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COLLEGE OF PHYSICIANS "
AND SURGEONS

Reference Library

Given by

AN INTRODUCTION TO PHYSIOLOGY

AN INTRODUCTION

TO

PHYSIOLOGY

BY

WILLIAM TOWNSEND POETEE, M.D.

ASSOCIATE PROFESSOR OF PHTSIOLOGT IN THE
HARVARD MEDICAL SCHOOL

THE UNIVERSITY PRESS

Cambrftgr, fflass.

1906

Copyright, 1906,
By W. T. Porter.

QT34-
?S3

\<\0G

PKEFACE TO THE SECOND EDITION

Concentration, sequence, and election are
fruitful principles in the higher education.

In 1898 the Committee on Medical Education,
appointed by the Harvard Faculty of Medicine,
reported in favor of the " concentration " system
urged in the committee by the author in com-
mon with Professor W. T. Councilman. By this
method, the first half-year in the Medical School
is devoted to anatomy and histology, the second
half-year to physiology and biological chemistry,
the third half-year to pathology and bacteriology,
and the fourth, fifth, and sixth half-years to
practical medicine and surgery. Work under
the new svstem began in the collegiate year of
1899-1900. In 1904, largely through the influ-
ence of Professor Bowditch, the seventh and
eighth half-years were made elective, each stu-
dent choosing for himself the studies best suited
to his needs.

Concentration provides that the student shall
not serve two masters, but shall study at one

vi PREFACE TO THE SECOND EDITION

time only one principal subject, such as physi-
ology or pathology, disciplines that do not yield
readily to a divided mind. Sequence provides
that a foundation shall be laid before the super-
structure is attempted. Students now have an
acquaintance with anatomy before they begin
the study of physiology. Election somewhat
tardily intrusts to university men rarely less
than twenty -five years of age a voice in the
decision of their nearest affairs. The application
of these principles to medical teaching has un-
doubtedly resulted in large savings of time and
energy.

The economy of force secured by concentra-
tion and sequence has been highly valuable,
though not indispensable, in the new teaching of
physiology introduced by the author in Feb-
ruary, 1900. The traditional teaching of physi-
ology consists of lectures illustrated by occasional
demonstrations and, in some instances, by experi-
ments performed by the students themselves.
The new method is fundamentally opposite. It
consists of experiments and observations by the
student himself. The didactic instruction, com-
prising lectures, written tests, recitations, confer-
ences, and the writing and discussing of theses,
follows the student's experiments and considers
them in relation to the work of other observers.

PREFACE TO THE SECOND EDITION Vll

In the old method, the stress is upon the di-
dactic teaching. In the new there is no less
didactic teaching, but the stress is upon observa-
tion. The old method insensibly teaches men to
rest upon authority, but the new directs them
to nature.

The new method requires :

1. Printed accounts of the fundamental experi-
ments and observations in physiology, taken from
the original sources, and arranged in the most
instructive sequence. The reference to the origi-
nal source should be given in each case.

2. Accessory data grouped about the funda-
mental experiments. The accessory data should
also be taken as directly as possible from the
original sources, and the reference given in each
case.

3. Apparatus of precision designed with the
utmost simplicity upon lines that permit its
manufacture in large quantities at small cost.

It is obvious that these conditions cannot be
met without prolonged labor. Meanwhile, the
annual classes in physiology must be taught.
The present volume is a collection of fundamen-
tal and accessory experiments in several fields
printed in an abbreviated form for the temporary
use of Harvard Medical students and other inter-
ested persons. This collection is being completed

Vlii PREFACE TO THE SECOND EDITION

and improved as rapidly as possible, and the data
for the remaining fields are being brought to-
gether. In its final form this material will con-
stitute " A Laboratory Text-book of Physiology."

The Harvard Medical School,
January, 1906.

CONTENTS

PART I

THE GENERAL PROPERTIES OF
LIVING TISSUES

I

Page

Introduction 3

Nerve-muscle preparation — Preliminary considerations
regarding energy, stimulation, and irritability.

II

Methods of Electrical Stimulation

Introduction 12

Kinetic theory — Osmotic pressure — Plasmolysis. Isotony
— Estimation of osmotic pressure in the blood serum —
Surface tension — Electrolysis — Electrolytic solution
pressure.

The Electrometer, the Rheochord, and the Cell 34
Surface tension altered by electrical energy — Electrom-
meter — Rheochord — Long rheochord — Square rheo-
chord — Simple key — Short-circuiting key — Polariza-
tion — Pole-changer — Polarization current — Dry cell.

Induction Currents 53

Inductorium — Magnetic induction — Magnetic field.
Lines of force — To produce electric induction, lines
of magnetic force must be cut by circuit — Electro-
magnetic induction — On the construction of the induc-
torium — Empirical graduation of inductorium — Plat-
inum electrodes — Flat-jawed clamp — Round-jawed

X CONTENTS

Page
clamp — Double clamp — Make and break induction
currents as stimuli — Extra currents at opening and
closing of primary current — Tetanizing currents — In-
duction in nerves — Exclusion of make or break current.

Unipolar Induction 71

in

The Graphic Method

The Graphic Method 77

Kymograph — Long paper kymograph — Light muscle
lever — Writing lever — Tuning fork.

The Electrical Stimulation oe Muscle and Nerve

The Galvanic Current 93

Non-polarizable electrodes — Moist chamber — Destruc-
tion of the brain by pithing — Paralysis of voluntary
motion by curare — Opening and closing contraction
— Changes in intensity of stimulus.

Polar Stimulation of Muscle 101

Ureter — Gaskell Clamp — Intestine — Electro-magnetic
signal — Tonic contraction — Physiological anode and
cathode — Polar stimulation in heart.

Polar Stimulation of Nerve 113

Law of contraction — Changes in irritability — Changes in
conductivity.

Stimulation of Human Nerves 127

Stimulation of motor points — Polar stimulation of human
nerves — Brass electrodes — Reaction of degeneration.

Galvanotropism 137

Paramecium.

Influence of Duration of Stimulus 138

Tonic contraction — Rhythmic contraction — Continuous
galvanic stimulation of nerve may cause periodic dis-

CONTENTS XI

Page
charge of nerve impulses — Polarization current — Polar
fatigue — Opening and closing tetanus — Polar excitation
in injured muscle.
Polar Inhibition by the Galvanic Current . . . 153

Heart — Polar inhibition in veratrinized muscle.
Stimulation affected by the Form of the Muscle 156
Effect of the Angle at which the Current Line*

cut the Muscle Fibres 157

The Induced Current 158

Chemical and Mechanical Stimulation

Chemical Stimulation 163

Effect of distilled water — Strong saline solutions — Dry-
ing— "Normal saline" — Importance of calcium —
Constant chemical stimulation may cause periodic
contraction.

Mechanical Stimulation 166

Idio-niuscolar contraction/

VI

Irritability and Conductivity

Irritability and Conductivity 168

Independent irritability of muscle — Irritability and con-
ductivity are separate properties of nerve — Minimal and
maximal stimuli; threshold value — Summation of in-
adequate single stimuli — Relative excitability of flexor
and extensor nerve fibres ; Ritter-Rollett phenomenon —
Specific irritability of nerve greater than that of muscle —
Irritability at different points of same nerve — Excitation
wave remains in muscle or nerve fibre in which it starts
— Same nerve fibre may conduct impulses both centrip-
etally and centrifugally — Speed of nerve impulse.

XU CONTENTS

PAET II
THE INCOME OF ENERGY

I

Fermentation

Page

Hydrolysis of Starch by Diastase 189

Conversion of starch to sugar by germinating barley — Con-
version of starch to sugar by salivary diastase (ptyalin) —
Extraction of diastase from germinating barley — Specific
action of ferments.

Proteid Digestion by Pepsin 192

Gastric digestion of cooked beef and bread — Artificial
gastric juice — Digestion with artificial gastric juice —
Extraction of pepsin — Change of proteid to peptone by
pepsin.

Splitting of Casein by Rennin 195

Rennin extract — Separation of rennin — Precipitation of
casein — Experiments of Arthus and Pages.

Precipitation of Fibrin by Fibrin Ferment . . . 199
Buchanan's experiment — Extraction of fibrin ferment —
Extraction of fibrinogen — Precipitation of fibrinogen by
fibrin ferment.

Ammonia* a i. Fermentation of Urea by Urease. . 201
Extraction of urease.

Splitting and Synthesis of Fats 205

Chemistry of fats and soups — Splitting of fats by the pan-
creatic juice — Preparation of neutral fat — The emulsion
tesl lor fatty acid — Extraction of lipase — Hydrolysis
of ethyl butyrate by lipase — Synthesis of neutral fat
by lipase.

V

CONTENTS Xlll

Page

Immunity 218

Ehrlich's ricin experiments — Ricin antitoxine — Theory
of immunity.
Haemolytic and Bacteriolytic Ferments .... 227
Bordet's experiments.

Oxidizing Ferments 230

Schonbein's experiment — Farther oxidations by animal
tissues — Oxidation by nucleo-proteid — Oxidation about
the nucleus — Glycolysis in blood — Oxidation not de-
pendent on living cells of blood — Relation of glycolysis
to the pancreas and the lymph — Glycolytic ferment of
pancreas.

Alcoholic Fermentation 238

The yeast plant — Chemical relations of carbohydrates.

Activating Ferments 243

Enterokinase — Conversion of trypsinogen to trypsin by
- enterokinase.

Absorption of Proteids 245

Diffusion of proteids through dead membrane — Diffusion
through living intestinal wall — Absorption velocity com-
pared with diffusion velocity — Assimilable proteids —
Non-assimilable proteids — Alimentary albuminuria —
Albumose and peptone not ordinarily present in the
blood or urine — Albumose and peptone changed in their
passage through the intestinal wall.

Absorption of Fats, Fat Acids, and Soaps . . . 259
Absorption of fat — Absorption of fat acids — Absorption
of fat acid as a soap.

Lymph 262

Permeability of vessel wall in inflammation.

II
Blood

Specific Gravity 264

Drawing the blood — Determination of specific gravity.

Counting the Corpuscles 266

Counting the red corpuscles — Counting the white cor-
puscles.

XIV CONTENTS

Page
Estimation of Haemoglobin 269

Oxygen capacity of the blood ; the colorimetric determina-
tion of haemoglobin.

Haemorrhage and Regeneration 273

Physical Aspects of Coagulation 273

Physical action of salts in the coagulation of colloidal
mixtures — Physical changes in coagulation.

Secretion 276

Speed of absorption and secretion.

Ill

Respiration

Chemistry of Respiration 277

Estimation of oxygen, carbon dioxide, and water.

Metabolism 278

Effect of muscular exercise on the oxygen, carbon dioxide,
and water of the respired air — Individual level of pro-
teid metabolism — Nitrogenous equilibrium — Effect of
muscular exercise on proteid metabolism.

PAET III

THE OUTGO OF ENERGY

I
Animal Heat

Animal Heat 285

Regional temperature — Effect of hot and cold drinks on
the temperature of the mouth — Hourly variation — Re-
action of cold and warm blooded animals to changes in
the external temperature — Chemical action the source
of animal heat.

CONTENTS XV

n

The Electromotive Phenomena of Muscle and
Nerve

Page

The Demarcation Current of Muscle 287

Demarcation current of muscle — Stimulation by demarca-
tion current — Interference between demarcation current
and stimulating current ; polar refusal.

Demarcation Current of Nerve 295

Nerve may be stimulated by its own demarcation current.

Hypotheses regarding the Causation of the De-
marcation Current 297

Action Current of Muscle 302

Rheoscopic frog — Action current in tetanus; stroboscopic
me.thod — Action current of human muscle — Action
current of heart.

Action Current of Nerve 315

Negative variation — Positive variation — Positive after
current — Contraction secured with a weaker stimulus
than negative variation — Current of action in optic
nerve — Errors from, unipolar stimulation.

Secretion Current 320

Secretion current from mucous membrane — - Negative vari-
ation of secretion current.

Electrotonic Currents 323

Negative variation of electrotonic. currents ; positive vari-
ation (polarization increment) of polarizing current
— Electrotonic current as stimulus.

Electric Fish 329

XVI CONTENTS

III

The Change in Form

Page

Volume of Contracting Muscle 331

The Single Contraction or Twitch 332

Muscle curve — Duration of the several periods — Exci-
tation wave — Contraction wave — Relation of strength
of stimulus to form of contraction wave — Influence of
load on height of contraction — Influence of temperature
on form of contraction — Muscle warmer — Influence of
veratrine on form of contraction.

Tetanus 346

Superposition of two contractions — Superposition in teta-
nus — Relation of shortening in a single contraction to
shortening in tetanus.

The Isometric Method 349

Graduation of isometric spring — Heavy muscle lever —
Isometric contraction.

Contraction of Human Muscle 353

Simple contraction or twitch — Ergograph — Isometric
contraction — Artificial tetanus — Natural tetanus.

Smooth Muscle 356

Spontaneous contractions — Simple contraction — Tetanus.
The Work Done 358

Influence of load on work done — Absolute force of mus-
cle — Total work done ; the work adder — Total work
done estimated by muscle curve — Time relations of
developing energy.

Elasticity and Extensibility 363

Elasticity and extensibility of a metal spring — Of a rubber
band — Of skeletal muscle — Extensibility increased in
tetanus.

Fatigue 366

Skeletal muscle of frog — Human skeletal muscle

CONTENTS XVll

IV

The Central Nervous System

Page

Simple Reflex Actions 370

The spinal cord a seat of simple reflexes — Influence of
afferent impulses on reflex action — Threshold value
lower in end organ than in nerve-trunk — Summation
of afferent impulses — Segmental arrangement of reflex
apparatus — Reflexes in man.

Tendon Reflexes 375

Knee jerk — Ankle jerk — Gower's experiment.

Effect of Strychnine on Reflex Action .... 377

Complex Co-ordinated Reflexes 377

Removal of cerebral hemispheres — Posture, etc. — Bal-
ancing experiment— Retinal reflex — Croak reflex.

Apparent Purpose in Reflex Action 381

Reflex and Reaction Time 382

Reflex time — Reaction time — Reaction time with choice.

Inhibition of Reflexes 384

Through peripheral afferent nerves — Through central
afferent paths; the optic lobes.

The Roots of Spinal Nerves 386

Ludwig's demonstration — Localization of movements at
different levels of the spinal cord.

Distribution of Sensory Spinal Nerves .... 388

Muscular Tonus 389

Brondgeest's experiment.

V

The Skin

Sensations of Temperature 390

Hot and cold spots — Outline — Mechanical stimulation
— Chemical stimulation — Electrical stimulation — Tem-
perature after-sensation — Balance between loss and gain

XVU1 CONTENTS

of heat — Fatigue — Relation of stimulated area to sen
sation — Perception of difference — Relatively insensitive
regions.

Sensations of Pressure 393

Pressure spots — Threshold value — Touch discrimina-
tion — Weber's law — After-sensation of pressure —
Temperature and pressure — Touch illusion ; Aristotle's
experiment.

VI
General Sensations

Tickle 398

Irradiation — After image — Topography — Summation —
Fatigue.

Pain 399

Threshold value — Latent period — Summation — Topog-
raphy— Individual variation — Temperature stimuli.

Motor Sensations 400

Judgment of weight — Sensation of effort — Sensation of
motion.

VII
Taste

Taste 401

Threshold value — Topography — Relation of taste to area
stimulated — Electrical stimulation.

VIII

Introduction to Physiological Optics

Reflection from Plane Mirrors 403

Angles of incidence and reflection.

Reflection prom Concave Mirrors 405

Principal focus — Conjugate foci — Virtual image — Con-
struction of image from concave mirrors.

CONTEXTS xix

Page

Reflection from Convex Mirrors 410

Refraction 410

Refraction by Prisms 413

Construction of the path of a ray passing through a prism.

Refraction by Convex Lenses 416

Principal focus — Estimation of principal focal distance —
Conjugate foci — Virtual image — Construction of image
obtained with convex lens.

Refraction by Concave Lenses 422

Refraction by Segments of Cylinders 422

Refraction through Combined Convex and Cylin-
drical Lenses 424

Aberration 426

Spherical aberration by reflection — Spherical aberration
by refraction — Dispersion circles — Myopia — Hyper-
metropia — Chromatic aberration — Aberration avoided
by a diaphragm,

Numbering of Prisms and Lenses 435

Numbering of prisms — Numbering of lenses.

IX

Refraction in the Eye

Refraction in the Eye 437

The eye as a camera obscura.

The Schematic Eye 438

Cardinal Points of the Cornea (System A) . . . 440
Construction drawing of System A — Principal focal dis-
tances — Construction of image — Calculation of position
to conjugate foci.

Cardinal Points of the Crystalline Lens (System B) 445
Construction drawing of System B — Optical centre — Nodal
points — Principal surfaces — The point s — Principal
points — Principal focal distances.

Cardinal Points of the Eye (System C) . . . . 451
Principal surfaces — Nodal points — Principal foci.

XX CONTENTS

Page
Calculation of the Situation and Size of Dioptric

Images 456

Reduced Eye 458

Relations of the Visual Axis 463

Visual angle — Apparent size — Size of retinal image —
Acuteness of vision — Smallest perceptible image —
Measurement of visual acuteness.

Accommodation 469

Schemer's experiment — Dispersion circles — Diameter
of circles of dispersion — Accommodation line.

Mechanism of Accommodation 473

Narrowing of pupil — Relation of iris to lens — Changes
in the lens.

Measurement of Accommodation 479

Far point — Determination of far point — Near point —
Determination of near point — Range of accommodation.

Ophthalmoscopy 484

Reflection from retina — Influence of angle between light
and visual axis — Influence of size of pupil — Influence
of nearness to pupil — Ophthalmoscope.

Direct Method 490

Emmetropia — Ametropia ; qualitative determination —

Measurement of myopia — Measurement of hypermetro-

pia — Measurement of astigmatism.
Indirect Method 496

Vision

Viston 499

Mapping the blind spot — Yellow spot — Field of vision.

Color Blindness 501

Method of examination and diagnosis.

CONTENTS XXI

XI

Mechanics of Respiration

Page

Mechanics of Respiration 505

Artificial scheme — Inspiration — Expiration — Normal
respiration — Forced respiration — Obstructed air pas-
sages — Asphyxia — Coughing ; sneezing — Hiccough —
Perforation of the pleura.

XII

The Circulation of the Blood

The Mechanics of the Circulation 508

Circulation scheme.
The Conversion of the Intermittent into a Con-
tinuous Flow 515

The Relation between Rate of Flow and Width

of Bed 519

The Blood-Pressure 521

Relation of peripheral resistance to blood-pressure —
Curve of arterial pressure in the frog — Effect on blood-
pressure of increasing tbe peripheral resistance in the
frog — Changes in the stroke of the pump; inhibition
of the ventricle — Effect of inhibition of the heart on
the blood-pressure in the frog.

The Heart as a Pump 525

Opening and closing of the valves — Period of outflow
from the ventricle — Sphygmograph tambour — Visible
change in form — Graphic record of ventricular contrac-
tion.

The Heart Muscle 530

All contractions maximal — Staircase contractions — Iso-
lated apex ; Bernstein's experiment — Rhythmic con-
tractility of heart muscle — Constant stimulus may cause
periodic contraction — Inactive heart muscle still irri-
table— Refractory period; extra-contraction; compen-
satory pause — Transmission of the contraction wave
in the ventricle ; Engelinann's incisions — Transmission

xxii CONTENTS

Page
of the cardiac excitation from auricle to ventricle;
GaskeU's block — Tonus — Influence of "load" on ven-
tricular contraction — Influence of temperature on fre-
quency of contraction — Action of inorganic salts on
heart muscle.

The Heart Sounds 541

The Pressure-Pulse 543

Frequency — Hardness — Form — Volume — Pressure-
pulse in the artificial scheme — Human pressure-pulse
curve — Low tension pressure-pulse — Pressure-pulse
in aortic regurgitation — Stenosis of the aortic valve
— Incompetence of the mitral valve.

The Volume Pulse 552

XIII

The Innervation of the Heart and Blood-Vessels

The Innervation of the Heart and Blood- Vessels 554

The Augmentor Nerves of the Heart 555

Preparation of the sympathetic — Action of sympathetic
on heart.

The Inhibitory Nerves of the Heart 558

Preparation of the vagus nerve — Stimulation of cardiac
inhibitory fibres in vagus trunk — Effect of vagus
stimulation on the auriculo-ventricular contraction in-
terval — Irritability of the inhibited heart — Intracar-
diac inhibitory mechanism — Inhibition by Stannius
ligature — Action of nicotine — Atropine — Muscarine
— Antagonistic action of muscarine and atropine.

The Centres of the Heart Nerves 564

Inhibitory centre — Augmentor centre — Reflex inhibition
of the heart ; Goltz's experiment — Reflex augmentation.

The Innervation of the Blood-Vessels .... 568
Bulbar centre — Vasomotor functions of the spinal cord —
Effect of destruction of the spinal cord on the distri-
bution of the blood — Vasomotor fibres leave the cord
in the anterior roots of spinal nerves — Vasoconstrictor
fibres in the sciatic nerve — Vasodilator nerves — Reflex
vasomotor actions.

ft

ILLUSTRATIONS

Diagrams which merely illustrate the grouping of apparatus for a par-
ticular experiment are omitted from this list.

Fig. Page

1. Muscles of left hind limb of frog, dorsal view . . 6

2. Nerve-muscle preparation 7

3. Muscle clamp, stand, and nerve-holder .... 8

4. Tension indicator 25

5. Stage electrometer 38

6. Long rheochord 43

7. Square rheochord 44

8. Simple key 45

9. Short-circuiting key 46

11. Pole-changer, early form 49

12. Rocking key 50

14. Inductorium 54

15. Platinum electrodes 65

16. Flat-jawed clamp and round-jawed clamp .... 66

17. Double clamp 66

19. Long paper kymograph 82

20. Smoker 84

21. Light muscle lever 86

22. Tuning fork 87

23. ISTon-polarizable electrodes 94

24. Moist chamber 95

25. Hind limb of frog, anterior view 99

25. Gaskell clamp 103

26. Electro-magnetic signal 105

28. Frog board 112

XXIV ILLUSTRATIONS

Fig. Page

35. Motor points on the anterior surface of the forearm

and hand 128

36. Motor points on the posterior surface of the forearm 129

and hand

38. Brass electrodes 132

42. Gas chamber, with bottle for generating curbon

dioxide 172

43. Sartorius 181

44. Gracilis 183

48. Scheme of myomeres in a parallel-fibred muscle . . 298

49. Scheme of myomeres in an oblique section . . . 299

50. Vibrating interrupter 303

51. Vibrating interrupter arranged to make one contact

per second 304

53. Heart lever 311

54. Scheme of differential rheotome 313

58. Volume tube 332

59. Muscle warmer 343

60. Heavy muscle lever 351

61. Ergograph 354

62. Work adder 359

63. Lantern and optical box 404

65. Reduced eye 459

67. Respiration scheme 504

68. Quantitative circulation scheme 512

69. Mercury manometer 523

70. Sphygmograph 527

71. Sphygmograph tambour 528

72. Scheme of sympathetic nerve in frog 556

73. Scheme of cervical nerves in frog 558

74. View of brain of frog from above 565

PART I

THE GENERAL PROPERTIES OF LIVING
TISSUES

PART I

THE GENERAL PROPERTIES OF
LIVING TISSUES

INTRODUCTION

Until recent times it was believed that many of
the compounds found in the tissues of animals
and plants could be made only by the action of
organized, i. e. living matter. Such compounds
were called organic to distinguish them from
those found in inorganic or inanimate nature.
The forces producing organic compounds were
thought to be partly the ordinary chemical
and physical processes known to science, and
partly certain mystical agencies termed vital
forces. The great discovery of Wohler in
1828 that urea (C02NH2), a typical organic
compound, could be made synthetically in the
laboratory, overthrew this conception and was
the beginning of a long and fruitful struggle to

4 GENERAL PROPERTIES OF LIVING TISSUES

bring the phenomena of living matter within
the operation of chemical and physical laws
without recourse to the supernatural and occult.
According to this new, unified view of nature,
which is the foundation of modern physiology,
all phenomena, whether animate or inanimate,
are alike the expression of chemical and physi-
cal processes, some known, some unknown, none
of which is fundamentally different from the
rest.

The physiologist, therefore, now looks upon
the reactions of living matter with the eye of
the physicist, and it is of the first importance
to beginners in physiology to acquire this point
of view. To this end it is desirable to consider
living tissues from the standpoint of energy and
to divide, even imperfectly, the functions to be
studied into those that have to do with the
income of energy and those that are active in
its outgo. These studies cannot, however, be
profitably undertaken without some acquaint-
ance with the general properties of living tissues,
such as irritability and contractility.

We shall begin, therefore, by examining a
motor nerve and the muscle in which its fibres
are distributed.

The Nerve-Muscle Preparation. — Wrap the
frog in the cloth, the head out. Pass one blade

INTRODUCTION 5

of the stout scissors between the jaws. Bring
this blade to the angle of the jaw, the other
blade over the junction of the head and trunk.
Cut off the skull with a single closure of the
scissors. Thrust the pithing wire into the cranial
cavity and then into the vertebral canal, destroy-
ing the brain and spinal cord. The frog ceases
to move; the muscles are relaxed. Divide the
body transversely behind the fore limbs. Ee-
move the viscera. Seize the spinal column with
the finger and thumb of one hand, and the
skin of the back with the other hand, covered
with a cloth to prevent slipping. Draw the
hind limbs out of the skin. Lay the limbs
down, back uppermost, upon a clean glass
plate, which the outside of the frog's skin has
not touched. The skin of the frog, like that of
the salamander and some other batrachians, is
provided with a protective secretion injurious to
sensitive tissues. Note on the outside of the
thigh the triceps femoris muscle ; on the median
side, the semi-membranosus ; between these, the
narrow biceps femoris. (Fig. 1.) Cautiously di-
vide the connective tissue between the semi-
membranosus and the biceps femoris. On
drawing these muscles apart, the sciatic nerve
and the femoral vessels will be seen. Clear the
nerve with scissors and forceps from the knee

GENERAL PROPERTIES OF LIVING TISSUES

to the vertebral column. The nerve itself should
not be touched with the instruments. Near the
pelvis it will be necessary to divide the pyriform
and the iliococcygeal muscles: carefully avoid

the nerve while do-
ing this.

With the forceps
lift the tip of the
urostyle (the 10th
vertebra, a long, slen-
der bone which forms
the caudal end of the
vertebral column)
and remove the bone
with the stout scissors
as far as the 9th
vertebra. Divide the
spinal column trans-
versely between the
Fig. i. Muscles of left hind limb of 6th an(^ 'th vertebrae.

frog, <lorsal view (Ecker and Wieders- Tiivyi the ffO0" back
heim ). °

down. Bisect length-
wise the 7th, 8th, and 9th vertebras. Grasp
the half from which the prepared nerve springs
and lift it gently, freeing the nerve with the
scissors down to the knee.

Puss now to the leg. Cut through the Achil-
les tendon of the gastrocnemius muscle below

INTRODUCTION

the thickening at the heel. Free the muscle up

to its origin from the femur, taking care not to

harm the branch of the nerve which enters the

muscle on its posterior surface near the knee.

Cut through the tibia about one

centimetre from the knee-joint.

Clear away the muscles of the

thi^h from the lower end of the

femur, avoiding the sciatic nerve.

Cut through the femur about

its middle. (Fig. 2.) Lay the

sciatic nerve for safety along the

gastrocnemius muscle. Fasten

the lower fragment of the femur Fi°- 2- Nerve-mus-

cle preparation; gas-
in the jaWS Of the mUSCle Clamp, trocnemius muscle

cinil scititic nerve F

Let the whole nerve rest with- end of femur jn.'sci-
out stretching on the adjustable l?ha™aS-
plate or nerve-holder, the filter meat of smaller ten-

don of gastrocnemius

paper Covering Which Should be to femur (Handbook

, . , , , . for the Physiological

moistened with normal saline Laboratory).
solution (0.6 per cent NaCl).
Take care that the nerve does not dry between
the nerve-holder and the muscle. (Fig. 3.) The
filter paper should reach from the nerve-holder
to the muscle.

Preliminary Considerations regarding Energy,
Stimulation, and Irritability. — Pinch the muscle
sharply with the forceps.

8 GENERAL PROPERTIES OF LIVING TISSUES

The muscle passes into the active state; it
shortens and thickens. The foot, which is rela-

Fig. 3. The muscle clamp, stand, and nerve-holder. The nerve-holder
supports the sciatic nerve, together with the portion of the spinal column
from which it springs. The handle of the nerve-holder is of thick lead
wire which may be bent as desired. The binding post on the muscle clamp
provides electrical connection with the upper end of the muscle.

tively less fixed than the leg, is extended. The
contraction is followed by a slower relaxation or
return to the original form.

INTRODUCTION 9

Observe that the mechanical act of pinching
caused the resting muscle to become active. Its
stored energy was transformed into external,
mechanical work, i. e„ the moving of the foot.
Not all of the energy set free takes this easily
visible form. It will be shown later that much
of it is made active as molecular motion, in the
form of heat, chemical action, and electricity.
Agents which occasion a transformation of
energy within the living body are termed stim-
uli, and tissues which convert energy of one
form into energy of another in consequence of
stimulation are said to be irritable. All living
tissues are alike irritable, but the form in which
their kinetic or active energy appears differs
with the nature of the tissue. The contrast
between muscle and nerve in this respect is
especially instructive.

Pinch the end of the nerve.

No change will be seen in the nerve, but the
muscle will contract.

Thus, while the most conspicuous form which
the energy of muscle takes, when set free, is
mechanical, the active nerve does not alter its
form, but spends its energy in a molecular
change, the nerve impulse, which passes from
point to point along the nerve to the muscle,
or gland, or other structure connected function-

10 GENERAL PROPERTIES OF LIVING TISSUES

ally to the nerve. The effect produced by
the nerve impulse depends on the nature of
the tissue in which the nerve ends ; for ex-
ample, the energy set free in secreting glands
is especially chemical; that set free in the
electrical organ of Torpedo is especially elec-
trical. In considering these illustrations of the
ways in which the energy of living tissue may
be set free, however, two facts should always
be kept in mind ; first, that by far the greater
part of the stored energy of the body is set
free as heat; and secondly, that while the sev-
eral tissues are characterized by the especial
prominence of some one form of energy, as
contractility in the case of muscle, and the
production and conveyance of a nerve impulse
in the case of nerve, yet the transformation of
energy in each tissue is a complex process,
many steps of which, for example heat and
chemical action, are common to all living
substance.

We have made, then, the fundamental obser-
vation that an adequate stimulus will occasion
in muscle a conversion of latent energy into
mechanical change in form and in the nerve a
molecular change that passes along the nerve as
a nerve impulse. We must now examine sys-
tematically the usual methods of exciting the

INTRODUCTION 11

transformation of energy and inquire concerning
their effect on muscle and nerve.

Apparatus

Normal saline. Bowl. Cloth. Pithing wire. Scissors.
Forceps. Pipette. Glass plate. Cement. Foil. Nerve-
holder (filter paper). Muscle clamp. Stand. Frog.

12 GENERAL PROPERTIES OF LIVING TISSUES

II
METHODS OF ELECTRICAL STIMULATION

Introduction

The stimulus most usually employed in the
laboratory is electricity, because electricity will
stimulate when used in quantities which do not
destroy the tissues, as do many mechanical,
chemical, and thermal stimuli, and because the
intensity and duration of the electrical stimulus
can be graduated with accuracy. It will be
necessary, therefore, to examine with especial
care the methods and the results of electrical
stimulation. These matters are involved with
problems of ionisation, surface tension, osmosis,
and other molecular actions highly important
in many fields of physiology. Such interde-
pendent phenomena cannot be studied profitably
without working hypotheses that shall attempt
to relate them as forms of energy.

Kinetic Theory. — The particles of a gas, the
simplest state in which matter exists, are identi-
cal with its chemical molecules. These particles

METHODS OF ELECTRICAL STIMULATION 13

are assumed by Clausius and Maxwell to be in
constant rapid motion in all directions. It is
this motion which causes the "disappearance"
of a gas " set free " in the open air. The mole-
cules of air are also in rapid motion and fre-
quently collide with each other and with those
of the escaping gas, but the air molecules are
far from rilling the space in which they move
and the molecules of gas rapidly pass off be-
tween them. In their flight, they strike with
a measurable force whatever opposes them, be
it another flying molecule or some boundary
wall. The force of the blow is the "pressure"
of the molecule. If the gas be confined by an
impermeable wall, that is, a wall the inevitable
openings in which are too small for the gas
molecules to pass, the sum of the blows of the
molecules dashing against this wall will be the
total pressure of the gas.

Partial pressure. — If the molecules of a second
gas be within the containing vessel, they also
will strike the boundary. The force of their
blows will be entirely independent of the force
of the blows struck by the molecules of the
first gas. It is as if black and white balls were
thrown at the same time against a wall ; their
blows would be independent of each other.

The molecules of gas and the confining walls

14 GENERAL PROPERTIES OF LIVING TISSUES

are assumed to be perfectly elastic, so that the
motion of a molecule is not lost when it collides
with another molecule or strikes the wall; the
direction of the flight is changed but the swift-
ness is unimpaired. The speed of the molecules
of a gas is inversely proportional to the square
root of its density. At 0° C. the molecule of
oxygen moves at the rate of almost eighteen
miles per minute.

Diffusion of gases. — The molecules of two
gases moving in the same space will intermix
or " diffuse," but the rate will be surprisingly
slow, for at ordinary pressures the molecules of
gases are so near together that they cannot move
far without colliding and rebounding. Their prog-
ress in any one direction is thus greatly hindered.

Every particle of matter attracts every other
particle. Van der Waal assumes that with gases
this attraction is proportional to the square of
the density of the gas. Where the density is
slight, that is, where there are few molecules in
proportion to the space in which they move, this
attraction need not be taken into account, but
where the confining space is small, thus crowd-
ing the molecules together, this attraction be-
comes important. It is still more important in
the case of liquids, for in liquids the molecules
are much nearer than in a gas.

METHODS OF ELECTRICAL STIMULATION 15

Vapor pressure. — Were it not for the attrac-
tive or cohesive force just mentioned, the mole-
cules of a liquid would rapidly pass into the
space surrounding the liquid and the liquid
would soon disappear (evaporation). But the
molecules are so close together that their attrac-
tion for each other largely prevents escape.
Nevertheless, the motion of many of the mole-
cules at or near the surface of the liquid is
sufficient to break through this force of cohesion.
These molecules escape and their places are
taken by molecules which may in turn escape.
Thus evaporation proceeds. In the vapor above
the liquid the escaping molecules collide with
other molecules and may be driven by the recoil
back into the liquid. If the liquid be in a
confined space, the number of vapor molecules
recoiling into the liquid will increase, partly
because they are brought nearer together and
collisions are thus more frequent and partly
because the molecules rebound from the con-
taining wall. When the number of molecules
returning equals the number leaving the liquid,
the vapor and the liquid are in equilibrium
(saturation). In other words, the vapor tension
or pressure or force with which the liquid mole-
cules tend to leave the liquid is balanced by the
gas pressure or force with which the gas mole-

16 GENERAL PROPERTIES OF LIVING TISSUES

cules strike against the liquid. As the speed
of the molecules and therefore their power to
escape from the liquid rises with the tempera-
ture, the vapc? pressure will also rise with the
temperature.

Solution of a gas in a liquid. — A liquid
brought near a gas is struck by many of the
moving molecules of the gas. Some of these are
held by the attractive force of the liquid. Some
will at length escape. Finally, as the number
of molecules striking the surface of the liquid
remains constant at the same pressure, the gas
molecules leaving the liquid will equal the number
entering (saturation).

Solution of a solid in a liquid. — When a crys-
talline solid is placed in a liquid solvent, particles
escape from the solid and enter the liquid. Some
of these particles again enter the solid and are
bound by it. Saturation is reached when the
number of particles entering and leaving the
solid is equal.

Solution tension. — The force with which the
particles of the solid pass into the solvent is
termed the solution tension. There is equili-
brium, i. e. saturation, when the solution tension
is balanced by the force with which the particles
in the solvent return to the solid.

Osmotic Pressure. ■ — It has been found that

METHODS OF ELECTRICAL STIMULATION 17

hydrogen gas will pass through the metal palla-
dium when the metal is heated to 200° C. Nitro-
gen will not pass through. Palladium at 200° C.
is therefore said to be semi-permeable, i. e. it is per-
meable to one gas, but not to another. If a tube
of palladium at 200° containing nitrogen gas at
a pressure of one half atmosphere be placed in a
vessel containing hydrogen gas at a pressure of
one atmosphere, the hydrogen will pass through
the palladium into the tube until the pressure
of the hydrogen inside equals that outside the
tube, namely, oue atmosphere. The pressure in
the tube will now be almost one and one half
atmospheres, which is the sum of the partial
pressure of the nitrogen (one half atmosphere)
and the partial pressure of the hydrogen (one
atmosphere), less an error due chiefly to the im-
perfect permeability of the palladium. Thus the
pressure on one side of the palladium will be
higher than that on the other side, as may be
shown by connecting the tube with a manometer.

Substances in solution may exert a force like
the partial pressure of a gas. This force is called
osmotic pressure.

Osmotic pressure is measured most readily by
the aid of semi-permeable membranes, first used
for this purpose by Pfeffer. For demonstration
they may be made as follows. Wash a porcelain

18 GENEKAL PROPEKTIES OF LIVING TISSUES

diffusion bulb twenty-four hours in running
water. Dry the bulb and coat its neck inside
and out with paraffin ; when this has become
firm, fill the bulb to above the lower edge of the
paraffin with solution of copper sulphate (2.5 gm.
per litre). Place the bulb in a beaker and pour
in a solution of potassium ferrocyanide (2.1 gm.
per litre) until the lower edge of the paraffin is
covered. Keep the bulb in this solution over
night. Where the two solutions meet within the
clay wall a precipitation membrane of copper
ferrocyanide will form. This membrane is sup-
ported by the clay wall. Pour out the contents
of the bulb and rinse with cold distilled water.
Through such precipitation membranes water
and some other solvents will readily pass, while
many salts dissolved in the solvent are kept
back.

Fill the bulb with one per cent solution of
cane sugar. Insert in the neck of the bulb a
tightly fitting rubber stopper pierced by a small-
bore glass tube about ten feet long. Stand the
bulb in distilled water and support the long
tube in suitable clamps. The sugar will not pass
out through the membrane, but water will pass
through it into the bulb, and the solution will
rise in the tube at the rate of several inches an
hour. The rate is slow because the friction in

METHODS OF ELECTRICAL STIMULATION 19

the artificial membrane is great ; the osmosis of
salts through living membranes may be very rapid.
When the liquid in the tube is high enough to
balance the force with which the water would
pass through the membrane, the flow ceases.
The difference in water level is the osmotic
pressure, the analogue of gas pressure. The maxi-
mum osmotic pressure is so great that only perfect
semi-permeable membranes will support it.

It will be obvious upon reflection that osmotic
pressure must be independent of the semi-per-
meable membrane. The solvent is continuous
through the membrane. The only function of
the membrane is to render the osmotic pressure
visible.

With constant temperature the osmotic pres-
sure is nearly proportional to the concentration
of the solution.

Concentration

Osmotic pressure

of solution of

in centimetres

Ratio.

cane-sugar.

of mercury.

Per cent.

1

53.5

53.5

2

101.6

50.8

2.74

151.8

55.4

4

208.2

52.1

6

307.5

51.3

The osmotic pressure increases as the tempera-
ture rises.

20 GENERAL PROPERTIES OF LIVING TISSUES

Ten years after these observations were pub-
lished by Pfeffer, Van't Hoff pointed out the
analogy between osmotic pressure and gas pres-
sure. It has just been shown that, if the tem-
perature be constant, the osmotic pressure is
proportional to the amount of dissolved substance
in a given volume ; thus the osmotic pressure
of a solution, like that of a gas, varies inversely
with the pressure. Moreover, the osmotic pres-
sure, like gas pressure, increases with the tempera-
ture. Pfeffer observed that the osmotic pressure
of a cane sugar solution at 14.2° C. was 51 cm.
Hg. Assuming that the osmotic pressure, like
gas pressure, is proportional to the absolute
temperature, Pfeffer then determined by calcula-
tion that the osmotic pressure of this same
solution at 32.0° C. should be 54.2 cm. Actual
observation gave 54.4 cm.

In short, the osmotic pressure of a dissolved
substance is numerically equal to the pressure
which the substance would exert were it present
as a gas.

Plasmoiysis. Isotony. — The cells of Trades-
cantia discolor possess a strong outer envelope
permeable by both water and salts, and a thin
inner envelope permeable by water, but not by
salts. The cell is filled with an aqueous solution
of glucose, salts of malic acid, etc. The osmotic

METHODS OF ELECTRICAL STIMULATION 21

pressure of the contents is from four to six
atmospheres. When the cell is placed in water,
the water penetrates both envelopes and the cell
swells so far as the resistant outer envelope
may permit. In a concentrated salt solution,
the osmotic pressure pushes the inner envelope
away from the outer envelope, contracting the
volume of the cell contents (plasmolysis), and
water leaves the cell until the concentration of
the cell contents equals that of the surrounding
solution. Solutions whose concentration is such
that cells immersed in them are not deformed
must possess the same osmotic pressure. Such
solutions are termed isotonic or isosmotic.

Estimation of Osmotic Pressure in the Blood
Serum. 1. The method of de Vries.1 — Make a
section along the midrib of the violet side of
the leaf of Tradescantia discolor and two other
sections one on each side, parallel to and about
2 mm. from the first. Now make transverse
sections across the three vertical sections about
5 mm. apart, and a final very thin section paral-
lel to the surface. Place some of these thin tan-
gential sections in the serum diluted with 20 per
cent of water, and others in salt solutions of
different concentrations (0.60, 0.65, 0.70, 0.75, 0.80

1 de Vries: Zeitschrift fur physikalische Chemie, 1888, ii,
p. 419.

22 GENERAL PROPERTIES OF LIVING TISSUES

per cent). From time to time remove the sec-
tions and observe under the microscope whether
plasmolysis is present. The serous fluid that
causes plasmolysis in half the cells immersed
in it, is isotonic or " normal " with the salt solu-
tion having the same effect.

For example, if there were used 5 c.c. serum
+ 1 c.c. water with 0.8 per cent solution of sodium
chloride, the original serum would be isotonic

with a sodium chloride solution of — — — x 0.8

5

= 0.96 per cent.

Should the osmotic pressure of the serum be
too slight to call forth plasmolysis in the cells
employed, add to the serum measured quantities
of a strong saline solution, e. g. 5 per cent sodium
chloride solution.1

2. The blood- corpuscle method of Hamburger?
— Place 5 c.c. serum in each of six test-tubes.
To these add from a burette 3.1, 3.0, 2.9, 2.8, 2.7,
and 2.6 c.c. water, respectively. Into each tube
let fall three drops of defibrinated blood, and mix

1 Hamburger : Osmotischer Drack und Ionenlehre, 1902,
i, p. 438.

The cells of Tradescantia cannot be used for the measure-
ment of osmotic pressure in acid solutions. For the urine, the
cells of Begonia manicata should be used.

2 HAMBURGER : Loc. tit. pp. 185 and 439. Also Archiv fur
Physiologic, 1887, p. 31.

METHODS OF ELECTRICAL STIMULATION 23

by shaking, taking care that the mixture does
not foam too much.

In each of six other test-tubes place 8 c.c.
sodium chloride solution of 0.62, 0.61, 0.60, 0.59,
0.58, and 0.57 per cent, respectively. Into each
tube let fall three drops of the same defibrinated
blood. Mix as before. After some hours the
red corpuscles will have settled to the bottom
in all the tubes.

In the first series the clear fluid will be red
in some of the tubes. For example, the fluid in
the tubes diluted with 3.1, 3.0, and 2.9 c.c. water
may be red, while in the three other tubes it may
not be red. In this case the mixture of 5 c.c.
serum + 2.9 c.c. water has caused the haemo-
globin to escape from the corpuscles (" laked "
the blood), while the mixture of 5 c.c. serum
+ 2.8 c.c. water has not accomplished this.

If the tubes with salt solution be now exam-
ined, escaped haemoglobin will be found only in
the 0.58 per cent and the weaker solutions. Con-

sequently the mixture of 5 c.c. serum H — : — ^ — —

water is isotonic with a sodium chloride solution

. 0.59 + 0.85 _ ^0_ _

of « = 0.5 8 o per cent. Hence the un-
diluted serum is isotonic with a sodium chloride

5 _l_ 2 85
solution of =^ — x 0.585 = 0.92 per cent.

24 GENERAL PROPERTIES OF LIVING TISSUES

In a solution of this concentration the red blood-
corpuscles of mammals are in osmotic equi-
librium.1 The isotonic (isosmotic or normal)

1 In this calculation it is assumed that the osmotic pressure
is proportional to the concentration. This is not strictly cor-
rect. When serum is diluted with an equal volume of water,
the osmotic pressure of the resulting liquid is not merely half
so large as before, but is somewhat greater than one half the
original pressure. For when the water is added, a part of the
molecules not yet dissociated are split into ions and each ion
has an osmotic pressure equal to that of an undissociated mole-
cule. If the serum upon dilution with water followed the
same dissociation curve as the sodium chloride solution of 0.92
per cent, the above method of calculation would be strictly
correct. This is, however, not the case ; on the contrary, the
dissociation curves separate from each other. But this devia-
tion, in the case of the dilutions considered here, lies within
the limit of errors of observation, probably because the osmotic
pressure of the serum is due chiefly to sodium chloride (Ham-
burger, p. 186).

The above calculation also leaves out of account the fact
that the blood-corpuscles are permeable for anions. It is evi-
dent that the exchange of ions between blood-corpuscles and
surrounding liquid will differ according as this liquid is dilute
serum or pure sodium chloride solution. For the partial ten-
sion of the ions in the two solutions is not the same. The
partial pressure of the CI' ions in the 0.6 per cent sodium
chloride solution is greater than in the serum diluted with 60
per cent water; while in the serum there is a pressure of
CO'" ions, lacking in the sodium chloride solution. Moreover,
the blood-corpuscles placed in these liquids acquire a different
composition. The osmotic pressure of the blood-corpuscles is
increased by immersion in sodium chloride solution.

Dissociation and permeability act with opposite sign, balanc-
ing each other. That the blood-corpuscle method is practically

METHODS OF ELECTRICAL STIMULATION

25

concentration for the corpuscles of frog's blood is
0.6 per cent.

Surface Tension. — The osmotic pressure of
solutions is very great. In the ordinary reagents
of the laboratory it amounts to many atmos-
pheres. Obviously, such solutions could not be
kept in thin glass beakers or
bottles were these enormous
pressures not restrained by
some opposing force. This op-
posing force is surface tension,
which acts with a pressure of
probably hundreds of atmos-
pheres upon the free surface of
a liquid, whether that surface
be bounded by air or glass.
The semi-permeable membrane
is filled with liquid, and there-
fore does not present a free
surface.

1. A thick wire is bent to enclose a right-
angled space and the end prolonged for a handle.
(Fig. 1.) A very fine slack-wire divides the space
in halves.

Fig. 4. The tension
indicator.

accurate may be shown by comparison with the method of
estimating osmotic pressure by the depression in the freezing-
point of the solution, which is proportional to the concentration
of the solution (p. 439).

26 GENERAL PROPERTIES OF LIVING- TISSUES

Dip the tension indicator into a soap solution.

A thin layer of the solution will span the
frame on both sides of the dividing wire. The
tension of the membrane on one side of the di-
viding wire compensates that on the other and
the wire will not move.

Hold the frame in a vertical position. The
cross wire will sink slightly, owing to the force
of gravity. Absorb the lower membrane with
filter paper.

The cross wire will at once be lifted against
the force of gravity by the surface tension of the
remaining membrane. Destroy the remaining
membrane and the wire will fall again.

2. Strew lycopodium1 upon a water surface.
In the centre place a few drops of alcohol.

The lycopodium will be driven in all direc-
tions. The surface tension of alcohol is less
than that of water. The water-air surface and
the alcohol-air surface are therefore not in
equilibrium. The water-air surface contracts
violently, and the alcohol-air surface expands,
producing the strong currents made visible by
the motion of the lycopodium.

Electrolysis. — 1. Connect two dry cells in
series (carbon of one cell connected with zinc of
other). Attach wires to the terminal zinc and

1 Be careful not to bring the tycopotliuni near a flame.

METHODS OF ELECTRICAL STIMULATION 27

carbon. Touch the ends of the wires together.
An electric current passes, as evidenced by the
spark when the contact is made or broken, but
no material change can be observed in the me-
tallic conductor.

2. Place two pieces of platinum foil in a solu-
tion of copper sulphate and connect them to the
terminal zinc and carbon as before. Copper will
be deposited on the platinum connected with the
zinc, and oxygen will be deposited on the plati-
num connected with the carbon. Thus the
passage of the current through the conducting
solution or electrolyte has caused a change in
the solution, evidenced by a movement of pon-
derable matter.

Faraday discovered that the quantity of matter
moved by the . current was always proportional
to the quantity of the current, independent of
its strength or speed. In the electrolysis of
hydrochloric acid 96,500 coulombs 1 will set free
1 gm. of hydrogen. Faraday also discovered
that the same quantity of current (96,500 cou-
lombs) which carries 1 gm. of hydrogen will
carry the chemical equivalent of any other sub-

1 A coulomb (ampere) of electricity is the quantity of cur-
rent which, when passed through a solution of silver nitrate in
water, deposits silver on the cathode, or negative pole, at the
rate of 0.001118 gram per second.

28 GENERAL PROPERTIES OF LIVING TISSUES

stance, for example 35.5 gm. of chlorine. In the
above experiment on the electrolysis of copper
sulphate solution, each 31.5 grams of copper
moved to the zinc pole requires the passage of
exactly 96,500 coulombs. The particles of matter
travelling in the solution toward the anode were
called by Faraday the anions and those travel-
ling toward the cathode were called cations. On
reaching the poles the ions give up their electric
charge and resume their simple chemical nature.
Thus each 31.5 grams of copper ions, on reaching
the cathode, gives up 96,500 coulombs of electric-
ity and becomes ordinary copper again, and each
96 grams of sulphate ions gives up 96,500 cou-
lombs and becomes the ordinary radical S04.
This radical cannot exist uncombined in water,
but forms sulphuric acid. S04 + H20 = H2S04
+ O. Thus the liquid around the anode becomes
acid, and actual measurement has shown that the
quantity of sulphuric acid formed at the anode
is exactly equivalent to the quantity of copper
deposited on the cathode.

The ions move very slowly. The high vis-
cosity or internal friction of the liquid opposes a
great resistance to the movement of ions as well
as to the osmosis of dissolved substances. To
drive 1 gm. of hydrion (OH) through pure water
at the rate of 1 cm. per second, a force equal to

METHODS OF ELECTRICAL STIMULATION 29

320,000 tons' weight is required. To diffuse
1 gm. urea through pure water at the rate of
1 cm. per second, 40,000 tons' weight is required.
In dilute aqueous solutions at 18° C. a difference
of potential of 1 volt between electrodes 1 cm.
apart will drive the cation H 10.8 cm. per hour,
the cation Na 1.26 cm., the anion OH 5.6 cm.,
and the anion CI 2.12 cm. per hour.

As the ions move so slowly and as the products
of electrolysis appear at each electrode the
moment the current is made, it is evident that
the ions which immediately appear at the anode
cannot be derived from the same molecules as the
ions which simultaneously appear at the cathode.

" Clausius explains this in the following way :
According to the theory of molecular motion, of
which he has himself been the chief founder,
every molecule of the fluid is moving in an ex-
ceedingly irregular manner, being driven first one
way and then another by the impacts of other
molecules which are also in a state of agitation.

" This molecular agitation goes on at all times
independently of the action of electromotive force.
The diffusion of one fluid through another is
brought about by this molecular agitation, which
increases in velocity as the temperature rises. The
agitation being exceedingly irregular, the encoun-
ters of the molecules take place with various

30 GENERAL PROPERTIES OF LIVING TISSUES

degrees of violence, and it is probable that even at
low temperatures some of the encounters are so
violent that one or both of the compound molecules
are split up into their constituents. Each of these
constituent molecules now knocks about among
the rest till it meets with another molecule of
the opposite kind, and unites with it to form a
new molecule of the compound. In every com-
pound, therefore, a certain proportion of the
molecules at any instant are broken up into their
constituent atoms.

" Now Clausius supposes that it is on the con-
stituent molecules in their intervals of freedom
that the electromotive force acts, deflecting them
slightly from the paths they would otherwise
have followed, and causing the positive constit-
uents to travel, on the whole, more in the positive
than in the negative direction, and the negative
constituents more in the negative direction than
in the positive. The electromotive force, there-
fore, does not produce the disruptions and reunions
of the molecules, but, finding these disruptions
and reunions already going on, it influences the
motion of the constituents during their intervals
of freedom." 1

1 Quoted from Clerk Maxwell by Walker in his admirable
"Introduction to Physical Chemistry," a book to which the
present writer is much indebted.

METHODS OF ELECTRICAL STIMULATION 31

Views of Arrhenius. — It was Arrhenius who
made these ideas regarding the dissociation of
the molecules of solutions into ions quantitative
and thus precise. Feeble electrolytes, i. e. poor
conductors of electricity, are but slightly dis-
sociated, whereas solutions that readily conduct
electricity are largely dissociated. Ionisation
may be measured by the degree of conductivity.
Undissociated molecules carry no electricity. Each
univalent ion has the same load : 96,500 coulombs.

Conductivity depends on the number of the
ions and upon their speed. In this connection
the following observation is of interest. If suc-
cessive quantities of pure water be added to a
salt solution, the conductivity will increase as
the dilution increases. The first factor to be
considered here is the viscosity of the solution,
for the viscosity determines the resistance of the
solution to the passage of ions, and thus determines
the speed of the ions. As the addition of water
continues a point is soon reached at which the
amount of water in the solution is so great in
relation to the amount of salt that the water may
be regarded practically as pure. The addition
of more water should not then appreciably affect
the viscosity and thus the speed of the ions. If
the conductivity were related solely to the speed
of the ions, the conductivity should not then

32 GENERAL PROPERTIES OF LIVING TISSUES

increase upon this further addition of water.
Observation shows that it does increase. It
must therefore depend on the degree of dissocia-
tion, i. e. the number of ions.

When the solution is heated, its viscosity and
thus its fluid friction diminishes ; the ions pass
through it with less difficulty and the conduc-
tivity rises. Non-conducting substances added
to aqueous solutions may affect both the number
and the speed of the ions. The first additions
of alcohol to a dilute solution increase the vis-
cidity, and lessen the speed of the ions ; after a
certain limit, further additions have little effect
on the speed, but markedly lessen the number
of the ions, i e. the degree of ionisation or dis-
sociation. Comparisons of electrical conductivity
in solutions of different concentration can be
made only when the rate at which the ions
move remains the same ; in other words, the
salt, the solvent, and the temperature must be
the same in the two solutions.

Electrolytic solution Pressure. — When a salt
is placed in water it dissolves until its solution
pressure or tendency to pass into solution is
balanced by the osmotic pressure of the dissolved
particles. If the osmotic pressure exceed the
solution pressure, salt will be deposited. As
the salt dissolves, positive and negative ions are

METHODS OF ELECTRICAL STIMULATION 33

formed in equivalent quantities, so that there is
no difference in electrical pressure.

When metallic zinc is placed in dilute sulphu-
ric acid, it dissolves, and positively charged zinc
ions enter the solvent, but no negative ions are
formed at the same time. The solution next
the metal becomes statically charged with posi-
tive electricity, and in consequence the zinc itself
becomes negatively charged. The electrical stress
thereby produced compensates the difference
between the osmotic pressure of the zinc ion and
the electrolytic solution pressure of the zinc.

When copper is placed in a solution of copper
sulphate, the osmotic pressure of the metal ion
exceeds the electrolytic solution pressure of the
metal and metallic copper is deposited on the
surface of the electrode. The metal becomes
positively charged and the solution negatively
charged through the sulphanions that gather at
the layer of solution next the metal. This pro-
cess continues until the electrical stress balances
the difference between the actual osmotic pres-
sure and the electrolytic solution pressure.

The electrical double layer about each elec-
trode is of only molecular thickness, so that the
solution or deposition of an extremely small
quantity of metal is sufficient to establish equi-
librium.

o4 GENERAL PROPERTIES OF LIVING TISSUES

In galvanic cells, in which two metals are
immersed in one or more electrolytes, there are
three sources of electromotive force: the junc-
tion of the metals with the electrolytes, the
junction of the two metallic conductors, and the
junction of the electrolytes. The junction of
the metals with the electrolytes is the principal
source ; the electromotive force produced by the
junction of the metals is slight, and the ions of
different neutral salts move at not far from the
same speed, so that the electromotive force at the
junction of the electrolytes is also relatively
small.

The Electrometer, the Eheocord, and
the Cell

In order to study differences in electrical
potential,1 a galvanometer or some other elec-

1 The difference of potential may be compared to the differ-
ence of water level between a reservoir and its distributing
pipes. It produces an electromotive force, comparable to the
force which moves the water from the higher to the lower level.
The unit of electrical pressure is the volt. The flow through
an hydraulic system is measured by the quantity of water pass-
ing any point in a given time ; similarly the quantity of elec-
tricity is the amount that flows through a cross-section of the
conductor in a given time. The unit of quantity is the ampere.
Electricity passing through a conductor meets with a resistance
which becomes greater as the cross-section of the conductor

METHODS OF ELECTRICAL STIMULATION 35

trometer is necessary. In the galvanometer, the
points of different potential are connected by a
coil of wire near which is suspended a magnet.
When the circuit is completed, the electrical
energy acts on the suspended magnet by induc-
tion, and deflects it to an extent proportionate
to the difference of potential. In the capillary
electrometer, which is the electrometer preferred
here, a capillary tube filled with mercury and
sulphuric acid dips in a wider tube which con-
tains sulphuric acid. The points the potential
of which is to be measured are connected with
the mercury and the acid respectively. When
the connection is made, the tension of the sur-
face of mercury in contact with the acid changes,
causing the mercury to move in the capillary.
The change in surface tension is proportional to

diminishes, just as water can be forced more easily through
wide channels than through narrow ones. The unit of electri-
cal resistance is the ohm. The precise definition of these units
is as follows :

A volt is the electromotive force that, steadily applied to a
conductor whose resistance is one international ohm, will pro-
duce a current of one international ampere. The practical
ampere {coulomb) is the unvarying current which, when passed
through a solution of nitrate of silver in water, deposits silver
on the cathode, or negative pole, at the rate of 0.001118 gram
per second. The ohm is the resistance offered to an unvarying
electrical current by a column of mercury at the temperature
of melting ice, 14.4521 grams in mass, of a constant cross-
sectional area, and of the length of 106.3 centimetres.

36 GENERAL PROPERTIES OF LIVING TISSUES

the difference in potential. The action of the
instrument will be more clear from the follow-
ing experiments.

Surface Tension altered by Electrical Energy. —
In a small porcelain evaporating dish place a
globule of mercury about one inch in diameter.

The cohesion of the mercury is stronger than
the attraction between the mercury and porce-
lain, — the mercury does not " wet " the porcelain.
The free surface of the mercury is curved and
not plane, as it would be were the molecules
acted upon by the force of gravity alone. Obvi-
ously the spreading of the mercury is resisted by
some force that strives to make the drop spher-
ical, i. e. to make the surface as small as possible.

This force is called the surface tension. It is
the attraction which the molecules beneath the
surface exert on the side of the surface layer
next them. The form of the drop is the result
of the equilibrium between these opposing forces
(Thomas Young, 1804).

Cover the mercury one centimetre deep with
5 per cent sulphuric acid. Note carefully the
degree of convexity. Add a trace of potassium
bichromate. The drop will flatten slightly.

When a metal is placed in an electrolyte, a
difference of potential is created at the surfaces
in contact. If the metal is positive compared

METHODS OF ELECTRICAL STIMULATION 37

with the electrolyte, an immeasurably thin layer
of positively electrified molecules may be said to
coat its surface, and in the electrolyte a parallel
layer of negatively electrified molecules will
collect. On every side of the parallel layer
electricity of the same sign will be repelled. In
the case of a liquid metal, for example mercury,
the form of the surface will be altered, for the
repulsion of like electricities will tend to stretch
the surface layer, and will thus oppose the sur-
face tension. The new form which the surface
will take is the equilibrium between the electri-
cal energy and the surface tension (Helmholtz).
If this equilibrium is changed by the introduc-
tion of new electrical energy, the curvature of
the surface will change (Henry).

Fasten an iron wire in the muscle clamp and
clamp the latter to the stand. Bring the wire
over the mercury and lower the muscle clamp
until the wire just touches the edge of the
mercury. Fix the clamp in this position.

The instant the two metals touch (iron and
mercury in chromic acid solution) the existing
difference of potential will be altered. The sur-
face tension will thereby be increased and the
globule will become more convex. This move-
ment withdraws the margin of the globule from
the iron and the globule flattens again, which

38 GENERAL PROPERTIES OF LIVING TISSUES

brings it again into contact with the iron. This
play is repeated until the chromic acid is all
reduced to chromic sulphate.

A , B

Fig. 5. Stage electrometer;1 about three-sevenths the actual size. A,
Side view. B, Front view.

The Electrometer. — -The electrometer consists of
a vertical tube drawn out at the lower end into a
fine capillary and filled with mercury. (Fig. 5.) The

1 Science, 1905, xxii, p. 602.

METHODS OF ELECTRICAL STIMULATION 39

upper end of the tube is joined to a cylinder in which
a piston is moved by a screw, thus making pressure
on the mercury column. The end of the capillary dips
in a reservoir containing twenty per cent sulphuric
acid. Platinum wires lead from the acid reservoir
and the mercury in the capillary to convenient bind-
ing posts. The platinum wire should never touch
the acid, but should be protected by a covering of
mercury. When mercury is placed in the vertical
tube it enters the capillary until the weight of the
column of mercury is balanced by the surface tension,
which is inversely proportional to the diameter of the
tube. If the capillary be now dipped in the reservoir
containing the sulphuric acid, and the piston driven
upward by its screw, mercury will be forced out of the
capillary into the acid ; and on lowering the pressure
the mercury will retreat within the capillary, drawing
the acid after it. Numerous advantages are presented
by this form of electrometer. It tits the stage of the
microscope. The microscope need not be tilted very
far, and the observer is therefore in. a comfortable
position. The position of the electrometer on the
stage may readily be changed. All the parts near the
acid are of hard rubber, thus excluding currents that
might arise from acid touching metal parts. The
acid tube is flanged so that the acid cannot creep
out along the capillary tube. The capillary can
easily be brought against the wall of the acid tube.
The tube from which the capillar}7 springs descends
within the acid tube, thus protecting the capillary

40 GENERAL PROPERTIES OF LIVING TISSUES

against breakage. Either tube may at once be re-
moved from its holder. The platinum wires extend
to the binding post, and are not simply short pieces
soldered to copper wire. The wire to the capillary
tube extends to the bottom of the tube, thus main-
taining the contact until all the mercury in the tube
is used.

About one cubic centimetre of paraffin oil should
be placed above the piston. Only absolutely clean
double-distilled mercury should be used.

As the mercury in the capillary is kept from
falling by the surface tension, it is obvious that
whatever increases or diminishes the surface
tension, for example an electric current, will
raise or lower in corresponding measure the
mercury in the capillary. The alteration in sur-
face tension is accompanied by the movement
of ions between the meniscus and the remaining
electrode of the electrometer (the mercury in
the acid reservoir). In practice it is found that
this movement can be neither very rapid nor
long continued, without injuring the sensitiveness
of the instrument. The potential difference
from even a single element (Daniell or dry cell)
is far too large to be used safely. It is advisable
to employ a potential divider, or rheochord, which
shall permit only a fraction of the original
potential (not more than 0.1 volt) to reach the

METHODS OF ELECTRICAL STIMULATION 41

electrometer. The platinum should never come
in contact with the acid.

The electrometer should be kept short-cir-
cuited, except during an observation, so that
the capillary and the mercury in the reservoir
may always be connected through a conductor.
The short-circuit key is shown in Fig. 5, B.
A strip of spring brass connected with one
of the binding posts of the electrometer rests
against a second piece of brass connected with
the other binding post, except when depressed
by the finger. The point of higher potential,
when known, should always be connected with
the capillary.

When the capillary electrometer is connected
with two points of unlike potential the meniscus
is displaced. The pressure necessary to bring
it back to its original position is proportional to
the electromotive force that displaced the me-
niscus. Thus by connecting the electrometer
with known differences of potential it may be
experimentally graduated. In practice, the re-
lation between the pressure and the potential
must frequently be redetermined. It is usually
easier to measure differences of potential, such
as the demarcation current of nerve or muscle,
by compensation (Fig. 47, p. 294). In this method
the electromotive force of the demarcation current

42 GENERAL PROPERTIES OF LIVING TISSUES

is measured in fractions of a Daniell cell, or any
other constant element, by bringing into the same
circuit with the current of injury, but in an op-
posite direction, so much of the current from the
cell as will exactly balance the current of injury,
i. e. so much as will keep the meniscus of the
electrometer from moving in either a positive
or negative direction when connected with the
circuit.

Advantages of the Electrometer. — The mass of
mercury displaced in the movement of the menis-
cus is very small, and the distance through which
it is moved is short. Hence the inertia of posi-
tion is easily overcome and the inertia of motion
(which is proportionate to the mass times the
square of the velocity) is practically wanting.
The absence of inertia errors, the almost instan-
taneous quickness with which the meniscus takes
its new position, the ease with which slight elec-
tromotive forces (io"o7nr vo^) may be measured,
and simplicity of construction, are the principal
advantages of this admirable instrument.

The Rheochord. — If two poles of a cell or
other points of different potential be joined by
a well-drawn wire, the potential through the
wire will fall uniformly from the anode to the
cathode. The greater the resistance in the wire,
the more uniform will be the fall in potential.

METHODS OF ELECTRICAL STIMULATION 43

The Long Rheochord. — In the long rheochord
(Fig. 6) a metre rule is screwed upon a wood
base. At each end is a binding post. To post 0 is
fastened the end of an unbroken German-silver wire
twenty metres in length. This wire is carried along
the metre stick to the second post, 1, then wound
upon a spool, and the end fastened to a third binding

Fig. 6. The long rheochord ; about one-thirteenth the original size.

post. The wire upon the metre rule is bare, the
remaining nineteen metres silk-covered. A conven-
ient spring contact with binding post slides along the
metre rule.

The Square Rheochord. — Upon a block of hard
maple, 12.5 cm. square, is placed a centimetre scale
beginning at the 0-post shown on the left side of
Fig. 7 and ending at the 1 -metre post visible in
the background to the left. For the sake of clearness
the numbers on this scale have been omitted from the
figure. Along the scale, between these two posts, is
stretched the first metre of a continuous German-silver
wire, 0.26 mm. in diameter and twenty metres long.
The remaining nineteen metres of this wTire are coiled
upon a spool, and the free end is fastened to the
tw7enty-metre post shown in the background to the
right of Fig. 7. One of the posts may be turned, in

44 GENERAL PROPERTIES OF LIVING TISSUES

order to keep the wire taut, in case changes of tem-
perature have caused it to lengthen. (This device is
not shown in Fig. 7.) The under surface of the con-
tact block is bevelled so that the metal touches the
wire only with one edge ; the opposite edge is sup-
ported by a piece of hard rubber.

A flexible cable leads from the contact block to the
binding post shown in the foreground to the right.

Fig. 7. The square rheochord ; two-fifths the actual size.1

The resistance in the 20 metres of thin Ger-
man-silver wire is so great (about 184 ohms)
that the internal resistance of the element fur-
nishing the electromotive force, together with the
resistance of the large copper connecting-wires,
practically disappears for such measurements as
we shall need to make. As the fall of potential
is uniform throughout the 20 metres, the differ-

1 American Journal of Physiol ogy, 1903, viii, p. xli.

METHODS OF ELECTRICAL STIMULATION 45

ence of potential between post 0 and post 1 will
be practically one-twentieth the electromotive
force of the element. Thus when the sliding
contact is at post 1, the capillary electrometer
receives one-twentieth the electromotive force of
the element. By moving the slider from post 1
towards post 0, any desired fraction of this one-
twentieth may be measured by the electrometer.

The Simple Key. — A copper bar with hard rubber
handle is pivoted at one end in a brass post with
binding screw for electrical

connection (Fig. 8). Xear CP /^ P

the other end of the bar is
a platinum ■ pin, which,
when the key is closed,
rests upon a platinum plate

borne Upon a Second bind- Fig. S. The simple key ; about

three -eighths the actual size. The
ing post. wire spriug which presses the bar

The contact bar is held afinst the contact plate is not

shown.

against the contact plate

partly by its own weight and partly by a wire spring
not shown in Fig, 8. When it is desired to break the
circuit the contact bar is turned back.

Many experiments in physiology require stimuli of
uniform intensity. Variations in the make or break of
the current due to faults in the contacts of the key in
the primary circuit are a frequent source of error.
With the key described here the break in the circuit
may be made practically uniform.

46 GENERAL PROPERTIES OF LIVING TISSUES

The Short-circuiting Key. — Two strips of brass,
provided with a binding post at each end, are fastened
to a block of dark slate (Fig. 9). At the centre of
one strip is a post in which is pivoted a copper bar
ending in a hard-rubber handle. The bar may be
lowered between edges of spring brass.

Polarization. — Connect a platinum and a zinc *
plate through a simple key with posts 0 and 20

Fig. 10.

Fig. 9. The short-circuiting key ;
about three-eighths the actual size.

of the rheochord as shown in Fig. 10. Connect
the zero post and the slider with the capillary
electrometer through a short-circuiting key.

1 It will be observed that the zinc is amalgamated. Chemi-
cally pure zinc does not need amalgamation. Commercial zinc
contains iron, arsenic, etc., as impurities. The contact of una-
malgamated zinc and these dissimilar metals with an electrolyte
creates a difference of potential, and parasitic currents run from
the zinc to the foreign metals. These currents are prevented by
covering the impurities with zinc amalgam, the electromotive
properties of which, toward sulphuric acid, are those of pure
zinc. As the zinc in the amalgam dissolves out, the film of
mercury unites with fresh zinc. Zinc is amalgamated best by

METHODS OF ELECTRICAL STIMULATION 47

Bring the capillary into the field of the micro-
scope (Leitz objective 3, micrometer ocular), par-
allel to the micrometer scale. The end of the
tube should be just visible at the upper margin
of the field. If the meniscus is not visible, turn
the pressure screw slowly to the right until the
meniscus enters the field. Note the position of
the meniscus on the scale. Close the battery key.
Let an assistant place the metals in a beaker con-
taining solution of sodium chloride. Open the
short-circuiting key of the electrometer.

When the metals touch the electrolyte a dif-
ference in potential will be set up, and the
meniscus will move in the capillary.

Note the number of divisions of the scale
traversed by the meniscus. Close the electrom-
eter key. Wait several minutes.

Now bring the meniscus back to its original
position on the scale. Open the electrometer key.

The meniscus will move to a much slighter
extent than when the circuit was first made.

adding 4 per cent of mercury to the molten zinc before casting ;
or the zinc may be dipped in 10 per cent sulphuric acid to clean
it, and mercury rubbed over the surface with a brush or a stick
padded with cloth ; or the zinc may be dipped in a solution
from which the mercury will deposit on the zinc. Formula for
amalgamating fluid : warm gently 4 parts mercury in 5 parts
concentrated nitric acid and 15 parts concentrated hydrochloric
acid until dissolved, and then add 20 parts more of concentrated
hydrochloric acid.

48 GENERAL PROPERTIES OF LIVING TISSUES

As the displacement of the meniscus is propor-
tional to the electromotive force of the cell, it is
obvious that the latter has rapidly diminished.
The solution contains the ions of water as well
as those of the salt. When the circuit between
the platinum and zinc is completed the cations
H+ and Na+ move towards the cathode. There
the more easily de-ionized H+ yields up its elec-
tricity, and hydrogen appears on the cathode.
The corresponding quantity of electricity is con-
veyed into the solution at the anode by ioniza-
tion of the zinc. The deposition of hydrogen
on the negative plate checks the electromotive
force setting from the zinc to the platinum in
two ways : first, because gas is a bad conductor,
and the effective surface of the platinum is
thereby diminished by the bubbles collecting
on it ; and secondly, because hydrogen is electro-
positive, and creates an electromotive force in
the direction from platinum to zinc, and thus
" polarizes " the cell. This new electromotive
force opposes the original current from zinc to
platinum.

The Daniell Cell. — Daniell discovered an elec-
tro-chemical method of avoiding polarization, and
thus was able to construct a cell that would
furnish a current of unvarying strength. In the
Daniell cell the two metals employed are zinc

METHODS OF ELECTRICAL STIMULATION 49

and copper. The amalgamated zinc is placed in
a porous cup filled with dilute sulphuric acid.
The copper is placed in a solution of copper sul-
phate kept saturated by crystals of the salt.
When the circuit is closed, the zinc "dissolves"
in the sulphuric acid, carrying with it the elec-
tricity with which the zinc ions are charged.
The electricity is carried through the solution
by the migration first of hydrogen and then of

O-x ,< o-... ( o

t

\

\

12 3

Fig. 11 A. Fig. 11 B.

A, earlier form of pole-changer. The rubber handle prevents the cross-
ing of the current from one side cup to the other. B, diagram of pole-
changer arranged (1) to change the direction of the current, (2) as a double
key, without cross-wires, (3) as a simple key.

copper ions. It leaves the solution at the cath-
ode where the copper ions are converted into
metallic copper and deposited on the cathode.
The quantity of zinc dissolved and copper de-
posited is proportional to the quantity of the
current. One ampere deposits per minute 19.75
milligrams copper, and dissolves 20.32 milligrams

zinc.

4

\

\

\
\

50 GENERAL PROPERTIES OF LIVING TISSUES

It is to be observed that each metal is placed
in a solution of its own salt. The ions carried to
the respective poles are of the same nature
chemically as the poles themselves, and hence do
not set up opposing electromotive forces when
they are de-ionized.

The current produced by the Daniell cell is
almost perfectly constant, so long as sulphuric
acid still remains uncombined, and so long as
the sulphate of copper solution is kept saturated.

Fig. 12. Rocking key, metal contact ; about one-half the actual size.

It may be remarked that the function of the
porous cup is to keep the copper from depositing
on the zinc.

The Pole-Changer.1 — The instrument illustrated
by Fig. 12 serves as a simple key, short-circuiting
key, and pole-changer. No mercury is used.

1 Science, 1905, xxi, pp. 752-754.

METHODS OF ELECTRICAL STIMULATION 51

The central binding posts are prolonged upwards
and each is slotted to receive a brass bar, which is
pivoted in the slot by a horizontal pin. The brass
bars are held parallel by two rubber rods which serve
as handles. When the bars are depressed to one side
or the other, they engage between plates of spring
brass set into brass blocks, each of which carries a
binding screw. Cross-wires enter these blocks, as
shown in the figure. At one end the cross- wires are
soldered into the blocks, thus making an electrical
contact. The two blocks at the other end are per-
forated by rubber cores or " bushings " through which
the cross-wires pass. The cross-wires, therefore, make
no electrical contact with these blocks. When a con-
tact is desired, the nut borne on the head of each
cross-wire is turned until its face presses against the
brass block outside the bushing. In this position the
key serves as a pole-changer, or commutator. When the
nut on the cross-bar between the central posts is turned
until its face presses against the post, it will short-
circuit the central posts.

Polarization Current. — Place two pieces of
platinum foil in a solution of copper sulphate,
and connect them to a pole-changer (without
cross-wires). Connect the remaining pairs of
posts with two dry cells in series (carbon of one
cell connected with zinc of other), and with the

52 GENERAL PROPERTIES OF LIVING TISSUES

0 and 1 metre posts of the rheochord, respectively.
Connect the zero post and the slider to the capil-
lary electrometer (Fig. 13). Turn the pole-
changer to pass the battery current through the
copper sulphate solution or " electrolyte." The

cation (copper) will be
partially de-ionized at
the negative pole, or
cathode, on which cop-
per will be deposited
in a fine film. The anion
(sulphion, S04) will pass
-~o) towards the positive pole,
or anode, where it gives
up its electric charge and
becomes the ordinary radical S04. This radical
cannot exist uncombined in water, but forms sul-
phuric acid, setting free oxygen, which therefore
appears at the anode.

The elements copper and oxygen deposited
respectively on the cathode and anode tend to
fly back into the ionic state ; and this ten-
dency, taken in connection with the opposing
osmotic force of the ions already in solution,
sets up an electromotive force equal to that
which caused the de-ionization, but in an op-
posite direction. Hence the polarization cur-

METHODS OF ELECTRICAL STIMULATION 53

rent. On cutting off the electrolyzing current,
the polarization current may be measured.

Note the position of the meniscus of the capil-
lary electrometer. Turn the pole-changer so that
the cell is cut off and the electrodes are brought
into the electrometer circuit.

The meniscus will indicate a current opposite
in direction to the current from the cell.

Dry Cell. — A "dry" cell is very convenient
for large classes. It usually consists of a zinc
cup, lined with plaster of Paris, saturated with
ammonium chloride, in the centre of which 'is a
carbon plate surrounded with black oxide of
manganese. When the cell is in action, the zinc
forms a double chloride of zinc and ammonium
while ammonia gas and hydrogen are liberated
at the carbon pole. These cells should never be
used continuously for many minutes, for they are
rapidly polarized by the accumulation of hydro-
gen on the carbon plate. The unused cell re-
gains its difference of potential by the union of
the hydrogen with the oxygen slowly given off
by the manganese dioxide, which therefore acts
as a depolarizer.

Induction Currents

A most useful method of electrical stimulation
of living tissues is by the induced current, and

54 GENERAL PROPERTIES OF LIVING TISSUES

a clear idea of the phenomena of induction must
now be gained.

The Inductorium * — The primary coil of the in-
ductorium (Fig. 14), wound with double silk-covered
wire of 0.82 mm. diameter, having a resistance of 0.5

Fig. 14. The inductorium ; one-third the actual size. (The set screw
holding the trunnion block tube against the side rod is not shown.)

ohm, is supported in a head-piece bearing three bind-
ing posts and an automatic interrupter. The core
consists of about ninety pieces of shellacked soft
iron wire. This core actuates the automatic inter-
rupter. The interrupter spring ends below in a collar
with a set screw. By loosening the screw, the inter-
rupter with its armature may be moved nearer to or

1 American Journal of Physiology, 1903, p. xxxv.

METHODS OF ELECTRICAL STIMULATION 55

farther from the magnetic core. Once set, the inter-
rupter will begin to vibrate as soon as the primary
circuit is made. The outer binding posts are used for
the tetanizing current. The left-hand outer post and
the middle post are used when single induction cur-
rents are desired ; they connect directly with the ends
of the primary wire, thus excluding the interrupter.
These several connections upon the head-piece are
simply arranged and are all in view ; there are no con-
cealed wires.

From the head-piece extend two parallel rods 22
cm. in length, between which slides the secondary coil,
containing 5000 turns of silk-covered wire 0.2 mm. in
diameter. Over each layer of wire upon the secondary
spool is placed a sheet of insulating paper. Each end
of the secondary wire is fastened to 'a brass bar
screwed to the ends of the hard-rubber spool.

The brass bars bear a trunnion wrhich revolves in
a split brass block, the friction of which is regulated
by a screw. The trunnion block is cast in one piece
with a tube 3 cm. in length, which slides upon the
side rods. A set screw, not shown in Fig. 14, holds
the trunnion block tube and the secondary spool at
any desired point upon the side rods. This screw
also serves to make the electrical contact between the
trunnion block tube and the side rod more perfect.
The secondary spool revolves between the side rods
in a vertical plane. When the secondary coil has
revolved through 90°, a pin upon the side bar of
the secondary coil strikes against the trunnion block

56 GENERAL PROPERTIES OF LIVING TISSUES

and prevents further movement in that direction.
The right-hand side bar bears a half-circle graduated
upon one side from 0° to 90°. An index pointer is
fastened upon the trunnion block. One side rod is
graduated in centimetres.

The side rods end in the secondary binding posts,
so that moving the secondary coil does not drag the
electrodes. Next the binding posts is placed a short-
circuiting key.

Magnetic Induction. — Faraday's experiment.
Eemove the secondary (larger) coil of the in-
ductorium (Fig. 14) from its slideway and con-
nect its terminals with the capillary electrometer.
Eaise the brass bridge between the binding posts.
(If this bridge is down its thick metallic mass
will offer such an easy path between the ends of
the secondary wire that nearly all — practically
all — the electricity produced in this coil will
pass over the bridge, instead of by the relatively
long, thin wires leading to the electrometer.)
Bring the meniscus into the field. Thrust
the north pole of a magnetized rod within the
coil.

The meniscus will move, indicating that an
electric current has been induced in the second-
ary coil. Note the direction of the current.

Let the magnet remain in the coil.

The meniscus will return to its former position.

METHODS OF ELECTRICAL STIMULATION 57

Evidently the induced current is of momentary
duration.

Withdraw the magnet quickly.

The meniscus will move in the opposite
direction.

Insert the south pole.

The induced current now has the direction
opposite to that of the current induced by the
insertion of the north pole.

Withdraw the magnet quickly.

The induced current has the direction opposite
to that of the current induced by the withdrawal
of the north pole.

These results may be thus expressed : the
moving of a magnet in the neighborhood of a
conductor, or of a conductor in the neighbor-
hood of a magnet, produces in the conductor an
electromotive force, which, on the circuit being
completed, creates a current that would impart
to the magnet or the conductor a movement in
the opposite direction.

