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AN INTRODUCTION TO BIOPHYSICS

PRINCIPLES OF HUMAN PHYSIOLOGY

By E. H. Starlixg, C.M.G., F.K.S., M.D. Fourth Editinn.
570 Figures, 10 in colour. 25s.

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J. & A. CHURCHILL

Q O

AN INTRODUCTION
TO BIOPHYSICS

<

BY

DAVID BURNS

M.A., D.Sc.

Professor of Physiology in the University of Durham

Late Grieve Lecturer on Physiological Chemistry

in the University of Glasgow

WITH A FOREWORD BY

Prof. D. NOEL PATON

M.D., LL.D., F.R.S., Etc.

SECOND EDITION

WITH 116 ILLUSTRATIONS

LONDON

J. & A. CHURCHILL

40 GLOUCESTER PLACE
PORTMAN SQUARE
1929

TO

I. R. V. M.

Printed in Great Britain

PREFACE TO THE SECOND EDITION

The scope of the book has been slightly altered to make it more in
accord with the Si/Uabus of Biophysics suggested by the General
Medical Council. Sections I. and II,, with the corresponding
exercises in Part II., cover the syllabus of the Physical Physiology
required by The Examining Board in England of the Royal College
of Physicians of London and the Royal College of Surgeons of Eng-
land. The text, however, has not been cut merely to suit examina-
tions, but an attempt has been made to view^ the human body as
far as possible as a physical machine. To do this adequately a
knowledge of mathematics beyond the stage usually professed by
medical and other students of the Biological Sciences is necessary.
Wc ha\'e therefore cut down mathematical treatment to the
mininunii and have indicated where the student who desires to
study the subject further inay get additional information.

In spite of efforts to keep the book reasonably small, expansion
has taken place. A new chapter on Emulsions and Soaps has been
added, and the chapters on Surface Tension, General Receptors,
Eye, Ear, Voice and Movements of the Limbs have been almost
entirely rewritten. The greatest changes have been made in
Part II., as the result of six years' teaching experience.

The main purpose of this preface is to record my thanks to all
who have helped me in the revision. My Staff at the College of
Medicine has generously come to my aid. Messrs. Seeker and
Saunders have read all the proofs and made many valuable sug-
gestions. Mr. Saunders and my wife have checked most of the
calculations. I am also indebted to my wife for much help in that
most tiring of tasks, the compilation of the index of subjects.

Illustrations have been drawn from various sources, and I desire
to thank the various authors who have given me permission to
use their blocks. Especial mention should be made of the permis-
sion freely given by Professor L. J. Henderson to use his " Align-
ment Chart," and by Professor Leathes for his series of " Myelin "
ligures.

Figs. 61, 75, 80, 81, 99 and 100 are from the late Professor
Starling's Principles of Human Physiology ; 2, 21, 2-t and 25 from
Pryde's Recent Advances in Biochemistry ; 68 and 88 from Lo\-att
Evans' Recent Advances in Physiology ; 72 from (ioulden's Rcfrac-

vi PREFACE TO THE SECOND EDITION

tion of the Eye ; 5 and 12 from Crocker and Matthew's Theoretical
and Experimental Physical Chemistry. To all these authors and
to their publishers, Messrs. J. and A. Churchill, I desire to express
my thanks.

I am indebted to Messrs. Baird and Tatlock, London, for the
loan of the blocks for Figs. 8, 18, 22, 45, 53, 67, 104, 106 and 109.

I wish to record my thanks to Miss E. M. Paul, of the King
Edward School of Art, Armstrong College, for the original drawing
for Fig. QQ, and to Mr. J. Robson for the rough drawings from
which all the other new illustrations were made.

DAVID BURNS.

University of Durham College of Medicine,
Newcastle-upon-Tyne.

PREFACE TO THE FIRST EDITION

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 particvilar, 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
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

vii

viii PREFACE TO THE FIRST EDITION

first three sections of the book in shp-proot' ; 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 Chapters XIX. and XXIX. have been
drawn. A book of this nature could not be written without con-
stant reference to the Principles of General Physiology. If my
Introduction 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. 41, 47, 85, 86, 95, 98, 101 and 116) ; to Professor Starling and
Messrs. Churchill for the following figures from Principles of
Human Physiology: 1, 10, 16, 31, 56-59, 63, 65, 73, 96, 97, 103,
105, 107, 112 and 114 ; to Mr. Crowther for Fig. 39 from Molecular
Physics, and to Mr. Emil Hatschek for Figs. 15, 19 and 20 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. 46) from his monograph on The
Secretion of Urine (Messrs. Longmans, (ircen and Co.) : to Pro-
fessor Soddy and " The Electrician " Publishing Co., for the
diagram of the gold-leaf electroscope (Fig. 40) from Radioactivity.

To Dr. Bradford for allowing me to reproduce, from the Bio-
chemical Journal, his photograph of adsorptive stratification
(Fig. 17), and to Professor Roaf for the pll-C\ graph reproduced
from the Proceedings of the Physiological Society (Fig. 115).

To Messrs. the Cambridge and Paul Scientific Instrument Co.
for the figures illustrating the electro-cardiograph (Figs. 91, 92 and
93) ; to Messrs. Hawksley for those of the viscosimeter (Figs. 108
and 110), and to Messrs. Gallenkamp for Figs. 3 and 102 of the
bomb calorimeter.

The remaining illustrations were drawn by Dr. G. M. Wishart,
Assistant in the Department of Chemical Physiology, and by Mr.

PREFACE TO THE FIRST EDITION ix

John Waters, a student ol' nRnlieinc here. To their skill and care
I owe much.

I am greatly obliged to Mr. A. V. Steen, B.Sc., one of om*
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 publica-
tion and to the printers for the care they haAC taken and the con-
sideration shown when my ignorance made large demands on their
time and patience.

Institute of Physiology,

University of Glasgow.

CONTENTS

PAGE

INTRODUCTION. Bv Professor D. Noel Paton, M.D.. LL.D.,

F.R.S. . . ^ xvii

PART I. SYSTEMATIC
SECTION I : ENERGETICS

CHAP.

I. LAWS OF ENERGY 1

Definition of Biophysics, 1 ; of Laws, 1 and 2 ; of
Matter and of Energy, 3. Equivalent Units of Work, 4.
First Law of Thermodynamics, 4. Corollaries of First
Law, 5. Second Law of Thermodynamics, 6. States
of Energy, Potential and Kinetic, 6-8. Physiological
Availability of Energy, 9. Principle of Le Chatelier, 9.
Inertia, 10-13.

II. THE STORAGE OF ENERGY 14

Chlorophyll, 14. Grotthus' Law, 15. Synthesis of
Carbohydrate, 15-18 ; of Fats and Proteins, 19.
Absorption Spectra of Chlorophylls A and B, 20.
Catalyst for Photosynthesis, 21.

III. LIBERATION OF ENERGY.— (1) CALORIMETRY . . 22

Measurement of Energy in Calories, 22. E.V. of Foods
by Ultimate Analysis, 22-25 ; by Calorimeter, 25-27 ;
by Direct Animal Calorimetry, 27 ; by Indirect Calori-
metry, 28. Respiratory Quotient, 29. Hiberna-
tion,*30.

IV. LIBERATION OF ENERGY.— (2) THE ANIMAL AS
MACHINE 31

Comparative Thermal Efficiencies, 32. Animal not a
Heat Engine, 33. Energy Changes in Living Cell, 33.

V. LIBERATION OF ENERGY.— (3) ENERGY OF SUB-
STANCE IN SOLUTION 35

State of Matter in Solution, 35. Kinetic Theory, 35.
Newton's Law, 36. Boyle's Law and Charles' or Gay-
Lussacs' Law, 37. Evaluation of R in Gas Equation,

37. Avogadro's Hypothesis, 37. Gaseous Diffusion,

38. Osmosis, 40. Osmolar Concentrations, 41.

VI. LIBERATION OF ENERGY.— (4) SURFACE ENERGY . 44

Du Noviy's Torsion Balance, 45. Drop-weight Method,
45. Capillary Rise and Air Bubble Methods, 46.
Ageing of Sxu-faces, 46 . Temperature Coefficient, 46.
Orientation on Siu-faces. 47. Utilisation of Surface

CONTENTS xi

CHAl'. lAGE

Energy. 48. Ostwaki's " Physical Heart," 49. Capil-
lary Electrometer. 50. Capillary Active Substances,
51. Adam's Experiments, 52. Adsorption, 53-55.

SECTION II : CELLULAR MECHANICS

VII. lONISATION 56

Definitions, 56. Charge on Ions, 56. Speed of Ions,
57. Hydration of Ions, 57. Effect of Temperature on
Dissociation, 58. Dielectric Constant, 59. Electron
Theory, 59-60. Properties of Water, 61. lonisation
Constant, 62. Hydrogen Ion Concentration, 63.
jM, 64. Acids and^Alkalis, 65. Salts, 68.

VIII. DISPERSE SYSTEMS.— I. COLLOIDS .... 71

Effective Surface, 71. Specific Surface, 72. Crystal-
loids and Colloids, 72-73. Nomenclature of Disperse
Systems, 74. Preparation of Colloids, 75.

1. Properties Depending on Size of Particles Dis^jersed.
(i.) Optical. 76. Faraday-Tyndall Phenomenon, 79.
Ultramicroscope, 80. (ii.) Kinetic, 81. Brownian
Movement, 81-83. Ultrafiltration, 84. Osmotic
Pressure, 84. Diffusion, 85. Electrical Diffusion,
86. Liesegang Phenomenon, 86-87. Dialysis, 87.
Vividiffusion. 88. Viscosity, 88-90.

2. Properties Depending on Charge on Particles Dis-
persed, 90. Isoelectric Point, 91-92. Coagulation, 92.
Salting out, 93. Protective Action of Emulsoids, 93.
Precipitation by Neutralisation, 95. Action of Radiant
Energy, 96.

3. Properties Depending on Size, Charge and Structure,
96. Imbibition, 97. " Bound " Water, 98. Pressure
and Heat of Imbibition, 99. Syneresis, 100. Colloids
as Reservoirs of Energy. 101.

IX. DISPERSE SYSTEMS.— II. SOAPS AND EMULSIONS . 103

Types of Emulsions. 103. Theories of Formation of,
105. Breaking of, 106. Soaps, 106. Effect of Cation
on Hydrophilic Properties of, 107. Emulsifying Pro-
perties of, 108. Liquid Crvstals, 108. Myelin Forms of
Lipoids, 109. Foodstuffs as Emulsions, 111. Effect of
Cooking, 113.

X. ENZYMES. THE TOOLS OF THE CELL . . . 115

Catalysts, 116. Types of Catalysts, 117. Charac-
teristics of Catalysts, 117-118. Properties of Enzymes,
118-120. Nomenclature, 120. Endo-enzymes and
Ecto-enzymes. 121. Zymogen Secretion, 121. Anti-
enzymes, 122. Enzymes as Catalysts, 122-123.
Specificity of Action. 123. Syntheses by Enzymes, 124.
Balanced Reactions, 124. Influence of /jH on Activity,
126. Optical Activity. 126-131. Snell's Law, 128.
Polarimeter, 129. Optical Isomerism. 130.

53628

xii CONTENTS

CHAP. TAOE

XI. MEMBRANES (PLASMAHAUT) 132

Need for Cell Membrane, 132. Nature of, 133. Forma-
tion. 134. Composition, 135. Structure. 136. Per-
meability, 136-145. Electrical Osmosis, 140. Nega-
tive Osmosis, 140. Donnan Equilibrium, 143. Polari-
sation, 145. Selective Permeability, 145.

XII. THE CELL 147

Composition. 148. Nucleus, 149. Phenomena of Life :
(o) Movement. 150 ; (b) Irritability, (c) Ingestion and
Excretion, 151 ; (d) Growth, (e) Electric Phenomena.
152. Current of Action, 153. Artificial Cell, 153.
Polarisation Current, 154.

XIII. RADIO-ACTIVITY 155

Electrons, 156. Kathode, X. a, j8 and y Rays, 157.
lonisation, 158. Potassium, 159-162. JPhysiological
Effects, 163-164. Ultra-violet Rays, 164. Ergosterol,
165.

SECTION III : CELL COMMUNITIES

XIV. THE ARMY WHEREWITH THE BODY WAGES WAR
WITH NATURE—THE MUSCLE CELLS 166

As Energy Transformers, 167. Structure, 168. Iso-
metric and Isotonic Contractions, 169. Muscular
Cycle, 171. Glycogen and Lactic Acid, 172. Lactic
Acid and Heat Evolved, 173. Function of Lactic Acid.
174. Theories of Muscle Action : (1) Surface Tension
Theory, 174. (2) Osmotic, (3) Imbibition. (4) Liquid
Crystal Theories, 176. (5) Condenser Theory. 177.
Temperature Coefficient, 177. Efficiency, 178. Elec-
trical Effects, 179. Rheoscopic Frog, 180.

XV. MANUFACTURING CELLS 182

Phases of Activity, 182. Conditions Controlling Secre-
tion, 183. Oxvgen Needs, 184. Mechanism of Secre-
tion, 185, 187^ Electrical Potential Developed. 186.
Heat Developed in Secretion, 187.

XVI. THE ARMY FOR HOME DEFENCE .... 189

Ciliated Cells, 189. Reticulo-Endothelial System. 190-
192. Formation of Gall-stones, 192. Kidneys, 193-202.
Structure, 193. Function of Bowman's Capsule, 194.
Saline Diuresis, 195. Gum Saline, 196. Sulphate
Diuresis. 196. Function of Tubules, 197. Work Done
by Kidney, 198. " Free " and " Bound " Water, 199.
Theories, 199-201. Other Glands of Elimination, 202.

XVII. THE CIVIL ENGINEERS OF THE BODY . . . 203

Epithelium. 203. Connective Tissues, 204. Stress and
Strain, 205. Hooke's Law, Young's Modulus, Shear
Modulus, 206. Bulk Modulus. Poisson's Ratio, Elas-

CONTENTS xiii

CHAl'. PAGE

ticity, 207. Strenoth of Materials, 208. Girders and
Trusses, 209. Mucoid Tissue, Fibrous Tissue, Elastic
Fibres, 210. Endothelium, Fat, 211. Pigment, 212.
Cartilage and Bone, 212-220. Relative Strength of
Bones, 213. Internal Structure, 214-218. Fractures,
218. Lubrication, 218. Joints, Tendon Sheaths, 210.

XVIII. THE INTELLIGENCE SERVICE. NERVE CELLS . 221

Neuron, 221. Structvn-e and Function, 222. Miiller's
Law, 223. " All or Nothing," 224. Nature of Impulse.
Electrical Changes, 225. Cause of Electrical Changes,
226. Refractory Period. Summation, 227. Fatiffue.
Metabolism, Temperature Coefficient. Polarisation. 228.
Negative Polarisation, Polarisation Model, 221). Elec-
trotonus, 230. Positive Polarisation, 231. Theory, 232.

XIX. OUTPOSTS OF THE INTELLIGENCE SERVICE.

(a) GENERAL AND INTRA-COMMUNAL RECEPTORS 233
Threshold. 233. Adaptation. Frequency of Discharge,
234. Stimulus and Sensation, Fechner's Law, 235.
' Classification of Receptors, 236. I. Phasic Receptors :
(1) Touch, 237 ; (2) Tickle, 238 ; (3) Pain, 239.
II. Phasic-Postural Receptors : (4) Pressure, 240 ;
(5) Temperature. 241. III. Postural Receptors, 242.
IV. Special Receptors : (6) Taste, 242 ; (7) Smell, 244 ;
(8) Hunger, 246.

XX. (b) DISTANCE RECEPTOR FOR SOUND. THE EAR . 249

Tympanic Membrane, 250. Ossicles, 252. Mechanism
of Middle Ear, 254. Cochlea, 256. Resonance Theory,
258. Displacement Theory, 262. Pressure-Pattern
Theory, 263. Differentiation of Sounds in Intensity,
264; in Timbre, 265. Advantages of Form of Cochlea,
265. Binaural Hearing, 266. Bone Conduction, 266.
Utricle and Saccule, 267.

XXI. (c) DISTANCE RECEPTOR FOR LIGHT. THE EYE . 272

Physics of Refraction, Lenses, etc., 272-275. Anatomy
of the Eye, 276-278. The Eye as an Optical Instru-
ment, 278. Refractive Indices of Media, 278. San-
son's Images, 279. Accommodation. 280. Prevention
of Optical Defects. 282. Mechanism of Retina, 285.
Effects of Light on Retina, 287. Movements of the Eye-
ball, 290, Binocular Vision, 292. Analysis of Retinal
Stimuli, 295. Ophthalmoscopy, 296.

SECTION IV : TRANSPORT

XXII. INLAND TRANSPORT. THE BLOOD .... 298

Development, 299. Function, 300. Composition. 300
-317. Plasma. 301. Clotting, 303-310. Crystalloids
of Plasma, 310. Blood Corpuscles, 312 321. Shape of
Erythrocytes, 313. Contents of Erythrocytes, 316.

XIV

CONTENTS

CHAP .

PAGE

Haemolysis, 317. Colligative Properties of Whole
Blood, 320. Viscosity, 321.

XXIII. INLAND TRANSPORT.
TION OF THE BLOOD

THE RESPIRATORY FUNG

XXVIII. OVERSEAS TRANSPORT. THE VOICE

I. Phonation, 404-409. Mechanism of Larynx, 404.
False and True Vocal Cords, 405. Notation, Frequency,
Pressure and Amplitudes of Air Waves of the Musical
Scale, 406. Pitch, 407. Overtones, 408.

II. Speech, 409-412. Vowels, 409. Consonants, 410.
Work Done in Speaking, etc., 411-412.

322

Law of Henry, 322. Absorption Co-efficients. 323.
Gas-holding Power of Plasma, 324. Dissociation of
Oxy-hsemoglobin, 325. Nature of Union Between Og
and Hb, 326. Influence of Various Conditions on the
Dissociation of Oxy-hasmoglobin, 327-332 ; Transport
of Carbon-Dioxidei 332-339 ; Alignment Chart, 339 ;
Integrative Action of Plasma, 342.

XXIV. INLAND TRANSPORT. LOADING UP . . . . 344

Vital Capacity, 345. Effective Absorptive Surface of
Lungs, 346. Passage of Gas through a Membrane. 347.
Diffusion of CO.,, 348. Diffusion of Oxygen. 349.
Effect of Muscular Work, 351. Effects of Altered Air
Pressure, 352. Decompression, 356.

XXV. INLAND TRANSPORT. THE CIRCULATION . . 360

General Scheme, 360. Harvey's work, 362. Htemo-
dynamics, 363. Piezometry, 364-366. Work Done
by a Force-pump, 366. Work Done by Heart, 368.
Efficiency of the Heart, 371. Conditions for Maximal
Efficiency, 372. Form and Function, 373. Valves in
the Veins, 375. A.V. Valves, 376. Semi-kmar Valves,
377. Sounds of the Heart, 378. Angle of Origin of
Branch Vessels, 380.

XXVI. INLAND TRANSPORT. THE ELECTROCARDIOGRAM 382

Rheoscopic Frog, 382. Capillary Electrometer, 382-
384. Leads for Electrocardiograph, 384. String Gal-
vanometer, 385. Analysis of Records, 387. Monocar-
diogram, 387. Triangle Method of Analysis, 388.
Effect of H"*^ Concentration on Cardiogram, 388.

XXVII. OVERSEAS TRANSPORT. EXTERNAL RESPIRATION 390

Principle of Mechanism, 390. Structure of Lungs, 391.
Mechanics of Respiration, 892. Mechanics of Dia-
phragm, 393. Thoracic Respiration, 395. Mechanics
of Thorax, 397. Elasticity of Lungs, 398. Efficiency
of Lung Mechanism, 400. Effect of the Respiratory
Movements on Mass Movements of the Blood, 401.
Modifications of the Respiratory Act, 402. Influence
of Heart Action on Respiratory Movements, 402.

404

CONTENTS

XV

ClIAl'.

XXIX.

OVERSEAS TRANSPORT. ALIMENTARY CANAL

General. 413. Mouth. 413-415 : Functions of Saliva,
Muscles ol' Tonpue, 414 ; Act of Swallowinp;, 41.5. The
Stomach, 416 418 : Cardiac and Pre-pyloric Sphincters,
417 ; Pyloric Sphincter, 418. The Intestines, 418-419 :
Faeces, 419 ; Secretion of Acid and Alkaline Juices,
420.

XXX. MOVEMENTS OF THE LIMBS

Levers, 423. Pulleys, 425. Centre of Gravity, 426.
Standing, Bending and Walking, 427-428.

PAGE

413

422

XXXI.

XXXII.

SECTION V: THE ANIMAL AS A WHOLE

THE PRESERVATION OF NEUTRALITY

Factors Tending to Preserve Neutrality, 430. Alkali
Reserve, 431, Part Played by Erythrocytes, 433.

XXXIII. TROPISMS— THE SLAVES OF THE LAMP .

Heliotropism, 455. Talbot's Law, 457. Heliotropic

" Dog," 458. Geotropism, Stereotropisni and Chemo-

tropism, 459. Galvanotropism, Orientation in Space,
460.

429

THE REGULATION OF TEMPERATURE . . 435

Instruments used to Indicate Animal Temperature,
436. Radiation, 439. Conduction, 440. Table of
Thermal Conductivities. 441. Temjierature Gradient,
442. Evaporation of Moisture, 443. Katathermo-
meter, 446. Physical Processes involved in the Regula-
tion of Temperature, 448. Chemical Processes, 449.
Heat Centre, 450. Ventilation, 450. Clothes, 451.

455

462

466

XXXIV. ADAPTATION

Survival of Fittest, 462. Nature of Engrams, 463.
Various Influences from Environment, 464.

XXXV. GROWTH

Nature of the Phenomenon, 466. " Free " and
" Bound " Water, 467. Normal Rate of Growth, 468.
" Expected " Weight and " Calculated " Length, 469.
Centimetre Index, 470. Factors Modifying Growth :

(1) Phase Differences, 472 ; Sex and Race, 473 ;

(2) External Factors, 473 ; Seasonal Variations, 474 ;
Nutrition, 475 ; Energetics of Growth, 476. Rubner's
Law of Constant Energy Consumption, 477. Growth
and Form, 478. Bohn's Laws, 479.

XXXVI. DEVELOPMENT 480

Cell Division, 480. Fields of Force, 481. Cause of Cell
Division, 483. Maturation of Germ Cells, 485. Ferti-
lisation, 486. Artificial Parthenogenesis : (1) Mem-

XVI

CONTENTS

CHAI'.

PAGE

brane Formation, 486 ; (2) Exosmosis, 487. Organo-
genesis, 489. Growth Tension, 490. Energy of Deve-
lopment, 491.

XXXVII. DEATH AND DISSOLUTION 492

Rubner's Law of " Length of Life," 492. Cloudy
Swelling, Fatty Degeneration, 493. Continuity of
Matter and of Energy, 494.

XXXVIII. THE EFFICIENCY OF THE ORGANISM . . . 495

By E. P. Cathcart, M.D., D.Sc., LL.D., F.R.S., Regius
Professor of Physiology, University of Glasgow.
Gross and Net Efficiency, 495. Basal Metabolism, 498.
Effect of Load on Efficiency, 499. Effect of Speed, 500.
Isolated Muscle, 501.

PART II. ILLUSTRATIVE EXPERIMENTS

LIST OF EXPERIMENTS 502-505

LIST OF PREPARATIONS 505, 506

EXPERIMENTS 506-557

PREPARATIONS 557-563

CONVERSION FACTORS 564-566

SOME PRACTICAL HANDBOOKS 567

INDEX OF NAMES 568

INDEX OF SUBJECTS .571

INTRODUCTION

By Professor D. No£l Paton, M,D., LL.D., F.R.S.

On looking back over a forty years' association with physiology
nothing is more striking than tlie 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 signili-
cance of Graham's colloids was not appreciated, and the pheno-
mena 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 " delomorphous "
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 consti-
tution, they promptly gave it a name with no connection with its
chemical nature, and these names have generally continued 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.

It was the " what happens ? " which interested these older
Avorkers : " 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

ii. xvii b

xviii INTRODUCTION

science of physics, based as it is so largely upon mathematics, has
had an enormous effect in getting rid of this habit of vague theoris-
ing 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 preparation.

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
curiosit}^, 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 physio-
logy 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 —
" 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 patho-
logy, of experimental medicine and of pharmacology : and the
knowledge of disease and of its treatment has thus been put upon
a sounder basis.

INTRODUCTION xix

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 biophysics has evolved in tlie same
way as that of biochemistry. Perhaps some attempt sliould
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

TAirr I. SYSTEMATK^
SECTION I.: ENERGETICS

CHAPTER I
LAWS OF ENERGY

" There is in reality only one general physics, only one chemistry, anci only one
mechanics, in which all the phenomenal manifestations of nature are included, both
those of living bodies and those of inanimate ones." Claude Bernard.

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

SODDY.

Biophysics deals with the appHcation of physical and physico-
chemical laws to the actions of living things. It is necessary
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 jurisprudence. 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 circum-
stances. 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 science is the most finidamental of the
experimental sciences and, so far as is known, its laws are applicable
to all non-living matter. Biochemists have attempted to break

2 LAWS OF ENERGY

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 synthesised 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, justifi-
able ? 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 accounted
for, and could be recorded as due to pressiu-e 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 not 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 alterations
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. metabole, to 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. kaia = down). If anabolism is greater
than catabolism, the organism grows ; if the two processes balance,
the organism exists. The predominance of catabolism leads to
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-

fc)

MEASUREMENT OE ENERGY 3

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. Energy, then, is that
which produces an effect on our senses. Our sense organs, as we
shall see later (Chap. XIX.), are stimulated by changes of energy in
their environment. We see, because radiant energy of a certain
frequency falls on our retinae ; we hear when the hair cells on the
basilar membrane are stimulated as the result of air waves of
definite frequencies transmitted to them via tympanic membrane
or via bone ; our senses of taste and smell depend on changes of
chemical energy, while changes in kinetic energy produce the
sensations of heat, cold, tickle, touch, pressure, position, etc.

Energy is measured by its power to do work. The kind of unit
used will therefore depend on the nature of the work done. In
the C.G.S. system the unit of work is the erg — that amount of
work which is done when unit force is overcome through unit
distance. The unit of force is the dyne, and is defined as the force
Avhich acting on a gram for a second would gi\e it the velocity of
one centimetre per second. An erg is, therefore, a dyne-centimetre.
If the power developed is electrical it would be measured in watts,
if mechanical, u\ foot-pounds per second, or in horsepower, and so on.
These various units may be converted into one another (Table I.).
For our piu'pose it is most convenient to measure energy in heat
units or calories.

1—2

4 LAWS OF ENERGY

In 1798, Count Rumford, who was engaged in boring cannon,
showed that the energy of a moving body, i-c kinetic energy, could
be transformed into heat. Later, Joule demonstrated the equiva-
lence of these two forms of energy. 427 kilogrammetres of work
always produce (under standard conditions) one Calorie of heat.
Conversely, 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 e\'en to influence the
rate of transformation have failed. Chap. XIII.)

TABLE I

Equivalent Units of Work

1 Calorie n / 41-9 X 10^ ergs.

or I ^^jy^^g^i- ' 98-8 X 10^ foot-poiindak.

l.OUO gram, calories - . - 42-6 X 10^ gram. cms.

or i ^'^^^ ^ ^^^ foot-lbs.

10^ microcalories / '4190 joules.

Equivalent Units op Power
1 Calorie per second = 41*9 X 10^ ergs per second,

= 4-19 X 103 ^.atts.
= 4-19 kilowatts.
= 5-61 horse-power.

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 (First Law of Thermo-
dynamics).

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 characteristic
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 + Oo^iC02 -|- HgO + heat energy.

LAW OF HESS 5

Corollaries of the First Law.

The followino- two (Icductions arc of biological interest :

1. The total energy of a system in a given state is for the system
in question a definite characteristic of iJuit state, and it is totally
independent of how the system reached that state.

The energy that would be liberated by the fall of a kiloerani, e.g., of lead,
from a height of 3UU 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.

[h) 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 he lifted as a series of chemical compounds weighing more than 1
kilogram as salts of lead and reduced to )netallic 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.

Law of Hess. — This second corollary w^as enunciated by Hess in
1840 as the result of experiments. He worded it, " The amount of
heat generated by a chemical reaction is the same whether it takes
place all at once or in steps."

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 (Second Law of Thermodynamics),

When a substance or group of substances is changed into a
substance or group of substances with a smaller energy-content,

6 LAWS OF ENERGY

the energy thus Hherated is, iiv theory, available for work. In
practice, it is found that all this surplus energy cannot be 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 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 how waves in ether, e.g. light or the
longer (wireless) waves, fall away in strength in widening concentric
zones as their influence spreads from the source, till at infinite
distance the most sensitive apparatus can only with difficulty
detect the disturbance. 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 a maximum." 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,
^'urther, 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
so " degraded " during a transformation from one form to another
may be taken as an inverse index of the efficiency of the transform-
ing 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 lueasured
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-

POTENTIAL EXKHaV 7

strated that it is storrd and is rccoN ci-ablf. 'I'lic simplest example
is the ap})heatioii of toree to a peri'ectly ehistie system. On
removal of the foree 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 distor-
tion. The hackneyed example of energy storage is, of course,
that of our coal supply.

There can be no liberation of energy without free energy. No
change can take place without free energy. Our senses make us
aware of free energy, but potential energy can be perceived only
as the result of reasoning from past experiences. Potential energy,
then, is a psychological concept.

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 explosiv'C 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.
In order to get w^ork out of these quiescent bodies, all that is
necessary is the application of a suitable and sufficient stimulus, i.e.
a small quantity of free kinetic energy (pp. 222 and 235). 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.

Free and Bound Energy. — In 1882 Helndioltz 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 delinition,
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 woidd have

8

LAWS OF ENERGY

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 environ-
ment. No work could be got from it without the previous expenditure 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 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

(1) V

Available for work,
i.e., Free Kinetic Energy

i (2)

Not directly available for work

i (4)

Potential Energy
Add trigger Energy from (1)

i (3)

Degraded Heat
(Entropy)
Totally unavailable

Free Energy
Total Available Energy

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. that of coal, requires the employment of only small quantities
of free energy to render it immediately available for work, while
other varieties, e.g. that of radio-active minerals, have their energy
boimd in such a way that it is evolved with excessive slowness.
Uranium contains the same amount of energy as 250,000 times or

more of its weight of coal, but little more than part

10,000,000,000

PRINCIPLE OF LE CHAT ELI ER 9

of this is given out in a year (Chap. XIII.). To enable mankind to
avail hiniscli' of this kind of energy, some means will have to
be devised for speeding up and eontrolhng 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
leading eramped lives and fighting among ourselves, whether in
peaee or war, for a modicum of the means of existence, science
tells us that, in the commonest materials that make up the frame-
work of the world, there is energy of a magnitude of which we ha\-e
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."

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 impassable
mountains. The water power, i.e. the stored energy of the former,
is utilisable, while the latter could not be tapped without 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-available. Future scientists may discover
how to draw upon this surplus energy supply.

Principle of Le Chatelier.

" Every system in chemical equilibrium, under the influence of a
change of any single one of the factors of equilibrium, undergoes a
transformation in such direction that, if this transformation took place
alone, it ivould produce a change in the opposite direction of the
factor in question. The factors of equilibrium are temperature,
pressure and electromotive force, corresponding to three forms of
energy — heat, electricity and mechanical energy.''

The above is the principle as enunciated by Le Chatelier in 1884.
Consider the energy changes in the formation of water where
hydrogen and oxygen combine with the evolution of 68-3 Calories
for every gram molecule formed. The equation of the reaction
may be written

2H2 + 02^ 2H0O + 136-6 Calories.

10 LAWS OF ENERGY

But at high temperatures the reaction is reversible, that is, H and O
are formed from the water :

tiHoO + 136-6 Calories -^ 2H2 + O^

Both reactions take place simultaneously, some of the water being
decomposed steadily and some water being formed, so that an
equilibrium is established between these two opposing forces :

2H2 + Oo := 2H2O + 136-6 Calories.

If we add either H alone or O alone to the system, the equilibrium is
shifted in the direction of the upper arrow so that some of the added
constituent undergoes combination. Similarly, if we alter another
of the intensity factors, say, temperature, and apply heat to the
reacting substances, the equilibrium is shifted in the direction of the
lower arrow and heat is absorbed. The principle of Le Chatelier
enables a prediction to be made of the direction in which a reaction
to a disturbance may take place. Only those predictions are valid
which involve changes in the intensity factors of the energy of a
system.

The principle has been broadened in order to apply it to the
dynamic equilibrium of living things. For example, almost simul-
taneously with the publication of Lc Chatelier's paper, Fredericq
stated, " The living organism is such that each disturbing influence
produces in the organism itself a compensatory reaction which
tends to neutralise the disturbance and restore the equilibrium."
Now Le Chatelier postulated that the systems to which his principle
applied were to be in stable equilibriimi, and so one cannot justly
apply his name to Fredericq's interesting hypothesis.

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 that of its environment.
Further, the degradation of energy follows the line of least
resistance. This is known as the " Law of Least Action." 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 imless 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 wull, in
the circumstances, give relief from strain with the least possible
expenditure of energy. This law was stated by Bert helot in a

INERTIA 11

sonieAvhat different form, and is known as the principle of the
necessity of reactions. It is, " Every eheniieal change which is
acconiphshed without the ad(iition of external energy necessarily
occurs if it is accompanied bij a disengagement of heat.'" This means
that, where possible, substances which can react spontaneously do
so, if the products of the reaction contain less energy than the
reacting substances. In other words, water, if allowed, runs
downhill. These two principles are important generalisations for
the biologist, but there are many exceptions to them. 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 (Chap. XVII.).

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 continuous 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 exchange, 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 deduction
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
wHll most permanently and w4th " 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.

12 LAWS OF ENERGY

is but a machine, working according to pliysico-cheniical principles,
reacting l)lindly 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 l^etween
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 can-
not 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
transformation involves the loss of some available energy. A

PRINCIPLE OF LEAST ACTION 13

certain anioinit finds its way into the great ocean (or " sink ")
of heat energy of nearly nniforni tcniperatnre. The attainment
of this dead level is the final goal of all energy whether it is utilised
or not.

Further Reading

SoDDY. " Matter and Energy." Williams and Norgate.
LoTKA. " Elements of Physical Biology." Williams and Wilkins.

CHAPTER II
THE STORAGE OF ENERGY

" All forces of the earth, all manifestations of life are modulations and variations
of the same heavenly melody which proceeds from the smi." Tyndall.

All life processes demand for their continuation and mainten-
ance a continuous supply of matter and energy. 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. Energy, however, must be supplied from outside
the cycle. The one essential physical factor that makes the
process possible is the supply of energy as simlight 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

IZOOO

lOOOO

8000

6000

■*ooo

20 oo

.y^

HEftT

VISUAL

ACTINIC

Fig. 1. — Cui-ves showinsi relative energy and hiuiiiiusity uf dittereut regions of tlie
spectrum. (Abney.) Tlie wave-lengths ^are given in Angstrom units. An Angstrom
unit (A.T'.) = one ten millionth of a millimetre = 0-1 /x/x

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 may act as trigger-energy starting a series of changes
in matter and its energy content whereby a liberation of free energy
is effected. This free energy will then be available for work.

The green plant is able to collect and conserve a portion of the
stream of energy emitted from the sun. This it does by virtue of
its content of a green pigment chlorophyll dissolved in the lipoids

14

GROTTIIUS' LAW 15

of the plastid. The existence of chlorophyll in fossil vegetation
shows that it is of prinuiry importance in the e\ohition and
maintenance of life. Man, lord of the earth, depends for his very
existence on the presence of an organic magnesium compound in
the humble grass of the field.

The light that falls on the leaf may be {a) reflected, {h) refracted,
or {c) absorbed. It is obvious that only absorbed energy can have
any effect on the metabolism of the leaf. This stateinent is known
as Grotthus' Law, and can quite readily be proved. For example,
a substance appears red to us because it is reflecting light whose
mean frequency is 375 X 10^^ cycles per second. It will, therefore,
absorb light of other frequencies. Grotthus showed that red iron
thiocyanate imderwent no change on exposure to red rays, but was
bleached when green light fell on it. Similarly the blue complex
formed by the action of iodine on soluble starch is decolourised by
yellow light and yellow gold choride by blue light.

Absorption Spectrum of the Green Leaf.

A mere glance at the absorption spectrum of the green leaf
is sufficient to show that the light liest absorbed is that having
a wave-length less than 500 aye, the amount absorbed becoming
greater as the wave-length becomes shorter, i.e. the chloroplasts
absorb the actinic rays (violet and a small amoiuit of the ultra-
violet rays). There is also a w-ell-marked absorption band in
the red portion of the spectrum between 665 and 685 /x/^. The
figure for the maximal energy of solar radiation is given by
S, P. Langley as 650 to 666 /x/x 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.

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 ))y
a very simple experiment. It is only necessary to screen a portion

16 THE STORAGE OF ENERGY

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
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 CO, is absorbed beyond the needs of respira-
tion, and that Og 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 (respiratory CO2).

(b) The CO2 absorbed in light of a definite intensity (total COg).
Total COo — respiratory COo, i.e. (b — a) = assimilated QO^.

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

(d) The O2 evolved in the light (total O^).

Total O2 — respiratory Og, i.e. (d — c) = non-respiratory Oo.

SYNTHESIS OF CARBOHYDKATE 17

(e) ^ ~^ - = ? = assimilation coefficient.

^^^ {d - c) O2

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

They find that under all conditions of light the assimilation
coefficient is 1. That is, for every volume of CO2 assimilated, there
is evolved a volume of O2. In short, the chloroplast acts as a
machine for converting CO.2 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 :

xR^O + crCOg + light energy = C^Hg^O^ + xO^.

It has been proved that the first step is the formation of
formaldehyde, i.e. a; = 1.

(i) HgO + CO2 + 112,090 gram cals (?) := O2 + CHgO

(formaldehyde).

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

If a^ = 2 then the formaldehyde would condense to form
glycollic aldehyde — a diose.

(ii) CH2O + CH2O + energy — C2H4O2.

Similarly, glucose could be formed.

(iii) C2H4O2 + C2H4O2 + C2H4O2 + energy ^ Q^YL^f^^.
Two molecules of glucose combine to form maltose.

(iv) C^HiaOg + CgHiaOe + 3.300 gram-calories

;= t!l2H220ll + HoO.

(v) The gums and dextrins are composed of condensed molecules
of maltose, e.g.

C12H20O11 + C12H22O11 + H2O + energy z:; C24H4e023,

and so on.

(3) Carbon-dioxide and water have small energy contents (2-1
and 6-5 gram calories per gram respectively, and these amounts are
not available for food), while starch has a value of 4-1 large
Calorics per gram. It is evident, therefore, that in some way the
plant has converted a certain amount of kinetic energy into poten-
tial energy. Now, as the formula for starch is imcertain, let us
consider the amount of energy required to form glucose from COo
and HoO. Carbon dioxide and water are fullv oxidised. Theo-
reticallv, they may be considered as undergoing a process of
reduction before combining to form the aldehyde, but as the energy
evolved during reduction would be balanced by the energy absorbed

18 THE STORAGE OF ENERGY

during formation, we may limit our problem to the total energy
change according to the two equations given above, viz. (i) and (iii).
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 HgO (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 particular concentration. Therefore, when six molecules of
formaldehyde are condensed to one molecule of glucose, a corre-
sponding 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
formaldehyde. Sunlight here acts as a catalyst (Chap. X.),
Moore and Webster have synthesised formaldehyde by exposing
an aqueous solution of COg to ultra-violet light (Chap. XIII.) in
the presence of inorganic colloids (Chap. VIII.).

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 CO2 into glucose 5-02 gram cals. are stored. Therefore, in
building 0-00034 c.cm. of COo into sugar the amount of energy
rendered potential would be 0-00034 x 5-02 = 0-0017 gram-cals.

Total incident light per sq.cm. per minute = 0-041 cals.

Total volume of CO2 per sq.cm. per minute = 0-00034 c.cm.

Energy rendered potential per sq.cm. per minute = 0-0017 cals.

That is, 17 cals. out of every 410 that fall on the leaf are stored
in starch. But as only 41 cals. (10 per cent, of the total incident
light) are absorbed, we may consider that 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 pro])ortion 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

SYNTHESIS OF PROTEIN 19

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
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 decomposi-
tion of 100 mg. mannitol, the parent alcohol of the carbohydrate,
mannose. Moore and Webster 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.

Baly suggests the following scheme as an indication of what
probably occurs in the plant.

Potassium Nitrate Carbon-dioxide and Water

Potassium Nitrite Formaldehyde

(Formhydroxamic Acid) Carbohydrates

I i

Nitrogen Bases a Amino Acids

Alkaloids and Xanthine derivatives Proteins

To conclude, the plant acts as a transformer of kinetic into potential
energy by the formation of carbohydrates, fats, proteins {the so-called

2—2

20

THE STORAGE OF ENERGY

proi'iniate 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 shown that pure chlorophyll, in alcohol,
absorbed the same amount of COo as the alcohol itself, and it

^oo

650

' ' 1 ' '
600

550

— 1 r—

II''
500

1 1 — T- r

450

< 1
400

B

1

C

1

t

1

F
1

^

K

CHLOROPHVLL A

ri I I I I ' '^'-' I I ' ' ' I '

700 650 600 550
B C D

500

450

400

KmLj:':^^

CHLOROPHYLL B

Fig. 2. — Absorption spectra of chlorophylls A and B. 00312 ?ram in ether
Thicknesses 5, 20 and 40 mm. (After Willstiitter, Stoll and Utzinger.)

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 quite similar to the
spectrum of tlie living green leaf. Knowledge is incomplete 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 COg is accompanied by alterations
in the electrical state.

Moore and his co-workers have proved that inorganic colloidal
uranium, iron and aluminium hydroxides act as catalysts in this

CIILOROPII YLL 21

conversion of kinetic to potential energy. They also found that
iron is present in the colourless part of the ehl()ro|)lasts of the green
plant. Snn and iron are necessary for the de\elopnient of the
chlorophyll although the pigment itself contains no iron. It,
hoAvever, according to Willstater, contains magnesium as an integral
part of the molecule. Fenton, in 1907, showed that carbon-dioxide
and water could combine to form formaldehyde when reduced by
metallic magnesium. From Moore's work, it may be inferred :

(1) That inorganic colloidal systems evolved in point of time
before organic colloids.

(2) That under the influence of sunlight and in the presence of an
inorganic catalyst, the chlorophyll system developed.

(3) The inorganic system is able to utilise light only of short
wave-length, while

(4) The chlorophyll system acts as a transformer (p. 164) and
utilises the more abundant longer waves (Fig. 1).

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
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 has 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 man 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 energy available. Then
and only then will he be able to dispense with plant life. The
energy available for each man is his income. Stored energy is a
legacy deposited in Nature's " bank."

Further Reading
Moore. " Biochemistry." Edward Arnold.

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. 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 through 1° C.

Jvist as a country must have a standard coin of the realm —
poimd 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. or $, 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.
Similarly, 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
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

22

CALORIE VALVES FROM ANALVSLS '2:i

from its chemical lormula. The amount of heat e\ol\ ed 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 = CO2 + 94-31 Cals.
2Ho + O2 = 2H0O + 136(5 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 indicates 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 :

Tri-olein has the formula . . . C^^Hk^^Oq

Deduct intramolecular water (6H2O) . H^gOg

Leaving for oxidation .... Cg^Hgg
Heat of combustion .= 57 X 94-3 + 92 X 34-15

= 53751 + 3141-8

= 8517 Calories.

That is, a gram molecule (884 grams) of triolein in being completely
oxidised to CO2 + HgO would liberate 8517 Cals. of heat, approxi-
mately 9-3 Calories per gram. Similarly, the energy stored in the
form of carbohydrate may be calculated :

Glucose = CgHigOfi

Intramolecular water = Hi20g

For oxidation = 6C

6C + 6O2 = 6CO2 + 566 Calories,
approximately 3-2 Calories per gram.

24

LIBERATION OF ENERGY

The value ioiiiul by direct combustion is 3-7, a considerably higher
figure. A difiiculty, however, occurs with proteins.

In the case of carbohydrates and fats the end-products are

Fig. 3. — Bertlielot-Mahler Bomb Calorimeter.
A. Boint) or autoclave (see Fig. 102).
H. Insulating vessel.

G. Manometer on stand with union.s to fix to oxygen cylinder and to bomb (at S, Fig. 102).
D. A steel mould for making pellets from the material to be burned.

those of complete oxidation, but in the case of proteins, the
final results of metabolism are not substances of the lowest
energy content, i.e. protein is not completely oxidised. Further,
these protein end-products are eliminated in solution, and this

CALORIE VALUES FROM COMBUSTION 25

r('(|uires some correction. Finally, to obtain tlie correct content
of the foodstuff of ('. H and O re(|uires a complicated chemical
techni(]ue, and the calorie \alue of an element may vary witii its
position in the molecule. For example, Barker states that

the E.V. of the CO group is 60-7 Calories
and „ „ OH „ 12-9 „

but the EV of a COOH group may not be obtained by adding
60-7 and 12-9. This investigator finds that carbon has lower
calorie values when it is arranged in such a position in an organic
chain that its bonds approach the tetrahedral position. 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 absorbed 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 instrument (Fig. 3) is described on p. 24.

On p. 5 we mentioned the Law of Hess, which enables us to
apply calorimetric combustion values to the food used by an
animal. Provided the final products of combustion in the boml)
are the same as the final products of metabolism, the energy
liberated from equal quantities of the same food material will be
the same. In the bomb the process of oxidation is rapid, in the
bodv it is slow. In the former case the intermediate steps are
known, in the latter they are not, but if the carbon becomes CO2 and
the hydrogen HgO in each instance, the same quantity of energy
will have been evolved. This law also permits us to calculate the
energy set free when the process stops before oxidation is complete.
For example, if C were only to combine with one instead of two
molecules of oxygen and we found from actual combustion that :

(1) C + O2 = 94-3 Cals.

and (2) i(2C0 + O2) = 68-1 Cals.

Then (1 — 2) = 26-2 Cals. would be the heat liberated in the
reaction i(2C + O2) = CO. This principle is of great importance
in arriving at a caloric value for proteins (see p. 26).

Determinations of the energy-value of the proximate principles
of food have shown that only minute differences exist betw'een
the various members of any class. For example, one gram of

26 LIBERATION OF ENERGY

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 (Physical value) . . 5-3 ,,

Protein (Physiological value) . 4-1 ,,

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 necessarily 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.

(6) 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 piu'cly
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.

ANIMAL CALORIMETRY 27

(ii) Certain substances are excreted in conibinatioii with protein
disintegration products, e.g. hip{)uric acid (protective syntheses).

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

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 ealorimetry — (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,
the heat evolved should, providing our hypothesis is true, be
exactly the same as would be evolved in direct food ealorimetry.
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) ealorimetry, 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-w^alled box
with a known amoimt 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 contributed
so much to the knowledge of nutrition. Crawford foimd 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 sufficient evidence for him to
conclude that, in each case, the heat produced was due to the
conversion of pure air into fixed air, or, as we should now say, to
the combination of C and Og.

A year later, Lavoisier and Laplace published the result of

28 LIBERATION OF ENERGY

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 amoimt of
carbon (a candle) and the volume of the COg evolved. A similar
experiment was then tried with a guinea-pig. They found that
for equal volumes of COg 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 condi-
tions were not the same. As we shall see later, cold raises the
CO2 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 O^.

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 oroportion of O to C.

(V) If a determination were made of the amount of heat and

INDIRECT CALORIMETRY 2!)

the amount of C and O, 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 Go
from the total O^ absorbed and the protein COg from the total
CO2 eliminated, one arrives at the figures corresponding to the
non-protein O^ and COg respectively.

(VI) Now, as we have said, carbohydrates differ from fats in
their respective contents of C and O2. Carbohydrates have the
general formula ^-'(CHgO), while fats contain less O^ compared
with their content of oxidisable matter, e.g. CjgHgeOg. There-
fore, when carbohydrates alone are used, the ratio of the volume
of CO2 eliminated to the volume of O absorbed will be 1, as may
be deduced from the equation :

C(H20) + O2 = CO2 + H2O ^^^ ^Q ^

1 vol = 1 vol R.Q = -^r^Trr =7 = 1-

Vol (Jo 1

Fats are compounds of glycerol, the trihydric alcohol, 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 CHg.

TABLE III

Saturated Series. C^^Hg^Oa-
E.g. HCOOH— formic acid CH2O2

CH3COOH— acetic acid C2H4d2
CHa-CHa-COOH— propionic acid Q^H^O^
CH3CH2CH2COOH— butyric acid C4H8O2

• •••••»

CH3-(CH2)i4COOH— palmitic acid C16H32O2
CH3-(CH2)i5COOH — margaric acid C17H34O2
CH3-(CH2)i6COOH— stearic acid Ci8H3e02

Unsaturated Series. C„H2„-202

CH3(CH2)7CH = CH(CH2)7COOH— oleic acid Ci8H3,02

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 Tri-palmitin

CigHaiCOOi^HO

Ci,H3iC0 0H HO-^CgHs = ^.i^.s^, + 3H2O

C15H31CO OH H O^

30 LIBERATION OF ENERGY

2(C5iH980e) + I45O2 = IO2CO2 + 98H2O.

Vol COo 102

Now ratio = ^j ^ r>." = ttt. = 0-70.
Vol O2 145

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

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

(«) 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.

(IX) 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 calorimetrv . . 2,244 Cals.

Direct 2,230 „

Difference . . . 14 .,

Percentage . . . 0-6 .,

(X) If the ratio is greater than 1, say, 1-5, it shows that for every
three volumes of CO2 evolved, only two volumes of oxygen are being
taken from the air. This type of result is obtained either during
severe exercise when an oxygen debt is being built up, or in a
hibernating animal just before it begins its winter sleep, i.e. when
fat is being formed from carbohydrate.

Further Reading

Crockeh and Matthews. " Theoretical and Experimental Physical

Chemistry." J. k A. Churchill.

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. Docs 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 wastefid 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, that is, 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 182-t Carnot determined, theoretically,
the percentage of heat that any heat engine could convert into
work. A theoretically perfect engine, working between the
absolute temperatures T^ and T^, takes up Q cals. from a heat
reservoir at the temperature T^ and transforms the part W into
work, then

W = Q ^^~ ^^^ (Carnot's Equation).
^ 1

31

32 LIBERATION OF ENERGY

T — T

Evidently the fraction ^ is that part of the Q units of heal

^ 1

which represents the amount of energy made available for work.

That is, even under unattainably perfect conditions no more heat

T — T

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

This equation gives the efficiency of the heat engine.

The most efficient steam engine yet constructed — a Nordbeg
air compressor of 1,000 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 fuel
burned have their energy converted into work.

TABLE IV

Comparative Thermal Efficiencies

I Compound (non-condensing) - 8-12 per cent.
Steam - --; ,, (condensing) - - 10-16

Parson's turbine _ _ _ 15-18 ,.

Petrol (motor) - _ _ _ 22-24

Internal ' ,, (aero) - - - - 26-28

Combustion -■ Coal gas (stationary) - - 29-31 ,,

( Diesel - - ' - - - 33-35

Combined I.e. ) q, n • a-i aa

J a^ Still engme _ _ _ _ 41-44

and Steam i "^

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 tempera-
tures 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.

Efficiency = ^IziZj _ E,

or transposing

T, = T,I{1 - E).

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

T, = ^y_ =:^H= 389° absolute or 116° C.
1—0-2 0-8

TRANSFORMERS OF ENERGY 33

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 Avork 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 the liberation of energy in the animal is
invariably followed by oxidation. 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 dispersed phase in various
colloidal complexes. The cell comes into intimate contact with
other cells, and all cell contents are not of the same chemical
composition nor in the same physical state. There will, thus, arise
differences in surface tension and 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 facts ascertained regarding
cell behaviour.

B. 3

34 LIBERATION OF ENERGY

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

Further Eeading

Crocker and Matthews. "Theoretical and Experimental Physical

Chemistry." J. & A. Churchill.

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 bringinir 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. Digestion
is merely the breaking down of the material supplied so that
it can pass through the absorl)ing medium in solution. It follows
(from this statement and from the physical state of the living
cell) that all energy manifested by an animal ccmes from sub-
stances in solution. No material is of any use for energy purposes
unless it is soluble, and imtil it is rendered soluble it cannot be
absorbed and utilised.

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.) 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 arrangement 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
resemblance 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 conceiv-
ably have passed into the gaseous state. Physical chemists are
agreed that this is the most probable course. They find that for
dUuic solutions, at any rate, the simple gas laws hold good.

In order to explain and correlate these gas laws and the
phenomena 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,

35 3—3

36 LIBERATION OF ENERGY

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 distance

m^ X 7^2
between them. Stress = 7- — , where m, and m^ are the masses

of the particles and d the distance between them.

(2) A Repellent Force (Real Kinetic Energy = \mv^). Every
molecule is free to vibrate in a straight line within the limits of
the intermolecular spaces. In a solid these spaces are small,
and therefore attractive forces are predominant. If a greater
kinetic energy be given to the molecules by means of heat, for
instance, their mean free path wdll be increased at a rate corre-
sponding to the coefficient of expansion. In a liquid the free path
of the molecules becomes sufficiently long to reduce the tractative
forces between the molecules to a value which is exactly balanced
by the forces keeping them apart. Pellation and tractation are
thus stalemate, leaving other forces, e.g. gravity, to determine the
arrangement of the molecules in space.

If the temperature of the liquid be raised, some of the mole-
cules will acquire 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 a liquid balances the gaseous pressure above it, a
stationary state w^ill be reached, i.e. the same number of molecules
will be freed from the liquid as are being absorbed by it. That

KINETIC THEORY 37

pressure is the Vapour Pressure of the substance at that tempera-
ture. (Cf. tension of i^as in sohition.)

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
tlie 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) BoyWs Lazv. 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
of any gas varies directly as the absolute temperature if the
pressure remains constant.

Vr, = Fo (1 + O.T).

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

Vr, = Po (1 + O.T).

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

8-315

0-8613 X 10*
008207
1-985

Joule (Volt — Coulomb)
Volt — Faraday
Litre — atmosphere .
Gram — calorie

The thermal constant w^ith the gratn caloric 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

PV= 2T.

What is the pressure of a gas ? The gas only manifests its

40 LIBERATION OF ENERGY

permeable membranes— that is, membranes whieh 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 wdll 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. XXIV.)

An attempt may now be made to apply these laws (which are
only absolutely true for perfect gases) to dilute solutions.

PV= RT

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 (Fig. 5) (Part II. p. 511)
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
pressure than the solution. Experiment has shown that for simple
dilute solutions the magnitude of the osmotic pressure depends on
the molecular weight of the substance dissolved, the amoimt of
substance in the solute per unit volimie and on the temperature of
the solution. That is, osmotic pressure is controlled by just those
factors which control gaseous pressure. It might be stated that
in a simple solution the osmotic pressure of a substance ivould be
numericcdly 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,

OS MOLAR CONCENTRATIONS 41

P varies as the number of molecules. De Vries (1884) fomid that
one ^ram-moleeule of sugar dissolved in water to make up a
litre, has at 0° C. an osmotie pressure of 22-4 atmos. (Practically
all gases at 0° C. and 760 nun. pressure ha^'e a gram 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 (undissociated) dilute
solutions. Van't Hol'f (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. It follows that vapour pressure
varies directly with temperature. 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 this 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
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 coUigative 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. 303 lbs, 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.

Class 1. O.P. Approximately 22-4 atmos., e.g. Sugar.

„ 2. O.P. Decidedly greater than 22-4 ,, e.g. Salt.
„ 3. O.P. „ less „ 22-4 ,, e.g. Starch,

The first class have been termed simple (undissociated) solutions.

42 LIBERATION OF ENERGY

According to the kinetic theory the second and third classes have
a larger or smaller number of particles in solution than theory
warrants.

Where have the extra particles in Class 2 come from ? Has
the molecule divided ? If one compares the osmotic pressure of
cane sugar and sodiimi chloride in gram-molecular solution,
one finds them (roughly) as 1 : 2. How can this be explained ?
In 1887 Arrhennius propounded his dissociation theory, which has
since been proved, amplified and universally accepted. According
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) + aq = cat-ion + an-ion

= Na + CI

= (Na(H20)ci') + {C\{B.^O)ij).

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 electro-
lyte (Chap. VII.).

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

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 at this concentration. The degree of ionisation may be
determined 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 freeezing point.
(For univalent strong electrolytes at concentrations not exceeding
0-1 molar, the error of this determination is in most cases between
1 and 4 per cent.)

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.

OSMOTIC PRESSURE OF COLLOIDS 43

111 solutions ol" the third class, the O.P. and otlicr coUigativc
properties point to a reduction in the number ol" j)artieles in
solution. A clubbing ol" molecules has taken place. Because most
of the substances that compose this group have a somewhat gluey
consistency, Ciraham called them colloids (Gr. koXXi-j = 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 a very low osmotic pressure, may be readily
hydrolysed to maltose, which is a crystalloid — non-electrolyte,
having a molal O.P. {i.e. belongs to Class 1). Glucose, which
similarly has a molal O.P., may be stored in the liver as glycogen — a
colloid, which again readily undergoes hydrolysis (to a crystalloid).
(See Chap. VIII., ColloidsO

Further Reading
FiNDLAY. '■ Osmotic Pressure." Longmans, Green & Co.

CHAPTER VI
LIBERATION OF ENERGY

(4) SURFACE ENERGY

" This Phaenomenon proceeds from a propriety wliich 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. XIV. Muscular Contraction ; XV. and XVI.
Secretion and Excretion ; XVIII. Nerve Conduction ; XXVII.
Respiration.)

Observation shows that the surface differs markedly in physical
state from the interior of a liquid. The surface between air and
w^ater, the air-water interface as it may be called, is able to with-
stand the application of a considerable distorting force without
rupture. This fact may be demonstrated in a variety of ways, e.g.,

(i) A sewing needle carefully placed on such a surface causes the
water to bend to accommodate its weight (Fig. 6).

(ii) A cold tea-spoon or other object
;e^=z^— -.^^#5^=^^^^^ lifted from the surface of a cold liquid

^^ ^~_j£r^ will stretch some of the surface film

J^i^z . adherent to it for quite a considerable

~ '- — -• distance (Fig. 7). If the fluid and spoon

are warm the film will break more readily.

Fig. 6. — To show the depression x x" j. j. i i?

of the surface of water when lucrcasc oi tcmperaturc lowcrs surface

a needle is floated on it. i

cohesion.

(iii) Water creeps up the sides of beakers, is soaked up by blotting
paper, sponges, charcoal, capillary tubes, etc., against gravity.

(iv) Water beetles walk safely over the surface of water, and
large heavy clams may suspend themselves from filaments anchored
to the undcr-surface of the water in aquaria. These examples
show that the film of water molecules at the surface possess a
remarkable tensile quality, surface energy, surface tension or
cohesion which in the case of a water-platinum interface is about
73 dynes per cm. at 20° C.

How Measured. — There are four methods in common use for the
determination of either the absolute surface tension or its value
relative to water.

44

MEASUREMENT OF SURFACE TENSION

45

1. By means of the torsion balance (Fig. 8) the force necessary to
lift a ring, plate or straight wire from the fluid-air interface is
determined.

Fig. 8. — Du Xouy's Surfacp Tension Ai)paraliis. One ruble centiiiutre of tlie liiniid to
be tested is plaeed in tbe wateli-glass. The force re(|uireil to luill a platinum ring
from the fluid snrfaee is applied by twisting a wire The amount of torsion, and
hcnee the value of the surface tension, is given on the graduated dial.

2. Drop-weight Method (Part II., p. 517). The weight of a drop
falling Ijy gravity under standard conditions (size of dropping
surface, etc.) gives a measure of the tension on the surface of the
drop.

46 LIBERATION OF ENERGY

3. Capillary Rise Method. The height to which a Hquid will rise
in a capillary tube held vertically on the surface is an inverse
measure of the surface tension of the liquid. (Part II., p. 518.)

4. Air Bubble Method. A value for the surface tension of a
liquid may be obtained by measuring the amount of force necessary
to blow a bubble of air into it from a capillary tube.

Ageing of Surfaces. — All these methods require the observance
of standard conditions. For instance, it takes time for a new
surface to attain its normal tension after it has been disturbed by
the placing of a ring on it, by the formation of a new drop, or by
forcing it out of a tube by a bubble of gas. In fact, the adjustment
of a surface may go on for hours, though the maximum change
takes place very rapidly. After the elapse of a minute an approxi-
mately normal value for surface tension may be obtained. Again,
the temperature at which the measurements are carried out is
important — the higher the temperature the lower the tension
developed, till at the critical temperature it reaches a mininnmi
value. That is, surface tension is a phenomenon with a negaiixe
temperature cocjjicieht.

These facts may be explained by reference to the forces which
act on all molecules — in solids, liquids and gases.

Two forces act on molecules :

(«) A repellent force — kinetic, revealed in vapour tension, etc.

{b) A cohesive or attractive force — Newton's " Gravity."

The latter gives rise within the liquid to intrinsic pressure,
whose magnitude we have no direct means of measuring, and
whose energy we cannot utilise — because the various tractati\"e
forces acting on each and every molecule zvithin 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 in any plane may be resolved 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 downwards, has no
opposing upward force to stabilise the molecule. There is, there-
fore, a state of strain in the surface area.

Orientation on Surfaces. — As the result of this state of strain the
molecules at the surface are arranged more regularly than those in
the body of the liquid. One may consider the internal molecules of
water as lying at random with their long axes in no particular
plane, while at the siu-face the long axes are practically parallel to

ORIENTATION AT AN INTERFACE

47

one another and at right angles to the surface. The surface layer
or layers, because of their orderly arrangement, will, therefore,
have a larger niuuber of niolecvdes per unit area than the interior
of the liquid with its higgledy-piggledy arrangement of molecules
(Fig. 9). That is, the surface will tend to decrease under the
micompensated Newtonian attraction of under surface molecule
for surface molecule, and the tension so produced will cause the
orientation of the molecules at the surface, the effect on any
individual molecule being determined by the extent to which the
surfaces of that molecule (on which equal forces are acting)

I'lG. 9. — To show how t)ie surface of water differs from the interior in tlie orientation of the
molecules. A similar orientation occurs at the fjlass-water interfaces.

deviate in shape from spheres- drawn about the centre of mass.
Various experiments ha\'e been devised to determine to Avhat
extent this orientation is transmitted to molecules lying at a
distance from the surface. Hardy's proof that the oriented layer
may be several molecules thick is both simple and unequivocal.
He allowed the fluid under test to be drawn in by capillarity
between, say, a microscope slide and a weighted cover-slip. The
force exerted is sufficient to lift the cover-slip and its weight from
their bed. Every molecule of fluid drawn in nnist, by the fact
that it is drawn in, be under the influence of the glass surfaces.
The fluid is now frozen, and the cover-slip broken away. The
layer of solidified fluid left is quite visible and is capable of measure-

48 LIBERATION OF ENERGY

ment in depth, in tensile strength and in resistance to shear. This
experiment indicates that the thickness of the layer under the
influence of surface forces is at least of the order of 1,000 molecules,
its value depending on the eccentricity of the equipotential
surfaces of the molecules. The greater the eccentricity of the
fields of force about the molecules {i.e. the greater their polarity)
the thicker will be the oriented layer.

Utilisation of Surface Energy. — As we have seen, the energy
developed at the surface is considerable. If some means could be
devised whereby this energy could be freed from the surface, or,
what comes to the same thing, if its intensity could be altered,
then it might be utilised to bring about changes in matter. Such a
potential power might have considerable significance in physiology.
The tissues of which organs consist and the cells that compose the
tissues abound in surfaces or interfaces where one liquid phase
subjoins another similar or dissimilar phase. Alterations in surface
tension, quite apart from gross energy changes, play a large part in
physiological processes, as we shall see later.

Alterations in Surface Tension.

A. Pure Liquids. — (1) Whatever alters the intrinsic energy of
the liquid will produce a corresponding alteration of the energy on
the surface. The attractive force between molecules of a liquid
(or gas) varies from absolute zero to the critical temperature
directly as a constant and inversely as the square of the distance
between the molecules. That is, increase of temperature will tend
to lower surface tension. In other words, surface tension has a
negative temperature coefficient.

This means of varying surface energy is not of great interest to
the biologist, as it implies alterations of temperature which to be
significant have to be considerably more than is compatible with
life.

(2) The electrical state of a surface layer is of interest in this
connection. Electrons accumulate on the aqueous side of a water-
air interface and they tend to cause the surface to expand. If
they are increased in number their mutually repellent power will
actually overcome the contracting power of Newtonian gravity,
and the surface will increase in curvature, i.e., expand, and the
surface tension be lowered. Examine the surface, for instance, of a
globule of mercury in water. The water molecules on this surface
are arranged with their polar ends, i.e., OH radicle, in the water
and the H"^ ion pressed against the mercury. A double electrical
layer thus exists. The metal, by virtue of the closely adherent H^
ions, takes on a positive charge on its surface, while just external

ALTERATIONS IN SURFACE TENSIONS 49

to this is a layer of ncjjjativcly charged hydroxyls. If these two
opposing charges balance one another, the shape of the globule will
be defined by surface forces alone, i.e., the surface will be reduced
to a minimum and the globule will appear spherical, except, of
course, at the mercury-glass interface. Now increase the con-
centration of positive ions in the water by adding a drop of sulphuric
acid to it, and so reducing the number of effective electrons on the
surface of the water adjacent to the mercury, and the balance
between protons and electrons is disturbed in favour of the former.

ABC

Fig. 10. — Form assumed by mercury globules under different electrical states. _B is a
mercury globule immersed in dilute HjS'Oi. It assumes a more spherical form A when con-
nected with the negative pole of a battery, while connection to the positive pole reduces
surface tension as shown at C.

The surface forces are, therefore, partially overcome l)y the
electrostatic repulsion of similarly charged surface molecules and
the globule will flatten out (Fig. 10, B). Increasing the positive
charge on the mercury by connecting it to the positive pole of a
battery and immersing the lead from the negative element in the
acidulated water will cause the surface forces to be still further
reduced (Fig. 10, C). The reverse effect occurs when the direction
of the electrical current is reversed. A very neat demonstration
of this, due to Ostwald, may be given by actually making the
mercury one of the elements in a galvanic couple. (Part II., p. 517.)

CORK.

5EWIN6 NEtCLE

.-WATCH GU\iS

GLOBULE OF MERCURV

Fig. 11. — Mercury " Heart."

In this experiment (Fig. 11) the mercury forms the positive
element and the carbon in the steel needle the negative element.
When connection is made between the + and — substances by
placing the needle so that it just touches the mercury the charge on
the mercury surface is decreased, the globule more nearly assumes
the spherical form and so breaks connection with the needle. This
allows the positive charge on the metal to accumulate, lower the
surface tension, and so again make contact. (To pre\'ent the
cessation of this rhythmic movement by polarisation, a little
potassium bichromate is added to the fluid.)

50

LIBERATION OF ENERGY

Capillary Electrometer. — Lippmaii made use of the electrical
alteration of surface tension in his capillary electrometer which

M

(A)

(B)

Fig. 12.— Diasraui of Capillary Electrometor (Crocker and Matthews).
12A.—T. the reservoir of mercury containing the insulated electrode E, communicates by t/
with the caiiillarv A. Above the mercury in A. and tilling the upper part of B, is dilute
sulphuric acid. F, the other electrode, passes into the mercury at the bottom ot -o and
F is kept out of contact with the acid. When not in use F and E are short circuited
by a key.
B represents the surface of the mercury M in contact with the acid S.

consists essentially of a capillary tube containing mercury and
dipping into dilute sulphuric acid (Part II., p. 520 and Fig., 12).
The mercury contains one leading in wire from a source of potential
difference, while the other lead is taken to a small amount of

CAPILLARY ACTIVE SUBSTANCES 51

mercury in the bottom of the vessel holding the acid. The position
of the meniscus in the capillary is observed through a microscope
or is projected on a screen. A very slight increase in the charge
on the mercury-acid interface will lead to a movement of the
mercury in the direction of the current. That is, if the mercury
holds the positive lead the meniscus will fall (S.T. lowered) ; con-
versely, if the negative pole from the battery is attached to the
capillary, the meniscus will rise (S.T. raised). The extent of move-
ment depends on the difference of potential developed (Figs. 38 and 43).

B. Solutions. — The surface layers of electrons may be increased
or decreased by the addition of solutes which, by altering the
intrinsic energy of the solution, cause a redistribution of energy,
and so new surface relationships are produced. The material
dissolved in a fluid is not dispersed regularly, but is generally found
more concentrated at surfaces. According to the Gibbs-Thomson
principle, those solutes which tend to lower surface tension are
found at the surface, while those which raise surface tension are
least concentrated at the surface, i.e., " The concentration throughout
a fluid tends to be so adjusted as to reduce the energy at every p)oint
in it to a minimum.'''' Very few substances raise surface tension,
and that to a very slight extent. Strongly dissociated inorganic
salts have very little effect either way, but are usually found
adsorbed to surfaces. This fact is attributed not to any property
of the salts, but to the unsatisfied valencies existing at any surface
wetted by the solvent. (See also Adsorption, p. 53.)

C. Capillary Active Substances. — The surface tension of water is
markedly diminished by certain organic substances with long
carbon chains. The longer the carbon chain, and the smaller the
number of decidedly electro-jjositive and (particularly) electro-nega-
tive groups (such as — OH and — COOH) they possess, the more
powerful is their action. These substances, which are also distin-
guished by a high degree of adsorbability (q.v.) and by poW'Crful
biological actions (cf. anaesthetics, etc.), are called capillary active
from their effect in lowering the level of water in a capillary tube.
They have also a low surface tension themselves and are of interest
because of the orientation of their molecules on the surface of water.
Typical physiological capillary active substances are found in
saliva, bile, blood and milk. These substances all have in their
carbon chain a radicle which is particularly soluble in w^ater, e.g.,
carboxyl (COOH), hydroxyl (OH), COOCH3 or CN. Apart from
this polar radicle, the remainder of the molecule is insoluble or
markedly less soluble in the solvent. They are, therefore, arranged
like a fisherman's floats with their soluble polar ends in the water
and the rest of the molecule standing vertically out of the water

4—2

50

LIBERATION OF ENERGY

Capillary Electrometer. — Lippman made use of the electrical
alteration of surface tension in his capillary electrometer which

M

(A) (B)

Fig. 12. — Diagram of Capillary Electrometer (Crocker and Matthews).
12a.— r. the reservoir of mercury containing the Insulated rlectrode E, communicates by U
with the capillary .1. Above the mercury in A. and Hlling the upper part of B, is ddute
sulphuric acid. F, the other electrode, passes into the mercury at the bottom of B and
F is kept out of contact with the acid. When not in use F and E are short circuited
by a key.
B represents the surface of the mercury M in contact with the acid S.

consists essentially of a capillary tube containing mercury and
dipping into dilute sulphuric acid (Part II., p. 520 and Fig., 12).
The mercury contains one leading in wire from a source of potential
difference, while the other lead is taken to a small amount of

CAPILLARY ACTIVE SUBSTANCES 51

mercury in the bottom of the vessel holding the acid. The position
of the meniscus in the capillary is observed through a microscope
or is projected on a screen. A very slight increase in the charge
on the mercury-acid interface will lead to a movement of the
mercury in the direction of the current. That is, if the mercury
holds tiie positive lead the meniscus will fall (S.T. lowered) ; con-
versely, if the negative pole from the battery is attached to the
capillary, the meniscus will rise (S.T. raised). The extent of move-
ment depends on the difference of potenticd developed (Figs. 38 and 43).

B. Solutions. — The surface layers of electrons may be increased
or decreased by the addition of solutes which, by altering the
intrinsic energy of the solution, cause a redistribution of energy,
and so new surface relationships are produced. The material
dissolved in a fluid is not dispersed regularly, but is generally found
more concentrated at surfaces. According to the Gibbs-Thomson
principle, those solutes which tend to lower surface tension are
found at the surface, while those which raise surface tension are
least concentrated at the surface, i.e., " The concentration throughout
a fluid tends to be so adjusted as to reduce the energy at every jjoint
in it to a minimum.'" Very few substances raise surface tension,
and that to a very slight extent. Strongly dissociated inorganic
salts have very little effect either w^ay, but are usually found
adsorbed to surfaces. This fact is attributed not to any property
of the salts, but to the unsatisfied valencies existing at any surface
wetted by the solvent. (See also Adsorption, p. 53.)

C. Capillary Active Substances. — The surface tension of water is
markedly diminished by certain organic substances with long
carbon chains. The longer the carbon chain, and the smaller the
number of decidedly electro-positive and (particularly) electro-nega-
tive groups (such as — OH and — COOH) they possess, the more
powerful is their action. These substances, which are also distin-
guished by a high degree of adsorbability (q.v.) and by powerful
biological actions (cf. anaesthetics, etc.), are called capillary active
from their effect in lowering the level of water in a capillary tube.
Thev have also a low surface tension themselves and are of interest
because of the orientation of their molecules on the surface of water.
Typical physiological capillary active substances are found in
saliva, bile, blood and milk. These substances all have in their
carbon chain a radicle which is particularly soluble in water, e.g.,
carboxyl (COOH), hydroxyl (OH), COOCH3 or CN. Apart from
this polar radicle, the remainder of the molecule is insoluble or
markedly less soluble in the solvent. They are, therefore, arranged
like a fisherman's floats with their soluble polar ends in the water
and the rest of the molecule standing vertically out of the water

52

LIBERATION OF ENERGY

(Fig. 13). Fatty acids (Experiment 11) lower the surface tension of
water because the unsatisfied valencies at the surface are satisfied
by the soluble COOH group, while the insoluble paraffin portion
remains out of the water. That is, the fatty acid or other capillary
active substance goes to the surface because that portion of the
molecule which does not wet tends to leave the water, but is
anchored to the water by the polar group. If there is sufficient
of the substance present to cover the surface with a layer at least
one molecule thick, then the surface tension will be decreased.
Compare this surface orientation with Experiment 18, where small
bits of paper coated on one side with lamp-black or printer's ink
orient themselves on the interface between paraffin oil and water
so that the blackened sides are turned towards the oil.

Adam has found that the gathering together of fats or fatty acids

COOH

Fig. 13. — To show how an oil like Olein containing Oleic Acid has its molecules oriented
on the surface of water, COOH radicle attracted to OH radicle.

in an orderly fashion like this on a surface produces changes in the
physical state of the substances so oriented. For instance,
palmitic acid at room temperature is solid, but if placed on the
surface of water at the same temperature is clearly liquid. Further,
the surface layer is able to withstand a considerable lateral force
without buckling. When the packing force is applied the molecules
on the surface fit into one another like spoons in a box and so allow
of more molecules per unit surface. If the polar portion is bulky
the molecules pack into a curved film having the hydrophobic
portion concave and the hydrophilic polar part convex. Not until
something like 100 atmos. pressure has been applied laterally
will buckling of the film occur. Some substances go completely
out of solution when so adsorbed on a surface. The molecules of
albumin, for instance, when oriented on a surface adhere together
and form an irreversible gel, i.e., they coagulate. This adherence

ADSORPTION 53

to one (mother is a common attribute of all long molecules capable of
forming a closely packed surface f hit. (See C'hap. XL, MeinlH-anes.)

Adsorption. — II has been found that surl'aees of soHds and
htjuids exert an attraction for gases. It is very diineuit, for
instance, completely to reniovx air from the surface of a glass
container. Repeated evacuation is necessary. The amount of gas
so adsorbed varies with the nature of the surface, and of the gas, as
well as with the pressure, and inversely with the temperature, and
is a reversible process. That is, the processes of adsorption and
de-adsorption will proceed together till a condition of equilibrium
has been reached which will remain undisturbed as long as
the temperature and pressure of the system remain unaltered.
(Principle of Le Chatelier.) Charcoal, which has an enormous
surface area per unit volume, will adsorb large quantities of gases,
e.g., 1 c.c. of coconut charcoal at 0° C. will adsorb 2 c.c. of helium,
4 c.c. of hydrogen, 15 c.c. of nitrogen, 18 c.c. of oxygen, 75 c.c. of
ethylene, 171 c.c, of ammonia. Use is made of this property in the
preparation of high vacua, in the manufacture of " gas masks," and
for the removal of foul gases, etc.

At a liquid-gas, liquid-liquid, or at a liquid-solid interface
adsorption readily occurs and may easily be demonstrated by the
use of coloured solutes. (Part II., Experiments 18/43 (c).) If
we increase the surface of a liquid by the introduction of a finely
divided gas, immiscible liquid, or solid, we may be able completely
to remove substances in solution. Here we find that the physical
and chemical nature of the adsorbing surface and of the adsorbed
material are of prime importance. Some adsorbents are almost
omniverous, e.g., charcoal in aqueous solutions, others, like kaolin
and ferric hydroxide, which have the greatest conceivable specific
surface (see p. 72), will only adsorb certain types of solute, due
to the sign of the electric charge which they develop in contact
with water. Most of them, like kaolin, become negative, but a
very few, like ferric hydroxide and haemoglobin, become positive.
The former adsorbent will, therefore, fix electro-positive dyes such
as the " basic " dye methylene blue and the latter electro-negative
dyes.

Practically all dyes are salts of a coloured and a colourless ion. If the
organic base, united generally with hydrochloric acid is coloured the dye is
termed basic. A coloured organic acid, may unite with a colourless inorganic
base to give an acid dye. The former because of its hydrion is electro- positive,
the latter is electro-negative on account of its natrion.

Chemical forces come into play in some adsorptions, for example,
the adsorption of that class of substances termed " capillary or
surface active " is determined not by the extent or the physical

54 LIBERATION OF ENERGY

nature of the surfaces to which they are exposed, but by the
chemical nature of the surfaces, Kaohn and ferric hydroxide will
not adsorb even a trace of tri-butyrin or acetone, or of any of the
higher alcohols, or, in fact, of any capillary active substance.

The amount of any solute adsorbed depends on its concentration
and temperature, as well as on the nature of the force causing the
adsorption. If the volume and temperature of a solution are kept
constant while the quantities of adsorbent and of material to be
adsorbed are varied, it is found that when adsorption equilibrium
has been established, the relation between the amount of substance
absorbed (cv) and its concentration unabsorbed in solution (c) is
given by Freundlich's equation :

- = ^T"
m

where m = weight of adsorbent present,

A; is a constant depending on the nature of the adsorbent and
is the amount adsorbed when c = 1
and n is a constant depending on the nature of the adsorbed
substance.

(The value of n is usually about 0-5.)
Four further points are of interest :

(1) The rapidity with which adsorption takes place.

(2) The reversible nature of adsorptions of the purely physical type.
If definite amounts of adsorbent and adsorbable substances are
allowed to attain equilibrium and then the concentration of either
of them altered, a new equilibrium point will be reached. For
example, if after charcoal has removed a certain quantity of a
solute from a solution, the solution be diluted with an equal
quantity of water, so reducing the concentration of the charcoal
and of the unabsorbed material by half, then some of the material
will be given up by the charcoal to the solution. The final con-
centrations will be the same as if one had started with half the
quantity of charcoal.

(3) The phenomenon of adsorption-displacement. If two or more
adsorbable substances are present in solution and no chemical action
takes place only one substance will be adsorbed — the more sparingly
adsorbable substances will remain in solution. On the other hand,
if a substance A is adsorbed and then B which is more powerfully
adsorbed is added to the solution, A will be completely expelled
from the surface. Capillary active substances, by powerfully
lowering surface tension, cause the expulsion of all less active
substances from a charcoal- water interface. (See Chap. XI.,
Adsorption Membranes, and Part II., Experiments 18 and 20.)

MICROPORES AND INTERFACES 55

(4) The minute nature of the qiicuitities of solute zvhich mui/ be
removed from solution. A 100 c.c. of a 1 in 10,000 solution of
crystal N'iolet or eosin is completely decolorised by 1 gram of char-
coal in less than 2 minutes.

The biological significance of adsorptions will be considered in
later chapters.

D. Suspensions. — When very tiny particles of insoluble matter,
e.g., gold, carbon, etc., are dispersed through water, a large increase
of surface is produced and the physical properties of the liquid
become so remarkable that a separate branch of science with a
technique of its own has been evolved to study them. They will
be dealt with in a subsequent chapter.

A special case of the multiplication of surface may be considered
now. A piece of charcoal has not only an external surface, but its
interior is ramified by a series of larger channels or macropores
(mean diameter 12|U,) and tiny capillary bores or micropores (mean
diameter 10 /x/x). When gas-free charcoal is immersed in water it
soaks up the fluid like a sponge, but takes in more water than its
volume would appear to justify. That is, some of the imbibed
water is compressed. This compression occurs in the micropores
with, of course, the evolution of heat. The net heat of adsorption
is closely proportional to the heat of compression under high
pressures. One gram of charcoal (not evacuated) immersed in
water gives off something like 18-5 gram cals. The molecules of
water in the micropores are arranged in parallel rows, closely
packed together, and so occupy less volume than either the
molecules in the macropores or in bulk.

Tissues abound in potential micropores and in interfaces, and,
therefore, we w^ould expect that surface forces would play an
important part (a) in the structure of living matter, and (6) in
maintaining a balance between free and potential energy.

Further Reading

Willows and Hatschek. " Surface Tension and Surface Energy." J. and A.
Churchill.

SECTION II.: CELLULAR MECHANICS

CHAPTER VII
lONIS ATION

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. 42), 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.

Electrical Charge. — It is obvious, 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).

so

HYDRATION OF IONS

57

Such a solution will therefore conduct electricity, aiul further,
its efficiency as a conductor will depend on the ninnlxr of ions
present, i.e. on the dissociation of the sohite.

Tills provides the basis on whicii the method for estinuiting
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. 522).

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 l)y 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
follow's :

TABLE VI

Cations +

Anions —

Ion.

Atomic Wt.

Relative Speed.

Ion.

OH

Atomic Wt.

Relative Speed.

H

1

318

17

174

K

39

64-6

ISO,

48

68

NH,

18

64-4

Br

80

67

iBa

68-5

55

I

127

- 66-5

iSr

43-7

51

CI

35-5

65-5

iCa

20

51

IC2O4

44

63

iMg

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, however,
comparatively slight.

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
of ions apart from hydration is proportional to their mass, e.g.
potassium and chlorine have approximately similar atomic w'cights
and similar speeds. Any variation from this proportion is usually
attributed to the different hydration of the ions. It is generally

58 lONISATION

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,

64-6 65-5
Now, as the speed of K to CI is as — — : — -, i.e. as 16 : 19, almost

as 4 : 5, it may be considered that K has 4 and CI 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 incre-
ment of temperature, different ions increase in speed according
to their degree of hydration. The more highly hydrated the ion,
the greater is its temperature coefficient. This is explicable on
the hypothesis that a rise of temperature will favour the disruption
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. 48), 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 oppositely charged ions.

There exists an enormous electrostatic attraction between ions
of opposite sign. The introduction of other electrolytes 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 HCl to a solution of KCl would increase the diffusion potential
that would be produced at the boundary between solutions of KCl

DIELECTRIC CONSTANT 59

at different concentrations ; tlic more HCl present, the greater the
diffnsion 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 CI ions, while the H ions move about five times as fast.
The boiuidary 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 equilibrium caused by the
introduction of electrodes 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
thing or on a process does not explain it.
Neither is it sufficient to say that the
dielectric constant or specific inductive
capacity of any medium is a measure of the cation anion

capacity of that medium to act as a dielectric fig. 14.— Model ot anion

^ •" . . and cation. Two pith balls

(non-conductmg) substance ot an electric suspended by siik threads

1 • 1 PI attract one another if carrv-

condenser. The higher the value of the ing opposite charges, when

. PI *'i^ charges are of the same

constant, the greater is the value ot the sign, the bails diverge, i.e.,

repel one another.

condenser.

According to the electron theory, an atom is composed of

protons and electrons. Electrons are all similar, and are supposed

to be not sensible matter, but the smallest possible unit of negative

electricity. Atoms of different substances owe their different

qualities to the varying number of electrons they contain and to

the diversity of their arrangement. 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. Now it can be

show^n that when two small electrically charged bodies (charges e

and e' respectively) are immersed in a medium at a distance r

ee'
apart, the force they exert on each other equals ^r-g, where K is a

constant for the medium and is known as the dielectric constant.

60 ION I SAT I ON

It is a measure of the obstruction produced as described above, i.e.

it measures the capacity of the mediuui to act as an insulator. When

the distance /• between the two charged bodies is increased so that

ee'
Kr^ is very large compared with ee', the force t^, becomes ncghgible,

and the two bodies will cease to attract (if of opposite signs) or
repel one another (if of the same sign). Suppose this happens at a
distance r^ in a medium with a dielectric constant K^, and at a
distance r2 when the medium has a dielectric constant of A'2,

ee' ee'

and as the charges e and e' are obviously the same in both instances,

then ^1^1^ = K^ro^ and /-g = r, v/ t^ .

From the following Table (VII.) it may be seen that air is
arbitrarily taken as having unit dielectric constant, and on this
basis water has a dielectric constant of 81-7.

TABLE VII

Air =1-0

Water =81-7

Co 2 =1-0004

Alcohol =25-0

H =0-9997

Formaldehyde =84-0
Acetic Acid = 6-46
Vaseline \ ^ ^
Paraffin j ~ "" *"
Liquid Fat =3-3-2

media r, and r<

> refer

red to above are air and water

If the
respectively, and substituting values in the equation for /'g, we have

r.

I

ri

2 = ^'i V SW ^ 9 ^PP^o^-

That is, the distance between charged ions in water may be nine
times less than in air without the one ion exerting an appreciable
influence on the other. Thus, when the molecules have been split
into their constituent ions, the high dielectric constant of water
lowers the probability of their recombination to such an extent
that the solution is stable in this dissociated form.

This does not, however, describe how the splitting of the mole-
cules into ions is brought about, nor why some substances are easily
and almost completely dissociated at a certain dilution, while
others under the same conditions undergo an almost negligible
dissociation. Many solutes dissolve in water to give highly
dissociated solutions without any great change in the sum total of

DISSOCIATION 61

the energy content of the reacting substances. Yet, out of soki-
tion, molecules can only be resolved into their atoms or dry gases
ionised, by the application of considerable external force. The
latter phenomenon has been much studied of late years, especially
in connection with the passage of X-rays and ultra-violet rays, and
it has been found to depend on the frequency of the incident
radiation. The former rays knock electrons off the molecules of
the oxygen and nitrogen of air 1,000 times more efficiently than the
latter rays because their frequency is 1,000 times as great. That is,
the energy of escape of electrons from gases is an accurately linear
function of the frequency of the incident radiation provided the fre-
quency exceeds a certain limit.

Without this tremendous display of energy, by merely putting a
substance in solution electrons are freed. The necessary energy
might come from all or any of the heat liberating actions that take
place during the process of solution {e.g., heats of hydration and
dilution, heat of combination of the anion with an extra valence
electron), and the process might be aided by the heat of hydration of
the ions as they are set free. 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 with 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." Aqueous solutions are
fundamental for all biological phenomena. The physical properties
of water are in general extreme — their numerical expressions are
cither 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. -il ) of water, have
constructed diagrams of the molecide of water. Discussion of
this work is somewhat without the bounds of this book.

In recent years it has been amply demonstrated that a triatomic
molecule could not possess the properties of water. For instance,

o2 lONISATION

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 temperature of
steam should be — 100° C. The inference from this is that the
molecule of water is bigger than HgO. 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 tempera-
ture, 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 HgO and the solid (H20)3, and between these extremes
the liquid (ft^HgO) + ^(H20)2 + c(H20)3), a, b and c being con-
stants 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 equilibriiun 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

HoO — H+ + 0H-.

According to Guldberg and Waage's Law of Mass Action,
the product of the concentrations of the reacting substances,
H+ and OH , bears a direct relationship to the mass of the
resultant substance H2O.

[H+J X [OH]"
That is FTTTTi = constant K,

HYDROGEN ION CONCENTRATIONS 63

where [H + ] = the molecular concentration of hydrogen ions.

fOH~] = the molecular concentration of the hydroxyl ions,
and [H2O] = the molecular concentration of the undissociated

water.

In practice it is found that so little water is dissociated that
relative to [H] and [OH], [H.O] is constant. A'[Ho()] is thus
constant and equal to K.^^„ which is defined as the dissociation
constant of water.

The value of K^^., the dissociation constant of ivatcr, depends only
on the temperature.

.... (1)

(2)
(3)
(4)

At 0° C.

Ky,

~ 10,000,000,000,000,000

At 22° C.

K,,

1

~ 100,000,000,000,000

At 40° C.

^IV

3-5

~ ioo,ooo,ooo,ooo;ooo

At 100° C.

K.

48

100,000,000,000,000

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

(1) is =

001

X

10-14

= K„ at 0° C

(2) is =

1

X

10-14

= K^, at 22° C

(3) is =

3-5

X

10-14

= /i,„ at 40° C

(4) is =

48

X

10-14

= K,, at 100° C

Since [H+] X [OH"] = i^„„

and obviously H+ and 0H~ are produced in equal amounts,
therefore [H+] = [OH"] = \/K^-

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, K^, = lO-i^ ;

.-. [H+] X [0H-] = 10-".

[H+] is therefore equal to VlO~" = 10" 7,

and [OH-] „ „ „ a/10-" = 10-^.

It is usual to write H- for H+ and OH' for OH".

Still further to shorten the symbols, S^rensen suggested the
use of the logarithm to denote the hydrogen ion concentration.

64

ION I SAT ION

Instead of writing 10'"'' one may write merely the positive index 7,
keeping the rest of the formula in mind. This is called the p^,
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

Pn
C

H

Poll = 7,

In words, neutral water has a hydrogen ion concentration of
10"^ or Si pyj of 7.

Appended is a list of values of ^% of water for various tempera-
tures.

TABLE VIII

Effect of Altebation of Temperature on the Dissociatton op Water

Temperature.

pH.

pOH.

jjH.O.

16° C

710

7-10

14-2

18° C.

7-07

7-07

1414

20° C.

7-03

7-03

14-06

22° C.

7-0

7-0

140

24° C.

6-96

6-96

13-92

26° C.

6-93

6-93

13-86

28° C.

6-90

6-90

13-80

37° C. (body temp.) .

6-75

6-75

13-5

Some people prefer a more cumbrous Ijut nevertheless a more
comprehensible method of recording ionic concentrations. In
S0rensen's method it is rather difficidt to see at a glance the
relative concentrations of ions at two temperatures. As the
temperature increases, dissociation increases, but the negative
exponent or pj^^^ decreases. At S°, for example, the p^ is 7-3,
and at 22° it is 7-0. Put in this way, one does not readily grasp
the fact that the p^^ at 22° is double the p^j^ at 8°. 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.,
8°Pjj = 7-3 = 0-5 X 10-7 = Ch,
22° Pjj = 7-0 = 1 X 10-7 = c^.

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

p^^ 7-6 = 10-7*5 ^ 10-70 X 10-06 ^ 0-25 X lO"'
antilog of — 0-6 = 0-25.
Conversely we find the short expression for

REACTIONS TO INDICATORS 65

log Cjj 5 X 10-6 = log 5 + log 10-6

= -6990 + ( — 6-0000)
= — 5-3 i.e. p^, — 5'3
or Ch 5 X 10-6 = 10-699 X 10-6 = 10-5 3^ j;^ 5-3.

Graph for conversion from one notation to other, Part II.,
p. 564.)

Reaction to Indicators.

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.
Litnuis, 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. XXXI.).

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 :

HCl = H+ + Cl-

HNO3 = H+ + NO3-

H2SO4 = H+ + HSO4-

CH3COOH = H" + CH3COO-

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+ + OR-
NH4OH = NH4+ + 0H-.
The concentration of 0H~ ions is increased.

66 ION I SAT ION

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- - + H+

Na2HP04 = 2Na+ + PO4 + H+

COOH

COONH4 = NH4+ + (C00)2" - + H+

{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(0H)2Cl = Fe+ + + + CI" + 20H-,

CH2 • NH • OH • COOK = K+ + CHgNHCOO + 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, Kj^ and -K^oh-
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 concentra-
tion of hydrogen ions is 1 X 10~', i.e.pjj = 7. If the concentration
is greater than this, e.g. 1 X 10" 5, or p^^ = 5, then the concentra-
tion of OH' must be correspondingly decreased according to the
equation,

[H+] [0H-] = 10-14

or [0H-] = 7.PJXT = 10-14 (-5' = 10-9.

A jjjj of 5 will be accompanied by a p^J^ 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.

if i^oH = 3, then (H+) = ^' = 10-^ = p„ of 1],
an alkaline solution.

NORMAL SOLUTIONS 67

Reaction may, therefcre, be expressed in terms of p^ or of j^oh-
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 jDj^. 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 p^^ 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 concentration 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 hvdrogen as H + . The concentration of acid commonlv used for

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

concentration of such a solution would be 1/10 gram per litre =
(H+) of 1 X 10-1 OP p^ of I and ^^g of 13.

Water of p^ = Pos = '^ i^ t^uis, at 23° C, N/10,000,000 acid and
N/10,000,000 alkaline. If the acid added to water is not com-
pletely dissociated {i.e. a weak acid), then, of course, the degree of
dissociation must be taken into account. A deeinormal solution of
acetic acid, for instance, at 23° is dissociated 1-36 per cent. There-

1-36
fore its (H+) would be equal to "— x lO'^ = 1-36 X 10~^ or p^ of

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

— HCl in water at 23° = j^b. 1 »r ^'h = 1 X lO"!,

N
10

N

— CH3COOH „ = Ph 2-86 or Cjj = 1-36 x lO-^.

5 — 2

68 ION IS ATI ON

That is, hydrochloric acid, under the above conditions, has

10-1 ^ 10-286 == 73.5

times the amount of liydrogen ions per Htre 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 H- 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, for H+ and A- ions are present.
According to the law of mass action

[H-l X [A'l

^HA] = ^^^ ^' 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.

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 zveak 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- ] ^

H2O = H+ + OH ) "^'^ ^ ^ + un .

This causes an alkalinity equal to that of potassium hydrate.
The alkalinity of solutions of sodium carbonate is due to the
reactions,

DISSOCIATION OF SALTS

69

Na.,CO..

CO3-

HCO3

HoCO.

HoO

2Na ■
H'

+ CO,

HoO = H2CO3
=zHoO

+ OH-
+ OH-
OH

+ COo

If the CO2 is allowed to escape, the last reaction will only cease
when all the H2CO3 has been decomposed. The total resnlt 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 =

= BOH + H

HoO =

where HA is a strong acid and BOH a weak base.

E.g.

NHXl

HoO

= NH4OH

H^ +C1

(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. 62 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 37° to 38°, causes the
[H] X [OH] to rise from 10"^^^ to 10"^^*^ an increase of about
10 per cent. Strong electrolytes have a low^ temperature coeffi-
cient of dissociation. It is, therefore, obvious that increase of

70 ION IS ATI ON

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 + strong base. Increase of temperature causes tlie degree
of dissociation of acid to increase. Anions combine with hydrogen ions
from HgO 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 HgO and liberate H^.

(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 correspond-
ingly 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 Kh,o ;
II. the alteration in Kgait-

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

Further Keading

Crocker & Matthews. "Theoretical and Experimental Physical

Chemistry." J. & A. Churchill."

CHAPTER VIII
DISPERSE SYSTEMS

I. 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."" Sorensen.

Protoplasm consists largely of water. For instance, about 85 per
cent, of the total body weight of a puppy is water. This water is
partly " free," i.e. may readily be removed Ijy gentle drying, and
partly " bound," removable only by destruction of the tissues.
The bound water may amount to as much as 1-8 grams for every
gram of dry matter in the animal. Obviously, some mechanism
must exist to keep this fluid in position and so to mask it as to give
the impression of more or less solid tissue. The part of water-
holders is played by colloids, emulsions and certain crystalloids.

In Chap. 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 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 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.).

This table shows how a molecular solution of particles of 0-1 /a/x
radius acquires an additional effective surface of 12,600 sq. metres
when the particles are increased in size sufficiently to bring them
into the colloidal realm. A surface is effective when its area is
large enough to accommodate the heads (or tails as may be) of
molecules which may be held end-on to it. The diameter of the
cross-section of most molecules can readily' be calculated, and so
the possibility of their adsorption to particles of any particular
size may be predicted. In this connection Wo. Ostwald has

71

72

DISPERSE SYSTEMS

TABLE IX

Increase in Surface of a Sphere when its Radius is Decimally

Divided

Length of Radius.

Number of
Spheres.

Total Surface.

1 cm. \ Small Shot

1

12-6 sq. cm.

1 mm. )

103

126

0-1 mm. ) Coarse

10«

1260

0-01 mm. • Suspensions

109

1-26 sq. metres

1]^^ )

1012

12-6

O-l^it

Typical

1015

126

0-01/x

Colloids

1018

1,260

1^^

1021

12,600

0-l)u.)u. True Solution

1024

126.000

introduced the term specific surface to denote the ratio of surface
to vohime or SjV. In a sphere S = 4-TTr^ and T" = ^nr^ : therefore

— ^ = '-= - . It has been found in physical chemistry that

V 477/"* r

adsorption to a surface becomes an important 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 X IC^ approx., i.e. when the material is so finely subdivided

that it is in molecular solution, adsorption phenomena cannot

be detected.

Crystalloids and Colloids. Protoplasm, composed of proteins,
lipides, carbohydrates, organic and inorganic salts and a large
amount of water, is enclosed within a plasma-membrane, which
permits of the free passage of water, certain salts and other sub-
stances, but not of protein and similar complexes. If a mixture
of, say, albumin, starch, glucose, common salt and water were
enclosed in a parchment bag suspended in water, the glucose and
salt would pass through the membrane into the external water,
while the albumin and starch would remain within the bag.
Substances which pass readily through membranes like parch-
ment are termed crystalloids, and the albumin-like substances
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 saturated solutions, and
colloids, which diffuse very slowly and in general have a gluey
consistency. " They appear," he writes, " like different worlds of

COLLOIDAL STATE 73

matter, and give occasion to a corrcspoiuliiio- (li\ jsion ol" clicinical
science." The process of separating crystalloids i'roni colloids by
means of a membrane is called dialysis^ (See.Part II., Experiment

26.)

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. As an illustration, attention may be
drawn to a disperse system having two phases and only one com-
ponent, 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
{b) 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 metastable.

74

DISPERSE S Y STEMS

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 Continuous
Pliase. Pliase.

Examples.

I.

Gas — Liquid

Gas Liquid
Liquid ; Gas

Foam, Suds, Lather.
Mist, Spray, Steam.

IL

Gas — Solid

Gas ' Solid
Solid Gas

Hydrogen in platinum ; lava,

meringues, meerschaum.
Smoke, dust and some fumes.

m.

Liquid — Liquid

Liquid Liquid

Milk (fat in water).

Lymph, egg white (raw).

IV.

Liquid — Solid

Liquid
Solid

Solid
Liquid

Rock inclusions. Opal.
Colloidal metals, etc.

V.

Solid Solid

Solid Solid

Ruby Glass (Gold in Glass).
Some precious stones.

Class III. (So-called Emulsoid) is of the most importance in
biology, but Class IV. (Suspensoid) has been most studied and is
of considerable industrial and therapeutic value.

