XPERIMENTAL
PHYSIOLOGY

E. A. SCHAFE

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D

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o

Experimental Physiology

BY THE SAME AUTHOR
Eighth Edition, 1910.

THE ESSENTIALS OF
HISTOLOGY

With 645 Illustrations. 8vo. 10s. 6d. net.

TEXT-BOOK OF
MICROSCOPIC ANATOMY

With 21 Coloured Plates and 1001 Illustra-
tions in the text. Royal Svo. 25s. net.

This has been published as part of the eleventh edition of
Quain's Anatomy, but is a complete work in itself. It contains
a full account of the minute structure of all the tissues and
organs of the body, ilhtstrated by drawings and photographs.

LIFE: ITS NATURE, ORIGIN

AND MAINTENANCE

Being the Presidential Address delivered before the
British Association at Dundee, September 1912.

Svo. Paper Covers. Is. net.

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Experimental Physiology

BY

E. A. SCHAFER, F.R.S.

PROFESSOR OF PHYSIOLOGY IN EDINBURGH

R

\VITH EIGHTY-THREE ILLUSTRATIONS

LONGMANS, GREEN, AND CO.

39 PATERNOSTER ROW, LONDON

NEW YORK, BOMBAY AND CALCUTTA

1912

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S

Pref;

ace

THE present volume is based upon a small book, entitled Directions
for Class Work in Practical Physiology, which was published in
1901, and consisted chiefly of an account of the methods employed
in the study of muscle and nerve physiology and of the heart, in so
far as these could be illustrated in preparations from the frog. To
that account have now been added descriptions of such other methods
of Experimental Physiology as may be performed by the student
either in class or individually, although a few which are given can—
at least in this country — only take the form of demonstrations.
The additions deal chiefly with the heart and vascular system,
respiration, secretion, the central nervous system, and the sense
organs ; but considerable changes have also been introduced in
the description of the methods of studying the physiology of muscle
and nerve, and not only have a large number of new illustrations — for
the most part in the form of diagrams — been added, but all the original
figures have been redrawn, so that the work has taken the character
of a new book, which it has been thought proper to furnish with
another name.

The descriptions of the methods employed are founded upon twelve
years' experience in conducting the classes of Practical Physiology
in the University of Edinburgh. These classes are of two kinds,
elementary and advanced, and some of the methods described are
intended only for advanced students. But no attempt has been made
in the work to discriminate between the experiments which are ex-
pected to be performed by the one or the other grade. Such selection
can be best made by the teacher of the subject, and would be
regulated by the requirements of the students and the nature of the
examinations for which they are preparing.

UNIVERSITY, EDINBURGH,
September 1912.

.

Contents

CHAP. . PAGE

PRELIMINARY 1

I. AMCEBOID AND CILIARY MOVEMENT ..... 2
II. THE ELECTRICAL APPARATUS IN COMMON USE IN PHYSIO-
LOGICAL WORK 4

III. SIMPLE EXPERIMENTS ILLUSTRATING THE USE OF ELECTRICAL

APPARATUS IN PHYSIOLOGY . . ... 17

IV. THE NERVE-MUSCLE PREPARATION 20

V. THE RECORDING OF MUSCULAR CONTRACTIONS . 26

VI. THE NERVELESS MUSCLE ...... 32

VII. EFFECT OF SUCCESSIVE STIMULI UPON A MUSCLE-NERVE

PREPARATION 36

VIII. WORK OF MUSCLE ; EXTENSIBILITY OF MUSCLE ... 39

IX. FATIGUE OF MUSCLE AND NERVE 42

X. CONDUCTION IN NERVE 46

XL CONDITIONS OF EXCITATION OF NERVE AND MUSCLE BY THE

GALVANIC CURRENT .... ... 50

XII. POLAR EFFECTS OF A GALVANIC CURRENT ; ELECTROTONUS . 54

XIII. EXPERIMENTS ON THE ELECTRICAL CONDITIONS OF MUSCLE

AND NERVE 57

XIV. INVOLUNTARY MUSCLE ... .... 62

XV. THE FROG-HEART .64

XVI, PERFUSION OF HEART 69

XVII. CARDIAC NERVES OF FROG . 72

XVIII. STRUCTURE AND ACTION OF THE MAMMALIAN HEART . . 75

XIX. THE CIRCULATION IN THE BLOOD-VESSELS .... 77

XX. THE PFLSE 83

XXI. PERFUSION OF VESSELS ; LYMPH-HEARTS . 86

XXII. MECHANISM OF SECRETION ....... 88

XXIII. RESPIRATION . . 90

XXIV. NERVE- ROOTS . 94

vii

viii EXPERIMENTAL PHYSIOLOGY

CHAl'. PAGE

XXV. REFLEX ACTION AND REACTION TIME. EXCITATION OF CORTEX

CEREBRI .... . 95

XXVI. CUTANEOUS SENSATIONS . 100

XXVII. EXPERIMENTS ON THE DIOPTRIC MECHANISM . . 102

XXVIII. STIMULATION OF THE RETINA . ... 106
XXIX. THE PRODUCTION OF VOCAL SOUNDS. ANALYSIS OF SOUNDS

AUDITION. THE SEMICIRCULAR CANALS .... 10!)

XXX. TASTE AND SMELL 111

EXPERIMENTAL PHYSIOLOGY

PRELIMINARY

As a preliminary to any course of Experimental Physiology, the following dis-
sections should be made : —

Frog. In this the following parts are to be displayed : —

(a) The brain and spinal cord, with the nerves passing off from them.

(b) The heart, with the main vessels leading to and from it.

(c) The lungs.

(d) The abdominal viscera, including stomach, small intestine, large

intestine, liver, spleen, kidneys, bladder, and reproductive
glands.

(e) The nerves and muscles of the leg.

Rabbit.

(a) The skull to be opened, and the several parts of the brain examined.

(b) The trachea and the blood-vessels and nerves on either side of it to

be displayed, and to be followed as far as possible both upwards
towards the head and downwards into the thorax.

(c) The contents and boundaries of the thorax to be examined. The

several parts of the heart to be observed and the vessels which
are connected with it. After removing the contents of the
thorax, the sympathetic ganglia and the nerves (splanchnic)
leading downwards from them towards the abdomen should be
noticed.

(d) The abdominal and pelvic viscera to be displayed.

(e) The nerves and muscles of one of the hind limbs to be dissected.

Since these dissections form a part of every course of Biology, the student
will probably already be familiar with them. If not, they should be made now.

CHAPTER I

AMCEBOID AND CILIARY MOVEMENT

The fresh-water amoeba. — Find an amoeba in a drop of pond water with
the microscope, and study its movements.

Amoeboid movements of frog's leucocytes. — Observe in a preparation of frog's
blood the amoeboid movements of the leucocytes.

Ciliary movement. — (1) Gently scrape some epithelium from the roof of a
frog's mouth, and shake the scrapings in a drop of normal salt solution or of
Ringer's solution.1 Observe with the microscope the ciliated cells and the
movements of their cilia.

(2) Take a small fragment of the gills of a sea-mussel and examine it under
the microscope in a drop of sea water. The cilia are much larger than those
of the frog, and their movements more easily watched, especially when they
become slow.

Experiments illustrative of amoeboid movement. — The following experiments
show that movements like those of the amoeba can be produced by purely
physical means (changes in surface tension).

1. Take on a glass rod a drop of ordinary olive oil which has been coloured
with Scharlach R., and place it gently on the surface of a 1 per cent, solution of
sodium bicarbonate. Sketch the changes of shape which it undergoes.

2. A globule of mercury is placed in a watch-glass of dilute nitric acid (1
per cent.). Introduce into the fluid near, but not touching, the drop a small
crystal of potassium bichromate. Observe the movements of the mercury.

Experiments on ciliary movement. — 1. In a model consisting of a thick
rubber ball from which a flat, curved rubber tube projects, notice that the tube
straightens out or curves over to one side according to the tension of the contents
of the ball. This movement, which resembles that of a cilium, is thus produced
by variations in tension within the part representing the cell.

2. In a frog which has just been killed, cut through the lower jaw and carry the
incision down the oesophagus to the stomach. Cut this organ across, seize the
cardiac end with forceps, and dissect out the oesophagus together with the
pharynx and a part of the mucous membrane of the mouth. Pin out the oeso-
phagus and pharynx and adjacent parts of the buccal membrane on a flat cork
with the inner surface uppermost. Rinse with Ringer's solution. Sprinkle a
few grains of charcoal over the buccal end of the preparation, and notice that
the charcoal is carried down as far as the stomach by the action of the cilia.
In the same way, pieces of cork or wax, or even small flat pieces of heavy materials
such as lead, may be passed over the surface.

1 Normal salt solution is made by dissolving six grams Nad in a litre of
water. Ringer's solution is an improved salt solution made by saturating one
litre of the above with calcium phosphate and adding ten milligrams of
potassium chloride. '' Ringer " should always be used in preference to ordinary
salt solution. For mammalian tissues it is made similarly but with 7—9 grams
NaCl to each litre of water.

2

AMCEBOID AND CILIARY MOVEMENT

3

3. Effect of temperature on ciliary movement. Fasten with, pins two pieces
of thread about half an inch apart across the above preparation of oasophagus,
and slightly raised above it. Rinse the membrane with ice-cold Ringer solution.
Drop a grain of charcoal on the buccal end, and with a watch record the number of
seconds which the charcoal takes to pass over the half-inch between the threads.
Again rinse the membrane, but this time with warm Ringer (25° C.), and repeat
the experiment. Note the difference in time taken to traverse the space marked
off by the threads. Lastly, rinse with Ringer heated to 50° C., and repeat the
experiment. The ciliated cells are killed at this temperature, and the charcoal
is no longer carried along.

'

CHAPTER II

THE ELECTRICAL APPARATUS IN COMMON USE IN
PHYSIOLOGICAL WORK

Batteries. — A voltaic element or cell usually consists of two metals—
e.g., zinc and copper — immersed in a fluid such as dilute sulphuric
acid, and the changes (movements of ions) which occur under these

Anode.

Copper.

Kathode.

Zinc.

Dilute sulphuric acid.

FIG. l. — VOLTAIC COUPLE.

circumstances in the fluid produce a disturbance of electrical equili-
brium in the cell which manifests itself as a difference of electrical
potential or pressure at the metals. If wires are connected to these
it is found that the end of the wire connected with the copper or
electronegative metal is charged with positive electricity, and that

connected with the zinc or electropositive metal is charged with

4

ELECTRICAL APPARATUS IN USE IN PHYSIOLOGICAL WORK 5

negative electricity ; these ends are called the positive pole, or anode,
and the negative pole, or kathode, respectively. The anode is said to
be in a condition of higher potential and the kathode in one of lower
potential, and when they are joined electrical equilibrium tends to
re-establish itself in the circuit thus closed. It is common to speak
of a current as flowing from the anode to the kathode outside the
battery and from the zinc to the copper inside.1 The amount of this
current depends upon the difference of potential produced within the
cell. This is diminished by any increase of resistance to the flow of
electricity, whether occurring within the cell or in the outside circuit.
Electromotive force (E.M.F.) is measured in volts ; thus the E.M.F. of a
Daniell cell is T079 volts. It may be increased by coupling two or
more cells together in series, the zinc of one connected with the copper
of the next, and so on.

FIG. 2. — DIAGRAM OF A VOLTAIC COUPLE. Z, ZINC ; C, COPPER.

If electricity be generated simply by immersing plates of zinc and
copper into acid the chemical action which ensues causes bubbles of
hydrogen gas to form on the copper, and this not only introduces a
resistance to the flow of current through the cell, but the hydrogen
being electropositive tends to set up a current (polarisation current)
in the opposite direction in the cell and circuit ; from both these
causes the original E.M.F. of the cell becomes rapidly weakened.

To obviate this effect Daniell placed the copper plate in a saturated
solution of copper sulphate and introduced a porous pot to separate
this from the dilute sulphuric acid in which the zinc is immersed (fig. 3).
The zinc then dissolves in the acid, displacing hydrogen ; the hydrogen
in its turn displaces copper from the copper sulphate, and the dis-
placed copper is deposited on the copper plate, so that no bubbles of
hydrogen are formed upon the metal, and if the copper sulphate
solution is kept saturated, the E.M.F. of the cell remains constant.
Commercial zinc, which is never pure, must always be " amalgamated "

1 Within the battery the electrical potential is highest at the zinc, which is
therefore here the anode, and lowest at the copper, which is here the kathode.

EXPERIMENTAL PHYSIOLOGY

Copper pot.

Zinc.

Porous pot containing
dilute sulphuric acid.

Sulphate of copper
(saturated solution).

FIG. 3. — DANIELL CELL.

Zinc.

Carbon.

Manganese dioxide
in porous pot.

Ammonium chloride
solution.

FIG. 4. — LECLANCH4 OBLL.

ELECTRICAL APPARATUS IN USE IN PHYSIOLOGICAL WORK 7

by rubbing its surface with mercury after it has been cleaned by
dipping into dilute sulphuric acid.

Other constant batteries which are frequently used in physiology are that of
Grove, where the negative plate is platinum and is plunged into strong nitric
acid, separated from the sulphuric acid containing the zinc plate by a porous
partition ; that of Bunsen, which is similar to Grove's, but with a negative plate
of carbon ; that of Leclanche (fig. 4), in which the acid is replaced by chloride
of ammonium and the place of the negative plate is also taken by carbon, which
is surrounded by manganese dioxide ; and that of Grenet, where carbon again
forms the negative plate, but where a single fluid is used (bichromate of potassium
dissolved in dilute sulphuric acid), in which both plates are immersed. The so-
called " dry" cells are modified Leclanches. The positive plate in every one
of these cells is amalgamated zinc.

Electrodes. — The wires used in physiological experiments must
always be insulated, either with gutta-percha or with silk or cotton ;
in the latter case the insulation is rendered more effectual
by dipping the covered wire into molten paraffin. For
experimental purposes it is usual to place the ends of
the wires (which must be clean and free from the
insulating material) in some sort of holder, so that they
can be more readily applied to the tissue which is to
be investigated ; these ends are usually termed the
electrodes.1 They are often made of platinum set in a

vulcanite holder ; but a FIG. 5.— PIN-
r • •,-, ,2 ELECTRODE.

•.-•^'.••:.:^:--y;^i Pair °* Pms with nne

^* wires soldered to their heads, which

FIG. SAMPLE CORK ELECTRODE-HOLDER, can on occasion be passed through

a small cork, with their points pro-

jecting for a few millimeters, constitute a readily improvised and
efficient pair of electrodes for most class purposes.

To determine which of the two electrodes in any case is the anode and which
the kathode, they may be placed in contact with a piece of blotting-paper moist-
ened with starch solution containing iodide of potassium (pole-testing paper).
Iodine is set free at the anode and turns the starch blue. Feeble differences of
electrical potential are determined and estimated by other methods (galvano-
meter, electrometer), which will be studied later.

Non-polarisable electrodes.— Like the plates of the battery itself,
metallic electrodes are capable of becoming polarised when they are
in contact with the moist tissues and a current is passed continuously
between them in one direction. For some experiments it is necessary
to obviate this polarisation of electrodes and to employ electrodes

1 The term electrode means literally the " path " of the electric current, and
in this sense the wires throughout are electrodes. But it has come to mean
technically the ends of the wires which are used to apply the electric current to
a given object (such as an animal tissue).

8 EXPERIMENTAL PHYSIOLOGY

which are not polarisable. These are usually made by taking two
small pieces of glass tubing open at both ends, either straight (fig. 7)
or curved (fig. 8), and having plugged one end of such tube with
china clay made into a paste with salt solution, the tube is filled
with saturated solution of zinc sulphate, and an amalgamated zinc

Zinc wire.
Cork.

• Saturated solution
of zinc sulphate.

Clay plug, moistened

with salt solution.

FIO. 7. — NON-POLABISABLE
ELECTRODE.

- Clay plug in
small glass
tube.

Zinc sulphate
solution.

PIG. 8. — SANDERSON'S PATTERN OP NON-
POLARISABLE ELECTRODE.

rod (to which one of the wires of the circuit is soldered or otherwise
attached) is plunged into the zinc sulphate.

The rod is amalgamated by dipping it for a few seconds into a solution of
mercury in nitric acid, washing under a tap, and polishing with cotton- wool.

A convenient form of non-polarisable electrode is that of Porter,
who uses a boot-shaped tube of unglazed porcelain which is soaked
with normal saline and filled with saturated solution of zinc sulphate ;
the amalgamated zinc rod is passed into the leg of the boot.

Keys. — Any apparatus which is used for interrupting or diverting
the course of a current is called a key or switch. The keys used in
physiological experiments are arranged to close and open a circuit

FIG. 9. — DIAGRAM OP MERCURY KEY.

(make and break the current) by connecting two wires together either
through a pool of mercury (mercury key — figs. 9 and 10) ; or by contact
between a platinum plate and platinum point (contact key — fig. 11),

ELECTRICAL APPARATUS IN USE IN PHYSIOLOGICAL WORK 9

as in the Morse key ; or by friction contact between two brass sur-
faces (friction key), as in that known as du Bois-Reymond's (fig. 12),

FIG. 10.— MERCURY KEY IN A BATTERY CIRCUIT.
and in the ordinary electric-light switches. They are used in two

PIG. 11. — CONTACT KEY IN A BATTERY CIRCUIT.
ways, viz. : either to simply close or open the circuit (direct method-

PIG. 12. — DIAGRAM OP SHORT-CIRCUITING KEY OP DU BOIS-REYMOND.
figs. 10, 11, 13) ; or by bridging across a part of the circuit a passage

PIG. 13. — FRICTION KEY IN A BATTERY CIRCUIT ; DIRECT METHOD OP USE.

with very little resistance is offered through the key, and the current
is thus diverted from the main circuit and from the electrodes (short-

10

EXPERIMENTAL PHYSIOLOGY

circuit method — fig. 14). For this purpose du Bois-Reymond's key is
especially well suited.

PIG. 14. — FRICTION KEY; SHORT-CIRCUIT METHOD OF USE.

A key which is constructed so as to cause a current to flow either in
one direction or in the reverse direction in part of a circuit is called a

FIG. 15.— DIAGRAM OP POHL'S COMMUTATOR.

reverser or commutator. One of the most frequently used is Pohl's
commutator (fig. 15), which consists of a plate of vulcanite or

FIG. 16.— POHL'S COMMUTATOR USED AS SWITCH (CROSS WIRES REMOVED).

other non-conducting material in which are six cups of mercury con-
nected with terminals. Four of the cups are joined diagonally, two

ELECTRICAL APPARATUS IN USE IN PHYSIOLOGICAL WORK II
and two, by crossed wires. A rocking double bridge of copper

FIG. 17. — WALLER'S COMMUTATOR.

PIG. 18. — DIAGRAM OP MALCOLM'S COMMUTATOR.

serves, on being moved to one side or the other, to effect the
reversal.

12

EXPERIMENTAL PHYSIOLOGY

If the crossed wires are removed the Pohl can be used as a
switch for diverting a current into one or other of two circuits
(fig. 16).

Other commutators have friction-contacts in place of mercury : of these
the simplest are Waller's (fig. 17), which has a rotating action; and Malcolm's
(fig. 18), which has a sliding action. The principle is the same as the mercury
commutator, and it is often convenient to dispense with mercury.

Rheochords. — A rheochord is an apparatus for dividing a constant
current by offering a circuit of relatively small resistance which is
capable of being varied so that a variable part only of the current
shall pass through the experimental circuit. It usually consists of a
german-silver or platinum-iridium wire of a certain known resistance

FIG. 19. — DIAGRAM OP BHEOCHORD.

(e.g., 20 ohms), to the ends (fig. 19, a and 6) of which the battery poles
are connected ; a certain difference of potential is thereby produced
at the two ends of the wire. With one of these ends (b) another wire
is connected ; this forms part of the experimental circuit through
which a portion of the battery current is to be conducted ; this circuit
is completed through a wire attached to a rider (r) which slides along
the rheochord wire.

When r is in contact with b the whole difference of potential between a and
b — which depends upon the E.M.F. of the battery and the resistance of the
rheochord wire relative to that of the experimental circuit- — is operative in pro-
ducing a current through the preparation. When r is at the middle of the
rheochord wire only one-half of this difference of potential comes into play,
and so in proportion to the distance between a and r as compared with the
whole length of the wire. Thus if the wire be 100 centimeters long and r be

ELECTRICAL APPARATUS IN USE IN PHYSIOLOGICAL WORK 13

placed at one centimeter from a, only , ,',,-, of the total difference of potential will
be operative and a proportional current will be diverted into the experimental
circuit. If r is in contact with a no current is led through the preparation.

When this kind of rheochord is used, the resistance of the experimental
circuit must always be relatively very great : as is invariably the case in physio-
logical experiments, where an animal tissue forms part of the circuit.

The wire of a rheochord may be stretched straight as in fig. 19, or, to
economise space, it may be zig-zagged upon a board (fig. 20), or arranged
spirally round a vulcanite cylinder, or circularly round a disc as in du Bois-
Reymond's form of instrument.

Via. -20. — DIAGRAM OP THE OXFORD FORM OP RHEOCHORD. a, 6, RHECHORD WIRE ZIG-ZAOHF.H
UPON A MAHOGANY BOAKD, MARKED Br CROSS LINES INTO HUNDREDTHS ; r, RIDER.

In another form of rheochord there are two wires, and a broad
metal rider (r) bridges across and forms a short circuit between the
two (fig. 21). The battery circuit and the experimental circuit are
both connected with the one end of each wire. When the rider is
brought up to these ends the battery current is completely short-
circuited, but when the rider is moved away from them a gradually
increasing resistance is inserted into the short circuit formed by the

14 EXPERIMENTAL PHYSIOLOGY

rheochord and its rider, and proportionally more of the battery
current passes into the experimental circuit.

Induction coil. — If the wires of two separate circuits are at any
point near to and parallel with one another and if, in the first or
primary circuit, the current of a battery is either made or broken by
the closing or opening of a key, an induced current is set up in the
other or secondary circuit at the instant of such closing or opening,
but not during the passage of the primary current. The induced or
secondary current is always of very short duration, but has a much
higher electromotive force than the primary or inducing current.

FIG. 21. — DOUBLE-WIRE RHEOCHORD.

