may be seen, e.g.
nucleated amoebae, cells undergoing division, nuclear spiremes, granular
and honeycomb structures, etc.

The figures are due to the strains produced in the silicate by the simul-
taneous formation of a colloid, calcium silicate and a crystalloid, calcium
fluoride. Silica, coagulated by a crystalloid, gives rise to a semipermeable
membrane, which, if it forms a sac round a crystalloid, may set up endos-
mosis. Slow amoeboid movements may be shown by some of the com-
plexes lying near the point of insertion of the CaCl2. Add a trace of alcohol
over the CaCl2, and more rapid diffusion ensues.

37. Emulsions. 1. Take four test tubes and place in each 10 c.c. of
olive oil. In addition add to (a) a few drops of oleic acid and a drop
of alcoholic NaOH ; to (6) some (soft) soap solution ; to (c) a few drops of
oleic acid and about the same quantity of cone. Ca(OH)2 solution and
allow to stand. Which gives the best emulsions ?

EMULSIONS

415

2. To determine the optimum concentration of colloid for the stabilisation
of an emulsion. Into each of three mortars introduce 20 c.c. of wa,ter,
(a) containing 1-25 per cent, of commercial soft soap, (6) 1-875 per cent,
and (c) 2-5 per cent. To each slowly add 120 c.c. of, say, cottonseed oil,
stirring regularly but not too vigorously meanwhile. If possible, put on
a mechanical shaker for | hour. Pour into tall cylinders and allow to stand
for some days.

3. Effect of concentration of oil on rigidity. Stir into four lots of 25 c.c.
of 25 per cent, soft soap in mortars, (a) 50 c.c., (6) 100 c.c., (c) 200 c.c.,
(d) 400-500 c.c. of cottonseed oil. Place in shallow dishes. Note rigidity.
What happens when the optimum concentration of oil has been passed.

4. Divide an emulsion of oil in water — (soap), (i.e. 120 c.c. oil in 20 c.c.
7 per cent, soft soap) into nine portions. No. (1) will serve as control.
To the others add a few drops of one of the following N solutions, (ii) HC1,
(iii) NaOH, (iv) Ca(OH)2, (v) CaCl2, (vi) NaCl, (vii) Alcohol, (viii) CHC13,
(ix) Ether.

5. Instead of soap any hydrophilic colloid may be used, e.g. albumin,
casein, acacia, dextrin, starch. The carbohydrate-stabilised emulsions
are the hardest to break.

6. To 5 grams of dry casein in each of three mortars add slowly (a) 50 c.c.
N/20NaOH, (6) 50 c.c. water and to (c) 50 c.c. N/20HC1. Allow to stand
overnight and then slowly stir 75 c.c. of cottonseed oil into each. Pour
into clear jars and allow to stand. Why does (6) separate out ?

38. Model of Mucoid Secretion. (Fischer.) Grind up in a mortar a
small quantity of gum acacia and one or two c.c. of cottonseed oil. Put
a drop of this mixture on a microscope slide with cover glass and examine.
Place a drop of water at the edge of the cover slip and note what happens
when it touches the oil layer.

39. Comparison of the Electrical Conductivity of Equimolecular Solutions
of Mineral and Organic Acids. Conductivity being the reciprocal of resist-
ance, obviously can be measured by a resistance method, e.g. by the

FIG. 78. — Diagram of Conductivity Apparatus.

Wheatstone bridge (Fig. 78). The current from 6 is divided between two
circuits (1) by R} and R2 and (2) by R3 and R± (where R = resistance in
ohms). The amount of current travelling by these circuits is such that the
drop of potential in both is the same. If then a lead be taken from the
junction between R: and R2 and connection made with the R3, R± route

416 ILLUSTRATIVE EXPERIMENTS

so that RI/RZ = RS/RV then no current will flow through the lead as shown
by the indicator (G), a galvanometer, lamp, telephone receiver, etc. Thus
Rv R2 and R3 being known, R^ can be found. In practice, the lead fixed
between R3 and R^ terminates in a jockey- piece which slides along a
platinum, iridium, or nickelin wire of uniform resistance and a metre long,
constituting Rlt R2. The length of R1 is read from an underlying scale
when G indicates that no current is passing.

Owing to polarisation occurring at the electrodes when a steady current
is passed through an electrolyte, it is necessary to employ an alternating
current which renders a galvanometer useless as an indicator. The alter-
nating current is usually got from the secondary terminals of an induction
coil. As an indicator, one may use a telephone receiver or a small A.C.
pea lamp.

Expt. (a). Eough Demonstration. Fit up a Wheatstone bridge, using a
4-volt accumulator with switch as b, and a pea lamp as G. Rs is a resistance
box and R± or x is a simple type of conductivity cell, e.g. a beaker containing
the solution to be tested with two sheet-silver electrodes. Find the point
on the metre wire when the light from the lamp is at its minimum = x.
Then conductance

and the molecular conductivity is equal to C<f>, where <£ is the volume in
c.c. in which 1 mole is dissolved. Suitable solutions =1/16 molar hydro-
chloric, acetic, and benzoic acids ; 1/8 molar NaCl and glucose. (N.B. —
Keep the switch from b open as much as possible to prevent polarisation
of the electrodes of x.)

(b) With the same apparatus the neutral point of a titration may be
determined. Place 20 c.c. of N/50NaOH in the conductivity cell and
arrange the resistance box (R3) so that the bridge reading is about 50 cm.
From a burette run in a standard (N/50) solution of H2S04 and mix as in
titration, determining the point of balance on the wire after each addition.
It will be found that the balance point will first tend towards the zero end
of the scale and later will move in the reverse direction. The point at which
it changes direction is the electrotitrametric neutral.

For any but very rough readings, many precautions have to be observed.
These will be found in any book on practical physical chemistry. Instead
of a lamp, the capillary electrometer may be used as an indicator.

40. (i) Buffer Solution. Sfirensen. (a) M/15 solution of KH2P04
(9-078 grams per litre). The salt should be chemically pure, and its solution
should be water clear and free from even traces of chloride and sulphate.

(b) M/15 solution of Na2HP04 . 2H20 (11-876 grams per litre). The
salt is prepared by exposing to the air the recrystallised Na2HP04 . 12H20.
After two weeks' exposure on a porous plate, dissolve the salt in water and
test for chloride and sulphate. 8 c.c. of (a) KH2P04 + 2 c.c. of (6) Na2HP04
2H20 gives a solution of pR 7-381.

(i) To demonstrate the acid-combining power of a " buffered " solution.
Take 50 c.c. of the above mixture or prepare a solution containing about
0-25 per cent, sodium bicarbonate. Place this in a tall cylinder and in
another similar vessel place the same quantity of water. Add about
20 drops of neutral red (0-05 per cent, in alcohol) to each. Add N/10 NaOH

ALKALI RESERVE OF BLOOD 417

to the water till it has approximately the same pH as the bicarbonate.
Titrate both with N/50HC1 to the same end point.

(ii) To demonstrate the effect of the tension of C02 on the pH of a solution
of bicarbonate. Put 5 c.c. of a 0-25 per cent, solution of NaHC03 in each
of three tall stoppered cylinders. To each add 2 drops of neutral red.
Fill (a) with air expired after a deep inspiration, (6) with alveolar air (Expt.
43) and (c) with C02 from a generator or cylinder. Stopper and shake.
Note colours. Remove the C02 in (c) by repeated changes of atmospheric
air. Note that the colour goes back from crimson through the red of (6)
to the orange of (a) or even to the yellow seen before any C02 was added.

41. An Approximate Determination of the Alkali Reserve of Blood.
(Rieger.) Principle. Erythrocytes are easily damaged by acid. This
will lead to agglutination and haemolysis on the addition of acid as soon
as the reserve of base has been used up.

Method. Twelve test tubes (8" x 1" or thereabout) cleansed thoroughly
and dried are set in a rack. The first or stock tube is charged with 18 c.c.
of a 0-85 per cent, solution of NaCl (pure salt in distilled water) and 2 c.c.
of whole blood (oxalated with 0-2 per cent, pure sodium oxalate). Mix
thoroughly by drawing up into the pipette several times, keeping the tip
of the pipette always below the surface of the liquid.