Colloids might be classified according to their degree of dispersion,
that is the ratio of total surface to volume, or the surface exposed to
each c.c. of the dispersed phase. This would give 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 suspended in water, range
of colloidal gold in water (Zsigmondy), solution of gold salt (un-
dissociated) and, finally, completely dissociated gold salt in aqueous
solution.

This state is not peculiar to the metallic colloids, but, as has
been amply demonstrated by Von Weimarn, can be obtained
from such materials as NaCl, A1(0H)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 irrespec-

LAW or COR RES PONDING STATES 75

tive 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.

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. Because of
their affinity for water such colloids are termed hydrophilic, i.e.
water-loving, in contradistinction to the hydrophobic suspensoids,
which are readily separated from their dispersion medium.

Colloidal matter may be further divided into two groups.
White of egg is a hydrophilic 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 semi-
soHd, 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. 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 (see p. 98).

Preparation of Colloidal Dispersions.

Some substances easily assume the colloidal state, but fairly
strenuous methods have to be adopted to induce others to do so.
The naturally occurring colloids, such as proteins of all kinds and
polysaccharides, are caused to crystallise with difficulty, while
substances which crystallise easily become colloids under compul-
sion. The methods used in the preparation of colloids fall, in
general, into two classes, chemical and electrical methods. In the
former class is included all methods which entail reduction, double-
decomposition, hydration, substitution of solvent, peptisation, etc.
In Part II. are given directions for the preparation of typical
colloids by these methods. Electrical dispersion methods con-
sist in the passage of an oscillating discharge between iron or
aluminium electrodes immersed in water (or other dispersion
medium) in which are suspended coarse fragments of the metal to
be dispersed.

76 DISPERSE SYSTEMS

Properties of a Colloidal Dispersion.

The properties of a dispersion depend in general either on the
size of the dispersed particles or on their electrical charge, or on both.

1. PROPERTIES OF COLLOIDS DEPENDING ON
SIZE OF PARTICLES

(i) Optical.

(rt) Colour. White light is composed of waves of different lengths
varying from 760/x/x to 4<50yu,^. 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 indices of
refraction of the dispersoid and the dispersant be kept constant.

The late Lord Rayleigh deduced a formula relating the size of the
particle and the wave-length of the scattered light in a quantitative
manner. A particle smaller in diameter than half the wave-length
of light will scatter light at the blue end of the spectrum about
twelve times as copiously as it does the longer red rays.

He explained the blue colour of the sky by considering that the
fine particles of dust, globules of water, etc., suspended in the
air, or even the molecules of the various gases of the atmosphere,
cause lateral diffusion of light of short wave-length giving a blue
colour, while the red rays are transmitted direct, producing the
gorgeous sunset colours. In one of Tyndall's experimental verifi-
cations 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 precipi-
tate. 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."

COLOUR OF DISPERSIONS 77

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 sullicient
depth appears blue l)ecause of 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 double 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 fine
unpigmented colloid particles suspended 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. In brown and black eyes,
pigment cells are found in the endothelium in front of the iris.
Except with people who have very black eyes, the pigment on the
anterior 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, if the pigment develops the colour changes from blue to
hazel, brown or black. The reverse change never takes place
(Bancroft).

Colour may be due, as we saw in Chap. II., to the reflection
of non-absorbed light. A surface which completely absorbed light
would give rise to the sensation of black, while a perfect reflecting
surface would be, of course, invisible. It follows that particles of
different sizes will " select " light of certain wave-length for
absorption, and, as a consequence, colour may result from " selec-
tive " absorption, reflection or diffraction.

In the table on p. 78, from Ostwald, is given the relationship
between size of particle and colour (a) from light absorbed, and
[b) from light transmitted (Table XI.).

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

As the particle becomes smaller, the colour transmitted alters to

78

DISPERSE SYSTEMS

TABLE XI

Corresponding Absorbed and Subjective Colours

{a) Wave-lengtli in ju.
Absorbed Colour

(h) Transmitted Colour

Wave-length in fx

•70
Purple

Green

•50

•65
Red

•60
Orange

Blue

Green-
Blue i

•48 ^45

■55
Yellow

Indigo

•43

•53
Green-
Yellow
Violet

•40

{a) Wave-length in /x

•50

•48

•45

•43

•40

Absorbed Colour

Green

Green-
Blue

Blue

Indigo

Violet

(6) Transmitted Colour

Purple

Red

Orange

Yellow

Green-
Yellow

Wave-length in fx

•70

•65

•60

•55

•53

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). 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).

Opticai, Resonance. — 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 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 tcmpcratui'e and a slight alteration

OPTICAL RESONANCE 70

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 ])endulum 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 movement may
attain an increased velocity because of incident light. Exner found that
exposure to light of a suitable wave-length had a slight but a positive
accelerating effect.

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 dye) 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, i.e. when the particles are large, this colloidal
dye appears red when observed laterally to the plane of incidence
of light. By transmitted light it is blue, i.e. appears blue when
looked at against the light. If a fine suspension is prepared it
reflects blue and transmits red,

{b) Faraday-Tyndall Phenomenon. 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 suspension to the invisible
solute. If the size of a particle is decreased below 200^^, it caimot
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. If mono-
chromatic light with a very short wave-length, say 2,000 A.u., were
to be used with a suitable microscope, particles of lOO^UjU. and
greater could be photographed. Such a microscope with quartz
lenses has been constructed by Barnard.

The tiny particles may also be made apparent in much the same
way as the innumerable specks of dust floating in the air become
sparkling motes dancing in a ray of sunlight which has penetrated
into a partially darkened room. 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

80

DISPERSE SYSTEMS

>^ \ / ,'

water, but ncj 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. 126), and is always produced when
light passes through any medium con-
taining particles whose diameter is
small in comparison with the wave-
length of light.

(c) The ultra-microscope is, in prin-
ciple, 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 objective
is that diffracted from the particles present in and optically
different from the fluid (Fig. 15). 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
particle and the dispersant. Nevertheless, by making certain
assumptions, the size of the particles may be calculated. The
essential featin*e of the ultra-microscope is not that it is a more
powerful kind of microscope, but a new method of illumination, so

Fig. 15. — Diagrammatic section
tlirousli a Wenham jsaraboloid con-
denser to show the direction taken by
the rays of light. (Hatscheli.)

TABLE XII

LOWER LIMITS OF DIAMETERS OF SMALL PARTICLES.

Visible under
Microscope

Microns
0-2;Li or
2-5 X 10^^ cm.

Sub-microns
(photographed

by U.V. light)

100/XjU, or
1-0 X 10 5 cm.

Not visible under microscope

8UB-MICRONS

Visible by ultra-microscope

Amicrons
Not visible by U.M.
under l-Oju/x

Electric arc

\b\i\x or

15 X 10-' cm.

Strongest
Sunlight
TOju,^ or
1-0 X 10-7 cm.

/i equals 10 ^ mm. = 10 * cm., jliju, = 10 ' cm.

BROWNIAX MOVEMENT 81

that ultra-microscopic particles arc rendered self-luminous. The
conditions under which these small particles can be made apparent
by this means are that (1) the light scattered is sufficient in intensity
and is suitable in wave-length to affect the retina ; (2) the particles
differ materially in refractive index from their dispersion medium ;
and (3) the particles are not so crowded as to overlap.

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 illumination, was 1-0 ju,/x 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 table on p. 80 (from Zsigmondy) shows the limits of size of the
various classes of particles (Table XII.).

Properties of Colloids Depending on the Size of the
Dispersed Particles

(ii.) Kinetic.

{d) The Brownian Movement. 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 is assumed to be made up of molecules
in a state of very rapid motion and having a mean free path inter-
mediate 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 con?iiderable 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 specifically
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
suspension of the water-colour gamboge, especially when the
diaphragm of the microscope is almost closed. The rate of mo ve-
il. 0

82

DISPERSE SYSTEMS

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. It has been observed in granite and in other rocks in small
pockets of liquid, which they must have occluded for millions of
years.

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. 16, obtained

Fig. 16. — Movements of two particle.s of iiidia-ruhber latex in colloidal solution, recorded
by cinematograph and ultramicroscope. (Henri.)

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
velocity. When the viscosity of the colloidal solution is increased
by the formation of a gel, the particles aggregate in one way or
another, their mean free path is reduced, and consequently their
motion is reduced in amplitude ; the resistance to movement is
increased, and so their velocity may become smaller and smaller
till they stop altogether. This phenomenon has been studied in
order to find out something about tlie structure of gels and will be
referred to later. The velocity may also be modified by alterations
in the hydration of the particles. Ramsay considers that the

INFLUENCE OF GRAVITY 83

particles in pure water do not touch one another at any time, each
particle being surrounded by a lifpiid layer. This layer is destroyed
by the addition of salts.

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.

{(') Distribution of Particles. If a fine suspension of gamboge or
mastic be kept imdisturbed at constant temperature for some time,
Perrin found that there was a distribution of the 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 atmosphere
with height above sea level, and Einstein argued that the distribvi-
tion 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 experiment
with mastic at four different levels 12/x apart he found 116,
146, 170 and 200 particles per unit. For the same levels the
following values were calculated : 119, 142, 169, 201. After this
adjustment of concentration to level has been reached, no other
change seems to take place. While this is true for the compara-
tively coarse suspensions used by Perrin, and even for finer
suspensions when examined in very thin sheets of liquid, it has
definitely been proved to be untrue for colloids, and even for
emulsions when the portions of the liquid within about lOO^u, of a
surface are neglected. In the body of the liquid gravity seems to
play no part in the arrangement of the particles, the concentration
being uniform throughout the non-surface portion and remaining
so for an indefinite length of time. This stability is due to the
electrical properties of the dispersed material.

Study of the optical properties of colloidal solutions leads one
to the conclusion that the individual dispersed particles, although
they are too small to be seen by the microscope luider any power,
i.e., cause no obstruction to the larger light waves, are still able to
cause deviation of the ripples of light. One would, therefore,
expect that they would show colligative properties indicative of
more sluggish particles than those in simple molecular solution.
Briefly, their osmotic pressure, activity of diffusion and power of
lowering the vapour pressure of water would be low, and their
viscosity and their resistance to the passage of salts through them

6—2

84

DISPERSE SYSTEMS

would be high. However, definite statements Hke that cannot be
made generally about colloids. They are true of physiological
colloids, especially of those in gel form, but are not all applicable to
the suspensoids.

(/) Ultrafiltration. Evidence tending to confirm the limits of
size found by optical methods of investigation is afforded by
experiments initiated by the classical series of ultrafiltrations of
Bechold. 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 also, equally necessarily, they must be larger
than the next filter in the series. The sizes of particles obtained
in this way arc in reasonable agreement with the values obtained
from ultramicroscopic calculations.

TABLE XIII

Size of Pores in Filter Paper

{H.

Bechold and R. Lucas.)

Number and type of paper.

Size of

pores in n approx

1,450 .

4-8

598 \
thick filter paperj

3-3

597 .

2-9

602 (hard) .

2-2

(baryta filters)

566 .

1-7

602 (extra hard)

1-5

Chamberland — Kerze

0-2-0-4

Reichel — Kerze

0-16-0-18

(g) Osmotic Pressure. Pure colloids in neutral water have a very
low osmotic pressure. This is just what one would expect when
one remembers that the osmotic pressure of a solution is related
to the number of particles dispersed in unit volume. The value of
the osmotic pressure of suspensoids is very small, and seems to vary
experimentally with the method of preparation of the colloid.
Hydrophilic colloids, both sols and gels, have a measurable
osmotic pressure, e.g. a 1-25 per cent, solution of pure egg albumin
(Lillie) gives a pressure of 20 mm. of mercury at room temperature.
It is very difficult to prepare pure hydrophilic dispersoids, because
of the way in which they retain crystalloids, and the presence of
these salts materially modifies the osmotic pressure of the colloid.
This modification is not simply additive as it would be if salts were

DIFFUSION 85

added to a molecular dispersion, hut varies with the salt used.
Some salts cause au increased and some a decreased osmotic pres-
sure to develop. In general, electrolytes belong to the latter class,
the extent of their depressing influence depending on the nature
of the ions composing the electrolyte. As regards the anions,
there is a defmite order of increasing depressing power as one passes
along the series

CNS < I< Br < NOo < CI < SO4

Similarly the cations may be arranged as follows : alkali metals <<
alkaline earths << heavy metals.

The hydrogen ion concentration of the whole colloidal system
has a very great influence on the nature of the osmotic change
produced by any added salt.

{}}) Diffusion. The large size of the colloidal particles, especially
those of hydrophilic sols, prevents their rapid diffusion through
still w^ater. In fact, coloured colloidal substances can readily be
arranged in the order of increasing size of the dispersed phase by
noting the rate with which the colour passes into water in a test
tube.

Diffusion of Salts. — Dissolved substances diffuse easily into or
out of gels, the rate of diffusion depending on the concentration
of the diffusing substance and on the nature of the colloid. Resist-
ance to the passage of the diffusant varies from gel to gel according
to their structure and viscosity. The obstructive power of a gel
may be altered by alterations of temperature, which alters both
the kinetic energy of the diffusing salt and the viscosity of the
gel. Some colloids, like albumin, develop a definite semi-solid
structure when heated, while others of a gelatin nature become
more liquid.

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 velocity of
diffusion.

The Cause of Diffusion. — What is the force that drives the
solute to all parts of a solution or of a sol or of a gel so that except
at interfaces it is equally distributed throughout the mass ? Just
that force which causes a gas to diffuse equally through a container

8(j DISPERSE SYSTEMS

and which causes a sokite to exert osmotic pressure, viz., the
kinetic energy of the particles (ions, atoms, molecules, or larger
aggregates).

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 adminis-
tration of drugs, — so called ionic medica-
tion. " Metal "-ions (cations) are carried
i into the tissues from the positive electrode

I of any current-supply device, while " acid "-

ions (anions) are driven in from the nega-
' five electrode (see Chap. XI. and Part II.,

p. 529).

LiESEGANG Phenomenon. — If a gel con-
tains 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.). These banded precipitates were
first prepared by Liesegang in a slightly
different form. A quantity of 4 per cent,
gelatin sol to which had been added 2 c.c.
of a concentrated solution of potassium
bichromate was poured on a clean glass
plate and allowed to set to a gel in a very
thin film. When firm, a large drop of 25
per cent, silver nitrate was placed in the
centre of the film, the plate being kept
horizontal. After remaining undisturbed
(in the dark) for two days or so, concentric
rings of silver bichromate were found round
the original drop, separated by clear zones
free from the precipitate, the distances

Fig. 17. — Adsorptive stratifl- i , , i • • i • ±.

cation of silver bichromate in betwecii the succcssivc Tiugs Dcmg greater

an agar gel. (Bradford, Bio- ,, i?j_i i? j_i j_ j_i

chemicaiJourmi.) the further from the centre they are

formed. Since the publication of the
details of the original experiment many different gels and
mutually precipitating salts have been tried. For example,
water-glass may be used as medium, or with certain precautions
agar-agar, or even a test tube full of a fine powder (flowers
of sulphur) or packed with vertically placed capillary tubes.
The illustration (Fig. 17) shows beautiful rings of silver-bichro-
mate in an agar gel. A very instructive modification of the

ifc ,1

^mmt»-

tefe Mi.^fjjLMfc Jia

DIALYSIS 87

experiment, also due to Liesegang, is to fill a glass tube with a
4-5 per cent, gelatin sol containing about 10 per cent, sodium
chloride. When the gel has set, the tube is immersed in a silver-
nitrate solution which will diffuse steadily into the gel from both
ends, leaving continuous bands of silver chloride. These bands
approach one another, but they do not meet. A clear space is left
in the middle of the tube.

The explanation of the phenomenon seems to be that as the silver
ions (of the original experiment) diffuse into the gel they meet the
bichromate ions, and some of the silver forms silver bichromate and
is precipitated. Now, as the diffusing ions move into the gel in
straight lines (Rcigel and Widjoff), and as conditions are similar
for the whole first line of advancing ions, they will undergo
precipitation practically sinudtaneously and form a layer of silver
bichromate in one plane. By the formation of the layer a certain
amount of gelatin has lost its bichromate. Diffusion of bichromate
ions will, therefore, occur to fill this gap. At the same time, silv^er
ions are advancing outwards and being precipitated. These
newly formed precipitates are at first attracted to the first ring and
adsorbed, so increasing the thickness of the ring. On account of
the greater concentration of the invading ions, they advance more
rapidly than the diffused solute and so pass beyond the first ring,
and after crossing a space with too low a concentration of opposing
ions to cause combination to take place, again form a ring of
precipitate, and so on. By the time that the silver has reached
the periphery of the plate, its concentration and, therefore, its
diffusion rate have become very low. The rings will, therefore,
have a longer time, i.e. greater opportunity to adsorb the solute,
and so they will be heavier and more widely separated.

Dialysis. — If a tube open at both ends and filled with a gel is
placed so that one end is immersed in water and the other end in a
solution, it will be found after a time that a considerable quantity
of the solute w'ill have passed through the intervening colloid and
be distributed in the water. If sufficient time were given, the
concentration of the solute in the water at both ends of the tube
would become equal. On the other hand, a colloid sol placed in
the solution would not have diffused appreciably into the gel.
This gives us a method of separating colloids from salts. The
thickness of the intervening gel is reduced to that of a thick film,
and instead of using for this purpose a gel soluble in water like
gelatin, a w^ater-holding substance like collodion is employed.
Instructions are given in Part II. for the preparation of various
types of dialysers, i.e. pieces of apparatus, principally consisting of
a film of collodion or a piece of parchment which can be used to

88

DISPERSE SYSTEMS

separate colloids and crystalloids from a mixture of these two
constituents. If instead of keeping one side of the dialysing
membrane immersed in water, running water is substituted, or the
water is changed often, the colloid in the dialyser can be freed from
practically all the crystalloid mixed with it. Fig. 18 is an illus-
tration of Abel's vividiffusion apparatus, by means of which
crystalloids — salts, glucose, amino acids, etc., can be removed
from the colloids — albumin, globulin, fibrinogen, etc., of the cir-
culating blood. It consists of a number of collodion tubes in
parallel, which may be interpolated between the two ends of a cut
artery in an anaesthetised animal so that they are functionally
part of an intact circulation. Now, as have we seen, a diffusible

substance will pass
out into the sur-
rounding water in
the glass con-
tainer, at a rate
depending on the
difference in the
concentration of
that solute on both
sides of the mem-
b r a n e (F i ck's
Law). If we want,
say, to study the
amino acid content
of the circulating
blood, all we have
to do is to arrange
matters so that our outer liquid starts with a concentration of no
amino acids and a concentration of all the other diffusible sub-
stances of blood equal at least to their concentration in the blood.
(i) Viscosity. It is obvious that some liquids offer a greater
resistance to stirring than others. Water and all true solutions in
water, even fairly concentrated ones, differ little from one another
in this respect. Even if small particles are suspended in the water
to form a suspensoid, or larger particles such as a precipitate of
barium sulphate in suspension, the additional resistance to shearing
is not very great. But when one comes to deal with hydrophilic
sols, and more so with gels, considerable force is required to push
a stirring rod through the liquid, i.e. the viscosity of hydrophilic
colloids is much greater than that of water, e.g. at 38° C. water has
a viscosity of 6-6 x 10~^ dynes per sq. cm., and blood serum about
twice that amount, viz. from 9-12 X 10~^ dynes per cm^.

Fig. 18. — Abel's vividiffusion apparatus.

COEFFICIEXT OF VlSCOSUrV 80

The \aliic of xiscosily is oi' soiiu' iniportancc in the study ol" the
circulation ol" the blood, because, if the resistance to the niovenicnt
of the blood in the capillary vessels is increased, the heart will have
to expel the blood at a greater pressure to force the fluid round the
circuit. Several methods have been employed to measure this
value. The one most commonly used is to measure the rate of
flow of a measured quantity of the fluid under test down a vertically
held capillary tube imder standard conditions. This rate, after
correcting for density, is usually compared with the rate obtained
under the same conditions for an equal quantity of water (Part II.,
p. 530). Sometimes it is desirable to determine the coefficient of
viscosity in C.G.S. units. The coefficient is defined as the tan-
gential force per cm.^ on either of two horizontal planes 1 cm. apart,
one of which is fixed while the other moves at 1 cm. per second, the
space between being filled with the liquid under test. Hatschek
used for this determination a piece of apparatus consisting essen-
tially of two concentric cylinders, the outer one of which can be
rotated at any desired rate while the inner one is suspended from a
wire. The liquid fills the space between the cylinders. When the
outer cylinder is rotated it carries with it the thin layer of liquid in
contact with it. This liquid layer in turn pulls at the layer next
to it, and so on till we come to the almost stationary layer in
contact with the inner cylinder. That is, we may consider the
fluid between the cylinders to be made up of a number of concentric
liquid cylinders, each exerting a certain fractional force on the
adjacent cylinders. The degree of torsion of the suspending wire
gives a measure of the viscosity of the liquid.

The main factor on which the large value of the viscosity of
hydrophilic colloids depends is that the shearing force has to over-
come not only the internal resistance of the liquid continuous
phase, but the resistance to distortion of the elastic colloid dispersed
phase.

Concentration. — The latter resistance, of course, increases with
the number of colloid particles encountered by the distorting force
i.e., on concentration. Up to a certain concentration limit, which
varies with different colloids, increase of concentration makes very
little difference in the value of the viscosity. Above this limit,
a very sharp increase of viscosity occurs. One may take this
limiting value as a measure of the hydrophilic properties of the
colloid, e.g. caseinogen starts to increase its viscosity markedly at
about 5 per cent., while glycogen goes up to 25 per cent, before
being effectively viscous.

Temperature. — Alteration of temperature produces marked and
regular alterations in the value of the viscosity of pure water, e.g.,

90 DISPERSE SYSTEMS

about 2 per cent, per degree. With hyclrophilic colloids it varies
with the colloid in both degree and sign, e.g. gelatin is less viscous
while albumin is more viscous at 60° than at 10° C.

Hydrogen ion Concentration. — At the isoelectric point (see
p. 92) physiological colloids have their lowest viscosity. Any
increase of H+ above this point leads to increased viscosity.
Decrease of H+ below the isoelectric point also increases viscosity,
but not so markedly. This increase of viscosity with altered pH
soon reaches a sharp upper limit. Any further alteration of pH
produces a decrease in viscosity due to a dehydration of the
colloidal micelle.

Salts. — The effect of salts on the viscosity of a colloid at its
isoelectric point is very slight. It is found that the addition of
salts to an acid or to an alkaline protein tends to reduce the
viscosity to that found at the isoelectric point. The various
neutral salts differ in the intensity of their power to antagonise
acid or alkali in colloids, depending principally on their valency
(see Part II.).

2. PROPERTIES OF COLLOIDS DEPENDING ON THEIR

ELECTRIC CHARGE

We have used terms in the discussion on viscosity above which
indicate that colloidal particles carry an electric charge. 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 opposite
charge. This electrical migration is called cataphoresis (Figs. 19
and 20). If, on the other hand, the colloid cannot move, say it is
in gel form or associated with a membrane impermeable to it, then
the molecules of the water in which it is immersed will move
relative to it. (See Electrical Endosmose, p. 142).

The charge on colloidal particles may be developed (a) electro-
statically, (b) by orientation of the molecules on the surface of the
colloid, or (c) by some adsorption effect. Most inert substances
when immersed in water collect a negative charge, while a very
few become positive. This is true whether we are dealing with
particles of colloidal size or with large masses, e.g. basins, beakers,
etc., and is generally considered as due to electrostatic causes, i.e.
the surface picks up electrons liberated by the energy of agita-
tion of the water molecules (ionisation, q.v.). Many colloids are
amphoteric, i.e. can give rise as occasion offers to either + or —
" ions." That is, they will have two ionisation constants — an
acid one and a basic one. Now if an ampholyte is immersed in
water and a strong acid added, the ionisation of the weak acid of

ISOELECTRIC POINTS OF PROTEINS

01

the colloid will he rc'})r(ssc(l, aiul so tiic colloid will a])j)car basic,
i.e., will act as if composed of cations. On the other hand, treat-

I

^

n

>•^

;.•'.:•.:••:

'.••;•.•.:..••.:

.••• '..'-.I

Fig. 19. — 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 ciu:rent the colloid
rises towards the electrode of opposite sign to
tiie sol. (Hatschek.)

Fig. 20. — Apparatus for ultramicroscopic
observation of the movements of colloids in an
electric field (see Part II.). (Hatschek.)

ment with a strong alkali will give the colloid acidic or anionic
properties. Hardy (1899) noticed that the particles of egg albumin

TABLE

XIV

Isoelectric

Points

OF Common Proteins

.\nimal.

Vegetable.

Nucleoprotein (Pancreas)

. 3-52

Glutenin

. 4-45

Serum Albumin

Edestin

. 4-5-8

Casein

- 4-7

Gliadin

. 9-0

Gelatin

Eg£f Albumin .

. 4-8

Fibrinogen

. 5-0

Serum Globulin

. 5-4

Oxyhsemoglobin

. 6-74

92

DISPERSE SYSTEMS

sol migrated to the cathode in acid sohitioii or to the anode in
alkahne sokition.

Isoelectric Point.

At a pH of -t-8 in Hardy's cataphoresis experiment the albumin
particles did not migrate to one pole or the other. This indicates

that the protein is equally
ionised as an acid and as a base,
and is electrically neutral. The
isolectric point of an amphoteric
colloid is that pH at which
certain of the characteristic
properties of the colloid are
minimal, viz., osmotic pressure,
viscosity, imbibition and sta-
bility, as is shown for gelatin in
Fig. 21 from Loeb's results.

The actual concentration of
H ions at which these minimal
values are reached is specific for
each colloid. Most animal pro-
teins are isoelectric on the acid
side of neutrality, while vege-
table proteins reach this point
on either side of pH 7.

Coagulation of Gels and Precipita-
tion of Sols.

As we have seen, at the
isoelectric point, the colloidal
particles become electrically
neutral, and, therefore, one of
the factors tending to keep
them apart has been removed,
viz., the repulsion of similarly
charged bodies. When, by
simple molecular agitation, some
of the particles pick up an
electron, as they are bound to
do, and so become differently
charged from their neighbours,
mutual attraction takes place ; these particles coming together form
larger aggregates, thus accounting for the lowering of osmotic
pressure and of the stability of the dispersion at this point.

RE6I0N OF GELATIN

ISOELECTRJC
BRDMIBE POIKT RESION OF (JEWTlN

too

90
BO
TO
60
SO
■4-0
30

1

I 5^^

\

I

\

>

V

\

\

^

^-^

I-—

20
lO
0
130
I20
1 lO
100

so

1

n

nAi

, j;

>EL

.INC

\

k/

j

V

\

k

\

c

\

^

,^

^^

80

70

60

175

1 50

125

100

T5

50

25

O

4-

3

2

U.

SCi

jsn

V

\

,^

Ph

3-

J 3

3 I

b 4

0 A,

\^.y'

\li

1 S'

5 5

8 6

0 fr

H

<

s<

s

\

N

S

^^

iz::

S

\

^

1,— <

r— '

\

/

a

HO

vc

'Rl

SLSi/

e£

\,

(

<

t

N

^

N

s

a

HD>

iCTt

vn

f

s

N.

^

-— '

—"'

~~'

'~~'

10,

'<?<?

^

y'

o>

M3

(

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cc

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iOi

IN

\

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CC

IP

K

'£N

:M

s

GE

jiri

H 3

UUT/O)^

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s

^rt

H

Br

M

e

16

M
3!

H
. 64

t 121

i U6

M Jl
5IZ lOZ

H
4 21^

M
t8409

M

M

I 163

s-.°

4.7
PH 4.1 4.i 4.2 43 44 4.S 4J H 5-4 55 5-6 5-6 S f

Fig. 21. — Curves showing that the total
swelling, viscosity, osmotic pressure, and con-
ductivity of gelatin are minimal at the isoelectric
point, pn 4-7. (.After Loeb.)

HARDY'S RULE 93

This coagulation may be brought about b\' adding [a) acids or
alkahes, (6) 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.
Hydrophilic colloids, on the other hand, are more stable than
hydrophobic colloids. They usually need the addition of a large
quantity of the coagulating substance and the resulting coagulum
is frequently irreversible. We have seen that they are diphasic
systems where the continuous phase is more or less a continuation
of the disperse phase. If a substance A is dispersed in water to
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 minimimi and on the other hand by a certain
maximum concentration of water in the continuous phase.

Salting Out.

There are two factors implicated in the precipitation of hydro-
philic colloids by salts, one of these (a) is determined by the degree
of hydration of the colloid (see p. 98), while the other (j8) is related
to the solubility of the colloid-hydrate at the isoelectric point. At
this pa, the two factors may be included in the equation

log s = am -\- ^Q

where s = solubility of the colloid and m the molecular concentra-
tion of the salt. If precipitation is not carried out at the isoelectric
point, but at some other hydrogen ion concentration, then instead
of /3q another constant ^^ has to be used, depending on the ^^H.
If the precipitations are not induced at the isoelectric point of the
colloid, the powers of various salts to flocculate any colloid
depends on the valency of the cation if the pJi of the fluid is greater
than the isoelectric pH, and on the valency of the anion if the
solution is on the acid side. That is, under these conditioiis onlv
those ions are effective coagvdants whose electric charge is opposite
to that of the colloid (Hardy's rule).

Protective action of Hydrophilic Colloids.

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

94

DISPERSE SYSTEMS

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 XV

Class.

Gold Number.

Examples.

I.

11.

III.

IV.

0- 005-0-1 mg.
01 -10 mg^
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 the globulins are emulsoids,
but they differ physically in at least three respects summarised
below.

TABLE XVI

Albumin.

Sol in water.

(Sol in 5 per cent. NaCl.)
Not ppt. by \ sat. (NH4)2SO.i.
Protects suspensoids.

Globulin.

In sol in water.

(Sol in 5 per cent. NaCl.)
Ppt. by i sat. (NHJoSOj.
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 are practically invariable
in health, but duriim the course of various diseases the balance
is u])sc't. If the globulin content is increased relatively to the
albumin, then the body fluid will lose a portion of its protective

MUTUAL PRECIPITATION 05

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.)

Precipitation by Colloids of Opposite Charge.

Colloids that are present together in the same medium may
mutually precipitate one another, either because being of opposite
sign they neutralise their charges, or because they sensitise each
other to electrolytes. As an example of the former action we may
consider the usual method of getting a protein-free filtrate from
serum by the addition of a calculated quantity of colloidal iron or
of tannic acid. The serum proteins are, as found, slightly alkaline,
and carry a small negative charge. This is neutralised by the
positive charge on the iron or on the tannin (Part II.).

A similar method could not be used for whole blood because the
haemoglobin at pH 7-4 carries only a feeble negative charge and
would very readily take on a + charge. A small quantity of
colloidal iron is added which distributes itself over the blood
colloids. If one now precipitates the liq. ferri oxidati dialysati by
an electrolyte to which it is sensitive, e.g. KgSO^, it will rapidly
separate out, carrying with it the blood proteins. This is an
example of the second type of mutual precipitation.

A special instance of this kind is found in the precipitation of
electro-positive dyes on filter paper, — colloidal cellulose with a
negative charge in water, intensified by the presence in it of
electrolytes, especially calcium silicate (Part II.).

Of great interest in this connection is the reaction of proteins to
dyes. In histological technique, various " basic " and " acidic "
dyes (see p. 53) are used to obtain a differential staining of various
tissues or to indicate cell structure. Gortner has found that at
physiological concentrations of hydrogen ions the dye combines
chemically with the protein, the dye anions forming a salt with the
protein cations, and vice versa. For example, the nuclear material
contains a predominant amount of acidic protein and so attracts
dye cations. If the cation of the dye is coloured, i.e. if the dye is
basic, it will stain the nucleus. On the other hand, at greater
acidities {pH 2-5-1) true adsorption takes place with a neutralisa-
tion of the electro-kinetic potential on the surfaces of the colloids.
That is, at hydrogen ion concentrations not far removed from the
isoelectric point of the proteins the amount of dye fixed is deter-
mined by the chemical composition of the proteins, and differs, of
course, for the various proteins concerned. When the deviation
from the neutral point is greater, more dye is taken up by adsorp-
tion. This extra amount is independent of the ehcmieal composi-

96 DISPERSE SYSTEMS

tion of the proteins, and is determined only by their concentration
and charge. Such stains as Van Gieson's depend on this reaction.

Action of Radiant Energy. (See also Chap, XIII.)

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 13 radiation. Schanz found that ultra-violet light by its power
of ionising water could decrease the solubility of albumin so that it
was precipitated along with the globulins. He attributed the
production of sclerosis and lack of elasticity of the lens of the eye
to light of short wave-length acting in this way on the mixture of
albumin and globulin composing it.

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.

3. PROPERTIES DEPENDING ON SIZE, CHARGE
AND STRUCTURE

Adsorption. Adsorption to a surface was considered in Chap. VI.
Colloids are characterised by their large specific surface, by the
development of surface charges due to this surface, or, in some, to
their amphoteric nature, and in the case of gels, by an internal
structure offering a surface to the dispersion fluid. If the colloidal
particles are free to move, i.e., if the colloid is in sol form, adsorption
may take place in either of two ways. The colloid may be adsorbed
to a surface or matter may be adsorbed to the colloid. Dyeing
with colloidal dyes offers an example of the first kind, while the
fact that natural colloids are always impure on account of adsorbed
mineral matter indicates the truth of the latter statement. The
gels with their internal structure present peculiar surface properties.
They have a special propensity for adsorbing their dispersion

IMBIIiiriON

!I7

medium (see below, Imbibition). In all cases of adsorption the
chemical and physical properties of the adsorbed material are
altered by the process. Not only are the adsorbed molecules
oriented, but they are held under comj)ression. It is in these
condensed layers that many typically ])hysiological reactions take
place — reactions which could only occur with great difliculty in
dilute solutions (Chap. X.), Further, the adsorbed salts are
rendered for the time being osmotically inactive. They are
removed from any active part in the solution.

The process of liberating the adsorbed material has been dealt
with in a previous chapter (VI.). The result of the process of
de-adsorption is the restoration of the physical properties of the
adsorbed material. We shall see later (Blood) when, how and with
what effect adsorption and de-adsorption take place.

Imbibition. The adsorption of water is of such biological
importance that it requires special consideration. All the physio-
logical colloids have the property of taking in relatively large
quantities of water even against enormous pressures, and of
holding this water against even strenuous methods of removal.
This " bound " water stored in the micropores (p. 55) is under
considerable compression, so much so that its density and all its
physical properties are altered. A very instructive demonstration
of this, due to Du Bois Reymond, is given in a modified form on
p. 537. A piece of the seaweed laminaria digitata, which can be
bought dried and ready for use under the name of tangle tents, is
attached by a thin copper wire to a piece of cork of such a size
that it just floats in water {i.e. the system cork-wire-laminaria has
a density of 1 approx.). The following table gives the results of its
immersion in water.

TABLE XVII

Compression of Water imbibed by Laminaria

Wj = Weight of Laminaria in Air.
Wo — Weight of Laminaria in Water.

B.

98

DISPERSE SYSTEMS

Laminaria balanced with cork and wire on zero day. On the first day it
floats, on the second it is as on zero day, and on the third day it sinks. If
more cork is now added so that the system just floats again, the laminaria
will sink again on the flfth day.

If IV = wt. of cork and wire, v = vol. of cork and wire.
Then on zero day, w + 2-64 = v + 1"81 (/."., density = 1)

.■ . v= w -\- 0-83.
Then on any day (say 10th)

' Density of whole system

. wt. m; + 20-31

IS

vol. ~ -y + 19-40
_w + 20-31
~ w + 20-23

which is > 1.

Hence on the lOth day the laminaria will have sunk if just balanced on the
zero day.

It will be seen that at first the density of the system decreases

Kl(i. -^-d

-(IvloniftcT for determining tlie swelling pressure of colloids.

slightly, and then rapidly increases — the system sinking in water.
The primary decrease, occurring when the macropores are filling
and the seaweed swells, is difficult to explain and is not relevant to
this discussion. During the period of increasing density, water is
being packed into the micropores in the interior of the gel. This
water is " bound " and can only be driven off by the application
of suction and heat. Many similar experiments have been devised
to show the same phenomenon. In Fig. 22 is an apparatus
designed to measure the swelling pressure of seeds or of powdered
gelatin. (See also Part II., p. 537.)

The " boimd " portion of the imbibed water which is held so
fiercely, and which may be so increased in density that it
occupies about 75 per cent, of its bulk at atiuospheric pressure,
has no aj^preeiable vapour pressure at ordinary temperatures
(Gortncr). It will, therefore, freeze with great difficulty, and if it

HEAT OF IMBIBITION 99

does, it forms such small crystals of ice that the colloid structuie is
not destroyed. Although it is so tlillicult to dri\e oil, that a silica
gel, for instance, can only partially be dried in a vacuum at 300° C,
about 5 per cent, of the water remaining after 6 hours' heating
(Neuhausen and Patrick), and an alumina gel cannot be dried by
heating for 2 or 3 days at 500° C, yet some relationship does
exist between the " free " and the " bormd " water. Under
certain conditions, as yet undefined, boimd water may become
free again, and the reverse. Many physiological processes may
depend on an equilibrium between free and bound water. For
example, certain enzymes proceed towards synthesis under one
set of conditions and towards hydrolytic splitting under the
opposite set. The former conditions are generally admitted to be
when the reacting substances are concentrated, ie., when by
imbibition colloids have removed water from the sphere of activity,
and the latter when dilution takes place.

Heat of Imbibition (p. 55). During the process of compression
a considerable amount of heat is set free. If the swelling takes
place relatively slowly, as with laminaria, it is not easy to demon-
strate the development of heat, but, in the case of colloids which
rapidly imbibe water, even such a value obtained by merely stirring
the collcid with a thermometer during the process of imbibition is
appreciable (Part II.). The amount of heat developed depends on
various factors. At the isoelectric point the main factor is the
amount of compression of water produced.

TABLE XVIII
Pressure and Heat of Imbibition of Hydrogels

Gel. ('oiiii)ressioii (atmos.). tJram calories per gram of gel.

Dry Gelatin . . over 300 5-7

Dry soluble Starch . over 2,500 (Rodewald) 6-6

Dry Gum Tragacanth . over 400 10-3

It is obvious from Table XVIII. that other factors besides
compression play a part. Starch always exerts a large osmotic
pull because it is never free from ions. This may, in part, explain
the large compression without a correspondingly large evolution
of heat.

The amount of water imbibed and the rate of imbibition are
lowest at the isoelectric point (Fig. 21;. The addition of either
acid or alkali greatly increases both rate and quantity. This effect
is due to the formation of salts of the colloid, and the colloidal ions
so produced exert a pure osmotic ])ull on the water — the gel
itself acting as a semipermeable membrane to its own ions. The

7—2

100 DISPERSE SYSTEMS

effect of a very slight increase in pH on swelling is much more
pronounced than a larger increase — e.g. 1 gram of gelatin at pH 4.-7
imbibes 7 c.c. of water, while at ^^H 4-4, 21 c.c, water will be taken
up. Increasing the hydrogen ion concentration still further
produces a fairly steady increase in swelling power till at jjH of 3-4
about 35 c.c. of water have been absorbed. The extra amount
absorbed by increasing the hydrogen ion concentration still further
is inappreciable. When acetic acid or similar weak acid is used
to acidify the gel atypically large results are produced, due, according
to Loeb, to a diminution in the cohesion of the gel brought about
by the high concentration of those acids necessary to give a pH
of 3-2.

It is obvious from our discussion of the isoelectric point that the
addition of salts to a gel will tend to depress its power of imbibition
to a value approximating that found at the isoelectric point due to
their inhibitory action on the io7iisation of the gel. Salts cannot
exert an osmotic effect of their own if the gel is freely permeable
to them (see Diffusion).

Explanations may now be offered as to why a limiting value
is placed on the amoimt of water imbibed by a gel. The force
causing swelling, whether due. as at the isoelectric point to pure
capillarity, or to the ionised gel exerting an osmotic effect, is
opposed by the elastic forces of the gel. The gel molecules or gel
ions exert a cohesive force which has to be overcome. In the case
of substances like laminar la, the cohesion is very great and does
not permit the molecidcs to be forced very far apart. On the other
hand, gelatinous substances have their particles separated suffi-
ciently to make the gel soft, and, finally, if water were freely
admitted, the gel would become more and more like a sol.

Syneresis. Graham found that if gels were left undisturbed for
some time they underwent contraction and expressed a quantity
of their dispersion medium containing some of all the colloidal and
crystalloidal matter present. This process he called syneresis
(coalescence), and it is common to all gels, but in different degree.
Tvpical examples are separation of serum from blood-clot, whey
from curded milk, and weeping of agar slants.

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
closelv 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 prac-

SYNERi:SIS 101

tically ins()liil)le in water. The /3 form is very soluble in water.
On warniino- some of tlie former willi water it gradually passes
into the soluble form and thus goes into solution. Insoluble
a partieles may be dispersed in larger particles of j8 + water.
They in turn form a true sol with water. Alteration of i)hysical
or chemical conditions will therefore alter the relative concen-
tration of a and ^. The jS 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 Emulsions, Chap. IX.)

A similar difficulty occurs in attempting to explain the colloidal
behaviour of some of the proteins. The globulins offer an interest-
ing and somewhat bewildering field of study. They are insoluble
in Avater, but soluble in neutral salt solutions in the neighbourhood
of their isoelectric points. In the list of isoelectric points given on
p. 91 you will find that edestin, a vegetable globulin, is given no
definite figure, but a range from jjH 4-5-8-0. That is, between
those wide limits of hydrogen ion concentration, the reactivity of
edestin is at its lowest. Somewhat similar figures could be
adduced for the blood globulins. They have large molecules, but
very few polar groups capable of combining readily with acid or
base — too few indeed to carry them into solution under physio-
logical limits of pH. They, therefore, carry the burden of retaining
salts, especially sodium chloride, within the body if they are to
remain in solution (see Blood).

It has been shown by Starling that the colloids of the blood were
the factors determining the volume of the blood, and that their
osmotic pull acting against the filtering force of the blood pressure
controlled the output of urine, the formation of lymph, etc.
Bayliss clearly demonstrated the function of these colloids,
especially in the neat balance between albumin and the globulins
in maintaining the viscosity of blood. Swelling of colloidal matter
in the erythrocyte under the influence of an acid (COg) plays a large
part in securing efficient oxidation in the body, and adsorption is
necessary for the life of the cell (p. 134). Further, colloids may be
regarded as great reservoirs of energy in the body —

(1) As colloids have extremely low osmotic pressures they are a.
suitable medium for the storage of potential energy. Carboliydrates
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 thus rendered osmotically
inactive, but may be set free again by alteration of the colloidal
electric charge.

102 DISPERSE SYSTEMS

(3) Some colloids imbibe water and compress it. A hydrated gel
(jelly) has therefore a store of hydraulic pressure within it.

Further Reading

E. Hatschek. " An Introduction to the Physics and Chemistry of Colloids."
J. and A. Churchill.

CHAPTER IX
DISPERSE SYSTEMS

II. SOAPS AND EMULSIONS

" When we have faniiharised ourselves with the physico-eheniie and colloid-
chemie behaviour of systems of the type water-dissolved-in-x, we shall liiid ourselves
possessed also of the laws whieh govern the behaviour of protoplasm under physio-
logic and pathologic circumstances. Martin H. Fischer.

Emulsions are systems consisting of two nuitually iiisoltible
liquids, one of which is very finely dispersed within the other.

They may be regarded as emidsoids 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
w^ater in such a way as to remain stable for an indefinite 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
maxinumi of 2 per cent, of the oil may be taken up by the water,
forming a stable dispcrsoid. Measurement of the particles, how-
ever, 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 condenser water of steam engines, which contains lubricating
oil in suspension.

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

If the generic term oil is used to denote any liqind that is not
miscible w4th water, we may note that there are two entirely
different types of enmlsions, the one being drops of oil suspended
in water and the other being drops of water suspended in oil
(cf. sol and gel). For example, milk belongs to the former and
butter to the latter class. It is important to know under what
conditions each of these types is formed. One might at first
imagine that the governing factor wotdd be the relative amoimts
of oil in water, much water and little oil producing the

103

104

DISPERSE SYSTEMS

oil-ill-water type and excess of oil over water producing the
water-in-oil emulsion. This is not so. The relative amounts
of oil and water have nothing to do with it. To understand

TABLE XIX

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
NaXOg, 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

75-2

Protein

2-8

Sugars,

K and Ca, etc.

Pharmaceu-
tical
Emulsions

Oil
50

Water
50

Egg white
Gum arable
Saponin

Sugar

Phosphates

Carbonates

Lubricating
Emulsion

Water
1

Oil
98

Soap
1

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

ST A n I LISA TIOX 105

cause nmtiial repulsion, and (c) nieelianieally keep the dioplets
separate. The presence oi' an ennilsoid seems to confer stalnhty
on an oil-water emulsion.

Various theories have been put forward to explain why the
presence of a hydrophilie colloid permits of the formation of a
permanent enudsion and why some stabilising colloids ])r()duce
a dispersion of oil-in-water while others favour the water-in-
oil type.

(1) Quincke, Hilly er, Donnan and Potts are of opinion that the
stability is due mainly to a lowering of interfaeial tension by a
thin layer of the colloid or semi-colloid deposited on the surface of
the droplets of the disperse phase. This interphase 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. That is, an emulsion is
triphasic.

(2) According to Bancroft, a deposition of the stabiliser in
accordance with the Gibbs-Thomson principle {q.v.) provides the
necessary electric charge and confers protection. He adduces as
proof the fact that if another surface is brought into competition
with the oil- water surface for the stabilising agent, some proportion
of the stabiliser will be adsorbed to this new surface. For example,
if the emulsion is allowed to stand the air-fluid interface will
capture some of the stabiliser, i.e. the cream will carry off some of
the colloid, and this, we know, it does.

(3) Fischer considers that an emulsion may be triphasic but need
not necessarily be so. His idea is that a diphasic system is all that
is required for stability, e.g. oil and a lyophilic colloid in water.
A film of the solvated colloid is adsorbed to the surface of the
disperse phase.

(4) R. E. Wilson is of opinion that the film on the dispersed
fluid is really a plastic solid, i.e. butter-like.

All these theories have one fact in common, viz. 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.

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.

106 DISPERSE SYSTEMS

Emulsions are broken throuoli tlie institution of conditions
that are the reverse of those that make for their stabihsation.
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 giun 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 difficidt
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.

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-to-use 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.

Soaps. 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, bloed, 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

107

OIL

■tSaCl

+ Ca CI2

+ NaCL
+ CaCl,

soaps of the lower fatty acids to the colloidal ^els of the higher
honiologues. This is largely due to the steady increase in water-
holding capacity with increase in the length of the carbon chain.
The sodium soaps of the acetic series show this gradation in imbibi-
tion very well. For instance, a gram-molecule of the sodium soap
of caprylic acid can hold 200 c.c. of water while that of arachidic
acid is capable of imbibing 37,000 c.c.

Still more important physiologically is the effect of altering the
cation. Sodium, potassium, ammonium, calcium and magnesium
soaps are found in physiological analyses and these differ from one
another, especially in their power to hold loater. 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
I 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.

Sodium soaps, used as
emulsifying agents, pro-
duce oil-in-water sys-
tems (secretions ?), while
the calcium and magnesium soaps favour the water-in-oil type.
Therefore, in a mixture of these soaps there wdll be a com-
petition for the surface of the oil drops. If the lime salt pre-
dominates interfacial tension will become greater, while it will
be markedly decreased w'hen a superabvmdancc of sodium is
present. This is clearly illustrated in Fig. 23. In tube («)
the oil is allowed to drop from a capillary tube (stalagmometer,
Part II.) into very dilute sodium hydrate (N/1,000). This may be
taken as the standard = 5 drops per unit time. The second tube
demonstrates unequivocally what happens when, under the same
standard conditions, sodium chloride (N/6) is added to the soda.
There are now 30 drops per unit time — ^the surface tension has been
lowered 3,650 times. The substitution of the chloride of calcium
for that of the monovalent sodium (N/1,000) cuts down the drops

Fig. 23. — To demonstrate the effect on the number and size
of drops formed from a ijiven vohime of olive oil dropping from
a standard tip tlirough solutions of O'ODl >', >'a<)H alone
(tube 1). and plus ()-15 N. XaCl (tube 2). plus 0-0007 X, Cal 1.,
(tube 3), and in tube 4 plus both Nail and CaCl,. (After
(i. H. A. Clowes).

108 DISPERSE SYSTEMS

to 3 per unit time. That is, surface area has been decreased and
surface tension increased. The final tube indicates graphically that
a balance may be struck between the mono- and the divalent
cations, producing a result differing not one whit from that shown
in the first tube where both chlorides were absent. In our later
studies we shall see in just how many reactions monovalent cations
like sodium, potassium and guanidine are antagonised by divalent
cations like calcium and magnesium.

The behaviour of sodium and calcium soaps 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. XVIII.).

Soap, above certain concentrations, exists as neutral undis-
sociated colloidal matter with a certain amount of water of
hydration " bound " in it. If the concentration of the soap is
decreased, some of it will become ionised, and so cause the " free "
water of solvation to give an alkaline reaction to litmus. Heating
a neat soap causes it to liquefy, i.e., to form liquid crystals. Mac-
lennan (1923) carried out work on the microscopic structure of
soaps, much of which is of interest to physiologists. He showed
that liquid neat soap had some kind of molecular structure or
orientation indicated by its power of rotating the plane of polarised
light (q.v.), i.e., the liquid is anisotropic like a solid crystal. The
crystal structure also produces characteristic X-ray photographs.
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 = NagSO^ + 2HA.

MYELIN FORMS

109

{b) On adding a powdered neutral salt to a soap solution the
soap is " salted out " as a curdy mass. The salt reduces the
hydrophilie powers of the soap and so reduces the stability ol"
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 aumioniiuii, sodiiuii or potassium a curdy precipitate is produced.
This curd is a calcium or magnesimii soap, which, as we have seen,
has little or no aflinity 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).

Myelin Forms. — If a drop of a soap of an unsaturated fatty acid
is allowed to come in contact with a drop of water, the soap will be
partially dissociated into base and fatty acid, and so cause a re-
arrangement of the internal structure of the fat droplet. The
visible sign of this alteration is the shooting out of a knob of
material into the water. Close examination of this extrusion
reveals that it is a coiled structure (Fig. 26 {a) ) with a distinct
adsorption membrane at the water-soap interfaces. If a micro-
polarimeter is used the coils will appear brightly coloured and
marked with a cross which rotates with the Nicol prism. One
associates this appearance with the fornuition of acicular crystals,
and, under the high power, bipyramidal crystals may be seen lying

— Successive jiliases in tlic dcvelop-
inent of myelin outgrowths from a streak of
lecithin in n'lOO hydrochloric acid. (Courtesy
of Professor l^eathcs.)

no

DISPERSE SYSTEMS

parallel to one another and at right angles to the myelin sheath
(Fig. 26 (/) ). If now the surrounding water be made slightly

alkaline, say, altered from pH 7 to 7-4,
the coil will steadily unroll (Fig. 26 (b) )
till it assumes the appearance in Fig.
26 (c) ). Fig. 26 (d) indicates that it is
still a double structure. This stretching or
unrolling, due in the first instance to in-
creased alkalinity on the surface of water
and soap, is carried out by the in-
creased internal tension developed in the
myelinated soap by the imbibition of
water. The addition of a quantity of a
weak acid just sufficient to ensure that
the water is merely acid (e.g. pH 6-9) will
cause the processes to retract (Fig. 26 (e)). If a greater acidity
is developed the sheath will be ruptured and the crystals dis-
seminated and dissolved. Leathes has demonstrated that lecithin
and cholesterol oleate, compounds very widely distributed in the
body, readily show the development of myelin forms. (See also
Chap. XL, Membranes.)

Bragg and others have shown that by means of X-rays, diffrac-
tion patterns of crystals can be obtained. For instance, a single

Fig. 25. — Myelin outgrowths from
lecithin after 24 hours in equal
parts of n'lOO calcium and sodium
hydro.Kides. (Courtesy of Trofessor
Leathes.)

Fig. 26. — Myelin forms of Ammonium Oleate, viewed in convergent polarised light.
See text. After J. H. ( lark, AiiiiTiain Journal of Physiology.

solid crystal gives a regular interference pattern of sharply defined
spots round a central image. If. now, we have a large number of
small crystals regularly arranged (as in (/) Fig. 26), the diffraction

RIGIDITY OF TISSUES 111

pattern I'roni the parallel planes in the niicrocrystals, lia\ ing une
direction in conniion, will appear as concentric rinj^s. The
distance between the reflecting planes is twice the length of the
nioleeides composing the crystals, so that if the length of the fatty
acid chain in a soap is increased, the parallel reflecting planes in
the crystals produced when the myelin form contracts will div^crge.
The amoimt of this divergence is just over 0-1 /x/x for every addi-
tional earl)on atom added.

When the soap contracts, that is, when the liquid crystals within
the myelin sheath are converted into true crystals and so become
more closely packed together, heat is evolved. This heat is, of
course, absorbed during the converse process. The former is an
example of an exothermic, the latter of an endothermie reaction.

As mentioned above, under the influence of the alkali set free
by the ionisation of the soap in contact with water, imbibition is
induced. Water passes in through the myelin membrane and is
incorporated in the soap, just as water is imbibed by gelatin and
laminar ia. This water-in-soap colloid is neutral or faintly acid to
phenolphthalein in contrast to a soap-in-water sol, which is
intensely alkaline.

The rigidity of tissues is to a large extent due to their emulsion
character. WV 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 (^f 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 ?
A cell is a water-in-protein complex, while its secretion (of similar
composition) is of the protein-in-water type. 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 deri\ed 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.
(«) The fat globules each seem to be enveloped by a covering
of adsorbed protein.

(6) The chief protein in milk is easeinogen, a phospho-proteiu

112 DISPERSE SYSTEMS

which exists in niilk as a sohible 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
emidsion. Whole, unchanged milk shows no tendency to form
butter. To form butter the fat particles are concentrated at the
siu'face 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 >vhich we call butter "
(Fischer and Hooker). That milk and cream are oil-in-water
emulsions can l)e 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
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 nuist be destroyed by
previous treatment, e.g., milling, cooking, chewing, etc., before

COLLOIDAL NATURE OF FOODS 113

the contents ean be utilised. Far and away the most important
of our foodstuffs are derived from cereals. From .*J() 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 molecidarly dispersed
salts, sugar, water, and adsorbed gases such as air and carbon
dioxide. Of the 10 per cent, of protein, gliadin forms a]:)out
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 fil)rous
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 COg 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
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

I

114 DISPERSE SYSTEMS

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.

Further Reading

Fischer AND Hooker. "Fats and Fatty Degeneratiou." Messrs. J. Wiley
& Sons.

CHAPTER X
ENZYMES

THE TOOLS OF THE CELL

" Instances of Magic ; . . . . By which I mean those wherein the material or
cHicieiit cause is scanty and small as compared with the work or effect j)rodnced ;
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
imable 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 commimities 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-
facturing cities are not spotless nor are our processes there
economical. Smoke, sound, and slag-heaps are universal accom-
paniments of a manufacturing conmiunity. Most of the processes
carried on in the cell have not been reproduced in the laboratory.

115 8—2

116 ENZYMES

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
mav 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 midway 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. 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
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 4-77/'^. If the original sphere be divided
into 100 small shot, then the new surface would be 100 X ^-nr-^
where r-^ = radius of small shot. Now 7\ = r v^xt)0' ^° *^^^^ *^^

CATALYSIS 117

ratio of the new surface a^ to the original surface a would be

47rr^ ( >JA^ X 100

^^^ = ^ ^^'

i.e. the surface would be increased over four and a half times. If
the subdivision were carried still further till there were 10^" 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 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 O-l^Lt diameter, then the adsorbing
surface becomes 60,000,000 sq. metres. Capillary active substances,
e.g. anaesthetics, by being themselves adsorbed to the surface of the
catalyst prevent contact catalysis.

2. Carriers. In some cases the catalytic agent combines
chemically with one of the reacting substances to form an unstable
intermediate compound. This, in turn, breaks up, regenerates
the catalyst, and liberates the reagent in the active atomic state —
so called nascent. Many oxidations and reductions are brought
about in this way. That is, if a reaction of the type

A -\-B^AB
takes place very slowly under ordinary conditions, a catalyst C
which interacts with A {e.g.), thus A -\- C = AC, and AC itself is
acted on by B,

B + AC = AB + C

may materially alter the rate at which the whole reaction proceeds.

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 pro])ortional 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 following statements are a brief survey of the characteristics
of catalysts :

(a) A very small amount of catalyst can produce a considerable
alteration in the rate of reaction.

(6) No amount of catalyst can start a reaction that would not
otherwise take place.

(c) A catalysed reaction reaches the same final state as ultimately
it would reach if no catalyst were present.

118 ENZYMES

(d) Catalytic acceleration (positive or negative) is proportional
to the concentration of the catalyst. This is true only within
limits. At very high concentrations of catalyst the acceleration
is not quite proportional to concentration.

(e) The catalyst is not destroyed during the reaction, but may
suffer a change in physical state or be altered chemically by some
subsidiary reaction.

(/) Some catalysts are specific in their action. They act best
in certain reactions. For example, hydriodic acid is slowlj^
oxidised by hydrogen peroxide and by persulphates. The former
reaction is activated by tungstic acid, but not the latter.

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 ultra-filtration. Chemically, they
resemble their substrate or are so closely associated with their
sulistrate 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."

(b) Enzymes retain their activity only over a very well-defined
range of temperature. It is common knowledge that physio-
logical processes take place most rapidly 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

FACTORS INFLUENCING ENZYME ACTION ll'j

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

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TEMPER.ATUR.E

Flti. 27.— Graph to show liow the effect of increase of temperature on tlie rate of enzyme
action is the result of the interaction of two factors, (1) increased chemical action and (2)
increased destruction of enzyme.

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. 27) 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
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

120 EN7A'MES

action. This 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 nuich to do with its activity. Each enzyme
is active only when the bathing fluid has a p^^ of a certain range
with an optimum p^^ at which the action proceeds at its best.
The extraordinary sensitiveness of colloids to the p^ 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, p^, 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
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
proteinase I

protease j "

aldehydase ,, aldehyde

lipase ,, lipides

peroxidase ,, peroxide

arginase ,, arginine

urease ,, urea.

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

oxidase accelerates oxidation (= peroxide + peroxidase)
catalase ,, breaking down of peroxides

invertase ,, inversion of cane sugar

desamidase ,, removal of amino groups.

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 ((ir. Pepsis — digestion) = acid or gastric proteinase.

protein

ACTIVATION 121

Tr\'psiii (CjV. Tribein — to rub — prepared by rubbing pancreas with
sand and glycerol) = alkaline or pancreatic proteinase.

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 reduc-
tions 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.

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.

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 P^. The moment that the juice comes in contact
with the substrate, digestion begins.

Zymogen Secretion. 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, pseudo-activation. The active principle of gastric juice
is secreted as pepsinogen, which becomes active pepsin on coming
into contact with a fluid of a certain P„. This is not a true
activation. Acid does not so much activate pepsinogen as form
a necessary concomitant for pepsin. That tiiis is so may be
demonstrated by neutralisation of the acid, with consequent loss
of activity in the enzyme. On reacidifying, digestive activity

122 ENZYMES

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 fimction 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 middleman.

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
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 P^ leads to alteration in their
power of adsorbing or being adsorbed by their substrate.

We are now in a position to consider if enzymes should be
admitted as catalysts. Do they have the six characteristics
detailed on p. 117 ?

(a) Minute Quantities. They undoubtedly accelerate reactions
when present in amounts even more minute than an inorganic
catalyst, e.g. in the reaction

Lactose + water = glucose + galactose

one might employ as catalyst either an enzyme or an acid. The
enzyme lactase is about 5,000 times as effective as an equal weight

SPECIFICITY

123

of hydrochloric acid. Pepsin can hydrolyse about 400,000 times
its weight of caseinogen.

{b) Do not Initiate Reactions. This is a much more difficult canon
to satisfy. Certainly cane sugar in solution slowly undergoes
inversion, but who is to say whether it would inv^ert in the process
of time if kept dry. The process might be proceeding at an
immeasurable rate.

(c) Final State of Equilibriiun. Enzymes do appear to change
the equilibrium point of reversible reactions in some cases, e.g.
No Catalyst. Starch + HgO -^ dextrin + maltose -\- glucose

Catalyst-HCl, ,, ,, — > glucose

,, Amylase ,, „ -^ maltose.

i.e. the reaction takes place in steps. In the presence of water all
the stages are shown, while when acid is added only the final
product appears in quantity. Various enzymes activate the
various steps — one enzyme aids in the production of dextrins
from soluble starch, another assists in the process of hydrolysing
the dextrins to maltose, while still another catalyses the step down
from maltose to glucose. Each of those steps should be considered
a separate reaction.

- {d) Activation Proportional to Concentration. This is strictly
true of enzymes, and may be proved in various ways (Part II.).

{e) Not Destroyed. That enzymes are altered during a reaction is
not surprising considering their unstable colloidal nature. The
change entailed is usually an alteration in physical state whereby
they are rendered inactive.

(/) 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 preferentially on one — maltose.

TABLE XX

Sugar.

Components.

Split by.

Maltose .

Glucose a glucoside .

Maltase.

Isomaltose

Glucose j8 glucoside .

Emulsin.

Centiobiose

Glucose ^ glucoside .

Emulsin.

Cellobiose

Glucose j8 glucoside .

Emulsin.

Lactose .

Glucose j8 galactoside

Lactase (crude emulsin).

124

ENZYMES

TABLE XX— continued

Sugar.

Components.

Split by.

Isolactose

Glucose galactoside .

! ?

Melibiose

Glucose galactoside .

Melibiase (crude emulsin).

Trehalose

. J Glucose + glucose .

Trehalase.

Cane Sugar

Glucose + fructose .

Invertase.

Turanose

Glucose + fructose .

? (not invertase).

Lactose and melibiose are both glucose galactosides differing only
in the position occupied by the hydroxyl of the glucose molecule
united to the galactoside. As galactosides, both are slowly hydro-
lysed 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
configuration of colloids by slight modifications of the surrounding
conditions might lead towards an acceptable explanation of
specificity. (See also Optical Activity, p. 126.) Weight is given
to this suggestion by examination of the synthesising power of
enzymes. Since enzymes accelerate reactions that would take
place without them, and since, theoretically, all reactions are
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. That is, a lipase should not only split
a fat into fatty acid + glycerol, but should regenerate fat from fatty
acid + glycerol.

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

BALANCED REACTIONS

125

as enter it. Now alter the conditions, (1) open the bottle to a dry
atmosphere, i.e. to unlimited air containing inlinitely little mois-
ture. The reaction will proceed almost entirely in one direction —
evaporation. (2) If the bottle be opened to an air supersaturated
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 shoAvn very clearly in the following
experiment in which the course of the digestion of the starch was
followed by the iodine reaction. In one case, the 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 XXI

Time (in mins.)-

Dialysed Starch Solution.

Not Dialysed.

0

Pure blue

Pure blue

20

Trace of violet

)) ))

40

Red with violet tinge

Violet

75

Colourless

Red with violet

100

))

Very faint red

125

?j

Colourless

Ecto-enzymes generally have a catabolic 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 functions.
The conditions under ivhich they zvork 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 /3 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 HCl is used as
catalyst, the equilibrium point is reached with glucose, maltose,
and isomaltose present in the same pr()j)()rti()ns, 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

126

ENZYMES

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 P^ on activity. The following table gives the optimum P^ for
certain enzymes :

TABLE XXII.

Ptyalin ....
Invertase ....

6-7
4-5

Maltase acting on maltose

6-6

,, ,, methyl-glucoside
Pancreatic lipase .

6-2
80

Pepsin on proteins

,, (plastein formation)
Rennin ....

1 •5-2-5

1-0

5-7

Trypsin on peptone
,, gelatin

7-7
9-7

Erepsin ....
Urease (Decomp. of urea)
,, (Synth. „ )

7-8
8-7
7-0

Much has been made of the fact that enzymes seem to be rather
finical as to what compounds they will attack. Two compoimds
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 hydrolysc 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 liooks are similarly placed or
when one has been placed upside down, i.e. rotated on its central
axis AC by 180° (Fig. 28). If, after passing through book one, the

Fig. 2S. — Model of polariinet.er. ^ = source of liylit, i>'i = polari8er, /) = point at which
twisting force is applied, B.. analyser, the amount of twisting at D can be estimated from
the angle through which B. has to be rotated to allow of the passage of the metal strip AC,
C = eyepiece.

OPTICAL ACTIVITY 127

strip of metal is given a twist, then booiv two will have to he 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 strij). 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.

{h) The length of the strip exposed to the twisting force. The
longer the strip between B^ and B^ the greater will be the twisting,
other conditions being equal.

(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 arc applied
to light. If a beam of light (at A) 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 B-^
and 1?2 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
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.

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

(c) Temperature as above.

(f/) 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 Nieol 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 ])lack dots will be seen. If now the crystal be rotated
without lifting it from the paper, one dark spot will remain

128 ENZYMES

stationary while the other will rotate round it as a centre. This
phenomenon 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 ])e
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.

L— :^

Fig. 29. — Diagram of the paths of the ordinary and extraordinary rays of liulit tlirough a
rhombohcdron of Iceland spar. The liglit, 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 (0) is the more refracted ray.

One ray, the stationary one, has travelled through the crystal

just as it would pass through glass — obeying the ordinary laws of

refraction (Snell's Law). It is called the ordinary ray. The other

ray is called the extraordinary ray, and it does 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

sin a
of refraction is constant, —. — 7, = u.)

sm 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. so. — 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 EC (Fig. 30)
perpendicular to the principal plane i'or the face AC. The cut
surfaces were carefully polished and then cemented in their
original position by a thin film of Canada balsam. If now the
ordinary ray falls on the surface BC at an angle greater than the

POLARlMKTFJi Vl\)

critical angle it 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 dilTers 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 colom-, 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 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

h\ Be [^d.D . "H

1

Fig. 31. — Diagram of Laurent Polarimeter. Monochromatic light from tlie source L
passes through the lens A which renders the rays of light parallel, and then through the
polariser B. 0 is the observation tube containing the fluid under examination, while I) is
the analysing Xicol 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.

light from the first, is called the analyser (Fig. 31, D). 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
on a similar laevorotatory piece would be optically inactive.
Physical examination of quartz crystals shows that <^/-crystals
differ from /-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

130

ENZYMES

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

(<rz?^

'A

k:

r\

Fig. 32. — Crystals of Ammonium Hydrogen Malate. (a) Symmetrical crystal, optically
inactive; (b) Asymmetrical crystal, dextrorotatory; (c) Asymmetrical crj'stal, laevo-
rotatory. (After van't Hoff.)

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

Fig. 33. — 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.

optical activity is impossible. Any perfect cube is an exact
duplicate of any other perfect cube. Such holohedral crystals
can be prepared. In Fig. 32, A represents a holohedral crystal of
i nactive ammonium hydrogen malate ; B represents a dextro-

ASYMMETRIC CARBON ATOM 131

rotatory crystal, while C represents its mirror image, a laevo-
rotatory crj^stal 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 asi/mmetric (Fig. 33). Compoimds
containing asymmetric carbon atoms exist in proteins, carbo-
hydrates and fats. Each member of a pair of optical isomers is
identically equal to its isomer in every respect but one.

As stated at the beginning of this section, enzymes preferentially
act on one isomer. For example, those sugars which are dextro-
rotatory are more readily hydrolysed than their laevorotatory
isomers. The mould peniciUium glaucum destroys Z-leucine and
(/-glutamic acid without having any extensive action on (/-leucine
or /-glutamic acid.

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

y— 3

CHAPTER XI

MEMBRANES (PLASMAHAUT)

THE HOUSE OP^ 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 and that 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, provided
that it is borne in rnind that in a coinplex animal, each cell will he
modified inform and somewhat in function not only by neighbouring
and similar units, but by comparatively remote and dissimilar cells.

Need for cell membrane.

We have seen that the cell consists of protoplasm, which may
be regarded as water dispersed through a colloidal complex con-
taining dissociated and non-dissociated crystalloids and substances
in suspension.

(i.) 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. For example, if an amoeba is deprived
of its coat, say by bringing the animalcule into contact with air at
the surface of water, the naked protoplasm lying below the surface
of the water after a moment or two generally suffers dispersion
throughout the surrounding water.

(ii.) 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. Nagcli, Pfeffer, De Vries
and others have demonstrated the existence of such a cell wall.
If plant cells are inmiersed 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

132

PLASMOLYSIS 133

will j)ass iVom \\\v (■ell, caiisino the cell snh.staiur to shrink. But
the cell icall docs not shrink and a space is left between the contents
and the container, so rendering the latter apparent. This process
is termed plasmolysis. 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 j)robably burst. This is called haemolysis, and luay be brought
about in other ways, which are, however, all obviously methods
for destroying a membrane (page 318). Artificial membranes may
be made which act in a way similar to animal cell coverings.

(iii.) The work of A. V. Hill, Meyerhof and others, which has in
recent years done so much to elucidate that process so essential for
our well-being, viz. muscular contraction, has also pointed to the
necessity for postulating membranes in and on the contracting
imits (Chap. XIV.). These experiments, together wdth 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.

Nature of the Membrane.

The cell w^all differs considerably from the cell contents in
chemical composition and in physical state. 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 mem-
branes should not be confounded with the true cell membrane or
plasmahaut, which term connotes the layer of cell protoplasm
which, in animal and plant cells alike, lies between cell and environ-
ment. Only through this layer or membrane can the cell be
influenced by changes in the surrounding medium. Animal cell
membranes are more elastic than those of plants. Microscopic
examination shows generally a difference in refractive index round
the border of cells.

Much research and nuieh 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 w^aste products of metabolism,, gaseous and liquid, must

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

(4) Finally, the mend^rane nmst be of such a nature as to allow

134 MEMBRANES {PLASM AH AIJT)

of expansion. Mere elasticity will not answer this end.

The membrane must be capal^le 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
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. A very simple experiment shows the intimate
relationship of cytoplasm and membrane. Amoebae immersed in
a dilute aqueous solution of eosin remain unstained as long as they
are alive. That is, the membrane is impermeable to the dye.
Eosin, on the other hand, injected into the body of the amoeba
remains evenly distributed throughout the protoplasm during life,
and does not diffuse into the surrounding water. In both experi-
ments the cell wall becomes permeable to the dye on the death of
the animal.

Formation.

The fourth essential quality of a cell membrane mentioned above
gives a clue as to the mode of its origin.

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 on the surfaces. Any substance
in the protoplasm which lowers surface tension will have a greater
concentration at the surface than in the interior. If there is more
than one capillary active substance present, then the one in
possession of the surface will be the substance having the greatest
power of lowering surface tension. Now a surface implies the
juxtaposition of two systems or phases, e.g. amoeba-water,
erythrocyte-plasma, cell-environment. The second system, the
environment, must, therefore, contribute its quota to the formation
of the membranes. That such a membrane can be formed is
readily demonstrable.

1. Brailsford Robertson's artificial amoeba (Part II., p. 516)
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. 544), yield life-like growths.

FUNCTION OF FATS 135

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
pseudo-adsorption.

Adsorption (including pseudo-adsorption) is, as we have seen
in a previous chapter, dependent on surface forces. 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 adsorbability of substances in solution. Can we associate with
this fact the \'arying thickness of animal membranes according to
their degree of exposiu'e to cold ?

There is no doubt that material adsorbed to a surface can in
turn take up other matter from the body of the solution. In fact
it might completely remove one component. (Cf. emulsions and
emulsifying agents.) Surface concentration alone cannot account
for all the properties of the plasmahaut.

Composition of Membranes.

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 wdiole. This is particularly true when
attention is directed mainly to the lipide content of protoplasm.
One is struck first of all with the way in which under physiological
conditions the amount of tissue lipide is kept constant in all cells
(except those of the liver). These unsaturated fats seem insepar-
able from the life of the cell. We have seen (Chap. VI,) how fats
spread over a surface in a layer one molecule thick, and how slight
alterations in the hydrogen ion concentration on either side of this
fatty layer may make extensive alterations in the structure and
intimate composition of the layer, and how fats solid at a particular
temperature become apparently fluid when adsorbed.

Couple with their insolubility in water, the chemical inertness of
the fats and their substitution products, and one can see how
suitable they are as building stones for the house of the cell. If
this view is correct, then fat solvents should cause disruption of
animal membranes. This is easily shown to be the case (cf.
Haemolysis by ether and by soaps, Chap. XXII.),

Cholesterol and lecithin are general constituents of cell membranes
and their relative proportions play an important part in controlling

KJG MEMBRANES {PLASM AH AUT)

the amount of water held by the cell. The ratio of water to sohds
in a cell depends directly on the cholesterol and indirectly on the
lecithin content. Now, Leathes has shown that if a monomole-
cular layer of lecithin is prepared on the surface of water, the area
so covered is markedly reduced by the addition of cholesterol. In
some way this alcohol causes the long-chained phospholipine to
pack its molecules more closely together. Protein, cell-albumin
and a globulin and a nucleoprotein (so-called /3 globulin) also
enter into the composition of the cell membrane, and contribute
to its apparently capricious behaviour by virtue of their ampho-
teric nature.

Structure.

In spite of many attempts to overthrow it, the most satisfactory
explanation of the structure of a cell memljrane 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.). 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, Init 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

PEUMKABILITY 187

is a function ol' the size (oi* speed) <>i" a particle in solution. Hy
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 " (p. 84).

Alterations in Permeability.

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
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.

Consider for the moment the passage of material across the
membrane of the erythrocyte. On the one side we have the
corpuscular contents, viz. haemoglobin, potassium, phosphorus and
small quantities of calcium, glucose, etc. ; and, on the other side, the
blood-plasma richer in water, proteins and salts than the corpuscle.
Haemoglobin is freely solulile in plasma, but is held in greater
concentration than would readily dissolve in the volume of fluid
within the corpuscle (Chap. XXII.). The corpuscle also retains
certain salts, organic and inorganic, in very different concentra-
tions from those in which they occur in the plasma. Now glucose,
chlorides and phosphates under certain conditions may pass easily
in or out of the corpuscle, while sodium and potassium cannot
permeate. Even when the plasma is diluted with water, provided
the haemolytic concentration is not reached, the contents of the
corpuscle are retained. If various samples of the plasma in which
erythrocytes are suspended are diluted with different solutions
isotonic with the plasma, e.g. (a) sodimn chloride, (6) glucose,
(c) urea, (d) ammonium chloride, it will be seen that the cell is not
impermeable to all alike. The urea and the salts of ammonia with
sufficient water to keep them in solution will pass into the cell,
while the sodium salts will be kept out.

M. H. Fischer has demonstrated with characteristic clearness
that the interface between a water-in-c^ phase and an ir-in-water
phase shows dilTerential permeability, where a; is a hydrophilic
colloid, or even a hydrophilic substance like phenol, quinoline, or
ether. Some coloured substances (such as neutral red, nile blue,
methyl violet, methyl green) all leave the iT-in-water phase, and
are concentrated in the water-in-a; phase so much that after a few

138 MEMBRANES {PLASMAHAVT)

hours they may be found ahiiost entirely in this phase. Iodine and
eosin and similar substances pass in the same direction, but more
slowly and less completely, while ferric chloride, cupric acetate, etc.,
take a very long time to leave the aqueous phase. On the other
hand, the interface seems quite impermeable to the chlorides of
cobalt, chromium and nickel. All the salts to which the living cell
is impermeable are also excluded completely, or almost so, from
passage across this laboratory-made interface.

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 be 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
from either side.

(1) The nature of the membrane is of great importance in
studies of permeability. The cell membrane is unique, and one
cannot guard too carefully against the adoption of generalisations
drawn from experiments in which collodion, parchment or other
artificial membranes have been used. Even the behaviour of dead
animal membranes or of that of the erythrocyte is quite different
from the true plasmahaut. Further, 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 combina-
tion, 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

ABNORMAL OSMOTIC EFFECTS 139

apparently ahiiorinal osmosis. Collodion nicmbrancs, for instance,
are practically indifl'erent as regards electrical charge. Water passes
through these membranes into solutions of non-electrolytes and
of electrolytes more concentrated than M/8 at a rate in accord-
ance with the van't Hoff theory of osmotic pressure, i.e. a linear
function of the concentration of the particles (colloidal 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, w^hile 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,
(6) 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 a
membrane may undergo alterations. This is a general statement
in which is included the effect of alterations of hydrogen ion
concentration on permeability. The diffusion of water through an
indifferent membrane depends on two forces, («) 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 increasing with the valency and 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

140 MEMBRANES (PLASMAHAVT)

the reverse to be the case. The water niolceules 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 electrostatic effect on account of the small ionic radius of the
hydrogen ion. It is important to note that certain salts of bio-
logical interest have a marked electrostatic value — very dilute
solutions of oxalates, phosphates, and citrates and of the tetra-
valent ion Fe(CN)6 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
attractive 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. IX.).

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 KCl 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
KCl solution. This transport of water must be due to the electrical
pull of the KCl. He then raised the concentration of the sugar
outside the bag till its osmotic pressure just balanced the attractive
forces of the KCl. 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 pressures of

7M 7 X 22-4

an M/8 and an M/64 solution of sugar = ^j- = — = 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 mem-
brane 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

N EG ATI VE OSMOSIS

141

attractive action of the ion with the opposite charge. The
appended curve (Fig 34, from Loeb) shows the effect of concentra-
tion on the attractive force of Na2HP04 on water. Various
concentrations of this salt from M/8192 to M/8 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

2'^o

2ZO

200
^ /so

H

s: /60

Z /^O

z

0

1-

D

_l
0

in

O

>

UJ

/20

/OO

ao

60

^o

20

REGION OF PREVAILING ELECTRICAL EFFECT
OF ELECTROLYTES

PREVALENCE OF ATTRACTIVE ACTION OF /^NION ''iS'^,^'?5'^''i
UPON THE POSITIVELY CHARGED PARTICLES OF WATER, F^tVALLNCE

CF REPELUNa
ACTION OF
CATION UPON
THE POSITIVE-
-LY CHARGED

PAR.TICLE5
OF WATER

R.ECION Cr PR.EVAILINO1 &AS
PRESSURE, EFFECT OF

ELECTROLYTES
(true 05KOTIC PRE55URE)

M

M

M

M

M

M M M M M

M

M

M

8I3Z

4C96

2048

I0Z4-

JIZ

266 128 64- 31 16

concentrations

8

4

2

IM

Fig. 34.

dipped 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
concentration, 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 ])e due to the predominance of the attractive
action of the anion upon the positively charged hydrols. With
an increase in concentration beyond ili/128 the rate of diffusion

14-2

MEMBRANES (PLASMAHAUT)

ELECTRICAL

OSMOSIS

ANODE

4-

+ +
— + +

CATHODE.

•5-04

ef

falls abruptly to reach a minimum at a concentration of M/16.
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 7-ate of diffu-
sion is decreased, i.e. where the curve falls (M/256 — MjlQ in the case
of N a^JlPO ,^) 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. 534, will be found
details of an experiment which
shows that water can be drawn
through certain colloidal membranes
by direct electrical means. If the
water is acidulated the attraction
is towards the anode, but if alkali
is added 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. of protein. Collodion does not
form such compounds and so cannot
form a membrane suitable for ex-
periments on electrical osmosis until
it has adsorbed an amphoteric col-
loid. In Fig. 35 is represented a
gelatin - collodion membrane in
acidulated water — i.e. in water with
a slight excess of hydrogen ions.
The membrane adsorbs some of these excess ions, interacts
chemically with them to form gelatin 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 0H~. 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 obvious that the hydrogen ion
concentration must increase at the cathode and decrease at the
anode. (Pole finding paper is blotting paper soaked in phenol-
phthalein — an indicator which while colourless in neutral solutions
becomes red in distinctly alkaline solutions.)

1+ +
K +

Fig. 35. — Diagrammatic section tlirough
a gelatin-collodion membrane showing a
single large pore to demonstrate electrical
osmosis.

DON NAN ECiUl LIBRIUM 1-13

Water passes through the membrane in the reverse way when
the sokition on both sides of the membrane is alkahne. A dihite
acid sohition separated from a dihitc alkahne sohition 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.

Whatever causes may be assigned to the \'ariations in permea-
bility of plasma membranes, we can definitely exclude (a) mere
variations in the size of the molecules presented to the membrane.
Metallic cations, we have seen, are not allowed to pass through,
while relatively large molecules like those of amino acids and
glucose are able to make their way into the cell, and urea easily
passes in or out, depending on which side of the membrane it is
most concentrated. Hamburger and others thought that they
had disproved Ciiirber's work on the lack of penetration of sodium
and potassium. Recent work, however, has confirmed the view
given above.

Bayliss separated a concentrated 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.

Donnan (1911) propounded a theory of membrane equilibrium
which is now classical. He studied a system such as that above
where a membrane separated two liquids, in one of which was an
ion (like the anion of congo red) which could not pass through
the membrane. From thermodynamic considerations, he deduced
formulae quantitatively connecting the ion concentrations on
either side of the membrane (when equilibrium had been reached)
and, by pure reasoning, predicted the presence of a potential
difference across the membrane, the magnitude of which depends
on the difference in the concentrations of the dijfusihle ions on both
sides of the membrane. That is, if a solution of congo red (XaR)
is separated from a solution of sodium chloride (NaCl) by a mem-
brane impermeable to the anion of the dye (HR), the Na coming
from the NaR would be prevented by electrostatic attraction from
wandering far from its anion, i.e. it could not pass through a
membrane except in minute quantities. The anion may be
likened to a large dog attached by a short leash to a terrier (cation).
The terrier could (and probably does) pass through between the
rails of a fence, but is prevented by its large companion from
penetrating far from the boundary. If we had a large mnnber of
such pairs, the chance of finding (at any particular time) a fair
proportion of terriers in the field would be small. Two small dogs,

144; MEMBRANES {PLASM AH iUT)

a terrier and a spaniel, on the other hand, similarly united might
pass into the field together. One woidd then find that the con-
centration of terriers on either side of the fence would bear a
definite relationship to the number of spaniels on that side.

Following Donnan's plan and indicating the membrane by a
vertical line and molecular concentrations by square brackets, we
have, to begin with :

(1) Na+ : Na+

R- Cl-

[i) inside outside (o)

The NaCl diffuses readily into the cell, so that when equilibrium is
established we have :

(2) Na

R
CI

Na

CI

It can be calculated that at this point

[NaJ [CI,]

[Nao] "^ [Cy

Since the concentration of the cation Na inside the cell must be
equal to the sum of the anions (R and CI) present in order to
maintain electrical equilibrium, whereas on the outside the con-
centration of Na is only equal to that of CI, it follows that

[Na,] > [Nao] and [CI,] < [Clo]

i.e. there is more cation (positive charge) inside the cell than out-
side. This difference of electrical potential is intensified by the
smaller amount of mobile anion (negative charge) inside than
outside. The potential difference thus created is balanced by the
osmotic energy developed in the opposite sense, i.e. the energy
which can be gained in this way is zero. Donnan has shown that
the potential difference developed is

[Na.] [CL] „ ,

58 log Y^J^^ ^ ^^ ^°S YtT] milli'^olts (at room temperature).

Where the amount of NaR is large compared with the amount of
NaCl, the P.D.- would be 58 log [NaR]/[NaCl] millivolts,
where [NaR] = initial concentration inside the cell
and [NaCl] = initial concentration outside the cell.

As a matter of fact, as we shall see in Chap. XXIII., other
balancing factors come into play as well {e.g. hydrostatic pressure).

Since many compounds in the cell are of the form NaR, and, as
readily diffusible substances and membranes permeable to them
abound both in the cell and forming a boundary to the cell, it

POLARISATION OF MEMBRANES 145

follows that potential differences due to the Donnan equililH-iuni
are common occurrences in the body.

Differential permeability docs not afford a sufficient explanation
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 electro-
positive. 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
gelatin, 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 (Fig. 35). This may
be confirmed by altering the charge on the membrane. Gelatin
may be induced to take up a positive charge. Mines found that
when a dilute solution N/80 was separated by a gelatin membrane
from a more concentrated N/8 solution of sodium chloride, the
dilute solution became electropositive. Gelatin is made positive
by treatment with the ions of polyvalent metals. When an
electropositive gelatin membrane was used, the dilute solution
became negative.

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 H^ 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. 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 convection currents. For
instance, such membranes are nmch 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

B, 10

146 MEMBRANES (PLASMAHAUT)

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 explained by analogy to known physical processes.

Further Reading

McClendon and Medes. " Physical Chemistry in Biology and Medicine."
Messrs. Saunders.

CHAPTER XII
THE CELL

'■ The life (if the cell is a dynamic equilibrium in u polyphasie system."

Sir F. G. Hopkins.

" 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. Logieally,
we ought next to study the system by whieh these absorbed
substanees 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 con-
venient 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 1838, 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 in refractive index 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. Appa-
rently 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 cut in two the part which did not contain the
nucleus would only live for a short time, while the other part would

147 10—3

148 THE CELL

function normally. The nucleus is, therefore, necessary for life.
Ultramicroscopic examination shows that the grey mass is a
hydrophilic colloid (emulsoid). Chemical analysis of dead amoebae
confirms the ultramicroscopic examination. Water to the extent
of about 75 per cent, is dispersed in the colloidal complex and acts
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. Hofmeister estimated that a
typical cell contains :

225 X 10^^ molecules of water

53 X 1012 molecules of protein

166 X 10^2 molecules of lipide

29 X 10^* crystalloid al molecules.

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, nitro-
gen, 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,
v/hereby the eye is pleased, so the life of a cell depends on the size,
consistency, etc., of the colloid-crystalloid complex forming its
protoplasm.

The water content of protoplasm is amazing in quantity and in
physical state. We have seen (Chap. YIII.) that certain colloids
have the property of imbibing large quantities of water and of
holding that water under considerable compression (see also
Experiment 39, Part II.). The physical properties of such
water differ markedly from those of free water. For example, its
vapour pressure will drop to a very low value and its removal
from the colloid will be very difficult.

So, too, as has been pointed out in Chapter XL, is the fat
content of the cell imique. Every cell has a fairly constant
content of lipide, although when stained by the usual methods to
demonstrate fat, no evidence is given of such a content. This
masked fat is only made visible when the cell is diseased or disin-
tegrated. The process of phanerosis or the unmasking of fat may

VISCIDITY OF PROTOPLASM 149

be likened to a chan^'o Iroin a water-in-oil eniulsion to an oil-in-
water one (Chaj). IX.).

The crystalloids, too, differ in their physical attributes from
similar salts in solution. A salt solution isotonic with a 0-9 per
cent, solution of sodium chloride exerts no osmotic effect either
positive or negative on the mammalian cells, but has an electrical
conductivity about five to thirty-five times as great as the cells.
That is. the cell offers a greater resistance to the passage of an
electrical current than its content of electrolytes would lead one to
expect. If now, the cell is injured so that its contents undergo
disintegration, its conductivity will approach that apparently
justified by its composition. The high electrical resistance of
living matter is due mainly to two factors — (1) the state in which
the water is held, and (2) the adsorption of a large proportion of
the electrolytes. (See also Chap. XXII., Blood.)

The w^ater and a large proportion of the salts are dispersed
through an apparently homogeneous colloidal mass. From ultra-
microscopic examination one learns that the protoplasm varies in
viscosity from cell to cell and more markedly from animal to
animal. Some cells are almost liquid, as demonstrated by the
Vigour of the Brownian movement of the smaller granules in them,
while other cells appear to be decidedly viscous with sluggish
granular movements. The annelid egg exemplifies the foimer
and the sea urchin^s egg the latter state.

The viscidity of protoplasm may be influenced by alterations in
the immediate environment. An excess of salts of monovalent
elements, e.g. Na, K, guanidine leads to an increase in liquidity,
while divalent cations produce the opposite effect. The presenta-
tion of a suitable mixture of mono- and divalent salts leads to the
optimum viscidity of any particular cell. Loeb showed that
Fundulus eggs, which were killed if placed in isotonic solutions of
the chlorides of either sodium or calcium, would thrive in a
definitely proportioned mixture of these two salts (cf. Salts and
surface action, Chap. IX.).

The nucleus, as is mentioned above, is absolutely necessary for
the continued integrity of the cell. It is, in amoeba, a spherical
body, with a refractive index slightly higher than the cytoplasm
and contains a nucleolus which is still more highly retractile . It
also carries the chromosomes, the bearers or indicators of hereditary
characteristics. The nucleus is surrounded by a men^brane and is
generally considered to contain a reticulum. Experiment has
shown that the nucleoplasm reacts to salts much in the same way
as the cell itself.

To sum up, the cell consists of three essential parts, (i) A mem-

150

THE CELL

brane, composed of lipide, protein and water ; (ii) cytoplasm, a
water-in-colloid dispersion ; and (iii) the nucleus, a still more
complex dispersion within its own membrane. All three elements
are easily altered in physical state by alterations in the balance of
electrolytes in the protoplasm or in the environment. The whole
cell may be regarded as a polyphase crystalloid-colloid complex in
unstable equilibrium. " When," says Sharpey-Schafer, " the
chemist succeeds in building up this complex it will, without doubt,
be found to exhil^it 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 mani-
fested by a imicellular animal ?

{a) Movement is the commonest phenomenon indicative of life.

Amoeba moves. It extrudes
footlike processes, pseudo-
podia (Gr. pseudio, false
(= similar to), podes, foot),
at one part and retracts
them at another and so
moves along. Similar amoe-
boid movements are cha-
racteristic of the white
cells or leucocytes (Gr.
leukos, white) of the blood.
Recently, Goodrich has care-
fully studied these move-
ments 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
Fig. 36. 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 (Part II.). These purely physico-chemical reactions
are produced by alterations of the surface tension of the fluids
under observation. Macallum has shown (pp. 173 and 185) 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. 36. — Leucocyte of invertebrate. (Redrawn after
Goodrich.)

IRRITABILITY

151

of nicrc'iiry iiiort- than an iiicli in diameter may be made to pidsate
with perfect regularity for hours. (See Ostwald's " Physical
Heart," Part II.).

[b) Irritability is a general property of Uving matter. When
amoeba is touched, it withdraws its pseudopodia (barotaxis)
(Chap. XXXIII.). It moves towards and over suitable food and
moves away from quinine or from a hypertonic solution of crystal-
loids (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 box. Ultra-violet rays
have a marked effect on
living organisms, for ex-
ample, the tubercle bacillus
is killed by ultra-violet light
and lupus is cured by pro-
jection of the Finsen arc on
the growth. Change of tem
perature 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 demonstrated 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 electri-
cally. 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

f'OL YMOftPHONUCLE^R.
LEUCOCVTa.

Fig. 37. — Large mono-nuclear cell (macrophage) from
the peritoneal fluid of a rabbit suffering from peritonitis
inrluced by inoculation with L5. coli, showing phagocytosis
of (1) a polymorphonuclear leucocyte, which has itself
ingested some bacilli, and (2) an eosinophil leucocyte.

152 THE CELL

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 be 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 71 small units are connected in series, the resultant
voltage is n times the voltage of the single unit. Dissection of an
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
(p. 145), or in alterations of the content of the protoplasm in
electrolytes.

Electrical effects are produced in living cells by suitable
stinuilation. 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 two sides of the membrane.
Inside will be a preponderance of negative ions while outside will
be an equal preponderance of positive ions (Fig. 38). 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-

BIO-ELECrniC PHENOMENA

153

positi\e. 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

CAPILLAfiY ELfCTffpMETER.

1^^

=-^VQ,= -::

■=-*

" - --

km'mTOW.'.'.wmmwmm^'.'.'mft'

ne.f(cuio'\

+ +▼ + + + + + + -!-▼+ +

+++++++▼++

-

CI

^

-

Z_-

. _

_ r

+
+
+
+
+
- +

+ H- + + + ++ + + + ++ +
RLSrill^ OKIfiTACT CCLL

++++++++++

INJUKlb OR. COHTKfiCTING C£U..
THE. SMOED PARJ U IHJUKP>
OR. 15 COHTRfiCTINQ

Fig. 38. — To show the origin and method of measuring the current of action or of injury
in a living cell. In the resting cell (central figure) all points on the surface of the cell are at
the same potential. >;ote position of Hg in the capillary tube. Action or injury produces
contact with the interior of the cell at the part active or injured, so that a current Hows with
the effect shown. Compare with the zinc-copper galvanic cell.

origin, but passes as a wave of increased stress over the whole cell
followed immediately by an electropositive wave (Fig. 43).

MacDougal and Moravek (1927) have constructed a cell that
answers several of Sir Edward Sharpey-Schafer's requirements
(p. 150). Their cell membrane consisted of a Soxhlet thimble
(cellulose + calcium salts) impregnated with a solution of choles-
terol in lecithin, which mixture is incorporated in a hydrophilic
gel (gelatin-agar). Various mixtures, solutions, etc., may be put
inside the cell and the cell immersed in various solutions. For
example, when the cell contained 20 per cent, sugar solution, an
increasing endosmotic series in Na > K >> Ca is given, implying
decreasing permeability with this series of cations. Further
addition of any of these cations further decreases permeability.
The cell wall shows excellent buffering power (Chap. XXII, ) — i.e.,
even when the hydrogen ion concentration of the external solution
varied as much as from pH 3-05 to ^H 8-2, the interior remained

154 THE CELL

practically neutral. This power is conferred on the " constructed
cell " by the lecithin incorporated in its membrane.

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
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. XI. 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.

Further Reading

McClendon & Medes. "Physical Chemistry in Biolog;v and Medicine."
Messrs. Saunders.

CHAPTER XIII
R A D I () - A C T I V I T Y

THE ATOM IN DISSOLUTION

" From liarniony, from lieavenly harmony
This universal frame began ;
\Vhen 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 radicles). Chemists
once defined the atom as the smallest non-divisible portion of
matter. Needless to say, many scientists were content to be
decryed as old-fashioned and refused to accept this opinion of
the atom. My old teacher. Prof. John Ferguson, would allow
no one to refer to atoms. He preferred the more cimibrous but
exact term " Combining Proportions." Modern work has con-
firmed these opinions of the atom. Physicists are now 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 — ■
electrons, all moving rapidly, eccentrically and regularlij round a
central positive charge or nucleus. An electron is nothing more
than a unit charge of negative 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 electronic rings exceeds or falls
below a certain critical value, the electrons are rearranged to
ensure stability for that speed.

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 verti-
cally in a small trough (Fig. 39), by having, say, their A'^ poles

155

156

RADIO-ACTIVITY

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, A^ pole upwards, below the trough. It will be
noticed that the needles arrange themselves in two rings. If ten
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

Fig. 39. — A " Model " Atom. (I'lom CiowtheT's' Molecular Physics.)

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 eccentric motion. If for
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.

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~ ' of atmo-

ROENTGEN RAYS 157

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 tin-ii
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
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 penetra-
tion 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-

1 58 RAD 10- A CTI VI T Y

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 uranow^ salts
which are not fluorescent, as well as by the fluorescing uranic
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, /S and y rays. The a rays arc particles of the gas
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 about 7 cm. 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. electrons. 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 vaciumi 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 a and ^ rays do not penetrate gases by pushing aside those
molecules of the gas that lie in their path. They actually pass
through the molecules (which, of course, are mostly " hole ") and
knock off, in their progress, some of the outlying electrons. In
passing through 7 cm. of air, the a particle chips off about 130.000
electrons and so " ionises " the air.

This power of ionising a gas is used as a means for measuring the
intensity of radiation. The simplest apparatus for this purpose is

a, y8 AND y RAYS

159

a gold-leaf electroscope. Fig. 40 represents the type of electro-
scope used by Soddy. It consists of a tin can with a movable
bottom E for the insertion ol' 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 ex-
tracted about 200 mgrms. of radium
chloride, which w^as responsible for over
80 per cent, of the radio-activity of the
raw material.

Subsequent investigations by the above
workers, and principally by Rutherford,
Soddy, and their collaborators, have shown
that there are three series of radio-acti\'e
elements. The appended chart from Soddy
show^s the relationship between the mem-
bers of the series and betw'een two of the
series themselves. This chart demon-
strates to us the remarkable fact that
the atom of the heavy elements at the
head of each series is 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
13 rays are emitted. Potassium is 1,000 times weaker than uranium
and 1,000,000,000 times weaker than radium in the emission of
13 rays.

Fig. 40. — Section tlirough gold-
leaf electroscope as used to deter-
mine the ionising power of radio-
active matter. See text. (From
Soddy's Radioactivity. Electrician
Press.)

160

RADIO-ACTIVITY

TABLE XXIII
TABLE OF RADIO-ACTIVE DISINTEGRATION.*
I. MAIN SERIES.
A. Uranium, Radium and Actinium Series.

Element.

Atomic
Weisht.

Radiation.

Period of Average Life.

Clieinieal Cliaractci'
(Isotopic with).

Uranium-I. .

238

a

8,000,000,000 years

Uranium.

Uranium-Xi

234

P

35-5 days .

Thorium.

Uranium-X-

234

i8

1-6.5 minutes

Eka-tantalum.

Uranium-II.

234

a

3,000,000 years (?)

Uranium.

Ionium

230

a

100,000 years

Thorium.

Radium

226

a

2,440 years

Radium.

Ra. Emanation

222

a

5-55 days .

Emanation.

Radium-A

218

a

4-3 minutes

Polonium.

Radium-B

214

iS

38-5 minutes

Lead.

Radium-C

214

(99-97%)

28-1 minutes

Bismuth.

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.

B. Thorium Series.

Thorium

232

a

25,000,000,000 years .

Thorium.

Mesothorium-I .

228

jS

9-67 years .

Radium.

Mesothorium-II . .

228

iS

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

Lead.

Thorium-C .

212

i8 (65%)

87 minutes

Bismuth.

Thorium-C .

212

l/100,000,000,000th .
sec. (?)

Polonium.

End Product

208

—

Infinitely long

Lead.

II. BRANCH SERIES. (.4.)

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

?nt. of the total

number of atoms disintegrating follow the branch Actinium &

eries.)

Uranium-Y .

— ■

P

2-2 days

Thorium.

Eka-tantalum

— -

a

1,000 to 10,000 years (?)

Eka-tantalum.

Actinium

—

pen

(?) .

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 .

—

jS

52-1 minutes

Lead.

Actinium-C .

—

a

3-1 minutes

Bismuth.

Actinium-D .

—

/3

6-83 minutes

Thallium.

End Product

Either 206
or 210

Infinitely long

Lead.

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

series.)

Radium-C

214

a

28-1 minutes

Bismuth.

Radium-C 2 .

210

P

1-9 minute .

Thallium.

End Product

210

1 r

Infinitely long

i \

Lead.

(D.)

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

eries.)

Thorium-C .

212

a

87 minutes

Lead.

Thorium-D .

208

P

4-5 minutes

Thallium.

End Product

208

Infinitely long

Lead.

* (From

Soddy.)

FUNCTION OF POTASSIUM

161

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 swtII 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 foimd which is capable of
acting as a substitute for potassium. Further, Zwaardemaker
was able to perform normal perfusions provided a substance
emitting ^ 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
to replace potassium. These radio-elements, as we have seen,
emit a rays in marked excess of the /8 rays necessary for physio-
logical purposes. They found that, as was to be expected, the
a radiation completely masked the ^ radiation. If means were
taken to exclude the a 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
XXIV.).

TABLE XXIV
I.

^ Radiating (negative).

Potassium.
Rubidium.
Caesium.

II.

(t Radiating (positive).

Uranium.

Thorium.