In order to multiply the induction effect the two circuits always
take the form of closely coiled wires (fig. 22) (that of the secondary
circuit being very fine and having very numerous coils), and to still
further increase the effect the primary coil is wrapped round a core
formed of a bundle of soft iron wires which are magnetized and de-
magnetized on the closing and opening of the primary circuit, thus
enhancing the induction effects.

For physiological purposes the induction coil was arranged by
du Bois-Reymond so that the secondary circuit can be made to slide
nearer to or farther from the primary circuit ; since with the same
strength of battery the nearer or further the coils are from one another
the greater or less is the strength of the induced current. The varia-
tion is not, however, proportional to the distance, but approximately
to the square of the distance. For producing single make and break
induced shocks the primary circuit is closed and opened with a simple
key (fig. 22). For multiple induced shocks most coils are fitted with
an apparatus for automatically breaking and making the primary

ELECTRICAL APPARATUS IN USE IN PHYSIOLOGICAL WORK 15

circuit (Neef's hammer). This will be understood from the diagram
shown in fig. 23. The battery current is conveyed from the terminal,
t3, to a steel spring, sp, having a bar of soft iron at its free end, and

t' t2

FIG. 22. — INDUCTION COIL ARRANGED FOR SINGLE SHOCKS.

the current passes from the spring, which has a plate of platinum
upon it, to the platinum point of a screw, s1, and thence through the
primary coil. Before passing back to the battery it is conducted

FIG. 23. — DIAGRAM OP DU Bois COIL ARRANGED FOR FARADISATION.
(FOR DESCRIPTION SEE TEST.)

through a small electro-magnet, m ; the electro-magnet being thus
set in action, draws down the iron bar and with it the spring, which
leaves the screw and breaks contact so that a break induced current
is set up in the secondary coil. But, the current being broken, the

16

EXPERIMENTAL PHYSIOLOGY

electro-magnet, m, is no longer active, the bar springs up again, and
contact is re-established between the spring and screw ; this produces
a make induced current in the secondary coil. Thus the spring vibrates
to and fro, and break and make induced currents are set up in the
secondary coil many times a second, according to the rate of vibration
of the spring.

These make and break shocks are unequal owing to the extra current which
is self-induced within the primary coil, and which diminishes the make effect
(see Chapter III.). This inequality is, however, overcome by a modification
introduced, by Helmholtz. In this arrangement (fig. 24) a wire, w, connects the
terminals t1, t3 ; the screw sl is raised altogether away from the spring, and does
not come into use ; the screw s2 is brought nearly up to the spring. The battery
current passes by the wire, w, from the terminal, t3, directly to t1, thence
through the primary coil and through the electro-magnet, m, which draws down

FIG. 24. — DIAGRAM OP THE ABRANGEMENTS EMPLOYED IN THE HELMHOLTZ MODIFICATION
OP DU BOIS-REYMOND'S INDUCTION COIL. (FOR DESCRIPTION SEE TEXT.)

the iron bar and brings the spring in contact with the screw, s2. A large part
of the battery current now goes directly back to the battery through this contact,
and is diverted from the primary coil and electro -magnet. This greatly weakens
the current through the primary coil, and the equivalent of a break induced
shock is obtained in the secondary circuit ; for any sudden variation in the current
of the primary coil is effective in producing an induced current in the secondary
coil. But the electro-magnet is also weakened, so that the bar and spring fly
up. This breaks the short-circuiting contact which was established between
the spring and s2, and the whole current again passes through the primary coil,
producing the equivalent of a make induced shock in the secondary circuit,
and so on automatically. It will be observed that the primary circuit is never
actually broken, but only short-circuited.

The Helmholtz arrangement should always be employed for tetanic stimula-
tion, unless the nature of the experiment contra-indicates it.

Kronecker's inductorium. — Most du Bois-Reymond coils are furnished with
a scale marked in millimeters to indicate the distance of the secondary from the
primary coil. But the Kronecker coil is so graduated as to indicate the relative
strength of the induced current when a standard battery of constant strength is
employed in the primary circuit, and the scale is marked in units as well as milli-
meters. Moreover, the contacts are between a platinum wire and mercury, the
latter being kept clean by passing water or dilute alcohol over its surface. This
gives much more constant make and break effects than the contacts between
platinum point and platinum plate which are supplied with ordinary coils.

CHAPTER III

SIMPLE EXPERIMENTS ILLUSTRATING THE USE OP ELECTRICAL

APPARATUS IN PHYSIOLOGY

1. Connect up a cell with a pair of wires, introducing a simple key
into the circuit (fig. 10). Place the free ends of the wires on the
tongue, and close and open the key.

2. Repeat this experiment, but use a short-circuiting key (fig. 14).
Note that the effect of the current upon the tongue is now only felt
when the key is open.

3. Connect a cell with electrodes through a commutator, as shown
in figs. 15, 17, and 18. Determine with pole-testing paper which
is the anode and which the kathode in the two positions of the
bridge of the commutator. Verify this by following out the course
of the wires.

4. Connect a cell with the upper terminals, t1, t2, of the primary
coil of the inductorium, introducing a simple key into the circuit.
Connect a pair of electrodes through a short-circuiting key with the
terminals of the secondary coil, and slide this coil to some distance
from the primary (fig. 22). Place the electrodes on the tongue.
Alternately close and open the key in the primary circuit. Notice
that induction shocks are obtained on making and breaking the
primary circuit, but not during the passage of the current. Notice
that the break shocks are much sharper than the make.

This is partly due to the fact that as the current of the primary circuit is
made and broken, induced currents (extra currents) are formed in its own coils ;
the make extra current of closure, being in the opposite direction to the battery
current, diminishes the make induced current in the secondary circuit, while the
break extra current is cut off by the opening of the primary circuit, and therefore
has no effect on the induced current. The sharpness of the break effect is also
partly due to the fact that with the keys generally used the opening of the
primary circuit is more sudden than its closure.

5. To show the existence of the " extra " currents, remove the
secondary coil altogether and connect up the primary coil

17 2

18

EXPERIMENTAL PHYSIOLOGY

with a battery and keys in the way shown in fig. 25. Place the
electrodes on the tongue. Make and break the battery circuit by
closing and opening the key, k1. If this is done when the primary
coil is included in the circuit (i.e., with kz open as in the diagram)

Fio. 25. — EXPERIMENT FOR SHOWING EFFECT OF EXTRA CURRENT.

the stimulus is sharp owing to the " extra " currents, but if the coil is
shunted out by closing k2 the stimulus is hardly perceptible to the
tongue.

6. Instead of placing the simple key in the primary circuit place
it in a side circuit (fig. 26). On closing and opening the key. shocks
are still produced in the secondary circuit, although the current

PIG. 26. — DIAGRAM OF EXPERIMENT TO SHOW THE EFFECT OF CLOSING AND OPENING A SIDE
CIRCUIT TO PRIMARY COIL, k, KEY m SIDE CIRCUIT ; V , KEY IN SECONDARY CIRCUIT.

through the primary coil is not made and broken, but only strength-
ened and weakened. The make and break shocks in the secondary
coil are now more uniform, but are both weaker. This is the same
effect as is obtained for rapidly interrupted shocks by the use of the
Helmholtz wire (see p. 16).

7. Take the secondary coil out and place it across the direction of
the primary coil instead of in its usual position. The making and
breaking of the primary circuit now produce no effect on the secondary
circuit, but induced currents begin to show themselves if the secondary
coil is placed obliquely to the primary, and are strongest when the two

EXPERIMENTS ILLUSTRATING THE USE OF APPARATUS 19

coils are again parallel. This principle is embodied in Bowditch's
induction coil.

8. Connect up the battery with the terminals, t3, fi, of the in-
duction coil (as in fig. 23), introducing a simple key into the
circuit. Set the Neef's hammer in vibration. The electrodes from
the secondary coil are to be applied to the tongue, and the distance of
the secondary from the primary coil found at which the induced
shocks can just be felt. Determine that these are the break shocks
by raising and lowering the hammer by the hand, and thus slowly
making and breaking the primary circuit (the mercury key being
closed).

9. Detach one of the wires of the electrodes from the secondary
coil so that only one electrode is connected with that coil. Slide the
coil home. Pass a strong current through the primary coil and set
Neef's hammer going as in the last experiment. It will be found that
shocks are faintly felt by the tongue, although only the one electrode
is in connection with the secondary coil and the secondary circuit is
broken (unipolar induction).1 It is on account of this possibility of
stimulating through only one pole that a simple key is never used in
the secondary circuit, but always a short-circuiting key, which is
introduced in the manner shown in fig. 22. No shocks can pass to the
electrodes when the key is closed, since the coil is then short-circuited ;
only when the key is open are the shocks conducted to the electrodes.
On the other hand, in the primary or battery circuit a simple key is
always used ; were a short-circuiting key placed here the battery
would rapidly run down.

10. Connect up a battery with the induction coil, using Helm-
holtz's modification (fig. 24). As in experiment 8, find the distance
of the secondary from the primary coil at which the induced shocks
can just be felt on the tongue, and determine that the make and break
shocks are now nearly equal by raising and lowering the spring by the
hand. Both are markedly diminished.

1 The explanation of this is that the body acts as a condenser which becomes
charged and discharged through the electrode applied to the tongue.

CHAPTER IV

THE NERVE-MUSCLE PREPARATION

THE central nervous system of a frog is destroyed by cutting through the spinal
cord at the occipito-atlantoid ligament and passing a blanket pin into the skull
and down the cord. Notice that the muscles of the trunk and limbs are thrown

Cut pectoral girdle - "\C~J

Small intestine

Testicle.
Rectum.
- Bladder.

FIG. 27. — VISCERA. OP FROO. THE LIVER is SHOWN IN OUTLINE, AND THE
PARTS CONCEALED BY rr ARE INDICATED BY DOTTED LINES.

into contraction when the cord is being destroyed. Make a circular incision
round the trunk just below the upper limbs through the skin only, and, seizing
the skin covering the lower part, strip it off from both hind limbs. Lay the frog
on its back on a glass plate, and open the abdomen and thorax freely but care-
fully. Notice the viscera (fig. 27) — heart and lungs, liver, stomach, intestines,

20

THK NERVE-MUSCLE PREPARATION

21

ovaries and oviducts or testes, bladder. Cut through the lower end of the rectum
and through its attached mesentery. On raising it, two elongated red bodies —
the kidneys — are seen at the back of the abdomen, partly covering the nerves
which are passing down to the hind limbs. Remove the kidneys without touching
the nerves. Now hold the frog up by its legs so that the viscera hang towards the
head, and cut through the lower end of the vertebral column with strong scissors
so as to separate the fore part of the trunk and the viscera from the pelvis and
hind limbs. Lay the latter preparation on a clean glass plate or on a piece of
paraffined paper on the frog-cork. Note the several muscles which are seen on
the front and back of the lower limbs (figs. 28, 29). The gastrocnemius is gener-
ally used for experiments. Tie a thread round its tendon (tendo Achillis), and

Hiac ext.

Tensor fasc. lat.

Triceps fern.

1'yriformia.

Seruimembranosus. Iliofibula.

Peroneus.

Tibial ant. long.

Tendo Achillis.

I *i* /!KAiA

• Tars. ant.

FIG. 28. — MUSCLES OF FROG-LEG : DORSAL ASPECT (GUupp).

cut this away from the calcaneum. Holding it by the thread, tear the muscle
upwards away from the tibia, and sever this bone just below the knee.

Next bring to view the sciatic nerve. Separate the muscles at the back of
the thigh by the aid of two pairs of forceps, keeping to the mesial of the two
chief intermuscular septa, and the nerve will be seen, accompanied by the
femoral vessels. On no account touch the nerve, but separate the muscles from
it so as to expose it freely.

If only a short piece of nerve is required, a wet thread may be tied round the
uppermost end of the length of nerve displayed, and the nerve may be cut
across above the thread. Then, holding it up gently by the thread and passing
a pair of straight scissors below and parallel to the nerve, its branches to the
thigh muscles are successively severed, and the nerve is separated as far as the
back of the knee-joint. Notice that as each branch is snipped the muscles which
it supplies contract. Lay the nerve thus isolated upon the gastrocnemius muscle.
Then cut through the middle of the femur, and clear the attachments of the
• thigh muscles away from the lower end of that bone. You now have a prepara-

22

EXPERIMENTAL PHYSIOLOGY

tion consisting of the knee-joint with portions of the femur and tibia, the gastro-
cnemius muscle, and the sciatic nerve ; this is termed a muacle-nerve preparation.
For many experiments a longer nerve is needed. To obtain this the sciatic
nerve is to be exposed as before from behind, but not tied or cut; it should
indeed not be touched in its course by any instrument. Then seize the
urostyle with forceps, and cut it and the muscles attached to it entirely away
with scissors. The nerves previously seen behind the kidneys are now exposed
from the back ; they are continuous on each side with the corresponding sciatic
nerve. To isolate the nerve along its whole length, sever the attachment of
the ilium to the sacrum. Split the end of the spinal column longitudinally with
scissors, and, holding one-half with forceps, lift it up obliquely, but not at too

mac.

Tensor fasc lat.

Triceps femoris (cruralis).
Add. magn.

Ext. crur. brev.

Tibialis ant. long.

Tibialis ant. brev

Tars, ant

Gastrocnemios .
Tibialis posticus.

Int. iliac.
Add. long.
Sartorius.

Pectineus.
Eect. abd.
Add. magn.
Gracilis major.

Gracilis minor.

Crural bone (tibia and fibula).

Tendo AchUlis.

FIG. 29. — MUSCLES OF FROG-LEG : VENTRAL ASPECT (GAUPP).

sharp an angle, along with the nerves issuing from it to form the sciatic.
Gradually dissect out the nerve from above down as before described, snipping
the lateral branches with scissors (without touching the main nerve) until the
back of the knee is reached. Lay the long piece of nerve thus isolated upon the
gastrocnemius muscle, and, as before, cut through the middle of the femur after
clearing the attachments of the thigh-muscles away from its lower end ; you
now have a nerve-muscle preparation with long nerve. Place a piece of paper
impregnated with paraffin on the frog-cork, and lay the nerve out clear of the
muscle, fixing a pair of electrodes so that the nerve lies across them. Keep
both muscle and nerve — but especially the latter — wet with normal salt solution
or Ringer's solution.

With a nerve-muscle preparation thus obtained perform the
following experiments, which are, for the most part, similar to those
already performed upon the tongue. Note down all your results.

THE NERVE-MUSCLE PREPARATION

23

1. Excitation by galvanic current. — Determine that making or
breaking the circuit of a battery is a stimulus to the nerve, whereas
the passage of the current usually 1 produces no obvious effect. It
is proper to use non-polarisable electrodes wherever the current of
a galvanic battery is led through a preparation.

A simple form of battery is furnished by two wires, one of copper, the other
of iron or zinc. If these are placed at one end in contact with the moist nerve-
muscle preparation, and if the other ends are made to touch one another, the
muscle will contract, as in Galvani's original experiment.

Fleischl's rheonome is designed to show that not only a change of potential
but also the suddenness of the change is an important factor in stimulation
by a galvanic current. The rheonome consists of a bridge composed of two
curved pieces of zinc capable of being rotated about a raised centre. One end
of each piece has a terminal attached to it (upper terminals); the other end —
which should be amalgamated — dips into saturated solution of zinc sulphate
contained in a circular groove in the wooden base of the instrument. Wires

FIG. 30. — DIAGRAM OP FLEISCHL'S EHEONOME.

from a battery are brought to opposite sides of the groove and come into
connection with the zinc sulphate solution by amalgamated zinc terminals
(lower terminals). The upper terminals are brought into relation with a muscle-
nerve preparation by other wires, and when the battery circuit is closed part of its
current passes to the preparation, part is short-circuited through the zinc sul-
phate. The amount of short-circuiting depends upon the position of the rotating
bridge. Most current passes through the preparation when the ends of the
bridge are opposite the lower or battery terminals. On now rotating the bridge
this current is diminished, and it vanishes when the rotation has attained 90°
of the circle, gradually increasing again as this point is passed. If the rotation
is slow, there is no stimulation of the preparation, in spite of the variation in
amount of current; but if quick, the muscle-nerve responds to each movement of
the bridge.

2. Excitation by induced current ; Determination of excitability of
a nerve. — An induction shock is a stimulus, and the break induction
shock a far stronger stimulus than the make. Get the minimal
effect of each by sliding the secondary coil to the necessary

1 For exceptions see Chapter XI.

24

EXPERIMENTAL PHYSIOLOGY

distance from the primary, and make a note as to the respective
positions of the secondary coil. This gives a measure of the
excitability of the nerve. Its excitability to tetanisation (use the
Neef's hammer and the Helmholtz wire) is determined in the same
way.

•

3. Reaction of nerve and muscle to galvanic and faradic excitation.— It the
above experiment be tried with a nerve-muscle preparation and with nerve-less
muscle (the nerves within the muscle are paralysed by curari), it will be found
that the nerve will react to a weaker stimulus than the muscle when induction
shocks are employed ; but if the make and break of a galvanic circuit be used
as the stimulus, the muscle will respond to the weaker stimulus. Plain muscle
shows this even more strikingly.

4. Gotch's experiment. — Cooling a nerve causes it to react to galvanic and
faradic stimulation in the same way as muscle. The upper end of the nerve of
a nerve-muscle preparation is cooled by laying it on a tube through which ice-
cold water is passing ; the muscle itself must not be allowed to come anywhere
near the cold tube. If, now, the cooled part of the nerve be stimulated, it will
be found to be less sensitive to faradic and more sensitive to galvanic stimu-
lation than a part nearer the muscle which has not been cooled. Cooling the
nerve also diminishes the rate of conduction of nerve impulses along the cooled
portion (see p. 48).

5. Unipolar induction. — It is possible to stimulate the nerve when
it is connected by only one wire with the secondary coil ; hence the
necessity for using a short-circuit key to prevent unipolar induction
(seep. 19). It is best for this experiment to place the secondary coil
close to the primary and to make use of the automatic interrupter.

6. Excitation by condenser discharge. — The discharge of a condenser through a
nerve acts as a stimulus. Arrange the apparatus as shown in fig. 31, in which

PIG. 31.— STIMULATION OP NERVE BY CONDENSER DISCHARGE.

C is a condenser made by covering a sheet of glass with tinfoil on both sides.
The sheets of tinfoil are first connected with the battery for a few seconds, and
then, by turning the switch, are connected with the nerve, the battery being
cut off by the same movement.

THE NERVE-MUSCLE PREPARATION 25

7. Mechanical excitation. — The nerve (or muscle) can be stimulated
by mechanical means — e.g., by tapping it gently or by allowing
mercury to drop (upon a nerve) from a height of three or four inches.
The effect of a mechanical stimulus is seen whenever a nerve is cut
or pinched, but any severe injury abolishes its conducting functions.

8. Thermal excitation. — The nerve (or muscle) is stimulated if it
be touched with a hot wire.

9. Osmotic excitation. — It can be stimulated by osmosis, as by
placing wet salt or pure glycerine upon it. The salt and glycerine
act by abstracting water.

10. Excitation by drying. — Drying acts as a stimulus, especially
to the nerve. When a nerve begins to dry, its muscle twitches.1

Addition of water may also act as a stimulus, especially with muscle. If
distilled water be injected into the blood-vessels of an animal, all the muscles
are thrown into contraction ; this is, however, followed by paralysis. These
effects are at least in part due to the abstraction of lime salts from the muscle.

1 This twitching is a frequent source of puzzle to the beginner ; it is always a
sign that be has not been careful to keep the nerve moist with Ringer's fluid.

CHAPTER V

THE RECORDING OF MUSCULAR CONTRACTIONS

MUSCULAR contractions are recorded by a lever upon a metal drum
covered with highly glazed paper, and caused to revolve by clockwork,
or some other form of motor, at a regular rate. With a drum of six
inches diameter one revolution in a second is a convenient speed.
The glazed paper is blackened by holding a gas flame containing
benzole vapour against it while the drum is revolving. The paper
must fit evenly and tightly, or it will become burnt.

The contraction of the muscle is amplified by the lever (myo-
graph lever), which may be straight (fig. 32), but which may also
conveniently take the crank form (fig. 33). In this case the ful-
crum of the lever is at the end of a cork plate, to which the muscle
is fastened by a pin passed through the knee-joint,1 the tendon is
attached to the short arm of the lever by means of a thread. The
cork plate must be covered with paraffined paper. The lever should
be weighted with a 20- or 30-gram weight, attached to it close to
the fulcrum, and should be so adjusted as to be nearly horizontal,
but with the end a little lower than the fulcrum.2 The muscle is

1 In the Keith-Lucas crank myograph the muscle-nerve preparation is
enclosed in a vulcanite trough ; the muscle is kept immersed in Ringer's
fluid ; the bony attachment of the muscle is fixed by a pin, and electrodes are
introduced through holes in the vulcanite. The whole is covered by a glass
plate to prevent evaporation.

2 The following points must be attended to in every graphic record in which
a lever is employed: — (1) On no account must the lever point be directed
obliquely upwards : the result of doing this is to distort the curves which are
recorded ; (2) the lever must be directed tangentially to the curve of the drum
with the point of the lever slightly curved in towards the surface of the drum ;

(3) the myograph stand, which carries the cork plate and lever upon a vertical
rod capable of being turned on its axis, must always be furnished with a stop,
so that the point of the lever can always be brought against the drum with
exactly the same amount of pressure as that with which it is originally adjusted ;

(4) the myograph stand must always be on the right-hand side of the drum,
so that the lever extends from right to left, and the drum itself must always be
arranged to move in the direction of the hands of a watch, never in the reverse
direction.

26

THE RECORDING OF MUSCULAR CONTRACTIONS

27

kept stretched by the weight, so that the connecting thread is taut.
Under these circumstances the muscle is said to be free-weighted.

There should always be a screw near the fulcrum which is intended to support
the lever in certain experiments. The screw can be adjusted so that the muscle
and thread are not fully stretched, and only become so after the muscle has
begun to contract ; the muscle is then described as after-loaded.