One c.c. of the diluted blood is placed in the bottom of each tube, avoiding
the sides, and then, starting on the left, N/100HC1 is added from a graduated
pipette. The first is given 0-7 c.c. acid, the next 0-75 and so on, increasing
the amount by 0-05 c.c. with each tube, the last tube thus receiving 1-20 c.c.
In about an hour examine the tubes. Those on the left should show no
haemolysis and the corpuscles should be settled in a sharply defined clump
in the centre of the foot of the tube. The tube on the right may show
haemolysis and have corpuscles scattered over the bottom in an irregular
manner, giving a speckled appearance. The tube with the greatest amount
of acid which shows no haemolysis or scattering of corpuscles gives an
indication of the alkali reserve of the blood.

For example : Normal blood — the first seven tubes (i.e. 0-7-1 c.c.) are
clear, tube 8 shows scattering and slight haemolysis. Therefore 0-1 c.c.
of blood can neutralise 1 c.c. of N/100 acid, or 100 c.c. of blood contains
base equivalent to 0-42 grams NaHC03. This would, in Van Slyke's
apparatus, give rise to 112 c.c. of " bound " C02 — a somewhat high result
(see 42 and 43), probably due to interaction of acid and protein.

42. Alkali Reserve. (C. J. Martin.) Principle. Dilution of a well-
buffered solution such as plasma does not alter its (7H. If an indicator
is used which has a low protein error the plasma may be titrated with acid.
The titration value indicates the acid-combining power of the plasma.

Apparatus. A small wooden stand to hold three "non-sol" glass test
tubes (8 x 0-8 cm.) vertically in a row and close together. The central tube
at its upper end runs through the rubber stopper of an inverted " non-sol "
flask (100-150 c.c.).

Method. The flask is removed from the central tube and 0-5 c.c. of
plasma or serum and 2 c.c. of neutral 0-9 per cent, sodium chloride added.
The side tubes are almost filled with a phosphate buffer mixture of pVL = 7-4.
These standard tubes are coloured by the addition of a drop of two aqueous
solutions of burnt sugar and flavine (1/100,000) till they match the fluid
in the central tube. To all of the tubes are then added 2 drops of 0-05 per
B.B. 27

418

ILLUSTRATIVE EXPERIMENTS

cent, (alcoholic) neutral red. The optical effect of the turbidity of the
plasma may be counteracted by placing a sheet of white tissue paper behind
the tubes. The plasma mixture is titrated with N/50HC1 (2 c.c. burette
with fine nose) till its colour matches the standards. This is done by run-
ning the plasma into the flask, adding a few drops of acid and rotating
gently but steadily for 1 minute, the flask meanwhile being in communica-
tion with the air. This readily allows the thin film of plasma to give up
the liberated C02. The fluid is run back into the tube and compared with
the standards. The process is repeated as often as necessary. . Rotation
for at least 1 minute is necessary after each addition of acid.

Titration value for 0-5 c.c. plasma =0-77 c.c. N/50HC1,
i.e. Alkali reserve of „ „ =0-77 c.c. N/50NaHC03
,, „ 100 c.c. „ =154c:c. „ „

= 3-08N „
= 3-08x224 c.c. C02,

i.e. 68-99 volumes per cent, of C02 are bound as bicarbonate in the plasma.

A sharper end -point is obtained by the
use of phenol sulphonephthalein as in-
dicator. In this case the standard
phosphate solutions are made of pH 7-2
to correct the protein error.

43. Alkali Reserve by Van Slyke's
Method. The Van Slyke apparatus is
illustrated in Fig. 79. It consists essen-
tially of a 50 c.c. pipette with three-way
stopcocks (e and /) at top and bottom,
and a 1 c.c. scale on the upper stem,
divided into 0-02 c.c. divisions. The
body of the apparatus is connected
through heavy walled rubber tubing
with a levelling bulb filled with mercury.
The whole apparatus is supported on a
stand so that, without unclamping, the
pipette may be rotated round a central
axis. The stopcocks are lubricated with
a rubber-vaseline mixture and may be
held in place by strong rubber bands.

Preliminary preparation. Open taps e
and / and fill the entire apparatus with
mercury by raising the levelling bulb,
allowing some mercury to run into a and
into b. Shut e, and lower the levelling
bulb till the mercury falls half-way down
c and d. The bulb is then slowly raised.
If the apparatus is gas-free, a sharp click
will be heard when the mercury strikes
the upper stopcock. If a gas cushion is
FIG. 79.— Apparatus for Estimation of present, open e, and force the gas out.

Carbonates in Solution. &nd repeat ^ evacuation proce8Sj

opening / alternately to c and d.

Determination. (1) Solutions required. It is convenient to have four

VAN SLYKE'S CO2 APPARATUS 419

dropping bottles with ground in pipettes and rubber teats containing
(a) 5 per cent. H2S04, (b) 1 per cent, carbonate-free NH3 water, (c) caprylic
alcohol and (d) distilled water. The carbonate-free ammonia is prepared
by adding a small amount of sat. barium hydrate solution to ordinary
ammonia solution. The barium carbonate is filtered off, and the excess
of barium remaining is precipitated with a little (NH4)2S04.

(2) Plasma. An ordinary centrifug% tube is fitted out with rubber cork
and glass tubes just like a wash -bottle. The longer tube bears at its upper
end a hypodermic needle. The whole apparatus — glass, tubes and needle —
is washed out with a saturated solution of neutral potassium oxalate.
(Van Slyke and Cullen point out that it is desirable that the subject should
avoid vigorous muscular exertion for at least an hour before the blood is
drawn. It is also best to avoid stasis, or when stasis is unavoidable the
ligature should be released as soon as the vein is entered. In this case,
the first sample of blood should be neglected.) The blood should run into
the tube without suction. By a gentle rotary motion, mix the blood with the
finely crystallised oxalate left adhering to the walls of the vessel, and centri-
fuge at once. The plasma is then transferred to sampling tubes (Fig. 80),

TUBE.

FIG. 80.— Alveolar Air Collecting Tube.

3-4 c.c. of plasma to each tube. These tubes (300 c.c.), or separating
funnels of the same capacity, are filled with alveolar air (of the subject, if
possible). This may be done by holding the tube horizontally, opening
both taps and, without inspiring more deeply than normal, expire as quickly
and as completely as possible through the tube, closing the further tap
just before the expiration is finished. A bottle containing large glass
beads must be interposed between mouth and funnel in order to prevent
dilution of the plasma by condensation of vapour from the breath. With
both taps closed, the funnel is rotated (not shaken) so that the plasma
forms a thin layer over the walls, and so readily comes into equilibrium as
regards C02 tension with the alveolar air.

(3) Procedure. The apparatus is entirely filled with mercury, including
the two capillaries (a and stem of 6) at the top. The cup 6 is washed with
C02-free NH3. 1 c.c. of plasma is run into the cup from an Ostwald-Folin
pipette, keeping the tip of the pipette immersed in the fluid. Placing the
mercury reservoir in the second ring (Fig. 79) and with cock / open to d,
open e and admit the plasma to the pipette, leaving sufficient in b to fill the
capillary. Wash the cup twice into the pipette using about 0-5 c.c. of
water each time, adding a very small quantity of caprylic acid to the
second wash water. Finally run in 0-5 c.c. of 5 per cent. H2S04 and seal
the capillary with mercury. The fluid must come to the 2-5 c.c. mark.
Wash out the cup with water and then with carbonate-free ammonia till
acid-free. The mercury bulb is now taken to a position (about 80cm.
below the second ring) so that a Torricellian vacuum is formed in the gas
pipette. Allow the mercury to run down almost to (but not below) the
B.B. 27*

420

ILLUSTRATIVE EXPERIMENTS

50 c.c. mark. Close / and replace the bulb on the upper ring. Slacken
the milled head of the screw that controls the central swivel. Holding the
pipette at the bulb with the right hand and gathering up the loose rubber
tubing with the left, rotate the bulb through 180° some 15 times. Set
vertically and tighten the milled head. Lower reservoir and, with / open
to d, rapidly empty the water solution into d without however allowing
any of the gas to follow it. Now op^en / to c and, by raising the reservoir,
fill the body of the pipette with clean mercury. Hold the reservoir in such
a position that pressure inside the reservoir is atmospheric and rapidly take
a reading. If thought desirable, re-extraction may be carried out.