Radium.

Ionium.

Lanthanum.

Cerium.

Niton (Emanation).

A heart beating with a fluid containing the appropriate quantity
of any of (iroup I. may he switched on to any other group I.
element in aequi-radio-active amounts. Similarly, the Ciroup II.
elements are interchangeable. But direct transference from a I.

B.

11

102 RADIO-ACTIVITY

fluid to a II. 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 ^ 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
radio-active 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 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 :

(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 2,000 Angstrom units), i.e.
the 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 nuclei 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 a unit
positive charge. Other atoms are composed, as we have seen, of a
positively charged nucleus about which are grouped sufficient
electrons to render the whole system neutral.

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, kathode rays, X-rays
and the a, j8, and y rays of radio-active inatter 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

LETHAL EFFECT OF RAYS 163

kind. In general, the lower the velocity of the ray, the greater its
physiological action, provided always that its xclocity is sullliciently
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 xelocity of the
ray than on its nature, e.g. a rays have mass while the others have
not, yet similar actions may be produced under proper conditions.
The physiological effect of any ray is proportional to its power to
ionise air. ^ rays have 00 times the ionising power of y rays, and
experiment has shown that y rays require to operate for 60 mins.
on li\'ing matter to ha\'e the same effect as one minute's exposure
to /3 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
air, then those having the greatest ionising effect have an inhibitory
rather than a beneficial effect on living organisms, while, con-
versely, the weaker rays promote the function of the organism.
The power of ionisation being equal, then generally a long exposure
produces inhibitory effects and a brief exposure beneficial. 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 /3 and y rays seem to act on different
parts of the egg. The nucleus, especially if it is undergoing
mitosis, is influenced by the y rays, while the j8 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 rays emitted by radio-active elements, especially radium,
have been employed extensively in the treatment of morbid cell
growths. The cells are not killed outright, but division of the
nuclei is inhibited, eventually leading to death of the cell. The
rays are capable of causing definite regressive changes even in deep
seated tumours such as mediastinal lympho-sarcoma, carcinoma of
the lungs, and abtloniinal metastases of carcinoma of the testis.

Several investigators have reported results to show that the

164 RADIO-ACTIVITY

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 destruc-
tion 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 radium emanation. 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. 96). Of
course, normal as well as pathological tissue may be damaged by
exposure to radium. The action is similar to exposure to cold.
Radium causes an immediate decrease in the total number of white
cells in the blood (Chap. XVI.). 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 I 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 (q.v.), matter
exposed to radio-active elements should develop some protective
mechanism against the action of the rays. Becquerel noticed
that /3 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.

Ultra-Violet Rays.

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
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.

The tissues may, however, be made sensitive to rays of some-
what longer wave-length by administering coloured substances
which act as sensitisers. For example, haematoporphyrin, an
iron-free disintegration product of haemoglobin, so sensitises the
tissues that ordinary daylight produces similar effects to idtra-
violet light. These effects are mainly psychological and photo-
chemical. The latter action has been carefully investigated, the

VLriiA- VIOLET RAYS 165

foriiRT is cxtcnsnc'ly fxploitcd. C'liicl' aiiionii' tlif pliott-t'licniical
actions is that of forming a j)rotective pigment in accordance with
the principle of Le ChateHcr, Some of the other chemical results
of exposure to ultra-violet rays are of interest, but can only l)e
mentioned here.

(1) Ergosterol has two well-defined absorption bands betw^een
2,500 and 3,000 AU. After irradiation these bands vanish and
new bands appear further in the ultra-violet region (about 2,100
and 2,400 AU). Irradiated ergosterol is extraordinarily effective
in curing rickets, and is thus of use where effective sunlight cannot
be directly applied to the body.

(2) Hydrophilie colloids on exposure to radiation " take on "
some extra electrons, and so become internally more mobile. If
they are incorporated in a membrane that membrane becomes
more permeable.

(3) Certain syntheses are accelerated by the irradiation of the
reacting substances, e.g. exposure to rays of 2,000-2,500 AU of a
solution of anmionium carbonate for two or more hours causes the
formation of urea. This synthesis is probably brought about by
alternate reduction and oxidation of carbonic acid.

Further Reading

Russell. " Ultra- Violet Radiation." Messrs. Livingstone.
MiLLiKAN. " The Electron." University of Chicago Press.
Crowther. "Molecular Phvsics." Messrs. J. & A. Churchill.

SECTION III: CELL COMMUNITIES

CHAPTER XIV

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.

" Lactic acid is the keystone of the arch which now joins the physiology of muscle
to the exact sciences." " A. V. Hiu..

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 conmiunities. In a big
complex concern like the manmialian 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 cell in such a commimity 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 and
might, if circumstances 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
(the nervous system) exists in large measure to suit the muscles.
In short, the muscles are the master-tissues of the soma. They

166

KNKR(; ) ' TR. I XSrORM EHS 1 C,7

are not a maiiiiracturing community but are power users. In
another sense, the nmscles are the servants t)!" the body. By
means of them, the body fights a war not merely of defence but
of aggression against its environment. As civihsation has ad-
vanced, man has found it convenient by means of tools and
machines to add power and speed to his muscle. By so doing, he
has been able to harness and utilise power from sources that could
not have been tapped otherwise. Tools and machines are thus
extended and detachable limbs.

The Muscles are Energy Transformers. In the first instance, they
act as accumulators accepting energy principally in two forms [e.g.
potential energy of glucose and osmotic energy of glucose, phos-
phates, etc.) and then storing that energy in potential form (in a
glycogen-nitrogen-phosphorus compound having a very low osmotic
pressure) till it is required, when it is liberated (in what form we do
not know) and converted into kinetic energy. That is, muscle is a
compound transformer, [a) It stores energy and, just like any
other accumulator, the amount of energy stored depends on the
size and number of the units, and the potential of the energy
released only on the number of units composing the muscle. When
a muscle has its full charge, it can take no more. The amount of
glycogen stored in muscle is definitely limited by the bulk of the
muscle for each particular type of muscle, (b) On activation, it
transforms portions of the stored energy into some form which
acts on the liquid colloidal mass within the fibres, causing the mass
to become less liquid and more viscous, and producing a shortening
and thickening of the muscle as a whole, (c) This latter process,
on account of the attachment of one end of the muscle to a fixed
point and the other end to a lever system, results in the perform-
ance of work. The muscle may now relax, and, after the lapse of a
suitable period, again undergo shortening, and so on, once every
five minutes or so, for about fifteen hours, before markedly showing
any sign of the accumulator running dow^n. This feat can be
performed in an atmosphere of nitrogen, thus excluding the
oxidative removal of the bye-products of the reaction. If one
attempted to get not only maximal discharges of energy, but tried
to get them as quickly as possible, one after the other, the accumu-
lator would show signs of weariness very early — whether it were one
of cellulose, lead, acid and water, or one of protein, polysaccharide,
lipide, water, etc.

This double process of contraction and relaxation can be carried
on quite readily without oxygen, but the next stage, that of
recovery — re-charging the storage battery — can only be effected
efficiently in the presence of oxygen and circulating water contain-

168

THE MUSCLE CELLS

□

JZL

ing glucose and other crystalloids. The length of time necessary
to make the muscle fit to perform again its full complement of
work depends, under ideal conditions, on the amount of work it
has been called on to do in the immediate past. As indicated
above, these are the findings of experiments in which the condi-
tions were not natural.

A muscle doing work in the body is supplied with adequate
means (as we shall see in future chapters) of keeping up its store of
energy. Like the starting-lighting battery of a motor car, it
stores and uses energy sinmltaneously. It has, moreover, at least
one advantage over the car battery : it is self-attending and self-
adjusting. It regulates (by means of the balance of hydrophilic
colloids and crystalloids) its own water level, and, by the " buffers "
in its complex, maintains its H^ concentration. It also carries

out (by means of circulatory changes) its
own cleaning and repairs. Further, if it
is asked to pro\'ide for a heavy discharge
fairly regularly, it meets this demand by
adding to the size and number of its cells.

This wonderful transformer has been the
subject of many investigations — as to its
structure and mechanism.

Structure. The units of the accumulator
are long cells, which, in muscles like the
semi-membranosus and sartorius, are prac-
tically as long as the muscle (excluding
tendinous attachments). In other muscles
{e.g. gastrocnemius) they are just a little
over half the length of the muscle. These
fibres, consisting of fibrils which lie side by side immersed in sarco-
plasm, though they, of necessity, all undergo the same amount
of shortening together, do not necessarily all develop tension
during this process. If the muscle is feebly stimulated only
a few fibres actively shorten, the others passively adjusting
themselves to keep their due place by their fellows. The
stronger the stinudus, the more fibres are involved till, with
a certain strength of stimulus, all the fibres are activated. No
further increase of stimulus can then produce any further effect.
That is, other factors remaining constant, the power exhibited by a
inuscle depends on the number of muscle fibres involved. Muscles
are, as we have just seen, of different lengths. If a maximal
contraction is induced, and each muscle is able to shorten to, say,
half its length, then obviously the longer the muscle, the greater
will be the distance through which it can pull its load (Fig. 41).

Fig. 41. — Influence of tlie
length of a muscle upon the
work done. A muscle one
Inch long (left-hand figure)
in contracting to half its
length lifts a weight over half
an inch. A muscle of two
inches, on the other hand, is
capable of Ufting the weight
over one inch.

(Noel Paton's Essentials of
Human Physiology.)

ISOMETRIC COXTRICTIOXS 169

These two faetors, nuiiihcT of (ibres (thickness) and length of
fibres (resting), determine the strength of the nuiscle. The
former gives a measure of the tension dexeloped (ef. volts and
number of cells), while the latter bears an obvious relationship to
the work which can be done.

Tension (dynes) X length (in cms.)
^ ' Work (ergs) ~ ^

Isometric and Isotonic Contractions.

It is usual (and simpler) to make the muscle develop tension
against a spring so adjusted that the muscle cannot shorten. In
an experiment of this sort, the tension developed bears a simple
relationship to the heat produced. Such an experiment is called
isometric because the length of the muscle is kept equal to its
resting length. In a maximal isometric contraction Tl/H is a
constant ratio (= 5 approx.) applicable practically to all muscles
of all animals and over a very wide range of temperatures. Now
H, which may be expressed as microcalories, or in work units as
ergs, bears a quantitative relationship to one of the metabolites of
muscle action, viz., lactic acid. Meyerhof expressed this relation-
ship by equating what he called the isometric coefficient for lactic
acid {K^) with Tl in this way :

^ _ Tension (in kgms.) x /(ems.)

lactic acid liberated (mgrms.)
or in c.g.s, units :

i^A K = T X 1-02 X 10~^ X /

lactic acid (grams)

From these two formulae one finds that :
(from 1) Tl = 5H, and

(from 2) T/ = ? -^ grams of lactic acid.

1-02 X 10-9 s

H (ergs) K

2

lactic acid (grams) 5 x 1-02 X 10""^
Substituting the value for K^ = 77-5, we find
H 77-5 1

lactic acid (grams) 5 X 1-02 X 10"^ 65 X lO^^'^'

That is, for every erg develojjed there should be liberated 65 X lO^^^
grams of lactic acid, and, conversely, for every gram of lactic acid
appearing one should have 1-5 X 10^" ergs.

170

THE MUSCLE CELLS

Now when 1 dyne is developed in 1 em. length of muscle, we have

Tl
H

= 5,orH

- ere\
5 ^

which should be accompanied by 65 X lO^^^/S = 13 X 10""^^ grams
of lactic acid, a figure which agrees fairly well with experimental
values.

Isotonic Contraction. In the body, of course, muscle naturally
shortens against a load, thus keeping the tension unaltered. This
introduces several fresh factors for consideration. The mechanical
act of shortening produces alterations in the thermo-elastic
properties of muscle whereby heat is absorbed, while the increase
of internal friction resulting from the increased viscosity produces
heat. Further, the resistance to movement of the load against
which the muscle has to shorten bears a very important quantita-
tive relationship to the heat generated. Fenn has shown that the
heat generated in an isotonic contraction is greater than the
amount generated in an isometric contraction by an amount
approximately equivalent to the extra work done if the work done
is maximal. To take a simple example, in an isometric contraction
a muscle evolved 24 X 10^* calories, while when it did 2-2 X 10*
ergs of external work it produced 30 X 10~* calories. The extra
6 X 10~* calories are equivalent to 2-5 X 10* ergs, corresponding
to the extra external work (2-2 X 10* ergs) and the internal
thermo-elastic and frictional factors.

TABLE XXV

Heat Production uxder Isometric and Isotonic Conditions
(Modified from Fenn, Jour. Physiol, LVIII., p. 180)

Mode of

Work done

Heat produced

Excess Heat

Contraction.

(ergs X IC).

(ergs X 10<).

(ergs X 10^).

Isometric

0

7-3

0

Isotonic

0-62

8-6

1-3

3 J

1-26

9-3

2-0

J J

1-88

10-5

3-2

>>

1-90

11-5

4-2

It will be seen from this Table (XXV.) that, under the conditions
of the experiment, the excess heat, measured in ergs, is about twice
the value of the external work done.

Muscle causes the conversion of the potential energy of the
greater part of the foodstuffs into kinetic energy, i.e., heat and
work. The process of conversion is ultimately an oxidative one.

ISOTONIC CONTRACTIONS

in

There must, therefore, he a close correlation between tlie enerf>y
evolved and the oxygen intake. 11 we were to measure the amount
of oxygen used by a man resting and kept warm, and then found
the extra amount of oxygen he used when he did a measured
amount of work, we would fmd the cost of the work in oxygen.
Every gram of glucose requires 1-06 grams of oxygen to convert it
into CO2 and H2O, and. therefore, we could calculate the cost of
the work in glucose from the oxygen consumption, presuming that
only glucose was oxidised (Chap. III.). That is, the basis of
muscular activitt/ is oxidation, just as the basis of the activity of a
steam engine is the oxidation of coal.

TABLE XXVI

Gaseous Exchange in M. Levator Labii Superioris of the Horse per
GRAM OF Muscle per minute (Chauveau and Kaupmann)

Rest.

Activity.

Oxygen absorbed.

CO; given out.

Oxygen absorbed.

0-054 C.C.

0-014

0-010

CO, given out.

1

2
3

0-0032 C.C.

0-0079
0-0028

0-0019 C.C.

0-0058

0-0026

0-063 C.C.

0-018
0-013

Heat Developed. Every one knows without the use of thermo-
meters or thermopiles that muscular action produces heat. The
employment of heat measuring devices applied to isolated muscles
or to man as a whole (calorimetric chambers) enables us to formu-
late equations relating the exact amount of heat generated to the
work done and to various other factors. For example, two of the
metabolites of muscular action, lactic acid and CO,, may be equated
with either the heat evolved or the tension developed in an isometric
contraction or with the work done in an isotonic contraction. As
during the cycle of muscular activity, lactic acid disappears at the
same time as COg appears, one might consider that the heat
developed came from the oxidation of the organic acid. In part,
this is the truth, but it is not the whole truth. Let us consider
briefly the various stages in the cycle of changes produced when
muscle does work.

Muscular Cycle. The muscular cycle from resting state to the
return to the resting state is divided into four well-defined stages,
e.g., (1) initiation of contraction, (2) maintenance of contraction,
(3) relaxation, and (4) recovery or restitution. The three earlier
Components do not necessarily require the presence of oxygen.

172

THE MUSCLE CELLS

111 the recovery stage the anaerobic processes are followed by
cht^iiieal changes involving the use of oxygen. Practically all the
simpler quantitative experiments have been carried out iso-
metrically, as that type of contraction is free from the complication
of the various extra factors involved in an isotonic contraction.
In the absence of oxygen a muscle produces heat equivalent to
3-8 X 10'^ ergs for every gram weight of muscle. This amount of
heat (0-9 calorie) is divisible over the three anaerobic stages as
follows :

1. Initiation of contraction

2. Maintenance of contraction

3. Relaxation .

12-5 X 10^ ergs.
6-2 X 10*5 ergs.

. n-7 X 10*5 ergs.

leaving 7-6 X 10^ ergs as equivalent to the heat evolved during
(4) imperfect anaerobic recovery.

If the contracting muscle has adequate supplies of oxygen, the
heat evolved during the last stage wall be spread over a considerable
period of time and will amount to about six times the anaerobic
recovery heat = 45-6 X \Q^ ergs. The earlier stages will have the
same heat production under both anaerobic and aerobic conditions.
During this process of restitution a large amount of lactic acid
liberated during the earlier phases disappears (Table XXVII.).
Some of it is rebuilt into glycogen absorbing a definite amount of
energy which may be produced by the oxidation of other lactic
acid molecules. For every gram of lactic acid formed in the earlier
stages in the absence of oxygen, about 0-81 gram is restored to
muscle to rebuild glycogen, while the remainder, 0-19 gram, is

oxidised to COg and H.^O. That is, 0-81 gram lactic acid > 0-81

gram (approx.) of glycogen with absorption of 1008 X 10^ ergs

= 240 cals. 0-19 gram lactic acid > COg + H2O + 2873 X 10^

ergs = 684 cals.

TABLE XXVII

Percentage of Glycogen and Lactic Acid in Muscle

Muscle.

Glycogen.

Lactic Acid.

(Bull frog)

Rest.

Fatigued.

Did.

Rest.

Fatigued.

Diff.

Gastrocnemius
Thigh

0-37
0-26

0-16
0-07

-0-21
- 0-19

0-09
OlO

0-30

0-28

+ 0-21
+ 0-18

Thi.s table of averages, taken from the experiments of Olmstead and
Coulthard (Anier. Journal of Physiology, LXXXIV., 1928), shows clearly that
what is lost in glycogen content during activity is quantitatively gained in
lactic acid content.

MUSCULAR CYCLE 178

The net result, heat evolved less the energy absorbed

= 2873 X 10' — 1008 X 10" ergs
= 1865 X 10" ergs = 444 calories.

Determinations of the heat evolved and the lactic acid liberated
(Hill and Hartree) show that on isometric contraction 444 calorics
are evolved during oxidative recovery for every gram of lactic
acid. Experiment and calculation agree.

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.

As 0-19 gram out of every gram of glycogen involved disappears
during activity, it nuist be replaced in some way in order to main-
tain the glycogen content of muscle.

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 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 during muscle restitution. Either because
carbohydrate is more readily mobilised or because it requires a
lower tension of oxygen for disintegrativ e 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 hydrion reacts on
the colloids in suspension in the muscle, causing them to alter in
electrical charge (Chaj). 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 contrac-
tion. Macallum proved that activity caused an alteration in the
concentration of salts in muscle, and Fletcher has demonstrated
the increase in water content after exercise.

What is the effect of temperature on the restitution |)hase ?
Theoretically, each of the five sequelae to the liberation of lactic

174

THE MUSCLE CELLS

acid as mentioned in the preceding paragraph has a positive
temperature coefficient. The building up of lactic acid into a
complex is accelerated by increase of temperature just like any
other chemical reaction.

Rest. During complete inactivity, energy is used for maintain-
ing the muscle in a state of preparedness for action, just as a nation
has to spend money maintaining an army in peace time, so the
muscle cell must always be ready for action. This is the fifth phase
of the muscular cycle — erroneously termed rest. This stage is
anything but restful. Just as in peace time the co-ordinating 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 4 per cent.

TABLE XXVIII
Oxygen used by Cat's Gastrocnemius M. (Verzar, 1912)

c.c. Oxygen used by nuisele.

per minute.

per gram
per minute.

Rest (Normal) ......

0-050

0-003

Contraction .......

0-178

0-010

Restitution 15 sees, loiter ....
11 ., „ .
11 „ ,

0-336

0-208
0-154

0-020
0-012
0-009

Rest (Normal) 146 ,, ,,

0-059

0-0035

Function of Lactic Acid. Lactic acid liberation is the pivot
round which all the modern theories of muscular contraction
revolve. Five such hypotheses deserve mention.

(1) Surface Tension Theory. Lactic acid lowers the surface
tension of water and so might alter the interfacial tension of oval
eleinents and their plasma.

A glance at Fig. 42 may make it clear how surface energy may
be made to do work.

SURFACE TENSION THEORY

175

A wire frame is made, to one side of which is attached a silk
thread. Over the w^hole area is a (ilin of soap. The thread M
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 i^ = 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. Howev^er 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

n

^S!-_--i-

^rrrr^

A

Fig. 42. — Frami? of wire enclosing a Soap Film.
In .-1 there is a loop of fine silk floating in the film.
In B the film enclosed by the loop has been broken. (After Van tier Mensbrugghe.)

how slight the difference on the two sides of the thread the rnovement
would be maximal — the " all or none " principle.

Muscle consists of a number of chains of long oval elements
immersed in sarcoplasm. The membranes (plasmahaut) of the
elements may be represented by the thread mentioned above, the
protoplasm of element and sarcoplasm as the soap film. Anything
which causes a difference of surface tension at the interface between
sarcous element and sarcoplasm will cause the element to become
spherical, i.e. its length would decrease without alteration in
volume.

We have seen (Chap. VI.) that a substance cannot produce any
effect on a surface unless it can spread over that surface completely.
The thinnest layer possible would be one a single molecule deep.
Adam has found that the area occupied by a fatty acid molecule
forming part of a condensed film on the surface of water is 21 X 10 ""^
sq, cm. Hill calculates that one molecule of lactic acid should
occupy a surface of 24 X 10"^*^. Giving the acid the benefit of the

176 THE MUSCLE CELLS

larger value, the total area occupied by the lactic acid liberated
when a fibre 1 cm, long develops a dyne would be 24 X 10"^^ times
the number of molecules. We have seen that under these condi-
tions 13 X 10^^^ grams of lactic acid are liberated (p. 170), that is
13 X 10-^2

— 7 7. \ Tj approximately 10^^ molecules. The area

wt oi a molecule ^ ^

coverable would, therefore, be 10^^ x 24 X lO^^^ = 24 X 10~^

cms^., approx. 40^00 of ^ square centimetre. The muscle fibre

being 1 cm. long, its circumference must be 4000 cm. On this

edge, a surface tension of 1 dyne has to be produced, i.e., the

coefficient of surface tension required would be 4,000 dynes — a

perfectly impossible figure. To have a surface effect much more

lactic acid is needed. Thus muscular contraction cannot be

purely a surface tension effect.

(2) Osmotic Theory. The release of lactic acid and other
substances of low molecular weight within a membrane known to
be semi-permeable in the resting state would produce an endos-
mosis which might conceivably lead to shortening. Against this
theory there is the fact that the muscle does not increase in
volume when it thickens and shortens.

(3) Imbibition Theory. The increased H+ concentration pro-
duced on stimulation might cause the cell-colloids thus removed
further from their isoelectric point to take up more water and
swell. This theory suffers from the defects of both the two former
theories. There is not enough lactic acid liberated to alter the /jH
of the muscle proteins from the alkaline side of their isoelectric
point to the acid side, especially in the presence of electrolytes.
(The pYi of muscle in situ is about 7, while the isoelectric point of
myoproteins lies between pYi 4-6 and 5. Myosin is isoelectric at
pYi 3-9.) There is a further objection, namely, it is known that
lactic acid is neutralised under ordinary conditions by inorganic
bases and to a very small extent (if at all) by proteins. The heat
of neutralisation of the acid by proteins is 138 calories and by
salts 19 calories per gram of acid. The former value would
disturb the energy balance sheet of muscle.

(4) Liquid Crystal Theory. Garner and also Clark have suggested
that if there is a film of lipoid liquid crystals in or upon the
anisotropic bands, then this film might be caused to contract or
expand by very slight alterations in 79H. Clark supposes that the
substance in the doubly-refracting bands passes abruptly from a
liquid crystal to a solid crystal form under the influence of acid.
The solid crystal lattice would have a closer form than the liquid
one, i.e. shortening would take place. She supports her hypo-
thesis by the production of X-ray diffraction patterns to shovv the

LIQUID CRYSTAL AND CONDENSER THEORIES 177

nature and extent of crystallisation. The X-ray figures, however,
do not agree with Garner's. The advantage of this theory — ■
Garner's or Clark's is that relatively large forces are brought into
play by an amount of lactic acid which does not need to be
sufficient to cover the whole area (see Chaj), TX. and Figs. 24
and 26).

These statements about the crystalline structure of elements in
nmscle are very similar to the modern view of the structure of
rubber. Examination of rubber at rest (neither stretched nor
pressed) by X-ray interference methods leads one to the con-
clusion that it is formed of colloidal aggregates of large size. These
aggregates consist of highly polymerised rubber swollen by
imbibition of rubber not so highly polymerised. In this state the
free path of the molecules is limited and they yield no clear inter-
ference figure.

If now the rubber is put under stress from any cause (Chap. XVII.)
the liquid phase is expelled from the aggregates to the continuous
phase. Clear interference figures — crystal like — are produced.
When released, the substance tends to regain its state of unstressed
equilibrium and the crystal structure disappears. The incorpora-
tion of a straight-chain fatty acid in the rubber leads to a great
increase in tensile strength, increasing with the length of the
carbon chain up to 14 carbon atoms, and giving marked X-ray
interference figures when put under torsion, stretch or compression.

(5) Condenser Theory. Hill (1925) brought forward a new
conception, viz., that the fibrils, of which there are somewhere
about 100 per fibre, are little negatively-charged cylinders of
protein, surrounded by a cloud of attendant electrons, the whole
constituting a tiny condenser. " Such a condenser would be in a
state of strain under the mutual repulsion of the elements of charge
occupying its plates. The sudden liberation of lactic acid in the
neighbourhood of the negatively-charged protein surface would
cause a discharge of the condenser by the formation of sodium
lactate and ionised protein. The mutual repulsion of the charges
would then be obliterated and the condenser would tend to shorten.
The force developed in such a condenser suddenly discharged can
be calculated, provided we know its dimensions and the density of
its charge." Hill calculates that a monomolecular film deposited
on the surface of the condenser could easilv account for the
liberation of a force of 5,000 dynes per cm. edge (cf. Fig. 14).

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

U. 12

178 THE MUSCLE CELLS

rate of the physical reactions of the contraction phases and the
increases in the physical and chemical reactions of the restitution
phase.

Efficiency of a Contraction. The mechanical efficiency of a
contraction is the fraction of the total energy expended which can
be recovered as external work.

It is found from the formula

E, = lx 100,

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.

a
Net efficiency E^ = -, x 100,

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 values obtained for a complete muscular cycle (contraction
and recovery) vary somewhat with the animal chosen and with
various other factors, such as temperature, rate of work, load, etc.
So far, only the efficiency of individual muscles acting isometrically
(or of the entire muscular machine (Chap. XXXVIII.) ) have been
estimated. The maximum gross efficiency is under 50 per cent.
Various attempts have been made to apply findings from experi-
ments on isolated muscles to muscles in situ. For example, the
biceps brachialis of man pulling against an immovable object for
about 1-4 seconds, turns 26 per cent, of the available energy into
realisable work and 74 per cent, to domestic purposes and to
warming the muscle. If the duration of the contraction is greater
or less than 1-4 seconds the efficiency of the biceps falls off.
Similarly the optimum load, the optimum rate of contraction,
as well as the optimimi duration of the contraction, could be
found for any muscle or group of muscles (see Chap. XXXVIII.).

Training. The regular use of a muscle or group of muscles in a
certain way leads to their more efficient use. Repetition not only
causes a " warming up " of the muscle, but leads to a decreased
shortening viscosity (cf. Expt. 31 (b), p. 531). Other factors,
cardiac and nervous, enter into the question of the effectiveness of
training as applied to a complete animal.

ELECTRICAL PHENOMENA 179

Character of the Electrical Variations in Muscle.

The existence of electrical currents in tissues did not find
direct proof until the year 1824, when Nobili de\ ised 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 conclu-
sively proved that these " natiu-al " currents are not natural
at all but arc 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 therejore currentless (Fig. 38).

Current of Injury or Demarcation Current.

The injured part of a muscle is like the injured part of any
cell (p. 152 and Fig. 38), " 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 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 electro-
motive 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. 153), to physico-chemical differences
at the junction of living and dying tissue. Dead tissue gi\'es no
current.

Current of Action (Fig. 43).

Similar physico-chemical changes are answerable for the wave
of " negativity " which precedes the mechanical change in a
contracting nuiscle. The part which is just about to contract
is electropositive, or " zincative," to the rest. Consider for a

180

THE MUSCLE CELLS

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 (Fig. 43 (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 (Fig. 4-3 {h) ). That is, A has first been

(pi RESULTAMT

"ACTION CURREMT"

ACTIVE. R^IOH

ACTIVE I?Ei:^ION

Fio. 43. — Diagram to show the diphasic character of the current of action in muscle.
(See text for explanation.) Fig. c (in centre) is a representation of the photographic
trace obtained liy protecting the shadow of the mercury in the capillary tube tluough a
IciLs on to a rotating strip of sensitised paper. See Fig. 92.

electropositive and then electronegative to B. Such a current is
termed diphasic and is an indication of a propagated change
(Fig. 43 (c) ).

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
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 stinuili 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.

CURRENT OF ACTION 181

Tlie current of action may be considered as inclusive of tlie
current of injury. Injury is stinuilation, or, conversely, stinuda-
tion is a temporary injury. 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. The diphasic
current of action is of short duration, while the monophasie current
of injury continues as long as the muscle lives in an injured
condition.

Further Reading

Hill. "' Living Machinery." Bell.

Hill. In "" Certain Aspects of Biochemistry." University of London Press.

Evans. Chapters in " Recent Advances in Physiology." J. and A. Churchill.

CHAPTER XV
MANUFACTURING CELLS

" The extreme assumption that the laws of Physics and Chemistry are inadequate
to explain the causation of vital phenomena is, of course, not justifiable, for it
postulates that we fully comprehend now all the laws of the physical world."

Macallum.

In the preceding chapter attention has been drawn to the muscles
as cell communities which consume poAver but do not produce
commodities for the use of the body as a whole. Other cell groups,
the glands, may be regarded as industrial communities manufactur-
ing goods for use elsewhere. Others again are mere handlers of
goods. These latter, the organs of absorption and of 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 secretory 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 is of value
to other cells in the body. They secrete into the blood stream.
The former may be termed organs of external secretion, or exocrine
glands. The latter are called organs of internal secretion, ductless
glands or endocrine organs.

As far as is known the principle underlying the activities of
all 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 phases — just as
we saw that muscle work could be so treated — viz. : {a) Activity,
(6) Restitution, (c) Rest or Maintenance.

(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

182

CYCLE OF ACriVITV 183

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 corresponding to their 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 depart-
ment where it is first packed small and ready for delivery and then
(IV.) the actual delivery department. Generally 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 ?
The same factors come into play w^hich operate in our industrial
world, viz. :

1. Stock on hand.

2. Rate of output from workshop.

3. Efficiency of the dispatchers.

4. 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. Under certain pathological condi-
tions, a state of temporary or chronic over-production occurs.
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 controUing rate of output is the demand for
goods. The store of goods is draw^n 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 (cf. Secretion of Milk).

These various conditions may be studied conveniently by
studying the intake of oxygen or output of COg. 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 Og intake goes to the dispatch department. That is, the
actual setting free of the secretion does not require much energy,

{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.

184

MANUFACTURING CELLS

(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 (44) it will be seen that the maximal rate of
secretion occurs some time before the maximal consumption of
oxygen, and 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
consumption 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

Fig. 44. — Oxvgen used by the salivary gland during rest, aotivity and restitution. From
a to b. the gland was not' secreting, but was using a fairly constant amount of oxygen.
From b to c, tlic 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-seeretory state, o-o = 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.)

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
of glucose used is parallel to the oxygen consumption, as one would
expect.

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 ?

MKCUAMSM or SECRETION 185

1. Microscopical exaniinatioii of the oland shows that during
inactivity the lumen (storehouse) becomes lilled 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 explana-
tion of the second of these phenomena. The postulation of a
semi-permeable membrane is sufficient. The first fact presents
difficulties.

(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 found that the
pressure of secretion was as high as 240 mm. Hg. with an arterial
pressure of 130 nnn.

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 w^hich had been killed and fixed almost
instantaneously. 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 ^d pow er 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 Avhich the secretion and the
leaching water pass.

He found that, during activity, there w'as 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, while when the gland was at rest there was
no marked difference between the interfaces. 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

[h) 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. Blood Supply. It is well know^n that during glandular activity

186 MANUFACTURING CELLS

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

(6) 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. XXV.).

5. Electric Potential. Alterations take place in electrical poten-
tial 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 latter is
accompanied by —

(6) A large difference of potential between the cell-lymph inter-
face and the cell-lumen interface, the former by a small potential
difference of the opposite sign from the latter.

The cause of the larger difference may be sought in the increased
permeability (lowered surface tension) of the cell-lumen 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. injured muscle).

An explanation of the potential difference developed 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
alterations 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

ENDOCRINE (i LANDS 187

gland to be Hooded with water, while " trophic " nerve fibres
have to do with the emission of the granular material of the
secretion. (Heidenhain, 18(38, and Habkin, ]013.) Hoth 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, {h) 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,
because the alkaline reserve of the blood is sufficient to keep the
cell-lymph interface normal or rather supernormal, while the cell-
cell interfaces obviously need not be considered.

In short, the arrival of the appropriate stimulus causes the
cell to draw on its store of material, alter the packing of the
material and launch it into the duet 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.

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 assume that a gland is 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.

Of the mechanism of those glands which secrete directly into
the blood stream little is known. Seemingly, the secretion is

188 MANUFACTURING CELLS

extruded from the cell and washed away by blood, lymph or cerebro-
spinal fluid. Their oxygen consumption has never been measured
nor yet their utilisation of glucose.

Further Reading

Swale Vincent. "An Introduction to the Study of Secretion." Ainold.

CHAPTER XVI
THE ARMY FOR HOME DEFENCE

■■ Whatever uncertainty and variety may appear in the world, \vc remark,
nevertheless, a certain secret concatenation and rejjiilar order at all times carried
on by rrovidence. which causes everything to proceed in its course, and to i'ollo\v
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. Ciliated Epithelial Cells. In certain parts of the body, where
it might be possible for solid matter in a fine state of division to
find its way into hollow visci, a pectiliar type of protective mecha-
nism is found. The entrance to the cavity is lined by a layer of
more or less cohmmar cells on the exposed surface of each of which
is a bunch of fine tapering filaments. During life the cilia move
in such a way as to prodtice a flow otitwards of the fluid bathing
them. Ciliated epithelitmi is found lining the whole extent of the
air-passages (except upper part of nares, lower part of pharynx,
terminal bronchioles and pulmonary alveoli, q.v.). It occurs also
in the uterus and uterine tubes ; in the efferent tubes of the testes.
[As we shall learn later, ciliated epithelium is found in other places,
e.g., central canal of spinal medulla and ventricles of the braiit
where it prov^okes movement of the cerebro-spinal fluid.]

There are two phases in the movement of any cilium, (a) a rapid
stroke in the direction in which the action is to be effective, and
(b) a slow return stroke. Further, although all the cilia attached
to any one cell or row of cells act synchronously, there is a meta-
chronical rhythm about the whole ciliated stirface, i.e., any indivi-
dual cell begins its effective stroke slightly later than the cell
immediately internal to it and slightly earlier than the cell lying
external to it. In this way a progressive wave motion is pro-
duced, carrying towards the exterior the extraneous matter, dust,
etc., entangled in the mucus deposited on the ciliated stirface from
numerous glands.

In considering the efficiency of this means of protection, one has
to take into account the amplitude of the strokes, the frequency
of the strokes of the cilia as a whole, and the exactitude of the
timing of their concerted rhythm. Human cilia are not very long,

189

190 THE ARMY FOR HOME DEFENCE

and we have no means of measuring the amphtude of their beat.
The frequency is somewhere about 10 per second. One may say
that the energy necessary for an effective stroke would be directly
proportional to the amplitude and to the square of the velocity.
E = k.sv^ (where k is a constant, s the amplitude, and v the velocity
of stroke). Therefore the work done in an effective (unloaded)
stroke would be ksv^/t, where t is time, or as

s 1

W = kv\

The value of TF varies from almost 0 to probably just under 30 ergs.
The activity of the cilia is modified by almost any factor that
modifies protoplasmic activity. The relative concentrations of
oxygen, carbon dioxide, hydrogen ion and various salts are factors

any alteration of which will cause

^ a change in activity. Increase of

Ifelrf j jif^ temperature up to a critical value

^ . i. " causes increased activity. Especially

^ interesting is the alteration produced

in rhythm and rate by loading the

^ C^ cilia. The placing of an inert

"^^ powder on the mucus-covered tips

Fig. 45. — To demonstrate turgor. The . rs:? • j_ . • . , • n i

sausage-shaped membrane filled with a sugar IS SUIUCient tO CXCltC actlVC nagcl-

solution is flaccid. When immersed in water, , .

endosmosis recurs and the vessel becomes latlOU.

We have no evidence as to the
mechanism involved in the production of this movement. Schafer
supposes an increase in liquid pressure in a hollow blind tube
(cf. Fig. 45 and Expt. 6 Part II.,), but gives no explanation as
to how this alternate flow and ebb of pressure into the cilia is
produced.

2. Reticulo-endothelial System. It has been found that when a
substance like the dye, lithium carmine, a colloid, is injected into
the blood stream of a living animal, it is not immediately excreted
nor is it uniformly distributed throughout the tissues. Muscle
fibres, ganglion and glial cells appear to take up none of the dye,
while (in the cat) about two-fifths is found in the liver, half in the
lungs, one-twentieth in the spleen, and the remainder in large part
in the kidney, lympoid tissue, and certain cells moving freely in
the blood stream, the true vascular endothelium being stained very
feebly. If, instead of killing the animal for examination an hour
after the injection, the animal were allowed to live for about twflve
hours, then most of the dye would be found in certain cells of the
liver. The cells which are capable of ingesting colloidal particles

RETICULOENDOTHELIAL SYSTEM 191

(suspensoids or emulsoids) have been grouped together under the
name of the reticulo-endothehal system. They are found in the
hnigs, spleen, hver, bone-marrow, lympoid tissue generally, and
in the blood.

Function. They have a special avidity for aeid suspensions
(colloids, small particulate suspensions, fat-dust, cholesterol,
bacteria and fragmented and moribimd erythrocytes). Those that
are free in the blood stream, e.g., monocytes (histiocytes) and endo-
theliocytes, are electrically charged bodies at the hydrogen ion
concentration of the blood (pH 7-4) and move to the cathode in an
electric field. The bacteria in a suspension of B. typhosus move to
the anode. When the smaller electro- negative colloidal mass
(bacterium) comes within the sphere of influence of the larger
oppositely-charged mass (histiocyte) the result is adsorption and
ultimately absorption. The processes whereby bacteria are
engulfed are hastened by a gathering together of the bacteria into
clumps which may be absorbed as such. The large cell thus
disposes of a larger number of the smaller cells at each encounter.
Agglutination (the clumping of bacteria) bears a general resem-
blance to the process of sensitisation of hydrophilic colloids. In this
connection it is interesting to note that the salts of the plasma
are essential for the process. If, by means of dialysis, they are
reduced appreciably, or if their balance is markedly disturbed
agglutination does not take place, and thus bacterial absorption
remains a slow process.

It has been mentioned above that the cells of the reticulo-
endothelial system show a special preference for acidic dyes, e.g.,
trypan blue or pyrrol blue, and thus have become known as
" pyrrol " cells. Compare with this the staining action (adsorp-
tion) of these dyes on colloids (p. 95). Solid particles may also
be taken up by these cells. The special endothelial cells of the
lung may be found full of carbon particles, silica powder, asbestos
dust, or finely divided metal in animals to which these substances
have been administered either by insufflation or by injection (cf,
protection of suspensoids by hydrophilic colloids, p. 93).

Substances of a fatty nature or substances soluble in fats tend to
collect, under certain conditions, in reticulo-endothelial cells.
The esters of the monohydric alcohol, cholesterol, may, in this way,
fill the reticular cells of the spleen to such an extent that that
organ undergoes enlargement. We can again, as a first a])j)roxima-
tion, suggest that lipide and reticulo-endothelial cells dilTer some-
what in electrical charge and thus tend to come more closely
together. The lipide may then be oriented in the first instance,
so that its polar group is in the plasma and its fatty portion in the

192

THE ARMY FOR HOME DEFENCE

lipide membrane surrounding the specialised cell (p. 51). As
the major length of the cholesterol molecule is fat soluble, the
tendency will be for the OH group to be pulled close to the surface
of the cell. In this position the hydrophilic cell-substance will
enter into competition with the surrounding plasma for the polar
group. The balance between Ca and K plays a very important
part in this tug-of-war. If the blood Ca is on the low side and the
cholesterol high {e.g., in starvation or diabetes) the cell contents
win, and the cholesterol and other fatty bodies are tucked away
in the cell. On the other hand, when the calcium is high (or K

Afferent
vessel

Efferen-t

\'essel

Glomerular
capsule

CapillAT-^"
tuft

Capsule

Tubule

VlG. 46. — IJianrain of Jiaipinhian porisust-k'. (From Ciisliny's Secretion of Urine.)

low) the tendency is for the cholesterol to form aggregates with
some calcium soap as nuclei (p. 107) and gall-stones may be
formed.

One of the most important functions of the reticulo-endothelial
system is hsemolyto-poietic. This is especially developed in bone
marrow, spleen, liver, and lymph nodes. These organs are rich in
sessile reticulo-endothelial cells, having the role (in bone marrow)
of forming or of destroying erythrocytes, and in the others of
destroying them (q.v.).

Ultimately the ingested particles or their derivatives are carried
by wandering cells to the liver and excreted with the bile into
the gut. That is, the heavy metals, the colloidal dyes and dis-
integrated blood pigment are eliminated with the f£eces (q.v.).

WORK OF KIDNEY' 193

3. 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 pelvds. 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 (Fig. 46).

The kidney does not manufacture any of the constituents of
its secretion except hippuric acid and probably a small quantity of
urea, 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. That is, when-
ever any substance capable of elimination by the kidney oversteps
its threshold value, it is, in general, excreted till the excess has been
removed. In this way, the kidney acts as a regulator of the water
and salt content of the system. Abnormal constituents of the
blood, except those entangled in the reticulo-endothelial cells and
excreted via bile and faeces, pass in their entirety into the urine.
Not only is there an alteration in the relative concentrations of the
various substances eliminated, but there is in general an increase
in the concentration of solutes. This process of concentration
necessitates 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 most of 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 (h) the tubules. Each capsule is lined
by flattened pavement cells supported by a delicate basement
membrane, A tubule passes from each capsule, joins with other

B. Vi

194 THE ARMY FOR HOME DEFENCE

tubules, and finally opens into the pelvis of the kidney. As the
structure of the kidney is intimately related to its function we
must briefly follow the course of a tubule from capsule to ureter
and note the type of epithelium with which it is lined.

Capsule, flat thin endothelial cells ; > neck of tubule, cylindrical epithe-
lial cells ; > first convoluted tubule, columnar epithelium, indefinite out-
lines, rows of granules arranged vertically to base of cells, striated free border ;

> U-shaped loop of Henle, descending limb has flattened epithelium while

ascending limb is similar to convoluted tubules, but with less striation

second convoluted tubule, as first ; > junctional tubule, cubical or

columnar cells with no granules ; > straight collecting tubule, same as

junctional.

3. Blood Supply. The artery supplying the kidney breaks up in
the cortex into a large number of arterioles, 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. In the mammal, the capillaries surround-
ing the tubules may receive some blood which has not passed
through the glomeruli.

4. Blood Pressure and Secretion. If the blood pressure is
lowered to between 40 and 30 mm. Hg secretion stops. Starling
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. (See Chap. XXII., O.P. of
Plasma.)

Function of Capsule. 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, 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 niay be under one-fifth of
this.

DIURESIS 195

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 a collodion membrane, a solution
of globulin in 0-15 per cent, sodium chloride lost practically no
salt in six hours. Any salt over the amount mentioned rapidly
passed through the membrane.

It does not matter whether the filtration or the dialysing function
of the capsule is accepted as correct, it is clear that no energy is
expended by the kidney in carrying out the process. If filtration
occurs, the energy to force the fluid through the filter comes from
the heart ; if dialysis be the process, molecular forces are involved.
Proof of this lack of work on the part of the capsular cells may be
sought in the oxygen consumption of the kidney when it is known
that the tubule cells are not particularly active. Such is the case
when a diuresis (free flow of urine) is caused by the injection of
Ringer's solution. This solution contains the various salts of the
blood plasma in their correct proportions, and thus its administra-
tion leads to a temporary dilution of the colloids of the plasma.
The dilution is merely temporary, because there is an almost
immediate increase in the amount of urine secreted, but the increase
in the oxygen consumption of the kidney is relatively small (Fig. 47).

Saline Diuresis. The introduction of the saline fluid has caused :

(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. Richards and Schmidt showed that ordinarily, blood
flows through only a part of the glomerular capillaries, but that
saline diuretics cause the closed capillaries to open, and so allow
the blood to flow through a greater nuinber.

(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.

The saline dimrsis may have been caused by all or any of these
concomitants. Thev mav be eliminated one bv one.

13—3

196 THE ARMY FOR HOME DEFENCE

(l, 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 : («) its lower osmotic
pressure (5 per cent, gum has an osmotic pressure of about 12 mm.
compared with 5 per cent, gelatine whose osmotic pressure is
23 mm. of Hg. Bayliss recommends a 7 per cent, solution of
gum), {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 experiments
is that the passage of fluid and salts through the kidney by filtration
or dialysis is controlled by the concentration of colloids in the blood
plasma.

Sulphate diuresis. Let us consider now a case where oxygen
is consumed and, presumably, work done. Sodium sulphate is a
diuretic, i.e., causes a free flow of urine. It is less diffusible than
sodium chloride, and may be retained by a collodion membrane
which will allow the chloride 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 solution 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 Na2S04 is followed by the secretion of
a urine almost entirely an aqueous solution of the sulphate. After
the injection of a solution containing 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 still
above the normal. These results point to the sulphate as having a

F I WCTIOX O F T VnVL FS

197

direct irritant action on the renal (•ells. The (piestion now is, docs
the kidney nsc up more oxygen during a sulphate diuresis than
during a Ringer diuresis ? Fig. 47 shows that the oxygen used
increases as the amount of urine increases under the inlluence of
sulphate, that is, sulphate diuresis entails an expenditure of energy.

The various factors dealt witli above as concomitants of saline
diuresis may now be dealt with in relation to sulphate diuresis.

1, 2, and 3. Increase in flow of blood, etc., do not here play a
part. Bainbridge and Evans showed that in a perfused living
kidney, sulphate diuresis may occur without any increase in
volume.

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.

Function of Tubules.
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 + NagSO^ 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.

so. Gins.

Fig. 47. — To show the relationship between the produc-
tion of urine and tlie consumpti(JU of axvfjen by the
kidney under tlie intluenre of Kingei-Solutiou and of
Sodium Sulpliate. The black area indicates the amount
of urine secreted, the thin line the consumption of oxygen.
(Harcroft.)

rine Gnis.

(1. Oms.

24

0-081

8

0-014

{a) Unobstructed side . . 24 0-081 0-108

(b) Obstructed side ... 8 0-014 0-067

He assumed that the filtrate from Bowman's capsule must be

of identical composition in both kidneys, as each had a similar

blood supply. Therefore, some change nmst 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

198 THE ARMY FOR HOME DEFENCE

sulphate must have been added to the Ihiid during its stay in the
tubule or chloride and water absorbed from it. The two main
modern theories of renal action differ on this point. The experi-
ment is quoted at this stage to demonstrate that it is probable that
sulphate stinuilates the cells lining the tubule, and that their
activity entails the consumption of oxygen and the expenditure
of energy.

Energy Used. The consumption of oxygen, as we have seen, is
an indication of energy usage, and the amount of oxygen used
gives a measure of the amount of energy used. Assuming that
the oxygen all goes to the oxidation of glucose, then- each cubic
centimetre of oxygen will cause the liberation of 0-005 Cal.
from 1-5 mgrms. of glucose.

Basal Metabolism of Kidney. When the kidney is at rest, that
is, when minimal amounts of urine are being formed, very little
work beyond the domestic upkeep of the kidney cells is being
performed and very little oxygen is consumed. A kidney in this
condition, forming 0-03 c.cm. of urine per minute, used 0-4 c.cm. of
oxygen corresponding to the evolution of 0-002 Cal. from the
oxidation of 0-6 mgrm. of glucose.

Metabolism by Secreting Kidney. During the secretion of 2 c.cms.
of urine per minute the kidney consumes about 2-4 c.cm. of oxygen.
Subtract from this amount the amount of oxygen necessary for the
upkeep of the cells (basal rate 0-4 c.cm. per minute) and you have
the amount of oxygen used in the formation of 2 c.cms. of urine.
That is, each litre of urine formed entails the consumption of about
an equal volume of oxygen and 1-3 grams of glucose (approx.) with
an energy utilisation of 5 Cals.

The COo 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.

Work Done by Kidney. 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 mininuun work done in the
formation of a litre of urine may be calculated from the Hill-Donnan
formula : —

Work = R.T. ^e{c„ log, ^^^ + ZC, - ZC^

where R = the gas constant, T = absolute temperature,

C^, = concentration in the blood of any constituent
a, b, c, etc.
and C„ = its concentration in the urine.

TIIKOIUKS OF KIDNEY ACTION 199

This, of course, would only give the minimum work of the
kidney, even if we knew the concentration and degree of dissocia-
tion of each and every urinary constituent. It may be advisable
again 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, as calculated from the
Hill-Uonnan formula above, is simply the minimum necessary to
cause the change in the molecular concentration. It is independent
of any process and commits one to no theory (see Chap. III.).

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 Cat., and similarly about 0-5 Cal. 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 (5 Cals.). We have seen above that for each
volume of urine excreted, the kidney consumes about an equal
volume of oxygen. There is thus a discrepancy between the total
energy absorbed and the apparent work done. In other words,
the efficiency of the kidney

actual work done (in Cals.) 1-2

= , ,. V, , , X 100 = ^ X 100 = 24 per cent.,

energy used (m Cals.) 5

a value closely approximating to the value found for the efficiency
of muscle.

Some of the apparently " wasted " energy goes to keeping the
machine warm and serves other domestic purposes. Some, again,
may be used in maintaining the permanent low surface tension on
the cell-lumen interface in the tubules (Macallum).

Theory of Mechanism. There are two series of facts which are
very difficult to explain.

(1) Some substances occurring in blood and urine have threshold
values, i.e., they are not excreted till their concentration in the
blood reaches a certain value, e.g., water, chlorides, uric acid,
glucose, etc. Others, like urea, creatinin, galactose, etc., have so
low a threshold value that they may be classed with foreign
solutes as non-threshold substances. Now water and chlorides
are more diffusible than urea and creatinin, and yet the latter
seem to be readily eliminated from the blood whenever they are
present irrespective of concentration. In the two chapters on
disperse systems we discussed the question of free and bound water.
Blood plasma is a complex disperse system, and when we come to

200

THE ARMY FOR HOME DEFENCE

study it (Chap. XXII.) we will see that the colloids in it have the
power of binding a large amount of water and certain solutes.
Serum globulin, for instance, binds a considerable amount of
chloride. That is, the threshold refers not so much to a differential
sill in the kidney as to the differential binding of water, organic and
inorganic solutes by the hydrophilic colloids and disperse lipoid
particles in the blood.

(2) The concentration of the substances in the urine differs
markedly from their concentration in the plasma. Not only is
this so, but similar substances, e.g., potassium and sodium, undergo
alterations in concentration to a different extent. The following
table illustrates this point (Table XXIX.).

TABLE XXIX

Concentration

Concentration

Number of times

Substance.

in plasma

in urine

concentrated

per 100 e.c.

per 100 c.c.

by kidney.

Urea

25-30 mgrms.

1-8-2 grms.

60-70

Creatinin .

2-3 „

80-90 mgrms.

40

Uric acid .

2 „

50-60 „

30

Sodium .

320 „

350

J

Potassium

20 „

150

;

7

Ammonium

1— '

40

)

40

Calcium .

8 „

15

J

2

Magnesium

2-5.,

6

5

2

Chloride .

370 „

600

,

2

Phosphate

9 „

270

5

30

Sulphate .

3 „

180

5

60

We ought actually to have in the first column of concentrations,
not the gross amount of these substances in the blood, but a much
higher series of figures, viz. the concentrations of the free salts in
free water. We know that the quantity of water free in the blood
is remarkably small, not over 10 per cent., and probably some-
w'here about 5 per cent., but we have lio reliable figures for the
distribution of the solutes. Even if this correction were made it
would account only for a few differences in concentration, and
would reduce the figures in the last column quite considerably, but
would not clear all our difficulties away.

The bone of contention between the two modern schools is the
function of the tubule. One group holds that the tubular epithc'
Hum absorbs water and threshold salts 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

TIIRKSUOLD VALVES JOI

oi' ccjLuil value to botli sets of thinkers. Maeallum'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 NaCl-ten*?'o/? must be equal to the blood ^a£\-tension,
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
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 an aqueous solution to one containing a
globulin.

Cushny's obstructed ureter experiment referred to abo\'e 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 grms.
water, 0-08 grm. NaCl and 0-11 grms. NaaSO^. Sodium chloride
is more diffusible than sulphate and readily penetrates cells, there-
fore the positive tension of NaCl in the tubule wdll 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 grams.
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 tubular 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-

202 THE ARMY FOR HOME DEFENCE

mcnt, and {b) a mechanical dialysis ol' water and crystalloids in
solution through the capsule under sufRcient 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 intestine. Much waste matter is excreted by the large
intestine and here the physico-chemical mechanism is more clearly
indicated (see Chap. XXVIII.).

Skin glands — sweat excretion will be considered under regula-
tion of temperature (Chap. XXXII.), and elimination by the lungs
under Transport (Chap. XXIV.).

Further Reauixg
CusHNY. '■ The Secretion of Urine." Longmans, Green & Co.

For Reticulo-Endothelial System
Evans. " Recent Advances in Physiology." J. nnd A. Churchill.

CHAPTER XVI T
THE CIVIL ENGINEERS OF THE 1?01)V

CONNKCnVK TISSriO C'KLLS

" Which (loth neatly cU'flarc how nature Geometrizeth and observetii ordei-
in all things/' Sih Thomas Bhowm:.

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 \'arious 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
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.

203

204 THE CIVIL ENGINEERS OF THE BODY

The form of a cell depends in great part on the magnitude of
the snrface 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 fill the space. No odd, empty 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,
drying, etc. These again affect tension. The result is that the
outer layers are flattened and scale-like.

The form of the inmost layer of cells 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 segmentation and of growth.

(c) The outmost layer, away from the nourishing fluids of the body,
undergoes keratinisation and resists the outwards push of young
cells which are thus put under stress.

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 withstand stresses. Before critically
examining their handiwork let us study some elementary engineer-
ing problems, so that we may the better understand the phenomena
of cell structures.

STRENGTH OF MATERIALS 205

If we make a list of the various ways in which mechanical force
can be applied in the human body, e.g., by pressing, pulling, twisting,
bending, etc., and examine them carefully, we find that they can
be resolved into two only, viz., pressing and pulling. Tu attempting
to bend something we apply simultaneously a compressing and a
stretching force. Torsion, too, mav be resolved into these two
forces applied tangcntially to one another.

As every substance develops within itself a force equal in
intensity, but opposite in sign from the applied force, we may
state that all the stresses developed in a material are of two kinds,
e.g. tensile and compressive.

It is obvious that substances may be so formed that they bear
up under compression, but are unable to maintain their integrity
of form or of structure when pulled, or vice versa. For example, a
chain will withstand a great pulling force, but crumples up when
compressed along its length. The stresses developed in a walking
stick are parallel to its length, i.e. it may be pressed or pulled
by forces acting axially without undue danger of fracture, but a
bending force easily produces distortion. The axial forces produce
stresses that lie wholly within the material and. with reasonable
force, no shear occurs.

Shear stress exists between two parts of a body in contact when
the two parts exert equal and opposite forces on each other
laterally in a direction tangential to their surface of contact. For
example, there is a shear stress on a l3olt or rivet when the two
plates which it holds together are pulled or pushed in opposite
directions in a plane parallel to the plane of normal cross-section
of the bolt.

On the other hand, force applied to a walking stick at both
ends so as to bend it, very easily produces fracture. The line
joining the points of application of the two forces in this case lies
almost wholly outside the stick.

There are two factors to be considered when we are dealing with
the ability of structures to maintain their integrity under applied
force. These are (1) strength of material, and (2) nature of
structure.

(1) Strength of Material. The ability of any material to with-
stand stress may be found from various elastic constants, the
so-called moduli, of which there is one for each type of stress and
strain.

Strain is the alteration of shape or dimensions resulting from
stress, and one has a tensile strain resulting from a stretch, com-
pressive strain from a thrust, and shear strain from shear stress.
If after the stress causing a strain has been removed, the strain

206 THE CIVIL ENGINEERS OF THE BODY

disappears, then the stress has not been beyond the elastic limit of
the material. If a stress beyond an elastic limit has been applied,
part of the resulting strain remains after the removal of the stress
and the material has become permanently distorted. In other
words, the residual strain has become a permanent set. The
determination of an elastic limit comes then to be the detection of
the minimum permanent set. Hooke's Law (1660) states that,
within the elastic liinits, the strain produced is proportional to
the stress producing it. This law holds for all kinds of stresses,
but is not exactly true for all materials. The deviations, however,
are few and slight. Hooke's law may be written as

Stress intensity = strain X constant.

The constant in this equation is of the same kind as the stress
intensity, and is measured in units of force per unit area. It
varies (a) with the material stressed, and (b) with the type of stress
developed. That is, for every material there will be a constant
or modulus for tensile, for compressive and for shear stress. The
modulus of elasticity might be defined as the intensity of stress
which would cause unit strain.

Young's Modulus is the direct or stretch modulus. It is always
denoted by the letter E. From Hooke's law —

Stress intensity = Strain X E,

tensile stress intensity

oyE

tensile strain
load on specimen -i- area of cross-section

alteration in length -i- original length

Wertheim sives the moduli of the following substances in grams weight

per sq. cm.

TABLE XXX

Bone

Tendon

Nerve .

Muscle (resting)

Vein

,

Artery .

•

2304-1

X 106

163-41

X 10«

18-89

X 10*^

0-95

X 10«

0-87

X 10«

0-052

X 106

The above values are given in order of increasing " perfection " and decreas-
ing ■■ strength " of elasticity. The figure last given, that of arterial walls,
may be taken as substantially that of elastic fibrous tissue.

The same values are obtained for most materials for a pure
compressive strain.

Shear Modulus (or modulus of rigidity, or of transverse elasticity)
is the modulus expressing the relation l)etween the intensity shear

ELASTICITY 207

stress and the amount of shear strain. It is denoted by the

shear stress
letter N (sometimes by C or G) = ^^ear strain'

Bulk Modulus is the ratio involved when, e.g., a red blood
corpuscle is immersed in a fluid pressing equally on it from all
directions. That is, when three mutually perpendicular and equal
direct stresses act on a body they produce a volumetric strain.
The volume may be increased or decreased as the result. The
bulk modulus is usually expressed as K. If the intensities of the
stresses are each = p, then

p . . change in volume

— = volumetric strain — r-; — -. -. .

K origmal volume

The volumetric strain is three times the accompanying linear
strain under these conditions.

Poisson's Ratio expresses the relation between lateral and
longitudinal strain. A cube of rubber, if pressed on opposite
sides between the finger and thumb, bulges on the other four sides,
or, conversely, if two of the parallel sides are pulled apart, the other
sides become concave. That is, direct stress produces a strain in
its own direction, and an opposite kind of strain in every direction
perpendicular to its own. These two opposing strains resolve into
diagonals, and if the body stressed ruptures it will do so along a
diagonal line. This is of some importance in explaining the
oblique course taken by fractures of bones due to indirect violence.

i lateral strain

Poisson's ratio = — = -. .^ ,. — -. — 7 — —.

m longitudmal strain

The value of m usually lies between 3 and 4.

Elasticity. 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 (6) 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 the distortion due to temporary forces
and intermittent forces, e.g., the elasticity of the costal cartilages
and of the ribs restores the chest wall to its original position when
the inspiratory muscles relax. (3) Intermittent movement is
transformed into a continuous movement by transmission through
an elastic medium (see circulation). (4) Elasticity economises

208

THE CIVIL ENGINEERS OF THE BODY

muscular work by coming into play in the intervals between
successive shocks (Marey).

Examination of Fig. 48 will reveal the fact that bodies with an
elasticity like rubber act under stress in exactly the opposite way
to bodies like the metals. The metals are at first resistant to the
distorting force, and lengthen only slightly till the " yield point "
is reached, when they lengthen rapidly with little or no increase
of applied force and then suddenly rupture. Rubber, on the other

hand, at first stretches easily,
and then enters on a stage
in which it offers greatly
increased resistance to the
pull and lengthens very
little, as the applied force
increases, till it breaks.
Almost similar graphs could
be prepared for compressive
and shearing stresses.

(2) Nature of Structure.
A moment's thought will
convince one that a quite
different structure is re-
quired to meet strains of the
stretching and of the thrusting varieties, (a) The material used
in the l^uilding of struts to withstand thrust must have a high
crushing limit, while that going to form ties requires high resistance
to stretching. In the following table drawn up by Sir Donald
MacAlister, are given the approximate values of the crushing and
tensile strengths of some building materials.

Fig

INTENSITY OF ^THESi

48. — Tensile stress-strain furves for rubber and
annealed steel wire (on ditfcient scales).

TABLE XXXI
Average Strength of Materials

(in kgs.

pet sq. mm.)

Material.

Crusliinti Strength.

Tensile Strength

Steel . . . .

145

100

Wrought Iron

20

40

Cast Iron

72

12

Wood (fibrous tissue)

2

4

Bone . . . .

. 13-16

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. This is very clear if we consider
such a substance as cast iron, which may withstand a compressive force of
40 to 50 tons per square inch before it breaks, but may be pulled to bits by
about one-sixtli of that force. It would be quite suitable for struts, but useless
for forming a sound tie-bar. On the other hand, bone is almost as well able
to resist distortion by pulling as by pressing. If anything, it requires a greater

TIES AND STRUTS

209

compressive force to do any clainage to bone which is as it should be (Table
XXXII.).

The engineer plans his structures to give the niaxiniuni strength
with the minimum weight. Examination of the girders holding a
roof will show that those running from wall to wall have a cross-
section like the capital letter " I." This girder is a tie rod and has
to withstand a stretching force. How has the engineer arrived

BEAM UNLjOADED

BEAM LOADED

Fig. 49. — To show lines of compression (darli) 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.

at this form ? Fig. 49 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
surface is compressed while the lower is stretched. Therefore
midwav 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.

LOAD

Fig. .50. — A simple triangular roof truss.

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 connec-
tion between them
which may be almost
as thin as he likes
without destroying 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. 50) the simple girder becomes a tie
between two struts. The horizontal member of the truss under-
goes tension only, while the sloping beams are compressed. 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

210 THE CIVIL ENGINEERS OF THE BODY

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 exudate from the cells. They
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
which do not branch arranged in bundles which do branch.

[b) The yellow fibres are highl}^ retractile elastic fibres which
branch and anastomose v/ith one another. The fibres are formed
by the coalescence of granules which appear in rows in mucoid
tissue subjected to intermittent stretching. They have no obvious
connection with any cell and are 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 eaplain difference in physical properties, it does
not make any clearer hoiv such a difference is brought about. If
elastic and non-elastic fibres existed side by side in definite pro-
portions 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 goNcrns 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.

FORM AND FUNCTION 211

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.

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) behveen 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. Tender
such circumstances the pressure of separation deforms the originally
spherical globules to form a beaded flattened honeycomb.

(2) Fat Cefls. The experiments detailed in Chap. IX. 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 protoplasm is comparable to an
emulsion. It depends for its permanence 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 demon-
strable 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 protoplasm as a sort of capsule. Reference to the
chapter on emulsions will show that when the colloid in an oil-
in-colloid ?mulsion decreases in hydrophilic power 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. (page 105.)

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. XXXII.). Then too,

14—2

212 THE CIVIL ENGINEERS OF THE BODY

fatty fibrous tissue has a considerable amount of resilience, acting
as a buffer protecting organs from external violence.

(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 filters — 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 epithe-
lium 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 fcetal
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-memhranous bone
formation. The long bones are preformed in cartilage into which

BONE

218

processes of fibrous tissue find their way and they in turn underjjjo
calcification. All bone is developed from Jihrous tissue. The
cartilage merely plays the part of scalTolding and is all replaced by
fibrous tissue before ossification takes place.

TABLE XXXII
Relative Strength of the Long Bonks
(Man aged 31)

Crushing Strengtli
(in kg. per sq. mm.).

Bending
Strength
(in kg.).

Shearing
Strength.

J'lace of Kupturp.

Torsion *
(in kg.).

liunc.

1st appear-
ance of
breakdown.

Complete
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 end

48

Fibula .

3

—

55

21

61

20

In the middle .

6

Torsion applied to the extremity of tlie bone with a leverage of 16 cm. produced a spiral fracturi;
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 w^U 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 pro-
teoses and peptones. Now, experiment has shown that calcium
salts dispersed in an albimiinous hydrogel are throw'n out of
solution when protesoses and peptones appear in the gel. Further,
calcium phosphate is much more insoluble in proteose-peptone
solution than the carbonate, w'hich is only slightly affected by the
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.

214 THE CIVIL ENGINEERS OE THE BODY

One cannot say why cells in certain sitnations 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 hones undergoes alterations to suit altera-
tions 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 w^as 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 othfr ivords, 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. Professor Culmann, an engineer from Zurich, hap-
pened to see some drawings by Professor H. Meyer of the cancellous
tissue of the femur and at once noticed how the trabeculae of the
bone coincided wnth 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. 51 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 w ith 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,
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

STRESS LINES

2 15

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-
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 conipression lines. In the cancellous

INCIDENCE OF lOAD

Fig. 51. — To show the stress lines in tlie head of the Femur, A, in section, and B, mi
the surface. The central diagram gives an idea of the location of the lines of stress in the
head of a crane. (After Culmann, Meyer and Dixon.)

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
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

216

THE CIVIL ENGINEERS OE THE BODY

Fig. 50. 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 tw^o systems of compression
lines. These tension lines will be seen in Fig. 52 forming curves
with their concavities upwards and orthogonal to the compression
lines. They are continued forward by the fibres of the plantar
ligaments which act as the tie-bar of the arch. It will be noticed
that these ties in the calcaneus are closer together at the arch
of the bone between the two struts, i.e. at the point where

-TIBIA

ARTICULAR CARTILAGE

CAPSULE

Fig. 52. — Diagram .sliowing some of the stress lines in the arch of the foot. (After
Hermann Meyer.)

(Tlie diagram is not strictly a section, and the stress lines are not all in one plane.)

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 tvould not ' row its
weight,' and it has been ' turned out '."

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

VI BRAT I OK

217

cells become enlarged and multinucleated. Histologists call these
cells osteoclasts. 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 hone, has
undergone remodelling to suit the nezo 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, where
being in equilibrium they will tend
to " solidify " in mass.

One may easily see this process
of " carding " in action in the siliceous sponges. These sponges
not only orient themselves in water so as to reduce their
resistance to the steady dominant flow of their environment,
but their siliceous skeleton which supports the softer tissues
has an internal structure like bone with the silica laid down
on stress lines so arranged as to take the load. Altering the
direction of the stream of water and thus setting up stresses
different from the previous ones, causes the laying down of
a new skeleton with an absorption of the old one. Chladni's
experiments (Fig. 53) demonstrate that fine grains are deposited
on a horizontal vibrating plate in certain patterns or figures,
depending on the nature of the vibration produced in the plate.
That is, the plate does not vibrate in all its parts at the same rate.
Some points or nodes are practically stationary, and it is at these
nodes that most grains are found. Dendy and Nicholson observed
that siliceous particles were first laid down on the nodal points of
the sponge. The basis, then, of each line of stress outlined in
silica is a series of points which remain stationary when the sponge

tliladni's exix-rimeiit.

218 THE CIVIL ENGINEERS OF THE BODY

vibrates on the impact of a stream of water. There is quite a
body of evidence that a similar vibration-theory may hold good
as well for the work of the osteoblasts as for that of their ancestral
relatives the scleroblasts. Compare, for example, the interlacing
spiral lines in which calcium is deposited (Fig. 51, b) in the femur
with the similar figure obtained when sand is scattered on the
surface of a rectangular bar clamped horizontally at one end and
caused to vibrate. The nodal lines are really lines separating two
parts which are vibrating in opposite phases and so correspond to
the stress lines. If now we dust the plate with two powders, one
heavy, say, blue sand, the other light like lycopodium, we will have
a pattern in blue on the nodal lines and a pattern in white at the
parts of maximum vibration. This deposition of the light powder
is due to the formation of small vortices in the fluid (gas or liquid)
near the vibrating body sweeping the powder to the centre of the
vortex (Faraday). Bone is subject to longitudinal, transverse and
to torsional vibrations, and has in it all the factors to produce
vibration figures.

Fractures. There are several ways by which a piece of black-
board " chalk " can be broken. Let us consider three of them.
{a) If we hold it by both ends and apply force directly at right
angles to the long axis of the chalk, it will snap transversely at the
point of contact of the distorting force. (6) An oblique fracture
results from smacking the chalk vertically on the table. The
force of compression applied along the long axis leads to an
extension at right angles to this (cf. rubber cube, p. 207). The
fracture is only indirectly due to the impact on the tabic, but is
directly due to the bulging being beyond the elastic limit of the
material, (c) A twisting force applied to the chalk produces a
spiral fracture. These types of fracture can all be produced in
bone, (a) Fractures caused by direct violence are transverse and
are located at the point of incidence of the force. (6) Oblique
fractures are a sign of indirect violence, e.g. fracture of the clavicle
from a fall on the outstretched arm. (c) Spiral fractures are
produced when the body is twisted with the limb fixed.

(5) Lubricating Cells. 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 vip " 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.

JOIXTS 21 «)

In spite of all precautions, however, "' seizinj>- " does take plaee.
The film of oil is rubbed away just at the point where it is most
required. Only one maehine 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 bone : tendons run like Howden wires in sheaths, and yet
the healthy animal body moves noiselessly and without " heating
up " or " seizing " at any speed.

(«) 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. 52). 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. Grow^th and destruction exactly
balance one another, (ii.) The waste synovia is drained into the
blood stream through villous processes w'hich project from the
synovial membrane into the cavities of the joints.

(6) 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
known all other cell connnunities 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

220 THE CIVIL ENGINEERS OF THE BODY

plasma wliicli reaches the cells from the rich v^ascular 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 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.

Further Reading

Thompson. " Growth and Form." Cambridge University Press.
Keith. " Engines of the Human Body." Williams and Norgate.

CHAPTER XVIII
THE INTELLIGENCE SERVICE

NERVE CELLS

" The messengers that preser\ed 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 inmost 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 of a nerve cell or cyton,
with the terminal processes of the axon of another cyton. The
cell with its processes is called a neuron. (See Fig. 54.)

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.

Some nerves have a sheath or coat composed of unsaturated
fatty acids and lecithin (and allied lipoids). This medullary
sheath is formed from separate cells, but it must retain some
connection with the nerve cell, as it dies and disintegrates when
dissociated from it,

221

222 THE INTELLIGENCE SERVICE

This sheath is present on the nerve fibres which are concerned
with rapid adjustments to alterations in environment. Peripheral
non-medullated fibres generally belong to the second system of
nerves and have a slower reaction rate as befits the slower adjust-
ments of the structures they innervate.

1. Structure. A nerve is really a compound structure composed
of parallel bundles of nerve fibres (funiculi), each of which is
enclosed in lamellar connective tissue (perineurium). The nerve
fibres in a funiculus are supported by a delicate fibrous investment
— the endoneurium. The whole collection of funiculi — the nerve —
is united together and to neighbouring tissues by epineurium.

Each fibre is an anatomical and physiological unit, and runs an
uninterrupted course between central cell (brain, spinal medulla,
sympathetic ganglion, etc.) and peripheral end organ (in muscle,
gland, sense organ, etc.). Each consists of a long thread of
protoplasm (axon) drawn out from and continuous with the
cytoplasm of the nerve cell.

The neuron (cell and fibres), like any other cell, is a colloidal
fluid mass, (i.) 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 large aggregates which again
dissociate, (ii.) Carlson has shown that nerves may be stretched
without altering their efficiency, judged by rate of conduction of
an impulse, (iii.) Macallum states that alterations in surface tension
can be detected especially in the growing nerve, (iv.) 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 (cf. Irritability of Cell, Chap. XII.).

3. The nature of the stimulus seems immaterial. Mechanical,
electrical or chemical stinudi all cause the nerve to propagate the
same kind of impulse. Furthermore, the excitatory result of the
propagated impidse depends not on the nature of the " trigger "
stimulus but on the nature of the mechanism to which the nerve
goes. That is, stinudation of the sciatic nerve by electrical,
mechanical, thermal or chemical means causes contraction of the
gastrocnemius muscle ; stimulation of the vagus ner\'c by any
means slows the heart, stimulation of the chorda tympani causes
the salivary glands to secrete, no matter how the stimulation is
effected. These are all outgoing nerves. The predominating
fibres in them carry impulses to the periphery to produce action of

SPECIFIC NERVOUS ENERGY 223

some sort. A similar investigation may be held concerning those
nerve fibres which carry impulses from the periphery. Stinuilation
of the optic nerve gives rise to the sensation of light, of the cochlear
nerve to sound, and so on. On these facts about sensory stinuila-
tion is based Midler'' s " Doctrine of Specific Nervous Energy,''''
which reads : " The specific sensations of each sensory nerve can
be evoked by different internal and external stimuli." " Sensation
is not the transmission to consciousness of a quality or state of an
external body, but of the quality or state of a sensory nerve as
produced by an extrinsic cause, and these qualities differ in the
different sensory nerves." They differ not because of any inherent
quality in the nerve, but because of the nature of the central body
to which they go. In the same way, as far as modern work goes
it shows that the concomitants of all nervous impulses are abso-
lutely similar. The sole difference between motor neurons and

NERVE CELL

DENDRITES IN
A

>

DENDRiTES IN

CONDUCTING AAON R£CEIVIN(3 AXON V^

KOTO:^ ORGAN ^ RECEPTOR. ORCAN

^ • CONTACT KEY

GALVANIC CELL

FiCt. 54. — 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.

sensory neurons is in the nature of the organ to which the nervous
disturbance is propagated.

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. 54b, where
a galvanic cell or other electrical unit is connected by wires F^ and
F.)^ to M, an electric machine. 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 (/;) the manifestation of the current will
depend 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 incan-
descent globe, light will be seen, if M is a motor, motion will result,
and so on. The electrical energy of the electric generator 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.

224

THE INTELLIGENCE SERVICE

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 as well 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
transmitter (see following chapter).

The neuron may be likened to this electrical model (Fig. 54a).
The nerve cell is similar to the galvanic unit, F is the axon or

XEACTING OR. EFFECTOR. UNIT : RECEIVING OR. KBCEPTOI^ UNIT

I

S

N,

'prr

I

! SYNAPSE C,

^

KEY

ELECTRDMAGNET

Fig. 55. — A. ])iagram showing a receiving (A',) and a reuctim) Neuron (N.,), eacli with

dendrites at its extremities, and their eoiiiiection to one another tlirougli a Synapsis {*').

B. Electrical Model to illustrate the functional contintiity of two neurons. See text.

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. 55). S may be
termed the synapse joining an effector and receptor neuron. The
student will notice that there is no material continuity 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
from Cj is a fixed quantity independent of the energy used to
close the circuit, and similarly the energy in the system of which
C^ 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." The existence of the " all or nothing " effect

ALL OR NOTHING 22

zzo

ill neurons forces us to look for some other way in wliich a strong
stimulus differs from a weak but effective one. The only possible
way in which to provide for a gradation is to consider the ninnber
of impulses per unit time, i.e., the frequency. Experiments have
shown that strong stimuli produce a large series of propagated
disturbances in nerve fibres. The stronger the stimulus, the
greater is the frequency up to a limit, but the " size " of each
impulse is invariable.

5. Nature of the impulse. About the nature of the " disturb-
ance " propagated along a nerve we know nothing. It is accom-
panied by electrical changes similar in nature to the action potential
of muscle, and by metabolic changes, e.g. evolution of C02and heat.

0. Electrical changes. The electrical changes have been much
studied by means of the capillary electrometer. Just as in muscle,
so in nerve, an electrical wave accompanies the nervous impulse.
The part excited becomes galvanometrically negative (zincative) to
the rest (see Muscle, p. 179), 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 (cf. Fig. 43). That is, a potential difference is produced
which, if conditions permitted, would cause a current to travel in
the electrometer circuit first from B to A, and then from A to B
(Fig. 43). The relation between impulse and action potential at
any point are found experimentally by damaging the nerve at,
say, B, so producing a constant demarcation negative potential
difference (current of injury) which remains constant even when
the wave of negativity (current of action) reaches it (cf. Fig. 38).
The potential difference shown by the electrometer in an experi-
ment of this kind will, therefore, be in one direction or monophasic,
and will indicate the rise and fall of a potential difference under
one electrode.

The monophasic response is brief, 0 to 8 a 10 '* seconds in the
frog. Increase of temperature shortens, and decrease of tempera-
ture lengthens the duration of the stay of the electrically excited
region at any spot. The duration is, however, the same in all
similar fibres in a nerve trunk.

7. Velocity of passage of electrical disturbance. The propagated
disturbance and the electrical disturbance pass along a nerve fibre
at the same rate and in the same direction. In the frog this rate
is somewhere about 28-33 metres per second. The rate varies,
however, from fibre to fibre. Even all the fibres in a nerve trunk
do not pass on the disturbance at the same rate, some having
velocities of propagation five times that of their neighbours. This

B. 15

226 THE INTELLIGENCE SERVICE

is due to differences in the structure and diameter of fibres. The
former has been referred to on p. 222 ; as regards the latter, we
may say that velocity is a linear function of the diameter of similar
fibres. The rate of transmission also alters with the temperature
level, as does the duration of the local electrical disturbance.

8. Cause of the electrical change. It is generally admitted that
the action potential difference is the sign of a local ionic change in
nature similar to that occurring in other protoplasmic units in
action. In the first place, let us consider why the electrical change
is local. That is, the nerve fibre is not to be looked upon as a simple
electrical conductor, but rather as a chain of membrane-bounded
chambers containing ionised protein, ionised salts, etc., and
developing a local Donnan membrane -potential (cf. muscle
fibrillae). When one of these chambers is " excited " there is a
heaping up of ions on the membrane separating it from the next
chamber in order of progression, and this in some ways leads to
an alteration in permeability— an injury of the membrane, and the
disturbance passes to the next chamber, and so on. The evidence
for the local nature of the change is primarily twofold.

(a) Resistance. The resistance of the nerve fibre to the conduc-
tion of an electric current is about 10'^ ohms per centimetre, and
varies with the cross-section of the fibre. According to Ohm's law,
the current flowing in a conductor varies directly as the potential
difference (E), and inversely as resistance (R) of the conductor,

E

i,e. C = p" If, for example, the value of 1 volt be given to E,

then the current flowing in a fibre 10 nun. long would be 10"**
amperes. We have no means at present of computing the E.M.F.
developed in nerve, but it would need to be well beyond physio-
logical limits to produce a current flow in, say, the sensory nerve
fibre bringing the sensation of tickle from the sole of the foot.

{h) 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. l)ut 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

REFRACTORY PERIOD 227

to cooling. The firing of a train of gunpowder is a series of local
acts. Moreover, an increased resistance in a straight electrical
circuit would produce a decrement of current which would not
recover its pre-resistancc value no matter how good a conductor
it passed into.

9. Refractory period. Tlic passage of a nervous impulse pro-
duces 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 : («) The ahsolutely
refractory period when no stimulus, however strong, is effective.
(6) During the relative refractory period the nerve is recovering
and will respond to stimuli of supernormal strength, (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
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. Take
a very simple analogy. In a game common to Boy Scouts, and,
I understand, borrowed from the NaAv, a row of players are so
arranged in unstable equilibrium that on the word or sign of
command (stimulus) number one falls towards number two, and
so on, till all the players are horizontal. The disturbance has been
propagated from one end of the line to the other. Note in the
first instance that the stimulus has not supplied any of the energy.
Secondly, that the disturbance alone has been propagated, and that
each unit of the team has supplied its own energy (+ gravity).
Thirdly, before a second impulse can be propagated all the players
must be restored to the vertical. Until this is done, no amount of
stinuilation is of any use. This is the absolutely refractory
period. We cannot push the analogy further.

10. Summation. If a second stimulus be applied to the nerve
during the third phase of the 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 projiagated along

15 — 2

228 THE INTELLIGENCE SERVICE

a nerve during the supernormal period may cause the motor end-
organ to act. Such a phenomenon is called summation.

11. 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.

12. Metabolism. This leads one to infer that the energy
exchanges during the conduction of ihipulses are small. 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. Ingenious methods have
been devised by Waller, by Tashiro, and by Hill for the measure-
ment of the COo evolved during activity. Hill has found that the
heat and CO., liberated in nerve activity represent an appreciable
amount of metabolic change.

13. Temperature coefficient of the nervous impulse. When a
length of nerve is cooled its power to conduct an impulse is
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 (Centigrade scale), 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° = — . has been estimated hy Lucas as approximately

V ait T

1-8. This value has been proved to be right by later workers.
Therefore, physical factors, as well as chemical reactions, are
involved in the propagation of a nervous impulse.

11-. Polarisation, {a) Negative polarisation. A disturbing arte-
fact is produced when a medullated nerve is stimulated and leads
are taken to a galvanometer from two points on its length. In
Fig. 56 we have a diagram of such a circuit. The upper circuit is
the polarising one, i.e. at the anode, positive charges develop in the
sheath (due supposedly to the dissociation of electrolytes by the

POLARISATION CURRENT 22!)

passage of the current through the sheath). Similarly, below the
cathode there is a collection of electrons. If now the current is
switched off and the lower circuit (through a galvanometer)
switched on, it will be found that a potential difference has
developed, causing a current to flow through the galvanometer in
the opposite sense to the polarisation current. The previous
anode has become the cathode,

i.e. the anode has been posi- /^ ^^^\\ Po'a'''sin<3

tively polarised and the
cathode negatively polarised

-?

Polarisation model. The '^^W''^ Neqative polarisation.

theory that the phenomenon j.-j^, 56._])iagram to sliow direction of tlic negative

is due to a heaping up of l^lan^ation .uirent in a meduUated nerve.

opposite charges in the sheath is svipportcd by a simple in-
organic model (Fig. 57). If for axon and sheath we substitute
a zinc wire and some cotton wool soaked in saline, we would
find that the cotton wool would collect positive charges under
the anode, negative charges under the cathode, and show a
negative polarisation in the same way as medullated nerve. The
substitution of zinc sulphate for the sodium chloride in the cotton
" sheath " prevents polarisation, indicating the probability that
the phenomenon is due (1) to the sheath, and (2) to some ionisable
substance therein.

When an electric field is developed in water, each water molecule in the
field becomes polarised, i.e., oriented so that the positive ends (H) all point
in one direction, and, of course, the negative ends (OH) in the opposite
direction. The result of this arrangement is the formation of a large number

Glass tube

containing O-6/o Na Cj.

Pt.wire

c d d b e f

Fig. 57. — Apparatus for iniitatinu the polarisation phenomena in medullated nerve.

of tiny condensers in series stretching from one electrode to the other, thus
giving water a high value as a dielectric {q.v.). The polarity of the water
molecules, in other words, the presence of efficient condensers, may account
for the power water undoubtedly has of causing the dissociation of electrolytes
into ions {q.v.). If we measure the charge on a condenser formed by immersing
two metal plates in pure, air-free water, and get a value, we can then alter the
value by dissolving various salts in the water. The addition of .salts, ioni.sed
proteins, etc., increases the potential of the condenser. A charged condenser
can, of course, give up its charge (cf. Leyden jar). This is apparently what
happens when a current is passed through the medullated sheath of a nerve.
The discharge of the condensers gives rise to the negative polarisation current.

o

230

THE INTELLIGENCE SERVICE

Electrotonic Currents. I'liat negative })()larisation oecurs while
the polarisation eurrent is running may be shown by an experiment
as indicated in Fig. 58. The centre circuit is supplying the
polarising current, x being the anode, and y the cathode. The two
lower circuits are merely leads to galvanometers, Gj and ^3.

t 1

y

I
c

G2

Fig. 58. — Diagram showing electrotonic currents. P. polarising circuit ; 6'', G-, galvanometers.

When the polarising circuit is closed and the polarising current
passes in the nerve from x to y, the galvanometers will both
indicate currents passing in the same direction, from a to b and
c to d respectively. These extra-polar, or as Du Bois-Reymond
called them, electrotonic currents, are due to the same causes as
negative polarisation. Consider Fig. 59, where the positive charges
are shown gathering on the surface of the axon at a-b. That is,
a-b will have a higher + potential than in the nerve at c or to the
left of c. The result will be a flow of current from left to right

-Itl tll+

+ + -f + + +

+ - + + -

.;;_-" - -y-^=j- ---

-_

c b a d e ^

riG. 59. — Diagram to show polarisation at the surface between conducting core and
electrolyte sheath.

along the surface of the axon to reduce this difference of potential.
In the same way, under the cathode at d-e the accumulation of
electrons in excess of what is at /and to the right of/ will cause the
passage of some of the excess towards the right. It is clear, then,
that all three currents, left to b {anelectrotonic), a to d (polarising),
and e to right {cateIectroto7iic) flow in the same direction.

The model referred to above responds in the same way (Fig. 57),

ELIX TROTOXIC CIRHEXTS 2:n

but if a zinc wire is used as core and the cotton wool soaked in
zinc sulphate to prevent polarisation, neither anelectrotonic or
catelectrotonic currents are produced.

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, (i.) The former have a much greater velocity
than the nerve impulse, as indicated by the wave of negativity.
(ii.) Their E.M.F. may attain a value twenty-five times that of the
current of injury, (iii.) 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.

{b) Positive polarisation. A special type of injury current,
unfortunately named the positive polarisation current, may be
obtained immediately after

the passage of a very strong /^l~^ Polarising

current along a nerve (Fig. 60). ^ /^'

When the " polarising " cur-

rent is broken and the anode a '^'^y^^ Pos.tive polarisation

connected through a galvano- W'

r,^f^^-p>T fr> fVi<^ noflinrlfi I- ( niv FiG. 60.— Diagram to sliow direction of the positive

lllCLCl to LUC CclLllOUe th \L-U- polarisation current, due to a break excitation at the

cuit 2), a current will be """'*''

apparent flowing in the same direction as the " polarising " current,
i.e. from a to k. This current is not due to polarisation at all.
but to injury at the anode by the strong " polarising " current used,
A very significant series of experiments due to Lillie may be
referred to here. If an iron wire is immersed in dilute nitric acid,
in time it will be covered with a film of iron oxide. It is now in a
passive state, and as long as the environment does not alter, no
further changes will take place in or on the wire. But when the
film of oxide is broken, say, by a mere scratch near one end of the
wire, the break in the oxide is transmitted without decrement
along the whole extent of the wire regardless of its length. This is
accompanied by electrical changes and by the e\'olution of gas, and
is followed by a restoration of the film of oxide. The wire is now
passive and ready for further scratching. The model illustrates
several principles of nerve action dealt with above and emphasises
the point of view that the nerve impulse is associated with changes
on the surface of the axon. It might repay the student to turn
back to Chaps. VI. and IX., where consideration is given to the
properties of monomolecular films on surfaces.

s

232 THE INTELLIGENCE SERVICE

Consider a^ain Fig, 58. Suppose that at a little to the right of d
the nerve entered a muscle. With the key of circuit P open,
stimulation of the nerve, say, at 6 by a drop of strong saline would
produce convulsive twitchings of the muscle. The closure of the
key completing the circuit P produces a cessation of the muscle
action. The polarising current has blocked the passage of the
nerve impulse. Careful experiment shows that this is due to a
depression centred at x, an anodic depression. In a similar way, it
can be shown that at y the nerve is more easily stimulated when the
polarising current is running than otherwise. There is cathodic
sensitisation. A drop of saline which, when placed at h or at c,
would produce only a series of muscle twitches with the polarising
current off, would cause complete tetanus at c only when the
polarising current was running.

To explain this we must consider again the series of little
condensers (Fig. 59). When the drop of saline acts on the nerve
it produces a brief current of action, i.e. it tends to cause a tempo-
rary accumulation of electrons at the stimulated point and the
propagation of a current of action along the nerve. When the
polarising current is flowing, the condensers near x (Fig. 58)
would be positively and those at y negatively charged. The action
potential developed by the saline (or other stimulating cause)
would, when applied in the neighbourhood of x, merely discharge
the condensers, while applied at y, it would augment the charge
already present leading to a more complete excitation of the
structure, motor organ or sensory area supplied by the nerve.

Under experimental conditions it may be shown that the nervous
impulse may be propagated in any direction in a nerve, but the
nervous system as a whole conducts only in one direction. The
unidirectional mechanism lies in the synapse, where a non-nervous
substance forms the connection between neuron and neuron.

Further Eeading
Adrian. " The Basis of Sensation." Christophers.

CHAPTER XIX
OUTPOSTS OF THE INTELLIGENCE SERVICE

(a) GENERAL AND INTRA-C OMMUNAL RECEPTORS

" By mine eye. I do not know tliat I see, or by mine eai' that I licar, bnt by my
eommon sense who jiidgeth of sonnd and eoloiirs." Burtox.

If an organism is to adapt itself to changes in the environment,
there must exist within it some mechanism whereby it is '' made
aware " of these changes. It is as if the Cabinet and the various
Local Government Boards of a country were shut up in seclusion
and had to learn of the progress of the areas governed and of the
various happenings abroad by messages sent in by agents from
without. These agents could transmit their information by special
messenger (hormones, CO^, etc.) or by coded telegram, either to
the special body controlling an area (local nerve centres), or a
function {e.g. respiratory centre), or to the central governing body
(consciousness). It is clear that 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." The other intelligence staff operates
on matters outside the organism. They are exteroceptors.

1. Threshold. The agents or receptors are specialised organs, so
constructed as to have a lower threshold for one particular type of
change in the environment than for all other changes. For
example, the eye is specially adapted for the reception of waves
in ether over a well-defined range of frequencies of quite a low
intensity. It can, however, respond to other forms of stimulation,
mechanical, chemical and electrical, if their intensity is sufficiently
great. That is, a specialised receptor responds readily to one
particular form of environmental change, even though that change

233

234 OUTPOSTS OF THE INTELLIGENCE SERVICE

merely whispers, while all other types of change have to shout for
attention.

f* 2. Adaptation. A change in the environment of suitable nature
and of sufficient intensity to be perceived by the central area
concerned, ceases after a time to produce any effect. Change,
ceaseless change alone, is capable of being conveyed to conscious-
ness. The steady state is unproductive of alterations in the
nervous system. We cease to be aware of the steady pressure of
our clothes, of the regular ticking of the clock, of the peculiar
odour of our laboratories and so on. Three structures are concerned
in this : (a) the receptor, (b) the sensory nerve, and (c) the central
sensory area. The adaptation may take place in any or in all of
these. From Adrian's work we know that sensory nerves adapt
themselves very rapidly and practically all at the same rate. This
information is obtainable from experiments where the electrical
changes that accompany the nervous impulse are made to record
their own fluctuations (p. 225). When a sensory nerve fibre is
stimulated electrically, only one wave of negativity passes along
the nerve. Continued similar stinuilation produces no further
effect. Adrian dissected out an end-organ with sensory nerve
intact, e.g. eye of eel and optic nerve, hair and cutaneous nerve,
etc. He found that when an adequate stimulus was applied to the
receptor, the electrometer, oscillograph, loud-speaker, or other
electrical device, showed a burst of electrical activity lasting only
a fraction of a second, even though the stimulation was continued.
That is, there is a rate of adaptation for nerve plus receptor which is
different from that of nerve alone. All the end-organs adapt
themselves more slowly than nerves alone. Some, like those of
touch and tickle, are fairly rapid, others, like pressure and muscle
joint sense, are very sIoav. The former are termed phasic, and are
concerned with stimuli demanding rapid action, e.g. touch-jump,
tickle-scratch, etc. The latter are jjostural, conveying information
about the position occupied by our limbs — resistance to move-
ment, weights held, etc., not necessitating any very rapid response,
but calling for the exercise of further mental processes, e.g.
discrimination. That is, we are given time for the sensation
aroused by the stimulation of a postural end -organ to " sink in."
About adaptation in the sensory area, nothing can be said in the
present state of knowledge.

3. Frequency of Discharge. In the previous chapter we con-
sidered the refractory period of nerve. This period, during which
the nerve cannot transmit any propagated impulse, is, for mam-
malian sensory nerves, somewhat less than 1/1,000 second. That
means that the nerve could conduct at least 1,000 impulses per

FKCIIXEirS L.tW 235

second if called on to do so. The receptors ure not capable of
such a rapid recovery. They all take about seven times as long
as nerve to recover. They are, therefore, capable of transnntting
as a maximum less than 150 impulses per second. This difference
in time constitutes a margin of safety, i.e. the ingoing nerve has
time completely to recover before the next impulse arrives for
propagation. " In fact,'' says Adrian, " the rapid recovery of the
nerve fibre makes it practically an aperiodic conducting system as
far as the slower end-organ is concerned.'' The message transmitted
to the nerve by a receptor will be carried without distortion to the
sensory area concerned.

4. Stimulus and Sensation. We cannot hope to explain on
physical grounds the relationship between the nature of the
stimulus and the nature of sensation {e.g. why ether waves of a
certain frequency falling on the end-organ for sight should give us
the sensation of redness, the same waves received by a heat spot
arouse a feeling of warmth, etc.) until we can state in physical
terms what consciousness is. We do know, however, that the
quality (intensity and striking value) of a sensation (emotional
factors being kept constant) bears a quantitative relationship to
certain physical attributes of the stimulus. Adrian's technique
has opened out a vast field for exploration, because consciousness
can, in a sense, be eliminated. If we admit that the electrical
response of a nerve is quantitatively and qualitatively a symbol of
the nervous impulse, then we have an experimental tool of great
importance. We can measure the stimulus in energy units and
we can measure the frequency, amplitude and duration of the
electrical waves induced in the sensory nerve.

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 stinudus. This threshold value is lowest, as has been said
above, for the form of stimulation specific to that organ. Once
this value is gained, the resulting sensation bears a definite relation-
ship to the incident stimulus until an upper limiting value has been
reached, after w^hich increase of stimulation is of no avail. In fact,
fatigue rapidly sets in, and the resulting sensation is submaximal.

Fechner's Law. This law states that the sensation varies as
the natural logarithm of the stimulus. Adrian showed that the
amplitude of movement of the mercury in the electrometer, and
hence the potential difference developed in the nerve, did not vary
whatever the intensity of the stimulus. The factors which do
vary are the duration of the discharge and, in some cases, the
frequency of the discharge. In the case of " phasic " receptors

236 OUTPOSTS OF THE INTELLIGENCE SERVICE

(rapid adaptation), touch, tickle, etc., a single .stimulation giv^cs
rise to the same electrical variations — frequency, amplitude and
duration — irrespective of the intensity of the stimulus. A graded
response can be obtained only if several end -organs are stimulated
simultaneously.

To offset this lack of discriminative power the phasic end-organs
have a very short refractory period, and so are able to accept and
transmit a subsequent stimulus in a fraction of a second. Per-
sistence of tickling, say by distortion of hairs, produces a rapid
series of electrical variations. Postural receptors are capable of
giving a graded response. We can recognise a pressure stimulus
produced by 1 gram as being less than that produced by 5 grams.
The movements of the mercury in the capillary electrometer
indicate that, in the former case, a very brief discharge has occurred,
while in the latter case, the duration of the discharge has been in-
creased. Amplitude [i.e. potential difference) and frequency {i.e. rate
of discharge) are the same for any weight giving rise to a sensation
of pure pressure. Similar findings from experiments on other end-
organs lead to the same conclusion, viz. the receptor when stimulated
causes an impulse to he propagated along a series of units containing
ions, so that each unit becomes first negatively and then positively
charged. The potential developed is a constant ; the rate at which
each cycle of electrical charges appears, varies from nerve to nerve
{between 5 and 100 cycles jjer second), but is characteristic for any
particular nerve fibre. The time during which the series of cycles
jjersists is a measure of the intensity of the stimulus where adaptation
is slow enough to allow of it.

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 are received by the tactile corpuscles of
the skin. They may be perceived as separate stimuli even when
they arrive as rapidly as 150 per second.

2. Slow vibrations especially in air are received by the ear. The
himian ear may be stimulated by vibrations ranging from 16 to
40,000 per second. Practice may extend this range.

3. Rapid vibrations in ether.

(«) Radiant heat. Vibrations with a frequency of between
3 billions and 400 billions per second stimulate the temperature
receptors of the skin.

(6) 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.

TOUCH 237

B. Chemical Energy.

The various chemical stiumli to which the organism is exposed
have receptors in the skin, giving rise to sensations of pain or
discomfort, and in the special end-organs to those of taste and
smell.

As receptors for tliese 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 bodv.

I. PHASIC RECEPTORS

1. 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
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 bieen 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
(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 XXXIII.

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 ....

Millimetres.

11
2-2-3

4-5
4-4-5
5-5-5

6-8

6-8
5-6-8
5-7-6
5-5-6

238 OUTPOSTS OF THE INTELLIGENCE SERVICE

volar surface

TABLE XXXIII— co;;^«me(^.

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
Lower third of the forearm
In front of the zygoma
Plantar surface of the great toe
Inner surface of the lip
Behind the zygoma .
Forehead
Occiput .
Back of the hand
Under the chin
Vertex
Knee

Sacrum, gluteal region
Forearm and leg
Neck
Back of the fifth dorsal vertebra ; lower dorsal

and lumbar region
Upper arm ; thigh ; centre
Middle of the neck

of back

Millimetres.

8-9

-11-3

13-5
15

15-8
15-8
20-3
22-6
22-6
27-1
29-8
33-8
33-8
36-1
44-6
45-1
54-1

54-1

67-7
67-7

The intensity of the contact sensation is increased in a mechanical
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.

2. Tickle is a sensation that may be classed among the surface
phenomena like touch, or among the deeper sensibilities like
pressure. Dealing exclusively with the former variety, we may
say that the stimuli producing it are light, intermittent or stroking
touches applied to the surface of the body. We must again
distinguish between stinmlation of a surface furnished with hairs,
such as the back of the hand, nape of the neck, etc., and those
surfaces that are hairless, such as the sole of the foot, dorsum of
the tongue, back of the throat, etc. In the former case, even a
gentle touch applied to the end of a hair, 'provided it is sufficient to
bend the hair, gives rise to a short burst of electrical waves along
the sensory nerve, and adaptation occurs rapidly, i.e. the receptor
is of the phasic type. Histological examination shows that the
hair acts as a lever transmitting pressure to the tissue surrounding
its root, in which are embedded arborisations of sensory nerve

TICKLE AND PAIN

23i)

fibres. The hairless surfaces when touched only give rise to a
sensation of tickle when the touch is intermittent or strokintv. It
need not necessarily be light, e.g. the sole of the foot may be tickled
intensely by rubbing vigorously with a hard nail brush (Greig).
The receptors for this type of stimulation arc also phasic, and
depend on pressure in the sublying tissues (Fig. 01).