Magnetic Field. Lines of Force. — The space
about a magnet in which the magnetic forces
act is called the " field " of the magnet. If very
fine iron filings are dusted through a muslin
cloth onto a thin card perforated near the centre
by a copper wire or other conductor, and a strong
current is passed through the wire, the filings will

58 GENERAL PROPERTIES OF LIVING TISSUES

arrange themselves in concentric circles around
the wire, particularly if the card be gently
tapped.

The position of these " lines of force " shows
the direction of the magnetic force, and their
number is an index of its intensity.

To produce Electric Induction, the Lines of
Magnetic Force must be cut by the Circuit. —
Hold the magnet at right angles to the axis of
the coil, and, keeping it in this position, rapidly
advance it towards the coil.

The electrometer will show no current, because
the number of the lines of magnetic force which
pass through the field of the conductor has not
been altered.

Electro-magnetic Induction. — An electro-magnet
may be used in place of the bar magnet to pro-
duce induction.

Connect a dry cell through a simple key with
posts 1 and 2 of the primary coil.1 Close the

key-
When the current passes through the primary

coil, the core of iron wire in the coil will be

1 It will be convenient to use the numbers 1 and 2 to desig-
nate the posts connected directly with the ends of the primary
wire, excluding the vibrating hammer ; the numbers 2 and 3
will indicate the posts that connect with the ends of the pri-
mary wire including the hammer. When the battery is con-
nected with posts 2 and 3 the hammer will vibrate.

METHODS OF ELECTRICAL STIMULATION 59

magnetized, as is shown by its attracting the
head of the Wagner hammer.

Bring the meniscus into the field. Approach the
primary coil to the secondary as in the experiment
with the magnet. "Withdraw the primary coil.

The electrometer shows the presence of in-
duced currents, as before. These currents are
momentary. The first induction current is in-
verse, i. e. it runs round the secondary coil in the
direction opposite to that taken by the battery cur-
rent in the primary coil. The second induced cur-
rent is in the same direction as the primary current.

Place the coils at right angles to each other.
Approach one towards the other.

No current will be induced.

Make and break Induction. — Close and open
the key in the primary circuit, thus making and
breaking the primary current.

The effect is the same as if the primary were
suddenly brought up to the secondary coil from
an infinite distance and removed aoain. The make
induction current is in the opposite, the break in
the same, direction as the primary current.

Turn the secondary coil on its pivot until the
axis is at right angles to the axis of the primary
coil. Make and break the primary current.

No induction will take place provided the
angle between the coils is precisely 90°.

60 GENERAL PROPERTIES OF LIVING TISSUES

On the Construction of the Inductorium. — Ex-
amine the construction of the inductorium. The
primary coil consists of a few turns of thick wire.
More turns would increase resistance and self-
induction, — the counter induction set up in each
turn of the primary wire by the passage of the
primary current through neighboring turns, —
without increasing the induction effect in the
secondary coil.

The iron core adds to the number of lines of
magnetic induction which pass through the coils.
It has been already shown (page 58) that the
lines of magnetic induction produced by the pas-
sage of an electric current through a wire are
closed circles. If the centre of the coil were
filled with air, most of these circles would remain
closed about their own wire, for air is not readily
permeable to magnetism. But when the iron core
is placed within the coil the greater part of the
magnetic induction follows the iron (because it
is more permeable) from end to end of the core,
returning outside through the air. Thus the
number of effective lines is increased. A bundle
of iron wires is used instead of a solid core, be-
cause no induced current is then possible through
the mass of the iron, as would be the case in a
solid core. Such a current would slow the speed
of magnetization and demagnetization.

METHODS OF ELECTRICAL STIMULATION 61

The secondary coil is made of many turns of
fine wire, because the object of the inductorium
is to transform the low electromotive force of the
cell into the high electromotive force of the in-
duced current. In the induction coil, as in other
transformers, the electromotive forces in the
primary circuit are to those produced in the
secondary circuit approximately as the number
of turns of wire in the primary is to the number
in the secondary circuit.

If the induced current is to be passed through
conductors of low resistance, the high internal
resistance of the secondary coil, due to its great
length of fine wire, will be of importance.

Place a dry cell with simple key in the pri-
mary circuit of an inductorium (posts 1 and 2).
Connect the secondary coil with a galvanometer.
Note the excursion of the needle with a break
induction current. Eeplace the secondary coil
with one of fewer windings (the primary coil of
a second inductorium will serve). Let the dis-
tance between primary and secondary coil be the
same as before.

The excursion of the needle with a break in-
duction current will be increased, or at least not
proportionately diminished.

If, on the other hand, the induced current is
to be passed through nerve, muscle, or skin, the

62 GENERAL PROPERTIES OF LIVING TISSUES

resistance of the secondary coil will practically
be nothing in comparison with the enormons
resistance of animal tissue.

Eepeat the preceding experiment, introducing
in the secondary circuit a high external resist-
ance, i. e. a nerve.

The secondary coil with many turns of fine wire
now causes a much greater deflection of the gal-
vanometer needle than the coil with fewer turns.

Interrupter. — Instead of making and break-
ing the primary circuit by hand, an automatic
interrupter is provided. The primary circuit
passes through a screw, the point of which con-
veys the current through a flat spring upon
which is mounted an iron disk opposite and near
to the core of wire in the primary coil. When
the current enters the primary coil, the core is
magnetized and draws upon the iron disk. The
spring, to which the disk is attached, is thereby
drawn away from the screw-point through which
the current is passing. Thus the current is
broken, and ceases to flow through the primary
coil ; the core no longer is magnetized, and re-
leases the iron disk ; the spring again makes
contact with the screw-point, the current is re-
established, only to be at once again broken.
Thus a rapid series of make and break induc-
tion currents is secured.

METHODS OF ELECTRICAL STIMULATION 63

Draw a diagram of the primary circuit, indi-
cating the connections of the inductorium.

Empirical Graduation of Inductorium. — Con-
nect the secondary coil with the galvanometer.
Join the primary coil to a dry cell, interposing a
simple key. Turn the secondary coil on its pivot
until it is at right angles with the primary coil.
Close the circuit.

The galvanometer needle will not swing.
There is no induced current.1

Turn the secondary coil on its pivot, closing
the key from time to time to test the induction.

The strength of the induction increases ap-
proximately as the cosine of the angle between
the coils increases. An empirical graduation is
sometimes placed on a circular scale beneath the
coil.

When the axes of the two coils lie in the same
plane, slide the secondary towards the primary,
making and breaking the primary current from
time to time.

The potential of the primary upon the second-
ary coil, i. e. the sum of the inductions of each
element of the primary upon all the elements of
the secondary coil, increases as the secondary is
brought nearer the primary coil. The increase is
not linear. As the distance between the coils

1 It is difficult to place the coil precisely at an angle of 90.°

64 GENERAL PROPERTIES OF LIVING TISSUES

diminishes, the increment of increase in the in-
tensity of the induced current is not the same
but greater for each centimetre of approach.

Graduation. — Fasten a strip of white gummed
paper at the side of the base of the inductorium,
beginning at the end block which holds the
primary coil. Place the secondary coil at the
end of the slideway. Make the primary current.
Kead the number of degrees of deviation for the
break induction current only. Make a line on
the paper band exactly opposite that end of the
secondary coil which is nearer the primary.
When the needle is again at rest, move the
secondary nearer the primary coil, and find the
distance at which the deviation of the needle in
response to the break induction current is n de-
grees (for example, two) of the scale larger than at
the former position of the coil. Mark on the white
strip the new position of the coil. Continue in
this way to find the positions of the secondary
coil at which the needle shows successively a
deviation two degrees greater at each new posi-
tion, and mark them on the paper band.

The marks on this empirical scale will be
nearer together as the secondary approaches the
primary coil.1

1 The rough method here employed serves merely to show
that the increase in the intensity of the induction current as

METHODS OF ELECTRICAL STIMULATION 65

The Platinum Electrodes. — The stimulating elec-
trodes are provided with platinum points projecting
about 10 mm., polished hard-rubber handle, 7.5 cm.
long, and very flexible silk-covered connecting wires
65 cm. long, ending in nickel-plated brass tips (Fig.
15). The rubber handle is in two pieces, screwed
together, permitting easy access to the connection
between the flexible wire and the
stiff wire into which the platinum
points are inserted.

The Flat-jawed Clamp. — The
flat-jawed clamp, or " Femur
Clamp" (Fig. 16), consists of
strong, smoothly working brass
jaws attached to a steel rod.
The jaws are separated by a spring
and brought together by a screw.
They will hold objects of widely
varying size, — for example, the
femur of a nerve-muscle prepara-
tion or a board a centimetre thick. The clamp has a
binding post for making electrical connection with a
muscle or other conductor held between its jaws.

The Round-jawed Clamp. — The round-jawed clamp
is convenient for holding burettes, tubing, rods, ther-
mometers, etc. (Fig. 16).

The Double Clamp. — This is a strong clamp of
enamelled iron with two brass nickelled screws (Fig.

the coils approach is not linear. An exact method of gradua-
tion has been given by Kronecker.

5

Fig. 15. The " platinum "
electrodes ; about one-third
the actual size.

66 GENERAL PROPERTIES OF LIVING TISSUES

17). The screws move into an angle, against the sides
of which a large or small rod may be held firmly and
without sidelash.

Make and Break Induction Currents as Stimuli.

— Make a nerve-muscle preparation. Connect a
dry cell with simple key to the primary coil
(posts 1 and 2). Fasten in the posts of the

Fig. 16. The flat-jawed clamp and the round-jawed clamp ; one-fourth
the actual size.

secondary coil the stimulation electrodes, i. c.
the prolongation of the ends of the secondary
wire which convenience demands. Put the
secondary coil at the end of the slide way and

turn the coil. Place the

^^_jr~xEE^\ electrode points against

(l^3^^<«QMf the nerve. Open and close

the primary circuit.

Fig. 17. The double clamp, one- r¥,, , ,

third the actual si/.. The muscle does not

contract.
Move the secondary towards the primary coil,
opening and closing the primary circuit.

METHODS OF ELECTRICAL STIMULATION 67

Presently the muscle will shorten. (Compare
pages 175 and 176.) Observe that this contrac-
tion was the result of a break induction current,
not a make.

Cautiously move the secondary coil still nearer
the primary, making and breaking the current as
before.

A point will be reached at which the make
induction also causes contraction. Obviously,
the break current is a stronger stimulus than
the make induction current. The cause of the
greater intensity of the break induction current
lies in the primary coil. The current which en-
ters the primary coil induces a current in this
coil as well as in the secondary coil. The direc-
tion of this "self-induced" current is opposite to
that of the primary current, and hence weakens
it and delays its development. The stimulating
power of electricity increases with both the inten-
sity of the current and the quickness with which
the intensity alters. Hence the stimulating power
of the make induction current is lessened by the
self-induction of the primary coil. When, on
the other hand, the primary circuit is broken,
the current stops, and although self-induction
again takes place, it cannot affect the primary
current, because the latter no longer exists. The
self-induced current at the break of the primary

68 GENERAL PROPERTIES OF LIVING TISSUES

current is in the same direction as the primary-
current before the break.

The Extra Currents at the Opening and Closing
of the Primary Current. — 1. Be move the secon-
dary coil from the inductorium. Connect posts
1 and 2 of the primary coil with a dry cell, inter-
posing a simple key. Fasten the ends of the
electrode wires in these same
^K ~ posts. Close the primary cir-

°) I cuit. Place the electrode

f <=j=p "] points against the tongue.

\ U I Open the key.

^ v0 — =±$f) J a shock from the self-
^-o^v y induced current developed in

2/ the primary coil will be felt.

Fig. is. Draw a diagram of the circuits.

2. Connect a dry cell through
a key to the metre posts of the rheochord (Fig.
18). Connect the positive post and the slider to
the primary coil of an inductorium arranged for
single induction currents. Bring wires from these
posts of the primary coil through a simple key
to the nerve of a nerve-muscle preparation. Close
the key in the primary circuit. Open and close
the key in the nerve circuit. The muscle will
contract at closure and possibly at opening. By
means of the slider, weaken the current through
the primary coil until opening and closing the

METHODS OF ELECTRICAL STIMULATION 69

key to the nerve no longer produces contraction.
Now let this key remain closed and make and
break the primary circuit.

The muscle will contract both on opening and
closure. The induction currents developed in
the primary coil when the primary current is
made and broken stimulate the nerve, al-
though the galvanic current itself is powerless
to do so.

Tetanizing Currents. — Connect a dry cell to
posts 2 and 3 of the primary coil. The vibrat-
ing hammer will automatically make and break
the current. Place the electrodes against the
nerve or muscle.

The muscle will contract once for each induc-
tion current, but the contractions are so rapid
that they fuse into a prolonged shortening termed
tetanus.

Induction in Nerves. — Faraday discovered that
currents can be induced in electrolytes as well
as in metallic conductors. Induced currents may
therefore appear in nerves lying sufficiently near
a primary circuit.

Lay the well-moistened nerve of a nerve-muscle
preparation around the primary coil protected by
a piece of paraffin paper in such a way that the
free end of the nerve touches the nerve near the
muscle or touches the muscle itself, so as to form

70 GENERAL PROPERTIES OP LIVING TISSUES

a closed circuit. Make and break the primary
current.

Make and break currents will be induced in
the nerve, and the muscle will contract.

Exclusion of Make or Break Current. — Con-
nect the dry cell with posts 1 and 2, interposing
a key. See that the short-circuiting key, i. e. the
thick brass bridge between the posts on the sec-
ondary coil, is down. Connect the electrodes
with the secondary coil, and place their points
against the nerve of a nerve-muscle preparation.
Close the primary key.

The muscle will not contract.

The resistance to the passage of the induced
current through the portion of nerve between
the ends of the electrodes is many thousand
times greater than the resistance of the brass
bridge or short-circuiting key. Practically none
of the electricity will pass through the nerve
when the short-circuiting key is closed.

Open the short-circuiting key and then open
the primary key.

The muscle contracts.

Eepeat the experiment, letting the make cur-
rent pass and short-circuiting the break.

With the primary key and a short-circuiting
key either break or make induced currents can
be used as stimuli at will.

methods of electrical stimulation 71

Unipolar Induction

1. Arrange the inductorium for tetanizing
currents (posts 2 and 3). Make a nerve-muscle
preparation. Lay it on a clean dry glass plate.
Let the nerve rest on a wire connected with one
pole of the secondary coil. Set the inductorium
in action. Connect the muscle with the earth
by touching the muscle with the end of a wire
the other end of which rests on a gas or water
pipe.

The muscle will show tetanic contractions,
provided the induced current is sufficiently
strong. If no tetanus is seen, move the second-
ary coil completely over the primary.

Unipolar induction may be produced by the
electric currents in the skin. This may be
demonstrated with a sensitive nerve-muscle prep-
aration.

2. Ligature the nerve between the electrode
and the muscle, and repeat the experiment.

Stimulation will still be secured. The uni-
polar discharge passes through the entire length
of nerve and muscle to or from the point at
which the connection with the earth is made, and
thus stimulates the entire preparation.

DuBois-Eeymond, who was the first to make
the preceding experiments, pointed out that

72 GENERAL PROPERTIES OF LIVING TISSUES

whenever the secondary circuit was open (i. e.
when the bridge between the ends of the second-
ary wire was np) the making and breaking of
the primary circuit caused free electricity to
gather on the ends of the secondary wire. When
the electro-static induction becomes great enough
the electromotive force overcomes the resistance
in whatever connecting path may be offered, and
the electricity passes from the coil to the earth.
If a part of the path is formed by irritable
tissues, they will of course be stimulated.

3. The quantity of electricity passing through
the nerve may be increased by approximating
the coils or by increasing the electrical capacity
of the conductor, as follows : —

Eemove the wire connecting the preparation
with the gas pipe. Set the inductorium in action.
Touch the muscle with the moistened finger.

Contraction follows.

Here the electrical capacity of the preparation
is increased by connecting the preparation with
the human body, a conductor of large surface
(and through it with the earth). A similar
result is obtained by unipolar stimulation of
nerves and muscles while still in the body of
the animal, as in many physiological experi-
ments. It is not necessary that the surface of
the conductor be enormously large. The follow-

METHODS OF ELECTRICAL STIMULATION 73

ing experiment shows that even very small sur-
faces will suffice.

4. On a carefully dried, clean glass plate lay
four nerve-muscle preparations. Let the nerve
of the first rest on a single wire the other end of
which is fastened in one of the binding posts of
the secondary coil. Place the end of the second
nerve on the tendon of the muscle of the first
preparation, the third on the second tendon, and
the fourth nerve on the tendon of the third.
Eemove the secondary coil some distance (a few
centimetres) from the primary, and set the in-
ductorium in action. Gradually approximate
the coils.

As the tension at the ends of the secondary
wire increases by the approximation of the coils,
the first preparation will contract. On further
approximation, the first and second; then the
first, second, and third ; and finally all four will
contract.

This instructive experiment shows that when
the conducting surface is small, as in the present
instance, the unipolar action is greater on the
parts nearer the secondary wire than on parts
farther away. The danger of unipolar action on
tissues lying near the electrodes in ordinary
artificial stimulation of nerves and muscles in
situ is obvious.

74 GENERAL PROPERTIES OF LIVING TISSUES

5. It is not even necessary that the conductor
should be actually in contact with the prep-
aration.

Connect a nerve-muscle preparation, insulated
on a glass plate, with one pole of the secondary
coil, and set the inductorium in action. The
secondary coil should completely cover the pri-
mary. Bring a moistened linger as near the
muscle as possible without touching it.

With the proper intensity of the primary cur-
rent, contraction will take place, though absent
when the finger is removed.

The sudden approach of a condenser charged
with static electricity will stimulate an isolated
nerve or muscle.

6. The danger of error from unipolar action is
particularly great in electrometer observations on
the current of rest or action current of nerve and
muscle, discussed and demonstrated experiment-
ally in Part III, Chapter II.

The errors due to unipolar action can usually
be prevented by the following precautions : The
secondary coil should always be connected with
the tissue to be stimulated through a short-
circuiting key, which should be kept closed ex-
cept during the intentional stimulation of the
tissue. With this good metallic connection be-
tween the ends of the secondary wire there will

METHODS OF ELECTRICAL STIMULATION 75

be no static electrification. Further, the appear-
ance of positive and negative electricity during
the period of stimulation must be provided
against, especially if that period is at all pro-
tracted, for it must not be forgotten that the
bridge of nerve, which completes the secondary
circuit by uniting the two electrodes, possesses
very high resistance, and thus affords but an
imperfect closure of the ends of the secondary
wire. This provision is made by connecting the
positive electrode with the earth by a good con-
ductor, for example by a copper wire leading
from the electrode to the gas or water pipe
In case of doubt, a control experiment should
be made. The nerve should be severed between
the stimulated point and the muscle, and one
end laid on the other. Excitation through the
passage of a nerve impulse along the nerve is
thereby made impossible. If the muscle still
contracts when the nerve is stimulated above
the section, it is because of unipolar stimulation.

An" additional reason for care is that the insu-
lation of the secondary spiral is injured by leav-
ing the secondary circuit open while the hammer
of the inductorium is in action.

It may be stated that the direction of the uni-
polar discharge is of importance. Excitation
takes place only where the positive charge enters

76 GENERAL PROPERTIES OF LIVING TISSUES

the nerve or the negative charge leaves the
nerve.

The break induction current is more effective
than the make, as the slower development of the
latter causes the terminals of the secondary wire
to be charged more slowly than by the rapidly
developed break current.

Apparatus.

Normal saline. Bowl. Towel. Pipette. Glass plate.
Zinc wire, 4 inches long. Copper wire, 4 inches long. Por-
celain dish. Mercury. 5 per cent sulphuric acid. 5 per
cent solution of potassium chromate. Iron wire, 4 inches
long. Muscle clamp. Iron stand. Capillary electrometer.
Rheochord. Microscope (micrometer ocular, objective 3).
Daniell cell. Dry cell. Two platinum electrodes. Zinc
electrode. Beaker. Sodium chloride. Simple key. 9
wires, 2 feet long. Saturated solution of copper sulphate.
Pole-changer (in paper dish). Inductorium (with elec-
trodes). Coil with few windings (primary coil of a
second inductorium). Bar magnet. Iron filings. Galva-
nometer. Card, with thick copper wire. Ligatures.
Frogs. Osmometer (for demonstration). Tradescantia
discolor. Serum. Sodium chloride solutions (0.60, 0.65,
0.70, 0.75, 0.80 and 5.0 per cent, also 0.62, 0.61, 0.60,
0.59, 0.58, and 0.57 per cent). Microscope. Defibrinated
blood. Twelve test-tubes. Tension indicator. Soap solu-
tion. Lycopodium. Alcohol.

THE GRAPHIC METHOD 77

III

THE GRAPHIC METHOD

The studies next to be undertaken make use of
the change of form of the contracting muscle as
a partial index to the transformation of energy
in the tissue. A permanent record is desirable.
Further, the changes in the dimensions of the
muscle are so small that it is necessary to have
the graphic record enlarged, rather than of actual
size. To satisfy these conditions, the muscle is
attached near the fulcrum of a lever furnished
with a recording point. The surface for the
writing is usually glazed paper which has been
covered with a thin layer of soot by passing the
paper through the luminous part of a broad gas
flame. The paper is fastened (before smoking)
on a plate or on a drum which moves past the
writing point, almost parallel to it, and furnishes
thus a continuously fresh surface.1

1 The paper is cut wider and longer than the surface of the
drum. The extra width is to protect the bearings of the drum
from soot that might otherwise collect there in smoking the

78 GENERAL PROPERTIES OF LIVING TISSUES

The writing point rubs off the soot in its path
and leaves a white magnified tracing of the
muscle's change in length or whatever dimen-
sion is the subject of record. The paper is then
removed, drawn through a saturated solution of

paper. The extra length allows the edge of the overlap to be
gummed to the paper below, permits the paper to be removed
from the drum by cutting through the overlap parallel to the
mucilage, — the surface of the drum being protected from the
knife by the underlying paper, — and provides an unsmoked
surface by which the paper can be handled on its removal from
the drum. The drum should be laid in the centre of the strip
of paper, the gummed edge to the left, and the axis of the drum
precisely at right angles to the long axis of the paper ; the
mucilage should be moistened, and the ends of the paper
brought around and fastened. If the paper is awry, the sur-
face will not lie uniformly against the drum and the record
will be deformed. The drum should now be placed in the
smoking apparatus, revolved uniformly and not too fast,
brought over the gas flame, lowered just below the upper edge
of the flame, and covered with a chocolate brown layer of soot,
beginning at the operator's left hand and passing gradually to
the right. The speed should be such that one passage from
left to right shall suffice. To trim the edges, hold the drum
in the left hand, inclined downwards, and pass a sharp knife-
blade around the lower edge. The handle of the knife should
be kept lower than the blade, to avoid tearing. In removing
the paper from the drum, hold the drum in the air with the
left thumb pressed on the edge of the paper near the overlap,
and cut through the overlapping edge near the mucilage. The
loosened paper will hang down and may then be seized by the
unsmoked overlap. In recording, let all the curves begin near
the overlap. Attention to these details is indispensable to the
best technical results.

THE GRAPHIC METHOD 79

white shellac in 95 per cent alcohol,1 and hung
up until the alcohol is evaporated. The soot
will thus be coated over and held in place by
a thin layer of shellac, and the record will be
secure.

The Kymograph. — The improved kymograph 2
is shown at the right of Fig. 19, in which it is mounted
as part of the long paper device. It consists of a
drum revolved by clockwork and also arranged to be
more rapidly revolved or " spun " by hand.

The drum is of aluminium, cast in one piece
turned true in the lathe to a circumference of 50 cm.
The height is 15.5 cm. The weight is about 600
grams. The drum slides upon a brass sleeve in bear-
ings 1.1 cm. deep (to prevent "sidelash"), and is
held at any desired height by a spring clip. The
sleeve ends in a friction plate, which rests upon a
metal disk driven by the clockwork. Sleeve and
friction plate revolve about a steel shaft which passes
through both the heavy plates containing the clock-
work, and is securely bolted to the bottom plate.
The sleeve bears upon the steel shaft only by means
of " bushings " at the ends of the sleeve, thus securing

1 To make this solution, the alcohol should be allowed to
stand on the shellac a month or more before using. A satisfac-
tory solution may be made in twenty-four hours by dissolving
375 grams of rosin in 2500 c.c. of alcohol.

2 Introduction to Physiology, 1901, p. 51. American Jour-
nal of Physiology, 1903, viii, p. xxxvii. Ibid., 1904, x, p.
xxxix. Science, 1906,

80 GENERAL PROPERTIES OF LIVING TISSUES

a bearing without " sidelash " and with little friction.
As the sleeve with the drum rests upon the friction
plate by gravity alone, it is easy to turn the drum by
hand either forward or back, even while the clock-
work is in action. At the top of the sleeve is a screw
ending in a point which, when the screw is down,
bears upon the end of the steel shaft and lifts the
sleeve, and with it the drum, until the sleeve no
longer bears upon the friction plate. The drum may
then be " spun " by hand about the steel shaft. The
impulse given by the hand will cause the drum to
revolve for about one minute. The speed during any
one revolution is practically uniform.

The clockwork consists of a stout spring about
6 metres in length, driving a chain of gears. The
speed is mainly determined by a fan slipped upon an
extension of the last pinion shaft in the chain. Four
fans of different sizes are provided.

The speed is regulated by a governor on the shaft
that carries the fan. When the milled head shown to
the right of the steel shaft in Fig. 19 is up, the gear
on the extreme right of the chain no longer engages
with the gear driven by the spring, but runs " idle,"
while the gear attached to the friction plate engages
with the lower of the two gears at the left ; the pinion
of this lower left-hand gear engages with the spring
gear. Fast speeds are then obtained.

When the milled head is down, the gear attached
to the friction plate falls below the left-hand gear,
while the right-hand gear engages with the spring

THE GRAPHIC METHOD 81

gear and through a pinion drives the friction-plate
gear. Slow speeds are then obtained.

These operations are easily and rapidly performed,
though, as in all gear mechanism, an instant's pause
is sometimes required to enable the gear teeth to
engage. The clockwork should be in motion, without
the fan, when the adjustments are being made.

With both fast and slow gearing four fans of
different areas may be used. They are slipped upon
an extension of the last pinion shaft in the chain.
Five slow and five fast speeds (exclusive of spinning)
are thus obtained. An additional slow speed (50 cm.
per hour) may be obtained with a very large fan.
All speeds are regulated by a friction governor fast-
ened to the same shaft that carries the fan. With
one winding the drum will revolve from about one
to about seven hours, or longer, depending on the
fan employed. x

The Long Paper Kymograph.1 — In Fig. 19 the
kymograph is arranged for use with a sheet of smoked
paper about eight feet long. A rigid bench of steel
about 97 centimetres long firmly supports two
^-shaped castings in which two aluminium drums
revolve on pointed adjustable bearings. One of the
castings slides along the bench, and may be fastened
at any desired distance from the remaining or clock-
work drum, so that paper from about 150 to 240
centimetres in length may be stretched between the

Science;, 1906
6

82 GENEEAL FE0PERT1ES OF LIVING TISSUES

a

C

<v
H

60

THE GRAPHIC METHOD 83

drums. Each drum is provided with an adjusting
screw, by means of which the drum may be inclined until
the strip of paper is stretched uniformly throughout its
height. This adjustment should preferably be made
upon the sliding drum. "When the adjustment is
complete, the abscissae drawn by a writing lever in
successive revolutions will exactly coincide. The
clockwork drum does not slide along the bench.
Both drums may readily be removed from their
bearings.

Beneath the clockwork drum is a circular plate of
the exact size of that of the medium spring kymo-
graph. This plate rests on two feet and in fact
supports the anterior end of the steel bench. The
clockwork drum is driven by a kymograph in which
the vertical steel drum-rod and sleeve are replaced by
a short rod the top of which is flush with the upper
plate of the kymograph. The feet of this kymo-
graph are hollowed to fit three rounded pins. "When
the kymograph is set upon these pins, it is at once
" centred " and all side motion is prevented. A
coupling sleeve is now let down from the shaft of the
clockwork drum until two projections on the under
surface of the coupler engage with corresponding
slots in the kymograph rod. The clockwork operates
like that of the medium-spring kymograph, having
ten changes of speed. The speeds are, however,
faster as a stronger spring is used, the maximum
being about seven centimetres per second.

To smoke the paper, the coupler is raised, the

84 GENERAL PROPERTIES OF LIVING TISSUES

kymograph clockwork is removed, and then the entire
bench together with its drums is placed horizontally
in the smoker frame (Fig. 20).

Fig. 20. The smoker, showing the long paper kymograph in place. The
paper is smoked with an oil lamp having a four inch wick. Near the
stand are the handle with which the drum is revolved to carry the paper
over the lamp flame, and the two rods which are inserted in the kymo-
graph clockwork when the latter is used independently of the long paper
arrangement.

The graphic record involves the use of appa-
ratus. It never should be forgotten that the use
of apparatus always introduces more or less
error. In every experiment the apparatus
should be criticised sharply. The numerous
imperfections which such scrutiny will bring
to light are of two sorts, — the errors that may
be neglected, and the errors that may not be
neglected without seriously impairing the value
of the method for the purpose in hand. For
example, a count of the pulse rate with an ordi-
nary watch will usually be incorrect by one or

THE GRAPHIC METHOD 85

two beats in the minute, but such a record is
quite accurate enough for most purposes. The
use of a stop-watch marking fifths of seconds
would add nothing to the value of the count,
for the error introduced by numberless causes
that slightly modify the heart-beat from minute
to minute is greater than the error introduced by
using an ordinary watch instead of a stop-watch.
The correction of errors that are too small to
alter essentially the value of the method for
the purpose to which it is applied is usually
wasteful.

With these points in mind, smoke a drum.
Arrange the inductorium with simple key for
maximal break induction currents. Prepare a
gastrocnemius muscle, fasten it in the muscle
clamp, tie a fine copper wire around the tendo
Achillis, wrap the wire about the hook on the
muscle lever, and fasten the end in the binding
post of the muscle lever (Fig. 21). Connect
the secondary coil with the posts on the muscle
clamp and muscle lever respectively. Weight
the muscle with ten grams. Arrange the lever
to write on the drum. Eecord single contrac-
tions with various speeds.

Note that the muscle writes its contraction
in the form of a curve, the ordinates of which
measure the height to which the load is lifted.

86 GENERAL PROPERTIES OF LIVING TISSUES

Light Muscle Lever.1 — A stout yoke (Fig. 21)
bears two set screws holding a steel axle upon which
is mounted a light piece of tubing and a hard-rubber
pulley. One end of the tubing tapers slightly to
receive the writing straw. The other projects behind
the axle, and may be pressed upon by the accurately
cut after-loading screw. The pulley is pierced with a
hole for securing a fine wire by means of which a

Fig. 21. The light muscle lever, with double hook straw fastener ; the
actual size.

weight may be suspended from the pulley when
it is desirable that the weight should be applied
near the axis of rotation. The muscle may also be
weighted directly by means of a scale-pan suspended
from the double hook to which the lower end of the
muscle is attached. If the tendon of the muscle be
fastened to the double hook by a fine wire, the free
end of the wire may be carried to the insulated bind-

1 First Catalogue of Harvard Physiological Apparatus, Sep-
tember, 1901.

THE GRAPHIC METHOD 87

ing post provided for convenient electrical stimula-
tion. The upper end of the muscle may be grasped
in the flat-jawed clamp (Fig. 16), and thus connected
electrically with the binding post upon it.

In obtainiug the extension curve of muscle this
lever, after-loaded, may be weighted to one hundred
grams without bending and thus deforming the curve.
The abscissa will be a straight line. The moving
parts are very light. The apparatus is compact and
occupies but little of the vertical space so valuable
where several recording instruments must be placed
upon the same stand.

Writing Lever. — A strip of aluminium, bent at
one end to fasten with the double hook, pointed at
the other, may be used in place of a straw.

Tuning Fork. — A nickelled polished steel fork
(Fig. 22) with steel handle is filed until it gives one
hundred double vibrations per second. The tuning
fork may be provided with a paper or foil writing

Fig. 22. The tuning fork ; about one-sixth the actual size.

point and clamped to the iron stand. It serves to
measure the latent period of muscular contraction and
similar phenomena of brief duration.

Start the drum at very rapid speed. Bring
the writing point of the vibrating tuning fork

88 GENERAL PROPERTIES OF LIVING TISSUES

(Fig. 22) against the paper below the point of
the muscle lever, and stimulate the muscle to
contract.

Observe that the tuning fork now gives the
time intervals on the abscissa of the muscle
curve, from which the duration of the periods
of shortening and relaxation may be known.
Note also the difference in appearance of curves
recorded on a slow and a rapidly moving
surface.

Measure the interval between the beginning
of contraction and the point of maximum
shortening.

In your laboratory note-book write a critical
account of the muscle lever.

Compare this account with the remarks which
follow : —

The object of the muscle lever is to write a
magnified record of the change in form of the
muscle. Usually the muscle is suspended in a
muscle clamp and its lower end attached to
the lever, which then records the shortening of
the muscle. The same lever may be used to
record the thickening of the muscle ; in this
case the muscle is of course horizontal and
the lever rests upon it. For either purpose
the weight of the lever is an objection, for
it tends to prevent the muscle from begin-

THE GRAPHIC METHOD 89

ning its movement (inertia of position). Once
in motion, the weight tends to keep moving,
and thus to continue the record of contraction
after the actual contraction has ceased (inertia
of motion). As the inertia of motion increases
with the mass and the square of the velocity,
the lighter the lever the less the error. The
disposition of the weight relative to the axis
is also of importance. In a swinging system,
the nearer the mass to the axis of rotation, the
less are the after vibrations or pendulum-like
oscillations which continue after the original im-
pulse has ceased. For this reason, in experi-
ments likely to be disturbed by after vibrations,
the weight which the muscle lifts is attached
to the small pulley, so as to be as near the
axis as possible. In this case, the weight on
the muscle is of course not the weight hung on
the pulley; the pulley weight must be divided
by the number of times the radius of the pulley
is contained in the distance between the axis
and the point of attachment of the muscle to the
lever.

It will be observed that the writing point is a
strip of tinsel bent slightly and placed parallel
to the writing surface. It is very easily moved
in a direction at rio;ht angles to the writing sur-
face, but resists movement in a vertical direction.

90 GENERAL PROPERTIES OF LIVING TISSUES

The bend makes the strip a weak spring, ena-
bling the point to remain in contact with the
drum throughout the excursion of the point on
the paper. The writing point should be as nearly
as possible parallel to the paper. Even in this
position, the distance of the end of the straw
from the paper is necessarily less when the lever
is horizontal than when raised by the contrac-
tion of the muscle, for the end of the lever
describes a curved line in a plane tangent to the
recording surface. Were it not for the spring
of the writing point, the latter would leave the
drum. To remain on the drum at the height of
the contraction, the point must at the beginning
of contraction press against the drum with much
more friction than is necessary simply for scratch-
ing through the layer of soot. Thus the distance
of the writing point from the axis is constantly
varying, and the magnification of the lever
is constantly changing. Within the limits ordi-
narily employed in physiology, the deformation
of the curve thereby produced is proportional to
the length of the arc through which the point
moves ; the curve should therefore be written
no larger than is necessary for clearness.

When the smoked surface is at rest, and the
contracting muscle lifts the lever, the writing
point describes an arc ; when the muscle relaxes,

THE GRAPHIC METHOD 91

the writing point returns in the same line. When
the drum revolves, the writing point describes a
curve as the muscle contracts. The maximum
shortening of the muscle, or height to which the
load is lifted, is measured by a perpendicular
drawn from the highest point of the curve to the
abscissa. The time required for the muscle to
reach this height, however, is not the distance on
the abscissa from the beginning of the curve to
the perpendicular, but to the point at which the
segment of a circle of a radius equal to the
length of the lever would cut the abscissa when
drawn from the highest point of the curve. Prac-
tically, this measurement is made by turning the
drum back until the point of the raised lever
rests at the summit of the curve, and then,
while the drum is at rest, allowing the lever
to write the ordinate by falling down to the
abscissa.

Perpendicular ordinates may be secured by a
long pin passed transversely through the end of
the writing lever, and bent twice at right angles,
first parallel to the paper and then towards it.
The lever is perpendicular to the paper and very
near it ; the weight of the pin keeps the point
against the paper as the lever rises. The perpen-
dicular writing has many faults in common with
arc writing.

92 GENERAL PROPERTIES OF LIVING TISSUES

Apparatus

Normal saline. Bowl. Pipette. Towel. Glass plate.
Kymograph. Glazed paper. Smoking apparatus. Shel-
lacking trough. Shellac in alcohol. Muscle lever (weight
pan). Muscle clamp. Stand. Inductorium. Electrodes.
Simple key. Dry cell. 5 Wires. Fine copper wire. Ten
gram weight. Tuning fork. Tin foil. Cement. Frogs.

STIMULATION OF MUSCLE AND NERVE 93

IV

THE ELECTRICAL STIMULATION OF MUSCLE
. AND NERVE

The Galvanic Current

The study of the changes occasioned in muscle
and nerve by electrical stimulation may profit-
ably begin with the action of the galvanic
current.

Non-Polarizable Electrodes. — "When metal
electrodes come in contact with an electro-
lyte, polarization currents develop (see page 51).
Electrodes of metal for this reason should be
avoided in the study of the effect of the galvanic
current on muscle and nerve. A "non-polar-
izable " electrode should be employed. Strictly
speaking, no electrode is non-polarizable, but
practically the polarization errors are excluded
by the device shown in Fig. 23.

The boot electrodes (Fig. 23) are made of potter's
clay, skilfully fired, and are unglazed. The leg is
pierced with a hole 28 mm. deep and S mm. in

94 GENERAL PROPERTIES OF LIVING TISSUES

diameter, in which is placed the zinc. The foot is
20 nam. long, measured from its junction with the
leg. In the foot is a well for normal saline solution
which shall keep the feet equally saturated. The
boots should ordinarily be kept in normal saline so-
lution. In use the hollow leg of the boot is half-filled
with saturated solution of zinc sulphate and placed in
the clip. The well in the foot of the boot is now filled
with normal saline solution. If metal clips are used

Fig. 23. Non-polarizable electrodes ; about
two-fifths the actual size.1

the boots should be mounted on separate rods, to
prevent the current passing through the unglazed
boot to the metal holder and thus to the other boot.
This difficulty is avoided by the rubber holders shown
in Fig. 24. The electrodes may be mounted on a
brass rod called the mounting-rod, or in the moist
chamber shown in Fig. 24. The boot electrodes
serve equally well for leading off the nerve or mus-

1 First described in " Science," 1901, xiv, pp. 567-570. The
well was added in Nov. 1905.

STIMULATION OF MUSCLE AND NERVE

95

cle current to the electrometer arid for stimulation.
After use, the boots should be emptied, rinsed in
tap water, drained, and placed in several hundred
cubic centimetres of normal saline solution until
wanted again. If the foot of the hoot is kept saturated
with normal saline solution these electrodes will remain

Fig. 24. The moist chamber ; about three-fifths the actual size.

non-polarizable. They may also be used with normal
saline clay.

The Moist Chamber.1 — The moist chamber (Fig.
24) consists of a porcelain plate which bears near

1 Science, 1901, n. s. xiv, p. 569.

96 GENERAL PROPERTIES OF LIVING TISSUES

the margin a shallow groove. In this groove rests a
glass cover which for the sake of clearness has been
omitted from the figure. To the porcelain plate is
screwed a rod, by which the plate may be supported
on a stand. Within the glass cover are two right-
angled rods. One of the rods carries a small clamp,
composed of a split screw on which moves a nut, by
means of which the femur of a nerve-muscle prepara-
tion may be firmly grasped. The holder for the split
screw is arranged to permit of motion in all directions.
Both right-angled rods carry unpolarizable electrodes.
Each of these is borne by a hard- rubber holder. By
turning the leg of the boot in the holder the foot may
be brought as near the foot of the neighboring elec-
trode as may be desired. It is desirable to mount
the boots on opposite rods as in Fig. 24. A thick
wire of freshly amalgamated zinc, provided at one
end with a hole in which a connecting wire may be
fastened with a set screw, is placed in the leg of the
boot, and the other end of the connecting wire
brought to one of the four binding posts shown in
Fig. 24. These four posts are in electrical connec-
tion with four other posts beneath the porcelain
plate. The air within the moist chamber may be
kept saturated with water vapor by applying moist
filter paper to the inner side of the glass globe.

Destruction of the Brain by Pithing. — The
next experiment requires a curarized muscle, and

STIMULATION OF MUSCLE AND NERVE 97

curarization is best accomplished by the injec-
tion of curare into the dorsal lymph sac of a
frog the brain of which has been destroyed.
Wrap the frog in the cloth, head out. Hold the
frog with the fingers of the left hand, pressing
down the tip of the frog's nose with the left
thumb. Pass the right forefinger along the mid-
dle line of the head. A slight depression will be
felt at the joining of the skull and trunk. Here
the cerebro-spinal canal has no bony covering.
Make at this point a cut about a centimetre
(I inch) long through the skin in the middle line.
Thrust the seeker vertically through the soft
tissues until the point is stopped by the bony
vertebrae. Turn the point of the seeker towards
the head, and push it along the brain cavity,
moving it gently from side to side.

Paralysis of Voluntary Motion by Curare. —
Make a very small hole in the skin of the back
into the dorsal lymph sac. With a fine glass
pipette inject a few drops of a straw-colored
solution of curare. The curare of commerce is
the dried juice of a species of strychnos. It is
not a definite chemical compound and cannot
therefore be given in an accurate dose. It is
customary to make a one per cent solution of the
crude mass. This solution may be kept from

7

98 GENERAL PROPERTIES OF LIVING TISSUES

decomposition by a small crystal of thymol. The
bottle should be shaken before the curare is with-
drawn. The curare should be injected at the
beginning of the laboratory day, so that there
may be time for its action in a dilute solution.
The motor nerves are paralyzed first and the
effect should, if possible, be limited to them.
Strong solutions paralyze other nerves, the heart,
and probably other muscles.

Opening and closing Contraction. — Place two
non-polarizable boot electrodes in rubber holders
upon a mounting-rod. Fill the boots half full
of saturated solution of zinc sulphate. Fill the
well in the toe of each boot with normal saline
solution. Place well amalgamated zincs in the
boots and connect them through an open simple
key with the poles of a battery. Prepare a
sartorius muscle (Fig. 25) from a curarized frog,1
preserving the pelvic and tibial attachments.
Lay the muscle upon the toes of the boot
electrodes. Close the key.

The muscle will twitch when the current is
made and probably when it is broken, but during
the passage of the current there will be normally
no contraction.

1 Be sure to cut off the head or otherwise destroy the brain
of curarized frogs before operating on them.

STIMULATION OF MUSCLE AND NERVE

99

In frogs used during the period of hibernation
and especially in those brought from a cold store-
room into a warm laboratory, the make and some-
times the break of the constant current may be
followed by prolonged
tetanus. In such frogs,
the irritability of the
muscles is greatly
increased, and the
changes, probably
ionic, which occur
while the current is
passing and after it is
shut off are sufficient to
produce contractions
not seen in the normal
state (see page 147).
Usually the muscle is
stimulated only by a
sudden change in the
intensity of the current.

Changes in Intensity of Stimulus. — Connect
one of the electrodes used in the preceding ex-
periment with one of the poles of a dry cell.
From the other pole lead a wire to a bowl of
salt water. To the other side of the same bowl
bring a wire from the remaining electrode.

When the wires are slowly brought nearer

e.c.

t.a.

Fig. 25. Hind limb of froj
view (Ecker-Wiedersheim).

anterior

100 GENERAL PROPERTIES OF LIVING TISSUES

together, there will be no contraction ; when they
are brought quickly together, thus quickly in-
creasing the intensity of the current, the muscle
will contract.

With Indirect Stimulation. — 1 . Smoke a drum.
Make a nerve-muscle preparation (sciatic nerve
and gastrocnemius muscle). Place the femur
in the clamp in the moist chamber. Let the
nerve rest on non-polarizable electrodes connected
through an open key with a dry cell. Attach
the tendo Achillis to the muscle lever. Let the
muscle lever write on a slowly moving drum.
Close and open the key.

Both closing and opening contraction will be
seen. (If the frog has been brought from a cold
room into the warm laboratory, opening and
closing tetanus will probably replace the usual
twitch. See page 147.)

2. Eepeat the experiment on page 99, using
the nerve-muscle preparation instead of the
curarized muscle.

It will again be found that the intensity of
the current must be increased with a certain
rapidity in order to stimulate.

The experiments just made support DuBois-
Reymond's statement that the electrical current
does not stimulate during the entire period of
its flow through the irritable tissue, but only

STIMULATION OF MUSCLE AND NERVE 101

when the intensity is rapidly altered by making
or breaking the circuit. These experiments,
however, were made on the rapidly reacting
skeletal muscle of the frog. The law does not
hold good for sluggish contractile tissue. In-
deed it can be disproved even for highly striated
muscle by a very careful examination of the
manner in which excitation takes place. Pfliiger
discovered that when the galvanic current is
made, excitation takes place only at the points
through which the current leaves the muscle or
nerve (cathodal stimulation), and that when the
current is broken, excitation takes place only
where the current enters the irritable tissue.
This "polar excitation" we must now consider.
We shall find, among many other facts, the
refutation of the idea that stimulation does not
occur throughout the passage of the current.

Polar Stimulation of Muscle

1. Slit the curarized sartorius muscle trouser-
like from the lower end. Lay each end on a
boot electrode. Make and break the current.

On making the current the cathodal side will
contract ; on breaking, the anodal side.

2. Lay the muscle on ice covered with a small
piece of paraffin paper, to shield the muscle from

102 GENERAL PROPERTIES OF LIVING TISSUES

water. When thoroughly cold, place the muscle
in the Gaskell clamp (Fig. 26), making very
gentle pressure across the middle, and bring the
non-polarizable electrodes against the ends. Make
and, after a minute, break the current.

The excitation wave passes so slowly through
cooled muscle that the contraction can be seen
with the unaided eye to begin at the cathode on
closing and at the anode on opening the circuit.

3. Ureter.1 — Place the extirpated ureter of
any mammal on a glass plate set as a cover on
a beaker containing hot normal saline solution,
so that the hot vapor of the water shall keep
the ureter warm. Bring the non-polarizable
electrodes against the ureter. Note which elec-
trode is the cathode. Close the key.

After a distinct latent period the ureter in the
cathodal region, and nowhere else, will contract,
and the contraction wave will spread from the
cathode in both directions along the ureter.

Open the key.

The Gaskell Clamp. — The tapered edge of a hard-
rubber block is brought against a similar edge by
means of a fine screw (Fig. 20). With this clamp
the heart muscle may be compressed, after GaskelFs

1 The experiment succeeds also with extirpated pieces of in-
testine :ili"iit lour iii<hcs long, provided they are kept warm
with normal saline solution.

STIMULATION OF MUSCLE AND NERVE 103

method, until conduction between auricle and ven-
tricle is partially or wholly interrupted. The clamp

Fig. 26. The Gaskell clamp j about one-third the actual size.1

is also used to press upon the sartorius until the con-
duction wave is blocked while the excitation wave
still passes.

The contraction takes place now only at
the anode, and the contraction wave spreads
from that point over the muscle (as making
the current is a less effective stimulus than
breaking it may be necessary to increase the
strength of the current, or to keep it closed a
considerable time, in order to secure making
contraction).

4. Intestine. — Place the non-polarizable anode
on the intestine of a freshly killed rabbit or frog,
the cathode on some indifferent point, for example
the liver. Close the key.

The intestine will constrict in the anodal re-
gion and remain constricted during the passage
of the current, provided it be not so long as to

1 This form was first described in the Catalogue of the Harvard
Apparatus Company, May. 1905.

104 GENERAL PROPERTIES OF LIVING TISSUES

cause fatigue. A peristaltic contraction wave
usually passes from the anode in both directions
along the intestine.

Place the cathode on the intestine, and the
anode on an indifferent point. Close the key.

A small, indistinct thickening will be seen in
the cathodal region.

Thus the intestine, while it serves admirably to
illustrate a polar action of the galvanic current, ap-
parently differs from the tissues already considered
in that closure causes contraction at the anode in-
stead of the cathode. The exception is only appar-
ent, and its explanation is that the point at which
the electrode touches the peritoneal surface of the
many-layered intestinal wall is not the physiologi-
cal anode or cathode ; i. e. not the point at which
the current actually enters or leaves the muscular
coat. This matter is discussed on page 110.

5. Smoke a drum. Eaise the drum off the fric-
tion bearing by turning the screw at the top of the
shaft to the right. Arrange two muscle levers 1
and the electro-magnetic signal (Fig. 27) to write
on the drum in the same vertical line. Place the
electro-magnetic signal, together with a simple
key, in the circuit between one dry cell and the
rheochord. Bring the slider near the positive
post of the rheochord.

1 Or heart levers (Fig. 53, page 311).

STIMULATION OF MUSCLE AND NERVE 105

Fig. 27. The signal magnet ; the actual size.

The Electro-magnetic signal.1 — A protecting metal
box (Fig. 27), open at the front and ends, contains a
strong magnet, the armature of which is mounted upon
a steel spring. An accurate fine adjustment screw reg-
ulates the excursion of the armature. One binding
post is mounted upon the metal box, the other is insu-
lated by a rubber block. This signal, in circuit with a
vibrating tuning fork, will record one hundred double
vibrations per second. In the primary circuit of the
inductorium it will record the make and break of the
current without after-vibrations which are prevented by
lead foil placed on the spring where it strikes the limit-
ing screw. Residual magnetism is obviated by parch-
ment paper, fastened to the spring with shellac at the
point where the spring would touch the core of the
magnet. The handle is long enough to bring the writ-
ing point directly above or below the writing point of
the muscle lever clamped to the same iron stand.

The metal box is of soft iron and serves as an
extension of the magnet core, thus completing the
magnetic circuit, and doing away with a second spool.
The magnetic power is further improved by boring
out the core, which is then " softened " by heat.

1 First Catalogue of Harvard Apparatus, September, 1901, p. 46.

106 GENERAL PROPERTIES OF LIVING TISSUES

Fasten a curarized sartorius muscle by the middle
in the Gaskell clamp ; the pressure should be
enough to prevent the contraction wave of one
part reaching the other part, but not great enough
to prevent the passage of the excitation. Place
the muscle vertical to the writing levers. Tie a
thread around the pelvic and tibial fragments
and fasten each thread to a muscle lever, so that
each half of the muscle may record its contrac-
tion independently of the other. Moisten two
strands of lamp wick with normal saline clay.
Tie one strand around each end of the muscle
and lay the free portion of the strands on the
toes of boot electrodes properly mounted. Note
which lever is connected with the cathodal end.
Make the current. If the muscle does not con-
tract, move the slider along the wire a short dis-
tance towards the positive post (so as to bring
a stronger current through the electrodes) and
make the current again. When both make and
break contractions are secured, see that the writ-
ing points record properly, and " spin " the drum,
but not too fast. As soon as the drum moves
steadily, make and then break the current.

The moment of making and breaking the cur-
rent will be recorded by the electro-magnetic
signal. An instant later the muscle levers will
begin their record of the contractions.

STIMULATION OF MUSCLE AND NERVE 107

It will be found that the cathodal half of
the muscle contracts first on closing, the anodal
half on opening the circuit. Evidently the
excitation began on closure at the cathode and
passed thence to the anode, while on opening
the circuit the excitation began at the anode
and passed to the cathode.

In order to measure this interval accurately
the drum should be turned back until the writ-
ing point of the signal lies precisely in the ordi-
nate drawn by it during the experiment. The
muscle should then be stimulated. The ordinate
now drawn by the muscle with the drum thus
at rest will be synchronous with that drawn by
the signal during the experiment, and will mark
upon the abscissa of the muscle curve the moment
of stimulation,

6. Tonic Contraction. — Connect a dry cell
through an open simple key with the metre
posts of the rheochord. Connect non-polarizable
electrodes with the positive post and the slider.
Fasten one end of the curarized sartorius (pre-
pared with fragments of pelvis and tibia attached)
in the muscle clamp. Tie a thread to the other
end and fasten the thread to the upright pin of
the muscle lever. Let non-polarizable electrodes
rest on the muscle near the respective ends.
Use a strength of current that will just cause

108 GENERAL PROPERTIES OF LIVING TISSUES

contraction on closure. Watch very closely the
cathodal region near the junction of the muscle
fibres with the tendon. Close the key.

After the closing contraction, the ends of the
muscle fibres next the tendon in the cathodal
region will show a faint but distinct thickening,
which will remain until the current is broken.

These several experiments demonstrate that in
galvanic stimulation of both skeletal and smooth
muscle the excitation takes place at the points
where the current leaves and enters the muscle.
Before inquiring whether this law holds good for
the heart, the muscle cells in which have a form
intermediate between the smooth muscle cell and
the cells of skeletal muscle, it will be necessary
to consider whether the points of contact with
the electrodes are always the real anode and
cathode.

Physiological Anode and Cathode. — When the
electrodes are placed directly on a nerve, or are
applied to a muscle with straight parallel fibres in
such a way that the current flows through each
fibre from end to end, the anode and cathode
obviously coincide with the points at which the
electrodes touch the muscle. When, however,
the fibres are of irregular shape, or are irregularly
disposed, the current lines can no longer traverse
the fibres from end to end, but will enter and

STIMULATION OF MUSCLE AND NERVE 109

leave fibres at points other than those in contact
with the electrodes.

The difference between the operator's elec-
trodes and the physiological anode and cathode
is also obvious when the electrodes are applied
to skin, connective tissue, mucous membrane, etc.,
covering the muscle or nerve, — the points at
which the electrodes touch the covering tissue
cannot be the points at which the current actu-
ally leaves or enters the muscle.

The failure to keep this distinction in mind
may lead to wholly erroneous interpretations.
Thus when the ureter is extirpated, or is raised
from the tissues on which it normally rests, its
reaction to the galvanic current follows the law,
— contraction begins at cathode on making, at
anode on breaking the current; but when the
ureter is stimulated in situ, exactly the opposite
effect is seen, — contraction begins at anode on
making the current. The explanation is that
the current lines in the latter case are very
widely diffused through the conducting tissues
on which the ureter lies, so that the current
passes into and out of the muscle fibres for some
distance either side of the positive electrode.
Each point at which the current leaves a fibre
is a secondary cathode, and if the number of
such points is large, cathodal stimulation will

110 GENERAL PROPERTIES OF LIVING TISSUES

take place in what, superficially regarded, is the
anodal region (compare page 131, and Fig. 37).
The same explanation holds good for the intes-
tine (see page 103). The formation of physio-
logical anodes and cathodes is well shown in the
next experiment.

Physiological Anodes and Cathodes in Bechis
Muscle. — Eemove the rectus abdominis muscle,
from a curarized frog. Note the tendinous cross
bands which divide the muscle from side to
side and divide it into parts. Lay the muscle
smoothly on a glass slide. Connect the non-
polarizable electrodes through a simple key with
a dry cell. Place one electrode on each end of
the muscle. Close the key.

On closure, the cathodal side of each division
of the muscle will show a sharply defined con-
tinued contraction of the ends of the fibres at
their insertion in the transverse tendinous bands.
On opening, the cathodal contraction disappears,
and a similar thickening of the fibres is seen at
the anodal side of each division. The twitch of
each segment on closure and opening of the cur-
rent also starts respectively from the cathodal
and anodal ends of each segment. These effects
are best seen through a magnifying glass.

Polar Stimulation in Heart. — The muscle cells
of the heart are not only of irregular shape, but

STIMULATION OF MUSCLE AND NERVE 111

they are so joined with each other as to make it
impossible to pass a current through the heart
muscle without the current lines cutting fibres
in every direction. It would seem therefore that
secondary anodes and cathodes would be formed
to such a degree that the demonstration of polar
excitation would be difficult or impossible. Ex-
perimentation shows however that this is not the
case. The heart behaves like a single hollow
fibre.

Monopolar Method. — The small size and conical
form of the ventricle of the frog's heart make the
ordinary method of stimulation, in which the
electrodes would both be placed on the heart,
less suitable than the monopolar method. This
method was suggested by the fact that the
stimulating effect of the galvanic current depends
on its density. If one electrode has a large sur-
face, and the other a very small surface, the
current lines will be distributed through a con-
siderable cross-section in the first instance and
converge to a small cone in the second. The
threshold value of stimulation will not be
reached at the large electrode, and stimulation
will occur only at the small electrode. Thus the
large "indifferent" electrode may be placed on
any part of the frog's body, and the convenient
small electrode be used to stimulate the heart

112 GENERAL PROPERTIES OF LIVING TISSUES

Cover the indifferent electrode (consisting of a
brass plate furnished with a binding post) with
cotton wet with saline solution. Mount a non-
polarizable boot electrode. Con-
nect a dry cell with the metre
posts (0 and 1) of the rheochord
through a simple key (Fig. 28).
Connect post 0 and the slider
through a pole-changer (with
cross-wires) with the electrodes.
Expose the heart, according
to the following method :
brainless frog, back down, in the
holder (Fig. 29). Cut through the skin across
the middle of the body from side to side.
Make a second cut in the middle line from the

Fig. 28

Place the

Fig. 29. The frog board, with spring clips ; about one-fourth the actual

first cut to near the lower jaw. Turn back the
flaps. Cut through the sternal cartilage near its
lower end, thus avoiding the epigastric vein.

STIMULATION OF MUSCLE AND NERVE 113

Cautiously remove the breast bone, doing no
harm to deeper parts. Open the delicate mem-
brane (pericardium) which surrounds the heart.
Tie a ligature about the sinus-auricular junction,
to stop the ventricular contractions. Place the
indifferent electrode over the larynx and the non-
polarizable electrode on the ventricle. Turn the
pole-changer so that the electrode on the heart
becomes the anode. Close and then open the
key.

Contraction will take place on opening only,
if at all. Eeverse the pole-changer so that the
cardiac electrode becomes the cathode. Close
and then open the key.

Contraction takes place at closure only.

Polar Stimulation of Nerve

Law of Contraction. — 1. Whether contraction
will follow the galvanic stimulation of a motor

O

nerve depends on the irritability of the nerve
and the direction and intensity of the current.
The current may pass through the intrapolar
portion of the nerve towards the muscle (de-
scending current) or away from it (ascending
current). The intensity may be weak, medium,
or strong ; intensity in this case is evidently
merely a relative term, depending on the irrita-

114 GENERAL PROPERTIES OF LIVING TISSUES

bility of the particular nerve in hand. We will
test first the effect of the ascending current.

Connect a dry cell through an open key with
the metre posts of the rheochord (Fig. 30). Join
the positive post and the slider through a pole-
changer (cross-wires in place), with the non-
polarizable electrodes placed in the moist

Fig. 30.

chamber (Fig. 24, page 95), in the holders farthest
from the opening for the muscle. Make a
nerve-muscle preparation. Secure the femur in
the femur clamp of the moist chamber. Let
the nerve lie on the non-polarizable electrodes.
Attach the Achilles tendon to the muscle lever.
Keep the air in the chamber moist by lining
the glass shade with filter paper saturated with
water. Arrange the pole-changer so that the

1 The inductorium shown in Fig. 30 is not used in this ex-
periment, but in the first experiment on page 116.

STIMULATION OF MUSCLE AND NEEVE 115

anode shall be next the muscle. Move the slider
near the positive post. Make and break the gal-
vanic current. If no contraction is secured,
move the slider to increase the current, and
repeat the experiment.

The first contraction will take place on mak-
ing the current. Continue to increase the cur-
rent strength by moving the slider.

A point will be reached at which contraction
will occur both on opening and closure.

Increase the intensity of the current by add-
ing dry cells in series (zinc to carbon), testing
the effect after each addition by closing and
opening the current.

An intensity will be reached at which opening
and not closure causes contraction.

In a similar manner, work out the law of con-
traction for descending currents. (It may be
necessary to take a fresh nerve-muscle prepa-
ration.)

Set down the results in a table.

Intensity

Ascending

current.

Descending current.

of current.

Make.

Break.

Make. Break.

Weak.

Contr.

Rest.

Contr. Rest.

Medium.

Contr.

Contr.

Contr. Contr.

Strong.

Rest.

Contr.

Contr. Rest (Weak contr.)

2. The remarkable nature of these results is
apparent on observing that contraction is easily

116 GENERAL PROPERTIES OF LIVING TISSUES

secured on closing a weak ascending current and
yet cannot be obtained with a strong one. The
first step in the inquiry into the causes of the
phenomena is to determine whether the stimu-
lation is polar. That the nerve impulse really
starts at the cathode on closure and at the anode
on opening is shown (1) by the fact that the
interval between stimulation and contraction,
with the ascending current, in which the anode
is next the muscle, is longer at closure than on
opening, while the opposite is the case when the
current is descending. (2) With descending
currents, it sometimes happens that opening
produces tetanus instead of a simple twitch.
If this tetanus appears, the student should sever
the nerve between the electrodes. Immediately
the contractions will cease. They must there-
fore have arisen at the anode, for the cathode
still remains in full connection with the muscle.

Changes in Irritability. — The second step in
this inquiry is to determine the nature of the
changes at the poles. For this purpose the
nerve should be stimulated in the cathodal and
anodal regions during the passage of the constant
current.

1. Pass two needles through a cork placed in
the rubber holder next the muscle in the moist
chamber. Connect them with the secondary coil

STIMULATION OF MUSCLE AND NERVE ' 117

of an inductorium (Fig. 30). Arrange the pri-
mary for single induction shocks, which must
not be maximal. Turn the pole-changer to bring
the cathode next the metal electrodes. Using a
weak induction current as stimulus, record on a
stationary drum three contractions: (1) before
the passing of the galvanic current through
the nerve, (2) during its passage, (3) after its
passage.

The second contraction — that obtained by
stimulating in the cathodal region during the
passage of the galvanic current — will be greater
than the other two.

Eeverse the galvanic current and repeat the
experiment, the stimulation now being in the
anodal region.

The stimulation in the anodal region during
the passage of the galvanic current causes less
than the normal contraction.

2. The stimulating current may be superposed
directly on the polarizing current by using the
same electrodes.

Connect a dry cell through an open key with
the 0 and 1 metre posts of the rheochord
(Fig. 31). Connect the positive post of the
rheochord with one of the non-polarizable elec-
trodes. Join the slider to one end of the second-
ary wire of an inductorium ; to the other end

Fig. 31.

118 GENERAL PROPERTIES OF LIVING TISSUES

join the remaining non-polarizable electrode. If
the positive pole of the secondary coil is not
known, determine it by the electrolytic method
(page 158). Arrange the primary coil of the

inductorium for single

====*wp\ submaximal induction

/\2^\ jj \] currents. Make and

Vo^o ^jw (^.Culi | break the induction

f ? = sf j current, and record

v*/\»-^ / the contractions on

the drum. Now pass
a weak polarizing cur-
rent through the nerve and stimulate again with
the induction current.

It will be found that the stimulating effect of
the induction current is increased when the
direction of the induction current coincides with
that of the polarizing current, i. e. when the
cathode (which is the sole source of the induc-
tion stimulus, as pointed out on page 160) coin-
cides with the cathode of the polarizing current.
When the cathode of the induction circuit falls
in the anodal region of the polarizing circuit, the
stimulating effect is diminished. Very strong
polarizing currents produce such alterations in
irritability that the additional alteration caused
by the brief induction current is not great enough
to be a stimulus.

STIMULATION OF MUSCLE AND NERVE 119

The law revealed by this experiment may be
thus expressed. The same stimulating current
has a greater stimulating effect when it coincides
in direction with a pre-existing current, and a
lessened effect when it is opposed in direction to
a pre-existing current. This law explains the
interference observed between stimulating cur-
rents and demarcation or injury currents of nerve
and muscle (see page 292).

3. Place a drop of saturated solution of sodium
chloride on the nerve in the extrapolar region
near one of the non-polarizable electrodes.
Eecord the irregular tetanus (chemical stimu-
lation) on a slowly moving drum. Make the
polarizing current.

Note that the tetanus is increased when the
cathode is nearer the stimulating solution, but
diminished when the anode is nearer.

Hence the irritability of the nerve is altered
during the passage of the electric current (elec-
trotonus);1 it is increased in the neighborhood
of the cathode (catelectrotonus) and is diminished
in the neighborhood of the anode (anelectro-

1 The change in the excitability of the nerve produced by
the electric current is so generally called electrotonus that the
term cannot well be changed. It should not be confused with
the electrotonus described on page 000, though it is possible
that the two phenomena have a similar if not identical first
cause.

120 GENERAL PROPERTIES OF LIVING TISSUES

tonus). Ill the intrapolar region, the cathodal
touches the anodal area at the so-called indifferent
point. This point approaches the cathode when
the intensity of the polarizing current is increased.

The greater the length of nerve between the
electrodes, the greater the extrapolar electrotonus.
Catelectrotonus rises rapidly to a maximum as
soon as the circuit is closed, and then gradually
wanes. Anelectrotonus develops more slowly and
does not reach its maximum for some time after
closure.

On the opening of the circuit, the conditions at
the anode and cathode are reversed, the irritability
falls at the cathode and rises at the anode. The
fall in the cathodal region is of short duration
and the irritability soon returns again towards
normal. In the anodal region, the rise on open-
ing is unbroken.

Changes in Conductivity. — We have seen
that the irritability is altered by the galvanic
current. The conductivity also is altered.

Connect a dry cell through a pole-changer with
cross-wires to a pair of non-polarizable electrodes
placed in the holders of the moist chamber
farthest from the muscle (Fig. 32). Leave one
wire uncoupled until the current is wanted.
Connect another cell with the primary coil of
the inductorium arranged for break induction

STIMULATION OF MUSCLE AND NERVE 121

shocks, placing in the circuit a simple key and
the electro-magnetic signal. Lead wires from the
poles of the secondary coil to the side cups of a
pole-changer (without cross-wires). In each of
the remaining two holders of the moist chamber
place a cork pierced by two metal electrodes.
One wire in each pair should be insulated from
its fellow by rubber
tubing drawn over the
part between the cork
and the end of the elec-
trode to be applied
to the nerve. Connect
the wire soldered to
the basal ends of these
electrodes with the re-
maining cups of the
pole-changer in the sec-
ondary circuit of the
indue torium

smoked drum beneath the writing point of the
muscle lever.

Make a nerve-muscle preparation. Let the
nerve rest on the non-polarizable electrodes near
the cross-section. Place one pair of the metal
electrodes beneath the nerve near the muscle, the
other pair near the non-polarizable electrodes.
The clockwork of the drum should be fully

Fig. 32.

Arrange the signal to write on the

122 GENERAL PEOPERTIES OF LIVING TISSUES

wound (not over wound), and the drum should
revolve at its most rapid speed. Write two
muscle curves. For the first stimulate through
the metal electrodes nearer the muscle ; for the
second through the metal electrodes farther from
the muscle.

While each curve is writing, let a tuning fork
record its vibrations beneath the point of the
the muscle lever. To mark on the abscissa of
the muscle curve the exact moment at which the
muscle was stimulated, turn back the drum until
the writing point of the signal lies precisely in
the line described by it when the current was
broken. Now stimulate the muscle with another
induction shock. The curved ordinate of the
muscle lever will be synchronous with the ordi-
nate of the signal.

The interval between the moment of stimula-
tion, as recorded by the signal, and the beginning
of contraction, is greater when the nerve is stim-
ulated far from the muscle. The difference is
the time required for the nerve impulse to tra-
verse the length of nerve between the electrodes,
provided of course that the interval between the
arrival of the nerve impulse in the muscle and
the beginning of the contraction is the same in
both cases, an assumption considered reasonable
by most physiologists.

STIMULATION OF MUSCLE AND NERVE 123

Write now three other pairs of curves : one
while a galvanic current passes through the non-
polarizable electrodes in a descending direction
(cathode nearer the muscle); a second while an
ascending current passes (anode nearer the mus-
cle) ; and a third, after, the galvanic current has
been some minutes broken, as a control. During
the writing of these curves measure the velocity
of the drum with the tuning fork as before.

The speed of the nerve impulse will be found
to be greater than normal when the nerve im-
pulse starting at the second pair of metal elec-
trodes passes through an extrapolar cathodal
area (i. e. stimulation during descending current),
and less than normal when that region is made
anodal by reversing the galvanic current. In
other words, the conductivity of the nerve has
been increased by cathodal and diminished by
anodal stimulation.

2. Conductivity is diminished by strong or pro-
tracted currents in the cathodal as well as in the
anodal region. — Place two non-polarizable elec-
trodes upon the nerve about 3 cm. apart. Con-
nect them through a pole-changer with two dry
cells (Fig. 33). In the middle of the intrapolar
region place two stimulating electrodes close
together. Connect one of the stimulating elec-
trodes directly to the secondary coil of an indue-

124 GENERAL PROPERTIES OF LIVING TISSUES

torium arranged for single induction currents.
Lead from the other stimulating electrode to a
piece of nerve or muscle about 4 cm. long, and
thence to the secondary coil. The introduction
of this great resistance will keep most of the
polarizing current in the short bridge of nerve
between the polarizing electrodes. Without this
resistance, the polarizing current would pass

through the stimulating
A3 v2^ circuit in preference to

N /Ct\/ crossing the nerve be-

/S7 tween the stimulating

I i electrodes. Observe that

the nerve impulse cre-
ated by the stimulus

Pig. 33> cathodal region, if the

current be descending, or
the anodal region, if the current be ascending, in
order to reach the muscle.

Find the position of the secondary coil at
which the muscle will barely contract on making
the stimulating current. Arrange the pole-
changer to brin^ the anode between the stiinu-
lating electrodes and the muscle, and make the
polarizing current. Stimulate with a make in-
duction current during the passage of the polar-
izing current. Open the polarizing current.

I

~"u\ ^ y^2) must pass through the

STIMULATION OF MUSCLE AND NERVE 125

After three minutes' rest, bring the cathode next
the muscle and make the polarizing current as
before. Then stimulate again with a make in-
duction current of the same intensity as before.

Contraction will be absent, or at most very
weak. The impulse will be blocked in the
cathodal region. In truth, during the passage of
strong or protracted currents, the conductivity is
more diminished in the cathodal than in the
anodal resrion.

Griitzner and Tigerstedt believe that the open-
ing contraction is due to the stimulation of the
nerve or muscle by the polarization current
which appears when the galvanic current is
broken. The polarization current may be said
to be closed when the galvanic current is opened.
These observers, therefore, hold that stimulation
takes place only at closure.

We are now in a position to account for the
phenomena described by the law of contraction.
The irritability of the nerve is increased at the
cathode on closing, and at the anode on opening
the galvanic current. This rise of irritability
stimulates the nerve. The rise at the cathode is
a more effective stimulus than the rise at the
anode ; consequently with weak currents the first
stimulus to produce contraction is cathodal, i. e.
at the closure of the circuit. As the current in-

126 GENERAL PROPERTIES OF LIVING TISSUES

tensity is increased, the anodal rise becomes also
effective, and contraction is secured by both mak-
ing and breaking the current.

But we have to deal also with a decrease in
irritability, and, still more important for the
explanation of the effects of strong currents, with
a decrease in conductivity. The irritability and
conductivity are decreased on closure at the anode
and on opening at the cathode. If the anode is
next the muscle (Fig. 34), the decrease in con-
ductivity on closure of a strong
current will block the nerve im-
m^^) ?""-? pulse coining from the cathode ;
it will therefore never reach the

«c^3 | — * muscle, and there will be no

Fig. 34. contraction on closure. If the

cathode is next the muscle, the
conductivity may be so decreased on opening that
the nerve impulse coining from the anode may be
blocked. The decrease at cathode, when the cur-
rent is broken, is, however, less marked than the
decrease at anode when the current is made, so
that the cathodal decrease, even writh strong
currents, sometimes fails to block the impulse
entirely. In that case, a weak contraction may
be obtained at the break of the descending
current.

stimulation of muscle and nerve 127

Stimulation of Human Nerves

Duchenne devised a method by which either the
motor or the sensory human nerves can be stimu-
lated at will, and the reaction of single muscles
or groups of muscles to electricity determined.
When electrodes are placed on the surface of the
skin and the circuit is made, the current entering
at the anode will spread in current lines through
the entire body. At the cathode, all these lines
will converge again. The density of the current
depends on the concentration of the current
lines. Thus the density is relatively great at
the electrodes, and becomes rapidly weaker as
the lines diverge between them. The smaller the
electrode, the greater the density. The stimulat-
ing effect depends on the density. With small
electrodes, a current not sufficient to cause stimu-
lation may gradually be increased in strength
until the density at the electrode becomes great
enough to stimulate, while in all other regions it
is not yet great enough. Thus a local stimula-
tion is secured. But this local stimulus does
not sufficiently distinguish between the sensory
nerves and the motor nerves and muscles ; for in
order to reach the deeper lying motor nerves and
muscles, the current must pass through the skin.
The resistance of the epidermis is very great, and

128 GENERAL PROPERTIES OF LIVING TISSUES

currents of considerable intensity are necessary
to overcome it. Once through the epidermis, the
current spreads immediately in all directions
through the cutis, where it stimulates the very

Mm. lumbricales

*

M. opponens digit, min

M. flexor digit, min.

M. abd. digit, min.

M. palmaris brevis

N. ulnaris (ram. vol.
prof.)

N. medianus

M. flexor digit, subl.
(ind. and minim.)

M. flexor, digit.
(II & III)

subl

M. flexor digit profund.

M. ulnaris internus

(flexor carp. uln. )

M. palm, longus

M. pronator teres

N. medianus

N. ulnaris

M. adductor poll.
M. flexor poll, brevis
M. opponens pollicis
M. abductor poll, brevis

M. flexor pollicis longus

— M. flexor digit, subl.

M. rad. internus (flexor
carp, rad )

M. supin. longus

Fig 35. The motor points on the anterior surface of the forearm and
hand.

numerous sensory nerves. When the muscles or
motor nerves are reached, the density is much
reduced, and may not suffice for stimulation.
Thus the result may be not motor stimulation,
but simply pain from stimulation of the sensory

STIMULATION OF MUSCLE AND NERVE 129

nerves. For painless motor stimulation it is,
therefore, necessary to increase the strength of
the current which reaches the muscle or motor
nerve and to diminish the density of the current

M. inteross. dors. IV
M. abd. digit, min.

M. ext. poll, brevis

M. abd. poll, longus

M. ext. indicis propr.
M. ulnaris extern.

M. rad. ext. brevis

M. ext. pollicis longus
M. ext. indicis propr.

M. ext. dig. min. propr
M. ext. dig. communis

M. supin. brevis

M. rad. ext. longus -
M. supin. longus ■

Fig. 36. The motor points on the posterior surface of the forearm and
hand.

at the electrodes. These ends are accomplished
by using for electrodes large metal plates cov-
ered with sponge or cotton wet with saline solu-
tion. The liquid diminishes greatly the resistance
of the epidermis, so that more current reaches

9

130 GENERAL PROPERTIES OF LIVING TISSUES

the deeper tissues ; and the large surface offers a
broad path for the current, so that the current lines
are not so concentrated as to stimulate painfully
the sensory nerves of the cutis. One sponge elec-
trode may be made considerably smaller than the
other without forfeiting this advantage, while the
smaller size makes it easier to localize the stimulus.

Muscles are best stimulated through their
nerves, for two reasons : the nerve responds to
a weaker stimulus than the muscle ; and, sec-
ondly, it is much easier to secure contraction of
the whole muscle by stimulating the nerve than
by attempting to pass a current through the
muscle directly. The smaller electrode should
be placed over the nerve, the larger on some in-
different region. The indifferent electrode may
be placed over the muscle itself, if it is important
that the resistance shall not be increased by the
too great separation of the electrodes.

Duchenne found that certain points were es-
pecially favorable for the stimulation of indi-
vidual muscles. Remak discovered that these
" motor points " were simply the places at which
the nerves entered the muscle. The motor points
of the forearm are shown in Figs. 35 and 36.

Stimulation of Motor Points. — Arrange the
inductorium for single induction shocks. .De-
termine by the electrolytic method which pole

STIMULATION OF MUSCLE AND NERVE 131

of the secondary coil is the cathode when the
primary current is broken (page 158). To this
pole connect the small (stimulating) electrode ;
to the other pole connect the large (indifferent)
electrode. Place the indifferent electrode on
the arm or neck. With the small electrode
make out the motor points indicated in Figs. 35
and 36.

Polar Stimulation of Human Nerves. — In the
hands of the earlier observers the stimulation
of nerves within the body gave results often
contrary to the law of polar stimulation so easily
demonstrated in extirpated nerves. The ex-
planation of these inconstant results lay in the
failure to comprehend the distinction between
the stimulating positive and negative electrodes
and the physiological anode and cathode (compare
page 108). Even when the monopolar method
is employed, and a small electrode is brought as
near as possible to the nerve to be stimulated,
while a large indifferent electrode is placed on
some other part of the body, it is impossible to
secure true monopolar stimulation. The current
entering at the anode does not remain in the
nerve, but very soon passes out into the sur-
rounding tissues (Fig. 37). Hence there are
physiological cathodes on both sides of the posi-
tive electrode, and for the like reason physiologi-

132 GENERAL PROPERTIES OF LIVING TISSUES

cal anodes on both sides of the negative electrode.
Thus both anodal and cathodal stimulation take
place, whichever electrode rests over the nerve.
It is therefore incorrect to speak of ascending
and descending currents in the case of nerves
stimulated in situ. It should be
pointed out, too, that the density

^~jk

cccccc

AAAAAA

Fig. 37.

of the current is greater on the
side of the nerve nearer the
electrode than on the more deeply

placed side cut by current lines already rapidly

diverging.

With these facts in mind, we may compare

the polar stimulation of human nerve with the

law already determined for the isolated nerves

of the frog (page 115).

The Brass Electrodes. — The brass electrodes,
used chiefly for the stimulation of human muscles

and nerves, are two in number:
an "indifferent" electrode, con-
sisting of a brass plate, 3x6
cm., with binding post, and
a " stimulating " electrode, of
brass rod, G cm. long, ringed
at one end and provided at the
other with a binding post. Be-

Fig. 38.

tween these the rod is insulated with rubber tubing.

The electrodes should be covered with cotton wet

STIMULATION OF MUSCLE AND NERVE 133

with normal saline solution. The larger electrode
may be fastened upon the arm or other indifferent
region, and the smaller may be used to stimulate the
nerves or muscles, for example the abductor indicis,
or to find the "motor points."

Connect 8 dry cells in series (the carbon of
one cell to the zinc of the next, etc.). Coupling
in this way enables the electromotive force of
each cell to be added with slight loss to that of
the others, provided the resistance in the circuit
outside the cells is so great that the internal
resistance of the battery disappears in compari-
son, as is the case where living tissues form part
of the circuit. Connect the terminal zinc and
carbon pole through a pole-changer (with cross-
wires) to a small and a large electrode covered
with cotton thoroughly wet with strong saline
solution. Place the small electrode over the
ulnar nerve between the internal condyle and
the olecranon, a little above the furrow. Make
and break the current. If no contraction is
secured, add cells to the battery until contraction
occurs.

It will be found that the first contraction
occurs on closure with the cathode over the
nerve. With this strength of current the opening
contraction will be absent.

Turn the pole-changer so as to bring the anode

134 GENERAL PROPERTIES OF LIVING TISSUES

over the nerve, and increase the intensity still
further.

A strength will be reached at which closure
with the anode over the nerve will cause contrac-
tion, but the opening of the current will still be
without effect. A slightly greater intensity will
now bring out the anodal opening contraction.1

In the mean time the cathodal closing con-
traction has increased in force with each addition
to the intensity of the current. With about 18
cells, the muscle twitch on closure may give
place to a continued contraction or tetanus, the
cathodal closing tetanus. Further increase gives
cathodal opening contraction, and finally very
strong currents sometimes cause anodal closing
tetanus. Thus we have

1. Cathodal closing contraction.

2. Anodal closing contraction.

3. Anodal opening contraction.

4. Cathodal closing tetanus.

5. Cathodal opening contraction.

6. Anodal closing tetanus (rare).
Sometimes the anodal opening precedes the

anodal closing contraction.

1 Sometimes anodal opening contraction precedes the closing
contraction. This inconstancy results from variations in cur-
p lit strength due to differences in the tissues surrounding the
nerve.

STIMULATION OF MUSCLE AND NERVE 135

The apparent deviation from the law of polar
excitation (cathodal on closure, anodal on open-
ing) is explained by the presence of a physi-
ological anode and cathode at each electrode,
as already mentioned. The appearance of cath-
odal closing contraction before anodal closing
contraction is due to the fact that when the
negative electrode lies over the nerve the physi-
ological cathode will be found on the side of the
nerve next the electrode. The nearer the elec-
trode, the greater the current density, and hence
the earlier the threshold value is reached. When,
however, the positive electrode lies over the
nerve, the physiological cathode will be found
on the side of the nerve farther from the elec-
trode, where the density is less, owing to the
divergence of the current lines. The threshold
value will be reached first at the point of higher
density, and consequently the first contraction
will appear while the negative electrode rests
over the nerve. The anodal opening contraction
appears before the cathodal opening contraction
for a similar reason.

Reaction of Degeneration. — Whenever a nerve
is severed, the portion separated from the cell of
origin of the nerve " degenerates." The degener-
ation does not begin at the section and advance
to the terminal branches, but takes place al-

136 GENERAL PROPERTIES OF LIVING TISSUES

most or quite simultaneously throughout the
nerve. Eanvier states that it begins first in the
end plates. Severed nerves in the brain and
spinal cord degenerate in the same way, and this
"Wallerian degeneration" (Waller, 1850) is a
valuable aid in tracing the path of nerve fibres
in the central nervous system. Degeneration is
accompanied by changes in the reaction to the
electric current which form a valuable aid in the
diagnosis of the seat of the lesion in cases of
paralysis. The muscle reacts imperfectly, or not
at all, to the brief induction current, while its
reaction to the long galvanic current may even
be greater than usual.