The simple muscle-curve. — Arrange the drum in the primary cir-
cuit of the induction coil (in the manner shown in fig. 33), so that, as
the drum revolves, a pin (c) which projects from it, by just touching a

PIG. 32. — MUSCLE-NERVE PREPARATION SUSPENDED AND ATTACHED TO A STRAIGHT
MYOGRAPH LEVER, a. AFTER-LOADING SCREW ; 6, ELECTRODES.

needle fixed outside, instantaneously makes and breaks the circuit at
each revolution. A pair of electrodes is either brought in contact with
the muscle itself or the nerve (ri) is laid upon the electrodes, which are
connected through a short-circuit key with the secondary coil. The
secondary coil is placed at such a distance from the primary that the
" make " shock is insufficiently strong to act ; the " break " shock
therefore alone furnishes the stimulus.1 Before the lever is allowed
actually to touch the cylinder, determine that the apparatus is all in
working order, and at what distance of the secondary from the primary

1 It is possible to employ a single induction shock as the stimulus by intro-
ducing a break key into the primary circuit and making the pin open this key
as the drum revolves.

28

EXPERIMENTAL PHYSIOLOGY

the break shock is effective in causing a full contraction when the
drum is made to revolve. Do not allow the muscle to be fatigued by
many excitations before recording its contraction.

Now bring the lever point so as lightly to touch the blackened
paper, using the stop of the myograph stand to prevent the point
pressing too hard against the paper. When the stop is used in this.

THE RECORDING OF MUSCULAR CONTRACTIONS 29

way the lever point can be removed at any time from the paper
and brought back again so as to press with exactly the same force as
before ; it is absolutely essential to make use of the stop in all recording
experiments in which comparisons of different curves upon the same
surface have to be made.

Start the drum revolving, but keep the short-circuit key (&') closed
so that no stimulus reaches the nerve ; the lever point will describe a
horizontal line (abscissa). Whilst the drum is still revolving open the
short-circuit key, but close it again the instant the muscle has con-
tracted ; immediately afterwards remove the lever point from the
drum, before this has had time to perform another revolution. A
simple muscle curve will thus be described.

To mark the point of stimulation, move the drum slowly round by
hand until the projecting pin just touches the needle where contact is
made (as in the diagram, fig. 33) ; bring the lever point against the
smoked surface as far as the stop will allow, and raise the lever about
half an inch by the finger. The distance between this mark, which
indicates the moment when the stimulus was put into the nerve, and
the rise of the curve, which indicates the commencement of the con-
traction of the muscle, gives the period of latent stimulation. To
measure this period, as well as the duration of the contraction and
relaxation of the muscle, remove the lever point from the smoked
surface, set the drum revolving at the same rate as before, and allow
a tuning-fork of known rate, e.g., one hundred vibrations per second,
to record its waves just below the abscissa of the muscle curve, putting
the bristle, which is attached to the tuning-fork, during a single
revolution only against the drum. Cut through the paper without
scoring the surface of the drum. Lay it on the table, and write
upon it date and description. Then pass it through the varnishing
trough, and hang it up to dry. When dry, cut out the part of the
tracing which is required.

Effect of heating and cooling the muscle upon its contraction.—
The same nerve-muscle preparation may be used, the apparatus being
arranged exactly as in the last experiment. Mark on a new abscissa
the point of stimulation. Then take the following curves on this
abscissa :—

1. A simple muscle curve at the room temperature.

2. A simple curve after warming the muscle by dropping Ringer's
solution, warmed to about 30° C., upon the muscle.

3. A simple curve after cooling the muscle by dropping upon it
ice-cold Ringer.

30

EXPERIMENTAL PHYSIOLOGY

Finally, take a tuning-fork tracing below the abscissa.
Notice the effect of heat and cold respectively upon the period of
latency and upon the amount and duration of the contraction.

Isometric contraction. — If the contracting muscle is prevented from shorten-
ing, or allowed only to shorten to so small an extent so that it practically re-
mains of the same length throughout, the contraction is said to be isometric.
It is recorded by attaching the muscle very close to the fulcrum of the muscle
lever, which is held down by a strong spiral spring (fig. 34) instead of by a weight.
All the other arrangements of the experiment are the same as with the ordinary
method where the muscle is free to shorten and raise a weight ; its tension
being constant (isotonic contraction).

FIG. 34. — METHOD OP STUDYING ISOMETRIC CONTRACTION, sp. SPIRAL SPRING ;

s. SCREW FOR REGULATING ITS TENSION.

Action of drugs on muscular contraction. — The hyoglossus muscles may be
used. Cut away the whole of the lower jaw, along with the tongue and hyoid
bone. Tie a thread to the tongue near its tip and another near its fixed ex-
tremity, and cut this away from the hyoid. The tongue thus separated includes
the hyoglossus muscles, which run through it from the hyoid bone, and the pre-
paration can be used in the same way as the gastrocnemius muscle, the hyoid end
being fixed by a pin to the myograph cork and the tip connected by its thread
with the myograph lever. A smaller weight must be used than in the case of
the gastrocnemius, since the hyoglossus muscles are far weaker. Probably the
weight of the lever alone will be sufficient. Insert pin electrodes on either side
near the fixed end so that induction shocks will stimulate all the fibres of both
hyoglossus muscles.

Veratrin. — Arrange the apparatus to take a muscle curve in the

THE RECORDING OF MUSCULAR CONTRACTIONS 31

usual way. If the speed of the drum is the same as before (one
revolution per second), the curve is more prolonged than that of the
gastrocnernius, for the contraction of the hyoglossus is slower than
that of the gastrocnernius. It is well, however, in investigating the
action of veratrin to use a slow rate of cylinder, since this drug enor-
mously delays the relaxation of muscle. The cylinder therefore
should be arranged to revolve once in about ten seconds.

A normal muscle curve is first described, the point of stimulation
being marked in the usual way. Then inject with a hypodermic
syringe a drop or two of veratrin acetate solution (1 in 300) under the
mucous membrane of the tongue, so that the drug is brought into
contact with the fibres of the hyoglossi. After three minutes take
another muscle curve. Describe a tuning-fork tracing below the
abscissa. If the preparation is excited repeatedly, it will be found
that the contractions lose their prolonged character, which, however,
returns after a period of rest.

This method can be used for investigating the action of other drugs upon
muscular contraction.

CHAPTER VI

THE NERVELESS MUSCLE

Action of curari. — The brain of a frog is destroyed by passing a
sharp splinter of wood through the occipital foramen after cutting
through the skin and occipito-atlantoid ligament. The blood-vessels
of one leg are ligatured, care being taken to avoid injuring the accom-
panying sciatic nerve. Or the leg can be tightly tied round with a
tape so as to stop the circulation within it. A drop or two of one per
cent, solution of curari is now injected under the skin of the back.
After a short time the drug will have penetrated to all parts of the
body except the ligatured leg.1 The following observations and
experiments may then be made :—

1. Notice that all the muscles are paralysed except those of the
ligatured limb.

2. On tapping any of the paralysed parts the foot on the ligatured
side is moved — i.e., the conducting power of the nerves both sensory
and motor, and the reflex functions of the spinal cord are not
abolished.

3. Strip the skin off both legs and isolate both sets of sciatic
nerves at the back of the abdomen. Tie their upper ends and cut
them away from the vertebral column. Excite both sets of nerves
high up, placing them upon the same electrodes and observe the differ-
ence of effect. Excitation of the nerve of the limb which has been
exposed to the poison produces no contraction of its muscles ; ex-
citation of the nerve of the ligatiired limb produces the usual effect.
Now stimulate the muscles of the two limbs, applying the electrodes
directly to them. The muscles of the poisoned lirnb react like those
of the normal limb, but the liminal stimulation 2 is greater. Deter-

1 This method is applicable to the study of the action of drugs in general
on nerves and muscles.

2 The stimulation which is only just effective, i.e. the least stimulation
which is responded to.

32

THE NERVELESS MUSCLE 33

mine at what distance of the secondary coil from the primary a
response is obtained in each case.

The conclusion is that neither the nerve fibres, sensory and motor,
nor the nerve centres, nor the muscular fibres are affected, but that
the poison has produced paralysis by severing the connexion between
motor nerve fibres and muscle fibres, probably at the end-plates.

The paralysing action of curari can also be shown by keeping a muscle-nerve
preparation in Ringer's solution to which a little curari solution has been added.
It will be found that after a time the muscle will cease to respond to stimulation
of its nerve, although it will contract readily if the muscle itself is stimulated.
As a control, another preparation may be taken, and its nerve alone placed in
the same solution during the same period, the muscle being supported just above
the level of the fluid. This preparation will respond to every stimulation of its
nerve.

It is best to use a sartorius muscle-nerve preparation for this experiment on
account of the length of time necessary for the curari to penetrate the gastro-
cnemius.

For the mode of preparing the sartorius — the nerve of which must be kept
in continuity with the main trunk — see p. 41.

Muscle wave. — Separate from the remaining thigh muscles the
adductor muscles (gracilis and semimembranosus ; see figs. 28, 29)
of a frog which has been poisoned with curari to eliminate the
intramuscular nerves. Leave the attachments to the tibia. Cut
this bone through just below these attachments, and also sever the
tibia from the femur at the knee joint. It is then easy to complete
the separation of the muscles up to their iliac attachments ; a small
fragment of the ilium may be cut away and removed along with them.
Tie a thread to the tibial and another to the iliac attachment, stretch
the muscular mass lightly between these threads, and fasten to the
cork by a couple of pins at one end and a pair of pin electrodes at
the other end of the muscle. Allow two long light levers (which can
be made of straws, working in simple brass holders capable of being
pinned to the cork) to rest upon the muscle near each end close
to their fulcra, and let the points of the levers write lightly on
the drum, one exactly above the other (fig. 35). When the muscle
contracts, its swelling raises first the lever nearer to the electrodes,
and later the one at the further end. The movements of the levers
are recorded upon the drum, and curves are obtained of the swelling
of the muscle during its contraction in the same manner as the
curves of shortening of the gastrocnemius were obtained in previous
experiments. The drum must move at a fast rate, and the levers
should be directed obliquely downwards : much more so than in the
ordinary method.

Connect the pair of pin-electrodes with a du Bois-Eeymond key

3

34

EXPERIMENTAL PHYSIOLOGY

in the secondary circuit. Describe an abscissa, and mark the
point of stimulation as in previous experiments by raising the end
of each lever by the hand when the projecting pin on the drum just
touches the vertical needle (see p. 29), making use of the slop. Then
take the two tracings of the contraction of the muscle, letting the
drum revolve once only, and removing the levers the instant the
curves are completed. The difference of latency of the two curves

PIG. 35. — DIAGRAM OP AEBT'S EXPERIMENT FOR RECORDING THE MUSCLE WAVE, a, Z>, LIGHT
STRAW LEVERS RESTING' ON THE MUSCLE, WHICH is CURARIZED ; k, V, KEYS IN PRIMARY
AND SECONDARY CIRCUITS.

represents the time which it has taken for the wave of contraction
to pass along the length of the fibres which intervene between the
two places on which the levers rest. Take a tuning-fork tracing, and
measure this time, and from it and the length of muscle traversed by
the wave (measure with compasses) calculate the rate of propaga-
tion of the muscle wave per second.

It is essential for the success of this experiment that the muscles used should
have most of their fibres running longitudinally and parallel with one another.
If very large frogs are obtainable the two sartorius muscles may be used with
advantage instead of the adductor preparation described.

THE NERVELESS MUSCLE

36

A method of obtaining the curve of swelling of a contracting muscle which
is better adapted for mammalian muscle is to use the pince myographique or
myographic forceps of Marey (fig. 36, F). The muscle is grasped by this, and

FIG. 36. — MYOGRAPHIC FORCEPS OP MAREY. F, FORCEPS FOR GRASPING THE MUSCLE THE CON-
TRACTION OP WHICH IS TO BE RECORDED. THE TWO BLADES OP THE FORCEPS ARE DRAWN TO-
GETHER BY AN INDIA-RUBBER BAND. T, RECEIVING TAMBOUR. THE AIR IN WHICH is COMPRESSED
BY THE SWELLIN-G OP THE MUSCLE. AND FROM WHICH THE PRESSURE is TRANSMITTED BY AN
INDIA-RUBBER TUBE TO T', THE RECORDING TAMBOUR, THE LEVER OF WHICH WRITES ON
A REVOLVING DRUM.

its contraction affects a tambour (T) which is connected by rubber tubing
to another tambour (T'), writing upon the drum. The muscle is stimulated
(1) at the point of application of the forceps, and (2) at some distance from the
forceps. The difference of time between the two resulting curves is measured,
and the rate of passage of the muscle wave calculated therefrom.

CHAPTER VII

EFFECT OF SUCCESSIVE STIMULI UPON A MUSCLE-NERVE

PREPARATION

Summation. — Make a muscle-nerve preparation and place the
nerve upon electrodes connected through a short-circuit key with the
secondary coil. Include the Neef hammer in the primary circuit, as
in fig. 23. Shift the secondary coil to such a distance from the primary
coil that a single-break induction shock, made by moving the Neef
hammer by hand, just fails to produce a contraction of the muscle.
The stimulation is therefore subliminal. Now allow the Neef hammer
to vibrate so that a succession of stimuli of the same strength act
upon the nerve. The muscle will contract, owing to the summation
of the effects of the repeated stimulations of its nerve, although indi-
vidually these stimulations were ineffective.

Superposition. — Arrange the muscle-nerve preparation on the
myograph and connect the drum in the primary circuit in the manner
employed to record a simple muscle curve (p. 27 and fig. 33). Place
the secondary coil at such a distance from the primary that the ex-
citation produced by a single pin projecting from its circumference
and striking the needle in its revolution produces a maximal effect ;
describe a normal muscle curve in the usual way. Then insert a
second pin at varying intervals so that the excitation which it produces
will affect the nerve at different intervals after the first excitation ;
viz., (a) during the rise of the first curve, (6) near the top of the first
curve, (c) during the decline of the first curve. Take these double
tracings at different levels of the paper, each one on its own abscissa.

Effect of several successive stimuli ; tetanus. — For studying the
effect on a nerve-muscle preparation of a rapid succession of stimuli a
vibrating steel reed is used to make or break the primary circuit of
the induction coil by allowing a wire attached to its end to dip into

and out of a cup of mercury. The rate of vibration of the reed

36

EFFECT OF STIMULI UPON A MUSCLE-NERVE PREPARATION 37

depends upon its length, which can be varied by clamping it at differ-
ent places ; it is marked at points for producing vibrations of ten,
fifteen, twenty, and thirty per second (fig. 37). The secondary coil
should be placed at such a distance from the primary that only the
break shock is effective. The drum should revolve at moderate
speed (one revolution in ten seconds).

Attach the muscle to the lever of the myograph in the usual way ;
place the nerve upon the electrodes ; set the drum revolving and
bring the lever point against it, using the stop ; set the reed vibrating ;
open the key in the secondary circuit for about a second ; take the

PIG. 37. — EXPERIMENT TO INVESTIGATE THE GENESIS OP TETANUS. a, FLAT STEEL SPRING
MARKED AT INTERVALS WITH THE NUMBER OP VIBRATIONS CORRESPONDING TO CERTAIN LENGTHS

OP THE SPRING ; 6, MERCURY CUP INTO AND OUT OP WHICH A PLATINUM WIRE ATTACHED TO THE
SPRING DIPS.

lever point away from the drum. A tracing is to be taken in this way
at each of the above rates, each tracing on its own abscissa ; add a
time marking.

Record of voluntary contraction. — A voluntary muscular contrac-
tion of the finger-muscles may be recorded by resting the hand across
the myograph plate and tying a thread to the abducted forefinger,
the other end of the thread being attached to the short arm of the
lever ; this is to be held down by a heavy weight or thick elastic band.
On adducting the finger the lever is raised, and a curve is described
on the moving drum which bears a close resemblance to an incomplete
and somewhat irregular tetanus produced by ten or twelve stimula-
tions per second.

38 EXPERIMENTAL PHYSIOLOGY

It must not be concluded that this represents the rate of the successive
individual contractions which fuse to form the voluntary contractions, for it
has been shown by photographic records of the capillary electrometer (see
p. 49) that in a voluntary contraction there are not less than fifty electrical
changes per second, and this probably also represents the number of mechanical
changes -which succeed one another in a voluntary contraction. The causation
of the waves of ten or twelve per second is not fully understood.

Another method of obtaining the curve of a voluntary contraction
is by the use of a transmission myograph, which consists of two tam-
bours connected by india rubber tubing. The first or receiving
tambour (which may be represented by an ordinary Marey's cardio-
graph ; see fig. 63) is fixed against the masseter muscle ; when this
muscle is made to contract voluntarily, its movements are com-
municated to the air within the cardiograph, and the differences
of pressure produced are transmitted to the second or recording
tambour, which writes against a revolving drum.

Sound of a voluntary contracting muscle. — Place the tips of the middle
fingsrs in the ears, and contract the muscles of the arm strongly. A rumbling
sound is heard,j,which is caused by the vibration of the contracting fibres. The
sound actually heard is modified by the resonance of the drum of the ear, and
cannot be taken to indicate the rhythm of contraction.

CHAPTER VIII

WORK OF MUSCLE J EXTENSIBILITY OF MUSCLE

THE experiments to be performed on these subjects are recorded
upon a stationary drum which must be moved onwards for about
five millimeters by hand after each record.

Make a muscle preparation, preferably the sartorius (see end of
chapter), place it on the myograph, and arrange that it shall be
stimulated, either directly or through its nerve, by induction shocks.
Arrange a mercury key in the primary circuit (which is not to include
the drum) and a short-circuit key in the secondary circuit. It is best
in these experiments to use tetanic stimuli furnished by the Neef's
hammer ; the Helmholtz modification should be employed (fig. 24).
The lever should have a light scale pan suspended from it ; such a scale
pan can readily be made from the lid of a pill-box. Determine :—

1. The effect upon the lift, the weight being constant (say about
thirty grams), of a gradual increase of the strength of the stimulus
from minimal to maximal.

Note down on the curve the distances of the secondary coil at which the
results recorded are obtained.

2. The amount of work which the muscle performs in lifting
different weights, the stimulus being constant and maximal and the
muscle free- weighted. Beginning with the weight of the scale pan
alone, weights are gradually added, and the muscle being stimulated,
an ordinate is described for each additional weight. The work of the
muscle is estimated as weight x height.

Note down the weight which corresponds with each ordinate and the height
of the ordinate. The exact height to which the weight is raised is calculated
by dividing the height of each ordinate by the magnifying extent of the lever.

Another result is yielded in this experiment ; viz. the effect of the gradually
increasing weights in producing extension of muscle in the resting and contracted
conditions respectively. For it is obvious that the lowermost point of any
ordinate described by the muscle represents the length to which the resting

39

40

EXPERIMENTAL PHYSIOLOGY

muscle is extended by the particular weight, and the top of the ordinate the
length to which the muscle when contracted is extended by the same weight.
If the ordinates are at regular distances apart, a line joining their lowermost
ends gives the curve of extension of the resting muscle, and a line joining the
tops of the ordinates the curves of extension of the contracting muscle. Further,
if the weights are removed in succession and ordinates are again described after
each such removal, curves of recovery from extension — i.e. of retraction — can
be obtained. This experiment can be conveniently performed with the sartorius,
large shot serving as the weights.

I

FIQ. 38. — EXPERIMENT FOR INVESTIGATING THE EFFECT OF HEAT ON THE EXTENSIBILITY

OF MUSCLE.

3. The effect of after-loading (p. 27). Take a series of contraction
ordinates, using a maximal stimulus and a constant weight (say
about thirty grams). Begin with the muscle free- weighted, and by
using the screw stop beneath the lever raise the latter so that the
muscle and connecting thread are somewhat slackened. Under these
circumstances the muscle will not begin to raise the weight until its
contraction has proceeded to a certain extent ; this shows the effect

WORK OF MUSCLE; EXTENSIBILITY OF MUSCLE

41

of after-loading. Describe a series of contraction ordinates with a
gradual increase of after-load. Calculate the amount of work done
under these conditions, and compare with that performed by the free-
weighted muscle.

Effect of heat on the extensibility Of muscle. — Take a sartorius muscle and fix
one end to a heavy disc of metal provided with a hook : place the disc and muscle
in a beaker of Ranger's solution (fig. 38). Attach the other end of the muscle by
means of a thread to the short arm of a lightly weighted lever of the first order, so
that when the muscle shortens the long arm of the lever is raised. Let the point
of the lever write on a very slowly moving drum. Arrange a small gas or spirit
flame under the beaker and slowly heat the Ringer's solution, which shouldfbe
provided with a thermometer. Notice the effect of the gradual rise of tempera-
ture upon the length of the muscle as recorded
by the lever. Note especially that at certain
temperatures — which correspond with the coagu-
lation temperatures of the muscle proteins — there
is a marked shortening. (The final contraction
corresponds with the coagulation temperature of
the collagenous matter, i.e. of the connective
tissue, and is not muscular.) After no further
shortening is produced, remove the flame and
allow the Ringer to cool. There is no reversal of
the contraction of the muscle, which remains stiff
and completely coagulated (heat rigor). If the
muscle is cut and tested with litmus paper it will
be found to be acid.

During contraction a muscle does not alter in
volume. — Take a wide-mouthed bottle with well-
fitting paraffined cork (fig. 39). Through the cork
are passed (a) a glass tube drawn out above the
cork to a capillary size ; (6) two copper wires of
unequal length coiled spirally, and each ending
below in a sharp hook : above each terminates in
a loop close to the cork. Fill the bottle to the
rim with Ringer's solution. Attach a fresh muscle
by its two ends to the hooks, lower into the

bottle, and press the cork in securely : the fluid FIG- 39.— EXPERIMENT TO DETER-
should completely fill the bottle and capillary to
the exclusion of air-bubbles. Draw a little of the
fluid out of the capillary by filter paper, and mark
the level at which the fluid then stands. Hook

wires from the secondary coil to the loops above mentioned, and tetanise the
muscle. If there were a diminution of volume the level of the water in the
capillary would fall.

Preparation of the sartorius muscle. — The thin, flat sartorius is seen crossing
obliquely over the front of the thigh. It is readily isolated by tying a thread
round its tendinous attachment to the tibia, cutting this attachment away from
the bone, raising the lower end by the aid of the thread, and snipping through
the fascia on either side of the muscle, thus separating it right up to its iliac
attachment. Notice the twitch which occurs when the nerve, which enters
the under surface about its middle, is cut through. The muscle may be left
attached to the ilium, or its bony attachment may be cut away with it and the
muscle thus completely isolated. Its uppermost part contains no nerve fibres,
and can be used to show that, independently of nerve, muscle responds to all
forms of stimulation (electrical, mechanical, thermal, and osmotic).