FIG. 81.— Van Slyke Micro Apparatus.

Cleaning. Lower the reservoir and run most of the mercury back
through c. Open f to d and, by raising the reservoir, run the water back
into the pipette. Open e to a and force the fluid out into a collecting jar.
The apparatus is now ready for another determination.

Micro apparatus (Fig. 81). This apparatus is easier to manipulate, and
as water, etc., never enters the gas pipette, it is easily kept clean. The
different parts are in the same relative proportions as the corresponding
parts of the larger apparatus. Each division of 0-002 c.c. on the smaller
corresponds to 0-01 c.c. on the larger.

(1) It is advisable to mark the course of the canals with pencil on the
butt end of the tap d.

DETERMINATION OF CH

421

(2) No froth preventer is necessary or advisable. It merely acts on the
tap lubricant.

(3) All quantities are reduced to 1/5 of those given above, e.g. 0-2 c.c.
plasma, 0-1 c.c. water, and 0-1 c.c. acid. In all, exactly 0-5 c.c. of fluid
is used.

Calculation of Results.

TABLE LXXXI.

TABLE FOR CALCULATION OP C02-CoMBiNiNG POWER OF PLASMA
(from Van Slyke and Cullen).

D

Observed Vol. x=w«.

C.c. of CO,,. Reduced to N.T.P. bound as
Bicarbonate by 100 c.c. of plasma.

15° C.

20' C.

0-2

9-1

9-9

0-3

18-8

19-5

04

284

29-0

0-5

38-1

38-5

0-6

47-6

48-1

0-7

574

57-6

0-8

67-1

67-2

0-9

76-8

76-7

1-0

86-5

86-2

Intermediate values may be obtained by interpolation.

B = observed barometric pressure.

Normal range — adult 53-77 c.c., infants about 10 per cent, lower.

44. Alterations of the Surface Tensions of Oil- Water Interface by Alter-
ations in Hydrogen Ion Concentration (Hartridge and Peters, Jour. Physiol.
LIV., Proc. XLI.). Oil free from fatty acids or soaps is essential. Pure
olive oil, castor oil, or cod-liver oil may be freed from these bodies by boiling
for a number of hours with frequent changes of a considerable excess of
tap water. A series of test tubes 6 x 5/8" each receives 5-10 c.c. of the
treated oil. Into each is put a capillary tube 4" long, open at both ends.
The test tube is almost filled with the fluid to be tested. Try solutions
having a pH of 9, 8, 7, 6. Measure the height to which the oil rises in the
capillary.

45. Principle of Measurement of H-ion Concentration by Potentiometer.
The principle is much the same as that of the conductivity measurements
(Fig. 78), only instead of having a single source of potential and an unknown
resistance, one has known resistances and two sources of E.M.F., one of
which is of unknown value.

In Fig. 78, b may be taken as a cell of standard E.M.F. sending its current
through the wire bridge R± - R2. If we lead into Rl - R2 the wires from
another battery x, taking care that the direction of the difference of potential
is the same, e.g. both negative poles leading to Rlt as the fall of potential
along R1 - R2 is regular, we can readily divide the wire so that the difference
of potential between the point of entrance and exit of the current from x
is equal and opposite to the difference of potential between the same points
caused by the standard cell, i.e. the galvanometer or electrometer will

422

ILLUSTRATIVE EXPERIMENTS

indicate no B.P.D. The cell x is of interest. It consists of two half cells
or electrodes. One of these is the ordinary standard calomel electrode,
i.e. an electrode of mercury covered with HgCl in the presence of a definite
concentration of KC1. The other half cell is a hydrogen electrode, i.e.
platinum black laden with hydrogen and immersed in a solution containing
H-ions. The difference of E.M.F. between electrode and solution depends
on the concentration of H-ions in the latter.

The difference of potential between the calomel and normal hydrogen
electrode can be ascertained. This value is subtracted from the total
E.M.F. of the cell to give a value from which the pH may be calculated.

46. Determination of the Relative Viscosity of Blood (see expt. 24).
Blood may be taken from the lobe of the ear or from the finger. The skin
is thoroughly cleansed with ether and pricked with a fine pointed lancet.

Fia. 82. — Denning- Watson Clinical Viscosimeter (Ilawksley).

The viscosimeter (at body temperature) is held vertically under the bleeding
spot and the receiver filled (Fig. 82). Measure as in expt. 24.

Immediately after an observation, the blood should be driven out by a
blast from an inflator attached by rubber tubing to the short arm of the
capillary.

It is advisable to make a blood count at the same time (p. 242).

47. Haematocrite. This apparatus consists of two similar graduated
capillary tubes, which, after clipping in a holder, may be spun hori-
zontally by a. centrifuge. A small measured quantity of Miiller's fluid
(Na2S04 - 1 gm. ; K2Cr207 - 2 gm. ; distilled water, 100 gm.) is placed
in a test glass. The same quantity of blood is added. Mix thoroughly
with a glass rod. Fix a short length of rubber tubing furnished
with a mouthpiece to each of the graduated tubes and suck up sufficient
of the mixture to fill the tubes. Place them in a holder and spin
for 5-7 minutes with a velocity of 8000 revs, per minute. Read off the
relative length of the column of corpuscles. As the glass walls of the

BLOOD PRESSURE MODEL

423

tubes are thick, it is advisable to aid the eye by looking along a glass
plate held at right angles to the tube. The tubes have a bore of one
square mm. and are divided into 100 equal parts. The reading multiplied
by 2 will give the volume of corpuscles in 100 parts of blood. The
function of the Miiller's fluid is to retard clotting and to fix the red
corpuscles in their natural size.

48. Blood Pressure Model, (a) General distribution. Examine the
schema (Fig. 83) of the circulation given you and identify the parts repre-
senting arteries, capillaries and veins. Disconnect the rubber ball H and
the two Bunsen valves V, V. Attach the arterial tube A to the water
supply and lead the tube from G to the sink. Cautiously turn on the water
and measure the pressure in the arteries (at B), and in the veins (at E).
(It is more economical to have single vertical tubes at B and E, the pressures
read off in mm. of water may be calculated in mm. of mercury.)

Arterial BP

FIG. 83.— Schema of the Circulation.

Note the effect of (a) varying the force of inflow by manipulation of the
water tap, (b) varying the resistance to flow by tightening the clip at D.
With a steady pressure over its whole length, compress G and note altera-
tion in manometer levels.

(6) Pulse. Fill with water and replace H and V-V in circuit. Gently
compress and relax H at regular rhythmic intervals of about a second.
Note the effect of this upon the arterial and venous pressures. Study the
further effect of constricting D.

(c) Place a finger on A and note the expansion with each contraction
of H. Study the same thing on D and on F.

49. (a) Conduction of Sound Waves by the Cranial Bones. Place a
vibrating tuning fork in the region of the interparietal suture. From where
does the sound apparently come ? Place the tip of the finger into the
auditory meatus of one ear and then block both ears. Explain.

(b) Binaural Localisation of Sound. With the eyes closed listen to the
ticking of a watch through a binaural stethoscope. Pinch one of the
tubes to prevent transmission of sound to one ear. Release and repeat
with other tube.

50. Vowel Sounds by Percussion. Place the mouth in the position
necessary for the pronunciation of the various vowels and then percuss

424

ILLUSTRATIVE EXPERIMENTS

over the cheek (Fig. 70). Now shift the point of percussion to a position
over the pharynx just behind the angle of the jaw and percuss again. Note
that the " cheek notes " rise as one passes from U — 0 — A — E — I, while
the " pharynx notes " rise U — 0 — A and fall to E and I. This demon-
strates the double nature of the mouth cavity in producing E and I.