Expose each gastrocnemius muscle in a frog,
the left sciatic nerve of which has been severed
ten days before this experiment. Stimulate each
muscle with weak induction currents and with
the galvanic current.

The muscle, the nerves of which are degen-
erated, reacts more readily to the galvanic current
than to the brief induction current. The normal
muscle shows the opposite reaction.

In man, the reaction of degeneration in the
case of muscle consists of a lessened or lost
excitability to the induced current with increased
excitability to the galvanic current. The duration
of contraction may be greater than normal. In

STIMULATION OF MUSCLE AND NERVE 137

polar stimulation, anodal closing contraction may
appear before cathodal closing contraction, — a
reversal of the normal sequence.

In degenerated nerve there is of course a total
loss of irritability, corresponding to the destruc-
tion of the axis-cylinder.

Galvanotropism

Paramecium. — Connect two non-polarizable
electrodes through a pole-changer with a dry cell.
On a glass microscope-slide make with wax an
enclosure about one centimetre square and a few
millimetres high. Place in this a little hay
infusion containing Paramecia. Bring near the
two opposite sides of the wax cell non-polarizable
electrodes, provided with a thick thread that shall
dip into the infusion. Examine the infusion with
a very low power. Close the key.

Upon closure each Paramecium turns the an-
terior end of the body towards the cathode and
swims in that direction. In a very short time
the anodal region is free, and the Paramecia are
gathered at the cathode, where they remain so
long as the current flows.

Change the direction of the current.

The Paramecia now turn to the anode and
swim in that direction, but the anodal grouping
is less complete than the cathodal, and lasts but

138 GENERAL PROPERTIES OF LIVING TISSUES

a short time. Careful observation shows that
in Paramecium the galvanic reaction consists in
placing the long axis of the bod)7 in the current
lines. The outermost individuals in the liquid
will therefore describe a curve corresponding to
the curved outer current lines.

All protozoa and many other animals (for ex-
ample, the tadpole and the crayfish) show gal-
vanotropism, but in some, movement on closure
is toward the positive pole (positive galvano-
tropism).

These experiments on skeletal, smooth, and
cardiac muscle, on nerve, and on infusoria, sug-
gest that polar excitation occurs wherever a gal-
vanic current passes through irritable tissue.
Further experience would confirm this view. We
have seen that the changes at the cathode when
the current is made are not momentary, as re-
quired by the hypothesis of DuBois-Eeymond,
but continue so long as the current flows. This
fact appears still more clearly when the influence
of the duration of the current is examined.

Influence of Duration of Stimulus

1. Smoke a drum. Arrange a muscle lever to
write on the smoked paper. Prepare non-polariz-
able electrodes and fasten them on the glass plate

STIMULATION OF MUSCLE AND NERVE 139

of the nerve holder. Arrange the inductoriuni
for maximal induction currents. Lead from the
secondary coil to a pair of the end cups of the
pole-changer (without cross-wires), as in Fig. 39.
To the opposite cups of the pole-changer bring
wires from a dry cell.
Connect the remaining
cups with the non-polar-
izable electrodes. Turn
the rocker towards the in-
duction coil. Fasten the
pelvic attachment of the Kg. 39.

curarized sartorius in

the muscle clamp. Tie a thread to the fragment
of tibia, and fasten the thread to the upright pin
of the muscle lever, so that the horizontal muscle
shall record its contraction on the drum. Start
the drum at moderate speed. Record contrac-
tions, (1) with maximal break shocks, (2) with
closure of galvanic current. Compare the curves.

The curve from galvanic stimulation will be of
greater height and duration, and the summit of
the curve will be less pointed, indicating that
the muscle remains longer in the stage of ex-
treme shortening.

Other evidence that the duration of the stimu-
lus modifies the character of the contraction is
afforded by the following experiments : —

140 GENERAL PROPERTIES OF LIVING TISSUES

2. Make two cuts, 5 mm. apart, through the
frog's stomach at right angles to the long axis.
Hang the ring thus secured in the moist cham-
ber. Pass a bent hook through the lower end of
the ring, and attach it by means of a fine copper
wire to the hook on the muscle lever. Carry the
end of the copper wire to the binding post on the
muscle lever.

Stimulate not more than twice with single in-
duction currents of a strength about the threshold
value for skeletal muscle of frog.

There will be no contraction.

Stimulate with galvanic current (two dry cells),1
writing three curves, the duration of closure be-
ing approximately one-fifth second, one, and five
seconds, respectively. Compare the curves.

The maximum shortening with currents of
brief duration (^ second) is very much less than
with currents of three or four seconds or over.
The briefer the current also, the quicker will the
maximum shortening be reached, and the quicker
will be the relaxation.

3. If the galvanic current is very rapidly made
and broken, the muscle will not contract.

1 If the muscle does not respond, wrap it with filter paper
moistened with normal saline solution, and wait until the tonic
contraction due to the cutting has passed off. The tonus may
sometimes be lessened by passing a galvanic current through the
preparation (p. 153).

STIMULATION OF MUSCLE AND NERVE 141

The same is true of the ureter (Engelmann).

4. Tonic Contraction. — Examine the contrac-
tion curve already recorded by the smooth
muscle of the frog's stomach. Note that the
muscle remains contracted during the passage
of the current. The curves secured from the
curarized sartorius (page 139) also show this,
but to a much less degree ; the sartorius does
not resume its former length after the twitch or
closure of the galvanic current, but remains con-
tracted to a slight extent. This tonic contrac-
tion appears much more plainly in fatigued
muscles.

Fatigue a sartorius muscle by stimulating it
with a galvanic current repeatedly made and
broken. After a time, the twitch on closure will
become very feeble, and finally will disappear,
while the tonic shortening during the passage of
the current is still very evident.

5. The influence of duration is shown also in
the opening contraction.

Fasten the pelvic attachment of a sartorius
muscle in the muscle clamp and connect the
other end with the upright pin of the muscle
lever, so that the horizontal muscle shall record
its contraction on a drum. Place the non-polar-
izable electrodes on the ends of the muscle.
Allow the "galvanic current from a dry cell to

142 GENERAL PROPERTIES OF LIVING TISSUES

pass through the muscle until the closure tonic
contraction has disappeared, then open the key.
Neglect the opening twitch.

The muscle will not return to its original
length, but will remain contracted for a time
(opening tonic contraction).

Close the key again.

The tonic contraction will disappear.

The galvanic current in this case checks (in-
hibits) a contraction. This new action is dis-
cussed on page 153.

6. Rhythmic Contraction. — That the galvanic
current acts as a stimulus so long as it continues
to flow is shown also by the fact that its passage
through contractile tissue may cause the muscle
to fall into rhythmic contractions. These are
easy to produce in muscles which normally con-
tract in rhythms, for example, the heart ; but
they may under some circumstances be observed
also in smooth muscle, and even in skeletal
muscles.

Connect a dry cell through a simple key with
the metre posts of the rheochord. Join the non-
polarizable electrodes to the positive post and the
slider. Bring the slider against the positive post,
so that no current shall flow through the elec-
trodes when they are joined by the tissue.

Expose the heart. With a sharp knife bisect

STIMULATION OF MUSCLE AND NERVE 143

the ventricle transversely. Best this "apex"
preparation between the tips of two non-polar-
izable boot electrodes. Keep the tissue moistened
with normal saline solution, but avoid excess.
Close the key. Move the slider along the wire.

When the current taken off reaches the thresh-
old value, the apex will begin to beat rhyth-
mically. Increasing the current strength will
increase (within limits) the frequency of con-
traction.

Skeletal Muscle. — The curarized sartorius may
sometimes be brought into rhythmic contraction
by constant currents (Hering). If the irrita-
bility of the muscle at the point of stimulation
be increased by applying to the cathodal region
a two per cent solution of sodium carbonate, the
constant current will produce strong rhythmic
contractions.

Smoke a drum. Fasten the pelvic end of the
sartorius in the muscle clamp, and attach the
tibial end by a thread to the vertical pin on
the muscle lever so that the horizontally extended
muscle may write its contraction on a drum.
Lay on the tibial fifth of the muscle a piece of
filter paper, wet with two per cent solution of
sodium carbonate. Connect a dry cell through
a simple key with the metre posts of the rheo-
chord. Connect the non-polarizable electrodes

144 GENERAL PROPERTIES OF LIVING TISSUES

with the positive post and the slider. Bring the
slider near the positive post. When the sodium
carbonate has acted for 15 minutes, bring the
cathode against the tibial end, the anode against
the pelvic end of the muscle. Close and open the
circuit, moving the slider meanwhile to find
the current which will give closing contraction.
At this point keep the circuit closed.

Rhythmical contractions usually appear.

Periodic contractions are observed also in
smooth muscle, stimulated with the constant
current. Any form of constant stimulus will
serve to produce them, pressure — as in the
heart, bladder, and intestine — and chemical
action, being especially noteworthy.

Continuous Galvanic Stimulation of Nerve may
cause the Periodic Discharge of Nerve Impulses. —
If two non-polarizable electrodes are allowed to
rest on the muscle (horizontally suspended), and
are connected to a capillary electrometer, the
meniscus of which is projected through a slit
onto rapidly moving sensitized paper, the shadow
of the meniscus will make a straight line on the
photographic paper so long as the muscle is at
rest. When, however, the nerve of the muscle
is stimulated with the galvanic current and
closing tetanus appears, the straight line will be
broken by 10-15 oscillations per second. These

STIMULATION OF MUSCLE AND NERVE 145

oscillations are produced by the difference of
potential created by each contraction wave as it
passes over the muscle (contracting muscle is
negative towards muscle at rest, see page 302),
and demonstrate that the tetanus is a fusion
of individual contractions produced by successive
stimuli.

Hence, nerve, like muscle, responds to a contin-
uous stimulus by a periodic discharge of energy.

Ulnar Nerve. — Connect 15 dry cells in series
(zinc to carbon), and join the last zinc and carbon
through a key to a small brass stimulating
electrode one cm. in diameter, and a large " in-
different" electrode (brass plate 6.5 x 3.5 cm.
covered with cotton wTet in solution of common
salt). Hold the indifferent electrode in the left
hand, and apply the stimulating electrode to the
ulnar nerve at the elbow.

A peculiar tingling sensation will be felt so
long as the current flows.

Polarization Current. — Let the sciatic nerve
rest on a pair of non-polarizable electrodes in
the moist chamber. Connect the electrodes to
the side cups of the pole-changer (without cross-
wires). Connect one end pair of the pole-changer
cups with a dry cell. Turn the rocker to the
opposite side to prevent the battery current from
reaching the electrodes until it is wanted. Con-

10

146 GENERAL PROPERTIES OF LIVING TISSUES

nect the remaining pair of cups through a closed
short-circuiting key with the capillary electrom-
eter. Let the galvanic current flow some min-
utes through the nerve, then turn the rocker
towards the electrometer and open the short-
circuiting key.

Note a movement of the meniscus in a direction
indicating that the former cathode is now posi-
tive to the former anode.
^^ _ /^~-\ J The nerve is polarized.

(2/- - JLJJ \ y\ [f| Positive Variation. —

\ / "x — ' If the polarizing current

1 1 is strong and brief, the

negative polarization
after-current will speed-
ily give place to a positive current, i. e. one in the
direction of the polarizing current. This positive
current is really an action current. When the
polarizing current is broken, the rise of irritabil-
ity at the anode stimulates points nearer the
anode more strongly than points farther away.
Points nearer the anode become, therefore, nega-
tive to points farther away, and a current flows
through the electrometer circuit from the less
negative to the more negative pole, and through
the nerve in the direction from anode to cath-
ode. This positive variation is seen only in
living nerves.

Fig. 40.

STIMULATION OF MUSCLE AND NERVE 147

Polar Fatigue. — Connect non-polarizable elec-
trodes through a simple key with a dry cell.
Fatigue a sartorious muscle by opening and clos-
ing the galvanic circuit (leave a brief interval
between opening and closure). Closure will at
length be followed by no contraction. Arrange
an inductorium for single induction currents (the
pole-changer may be placed in the primary cir-
cuit as a simple key). Test now the irritability
of the muscle by stimulating it with single induc-
tion currents.

The muscle will be irritable except in the cath-
odal region. The fatigue has been local (polar).

Opening and Closing Tetanus. — 1. Arrange a
moist chamber with a muscle lever to write on a
smoked drum. Place two non-polarizable elec-
trodes in the moist chamber and connect them
through a pole- changer with a dry cell. Make a
nerve muscle preparation from a frog that has
just been brought from a cold room into the warm
laboratory. Secure the femur in the femur clamp
of the moist chamber. Let the nerve rest on the
non-polarizable electrodes. Attach the muscle
to the lever. Bring the writing point against the
slowly moving drum. Close the key.

If the frog has been well cooled (below 10° C),
the muscle will fall into tetanus both on closing
and on opening the circuit. Note that the curve

148 GENERAL PROPERTIES OF LIVING TISSUES

is quite regular. If tetanus fails to appear, paint
the cathodal region with one per cent solution of
sodic carbonate, thus raising the irritability, and
repeat the experiment. The curve secured in
this way is likely to be irregular.

Produce opening tetanus, and while the muscle
is contracting close the current again.

The tetanus will disappear ; the irritability
will be reduced in the anodal region, from the
polarization of which the tetanus was produced.

Open the current again. When the tetanus
reappears reverse the pole-changer and close the
current.

The tetanus will be increased ; the irritability
in the former anodal region will suffer a catelec-
trotonic increase.

2. A beautiful demonstration of polar excitation
may be made in this experiment. Connect the
electrodes in such a way that the intrapolar cur-
rent shall be descending (i.e. towards the muscle).
When the opening tetanus appears, cut away
the anode by severing the nerve between the
electrodes.

The contraction ceases witli the removal of the
source of stimulation.

3. The stimulating effect of the salts of the
alkalies has been explained by their attraction
for water, the loss of which increases the effect

STIMULATION OF MUSCLE AND NERVE 149

of the galvanic current on nerve. When the
irritability of the nerve is raised by drying, weak
currents may give opening contractions, although
they are absent in normal, uninjured nerves.
The interval between the opening of the current
and the resulting contraction is then markedly
long. In nerves in the first stage of drying the
intensity of the nerve impulse (height of con-
traction of attached muscle) is also more than
usually dependent on the duration of the
current.

4. The opening tetanus (so-called Eitter's tet-
anus) is probably caused by the rise of irritabil-
ity, which takes place in the anodal region when
the current is shut off, acting on a nerve already
in latent excitation. A similar condition can be
produced as follows : —

Smoke a drum. Connect a dry cell through an
open key and an electro-magnetic signal with the
metre posts of the rheochord (Fig. 41). Connect
the zero post and the slider of the rheochord with
the pole-changer (with cross-wires), and the latter
with two non-polarizable electrodes placed in the
moist chamber. Make a nerve-muscle prepara-
tion, and secure the femur in the femur clamp
of the moist chamber. Attach the muscle to the
muscle lever. Bring the writing points of the
muscle lever and the electro-magnetic signal

150 GENERAL PROPERTIES OF LIVING TISSUES

against the smoked surface in the same vertical
line. Let the nerve rest on the non-polarizable
electrodes. In the remaining two posts in the
moist chamber fasten stimulating electrodes.
Connect the latter to the inductorium, arranged
for tetanizing currents, short-circuiting key closed.
Bring the stimulating electrodes against the nerve
between the non-polarizable electrodes and the

Fig. 41.

muscle. Let the secondary coil be at such a dis-
tance that the tetanizing current will be just
below the threshold value. Turn the pole-changer
so that the anode shall be next the tetanizing
electrodes. Make and break the galvanic current,
recording the contraction on a slowly moving
drum. Now open the short-circuiting key, and
after half a minute, and while the sub-minimal
tetanizing current is still passing through the

STIMULATION OF MUSCLE AND NERVE 151

nerve, make and break the galvanic current
again.

A moderately strong galvanic current will now
produce an opening tetanus (anodal stimulation
of a region the irritability of which has been
raised by the sub-minimal tetanizing current).
Other effects are a lengthening of the latent
period, and an increased dependence on the
duration of the galvanic current (see page 138).

Ee verse the pole-changer, so that the tetanizing
electrodes fall in the cathodal region. Eepeat
the experiment, comparing the results of cathodal
stimulation without and with the sub-minimal
tetanizing current.

With sub- minimal tetanization, an increase in
the height of the closing contraction, when the
galvanic current is not too strong, will be seen ;
when the galvanic current is stronger, closing
tetanus will also be observed.

Polar Excitation in Injured Muscle. — Smoke a
drum. Make non-polarizable electrodes. Con-
nect a dry cell through a simple key and
pole-changer (with cross-wires) with the non-
polarizable electrodes. Prepare a sartorius mus-
cle with bony attachments. Fasten the pelvic end
in the muscle clamp. Tie a thread to the tibial
end, and fasten the thread to the upright pin of
the muscle lever, so that the muscle is extended

152 GENERAL PROPERTIES OF LIVING TISSUES

horizontally. Bring the writing point against the
drum. Light a Bun sen burner. Heat a wire,
and kill the pelvic end of the muscle by laying
the hot wire against it. Bring one non-polar-
izable electrode upon each end of the muscle.
Arrange the pole-changer so that the cathode
shall be at the pelvic end, and the current there-
fore " atterminal," i. e. directed toward the
"thermal cross-section." Close the simple key.

No contraction, or a very slight contraction,
will be seen.

Open the key. Eeverse the pole-changer, so
that the current shall be " abterminal." Close
the simple key.

The ordinary closing contraction will be seen.

The great difference here shown between the
polar excitability in the uninjured and injured
region is probably due to chemical changes in
the injured part. Similar results can be obtained
by painting the end of the muscle with one per
cent solution of acid potassium phosphate. The
irritability is lessened by this salt, but returns to
normal if the altered end of the muscle is bathed
in 0.6 per cent sodium chloride solution.

Sodium carbonate has an effect opposite to that
of the potassium salts.

Wet the pelvic end of a fresh muscle with one
per cent solution of sodic carbonate. After a

STIMULATION OF MUSCLE AND NERVE 153

short time, test the irritability to weak, ascend-
ing (i. e. cathode at pelvic end) currents.

The closure of ascending currents will give
extraordinarily large contractions.

The cause of this change in irritability is not
the presence of dead contractile tissue, for elec-
trodes can be wrapped in dead muscle and used
to stimulate normal muscle without loss of irri-
tability being noticeable.

When the end of the fibre is killed, the patho-
logical change passes gradually through the
whole of the fibre.

Polar Inhibition by the Galvanic Current

It remains now to consider the inhibitory
action of the galvanic current, to which attention
was called on page 142.

Heart. — Connect a dry cell through a simple
key with the 0 and 1 metre posts of the rheochord.
Connect non-polarizable electrodes through a pole-
changer with cross-wires (Fig. 30), with the slider
and the positive post of the rheochord. Pith the
brain, not the cord, of a frog, and place the animal,
back down, in the holder (Fig. 29, page 112), and
expose the heart, without unnecessary loss of
blood, according to the method described on page
112. Open the delicate membrane (pericardium)

154 GENERAL PROPERTIES OF LIVING TISSUES

which surrounds the heart. Let one electrode
rest on the larynx. Lay upon the tip of the
other electrode a strand of lamp wick or absor-
bent cotton wet with normal saline solution.
Bring this electrode over the heart so that the
free end of the strand rests on the ventricle and
moves with it. Turn the pole-changer to make
this electrode the anode. Make the current.

At each systole, the portion of the ventricle
immediately about the anode will not contract
with the rest, but will remain relaxed (local dias-
tole). Thus while the greater part of the ven-
tricle becomes pale as the blood is squeezed out
of its wall by the contraction, the anodal region
remains dark red. From this region the relaxa-
tion spreads over the rest of the ventricle. Re-
verse the pole-changer. Break the current.

The cardiac electrode is now the cathode. In
the systole following the breaking of the current,
the cathodal region will remain relaxed during
contraction of the ventricle.

This experiment demonstrates that the galvanic
current not only may stimulate, but may check
or inhibit contraction. In the former case, the
conversion of potential into active energy is set
going; in the latter, it is prevented. Inhibi-
tion plays a large part in the physiology of the
day.

STIMULATION OF MUSCLE AND NERVE 155

Polar Inhibition in Veratrinized Muscle. — A

similar inhibitory effect can be demonstrated in
skeletal muscle previously placed in continued
("tonic") contraction by veratrine poisoning.
Inject with a fine glass pipette seven drops of
one per cent solution of veratrine acetate in the
dorsal lymph sac of a frog.

Arrange two muscle levers to write on a drum.
Between them place an electromagnetic signal.
Let all three writing points be in the same vertical
line. Connect a dry cell through a simple key
with an inductorium arranged for single induc-
tion shocks. Connect non-polarizable electrodes
through another simple key and the electro-
magnetic signal with a dry cell. Prepare a
sartorius muscle with pelvic and tibial attach-
ments. Fasten the muscle about the middle in
the cork clamp. Fasten the cork clamp verti-
cally in the jaws of the muscle clamp. Carry
threads from each end of the muscle to one of
the muscle levers. Place the non-polarizable
electrodes near the respective ends of the mus-
cle. Note which is the anode. Bring wires
from the secondary coil of the inductorium to
the ends of the muscle. Start the drum mov-
ing slowly. Stimulate the muscle with a single
induction shock. There will be a prolonged con-
traction, characteristic of veratrine poisoning. So

156 GENERAL PROPERTIES OF LIVING TISSUES

soon as this contraction is well under way, make
the constant current.

The anodal half of the muscle will show a dis-
tinct relaxation ; the cathodal half will not relax,
but may even contract a little more.

Stimulation affected by the Form of the
Muscle

Connect a dry cell through a simple key to
the metre posts of the rheochord. Bring wires
from the non-polarizable electrodes to the positive
post and the slider, interposing the pole-changer
with cross-wires so that the direction of the cur-
rent can be changed. Place the slider against
the positive post, so that all the current passes
back to the cell.

Prepare a curarized sartorius muscle with its
bony attachments. Fasten the pelvic fragment
in the muscle clamp. Tie a thread about the
tibia and fasten the thread to the upright pin of
the muscle lever. Let the cathode rest on the
tibial end of the muscle, the anode on the pelvic
end ; the current will then be descending. Move
the slider a few centimetres away from the posi-
tive post, and make the current. If no contrac-
tion follows, move the slider farther along, and
make the current again.

With careful work, it will be shown that with

STIMULATION OF MUSCLE AND NERVE 157

descending currents, the first contraction will
be on closure only. With ascending currents,
the first contraction will be on opening the
current.

The explanation is that, with currents which
pass through the sartorius from end to end
the point of greatest density is the smaller,
lower end. This is cathodal in descending
currents, anodal in ascending currents.

Effect of the Angle at which the Current
Lines cut the Muscle Fibres

Connect non-polarizable electrodes through
a key with a dry cell. Build on a glass plate
with normal saline clay two parallel walls a
little longer than the sartorius muscle and
one centimetre apart. Join the ends with
wax, to make a rectangular trough. Eemove
a sartorius muscle from a curarized frog,
avoiding all injury to the muscle. Place the
muscle in the trough, and cover it with normal
saline solution. Bring a non-polarizable elec-
trode against the centre of each long side, so
that the current lines shall cut the muscle
fibres at right angles. Close the key.

There will be no contraction. The muscle is
inexcitable to currents that cross its fibres at
right angles.

158 GENERAL PROPERTIES OF LIVING TISSUES

Alter the angle by moving one electrode to
the right, the other to the left, and repeat the
experiment.

The stimulating effect will increase as the
angle between current lines and the long axis of
muscular fibres diminishes.

Nerves also are inexcitable to transverse cur-
rents. Differences in resistance play a great
part here. The resistance of nerves is said to
be 2 J million times that of mercury, when the
current passes along the nerve, and 12J million
times when it passes transversely.

The Induced Current

The break induction current, owing to its rapid
rise from zero to maximum intensity, is a more
effective physiological stimulus than the make
current, and may therefore be chosen for
experimentation.

1. The direction of the induction current in
the secondary coil is most easily determined
electrolytically.

Arrange the inductorium for maximal currents.
Bring wires from the posts on the secondary coil
to a piece of filter paper wet with starch paste
containing iodide of potassium. Exclude the
make currents with the short-circuiting key ;

STIMULATION OF MUSCLE AND NERVE 159

pass the maximal break currents through the
electrolyte.

Iodine will be set free at the anode and will
combine with the starch to form blue iodide of
starch.

Mark the positive post on the secondary coil
with a plus sign.

2. Connect the poles of the secondary coil
through a pole-changer with non-polarizable
electrodes. Make a nerve-muscle preparation.
Tie a ligature about the nerve about two cen-
timetres from the central end. Place one elec-
trode on each side of the ligature. The passage
of a nerve impulse from the central electrode
to the muscle will be prevented by the lig-
ature, although the electric current can still
pass between the electrodes. Turn the pole-
changer so that the electrode on the periph-
eral (muscle) side of the ligature shall be first
the anode and then the cathode, and test the
irritability to weak induction currents, begin-
ning with the secondary coil some distance from
the primary, and gradually increasing the intensity.

Only cathodal stimulation will produce con-
traction. The same result can be secured by
separating the cathode and anode with ammonia.
If the nerve is painted with ammonia in the
intrapolar region, break currents cease to cause

160 GENERAL PROPERTIES OF LIVING TISSUES

contraction when the cathode is on the central
side of the painted zone. Painting the cathodal
region directly also prevents excitation.

The failure of the induction current to stimu-
late at the anode, on opening the current, is due
to the exceedingly brief duration of the induced
current; there is not time for a sufficient anelec-
trotonic alteration in excitability. If the current
is shortened still more (if it be less than 0.0015
sec), the cathodal excitation also disappears.
With very strong currents, however, opening the
current stimulates as well as closure.

3. Additional evidence of polar action is
secured by connecting the electrodes with the
capillary electrometer through a closed short-
circuiting key. The meniscus is brought into
the field, the nerve is stimulated repeatedly
with maximal break currents, and then stimu-
lation is stopped, and the short-circuiting key
in the electrometer circuit, opened. The menis-
cus will move in a direction indicating a higher
potential at the anode (positive anodal polariza-
tion current).

4. Finally, it may be added that the galvanic
current may increase the stimulating effect of the
induced current as pointed out on page 80, but only
when the cathode of the induced current falls ir:
the cathodal region of the polarizing current.

STIMULATION OF MUSCLE AND NERVE 161

The law of polar excitation holds good then
for the induced as well as the galvanic current.
In fact, there is no essential difference between
the physiological effects of induced currents and
very brief galvanic currents.

Increasing the intensity of the induced cur-
rent increases at first the excitation (height of
contraction). At length, however, with ascend-
ing currents, a point is reached beyond which
further increase in strength is followed first by
the diminution and at length by the disappear
ance of contraction. With still higher intensi-
ties, the contractions reappear. This gap in the
contraction series is explained by the increasing
depression of irritability at the anode blocking
the cathodal impulse ; when the intensity is still
further increased, the opening of the current acts
as a stimulus. A similar result may be secured
with the galvanic current.

Apparatus

Normal saline. Bowl. Pipette. Towel. Simple key.
Non-polarizable electrodes. Nerve holder. Potter's clay
mixed with 0.6 per cent solution of sodium chloride.
Saturated solution of zinc sulphate. Muscle clamp.
Stand. 13 wires. Kymograph. Glazed paper. Two
muscle levers. Thread. Eheochord. Two dry cells.
Moist chamber. Glass plate. Ice. Paraffin paper. Cork
clamp. Pole-changer. Beaker. Tripod, Sodium chloride.

11

162 GENERAL TKOPERTIES OF LIVING TISSUES

Inductorium. Electrodes. Bunsen burner. Intestine of
a rabbit. Electromagnetic signal. Tuning fork. Brass
electrodes. Fine copper wire. Frog board. 2 pairs • of
metal electrodes, each passed through cork. Electrom-
eter. Paramecia. Microscope. Glass slide. Bent hooks.
One per cent solution of veratrine acetate. Fine glass
pipette. Filter paper saturated with starch paste con-
taining potassium iodide. Frogs. Fine rubber tubing
for insulating electrodes. Ammonia. One per cent solu-
tion of acid potassium phosphate. Two per cent solution
of sodic carbonate. Ligatures. Filter paper.

CHEMICAL AND MECHANICAL STIMULATION 163

CHEMICAL AND MECHANICAL STIMULATION

Chemical Stimulation

The contractility, heat production, and other
phenomena of the life of muscle rest at base on
chemical processes. Anything that sufficiently
alters these processes may be a stimulus. A most
important source of stimulation is the alteration
of the chemical composition of muscle through
osmosis.

Effect of Distilled Water. — Place a sartorius
muscle in distilled water.

Irregular contractions usually occur. The
muscle soon swells, and becomes white, turbid,
cadaveric.

These striking changes depend on the with-
drawal of certain bodies by osmosis. Muscle
contains large quantities of proteid, particularly
proteids of the globulin class ; certain carbo-
hydrates, such as glycogen ; nitrogenous and
other extractives ; water ; and a number of in-
organic salts. Most of these bodies are largely
or wholly insoluble in water, and require for
their solution the presence of inorganic salts.

164 GENERAL PROPERTIES OF LIVING TISSUES

The globulins, for example, are insoluble in dis-
tilled water, but soluble in dilute solutions of
sodium chloride. The osmosis of salts into the
distilled water in the above experiment first
stimulates and then destroys the contractility
of the muscle.

An increase in the saline content of the muscle
juice or "plasma" also acts as a stimulus, and, if
excessive, may be fatal.

Strong Saline Solutions. — Place a sartorius
muscle on a slightly inclined glass plate. Cover
the lowest fourth of the muscle with crystals of
sodium chloride.

Irregular contractions will appear.

Drying. — The effect of loss of water is best
shown in nerve.

Let the nerve of a nerve-muscle preparation
dry. Note the twitching of the muscle as the
water content diminishes. Test the irritability
of the nerve from time to time with induction
currents. It will first increase, then disappear
as the nerve dries.

Wet the nerve with 0.6 per cent sodium
chloride solution.

The irritability will reappear.

To keep muscles and nerves in good condition
for experimentation, it is necessary to moisten
them with a solution containing the inorganic
salts most abundant in the tissue-liquids in the

CHEMICAL AND MECHANICAL STIMULATION 165

proportions in which they are present in those
liquids. Practically, a 0.6 per cent solution of
sodium chloride has commonly been employed,
in the case of the frog. Such a solution is said
to be isotonic, i. e. neither giving nor taking
water from the tissue.. That it is not perfectly
indifferent appears from this experiment.

"Normal Saline." — Allow a sartorius muscle
to stand half an hour in normal saline solution
(0.6 per cent NaCl). Eecord its contraction in
response to a maximal break induction current.
In place of a simple twitch, a prolonged contrac-
tion of abnormal height and duration will usually
be secured.

Importance of Calcium. — Place the " normal
saline " sartorius in 0.6 per cent sodium chloride
solution containing 10 per cent of saturated solu-
tion of calcium sulphate. After ten minutes
record the maximal break contraction.

The abnormal contraction will have disap-
peared.

Constant Chemical Stimulation may cause Peri-
odic Contraction. — Place a sartorius muscle in a
solution of 5 grams NaCl, 2 grams Na2HP04, and
0.4 gram Na2C03 in one litre of distilled water.

Usually rhythmic contractions are seen. All
contractile substance shows a tendency to peri-
odic contractions in response to a constant stimu-

166 GENERAL PROPERTIES OF LIVING TISSUES

lus, whether chemical, mechanical, or electrical.
There are reasons for believing that the rhythmi-
cal contractions of the heart are the consequence
of a constant chemical stimulus.

Mechanical Stimulation

Stimulate a nerve mechanically by pinching
the cut end with forceps.

No change will be seen in the nerve, but the
muscle will shorten, and then relax.

Mechanical stimulation has the advantage that
it can be localized accurately, and for this reason
it has been used where electrical stimulation
seemed inapplicable. Tetanomotors have been
constructed by Heidenhain and others to give a
rapid succession of slight blows upon the nerve.

Sudden pressure on a muscle or sudden exten-
sion may cause contraction. Sometimes the
whole muscle contracts, sometimes only the
portion directly stimulated.

Idio-Muscular Contraction. — With the point
of the seeker stroke the diaphragm and other
muscles of a recently killed rat, or other small
warm-blooded animal, in a direction at right
angles to the course of the fibres.

A wheal, i. e. a long-continued shortening and
thickening of the fibre stimulated, will be seen.
If the animal be not too long dead, a momentary

CHEMICAL AND MECHANICAL STIMULATION 167

twitch of the whole of the fibre stimulated will
precede the continued local contraction or wheal.
The same phenomenon is seen for a briefer
time on sharp mechanical stimulation of muscles
in living animals, for example, the wheals raised
by the blow of a whip. In men long ill of wast-
ing diseases, e. g. phthisis, the idio-muscular con-
tractions appear on drawing a pencil point across
the muscles. Direct total stimulation of frog's
muscle, especially in the spring months, may be
followed by long continued contraction. Fatigue,
cold, and many poisons, such as veratrine, favor
the prolongation of the phase of shortening. The
idio-muscular contraction is not a " tetanus,"
i. e. not a prolonged shortening clue to successive
contractions, the interval between which is too
short to permit of relaxation, but a prolonged
single contraction, the cause of which lies in the
muscle and not in the nerve.

Apparatus

Normal saline. Bowl. Pipette. Towel. Glass plate.
Distilled water. Sodium chloride. Solution of sodium
chloride (0.6 per cent), containing 10 per cent of saturated
solution of calcium sulphate. Solution containing 5 grams
sodium chloride, 2 grams di-sodium hydrogen phosphate,
and 0.4 gram sodium carbonate, in 1000 c.c. water. Small
warm-blooded animal recently killed. Introduction coil.
Dry cell. Key. Electrodes. 3 Wires. Frogs.

168 GENERAL PROPERTIES OF LIVING TISSUES

VI

IRRITABILITY AND CONDUCTIVITY

Irritability is the power of discharging energy
on stimulation. The form in which the kinetic
energy of muscle appears is partly mechanical
work (the visible contraction) and partly molec-
ular, — heat, chemical action, and electricity.
In the nerve, the kinetic energy is wholly molec-
ular ; an electromotive force is generated, prob-
ably heat is set free (though this statement —
which is based simply on analogy — is frequently
disputed), and a molecular change — the nerve
impulse — arises at the seat of stimulation. In
both muscle and nerve, by virtue of their con-
ductivity, the change induced by stimulation is
as a rule not limited to the region stimulated, but
passes in both directions along each stimulated
fibre. In neither muscle nor nerve can the
changes in energy spread transversely ; they are
limited to the muscle- or nerve-fibre in which
they arise.

It will be shown that conductivity and irrita-
bility are essentially different functions.

IRRITABILITY AND CONDUCTIVITY 1G9

The Independent Irritability of Muscle. — The

stimulus that causes the contraction of a muscle
may be applied either to the nerve or to the
muscle itself. If to the nerve, the muscle will
be thrown into the active state not by the origi-
nal stimulus, but by a nerve impulse. If to the
muscle, the nerve will still be stimulated, for
examination shows terminal fibres distributed, in
skeletal muscle at least, probably to every fibre,
and with few exceptions to all parts of the
muscle. The fact that muscles may contract
when an electric current flows through them, or
when otherwise stimulated, does not therefore of
itself indicate that electricity is a stimulus to
muscle protoplasm. Before this can be estab-
lished, it will be necessary to demonstrate con-
traction in parts of muscle not provided with
nerves ; for example, the distal part of the sar-
torius, or in muscles in which the nerves have
been destroyed by curare or by degeneration.

Nerve-free Muscle. — Beniove the sartorius
muscle, together with the portion of the pelvis
and the tibia to which the muscle is attached,
and lay it on a glass plate. Stimulate the distal
(tibial) fifth, in which examination with the
microscope would show the absence of nerve
fibres, with a strong break induction current.

The nerve-free muscle will contract.

170 GENERAL PROPERTIES OF LIVING TISSUES

Muscle with Nerves Degenerated. — A nerve
fibre severed from its cell of origin dies or " de-
generates " down to its ultimate endings. Expose
the sciatic nerve in the middle of the thigh of a
frog in which the nerve has been severed near
the pelvis ten days before, so that the whole of
the nerve distal to the section shall have degen-
erated. Stimulate the degenerated trunk.

No contraction is seen in the muscles of the
leg. Stimulate the muscles directly.

Contraction takes place.

The Nerve-free Embryo Heart. — Embryological
studies show that the nerves of the heart are
formed from epiblast in the walls of the neural
canal, and do not grow into the heart until the
close of the third day of incubation (chick).
The heart, however, begins to beat during the
second day of embryonic life, before even the
blood which it shall pump is formed. Thus
the heart muscle, in the embryo, is capable of
contraction in the absence of nerves.

Cover an egg which has been incubated 60-70
hours with 0.75 per cent solution of sodium
chloride warmed to 38° C. Eemove the shell
with the forceps over one third of the egg, be-
ginning at the broad end, and leaving the shell
membrane behind. Now remove the shell mem-
brane. Note the buating heart.

IRRITABILITY AND CONDUCTIVITY 171

Paralysis of Nerve Endings with Curare. —
Make two nerve muscle preparations A and B,
and fill two watch glasses with curare solution.
In one watch glass lay the nerve trunk of prep-
aration A and in the other watch glass the muscle
of preparation B. Cover muscle A and nerve B
with filter paper moistened with normal saline
solution, to prevent drying. At intervals of ten
minutes stimulate nerve B with induction
currents.

When the poison has acted the stimulation of
nerve B will produce no contraction of the at-
tached muscle, which lies in the curare. Either
the muscle or the nerve has been poisoned.

Stimulate muscle B directly.

It contracts. Hence the curare has poisoned
the nerve ; probably the terminals of the nerve
within the muscle.

Now remove nerve A from the curare and
stimulate the trunk of the nerve.

The attached muscle will contract. Hence
the trunk of the nerve has not been poisoned
by the curare.

It follows that curare poisons the endings of
the nerve within the muscle. Therefore, the
contraction of muscle B, in which the nerve end-
ings were paralyzed, must have been due to the
independent irritability of the muscle fibres.

172 GENERAL PROPERTIES OF LIVING TISSUES

The occurrence of idio-muscular contraction
(see page 166) is an additional proof of the
independent irritability of muscle.

Irritability and Conductivity are Separate Prop-
erties of Nerve. — 1. Carbon-dioxide. — Arrange
the inductorium for tetanizing currents. Connect
the secondary coil with the mam posts of the
pole-changer (cross-wires out). Connect the

Fig. 42. The gas chamber, with bottle for generating carbon dioxide,
and a pole-changer arranged to stimulate the nerve either within or without
the chamber. The holes in the glass through which the nerve passes are
plugged with normal saline clay.

two other pairs of posts with the usual stimula-
tion electrodes and the electrodes of the small
gas chamber (Fig. 42). Join the inflow tube of
the gas chamber with the outflow tube of the
carbon-dioxide bottle. The gas chamber should
rest on a glass plate. Make a nerve-muscle
preparation, preserving the full length of the
sciatic nerve up to the vertebral column. Tie

IRRITABILITY AND CONDUCTIVITY 173

a silk thread to the extreme end of the nerve,
and fasten the thread to the end of the seeker
by a drop of wax cement. With the aid of the
seeker, pass the thread through the holes, and
draw the nerve after, so that the nerve lies on
the electrodes. The. nerve should be drawn
through until the muscle is close to the gas
chamber. Stop the holes through which the
nerve passes with normal saline clay. Bring the
outer pair of electrodes against the central end
of the nerve near its exit from the gas chamber.
Determine which position of the pole-changer
corresponds to each pair of electrodes. Stimulate
the nerve first within the chamber, and then on
the central end of the nerve, using a current just
sufficient to cause tetanus. In both cases tetanus
will result. Now pour 20 per cent hydrochloric
acid on the marble in the generator. After the
gas has passed through the chamber for a moment,
stimulate as before.

Stimulation of the portion of the nerve exposed
to the carbon-dioxide is no longer effective, while
stimulation of the part central to the gas chamber
still produces tetanus.

But the nerve impulses created by stimulation
of the nerve central to the gas chamber cannot
reach the muscle except by passing along the
nerve and through the carbon-dioxide. The con-

174 GENERAL PROPERTIES OF LIVING TISSUES

ductivity of the nerve therefore is still sufficient,
while the irritability has been suspended by the
action of the gas. Hence, conductivity and irri-
tability are by no means interchangeable terms.

Their essential difference is further shown by
the effect of alcohol vapor, which impairs con-
ductivity while irritability is little changed.

2. Alcohol. — Disconnect the rubber tube from
the gas generator, and blow through the gas
chamber until the carbon-dioxide is driven out.
The nerve will recover its irritability. Deter-
mine this by stimulating from time to time.
When the nerve has recovered, drop a little
alcohol through the long glass tube of the gas
chamber, being careful that only the vapor of
the alcohol comes into contact with the nerve.
Stimulate both within and central to the chamber.

After a time, tetanus will no longer be pro-
duced by stimulating central to the chamber.
Stimulation within the latter is still effective.
Thus conductivity is impaired, while irritability
remains intact, or at least is affected to a less
extent. (The electrodes within the alcohol at-
mosphere should not be too far from the opening
through which the nerve passes to the muscle,
else the loss of conductivity in this part of the
nerve may make difficult the demonstration of
irritability.)

IRRITABILITY AND CONDUCTIVITY 175

Minimal and Maximal Stimuli ; Threshold Value.
— Arrange the gastrocnemius muscle to write on
a smoked drum. Connect one binding post of
the secondary coil to the muscle clamp, the
other binding post to the post on the muscle
lever. Load the muscle with 10 grams. De-
scribe an abscissa on the smoked paper, turning
the drum by hand. Send a feeble break induc-
tion current through the muscle.

There will be no response.

Eepeat the break currents, gradually moving
the secondary closer to the primary coil.

At a certain point the muscle will just con-
tract (" threshold value "). This is a minimal
contraction produced by a minimal stimulation.

Turn the drum 5 mm., move the secondary
coil 5 mm. nearer the primary, send in another
break current, and record the contraction. Con-
tinue this.

The contraction in answer to each break cur-
rent increases with the strength of the currents
at first rapidly, then slowly, up to a certain point.
Further increase in the strength of the stimulus
produces no further increase of contraction. The
stimulus and the resulting contraction have now
become maximal.

There is a striking disproportion between the
energy of the stimulus necessary to throw a

176 GENERAL PROPERTIES OF LIVING TISSUES

nerve or muscle into the active state, and the
energy that the stimulus sets free. It is as if a
spark fell into powder; the active process is to
be regarded, with some reservations, as an explo-
sion. But only a part of the latent energy of
muscle can be set free by any one stimulus.

Threshold Value Independent of Load. — Re-
peat the preceding experiment, and load the
muscle with 50 grams instead of 10.

The threshold value will not be changed.

Summation of Inadequate Single Stimuli. —
Place the secondary coil of the inductorium at
such a distance from the primary that a break
current shall be nearly, but not quite sufficient
to cause a contraction. Let the muscle rest
without stimulation for about a minute. Repeat
the inadequate single stimulation at intervals of
five seconds. No curve need be written.

After a time, contraction will be secured.

The excitation outlasts the stimulus, and rein-
forces subsequent stimuli : finally, the summed
excitations call forth a contraction. Summation
is of frequent occurrence probably in all living
tissues.

Relative Excitability of Flexor and Extensor
Nerve Fibres ; Ritter-Rollett Phenomenon. — Ex-
pose the sciatic nerve in a brainless frog in
the pelvic region. Set the hammer of the in-

IRRITABILITY AND CONDUCTIVITY 177

ductorium in action (binding posts 2 and 3),
and stimulate the nerve with weak induction
currents.

The leg will be flexed.

Use stronger induction shocks.

As the intensity increases extension as well as
flexion is seen. A still further increase causes
extension only.

The gradations of intensity necessary to show
these results are sometimes difficult to secure.
The phenomenon of relative excitability is not lim-
ited to the case just cited. Weak stimulation of
the vagus causes adduction of the vocal bands ;
stronger stimulation, abduction. Weak stimula-
tion causes opening of the claw of the lobster, while
stronger stimulation of the same nerve causes clo-
sure. Weak stimulation of the hypoglossal nerve
in the dog and rabbit causes the tongue to be thrust
from the mouth, while with strong stimulation the
tongue is withdrawn into the mouth. It must not
be forgotten that the anatomical nerves stimulated
in these experiments are composed of many axis
cylinders, each of which is a physiological nerve.
That they should vary in excitability is to be
expected.

A second and probably better explanation of
the Eitter-Eollett phenomena is found in the dif-
ference in structure of the flexors and extensors.

12

178 GENERAL PROPERTIES OF LIVING TISSUES

Muscle fibres consist of contractile substance im-
bedded in sarcoplasm. The relation between
the contractile substance differs in the same
muscle in different species and individuals, and
differs further in the muscles of the same indi-
vidual. In striated muscles of vertebrates, those
rich in sarcoplasm have a turbid, opaque appear-
ance, while those poor in sarcoplasm are translu-
cent. Important differences in contractility,
irritability, etc., depend on this difference of
structure. Muscles which contain many u clear"
fibres (poor in sarcoplasm) are more irritable
than those containing many of the fibres rich in
sarcoplasm. In the flexors of the frog the " clear "
fibres are relatively more numerous than in the
extensors.

Specific Irritability of Nerve Greater than that
of Muscle. — Arrange an inductorium for single
induction currents. Make as rapidly as possible
two nerve-muscle preparations, A and B. Bring
a wire from the secondary coil to each end of
muscle A. Let the nerve of B rest on muscle A.
No stimulation can now reach B except through
that part of the nerve of B which rests on muscle
A. Place the secondary some distance from the
primary coil. Stimulate muscle A with make
induction shocks, the strength of which is gradu-
ally increased by approximating the coils.

IRRITABILITY AND CONDUCTIVITY 179

Muscle B, which is stimulated only through
its nerve, will contract before muscle A, which
is stimulated directly. Hence, the specific irri-
tability of nerve is greater than that of muscle,
provided (1) that the intensity of the stimulating
current is equal for both nerve and muscle, and
(2) that the irritability of the two muscles does not
differ, and (3) that the stimulation of the nerve
of B is not by unipolar induction. The first
source of error may be excluded, because the
density of the current passing through the por-
tion of nerve lying on muscle A is certainly not
greater than the density of the current passing
through the muscle itself. The second possibil-
ity is tested as follows : —

Eeverse the muscles and repeat the experi-
ment.

The result will not be altered.

The third source of error is excluded as follows.

Tie a ligature about the nerve of B, between
muscles A and B. The physiological conduc-
tivity of nerve B is thereby destroyed, and the
nerve impulse cannot pass ; but the physical con-
tinuity of the nerve, and hence its power to con-
duct electricity, is still present.

The strongest induction currents applied to
muscle A will now fail to produce contraction
of B.

180 GENERAL PROPERTIES OF LIVING TISSUES

Irritability at Different Points of Same Nerve. —
Determine the threshold value for the sciatic
nerve near the gastrocnemius muscle and about
two centimetres from the cut end of the nerve.

The farther from the muscle the nerve is stim-
ulated, the lower will be the threshold value. It
has been suggested in explanation of this that
the nerve impulse gathers force as it passes
along the nerve, and is the more powerful the
longer the nerve which it traverses (avalanche
theory). It has also been suggested that the
nearer to the nutrient cell of origin the stim-
ulus is applied, the greater the effect. The true
explanation lies in the fact that the irritability
of the nerve is raised in the neighborhood of the
cross-section by the passage of the demarcation
current through that portion, as explained on
page 296. Tigerstedt has shown with mechani-
cal stimuli that the uninjured nerve has equal
irritability throughout.

The Excitation Wave remains in the Muscle or
Nerve Fibre in which it starts. — In order to
limit the stimulus to one or two fibres, the
method of unipolar stimulation may be adopted.

Fasten in one post of the secondary coil of
the inductorium arranged for tetanizing currents
a wire soldered to a blunt needle. The needle,
except near the free end, and the lower part of

IRRITABILITY AND CONDUCTIVITY 181

the connecting wire, should be inclosed in a
glass tube for insulation.

Expose the sacral plexus in a brainless frog in
which the skin has been removed from the hind
limbs. Connect the preparation by means of a
copper wire with the earth through the gas or
water pipes.

Touch the sacral nerves here and there with
the needle electrode, watching meanwhile the
sartorius muscle.

Partial contractions will be seen in the sar-
torius, now of the inner, now the outer fibres,
according to the nerve fibres touched
by the needle.

Stimulate the sartorius directly.
Only the fibres touched by the
needle contract.

Evidently the excitation wave re-
mains limited both in the muscle
and the nerve to the fibres in which

sartorius. It Starts.

The same Nerve Fibre may conduct Impulses
both Centripetally and Centrifugally. — 1. The
nerve of the sartorius divides at the muscle, part
going to each half of the muscle (Fig. 43).
Microscopical examination shows that the divi-
sion is not simply a parting of individual nerve
fibres, but that each axis cylinder forks, one

182 GENERAL PROPERTIES OF LIVING TISSUES

limb going upwards, the other downwards. If
the muscle be severed between the forks, no
impulse started in one half of the muscle could
reach the other half, except by going up one
branch to the original axis cylinder and down
the remaining branch ; for it is known that the
nerve impulse does not escape transversely from
one axis cylinder to other neighboring ones.

Eemove a sartorius muscle with great care.
Split the muscle in the middle line for one third
of its length, beginning at the broad end, as in-
dicated in the diagram. Stimulate the muscle
fibres of the right segment mechanically, by
snipping the preparation with scissors in the
line a. Do not cut quite through the segment.

Only the right half twitches.

Eepeat 'the stimulus by snipping in the line av

Again only the right half twitches.

Stimulate in the line b.

Both segments twitch, or at least some fibres
in each.

Repeat at bv

Both segments twitch again.

2. The gracilis of the frog is divided into an
upper, shorter part and a lower, longer part by
a tendon (Fig. 44, j). Each axis cylinder in
the nerve N, on approaching the muscle, divides
into two branches, one of which goes to the

IRRITABILITY AND CONDUCTIVITY

183

Fig. ±i. The gracilis.

upper and the other to the lower portion of the
muscle.

Eemove the muscle together with a portion of
its attached nerve, and examine
the inner surface (Fig. . 44).
The nerve (N) divides into two
branches, of which the upper
(K) runs. to the shorter portion
of the muscle and is mibranched
for some distance, while the
other (L) has a very short stem
and sinks almost at once into the
substance of the lower part. One of the branches
(H) perforates the muscle and goes to the skin.

With a sharp
pair of scissors cut
out entirely the part
shaded in the dia-
gram, without in-
juring the nerves.
The halves of the
muscle are now
united only by the
forked nerve.

Stimulate the end branches of the nerve in
one of the pieces of muscle by snipping with
scissors ; also chemically, with a lump of salt.

Both pieces will contract.

Fig. 45.

184 GENERAL PROPERTIES OF LIVING TISSUES

Speed of Nerve Impulse. — Smoke a drum, and
adjust it for " spinning." Place two pairs of
needle electrodes in corks in the moist chamber.
Arrange the inductorium for maximal make
currents, placing a simple key and the electro-
magnetic signal in the primary circuit (Fig. 45).
Connect the secondary coil to the side cups of
the pole-changer. Connect the end pairs of
cups each with one pair of the electrodes in
the moist chamber. Make a nerve-muscle prep-
aration, preserving the full length of the sciatic
nerve. Fasten the femur in the clamp in the
moist chamber. Connect the Achilles tendon
to the muscle lever. Bring the point of the
lever against the drum immediately over the
writing point of the electro-magnetic signal.
Let the nerve rest on the electrodes, one
pair near the end of the nerve, the other
near the muscle. Spin the drum slowly.
Hold the writing point of a vibrating tuning
fork against the smoked paper beneath the
line drawn by the signal. Send a maximal
induction current through first one pair of elec-
trodes and then the other. Determine the inter-
val between the moment of stimulation and
the beginning of contraction in each instance.
[This is done by turning the drum back until
the writing point of the signal lies precisely in

IRRITABILITY AND CONDUCTIVITY 185

the vertical line marked by it when the current
was made, and then stimulating the muscle to
contract. The ordinate drawn by the muscle
lever (the drum being still at rest) will be
synchronous with the ordinate drawn by the
signal during the experiment.]

It will be found that the interval between
stimulation and contraction is greater when the
nerve is stimulated far from the muscle than it
is on stimulation near the muscle. The differ-
ence is the time occupied by the passage of the
excitation wave along the nerve between the
electrodes.

Measure the length of nerve between the elec-
trodes, and calculate the speed of the nerve im-
pulse per second.

It is assumed in this method that the interval
between the closure of the primary circuit and
the beginning of the nerve impulse is the same
in both instances, and that the interval between
the arrival of the impulse in the muscle, and the
visible change of form, is likewise the same in
both. If the mean and the probable deviation of
a series of measurements are taken, a fairly accu-
rate result may be expected. A better method,
however, is to record the passage of the negative
variation over a measured length of nerve by
photographing the meniscus of the capillary

186 GENERAL PROPERTIES OF LIVING TISSUES

electrometer. Similar measurements can be
made with a differential rheotome (page 313).

Helmlioltz found in motor nerves of the frog
an average speed of 27 metres per second, but
the individual variation is considerable. The
speed is very slow compared with that of light, or
even sound. It is modified by changes in tem-
perature, nutrition, anaesthetics (alcohol, ether,
chloroform, carbon dioxide), the intensity of the
stimulus, — above a certain value, the greater
the stimulus, the more rapid the conduction, —
and by many other factors. Specific differences
are found depending on the structure of the
nerve. Thus the velocity has been found in mam-
malian nerve to smooth muscle to be about 9
metres per second, while in the bivalve Anodonta
it is said to be only 1 centimetre per second.

Apparatus

Normal saline. Bowl. Towel. Pipette. Glass plate.
Dry cell. Inductorium. Key. Wires. Frog with sci-
atic nerve degenerated. Hen's egg incubated 60-70 hours.
NaCl solution (0.75%). Ligatures. Filter paper. One
per cent solution of curare. Pole-changer. Gas chamber.
Carbon dioxide generator. Twenty per cent hydrochloric
acid. Broken marble. Alcohol. Muscle clamp. Stand.
Muscle lever with scale pan. Millimetre rule. Ten gram
weights. Needle electrodes (glass tube). Moist chamber.
Two pairs of non-polarizable electrodes. Electro-magnetic
signal. Recording drum. Glazed paper. Tuning fork.
Normal saline clay.

PART II

THE INCOME OF ENERGY

PART II
THE INCOME OF ENERGY

I FERMENTATION

Hydrolysis of Stakch by Diastase

Conversion of Starch to Sugar by Germinating
Barley. — To 5 grams crushed, germinating barley
add 10 grams potato starch, and 20 c.c. of cold
water. Then add gradually 70 c.c. of hot water
with constant stirring. Keep the mixture in a
temperature of about 60° C. for one hour.

The insoluble starch will be converted to a
sweet liquid.1

Boil 10 c.c. of Fehling's solution,2 dilute the
syrup with water and add it drop by drop to the
boiling Fehling's solution.

1 Kirchoff : Schweigger's Journal fur Chemie und Physik,
1815, xiv, p. 389. There is a small amount of sugar and starch
in the barley itself.

2 Fehling's solution. — In a large watch glass weigh 34.639
gms. pure cupric sulphate (clean crystals). Dissolve the crystals
by warming them with about 150 c.c. water in an evaporating
dish. Place the solution in a 500-c.c. measuring flask. Wash the
remnant from the dish into the flask. Allow the liquid to cool
completely. Add water to the mark on the neck of the flask.

Warm about 173 gms. potassium sodium tartrate in a little
water until dissolved. Place the solution in a 500-c.c. measur-
ing flask, add 100 c.c. sodium hydroxide, sp. gr. 1.34 (about
31 per cent), and, after the mixture has completely cooled, fill
the flask to the mark on the neck.

In use, mix equal volumes of each solution in a dry glass.

One molecule grape sugar reduces five molecules cupric oxide
to cuprous oxide ; 10 c.c. of Fehling's copper sulphate solution
equals 0.05 gm. grape sugar.

190 THE INCOME OF ENERGY

Eed cuprous oxide or its yellow hydrate will
separate.

The germinating barley causes the starch to
take up water, thus changing to a reducing sugar.
In this instance the agent is a living cell, or
some substance or " ferment " secreted by the
cell. It is now necessary to inquire whether
ferments are separable from living cells.

Conversion of Starch to Sugar by Salivary Dias-
tase (Ptyalin). — To 10 c.c. of starch paste1 col-
ored blue with iodine (blue iodide of starch) add
about 2 c.c. of filtered saliva and keep the mixture
at 35-40° C.

The starch paste will liquefy and become sweet.
The blue color will become lighter and finally
disappear.

Test with Fehling's solution. Eeduction will
take place.

Saliva hydrolyzes starch to a reducing sugar.

Saliva is secreted by the cells in the salivary
gland, placed some distance from the mouth.
The saliva itself contains no secreting cells.
There are ferments, then, which act at a distance

1 Starch paste. — Rub 1 gm. potato starch in a mortar with
25 c.c. cold water. Pour the mixture into an evaporating dish.
Wash the remnant from the mortar and pestle into the dish with
75 c.c. water. Heat the mixture to boiling point with constant
stirring. The starch paste will turn blue upon addition of iodine
(iodide of starch).

FERMENTATION 191

from the cells that produce them. There seems
thus an important distinction to be made between
organized ferments, those acting apparently with-
in the living cell, and unorganized ferments, like
the salivary diastase, which is secreted by a
living cell but remains active after leaving the
cell. It will be seen that this distinction cannot
be maintained.

Extraction of Diastase from Germinating Barley.1
— Crush freshly germinating barley in a mortar
with about half its weight of water. Keep the
mass two hours at 35-40° C. Squeeze out the
watery extract in a press, or strain by strong
pressure through a linen cloth. Add excess of
alcohol.

Diastase will be precipitated. It may be puri-
fied by dissolving it in water and reprecipitating
with alcohol.

Add a little diastase to 10 c.c. starch paste,
colored blue with iodine. The starch will be con-
verted to sugar. The blue color will disappear.

It appears, therefore, that ferment action is
not dependent on the life of the cell that secretes
the ferment.

Specific Action of Ferments. — The question
now arises whether the diastase acts only to

1 Payen and Persoz : Annates de chimie et de physique,
1833, liii, p. 78.

192 THE INCOME OF ENERGY

change starch to sugar or whether it causes the
decomposition of other substances.

Place a small piece of fibrin in a test-tube and
add 2 c.c. filtered saliva. Keep the tube several
hours at a temperature of 35-40° C

The fibrin will not change.

Place 0.5 c.c. neutral olive oil (page 207) and 2
c.c. filtered saliva in a test-tube.

Noteworthy changes will be absent.

From these experiments it is evident that
diastase decomposes starches, but does not de-
compose proteids and fats. Its ferment action is
thus far " specific." The belief that each ferment
has its own characteristic product will be in-
creased by the study of the following typical
ferment actions.

Proteid Digestion by Pepsin

Gastric Digestion of Cooked Beef and Bread. —

At 7 a.m. feed cooked beef and bread to a cat
which has fasted twelve hours. At 11 a. m. kill
the cat, expose the stomach, and apply double
ligatures about 1 cm. apart to the duodenum at
the pylorus and to the oesophagus at the cardiac
orifice. Ptemove the stomach. Open the stomach
very cautiously by drawing a knife along the
greater curvature.

" The stomach is very full, and still contains

FERMENTATION 193

much meat and bread not wholly softened. The
softening is greater in the portal region and in
those portions of the food next the mucous mem-
brane than in the middle of the stomach contents.
The mucus secreted by the gastric mucous
membrane is very abundant and is strongly acid.
The stomach contents have a sour odor." 1

Artificial Gastric Juice.2 — 1. Strip the mucous
membrane from the fourth stomach of a calf.
Wash the membrane with cold water until the
acid reaction disappears. Dry the mucous mem-
brane in the air. Divide some of the dried
membrane into small pieces and add dilute hy-
drochloric acid.3

2. Strip the mucous membrane of the pig or
rabbit from the deeper layers of the stomach, cut
the mucous membrane into the smallest pieces,
wash slightly with water, pour off the water with
all possible care, and cover the slightly moist
residue with glycerine.4 Before using, add dilute
hydrochloric acid.

1 Eberle : Physiologie der Verdauung, 1834, p. 100.

2 Eberle : loc. cit., p. 79.

3 Dilute hydrochloric acid. — Add to 10 c.c. officinal HC1,
sp. gr. 1.124 (about 25 per cent HC1), enough water to make
1000 c.c. This solution will contain about 0.281 per cent HOT.
(Salkowski's Practicum, 1893, p. 130.)

4 Von Wittich : Archiv fur die gesaramte Physiologie> 1869,
ii, p. 194.

13

194 THE INCOME OF ENERGY

Digestion with Artificial Gastric Juice. — Pre-
pare three flasks, A, B, and C. In A place 100 c.c.
artificial gastric juice; in B, 100 c.c. 0.2 per cent
HC1; and in C, a piece of dried gastric membrane
and 100 c.c. distilled water. In each of the three
flasks place a small piece of cooked meat, and keep
the flasks about five hours at 35-40° C.1 Com-
pare the result with that observed in natural
digestion.

The artificial gastric juice will digest the meat
as did the natural juice in the stomach, but neither
the acid alone, nor the mucous membrane free
from acid, will digest. There is a ferment in the
mucous membrane, but it will not act except in
an acid medium.

Extraction of Pepsin. — Pepsin more or less con-
taminated with proteid (pepsin may itself be a proteid)
may be precipitated from a glycerine extract by alco-
hol.2 The pepsin may also be carried down mechani-
cally by an indifferent precipitate as in Brucke's
method,3 in which the mucous membrane, acidulated
with phosphoric acid, is allowed to digest until the
proteids are mostly converted into soluble peptone.
The mixture is then neutralized with lime water.
The insoluble calcium phosphate thus formed falls as

1 Eberle : loc. cit.

2 Von Wittich: loc. cit., p. 195.

3 Briicke : Sitzungsberichte der konigliche Akadeniie cler
Wissenschaften zu Wien, 1862, xliii, p. 601.

FERMENTATION 195

a fine powder carrying the pepsin with it. The precip-
itate is dissolved in very dilute hydrochloric acid, and
to this solution is added a solution of cholesterin in
alcohol and ether. When the two solutions are mixed,
the cholesterin separates as an abundant, fine powder
bearing the pepsin with it. The cholesterin is removed
with ether, leaving the pepsin.

Ammonium sulphate may also be used as the me-
chanical precipitant.1

Change of Proteid to Peptone by Pepsin. — 1.

Place in a test-tube five drops of the glycerine
extract of pepsin with 5 c.c. 0.2 per cent hydro-
chloric acid and a small piece of fibrin.2 Keep
the mixture at 35-40° C.

In a short time the fibrin will be dissolved.
Appropriate tests will show that it has been con-
verted to peptone. 2. Repeat the preceding ex-
periment, using commercial pepsin (never very
free from proteid).

Splitting of Casein by Eennin.

Rennin Extract. — Allow the mucous membrane
of the stomach (preferably the fourth stomach of

1 Kiihne and Chittenden: Zeitschrift fur Biologie, 1886,
xxii, p. 428.

2 Preparation of fibrin. — With a bundle of smooth rods
whip blood as it flows from an artery until the fibrin gathers on
the rods. Wash the fibrin in running water until the red cor-
puscles are removed and the fibrin shows its natural color.
Preserve the fibrin in glycerine.

196 THE INCOME OF ENERGY

the suckling calf) to stand twenty-four hours in
150-200 c.c. 0.1-0.2 per cent solution of hydrochlo-
ric acid. Then neutralize the acid with great care.1

Separation of Rennin. — The extract just prepared
contains pepsin as well as rennin. The rennin may
be separated as follows. The neutralized extract is
repeatedly shaken with fresh amounts of magnesium
carbonate. The resulting precipitates carry down
almost all the pepsin and very little rennin. The
filtrate still rapidly coagulates milk, but contains only
traces of pepsin. This filtrate is now precipitated
with lead acetate, the precipitate is decomposed with
very dilute sulphuric acid, and the mixture filtered.
To the filtrate, which contains the rennin, is added a
solution of stearin soap in water. Thereupon the
soap is thrown out of solution and falls, carrying the
rennin with it. The soap is then removed by shaking
with ether, and the rennin remains.2

Precipitation of Casein. — Add 1 C.C. of the
neutral extract to 25 c.c. fresh milk at 36-38° C.
(Normal milk is amphoteric. If the reaction
be acid, the acid should be very carefully
neutralized.)

In a few minutes the milk will separate into

1 Hammarsten : Upsala Lakareforenings Fbrhandlingar, 1872,
viii, pp. 63-86. Abstract by author in Maly's Jahresbericht
uber die Fortschritte der Thierchemie, 1872, ii, pp. 118-125.

2 Hammarsten : Lehrbuch der physiologischen Chemie, 1895,
p. 241.

FERMENTATION

197

curd and whey. The curd is casein together
with the fat globules carried down as it precipi-
tates. The whey is a dilute saline solution of
milk-albumin, milk sugar, etc.

Test the chemical reaction. The mixture is
still neutral. Milk may also be curdled by acid,
either added artificially or produced in the milk
itself by lactic acid fermentation of milk sugar.
The absence of an acid reaction in the above exper-
iment excludes precipitation through acid fermen-
tation of milk sugar. Casein prepared free from
milk sugar is also precipitated by rennin. Finally,
rennin, extracted by the method given above, does
not act upon milk sugar, but rapidly precipitates
casein.

Analogy suggests that the specific action of
the rennin may be the splitting of casein and that
the precipitation may be a secondary process.
The following experiments determine this matter.

Experiments of Arthus and Pages.1 — Prepare
two solutions, A and B.

A.
Milk 100 c.c.

Neutral oxalate of

potassium 1 % 5 c.c.

Rennin 1 to 250 4 c.c.

B.
Milk 100 c.c.

Neutral oxalate of

potassium 1 % 5 c.c.
Water 4 c.c.

1 Arthus and Pages : Archives de physiologie, 1890, p. 334.

198 THE INCOME OF ENERGY

(Kennin, 1 to 250, is a pastille of Hansen dis-
solved in 250 c.c. H20.)

Keep both mixtures at 38° C. during forty
minutes. 1. Boil 25 c.c. from each solution.
Solution A coagulates, while solution B shows
no trace of coagulation. Hence the action of
rennin has rendered the casein in A coagulable
on boiling.

2. To 25 c.c. from each solution add 8 c.c. of
a solution of calcium chloride capable of pre-
cipitating exactly, in equal volumes, the solution
of potassium oxalate. By this addition any ex-
cess of potassium oxalate is removed and the
calcium chloride remains in slight excess.

A will coagulate ; B will not. Hence the casein
in solution A has been so changed by rennin that
it is precipitated on the addition of a small quan-
tity of calcium chloride. Solution A may also
be precipitated by restoring its original content
of calcium chloride, i.e. by adding 5 c.c. of the
above calcium chloride solution, which will exactly
combine with the 5 c.c. of potassium oxalate.

If small quantities of rennin be added to
natural milk and equal portions of the milk be
tested from time to time by boiling, the amount
coagulated will be greater the longer the rennin
acts. An amount of calcium chloride too small
to produce coagulation in the early stages of

FERMENTATION 199

rennin action is sufficient to produce coagulation
when added in the later stages.

Evidently, in the clotting of milk by rennin
two separate phenomena must be distinguished:
(1) the chemical transformation of casein by
rennin, (2) the precipitation of the transformed
casein by the calcium chloride. (This salt favors
also the splitting of the casein.) Eennin may
therefore be classed with pepsin and trypsin.

According to Hammarsten the casein is split
into phosphorus-free albumose and phosphorus-
holding paracasein. Heat is set free. It is the
paracasein which precipitates. It is less soluble
than casein.

Precipitation of Fibrin by Fibrin Ferment

Buchanan's Experiment. — Press blood clot
through a linen cloth. Add the liquid thus ob-
tained to a serous fluid, which does not clot spon-
taneously, such as ascitic fluid, pleural effusion,
hydrocele fluid.

After some hours a firm, translucent clot will
form.1

Extraction of Fibrin Ferment. Schmidt's Method.
— Coagulate one part of serum from the blood

1 Buchanan: London Medical Gazette, 1835, xviii, p. 51;
idem, 1845, xxxvi, p. 617. This discovery was first announced
in 1831.

200 THE INCOME OF ENERGY

of ox, dog, or horse, by adding 15-20 parts strong
alcohol. After at least fourteen days, filter, dry
the moist residue over sulphuric acid, pulverize
the dried substance, stir it with water (twice the
volume of the serum originally taken) and after
allowing sufficient time for solution, filter. The
filtrate contains the fibrin ferment.1

Gamgee's Method. — Allow freshly prepared fi-
brin (obtained by washing a blood clot free from
corpuscles) to stand three days in 8.0 per cent
solution of sodium chloride. Filter.2

The filtrate is rich in fibrin ferment.

Extraction of Fibrinogen. — Eeceive three
volumes of blood directly from an artery into
one volume of saturated solution of magnesium
sulphate, which will prevent the blood from
clotting. Separate the corpuscles from the liquid
plasma by the centrifugal machine. Add to the
plasma an equal volume of saturated solution of
sodium chloride. Flakes of fibrinogen will be
precipitated. Filter as quickly as possible, for
that purpose dividing the liquid among several
funnels each with a folded filter paper. Press
the filter papers containing the residue between
fresh filter paper, in order to remove the adherent

1 Schmidt : Archiv fiir die gesammte Thysiologie, 1872, vi,
p. 457.

2 Gamgee : Journal of physiology, 1879, ii, p. 151.

FERMENTATION 201

liquid. Tear the filter containing the fibrinogen
into small pieces. Dissolve the fibrinogen which
sticks to the filter as a tough, elastic mass, in a
quantity of 8 per cent sodium chloride solu-
tion equal to about one-third the quantity of the
magnesium sulphate solution originally taken.
Filter off the fragments of paper. Purify by
reprecipitation with an equal volume of saturated
solution of sodium chloride. Filter. Dry as
before, and add a small quantity of water to the
finely divided filter to which the precipitate
clings. This water will take a small quantity of
salt from the precipitate, and in this dilute saline
solution the fibrinogen will dissolve.1

Precipitation of Fibrinogen by Fibrin Ferment. —
Add to the dilute saline solution of fibrinogen a
solution containing fibrin ferment.

Fibrin will gradually form.

Ammoniacal Fermentation of Urea by
Urease

1. Place 100 c.c. fresh human urine in each
of three clean flasks marked A, B, C. To B and
C add 1 c.c. of urine that has become ammoniacal
upon standing in the atmospheric air. Add also

1 Hammarsten : Archiv fiir die gesammte Physiologie, 1879,
xix, p. 563. Also idem, 1880, xxii, p. 431. Hammarsten's first
publication was in Nova acta regia societas scientiarum Upsali-
ensis, 1878, (3), ix.

202 THE INCOME OF ENERGY

to G 2 per cent of a saturated solution of carbolic
acid in water. Let B and G stand in a warm
place sixteen days.

2. Withdraw 5 c.c. from flask A. Note
whether the urine is clear or turbid, and
whether it effervesces on the addition of a
dilute acid. Withdraw 2 c.c. from flask A and
determine its percentage of urea by the hypo-
bromite method.

Centrifugalize a portion of the remaining con-
tents of flask A. With a microscope examine
the sediment for crystals of ammonio-magnesium
phosphate and for micro-organisms, especially the
micrococcus ureas, which occurs in long curved
chains of round cells about 1.5 /jl in diameter.

3. After sixteen days repeat these observa-
tions on the urine in flasks B and G. Eecord
the results obtained from all three flasks in the
table on page 203.

The table shows that the hydrolysis of urea
into ammonium carbonate still takes place in
urine containing enough carbolic acid to destroy
the micro-organisms long known to be the cause
of the ammoniacal fermentation.1 It is therefore
probably due to a ferment, which escapes from
the cells after their death.

1 Hoppe-Seyler : Medicinisch-chemische Untersuchungen,
Berlin, 1866, p. 570.

FERMENTATION

203

GO

" to
O

Crystals of
Ammonio-
Magnesium
Phosphate.

Per cent

of

Urea.

Reaction

to

Acids.

Clear

or

Turbid.

•

Content

of

Carbolic

Acid.

CO

A

Normal

B

Septic

C
Aseptic

204 THE INCOME OF ENERGY

Prior to 1860 ammoniacal decomposition of
urine was vaguely classed as a fermentation. In
that year Miiller1 suggested that it might be due
to a body like beer-yeast. In 1862 Pasteur2
discovered such a yeast, which he called Torula
urece. Cohn first classed it with the micrococci.
It is aerobic. Miguel finds seven species of
bacilli, nine micrococci, and one sarcina, that
decompose urea. These obtain their nitrogen
ordinarily from proteids, but in the absence of
proteids may utilize urea.

Extraction of Urease. — To 10 C.C. of urine
undergoing an active ammoniacal fermentation,
add 50 c.c. of strong alcohol, and allow the
mixture to stand in a well-corked flask. After
five days place the precipitate upon a very small
filter and wash it with 50 c.c. of fresh alcohol.
(Preserve both filtrates for recovery of the alcohol
by redistillation.)

1. Add a very small quantity of this precip-
itate to a neutral 2 per cent solution of urea.
Test the reaction. Place the mixture in a water
bath at 38° C.

After a few minutes again test the reaction.

It will be strongly alkaline.

1 Miiller: Journal fur praktische Chemie, 1860, lxxxi, p. 467.

2 Pasteur : Comptes rendus de l'academie des sciences, Paris,
1860, 1, p. 869. See also Van Tieghem, idem, 1864, p. 210.

FERMENTATION 205

After a short time the odor of ammonia will be
perceptible. The alcoholic precipitate contains a
ferment capable of quickly hydrating urea.

"The alcoholic precipitate from the unfiltered
urine consists chiefly of various salts together
with the cells of the Torula, hence when treated
with water some of the salts are dissolved and
pass with the ferment through the filter. If this
first aqueous extract be again precipitated with
alcohol, a portion of the salts will be again
removed, and if this second precipitate be several
times redissolved in water and reprecipitated
with alcohol, the body with the ferment proper-
ties may be ultimately separated — as an amor-
phous white powder soluble to a clear solution
in distilled water and not characterized by any
special chemical reactions."

The ferment is not secreted by the cells into
the surrounding liquid, but is retained within the
cell bodies, for the living cells may be filtered off,
and the filtrate will not hydrate the urea.1

Splitting and Synthesis of Fats

Chemistry of Fats and Soaps. — When olive oil
is saponified, glycerine appears (Scheele, 1779).

1 Lea : Journal of Physiology7, 1885, vi, p. 138. See also
Musculus : Comptes reudus de l'academie des sciences, Paris,
1874, lxxviii, p. 132 ; idem, 1876, lxxxii, p. 333 ; Archiv fur
die gesammte Physiologie, 1876, xii, p. 214.

206 THE INCOME OF ENERGY

It is related to the alcohols (Chevreul, 1813),
being a compound ether or ester, a combination
of an alcohol with an acid. Commercially gly-
cerine is prepared by exposing neutral fats, such
as stearin, to superheated steam, whereby the
neutral fat is split into glycerine and fatty acid.

CH20

•CO(CH2)16

CH3

H

OH

CHO

• CO(CH2)16

•CH3

+

H

OH

=

CH20

'CO(CH2)16

CH3

H

•OH

STEARIN

WATER

CH2

•OH

CO

1

•OH(CH2)16-CH3

CH

•OH

+

1
CO

1

•OH(CH2)16-CH3

CH2

•OH

1
CO

•OH(CH2)16'CH3

GLYCERINE

STEARIC ACID

If an alkali be present, it will combine with
the fatty acid to form a soap.

CO-OH(CH2)16-CH3
CO'OH(CH2)16-CH8
CO-OH(CH2)16-CH3

STEARIC ACID

Na-OH

+ Na • OH =

Na-OH

SODIUM

HYDROXIDE

CO • ONa(CH2)16 • CH3

HOH

GO-ONa(CH2)16-CH8

+

HOH

CO-ONa(CH2)16.CH3

H-OH

SODIUM STEARATE

WATER

Splitting of Fats by the Pancreatic Juice. Ber-
nard's Experiment. — Place 2 c.c. neutral olive

FERMENTATION 207

oil in a test-tube and add a small quantity of
pancreatic juice (or a piece of fresh pancreas or
extract of pancreas). Test the reaction of the
mixture. It is alkaline. Note that a white,
creamy liquid forms almost immediately. This
" emulsion " is composed of a multitude of small
fat globules.

Test the reaction again. It gradually becomes
acid.

It is evident that under the influence of the
pancreatic juice the fatty matter is not simply
finely divided and emulsified, but that it has also
been modified chemically.1

In order to study the splitting of neutral fats
by lipase, a ferment found in the pancreatic juice,
it is necessary (1) to prepare a perfectly neutral
fat, and (2) to recognize the fatty acid as soon as
it is set free.

Preparation of Neutral Fat. — Shake commer-
cial olive oil (which always contains fatty acid)
for two hours at 95° C. in a separating funnel
with a saturated solution of barium hydroxide.
Allow the mixture to stand until the oil sepa-
rates from the hydroxide. Kemove the hydrox-
ide. Filter the oil.

The Emulsion Test for Fatty Acid. Briicke's

1 Bernard : Comptes rendus de l'academie des sciences, Paris,
1849, xxviii, p. 250.

208 THE INCOME OF ENERGY

Experiment. — 1. Shake 1 c.c. neutral olive oil
in a test-tube with 5 c.c. 0.25 per cent sodium
carbonate solution.

The oil will be broken up into large globules
which will speedily reunite, leaving the liquid
clear.

2. Shake 1 c.c. rancid olive oil (containing
about 5.5 per cent fatty acid) with 5 c.c. 0.25 per
cent sodium carbonate solution.

The mixture becomes instantly milky. The
oil is divided into globules of microscopic size.
The emulsion is permanent.

3. Shake 1 c.c. neutral olive oil with 5 c.c. water.
The water and oil will not mix.

4. Shake 1 c.c. neutral oil with water con-
taining soap.

The oil will be emulsified. It is probable
therefore that soap contributes to the emulsion,
perhaps by coating the fine particles of oil with a
membrane that prevents their reunion.1

Gad's Experiment. — 1 . Fill a watch glass
about 5 cm. in diameter with 0.25 per cent solu-
tion of sodium carbonate. With a glass rod
carefully place a large drop of rancid olive oil
(containing 5.5 per cent fatty acid) upon the
surface of the soda solution.

1 Briioke : Sitzungsberichte der kaiserlichen Akadeniie der
Wissenschaften zu Wien, 1870, lxi, pp. 613-614.

FERMENTATION 209

The drop will come to rest, and for a moment
both the drop and the surrounding liquid remain
clear. Very soon, however, the oil is covered
with a white layer, and through the soda solu-
tion spreads a white cloud which becomes denser
and denser until the oil drop, steadily diminish-
ing in size, floats in a milky white liquid.

2. Eepeat the experiment, observing the oil
drop under a low power of the microscope.

Note the extraordinary motion in the neigh-
borhood of the oil drop, and how the particles of
oil are thrown out in strong eddies.

3. Examine the completed emulsion under a
higher power of the microscope.

There appear exceedingly small fat drops of
very uniform size. The milky fluid is the finest
and most uniform emulsion.1

RachforcV s Experiment. — " Arrange a series of
watch glasses containing 0.25 per cent solution
sodium carbonate. Place in a test-tube 2 c.c.
neutral olive oil and 1 c.c. pancreatic juice (or
extract). Shake the tube and allow the juice
and oil to separate, then pipette a drop of oil
from the surface and place it on the soda solu-
tion-in watch glass 1. Again shake the tube
and allow the oil and juice to separate, then
pipette as before, placing a drop of oil in watch

1 Gad: Archiv fur Physiologie, 1878, p. 183.
14

210 THE INCOME OF ENERGY

glass 2. Again shake and pipette as before, and
repeat this process every three or four minutes
until the experiment is completed. The begin-
ning of the experiment and the time of each
pipetting must be carefully noted. If the pipet-
tings are three minutes apart, then the first drop
of oil will have been exposed three minutes to
the action of the pancreatic juice, the second
drop six minutes, the third nine minutes, and
so on.1

The gradual increase in fatty acid will be
shown by the gradual increase in the amount
of the spontaneous emulsion.2

It has just been shown that lipase will hydro-
lyze neutral fats into fatty acid and glycerine.
We must now enquire whether this ferment
ean effect the synthesis of fats, in other words
whether its action is reversible. For this pur-

1 Raehford: Journal of physiology, 1891, xii, p. 81. Rach-
ford used J c.c. fresh pancreatic juice obtained by placing a
glass tube in the pancreatic duct of the rabbit (see page 80).

2 " There is a possible error in this method which had better
be spoken of here. It would seem that the alkali of the pan-
creatic juice would combine with the fatty acids forming soap,
and in this way the oil would soon be emulsified in the juice
itself and not separate after shaking. This would indeed be a
serious drawback if it actually occurred, but in truth it does not
occur until late in the experiment after we have obtained the
information we have sought by the spontaneous emulsion
method." (Raehford, loc. cit., p. 82).