MINE IP A MUSCLE ALTERS IN
VOLUME DURING CONTRACTION.
a, MUSCLE IN RINGER SOLUTION;
6, CAPILLARY.

CHAPTER IX

FATIGUE OF MUSCLE AND NERVE

Effects of fatigue on muscle : (a) On the form of the muscle curve.-

Take a nerve-muscle preparation and fit it up as for recording the
simple muscle curve (p. 27). Make an abscissa, and mark, as usual,
upon it the point of stimulation. Take a normal curve with the
muscle free-weighted. Remove the writing point from the drum,
which is then allowed to revolve continuously and to stimulate the
muscle with each revolution. After fifty of such excitations without
record, apply the lever point again to the drum (making use, of course,
of the stop), and let the muscle describe another curve at the same
place as the first. Remove the writing point again for the duration
of fifty excitations, and repeat the above procedure, and so on a
number of times until the fatigue curves are pronounced. Notice
the effects of fatigue upon muscle, in prolonging the latency
period, diminishing the amount and slowing the course of its con-
traction, and greatly delaying, and at length even preventing, its
relaxation.

A fatigue curve or series of curves can also be obtained by allowing the lever
point to remain in contact with the cylinder during the whole of the experiment,
and thus recording every contraction ; but the individual curves in a tracing so
obtained are very numerous, and tend to obscure one another.

(&) On the extent of contraction. — The effect of fatigue upon the
extent of contraction is best recorded upon a stationary drum,
moved by hand about half a millimeter after each excitation, or on a
very slowly moving drum ; the extent of the contraction is shown by
the ordinates described by the lever. Use the slowest rate of move-
ment of the drum (1 mm. per second or less), and arrange the primary
circuit so that it is made and broken about every half-second. This
can be done either by closing and opening a key by the hand, or
by allowing a metallic bridge, actuated mechanically (e.g. by a

42

FATIGUE OF MUSCLE AND NERVE 43

metronome), to close and open a gap between two mercury cups
in the circuit. Use maximal stimuli. Keep the point of the lever
—which must be free-weighted — against the smoked paper, and
record every contraction. In this way a continuous fatigue curve
is obtained, exhibiting the effect of fatigue, not only in the extent of
contraction but also on the extensibility of the muscle both in rest
and in contraction. Notice the " staircase " (gradual rise of the
ordinates) at the beginning of the curve and the " contracture "
(permanent contraction remainder) near its termination. Carry the
experiment to complete exhaustion — i.e., until the stimuli produce no
further perceptible effect. Then allow the preparation to rest,
keeping it moist with Ringer's solution. After 15 or 20 minutes
again test the effect of a stimulus. Notice that there is a certain
amount of recovery from the fatigue, even in a preparation such as
this in which no blood is circulating. In muscle in which the circula-
tion is maintained fatigue comes on more slowly and is more rapidly
recovered from, since the circulating blood removes the fatigue
products.

Reaction of the fatigued muscle. — Cut across a muscle which is completely
fatigued, and apply blue litmus paper to it. Notice that the paper is reddened
(production of acid fatigue products). Compare the reaction with that of a
piece of fresh, unfatigued muscle. Muscle which has died and passed into
rigor — whether natural or the effect of heat (see p. 41) — is also acid.

Onset of the fatigue in a muscle-nerve preparation : Bernstein's
experiment. — Arrange an experiment in the manner shown in the
diagram (fig. 40). Dissect out both nerve-muscle preparations of a
frog and place both nerves near the spinal cord on a single pair of elec-
trodes connected through a short-circuit key with the secondary coil.
Another pair of electrodes — which should be non-polarisable (p. 7)—
is connected with one of the nerves in such a manner that the current
furnished by three Daniell cells (shown below in the diagram)
can be led into the nerve in an ascending direction. When the
mercury key of this circuit is closed the constant current from the
Daniell cells blocks the nerve, and the nerve impulses generated by
the induction shocks fail to pass to the muscle. Stimulate both nerves
by induction shocks. The muscle the nerve of which is free to conduct
is speedily fatigued : the other one shows no signs of contraction ;
on removing the block by opening the mercury key it at once
responds to the stimuli, and its contractions show no evidence of
fatigue even after long faradisation of its nerve.

Fatigue in voluntary contraction. — This is investigated by the

44

EXPERIMENTAL PHYSIOLOGY

ergograph, the muscles of the fingers being fatigued by causing them to
repeatedly raise a heavy weight or repeatedly deflect a strong spring.

PIG. 40. — DIAGRAM OP BERNSTEIN'S EXPERIMENT TO ILLUSTRATE THE BLOCKING EFFECT OF A
CONSTANT CURRENT UPON CONDUCTION OF NERVE-IMPULSES.

The extent of the contractions is recorded upon a very slowly
revolving drum, and a fatigue curve or ergogram — which shows

FIG. 41. — DIAGRAM OF Mosso's ERGOGRAPH FOR THE INVESTIGATION OF FATIGUE

IN THE HUMAN SUBJECT.

individual peculiarities — is thereby produced in the same manner
as with the frog muscle-nerve preparation (p. 42, (6)).

FATIGUE OF MUSCLE AND NERVE 45

In Mosso's ergograph (fig. 41) the record is made upon a horizontal drum ;
in Waller's and Porter's modifications the drum is vertical.

In the case of voluntary contractions the result is complicated by the fact
that fatigue of nerve-cells in the central nervous system occurs before that
either of the muscle itself or of the nerve endings in the muscle. This fact can
be shown by direct faradic stimulation of the median nerve (or of the finger
muscles) after the fatigue curve is complete. It is found that the muscle can
still be made to contract by such peripherally applied stimuli.

CHAPTER X

CONDUCTION IN NERVE

Conduction of nerve-impulses may take place in both directions :
Kiihne's experiment. — Remove the gracilis with part of its entering
nerve ; lay it on a glass plate, with its inner surface uppermost. The
nerve is seen to give branches upwards and downwards ; as a matter
of fact each nerve fibre divides into two branches, one for the upper
and the other for the lower part of the muscle, which has a tendinous
intersection obliquely across its middle. The middle part of the
muscle can be entirely cut through here without injuring these
nerves, and the two parts of the muscle will then only be united by
the forked nerves.

If the ends of the nerves in either of the pieces of the muscle are
stimulated, whether electrically, osmotically (salt), or mechanically
(by snipping with scissors), both pieces contract.

Rate of transmission of nerve impulse. — Make a nerve-muscle
preparation in the usual way ; fix it upon the myograph, and lay the
nerve out upon two pairs of electrodes, one placed as near the muscle
as possible, the other close to the vertebral column. With a large
frog nearly two inches will intervene between the two. Place a
commutator without cross wires in the secondary circuit, and arrange
so that by moving the bridge of the commutator the induction shocks
can be switched on to one or other pair of electrodes. The drum is
to be included in the primary circuit, and a short-circuit key in the
secondary (fig. 42).

Two muscle curves are now successively taken with a fast rate of
cylinder and a maximal stimulus. The stimulus is applied to the nerve,
first, close to the muscle, and, second, close to the vertebral column.
The muscle curves are both taken in exactly the same way, and with
exactly the same precautions as to the use of the stop, etc., detailed

in Chapter III., and both curves are to be traced upon the one abscissa,

46

CONDUCTION IN NERVE

47

a time tracing being written beneath this. It will be found that the
curves are not quite coincident, but that one succeeds the other by a

very small interval. This interval represents the time occupied by
the transmission of the nerve impulse along the length of nerve
between the two pairs of electrodes.

48

EXPERIMENTAL PHYSIOLOGY

The interval is relatively small compared with the total latency period of
the muscle-nerve preparation. It can be rendered more evident if the nerve (not
the muscle) be cooled (p. 24). To measure it accurately a longer nerve and faster
rate of movement must be taken. This is obtained by the use of the pendulum
myograph, upon which the contraction of the human thumb muscles is recorded.
The electrodes used consist of wash-leather pads soaked with strong salt solution.
One electrode, large and flat, is fixed against the skin of the upper part of the
back, the other smaller one being applied respectively over the median nerve
at the elbow and over the brachial plexus above the clavicle ; the length of
nerve between these points is about 12 inches. The muscle-contraction in this
case is recorded by means of two tambours or by the pince myographique (p. 35).

Effect of various agencies on nerve-conduction : blocking of
nerve by current ; carbonic acid ; ether vapour ; chloroform.— Take

a nerve-muscle preparation and lay the nerve across and partly
imbedded in a ring of putty or soft modelling clay placed upon a glass
slide, to which a tube is cemented so that a current of C02 can be

FIG. 43. — EFFECT OF OAEBON DIOXIDE ON CONDUCTION IN NERVE.

conducted over the nerve. A cover glass is placed upon the ring :
the end of the nerve projects beyond this and rests upon a pair of
electrodes (fig. 43).

Find the minimal stimulus which will produce contraction of the
muscle ; then pass a current of C02 over the intervening nerve, and
notice its effect in blocking the nerve-impulse. Remove the C02 by
a current of air, and repeat the observation.

Other experiments may subsequently be made with ether vapour
and chloroform vapour instead of C02. It will be found that ether
acts like C02, but more powerfully. Chloroform vapour is more
powerful than ether ; and after a short exposure to it the nerve
does not recover its power of conduction on readmitting air ; it
has, in fact, been killed.

Blocking by a galvanic current. — The blocking effect of a constant current
has been made use of in Bernstein's experiment on fatigue (p. 43). To exhibit

CONDUCTION IN NERVE 49

it graphically, take a muscle-nerve preparation with long nerve and attach the
muscle to the myograph lever in the usual manner, so that its contractions may
be recorded upon a slowly moving drum. Apply stimulating electrodes from
the secondary coil to the part of the nerve near the vertebral column, using the
Neef's hammer (with Helmholtz wire) for tetanisation. Apply a pair of non-
polarisable electrodes connected through a mercury key with a 3-cell Daniell
battery, arranged so that the current can be passed up the nerve (polarising
circuit). Take a tracing of the tetanised muscle, and whilst this is progressing
close the polarising circuit. The tetanus at once ceases, to be renewed on again
opening that circuit, and so on repeatedly.

CHAPTER XI

CONDITIONS OF EXCITATION OF NERVE AND MUSCLE BY THE

GALVANIC CURRENT

THE passage of a galvanic current through a nerve or muscle produces secondary
polarisation of these tissues, caused by the accumulation of positive and negative
ions at or near the poles of the constant current. This polarisation is accom-
panied by certain physiological changes, the tissue being more excitable in the
neighbourhood of the negative pole or kathode, and less excitable in the neigh-
bourhood of the positive pole or anode. These effects — both physical and
physiological — spread for some distance beyond the actual poles. And not only
is the tissue rendered more excitable by the kathode, but this itself sets up
excitation, which, in the case of a muscle, may cause its contraction not only
at the moment of closure, but during the whole time of passage of the current.
On breaking the circuit the part of the nerve which was more excitable
during the passage of the current becomes instantaneously less so than the rest
(physiological rebound). On the other hand, the presence of the anode of a
constant current not only renders the tissue less excitable whilst the current is
passing, but on breaking the circuit there is again a rebound ; the part which

was the less excitable becom-
ing the more excitable ; this
passage from less to greater
excitability again acts as a
stimulus. Hence, when a con-
stant current is sent through
a nerve or muscle, there is
excitation at the kathode on
making and at the anode
on breaking the circuit. But
the latter furnishes a rather
weaker excitation than the
former.

Polar excitation of muscle.
— 1. Engelmann's sartorius
experiment. — A curarised sar-
torius is connected with a
pair of non-polarisable elec-
trodes which are joined up
through a mercury key with
a battery (fig. 44). It will
be observed that the twitch
begins at the kathode when
the current is closed ; indeed,
the muscle may remain more or less contracted at that end during the whole time
of the passage of a strong current. On the other hand, on opening the circuit
the twitch begins near the anode, and may again be followed by a prolonged

50

PIG. 44. — POLAR EFFECTS OF CONSTANT CURRENT
UPON CURARISED SARTORIUS.

EXCITATION OF NERVE AND MUSCLE BY GALVANIC CURRENT 51

contraction. These prolonged contractions show that excitation is produced
not only at the make and break but also during the passage and for a short time
after the cessation of a strong constant current.

2. An instructive variation of this experiment is to dissect out the rectus
abdominis muscles of a curarised frog, and place the non-polarisable electrodes
one in contact with the anterior, the other with the posterior end of the flat
muscular mass (iig. 45). The muscles are divided into several parts by tendinous

FIG. 45. — POLAR STIMULATION OP EECTUS ABDOMINIS. m, MUSCLE CURAKISED AND

STRETCHED BETWEEN TWO PIECES OF CORK (AFTER VERWORN).

septa, and it will be seen that during the passage of the constant current each
of these parts has the part directed towards the kathode in a condition of con-
traction, and the part directed towards the anode in a condition of relaxation.

3. The effect of the poles of a constant current upon cardiac muscle can
be exhibited on the frog's heart. The frog is killed by destroying the brain,
and the heart is exposed in situ. Using non-polarisable electrodes and the
whole current of a Daniell cell with a mercury key and a commutator in
the circuit, place one electrode either in the mouth or on any part of the body
of the frog, and connect the other, by means of a short piece of cotton- wool
wetted with Ringer solution and drawn to a point, with the heart so as to touch
it near the base of the ventricle. If this electrode is the anode, on closing the key
it will be observed that the part of the ventricle underneath it does not partici-
pate in the contractions, but remains quiescent, and, if the heart be filled with
blood, even bulges during general systole : on opening the key this part passes
into systole — even during general diastole (physiological rebound). If the
current be reversed and the cotton-wool be made the kathode, the reversed
effects are obtained.

Polar excitation of nerve. — Take a muscle-nerve preparation with as long a
nerve as possible and arrange it on the myograph. Non-polarisable electrodes,
connected with a constant battery through a mercury key, are placed — the
anode in contact with the uppermost end of the nerve, the kathode in contact
with the lowermost end, i.e. close to the muscle. Insert an electro-magnetic
signal into the circuit and cause it to mark on the drum just below the myograph
lever. Record two contractions, one produced by closing the mercury key,
the other (on a different abscissa) by opening it. Make a tuning-fork tracing
below, and measure exactly the period of latency in each case, i.e. the time
elapsing between the current of the electromagnetic signal and the commence-
ment of rise of the curve. Notice that it is slightly greater as the result of
breaking the circuit than on making (by the time taken for the nerve impulse to
traverse the length of nerve), since the excitation at breaking is at the anode, i.e.
at a point of the nerve furthest from the muscle, whereas on making the excita-
tion was at the kathode, i.e. close to the muscle.

If, as represented in fig. 46, an ascending current is used instead of a
descending one, the result is complicated by the blocking effect of the con-
stant current on conduction (see pp. 43 and 48). Thus, on making such an
ascending current, if it were a strong one, the excitation being at the kathode,
i.e. at the uppermost end of the nerve, and the intermediate part of the nerve
being at the same moment traversed by the current, this would block the passage
of the nerve-impulse generated at the kathode, and no contraction would result.

52

EXPERIMENTAL PHYSIOLOGY

Therefore, Instead of obtaining a contraction at both make and break, only the
break would produce a visible effect under these circumstances. On the other

hand, if the constant current is weak, its removal may not be followed by con-
traction of the muscle, because the breaking of such a current furnishes a smaller
excitation than its making.

EXCITATION OF NERVE AND MUSCLE BY GALVANIC CURRENT 63

Pfliiger's law. — The above (which has been misnamed " the law of con-
traction ") is illustrated by an experiment devised by Pfliiger. The nerve^jof a
nerve-muscle preparation is placed on non-polarisable electrodes, which are
connected with a battery of at least three cells through a commutator and
rheochord : a mercury key is introduced into the circuit (fig. 47). Beginning with
a very weak current, the rider of the rheochord being brought near to the end a
of the rheochord wire (see figs. 19, 20), determine the effect upon the nerve, as
indicated by the contraction of the muscle, of making and breaking the current

t

•

IEZ

9 I

BH

1 1

mm

1 6

SB

'T

r

r

3

/

1

BB

1 1

sac

1 t

££

1 1

KB

S I

m

FIG. 47. — To TEST PPLUGEK'S ' ' LAW OP CONDUCTION."

when it is (1) ascending and (2) descending. Repeat the experiment, using
a moderate strength of polarising current — i.e. with the rider of the rheochord
near the end b of the wire. Finally, the effect of a strong current is to be studied
by eliminating the rheochord altogether. Note down in tabular form all the
results obtained. (The contractions of the muscle need not be recorded
graphically.)

If the nerve be very excitable 1 the muscle may remain in contraction during
the whole time of the passage of a strong descending current (closing tetanus),
and may also remain contracted for a considerable time after the removal of a
strong ascending current (Hitter's opening tetanus). If Ritter's tetanus is ob-
tained the nerve may be cut between the electrodes. The tetanus instantly
ceases because the point where the stimulus occurs (the original anode) is cut off.

1 The excitability of a muscle-nerve preparation is greater when the latter is
made from a frog which has been in a cold place or in contact with ice, and then
kept for half an hour at the ordinary room-temperature before being killed.

CHAPTER XII

POLAR EFFECTS OF A GALVANIC CURRENT ; ELECTROTONUS

A POLARISING current produces changes of excitability not only at its poles but
also in the adjacent parts of the nerve, and even some distance away from
them. This is due to the fact that owing to spread of current in the extra
polar regions as well as at and between the poles, changes of potential are
manifested in those regions during the passage of the current, these being accom-
panied by physiological changes, viz. increased excitability near the kathode,
and diminished excitability near the anode. Such a condition is known as
electrotonus ; that obtaining at and near the kathode being termed katelectro-
tonus ; that obtaining at and near the anode, anelectrotonus.

The spread of the electrical changes beyond the poles is illustrated by the
following experiment.

Paradoxical contraction. — Dissect out the sciatic nerve of a frog, cutting all
the branches save that to the calf muscles, but leaving the cut branch to the
peronei muscles as long as possible. Place the cut end of this branch upon
non-polarisable electrodes connected with a battery and rheochord and have
a mercury key in the circuit. On making or breaking the circuit the gastro-

PIG. 48. — PARADOXICAL CONTRACTION SHOWN BY INDUCED CURRENTS.

cnemius will contract. Owing to the electrotonic spread of the current in the
fibres of the peroneus nerve the fibres to the gastrocnemius in the trunk of
the sciatic become stimulated ; in an excitable preparation this will occur even
with very weak currents. The experiment can also be performed with ordinary
metallic electrodes connected with the secondary coil of an inductorium (fig.
48). On stimulating the peroneus nerve by closing the merciiry key the
gastrocnemius is made to contract. If the peroneus branch is tied or crushed
near its junction with the sciatic the effect can only be got with strong currents.
The experiment should be repeated by placing a thread, wetted with Ringer,
along the sciatic nerve, and laying its free end on the electrodes. In this case
also the excitation caused by spread of current will only show itself with strong

54

POLAR EFFECTS OF GALVANIC CURRENT

55

currents. These experiments show that the spread of current is assisted by the
structure of the nerve ; even with a weak current it takes place for a consider-
able distance along an intact nerve, but it is easily blocked if the nerve be tied
or crushed.

Electrotonic effects of constant current on excitability. — Take a
pair of non-polarisable electrodes and connect with a battery of at
least two cells, inserting a rheochord, a commutator, and a mercury
key into the circuit (polarising circuit). Another circuit is also pre-
pared (exciting circuit),1 including battery, induction coil, and mercury
key in the primary circuit ; the secondary circuit is to have a short-
circuit key, with which a pair of ordinary metallic electrodes are

FIG. 49. — To TEST THE POLAR EFFECTS OF A CONSTANT CURRENT ON NERVE EXCITABILITY.

connected ; these electrodes are brought in contact with the nerve
of a muscle-nerve preparation near the muscle. The non-polarisable
electrodes, which may be of the boot pattern, are fixed to the
myograph cork, but slightly raised above it ; the upper part of
the nerve is laid upon them (fig. 49). The record of the muscular
contractions obtained is made on a stationary drum. Be careful to
keep the nerve moist.

Place the secondary coil at such a distance from the primary coil
that faradisation (Helmholtz modification) just produces a small
contraction. Now put in the polarising current (1) in an ascend-

1 A variation of the experiment is to replace the exciting circuit by a few
crystals of salt and wait until the penetration of this begins to excite the nerve
fibres. The rheochord also may be dispensed with in the polarising circuit, in
which case two Daniell cells will suffice.

56 EXPERIMENTAL PHYSIOLOGY

ing and (2) in a descending direction, and determine the effect
of its poles in diminishing or increasing the excitability of the nerve
as tested by the height of the ordinates described by the myograph
lever.

This experiment can be performed without taking a graphic record by noting
at what distance the secondary coil must be placed in order just to produce a
contraction. In this way the varying conditions of excitability produced by
the polarising current are tested and may be recorded numerically.

CHAPTER XIII

EXPERIMENTS ON THE ELECTRICAL CONDITIONS OF MUSCLE

AND NERVE

A galvanometer or electrometer is necessary to study these con-
ditions, but certain facts can be demonstrated without any special
apparatus.

Demarcation current of muscle: Contraction without metals.—
By means of a glass rod loop up the
nerve of a nerve-muscle preparation,
and allow its cut end to come in contact
either with an injured part of the sur-
face of its own muscle (fig. 50) or with
other muscles. There will be a con-
traction of its muscle each time that
the contact is made or broken. The
excitation is caused by the passage

through the nerve of part of the
, . . ~ , , , Fio. 50. — EXPERIMENT OF THE CON-

demarcation current OI the muscle. TRACTION WITHOUT METALS, gl,

BENT GLASS KOD ; n, NERVE ;

The result can sometimes be obtained if m> MUSCLE.

the cut end of the nerve be allowed to touch

a part of the nerve nearer the muscle : in thib case it is the demarcation current
of the nerve which stimulates its own fibres.

This experiment is only likely to succeed if a very excitable preparation,
auch as is obtained from a cooled frog (see footnote, p. 53), is employed^

Action current of muscle ; Secondary contraction. — Take a nerve-
muscle preparation, and lay its nerve over the muscles of another leg,
the nerve of which is placed upon electrodes (fig. 51). Tetanise these
muscles ; the nerve of the first-named preparation will be stimulated
by the electrical variations which accompany the contraction of the
tetanised muscles. A nerve-muscle preparation thus used in place of
a galvanometer to indicate electrical variations is known as a rkeoscopic
frog preparation.