51. Prepare a series of bladders filled completely with (a) air, (&) water
and (c) some viscous fluid like syrup and (d) lard. Percuss and palpate
each.

52. Demonstration of the effect of colour on the absorption of radiant
energy (L. Hill). Two similar pieces of cotton tape, one white and the other
black, are suspended so that the end of each dips in a graduated cylinder
filled with water. Place first in the shade and measure the amount of
water evaporated from each cylinder during a period of 30 minutes. Refill
with water to the same level and repeat the experiment in direct sunlight.

-log[H']or

FiG. 84.— Graph for Conversion of pH to CH.

Graphic Conversion of Sdrensen's /> 1 1 ( - log ( H ")) into Concentrations of
Hydrogen Ions and the reverse (Roaf, Journ. of Physiol.). Fig. 84 is a graph

425

whereby the logarithmic notation of S0rensen can be converted at sight
into true concentrations. It would be advisable to redraw the figure on
semi-logarithmic paper and so enable the reading to be taken to two
places of decimals. For example, to convert pHQ-1 into CH, pH = 6 is
CH = 10~6; 0-7 cuts the diagonal line opposite 0-2; therefore

pKot 6-7 = CHof 0-2xlO-«.

Estimation of the Surface Area of the Body. Rubner announced that
the amount of heat produced by an animal is proportional to its superficial
area. This law of surface area has rendered necessary the accurate deter-
mination of the skin surface in most metabolism experiments.

Since the surface of a figure varies as the square, and that of volume as
the cube of its linear dimensions, it follows that

where S = surf ace, F = volume and K = constant, or, as weight (W) varies
directly as volume,

S = K 2/W*.

Meeh, from sixteen experiments, suggested that K should be = 12-3 for
adults ; and Lissauer used the value 10-3 for children. The average error
of this calculation is about 16 per cent.

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FiG. 85. — Du Bois Graphs for Estimating the Area of Body-Surface.

The brothers Du Bois covered the body-surface of their subjects with
" tights " and applied melted paraffin. Paper strips were affixed to
prevent change of area during the process of removing the " shell." The
model of the surface, cut into pieces sufficiently small to be flat, was photo-
graphed upon squared paper of uniform thickness. The weight of each
square on the paper was known. The darkened portions of the paper
were carefully cut and weighed, and from this was calculated the area of
body surface. The formula resulting from this work involved nineteen
measurements. From this they have evolved a two -measurement formula
on which the appended chart is based (Fig. 85).

The Field of Vision (see p. 225). The extent of the field of vision may be
measured approximately as follows :

Describe a semi-circle on a blackboard with the free ends of the line
finishing at one side. Mark the centre of the circle at the edge of the board,

426 ILLUSTRATIVE EXPERIMENTS

and the middle point of the circumference with an X . This forms a rough
" Perimeter."

The subject of the experiment closes one eye and places the other at
the centre of the semi-circle, directing his gaze at the middle point of the
circumference. The observer slowly draws a small object, say a piece of
chalk, along the circumference from below. The subject states when it
becomes visible and the other marks this point. The process is repeated,
starting from above, and the point when the object comes into view is
again marked. The angle formed by joining these points to the centre of
the circle subtends the vertical field of vision.

By turning the blackboard into the horizontal plane, or by using the top
of a table, the horizontal field of vision may be mapped out.

Movements of the Eyeball. The movements of the eyeball may be
studied by means of a ball of wool. Make some mark on it to represent
the pupil, and thrust three knitting needles through the ball to represent
the axes round which the eyeball rotates (Fig. 51, p. 223). The movements
can then be reproduced with a fair degree of accuracy.

INDEX

(References to Part II. are in italics.)

Absorption coefficient of gases in liquids,
247 ; from alimentary canal, 317, 318 ;
of light, 15, 18, 71, 72 ; of heat, 343,
345, 424 ; of solutes by renal tubules,
163 ; spectrum of chlorophyll, 14.

Accessory factors of diet, 372.

Acclimatisation, 267.

Accommodation in eye, 220.

Acid, action of, on emulsions, 86, 378,
381, 389 ; on fats, 421 ; on soaps, 82 ;
on tissues, 381, 389.

Acid, effect of, on dissociation curve of
Hb02, 253 ; on imbibition of water
by colloids, 378, 389, 411.

Acidity, numerical expression of, 57,
58, 424.

Acquired characters, transmission of, 361.

Adaptation, 360.

Adipose tissue, 173.

Adsorbed material, state of, 66, 153.

Adsorption, 66, 98, 111, 378.

Adsorption and osmosis, 66, 153.

Adsorption by enzymes, 94, 98 ; cause
of, 48 ; demonstrations, 411 ; effect of
temperature on, 94, 109 ; of gases by
colloids, 248, 332 ; of carbon dioxide
by haemoglobin, 254, 334 ; of oxygen
by haemoglobin, 248, 251 ; specific
surface for, 66, 94.

Adsorptive stratification (Liesgang pheno-
menon), 79, 413.

Agar-agar, 82.

Agglutination, 79.

Alimentary canal, general plan of, 313.

Alkali reserve of blood, 241, 333, 417,
418, 419.

" All or nothing," in nerve, 185.

Alveoli, 260.

A micron, 74.

Amoeboid movement, 130, 403, 404.

Amphoteric colloids, 332 ; electrolytes,
59.

Anabolism, 2, 374.

Anaesthetics, action on colloids of, 83, 86.

Analyser, 102, 104.

Angle of origin of blood vessels, 292.

Angstrom units, 14, 127.

Anion and cation, 49, 52.

Anode, 50.

Anti-enzyme, 97.

Anti-pro-thrombin, 236, 238.

Anti-thrombin, 236, 238.

Antrum pylori, 317.

Aortic valves, 289, 290.

Arrhenius' theory, 44.

Arteries, pressure in, 281.

Arterioles, pressure in, 281.

Artificial laccase, 94 ; membranes, 41,
109, 398, 399, 405, 407; partheno-
genesis, 378.

a rays, 120.

Astral rays, 383.

Asymmetric carbon atom, 105, 106.

Autocatalysis and growth, 365.

Autolysis, 389.

Available energy, 9 ; of cell, 36.

Avogadro's hypothesis, 38.

Axial repulsions, law of, 376.

Bacon, Instances of Magic (quoted), 91.

Balanced chemical reactions, 99, 376, 381.

Barger's vapour pressure method for
determination of osmotic pressure, 402.

Barotaxis, 131.

Basilar membrane, 209.

Beckmann thermometer, 400.

Benzol, imbibition of, 410.

Bicarbonate system, 241, 332, 416.

Bile, function of, 318.

Binocular vision, 225.

Bio-electric phenomena, 133.

Bjerknes' phenomenon, 382.

Blood, alkali reserve of, 241, 333, 417 ;
coagulation of, 235 ; colloids of, 233,
243 ; composition, 232 ; corpuscles,
241 et seq., 398, 422 ; crystalloids, 238 ;

427

428

INDEX

development of, 230 ; flow, 163, 277 ;
function of, 229, 231 ; hydrogen ion
concentration of, 232, 421, 424; in-
tegrative action of, 256 ; osmotic
pressure of, 157, 233, 244 ; plasma,
q.v., 232; pressure, 162, 279, 423;
viscosity of, 242, 422.

Bone, 174; adaptation of, 176, 179;
conduction of sound by, 213, 423 ;
development of , 174 ; internal structure
of, 176 ; strength of, 175 ; stress lines
in, 175.

Bowman's capsule, 156.

Boyle's law, 38.

ft rays, 120.

Brownian movement, 73, 75, 409 ; in
neuron, 183.

" Buffers," 241, 416.

Bunsen-Roscoe, law of, 354, 356:

Caisson disease, 267.