FERMENTATION 211

pose an extract of lipase may be used, first, to
split a neutral fat (or glycerol ester) into its con-
stituent fatty acid and alcohol (glycerine is a
trihydric alcohol), and second, to form a neutral
fat from fatty acid and alcohol.

Extraction of Lipase. . From Pancreas. — Ee-
move the pancreas of the pig within thirty min-
utes after the death of the animal. Dissect off
as much of the fat as possible. Eeduce the pan-
creas to a fine pulp in a mortar with coarse well-
washed white sand. Extract the lipase with a
little water or glycerine.

From Liver. — Eemove the liver of the pig
within thirty minutes of the death of the animal.
Eeduce 50 gms. to a fine pulp in a mortar with
about 200 c.c. water. Filter. Dilute the watery
extract to 500 c.c.

Hydrolysis of Ethyl Butyrate by Lipase. —
Place in each of two test-tubes, A and B, 4 c.c.
water, 0.1 c.c. toluene,1 and 0.26 c.c. ethyl buty-
rate.2 Cork the tubes tightly. Place them in the
water bath for five minutes, to bring them to
the temperature of the bath, 40° C. Add 1 c.c. of

1 Toluene is an antiseptic, which prevents the splitting of
the neutral fat by bacteria.

2 Ethyl butyrate hydrolyzes more rapidly than butter fat.
It has the further advantage that the amount split by the
temperatures employed during the time of the experiment is too
small to be measurable.

212 THE INCOME OF ENERGY

the aqueous extract of lipase to each. Boil tube
B. Place both tubes at 40° C. for fifteen min-
utes. Eemove them from the bath and plunge
them into ice-water (to check further ferment
action). Titrate with ^ KOH, using neutral lit-
mus as the indicator.1 The initial acidity of the

1 A normal solution contains in each litre one equivalent
weight of the active substance, i. e. that mass of the active sub.
stance which is equivalent to the atomic weight of a univalent
element in the reaction for which the normal solution is to be
employed. Equal volumes of different normal solutions are
equivalent to each other. Thus, 1 c.c. normal alkali solution
requires for neutralization exactly 1 c.c. normal acid, no matter
what acid is employed to make the normal solution.

Preparation of Normal Potassium Solution. — The content of
KOH in 1 litre is 56.16 grams. Dissolve 60 gms. purest com-
mercial KOH (which always contains considerable water) in a
graduated cylinder in about 950 c.c. water. Determine the
true content of KOH by titration with a normal oxalic acid
solution (prepared by dissolving its equivalent weight 63 gms.
in 1 litre water) as follows. Thoroughly stir the potassium hy-
droxide solution, fill a burette with a portion of the well-mixed
solution. Place 10 c.c. normal oxalic acid solution in a beaker
and add a few drops of solution of rosolic acid as indicator.
Add the alkali from the burette cautiously until the end point
of the reaction is reached, i. e. until the indicator gives a red
color which does not quickly disappear. As 10 c.c. of acid solu-
tion should exactly neutralize 10 c.c. of alkali solution, pro-
vided both were normal, it follows that the quantity of KOH
solution necessary to neutralize is to 10 c.c. as the total quantity
of the original KOH solution is to x. x will be the number of
cubic centimetres to which the KOH solution must be diluted
in order to make it normal. A portion of the normal solution
should then be diluted 1:20, and preserved in an air-tight

FERMENTATION 213

enzyme solution, usually 0.1 to 0.2 c.c. ^V KOH,
should be deducted from the cubic centimetres
KOH required to neutralize the fatty acid
formed.1

Fatty acid will appear in tube A, but not in
tube B, in which the enzyme was destroyed by
boiling.

Synthesis of Neutral Fat by Lipase. — 1. Place
5 c.c. t^-q butyric acid, 2 c.c. 13 per cent alcohol,
1 c.c. diluted glycerine extract of pig's pancreas
(or aqueous extract of liver) in each of two test-
tubes, A and B. Boil the contents of test-tube
B. Seal both tubes. Keep them thirty-six
hours at 48.5° C.

On opening the tubes, A will give a distinct
odor of ethyl butyrate ; none will be found in B,
in which the ferment was destroyed by boiling.2

2. Place 5 gms. glycerine, 2 gms. isobutyric
acid, 125 gms. water, 1 c.c. neutralized blood serum
(or aqueous extract of pig's liver) in each of two

flask. (Compare Miiller and Kiliani : Kurzes Lehrbuch der
analytischen Chemie, 1900, p. 31 and p. 83).

At 30° (summer temperature) 0.26 c.c. ethyl butyrate weighs
0.2300 gram. This quantity, if completely hydrolyzed, would
require 39.7 c.c. ^ KOH.

1 Kastle and Loeveuhart : American chemical journal, 1900,
xxiv, pp. 491-525. Also Loevenhart : American journal of
physiology, 1902, vi, pp. 331-350.

2 Kastle and Loevenhart : loc. cit., p. 518.

214 THE INCOME OF ENERGY

test-tubes, A and B. Boil the contents of tube
B. Place both at 37° C. At intervals of half
an hour titrate a portion from each tube with
7tq KOH solution. The acidity will diminish in
both, but much more rapidly in the tube contain-
ing the active ferment.

The acidity is diminished by the combination
of the fatty acid with the glycerine to form a
neutral fat.1

Fats are hydrolyzed to some extent in the stomach,2
but stomach lipase is active only in neutral solutions.
It is inhibited or destroyed by 0.3 per cent hydro-
chloric acid. Other ethereal salts besides the fats are
hydrolyzed in the intestine, e. g. salol.8

The rate of change by lipase increases with the
amount of the enzyme present.4

Reversible action is seen in ferments other than
lipase, as in the following experiments.

Splitting of Hippuric Acid by Histozyme. — A pig's
kidney was perfused four hours with one litre defibri-
nated pig's blood to which 0.8 gram hippuric acid

1 Hanriot : Comptes rendus de la societe de biologic, 1901,
p. 70.

2 Marcet: Proceedings Royal Society, London, 1858, ix.
p. 306. Ogata : Archiv fur Physiologie, 1881, p. 515. Cash :
Archiv fur Physiologie, 1880, p. 323.

3 Baas: Zeitschrift fur physiologische Chemie, 1890, xiv,
p. 416.

4 Kastle and Loevenhart : loc. cit., p. 511.

FERMENTATION 215

(sodium salt) had been added. The blood passed
through the kidney 9-10 times.

Upon analysis, there appeared 0.087 gram benzoic
acid, produced from 0.1276 gram hippuric acid.

Synthesis of Hippuric Acid by Histozyme. — A pig's
kidney was perfused three hours with one litre defibri-
nated pig's blood containing a neutral solution of 0.5
gram benzoic acid and 0.6 gram glycocoll. The blood
passed ten times through the kidney.

Found : 94 mgm. hippuric acid.1

These actions depend upon a ferment, histozyme,
extracted by Schmiedeberg.

Some hypothetical considerations will be of value
here. Compounds of carbon may be divided into
those in which the carbon atoms are arranged in an
open chain, for example ethane, C2H6,

H H

I I
H— C— C— H

I I
H H

ETHANE

and those in which the chain is closed to form a " car-
bon ring," for example, benzene, C6H6, which consists
of six carbon atoms, in a closed, ring-shaped chain, the
"benzene nucleus," with a hydrogen atom joined
to each carbon atom by its fourth affinity (Kekule,
1865).

1 Schmiedeberg : Arehiv fur experiments le Pathologie mid
Pharmakologie, 1881, xiv, pp. 382-383.

216 THE INCOME OF ENERGY

\

/

c

= c

/

\

-c

c-

. %

//

c

-c

/

\

BENZENE

NUCLEUS

OR

RING

H H

\ /

C = C

/ \

H-C C-H

% //

c-c

/ \

H H

BENZENE

The benzene ring is not easily opened, but deriva-
tives of benzene may be readily obtained by replacing
hydrogen atoms. Thus, in aniline or amido-benzene,
C6H5.NH2, one hydrogen atom is replaced by amide
radical ; in carbolic acid, or phenol, C6H5.OH, by
hydroxyl ; in toluene or methyl benzene, C6H5.CH3,
by the radical CH3. The carbon atom in methyl
benzene is not a part of the benzene ring, but is
chained to the side of the ring. The hydrogen atoms
in the side-chain differ in their affinities from those
attached to the ring; the hydrogen in the ring may
be replaced by groups {e.g. N02) which will not readily
replace the hydrogen of the side-chain. This is a
matter of special interest in relation to the specific
action of poisons, ferments, etc. By substituting
hydroxyl for the hydrogen of the side-chain, benzyl
alcohol, C6H6.CH2.OH, is formed. By introducing
carboxyl, benzoic acid, C6H5.CO.OH, is obtained. It
has been shown above that benzoic acid and glyco-
coll are united in the kidney to form hippuric acid.
Glycocoll is amido-acetic acid, CH2(NH2).CO.OH. It

FERMENTATION 217

unites with benzoic acid by replacing the hydroxy 1 in
the side-chain, thus forming

C6HB.CO.NHx
CO.OH''

HIPPURIC ACID

CH2

Cinnamic acid, toluene, and other aromatic substances
are similarly excreted as hippuric acid when taken
internally.

The reversible action of the kidney ferment is im-
portant in hastening the establishment of the equi-
librium between benzoic acid and glycocoll. If these
two bodies pass through the kidney, a certain amount
of hippuric acid is formed ; if hippuric acid itself
passes through the kidney, a certain quantity is hy-
drolyzed.

Relation of Reversible Action to Absorption of Fat. —
"Pancreatic juice is capable of hydrolyzing all the fat
of a fatty meal in the period of pancreatic digestion.
In the living intestine the hydrolysis should be com-
plete, inasmuch as the removal of the products of the
hydrolysis by absorption prevents the establishment
of equilibrium. On the other hand, the products of
the hydrolysis in their transition through the epithelial
cells come in contact with a lipolytic enzyme, the pres-
ence of which in these cells has been demonstrated in
the above.

" The lipase now finds itself in contact with only
fatty acid and glycerine, and hence in acting catalyti-
cally to bring about the chemical equilibrium, it effects

218 THE INCOME OF ENERGY

the synthesis of a fat. This would offer a satisfactory
explanation of the presence of fat granules in these
cells. As the fatty acid and glycerine diffuse out of
the cells through the basement membrane, the fat
in these cells would speedily disappear were it not that
these substances were constantly being absorbed from
the lumen of the intestine. When absorption ceases,
however, the fat present is at once hydro lyzed by the
lipase present. This hydrolysis is in all probability
complete for the reason that the products of the
hydrolysis, viz., glycerine and fatty acid, are being
constantly removed by diffusion. According to this
view, therefore, no fat ever enters or leaves the epi-
thelial cells as such, but as fatty acid and glycerine.

" These two substances then enter the central
lacteal, where equilibrium is again established and
there is a large production of fat." *

Immunity

Ehrlich's Ricin Experiments.2 — Powder Albert
biscuits weighing 6.75 grams. Add to each cake

1 Kastle and Loevenhart: loccit., p. 522.

2 Ehrlich : Deutsche medicinische Wochenschrift, 1891,
xvii, pp. 976-979.

Ricin is a toxalbumin extracted from the seeds of the castor
oil plant. It is poisonous in the slightest traces. Weight for
weight it is a billion timss more poisonous than corrosive sub-
limate. Intravenous injection of 0.03 milligram (0.00003 gram)
per kilo of body weight is fatal. One gram commercial ricin
would kill one and one-half million guinea-pigs. The effect is
about one hundred times less when taken by the mouth, yet

FERMENTATION 219

3.2-3.5 c.c. of water containing ricin. The be-
ginning content of ricin should be 0.02 gm. ricin
for each cake ; 0.035 gm. is fatal in the course
of five or six days. Mix the biscuit powder and
ricin solution to a stiff dough, roll the dough into
rods, divide them into equal lengths, and dry
the portions quickly on a wire sieve. Determine
the effect on white mice of successively increas-
ing doses, as follows :

DAY DOSE

1

0.002 c

2

. . .

3

0.006

4

0.008

5

. . .

6

0.01

7

0.0125

8

0.015

DAY

DOSE

9

0.02

10

0.03

11

0.04

12

0.05

13

0.06

14

• . .

15

0.08

16

0.01

On the 17th day inject subcutaneously a fresh
mouse with the fatal dose — 1 c.c. of a Ytnfowo so~
lution per 20 gm. of mouse. At the same time

even thus 0.18 gram will kill a full-grown man. The cause of
death is agglutination of red blood corpuscles, and hence
multiple thrombosis, especially of the abdominal vessels.
Clinically, violent diarrhcea and progressive exhaustion are ob-
served. The toxicity is greatly dependent on species. Guinea-
pigs are far more susceptible than white mice. With white
mice the fatal subcutaneous injection is 1 c.c. of a solution con-
taining ^sWiJ ricin per 20 grams of body weight.

220 THE INCOME OF ENERGY

inject the immunized mice with a dose one
hundred times as great.1

Observe the non-immune and the immune mice
for several days and note the results.

Ehrlich continued the above experiment until the
immunized mouse received daily 0.5 gm. of the ricin
by the mouth. Such animals bore safely subcutaneous
injections of z^q and even more. The immunity also
appeared in that solutions of 0.5-1.0 per cent applied
to the eyes of non-immune mice caused violent pano-
phthalmitis, while immune mice bore easily the appli-
cation of 10 per cent solutions.

This absolute local immunity was fully established
when the general immunity had attained only a
middle grade. Normally the subcutaneous injection
of ^ooVou ricm solution causes severe local inflamma-
tion, but thoroughly immunized animals bear toVq.
Quantitative experiments show that the resistance to
the poison is not increased during the first four days,
and the increase is doubtful on the fifth day, but on
the sixth day a relatively high (for example thirteen-
fold) general immunity is suddenly established. The
sudden fall toward normal temperature observed in
diseases with a "crisis," such as pneumonia, may de-
pend on the " critical " establishment of immunity.

Immunity is not increased by continued administra-
tion of the same dose, day by day. An equilibrium
appears to be established.

1 The mice in these experiments must be carefully protected
against cold and wetting.

FERMENTATION 221

The immunity once established endures a consider-
able time ; six months and possibly much longer.

Ricin Antitoxine. — Defibrinate the blood of the
immunized mice. Divide it into two portions.
1. To one portion add ricin solution in such a
ratio that the mixture shall contain yo 0V0 o> *■ e-
twice the fatal amount.

Inject a fresh mouse subcutaneously with 1 c.c.
of this mixture per 20 grams of weight.

The poison will be borne. It has been neu-
tralized by the serum of the immune animal.
This result accords with the discovery of Behring
and Kitasato that immunity in diphtheria and
tetanus depends on the power of the serum to
neutralize the poison.

2. Divide the second portion of the antitoxine
blood among six small test-tubes. To the first
add a few drops yo'oVo o" ri°m solution. To the
others add amounts increasing in a definite ratio.

At first there will be no effect (immunity).
As the amount of ricin added is increased, a point
will be reached at which agglutination of red
corpusles will be produced. This is the neutrali-
zation point.

Evidently, there is a definite quantitative
chemical relation between the toxine and the
antitoxine.

222 THE INCOME OF ENERGY

Theory of Immunity.1 — Jenner discovered the
protective action of vaccinia against small-pox. The
sni all-pox virus when passed through a susceptible
animal becomes attenuated. This weakened poison
introduced into the circulation in man protects the
individual for long periods against the original disease
— it establishes an artificial immunity against small-
pox. Schwann found that fermentation and putre-
faction arose through the agency of micro-organisms
coming from without. Pasteur and Koch demonstrated
that the inoculation of animals with pure cultures of
certain bacteria produced specific infectious diseases,
and that these cultures could be modified at will,
either by passing through the animal body, as in
Jenner's method, or in artificial culture media. Pas-
teur produced artificial immunity by using attenuated
virus. Behring discovered that the blood-serum of
animals immunized against diphtheria contained a sub-
stance which would protect other animals against the
toxine of diphtheria. So also with tetanus. Ehrlich
introduced the quantitative study of toxines and anti-
toxines by means of test-tube experiments, thereby
eliminating the uncertain factor of the animal body.
Thus it was shown in experiments on tetanus toxine
that the action of antitoxines is accelerated by heat,
retarded by cold, dependent on concentration — in
short, that it is a chemical action. In the above ex-
periments on ricin, it is shown that the relation

1 Ehrlich : Croonian Lecture, Proceedings of the Royal
Society, London, 1901, lxvi, pp. 424-448.

FERMENTATION 223

between toxine and antitoxine is quantitative. These
results, obtained by test-tube experiments, have been
confirmed by observations on living animals. Thus it
was established that a fixed quantity of toxine is neu-
tralized by a fixed quantity of its specific antitoxine.

Chemical substances affect only those tissues with
which they are able to come into chemical contact.
They must first reach the tissue. This general law is
illustrated by the experiments of Douitz with tetanus
toxine.1 When the toxine is injected directly into
the circulation and immediately followed by a chemi-
cally equivalent amount of antitoxine, the animal is
not poisoned ; all the toxine circulating in the blood
is neutralized. When the same neutralizing dose is
injected eight minutes after the toxine, death occurs
from tetanus exactly as if no antitoxine had been used.
In these eight minutes a lethal quantity of toxine
must have left the blood and entered the tissues.
This toxine which has entered the tissues may still
for a time be withdrawn by injection of the specific
antitoxine in quantities much greater than the simple
neutralizing dose. The longer the delay, the larger
the saving dose. But after a fixed interval, or "period
of incubation," no amount of antitoxine, however
large, will prevent tetanus. There must, therefore,
be present in the brain or cord (the organ princi-
pally affected by tetanus toxine) certain atom groups
which, like the antitoxine, have a chemical affinity
for the toxine. At the close of the period of incuba-

1 Donitz : Klinisches Jahrbuch, 1900, vii.

224 THE INCOME OF ENERGY

tion the chemical union between these atom groups
and the toxine is complete and the antitoxine is shut
out. Wassermann 1 found that when tetanus toxine
was mixed with fresh brain or cord substance from the
guinea-pig, the toxine united chemically with the nerve
centres so that neither the surrounding liquid nor the
mixture itself was poisonous when injected into an
animal.

The stable benzene ring and the less stable side-chains
of the benzene derivatives 2 suggested to Ehrlich that
living cells also consist of a stable centre and less stable
side-chains. The side-chains enable the cell to form
chemical combinations with food stuffs and other bodies
that possess atom groups having a chemical affinity
with the atom groups in the side-chains. It is in this
way that the toxine is bound to the cell. Experiments
have shown that the binding atoms in the toxine
molecule are not the poison atoms. If for a portion
of fresh toxine there be determined quantitatively (1)
the killing power and (2) the amount of antitoxine
required to neutralize the toxine, and if the remainder
of the toxine be then allowed to stand for a time, it
will be found, on again determining the toxic power
and the combining power, that the toxic power has di-
minished, while the combining power remains almost
the same. Hence, two separate and independent groups
exist. Ehrlich terms the combining atoms the hapto-
phore group, while the poison atoms are the toxophore

1 Wassermann : Berliner klinische Wochenschrift, 1898.

2 Seepage 216.

FERMENTATION 225

group. The haptophore atom group (Sltttw, I cling to)
unites with the antitoxine, if there be any present, or
with any other atom group for which it lias chemical
affinity. If this latter atom group be in the side-chain
of a living cell, its union with the haptophore atoms
of the toxine will necessarily bring the poison atoms of
the toxine into intimate chemical relationship with the
central atoms of the cell. Poisoning will then take
place. If the cells of vital organs have no atom groups
with chemical affinity for the haptophore group of a
toxine, no union between cell-atom group and hapto-
phore takes place, the toxophore is not brought into
intimate contact with the cell, and poisoning does
not occur. The animal is naturally immune to this
particular toxine. Thus a toxine in sausages is exces-
sively poisonous to man, the monkey, and the rabbit,
while even large amounts are not injurious to the
dog.

The haptophore group of the toxine acts immediately
after injection into the organism, while in most or all
toxines the toxophore group becomes active only after
a longer or shorter incubation period. During this
period the animal may often be saved by placing it in
conditions in which the toxophores cannot act. Thus
frogs kept at less than 20° C. are not poisoned by large
doses of tetanus toxine, though much smaller doses are
fatal at a higher temperature (Morgenroth).

The toxophile atom group of the cell was not pre-
destined to unite with a remotely possible toxine, —
it has a normal function, probably that of attaching
food to the cell. When it enters into its firm and

15

226 THE INCOME OF ENERGY

enduring union with the haptophore group of a toxine,
this normal function is lost. Such a loss acts as a
physiological stimulus.1 New side-chains are produced
by the cell, only to unite with fresh toxine. The pro-
duction and the loss of side-chains continue until all
the toxine in the blood is neutralized. By this time
the cell has become habituated to a more than normal
production of these special atom groups. The excess
is cast off like a secretion and circulates in the blood.
These free side-chains, possessing a special affinity for
one specific toxine, constitute the antitoxine of that
toxine.

Their continued production after the neutralization
of all the toxine protects the animal against fresh
toxine, i. e. establishes continued immunity.

It has already been stated that by special means the
toxophore group of a toxine may be weakened or
destroyed while its haptophore group is unchanged.
Such altered and non-poisonous toxines are termed
toxoids. As their affinity for the side-chains of the
cells remains unaltered, the toxoids by continuing to
unite with the side-chains of the cells may stimulate
the production of such side-chains in excess, or, in
other words, may assist in making antitoxine and thus
establishing immunity.

1 Weigert : Deutsche medicinische Wochenschrift, 1896.

fermentation 227

Haemolytic and Bacteriolytic Ferments

Bordet's Experiments.1 — Inject into the perito-
neum of a guinea-pig 10 c.c. defibrinated rabbit
blood on five successive days. After two more
days bleed the guinea-pig and obtain the serum,
by allowing the blood to stand in test-tubes in a
cool place until the shrinking clot has pressed
out the serum.

1. Mix a drop of serum from a fresh guinea-
pig (one not injected with rabbit blood) with a
drop of defibrinated rabbit blood and examine
under the microscope. The corpuscles show a
very slight agglutination, but are otherwise un-
injured. The normal serum of the guinea-pig is
almost inactive upon rabbit blood.

2. A. Mix a drop of the serum from the
injected guinea-pig with a drop of defibrinated
rabbit blood and examine under the microscope.
The corpuscles are strongly agglutinated.2

B. Mix 0.5 c.c. of the serum with 1.5 c.c.
defibrinated rabbit blood.

1 Bordet : Annales de 1'Institut Pasteur, 1898, xii, pp. 692-
694.

2 Agglutinated blood looks granular, especially on gentle
shaking ; the massed corpuscles sink rapidly ; they will not pass
through filter paper. Agglutination of blood corpuscles is
similar to the clumping of the typhoid bacillus in the serum of
a typhoid-fever patient.

228 THE INCOME OF ENERGY

The corpuscles are agglutinated and their hae-
moglobin is set free. The mixture becomes red,
clear and limpid in two or three minutes. With
the microscope nothing can be found but the
stroma of the corpuscles, more or less deformed,
very transparent and scarcely visible.

The continued presence of blood corpuscles
of the rabbit in the blood of the guinea-pig has
developed in the latter the power to agglutinate
the corpuscles and to set free their haemoglobin.
It is thus that the guinea-pig protects itself ; it
acquires immunity.

3. Heat 1 c.c. of serum to 55° C. for half an
hour. Add 0.5 c.c. of this to 1 .5 c.c. defibrinated
rabbit blood as in Experiment 2 B.

The serum which was heated to 55° C. no
longer destroys the corpuscles, but still strongly
agglutinates them.1

Evidently the agglutination of the corpuscles
and the setting free of the haemoglobin (termed
"laking") are effected by different substances.
The agglutinating body resists a temperature that
destroys the blood-laking body.

4. To the mixture used in the preceding experi-
ment, add 2 c.c. of fresh serum from a normal

1 A very slow destruction of the red corpuscles may be ob-
served. This, however, is due to the fresh serum in the 1.5 c.c.
defibrinated rabbit blood, as will be evident from Experiment 4.

FERMENTATION 229

guinea-pig (one that has not been injected with
rabbit blood).

In a few minutes the mixture becomes limpid
and red. The laking power is restored.

Obviously, with the fresh serum was added
the unstable body destructive to red corpuscles.
Ehrlich and Morgenroth have shown that at low
temperatures the stable body unites with the red
corpuscles while the unstable body remains in
the serum ; in this case the haemoglobin is not
set free. At higher temperatures the haemoglo-
bin separates and the unstable body is found to
have left the serum. It has joined the stable
body in the sediment.

Following the side-chain theory already men-
tioned, Ehrlich and Morgenroth assume that the
stable substance has two combining powers;
on the one hand it unites with the red corpus-
cles, on the other with the unstable substance,
thus bringing it to the cell which it may then
destroy.

Immunity against toxines and foreign red cor-
puscles are only two of the protective actions of
the blood. The injection of cells of the most
varied kinds is followed by the production of
specific protective bodies;1 thus, the injection of

1 Metchnikoff: Annales de l'lnstitut Pasteur, 1900, xiv,
p. 369.

230 THE INCOME OF ENERGY

bacteria causes the formation of bacteriolysines,
which destroy the injurious organism.

Many haemolysines and agglutines are found
in plants ; others, for example, the tetanus bacil-
lus, are bacterial; still others, such as snake
venom, are animal secretions.

Oxidizing Ferments

Schdnbein's Experiment.1 — 1. To five c. c. hy-
drogen peroxide add tincture of guiac (freshly
prepared by dissolving guiac resin in alcohol)
drop by drop until the liquid is milky. Now
add from eight to ten drops of a somewhat con-
centrated extract of malt, prepared in the cold.

The guiac will be oxidized and will turn blue.

2. Eepeat the experiment, adding in place of
the malt extract from eight to ten drops of blood.

The guiac will be oxidized, as before.

Further Oxidations by Animal Tissues.2 —
1. Soak strips of bibulous paper in a diluted solu-
tion made as follows :

a-naphthol 1 mol.

sodium carbonate .... 3 "
para-phenylenediamine . . 1 "

1 Schonbein : Zeitschrift fur Biologie, 1868, iv, p. 367.

2 Spitzer : Arcbiv fur die ge.sannnte Physiologie, 1895, lx,
pp. 322-323.

FERMENTATION 231

This solution, left in the atmosphere, oxidizes
slowly to indophenol (violet color).

Place a drop of a known oxidizer, e.g. ferri-
cyanide of potash or potassium bichromate, on
the saturated paper.

The color will change at once, in consequence
of immediate oxidation.

(1) C6FT4(NH2)2 + C10H7OH + 0 =

PARA-PHENYLENEDIAMINE A-NAPHTHOL CcTrLNHo

NH<C10H6OH + H*°

(2) NH<C6H4NH2 + 0 = N<C°H*NH* +H.0

C10H6OH I C10H6O

INDOPHENOL

Each of the combining molecules has been acted
upon by a different oxygen atom; hence the oxy-
gen molecule must have been split.

2. Eub the test paper with finely divided tissue
from the liver or any other organ.

Oxidation will occur.

A drop of blood placed on the test paper is
soon surrounded by a characteristically colored
ring.

Extraction of Nucleo-Proteid from Liver} —
Perfuse a fresh liver (dog) with tap water until
the washings are no longer colored by haemo-

1 Spitzer : Archiv fur die gesammte Physiologie, 1897, lxvii,
p. 616.

232 THE INCOME OF ENEEGY

globin. Grind the liver to a pulp and press
through several thicknesses of gauze. Add five
volumes of distilled water. Allow the mixture
to stand twenty-four hours at low temperatures.
Remove the opalescent watery extract with a
pipette and filter through linen. Demonstrate
with the microscope that liver cells are absent
from the liquid. Add T^ HC1 drop by drop until
there is no further precipitation, and the super-
natant fluid is clear. Since the precipitate redis-
solves in acid, use lacmoid as an indicator. Cease
when the lacmoid shows a trace of excess. De-
cant the precipitate, filter, wash the residue with
water.

Oxidation by Nucleo-Proteid. — Place in a wide-
necked flask 50 c.c. water containing 0.2 gram
of the fresh, brown substance and 10 c.c. hydro-
gen peroxide in a small glass cup. The hydrogen
peroxide must be neutralized with from 1 to 1.5
c.c. {\ NaOH. Connect the flask with the lower
end of a eudiometer by means of a bent tube.
Shake the flask so that the hydrogen peroxide
shall come in contact with the tissue. Oxygen
is at once set free. Kead in the eudiometer
the oxygen developed from minute to minute.
Spitzer found :

After minutes . . 1 2 3 4 5 8 9 1G
C.c. 02 developed 19 28 41 55 69 85 87 95

FERMENTATION 233

Oxidation about the Nucleus.1 — Introduce the
oxidizable solution of a-naphthol and para-phe-
nylenediamine (page 230), beneath the cover
glass of a fresh preparation of teased thymus
or spleen.

" Granules of the intense greenish-blue oxi-
dation product shortly make their appearance
within the leucocytes. Their first appearance is
typically at the boundary between nucleus and
cytoplasm ; eventually the latter may become
so densely laden as completely to obscure the
nucleus. . . . The nucleus is the chief agency in
the intracellular activation of oxv^en. The ac-
tive or atomic oxygen is in general most abun-
dantly freed at the surface of contact between
nucleus and cytoplasm."

Glycolysis in Blood. Bernard's Experiment? —
125 c.c. dog's blood were divided into five equal
parts. The sugar in each was estimated as
follows :

Sugar
Grams per 1000.

1.07

1. Analysis made at once

2. " " after 10 minutes

3. " " " 30 "

4. " " " 5 hours .
5 (t " " 24 "

1.01

0.88
0.44
0.00

vii, p. 420.

1 Lillie : American journal of physiology, 1902,

2 Bernard : Comptes rendus de 1'ae.ademie des sciences, Paris,
1876, lxxxii, p. 1406.

234 THE INCOME OF ENERGY

Sugar disappears from the blood on stand-

ing.

It has been found by Lepine and Barral 1 that
the glycolytic power of the blood increases as the
temperature rises to 52.5° C, which is the opti-
mum. At 54° the ferment is destroyed.

Oxidation not Dependent on Living Cells of Blood.
— Place the following solutions at 34-35° C. for
six hours, allowing a stream of air to pass through
the. liquid. Then estimate the sugar.2

A. Calf's blood 100 c.c.

Water containing 1.14 gram grape sugar 10 c.c.
Seegen 3 recovered 1.000 gram.

1 Lepine and Barral : Comptes rendus de l'academie dea sci.
ences, Paris, 1891, cxii, p. 146.

2 Test the filtrate by adding a drop of acetic acid and a little
ferrocyanide of potassium.

The absence of a precipitate shows freedom from proteids and
ferric salts. Concentrate filtrate to 150-200 c.c.

Titration of the Sugar Extract. — Make the volume of the
solution such that its probable content of sugar shall lie
between 0.0004 and 0.0010. Causse (Bulletin de la Societe
chimique de Paris, 1, p. 625) recommends that 1750 c.c. of
water containing 5 grams of ferrocyanide of potassium be added
to each 250 c.c. of Fehling's solution. Boil 10 c.c. of this
mixture, and add the sugar solution drop by drop until the bin*
liquid is decolorized (Arthus : Archives de physiologie, 1891,
p. 425).

3 Estimation of Sugar in Blood. Extraction of the Sugar
from the Blood. — To 350-400 c.c. boiling water add all at once
50 c.c. blood containing 5 c.c. one per cent acetic acid. Let

FERMENTATION 235

B. Calf's blood 100 c.c.

Water containing 1.14 gram grape sugar 10 c.c.

Chloroform 1 c.c.

Seegen recovered 0.960 gram.

The chloroform destroys the cells, but fails to
check the oxidation.

Relation of Glycolysis to the Pancreas and the
Lymph.1 — Remove the pancreas aseptically from an
anaesthetized dog which has fasted thirty-six hours.
Estimate the sugar in the urine at intervals of a few-
hours.

Sugar will be present in large and increasing quanti-
ties,2 rising even to twenty per cent.

Inject into the jugular vein 15-20 c.c. of lymph
from the thoracic duct of a dog fed a few hours before
upon one litre of milk.

the mixture boil for a few minutes. Filter through a small
linen cloth.

Separation of Proteids. — Boil the filtrate. Most of the pro-
teids will separate by coagulation. The remainder, if necessary,
may be removed by adding to each 300 c.c. of filtrate, 5 c.c.
saturated solution of sodium acetate, and a small quantity of a
dilute solution of ferric chloride, neutralizing almost completely
with dilute soda solution, and boiling. The ferric chloride will
precipitate as ferrous chloride and will carry down the last
traces of proteid substances. Filter. Wash with boiling water.
(Seegen : Centralblatt fur Physiologic, 1891, v, p. 824.)

1 Lepine : Comptes rendus de l'academie des sciences, Paris,
1890, ex, p. 742.

2 Von Mering and Minkowski : Archiv fur experimentelle
Pathologie und Pharmakologie, 1890, xxvi, p. 371.

236 THE INCOME OF ENERGY

The glycosuria will greatly diminish.

After a few hours, the glycosuria will become once
more intense, continuing until death. The quantity of
sugar in the blood is also greatly increased.

Glycolytic Ferment of Pancreas.1 — Remove the

pancreas aseptically from a dog immediately after
death. Crush it at once in 100 c.c. sterile water
containing 0.2 gram sulphuric acid. Allow it to
macerate two hours at 38° C. Neutralize the
acid with soda, add 0.5 gram pure glucose, and
keep the mixture one hour at 38° C. Estimate
the sugar.

The loss will be from ten to fifty per cent.

When pancreatic extract made without acid is used,
the loss of sugar is much less. Probably, therefore,
the glycolytic ferment is produced from a zymogen by
hydration.

Malt diastase, or salivary diastase, kept three hours
at 38° in water containing one tenth per cent sulphuric
acid loses the power to change starch to sugar, but ac-
quires a glycolytic power.

If the pancreatic juice which flows upon stimulation
of the peripheral end of the vagus (Pavvlow) is treated
with dilute acid, 1 : 1000, the amylolytic power is lost,
but glycolytic power is acquired. During the excita-
tion of the nerve — while the juice is flowing — the

1 Lepine : Comptes rendus de l'academie des sciences, Paris,
1895, cxx, p. 139.

FERMENTATION 237

blood in the pancreatic vein has almost no glycolytic
power; after the juice ceases to run, the blood has
considerable glycolytic power. Here the external is
balanced against the internal secretion of the pancreas.

Oxidative ferments are very widely distributed both
in animals and plants. The above experiments show
their presence in the blood; pancreas, liver, and lymph.
They are present also in the urine.

The stomach contains a ferment that oxidizes lactose
to lactic acid.1

Urushi, the milky secretion of Rhus vernicifera, dries
in the air to a translucent varnish (Japanese lacquer).
It contains urushic acid, which does not dry sponta-
neously, and a ferment, the addition of which to
urushic acid causes the latter to dry to lacquer. A
sample of fresh juice boiled to stop the action of the
ferment on urushic acid contained 15.01 per cent
oxygen ; lacquer dried in the usual manner contained
20.52 per cent oxygen.

Many oxidations are effected by the tissues without
the aid of ferments, so far as is yet known. These be-
long properly to metabolism, but in passing, it may be
noted that while substances exceedingly resistant to
oxidation, for example, proteids, are oxidized in the
body, other substances very easily oxidizable may be
excreted unchanged ; oxalic acid is one of these.2

1 Hammarsten : Maly's Jahresbericht der Thierchemie, 1872,
ii, p. 118. (Original in Swedish.)

2 Pohl : Archiv fur experimentelle Pathologie und Pharraa-
kologie, 1896, xxxvii, p. 413.

238 THE INCOME OF ENERGY

Hoppe-Seylers Theory.1 — Living tissues consist of
easily combustible reducing substances, which split
the oxygen molecules, taking to themselves one atom
of 0 and setting the other free in active state to
unite with any oxidizable substance present.

Traube's Theory.2 — In living protoplasm oxygen is
rendered active by an oxidizing ferment, which brings
the oxygen to bodies ordinarily oxidizable only by such
powerful agents as heat and strong alkalies.

Inorganic bodies, e. g. platinum black, the oxides of
copper, silver, mercury, and vanadium, and certain iron
salts similarly act as oxygen carriers. Thus

(1) Pt + 02 + H2 = PtO + H20

(2) PtO + H2 = Pt + H20

The oxygen carrier reduces H202, takes one atom 0
to itself, then gives off this atom in an active or
nascent state to oxidize any oxidizable compound
present ; e. g. guiac. Grape sugar takes 0 from
indigo-blue, producing thereby indigo-white. The
indigo-white oxidizes itself to indigo-blue, then gives
up another atom of 0, and so on.

Alcoholic Fermentation
The Yeast Plant. — Observe a solution of sugar
undergoing alcoholic fermentation.3 Note the
bubbles of gas, the scum, the sour odor.

1 Hoppe-Seyler: Zeitschrift fur physiologische Chemie, 1879,
ii, p. 1.

'2 Traube : Berichte der deutschen chemischen Gesellschaft,
1883, xvi, pp. 123, 1201, and earlier papers in volumes x and xv.

8 The fermentation is assisted by providing the yeast plant

FERMENTATION 239

Examine some of the mixture under the micro-
scope. Xote the multitude of globular or slightly
ovoid bodies, the largest about T^o mm- m diame-
ter. They are motionless. Many have put forth
buds. They seem to be plants in active growth.1

1. Place 300 c.c. of the nutrient liquid (Ex-
periment 1) in a flask holding 500 c.c. Add a
piece of fresh compressed yeast the size of a pea.
Place the flask in a temperature of 35° C.

Note that as fermentation advances the yeast
increases in quantity.

2. Place a small piece of fresh compressed
yeast in a test-tube. Fill the tube with nutrient
liquid and invert it in a dish of similar liquid. The
tube may be kept upright by a elamp. Let the
mixture stand twenty -four hours in a warm room.

with the salts present in the ash of yeast (Pasteur). A useful
substitute is

Potassium phosphate ... 20 gms.

Calcium phosphate ... 2

Magnesium sulphate ... 2

Ammonium tartrate . . . 100

Cane sugar 1,500

Water 8,376

10,000
(Practical biology, Huxley and Martin.)
1 Cagniard-Latour : L'Institut, 1835, iii, p. 150 ; also Annales
de chimie et de physique, 1838, Ixviii, p. 206. The yeast plant
was first observed microscopically in beer-yeast by Leeuwen-
hoek, 1680, but he did not associate fermentation with the
growth of the yeast.

240 THE INCOME OF ENERGY

The tube will fill with gas. With a bent pipette
introduce about 1 c.c. of a solution of sodium
hydroxide (sp. gr. 1.12 = 11 per cent). The gas
will be absorbed, with formation of sodic carbon-
ate, and the liquid will rise in the tube.

The growth of the yeast plant is accompanied
by the production of carbon dioxide.

3. Eeturn to Experiment 1. After the fer-
menting liquid has ceased to give off gas, place a
stopper with a bent tube in the mouth of the
flask and distill the contents of the flask in a
water bath. Condense the first fifth of the dis-
tillate. Saturate this with sodium carbonate.
Eedistill, and condense.

Test for alcohol by warming the distillate with
potassium dichromate and dilute sulphuric acid,
whereby the alcohol will be oxidized to aldehyde,
with characteristic odor.

Alcohol is present.

The production of alcohol by the yeast is the work
of the ferment zymase.1 This body is closely bound
to the protoplasm of the cell, very easily destroyed, not
produced in excess, and not secreted free. Only sugars
containing three, six, and nine carbon atoms are at-
tacked. The saccharobioses must be " inverted " be-
fore they can be fermented. Thus, cane sugar must

1 Buchner : Berichte der deutschen cheuiischen Gesollscliaft,
1897, xxx, pp. 117, 1110, 2668.

FERMENTATION 241

first he inverted to grape sugar by invertin,1 and
malt sugar by maltase. Lactase is present in some
yeasts, enabling them to ferment milk sugar. Diastase
is also found.

The action of these several ferments becomes clear
when the chemical nature of the carbohydrates is
recalled.

Chemical Relations of Carbohydrates. — Carbohy-
drates were formerly defined to be compounds con-
taining six, or a multiple of six carbon atoms, together
with hydrogen and oxygen atoms in the proportion in
which they exist in water. The researches of E.
Fischer have shown that all aldehydes (bodies which
are the first oxidation products of primary alcohols, and
which contain the carbonyl group CO) and all ketones
(bodies which are the first oxidation products of second-
ary alcohols and which likewise contain the carbouyl
group CO) contain carbon, hydrogen, and oxygen, there
being two atoms of hydrogen to one atom of oxygen,
as in water.

The carbohydrates, therefore, no longer occupy an
isolated position, but are to be classed with the fats,
being methane derivatives in which the carbon atoms
are arranged in an open chain; thus, grape sugar is an
aldehyde alcohol, and fruit sugar a ketone alcohol.

The carbohydrates are divided, according to the size
of their molecule, into monosaccharides, disaccharides,
and polysaccharides. The monosaccharides (e. g. grape

1 For extraction, see Lea : Journal of physiology, 1885, vi,

p. 142.

16

242

THE INCOME OF ENERGY

sugar) are the first oxidation products of the hexahy-
dric alcohols ; the higher carbohydrates are anhydrides
of the monosaccharides. Most of the higher carbohy-
drates cannot be fermented directly, but must first
be hydrolyzed (i. e. take up water). This hydrolysis
may be accomplished by the prolonged action of dilute
acids at high temperatures, by the action of water at
still higher temperatures, or by specific ferments, e. g.
diastase, at the relatively low temperature of the body.
The polysaccharides, consisting of the starches, the
gums (e. g. dextrine or starch gum) and the celluloses
(wood fibre) differ greatly from the lower carbohy-
drates. The polysaccharides are usually amorphous
and are not easily soluble in water.

Carbohydrates.1

Glucoses, Monoses
C6H1206.

Saccharobioses

Polysaccharides

(C6H10O5)x.

Grape sugar —

—

-Malt sugar —

— Starch

Grape sugar —

—

Grape sugar —

—

-Cane sugar

Fruit sugar —

Grape sugar —

— ■

Milk sugar

Galactose —

"

—Dextrine

1 Richtci's Organic Chemistry, Third American Edition, i,
p. 121.

FERMENTATION 243

The zymase attacks only those sugars which present
a specific stereo-configuration. The position of their
atoms in space must fit the position of the atoms of
the ferment (the lock and the key). Thus, only the
dextro-rotatory forms of the aldehyde sugars (d-glu-
cose, d-mannose, d-galactose) are attacked ; the sugars
that rotate the plane of polarized light to the left
are not attacked. It is probable that the zymase
of different species of yeast presents characteristic dif-
ferences. It is known that the products formed in the
fermentation of sugar by different species of yeasts are
to a large degree characteristic. Often these products
are injurious. Upon this specific action of ferments
rests the work of Hansen,1 who taught the brewers to
make pure cultures of the most favorable species of
yeast, and thereby raised the brewing industry to the
level of an applied science.

Activating Ferments

Enterokinase. — In 1899, Chepowalnikow, 2 in
Pawlow's laboratory, found that pancreatic juice
obtained by Pawlow's 3 method contain ed very

1 Hansen : Untersuckuugen an der Praxis der Gahrungs-
Industrie, 1895.

2 Chepowalnikow.: Thesis (Russian), St. Petersburg, 1899,
Paris, 1901.

3 In Pawlow's method the intestine is resected and the
portion of the intestinal wall containing the opening of the
pancreatic duct is stitched to the edges of the abdominal wound,
where it soon unites ; the pancreatic duct then discharges upon
the surface of the abdomen, where the juice may be caught by
applying a suitable vessel.

244 THE INCOME OF ENERGY

little trypsin and had a correspondingly slight
action on proteids. When intestinal juice was
added to this pancreatic juice, the pancreatic
juice at once became active in proteid digestion.
Pawlow called the activating body enterokinase.1
In 1902, Delezenne and Frouin 2 found that
pancreatic juice obtained by catheterizing the
pancreatic duct contained no trypsin whatever;
their procedure prevented any contact between
the juice and the intestinal mucous membrane
at the orifice of the pancreatic duct. It has been
shown that enterokinase is a ferment, secreted
in the small intestine, and that it converts tryp-
sinogen contained in pure pancreatic juice into
trypsin, the active proteid ferment.

Preparation of Enterokinase. — Scrape lightly
with the handle of a scalpel the upper part of
the mucous membrane of the small intestine
(dog or cat). Digest the scrapings during two
days in a closed vessel of water to which a few
drops of chloroform have been added to prevent de-
composition. Filter through paper, then through
a Berkefeldt filter. The resulting solution is
perfectly clear, contains a certain amount of
coagulable proteid, and will retain its activity

1 Pawlow : The Work of the Digestive Glands, translated
by W. H. Thompson, 1902, p. 160.

2 Delezenne and Frouin : Comptes rendus de la societe
de biologic, Paris, 1902, pp. 691-693.

FERMENTATION 245

at room temperature for many months. It is
rapidly destroyed at 35°-40°C.1

Conversion of Trypsinogen to Trypsin by En-
terokinase. — Place 5 c.c. of 0.25 per cent solution
of sodium carbonate in each of two test-tubes
A and B, containing gelatine prepared by Fermi's2
method. To A add a few drops of pure pancreatic
juice ; 3 to B add the same quantity of pure pan-
creatic juice and a few drops of enterokinase.
Place at a temperature of 30°-35° C. The pure
juice will not act on it, but the juice to which
enterokinase was added will dissolve the gelatine.
In order to determine accurately the amount of
gelatine dissolved, the tubes often must be cooled
to 10° C.

Absorption of Proteids

Diffusion of Proteids through Dead Membrane.

— Bend a cylinder of parchment paper and fasten
the ends to a glass rod. Place in the parchment
tubes thus formed 25 c.c. of each of the follow-

1 Bayliss and Starling: Journal of Physiology, 1903,
xxx, p. 80.

'2 Fermi and Repetto : Central blatt flir Bakteriologie und
Parasitenkunde, 1902, xxxi, p. 404. Narrow glass tubes, pref-
erably graduated, are tilled one half full of gelatine (5 to 10
per cent) containing one per cent of sodium fluoride.

3 Obtained by catheterizing the pancreatic duct of the rabbit
(Rachford's method), Journal of Physiology, 1891, xii, p. 81.

246

THE INCOME OF ENERGY

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FERMENTATION

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248 THE INCOME OF ENERGY

ing solutions : 1 (1) Egg-albumin, (2) Myosin, (3)
Alkali-albumin, (4) Peptones. Suspend the egg-
albumin and the peptone in vessels containing
one litre of normal saline solution (0.8 per cent
sodium chloride) ; the alkali-albumin in one litre

1 Preparation of egg-albumin. — Thoroughly mix the whites
of twelve or more eggs with saturated solution of magnesium
sulphate at 20° C. Filter from the precipitated globulin.
Saturate the filtrate at 20° C. with sodium sulphate. Filter
the precipitated albumin. Press in filter paper. Dissolve in
water. Dialyse until the dialysate is free from sulphates.
(Starke, quoted by Haminarsten : Lehrbuch der physiologischen
Chemie, 1897, p. 372.) Determine the albumin in a measured
quantity of the solution, as follows.

Quantitative Estimation of Egg -albumin. — To 25 c.c. of the
albuminous liquid add an equal quantity of 4 per cent sodium
chloride solution. Neutralize exactly. Boil 5 c.c. of this mix-
ture in a test-tube. To the boiling liquid add one drop of acetic
acid from a burette. Filter from the precipitated proteid. Pour
the filtrate carefully down the side of a conical glass containing
about 5 c. c. concentrated nitric acid, so that the lighter liquid
rests on the heavier acid. If the surface of separation remain
clear, all the albumin in the 5 c.c. was precipitated by adding
to the boiling liquid one drop of acetic acid. If a white ring
form, albumin is still present (Heller's test). In this case boil
a fresh portion (5 c.c), add two drops acetic acid, filter, and
test the filtrate. Determine in this way how much acetic acid
must be added to each 5 c.c. of the albuminous liquid to pre-
cipitate all the albumin when the liquid is boiled. Heat 25 c.c.
of the remaining portion of the albuminous liquid in a water
bath. Add slowly with constant stirring the calculated quan-
tity of acetic acid. Heat ten minutes longer. Filter through
weighed paper. Test filtrate once more for albumin. If none be
present, wash with water, alcohol, and ether, dry at 40°, weigh,

FERMENTATION 249

of 0.1 per cent sodium carbonate solution ; and
the myosin in one litre of 5 per cent sodium
chloride solution.

After three hours determine the amount ot

subtract the weight of the filter. There remains the weight of
the albumin in 25 c.c. of the original solution.1

Preparation of Myosin. — Use muscle containing little blood
(calf, rabbit, fowl, frog). Hash the muscle. Wash with water
until the washings are free from proteid. Remove excess of
wash water by pressure. Mix with enough 15 per cent solu-
tion of ammonium chloride to cover the mass. After four hours,
filter through cloth and then through paper. The filtrate should
be clear, opalescent, somewhat thick. Dialyse in running water.
As the neutral salt is removed, the myosin will separate in fine
flocks (Danilewsky). Redissolve in 5 per cent sodium chloride
solution.

Quantitative Estimation of Myosin. —Dialyse 25 c.c. of the
saline solution of myosin until the dialysate is free from salt.
Wash the precipitated myosin into a tall narrow beaker. When
the myosin has settled, decant as much of the supernatant liquid
as possible. To the remainder add alcohol in such proportion
that the mixture shall contain 80 per cent. After coagulation,
filter through a weighed filter. Wash with alcohol and ether.
Dry at 100°. Weigh. Subtract the weight of the filter.

Preparation of Alkali-albumin. — Warm the whites of twelve
or more eggs with 1 per cent sodium hydrate at 40° C. Filter.
Neutralize very cautiously with hydrochloric acid, at first 1 per
cent, later 0.1 per cent. The alkali-albumin will be precipi-
tated. Allow to stand several hours. Filter. Boil the filtrate.
Filter from the fresh precipitate and add residue to first pre-

1 Literature. — Ku'hne: TJntersuchungen liber das Protoplasma, 1864,
p. 2. Danilewsky : Zeitsehrift fiir physiologische Chemie, 1881, v. p. 15S.
Halliburton : Journal of Physiology, 1887, viii, p. 132. Kuhne and
Chittenden : Zeitsehrift fiir Biologic, 18S9, xxv, p. 358.

250 THE INCOME OF ENERGY

proteid in each tube and state the per cent that
has passed through the membrane.

Diffusion through Living Intestinal "Wall.1 —
Through a small opening in the linea alba of a
fasting anaesthetized cat2 draw out a loop near
the middle of the small intestine. Eemove the
contents by careful stroking. Tie double liga-
tures 0.5 cm. apart around the intestine at one
end of the loop and similar ligatures at a point
30 cm. from the first pair. With a hypodermic

cipitate.1 Wash with water. Redissolve in water containing
0.1 per cent sodium hydrate.

Quantitative Estimation of A Hcali- albumin. — Neutralize a
measured quantity of the solution. Separate the neutralization
precipitate upon a weighed filter. Wash with water, alcohol,
and ether. Dry and weigh.

Preparation of Peptones. — The separation of peptone from
the albumoses2 with which it is obtained in the tryptic diges-
tion of proteids is so difficult that it should not be attempted
in these experiments. Add commercial peptone, often contain-
ing albumoses as an impurity, to a small quantity of boiling
neutral distilled water. Filter.

Quantitative Estimation of Peptone. — To 10 c.c. of the liquid
add alcohol in such proportion that the mixture shall contain
80 per cent. Filter through weighed filter paper. Dry at
40° C. Weigh. [This method is not exact, but is to be pre-
ferred for the purpose in hand.]

1 Voit and Bauer : Zeitschrift fiir Biologie, 1869, v, p. 562.

2 These and subsequent operations will be done by an in-
structor assisted by a committee of the class.

1 Hawk and Oies : American Journal of Physiology, 1902, vii, p. 4C0.

2 Kuhne : Zeitsclirift fiir Biologic,, 1892, xxix, p. 1.

FERMENTATION 251

needle attached to a burette inject into the
loop sufficient egg-albumin solution to distend it
slightly. Measure the volume of the solution
injected. The content of this solution was found
in the course of the experiment on diffusion
through dead membranes (page 245).

Eeplace the loop in the abdomen. At some
distance from this loop prepare a control loop
with double ligatures in the same way, but leave
the control loop empty. Sew up the abdominal
wound.

After three hours, kill the animal (best by
puncture of the spinal bulb). Eemove the loops
by cutting between the double ligatures. Eapidly
wash the outer surface with water, dry the sur-
face with filter paper, open the loops, measure
the volume of the contents, wash the inner sur-
face, add the washings to the contents, and
estimate the proteid in a measured portion.

Perform a similar experiment with solutions of
(2) myosin, (3) alkali-albumin, and (4) peptone.

Compare the results of absorption of proteids
through the living intestinal wall with absorp-
tion through dead membranes. It will appear
that the living cells of the intestinal wall modify
absorption so that it does not follow the law of
diffusion through dead membrane.

It is also evident that egg-albumin, myosin,

252 THE INCOME OF ENERGY

alkali-albumin, and peptone may be absorbed
unchanged. Indeed, the absorption of alkali-
albumin is almost or quite as complete as that
of peptone. The conversion of proteids to
peptones is advantageous but not essential to
absorption.

Absorption Velocity Compared with Diffusion
Velocity.1 — Prepare a cat as in Experiment 2.
Fill one intestinal loop with a measured quantity
of 5 per cent dextrose solution, the other with
0.25 per cent solution of sodium sulphate. After
one hour kill the animal, measure the liquid re-
maining in the two loops and estimate its content
in dextrose and sodium sulphate respectively.2

The dextrose solution will be found to have
been largely or completely absorbed, while rela-

1 Rohmann: Archiv fur die gesammte Physiologie, 1887,
xii, p. 456.

2 The quantitative estimation of dextrose is described in
"Experiments for Students in the Harvard Medical School,"
third edition, p. 38.

Quantitative Estimation of Sodium Sulphate. — Boil the solu-
tion, make the reaction acid with a few drops of hydrochloric
acid, add hot solution of barium chloride in slight excess (until
barium sulphate ceases to be precipitated). Boil a few minutes.
Wait for the precipitate to settle. Decant the clear liquid
through a filter, the ash of which is of known weight. Boil the
precipitate in the beaker repeatedly with water. Place the pre-
cipitate on the filter. Wash with boiling water. Dry. Heat to
redness in a weighed crucible. Weigh when cold. (The atomic
weights are: barium, 137.4; sulphur, 32.06; oxygen, 16.)

FERMENTATION 253

tively little of the sodium sulphate will have
left the intestine. Yet sodium sulphate is some-
what more diffusible than dextrose.1

Assimilable Proteids. — With a catheter re-
move the urine from the bladder of an anaesthe-
tized female cat, and apply Heller's test for
albumin (page 248). Albumin should be absent.
Slowly inject into the jugular vein 25 c.c. of
solution of alkali-albumin (page 249) at the tem-
perature of the body. Test the urine for albumin
twice, at intervals of half an hour.

No albumin will be found. The alkali- albumin
has not been removed from the blood by the
kidneys.

Non- Assimilable Proteids. — Perform a similar
experiment on another cat, injecting solution of
egg-albumin instead of alkali-albumin.

Albumin will be found in the urine. Egg-
albumin, present in the blood, is at once re-
moved by the kidneys. It cannot be used unless
changed ("digested") in the intestine.2 Albu-
moses and peptones are also non-assimilable ;
they produce a dangerous fall in blood-pressure.

1 Compare Hoffmann: Eckhard's Beitrage zur Anatomie
und Physiologie, 1860, ii, p. 65.

2 Munk, J., and M. Lewandowsky (Archiv fur Physiologie,
1899, Supplement, pp. 73-88) find the non-assimilable proteids
of Neumeister (not including albumoses and peptones) may be
assimilated if injected very slowly into the blood.

254 THE INCOME OF ENERGY

Alimentary Albuminuria. — Test the urine of a
human subject for albumin at half-hour intervals.
After the first test let the subject swallow the
whites of six raw eggs.

Albumin will probably be found. In many
subjects a portion of any unusual quantity of
egg-albumin may be absorbed unchanged into the
blood, whence it is removed by the kidneys.

Albumose and Peptone not ordinarily Present
in the Blood or Urine. — Dissolve as completely
as possible ten grams of commercial peptone,
which contains albumose as an impurity, in a
small quantity of water. Boil. Filter. Measure
the filtrate.

Through a small opening in the linea alba of a
fasting anaesthetized cat draw out a loop near the
middle of the small intestine. Kemove the con-
tents by careful stroking. Tie double ligatures
0.5 cm. apart around the intestine at one end of
the loop and similar ligatures at a point 30 cm.
from the first pair. With a hypodermic needle
inject into the loop sufficient peptone solution to
distend it slightly. Measure the amount injected.
Replace the loop in the abdomen and close the
wound. Keep the animal in a cage arranged to
collect voided urine.

After two hours, withdraw the urine from the
bladder and add it to any that may have been
spontaneously voided.

FERMENTATION 255

Bleed the animal from the carotid artery, re-
ceiving the blood into an equal volume of satu-
rated solution of ammonium sulphate, to prevent
coagulation. Kemove the intestinal loop by cut-
ting between the double ligatures. Measure the
liquid remaining in the intestine. It will be
found that most of the peptone has disappeared.
Test the blood and the urine for peptone 1

1 Recognition of Peptone in Blood. — To the blood already-
mixed with an equal volume of ammonium sulphate solution
add crystals of ammonium sulphate to saturation. Filter from
the precipitated proteids. To the clear filtrate apply the biuret
test for peptone.

Biuret reaction. — To the saturated ammonium sulphate
filtrate add half its volume of saturated solution of potassium
hydrate. Shake the dense precipitate. Allow the tube to
stand two or three minutes until the heat developed by the
chemical action passes off. Add a drop of very dilute solution
of cupric sulphate. The fluid, dense white from the precipitated
salts, assumes a pale blue color, due to the solution of hydrated
cupric oxide in the ammonia generated. The same quantity of
saturated potassium hydrate as before is now allowed to flow
down the tube, and to form a layer at the bottom. If peptone
is present a rose red ring is formed at the junction of the two
layers. The contrast of the red ring with the pale blue above
it renders the test very delicate (Neumeister's method modified
by Shore : Journal of Physiology, 1890, xi, pp. 532-534).

Recognition of Peptone in Urine. — Remove the coloring
matter by (1) adding solid lead acetate and filtering from the
heavy precipitate ; (2) adding to the filtrate ammonium sul-
phate, and filtering from the copious precipitate of lead sulphate ;
(3) saturating the filtrate with crystals of ammonium sulphate
and filtering from the additional precipitate. On filtration the

256 THE INCOME OF ENERGY

with the biuret reaction. No peptone will be
found.1

An examination of the lymph would show
that it also contains no peptone. Apparently
the peptone absorbed from the intestinal loop is
changed in its passage through the intestinal
wall. This conclusion is made secure by the ex-
periments of Salvioli,2 who removed the jejunum
of the dog or rabbit, tied a cannula in the mesen-
teric artery and vein, and established through
these vessels an artificial circulation of defibri-
nated blood diluted with isotonic saline solution.
One gram of peptone was dissolved in 10 c.c. of
normal saline solution and placed in the intes-
tine, and the artificial circulation maintained four
hours. The peptone disappeared from the intes-
tine, but none could be found in the blood.

Albumose and Peptone changed in their Passage
through the Intestinal "Wall. — - Kill a fairly large
anaesthetized rabbit by bleeding. Beat the blood

solution is free from lead, but usually still contains a trace of
yellow pigment. Apply the biuret reaction as above. If the
urine requires to be concentrated, it is better to evaporate the
final ammonium sulphate filtrate, as boiling the urine at first
deepens the color. (Neumeister and Shore, lot. cit.)

1 Neumeister: Zeitschrift fur Biologie, 1888, xxiv, pp.
278-279.

2 Salvioli : Archiv fur Physiologic, 1880, Supplemental
volume, p. 112.

FERMENTATION 257

until all the fibrin separates. Filter through
gauze into a cylinder holding 100 c.c. To the
30 c.c. defibrinated blood add 30 c.c. sodium
chloride solution (0.5 per cent) containing 0.6
gram salt-free peptone. The mixture will thus
contain 1.0 per cent of peptone. Eeserve 5 c.c.
of the mixture. Place the rest in a half-litre
flask, provided with a stopper pierced by two
glass tubes, one reaching to near the bottom
of the flask, the other ending just beneath the
stopper so that air may be drawn through the
blood-peptone solution by an aspirator. Place
the flask in a beaker with a heavy iron ring
around the neck to prevent the flask being driven
upward, fill the beaker with water at 40° C. and
place it in a water bath also at 40°.

Separate the intestine carefully from the mes-
entery and especially the pancreas. Slit the
intestine from the pylorus to the ilio-csecal valve
with scissors, cut it into several pieces, wash it
in a large water-bath filled with 0.5 per cent
sodium chloride solution at 40° C. Eepeat the
washing in a second and a third bath. Cut the
intestine into finger-lengths. Collect the pieces
on a porcelain sieve, wash them with 1 per cent
peptone solution, and then place them in the
blood-peptone solution. Draw air through the
solution, with every possible care against foam-

17

258 THE INCOME OF ENERGY

ing. These several operations, beginning with
the bleeding of the rabbit, should take not more
than fifteen minutes.

After two hours interrupt the experiment,
pour the solution through a sieve, stir into the
filtrate solid ammonium sulphate to saturation,
filter off about 10 c.c., add to the water-clear fil-
trate an equal volume of absolute sodium hydrate
(70 per cent), stir thoroughly with a glass rod,
and let the precipitated sodium sulphate settle.

Add to the clear liquid drop hy drop 2 per
cent cupric sulphate solution. No biuret reaction
will be obtained, but the liquid will show at once
a pure blue color.

Eepeat the test, with the same quantitative
relations, upon the reserved 5 c.c. of the blood-
peptone solution : a purple color will be obtained.

Hence the not inconsiderable quantity of pep-
tone in the blood covering the pieces of intestine
lias disappeared.

Rub the pieces of intestine with sand to a
pulp, boil with as little water as possible, saturate
with ammonium sulphate, and test as before.

No biuret reaction will be obtained. Hence
the peptone which disappeared from the blood-
peptone solution is not stored in the intestine.1

1 NbUMBISTER : Zcitschrift fur Biologie, 1890, xxvii, pp. 324-
327.

FERMENTATION 259

Cohnheim 1 attempted to find in the intestinal
wall the peptone which disappears from the
intestine without enterinG: the intestinal blood
and lymph. His failure led him to the dis-
covery of a new ferment Erepsin (epziTrw, I de-
stroy), the action of which is to split peptone into
crystallizable substances. This ferment, which is
found in many tissues, was isolated by fractional
precipitation with ammonium sulphate. Two
parts of intestinal extract were mixed with three
parts of concentrated ammonium sulphate. The
resulting thick precipitate, consisting largely of
proteid was dialyzed, and the erepsin found in
the dialysate.

The disappearance of peptone from the intes-
tine is probably therefore not to be explained by
the assimilation of the peptone or its reconver-
sion into other forms of proteid, but by the split-
ting of the peptone through the action of the
ferment erepsin.

Absorption of Fats, Fat Acids, and Soaps2

Absorption of Fat. — 1. Place a few drops of
neutral olive oil in the pharynx of a frog that

1 Cohnheim: Zeitschrift fur physiologische Chemie, 1901,
xxxiii, pp. 451-465.

2 Will : Archiv far die gesammte Physiologie, 1879, xx,
pp. 255-262. These experiments are best performed upon
summer frogs, i. e. not during the normal period of hibernation.

260 THE INCOME OF ENERGY

has fasted at least fourteen days. After about
twenty-four hours, remove the intestine and im-
merse it from thirty to forty minutes in 0.25 per
cent osmic acid solution.1

Slice the epithelial layer from its base. Tease
on a glass slide and examine under the micro-
scope.

Particles of fat stained deep-brown by the osmic
acid will be found in the epithelial cells.

In a " control " frog that has fasted fourteen
days, show that the intestinal epithelium is free
from fat.

2. Open the stomach of a frog the brain and
spinal cord of which have been destroyed. Tie
a glass cannula in the pylorus. Tie a ligature
around the lower end of the intestine. Eemove
the intestine. Place about 1 c.c. normal saline
solution in a test-tube. Hang the intestine in
the test-tube by passing the cannula through
the cork. Place a little neutral olive oil in the
intestine. After about twenty-four hours stain
the epithelium with osmic acid and examine as
before.

Drops of fat will be found in the cells, but the

1 Preparation of Osmic Acid Solution. — The glass capsule
containing a known quantity of osmic acid is placed in a bottle
and enough water is then added to make the required solution.
The capsule is then broken. [The vapor of osmic acid is very
irritating.]

FERMENTATION 261

quantity absorbed will be less than in the living
animal.

3. Kepeat Experiment 2, using an emulsion of
commercial olive oil and 0.25 percent solution of
sodium carbonate.

Absorption will be increased by the giving of
the fat in an emulsion.

Absorption of Fat Acids. — Place in the pharynx
of a frog a pill of pure palmitic acid made with a
few drops of glycerine. After about twenty-four
hours examine as before.

Numerous drops of fat will be found in the in-
testinal epithelium. These globules are not free
fat acid absorbed as emulsion, for miscrocopic
examination of the contents of the intestine
shows no emulsion. Moreover, palmitic acid
must be liquid to be emulsified, and as its melt-
ing-point is 62° C. it could not melt in the
intestine of a cold-blooded animal at room tem-
perature.

Absorption of Fat Acid as a Soap.1 — Feed a
frog with palmitin soap containing a few drops of
glycerine. After about twenty-four hours exam-
ine the intestine for fat, as before.

1 Preparation of Palmitin Soap. — Dissolve ten grams pure
palmitic acid in hot alcohol. Add enough 5 per cent potassium
hydrate to combine with the fat acid. Drive off the alcohol
by heating on a water-bath. Dilute with water and add a few
drops of glycerine.

262 THE INCOME OF ENERGY

Fat globules will be found in the epithelial
cells.

Lymph

Permeability of Vessel Wall in Inflammation.
— 1. In a curarized frog whose brain has been
destroyed by pithing spread the mesentery over
the glass plate of the mesentery board, and ob-
serve the capillary circulation under the micro-
scope. Note the following changes. Dilatation
of the arteries, veins, and capillaries, in the order
named. With the dilatation an increase in the
speed of the blood-stream, most noticeable in
the arteries. After half an hour to an hour the
acceleration gives place to slowing. All the
vessels are now dilated, many capillaries are
plainly visible that could hardly be made out in
the normal state, the pulsation in the arteries
is uncommonly strong down to their smallest
branches, yet the circulation is everywhere slug-
gish. In consequence of the slow blood-stream,
the capillaries become crowded with corpuscles,
so that they appear redder and more volumi-
nous than normal, yet their cross-section is only
slightly increased. In the veins the normally
almost clear plasma next the wall fills gradually
with leucocytes. The white corpuscles pass
through the walls of the veins and capillaries.

FERMENTATION 263

Eed corpuscles escape from the capillaries.
Hand in hand with the extravasation of cor-
puscles, there is an increased transudation of
lymph. The tissue swells with lymph, which
soon exudes upon the free surface of the mes-
entery, where it clots. The surface is then
covered with a fibrinous membrane, crowded
with white corpuscles, and containing also some
red corpuscles.1

2. Place on the frog's tongue a small drop of
croton oil mixed with fifty times its volume of
olive oil. After thirty seconds wipe off the
croton oil. Observe the inflammatory process
under the microscope.

3. Place a rubber band around the base of a
white rabbit-ear and thus interrupt the venous
flow. Hold the tip of the ear in warm water
until it has a temperature of about 44° 0.
Take the ear from the water and remove the
band.

• Note the rosy swelling (oedema with slight
extravasation of blood-corpuscles) in the in-
flamed area.2

1 Cohnheim: Allgemeine Pathologie, 1882, i, pp. 237-241.

2 Id. : Loc. cit., pp. 244-245.

264 THE INCOME OF ENERGY

II BLOOD
Specific Gravity

Drawing the Blood. — Wash the lobe of the ear
with a bit of absorbent cotton dipped in clean
water.1 Bub the lobe dry with another piece
of cotton. Pass a three-sided surgical needle
through a Bunsen name. (Do not heat the
needle red or the temper will be drawn and the
sharpness lost.) Stretch the skin of the lobe
between the fingers of the left hand. Make a
quick puncture one -eighth inch deep in the edge
of the lobe. Press gently to start the flow. The
blood must now flow freely. On no account use
blood squeezed out.

Determination of Specific Gravity.2 — Fill a
small beaker half full of a mixture of benzol and
chloroform of a specific gravity of about 1059.
Let a drop of the blood fall into this mixture.
The drop will remain spherical, for blood does
not mix with benzol and chloroform. If the
drop sinks, add chloroform drop by drop, mean-
while stirring the mixture with a glass rod, until

1 Subjects who are " bleeders" are not to be used for this
observation .

2 Roy: Journal of Physiology, 1884, v, p. ix. Ham-
MEU8CHLAG, A. : Wiener klinische Wochensehrift, 1890, iii,
p. 1018.

BLOOD 265

the drop neither rises to the surface nor sinks
to the bottom but swims with the mixture. If
the drop rests upon the surface, add benzol in
a similar manner. When the drop neither sinks
nor floats, its specific gravity must be that of the
benzol-chloroform mixture. Pour the mixture
into a glass cylinder, through a piece of linen to
hold back the blood-drop, and take the specific
gravity of the benzol-chloroform with an areom-
eter. The result is also the specific gravity of
the blood.

The values obtained are slightly too low. The
error is one unit in the third decimal place.

Determine the specific gravity of the blood
under the following conditions. Record the re-
sults in the laboratory note-book. Hand to the
instructor a copy of your observations written in
ink upon a laboratory blank. The material col-
lected by the class will be analyzed statistically
by a committee and a report made.

1. The specific gravity of the blood in a healthy
man.

2. In the same man half an hour after drink-
ing 750 c.c. of water.

3. In the same man one hour after drinking
750 c.c. of water.

4. In the same man after profuse sweating.
Note any feeling of thirst.

266 THE INCOME OF ENERGY

5. In a healthy woman.

Haromerschlag found the specific gravity in
chlorosis and nephritis diminished as the haemo-
globin diminished. No relation was observed
between the appearance of oedema and a reduc-
tion in the specific gravity.

Counting the Corpuscles

Counting the Red Corpuscles. — See that the
pipettes of the Thoma-Zeiss apparatus are per-
fectly clean and dry. Open the bottle contain-
ing Gower's solution (sodium sulphate, 7.3 grams ;
acetic acid, 20 c.c. ; water, 125 c.c). Prick the
ear as directed on page 264. In a large drop
which has collected without pressure put the
point of the smaller Thoma-Zeiss pipette ( " red
counter " ). Fill the pipette to the mark 0.5 by
careful suction. Should the mark be passed,
lower the column to the mark by touching the
point of the pipette to filter paper. When the
mark is reached, clean the outside of the pipette,
dip the end in Gower's diluent solution, and
draw the liquid very carefully up to the mark
101. (Should the liquid pass the mark, the
pipette must be cleaned and dried and the whole
process repeated.) Close the ends of the pipette
with the fingers, and shake it gently for one

BLOOD 267

minute in order to mix the blood thoroughly
with the diluent. The blood will now be diluted
200 times its volume.

Eemove the rubber tube from the pipette.
Blow out the unmixed solution in the capillary
tube, between the point and the bulb, and several
drops of the mixture in the bulb. Wipe off the
end of the pipette. Touch it to the ruled disc.
Let a very small drop flow out. Place the cover
glass on the drop. The flattened drop should
almost cover the glass. If it spread into the
moat, clean the disc and use a second, smaller
drop. If Newton's color-rings cannot be seen
between the cover-glass and the disc by placing
the eyes near the level of the cover-glass, another
preparation must be made, with cleaner disc and
cover-glass.

Use Leitz No. 5 or Zeiss D objective. Bring
the drop into focus and then, using the microm-
eter screw, find the ruled field.

On the central portion of the disc 1 square
millimetre has been ruled into 400 squares, each
square having therefore an area of ^-j-g- square
millimetre. Each 16 small squares are sur-
rounded by double lines, thus forming a " large
square." In the Zappert-Ewing slide, the cen-
tral square of 1 mm. is surrounded by eight other
squares of 1 mm. each, and the central ruling is

268 THE INCOME OF ENERGY

extended through the surrounding squares, which
are intersected by lines ^ mm. apart. Count the
number of corpuscles, square by square, in 200
small squares. Corpuscles touching the north
and south lines of each area are to be counted
in, those touching the east and west lines are to
be omitted from the count.

Each square has an area of ^^ square milli-
metre. The thickness of the layer of blood, i. e.
the distance from the ruled disc to the cover-
glass, is 0.1 mm. The volume of the space above
each square, therefore, is 4 oVo CUDic millimetre.
As the blood is diluted 200 times its volume, and
the number of squares counted is 200, the total
number of corpuscles in a cubic millimetre is
x X 200 X 4000
200
x being the total number of corpuscles counted.
In short, to obtain the number of corpuscles in a
cubic millimetre, multiply by 4000 the number
counted in 200 squares. Clean the pipette as
soon as the counting is done.

Cleaning the Pipette. — Draw clean Gower's
solution through the pipette, then alcohol, and
finally ether. Dry the pipette by sucking (not
blowing) air through it.1

1 Do not use alcohol and ether in cleaning the disk. Pi-
pettes left dirty will be cleaned at the student's expense, or,
where necessary, a new;one purchased.

BLOOD 269

Control Counting. — Count the red corpuscles
in a second drop. If the result differ greatly
from that of the first count, the corpuscles in a
third drop must be counted.

Counting the White Corpuscles. — Have ready
a diluting solution of glacial acetic acid (one-
third of one per cent). This solution will make
the red cells invisible. Obtain a very large drop
of blood. By very gentle suction fill the large
Thoma-Zeiss pipette to the point 0.5. Keep
the pipette nearly horizontal, both in obtain-
ing the drop and in drawing in the diluting solu-
tion ; the bottle should be tilted. Count the
white corpuscles in the entire ruled disc. Eepeat
with a second drop. Calculate the number of
white corpuscles in a cubic millimetre.

Estimation of Haemoglobin

Oxygen Capacity of the Blood ; the Colorimetric
Determination of Haemoglobin. 1 — Haldane and
Smith 2 have shown that " the coloring power of
the blood of different mammals varies in exact

1 Haldane : Journal of Physiology, 1901, xxvi, pp. 497-
504. This experiment should be substituted for that given in
"Experiments for Students in the Harvard Medical School,"
third edition, pp. 100, 101.

2 Haldane and Smith : Journal of Physiology, 1900, xxv,
pp. 331-343.

270 THE INCOME OF ENERGY

proportion to its oxygen capacity. The latter
can be easily and accurately determined by
means of the ferricyanide method.1 Thus blood
of a certain oxygen capacity has also a certain
coloring power ; and it is possible to standardize
the coloring power in terms of the oxygen capa-
city. We can therefore make the unit of volume
the basis of our definition of the unit of color-
ing power employed in haemoglobin estimations.
Since, however, oxy-lnemoglobin is not stable,
I have adopted as a standard a dilute solution
of blood of known oxygen capacity saturated
with coal gas.2 This solution is sealed up in
a narrow test-tube after all the contained air
has been displaced by coal gas, and when thus
completely sealed is permanent."

The standard solution for the ruemoglobin-
ometer is a one per cent solution, saturated with
coal gas, of ox or sheep's blood of the average
oxygen capacity of the blood of normal adult
males, found to be 18.5 per cent. If it be borne
in mind that 100 per cent on the hsemoglobin-
ometer scale corresponds to an oxygen capacity

1 In this method the oxygen is displaced from laked blood
by ferricyanide of potassium, and the resultant gas measured.
HALDANB: Journal of Physiology, 1900, xxv, pp. 295-302.

2 Coal gas contains carbon monoxide as an impurity, and
thus converts the oxy-haemoglobin to CO-hsemoglobin.

BLOOD 271

of 18.5 per cent, it is of course easy to express
the results in terms of oxygen capacity. The
exact percentage of haemoglobin corresponding to
18.5 per cent oxygen capacity is still uncertain.
According to Hufner's latest results it would be
13.8 per cent.

In using the haemoglobinometer, place 15-20
c.c. water in the graduated tube, for dilution of
the blood. Draw 20 cb. mm. of blood into the
pipette, with, the necessary precautions.1 Gently
blow the blood out of the pipette on to the sur-
face of the water in the graduated tube. Before
mixing the blood with the water introduce into
the free part of the tube a narrow glass tube con-
nected with the gas-tap, turn on the gas, and
push the gas-tube down to near the level of the
water, so that the air may be instantly displaced
from the tube. Avoid any loss of liquid. If
the upper part of the tube, or the liquid itself,
is warmed by the fingers while the solution is
being mixed or saturated with carbon monoxide,
a little liquid is apt to spurt out. This can be
avoided by holding the tube in a cloth. With-
draw the gas-tube while the gas is still flowing.
Close the top of the graduated tube with the
finger and invert the tube about a dozen times,

1 See page 264 ; remember not to use blood squeezed from
the ear.

272 THE INCOME OF ENERGY

so that the haemoglobin is thoroughly saturated
with carbon monoxide and the full pink tint
of the CO-haemoglobin appears. Then add water
drop by drop from a pipette until the tint in
the graduated tube equals that in the standard
tube. In comparing the tints of the two tubes,
it is best to hold them up against the light from
the sky. The precaution must always be taken
of repeatedly transposing the tubes from side to
side during the observations : otherwise very
considerable error may arise. The percentage
is read off on the tube after half a minute has
been allowed for the liquid to run down. An-
other drop is now added, and if necessary another,
until the tints again appear unequal. Usually
the tints will appear equal for two or possibly
three additions. The mean of the readings which
gave equality is taken as the correct result. The
results in successive experiments with the same
blood should agree within one per cent of the
mean.

The average percentage of haemoglobin in the
blood of women is 11 per cent, and in the blood
of children 13 per cent below that of adult men.
In calculating the proportion of haemoglobin in
the blood of women and children as percentages
of the average normal proportion, it is evidently
necessary to add about one-eighth for women

BLOOD 273

and one-seventh for children to the percentage
found by the haetnoglobinometer, with the stand-
ard solution described above.

HEMORRHAGE AND EEGENERATION

Determine the specific gravity, number of red
and white corpuscles per millimetre, and per-
centage of haemoglobin in the same animal under
the following conditions : Normal ; two hours
after a profuse haemorrhage ; one day, three days,
and five days after the haemorrhage. Plot all
three curves upon one co-ordinate system.

Physical Aspects of Coagulation

Physical Action of Salts in the Coagulation of
Colloidal Mixtures. — 1. Boil egg-albumin diluted
with about eight volumes of water. The colloid
will not coagulate. Add crystals of magnesium
sulphate gradually. Coagulation will take place.1

2. Dip a thin thread of silk in 2 per cent
solution of calcium chloride and lay the thread
upon a glass slide beneath a cover-glass. Allow
boiled solution of egg-white (1 : 8) to run under
the cover-glass. Examine the process of coagu-
lation under a magnification of about 500 diam-

1 Hayciiaft and Duggan : British Medical Journal, 1890,
p. 167.

18

274 THE INCOME OF ENERGY

eters. The fluid at first is free from visible
particles. Near the silk thread appears a fine
cloud, the particles in which grow in size until
they form spherules having a maximum diameter
of 0.75 to 1/n. They are now seen to be arranged
in patterns forming an open net with regular
polygonal meshes, having diagonals as long as 6/x.
The threads of the net are formed of contiguous
spherules. This stage, however, is not one of
equilibrium — the net shrinks, the meshes become
smaller, and the spherules apparently shift their
points of attachment until, in place of being-
bounded by threads composed of several spher-
ules, the image has the appearance of the typical
fine net with spherules at the nodal points joined
by tiny threads. Whether these joining-threads
or bars have a real existence, or whether they
are purely optical and the spherules actually
touch one another, it is impossible to say at
present. When the particles are large enough
to be clearly visible with a magnification of 500
diameters they do not show Brownian movement
— in other words they are probably already in
some way linked to one another.

The following explanation of these phenomena
may be given. On boiling the egg-albumin, the
heat chemically alters the dissolved proteid and
produces a suspension of particles having an

BLOOD 275

average diameter commensurable with the mean
wave-length of light.1 Under the influence of
electrolytes (the salt solution) the particles
aggregate to larger and larger masses. When
these molecular aggregates attain a certain size
the fluid condition is no longer possible ; this
would follow immediately from Graham's ob-
servation that actual coagulation is preceded by
a continuous increase in the viscosity of the liquid.
The following conditions determine this generic
action of salts as coagulants, as distinguished
from any specific chemical action. 1. The point
at which coagulation appears is determined by
the concentration of the solid in the colloidal mix-
ture, and the temperature, molecular concentra-
tion (gram-molecules per litre), and nature of
the electrolytes present. 2. The concentration
necessary for coagulation is lowered by a rise of
temperature, or by an electrolyte. 3. The coagu-
lative energy of electrolytes as measured by the
number of gram-equivalents per litre necessary
to produce coagulation is determined almost
solely by the nature of the metal of the salt ;
and among the metals themselves it is deter-
mined by the valency of the metal.2

1 Picton and Likder: Transactions of the Chemical
Society, 1895, lxvii, p. 63.

2 Haedy : Journal of Physiology, 1899, xxiv, pp. 181-183.

276 THE INCOME OF ENERGY

Physical Changes in Coagulation. — 1 . Clotting
of Plasma. — Wet a small filter with cane-sugar
solution (0.5 per cent). Cut a frog's ventricle
across near the base so that 0.5 c.c. blood shall fall
into a beaker containing an equal quantity of cane-
sugar solution. Pour the mixture on the filter.
Eeceive the filtrate on a watch-glass. Note the
physical changes in this filtrate.