The muscles at certain places are extremely sensitive to inter-

PACINIAN

CORPUSCLE

D££P PK£SSL:-Z)

NERVE

£ND BULB
KR/^ use's
'HEAT OR COLO '1

M£ISShl£RiS

\ corpuscle
(touch)

NERVE PLEXUS
OF A HAIR.

I NERVIL

NERV£

fJ£Rve PLEKUi
f'ROM CORI^EA

I pain)

Fig. 61. — Various types of receptors found at or near the surface of the body.

mittent pressure, e.g. at ribs and knees. Here the stimulus is
distinct pressure, and is allied with the sense of pain. Continued
tickling has been used as a means of torture by Eastern peoples.
Simon de Montfort is said to have put the Albigenses to death by
tickling, and a certain Anabaptist sect, unwilling to shed blood,
are reported to have used this method of executing offenders.

3. Pain is aroused by mechanical, thermal or chemical stimuli
of sufficient intensity, and is considered by some to be caused by
overstimulation of any receptor, e.g. too loud a sound, too bright a

240 OUTPOSTS OF THE INTELLIGENCE SERVICE

light, too hot or too cold an object touching the body. Recent
work, however, leads one to the conclusion that although abnor-
mally intense stimuli may cause a painful sensation, there are
specific receptors for pain. For example, pain spots may be
demonstrated in the skin, in much the same way as touch spots,
using a needle in place of a soft bristle. Further, pain may be
elicited by the stimulation of surfaces known to contain no other
receptors, e.g. cornea. The electrical response on stimulation of a
pain spot is of similar frequency (5-100 a second) to that produced
by touch. It differs in its duration and intensity. A slight pain
would be one accompanied by an electrical discharge lasting, say,
1 second, while the discharge during acute pain may last about
20 seconds. Touch produces an electrical burst lasting about
0-2 second. It may be that a brief discharge passing along a
nerve fibre is the sign of the passage of a nervous impulse producing
a change in consciousness which we have learned to associate with
touch, while a longer discharge in the same fibre signifies pain.
This is not true of all touch receptors. For instance, Meissner's
corpuscles never give rise to pain when stimulated. The naked
terminations of nerve fibres arborising in the skin may, as Sherring-
ton suggests, act as receptors for touch and pain — -touch when the
stimulus is slight, and pain when it is massive.

Pain may be produced by direct stimulation of the nervous
system, either by the application of induction shocks, by mecha-
nical force (pulling, tearing, pressing, etc.), or by chemical
means (drying, application of solutions, etc.), and in this case the
intensity of the pain depends on the number of nerve fibres in the
nerve trunk stimulated. The central sensory area may also
receive painful stimulation without the apparent intervention of
specialised receptors. A rise in blood pressure, for example,
results in a headache relieved by the administration of a vaso-
dilator. Pain, then, may be considered as allied to both touch and
pressure, but possessing the characteristic of a massiveness in the
electrical variations accompanying its transmission to the cortex.

II. PHASIC-POSTURAL RECEPTORS

4. Pressure. The receptors for pressure are more of the ijostural
than of the phasic type. That is, a single continued stimulation
produces a prolonged sensation. In fact, the sensation outlasts
the stimulus by quite an appreciable time. Absolute sensitiveness
as indicated by a sense of pressure is generally determined by
finding a minimum pressure necessary to evoke a minimal sensa-

PRESSURE AND TEMPERATURE

2U

tion. 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 XXXIV.). Practice may increase
the discriminating point. Every one knows how a blind man
" sees " with his fingers.

TABLE XXXIV.

Tougue 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 foot

28

Back of the forearm .

33

Gluteal region ....

48

Adrian and Zotterman have shown that the electrical discharge
in the sensory nerve supplying the toe-pad of a cat varies in fre-
quency with the intensity of the pressure applied to the pad and
with the rate at which the pressure is increased. The frequency
declines when the pressure is kept constant, i.e. adaptation takes
place. The rate of decline is not, however, as rapid as in a truly
phasic unit, but is more rapid than in a typical postural unit like
the muscle-spindle {q.v.).

5. Temperature. 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 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 XXXV.).

TABLE XXXV.

Back
Leg

Thigh

Back of foot
Cheek
Temple .
Palm of hand
Back of hand
Arm

0-9

0-6-0-2

0-5

04

04

0-3

0-3
0-2

10

242 OUTPOSTS OF THE INTELLIGENCE SERVICE

III. POSTURAL RECEPTORS

In this class fall the receptors in muscles, tendons and joints,
the proprioceptors of Sherrington's classification. They convey
information to the central nervous system about the position of
the limbs, etc. (To this group also belong the organs which have
to do with the sensations of equilibrium, which will be considered
in the next chapter.) Of their physics nothing is known. Recently
Adrian has studied the electrical variations in the sensory nerves
supplied by them and finds that the electrical discharge is con-
tinuous with the stimulation for quite a long time. That is,
adaptation is slow. A frog's muscle spindle may continue to
discharge impulses for 10 minutes or more when a steady stretching
force is applied to the muscle during that time. (See also the
vestibular apparatus at the end of the next chapter.)

IV. SPECIAL RECEPTORS

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.

6. Taste. The end-organs for the sense of taste, the so-called
taste-buds, are found on the tongue except in the mid-dorsal
region, on both the anterior and posterior surfaces of the epiglottis,
on the inner surface of the arytenoid process of the larynx, on the
soft palate above the uvula, on the anterior pillars of the fauces,
and on the posterior wall of the pharynx. They differ in structure
and markedly in threshold value with their position. For instance,
at the tip of the tongue the structure of the end-organs is such that
substances like sugars, amino acids, etc., penetrate easily into the
cells surrounding the nerve endings and cause the liberation of
something which stimulates the terminations of the nerve. Bitter
substances, like quinine, saccharine, etc., affect the receptors near
the back of the tongue, the hydrogen ion finds a lower threshold
in the receptors at the sides, while chlorides and other salty anions
are catered for by end-organs all o^'er the surface of the tongue.
Most work has been done on the receptor structures at the tip and
on the sides of the tongue.

Sweetness. This has been investigated almost solely from the
chemical standpoint, and the result has been the drawing up of
two lists of groupings, e.g. gluciphores and auxoglucs. A substance
is sweet, i.e. capable of penetrating the cells and stimulating the

TASTE

243

special end-organs at the tij) of the tongue, if it contains both a
ghiciphoric and anxoghic grouping. The classification is not quite
satisfactory. Progress will be made when the problem is attacked
by physical chemists from the aspect of permeability, much in the
same way as we shall see has been done for sour tastes.

Sourness. This sensation is produced when acids penetrate
certain cells on the sides of the tongue. The threshold value for
sourness does not depend on the strength of the acid alone. For
example, acetic acid, a weak acid, is able to affect the cells at a
H ion concentration less than that necessary for strong acids like
HCl, HNO3, etc. This is probably due to the greater penetrating
power of the weaker acid in an undissociated state. It then
dissociates in the cell, liberating H ions to act on the end-organs.
In the following table, XXXVI., is given a list of some organic
acids with their minimum concentration just to be appreciated as
sour, i.e. threshold value (from Taylor), and with the concentration
gradient necessary to produce a pYi of 5-6 in Ckromodoris tissue
in 20 minutes (from Crozier, 1916).

TABLE XXXVI.

Thieshold Value for Taste.

Penetration.

Concentration.

Ae-id.

Concentration
X 10— ' N

H Concentration

X 10— 'N

Concentration.
X 10— 'N

H Concentration
X 10-' N

Formic

18

5-5

33

7-5

Oxalic .

20

11-6

10

9-5

Tartaric

22

7-0

33

10-5

Acetic .

28

2-8

188

5-8

Lactic .

28

11-7

52

7-9

Succinic

32

34

42

3-6

Butyric

35

2-7

93

3-6

It will be seen from this table (1) that weak acids, like acetic,
butyric and succinic, are effective at a remarkably low H^ con-
centration, both in causing taste and in penetrating tissue ; and
(2) that the introduction of a hydroxy group generally (not always)
decreases the power of stimulation and penetration, e.g. lactic
acid (hydroxy-propionic) is about half as active as propionic acid,
and salicylic about one-third as penetrating as benzoic acid.
Carbonic acid, which may be considered as hydroxy-formic acid,
apparently is an exception to this generalisation, as it is about
fifty times as active as the fatty acid. This is probably due to its
passage into the tissues not as HgCO.,, but as COo? ^vhich is soluble

both in water and in fats.

ic— 2

244 OUTPOSTS OF THE INTELLIGENCE SERVICE

That only four kinds of taste can be recognised is readily under-
stood when consideration is given to the four types of receptors,
each with a lower threshold for one particular form of chemical
stimulation. Some substances are able to stimulate more than one
group of gustatory end-organs. For example, saccharine pene-
trates and stimulates the receptors at the back as well as those at
the tip of the tongue. It is, therefore, perceived as both bitter
and sweet. In the same way, acetate of lead is sweet and sour ;
acetone, sweet and bitter ; potassium sulphate, bitter and sour ;
magnesium chloride, bitter and salt, and so on. Then other tasty
solutions are mixtures of substances, each stimulating at a different
part of the tongue, i.e. a compound stimulation. Proof of this
fourfold taste coniplex has been obtained in man by stimulating
the afferent nerve fibres for taste in the chorda tympani of an
individual with a fistula in his ear. Trials were made at different
times and by various direct means of stimulating the nerve, and,
in every case, the subject reported sensations of sweetness, sour-
ness, bitterness or saltness only. One must conclude, in view of
Adrian's work, that we differentiate between tastes not so much
because a different stimulus is applied, but because it is applied
at a different place, i.e. a primary analysis takes place at the end-
organ. As far as one can judge, the nature of the nervous impulse
is the same for all tastes and, therefore, final analysis must take
place in the sensory centre. That is, we appreciate the difference
between sweet and bitter, say, in the same way as we differentiate
between a touch on the arm and a similar stimulus applied to the
calf of the leg.

7. Smell. The sense of smell added to that of taste contributes
in large measure to the pleasures of the table and serves as an
excellent substitute-stimulus for the fiow of saliva and gastric juice
(conditioned reflex). Flavours, as a matter of fact, are olfactory
and not gustatory stimulants. If we lose our sense of smell, say
by a cold in the nose or by experimentally preventing the entrance
of gases into the upper nasal passage, much of our food seems to
become tasteless. We are unable in these circumstances to tell
whether Ave are chewing raw potato or raw apple.

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 arc small rectangular strips in the upper part of each
nasal cavity, just above the superior turbinate bone. In ordinary
respiration, air docs not pass directly over the olfactory mucous

SMELL

245

membrane, but some air diffuses backways throuji^h I lie j)ostcrior
nares (Fig. 62, upper portion). This is important for the preserva-
tion of the sense. The receptor neurons have retained their
primitive condition of cell l)ody 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

OLFACTORY BULB

OLFACTORY EPITHEUUM

OPENING OF

EUSTACHIAN

TUBE

ARYTENOID

HYOID BONE
THYREOID CARTILAGE-'
EPIGLOTTIS-''

VOCAL CORD-'

' CE50PHAGUS

TRACHEA--

Fig. 62. — Diagram of antero-posterior section througli nasal fossw, moutli and neclc. In
the upper portion of the figure tlie arrows show the direction of the air ('urrents during
inspiration. The soft palate should, of course, be down to allow of the passage of air. The
lower portion uf the diagram represents the position of the structures during the act of
swallowing.

with high concentrations of odoriferous substances and, further-
more, 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
gram per litre of air, can be detected. Training renders the sense
more acute. The working chemist relies on his sense of smell to

246 OUTPOSTS OF THE INTELLIGENCE SERVICE

a great extent to lielp him in the identification of compounds.
The tea blender and the wine expert can detect very shght differ-
ences in " flavour."

It is worth while noticing that receptors all depend for stimula-
tion on the existence of an alteration in external energy. This
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 which have, for the time being, become
permanent in their environment. A room may be stufl'y to an
incomer but quite comfortable to the tenants. The physiological
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.

The primary odours are (i.) flowery (violet), (ii.) fruity (lemon),
(iii.) spicy (nutmeg), (iv.) resinous (frankincense), (v.) putrid (H2S),
and (vi.) burning (tar). Other olfactory sensations are mixtures
of two or more of these, e.g. vanilla = (i.) + (ii.), garlic = (ii.) + (v.),
and so on.

How do these substances produce a stimulation of the olfactory
epithelium ? The present idea is that in the gaseous state they
produce a series of waves in ether, part of the electro-magnetic
spectrum, having frequencies much greater than those of light.
This is quite plausible, as odorous substances belong almost
exclusively to the fifth, sixth and seventh groups of the periodic
classification, in which the elements are characterised by the
possession of variable valences , i.e. can set free electrons. The
" strength " of a smell appears to be related to the speed of
rotation of the valence electrons (Chap. XIII.). It is interesting
to note that ultra-violet light, which is known to have the property
of stabilising these substances by destroying the double bonds in
them, also destroys their odour.

8. 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 bv which the lack of nourishment
is signalled to consciousness. The evolution of knowledge of this
sensation is largely due to 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

HUNGER 247

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 indivi-
duals— headache in one and faintness in another, for example —
indicates that they do not indicate the central fact of hunger,
but are more or less 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, therefore, as
the constant characteristic, the central 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
transport (Chap. XXVIII.), 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.

248 OUTPOSTS OF THE INTELLIGENCE SERVICE

The signilicanee 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 alimen-
tary 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."

Further Reading

Adrian. " The Basis of Sensation."' Christopliers.

Cannon. " Bodily Changes in Pain, Hunger, Fear and Rage." Apj)leton

Harris. "The Functional Inertia of Living Matter." J. & A. Churchil]

CHAPTER XX
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-Hke appendages, either on the free surface or
in a depression, more or less protected. In the higher vertebrates it
is a nmch more complicated structure. The human organ of hearing
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 move-
ment of a hinged piston-like lever and the accentuation of
these movements.

Part of internal ear — transformer of mechanical pressure, via
hydraulic pressure, into touch stimulus.

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. 63).

(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 twofold, (i.) On account of its shape,
secretion, and hairs (at orifice) it protects the delicate tympanic
membrane from draughts, dust, and from the incursion of insects,
and maintains an equable temperature. These are its main
functions, (ii.) The sound waves are conducted by reflection from
the walls without loss of intensity, and directed almost per-
pendicularly on to the drum which lies at an angle of 150° to the
axis of the canal.

249

250 OUTPOSTS OF THE INTELLIGENCE SERVICE

2. Middle ear. The mechanism found m the middle ear converts
vibrations in air into vibrations in fluid by means of membranes
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 car by the tympanic membrane, and 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

Fig. fi3. — Diagrammatic view of auditory organ. (After Scliafer.)
1, Auditory nerve; 2, internal acoustic meatus; ;?, utricle: 4, semicircular duct;
.5, saccule; 6, .scala media of cochlea; 9, vestibule containing lymph; 10, semicircular
canal ; 12, stapes ; 13, fenestra rotunda ; 19, incus ; 18, malleus ; 17, niembrana tympani ;
16, external acoustic meatus ; 14, auricle or pinna ; 23, Eustachian tube.

filling the foramen 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.
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

MIDDLE EAR 251

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 (umbo). 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."

Hence it may be shown that " 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

252 our POSTS OF THE INTELLIGENCE SERVICE

regulating the action of the le\'er, as the force which fibres exert
upon the handle of the malleus increases, aniphtude 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

-SUPERIOR. LIGAMENT OF^MALLEUS

ANTERIOR LIGAMENT OF MALLEU5

i^ORT PROCESS <y
POSTERIOR LIGAMENT
OF INCUS

LONG PROCESS OF 1NCU5

EMINEtlTIA PYRAMIDAL15
TO WHICH THE TEMDON OF
M. STAPEDIUS IS ATTACHED

^=^S= M. TENSOR TYMPANI

^^ SEPTUM CANALIS
MUSCULOTUBARII

MANUBRIUM MALLE.I

Fig. 64. — 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 inciis. 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.

the fluid of the internal ear. The Malleus, or hammer, is about
18-19 mm. long, and has an average weight of 23 mg. 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 miibo. Near the insertion of the head and
handle arises a bony process — the processus gracilis 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 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

TYMPANIC OSSICLES 2.):i

rotating on any other axis than a horizontal one whose line
passes through the head of the malleus and the anterior ligament
(Fig. 64). The posterior surface of the head of the hanniier 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 aN-erage 25 mg. 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
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 mg., is set almost at right angles to the
long process of the incus. Its oval footplate is attached to the
margin of the fenestra ovalis by a short stiff membrane, the annular
ligament.

Muscles oJ 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 on the fenestra ovalis. Its line of
traction (Fig. 64), 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 nmscles prevents a slack engagement

254 OUTPOSTS OF THE INTELLIGENCE SERVICE

between the ossicles. If the bearings were not kept together with
sufficient force, sUpping, 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
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. XXVIII.), 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. 62 and 63),

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. 64
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 mamibrium will cause the head of
the malleus to swing outwards, carrying with it the upper part
of the incus and so mo^'ing the long process of the incus in the same

MECHANISM OF MIDDLE EAR 255

direction as the mcmubrhnn. 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
Helmholtz, the distance p^ — a is 9-5 mm., and i — a is 6-3 mm. The
movement at i therefore will be only two-thirds of the move-
ment 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 (loAver annular ligament) to d the centre of the
foot of the stapes, and c — i the distance from the tip of the long
process of the incus to the lower end of the stapes, then the range of

motion of the centre of the foot of the stapes will be -, r:

{c-i)

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 verv 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

* a = junction of dotted line witii the axis .4 — B ; i = tip of lony process of
incus ; p = point of application of power, i.e. tip of manubrium mallei (Fig. 04).

256 OUTPOSTS OF THE INTELLIGENCE SERVICE

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
as not less than 1^ — 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 modiohis 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 extend-
ing from the modiolus about two-thirds 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 fenestra
rotunda does similar service to the lower duct, the scala tijmpani.
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. 65). 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 ynembrane,
which divides it from the vestibular duct. The short side is
separated from the outer wall of the osseous 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 tjpnpani 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 conmmnication exists
between the scala media and any other part of the cochlea. There

INTERNAL EAR

257

is a narrow tube, the canalis reuniens, which runs from this duet
to the saccule — part of the organ for maintaining eciuihln-ium.

The reason for the attention that has been directed to the scala
media is that the cochlear division of 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

Fig. 65. — Vertical section oi the first turn of the human cochlea (G. Retzius).
s.v, scala vestibuli ; s.t, scala tj'mpani ; D.C, scala media ; sp.l, spiral lamina ; n, nerve
fibres; /.sp, spiral ligament ; .s//-.c, stria vascularis ; ?K.f, membrana tectoria ; ft.;?;., basilar
membrane ; /;.;', and h.e, internal and external hair cells ; R, section of Keissner's membrane ;
t.C, tunnel of Corti ; Z, limbus laminae spiralis.

elements. (1) Certain columnar cells with short stiff hair-like
processes projecting from their free border, the hair cells, to which
pass, as we 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 {membrana tectoria).

The arch of Corti, which lies just outside the single row of inner

B. 17

258 OUTPOSTS OF THE INTELLIGENCE SERVICE

hair cells, is composed of a row of inner " rods," shaped like ulnar
bones, attached by their terminal end to the basilar membrane, and
fitting on to the heads of the outer " rods." The latter resemble
swan's 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 communicated
by the perilymph to the membranes of the sccda 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. The only
structures placed so that their movements can be transmitted to
these hair cells are («) the basilar membrane, {b) the tectorial
membrane, and (c) the pillars of the arches of Corti. We may
dismiss Corti's arches as the basis whereby fluid motion is converted
into the movements of the hairs, because the cochlea of birds is
free from them. Opinion is sharply divided as to the comparative
importance of the two membranes. Because of its structure,
position and marked differentiation at different levels, most
modern investigators are of the opinion that the basilar membrane
plays the more important part.

Several theories have been put forward as to the mechanism of
the inner ear. The most important are (i.) the resonance theory
associated with the names of Helmholtz, McKendrick, Hartridge
and Wilkinson; (ii.) the displacement theory of Wrightson and
Keith; and (iii.) the pressure-pattern theory of Rutherford as
elaborated by Ewald.

Resonance Theory.

Although Helmholtz was not the first to suggest that possibly
the fibres of the basilar membrane acted as resonators like the
strings of a piano, he may be considered the originator of this
theory, as he worked out a connected theory of hearing based on
the physics of sympathetic resonation.

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

RESONANCE THEORY OF HEARING

250

higher particles under the supposed conditions, would fall to the
lot of different nerve fibres, and hence l)e produced perfectly,
separately and independently. Now, as a matter of fact, later
microscopic discoveries respecting the internal construction of
the ear, 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 radial fibres of the basilar membrane
constituted 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 sub-
stance (Fig. 66).

To quote again from
Helmholtz, " If the
tension in the direction
of its length is infini-
tesimally small in com-
parison with the tension

in the direction of its fig. 66. — interior of right cochlea (human) expo.sed to show

(«) modiolus, (b) ba.silar membrane, and (c) lamina spiralis
breadth then the radial seconuarlus. Between («) and (6) is the lamina spirahs. (E. M.
' ., F'aul.)

fibres of the basilar

membrane may be approximately regarded as forming a system of
stretched strings, the membranous connection only serving to give
a fulcrum to the pressure of the fluid against these strings. In
that ease the law of their motion would be the same as if every
individual string moved independently of all the others, and
obeyed by itself the influence of the periodically alternating
pressure of the fluid of the labyrinth contained in the vestibule
gallery. Consequently, any exciting tone would set that part of
the membrane into sympathetic vibration, for which the proper
tone of one of its radial fibres that were stretched and loaded with
the various appendages already described corresponds most nearly
with the exciting tone ; and thence the Aibrations will extend
with rapidly diminishing strength on to the adjacent parts of the
membrane."

That is, three factors are implicated, viz. length, tension and

17—2

260 OUTPOSTS OF THE INTELLIGENCE SERVICE

mass, by variations in which a range of 16 to 20,000 complete
vibrations per second could be detected.

Length. It is clear from Fig. 66 that the fibres progressively
increase in length from base to apex. Various estimates have been
made of the length of the fibres and values ranging from 0-041 —
0-495 mm. (Hensen) to 0-176 — 0-4 mm. (Keith), i.e. according to
Hensen there is a twelve-fold increase in size, while Keith and other
modern workers give only a fourfold variation. If the fibres
varied in length alone, a thousandfold variation would be necessary
to provide resonators tuned to the highest and the lowest note
perceptible.

Tension. Reference to the figure (66) will show the presence in
the spiral ligament of radiating fibres attached at one end to the
outer wall of the cochlear galleries, and at the other end running
in a direction continuous with the basilar fibres to which they are
attached. At the basal end the ligament is about 0-5 mm. thick,
and is full of closely-packed fibres, while at the apical turn it is
only about 0-1 mm. thick and contains only a few fibres. Gray
and Wilkinson consider that the function of these fibres is to exert
a progressively increasing tension on the basilar fibres — applying
the greatest tension where the fibres are shortest and thus raising
the pitch of the resonators responding to the high notes, and least
on the longer fibres, i.e. making them capable of resonating to
notes lower than they would accept if stretched. (Cf. vibration of
stretched string.)

Mass. Most investigators consider that the progressive varia-
tion in the length and in the tension of the fibres of the basilar
membrane is sufficient to account for the 10-| octaves of the audible
range, but Helmholtz vaguely suggested a third physical factor,
the load on the fibres. The load is made up of two components,
viz. (i.) the organ of Corti and appendages, and (ii.) the endolymph
or fluid load. The main reason for postidating load as well as
tension and length is to explain why we can hear very low notes,
e.g. 15-30 vibrations per second. The variation in tension seems
adequate for the higher frequencies, but when we come to the lower
ones we would need to have very slack strings as resonators on
account of their shortness, (i.) The weight of the arches of Corti,
the hair cells, sustentacular cells, etc., loads the fibres of the
basilar membrane, and so increases their period of vibration.
(ii.) Wilkinson considers the fluid load as of fundamental import-
ance. He has constructed models to demonstrate his case, and,
if we can accept models as evidence, then he has gone far to prove
the correctness of his assumption. The essential feature of his
modification of the resonance theory is that the fluid filling the

DAMPING 261

cochlea acts as a progress! \cly graduated load on the basilar
libres. " Supposing a small traiisxerse sector of the basilar
membrane to mo\ c from its central position towards the scala
tympani, its movement will displace a certain amount of fiuid, and
the displacement will travel along the scala till the membrane
closing the round window is bulged to an extent sullicient to
accommodate the amount of fluid displaced. It follows that an
equivalent quantity of fluid will be displaced across each cross-
section of the scala from the level of the vibrating sector to that
of the round window. The mass of the fluid moved will equal
that of a column the base of which is equal to the area of the
vibrating sector, and the height to the distance from the sector to
the round window. A similar mass of fluid will be displaced in the
scala vestibuli, but in the opposite direction " (Wilkinson). The
mass (weight of double column) progressively increases from the
base to the apex of the cochlea. This Avill cause a differentiation
in the periodicity of the vibrations in the same sense as the varia-
tions of length and tension, i.e. length and mass are greatest on the
longer fibres, while tension is greatest on the shorter fibres.

Now if we consider the mean length of the basilar membrane as
35 mm., we may state as an approximation that the shortest
distance (following round the inner curve of the scalae) between
the longest fibre of the membrane and the windows woidd be
2 X 20 = 40 mm. The distance between the windows and the
shortest fibre is about 2 mm., i.e. a twenty-fold variation in fluid
load is possible.

Damping. Some mechanism must exist to prevent a resonating
fibre from continuing its vibrations after the stimulating sound
has ceased. Hartridge has devised many demonstrations of the
presence of dampers. In one experiment he used a siren arranged
to produce instantaneously a change of phase of half a wave-length
in the successive pulses emitted by it. When the change of phase
occurred, there was apparently a period of silence. That is, at that
moment, the resonators were damped before a fresh set of resonators
took up the new vibrations.

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.

(3) If one ear be fatigued by prolonged stimulation from a

262 OUTPOSTS OF THE INTELLIGENCE SERVICE

constant note, its response to the same note is found to be
inhibited, but notes of sHghtly higher or lower pitch are readily
heard.

Against this theory are arrayed most psychologists and not a
few physiologists and anatomists. They find in it no adequate
explanation of certain phenomena, e.g. :

(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 one-fifth that
of the mammal, but has numerous hair cells. These cells are set in
the bird in rows of thirty or forty, and in the mammal in rows of
four. 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) The fibres of the basilar membrane are not separate struc-
tures, but are bound together so that we have to deal with a
triangular sheet of membrane with the tension applied across the
shorter distance. Such a sheet, as we shall see when we consider
the pressure-pattern theory, does vibrate as a differential resonator.
As a matter of fact, Helmholtz met this difficulty by calculating
that a uniform membrane in which the tension was greater from
side to side than longitudinally w^ould answer in the same way as
a series of fibres as his theory required.

Displacement Theory.

The latest form of this theory is put forward by Sir Thomas
Wrightson, an engineer. He is supported by Sir 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, wath 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 THEOR V

263

hdicolrcma. He believes thaL the luiir eells and not the basilar
niembraiic are the sensitive organ. They pass throngii the meshes
of the reticulate membrane, and, according to Wrightson 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-fro 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 succession
of bendings of the innumerable hairlets can be obtained to convey
to the auditory nerve every impulse required to produce 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 mem-
l)rane, 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 reach-
ing it simultaneously, and it does not give a very clear explana-
tion of " tone-gaps," nor does it explain why fatigue to one note
leaves the response to all other notes apparently unaffected in
intensity.

Pressure-Pattern Theory.

This theory, originated by Waller and elaborated by Ewald, is
based on the sand and powder patterns produced on vibrating
plates (Fig. 67) (see Chladni's plates. Chap. XVII.). The pattern
traced by the sand depends on three main factors : (1) the part of
the plate where the vibrations start, (2) the parts of the plate that
are fixed or damped, and (3) the frequency of the induced vibra-
tions. Ewald showed that the membrane in his " acoustic
camera " vibrated like Chladni's plates, and that the distance
between the nodes varied with the pitch of the note entering the
camera. The sand comes to rest on the nodal lines, or lines of rest,
and makes a pattern, so translating a sound figure into a light

Fig. 67. — Chladni's plate.

264 OUTPOSTS OF THE INTELLIGENCE SERVICE

figure. A light powder like lycopodiuni, on the other hand, is
caught up in the air whirling above the moving parts of the plate
and comes to rest in heaps where the greatest movements of the
plate have been.

Ewald used a rubber membrane stretched over a frame and
innnersed in fluid. Instead of producing figures in sand, he smeared
the surface of the rubber with oil and examined it under oblique
illumination by means of a very low-power microscope set at an
angle. The acoustic images so produced can readily be photo-
graphed, and are found to be characteristic for each note sounded
near the apparatus. These images produced on the basilar
membrane cause some hair cells to move and so transmit a
stimulus to the fibres of the cochlear nerve with which these cells
are richly provided. (According to some investigators, the moving
part is the membrana tectoria, which by coming against the hairs
of the cells excites the nerve fibres.)

This theory and that of Helmholtz have this in common, that
the primary analysis of the sound takes place in the ear. This is
as one would expect from a study of all other external receptors,
and, as is the case with the other receptors, the ultimate analysis
must take place in the cortex. This final analytical act is not an
inborn process, but is acquired through experience.

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."

Intensity. Sounds differ not only in pitch, but in loudness and
in quality. We must go to Adrian's experiments to find out how
the ear differentiates between sounds differing in intensity. It
has been found that the frequency with which the electric impulses
pass towards the sensory centre when a sensory nerve fibre is
stimulated, varies with the intensity of the stimulation. That is, a
loud sound of a certain pitch would cause a rapid succession of
impulses to pass along certain fibres of the cochlear nerve, while
less intense sound of the same pitch would produce probably only
a single volley of impulses. Now although these sounds were
])rodueed, say, by the same tuning fork, vigorously banged or
gently touched, and, therefore, of the same pitch, the louder sound
would appear to us to be of higher pitch than the less intense
sound. This is due to the more intense sound producing some
vibration in the hair-cells lying nearer the entrance of the disturb-
ance into the cochlea, i.e. nearer the base where the fibres are

DIFFEREXritrrOX OF SOUNDS 265

shorter. This may be shown clearly on a iiuxlel ear built to
demonstrate either Helmholt/Zs or Ewakrs tlieory.

Timbre or (-liiality. Most sound-producing instruments impart
a characteristic quality to the sounds emitted by them. Anyone,
for instance, could tell whether a specific note were produced from
a piano, a violin, a pipe-organ, a harmonium, etc. This is due to
the fact that not only does the instrument vibrate as a whole, but
each individual part tends to vibrate in a characteristic way.
These partial viln-ations give rise to overtones, which impart
quality to the production in accordance with their number, their
pitch and their relative intensities. The ear, therefore, has no
need to develop a special mechanism for the purpose of appreciating
timbre.

We must now consider the physical reasons for the peculiar
shape of the cochlea. Why should it take two and a half turns up to
the helicotrema, and why should it be a double body, e.g. scala
media sandwiched in betw^een the sccdae vestibuli and tiimpani?
If the cochlear tube w^ere straight, having at one end the oval
window with the stapes and at the other the round window with
its compensating membrane, the floor of the tube being the basilar
membrane with appendages, and the tube being practically of
uniform width throughout, w^e would ha\-e a receptor capable of
the maximum distortion possible, and also liable to have induced
in its fluid ripples and changes of pressure due to physical changes
other than sound waves. Every time that we started to move
our heads in space with or relatively to our bodies we would cause
a movement of the cochlear fluid and w^ould receive the sensation
of sound. The same thing would happen every time we changed
either our rate of movement or its direction. What a deafening
crash there would be when we violently applied negative accelera-
tion, e.g. express train stopping suddenly. This disadvantage
could be overcome partially by bending the tube into a U with
the two windows close together. A stricture at the bend of the U
would further help matters. We would now be able to move
linearly in any direction and alter our rate of progression without
hearing about it. An angular displacement would still disturb
hearing, especially if the movement were at all rapidly initiated or
stopped. The winding of the tube into a narrow spiral gives us
an organ of hearing containing a liquid that undergoes very little
relative displacement with the ordinary movements of the body.
It still tends to generate sounds when extraordinary motion or
acceleration is applied to the body.

The double nature of the organ is a structural necessity. The
basilar membrane must vibrate in some fluid (gas or liquid)

266 OUTPOSTS OF THE INTELLIGENCE SERVICE

medium. As fluid lills the space on one side of the membrane,
efficiency demands a fluid on the other side. One may also say
that the separation of the scala media from the scala vestibuli
enables (i.) damping to take place readily, and (ii.) a simpler and
more efficient balance-organ (labyrinth) to be constructed.

Binaural Hearing.

Quite apart from the undoubted fact that having two ears
enables us to hear more distinctly and allows of the damage of one
ear without completely shutting us out from the variations in
external sound, the possession of two listening points alone permits
of the localisation of sound. The head is oriented so that an equal
intensity of sound falls on each ear, i.e. if our ears are equally
sensitive, we face the sound — we are positively audiotropic
(Chap. XXXIII.).

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 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 membrane
is flaccid, sounds may be heard by bone conduction, and ordinary
hearing is not impossible. The vibrations are transmitted directly
through the thick, exceedingly dense but elastic bony walls of
the aural cavity, and produce a movement of the basilar mem-
brane, 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.

UTRICLE ANT) SACCULE 267

Further, if both the slopes and round nuMnl)r<uu' wci-c free to
move, hearing' in the ease of a diseased middle ear would not be
so good as when t>nly one ol" 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. Peo{)le may hear fairly well after the stapes has
become inmiovably 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 car 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, if a vibrating tuning-fork is placed on
the region of the interparietal suture, when both ears are un-
obstructed 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. When both ears are treated
in this way, localisation is again median. A conuuon 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 transmitted through the parietal bone direct to the fluid of the
cochlea.

Balance.

The ear is a double organ. We have just dealt with its function
as the receiver and analyser of certain vibrations in matter trans-
mitted to it generally through the air, but capable of transmission
through much denser media. The other and more ancient function
is that of giving information as to (i.) the position of our head in
space, and (ii.) the acceleration of the head in space.

Structure (Fig. 63). The vestibule (Fig. 63 (9) ) and the semi-
circular canals (10), like the cochlea (6), are double organs. The
outer or osseous part is hollowed out of the substance of the bone,
lined by periosteum and filled with perilymph in which the mem-
branous part is placed. The various parts of the membranous
labyrinth, viz. {a) utricle and saccule, contained in the vestibule,
(6) three semicircular ducts, with their ampullae, in the osseous
semicircular canals, and (c) the scala media in the cochlea are filled
with endolymph and are in fluid connection with one another.
The semicircular ducts open into the utricle, the utricle into the

268 OUTPOSTS OF THE INTELLIGENCE SERVICE

saccule through the ductus cndohjiuphuticus, and the saccule into
the scala media through the cattali.s rcunicns. Ner\'e fibres from
the vestibular division of the auditory nerve end in naked fibrils
between the hair-cells of the maculae of the utricle and saccule
and of the cristae ampullares of the semicircular ducts. The
maculae and cristae are little thickenings on the internal surfaces
of these cavities, one in each. The epithelium on the surface of
the humps is columnar, and consists of (i.) fusiform supporting
cells, the free ends of which unite to form a thin cuticle, and
(ii.) flask-shaped hair-cells, whose free ends are surmounted by a
long, tapering, hair-like filament. Two small rounded calcareous
bodies termed otoconia, or otoliths, lie in contact with the free
ends of the projecting hairs of the maculae.

Mechanism of Utricles and Saccules.

It is obvious that any movement of the hairs will cause a

Fig. 68. — Eabbit's skull with oriented magnified models of the utricle and saccule
maculae. Skull in normal position. The suriface of the macula to which the otolith is
attached is indicated in the utricle by white dots and in the saccula by white stripes on the
black I'late. Stereoscopic. (Magnus, " Korperstellung.")

stimulation of the filaments of the vestibular nerve, and that the
otoliths are an excellent means of providing this stimulation.
But the exact way in which this occurs does not appear to be so
simple a matter to determine. The literature on this question
contains somewhere about 2,000 papers, and they do not all
convey the same impression. To begin with, most of the work has
been done on fishes, where operative procedure is simpler than in
the mammal. One cannot directly apply knowledge so gained to
the human being, because the structure and function of the organs
are somewhat different. The present ^'iew, largely due to experi-
ments on the rabbit and other manmials by Magnus, is that an
alteration of the position of the head brought about by allowing
gravity to act on the otoliths causes them to exert a slight pull on
the hairs, and so to induce the passage of a nervous impulse which
in turn affects the muscular tone of the body.

Utricles. The utricle in each ear has one macula with its otolith.

SEMICIRCULAR CANALS 200

The maculae are so placed that when the head (of the rabbit) is
held in its normal position they lie with their hairs vertical,
bearing the otoliths above them. Now. if the rabbit is held so
that the head has turned through 180 degrees and the macular
hairs are again vertical, but the otoliths arc now hanging from them,
it has been found that the limbs are extended maximally. That is,
when the otolith in each macula presses against the hairs, one has
minimal limb tonus, and, conversely, when the otolith in each
macula pulls on the hairs, one has maximal tonus. Degrees of
tonus may be obtained by degrees of rotation.

Saccules. The saccule of each ear has its macula on the inner
lateral wall, i.e. in the normal position of the head (of the rabbit)
the hairs will be horizontal and pointing in opposite directions in
each ear. The macula of the saccule is least stimulated when the
otolith presses against the hairs, and undergoes maximal stimulation
when the otolith hangs vertically from the hairs (cf, utricle).
That is, e.g. when the head is hanging over towards the left side of
the animal, the right saccule will receive minimal and the left
saccule maximal stimulation, producing an asymmetric alteration
of muscle tonus, the extensor muscles of the limbs on the left side
having their tone increased and those on the right side undergoing
diminution of extensor tone, whereby a " righting " action is
developed (Fig. 68).

Semicircular Canals. These structures, of which there are six,
are arranged so that the three on each side are in three planes at
right angles to one another. The two canals, which lie externally
in each ear, are situated in a plane which is almost horizontal in
the erect position of the human head. The two other pairs of
canals are, therefore, vertical, as they are at right angles to the
external canals. The two groups of three canals each are set, as
it were, back to back, i.e. mirror images of one another, so that
any rotatory movement of the head will tend to produce equal and
opposite movements of the fluid pressure in the canals and their
membranous ducts. The ducts running within the osseous canals
occupy about one-fourth of the volume of the canals except where
they are widened to fill the ainpullae, which are bulbous cavities
at one end of each canal (anterior end of external canals and
external ends of anterior and posterior canals). The bony ampullae
are about twice the diameter of the canals, and, therefore, each of
the membranous ducts undergoes an 800 per cent, enlargement.
On the concave side of each membranous ampulla is a thickened
ridge rising almost to the axis of the duet and covered with
columnar cells forming the crista ampidlaris. From the surface of
the crista project long flexible hairs, thicker and more bristle-like

270 OUTPOSTS OF THE INTELLIGENCE SERVICE

than ordinary ciliated epithelium {q.v.), and held together by a
nnicous gelatinous mass so that they cannot move freely in the
endolymph. The hair-cells are supplied with fine filaments from
the vestibular division of the eighth nerve.

The ducts on each side open into the corresponding utricle by
five orifices, i.e. two of the ducts (the anterior and the posterior)
join in a common canal {cms commune) and have a common opening
into the utricle.

Mechanism. The structure of the organ indicates that altera-
tions of the pressure of the viscous fluid in the membranous
ampullae will tend to bend the hairs and, following the same
scheme as in the maculae, will alter muscle tone. When a rotatory
movement round any axis is initiated or accelerated positively or
negatively, positive or negative fluid pressure beyond the normal
will tend to develop in certain ampullae and so produce stimulation
of the cristae. Initiation of rotation, for instance, of an animal
about its dorso-ventral axis, i.e. in the plane of the horizontal
canals, produces t'ne same results as mechanical stimulation of the
hairs with a tiny pledget of cotton wool. Adaptation occiu-s
gradually on continuing the rotation at a steady rate. That is,
like the proprioceptors already studied, adaptation is a slow
process. Any alteration of rate, quickening, slowing or stopping
acts as a fresh stimulus.

It has been shown conclusively by Mach that actual currents
cannot be produced either in the perilymph of the canals or in
the endolymph of the ducts. Maxwell has disposed of the theory
that fluid pressure is developed in the duct and transmitted to the
ampulla. He tied off the posterior end of the external canal
(horizontal) and, after cutting it, raised it so that its plane was
vertical. He then rotated the animal about its dorso-ventral axis
and produced the usual reactions. That is, the animal reacted
normally when it was possible only for fluid to enter the ampulla
from the utricle. The normal mechanism, therefore, for excitation
of the nerve-endings in the cristae is the transmission of fluid-pressure
from the utricle to the ampullae. This pressure is prevented from
rapid dissipation by the narrowing of the duct by eight times as it
leaves the ampulla.

The otoliths of the maculae and the hairs of the cristae are both
capable of responding to angular and linear acceleration. Maxwell
has shown that the otoliths, because of their greater specific
gravity, have a greater inertia than the fluid they displace and,
therefore, are as likely to suffer displacement during rotation as the
endolymph. There is also a physical possibility that during linear
and angular accelerations the utricular fluid would tend to lag and

MECHANISM 271

heap up pressure in some ampulla. Some work on fishes by
Maxwell and others gives an indication that this co-operation is
extremely probable.

The alterations in extensor tone produced by stinnilatino of the
hair-cells of the vestibular apparatus are augmented by stimuli
coming from the muscles themselves, especially from those of the
neck, and by auditory and visual stimulation. The following
sentences taken from " Recent Advances in Physiology " may
make this clear. '' Suppose that a cat hears a mouse moving on
its right. The head is turned to the right ; this alters the centre
of gravity, but as a result of the tonic neck reflex, there is an
increase of tonus in the muscles on the right side of the body,
which preserves the balance by throwing the weight on the right
limbs. Now, because the left limbs are less loaded, they will ])e
the first to move if the animal springs to its prey, so that the cat
will automatically move in the right direction." Compare with
this statement the description given in Chap. XXXIII. of Ham-
mond's heliotropic dog.

Further Reading

Hartridge. In Starling's " Principles of Physiology." J. & A. Churchill.
LovATT Evans. " Recent Advances in Physiology." J. & A. Churchill.

CHAPTER XXI
OUTPOSTS OF THE INTELLIGENCE SERVICE

(r) DISTANCE RECEPTOR FOR LIGHT

THE EYE

" I had rather not describe it at all, so that neither the difficulty of the explana-
tion nor its length might cause me to be hated." Galen.

The following points in connection with light are recalled to the
student's memory.

(1) It can be shown in various ways that light travels in straight lines, e.g.
interception of light by opaque objects.

(2) The path along wliich light travels from each point of a luminous object
is a ray. A collection of such rays converging so as to form a cone is termed
a pencil of rays. When the apex of the cone is at the source of light the pencil
is diven/oif : wlien the reverse is the case, one has a convergent pencil. When
a pencil of rays diverges from or converges to a point 6 metres or more away
(infinite distance) tlie rays are considered to be 'parallel.

(3) The simplest instrument with which to obtain an image of an external
object is a pinhole camera, which consists of a rectangular box. One end of
the camera is made of ground glass, and in the centre of the opposite side is a
pinhole. Rays of light diverge from a luminous object, say an arrow [A — W)
placed in front of the pinhole (0). A divergent pencil of rays proceeds from
the arrowhead A. A certain very small collection of rays from A will pass
through 0, and reach the screen S. The result will be an image A' of A on
the ground glass. Similarly, every other point, RRO and W , of the arrow-
will produce divergent pencils of rays, some of which rays will pass through 0
to give a complete image, A'R'R'O'W . Now as all the rays entering the
camera have passed through the pinhole, it follows that they must liave
crossed at 0, and, therefore, the image will be inverted, viz. ,14' . . . A' . There
is a definite relationship between the relative sizes of object and image and the
relative distances of pinhole to screen 08 and pinhole to object OR. i.e. :

size of image distance OS
size of object ~ distance OR

By varying the position of the screen, the image may be made to vary in
size, and similarly, but in the reverse way, the size of the image depends on
the distance of the object from the camera. By increasing OS or reducing
OR within certain limits, the image nuiy be made larger. When OR is
reduced to a certain size, the pencils of rays coming from the points A and R,
0 and W miss the pinhole with the exception of the most divergent rays.
The image is, therefore, blurred. The further the object is from the camera
(within limits) the more will the less divergent rays from the extremities of the

REFRACTION

273

arrow liave a chance to pass into the camera, producing a well-deHned image.
That is, the pencils from every point of the image consist of parallel rays.

In the pinhole camera the rays of light traverse an optical medium which is
hoiiiof/eiu'ous, i.e. it is identical in its properties at all parts. The rays would
take a somewhat different path if the optical medium were heterogeneous.
For example, the medium might be denser or rarer at one part. When the
ray came to pass through this part it would suffer refraction.

(4) 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 (or away from)
the perpendicular to the surface at the point of incidence. This perpendicular
is called the normal. Snell's Law 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.

Refractive Index. In Fig. 69 PO is the incident ray, OQ the refracted ray,

Fig. 60. — Befraction of incident ray PO at interface AB.

NOM the normal to the interface AB between the media (the upper being

sin PON

the less dense). Then t, — = constant. This constant is called the

sin QOM

refractive index, and is usually denoted by the letter jx.

(5) Reflection. 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.

(6) Lenses. A lens is a portion of any transparent medium bounded by
surfaces that are parts of a spherical surface. The line joining the centres of
the two spheres which bound a lens is called the principal axis of the lens.
There are two main types of lenses, viz. convex and concave. The former
cause rays to converge to a point on the principal axis, whereas the concave
lens causes rays apparently to diverge from a point on the principal axis.
The point to which or from which the rays appear to converge is, i)i the case
of parallel rays, the principal focus of the lens.

Focal Length. The distance between the principal focus and the lens is

B, IS

274 OUTPOSTS OF THE INTELLIGENCE SERVICE

(for a thin lens) its focal length. If the focal lengths are given in metres,
then their reciprocals give the power of the lens in dioptres. For example,
a lens with a focal length of 1 metre is of 1 dioptre : of 2 metres of 0-5 dioptre ;
of 0-3 metres of 3 dioptres, and so on. Convex lenses are positive, and their
power in dioptres is given with the sign -\-. The negative sign is placed with
the dioptric value of concave lenses.

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 con-
vexity of the lens increases. Its brighf)iess 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.

If we now replace the pinhole of the camera with a convex lens, we will
find that we still obtain an image of the arrow on the screen. The introduc-
tion of the lens brings advantages and disadvantages. Two of the chief
drawbacks are chromatic and spherical aberration.

Chromatic Aberration. When white light, which is a mixture of waves of
various frequencies (q.v.), passes through a lens, each monochromatic con-

FiG. 70. — Chromatic Aberration.

stituent is refracted to a degree depending on its frequency. That is, the
refractive index of the lens has a different value for each type of light, and
therefore the different waves, when they strike the bounding surfaces of the
lens, will undergo different deviations. Those of high frequency, violet rays,
are refracted to a greater degree than the slower, longer red rays.

In Fig. 70 the dotted lines represent the path taken by limiting parallel
violet rays, while the continuous lines coming to a focus further away from
the lens represent the paths of the red constituent rays of white light. If the
screen is placed as in the diagram midway between the principal foci for
violet and red rays, the image of the arrow will appear surrounded by a red
and violet lialo.

Chromatic Difference of Magnification. This defect also is due to the
unequal refraction of waves of different frequencies. Not only do the foci
of the various monochromatic components of white light fall on different parts
of the principal axis, but their pencils form different angles with the optic
axis. Thus, rays entering the lens at a considerable angle come to a focus
at a point depending on the colour of the light and therefore the size of the
image produced will also depend on the colour of the light. That is, violet
rays will produce an image smaller than that produced by blue rays, blue
smaller than green, green smaller than yellow, while the largest images will
come from red rays.

These defects may be overcome by the use of a combination of lenses.

DISTORTION DUE TO LENSES 275

convex and concave, made of substances of different refractive index, or by
the insertion of colour filters to cut out a series of frequencies.

Spherical Aberration. Eays of light passing through the peripheral part
of a lens are refracted more than those passing through the central part.
This tends to prodixce distortion of the image at the periphery.
. Curvature of Field is found in all convergent lenses of simple formula. For
example, the lines on a piece of squared paper examined through a positive
lens of about 1 or 2 inches focus will appear definitely curved, all except the
two lines at right angles to one another occupying the centre of the field of
vision. Pliotographs taken with the iris diaphragm wide open, if only a single
lens is used, will exhibit this aberration to a marked degree, e.g. sides of
buildings, etc., will appear curved, each part of the picture will be confused,
being formed by pencils refracted through various parts of the lens.

Spherical aberrations may be avoided by the employment of a lens whose
curvature gradually decreases from centre to periphery, and by placing an
iris diaphragm or stop in front of the lens to cut off peripherally incident
rays.

For a lens (of crown glass) to produce absolutely the smallest possible
amount of aberration it should be biconvex, the radii of curvature of its
surfaces being in the ratio of 1 : 6, the more strongly curved surf ace facing the
incident rays. Such a lens is termed a crossed lens. Crown glass has a
refractive index of 1-5. If a glass with a ^u, = 1-6 (flint glass) were used the
side away from the incident light woidd be flat, i.e. the lens would be plano-
convex.

Comma. Kays coming from a point source form, with some lenses, an
image with a fine tail pointing towards the optical axis — just like an illumi-
nated comma. This aberration is seen easily with the old-fashioned carafe,
which when filled with water acted as a lens. The distortion is due to a
difference in the position of the image produced by different zones of the
lens. If the lens obeys the sine law it is free from comma.

The camera, whether of the pinhole variety or fitted with a good lens and
diaphragm, may produce images which suffer from defects not due to the
optical system, e.g. halation, flare, irradiation and scattered light.

Halation is noticeable only when the photographic plate or screen is
sutticiently thick for the image formed on the surface to be reinforced by a
reflection of the image from the internal glass surface, so producing a blurred
outhne or halo. Photographic films, owing to their thinness, do not exhibit
halation noticeably.

Flare is due to the illumination of the screen by light reflected from the
internal surfaces of the compound lens. It is least when the refractive indices
of the heterogeneous optical medium are almost identical and when the light
passes through the lens along the optic axis. The greater the angle of
incidence of the rays and the greater the dift'erences in refractive index of the
components of the optical medium, the greater will be the possibility of
flare.

Irradiation is the spreading of the image on the screen due to excess
illumination of the object. It is easily produced in jihotography, e.g. by
pointing the camera directly to the sun and getting apparently a " moonlight
scene."

Scattered light is light reflected from the inner surface of the camera, e.g.
shiny bellows, badly blacked walls, etc.

We will deal later with the ways in whicli the eye avoids these defects,
meanwhile we will consider the structure of the organ.

18-3

276 OUTPOSTS OF THE INTELLIGENCE SERVICE

Anatomy of Eye.

To understand the mechanism of the eye even from the purely physical
standj^oint, i.e. as an optical instrument, it is necessary to have a clear
conception of its structure.

Anatomy (contributed by J. Seeker). The human eyeball (Fig. 71) is a
hollow sphere of about 20 mm. in diameter. It consists of three concentrically
arranged coats enclosing a cavity containing three refracting media. These
coats are (i.) an outer fibrous envelope which is divided into an opaque portion,
the sclera, and a transparent portion, the cornea. The sclera constitutes the
posterior five-sixths of the coat, and the cornea, which has a greater convexity
than the sclera, the remaining anterior one-sixth, (ii.) A richly pigmented
coat, the chorioid, which is the vascular tunic of the eyeball, and contains
the intrinsic muscles of the eye, is the intermediate coat. At the junction

IRIS

FILTRATION ANGLE

CORNEA,

i

>» \ Xi .CILIARY,

-A.^' muscle"

5CLEKOTIC,

OPTIC NERVEI

Fig. 71. — Diagrammatic section tliroiigh c(juator of tlie left eye seen from above.

of the sclera with the cornea, the chorioid ceases to be in intimate contact
with the sclera and projects as a curtain, the iris, into the cavity of the eye,
dividing the space between cornea and vitreous humour into an anterior and a
posterior chamber. In the centre of this curtain there is a central circular
aperture of variable size, the pupil. In the substance of the iris are two sets
of muscle fibres, one set, the constrictor muscles, arranged concentrically
with the pupil, and the other set, the dilator muscles, arranged radially. At
a point immediately posterior to the iris a series of about seventy radially
arranged processes project into the cavity. These projections or ciliary
processes consist of connective tissue containing blood vessels, and supplied
with muscular fibres from the ciliary muscle, which has its main body in the
chorioid coat at the region from which the ciliary processes originate. The
ciliary muscle arises from a spur of the sclera at the corneo-sclerotic junction
and consists of two sets of fibres, a circular and a radial set. The latter passes
into the ciliary processes, and together with them constitutes the ciliary
body, (iii.) The innermost coat, the retina, is the sensitive layer of the visual

ANATOMY OF THE EYE 277

a])|tai;itus and corrcspniKls to tlu' plate of a camera. Histologist.s divide the
substance of the retina into eight layers, viz. .starting from the si(U' on whii li
the light falls, i.e. next to the vitreous hiinioiii- :

1. Stratum opticum. Layer of non-myelinated nerve fibres.

2. (Janglionie nerve cell layer.

3. Inner molecular layer. Interlacing dendrites of 2 and -i.

4. Inner nuclear layer. Bipolar nerve cells.

5. Outer molecular layer. Dendrites of 4 and fi.

6. Outer nuclear layer. Neurones of rods and cones.

7. Bacillary layer. Layer of rods and cones.

8. Stratum pigmenti.

For our purpose we may consider four sets of elements in the retina, viz.
neurones, rods, cones, and pigment-containing cells.

(fl) The bacillary layer contains structures known as rods and cones.
These structures are believed to be the actual sensitive structures of the eye.
Lender certain conditions, e.g. when the eye has been in the dark for some time
before death, fine processes of the pigment cells can be seen to pass up between
the cells of this layer. (6) An intermediate layer of bipolar cells which
function as connector neurones and link up the rods and cones with the next
layer of neurones, (c) The ganglion cells.

The axons of the ganglion cells pass horizontally across the inner surface of
the retina and converge on a point at the back of the eyeball slightly internal
to and just below the antero-posterior axis, to pierce the chorioid and sclera
to form the optic nerve. These layers, as mentioned above, do not, however,
extend so far anteriorly as the ciliary region, but are represented in this
region by a double layer of pigmented cells constituting the }xirs ciliaris
retin(e. The sensitive retina itself shows variations in structure in different
regions.

At a point where the antero-posterior axis meets the retina there is an
area which is yellow in colour, the macula lutea, in the centre of which is a
depression, the fovea centralis. At the fovea, which is the area for direct
vision, only cones are found, and here the cones are larger than in other areas
of the retina. In addition to the absence of rods at the fovea the remaining
layers of the retina are not represented, the centrally directed processes of the
cones diverging towards the periphery of the macula to end in relation to the
ganglion cells, which are at this region found to be of several layers deep.

The retina receives its own arterial blood supply from the arteria centralis
retinae, a small artery which enters the eyeball at the site of exit of the optic
nerve. Branches of this artery radiate on the inner surface of the retina,
supplying all areas excepting the fovea centralis.

The three coats as described constitute the walls of the eyeball and enclose
the three refractive media, i.e. the aqueous humour, the lens and the vitreous
body.

The lens is a laminated biconvex, transparent, elastic structure, the posterior
surface of which is more convex than the anterior surface. The lens is placed
just behind the iris and centred with the pupil, and is enclosed in an elastic
membrane called the capsule. The periphery of the capsule is attached by a
thickened portion of the hyaloid membrane {vide injra), known as the
suspensory ligament, to the ciliary processes.

The anterior compartment of the eyeball contains a clear fluid, the aqueous
humour, and the posterior portion a more jelly-like substance, the vitreous
body. The vitreous body (or humour) is enclosed in a membrane, the

278 OUTPOSTS OF THE INTELLIGENCE SERVICE

hyaloid uienibraiie. At the back of tlie eye, this ineinbraiie i.s in intimate
contact witli the retina, but on reaching the ciliary region it splits into two
layers, the posterior of which is continued over the anterior surface of the
vitreous body, and the anterior, gaining attachment to the ciliary processes,
becomes thickened to form the suspensory ligament of the lens.

On the anterior surface of the vitreous body is a cavity, the hyaloid fossa,
in which the posterior surface of the lens is lodged. From this fossa a
minute canal, the hyaloid canal, passes obliquely backwards to the point of
exit of the optic nerve.

Eecent work on the anatomy of the living eye with the slit-lamp seems to
suggest that a small space, the retro-lental space, exists between the posterior
surface of the lens and the anterior surface of the vitreous body, and that the
aqueous humour is able to j^ass between the fibres of the suspensory ligament
into this space, which is drained by the hyaloid canal into the lymphatics of
the sheath of the optic nerve, or into the retinal vessels.

The Eye as an Optical Instrument.

The physics of vision may be considered under two heads,
viz. (1) the way in which the image is produced on the retina,
and (2) how that image stimulates the end-organs for vision in the
retina so that impulses pass to the optic nerve, producing finally
a change in consciousness. Under the former head will fall the
study of the defects common to a camera and the means by which
they are overcome in the eye.

(1) There can be no doubt as to the actual formation of an
inverted image on the retina. If a small window be cut through
the back of a freshly excised eye, and the space covered with a
sheet of tissue paper or a small bit of ground glass inserted,
inverted illuminated images of objects placed before the eye may
be seen on the screen. The optical system consists of {a) cornea,
[b) lens, and (c) iris. Light will undergo refraction at three
surfaces, e.g. where it enters the cornea and where it enters and
leaves the lens. This may be deduced from consideration of the
refractive indices of the various media of the system given below.

Refraction also occurs at the posterior surface of the cornea,
but as the R.I. of cornea and aqueous humour differ only slightly,
we may neglect refraction at this surface.

TABLE XXXVII

Kefractive Indices of Media

Air . . . .
Cornea

Aqueous humour

Lens (periphery)

(central nucleus)
(total equivalent)

Vitreous humour

1-00
L37
L33
L37
L41
1-42
1-33

THE FAE AS AN omCAL INSTRUMENT 270

At each of these three surfaces the light passes from a medium
of one density to auotlier and, therefore, as the surfaces are
convex, the incident rav is bent towards the central axis.

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 Sansori'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 1-37 is much brighter than the images from the lens,
where the change is from 1-33 to 1-42 and from 1-42 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.

Curvature of the Surfaces. The
images of the candle are not all of
the same size, because the radii of
curvature of the three reflecting and
refracting surfaces are different. The
central image is the largest because
the anterior surface of the lens is
the least curved, while the inverted
image is the smallest because it is
reflected from the posterior concave
surface of the lens which has the greatest curvature, i.e. smallest
radius of curvature (Table XXXVIII.).

no.

-ansDu's Images.

The images, from left to riglit, are
from the anterior surface of tlie cornea,
anterior surface of lens, and posterior
surface of the leas. (From Goulden'.s
" Refraction.")

TABLE XXXVIII

Radii of Curvatures of Cornea and Lens

Cornea (anterior surface) .....

(posterior surface) .....

Lens (anterior surface) ....

(posterior surface) ....

mm.
7-98
6-22
10-20
6-17

Positions on Optic Axis. If we add to our knowledge of the
refractive indices and radii of curvature of the components of the
optical system of the eye, measurements of their distances from the
retina, we shall be in a position to calculate the dioptric values of
these media.

The distances are given in Table XXXIX.

280 OUTPOSTS OF THE INTELLIGENCE SERVICE

TABLE XXXIX

mm.
Anterior surface of cornea to aqueous humour . . .1-15

Anterior surface of cornea to lens ..... 3-54
Anterior surface of cornea to vitreous humour . . . 7-60

Anterior surface of cornea to retina ..... 22-6

The cornea will, therefore, have a focal length of 32 mm,, and
the lens of 56-3 mm. The dioptric value is, as we have seen, the
reciprocal of the focal length, i.e. cornea 31 and lens 18 dioptres.
It will be seen from these figures that the cornea plays the major
part in the formation of the image. When one attempts to see
while immersed in water, one finds it impossible clearly to perceive
objects near at hand, while more distant objects appear reasonably
distinct. Water having a refractive index of a value close to that
of the cornea, lengthens the focal distance of the cornea, i.e. the
eye becomes long-sighted and cannot bring near objects into focus.
When the lens is removed for cataract, the cornea has to be
strengthened optically by a spectacle lens of about 10 dioptres.

The lens is an interesting structure. It is not homogeneous,
but is formed of a series of concentric layers of material graded in
optical properties, so that the refractive index increases layer by
layer from capsule to nucleus. The curvature of these layers also
increases in the same direction, i.e. the nucleus has the greatest
curvature, appearing almost spherical. This peculiar structure
gives the lens increased power. If its composition were uniform,
with a mean refractive index of 1-39, its power would be proportional
to the difference between its R.I. and the R.I, of the adjacent
medium, i.e. 1-39 — 1-34 = 0-05. But its actual R.I. is 1-42.
It has thus increased in power in the ratio 8/5.

Focussing.

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 has
virtually a series of lenses of varying strength, from which it
selects the one most suited to the requirements of the moment.

PURKINJE-SANSON IMAGES

281

'J'Ik' kiis .sus|)<.'iRltcl in llu- resting eye lias not its natural shape :
it is kept somewhat flattened by the tension ol' the capsule. U'
this tension can he relaxed, the lens will heeoine more convex
on account ol" its iidierent elasticity. A mechanism for bringing
this about is })resent. The ciliary nuiscle is lixed at the cornco-
sclerotic junction. When its radial fibres contract they drag the
ciliary processes, with the adherent hyaloid membrane, forward.
Simultaneously the circular fibres by their contraction constrict
the circle round which the suspensory ligament is attached. The

venosus

Conjunctiva

Retina

Fig. 73. — IScction of anterior parts of eyeball, slinwing structures concerned in accommoda-
tion. (After Merl<el anil Ivallius.)

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 nmi. fully accommodated. The
normal adult is thus enabled to see objects distinctly to within
10 or 15 cm. distance.

The Purkinje-Sanson images during the process of accommoda-
tion provide a clear demonstration that the main surface affected
is the anterior surface of the lens. The central, larger but less bright
erect image is reflected from this surface. If, therefore, the two
other images remain almost unchanged, and only this image alters
in size and position when the eye of the subject, resting on a

282 OUTPOSTS OF THE INTELLIGENCE SERVICE

distant object, is brought to bear on something near the eye, it is
proof that tlic main change of curvature is that of the front of the
lens. In acconniiodation, the central image becomes smaller and
moves towards the other erect image. (There are other theories
of the mechanism of accommodation, but the above has, at present,
the greatest weight of evidence in its favour.) (Fig. 72.)

The iris corresponds to the stop or diaphragm of the camera and
is used for the same ends. The way in which the size of the aper-
ture, the pupil, is altered has been considered. It is controlled
from the retina, light falling on the retina producing constriction.
The function of the iris in accommodation is to increase the depth
of focus of the eye. The depth of focus in the case of the eye is the
greatest distance through which a luminous point can be moved
and still produce a sharp point image {i.e. falls on one cone) on
the retina. For example, a point may be seen clearly at, say,
100 metres, and at 0-5 metre, i.e. the depth of focus, in this case,
would be 100 — 0-5 = 99-5 metres. Now in any lens system the
depth of focus may be modified by the size of the aperture in front
of the lens. The depth increases as the diameter of the aperture
decreases. In other words, when we are near an object we use a
small stop so that light which might cause the image to spread
itself over the retina is shut out, i.e. we get definition.

How Optical Defects are Prevented in the Eye.

At the beginning of this chapter we mentioned some of the
commoner faults found in lens cameras, e.g. spherical and chro-
matic aberration, comma, halation, flare, irradiation and scattered
light, and we discussed methods of overcoming these defects {q.v.).

Spherical Aberration. In ordinary circumstances this aberration
of the eye is negligible, due {a) to the special structure of the lens
whereby the rays are refracted in exactly the opposite way from
that produced by an ordinary biconvex lens ; that is, the rays
passing through the nucleus are more highly refracted than the
rays falling on the peripheral parts of the lens, and (6) to the
stopping action of the iris.

Curvature of the Field. This is avoided completely by the
curved screen on which the image is formed. The focal length
of the eye (15-5 mm.), being somewhat longer than the radius of
curvature of the retina (10 mm.), gives an optical system practically
perfect in this respect.

Chromatic Aberration. Experiment shows that the curvature
of the anterior surface of the lens and the diameter of the pupil are
so adjusted that the image is formed on the retina by the com-
ponent rays of white light Dresent in greatest intensity. For

PREVENTION OF OPTICAL DEFECTS 283

suiilighl these are tlie yellow rays (Fi<4'. 1), and other faint blurred
images are produced by the vioiet-blue-grceu which come to a
I'ocus in I'rout of the sensitive surface and by the red rays wliich
would focus behind the retina.

Chromatic Differences of Magnification. Tlie fo\'ea, the area of
the retina most sensitive to light (q.v.), is eccentric and, therefore,
violet, blue and green images should appear smaller on it than
yellow and red ones. This manifest fault, however, acts as a
corrective to chromatic aberration.

Comma. This is not shown by lens systems obeying the sine
law. Apparently the optical system of the eye fulfils this condition.

Halation does not occur in the normal eye, as the reflecting
layer and the sensitive layer are practically identical.

Flare. Table XXXVII. shows that the refractive indices of the
media bounding the lens differ only slightly from that of the lens
itself. Further, the R.I. of the peripheral parts of the lens is even
closer to the R.I. of the humours. Flare is therefore negligible.

Irradiation. This does occur in the eye if the illumination is
very bright, and causes bad definition of objects.

Scattered Light. In spite of the liberal supply of protective
pigment in the layer of the retina lying immediately under the
layer of rods and cones, some light is reflected back into the
viscus of the eye. It is this reflecte'd light that makes retinoscopy,
etc., possible. The reflected light, however, is in great part
absorbed by the pigment of the iris and by the insensitive anterior
portion of the retina. On the other hand, light entering the eye
at a great angle would first strike the anterior retina and be
reflected to the posterior sensitive part.

The possibility of the entry of oblique rays is reduced by shelter-
ing the eye by the barriers of eyebrows, eyelids, eyelashes, cheeks
and nose, and by the smallness of the pupil when light is intense.
Under ordinary conditions one is not much troubled by scattered
light in the eye.

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.

Neither of these defects interferes appreciably with the accuracy
of vision

(iii.) Slight degrees of astigmatism are almost always present.

284 OUTPOSTS OF THE INTELLIGENCE SERVICE

This is a " defect " of the cornea and is due to the fact that the
surface is not uniformly part of a sphere. For example, the top
of an egg is spherical, but a portion of the shell removed from the
side would correspond in greater or less degree to the normal
astigmatic cornea. Astigmatism is termed rvgular when the
different meridians which cut the anterior surface present a gradual
change in passing from one meridian to the other, the curvatures
that are most different being at right angles to one another. The
eye has, therefore, two anterior focal points, the one corresponding
to the meridian of greater curvature nearer the eye than the one
corresponding to the lesser curvature. The emmetropic eye has a
certain amount of radial astigmatism, which is neutralised to a
considerable extent by a positive axial astigmatism, i.e. a circular
object appears as if compounded of two almost circular ovals in
the same plane with the same " centre," but at right angles to one
another. Such an astigmatism does not require correction by
lenses.

Defects of the abnormal eye as an optical instrument.

In the normal or emmetropic eye, parallel rays, which in
practice are those coming from a distance greater than 6 metres,
are focussed in the resting state. Within 6 metres accommodation
begins, and it increases as the object approaches, reaching its
maximum at about 10 or 15 cm. This is called the near point
of vision, and the point at which accommodation begins is called
the far point.

The eyes of a considerable proportion of persons do not produce
sharply focussed 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 focussed 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.

Presbyojjia is the result of a gradual diminution of the power

BOnS ANT) CONES 285

of accoinniodatioii tlirouj^ih loss ol" elasticity of the lens as age
advances, the retina retaining its normal position relative to
the lens.

The Retina. ( 1 ) The Mechanism.

This, as we have seen, is the end-organ for vision. Our aim is
now to endeavour to find out how light falling on this surface
becomes an effective stimulus for the occipital cortex so that very
slight dilTerences in wave-length can be appreciated. There can
l)e no doubt that the rods and cones are the actual irritable organs.
Once they are stimulated, the disturbance is passed through their
cell bodies to their processes in the outer molecular layer where the
impulse passes across a synapse to bipolar neurones. These hand
on the disturbance to the large oval ganglion cells whose axones
form the stratum opticum. The axones are given a myelin
sheath as they pass out of th^ eyeball and form the optic nerve.

Rods and Cones. As both rods and cones make connection
in this way with the optic nerve, we have to consider these two
types of receiving units. They differ in structure, in distribution,
in their associations in the outer molecular layer and in function.

Structure. Briefly the rods, as their name implies, are columnar
structures lying in contact with and normal to the pigmented
layer of cells. Their inner portion is attached by a process to a
small bipolar cyton whose other process gives off dendrites in the
fifth layer (p. 277), several rods forming synaptic connection with
one bipolar neurone of the inner nuclear layer.

Distribution. Rods are not found at the fovea and are associated
with the visual purple.

Function. As more than one rod forms nervous connection
with a single bipolar cell, their function cannot be that of exact
minute definition. Further, as rods are not found at the fovea,
the area of direct vision, they are not necessary for clear vision.
Experiment shows that they are sensitive to light of low intensity,
i.e. they are effective in twilight vision. When lighting is poor we
readily detect movements. The rods, therefore, are easily stinni-
lated by light of short duration provided it is not too bright.
In the twilight everything appears dressed in shades of grey. Some
greys are more easily seen than others. Examination of these greys
in a good light shows that they are actually yellows and yellow-
greens. From this we infer that the rods are colour blind, but have
a lower threshold for light belonging about the middle of tlie
visible spectrum.

Cones are shorter elements and are directly incorporated with
their cyton, i.e. they are part of the first order neurones. They

286 OUTPOSTS OF THE INTELLIGENCE SERVICE

form synaptic connection exclusively with one bipolar neurone
each, i.e. the stimulation of one cone is not associated with the
stimulation of any other cone till the disturbance has reached the
cortex. They are thus fitted for point vision and are capable of
transmitting fine detail if the light is not too intense. The fovea
contains cones closely packed together ; the surrounding area, cones
and some rods. Then comes an area peripheral to this, with rods
and some cones, and, finally, at the very edge of the effective
sensitive surface very few cones are found. They are, therefore,
the elements responsible for direct vision in good light, are capable
of transmitting detail and are sensitive to all parts of the visible
spectrum. They are not fitted for twilight vision and are not
associated with the visual purple.

Fovea Centralis. As this tiny depression in the retina is the
screen on which inverted images of external objects are clearly
focused under ordinary conditions, ^e must devote a little more
attention to it. In this area the rays of light transmitted through
cornea, aqueous humour, lens and vitreous body and " stopped
down " by the iris, come otherwise undistorted into direct contact
with the bases of the cones, which here are larger, more highly
developed, and more rod-like than elsewhere. In order to get this
freedom from the dissemination of light by the colloidal structures
interposed in other parts of the retina, the nervous connections of
the cones are led away from the fovea into the surrounding
macula lutea. There are no blood vessels in the fovea, and this,
also, contributes to exactness of vision. The cones, too, are so
closely packed together that, in section, they become hexagonal,
each flat side being in contact with the flat side of a neighbour.
That is, in the fovea, there are essentially only two sets of elements,
viz. cones and the cells of the stratum pigmenti.

Pigments. Several coloured substances have been described as
being present in the retina. (1) In the outer layer, i.e. the layer
lying between the layer of rods and cones and the chorioid coat,
there is a pigment fucsin, which acts as a " damper " for the
ethereal waves, i.e. the needles, prisms or plates of this pigment
found in the processes of the cells of the stratum pigmenti prevent
light from spreading by reflection from the outer limbs of rods and
cones. (2) Visual purple, or rhodopsin, is found associated with the
rods. In fact some investigators, like Edridge-Green, are inclined
to consider that the main if not the sole function of the rods is to
elaborate and secrete this pigment. Rhodopsin has been extracted
from retinae and its photo-sensitiveness tested. Strong light
bleaches it very rapidly, forming probably two substances, a
principal one and an accessory one. These products of photolysis

EFFECT OF LIGHT ON THE RETINA 287

are, in the eye, resynthesised into rhodopsin. Removed from the
retina, the pigment bleaches at a rate which varies in velocity with
the intensity and wave-len»th of the incident light and remains in
its bleached state. That is, the rods or their adnexa are essential
for the restoration process. (3) Other pigments, such as visual
yellow and pigmented oil drops (amphibians, reptiles and birds)
have been described, but their nature, distribution and function
are not yet clear. It has been suggested that these red, yellow and
green globules act as colour filters in much the same way as the
coloured starch grains do in the Lumiere process for colour
photography.

The Retina. (2) Effect of Light on it.

When light falls on the sensitive surface of the retina physical
and chemical changes occur.

(1) PhysicaJ. »

(a) Pigment moves inwards (Boll and Kuhne, 1877).

(6) Cones retract (Angelucci, 1882).

(c) Outer parts of rods swell.

{d) Ganglionic chromatin is decreased.

{e) Electrical changes occur.

(2) Chemical.

(f) Retina develops an increase in H+ concentration.
{g) Rhodopsin and fucsin, two pigments, are bleached,

and a physiological change is produced, whereby we see. Of
these changes, («) and {b), and probably (c) and [d] as well, are
secondary products. They only occur if the nervous mechanism
is intact, and may be produced by stimulation of either optic
nerve by any means, i.e. they are caused by retinomotor impulses
from the brain. That leaves three factors to be reckoned with in
any explanation of the mechanism of the retina, viz. the electro-
motive force developed, the alteration in hydrogen ion concentra-
tion, and the bleaching of the pigments.

(1) Electromotive Force. Du Bois Reymond in 1840 noticed
that alteration in the nature and intensity of illumination altered
the potential of the retina as a whole. His work has been con-
firmed and amplified by Holmgren (1880) and later workers. In
general, illumination causes a negative variation in the electro-
motive force of any point of the retina, i.e. a current would flow
in the retina from an ilhmiinated point to the rest of the structure.
In other words, the ilhuninated part becomes zincative just like
the injured part of any cell, the contracting part of a muscle or the
momentary site of the impulse in a nerve. This is not strange when

288 OUTPOSTS OF THE INTELLIGENCE SERVICE

we remember that the retina is primarily part of the nervous
system, and that the electrical variations found are actually those
accompanying the nervous impulse, and do not differ materially
from those found by Adrian in the optic nerve itself. The change
in E.M.F. does not occur exactly at the moment when the stimu-
lating light falls on the retina. There is a definite latent period
during which, it is presumed, some photochemical change takes
place. In the case of peripheral vision, where rods are the main
elements present, this latent period is occupied by the bleaching
of the visual purple and the liberation of whatever substance is
responsible for stimulating the rods, but in the fovea there is no
visual purple to bleach. We can only assume at present that some
substance is formed or altered by the incidence of light on the
fovea, which in turn stimulates the cones. Edridge-Green has
brought forward evidence that visual purple may diffuse from the
surrounding rods into the fovea, be bleached by light there, and so
stimulate the cones, Hecht and others have studied the relation-
ship between the intensity and colour of the incident light on the
one hand and the })hotochemico-clectrical response on the other.
With monochromatic light a geometric rise in the intensity of the
light causes an arithmetic increase in the E.M.F. produced, i.e.
if we increase the illumination from 60 candles to 3,600 candles
we would double the potential developed. With coloured lights of
apparently equal intensities, the yellows are more effective as
stimulants when the general intensity is fairly high, and the greens
when the intensity is low.

The following table from Frohlich (1013) shows that, in order to
produce the same E.M.F., it is necessary to have a greater intensity
of blue light than of white light, and a much greater intensity of
light when it is red than when it is blue.

TABLE XL

E.M.F.

Relative

Intensity of Light.

Millivolts.

White.

Blue.

Rel.

Minimal

1

20

0-2
04

1-25

5
11-2

1,020
12,500

0-6

5

80

—

0-8

80

12,500

(2) Chemical Changes. We have seen that rhodopsin is bleached
by incident light, with a velocity related to the intensity of the

ADAPTATION 289

light and to its colour. Proof has been given that Grotthus' law
{q.v.) of photochemical action applies to this photolysis, and that
the amount of light absorbed when light of various frequencies
falls on the pigment is related quantitatively to the amount of
chemical action produced. That is, if we constructed two curves,
one showing the relative bleaching ])owers of light of various wave-
lengths and the other showing the amount of light absorbed by the
visual purple with light of the same wave-lengths, these curves
would run a similar course. Further, a third curve produced by
plotting wave-lengths against the intensity necessary to produce a
minimal peripheral sensation of grey-blue would be of the same
form as the other two. From this we infer that the amount of
visual purple bleached to produce similar sensations is the same
for all wave-lengths.

Peripheral Vision. When light strikes the peripheral parts of
the retina it bleaches a certain amount of visual purple, producing
two substances, either or both of which stimulate the irritable
element. The general view is that the irritable elements concerned
are the rods. Some people, however, are of opinion with Edridge-
Green, that the rods merely produce the pigment and are necessary
for its restoration, but have nothing to do with actual perception.
That function they attribute exclusively to the cones which are
present in decreasing concentration as the distance from the fovea
increases. While admitting the validity of the evidence on which
this theory is founded, one may draw other conclusions from it.
It is difficult to shut one's eyes to the histological nature of the
nervous connections of the rods (q.v.). It has been suggested that
while the cones undoubtedly are stimulated by the bleaching of
the rhodopsin, the rods might be stimulated by the decrease of the
concentration of the pigment in their substances.

Acidity. Dittler (1907) showed that the illuminated retina
became acid. This acidity decreased rapidly to the normal value
when the eye became dark-adapted, i.e. remained in the dark.

Adaptation of Retina. The retinal mechanism has a rate of
adaptation to a constant stimulus that is similar to that of the
receptors for pressure, i.e. more rapid than that of the proprioceptors
in general, e.g. muscle-spindle, and a good deal less rapid than that
of touch, e.g. hair. A constant stimulus, therefore, ought to cease
to be effective in a few seconds. That is, after a latent period the
retina will send a burst of impulses to the cortex which will decline
rapidly at first and then gradually fade away. This appears to be
contradictory to our daily experience. But is it so ? If you fix
your eye steadily on this page and prevent your head and your
eyes from moving, you will find that the print becomes rapidly

li. 19

290 OUTPOSTS OF THE INTELLIGENCE SERVICE

blurred, then remains in this blurred state apparently without
change for a few seconds before involuntary movements of the
body as a whole (respiratory or cardiac) cause a slight improvement
in vision j^ro tern. The blurriness is primarily due to points of
the image on the fovea alternating between adjacent cones and so
allowing one cone to have its irritability restored while its neighbour
is being excited. This rhythmic alternation of ability to function
is a universal characteristic of biological systems and permits of
a function being effectively carried out almost continuously over a
reasonable period of time by any collection of units, e.g. cones,
capillaries to an area, touch receptors, etc.

Movements of the Eyeball.

The eyeball lies at the front of the bony orbit, a cone-shaped
^anal with its apex directed backwards and pierced by the optic

TRANSVEKSE

Fig. 74. — Diagram of extrinsic muscles of eye.

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 move-

MOVEMENTS OE THE EYEBALLS 291

ments of the eyeball are carried out by the extrinsic muscles,
Avhich are six in number. Of these, four (called the recti) originate
in a common tendon surrounding the optic foramen, and pass
forward to be inserted a short distance in front of the equator
of the eyeball. One is placed above (R. superior), one bel(nv
(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 inferior oblique arises from
the inner anterior part of the orbital floor, and passes outwards

INF OBLIQUE
ipiH)<,

EXT. RECTUS I /^mW>>. \ '^"^^ f^ECTUS

tsnN.)< — SBIH ^ (™^) <:

SUP. RECTUS

-> CniN.) ^

(iyn)< x.^________^^-£ ^ (niN.)

SUP. OBLIQUE I I INF. R.ECTUS

Fig. 75. — Diagram showing the directions in wliich tlie different external muscles of the eye

rotate the eyeball.

and backwards to its insertion rather beyond the equator. It acts
on the same line as the superior oblique.

All the movements of the eyeball are rotations round axes passing
practically through the centre of the sphere, but it can be proved
experimentally that rotation never occurs round the visual axis.

The internal and external recti rotate the eye roimd 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 tending
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 simul-
taneously. Its force can likewise be resolved, one component
tending to rotation round the horizontal axis at right angles to the
visual axis, the second component tending to rotation round
the visual axis, clockwise. The two rotations round the visual

292 OUTPOSTS OF THE INTELLIGENCE SERVICE

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 (Fig. 75),

Binocular Vision.

1. 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. 76). If this
mechanism is defective, strabismus or
squint results. The amount of con-
vergence varies inversely as the distance
of the object. The power of conver-
gence is rather less than that of accom-
modation, for we can focus an object
with one eye at a slightly shorter distance
than when we use both eyes.

It is only in the emmetropic eye that
convergence and accommodation corre-
spond exactly in amount. A hyper-
metropic 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 emme-
trope 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 acconnnodation sufficiently to neutralise their
effect. The object still remains at the same distance, i.e. the
convergence does not alter. Hence we see that accommodation
and convergence are to some extent independent.

2. Heterophoria. In strabismus the deviation of the two visual
axes is manifest, but the majority of people, with otherwise normal
eyes, have a latent squint, only exhibited as an actual deviation
when the eyes are dissociated by Maddox rods or other apparatus.

riG. 76. — Convergence. OandO'
are the far and near points respec-
tively, and OEF and O'EP the
angles of convergence.

BINOCULAR VISION

203

We have seen tliat the I'linctions of acconmiodation and con-
vergence are within hnnts co-ordinated, i.e. there is a movement
inwards of each eye of 1 metre angle for each dioptre of accom-
modation. Now when the eyes are dissociated, and this may
easily be done by holding a card sufficiently near one eye to prevent
vision of the object by it and yet far enough aw^ay to permit of
observation of that eye, and an object brought gradually from the
far point (6 metres away) to the near point (7-17 em.), accom-
modation and convergence do not keep pace with one another.
The occluded eye will deviate about 3° or 4° outwards, i.e. at
the near point all emmetropes are exophoric. As the object is
taken further away from the eye the exophoric deviation of the
dissociated eye tends to become less, and
at a certain point, usually about 30-50 cm.
away, no deviation is noticeable ; that
is, the extra-ocular muscles are perfectly
balanced. The mechanism is, therefore,
orthophoric. The latent deviation, or
heterophoria, may be in a variety of
directions, depending on which of the
extra-ocular muscles are unbalanced. The
directions may, however, for purposes of
description, be resolved into four com-
ponents pulling at right angles to the
visual axis, e.g. upwards or downwards ;
inwards or outwards. The former two are
deviations due to unbalanced action round
a horizontal axis, and are termed hyper-
phoria or latent vertical deviations.
Latent convergence is called esophoria, and latent divergence is
exophoria. About three-quarters of the people with emmetropic
eyes are esophoric, less than one-fifth are exophoric, and only
about one in twenty is orthophoric. The value of the deviation
is generally given as so many dioptres — the power of the lens
required to correct it. The type of lens used depends on whether
the object is to be " brought in " or " taken outwards." Con-
sequently to correct heterophoria decentred lenses are used,
convex lenses displaced against the deviation, and concave
lenses with the deviation found by tests.

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.

<a

Fig.

-Artificial divergence of
visual axes.

294 OUTPOSTS OF THE INTELLIGENCE SERVICE

4. Visual Judgments. On account of the distance between the
eyes, objects are viewed from a sHghtly 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
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 ^ 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 be
demonstrated by looking ' at a wall
between which and the observer an
object, such as the wire of an electric 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 imper-
fectly, 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

1 IS I J A L J I DGMKNTS

295

stereoscope. This instrument consists of two prisms or half
lenses placed, with the thin edge inwards, about the same distance
apart as the eyes. The dissimilar pictures P^ and Pg ^^^ fixed
one in front of each lens, and a median screen cuts off each opposite
picture. By means of this apparatus we obtain a single picture
in the most pronounced relief, and situated apparently at P.
(Fig. 79).

6. 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. Witli
both eyes opened and fixed we command
a greater range. — :> —

We may summarise the advantages of / ',

binocular vision as follows : < '>

(i.) The visual field is increased. ,' *

(ii.) W^e receive impressions of solidity. ,' \

(iii.) We have a most important means p
of judging distances. ~

(iv.) The loss of one eye does not reduce
us to blindness.

./ n

w

Fig. 79. — Diagram of stereoscope.

Analysis of Retinal Stimuli.

We have examined the eye as an optical
instrument and discussed the mechanism
whereby an inverted image of the external
object is formed on the retina. We have
also indicated that this image may be
imprinted on the retina photoehcmically—
a rapidly reversible reaction. It may
puzzle the student as to why, the image
being inverted on the retina, we see things right side up.
Seeing is an acquired reaction, i.e. it implies learning. We do not
see the image on the retina. What we do get is a series of nerve
impulses coming to the cortex from one or more of our seven
million cones. Just as with the other receptors, primary analysis
takes place in the retina — number and position of cones stimulated,
rate of bleaching of visual purple, etc. — and these changes, in the
light of previous experiences, are analysed and interpreted in the
cortex.

Purkinje Figures. Certain parts of our retina may be seen by
ourselves, as shadows it is true, but nevertheless objectively.
These are the blood-vessels and certain bundles of nerve-fibres.
If, in a dark room, the eye is kept motionless, and light from a

296 OUTPOSTS OF THE INTELLIGENCE SERVICE

candle, held near the temple, allowed to fall obliquely on the
sclera, the shadows of the vessels are projected on to the retina.
The eyes should have their accommodation fully relaxed and a
suitable dark screen be placed in a plane parallel to the antero-
posterior plane of the head. Under these conditions the vascular
network of the retina appears, in a highly magnified form, as if
projected on the screen. If the light is focused on the sclera by
means of a biconvex lens, or if a brighter source of light is used,
flashes of light following definite paths are seen. These flashes are
produced every time a transparent leucocyte passes across the
path of light. The interposition of a dark blue-violet light filter

will make this phenomenon clearer.
The red cells of the blood absorb the
blue rays and appear as an almost
continuous shadowy stream broken
here and there by a leucocytic flash.
By holding the breath one alters the
rate of blood-flow, and so produces a
definite alteration in the rate at which
these flashes appear (Fig, 80).

Arc Phenomenon. Under suitable
conditions nerve bundles lying on the
upper and lower borders of the tem-
poral half of the macula and extending
to the optic disc may be seen (Ellis).
If one is looking at a distant street
lamp (a doctor's red lamp serves well)
in the evening, when it is possible to
use a wall in shadow as a dark screen
for projection purposes, two arcs of a
bluish colour are seen, set with their concavities facing. The oval
space between the arcs is filled with a bluish haze. If the distant
light is feeble or poor in the more refrangible red rays, the arcs
may be difficult to see and only the haze be perceptible.

Muscae Volitantes. These motes, which move steadily down-
wards as the eye is directed upwards, are parts of a diffraction
pattern produced by substances in the vitreous body.

Ophthalmoscopy.

The interior of another person's eye may be viewed quite readily
by suitable methods.

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

ti M

Fig. 80. — Diagram of the path of the rays

of hght in the formation of Purkinje's

figures.

F represents a retinal vessel. When
this is illuminated from A, a shadow is
formed on the sensitive layer of the retina
at a'. This is jrojected along a line
passing through the optic axis and
appears to come from a joint (a") on the
screen. On moving the light from A to
£, the image of the vessel on the screen
appears to move from a" to b" ,

OPHTHALMOSCOP Y

297

up the interior it would become visible by refieetecl light, 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 nuist interpose our head between it and
the source of light in our attempts to peer into it. This difliculty
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

AERIAL

IMAGE

OF FATIENT'S

R.ETINA

Fig. 81. — Diagram to show paths of rays from eye of patient (on left) to observer when tlie
indirect method of ophthalmoscopy is in use (Hartridge).

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 (Fig. 81).

Further Reading

Edridge-Green. " The Physiology of Vision." Bell.
GouLDEN. "Refraction of the Eye." J. & A. Churchill.

SECTION IV: TRANSPORT

CHAPTER XXII

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 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 com-
munication— 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 in, 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
repacking and transmission to the consumer. Others have to
undergo some change before they can be transported inland. That
is, there are tzvo classes of raiv material arriving at the same port,
viz. : gas and liquid-solid food. By a mechanism which will be
considered in a subsequent chapter, the gas is diverted to one
basin of the harbour, while the food material is passed to a canal —
the alimentary canal. The gas 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. 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 distributed 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

298

DEVELOPMENT OF BLOOD 299

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
evidence 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 {q.v.)
The ciliary waves force the water through the tubes into the
lacunae of the tissues. Such a system is difflcult 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
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

300 THE BLOOD

a closed system in whieh 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.
camel's hair brush experiment, Part II.). 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. 310). 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 materials for building, repair and
renewal of tissues, as well as oxygen, water and potential energy
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. XXXII.).

{e) It plays a very important part in the defence of the organism
against parasites, etc.

(/) The preserv'ation of the H-ion concentration of the body
is principally a function of the circulating fluid (Chap. XXXI.).

{g) It maintains the water and salt content of the body at a
certain level.

3. Composition.

Since the function of the blood is to act as common carrier
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 (urea, etc.), COg and HgO, and
carries them away to the excretory organs, kidneys, lungs, skin,
etc., by which they are eliminated. It is therefore evident that the

PROPERTIES OF PLASMA 301

composition of the blood must vanj from time to time ami from place
to place, act'orciing to the activity and the function of the organ
which it is traA ersing. The cells of the body are adjusted to respond
to very minute changes in the composition of the blood and, there-
fore, changes are kept within infinitesimal limits.

The term blood or whole blood is usually applied to the fluid
content of the vascular system, plus the formed elements suspended
in it.

I. Fluid or Plasma
(a) Physical Characters.

(i.) Colour, light straw.

(ii.) Opacity, practically transparent.

(iii.) Specific Gravity, about 1,030. 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. 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~^. It is acid to phenolphthalein
and therefore has an H-ion concentration greater than 10"^. Exact
determinations have shown that the jjH. of plasma is 7-4, i.e. just
on the alkaline side of neutrality. This alkalinity is due to the
presence of sodium bicarbonate (see below).

(vi.) Colligative Properties. It is of academic interest to ascer-
tain the values of the vapour pressure, osmotic pressure, and
depression of the freezing-point of plasma, and many attempts
have been made to correlate changes in these values with the
symptoms of disease. As we have seen in studying the colligative
properties of dilute solutions (Chaps. V. and VI.), the temperature
at which the determinations are made is of great importance.
Grollman has determined the values for " separated " plasma

302 THE BLOOD

saturated with COg at its tension in alveolar air and at body
temperature (37-5° C). For dog's plasma he finds the depression
of the freezing-point = 0-61° C, for vapour pressure 48-1 mm. Hg,
and calculates from these an osmotic pressure of 8-2 atmospheres.
This value for the osmotic pressure is due very largely to the crys-
talloids present, as shown by separating colloids from crystalloids
by the process of ultrafiltration [q.v.). It is then found that over
8 atmospheres pressure is given by the diffusible salts, leaving only
about 0-06 of an atmosphere, i.e. 46 mm. Hg., due to the colloids.

That is, the osmotic pressure of separated 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 crystalloids, but to colloids. Further, plasma
divorced from its formed elements, especially the red corpuscles,
is very different from " true plasma," which is plasma removed
with such precautions that for any given tension of COo it is in
equilibrium with the cells of the blood.

(vii.) Refractive Index (see p. 273). 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.

(6) Components, (i.) Colloids.

The major colloidal constituents of plasma are protein in
chemical nature. These proteins are :

(a) Albumin . . 2-5 per cent, circa.

(/3) Globulin . . 3-8 per cent, circa.

(y) Fibrinogen . . O15-0-6 per cent.

(a) Albumin, probably a mixture of three albumins. At least
it is possible by careful heating to discover three separate coagula-
tion temperatures.

(j8) Globulin is similarly a mixture of two or more globulins.
Globulins are insoluble in distilled water, but soluble in dilute salt

COLLOIDS OF PLASMA SO.'i

solutions. They therefore require to have a certain concentration
of electrolytes present if they are to remain in solution. They
may l)c partially separated from albumin by dialysis. When the
salt content 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
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. Cilobulin is precipitated by an increase in hydrogen
ions. It is specially sensitive to COg.

(y) Fibrinogen, a globulin formed in the reticulo-endothelial
cells of the liver (Faludi).

The osmotic pressure in the vessels is due to proteins. They
are also responsible for the viscosity of blood. The removal of
the proteins from 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 arable 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.

304 THE BLOOD

Mammalian plasma, if left standing in a tube exposed to the air,
clots to a jelly in 2 to 10 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 exjjresses a clear straw-yellow liquid, the
serum,

i.e. Plasma = Clot + Serum.

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 clean air. This latter
fact has been confirmed by the observation that blood clots as
readily in a vacuum as in air. 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 explana-
tions of the process to the Glasgow Philosophical Society, in March,
1844, and February, 1845. Using hydrocele fluid from the tunica
vagiiialis 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.

(iii.) He later showed that this fibrin-former (now called throm-
bin) 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) :

1. Thrombokinase -f Prothrombin — >- Thrombin.

2. Thrombin + Fibrinogen — > Fibrin (Clot).

CLOTTING OF PLASMA 305

Arthus and Pages in 1890 showed the need of calcium in the
clotting process.

Haniniersten confirmed this, and found that the calcium acts
on the prothrombin producing active thrombin.

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 from activating
the prothrombin. This hypothetical substance they called anti-
prothrombin. When a vessel is ruptured and blood comes into
contact with the tissues or into contact with disintegrating blood-
cells, it takes from them a substance which neutralises the inhibi-
tory action of the anti-prothrombin and so allows the calcium to
act. This substance was, at that time, believed to be a ferment,
or kinase, and was, therefore, named " thrombokinase.'' That is,
in all cells there is a large or small quantity of thrombokinase,
which is the trigger setting off the whole clotting process. It is
now known that this substance is not a ferment or kinase. Some
people, therefore, prefer to call it thrombojjiastin.

That is, we have in the blood-stream prothrombin, anti-pro-
thrombin, fibrinogen and calcium salts. In order to start the pro-
cess of clotting, thrombin must be liberated from its precursor.
This duty falls on thromboplastin, a substance present in all tissues
and, in vertebrates, also in the white corpuscles, and perhaps in
the platelets {q.v.). Can we form a picture of the process ?
Examination of plasma during the process of clotting on a micro-
scope slide with dark-ground illumination shows how, on the
introduction of a drop of serum, tissue juice, etc., fine needles of
fibrin seem to radiate /rom the added fluid. These liquid crystals
pack together to form a felt-work of fibrils of fibrin — a very similar
process to that studied in an earlier chapter, viz. myelin forms of
lecithin (p. 109).

Pickering and Hewitt have produced evidence to show the
lines on which the clotting process runs. Their scheme may have
to be modified in detail as our knowledge of the physical chemistry
of colloidal systems like blood increases, but it gives a plausible
explanation of all the known facts. According to their theory,
blood contains all the elements necessary to form a clot, but it
maintains its fluidity because of the presence of a protective
substance. That is, we have two substances — a sol and a solution,
fibrinogen and thrombin respectively, which would interact to
form a liquid-crystal complex — a gel, but for the presence of an
inhibiting body. This inhibiting body may be a substance acting
in a manner similar to the protective emulsoids (Chap. VIII.), or
it may interfere with the process of gelation like certain solutes

B. 20

306 THE BLOOD

(Chap. VIII. and Part II.), or, according to Tait, it may be the
membrane siirroimding one type of the cells in the blood (thigmo-
cytes or platelets). The addition of a phospholipin, thrombo-
plastin, with the aid of the calcium of the blood, overcomes the
protective power of the anti-prothrombin, neutralises the inhibi-
tory solute, or causes the membrane of the thigmocyte to be
ruptured, depending on which view one adopts.

(1) Surface. Howell presents experimental proof that the
thromboplastic substance is either kephalin or some other phospho-
lipin of similar composition and structure. Pure kephalin has not
been prepared in sufficient quantity to allow of complete analysis,
but its molecule probably consists of :

m J. , , -1 ( Stearic (saturated)
i wo ratty acids ]-r ■ , • ; , / -,.
•^ iLinolic (unsaturated),

+
an amino alcohol, NH2-CH2-CH2-OH

(amino ethyl alcohol),

+
a glycero-phosphoric acid.

It is optically active, rotating the plane of polarised light to
the right (p. 126).

The main point of interest for us apart from its presence in all
tissues is its colloidal and fatty 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 first step in the formation of the clot is the liberation of
kephalin or some such thromboplastic substance which, by inter-
action with calcium soaps or other colloidal calcium complex,
offers water-wettable surfaces to which the thigmocytes (Tait) or
other blood cells may adhere and over which they Mill spread.
The spreading process causes mechanical rupture of the cells, with
the liberation of thrombin (a proteose) from their contents. Then,
as we have seen, thrombin acts on fibrinogen and a clot of fibrin is
produced.

That the introduction of a hydrophilic surface can initiate the
process of clot formation can easily be demonstrated. Almost any
hydrophilic substance with an effective surface (p. 71) will answer
as well as thromboplastin, e.g. powdered glass, quartz particles,
bubbles of carbon-dioxide gas, etc. Emboli (bubbles of gas) are
apt to cause clotting in the vessels where they stick, i.e. in the
smaller vessels. Other foreign substances whose surfaces can be
wet by plasma have the same effect.

It is worthy of note that kephalin particles of a size just visible

THEORIES OF CLOTTING

307

under an oil-inmicrsion microscope arc capable of producing
intravascular clotting when injected into the blood-stream, while
powdered glass or quartz particles of apparently the same size
are without effect. Coarser glass suspensions arc necessary to
produce the effect. Some other factor in addition to surface must
come into play or kephalin particles must have a wrinkled surface.
(2) H-ion concentration. This view of the process of blood-
clotting has been challenged by Pickering and Hewitt and by others
as an incomplete picture. It does not accoiuit for the fact that, if
due precautions are taken, l)irds' l)lood, which contains all the
constituents necessary for the formation of a clot, remains liquid
for a considerable time after removal from the vessels. The
addition of a mere trace of acid causes immediate and extensive
clotting. From this one may infer that in avian blood the forma-
tion of a clot depends primarily on the attainment of a definite
hydrogen ion concentration. That this inference is justifiable,
not only for birds' blood, but also for mammalian blood, is indicated
by experiments where blood was prevented from coagulating by
the liberation of alkali in it. Tri-calcium phosphate, the salt of a
weak acid, H3PO4, and of a strong base, Ca(0H)2, dissociates in
aqueous solution as shown on p. 68, liberating -OH ions, and so
tending to reduce the hydrogen ion concentration of the solution.
Thus :

Ca3 (POJ^

+ 2P0,

6H2O

^ 3Ca (OH), + 2H3PO4

(strong base) (weak acid)

Now, when tri-calcium phosphate is added to mammalian blood,
some of the salt dissociates, liberating alkali, and so preventing
clotting. Further, it has been found that fibrinogen in the
presence of the serum proteins, with their non-diffusible calcium,
readily forms an insoluble complex gel with a phosphatide in a
slightlij acid medium. Confirmation of the part played in this
process by the ^^H of the blood is deducible from Kugelmass'
investigations on the change in /jH of the blood during coagulation.
Blood has a pH of 7-4, but the optimal pH for the process of clot-
ting is 7. From such experiments, the conclusion may be drawn
that alkali is the factor in the blood which prevents intra-vascular
clotting. As we shall see later, blood has a considerable alkali
reserve (buffering power), so that a tendency to reduce the
hydrogen ion concentration is restricted within narrow limits.