The result can also be obtained with single contractions.

57

58

EXPERIMENTAL PHYSIOLOGY

Secondary contraction from the heart. — Lay the nerve of a muscle-nerve
preparation upon the beating heart of the frog. If the preparation is very
excitable the muscle will twitch with each beat of the ventricle. If the heart-
beat and the twitch are simultaneously recorded on a drum the twitch will be
found to slightly precede the beat — i.e. the electrical change precedes the
mechanical ; this is seen best with a cooled heart.

Measurement of demarcation current ; Capillary electrometer. — The capillary
electrometer consists of a thread of mercury, which is forced by pressure from
behind for a certain distance along a glass tube drawn out to a capillary ter-
mination ; the free end of the capillary is filled with dilute sulphuric acid and
dips into a vessel containing the same fluid. The capillary is observed with a
microscope. If the mercury and the sulphuric acid be now connected with wires
which are charged with electricity, there is produced a movement of the mercury
in the direction which the current would take — i.e. from positive to negative —
the ultimate extent of movement of the meniscus being, for the same electrometer,
proportioned to the difference of potential. From the direction and extent of
the movement the direction and electromotive force of any constant current
can therefore be gauged. The movements of the meniscus can also be photo-
graphed, and a graphic record thus obtained.

PIG. 51. — EXPERIMENT TO SHOW SECONDARY CONTRACTION, k, MERCURY KEY IN PRIMARY CIRCUIT ;
k1, SHORT-CIRCUIT KEY IN SECONDARY CIRCUIT ; a, FIRST MUSCLE ; 6, SECOND MUSCLE WITH
ITS NERVE LAID OVER THE FIRST.

Join a pair of non-polarisable electrodes up in circuit with a capillary electro-
meter and Daniell cell through a rheochord and commutator in the manner shown
in the diagram (fig. 52), but with a piece of blotting-paper moistened with salt
solution placed across the electrodes instead of the muscle shown in the figure.
Put a short-circuiting key between the electrometer and the electrodes. Have the
short-circuiting key (k') shut at first so that the electrometer is short-circuited,
and the battery key (k) open. Bring the mercury meniscus into the field of the
microscope. Now open the short-circuiting key. If the electrodes are themselves
without current there will be no effect on the electrometer ; but usually there is
a slight effect, the direction and the amount of which should be noticed. Next
close the battery circuit, leaving the short-circuiting key open. Part of the
battery current is now sent through the electrodes and electrometer in a particular
direction (which can be reversed by the commutator), and there is a correspond-
ing movement of the mercury. Note the direction of this movement, and
by following out the wires from the battery determine with which part of
the electrometer the anode and kathode are respectively connected. By
means of the rheochord and commutator a definite proportion of the battery
current can be sent in either direction through the electrodes and through
any preparation with which they may be connected. Open the battery key
and close the short-circuiting key ; the meniscus should return to its original
position.

Lay the muscle of a nerve- muscle preparation, which may have the distal end
cut or injured, upon the electrodes in place of the wet blotting-paper. Place it

THE ELECTRICAL CONDITIONS OF MUSCLE AND NERVE 59

with one electrode touching the longitudinal surface and the other at or near
the injured end. Then open the short-circuiting key to allow the demarcation
current of the muscle to aifect the electrometer. From the direction of move-
ment of the mercury determine the direction of the muscle current through the
apparatus — i.e. which part of the muscle led off from the electrodes is negative
to the other. The electromotive force of the current can be measured by closing
the battery key, so that the battery current is brought into the circuit, and by
aid of the rheochord and commutator sending a current through the circuit
in a direction the reverse of the demarcation current and of exactly such a
strength (measured by the known electromotive force of the battery employed
and the position of the rider on the rheocord) as to bring the mercury back
to zero.

CJCC

FIG. 52. — DIAGRAM OP CAPILLARY ELECTROMETER. A, RESERVOIR CONTAINING SULPHURIC ACID.
s, AND MERCURY, m' ; m, MERCURY IN GLASS TUBE DRAWN OUT TO CAPILLARY TERMINA-
TION ; B, CAPILLARY AS SEEN UNDER MICROSCOPE ; n.p. NON-POLARISABLE ELECTRODES ; exc,
EXCITING ELECTRODES ; k, A-', KEYS ; c, COMMUTATOR ; rl>, RHEOCHORD.

Action-current. — Place the upper end of the nerve of the preparation on a
pair of exciting electrodes connected with an induction coil arranged for tetanisa-
tion. Observe the meniscus with the microscope, and tetanise the muscle,
using the weakest possible stimulus. Notice that the meniscus moves in a
particular direction. This movement is caused by a change in the electrical
condition of the muscle accompanying its contraction. From the direction of
movement of the mercury determine which part of the muscle is now negative
to the other. The action-current can only be properly studied in photographs
of the end of the mercury column, the image of which is thrown on a slit in
front of a moving plate.

String galvanometer of Einthoven. — This consists of a microscopically fine
thread of silvered quartz stretched between the poles of a powerful electro-
magnet (fig. 53). When a galvanic current is passed along it the thread

60

EXPERIMENTAL PHYSIOLOGY

is deflected to one side or the other to an extent varying with the E.M.F. — the
tension of the thread being supposed constant. The movement is observed with

a microscope, or the magnified image of
the thread is photographed on a moving
sensitised surface. The method of con-
ducting the experiment is very similar
to that employed for the capillary
electrometer. For certain investigations,
especially those relating to the electrical
conditions accompanying the action of
the heart, the string galvanometer is
more convenient than either the capil-
lary electrometer or the needle galvano-
meter. It has been largely adopted by
clinicians, since the heart-records ob-
tained by it (electro-cardiograms) furnish
valuable indications as to the nature of
cardiac affections which might be other-
wise difficult to diagnose. When used
for the human subject the two hands,
or one hand and an opposite foot, are
placed in vessels of salt solution, and
these are connected, by wires, with the ends of the quartz thread.

Reflecting needle galvanometer. — Reflecting galvanometers of high resistance

k

FIG. 53. — DIAGRAM OP EINTHOVEN STKTNO
GALVANOMETER, s, s', SILVERED QUARTZ
THREAD, STRETCHED BETWEEN POWERFUL
MAGNETS m, m, WHICH ARE PERFORATED
TO ALLOW A MICROSCOPE TO BEAR UPON
THE THREAD.

a

FIG. 54. — DIAGRAM OF ABRANGEMENT OF APPARATUS FOR STUDYING MUSCLE CURRENTS WITH
GALVANOMETER, g, GALVANOMETER. THE OTHER LETTERS AS DJ FIG. 52.

were, until recent years, almost exclusively used for experiments in electro-
physiology (fig. 54), but have been largely superseded by the instruments that
have just been described.

THE ELECTRICAL CONDITIONS OF MUSCLE AND NERVE 61

Demarcation and action currents of nerve. — These are examined and measured
in exactly the same way as those of muscle.

Action current of frog-heart. — Non-polarisable electrodes are connected with
a beating frog-heart, which may either be removed from the body and laid with
the base upon one electrode and the apex on the other, or left in situ and the
electrodes connected with apex and base by thick threads wetted with salt
solution. The electrodes are joined by wires to any of the above instruments.
Each contraction of the heart is accompanied by movements of the respective
indicators (mercury column, quartz thread, or magnetic needle), the direction
of which may be recorded and the alterations in electrical potential of base and
apex deduced therefrom.

CHAPTER XIV

INVOLUNTARY MUSCLE

Stomach or bladder of frog. — Take either a transverse strip from the
stomach — the frog should have been recently fed — or preferably the
whole urinary bladder, fastening a thread to each end. Attach one
end to the metal disc used in the experiment on the effect of heat on
extensibility (fig. 38) ; let this lie in a small vessel of Ringer's solution,
and, as in that experiment, attach the other end to the short arm of a
light lever. Bring fine wires from the induction coil — one in contact
with the bottom of the strip, the other with the top. This upper wire
must be spirally coiled or otherwise so arranged that the piece of tissue
can be stimulated and can contract without interference. Use a very
slow drum. Stimulate by making and breaking the primary circuit.
With a single make or break there is usually no response owing
to the short duration of the induction shock, but by repeating
the stimulus the tissue will contract and the lever will describe
a simple prolonged muscle curve on the drum. The contraction is
best obtained by a rapid succession of stimuli, using the Neef's
hammer, but in this case also it is a simple contraction, not a
tetanus ; it furnishes an example of the effect of summation of
stimuli (see p. 36). Involuntary muscle does not show superposition
nor tetanus, in this respect resembling the heart. On the other
hand, it exhibits great variations in tone — i.e. a condition of greater
or less continuous contraction.

Intestine of rabbit : Magnus' method. — The same apparatus is
used, but the Ringer's solution must be kept warm (35° C. to 40° C.).
A longitudinal strip of rabbit intestine (descending colon), which
may be divested of its mucous membrane, is attached below to the
disc and above to the lever. Rhythmic contractions occur and

should be recorded. Add to the Ringer solution of one preparation

62

INVOLUNTARY MUSCLE 63

a few drops of pituitary extract, and to another a few drops of
suprarenal extract, and observe the effect in both cases.

This method is used for investigating the action of drugs upon the
muscular tissue of the intestine. For prolonged and exact experi-
ments oxygen is allowed to bubble through the Ringer so as to keep
the solution saturated with this gas.

CHAPTER XV

THE FROG-HEART

MAKE a special dissection of the upper part of the body of a large frog to show
the situation and connexions of the heart, its several cavities and the blood-
vessels leading to and from it. It is advantageous to distend the cavities with
gelatin solution and allow this to set. Notice a small nerve entering it on each
side along the superior vena cava ; this is the cardiac nerve, and is given off
from the vagus ; it contains also fibres from the sympathetic which reach the
vagus near the skull. Cut out a piece of the interauricular septum ; place
it in dilute methylene blue for five minutes ; wash with water, and examine
in water under the microscope for nerve fibres and groups of nerve cells. The
dissection of the heart may be made beforehand and kept for reference in dilute
formalin.

Examine the contracting heart of a frog the brain and spinal cord
of which have been destroyed ; cut away the sternum and ensiform
cartilage and the front of the pericardium. Very gently raise the

Common carotid.

Right auricle.
Aortic bulb.

Ventricle.

Aorta.

Pulmuno-cutaneous artery.
Left auricle.

Aortic trunk.
Coronary sulcus.

FIG. 55. — HEART OP FROG : VENTRAL ASPECT (GAUPP).

tip of the ventricle with a blunt instrument, and sever the peri-
cardial ligament which binds the ventricle to the back of the peri-
cardium. Do not grasp the heart with forceps or injure it in any way
by manipulation.

On raising the ventricle the sinus venosus comes into view,

64

THE FROG-HEART

65

receiving the two vense cavas superiores and the vena cava inferior ;
above, it is continuous with, but marked off by a whitish line (the
sino-auricular junction) from, the auricle, which is double and receives
on the left side the pulmonary vein ; the two auricles open into a

Aortic trunk.

Left auricle. —
Pulmonary vein.

Sinus venosus.

Superior (ant.) vena cava.
Bight auricle.

Bulb of aorta.
Coronary sulcus.

Pericardial fold with vein.
Vena cava inf. (post.).

Fid. 56.— HEART OP FROG PROM DORSAL ASPECT (GAUPP). ?•

single ventricle. On the front the bulbus aortse is seen leaving the
ventricle and dividing into two trunks, the right and left aortse,
each of which again soon divides into three branches.

Notice that with each systole the venous part of the heart (sinus
venosus) contracts first ; its contraction is immediately, followed by

Ext. jugular vein.

Superior (ant.) vena cava.

Bight pulmonary vein.
Sinus venosus.

Innominate vein.

Subclavian vein.
Bight auricle.
Bulb of aorta.
Coronary sulcus.

Pericardial fold with vein.

Ventricle apex.
FIG. 57. — HEART OP FROG, SEEN PROM THE BIGHT SIDE (GAUPP). 5.

that of the auricles, which contract together, and this by that
of the ventricle. In a frog the spinal cord of which has been
destroyed, there is usually little or no blood passing through the
heart. But if blood is being pumped through, notice the sudden
distension (diastole) of each cavity which immediately succeeds
its contraction (systole). If the finger be very lightly placed on the
ventricle the hardening which accompanies systole may be felt.

5

G6

EXPERIMENTAL PHYSIOLOGY

Using a watch, count the number of beats per minute during
several minutes and record the result.

Effect of heat and cold on rate of beat. — Now apply, first, an ice-
cold and, second, a warmed thick wire (a) to the ventricle, (6) to one
of the auricles, (c) by turning up the heart, to the sinus. Count the
rate during each application, and record the results.

Out edge of septum.

Auricular septum.

Left auricle.

Aur.-ventr. valve.

Eight auricle.

Ventricle.

FIG. 58. — SECTION THKOUGH HEART OP FROG. FRONT HALF SEEN FROM BEHIND
(GAUPP). ?. THE SPONGY STRUCTURE OP THE VENTRICLE is WELL SHOWN.

Stannius' experiment. — Raise the ventricle very carefully without
pinching or injuring it in any way, and, after cutting a ligament or
fold of pericardium which encloses a small vein, pass a thread under
the sinus, and tighten it round the sino-auricular junction, which is
marked by a whitish line. The sinus continues to beat as before
(count the rate), but the auricle and ventricle come to a standstill
in diastole. Such a heart is termed a Stannius heart.

Septum of auricles.

Orifice of pulmonary vein.

Left vagus nerve.
- Bidder's ganglion.

Right vagus nerve. -

Ventricle.

FIG. 59. — HEART OF FROG WITH LEFT AURICLE cur OPEN TO SHOW THE VAGUS
NERVES IN THE AURICULAR SEPTUM (GAUPP). j.

Stimulate auricle or ventricle, and notice that each stimulation is
followed by a contraction. They are therefore not inhibited, but
have ceased to contract owing to their being cut off by the ligature
from the sinus (in which the contractions normally begin).

Now tie a second ligature round the auriculo- ventricular junction.
The ventricle usually gives a few (three or four) beats, and then both

THE FROG-HEART

67

it and the auricle again come to a standstill. Either can, however,
be made to beat by artificial stimulation (prick, electric shock).

After a certain lapse of time (sometimes very soon after the appli-
cation of the first ligature) the auricle and ventricle may recommence beating
regularly and rhythmically, but it will be found on counting the rate that it is
never as fast as that of the sinus. If the auricle is cut off from the ventricle,
as by the second Stannius ligature, all three parts may ultimately be found
beating spontaneously, but it will always be noticed that the rate of the sinus
is the fastest, that of the auricles next, and that of the ventricle the slowest.
The bulbus aortse is also spontaneously contractile ; even small pieces can be
observed to beat rhythmically.

Peculiarities of cardiac contraction.— Apart from its regular
rhythm the heart muscle shows certain peculiarities as compared with

FIG. 60. — PROG CARDIOGRAPH. /, PROG ; /;, HEART ; I, LEVER.

skeletal muscle. To investigate these, apply a ligature at the base
of the ventricle ; cut out the heart and attach the apex of the ventricle
by means of a fine hook or serafin and thread to a muscle lever (such
as is shown in fig. 60), the preparation being fixed by a pin
passed through the ligatured base. The heart may, if desired, be left
in situ as shown in the figure. Contractions are recorded by the lever
in the same way as those of any other muscle, but on a very slow
drum. Be very careful not to injure the preparation. As a rule there
are no spontaneous contractions, but the ventricle responds to the
least stimulus applied to any part of its surface. The following
experiments are to be made with this preparation :—

1. "All or none " contraction. — Allow a pair of electrodes, con-
nected with an induction coil, to touch the base of the quiescent
heart. They must be fixed (this can be done with plasticine), not

68 EXPERIMENTAL PHYSIOLOGY

held in the hand. Put the secondary coil far from the primary,
and break the primary circuit. Determine the excitability of the
preparation by ascertaining to what division of the scale the secondary
coil must approach the primary before a contraction is produced.
This represents the liminal stimulus. Now bring the secondary
nearer the primary and again stimulate. The contraction is not
appreciably larger. Repeat with a still stronger stimulus. In every
case the extent of contraction is the same1 (compare with skeletal
muscle, p. 39).

2. Refractory period. — Put in a second stimulus (with the hand)
at varying intervals after the first. If put in very soon after so as to
reach the heart whilst it is still in process of contraction, no additional
effect is produced ; there is no superposition (compare with skeletal
muscle, p. 36). In other words, whilst the contraction produced by
the first stimulus is proceeding, cardiac muscle is refractory to a
second stimulus. This refractory phase is continued to a less extent
during the period of relaxation of the muscle. A consequence of the
refractory phase and of the lack of superposition is that cardiac
muscle never shows a true tetanus, although by sending in successive
stimuli so that they reach the muscle always at the commencement
of the period of relaxation, there is an appearance of fusion of the
successive contractions ; but they never overtop one another as in
tetanus of skeletal muscle. To show this, put in a succession of
stimuli by rapidly making and breaking the primary circuit with the
hand (compare with tetanus of skeletal muscle, p. 36).

3. Staircase phenomenon. — This is not peculiar to cardiac muscle
(^ee p. 43), but is often well shown by it. Using the Stannius prepara-
tion, and after a period of rest, stimulate a number of times in suc-
cession at intervals of about two seconds, keeping the strength of
the stimulus the same throughout. Notice that there is a slight
increase in the extent of the first few successive contractions, the
second ordinate being a little higher than the first, the third than the
second, and so on.

1 See, however, what is said as to the staircase phenomenon (paragraph 3).

CHAPTER XVI

PERFUSION OP HEART

Perfusion of frog-heart. — -Kill a large frog and expose the heart ;
remove the pericardium and cut through the pericardial ligament.
Very carefully raise the apex of the ventricle with a blunt instrument,
remembering that the least injury to the surface of the ventricle will
spoil it for this experiment. Make a free cut with scissors into the
auricles thus exposed, near to the sino-auricular junction ; insert the
scissors into the auricles and snip through their septum. Wash all
blood away with Ringer's solution. Place a ligature of wet cotton
round the auricles near their junction with the ventricles ; insert the
double perfusion Kronecker cannula (fig. 61,/') through the auricles
and into the ventricle, and tie it in firmly by means of the ligature ;
cut through the sinus, and remove the heart upon the cannula.
The inlet tube of the perfusion cannula is connected to a reservoir
(Mariotte bottle) containing about 100 c.c. Ringer's solution, and the
outlet tube conducts to a receptacle into which the fluid may flow
after passing through the heart. Whilst the heart is being fastened
over the cannula, let Ringer's fluid flow very slowly (drop by drop)
through the cannula so as to expel and keep all air out of the
cannula and heart.

Now place the heart in the plethysmograph. The lower part of
the plethysmograph contains Ringer's solution : the upper part and
the tubes leading horizontally from it contain pure, moderately thin
paraffin oil.1 Both stop-cocks are closed whilst the heart is inserted ;
then the one belonging to the bent tube is opened. If the reservoir of
Ringer's fluid be at a height of three or four inches above the heart,
the ventricle will soon begin to beat, and its changes in volume will
cause a movement of the oil to and fro in the open tube. If this tube

1 Not olive oil. Ringer's solution may be substituted for oil in the plethys-
mograph, but for the piston-tube oil is required.

69

70

EXPERIMENTAL PHYSIOLOGY

be now closed and the one containing the piston opened, the piston
will move to and fro, and its movements can be recorded on a very
slowly rotating horizontal drum.

It may happen that the perfused heart (which is a Stanniused heart) does not
begin to beat spontaneously, although the salts and the pressure of fluid serve
as a slight stimulus. In that event the beats may be started by faradic excita-
tion from an induction coil, one electrode being attached to the metal cannula
and the other to a wire which passes up through a cork in the bottom of the
plethysmograph, and is brought in contact with the ventricle.

The influence of various salts, such as chloride of calcium and chloride of
potassium, of anaesthetic agents such as ether and chloroform, and of drugs such

PERFUSION OF HEART 71

as digitaline and veratrine, can bo studied by adding definite amounts of thcso
to the Ringer's solution used for perfusion. For such purposes it is convenient
to have two reservoirs of Ringer's solution (fig. (51), one for addition of the
drug to be investigated, and the other to flush out the heart after the action
of the drug is complete. Both reservoirs are connected with the inflow of the
cannula by a three-way tube (e) furnished with a stop-cock or with small flips.

Influence of calcium and potassium on the cardiac contractions : Ringer's
experiment. — Place in the second reservoir a solution containing 6 parts of pure
Nad to 1000 of distilled water, and keep it filled with this solution. Flush the
heart with it ; the organ will soon cease to contract and to respond to excitations.
Now mix with the 100 c.c. of fluid in the second reservoir 2 c.c. of a 1 per cent,
solution of calcium chloride and flush the heart with the mixture. Contractions
will be resumed, but each one will be too prolonged, and the heart will again
soon stop : this time in systole. Next add 4 c.c. of a 1 per cent, solution of
potassium chloride to the contents of the second reservoir, mix thoroughly,
and flush the heart With the mixture. The beats will recommence, either
spontaneously or in response to stimulation, the normal character being
resumed. If the potassium salt is added in excess, the heart will be arrested
in diastole.

Perfusion of the heart in situ. — In large frogs the heart can be perfused in situ
by introducing a very fine glass or metal cannula into the vein which runs along
the middle line of the ventral wall of the abdomen. The vein is exposed by
making a longitudinal incision through the abdominal wall a little to the right
of the middle line, and a transverse incision at the level of the ensiform cartilage
starting from the upper end of the longitudinal cut and carried outwards. The
triangular flap thus made is turned down, and the vein will be seen passing
from the abdominal wall towards the heart. The cannula is connected with a
reservoir of Ringer's fluid, which is allowed to drop very slowly from its end
during insertion, so that no air-bubbles can enter. It is then tied in, and the
heart, previously exposed and attached to a heart lever (as in fig. 60), is flushed
with the solution, which is allowed to flow out from a small cut near the apex of
the ventricle. Drugs are introduced by means of a second reservoir as before.