2. Fibrin Threads. — Place a blood-drop under
a cover-glass. With the microscope observe the
appearance of fibrin threads.

3. Eeceive 1 c.c. blood into 0.5 c.c. saturated
solution MgS04. Note (1) absence of clotting,
and (2) its appearance after dilution.

4. Receive 0.5 c.c. blood in a watch-glass.
Let it stand twenty-four hours. Note physical
changes during the first ten minutes and at
end of period.

Secretion

Speed of Absorption and Secretion. — Place
5 c.c. of thin starch paste and 2 c.c. concentrated
nitric acid in each of ten test-tubes and mark
them 2, 4, 6, 8, 10, 12, 14, 16, 18, and 20
minutes. Let one of each pair of students swal-
low a gelatine capsule containing ten grains of
potassium iodide.1 Immediately rinse the sub-

1 The subject should have had a small, early breakfast.

RESPIRATION 277

ject's mouth until the wash water gives no blue
color (iodide of starch) on the addition of potas-
sium iodide and concentrated nitric acid (to set
free the iodine). Let the subject chew a small
piece of clean black rubber-tubing to increase
the secretion of saliva. At intervals of two
minutes, beginning with the swallowing of the
potassium iodide, empty the mouth into the cor-
responding test-tube, at once rinse the mouth
with water, and begin a fresh collection.1

Note the moment at which the drug appears
in the saliva.

RESPIRATION
Chemistry of Kespiration

Estimation of Oxygen, Carbon Dioxide, and
Water.2 — Weigh bottles 3, 4, and 5 (4 and 5

1 If the saliva secreted during two minutes cannot be held
in the mouth with comfort and without loss by swallowing, the
mouth may be emptied into a freshly washed porcelain dish,
from which the saliva should be poured into the proper test-
tube at the end of each two-minute period.

2 Apparatus. — Two aspirator bottles, with box. A wooden
tray, containing a jar for the guinea-pig, and six bottles, viz. :
Nos. 1 and 4, filled with soda-lime, to absorb carbonic acid ;
N"os. 2, 3, and 5, filled with pumice stone soaked in sulphuric
acid, to absorb moisture ; No. 6, a Miiller valve, to prevent air
being forced back through the series of bottles by a wrong
coupling of the aspirator tubes.

278 THE INCOME OE ENERGY

together). Place the guinea-pig in the jar and
weigh. During one hour draw air through bot-
tles 1 to 6 by placing an aspirator bottle on its
box and allowing the water to flow from this
bottle to the one remaining on the desk. The
rubber connecting tube must be changed when
the aspirator bottles are changed. After one
hour weigh bottle 3, and bottles 4 and 5.
Tabulate results as follows :

grams

Weight of jar and guinea-pig at beginning
" " " end . .

Loss

Wt. of bottle 3 (sulph. acid) at beginning
" " " end . .

Gain (= water absorbed) . . .

Weight of bottles 4 and 5 at beginning .
" " " end . . .

Gain (= carbon dioxide absorbed)

Total water and carbon dioxide absorbed
Loss in weight of jar and guinea-pig . .
Difference (= oxygen absorbed) .
Respiratory quotient

Metabolism

Effect of Muscular Exercise on the Oxygen, Car-
bon Dioxide, and Water of the Respired Air. —

Repeat the estimation of oxygen, carbon dioxide,

RESPIRATION 279

and water in the respired air (p. 277), slowly
turning the guinea-pig jar from side to side, so
that the animal shall be kept in gentle motion
during an hour.

The excretion of carbon dioxide is increased by
muscular exercise.

Individual Level of Proteid Metabolism. — Each
group of eight students will select two subjects
for experiment. They should be thin men in
good health. Let each subject collect the twenty-
four hours' urine in a thoroughly clean bottle of
about 2000 c.c. capacity. Measure the quan-
tity. Determine in a measured portion of the
total mixed urine the quantity of urea (hypobro-
bromite method). Calculate the nitrogen in the
urea. Add 2.5 grams for the nitrogen excreted
in the faeces, sweat, and as uric acid in the
urine.

Eepeat these determinations for three days, the
subject maintaining his usual diet and mode of
life.

The excretion of nitrogen will probably be
found to be fairly uniform in each individual
though the different nutritive habits of different
individuals may cause them to be on different
proteid planes, characterized by high, medium, or
low nitrogen excretion.

Nitrogenous Equilibrium. — When the daily

280 THE INCOME OF ENERGY

excretion of nitrogen has been found to be fairly
uniform, place the subject upon a simple diet
of eggs, bread, milk, and butter, containing as
much nitrogen as he excretes.1

The diet may be chosen from the following-
table.2

The relative proportion of proteid, fat, and car-
bohydrate per day should be about as follows :

Proteid 100 grams

Fat 100 grams

Carbohydrate . . . 250 grams

450 grams

Eepeat the determination of urea in the urine
during four more days.3 Calculate the nitrogen

1 Owing to the variation in the nitrogen content of meats,
they should be omitted.

Physiological heat values : —

1 grain proteid = 4000 small calories

1 " fat = 9423 "

1 " carbohydrate zr 4182 " "

Proteids contain about 16 per cent nitrogen. Hence to obtain
the amount of metabolized proteid from the nitrogen in the
urine multiply the latter by 6.25.

In one pound there are 453.6 grams.

2 Coffee and tea contain so little nitrogen that they may be
added to the diet in small amounts to suit the individual taste.

3 The twenty-four boms should begin in the morning im-
mediately after passing the mine excreted dining the night.

RESPIRATION

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282 THE INCOME OF ENERGY

excreted in urea, adding 2.5 grams for the nitro-
gen of the faeces, sweat, uric acid, etc.

It will probably be found that the nitrogen
excreted equals that ingested (nitrogenous equi-
librium).

Effect of Muscular Exercise on Proteid Metab-
olism. — On the third day of the preceding ex-
periment, the subject should take an unusual
amount of measurable exercise. Hill-climbing
is a suitable form. The protocol of the experi-
ment must contain an approximate estimate' of
the work done in foot pounds.

It will be found that muscular work, unless
pushed to great fatigue, does not increase pro-
teid metabolism, as measured by the nitrogen
excreted.

PART III

THE OUTGO OF ENERGY

PART III
THE OUTGO OF ENERGY

I Animal Heat

Regional Temperature. — Record the tempera-
ture taken with a clinical thermometer placed
under the tongue, in the axilla, and in the
rectum.

Effect of Hot and Cold Drinks on the Tempera-
ture of the Mouth. — Record the temperature
taken under the tongue soon after drinking (1)
cold water. (2) warm water.

Hourly Variation. — Record the temperature
taken under the tongue every two hours through
the day and plot the results on clinical tempera-
ture paper.

Reaction of Cold and Warm Blooded Animals to
Changes in the External Temperature. — 1. Record
the temperature in the gullet of a frog placed in
water of varying temperature. 2. Record the
(rectal) temperature of a guinea pig in a bath at
40°, gradually cooled to 15° C.

Chemical Action the Source of Animal Heat. —
Calculate the heat values observed by Rubner 1

1 Rubnee : Zeitschrift fur Biologie, 1894, xxx, p. 134.

286 THE OUTGO OF ENERGY

in a dog weighing 11.8 kg., receiving 580 gms.
flesh daily.1

Date
1890.

Nitrogen
excreted.

Fat
C

Calories
from Proteid ; from Fat.

Total
calories,

April 11

18.75

14.6

12

17.39

18.2

13

19.43

13.7

14

18.35

17.5

15

18.57

17.5

16

18.50

16.8

17

18.31

17.1

Compare above results with those actually ob-
tained by Eubner when the dog was placed in
the calorimeter.

Date
1890.

Heat given
to calorimeter.

Heat lost in
ventilation. evaporation
of water.

Total
calories
in 24 hrs,

ril 12

469.4

44.8

165.1

679.4

13

483.0

56.4

148.6

687.9

14

455.3

32.9

178.0

666.1

15

485.1

34.4

179.1

698.7

16

447.9

34.7

199.3

681.8

17

465.9

34.1

174.2

674.2

18

456.9

35.1

187.3

679.4

1 1 gm. proteid = 4.1 cal. (Rubner used 4.0 cal.)
1 " fat = 9.3 " ( " " 9.423 " )

To find the fat from the carbon multiply the carbon by 1.3
(fat contains 76.5 per cent of carbon).

THE ELECTROMOTIVE PHENOMENA 287

II

THE ELECTROMOTIVE PHENOMENA OF
MUSCLE AND NERVE

The stored energy of muscle is set free in molec-
ular movement, — heat, chemical action, and
electricity, — and in mechanical work, the change
in form. It will be convenient to consider the
electromotive phenomena first.

The Demarcation Current of Muscle

Demarcation Current of Muscle. — 1. Mount
two non-polarizable electrodes. Connect them
to the capillary electrometer through a short-
circuiting key. Remove a sartorius muscle. Cut
off each end with a sharp knife by a clean cut at
right angles to the fibres. Observe that the
muscle is thereby converted into a " muscle
prism." It possesses two artificial cross-sections,
at each of which the muscle has been injured,
and is, in fact, dying, and an uninjured natural
longitudinal surface. Place the muscle across
the electrodes so that the cross-section rests on
one electrode and the middle of the longitudinal
surface rests on the other. Bring the meniscus
of the capillary into the field. Note its position
on the micrometer scale. Open the key.

288 THE OUTGO OF ENERGY

The meniscus will be displaced in the direc-
tion indicating a higher potential at the middle
or " equator " of the longitudinal surface than
at the cross-section. Note the divisions of the
scale, traversed by the meniscus — the displace-
ment is proportional to the difference of potential.

2. Move the electrode on the longitudinal sur-
face a few millimetres towards the cross-section.
Determine the difference of potential here. It
will be less than before. Measure the potential
in similar manner at intervals of 5 mm. between
this point and the cross-section. On co-ordinate
paper set down on the abscissa the number of
millimetres from equator to cross-section. Set
down as ordinates the number of divisions of the
micrometer scale traversed by the meniscus when
the electrode on the longitudinal surface is placed
successively on the equator, and at intervals of 5
mm. between equator and cross-section. Draw
the curve uniting the summits of the ordinates.

As the cross-section is approached, the curve of
potential will fall more and more rapidly. The
centre of the cross-section is negative towards
the outer parts of the section. Points on the
equator, or equidistant from it, have the same
potential. Points on the longitudinal surface
at different distances from the equator, and on
the cross-section at different distances from the

THE ELECTROMOTIVE PHENOMENA 289

centre of the section, show a slight difference of
potential.

Prove these several statements.

Oblique Section. — When the artificial cross-
section is oblique to the long axis of the muscle,
the maximum difference of potential is no longer
at the equator and the centre of the cross-section.
The most positive point is on the longitudinal
surface near the obtuse angle made by the oblique
section, and the most negative point is on the
cross-section near the acute angle. The structure
of certain muscles, the frog's gastrocnemius, for
example, is such as to make their natural cross-
section oblique. In consequence, their differ-
ences of potential are not distributed as in a
regular parallel-fibred muscle like the sartorius.
In the gastrocnemius, owing to the peculiar inser-
tion of the muscle fibres into the tendon, the
upper end of the muscle is really the middle of
the longitudinal section, while the lower end
is the acute angle of an oblique cross-section.
When the ends are connected with an electrom-
eter, a strong current is observed flowing (out-
side the muscle) from the upper to the lower end.

Uninjured Muscle. — Prepare .a sartorius muscle
with extreme care to prevent injury. Connect
the tendon (the natural "cross-section") and
the longitudinal surface with the electrometer

19

290 THE OUTGO OF ENERGY

through a short-circuiting key. Note the posi-
tion of the meniscus on the micrometer scale.
Open the short-circuiting key.

The meniscus will move but little. It will not
move at all, provided the muscle has not been
injured; but the difficulty of preparation is such
that some difference of potential will probably
appear.

Close the key. Injure the muscle by drawing
a hot wire across one end. Open the key.

A strong demarcation current will appear.

Stimulation by Demarcation Current. — 1. Make
a nerve-muscle preparation (sciatic nerve and
gastrocnemius muscle). Let the nerve near the
muscle touch a cross-section of the sartorius.
Now let the end of the nerve fall on the longi-
tudinal surface near the equator.

The gastrocnemius will contract; the nerve
acts as a conductor between the positive longi-
tudinal surface and the negative cross-section.

It should be pointed out that the conclusion
here drawn is not entirely free from criticism.
The muscle is a conductor as well as the nerve,
and may close the demarcation current of the
nerve, as the nerve may close that of the muscle.
Thus it is possible that the nerve is stimulated
by its own demarcation current. The former
explanation is the more probable.

THE ELECTROMOTIVE PHENOMENA 291

2. Place non-polarizable electrodes on the
longitudinal surface and cross-section of the
sartorius. Fasten the wires of the stimulating
electrodes in the binding posts of the non-polar-
izable electrodes. Drop the nerve of the nerve-
muscle preparation across the electrode points.

The gastrocnemius will contract when the
nerve bridges the space from one electrode to
the other, and thus completes the circuit be-
tween the longitudinal surface and cross-section
of the sartorius.

3. Place a little 0.6 per cent solution of sodium
chloride in a porcelain dish. Fasten one end of
the sartorius gently between two pieces of cork
in the jaws of the muscle clamp. Bring the
muscle over the saline solution. Make a fresh
clean cross-section, and lower the clamp on its
stand until the cross-section dips (not too far)
into the solution.

The muscle will twitch. The twitch will pull
the end of the muscle out of the solution. When
the muscle relaxes, the contact between positive
longitudinal surface and negative cross-section
is once more made by the saline solution, the
current of rest flows from the point of higher to
•the point of lower potential, and again stimulates
the muscular tissue through which it passes.
Thus the muscle is stimulated by its own cur-

292 THE OUTGO OF ENERGY

rent. A long series of contractions may be
secured. Other liquid conductors will serve.
When the solution touches only the cross-sec-
tion, there is no contraction.

4. Prepare a fresh sartorius muscle with bony
attachments. Fasten the pelvic end in the
muscle clamp. Make a fresh cross-section in
the first sartorius. Hold the tibial end of the
second muscle in such a way that the muscle
lies horizontally with its upper surface some-
what concave. Against this surface bring the
fresh cross-section of the first sartorius. The
longitudinal surface will naturally also touch
to some extent.

The second muscle will close the circuit be-
tween longitudinal surface and cross-section of
the first, and, if very irritable, both muscles will
contract.

Interference between the Demarcation Current
and a Stimulating Current ; Polar Refusal. — Con-
nect a dry cell through an open key with the
0 and 1 metre posts of the rheochord (Fig. 46).
Mount two non-polarizable electrodes, and con-
nect them through a pole-changer (with cross-
wires) to the positive post and slider of the
rheochord. Tie a thick cotton thread to the
foot of the positive electrode in such a way
that the thread shall hang down in a small loop.

THE ELECTROMOTIVE PHENOMENA 293

Let a sartorius muscle rest on a clean glass
plate. Make an artificial cross-section by draw-
ing a hot wire across the muscle near the pelvic
end. Pass the loop of thread on the positive
electrode over the muscle about 5 mm. from the
thermal cross-section. Let the negative electrode
rest on the cross-section. Arrange the rheochord
for weak currents. Moisten the electrodes with
normal saline solution. Close the key.

The usual closing contraction
will be absent (polar refusal).

Note that the galvanic cur-
rent is now passing through
the muscle in an atterminal
direction, i. e, towards the in- s — <* ^Q — ^^
jured portion (admortal), while \^^
the demarcation current is
passing through the muscle in Fig. 46.

the opposite direction. The two currents more
or less compensate each other. Hence, the ab-
sence of the closing contraction. Observe, also,
that opening the key will break the galvanic cir-
cuit, but that the circuit for the demarcation
current will still be closed — through non-polariz-
able electrodes and rheochord.

Open the key.

An opening contraction will take place,
obviously because the muscle current is no
longer compensated.

294 THE OUTGO OF ENERGY

Keverse the pole-changer, so that the anode
lies at the cross-section. Open and close the
galvanic current.

Contraction will take place at closure only.
The electrode at the cross-section again refuses.

2. Compensation Method. — The electromotive
force of a current of injury may be expressed in
fractions of a Daniell cell, or any other constant
element, by bringing into the same circuit with the

current of injury, but in an
opposite direction, so much
of the current from the cell
as will exactly balance the
current of injury, i. e. so
much as will keep the menis-
cus of the electrometer from
moving in either a positive
or negative direction when
Fie- 47- connected with the circuit.

Prepare a sartorius muscle. Connect a Daniell
cell with the 0 and 10 metre posts of the rheo-
chord. Connect the capillary electrometer to a
closed short-circuiting key. From the post joined
to the capillary lead to the 0 post of the rheo-
chord. Connect the remaining post of the key
to a non-polarizable electrode placed on the cross-
section of the muscle. Join the slider of the
rheochord to another non-polarizable electrode

THE ELECTROMOTIVE PHENOMENA 295

placed on the equator of the muscle (Fig. 47).
Bring the slider to the zero post. Bring the
meniscus into the field. Note its position on the
micrometer scale. Open the short-circuiting key.
When the meniscus comes to rest, move the slider
along the rheochord -until the meniscus returns
to its original position. Eead the number of
millimetres between the positive post and the
slider. This number divided by 10,000 is the
fraction of the electromotive force of the Daniell
cell (1.1 volt) necessary to balance the current of
injury of the muscle (from 0.035 to 0.090 volt).

Demarcation Current of Nerve

Place non-polarizable electrodes on the cross-
section and longitudinal surface of a long piece
of sciatic nerve. Connect the electrodes through
a short-circuiting key with the electrometer.
Bring the meniscus into the field and open the
short-circuiting key.

The meniscus will move in a direction indicating
a current in the nerve from cross-section to loncn-

o

tudinal surface, as in muscle.

Measure the electromotive force of this demar-
cation current.

The demarcation current is much weaker in
nerve than in muscle, being in the former about

296 THE OUTGO OF ENERGY

0.025 volt, as against about 0.060 volt in
muscle. The demarcation current of muscle is
maintained in force for a long time, whereas that
of nerve diminishes rapidly. The nerve current
is restored on making a fresh cross-section.

The demarcation current from the cut branches
of a nerve may reach electrodes placed on the
main trunk, and thus confuse the electrometer
measurements. To this same cause must be
ascribed the increased irritability observed in the
main trunk in the neighborhood of branches ;
the irritability is raised by the demarcation cur-
rent of the severed branch.

Nerve may be stimulated by its own Demarca-
tion Current. — On a glass plate make a U shaped
wall of normal saline clay, each limb about 1 cm.
long and 3 or 4 mm. wide. Carefully remove the
moisture between the clay walls with filter paper.
Lay the longitudinal surface of the nerve of a nerve-
muscle preparation on one limb of the U, and with a
glass rod let the cross-section fall on the other limb.

When the circuit between the cross-section and
the longitudinal surface is completed by contact
with the clay, the demarcation current will
stimulate the nerve, and the resulting nerve im-
pulse will cause the muscle to contract.

Other Examples. — The dropping of the central
end of the severed vagus nerve into the wound
from which it was lifted has caused the slowing

THE ELECTROMOTIVE PHENOMENA 297

of respiration, presumably by the stimulation of
the nerve through the closure of its own demar-
cation current by the lymph or blood, though
the possible influence of demarcation currents
from the wounded tissues cannot be forgotten.
Definite results, such -as inhibition of the heart,
have not been observed to follow the closure of
the current of the peripheral segment. To avoid
any chance stimulation from the closure of the de
marcation current, nerves are sometimes severed
physiologically by freezing, — a process wdiich
not only does not stimulate, but which does not
destroy permanently the conductivity ; the latter
returns upon the restoration of the nerve to
normal temperature.

The olfactory nerve of the pike shows a strong
demarcation current, as does the optic nerve.

Hypotheses regarding the Causation of
the Demarcation Current

Make artificial cross-sections in a sartorius
muscle, and test the difference of potential be-
tween the longitudinal surface and a cross-section
with the electrometer. Divide the muscle, lonoi-
tudinally, and make fresh cross-sections ; test the
difference of potential again.

However small the muscle prism may be

293

THE OUTGO OF ENERGY

made, the longitudinal surface will still be posi-
tive to the cross-section.

Molecular Hypothesis. — The fact that the
smallest possible muscle prism is still positive
on the longitudinal surface, and negative on the
cross-section, suggested to DuBois-Keymond that
muscle (and nerve) are composed of electrical
particles or molecules something like the mole-
cules of a magnet. A magnet has two poles,
and, however it may be divided, the pieces still

ill

mmmmmmmmmw

■■iBinnnainni

[■■■■■JMMBIBll

A

Fig. 48. Scheme of the myomeres ill a parallel-fibred muscle (Rosenthal).

possess a north and a south pole. The magnet is
therefore believed to be composed of molecules,
each possessing a north and a south pole. These
molecules lie with the north poles all pointing in
one direction, the south poles in the other. The
structure of muscle favors, in a measure, a simi-
lar hypothesis ; for it is known that a striated
muscle consists of fibrilhe, each of which is com-
posed of a row of particles arranged in quite
regular fashion. The electromotive molecules, or

THE ELECTROMOTIVE PHENOMENA

299

myomeres, may be conceived to be positive on
their longitudinal surfaces, and negative on their
cross-sections (Fig. 48). They are assumed to
have their negative surfaces turned towards the
ends of the muscle or nerve, and the positive
equatorial region turned towards the longitudi-
nal surface. A non-electric conducting substance
surrounds them. An electrode placed on the
longitudinal surface would touch only the posi-
tive sides, while an electrode placed on the cross-

Fig. 49. ScLeme of myomeres in an oblique section (Rosenthal).

section would touch only the negative poles.
However small the muscle prism was made, the
relation would still be the same. Thus the dis-
tribution of potentials would correspond with
that actually observed.

When the cross-section is oblique, the myo-
meres at the cross-section are exposed as shown
in Fig. 49, and the currents which pass from the
longitudinal surface of each myomere to its cross-
section are added to the main currents passing

300 THE OUTGO OF ENERGY

from the longitudinal surface to the cross-section
of the "whole muscle. The region of maximum
positive potential is thereby brought towards the
obtuse angle of the oblique cross-section, and the
region of maximum negative potential is dis-
placed towards the acute angle, as actually
observed.

When it was found by Bernstein, Hermann,
and others, that uninjured muscle showed no
difference of potential, DuBois-Beymond as-
sumed that in the natural, uninjured state the
end of the muscle in contact with the tendon
(the " natural cross- section ") is composed of a
layer of molecules which have their positive in-
stead of negative surface turned towards the
tendon.

The highly artificial and complicated structure
which DuBois was compelled to erect on this
foundation in order to explain all the electrical
phenomena of living tissue, cannot be discussed
here. The chief argument against the molecular
theory of muscle and nerve currents is that the
phenomena can be explained in a simpler way.

Alteration Theory. — This hypothesis, in the
making of which Hermann and Hering have
been especially active, explains the electromo-
tive forces of nerve and muscle by alterations in
the chemical composition of the tissue at the

THE ELECTROMOTIVE PHENOMENA 301

cross-section. When the cross-section is made,
the tissue next the section passes through the
series of catabolic changes which constitute
muscle death ; carbon dioxide is given off, lac-
tic acid is developed, a soluble proteid is con-
verted to a less soluble form, etc. The contact
of this dying layer with the uninjured tissue is
believed to create a difference of potential. The
potential difference, therefore, appears at the de-
marcation between dying and uninjured tissue,
— hence the term "demarcation current." The
action current finds its explanation in the chemi-
cal changes accompanying contraction. It would
be interesting to consider here the parallel be-
tween the chemical transformations in contrac-
tion and those which usher in the death of the
muscle, but we must be content with mentioning
the apparently close relationship. In its most
general form, the alteration hypothesis rests on
the fact that living substance is everywhere the
seat of constant constructive and destructive
changes. Where these are nearly in equilibrium,
as, for example, in the resting uninjured muscle,
the tissue is equipotential ; where, on the con-
trary, either form of chemical change has the
upper hand, as in the explosion which we term
contraction, and in dying muscle, it is assumed
that a difference of potential is created.

302 THE OUTGO OF ENERGY

For many years the weight of physiological
opinion has been largely on the side of the alter-
ation hypothesis ; but it would be unsafe without
further evidence to decide finally against the
molecular theory.

Action Current of Muscle

The demarcation current (current of injury,
current of rest) just studied has been shown to
be due to the injury of the tissue. We have
now to examine the electromotive forces which
appear when a nerve or muscle becomes active.

1. Rheoscopic Frog. — Make two nerve-muscle
preparations, A and B. Let the nerve of B
rest on muscle A. Stimulate the nerve of A
with single induction shocks, and with the
tetanizing current.

Muscle B will contract once for each contrac-
tion of A. The current of action of muscle A
stimulates the nerve of B.

Secondary contraction can take place also from
muscle to muscle, but only under circumstances
that suggest increased irritability, as, for example,
through partial drying. No secondary contrac-
tion has been secured from voluntary muscular
contraction.

2. That the stimulus to the nerve of the rheo-
scopic muscle is really an electrical current, is

THE ELECTROMOTIVE PHENOMENA

303

shown by the capillary electrometer. Place
muscle A in the moist chamber upon two non-
polarizable electrodes. Let the tendon rest on
one electrode and the equator on the other. Lead

T37

Fig. 50. The vibrating interrupter. A platinum wire on the end of a steel
spring dips into a mercury cup. By varying the length of the spring, con-
tacts from once a second to more than one hundred per second may be
secured.

from the non-polarizable electrodes through a
closed short-circuiting key to the capillary elec-
trometer (the tendon should be connected with

304

THE OUTGO OF ENERGY

the capillary). Lay the nerve on stimulating
electrodes. Connect the latter with the secondary
coil of an inductorium arranged for single induc-

Fig. 51. The vibrating interrupter arranged to make one contact per

second.

lion currents. Place the vibrating interrupter
(Figs. HO, 51) in the primary circuit. Bring the
meniscus into the field. Open the short-circuiting

THE ELECTROMOTIVE PHENOMENA 305

key. The meniscus will be displaced by the
demarcation current. When the meniscus has
come to rest, stimulate the nerve with single and
repeated induction currents.

With each stimulus there will be a negative va-
riation (action current) of the demarcation current.

When the number of stimuli per second passes
a certain point, which differs with different in-
dividuals, the hitherto separate excursions of the
meniscus will be fused, and a gray blur will
appear at the end of the vibrating column.
Movements of this rapidity may of course be
studied by photographing them on sensitive paper
moving rapidly enough to draw the fused image
out into a line in which its component oscilla-
tions are each distinct, or they may be observed
directly by the stroboscopic method.

The Action Current in Tetanus ; Stroboscopic
Method. — 1. If a piece of thin black paper about
1 cm. square is fastened vertically on the end of
the electro-magnetic signal lever, and the signal
placed in the primary circuit of the inductorium
arranged for tetanizing currents, the piece of
paper will move each time the primary current
is made or broken by the vibrating hammer of
the inductorium. The movement is so rapid
that the paper seems stationary and a gray haze
appears on its upper and lower border.

20

306 THE OUTGO OF ENERGY

Connect the electrometer with the secondary
coil of the inductorium, and bring the vibrating
meniscus into the field.

Bring the stroboscopic paper next the acid
reservoir of the electrometer at such a height
that the ed^e of the meniscus shall be seen
through the gray blur. The meniscus will no
longer appear blurred, but will be as sharp as
if the mercury were stationary. This appearance
is produced only when the stroboscopic paper
and the object seen by its aid have the same
periodicity of vibration. If the periodicity of
the vibrations is unequal, interference results,
and from this interference the rate of vibration
of the observed body can be calculated. For
example, if the observed body shows three vibra-
tions per second, when observed through the
stroboscope, its rate is three more per second
than that of the stroboscope.

In the present instance, the meniscus remains
apparently at rest. The number of action cur-
rents is therefore identical with the number of
stimuli.

2. Rheoscopic Muscle Tetanus. — The same
method may be applied to the analysis of the
rheoscopic tetanus in the rheoscopic muscle.

Place two nerve-muscle preparations in the
moist chamber. Place the tendon of muscle B

THE ELECTROMOTIVE PHENOMENA

307

on one electrode and the longitudinal surface on
the other, and connect them through a short-
circuiting key with the electrometer. Lay the
nerve of B on muscle A. Place the nerve of A
on electrodes connected with the secondary coil
(the coil should be well over the primary).
Bring the meniscus into the field, and open the
short-circuiting key. Place the stroboscope, still
in the primary circuit, near the meniscus. Tet-
anize the nerve of A.

Fig. 52.

For each stimulus received from nerve A,
muscle A contracts ; the contractions are so fre-
quent that they fuse into tetanus. At each
contraction of A, its current of action stimulates
the nerve of B, and B also contracts. At each
contraction of B, the action current displaces
the meniscus, which falls therefore into very
rapid oscillation. Observe the meniscus through
the stroboscope. It will seem to be standing
still.

308 THE OUTGO OF ENERGY

Thus the apparent continuous contraction of
muscle B is in reality a series of simple contrac-
tions, as stated, corresponding in number to
the make and break currents of the inductorium.
For each contraction there is one action current
in each muscle.1

When a muscle and its nerve are removed
without injury to the muscle, electrodes placed
on the latter will show no difference of potential,
as already stated (page 289). Stimulation of such
a muscle through its nerve causes a current of
action to start at the point at which the nerve
enters the muscle fibres. The contraction wave
begins also at this point, as may be shown very
beautifully by " fixing " the contraction in the
muscles of certain insects by plunging the con-
tracting muscle into a solution which arrests and
" sets " the fibre instantly. In such cases fibres
will be found in which the contraction wave is
caught at its beginning in the neighborhood of
the nerve end-plate.

The action current, beginning at the entrance
of the nerve into the muscle fibre, passes in both
directions along the fibre. As may be shown
with the differential rheotome, or by photograph-
ing the meniscus of the capillary electrometer,

1 The experiment also demonstrates that the meniscus has no
after vibra Lions, but follows unerringly the changes of potential.

THE ELECTKOMOTIVE PHENOMENA 309

the current is diphasic. In the first phase, the
current is directed away from the nerve, in
the second phase, towards it. In extirpated
muscle, the second phase is much weaker than
the first. In normal muscle in situ (human
muscle), this difference or decrement does not
appear.

The direction of the current obtained with
the electrometer from the ivhole muscle is de-
termined by the position of the electrodes with
reference to the nerve equator, namely, a trans-
verse line drawn at the mean distance from the
entrance of all the nerve fibres. Points nearer
the equator are negative to points further away.

Action Current of Human Muscle. — Cover
the brass electrodes with cotton saturated with
saline solution, and connect them with an
inductorium arranged for tetanizing currents.
Close the short-circuiting key of the second-
ary coil. Tie about each of the non-polarizable
electrodes a piece of well washed candle-wick a
foot long. Saturate the wick with sodium
chloride solution. Place one of these elec-
trodes around the forearm near the elbow, the
other around the wrist. (The nerve equator lies
about the upper third of the forearm.) Connect
the electrodes through a short-circuiting key
with the capillary electrometer. Place the brass

310 THE OUTGO OF ENERGY

electrodes over the brachial plexus in the axilla.
Bring the meniscus into the field. Open the
short-circuiting key leading to the electrometer.
If the meniscus is displaced by a skin (secretion)
current bring it back by means of the pressure
apparatus. Set the inductorium in action. Open
the short-circuiting key of the secondary coil,
thus stimulating the nerves.

The meniscus will be displaced by an action
current.

Action Current of Heart. — 1. Expose the
heart of a frog (page 112). Lay the nerve of an
irritable nerve-muscle preparation on the beating
ventricle.

During diastole, the rheoscopic muscle will be
quiet ; at each systole, it will contract.

2. Tie a cotton thread one inch long about the
foot of each non-polarizable electrode, and let
the ends, wet with normal saline solution, rest
on the beating heart, one on the base, the other
on the apex. These electrodes will follow the
movements of the heart. Connect the elec-
trodes through a short-circuiting key to the
electrometer.

During the diastole, the meniscus will remain
at rest. At each beat of the ventricle, the
meniscus will move ; first in a direction indicating
that the base is negative to the apex, and then

THE ELECTROMOTIVE PHENOMENA 311

in the opposite direction. The action current
passes over the heart from base to apex.

These experiments show not only that there
is an action current at each systole of the heart,
but are evidence also that the resting heart
muscle is iso- electric- (i. e. of uniform potential).

The Action Current precedes the Contraction. —
Expose the heart. Fasten a very fine copper wire
to the ventricle ; the end of the wire may be
thrust through the tip of the ventricle. Mount

Pig. 53. The Heart Lever.

the heart lever (Fig. 53) on a stand so that the
writing point will write on the smoked paper of
the kymograph. Bring the free end of the wire
to the heart lever, on which it may be fastened
with a drop of colophonium cement. Make a
nerve-muscle preparation. Fasten the femur in
the upper side of the muscle clamp, at right
angles to the long axis of the clamp. Bring the
latter near the heart lever, so that the nerve may
rest on the ventricle. Fasten the tendon Achilles
to the muscle lever by a thread which passes over
the pulley on the axis of the lever before being

312 THE OUTGO OF ENERGY

secured to the lever. Thus the muscle, though
below the lever, will pull it upwards when con-
traction takes place. Let the two writing points
be in the same vertical line. Start the drum at
rapid speed. Two curves will be recorded : one
by the contraction of the ventricle, the other by
the rheoscopic muscle, stimulated to contract by
the action current. The contraction of the rheo-
scopic muscle will slightly precede the contraction
of the ventricle.

Current of Action of Human Heart. — Place
normal saline solution in two beakers. In each
let the foot of a non-polarizable electrode dip.
Connect the electrodes through the usual short-
circuiting key with the electrometer. Bring the
meniscus into the field. Let an assistant place a
finder of each hand in the saline solution.

When the short-circuiting key is opened the
meniscus will be displaced by the skin (secretion)
current. Careful observation will show also a
periodic variation synchronous with the systole
of the heart.

The diphasic character of the action current of
the heart, shown so well by the capillary elec-
trometer to the unaided eye, appears even more
clearly when the movements of the meniscus are
recorded by projecting them on a quickly moving
photographic plate. By photography, too, the di-

THE ELECTKOMOTIVE PHENOMENA

o-i o

phasic character of the action current in the more
rapidly contracting skeletal muscle is made visible,
and the form of the action current wave recorded.
Before the capillary electrometer was used for

Fig. 54. Scheme of differential rheotome.

this purpose, the differential rheotome of Bern-
stein was employed. This celebrated invention
consists of a wheel which revolves at uniform
speed and carries contacts by which the primary
circuit of an inductorium and a galvanometer

314 THE OUTGO OF ENERGY

circuit may be made. By means of the induc-
torium, the muscle is stimulated at one end.
The galvanometer records the current of action
by means of electrodes placed at the other end
of the muscle. The position of the galvanometer
contact on the wheel can be shifted nearer to or
farther from the stimulating contacts ; thus the
interval between stimulation and the making of
the galvanometer circuit may be chosen at will,
and the electromotive force at any point in the
action wave registered. By repeatedly changing
the interval, the several portions of the wave
can be investigated successively, and the results
plotted. With Hermann's rheotachygraph, the
whole electrical change may be recorded at one
time. In this instrument the stimulating con-
tacts revolve rapidly, and the galvanometer con-
tact less rapidly, so that the interval between
stimulation and the closure of the galvanometer
continually alters. The effect of the electrical
change on the galvanometer is thus prolonged so
that the galvanometer mirror is able to follow it.
The results from these different methods agree
in showing that the electrical change sweeps
over the muscle (and nerve), in the form of a
wave at a rate, in frog's muscle, of about three
metres per second. The duration of the wave
is from 0.0033 to 0.0040 second. The ascent is

THE ELECTROMOTIVE PHENOMENA 315

quicker than the descent. The latent period is
probably absent ; the process begins as soon as
the stimulus reaches the muscle. The electro-
motive force of the action current for a single
contraction of the frog's gastrocnemius is about
0.08 volt.

Direct stimulation of the whole of a normal
uninjured muscle produces no action current
whatever, because the whole muscle becomes
active at the same moment.

Action Current of Xerve

1. Negative Variation. — Sever the nerve of a
nerve-muscle preparation close to the muscle,
and lay the nerve in the moist chamber on non-
polarizable electrodes placing the equator on one
and a cross-section on the other. Lead them
through a short-circuiting key to the capillary
electrometer. Place a second pair of non-polar-
izable electrodes near the other cross-section
of the nerve. Connect this second pair to the
secondary coil of an inductorium. Connect the
primary coil through a key and the wheel inter-
rupter with a dry cell. Bring the meniscus into
the field. Open the short-circuiting key. The
meniscus will be displaced by the demarcation
current. Stimulate the nerve with induction
shocks at different rates.

316 THE OUTGO OF ENERGY

A negative variation will be observed each
time the nerve is stimulated.

2. The current of action is not dependent on
the electrical stimulation, but is an expression of
the changes in the nerve which constitute the
nerve impulse. It follows mechanical as readily
as electrical stimulation.

Lead to the capillary electrometer from non-
polarizable electrodes placed on the longitudinal
surface and cross-section. Note the position of
the meniscus. Stimulate the nerve mechanically
by snipping the end with the scissors.

There will be a negative variation as before-
Positive Variation. — The direction of the cur-
rent of action is not always opposite to that of
the demarcation current. Biedermann obtained
a current in the positive direction on stimulating
the nerve to the abductor muscle in the lobster.
In the tortoise, the cardiac auricle may be cut
away from the sinus, without injury to the cor-
onary nerve, which in this animal carries to the
auricle the cardiac fibres of the vagus. After
this operation, the auricle and ventricle remain
motionless for a time. In a heart thus prepared,
Gaskell made a thermal cross-section by im-
mersing the tip of the auricle in hot water, and
led the demarcation current to a galvanometer.
The stimulation of the vagus in the neck — the

THE ELECTROMOTIVE PHENOMENA 317

heart still resting — caused a marked increase in
the demarcation current, in other words, a posi-
tive variation. No visible change in the form of
the heart was observed.

Positive After Current. — Compensate the de-
marcation current of nerve by the method de-
scribed on page 294. When compensation is
secured, note the position of the meniscus on the
scale, and tetanize the nerve. The meniscus will
be displaced by the current of action. Note the
direction of the current. Break the stimulating
current. The meniscus will return to and pass
the position which it held when the demarca-
tion current was compensated, showing thus a
current opposed in direction to the action
current.

The positive after current is absent in weak-
ened or fatigued nerves.

Contraction secured with a Weaker Stimulus
than Negative Variation. — Place the non-polariz-
able electrodes on the longitudinal surface of the
nerve of a nerve-muscle preparation. Connect
them through the usual short-circuiting key
with the electrometer. Bring the meniscus into
the field. Arrange the inductorium for break
currents. Place the secondary coil some dis-
tance from the primary. Stimulate the nerve
in the extrapolar region. Approach the coils

318 THE OUTGO OF ENERGY

until the threshold value is reached and the
muscle contracts.

At the threshold value of muscular contrac-
tion, the current of action in the nerve will not
yet be demonstrable. The coils must be still
nearer together before the action current be-
comes visible.

This experiment has a certain suggestive
value. It would not, however, be safe to con-
clude from it that the action current is not
an essential part in the passage from the resting
to the active stage. The failure to recognize the
action current probably lies in the method.

Current of Action in Optic Nerve. — Place two
non-polarizable electrodes in the moist chamber,
and connect them through a short-circuiting key
with the capillary electrometer. Eemove the
eye of the frog, together with a portion of the
optic nerve, and lay the preparation on the elec-
trodes in the moist chamber, letting the edge of
the cornea touch one electrode and the optic
nerve the other. Cover the electrodes and the
preparation with a black pasteboard box or
other opaque screen to shut off the light. Note
the position of the meniscus in the field of
the microscope. Open the short-circuiting key.
A demarcation current from the injured optic
nerve to the cornea will be indicated. Ee-

THE ELECTROMOTIVE PHENOMENA 319

move the box so that light shall fall on the
retina.

The demarcation current will undergo a nega-
tive variation.

Shut off the light by replacing the box.

There will now be a, positive variation.

Currents of action have also been demonstrated
in the central nervous system. Gotch and
Horsley find that when the spinal cord of the
monkey is severed, and non-polarizable electrodes
are applied to the longitudinal surface and the
cross-section, a negative variation of the current
of injury appears whenever the cortex of the
cerebrum is stimulated in the neighborhood of
the fissure of Bolando, — the "motor " region. A
considerable decree of localization in the cord is
possible. It may be shown that the negative
variation from the motor region of the cortex
descends the cord chiefly in the crossed pyramidal
tract, — a collection of white fibres in the lateral
column of the cord near the gray matter. It is
known from pathological evidence that the nerve
impulse from the motor cortical cells passes
through these fibres, and the demonstration of
their negative variation justifies the hope that
this method may be useful in determining the
course of other nerve fibres in the brain and
cord.

320 THE OUTGO OF ENERGY

Errors from Unipolar Stimulation. — Attention
already has been called to the danger of unipolar
induction currents entering the electrometer
circuit in observations of the action current with
the capillary electrometer or galvanometer (page
74).

Place a nerve in the moist chamber. Connect
the capillary electrometer through a short-circuit-
iug key with non-polarizable electrodes placed on
the longitudinal surface and cross-section, about
5 mm. apart. Let a wire connected with one
pole of the secondary coil rest on the nerve about
2 cm. from the non-polarizable electrodes. Open
the short-circuiting key. When the meniscus
has come to rest, set the inductorium in action.

If the meniscus remains at rest, bring the
secondary coil nearer the primary, until unipolar
effects appear.

Secretion Current

Secretion Current from Mucous Membrane. —

Remove the skin from the lower jaw of a frog, the
skull of which has been cut away. Be very care-
ful not to touch the tongue with metal instruments
or with fragments of skin. Make a normal saline
clay electrode about 1 cm. square and 3 mm.
thick on the glass of the cork clamp near the

THE ELECTROMOTIVE PHENOMENA 321

cork. Lay the denuded jaw on the glass, and
turn the tongue forward with a glass rod until
the tip can he secured in the clamp. Avoid all
roughness. The normally upper surface of the
tongue will now rest on the clay. Bring one
non-polarizable electrode into contact with the
clay, and let the other touch the upper (normally
lower) surface of the tongue. Connect the elec-
trodes through an open key with the capillary
electrometer. Bring the meniscus into the field,
and note its position on the micrometer scale.
Close the key.

A strong difference of potential will be shown.
The normal under surface is usually positive
towards the normal upper surface.

The difference of potential thus demonstrated
is probably chiefly due to secreting glands in the
mucous membrane. If the "secretion current"
is compensated after the general compensation
method described on page 294, and the glosso-
pharyngeal nerve then stimulated, the electrom-
eter will show an electromotive force, in a
direction opposite to the original difference of
potential, — in other words, a " negative variation."

Negative Variation of Secretion Current. — Place

a frog curarized until voluntary motion is just

paralyzed back uppermost on the frog board.

Strip the skin from one thigh, and expose

21

322 THE OUTGO OF ENERGY

the sciatic nerve of this side. Place non-polar-
izable electrodes on the bare muscle of the
thigh and on the skin of the leg. Connect the
electrodes to a rheochord arranged for compensa-
tion by the bridge method, as shown in Fig. 47.
Place the capillary electrometer in a short cir-
cuit. Bring the meniscus into the field, and
note its position. Open the short-circuiting key.
Move the slider along the wire until the meniscus
returns to its original position. Now stimulate
the sciatic nerve with the tetanizing current.

A negative variation will be seen. If the skin
current was slight, the variation may be positive.

The greater part of the skin current is doubt-
less a secretion current, but not all. Weak cur-
rents have been obtained from skin devoid of
glands, for example, the eel's skin. Hermann
attributes this current to the degeneration which
accompanies the change of the nucleated cells of
the corium to the dead scales of the outer
epidermis.

A strong secretion current may be obtained
from the skin of the foot (cat). On stimulation
of the sciatic nerve, the current is increased
(positive variation).

In the submaxillary gland, the hilus is positive
to any point on the external surface of the gland.
Stimulation of the chorda tympani nerve, secre-

THE ELECTROMOTIVE PHENOMENA 323

tory fibres from which are supplied to the gland,
causes the surface to become still more negative,
i. e. the secretion current is increased (positive
variation). Stimulation of the sympathetic, which
also sends fibres to the gland, causes the secretion
current to lessen (negative variation).

Electrotonic Currents

It has already been shown that the irritability
and conductivity of the nerve are altered by the

Fig. 55.

galvanic current. So also are the electromotive
properties.

Place one pair of non-polarizable electrodes
near the middle of a long piece of extirpated
nerve, and one other pair at each end, on the
cross-section and longitudinal surface as in Fig.
55. Connect the middle pair through a key
with two dry cells. Connect each of the other
pairs through a short-circuiting key with a

324 THE OUTGO OF ENERGY

capillary electrometer. Let one observer watch
each meniscus, while a third experimenter
manages the polarizing current. Note the posi-
tion of each meniscus. Open the short-circuiting
keys. In each electrometer, the meniscus will he
displaced by the demarcation current. It should
be noted that the demarcation currents are of
opposite direction, flowing in the nerve from the
cross-section towards the longitudinal surface.
Make the polarizing current.

When the polarizing current enters the nerve,
there will be a twitch in each electrometer,
caused by the negative variation of the demar-
cation current; this may be neglected. Each
meniscus will be displaced; on the side of the
anode of the polarizing current, the demarcation
current will be reinforced, but on the side of the
cathode it will be diminished.

Thus the passage of the galvanic current
through a part of the nerve has polarized the
nerve on both sides of that part. The extra-
polar region on the side of the anode becomes
positive ; the extrapolar region on the side of the
cathode becomes negative ; similar changes prob-
ably occur in the intrapolar region. In short, an
electrotonic current is set up, having the same
direction as the polarizing current. This electro-
tonic current augments the demarcation current

THE ELECTROMOTIVE PHENOMENA 325

on the side of the anode, but is opposed to that
on the side of the cathode. It appears when
any two points on the longitudinal surface are
" led off " to the electrometer, and is entirely
independent of the demarcation current.

The intensity of the electrotonic current de-
pends on the intensity of the polarizing current.
The greater the separation of the polarizing elec-
trodes, the less the electrotonic effect, as might be
expected from the great resistance of nerve. If
this factor be excluded by placing in the circuit
a much greater resistance than that of nerve, the
electrotonic effect will be found to increase with
the length of the intrapolar region. The electro-
tonic current is absent in dead nerves, in strongly
cooled nerves, and in those ligated between the
polarizing electrodes and the electrodes leading
to the electrometer.

In muscle, the electrotonic currents are much
stronger than in nerve.

Negative Variation of Electrotonic Currents ;
Positive Variation (Polarization Increment) of Polar-
izing Current. — Place the polarization electrodes
near one end of the nerve. Connect them through
a short-circuiting key with a dry cell. From the
short-circuiting key lead to a capillary electrom-
eter (Fig. o6~). From the middle of the nerve
lead off the electrotonic current through a short-

326 THE OUTGO OF ENERGY

circuiting key to a second capillary electrometer.
Near the other end of the nerve place stimu-
lating electrodes connected with the secondary
coil of an inductorium arranged for tetanization.
Make the polarizing current. Open the short-
circuiting key leading to the electrotonic elec-
trometer, and note the position taken by the
meniscus under the influence of the electrotonic
current. Make the tetanizing current.

^- z#=J Q;

Fig. 56.

The strength of the electrotonic current will
be diminished. At the same time the strength
of the polarizing current will be increased (polar-
ization increment).

These are in reality action currents.

The electrotonic currents are absent in nerves
which lack a myelin sheath. This suggests that
the myelin in some way divides the nerve into a
core and a sheath. If a zinc wire connecting
two electrodes is surrounded by a layer or sheath

THE ELECTROMOTIVE PHENOMENA 327

of saturated solution of sulphate of zinc, there
will be no polarization, and the current will not
spread to any extent beyond the electrodes. If,
however, the wire is platinum instead of zinc,
polarization will take place where the current
passes from the electrodes through the electrolyte
into and out of the wire, and the polarization
may be recognized by connecting the extrapolar
region with the electrometer as in the foregoing
experiment. The resistance to the spread of the
electrotonic current in a longitudinal direction is
relatively slight, so that it passes almost instantly
along the core.

In nerve, also, the greater resistance in the
transverse direction (five-fold greater than the
resistance in the longitudinal direction) would
favor the spread of electrotonic currents length-
wise along the nerve.

Certain observations of Biedermann make it
difficult to accept without reservation the simple
physical explanation just offered. For example,
the narcotization of a nerve with ether or chloro-
form causes the electrotonus to disappear a
short distance from the electrodes, although
still strongly present in their immediate neigh-
borhood. These experiments cannot be discussed
here, but they indicate that to the purely physi-
cal must be added a physiological electrotonus.

328 THE OUTGO OF ENERGY

The Electrotonic Current as a Stimulus. — As

would naturally be expected, the electrotonic
current may be an effective stimulus. Bring the
end of an extirpated nerve A into contact with
the distal portion of the nerve of a nerve-muscle
preparation, B, as in Fig. 57, and place on the
other end of A non-polarizable electrodes joined
through a key to a battery of two cells. Make
the galvanic current.
Muscle B will contract.

The galvanic current polarizes nerve A, and
the electrotonic current thereby
set up passes into the nerve of
B through the contact, and occa-
sions in nerve B an impulse
which descends to the muscle

Fig. 57.

and stimulates it to contract.

Paradoxical Contraction. — Expose the bifur-
cation of the sciatic nerve into tibial and peroneal
branches. Polarize either of these branches.
(The electrodes should not be placed too near
the bifurcation.)

On making and breaking the polarizing cur-
rent, the muscles supplied by each branch will
contract.

In this instance, the extrapolar region of the
branch polarized lies in part in the main trunk.
The electrotonic current there spreads into the

THE ELECTROMOTIVE PHENOMENA 329

contiguous axis cylinders, anions them those
of the other branch.

Electeic Fish

There are several species of fish which possess
the power of discharging electrical currents when
stimulated. The best known are Torpedo, a ray
.found on the coasts of Europe ; Gymnotus, the
electrical eel of South America ; and Malaptera-
rus electricus, a catfish found in the Xile and
other African rivers. The electromotive force of
these fishes is derived from a special organ placed
beneath the skin. This electrical organ is bilat-
eral and is formed of parallel plates. One side
of each plate receives a branch of the electrical
nerve, which in Malapterurus is a single great
axis cylinder derived from a giant nerve cell.
The side of the plate receiving the nerve becomes
negative to the other side when the electrical
organ is active ; it behaves like the negative plate
of the ordinary cell. When the nerve is at rest,
there is no difference of potential in the electrical
organ. The discharge in the active state is peri-
odic, and may rise to 200 per second. The elec-
tromotive force is considerable : in Torpedo, 30-35
volts, 5 volts for each cubic centimetre of the
organ, 0.08 volt for each plate. The fish itself

330 THE OUTGO OF ENERGY

is not injured by the current ; its tissues are
not easily excitable by electricity, though they
respond readily to mechanical stimulation.

Apparatus

Normal saline. Bowl. Towel. Pipette. Glass plate.
Sharp knife. Two dry cells. Four non-polarizable elec-
trodes. Simple key. Capillary electrometer. Co-ordi-
nate paper. Millimetre scale. Inductorium. Electrodes.
Thirteen wires. Porcelain dish. Muscle clamp. Muscle
lever. Stand. Cork. Kheochord. Normal saline clay.
Filter paper. Wheel interrupter. Candle-wick. Electro-
magnetic signal. Pole-changer. Bent hooks. Black paper
(stroboscope). Moist chamber. Large and small brass
electrodes. Cotton. Common salt. Two beakers. Satu-
rated solution of zinc sulphate. Cotton thread. Frog
board. Heart-holder. Black box for covering retina.
Bunsen burner. Glass slide. Cork clamp. Frogs.

THE CHANGE IN FORM 331

III

THE CHANGE IN FORM

The change in form or the contraction of muscle
is the most conspicuous of the several ways in
which its energy is set free. It has already been
shown that this change consists of a shortening
of the contractile mass followed by a return to
the original length. It is necessary now to de-
termine whether the muscle becomes smaller on
entering the active state or whether the altera-
tion in form is simply a shifting — a transloca-
tion — of the muscular units.

Volume of Contracting Muscle

Strip the skin from the hind limb of a frog.
Hang the limb from the hooked electrode in the
stopper of the volume tube (Fig. 58) and place
the stopper loosely in the tube. Hook the elec-
trode at the other end of the tube into the limb
near the foot. Fill the tube absolutely full of
boiled normal saline solution, slightly withdraw-
ing the stopper for the purpose. Eeplace the
stopper in the tube in such a way that all air

332

THE OUTGO OF ENERGY

Fig. 58. The
volume tube.

bubbles shall be excluded. If the height of the
water-column in the capillary tube
does not permit the meniscus to be
readily observed, move the glass rod
in the stopper in or out until the
meniscus is adjusted. Connect the
electrodes with the secondary coil
of an inductorium arranged for
single induction currents. Note
carefully the level of the water in
the capillary tube. Stimulate the
muscle with a maximal break
current.

The level of the water in the
capillary will not change. The
change in the form of the contracting muscle
is not accompanied by a change in volume.1

The Single Contraction or Twitch

The change in the form of the muscle on
entering the active state is usually studied from
the graphic record made on a smoked surface
by a writing lever the shorter arm of which is
attached to the end of the muscle. Such a
record, it should be remarked, gives the extent

1 This experiment must not be regarded as excluding a very
slight change in volume, because of the difficulty of expelling,
by boiling or otherwise, all the air in the saline solution.

THE CHANGE IN FOEM 333

and the time relations of the shortening, but not
the thickening of the muscle. (See page 339. J

The Muscle Curve. Prepare a gastrocnemius
muscle together with the distal third of the
femur. Fasten the latter in the muscle clamp.
Attach the tendo Achillis to the hook on the
muscle lever by means of a fine copper wire
which should be wrapped round the hook and
the end then carried to the binding post on the
muscle lever. Place a ten-^ram weight in the
scale-pan. Connect the posts on the clamp and
the lever with the secondary coil of an inducto-
rium arranged for maximal induction currents.
In the primary circuit place an electromagnetic
signal. Bring the writing points of the signal
and the muscle lever against the smoked paper
in the same vertical line. Start the drum at its
most rapid speed. Stimulate the muscle with a
maximal break current.

The muscle will shorten and then extend,
marking a period of rising energy and a period
of sinking energy. Note that the period of rising
energy is shorter than the period of sinking
energy. Close observation will show that the
lever does not begin to move at the instant the
muscle is stimulated, — there is here an interval
or latent period.

The Duration of the Several Periods. — Turn to

334 THE OUTGO OF ENERGY

the right the screw at the top of the sleeve bear-
ing the recording drum until the sleeve is raised
from the friction bearing. The drum can now
be "spun." Start the tuning fork vibrating,
spin the drum, lay the writing point of the tun-
ing fork on the smoked paper near the line
traced by the electro-magnetic signal, and stim-
ulate the muscle with a maximal induction
current.

An interval will be found between the moment
of stimulation (marked by the electromagnetic
signal) and the beginning of contraction. This
interval is the mechanical latent period. Meas-
ure its duration by means of the tuning fork
curve. Measure also the duration of the period
of rising energy and the period of sinking energy.

Helmholtz, who first measured the latent period
of frog's muscle, found a mean duration of 0.01
sec, while the phase of rising energy measured
0.04 sec, and the phase of sinking energy 0.05
sec. More recent measurements by Tigerstedt
and others have reduced the latent period
given by Helmholtz to from 0.0025 to 0.005
sec. The interval observed grows less as the
intensity of stimulation is increased from the
threshold to the maximal value ; further in-
crease in intensity (supermaximal stimulation)
causes no further diminution in the latent period.

THE CHANGE IN FORM 335

The period is shorter at high temperatures than
at low, with maximal break induction currents
than with make induction currents, with break
induction currents than with closure of the gal-
vanic current. Changing the load of the muscle
is without effect on the latent period.

When the muscle is stimulated through its
nerve the latent period is longer by about 0.002
sec. than when the electrodes are placed on the
muscle itself (Bernstein), due allowance being
made for the time occupied by the passage of
the nerve impulse along the trunk of the nerve
from the point of stimulation to the muscle. The
additional time is taken perhaps in the passage
of the impulse through the end plate into the
contractile substance.

Griitzner has shown that the striated muscle
fibres, particularly of vertebrates, differ in their
histological elements. Some are rich in sarco-
plasm, and when seen by transmitted light appear
cloudy and granular ; others have less sarcoplasm
and are relatively translucent. This difference
in structure is associated with a striking differ-
ence in the character of the contraction. The
muscles composed chiefly of turbid fibres contract
slowly, while " clear " muscles contract rapidly
(compare page 178). Thus in the rabbit the
duration of the contraction of the red soleus

336 THE OUTGO OF ENEKGY

muscle, which is rich in sarcoplasm, is about
1.0 sec, while in the white gastrocnemius — a
" clear" muscle —it is 0.25 sec. In the frog, the
contraction period of the hyoglossus is 0.205,
the gastrocnemius 0.120, and the gracilis 0.108
sec. (Cash). The latent period is longer in the
red muscles. The amplitude of contraction is
less in the red than in the white.

The mixture of quickly and slowly contracting
fibres in the same muscle is sometimes obviously
an advantage. Thus in certain bivalves the quick
fibres in the shell-closing muscle close the shell
rapidly, and the slow fibres keep it closed after
the contraction of the quick fibres has ceased.

The form of the contraction is influenced by
the mixture of fibres. The clear fibres reach
their maximum shortening sooner than those
rich in sarcoplasm. In some instances, indeed,
the contraction curve may show two summits.
These differences may perhaps explain the char-
acteristic differences in the form of the contrac-
tion wave of different muscles, observed by Cash
and others. The white fibres are more easily
fatigued than the red. Thus the triceps humeri
of the rabbit contracts at the beginning of stimu-
lation like an unmixed white muscle (quickly),
hut later like a red muscle (slowly).

The Excitation Wave. — Prepare a plate of

THE CHANGE IX FORM 337

cork one inch long and just narrow enough to be
held in the Gaskell clamp (Fig. 26). Smoke a
drum. Raise the drum off the friction bearing
by turning to the right the milled screw at the
top of the shaft. Fasten the end of a curarized
sartorius muscle to the cork plate by means of
two needles to the ends of which conducting
wires are soldered. Place the preparation in the
Gaskell clamp in such a way that the clamp
shall compress the equator of the muscle suffi-
ciently to prevent the passage of a contraction
wave from one part of the muscle to the other,
but not sufficiently to prevent the passage of the
excitation. Let a second pair of needle elec-
trodes rest on the muscle near the upper side of
the clamp. Fasten the clamp to the iron stand.
Connect the two pairs of electrodes to the end
cups of a pole-changer (without cross-wires), the
side cups of which are connected with the secon-
dary coil of an inductorium arranged for single
maximal induction currents. In the primary
circuit of the inductorium place the electro-
magnetic signal. Fasten the tibial end of the
muscle to a muscle lever. Bring the writing

o o

point against the smoked surface exactly under-
neath the point of the electro-magnetjc signal.
" Spin " the drum slowly. Place the writing
point of a vibrating tuning fork against the

22

338 THE OUTGO OF ENERGY

smoked paper below the recording levers. Stim-
ulate the muscle with a maximal break current
first through one pair of electrodes and then
through the other. In each of the resulting
curves measure the interval between stimulation
and contraction (for method see page 184).

This interval will be longer when the muscle
is stimulated farther from the portion the con-
traction of which is recorded. The difference is
the time taken by the excitation to traverse the
part of the muscle lying between the two pairs
of electrodes. Measure the distance and calcu-
late the speed of the excitation.

The nature of the excitation process is un-
known. The current of action has been shown
to precede the visible change in form of muscle.
It is usually assumed to be a manifestation of the
excitation process, but the precise relation be-
tween the two has never been ascertained. The
speed of the excitation is the same as that of the
contraction wave.

The Contraction Wave. — Eemove from a CU-
rarized frog the long parallel-fibred muscles ex-
tending along the inner side of the thigh from
the pelvis to the tibia. Let the preparation rest
horizontally on a glass plate supported on a stand.
With fine wire fasten near the axle of each of
two heart levers a small piece of cork into which

THE CHANGE IN FORM 339

the point of a long pin has been thrust. Place
the levers so that the head of the first pin rests
on the muscle near one end, while the head of
the second pin rests near the other end. Place
needle electrodes at one end of the muscle.
Bring the writing points of the two levers
against a smoked drum in the same vertical line.
Let a tuning fork write its curve near that of the
muscle levers. Set the tuning fork vibrating.
Let the drum revolve rapidly. Stimulate the
muscle at one end with a maximal make induc-
tion current.

The lever near the point of stimulation will
begin to rise before that farther away. Evidently
the contraction starts at the point stimulated and
spreads along the muscle in the form of a wave
(compare pages 308 et seq.}.

Determine the speed per second of the wave
of contraction by measuring with the tuning-fork
curve the time occupied by the wave in passing
along the muscle from one lever to the other.

It is evident that a lever resting on a horizontal
muscle will register the change in form of the
cross-section on which the lever lies, while a lever
attached to the end of a muscle suspended verti-
cally will be moved by the change in form of all
the cross -sections of which the muscle is com-
posed. The curves secured by the two procedures

340 THE OUTGO OF ENERGY

are similar in form, but different in duration.
The curve of thickening is shorter by the differ-
ence between the time taken by the contraction
wave to pass over the single cross-section, on the
one hand, and the whole length of the muscle on
the other.

An extirpated muscle is apt to remain short-
ened after contraction. To bring muscles back
to their original length it is usually necessary to
weight them, or — as in the bodv — to submit
them to the pull of antagonists. Even the
weighted muscles may return very slowly and
imperfectly to their normal length. This con-
tracture, as it is termed, is seen especially in
strong direct stimulation, in poisoning with vera-
trine, and as death comes on. Contracture is
not the result of fatigue, for when the muscle
is repeatedly stimulated contracture diminishes,
instead of increasing. During contracture, the
irritability of the muscle for stimulation through
the nerve is diminished.

Relation of Strength of Stimulus to Form of
Contraction Wave. — Fasten the femur of a gas-
trocnemius preparation in the muscle clamp and
attach the Achilles tendon to the muscle lever
with a fine copper wire the end of which should
be carried to the binding post on the handle of
the lever. Connect this post and that on the

THE CHANGE IN FORM 341

muscle clamp with the secondary coil of the in-
ductorium. Bring the writing point against the
smoked drum. Stimulate the muscle with break
induction currents of varying intensity and record
the contraction curves.

It will be found that the contraction is longer
with weak stimuli than with strong.

Influence of Load on Height of Contraction. —
Attach a curarized gastrocnemius preparation
to the muscle lever and bring the writing point
against a smoked drum. Connect the binding
posts on the lever and the muscle clamp with
the secondary coil of the inductorium. Load
the muscle with the lever and scale-pan only.
With the drum at rest record the contraction
on stimulation with a maximal induction current.
Turn the drum by hand one millimetre. Place
a one-gram weight in the scale-pan, and record
the contraction produced by a make induction
current of the same intensity as before. Con-
tinue to add gram weights and to record the
contractions until ten one-gram weights have
been placed in the scale-pan. Now increase the
load each time by ten grams, recording the con-
traction after each increase, until the muscle is
weighted with one hundred grams. (Care should
be taken not to fatigue the muscle by stimulating
it oftener than is necessary to obtain the record.)

342 THE OUTGO OF ENERGY

Within certain narrow limits the height of the
contraction will be increased by the increase in
the load. With increasing loads the height of
contraction diminishes at first quickly, and then
more slowly.

Influence of Temperature on the Form of the
Contraction. — Prepare a gastrocnemius muscle
together with its attachment to the femur.
Fasten the femur in the " muscle warmer " (Fig.
59). Tie the end of a fine copper wire about
ten centimetres long around the Achilles tendon.
Bring the wire through the opening in the muscle
warmer and fasten the wire around the pulley
of the muscle lever. If the pulley is of metal
the muscle lever should be supported on a stand
separate from that bearing the muscle warmer
or should be otherwise insulated. Connect the
muscle warmer and the muscle lever with the
secondary coil of an inductorium arranged for
single induction currents. Fill a beaker with
cracked i'ce and add a little salt. Immerse the
muscle warmer in the beaker and support the
latter on a suitable stand. Bring the writing
point of the muscle lever against a smoked
drum. Let the drum revolve at fairly rapid
speed. Stimulate the cooling muscle at inter-
vals of 5° with a maximal break current.

THE CHANGE IN FORM

343

It

iii

^^

The Muscle Warmer. 1 — A disk, supported by a
rod, bears three pins (Fig. 59). One of the three pins
is prolonged and bent at a right angle near its lower
end. To the bend is fas-
tened one end of the mus-
cle under experimentation.
About the other end is tied
a fine copper wire which
passes through a hole in
the disk to reach a muscle
lever. A second opening in
the disk is provided with a
short metal tube, in which
a thermometer is held by
a piece of rubber. The
bulb of the thermometer
may be placed on a level
with the belly of the
muscle. When these ad-
justments are complete, a

glass cylinder is brought FlG- 59' The muscle warmer;

J an apparatus for studying the in-

against the Under Surface fluence of temperature on mus-

„,, ,., , ■■•iii cular contraction.

of the disk, where it is held

in position by the "spring" of the three pins. A
beaker or other vessel containing water is now
placed beneath the cylinder and raised until the
cyclinder is sufficiently immersed. The temperature
of the muscle is altered by heating or cooling this

American Journal of Physiology, 1904, x, p. xliii.

344 THE OUTGO OF ENERGY

water. Direct electrical stimulation of the muscle
may be made by connecting one electrode with the
metal parts of the apparatus and the other with the
copper wire attached to the upper end of the muscle.

Note that as the temperature falls the contrac-
tion curve becomes longer. The phase of rising
energy is lengthened more than the relaxation.
The earlier portion of the relaxation is lengthened
less than the later ; the muscle shows a tendency
to contracture (see page 340).

Place fresh paper on the drum. Let the drum re-
volve very slowly. Place a lighted Bunsen burner
under the arm of the muscle warmer. At intervals
of 5° stimulate the muscle with a maximal break
current. Note the changes in the contraction.

The height of contraction is least at the freezing
point of the muscle (-5°). It rises from the
freezing point to 0°; falls from 0° to 19°; in-
creases to 30°, which is the maximum ; from 30°
to 45° diminishes again; and at 45° the frog's
muscle usually enters into a state called rigor
caloris; the muscle becomes opaque, inelastic,
resistant to the touch, shortens very considerably,
and undergoes chemical changes of great impor-
tance. The duration of contraction lessens with
the rising temperature, being least at 30°. Above
30° the duration remains approximately un-
changed. The latent period is increased at low

THE CHANGE IN FORM 345

temperatures, diminished at high. Above 30° the
excitability to electrical stimuli diminishes stead-
ily ; it disappears almost entirely before rigor is
reached.

Influence of Veratrine on the Form of the Con-
traction.— With a capillary pipette inject in the
dorsal lymph sac 5 drops of a 1 per cent solution
of veratrine sulphate or acetate. After a few
minutes, test for symptoms of veratrine poisoning
by pinching the foot from time to time.

Soon the mechanical stimulation will be fol-
lowed by prolonged contraction of the extensor
muscles and still more prolonged relaxation.

Make a gastrocnemius muscle preparation.
Fasten the muscle to a muscle lever and bring the
writing point against a smoked drum. Eecord a
single contraction.

Note the increased height of the phase of
shortening, and the prodigious increase in the
duration of the phase of relaxation. This con-
tracture (page 340) is lessened by repeated stimu-
lation, but reappears if the muscle be allowed
to rest. Cooling or warming usually causes the
veratrine effect to disappear temporarily.

A quick initial contraction may precede the
characteristic veratrine contraction, possibly be-
cause the veratrine affects differently the red and
the clear fibres.

346 THE OUTGO OF ENERGY

Tetanus

Superposition of Two Contractions. — Arrange
a gastrocnemius muscle to write on a smoked
drum. Connect the binding posts on the muscle
lever and muscle clamp with the secondary coil
of an inductorium. In the primary circuit (posts
1 and 2) place the electro-magnetic signal and a
simple key. Let the drum revolve at a rapid
rate. Send two maximal induction currents
through the muscle at varying intervals, begin-
ning with the shortest interval possible. The
secondary should be at such a distance from
the primary coil that both make and break cur-
rents shall cause maximal contraction.

If the second stimulus fall in the latent period
of the first contraction, the stimulus will be with-
out effect. If the second stimulus fall between
the beginning of shortening and the end of relax-
ation caused by the first stimulus, the contraction
following the second stimulus will not begin from
the base line, but will be superposed on the first,
as if the state of shortening from which the
second contraction begins were the resting stage
of the muscle. The height readied by the
second contraction will be greater than that
reached by the first. The summed height is

THE CHANGE IN FORM 347

usually greatest when the second contraction
starts from the summit of the first, but this rule
is not invariable. The summit of the summed
contraction does not necessarily coincide with the
summit of the second contraction ; the higher the
summed contraction, the quicker the summit is
reached.

Superposition in Tetanus. — Place the vibrat-
ing interrupter (Fig. 50) in the primary circuit.
Eepeat the preceding experiment, but use a series
of stimuli instead of only two. It will be ob-
served that a third contraction may be super-
posed on the second, a fourth on the third, and
so on. The shortening of muscle, however, has a
limit ; and when this is reached, further stimu-
lation merely maintains this maximum degree of
shortening until fatigue sets in. When the in-
terval between successive stimuli is very brief
the successive contractions appear to fuse to-
gether and the contraction curve becomes a con-
tinuous line. The more rapid the contraction,
the shorter must be the interval between succes-
sive stimuli in order to cause the disappearance
of the individual contractions. Thus a more
rapid rate of stimulation is necessary to produce
complete fusion in fresh, highly irritable muscles
than in those the irritability of which has been
diminished by cold or fatigue. For this reason

348 THE OUTGO OF ENERGY

contractions which at the beginning of the stim-
ulation period are marked by notches in the curve
fuse completely as longer stimulation brings on
fatigue. Here also the differences in the structure
of muscles already mentioned play an important
part. Thus the red muscles of the rabbit are
thrown into tetanus by a much smaller number
of stimuli per second than are the more quickly
contracting white muscles.

Relation of Shortening in a Single Contraction
to Shortening in Tetanus. — 1. Kecord side by
side the contractions of a muscle unloaded except
by the muscle lever. Stimulate with a single
maximal induction current ; stimulate with a
brief tetanizing current.

The shortening of the single twitch of the un-
loaded muscle is as great as the shortening in
tetanus.

2. Load the muscle with ten grams and repeat
Experiment 1.

The shortening in tetanus will now be con-
siderably greater than that of the single twitch.

3. Load the muscle with ten grams but sup-
port the weight by the after-loading screw, so
that the weight cannot pull on the muscle until
the contraction begins. Record one contraction
on a stationary drum in response to a maximal
make induction current. Turn the drum one

THE CHANGE IN FORM 349

millimetre. Kaise the writing point of the lever
one millimetre by means of the after-loading
screw. Stimulate the muscle with a make in-
duction current of the same intensity as before.
Again turn the drum and raise the point of the
lever one millimetre, and stimulate the muscle
as before. Continue this until the after-loading
screw is raised so high that the muscle no longer
shortens sufficiently to raise the lever.

Obviously in this experiment the weight is arti-
ficially supported during a progressively greater
portion of the contraction. It will be found that
the total shortening of the muscle loaded only
during the latter portion of the contraction is
as great as the shortening of a loaded muscle in
tetanus.

The Isometric Method

Thus far we have observed the development
of energy in a muscle stretched by a small, un-
varying load. The principal part of the energy
set free in this isotonic process appears as the
mechanical energy of a visible change in form ;
a small part of the energy of the muscle is con-
verted into tension. Fick has pointed out that
if the muscle be made to pull against a strong
spring, the change in the length of the muscle

350 THE OUTGO OF ENERGY

will be very slight, and the greater portion of the
energy will be converted into tension and stored
in the spring. If the excursion of the spring be
recorded by a writing lever, the curve will be
practically a record of the course of transforma-
tion of energy into tension, and will be only to a
slight extent the record of a change in form.

In order to determine the amount of energy
converted into tension in the isometric contrac-
tion, it is necessary to graduate the spring against
which the muscle pulls.

Graduation of Isometric Spring. — Attach the
large scale-pan to the strong spring of the appa-
ratus shown in Fig. 60. Place a long straw on
the end of the spring. Bring the writing point
against the smoked paper of a kymograph. Turn
the drum once round to record an abscissa. Re-
turn the drum to its former position, and place
80 grams in the scale-pan attached to the spring.
When the spring is stretched turn the drum once
round to record the bending under 100 grams'
weight.1 Restore the drum to its former posi-
tion, add 100 grams, and make record of the
extension at 200 grams. Continue the record
up to 1000 grams. Preserve the curve for ref-
erence (page 363).

i The scale-pan weighs about 20 grams.

THE CHANGE IN FORM

351

The Heavy Muscle
Lever.1 — It is sometimes
necessary to after- load a
muscle lever with weights
far in excess of those that
a light muscle lever will
bear without " springing"
and thus altering the ab-
scissa. Such heavy loads
are borne by the heavy
muscle lever illustrated in
Fig. 60. A tripod of ja-
panned malleable iron, 27
cm. high and 17.5 cm.
broad at the base, supports
a femur clamp and a mus-
cle lever. The latter is
a steel tube 5 cm. long,
pierced by a steel axle 9 mm.
long, revolving between
heavy brass posts. The
lever weighs about 2.5 gms.
The aluminium scale-pan
weighs about 20 gms. ; it
holds one hundred 10-gram
weights. The lever may be
turned completely over in
a backward direction, and

Fig. 60. The heavy muscle
lever.

1 American Journal of Physiology, 1903, viii, p. xl.

352 THE OUTGO OF ENERGY

thus be entirely out of the way. The steel spring
shown upon the left of Fig. 60 may then be turned to
the right to bring its wire hook into the opening
through which the scale-pan is reached. The scale-
pan may then be attached to this isometric spring and
the spring empirically graduated. When the gradua-
tion scale has been written, the milled screw that
holds the isometric spring upon the left-hand post
(Fig. 60) may be loosened, the spring turned with the
hook up, and the screw made fast again. The lower
end of the muscle may now be attached to the
hook upon the spring and an isometric curve written.

The screw clamp holding the muscle clamp is
insulated. A binding post upon the muscle clamp,
and another binding post upon the right-hand post
supporting the axle of the lever, allow direct stimula-
tion of the muscle.

This lever serves especially well for the double
abductor preparation of Fick, consisting of the semi-
membranosus and gracilis of both sides.

Isometric Contraction. — Invert the spring.
Fasten the femur of a gastrocnemius preparation
in the muscle clamp, and the Achilles tendon to
the spring. Connect the binding posts on the
lever and the clamp with the secondary coil of the
inductorium, arranged for single maximal induc-
tion currents. Let the drum revolve at a rapid
speed. Stimulate the muscle with a maximal
break current.

THE CHANGE IN FORM doo

An isometric contraction will be recorded.

Eemove the spring, and attach the tendon to
the lever weighted with ten grams. Stimulate
the muscle with a break induction current of the
strength used before.

The usual isotonic curve will be written.
Comparison of the isometric and isotonic curves
reveals as a rule in the isometric curve a longer
phase of rising energy and a flattened summit
or plateau. The muscle reaches its maximum
tension sooner than its maximum shortening and
maintains the maximum tension longer than the
maximum shortening.

Contraction of Human Muscle

Simple Contraction or Twitch. — Place the
middle, ring, and little fingers in the support of
the ergograph (Fig. 61). Let the adjustable rod
rest on the index finger near the distal end of
the middle phalanx. Place the point of the rod
in the hole nearest the free end of the spring.
Adjust the writing point to write on a smoked
drum revolving at moderate speed. With the brass
electrodes covered with wet cotton (page 129),
stimulate the abductor indicis with a single max-
imal break induction current. Compare the form
of the curve thus obtained with the contraction
curve of the skeletal muscle of the frog.

23

°54

OD-

THE OUTGO OF ENERGY

The Ergograph.1 — A flat, steel spring provided
with a writing point is fastened in a stout iron support
clamped to the table (Fig. 61). The second, third, and
fourth fingers of the subject's hand are fastened with
tapes to the wooden support. Upon the index finger

C3CP=

Fig. 61. The ergograph ; also employed for recording the isometric and
i si. tonic contractions of human muscle.

near the distal end of the middle phalanx is placed a
rod the length of which is adjustable. The point of
the rod passes through a rubber ring and presses
against the under side of the spring. When the point

1 First described in the " Introduction to Physiology," 1901,
p. 220.

THE CHANGE IN FORM 355

is near the free end of the spring, contractions of the
abductor indicis muscle with voluntary and electrical
stimuli may be recorded. When the point of the
rod is placed near the cast-iron support of the spring,
the movements of the spring will be so much less that
almost none of the energy of the muscle will be con-
verted into mechanical motion. An isometric con-
traction will be recorded.

Isometric Contraction. — Place the point of the
adjustable rod in the hole nearest the cast-iron
support of the spring. The movement of the
spring is so much less at this point that almost
none of the energy of the muscle will be con-
verted into mechanical motion. Stimulate the
muscle as before with a maximal break induc-
tion current. Compare the isometric curve thus
recorded with the largely isotonic curve previ-
ously obtained.

Artificial Tetanus. — Eeplace the adjustable rod
in its former position (isotonic arrangement).
Stimulate the abductor with the tetanizing cur-
rent of the inductorium. Compare the curve
with the tetanus of frog muscle.

Natural Tetanus. — 1. Contract the abductor
by voluntary impulse. This also gives a tetanus
curve. When the natural tetanus is prolonged,
it frequently is marked by oscillations having a
periodicity of about ten per second.

356 THE OUTGO OF ENERGY

2. Place the adjustable rod in the hole nearest
the iron support (isometric arrangement). Stimu-
late the muscle (1) with the tetanizing current
of the inductorium ; (2) by voluntary impulse.

It will be seen that the energy set free by the
natural stimulus is much greater than when the
muscle is stimulated artificially.

Smooth Muscle

Spontaneous Contractions. — Make two cuts,
5 mm. apart, through the frog's stomach at
right angles to the long axis. Pass a bent hook
through the ring (i. e. through the cavity of the
stomach), and fasten the hook in the muscle
clamp. Pass a second hook around the lower
margin of the ring and attach it by means of a
fine copper wire to the straw of the heart lever
(Fig. 53). Contraction of the circular fibres, can
thus be made visible. Bring the writing point
against a drum revolving about once an hour.
Wrap filter paper saturated with normal saline
solution about the muscle ring. Keep this
thoroughly moist. Proceed to the remaining ex-
periments, observing the stomach preparation
from time to time.

Spontaneous rhythmic contractions will appear.
Note the changes in tonus.

THE CHANGE IX FOEM 357

Simple Contraction. — Prepare a second ring
of frog's stomach in the manner described in
the preceding experiment. Attach the lower
margin of the ring to the muscle lever by means
of a fine copper wire. Carry the end of the
copper wire to the binding post on the muscle
lever. Connect this post and the post on the
muscle clamp with a dry cell, interposing a sim-
ple key. Place the electro-magnetic signal in the
primary circuit. Bring the writing points of the
muscle lever and the signal against a smoked
drum in the same verticle line. Let the drum
move at slow speed. Stimulate the muscle by
making and breaking the galvanic current once,
not oftener.

Compare the duration of the latent period with
that of skeletal muscle. Compare the form of
the contraction curve with that of skeletal
muscle.

Tetanus. — Determine how frequent the stimuli
must be in order that the separate contractions
may be fused into a smooth curve.

Usually the muscle after contracting loses its
irritability for several minutes. If this occur,
the ring may be laid aside, covered with filter
paper saturated with normal saline solution.
Excellent curves are often obtained from muscle
preserved in this way for halt" an hour or more.

358 the outgo of energy

The Work Done

Influence of Load on Work done. — In the

tracings obtained in the experiments on page 341
with loads of 10 grams and upwards measure
the distance from the summit of each curve to
the abscissa. Calculate the gram-millimetres of
work done at 10, 30, 50, 70, and 90 grams,

using the formula W= — in which W is work
° m

done, in gram-millimetres ; iv, the weight lifted

in grams, — i. e. the weight of the scale-pan and

lever (about 12 grams) plus the weight put into

the scale-pan (the weight of the muscle itself

may be neglected) ; h, the height, in millimetres,

to which the load is lifted ; m, the magnification

of the lever.

Write the results on the smoked paper.

Note that within wide limits an increase in the
load increases the work done by the muscle.

Absolute Force of Muscle. — Secure the femur
of a gastrocnemius muscle preparation in a mus-
cle clamp and fasten the tendon to the rigid
muscle lever. After-load the muscle until it
just fails to lift the load when stimulated with
tetanizing induction currents.

The load which neither extends a contracting
muscle nor allows it to shorten is a measure of
the "absolute force" of the muscle.

THE CHANGE IN FORM

359

Total Work done ; the "Work Adder — Attach
a scale-pan to the cord that passes over the
pulley on the axle of the
work adder (Fig. 62).