(3) Calcium. During coagulation the electrical conductivity of

20—2

308 THE BLOOD

the blood decreases markedly, i.e. the concentration and mobility
of ions has been reduced. From a study of the form of the
curves produced by plotting the rate of diminution of electrical
conductivity against time, and the rate of fibrin formation against
time, etc., one arrives at two conclusions, viz. {a) that the process
is auto-catalytic {q.v.) and is in two stages ; and {h) that calcium
is necessary only in one of these stages, i.e. in the liberation of
thrombin from its precursor.

Stewart and Percival have carefully examined the part played
by calcium in the coagulation process. This metal exists in the
blood in three forms, viz. ionic, molecular and colloidal. The
last is non-dialysible, while the two other forms readily pass
through a dialysing membrane. According to these investigators,
it is the non-diffusible calcium that is effective in the formation of
a clot. Ionic calcium seems definitely to inhibit the process.

Certain substances by preventing the calcium from acting on
prothrombin prevent clotting. One of these, called heparin by
Howell, arises in the liver. Certain salts act on the calcium. For
example, oxalates, fluorides, etc., form insoluble calcium salts, and
when they are added in sufficient quantity they will cause the
precipitation of the major portion of the total calcium of the
blood. Citrates, on the other hand, reduce both the ionic and the
non-diffusible calcium, and if enough citrate is added, all the
calcium of the blood will be in the non-ionised but diffusible form.
The addition of a soluble calcium salt to oxalated or citrated blood
causes, in time, an increase in the non-diffusible calcium. When
this latter reaches a certain concentration coagulation occurs.

(4) Platelets. The platelets (q.v.) have recently received renewed
attention as clot-formers. Bedson and others have noticed that
in whole blood, clotting seems to start at the platelets, i.e. they
may initiate the process. Further, when the platelets are excluded,
a clot may still be formed, but it does not undergo typical retrac-
tion and lacks firmness. If such a clot is plugging a wound it is
very easily dislodged. A good clot normally formed in the presence
of sufficient platelets would have a considerable tenacity, holding
firmly to the edges of the Avoimd and so knitting these edges
together, Bedson attributes to the platelets the production of
thrombokinase (cf. Tait, above).

Most of the work mentioned above has been done in vitro ;
that is, blood has been collected into a vessel, or plasma has been
separated from the corpuscles by centrifuging, and allowed to clot
under observation. Such experiments may lead to quite a mis-
taken idea of the process as it occurs in vivo. When a blood
vessel is punctured and the blood allowed to flow to the surface

COAGULANTS AND ANTI-COAGULANTS 309

of the skin, one finds tliat tlie platelets gather at the edge of the
wound, forming a gelatinous annular mass. As this mass grows
in size a fine interlacing network of hbrin appears in it, with
platelets at the nodes or crossings of the net. White cells are
incorporated, and as the network becomes more felt-like, red cells
are entangled and imprisoned. Sometimes the clot seems to be
merely a mass of closely-packed platelets, leucocytes and erythro-
cytes (with very little fibrin) plugging the wound.

Anti-coagulants. The removal of any one of the participating
substances from the sphere of activity will naturally prevent
clotting. Let us take the process step by step.

(1) Liberation of thromboplastic substance is prevented by
carefully drawing the blood through a paraffined tube into a
vaselined or waxed vessel. If there is no contact with a water-
wettable surface, there will be no clot. One of the old experi-
menters found that blood placed with due precautions on a
nasturtium leaf would remain liquid for long. It is well known
that water runs off the leaf of this plant.

(1«) Platelets may be reduced below their effective concentration
by anti-platelet serum. In this way (and in purpura in man)
clotting power may be poor, wounds hard to heal, and capillary
bleeding dangerous.

(2) We have dealt with the inactivation of the calcium above.

(3) Thrombin may be rendered ineffective by the action of
substances such as hirudin, a proteose prepared from the buccal
glands of the medicinal leech. It is injected in blood-pressure
experiments to prevent clots from forming in the arterial cannula.

(4) The fibrin may be removed as rapidly as it is formed by
agitating the blood with glass beads or whipping it with twigs.
The sticky fibrin adheres to the beads or twigs and may be
removed. These methods and some others are summarised in
Table XLI.

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. Peptonisa-
tion and the injection of venom may cause some alteration in the
state of the thigmocytes. This has not been investigated.

Coagulants. Extracts of organs rich in kephalin, e.g. thymus,
testes, lymph glands, produce intravascular clotting.

310

THE BLOOD

TABLE XLI
Non-clotting Plasma

Nature of Plasma.

Reason.

To cause Clotting.

Whipped

Fibrin removed as soon as

Add fibrinogen to whip-

(Defibrinated).

formed by whipping with
a bunch of twigs.

ped plasma (or blood).

Salted.

Fibrinogen precipitated.

Dilute with water and

1 sat. with

so reduce concentra-

(NH)oS04.

tion of electrolytes.

Cooled to 0° C.

Cooling slows the physico-
chemical changes which
are optimum at about
40° C.

Warm,

Oxalated.

Ppts. calcium of all forms.

Add soluble calcium salt.

Addition of

soluble oxalate.

Citrated.

Reduces concentration of
non-dii?usible Ca.

Add soluble calcium salt.

Addition of

Reduces H-ion concentration

Add acid.

Ca3(PO,)2.

Hirudinised.

Combines with thrombin.

Add thrombin.

Peptonised.

Stimulates production of

Dilute to decrease con-

anti-prothrombin.

centration of anti-pro-
thrombin, or add tis-
sue extract or kephalin
or pass in CO^ gas.

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
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. Bungc, 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 mannualian 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

CRYSTALLOIDS OF PLASMA 311

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

C'a

Mg

Serum (defibrinated. plasma) .

100

6-69

2-58

0-8

Ocean ....

100

3-66

3-84

11-99

The similarity in proportion is not very striking because the
figm'cs given are from analysis of the ocean as it is to-day. What
we should have is the analysis of the ocean in pre vertebrate 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 concentration 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 (CaS04) and limestone
(CaCOg) and in the formation of calcareous skeleta (CaHPO^).

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.

Present day

Cambrian

Serum

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 = 4.00, Ca = 9-3, Mg = 26-4. This may be in part
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 NaHCOg absorbs the acid.

The amount of NaHCOg 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

NaHCOg + HA - NaA + H^O + CO,.

Na

K

Ca

Mg

100

3-6

3-9

11-9

100

6-0

3-0

2-0

100

6-6

2-5

0-8

312 THE BLOOD

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. XXXI.).

II. Formed Elements

The formed elements borne by the plasma have a volume about
equal to that of the plasma and weigh about the same amount.

Plasma. Corpuscles.

Volume . . 52-48 per cent. 48-52 per cent.

Weiglit . . 3 2

'fci'

This may be determined by the haematocrite (see Part II.) 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.

The Corpuscles

The blood corpuscles are of three kinds : (i.) coloured corpuscles
or erythrocytes ; (ii.) colourless corpuscles or leucocytes ; and
(iii.) blood platelets. The colourless corpuscles have been men-
tioned already in Chaps. XII. and XVI., and two types of them
have been portrayed in Figs. 36 and 37.

The blood-platelets {q.v.) are oval, colourless, refractile discs,
varying somewhat in size, but with an average measurement of 3/x
in their longest diameter. There are from 200,000 to 300,000 of
them in a cubic millimetre of blood. There is some doubt as to the
title of the platelet to be considered a cell. It has no nucleus or
chromatin material, and seems to consist of a homogeneous matrix
in which highly refractile granules are embedded. These granules
stain with basic stains {q.v.) like cresyl blue, and so are called
azurophil granules. Many haematologists are of the opinion that
the platelet is a complete cell budded off from the giant cells or
megakaryocyte of the bone marrow. Others consider that they are
fragments of cells or are the nuclei from young erythrocytes, or
even are some of the protein matter of the plasma gelatinised.
Whatever their origin, their function in the initiation of clotting
and in the formation of a firm thrombus is unquestioned {q.v.).

The erythrocytes are the carriers^ submerged barges into which
are packed the oxygen for the tissues and some of the carbon
dioxide from the tissues. They are born in the red bone marrow.

THE CORPUSCLES 313

The young corpuscle is called an erythrohJost 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 undergo
pyknosis and the enucleated corpuscles pass into the blood stream
on their way to the liver and spleen, where they are alleged to be
destroyed after 10 to 40 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.
In the next chapter we will consider the function of the red cells
in the transport of the respiratory gases, and later will give con-
sideration to the part they play in the preservation of a constant
pH in the blood. There are one or two interesting physical
problems in connection with the shape, structure and composition
of the red cell which must first be considered. Why should the
mammal (except camelidae) have circular biconcave discoids ?

Shape, Volume, etc., of Red Cells.

The 5,000,000 (± 1,000,000) of these cells found on the average
in every cubic millimetre of healthy human blood vary in diameter
and in thickness with variations in the composition of the plasma
in which they are suspended. Variations in size and shape are
also introduced whenever these cells are measured away from their
natural environment. Let us consider these artificial variations
first.

The usual methods of examination entail one or other of the
following manipulations : drying in air, dehydrating by alcohol,
washing free from plasma, staining, mounting on a glass slide, etc.
All of these introduce errors. For example, drying in air, by
reducing the water content from about 60 per cent, to almost
nothing, is bound to cause shrinking and distortion of the membrane,
alteration in the pH of the colloidal matter of the corpuscle due
to loss of CO2, etc. Fixation, even by such a rapid fixative as
osmic acid, produces peculiar bell-shaped forms. Nevertheless,
drying, fixing and staining methods are universally employed, and
the results obtained by them appear in most text-books as stan-
dard. The best that one can say of methods which take such
liberties with a delicate colloidal structure is that they are rapid,
and if applied in a standardised way, that they will give compara-
tive results.

The cell and its environment, the erythrocyte and its plasma,
must be considered together. Measured in this way, at a constant
tension of CO,, the human red cells are 8-8/x in mean diameter as

314 THE BLOOD

against 7-l~8-3/>t in dried films and 6-8-7-5 in dried and stained
specimens. Their greatest thickness is very nearly 0-3 of the
diameter, i.e. in man, from 'i-i/x in a dried specimen to 2-7/x for a
natural cell. It will be seen, therefore, that if the shape is the same
in both cases, the cell as it occurs in the blood stream is larger
in every way than when dried in a film. The thickness across the
narrowest part is about 2ja.

The volume and surface area of the cell can be calculated from
the diameter and thickness. This gives the human red cell a
volume of between 70 and 80/x^ and an area of 120/x2. The value
thus obtained for the volume agrees reasonably with that found
from dividing the percentage volume of cells found by the
haematocrite by the number of cells actually counted per unit
volume.

The size of the red cell is markedly altered by the j^H of the
plasma in which it is suspended. Increase of COg, by decreasing
the alkalinity of the blood, produces swelling (cf. swelling of
colloids, Chap. VIII.). Therefore venous blood will always
have larger erythrocytes than arterial blood. We shall discuss the
significance of this in the next chapter.

Shape. In contact with plasma the human red cell is a circular
biconcave discoid. A peculiar shape like this gives one the
impression of the application of a constant distorting force. If
the corpuscle, as is the almost general opinion to-day, is an elastic
bag filled with fluid containing, it is said, colloidal matter dispersed
through it, one would expect it to be spherical. Several views
have been advanced to explain the central cavities.

1. Those who consider that the cell is a sponge-hke body easily
find an explanation of the persistence of the shape, i.e. it is imposed
on the cell by the stroma within it. The flattening they attribute
to the loss of the nucleus and the consequent loss of some water.
Nucleated red cells have about 70-90 per cent, water, while non-
nucleated cells have only between 60 and 70 per cent, by volume.
Unfortunately the change from the practically spherical erythro-
blast to the typical disc-like erythrocyte is not synchronous with
the disappearance of the nucleus from the former. Further, the
nucleus is not thrown out of the cell. It undergoes disintegration
in situ, and its fragments are gradually absorbed by tlie cell.
Flattening occurs later.

2. The shape may l3c due to surface forces. Since the membrane
of the cell is mainly lipide, the cell, as a whole, may be regarded as
a lipide drop. Shape is imposed on any such drop by surface
forces. If these forces are uniformly applied, a spherical form
results ; if unevenly, an egg-shaped body, and so on. It is difficult

SHAPE OF ERYTHROCYTES'^ 315

to conceive how differences of snrface tension could 1)e produced at
different parts of a cell surface hounding two fluids such as cell
contents and hlood plasma.

3. Ponder's view is that the erythrocyte contains Huid or semi-
fluid material, and if the volume of the cell be increased by the
passage of fluid into it, the diameter (equatorial axis) must
diminish at the same time as the polar axis increases, until the
ratio of the axis is about 1 to 1-6. Thereafter both axes increase.
This investigator has worked out his theory mathematically from
the principles governing the stretching of clastic membranes of
spheroidal form and has constructed models which when distended
assume a discoid form.

Experiments by Gough and by Seeker may be considered as
supporting this theory. The former's experiments also give a
clear indication of the intimate relationship between the red cell
and the blood plasma. On removing the last traces of plasma and
suspending the red cells in isotonic saline, they assume the spherical
form. The addition of serum, however, causes them to reassume
their discoid form. The volume of the cell in both forms is the
same. Seeker showed that unleashed corpuscles retained the
discoid form in various saline solutions, but if to any of the solu-
tions a small quantity of insulin or of guanidine carbonate solution
were added, the corpuscle became spherical. If the saline were
isotonic or hypertonic the sphere had a smaller diameter than the
disc. On the other hand, when a hypotonic saline was used,
although the sphere was of the same diameter as before, the
haemoglobin of these corpuscles gradually diffused out without
apparent rupture of the plasma membrane, leaving spherical
" ghosts."

Now we must admit that, at all times, as long as the cell
membrane is intact, the contents of the cell must be in hydrostatic
equilibrium with the plasma. That is, the forces applied to the
cell membrane from without the cell must be exactly balanced by
the forces applied to the membrane from within the cell. The
forces tending to compress the cell are (i.) the elastic pressure of the
membrane; (ii.) the osmotic pressure of the plasma colloids
and of those crystalloids to which the membrane is impermeable.
On the other hand, the opposing forces are the osmotic pressures
of the cell colloids, viz. haemoglobin and cell-globulin ^8, and
possibly of some crystalloids like potassium. If this balance is
altered the cell will alter in size but not necessarily in shape.
An increased power of imbibition conferred on the cell colloids by
increased COg tension, for instance, leads to a swelling of the
corpuscle but no alteration in shape. Disturbance, however, of

316 THE BLOOD

the orientated surface layers, by removal of plasma or by disturb-
ance of the K/Ca ratio, leads at once to altered permeability and
an alteration in shape. From such experiments one infers that
the corpuscular capsule in contact with plasma is not of uniform
elasticity. This lack of uniformity is abolished when the cell is
completely removed from plasma or serum.

The conclusion at present drawn from experiments mentioned
in this chapter, viz. conductivity of whole blood compared with
that of laked blood, haemolysis in general, and, finally, the colliga-
tive properties of blood and plasma about to be considered, is that
the red corpuscle is a bag containing fluid and no spongework or
stroma. In other words, the continuous phase of the corpuscular
contents is water + crystalloids + cell globulin ^, while the disperse
phase is haemoglobin with some " bound " water and possibly
adsorbed crystalloids. The blood as a whole, then, consists of a
water-in-colloid complex in which is suspended small encapsulated
drops of a colloid-in- water complex. These two systems may be
compared in their properties to a series of little gelatin + collodion
bags filled with phenol-dispersed-in-water, suspended in a fluid,
water-in-phenol.

Contents of erythrocyte. The nature and volume of the disperse
phase in the contents of the corpuscle is of considerable academic
interest. The next chapter will be devoted almost entirely to the
study of the function of the haemoglobin, which is the main
constituent of the disperse phase wdthin the cell. It is a conjugated
protein composed of about 94 per cent, of a colourless protein —
globin — belonging to the histone group, and 6 per cent, of a
brownish ferro-porphyrin called haem. Haem is completely
insoluble in water at a jjH of about 7 and less, i.e. in neutral
and acid aqueous solutions, but dissolves in the presence of alkali.
Such a solution gives a diffuse absorption spectrum in the yellow
region not at all like that characteristic of haemoglobin. On
combining with globin, however, the spectrimi of reduced alkaline
haematin (haemochromogen) is obtainable from the compound.
Probably four haemochromogen molecules (mol. wt. about 17,000)
polymerise under the influence of an increase in the H+ ion con-
centration to form one haemoglobin molecule (mol. w't. about
68,000). The pigment is dispersed in gel form through a sol
within the membrane of the corpuscle. Actually about 32 grams
of Hb and 63 grams of water are found in every 100 grams of red
cells, while only 18 grams of Hb can be dissolved in 100 grams of
water.

Various estimates have been made of the volume of the dispersed
phase relative to the volume of the continuous phase. A know-

HAEMOLYSIS 317

ledge of this is necessary if one is to explain the partition of
diffusible non-eleetrolytes between the disperse phases of plasma
and corpuscle which have been found by experiment. For
example, if it were found that the partition of urea between
corpuscle and plasma corresponded to the relative magnitudes of
the continuous phase in those two bodies, then the conclusion
could be drawn that the urea was in solution only in the dispersion
media. On the other hand, if one found that the ratio of con-
centration of a substance in corpuscle to its concentration in
plasma were greater or less than the ratio between the volumes
of the continuous phases in corpuscle and plasma, then some of the
substance must be adsorbed to or soluble in the disperse phase of
one of the systems. Various values have been obtained for the
volume of the disperse phase in the corpuscle, ranging from
33 to 65 per cent. The reason for this wide variation is to be
sought in the methods employed in the investigation. The larger
values are obtained w^hen a haematocrite {q.v.) or other apparatus
depending on centrifugal force is used. If sedimentation is not
complete, and it very seldom is, high values are obtained for the
volume of the red cells. Ege's method is simple and ingenious,
and depends on the determination of differences in the depression
of the freezing point {q.v.) of solutions of non-electrolyte in equal
volumes of water and of red corpuscle press-juice. For example,

if the A of 8 grams of cane sugar in water = 1-22° C.
and of 8 grams of cane sugar in press-juice = 1-81° C.

(allowance having been made for the A of the press-juice alone)
then the volume (D.P.v.) of the disperse phase of the corpuscular
juice w'ould be found from the equation :

(100 —D.P.v.) X 1-81 = 100 X 1-22

122

100 —D.P.v. = = 67 = continuous phase

1-81

.'. volume of disperse phase = 33 per cent.

It is inferred that the dispersed phase consists almost wholly of
water in haemoglobin in a continuous phase of cell-globulin ^ in
water, both phases being enclosed in a membrane composed of
protein, lecithin and other phosphatides, cholesterol, etc.

Haemolysis.

As the haemoglobin is held in the corpuscle in a state in which
it is more concentrated than it could possibly l)e when in solution,
the process of putting it into solution ought to alter some of the
physical characters of blood. Blood diluted wdth an isotonic

318 THE BLOOD

solution, so that the corpuscle is not subjected to osmotic strain,
appears yellow and somewhat opaque. If now, the capsules of the
corpuscles are damaged so that the Hb is set free and goes into
solution in the aqueous saline solution, the liquid will become
translucent and a deep red in colour. 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.

2. Physical, freezing and thawing, heat, condenser discharges,
or similar methods.

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. 138).

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 capsule of the erythrocyte. Normally this membrane is

CHEN AT ION 319

inipernioablc to colloids and to most crystalloids. This has
Ijccii determined by estimating the electrical conductivity 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
be shown by fixing the corpuscles with formalin, which prevents
the egress of the pigment but not of the salts.

Laked blood has a lower viscosity than whole blood due to the
lack of 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 understood.
Possibly the withdrawal of water from the membrane to form
ice might be adduced as sufficient reason (Guthrie). (Cf. Test for
frozen meat.)

Endosmotie 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. Y.).
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

320

THE BLOOD

shrink and shrivel. They then break up into fragments, due to
inequahties 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.

Colligative properties of whole blood.

The suspension of small bodies like blood corpuscles in plasma
should not materially affect the values of vapour pressure, osmotic
pressure, etc. This is found to be the case. Using average values
taken from Grollman's paper referred to above, we find that blood
has practically the same vapour pressure and osmotic pressure as
its plasma at body temperature. Plasma is, however, slightly
richer in free salts, as shown by a slightly greater depression of the
freezing point. The difference is so slight that one might hesitate,
in view of the unstable nature of the bound salts of " separated "
plasma, to accept it as significant.

TABLE XLII

Colligative Properties of Blood and "' Separated " Plasma

AT 37-5° C. (Dog)

Vapour Pressure,
mm. Hg.

Depression of Freezing
Point. °C.

Osmotic Pressure.
Atmospheres.*

Blood

48-08

0-602

8-8

48-12

0-585

7-6

48-09

0-590

8-5

Plasma

48-09

0-616

8-5

48-12

0-605

7-6

48-11

0-604

7-9

48-08

0-620

8-8

* Calculated from vapour pressures.
XL, 1928.

Grollman : Jour. Gen. Physiol.,

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.

VISCOSITY OF BLOOD 321

TABLE XLIII

Serum + X 0 Corpuscles

„ + 3-2 X 10"
„ + 6-3 X 10«
„ + 12-6 X 10«

Viscosity at 32° C.

1-9

3-3

4-9

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.

The capsule and its contents are colloidal in character. Acids
increase the power of colloids to imbibe water, and, therefore, one
would expect that COg 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 (b) the swelling of the
corpuscle itself. The experimental 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 another 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 fornuda

1 ^ K = ^.

pc

If the total number of corpuscles per unit volume be A^ then
the average volume of each will be KjN .

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).

Further Reading
Ponder. '" The Erythrocyte and the Action of Simple Haemolysins."
Oliver and Boyd.

21

CHAPTER XXIII
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 respira-
tory gases, oxygen and carbon-dioxide. Air has an average
composition of about 79 vohniies 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 ^j^fj X 760 = 159-6 mm. of mercury. The partial pressure of
oxygen in the limg 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 CO,, 13 vols, of O^ and 79-5
vols, of N. Their partial pressures will be (at normal barometric
pressure)

O2 = ^ X 760 = 98-8 mm. Hg.
CO2 = f^ X 760 = 41-8 mm. Hg.
N = ^ X 760 = 604-2 mm. Hg.

The partial pressure of the oxygen in the limg 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 |l*|j 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 amovmts to about 50 mm. of Hg. That is, dry
air at normal temperature and pressure 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 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.

322

HENRY'S LAW 323

TABLE XLIV

Solubility of CO^ in Water at 15° C.
1'. 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 Ha; of CO.^,

V = volume of CO., (measured at N.T.P.) absorbed by 1 c.c. of water
atl5°C.

(The same volume of gas at constant temperature is absorbed by the fluid,
no matter what the pressure is. Increase of pressure proportionately increases
the weight of unit volume. Thus, if 1 volume of water dissolves 1 volume of
gas weighing 1 gram at 1 atmosphere pressure, then, if the pressure be raised
to 2 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 ot the gas w^eighing 2 grams.)

Absorption coefficient (u.sually denoted by the Greek letter a).

Uifi'erent gases, just like different solids, vary in their solu-
bilities. The vohime of gas (at N.T.P.) which dissolves in 1 c.c.
of water under a pressure of 1 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 = aJJ,
where L = amount of gas dissolved,
a = absorption coefficient,
}) = pressure in atmospheres.

Variations in temperature alter the amount of gas a fluid may
take up.

The amount of gas absorbed by a fluid decreases as the tempera-
ture of the fluid (and gas) is increased and vice versa.

TABLE XLV

Absorption Coefficients at Various Temperatures

Temperature.

Oxvucn.

Nitrogen.

t'arbon-dioxidi

o°c.

0-()489

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. 00231 0-0118 0-530

Effect of solutes.

Plasma, as we have seen, is a hydrophilic colloid in which a large
amount of water is dispersed through a hydrated protein-crystalloid

21--2

32J- RESPIRATORY FUNCTION OF THE BLOOD

complex ; that is, only a certain amonnt of the water present
(the true disperse phase) is chemically free. The large bulk of the
fluid present is firmly bound and closely packed in orientated
layers to the colloid, or serves as water of hydration for the
crystalloidal components. The colloidally bound water is con-
sidered by R. A, Gortner to be capable of " dissolving " more gas
than free water. On the other hand, many experiments in which
various solutes were added to plasma tend to show that the
presence of free crystalloids decreases the amount of gas that it is
able to hold.

Gas -holding power of plasma.

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.). If we consider
that the tension of oxygen in the tissues cannot be less than zero,
and 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
gastrocnemius muscle weighing 20 grams and using about 0-24
c.c. of oxygen per minute would, therefore, 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 weight of its own circulating fluid. For
example, the average man weighing 66 kg. would have to carry, in
addition, at least 140 kg. 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 minute — just under a
twentieth of the amount necessary when plasma alone was con-
sidered. 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 XLVI

Oxysen. Nitrogen. Carbon-dioxide.

Water .... 2-37 1-2 55-5

" Separated " plasma . 2-3 1-2 54-1

" True " plasma . .2-2 1-1 51 -1

In addition to the amount dissolved in " true " plasma one has to
consider the amount held by the haemoglobin. The table given

DISSOCIATION OF OXY-HAEMOGLOIilN

325

below contains the results of a series of experiments on the blood
of a horse, where the amount of oxygen in the blood was determined
at various pressures.

TABLE XLVTI

Oxygen tension

Oxygen in c.c. (at N.T.P.)
per 100 c.c. of blood.

Degrrc of
Satiirati<iii
of Hb. %.

Degree of
Dissoeiatiou %

in mm. of Hd.

(unsaturation).

(1)

Bound by
Haemoglobin.

C-'J

Dissolved in
Plasma.

(4)

[100-(4)]

10

6-0

0-020

30-0

70-0

20

12-9

0-041

64-7

35-3

30

16-3

0061

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

0141

98 8

1-2

80

19-9

0162

99-5

0-5

90

19-95

0182

998

0-2

150

20

0-303

loo

(»•()

From the figures in Table XL VII. it may be seen that much
the greater proportion of the oxygen is carried in combination with
the haemoglobin of the cells, and a relatively negligible proportion
in solution in the plasma.

Oxygen load of corpuscle.

The average normal man has about 5 litres of blood ; 2-5 litres
of this is occupied by 25 X 10^^ red corpuscles with a total surface
of about 3,000 sq. metres. When fully saturated with oxygen at
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

Total number of corpuscles

1000
25 X 10^2

4 X 10-11 c.c.

Each cubic centimetre of oxygen will need 25x10*^ 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-

326 RESPIRATORY FUNCTION OF THE BLOOD

mental finding of 401 c.c. Normal blood contains 14 grams per
cent, of haemoglobin. It follows that each corpnscle carries

= 28 X 10" 1- grams of haemoglobin. In other words,

25 X 1012 s

each cubic centimetre of oxygen postulates the presence of

28 X 25 X 109

= 0-7 gram oi Hb.

1012

The iron content of Hb must therefore be = gram

7 X 400 280

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.

Nature of union between oxygen and haemoglobin.

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 FeOg in haemoglobin. That may be. On the other
hand, the idea of a chemical combination between haemoglobin
and oxygen raises hosts of difficulties which w'ould 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 undisputed.

Conditions controlling the reaction between haemoglobin and oxygen.

Whatever may be the nature of the union between oxygen and
haemoglobin, it is established that the reaction between them is a
reversible one, the equilibrium point being determined by the
tension of oxygen and the active mass of haemoglobin, wdien all
other conditions, such as temperature, hydrogen ion concentration,
etc., are kept constant.

In Table XL VII., if the tensions (1) are taken as abscissae, and
the degree of saturation (4) as ordinates, a curve (Fig. 82, heavy
line) is obtained, called the dissociation curve of blood. It has been
shown by Hill that this curve can be approximately represented
by the equation

_ [Hb] [O,]-

[HbO,]

CONDITIONS INFLUENCING DISSOCIATION 327

The dissociation curve for pure haemoglobin is also foiiiui in
Fig. 82, dotted line. It differs from that of whole blood in that its
eontour is that of a rectangular hyperbole, wliieh ean be represented
approximately by the equation

[Hb] X [O,]

K

[HbO^-J

(Henderson)

Influence of the solutes of blood on the dissociation curve.

From Fig. 82 it may be seen that, at all oxygen tensions, the

DISSOCIATION CURVE. OF H/EMOGLOBIN AT 37°C.

too

lo 20 30 'ND SO 60 ro 80

TE-NSION OF OXVGEN IN MM OF Mq

90

/OO

Fig. 82. — Dissociation curve representing tlie cciuilibrium between oxygen tension^
oxy-haemoglobin and reduced haemoglobin :

= Curve from pure 14% haemoglobin .solution.

= „ „ 14% haemoglobin in plasma.

— „ „ ,, ,, ,, with increased

tension of carbon-dio.Nide.
Tlie hatched portion represents the amount of haemoglotiin wliieli gives up its oxygen
when the oxygen tension is reduced from 100 to 15 nun. Hg.

percentage saturation of haemoglobin with oxygen is less in blood
than in a solution of pure haemoglobin, although the difference is
small at tensions above about 80 mm. of Hg.

The dissociation curves of haemoglobin in solutions of sodium
chloride of approximately the same osmotic concentration as
plasma (about 0-9 per cent.) (q.v.) are found to lie nearer the

328 RESPIRATORY FUNCTION OF THE BLOOD

dissociation curve of blood, but to retain the same general shape
as the curve for pure haemoglobin.

Influence of H * concentration.

An increase, however, in the carbon-dioxide tension of the
haemoglobin solution produces a curve of the sigmoid shape,
typical of the blood dissociation curve, and, in fact, the dissociation
curve of haemoglobin in a solution containing the solutes of blood,
including COc>, in the projjortion in ichich theij occur in blood, lies
point for point on the dissociation curve of that blood. The presence
of any other acid in the blood, tending to increase the H+ con-
centration, as will be shown later, liberates COg from bicarbonates
present, and, therefore, has the same effect on the oxygen dis-
sociation curve as an equivalent increase in CO2 tension. It might
be thought that this influence of carbon-dioxide on the union
between haemoglobin and oxygen was a direct one, the oxygen in
the oxy-haemoglobin being simply replaced by carbon-dioxide, but
there is no molecular equivalence between the amounts of the two
gases involved in the reaction, and, therefore, this simple replace-
ment cannot be the explanation of the influence.

Examination of the curves of Fig. 82 reveals the importance to
the body of the part played by the solutes of the blood in the
transport of oxygen. At high oxygen tensions, the presence of
salts and COg in the blood does not materially decrease the per-
centage saturation of the haemoglobin, but at low oxygen tensions,
such as are found in the tissues, it enables much more oxygen to be
given off by the blood than would be the case in a solution of
pure haemoglobin.

In the tissues the tension of oxygen is low, say 15 nun. Hg. 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 (where the
blood in the lungs is supposed to be 92 per cent, saturated). 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 re})resented by the space between the heavy curve and the
dotted curve in Fig. 82. That is, solutes so aid in the unloading of oxygen that
50 j)er cent, of the haemoglobin that tcould otherwise have retained its oxygen is
induced to give it up to the tissiies. 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.

The effect of the carbon-dioxide tension is particularly important
at very low oxygen tensions, as with increasing carbon-dioxide

Ch and dissociation 329

tension the percentage saturation of haemoglobin with oxygen
at these low oxygen tensions becomes very small.

In the lung. CO2 passes from the blood into the alveolar air, and
the hydrogen ion concentration of the plasma tends to decrease.
At the ordinary alveolar tension of oxygen this has little effect on
the combination of oxygen and haemoglo})in, })ut where the
alveolar tension of oxygen is reduced, as at high altitudes, the
exchange of gases occurs under conditions in which the COg tension
is increasingly important, and the adequate removal of the COg,
and consequent decrease of H^ concentration in the plasma, is
an important factor in permitting the picking up of an adequate
load of oxygen by the haemoglobin.

From curve 82 it may be seen that, if the exchange of gases
were to take place in the lungs at an oxygen tension of 50 mm.,
and if the curve indicated by the broken line represented the
haemoglobin dissociation curve at the COg tension of venous
blood, and the thick line represented the same curve at the COg
tension of the alveolar air, then the mere passage of the COo from
the blood into the alveolar air would enable the haemoglobin to
take up more oxygen. Thus the action of the CO^ on the reaction
between haemoglobin and oxygen is such that the taking up of oxygen
in the lungs and the unloading of it in the tissues are both facilitated.
So it appears that the COg tension of the blood is an important
factor in defining the oxygen dissociation curve, and that the con-
stant K in Hill's equation must be a function of the carbon-dioxide
tension.

It has been found that Hill's equation may be written

H,C03 + 7-7 _ [Hb] [0,r
0-014 [HbOg] '

where K = [^^^^3] + 7-7^

0014

How the tissues unload the oxygen.

(1) Distortion. The corpuscle is considered as a fluid drop with
an outer coat of orientated lipoid matter. The colloidal haemo-
globin is dispersed through the liquid contents. These little
barges, 8-8/x in diameter (p. 313), 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.

330 RESPIRATORY FUNCTION OF THE BLOOD

(2) 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. XXXII.). Increase in temperature increases
the desaturation of haemoglobin. 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

Hb + Oo :;^ HbO^.

The velocity of this reaction depends, other things being equal,
on the active masses of oxygen, C,), and of haemoglobin, C^.,

i.e. V = k (Co X Cjj).

Now A'l, the velocity constant of the saturation process, and k2,
the corresponding constant for desaturation, vary with the
temperature. We have seen (p. 323) that a, the absorption
coefficient of oxygen in blood, varies inversely with the temperature.

where Cjj = concentration 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 T^ and To
are related by the equation

-q T., - T.

(e = base of Napierian logs, q = heat evolved when 1 gram
molecule of Hb unites with 1 gram molecule of oxygen).

For example, let us try to determine what desaturation would
arise from raising the temperature from 36° C. to 39° C.

Here T, = 273 + 36 = 309 absolute,

Ta = 273 + 39 = 312
and q = 28,000 cals.,

- 28000 3

If ^36 be 30 per cent., then K^^ is equal to 30e-°'^3^'^ = 19-4,
we find that haemoglobin which was 30 per cent, saturated at
36° becomes only 19-4 per cent, saturated at 39°.

TISSUE ACTIVITY AND DISSOCIATION .331

An increase in 3° C. betxveen the values of 36 and 30 causes the
IlbO., to lose oxygen to the extent of about 10 per cent, of full saturation.

(3) Carbon-dioxide. A physico-chemical factor, however, is
much more potent than temperature in })roducing desaturation.
Active tissues tend to become acid. In deahng 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 COg in the capillaries.
The molecules of COg are to be the new passengers on the erythro-
cytes, and because of their acidity they cause an aggregation of
the colloidal particles of haemoglobin and, as has already been
indicated, 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 of24< mm. Hg. as if the tension of oxygen were
only 10 mm. For example, blood which in the absence of CO 2
would be 30 per cent, desaturated is actually desaturated to the
extent of 78 per cent, by the presence of a CO2 tension of 40 mm.
Hg. The blood becomes now a carrier of CO2 from the tissues to
the lungs (Fig. 82, 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
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 + Na2HP04 — NaHoPO, + NaHCOg.

The sodium bicarbonate so formed finds its way into the blood
stream, where it is in equilibrium with free dissolved carbon-
dioxide, so that the volume of COg in solution is 1/20 of the volume
of combined COo.

The result of the influx of NaHCOg is to increase the volume of

332 RESPIRATORY FUNCTION OF THE BLOOD

CO free 1
free COg in order to preserve this ratio -, = . That

CO2 combined 20

is, the CO2 tension in the muscle capillaries tends to increase,
and increase of COg tension causes increased unloading of oxygen
from oxy-haemoglobin.

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 CO^ — the
inain 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 oJ 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. The
erythrocyte, once freed from its load of oxygen, takes on a cargo of
carbon-dioxide. Part of this cargo is carried by the haemoglobin
and part is dissolved in the corpuscular lipoid envelope causing it
to swell. Lipoid is capable of dissolving very large amounts of
COo. But the erythrocytes are not the sole means of transport.
Carbon-dioxide is about twenty-five times as soluble in water
as oxygen under similar conditions. Relatively more COg 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
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 XLVIIT

Partition op Co, in 100 c.c. of Depibrinated Blood
(Haematocrite Value = 51)

Vol. of COo

Vol. of CO,

Vol. of CO,

CO J tension.

in blood.

in serum.

in corpuscles,

Oxygenated .

40

45-0

25-9

191

Reduced

40

50-4

28-0

22-4

That is, in arterial (whole) blood there is about 50 c.c. of COg,
of which amount the fibrinogen carries about 5 c.c, the serum

TRANSPORT OF CARBON-DIOXIDE 333

(proteins, water and crystalloid bases) about 26 c.c., and the
corpuscles about 19 c.c.

As stated above, the free carbon-dioxide of the blood represents
only about 1/20 of the total carbon-dioxide carried. The forms in
which the combined carbon-dioxide of the blood is carried must
therefore be sought.

Transport of COo in chemical combination with the blood constituents.

It is assumed that the CO2 carried in the blood in chemical
combination is found there as bicarbonates, because the whole of
it may be removed if the blood is treated with an acid stronger
than H2CO3. This latter reaction is assumed to be of the nature
expressed by BHCO3 + HA =- BA + HgCOg, where B is a basic
radicle and HA is an acid. It is, however, found that the whole
of the COo of the blood may be removed by subjecting the blood to
a high vacuum. This is not the case for a simple bicarbonate
solution, which under a vacuum only gives off half its COo (2BHCO3
= B0CO3 + H2O + CO2). Plasma subjected to a vacuum reacts
like a pure solution of bicarbonate and gives off only half its COg.
The re-addition of erythrocytes to such plasma, which is again
subjected to a high vacuum, permits the removal of the remaining
CO2. There is, therefore, some substance in the red cells, which
acts as a weak, non-volatile acid in its relation to the carbon
dioxide of the blood, and can displace the latter from its combina-
tion as carbonates if each small amount of the latter is removed as
produced, owing to the low pressure at which the reaction is
carried out. It has been found that this substance is the haemoglobin
of the red blood corpuscle.

BHCO3 + HA — BA + H2O + C02*(*volatile-removed as formed).

(weak)

Absorption curve of CO 2 in blood.

A curve showing the volume of gas absorbed by blood under
different pressures of the gas can be drawn for carbon-dioxide as
for oxygen. The general shape of the curve is rather like that of
the absorption of oxygen by a solution of pure haemoglobin than
like the oxygen absorption curve of the blood, i.e. it is not sigmoid.
The volume of carbon-dioxide absorbed at a given tension is found to
depend on the degree of oxygenation of the haemoglobin. The higher
the saturation of the haemoglobin with oxygen, the less the CO2
absorption. (The converse influence of COg in O2 absorption has
already been noted.)

The hydrogen ion concentration is also an important factor in

334 RESPIRATORY FUNCTION OF THE BLOOD

determining the volume of COg absorbed, the vohmie increasing as
H+ decreases.

It has been stated that the bound COg of the blood is found as
bicarbonates produced by the combination of COg in solution as
H2CO3 with bases of the blood. But the blood, either venous or
arterial, has a pfL very near the neutral point, and cannot contain
any considerable quantity of free base to be neutralised by the
carbonic acid. The mechanism by which base is liberated for
combination with the respiratory COg without any considerable
change in the pH of the blood has been shown to be dependent on
the physical and chemical characteristics of haemoglobin and its
compounds. The part played by this compound in the transport
of oxygen has been indicated. It is equally important in the
transport of carbon-dioxide.

By virtue of its chemical composition, haemoglobin in solution
can dissociate, either as an acid or as a base, according to the pH
of the solution ; in other words, it is amphoteric {q.v.). Therefore,
in solutions at a pH on the alkaline side of its isoelectric point
(about pH 6-8), haemoglobin reacts as a weak acid and can combine
with bases. In solutions of |?H less than 6-8 {i.e. more acid),
haemoglobin reacts as a weak base and can combine directly with
carbon-dioxide. Blood under ordinary conditions in vivo does not
reach a ^;H less than 6-8, and, therefore, the haemoglobin in it
always reacts as a weak acid, and cannot combine directly with
carbon-dioxide. Its action in the transport of the latter is, there-
fore, an indirect one.

When carbon-dioxide enters the blood it reacts with the weak
salts of haemoglobin to liberate the free acid haemoglobin and form
bicarbonates, i.e. B.Hb + H2CO3 = BHCO3 + H.HB. Haemo-
globin is a very weak acid, and exerts a very slight influence on
the pH of the red cell contents, Oxy-haemoglobin, on the other
hand, acts as though it is a much stronger acid.

It is known that where a base insufficient for the neutralisation
of both is added to a mixture of two acids, the proportion of the
salts formed from the two acids depends on the relative " strengths "
of the acids and also upon their relative concentrations in the mix-
ture. In the cells there appears to be a fixed quantity of base
which is distributed between the acids, haemoglogin and carbon-
dioxide, according to their relative strength and concentrations.
The concentration of haemoglobin can only be varied by variations
in total cell volume, as the cell is impermeable to haemoglobin, but
the concentration of carbon-dioxide in the red cell depends on the
carbon-dioxide tension of the plasma, which again is determined
by the COg tension in the lungs or tissues. The concentration of

SALTS OF HAEMOGLOBIN 335

carbon-dioxide in the erythrocyte is, therefore, subject to consider-
able variation, and will tend to decrease in the lung, since the
alveolar carbon-dioxide tension is low. The " strength " of the
carbon-dioxide in solution as carbonic acid is unchanged, but, as
has already been indicated, oxygenation in the lung causes a marked
increase in the acid strength of haemoglo})in. The reaction
BHCO3 + H.Hb z= B.Hb -f HgO + CO2 is facilitated in the
direction from left to right, both by virtue of the increased acidity
of the oxyhaemoglobin, which, therefore, needs more alkali to
neutralise, and also by the escape of the carbon-dioxide, which
lowers the concentration of carbonic acid in the cells relative to the
concentration of haemoglobin.

The quantitative importance of this redistribution of base may

be appreciated from the following figures taken from Van Slyke.

At the ordinary hydrogen ion concentration of blood (pH 7-4),

1 mol. reduced haemoglobin (= 1 mol. O2) combines with about

1-5 equivalents of alkali.

This same haemoglobin, in oxygenated form, combines with a

little over 2 equivalents of alkali.
.'. the reduction of 1 molecule of oxygenated haemoglobin in
the tissues sets free about 0-6 equivalents of alkali to combine
with the CO2 produced in the tissues.

If the respiratory quotient is 0-8, and 0-8 molecules of COg are
produced for every molecule of oxygen absorbed, then 0-6 molecules
of CO2 {i.e. 75 per cent, of the total) will be carried by alkali
liberated from combination with oxy-haemoglobin by the reduction
of the latter. The remaining 25 per cent, of the carbon-dioxide is
carried by reaction with certain salts of weak acids, including
H2HbOo, present in the blood, the reactions being of the type
B2HPO4 + H2CO3 = BH2PO4 + BHCO3.
These latter reactions are accompanied by a very slight increase
in hydrogen ion concentration. The weak acids involved in these
reactions are mainly phosphates and the proteins of plasma and
cells.

It would seem, then, that cells carry at least 80 per cent, of the
respiratory carbon-dioxide of the blood {i.e. the carbon-dioxide
picked up by the blood from the tissues, and excreted in the lungs,
as distinct from that concentration of carbon-dioxide which is
present alike in venous and arterial blood). Examination of
arterial and venous blood from any individual under given condi-
tions reveals, however, that the excess of carl)()n-dioxide carried
by the venous blood over that carried by the arterial blood is
distributed in approximately the ratio of 3 : 3 between serum and
cells. (Table XLVIII.)

336 RESPIRATORY FUNCTION OF THE BLOOD

TABLE XLIX

100 c.c. OF Arterial Blood (CO2 tension 40 mm., Og tension 100 mm.).

Corpuscles | | in solution . . 0-85 c.c.

51 % by volume |- carry | of total CO2 - bound {e.o. NaHCOg) . 8 45 c.c.

[adsorbedby Hb, etc. . 9-7 c.c.

19 c.c.

Plasma

49% by volume

^carries f of total COn

in solution . . 1-2 c.c.

bound (NaHCOg) . 23-8 c.c.
adsorbed by fibrinogen 5 c.c.
adsorbed by serum

proteins. . . 1 c.c.

31 c.c.

100 c.c. OF Venous Blood (CO2 tension = 45 mm., 0_> tension = 40 mm.).
Corpuscles carry . 22 c.c. = + 3 c.c. over arterial blood.
Plasma carries . 34 c.c. = + 3 c.c. ,, ,, ,,

56 c.c. + 6 c.c. ,,

The conclusion might be drawn that some mechanism for carbon-
dioxide transport in the serum, quite other than that in the cells
involving haemoglobin, must be sought. The explanation of the
apparent inadequacy of the latter mechanism has been found by a
study of the inter-relationship between the electrolytes of serum
and cell contents.

The function of serum and cell electrolytes in the transport of CO 2.

Increase in the carbon-dioxide tension of plasma causes a re-
distribution of chlorides as between the blood cells and the plasma,
resulting in an increase in cell chloride and a decrease in plasma
chloride. Some carbon-dioxide also passes into the red cells. This
brings about a considerable increase in the electrolyte concentration
in the cells, and, therefore, of the osmotic pressure, and water is
drawn from the plasma into the cells to restore osmotic equilibrium.
If the consequent increase in erythrocyte volume (q.v.) is taken
into account, chemical analysis shows that a quantity of hydro-
chloric acid equivalent to the bicarbonate taken up by the plasma
has passed from the plasma into the cells, and the reactions
supposed to occur are as follows : —

NaCl + H2CO3 = NaHCOg -f HCl.

This is followed by the passage of the liberated HCl through
the cell membrane. The hydrochloric acid then reacts with the
salts of haemoglobin in the same way as was previously described
for carbonic acid, viz.

HCl + B.Hb = BCl + H.Hb.

FUNCTION OF CELL CHLORIDES 337

This means that a considerable proportion of the respiratory
carbon-dioxide (quite 90 per cent, of the total respiratory carbon-
dioxide carried by the plasma) is transported in combination with
bases of the plasma, which previous to the loading up with carbon
dioxide w^re combined with hydrochloric acid. While the respira-
tory carbon-dioxide is " on board " this hydrochloric acid is carried
in the cells in combination with base liberated from haemoglobin.
In determining the actual contribution of the haemoglobin to the
transport of respiratory carbon-dioxide, it is therefore necessary to
take into account not only the excess of carbon-dioxide in the cells of
venous blood over that in arterial blood, but also the excess of cell
chlorides. When this is done it is found that, as stated above, the
haemoglobin provides for the transport of at least 80 per cent, of
the respiratory carbon-dioxide.

When the carbon-dioxide is excreted in the lung, the processes
described above occur, of course, in the reverse order, although,
owing to the fact that under all physiological conditions plasma
contains a higher concentration of both chlorides and carbonates
than the cells, this involves the passage of chlorides and car-
bonates from a lower to a higher concentration.

This simple explanation of the mechanism of the transport of
carbon-dioxide needs, therefore, further exploration, since it would
seem to entail first the displacement of the strong acid hydrochloric
by the weak acid carbonic in the plasma, and then later the replace-
ment in the cells of the relatively stronger acids hydrochloric and
carbonic by the very weak acid haemoglobin (which even in its
oxygenated form is still a very weak acid). It is well knozvn that
a weak acid will replace a strong one in combination if the strong one
is removed as it is formed, and, as indicated above, it is on this basis
that the removal of carbon-dioxide from the blood, in the lung, is
explained. But it is necessary to consider why the displacement
of chlorides should take place, since there is no variation in chloride
tension in lungs and tissues.

It has been stated that carbonic acid displaces the stronger
hydrochloric acid from combination as the chlorides of the plasma,
because the hydrochloric acid so liberated diffuses through the cell
membrane and is thus removed from the sphere of action, and that
therefore the reaction NaCl + HoCOg r^ NaHCOg + HCl pro-
ceeds from left to right. It must, however, be remembered that
the cell membrane is freely permeable also to carbon-dioxide, and
that, in fact, at least 40 per cent, of respiratory carbon-dioxide
passes into the cell and there displaces base from combination with
haemoglobin. Since, moreover, enough base can be liberated from
combination with haemoglobin to combine with the whole of the

838 RESPIRATORY FUNCTION OF THE BLOOD

respiratory carbon-dioxide, it is obvious that some other factor
must be involved which determines how much carbon-dioxide
shall enter the red corpuscle and how much shall react with
chloride in the plasma, liberating hydrochloric acid, which then
enters the red cell.

Since the passage of carbon-dioxide into the cell under increased
carbon-dioxide tensions, and the passage of carbon-dioxide out of
the cell under lowered carbon-dioxide tensions, is accompanied by a
transfer of chlorides in the same direction, it would seem that the
distribution of one of these electrolytes is related to the distribution
of the other. For information on this point, the distribution of all
the main solutes of the blood between plasma and cells must be
studied. It is then found that : — ■

(1) The solutes of the blood are so distributed that the red cell
contents and plasma are isotonic (q.v.). This is indicated by the
shape of the cells (Chap, XXII,).

(2) The red cells are impermeable under physiological conditions
to the bases of the blood (excepting the hydrion),

(3) The red cells are freely permeable to the non-colloidal
anions of the blood,

(4) The red cells are impermeable to the protein anions of the
cells and plasma.

From Donnan's theory of membrane equilibria (q.v.) it may be
deduced that under these four conditions, for thermodynamic
equilibrium

[Cy _ [HCO3J _ [HJ _ [AJ

[CIJ [HCO3J [HJ [AJ

Where [AJ is the ionic concentration of anions in the cell.

[A J is the ionic concentration of anions in the serum, etc.

[A 1
The ratio — ^ has been called r.

[AJ
Thus it is seen that when carbon-dioxide enters the blood, thus

riTCO 1

altering the ratio '—, a re-distribution of the other mono-

[HCO3J'

valent anions (mainly chlorides) must occur to preserve thermo-
dynamic equilibrium. But this is not the only condition governing
the electrolyte distribution in blood. For osmotic equilibrium the
total osmolar concentration in plasma and cells must be equal, and
therefore the passage of carbon-dioxide and chloride from plasma
to cells must be accompanied by a passage of water in the same
direction, with a consequent increase in cell volume. Also for
electrical equilibrium the total positive ions of the serum must equal

ALIGNMENT CHART 339

the total negative ions of the serum, and hkewise for the eclls.
These three conditions absohitely determine the relative distribu-
tion of eleetrolytes under given eonditions. If the eomparatively
low osmotic pressures of haemoglobin and serum protein are
ignored, an approximate value for r may be deduced, viz. :

[Hb,]

r = 1

2 [A J

As — cannot be negative, r must always be less than 1, i.e.

2 [A J

there will always be an unequal distribution of anions about the
membrane, the concentration in the cells being always less than
that in the serum.

Hence the transport of respiratory carbon-dioxide in the blood
involves the passage of carbonate, chloride and water from plasma
to cells, a change in cell volume " i'," a change in the anion ratio
" r " and a slight change in hydrogen ion concentration ; the
changes which occur when the haemoglobin is reduced and the
carbon-dioxide is picked up occur in the reverse order when the
haemoglobin is oxygenated and the carbon -dioxide excreted.
Thus it may be seen that in determining equilibrium eonditions in
the blood, it is necessary to consider oxygen tension, carbon-dioxide
tension, j^H, r, v, the percentage of haemoglobin combined with
oxygen, and the percentage of carbon-dioxide free and in combina-
tion with base as bicarbonate. The relationship between any
two of these factors, when other conditions are constant, may
be represented by curves.

In studying the mechanism of the gaseous interchange of blood,
it is convenient to begin by studying the reaction of blood in vitro,
under specified conditions. From such studies, curves like Fig. 82
may be deduced. These curves do not, however, at all represent
the gaseous exchange of blood in the body. They represent the
variation of one gaseous constituent {e.g. O^) with one other
condition {e.g. oxygen pressure), assuming that other conditions
{e.g. tensions of other gases) are constant. In the circulating blood,
however, in lungs and tissues, not only oxygen tension, but carbon-
dioxide tension, vary from point to point, and the oxygen absorp-
tion curve for blood in vivo is one which intersects the curves
representing oxygen absorption at different oxygen pressures
under different constant carbon-dioxide tensions of physiological
range.

To define the complete equilibrium conditions of blood at any
point a large number of curves would be necessary, indicating the
relationship between oxygen and carbon-dioxide content and ten-

340 RESPIRATORY FUNCTION OF THE BLOOD

sion, hydrogen ion concentration, free and bound carbon-dioxide,
r, cell volume, etc. It has, however, been shown that for any
given sample of blood an " alignment chart " may be drawn, and
graduated in such a way that each curve on it represents one
variable factor in the blood, and a straight line drawn to cut all the
curves will do so at points which give the value of each of the
respective factors in the blood at any one time. Hence, if the
simultaneous values of any two factors in the blood be known, all
the others may be deduced from the chart by joining the points

\^ fv4 TotaJ CO^ COJension

Oz HbO,

Fifi. 83. — D'Ocagne tomogram or Aliannient Chart for the blood of A.V.B. (By courtesy
of L. .7. Henderson, from Ifecent Admnccs in Physiology. Kxplanation in text and also in
Lectures on Certain Aspects of Biochenn.itry.)

corresponding to these values on their respective curves and
producing the line to intersect the other curves.

In the alignment chart (Fig. 83) the seven graduated lines, taken
from left to right, represent respectively (1) the ratio, r = (anions
of cell)/(anions of serum) ; (2) the volume of the erythrocytes, v ;
(3) the total COg of the blood ; (4) the CO2 tension ; (5) the joH of
the serum ; (6) the oxygen tension ; and (7) the percentage satura-
tion of haemoglobin with oxygen. If any two of these values are
known for the blood for which an alignment chart has l:)een
constructed, then the five other concomitant values may be
obtained by drawing a line through the two known points. This
line will cut all seven lines, and the point at which it cuts a

CELL VOLUME 341

graduated line will gi\e the \alue for that faetor. For example,
ill Fig. 83, wliieli is the aliguuieut ehart for A.V.B.'s blood, if one
knew that, at any time, the blood, under a tension of 40 mm. Hg
of CO2, would give a serum with a^;!! of 7-45, then, by joining these
points and produeing the line to eut the other curves {i.e. the
line a — b in the figure) the values of r, v, total CO2, Oo
tension, and percentage saturation of Hb with oxygen are given
by the points of intersection of a — b with the respective graduated
curves. This shows us that when this blood has a COg tension of
40 mm. Hg, and its serum a p¥l of 7-45, the chlorides and biear-
bonates are so divided between cells and serum that [BHCOaJj
[BHCO3], = [C1],/[C1], = r = 0-723 ; the cell volume, v = yo\ =
100-1 ; the total COg = 48 per cent. ; the oxygen tension =
70 mm. Hg ; and the percentage saturation of haemoglobin with
oxygen = 92.

A word of explanation is necessary concerning the value (vol)
of the cell-volume. Professor L. J. Henderson, to whom we are
indebted for the ehart, took the normal cell-volume (70/z") as
100 per cent., when the O2 tension was 80 mm. Hg and the CO2
tension was 39 mm. Hg. At this point the haematocrite reading
was 40 per cent., i.e. the cells occupied two-fifths of the total blood
volume and the plasma the remaining three-fifths.

The line a — b represents a typical set of conditions for arterial
blood. Another line, c — d, could be drawn to represent the values
of the seven factors in typical venous blood. Here the COo
tension has risen to 47-5 mm. Hg, and the Hb saturation has fallen
to 65 per cent. It is evident that this produces marked alterations
in the values of r and v, and a less marked increase in hydrogen ion
concentration. Between the extremes represented by the oxygen
and carbon-dioxide tensions indicated by the lines a — b and c — d,
i.e. between arterial and venous conditions, a large number of
lines are possible, representing the conditions in capillary blood.
For example, blood with an oxygen tension of about 60 mm. Hg.
might pass through a very active tissue producing large quantities
of CO2. The blood as it reached this tissue might have the
following characteristics, viz. r = 0-73 ; vol. = 100-4 ; total COg
= 48 per cent. ; CO2 tension = 42 mm. Hg ; pH (serum) = 7-41 ;
and percentage Hb02 = 90 per cent. Interchanges with the active
tissue would cause a decrease in factors 6 and 7 on the chart, and
an increase in the factors represented by the first five lines, e.g.
r = 0-75 ; vol. = 101 ; total COg = 52-5 per cent. ; CO2 tension =
45 ; ^H serum = 7-42, all increase ; while Og tension = 36 mm.
Hg and HbOg per cent. = 70, show a decrease. Oxygen has been
given to the tissues, and CO2 accepted from the tissues with a

342 RESPIRATORY FUNCTION OF THE BLOOD

consequent adjustment of r, vol and pH^ to meet the new con-
ditions. Thus, by this simple diagram, the complicated changes
occurring in the blood during respiration or following on the
activity of any organ, can be depicted.

It must be noted that each alignment chart represents the
conditions in the sample of blood from the analysis of which it was
constructed, and must not be applied generally to any blood under
any conditions. Any change of condition necessitates the con-
struction of a new chart.

Integrative action of blood plasma.

Plasma must be considered as a solution of water in colloid
separated from other fluids (with which it is in equilibrium) by
membranes permeable to certain solutes. The whole transport
system is a multi-phase colloidal complex in equilibrium. Altera-
tions in any phase produce regulatory 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 would 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 inefiicient. 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

INTEGRATIVE ACTION OE PLASMA 343

a scarcity of oxygen in the air hreatlied — analysis will show
that, (ii.) The lung mechanism may he out of order (Chap.
XXVII.). (iii.) The memhrane separating lung-air from blood
may have lost its permeability. Comparison oi" 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 fidl load. {\.) 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.

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
physico-chemical force brought about mainly via the inland
transport system that goes to make up the metabolism of the
organism.

Further Readixs

Barcroft. '' The Respiratory Function of the Blood." Cambridge Univer-
sity Press.

L. J. Hexderson. In " Certain Aspects of Biochemistry." University of
London Press.

Van iSlyke. " Factors Affecting the Distribution of Electrolytes, Water
and Gases in the Animal Body." Lippincott.

CHAPTER XXIV
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 handhng 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 sjDecial 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.
Indissohibly associated with any system of importation is the
provision of exports. Any barge travelling empty on the blood
stream as on any 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.

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 air sacs, and after a very short interval is
expelled into the outer air altered in content.

In the average resting man, somewhat over 500 c.c. of air come

344

VITAL CAPACITY

345

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
is given below (Table L.) :

TABLE L

Age.

0-6 months.
6-12 months.
3- 7 years.
8-14 years.
Adult.

48

85-130
124-220
220-400
300-550

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 complemental air.
By a forced expiration after a normal expiration the reserve air
may be expelled from the lungs. The volume so expelled varies
very much, and may markedly be increased by practice. Some
people can breathe out only an additional 500 to 700 c.c, while
singers, physical training experts and others who practise abdomino-
thoracic breathing, may register a volume of 1,500 to 2,500 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 :

Vital capacity

Residual air

Tidal air

Complemental air
Reserve air

500 c.c.
1,500 c.c.
1,500 c.c.

3,500 c.c.
1,000 c.c.

Volume of fully distended respiratory apparatus . 4,500 c.c.

This volume of 4,500 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

346 LOADING UP

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 CO., and
imported Og.

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 sac 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 volume of lung substance is 1617 c.c.
This provides for the possible presence of 404,500,000 air sacs,
with a surface of 50*56 square metres. Of course this is a maximum
value for the number. From the volume of lung substance has
to be deducted the volume of the supporting cells of the lung, of
the blood vessels, 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 lumina of the alveoli. Various estimates have been made
of the surface area of the alveoli, ranging from that of von Huschke
of 2,000 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
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. XXV.). The sudden increase in the

EFFECTIVE ABSORPTIVE SURFACE 347

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 {b) 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 COg 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 CO2 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, {b) 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 two layers of flattened cells separating blood from
alveolar air differ little in chemical nature from any other similar
structure. Ofie may note, however, their richness m lipoids,
{b) They are constructed of large irregular flattened cells forming
an extremely delicate layer as thin as the film of a soap bubble.
The average thickness of the membranous layer is 0-004 mm.
(c) Not only does the protoplasm forming the membrane contain
about 90 per cent, of water dispersed through it, but its surface is
kept moist on both sides, (d) Carbon-dioxide is very soluble in
water, and more soluble in lipoid. Water at body temperature
and atmospheric 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.

It is worth while to look a little more closely at this problem.
In Chap. XXIII. is given a table (XLV.) 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

348 LOADING UP

absorption coefficient of the gas, but also on a factor Ic — the
diffusion coefficient. Ic is a constant for each gas and each
temperature. The appended Table LI. (from Loewy) will amplify
this.

TABLE LI

Diffusion Coefficients

Temperature

Oxygen .
Carbon-dioxide .

. 16° C.
. 1-62
. 1-38

37° C
1-68
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. X 1 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"815 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 kym 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 jjH 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 COg 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 1 sq. cm.
of alveolar wall may be calculated from this formula :

V

760 Vni • d
Dealing with carbon-dioxide we may evaluate as follows :

a at 37° = 0-57,

Pj^ = COg tension in the blood of the pulmonary artery
= about 46 mm. Hg.

^2 = CO2 tension in alveolar air = about 40 mm. Hg,
Pi — P2 = -i^ — 40 = ^ mm. Hg.

GASEOUS DIFFUSION 349

This difference of pressure, of course, only exists at the beginning of the
experiment. The blood loses carbon-dioxide, i.e. p^ decreases ; COg passes
into the alveolar air, i.e. p^ increases, and p^ — ^g-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,
\/m = V44 = 6-63,

d = thickness of alveolar wall = 0-004 mm.,

_ 0-57 X 3 X 0-139
~ 760 X 6-63 X 0-004
= 0-01 c.c. 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 X 0-01 = 10,000 c.c.

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 X 760 -y/m X d

Pi -P2

a X c

Evaluating this,
Pi ~Pz

_ 250 X 760 X 6-63 X 0004
"~ 0-57 X 0-139 X 100 X 10,000
= 0-063 mm. Hg.

That is, a difference of COg tension between blood and alveolar
air of only 2 X 0-063 = 0-12 mm. Hg would be quite sufficient to
cause 250 c.c. of COg 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.

(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 structuralh' do

350 LOADING UP

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 COg 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 dis-
agree with the earlier flndings, 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 3,000 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.

Employing the same formula as for COo, one finds with a differ-
ence of pressure of 7-6 mm. Hg that

00239 X 3-8 X 013!> ^^ ^^^^

V = = 00006 c.c.

760 X 5-66 X 0-004

per minute per sq. cm. This gives a value of

100 X 10,000 X OOOOG = 600 c.c.

passing through the total effective absorptive surface of the lung.
Thus we see that the physical conditions allow for an ample supply

VENTILATION OF LINGS 351

of oxygen for ordinary purposes. As a matter of faet a difference
in pressure of less than 4 nmi. would ])e 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 3,000 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 (LII.) shows that the
ventilation of the lungs is markedly increased by the performance
of work.

TABLE LII
Ventilation of Lungs

Litres per iiiiu. Kosijir. ]kt niiii.

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.

TABLE LIIT

HT ON Barometric

Pressure

Barometer
mil). Hg.

760

Per cent, of an
atmosphere.

100

670

88

593

78

524

69

463

61

410

54

357

47

320

42

Height above sea level
in metres.

0
1,000
2,000
3,000
4,000
5,000
6,000
7,000

It is well known that ballooning, for instance, causes respiratory
distress ; so, too, does mountaineering. Mountain sickness fre-

352 LOADING UP

quently begins at altitudes of 2,000 to 3,000 metres, particularly if
the ascent has been fairly rapid by railway. Airmen usually suffer
after ascending 5,000 to 6,000 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 LIV

Effect of Atmospheric Pressure on Alveolar Oxygen

Tension

Height above sea

0.

tension of

Alveolar 0, tension

level in metres.

air.

mm. Hg.

mm. Hg.

Berlin .

54

157

105

Brienz .

500

148

88

Brienzer Rothorn .

. 2,130

121

62

Col cl'Olen .

. 2,900

110

60 .

Monte Rosa

. 4,560

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
iiaemoglobin content of the blood is increased, as in the case of
acclimatisation to high altitudes ?

TABLE LV
Atmospheric Pressure and Number op Erythrocytes

Height above sea

Red

level in metres.

corpuscles.

Christiania

0

4,970.000

Zurich

412

5,752,000

Davos

1,560

6,551,000

Arosa

1,800

7,000,000

Cordilleras

4,392

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

EFFECTS OF ALTERED AIR PRESSURE 353

ordinary state of affairs ; but as improvements were made in experimental
nietliods, 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 jihenomena." — Bayliss, Principles of
General Physiology.

Let us now consider what happens to the inland transport
service when the port becomes congested with incoming traflftc.
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 conciousness, 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
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

B. 23

354 LOADING UP

simple solution in the plasma. («) 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. 82). {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
s()lul)ility 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
pressure 1 litre of blood contains 200 c.c. of oxygen carried by
haemoglobin and only 3 c.c. in simple solution (measured at
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 3h 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 oxvffen in its
passage through the pulmonary capillaries, we may take for
granted that saturation with nitrogen under the same conditions

EFFECT OF COMPRESSED AIR 355

is just as complete. It is also reasonable to suppose that Daltou's
Law of partial pressures is just as applicable to blood as to any
ordinary solution exposed to compressed air. 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 («) to the absorption coefficient of the gas in
blood and tissues and (6) to the partial pressure of the gas in
blood and tissues. («) 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 tissvie 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 3 atmospheres brought about
by a rapid descent through 60 ft. of Avater to the bed of the sea.
The volume of gas in solution in the body is at once reduced
to one-third, 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.

23—2

356

LOADING UP

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.

Distribution of Nitrogen in the Tissues of Men Weighing 70 Kg.

TissTie.

Per cent, of
body wt.

wt. of tissue.

Vol. of nitrogen.

Blood .
Fat
Bone
Residue .

5

15

3

77

100

3-5 kg.
10-5 „

2-1 „
53-9 „

30 c.c.
530 „
0 „
435 „

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 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 calcula-
tion, considered as spread uniformly and at a uniform rate through-
out 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 circula-
tion would add 1/32 of the remaining deficit in saturation, 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. 84). As about 3-5 litres
of blood pass through the lungs every minute, and as the total

DECOMPRESSION

357

blood volume is also 3-5 litres, we may substitute minutes for
rounds of the circulation, and state that it requires 23 miiuitcs 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

MINUTES
(l20) (iSO)

O 1 Z 3 '^ 5

MULTIPLES OF THE. TIME REQUIRfO TC PRODUCE HfiiLfSfiiTURfiiTiOH

Fig. 84. — Curve showin<; the progress of saturation of any part of the body with nitrogen
after any given sudden rise of air pressure (after Haldane).

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
about 15 minutes altogether. As a result of this haste to get into

358

LOADING UP

" free air," constructional engineers are afraid to put their men
under more than -|- 3-5 atmospheres. Bulhon 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
periods of decompression which seem necessary for safety, put
the men in charge in an awkward dilemma wdien, on account of
some mishap, it is necessary to bring men at once to the surface.

From Table LVI. it will be seen that the diver is brought to
the surface from the bottom in stages. These stages are 3 metres
apart, and the time spent at each one depends on the duration of
his stay on the bottom. This method of decompression by stages
depends on the empirical fact that no untoward results arise from
even a rapid decompression of 1 atmosphere or less.

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 LVI
A Portion of a Diving Table used by Naval Divers

Depth.

Total
pressure in
atmospheres

Time from surface

to beginning of

ascent.

Depth and duration in
minutes of stoppages dur-
ing ascent.
Metises.
12 9 G 3

Time for

Fathoms.

Metres.

totalascent
in minutes.

/

Up to 15 min.

- 2 3 7

15

15-25 „

- 5 5 10

25

18-20

33-361

4-6

25-35 .,

- 5 10 15

33

35-60 ,,

5 10 15 25

57

60-120 ,,

10 20 30 35

97

V

Over 120 ,.

30 35 35 40

192

Haldane and his collaborators liave 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 1 atmosphere (1-25 atmospheres to be exact) to
normal, then it nmst be equally safe to decompress rapidly to half
pressure for any value. For example, if the total pressure were
8 atmospheres, these workers advise a rapid decompression
to 4 atmospheres, and after a pause to 2 atmospheres, and, after

RELEASE OF ABSORBED NITROGEN 350

a pause, more slowly to normal pressure. The principle under-
lying 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.

CHAPTER XXV
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-

FiG. 85. — Vertical Mesial Section through Heart to show Aortic and Mitral Valves.
R.V., right ventricle; L.V., left ventricle with papillary iimscle ; L.A., left atrium 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.)

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 blood in motion. The accompanying figure (Fig. 85) is a
diagrammatical view of a vertical-mesial section through the

360

GENERAL SCHEME OF CIRCULATION

301

lieart. From it we learn that tlie heart is not a simple structure.
In the diagram lour distinct cavities can be seen, viz. : right antl
left ventricles, left atrium and aortic space — the right atrium is
not shown. The heart is really a double pump consisting of a
main pump or systemic heart (left atrium and ventricle) and
a subsidiary pump or j)ulmonary heart. In Fig. 80 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

CAP

Art.

Fig. 86. — Scheme of tlie Circulation. S.H., systemic lieart .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 alimentary canal, Al.C, and from that to the
liver, Lir. ; blood also sent to the kidneys. Kid. ; the blood before again being sent to the
body is passed through the lung.s by the pulmonic heart, P.H.

(Noel Paton's Essentials of Human Physiology.)

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
walls of the intestine {Al.C). Some waste matter is eliminated,
as we have seen, by a capillary mechanism in the kidney. Chemical
changes occur on the passage of the blood through the capillaries
of certain factories, e.g. liver and spleen. The loss of oxygen is
not made good until the blood has been carried by the veins into
the right atrium, 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

362 CIRCULATION

and makes up its deiicit 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 pinnp.

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 mecha-
nism. Harvey found that the left ventricle of a man's heart
held 2 oz. 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 oz. 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 argued the necessity of some communication
between the arteries and veins. That is, after experiment,
observation, analysis and argument, come 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 Leeuwenhoek, the illiterate
janitor of the aldermen of Delft.

Haemodynamics. Dynamically considered, the blood acts in

HAEMODYNAMICS 363

iimch the saiiK' wuv as any other cciiiallv viscous (luid drixfu
through a series oi" tubes. In order to understand many of the
prol)lenis wliich 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.

(1) Gravity. In a liquid the molecular forces are in equili-
brium ; 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 iDellation and
tractation woidd 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 V'igh, g being the accelera-
tion produced by gra\'ity.

(2) Resistance at Outlet. 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.

(3) Resistance to Flow. 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 resist-
ance 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 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.

(a) Friction. 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

364 CIRCULATION

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
uniform 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 over-
coming the peripheral resistance caused by pure friction. 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. Liquid, in a tube
so narrow that only an outer layer and a central column could
pass along it, woidd 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. Further, the resistance in a tube of uniform diameter is
proportional to its length. Therefore, the energy of the fluid must
decrease gradually from the reservoir to the outlet of the tube.

{b) Viscosity. The internal friction or viscosity depends on the
nature of the fluid, and, as indicated in Table XLIII., on the size
and concentration of the bodies suspended in it. The mean
viscosity of blood compared with water is 4-45, and, therefore, it
would require 4*45 times as much pressure to force blood along
a tube at the same rate as an equal volume of water. The blood
cells do not materially affect viscosity till they occupy about
two-thirds of the total volume, i.e. till the haematocrite reading is
about 66 per cent. When that concentration has been reached, the
value of the viscosity rises owing to the friction of one erythrocyte
against another. The values of the viscosity of blood vary at
different parts of the circulation, due principally to alterations in
the size of the corpuscles {q.v.). The total frictional loss (friction +
viscosity) reaches a maximum in the capillaries, where not only do
the corpuscles tend to increase in volume but the bore of the
individual vessel becomes so small that the corpuscles undergo
considerable distortion in their passage along it.

Pressure. 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.

PIEZOMETERS

365

Tho fluid rises in tlu'se coUateral tubes or piczonwicr.s to a height
proportional to the pressure in the main conduit. In otlier 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. 87. 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
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

FALL OF PRESSURE.

fNCA^TUBE OF UNlFORJn DIAMF.TtR )N(B) TUBE OF VARYING DIAMETER.

y 6 5 •* 3 2 1 R£5E<?vr>lR. I 2345676 9 10

R.

FIG. 87.

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).

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

366

CIRCULATION

augmented, and therefore there is a heaping up of the fluid in the
earher 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.

Pressure by Force-Pump. In the preceding experiment, the

A

RUBBER

COMt

1 COMPRESSION CHAMBER j

MEAN AORTIC
PR£55UR£-I05MH5.

KtflN BRACHML
rR£55UR£ -90 HM5.

Fig. 88. — Diagram of a simple force pump (outer circuit) to compare witli diagram of
circulation from left side of lieart (inner circuit).

head pressure has always been kept constant by making provision
for a steady influx of water to the reservoir to compensate for the
outflow. If, however, 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 piezometers will vary from a maximum to a minimum as the
wave of pressure passes down the system after each stroke. Such
conditions entail great loss of power.

Elastic Regulator. In order to reduce this loss to a minimum,

WORK DONE BY A PUMP 367

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 ekistic power
exactly counterbalances the extra energy, and the fluid has an
outflow velocity of (v). The inflvix of water having ceased, the
steady pressure of the distended walls of the tube as they recoil
keeps the fluid 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 interjnittent inflow into
a constant outflow, the property of elasticity preserving 7iormal
conditions of flow even during periods when the piston is not
descending.

The value of the work done by a pump may be calculated
approximately by the formula

W=QR + — + 0,

where W (gram-metres), is the work done at each stroke, m is the
mass in grams and Q the stroke volume, 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,

niv^
QR represents the resistance pressure (r in Fig. 87) and (v in

"a
Fig. 87) the velocity pressure, while O is the energy expended in
overcoming the resistance to outflow at the orifice of the pump.

Such a system of single stroke pump and elastic regiflator 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. 88 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 pi])e. The ])ower necessary
to drive the phuiger 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,

368 CIRCULATION

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.

Work done by the Heart

If we take average figures for the human left heart as follows :

Q = 60 c.c,

/? = 100 mm. Hg pressure in aorta

= 0-1 X 13-6 grams (1 c.c. of Hg weighs 13-6 gm.),

the expression QB may be evaluated as

60 X 0-1 m. X 13-6 = 81-6 gram-metres.

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
0-4 metre per second, the velocity pressure will have a value

mz;2 60 X (0-4)2

~ir~ = ^~i^ TTTT' = 0'5 gram-metre.

2g 2 X 9-8 ®

This quantity is so small compared with the former during rest
that for all practical purposes the work of the heart may be taken
as proportional 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 X 0-02 X 13-6 = 16-1, say 16 gram-metres per beat. The
average heart beats 70 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. When
the output is increased to 20 litres per minute, as it may easily be
during exercise, as is shown in Table LVIII., the velocity factor
becomes about 10 per cent, of the total work of the heart and must
be taken into account. The following table (LVII.), taken from
Lovatt Evans, indicates the variation in the magnitude of the
velocity factor with the output of the heart.

WORK DONE BY THE HEART

TABLE LVII

Output and Mean Aortic Velocity of Blood from the Dog's

Heart (Lovatt Evans.)

360

Output
(Litres per liour).

Jlcan Aortic Velocity
(Metres per second).

Kinetic Factor for both
Ventricles * (in kg.
metres per hour).

3
12

48

96

120

0-042

0-169

0-67

1-35

1-69

0-0038
0-253
15-4

125-0

245-0

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 X 0-12 X 13-6 = 294 gram-metres.

and Qi2 (pulmonary) =180 X 0-025 X 13-6 = 61 gram-metres.

If the time of outflow is considered as three-eighths 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 32-4 litres
per minute. If the cross-section of the root of the aorta be taken
as 625 sq. mm., then the mean aortic velocity will be 540/625 =
0-86 metres per second. Now, as blood is expelled only during a
period not greater than about three-eighths of the cardiac cycle,
the average velocity of expulsion must be, at least, 8/3 times as
much as the mean aortic velocity ; hence

0-86 X 8/3 = 2-3 metres per second.

Therefore, wv^l2g = 180 X (2-3)2/2 X 9-8 = 48-8 gram-metres.

That is, the total work on both sides of the heart will be

Left side. Right side. Total.

During rest (81-6 + 0-5) + (16-1 + 0-5) =98-7 gram-metres.

During work (294 + 48-8) + (61 + 48-8) = 452-6 gram-metres

per beat.
= 81-5 kilogram-
metres per minute.

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

7mv^

* Calculated from Lovatt Evans' formula

8

B.

24

370

CIRCULATION

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 one-fifth 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 ventricles must each discharge
equal amounts of blood, the output of the left ventricle is found.

Total Work of the Heart

Lovatt Evans has shown that if the pressure in the right
ventricle be assumed to be one-sixth that of the left, a close
approximation to the total work of the heart can be obtained
from the expression :

^y_nJl ^ mjVCf

6

gE'

where

E = duration of period of expulsion,
C — duration of cardiac cycle, and
V = mean aortic velocity.

Stroke Volume. 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 thus to increase its

TABLE LVIII

Effect of Work on Cardiac Output

Muscular work per min. in Kgins.

Pulse rate per
min.

Output per beat
in c.c.

Output per min.
in c.c.

At rest . . 0

Moderate exercise . 270

Light labour . 735

Very hard work . 1000

70
100
110
130
180

45

75

120

115

117

3,150

7,500

13,200

14,950

21,060

EFFICIENCY OF THE HEART 371

capacity is limited. By a reflex mechanism the heart rate is
increased and so the output per minute is augmented. The
table on p. 370 shows approximately the share of the burden
of increasing the output borne by increased distension of the
ventricular walls and by increased pidse rate.

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
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 kilogram-
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 one-tenth of that done by the
skeletal muscles.

Efficiency of the Heart under Various Conditions

The efficiency of the heart may be taken as the percentage
amount of the energy taken in as fuel that is converted into w^ork.
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 table on p. 372 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
hour. The resistance to outflow was increased by steps of 40 mm.
Hg from 80 to 160 nmi. 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 cubic centimetres)

24—2

372 CIRCULATION

TABLE LIX

Efficiency of the Heart under various Conditions

Pulse-rate.

Arterial

pressure in

mm. Hg.

Total
output per
hr. Litres.

Oj used per
hour in c.c.

Energy
generated in
Kg. metres.

Work of

heart in

Kgs. per hr.

Per cent.
Efficiency.

Venous
pressure,
mm. HjO.

A 134

150

80
120
160

17-4
16-3
14-7

139
175
249

288
362

518

211

30-7
40-8

7-3

8-5
7-9

38

50

80-103

B 143
146

80
80
80

27-8

52

92

217

277
649

448

572

1,343

34-1

65-6
126-3

7-6

11-5

9-4

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 propor-
tional 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 1,343 kg. 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.

Maximal Efficiency. 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

PRESSURE DEVELOPED IN VENTRICLES 373

during the isometric 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.

We have seen (Chap. XIV.) that when skeletal muscle contracts
about two-fifths of the energy used is actually converted into
tension. If all the tension energy were then converted into
external work, the mechanical efficiency of this type of muscle
would be about 40 per cent. The realisable efficiency differs from
this theoretical value, because, even provided the load and rate
are optimal (q.v.), a considerable amount of energy is rendered
unavailable for work because it is dissipated in overcoming the
resistance of the viscous muscle to shortening. The more rapid
and the more complete the shortening, the greater will be the
amount of energy lost. The optimum efficiency is obtained when
the muscle pulls on a load that is always optimal, i.e. varies so as
to be always as great as the muscle can move. At the beginning
of contraction the load should be great, and it should gradually be
decreased as the shortening process proceeds.

This desideratum is found in the heart. As soon as the ventricles
start to empty, the shortening cardiac muscles have a steadily
decreasing mass of blood to act against.

It is of further interest to note that during severe muscular
exercise optimal conditions are found for cardiac efficiency, i.e. a
high output at moderate arterial pressure. Under these circum-
stances the efficiency of the heart is about 26 per cent. (cf. Muscle).

Form and Function

Pressure Developed in Ventricles. The diagrammatic section of
the heart (Fig. 85) 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 indicating that the left ventricle develops six to
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.

374 CIRCULATION

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 altera-
tion in wall thickness.

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 = TjR, 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. i^ = ^•

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 = TjR -\- TjR^.

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

t{llR + l/i?i) = C,
where t — thickness of the walls and C a constant.

VALVES OF THE VEINS

375

The wall of the apex of the heart has the largest mean curvature
{R is least and, therefore, t is least).

Similar reasonino- may l)e a})|)lie(l 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
(7^) divided by the radius of curvature (R), and (2) by the pressure
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 t = 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 LX
Thickness of Walls and Diameter of Lumen or Arteries in mm.

Artery.

Intiina.

Media.

Adventitia.

Total.

Lumen.

Brachial (human)
Carotid (ox)

„ (sheep) .
Metacarpal (horse)

0-03
0-84
0-028
0-03

0-5
1-176
0-420
0-513

0-25
0-484
0-168 .
0-31

0-78
1-744
0-616
0-853

4-17

6-0
3-0

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 RIR^ = 2/1 and p/p^ = 3/2.

Now t/t^ = RjR^ by pjp^ == 6/2 = 3/1.

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 approximation
to the ratio 3 to 1 (Table LX.).

Valves.

The valves of the heart and veins are interesting mechanical
structures. During the t^^'o 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

376 CIRCULATION

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
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, by
noting the direction in Mdiich 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. 85 and 88.

(1) The atrio- ventricular valves are triangular sheets of fibrous
tissue — tough but flexible — fixed by one side to the atrio-
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 tendirieae. 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. The bases of the
valve-flaps are approximated by the ventricular contraction which
begins at the base. When the ventricles contract so do the papillary
muscles- — pulling on the chordae and thus preventing the cusps
from being pushed through into the atria. The increasing pressure
of the blood in the ventricle causes the flaps to belly out and block
the passage-way so that the blood cannot pass back into the
atria. The greater the pressure developed in the ventricle, the
more tightly is the valve shut. The cusps may even bulge up
into the atria. Valves constructed 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

VALVES OF THE HEART

377

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 atrium to right ventricle is guarded by the three
cusps of the tricuspid valve.

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 arc 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

CORPUS ARANTll

Fig. 89. — Semilunar valves. A, in longitudinal-mesial section. B, Artery laid open and
exposed, and C, closed valves from the arterial aspect.

contraction of the ventricles, stretches the atrio-ventricular valves
it causes them to emit a sound which is a component of 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) Semilunar Valves. 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. 89). 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

378 CIRCULATION

cusp is mounted on a muscular septum which acts as a cushion,
absor})ing 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 of the
heart.

A third sound has been described. It has been attributed to
the rebound of the atrio-ventricular valves when the ventricle
relaxes and the atrio-ventricular orifice 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
atrium to ventricle is narrowed. During the whole period when
the ventricle is filling up from its atrial reservoir, the blood
flowing through the narrowed opening is set into ^'ibrations 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
narrozver 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.

The efi'ect of the narrowing of the aortic orifice on the magnitude
of the velocity component of cardiac work is considerable. If the
orifice be decreased in area to 1 cm. 2, for instance, the velocity of
the blood in passing this very narrow orifice is so much increased
above the normal value of 0-4- metre per second that, in spite of the
decrease in heart rate characteristic of this condition, the velocity
component may reach a value of about half that of the total work
of the heart. An enormous hypertrophy of the left ventricle is,

SOUNDS OF THE HEART 370

therefore, produced to allow of this extra work being done. In
a case like this, it is not surprising to find later that the heart is
unable to respond to the call for any extra effort, and that even
slight exercise results in distress.

(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 atrio- ventricular valves— if during ventricular
diastole, the aortic or pulmonary valves are at fault.

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 murmur will be best
heard 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 (Fig. 93, Chap. XXVI.), 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 1 00 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 pressure is
provided to carry the fluid within range of the atrial 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. XXVIII.).

380 CIRCULATION

Angle of Origin of Vessels

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
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 D, making an angle of 6
with the main trunk. Then the distance from X to C would be
Vos^ + h^ (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) :

. , . . ^ AC AX

I.e. loss IS proportional to + -^•

If the whole distance from A to D be put = b, then AX =^ b — x.

Vx^ -{- h'^ b — X
Substitutmg, we have }- — ^ — ,

multiplying by Rr gives us the value

S ^ R V cTa + K + {b - x)r,

where S = loss due to friction.

Differentiating and equating to zero we obtain a value for x
^vhich makes S a minimum.

dS 2Rx

Thus J— — ^ ,' = — /• =^ 0 ;

dx 2\^x^ + h^

r _ X _XD _

R " V^^Th^ - AC - ^"' ^'

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 7nain trunk.

The size of the angle of origin is governed neither by the radius

ANGLE OF ORIGIN OF VESSELS 381

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 rjR, we have therefore a constant value of d ; 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

be infinitely small, i.e. angle 6 will be close to 90°.

(3) If r differs but slightly from R it is obvious that cos 6 tends
towards the limiting value = 1, 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.

Further Eeading

LovATT Evans. " Recent Advances in Physiology," J. & A. Churchill.
Bainbridge. "The Physiology of Muscular Exercise," Longmans, Green
&Co.

CHAPTER XXVI
THE ELECTROCARDIOGRAM

" Providence . . . can make a harmony
In things that are most strange to human reason."

MiDDLETON.

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-positive 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 at the sino-atrial node. Therefore, the
node will become electro-positive (galvanometrically negative) to
the rest of the heart. The atria next contract as a whole, passing
on the excitation through a piece of primitive tissue (Bundle of
His) to the ventricles. Node, atria and ventricles, as they contract,
become electro-positive (zincative) to all other parts of the heart.

(1) Rheoscopic Frog. The existence of this change in the sign
of the potential developed as the wave of contraction passes
over the various parts of the heart may be demonstrated, as it was
in muscle (p. 179), by the use of a fresh nerve- muscle preparation.
The nerve laid across the beating ventricle produces two muscle
twitches per beat.

(2) Capillary Electrometer. Earlier experimenters used the
capillary electrometer (Fig. 12) as the instrument wherewith to
detect and measure these potential differences. They found, on
leading two electrodes from different points of the atrium, that the
amplitude of movement of the mercury produced at each heart-
beat is greatest when the line forming the shortest distance between
the electrodes would pass through the sino-atrial node. This is
interpreted as an indication that the electrical disturbance has its
origin at the node.

Consider, for a moment, a large circular sheet of muscle, and
near the centre of the sheet are placed two electrodes {A and B)

382

CAP ILL A E Y ELECT ROM ETER

383

leading to an electrometer. If the edge of the sheet is now
stimulated at various points, it will he ohvious that the greatest
movement of the mercury will he produced when the point of
stimulation of the muscle lies on the extension of the straight line
joining the electrodes. That is, the wave of negativity takes a
longer time to pass to B when it starts radially opposite to A than
when it radiates from any other point on the periphery of the
sheet. Further, if A is placed so near to the point of stimulation
that it is practicalh^ on it, then no matter where B is put, A will
always be zincative (galvanometrically negative) to B.

Evidence as to the origin of the cardiac contraction at the sino-
atrial node may be deduced in a similar way from electrometer
readings. If one lead is taken from an electrode placed on the

POSITIVE
VARIATION

AURICLE.

VENTRICLE

Fig. so. — Record of the electrical variations in the beating heart of a tortoise, taken by a
capillary electrometer (after Gotch).

node and the other lead from an electrode moved about from place
to place on the atria, the electrode on the node will be found
always electro-positive (zincative).

The figure (00) was obtained by leading one electrode from a
point near the atrial sinus and the other from a point near the
apex of the ventricle. In order to standardise such records, the
leads are always arranged so that any upward movement of the
shadow of the mercury (or of the string of the galvanometer)
above the line of equal potential (rest) indicates negativity (zinca-
tiveness). This may be done by leading the atrial electrode to the
mercury in the capillary of the electrometer (Fig. 43) and the
ventricular electrode to the mercury in the cup. On the initiation
of contraction the mercury runs up the capillary away from the
tip, indicating that the atrium was electro-positive to the ventricle.
This is followed immediately by a tiny downward movement of the
mercury, showing that the wave of negativity had passed the site

384

THE ELECTROCARDIOGRAM

of the atrial electrode. This constitutes the second part of the
atrial diphasic response. Similarly a large upward excursion of
the 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.

Using these leads, one may easily identify on the record the
P wave (Fig. 90) which may readily be shown to correspond to the

I'lG. 91. — Diagram of tlie essential parts of the string galvanometer. N and .S' are the poles
of a powerful electromagnet, between which is stretched the fibre C.

contraction of the atrium. As potential differences radiate from
the heart to the surface of the body, and may even be com-
municated to the air and detected at a reasonable distance from
the body (Potter), leads might be taken from any tAvo points on or
near the surface of the body. Certain leads, however, give better
results than others, due to the fact that the heart lies obliquely,
and, therefore, produces an asymmetrical distribution of lines of
equal potential. For this reason and for convenience three pairs
of leads have been adopted for standard practice, namel}' : —

Lead I. — Right arm and left arm.

Lead 11. — Right arm and left leg.

Lead III. — Left leg and left arm.

STRING GALVANOMErER

385

0.

',(...>■

Records from these three pairs of leads dilTcr from one aiiotlier,
and information may be gained from these differences as to the
state of the myocardium at various
parts.

(3) String Galvanometer.
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 instrument at present
generally eiuployed 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 appara-
tus for such work must be as " dead
beat " as possible — ^moving in exact
accordance witli 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. 91),
which is an extremely light fibre of
silvered glass, quartz, or platinum, is
stretched between the poles (A'^, 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 direc-
tion of the deflection (observer's left
or right) depending on the direction
in which the current is passing. If

the current 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

B. 25

886

THE ELECTROCARDIOGRAM

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 fibre by a lens F and throwing the shadow on
to a moving photo-sensitive surface. Fig. 92 shows diagram-
matically the arrangements 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

ii^^^d^^BAiAW^^^k^i^^^^AiAiteiiAriii^Ai^JiiliAriiiAiAAiMMWMti

Fig. 93. — Electrocardiogram from lead II. and Phono cardiogram talcen simultaneously
from a normal subject.

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 b}' the
sHt. 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
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 record (Fig. 93) shows vertical and horizontal markings
as well as the electrocardiogram itself. The horizontal mark-
ings enable one to find by inspection the potential difference

ANALYSIS OF RECORDS 387

generated at dilTcreiit phases of the eardiac eycle. The space
between eaeh line is generally 1 mm. = 1/10, ()()() volt (Einthoven's
standard). The lines are engraved across the ividth of the eyHn-
drical 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 record illustrated, are a measure of
time — in the case given = one-thirtieth of a second.

They are produced by the interruption of the focused beam of
light by a serrated wheel (Fig. 92) so that for a short interval no
light falls on the whole (or on part of the sensitised 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 resist-
ance 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 counterbalanced by sending an equal current through
the fibre in the opposite direction. The resistance of the body to
the passage of a current is very rarely considered in routine
clinical electrocardiography.

The analysis of electrocardiograms (Fig. 93) is liy no means
simple. Considerable uncertainty exists as to the exact interpreta-
tion of certain units in the trace. If Einthoven's symbols PQRST
are 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 doubt the wave of negativity produced by the contraction
of the ventricles. The upstroke of R is inscribed just before
ventricular systole starts. S is the second phase or positive
reaction of the ventricles. 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, culmi-
nating at the moment that the ventricles begin to relax. The
QRS complex is a composite picture consisting of the algebraic
sum of the electrical elTects in both ventricles. Other interpreta-
tions 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.

Consider again the sheet of muscle mentioned above. The line
joining AB and projected to the periphery will be the electrical axis
when the point of stinnilation lies on it, i.e. the electrical axis is the
resultant direction of the electromotive changes. It is obvious

25—3

388 THE ELECTROCARDIOGRAM

that, in the heart, it is not constant, but varies in direction with
every phase of the cardiac cycle.

The three leads are represented on paper by the three sides of an
equilateral triangle, vertex pointing downwards, and a drawing of
the heart is placed in the triangle, having its base on one side
(corresponding to lead I.) and its right side (on the left of the
drawing) = lead II. Now, if a line be drawn on the heart in the
triangle to represent the electrical axis at any moment, and the
line be projected by drawing perpendiculars on the three sides of
the triangle, then the algebraic sum of the projections on any two
sides is equal to the projection on to the remaining side. The
projection of the electrical axis will be greatest on that side of the
triangle which is more nearly parallel to it. From this mathe-
matical truth Einthoven has formulated the rule that the potential
values represented in the cardiogram from lead II. are equal to the
sum of the corresponding values obtained in the graphs from leads
I. and III. That is, the height of Rj, (R in cardiogram from
lead II.) is equal to the sum of the heights of R, and Rjj,. Knowing
the potential values of a given wave, P, R, S or T in the three
leads, the direction of the electrical axis during the production of that
wave can be calculated by use of a trigonometrical formula.

Since the potential values in the three leads are the projections
of the line of the electrical axis on the three sides of the triangle,
it follows that the maximum manifest value for any wave will
appear on the cardiogram when the representation of the electrical
axis is parallel to the line representing the lead. It will have a
minimum value when the axis line is at right angles to the line of
the lead. The magnitude of any wave from any lead, therefore,
depends on the angle which the electrical axis makes with the side
of the triangle representative of the particular lead taken at that
time. That is, the deflection of the string will be greatest in
lead I. when the electrical axis is parallel to the base of the heart,
in lead II. when parallel to a line drawn from apex to right side of
base and making an angle of 60 degrees with it, and in lead III. with
a corresponding line on the left side of the heart.

Effect of H ion Concentration. It is well known that the rate at
which the excitation is conducted over the heart muscle varies
considerably with the /?H of the fluid medium in a perfused heart.
Increase in alkalinity, for instance, increases the conduction rate
and decreases the refractory period. Acid, naturally, has the
opposite effect. It has been found that the current of injury of
skeletal muscle {q.v.) can be reversed by decreasing the /?H below
7*4, the critical level. It is, therefore, suggestive to find that the
P. R and T waves of the electrocardiogram can be reversed in sign

EFFECT OF pll OX i'ARDIOOR.lM 389

by changing to a more alkaline [K-rlnsino- Huid. Tliis gives us
gromid for a plausible explanation of the eJTeet of the \ agus and
of the sympathetic nerves on the rate of conduction in the heart.
Some evidence has been t)roduced to show that acid ions are
liberated in heart muscle when the peripheral end of the cut
vagus is stimulated. The inhibitory power of the vagus is increased
also on the addition to the perfusion fluid of certain salts of
calcium w'hich are known to dissociate wdth the liberation of acid
ions (see Blood-clotting).

Further Reading

Lewis. " The Mechanism and Graphic Registration of the Heart Beat."
Sliaw k Son.

CHAPTER XXVIT
EXTERNAL RESPIRATION

" The body is sustained by three kinds of nutriment, food, drink, air (nuevixaTa),
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 imtriment " 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 o5 Mechanism.

The lung mechanism may be considered as an clastic bag with
one opening, the whole suspended in an air-tight box with movable
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-

390

STRVCrrRE OF LUNGS

301

wards is released, the box and bag' resume their i'oriiier \ ohuues, and
air is expelled. In short the lungs are a form of suction pump or
bellows (Fig. 94).

Structure of Mechanism.

While the foregoing accoimt of the principle underlying the
respiratory mechanism may be taken as substantially 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 — forming an
elastic sponge-work.

(6) Each lung is subdivided into lobes,
the left lung having two lobes and the
right lung three lobes, and is in com-
munication with the external air through
the trachea and bronchi. The windpipe,
or trachea, divides into two bronchi, one
of which, with the pulmonary blood and
lymph vessels, etc., enters each lung at
the root of the lung. The bronchi on
entering the lungs undergo repeated
branchings, and finally each tiny termmal
bronchiole subdivides into a number of
alveolar ducts. On these are little ex-
pansions, the atria, from which the air
sacs or alveoli open. Each bronchial
branch is accompanied by a branch of the
pulmonary artery, which ultimately breaks
up into a fine network of blood capillaries
on the walls of the air sacs. The blood
from the capillaries is returned to the left
side of the heart by the pulmonary veins.

(c) These complex bags are suspended in and ahnost fill the
thoracic cavity. Each lung is enclosed in a membranous sac — the
pleura, which, on reaching the root of the lung, bends back from
the bronchi and lines the entire internal surface of the chest wall.
Each lung has, in its development, pushed into a closed sac, and,
carrying the walls of that sac with it, has l^ecn completely
enveloped by it. That is, the pleura consists of two layers — an
outer, parietal or chest wall layer, and an inner, visceral or lung
layer. The surfaces of the two layers 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

FlCJ. 94. — Model to demonstrate
aclion of diaphragm. On pulling
the rubber sheet downwards, air
enters the lungs and they expand.

392 EXTERNAL RESPIRATION

pleura arc always uornially in close contact with one another
and with the underlying and overlying surfaces. In other 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
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 w^iich 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 ;

MKCIIAXICS or DIArilRAGM ;j!»3

(3) by their (lilTerciil l)l()()d .supply I lie lonucr directly from the
aorta and the latter Iroiii the intercostal and internal manniiary
arteries ; and (4) by their difierent nerve supply, the crural 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
dio'ing quiet breathing. The majority of individuals employ
both parts of the muscle in varying degrees.

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 on the vertebral column. The resistance to be overcome
is mainly the pressure of the contents of the abdomen, the peri-
cardial 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 equiva-
lent to a drop of about \ in. all over. For ease in calculation,
say that the distance through which the diaphragm moved in an
ordinary quiet respiration w^ere 10 mm. and that the mean area
of the piston were 250 sq. cm., then the volume of air sucked
in w^ould 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.

Synergic Muscles. Acting along with the diaphragm there are
those muscles w^iich 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 w'here 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

394 EXTERNAL RESPIRATION

muscles of the abdominal wall, viz. : external oblique, internal
oblique, transversalis and rectus abdominis on each side.

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 ivall zvhich ivill move forwards. Correspond-
ingly, 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.

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. In the mammal, without the constant tension of the
abdominal muscles applied to the abdominal viscera, the larger
veins would become distended with blood, and these veins are
capable of holding the entire amount of blood in the body. So, if
for any reason the muscles of the abdominal wall lose tone, a
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 thoracic 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 vertically erect, the abdominal veins
distend under the haemostatic pressure. In them such a large

Til OR. I CIC RESPIR. t TI()\

31)5

projjortioii o\' the hlooci collects that there is iiisudicient i)lo()(l to
lill 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 (sixth to ninth or tenth rib).

Tliis segment moves along with the diaphragm and leads to
the expansion downwards of the low^er lobes of the lungs. The
ribs are articulated to the spinal colunm
so that during inspiration the lateral and
anterior part of each moves outward more
than the one above it. Two movements
may be noted :

(i.) The 50 to 70 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 forw-ard
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 in-
spiration. At the centre of each pair is the
sternum-cartilage complex w^hich is raised
and forced forwards during inspiration.
The muscles concerned in this increase of
the volume of the lower thorax, trans-
versely and antero-posteriorly, are the
external intercostals.