Perfusion of the mammalian heart. — The heart is excised from a recently
killed cat or rabbit, and the aorta is at once tied on to a cannula through which
Ringer's solution, saturated with oxygen, is slowly dropping. The solution is
warmed to about 38° C. before reaching the heart — which is itself kept in a
warmed chamber. The cannula is directed towards the aortic valves, which are
closed on raising the pressure of the perfused fluid ; this runs through the
coronary vessels and escapes through the right auricle. The amount of fluid
perfused can be measured by a tilter (see p. 87). The contractions of the heart
can be recorded by one or more light levers, attached to it by threads which
are passed over pulleys. The action of drugs is investigated by adding them to
the Ringer's solution.

CHAPTER XVII

CARDIAC NERVES

DESTROY by a wire the spinal cord of a frog, and also remove the
cerebral hemispheres ; this can be done without special dissection by
cutting away the upper jaw and anterior part of the skull at the level
of the front of the tympana (see fig. 77, p. 95). The posterior part of the
brain with the medulla oblongata must not be injured. Fix a pair of
pin electrodes connected with an induction coil into this part of the
skull and arrange for tetanisation of the medulla oblongata — using the
Helmholtz method (p. 16). Lay the frog upon its back on the frog-cork,
and fix it securely by strong pins or rubber bands ; expose the heart
and the chief nerves which are proceeding from the base of the skull
to the hyoid region (vagus, glosso-pharyngeal, and hypoglossal ; see
fig 62). The vagus gives off a small branch on each side, which runs
close along the superior vena cava to the sinus venosus. Place one
vagus trunk upon a fine pair of wire electrodes passed through a flat
piece of cork (which must itself be fixed by plasticine to the frog-
cork, not held in the hand), and connect these electrodes, and also
those which are fixed into the skull, to a commutator without cross
wires so that the faradising shocks can be sent to one or other pair as
may be desired. Place the frog-cork upon the stand of a frog cardio-
graph (fig. 60), and by means of a thread and fine steel hook attach
the apex of the ventricle to the short arm of the light lever. Record
the contractions of the heart upon a very slowly moving drum (one
revolution in four or five minutes). Use the " stop " for adjusting
the lever and for readjusting it after removal from the drum, so that
the pressure of the lever point is always exactly the same. Without
this precaution the strength of the contractions may be wrongly
judged, for if the lever is pressing more at one time than at another,
the lever will not be raised so high, even if the force of the heart's
contractions is unaltered.

72

CARDIAC NERVES

73

Be careful not to injure the heart more than is absolutely necessary.
Jn order to fix the base securely, pass a strong pin close to the base
of the heart and through the vertebral column into the frog-cork.

The following experiments may be performed upon this prepara-
tion :—

1. Take a normal tracing of the beats during a short period and
record by an electromagnetic signal a time-tracing (seconds) upon the

Glossopharyngeal. . — -/- ->

Vagus.

Laryngeal branch of vagus.
Hypoglossal. -

2nd spinal (or brachial) nerve. _ -Nv^

Cardiac branch of vagus.

Superior vena cava.

i'ulrnoiiary branches of vagus. -V

Glottis.

Left auricle.
Bulbus aortee.
^ Right auricle.

Sinus venosua.

FIG. 62.— RELATIONS OF VAGUS NERVE TO OTHER STRUCTURES IN THE NECK AND THORAX. THE
VENTRIOI^E HAS BEEN DRAWN OVER TO THE LEFT SIDE BY A HOOK AND THE SINUS VENOSUS is
THUS EXPOSED, x , LINE OF JUNCTION BETWEEN SINUS AND AURICLES.

drum. This time-tracing is to serve for determining the exact rate
of the heart-beat under the different circumstances of the experiments.

2. Whilst this is proceeding, stimulate, not too strongly, the
medulla oblongata, allowing the result to be recorded continuously
at the same level of the drum.

3. Cut both vagus nerves near the skull and repeat the above
stimulation of the medulla oblongata, recording the result at another
level of the drum.

4. Alter the commutator and stimulate the vagus, recording the
result at a third level of the drum. With weak stimulation of the
vagus in the frog the heart may beat faster and more strongly owing

74 EXPERIMENTAL PHYSIOLOGY

to excitation of the sympathetic fibres which have joined the vagus
near the skull and are running with the cardiac branch to the heart ;
with stronger stimulation the heart will beat more slowly and less
vigorously or may stop altogether.

5. Place one drop of a weak solution (0'2 per cent.) of nicotine upon the sinus ;
the effect of this is at first to slow the heart, because the nerve cells to which
the vagus fibres are distributed are stimulated by the drug ; subsequently they
are paralysed, and the heart resumes its normal rate. After a short interval
stimulate the vagus. No effect should be obtained, since nicotine blocks the
junction of its nerve fibres with the distributing nerve cells within the heart.
Wash away the nicotine with salt solution ; the effect will return after a time.

6. Stimulate the heart at the white line of the sino-auricular junction. (The
electrodes must not be held in the hand, but must be fixed in position by a pin
through their cork or by plasticine.) The heart comes to a standstill in diastole.
Record this effect by a continuous tracing. This standstill is not due to the
stimulation of an inhibitory centre, but to the fact that the inhibitory fibres are
close to the surface at this place.

Notice that in each case of acceleration or retardation of the pulse-rate there
is an after-effect of a nature contrary to the immediate effect.

7. Place a single drop of dilute solution of muscarine upon the sinus, recording
the effect produced upon the rate and force of the heart, which will soon come
to a standstill in diastole. Now wash away the muscarine with two or three
drops of solution of atropine sulphate (1 in 300). Notice the gradual restoration
of the rate and force of the beats. Notice further that no inhibition can now be
produced on stimulating either the vagus or the sino-auricular junction. There
may, however, be acceleration, from stimulation of the sympathetic fibres which
are running to the heart in the cardiac branch of the vagus.

CHAPTER XVIII

STRUCTURE AND ACTION OF THE MAMMALIAN HEART

THE heart of a sheep or man should have been previously dissected to show
its cavities and the blood-vessels connected with them, as well as the arrangement
and action of the auriculo-ventricular and semilunar valves.1 A dissection
should also have been made in a rabbit of the nerves accompanying the carotid
artery (vagus, sympathetic, depressor).

Action of the heart in man. — Observe the chest wall over the
situation of the heart ; notice and feel the impulse or apex beat,
strongest at one spot ; mark this with ink. Apply the ear directly or
through a binaural stethoscope over this spot, and also over the second
right costo-sternal articulation Whilst listening to the sounds of the
heart feel the carotid pulse of the subject, and determine that the
first sound is systolic — -i.e., is synchronous with the rise of pressure
in the artery due to the contraction of the ventricle.

Cardiographie tracing. — Apply the button of a cardiograph (fig. 63)
to the point where the impulse is most distinct, and take a tracing
upon a moderately fast drum by the aid of a recording tambour.

The breath should be held whilst the tracing is taken, to eliminate the
movements caused by respiration. To obtain a distinct record it is best to select
a thin subject, and to place him on a couch in the recumbent position on his
left side.

Rate of rhythm of the heart. Effect of position. — Count the rate
of the heart's beat by placing the finger either over the apex beat or
upon an artery (pulse). Do this with the subject (1) recumbent,
(2) sitting up, (3) standing up. Note down any differences you may
observe in the rate and also in the character of the beat in these
different postures.

Observation o£ the heart of a mammal in situ. — This observation may be made
upon a " Sherrington " preparation. The animal (cat) has been killed under
chloroform anaesthesia by decapitation, the carotids having first been ligatured,
and the vertebrals occluded by a wire passed immediately in front of the axis
vertebra, drawn tightly and securely fastened behind. Another ligature is

1 The mode of dissecting a sheep's heart is described in Pembrey's Practical
Physiology and in Stewart's Physiology.

75

76

EXPERIMENTAL PHYSIOLOGY

made to include all the remaining structures of the neck except the trachea.
The head is cut off by an incision in front of these ligatures passing between the
occiput and atlas. Oozing of blood is stopped by application of dilute supra-
renal extract, and the skin is fastened over the cut end of the neck. Before
tying the arteries, a tube has been inserted into the trachea, and artificial
respiration kept up by pumping air into the lungs and allowing it to escape by a
side tube. This air is warmed, and the body is further kept warm after decapi-
tation by placing it on a warmed plate and covering it with cotton-wool. In
such a preparation the circulation is maintained, although the pressure is some-
what low, and the tissues continue to live for several hours. Spinal reflexes can
be studied in it (see Chapter XXV.). The heart is exposed by severing four or five
ribs or rib-cartilages on each side by bone forceps, and with the same instrument

FIG. 63.— DIAGRAM OP MAREY'S CARDIOGRAPH, a, RECEIVING TAMBOUR FOR FIXING OVER APEX-
BEAT ; 6, RECORDING TAMBOUR CONNECTED WITH, a, BY RUBBER TUBING, WITH A LATERAL

OPENING CLOSED BY A CLIP.

cutting through the sternum near its lower end, and raising the detached part
forcibly, along with the cut ends of the ribs. This bony and muscular flap may,
if necessary, be removed altogether after tying a string or wire tightly round its
anterior end to arrest bleeding from the internal mammary arteries. The window
thus opened discloses the heart within the pericardium ; the latter may be cut
open and the heart fully exposed. The systole, followed by diastole, of auricles
and ventricles can be watched, and the hardening of the ventricles during their
systole felt by applying the finger to their surface. By attaching one of the
ventricles and one of the auricles by fine hooks and threads to light levers
suspended by rubber threads, the contractions of these parts can be recorded
separately on a drum. The effect of stimulating the vagus in the neck and of
atropine in abolishing this effect can be demonstrated ; also the effect of stimu-
lating the accelerator fibres which pass from the inferior cervical ganglion of
the sympathetic to the cardiac plexuses. The same effect is obtained by
stimulating the ganglion itself, which may be found by following the cervical
sympathetic downwards. (In the cat the vagus and sympathetic run in the
same sheath in the neck, but they separate below and above as the sym-
pathetic passes out of and into its inferior and superior cervical ganglia.)

CHAPTER XIX

METHODS OP INVESTIGATING THE CIRCULATION IN THE

BLOOD-VESSELS

THE chief methods used can be practised upon a long india-rubber tube
through which water is pumped from a low reservoir by a Higginson
syringe actuated by some form of motor. After passing through the
system the fluid is again delivered into the reservoir (which represents
the capillary and venous systems). A mercury kymograph (fig. 64)
and other manometers such as Fick's C-spring (fig. 65), Hiirthle's
tambour (fig. 66), as well as the stromuhr (fig. 69) and other
instruments for measuring or estimating velocity, are connected
by means of T-tubes with the main india-rubber tube. The
use of each instrument is to be studied separately, the others being
temporarily shut off by screw clips. Notice how the movement
of any of the recording manometers may be damped by partially
closing the tube connecting it with the main system. Observe
the effect upon the pressure within the system (1) of increasing either
the rate of the pump or the amount delivered at each stroke ; (2) of
diminishing or enlarging the outflow from the main tube by a screw-
clip. This is equivalent to contraction or dilatation of the arterioles.
Take a tracing with each form of manometer. Also record the amount
of fluid passing through the stromuhr in one minute. Measure the
diameter of the artery in whose course the instrument is inserted,
and calculate from these data the velocity of flow.

A dog's or lamb's kidney enclosed in a plethysmograph (such as is shown in
fig. 68) may also be connected laterally with the main system, and Ringer's
fluid allowed to flow in by the renal artery and out by the renal vein ; from
this it must be conducted straight to the reservoir.

77

78

EXPERIMENTAL PHYSIOLOGY

Fm. 64. — DIAGRAM OP MERCURY KYMOGRAPH ARRANGED FOR AN EXPERIMENT, a, BENT GLASS
TUBE CONTAINING MERCURY FORMING THE MANOMETER ; 6, ALUMINIUM FLOAT WITH ROD,
BENT AT RIGHT ANGLES AND ENDING IN A WRITING POINT ; c, SMALL WEIGHT ATTACHED TO SILK
THREAD SUSPENDED ABOVE WRITER AND SERVING TO KEEP IT AGAINST THE SMOKED PAPER ;
d, THREE-WAY STOPCOCK ; <?, ARTERY CANNULA ; /, BOTTLE OP SODIUM CARBONATE SOLUTION ;
g, BICYCLE PUMP.

CIRCULATION IN BLOOD-VESSELS

79

FIG. 65. — DIAGRAM OP FICK'S O-SPRING KYMOGRAPH. ANY INCREASE OP PRESSURE WITHIN THE
HOLLOW METAL SPRING (WHICH is PILLED WITH FLUID) CAUSES THE 0 TO OPEN ; ANY DECREASE
OP PRESSURE CAUSES IT TO CLOSE. THESE MOVEMENTS ARE COMMUNICATED TO THE LEVER.
THE ADVANTAGE OP EMPLOYING THIS OR THE HURTHLE MANOMETER IS THAT THEY HAVE LITTLE
INERTIA AS COMPARED WITH THE MERCURY KYMOGRAPH. THEY MUST, HOWEVER, BE GRADUATED
BY AID OP A MERCURY MANOMETER.

FIG. 66. — DIAGRAM (AFTER SCHENCK) TO SHOW THE PRINCIPLE OP THE HPRTHLE KYMOGRAPH, a,

TUBE TERMINATING ABOVE IN A TAMBOUR-LIKE ENLARGEMENT COVERED BY A STOUT RUBBER

MEMBRANE UPON WHICH is A METAL DISK AND A WEDGE ACTUATING A VERY LIGHT LEVER.
THE TUBE is CONNECTED BY RUBBER PRESSURE TUBING WITH AN ARTERY CANNULA LIKE THAT

SHOWN IN FIG. 64, AND THE WHOLE IS PILLED WITH SODIUM BICARBONATE SOLUTION.

80

EXPERIMENTAL PHYSIOLOGY

FIQ. 67.— MOSSO'S AIW-PLETHYSMOGRAPH.

p.r.

pi. gl

68 —DIAGRAM OP KIDNEY PLETHYSMOGRAPH. pi., PLETHYSMOGRAPH; gl., GLASS COVER;

ff, GAP FOR PASSAGE OP BLOOD-VESSELS AND URETER ; p.r. PISTON RECORDER.

CIRCULATION IN BLOOD-VESSELS

81

Plethysmography. — -The arm of a subject (who is to be seated com-
fortably) is placed in a Mosso plethysmograph (fig. 67), and this is
allowed to rest on a table or in a sling. The junction with the arm
is made by a broad rubber band. The interior of the plethysmograph
is connected by rubber tubing with a recording tambour or a
bellows- or piston-recorder ; the whole is to be airtight. The lever
of the recorder registers respiratory and cardiac movements upon the
smoked surface, since these movements produce changes in general
arterial pressure, and thus in the amount of blood driven into the arm.
Compress the brachial vein above the elbow ; the swelling of the
arm due to retention of blood is at once shown.

Plethysmographs for the kidney (see fig. 68), spleen, and other organs may
be also studied. The principle of their
action is the same as that used for the
arm, but the form is adapted to each
particular organ. The gap (g) in the
instrument through which the vessels
and duct pass is made airtight by
vaseline.

Study of blood pressure, and the
effects of nerves and drugs upon the
heart and arteries in animals. — Either an
anaesthetised animal may be employed as
the subject of a demonstration on blood-
pressure, or a " Sherrington " preparation
(p. 75) can be used by the student. A
cannula (fig. 64, e) is inserted into one of
the carotids towards the thorax and tied
securely in. The artery is previously
ligatured above and clamped below the
place of insertion. The cannula is con-
nected by a tube containing solution
of sodium bicarbonate with the proximal
limb of a mercurial manometer ; a
lateral tube affords communication with
a reservoir of the same solution, which
is under pressure. By this pressure the
mercury is forced up in the distal limb
of the manometer, so that the recording
style is about 50 mm. above the abscissa
or zero line. The clamp on the artery
is then removed, and a record of the
arterial pressure taken, a time record
(in 10-second intervals) being also in-
scribed. It is useful to record the
respiratory movements at the same
time : this is conveniently done either
by tambours or by attaching a thread
by one end to the skin of the epigastric
region and causing the other end to
activate a lever. A blunt metal cannula,
which fits the nozzle of a hypodermic
syringe, is tied into} one of the jugular
veins towards the thorax : this is for the purpose of giving intravenous in-
jections of drugs and extracts. A kidney or the spleen or a loop of intestine,

6

e

FIG. 69. — LUDWIG'S STROMUHR. a, a', CAN-

NULAS FOR TYING INTO CUT ARTERY ;

6, BLOCK ON WHICH THE PART c ROTATES

ABOUND THE AXIS, d \ e, KESERVOIR CON-
TAINING OIL ; e1, RESERVOIR CONTAINING
DEPIBRINATED BLOOD ; /, APERTURE FOR
FILLING RESERVOIRS, CLOSED BY CORK, g.

82 EXPERIMENTAL PHYSIOLOGY

or a limb, may be placed in a plethysmograph, and the changes of volume
recorded. In the anaesthetised animal the following experiments can be made :
for many of them the Sherrington preparation can be used : —

1. Effect of exciting the afferent fibres of a peripheral limb-nerve. Expose
any limb nerve, tie a ligature tightly round the distal end of the part exposed.
Stimulate the central end. Observe the effects on arterial pressure, on heart
rate, and on respiration.

2. Put a drop or two of amyl nitrite on cotton -wool and allow the animal to
inhale the vapour. Note the effect on blood-pressure.

3. Effect of exciting the vagus. One of the vagi in the neck having been
isolated for a short distance, taking care to avoid injuring it, a thread is tied
tightly round it : this serves to hold it, and also severs the continuity of its
fibres, and is therefore equivalent to cutting it across, (a) Stimulate the end
below the ligature. Observe the effect on blood-pressure caused by cardiac
inhibition. (6) Stimulate the upper end. Observe the reflex effects on blood-
pressure and on respiration which are produced, (c) Stimulate the superior
laryngeal branch, which can be seen passing to the larynx. Observe the effect
on respiration and blood-pressure.

4. Effect of cutting both vagi. The ligature of the one vagus — which, as
just explained, severs its fibres — produces little or no permanent effect on blood-
pressure or respiration. Now tie or cut the other vagus also. Notice the effect
(a) on respiration, (6) on blood-pressure. Repeat the excitation experiments.

5. Inject solution of atropine sulphate (about 2 milligrams) into the jugular
vein. Notice the effect, if any, upon blood-pressure and respiration. Repeat
the excitation of lower and upper ends of vagus as in (1), and note results.

6. If a rabbit is used, two other very fine nerves can be found in the neck
accompanying the carotid artery and vagus. One of these is the depressor :
it is a branch of the vagus or of the superior laryngeal. The other is the cervical
sympathetic : it passes above into the superior ganglion. Both these nerves
are to be tied low down. After tying the sympathetic, the pupil of the eye on
that side will be more contracted than the other, and the ear of that side will be
warmer and redder, (a) Stimulate the upper end of the sympathetic : the
pupil dilates, the third eyelid is retracted, some of the hairs on the side of the
head may be erected, and the arteries of the ear contract, so that the whole ear
becomes pale. (6) Stimulate the upper end of the depressor whilst the blood-
pressure is being recorded. After a long period of latency there is a fall of
pressure which lasts during stimulation of the nerve and for a short time after
its cessation.

7. Inject into the jugular vein a few drops of an extract of the supra-
renal capsule of any animal. The extract is made by taking 20 c.c. of
Ringer's solution to each gram of suprarenal capsule, boiling and filtering.
Record the effect on blood-pressure. Notice the dilatation of the pupils, the
retraction of the third eyelid, and the pallor of the ears. If a plethysmo-
graph is being used, the record of the effect on the contained organ indicates
contraction of arteries. The experiment can be repeated more than once.

8. Inject into the jugular vein a few drops of an extract of ox-pituitary.
The extract is made in the same way as the suprarenal extract. The posterior
lobe only should be used. Notice the effect of the extract upon the blood-pressure
and upon the plethysmograph record. If the injection is repeated after a short
interval, most of the results are not shown, or are much less marked.

9. Kill the animal by asphyxia — which may be effected by occluding the
trachea or by allowing carbon monoxide gas (or coal gas) to be respired. A con-
tinuous tracing showing the effects of asphyxia, both upon the respiratory
movements and upon the blood-pressure and heart-beats, may be recorded.

The capillary circulation. — The flow of blood in the smallest arteries and
veins and in the capillaries is observed with the microscope in transparent
parts of animals such as the web and mesentery of the frog, the tail of the
tadpole, and the mesentery of small mammals.1

1 For the methods of displaying these parts, see the author's Course of
Practical Histology, in which full details are given.

CHAPTER XX

THE PULSE. ARTERIAL PRESSURE IN MAN

The pulse in the arteries. — Feel the pulse in the radial artery and
determine and note (1) its rate, (2) its quality, whether hard or soft,
bounding, readily compressible, etc. Apply a sphygmograph, either

Fin. 70. — DIAGRAM OP MAREY'S SPHYGMOGRAPH. xpr, SPRING WITH BUTTON FOR RESTING ON RADIAL

ABTERY ; c, 0AM, FOR EXERTING PRESSURE ON THE SPRING ; scr, SCREW CONNECTING SPRING

WITH DOUBLE LEVER ;, V ; gi, SMOKED GLASS OR PAPER FOR WRITING THE PULSE.

Marey's original pattern (fig. 70) or the modification devised by
Dudgeon (fig. 71). Using the cam, exert such pressure upon the
spring of the sphygmograph as will allow the variations in pressure
within the artery to be most manifest. The tracings are taken on
slips of paper smoked over a candle. Write on each slip the name
of the subject of the experiment and the pressure which was em-
ployed ; varnish and preserve.

83

84 EXPERIMENTAL PHYSIOLOGY

The venous pulse. — In a recumbent subject fix a small open
receiving tambour (a small thistle funnel will do) at the place in the
lower part of the neck where the venous pulse in the jugular is most
distinct. The receiving tambour is connected by rubber tubing to a
small recording tambour, and the curve is written on paper moved
slowly by clockwork. A tracing of the carotid pulse can be ob-
tained on the same paper, another tambour being fixed over the
artery. A convenient apparatus for taking such tracings is the
polygraph of Mackenzie. In this instrument there is a continuous
roll of white paper on which the tracings are recorded with ink.

Fia. 71. — DIAGRAM TO SHOW THE LEVER-MECHANISM OP THE DUDGEON SPHTGMOGRAPH. a, SPRING ;
6, BUTTON TO BE APPLIED TO THE RADIAL ARTERY ; c, WRITING POINT OP JOINTED LEVER

ATTACHED TO SPRING ; d, GLASS PLATE OR PAPER ON WHICH THE TRACING IS RECORDED.