Calcium, action of, in coagulation of

blood, 235 ; in breaking emulsions, 86,

87, 113, 415; on water-holding

capacity of soap, 82, 236, 237.
Calorie, 3, 21 ; value from oxygen usage,

31 ; value of diet, 26.
Calorie, value of diet (physiological), 27.
Calorimeter, bomb, 24.
Calorimetry of animals, direct, 27 ;

indirect, 29.

Cambrian period, sea water in, 240.
Capacity of a conductor, 53.
Capillary analysis, 411.
Capillary circulation, 252, 279, 423.
Capillary electrometer, 47, 259, 404.
Carbohydrate, formation of, 15-18 ;

oxidation of, 19, 29, 136, 139, 150.
Carbon dioxide, effect of, on dissociation

of HbO2, 253 ; excretion of, 261 ;

production of, 22, 28 ; specific function

of, 253 ; tension in blood and alveoli,

255 ; transport of, 254.
Carnot's principle, 32.
Cartilage, 174.
Catabolism, 2, 350.
Catalase, 96.
Catalysis, 92, 380.
Cataphoresis, 78, 413.
Cathode, 50.
Cathode rays, 119.
Cation and anion, 49.
Cell as factory, 91.
Cell division, cause of, 375.
Cell pressure and growth, 375.
Centimetre index, 367.
Charles' law, 38.
Chemical energy, receptors for, 192, 196.

Chemical gardens, 399.

Chemiotaxis (Chemotropism), 131, 155,

359.
Chloroform : effect of, on dispersoids, 83,

86 ; on membranes, 244.
Chlorophyll, absorption spectrum of, 14;

function of, 19 ; efficiency of, 18.
Chromatic aberration, 217.
Circulation of blood, general plan of, 274,

281, 423.

Coagulation of colloids, 79, 234.
Coefficient of variability, 369.
Co-enzyme, 97.
Cold, reaction to, 349, 350.
Collagen, 172.

Colligative properties of solutions, 43.
Collodion membranes, 405
Colloidal aggregates, dimensions of, 65,

74.

Colloidal gold, 72, 412.
Colloidal solutions, coagulation of, 79,

409 ; osmotic pressure of, 66, 233, 234 ;

viscosity of, 232, 234, 409.
Colloidal state, 67.
Colloids, elasticity of, 169 ; hydrophilic,

173.
Colour, of colloidal solutions, 71, 72 ; of

iris, 71 ; of sky, 70.
Compensation, law of, 376.
Complemental air, 259.
Compound interest law, 365, 367.
Condensation in surface layer, 48, 109,

151, 189.
Conduction of nerve impulse, 185 ; of

heat, 340 ; of sound, 423.
Connective tissues, 168.
Conservation of energy, 4, 32.
Continuous phase, 67.
Cooking, 89.
Copper ferrocyanide membranes, 41, 110,

398, 399.

Corti, organ of, 210.
Crenation, 245.
Crooke's tube, 119.
Crystalloids, 66.
Current, electrotonic, 189 ; demarcation,

134, 143, 145 ; of action, 134, 144, 145,

190 ; of injury, 134, 143, 145, 190, 405 ;

polarisation, 133, 188.

Dalton's law of partial pressures, 40.
Dark ground illumination, 74, 409.
Dead space, 260.

Decrement in nervous impulse, 186.
Degeneration, fatty, 389.
Degraded energy, 5, 8.
Dehydration of fertilised eggs, 379 ; of
tissues, 364.

INDEX

429

Demarcation current, 134, 143, 145.

Dendrites, 182, 184.

Depolarisation, law of, 376.

Dermatoptic function, 174.

Destruction of enzyme, 94, 95.

Dialysis, 67 ; experiments on, 408.

Diaphragm, mechanics of, 304 ; structure
of, 303.

Dielectric constant, 52, 53.

Diffusiometer, 40, 398.

Diffusion, coefficient, 262 ; factor, 262 ;
field of force of, 382 ; of colloids, 67,
413 ; of electrolytes, 413 ; of gases,
40, 398 ; of gases through membranes,
40, 41 ; potential, 52.

Dimension of colloidal particles, 65, 74.

Dioptric system of eye, 222.

Diphasic electrical response, 144, 188,
296.

Dispersant, 68.

Dispersed phase, 67.

Dispersion, degree of, 68.

Dispersoid, 68.

Displacement theory of hearing, 212.

Dissociation constant of water, 55.

Dissociation curve of oxyhaemoglobin,
249 ; effect of acid on, 253 ; effect of
carbon dioxide on, 253 ; effect of
electrolytes on, 248 ; effect of oxygen
tension on, 249, 250 ; effect of heat on,
252.

Dissociation, temperature coefficient of,
63 ; theory of solutions, 44.

Distance receptors, 191, 200, 215.

Diuresis and oxygen consumption, 160.

Diuretics, model to imitate action of,
414.

Dynamic equilibrium, 163, 257.

Ear, 200.

Ecto-enzymes, 97.

Effective surface of blood corpuscles, 243 ;

of solvents, 65.
Efficiency, factors influencing, 395 ;

" gross " (physiological), 391, 393 ;

"net" (industrial), 391.
Efficiency of an engine, 6, 392 ; of animal

as a machine, 34 ; of heart, 284 ; of

lung mechanism, 311 ; of muscle, 138,

141, 142, 143, 397 ; of organism as a

whole, 391 ; of secretory glands, 154 ;

of tympanic membrane, 203.
Elasticity, 168; of tissues, 169, 310.
Elastin, 172.
Electric charge on colloids, 78, 79 ; on

ions, 50, 52 ; on surfaces, 47, 48,

51.
Electric endosmose, 115, 399.

Electric phenomena of cell, 132 ; of
muscle, 143, 405 ; of nerve, 188 ; of
secretion, 153, 154.

Electrical conductivity, 50, 379, 415.

Electrocardiogram, 295.

Electrodes (anode and cathode), 50.

Electrolytes, 44, 49 ; action of, on
colloids, 79 ; effect of, on dissociation
of Hb02, 249.

Electromagnetic theory of light, 53.

Electrometer, capillary, 47, 259, 404.

Electromotive force, 52.

Electron, 117.

Electron theory, 53.

Electroscope, gold leaf, 121.

Electrostatic attraction of ions, 52, 189.

Electrotonic currents, 189.

Emulsifying agents, 85.

Emulsions, 83, 173, 414 ; effects of acid
on, 86, 378, 389, 415; effects of
anaesthetics on, 86 ; experiments on,
414, 415 ; fatty degeneration in, 389 ;
types of, 84.

Emulsoids, 68 ; protective action of, 80,
413.

Endocrinetes, 368, 373, 388.

Endo-enzymes, 97, 389.

Endosmosis, 399.

Endothelium, 173.

Endothermic reactions, 18.

Energetics of karyokinesis, 383.

Energy, absorbed by chlorophyll, 17 ;
available, 9 ; available, of cell, 36 ;
bound, 7 ; chemical receptors for,
192 ; conservation of, 4 ; consump-
tion of, by glands, 150 ; by kidney,
156 ; by muscle, 143 ; by nerve,
187 ; by organism, 388 ; by respira-
tory musculature, 311 ; degradation
of, 5, 8 ; free, 3, 8 ; index of heart,
286 ; kinetic, 6, 7, 8 ; laws of, 3 ;
necessary for dissociation, 54 ; of
food, 26 ; of growth, 373 ; of radiation
from sun, 14 ; potential, 6, 8 ; vibra-
tory, receptors for, 192, 193, 194, 200,
215*.

Enterokinase, 97.

Entropy, 6.

Enzyme action, 92 ; effect of anaes-
thetics on, 95 ; effect of hydrogen ion
concentration on, 95, 101 ; effect of
solutes on, 95 ; effect of temperature
on, 94 ; inhibition of, 100 ; reversal
of, 99.

Enzyme activators, 97.

Enzymes as catalysts, 93 ; chemical
nature of, 93 ; physical nature of, 93.

Epithelium, 166, 375.