(b) Upper costal series (second to fifth
rib).

These ribs differ from the lower series in
shape, articulation, ligamentation, musculature and, consequently,
in their movements.

(i.) Shape. The upper ribs have a concave upper margin and
do not have such a marked twist as those in the lower costal
series. The second rib as a matter of fact may be laid flat on a
table.

(ii.) Articulation. The spinal articulation differs from the lo\ver
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. The costal articulations are nearly in a
transverse axis (Fig. 95), and movement occurs at the manubrio-

— Rib and vertebra
in upper and in lower costal
series to sliow the difference
in the obliquity of articulation
and the resulting difference in
the expansion of the chest.
Note direction of arrows.
(From Noel Paten's " Essentials
of Human Physiology.")

39G EXTERNAL RESPIRATION

sternal articulation. Each transverse process from above down-
wards is tilted a little more l^aekwards so that the angle of
articulation becomes more oblique as one passes down the
series.

(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 increases, e.g. the
second costal cartilage joins the sternum at right angles while the
third ascends to the sternum.

(iv.) Musculature. The musculature of these ribs is the inter-
costal interchondral and external intercostal.

(v.) Movements. Because of the nature of the 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 trans-
verse, 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
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 fibro-cartilage are bound together firmly by longitudinal
fibres developed from the strong and thick periosteum. The
limitation of movement thus imposed at the joint is counter-
balanced by the greater freedom of movement which is allowed at
the articulation of the heads of the first pair of ribs with the
thoracic vertebra.

Great importance has been attached to the movements of this
joint. Its amplitude varies, of course, wdth the type of respiration,
being greatest with those who make least use of the muscles of the
abdominal w^all 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
l)reathing), 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

MECHANICS OF THORAX 397

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 colunm 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
mentioned when dealing with the ribs of the various thoracic
segments.

(2) The power applied differs according to whether inspiration
or expiration is being performed (p. 423).

(«) Inspiration.

(i.) The lid or operculum is raised by the action of a flat tri-
angular muscle {.scaleni). The scalenus anticus is inserted into
the inner border of the first rib and passes almost vertically to
the transverse processes of the third, fourth, fifth and sixth
cervical vertebrae. The scalenus medius lies posteriorly to the
anticus and passes to the transverse processes of the lower six
cervical vertebrae.

(ii.) The external intercostal muscles may be regarded as a
triangular sheet of muscle having its origin in the posterior part
of the lid and being inserted into the upper surfaces of the ribs.
It pulls upwards.

(6) 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 towai-ds the end of insj^irntion than at the
begiiming.

(ii.) The elasticity of the chest wall — the costal cartilages ha\e

398 EXTERNAL RESPIRATION

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 colunni 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
(Chap. XXX.).

(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
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 clastic 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 t(j 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 part contains much fil)rous tissue and. tlierefore,
offers considerable resistance to distortion. Using physical terms
one may say that its elasticity is strong, but far from j^erfect (p. 206).

(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 perfect! 1/ hut feeblfj elastic and the capillaries (em])ty) have
a modulus of about 0-04 X 10^^ — not quite so perfect as the lung

EFFICIENCY OF UWC MECHANISM ;3l)9

substance, but offering a greater resistance to distortion. P^ven
within this zone extensibiUty is not uniform. The stratum lying
immediately below the pleura is nuich 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 flrst and that the inflation of certain parts of the sub-
pleural stratum spreads from these points.

(3) The middle zone, lying between the root 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.

(6) 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
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 the 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 directUj expand, viz. —

(i.) the mediastinal surface in contact with the pericardium and
with the structures of the mediastinum, (ii.) the medial surface
lying close against the vertebral column and spinal portions of the
ribs and its anterior portion, in contact with the mediastinal pleura,
(iii.) The posterior 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 (vcntro-lateral aspect) and (vi.) upper

ribs (sternal asp(»ct) undergo direct expansion at each inspiration.

VI, The efficiency of the lung mechanism, If figures could be

400 EXTERNAL RESPIRATION

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 0-9 c.c. of
oxygen per litre of ventilation. Assuming that all the energy
used is obtained from glucose, these figures indicate that from
0-0015 to 0-005 Calorie is expended for each litre of air breathed.
This amount of energy is liberated from 0-0004 — 0-0012 gram of
glucose. During quiet breathing each breath (400 c.c.) costs at
most 0-002 Calorie obtained from just about 0-0005 of a gram of
glucose and 0-36 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, 0-00014 — 0-0004 Calorie is
converted into work = 0*06 to 0*17 kilogram-metre.

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 CO.^ 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 (see Voice, Chap. XXVIII.).

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 COg 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
COo in the alveolar air, as we have explained (Chap. XXIV.), are
always in dynamic equilibrimn, 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 of man, i.e. a rise of tension of from 40 to 41-6 mm. Hg, is
sufficient to double the alveolar ventilation. 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

EFFECT OF RESPIRATION ON CIRCULATION 401

of CO2 in alveolar air is maintained at an almost constant level
of about 40 mm. Hg (see Chap. XXXI.).

Regulation of Depth. Impulses are constantly passing from
the lungs, through the N^agi, 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.

Effect of the Respiratory Movements on Mass Movements of the Blood.

Thoracic Respiration. During each inspiration the increase in
the capacity of the thorax not only tends to produce a negative
pressure in the trachea and pharynx, so causing air to be sucked
into the lungs, but negative pressure is effectively applied to the
thin-walled veins in the thoracic cavity, causing them to dilate
with blood aspirated from the extra- thoracic venous system.
This dilatation causes more blood to collect in the intrathoracic
vessels, and to some extent delays the passage of this blood to
the atria. During expiration, however, positive pressure is applied
to these veins ; the extra blood is forced into the heart. As we
have seen in a previous chapter, the increased venous filling leads
to an increased ventricular output and a rise of blood-pressure.

Diaphragmatic Respiration. During inspiration the diaphragm
contracts and presses down on the abdominal viscera. They, in
turn, pass on the pressure to the blood in the vena cava, with the
result that, at first, more blood is forced into the thoracic vena
cava, and, consequently, to the right atrium ; and the blood pressure
tends to rise a little. Continued compression of the abdominal
vena cava cuts down the supply of blood to the thorax, and blood
pressure falls. During the expiratory relaxation of the diaphragm
the reverse process takes place.

Most people breathe diaphragmatically with a slight rising of the
thoracic cage. The effect on their blood pressure will, therefore,
be the algebraic sum of the two opposing effects : viz. an initial
rise due to thoracic negative pressure and abdominal pressure
on the veins. This rise, which would continue in purely chest
breathing, is cut short by the fall of pressure due to continued
abdominal pressure.

Exercise. The above factors are more marked in their influence
on cardiac output during ordinary nniscular exercise. There are
certain types of exercise, however, in which, in order to produce a
maximum leverage (q.v.), the chest wall is fixed and respiration is

B. 26

402 EXTERNAL RESPIRATION

suspended. For example, in attempting to push a heavy body,
pull against an almost unyielding resistance, or lift a heavy weight,
a deep inspiration is taken and then, by powerful muscular action,
the whole body is knitted into a single lever with a long power arm.
The contracted abdominal muscles press the diaphragm, etc., up
into the thoracic cavity. This compression at first causes blood
to be squeezed from the abdominal veins into the thoracic veins
and so into the heart, producing a marked rise in arterial pressure.
Later there is a damming back of blood into the peripheral vessels,
causing them to stand out like knotted cords. When the effort
ceases and the compression on the abdominal contents is released,
the large abdominal and thoracic veins fill up with blood, producing
a marked fall in arterial pressure. The tissues during the period
of sustained effort have removed oxygen in large quantities from
the blood in the peripheral vessels, and if the effort is long continued
an oxygen debt is incurred (q.v.). Marked cyanoses may even
develop.

Modifications of the Respiratory Act. A similar positive pressure
is brought to bear on the veins entering the thorax during such acts
as coughing, sneezing, defsecation and parturition. In the first
stage of coughing and in defsecation, after a forced inspiration, the
glottis {q.v.) is closed and the expiratory muscles put into strong
contraction. The enormous positive pressure produced, in the
former case, in thorax or abdomen, and, in the latter case, in the
abdomen, dams back the blood in the veins, causes a fall of arterial
pressure, and, if sustained, cyanosis follows. In sneezing, the air
is compressed after a forced inspiration by the contraction of the
pillars of the fauces, descent of the soft palate and pressure of the
tip of the tongue against the hard palate. The effect on blood
pressure is similar to that of coughing. Sighing and yawning,
which are alleged to be controlled by separate centres in the
medulla, are deep inspiratory acts almost entirely thoracic in
character and, therefore, tend to encourage diastolic filling and a
general increase of blood pressure.

Influence of Heart Action on Respiration.

As the heart contracts and dilates it nuist alternately decrease
and increase the intrapleural pressure, causing a slight inrush and
outrush of air with each cycle. These cardio-pneumatic move-
ments may be demonstrated in a very simple manner by filling
the mouth with tobacco smoke, inserting a glass tube about
18 in. by | in. in the mouth. Hold the tube vertically (preferably
with the upper end gently plugged with cotton wool). Allow a
little smoke to enter the tube and then hold the breath. The

HEART ACTION ON RESPIRATION 403

column of smoke will be seen to pulsate. These movements may
be timed with the pulse.

If a simultaneous record be obtained of the heart beat and of
the movements of the air in the external respiratory passages
(e.g. nares), it will be seen that there are three phases of the cardiac
cycle in which the influence of the heart on the movements of the
air column are manifest : —

(1) At the beginning of ventricular systole intrapleural pressure
is suddenly increased. At this moment the ventricles are closed
cavities.

(2) During ventricular systole intrapleural pressure decreases as
systole proceeds.

(3) During ventricular diastole there is a gradual increase of
intrapleural pressure.

These phases may be seen easily in the smoke-filled tube referred
to above, viz. (1) smoke-level suddenly rises when the heart beats ;
(2) smoke-level drops ; (3) smoke-level slowly rises. During the
period of passive diastole the smoke-level remains steady.

If a bronchitic patient has a plug of nuicus in a small air passage
near the heart, every time air is forced past the plug by the cardio-
pneumatic movements the air will be thrown into vibration, and a
murnun- will be heard very similar in character to a cardiac
nuirmur.

It is alleged that the movement of air produced in this way by
heart action is quite sufficient to keep up the necessary gaseous
exchange in hibernating animals.

^6—3

CHAPTER XXVIIl
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. . . ."

Vesalius (1543) quoted by Foster.

The production of sound by the larynx or by the hps is so essen-
tially a modification of respiration that we may conveniently deal
with phonation, whistling and speech at this point. By means of
soimd production we act on matter at a distance, and so one would
naturally consider the problems of phonation, and especially of
articulation, after one had reviewed the various types of levers,
pulleys, etc., by means of which the body reacts on its environ-
ment.

I. Phonation. At least two essential factors are concerned in
phonation, namely, («) a means of producing a flow of air, and (b) a
means of interrupting that flow so that alternate condensations
and rarefactions follow one another in the air at a certain rate.
The lungs provide the current of air, and either the sudden expan-
sion of the bore of the wind-pipe at the ventricle, the pursing of the
lips to form a small orifice (whistling), the juxtaposition of tongue
to palate and closure of teeth (hiss), or the vibrations of the vocal
cords account for the breaking of the continuous column of air into
waves.

Mechanism of Larynx. The larynx or sound box is situated
between the root of the tongue and the trachea. Above, it opens
into the laryngeal part of the pharynx, of which it forms the
anterior wall ; below, it is continuous with the trachea. It is
composed of nine cartilages, three single and three paired. They
are connected by ligaments and membranes, and moved by some
ten muscles — some of which open and close the glottis and some
regulate the degree of tension of the vocal ligaments. The larynx
is lined by a mucous membrane which is continuous above with
that of the mouth and pharynx and below with that of the trachea.
Except over the vocal folds, where it is stratified, the epithelium is

404

MECHANISM OF LAlllW \ 405

of the ciliated variety. Except also on the free edges of the vocal
folds the mucous nienibrane is studded with nnicous glands. These
are especially plentiful upon the epiglottis (q.v.) where they are
lodged in little pits.

The cavity of the larynx is divided into three parts by two pairs
of folds of the mucous membrane which project from the sides of
the cavity into its interior. The upper or ventricular folds are the
so-called false vocal cords. Each encloses a narrow band of
fibrous tissue (the ventricular ligament), which is fixed in front
to the thyreoid cartilage and behind to the arytsenoid cartilage.
The fissure between the false cords is termed the rima vestibuli.
The lower or vocal folds are the true vocal cords. Each encloses a
band of yellow elastic tissue (the vocal ligament), which is fixed to
the same cartilages as the corresponding ventricular ligament, but
a little lower down. The vocalis muscle lies lateral to and parallel
with the vocal ligament. The fissure between the true cords is
called the rima glottidis. Between the false and the true cords is a
recess known as the ventricle of the larynx (or of Morgagni),

False Cords. The ventricular folds play only a protective part
in phonation, keeping the true cords moistened by the secretion of
the numerous mucous glands with which they and their appendices
are provided. They are of use in " holding the breath." Animals
which have to do this often in fight or flight have w^ell-developed
ventricular folds.

True Cords. The alterations in the width and shape of the
rima glottidis, brought about by the movements of the vocal folds
and arytaenoid cartilages during phonation, can be studied readily
by the use of the laryngoscope. This instrument consists of two
mirrors, a small one which is held by means of a long handle at the
base of the uvula with the mirror directed at an angle towards the
larynx, and a larger mirror with a central hole through which the
observer examines the image in the small mirror. The practical
details of this method of examination are given in any practical
text-book of physiology (" Practical Physiology," by Anrep and
Harris) and are out of place here.

In order that the vocal cords may set the air current into vibra-
tion they must be put into a state of tension. In the dead
larynx it is possible to produce sounds by forcing air from bellows
through the larynx, meanwhile applying tension to the cords by
pulling the arytaenoid cartilages backw^ards.

From experiments on the cadaver and on tracheotomised
patients it has been found that with a constant tension on the
cords sounds vary in loudness and in pitch with the air pressure
developed. In the following table (LXI.) is given the limits of

406

THE VOICE

oscillatory pressure (R.M.S.) for various frequencies of vibration
detectable by the hiuiian ear {q.v.). Starling states that in patients
on whom tracheotomy had been performed, the pressure of air in
the trachea necessary to cause the production of an audible sound
was from 140 to 240 mm. HgO, and for loud shouting a pressure of
945 mm. of water was necessary. This pressure is furnished by
the contraction of the expiratory muscles {q.v.).

TABLE LXI

Notation, Frequency, Pressure and Amplitudes of Air Waves

OF the Musical Scale

Notation.

Frequency.

R.M.S. Oscillatory Pressure.

Amplitude.

For Minimum

For Maximum

For Minimum

For Maximum

Helniholtz

Sabine

Double* Vibra-

Intensity.

Intensity.

Intensity .

Intensity.

(European).

(U.S.A.).

tions per Sec.

Dynes per
sq. cm.

Dynes per
sq. cm.

em. ■ 10" «

cm. X 10^2

C^

32

1-0

17,000

c

Ci

64

0-15

300

1,200

2-5

c

C2

128

0-03

900

120

4

c'

c,

256

0-006

3,000

12

6

c"

C4

512

0-002

6,000

2

6

c"i

Cs

1,024

0-0009

4,000

0-5

2

c^^

c«

2,048

0-0006

1,500

0-2

0-4

c^'

C7

4,096

0-0007

0-1

8,192

0-0015

0-1

16,384

0-1

3-2

* In France frequency is mea.sured in single vibrations, and so all the figures in
this column are half the French values.

The first muscular act in breathing for the purpose of phonation
is a slight inspiration. When this is done properly, the column of
air, resting as it were on the diaphragm, is ready for its impact on
the vocal cords, an impact which must be made with the greatest
nicety and control. Hudson-Makuen states that the expiratory
act necessary for phonation is produced by a contraction of the
diaphragm which pulls the lower ribs downwards and inwards,
i.e. a muscle which in ordinary breathing is inspiratory, here acts
in the opposite sense. Proper co-ordination of the intercostal and
abdominal muscles are, of course, just as essential for phonation as
for respiration.

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 407

Pitch, or tone-height, is a function of the frequency, i.e. rate of
vibrations. This may be proved by ruiniing 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 second, 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 av^erage limits for the human voice are given in Table LXII.

TABLE LXII

(Sabine's Notation)

Bass

Fj to Dg

85 to 288

Baritone

A., to Fg

106 to 340

Tenor

C2 to A4

128 to 424

Alto

E^ to C4

160 to 512

Soprano

B3 to G^

240 to 768

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 the voice may be altered by
voluntarily lowering the position of the larynx during phonation —
a knack acquired by training. Hudson-Makuen has used this fact
in correcting the high-pitched or eunuchoid voice which occasion-
ally occurs in men otherwise normal. A somewhat similar process
occurs in the acquirement of the deep voice cultivated by many
women who have occasion to lecture regularly. Prolonged use of
the lower register gives these people a peculiar " falsetto " booming
voice. The pitch of a tone, from a physical 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 arytsenoid
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-.

408 THE VOICE

or thick-register, while high liotes 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 w^hole extent. In taking the lowest
notes the posterior portion of the arytaenoid cartilages are close
together with a wide elliptical chink between the cords. As the
pitch of the note rises the arytaenoid 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 F4.
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
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 (see Ear, Chap. XX.).

If the intensity ranges of the ear are again referred to (Chap. XX.)
it will be seen that while the range of intensities covered by the
human ear is large, covering frequencies from 32 to 16,000 vibra-
tions per second, it is particularly sensitive to those frequencies
lying between 1,000 and 5,000 d.v. per second. In this middle
region it can pick up a pressure variation as small as one-thousand-
millionth of an atmosphere. Now, frequencies of this order occur
in phonation only in overtones. The main energy of the voice is
of much lower pitch. The male voice has a very pronounced low
component of about 120 d.v. per second, while the female voice
has one about an octave higher. About 60 per cent, of the energy
of the air emitted is due to vibrations having a frequency of less
than 600 d.v. per second. Under 5 per cent, of the energy is
associated with the production of overtones having a frequency of

SPEECH

409

'2,000 d.v. and over per seeoiid. We w ill return to this iii dealing
with speeeh.

Timbre or (juality 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 ada])t the
shape of the mouth so as to secure for each tone the most suitable
overtones.

II. Articulate speech may be considered as the resultant of
essentially two component factors, {a) the production of sound,
and {h) the modification of the sound to produce speech.

Speech sound-units may be classed as vowels and consonants.

The vowels U, O, A, E and I are produced by the continuous
issue of a blast of air through the mouth. U, 0 and A, pro-

A {ah) U {oo) I (ee)

Fig. 96. — Changes in the Shape of the Mouth in Sounding the Vowels, A, U, and I. (Griitzner.)

nounced oo (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. 96).
This cavity is widest and shortest with A, longest and narrowest
with U, while 0 is intermediate. On the other hand, E (as in
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. 96).

By w^hispering the vowels one may readily determine the
resonance-pitch characteristic of each. U has the lowest pitch,
followed by O and A. It is thus easier to sing U and O on low
than on high notes. An attempt to go up the scale by sounding
" oos " will cause a tendency to clip the full vow^el and sound a
short " ee." The characteristic notes of each of these vowels
(by percussion, Expt. 72, p. 556) is given by Helmholtz as follows
(Fig. 97) :

410

THE VOICE

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

U = F

0 =B^
A = B"

1 = F, Z)^^

at

u

-Gh-

o

E

I

Fig. 97 (Starling). — Values obtained by percussing mouth cavity wliile sliaped for the
pronunciation of the vowels.

w&y some of the air comes continuously through the resonant
nasal passages.

TABLE LXIII

Consonants

Class

Labial.

Dental.

(iuttural.

Explosives
Aspirates .
Vibratives
Nasals

P. B. V.
F.

M.

T. D.

S. L. Th.

N.

K. G.

Ch. (Scots)
E. (Scots)

Ng.

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.

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 co
versation amounts to between 140 and 240 mm. of HoO, wh-i
nearly 1,000 mm. are required when shouting is indulged in.

WORK DONE IN SPEAKING 411

If zvork (})h()nati()ii only) is taken as ('(jiial to the produet of
the pressure and vohnne of air expelled, i.e. W — VH, we may
make a rough assessment of the amount of work done. During
ordinary eonversation, a man with a tracheal cannula developed
an air pressure of 200 mm. (HoO) and expired 300 litres of air
per hour, i.e.

300 X 200
VH = — — = 60 kilogram-metres = 0-14 Cals. per hour.

Speaking in a large hall the same man expired 1,440 litres of air
per hour and developed a mean pressure of 700 inm. (H2O).

W = 1,440 X 0-7 = 1,008 kilogram-metres = 2-36 Cals. per hour.

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 per hour. 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 11-82 X 4-9 = 57-9 Cals. per hour.

The value just obtained is about 25 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
additional muscles in gesticulation, etc. A speech of an hour's
duration may tax his entire powers. To add to his troubles
he had to make himself heard in a large reverberating hall.

Experiments have been carried out to determine the most
economical way of using the voice so as to obtain distinct enuncia-
tion and carrying power. During ordinary conversation in a
quiet room the oscillatory pressure (R.M.S.) in the sound wave
at 1 foot from the mouth appears to be about 1 dyne per cm. 2.
This value may be decreased or increased by about ten times
without appreciably decreasing distinctness. At the lower energy
level some of the consonants are difficult to differentiate. We
have seen that the main energy of the voice is, speaking broadly,
of low^ pitch. If we filter off the 60 per cent, or so of vibration of
lower frequency, the distinctness and carrying power of the voice
is not impaired, but if we filter off the 5 per cent, of the higher
frequencies we reduce the audibility of articulation by about
25 per cent. This applies especially to the dental consonants — the
" hiss " sounds having components of very high frequency, even
above 4,000 d.v. per second.

The rate of emission of sound energv for ordinarv conversational
speech is about 125 ergs per second ; for ])ublic speech about

412

THE VOICE

2,500 ergs per second ; and for tub oratory ])robably five times
that amount.

R. L. Jones (Amer. Telegraph Co.) considers that the energy
actually emitted in speech is very small. He calculates that if a
million persons were to talk steadily, and the energy of their voices
were to be converted into heat, they would have to talk for an
hour and a half to produce enough heat to boil half a pint of water.

Sabine, who experimented largely with organ pipes as his source
of sound, found that an open diapason organ pipe at a wind
pressure of 9-14 grams per sq. cm. emitted 1,400 to 32,000 ergs per
second according to the pitch of the note.

Table LXIV. gives the relative values of the expenditure of
energy in the utterance of a single perceptible note in various
sizes of halls. The notes were produced by an artificial larynx
(syren).

TABLE LXIV

Nature of Hall.

Tenor.

Baritone.

Bass.

Theatre .....
Church .....
Lecture room . . . .
Dining hall (bad acoustics)

1-0
4

1-4
4

3
6
4
6

7
42
12
66

These figures, multiplied by 2 X 10 ~\ give, in kilogram-metres per
second, 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.

CHAPTER XXIX
ALIMENTARY CANAL

" I receive the general food at first,
\\'hich 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. XXII.) the non-gaseous imports
are submitted to a certain amoimt 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 oiu' foodstuffs are solid or semi-solid, and in such a state
are useless to the organism. Before they can be split into their
constituent imits they must be rendered soluble.

General. In brief, the f miction 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,
(-t) 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 may be co-ordinated.

In structure, the alimentary canal is a tube passing longitudi-
nally through the body, having anteriorly a voluntary mechanism
for receiving and grinding food ; intermediately, stations, not
controlled by the will, for completely breaking down the food
mass to convenient units and for absorbing the same, and pos-
teriorly, 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

413

414 ALIMENTARY CANAL

the ship reaches port (conditioned reflexes). By means of the
taste buds on the tongue, the nature of the cargo is further ascer-
tained and appropriate secretions from the sahvary glands take
place (reflex). Bitter or saline substances provoke a profuse
secretion of watery saliva. Flesh is met by a secretion containing
a large proportion of the lubricating 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
(par. (c) below). It acts as a lubricant : moistening the surfaces
of the mouth and the passage from it ; infiltrating 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 i7i the mouth. It contains a diastatic enzyme, ptyalin, which,
however, carries out its action on polysaccharides during the earlier
period of digestion in the stomach (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.

The tongue has a threefold duty to perform as a unit of this
transport system^ — (a) working in conjunction with the lip-
sphincter^ — orbicularis oris, and with the triangidar and other
muscles it acts as a suction-plunger ; (/3) diu'ing deglutition it

THE ACT OF SWALLOWING 415

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 lower 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 kg.
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 kg., 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. XVII. 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,
faces are elongated and narrow instead of short and roimd 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 nuiscles. The jaws are closed and the
tip and sides of the tongue are pressed against the hard palate and

416

ALIMENTARY CANAL

teeth. A rapid contraction of the mylo-hyoid muscles, which form
a floor for the front portion of the mouth {diaphr'agma oris), pushes
the tongue up against the hard palate. At the same time the
hyoglossas 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. 62 (lower portion), 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 :

(«) The oral 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 veil palatini nuiscles. (6) The laryngeal aperture is kept
closed by the action of the crico-arytcenoideus lateralis, arytcenoidei,
and the thyreoarytcenoidei muscles, which pull the aryta^noid
cartilages forwards against the back of the epiglottis. Accom-
panied 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. The following table (LXV.) shows the time relations of
the chief muscles engaged in deglutition (from Kronecker and
Meltzer and others) :

TABLE LXV

Time from
Commence-
ment.

Interval
(seconds).

iluscle llovciucnt.

Duration of

Contraction

(seconds).

0-03

Mylohyoid

Deglutition apnoea starts

0-6
5-6

0-07

Elevation of larynx .

0-8

0-3 sec.

0-2

Constriction of j)liarynx

1-2

0-9

1st section of cesophagus

2-2-5

3-0 sec.

1-8

2nd section of oesophagus

6-7

6-0 sec.

3-0

3rd section of oesophagus

About 10.

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 of
the stomach. This aperture, in common with the exit from the
stomach, is guarded by a thick ring of \isceral nmscje. When

CONTROL OF GASTRIC SPHINCTERS 417

contracted, i.e. during the iu)rnial state ol' tonus, tliese 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 foodstnlTs by
enzymes now^ commence (Chap. X.). Polysaccharides are broken
down to maltose by ptyalin and the native proteins first converted
to mctaprotein 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.

Pre-pyloric Sphincter.

Even a casual examination of the stomach will show that it
is divided into two parts, each w^ith a distinct function. Wepfer
(1679), Spallanzani, Haller and others observed that a transverse
band of muscle formed a " potential " sphincter to the antrum
pylori in various animals including man. " This band," writes
Beaumont, the obser^'er in the now classical St. Martin experi-
ments, " is situated near the commencement of the more conically
shaped part of the pyloric extremity, 3 or 4 in. from the smaller
end. In attempting to pass a long glass thermometer tube through
the aperture into the pyloric portion of the stomach, during the
latter stages of digestion, a forcible contraction is first perceived
at this point and the bulb is stopped. In a short time there is a
gentle relaxation, w^hen the bulb passes without difficulty and
appears to be drawn quite forcibly for three or four inches toAvards
the pyloric end. It is then released and forced back, or suffered
to rise again ; at the same time giving to the bulb-tube a circular
or rather spiral motion and frequently revolving it completely
over." Other observers, using more modern methods involving
bismuth feeding, etc., have confirmed these older findings, and
have shown definitely that this constriction takes place during
normal digestion in man, dividing the stomach into an upper,
fundie part, which may be completely separated physically and
functionally from the lower, antrum pylori. 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 eardia, the nnishy 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

418 ALIMENTARY CANAL

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 pre-
pyloric sphincter w^as controlled by the hydrogen ion concentration
of the duodenum and of the pyloric part of the stomach. Acid
entering the intestine undoubtedly causes constriction of the
sphincter. While the pH 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 H ion
concentration 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.

Pyloric Sphincter.

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, {h) 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 distal end of the food-mass undergoes relaxation while a
corresponding proximal 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.

{b) These driving peristaltic waves are not the only movements
of the intestinal musculature. While these movements are going
on in some loops of the small intestine, in other loops 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 wdth 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

SOAPS IN FMCES 419

thcni into their coniponciit 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) Absorpti(jn 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 one-third of the fa?cal 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. 107) 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 (liqiud 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
of the rectum by the faeces. When the pressure of the faeces in
the rectum reaches a value of about 30 to 40 mm. Hg., there is a
call to defaecate. If no response be made, the call is not repeated
immediatelv, as the rectal walls relax and so lose their irritabilitv
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 gi\'en by attempting to trace
the development of the higlily complex system of the vertebrate
from the apparently sim])le physico-chemical response of the
amoeba to contact with food (Tropisms, Chap. XXXIII.).

27—2

420 ALIMENTARY CANAL

Secretion of Acid and of Alkali.

According to Carlson, the total amount of gastric juice secreted
by a man with a gastric fistula (on an ordinary diet of meat, bread,
vegetables, coffee or milk and fruit) is about 700 c.c. per meal.
Somewhere about 2,500 c.c. of water with sufficient hydrochloric
acid to make about a 0-03 N solution is secreted per day. This
concentration of a mineral acid is greater than is apparently
compatible w^ith life, and yet it exists in contact with the stomach
wall. Further, the blood from which the acid undoubtedly comes
is practically neutral {pH = 7-4). How% then, do the cells of the
acid-secreting glands cause the separation of this strong acid from
its salts and, having made the acid free, how do they maintain their
integrity ?

(1) Where is the acid formed ? After intravenous injection of
solutions of potassium ferrocyanide and of some inert salt of iron
which will combine with the ferrocyanide to form Prussian blue
only in the presence of free mineral acid, a blue colour is found in
certain of the parietal cells. This seems to point to the presence
of free mineral acid in these cells, but imfortunately for this
thesis, some cells known to be secreting HCl, do not stain, while
others incapable of forming HCl {e.g. liver, blood cells, etc.) do
stain.

(2) How is the acid formed ? The present view is that the protein
chlorides of the blood are dissociated slightly, as we have seen.
Some of the free chlorions pass into the parietal cells and are seized
upon by a weak base like ammonium. This weak chloride is
secreted by the cells into the lumen of the gland where, meeting
water, it is dissociated on the cell-lumen interface. The weak
base passes back into the gland cells, and the strong [Cl]~ vmites
with some [H|^ from the water and passes into the stomach as HCl.
It is known that cells, in contact with NH4CI and H2O, can carry
out such a chemical shuffling. For example, the mould Penicilliiim
glaucum readily absorbs the anmionia from a solution of ammonium
chloride, leaving hydrochloric acid. Evidence in support of this
view is afforded by chemical analyses of tissues which show that
while all contain ammonium salts those of the mucosa of the
stomach contain the highest percentage. We have also seen
(Chap. XXIII.) that there exists in blood a definite ratio between
[protein HCl] and [NaCl], so that any decrease in the [protein HCl]
will lead to a dissociation of (NaCl] to preserve the balance (see
also Donnan Equilibrium, Chap. XI.) A disturbance like this
has far-reaching effects (see alignment chart, Fig. 83).

When HCl is secreted there will remain an excess of base in the
blood, hence, the denominator of the ratio HaCOg/NaHCOg tends

ACID SECRET I OX 421

to rise and COg has to be retained to preserve the balance at 1/20
]^ut ill doing so, the |H2C'();j] rises, and this will cause the alveolar
C'Oa tension to rise. Dodds has shown that tliree-(|uarters of an
hour after an average meal the alveolar CO., tension may rise by as
nuich as 5 nnn. Hg. In hyperchlorhydria the excessive withdrawal
of [Cl]~ from the blood leads to over double this increase of alveolar
C"Oo tension. Those suffering from a low concentration of HCl
in their gastric juice have a very slight increase in the output of
CO2, while achlorhydrics show no change.

The same problem, that of the secretion of alkali at a later stage
of digestion, may be tackled in a similar way. It has been shown
by Dodds that during the secretion of the alkaline juices (succus
entericus, pancreatic juice and bile) the base of the blood suffers
a decrease with a consequent fall in alveolar COg tension.

Whatever be the mechanism by which these juices are formed,
the epithelial cells can remain in contact with a considerable
concentration of [H^] or of fOHJ^ without damage. Lowering of
vitality, by anaemia, HCN, etc., permits digestion of the walls of the
alimentary canal to take place.

CHAPTER XXX
MOVEMENTS OF THE LIMBS

" If the mountain will not come to Mohammed,
Mohammed must go to the mountain."

It is SO obviovisly to the benefit of the organism to have the power
rapidly to change its position relative to its prey and to those
elements in its environment not in accordance with its comfort,
that we take for granted that the process of the evolution of the
means of locomotion is both natural and beneficial, and do not
pause to consider how alterations in the external medium impressed
the first organ of movement on gradually differentiating proto-
plasm. We refrain from embarking on this fascinating and highly
speculative theme and leave to the student's imagination the
progress from the surface tension changes occurring in the pro-
trusion of pseudopodia ; through movement produced like that
of the "rocket car" by a backward expulsion of fluid ; to the
controlled ciliary whipping progression of free swimming ]jara-
mecium. Then come probably problems of the laying down of
fibrous tissue {q.v.) and the deposition of salts of lime, silica, etc.,
in this medium, forming a pattern such as we have seen on
Chladni's plates {q.v.). The lever is an essential tool whereby
muscle may be caused to do external work. Some animals lay
down the solid mineral matter outside the limbs forming an exo-
skeleton. They have certain advantages in the matter of autotomy,
but the disadvantages due to clumsiness and to the upheaval
necessary to accommodate the growing bulk of the limb clearly
outweigh these. The mammalian limbs contain their levers
within, and the limbs carry the muscles outside the system of
levers. We have already studied the structure of the levers
(Chap. XVII.) and the intimate nature of muscular action (Chap.
XIV.). We must now give consideration to the mechanism of the
lever system of the body.

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.

422

LEVERS 423

In general, a lever is a rigid bar either straight or eiirved which
is capable of a rotatory motion round a fixed point — the i'ulcruni.
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 point of application of the
power and that of the load. In this class of lever, if the power arm
is equal to the load arm, we have a balance. The application of
1 kg. of power will lift 1 kg. of load. If the power arm is lengthened
by shifting the fuleriun nearer to the load, thtni power will be
increased proportionalltj as speed is decreased. For example,
dealing with a straight lever and putting P = point of application
of power, F = 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.
the nod of 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
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 LFjPF.
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 oecipito-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 liy the toes on contraction of the gastrocnemius.

Class II. The fidcrum 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

424 MOVEMENTS OF THE LIMBS

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 Brachialis muscle is inserted about 1 cm. beyond
the fulcrum (ell)ow), while the total length of the load-arm (fore-
arm) is about 30 cm. 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-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 climl)ing, the upper
arm is the lever employed to lift the body, mainly by the con-
traction of the Brachialis muscle ; and the origin of the Brachialis
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 length of the effective power and load arms may be

PULLEYS 425

obtained by dropping perpendiculars from the fulcrum to the Hnes
of application of power and load. The ratio of these perpen-
diculars oivcs the ratio of the distrihutioii of j)ower 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 nniscle. For each
of its positions, the lev^er will have a moment of rotation determined
by the size of the angle made by the line of traction (axis) of the
nuiscle and the axis of the bone. By resolving the force of the
nniscle 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
})arallel 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),
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 nniscle 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 tendon of the
superior oblique muscle on its way to the eyeball : and the
peroneus longus looping round the lateral malleolus on its passage
to the medial 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 Brachialis, and it is pulled downwards by
gravity and the action of the Triceps brachii nuiscle. Both
sets of muscles act together and harmoniously, so that in any
position of the ulna relative to the humerus, the opposing (nmscular
and gravity) forces exactly balance one another. That is, the

426 MOVEMENTS OF THE LIMBS

arm may come to any position and remaiii there without the
expenditure of any extra energy (not taking into account gravity).

Synergists. 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 nuiscles 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
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 rhomboids 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
lengthened and the position of the fulcrum altered.

Centre of Gravity. One of the first problems to be tackled is
the maintenance of the body in a vertical position in a state of
stable equilibrium. To produce this state of affairs the body must
be balanced over the two feet so that the centre of gravity lies
vertically over the area between the feet. In this position the
centre of gravity of the whole body lies just above and half-way
between the anterior sujyerior iliac spines. As the body is bent
forwards, backwards, or sideways the centre of gravity moves
accordingly, and may lie outside of the body. As long as the
vertical dropped from the centre of gravity lies within the area
between the feet (underpropping area) the body will be in equili-
brium. The maintenance of this balance is a function of the
skeletal muscles. Whenever the centre of gravity tends to move
beyond the underpropping area muscular contraction pulls it back.

Standing. In order to maintain a vertical position the tibia has
to be balanced on the ankle-joint, the femur on the knee-joint, and

STANDING AND WALKING 427

the pelvis on the hip-joint. Just try to l)aUincc an articulated
skeleton on its two feet and you will get some idea of the com-
plexity of the process. P^^ach foot has three points of contact
with the ground, viz. heel, base of hallux, and varying proportions
of the outer digits. Thus, the body is balanced on two tripods
(Fig, 52). These tripods can be placed in various positions
relative to one another so as to spread the area of support and keep
the plumb from the centre of gravity within it. With the feet in
the position adopted when one stands erect and at ease, one has got
to place the tibia? on the tripods so that the centre of gravity of
the parts superior to the ankle-joint lies as nearly as possible over
the axis of the joint. Having done this, we have, in a similar way
to balance the femur, and then the pelvis with vertebral column,
thoracic cage and arms. Finally, the head has to be placed on
the atlas.

Bending. The further the vertical from the centre of gravity
moves from this " at ease " position, the greater is the difficulty of
maintaining equilibrium. More muscles are called into play and
they have to bear a greater load. Fatigue, which we have seen is
rapidly produced by continuous exertion, soon sets in.

In bending forward the centre of gravity passes forward out of
the body and lies well in front of it. To counterbalance this, the
hips are thrust back and the body assumes a > position. If this
is not done, we would fall forward, as any one may find out if he
tries to pick from the floor a coin placed between his feet, protrusion
to the posterior being prevented by standing against a wall. This
function of the hip movement is apparent also when one tries to
stand on one foot. On shifting from both feet to one foot, the hips
shift towards that side on which the foot is being used, and com-
pensatory movements of the shoulders and other parts occur. If
one stands vertically upright, heels against a wall which prevents
the backward movement of the hip, it is just as impossible to stand
on one foot as it is to touch the toes without falling.

Walking, The process of walking is a series of acts whereby a
state of unstable equilibrium is first produced, and then corrected
by altering the position of the underpropping area of the body.
It might be described as falling forward followed by recovery. It
has been extensively studied by Hill and others by means of the
ultra-rapid cinematograph camera producing the so-called " slow-
motion " pictures. These records show that, from the standing
position, natural walking is accomplished by leaning forward and
when the angle of slant assumes a critical value indirectly related
to the height of the walker's centre of gravity from the ground, one
foot is raised, swung forward, and its heel placed on the ground.

428 MOVEMENTS OF THE LIMBS

The body then falls forwards and towards that side on which the
foot has moved. This brings the centre of gravity over that foot,
and to prevent undne nuiscnlar action this leg is straightened,
bringing the centre of gravity right over the ankle-joint, etc., as
already explained. The other foot aids this process of the re-
distribution of the incidence of the weight of the body by pushing
against the ground with its toes and raising the heel from the
ground to do so. The second foot is now raised clear of the ground
by flexion at the knee and lifting of the toes. This foot follows a
similar path to the first foot, i.e. is swung forward by muscular
contraction until it reaches a position where the heel is placed on
the ground by the extension of the knee.

The leg thus acts, in walking, like a compound pendulum, and,
therefore, the amplitude of its swing, i.e the length of the stride,
will be determined by the length of the pendulum, i.e. by the
distance between the centre of gravity of the limb and the hip-
joint. A short leg will, therefore, have a short quick sw'ing, and
a long leg a long slow one. By altering the effective length of the
pendulum by lowering or raising the centre of gravity of the limb
one produces an amplitude of swing to which the leg muscles are
not accustomed. Fatigue wdll in these circumstances set in more
rapidly than normally. The alteration in the centre of gravity
may be accomplished quite simply by wearing extra heavy or
extra light-weight shoes.

As was mentioned above, the hip moves backw^ards to compen-
sate the shift forwards of the centre of gravity. One would,
therefore, expect to find a compensatory movement of the hips in
walking in order to keep the centre of gravity near the inner
border of each foot in turn. Not only does this side-to-side
movement take ])lace, but two other hip movements occur which
together cause the hips to follow the line of a double sigmoid
curve with each complete step. (1) When the body is falling
forward the hip moves in the arc of a circle, of which the centre is
the ankle-joint and the radius is the distance between hip and
ankle, (2) During the period when the weight of the body is being
shifted to the other leg the hips trace the arc of a circle whose
radius is half the distance of foot to ground.

Owing to the shortness of the ileo-fcmoraJ ligament in the
female, her leg cannot swing back as far as that of the male. If
she wishes to lengthen her stride to keep ])ace with a male partner,
she must twist her pelvis on the vertebral column. Because of the
ileo-femoral ligament and the wide pelvis, the adult female has a
gait characterised by a greater degree of rotation than that of the
male or of the younger female.

SECTION v.: THE ANIMAL AS A WHOLE

CHAPTER XXXI
THE PRESERVATION OF NEUTRALITY

" To test a principle by its ronsequences is allowed by good logic and enjoined by
sound reason." Joi bkut.

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. So, in discussing the relationship
existing between cell and environment, individual and world, etc.,
we find it convenient to consider how the organism so adjusts itself
to meet changes in its environment that it remains apparently an
independent entity. There is, of course, no such somatic inde-
pendence. Body and environment together are in indissoluble
partnership. In fact, they are a unity. The organism no more
adjusts itself to suit its environment than the enviroimient alters
itself to suit the organism. Both are subject to change, but the
change is equally impressed on both.

Further, a change in the nature or incidence of any force on
organism or environment produces far-reaching results. Every
imit of the entire system (organism + environment) is affected
more or less by quite a small change in the energy content applied
apparently locally. For example, we dealt (Chap. XVII.) with the

429

430 THE PRESERVATION OF NEUTRALITY

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
acts as a trigger, setting off a series of reactions resulting, finally,
in the restoration of the status quo. 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 oxyhsemoglobin (p. 328) setting free the needed
quota of oxygen, secondly, by stimulating the respiratory centre
(Chap. XXVI.), it speeds up the intake of oxygen, and lastly, the
blood flow is increased, both locally by vasodilatation, and generally
by increased cardiac action.

In the Avork 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 and carbonates are unknown. At the hydrogen ion
concentration of blood, however, the proteins may act as weak
acids and combine with some of the plasma base. When carbon-
dioxide passes into the plasma it reacts with the protein salt,
liberating the protein as a weak acid, and forming sodium bicarbo-
nate with the base. The weak protein acid is so slightly dissociated
as to have a negligible influence on the hydrogen ion concentration.

Some carbon-dioxide may also be absorbed by the colloidal
particles, but the part played by the serum proteins in the preserva-
tion of neutrality is quite small.

(6) As has been stated, the main crystalloids of the plasma are
sodium bicarbonate and sodium chloride, but there are small

ALKALI RESERVE

431

quantities of other salts sueh as phosphates also present. These
latter are, however, quantitatively unimportant. In the regula-
tion of the hydrogen ion coneentration, the sodium bicarbonate is
the most important plasma constituent. It has been shown
practically, and it may be deduced theoretically, by consideration
of the law of mass action, that where a solution contains a weak
acid, and a salt of that acid, the hydrogen ion concentration of the

, ^. . J.- 1 J. ^1 i.- [concentration of free acid]

solution IS proportional to the ratio ^ ; -:, \

[concentration of salt]

Of the crystalloids in solution in the plasma, sodium bicarbonate
has the most 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 sodium.

For instance.

Na
CH3COO

+

= Sodium bicarbonate.
= Acetic acid.

CH3C00Na

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. The dissociation of

NaHC03 is a reversible reaction

NaHCOg —
HoO —

Na+
OH-

+
+

HCO3-
H+

Strong. Weak.

This means that the direction of the reaction will, in the main,
depend on the relative amount of C02(HoO) present compared
with the amount of NaHC03. For plasma, this ratio has been
determined experimentally. To give the normal |jH of 7-4, plasma
must have 3-75 grams of CO2 bound in NaHCOg present for every
gram of uncombined CO2 : or, by volume, one volume of COg
remains constant when associated with 20 volumes combined as
carbonate. In tabular form this reads :

Free CO, 1 1

TS 1 r.A = 771^' by weight, -- by volume.

Bound to, 3-75 -^ "^ ' 20 -^

this ratio is present owing to reduction
in the CO., tension some will dissociate to balance the dissociation

If excess of NaHC03 over

432 THE PRESERVATION OF NEUTRALITY

pressure. If too much CO2 is present it will in the first instance
combine with any available base to form a bicarbonate ; if no
base is available, the excess COg wdll be eliminated by the lungs.
If any acid stronger than carbonic acid finds its way into the
blood it replaces some of the bound CO2, thereby increasing the
free CO2 temporarily. This causes increased ventilation of the
lungs and elimination of the excess COo, bringing the ratio

free CO
-_ \ — back to its original level, and hence restoring the

combined CO2

original pYi.

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 that CO^ 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 drazvn 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 widoiv's cruse of oil —
always magically replete. If the ratio of H0CO3 to NaHCOg 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.

II. The lungs eliminate COg. 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 COg 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 COo in the blood. It has been stated that
this regulatory action of the medulla is caused not by COg, but by
the hydrogen ion concentration of the blood, i.e. any acid perfusate
will quicken respiration. But, as is ob\i()us from the context,
)U) 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 in health, so nice is the regulation.

ACTION OF ERYTHROCYTES 433

III, Excess of base, and acids in condiination with bases are
eliminated by the kidney. The cells of this organ have a low
threshold for such salts.

IV. The part phit/cd hi/ ihc red blood corpuscles- in preserving
neutraliUj. In conmion with other tissue elements, the erythrocytes
have a phosphate buffer system. Potassium dihydrogen phos-
phate, KH0PO4, is an acid salt and reacts with bicarbonate^ for
instance, to form the basic salt KoHPO^,

viz. : 2KH2PO4 + 'iNaHCOgirNaaHPO^ + K^HPO^+HaO-l-COa

acid phosphate. basic i^hosphate.

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, the pigment haemoglobin plays a very
important part in the preservation of neutrality, as might be
deduced from its function in the transport of respiratory carbon-
dioxide. As explained in the chapter on respiration, haemoglobin,
either in the reduced or oxygenated form, appears to be present
in the cells either as a weak acid, or in combination with cell base
as a salt. Increase in the concentration of acid in the cell due to
increase in the acid in the plasma results in reactions of the type
BHb + HA — BA + H • Hb, as long as the acid HA is a stronger
acid than haemoglobin. Acids weaker than hi^moglobin would
have a negligible effect on the hydrogen ion concentration because
of their slight dissociation. Thus in the presence of a stronger acid,
base is liberated from combination with haemoglobin to neutralise
the stronger acid, while the resulting acid haemoglobin has a
minimal effect on the hydrogen ion concentration because of its low
dissociation.

In addition to this " buffer " action of the haemoglobin, in
which it acts simply as a weak acid and salt buffer system like the
free and bound carbon-dioxide of the plasma, the pigment has a
still more important influence on the preservation of neutrality by
virtue of its change in acidity on oxygenation as described in
Chap. XXIII,, whereby, without change in hydrogen ion con-
centration, the mere passage of haemoglobin from oxygenated to
reduced form renders available about 25 per cent, of base combined
with it for cond^ination with other acids. It is these physical and
chemical properties of luemogl()l)in, together with the re-distribu-
tion of electrolytes between cells and serum which accompanies the
reactions between haemoglobin and acids, which confer on blood
a " buffering " power su})erior to that of plasma.

B. 28

434 THE PRESERVATION OF NEUTRALITY

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 j;H = 7-4.

Alterations caused.

1. Tending towards alkalinity — Alkaline tide after digestion.

2. Tending towards acidity.

A. Normal. (1) Muscular activity. COo.

Lactic acid.
(2) Protein disintegration, food fHoS04

muscle [P2O5

B. Abnormal. Mal-oxidation acidosis.
Alterations checked.

1. Tissue compensation — Phosphates.

2. I Alkali reserve^ — NaHCOa.

^ ' ... ( COo stimulates respiratory centre.

3. Respiration ' " „ „ ^^ , ^

y ^ \ Lack of free LU, depresses centre.

, ,^. T la) increased elimination of -< „ -,. : as salts.

4. Kidney - ^ ' alkali ;

[(/^) 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 pH. in spite
of additions of acid or alkali. The late Professor 8ir Wm. 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 XXXII
THE REGULATION OF TEMPERATURE

" Where hot and cold, and dry and wet
Strive each the other's phice to get."

Prior.

The problems associated with the regulation of the temperature of
man are so closely connected physically and physiologically with
those involved in the provision of an adequate ventilation in
rooms, etc., that these two subjects may conveniently be con-
sidered together.

One of the most striking phenomena in the life of man and of
the warm-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 tcmperatiu'c. Contrast
this freedom from variation with the continuously changing
temperature of the cold-blooded animal as the temperature of its
environment changes.

TABLE

LXVI

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 wliich hibernate become,
for that time, as if cold-blooded. The advantages that warm-

435 28—3

436 THE REGULATION OF TEMPERATURE

blooded animals possess by reason of their higher temperature are
due to the well-known fact that most chemical and some physical
reactions are increased in rate by increase of temperature (see
Temperature Coefficient). They also are free 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.

Honioiothennic Animals maintain a constant temperature.
Mammals and Birds . . . Birds . . . about 42° C.

Adult and not during hiberna- f Mammals (except man) ,, 39° C.
tion or activity . . . ( Man . . ,, 37° C.

II eterothermic or Poikilothermic Animals.

{a) Lethal temperature, about New born Homoiothermes.

20° C. The young of rats, mice and man

are practically poikilothermic, and
maintain an internal temperature
of from 0-01 to 3-0° C. above the
temperature of the environment.
(6) Hibernation starts when Hibernating animals,
temperature falls to about
20° C.
(c) Still active below 20° C. Eeptiles, Batracia, Fish, Molluscs,

Insects, etc.

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.

Instruments Used to Indicate Animal Temperature.

(«) Mercury thermometer.

(/)) Electrical resistance thermometers.

{(•) Thermo-electric couple (Thermopile).

(rt) 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 attain-
ment 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

THE THERMOMETER 437

mercury that mijflit l)c drivcii over by accidental heating beyond 46° C.
Usually the tlienuonieter is made self-registering by having a small detached
thread of mercurv which is pushe<l up by the expanding fluid and remains
at the highest temperature reached.

Where a continuous record lias 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 resisla))ce
of a platinum (or other metal) wire caused by a slight increase in its tempera-
ture. The alteration in conductivity may be measured by a Wheatstone's
bridge or may be recorded photographically as in the study of the electrical
changes in tissues (q.v.). 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. A half-minute
thermometer should remain at least 3 minutes 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. (Average value = 36-87° C.)

(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. (Average value = 37-2° C.)

(h) 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. (Average value = 36-9° C.)

(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 clinieal sign, yet it does vary regularly by about
± 0-5° C. during the 24 hour day. From the chart (Fig. 98) it

438

THE REGULATION OF TEMPERATURE

will be seen that between 3 and 4 o'clock in the morning body
temperature is at its lowest and between 3 and 4 o'clock 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. After a very few days they become " acclimatised " to their

nHBIRHinB

I 2 3 4 5 6 7 8 9 10 H My; I Z34S67AS lo ii 'u,

Fig. 98. — Cliart of the Daily Variation of Tempprature in tlie Jformal Human Subject, in
degrees Centigrade. The liours are niarlied from midniglit. (Kichet.)

reversed " day," and thereafter have their peak temperature at
about 4 a.m. and their lowest temperature in the early afternoon.
Some people adapt very slowly. For instance, Benedict tells of a
night watchman who for seven years had been working during the
night and sleeping during the day, and had his maximum tempera-
ture 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 {'j-t'.)

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

RADIATION OF HEAT 439

temperature, fold much more severe thcUi is experienced in Hritain may
be enjoyed in the dry, Canadian climate.

For example, a temperature of — 40° may he borne if the air be dry and
still, while a iiiucli wanner 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 variation in rectal temperature.

What we want to get at i^. the mechanism whereby the body
temperatnre of the higher mammal is kept fairly constant despite
variations of outside and " inside " temperature. In this respect,
the ordinary laws of cooling-surface phenomena, are obeyed.
Heat may be lost by :
I. Radiation.

II. Conduction and convection.

Ha. Ingestion and excretion. Inspiration and expiration.

III. Evaporation of moisture.

I. 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 b\' contact with the warm body. This second body
passes the heat on, i.e. there is molecular continuity. By radiation,
on the other hand, one body can effect 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 absorp-
tive power of such a body is unity. The emissive power of a body
is the ratio of the quantity of heat radiated per square centimetre

440 THE REGULATION OF TEMPERATURE

of surface to the quantity radiated per em.- of a " perfectly
black body under the same conditions. (Expt. 74, p. 556.)

TABLE LXVII

Radiating and Absorbing Po\vp:rs of Bodies

Lamp black . . . . . . .1-0

Cinnabar .
White paper

White lead
Polished silver

0-28
0-9
0-21
0-03

(ii.) Temperature of the surface. 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 environment 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)* = 310* — 290* = 216 X 10^ 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 the black-skinned
man in a tropical climate.

II. 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) Area. The loss of heat varies directly with the area of the
surface exposed. For example, the flow across 2 sq, metres is
double that across 1 sq. metre. The area of surface of a child of
2 years weighing 10 kg. is 5,120 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.

CONDUCTION OF HEAT

441

(b) Moistness. 'Vhv loss of heat depends on iiie luoistness of the
surface. The thermal coiuluetivity of all li(|iii(ls except mercury
is very low. Water may be boiled in the toj) portion of a test tube
without aft'eetinti; a piece of ice at the bottom.

TABLE LXVIII
Thermal Conductivity

Substanfo.

Conduotivity (r).

Substance.

Conductivity (e).

Silver

1-52

Cotton flock .

4 X 10-^

Platiiuun

M4 X 10-^

Water at 37° C.

135 X 10-'^

Marble .

180 X 10-^

Sea water

108 X 10-3

Wood

10 X 10-^

Olive oil

39 X 10-'

Paper

30 X 10-"'

Human skin .

60 X 10-'

Vulcanised rubber

8-9 X 10-^

Lard

48 X 10-3

Wool

5 X 10-'

Leather

42 X 10-'

Compressed cotton .

3 X 10 •'

Air (dry)

5 X 10-'

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 em. is
reached. It continues to rise much more slowly for the next
2 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 50-4 Cals. of heat had been rendered latent.

(c) Fat. The loss of heat depends on the nature of the surface
and of the subcutaneous tissue. A good layer of subcutaneous fat
which has a low thermal conductivity will decrease the rate at
which heat arrives at the surface and retard heat loss. The
epidermis is a poor heat conductor. It is twice as bad as fat and
three times as poor as the corium.

442 THE REGULATION OF TEMPERATURE

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, wdiich 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.

(d) Duration of exposure. The loss of heat varies directly with
the duration 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 arc 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.

EVAPORATION OF MOISTURE 443

(iii.) Force of Wind.

Ill still air the loss by conduction is very sliojit. 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.

The cooling effect of an air current is appreciable when the air
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 temperature of 20° C. causes more rapid chilling of a naked
man than exposure to still air at 2° C. (see also p. 445).

(iv.) Humidity of Atmosphere.

Water is a better conductor of heat than is air. A moment's
consideration of the feeling of cold in cold air before entering
water at the same temperature 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 produced by a wind of even a much higher temperature
but laden with moisture.

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 wdll become
inadequate, and the body temperature would increase synchron-
ously with that of its surroundings. That normally this is 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 knowdedge of the
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.

444 THE REGULATION OF TEMPERATURE

TABLE LXIX

Time to Kill Spores of Hay Bacilli at Variolas
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

That the time factor is of immense importance may be adduced
from the preceding experiment (Table LXIX.) 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 liave entered ovens heated
to over 126° C. When the temperature approached 160°, they experienced
extreme superficial vasodilatation. Young girl labourers are said to experience
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 withstood a
temperature of between 226° and 315-5° C. Yet immersion in a bath of
water at 45° C. is unbearable.

It i« 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 ivhich is vaporised entails the use of 536 calories. This is
in accordance with the principle of energetics laid down by Le Chatelier
(p. 9 et seq.). 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 expan-
sion. 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 eva])oration of moisture from the surface thus causes cooling of
the body (see also clothes, p. 452) .

The quantity of heat lost by the evaporation of moisture («) in
the bronchial passages, etc., {b) in the form of sensible and in-
sensible perspiration, dejjends mainly on five factors, viz. :

1. Area and nature of moist surface exposed.

2. Colour of moist surface exposed.

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

HUMIDITY OF AIR 445

in great measure on the state of the superfieial blood vessels.
Dilatation of these enormously inereases the area. It is interesting
to note that the water content of the tissues varies with the age of
the person. Young and old {)e()ple have a higher water content
than adults in their prime (Chap. XXXV.). From age 20 to 50
man loses about 29 grams of water per hour in insensible perspira-
tion. Boys and old men lose more.

(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.

(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 mininumi. {^) 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 (over 70° F.),
the latter operates maximally in cold climates (imder Q5° F.).
This effect of humidity is clear when one considers the conditions
under which tobacco leaf is dried in Rhodesia. In the first stage
(drying at 40° C.) it is impossible for any one to enter the drying
sheds. The sheds are quite enterable during the second stage (at
almost 100° C). At this stage the leaf and, therefore, the air is
quite dry, while at 40° the leaf is fresh and giving oil moisture.

446 THE REGULATION OF TEMPERATURE

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 modification —
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 connec-
tion 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 thermo-
meters 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 — — and/ = F — AH{t — 9),

where A = the constant of the instrument,

F = the tension corresponding to 6°, the reading on the wet

bulb thermometer,
H = atmospheric pressure,
t = reading on dry bulb thermometer,
and »i = maximal vapour tension at t° C.

If ^ = 0-00082, t = 20° C, 9 = 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 = 7" = T^Tm ~ 0"637.

Valuable as this information is, it does not give us a true idea of the cooling
power of any atmosphere. It fails to register the cooling due to air move-
ment, for instance ; so L. Hill devised the kata-thermometer, whereby the
rate of cooling is measured directly.

The "Kata" thermometer is a large bulbed spirit thermometer with
only two marks on the scale indicating a difference of 5° F. in their difference
of level. That is, the top mark = 100° F. and the lower mark = 95° F.,
with a mean value about the mean value of body temperature = 97-5 F.
or 36-5° C. The instrument has inscribed on its stem a factor F, relating
principally to the cooling area of the bulb. The kata-thermometer is placed
in warm water (about 105° F.) till the spirit rises and enters the top bulb.
The bulb is now wiped dry and suspended well away from the body or any
other source of heat. A stop-watch is started when the meniscus passes the
top mark and stopped when it reaches the lower mark. Three to five readings
are taken. The average time in seconds occupied by the meniscus in falling
from 100° to 95° F. divided into F gives the cooling power of the atmosphere
in that place due to conduction and radiation in millicalories per cm.^ per sec.

To determine the cooling power due to the evaporation of moisture a little
silk-net finger-stall is fitted on the bulb and the experiment carried out as
above. Excess water, of course, is removed from the finger-stall. Suppose
F = 470, the dry reading = 78 seconds, and the wet reading = 26 seconds,
then the loss of heat due to radiation, conduction and convection is just
over 6 millicalories per square centimetre per second. The humidity of the

THE " KATA " THERMOMETER

447

atmosphere raises this value three times. These values 6 and 18 are maximal
values for the cooling power of the atmosphere in rooms where sedentary-
work is being carried out. For heavy physical work, the cooling power must
be increased in proportion to the severity of the work.

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 imme-
diate indication of the cooling property of the air in rooms. It consists of a
cylindrical metal box in which is inserted an electric incandescent 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 two-thirds of its length remains outside the instru-
ment. 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. Professor L. Hill, says
that as long as schools, factories, etc., are kept with the comfimeter indicating
somewhere about 30° C, conditions suitable for work will be maintained.

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 1° C, depending on the
cooling value of the environment as well as on the severity of the
work. The following figures from Pembrey (Table LXX.) illus-
trate the influence of the rate of cooling on the body temperature
after severe work :

TABLE LXX

Soldiers on Completing a March of Seven Milks

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 colder 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

448

THE REGULATION OF TEMPERATURE

only a slight increase, while on the warmer clay with almost the
same humidity, the men became uncomfortably hot, and the heart-
rate was increased. Under these conditions man is not an efficient
machine.

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 (LXXI.) gives a rough indication of the
amount of heat lost per day through the various channels :

TABLE LXXI

1. Radiation and conduction

2. Evaporation (a) lungs, etc.

(6) skin
a. Excreta (a) CO. .

(6) urine and faeces

Total heat loss per day

Calories per day.

1,792
182
364

84
48

2,470

The question now under consideration is, provided some 2,500
Calories of heat are lost per day, («) how is excessive heat loss
prevented, and (b) how is the amount lost made good ?

A. Physical Regulation — Preventative. (Usually effective up to
30° C. and over 40° 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 effective cooling siu'face, 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

sin 1 ERING 449

have been covered with a layer of inipcnetrablc 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 one-sixth of the normal,
i.e. metabolism was at a low ebb. If the animal were kept
normally warm, the carbon-dioxide output retin^ned to a normal
figure. On the other hand, Senator states that the human body
can be covered for 8 to 10 days with an impenetrable layer of
varnish without producing any disturbance of metabolism. He
avers that, in those cases where vasodilatation occurred, some
toxic substance must be absorbed from the varnish.

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^
26° C. and over 40° C.)

These mechanisms come into play to replace heat which has
been lost or when the surroundings are warm to prevent the body
from liberating heat from potential energy.

(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
skin temperature is allowed to drop below a certain value.
Anything 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
development are, obviously, unable to keep themselves warm
by exercise and have to be carefully protected against inidue
heat loss.

{b) 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. Cold blood
augments the sugar consumption of the heart-lung preparation,
while warm blood has the opposite effect. Natives of the colder
climates introduce much fatty matter into their diets, while

B. S'J

450 THE REGULATION OF TEMPERATURE

tropical dwellers cut down their protein intake (specific dynamic
action).

(c) Subjection of an animal to great external heat leads not only
to a disinclination to do external work or to take food, but definitely
decreases the flow of the digestive juices. A dog with a gastric
fistula (Pavlov, q.v.) gave neither a psychic nor a hormonic flow
of gastric juice when its body was overheated.

One may just glance at a problem connected wdth 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 striatum. 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 })ody 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.

Ventilation. The purpose of ventilation is to provide such a
change in the air of rooms, that the cooling power of the atmo-
sphere of the rooms shall be suitable for the nature of the work
being done. Some experiments by L. Hill make this perfectly
clear, and show how erroneous were the older ideas concerning
ventilation. A mmiber of healthy young men were crowded into
an airtight cabinet, provided with an electric fan, and with the
necessary apparatus for sampling the air for analysis, etc. " After
44 minutes the dry-bulb thermometer stood at 87° F., the wet
bulb at 83° F. The carbon-dioxide had risen to 5-26 per cent.
The oxygen had fallen to 15-1 per cent. The discomfort felt was
great ; all were wet with sweat and the skin of all was flushed.
The talking and laughing of the occupants had gradually become
less and then ceased. On putting on the electric fan and whirling
the air in the chamber the relief was immediate and very great,

CLOTHES

451

and this in spite of the temperature of the ehamber continuing to
rise. On putting off the fans the discomfort returned. The
occupants cried out for the fans " (Leonard Hill). Long bei'orc
the discomfort had become extreme the oxygen percentage became
so low that matches would not burn. The disinclination to smoke
cigarettes was not noticed until some time after it was impossible
to light them. In other experiments, Hill allowed the persons in
the cabinet to breathe fresh air through tubes and mouthpieces
piercing the walls of the chamber, or induced people outside the
chamber whose bodies were adequately cooled to breathe the
" vitiated " air from the cabinet. The former subjects received
practically no benefit from their " fresh " air, but suffered just as
they did in the experiment quoted above. The starting of the
fan brought relief as before. In the latter experiment the
" vitiated " air breathed by those whose bodies were in moving
air had no effect. They did not experience discomfort nor had
they any headaches nor other after effects popularly supposed to
be due to breathing " polluted " air. Clearly, then, neither the
lack of oxygen nor the presence of carbon-dioxide or other
excreted substance has any influence on the " badness " of the
atmosphere of a room. Discomfort is due to lack of cooling
power, i.e. to stagnation and the loading up of the air with
moisture.

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

TABLE LXXII

(From Rubner)

Substance.

Coefficient of Conductivity.

Air ....

53 X 10-"

Brown human hair

76 X 10-«

Grey human hair .

74 X 10-''

Feathers (eiderdown)

57 X 10-«

Horse hair .

57 X 10-«

Cotton clotli (smooth) .

81 X 10'«

Woollens

68 X 10-«

Silk ....

68 X 10-«

Cashmere wool

68 X 10-«

Cambric

81 X 10-«

Flannel

72 X lO-"

Flannelette .

75 X 10-«

29—2

452

THE REGULATION OF TEMPERATURE

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.

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 conductivitv of various materials is
given in Tables LXVIII. and LXXII.

Coefficient of Protection. In order to calculate the coefficient of
protection of clothing one must know the thickness of the
material. Table LXXIII. 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 LXXril

Thickness in mm.

Pi^rcentage

Rubs tan OP

Mean Oensitv.

volume of

t^ U K^<r lyUfU^V' «

Total.

Of the Skin.

air
enmeshed.

Black cat fur .

12-6

0-6

0-0429

96-7

Black lamb's wool .

130

0-3

0-0484

96-4

( Astra kan)

Rabbit skin .

13-0

0-5

0 0304

97-7

Musk rat skin

U-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

00514

961

Skunk ....

26-0

0-5

0-0410

96-8

Sheepskin

400

0-7

0-0461

96-4

Cashmere wool

0-37

0-364

72-0

Cambric

0-29

0-179

86-7

Silk ....

0-25

0-329

74-7

A man entirely clothed in a garment of a total surface (.9) of
19 X 10^ sq. cm., of a thickness [t) of 75 X 10"^ cm. and having a
difference of temperature {d) on the two sides of 10° C, loses
heat (Q) as shown by the following formula :

Q

c X s X d
i

calories per second,

where

I.e.

Q =

coefficient of conductivity,
c X s X d X 3,600 X 24

t X 1,000

Calories per day.

EFFICIENCY OF CLOTHING 453

If the garment were of wool, (^ = 68 X 10 '^j we have

68 X 19 X 36 X 24 X 10 " X 10=^ X 10^ x 10
^ 75 X 10' X 10^

= 1,488-3 Calories per day.

The coefficient of utiHty of elothing materials may be determined
by covering with them a number of similar copper spheres lilled
with warm water and fmding 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 l)e t, then t/Q = U (coefficient of utility).

TABLE LXXIV (From Bergonie)

Clothing.

Values of ('.

Cycling vest (tight fitting) .

11

Woollen shirt

1-5

Black leather waistcoat

1-6

Flannel shirt

1-75

Rough tweed coat

1-9

Weatherproof cloak

21

Woollen undervest

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 LXXV.) from Lefevre gives an
idea of the protective value of clothing. His subjects were })laced
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,
the mass of air passing in t minutes, is heated by 6°, then the heat

0-237 X 6 X li ^ , . , . ,

lost per mmute = Calories, where 0-237 is the

specific heat of air.

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 o})vious 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-

454

THE REGULATION OF TEMPERATURE
TABLE LXXV

Rate of

Wind.

Metres per

sec.

'reni])era-
ture of air
entering.

Loss pvT liour in Calorics.

Ratios.

Naked.

Clotlied.

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

'^' 1-5
134 ~ ^ ^

130 ,

98 - 1-32

277-5 , _

185 - 1-^

143 ~ ^ "

134

98 - l"^*'
201
130 ~ l'^'^

148 ~ ^ "

''77-5 1 fii
172 -1-^1

313 , ,
170 -l-«^

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.

Further Reading
L. Hill. " Sunshine and Open Air." Arnold.

CHAPTER XXXIII
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 VI 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 eqiiihbrium 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
tmdergoing 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 held, 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.

(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
Porthi'sia chrysorrhoea are of the former class. They move towards
the light and may starve, wdth abundance of food just behind them.

(2) If positively and negatively heliotropic animals are placed

465

456 TROPISMS—THE SLAVES OF THE LAMP

ill 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 ra>^s
of light. The most efficient rays for heliotropic reactions are
{a) the blue between 460 and 490^ju, and (/>) the yellow-green
betwTcn 520 and 580/x/;t. 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 orientated 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 introduced
into the sunny end of the tube. They promptly and invariably
move towards the window, i.e. out of the sunlight into the shade
towards the source of linht.

(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
photochemical reaction is equal in both eyes, this effect on the
symmetrical 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
through the source of light, provided only one source of light be
present. If, however, the light falls sidew^ays 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 positively
or negatively heliotropic."

In manmials, at least, the rods of the retina (g.v.) appear to be

TALBOT S LAW

457

the elements sensitive to light. Rodless mice are not photo-
tropically sensitive (Keiler).

(5) If this is true, it follows that the animal will olx-y the
Bunsen-Roseoe Law. This is rather troublesome to prove for
free-moving animals. The following table shows the applicability
of the law to regenerating polyps of Eiidcndrium. The intensity of
the light was altered by varying the distance between the source of
light and the polyps.

TABLE LXXVI

Distance between Polyps
and source of liiiht

Time in minutes required to cause 50 per cent, of Polyps to
bend towards the source of light.

(metres).

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 })
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 light from two sources ? One might predict that, if
Loeb's hypothesis is correct, the organism will be orientated so that
it comes to rest in a position where it is symmetrically stimulated.
(«) If the two sources of light are of equal intensity and duration
and are set at an equal distance from the organism it should be
orientated 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 straight path

458 TROPISMS—THE SLAVES OF THE LAMP

outlined at first. The relative intensities should be the governing
factor. These three predictions have been amply proved experi-
mentally. The following results (Table LXXVII.) from Patten's
investigations illustrate the nature of the findings.

TABLE LXXVII

No. of lainiis

Difference of intensity hetween tli
jiereentages.

e two lights in

used.

0

25

r)0

Deflection in ilefirees.

. 1

0-55

9-04

19-46

9

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 line of the original path. 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. 235).

(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
cells. The heliotropic machine consists of a rectangular box
about 3 ft. long, 1 J 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

GEOTROPISM 459

driving motors and hence their speed is determined by the intensity
of the Hght falling on the lenses. The steering magnets arc opposed,
i.e. if both seleniinn 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 asynmietrically. 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 minute. 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. Geotropism. Most animals so orientate themselves that
their plane of symmetry passes through the centre of the earth.
They, therefore, either move towards the earth and are positively
geotropic like the tap roots of plants or, more commonly, are
negatively geotropic and climb. Rodless mice or other blind
animals if placed in any position on a steeply inclined plane, after a
few orientating movements, move straight up the plane. The
steeper the plane, the fewer are the initial exploratory movements.

III. Stereotropism is the term applied to the tendency of certain
organisms to bring their bodies as much as possible on all sides
in contact wdth solid bodies. " The butterfly Amjjhipijra, 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 orientates 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 orientating
influence of the eyes is removed, the patient finds difliculty in
standing and in walking (Romberg's sign).

IV. Chemotropism plays an important part in the life of the

460 TROPISMS—THE SLAVES OF THE LAMP

lower organisms. By it, the animal is drawn towards or draws
away from certain chemical substances. The organ stimulated
asymmetrically is orientated so that the stimulating impacts on it
are symmetrical (see Chap. XII.).

V. Galvanotropism. It is easy to see that a simple animalcule,
like amoeba, would come readily under any influence which
altered either its surface energy or the distribution of its colloidal
contents or both. We have seen how colloids are attracted
according to Hardy's Rule {q.v.) to anode or cathode according to
which side of their isoelectric point the /jH of the medium lies.

The isoelectric points of all body proteins (Table XIV.) are on
the acid side of pH 7, and, therefore, if free to move, they would
tend to collect on the side of the cell nearest the anode (p. 92).
Either this produces some changes in the tension of the cell (cf.
geotropism) or the lipoids or some other factors unknown as yet
come into play and produce movement towards the cathode.
Various experiments indicate that the former hypothesis is, at
least, plausible.

VI. Orientation in space is determined mainly by three factors,
liglit, tactile sense and gravitation. Normal equilibrium or normal
geotropic orientation is defined as that position in which the plane
of synmietry 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, voluntarily (though generally subconsciously),
corrects his balance. In the labyrinths, we have a delicate
mechanism for detecting alterations in our orientation in space
{q.v.).

Crozier and his co-workers have applied simultaneously two
types of stimuli to which their experimental animals were sensitive.
For example, negatively phototropic animals which when left in
the dark would follow a path perpendicularly straight up a vertical
plate (negatively geotropic) were subjected to a series of rays of
light applied at right angles to and in the same plane as their path.
The result invariably was a deviation of the path through an angle
which was constant for that type of animal for each intensity of
light. One can then standardise the geotropic intensity as equal
to the effective light intensity when the angle of deviation is
45 degrees from the perpendicular.

In the same way one could apply any two other types of stimula-
tion, and so on till all types of stimulation were standardised as to
their tropic intensities in terms of one another. One would then
be able to predict the angle of deviation of the path of any tropic

ORIENTATION IN SPACE 461

animal under any circiinistanccs. Take, for example, the trielad
Leptoplana variabilis, whieh is cathodally fjaKaiiotropic and
negatively phototropie, and place it in a black rubber plu^tographic
developing dish. The dish is furnished with cotton electrodes at
either short end and a potential difference of about 0-4 volt estab-
lished between them. Three opal electric lamps placed at one side
of the dish supply the light. When the light is off, the planaria
move straight to the negative electrode, and, when the current is
off, they move straight away from the source of light. By varying
the intensity of either form of stimulation, it has been fovmd that
the trielad moves half-way between these extreme paths, i.e. with
an angle of deviation of 45° C. when the current intensity is pro-
portional to the logarithm of the intensity of the light (Crozier and
Steer) (see also Adaptation, Chap. XXXIV.).

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 XXXIV
ADAPTATION

" 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 have
paid the penalty consequent on their easy visibility against a white
backgroimd. It has been said that trypanosomes may be obtained
which are almost unaffected by treatment with arsenic. The pro-
cess 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.

To be brief, one nuist consider that, as anything but a rapid
response to the distribution of forces in the environment is in-
compatible with life, the animal capable of adapting itself to
circumstances will live and probably propagate. Man, because of

462

EN GRAPHIC RECORDS 463

his highly organised nervous and muscular systems, is able to
adapt himself readily and, therefore, reigns supreme.

In the previous chapter we referred to some experiments in which
planarians were subjected to two stimuli — geotropic and photo-
tropic — and stated that the movements of the animal were
governed by the angle of incidence and relative intensities of the
effective stimuli falling on it. Crozier and Wolf found on carrying
out repeated experiments on the same animals that adaptation
to light gradually took place. This adaptation occurs according
to a definite mathematical formula, so that one could predict, for
any intensity of light, how soon the animal would cease to be
influenced by it and follow undisturbed its geotropic path. Some
change had, therefore, occurred in the protoplasm of the animalcvde
which rendered it insensitive to light.

A somewhat different type of experiment leads us to the same
conclusion. If we arrange the stage of a microscope so that a
tiny strongly illuminated square appears in the field, and observe
the movements of an amoeba near the square, we will find that, by
chance, a pseudopod will enter the illuminated part for about
1 or 2 microns. Protoplasmic flow in the pseudopod will stop for
a moment, then begin again, but in the reverse direction. Finally,
the pseudopod will withdraw from the illuminated area. Later,
another pseudopod will be advanced towards the square, thrust in,
and the above process repeated, and so on. " After the animalcule
had repeated this process several times, thrusting one pseudopod
after another into the square, a general change in the course of
action took place. Pseudopods were no longer formed on that side
of the organism. It was noted that the number of attempts to
enter the square decreased with every succeeding pseudopod
formed, till wdth the last pseudopod thrust out in that direction a
single attempt sufficed and the square was barely entered.
Repeated experiments with the same specimen of amoeba proteus
led to such a change in the protoplasm that after ten or fifteen
experiments the moment the organism touched the square it
withdrew that pseudopod and, thrusting one out in the opposite
direction, moved away from the light''' (Mast).

McClendon, in a modification of Mast's experiment, tapped the
amoeba with a glass rod, and found that the strength of the stimu-
lus, the number of shocks and their frequency, all influence the
response. That is, the amoeba can profit by experience and be
taught just like the higher animals.

Careful examination of the proto])lasm during these lessons
shows that a different mass of protoplasm is thrust into the square
each time in any one experiment. That is, the shock leaves some

464

ADAPTATION

record on the protoplasm. This record or " engrani " is the basis
of memory, and the abiHty of protoplasm to retain the engraphic
record, i.e. its teachableness, is the basis of adaptation. " The
engram has a nature which is essentially dynamic. It is not to be
thought of as a mote left in the protoplasm by the stimulating
agent. It is rather a process." (Bovie.)

No case is known where acquired characters have been transmitted
to offspring.

On the other hand, the environment may have profound effects,
not in the nature of adaptation, })ut on the development of the
organism.

Temperature. In Chap. XXXII. the effect of alterations in
temperature on physical, chemical and physiological phenomena
was considered. Temperature influences all life phenomena.

(«) 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 LXXVIII. (Loeb and Chamberlain) gives the
time in minutes required from insemination to the first cell-
division for ^'arious temperatures.

TABLE LXXVIII

Effect of Increase of Temperature on Cell-division
IN Egg of Sea-ltrchin

Temperature (" C.^

8

10

15

20

25

Time (mimites) .

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 Fundalus (embryo) keeps
such regular pace with alterations in external temperature that
it could form the basis for a rough thermometer, as Table LXXIX.
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.

(c) The time necessary to reach sexual maturity is decreased
by increase of temperature. Stefansson reports that the Eskimo

RATE OF METABOLISM

TABI.K LXXIX
Relation between Temperature and Rate of Heart

4G5

Beat

IN FUNDULUS

Embryo

Temperature (° C.)

20

15

10

5

10

15

20

Time for 19 beats (minutes) .

11-5

19-0

32-5

61

33-5

18-8

12

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 observ^ers have
noticed that growth in height and in weight is increased during
periods of increased temperature, e.g. summer (see Growth).

B.

30

CHAPTER XXXV
GROWTH

" The living organism is so constituted that each disturbing influence stimulates
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 to 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 fcrrocyanide-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. Inmicdiately
this happens, a new membrane will form round the copper-glucose
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. 544).

Botanists are agreed that osmosis plays an important part in
plant growth. An experiment is given in Part II., p. 515, to
illustrate the production of turgescence and consequent rigidity

466

ALTERATIONS IN WATER CONTENT

467

as the result of endosmosis (Fig. 45). Plant growth is con-
spicuously associated with turgor, and depends in great measure on
the amount of water taken up. Another and more plausible
explanation may be given of tlie swelling of plant tissues. In
Chap. VIII., p. 97, Table XV^II., we mentioned tiie 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 concentration of the tissue.

It has been definitely proved that animal growth is accompanied
bj' alteration in water content as shown in Tables LXXX. and
LXXXI.

TABLE LXXX
Water Content of Human Embryo (FEHUNti)

Age (weeks).

Weight (grams).

Increment.

Increment
per week.

Water per cent.

6

0-975

97-5

IT

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

Water Content of Frog Embryo. (D.wenport.)

Age (weeks)

1

2

5

7

9

14

41

84

Water percent. .

56-3

58-5

76-7

89-3

93-1

95-0

90-2

87-5

TABLE LXXXI

Percentages of Free and Bound Water in Animal
Tissues at Certain Ages (From Thoenes)

Bound

Total

Free

Bound

Water

Animal.

Age.

Water

Water

Water

(grams) for

each gram

of Dry

per cent.

per cent.

per cent.

Matter.

Guinea pig .

Young (160 gm.)

81-6

61-5

20-1

1-09

))

Okl (600 gm.) .

79-6

60-5

19-2

0-94

Dog

1 day

85-7

59-0

26-7

1-86

)■>

3 weeks

83-8

60-4

23-4

1-44

3)

4 weeks

83-3

59-7

23-6

1-40

• * •

Several months

79-3

55-1

24-2

116

Several months

82-0

62-9

19-1

1-06

5J

Several months

79-7

58-3

21-4

105

30—2

468 GROWTH

Free and Bound Water. Reference to the table above (LXXXI.)
will make it clear that this change of water content with age refers
almost exclusively to the bound water (q.v.) which we saw in an
earlier chapter is held with extreme avidity by the tissues.

In the later stages of growth and especially in the higher
mammals the ratio of water to solids tends to diminish. Inhibi-
tion of growth occurs when means are taken to prevent the
entrance of water. For example, Loeb put Tuhidaria and Ccri-
anthus, which live and grow in sea-water having about 3 to 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
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 Rate of Growth.

(a) Weight. Brailsford Robertson has shown that the rate of
increase in weight follows a curve characteristic of auto catalytic
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 X 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 :

hx

1 ax
or, on integratmg, k = — log ,

QX (I- lC

where k is a constant.

As the result of a series of experiments on auto-inversion at
100° C, the value of k for this reaction has been put = 122 X 10"^.
With this value we can tell at any time after the inception of the
reaction just how much sugar has been inverted. Fin-ther, 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

AUTO-CATALYTIC REACTIONS

469

velocity due to definite concentrations of a and iT. In an auto-
catalytic reaction this niaxiniuni 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/.,.

Do statistical results bear out the statement that growth is an
autocatalytic reaction ? In the following table (LXXXII.) 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.

TABLE

LXXXII

Body weight (Kg.).

Age (years).

dumber nf rases.

Found.

Calculated.

0-5

34

34

100

5-5

22-7

16-5

176

6-5

24-6

204

327

7-5

25-9

234

631

8-5

27-0

26-2

1,038

9-5

28-3

284

1,262

10-5

304

304

1,200

11-5

32-3

32-2

1,129

12-5

35-0

34-0

863

15-5

474

44-8

1,451

20-5

664

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 " exjjected "

weight is —— — , where A = conceptional age in years and m is a

constant for each age (see Table LXXXIII. 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. : I = ■\/mw, w^here I = length in metres, w = weight in
kilograms, and m is a constant for each age (and each type). As

A 3

w =

4-75m

, therefore A = 4-75/3 or /

4-75

(Pfaundlcr.)

470

GROWTH

Pfaundler gives the following examples :

(i.) A boy aged 1 year has a conceptional age A = 175 yr.

Hence lengtli =

1-75 _

4-75

— \/0'36 ^ 0*72 metre, which compares favourably

with the value given in Table LXXXIII.
(ii.) A boy aged 8 yrs. has A = 8"75.

Hence length = . /^ = JVU = 1-23 metres.
V 4-75

(Average length of boy of 8 yrs. = 1-20 metres.)

TABLE LXXXIIT

Concep-

Length

(metres).

Weight (Kg.).

Age from

tional
age .4

Constant
m.

Weiglit

birth.

Height -^ ^'^^^

(yrs.)

Found.

Calo.

Found.

Calc.

3 months

0-225

0-08

25-6

20x10-=^

0-025

6 ,, 3

0450

0-31

0-45

46-91

635x10 =^

2

8 „ j^

0-600

0-42

0-50

36-1

2,100x10-3

5

10 „ )

0-750

0-50

0-53

39-73

3,300x10-3

3,975x10-3

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

1-75

0-74

0-72

42-88

9-4

8-59

12-6

2 years

2-75

0-84

0-83

48-98

12-1

11-82

14

3 „

3-75

0-90

0-92

55-06

13-2

14-34

14-6

6 „

6-75

Ml

1-12

68-17

18-1

17-76

16-3

9 „

9-75

1-24

1-27

78-41

24-9

26-15

20

12 „

12-75

1-38

1-39

84-94

30-9

31-60

22

Table LXXXIII. is from Pfaundler's data. It gives the calcu-
lated and observed weights for each age as well as his values for ?/?
and the centimetre index.

The ratio, weight in Kg. /length in centimetres, is called the centimetre
index. Sometimes the ratio is modified as in Levi's ratio, which is

100 i^/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 '-''l/l ;

Females W = 0-36093 " ■'>V^ ;
W = weight of the body in grams.

where
and

I = length of trunk in cm.

Note. — The values of m in Table LXXXTII. have been multiplied by 10^ for convenience.

FACTORS MODIFYING GROWTH 471

Some organisms when their size reaches a certain limiting value
tend to divide into two ecjual })ortions (Sach's Rule). Therefore,
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 ninnber of cells
follows the compound interest laiv, i.e. is an autocatalytic reaction

To summarise : ^Vhen it is said that growth is an autocatalytic
reaction it is inferred that (i.) superimposed on the velocity of
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 to 9 hmar 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 50 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

472

GROWTH

certain \'ariations in the rate of growth which may be correlated
with alterations in the conditions to which the subjects are
subjected.

1. Phase Differences.

(ft) Individual. Quetelet found that, under normal conditions,
the variations in the rate of growth of man were just what might
be predicted from the application of the mathematical law of
probability. This law is represented by the equation

y = —r- • ^ .

where <r and y are rectangular co-ordinates and h — parameter
of the curve. Riedel tabulated the heights of nearly 4,000 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 a, 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.
CT is a measure of this divergence.

The coefficient of variability (Table LXXXIV.) is obtained by
dividing a by the mean and, for convenience, multiplying by 100,

I.e.

C

M

X 100.

TABLE LXXXIV

Coefficient of Variability in Man at Various Ages

Age (yrs.).

Height C.

Weight C.

0

6-5

15-66

5

41

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."

TEMPERATURE COEFFICIENT 473

{b) bex introduces a ])hase difference in the rate of growth.
Girls rini through the various phenomena of growth at a more
rapid rate than boys.

(c) Difference in race, even under siniihir ehmatic 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
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 grozvth
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 ^•an't Hoff, it
may be said that if x is the temperature coefheient of a reaction,
and the temperature of the reacting mass is raised n degrees, the
consequent alteration in velocity will be as x". Usually the
interval taken [i.e. n) is 10° C. and x is written as Qjq. For most
chemical reactions Q-^q is = 2. This may be taken to mean that
for an increase of temperature of 10° C. the velocity of the reaction
will be doubled, Van't Hoff noticed that, at low temperatures,
very high temperature coefficients were obtained — in some cases
Qjo reached the value of 5 or 6. Most physical reactions, 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 (pp. 9 et seq.). It is, there-
fore, 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,

474

GROWTH

X

10

= 3-25,

I.e.

Therefore
and

10 log X = log 3-25 =- 0-5119.
\ogx = 005119,
X =- 1-125.

The temperature coefficient for the development of the tadpole
is thus (Qio) = 1*12- That is to say, if it takes t days at a certain
temperature 9° (between 10° and 20°), for a certain amount of
growth to take place, then it will take t X 1-12" days when the
temperature has fallen to ^ — n° C.

{e) Climate. The various meteorological conditions — tempera-
ture, 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 LXXXV.).

TABLE LXXXV

Growth in Height of German Military Cadets in Half-

Yearly Periods (Dafpner)

Age.

Increment in cm.

Winter, 6 months.

Summer, G months.

12

80

146

162

162

150

82

22

6

11 12
12—13

13 14

14 15
15—16
16—17
17 18
18—19
19—20

1-6
1-5
2-0
2-5
2-3
1-9
1-2
0-8
0-4

2-3
2-9
3-0
3-5
3-0
2-3
1-5
0-9
0-4

Other investigations (West Point, Sing-Sing, etc.) do not yield
such a marked seasonal variation.

NUTRITION AND GROWTH

475

(g) Diurnal variations. Botli wei<jht and height vary in the
course of 24 hours. The weight is lowest in the niornino- before
breakfast, and is highest after supper in the evening. This may
be aeeounted 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 trilling 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
LXXXVI.).

TABLE LXXXVI

Comparative Weights and Lengths of Full Fed and

Underfed Rats

Age (weeks).

Length of body.

Weight.

Full fed.

Underfed.

Full fed.

Underfed.

0

6

10

48 mm.
128
173

48

98

100

5-4 gm.
42
150

5-4 gm.
24
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 ^ysin, 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.

476 GROWTH

Of their chemistry a Httle is known^ — of their physics or of the
mechanism of their action nothing positive can be said (Chap.
XIIT.).

(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.

(j) Endocrinetes. Considering the factors which influence the
rate of growth, and keeping well in mind the imthinkable 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.

rv. 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. XXXII., 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.

2,820 320 348

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
5,600 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 = 2,491 Calories + 385 X 9-3 =
3,580-5 Calories = a total of 6,071-5 Calories for the period, or about

THE ENERGY OF GROWTH 477

35 Calorics per day. A child of that age has an intake on the
average of about 500 Calories 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 substance
has a value of 1-87 Calories. 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 1,726 Calories. Experiment has shown that in building
this up the animal uses about 4,800 Calories. Man is an exception,
and requires six times this amount.

The growth quotient is the percentage of the energy intake

C-f)

which is " fixed " in the animal tissues. It is about 36 I 1 for

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. Thev found that if the skin is

478 GROWTH

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. XVII.). 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 interna,! 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 (6) 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 hi/ 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
than another, or may have a higher surface tension and so on.
Although it has been pointed out that the presence of external

LAWS OF GROWTH AND FORM 479

resistance acts as a stinmhis to f^rowth, it has also l)ecu 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
l)orne on the principal axis of a plant or animal, a reciprocal
repulsive force is developed betw^een 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 amoimt 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.

CHAPTER XXXVI
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 witli a hollow
sphere, or vesicle, whatever he is going to make."

Oliver Wendell Holmes.

OccuREiNG 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.

'to'

Cell Division.

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 cellidar activity can be eliminated with sufficient
rapidity. A freely suspended unicellular animal is spherical.
Its surface-volume ratio is 3/1. Doubling the radius increases
the surface four times while increasing the volume eight times,
i.e. SIV='^, i.e. the effective surface has been halved. The
immediate result of decreasing the specific surface to a vcdue below the
minimal effective value is to decrease the suppJij 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

480

CELL DIVLSION 481

on an alkaline gel-emulsion has already been eonsidered and may
possibly be the cause of cell dixision. We have, however, to
inquire into the reason for the sijiiiiiu'trical 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 separa-
tion 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 di\ision is accompanied by a complex
but regular series of changes in the distribution of the nuclear
chromatin. These mitotic or karijokinetic changes are dependent
on the bipolaritij 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 l)ipolar cell there are tw^o " 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.
XVII.) 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 them-
selves. Friction prevents the filings from collecting in mass round the poles
while the specific inductive capacity (q.v.) 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 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 toivards regions of greater or less
ifitensity of stress according as its " pernteability " to the particular form of
energy in question is greater or less than that of the surrounding 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

Bi 31

4 82 DE VELOPMENT

obvious that, within certain limits, a longer path through a more permeable
mass would be more advantageous than a shorter path through a less perme-
able 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 hyper-
tonic solution of common salt is placed on either side of this central drop.
In a short time the pigment seems drawn out into threads {fiLros) 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 cell division consists in the division of the
centrosonie into two equal parts which draw away from one
another. A field of force is set np 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 mentioned above. On the
" outer " side of the centrosomes can be seen starlike radiations
(astral rays) recognisable as indications of incomplete lines of force
which run externally to those stronger interpolar lines which
constitute the achromatic spindle.

The chromatin of the nucleus is drawn into a continuous thread,
making a skein, which is then broken into short V-shaped lengths,
the chromosomes, of which there are 24 in human somatic cells.
These chromosomes become arranged round the equator of the
achromatic spindle with the apex of the V pointing to the centre.
This completes the first or prophase.

The second phase of karyokinesis conmiences by the longitudinal
splitting of each chromosome (metaphase). One longitudinal
half of each chromosome then passes (anaphase) to each pole of the

KARYOKINESIS 483

spindle, so that we have, in all, 48 chromosomes, 24 at each pole.
This completes the second and third phases of division.

The fourth or telophase consists of retrogressive changes, that is,
the chromatin of the daughter nuclei is formed by the fusion of
the chromosomes of each group to form a skein at each pole,
which then becomes transformed into the karyomitomc charac-
teristic of the nucleus. At this time, constriction of the proto-
plasm of the cell takes place in the neighbourhood of tiie equator
of the spindle ; the spindle disappears, and linally each daughter
cell, with its full complement of chromosomes, becomes an entity.

The nucleus is composed of material of fairly high " permea-
InHty " 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 woidd 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.

Cause of cell division. We are now in a position to consider the
actual cause of cell division. To state xvhy 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 outside 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. Considera-
tion must be given to the forces at work in the cell. Further,
experiments such as the much quoted one of Brailsford Robertson.

31—2

484 DEVELOPMENT

where an oil drop is divided by the imposition on it of a thread
soaked in alkah, are not very ihuminating. The energy of cell
division is not external to the cell, but depends entirely on a
redistribution of forces inside the cell.

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 ot radial lines of
force. The high tension of the surface of the Gg,g 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 fdings in a magnetic
field of force between two similar poles. The position of the nucleus
determines the first plane of segmentation, since apparentl\
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 ccntrosomes 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

MATURATION OF GERM CELLS

485

ol' the sui-rat'C'-iiK'mhi'uiie ol" tacli of tlir (laughter cells. These
(laughter cells adhere to oue another but do not coalesce. From
this it is inferred that the cell ineinhrane is insoluble in the sur-
rounding medium and in the cytoplasm as well. (It has been

Priinoniial {jcriii crll.

S])priimtogonia.

■ IJivision period (the number of
divisions is iiuich greater).

^ratllration iierioil.

Growth jjeriod.
Primary spermatocyte.

Secondary spermatocytes.

Spermatids.

Spermatozoa.
Fig. 99. — Scheme of the Processes involved in the Maturation of Spermatozoa.

Primordial germ cell.

Oogonia.

Primary oiicyte or ovarian egg.

Secondary oocytes (egg and

first polar body)

Mature egt; and three polar bodies.

Division period (the number of
divisions is much greater).

Growth period.

Maturation period.

Fic. 100. — Maturation of Ovum.

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.)

Maturation of Germ Cells. The cells of the body may be divided
into somatic or true l)ody-cells and gonads or reproductixe cells.
Certain of the cells of the gonads become germ cells. The process

486 BE VELOPMENT

of mitosis follows a path somewhat different in the germ cells from
that of the somatic cells. The primordial germ cell, after dividing
in the same manner, as we have seen somatic cells do, undergoes
a process of maturation which is an additional series of divisions
resulting in cells with only half the number of chromosomes that
the parent cell possessed (Figs. 99 and 100).

Fertilisation. This is the union of a male cell and a female cell,
whereby incidentally the full number of chromosomes is restored
and a further series of cell divisions instituted.

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 differen-
tiated 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 developinent of unfertilised eggs l^y alteration of the
environmental conditions. No change in a system in equilibriimi
can take place unless the relative amount or incidence of the free
energy of the environment is first altered. The two series of
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 foimd that all those substances or agencies which can
bring about haemolysis (Chap. XXII., p. 318) also induce mem-
brane formation. The best agent for this purpose is dilute butyric
acid. Immersion of sea-urchins' eggs (unfertilised) in sea-water
containing about 5 per cent, of A'^/10 butyric acid for 2 to 4 minutes
})rings about typical membrane formation. This membrane 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-

ARTIFICIAL PARTHENOGENESIS 487

stances makes manifest the mechanism oC tlie 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. IX., just those substances which break enudsions.
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 aqueous protein-in-oil type to an oil-in-aqueous-
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. XI.).

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.

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 15 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 so 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.
In order to induce an exosmotic flow, the membrane must be
impermeable to sugar. If the membrane had increased in per-
meability during fertilisation the fertilised egg would probably be
less easily plasmolysed than the unfertilised egg (see Chaps. V.
and XI.) In addition, it is probable that an alteration takes place
in the ratio of the free to the bound water in the egg, and that

488 DEVELOPMENT

adsorbed electrolytes are set free, so increasing the electrical
conductivity of the cell. 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 zvhich 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
(^10 = - 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

210 .

Hence, superimposed on the physical process of exosmosis are
secondary chemical reactions initiated by it.

Spermatozoon. Attempts have been made to determine what
part the spermatozoon plays in the process of fertilisation,
Brailsford Robertson has extracted a substance, oocytin, fVom 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 docs it counteract some obstacle to
development ? " To the first jjart of the question a negative
answer can be given. The velocity of the process of development
is not catalytic. It docs not follow Schiitz's law and vary in
velocity with the square root of the concentration. If two
spermatozoa are caused to enter an ovimi, the rate of segmentation
should increase by 1-4 {i.e. V2) 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.

FERTILISATION 480

Loeb is inclined to believe thul the spermatozoon removes
from the egg a siibstanee or condition which inhibits or prevents
the process of development.

On the otiicr hand, it is conceivable that tiie entry of the
spermat()ZO()n increases the free energy of the now fertilised o\um.
The potential energy of the system cannot be ntilised withont
the employment of a small quantity of free energy. This (piantity
of free energy may be extraordinarily small as long as it is sullicicnt
to start the series of reactions which, once started, arc niito-
catalytic.

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 calorimetrie methods (direct and indirect)
adopted in the study of the energy exchanges of the mature
organism.

Differentiation. The mammalian ovum is holoblastic, that is,
undergoes coiuplete segmentation, and forms a nnilberry-like mass
of cells which divides into two sets, viz. a group of large central
cells and a layer of small cells surrounding these. That is, there
is now 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 gives rise to a
definite part of the developed egg. Thus, up to this division
every constituent of the original egg is present in the segments
in the original proportions. The division now 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 .^, and four larger pigmented cells (intestinal
cells). Eight 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 1,024, the
processes of invagination and differentiation begin.

Organo-genesis. Various parts of the egg give rise to various
organs. The same organ is formed always from the same ])art.
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

490 DEVELOPMENT

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. XVII., 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 sets up mutual strains and
produces a considerable folding and distortion of the whole (Roux).

Both the circulatory systems and the alimentary canal are
evolved from tubular structures, and it is suggestive to hnd 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 track 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, how^ever, 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
growdng 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 491

Energy of Development.

Interesting observations have been made ol" the anioinit of
energy used by a develojjing 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
liad been formed at the cost of the energy represented by 058 small
calories.

l^'urther, 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 lien'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 XXXVII
DEATH AND DISSOLUTION

It is easy to show that these differences in temperature which are required
to secure oroanic hquids from ultimate chauffc 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. Riibner considers that death takes place naturally
after the organism has utilised a certain amount of energy per
kilogram. His second law, that of " length of life," is as follows,
" The amount of energy cons^imed in a kilogram of living protoplasm
from maturity to death is constant for all animals {and equals
191,600 Calories), except in the case of man, zvho 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 ha\'e 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 plentifid supplies of material and energ}', 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 consimmiation, 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
of oxygen in the tissues leads, as we have seen, to the accunndation
of acids. This, after death of the organism, occms 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

402

FATTY DEGENERATION 493

metals, j)h()sj)h()rus, potassium cyanide, oxidation processes arc
inhibited and acids accunndate. The first \isible change after
the inhil)ition 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 enudsion. The
enudsifying colloidal proteins, under the influence of acid, develop
an increased capacity for the ind>ibition of water. If water is
available, the proteins swell and become extremely dilute and the
emulsion is broken. The " groi/ing " 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 enudsion. 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 enudsion woidd
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 coincident with the cessation of respiration, the endo-
enzymes begin to accelerate the processes of hydrolysis of the
tissues (p. 121). Under sterile and anaerobic conditions, the tissues
may be con^'erted 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
fatty acids and soaps. This self-digestion is a consequence of the
lack of free oxygen in the tissues, Avhich 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. X. we mentioned the interesting fact that the enzyme
which hydrolyses maltose builds up another carbohydrate, iso-

494 DEATH AND DISSOLUTION

maltose, 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 dozvn 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 XXXVIII
THE EFFICIENCY OF THE ORGANISM

By E. P. Catiicart, M.l)., D.Sc, LL.D., F.R.S., Rcoius Professor of Physio-
logy, University of Glasgow.