The Work Adder.1 — A wheel
of aluminium (Fig. _G2) bears
upon its axle a counterpoised
muscle lever ending in a pawl
through which the wheel is
caused to revolve when the lever
is pulled upward by the attached
muscle. A second pawl pre-
vents the wheel from turning
hack when the muscle relaxes.
The axle of the aluminium wheel
bears on the other side a pulley,
from which the weight is sus-
pended. The turning of the
wheel winds the suspending cord
upon the pulley and thus raises
the weight.

Fig. 62. The work ad-
der ; about six-sevenths
the original size. The han-
dle is not shown. The
muscle preparation is the
double abductor suggested
bv Fick.

Clamp the work adder to

a stand in such a way that

the scale-pan hangs free of the table. Fasten the

tendon of the gastrocnemius muscle preparation

1 Introduction to Physiology, 1901, p. 225. The first work
adder was devised by Fick.

360 THE OUTGO OF ENERGY

to the lever of the work adder at a distance from
the axis of the pulley equal to the radius of the
pulley. Connect the muscle with the secondary
coil of an inductorium arranged for single maxi-
mal induction currents. Measure the distance of
the pulley weight from the level of the axis of
the pulley. Stimulate the muscle with induc-
tion currents at intervals of one second until the
fatigued muscle ceases to contract. (Stimulation
may be made by opening and closing a simple
key in the primary circuit in unison with the
beat of a metronome.)

Measure the height in millimetres to which
the pulley weight has been lifted. Multiply this
height by the weight. The product is the total
work done in gram-millimetres.

Total Work done estimated by Muscle Curve. —
The total work done by the muscle may also be
estimated by measuring in millimetres the height
of each successive contraction recorded on the
smoked paper, adding the several heights together,
dividing the sum by the number of times the
distance from the fulcrum of the recording lever
to the point of attachment of the muscle is con-
tained in the distance from the fulcrum to the
writing point, and multiplying this quotient by
the sum of the pulley weight plus the weight of
the lever.

THE CHANGE IN FORM Sbl

In tetanus no weight is raised and no visible
mechanical work is performed. That internal
work is performed is shown by the rise in
temperature.

Time Relations of Developing Energy. — The
simple muscle curve is a graphic record of the
mechanical energy set free by the muscle in lift-
ing a certain load. It is desirable to measure the
maximum energy that the muscle can set free at
each moment from the beginning of contraction
to the point at which the greatest shortening is
reached.

Place the electromagnetic signal in the primary
circuit of an inductorium arranged for maximal
make induction currents. Arrange a tuning fork
to write on a smoked drum beneath the line
drawn by the writing point of the signal. Fasten
the femur of a gastrocnemius muscle in the
muscle clamp and attach the tendon to the heavy
muscle lever. Place the three writing points in
the same vertical line. Connect the binding posts
on the muscle clamp and the lever with the posts
of the secondary coil of the inductorium. " After-
load " the muscle with 50 grams. Set the tuning
fork vibrating. Spin the drum. Stimulate the
muscle with a single maximal make induction
current.

The muscle will not shorten until the energy

362 THE OUTGO OF ENERGY

set free is sufficient to lift a load of 50 grams.
Turn the drum until the writing point of the
signal rests in the line made by the signal when
the muscle was stimulated. Let the drum be
stationary. Set the tuning fork vibrating. Its
writing point will mark a line synchronous with
that drawn by the signal during . the experiment.
Eevolve the drum a little farther, until the
writing point of the muscle lever reaches the
point at which contraction began. Set the
tuning fork vibrating again. Its writing point
will mark a line synchronous with the beginning
of contraction. The number of vibrations in the
tuning fork curve between the two points just
recorded is the interval between the stimulation
of the muscle and the point at which the energy
set free was sufficient to move a load of 50
grams. Note this interval.

After-load the muscle with 100, 150, 200, 250,
and 300 grams, and repeat the above experiment
after each addition of 50 grams.

On coordinate paper set down as ordinates
the several loads employed and along the abscissa
the time intervals in hundredths of a second.
Place a dot at the junction of the 50-gram line
with the perpendicular cutting the abscissa at the
figure indicating the interval observed between
stimulation and the moment when the energy

THE CHANGE IN FORM 363

developed sufficed to raise the load. Eepeat this
with other loads. Join the dots. The resulting
line is a curve showing the absolute force of the
muscle at successive intervals from the beginning
to the end of the phase of rising energy.

Eecord with this same muscle an isometric
contraction (page 350). With the aid of the
graduation scale of the isometric spring ascer-
tain the maximum tension developed in the
isometric contraction. Compare this result with
that secured in the experiment just concluded
on the time relations of developing energy.

Elasticity and Extensibility

Elasticity and Extensibility of a Metal Spring. —

Clamp the ergograph (Fig. 61) to the table in
such a way that the writing point of the ergo-
graph spring shall rest against a smoked drum.
Attach a scale-pan to the spring near the free
end. Turn the drum once round by hand, thus
describing an abscissa on the smoked paper.
With the forceps place 2 ten-gram weights very
carefully on the scale-pan.

The spring extends. Turn the drum 2 mm.
and add another 20 grams to the scale-pan.

A further extension of the spring will be
recorded.

364 THE OUTGO OF ENERGY

Turn the drum 2 mm. again. Continue to
record the extension of the spring after each
addition of 20 grams until a load of 200 grams
has been reached.

It will be found that the extension curve is a
straight line. The extension is directly propor-
tional to the weights employed.

Eemove the weights 20 grams at a time, turn-
ing the drum 2 mm. after each lightening.

The spring will return to its former length.
Its elasticity (within the limits of extension here
used) is perfect.

Of a Rubber Band. — Place the muscle clamp
in the stand of the heavy muscle lever (Fig. 60).
Secure a rubber band in the jaws of the clamp
and fasten the other end of the band to the
muscle lever. Eepeat the preceding experi-
ment, using 10-gram loads instead of 20-gram
loads.

The extension curve will again be a straight
line. The return to the original length will not
be complete. The elasticity of the rubber band
is not perfect. An " extension remainder " is
present. After a considerable time the exten-
sion remainder will disappear and the band will
return to its former length, provided the exten-
sion was not too violent nor too long-continued.

Of Skeletal Muscle. — Isolate in both limbs the

THE CHANGE IX FORM 365

mass of long, parallel-fibred muscles extending
along the inner side of the thigh from the pelvis
to the tibia. Separate from the remainder of the
pelvis the portion to which the muscles of both
sides are attached. Eemove the muscles of both
sides together with the part of the tibia and the
pelvis in which they are inserted. The muscles
of the two sides thus form practically one long
muscle held together in the middle by the small
piece of bone into which they both are inserted
(Tick's preparation, Fig. 60).

Eepeat the preceding experiment, using this
preparation in place of the rubber band.

The extension curve is no longer a straight
line, but approximately a parabola. In organic
bodies, the increase in length is not proportional
to the extending weights, but grows smaller as
the weight increases.

A perfectly fresh muscle weighted lightly (e. g.
10 grams) usually returns to its original length
when the extending weight is removed. With
larger weights, the return is not at first com-
plete : an extension remainder is observed, and
the original length is reached only after a con-
siderable time.

Extensibility increased in Tetanus. — With the
gastrocnemius muscle (unloaded except by the
writing lever and scale-pan) draw an abscissa (1)

•->

66 THE OUTGO OF ENERGY

with the muscle at rest; (2) with the muscle
tetanized. These abscissae record the length of
the practically unloaded muscle in the resting
and the active states. Place 10 grams in the
scale-pan and again record the length of the
muscle (1) at rest ; (2) tetanized. Make similar
records for each 10 grams up to 100.

It will be found that the extension curve falls
more rapidly in the active than in the rest-
ing muscle; the extensibility is increased in
tetanus.

Fatigue

Skeletal Muscle of Frog. — 1. Let a gastro-
cnemius muscle loaded with 10 grams write its
contractions on a very slowly moving drum.
Connect the secondary coil with the binding-
posts on the muscle clamp and the muscle lever.
Stimulate the muscle once in two seconds with a
maximal induction current, using make and break
currents alternately. The correct interval may be
obtained by listening to the beat of a metronome.
Continue to record the contractions until the
muscle will no longer shorten when stimulated
(exhaustion).

State the characteristic features of the fatigue
curve.

2. With a fresh muscle repeat the stimulation

THE CHANGE IN FORM 367

every two seconds until the height of contraction
has diminished about one half. Now record the
duration of the latent period, phase of rising
energy, and phase of sinking energy (page 334)
on a rapidly moving drum.

Note the absolute and relative duration of
these periods as compared with those of muscle
not fatigued.

3. Stimulate a sartorius from the same frog
continuously with tetanizing currents and record
the tetanus curve.

State the differences between the fatigue curve
thus secured and the curve obtained by less fre-
quent stimulation.

Attention has already been called to the dif-
ferences which depend on the relative proportion
of red and clear fibres (page 336). The latter
are more easily fatigued.

Human Skeletal Muscle. — 1. Arrange the ergo
graph to record the contractions of the abductor
indicis, as directed on page 353. Place the point
of the adjustable rod in the hole nearest the free
end of the spring.

Prepare also the large and small brass elec-
trodes for artificial stimulation of the muscle and
place them in position.

Bring the writing point against a very slowly
moving drum. Contract the muscle voluntarily

368 THE OUTGO OF ENERGY

twice every second, keeping time with the beat of
a metronome, until two hundred contractions
have been made.

Now stimulate artificially every two sec-
onds, using maximal make and break currents
alternately, until two hundred contractions have
been made.

State the characteristics of the twro fatigue
curves, and compare the curves with those
obtained from frog's skeletal muscle.

2. From a fresh subject obtain a fatigue curve
by artificial stimulation of the abductor indicis,
using maximal make and break induction cur-
rents alternately every two seconds, as directed
in the preceding experiment. When the muscle
has been stimulated two hundred times, contract
it voluntarily every two seconds until two hun-
dred contractions have been made.

Compare the curves with those obtained in
Experiment 1.

Explain these paradoxes.

It has been pointed out on page 357 that
smooth muscle loses its irritability much more
rapidly than striated muscle.

Apparatus

Normal saline. Bowl. Towel. Pipette. Glass plate.
Volume tube, ljuuseu burner. Inductorium. Two dry

THE CHANGE IN FORM 369

cells. Wires. Muscle clamp. Fine copper wire. One
hundred ten-gram weights. Muscle lever. Electro-mag-
netic signal. Kymograph. Tuning fork. Cork clamp.
Four needle electrodes. Pole-changer. Pin. Cork. Two
stands with clamps. Ten one-gram weights. Muscle-
warmer. Split shot. Ice. One per cent solution of
veratrine acetate. Wheel-interrupter. Vibrating reed.
Straw 36 cm. long with- platinum contact. Mercury cup.
Eigid muscle lever. Spring ergograph with rod. Hand
clamp. Ergograph clamp. Large weight pan. Cotton.
Two bent hooks. Heart-holder. Filter paper. Simple
key. Work adder. Co-ordinate paper. Rubber band.
Metronome.

370 THE OUTGO OF ENERGY

IV

THE CENTRAL NERVOUS SYSTEM
Simple Eeflex Actions

The Spinal Cord a Seat of Simple Reflexes. — -
1. By means of a hook or thread passed through
the lower jaw suspend vertically a frog the brain
of which has been destroyed with the seeker ; the
legs must not touch the table. Pinch a toe with
the forceps.

The leg will be drawn up.

A stimulus to the skin has caused the con-
traction of muscles. The afferent impulse set
going by the sensory stimulus is changed into
a motor efferent impulse. This is an example of
reflex action.

2. Destroy the spinal cord with the seeker.
Stimulate the skin of the right leg electrically
and mechanically.

In no case will the sensory stimulus call forth
the reflex contraction of a skeletal muscle. Yet
the nerves coming from the skin and going

THE CENTRAL NERVOUS SYSTEM 371

to the muscles are still intact. Only the spinal
cord has been destroyed.

The conversion of sensory into motor impulses
for skeletal muscles is a function of the central
nervous system.

Influence of Afferent Impulses on Reflex Action. —
Destroy the brain of a strong frog with the seeker.
Gently pinch a toe of the right foot.

Only the right leg will be drawn up.

Pinch a toe of the left foot.

Only the left foot will be drawn up.

Pinch a finger.

Only the corresponding arm will move.

Pinch the whole foot sharply.

More extended movements will be made.

The character and location of the stimulus
affect the resulting contraction.

Threshold Value Lower in End Organ than in
Nerve-Trunk. — 1. Carefully expose the sciatic
nerve. Determine the least strength of tetanizing
current that will cause a crossed reflex when
applied to the skin of the foot. Now apply the
same stimulus to the trunk of the nerve.

As a rule, the intensity required to produce
reflex action is less when the stimulus is applied
to the peripheral endings of the sensory nerves
than when the nerve-trunks are stimulated.

372 THE OUTGO OF ENERGY

2. Divide the skin over the back in the median
line. Eaise the skin on one side until the small
nerves which pass across the dorsal lymph sac to
innervate the skin come into view. Sever from
the surrounding skin a piece about one centi-
metre square containing the endings of one of
the nerves. Let the isolated piece with its nerve
endings remain connected with the body only by
the trunk of the nerve. As before, determine
the least strength of tetanizing current that will
cause a reflex movement when applied to the
nerve-endings in the skin and to the nerve-trunk
respectively.

The threshold value for reflex action will again
be found lower in the nerve-endings than in the
nerve-trunk.

Summation of Afferent Impulses. — Pass two
fine copper wires about the frog's foot a centi-
metre apart and connect them with the secondary
coil. Connect the primary coil through a simple
key with a dry cell. Stimulate with regularly
repeated make induction currents of such strength
that single stimuli cause no reflex contraction.

Summation of the subminimal stimuli will
finally cause reflex contraction.

Determine that the number of stimuli neces-
sary to produce a reflex becomes smaller when (1)

THE CENTRAL NERVOUS SYSTEM 373

the strength of the induction currents is increased,
and (2) when the interval between the stimuli is
lessened.

Segmental Arrangement of Reflex Apparatus. —
1. Gently pass the seeker over the abdominal
walls on one side.

The muscles in that region only will twitch.

Eepeat the stimulus, but use a stronger
pressure.

The area contracting will increase in extent
approximately in proportion to the increase in
the stimulus. The afferent nerves from any one
region are more closely related to the efferent
nerves of that same region than to those of other
regions. The fact that both afferent and efferent
fibres spring from the cord at the same level
suggests that their nerve cells lie also at approxi-
mately the same level. On increasing the stim-
ulus the afferent impulse spreads from segment
to segment of the cord. Further evidence of the
segmental arrangement will be gained by the
following experiment.

2. With a clean, sharp knife make transverse
sections of the spinal cord, beginning in the cer-
vical region. A short time after each section
test the reflexes from the hind limb by mechani-
cal stimulation.

374 THE OUTGO OF ENERGY

Note the level below which no section can be
made without rendering the reflex impossible.
The nerve cells concerned in this reflex lie on
the caudal side of this line.

Now in a second frog make transverse sections,
beginning at the caudal end of the cord, and test
the reflexes as before, until the level is reached
beyond which a section will destroy the reflex.

Observe that the portion of the cord comprised
between the two levels determined forms a seg-
ment which contains the central apparatus con-
cerned in the reflex studied.

Reflexes in Man. — 1. From the Skin. — Kub
the plantar surface of the foot gently with some
hard object.

The foot will be retracted reflexly.

Similar results may be obtained by rubbing
the skin of the inside of the thigh, which will
cause contraction of the cremaster muscles ; or by
rubbing the skin of the abdomen, which will be
followed by contraction of the abdominal muscles.

These reflexes are of importance in clinical
diagnosis because by means of them the seat of a
diseased area in the central nervous system may
sometimes be defined, since the reflex depends on
the integrity of the corresponding reflex arc;.

2. Cornea Refleto. — Touch the cornea gently
with a thread.

THE CENTRAL NERVOUS SYSTEM 375

The eye will be closed involuntarily.

3. Throat Reflex. — Touch the posterior wall
of the throat.

The movements of swallowing will usually
follow.

4. Piopil Reflexes ; Light Reflex. — Close one
eye for several seconds, then open it quickly.

Note the contraction of the pupil.

5. Consensual Reflex. — Close one eye as before,
but watch the pupil of the other eye when the
first is opened again.

The pupil wTill contract.

6. Accommodation Reflexes. — Look alternately
at a near and a far object. The pupil will con-
tract when the eye adjusts itself to see the near
object.

Tendon Eeflexes

Knee Jerk. — Sit in such a position that the
knee is bent at a right angle, and the foot hangs
free. Let an assistant strike the patellar liga-
ment with the side of the hand.

Note the sudden contraction of the extensors
of the thigh, the so-called knee jerk.

Flex the knee at different angles and deter-
mine in which position the resulting contraction
is greatest.

Knee jerk can be obtained only within certain
limits of extension.

376 THE OUTGO OF ENERGY

Let the subject immediately before the stimu-
lus is applied forcibly contract some other group
of muscles ; clench the hand, for example.

The knee jerk is reinforced.

Ankle Jerk. — Bend the foot at right angles to
the leg, and strike the tendo Achillis. The ex-
perimenter should hold the end of the foot in his
left hand.

Contraction of the gastrocnemius muscle will
be observed.

Gower's Experiment. — Strike the side of the
tendo Achillis.

A contraction will result.

Support the other side of the tendon so that
the gastrocnemius muscle will not be stretched
by the blow. Eepeat the experiment.

No contraction follows. The tendon jerk re-
quires for its production a rapid stretching of the
muscles involved in the contraction.

Try to obtain tendon jerks from other muscles ;
for example, the triceps humeri, flexors of hand,
and masseter muscles.

Normally no response will be obtained.

The experiments are of value in diagnosis of
diseases of the central nervous system.

the central nervous system 377

Effect of Strychnine on Eeflex Action

Inject with a glass pipette a few drops of 0.5
per cent solution of sulphate of strychnine into
the dorsal lymph sac of a frog the brain of which
has been destroyed with a seeker.

After a few minutes, very weak afferent-
impulses will be sufficient to call forth general
spasmodic reflex actions. Note that (1) the
strychnine reflexes are paroxysmal, (2) the mus-
cles fall into more or less prolonged rigidity (teta-
nus), and (3) the extensors overcome the flexors,
the limbs being strongly extended.

The characteristic action of strychnine is evi-
dently not dependent on the brain.

Destroy the spinal cord with a seeker.

Stimulation of muscles and nerves will not
cause spasmodic contractions.

Strychnine acts on the spinal cord, but not on
the muscles or the peripheral nerves.

Complex Co-ordinated Eeflexes

Removal of Cerebral Hemispheres. — Place a
frog under a glass jar containing a small sponge
wet with ether. Be very careful not to kill the
frog. When insensibility is complete, place the
animal on a frog-board. Cut through the skin in
the median line of the skull, from the nose to the

378 THE OUTGO OF ENERGY

vertebral column. Connect the front margins of
the two tympanic membranes by a transverse in-
cision through the skin. This transverse line
will pass over the junction of the cerebral lobes
with the optic lobes. Strip off the parietal bones
with forceps, beginning at the anterior end oppo-
site the anterior margin of the orbit. When the
cerebral hemispheres are uncovered, they may be
removed from before backwards. Avoid injuring
the optic lobes. Work rapidly but carefully. If
the ether effect diminish before the operation be
finished, replace the frog under the glass jar for
a few moments. As soon as the hemispheres are
removed, sew up the wounds in the skin.

Note the signs of profound inhibition.

If the operation be done carefully, the shock
will gradually pass away, and the functions possi-
ble in the absence of the cerebrum may then be
determined. Put the frog aside, moistening his
skin occasionally, but not otherwise disturbing
him, and prepare a second frog for the experi-
ment upon the " croak reflex " (page o79). When
tli is operation is completed, resume the observa-
tions on the first frog, while the second frog re-
covers from the shock.

1. Posture, etc. — Write down the differences
between the frog from which only the cerebral
hemispheres have been removed and a frog in

THE CENTRAL NERVOUS SYSTEM 379

which the whole brain has been destroyed with
the seeker, in respect to posture, power to regain
feet when laid on back, respiratory movements,
position of eyelids, leaping and swimming.

2. Balancing Experiment. — Place the frog on a
somewhat roughened board, about 20 inches long,
8 inches wide, and 1 inch thick. Tilt the
board gradually.

The frog remains motionless until his centre
of gravity is disturbed. He then moves forward
in an attempt to reach a stable position. By
careful management, he can be made to climb up
the inclined board, perch upon the narrow edge,
and, the board still turning, descend head-first on
the opposite side.

3. Retinal Reflex. — Place the frog deprived of
cerebral hemispheres in front of a bright light \
for example, an incandescent electric lamp. In-
terpose some object, such as a small instrument
case, between the light and the frog, so that a
strong shadow is cast upon the frog's eyes.
Stimulate the frog by pinching the skin of the
back.

The frog will jump, but will avoid the object
which casts the shadow.

4. Croak Reflex. — Sever the large hemispheres
from the remainder of the brain of another frog
by passing a knife through the cranium to the

380 THE OUTGO OF ENERGY

base of the skull from side to side in a line join-
ing the anterior margins of the tympanic mem-
branes. (Where possible, a male frog should be
selected for this experiment. Males may be rec-
ognized by the cushion-like thickening on. the
innermost digit of the manus, or hand ; the male
Eana esculenta possesses bladder-like, resonating
pouches connected on each side with the month
cavity.) After the immediate shock of the opera-
tion has passed, stroke the back over the anterior
half of the spinal cord.

Keflex croaking will be observed.

The croak reflex can be inhibited by simultane-
ous pinching of one of the limbs or other strong
stimulation. (Compare page 384.)

If the experiments on the frog in which the
cerebral hemispheres were extirpated were not
satisfactory, repeat them on this frog in which
the hemispheres were simply separated from the
remainder of the brain.

These observations teach that very complicated
co-ordinated actions are possible in the absence
of the large hemispheres. Only simple reflexes
are possible when the whole brain is removed.
Consequently, the seat of these complicated re-
flexes must lie in the brain between the cord and
the cerebral hemispheres.

the central nervous system 381

Apparent Purpose in Eeflex Action

1. Destroy the brain of a frog with the seeker.
Dip small pieces of filter paper in strong acetic
acid. Remove the superfluous acid, lay the
paper bearing the acid on (1) the frog's thigh,
(2) the foot, (3) the back. After each stimulation
note the character of the reflex movement, and
then carefully wash the acid from the skin.

The movements are related to the areas stimu-
lated in a certain purposeful way. Efforts are
made apparently to brush away the acid paper.

2. Place the acid on the flank of the right leg.
Usually the leg stimulated strives to brush away
the paper. Hold this leg fast.

The other leg (the left) will be used to re-
move the acid from the opposite limb. (This
experiment succeeds best in strong, lively frogs.)

3. Place an uninjured frog in an evaporating
basin containing sufficient water to immerse the
frog to the neck and covered with wire gauze
to keep him from jumping out. Warm the
water.

As the temperature rises to from 20°-30° C.
the frog will attempt to escape.

Repeat the experiment with the frog the brain
of which has been destroyed.

No movements of escape will be noticed.

382 THE OUTGO OF ENERGY

About 35°, muscular twitchings will be seen.
At 38°-40° death takes place and the muscles
become rigid (heat rigor).

This observation shows that volition in all
probability is absent in the brainless frog. It
follows that reflex actions are not volitional;
their " purpose " is only apparent.

Keflex and Eeaction Time

Reflex Time. — Destroy the brain of a frog with
the seeker. Hold one leg of the frog aside with
the glass rod. Bring beneath the other a small
beaker almost full of dilute sulphuric acid
(2:1000). Eaise the beaker until the foot is
immersed to the ankle. Count the seconds be-
tween the application of the stimulus (sulphuric
acid) and the withdrawal of the foot.

This interval is the reflex time.

Wash the foot carefully in the bowl of water.

Reaction Time. — Smoke a drum. Eaise the
drum off its friction bearing by turning the screw
at the top of the shaft. Place the writing point
of an electromagnetic signal against the smoked
paper. Arrange a tuning fork to write its curve
near that of the signal. Connect the signal
through two simple keys and a dry cell with the
primary coil of an inductorium arranged for
maximal single induction currents (posts 1 and

THE CENTRAL NERVOUS SYSTEM 383

2). Let stimulating electrodes pass from the
secondary coil (bridge up) to the tongue of the
subject. Let the subject hold one key closed un-
til he feels the stimulus on the tongue.

Direct the subject to shut his eyes. Let the ob-
server start the tuning fork, spin the drum, and
stimulate the subject by completing the primary
circuit. The instant the subject perceives the
stimulus, he will break the circuit by releasing
his key. By means of the tuning fork curve
determine the interval between stimulation and
response. This interval is the reaction time plus
the errors of observation ; for example, the latent
period of the electromagnetic signal. Eepeat the
experiment three times and take the mean of the
results.

In the laboratory note-book make a list of the
links in the chain between stimulus and re-
sponse, and state as far as possible the errors of
observation.

Reaction Time with Choice. — Connect the
side cups of a pole-changer (without cross wires)
to the posts of the secondary coil. Connect one
pair of end cups with the usual stimulating elec-
trodes, the other pair with large brass electrodes
covered with wet cotton. Let the ordinary elec-
trodes touch the forehead, the other pair the hand
of the subject. The other connections should re-

384 THE OUTGO OF ENERGY

main as before. Eepeat the preceding experi-
ment but tell the subject to signal only when
the tongue (or hand) is stimulated. In order to
do this he must add to his former reaction a de-
cision as to the part stimulated.

Eeaction time with choice is longer than sim-
ple reaction time. In general, the more compli-
cated the mental processes involved, the longer
will be the reaction time.

Inhibition of Eeflexes

Through Peripheral Afferent Nerves. — Expose
the left sciatic nerve for a distance of about 15
mm. in a frog the brain of which has been de-
stroyed. Tie a thread around the distal end, and
sever the nerve at the peripheral side of the liga-
ture. Place the central stump of the nerve on
the electrodes of the inductorium, the short-cir-
cuiting key being closed. Make the primary
circuit, and set the hammer vibrating. Now open
the short-circuiting key, bring the right foot of
the frog into the dilute sulphuric acid up to the
ankle, and count the seconds from the moment
of immersion to the moment of withdrawal, con-
tinuing meanwhile the stimulation of the central
end of the left sciatic nerve.

The latent period will be much prolonged.

Wash off the acid carefully.

THE CENTKAL NERVOUS SYSTEM 385

Keflex actions may be inhibited by the simul-
taneous stimulation of sensory nerves.

Through Central Afferent Paths ; the Optic
Lobes. — 1. Expose the brain according to the
directions already given (page 377). Immediately
posterior to the cerebral hemispheres lie the optic
lobes, two gray spherical bodies. Separate the
cerebral hemispheres from the optic lobes by a
transverse incision, and carefully remove the
hemispheres. Wait until the shock of the opera-
tion has passed. Now suspend the frog so that
the tips of ,the toes hang above a shallow dish
containing water made strongly sour to the taste
with dilute sulphuric acid. Determine the reflex
time. Wash off the acid and, after a moment's
rest, sprinkle a very little finely powdered com-
mon salt on the cut surface of the optic lobes.
Again determine the reflex time.

The reflex time will be found to be markedly
increased by the stimulation of the optic lobes.

2. Prepare a second frog in the same manner.
Determine the reflex time. Now instead of stim-
ulating the optic lobes, remove them, and again
determine the reflex time.

The removal of the optic lobes shortens the
reflex time.

25

386 the outgo of energy

The Eoots of Spinal Nerves

Destroy the brain of a strong, large frog with
a seeker. Divide the skin over the vertebral
colnmn from the upper end of the urostyle to
the level of the fore limbs. Hook back the
flaps of skin. Remove the longitudinal muscles
on either side of the spines of the vertebrae, thus
exposing the bony arches. Saw through the
arches of the 8th, 7th, and 6th vertebrae (there
are ten vertebrae in the frog, counting the uro-
style) in the order named. Clear away the bone
and the underlying tissues until the last three or
four pairs of roots shall be plainly seen. Grasp
the filum terminale and cautiously lift the cord
until the spinal nerve roots are clearly displayed.

The anterior roots are hidden by the large,
superficial posterior roots. The conspicuous pos-
terior root which seems to be the last is, in real-
ity, the 9th, the next to the last ; the last, or
10th, is smaller and lies close to the filum termi-
nale. Place a silk ligature about the middle
of an anterior and a posterior root on the right
side. With single induction currents as stimuli
ol (serve that (1) the stimulation of only the cen-
tral end of the posterior root calls forth a (re-
flex) movement, and (2) the stimulation of only
the peripheral segment of the anterior root causes,
movement.

THE CENTRAL NERVOUS SYSTEM 387

On this same side cut all the posterior roots.

No stimulus applied to the right leg will now
discharge a reflex action. But stimuli applied to
sensory nerves elsewhere may still cause reflex
movements of the right leg. Motor impulses still
pass to these muscles. But only the anterior
roots remain.

Hence the anterior roots of spinal nerves trans-
mit motor impulses from the spinal cord towards
the muscles (efferent impulses) ; the posterior
roots transmit sensory impulses from sensory sur-
faces towards the spinal cord (afferent impulses.)

Ludwig's Demonstration. — Destroy the brain
of a large frog with the seeker. Remove the
thoracic and abdominal viscera, taking care not
to injure the sciatic nerve plexus. Remove the
7th and 8th vertebra?, taking the greatest pains
not to injure the nerve roots. Divide the body
transversely at this level, so that the anterior
and posterior halves shall remain connected only
by the anterior and posterior sciatic roots. Keep
the roots moist with normal saline solution.

Demonstrate again that the anterior roots
transmit efferent, and the posterior roots afferent
impulses.

Localization of Movements at Different Levels of
the Spinal Cord. — Separate the three roots which
form the sciatic nerve. After tying a thread

388 THE OUTGO OF ENERGY

about each root sever it from the spinal cord by
a cut on the proximal side of the thread. Stimu-
late each nerve with a very weak tetanizing cur-
rent. Note the different results obtained from
nerves arising at different levels of the cord.
Stimulation of the most anterior root causes
marked flexion of the limb ; stimulation of the
middle roots, extension and internal rotation ;
and of the most posterior, simple extension.

In a frog whose nerves have not been cut
expose the spinal cord and stimulate it at differ-
ent levels in both directions along its length.
The various movements of the hind limbs are
localized at different levels of the cord.

Distribution of Sensory Spinal Nerves

Destroy the brain of a large frog with the
seeker. Expose the lower half of the spinal cord
by the method already described. On one side
cut the dorsal sensory root of the 8th spinal nerve
and on the other cut the sensory root of the 7th,
9th, and 10th. After the section of each root
test the cutaneous sensibility of the limbs by
placing upon the skin small pieces of filter paper
(two mm. square) moistened, not dripping, with
0.2 per cent sulphuric acid. Make a map of the
anaesthetic areas in each leg, and note the lack
of correspondence.

THE CENTRAL NERVOUS SYSTEM 389

Many skin areas are supplied by fibres from at
least two sensory roots. The fields of distribution
overlap.

Muscular Tonus

Brondgeest's Experiment. — Fasten a lightly
etherized frog back uppermost on the frog-board.

In a line between the ilium and the coccyx
open the pelvic cavity by cautiously dividing the
skin, fascia, and muscle. Divide the sciatic nerve
roots on the operated side. Pass a hook or thread
through the jaw and hang the frog up.

Observe that the limb the nerves of which
have been cut is relaxed, so that the toes hang
lower than those of the limb which still retains
its connection with the central nervous system.

Apparatus

Normal saline. Bowl. Towel. Pipette. Stand.
Muscle clamp. Bent hook. Inductorium. Dry cell.
Electrodes. Large brass electrodes. Cotton. Key.
Frog-board. Fine copper wire. One-half per cent solu-
tion of strychnine sulphate. Glass jar with ether and
sponge. Balancing board. Strong acetic acid. Filter
paper. Evaporating basin. Wire gauze. Bunsen burner.
Thermometer. Dilute sulphuric acid (0.2 per cent).
Beaker. Kymograph. Electro-magnetic signal. Tuning-
fork. Pole-changer. Vertebral saw.

390 THE OUTGO OF ENERGY

V

THE SKIN
Sensations of Temperature

Hot and Cold Spots. — With a lead-pencil point
carefully explore an area about an inch square
on the back of the wrist or hand. Mark with
black ink the places where a distinct sensation of
cold is felt, and with red ink those where the
sensation is one of warmth.

The places indicated are the so-called hot and
cold spots.

Outline. — Attempt to define more exactly the
outline of one of the cold spots.

The spots are of irregular shape, — blotches
rather than points.

Mechanical Stimulation. — 1. Gently tap one
end of a small wooden rod the other end of which
is placed on a well-defined cold spot.

The mechanical stimulation of the cold spot
will give a sensation of cold.

2. Stimulate a warm spot mechanically.

Chemical Stimulation. — Rub a menthol pencil
over a small area on the back of the hand.

THE SKIN 391

A sensation of cold will be perceived. This is
due to chemical irritation of the cold spots. The
temperature of the area does not fall.

Electrical Stimulation. — It has been found that
the stimulation of a well-defined cold or warm
spot with moderately strong induced currents
causes a sensation of cold or warmth respectively.

Temperature After-Sensation. — Stimulate a cold
spot mechanically with a pencil point. Eemove
the point.

The sensation of cold outlasts the stimulus.

Balance between Loss and Gain of Heat. — Pro-
vide three beakers of water. Heat them to 20°,
30°, and 40° C, respectively. Place a finger of
one hand in the water at 20°, and a finger of the
other hand in the water at 40°. After the re-
spective sensations of cold and warmth have
disappeared, place both the fingers in the water
at 30°.

The finger from the cold water will seem warm
and that from the warm water cold. The tem-
perature of the skin equals the balance between
its heat loss and heat gain. When this tempera-
ture is raised or lowered, the warm spots or cold
spots respectively are stimulated.

Fatigue. — Provide three beakers containing
water at 10°, 32°, and 45° C. respectively. Place
a finger of one hand in the beaker at 32°, and a

392 THE OUTGO OF ENERGY

finder of the other hand in the beaker at 45°.

o

After 45 seconds place both fingers in the water
at 10°.

The finger taken from the water at 32° (which
is about the normal temperature of the hand) will
feel colder than the other finger. Extreme tem-
peratures of heat or cold fatigue the temperature
spots.

Relation of Stimulated Area to Sensation. — In-
sert a finger of one hand in a beaker of warm or
cold water. Note the sensation. Insert a finger
of the other hand in the water.

The intensity of the sensation will increase
with the extent of the surface stimulated.

Perception of Difference. — Provide two beakers
of water, one at 30°, the other slightly warmer or
colder. By introducing a finger first into the one
and then into the other, and varying the tem-
perature of the water, ascertain how small a
difference in temperature can be detected.

Usually a difference of 0.5° C. is easily recog-
nized.

Relatively Insensitive Regions. — 1. Compare
the temperature sensation perceived on touching
with a pencil point the median line of the fore-
head, nose, and chin with that perceived on
touching the skin on either side of the median
line.

THE SKIN 393

The skin in the median line of the body is
comparatively insensitive to temperature varia-
tions.

2. Similarly compare the mucous membrane
with the skin.

The mucous membranes are much less sensitive
than the skin.

Sensations of Pressuee

Pressure Spots. — Explore the surface of the
forearm by bringing the blunted point of a needle
gently in touch with the skin.

At certain spots a distinct sensation of contact
will be perceived. Other spots will give only
dull sensations. Pressure, like heat and cold, is
appreciated by scattered sense-organs in the skin,
not by diffuse general sensation.

Note the relation of the pressure points (1) to
the hair follicles, and (2) to the warm and cold
spots mapped out in previous experiments.

Threshold Value. — Take from the human head
several straight, strong hairs. Cement each to
the end of a little stick of soft pine to serve as
a handle. Provide a special lever, made as fol-
lows : With a hot pin burn a small hole at the
middle of a straw about 25 cm. in length. Pass a
needle through this hole into a cork held in the
muscle clamp. Press the free end of the hairs

394 THE OUTGO OF ENERGY

against different parts of the skin of the hand,
arm, and face. Select hairs which when pressed
against the skin of the respective regions give no
sensation of pressure. Shorten the hairs until
the pressure is just perceptible. This will be the
"pressure threshold." Make a loop in a short
silk thread and pass the loop about the lever
exactly one millimetre from the axis. Hang on
the end of the thread a light bent hook. Coun-
terpoise the lever very exactly, so that the
slightest force applied to the end of the straw
will raise the lever from the after-loading screw.
By counterpoising in this way, the lever becomes
a balance. On the bent hook hang a ring of
German silver wire weighing one decigram (0.1
gram). Find a point on the lever 100 mm. from
the axis. The weight of one decigram suspended
1 mm. from the axis of the lever will be raised
by a force of j^q of a decigram, equal to one
milligram (0.001 gram) applied 100 mm. from
the axis. At HO mm. from the axis, 0.1 gram,
suspended 1 mm. from the axis, will be lifted by
a force of -gjjr gram (0.002 grain). Find the dis-
tance from the axis at which each testing-hair,
when pressed vertically against the lever, will
just fail to lift the lever; in other words, the
point at which the pressure will be just sufficient
to bend the hair. The number of millimetres

THE SKIN 395

between this point and the axis of the lever,
multiplied by one-tenth, will give the bending
pressure of the hair in the fraction of a gram.
Make ten observations on each hair and mark the
mean bending value on the wooden handle.

Touch Discrimination. — 1. Close the eyes and
let an assistant test the different parts of the
skin of the hand, arm, and face for discrimina-
ting power. For each test separate the points of
the aesthesiometer until they can be felt as two
(ordinary drawing dividers or compasses can be
used for an aesthesiometer).

Record your results in millimetres for finger-
tips, palm of hand, back of ringers, back of hand,
back of wrist, flexor and extensor surfaces of fore-
arm, forehead, cheeks, lips, and tongue.

2. Separate the points of the aesthesiometer
about 20 mm., and draw them gently side by
side along the extensor surface of the forearm
from the elbow to the wrist. Repeat the experi-
ment on the flexor surface. Try the same for
the cheek and lips, beginning near the ear and
drawing the points so that one shall go above
and the other below the mouth.

Describe the sensation in each case, and sug-
gest an explanation.

Weber's Law. — Place the hand palm upward
in a comfortable position on the table. Close

396 THE OUTGO OF ENERGY

the eyes. Let an assistant place on the last
phalanx of the middle and index fingers a small
round box containing ten small shot.

When the subject has formed a clear percep-
tion of the weight, let an assistant add or
subtract shot, and record the number of shot cor-
responding to the smallest difference in weight
perceived by the subject (whose eyes of course
should be kept closed). Kepeat the experiment
with 20, 30, 40, and 50 shot in the box respec-
tively. Determine in each instance the ratio of
the number of shot added or subtracted to the
number with which each experiment was begun.

This ratio will be approximately constant.
The degree of stimulation necessary to cause the
perception of difference always bears the same
ratio to the degree of stimulation already applied.
Weber's law is less true for very small and very
large weights than for those of medium value-
It is a general law and holds good for visual
judgments, etc.

After-Sensation of Pressure. — Place a rubber
band about the head and allow it to remain for
several minutes.

On removing the band, a distinct after-sensa-
tion of pressure will l)e felt.

Temperature and Pressure. — Place oil the back
of the hand supported on tin; table a coin the

THE SKIN 397

temperature of which has been made such that
it feels neither warm nor cold. Compare the
pressure sensation (apparent weight) of this "nor-
mal" coin with that of similar coins warmed
and cooled.

The hot or cold coin will seem heavier than
the " normal " coin of equal weight.

Touch Illusion ; Aristotle's Experiment. — Cross
the right middle finger over the right index finger
and place them on the palm of the left hand.
Place a small shot between the crossed fingers in
such a way that it shall touch the ulnar side of
the middle finger and the radial side of the index
finger. Eoll the shot in the palm of the hand.

A sensation of two objects will be felt.

Apparatus

Black and red ink. Small wooden rod. Menthol pen-
cil. Inductorium. Dry cell. Electrodes. Key. Three
beakers. Stand. Ring. Wire gauze. Bunsen burner.
Thermometer. Needle with blunted point. Muscle lever.
Gram and ten-gram weights. German silver ring weigh-
ing 0.1 gram. Silk thread. Four small wooden handles
for pressure-hairs. Bent hook. Drawing dividers (as
eesthesiometer). Small round box containing at least 50
shot. Rubber band large enough to go around the head.

398 THE OUTGO OF ENERGY

VI

GENERAL SENSATIONS
Tickle

Irradiation. — Gently touch the skin near one
nostril with a dry camel' s-hair brush.

Note (1) the strong sensation produced by
the slight stimulus ; (2) the irradiation beyond
the spot stimulated.

After image. — Repeat the stimulus of the pre-
ceding experiment.

Measure in seconds the time during which
the sensation outlasts the stimulus (after image).

Topography. — Test the tickle sensation at vari-
ous points on the skin of the face, hands, and
forearms. Determine whether the sensation is
greatest about the several openings, where skin
joins mucous or serous membranes ; e. g., the
nostrils, the conjunctival sac, the auditory canal.
Do the results indicate a protective mechanism ?

Summation. — In one of the sensitive areas
found in the preceding experiment determine the
difference between the response to a single stim-
ulus and to successive stimuli.

Fatigue. — In any sensitive area determine (1)
the quickness with which the apparatus for the
sensation of tickle is fatigued; (2) the duration
of fatigue.

general sensations 399

Pain

Threshold Value. — Arrange an inductorium for
tetanizincj currents. Place the electrodes on
the tip of the tongue, and move the secondary
toward the primary coil until no farther move-
ment can be made without causing the stimula-
tion to become painful. Determine for this
region and for others of the mucous membrane
of the mouth and of the skin what distance of
the secondary coil from the primary separates the
stimulus at which pain is just perceived from
that at which the pain is distinct.

Latent Period. — In several individuals measure
approximately the interval between the applica-
tion of the stimulus (single break shock) and the
resulting painful sensation.

Summation. — Determine the number of sub-
minimal stimuli necessary to produce pain.

Topography. — Map upon the skin of the face
and arm the areas specially sensitive to pain.

Individual Variation. — Compare the reactions
of several individuals, and note the differences in
threshold value, latent period, summation, and
topography.

Temperature Stimuli. — Fill two bowls or large
beakers with water twenty-five degrees respec-
tively, hotter and colder, than the temperature

400 THE OUTGO OF ENERGY

of the hand. Determine whether the increase
or the corresponding decrease in temperature is
the more painful to the immersed hand.

Motor Sensations

Judgment of Weight. — Lift the same weight
twice, at first very slowly and then quickly.

The weight will appear lighter when raised
quickly.

Sensation of Effort. — " Hold the finger as if to
pull the trigger of a pistol. Think vigorously
of bending the finger, but do not bend it.

" An unmistakable feeling of effort results.

" Eepeat the experiment, and notice that the
breath is involuntarily held, and that there are
tensions in other muscles than those that would
move the finger." {Sanforcl.)

Sensation of Motion. — Let the forearm and
hand rest upon a table. Bring the four fingers
of the hand together, and turn the hand so that
it shall rest upright upon the ulnar side of the
little finger. Close the eyes. Abduct the first
finger.

The second, third, and fourth finger will seem
to move in a direction opposite to the movement
of the first.

TASTE 401

VII

TASTE

Threshold Value. — Prepare solutions of cane
sugar of the following strengths : 1 : 1000, 1 : 800,
1 : 600, 1 : 400, 1 : 200, 1 : 100. Take half a
teaspoonful of the weakest solution into the
mouth, roll it upon the tongue, and swallow
it. Note whether a sweet taste can be per-
ceived. Einse the mouth thoroughly. Proceed
with solutions of increasing strength until the
sweet taste is just perceptible.

Topography. — 1. Select a solution of sugar
slightly more concentrated than that just per-
ceived to be sweet. With a small camel's-hair
brush apply this solution to the several parts
of the tongue and the palate. Determine the
regions sensitive to taste. The mouth must be
rinsed frequently. 2. Dry the upper surface of
the tongue with a handkerchief. With a finely
pointed camel's-hair brush apply a twenty per
cent sugar solution to the individual fungiform
papillse and to the mucous membrane between
them. Determine whether only the papilke
perceive taste.

Relation of Taste to Area stimulated. — Swallow
a very small quantity of a minimal solution of
sugar, as determined in the experiment upon

26

402 THE OUTGO OF ENERGY

threshold value. Einse the mouth, and then
swallow a much larger portion of the solution.

The taste will be perceived more strongly, the
larger the area stimulated.

Electrical Stimulation. — 1. Connect two small
zinc electrodes through a simple key to a battery
of four dry cells. Apply one electrode to an in-
different region, the other to the tongue. Close
the key.

Note the sour taste at the positive pole and
the alkaline taste at the negative.

INTRODUCTION TO PHYSIOLOGICAL OPTICS 403

VIII

INTRODUCTION TO PHYSIOLOGICAL
OPTICS

All visible objects give out light, either of their
own making, like the sun, or that which comes
from some external source and falls upon their
surfaces. Bays that fall upon any surface may
disappear (absorption), or be thrown back from
the surface (reflection), or, if the body be trans-
parent, pass into it, in which case they are often
bent from their course (refraction).

Eeflection from Plane Mirrors

Angles of Incidence and Reflection. — Place in
front of the condenser in the lantern (Fig. 63)
the diaphragm with 2 mm. aperture. Cover the
round window in the optical box with the plain
glass slide. Kemove the cork from the tin cylin-
der. Put a piece of lighted Japanese incense in

404

THE OUTGO OF ENERGY

INTRODUCTION TO PHYSIOLOGICAL OPTICS 405

the hole in the cork. Put back the cork. Place
the incense-holder in the optical box and put the
glass lid on the box. Arrange the lantern to
throw a beam of light through the window into
the box. The smoke will be made luminous by
the light so that the path of the rays can be seen.
Make the rays parallel by pushing in the draw-
tube holding the outer projecting lens of the
lantern. Set the plane mirror against the side
of the box. Let the rays fall obliquely upon
the mirror. Accurate measurement would show
(1) that the incident ray, the reflected ray, and
the perpendicular to the point of incidence, all
lie in the same plane, and (2) that the angle
between the incident ray and the perpendicular

— angle of incidence — is equal to the angle
between the perpendicular and the reflected ray

— angle of reflection (Hero of Alexandria, about
100 B. C).

Reflection from Concave Mirrors

Principal Focus. — 1. Place the concave mirror
(the polished inner surface of the segment of a
sphere of 5 cm. radius) at right angles to the
pencil of parallel rays.

The rays will be reflected to a point 2J cm.
from the mirror.1 This point, to which parallel

1 Much smoke will make the rays less visible. The incident

406 THE OUTGO OF ENERGY

rays are converged, is the principal focus of the
concave mirror. The distance between the prin-
cipal focus and the reflecting surface is termed
the principal focal distance ; it is one half the
radius of curvature. Accurate measurement
would show that the angle between the incident
ray and the perpendicular,1 in this case the radius
of the spherical surface, equals the angle of
reflection.

2. Take the mirror from the box and set it
in the principal axis of the beam coming from
the lantern. Replace the 2 mm. diaphragm by
the diaphragm with L-shaped aperture. At the
principal focus of the concave mirror hold the
small round screen with slender handle.

The inner rays of the beam will be inter-
cepted by the screen. The outer rays will be
reflected from the mirror and an inverted, real
image of the L_-shaped aperture will be seen upon
the screen. The image will be smaller than the
object. When the distance between the mirror
and the object is less than the radius of curvature
but greater than the focal distance, the image
is real, inverted, and larger. With concave
mirrors, real images are always inverted.

and tin: reflected beam may be compared l>y turning the mirror
slightly, so that they lie side by side.

1 It is assumed that the spherical surface is composed of an
infinite number of plane surfaces.

INTRODUCTION TO PHYSIOLOGICAL OPTICS 407

3. Obtain a luminous point as follows. In-
sert in front of the condenser the diaphragm with
2 mm. aperture. Place the glass slide over the
window of the box. Pull out the draw-tube to
make the pencil of rays convergent. Throw this
convergent pencil into the box. Determine its
focus by finding the place at which a clear image
of the aperture of the diaphragm is formed upon
a screen. This focus will serve as a luminous
point.

After converging to the focus, the rays will
diverge again. Place the mirror 2.5 cm. from the
luminous point. The luminous point will then
lie at the principal focus of the mirror. Turn
the mirror at a small angle with the axis of the
pencil.

The reflected rays will be parallel.

Conjugate Foci. — 1. Place the mirror at a dis-
tance from the luminous point greater than the
radius of curvature of the mirror.

The diverging incident rays will be reflected
from the spherical surface to a point between the
luminous point and the mirror. At this point a
real image of the luminous point will be seen.

The point from which the rays diverge, and
the point to which they converge by reflection
from the mirror are termed conjugate foci.

2. Draw back the lantern and thus increase

408 THE OUTGO OF ENERGY

the distance between the luminous point and the
mirror.

As the distance between the luminous point
and the mirror increases, the distance between
the mirror and the image diminishes.

Move the lantern towards the optical box, and
thus bring the luminous point towards the mirror.

As the distance between the mirror and one
conjugate focus diminishes, the distance between
the mirror and the other conjugate focus in-
creases. As one focus approaches the mirror, the
other recedes.

3. Place the mirror 5 cm. from the luminous
point. The luminous point is now at the centre
of the sphere of which the reflecting surface is
a segment. The incident rays are therefore all
radial, i. e. perpendicular, to this surface. Con-
sequently all the rays will be reflected to the
point of origin. The incident and the reflected
rays will coincide. The centre of the reflecting
surface and its optical image will also coincide.
The conjugate foci coincide.

Virtual image. — • 1. Place the mirror at a
distance from the luminous point less than the
principal focal distance.

The reflected rays will diverge. They will
appear to proceed from a point lying behind the
mirror. The distance between this unreal or

INTRODUCTION TO PHYSIOLOGICAL OPTICS 409

virtual image and the mirror will be greater than
the distance between the mirror and the lumi-
nous point. As the luminous point approaches
the mirror, its virtual image will also approach.

2. Hold a small object nearer the mirror than
its principal focal distance.

Note that the image is virtual, upright, and
larger than the object.

Construction of Image from Concave Mirrors. —
Determine by construction the length of the
image of an arrow 2 cm. long, placed 10 cm; from
the middle point of a concave mirror of 5 cm.
radius of curvature.

Draw a horizontal line. With any convenient
point on this line as a centre describe an arc
of 5 cm. radius, that shall intersect the line.
This arc will be the section of a concave mirror.
The horizontal line will be the principal axis,
and the intersection of the principal axis and
the arc, the middle point of the mirror. The
principal focus of the mirror will lie halfway
between the centre of curvature and the middle
point. At right angles to the principal axis
and 10 cm. from the middle point draw a vertical
arrow 2 cm. long. Determine first the position
of the image of the point of the arrow. Draw
from the point to the mirror an incident ray
parallel to the principal axis. This parallel ray

410 THE OUTGO OF ENERGY

will be reflected through the principal focus.
Draw a second incident ray from the arrow point
through the centre of curvature. This ray will
be perpendicular to the spherical surface and
will be reflected in the same line. The inter-
section of these two reflected rays will be the
image of the point of the arrow.

Determine in like manner the position of the
image of the other end of the arrow.

Keflection fkom Convex Mirrors

The laws of reflection from convex mirrors
may be deduced from those already stated for
concave mirrors. The image reflected from con-
vex mirrors is virtual, upright, and smaller than
the object.

Determine by construction the length of the
image of an arrow, 2 cm. long, placed 10 cm.
from the middle point of a convex mirror of
5 cm. radius.

Effraction

1. Place the diaphragm of 2 mm. aperture in
front of the condenser. Push in the draw-tube of
the lantern until a beam of parallel rays enter
the box. In the box lay the square glass bottle
on its side upon a wooden block and at right

INTRODUCTION TO PHYSIOLOGICAL OPTICS 411

angles to the pencil of light. Neglect the re-
flected rays.

Observe that the incident rays pass through
the bottle and its contents, and are not bent from
their course. Light, passing from one medium
into another of different density, is not refracted,
provided the course of the ray be perpendicular
to the surface separating the media.

2. Turn the bottle so that the incident ray
shall enter it at an angle.

On passing from the air into the denser
medium of the glass and the contained liquid,
the incident ray will be bent from its course.
On passing from the denser medium into the air
again, the ray will once more be bent from its
path. Imagine a perpendicular erected at the
points of incidence and emergence. The re-
fracted ray will be bent toward the perpendicu-
lar on passing into the denser medium, and away
from the perpendicular on leaving the denser
medium.

Turn the bottle and thus alter the angle be-
tween the incident ray and the perpendicular
(angle of incidence).

The angle between the refracted ray and the
perpendicular (angle of refraction) increases with
the ancde of incidence. Exact measurements
made by Snellius and Descartes, about 1621,

412 THE OUTGO OF ENERGY

showed that — (1) the refracted ray lies in the
same plane with the incident ray and the per-
pendicular, and (2) the sine of the angle of in-
cidence stands in an unalterable relation to the
sine of the angle of refraction.

The sine of the angle of incidence is to the
sine of the angle of refraction as the velocity of
the light ray in the first medium is to its velocity
in the second, or refracting medium. The ratio
of the velocity of light in a vacuum to its velocity
in any medium is termed the index of refraction,
or refractive power of that medium. If the
velocity of light in a vacuum he taken as 1, that
A light in air at 0° temperature and 760 mm.
pressure, will be 0.9997, a difference so slight
that the velocity in air is usually taken as the
unit. The law of refraction is commonly ex-
pressed as follows : Let n represent the index of
refraction, a the angle of incidence, and b the
angle of refraction ; then

. 7 sin a

sin a = ?i sin o, or n = — — r.

sin b

As a rule, the physically denser medium is
also optically denser. Thus the refractive index
for the Frauenhofer line1 I), on passing from air

1 White light is composed of rays of different refrangibility ;
hence the use in such measurements of pure spectral rays.

INTRODUCTION TO PHYSIOLOGICAL OPTICS 413

into crown glass, of which spectacle lenses are
made, is 1.530; into flint glass, 1.635; into water
at 15° C, 1.332.

Refraction by Prisms

A refracting medium bounded by two plane
surfaces not parallel is termed a prism. The
planes are termed the refracting surfaces. The
angle which they make with each other is termed
the refracting angle of the prism.

1. Place a prism in the optical box in the
beam of parallel rays. The beam will be bent
from its course on entering and on leaving the
prism. The emerging pencil will be divergent,
for the homogeneous rays, the union of which
produces the sensation of white light, are not
equally refracted, — the rays towards the red end
of the spectrum are bent less strongly than those
towards the violet end, the order being red,
orange, yellow, green, blue, violet.

Construction of the Path of a Ray passing through
a Prism. — Draw a horizontal line 5 cm. in length.
Upon this line construct the section of a prism.1

1 To construct the section of a jwism: Let the horizon-
tal line be the base of the prism. Place the brass leg of the
drawing compasses at one end of the base line. Draw a circle
of 3 cm. radius. Place the brass leg at the other end of the
base line and draw a circle of the same radius. A line joining
the intersections of the two circles will be perpendicular to the

414 THE OUTGO OF ENERGY

Draw with ink a ray incident to the refract-
ing surface.1 Find the sine of the angle of in-
cidence.2 For the Franenhofer line D passing
from air into crown glass the ratio of the sine
of the angle of incidence an to the sine of the
angle of refraction bn is

an : bn \\ 1.53 '. 1

For the same light passing from crown glass
into air the ratio of the sine of the angle of in-
cidence to the sine of the angle of refraction is
the reciprocal of the ratio from air to crown glass

an °. bn '. '. 1 '. 1.53

middle of the base line. Let a point on this perpendicular
5 cm. above the base line be the apex of the section. Join the
apex with the ends of the base line. Ink the boundarj' lines of
the cross-section thus obtained. Erase the pencil construction
lines.

1 For convenience let the incident ray come from the pro-
longed base line of the prism 10 cm. from the nearest refract-
ing surface. Let the point of incidence — the point at which
tin- incident ray meets the refracting surface — be about the
middle of the refracting surface.

2 To find the sine: With the point of incidence as a centre
draw a circle of convenient radius (2 cm.). Construct a radius
of this circle perpendicular to the refracting surface at the point
of incidence. From the intersection of the circle with the in-
cident ray draw a line perpendicular to the radius (a line drawn
from the point of intersection parallel to the refracting surface
will be perpendicular to the radius). This is the sinus line of
the angle. The ratio of this line to the radius of the circle is
the sine of the incident angle.

INTRODUCTION TO PHYSIOLOGICAL OPTICS 415

Measure the length of the sine of the angle of

incidence in millimetres. Suppose that an in

the present instance is 13 mm. Then with
equation ( 1 )

1.53 : 1 : : 13 : x

x = 8.5 mm., the sine of the angle of refraction.

Find on the construction circle within the
prism a point 8.5 mm. in a perpendicular line
above the diameter at right angles to the refract-
ing surface. Continue the ray through this point
to the second refracting surface. Ink the path
of the ray within the prism. Erase the con-
struction lines within the prism, but leave un-
touched those without the prism. Find the sines
of the angles of incidence and refraction at the
second refracting surface. Draw with ink the
path of the emergent ray. Preserve all these
construction lines. Write the equations in ink
in the upper left-hand corner of the paper, and
the four sines in the upper right-hand corner.

The degree to which light is refracted on pass-
ing through a prism depends on the refracting
power of the substance of the prism, the size of
the refracting angle, and the size of the angle of
incidence.

416 THE OUTGO OF ENERGY

Effraction by Convex Lenses

Principal Focus. — 1. Place the diaphragm of
2 mm. aperture in the lantern. Throw a beam
of parallel rajs into the optical box. Place the
double convex lens in the axis of the beam about
5 cm. from the window of the box.

The parallel rays will be brought to their
principal focus about 10 cm. (4 inches) from the
lens. Note the increase in intensity as the rays
converge.

Place the black wooden screen at this point.

A real image of the luminous aperture of the
diaphragm will be perceived.

2. Place the diaphragm of 2 mm. aperture over
the window of the box. Direct the light of the
lantern upon the opening in the diaphragm.
From the illuminated opening rays will diverge
in all directions. Place the lens 10 cm. from this
luminous body, so that it shall lie in the princi-
pal focus of the lens.

The diverging rays will be rendered parallel.
Pays diverging from the principal focus are
rendered parallel by passing through a convex
lens.

A lens may be regarded as an infinite series of
prisms. In a convex lens the refracting angle

INTRODUCTION TO PHYSIOLOGICAL OPTICS 417

of each hypothetical prism is directed to the
periphery of the lens. As the periphery is ap-
proached the refracting angles increase, and
hence refraction increases. The increased refrac-
tion of the outer rays diverging from a luminous
point compensates in part for their greater angle
of incidence, and hence most of the rays converge
approximately to the same focus.

Estimation of Principal Focal Distance. — Re-
move from the lantern the tubes holding the projec-
tion lenses. Place in front of the condensing lens
the diaphragm with L-shaped aperture each limb
of which is 5 mm. long and 1 mm. broad. Place
the convex lens in the axis of the pencil emerg-
ing from the illuminated slit and at a distance
from it a little greater than the principal focal dis-
tance as determined roughly in the preceding ex-
periment. On the other side of the lens place a
screen at such a distance as to give a strongly
enlarged clear picture of the l_. Measure

I = the length of one limb of the |_,
L = the length of its image,
A = the distance of the screen from the lens,
/ = the principal focal distance of the lens,

then1 f=ATTl

1 This formula is derived as follows ; Let a "be the distance

27

418 THE OUTGO OF ENERGY

The principal focal distance of a double con-
vex lens is approximately equal to the radius
of curvature.

Conjugate Foci. — Place in the lantern the dia-
phragm of 2 mm. aperture. Eemove the tubes
holding the projecting lenses. Place the convex
lens against the window of the optical box.
Place the black screen twice the focal distance
from the lens. Move back the lantern until a
clear image of the luminous aperture appears
on the screen.

The point from which rays passing through
a lens diverge, and the point to which they con-
verge, are termed conjugate foci. Measure the
distance of the luminous aperture from the lens.
It will be found to be twice the focal distance.
When the point of divergence is separated from
the lens by twice the focal distance, the point
of convergence is equally distant from the other

of the object from the principal surface of the lens (see page 46);

then — - + — = . The relation between the size of the image
A a f to

and the size of the object is L '. I '.'. A I a; then - = -j-r,
and, by substitution,— = — -+- —, whence f = A -

f A AV J L+l'

Compared with the thickness of the lens, the distance of the
object from the lens is so great that it may be used in place of
the unknown distance from the principal surface (Kohlrausch,:
Leitfaden der praktischen Physik, 1887, p. 142).

INTRODUCTION TO PHYSIOLOGICAL OPTICS 419

side of the lens, — the conjugate focal distances
are equal.

Move the lantern farther from the lens.

The conjugate focus will approach the lens.
As one conjugate focus recedes the other ap-
proaches the lens.

Virtual image. — 1. Place the 2 mm. diaphragm
over the window of the optical box. Let the di-
verging rays pass through the convex lens placed
at a distance from the lumiuous point less than
the principal focal distance.

After passing through the lens, the diverging
rays will continue to diverge though the degree
of divergence will be less. Prolonged backwards,
they would unite in a virtual image on the same
side of the lens as the luminous object. The
virtual image is farther from the lens than the
object, is never inverted, and is always enlarged.
(Compare the construction, directions for which
will be given on page 421.)

2. Look through the convex lens at printed
words placed between the lens and its principal
focus.

The image is virtual and enlarged.

Construction of Image obtained -with Convex
Lens. — The line which joins the centres of curva-
ture of a double convex lens is termed the prin-
cipal axis or optical axis. In every lens there

420 THE OUTGO OF ENERGY

are in the principal axis two points so placed
that when the entering ray is directed toward
the first, the emergent ray will appear to come
from the second in a direction parallel to the
entering ray. These are termed nodal points.
In ordinary glass lenses the distance between the
two nodal points is about one third the thickness
of the lens. When this distance is so small that
it may be disregarded, the two nodal points may
be assumed to meet in an intermediate point
termed the optical centre (compare page 444) of the
lens. A ray directed to the optical centre is not
refracted but passes through the lens in a straight
line. The position and size of an image formed
by a lens can be found by drawing one line from
each extremity of the object through the optical
centre, and another from each extremity parallel
with the principal axis to the lens and thence
through the principal focus. The intersections
of these lines mark the position of the image and
its upper and lower limit. It is necessary to
remember that parallel rays are refracted through
the principal focus only when the aperture of the
lens does not exceed approximately ten degrees.

Draw a horizontal line to serve as the principal
axis. Let a point near the middle of the line be
the optical centre of a double convex lens of 10°
aperture and 5 cm. radius. The radius of curva-

INTRODUCTION TO PHYSIOLOGICAL OPTICS 421

ture being 5 cm., the principal focus will lie
approximately 5 cm. from the optical centre.
Draw through the optical centre a line 10 mm.
long at right angles to and bisected by the prin-
cipal axis. Connect the ends of this line with
the principal focus. The angle included will
be approximately 10°. The vertical line will
then represent a double convex lens of 10° aper-
ture, assumed to be without thickness in order
that the nodal points may coincide with the opti-
cal centre. At any distance greater than 5 cm.,
draw an arrow at right angles to and bisected
by the principal axis. The height of the arrow
must not exceed the diameter of the lens, so
that rays emitted from the ends of the arrow
parallel to the principal axis of the lens shall
pass through the lens. From the ends of the
arrow draw to the lens and thence through
the principal focus incident rays parallel to the
principal axis. From each end of the arrow
draw a line through the optical centre of the
lens.

The intersections of these lines mark the upper
and lower limits of the image. Note that the
image is real and inverted. If the object be situ-
ated at twice the focal distance from the lens,
the image will be the size of the object ; if at less
than twice the focal distance, the image will be

422 THE OUTGO OF ENERGY

larger than the object ; if at more than twice the
focal distance, the image will be smaller than the
object ; finally, if the object be situated between
the principal focus and the lens, the image will
no longer be real, but virtual and larger than the
object, as mentioned on page 419.

Eefraction by Concave Lenses

Place the diaphragm with 2 mm. aperture in
front of the condenser. Throw a pencil of paral-
lel rays into the box. Let the rays fall upon a
concave lens.

The parallel rays will be rendered divergent.

Look through the concave lens at printed
words. The image is virtual, upright, and
smaller than the object. It is nearer the lens
than the object, and is always within the prin-
cipal focal distance.

Kefraction by Segments of Cylinders

1. Place the diaphragm with 2 mm. aperture
in front of the condenser. Throw a pencil of
parallel rnys into the box. Place the cylindrical
lens in the axis of the pencil in such a position
that the curvature shall be from side to side, i. e.
in the horizontal meridian.

INTRODUCTION TO PHYSIOLOGICAL OPTICS 423

The image of the circular aperture in the dia-
phragm will be a vertical line with blurred con-
vex ends.

Turn the cylinder so that the curvature shall
be in the vertical meridian.

The imacre will be a horizontal line with
blurred convex ends.

2. Place the diaphragm with horizontal slit in
the lantern. Throw parallel rays into the box.
Place the cylinder in the axis of the pencil with
its curvature vertical.

The horizontal line is a fusion of illuminated
points. From each point rays diverge in all
directions. Those passing from any point in
vertical planes through the cylinder convex in
its vertical meridians will be focussed by the
convex surface in a corresponding point in the
image. The overlapping of such points will form
a horizontal line with clear upper and lower
edge. The rays passing from any point in the
illuminated line in horizontal planes through
the cylinder with vertical curvature will be
refracted by plane glass surfaces and will not
come to a point but will form a faint horizontal
line. The overlapping in the image of the
bright points in which unite the rays passing
in vertical planes and the faint horizontal lines
formed by rays passing in horizontal planes will

424 THE OUTGO OF ENERGY

form upon the screen a horizontal line with
blurred ends.

Place the vertical slit in front of the con-
denser.

A broad, faint, horizontal line with blurred
ends will be observed. Draw a diagram illus-
trating the formation of this image.

Turn the cylinder, so that the curvature shall
lie in the horizontal meridian.

The horizontal rays are at once united in a
narrow sharply defined vertical line with blurred
ends.

Eefraction through Combined Convex and
Cylindrical Lenses

Thus far segments of perfect spheres or cylin-
ders have been considered separately. In the
eye both the cornea and the lens are frequently
more convex in one meridian than in another.
Such surfaces can be obtained by combining a
convex with a cylindrical lens.

1. Place the diaphragm of 2 mm. aperture in
front of the condenser. Throw parallel rays
into the box. Place the convex lens in the axis
of the pencil next the window. Keceive the
image of the illuminated aperture upon a screen
placed at the principal focus. The image will be
a well-defined circle. Place the cylindrical lens

INTRODUCTION TO PHYSIOLOGICAL OPTICS 425

as close as possible to the convex lens. Let the
curvature of the cylinder be in the vertical
meridian.

The circle will give place to a vertical line.

Move the screen about 4 cm. nearer the lenses.

The image of the circle will now be a horizon-
tal line.

Place the screen half way between the nearer
and the farther focal lines.

The image will be circular. At other points
in the focal interval or space separating the two
focal lines the image will be an ellipse.

2. Hang the block containing the cylindrical
lens on the end of the draw-tube of the lantern.
Leave the convex lens in its former position.
Fill the box with smoke. Let the curvature of
the cylindrical lens be in the vertical meridian.
Observe the pencil of rays.

The pencil will be drawn out to a vertical line
at the farther focus. Seen from above the cross-
section of this line will be a bright spot. At the
nearer focus the pencil will be flattened to a
horizontal line.

Eotate the cylinder through 90°. The curva-
ture will now be in the horizontal meridian.
Watch the pencil as the lens turns.

As the cylinder revolves the contour of the
pencil will change. When the curvature is

426

THE OUTGO OF ENERGY

finally horizontal the nearer focal line will be
vertical, the farther focal line will be horizontal.

Eotate the cylinder through 45°.

By looking at the pencil first from one side of
the box and then from the other, the focal lines
may readily be seen in profile, as well as in
cross-section.

Aberration

Spherical Aberration by Reflection. — In Fig.
64 a concave mirror, AB, has the centre of curva-
ture, C, and the principal focus, F. BE is one
of several incident parallel rays. CE is perpen-
dicular to the point of incidence. EF is the ray
reflected from E to the principal focus, G the

Pig. 64.

point at which the reflected ray cuts the axial
line CK. DEWC G, therefore ZGCE=CEB

INTRODUCTION TO PHYSIOLOGICAL OPTICS 427

= 0 E G, and C G E is an isosceles triangle. Then
if r be the radius and x the angle formed by the
perpendicular CE with the axial ray C G, CG

T

= . So lon^ as angle x is small, cosine x

2 cos x ' °

will be nearly 1. C G will then be nearly one
half the radius OK. Hence incident rays near
the axial ray CiT will be reflected approximately
to the principal focus F, which lies half way
between the centre of curvature and the mirror.
As the aperture 2 of the mirror increases, angle x
also increases. The larger x, the smaller will be
the denominator of the expression for C G, and the
greater the distance of G from C. Bays reflected
from the outer portion of a mirror of larger aper-
ture meet the principal axis nearer the mirror
than those reflected from the central portion.
The intersection of the reflected rays produces a
curved line — the caustic curve or focal line. By
revolving Fig. 2 about the axis C K, a caustic or
focal surface will be obtained.2

Spherical Aberration by Refraction. — 1. The
observations just made concerning concave mir-
rors are applicable also to lenses. Bays entering

1 The aperture is the angle included between lines drawn
from the principal focus to the margins of the mirror or lens.

2 Jochmann and Hermes. Grundriss der Experimental-
physik, 1890, p. 153.

428 THE OUTGO OF ENERGY

a lens with aperture greater than 10° are not
refracted to the principal focus but cross the
principal axis between the principal focus and
the lens. The caustic surface formed by the
intersection of these peripheral rays may readily
be shown with any lens or cylinder of small
radius of curvature.

2. Place the diaphragm with 2 mm. aperture
in front of the condenser. Throw parallel rays
into the optical box. Set in the box near the
window the cylindrical bottle of clear glass filled
with water. The bottle will serve as a powerful
refracting cylinder.

The circular pencil of parallel rays will be
brought to a focus in a vertical line (compare
page 422). The outer rays of the pencil pass
through the outer portion of the cylinder, and
are therefore more strongly refracted than those
near the optical axis. Each refracted ray inter-
sects the refracted rays nearer than itself to the
principal axis. These intersections form two
curved surfaces extending from the principal
focus — in this case a vertical line — towards
the cylinder. On regarding these surfaces from
above, their curvature will be apparent.

3. Remove the projecting lenses; place the
ground glass plate and the diaphragm with 2 mm.
aperture in front of the condenser. Let the rays

INTRODUCTION TO PHYSIOLOGICAL OPTICS 429

diverging from the illuminated aperture pass
through the refracting cylinder.

The curvature of the caustic surfaces will be
more noticeable than in Experiment 2.

Dispersion Circles. — 1. Let the parallel rays
pass through the double convex lens. Place a
screen at the principal focus. A clear image of
the circular aperture in the diaphragm will be
seen. Move the screen away from and then
towards the lens.

When the screen is either nearer or farther
from the lens than the principal focus, the image
will be larger and less distinct. The screen will
cut the pencil in the one case before it has con-
verged to the focus, and in the other case after
it has passed the focal point and is diverging.
Under such circumstances the image of a point
becomes a circle, termed a dispersion circle or
circle of confusion.

2. Substitute the diaphragm with L-shaped
aperture for that with circular aperture. Place
the screen a little nearer or farther than the
focal point.

The image will be a broad blurred line with
convex ends. The pencils proceeding from each
luminous point in the line will fall upon the
screen in dispersion circles. The broad line is
caused by the overlapping of the dispersion cir-

430 THE OUTGO OF ENERGY

cles. Similar blurring by dispersion circles is
caused by the rays which pass through the outer
parts of a lens coming to a focus sooner than
the axial rays.

Myopia. — In the normal eye at rest parallel
rays are brought to a focus upon the retina. In
the myopic eye parallel rays, and even rays to a
certain degree divergent, are brought to a focus
in the vitreous, whence they fall in dispersion
circles on the retina. The most common cause
of myopia is the abnormal length of the antero-
posterior diameter of the eye. The defect can be
remedied by placing a concave lens before the
eye. The entering rays are thereby rendered
divergent, or their divergence is increased, so that
their focus is displaced backwards towards the
retina. The degree of the myopia is measured
by the strength of the concave lens which, placed
before the eye, will bring the principal focus
exactly to the retina.

Let parallel rays pass through the convex lens
of 10 cm. (4 inch) focal distance placed against
the window of the optical box. Find the prin-
cipal focus and then move the screen 2.5 cm.
farther from the lens.

The image will be blurred. The screen will
intersect the rays diverging from the focal point.

Hold the weak concave lens, marked — 2, in

INTRODUCTION TO PHYSIOLOGICAL OPTICS 431

front of the window. This lens has a focal dis-
tance of two dioptres or one-half metre (see
page 435).

The image will be clear again. The myopia
in this case is therefore —2D.

Hypermetropia. — In the hypermetropic eye at
rest parallel rays and even those to a certain
degree convergent meet the retina before they
have come to a focus. The most frequent cause
of hypermetropia is the abnormal shortness of the
antero-posterior diameter of the eye. The defect
can be remedied by placing a convex lens before
the eye. The entering rays are thereby rendered
convergent, or their convergence is increased.
The degree of the hypermetropia is measured
by the strength of the convex lens which, placed
before the eye, will so increase its convergent
power that parallel rays will come to a focus on
the retina.

Place the screen 2.5 cm. nearer the lens than
the principal focus.

The image will be blurred. The screen will
intersect the rays before they have converged
to the focal point.

Hold the weak convex lens, marked + 2, in
front of the- window.

The image will be clear. The hypermetropia
in this case is therefore 4-2D.

432 THE OUTGO OF ENERGY

Myopia and hypermetropia will be further
considered under refraction in the eye.

Chromatic Aberration. — The velocity of the
homogeneous spectral rays composing white light
is believed to be the same in a vacuum and in
gases, but differs in transparent liquids and solids.
The front of the light wave strikes the refracting
surface obliquely. As the wave front enters the
medium, its speed lessens. Thus the part of the
front which enters first travels in the refracting
medium at a speed less than the remainder which
has not yet entered. The wave front is therefore
bent towards the retarded portion. The shorter
the wave length, i. e. the greater the wave num-
ber, the slower will the wave advance in the
refracting medium. Hence the wave front of the
violet ray moves more slowly in the medium
than the front of the red ray, and is therefore
bent more from its course. The reverse of this
process takes place when the wave emerges from
the refracting medium. The violet rays are there-
fore more refrangible than the red, and on enter-
ing a refracting medium pursue a different path.
Thus each spectral ray passing through a lens
has its own principal focus. In other words, the
images for the several spectral colors do not coin-
cide precisely. The order in which the refracted
spectral rays cross the principal axis is that of

INTRODUCTION TO PHYSIOLOGICAL OPTICS 433

their refrangibility ; violet crosses nearest the
lens, then blue, green, yellow, orange, and red in
the order named. The principal focus will thus
be a line of colors lying in the principal axis, the
end nearest the lens being violet. The peripheral
portions of a lens refract rays parallel to the prin-
cipal axis more strongly than the axial portion.
Hence the chromatic aberration will increase
with the aperture of the lens.

Put the ground glass plate and the diaphragm
with 2 mm. aperture in front of the condenser.
Let the rays from the illuminated spot of ground
glass pass through the 10 D lens placed about
15 cm. in front of the ground glass, i. e. a dis-
tance somewhat greater than the focal distance
of the lens (10 cm.). Place a white screen about
15 cm. in front of the lens.

The image of the white spot upon the ground
glass will be a disk with violet centre and red
margin.

Eemove the white screen farther from the lens.

At a distance of about 30 cm. the centre of the
image will be red and the border violet.

The image in this experiment is blurred be-
cause the rays which pass through the peripheral
portion of the lens cross the principal axis sooner
than the rays which pass through the axial por-
tion. If the screen be placed at the focus of the

28

434 THE OUTGO OF ENERGY

more axial rays, this focal point in the image will
be surrounded, by dispersion circles made by the
rays which have been refracted from the periph-
ery through foci nearer the lens and which are
now diverging from these foci. If the screen be
placed at the principal focus for the peripheral
rays, this focal point will be surrounded by dis-
persion circles made by the rays that have not
yet converged to the principal axis. (Compare
spherical aberration, page 428.)

Aberration avoided by a Diaphragm. — Place
before the condenser the paper diaphragm with
1 cm. aperture.

The image at once becomes distinct, and the
colors practically disappear. The outer rays,
which when refracted would cross the principal
axis far enough from the principal focus to cause
dispersion circles, have been cut off'. When the
aperture of a lens or mirror is reduced by a
diaphragm to 10°, the greater part of the spheri-
cal aberration is prevented.

Spherical aberration is still further reduced by
combining several lenses in an objective (apla-
natic system).

With an achromatic lens, consisting of a col-
lecting lens of crown glass united with a dispers-
ing lens of flint glass, all the spectral rays may
be brought to the same focus, and chromatic
aberration altogether avoided.

INTRODUCTION TO PHYSIOLOGICAL OPTICS

Numbering of Prisms and Lenses

Numbering of Prisms. — Prisms may be num-
bered according to refracting angles or according
to the extent to which they turn the light ray
from its course (angular deviation). Angular
deviation is expressed by the methods of Dennett
and of Prentice.

Dennett's method. — The length of an arc of
57.295° equals its radius of curvature. A prism
which will bend the ray one hundredth part of
this arc is called one centrad. The angular
deviation produced by the prisms are by this
method expressed in hundredths of the radius
measured on the arc.

Prentice's method. — The unit of comparison is
a prism-dioptre, i. e. a prism that deflects a ray
of light one centimetre at a plane one metre dis-
tant, or, in other words, the hundredth part of
the radius measured on the tangent.

Numbering of Lenses. — Lenses are numbered
according to their refractive power. The unit is
a lens with a focal distance of one metre. This
unit is termed a dioptre, D. A lens of two
metres focus is one half the refractive power, or
J D. The lenses ordinarily employed in ophthal-
mic practice extend from 0.12 D to 22 D. The

436 THE OUTGO OF ENERGY

principal focal distance of any lens in the dioptric
system may be found by dividing one metre, or
100 cm., by the number of dioptres ; thus the
focal distance of a lens of 4 I) = •1|^- = 25 cm.

Convex lenses are marked -f, concave lenses -.

If two or more lenses are placed together, the
dioptric power of the system thus formed equals
the algebraical sum of the dioptric powers of
the lenses in the system.

REFRACTION IN THE EYE 437

IX
REFRACTION IN THE EYE

The Eye as a Camera Obscura. — 1. From the
eye of an ox remove the posterior part of the
sclerotic and choroid coats over an area about
1 cm. in diameter near the outer (temporal) side
of the optic nerve. Cover the retina with a watch
glass. Turn the cornea towards an incandescent
lamp.

A small, real, inverted image of the lamp
will be seen upon the transparent retina. In the
white rabbit the choroid has so little pigment that
the retinal image may be seen without removing
the outer coats of the eye.

2. In a darkened room, direct a blond, blue-
eyed individual to turn the eyes so that one
cornea shall lie in the outer angle of the eye.
Hold a candle near the temporal side of that
eye.

The small, inverted retinal image of the
candle can often be seen shining through the
sclerotic coat at the nasal side of the eye.

438 THE OUTGO OF ENERGY

The Schematic Eye

In passing from the external air to the retina,
the rays of light undergo refraction at the layer
of tears on the anterior surface of the cornea, the
surfaces bounding layers of unequal refractive
power in the substance of the cornea, the ante-
rior surface of the aqueous humor, the anterior
surface of the lens, the surfaces bounding layers
of unequal refractive power in the substance of
the lens, and the anterior surface of the vitreous
humor. To determine the size and position of
visual images, it is fortunately not necessary to
calculate refraction at each of these many sur-
faces. The problem is much simplified by the
following considerations.

The irregularities in the refractive power of
the different parts of the cornea are small ; and
the refractive index of the layer of tears which
covers the anterior surface is almost identical
with the index of the substance of the cornea
and that of the aqueous humor. Practically
therefore the layer of tears, the cornea, and the
aqueous humor may be regarded as a single re-
fracting medium. Further, although the layers
of which the lens is composed increase in refract-
ing power towards the centre of the lens, it is

KEFR ACTION IN THE EYE 439

known that the error introduced by assuming
the lens to be homogeneous is unimportant.
Thus the simplified dioptric system of the eye
consists of three refracting surfaces : the anterior
surface of the cornea,1 the anterior surface of the
lens, and the anterior surface of the vitreous
humor. The index of refraction of the aqueous
and vitreous humors is practically the same.

The several refracting surfaces of this optical
system are approximately " centred," i. e. placed
with their centres of curvature upon a right line,
the optical axis. The diaphragm (iris) is of such
a size and position that the rays entering the eye
intersect the axis at small angles ; the aperture
of the system is therefore small. Under such
conditions it is possible to find upon the princi-
pal axis of the system certain cardinal points,
discovered by Gauss, by the aid of which the
situation and size of the visual images may be
determined. The cardinal points are (1) the an-
terior principal focus, (2) the anterior principal
point, (3) the posterior principal point, (4) the
anterior nodal point, (5) the posterior nodal point,
(6) the posterior principal focus. These points
are reciprocal.

As the dioptric system of the eye consists of a

1 For convenience, the anterior surface of the cornea will be
held to include the layer of tears.

440 THE OUTGO OF ENERGY

spherical surface 1 (the cornea) and a double con-
vex lens (the crystalline lens) it will be advis-
able to consider first the cardinal points of the
cornea (System A), next those of the lens (Sys-
tem B), and finally those of the two combined
as in the eye (System C).