430

INDEX

Equilibrium, 97, 99, 164, 363 ; is death,

2, 331, 377.
Erepsin, 101.
Ergometer, 393.
Errera's rule, 370, 376.
Erythrocyte, 164, 241, 242, 267, 398.
Eustachian tube, 206, 207.
Evolution of alimentary canal, 132, 313 ;

of nervous system, 131, 182 ; of

temperature regulation, 337.
Excitation of cell, 131, 134 ; of muscle,

137, 138; of nerve, 183, 192; of

secretion, 149, 153.
Excretion, 132, 156, 164, 318.
Exosmosis and development, 379.
Exothermic reactions, 19.
Exteroceptors, 191.
Eye, 215.

Faraday-Tyndall phenomenon, 70, 409.
Fat, energy value of, 22 ; function of,

173, 341 ; formation of, 18 ; invisible

in cells, 173, 389 ; visible in cells, 173,

389.
Fatigue, in muscle, 141, 147 ; (forced

respirations), 312 ; in nerve cells, 187 ;

in nerve fibres, 187.
Fatty degeneration, 87, 173, 389 ; role

of acids in, 86, 389.
Ferrocyanide membranes, 398, 399.
Fertilisation, increased permeability in,

384 ; spermatozoon and, 380.
Fibrin, 235.
Fibrinogen, 234.
Fibrous tissue, 171.
Flow through tubes, 277.
Food, changes of, in digestion, 316 ;

composition of, 87 ; energy value of,

26 ; requirements for growth, 372.
Force, fields of, 381.
Form, symmetry of, 381.
Formaldehyde in photosynthesis, 17.
Free energy, 7, 138, 377, 380, 381.
Freezing point, determination of, 399 ;

of urine, 157.
Friction, 243, 336.

Galvanometer, string, 296.

Gas constant, S, value of, 39.

Gas dispersions, 68.

Gas laws, 38, 39.

Gas, pressure of, cause of, 39.

Gay Lussac's law, 38.

Gel, 69.

Gelatine, imbibition by, 411.

Gelation, 79, 409.

Gijbbs -Thomson principle, 48, 152, 175.

Glands, mode of stimulation of, 153. *

Glomerulus of kidney, 162.
Gold number, 80.

Gold, preparation of colloidal, 412.
Graham, 40, 41, 69.
y rays, 120.

Growth, 132, 315, 363 ; and form, 375.
Guanidin salts, dissociation of, 49.
Guldeberg & Waage, Mass action, 55,
61, 368.

Haematocrite, 241, 422.

Haemodynamics, 278, 423.

Haemoglobin, 242, 248, 334.

Haemolysis, 108, 243, 378.

Harvey's work on circulation of blood,
276.

Hearing, 211.

Heart, efficiency of, 284 ; physical
(Ostwald's), 404 ; structure of, 275,
286 ; sounds, 290 ; thickness of walls
of, 286 ; valves of, 288 ; work done
by, 280.

Heat, action of, on chemical reactions,
370 ; on efficiency, 141 ; on emulsoids,
81 ; on enzymes, 94 ; on physical
phenomena, 370.

Heat centre, 350.

Heat, of combination, 54 ; of combus-
tion, 22 ; of dilution, 22, 54 ; of
hydration, 54 ;

Heat production, 34, 347, 349 ; in glands,
154 ; in muscle, 138, 145 ; in nerve,
188.

Helicotrema, 209.

Heliotropic machine, 357.

Heliotropism (phototaxis), 131, 354.

Helmholtz-Lippmann, double layer, 47,
51, 151, 152.

Helmholtz on ear, 211, 213.

Henry's law, 247.

Hess's law, 293.

Hibernation, temperature regulation
during, 337.

Hirudin, 238.

Hoff, J. H. van't, 37, 43, 111, 186.

Hoffmeister series, see Lyotropic series.

Homoiothermic animals, 337.

Hormone, 231.

Hunger, sensation of, 198.

Hydration of colloids, 66, 69, 82 ; ions,
50, 110.

Hydrogen electrode, 422.

Hydrogen ion concentration, 56 ; mea-
surement of, 421 ; of blood, 232.

Hydrol, 55.

Hydrolysis, by enzymes, 96, 389.

Hydrophilic colloids, 173.

Hydrosol and hydrogel, 69.

INDEX

431

Hypertonic and hypo tonic solutions, 107,
398.

Illumination, dark background, 74, 409.
Imbibition by colloids, 66, 153, 172, 245,

410, 411.
Incus, 204.

Index of variability, 369.
Inertia, 9, 354, 357, 378.
Infundibula, 260.
Injury, current of, 134, 143, 145, 190,

405.

Integrative action of blood, 206, 231.
Interface, 47, 151.
Interoceptors, 191.
Intrinsic pressure, 47.
Ion, definition of, 44.
Ionic micelle, 45.
lonisation, 49.

lonisation constant of water, 56.
Ions, electrical charge of, 50 ; hydration

of, 45, 50, 51 ; relative speed of, 50.
Iris, 218.

Iron content of haemoglobin, 251.
Irritability of matter, 131, 193, 319.
Isoelectric point, 79.
Isomeric compounds, 106, 390.
Isometric contraction, 136.
Isotonic solutions, 43, 233.

Joints, 180 ; lubrication of, 179.
Joule's heat, 147.

Karyokinesis, 381.

Kathode, see cathode.

Kephalin and blood clotting, 236, 237.

Kidney, model of, 414 ; structure of, 156,

161.
Kinetic energy, 6, 7, 8, 138 ; of substances

in solution, 36, 46.
Kinetic theory, 37, 75.

Laccase, artificial, 94.

Lactic acid, of muscle, origin of, 138.

Latent heat, 341, 345.

Latent period of tympanic membrane,
202.

Law, natural, 1.

Law of Avogadro, 38 ; Boyle, 38 ;
Bunscn and Roscoe, 354, 356 ; Charles,
38 ; Dalton, 40 ; Gay Lussac, 38 ;
Guldberg and Waage, 55, 61, 368 ;
Henry, 247 ; Hess, 293 ; Miiller, 183,
184, 193; Newton (cooling), 342;
(energetics), 37 ; Schutz, 380 ; Snell,
103 ; Talbot, 356 ; von Weimarn, 69.

Law of autocatalysis, 365 ; catalysis,
380 ; cooling, 340 ; corresponding

states, 69 ; least action, 9 ; length of

life (Rubner), 388 ; mass action, 55,

61, 368; probability, 369.
Laws of energetics, 3, 37 ; growth, 374,

376.
Le Chatelier, principle of, 9, 128, 345,

360, 370.
Leduc's diffusion experiment, 382 ;

osmotic growths, 109, 399.
Length of muscle fibre, energy pro-
portional to, 136, 142.
I^ens of eye, 219.
Leucocytes, 130, 155, 241.
Levers, 202, 207, 308, 315, 320.
Liesgang phenomenon, 79, 413.
Light, absorption of, by chlorophyll, 14 ;

by colloids, 70, 72.
Light, electromagnetic theory of, 53 ;

energy of, 14 ; polarised, 70 ; receptors,

215, 355.
Lippmann's capillary electrometer, 47,

404.

Load, influence of, on efficiency, 395.
Locomotion, movements of, 320.
Lubrication of joints, 179.
Lung, mechanism of, 302 ; structure, 260,

301.

Lungs, oxygen consumption of, 311.
Lymph, 276.
Lyotropic series, 78, 409, 411.

Maintenance of metabolic level, 150.

Malignant growths and radiation, 126.

Malleus, 202, 204.

Malpighian corpuscle, 156, 162.

Mannitol, 19.

Mass action, law of, 55, 61, 368.

Mastication, 314.

Maximum energy of solar spectrum, 14.

Mean free path of molecules, 47.

Measurement of, alkaline reserve of
blood, 417 ; electrical conductivity,
415 ; electric potential differences,
404 ; energy values, 22 ; hydrogen
ion concentration, 421 ; lowering of
vapour pressure by solutes, 402;
osmotic pressure, 398, 399, 402;
surface area of tody, 425 ; viscosity,
409.