Arterial pressure in man. — The pressure of the blood within the
human arteries is determined by the sphygmometer, of which many
forms are available. All have a circular rubber bag (fig. 72, a) which
is enclosed by leather and is placed round the upper arm. The bag is
distended with air by a pump (c), the amount of pressure used being
recorded either by a mercury manometer (Riva-Rocci) (6) or an aneroid
(Hill and Barnard) or by compression of air in a closed tube, using a
mercury index (Gr. Oliver). As the distension progresses the manometer
shows not only the gradual increase of pressure but also oscillations due
to the pulse. These oscillations increase in magnitude up to a certain
point. The point around which the oscillations are greatest is the
measure of diastolic or average pressure. On further raising the pres-
sure the oscillations again become smaller, for the brachial artery is
now becoming occluded. When it is completely occluded the pulse

ARTERIAL PRESSURE IN MAN

85

ceases to be felt at the wrist ; this point is the measure of systolic or
maximal pressure.

It is not always easy to determine the exact point at which the pulse ceases
to be felt. The difficulty is got over by Oliver, who attaches a small tambour

over the brachial artery at the elbow and connects this with a binaural stetho-
scope. As the pressure is raised over the upper arm the pulse beats become very
distinctly heard in the artery at the elbow, but when the pressure is sufficient to
occlude the brachial the beats instantly cease. This observation enables the
systolic pressure — which is the point of most value clinically — to be determined
with great exactitude.

CHAPTER XXI

PERFUSION OF VESSELS. LYMPH-HEARTS

Estimation of contraction or dilatation of vessels by measurement
of perfusion rate. — Tie a small glass cannula, bent round so that its
limbs are parallel, into the aorta of a large frog killed by destruction
of the nervous system ; it can either be passed directly into the cut
aorta or more easily through an incision in the ventricle.

In exposing the heart and aorta make as small an opening as possible. First
remove a flap of skin, then cut through the upper part of the ensiform cartilage
and extend the incision on either side of the sternum : force this up like a flap
until the heart is sufficiently exposed.

The cannula must be filled with Ringer's solution, and connected
through an india-rubber tube with a reservoir of the same fluid so
that the fluid is slowly dropping from it during its introduction;
this is for the sake of excluding air bubbles.

Suspend the frog by a pin through the jaw, and fix the reservoir a
short distance above the head so that the fluid flows into the vessels
by gravitation. Make a cut into the sinus venosus to enable the fluid
to flow freely out after it has traversed the blood-vessels of the body ;
the escaping fluid will drop from the toes, which should be tied together.
A cut must also be made through the skin of each foot to prevent any
accumulation in the lymph-spaces of the legs. Count the number of
drops per minute, and repeat the counting twice ; after the blood
is completely washed out the flow should be fairly regular.

To test the effect of drugs or reagents upon the muscular tissue of
the arterioles the reagent is added in known quantity to the perfused
fluid. The Ringer's fluid to which the drug is to be added is placed
in a second reservoir as in perfusion of the frog heart (see fig. 61, p. 70).
Again count the number of drops per minute (3 estimations), and
thus determine whether the arterioles are becoming dilated or con-
tracted as the effect of the reagent. This experiment may be tried

86

PERFUSION OP VESSELS. LYMPH-HEARTS

87

with Ringer's solution containing acid (HC1, 1 in 5000) and alkali
(NaOH, 1 in 5000), with a very dilute extract of suprarenal, and
with solutions of chloroform and ether in Ringer's solution. Normal
Ringer's solution must invariably be substituted afterwards for that
containing the drug, and a third determination made in the same
way (average of three counts).

The same method is used for perfusion of the organs of mammals. The can-
nula is tied into the artery of the (excised) organ, which is placed in a jacketed
funnel warmed to 40° C. : the perfused
fluid, which must also be warmed before
entering the organ, escapes by the vein and
runs down the funnel into a measuring
vessel. In this way perfusion can be con-
ducted through the kidney of the dog or
sheep, or through the vessels of a limb.
In the case of mammals it is important to
allow oxygen to bubble through the Ringer
solution used for perfusion.

Methods o£ recording the outflow of
fluid. — 1. The sequence of drops can be
recorded by aid of an electric drop re-
corder connected with an electro- magnetic
signal, which writes upon the smoked paper
of a drum.

2. Another method of graphically re-
gistering the rate of flow, especially if the
drops follow one another too fast to be
recorded individually by a drop-recorder,
is furnished by the " tilter " shown dia-
gramniatically in fig. 73. This is a small
vulcanite or celluloid trough with open
ends with a septum across the middle ;
the trough is balanced on a vulcanite knife-
edge. The drops are led over the middle,
and, falling on the side of the septum
which happens to be uppermost, they
gradually fill that side of the trough.

When full, it overbalances, and the trough tilts over to the other side, when
the process is repeated. Each double movement of the tilter is registered, either
by an electrical or a pneumatic arrangement, upon the recording paper, on which
the time is also written. The capacity of the tilter being known, the amount
of fluid flowing in a given time is ascertained. The record will continue auto-
matically for long periods.

The above methods are also used to record the flow of secretions
(Chapter XXII.).

Lymph-hearts. — Place a frog the brain of which has been destroyed, or which
has been decapitated, in the prone position on the frog-cork, and reflect the skin
from either side of the urostyle. Notice the pulsation of the lymph-hearts
beneath the fascia on each side : usually they do not synchronize. Destroy the
spinal cord completely by a wire. The lymph-hearts now cease to beat : their
pulsations are dependent on the spinal cord.

FIG. 73. — DIAGRAM OF TILTER. THE ROCK-
ING MOVEMENTS ARE RECORDED EITHER

BY ALLOWING THE ACCUMULATED FLUID
TO ACTUATE A TAMBOUR, OR BY AN
ELECTRO-MAGNETIC SIGNAL.

CHAPTER XXII

MECHANISM OF SECRETION

THE process of secretion may be studied in the salivary glands, the pancreas, the
kidneys, and the mamma. The influence of nerves upon secretion is illustrated
by the salivary glands, that of hormones by the pancreas and mamma : the
secretion of the kidneys is also dependent partly upon chemical agents, but
largely upon the blood-pressure and blood-flow through the organ.

The submaxillary gland. — A dog, having been anaesthetised, is fixed on its
back and a vein cannula inserted into a saphenous vein. An incision is then
made on one side through the skin and fascia below the mouth extending from
the chin backwards for three or four inches nearly parallel with the line of the
lower jaw. At the posterior part of the wound the submaxillary gland may be
observed. The anterior belly of the digastric, which comes into view and con-
ceals the hilum of the gland, is drawn over laterally by a weighted hook: or it
may be cut away. Any oozing from small vessels is controlled by rinsing the
wound with dilute extract of suprarenal : larger vessels are tied. A muscle —
the geniohyoid — is now exposed : it is composed of transverse fibres. When it
is cautiously cut through, the duct of the submaxillary gland (Wharton's duct)
is seen passing obliquely forwards towards the floor of the mouth. It is accom-
panied by a smaller duct, that of the sublingual. Crossing these ducts is a
conspicuous nerve — the lingual branch of the 5th. If this is drawn towards
the middle line with a blunt hook, it is seen that just before it crosses the ducts
it gives off a small nerve — the chorda tympani — which runs sharply backwards
and enters the hilum of the submaxillary gland, where the duct is emerging.
Tie a thread around the lingual above the place where the chorda leaves it,
and, without injuring it, clear a short length of the chorda so that a small pair
of flat electrodes can be placed underneath it. Stimulate by induction shocks :
the duct will fill with saliva.

Place a wet thread round the duct and slip a pointed piece of paraffined paper
under it. Make a snip into it with fine scissors ; pass a " finder " into the aper-
ture. Substitute for the " finder " a very fine metal or glass cannula, and tie
this in : a piece of small rubber tubing can be used to conduct the secretion
beyond the edge of the jaw, where it can be allowed to drop into a beaker.

On the same side of the neck make a longitudinal incision through the skin
and fascia, and separate the muscles so as to expose the carotid artery and the
common trunk of the vagus and sympathetic nerves. Ligature this combined
nerve low down, and place the upper end on a second pair of electrodes. The
two pairs of electrodes — for chorda and sympathetic respectively — are con-
nected to a commutator without cross-wires, and this with the secondary coil,
so that stimulation can be led into either pair at will.

1. Stimulate the sympathetic. A few drops of thick viscid saliva are
secreted.

2. Stimulate the chorda. There is a rapid flow of watery saliva lasting aa
long as the excitation is continued.

88

MECHANISM OF SECRETION 89

3. Inject a small amount of pilocarpine nitrate (2 or 3 milligrams) into the
saphenous vein. This produces an intense secretion.

4. Inject a small amount of atropine sulphate (5 milligrams) into the vein.
The flow produced by pilocarpine immediately stops.

6. Stimulate the chorda. The strongest stimulation produces no effect.
Atropine has paralysed the nerve endings.

6. Stimulate the sympathetic. A few drops of saliva may be secreted.
The dose of atropine is insufficient to abolish the action produced through the
sympathetic.

The pancreas. — A dog is anaesthetised and a cannula tied into the saphenous
vein. Open the abdomen by an incision in the linea alba. Find the duodeum
and bring it up to the surface : the pancreas is seen in the mesentery within
its curve. The duct of the gland — canal of Wirsung — may be found without
difficulty near the lower end of the part of the gland which is in contact with
the duodeum. Isolate a short length of the duct with forceps ; pass a wet ligature
round it and slip a pointed piece of paraffined paper under it. Make a snip
into the duct with fine scissors, introduce a finder, substitute for the finder a
fine metal or glass cannula, and tie this in. Attach a short piece of rubber
tubing to the cannula, bring the end of this outside the wound, and let the drops
of secretion fall into a beaker.

1. Inject into the saphenous vein 5 c.c. of an extract of duodenal mucous
membrane of any animal. The extract is made by boiling the clipped mucous
membrane with -5 per cent, hydrochloric acid, cooling the decoction, neutralising
with dilute alkali, and filtering. It contains secretin, which has the effect of
producing a rapid flow of pancreatic juice when injected into the circulation.

2. Inject pilocarpine nitrate and compare the effect with that of secretin.
The mamma. — A lactating animal (cat) is anaesthetised and a cannula tied into

the external jugular vein. Vaseline the fur over one of the mammas, and arrange
the animal so that this gland slightly overhangs the edge of the animal board.
Cut away the nipple of that mamma and make a short transverse incision into
the substance of the gland. Still any bleeding with cotton-wool or with dilute
suprarenal extract. Some milk may ooze out : it will run down the vaselined
fur, and can be caught in a beaker.

1. Inject into the vein 1 c.c. of a 10 per cent, decoction of corpus luteum
(filtered). Milk will, in a minute or two, exude and drop rapidly from the gland.

2. Inject into the vein 1 c.c. of a 10 per cent, decoction of posterior lobe of
pituitary body. The same result will ensue, but the flow will be more rapid.

The kidney. — In an ansesthetised rabbit or cat tie a cannula into the jugular
vein and connect the carotid with a manometer for taking blood-pressure.
Make an incision through the skin and muscles on the left side of the abdomen
near the back over the situation of the kidney, which is easily felt. After ex-
posing the kidney, bring it towards the surface, clear it partly of fat, and allow
it to lie in a suitable plethysmograph (fig. 68) the margins of which have been
vaselined, and place over it a glass cover also well vaselined : the cover is clipped
down on to the plethysmograph. The blood-vessels and ureter pass out at a
chink (g) left on one side of the plethysmograph ; the chink is made airtight
with vaseline. A tube leads from the plethysmograph to a piston recorder (p.r.)
writing on smoked paper. Make another incision in the lower part of the
abdomen in the middle line ; find the urinary bladder ; hold it up with two pairs
of clamp forceps ; loop a ligature round it just outside these ; make an incision
into it, and introduce a glass cannula, which must then be tied in. The urine
can be led from this cannula over the side of the animal by a rubber tube, and
the drops can be registered by a drop-recorder.

1. Inject pituitary extract into the vein, and record the effect on blood-
pressure, kidney, volume, and urine.

2. Inject a few milligrams of caffeine citrate into the vein, and record its
effect in the same way.

3. Inject atropine sulphate (5 milligrams). This has no effect on the secretion
of the kidney (compare with its effect on salivary secretion).

CHAPTER XXIII

RESPIRATION

The respiratory movements in man.— Examine the chest during quiet
respiration, and notice the parts in which movement is most evident ;
the same with forced respiration. Observe the alteration in obliquity

sp

fr

FIG. 74. — BURDON-SANDERSON'S STETHOGRAPH. fr, FRAME SUSPENDED OVER THE SHOULDER BY

CORD, c ; b. V, BUTTONS APPLIED TO OPPOSITE SIDES OP THE CHEST WALL ; sp, STEEL SPRING ;
t, RECEIVING TAMBOUR ; t', RECORDING TAMBOUR.

and other changes in position of the ribs, rib-cartilages, sternum, and
epigastrium. Apply the ear directly or through a stethoscope to the
chest wall and listen to the vesicular murmur. Count the rate of

respiration and compare it with that of the pulse of the same individual.

90

RESPIRATION

91

For the following experiments the slowest rate of drum is to be used, and
the subject must not be allowed to see the tracing which is being taken.

Record of respiratory movements. — Apply a stethograph (Marey's
or Sanderson's) (fig. 71) to the chest, and register the movements of
respiration by means of a recording tambour.

m

FIG. 75. — SPIBOMETEE ARRANGED TO REGISTER, UPON A SLOWLY REVOLVING DRUM. THE AMOUNT
OF AIR RESPIRED, sp., BODY OP SPIROMETER ; cy, MEASURING CYLINDER WITH SCALE AND
WRITER ATTACHED ; v., v'., WATER VALVES ; m, MOUTHPIECE.

Apno3a. — Remove the lever of the recording tambour from contact
with the drum. Cause the subject to take a number of deep respira-
tions at a rapid rate. Then let him cease these voluntary efforts, and
take a record of the ordinary breathing which succeeds to them.
There will probably be a pause (apnoea) followed by respirations which
are at first shallow but gradually become of the ordinary character.

Measurement of amount of air passing into and out of lungs.—
Using either an airtight mask or a niouth-tube (in this case the nostrils

92

EXPERIMENTAL PHYSIOLOGY

must be closed by a clip) provided with valves (see diagram, fig. 75),
allow the subject to breathe during one minute into a carefully
balanced spirometer. Count the number of respirations in the given
time and note the amount of air which has been breathed in that
time. From these results calculate the tidal air passing through
the lungs with each respiration. The observation should not be

A

1!

FIG 7c. PRONE-PRESSURE METHOD OP ARTIFICIAL BESPIRATION. A, PRESSURE

BEING APPLIED ; B, PRESSURE REMOVED.

begun until the subject is breathing regularly arid unconsciously, and
he must not be permitted to see the spirometer.

Reserve air, supplemental air, vital capacity. — Determine in your
own person with the spirometer the amounts of each of these and
note down the results.

Measurements of the chest and abdomen in deepest inspiration
and in deepest expiration. — Determine these upon yourself (a) at the
level of the armpits, (6) at the level of the lower end of the
sternum, (c) at the level of the umbilicus, using a tape measure.
Note down the results.

Artificial respiration in man. — Place the subject flat on the ground

RESPIRATION 93

in the prone position with the head on one side. Kneel or squat by
the side of or across the lower part of the body, facing the head, and
place your hands flat on the loins with the thumbs nearly touching at
the spine (fig. 75). Throw the weight of your body forwards on the
hands, keeping your arms straight (^4), and count slowly one, two, three,
four, five. Whilst counting four, five, swing backwards (B) so as to take
the weight off your hands. Then swing forward again, counting, as
before, one, two, three, and backwards, counting four, five ; and so on
about twelve to fifteen times a minute. The effect of the pressure is
to force the abdomen and lower part of the chest against the ground
so that the viscera are pressed against the diaphragm. In this way
air is driven out of the lungs. On relaxing the pressure the parts
resume their former position ; the diaphragm descends and air is
drawn into the lungs.

The amount of air thus pumped through the lungs in a minute can
be measured by the spirometer in the same way as the tidal air
measured in natural respiration.

Negative pressure within thorax. — Introduce through an intercostal space Into
the pleural cavity in the human cadaver or in any dead animal a sharp-pointed
cannula or hollow trochar connected by rubber tubing to a water manometer.
Notice that as soon as the trochar passes into the pleural space the water hi the
distal part of the manometer sinks and registers a certain amount of negative
pressure within the thorax.

Effects of stimulation of nerves and of asphyxia upon the respiratory move-
ments of animals. — These have been studied hi connexion with blood-pressure
(see pp. 81, 82).

CHAPTER XXIV

PERIPHERAL NERVES

Nerve-roots ; Magendie's experiment. — Decapitate a large frog and
fix it securely in a prone position on the frog-cork. Cut away the skin
along the whole length of the spine. With a pair of strong but fine
scissors sever the neural arches on each side, working from above
down, and removing them so as to expose the spinal cord and the
nerve roots. The dorsal roots are distinguished both by their position
and by the ganglia through which they pass ; they are especially large
and long in the lumbo-sacral region. Cut them here on one side of
the body.

1. Tetanise the skin of the corresponding foot. No reflex move-
ment is produced : although if the skin of the opposite foot be
stimulated, strong movements are produced in both limbs.

2. Stimulate the distal end of one or more of the cut roots. If
care be taken that the current does not spread to a ventral root, no
movement results.

3. Stimulate the proximal end. Strong reflex movements are
caused. Now cut the ventral roots on the same side in the same
region. Notice that on cutting them the leg muscles contract.

4. Stimulate the peripheral end of one or more of the cut ventral
roots. There is strong contraction of muscles of the corresponding
limb.

5. Stimulate the central end of the same. No effect is observed.
N. B. — The excitation used for the roots may be mechanical, such

as a pinch or snip of the scissors near the cut end. In this case errors
which with electrical stimulus may arise from spread of current are
obviated. But if the Helmholtz arrangement is used and only weak
induction shocks employed, the risk of spread is much reduced.

94

CHAPTER XXV

REFLEX ACTION : REACTION TIME

A PROG the brain of which has been removed 1 is used for the follow-
ing experiments. Note the position of the animal when placed on
the table, and the absence of spontaneous movements. Suspend the
preparation by the lower jaw (fig. 78). Have ready a large jar or
beaker of water (a), a small beaker of 2 per 1000 sulphuric acid (&),

Nares..

Olfactory lobes.

Cerebral hemispheres.
-Thalamus with pineal gland.

" Optic lobes.
" Cerebellum.

- Medulla oblongata.

Spinal cord.
FIG. 77, — BRAIN IN FROG in situ, EXPOSED BY REMOVING THE ROOF OP THE CRANIUM.

and some small pieces — about 2 mm. square — of filter paper,
moistened with 5 per cent, acetic acid. A watch, with seconds
hand, or a metronome is also required.

Effect of strength of stimulus. — Gently pinch the toe of one foot
with forceps ; the leg is drawn up. When again quiescent pinch
the toe more firmly ; not only the one, but both legs are drawn up,

1 For some of the experiments on reflex action the whole contents of the
skull are destroyed. This can be done without haemorrhage by inserting a
sharp-pointed plug of wood through the occipital foramen. For other experi-
ments only the cerebrum or brain proper is destroyed, the optic lobes and
medulla oblongata being left. This is effected either by crushing the anterior
part of the skull with Spencer Wells forceps ; or by opening the skull and
removing the hemispheres in an anaesthetised animal; or simply by cutting
away all the part of the skull in front of the tympanic membranes with stout
scissors.

95

96

EXPERIMENTAL PHYSIOLOGY

and there may also be a movement of the upper limbs (spread of
excitation).

Effect of summation of stimuli.— Stimulate the toe (1) with single
and (2) with interrupted induced currents. Determine and note down

FIG. 78; — TURCK'S METHOD OP DETERMINING TURN OP BEPLEX TO ACID-STIMULUS APPLIED TO TOES
OP DECAPITATED FROG, a, BEAKER OP WATER ; 6, BEAKER OP DILUTE ACID ; c, METRONOME ;

d, HOOK SUSPENDING FROG BY LOWER JAW.

at what distance of the secondary coil from the primary the reflex
response is elicited in each case.

Purposeful reflex action. — Place on one flank a piece of paper
moistened with acetic acid ; the foot of the same side is raised to
rub off the irritant ; if that foot is held down, the other foot may
be used.

After the observation do not leave the acid in contact with the flank, but
wash it off by bringing a large beaker of water up over the legs and lower
part of the trunk. The experiment may be repeated upon other places ; e.g.
the inside of one thigh, the upper pait of the body, and the abdomen, always
•washing the acid away after each observation.

REFLEX ACTION : REACTION TIME : EXCITATION OF CORTEX 97

Time of reflex response ; Turek's method. — Having allowed the
frog to become quiescent, allow the extremity of the toes to dip into
a small beaker of dilute sulphuric acid (2 per 1000). Count the time
in half-seconds which elapses between the application of the acid and
the withdrawal of the toe. Wash the acid off immediately after the
withdrawal. Kepeat this observation three times at intervals of a
few minutes ; calculate and record the average time of response.

Inhibition of reflex by an accompanying excitation ; Setschenow's
experiment. — Place a crystal of chloride of sodium upon the optic
lobes (or on the upper cut end of the cord if the whole brain have been
removed), and again determine the time of response after application
of the dilute sulphuric acid to the toes.

Reflex inhibition of heart. — Fix the frog securely on its back upon
the frog-cork ; expose the heart sufficiently for its beats to be ob-
served. Tap the abdomen smartly with some small heavy instrument
such as a metal rod or the handle of a knife. The effect will be to
produce a slowing or complete stoppage of the heart, which will, how-
ever, soon recommence beating. The same result is obtained if the
abdomen be opened and a loop of intestine strongly stimulated.

For this experiment the medulla oblongata must be left.

Effect of strychnine on reflex action. — Inject a very small dose
of strychnine nitrate (1 drop of a 1 per 1000 solution) under the skin
of a decerebrate frog, and wait for a few minutes until it is absorbed
into and distributed by the circulation. It will be found that pinching
the skin eventually produces not simple purposeful reflex actions,
but convulsive contractions of all the muscles in the body.