Cardinal Points of the Cornea (System A)

Construction Drawing of System A. — Draw
a horizontal line to serve as the optical axis.2
Take any point, k, in this line for a centre of
curvature.3 From this point describe an arc

1 The cornea is not strictly a spherical surface, but more
nearly that produced by the revolution of an ellipse about its
major axis.

2 This construction drawing should be placed near the top of
the page, in order to permit the construction drawings for the
lens and the compound optical system to be made beneath it.
All these drawings will be the natural size.

8 The following list will be found convenient :
k, centre of curvature.
r, radius of curvature.
hlt intersection of the first spherical surface of any system with
its principal axis (" first " is used in the sense of nearest
the source of light).
h2, intersection of the second spherical surface with its principal

axis.
nlt the first medium, that which bounds the refracting surface
on the side from which the ray conies ; also the refractive
index of this medium.
u2, The second medium, that which bounds the refracting sur-
face on the side from which the ray emerges ; also the
refractive index of this medium.

REFRACTION IN THE EYE 441

with the radius r = 7.829 mm., the radius of
curvature of the cornea. The intersection of
the arc with the axis is termed the principal
point hx of the axial ray. The spherical surface
separates two media : nv the air, and n2, the
aqueous humor.

Principal Focal Distances. — 1. Kays passing
from the first medium through the cornea into
the second medium unite nearly in a point, the
posterior principal focus, <£2. The distance, h^*,
between this point and the principal point is the
posterior principal focal distance, F2. Eays pass-
ing from the aqueous humor through the cornea

<pi, anterior principal focus.

02> posterior principal focus.

Fx, anterior focal distance.

F2, posterior focal distance.

fl, anterior conjugate focal distance.

f2, posterior conjugate focal distance.

o, optical centre.
Klt first nodal point.
K2, second nodal point.
Hi, first principal point.
H2, second principal point.

5, point between two refracting surfaces at which an object
must be in order that the images of the object formed by
the refracting surfaces shall be similar, i. e., images of
one another, lying therefore in the principal surfaces.

Where confusion might arise in applying these terms to Sys-
tem A, B, orC, they will be distinguished by placing with them
the letters A, B, C, respectively. Thus the anterior focal dis-
tance of the lens will be written Fi B, wherever it might other*
wise be confused with that of System A or C.

442 THE OUTGO OF ENERGY

to the air, parallel to and near the axis, unite in
front of the cornea nearly in a point, the anterior
principal focus, <£i. The distance, ht </>b between
this point and the principal point is the anterior
principal focal distance, Fx. The principal focal
distances are proportional to the coefficients of
refraction of the first and last media. The pos-
terior principal focal distance is calculated by
the formula *

(la.) F2= "*r

no — n.

In comparing refractive powers the air, nlt is
taken as the unit. Thus the formula becomes

(1 b) F2

n2 r

n2 — 1

The anterior principal focal distance is calcu-
lated by tne formula

(2 a) FX= *'

no — n.

As %i = unity, the formula becomes

(2 b) Ft = —^-r

n2 — 1
The refractive index, nu of the air = 1 ; accord-

1 For the derivation of the formulas in this chapter the
reader is referred to the works of Donders (Accommodation and
Refraction of the Eye) and Helmholtz (Handhuch der physio-
logischen Optik).

REFRACTION IN THE EYE 443

ing to Helmholtz,1 the refractive index, n2, of the
aqueous humor is 1.3365 ; the ratio is f.

Calculate F1 and F,. The result is,^i = 23.266,
F2 = 31.095.

2. The principal foci may also be approximately
found by construction. Erect at the principal
point and the nodal point 2 perpendiculars to the
optical axis. Set off on each perpendicular dis-
tances from the optical axis proportional to the
rapidity of light in the first and second medium.
The ratio in the case of the air and the aqueous
humor is 4 '. 3. Mark therefore points 20 mm.
and 15 mm. from the axis. Draw a line from the
20 mm. point of the first perpendicular through
the 15 mm. point of the second, and produce the
line to the optical axis. Its intersection with
the optical axis is the posterior principal focus.
Find in a similar way the anterior principal
focus. Indicate upon the axis the cardinal points,
remembering that the construction drawing is to
be the natural size.

Construction of Image. — About 10 cm. in
front of the cornea draw an arrow, ij, which
shall intersect the optical axis at right angles.

1 The figures for this and subsequent calculations under " Re-
fraction of the Eye," are those given by Helmholtz. They are
collected in a convenient Table on pages 461 and 462.

2 The centre of curvature is the nodal point of a system con-
sisting of a single spherical surface.

444 THE OUTGO OF ENERGY

Draw a line from the point i of the arrow
through k. This line, since it passes through
the centre of curvature, will coincide with the
perpendicular to the refracting surface, and there-
fore will not be refracted. Draw from the point
i to the cornea a line parallel to the axis. This
parallel ray will be refracted through the poste-
rior principal focus <f>2. The two rays will unite
at their point of intersection, i2, which point is
the image of i and is its conjugate focus. The
arrow ij was vertical to the axis. Hence its
image will also be vertical to the axis. Draw,
therefore, from i2 a line vertical to the axis.
From the end j of the arrow draw a line through
k. The intersection of this line witli the verti-
cal line just drawn will be the image j2 of the
point j.

Calculation of the Position of the Conjugate
Foci. — The conjugate foci may be found by the
following formulas. Let /i be the conjugate
focal distance hi i, and f2 be the conjugate focal
distance h\jr

\o a) fx = - — (4 a) f2 -

A- Ft v J "* fi-Fi

For virtual images the formulas become

(3b) /. = ^4 <4b) fi^TT**

REFRACTION IN THE EYE 445

Cardinal Points of the Crystalline Lens
(System B)

Construction Drawing of System B. — When
the lens is accommodated for distant vision the
radius of the anterior surface is about 10 mm.,
the radius of the posterior surface about 6 mm. ;
the thickness at the principal axis 3.6 mm. The
index of refraction of the lens is 1.4371. The in-
dex of the aqueous and vitreous humors is 1.3365.

Beneath the construction drawing of the
cardinal points of the cornea (System A) draw
a horizontal line parallel to the optical axis
of the cornea. This line will serve as the
optical axis of the lens. From the intersection
of the cornea with its optical axis let fall a
perpendicular to the optical axis of the lens.

The anterior surface of the lens intersects the
optical axis 3.6 mm. posterior to the cornea.
The radius of the anterior surface of the lens is
10 mm. Find therefore on the optical axis a
point 3.6 + 10 = 13.6 mm. behind the cornea.
From this point as a centre describe an arc with
a radius of 10 mm. that shall intersect the optical
axis 3.6 mm. behind the cornea. A segment of
this arc will represent the anterior surface of
the lens.

446 THE OUTGO OF ENERGY

The thickness of the lens, accommodated for
distant objects, is 3.6 mm. Mark this point.
Here the posterior surface of the lens intersects
the optical axis. The radius of the posterior sur-
face is 6 mm. Find therefore a point on the
optical axis 6 mm. in front of the posterior sur-
face of the lens. With this point as a centre
describe with a radius of 0 mm. the segment of
the arc that shall represent the posterior surface
of the lens. Mark upon this drawing the cardi-
nal points of the lens, as follows.

Optical Centre. — In the cornea, a simple spher-
ical surface, rays directed to the centre of curva-
ture, k, were found to pass through the refracting
surface unchanged in direction. In thin convex
lenses having a long focal distance it is generally
assumed that any ray passing through a point
within the lens termed the optical centre, o, is not
refracted. In thick lenses, on the contrary, every
ray excepting that coinciding with the principal
axis is refracted (see Nodal Points).

The optical centre is situated in the prin-
cipal axis within the lens. In a lens bounded on
both sides by media of equal refracting power,
for example, the crystalline lens bounded by the
aqueous and vitreous humors, the optical centre
is found by dividing the axis of the lens, i. e.}
the distance between the refracting surfaces on

REFRACTION IN THE EYE 447

the principal axis, into two parts proportionate
to the radii of the refracting surfaces.
Then

10 + 6 : 3.6 = 6 : x

x— 1.35 mm., the distance of o from the pos-
terior refracting surface.
Then

3.6 - 1.35 = 2.25 mm.,

the distance of o from the anterior refracting
surface.

Nodal Points. — In thick lenses (such as the
crystalline) with short focal distance, all the rays
except that which coincides with the principal
axis are refracted at one or both of the spherical
surfaces. In order to determine the path of rays
passing through the lens it is necessary to find
the nodal points. These are two points so placed
that a ray directed to the first point appears on
leaving the lens to have come from the second
point, in a direction parallel to the entering ray.
All rays coming from the optical centre, o, to the
anterior refracting surface will after refraction
appear to have come from the first nodal point,
Kx, situated within the lens on the principal axis,
between o and h*. Similarly, all rays from o to
the posterior refracting surface will appear to
have come from the second nodal point, K%, situ-

448 THE OUTGO OF ENERGY

a ted between o and h2. Thus o and Kx are con-
jugate foci for the surface hi, and o and K2 are
conjugate foci for the surface h2. K\ and K2
are virtual images of o; that is, if o were observed
through the surface hx the image would appear
to be A'i, while if o were observed through hz
the image would appear to be K2. As the nodal
points are images of the same point o, they must
therefore be images of each other.

The first nodal point, Ku which is the virtual
image of the optical centre, o, formed by rays
passing from o through the anterior refracting
surface, hu and which lies at the conjugate focus
of o, is situated 2.126 mm. behind the anterior
surface of the lens (accommodated for distant
objects). The second nodal point, K2, the virtual
image of o formed by rays passing from o through
the posterior refracting surface, h2, is situated
1.276 mm. in front of the posterior surface of the
lens (accommodated for distant objects). The dis-
tance between the two nodal points is 0.198 mm.

Principal Surfaces. — Within a double convex
lens are two parallel planes, termed the principal
surfaces. They are perpendicular to the prin-
cipal axis and are so placed that the emerging
ray appears to come from a point in the second
principal surface that exactly corresponds to the
point in the first principal surface to which the

REFRACTION IN THE EYE 449

entering ray is directed. Thus the point in
the second principal surface from which the
emergent ray appears to come is the same dis-
tance from the axis as the corresponding point
in the first principal surface to which the enter-
ing ray appears to pass. In short, each principal
surface is the image of the other, and is of equal
size.

To determine the position of the principal sur-
faces there must be found between the two
refracting surfaces a point, s, at which an object
will form similar images with each refracting
surface. These images being similar are images
of each other and of equal size. The planes in
which they lie are the principal surfaces.

The Point s. — The point s lies between the
two refracting surfaces at distances proportional
to the principal focal distance of each. It will
be remembered that the point o was found by
dividing the distance between the two refracting
surfaces into two parts, proportional to the radii
of curvature of the two surfaces. In System B
the two refracting surfaces are the anterior and
posterior surfaces of the crystalline lens, which
is bounded by the aqueous and vitreous humors,
media of equal refractive power. The focal dis-
tances of the refracting surfaces are in this case

proportional to the radii of curvature. Thus the

29

450 THE OUTGO OF ENERGY

division of the distance between the refracting
surfaces is the same for both s and o, and there-
fore s and o coincide. In System C, on the con-
trary, the first medium is the air, and the last
the vitreous humor. The principal focal dis-
tances are proportional to the coefficients of re-
fraction of the first and last media ; they are
no longer proportional to the radii of curvature ;
therefore s and o no longer coincide, and their
images, lying in the principal surfaces and at
the nodal points, respectively, no longer coincide,
but must be found separately.

Principal Points. — At the intersection of the
principal surfaces with the principal axis lie the
principal points,1 Hx and ff2. The second princi-
pal point is the image of the first. Kays which
in the first medium are directed to the first
principal point are directed to the second princi-
pal point in the last medium, i. e., after the last
refraction. The anterior principal focal distance
is calculated from the first principal point, and
the posterior principal focal distance from the
second principal point

Principal Focal Distances. — The posterior focal
distance of the lens (accommodated for distant

1 The principal points, Hx and 7f2, coincide with the nodal
points, A\ and K2, when the first and last media of the optical
system have the same refractive power.

KEFRACTION IN THE EYE 451

objects) is 50.617 mm. The anterior focal dis-
tance is the same, for the lens is bounded by
media of equal density.

Cardinal Points of the Eye (System C)

Examine construction drawings of System A
(the cornea) and System B (the lens). System C
must be a combination of A and B.

Note : 1. With System C as with System A
the first and last media have different refractive
powers. Therefore the principal points cannot
coincide with the nodal points. 2. The relation
between the nodal point k of System A and
the nodal points K\ and K2 of System B is such
that the nodal points of System C will lie near
the posterior surface of the crystalline leus.
3. The principal point hi of System A lies on
the anterior surface of the cornea, and the prin-
cipal points H\ and H2 of System B lie in the
lens. Hence those of System C must lie in the
aqueous humor. 4. In System C the collecting
power of System B is added to that of System
A. The focal distances in System C will there-
fore be less than those of A or B.

Principal Surfaces. — The principal surfaces are
found from the point s. If a perpendicular be
drawn at s the image of that perpendicular formed

452 THE OUTGO OF ENERGY

by the cornea will be of equal size with the image
of it formed by the crystalline lens. These simi-
lar images will lie in the principal surfaces. The
image which the cornea forms of the point s will
be the first principal point, Hx of System C, and
the image which the lens forms of s will be the
second principal point, H2 of System C. The
point s lies between hi of System A and H1 of
System B, at distances proportional to the pos-
terior focal distance (i^ = 31.095 mm.), of System
A and the anterior focal distance (Fx = 50.617
mm.) of System B. The distance between hi, which
lies at the anterior surface of the cornea, and
HXB, which lies 2.126 mm. behind the anterior
surface of the lens, is 3.6 mm. (the distance be-
tween the cornea and the lens) plus 2.126 mm.
= 5.726 mm. This distance is to be divided in
the proportion 50.617 : 31.095.

50.617 + 31.095 : 31.095 :: 5.726 : x.

x— 2.179. Hence s lies 2.179 mm. behind the
cornea, and 5.726 — 2.179 = 3.547 mm. in front of
the anterior principal point of the crystalline lens.
The first or anterior principal point of the eye,
H\G, is the virtual image of s formed by the
cornea ; it lies at the conjugate focus of s, and
its position is determined by the formula (3 b),
page 444.

REFRACTION IN THE EYE 453

Fx A = 23.266 mm.

F2 A = 31.095 mm.

f2A* = 2.179 mm,

The first principal point, Hx C, is

23.266 x 2.179 1 _. , ,. , , .,

= 1.75 mm. behind hi the an-

31.095 - 2.179

terior surface of the cornea.

The second or posterior principal point of the

eye, H2 C, is the virtual image of s formed by the

lens. It also is found by formula (3 b).

F1 B = 50.617 mm.

F2 B = 50.617 mm.

f2£^ = 3.547 mm.

The second principal point, H2 C, is

50.617 x 3.547 0 oi , , . .,

xfrwTTj q ca7 = 3.814 mm. before the posterior

principal point of the lens ; this point lies 5.924
mm. behind the cornea ; hence H2 C lies 5.924
— 3.814 = 2.11 mm. behind the anterior surface
of the cornea. The distance between the two
principal points is 2.11 — 1.75 = 0.36 mm.

Nodal Points. — The nodal points are virtual
images of the point o, which divides the distance
between the nodal points of System A and Sys-

* The distance of the object s from the refracting surface,
in this case, the cornea.

t The distance of the object s from the anterior principal
point of the crystalline lens.

454 THE OUTGO OF ENERGY

tera B iuto two parts, proportional to the anterior
focal distance of the cornea (23.266 mm.) and the
focal distance of the lens (50.617 mm.). As K1 A
lies 7.829 mm. and Kx B 5.726 mm. behind the cor-
nea, the distance between them is 2.103 mm. This
is to be divided in the proportion 23.266 : 50.617.
23.266+ 50.617: 50.617:: 2.103 : x. £ = 1.4408.
Thus o lies 1.4408 mm. behind the first principal
point of the crystalline lens (S}7stem B) and
consequently

5.726 + 1.4408 = 7.167 mm.

behind the cornea.

By formula (3 b), A^i C, the first nodal point or

the image of o formed by the cornea, is found to be

23.266 x 7.167 „ nr7 , - . , ,,

01 ~n^ — _ ., ._ = 6.9 / mm. behind the cornea.

oLU9o — 7.1b7

The second nodal point, K2 C, or image formed

. . ^ „. . 50.617 X 1.4408

or o by the crystalline lens, is rn n17 _ -. ^<ao

= 1.401 mm. behind the second principal point
of the crystalline lens, and consequently 5.924
+ 1.401 = 7.33 mm. behind the cornea.

The distance K\ K2 between the first and
second nodal points of System C is 7.33 —
6.97 = 0.36 mm. The distance Hi H2 = Kx K2.

Principal Foci. — Kays falling on the cornea par-
allel to the principal axis are refracted by hi A and

BEFBACTION IX THE EYE 455

converged to the point <f>2A, situated 31.095 mm.
behind the cornea. On their way they are further
refracted by System B. Hi B is 5.726 mm. behind
the cornea. The point <j>.2 A is 31.095 — 5.726
= 25.869 mm. behind Hx. Calculated from H2 B,
the posterior principal focal distance F2 of System
B is 50.617 mm. The posterior focal distance of
System C is calculated by the formula

- fiF2 25.369 x 50.617

/2 =& + *[ A = 25.369 + 50.617 = 168" mm«

behind Hz B, and hence 16.899 + 5.924 =
22.823 mm. behind the cornea, and 22.823 —
2.11 = 20.713 mm. behind H, of System C.
The posterior principal focal distance of the eye
is therefore 20.71 mm.

Parallel rays falling on the posterior surface of
the lens are refracted by the lens and converge
at a point (f)1 B — 50.617 mm. in front of Hi B.
They meet the anterior surface of the cornea
50.617 - 5.726 = 44.891 mm. from H1 B. They
are further converged by the cornea to

23.266 x 44.891 .0fTK
31.095 + 44.891 = 13-'omm-

before the cornea, or 13.75 + 1.75 = 15.5 mm.
before Hr C. The anterior principal focal dis-
tance of the eye is therefore 15.5 mm.1

1 In this discussion I have followed closely, in some places

456 THE OUTGO OF ENERGY

Calculation of the Situation and Size of
Dioptric Images

Draw perpendiculars through the optical axis
of System C at the following points : the anterior
principal focus, </>i 0, the first principal point,
Hi C, the second principal point, H2 C, and the
posterior principal focus, <£2 0 (retina). Mark on
the optical axis the first and second nodal points,
Kx C and K2 C.

The following facts should he borne in mind :

1. Every ray which in the first medium is
directed to the first nodal point appears in the
last medium to come from the second nodal
point and is parallel to its original direction.

2. The point at which the ray cuts the second
principal surface is the same distance from the
optical axis as the point at which the ray cuts
the first principal surface ; between the prin-
cipal surfaces the ray is parallel to the optical
axis. 3. All rays parallel in the first medium
unite in one point in the second or posterior focal
surface (the plane passing through the posterior
principal focus vertical to the optical axis) ; if

almost literally, the valuable works of 1 londers ( A ceo vn modal inn
ami Refraction of tin; Eye, New Sydenham Society, London,
1864) and Helmholtz (Handbuch der pliysiologischen Optik,
2te Auflage, 1896),

REFRACTION IX THE EYE 457

these rays be parallel to the axis they will unite
in the posterior principal focus. Conversely, all
rays parallel in the second medium unite in one
point on the first or anterior focal surface, and if
parallel to the axis they unite at the anterior
principal focus (Gauss).

1. Find the course in the vitreous humor of
any ray, ab, which enters the. eye.

Draw in the first medium a ray, a1 b', parallel
to a b, directed to the first nodal point. In the
second medium draw this ray, parallel to its origi-
nal direction, from the second nodal point to the
posterior focal surface. Then a b must also meet
the posterior focal surface at this same place ; for
all rays parallel in the first medium converge in
the second medium to one point in the posterior
focal surface. Produce a b to the first principal
surface, thence, parallel with the optical axis, to
the second priucipal surface, thence, through the
vitreous humor, to the point already found in the
posterior focal surface.

2. Let i be any point in the first medium (the
air). Find its image (for convenience i should
be placed at least 10 cm. in front of the cornea).

Draw from i a ray, iij\, through the first and
second nodal points, as directed above. Draw
from i a second ray, i2j2, parallel with the optical
axis. This rav will cut the second focal surface

458 THE OUTGO OF ENERGY

at the principal focus. Produce i2j>2 until it meets
tijfi. The point of intersection will be the image
of the point i.

Eeduced Eye

The distance of less than one fourth millimetre
which separates one principal point from the
other is so small that it may be neglected with-
out any error of practical importance. Thus the
two principal points may be combined in one point
lying 2.34 mm. behind the anterior surface of the
cornea of the normal.1 Similarly the two nodal
points may be combined in one point lying
0.48 mm. in front of the posterior surface of the
lens, or about 16 mm. in front of the retina.
The nodal point k of the cornea (System A) is
about 14 mm. in front of the retina. The nodal
point of the lens and that of the cornea are com-
bined in the reduced eye in a nodal point situated
15 mm. from the retina. The lens may therefore
be omitted. Indeed, the cornea is normally the
principal refracting surface ; its focal distance is
31.095 mm., while that of the crystalline lens is
50.617 mm. ; if the lens were not present, parallel
rays entering the eye would be focussed by the

1 Listing: Wagner's Handworterbuch der Physiologie, 1853,
iv., p. 495.

HEfHACTION IN THE EYE 459

cornea in a point about 10 mm. behind the retina.
Thus the eye is reduced to a single refracting
surface, the cornea, separating two media, the air
and the vitreous humor. The index of refraction
of these media is -|. The principal focal distances
are proportional to the coefficients of refraction
of the first and last media ; i<\ is 15 mm. and Fs
20 mm., measured from the principal point. The
visual axis (from the cornea to the retina of the
reduced eye) is therefore 20 mm. In order to
bring parallel rays to a focus at 20 mm., the
index of refraction being J, the radius of curva-
ture of the cornea of the reduced eye should be
5 mm.

In such a reduced eye trie retinal images have
the same position and size as in the ordinary
eye. The reduced eye is shown in normal size
in Fig. 65.

Fig. 65. The reduced eye. Normal size (Bonders).

K is the optical centre or nodal point.
h, the principal point.

K h = 5 mm., the radius of curvature of the
refracting surface.

460 THE OUTGO OF ENEKGY

</>!, the anterior principal focus, — the focus of
rays parallel in the vitreous.

<fi2, the posterior principal focus, — the focus
of rays parallel in the air.

h cf>1 = 2*1, the anterior focal distance, = 15 mm.

h cf>2 = F2t the posterior focal distance, = 20 mm.

n1~3~ Ft 7" 15'

With the reduced eye many calculations may
be rapidly and easily performed.

REFRACTION IN THE EYE

461

AVERAGE MEASUREMENTS OF NORMAL
(EMMETROPIC) EYE1

mm.

12

4

1

Thickness of lens accommodated for near

4

Thickness of lens accommodated for distant

3.6

0.2-0.3

Distance between retinal vessels

5 and rod

0.2-0.3

1.5

1.25

Diameter of fovea centralis . =

.

0.22

0.004-0.005
0.0018

Accommodated for

Distant

Near

objects.

objects.

Refractive index of aqueous

and vitreous humors . .

1.3365

1.3365

Total refractive index of crys-

1.4371

1.4371

Radius of curvature of cornea .

7.829

7.829

Radius of curvature of ante-

rior surface of lens . . .

10.00

6.0

Radius of curvature of poste-

rior surface of lens . .

6.0

5.5

1 It should be understood that the figures given in this table
are the mean of numerous observations. The variation in
different eyes is considerable, though in most cases not great
enough to be of practical importance.

462

THE OUTGO OF ENERGY

Accommodated for

Distant

Near

objects.

objects.

Distance from anterior surface

of cornea to anterior sur-

face of lens

3.6

3.2

Distance from anterior surface

of cornea to posterior sur-

face of lens

7.2

7.2

Calculated

Anterior principal focal dis-

tance of cornea ....

23.266

23.266

Posterior principal focal dis-

tance of cornea ....

31.095

31.095

Anterior and posterior princi-

pal focal distance of lens

50.617

39.073

Distance of anterior principal

point of lens from anterior

surface of lens ....

2.126

1.989

Distance of posterior principal

point of lens from poste-

rior surface of lens . . .

-1.276

-1.823

Distance of the two principal

points of lens from each

0.198

0.188

Posterior principal focal dis-

20.713

18.689

Anterior principal focal dis-

15.498

13.990

Distance from anterior sur-

face of cornea to

First principal point . . .

1.753

1.858

Second principal point . .

2.106

2.257

First nodal point ....

6.968

6.566

Second nodal point . . .

7.321

6.965

Anterior principal focus . •

—13.745

-12.132

Posterior principal focus

22.819

20.955

Distance upon optical axis

from anterior surface of

cornea to retina . . .

23.0

23.0

In accommodation a clear image of an object 152 mm. in
front of the cornea, or 140 mm. in front of the anterior prin-
cipal focus, will be formed upon the retina.

REFRACTION IN THE EYE 463

Eelations of the Visual Axis

It has already been stated that the refracting
surfaces of the eye are centred, often imperfectly,
upon a right line, the optical axis. This line
normally meets the retina between the yellow
spot and the optic papilla or exit of the optic
nerve. To see a luminous point clearly, the
image of the point must fall on the centre of the
yellow spot. The line passing from the centre of
the yellow spot through the nodal point to the
luminous point is termed the visual axis. Unless
the luminous point already lie in the visual axis,
it must for distinct vision be brought there by
the rotation of the eyeball. The object is then
said to be " fixed " by the eye. The point about
which the eye rotates is the centre of rotation.
The line between the luminous point and the
centre of rotation is the line of fixation.

The line of fixation and the visual axis should
nearly coincide. Generally, the visual axis
and the optical axis do not coincide. In other
words, the visual axis is generally a secondary
axis, and the planes of the refracting surfaces
are oblique to it. The optical axis passes to
the inner side of the yellow spot. It inter-
sects the visual axis at the nodal point. Hence

464 THE OUTGO OF ENERGY

the nodal point becomes the vertex of an
angle, the angle gamma, 7, the legs of which
are the anterior portion of the optical and visnal
axes. The angle 7 usually reaches 5°, but may
reach 10°.

In emmetropia and hypermetropia, the visual
axis passes through the cornea on the inner side
of the optical axis ; angle 7 is then positive. The
eyeball must rotate outwards in order to fix an
object. Thus the visual axes seem to diverge.
Hence the angle 7 must be considered in esti-
mating the degree of a divergent squint.

In myopia, the visual axis may coincide with
the optical axis or pass through the cornea on
the outer side of the optical axis. In the latter
case, angle 7 is negative. In this condition the
eyeball must rotate inwards in order to fix the
object. The deviation inwards may be confused
with convergent squint.

Draw a diagram showing angle 7.

Visual Angle. — Draw an arrow in front of a
diagram of the reduced eye. Draw lines from
the nodal point through and beyond the two ex-
tremities of the object.

The angle included between the lines drawn
from the nodal point to the extremities of the
object is termed the visual angle.

Apparent Size. — Within the lines marking the

REFRACTION IN THE EYE 465

visual angle draw a second arrow parallel to the
first and twice its distance from the nodal point.
Produce the visual lines from the nodal point to
the retina.

Observe that the retinal images of the large and
the small arrow are of equal size. The two ob-
jects subtend the same visual angle. Thus the
apparent size of an object depends upon the visual
angle.

Size of Retinal Image. — In the emmetropic eye
( the eye accommodated for distant vision ) the
size of the object B is to the size of the retinal
image h as the distance from the object to the
nodal point of the reduced eye, g1} is to the dis-
tance from the nodal point to the retina, g2.

(5) B : b : : g1 : g2

The retinal image is smaller than the object by
the number of times g2 = 15 mm. is contained in
the distance, in millimetres, of the object from the
nodal point.

Calculate the size of the retinal image of a
post one metre high placed 300 metres from the
observer's eye.

Acuteness of Vision. — Draw upon the visual
axis of the reduced eye a series of arrows of equal
size, each bisected by the axis. Draw lines from

30

466 THE OUTGO OF ENERGY

the extremities of these arrows to the nodal
point.

Observe that as the object recedes from the
eye the visual angle and the retinal image become
smaller. When the visual " angle is less than
one minute, the retinal image will be too small
to be perceived ; the limit of perception will be
reached.

Smallest Perceptible Image. — On a black card
gum one millimetre apart, and parallel with each
other, two slips of white paper one millimetre
in width. "Place the card about six metres in
front of a window or other sufficient light. Face
the card and move backward until the millimetre
space between the two white slips disappears be-
cause the slips can no longer be seen separately.
Measure the distance gx from the object to the
nodal point. Calculate the size of the retinal
image ( formula 5). Compare this result with
the diameter of the cones in the region of dis-
tinct vision (page 461).

Measurement of Visual Acuteness. — Taking V
as the average smallest visual angle at which an
object is perceptible, Snellen built up a set of
test letters by combining small squares each of
which subtends an angle of 1'. Thus the lines
of which the letters are formed subtend an angle
of 1'. The spaces between the lines also subtend

REFRACTION IN THE EYE 467

this angle. Only such letters are used as can
be drawn approximately within a square that
shall contain twenty-five of the smaller squares,
and shall subtend an angle of 5'. Thus the
strokes and, so far as possible, the spaces between
the strokes are one fifth the size of the letter.
The size of the letter the perception of which
constitutes normal vision at a given distance
(that is, the letter that subtends a visual angle
of 5' at the given distance) is obtained by multi-
plying the distance by 0.001454 mm., which is
the tangent 1 of the angle of 5'. At the distance
of one metre the size of the standard letter is
1000 X 0.001454 = 1.45 mm. Near each of Snel-
len's test letters is recorded the distance viewed
from which the letter will subtend a visual angle
of 5r in the emmetropic eye.

As some of the letters are not easily recognized
by the astigmatic eye (D, for example, being some-
times mistaken for B), the acuteness of vision
should not be pronounced normal unless each
letter of the entire series can be read at the dis-

1 To obtain the tangent of an angle draw a circle with the
vertex of the angle as the centre. The two legs of the angle
are radii of the circle. Draw a perpendicular (tangent line)
from the end of one radius to the prolongation of the other.
Divide the length of the perpendicular by the length of the
radius ; the quotient is the function called the tangent of the
angle-

468 THE OUTGO OF ENERGY

tance corresponding to the number of the series.

d
The acuteness of vision is expressed by — ; where

d is the greatest distance at which the letters
in any line are seen distinctly by the eye exam-
ined, and D the distance at which they can be
seen by the normally acute eye.

Place the subject in a well-lighted room six
metres (approximately 20 feet) in front of a
card of Snellen's test types. Eays from an object
six metres distant are practically parallel. At
this distance the letters numbered VI should

be read. If they are clearly visible, V = - ; acute-
ness of vision is normal. If the subject at 6 metres
cannot see distinctly letters larger than those
marked XVIII metres (approximately 60 feet),

V = — ; acuteness of vision is one third the

lo
normal.

In some eyes vision is so acute that types
constructed with a visual angle of 4 minutes
(J the normal angle) can be seen clearly.

REFRACTION IN THE EYE 469

Accommodation

Accommodation. — Look at any distant object.

The object will be seen clearly. The (practi-
cally) parallel rays proceeding from the object
are brought to a focus on the retina.

Look at an object ten inches from the eye.

The rays proceeding from this object are evi-
dently divergent, yet the object is seen clearly.
The divergent rays have also been focussed on
the retina. This power of voluntarily bringing
divergent rays to a focus on the retina is termed
accommodation.

Schemer's Experiment. — With a tine needle
pierce in a card two holes at a distance from each
other a little less than the diameter of the pupil
(average 4 mm.). Hold the card with the holes
horizontal and near the pupil. Look through the
holes at a pin or needle held vertical about 15 cm.
(6 inches) in front of the eye.

The needle will be seen clearly.

Move the index finger over one of the holes.

There will be no change except that the visual
field will be darker.

Fix a distant object, for example, a cloud.

The needle will appear double, and each image
will be rendered indistinct by dispersion circles.

Move the index finsjer over the left-hand hole,

470 THE OUTGO OF ENERGY

The right-hand image will disappear.

Hold the needle about 100 cm. away and fix
some nearer object. The needle will appear
double. Close the left-hand hole.

The left-hand image will disappear.

Draw a diagram to explain these observations.
Eemember that a separate image of the needle
will be formed by the rays passing through each
hole in the card.

Dispersion circles. — Place a printed page
about two feet in front of one eye, and shut the
other eye. Observe the letters through a piece
of wire gauze held six inches in front of the eye.

Either the wire or the letters can be distinctly
seen, bat not both at once. If the letters are
seen clearly, each wire will appear as a broad
indistinct line made up of superposed dispersion
circles and vice versa.

Diameter of Circles of Dispersion. — 1 . If the
eye be accommodated for objects at an infinite
distance (practically twelve metres or more), the
image of a near object will fall behind the
retina. The image will lie in the conjugate focus
of the object, and the position of the image can
be calculated by the formula for conjugate foci
(page 444). From this formula may be derived

y =

a

REFRACTION IN THE EYE 471

y =/2 — F2, the distance from the retina to the

image behind it.
g, the distance from the anterior focus <f>i to the

object.
(f>l lies 20 mm. from the nodal point K.
F2 Fv in the reduced eye, is 20 x 15 = 300 mm.
from K.

Find the distance behind the retina of an
image whose object is 320 mm. from K.

The distance is 1 mm.

2. If y is known, the diameter of the dispersion
circles can be calculated. In the example just
given, the pencil of rays diverging from each
luminous point in the object was reunited in a
single point one millimetre behind the retina.
At the retina, the converging cone had a certain
section, i. e. the circle of dispersion. The base of
the cone is evidently the pupil, which in the
reduced eye is taken to be 19 mm. in front of the
retina and 4 mm. in diameter.1

The length of y divided by the length of the
whole cone (19 mm.), gives the proportion in

1 The diameter of the cone is not precisely that of the pupil.
The rays in the vitreous would appear to come from the image
of the pupil formed by the lens. Thus the diameter changes
from 4 to 4.23 mm. At the same time the position of the base
is changed from 3.6 mm. (the distance of the plane of the pupil
behind the cornea) to 3.7 behind the cornea. This brings the
base of the cone 19 mm. in front of the retina, which is the
position assumed for it in the reduced eye.

472 THE OUTGO OF ENERGY

which the diameter of the cone at its base
(4 mm.) is reduced at the retina. In the example
taken y = 1 mm. Then the proportion sought is
1 '. 19 + 1 = oV Thus the diameter of the dis-
persion circle is 2V °f 4 mm. = J mm.

3. Calculate the size of the dispersion circle
produced by an object twelve metres from the
emmetropic eye. At this distance the dispersion
circles are so small as to cause no perceptible
lack of clearness in the image.

Accommodation Line. — Hold a needle two
inches from a printed page. Bring the eyes as
near the needle as is possible without causing the
image of the needle to blur. When the needle
is at this " near point " of accommodation it will
be seen clearly, but the printed words will be
indistinct. Draw back the eyes gradually.

Soon a point will be reached at which both
needle and print will be seen distinctly. The
greatest distance between two objects on the
visual line at which the two may both be seen
clearly while the eye is accommodated for either,
is called the accommodation line. The length of
the accommodation line increases as the object is
removed from the eye.

REFRACTION IN THE EYE

473

Mechanism of Accommodation

Narrowing of Pupil. — 1. Watch the pupil while
the subject accommodates first for a distant and
then fcr a near object.

In accommodation for near objects the pupil
contracts.

2. Hold a pencil about thirty centimetres in
front of one eve. Close the other eve. The
pencil is seen clearly. Move the pencil towards

Fig. 66.

the eye until its image becomes indistinct from
dispersion circles. Now observe the pencil
through a pin-hole in a card placed in front
of the pupil.

The image is sharper. The size of the dis-
persion circles is diminished by making the
aperture smaller and thus cutting off the rays

474 THE OUTGO OF ENERGY

that meet the refracting surfaces at a distance
from the optical axis (compare page 434).

Relation of Iris to Lens. — 1. Stand the convex
mirror upright on a level with the eye of the
observer. Over the mirror (Fig. 66, C M) place
a diaphragm of black paper, I V , with an aperture,
P P', four millimetres in diameter. Let this aper-
ture be the pupil and the convex mirror be the
crystalline lens. The wooden block in which the
mirror is held will support the diaphragm so that
there will be a space between the border of the
pupil and the surface of the mirror. Let the
lamp, L, be on one side of the aperture and
the observer's eye, E, on the other. By means
of the convex lens of 6.5 cm. focal distance fur-
nished with the ophthalmoscope concentrate the
light upon the margin of the pupil in the direc-
tion LH. It will pass the margin P and be
reflected from the mirror to the eye in the direc-
tion H E. No rays from L can reach the mirror
between H and C. This portion of the mirror
will reflect the posterior side of the diaphragm.
Thus the light from S falling on the mirror at J
will Ik; reflected in the direction J E to the ob-
server's eye, and a dark band, the image of the
back of the diaphragm, will appear in the mirror
between the image of L at H and the margin of
the pupil.

REFRACTION IN THE EYE 475

Depress the paper diaphragm until the margin
of the pupil lies against the mirror. The black
line will disappear, because the ray J E, reflected
from the back of the diaphragm, is intercepted.
The space P H is closed (Helmholtz).

2. In a dark room repeat Experiment 1 upon
the eye. The iris will be the diaphragm, I V, and
the anterior surface of the crystalline lens will
be the convex mirror. The light and the ob-
server's eye should be placed as in Fig. 66.

The bright image of the light formed by the
cornea, should be neglected. Near this image
are two others, very much fainter. The larger
of the two is indistinct and upright ; it is re-
flected from the anterior surface of the crystal-
line lens. The smaller is a sharp, inverted image
from the posterior surface of the lens. By mov-
ing the glass lens the light may be thrown at
will on all parts of the border of the pupil.

No dark line or image of the posterior surface
of the iris will be seen. The maroiu of the iris
lies upon the lens.

Changes in the Lens. — 1. Direct the subject to
cover one eye. Place a needle at the near point
of the other eye in line with some distant object
that can be clearly seen. The two objects must
be kept accurately in line throughout the experi-
ment. Let the observer stand at one side of and

476 THE OUTGO OF ENERGY

a little behind the subject, so that he shall see
about half of the corneal image of the black
pupil of the subject's eye projecting beyond the
corneal border of the sclera. Note, from within
outwards, the optical section or profile of the
margin of the sclera, the anterior half of the
pupil, a clear portion of the cornea, and finally
a dark stripe which is the most anterior portion
of the cornea.1

Watch carefully the clear interval between this
dark stripe and the profile of the pupil while the
subject, keeping the eye steadily in one position,
accommodates first for the distant and then for
the near object.

The interval between the corneal stripe and
the border of the pupil diminishes on accommo-
dation for near objects. Hence the border of the
pupil moves forward. If this were not the case,
the interval would become larger, for the pupil
narrows in accommodation. Accidental turning
of the subject's eye towards the observer would
also cause the interval to appear larger. As the
margin of the iris lies upon the lens, this obser-
vation is evidence that the anterior surface of the

1 The sclera projects over the iris. The inner surface of the
projecting portion is in shadow. The profile view of the image
formed of this projecting portion by the refraction of the cornea
is the dark line observed in the above experiment. It is dark
hy contrast with the image of the welMighted iris.

REFRACTION IN THE EYE 477

lens moves forward in accommodation (Helm-
holtz).

2. Place the diaphragm with L-shaped aper-
ture in the lantern. In a dark room place the
lantern in front and to the inner side of the
subject's eye, so that the rays shall make an angle
of about 40° with the visual axis of the eye
directed forwards. Let the observer's eye be in
a corresponding position to the outer side of the
subject's eye. In the visual axis of the subject's
eye place an object at the near point and one at
the far point (six metres). Let the subject
accommodate for the far point.

Note the sharp, very bright, upright image
reflected from the cornea, the indistinct, faint,
upright, slightly larger image from the convex
anterior surface of the crystalline lens, and lastly,
the sharper, faint, inverted, small image reflected
from the concave posterior surface of the lens.1
The image from the anterior surface of the lens
lies apparently 8-12 mm. behind the pupil, and
therefore disappears behind the border of the
iris upon slight changes in the position of the
light or the observer's eye. The image from
the posterior surface lies apparently about 1 mm.

1 These images may be magnified with advantage by looking
at them through the lens of 7.5 cm. focal distance furnished
with the ophthalmoscope.

478 THE OUTGO OF ENERGY

behind the pupil, and therefore is not much dis-
placed towards the pupil and the corneal image
upon slight movements of the light or the ob-
server's eye.

Let the subject accommodate for the near point.

The image from the anterior surface of the
lens will become considerably smaller, and usually
it will approach the middle of the pupil. The
image formed by a convex mirror becomes smaller
the smaller the radius. Hence in accommoda-
tion the anterior surface of the lens becomes
more convex.1

The image from the posterior surface also
becomes smaller, but the change is too slight
to be observed by the method employed in this
experiment. Some diminution in size would be
expected from the shifting of the cardinal points
in accommodation. Exact measurements with
the ophthalmometer show that the change is too
great to be explained in this way.

Thus in accommodation the focal distance of
the lens is shortened and its principal points
move forwards.

1 If in accommodation the anterior surface approached the
cornea, the image would hecome smaller through refraction in
the cornea, even though the anterior surface did not become more
convex. Calculation shows that the change thus produced is
very small relative to that actually observed in the above
experiment.

REFRACTION IN THE EYE 479

Measurement of Accommodation

Far Point. — The most distant point of which
the eye at rest, i. e. the ciliary muscle entirely
relaxed, can form a clear image on the retina was
termed by Donders the far point (ptcnctum re-
motum = r). The distance of r from the eye
= B. In the emmetropic eye parallel rays are
brought to a focus on the retina ; r is theoret-
ically at an infinite distance. Practically, if the
accommodation be kept at rest by voluntarily re-
laxing the ciliary muscle or by paralyzing the in-
nervation of the muscle with atropine, the far
point will be found at twelve metres, at which
distance objects produce dispersion circles so
small as to cause no perceptible lack of clearness
in the image.

In the myopic eye, r is a short distance in front
of the eye.

In hypermetropia, only convergent rays can be
f ocussed on the retina of the eye at rest. Parallel
and divergent rays can be f ocussed only by use
of the accommodation mechanism; r is therefore
negative.

Determination of Far Point. — Place the subject
in a well-lighted room six metres in front of a
card of Snellen's test-types. At this distance the

480 THE OUTGO OF ENERGY

normal eye can read the letters numbered VI
If the subject sees these letters clearly the acute-
ness of vision is normal, and R is infinite. If the
subject reads I at one metre, II at two metres,
but cannot read VI at six metres, bring the test
card towards the eye until a point is reached at
which the letters numbered VI are seen clearly.
This is the far point.

Near Point. — 1. Look through the holes in
the card used for Schemer's experiment at a
needle placed vertically about 30 cm. (twelve
inches) in front of one eye. Obtain a single
clear image of the needle. Bring the needle
nearer the eye. As the distance between the
needle and the eye becomes shorter, the rays pro-
ceeding from the needle become more divergent
and require a greater convexity of the lens to
bring them to a focus on the retina. A point
will be reached at which the divergence exceeds
the utmost converging power of the dioptric ap-
paratus and the images received through the two
holes in the card can no longer be made to co-
incide on the retina ; the needle will then appear
double. This is the near point of accommodation
(punctum proximum = pi). The distance from p
to the eye — P.

Determination of Near Point. — Hold ill front of
the eye a test card containing print so small that

REFRACTION IN THE EYE 481

it shall subtend the standard angle of 5' when
placed 25 cm. from the cornea. The distance from
the eye at which this type can be read clearly
= P. '

Range of Accommodation. — The range of accom-
modation is the expression of the total accommoda-
tive power of the eye. With the eye at rest rays
diverging from the far point r are brought to a
focus on the retina. With the ciliary muscle
fully contracted, rays diverging from the near
point p are focussed on the retina. To bring the
more divergent rays from p to the same focal
plane as the less divergent rays from r, an auxiliary
lens must be employed, as hi the following ex-
periment.

Place the diaphragm with L-shaped aperture
in front of the condenser. Eemove the tubes
holding the projecting lenses. Bays will now
diverge from the illuminated I Place this illu-
minated object at a convenient far point, for ex-
ample, 26 cm. in front of the convex lens of 10 cm.
focal length. Place a screen at the conjugate
focus. Note the clear image. Move the object 8 cm.
nearer the lens. Let this be the near point. The
conjugate focus now falls behind the screen and
the image is blurred by dispersion circles. Place
in front of the 10 D lens an auxiliary lens of + 2
D. The image will be clear. The rays diverg-

31

482 THE OUTGO OF ENERGY

ing from the near point will be united by the two
lenses in the same focal plane in which the rays
diverging from the far point were united by the
first lens. The second lens has " accommodated "
the optical system to the distance R — P.

In this experiment the power of the +2D lens
represents the distance R — P, or range of accom-
modation. The power of a lens is inversely pro-
portional to its focal distance A. Consequently,

the range of accommodation 1 = 1 : A or -r. Then

L 1 1

A~ P~ R

In the eye the auxiliary lens necessary for
focussing the rays diverging from the near point
is provided by an increase in the convexity of the
crystalline lens. The difference in refractive
power of the two lenses (the crystalline in its
least convex form and the crystalline in its most
convex form) is the measure of the range of
accommodation of the eye. If the lens remain in
its least convex form, an auxiliary lens must be
placed before the cornea in order to bring rays
diverging from an object at the near point to a
focus on the retina. The strength of this auxil-
iary lens becomes then the practical measure of

1 When 1 = 1 metre.

REFRACTION IN THE EYE 483

the range of accommodation, and - = — — —

A. Jr R

becomes its numerical expression l

In myopia P may be 10 cm. and R 25 cm.,

ti 1 10° inn1 10° i -r, m

Then p=ur =10J)>Tr-25=+I)' The

myopia is of 4 dioptres, -r — 10 D — 4 D = 6 D.

In this case Pis greater than A,

In hypermetropia P may be 50 cm. and R neg-

0K ™ i ioo 9r. , 1 100

ative, — 2o cm. I hen — = -7^= 1 D, and — = ~^—

r 5U ./*; — zo

= -4D. The hypermetropia is of 4 D. — =

2-(-4) = 2 + 4rr6D, which is the sum of

P and R.

In emmetropia P may be 20 cm. and R in-

1 1 1- 100 rTX T

finite. Then -.- = ~. -^ = -^tt = o D. In
J. P P 20

1 Theoretically the auxiliary lens should be placed in the
eye and not in front of it, and its second nodal point should
coincide with the first nodal point of the eye. The placing of
the auxiliary lens in front of the cornea alters the position of
the cardinal points of the combined system, and also alters the
focal distance of the auxiliary lens. Rut the actual changes
in the lens during accommodation are nearly proportional to

— = — , so that the formula serves practically for propor-
tional magnitudes, i. e., for comparing reciprocally the different
values of the range of accommodation under different circum-
stances.

484

THE OUTGO OF ENERGY

other words, a convex lens of 5 D must be placed
before the cornea in order to enable the eye with
ciliary muscle relaxed to see clearly an object
situated at the near point.

The near point recedes as the lens becomes
harder with advancing age until about the seven-
tieth year, when B = infinity, and accommodation
is lost.

RANGE OF ACCOMMODATION AT DIFFERENT

AGES

Age

P

P

in years.

in dioptres.

in cm.

15

12.0

8.3

25

8.5

12

35

5.5

18

45

3.5

28

55

1.75

55

65

0.75

133

70

0

00

Ophthalmoscopy

Reflection from Retina. — 1. Copy the construc-
tion used to find the image of the point i formed
by the dioptric system C (page 457). Assume
that the image is itself luminous, and that rays

REFRACTION IN THE EYE 485

in the last medium are passing from the image
to the second (now the first) refracting surface.
Find the point at which these rays unite in the
first medium (now the second).

The rays will unite at the original luminous
point. If the eye be accommodated £or a light
placed in front of it, an image of the light will
be formed upon the retina. A portion of the
light rays entering the eye will be reflected from
this image. Passing back over their original course,
they wTill form in turn an image which will ex-
actly coincide with the luminous object,

2. Draw a horizontal line as a visual axis.
Upon this visual axis draw two reduced eyes,
normal size (Fig. 65), facing each other a conven-
ient distance apart (5 cm.). Let the left be the
observer's eve, and the right the eve of the sub-
ject. On the visual axis behind the observer's
eye draw a lamp flame. Assume that the sub-
ject's eye is accommodated for this flame.

The construction shows that were the observ-
er's eye away, an image of the flame would be
formed on the retina of the subject's eye. The
image would reflect light toward the flame. This
reflected light would enter by the observer's
eye, and the illuminated area of the subject's
retina thus be made visible, were it not that the
observer's eye is necessarily placed in the visual

486 THE OUTGO OF ENERGY

axis, and thus intercepts the rays from the source
of light to the subject's eye. The interior of the
eye is therefore not illuminated, and the pupil
remains dark.

3. Three millimetres behind the principal
point of each of the two reduced eyes draw a
diaphragm (iris) with an aperture (pupil) four
millimetres in diameter. Assume that the sub-
ject's eye is accommodated for the pupil of the
observer's eye.

Note that a dark image of the pupil of the ob-
server's eye will be formed on the retina of the
subject's eye. The rays reflected from this image
will form a second dark image which will exactly
coincide with the pupil of the observer's eye.
Thus the observer will see only the reflection of
his own black pupil in the subject's eye.

4. Throw light into the subject's pupil from a
lamp held as near the observer's eye as possible.
The subject should not look at either the observer
or the light, and his eye should be accommodated
for a distance much less or much greater than
that of the observer or the light.

Part of the pupil will appear red. It has been
shown in Constructions 2 and 3 that the pupil or-
< I i 1 1 arily appears black. When, however, a part of
111'- image of the light on the retina of the subject
coincides with that of the pupil of the observer,

KEFfi ACTION IN THE EYE 487

and when the subject's eye is not accommodated
for either the light or the observer 's pupil, some
of the light reflected from the subject's retina will
reach the retina of the observer (Helmholtz).

Influence of Angle between Light and Visual
Axis. — 1. Draw a reduced eye with pupil of
four millimetres diameter as described above.
Draw to the margins of the pupil an illuminating
pencil of parallel rays that shall make with the
visual axis an angle of about 20°. Draw the
course of these rays from the pupil to the retina
(seepage 457). On the opposite side of the visual
axis mark the nodal point of the observer's eye
in such a position that the observer's visual axis
shall make also an angle of about 20° with the
visual axis of the subject's eye. Draw rays from
this nodal point to the pupil, and thence to their
focus on the retina.

The portion of the interior of the eye visible
to the observer will be that included between
the outermost rays of the two conical pencils, the
common base of which is the pupil. Note that
the apex of the cone is a short distance behind
the nodal point. The visible portion includes
therefore only a part of the anterior chamber, a
small portion of the lens, and a very small por-
tion of the vitreous.1

1 This matter is clearly presented by Dr. John Green in his

488 THE OUTGO OF ENERGY

2. Eepeat Construction 1, but bring the light
nearer the observer's eye.

Diminishing the angle between the axis of the
observer's eye and the axis of the illuminating
pencil increases the length of the cone formed by
the intersection of the illuminating pencil and
the pencil to the observer's eye. Thus the ob-
server sees a larger cross-section of the lens and
vitreous, and sees farther into the eye.

3. Repeat Construction 1, but place the ob-
server's nodal point in the axis of the illuminat-
ing pencil.

The point of the cone will reach the retina.
The light reflected will emerge from the emme-
tropic eye in parallel rays which will enter the
observer's eye and form upon his retina an image
of the illuminated area of the subject's retina.

Influence of Size of Pupil. — Repeat Construc-
tion 1 of the preceding section, but enlarge the
diameter of the pupil to eight millimetres.

The visible portion of the interior of the eye is
greater with a large pupil than with a small one.

Influence of Nearness to Pupil. — Repeat Con-
struction 1, but draw the observer's eye nearer the
subject's eye.

Note that rays from a larger portion of the

article on the Ophthalmoscope printed in the first edition of
Wood's Reference Handbook of the Medical Sciences.

REFRACTION IX THE EYE 489

subject's retina enter the pupil of the observer
when the eves are near.

Ophthalmoscope. — 1= The eye of the observer
cannot be placed in the axis of the illuminating
pencil without shutting off the illuminating rays.
This difficulty was obviated by the invention of
the ophthalmoscope.

Place the electric lamp at the same height as
the artificial eye, and a little in front of and to
one side of it, so that the axis of the illuminating
pencil shall be at right angles with the visual
axis of the artificial eye. In front of the artificial
eye set a clear glass plate at an angle of 45° to
the axis of the illuminating pencil. A portion
of the rays which fall upon this plate will pass
through the transparent glass and be lost. An-
other portion will be regularly reflected, and will
be thrown into the artificial eye. A portion of
the light returning from the interior of the ob-
served eye will be reflected by the glass plate
and lost. Another portion will be transmitted
through the glass plate in the direction of the
visual axis of the observed eye, and may be
received by the eye of an observer placed in this
axis, as shown in the preceding construction
(Helmholtz).

2. Examine the Loring ophthalmoscope. Its
essential parts are (1) the mirror of concave

490 THE OUTGO OF ENERGY

glass, silvered, pierced at its middle point with
an aperture of about 2.5 mm., pivoted to turn to
either side ; (2) two rotating disks carrying a
series of concave and convex lenses in front of
the aperture.

The silvered mirror reflects more light than
the mirror of transparent glass. Further, it
allows the lamp to be placed at the side of the eye
to be examined, and at any required distance from
the mirror. The turning of the mirror upon a
pivot permits the more or less oblique incident
rays to be thrown into the eye without tilting
the disks carrying the lenses, and thus rendering
the lenses astigmatic by placing them at an
angle to the optical axis which passes from the
subject's retina through the aperture of the mir-
ror and through the lens behind the aperture
into the observer's eye.

The disks may be used singly or in combi-
nation. A series of concave lenses (marked — )
from 1 D to 24 D, and a series of convex lenses
(marked +) from 1 D to 23 D, are thus secured.

Direct Method

Emmetropia. — 1. Eemove from the lantern
the tubes holding the projecting lens. Place the
ground glass screen before the condenser. See

REFRACTION IN THE EYE 491

that the inner tube of the artificial eye is drawn
out to the line marked zero upon its scale ; the
eye is then accommodated for distant vision. Set
the eye at the level of the observer's eye and
near the edge of the table. Place the light on the
right side of the artificial eye and slightly behind
it. Hold the ophthalmoscope in the right hand
close to the right eye at a distance of about fifty
centimetres from the artificial eye, and look
through the aperture in the mirror. The elbow
should be close to the side. The head should
be vertical so that the observer's eye and the
artificial eye may have the same visual axis.
Keep the reflected light upon the pupil of the
artificial eye. It will be illuminated by the red
reflection from the choroid coat. With the pupil
illuminated, approach the artificial eye until the
lens-bearing disk lies in the anterior principal
focus (50 mm. in front of this eye, 13 mm. in
front of the cornea of the normal human eye;
seepige!94.) The artificial eye is accommodated
for distant objects. The observer's eye must also
be accommodated for distant vision. The power
of voluntarily relaxing the ciliary muscle is at-
tained by practice ; the observer should endeavor
to look through and beyond the eye at some dis-
tant object. If the observer be myopic or hyper-
metropic, his refractive error should be corrected

492 THE OUTGO OF ENBEGY

by placing the appropriate lens before the opening
in the mirror.

As the eye is approached, the details of the
fundus will come into view. Find the optic disk.
Trace the branches of the central artery and vein
which perforate the disk. The image of these
parts is virtual, magnified about sixteen times,
and erect.

2. Copy Construction 2, page 485, in which
two reduced eyes are placed on the same visual
axis facing each other. At the anterior prin-
cipal focus of the subject's eye draw a concave
mirror of 175 mm. focal distance with an aper-
ture of 2.5 mm. through which passes the visual
axis.

The rays converging from the mirror and pass-
ing through the pupil are still further converged,
and are brought to a focus in the vitreous,
whence they diverge to fall in dispersion circles
upon the retina, a large area of which is thus
illuminated.

Draw rays reflected from the retina to the
pupil of the subject's eye. They must emerge
from the eye parallel. Entering the observer's
eye, with accommodation relaxed, they will be
brought to a focus on the retina. Show by a
construction that the image of the optic disk
formed in the observer's eye will be inverted but

REFRACTION IN THE EYE 493

will appear to be upright and of its natural size

(1.5 mm.).

The apparent size of this image depends upon

a visual judgment. The observer knows that

small objects are usually held about 250 mm. in

front of the nodal point. The size of an object

which at this distance would give a retinal image

1.5 mm. in diameter, can be found by formula 5,

page 465.

B : 1.5 :: 250 : 15

B = 25 mm., the apparent size of the optic
disk viewed by the direct method.

Ametropia ; Qualitative Determination. — 1.
Let an assistant make the artificial eye ametropic
by moving the draw-tube until the optical axis is
shorter or longer than normal. The observer
should not know which form of ametropia has
been produced. Examine the retina with the
ophthalmoscope held from 30 to 50 cm. in front
of the artificial eye.

If the details of the fundus can be seen, the
eye is either myopic or hypermetropic.

Move the head with the ophthalmoscope from
side to side.

If the vessels appear to move in the same
direction, the eye is hypermetropic ; if in the
opposite direction, the eye is myopic.

Measurement of Myopia. — The accommoda-

494 THE OUTGO OF ENERGY

tion of the observer's eye and the eye to be ex-
amined should be relaxed. The observer's eye
must be emmetropic ; if it be myopic or hyper-
metropic, the defect should be corrected by the
proper glass before the subject's myopia can be
measured. The correction may be made with
spectacles, or with one of the lenses in the disk
of the ophthalmoscope. The ophthalmoscope
should be placed in the. anterior focal plane of
the eye examined (13 mm. in front of the cornea
of the human eye, 50 mm. in front of the artifi-
cial eye). If the observer cannot reach this
point, in examining the human eye, the distance
between the correcting lens and the anterior
principal focus must be subtracted from the
focal distance of the correcting lens in order to
find the degree of hyperrnetropia, and be added
to the focal distance of the correcting lens in
order to find the degree of- myopia. Viewed
from the anterior principal focus, the fundus will
be blurred.

If myopia be present, turn the disk until that
concave lens is found which will render clear the
image of some one of the vessels 1 near the border
of the optic disk. The rays emerging from the
myopic eye are convergent. This lens makes

1 The error introduced by neglecting the distance between the
vessels and the nerve elements of the retina is inconsiderable.

REFRACTION IN THE EYE 495

them parallel, and its focal power is the measure
of the myopia.

Measurement of Hypermetropia. — If the image
of the fundus be blurred by hypermetropia, place
convex lenses before the eye until the strongest
convex lens is found through which the observer
can see clearly the retinal vessel or other point
selected. The rays emerging from the hyperme-
tropic eye are divergent. This lens renders
them parallel, and its focal power is the measure
of the hypermetropia.

Measurement of Astigmatism. — Set the retinal
tube of the artificial eye at zero. The eye is now
emmetropic. Place before the eye the cylindrical
lens of + 2 D. Examine the fundus with the
ophthalmoscope. The observer's accommodation
must be relaxed.

The optic disk will no longer appear circular,
but will be elongated in the direction of the
meridian of greatest curvature. The retinal ves-
sels will not all be in focus. If a horizontal ves-
sel be seen distinctly, and the vertical vessel at
right angles to it is blurred, the eye is astigmatic
in the horizontal meridian (compare page 423, and
remember that the breadth of the image of the
vessel is determined by means of the rays passing
through that meridian of the cornea which lies at
right angles to the vessel's course.) With the aid

496 THE OUTGO OF ENERGY

of the graduated circle on the front of the artifi-
cial eye determine the meridian in which the eye
is astigmatic. Find the lens which will make the
blurred vessel distinct. If the lens, for example,
have a focal power of + 2 D, there is simple hyper-
metropic astigmatism of + 2 D in the given
meridian. If a lens of — 2 D be required, there
is simple myopic astigmatism of — 2 D in the
given meridian.

In compound astigmatism, the eye is asymmet-
rical in more than one meridian. Thus a clear
image of the vertical vessels may be obtained
with a convex lens of + 2 D, while the horizontal
vessels may require a lens of -f 1 D.

The ophthalmoscopic measurement of astigma-
tism in the human eye is exceedingly difficult,
and should always be corrected by more reliable
methods.

Indirect Method

1. Arrange the light and the artificial eye as
directed for the examination by the direct
method. Hold the ophthalmoscope 30 cm. from
the artificial eye. With the other hand hold a
convex lens of 20 D at its own focal length of
50 mm. in front of the cornea. The rays return-
ing from the fundus pass through this lens and
form an image in the air between the observer

REFRACTION IN THE EYE 497

and the lens. Examine this image through a
magnifying glass of + 5 D placed behind the
aperture of the mirror. If the observer be
myopic in moderate degree, the aerial image will
lie near his far point, and he will need no mag-
nifying or correcting . glass ; if the myopia be
excessive, a weak concave glass should be used.
If the observer be hypermetropic, the degree of
his hypermetropia should be added to the focal
distance of the magnifying glass. The confusing
bright reflexes from the surfaces of the 20 D lens
may be avoided by holding the lens slightly
oblique to the optical axis.

The subject's eye and the 20 D lens form a
refracting system like the objective of the com-
pound microscope; the ophthalmoscopic lens
plays the part of the ocular.

The image is real, inverted, and magnified.
But it will appear to be upright. In it all the
relations of the retinal objects are reversed. If
the observer move, the image will move in the
opposite direction. The size of the image is found
by formula 5, p. 61. B is the size of the aerial
image, h the size of the optic disk — 1.5 mm., gx
the focal distance of the 20 D lens = 50 mm., g2
the distance from the nodal point to the retina
= 15 mm. Then

B : 1.5 : : 50 : 15, and B = 5 mm.

32

498 THE OUTGO OF ENERGY

Thus the enlargement of the retinal details is
less than with the direct method. When the
aerial image is viewed through the ophthalmo-
scopic lens of -|- 5 D, an enlarged virtual image
of the first image is formed, as in the microscope.
2. Draw constructions showing the formation
of the image in the direct and indirect methods.
Kemember that in the indirect method the rays
from the mirror come to a focus before reaching
the convex lens. Their second focus is in the
vitreous.

vision 499

X

VISION

Mapping the Blind Spot. — Fasten a rod fifteen
inches from the table. Beneath the rod place
a well-lighted sheet of white paper (a page of
the laboratory note-book will serve). Make a
small black cross near the left margin. Eest
the chin upon the rod in such a way that the
right eye shall look directly down at the cross.
Place the hand over the other eye. A straw
bearing a black pin-head will be drawn by an
assistant from the cross along the horizontal
meridian toward the temporal side of the eye
under observation. The assistant will mark the
point where the black object ceases to be visible,
and the point at which it reappears. These are
the boundaries of the blind spot of the right
eye in the horizontal meridian. Determine the
boundaries in other meridians. Obtain similarly
the outlines of the blind spot of the left eye.

Yellow Spot. — Close the eyes for half a
minute, and then look at the clear sky or a
brightly lighted surface through a solution of
chrome alum in a glass bottle with parallel
sides. The yellow spot will appear rose-colored

500 THE OUTGO OF ENEEGY

in the blue-green-red solution. The yellow pig-
ment absorbs some of the blue and green rays.
The remaining rays form rose color.

Field of Vision. — Fasten in a vertical position
a sheet of white paper about 50 cm. high and
60 cm. broad. (It may be pinned to the wooden
stand set on edge upon the electrometer box.)
About 20 cm. from the left margin and 30 cm.
from the lower margin of the paper mark a small
cross. Let the subject rest his chin upon a rod
clamped to the iron stand in such a way that
the right eye shall look directly at the cross.
Cement the squares of black, red, green, and
blue papers to the ends of separate straws.
Carry the black square from without inwards
along the horizontal meridian intersecting the
cross. Mark the point at which the black
object enters the field of vision. This point is
the temporal boundary of the visual field in the
horizontal meridian. Determine in the same
way the boundary on the nasal side. Eepeat
for several other meridians. A line joining the
points obtained will bound the visual field.

Determine the visual field for red, green, and
blue. Always pass the test color from without
inwards. The subject should be ignorant of
the color to be used, and should name the color
as soon as it enters his visual field.

VISION 501

Color Blindness

The three large skeins show the test colors.

1. Light Green. — Palest (lightest) shade of
very pure green, — neither yellow-green nor
blue-green to the normal eye. Light green is
chosen because, according to the Young-Helm-
holtz theory, it is the whitest of the colors of
the spectrum, and, consequently, is most easily
confused with gray. Light shades are employed
because it is difficult to distinguish between
strongly illuminated shades.

2. Purple {Rose). — A skein midway between
lightest and darkest purple. Chosen because
purple combines two fundamental colors which
are normally never confounded.

3. Red. — A vivid, slightly yellowish red.
Chosen because it represents the color-group in
which red (orange) and violet (blue) are com-
bined in nearly equal proportions.

Method of Examination and Diagnosis. — Place
the Berlin worsteds on the white cloth in which
they are wrapped. They should be well mixed,
and not spread out too much. Lay a skein of
the first test-color in a well-lighted position two
or three feet from the group. Inform the person
examined :

502 THE OUTGO OF ENERGY

(1) That he must not speak during the test.

(2) That the skeins are not to be fingered or
tossed about. A skein should be touched only
after its selection.

(3) That he must endeavor to pick out skeins
resembling the test skein, i. c, a little lighter or
darker in shade ; the resemblance cannot be per-
fect, as no two shades are exactly alike.

Green Test. — The subject must pick out all
the other skeins approximately the same shade.

The color-blind selects some shade of gray.

Purple {Rose). — The subject should pick out
the skeins of the same color, as before.

(1) He who is color-blind by the first test, and
who, upon the second test, selects only purple
skeins, is incompletely purple-blind.

(2) He who, in the second test, selects with
purple only blue and violet, or one of them, is
completely red-blind.

(3) He who, in the second test, selects with
purple only green and gray, or one of them, is
completely green-blind.

Remark. — The red-blind never selects the
colors taken by the green-blind, and vice versa.
Often the green-blind places a violet or blue
skein by the side of the green, but only the
brightest shades of these colors. This does not
influence the diagnosis.

vision 503

Bed. — This test is applied to those completely
color-blind. Continue the test until the person
examined has placed beside the specimen all the
skeins belonging to this shade, or else, separately,
one or more " colors of confusion."

The red-blind chooses (besides the red, green,
and brown) shades which to the normal sense
seem darker than red. The green-blind selects
opposite shades, which seem lighter than red.

Violet Blindness. — Very rare. Recognized by
a confusion of purple, red, and orange, in the
purple test (see 2). Much care is required to
diagnosticate this form.

The Respiration Scheme.1 — The glass cylinder
(Fig. 67) represents the thorax. The surface of the
water in the glass cylinder represents the diaphragm,
and movable chest walls ; its level may be changed
by raising or lowering the large rubber tube, in the
free end of which is placed a second glass cylinder,
not showu in Fig. 67. The interior of the cylinder
above the water represents the thoracic cavity, and
the rubber balloon the lungs. The paraffined cork
is pierced by a pleural and a tracheal tube. The
upper end of the pleural tube enters a rubber tube,
in the wall of which is a small hole closed by a short
glass rod. Through this hole the pleural cavity may
be opened to the atmospheric air. The tracheal tube

1 American Journal of Physiology, 1904, x, p. xlii.

504

THE OUTGO OF ENERGY

opens below into the lung, above into a rubber tube
in the wall of which is a small opening, which repre-
sents the glottis, and which may be partly or wholly
closed by a glass rod. The left manometer shows the
intrathoracic pressure, the right manometer the intra-

Fig. 67. The respiration scheme; about one-third the actual size.

pulmonary pressure. The normal relations between
intrathoracic and intrapulmonary respiration may be
reproduced with this apparatus. The pressure changes
in forced respiration, obstructed air passages, asphyxia,
coughing, sneezing, hiccough, and perforation of the
pleura may also be studied.

RESPIRATION 505

XI Mechanics of Eespiration

Artificial Scheme. — Eaise the left glass rod
above the opening in the rubber tubing (Fig. 67).
Hold the lower end of the free cylinder even with
the rubber balloon, and pour in water till the
level just reaches the balloon. Lower the left
glass rod to cover the opening.

The surface of the water in the attached
cylinder represents the diaphragm and movable
chest-walls; the interior of the cylinder above
the water, the thoracic cavity; and the rubber
balloon, the lungs. The left manometer shows
the intra-thoracic pressure ; the right manometer
shows the intra-pulmonary pressure. The left
glass rod closes the entrance to the -cylinder,
i. e. makes the thoracic cavity a closed cavity,
as is normal ; the right glass rod, with its lower
end partly covering the opening in the rubber
tubing, controls the entrance to the balloon (the
respiratory passages).

Inspiration. — Nearly close the respiratory pas-
sage. Lower the water level to the base of the
thoracic cylinder.

Xote the change in the size of the lung, and
in the pressure in the lung and in the thorax.
Give reasons for these changes.

Expiration. — Widen the respiratory passage

506 THE OUTGO OF ENERGY

slightly. Eaise the water level slowly till the
lung is slightly but evenly distended.

Note the pressure in the pleural cavity. Is it
positive or negative ? Why ?

Normal Respiration. — Slowly and rhythmi-
cally raise and lower the diaphragm (water level)
between the inspiratory and expiratory level,
taking care that the lung never becomes even
slightly collapsed at the end of expiration.

Give reasons for the changes in the intra-
pulmonary pressure.

Forced Respiration. — Eaise and lower the
diaphragm more quickly.

Observe that the differences in pressure are
increased.

Obstructed Air Passages. — Diminish the inlet
in the respiratory tube by moving the glass plug.
Raise and lower the diaphragm.

The differences of pressure will be increased.

Asphyxia. ■ — Close the entrance to the lungs
entirely.

Note the effect of movements of the diaphragm
upon the intra-thoracic and* intra-pulmonary
pressures.

Coughing : Sneezing. — Remove the glass rod
from the respiratory passage. . Bring the lung to
full inspiration. Close the respiratory opening
with the moistened thumb. Raise the diaphragm

RESPIRATION 507

half-way toward expiration. Suddenly open the
respiratory passage.

Air is quickly and forcibly expelled from the
lung (cough, sneeze).

Hiccough. — Lower the diaphragm quickly
toward full inspiration, and while the lung is
expanding close the respiratory opening with
the moistened thumb (hiccough).

Note the sudden changes of pressure in the
two cavities.

Perforation of the Pleura. — Open the inlet to
the pleura.

Note the effect of the opening into the pleural
cavity upon the lung and upon the intra-pulmo-
nary and intra-thoracic pressure.

Observe the result of movements of the
diaphragm.

508 THE OUTGO OF ENERGY

XII
THE CIRCULATION OF THE BLOOD

The Mechanics of the Circulation

The spaces between the cells of which the body
is composed are filled with a liquid called the
lymph, from which the cells take their food and
into which they pour their waste. The materials
and the products of metabolism diffuse from
lymph to cell and from cell to lymph. In
animals in which the division of labor has
produced separate organs for digestion, excre-
tion, and the like, the lymph serves as a medium
of exchange. For this purpose the relatively
slow processes of diffusion are not sufficient.
Food must be more rapidly brought and waste
more rapidly removed. A circulation must be
provided. There are many ways in which the
necessary circulation is secured. In Cyclops a
flow is caused by movements of the alimentary
canal. In Daphnia, the lymph enters a hollow
muscle and is then expelled. In the higher
animals the provision for rapid exchange is two-
fold. The intercellular spaces are traversed by a

THE CIRCULATION OF THE BLOOD 509

countless number of tubes of capillary size, the
walls of which are so thin that substances in
solution pass through them with great ease.
These capillaries are the ultimate branches of
a single tube, and, after fulfilling their function,
the capillaries unite into a single tube again. A
closed system is thus formed. This system is
filled with a modified lymph called the blood,
which is kept in constant circulatioiic Thus the
lymph in the intervascular spaces is in intimate
contact with a continually changing liquid.
Further provision for rapid exchange is found
in the circulation of the lymph itself. The
spaces between the cells are drained by channels
which gradually become definite tubes, the lym-
phatics, and these finally join to form two ducts
which empty into the blood vessels.

The unbranched portion of the vascular tube
is dilated into a cavity with thickened muscular
walls termed the ventricle of the heart. The
ventricle contracts rhythmically. Each contrac-
tion raises the pressure in the ventricle until it is
higher than the pressure in the remaining blood
vessels. The blood in the ventricle is thereby
forced into the blood vessels against the resist-
ance of friction. The high pressure in the ven-
tricle during contraction is transmitted into the
blood vessels and through them. At each cross-

510 THE OUTGO OF ENERGY

section of the vascular system some of the pres-
sure is lost in overcoming resistance ; hence the
pressure gradually falls. The blood flows from
the area of higher pressure, near the ventricle, to
the area of lower pressure. Thus the contrac-
tions of the ventricle establish a difference of
pressure in the blood vessels, which causes a
movement of the contained liquid.

At the two points at which the vascular
tube joins the ventricle membranous valves are
placed. One of these valves opens into the
ventricle. It is an inflow valve. The inflow
valve closes when the ventricle contracts. Con-
sequently the contractions cannot drive the
blood through this orifice. The ventricle can
drive the blood only through the remaining
orifice. Thus the ventricle becomes a pump
and its contractions move the blood always
in one direction. The vessels by which the
blood is carried from the ventricle to the cap-
illaries are called arteries ; those which bring
the blood from the capillaries back to the ven-
tricle are called veins. Adjoining the ventricle
the great veins meet in a common enlarge-
ment called the auricle. It is at the junction of
the auricle with the ventricle that the inflow
valve is placed.

The outflow valve is placed at that orifice of

THE CIRCULATION OF THE BLOOD 511

the ventricle which opens into the arteries.
When the ventricle, having by its contraction
raised the pressure in the arteries, begins to
relax, the pressure within its cavity becomes less
than that in the arteries. The outflow valve
then shuts. Otherwise the arteries would be
placed in direct communication with an area of
low pressure and the relaxation of the ventricle
would undo in part the work of the contraction,
the purpose of which was the creation of a pres-
sure in the arteries great enough to force the
blood through all the blood vessels.

It is obvious from these general considerations
that the problems of the circulation are in the
first instance those presented by any system of
closed tubes through which liquid is driven by a
pump.

The Circulation Scheme.1 — The artificial scheme
(Fig. 68) to illustrate the mechanics of the circulation
in the highest vertebrates consists of a pump, a sys-
tem of elastic tubes, and a peripheral resistance. The
inlet and the outlet tubes of the pump are furnished
with valves that permit a flow in one direction only.
The peripheral resistance is the friction which the
liquid undergoes in flowing through the minute chan-
nels of a piece of bamboo. To this must be added

1 Science, 1905, xxi, pp. 752-754.

512

THE OUTGO OF ENERGY"

the slighter resistance due to friction in the rubber
and glass tubes.

In this system the pump represents the left ven-
tricle ; the valves in the inlet and outlet tubes, the

Fig. 68. Quantitative circulation scheme ; about one-fourth the actual
size.

mitral and aortic valves, respectively ; the resistance
of the channels in the bamboo, the resistance of the
small arteries and capillaries. The tubes between
the pump and the resistance are the arteries ; those
on the distal side of the resistance are the veins.

THE CIRCULATION OF THE BLOOD 513

The side branch substitutes a wide channel for the
narrow ones, and thus is equivalent to a dilatation of
the vessels.

The pressure in the ventricle is varied through a
tambour covered with rubber membrane. The mem-
brane is grasped between two disks, one below and
one above. The upper disk is screwed down upon
the lower until the membrane is tightly held. To
these disks is fastened a rod which ends in a yoke.
The yoke rests upon a small wheel, which in turn is
supported by a brass plate eccentric in form. This
brass plate is revolved by turning a handle attached
to the axle. As the plate revolves the small wheel
bears upon the eccentric rim and rises and falls with
the rise and fall in the rim of the plate. The motion
of the small wheel is transferred through the yoke,
rod, and disk to the rubber membrane, and thus to the
interior of the ventricle.

The rim of the eccentric brass plate reproduces the
intraventricular pressure curve in the dog. In pro-
jecting this curve upon the plate the periphery is
divided into fractions of a second, and the radii are
divided into millimetres of mercury pressure.

Each revolution of the eccentric plate reproduces in
the ventricular tube both the time and the pressure
relations of the ventricular cycle in the dog. The
intraventricular pressure curve may be written by
connecting the side tube with a membrane manometer,
and clamping off the arterial mercury manometer to
be mentioned shortly.

33

514 THE OUTGO OF ENERGY

When the pressure rises in the ventricle to a suffi-
cient height the contents of the ventricle will be dis-
charged through the aortic valve into the aorta, and
thus (through a convenient metal tube) into the
arterial tube, leading to the capillary resistance.
Here two paths may be taken : the liquid may pass
either through the capillary channels in the cane, thus
meeting with a high resistance, or this resistance may
be lessened to any desired degree by unscrewing a
clamp and thus opening the side tube. Both paths
lead to the venous tubes, whence the liquid passes
through the mitral valve into the ventricle. The
mitral and aortic valves are of a modified Williams
type. Metal tubes closed at one end conduct the
liquid respectively to or from the ventricle. The
liquid enters or leaves the valve-tube through a
hole covered by a rubber valve-flap, not shown in
Fig. 68. Each valve is surrounded by a glass tube
through which the working of the valve may be
inspected.

Mercury manometers measure the pressure in the
arteries and veins near the capillary resistance. The
arterial manometer is provided with a glass thistle-
tube to catch any mercury that may be driven out by
a careless operator.

If the arterial mercury manometer be replaced by a
membrane manometer, or if it be provided with a float
and writing point arterial-pressure curves may be writ-
ten, identical with those obtained from the carotid
artery of the dog.

THE CIRCULATION OF THE BLOOD 515

Normal sphygmographic tracings may be obtained
by using a sphygmograph on the aortic tube.

Palpation of the arterial tube will give a pulse the
"feel" of which cannot be distinguished from that of
the pulse in the normal subject ; the pressure waves
in the quantitative scheme and in the living animal
are identical in respect of both time and pressure.

The Conversion of the Intermittent into a
Continuous Flow

When a pump forces water or any other
incompressible fluid through tubes with rigid
walls, the inflow and outflow are equal and in the
same time. The outflow ceases the instant the
inflow ceases. The same is true in a system of
elastic tubes so short and wide that friction be-
tween the liquid and the walls causes practically
no resistance to the flow. Here the quantity
received from the pump can still escape from the
distal end of the system during the stroke of the
pump. When the resistance is increased by
narrowing the tubes, or by increasing their
length, or in both these ways, not all the liquid
received from the pump can pass by the resist-
ance during the stroke of the pump, — the re-
mainder must pass during the interval between
one stroke and the next. The portion which
cannot pass during the stroke finds room be-

516 THE OUTGO OF ENERGY

tween the pump and the resistance in the dilata-
tion of the containing vessels. To effect the
dilatation the force or pressure transmitted from
the pump presses out the vessel walls until this
pressure is held in equilibrium by the elastic re-
action of the walls. As the pressure from the
pump wanes, the energy stored by it in the ten-
sion of the vessel walls is reconverted into
mechanical motion, and the walls return towards
their original position, driving the liquid out of
the tube past the resistance.

1. Open the side branch by unscrewing the
pressure-clip. See that the tubes are well filled
with water. Make a single brief gentle pressure
on the ventricle.

Note (1) that practically ail the liquid driven
out by the stroke escapes through the side
branch, in which the resistance is low, rather
than through the high capillary resistance.
(2) Only a portion of the liquid escapes during
the stroke. (3) The portion which cannot
escape by the resistance during the stroke finds
space in a very evident dilatation of the tubes
nearer the pump, i. e. between the pump and
the principal resistance. (4) A membrane ma-
nometer coupled to the side tube of the ventricle
would show a sudden rise and fall indicating
a sudden rise and fall in the intraventricular
pressure. (5) Close observation shows that on

THE CIRCULATION OF THE BLOOD 517

the stroke of the pump the tubing just distal to
the aortic valve begins to expand sooner than
that farther away. Evidently the change of
pressure produced by the stroke of the pump is
transmitted from point to point through the
liquid in the tubes. (6) The arterial manometer
shows a sudden rise and fall. Observe that the
rise is not synchronous with the stroke of the
pump, but begins an instant later. This interval
is occupied by the transmission of the pressure
change from the pump to the mercury column,
and in part by the time required to overcome the
inertia of position of the mercury. The oscilla-
tions of the mercury following the primary rise
and fall are due to inertia. (7) Observe the action
of the valves (they consist of a metal tube, closed
at one end, and pierced with a hole which is
covered with a rubber flap tied on both sides of
the hole). (8) Place a finger on the "aorta"
near the valve and note the pressure wave (pulse)
as it passes along the vessel.

2. With the side branch open as in Experiment
1, compress the bulb rhythmically and gradually
increase the frequency of stroke.

It will be found that at about twenty strokes
to the minute the stream will be intermittent.
As the interval between the strokes is shortened
the liquid received from the pump in any one

518 THE OUTGO OF ENERGY

stroke cannot all escape by the resistance during
the stroke and the succeeding interval. The
next stroke comes before the outflow from the
preceding stroke is finished, and the stream be-
comes remittent.