Mechanical equivalents of heat, 3, 4 ;
heart (Ostwald), 404.

Mechanics of, bone formation, 175, 331 ;
locomotion, 320 ; mastication, 315 ;
respiration, 303 ; speech, 325.

Mechanism of ear, 211 ; kidney, 163.

Membrana tympani, 201.

Membrane, basilar, 209 ; Reissner's,
209.

432

INDEX

Membranes, adsorption, 109 ; cell, 107,
108, 378 ; for dialysis, 67, 405 ; lipoid,
242, 243 ; of variable permeability,
111, 132; polarised, 116; selective
permeability of, 116; semi-permeable,
41,110,398,399.

Mercury, amoeba, 404.

Mercury heart (Ostwald's), 404.

Metabolism, definition of, 2 ; effect of
intensity of temperature on, 337, 34],
361 ; of nerve centres, 187.

Metabolites, function of, 381.

Micelle, ionic, 45.

Micron, 74.

Milk, 87.

Mimicry, of amoeboid movements, 131,
403, 404 ; of cell structure, 414 ; of
mucoid secretions, 153, 415.

Mirror images (optical activity), 101, 105,
106.

Mitosis, 381, 382.

Model of kidney, 414 ; nerve cell, to
illustrate Miiller's law, 184 ; polari-
meter, 102 ; receiving and reacting
neuron, 185.

Muller's law, 183, 184, 193.

Muscle, efficiency of, 143 ; electrical
changes in, 143 ; energy of, a surface
phenomenon, 137 ; excitatory process
in, 146 ; heat production in, 145 ;
oxygen consumption of, 138 ; phases
of action, 136, 145.

Narcotics, action of, on nervous impulse,
186 ; on soaps, 83.

Narcotics and stability of emulsions, 86,
389.

Negative osmosis, 113, 115.

Negative polarisation, 189.

Nerve, carbon dioxide production in, 187.

Nerve cells, 182.

Nerve, conductivity of, 183 ; elasticity
of, 169 ; electrical change in, 188 ;
fatigue of, 187 ; heat production in,
188 ; mechanical stimulation of, 183.

Nervous impulse, decrement of, 186 ;
nature of, 188 ; refractory period in
conduction of, 186 ; temperature co-
efficient of, 185.

Neuron, 182 ; Brownian movement in,
183.

Neutrality, definition of, 57 ; preserva-
tion of', 241, 252, 331.

Newton's laws of cooling, 342 ; of thermo-
dynamics, 37, 46, 49.

Nicol's prism, 102.

Nitrogen cycle, 390.

Normal solutions, 60.

Nucleus, 129.

Nucleus and mitosis, 381 ; and oxidative
changes, 384.

Oil in water dispersions, 84, 414.

Olfactory nerve, 196.

Oocytin, 380.

Ophthalmoscopy, 224.

Opsonins, 155.

Optical activity, 101 ; due to asym-
metric forces, 105 ; factors modifying,
102 ; measurement of, 104.

Optical isomers, 105, 106 ; and enzyme
action, 98, 106.

Optical resonance, 73.

Optimal, incidence of energy to nerve,
184 ; rate of work, 396 ; temperature
for enzyme action, 94.

Organ of Corti, 210.

Organogenesis, 385.

Osmometer, preparation of, 41, 398.

Osmosis, electrical, 112, 115, 399.

Osmosis in cells, 107, 108.

Osmosis, negative, 113, 115.

Osmotic growths, 399.

Osmotic pressure, and lowering of freez-
ing point, 43 ; and growth, 379 ; and
secretion, 153 ; and turgor, 364, 399 ;
and vapour pressure, 43 ; cause of, 37 ;
definition of, 42 ; demonstrations of,
398, 399 ; measurement of, 399, 402 ;
of blood, 157, 398; of colloids, 45;
of electrolytes, 44, 398 ; of urine, 157,
399.

Ossicles, auditory, 202, 204.

Ostwald, Wo., 66, 72 ; (physical heart),
404.

Oxidase, 96.

Oxidative removal of lactic acid, 138,
140.

Oxygen, calorie equivalent of, 31.

Oxygen, consumption of, glands, 150 ;
heart, 284 ; kidneys, 156, 160 ; lungs,
311 ; muscle, 142 ; organism, 380.

Oxygen, effects of want of, 381, 389 ;
solubility of, 247 ;

Oxygen tension and barometric pressure,
266.

Oxygen tension in air, 246 ; in alveoli of
lung, 249 ; in arterial blood, 249 ; in
tissues, 249 ; in venous blood, 249.

Oxygen transport by blood, 246.

Oxyhaemoglobin, 249.

Pacinian corpuscles, 194.
Parchment paper for dialysis, 407,
Parthenogenesis, 377 ; artificial, 378 ;
stages of, 378.

INDEX

433

Partial pressure of gases, 40.

Perilymph, 209.

Peripheral resistance in vascular system,

281.

Peristalsis, 317.

Permeability as affected by calcium, 113.
Permeability, differential, 133 ; selective,

111.

Peroxidase, 96.
Phagocytes, 155.
Phases of action, of gland, 148 ; of

muscle, 136, 145, 147.
Phases of growth, 368.
Phosphate buffer system, 334, 416.
Photosynthesis, 15, 355.
Phototaxis, see Heliotropism.
Physiological availability of energy, 9,

27.
Pigment, 174 ; cells stimulated by light,

174 ; of iris, colour of, 71.
Plasma, blood, coagulation of, 234 ;

colloids of, 233 ; composition of, 233 ;

crystalloids of, 238 ; CH of, 232 ;

function of, 234, 241 ; osmotic pressure

of, 233 ; oxygen carrying power of,

248 ; refractive index of, 233 ; specific

gravity of, 232 ; viscosity of, 232.
Plasmolysis, 107.
Poikilothermic organisms, 337.
Polarimeter, 104 ; model to explain, 102.
Polarisation, 116; at electrodes, 116;

currents, 133, 188, 189 ; of membranes,

116.

Pole-finding paper, 116.
Positive polarisation current, 188.
Potassium, in Helmholtz double layer,

152 ; radioactivity of, 122, 124 ;

soaps, 82.

Potential energy, 6, 8.
Potentiometer, 421.
Preparation of artificial amoeba, 403.

404 ; chemical gardens, 399 ; colloidal

solutions, 412, 413 ; dialysing vessels,

405, 407; diffusiometer, 398 ; osmo-

meter, 398.

Prepyloric sphincter, 317.
Preservation of neutrality, 241, 252, 331,

416.

Pressure and growth, 374, 386.
Pressure of gas, 39.
Principle of Avogadro, 38 ; Carnot, 32 ;

Gibbs, 48, 152, 175; least action, 9,

11 ; Le Chatelier, 9, 128, 345, 360, 370.
Production of heat, 34, 347, 349.
Proprioceptors, 191.
Protective action of emulsoids, 80.
Protein, energy of, 19, 26 ; energy value

of (physiological), 27.

Proteins as colloids, 80 ; digestion of,

317, 318 ; function of, in preserving

neutrality, 332.
Proteins of blood, 233 ; function of, 239 ;

osmotic pressure of, 233 ; viscosity

of, 232.
Protoplasm, 2, 130 ; as an emulsion, 87,

378 ; Brownian movement in, 183 ;

colloidal nature of, 34, 130; liquid

nature of, 34, 130 ; structure of, 130.
Proximate principles of food, 19, 26.
Pseudo-activation of enzymes, 97.
Pseudo-adsorption, 109.
Pulleys, 323.
Pulse wave, 280, 283.
Putrefaction and anaerobic action, 390.
Pyloric sphincter, 317.

Quantum of energy as stimulus, 194.
Quinine, action on haemoglobin, 244.

Radio-active phenomena, 117.
Radio-activity of potassium, 122 ; effect

on heart, 124.

Radium, effect on colloids, 81.
Rate of adsorption, demonstration on,

411.