The consideration of the efficiency {i.e. the relation of the con-
siunption 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 jjhysiological " 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

TABLE LXXXVII

Heat output per niin.

Heat equivalent of
external nuiseular

work per min.
(425Kgin. = lCal.).

{'I).

Eftlcieney.

Work.

No Work.
(6).

Increase of

work over no

work = «—/;.

(<■).

(iross.

fl ■ 1(10

a

Net.

d X 100

c

Cals.

9-50
5-71

Cals.

3-08
114

Cals.

641
4-57

Cals.

1-96
106

Per cent.

• 20-6

18-6

I'er cent.

30-6
23-2

495

496 THE EFFICIENCY OF THE ORGANISM

other hand, is the vahie 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 table on p. 495 will make the point clear.

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 efhciency 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 ha^'e found it
a comparatively simple matter to determine the efficiency of
ordinary thermodynamic machines })y the use of a simple formula
E = (Tj — T<y)lT^, where T^ is the absolute temperature at the
source of the heat (the steam in the boiler in the case of an engine)
and To the temperature at the sink (the condenser of 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 fcAv ju, (10-=^ nmi.). The mechanism
of muscular activity, it is true, is not >et 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

ASSESSMENT OF EFFICIENCY

497

the determination of the efficiency both of isohitcd 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 LXXXVIII

Gross and Net Efficiency of the Body as a Whole

Efficiency.

Autnonty.

Gross.

Net.

per cent.

per cent.

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
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.

■■yj.

498 THE EFFICIENCY OF THE ORGANISM

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 LXXXIX

Base line.

Net efficiency.
Average value.

(1) At rest .

(2) Sitting .

(3) Internal friction

(4) Free wheel

(5) Low to high speed

21 per cent.
Similar to (1)
27 per cent.
30 per cent.
30-33 per cent.

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
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

FACTORS INFLUENCING EFFICIENCY

499

ILO

IDS

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 zvithin 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
done in unit time, is of much greater moment. Experimentally
it has been found that the total energy expenditiu-c per revolution
of the pedals is constant for all speeds, but that although there is

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e

1

/^

1

,4

1 1

(

1

//

i

1/

'i

j

1/

1

70 » 90 100 no ua 130 lO

Flf). 101.

500

THE EFFICIENCY OF THE ORGANISM

naturally an increase in the amount of the total work done, the
effective muscular work per revolution decreases as the speed
increases, and there is therefore a steady fall in efficiency (see Fig.
101). 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 XC. :

TABLE XC

Kevs. per min.

Heat equivalent of

external nmseular work

per min. in Cals.

Net efticieney.*

90
124

1-94
1-96

per cent.
22-6
15-7

80
105

1-77
1-83

221

17-7

71
108

1-57
1-58

24-5
15-6

71

94

105

1-34
1-29
1-35

23-1
20-4

17-0

72
88

1-20
1-26

21-5
19-5

* Base line — complete rest, lying.

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. VV/H, the heat equivalent of the
work done, divided by the energy output determined as heat,
was of no real im])()rtance. The true efficiency of the nniscle is
the ratio between the " potential energy thrown into an active
muscle by excitation " and tlie " total chemical energy liberated
as heat." He found, further, that the heat production varied
according to whether the nnisclc 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

EFFICIENCY OF ISOLATED MUSCLE

501

prevented from shortening. On examination of the potential
energy developed by a stinuilatcd muscle not allowed to shorten,
it was found to be approximately 1/6 Tl, where T = the maximum
tension and / = the length of the nuisele. 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~*/-t-26 calories. (See Table XCI.)
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 XCI

ExPT. — Length of muscles, 3-3 cm. ; weight of muscles, 0-135 gm. ;
1 scale division of deflection =
contractions.

Duration of excitation : sees.
Initial tension : grm. wt.
Heat production H : cal. X 10-
Tension T : grms. wt.
TII6H . .

Incidentally he found that different types of muscle {e.g. semi-
membranosus 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.

8-32 X 10-" cal. Sartorius and

isometric

. 0-075

0-075

0-07,^

. 10-5

10-5

10-5

0-« . . 574

740

757

. 44-8

47

47

1-01

0-82

0-80

PAirr 11

ILLUSTRATIVE EXPERIMENTS

•• Science has but one language, that of quantity, and but one argument, that of
experiment." Starling.

■• The laboratory is the fore-court of the temple of philosophy ; and whoso has
not offered sacriliees and undergone purification there, has little chance of admission
into the sanctuary." Huxley.

Those marked
students.

*

Chapter III. —
Chapter V. —

*1.
2.
3.
4.

5.

List of Experiments

are suitable for demonstration

or for more advanced

Chapter VI. —

6.

7.

8.

9.
10.
11.
12.
1.3.
14.
15.
16.
17.

18.

*19.

20.

Chapter

*21.
VII.— 22.

Bomb calorimeter.
Diffusion. Gaseous.
Diffusion. Liquid.

Partial separation of two solutions by diffusion.
Osmotic pressure of crystalloids,
(a) By osmometer.

*(6) By determination of the depression of the
freezing-point.

*(c) By Barger's method.
Turgor.
Soap films.

Camel's hair brusfi experiment.
Cohesion — a surface tension phenomenon.
Work done by altering surface tension.
Effect of soap formation on surface tension.
Camphor, ' ' Water-beetle ' '
Camphor-benzene " amoeba."
Mercury " amoeba."
Electrical alteration of surface tension.
Oshvald's " Physical heart."
Measurement of surface tension.

(1) Stalagmometer method.

(2) Capillary rise method.
Adsorption to a surface.

(1) Charcoal and crystalloids.

(2) Hay's test for bile salts.
*(3) Flotation.

Demonstration of the oxidation of oxalic acid when

adsorbed to charcoal.
Effect of capillary active substances on the rate of

sedimentation of suspensions.
Capillary electrometer.
Strength of acids.

(a) By taste.

(b) By hydrolysing power.

502

LIST OF EXPERIMENTS 503

(r) By indicators.
*((/) By cundiictivity.
*23. H ion concentration by potentiometer.
*24. pH and surface tension.
25. Buffer solutions.

{n) S<)r('iis('ii\s (range pK 4-5-9-2).
*(6) C^a/-/; and Lubs. (I.) ;jH 2-2-3-9.

(II.) 4-6-3.

(III.) 5-8-8-0.
(IV.) 7-8-10-0.
Chapter VIII.^ — 26. Separation of colloids from crystalloids.

(1) Preparation of dialysers.

(2) (a) Albumen -(- sodium chloride, etc.

(b) Congo red and hydrochloric acid.

(c) Blood serum.

((/) Colloidal iron and hydrochloric acid.

Optical properties of colloids.
*27. A. Faraday-Tyndall phenomenon.

B. Polarisation of the Tyndall cone.
*28. A. Ultramicroscope.

B. Brownian movement.

29. Diffusion.

(a) Colloid into colloid.
(6) Crystalloid into colloid.

(c) Acid into colloid.

(d) Electrical diffusion.

30. Liesegang phenomenon.

*{a) Plate rings.

(6) Tube strata.

(c) Efiect of capillary active substances on the
formation of strata.

{d) Dead space.
*(e) In air.

31. Viscosity.

(a) Compare solution, sol and gel.
(6) Effect of mechanical agitation on the viscosity
of gelatin.

(c) Effect of concentration on the viscosity of

colloids.

(d) Effect of temperature on the viscosity of gelatin.

(e) Effect of electrolytes on the viscosity of gelatin.
(/) Effect of pH on the viscosity of acacia.

32. Determination of the isoelectric point of a protein.

(«) Casein by acid precipitation.

(6) Gelatin (Loeb's method).

(c) Gelatin by alcohol precipitation.
*33. Osmotic pressure of gelatin.
*34. Cataphoresis.
*35. Electric endosmose.
36. Coagulation of sols at isoelectric point.

(a) Ijy heat.

(6) By electrolytes.

(c) By mutual precipitation.

504

ILL USTRA TI T E EXPERIMENTS

37.

38.

39.

40.

41.

Chapter IX.

42.

Chapter X.

43.

44.

45.
*46.

*47.

48.

*49.

Chapter XI. — 50.

Protection from precipitation of hydrophobic sus-
pensoids by hydrophilic emulsoids.
(a) Colloida] iron and gelatin.
(6) Colloidal gold and gelatin.

* (c) Lange's test.
Adsorption.

(a) Colloid to surface.

(b) Colloid to colloid.

(c) Crystalloid to colloid.

(d) Electrochemical adsorption.
Imbibition.

(a) Plates of gelatin or glue and water.
(h) Rubber and benzene.

* (r) Effect of the dielectric value of the imbibed fluid

on the amount of swelling.

(d) Pressure of imbibition.

(i.) Laminaria.
*(ii.) Gelatin by cedometer.

(e) Heat of imbibition.

(/) Effect of electrolytes on imbibition.
*(7) Effect of acid on imbibition.
Gelation.

(a) Reversible and irreversible.
{b) Effect of solutes on gelation.

(c) Effect of non-electrolytes on gelation

[d) Effect of electrolytes on gelation.
Syneresis.

(a) Gelatin.

(b) Starch.

(c) Curds and whey.

{d) Blood-clot and serum.
Emulsions.

(a) Preparation of emulsions.

(b) Optimum concentration of stabiliser.

(c) Optimum pH of stabihsing colloid.
*{d) Rigidity and concentration of oil.

(c) Breaking of emulsions.
Foams.

(a) Conditions necessary for their formation.
(6) Breaking of foams.
*{c) Adsorption of enzymes by froth.
Enzymes. General conditions governing enzyme

action.
The influence of pK on enzyme action.
The effect of the removal of the end products of

enzyme action on the end point of the reaction.
Estimation of the relative activity of an enzyme.
Demonstration of the presence of a lipase in a tissue

extract.
Estimation of the relative lipolytic activity of an

extract of pancreas.
Preparation of semi-permeable membranes. Chemical
" gardens.''

LIST OF EXPERIMENTS

505

Chapter XIT.

Chapter XIII.

Chapter XIV.-

-*57

*58,

*59,

Chapter XV. —

*60

Chapter XVI.-

-*61.

Chapter XXII.

—62,

63,

64.

65.

66.

67.

*68.

69.

70.

Section IV.

5]. Leduc's " growths."

*52. " Shell " formation.

53. Study of living cells.

{a) Exainiuatiou of amoeba.
(6) Rxaniinatioii of blood corpusicles.
51. ConditioiLS affecting growth, etc.
*55. Mimicry of cell structure.
-*56. Action of ultra-violet light.

(«) Un fluorescent sub.stances.

[b) Bleaching effect.

(c) Schanz's experiment.
{d) On enzymes.

(f) On Cyclops.

(/) On human skin.
Indicators of potential difference.
Current of action and current of injury.
Membrane potential of the skin of an apple.
Model of mucoid secretion.
Model to illustrate some phases of urine formation.

BLOOD

Specific gravity of blood.

Haemolysis.

Fragility of erythrocytes.

Viscosity of blood.

Clotting time of blood.

Bleeding time.

Haematocrite.

Effect of CO, on a buffered solution.

Alkali reserve.

(«) Approximate.

*(6) C. J. Martin's method.

*(c) Van Slyke's method.

*{d) Van Slyke's micro method.

71. Blood pressure model.

72. Vowel sounds by percussion.

73. Percussion of bladders.

*74. Effect of colour on the absorption of heat.
*75. Use of the kata-thermometer.

PREPARATIONS

76. Distilled water for the Faraday-Tyndall phenomenon

and for the ultramicroscope.

77. Collodions.

78. Collodion membranes, etc.

79. Parchment dialysers.

Typical colloids.
(«) Sols.

80. Gold.

(a) Partially protected.

(6) Unprotected.

(c) Determination of C^ of colloidal gold.

506 ILLUSTRATIVE EXPERIMENTS

81. Iron.

82. Sulphur.

83. Purple of ( 'assius.

84. Gelatin, 1 per cent.

85. Starch, 1 per cent.

86. Gum mastic.

87. Silicic acid.

• 88. Coarse suspensions.

89. (i.) Egg albumin from eggs.

(ii.) Egg albumin from commercial egg albumin.

90. Finely divided suspensions of protein for use in experi-
ments on proteases.

(6) Gels.

91. Egg albumin.

92. Gelatin.

93. Preparation of non-polarisable electrodes.

94. Graphic conversion of Sorensen's pH into concentra-

tions of H ions.

95. Estimation of the surface area of the body.

VARIOUS CONVERSION FACTORS

Graphic conversion of S0rensen's pH into concentrations of hydrogen ions,

and the reverse (Eoaf).
Estimation of the surface area of the body.
Conversion factors.
A list of some practical handbooks.

I. Bomb Calorimeter.

Measurement of E.V. of Foods by Calorimetric Combustion. — The prin-
ciple 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 absorbed by a known amount of water and by the apparatus itself (which
is of known heat capacity). Some form of bomb calorimeter is now univer-
sally employed for this purpose. The instrument (Fig. 3, p. 24) consists of
three main parts.

1. The bomb itself (Fig. 102) is constructed of steel, nickel-plated, with a
cover to be screwed on firmly against a lead washer. It is lined with a special
enamel to resist corrosion. Its capacity is about 400 c.c. Through the cover
the entrance and exit gas channels pass ; K2 with its continuation platinum
tube, R, is for the introduction of oxygen, and /il for the withdrawal of the
gaseous products of combustion. Both channels are closed by means of the
screw spindles VI and V2, running in stuffing boxes. >S1 and 82 are screws
to stop the lateral communication with /il and K2. Throush the centre of
the cover passes a strong platinum wire, D, and this, as well as R, is fitted
with short pegs, a}, a^, 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.

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 white enamel, and contains within it,
but insulated from it by a thin ebonite stand, 3, the water holder or calori-
meter vessel.

BOMB CALORIMETER

507

3. The calorimeter vessel is a cylindrical copi)or can heavily nickel plated
and capaltle of containing the bomb and about 2,000-2,500 c.c. of water.
On the floor of the can is a pad of cork or fibre, ois which the bomb rests.

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

Calibration. — Certain values have 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 employed.
Some workers prefer to suspend a dried cotton thread of known weight from
0 platinum wire connecting D and 7?. The thread
(lips 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 oft' the cellulose match, which in
turn causes the foodstuff to ignite. Others prefer
to weigh out a piece of iron wire, 5-6 cm. 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 incorporated
in the correction called 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 calori-
meter 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.

If we burn a certain quantity of naphthalene (9,668 calories) or of cane
sugar (3,988 calories per gram), which would evolve Q gram cals.. the actual
rise of temperature shown by the thermometer is t° C, then Q = {m -\- ii)t
where m = water equivalent of the apparatus and ju. = weight of water
(in grams) in the apparatus. Transposing, we have

Fig. 102. — Section tlirough
a Kroeker bomb (see text).

m

Q

(

That is, the water equivalent is :

Total heat generated (calculated)
Observed increase in temperature of calorimeter water

(Quantity of water in

apparatus (in gms.) ]

(3) Calibration of Thermometer. — The thermometer has to be calibrated,
and a correction applied for this.

(4) Cooling Constant. — Another correction to be made in the final calcula-

508 ILLUSTRATIVE EXPERIMENTS

tion is that of the coohng 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 («) the
chemical action must go on as fast as possible, hence the use of oxygen under
pressure ; {h) 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 in 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 we 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 H^O. which
undergo little or no further energy changes. N and S, on the other hand, are
converted into sulphuric 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 CO^.

Preparation of the Bomb. Unscrew the cover of the bomb and remove
the small bottle or other vessel containing soda lime (which is left in the
bomb after each experiment for absorbing moisture). Press the material
under investigation into cylindrical shape ; weigh accurately (0-5-1 gram)
and place it in the quartz (or platinum) crucible (Fig. 102). Fix the crucible
T firmly in place with the two little arms of the holder, a^ and a^, passing
through the two holes in its side. Attach a piece of the ignition wire {q.v) to
the conducting rods so that it passes straight across and above the crucible.
To the centre of this wire, attach the fuse of cotton thread {q.v.). The other
end of this thread may be incorporated in the substance whose calorie value
is being estimated. Examine the lead washer in the cover to ensure the
absence of any grit or burr which would interfere with its function as a seal.

After these arrangements are completed, place the bomb in the cast-iron
holder (as in A, Fig. 3, p. 24), and put the cover on as far as possible by hand.
Finish the process with the spanner C provided for this purpose. Note that
the part of the spanner coming in contact with the bomb is furnished with
card gaskets to prevent damage to the plating.

By means of the cone and nut G connect the bomb through the pressure
gauge and union to a cylinder of compressed oxygen, (i.) Open the inlet
valve F2 (Fig. 102) of the bomb, (ii.) close the fine adjustment release valve
(needle valve) on the cylinder, and then (iii.) open the cylinder (niain) valve.
Gmdually open the release valve of the cylinder. If this valve is opened too
rapidly, the inrush of oxygen will tend to scatter the contents of the crucible.

When the gauge indicates a pressure of 15-20 atmospheres, close (i.) release
valve, (ii.) inlet valve of bomb, and (iii.) cylinder main valve. Disconnect
and place bomb in inner calorimeter vessel.

Preparation op Calorimeter. The calorimeter — a heavily nickel-plated
polished cylinder of copper should have placed in it about 2,000 grams of
water (accurately weighed). The calorimeter vessel and its charge of water
are best kept in an outer room with a temperature about 1° C. below that of
the room in which the calorimetric combustion is to be done. When the
bomb is placed in it, the water should cover the oblong excrescence, but not
the terminals P^ and P, ^^or the valve spindles V^ and Fg. One can now see
whether the bomb is gas tight or not. Small leaks do not render the experi-

BOMIi CALORIMETER

509

ment useless, ))ut tliey are best avoided. Leave for hall an hour. Place the
calorimeter, carefully carried in a cloth, on the cork studs on the thin sheet
of ebonite on the bottom of the large double-walled insulating vessel H
(Fig. 3), which has been filled with al)out 11 litres of water. Connect the
terminals P, and P., by well-insulated flexible leads to a battery (4-6 volts)
provided with a simple contact key. Place the ebonite cover, stirring gear
and thermometer in position.

Start the stirring device (best activated by a small electric motor) and after
the lapse of a few minutes take readings of the thermometer regularly every
half-minute. As the water in the calorimeter is about 1° C. below the tem-
perature of the room, the readings will tend to rise, e.g.

I. Pre-ignit'ION Period.

Time (minutes)
Teni]).' (° C.)

0
14-953

0-955

1

0-957

U

0-958

2
0-960

Time (minutes)
Temp. (° C.)

91

0-963

3

0-964

3*

0-966

4
0-969

i.e. rate of warming at 14-9° C. is 0-002° C. per half minute.

Ignition. At a known moment, fire the charge by pressing the button at
the battery. The temperature rapidly rises. Take readings every half-minute
as under.

II. Ignition Period.

Time (minutes)

Temp. °C. (14 omitted) .

41
1-5

5
2-1

51
2-3

6
2-4

61
2-4"5

7
2-47

Time (minutes)

Temp. °C. (14 omitted) .

n

2-496

8
2-503

81
'2-508

9
2-510

91
2-512

10
2-511

i.e. the temperature reaches a maximum value six minutes after ignition and
then begins to fall. Headings are continued every half-minute till the fall of
temperature has become quite regular, e.g.

III. Cooling Period.

Time (minutes)
Temp °C. (14 omitted)

1()1
2-51

11

2-508

lU

2-507

12

2-505

121
2-5()4

13
2-502

Time (minutes)
Temp. "C. (14 omitted)

131
2-5

14

2-498

141

2-49"6

15
2-493

151
2-490

16

2-488

i.e. the rate of cooling during this pcrioil is 0-002° C. per half-minute.

From these two cooling values, e.g. ()-(l02° in the pre-ignition j)eriod and

510 ILLUSTRATIVE EXPERIMENTS

+ 0-002° in the cooling period a cooling curve may be constructed with the
temperatures from 0-9 to 2-9 as abscissae and cooling loss from — 0-002 to
+ 0-002 as ordinates. The function is purely linear and extrapolation is
simple.

Calculation of E.V. (a) Correction of Teniperature. From the cooling
curve it is easy to discover the loss of heat due to cooling in the ignition
period. This value should be placed in a third column for every temperature
recorded during the second and third periods. For any reading of the thermo-
meter, the total loss by radiation is obtained by summing up the losses in all
the preceding intervals after ignition, e.g. in the second period the losses were
-0-001, +0-001, 0-0015, 0-0016, 0-0018, 0-0018, 0-0019, 0-002, 0-002,
0-002, 0-002, 0-002. This gives a total loss of 0-0175 at the maximum tem-
perature observed. This value added to the observed temperature gives the
corrected temperature. The corrected temperature during the third period
varies so little that the arithmetic mean of the values is taken as the cor-
rected maximum temperature. In this case = 16-5325.

(b) Calculation.

Temperature before firing, 14-969.

Temperature after firing (corr.), 16-5325.

.". Rise in temperature, 1-5635.

Water in calorimeter — 2,100 gram.

Water equivalent of calorimeter = 767-5 gram.

.•. Total water value = 2867-5 gram.

Heat of combustion = 2867-5 X 1-5635 = 4484.

Amount of N free food burned = 1-2 gram.

.-. EV of food = 4484/1-2 gram.

= 3737 cals. per gram.
= 3-73 Cals. per gram.

As soon as possible after each estimation, the gases are let off and the bomb
opened. Wash out the bomb with dilute sodium hydrate to remove any
nitric acid formed, dry and replace the bottle containing soda lime. Close
the bomb.

2. Gaseous Diffusion.

Experiment on p. 38, Fig. 4. Try this first with coal-gas and then with
CO,,. Soak the porous pot in water and compare the rate of diffusion inwards
of carbon-dioxide with the outwards dift'usion of air. What part does
solubility play in dift'usion through a membrane 1

3. Liquid Diffusion.

Place a number of coloured solutions varying in nature and in concentra-
tion in test-tubes. Carefully fill the tubes with distilled water and note the
rate at which the colour diffuses upwards into the water (Fig. 5 (a), p. 39).

(a) Nature. Use concentrated solutions of copper sulphate, potassium
bichromate, methylene blue, congo red, black Indian ink, etc.

(b) Concentration. Take four test tubes and put 5 c.c. of distilled water
in each. To the first tube add 5 c.c. of cone. CUSO4 and mix thoroughly.
Remove 5 c.c. of this mixture and add it to tube 2. Mix and take 5 c.c. for
tube 3 and so on, rejecting 5 c.c. of the mixture in tube 5. This will give you
five samples of 5 c.c. each varying in concentration from tube 1, having
0-5 cone. ; tube 2 = 0-25, tube 3 = 0-125 and tube 4 = 0-0625. In tube 5
place 5 c.c. of the cone, solution. Now carefully fill the tubes with water so
as to form a clea r layer of water above the blue sulphate and measure the rate

OSMOTIC PRESSURE 511

of diffusion. A narrow strip of translucent squared paper pasted over the
length of the test tube will aid in the determination.

(c) Temperature. Use two sam])les of cone. CuSO^ — one at 0° C. and the
other at 40° C.

Note that the water added should be at the same temperature as the solu-
tion and the tubes should be kept at constant temperature during the duration
of the experiment.

4. Partial Separation of two Solutions by Diffusion.

(i.) Add sufficient dilute alkaline aqueous eosiji to a solution of night blue
to give a dark violet mixture. Allow this mixture to stand in contact with
water (as above) for a day. The supernatant fluid will be stained red and the
underlying fluid will be a bluish violet.

(ii.) Make some congo red just blue by the addition of a few c.c. of N/10
sulphuric acid and allow this blue liquid to lie in contact with water tinged
with phenol red for twenty-four hours. The acid diffuses from the congo
red into the water. The result is a yellow fluid lying over a red one.

(iii.) Other pairs of rapidly diffusible and slowly diffusible substances are :
picric acid -j- alkali blue, picric acid -|- alizarin red, alkali blue -f acid
fuchsin.

5. Osmotic Pressure of Crystalloids.

(a) By Osmometer. Preparation of 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. 50). 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.

(i.) What happens after 24 hours or so when a 10 per cent, cane sugar
solution is placed in the pot and the pot immersed in water ?

(ii.) 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.

(iii.) Increase the concentration of sugar outside and note the effect on
the level of fluid in the manometer.

(iv.) Clean out the pot and fill it, in turn, with the following solutions : —

ilf/64 cane sugar.
ilf/128 sodium chloride.
M/192 calcium chloride.
ilf/192 sodium sulphate.
They should all rise to the same height in the same time, i.e. they are isotonic
solutions.

(v.) Prepare an osmometer with a collodion membrane (as in Expt. 33)
and again determine the relative osmotic pressures of the above four solu-
tions. The rise in hydrostatic pressure, in the case of a collodion membrane,
is not equal for solutions of equal osmotic pressure. The cane sugar in half
an hour shows scarcely any osmotic pressure, the CaClg solution gives the
greatest rise, about 50-60 mm., next comes the NaCl with about 15 mm.,
and the NagSO^ at from 4^ 5 to — 3 mm. Why tlo these values differ

512

ILL I hSTRA TI VE EXPERLMENTS

from those obtained in Expt. (iv.) above 1 Why should a negative pressure
be found in some cases ?

(vi.) Fill the collodion osmometer with distilled water and immerse it in
iV/1000 HCl. The water rises in the pressure tube. Why is this so ?

{h) 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.

Apparatus. Beckmann's(Fig. 103). It consists
of a specially devised test tube A with a side
neck. Through the rubber stopper, closing the
main neck of this tube, 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 thermo-
meter, if made in the ordinary way, unless it were
inconveniently long, w^ould 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 per-
mitting of alterations being made in the amount
of mercury in the bulb. At the upper end of
the thermometer (Fig. 104) there is a small reser-
voir 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° higher than the highest temperature
to be met with in the experiment and see whether or not the to]i 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, {h) When the mercury passes to the top of the capillary tube and

Fig. 1U3. — Kreezing-puint
Apparatus.

DETERMINATION OE EREEZlNd POINT

513

forms a small drop there, the thermometer should be carefully inverted
and tapped srently 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, cai;sing 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 top
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 thernioiiefer l)i baths having temperatures equal
to the highest and loicest to be encountered in the erperivient,
and noting that the top of the colmnn of >nercicry 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 wnth 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 deter-
mined.

(7) First make an approximate determination by placing FiG,i04.—T:ppcr portion

. . ^ '- . , . ■ ^ ~ of the stem of a liuck-

the freezing-point tube directly in the cooling bath so mann ' Thermometer,
that s. rapid fall of temperature occurs. ^^^ ""'^''"^y "'

(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 ice by w^arming 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 temperature will
now begin to rise.

6

r4'

="0

1-5!

514 ILLUSTRATIVE EXPERIMENTS

(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 determi-
nations 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.

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.

Precautio))s. (a) The temperature of the cooling bath must not be too
low. It should not exceed 3" below the freezing-point of the li<]uid.

/ e 3 f 5 6 7 s 9

-11 ¥ 11 » U M TT-

V/////y//////A'/AV///^/////Ay/////////yy/y^^^^^

]"'l(i. 105. — Barfcer't: Method for Determining Moleeular C'oneentration.

tplier figure, actual size. Lower figure, as seen under tlie microscope ; micrometer

scale in eyepiece.

(/3) Excessive supercooling should be avoided. It should not be greater
than half a degree.

(y) Stirring should not be too rapid — say one 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 sufHces to start
solidification.

(c) Osmotic Pressure by Barger's Method (Fig. 105). Trans. Chem. Soc.
85, p. 286. Prepare a number of capillary tubes by drawing out soft glass
tubing of ^ in. bore into capillaries 1-2 ft. 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

SURFACE TENSION 515

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
in a slanting position, and, by diminishing the pressure of the index finger
on the lower end, the globule of licpiid 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
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. 105, shows the appearance (actual size)
of a filled and sealed tube. The dark drops are A. The first and last
dro{)s, 1 and 9, are large and are not taken into account. The drops are
numbered in the order in which they were put 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. 105, 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 5 drops increase in
size it shows that the vapour pressure of B is less than that of A, and, conse-
quently, 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 w^ater. Time
about 20 hours.

6. Turgor.

(See Expts. 26 and 79 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 (Fig. 45).

7-21. Experiments on Surface Tension.

Soap Solution. In performing these experiments it is necessary to have
a good soap solution. It may be made as follows from pure sodium oleate
and glycerol. To 600 c.c. of distilled water in a stoppered bottle of 1 litre
capacity add 15 grams of pure sodium oleate (in flakes), and by occasional
shaking in the cold get it into solution. This may take a day or two. Then
add 200 c.c. of pure glycerol, shake and allow to stand, undisturbed in the
dark, for a week. Siphon off the clear undeiiyiiig fluid and add 4 drops of
concentrated ammonia. Kee]) well stoppered and away from light.

7. Experiment with Soap Films.

Make a film on the wade 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 rost and why ?

8. Camel-hair Brush Experiments.

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

33—2

516 ILLUSTRATIVE EXPERIMENTS

water-liair surface is increased, e.g. by removing the brush from the water, the
hairs form a compact pencil.

9. Boy's Leather Sucker (p. 392).

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 experiment under
various conditions, e.g. trace of oil ester, bile salts, etc.

10. Work Done by Altering Surface Tension.

In performing the experiment detailed on p. 175 (Fig. 42), it is convenient
to have a clean copper frame, easily prepared by bending a piece of copper
wire (No. 16 gauge) into a circle about 2 inches in diameter, with a handle
about 2 inches long. The frame is freed from grease by washing in dilute
soda and then thoroughly rinsed. A piece of silk thread is attached to one
portion of the frame and a loop n::ado on its loose end. Some of the soap
solution is placed in a large Petri dish. The frame is dipped into this and
removed horizontally with a fine film of soap covering the circle. Satisfy
yourself that the loop moves freely over the film by gently rotating the
frame. Now break the film inside the loop, using for this purpose a bluntly
pointed piece of blotting pai)er.

11. Effect of Soap Formation on Surface Tension.

Take four simihir watch-glasses. In the first two put a few c.c. of water,
and in the other two about the same quantity of a 1 per cent, solution of
sodium carbonate. With a fine pipette place one drop of rancid olive oil
on the surface of the lic[uid m glasses 1 and 3. Place drops of liquid
paraffin of similar size on the fluid in glasses 2 and 4. Note {a) whether the
rancid oil and the paraffin differ in spreading power on a water surface, and {h)
the movements occurring in glass 3. Can you explain these movments in the
light of what you have learned from experiments 9 and 10 ?

12. Camphor "Water-beetle."

Prepare a rectangular piece of camphor. To one short side aflnx 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.

13 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 dean Petri dish. The movements may be
slowed down by the addition of the faintest trace of oil. Generally the
first ■■ amoeba " disintegrates rapidly. Do not throw out the fluid in the
dish, but add another drop of the camphor solution. What eft'ect 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, {h) 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 ?

14. Mercury "Amoeba."

Place a small globule of mercurv in a large Petri dish and cover it with

MEASrnKMENT OF SURFACE TENSIOX 517

potassium bichromate (sat. solution) to uhidi has been added some nitric acid
(bench rea<j,ent). TTow do you ex])laiii the movements ?

15. Electrical Alteration of Surface Tension.

Carry out the exporinu-nt detailed on ]). 49. 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 ? ILxplain. 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 cotnnuitator.

16. Ostwald's Physical "Heart." (N'erworn's Physiuloijiachen
Pmktikuui.)

The method of carrving out this demonstration of electrical alterations in
surface tension is indicated in the diagram (Fig. 11, p. 49). A globule of
mercury about an inch in diameter is placed in a clock glass almost filled
with 10-15 per cent, sulphuric acid. Potassium bichromate solution (say
iV/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 pulsations may go on for hours. When
the action has stopped remove the needle and note the odour of acety-
lene. How do you account for this ? What is the reason for adding
bichromate ?

17. Measurement of Surface Tension.

Simple Stcdugmometer. A simple stalagmonieter which is sufhciently
accurate for any of the experiments detailed here may be made from com-
mercial capillary glass tubing. Cut a piece of this tubing into sections of 7
to 10 cm. long and grind the ends flat on fine emery cloth moistened with
paraffin oil. By means of a short length of pressure tubing fix the capillary
tube (glass to glass) to the lower end of a .3 to 5 c.c. pipette graduated to
1/10 c.c. and clamp rigidly in a vertical position over a narrow graduated
cylinder or other vessel to catch the drops.

Note. — The stalagmometer should be dissociated into its component parts
except when actually in use and the glass parts kept in cleaning mixture.
Before use they should be thoroughly rinsed with warm distilled water and
dried by attachment to a sucking or blowing apparatus.

To Calibrate the Stalagmometer. It is convenient to calibrate the apparatus
at room temperature. Fill it to above the top graduation mark with dis-
tilled water which lias attained room temperature. Start counting and
collecting the drops when the meniscus just passes the top mark. Note
the graduation mark when the sixtieth drop falls. Repeat the experiment
to confirm this point and then by a deep file mark or other means intensify
this jnark.

To compare the surface tensions of distilled water and 0"i per cent, soap
solutions.

(i.) Stalagmometer Method.

[a] Confirm the calibration of tlie stalagmometer by counting (i.) the
number of drops, (ii.) the volume of the fluid dropped, and (iii.) the time
taken in dropping between the two marks.

(ft) Wash out the apparatus with the soap solution and then fill to above
the top mark with the soap solution and proceed as in (a).

518 ILLUSTRATIVE EXPERIMENTS

TvpirAL Resi-lts at 17° C.

Liquid to be tested ..... Water. Soap Boln.

Number of drops . . . . . .60 112

Total volume of dro})s ..... 3 c.c. 3 c.c.

Time taken for fluid to fall from upper to lower

mark ....... 43 sees. 50 sees.

Surface tension relative to water . . . — — = 0-5 approx.

(ii.) Capillary-Tube Method. A fluid wliicli wets the tube will rise in it

2ct
to a height /(, which may be calculated from the formula h =^^ where a =

surface tension, r = radius of the capillary, and D = specific gravity of the
liquid. For approximate determinations, the height h may be measured by
calipers against a millimetre scale. Short lengths of thermometer tubing
may be used, having an internal diameter of from 0-3 to 2 mm. The tubes
should be prepared and cleaned as directed in Experiment 17 (i) above.

(a) Select a tube, thoroughly rinse it in distilled water and clamp it verti-
cally, dipping into distilled water. Be certain that the meniscus moves freely
in the tube, and that no drops of liquid adhere to the internal walls above the
meniscus. If this is not so, the tube is dirty and a fresh clean one should be
selected.

{b) Measure the height to w^hich distilled water (at room temperature) rises
in the tube. Repeat, using the soap solution above. See also Experiment 48.
18. Adsorption to a Surface.

(1) Adsorfition by Charcoal. («) Put 10 c.c. of a 0-1 per cent, solution of
crystal violet -\- 1 gm. of bone charcoal into a tube. Shake. Filter. The
filtrate is colourless. Return the precipitate to the cleaned tube. Add
10 c.c. of distilled water. Shake. Practically no colour leaves the charcoal
for the water. Now add a few cubic centimetres of methylated spirit and
shake. The dye leaves the charcoal.

(6) Repeat the experiment, using N'lOOHCl in place of the dye. Te.st the
filtrate with inetJiyl red. The hydrochloric acid has been adsorbed completely.

(2) Hay's Test for Bile Salts. The surface tension of water is sufficient to
permit of placing "' flowers of sulphur "' on it without rupturing the surface.

Take three test tubes and place in (i.) about 10 c.c. of w^ater : in (ii.) about
5 c.c. of water -)- 5 c.c. of methylated spirit well mixed together ; and in
(iii.) 10 c.c. of water containing bile salts (or ox bile). On to the surface of
each tube, sprinkle a small pinch of powdered sulphur. In tubes (ii.) and (iii.)
the sulphur will rupture the surface and sink to the bottom of the tube.

(3) (a) Flotation. Prepare a finely ground mixture of 9 parts of animal
charcoal and 1 part of aluminium silicate (clay). Shake 3 or 4 gms. of this
mixture with about 100 c.c. of water, so as to get a suspension; Allow" to
stand and decant off the supernatant liquid. Repeat this process so as to
get rid of the coarser particles of the clay.

Now shake the greyish black siispension with any capillary active sub-
stance iq.v.), and pour the mixture into a clean boiling-tube. The mixture
will separate into two sharply defined layers. The charcoal will adhere to
the glass-, air- and water-interfaces of the upper liquid {e.y. benzol), while the
lower aqueous layer will contain practically all the clay.

(b) Flotation. (Ostwald.) Cut a few pieces from a sized paper heavily
printed on one side, and the same number of similar size from a similar un-

ADSORPTION 519

])riiitod sheet. Sliake the pieces nf ])a]ier in an Krlciiiiicyer Hask containing
water till the papers have l^ecoine waterlojij^ed and sink to the bottom of the
flask. Cover the water with a tliiii layer of a light mineral oil, and shake
thoroufrhly. When tlie oil and water have separated, the printed bits of
paper will be fonnd floating, print side upwards, at the oil-water interface.
The unprinted bits sink. Paraflin oil, the usual dispersion medium for printer's
ink, is a satisfactory oil to use.

19. Demonstration of the Oxidation of Oxalic Acid when Adsorbed to
Charcoal.

Air freed from COo (by passing over soda lime, caustic soda and baryta)
is sucked through a vessel containing charcoal, oxalic acid and water. The
CO., liberated bv the oxidation of the oxalic acid is pas.sed into lime or baryta
water which becomes turbid.

Arrangement of . apparatus. 1 Suction pump, 2 trap, 3 Woulfe's bottle
with lime w^ater, 4 Erlenmeyer flask, 5 Woulfe's bottle with lime water,
tj and 7 two gas wash bottles with a layer of 40 per cent, sodium hydroxide,
and 8 a soda lime tower. By means of a clip on the inlet tube of the tower,
the flow of air is regulated through the series of vessels so that the bubbles in
bottle 3 can just be counted.

Method. See that the bottles and flasks are connected in the riglit way so
that the air enters by the long tube dipping into the fluid in the bottle. The
reaction vessel (No. 4) is a flask fitted with a rubber stopper carrying three
tubes. Of these, two tubes are like those of the other flasks. The third tube
goes almost to the bottom of the flask and at its upper end bears a fuuiiel and
stop-cock. This flask is kept at about 100° C. by immersion in a bath of
boiling water.

First test the apparatus for leaks by running it with the inlet on the tower
closed. Now run in the charcoal mixture. (In order to free the charcoal as
far as possible from adsorbed COg, it is heated dry and allowed to cool in a
desiccator over NaOH.) For our purpose, take 5 gms. of Merck's blood
charcoal and suspend it in 50 c.c. of boiled water. Boil the suspension for
15 minutes and run it, while still w^arm, into the already warmed reaction
chamber. Wash the final grains into the reactioii flask v.ith 50 c.c. of boiling
water. Run the pump for a short time to remove the last traces of COn
from the charcoal. This may require an hour or so. Now put fresh lime
water into bottle 3. Start the pump again. If no turbidity develops in
3, the experiment may be begun. If turbidity does develop, proceed as
before.

E.rppriment. Stop the suction and through the funnel add 2 gms. of oxalic
acid (dissolved in the minimum amount of water) to the reaction vessel. Start
the pump. In the course of a few minutes the lime water in bottle 3 will be
quite milky in appearance. It is advisable to run a blank experiment with
oxalic acid and 100 c.c. of water but no charcoal in flask 4.

20. Effect of Capillary-active Substances on the Rate of Sedimentation.
Take three test tubes and put about 20 c.c. of water into each. To one tube

add a few grains of camphor ; to the second a drop of tributyrin. Shake
thoroughly and add to all three about 2 gms. of finely ])owdered kaolin.
Shake vigorously and leave for about an hour. The kaolin slowlv sinks to
the bottom in all the tubes. The camphor and the tributyrin almost doul)le
the rate of sedimentation. Repeat the experiment, using powdered charcoal
instead of kaolin. Can you explain why the capillary active substances
increase the rate of sedimentation of the kaolin and not of the charcoal ?
(See Experiment 18.)

)20

ILL USTRA TI VE EXPERIMENTS

mercury
acidified

witli

21. The Capillary Electrometer.

This iustruinent tor measuring differences of electric potential depends for
its action upon the alteration of surface tension between mercury and
sulphuric acid with alterations of the potential diiTerence at the interface
(see p. 50, and Experiments 16 and 17). For class use the simplest satis-
factory 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 containins; dilute sulphuric acid
and a drop of mercury to make good contact with the 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
shake for 10-20 minutes -with a solution of mercurous nitrate
nitric acid. Wash thoroughly with distilled water and dry
with filter paper.

(If) Sulphuric acid. The pure (boiled) acid in six times
its volume of distilled water is shaken i;p 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.

Filli)ifi and Settinr/ 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 niercury into the test tube to cover the platinum
contact. Adjust by means of the plunger screw till the
Hg-H.SOj interface lies in the middle of the microscopic
field. The definition of the mercury meniscus may be improved 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.

For finer work, the closed type of electrometer (Fig. 106) gives excellent
results, and, once adjusted, needs no further attention for months.

Before this piece of apparatus is set u]), tilt the tube until the greater ])art
of the mercury has run over from B to T (Fig. 12). Set the tube with the bulb
limb {B) sloping slightly downwards and allow mercury to pass along f7and A
from T and to drip into B until, on suddenly righting the tube, the mercury
stands midway in A as in the figure. Fix in the stand and focus the micro-
scope on the meniscus. Affix the leads E and F as in the diagram (Fig. 12),
taking care to see that the short-circuiting key is across them and is kept
closed.

After any capillary electrometer has been readjusted so that a new surface
has been formed at the meniscus, it is essential to allow this surface to come
into electrical equilibrium with the glass and the sulphuric acid. (See Ageing
of Surfa,ces.) For rough work a few hours' rest is enough, but about 24 hours
is a preferable interval. Test the sensitivity of the electrometer by opening
the short-circuiting key and noting the movement, if any, of the meniscus.

Fig. 106.— Capillary
electrometer.

CAP ILL A A' 1 ' ELECTROMETER 521

The meniscus should either remain steady or should move only slightly.
To ensure that the lack of movement is not due to lack of sensitivity, pass a
weak current momentarily from F to E and note whether the electrometer
responds with a movement of the mercury from A towards U. A suitable
weak current may be generated by attaching a piece of brass wire to the
distal end of P and a copper wire to the corresponding part of i'^ and, after
opening the s.c. key, touching these wires with different hngers. Reverse the
wires and note whether a movement of the mercury in the reverse direction
is obtained.

To Test the Sensitivity of the Electrometer. Place a 2-volt accumulator which
is needing to be recharged {i.e. E.M.F. of about 1-85 volts) at Z in the circuit
of Fig. 12 with its + pole attached to R and — pole to P. Close the main
circuit and open the short-circuiting key for a moment (1 to 2 seconds),
observing meanwhile the mercury meniscus. It should move apparently
upwards in the microscope (actually downwards). Move the slide-wire Q
either towards P or R, and again fully depress the key so completing the
electrometer circuit and removing the short between E and F. If the meniscus
has a smaller excursion than before, release the key {i.e. short the terminals
and open the accumulator circuit) and move the slider a little more in the
same direction as before. (If the excursion of the mercury, on the other hand,
were increased, the slider would have to be moved in the opposite sense.)
Continue the process of moving Q, and completing the electrometer circuit
till a point of balance between P and R is reached. A sensitive electrometer
should show a deflection of 2 to 4 scale divisions in the eye-piece micrometer
when the slider is 1 mm. from the point of balance. From this division of the
potentiometer wire can be calculated the potential at the mercury surface in
the bulb, or if an accumulator of unknown strength is placed at Z and a
standard cell {e.g. cadmium cell) is placed between P and E to give a negative
potential to the mercury in T, one can measure the E.M.F. of the unknown as
follows. Since the combined resistances of the leads are negligible compared
with the resistance of the potentiometer wire P R, there exists the same
difference of potential between the points P and R as between the terminals
of the unknown source of E.M.F., i.e. E^,,. = E.M.F. of the accumulator.

When the point of balance has been obtained with Q, the potential difference
between Q and P {= Ep^^) is equal to the E.M.F. of the cell E{cnd).

Now En^ : £'pR = Length PQ : Length PR,

PP
E.M.F. of accumulator = E{cad) -^

For example, if ^(cad) ^ 1-0185 volts and PR = 1,000 mm. and PQ =

550-5, then E{acc) = i^^^t^ = 1-85 volts.

550-5

If the electrometer is used to find the point of balanced E.M.F. on a Wheat-
stone bridge (Experiment 22 (d) ), 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 he 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 he opened for as brief periods as possible.

Fine instruments may be purchased filled, adjusted and sealed ready
for use (Figs. 12 and 106).

522

ILLUSTRA TI VE EXPERIMENTS

22. Strength of Acids.

(a) By Taste. Prepare a imniher of N/'lO solutions of acids, e.g. hydro-
chloric, acetic and boric acids. JJry the side of the tongue and apply a small
quantity of the acids in turn with a camel's-hair brush, rinsing the mouth
out after each application. Place them in their order of sourness. Dilute
each of them ten times and repeat the experiment.

(6) By hydrolysing poiver. Take three test tubes and put 2 c.c. of a 0-5
M solution of cane sugar in each. Add to each respectively 5 c.c. of one of
the acids prepared above, e.g. N'lOHCl. N/IOHA and N/IOHBO.,, and place
all three in boiling water at the same time. Leave them there for IJ- to
2 minutes. Remove all together and cool. Add 5 c.c. N/lONaOH to each
tube, mix and then add 5 c.c. of Benedicf\s qualitative sugar reagent. Boil
and com[)are the amount of copper reduction in each tube.

(c) By indicators, (a) Prepare a series of graded concentrations of a
strong acid like hydrochloric and a similar series of a weak acid such as
acetic, e.g. :

Take seven test tubes, and in every tube except the first put 9 c.c. of dis-

FiG. 107. — Diagram of conductivity apparatus.

filled water. In the first tube put 10 c.c. of N acid. Transfer 1 c.c. of this
to the second tube, mix and transfer 1 c.c. of the N/10 acid so prepared to the
third tube, and so on, rejecting the 1 c.c. removed from the last tube. You
will then have a series of tubes containing 9 c.c. of (1) N, (2) N/10, (3) N/KM),
(4) N/1,000, (5) N/10,000, (6) N/100,000. (7) N/1,000,000 acid.

To each tube add a few drops of B.D.H. " Universal " indicator, mix and
compare the colours produced with those of the standard labelled tubes
provided. Why does tube 3, which gives a reading of about _/jH 2 with
hydrochloric acid, only give a pH of between 3 and 4 when acetic acid is
used ?

(^) Determine the same range more accurately, using thyniol blue {pK
1 •2-2-8), bro)iio-phei)ol blue (2-8-4-6), and methyl red (4 •2-6-3) in turn as
indicators.

(d) By conductivity. Comparison of the electrical conductivity of equi-
molecular solutions of mineral and organic acids. Conductivity, being the
reciprocal of resistance, obviously can be measured by a resistance method, e.g.
by the Wheatstone bridge (Fig. 107). The current from b is divided between
two circuits (1) by B^ and R.^ and (2) by i?3 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

STRENGTH OF ACIDS 523

juiictioii hetween R^ and R., mid couiioction iiiailc with ttic //.,, /i*, route
so that R^IR., = JisJJ^A, then im curroiit will How throiiiih the lead as shown
by the indicator (G), a galvanometer, lamp, telephone receiver, etc. Thus
i?j, R2 and R.^ being known, R^ can be found. In |)ractice, the lead fixed
between R^ and R^ terminates in a jockey-piece which slides along a plati-
num, iridium, or nickelin wire of uniform resistance and a metre long,
constituting R^, R.^- The length of R^ 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 em[)loy 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.

Experiment (a). Rough Demonstration. Fit up a Wheatstone bridge,
using a 4-volt accumulator with switch as h, and a pea lamp as G. R^ 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

i?3(100 - x)'

and the molecular conductivity is equal to C(j), where ^ is the volume in
cubic centimetres in which 1 mole is dissolved. Suitable solutions = 1/16
molar hydrochloric, acetic, and benzoic acids ; 1/8 molar NaCl and glucose.
{N .B. — Keep the switch from h open as much as possible to prevent polarisa-
tion of the electrodes of x.)

(|8) 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 [R^) so that the bridge reading is about 50 cm.
From a burette run in a standard (N/50) solution of HgSOj 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 w^ill move in the reverse direction. The point at w^hich
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.

23. Principle of Measurement of H-ion Concentration by Potentiometer.

The principle is much the same as that of the conductivity measurements
(Fig. 107), only instead of having a single source of potential and an unknown
resistance, one has known resistances and tw'o sources of E.M.F., one of
which is of unknown value.

In Fig. 107, 6 may be taken as a cell of standard E.M.F. sending its current
through the wire bridge, R^ — i?._,. If we lead into i?j — R.^ 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 7?j, as the fall of potential
along R.^ — i?2 is regular, we can readily divide the wire so that the ditTerence
of potential between the ])oint 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 indicate
no E.F.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

524 ILLUSTRATIVE EXPERIMENTS

mercury covered with HgCl in the presence of a definite concentration of KCl.
The other half-cell is a hydrogen electrode, i.e. ])latinuni 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 pJi may be calculated.

24. Alterations of the Surface Tensions of Oil-Water Interface by
Alterations in Hydrogen Ion Concentration (Hartridge and Peters, Jour.
Fhystol. LIV., Proc. XLL).

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 te.st tubes 6 X | in. each receives 5-10 c.c. of the treated oil. Into each
is put a capillary tube 4 in. long, open at both ends. The test tube is
almost filled with the fluid to be tested. Try solutions having a /jH of 9, 8,
7, 6. Measure the height to which the oil rises in the capillary.

25. Buffer Solutions.

(A) 8orensen's Phosphate Buft'ers. Two solutions are required, (a) M/15
solution of KHoPO, (9-078 gm. per litre). The salt should be chemically
pure, and its solution should be water clear and free from even traces of
chloride and sulphate.

(6) M/15 solution of Na.,HP04 . 2H2O (11-876 gm. per litre). The salt
is prepared by exposing to the air the recrystallised Na2HP04 . I2H2O.
After two weeks' exposure on a porous plate, dissolve the salt in water and
test for chloride and sulphate : 8 c.c. of (a) KH.^PO^ + 2 c.c. of (6) Na2HP04
2Ho0 gives a solution of /)H 7-381.

The water used for making these solutions must be free from CO^. This is
obtained by boiling the glass-distilled water in a hard glass flask for at least
5 minutes, and then fitting the flask with a bored rubber stopper carrying a
soda-lime tube so that the water may cool in an atmosphere free from COo.
The solutions may be kept in a hard glass double-necked bottle, of which one
neck is connectecl to a soda-lime tower fitted with a blow-ball, and the other
neck to the side tube of a burette. The burette is provided with a soda lime
tube at the upper end. It is as well to coat the inner surface of the bottle
with paraffin wax (see p. 557).

(B) Clark and Lubs. Five solutions are necessary to provide a complete
^H range.

(i.) 0-2 M acid potassium phthalate. Recrystallise the salt from distilled
water and dry at 110° C. for some hours. Dissolve 40-828 gm. in distilled
water and make up to a litre.

(ii.) 0-2 M acid potassium phosphate. Recrystallise the salt from distilled
water and dry as above. Dissolve 27-231 gm. in distilled water and make
up to a litre.

(iii.) 0-2 M boric acid in 0-2 M KCl. Dry the boric acid in air on a porous
plate. Use pure ignited KCl. Dissolve 12-4048 gm. of HBO., and 14-912 gm.
of KCl in distilled water and make up to a litre.

(iv.) 0-2 N sodium, hydroxide. Standardise this solution against weighed
amounts of pure potassium phthalate, using phenolphthalein as indicator.

(v.) 0-2 N hydrochloric acid. Prepare this from a freshly distilled 20 per
cent, solution and standardise it against the standard N/5 soda, using methyl
red as indicator.

BUFFER SOLUTIONS

525

pK Ranok 4-49-918
Indicator, B.D.H. (Universal).
More accurate determinations may be made with (jne of the indicators

given ill the next section.

pn.

c.c.M/15Na„HPO,.

c.c. M/loKHoPO,.

4-49

0

100

4-94

0-1

9-9

5-29

0-25

9-75

5-59

0-5

9-5

5-91

1-0

9-0

6-24

2-()

8-0

6-47

3-0

7-0

6-64

4-0

6-0

6-81

5-0

5-0

6-98

(M)

4-0

7-17

7-(i

3-0

7-38

8-0

2-0

7-73

9-0

1-0

8-04

9-5

0-5

8-34

9-75

0-25

8-68

9-9

0-1

9-18

10-0

0

T. pH Range 2-2-3-9

Vl'Ace 50 c.c. of solution (i.) in a number of flasks, add a drop of either
thymol blue or brom-phenol blue to each and various amounts of solution (v.)
as under :

c.c.

N/5 HCl .

46-7

42-5

39-6

37-0

32-95

29-6

26-42

22-8

20-32

pR

•

2-2

2-3

2-4

2-5

2-6

2 7

2-8

2-9

3-0

c.c.

N/5 HCl .

17-7

14-7

11-8

9-9

7-5

5-97

4-3

2-63

1-0

pR

.

31

3-2

3-3

3-4

3-5

3-6

3-7

3-8

3-9

Make each up to 200 c.c. with distilled water.

II. pB. Range 4-6-3

To 50 c.c. of solution (i.) add a drop of either brom-phenol blue, methyl red
or brom-cresol purple, and the number of cubic centimetres of solution (iv.)

given below. Mak

e up to 200 c.c

c.c. N/5 NaOH .
pK . . .

0-4
4-0

2-2
4-1

3-7
4-2

5-17
4-3

7-5
4-4

9-G
4-5

12-15
4-6

14-6

4-7

526

ILL USTRA TI VE EXPERIMENTS

CC. N/5 NaOH .
pll .'

17-7

4-8

20-95
4-9

23-85
5-0

27-2
5-1

29-95
5-2

32-5
5-3

35-45
5-4

37-7
5-5

CC. N/5 NaOH .
pR .

39-85
5-6

41-9
5-7

43-0

5-8

44-55
5-9

45-45
6-0

46-2
6-1

47-0
6-2

48-1
6-3

III. jM . 5-8-8-0 (Physiological Range).
Solutions : 50 c.c. solution (ii.), and cT c.c. of N/5NaOH.

Indicators,

Brom-cresol purple ; brom-thyniol blue ;
or Phenol red.
Dilute to 200 c.c.

X c.c.

^H

X c.c.

y,H

X c.c.

;.H

3-72

5-8

17-8

6-6

39-5

7-4

4-7

5-9

21 0

6-7

41-2

7-5

5-7

60

23-65

6-8

42-8

7-6

7-4

6-1

26-50

6-9

44-2

7-7

8-6

6-2

29-63

7-0

45-2

7-8

10-19

6-3

32-5

7-1

46-0

7-9

12-6

6-4

35-0

7-2

46-8

8-0

160

6-5

37-4

7-3

IV. Range 7-8-10-0

Place 50 c.c of solution (iii.) in a number of 200 c.c. flasks. Add to each
a drop of one of the indicators cresol red or thymol blue and the number of
cubic centimetres of solution (iv.) given below.

c.c. N/5 NaOH .
pH .

2-61

7-8

3-3

7-9

3-97

8-0

4-8
8-1

5-9

8-2

7-3

8-3

8-5
8-4

10-4

8-5

CC N/5 NaOH .
pH . . .

12-0
8-6

14-3

8-7

16-3

8-8

19-0
8-9

21-3
9-0

24-3
9-1

26-7
9-2

29-95
9-3

c.c. N/5 NaOH .

pn : . .

32-0
9-4

34-5

9-5

36-85
9-6

39-0
9-7

40-8
9-8

42-5
9-9

43-9
10-0

To demonstrate the acid-combining power of a "buffered" solution.

Take 50 c.c. of the above nu.xture { pH = 7'8) or prepare a .Mjlution con-
taining about 0-25 per cent, sodium bicarbonate. Place this in a tall
cylinder and in another similar vessel place the same quantity of water.

COLLOIDS 527

Add ahout 20 drops of neutral rod (O-Of) per cent, in alcoliol) to each. Add
N/IO NaOH to the water till it has approximately the same pR as the
bicarbonate. Titrate liotli with N'nOHCl to the same end jxiiiit.

26. Dialysis (see pp. 557-560).

(1) In using any dialvser it is advisabh' to look to the following points : —

1. Test for leaks.

2. See that neither the preservative nor tlie fluid to be dialysed act on
the substance of the membrane, e.g. bile ])igment increases the permea-
bility of collodion. (Bile may be dialysed through a double dialyser. ?.e. a
collodion tube suspended in a larger tube of the same material. Blood
pigment occasionally presents the same difficulty.)

3. II 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.

(2) [a) Dialyse {a) Egg albumin + Sodium Chloride. (/)) Starch + Iodine +
HCl. {(') Starch + Gkicose. Test dialysate for both constituents.

{b) Using a glass dialyser with a collodion membrane dialyse a mixture
of either congo red, litmus or alizarin and hydrochloric acid.

(c) Dialyse some blood serum. What is the precipitate ? How do you
explain this ?

[d] An acid Perfusate from an Alkaline Solution Prepare some colloidal
ferric hydrate either by dialysing 5 ])er cent, ferric chloride or by gradually
adding 1 c.c. of 30 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 K4FeCy.; solution. When
the iron content becomes very small (after 48 hours) add some HCl to the
colloid. Note the increase in the dif?usibility of the Fe. How can you
explain this ? Why does an acid perfusate come from an electro-negative sol ?

27. Faraday-Tyndall Phenomenon (p. 79).

Arrangement of apparatus. The fluid to be examined is placed in a prismatic
cell (small flat-sided specimen jar, say 5 X 5 X 2| in.). 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.

A. (1) Fill the cell with water and show that the beam is hardly shown.
(With conductivity water the beam is not seen, see preparation of special
water, p. 557.)

(2) Dust lycopodium or puff smoke into the beam outside the cell to
show how small particles in air af?ect 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) Replace the solution with another containing a red gold sol. ^^ hy
is the cone green ?

(5) Try also 1 per cent, starch, 1 per cent, mastic, a saturated solution of
cane sugar or milk whey.

528 ILLUSTRATIVE EXPERIMENTS

B. Polarisation of the. Tyndall Cone. Fill the cell with a mastic sol. Cut
down the light from the lantern to the minimum, which will still give a well-
defined cone. Examine the cone with a Nicol prism [q.v.) held at right angles
to the beam of light and rotate the prism. The cone of light will become very
dim twice in every complete revolution of the prism. That is, the light is
partially plane polarised.

Another similar cell should be ready to be substituted for the one containing
the mastic sol, or should be placed in series with it and nearer to the source
of light. Fill the second cell with a fluorescent solution such as that of
quinine bisulphate or of fluorescein or of eosin. Fluorescent solutions pro-
duce a cone, but no polarisation of the light.

28. Ultra-microscope.

The ■■ slit "" ultramicroscope and the cardioid condenser require special
lighting, but the coarser ultramicroscopic particles can be seen by the use
of a dark-ground condenser such as that shown in Fig. 15 on p. 80 (or
Watson's or Zeiss' " Paraboloid,"' Reichert's " Table," Jentzschs "' Con-
centric,"' or Watson's '" Nelson Cassegrain "). The last-named condenser
can be used with any oil immersion objective utilising its full aperture
without a funnel-stop in the objective. It is effective through the thickness
of an ordinary microscope slide.

Paraboloid Condensers (Watson or Zeiss). These condensers are simply
substituted for the optical part of the Abbe condenser. A funnel-stop must
be placed in the oil immersion objective to reduce their aperture below 1-0.
The following points require attention.

(i.) The ])araboloid must, in every case, have oil between it and the micro-
scope slide. All air bubbles must be excluded, and sufficient oil used to
maintain a perfect contact between slide and condenser.

(ii.) The condenser must be accurately centred.

(iii.) The fluid under examination should be placed on the slide in as thin
a layer as possible.

(iv.) The illumination should be as brilliant as possible. Good results will
be obtained by the use of an Ediswan " Point-o-lite " with bull's-eye con-
densing lens.

(v.) The slides and coverslips must be clean. The best method is to
immerse them in hot bichromate-sulphuric acid mixture for 5-10 minutes.
Rinse thoroughly in distilled water. Pick up the slides and slips one at a
time with forceps ; shake off the bulk of the water and place in dry alcohol
till required. When required withdraw a slide from the alcohol {using
forceps) and burn off the adherent alcohol in a spirit lamp. As soon as the
slide has cooled place it on the oil on the condenser. The slips may be treated
in the same way, or, if they crack readily, the alcohol may be removed by
evaporation near the flame. The cover slip, as soon as it has cooled, is placed
gently on the drop of sol to be examined. At no time should the slips or slides
be touched by hand or by cloth.

A. Mastic sols, gold sols and suspensions like gamboge and India ink show
up well.

B. Brownian Movement (p. 82 and Fig. 16). (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 (see
Experiment 28 above).

(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

DIFFUSION INTO OKLS 529

glass, prepared like the slide, is gently placed on the drop. Use a good
electric light, such as the Ediswan " Point-o-lite," and focus on the central
portion of the fluid. A 1 per cent, suspension of gamboge shows the Brownian
movement well.

2'). Diffusion.

[a) Colloid into colloid . Two-thirds fill four te.st tubes with sterile 3 per
cent, gelatin. Plug tubes with cotton-wool. When the gel has set firmly,
place 0-1 per cent, sols of (1) Congo red, (2) Prussian blue, (3) colloidal iron,
and (4) black India ink, one to each tube. Keep tubes plugged with cotton-
wool and in a cool place. Examine after two days and again after two
weeks.

(h) Crystalloid into colloid. Prepare a number o^ tubes of gelatin as above.
When the gelatin has set, pour various coloured solutions over the jelly and
examine as above. Try copper sulphate, methylene blue, methyl violet,
picric acid.

(c) Diffusion of acid into fidatin. Mix a 4-5 per cent, gelatin sol with just
alkaline phenolphthalein. When set cover with acidified night blue. The
acid diffuses rapidly from the dye. Two coloured layers separated by a
colourless layer are ])roduced in a very short time.

{d) Electrical diffusion (p. 86). Fit up a U-tube with an electrorle of
platinum- or silver-foil rolled cylindrically at the top of each tube. Fill tiie
tube two-thirds full with 3 per cent, gelatin containing a trace of citric acid,
and allow to stand overnight to form a gel. Fill one limb with a coloured
electrolyte {e.g. CuSOj), 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.

30. Adsorptive Stratification. (Liesegang Phenomenon, p. 86.)

(a) Four grams of gelatin 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. in. 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 suc-
cessive 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 gelatin. (2) Do not disturb
the plate after adding AgNOg, 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.

(6) (i.) Fill a test tube to about two-thirds with the bichromate-gelatin
mixture mentioned above. When the gelatin has set fill the remaining
one-third with (approximately) 10 per cent, silver nitrate. Keep in the
dark and reasonably cool.

(ii.) Prepare a gelatin sol containing 3 gm. of gelatin and 80 c.c. of water.
When solution is complete add 20 c.c. of a 50 per cent, solution of MgCL . 6H.,0
and mix. Allow to set and then cover with concentrated ammonia. Cork
well. Examine after a week. The rings are scarce and well separated.

(c) Saturate the gelatin in Experiment (6) (ii.) above with a ca[)illary
active substance like quinine. Whv are no rings formed ?

530

ILL USTRA TI VE EXPERIMENTS

(d) Dead-space experivient (p. 87). Fi]i a glass tube,' of about 4 in. diameter
and 6 in. in length, and open at both ends, with a 5 per cent, gelatin sol to
which sufficient silver nitrate has been added to give a Normal solution.
Immerse the tube, when the gelatin has set, in a 10-15 per cent, solution of
sodium chloride. Ring formation, starting from each end, stops before the
middle is reached.

(e) Rings formed between gases in air. Put a cork into a 1 oz. bottle.
Through the cork pass a glass tube about a metre long and between 1 and
2 cm. in diameter. Plug the upper end of the tube loosely with glass wool.
Put a few cubic centimetres of HCl into the bottle and moisten the wool with
concentrated ammonia. Leave overnight.

31. Determination of the Relative Viscosity of a Liquid.
When a liquid flows through a narrow tube the velocity of flow depends
mainly (a) on the force producing the flow and (/3) on the resistance to flow
produced by the viscosity or internal friction of the liquid. In Chap. XXV.
we considered the shearing of the difTerent layers of the blood stream. The
liquid, we saw, coiild be regarded as made up of a number of concentric
tubes sliding past one another. When the liquid is
-^TTT-T' moving through the narrow tube there will be, under
constant conditions, a constant difference in velocity
between the different tubular layers. The force per unit
area necessary to maintain this condition is proportional
to the difference of velocity, v, of two adjacent layers,
and inversely proportional to their distance apart, x.

V

Briefly, Force = r] X -, where rj is the coefficient of vis-
cosity, which is the 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

V Iv =^ s t js t .
Neglect of the difference of density introduces an error
of less than 1 per cent, and materiallj' simplifies the
o])eration, i.e.

rj'j-q" = t'jt".

Apparatus (Denning- Watson Viscosimeter). The instru-
ment is a modification of the Ostwald-Poiseuille viscosimeter. It consists of
a U-tnbe with a long and a short arm (Fig. 108). 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 ni' 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 in' and stopped when
it reaches ;;/". The time taken is compared with the time reading of water
which is recorded on the back of the tube used. Denning and Watson urge
attention to the following points. (1) The tubes should be scrupulously
clean and jirrferlly dig. (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

m

'-V

m

I'lG. 1(18. — ViscosiiiK tor
(HairMcii).

VISCOSITY

531

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. HNO3 (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.

{a) Compare the viscosities of (i.) water, (ii.) 1 per cent, sodium ddoride
(iii.) colloidal iron, (iv.) 1 per cent, starch, and (v.) 1 per cent, gelatin.

(b) Effect of inecha II ical agitation on the viscosity of a f/elatiii solution. Pre-
pare a 0-5 i^er cent, solution of gelatin and divide it into two parts A and B.
Leave A undisturbed for 12-24 hours. Cause B to be agitated for a few
minutes before the final experiment by sucking it up and blowing it down a
capillary pipette or by blowing bubbles through it. Compare the viscosities of
A and B.

(c) Effect of concentration on viscosity. Prepare various concentrations of
gelatin and of aqueous acacia resin, e.g. 0-5 per cent., 2-5 per cent., 5 per cent.,
10 per cent., and 15 per cent. Compare the viscosities. (The gelatin experi-
ments will have to be carried out at about 20-30° C.)

(d) Effect of temperature on the viscosity of gelatin. A 5 per cent, solution is
divided into three tubes, and after standing overnight the tubes are put for
half an hour {a) into a freezing mixture, (b) into water at 40° C, and (c) into
water at room temperature. Compare viscosities.

(e) Effect of electrolytes on the viscosity of gelatin. A 1 per cent, solution of
gelatin is taken, and the following dilutions and admixtures prepared :

(i.) 10 c.c. 1 per cent, gelatin + 10 c.c. water.

(ii.)

(iii.)

(iv.)

(v.)

(vi.)
(vii.)

N

9 c.c. water + 1 c.c. ^ HCl

N

100"

10 c.c. — NaOH.

10 c.c. ~ HCl

N

10
N_

100

10 c.c. N NagSO^.
10 c.c. N NaCNS.

10 c.c.

NaOH.

(/) ^Jl^'^'f ^I '^(i'f'yiitg the pH 0)1 the viscosity of acacia. Make a 5 per cent,
aqueous solution of acacia resin and dilute it with hydrochloric acid as under
to give the following concentrations of H^ in a 2-5 per cent, solution of acacia.
Take six test tubes and put 5 c.c. of water in each. Leave the first tube as
control, and add 5 c.c. 2 N . HCl to the second tube, mix and transfer 5 c.c. of
the mixture to the tliird tube, and so on, rejecting the 5 c.c. of the mixture
taken from tube 6. Now add .5 c.c. of the 5 per cent, acacia solution to each
tube.

Tube No.

1

■>

3

4

5

G

Water, c.c. .

5

5

5

5

5

5

Acid, c.c.

0

5

5

5

5

5

Acacia, c.c.

5

5

5

5

5

5

Normality .

0

N

N/2

N/4

N/8

N'16

34-S

532

ILL USTRA TI VE EXPERIMENTS

Acacia per cent., 2-5 in all tubes.

Determine the viscosity of the mixture in each tube. The lowest viscosity
will be found in tubes 4 and 5. If a new series of tubes is prepared with
concentrations of acid lying between these values, e.g. 0-25 N to 0-125 N, the
lowest reading will be obtained with about 0-2 X . HCl.

32. Determination of the Isoelectric Point of a Protein (p. 91).

(a) Preparation of solutions of definite {temporary) pH. Seven clean, dry
tubes are treated as under.

Tube No.

1

o

3

4

5

6

7

Water, c.c.

2

9

9

9

9

9

9

Acetic acid, c.c. .

16

9

9

9

9

9

9

+ 9

pB. . . .

3-8

4-1

4-4

4-7

5-0

5-3

5-6

Place 2 c.c. of distilled water in tube 1 and 9 c.c. in each of the other tubes.
To tube 1, add 16 c.c. N/10 acetic acid. Mix and transfer 9 c.c. of the mixture
to tube 2. Mix and transfer 9 c.c. to the next tube, and so on, rejecting the
9 c.c. withdrawn from tube 7.

Determination of the isoelectric point of casein. Put 1 c.c. of a casein sol
(q.v.) into each of seven clean, dry test tubes. Add the contents of acid
tube 1 {pB. 3-8) to the first casein tube, tube 2 (pB 4-1) to the second casein
tube, etc. Shake each of the tubes and record your observations on a chart
as below. — = no change, 0 = opalescence, + = precipitate.

Tube No.

1

o

3

4

5

6

0
0
0

7

On mixing ....
After 10 minutes
After 20 minutes

0
0
0

0
0 0
0 0

0 0

+ +
+ +

0 0 0

+ + +
+ + +

0 0
0 0 0

+

pB

3-8

4-1

4-4

4-7

5-0

5-3

5-6

Tube 4 (pB = 4-7) shows the greatest change, and so it is inferred that the
isoelectric point of casein lies near that value.

(b) Determination of the isoelectric point of gelatin. Make up a series of
buffer solutions of pB 4, 4-2, 4-4, 4-6, 4-8, 5, 5-5 from the phthalate series
given in Experiment 25. To each of a series of seven clean boiling tubes
containing 10 c.c. of these buffers, add 1 gm. of powdered gelatin and 1 c.c.
of M/128 potassium ferrocyanide solution. To another similar series, add
I c.c. of M/128 copper acetate solution. After the gelatin has been in contact
with the ferrocyanide or the copper solution at a definite pB for about an
hour, pour off the supernatant fluid, wash several times with cold water to
remove any metal salt not combined with the gelatin and dissolve the gelatin
by adding warm water to each tube and immersing the tubes in warm water
(40° C). The volume is made up to 50 c.c. Allow to stand for two or three
days. The tubes of the first series, in which the pB was less than 4-7, turn
blue because the gelatin forms tlie cation of a salt in which Fe(CN)g is the

OSMOTIC PRESSURE OF COLLOIDS

533

anion. The latter forms a h]no feiric salt on standinji for a few days. The
other tubes in this series are coh)urlcss. Similarly, the second series shows a
blue ranfie from pK 4-8-5-5 due to the combination of the gelatin with the
(■()|)|)ci- to give a coj)j)er gelatinatc. Fnuii these experinieiits one infers that
at a /;H between l-f) and 1-8 gelatin acts neither as a cation nor as an anion.
4-7 is, therefore, approximately the isoelectric point of gelatin.

(c) Detennination of the isoelectric point of gelatin by the alcohol precipitation
method (Pauli). Prepare a series of buffer solutions of the sodium acetate-
acetic acid series, having a range about the isoelectric point of gelatin, e.g.
4-1 to 5-3 as follows :

Take five boiling tubes and put 8 c.c. of distilled water in the first and
5 c.c. of distilled water in each of the others. To tube 1
add 2 c.c. of N acetic acid and mix. Transfer 5 c.c. of
this N/5 acid to tube 2 and mix, and so on, rejecting the
5 c.c. of N/80 acid removed from tube 5. That is, a
series of tubes having 5 c.c. of fluid of the following pH
values has been prepared :

Tube No. 12 3 4 5

^H

4-1

44 4-7

5-3

To each tube add 2 c.c. of N/10 sodium acetate. Mix
and add 2 c.c. of a 1 per cent, gelatin sol. Shake. Now
slowly add methylated spirit to tube 3 till a cloudiness is
just visible. This will require about 8 c.c. Add this
amount to each of the other tubes and leave for half an
hour. In which tubes is turbidity most pronounced ?

33. Osmotic Pressure of Gelatin.

(1) Fit up an osmometer with a collodion membrane
(as described on p. 557). Fill the collodion sac with
a 1 per cent, gelatin sol and place the osmometer in
water up to the level of the rubber stopper. It is
necessary to keep the apparatus and its contents at
about 16-20° C. to prevent gelatinisation. In about
20-30 hours the level of the fluid in the vertical tube
will be steady and there ought to be about 40 mm. of
solution above the level of the fluid outside.

(2) A simple comparative experiment to illustrate
the low osmotic pressure of gelatin at its isoelectric
point may be carried out by means of three thistle
funnels (Fig. 56). Over the mouth of each funnel is placed a collodion
membrane B (in the same way as is described in the preparation of a collodion
dialyser). Into the first osmometer put enough acid gelatin to come above
the wide part into the tube. Charge the second one similarly with isoelectric
gelatin and the third with alkaline gelatin, and place all three vertically
in the same water. After a day one can see that tube 2 has practically no
osmotic pressure, while the other two exhibit a pressure of about 70 mm. of
solution. The results are not quite accurate because the unprotected collo-
dion forming the floor of this simple osmometer is distensible and yields more
with the greater hydrostatic pressure. Another disturbing factor is the
electrostatic attraction of the gelatin for the CI ions and the Na ions, whereby
both CI and Na are prevented from diffusing freely through the membrane
(.see Donnan Equilibrium, p. I'^S). They thus cl.^.o exert an osmotic effect and
exaggerate the rise in the first and third tubes.

Fig. 109.— Osmometer
with collodion or parch-
ment membrane (see

text).

534 ILLUSTRATIVE EXPERIMENTS

34. Cataphoresis.

(a) Mac rosea pre uhscivalion of the titoveinciU of colloids in, (di. electric
Jldd. Material, etc., required :

U-tiibe, 15-25 cm. high x 2-3 cm. inside diameter, fitted with rubber
corks pierced by two holes (]). 91, Fig. 19). In one hole in each cork put a
short length of glass tubing to act as a vent for gas and water. The other
hole carries the electrodes, preferably of platinum or silver, but copper will
answer quite well. These electrodes may be flat, but more rapid results will
be given if the metal foil is rolled into cylindrical form. (Diameter of cylinder
2 mm. less than that of the tube.)

Eyg white sol (p. 562). Fill the lower third of the U-tube with the neutral
solution, and gently drop a small disc of smooth waiting paper on top of each
surface. With a pipette fill each limb with distilled water, so that there is a
clear demarcation at the water sol interface. Gently insert the corks carrying
the electrodes. Allow to stand undisturbed for 15 minutes. Now pass at
least 110 volts D.C. across the electrodes for half an hour or so and note the
alteration in the levels of the sol in each limb. With a D.C. voltage of about
200 the gradient in this tube would be about 5V/cm., so that in 15 minutes the
level of the sol should move quite distinctly. Reverse the direction of the
current for a similar time. Repeat the experiment with some egg white sol
which has been made (a) slightly acid with acetic acid, or (b) faintly alkaline
with dilute sodium hydrate.

A rough demonstration of the movement of colloids in an electric field may
be given by fitting up a small cylindrical zinc water bath (or even a cocoa tin)
with a central cylindrical roll of copper foil suspended from a glass or wooden
cross-piece. Fill the jar with the colloid to be studied and leave overnight.
Positively charged colloids will adhere to the copper foil, while those carrying
a negative charge will be found in association with the zinc.

Colloids to try. 1. Egg white (a) neutral to litmus, slightly electronegative,
(6) acidified with acetic acid, (c) made just alkaline with sodium hydrate.

2. 1 per cent, gelatin, (a) isoelectric, (b) electropositive, (c) electronegative.

3. 0-2 per cent, night blue. 4. 0-2 per cent, alkali blue. 5. Mixture of 100 parts
of 2 per cent, alizarin red and 2 c.c. saturated picric acid.

(6) Microscopic observation of movement of colloids in an electric field
(Fig. 20, p. 91, and letterpress, p. 92). The electrodes (Fig. 20) 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 the centre of the
space between the electrodes, making contact with them and covered with
a I in. slip. 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 centimetres per volt per second.

35. Electric Endosomose.

(a) The passage of water through a membrane by electrical means may be
observed in the preparation of a semipermeable copper ferrocyanide mem-
brane when the solutions are forced into the pores of the earthenware pot
by an electrical current (Experiment 5).

(6) A clean porous pot, fitted with a manojneter and a non-polarisable

COAGULATION AT ISOELFX'TRIC POINT 535

electrode, is filled with and placed in a solution of Ko'SU, ((JU5 per cent.).
A current of 2— t volts is passed so that the electrode inside the pot is the
cathode. Note the rise in level of tlic lliiid inside the pot. Note also the
increase in the alkalinity of the fluid outside the ])()t.

(c) Make a collodion tube to fit one linih of the U-tube (Fi^^ 19).

(1) Fill both limbs with dilute K.2SO, solution. Mark the level of the
fluid in both limbs and, using non-pohvrisable electrodes, pass a current of
4 volts for some time throup;h the sohition. Note that water passes towards
the cathode and that the cathodal fiuid becomes acid.

(2) Repeat, using tartaric acid in the collodion sac and pure water outside.
Test for tartaric acid.

(3) Fill the sac with gelatin sol and leave overnight. Wash out the
sol and repeat the experiments (r) 1 and 2.

30. Coagulation of Sols at the Isoelectric Point (see also Isoelectric Point).

(a) By heat. Prepare some egg albumin sol. Divide it equally into thres
lots. To lot 1 add 1 c.c of N . HCl for every 20 c.c. of sol. Leave lot 2 alone.
Add 1 c.c. of N . NaOH to lot 3 for every 20 c.c. of sol. Place in water bath and
gently w^arni to 60° C. Cool and examine. Filter if necessary.

Heat 5 c.c. of each lot to the boiling-point. Only No. 2 coagulates. Care-
fully neutralise No. 1 with N/10 NaOH and No. 3 with N/10 HCl. A precipi-
tate is formed. Add more alkali or acid as the case may be. The precipitate
dissolves. This precipitation by neutralisation is reversible. Repeat the
neutralisation experiment on the remainder of 1 and 3. Filter oft' the precipi-
tates and suspend each in about half a tube of water. Now heat to boiling.
A coagulation forms. Coagulation is irreversible.

(b) Effect of electrolytes on colloids. MetJiod. Take three test tubes (cZfa^i')
for each experiment. To tube 1 add 10 c.c. of the salt solution. To tube 2
add 10 c.c. of water + 1 c.c. of salt solution, mix and transfer 1 c.c. to tube 3.
To tube 3 add 10 c.c. of water -\- 1 c.c. from tube 2. Mix, withdraw 1 c.c. and
reject it. To each tube add 1 c.c. of colloid. Mix and leave alone for one
hour.

Colloids to use. (l)Suspensoid. Dialysed iron (B.D.H.) (1 m 10). (2) Emul-
•soid. Gum mastic {q.v.).

Salts to use. (i.) To show the effect of varying the anion : 2 N solutions of
the nitrate, chloride, acetate and sulphate of potassium.

(ii.) To show the effect of varying the cation : 2 N solutions of the chlorides
of sodium, calcium, magnesium and ammonium.

(c) Mutual precipitation of colloids, (i.) Add gum mastic to colloidal iron
till precipitation occurs. Filter and test filtrate for iron.

(ii.) Add colloidal iron to diluted blood ssrum. Filter through cotton-wool
and test filtrate for iron and for protein.

(iii.) Add tannic acid drop by drop to diluted blood serum till precipitation
is complete. Now add more tannic acid. The precipitated colloid again
resumes the sol form.

(iv.) Capillary analysis {q.v.).

37. Protection of (Hydrophobic) Suspensoids by (Hydrophilic) Emulsoids.

(a) Five cubic centimetres of colloidal iron (B.D.H. diluted 1 in 0) is jilaced
in each of two test tubes. To one add 5 c.c. of 0-1 per cent, gelatin (slightlv
acidified) and to the other 5 c.c. of water (also slightly acidified). To each add
enough of any of the salts (given in Experiment 36) to precipitate the iron.
Precipitation occurs rapidly only in the tube free from gelatin. Determine
how much more of the salt solution has to be added to precipitate the
gelatinised iron.

536

ILL I STB A TI IE EXPERIMENTS

(6) Protective action of e))udsoids (p. 93). Two equal portions (9 c.c.)
of neutral gold sol are treated (1) Avitli 1 c.c. of a 0-1 per cent, gelatin sol
and (2) with 1 c.c. of distilled water. To lioth 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 ])aper.

(c) Six tubes are prepared as follows and examined as in (6) above :

Tube No.

1

•>

3

4

5

6

Colloidal gold, c.c. ....
()01 per cent, gelatin, c.c. .
Redistilled water, c.c.
2N.NaCl, c.c

7
5
0
4

7
4
1
4

7
3
2
4

7
2
3
4

7
1
4
4

7
0
b
4

38. Adsorption.

(a) Adsorption of colloid to a surface. Pour into a series of Erlenmeyer
flasks faintly coloured suspensions of various colloidal dyes. Add a gram
of blood- or bone-charcoal to each flask. Shake several times. Filter
through ordinary pleated papers. Note the practically colourless filtrate
obtained. Return the charcoal to the cleaned flasks and shake with water.
Is any colour given of? ? Now add some substance w^hich lowers the surface
tension of water, e.g. methylated spirit, tributyrin, etc. The colour appears
in the fluid.

Dyes to try. Congo red, 0-05 per cent. ; Night blue, 0-01 per cent. ; Prus-
sian blue, 0-01 per cent. ; Berlin blue, 0-01 per cent.

(b) 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 licjuid-paper interface, while negatively charged
colloids will ascend with their dispersion media. (i.) Flask i. Water,
ii. Aqueous night blue or Prussian blue. iii. Aqueous alkali blue. In 10-15
minutes examine the height of w^ater 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.

(c) Adsorption of Salts to Colloids. Cut a series of discs 3-4 mm. thick
from a fairly concentrated gelatin gel and place them in a Petri dish con-
taining a 2 per cent. a(]ueous solution of commercial aluminium sulphate
(contains iron) and leave for some days. In three days or so the gelatin
becomes tinged reddish brown (ferric salts). Now test the original solution,
the solution after standing with gelatin, and the gelatin itself for iron
by adding a few drops of ammonium thiocyanate to each. Note the depth
of colour.

IMBIBITION

537

{il) Elect roclioin'ra] (idsorplloii. Prepare three sdliitions of :i dve, one in
each of three test tubes as follows :

1. lOc.c. of dye + 1 c.e. N . 1 1. SO,

2. 10 c.c. of dye + 1 c.c. water.

n. lOe.c. of dye + 1 c.c. N . NaOll.

I^it a strip of filter paper into each tube. In a few minutes, iciiiove the
papers and wash them in cold water. Only one paper is periiianently stained
— which paper depends on the dye used.

Dyes to try (all 0-01 per cent.). Methylene blue, crystal violet, brilliant
green, night blue, Nile blue, and (O-Oo per cent, solution) Congo red, and
Ol per cent, ponceau GR.

Note tliat this type of adsorption is irreversible.

39. Imbibition.

(a) 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 ]Jortion and also the alterations in
colour, opacity, elasticity, etc.

(6) X strip of thin sheet rubber (dental or patching rubber) about
12 in. X Ih in. 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.

(c) Effect of the dielectric value of the imbibed fluid on the amount of swelling.
Cut a number of exactly similar strips of dental rubber, say, 6 in. x h in.,
and suspend one in each of the following fluids in test tubes : Water, ethyl
alcohol, acetone, amyl alcohol, benzol, toluol, xylol. Examine and measure
the strips after about half an hour. It will be found that the rubber has not
swollen in the water, slightly in the ethyl alcohol, and so on, till the largest
increase is found in xylol. That is, the power of imbibition varies inversely
as the value of the dielectric constant (q.v.).

{d) (i.) 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 (see experiment on p. 97).

(ii.) Pressure by CEdometer (Fig. 22, p. 98). Place two large teaspoonfuls
of Cox's powdered gelatin in the foot of the cylindrical glass container.
Re])lace the plunger and attach the indicator clip. The pointer should be
adjusted to read zero. Add sufficient water to reach two-thirds up the
cylinder. When the apparatus is examined next day it will be obvious from
the drop of the pointer on the scale that the gelatin has swelled. The scale
may be calibrated to give readings in cubic centimetres. Repeat the experi-
ment, adding weights to the balance pan. For example, the addition of a
weight of 1 kilo slows the rate of imbibition, 2 kilos slows it still further, and
so on. till with a certain weight, say, 30 kilos, the swelling is inappreciable.

Swelling of Gelatin in Water.

Pressure (mm. Hg.)

Grams HgO per gram of gelatin

40
2-5

80
2-0

156

1-5

240
1-3

303
11

377

0-9

538 ILLUSTRATIVE EXPERIMENTS

Another experiment illustrating the effect of electrolytes may be tried.
During the tirst tt-10 hours cover the gelatin in the cedometer with a M/8
sodium chloride solution. Compare the rate and amount of swelling with
that in pure water. Now drain oft' as much of the salt solution as possible and
fill up again with pure water. Both rate and amount of swelling are now
increased.

(e) Heat of imbibitio)> . Dry some commercial starch powder at 105° C. and
leave to cool in a desiccator. Put about 50 gm. of this into a small beaker,
insert a thermometer and read off the temperature. Add about 50 c.c. of
water and stir with the thermometer. An increase of temperature of from
10-14° C. will be obtained in a few minutes.

Somewhat better results may be obtained by substituting a vacuum flask
for the beaker.

Potato meal, pease meal, etc., give + 8° to + 10° C.

(/) EJI^^' ^f various electrolytes on imbibition. First of all, prepare a
number of standardised gelatin discs as follows. Make a concentrated
solution of gelatin, adding a trace of a colloidal dye {e.g. Congo red) to
render the gelatin 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/lOHCl or
H2SO4, (iii.) N/lONaOH, (iv.) N/2KI, (v.) N/2NH^CNS, (vi.) N/SCaCl.,,
(vii.) Sat. MgS04.

Put a few gelatin 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 1 Arrange the electrolytes in a descending
order as they have favoured imbibition. This is the so-called hjtropic series.
Instead of gelatin, 1 per cent, agar may be used. The lytropic series will be
in the same order (see also Experiment 40).

(g) Effect of Acid on Imbibition, (i.) 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.

(ii.) Prepare a series of tubes covering a wide range of acidity and
alkalinity, e.g. HCl approximately 5 per cent., 2-5 per cent., 1-25 per cent.,
0-6 per cent, and 0-2 per cent., and a similar range for NaoCOo. Place a
weighed piece of blood fibrin in each and in a tube of water. After half an
hour remove the fibrin, dry with blotting paper and weigh. Fibrin absorbs
more water in any solution of acid or alkali than in piire water (cf. Experi-
ment 42 (c) ).

(iii.) Remove the eyes from a dead experimental animal or get sheep's eyes
[rom the abattoir. Measure the diameters of each eye. Weigh the eyes.
Place one eye in one of each of the following solutions, 0-5 per cent. HCl,
0-5 per cent. HCl + 3/20 M . Ca(N03)2, 0-5^ per cent. HCl -f N/IO NaCl,
0-5 per cent. HCl 4- N/10 Na^SO^. Leave for 6-10 hours and then dry with
blotting paper, measure and weigh. The eyes in the pure diluted acid swell
very rapidly. The presence of salts prevents much swelling and, in the case
of sodium sulphate, may even cause a decrease in weight. Similar results
may be obtained with pure gels placed in collodion bags.

GELATION 539

40. Gelation.

[a] Heat a .suialJ (|uant it y of I per cent, solution i)[ (J) gelatin, (2) scruiu,
(3) dextrine. Cool. What is the result ? Has reheating any effect ?

[b] Effects of soluleti on gelation. Into four boiling tul)es put the same
quantity of 2h per cent, gelatin. In (uie tube dissolve about 5 7 per cent,
magnesium sulphate crystals. Potassium iodide crystals are added to the
second tube, while a few drops of 1<) per cent, formalin are mixed with the
gelatin in the third tube. The fourth tube is left as a control. Allow all
tubes to stand overnight and examine by tilting and shaking. Flow do
you explain the varied viscosity '(

Sulphates, citrates and phosphates increase tlie viscosity of aqueous
emulsoid gels. Iodides, bromides, cyanides and some chlorides similarly
decrease viscosity. Alcohol, formaldehyde, etc.. in small amounts increase
viscosity.

(c) Effect of non -electrolytes on the setting of gelatin. A 6 per cent, solution
of gelatin is prepared and divided into three exactly similar tubes. To one
tube is added enough cane sugar to make a 10 per cent, solution. To another
sample sufficient urea to make a 5 per cent, solution. The third tube will
contain gelatin alone. Warm all tubes in a water batli to ensure complete
liquidity and uniformity. Put 1 c.c. of fluid from each tube on to three
separate watch-glasses and add a small lead shot to each, cover wuth a second
w-atcli-glass to prevent evaporation and gently rock the glasses from time to
time and note how^ long the fluid in each takes to set (lack of mobility of
shot).

Examine the firmness of the gelatin w^hen set.

When the gelatin left in the tubes has set, turn out the little cylinders of
gel. Weigh, and measure each diameter.

Place them in a relatively large volume of water oveniight. Dry with
blotting paper and again weigh and measure.

Sugar causes the gel to set more rapidly and swell less than either of the
other two. Urea retards gelation and causes the largest imbibition of water.

Similar experiments may be made with other non-electolytes,. e.g. :

1. Control . . 6 c.c. of 6 per cent, gelatin + 1 c.c. of water.

2. Urea . . ,, ,, + 1 gram of urea.

3. Aldehyde . „ ,, -f- 1 c.c. 40 per cent, for-

malin.

4. Alcohol . ,, ,, +1 c.c. methylated spirit.

5. Cane Sugar . ,, ,, +1 gram sucrose.

(d) Effect of electrolytes o)t gelation, (i.) Eft'ect of various anions.

1. Control tube . 3 c.c. 6 per cent, gelation -f 3 c.c. water (very faintly

acid) .

2. Sulphate . ,, ,, -|- 3 c.c. normal K.2SO4.

3. Sulphocyanide „ „ -f 3c.c. N. K.CNS".

4. Chloride . „ „ + 3 c.c. N. K.Cl.

5. Salicylate . „ ,, -|- 3 c.c. N. K.C7H5O3.

(ii.) Effect of various cations.

1. Control tube . 3 c.c. 6 per cent, gelatin + 3 c.c. faintly acid water.

2. Sodium . . „ „ +3 c.c. N. NaoSO^.

3. Calcium . ^^ ^^ ^ 3 c.c. 0-03" N. CaSO.,.

(sat. sol.)

4. Magnesium . ,., „ -f 3 c.c. N. MgS04.

540 ILLUSTRATIVE EXPERIMENTS

5. Potassium . 3 c.c. 6 per cent, gelatin -\- 3 c.c. N. K28O4.

6. Ammonium . ,, ,, + 3 c.c. N (NH^)., .SO4.

7. Iron . . „ „ + 3 c.c. N. FeoCSO^)..

41. Study of Syneresis.

(a) Make up about 30 c.c. each of 3 per cent., 1-5 per cent., and 0-75 per
cent, gelatin. Add a drop of thymol in chloroform to each sol, and place in
stoppered weighing bottles for three or four days. Note contraction of the
gel with expression of clear fluid. Examine both gel and fluid in each case
and note that qualitatively they are alike. That is, the separated phases
contain gelatin and salts dispersed through water and the gels, water and
salts dispersed through gelatin.

(b) A similar series of experiments may be performed with 4 per cent, and
2 per cent, starch.

(c) Examine the curd and the whey produced (a) by the addition of essence
of rennet, or (b) by a drop of acid to 20 c.c. of warm (30-38° C.) milk.

(d) Put about 5 c.c. of freshly drawn blood into each of a pair of centrifuge
tubes and spin gently for about 10 minutes. Remove from centrifuge, add a
drop of preservative, cork firmly and allow to stand overnight. Draw of? the
clear fluid (serum) and test for proteins and chlorides. Examine the clot.
Note clear layer on top — the buffy coat. Cut this part away and test it for
proteins and chlorides. Put the lower red portion in a fold of muslin and
knead it in a little 0-9 per cent, saline in a small evaporating basin. Note
(1) emergence of red corpuscles, (2) residue of tough fibrin. Treat the
remainder of the buffy coat in the same way and note the fibrin residue.

42. Emulsions.

(a) (i.) 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 {^) some (soft) soap solution : to (y) a few drops of oleic acid and about
the same quantity of cone. Ca(0H)2 solution, shake and allow to stand.
Which give the best emulsions ?

(ii.) Another method of preparation. Place some gum acacia in a large
mortar. Powder it thoroughly. While continuing the rotatory movement of
the pestle, add the oil to be emulsified in a very slow stream. Keep the pestle
going, always in the same direction. After a thorough mixture has been
produced add sufficient water to emulsify the gum, starting with a few
cubic centimetres and gradually increasing the rate at which the water is
run in. Keep the pestle going. When the emulsion gives forth a cracking
sound, the rest of the water may be added in one lot.

{})) To determine the optimum concentration of colloid for the stabilisation
of an emulsion. Into each of three mortars introduce 20 c.c. of water,
(a) containing 1-25 per cent, of commercial soft soap, (/3) 1-875 per cent.,
and (y) 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 half an hour. Pour into tall cylinders and allow to
stand for some days.

(c) To determine the effect of the pR of the colloid on the stability of the emul-
sion. To 5 gm. of drv casein in each of three mortars add slowly (a) 50 c.c.
N/20NaOH, '(^) 50 c.c. water, and to (y) 50 c.c. N/20HC1. Allow to stand
overnight and then slowly stir 75 c.c. of cottonseed oil into each. Pour
into clean jars and allow to stand. Why does (jS) separate out ?

(d) 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, (j8) 100 c.c, (y) 200 c.c,

EMULSIONS AND FOAMS 541

(8) 400 500 c.c. of cottonseed oil. i'lacc in slialiow dishes. Note rigidity.
What happens when the optimum concentration of oil has been passed.

(e) 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 [)ortions. No. (i.) will serve as control.
To the others add a few drops of one of the foUowinjj; N solutions, (ii.) HV\,
(iii.) NaOH, (iv.) Ca(OH).,, (v.) CaCl.,, (vi.) NaCI. (vii.) Alcolu.l, (viii.) (TIC^,
(ix.) Ether.

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.

43. Foams.

{a) Place about 10 c.c. of distilled water, absolute alcohol, and jiiacial
acetic acid in separate test tubes and shake vigorously for two minutes. Does
a foam appear ? Now mix 5 c.c. of water with 5 c.c. of the alcohol ; and also
with 5 c.c. of the acetic acid ; and the remaining 5 c.c. of the alcohol with 5 c.c.
of the acetic acid. Again shake vigorously. {Caution. — Release pressure
occasionally.) Do foams appear ? How long do they last ? Dust a little
lycopodium powder on to the aqueous alcohol, and a little finely powdered
lamp-black on to the surface of the aqueous acetic acid. Again shake for
two minutes. The foams last much longer.

(6) Shake up some protein sol, e.g. diluted blood serum, 1 per cent, egg
albumin, or 1 per cent. Witte's peptone in 0-5 per cent. NaCl. Touch the
froth with a glass rod on which is a drop of either olive oil, caprylic acid or
cheese. Why does the froth subside.

(c) Put 5 c.c. of a rennin solution into each of three test tubes. Leave
tube 1 as control. Add a trace of saponin to tube 3. Shake tubes 2 and 3
vigorously for two minutes. Withdraw 2 c.c. from each tube and compare
their activity in curdling a calcified milk (see Experiment 47). Why has
the saponin prevented the inactivation of the enzyme produced by shaking.

44. Conditions Governing Enzyme Action.
Collect 10-20 c.c. saliva, filter.

(1) Optimum temperature for the action of ptyalin on starch. Measure
5 c.c. of 1 per cent, boiled starch solution into a test tube and add 1 c.c. of
saliva. Set up the tubes at the following temperatures, {a) 0° C, {b) 20° C.
(c) 40° C, {d) 60° C, (e) 100° C. Test every minute with dilute iodine solu-
tion until the achromic point is reached. Note the time taken.

(2) Optimum pH. One cubic centimetre of 1 per cent, starch solution, 5 c.c.
of a buffer solution, 1 c.c. of 0-9 per cent. NaCl solution, 1 c.c. saliva and 4 c.c.
distilled water are measured into a test tube, the tube is set in a water bath at
37° C. Note the time taken to reach the achromic point. Buffer solutions
of the following pR values to be used : {a) 8, {h) 7-4, (c) 6-8, {d) 5-8, (e) 4-8.

(3) The action of salts in enzyme action, {a) Take 1 c.c. of starch solution,
1 c.c. of distilled water, and 1 c.c. of dialysed saliva.

{b) Take 1 c.c. of starch solution, 1 c.c. of 0-9 per cent. NaCl solution, and
1 c.c. of dialysed saliva.

Set the tubes in a water bath at 37' C.. and note the time taken to reach
the achromic point.

(4) Effect of boiling on saliva. To 1 c.c. of starch solution add 1 c.c. of
boiled saliva. Does the saliva have any action when placed at 37° C. ?

(5) Effect of boiling on starch. Add a little raw starch to 10 c.c. of
water. Divide into two equal portions, boil {a) and allow to cool, then add
1 c.c. of saliva to each portion and ])lace the tubes in a water bath at 37° C,
Note the tiine taken to reach the achromic ])oint.

542

ILLUSTRATIVE EXPERIMENTS

45. The Influence of the Hydrogen Ion Concentration on the Activity of
an Enzyme. Ptyalin (adapted from Ringer, Zeits.f. physiol. Chem., 1910).