Still further increase the frequency of the
stroke. A rate will be reached at which one-
half the quantity received from the pump will
pass by the resistance during the stroke of the
pump and the remaining half will pass in the
interval between that stroke and the next ;
the intermittent will be converted into a con-
tinuous flow.

Observe that the duration of the intervals is
greater than the duration of the strokes of the
pump. Thus the time during which the circula-
tion is carried on by the energy stored by the
pump in the elastic walls of the vessel is greater
than the time during which it is carried on by
the direct stroke of the pump.

Note that the arterial pressure remains low
even after the stream becomes continuous. An
increase in the frequency of the beat has little
influence on the blood pressure where the peri-
pheral resistance is very slight.

3. Close the side branch, so that the liquid
must pass through a high peripheral resistance.
Compress the bulb at such a rate that the outflow
shall be continuous.

THE CIRCULATION OF THE BLOOD 519

The frequency require! to make the flow con-
tinuous is now much less than when the peri-
pheral resistance was low.

The Eelation between Eate of Flow and
Width of Bed

In a frog slightly paralyzed with curare destroy
the brain by pithing, with the least possible loss
of blood. Lay the frog back down on the mes-
entery board. Open the abdomen in the median
line. Draw the intestine over the cover glass
upon the cork ring so that the mesentery may
lie upon the glass evenly and without stretch-
ing. The mesentery must be kept constantly
moist with normal saline solution. Examine
the blood vessels in the mesentery with No. 3
Leitz objective.

Note the swift flow in the larger vessels and
the slow movement of the blood through the
capillaries.

The combined cross-sections of the capillaries in
the body are vastly greater than the cross-section
of the arteries or the veins. The total quantity
of blood passing in a unit of time through the
arteries or veins and the capillaries is the same.
If less passed through the capillaries than through
the arteries, the capillaries would soon be gorged

520 THE OUTGO OF ENERGY

to bursting. If more, the arteries would soon be
empty. As the quantity passing through the
capillaries and the arteries and veins in a unit of
time must thus be the same, it follows that where
the' combined cross-section of the channel or
" bed " is small, the blood must flow faster than
where the cross-section is large. A river rushes
rapidly through a gorge, but moves sluggishly
where meadow-lands afford a wider channel.
Thus the blood flows with great velocity in the
great arteries, less rapidly in their branches, and
very slowly indeed in the capillaries, the com-
bined width of which is so great compared to
that of the arteries. And as the capillaries unite
into the smaller veins, and these into the larger
veins, the combined cross-section or bed becomes
ever smaller and the blood moves ever more
swiftly. Were the slow passage of the blood in
the capillaries due simply to friction, the blood
would move still more slowly in the veins be-
cause the retarding influence of the friction in
the veins would be added to that of the capillaries.
There is an inverse relation between the rate of
flow and the area of bed.

the circulation of the blood 521
The Blood- Pressure

The Relation of Peripheral Resistance to Blood-
Pressure. — Revolve the disk of the artificial
scheme at a rate that will produce a continuous
outflow.

With each successive stroke the portion of
liquid unable to pass the resistance during the
stroke and the succeeding interval is added to
that left behind from preceding strokes. The
arteries become more and more full. The arte-
rial manometer registers a higher and higher
pressure. At length the pressure ceases to rise.
The mercury remains at a mean level broken by
a slight accession at each stroke. The pump
now merely maintains the constant high arterial
pressure. This pressure suffices to drive through
the resistance during each stroke and the sue-
ceeding interval all the liquid received from the
pump during the stroke.

The venous pressure remains very low. The
capillary resistance (to which must especially be
added the resistance of the smallest arteries)
almost entirely exhausts the pressure in the
arteries. Hence the sudden and profound dif-
ference observed between the arterial and the
venous pressure. A second arterial manometer
placed near the aorta would show that the

522 THE OUTGO OF ENERGY

loss of pressure between the ventricle and the
smallest arteries is relatively slight.

The pulse is absent on the venous side of the
resistance.

The Curve of Arterial Pressure in the Frog. —
Expose the heart of a frog, the brain of which has
been pithed without haemorrhage. Provide a fine
cannula with a short piece of rubber tubing.
Fill cannula and tube with one per cent sodic car-
bonate solution, and close the end of the tube with
a small glass rod. Tie a ligature about one aorta
as far as possible from the junction of the two
aortas. Knot the ends of the ligature together.
Pass a second ligature beneath the same aorta, but
do not tie it. Lift the vessel by the second
ligature so that the vessel is constricted by lying
across the thread. Between the two ligatures
open the aorta with sharp scissors and introduce
the cannula. Fasten the cannula in place by
means of the ligature. Place the frog-board on
the wooden stand to bring the heart on a level
slightly higher than the level of the mercury in
the mercury manometer (Fig. 69). See that the
proximal limb of the manometer is filled with
one per cent sodic carbonate solution to the ex-
clusion of air. Bring the writing point of the
manometer against a smoked drum and revolve
the drum once by hand to record a line of atmos-

THE CIRCULATION OF THE BLOOD

523

pheric pressure. Close the aorta containing the
cannula by gentle pressure with a forceps the
blades of which are covered with rubber tubincr.

o

Join the cannula-tube to the manometer, exclud-
ing air bubbles. Remove the forceps.

The mercury will fall in the proximal and rise
in the distal limb until the blood-pressure in the
aorta is balanced by the column of mercury.
With each ventricular beat,
the column rises a short dis-
tance above the mean level
and sinks again.

Record the blood-pressure
curve on a very slowly
moving drum. To get the
actual pressure in milli-
metres of mercury multiply
by two the mean height of
the curve above the atmos-
pheric pressure line.

The Effect on Blood-Pressure of Increasing the
Peripheral Resistance in the Frog. — The peri-
pheral resistance may be increased by the nar-
rowing of the small arteries which follows the
stimulation of special vaso-constrictor nerve fibres.
The vaso-constrictor nerves may be stimulated
directly or reflexly. The latter method is chosen
here.

Fig. 69. The small mercury
manometer.

524 THE OUTGO OF ENERGY

Expose the sciatic nerve. Tie a ligature about
the nerve near the distal end of the wound, and
sever the nerve on the distal side of the ligature.
Stimulate the central end with a tetanizing
current of moderate strength.

The afferent impulses set up by the stimula-
tion proceed to the spinal cord and thence to the
bulb, where they excite nerve cells which dis-
charge impulses that cause the smaller arteries
(and probably the veins) to constrict. This
narrowing causes the arterial pressure to rise.

Changes in the Stroke of the Pump ; Inhibition
of the Ventricle. — While the arterial pressure in
the artificial scheme is at a good height (120 mm.
Hg) arrest the ventricular stroke (the ventricle
in animals may be thus inhibited by stimula-
tion of the vagus nerve, page 316).

So soon as the ventricle ceases to beat, the less
distended arteries will empty themselves through
the peripheral resistance, and the arterial man-
ometer will show a continuous fall in blood-
pressure.

Resume the ventricular beats.

The mercury in the arterial manometer will
rise in large leaps, corresponding to the ease with
which the early strokes of the pump distend the
lax arteries (the inertia of the mercury somewhat
exaggerates the rise at each stroke). As the

THE CIRCULATION OF THE BLOOD 525

blood-pressure rises, however, the excursion of
the mercury for each ventricular stroke becomes
less and less, corresponding to the smaller and
smaller difference between the pressure in the
arteries and the maximum pressure within the
ventricle, until at length equilibrium is restored
between the peripheral resistance and the force
and frequency of the ventricular beat.

The Effect of Inhibition of the Heart on the
Blood-Pressure in the Frog. — Arrange an induc-
torium for strong tetanizing currents. Insert
the electromagnetic signal in the primary circuit
and bring its writing point beneath that of the
manometer. Eaise the heart gently. Note the
white "crescent" between the sinus venosus and
the right auricle. Put the points of the elec-
trodes on the crescent, and close the circuit
for a moment. After one or two beats the
heart will stop.

Observe the great fall in blood-pressure.
Cease the stimulation.

The mercury returns in leaps to its former
level.

The Heart as a Pump

The Opening and Closing of the Valves. — Secure
a high arterial pressure (120 mm. Hg) in the
artificial scheme. Now greatly slow each ven-

526 THE OUTGO OF ENERGY

tricular beat and at once observe closely the
action of the valves.

It will be seen that the mitral valve closes as
soon as the ventricle begins to contract, but the
aortic valve does not open until the intraventric-
ular pressure has risen above that in the aorta.
Time is required for this rise in the pressure in
the ventricle. During this period both mitral
and aortic valves are closed. When the ventri-
cle begins to relax, the intraventricular pressure
speedily falls below that in the aorta, and the
aortic valve shuts, but the intraventricular pres-
sure normally must fall at least 100 mm. Hg
farther before it shall be lower than that in the
auricle. During this fall all the heart valves are
again closed ; the aortic valves are already shut,
and the mitral not yet open.

The Period of Outflow from the Ventricle. — Tie
a rubber membrane over the smaller thistle-tube
of the sphygmograph (Fig. 70) and cement a bone
button in the centre. Connect a membrane ma-
nometer : with the side tube of the ventricle.
Bring the writing points of the recording tam-

1 If such a manometer is not at hand, carry a thin wire from
the yoke of the disk of the circulation scheme to a light muscle
lever, counterweighted from the pulley or pulled gently upward
by a rubber band attached to the lever. This lever will record
the up and down movement of the disk and thus mark the
beginning of the ventricular stroke.

THE CIRCULATION OF THE BLOOD

527

boui and the manometer into the same vertical
line against a smoked drum. Let the drum re-
volve at a fast speed.

Place the button of the receiving tambour on
the aorta. It will record the aortic pulse and
the membrane
manometer will
record the intra-
ventricular pres-
sure. Let the
ventricle pump
with the usual
force and fre-
quency. When
the two curves
have been writ-
ten stop the

clockwork and turn back the drum until the
point of the lever recording the ventricular pres-
sure lies at the exact beginning of the upstroke
in the aortic pulse curve. Cause each lever to
write an ordinate on the stationary drum. These
ordinates will indicate synchronous points and
will mark the beginning of the "outflow" period.

The Sphygmograph Tambour.1 — This small and
very sensitive tambour (Fig. 71) is mounted upon a

1 First Catalogue of Harvard Physiological Apparatus, 1901,
p. 47.

Fig. 70. The sphygmograph.

523

THE OUTGO OF ENERGY

hollow tube through which the air waves reach the
rubber ruerabraue. A right-angled piece of alumin-
ium transmits the motion of the membrane to the
writing lever. The moving parts are of the lightest

Fig. 71. The sphygmograrih tambour ; about twice
the actual sLse.

construction. The axle of the writing lever is held in
a yoke, the distance of which from the fulcrum of the
lever is readily adjustable. The rubber membrane is
not tied, but is held in place by a removable ring, —
a time-saving device.

If a small glass thistle-tube placed over the carotid
artery be connected with this tambour by a rubber
tube, preferably with a side branch, admirable pulse
tracings may be recorded. By covering the thistle-
tube with a rubber membrane upon which a bone but-
ton is cemented, sphygmograms may be taken from
the radial artery or from the tubes of the circulation
scheme. The same tambour is used with the plethys-
mograph tube.

THE CIRCULATION OF THE BLOOD 529

Now turn the drum until the point of the
aortic lever lies beneath the notch seen in the
down stroke of the pulse curve (the dicrotic
notch, see page 546). Describe synchronous
ordinates. It is known that the dicrotic notch
in the aortic pulse curve corresponds closely to
the moment of closure of the aortic valves. It
marks, therefore, the end of the outflow period.
Note that this point is reached soon after the
ventricle begins to relax. Thus the period dur-
ing which the intraventricular pressure is higher
than the pressure in the aorta embraces part of
the relaxation as well as part of the contraction
of the ventricle. It includes approximately the
highest third of the intraventricular pressure
curve.

Observe also the considerable interval between
the beginning; of ventricular contraction and the
opening of the aortic valve, as shown by the
upstroke in the pulse curve consequent upon
the entrance of liquid into the aorta.

The Visible Change in Form. — Expose the heart
of a frog;. Observe the Great veins, the auricles,
the single ventricle, the two aortas, and the dila-
tation, or bulbus, by which the aortas are con-
nected with the ventricle. All these parts except
the two aortse are contracting. The veins con-
tract first ; the auricles next ; then the ventricle ;

34

530 THE OUTGO OF ENERGY

last the bulbus. Note the pallor of the contracted,
empty ventricle.

Graphic Record of Ventricular Contraction. —
Pass a fine wire through the tip of the ventricle
and fasten the free end to the heart lever (Fig. 53).
Let the lever write on a slow-moving drum.

Note the characteristics of the curve.

The Heart Muscle

All Contractions Maximal. — Inhibit the heart
by a Stannius ligature (see page 562). Find the
least strength of stimulus that will cause the ven-
tricle to contract. Increase the strength of the
stimulus, but do not stimulate oftener than once
in ten seconds (to avoid the staircase contractions
described below).

The force of ventricular contraction will re-
main the same, notwithstanding the increased
stimulus.

If the heart responds at all to a stimulus, it
responds by a maximum contraction. There is
no interval between the minimal and maximal
value (compare page 175).

Staircase Contractions. — Find the least stimu-
lus that will cause the ventricle to contract.

THE CIRCULATION OF THE BLOOD 531

Kepeat this minimal stimulus every 5 seconds,
recording the contractions on a drum turned
about 5 mm. by hand after each contraction.

The contractions of the ventricle will be suc-
cessively stronger, so that the apices of the curves
will form an ascending -line (" staircase "). The
form of the staircase is always an hyperbola.
Successively stronger responses to repeated stim-
uli of uniform strength can also be obtained
from the curarized gastrocnemius of the frog,
perfused with blood, and from mammalian and
invertebrate muscles. The contraction appears to
increase the irritability. Thus the same stimu-
lus causes a greater contraction after a brief
tetanus than before. Rossbach and Bohr have
observed this after-effect continuing more than
thirty minutes.

The Isolated Apex ; Bernstein's Experiment. —
Draw a ligature about the ventricle halfway be-
tween base and apex tightly enough to crush the
tissues without wholly separating them. The
anatomical continuity between the two halves
of the ventricle will thereby be maintained, but
the physiological continuity will be lost. Eelease
the ligature.

The isolated "apex" as a rule does not con-
tract. The exceptions can probably be explained

532 THE OUTGO OF ENEKGY

as the effect of a constant stimulus (see page
533).

The apical half of the normal ventricle con-
tains no nerve cells. Consequently its failure to
contract after its separation from the remainder
of the heart would indicate that the adult heart
muscle is incapable of spontaneous rhythmical
contraction. It has been shown, however, that the
" apex " of the mammalian heart will beat after
its complete removal from the remainder of the
heart, provided the circulation in the extirpated
piece is maintained by supplying it with blood.

Rhythmic Contractility of Heart Muscle. — Fur-
ther evidence of the rhythmic contractility of
the heart muscle is found in the bulbus arteriosus.

Place very small pieces of the bulbus arteri-
osus in normal saline solution under the
microscope.

They will contract rhythmically.

Histological examination shows that nerve
cells seldom occur in the bulbus. It is scarcely
credible that they are present in each of the small
pieces seen contracting under the microscope.

Constant Stimulus may cause Periodic Contrac-
tion. — In a frog with ventricular apex isolated
by Bernstein's ligature, compress one or both
aortaB, thus raising the pressure in the ventricle.

THE CIRCULATION OF THE BLOOD 533

The increased intracardiac pressure acts as a
constant stimulus to the cardiac muscle and the
hitherto inactive apex begins to contract again.

Thus a constant stimulus may discharge peri-
odic contractions in a muscle habituated to
periodic contractions -(compare page 144) ; the
galvanic current and chemical stimuli, such as
delphinin, are further examples of constant stim-
uli which call forth rhythmic contractions of the
heart muscle.

The Inactive Heart Muscle still Irritable. — Stim-
ulate the inactive " apex " mechanically and with
single induction shocks.

The apex, though incapable of spontaneous
rhythmic contractions, is still irritable, and will
respond by a single contraction to each stimulus.

Refractory Period : Extra-Contraction ; Compen-
satory Pause. — Put the electromagnetic signal
in the primary circuit. Connect the binding-
posts on the heart-holder to the secondary coil of
the inductorium. Arrange the latter for single
induction currents. Place the ventricle on the
heart-holder. Send maximal make and break
induction currents through the ventricle from
time to time in each phase of the cardiac cycle.

Note that (1) the stimulus sometimes calls
forth an extra-contraction ; (2) at other times
the stimulus causes no contraction, having fallen

534 THE OUTGO OF ENERGY

into the ventricle during the period in which it
is refractory towards stimuli ; (3) the extra-con-
traction is followed by a pause, called the com-
pensatory pause because it usually restores the
rate of beat to that existing before the extra-
contraction took place.

Using induction currents of equal intensity,
find the limits of the refractory period and note
them on the drum. Note also the point in the
cardiac cycle at which the maximum extra-
contraction can be obtained.

The Transmission of the Contraction Wave in the
Ventricle ; Engelmann's Incisions. — The action
current of the heart is taken to be an expression
of the excitation process, although the nature of
the latter is not yet understood. It has already
been shown (page 310) that the action current
sweeps rapidly over the ventricle preceding the
contraction. The excitation might be propagated
by nerves or by muscle fibres. The following
experiment affords some evidence that the
transmission is by means of muscular tissue.

Leaving the heart in situ, cut the ventricle
into a zigzag strip by obliquely transverse in-
cisions beginning near the apex. The nerve
fibres in the ventricle will thereby be severed
at some part or other of their course, but muscular
continuity will be preserved.

THE CIRCULATION OF THE BLOOD 535

The contraction wave will pass over the entire
zigzag strip. Normally the wave starts at the
base and proceeds to the apex, but by artificial
stimulation it can be made to pass from the
apex towards the base. A similar result can be
secured with the auricle.

The Transmission of the Cardiac Excitation from
Auricle to Ventricle ; Gaskell's Block. — The con-
traction wave can be seen to begin normally in
the sinus and thence to pass rapidly over the
auricle ; on reaching the auriculo-ventricular
junction there is a distinct pause termed the
auriculo-ventricular interval ; finally, the excita-
tion reaches the ventricle, and the contraction
wave is seen to traverse the ventricular muscle
as noted above. The auriculo-ventricular inter-
val may be lengthened by any natural or arti-
ficial hindrance to the passage of the excitation
wave.

1. Place the Gaskell clamp about the auriculo-
ventricular junction. Very cautiously turn the
screw until the rubber edge makes a gentle
pressure on the cardiac tissues at that point.

With careful work a degree of pressure will be
reached that diminishes the conductivity of the
muscle fibres joining the auricle and ventricle so
far as to permit only every second or every third
excitation to pass. The auricle will beat with-

536 THE OUTGO OF ENERGY

out change of frequency, but the ventricle will
contract only when the excitation succeeds in
passing the block.

2. Divide the auricles in two pieces con-
nected by a small bridge of auricular tissue.
Stimulate one piece.

The stimulation of one piece will be followed
immediately by the contraction of that piece,
and, after an interval, by the contraction of the
other. The smaller the bridge, the longer the
interval.

Gaskell has pointed out that a natural block
is furnished by the small number of the muscle
fibres joining the auricle to the ventricle, and
that this natural block explains the auriculo-
ventricular interval, i. e. the delay which the
excitation experiences in passing from the auricle
to the ventricle.

3. Eepeat Experiment 1, but place the screw-
clamp across the middle of the ventricle.

The passage of the excitation from one part of
the ventricle to another will be delayed or inter-
rupted by the lowering of the conductivity in
the compressed portion.

Many irregularities in the frequency and force
of the heart can be explained by variation in the
conductivity of its several parts. They can be

ni>7

THE CIRCULATION OF THE BLOOD 537

explained also, by variations in the irritability of
the several parts. In the latter case, the excita-
tion would pass as usual, but its action on any
part, for example the ventricle, would be in-
creased or diminished by changes in the irri-
tability of the cardiac muscle in that region.
Engelmann has found that ventricular systole
lowers the conductivity of the ventricle for a
time.

Tonus. — Pass the very fine copper wire through
the wall of the auricle of the tortoise and attach
the wire to the heart lever, so that the contrac-
tions of the auricle may be recorded. Let the
drum move so slowly that the individual contrac-
tions will be nearly but not quite fused.

Two sorts of contractions can be distinguished,
(1) the usual frequent contraction or beat of the
auricle, (2) the tonus oscillations. The tonus
oscillations include from twenty to forty beats.
•In the tortoise auricle, the beats usually become
less extensive during the rise of tonus.

The Influence of "Load" on Ventricular Contrac-
tion.— Eecord the contractions of the frog's
ventricle. Increase the intraventricular pressure
(i. e. the load against which the ventricular muscle
contracts) by clamping the aortas with forceps

538 THE OUTGO OF ENERGY

the blades of which are covered with rubber
tubing.

The force of the individual contractions
will be increased but their frequency will be
diminished.

The Influence of Temperature on Frequency of
Contraction. — Let the drum move at such a
speed that the individual heart-beats in the
curve shall be close together, but yet separate
and distinct. Surround with normal saline solu-
tion at 25° C.

The frequency of contraction will be increased.

Keplace the warm solution with normal saline
solution at 5° C.

The frequency of contraction will be dimin-
ished.

The Action of Inorganic Salts on Heart Muscle. —
Sever the apical two-thirds of the ventricle of the
tortoise heart from the remainder of the ventricle
by a cut parallel with the auriculo-ventricular'
furrow. With a second parallel cut remove
from the severed portion a ring two or three
millimetres wide. Divide the ring to form a
strip. Fasten one end of the strip to the short
limb of a glass rod bent at a right angle. By
means of a silk thread connect the other end of
the strip to a heart lever arranged to record the

THE CIRCULATION OF THE BLOOD 539

contractions of the strip on a very slowly moving
drum.

Sodium. — Immerse the strip of ventricular
muscle in a beaker containing 0.7 per cent solu-
tion of sodium chloride.

After a latent period, which may be protracted,
but usually is brief, a series of rhythmic con-
tractions will be observed. The contractions
soon reach a maximum and then gradually die
away. Sodium, although an important stimulus
to contraction, cannot maintain the ventricle in
continued activity.

The tonus of the heart muscle is diminished
by sodium chloride.

Calcium. — Surround a strip of contracting
ventricular muscle with a solution of calcium
chloride isotonic with 0.7 per cent sodium chlo-
ride solution (approximately 1.0 per cent).

Contractions will cease. Calcium added to
solutions of sodium chloride, however, will
lengthen the period during which the heart
muscle contracts and will increase the strength
of the individual contractions. Strong solutions
of calcium chloride greatly increase the tonus.

Potassium. — Surround a non-beating strip of
ventricular muscle with a solution of potassium
chloride isotonic with 0.7 per cent sodium
chloride solution (approximately 0.9 per cent).

540 THE OUTGO OF ENERGY

Contractions will not be produced. If potas-
sium be applied to a contracting strip, the con-
tractions will cease.

Combined Action of Sodium, Calcium, and
Potassium, — Surround the ventricular muscle
with a solution containing sodium chloride (0.7
per cent), calcium chloride (0.0026 per cent),
and potassium chloride (0.035 per cent). This
is a modified " Einger " solution.

Long-continued, rhythmic contractions will be
secured.

Observers are not entirely agreed as to the
action of potassium and calcium on heart muscle.
The matter is of importance because there is
much probability that the rhythmic contractions
of the heart are the result of the constant chemi-
cal stimulus of inorganic salts present in the
blood. Most observers are agreed that the inter-
action of salts of sodium, calcium, and potassium
is essential.

The fact that the contraction of the heart
begins normally in the sinus may be due to a
greater sensitiveness of that part to chemical
stimulation.

THE CIRCULATION OF THE BLOOD 541

The Heart Sounds

With a binaural stethoscope auscultate the
chest over its entire extent during normal respi-
ration and while the subject holds his breath.

1. Xote that two sounds are heard in the
heart region.

2. Determine at what point each of the sounds
is most distinct.

It will be found that one, termed the " first
sound," will be most distinct where the ventricle
comes nearest the surface, near the apex of the
heart, in the space between the fifth and sixth
ribs, about 2.5 cm. below and 2.5 cm. within the
left nipple. Close inspection of this region in
persons not too fat will show that the chest wall
is raised at each contraction of the heart. The
cardiac impulse, as it is called, may be felt dis-
tinctly by one or two fingers laid in the fifth
intercostal space. It is caused by the rapid
increase in the tension of the ventricle.

The " second sound " will be heard most dis-
tinctly immediately over the aortic arch, near the
junction of the second right costal cartilage with,
the sternum.

3. Observe the two sounds with relation to
their duration, pitch, intensity, and quality.

542 THE OUTGO OF ENERGY

The first sound in comparison with the second
is of longer duration, lower pitch, and greater
intensity. The quality of the first sound is dull,
booming ; that of the second is sharp, valvular.

4. With one finger feeling the cardiac impulse
observe the sounds with reference to systole and
diastole.

The first sound will be found to be systolic,
i. e. it occurs with the contraction of the ventricle,
while the second sound is diastolic, being heard
at the beginning of ventricular relaxation. The
interval between the first and second sounds is
therefore very brief. The pause after the second
sound before the first is heard again, is consider-
ably longer.

The first sound can be heard in the extirpated,
bloodless heart (dog). The contraction of the
ventricular muscle is therefore alone sufficient
for its production. But the sound is modified or
replaced by a murmur when the auriculo-ven-
tricular valves are sufficiently injured. It is
probable, therefore, that the sudden increase in
the tension of the auriculo-ventricular valves con-
tributes to its production. The second sound
obviously is due to the sudden increase in the
tension of the semilunar valves. It is replaced
by a murmur when these valves are rendered
incompetent.

THE CIRCULATION OF THE BLOOD 543

Ordinarily the ratio between the blood-pressure
in the pulmonary artery and right ventricle so
nearly equals the ratio between the blood
pressure in the aorta and left ventricle that the
semilunar valves in the pulmonary artery and
aorta close together, or nearly together, and their
respective sounds are heard as one. Pathologic-
ally, for example in distention of the right heart
from prolonged violent exercise, these relations
may be so altered as to produce between the two
sounds an interval perceptible to the ear. The
sound is then said to be reduplicated.

The Pressure-Pulse

Frequency. — Palpate the radial pulse by
laying on the artery at the wrist the ball (not
the tip) of the first, second, and third fingers of
the right hand. The forearm of both subject
and observer should be supported in a comfort-
able position. Count the pulse in four successive
periods of fifteen seconds. The counting of the
observer's instead of the subject's pulse may be
avoided by noting whether the subject's supposed
pulse is synchronous with the observer's heart-
beat.

Note the frequency per minute when the sub-
ject is standing, sitting, lying, swallowing, hold-
ing the breath ; and before and after exercise ;

544 THE OUTGO OF ENERGY

for example, before and after lifting the weight
of the body ten times by rising on the toes.

Sex, eating, the time of day, the temperature,
and many other factors also influence the fre-
quency of the pulse.

Hardness. — ■ When pressure is made upon an
artery in any part of its course, the pressure is
transmitted in all directions through the liquid
contained in the peri-arterial tissues, and the
artery becomes smaller. Part of the pressure is
used upon the peri-arterial tissues themselves.
When the remaining pressure equals the maxi-
mum blood-pressure in the artery at the point of
compression, the blood-pressure on the distal
side of this point will sink to the level of the
blood-pressure in the nearest .anastomosis. If
the anastomosis is of capillary size, the pulse will
disappear. A pulse which is obliterated by slight
pressure is termed " soft ; " if the pressure re-
quired is relatively considerable, the pulse is
termed " hard." The hardness of the pulse is
therefore a measure of the maximum blood-
pressure at the point of compression, less the
variable and unknown quantity required for the
compression of the elastic tissues.

Form. — 1. The vibrations which follow the
primary pulse wave cannot ordinarily be recog-
nized by the palpating finger. When, however,

THE CIRCULATION OF THE BLOOD 545

the usual amplitude of the principal secondary
vibration is much increased and the interval be-
tween the primary and this secondary vibration
is not too brief, the pulse may be felt to be
double, or " dicrotic." For example, dicrotism
can be felt in some ca~ses of continued fever.

2. A pulse which is felt to reach its maximum
slowly is called a " slow pulse " (pulsus tardus).
One which reaches its maximum rapidly, giving
the palpating finger the sensation of a quick
push, is said to be a " quick pulse " (pulsus celer).
Quick and slow pulses should be carefully dis-
tinguished from frequent and infrequent pulses.

Volume. — The extent to which the arterial
wall is driven from its position of equilibrium
(volume or size of pulse) is a function of the
output of the ventricle, the outflow period,
the peripheral resistance, and the elasticity of
the arteries. It is measured very inexactly by
the palpating finger and the sphygmograph, accu-
rately by the plethysmograph (page 552).

The Pressure-Pulse in the Artificial Scheme. —
Eevolve the disk of the artificial scheme until
the arterial pressure is maintained at 50 mm.
Hg. Close the tube leading to the arterial
manometer, so that the oscillations of the
mercury may not influence the curves to be
taken. Attach the small thistle-tube (without

35

546 THE OUTGO OF ENERGY

rubber membrane) to the sphygmograph (Fig.
70) and adjust the tube upon the aorta. Close
the side branch of the sphygmograph tube. Bring
the writing point of the sphygmograph lever
against a slow-moving, lightly-smoked drum.
Kecord a series of pulse curves.

Note the quick upstroke, corresponding to the
quick distention of the artery by the emptying
of the ventricle, and the gradual downstroke,
corresponding to the gradual emptying of the
artery through the resistance during the diastole
or interval between two beats. Near the apex
of the more delicately written curves may be
seen a slight depression, the dicrotic notch.

It is obvious that the changes observed in the
size of the artery are the expression of changes
in the blood-pressure. The pulse is a function
of the blood-pressure at the point observed.
Hence the term pressure-pulse.

The Human Pressure-Pulse Curve. — 1. Adjust
the lever of the recording tambour so that it shall
write with the least friction possible on a thinly
smoked drum. Let the drum revolve slowly
(two revolutions a minute). Be sure that the
side branch is open. Place the larger thistle-
tube, which serves as a " receiving tambour,'*
over the carotid artery, anterior to the stern o-
cleidomastoideus muscle, about the level of the

THE CIRCULATION OF THE BLOOD 547

thyroid cartilage. When the tambour (without
rubber membrane) is pressed well down over the
artery, let an assistant close the side branch. If
the receiving tambour has been properly placed,
the recording tambour will write a sharply
marked pulse curve. If none such appears, open
the side branch and move the receiving tambour
into a better position.

Indicate the primary wave, the predicrotic
elevation, and the dicrotic notch.

2. Cover the thistle-tube with a rubber mem-
brane. Cement in the centre of the membrane a
bone collar-button. Place the button upon the
radial artery at the wrist and record the radial
pulse.

It will be found that the degree of pressure
must be carefully regulated in order to secure a
satisfactory curve. The blood-pressure in the
artery normally is held in equilibrium by the
elastic tension of the wall of the artery and the
surrounding tissues. The pressure of the sphyg-
mograph increases the tension of the peri-arterial
tissues and thus assists in holding the blood-
pressure in equilibrium. The greater the pres-
sure of the sphygmograph, the larger the part of
the blood-pressure borne by it and the more com-
pletely will variations in the blood-pressure be
made visible in the pulse curve. The record,

548 THE OUTGO OF ENERGY

however, is not a measure of the absolute blood-
pressure, because it is not possible io estimate
accurately how much of the blood-pressure is
still held in equilibrium by the elastic tension
of the arterial wall and the surrounding tissues.
The pulse curve does give with approximate
correctness the variations in the blood-pressure.
The correctness would be complete were it not
that the part of the blood-pressure held in
equilibrium by the elastic tension of the arterial
wall varies with the size of the vessel, and the
size of the vessel increases as the blood-pressure
increases. Thus the portion of the blood-pres-
sure which fails of record constantly varies.
The error thus introduced is not important.
The sphygmograph, therefore, gives a practically
true record of the form of the pulse, i. e. the
time-relations of the changes in blood-pressure.
This knowledge cannot possibly be secured by
the palpation of the pulse. The sphygmograph,
it may be repeated, does not give a true record
of the absolute blood-pressure (hardness) or of
the amplitude (size) of the pulse. Both hardness
and amplitude are better measured by the pal-
pating finger.

In many sphygmographs, for example, Marey's
and Dudgeon's, the pressure on the artery is
made by a metal spring, the movements of which

THE CIRCULATION OF THE BLOOD 540

are recorded by a lever. In the record just taken
from the radial artery, the pressure was made by
the elastic tension of the rubber membrane clos-
ing the thistle-tube. In the case of the carotid
artery, this membrane is replaced by the skin of
the neck.

In every instance, the sphygmograph records
the changes of blood-pressure in a section of the
artery so short in comparison with the length of
the whole arterial tree as to be practically a
cross-section.

Low Tension Pressure-Pulse. — 1. In the arti-
ficial scheme open slightly the side-branch that
permits the liquid in the arterial tubes to flow
out without passing through the resistance. The
arterial pressure will fall in consequence of the
diminished peripheral resistance. Normally this
effect is produced by a dilatation of the smaller
arteries. Let the arterial pressure fall to about
20 mm. Hg. Eecord a series of pulse curves.

Note that the oscillations of the mercury
column with each ventricular beat are much
higher than with normal pressure (120-150 mm.).
Feel the pulse with the finger. With each beat
the artery quickly expands and as quickly re-
laxes. The artery is "softer" than usual.

2. Feel the normal pulse in the radial artery.
Note the normal " hardness." Let the subject

550 THE OUTGO OF ENERGY

inhale two drops (on no account more than two)
of the nitrite of amyl (to be dropped on a hand-
kerchief by one of the instructors). This power-
ful drug causes dilatation of the blood vessels,
particularly the smaller arteries.

Observe that as the face flushes, indicating the
vascular dilatation, the pulse will be softer.

Do not repeat the experiment.

Pressure-Pulse in Aortic Regurgitation. — Empty
the principal tubes of the artificial scheme. Re-
move the rubber from about the aortic valve.
Replace the valve tube. Till the apparatus with
water. Revolve the disk at the rate and with
the force employed to imitate the normal circula-
tion (page 545).

Feel the pulse with the finger.

After each systole the liquid streams back
through the incompetent valve. The ventricle
is thus fuller than normal at the beginning of
the stroke, while the arteries are less than
normally full. Consequently more than the
usual quantity is discharged by the ventricle
into relatively undistended arteries. The rela-
tively lax artery is thereby quickly and largely
expanded, as indicated by the quick thrust given
the palpating finger and by the large excursion
of the mercury in the arterial manometer.

Record pulse curves.

THE CIRCULATION OF THE BLOOD 551

The upstroke is unusually high and quick. It
is at once followed by a great and sudden fall.
Obviously a relatively empty artery has been
suddenly filled by an unusually large inflow and
has been suddenly emptied again through the
broken valve and the capillaries. The pulse-
curve shows low arterial tension, but is of greater
amplitude than the pulse in which low tension
results from lowering the peripheral resistance.
In the body, the amplitude of the pulse in aortic
regurgitation is increased by the greater force
with which the ventricle contracts, as well as by
the larger quantity discharged at each beat, for
the back-flow from the aorta dilates the ventricle
and usually causes the walls of the ventricle to
increase in thickness (dilatation with hypertrophy
of the ventricle).

Stenosis of the Aortic Valve. — Eeplace the rub-
ber flap upon the aortic valve-tube, and tie a
string around the flap and tube just over the
opening in the tube. Stenosis, i. e. narrowing, of
the opening will thus be secured. Put the valve-
tube in place, and compress the bulb at the usual
rate. Eecord pulse curves.

The slow difficult emptying of the ventricle
will be evident in the curve and to the hand.
The movements of the arterial manometer are
sluggish and of diminished amplitude. The

552 THE OUTGO OF ENERGY

pulse wave is small and the upstroke slow,
corresponding to the small slow inflow through
the stenosed valve.

Eestore the valve to its normal state.

Incompetence of the Mitral Valve. — Remove
the rubber flap from the mitral valve. Record
pulse curves as before.

The pulse will be small, because the pressure
in the auricle (in this case the reservoir of water)
is always low, while the pressure in the arteries
is always high. Hence the ventricle will partly
empty itself through the incompetent mitral
valve, in the direction of low resistance, before
the pressure in the ventricle rises high enough to
open the aortic valve against the high aortic
pressure. The quantity remaining in the ventri-
cle when the intraventricular pressure rises high
enough to open the aortic valve is not sufficient
to distend the arteries to the normal degree.

In mitral stenosis the pulse is also small
because the narrowing of the mitral orifice per-
mits less than the usual quantity of liquid to
enter the ventricle.

The Volume Pulse

Remove the receiving tambour of the sphygmo-
graph from its tube, and insert the plethysmo-
graph cylinder (this is the tube used in the

THE CIRCULATION OF THE BLOOD 553

experiment on the volume of contracting muscle,
Fig. 58). Place the middle finger in the cylinder,
making sure that the rubber collar fits around
the finger tightly, but without impeding the
venous circulation. Close the side branch.

Periodical alterations in the volume of the
finger will be recorded ; they have the rhythm of
the heart-beat. (The friction of the writing-lever
must be very slight to insure success, and the
curve at best will be small.)

Determine the effect of straining and forced
respiration upon the curve.

Apparatus

Normal saline. Bowl. Towel. Pipette. Artificial
scheme. Microscope. Mesentery board. Mercury man-
ometer. Aortic cannula. One per cent solution of sodic
carbonate. Ligature. Glass rod one inch long. Frog-
board. Wooden stand. Kymograph. Inductorium. Dry
cell. Electrodes. Key. Electromagnetic signal. Sphyg-
mograph with large anu small thistle-tubes. Rubber
membrane. Bone collar-button. Heart-holder. Screw-
clamp. Muscle lever with scale-pan and weights. Stand.
Fine copper wire. Tortoise with heart exposed. Ice.
Solution of sodium chloride, 0.7 per cent. Solutions of
calcium chloride, and potassium chloride, each isotonic
with 0.7 per cent solution of sodium chloride. A solu-
tion containing sodium chloride, 0.7 per cent ; calcium
chloride, 0.026 per cent; and potassium chloride, 0.035
per cent. Binaural stethoscope. Nitrite of amyl. Ple-
thysmograph.

554 THE OUTGO OF ENERGY

XIII

THE INNERVATION OF THE HEART AND
BLOOD-VESSELS

The quantity of blood required by the tissues
varies from time to time. For example, the
digestive organs require more blood when food
is taken than at other times. Variations in the
blood supply of the individual organs are accom-
plished chiefly by varying the size of their blood
vessels. To this end the blood vessels are pro-
vided with muscular coats which are made to
contract or relax, and thus to constrict or dilate
the vessels. The impulse to contraction or relax-
ation is given by the vasomotor nerves. It is
necessary, too, that the force and frequency of
ventricular contraction should vary with the
resistance to be overcome, the need for more
rapid oxygenation of the blood, etc., and special
nerves are provided for this purpose also. The
control or innervation of the heart and blood
vessels will now be considered.

The heart is provided with nerves that aug-
ment and nerves that inhibit its action.

innervation of heart and blood-vessels 555

The Augmentor Nerves of the Heart

In the frog both the augmentor and the inhibi-
tory nerves reach the heart through the splanch-
nic branch of the vagus. The augmentor fibres
leave the spinal cord in the third spinal nerve, and
pass through the ramus communicans of this
nerve into the third sympathetic ganglion, where
they probably end in contact with the body or
processes of sympathetic cells. The axis-cylin-
ders of these sympathetic cells pass up the cer-
vical sympathetic chain to the ganglion of the
vagus (Fig. 72), and thence down the vagus trunk
to the heart. Thus in the greater part of its
course the vagus cannot be stimulated without
exciting both the augmentor and the inhibitory
cardiac fibres. To excite either alone it is neces-
sary to stimulate the respective nerves above
their junction.

Preparation of the Sympathetic. — Cut away the
lower jaw of a large frog, the brain of which has
been destroyed by pithing, and continue the slit
from the an^le of the mouth downwards for a
short distance. Avoid cutting the vagus nerve
(Fig. 73). Turn the parts well aside, and expose
the vertebral column where it joins the skull.
Eemove the mucous membrane covering the
roof of the mouth. The sympathetic is situated

556

THE OUTGO OF ENEEGY

immediately under the levator anguli scapulse
muscle, which must be carefully removed. The
nerve will then be visible. It is commonly pig-
mented and usually lies under an artery. Care-
fully isolate the nerve. Put a ligature around it

LAS

.*V\ :> *■

LAS

i r> «.

LjAo

Fig. 72. Scheme of the sympathetic nerve in the frog. OC. Occiput.
LAS. Levator anguli scapulse. Sym. Sympathetic. GP. Glosso-pharyn-
geus. V-S. Vago-sym pathetic. G. Ganglion of the vagus. Ao. Aorta.
HA. Subclavian artery. (After Stirling's reproduction of Gaskell and
Gadow's plate.)

as far away from the skull as practical >le, and
cut the nerve caudal to the ligature.

Action of the Sympathetic on the Heart. —
Arrange the inductorium for weak tetanizing cur-
rents. In the primary circuit place the electro-

INNERVATION OF HEART AND BLOOD-VESSELS 557

magnetic signal. Prepare the sympathetic as
directed above. Expose the heart (page 75).
Place it in the heart-holder. Should the heart
beat rapidly, slow it with ice. Let the writing
point record above the point of the electromag-
netic signal on a drum revolving so slowly that
the individual beats shall appear in the curve
very close together, yet far enough apart to be
readily counted. Divide the observation into
nine periods of twenty seconds each. Place the
electrodes beneath the sympathetic, with the
short-circuiting key closed. Adjust the heart
lever to write its curve. Let the assistant call
the beginning of each period as he marks it on
the drum. At the beginning of the second pe-
riod, open the short-circuiting key ; at the begin-
ning of the third period, close the short-circuiting
key. Lower the drum when one circuit is
completed.

Count the number of beats in each period. The
frequency will be increased. The force of con-
traction will also be increased.1 The latent period
of excitation is long and there is a prolonged
after-effect. The former frequency is regained
more rapidly after short than after long stimula-
tions. The speed of the cardiac excitation wave

1 The stimulation of the augmentor fibres is difficult and
often fails in winter frogs.

558

THE OUTGO OF ENERGY

(compare page 336) is increased and the time of
its passage across the auriculo-ventricular groove
is shortened, though this cannot be observed by
the method used in the present experiment.

The Inhibitory Nerves of the Heart

The Preparation of the Vagus Nerve. — Fasten
a lame fros? on the board, back down. Pass the

Fig. 73. Scheme of the cervical nerves in the frog (after Schenck).
G. P. Glosso-pharyngeus. Hg. Hypoglossus. V. Vagus. L. Laryngeus.
K. Posterior end of lower jaw. The glosso-pharyngeus has been drawn
to one side of the hypoglossus for the sake of clearness.

glass tube through the oesophagus into the
stomach. Eemove the muscles lying over the
petrohyoid muscle, which passes from the base of
the skull to the horn of the hyoid bone. Lying

INNERVATION OF HEART AND BLOOD-VESSELS 559

near the line between the angle of the jaw and
the auricle are four nerves (Fig. 73) : (1) The
hypoglossals. This nerve is superficial. Near
their emergence from the skull it is the lowest
of the nerves, but later, the uppermost. It crosses
the remaining nerves and the blood-vessels, and
passes forwards and inwards towards the tongue.
(2) The glosso-pharyngeus, which soon turns for-
wards beneath the hypoglossus parallel to the
ramus of the jaw. (3) The vagus, and (4) the
laryngeus, the two lying almost parallel in the line
between the angle of the jaw and the auricle.
The laryngeus rests on the petrohyoid muscle, and
passes upwards and inwards beneath the arteries
towards the larynx. The vagus runs at first
along the superior vena cava to the auricle ; a
branch is given off to the lungs. Clear the vagus,
tie a silk thread around the nerve and sever the
nerve on the cranial side of the ligature, so that
the peripheral stump can be placed on the elec-
trodes for stimulation. Divide the laryngeal
branch. Keep the preparation moist with nor-
mal saline solution.

Stimulation of Cardiac Inhibitory Fibres in
Vagus Trunk. — Arrange the inductorium for
weak tetanizing currents. In the primary circuit
place the electro-magnetic signal. Expose the
heart. Place it in the heart-holder. Let the

560 THE OUTGO OF ENERGY

writing point record exactly above the point of
the electromagnetic signal on a drum revolving so
slowly that the individual beats shall appear in
the curve very close together and yet far enough
apart to be readily counted.

Lay the vagus nerve on the electrodes. Start
the drum. As soon as good curves are writing,
start the inductorium, and open the short-circuit-
ing key for about twenty seconds. The heart will
be inhibited. Note that the arrested heart is al-
ways relaxed, i. e. in diastole. The latent period
is short (one or two heart-beats). A brief after-
effect is present. If the stimulus is continued,
the heart will begin to beat even during the
stimulation, showing that the inhibitory mechan-
ism can be exhausted. The heart beats more
rapidly, and usually more strongly, immediately
after inhibition than before ; this probably is due
to the after-effect of the stimulation of augmentor
fibres in the vagus trunk, as explained below.

Eepeat the stimulation, but weaken the stimu-
lating current by moving the secondary farther
from the primary coil.

With a suitable strength of current, the heart
will be slowed but not arrested. The duration
of diastole will be markedly less, while the dura-
tion of systole will be changed but little if at
all. A stronger excitation would lengthen both

INNERVATION OF HEART AND BLOOD-VESSELS 561

systole and diastole. The diminution in force often
appears before the diminution in frequency.

Effect of Vagus Stimulation on the Auriculo-Ven-
tricular Contraction Interval. — Counterpoise two
inverted muscle levers. Place their writing points
exactly above the writing point of the electro-
magnetic signal. Pass fine bent pins through
the auricle and ventricle, respectively, and con-
nect them by silk threads with the muscle levers
("Suspension method"). Let the drum revolve
at its fastest speed. When good auricular and
ventricular contractions are obtained, stimulate the
vagus trunk with a current not quite sufficient to
cause arrest.

Note that the inhibition affects both the auricle
and the ventricle. Weak stimuli affect primarily
the auricles. The auriculo-ventricular contrac-
tion interval is lengthened.

Irritability of the Inhibited Heart. — Arrest the
heart by stimulating the vagus trunk. When
complete inhibition is secured, touch the ventricle
smartly with the point of the seeker.

The ventricle will respond by a single contrac-
tion.

When the inhibition is profound, the irritabil-
ity may be so far reduced that the heart will not
contract on direct stimulation.

In addition to the effects already enumerated,

36

562 THE OUTGO OF ENERGY

appropriate methods of observation would show
that vagus excitation increases the intraventricu-
lar pressure during diastole, lessens the intake
and the output of the ventricle, and diminishes
the tonus of the heart muscle. The action of the
vagus is accompanied by a positive electrical
variation. The action on the sinus and on the
bulbus does not differ essentially from that upon
the ventricle.

It has already been pointed out that the vagus
of the frog contains both inhibitory and augment-
ing fibres. The stimulation of the mixed nerve
usually causes inhibition, as described above, but
sometimes augmentation. The augmentation ob-
served after cessation of the inhibitory effect is
probably explained by the longer after-effect of
the augmentor excitation.

Intracardiac Inhibitory Mechanism. — Arrange
an inductorium for tetanizing currents. Close
the short-circuiting key. Expose a frog's heart.
Eaise the heart with a glass rod. Note the white
" crescent " between the sinus venosus and the
right auricle. Set the inductorium in action.
Put the points of the electrodes on the crescent,
and open the short-circuiting key for a moment.
After one or two beats the heart will stop.

Inhibition by Stannius Ligature. — Turn up the
heart to expose its posterior surface, and note the

INNERVATION OF HEART AND BLOOD-VESSELS 563

line of junction of the sinus venosus and right
auricle. Tie a ligature around the heart exactly
at this line, passing the thread beneath the aortas,
so that they shall not be included in the ligature.

The auricles and ventricle cease to beat, for a
time at least, while the sinus venosus continues
with unaltered rhythm. (The result is usually
ascribed to inhibition, from the mechanical stim-
ulation of the intracardiac inhibitory mechanism.
If the ventricle begins spontaneously to beat, as
may happen if the ligature is not accurately
placed, tie a second ligature around the junction
of sinus and auricle.)

Action of Nicotine. — Apply nicotine solution
(0.2 per cent) to the ventricle. After a few
minutes, stimulate the trunk of the vagus nerve.
No curve need be written.

The heart is not inhibited.

Now lift the heart with a glass rod, and stimu-
late the intracardiac inhibitory nerves.

The heart is inhibited. Nicotine paralyzes
some inhibitory mechanism between the vagus
and the intracardiac inhibitory nerves. But it is
known that nicotine does not paralyze nerve
trunks. Hence it is probable that the cardiac
inhibitory fibres do not pass to the cardiac muscle
directly, but end in contact with nerve cells,
which take up the impulse and transmit it

564 THE OUTGO OF ENERGY

through their processes to the muscular fibres of
the heart.

Atropine. — With a clean pipette apply a few
drops of a solution of atropine (0.5 per cent) to
the heart. After a few moments lift the ventri-
cle and stimulate the crescent.

The heart is not inhibited. Atropine paralyzes
the intracardiac inhibitory nerves.

Muscarine. — With a fine pipette put upon the
ventricle a few drops of normal salt solution con-
taining a trace of muscarine (a poisonous alkaloid
extracted from certain mushrooms).

The ventricle will gradually be arrested in
diastole, much distended with blood.

Antagonistic Action of Muscarine and Atropine.
— With a fresh pipette apply a little normal salt
solution of atropine (0.5 per cent).

The heart will commence to beat again.

The Centres of the Heart Nerves

It has been shown that the heart receives in-
hibitory and augmenting nerve fibres. The sit-
uation of the inhibitory and augmenting " centres,"
i. e., the nerve cells from which the inhibitory
and augmenting fibres spring, should now be
considered.

Inhibitory Centre. — Place a frog and a small
sponge wet with ether under a glass jar. Be very

INNERVATION OF HEART AND BLOOD-VESSELS 565

careful not to kill the frog by an overdose of
ether. When insensibility is complete, place the
animal, back uppermost, on

a frog-board.

Cut through

the skin in the median line
from the nose about half
way to the urostyle. Care-
fully uncover the roof of the
skull. Eemove the longitu-
dinal muscles on either side
of the 1st, 2d, and 3d verte-
bras. Strip off the parietal
bones with forceps, begin-
ning at the anterior end,
opposite the anterior margin
of the orbit. Clear away
the occipital bones. Saw
through the laminae of the
first three vertebrae, and re-
move the laminae to expose
the spinal cord. Expose the

Fig. 74. View of the brain
of a frog from above, en-
larged. L.ol. Olfactory lobes,
heart by Cutting away the H.c. Cerebral hemispheres.

G.p. Pineal body. Th.o.

chest wall over the pericar-
dium. Hold the frog in such
a way that the heart can be
observed while the brain and
cord are stimulated. With
needle electrodes, the points of which should be

Optic thalami. L.op. Optic
lobes. C Cerebellum. M.o.
Medulla oblongata. S.rh.
Sinus rhomboidalis. (After
Foster's plate in Bunion-
Sanderson's Handbook.)

566 THE OUTGO OF ENERGY

one millimetre apart, stimulate the spinal cord
with a tetanizing current of a strength easily
borne on the tongue.

Stimulation of the spinal cord will not inhibit
the heart. Stimulation of the cerebral hemi-
spheres will be also ineffectual. Now stimulate
the medulla oblongata. (Fig. 74.)

The heart will be inhibited.

This method of locating the cardio -inhibitory
centre is unsatisfactory, because the inhibition
produced may possibly be the result of the stimu-
lation of nerve paths to or from the centre. Its
results can be controlled by the method of suc-
cessive sections, to be explained in connection
with the vasomotor centre, page 565.

The cardio-inhibitory centre is always in ac-
tion, for section of the vagi causes the heart to
beat more frequently.

Augmentor Centre. — It is probable that this
centre, like the inhibitory centre, is situated in
the bulb, but the location is not definitely known.
The constant activity of the augmentor centre is
shown by the fall in frequency of beat after sec-
tion of the vagi followed by bilateral extirpation
of the inferior cervical and first thoracic ganglia
in mammals.

The neuraxons, or axis-cylinder processes, of
the augmentor cells lying in the central nervous

INNERVATION OF HEART AND BLOOD-VESSELS 567

system pass out of the spinal cord in the white
rami and terminate in the sympathetic ganglia
(for example, the inferior cervical and stellate
ganglia of the dog) in contact with sympathetic
cells, the neuraxons of which convey the impulse
to the heart.

The cardiac centres are readily affected by
afferent impulses from many sources.

Reflex Inhibition of the Heart; Goltz's Experi-
ment. — In a very lightly etherized frog, expose
the pericardium by cutting away the chest wall
over the heart. Count the number of beats in
periods of twenty seconds. Continue the count
while an assistant strikes gentle blows with the
handle of a scalpel upon the abdomen at the rate
of about 140 per minute.

The frequency will usually diminish and, in fa-
vorable cases, the heart will at length be arrested.

Cut both vagus nerves and repeat the experi-
ment.

The reflex inhibition of the heart cannot be
obtained after section of the vagi.

It has been shown by Bernstein that the affer-
ent nerves in this experiment are abdominal
branches of the sympathetic nerve. The stim-
ulation of the central end of the abdominal
sympathetic in the rabbit also produces reflex
inhibition of the heart.

568 THE OUTGO OF ENERGY

Reflex Augmentation. — Count the human radi-
al pulse during four consecutive periods of fifteen
seconds. Let the subject sip cold water slowly.
Eepeat the count while the subject swallows.

The frequency will be increased.

Variations in the force and frequency of the
heart-beat follow the stimulation of most afferent
nerves, for example the central end of the divided
vagus, the sciatic, and other mixed nerves, the
nerves of special sense, and the afferent nerves
which arise in the heart and pass to the bulb.

The most conspicuous of the nerves which bear
impulses from the heart to the central nervous
system in mammals is the depressor. This nerve
occurs as an isolated trunk in the rabbit, and is
found mixed with other fibres, for example in the
vagus, in many other animals. The stimulation
of the end of the severed depressor nerve in con-
nection with the heart is without effect. The
stimulation of the end in connection with the
bulb slows the heart and dilates the blood-vessels,
thus causing a great fall in the blood-pressure.

The Innervation of the Blood-Vessels

The Bulbar Centre. — 1. Lightly etherize a large
frog. Expose and cut both vagus nerves (in
order to exclude inhibition of the heart). It is
of the first importance to avoid excessive hemor-

INNERVATION OF HEART AND BLOOD-VESSELS 569

rhage. Expose the brain and the anterior half of
the spinal cord (page 565). Place the frog on the
web-board. Note carefully the speed with which
the corpuscles pass through the smaller vessels
of the web. The rate of flow in the capillaries is
the best practical index .of the diameter of the
small arteries. When the arteries constrict, the
flow in the capillaries will be less rapid. Eemove
the cerebral hemispheres and the optic lobes.
After five minutes or more (to allow the frog to
recover from the shock of the operation), note the
condition of the web vessels.

There will be no significant change.

The removal of the brain anterior to the bulb
has not destroyed the tonus of the blood-vessels.

Note the slow rhythmic changes in the diam-
eter of the vessels. The changes are not uniform
throughout the length of the blood-vessel.

2. Curarize the frog sufficiently to paralyze
the motor nerves. Stimulate the bulb with very
weak tetanizing currents.

The flow in the capillaries will be less rapid.
Obviously the bulb contains nerve cells, the ex-
citation of which causes the narrowing of the
blood-vessels. These cells are termed the bulbar
vasoconstrictor centre. Eepeated sections show
that the vasoconstrictor cells are placed (in the
rabbit) on both sides of the median line from

570 THE OUTGO OF ENEEGY

about one millimetre posterior to the corpora
qnadrigemina to a point about four millimetres
posterior to those bodies.

The Vasomotor Functions of the Spinal Cord. —
1. Divide the cord just posterior to the bulb.
(A fresh frog may be required. In that case,
remember to curarize.)

The division of the fibres connecting the vaso-
constrictor centre with the cord will be followed
by the dilatation of the vessels in the web (i. e.
the flow will be more rapid).

2. Stimulate the peripheral segment of the
divided cord.

The blood-vessels will constrict.

Thus the neuraxons (axis-cylinder processes)
of the bulbar vasomotor cells pass through the
spinal cord on the way to their respective blood-
vessels.

It should now be determined whether these
fibres pass to the blood-vessels without interrup-
tion, or whether they end in contact with spinal
vasomotor cells through which the connection
with the blood-vessels is made.

3. Wait five minutes and then note the flow
through the capillaries.

The dilatation observed immediately after the
separation of the cord from the medulla has given
place to moderate constriction. The tonus of the

INNERVATION OF HEART AND BLOOD-VESSELS 571

blood-vessels has returned. The spinal cord has
taken up the vasomotor function of the bulb.
Evidently the spinal cord contains vasomotor
cells, which ordinarily are subsidiary to those of
the bulb, but which, when separated from their
master cells, acquire^ the power of independent
action.

Effect of Destruction of the Spinal Cord on the
Distribution of the Blood. — Further evidence of
the vasomotor function of the spinal cord is
afforded by the following experiment.

Expose the heart, avoiding unnecessary loss of
blood. Lay bare the upper part of the intestine
by an incision on the left side of the umbilical
vein, which lies in the median line. Suspend the
frog vertically. Note that the heart and the great
vessels are filled with blood. Note also the size
and number of the vessels in the walls of the
stomach and intestines.

Bend the frog's head. Put the seeker into the
vertebral canal and pass it gently downwards to
destroy the spinal cord. The seeker will move
easily, if really in the canal. Look at the heart
and great arteries.

The heart will soon be bloodless, though beating
regularly. Examine the vessels of the stomach
and intestine. They are distended. Evidently,
the contents of the heart and the great arteries

572 THE OUTGO OF ENERGY

have passed into dilated smaller arteries and
veins. It would be found, on waiting, that this
effect is not a passing consequence of inhibition.
The destruction of the spinal cord has changed
the distribution of the blood.

The Vasomotor Fibres leave the Cord in the
Anterior Roots of Spinal Nerves. — 1. Eeniove
the arches of the 5th, 6th, 7th, 8th, and 9th ver-
tebrae and lay bare the cord in a large frog in
which the motor nerves have been paralyzed with
curare. Note the capillary flow in the web. On
the side on which the web-vessels are examined,
tie a silk thread around each of the anterior roots
near their origin from the cord, and sever the roots
between the ligature and the cord.

The vessels will dilate.

2. Stimulate the peripheral ends of several of
the divided roots.

Constriction will follow.

The vascular dilatation which follows the de-
struction of the spinal cord is not permanent.
After a time the vessels regain their tonus. It is
probable, therefore, that vasomotor nerve cells
exist outside the spinal cord, and this conclusion
is confirmed by the results gained on warm-blooded
animals with the nicotine method. Langley has
found that the injection of about ten milligrams
of nicotine into a vein of a cat will prevent, for a

INNERVATION OF HEART AND BLOOD-VESSELS 5<3

time, the passage of nerve impulses through sym-
pathetic cells. Painting the ganglia with nicotine
has the same effect. In animals the sympathetic
cells of which have thus been paralyzed, the stim-
ulation of the lumbar nerves in the spinal canal
produces no change in the vessels of the genera-
tive organs, though in animals not poisoned with
nicotine this stimulation causes marked constric-
tion. The lumbar vasomotor fibres must there-
fore end in connection with sympathetic nerve
cells which transmit the constrictor impulse to
the blood-vessel. Similar observations in other
regions warrant the belief that all the vasomotor
fibres emerging from the spinal cord end in like
manner.

Thus the vasoconstrictor system probably con-
sists of three neurons. The first is a sympa-
thetic cell, lying apart from the central nervous
system. Its neuraxon (axis-cylinder process)
passes directly to the blood-vessel. The second
is a spinal cell, the neuraxon of which leaves the
cord and terminates in contact with the sympa-
thetic cell or its branches. The third has its
cell body in the bulb and its neuraxon termi-
nates hi contact with the second neuron.

Commonly, as for example in the nerves of the
extremities, the sympathetic neuraxon passes
from the ganglion along the gray ramus into the

574 THE OUTGO OF ENERGY

corresponding spinal nerve, in which it continues
to its distribution.

Vasoconstrictor Fibres in the Sciatic Nerve. —
Curarize a frog sufficiently to paralyze the volun-
tary muscles (any excess of curare will paralyze
the vasomotor fibres also). Carefully destroy the
brain with the seeker, avoiding loss of blood.
Expose the right sciatic nerve for a short distance
on one side, using the greatest care not to injure
the blood-vessels. Tie a thread tightly around
the nerve near the upper end of the exposed por-
tion. Lay the frog, back upward, on the web-board,
placing the web of the right foot over the notch,
and securing it with fine pins. Examine the web
under a low power, to make sure that the circu-
lation has not been interrupted by stretching the
web. Place the secondary at such a distance
from the primary coil that the induced current
shall be barely perceptible to the tongue. Set
the hammer vibrating, and close the short-circuit-
ing key. Put the electrodes under the sciatic
nerve on the peripheral side of the ligature. Let
a second observer watch a small vessel of the web
through the microscope. Open the short-circuit-
ing key for a moment only.

The blood-stream slows from constriction of
the supplying vessels, the contraction increasing
during a few seconds and then subsiding.

INNERVATION OF HEART AND BLOOD-VESSELS 575

This experiment requires much care and close
observation. The curare effect must be very
slight ; a small quantity of the drug should be
given an hour before the observation is made.
Great pains must be taken to use feeble currents
and not to prolong the excitation, for the vaso-
motor nerves are rapidly exhausted. The nar-
rowing of the arteries of the web is usually
evident only in the slowing of the blood-stream
during excitation.

Vasodilator Nerves. — 1. Eepeat the preceding
experiment in a frog in which the sciatic nerve has
been four days severed (without injury to the fem-
oral vessels). On stimulation of the peripheral
segment of the divided sciatic nerve, the vessels
of the web will dilate instead of constricting.

Evidently the sciatic nerve contains vasodilator
as well as vasoconstrictor fibres. When the
sciatic fibres are separated from their cells of
origin by the section of the nerve, the fibres distal
to the section degenerate. But the degeneration
does not proceed at the same rate in all the fibres.
The vasoconstrictors die before the vasodilators.
In ordinary stimulation of the normal nerve, the
action of the constrictors overpowers that of the
dilators. In the partially degenerated nerve,
the same stimulation causes dilatation because
the constrictor fibres are dead or dying.

576 THE OUTGO OF ENERGY

2. Note the rate of flow in the web-vessels in
the uninjured limb. Stimulate the sciatic nerve
with the single induction current repeated at
intervals of five seconds.

The vessels of the web will dilate.

The vasoconstrictor and vasodilator fibres also
react differently to cold. If the hind limb (cat)
be cooled, the stimulation that normally causes
vasoconstriction will cause vasodilatation.

Vasoconstrictor and vasodilator fibres are not
always found in the same nerve-trunks ; in the
chorda tympani nerve, for example, there are only
dilator fibres.

The central relations of the dilator nerves have
not been sufficiently studied to warrant their
discussion here.

Reflex Vasomotor Actions. — 1. Note the rate
of flow in the vessels of the web in a lightly
curarized frog. Stimulate the skin (not too near
the bulb or cord) with tetanizing currents. The
stimulus must not be repeated often, or fatigue
will obscure the result.

Keflex constriction of the vessels will take place.
The sensory impulse is carried by afferent fibres
to the vasomotor centres.

Eepeat the experiment, using in place of the
electrical a mechanical stimulus, such as pinching
the skin with forceps.

INNERVATION OF HEART AND BLOOD-VESSELS 577

Apparatus

Normal saline. Bowl. Towel. Pipette. Glass plate.
Inductorium. Key. Wires. Dry cell. Electrodes.
Needle electrodes. Frog-board. Electromagnetic signal.
Heart-holder. Kymograph. Glass tube for oesophagus.
Two muscle levers. Solutions of nicotine (0.2 per cent),
atropine (0.5 per cent), muscarine (a trace in normal salt
solution). Curare. Ether. Sponge. Glass jar. Ver-
tebral saw. Web-board. Fine pins. Microscope. Frog,
the sciatic nerve of which has been severed four days.
Millimetre rule. Silk thread.

37

INDEX

Aberration, chromatic, 432, 434 ; diaphragm, 434 ; spherical,
by reflection, 426 ; spherical, by refraction, 427, 434.

Absolute force of muscle, 358.

Accommodation, 469 ; angle between light and visual axis,
487 ; far point, 479 ; iris, 474 ; lens, 474, 475, 477 ; liue, 472 ;
measurements, 479 ; mechanism, 473 ; pupil, 473 ; pupil, near-
ness, 488 ; pupil, size, 488 ; range, 471, 484.

Acuteness of vision, 465, 466.

Action current, brain and cord, 319; decrement, 309; dura-
tion, 314; glands, 320; heart, 310, 312; threshold value,
318; human muscle, 309; muscle, 300; nerve, 315; optic
nerve, 318; positive after current, 317; positive variation,
316; precedes change in form, 311; tetanus, 305; voltage,
315.

Afferent impulses, reflex action, 371 ; summation, 372.

Alteration hypothesis of nerve and muscle current, 299.

Amalgamation, 46

Ametropia, determination of, 493.

Angle, construction of tangent, 467 ; incidence, 403 ; reflection,
403 ; refraction, 411 ; sine, 414 ; visual, 464.

Angle gamma, 464.

Animal heat, 285.

Ankle jerk, 376.

Anodes and cathodes, physiological, 110.

Anterior roots, vasomotor fibres, 572.

Aortic regurgitation, 550.

Aortic stenosis, 551.

Aperture, 420, 427.

Apparatus, criticism of, 84.

Arrhenius, theory of dissociation, 31.

Artificial scheme, 511.

Astigmatism, 464 ; measurement, 495.

Atropine, action on heart, 564.

Augmentor centre, 566.

Axis, optical, 419 ; optical, eye, 439 ; principal, 419 ; visual 463.

5S0 INDEX

Balancing experiment, 379.

Bernstein's experiment, 531 ; rheotome, 313.

Blood pressure, arterial in frog, 522 ; influenced by inhibition,

525 ; peripheral resistance, 523.
Blood-vessels, innervation, 568.
Brain of frog, 565.
Brain, destruction by pithing, 97 ; dorsal view, 293.

Calcium, in normal solution, 165.

Calorimeter, Rubner's experiment, 285.

Carbon dioxide, action on nerve, 172; apparatus, 173.

Caustic surface, 427-429.

Cell, dry, 52 : Daniell, 48 ; galvanic, 34.

Cell, in series, 133.

Centre, rotation, 463 ; optical, 420 ; optical, crystalline lens, 446.

Centres of heart nerves, 564.

Cerebral hemispheres, removal of, 378.

Chemical stimulation, 163.

Circle, dispersion, 429, 470-472.

Circulation, artificial scheme, 511; capillary, 262, 569; inter-
mittent and continuous, 515 ; mechanics of , 508 ; mesentery,
519 ; rate of flow and width of bed, 519.

Clamp, double, 65 ; flat-jawed, 65 ; Gaskell, 103 ; round-jawed,
65.

Clausius, theory of dissociation, 29.

Closing contraction, 98.

Color blindness, 501.

Compensation of demarcation current, 294.

Compensatory pause, 533.

Conductivity, 168; centripetal and centrifugal, 181; during
constant current, 123.

Contraction, tonic, 141.

Contraction, direction of current, 157; human muscle, 353;
idiomuscular, 166; law, 113; load, 341 ; opening and closing,
98 ; rhythms, 142 ; single, 332 ; temperature, 342 ; torn"., 107,
140; veratrine, 345 ; wave, 338 ; heart muscle, 534.

Contracture, 340.

Coordinated actions, 378.

Croak reflex, 379.

Curare, 97 ; poisons end plates, 171.

Daniell cell, 48.

Decrement of action current, 309. »

Demarcation current, 287, 295 ; hypotheses, 297 ; interferes
with stimulating current, 292 ; measurement, 292 ; muscle,
287 ; negative variation, 305 ; nerve, 296; stimulus, 289, 296.

Dennett's method, numbering prisms, 435.

INDEX 581

Depressor nerve, 568.

Deviation, angular, 435.

Dicrotic notch, 545.

Diffusion of gases, 14.

Dioptre, 435.'

Dispersion circle, 429, 470, 471, 472.

Distance, focal, crystalline leus, 450 ; principal focal, cornea,

441.
Distilled water, a chemical stimulus, 163.
Drying, 149, 164.

DuBois-Reymond, molecular theory, 298.
Duchenne's points, 127.
Duration of stimulus, 138.

Elasticity and extensibility, of a metal spring, 364 ; of a rub-
ber band, 364 ; of skeletal muscle, 365.

Electric fish, 329.

Electrical units, 35.

Electrodes, for human nerves, 132 ; indifferent, 111 ; non-polariz-
able, 93 ; platinum, 65.

Electrolysis, 26.

Electrolytic solution pressure, 32.

Electrometer, 34.

Electromotive force, 34, 287 ; demarcation current, 292.

Electrotonic currents, 323 ; as stimulus, 328 ; negative and
positive variation, 325 ; polarization increment, 325.

Energy, set free in various forms. 10 ; stimulation, and irrita-
bility, 7 ; developing, 361.

Emmetropia, 490; angle of,1 464.

Engelmann's incisions, 534.

Ergograph, 354.

Excitation wave, 336 : remains in original fibre, 181.

Extensibility, 364, 366.

Extra contraction of heart, 533.

Eye, artificial, ophthalmoscopic, 489 ; as camera obscura, 437 ;
normal measurements, 461 ; see optical box, 404 ; reduced,
458 ; schematic, 438.

Extra current in inductorium, 68.

Fatigue, 367 ; human muscle, 368 ; polar, 147.

Fixation, line, 463.

Focus, conjugate, concave mirror, 427 ; conjugate, convex lens
418 ; conjugate, cornea, 444 ; principal, concave mirror, 405
principal, construction, 443; principal, convex lens, 416
principal, eye, 454.

Focal distance, concave mirror, 406 ; principal, convex lens, 417

Focal line, 427.

582 INDEX

Food materials, composition of, 281.

Flexors and extensors, relative excitability, 177.

Frog board, 112.

Galvanic cells, electromotive force in, 34.

Galvanic stimulation may cause periodic impulses, 144.

Galvanotropism, 137.

Gas chamber, 173.

Gaskell's block, 535 ; clamp, 103.

Goltz's experiment, 567.

Gower's experiment, 376.

Graphic method, 77.

Heart, action current, 310, 312 ; apex, isolated, 531 ; atropine,
564 ; augmentor centre, 566 ; augmentor nerves, 555 ; auric-
ulo-ventricular interval, 561 ; Bernstein's experiment, 531 ;
calcium, 539 ; change in form, 529 ; chemical theory, 540 ;
compensatory pause, 533 ; constant stimulus, 532 ; contrac-
tion curve, 530 ; contraction wave, 534 ; excitation from auri-
cle to ventricle, 535; exposure, 112; extra contraction,
533 ; Gaskell's block, 535 ; graphic record, 530 ; impulse,
541 ; inhibited, 559 ; inhibitory centre, 564 ; inhibitory mech-
anism, 562 ; inorganic salts, 538 ; irregularities, 536 ; irritable
though inactive, 533; irritable though inhibited, 561 ; load,
537 ; maximal contraction, 530; monopolar stimulation, 111 ;
muscarine, 564; nerve-free, 170; nicotine, 563; outflow
period, 526; polar inhibition, 153; polar stimulation, 110;
potassium, 539 ; pump, 525 ; reflex augmentation, 568 ; re-
flex inhibition, 567 ; refractory period, 533 ; rhythmic con-
tractility, 532 ; sounds, 541 ; staircase contraction, 531 ; tonus,
537 ; Stannius inhibition, 562 ; sympathetic, 556 ; tempera-
ture, 538; vagus, 559; valves, 511, 525, 550, 551, 552.

Heat values, calculation, 285.

Hypermetropia, 431 ; angle of, 464 ; measurement, 495.

Idio-muscular contraction, 166.

Image, concave mirror, 405, 409 ; convex mirror, 410 ; convex
lens, 419, 420; cornea, 443; dioptric, 456, 457 ; retinal, 437,;
retinal, actual size, 465; retinal, apparent size, 464; smallest
perceptible, 466; virtual, concave mirror, 408; virtual, con-
cave lens, 419.

Index of refraction, 412.

Induction currents, 54 ; direction, 158 ; gap in resulting contrac-
tions, 161; magnetic, 56, 58; nerves, 69 ; stimulus, 66, 158;
unipolar, 71.

Inductoiium, 54; construction, 60; graduation, 83.

INDEX 583

Inhibition, galvanic, 153; heart, 559; polar, 155 ; reflex of
heart, 567 ; ventricular, 524.

Inhibitory nerves of heart, 558.

Inhibitory centre, 564.

Interrupter, 62, 303.

Ions, 28.

Iris, accommodation, 474.

Irritability, 169 ; definition, 9 ; different points of same nerve,
180; flexor and extensor nerves, 177; muscle, independent,
169 ; nerve greater than muscle, 179 ; separable from conduc-
tivity, 172.

Isometric contraction, 352, 355 ; method, 349.

Isotonic method, 349.

Isotony, 20.

Key, short-circuiting, 46 ; simple, 45 ; rocking, 50.

Kinetic theory, 12.

Knee jerk, 375.

Kymograph, 79; long paper, 81.

Lantern, 404.

Latent period of muscle, 334.

Lens, accommodation, 474, 475; concave, 422; convex, 416;

numbering, 435.
Lever, light muscle, 86 ; heavy or rigid, 351 ; writing, 87.
Light, spectrum, 413.

Line of fixation, 463 ; focal, 427 ; force, 57.
Load, influence on contraction, 537.

Magnetic field, 57 ; induction, 57.

Make or break current excluded, 70; stimuli, 67.

Manometer, mercury, 523.

Mechanical stimulation, 166.

Mirror, concave, 405 ; convex, 410 ; plane, 403.

Mitral incompetence, 552.

Moist chamber, 95.

Molecular hypothesis of nerve and muscle current, 298.

Monopolar stimulation, 111.

Motor points, 128.

Muscarine, action on heart, 564.

Muscle, action current, 300 ; clamp, 8 ; curve, 333 ; demarca-
tion current, 287 ; form affects stimulation, 156 ; left hind
limb of frog, 6, 99; lever, 86, 351 ; tonus, 389; turbid and
clear, 335 ; warmer, 343.

Myomeres, 298.

Myopia, 430 ; angle of, 464 ; measurement, 493.

584 INDEX

Negative variation, 321 ; electrotonic currents, 325 ; secretion
currents, 321.

Nerve, action current, 315 ; cervical in frog, 558 ; conducts in
both directions, 181; conductivity, 120; conductivity and
irritability, 172 ; demarcation current, 295 ; drying, 149
electrical resistance, 327 ; electromotive phenomena, 295
impulse, speed of, 184 ; induction, 69 ; inhibitory, 558
irritability, 116; irritability compared with muscle, 179
irritability, different points, 180; irritability, specific, 179
polarization, 323; polar stimulation, 113, 131 ; stimulated by
own demarcation current, 296.

Nerve-muscle preparation, 4.

Nicotine, action on heart, 563.

Nitrite of amyl, 550.

Normal saline solution, 165.

Ophthalmoscope, 489.

Ophthalmoscopy, 484 ; direct, 490 ; indirect, 496.
Optic nerve, action current, 318.
Optical box, 404.

Opening and closing contraction, 98, 125 ; tetanus, 147.
Ordinates, 91.
Osmometer, 18.

Osmotic pressure, 16; blood-corpuscle method, 22; blood
serum, 21.

Paper, smoked, method of usiug, 78.

Paradoxical contraction, 328.

Paramecium, galvanotropism, 137.

Partial pressure, 13.

Periodic contraction from chemical stimulation, 165 ; galvanic
stimulation, 144.

Peripheral resistance, 521.

Permeability, 24.

Pithing, 97.

I'lasmolysis, 20.

Plethysmograph, 545.

Point, cardinal, cornea, 440; cardinal, crystalline lens, 445;
cardinal, eye, 439, 451 ; far, accommodation, 479 ; far, deter-
mination, 479 ; near, accommodation, 480 ; near, determina-
tion, 480; nodal, 420; nodal, crystalline lens, 447; nodal,
eye, 453 ; principal, crystalline lens, 450 ; s, 449, 453.

Polar excitation, 148; fatigue, 147; inhibition, 153, 155; in-
jured muscle, 151 ; refusal, 292; stimulation, 101, 113, 159.

Polarization, 46; current, 51, 145; increment, 325; positive
variation, 146.

Pole-changer, 49, 50.

INDEX 585

Positive after current, 317.

Positive variation, action current, 316 ; polarization current,
146 ; polarizing current, 325.

Prentice's method, numbering prisms, 435.

Prisms, 413; construction, 413; numbering, 435; path of en-
tering ray, 413.

Pulse, aortic regurgitation, 550 ; curve, 546 ; dicrotic, 545 ;
form, 544 ; frequency, 543 ; hardness, 544 ; low tension, 549 ;
pressure, 545; valvular disorders, 551, 552; volume, 545,
552.

Pupil, accommodation, 473.

Reaction of degeneration, 135.

Reaction time, 382.

Reflection, concave mirror, 405; convex mirror, 410; plane
mirror, 403.

Reflex actions, 370 ; afferent impulses, 371 ; cornea, 374 ; inhi-
bition, 384 ; man, 374 ; pupil, 375 ; purpose, 381 ; segmen-
tal, 373 ; strychnine, 377 ; tendon, 375 ; threshold, 372 ;
throat, 382 ; vasomotor, 576.

Reflex time, 382.

Refraction, 410; concave lens, 422 ; convex lens, 416; convex
and cylindrical lenses, combined, 424 ; cylinders, 422 ; eye,
437 ; index, 412 ; prism, 413.

Refractory period, 534.

Respiration, mechanics of, 505.

Respiration scheme, 505.

Retina, reflection, 484.

Rheochord, 42.

Rheoscopic frog, 302, 306.

Rheotachy graph, Hermann, 314.

Rheotome, differential, Bernstein, 313.

Ringer solution, 540.

Ritter-Rollett phenomenon, 177.

Salts, influence on contraction of heart, 538.

Saturation, 16.

Scheiner's experiment, 469.

Sciatic nerve, vasomotor fibres, 574.

Secretion current, 320; negative variation, 321.

Semi-permeable membrane, 17.

Shortening in single contraction and in tetanus, 348.

Sensation, effort, 400; general, 398; irradiation, 398; motion,
400 ; motor, 400 ; pain, 399 ; pressure, 393 ; taste, 401 ; tem-
perature, 390 ; tickle, 398 ; touch, 395 ; Weber's law, 395.

Signal, electro-magnet, 105.

Size, apparent, 456, 465.

586 INDEX

Skin, hot and cold spots, 390; irradiation, 398; pressure spots,
393.

Smooth muscle, 356.

Solution, gas in liquid, 16; normal, 165; solid in liquid, 16;
tension, 16.

Spectrum, 413, 432.

Sphygmograph, 527.

Spinal cord, localization of movements at different levels, 387 ;
destruction changes distribution of blood, 571.

Spinal nerve roots, 386 ; sensory nerves, 388.

Spontaneous contractions, 356.

Staircase contraction, heart, 531.

Stannius ligature, 562.

Stimulation, 9 ; angle of current lines, 157 ; chemical, 163, 164 ;
constant, may cause periodic contraction, 165 ; demarcation
current, 290, 296; distilled water, 163; drying, 164; form
of muscle, 10, 156; induction current, 158; intensity changes,
99; mechanical, 166; minimal and maximal, 175; monopo-
lar, 111; polar, in heart, 110; summation of impulses, 176;
threshold value, 174; unipolar, errors, 320.

Stroboscopic method, 305.

Surface, caustic, 427, 428, 429 ; principal, crystalline lens,
418 ; principal, eye, 449.

Surface tension, 25, 36.

Summation of stimuli, 176.

Superposition in tetanus, 347.

Superposition of two contractions, 346.

Sympathetic, action on heart, 556 ; frog, 556 ; preparation,
555.

Synchronous poiuts, method of obtaining, 120.

System A, schematic eye, 440 ; B, schematic eye, 445 ; C,
schematic eye, 451.

Temperature, hourly variation, 285 ; mouth, affected by food,
285; reaction to variations in, 285 ; regional, 285.

Tension indicator, 25.

Tetanus, 69, 346 ; electrical phenomena, 305 ; natural and arti-
ficial, 355 ; opening and closing, 147 ; Ritter's, 149.

Threshold value of stimulation, 175.

Tonus of heart muscle, 537.

Tradescantia discolor, 20.

Tuning fork, 88.

Unipolar induction, 71, stimulation, errors, 320.

Van I'll: \V.\ai.'> hypothesis, 14.
Van't Iloff's discoveries, 20.

INDEX 587

Vagus, preparation, 558; inhibits heart-beat, etc., 559, 560,

561.
Vapor pressure, 15.
Vasodilator nerves, 575.
Vasomotor centre, 570 ; fibres in anterior roots, 572 ; functions

of cord, 570 ; reflexes, 576 ; sciatic, 574.
Veratrine, influence on contraction, 345.
Vision, acuteness, 465, 466 ; blind spot, 499 ; color blindness,

501 ; field of, 500; yellow spot, 499,
Volume of contracting muscle, 331.
Volume tube, 332.

Wohler's discovery, 3.

"Work adder, 359.

"Work done, influenced by load, 35S.

— ~T ^r ^ A — #-

JUN 2 6 1928

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