Rate of conduction in nerve, 185.
Rate of growth, 365.
Rate of respiration, 265, 311.
Reaction, 58.
Receptors, 191.
Refraction, 103, 215, 219.
Refractive index, 53, 103, 216.
Refractory period of nerve, 186.
Regulation of rate of growth, 375 ;

respiration, 312, 334 ; temperature,

336.

Reissner's membrane, 209.
Reserve air, 259.
Residual air, 259.

Resonance, optical, 73 ; theory, 211.
Respiration, 258.
Respiratory centre, 312, 334 ; reaction

to CH, 312, 334.
Respiratory quotient, 30.
Retina, 218, 358.

Reversibility of enzyme action, 100, 390.
Reversible reactions, 99, 376, 381.
Rheoscopic frog, 145.
Rhythmic movement, model producing,

404.
Rigidity of tissues, 87, 389 ; experiments

to demonstrate, 399, 415.
Rivers, dissolved matter and colour of,

71.

Roentgen rays, 119.
Roux's experiment on growth, 385.

434

INDEX

Rubber, an emulsion, 84 ; imbibition of
benzol by, 410.

Rubner's law of constant energy con-
sumption, 374 ; length of life, 388.

Sach's rule, 367.

Saliva, function of, 314.

" Salting out " of colloids, 79 ; of soaps,
83. .

Salts, effect on pK, 61, 62.

Saponin haemolysis, 244.

Scala media, tympani vestibuli, 209.

Scheme of circulation, 281, 423.

Schutz's law, 380.

Secretion and osmosis, 151, 153 ; and
permeability, 154 ; by renal tubules,
163 ; electrical change in, 154 ;
mechanism of, 151 ; mucoid, 153,
415 ; phases of, 148 ; source of energy
for, 150 ; work done in, 154.

Secretory hypothesis of respiration, 265,
267.

Selective permeability of membranes, 116.

Semipermeable membranes, 41 ; pre-
paration of, 338.

Sensation and stimulus, 194.

Sense organs, 192.

Sensitiveness, absolute, 195.

Serum, blood, 234.

Shell formation, 411.

Simpson light, 126.

Slyke, van, alkali reserve, 241, 333, 418.

Smell, sense of, 196.

Snell's law, 103.

Soap, 82 ; calcium, 82, 318, 415 ; films,
137, 403 ; in faeces, 318 ; loss of
hydrophilic properties of, 82, 318, 415 ;
potassium, 82, 415 ; sodium, 82, 415 ;
soft, 82.

Soap solution, effect of acids on, 82, 415 ;
effect of anaesthetics on, 83 ; prepara-
tion of, 403.

Sodium bicarbonate and C02 tension,
241, 332.

Sodium bicarbonate system, 62, 332, 416.

Sodium soap, 82, 415.

Sol and gel, 69, 234.

Solutions normal, 60.

Solution tension, 163.

Soma, 135.

Sounds of the heart, 290, 299.

Source of energy, for food formation, 17 ;
muscular contraction, 140 ; secretion,
150.

Specific action of enzymes, 98.

Specific inductive capacity, 52, 381 ;
irritability, 193 ; nerve energy, 183 ;
surface, 66, 93, 381, 384.

Spectrum, 14.

Speech, 325.

Spermatozoon, function of, 380.

Sphincter muscles, 316.

Spleen, 164.

Stabilisation of colloids, 78 ; emulsions,

85.

Stapedius, 206.
Stapes, 204.
Stereoscope, 227.
Stereotropism, 358.
Stimulus for growth, 315, 376.
Stomach, 316.

Streaming of protoplasm, 131.
Stress and strain, 168, 381 ; lines of, in

bone, 176.

String galvanometer, 296.
Stroma of blood corpuscles, 243.
Structure of bone, 175 ; cell, 129 ; ear,

200, 205, 209 ; erythrocyte, 243 ;

eye, 218 ; lung, 260.
Struts and ties, 169, 170, 171.
Submicron, 74.
Substrate, 93.
Summation of stimuli, 187.
Surface area of body and heat loss, 340,

343.

Surface area of body and mass, 65, 381.
Surface area of body measurement, 425.
Surface condensation, 151, 158, 175.
Surface energy in cell mechanics, 131 ;

source of, 46 ; temperature coefficient

of, 47, 109, 137.

Surface, extent of, in colloidal suspen-
sions, 65, 237.
Surface tension, 46-48 ; and electrical

charge, 47, 153 ; and growth, 375 ;

and CH, 421 ; effect of solutes on,

48, 237 ; experiments on, 403, 404 ;

in muscle processes, 137 ; in nerve,

183 ;\ in urine formation, 158, 163.
Survival of fittest, 360.
Synapse, 182, 185.
Syneresis of gels, 235.
Synergetical muscles, 323.
Synkinetic movement, 202.
Synovial fluid, 180 ; sheath, 323.
Synthesis by enzymes, 100, 390.

Taste, 196.

Temperature coefficient, 47, 370 ; of
absorption of gas by a liquid, 247 ;
of development, 361, 379 ; of dissocia-
tion, 51, 63 ; of growth, 370 ; of
muscular contraction, 137 ; of nervous
conduction, 185 ; of surface tension,
47, 109, 137.

Temperature regulation, 336, 349.

INDEX

435

Tendon, 172 ; sheaths, 180.

Tension and rate of growth, 374.

Tension of gases, 246.

Tension, see surface tension.

Tetanus, 145.

Thermal conductivity, table of, 340.

Thermal efficiency, 33.

Thermodynamics, laws of, 3, 5.

Thermometer, Beckmann's, 400 ; clinical,

337.

Thermopile, 145, 338.
Thigmocytes, 237, 241.
Thorium, 123, 124.
Threshold values, 163, 193.
Thrombin, 235, 236, 237.
Thrombokinase, 235.
Thromboplastin, 236.
Thymus, 238, 373.
Thyreoid, 373.
Tidal air, 259.
Tissue, connective, 168 ; elasticity of,

169 ; fibrous, 171 ; strength of, 170 ;

vegetative, 166.
Tone of muscle, 142.
Tongue, 196, 314, 325.
Touch, 193.

Touch-button mechanisms, 312, 318.
Transmission of acquired characters, 361.
Trigger action, 183.
Trigger energy, 7, 8, 138, 146.
Trophic and secretory nerves, 153.
Tropisms, 131, 354.
Trypsin, 96, 97, 101.
Turgor, 364, 399.
Tympanic membrane, 201.
Tyndall phenomenon, 70, 409.
Types of colloids, 69 ; dispersoids, 68 ;

emulsions, 84.

Ultra-filtration, 75.

Ultra-microscope, 74.

Ultra-violet light, 14, 20, 126 ; action of,

on organisms, 126, 127, 132.
Uranium, 120, 121.

Urine, formation of, 162 ; work done in
formation of, 157.

Valves of heart, 288 ; veins, 288.

Vapour pressure, of a liquid, 38 ; and
osmotic pressure, 43 ; Barger's de-
termination of, 402.

Variations in growth, factors causing,
368.

Vectors, law of, 376.

Vegetative tissues, 166.

Velocity of growth, 368.

Vibratory energy, receptors for, 192,
193, 194, 200, 215.

Viscosity, measurement of, 409, 422 ; of
blood, 242, 243, 422; of emulsoids,
389 ; of plasma, 232.

Visual judgments, 226, 227.

Vital capacity of lungs, 259.

Volition, 11.

Volume of blood, 250.

Volume of blood corpuscles, 243.

Waller's characteristic, 184.

" Waste " heat, 6, 12, 390.

Water, chemical formula of, 54 ; di-
electric constant of, 53 ; dissociation
of, 55 ; electric conductivity of, 53,
55.

Water equivalent of calorimetric bomb,
25 ; of human body, 341.

Water, heat conductivity of, 340, 345.

Weimarn, von, law of, 69.

Work, done in formation of urine, 15'3;
done in secretion, 150, 154 ; of heart,
280 ; of lungs, 310 ; of muscle, 136,
142 ; of phonation, 359.

X-rays, 119, 120.

Young's modulus, 168, 169.

Zymase, 97.
Zymogen, 97.

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