Material required. (1) About 50 c.c. of a 1 in 50 dilution of saliva. (2) Seven
large boiling tubes or small Erlenmeyer flasks of about 50-100 c.c. capacity.
The tubes should contain phosphate buffers made up as on p. 525, so that
each tube has 5 c.c. of a phosphate solution with the following pK values :
6-24, 6-47, 6-64, 6-81, 6-98, 7-17, 7-38. (3) 0-5 per cent, solution of boiled
starch made up in 0-3 per cent, sodium chloride solution. (Ptyalin operates
best in the presence of the CI ion.) (4) A series of about 30 small tubes, each
containing 5 c.c. of an approximately N/1,000 iodine solution to act as
indicators.

Method. To each boiling tube in turn add 5 c.c. of the diluted saliva and
mix. Starting from the left and at an interval of exactly two ininutes between
each flask, add 25 c.c. (or 50 c.c. if your tubes will contain it) of the starch sol.
Then at tAVO-minute intervals, 2 c.c. of tube 3 are transferred to an iodine
tube. At first the colour will be blue, later violet, later still red. At this
stage, without delay, remove in turn 5 c.c. of the contents of each tube and
transfer to separate iodine tubes. Note that as before, exactly two minutes
should elapse between the withdrawal of the reaction mixture from successive
tubes. The following is a typical resvdt :

Tube Xo.

_pH (approx.)
Iodine colour

1

2

3

4

5

6-3

6-5

6-7

6-8

7-0

blue

violet

red

yellow

red

7-2
red violet

7-4
violet

In tube 4 the reaction has proceeded most rapidly, i.e. fR 6-8 (approx.) is
the optimum jpH for ptyalin.

46. Effect of Removal of the End-products on the Rate of Action of
Ptyalin (p. 125).

Place a small quantity of saliva in a test tube and dilute w^ith an equal
volume of water. Divide this amount equally between a dialysing cylinder
A and a slide-tube B of approximately the same diameter. Add an equal
quantity of 0-5 per cent, boiled starch (in 0-3 per cent. NaCl) to each tube
and mix the contents. Place the tubes in a beaker and maintain a
constant flow^ of water in the beaker. The flow of water will maintain a
comparatively steady temperature in both tubes and will hasten dialysis
in tube A. By means of a glass rod (one to be kept for each tube) transfer,
from time to time, a drop from each solution to a white glazed tile and add
to each drop a little iodine solution. In the drops from tube A a blue colour
with iodine is given at first ; later drops give a purplish, later still a reddish
brown colour, and after about an hour no reaction with iodine is obtained.
At this stage the drops from tube B still give a clear indication of the presence
of starch. A typical result is given in Table XXI. on p. 125.

A suitable exercise is now to estimate the amount of reducing sugar present
in each tube.

47. Estimation of the Relative Activity of an Enzyme (Rennin).
Material required, (i.) Boiled milk, to which has been added one-tenth of

its volume of 10 per cent, calcium chloride solution, (ii.) Arbitrary standard
of activity — prepared by diluting either commercial " Essence of Rennet "" or
Benger's "' Liquor Pepticus " to such a strength as will produce the curdling
of an equal volume of CaClo milk mixture in about 10-12 minutes at room

RELATIVE ACTIVITY OF AN EXZYME

543

temperature, (iii.) Filtered gastric juice or an artificial gastric juice made
from pepsin porci or from one of the above-mentioned commercial extracts.
Method. Take nine test tubes and put 1 c.c. of water into each except the
first. Into the first two tubes put J c.c. of the juice to be examined. Mix the
contents of the second tube by repeated sucking up into the pipette and blow-
ing out. Transfer 1 c.c. of the mixture to the third tube, from which, after
similar mixing, remove 1 c.c. and put it into the next tube, and so on, rejecting
the 1 c.c. removed from the ninth tube. The tubes now contain 1 c.c. of
fluid consisting of the juice of unknown strength diluted as follows :

Tube >'o.

1

2

3

4

.T

6

7

8

9

Dilution .

1/1

1/2

1/4

1/8

1/16

1/32

1/64

1/128

1/256

Place the tubes in a rack with a space between tubes 5 and 6. In this
space put a tube containing 1 c.c. of the prepared standard juice. To each
in turn add 1 c.c. of the calcium-chloride-milk mixture. This must be done
as rapidly as possible. Use a graduated 10 c.c. pipette for the purpose. The
operation should then take less than a minute to perform. Hold the rack of
tubes in the hand and gently tilt it occasionally, observing the way in which
the milk mixture flows on the sides of the tubes. Determine which tubes
show curd formation simultaneously with the standard tube. Suppose the
fourth tube curds a little before the " standard," which curds a little before
tube 5. The unknown juice, therefore, is between eight and sixteen times as
strong in rennin action as the standard.

A new series of dilutions should now be made. Dilute the unknown juice
eight times, and with a graduated 2 c.c. pipette put the following amounts of
juice and water into six tubes.

Tiihp No.

Diluted juice (c.c.)
Water (c.c.) .

1

o

3

4

5

2

1-6

1-3

1

0-7

0

0-4

0-7

1

1-3

0-4
1-6

A control tube containing 2 c.c. of the standard enzyme solution is placed
near the middle of the series ; 2 c.c. of the milk mixture is added "as before
and the above procedure carried out. Suppose now the control tube and
tube 3 almost coincide in clotting time. If tube 3 is just a little earlier in

Then 1-2 c.c.
= 2 c.c. of the
2/1-2 times as

clotting than the control, take an interpolated value, 1-2
of a 1/8 solution of the unknown has an " enzyme strength "
standard strength. That is, the unknown juice contains 8 x
much enzyme as the standard = 13-3.

Similar experiments may be carried out with other enzymes, using suitable
substrates. For example, determine the " strength " of the ptyalin in your
own saliva, using a diluted solution of Taka diastase as standard.

In determining the strength of j)roteolytic and lipolytic enzymes a water
bath capable of containing the labelled tubes and of being maintained at a
con.stant temperature (38-40° C.) is essential. For substrate for the proteo-
lytic enzymes either the coagulated egg albumin suspension or the turbid
suspension produced by the precipitation of the serum proteins by sulpho-

544

ILL USTRA TI VE EXPERIMENTS

salicylic acid may be used (p. 562). It is necessary, of course, to maintain
the correct /jH for the particular enzyme.

48. Demonstration of the Presence of a Lipase in an Extract. (Benger's
Liquor Pancreaticus.)

Take 90 c.c. of distilled water, 10 c.c. of M/3 secondary sodium phosphate
and 20 drops of tributyrin, and shake together for 10 minutes. Filter,
rejecting the first few cubic centimetres of the filtrate. This gives a fine
suspension of fat in a buffered solution of about ;;H 8. To 50 c.c. of this
mixture at 38° C. add 2 c.c. of Benger's Liquor Pancreaticus. Mix and rapidly
withdraw about 5 c.c. for stalagmometric investigation (Experiment 17 (1) ).
The drop number so obtained is taken as that of a diluted tributyrin mixture.
If a pancreatic lipase is present in the liquid under test, it should cause the
splitting of the fat into butyric acid and glycerol, which mixture has a higher
surface tension than the parent substance, and so gives fewer drops per
3 c.c. The mixture is kept at about 38° C, and lots of 5 c.c. are removed,
cooled, and the drop number taken every 5-10 minutes, depending on the
activity of the lipase.

Time (minutes) .
Drop No.

0
120

5
120

15
113

25
109

35
101

49. Estimation of the Relative Lipolytic Activity of an Extract of
Pancreas.

Prepare a series of test tubes with 2 c.c. of the following dilutions of
1/20 Benger's Liquor Pancreaticus : 1/1, 1/2, 1/4, 1/8, 1/16, 1/32. Place a
seventh tube about the middle of the series and put in it 2 c.c. of the extract
of pancreas. Now add as rapidly as possible to each tube in order 5 c.c. of the
phosphate-tributyrin mixture used in the previous experiment. Immerse
all the tubes in a water bath at 38° C. for 30 minutes. Cool. Estimate the
relative surface tension of the mixtures by the capillary rise method (Experi-
ment 17 (2)), starting at the right, i.e. with the greater dilutions of the
enzyme. Suppose the unknown fluid rose in the tube just a little less than
in tube 3 but a little more than in tube 4, then the pancreatic extract would
approximately be in strength between 1/4 X 1/20 = 1/80 and 1/160 of the
liquor pancreaticus. One may then proceed as in the experiment above to
define the strength more accurately.

50. Chemical Gardens.

(a) Place 50 c.c. of potassium ferrocyanide in a glass jar or beaker and
add a small particle of ferric chloride (small pea). A semipermeable mem-
brane of ferric ferrocyanide (Prussian blue) is formed round the solid.
Endosmosis occurs and peculiar growths may be formed,

(6) 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 concentration
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 (see also Experiment 5 {a) ).

51. Leduc's Growths.

A small flat-sided jar, e.g a specimen jar, is filled with a 1-2 per cent,
solution of gelatin to which is added just enough potassium ferrocyanide to
give it a pale green colour. Just before the gelatin has set, a little seed

STUDY OF LIVING CELLS 545

made from a mixtiire of glucose and copper sulphate is planted on the bottom
of the jar. Within an hour, growth will be visible and may procood for
several days.

See Leduc, Etudes de Biophysique, I. Theorie Physico-Chimiqiie de la
Vie (1910) : TI. La BioIn(/ie Sijuthetique (1912),

52. 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.

53. Study of Living Cells.

[a) Amoeba. The large form may be found in water trickling from a
boggy spot. Collect some of the upper layers of ooze from the bottom of the
ditch or boggy runlet and leave for a few days in tall jars to allow the ooze to
settle. Pipette ofT the surface layer and transfer to a test tube containing
clear pond water with some green algae in it. The amoebae will be found on
the surface of the ooze.

Small amoibae may readily be obtained from garden soil by the following
method (Goodey, Nature, 1918). Boil some hay or grass in water. Filter.
Neutralise filtrate. Take 2-3 gm. of garden earth in each of several Petri
dishes and mix with the filtrate from the hay infusion to give a depth of
about 2-3 mm. of moist soil. Place in a good light and keep moist. After
2-3 days float some cover-slips on the surface of the fluid in the dishes. The
amoebae will attach themselves to the under surface of the slips. Remove
slips and rinse gently in water in an evaporating basin. Mount in a
hanging drop slide with a hair or thread placed below the slip to aid in
focussing.

Examine the slide. Select as large an amoeba as possible and make
drawings of it from minute to minute. Place a small drop of N/10 HCl at one
side of the preparation and note what happens. Now place 2 drops of
N/lO NaOH on the same spot and observe any changes.

Electrical stimulation. Use a slide with electrodes (Fig. 20) and attach the
electrodes through a short-circuiting key to the secondary coil of an induction
apparatus. Pull the coil well out, start the interrupter, and open the short-
circuiting key for a moment. If no change occurs, gradually push in the coil
and try again. Do not expose the amoeba to too strong or too long a shock or
it will be disintegrated.

(6) Blood corpuscles, (i.) 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 (/3) as to depth
of colour. Take a drop of the fluid from each and examine under the micro-
scope. Measure the diameter of a number of corpuscles and average those
from each tube.

(ii.) 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.

(iii.) Experiments similar to those detailed above for amceha may be
performed on the leucocytes.

■ B. 35

546

ILLUSTRATIVE EXPERIMENTS

54. Conditions Affecting Growth, etc.

To a test tube Jilled with a nutrient medium add 1 drop of yeast emul-
sion. (Nutrient mediimi contains the elements C, 0, H, N, S, and P, e.^r.Urea
CO(NH2)2, glucose CeHi^Oc, with traces of Na2HP04, and Ca3(P04)2.) Add
a similar drop to a test tube filled with distilled water. Shake the tubes
well and examine a drop of the mixtixre from each microscopically, counting
the number of cells in three fields ; take the average. Note the appearance
of the mixtures.

Student at bench (1). Insert a cork fitted with a glass tube into the test
tubes, and place them in the incubator at 37° C.

(2) As in (1), placing the tubes in ice.

(3) Introduce a few drops of pure phenol into each of the tubes, insert the
corks as in (1) and place the tubes in the incubator.

(4) Boil the mixtures, cool the tubes under the tap, insert the corks and
place the tubes in the incubator.

The tubes are left under these conditions for 24 hours.

Results. . Examine the tubes before and after shaking. A drop from each
tube is to be examined microscopically after shaking, counting the number
of cells in three fields ; take the average.

Record the results on the sheet provided, using the signs -(- and — .

Tubes witli sugar (l)\t 37° C.
Tubes with sugar (2) at 0° C.
Tubes with sugar (3) with phenol
Tubes with sugar (4) ^boiled .
Tubes with water (5)'at 37° C.

Gas

Opacity.

dumber.

Test (1) is also carried out in bulk, the yeast cells are removed by filtration.
Use some of the filtrate for the followmg tests.

(a) Disappearance of sugar. To about h in. of the fluid in a test tube add
an equal volume of Folin's copper sohition and boil for one minute. Note
the extent of reduction. Repeat, using the original nutrient medium. Com-
pare the reduction obtained with that obtained in the preceding test.

[h) Formation of alcohol. Some of the filtrate from (1) is distilled. Test
the distillate for alcohol. To about | in. of the distillate add a few drops of
Pot. bichromate and a little H2SO,, cone, warm.

Note. (1) Pungent odour, aldehyde. (2) Green colour.

Nature of the gas evolved. Fill a test tube with the nutrient medium, and,
covering the mouth of the tube with a coin, invert it into a dish containing
nutrient medium ; care must be taken to avoid entrance of air bubbles into
the tube. Introduce a piece of yeast about the size of a pea so that it comes
to lie in the mouth of the inverted test tube, which is now allowed to rest on
the dish. Su})port the tube by means of a burette stand and place in the
incubator at 37° C. for 24 hours.

With the mouth of the tube still beneath the surface of the fluid in the dish,
introduce into the tube a few cubic centimetres of 40 per cent. NaOH using a
bent pipette.

Conclusions. (1 ) What has happened to the yeast cells in each of the tubes ?

(2) What conclusions do you come to as to the influence upon the yeast
})rotoplasm of the various conditions to which it has bean subjected ?

ULTRA-VIOLET LIGHT 547

(3) Where does the yeast protoplasm get material for growth ?

(4) Wliero (loos veast ])r(it()plasm get the energy for growth ?

55. Mimicry of Cell Structure (Herrera after Harthig).

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 l-02() may be
used instead of colloidal silica.) At one edge of the crystallising dish place
10-20 mgrm. of recrystallised potassium bifluoride. At the diametrically
opposite side of the dish place 5 gm. pure powdered anhydrous calcium
chloride. Cover and keep at 20° C. for 24 hours. Various structures which
nuiy be stained by any of the dyes used by histologists may be seen, '.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 JFormation of a colloid, calcium silicate and a crystalloid, calcium
fluoride. Silica, coagidated 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 complexes
lying near the point of insertion of the CaCU. Add a trace of alcohol over
the CaCU. and more ra]5id diffusion ensues.

56. Action of Ultra-violet Light.

The light used is passed through a Wood's filter which cuts ofT all the
visible rays. Caution must, therefore, he exercised to prevent any of the direct
rays from enter inq the eye. If an adequately screened lanij:) like the K.B.B.
microscope lamp is used, goggles need not be worn. With unscreened lamps
thev are essential.

(a) To render the rays visible. Thin glass test tubes may be used, but
better results are obtained with flat-sided quartz vessels. Place vessels
containing solutions of fluorescent substances in the rays and about a foot
away from the Wood's filter. Try quinine, eosiu, fluorescein, and dilute
hsematoporphyrin.

It is interesting to note the beautiful fluorescence obtained with " natural "
pearls and the absolute lack of it with imitations. " Cultured " pearls vary.
They all fluoresce, and some of them are almost as fluorescent as the " natural"
pearl.

{h) Bleachina effect. Expose the following solutions for one minute at 1 ft.
from the lamp. Acetone-methylene blue, 20 per cent, potassium ferro-
cyanide, carbon-tetrachloride -f potassiimi iodide. Rays below 2,650 A°
cause the liberation of nascent chlorine from the tetrachloride. The chlorine
replaces the iodine in the KI. The iodine thus set free gives the tetrachloride
a reddish violet tinge.

Filter paper if soaked in potassium ferrocyanide is bleached, and if soaked
in paraphenylenediamene nitrate turns violet on exposure to the short rays.

(c) Schanz' experiment. A dilute solution of egg albumin exposed for an
hour in a quartz vessel close to the lamp (within 5 cm.) is so changed in
colloidal state that it acts to half-saturation with ammonium sul])hate like a
globulin, 'i.e. it tends to lose its emulsoid character and become more like
a suspensoid. It ceases to protect gold (Experiment 37).

{d) Effect on enzymes. Expose an active solution of any of the digestive
enzymes for an hour near the lamp and comy)are their activity with that of
some of the unexposed solution. Maltase reacts very rapidly.

35—3

548 ILLUSTRATIVE EXPERIMENTS

(e) Effect Oil Cyclops quadricornis. Place one or two of these pond crus-
taceans in two Petri dishes containing the niinimuni amount of tap water.
Cover one dish with a 26-oz. glass. Note movements. Now place both
dishes below the lamp so that they are equally radiated. Note the time. At
first mobility in the uncovered dish is greatly increased. Soon, liowever,
movement is gradually slowed down and stops in less than 1-2 minutes.
Note time. The cyclops in the covered glass should now receive attention.
They live eight or nine times as long as the uncovered ones. Glass, therefore,
cuts off some of the abiotic radiations. If vita-glass or other similar glass is
available it is instructive to cover a third Petri dish with it.

(/) Effect on living skin. Cut three holes of various patterns in line on a
piece of thick brown paper. Clean a part of the back of the arm with spirit
soap and dry wnth methylated spirit. Fix the brown paper over this part of
the arm with rubber bands. Cover hole No. 1 with a thin layer of vaseline ;
leave No. 2 uncovered, and cover No. 3 with either one layer of muslin or a
piece of vita-glass. Expose to the rays at a distance of 1 metre for two
minutes. Remove the paper and examine the arm immediately and one hour
afterwards. Compare notes next day with the rest of the class. Does
the colour of hair and eyes have any influence on the amount of erythema
produced ?

57. Indicators of Potential Difference.

Two of the more common indicators of the existence of a potential
difference between two points have been considered in detail, viz. the
capillary electrometer (on p. 50, Experiment 21) and the string galvanometer
(Chap. XXVI.). If the potential difference is sufficiently great or if it is
amplified (one valve resistance-capacity amplifier) it may be demonstrated
and measured by an ordinary mirror galvanometer. A wireless head-
phone or, if two or three valves (resistance-capacity coupled) are used
in series, a loudspeaker makes a very efficient detector of differences of
E.M.F.

58. The current of injury, etc., of muscle (pp. 152 and 179) 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. 107 and Experiment 23). By moving the jockey along the slide wire
(E-^-R.) 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.

59. The Membrane Potential of the Skin of an Apple.

Select an undamaged apple. With a cork cutter remove a small circle of
skin from one side. Place the apple whole side downwards in a Petri dish
containing some OT N . KCl solution. A non-polarisable electrode is placed
in this solution in contact with the apple. The other similar electrode is
brought into contact with the upper cut surface of the apple, taking care not
to touch any of the skin. Lead these electrodes to a capillary electrometer
or to a sensitive mirror galvanometer. The damaged portion is, of course,
the negative pole.

60. Model of Mucoid Secretion. (Fischer.)

Grind up in a mortar a small quantity of gum acacia and 1 or 2 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.

liLOOl)

549

61. Model to Illustrate some Phases of Urine Formation. (Fischer and
MiicLaughliii.)

Prepare some cujjs of .sodium stearate l)y ])Ourin<f the liot stearate sohitioii
(1/10 molar) into a moidd consisting of one beaker (120 c.c.) suspended within
another similarly shaped (350 c.c). A cup is supported on a filtration 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 hours), (6) molar sodium
oleate (24 hours), (c) NaCl 1/8 M., 1/4 M., and 1/1 M. (3-6 hours), [d) 1/8 M.
CaCl.2 (1-4 hours), (e) 1/8 M. NH^Cl (7 hours).

Note increased flow with (c) and {d) ; initial increase and final decrease
of flow with (e) and total inhibition W'ith [h). Test, in each case, the per-
fusion fluid, the perfusate and the cup, with phenolphthalein. How do
you account for your results I Test the perfusates for fatty acids. Why
does pure water dissolve out more of the acid than do the salt solutions ?

62. Specific Gravity of Blood.

Make up a series of solutions of sodium sulphate or of mixtures of benzene
and chloroform to give specific gravities ranging from 1-04 to 1-07. Puncture
the finger (use a sterile blood lancet, i.e. one with a flat .sharp edge and not a
sewing needle) and allow a drop of blood to fall into each tube of liquid.
f)ee that the drop pierces the surface of the liquid. Note in which tube the blood
drop remains suspended or sinks verj' slowly. The specific gravity of the fluid
in that tube is equal to or almost equal to the specific gravity of the blood.

Preparation of (a) Sodium sulphate solutions.

Specific gravity .

1-04

1-045

105

1-055

1-06

1-065

1-07

Grams Na^SO.^ in 500 c.c.
water

of

50

55

70

85

90

95

100

(6) Benzene and chloroform mixture. Make a mixture of chloroform and
benzene of specific gravity 1-07. Stir in benzene to get the smaller values of
the specific gravity.

Another method. Place the mixture of chloroform and benzene with a
specific gravity of 1 -07 in a urinometer tube. Drop one drop of blood from the
finger into the tube. If the drop floats add benzene and stir with a glass rod.
Continue addinti benzene and stirring till the drop of blood neither floats nor
sinks. The specific gravity of this mixture taken with a hydrometer is the
specific gravity of the blood under test.

63. Haemolysis (see also Experiments 53 (6) and 64).

(i.) Mix a drop of your blood with a drop of distilled water on an uncovered
microscope slide and observe. The corpuscles swell up, burst and liberate
haemoglobin.

(ii.) Repeat, using instead of water some fat solvent like ether, chloroform etc.

(iii.) Repeat, using a capillary active substance in dilute solution, e.g. bile
salts, saponin, etc.

64. Estimation of the Fragility of Human Red Blood Corpuscles.
Twelve clean small test tubes (4 x ^ in.) are placed in a row in a rack and

numbered from left to right 25, 24, 23, 22, 21, 20, 19, 18, 17, 16, 15 and 14.

530

ILL USTRA TI VE EXPERIMENTS

With a pipette drawn to a fine point put into each tuhe the number of drops
of 0-5 per cent, sodium chloride indicated by the figure on the tube. Rinse the
pipette thoroughly with distilled water. Using the same pipette, add 1 drop
of distilled water to tube 24, 2 drops to tube 23, and so on, till 11 drops are
put into tube 14. Mix. That is, there are now 25 drops of fluid in each tube,
giving a graduated series of percentages of NaCl. Thus :

Tube No.

25

24

23

22

21

20

Per cent. NaCl

0-5

0-48

0-46

0-44

0-42

0-4

Tube No.

19

18

IT

16

15

14

Per cent. NaCl

0-38

0-36

0-34

0-32

0-3

0-28

Add 1 drop of blood (0-1 c.c.) to each tube. Allow to stand at room
temperature for 1-2 hours. The test is recorded by + signs, + + + repre-
senting complete haemolysis, -\ — |- partial and + initial haemolysis. The
dilution in which there is just a slight haemolysis is noted as the point of initial

haemolysis. Complete haemolysis is
indicated by the absence of intact
corpuscles at the bottom of the tube.

65. Determination of the Relative
Viscosity of Blood (see Experi-
ment 31).

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. The
viscosimeter (at body temperature) is
held vertically under the bleeding
spot and the receiver filled (Fig. 110).
Measure as in Experiment 31.

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.

66. Clotting Time of Blood.
Thoroughly clean two watch

glasses (1-J- in. diameter).
Clean the lobe of the subject's ear with ether and puncture it with a sterile
lancet. Allow a large drop of blootl to fall on to one of the watch glasses (as
the blood falls set a stop watch going). Add a small lead shot to the blood
and cover by inverting the second glass over the first one. Rock the glasses
gently and note that, with increasing viscosity of the blood, the extent of
movement of the shot is diminished. When the shot ceases to move, stop the
watch and note the time taken for the blood to clot. Repeat.

Fig. 110. — Deiiniiisx- Watson cliiiiral visr-osiinctrr
(Iliiirk-yh'H).

ALKALI RESERVE OE BLOOD 551

(37. Bleeding Time.

Clean the lobe of the ear with ether and puncture with a sterile lancet. As
the first drop of blood appears, start a stop watch goinj?. Using the edge of
a circle of filter paper, remove the drops of blood as they form. Note the time
when no further drop appears.

Repeat. Compare the clotting time and the bleeding time of the same
subject.

(kS. Haematocrite.

This apparatus consists of two similar graduated capillary tubes, which,
after clipping in a holder, may be spun horizontally by a centrifuge. A
small measured quantity of Midler's fluid (Na2S04 - 1 gni. ; K2Cr.07 - 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 8,000 revs, per minute.
Read off the relative length of the column of corpuscles. As the glass
walls of the tubes are thick, it is advisable to aid the eye by looking along
a glass plate held at right angles to the tube. The tube^^have a bore of one
square millimeter and are divided into 100 equal parts. The reading multi-
plied 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.

69. To Demonstrate the Effect of the Tension of COo on the /)H of a
Solution of Bicarbonate.

Put 5 c.c. of a 0-25 per cent, solution of NaHCOa in each of three tall
sto})pered cylinders. To each add 2 drops of neutral red. Fill (a) with air
expired after a deep inspiration, (6) with alveolar air ( Experiment 70 (6) ) and (c)
with COj; from a generator or cylinder. Stopper and shake. Note colours.
Remove the COg 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 CO2 was added.

70. Determination of the Alkali Reserve of Blood.

(a) An approximate method. (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. Ten test tubes (8 in. X 1 in. or thereabout) cleansed thoroughly and
dried are set in a rack. The first or stock tube is charged with 9 c.c. of a
0-85 per cent, solution of NaCl (pure salt in distilled water) and 1 c.c. of
whole b'.ood (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 cubic centimetre of the diluted blood is placed in the bottom of each
tube, avoiding the sides, and then, starting on the left, N/lOOHCl is added
from a graduated pipette. The first is given 0-75 c.c. acid, the next 0-8 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.

552

ILL USTRA TI T E EXPERIMENTS

For example: Normal blood — the first six tubes {i.e. 0-75 1 c.c.) are
clear, tube 7 shows scattering and slight haemolysis. Therefore (>1 c.c.
of blood can neutralise 1 c.c. of N/100 acid, or 100 c.c. of blood contains
base equivalent to 0-84 grams NaHCO;^. This would, in Van Slyke's apparatus,
give rise to 224 c.c. of '" bound " COg — a somewhat high result (see p. 334),
due probably to interaction of acid and protein and to the buffering action
of the oxalate.

In using this method for the determination of the alkali reserve of human

blood, the endosmotic effect of the dilu-
tion of the blood by the acid ma;f* be
neglected as the salt concentration does
not fall to a value low enough to affect
the fragility of the corpuscles. It is ad-
visable, when sheep's or rabbit's blood is
used, to make up the acid in 0-75 per
cent, sodium chloride. It is also essential
to see that, if the blood is not used
immediately it is shed, that it is kept in an
ice chest and is brought to a tension of
COo equivalent to alveolar tension. (See
Van Slyke's method below.)

(b) Alkali reserve. (C. J. Martin.)
Principle. Dilution of a well-buffered
solution such as plasma does not alter its
C^. 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
(100-1.50 c.c).

Method. The flask is removetl 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 pH — 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 cent, (alcoholic)
neutral red. The optical effect of the turbidity of the plasma may be counter-
acted by placing a sheet of white tissue paper behind the tubes. The plasma
mixture is titrated with N'50HC'l (2 c.c. burette with fine nose) till its colour
matches the stantlards. Tliis is done by running the plasma into the flask,
adding a few drops of acid and rotating gently but steadily for 1 minute, the
flask meanwhile being in communication with the air. This readily allows
the thin film of plasma to give up the liberated COo. The fluid is run back
into the tube and compared with the standards. The process is repeated as

VlH. 111. — Apparatus for cstiinalidii of
carbonates in solution.

FREE AND HOUND CO^ 553

often as necessary. Rotation for (it Inisl 1 minute is necessary after each
addition of acid.

Titration value for 0-5 c.c. [)lasma = 0-77 c.c. N/50H('l,
i.e. Alkali reserve of ,, ,, = 0-77 c.c. N/SONaHCOa

100 c.c. ,, = 154 c.c.

= 3-08 N

= 3-08 X 224 c.c. CO2,
i.e. 68-99 volumes per cent, of CO2 are bound as bicarbonate in the plasma.

A sharper end-])oint is obtained liy the use of ])henol sulphonephthalein as
indicator. In this case the standard phosphate solutions are made of pH 7-2
to correct the protein error.

(c) Alkali reserve by Van Slyke's method. The Van Slyke ap])aratus is
illustrated in Fig. 111. It consists essentially of a 50 c.c. pipette with three-
way sto})COcks (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.

Prelim innry preparation. Open taps e and / and fill the entire apparatus
with mercury by raising the levelling bulb, allowing some mercury to run into

/l^oi/r/z-p/ecc.

S/IMPL/A/G TUBE.

riG. 112. — Alveolar air collecting tube.

a and into h. 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 present, open e, and force the gas out, and repeat the evacua-
tion process, opening/ alternately to c and d.

Determination. (1) Solutions refpiired. It is convenient to have four
dropping bottles with ground in ])ipettes and rubber teats containing
(a) 5 per cent. H2SO4, (6) 1 per cent, carbonate-free NII3 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 of¥, and the excess of
barium remaining is precipitated with a little {NH4)2S04.

(2) Plasma. An ordinary centrifuge 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 tliis 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 centrifuge at once. The

554

ILL USTRA TI VE EXPERIMENTS

plasma is then transferred to sampling tubes (Fig. 112), 3-4 c.c. of plasma to
each tube. These tubes (3UU 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 COg tension
with the alveolar air.

(3) Procedure. The apparatus is
entirely filled with mercury, including
the two capillaries (a and stem of b)
at the top. The cup b is washed with
COo-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. Ill) 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. HoSOj 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 80 cm. 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 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 open /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.

Cleanivg. Lower the reservoir and run )i)ost of the mercury back through c.
Open/ to d and, by raising the reservoir, run the water back into the pipette.

''10. 113. — Van Slyke mii-ro apparatus

BLOOD I'RESSVRE MODEL

SSi'S

Open e to a and force the fluid out into a collecting jar. Tlie a]>[)aratus is
now ready for another determination.

{d) Micro appamfua (Fig. 113). This apparatus is easier to iuaiii|)ulate, and
as water, etc., never enters the gas pipette, it is easily kept clean. The
different parts are in the same relative pro{)ortions as the corresponding
parts of the larger apparatus. Each division of U-U02 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.

(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 Huid is
used.

Calculation of Results.

Table for Calculation of CO2-C0MBINIXG Power of Plasma
(from Van Slyke and Cullen).

Observed VoL x

B

760'

C.c. of CO 2. Reduced to X.T.P. bound iU
Bicarbonate by 100 c.c. of plasma.

15' C.

•20° C.

0-2

9-1

9-9

0-3

18-8

19-5

0-4:

28-4

29-0

0-5

38-1

38-5

0-6

47-6

48-1

0-7

57-4

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.

71. Blood Pressure Model.

(a) Goieral distribution. Examine the schema (Fig. 114) of the circulation
given you and identify the parts representing 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 of¥ in millimetres of water may be
calculated in millimetres of mercury.)

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 alteration
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

556

ILL USTRA TI VE EXPERIMENTS

the effect of this upon the arterial and venous ])ressures. »Study tlie further
effect of constricting D.

{(■) Place a finger on A and note the expansion with each contraction of H.
Study the same thing on D and on F.

72. Vowel Sounds by Percussion.

Place the mouth in the position necessary for the pronunciation of the
various vowels and then percuss over the cheek (Fig. 96\ 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 demonstrates the double nature of the mouth cavity in
producing E and I (Fig. 97).

73. Prepare a series of bladders filled completely w^ith (a) air, {b) water
and (c) some viscous Huid like svrup and (rl) lard. Percuss and pal])ate each.

74. 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

Arterial BP

Veins Splanchnic area

Helrt
H

Fig. 114. — Schema of the ein-ulatioii.

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.

75. The Kata-thermometer.

The instrument is fully described in Chap. XXXIL Before attem])ting
to use it the student should study the description and the theory outlined
there.

Cautions, (i.) The bulb is very fragile, and should be handled carefully.
With reasonable use the kata-thermometer should have a life as long as an
ordinarv thermometer and longer than a clinical thermometer.

(ii.) The kata-thermometer should never be put into boiling water and
should never be left without attention in warm water.

Method, (a) See that there is a eontinuous thread of spirit in the stem
reaching from bulb to upper reservoir (see text, Chap. XXXIL). Dry the
bulb.

(6) Hang the instrument by a thin cord to a stand (a wooden filter stand
answers well) and start a stop-watch when the meniscus reaches the upper

PREPARATION OF COLLODION MEMBRANES 557

mark. Stop the watch whon tho nionisnis reaches the lower mark. Note the
interval of time.

(c) Repeat the experiment, wanniiiii the hull) as in (a).

(r/) Repeat as in (c).

If the readings are reasonably consistent average them and calculate the
heat loss as in Chaj). XXXII.

(e) Put on the silk thimble and repeat {((), {!>), (r) and (d). tSee text.

PREPARATIONS

76. Water for Faraday-Tyndall Phenomenon.

Store a large volume of glass-distilled water in a paraffin covered jar
stoppered with a paraffined cork through which jiass two tubes, viz. a syphon
delivery tube reaching only one-third of the way down inside the jar, and an
air inlet tube protected by a plug of glass wool. The water should stand
undisturbed for at least three months before use.

77. Collodions.

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 Aci<l 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.) 7-5 c.c. of ethyl
ether are poured on .3 gm. of gun-cotton in a wide-mouthed stoppered bottle
as above. After 10-15 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.

The permeability of collodion ineuibraues may be standardised for any
particular make of collodion by standardising the conditions under which they
are freed from ether and alcohol. Permeability can be increased by allowing
the collodion membrane to set in a moist atmosphere or under a bell-jar
whose content of air is saturated with alcohol, or, better still, acetone vapour,
before immersion of the fihn in water. Another and more reliable method of
attaining the same end is to add a less volatile constituent than ether and
alcohol to the stock solution, and, during the pre-immersion period, evaporat-
ing completely the volatile solvents in a dry atmosphere. The formula for
such a solution, due to Pierce, is as follows : Stock solution, 1 gm. nitro-
cellulose, X c.c. ethylene glycol, 25 c.c. absolute alcohol and enough anhydrous
anaesthetic ether to make 100 c.c. The permeability is controlled by varying
the amount (x c.c.) of the ethylene glycol from 0-5 c.c. for the least permeable
membrane (about 0-02 c.c. of water per cm." per min.) to 15 c.c. for a mem-
brane giving a filtration rate of about 0-5 c.c. per cm.^ per minute.

78. Preparation of Collodion Membranes.

Membranes are easily made in any size or shape, and, as they are trans-
parent, are very convenient for general use. They are, as ordinarily prepared,
unsatisfactory for the dialysis of whole blood or of bile.

(i.) To cover a vessel siuular to a Grahcun diahjser. 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

558 ILL USTRA TI VE EXPERIMENTS

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 in. 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 tlie 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 ')iot 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 treat-
ment 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,
is filled with collodion sol, care being taken to pour the fluid slowli/ 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

PARCHMENT DIALYSERS 559

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 lit 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 degrees 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.

79. Parchment Dialysers.

Parchment 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 2 in. 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 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 parchment
Biay 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 in. 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 ilat in lengths
of about a metre and are very easily damaged. They are best kept hanging

560 ILLUSTRATIVE EXPERIMENTS

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 \ in. from the opening. Bend the tube into U-t^hape 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.

TYPICAL COLLOIDS
(a) SOLS

80. 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 OT 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. maybe 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 adtl more hydrazine. If it is greenish, too much
hydrazine has been added.

"(2) Gold Sol for Colloidal Gold Test. 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 2-5-3 c.c. N/5 pure KX'Oo. Bring to the boil, stirring
vigorously. Add gradually, but not too slowly, 2-3 c.c. of 1 per cent,
commercial formalin (1 c.c. 40 per cent, formalin 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 C^ of Colloidal Gold. Take a series of small test
tubes of equal bore, etc., and range them in two equal rows. Into each
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 HCl as the
case may be.

81. Colloidal Iron (Experiment 26 (d) ).

Heat 250 c.c. of distilled water in a 500 c.c. Erlenmeyer flask or in a tall
beaker flask. When the water is boiling vigorously, place the burner a little
out from the centre of the flask so as to produce a rotatory movement of
the water. Add to the boiling water, drop by drop, 1 c.c. of a 30 per cent,
solution of ferric chloride. The liquid turns a clear reddish brown colour.

PREPARATION OF COLLOIDAL SOLS 561

The sol contains 2-2 millimoles per cent, of hydrochloric acid from the 0-3
gm. of FeCl.,. Most of this acid can be removed by dialysis. Caution. Do
not push dialysis too far or the sol will undergo coagulation. The un-
dialysed sol may be used for the experiments on cataphoresis, diffusion,
precipitation and protection. The dialysed sol or B.P. dialysed iron are
necessary for the experiment on mutual precipitation.

82. Sulphur Sol.

(i.) Ode'n's. Prepare 100 c.c. of 2N (approx.) sulphurous acid by titration
against phenolphthalein. Pass clean H2S for an hour or so through it and
continue till the smell of SO2 has practically disappeared. Allow the fluid
to stand for 24 hours and then decant off the milky yellow supernatant sol.
Before use dilute the sol 100 times with distilled water.

(ii.) A sulphur sol may be prepared by neutralising a very dilute solution
of ammonium sulphide with hydrochloric acid.

83. Purple of Cassius.

Add a few cubic centimetres of a 0-01 per cent, solution of stannous
chloride to a 0-05 per cent, solution of gold chloride. The stannous chloride
reduces the gold chloride (cf. tannic acid and formalin), producing colloidal
gold, and itself being converted in the process to the stannic form. The
colloidal stannic amdioTxned from this is a hydrophilic colloid and " protects "
the gold. The purple-red colour is, therefore, due to an adsorption complex
of gold and tin.

84. Gelatin i per cent. Sol.

(a) Free the gelatin from the bulk of extraneous matter by immersing it in
a large bulk (about 100 vols.) of cold distilled water. Change the water
several times.

(b) Boil about 75 c.c. of distilled water for every 100 c.c. of sol required.
Remove the flame and add the cleaned and sivollen gelatin as free as possible
from wash water. Stir continuously till the gelatin has completely dissolved.
Cool.

(c) When quite cold stir in the amount of distilled water necessary to give
100 c.c. or whatever multiple of 100 c.c. is desired. Accuracy may be obtained
by first weighing the beaker, then beaker plus cooled contents, and so arriving
at the weight of additional water necessary.

85. Starch i per cent.

{a) Put the weighed potato starch in a mortar, and, adding small quantities
of cold water at a time, grind into a smooth thick cream.

(6) Gradually stir in about half of the total volume of water required to
make a 1 per cent. sol. This water should be fairly warm, but not hot.

(c) Dilute to about twice its volume with warm water.

(d) Boil on a sand bath for half an hour to convert dispersoid to a true
colloid.

(e) Cool, and when cold make up to the desired volume with cold water.
(/) Filter through a well washed grey paper.

{g) Cover the surface with a thin film of toluene to prevent rapid bacterial
infection.

86. Gum Mastic.

One to five grams of gum mastic are placed in a medium-sized mortar and
dissolved by trituration with repeated amounts of 96 per cent, alcohol. The
solution is made up to 100 c.c. with alcohol and filtered ; 10 c.c. of this
solution are placed in a 500 c.c. beaker and 200 c.c. of distilled water added
at once in one portion. Filter and allow to stand for about an hour. Use
the upper two-thirds of the suspensoid.

562 ILLUSTRATIVE EXPERIMENTS

87. Silicic Acid Sol from Water-glass.

Dilute some " water-glass," "" keep-egg" or other commercial preparation
of the same nature with enough freshly boiled (CO2 free) distilled water to
reduce its specific gravity to 1-16. This stock solution can be kept for years
in a wide-mouthed bottle closed by a rubber bung or a well-vaselined glass
stopper.

To prepare a sol (Hatschek) dilute 30 c.c. of concentrated hydrochloric
acid (1-2 specific gravity) with 100 c.c. of water, and pour 75 c.c. of the stock
sodium silicate solution info the dilute acid. Dialyse the mixture in a parch-
ment bag against repeated changes of water. Caution. Do not push the dia-
lysis too far or the sol will set to a gel.

The sol should be perfectly clear and colourless, and absolutely free of any
bluish tinge (which is indicative of impending gelation). The sol may be
kept in wide-mouthed bottles as above. It is very sensitive to COo, either free
or bound.

88. Coarse Suspensions.

Gamboge, Indian Ink, Chinese Ink, etc. A small quantity (1-2 gm.) of the
block is placed in a mortar and ground with a few cubic centimetres of w^ater.
The resulting mixture is diluted with a large volume (500-1,000 c.c.) of water.
The coarser particles are removed by filtration.

89. (i.) Egg White Solution (from Eggs).
[a] Separate white from yolk.

(6) Beat white to a foam and allow to stand.

(c) Remove membranous foam from the clear fluid below.

(d) Add 0-9 per cent, solution of sodium chloride to make the volume
five times the volume of (c).

(e) Add 300 c.c. of water slowly, stirring regularly.

(ii.) Egg Albumin Sol (from commercial dried egg albumin). Put 10-15 gm.
of the commercial albumin ex ovis crushed in a coffee mill or large mortar
into 100 c.c. of w^ater in a bottle and leave overnight to allow of imbibition.
Add 5 drops of 1 per cent thymol in chloroform and put the bottle on a me-
chanical shaker to break up most of the larger lumps. Leave standing a few
hours to let the larger lumps settle. Filter through a large glass funnel with
a short stem into which has been placed a plug of cotton-w^ool. This filtration
will require twelve hours or more, but should yield a yellowish opalescent
fluid.

A more economical but more tedious method is to add the dried egg white
to the w^ater in small portions, stirring regularly and attempting to break up
the lumps with the glass rod.

90. Finely Divided Suspension of Protein for Use in Experiments on
Proteolytic Enzymes.

(i.) Take a measured quantity of sheep's blood serum and dilute it with 15
volumes of distilled w^ater. Add 10 per cent, sulpho-salicylic acid solution
until the mixture imparts a faint violet tint {not blue) to Congo red paper.
At this point the diluted serum appears a homogeneous white due to the fine
permanent suspension of protein produced.

(ii.) Milk, centrifuged and filtered from fatty particles through wet paper
is a very sensitive substrate for proteolytic enzymes.

(b) GELS

91. Egg Albumin.

(i.) If at {e) in Experiment 89 (i.) the 300 c.c. of water added to the sol
were boiling, a fine suspension of coagulated egg white would result.

PREPARATION OF GELS 563

(ii.) For Mett'fi tubes. Suck up some of sol 89 (d) or undiluted blood seruiu
stained with methylene blue or gentian violet into capillary tubes (about
2 mm. bore). See that the aspirated sol is free from air bubbles. Lay the
tubes horizontally on a piece of gauze, wrap them and tie the gauze into a
bag. Immerse the tubes in water (whicli has been boiled and allowed to
cool to 85° C.) for 2-3 minutes. Cool and dry the tul)es on filter paper. Dip
the extreme ends in melted paraffin to seal the tubes. When required cut
the tubes into lengths of about 1 cm., discarding about 1 cm. from each end.

92. Concentrated Gelatin.

Sheets of Coignets "Gelatin A" washed for 48 hours in three changes of
ice-cold water acidified to ^H 4-6 originally (falling to 4-9 eventually).
Warm (below 60° C), and it dissolves in its own water of imbibition. Keep
liquid under 40 c.c. Add some toluene as preservative.

93. Non-polarisable Electrodes.

Brush electrodes of FleiscM (for Experiments 54, 55, etc.). The electrodes
consist of glass tubes (4 cm. x 5 mm.). In one end fits a perfectly clean
camel's-hair pencil, and into the other dips a well-amalgamated rod of zinc
with a binding screw at its free end. A piece of indiarubber tubing fits as a
cap over the upper end of the tube, holding the zinc rod in position.

Preparation of the electrode. Make a paste of kaolin, using normal saline
solution as the moistening agent. Pack the paste into the tube to cover the
fixed end of the brush and to give a layer of about ^ cm. in thickness.

(At this stage in the preparation the electrodes are placed in normal saline
solution until required for use.)

When required the tubes are filled with a saturated solution of ZnS04 and
the zinc rods are inserted.

■M—-J.

564

ILLUSTRATIVE EXPERIMENTS

CONVERSION FACTORS

94. Graphic Conversion of Sorensen's />H( — log (H) ) into Concentrations
of Hydrogen Ions and the Reverse (Roaf, Journ. of Physiol.).

Fig. 115 is a graph whereby the logarithmic notation of Sorensen 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

[H-] or C„ = 10 ■" - log [H-] or pH = » + . . .
Fig. 115. — Graph for conversion of pH to (' ^^.

to two places of decimals For example, to convert yjHG-T into C„, p\i — 6,
i.e. C„ = 10^ ; 0-7 cuts the diagonal line opposite 0-2 ; therefore

/;Hof fi-7 = C„ of ()-2 X 10-«.

95. 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 determination of the skin surface in most metabolism
experiments.

SURFACE AREA OF BODY

565

8iiu-e the surface of a figure varies as the square, and that of volume as the
cube of its linear dimensions, it follows that

S = K VF,

where S = surface, F = volume and K = constant, or, as weight (W) varies
directly as volume,

S = K l/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.

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 snuill to be flat, was photographed upon

?00
ISO
ISO

: 170

^ 130

110

100

IS

1-6

'^

\

^!

\

\

^0

V

^'J

^

V

\

\

12

13

1-4

\

S

\,

\

\

N,

\

S

N

V,

N

\

X

\

\

s

II

V

V

\

\

\

S,

\

\

\,

X

N

X

N

N

N

^

^

\

V

\

\

s

s.

\

S

\

\

N

\J

\

v?0

^il

V

\

\

\

s

N

Ad

N

N

N

\

\

'\

vL'

\

\

v

\,

\

\

s

\

s

V

V

\

•^17

^18

^r-''

5

V

\

\

\

\,

N

•s

N

X

\

^^

»l 6

S<!^

.^

\,

\

\,

\

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S

kl.3

14

IS

V^

k

\

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k

II

S^2

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<>^,

30

SO 60 70

Fig. 116. — Du Bois graphs for estimating tlie area of body-surface.

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
liave evolved a two-measurement formula on which the appended chart is
based (Fig. 116).

Sundry Conversion Factors

Length

Area

Volume

Weight

Force
Velocity

Inches to centimetres

Square inches to square centimetres

Cubic inches to cubic centimetres

Gallons to litres

Ounces to grams

Grains to grams

Pounds (avoirdupois) to kilos .

Poundals to dynes

Pounds weight to dynes

Miles per hour to centimetres per second

Multiply by
2-54.
64516.
16-387.
4-546.
28-349.
0-0648.
0-4536.
13,825.
4-45 X 105.
44-70.

566

ILL USTRA TI VE EXPERIMENTS

68,971.
14-7.

1-0132 X 106.

043.

0-01602.

10'.

4-19.

0-4266.

0-1382.

1-356.

0-102.

746.

76-04.

Pressure . . Pounds per square inch to dynes per

square centimetre ....

Atmospheres to pounds per scpiare inch .
Atmospheres to dynes per square centi-
metre ......

Head of water in feet to pounds per square
inch ......

Density . . Pounds per cubic foot to grams per cubic

centimetre .....

Energy . . Joules to ergs (1 erg = 1 dyne per second)

Gram-calories to joules
Gram-calories to kilogram-metres .
Foot-pounds to kilogram-metres
Foot-pounds to joules ....

Power . • (1 watt = 1 joule per second = 1 volt-

ampere.)
Watts to kilogram-metres per second
Horse-power to watts ....

Horse-power to kilogram-metres per second
1 B.T.U. = power of 1 kilowatt for one hour.
= 3-6 X 10^ joules.
= 8-59 X 10^ gram-calories.
German candles to English candles . . 1-25.

Thermometers. To convert degrees F. into degrees C, deduct 32 and
multiply by 5/9. To convert degrees C. into degrees F., multiply by 9/5
and add 32.
1 litre of oxygen at 0° C. and 760 mm. weighs 1-429 grams.
1 litie of carbon-dioxide at 0° C. and 760 mm. weighs 1-965 grams.
1 litre of nitrogen at 0° C. and 760 mm. weighs 1-254 grams.
1 litre of air at 0° C. and 760 mm. weighs 1-292 grams.
1 litre of hydrogen at 0° C. and 760 mm. weighs 0-900 gram.
1 litre of water vapour at 0° C. and 760 mm. weighs 0-8132 gram.
1 gram of protein = 966-3 c.c. oxygen intake and 773-9 c.c. of carbon-dioxide

output.
1 gram of fat ~. 2019-3 c.c. oxygen intake and 1427-3 c.c. of carbon-dioxide

output.
1 gram of starch = 828-8 c.c. oxygen intake and 828-8 c.c. of carbon-dioxide

output.
1 gram of urinary nitrogen = 26-51 Calories.

= 5-91 litres (8-45 grams) of oxygen.
=E 4-75 litres (9-35 grams) of carbon-dioxide.
IjU. = 1 micromillimetre = 10"^ mm.
Ifxix = 1 millimicrometre = 10"^ mm.
1 A = 1 Angstrom unit = 0-1 /x/x = 10~' mm.

567

SOME PRACTICAL HANDBOOKS

General.

Bayliss. '■' Introduction to General Physiology." Longmans, Green
& Co.

Physical Chemistry.

MiCHAELis (trans, by Parsons). " Practical Physical and Colloid
Chemistry for Students of Medicine and Biology." Heft'er.

Kerridge. ■■ Principles of Physical Chemistry for Medical Students."
Oxford Medical Publications.

Cocking. "jaH Values. What They Are and How to Determine Them."
British Drug Houses.

Colloids.

Hatschek. " Laboratory Manual of Elementary Colloid Cliemistry."

J. & A. Churchill.
OsTWALD (trans, by Kugelmass and Cleveland). " Practical Colloid

Chemistry." Methuen.

Special Senses and Experimental Physiology.

Anrep and Harris. " Practical Physiology." J. & A. Churchill.
Cathcart, Paton and Pembrey. " Practical Physiology." Arnold.

Chemical Physiology.

Hawk. " Practical Physiological Chemistry." J. & A. Churchill.
Cathcart. Li "" Practical Physiology " {il)id.).

Histology.

Watson. '" Handbook of Histology." Livingstone.

NAME INDEX

{Befercnces (o Part II. are m iialia^.)

I

Abel, 88

Abney, 14

Adam, 52, 175

Adrian, 232, 234, 235, 241. 242, 248, 264,

288
Aeb3% 346
Amar, 213, 497
Angelucci, 287
Anrep and Harris, 405, ,567'
Aristotle, 390
Arrhenius, 330
Arthus, 305
Asher, 184
Avogadro, 37

Babkin, 187

Bacon, 115, 298

Bainbridge, 197, 381

Baly, 19

Bancroft, 77, 105

Barcroft, 184, 196, 197, 324. 325, 343

Barger, 502, 514

Barker, 25

Barnard, 79

Bayliss, 101, 122. 143, 186, 187, 196. 303.

311, 353, 434, 567
B aumont, 417
Bechhold, 84
Bechmann, 512
Bedson, 308
Benedict, 27, 438, 497
Bergonie, 453
Berkeley, 221
Bernard, 1
Bert, 353, 357
Berthelot, 24
Bigelow, 557
Bjerknes, 482
Bohn, 479
Boll, 287
Boltzmann, 8
Bovie, 464
Bowen, 426
Boyle, 353
Boy sen-Jensen, 15
Bradford, 8. C. 86
Bradford, J. R., 186
Bragg, 110
Bredig, 57
Brown, 81
Browne, 203
Buchanan, 304
Bunsen, 455, 457
Burton, 233
Burton-Opitz, 319

Cameeer, 476
Campbell, 159
Cannon, 246, 247. 248
Carey, 490

Carlson, 420

Carnot, 31

Cassius, 506, 561

Cathcart, 418, 495, 567

Chamberlain, 464

Chauveau, 171

Chladni, 217, 263, 422

Christen, 444

Clark, J. H., llO, 176, 177

Clark and Lubs, 503, 524

Clowes, 107

Cocking, 567

Coulthard, 172

Crawford, 27, 28

Crocker and Matthews, 30, 34

Crookes, 156

Crowther, 156, 165

Crozier. 243. 460, 461, 463

Culmann, 214, 215

Cushny, 192, 197, 201, 202

Daffnek, 474

Dalton, 38, 354. 355

Davenport, 467

Dendy, 217

De Vries, 41, 132

Dittler, 289

Dixon, 215

Dodds, 421

Donnan, 105. 143, 144, 198, 199, 226, 338,

420, 533
Donnegan, 195, 201
Douglas, 350. 497
Dreyer. 470
Dryden. 360
Dubois, R., 212
Du Bois, 565

Du Bois Reymond. 97, 230. 287
Du Nouy. 45
Dutrochet, 140

Edridge-Green 286, 288, 289, 297

Ege, 317

Errera, 473, 479

Evans, Lovatt. 181. 197, 202, 271, 368

369, 370, 371, 381
Ewald, 258, 263, 264, 265

Faludi, 303

Faraday, 79. 503, 505, 527, 557

Fechner, 235

Fehling, 467

Fenn, 176

Fenton, 21

Tick. 88

Findlay, 43

Fischer, E.. 116. 124. 131

Fischer, M!, 103, 105, 112, 114, 137, 54S

Flack, 185

Fleischl, 563

568

NAME INDEX

569

Fmloiicti, U), 4t)ti
Freundlich, 54:
Fiohlich, 288

Galen, 272, 390

(Talileo, 436

(Tulloway, 462

Garner, 176, 177

Gemberling, 557

Gibbs, 51, 73, 105, 134, 185, 213

Goodej\ 545

Goodrich, 150

Gortner, 95, 98. 324

Gotch, 383

Gothlin, 222

Goiigh, 315

Goulden, 279. 281, 297

Graham. 38. 39. 43. 72, 75, 100

Greenwood. 358, 499

Grollman, 301, 320

Grotthus, 15. 289

Grutzner, 409

Guldberg and Waage, 62

Giirber. 143

Guthrie, 319

Hales, 441

Haller, 435

Hammersten, 305

Hammond, 458

Hardy, 47, 91. 92, 460

Harris, F., 248

Hartree, 173

Hartridge. 258, 261, 271, 297, 524

Harvey, 362, 376

Hasselbalch. 352

Hatschek, 55, 80, 89, 91, 102, 109, 559,

562, 567
Haudek, 248
Hawk, .567
Hay, 502, 518
Hearne, 445
Hecht, 288
Heidenhain, 187
Helmholtz, 7, 58, 255, 258, 260, 262, 264,

265, 331, 409
Henderson, 327, 340, 341, 343
Henri, 82
Henry, 323
Herrera, 547
Hertwig, 473
Hess, 5, 25, 381
Hewitt, 305, 307
Hill, A. v., 133, 166. 173, 175, 177, 181,

198, 199, 228, 326, 329, 427, 500, 501
Hill, L., 185, 446. 447, 450, 451, 556
Hippocrates, 390
Hofmeister, 148
Holmes, 480
Holmgren, 287
Hooke, 44, 206
Hopkins, 147
Howell, 306, 308
Hndson-Makuen, 406, 407
Hiifner, 346

Hunter, 380
Huxley, 502

Jones, 412
Joubert, 429

Kallius, 281

Karalov, 184

Keiler, 457

Keith, 220, 249, 258, 260, 262

Kerridge, 567

Kesson, 375

Kniep, 16

Knowlton, 196, 197

Kohlrausch, 57

Kremann, 20

Krogh, 347, 348, 350

Kronecker, 416

Kugelmass, 307, 567

Kuhne, 287

Langley, 15

Laplace, 27

La Rochefoucauld, 189

Lavoisier, 27

Leathes, 109, 110, 136

La Chatelier, 9, 10, 53, 164, 165, 203, 204,

444, 462, 473
Leduc, 134, 466, 482, 544
Leeuwenhoek, 362
Lefevre, 453
Levi, 470
Lewis, 389
Liebig, 451

Liesegang, 86, 87. 50?,, 529
Lillie, 84, 151, 231
Lindhard. 497. 498
Lippmann, 50
Lissauer, 565
Lister, 304
Loeb, J., 92, 100, 140, 141, 149, 456, 457,

464, 468, 477. 480. 486, 488, 489, 492.

503
Loeb, L., 477
Loewy, 348
Lotka, 13
Ludwig, 185

MacAlister, 208. 216

Macallum, 150. 173, 182, 185, 199, 201, 222

Macdonald, 499

MacDougal, 153

Mach, 270

MacLaughlin, 548

Maclennan, 108

MacWilliam, 375

Maddox, 292

Magnus, 268

Marey, 208

Martin, 505, 552

Mast, 463

Maxwell, 270, 271

McClendon. 146. 154, 463

M'Kendrick, 251, 252, 258

Meeh, ,56-5

Meltzer, 416

570

NAME INDEX

Merkel, 281
Metchnikoff, 492
Meyer, 214, 215, 216
Meyerhof, 133, 169
Michaelis, 567
Middleton, 382
Millikan, 165
Milroy, 195, 201
Mines, 145
Moore, 18, 19, 20, 21
Moravek, 153
Miiller, 223

Nageli, 132
Neuhausen, 99
Newton, 1, 36, 47, 56, 442
Nobili, 179

Oden, 561
Olmstead, 172
Orbelli, 186

Ostwald, 49, 71, 78, 151. 502, 517, 518, 530,
560, 567

Pages, 305

Parker, 245

Pasteur, 492

Paton, Noel, 360, 361, 395, 567

Patrick, 99

Patten, 458

Paul, 259

Pauli, 533

Pembrey, 447, 567

Perrin, 83

Peters, 524

Pfaundler, 469, 470

Pfeffer, 41, 132

Pickering, 305, 307

Pierce, 557

Poiseuille, 530

Ponder, 315, 321

Pope, 166, 455

Potter, 384

Prior, 435

Purkinje, 281, 295, 296

quetelet, 471, 472

Ramsay, 82

Rayleigh, 76

Rhorer, 199

Rhumbler, 545

Riedel, 472

Rieger, 551

Ringer, 542

Roaf, 173, 564

Robertson, Brailsford, 134, 150, 483, 488,

516
Romberg, 459
Roscoe, 455, 457
Roux, 490

Rubner, 26, 451, 452, 477, 492, 564
Rumford, 4
Russell. 165

Rutherford, C, 158, 159, 162
Rutherford, W., 258

Sack, 471

Sanctorius, 436

Sanson, 279, 281

Schafer, 150, 153, 250

Schanz, 96, 505, 547

Schmidt, 304, 325

Schnidlerschitsch, 20

Schiitz, 488

Schwarzschild, 457

Seeker, 276, 315

Senator, 449

Servetus, 363

Shakespeare, 344, 413

Snell, 128, 273

Soddy, 1, 3, 9, 13, 14, 35, 159. 160, 363

S0rensen, 63, 64, 71, 503, 506, 524

Spallanzani, 118, 417

Starling, lOl, 132, 194, 406, 410, 502

Steer, 461

Stefansson, 464

Stewart, 308, 312

Stoll, 16, 20, 21

Tait, 306, 308
Talbot, 457
Tangl, 491
Taylor, 243
Thales, 61
Thoenes, 467

Thompson, D'A., 31, 220, 462, 478
Thomson, 105
Traubc, 134, 136
Trautz, 18

Tyndall, 14, 76, 77, 80, 503, 505, 527, 528,
557

Valentin, 449

Van der Mensbrugghe, 175

Van Slyke, 335. 343, -561.5, 553, 555

Van't Hoff, 41, 130, 139, 228, 330, 473

Vernon, 122

Verworn, 151, 57?'

Vesalius, 404

Vincent, 188

Von Weimarn, 73, 74, 75

Watson, 567

Webster, 18, 19

Welter, 23

Wenham, 80

Wertheim, 206

Wilkinson, 258, 260, 261, 262

Willows, 55

Willstatter, 16, 20, 21

Wilson, 105

Wolf, 463

Wolff, 217

Wood, 159

Wrightson, 256, 258

Young, 206

zotteeman, 241
Zsigmondy, 74, 81, 94
Zuntz, 30, 369, 497
Zwardemaker, 161

SUBJECT INDEX

{References to Part II. are in italics.)

Aberration, chromatic, 274, 282

spherical, 275, 282
Absorption coefficient of gases in liquids,
:}2.S, 347
from alimentary canal, 418, 419
of heat, 439, 445
of light, 15, 18, 78
of solutes by renal tubules, 185
spectrum of chlorophyll, 20
ergosterol, 165
green leaf, 15
Acceleration, catalytic, 117
Accessory factors of diet, 475
Acclimatisation, 353
Accommodation in eye, 280, 293
Acid, action of, on emulsions, 106, 481,
487, 493
on fats, 480, 493
on soaps, 108

on surface tension, 187, 524
on tissues, 481, 493
definition of, 66

effect of, on dissociation curve of
oxyhsemoglobin, 328
on imbibition of water by colloids, 486,

493, 538
on surface tension, 524
on viscosity of colloids, 531
lactic, in muscle, 172
Acidity, numerical expression of, 63, 64,
563
of gastric juice, 420
of retina, 289
Acidosis, 432
Acoustics, 412
Acquired characteristics, transmission of,

464
Adaptation to environment, 462
of bone, 214, 217
of receptors, 234, 242, 289
of sensory nerves, 234, 289
Adipose tissue, 211, 441, 448
Adsorbed material, state of, 72, 187
Adsorption, 53—55, 96, 122, 139, 487
and osmosis, 187
by enzymes, 119, 122
cause of, 52

demonstrations of, 518, 530
intensity of, 117

of carbon-dioxide by haemoglobin, 332
of enzymes, 541
of gases by colloids, 325, 430
of oxygen by haemoglobin, 326
pseudo-, 135

Adsorption, specific surface for, 72, 119

temperature coefficient of, 119, 135
Adsorptive stratification (Liesegang phe-
nomenon), 86, 87, 529
Agar-agar, 86, 100
Ageing of surfaces, 46
Agglutination, 191
Alignment chart, 340
Alimentary canal, general plan of, 413

mechanics of development, 490
Alkali, definition of, 66

reserve, 311, 432, 551

secretion of, 421
" All or nothing " in muscle fibril, 175

in nerve, 224
Alveolar CO, tension, 421
Alveoli, 346 "

area of, 346
Amicron, 81
Amoeba, 147, 545

camphor-benzene, 150, 516

mei'cury, 516
Amphioxus, 299
Amphoteric colloids, 96, 138, 430

electrolytes, 66
Ampulla, 269
Anabolism, 2, 477

Ansesthetics, action on emulsions, 10(), 109
on enzymes, 120
on membranes, 135
Analyser, 126, 128
Angle of origin of blood-vessels, 380
Angstrom units, 14, 165, 567
Anion and cation, 56, 59
Anode, 56
Anti-enzyme, 122
Anti-pro-thrombin, 305, 306
Antrum pylori, 417
Aortic valves, 377
Apnoea, 416

deglutition, 416
Arrheuius' theory, 42
Arterial walls, 375, 379
Arteries, pressure in, 367
Arterioles, pressure in, 367
Artificial amoeba, 150, 516

cell, 153

laccase, 118

membranes, 40, 134, 544, 557

parthenogenesis, 487
a rays, 158
Astigmatism, 283
Astral lays, 482
Asymmetric carbon atom, 130, 131

571

1

572

SUBJECT INDEX

Autocatalysis and growth, 468
Autolysis, 493
Available energy, 8

of cell, 33, 35
Avogadro's hypothesis, 40
Axial repulsions, law of, 479
Axis, visual, 283, 290, 292, 293

Balanced chemical reactions, 124
Barger's method for determination of

osmotic pressure, 514
Barometric pressure and alveolar tension,
352
and height, 351

and number of erythrocytes, 352
Barotaxis, 151
Basilar membrane, 259
Bending, 205, 427
Bicarbonate system, 311. 432, 551
Bile, function of, 419
Binaural hearing, 266
Binocular vision, 292
Bio-electric phenomena, 152, 179, 225, 287,

382, 54S
Bjerknes phenomenon, 482
Bone, 212

adaptation of, 214, 217

conduction of sound by, 266

development of, 212

internal structure of, 214

strength of, 213

stress lines in, 214

trabecular structure of, 217
Bowman's capsule, 193
Boyle's law, 37
,rf rays, !»6, 158
Brownian movement, 79 — 81, 52S

in neurone, 222
Buffers, 433. 524
Bunsen-Roscoe law, 455, 457

Caisson disease, 361
Calorie, definition of, 22

value from oxygen usage, 30, 198
of proximate principles of food, 26
Calorimeter, bomb, 24, 500

( 'raw ford's, 27
Calorimetry, direct, 27

indirect, 28
Cambrian period, sea- water in, 311
Capillary active substances, 51, 519

analyses, 536

circulation, 194, 361, 362

electrometer, 50, 153, 180, 382, 520

method for estimating surface tension,
46, 518

pressure, 194, 366
Carbohydrates, formation of, 16

oxidation of, 30
Carnot's principle, 31, 496
Cartilage, 212
Catalase, 120
Catalysis, 117.

auto-, 468

Catalyst, 116

ionic, 117
Cataphoresis, 90, 534
Cathode, 56

rays, 157
Cell, as an energy transformer, 33, 167

chemical and physical characteristics of,
148 et seq.

division, cause of, 478

polyphasic nature of, 147, 150, 429
Cellular dynamics, 203, 478
Centimetre index, 470
Centre of gravity of body, 426
Charles' law, 37
Chemical energy, receptors for, 242

'■ gardens," 544
Chemiotaxis (chemotropism), 151, 192, 459
Chladni's plates, 217, 263
Chlorophyll, absorption spectrum of, 20

catalytic action of, 21

chemical natui'e of, 21

efficiency of, 21

function of, 21
Cholesterol, 135, 191, 192
Chorioid coat, 276
Chromatic aberration, 274, 282
Cilia, 189, 299
Ciliary processes, 276

body, 276
Ciliated epithelium, 189
Circulation of blood, development of, 299

general plan of, 361, 566
Clotting, 303 et seq.
Coagulation of colloids, 92, 302, 535
Cochlea, 256

Coefficient of variability, 472
Ccelomic system, 299, 300
Co-enzymes, 122
Cold, reaction to, 135, 226, 304, 449

spots, 241
Collagen, 210
Colligative properties of plasma, 301

of solutions, 41
Collodions, 557

membranes, 557
Colloidal aggregates, dimensions of, 71, SO

gold, 74, 77, 80, 94, 536. 560

solutions, 72 et seq.
coagulation of, 92
colour of, 76

osmotic pressure of, 43, 84
precipitation of, 93, 95
preparation of, 560 et seq.
properties of, 76 et seq.
viscosity of, 88
Colloids, diffusion of, 85

hydrophilic, 75, 93, 211

hydrophobic, 75, 93

physiological, 75
Colour of colloidal solutions, 76

of iris, 77

of skv, 76
Comma", 275, 283
Compensation, law of, 479
Complemental air, 345
Compound interest law, 468, 471

SUBJECT INDEX

573

Condensation in surface layer, 73, 1U5, 134,

185, 213
Cones (and rods), 285, 289
Constant, dieiectrie, 59, 60

gas, 37

ionisation, (i2
Contraction, isometric, 1()9

isotonic, 170
Cooking, 113
Copper ferrocyanide membranes, 130, 511.

■U4
Cornea, 276, 278, 279, 280, 284
Corresponding states, law of, 74
Corti, organ of, 257
Crenation of corpuscles, 319
Crooke's tube, 156
Crystalloids, 72, 73
Current of action, 153, 179

demarcation, 152, 179, 231

electrotonic, 229

polarisation, 154, 228
Curvature of refractive media of eye, 279

uf ventricular walls, 374

Dalton's law of partial pressures, 38, 354,

355
Dark ground illumination, 80, 52S
Dead space, 345
Decompression, 356

Decrement of the nervous impulse, 226
Degeneration, fatty, 211, 493
Deglutition, 415

apncea, 416
Degraded energy, 5, 8, 494
Demarcation current, 152, 179, 231
Dendrites, 221
Depolarisation, law of, 479
Dermatoptic functions, 212
Destruction of enzymes, 118, 119
Dialysis, 73, 87, 527
Diaphragm, 392

Dielectric constant, 59, 60, 229, 537
DifEusiometer, 38, 510
Diffusion cause of, 85

coefficients, 348

electrical, 86, 529

field of force of, 482

of colloids, 85, 529

of crystalloids, 85, 195, 52!J

of gases, 38, 348, 510

through membranes, 38, 39
Dioptre, 274

Dioptric system of eye, 278
Diphasic electrical response, 180, 383
Dispersion, 73 — ^75
Displacement theory of hearing, 262
Dissociation of oxyhaemoglobin, 325 el seq.

of water, 63

temperature coefficient of, 64, 69

theory of solution, 42
Distance receptors, 249, 272
Diuresis, definition of, 195

and oxygen consumption, 197
Diuretics, model to imitate action of, ol'J
Donnan equilibrium, 143, 144

Ear, 249 et .seq.
Ecto-enyzmes, 121

Effective area of surface of erythrocytes, 321

lungs, 346
solvent, 71, 72
Efficiency, definition of, 32, 495

factors influencing, 499

gross, 495

net, 495, 497

of an engine, 31, 32, 496

of animal as a machine, 32, 497

of chlorophyll, 21

of clothing, 453

of heart, 371

of isolated muscle, 169, 178, 501

of lung mechanism, 399, 4(10

of organism as a whole, 497, 498

of secretory glands, 187

of tympanic membrane, 252

thermal, 32
Elasticity, 207

of arteries, 366

of lungs, 392, 398

of rubber, 177, 208

of tissues, 207
Elastin, 210
Electric endosmose, 142, 531

phenomena of cell, 152
of muscle, 179
of nerve, 225
of retina, 287
of secretion, 186
Electrical conductivity, 57, 149, 487, 522
Electrocardiogram, 385

analysis of, 387
Electrodes, non-polarisable, 563
Electrometer, capillary, 50, 153, 180, 382,
520

leads, 384

string, 385
Electron theory, 59

Electrostatic attraction of ions, 59, 229
Electrotonic currents, 230
Emulsifying agents, 102, 106 et seq.
Emulsoids, 74, 191

protective action of, 93, 535
Endo-enzymes, 121, 493
Endosmosis, 40. 108, 317, 511

electrical, 142, 534
Endotheliocytes, 191
Endothelium, 211, 347
Endothermic reactions, 18, 111
Energetics of growth, 476

of karyokinesis, 481
Energy absorbed by chlorophyll, 18

available, 7, 9

bound, 7, 8

chemical, receptors for, 237, 242, 244

conservation of, 4

consumption in ])honation, 411
of by glands, 183, 184
by kidneys, 198
by muscle, 172
by nerve, 228
by organism. 477
by respiratory muscles, 400

574

SUBJECT INDEX

Energy, degradation of, 8

free, 8, 486, 489

kinetic, 6

laws of, 4 — 10

necessary for dissociation, 61

of food, 26 et seq.

of growth, 411

potential, 7

radiation from sun, 15, 16

trigger, 8

values, 22, 25

vibratory, receptors for. 236
Enterokinase, 122
Entropy, 6
Epithelium, 203

ciliated, 189

growth, pressure of, 478
Equilibrium, 11, 116

Uonnan, 143
Erepsin, 126
Ergometer, 497
Errera's rule, 473, 479
Erythrocyte, 312, 322

area of, 314

ghosts, 315

shape and volume, 313
Eustachian tube, 258
Excretion, 151, 192, 193, 419
Exosmosis, 317, 511

and development, 487
Exothermic reactions, 23, 111
Exteroceptors, 233
Eye, 276 ef seq.

FECces, 192, 419

function of soap in, 419
Faraday-Tyndall phenomenon, 79,

557
Fat energy, value of, 23, 26

formation, 19

function of, 52, 211, 212, 441, 448

invisible in cells, 148, 211, 493

visible in cells, 148, 211, 493
Fatigue, in muscle, 167

in nerve cells, 228
fibres, 228
Fatty degeneration, 211, 493

n'le of acid in, 492
Ferrocyanide membranes, 511, 541
Fertilisation, 486

increased permeability in, 487

spermatozoon and, 488
Fibrin, 305 et seq.
Fibrinogen, 303
Fibrous tissue, 210 et seq.
Flare, 275, 283
Flow through tubes, 363
Focal length, 273
Food, animal. 111 ; vegetable, 112

changes of, in digestion, 35, 418

energy, value of, 22

proximate principles of, 20

requirements for growth, 475
Force, helds of, 481
Form, symmetiy of, 373

527,

Formaldehyde in photosynthesis, 17

Fovea centralis, 277, 286

Fractures, 218, 490

Freezing point, lowering of, 41, 512

Friction, 170, 363

Fucsin, 286

Gall-stones, formation of, 192
Galvanometer, string, 385
Galvanotaxis, 151, 460
Gas constant, R, value of, 37

dispersions, 74, 530

laws, 37

pressure, cause of, 37
Gay-Lussac's law, 37
Gel, 52, 75, 562

coagulation of, 92, 535
Gelation, 75, 92, 303, 539
Gibbs-Thomson principle, 73, 105, 134,

185, 213
Glands, activity of, 182

blood supply of, 185

endocrine and exocrine, 182

maintenance of, 184

mechanism of secretion, 187

mode of stimulation, 181

of elimination, 202

restitution of, 183
Glomerulus of kidney, 194
Glutelin, 113
Gluten, 113
Glutenin, 91
Gold uTimber, 94, 536

colloidal, 94, 560
Growth quotient, 477
7 rays, 158, 163

Guanidine salts, dissociation of, 56
effect on erythrocyte, 315

" free " water of protoplasm, 149
Gum saline, 303

Haem, 316
Hsematin, 316
Hsematocrite, 312, 317, 551
Hsemodynamics, 362
Haemoglobin, 316, 325

salts of, 335
Hemolysis, 133. 317, 549
Haemorrhage, 303
Halation, 275, 283

Harvey's work on circulation of blood, 362
Heat, action of, on chemical reactions, 62,
118, 173, 174, 177
on efficiency, 438, 447
on eraulsoids, 96, 119
on enzymes, 118

on physical reactions, 48, 58, 62, 69,
473
centre, 450
of combination, 25
of combustion, 23 et seq., 171
of dilution, 23, 61
of hydration, 57, 58, 61

SUBJECT INDEX

575

Heat of iiiil)il)itioii, it9, o3S

of neutralisation, 176

production in brain, 45U
in glands, 187
in muscle, 170, 171, 447
in nerve, :.'l'8

spots, 241
Helicotrema, 2f)5
Heliotropic machine, 458
Heliotropism (pliototaxis), 455
Helmholtz-Lippmann, double layer, 50, 58
Heterophoria, 2!»2
Hibernation, 4,'56
Hirudin, :iO!t
Histiocytes, \'i^\
Homoiothermic animals, 436
Hormone, 300
Humour, aqueous, 276

vitreous, 277
Hunger, sensation of, 246
Hydrocele fluid, 304
Hydrogen electrode, 523

ion concentration, 64-68
measurement, 522
of blood, 301
Hydrophilic colloids, 75, 93, 192, 211
Hydrophobic colloids, 75
Hydrosol and hydrogel, 75
Hypermetropia, 284
Hypertonic solutions, 132, 318, 488, 511,

544, 545
Hypotonic solutions, 133, 318, 511, 545

Imbibition by colloids, 97, 105, 487, 537

Incus, 252

Index, centimetre, 470

of variability, 472
Inertia, 10, 235, 455, 458, 486
Infundibula, 346

Injury, current of, 152, 179, 231, 548
Integrative action of blood, 300, 342
Interface, 44, 52, 53, 54, 55, 105, 137, 175,

185. 201, 420
Interoceptors, 233
Interphase, 73, 105, 134
Intestines, 418
Ionic micelle, 42
Ions, definition of, 42

electrical charge of, 56

hydration of, 57, 58

relative speeds, 57
Iris, 276, 278, 281, 282

colour of, 71

diaphragm, 81, 275, 282
Iron content of haemoglobin, 325
Irradiation, 275, 283
Irritability of matter, 151
Isoelectric point, definition of, 90, 92
and coUigative properties, 92
of muscle proteins, 176
of proteins, 91, 532, 533
Isomers, optical, 131
Isometric contraction, 169
Isotonic solutions, 315, 317, 5JI

Joints, 218

lubrication of, 218

Karyokinesis, 481 et seq.
Kathode. See Cathode.
Kephalin in blood-clotting, 306
Kidney, 193 et seq.

function of, 194-198

model of, 549
Kinetic energy, 6

of substances in solution, 36

Laccase, artificial, 118
Lactic acid of muscle, 172
function of, 174
origin of, 172
Larynx, 404

Latent heat of water, 441, 444.
Law of Avogadi-o, 37

of Berthclot, 10

of Bohn, 479

of Boyle, 37

of Bunsen and Roscoe, 455, 457

of Charles, 37

of Dalton, 38, 354, 355

of Fechner, 235

of Fick, 88

of Fredericq, 10

of Gay-Lussac, 37

of Grotthus, 15, 289

of Guldberg and Waage, 68

of Henry, 323

of Hess, 5

of Hooke, 206

of Le Chatelier, 9

of Midler, 223

of Newton, cooling, 442
thermodynamics, 1

of Rubner,' 477, 492, 564

of Schutz, 488

of Snell, 128, 273

of Talbot, 457

of \^on Weimai'n, 74

of Welter, 23
Laws of autocatalysis, 468

of axial repulsions, 479

of catalysis, 117, 118, 488

of compensation, 479

of compound interest, 468, 471

of constant energy consumption, 477

of cooling, 442

of corresponding states, 74

of depolarisation, 479

of energetics. 4 — 6

of growth, 479

of least action, 10

of length of life, 492

of mass action, 68

of necessity of reactions, 1 1

of probability, 472

of surface area, 564

of thermodynamics, 4 — 6

of vectors, 479

576

SUBJECT INDEX

Leduc's diffusion experiment, 482

osmotic growths, 134, 466, 544
Lens of eye, 277

Leucocytes, 150, 190, 296, 312. 545
Levers, 397, 423, 424
Liesegang phenomenon, 86, 87, 529
Light, absorption of, by chlorophyll, 2(>
by colloids, 78
by ergosterol, 165
by green leaf, 15

energy of, 14

polarised, 80, 108, 110, 127, 528

receptors for, 212, 278, 456

scattered, 275, 283
Liquid crystals, 108, 111, 176
Load and efficiency, 178, 499
Localisation of sound, 266
Locomotion, movements of, 427
Lubrication of joints, 218
Lungs, area and volume, 346

mechanism, structure, etc., 390 et seq.
Lymph, 362
Lyotropic series, 538

Macula lutea, 277

Maddox rod, 292

Magnification, chromatic dift'erences in,

274. 283
Malleus, 250

Malpighian corpuscles, 192
Mannitol, 19
Mass action, law of, 68
Mastication, 415

Maximum energy of solar spectrum, 15
Mechanical equivalents of heat. 4
Mechanics of bone formation, 214, 462

of locomotion, 427

of mastication, 415

of respiration, 392

of speech, 404, 409
Mechanism of ear, 254, 258

of kidney, 199

of larynx, 404
Meissner's corpuscle, 240
Melanoidins, 212
Membrane, basilar, 259

Ileissner's, 256

tectorial, 263

tympanic, 250
Membranes, 132 el fcq.

adsorption, 109, 134, 466, 544

cell, 136

for dialysis, 87, 88, 527, 557, 559

lipoid, 135, 318

permeability of, 136, 137

polarised, 145

selective permeability of. 145

semi -permeable, 40, 136, 511, 544
Metabolism, definition of, 2

effect of temperature on. 449
Metabolites, function of. 480
Micron, 81

Micropolarimeter, 109
Milk, 111
Mimicry of aiULcboid movements, 150, 510

Mimicry of cell structure, 153

of karyokinesis, 482

of kidney action. 549

of mucoid secretion, 548

of shell formation. 545
Mirror images (optical activity), 130
Mitosis, 482 et seq.
Model of cell, 153

of circulation, 556

of kidney, 549

of nerve cell to illustrate Miiller's law,
223

of polarimeter, 128

of receiving and reacting neuron, 224
Modulus bulk, 207

shear, 206

Young's. 206
Monocytes, 191
Mountain sickness. 351
Mouth, 413

Mucous membrane, olfactory. 244
Miiller's law, 223
Murmurs, cardiac, 378, 379
Muscse volitantes. 296
Muscles, antagonistic and synergic, 253,

393. 395, 400, 425, 426
Musical scale, 406
Myelin growths, 109. 110
Myopia, 284

Negative osmosis. 140

polarisation, 228

temperature coefficient, 46, 48, 58. 69,
174, 177
Neuron, 221, 222

Brownian, movement in, 222
Neutrality, definition of, 64

preservation of, 429 et aeq.
Newton's laws of cooling, 442

of thermodynamics, 1
Nicol's prism, 128
Nitrogen cycle, 19, 494
Normal solutions, 67
Nucleus, 149

and mitosis, 482

and oxidative changes, 484, 489

GEdometer, 98
Olfactory nerve. 245
Obcytin, 488
Ophthalmoscopy, 296
Optical activity, 126

due to asymmetric forces, 131
measurement of, 129
isomers, 131

and enzyme action. 123
resonance. 78
Optimal incidence of energy to nerve, 227,
234
load for muscular efficiency, 499
pK for enzyme action, 120, 126, 541, 542
rate of work, 500

temperature for enzyme action, 118, 541
Organ of Corti, 257

SUBJECT INDEX

577

Organogenesis, 489

Orientation on surfaces, 46, 52, 110,-231

Osmometer, 39, 511, 533

Osmosis, electrical, 139, 142, 534

negative, 140
Osmotic growths, 134, 466, 544
pressure, 35 et seq.
and growth, 466
and secretion, 185
and tui-gor, 190, 467, 515
and vapour pressui'e, 41
of blood, 302, 303
of colloids, 43, 84
of electrolytes, 41
of urine, 199
Ossicles, auditory, 251
Oxidase, 120

Oxygen, caloric equivalent of, 30, 198
consumption of by glands, 184
by heart, 370
by kidneys, 198
by muscle, 171
by organism, 480, 492
by respiratory muscles, 400
tension and barometric pressure, 352
in air, 322

in alveoli of lungs, 322
in arterial blood, 341
in tissues, 328
in venous blood, 341
transport, 325-332
Oxyhsemoglobin, 325, 326, 327, 328
acidity of, 335, 433
dissociation of, 327, 328, 329, 330, 331
salts of, 335, 337, 433

Pacinian corpuscle, 239
Pain, 239

spots, 241
Parchment paper for dialysis, 559
Parthenogenesis, 489

artificial, 487

stages of, 489-490
Partial pressure of gases, 38
Pellation, 36, 46, 363
Perilymph, 258
Peripheral resistance in vascular system,

367
Peristalsis, 418

gastric, 248
Permeability as affected by calcium, 140,
153

differential, 145

selective, 145
Peroxidase, 120
Phagocytes, 191
Phanerosis, 148, 211, 493
Phase rule, 73

Phases of action of gland, 182, 183
of muscle, 171-174

of growth, 471
Phasic receptors, 237, 240
Phonocardiogram, 386
Phosphate buffer system, 433, 575
Photosynthesis, 17, 456

Phototaxis (lieliotropism), 151, 455 et seq.
Pigment and heat regulation, 440

cells stimulated by light, 212

of iris, 71

of retina, 286
Pitch, 407
Plasma (blood), 301

coagulation of, 303 et seq.

coUigative properties of, 301

colloids of, 302

composition of, 302, 310

crystalloids of, 310

function of, 300

osmotic pressure of, 302, 303

oxygen, carrying power of, 324

^H of, 301, 431

refractive index of, 302

separated, 301, 324

specific gravity of, 301

" true," 302, 324

viscosity of, 301
Plasmolysis, 133
Poikilothermic organisms, 436
Poisson's ratio, 207
Polarimeter, 129
Polarisation at electrodes, 145

currents, 154, 228

negative, 228

of light, 80, 128

of membranes, 145

positive, 231
Pole-findmg paper, 142
Postural receptors, 240, 242
Potassium, effect on living cell, 162

in surface layers, 185

radioactivity of, 159

soaps, 107
Potentiometer, 523
Precipitation of sols, 92, 535

mutual, 95, 535
Prepyloric sphincter, 417
Presbyopia, 284
Pressure and growth, 204, 478

pattern theory of hearing, 263

receptors, 240
Proprioceptors, 242

Protective action of emulsoids, 93, 535, 530
Proteins as colloids, 94

digestion of, 417, 418

energy of, 26

function of, in preserving neutrality,
430, 433

isoelectric points of, 90, 91, 92, 176, 532,
533

synthesis of, 19
Protoplasm, 2, 148, 150

as an emulsion, 108

Brownian movement in, 222

colloidal nature of, 33, 148-150

liquid nature of, 33, 148

structure of, 148-150

water content of, 148
Proximate principles of food, 20
Pseudo-activation of enzymes, 121
Pseudo-adsorption, 135
Pseudo-colloid. 101

37

578

SUBJECT INDEX

Pulleys, 425

Pulse wave, 366, 556

Pump, 366

Pupil of eye, 276

Purkinje's figures, 295

Purple of Cassius, 561

visual, 286
Putrefaction and anaerobic action, 494
Pyloric sphincter, 418
Pyrrol cells, 191

Quantum of energy as stimulus, 235
Quinine, action on ha?moglobin, 318
on Liesegang phenomenon, 529
Quinine and chemiotaxis, 151
Quotient, respiratory, 335

Radiant energy, 15, 157, 164
effect on albumin, 96
on colloids, 96
on fertilised eggs, 163
Radio-activity, 155 et seq.

of potassium, 159
effect on heart, 161
Rate of conduction in nerve, 225

of growth, 468

factors influencing, 471
Rays, a, 158

astral, 482

/3, 158

y, 158

cathode, 157

pencil of, 272

ultra-violet, 164
Reaction to indicators, 65
Receptors, 233

phasic, 237

postural, 240

pressure, 240

special, 242
Reflection, 273
Refraction, 128, 273
Refractive index, 78, 273, 278, 302
Refractory period of nerve, 227
Regulation of respiration, 400
Reissner's membrane, 256
Reserve air, 345
Residual air, 345
Resonance, optical, 78

theory of hearing, 258
Respiratory act, modifications of, 402

centre, 400

quotient, 335
Reticulo-endothelial system, 190, 303
Retina, 277, 285

Reversibility of enzyme action, 123, 494
Reversible reactions, 53, 124, 479, 480
Rheoscopic frog, 180, 382
Rhodopsin, 286, 287, 288
Rigidity of tissues. 111, 467

model to demonstrate, 190, 515
Rivers, dissolved matter in and colour of,

77
Rods (and cones), 285, 289

Roentgen rays, 157
Roux's experiment on growth, 490
Rubber an emulsion, 104, 177
elasticity of, 208
imbibition of benzol by, 537
Rubner's law of constant energy consump-
tion, 477
of length of life, 492

Saccule, 268, 269
Sach's rule, 471
Saliva, function of, 414
"Salting out " of colloids, 93, 535
of soaps, 109
diffusion of, 85
Salts, effect on pK, 68, 69, 431, 510, 529
Sanson's images, 279, 281
Saponin haemolysis, 318
Scala media, 256
Schutz's law, 488
Sclera, 276
Sclerosis, 96
Secretion and osmosis, 187

and permeability, 185

by renal tubules, 200

electrical change in, 186

mechanism of, 187

mucoid, 548

of acid, 420

of alkali, 421

phases of, 183

source of energy for, 184

work done in, 182, 183

zymogen, 121
Secretory hypotheses of respiration, 349,

352
Segmentation of egg, 489

of intestines, 418
Selective action of enzymes, 123

Ijermeability of membranes, 145
Semi-circular ducts, 269
Semi-permeable membranes, 40, 136, 511,

541
Sensation, 235

and stimulus, 235

of hunger, 246

olfactory, 244
Sense organs, 237, 240, 242, 249, 272
Sensitiveness, absolute, 240
Shear modulus, 208
Shell formation, 545
Simpson light, 164
Smell, 244
Snell's law, 273
Soap, 106

breaking of solutions of, 108

calcium, 106, 107, 419, 541

effect of ansesthetics on, 109, 541

films, 175, 515

in faeces, 419

loss of hydrophilic properties of, 109, 541

potassium, 107, 541

sodium. 107, 541

soft, 107

SUBJECT INDEX

579

Sodium bicarbonate and CO, tension, 311,
431
system, B9, 431, 551
Sol and gel, 75, 92
Solution, colligative properties, 41

hypertonic, 132, 318, 488. 511, 544,

545
hypotonic, 133, 318, 511, 545
isotonic, 315, 317, 511
tension, 201
Soma, 485

Sound, conduction by bone, 266
localisation of, 266
production, 405 et seq.
Sounds of the heart, 377. 378, 379, 386
Source of energy for food formation, 17, 18,
19
for muscular contraction, 172
for secretion, 184
Specific action of enzymes, 123
inductive capacity, 60
irritability, 223
nerve energy, 222, 223
surface, 72, 484
Speech, 409

Spermatozoon, function of, 488
Spleen, 189, 190, 192
Stabilisation of colloids, 83
of emulsions, 103, 105, 540
of organism, 132
Stalagmometer, 107, 109, 517
Standing, 426
Stapedius, 253
Stapes, 253
Stenosis, 378
Stereoscope, 294
Stereotropism, 459
St. Martin, experiments on, 417
Stomach, 416
Strabismus, 292

Streaming of protoplasm, 151, 463
Strength of materials, 208
Stress and strain, 177, 205
lines in bone, 214
in diffusion, 482
in fields of force, 481
String galvanometer, 285
Stroma of erythrocytes, 314
Struts, 208
Submicron, 81
Substrate, 118, 121
Summation of stimuli, 227
Surface area of body, 564

and heat loss, 439, 440, 444, 446
and mass, 72, 116, 480
measurement, 564
condensation, 51
electrical charges on, 49
energy, 44

measurement, 45
source of, 46

temperature coefficient of, 46
utilisation, 48
extent of, in suspensions, 72
multiplication, 55
orientation, 46, 52

Surface tension, 46 et seq., 517

alterations in, 48

and electrical charge, 48

and growth, 466

and pH, 48

efifect of solutes on, 51

in muscle processes, 174

in nerve, 222

in respiration, 392

in urine formation, 199, 201
volume ratio, 480
Survival of the fittest, 462
Suspensory ligament, 277
Swallowing, 415
Synapse, 221
Syneresis, 100, 540
Synergetical muscles, 426
Synkinetic movement, 251
Synovial fluid, 219
Synthesis by enzymes, 125, 494
of carbohydi'ates, 17
of fats, 19
of proteins, 19

Taste, 242

Tectorial membrane, 263
Temperature coefficient, 48, 58, 69, 174,
177, 473
of development, 488
of dissociation, 63, 64, 69, 330
of growth, 473
of muscular contraction, 177
of nervous impulse, 228
of surface tension, 46
lethal, 33, 444
Tendon, 210

sheaths, 219
Tension and rate of growth, 478

of gases, 323, 328
Tetanus, 180

Thermal conductivity, 441
efficiency, 32
gradient, 441
Thermodynamics, laws of, 4-6
Thermo-elastic properties, 169, 170
Thermometer, Beckmann's, 512
clinical, 436
Kata, 446, 556'
Thermopile, 436, 437
Thermotaxis, 151
Thigmocytes, 306, 309
Threshold values, kidney, 200

receptors, 233
Thrombin, 305
Thrombokinase, 305
Thromboplastin, 305
Tidal air, 345
Ties, 208
Timbre, 409
Tissues, adipose, 211
connective, 204

elasticity of, 207
development of, 489
fibrous, 210
rigidity of. 111

580

SUBJECT INDEX

Tissues, strength of, 208

vegetative, 203
Tone, 407
Tongue, 414
Tonus of muscle, 174
Torsion, 205

balance, 45
Touch, 237

button mechanisms, 419, 464
Tractation, 36, 46, 363
Training and efficiency, 178, 499
Transport of carbon-dioxide, 332 et seq.

of oxygen, 324 et seq.
Trigger action, 222

energy, 14
Trophic and secretory nerves, 186, 187
Tropisms, 455
Truss, 209
Trypsin, 122
Turgor, 190, 467, 515
Tympanic membrane, 250
Tyndall phenomenon, 80, 528
Types of colloids, 75

of emulsions, 104

of levers, 423

Ultra-filtration, 84, 137
Ultra-microscope, 80, 528
Ultra-violet rays, 164, 547, 548

action of on albumin, 96, 505, 547
on organisms, 164, 548
on skin, 164, 548
Urine, formation of, 194-198

work done in formation of, 199
Utricle, 268

Valves of heart, 376

of veins, 375
Vapour pressure of a liquid, 37
and osmotic pressure, 41
Barger's determination of, 514
Variability, coefficient of, 472

index of, 472
Vectors, law of, 479
Vegetative tissues, 203
Velocity of growth, 471

of passage of electrical disturbance, 225
Ventilation of lungs, 351

of rooms, 450
Vibratory energy, receptors for, 236, 249,

272
Viscosity, 88, 530

coefficient of, 89

of blood, 320, 550

of colloidal solutions, 88, 89, 90, 531

Viscosity, of proteins, 303, 321, 531

of serum, 301, 321

of solutions, 88
Vision, binocular, 292

central, 286

peripheral, 285, 289
Visual axis, 283, 290, 292, 293

field, 295

judgments, 294

purple, 286
Vital capacity, 345
Vitalism, 352
Vividiffusion, 88
Vocal cords, 405
Volition, 12
Volume of blood, 325

corpuscles, 339 — 341, 551

of erythrocyte, 314

of heart, 370

of lungs, 346
Vowels, 409, 556

Walking, 427

" Waste " heat, 6, 13, 450, 494

Water as a catalyst, 117

as a solvent, 61

dielectric constant of, 60

dissociation of, 63, 64, 69

electric conductivity of, 62

equivalent of calorimetric bomb, 507
of human body, 441

free and bound, 98, 467, 468

heat conductivity of, 441

molecular formula of, 62

smface tension of, 44, 517
Work done in formation of urine, 199
in secretion, 182, 183

of heart, 368

of lungs, 400

of muscle, 169 — 173

of phonation, 410

of pump, 367

units of, 4

X-rays, 157

and crystal structure, 110, 176

Yeast, 490, 546
Yield point, 208
Young's modulus, 206

Zincative, 287
Zymogen, 121

PRINTED IN GREAT BRITAIN BY THE WHITEFRIARS PRESS, LTD.,
LONDON AND TONBRIDGE.

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BOOKS ON

NATURAL
SCIENCE

J. &

Published by
A. CHURCHILL

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INDEX TO

SUBJECTS

PAGE

Analysis . . . 2 — 7

Microscopy

PAGE

15

Bacteriology . 1 2
Biochemistry . 13

Pharmacognosy
and Materia
Medica . .

10, 1 1

Biology . . . 14, 15

Pharmacy . .

10. 1 1

Chemistry . . 2 — 7

Physics . . .

8

Hygiene . . 9

Miscellaneous ,

15

Index to Autho

rs, see page 16

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15

Adams, T.
Allen, A. H. .
Appleyard, F. N
Arloing, S.
Arnall, F.
Arup, P. S. .

Bamford, F.
Barnett, E. de B
Barton-Wright, i
Beale, J. F. .
Beaslev, H. .
Bennett, R. R.
Bergeim, O. .
Blair, G. W. Scott
Bloxam, A. G.
Bloxam, C. L.
Bolton, E. R.
Braithwaite, J. O.
Burn, J. .
Burns, D.
Bywaters, H. W

Caldwell, W.
Cameron, A. T.
Candy, H.
Carpenter, J. A.
Castelfranchi, G.
Chauveau, A.
Clayton, W. .
Clowes, F.
Cocking, T. T.
Coleman, J. B.
Collis, E. L. .
Cooley, A.
Corbin, H. E.
Cox, H. E. .
Crookes, Sir W.
Crowther, J. A.

Darling, H. C. R
Darlington, C. D
Daw, B. . .
Dexter, J.
Dible, J. H. .
Dreaper, W. P.

Edelmann, R.
Eichhorn, A.

FlERZ-DAVID, H.
Findlay, G. M.
Fleming, G. .
Fourneau, E.
Fowweather, F.
Fresenius, R.
Fyleman, E.

Gatenby, J. B.
Gibbs, W. E.
Gilmour, C. R.
Giltner, \V. .
Giua, M. . .

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Glasstone, S.
Grant, J. .
Gray, A. . . .
Green, J. R. .
Greenish, H. G. .
Greenwood, M. .
Groves. C. E.

Hackh, I.
Hampshire, C. H.
Harris, L.
Harrison, G. A. .
Harshberger, J. W.
Haslam, J. F. C.
Hatschek, E.
Hawk, P. B.
Henry, T. A.
Hewlett. R. T.
Hodges, F. W.
Hodgkinson, W. R.
Holder, J. T.
Hood, G. F. .
Horwood, A. R.
Hunter, H.

Imms, a. D. .
Ineson, W. I.

Jameson, W. W
Jensen, H. R.
Jobling, E. .
Johnson, A. E.
Johnston, J. H.

Kirk, J. B. .
Kloes, J. A. van der
Knott, F. A. .

Lathrop, E. C.
Leake, H. M.
Lee, A. B. .
Lewis, S. Judd
Ling, T. M. .
Liverseege, J. F.
Lloyd, D. J. .
Lucas, C. E. L.
Lucas, E. W.
Lyons, C. G.

Macfayden, a.
Mackie, H. B.
Maplestone, P. A
Marrison, L. W
Marshall, A. .
Mason, F. A.
Maxted, E. B.
Mayneord, W. V
Mcintosh, J.
Micks, R. H.
Mitchell, A. D.
Mitchell, C. A.
Mohler, J. R.
Molinari, E.

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Nierenstein, M.
North, W. .

Orla-Jensen

Painter, T. S.
Parkinson, G. S.
Parry, E. J. .
Pauli, W.
Piney, A.
Pope, T. H. .
Porter, A. E.
Pregl, F. . .
Pryde, J.

Robinson, G. W
Robson, J. M.
Rogers, Sir L.
Roth, H.

Sadtler, S. S.
Sansome, F. W.
Sartori, M. .
Searle, A. B.
Shore, A.
Silvester, W. A.
Simpson, R. H.
Small, J. .
Smith, E. A..
Smith, K. M.
Spear, R. H.
Stead, G.
Stevens, H. B.
Stewart, A. M.
Stiles, W. S. .
Stockdale, D.
Sutton, F.
Svedberg, T.

Thomas, M. .
Thorne, P. C. L
Thorpe, W. V.
Thresh, J. C.
Tilden, Sir A. W
Tognoli, E. .

Vacher, a. .
Valentin, W. G.
Villavecchia, V.

Waeser, B. .
Wagner, R. .
Wallis, T. E.
Walsh, J. W. T.
Watts, H. .
Whitby, L. E. H
White, F. D.
Whitfield, F. G.
Whymper, R.
Wiley, H. W.
Wood, A. H.

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