Tendon reflex ; knee jerk. — In a subject seated in a chair with
one leg crossed over the other, or seated on a table with the legs
dangling, strike the patellar tendon with the handle of a knife or
the back of a thin book. Notice the sudden jerk forward of the
leg owing to the contraction of the vastus internus. This can be
recorded by a transmission myograph (see p. 38).

Reinforcement of tendon reflex. — Just before striking the patellar
tendon cause the subject to clench his fist. The movement of the
leg will be stronger, or will be elicited with a slighter tap on the
tendon.

Reflex action in mammals.— The reflex actions which depend upon the spinal
cord can be studied in a Sherrington preparation (see p. 81), reflexes being
elicited in various ways, as by pinching or pricking one of the paws or the skin
of the flank or side of the thorax. Tendon-reflexes, such as the knee jerk (see
above) and the ankle-clonus, obtained by forcibly bending the foot at the
ankle, can also be well observed in such a preparation.

7

98

EXPERIMENTAL PHYSIOLOGY

Reaction time in man. — The reaction time in man may be deter-
mined by an arrangement of electric signals, but is done more simply
by Waller's apparatus (fig. 79). This consists of two wooden levers
lying across a piece of india-rubber tube, one end of which is closed,
the other being connected with a tambour which writes upon a
drum, the speed of which should be moderate. A screen hides the
movements of the experimenter from the person experimented on,
who sits at the table with one finger resting lightly on the
extremitv of one of the levers. He is to respond by pressing the

FIG. 79. — WALLER'S APPARATUS FOR REACTION TIME, a, RUBBER TUBE CLOSED AT ONE END AND AT

THE OTHER CONNECTED BY 6 WITH A TAMBOUR (NOT SHOWN) ; C, d, d, d', LEVERS (WITH COLOURED

PATCHES) HINGED NEAR c\ d', AND RESTING ON TEE RUBBER TUBE, a ; e, WOODEN SCREEN.

lever the instant he (1) feels a movement of that lever, his eyes
being shut ; (2) hears a tap on the second lever ; (3) sees a move-
ment which is imparted to the second lever by the experimenter,
who presses it down on the other side of the screen. In each case
two marks are recorded upon the abscissa : one being that which
is made by the experimenter in imparting the stimulus, and the
other that made by the observed person in responding. The interval
between the two marks, which can be accurately measured by the aid
of a time tracing, indicates the time between stimulus and response—
i.e. the reaction time — in the case of each of the three senses. To
record this with any accuracy several observations must be made
with each method of stimulation and the average time calculated.

REFLEX ACTION : REACTION TIME : EXCITATION OF CORTEX 99

Discrimination time. — -For the measurement of this the observed
person places one finger over each lever. It is agreed beforehand
that he is only to react to a stimulus received on the one side, not
on the other. The experimenter may stimulate either. It will be
found that the reaction time is lengthened by a certain interval,
and this increase of reaction time is termed the discrimination time.
Determine and record this.

Volitional time. — Similar arrangements are made, but with the
understanding that it is only the hand on the side which receives the
stimulus which is to be used for the response. The reaction time is
now found to be still more lengthened because the observed person
has to make a double decision ; viz., to determine not only which of
the two hands has been stimulated, but also which one he has to use in
response to the signal.

Variations of the above experiments can be made with the employment of
different sounds and the exhibition of different colours, but the methods for re-
cording the reaction times are essentially the same. For rapid and accurate
work it is usual to employ a specially constructed clock which can register the
time of a reaction to a fraction of a second.

Excitation of the cortex cerebri.— A monkey, anaesthetised with ether, is
used for this demonstration. A considerable portion of the skull cap is
removed on one side by trephining the skull and enlarging the aperture by
bone-forceps. The dura mater is then cut through below and reflected towards
the middle line, thus exposing the cerebral surface. A pair of blunt-pointed
platinum electrodes, with their points 1 mm. apart, is connected with a
du Bois key in the secondary circuit of an induction-coil (use the Helmholtz
modification) and applied to various spots in the excitable region of the frontal
lobe, the first temporal gyms, and the occipital lobe, and the results are
noted.

The rnonopolar method of stimulation may also be employed for these
observations. In this case one electrode is a flat pad of wash leather wetted
with strong salt solution, and the other [stimulating] electrode is a small spiral
platinum wire with blunt point, which is applied to the excitable areas of
the cortex.

CHAPTER XXVI

CUTANEOUS SENSATIONS

Cutaneous sensations ; Pain spots. — Explore with an ordinary pin
a portion of the skin of the forearm or back of the hand of another
person (who should keep his eyes closed), pressing the point firmly
here and there, but without penetrating the surface. Notice that
whereas at some places the prick is painful, at others no pain is
caused, the feeling being either one of touch or pressure or no
sensation is produced.

Warmth spots. — Substitute for the pin a steel or copper rod with a
smooth blunt point, like a knitting-pin ; the rod may be provided with
a wooden handle. Warm the rod by immersing it in water heated to
50° C. Explore the skin by drawing the warm point of the style
slowly over it. It will be found that the sensation is only one of
warmth at certain points, where it is very distinct ; at others it is
merely a sensation of touch.

Cold spots. — Repeat after cooling the rod by immersing it in ire-
cold water. In this way spots sensitive to cold alone can be picked
out : they are not the same as those which are sensitive to warmth.

The various spots may be mapped out upon a patch of the skin with coloured
inks or pencils, and may be tested again later. They are constant in position.

Touch sensations ; Determination of the relative delicacy of different
parts to touch. — Take a fine bristle or coarse hair two inches long, and
fix it with sealing-wax to a match to serve as a holder (fig. 80). Ex-
plore in another person (who is not to see the part which is touched) any
part of the skin, determining the spots which are most sensitive to the
pressure of the hair. The point of this is to be brought vertically on the
skin without lateral movement and pressed down only just enough 'to
bend it slightly. By using a number of bristles of different thickness

a certain rough scale of delicacy of touch on different parts of the body

100

CUTANEOUS SENSATIONS 101

can be made out. Notice that the slightest side-movement greatly
increases the sensitiveness of any part to the touch, especially if any
hairs are deflected. This can also
be shown with a scrap of cotton-
wool, the touch of which may be
imperceptible until it is moved.

The series of bristles just de-
scribed form collectively v. Frey's
jesthesiometer. In place of these,
an instrument is sometimes used FIG. so.— v. FRET'S HAIR JSSTHESIOMETER.
consisting of a fine blunt needle

set in a handle, within which is a delicate spiral spring furnished
with an index to show the amount of pressure required before a
sensation is caused. But in general this is found more difficult to
apply than the bristles.

Graham Brown's aesthesiometer consists of a convex piece of
steel with a polished surface, a part of which can be made to
project beyond the rest by turning a truly cut micrometer screw.
The surface is passed lightly over the surface of skin to be tested, or
vice versa. The relative delicacy of touch is gauged by the power
of feeling different degrees of projection.

Discrimination of two points. — For this purpose a pair of compasses
with blunt points is used ; their distance apart is measured upon
a scale after each observation. Or the points may be permanently
connected with the scale, one being fixed at its zero and the other
sliding along it (Sieveking's sesthesiometer). Test in this manner in
another person various parts of the integument (back and front of arm,
fingers, lips, tip of tongue, etc.) and record the distances at which the
two points are discriminated as separate, causing them always to
touch simultaneously, and without lateral movement.

Accuracy of localisation. — This is investigated by lightly touching
any part of the skin and immediately causing the subject to place
his finger upon the part touched.

In all the above experiments the subject should be blindfolded.

CHAPTER XXVII

EXPERIMENTS ON THE DIOPTRIC MECHANISM

AN eye (ox, sheep, or pig) is to be dissected. (1) After cleaning away from the
globe all remains of muscles, fat, etc., cut a window out from the back, removing
the sclera and choroid and exposing the retina. Notice that when the cornea
is turned to the window an inverted image of this is formed upon the retina.
(2) Cut away a small portion of the sclera at the edge of the cornea. A grey-
looking ring of plain muscular tissue is exposed, the fibres passing from the
corneo-sclerotic junction backwards over and into the choroid. This is the
ciliary muscle. (3) Cut the eye in two at its equator. Notice, in the posterior
half, from which the jelly-like vitreous humour flows away, the retina — usually
somewhat opaque and crumpled after death — spreading out from the entrance
of the optic nerve ; in the anterior half the lens within its capsule, the suspensory
ligament around the margin of the lens, the radiating ciliary processes. (4) Snip
through the suspensory ligament all round the lens, which can be removed
within its capsule ; the iris is now seen projecting into the anterior chamber.

Accommodation; Change in shape of the lens. — That the lens
bulges forward in accommodation is shown in various ways.

1. Stand at the side of another person and let him fix his vision
on a distant object, looking beyond a near object such as a needle or
pencil held a few inches from the eye. Notice his iris which can be
seen through the edge of the cornea lying against the front of the lens.
Now let the subject look at the near object. His iris is seen to advance,
being pushed forwards by the bulging lens ; the pupil at the same
time contracts.

2. Sansoris images. — In a dark room hold a candle at one side of
the eye of a subject, and, standing on the other side, observe the
reflected images — a bright one from the front of the cornea, a less
bright one from the front of the lens, and a duller, small, and inverted
image — difficult to see — from the back of the lens. The subject as
before is to have his vision fixed at first on a distant object, and is
then to transfer his gaze to a near object in the same line. The
image reflected from the front of the lens becomes smaller and moves
nearer to that reflected from the front of the cornea ; the other

102

EXPERIMENTS ON THE DIOPTRIC MECHANISM

103

n

G- si.— PHAKOSCOPE ; a, SITUATION- OP
OBSERVED BYE ; 6, DITTO OP OBSERVER'S
ETE ; c> LENSES ; n, APERTURE WITH
NEEDLE.

images remain unaltered. This change of the second image is due to
bulging of the anterior surface of the lens.

3. Phakoscope. — The same experiment may be performed with a
phakoscope (fig. 81) with less trouble, since all the points are fixed. The
instrument — a triangular box with truncated angles a, b, c — is used
in a darkened room. A lamp is placed in such a position that the
light from the two square window prisms at c falls upon the observed
eye at a. The observer looks
through the opening at b and sees
in the observed eye three pairs
of images — two bright squares
(reflected from the anterior surface
of the cornea), two larger but less
distinct squares, and two smaller
and much dimmer squares. The
two last pairs, being reflected from
the anterior and posterior surfaces
of the lens respectively, can, of
course, only be seen within the
pupil. The last pair is difficult to
make oat. If the subject be asked, first to look through the needle n
at a distant window and then at the needle, the middle pair of images
become smaller and slightly brighter ; they also approach each other
and come nearer to the corneal images during accommodation for
the near object ; the other two pairs remain unaffected.

Near and far points of distinct vision. — A wooden scale about
twelve inches long is marked in inches or centimeters. One end of
this is placed close to the eye, and a needle is put in about five
inches off. If the eye is normal, it should be seen sharply at this
distance and at any point beyond ; but if it is brought nearer the
eye its image becomes blurred. If the eye is myopic the needle may
be brought nearer than five inches without its image being blurred ;
when this occurs the near point for that eye has been passed.

If the eye is hypermetropic the needle will already appear blurred
at five inches, and it may be required to be moved considerably
further from the eye before the near point of distinct vision is
passed.

Pater Scheiner's experiment. — The observation is rendered easier
and more striking by Scheiner's device of observing the needle
through two pinholes made close to one another and side by side in
a card fixed vertically at one end of the scale (fig. 82). In this

104

EXPERIMENTAL PHYSIOLOGY

case, when the needle is nearer to or further from the near or far
points of distinct vision, its image appears not blurred but double.

That the eye cannot obtain a sharp image simultaneously of a
near and a distant object is shown by taking two needles and fixing
one at about five inches along the scale and the other some inches
further. If now, in Schemer's experiment, the eye is focused on the
near needle the far one looks double, and vice versa.

FIG. 82.— BOARD WITH PERFORATED CARD FOR SCHEINER'S EXPERIMENT, a, 6, NEEDLES ;

c, PERFORATIONS IN CARD.

Changes in the pupil produced by drugs.1 — Carefully enucleate
the eyeballs of a frog which has just been killed and place each in
a watch glass of Ringer's solution. Measure the diameter of the
pupils with compasses and note down the size of each. Add to the
contents of one watch glass a drop or two of extract of suprarenal
capsule or of dilute solution of eserine or of atropine. After a short
time again measure the pupils. Repeat the measurement after an
hour or more.

The effects of drugs are also investigated, in man or animals, by
dropping them on the conjunctiva, and, in animals, by injecting
them into a vein.

The Ophthalmoscope. — This instrument, which is used for examining the
interior of the eyeball, consists essentially of a small concave mirror with a
hole in the centre. (For the indirect method a biconvex lens is also required.)
Practise first on an artificial model of the eye and then on the living subject.
It can be practised upon a rabbit : a drop or two of a 1 per cent, solution of
atropine should previously be instilled into the eye. Or a frog, with the body
wrapped in a cloth, held up near the source of light may be employed.

Direct method. — Only a limited part of the retina is seen at one time, but it
is much magnified. The subject is seated in a darkened room with a light, not
too bright, near his ear. The observer sits in front of, and on a slightly higher
level than, the subject, close to him. The observer holds the mirror in front
of and close to his own eye, and, throwing the beam of light into the subject's

1 The effects upon the pupil of cutting and stimulating the sympathetic have
already been studied (see p. 82).

EXPERIMENTS ON THE DIOPTRIC MECHANISM 105

eye, asks him to look upwards and inwards. The observer then moves the
mirror, with his eye close behind it, backwards and forwards, looking through
the hole in the centre, and when the proper distance is found (two to three
inches), the retina comes into view with its vessels running in different directions
on a red ground. The mirror 'is moved about until the optic disk (entrance of
optic nerve) is seen as a whitish circular area with the central artery and vein
of the retina emerging at its centre. The image of the fundus is virtual
(erect), and it is enlarged because the lenses of the subject's eye magnify the
parts behind.

Indirect method. — With the subject as before, the observer places himself
about eighteen inches in front of the patient and throws the light on the pupil
as in the direct method. He then takes a small biconvex lens (two to three
inches focus) in his left hand, and, holding it vertically between the thumb and
forefinger at a distance of two to three inches from the patient's eye, moves his
own eye with the mirror in front of it backwards and forwards and from side to
side until the optic disk and other parts of the retina are seen. The image is
real (inverted), and is only slightly magnified.

Retinoscopy is difficult in the human subject unless the pupil has been
previously dilated by atropine. If the patient or observer has abnormal vision
this is corrected by suitable lenses placed behind the aperture in the mirror.

CHAPTER XXVIII

STIMULATION OP THE RETINA

Electrical changes. — That an electrical change results from the action of light
upon the retina can be shown in the frog. The eye is enucleated and is placed
on non-polarisable electrodes, one of which is in contact with the cut optic
nerve, and the other with the front of the eye. The electrodes are connected
with a galvanometer, and the preparation is placed in a dark box. On letting
light into the box an electric change is produced in the retina, and the galvano-
meter is deflected. On removing the light there is another deflection in the
same direction.

Blind spot; Mariotte's experiment. — Make a mark of any sort
(such as a cross) upon a piece of paper, and fix one eye — say the right
—upon it, closing the other eye and placing the head about 6 inches
from the paper. It will be found that over a considerable area of
irregular shape, about 3 or 3| inches from the cross, the point of a pen
or pencil will not be visible because its image falls upon the place
where the optic nerve enters the retina. Even a large black dot made
in this area upon the white paper is quite invisible as long as the eye
is fixed upon the cross. The experiment shows that the optic nerve
fibres are insensitive to light. Map out the blind area.

Macula lutea ; Maxwell's experiment. — Close the eyes for a minute
and on opening them hold a bottle with parallel sides containing a
solution of chrome alum — which has a greenish colour — between one
eye and a uniform source of light such as a cloud. The middle
of the field of vision will be occupied by an oval rose-coloured area ;
the alteration in colour of this part is due to absorption by the
yellowish pigment of the macula of some of the rays transmitted
through the chrome-alum, which is dichroic, transmitting greenish-
blue and red rays ; the former are absorbed.

Purkinje's experiment. — This is to be attempted in a darkened
room. Stand about 8 feet from a sheet of white or grey paper fixed
to the wall and get an assistant to illuminate the retina through the
sclerotic by means of a converging lens and lamp or candle held at

106

STIMULATION OF THE RETINA 107

one side of the eye. Look steadily at the paper with one eye, accom-
modating it for distance. In a minute or two a number of branching
figures will be seen Like the roots of trees. These are the shadows
of the retihal blood-vessels. When the light is moved the shadows
are also seen to move. This experiment shows that the visual cells
lie behind the blood-vessels of the retina.

Perimetry. — The perimeter is an instrument for testing and re-
cording light perceptions in different parts of the retina. The eye is
fixed upon a point in the centre of the concave hemisphere forming the
perimeter, and a white disc is brought gradually from the edge of the
hemisphere nearer and nearer to the centre until it is perceived. This
is repeated along different meridians and the results are marked on a
chart at the back of the instrument. By using coloured discs instead
of white the area of the retina which is sensitive to each colour can
also be ascertained.

The field of vision of a person may be compared roughly with that of the
observer in the following manner: — Stand 2 feet in front of the subject, close
one eye, ask him to do the same and to look steadily at your eye. Move the
fingers of both your hands held in a vertical plane midway between yourself
and the subject, drawing the hands apart in the horizontal, vertical, and oblique
directions, and note when the moving fingers pass out of his field of vision.
If the field is normal in both cases, the observer and the subject should cease to
see the fingers at the same time. If it is much restricted in the subject, the fact
will easily be detected.

Testing for colour vision. Edridge-Green's lamp and spectroscope.
Holmgren's wools. — The best practical method for testing colour
vision is by the use of a lamp provided with glasses of different colour,
the subject being expected to name the colour which is exhibited. A
more accurate method of obtaining spectral colours for testing purposes
is the employment of a spectroscope so arranged that only a definite
part of the spectrum with a pure spectral colour is visible at one time

A method which has been considerably used for testing colour
vision is to take a box full of skeins of wool dyed with different colours,
and, selecting one skein, to ask the person who is being tested to pick
out any that match it. If he is colour-blind he is liable to make
serious mistakes, matching grey with red, green with grey or red, and so
on ; but it occasionally happens that persons who fail completely with
the lamp test are able, probably by judging from the intensity of the
reflected light, to match the Holmgren wools fairly well.

Successive contrast. — Fix the vision upon a white spot on a dark
ground. After one minute look at a uniform white surface such as a
white ceiling. A dark spot now occupies the centre of the field of
vision.

108 EXPERIMENTAL PHYSIOLOGY

This experiment is varied by employing colours— e.g. a yellow
spot on a blue ground or vice versa ; and a red spot on a green ground
ot vice versa. In each case the vision is transferred to a uniform white
surface and the contrast colours are observed.

For the grounds coloured paper is used ; for the spots either disks
cut out of the paper, or wafers laid upon it.

Meyer's experiment. — Place a grey disk upon a yellow ground, and
cover the whole with thin tissue paper ; the grey disk at once appears
blue : the contrast colour of the yellow. If a blue ground be used the
disk will appear yellow. The same experiment may be repeated with
red and green grounds. On a white ground the grey disk will appear
darker ; on a black ground lighter.

Colour mixer. — -This usually takes the form of a revolving circular
plate on which sectors of different coloured cards can be fastened.
Owing to the fact that retinal impressions have an appreciable dura-
tion, the colours appear blended during the revolution of the plate,
and the mixing of the colours on the retina can thus be studied.

Stereoscope. — The fact that in stereoscopic vision the mind com-
bines the effects produced by slightly dissimilar pictures falling on
the two retinae is illustrated by the ordinary stereoscope.

CHAPTER XXIX

THE PRODUCTION OF VOCAL SOUNDS. ANALYSIS OF SOUNDS.
AUDITION. SEMICIRCULAR CANALS

Use of the laryngoscope. — The laryngoscope consists of a small circular plane
mirror fixed to a handle at a suitable angle ; a large concave mirror with a hole
in the centre is strapped to the operator's forehead.

Method of procedure. — Practise first on an artificial model of the larynx
and afterwards on the living subject. The latter is placed on a stool with a
lamp over his right shoulder, a little above the level of his mouth. The observer
sits opposite and close to the subject with the large mirror attached to his fore-
head. The subject is asked to open his mouth, incline his head slightly back-
wards, protrude his tongue, and to hold it down with a handkerchief. The
observer manoeuvres his head until the back of the subject's throat is brightly
illuminated ; he then takes the small mirror in his right hand, warms it slightly
in a flame to prevent moisture condensing on its surface (the back of the mirror
should be just perceptibly warm to the cheek), and, holding the handle as one
does a pen, pushes it horizontally backwards until it touches the uvul&. First
the dorsum of the tongue is seen in the mirror, then, as the handle is depressed, the
epiglottis ; then the glottis and vocal cords come into view. The image of the
larynx thus obtained is an inverted one. In ordinary breathing the glottis is
open ; if the patient be asked to sound a high note the vocal cords may be seen
to come together and to vibrate, and if he be asked to take a deep breath they
separate, and the interior of the trachea and even its bifurcation may be seen
through the widely open glottis.

Should there be a tendency to retch when the mirror comes in contact with
the soft palate, this may be diminished by the application of a solution of
cocaine to the mucous membrane.

The movements of the laryngeal cartilages are studied in a model which re-
presents them articulated together. The action of the muscles can be imitated
by threads, and the vocal cords by thin flat rubber bands stretched between the
thyroid and arytenoids.

The production of vowel sounds. — Notice that the production of the vowel
sounds (ah, eh, ee, o, oo) is accompanied by changes in the shape and size of
the resonating chamber formed by the throat and buccal cavity.

The production of consonants. — Notice that most of the consonants are
produced by an interruption, completed and incompleted, of the blast of air
which is producing the vibration of the vocal cords, the interruption occurring
either at the back of the palate (gutturals) or at the front of the palate (linguals),
or at the lips (labials). Notice also that the character of the interruption is a
factor in determining the quality of the consonant : thus, with some, such as
k, b, and t, it is sudden or explosive : with others, such as m and n, the nasal
cavities are brought in as resonators : with others, such as ch, f, and s, the
blast is continuous, but is made to traverse a narrowed part of the cavity :
whilst with q there is an actual vibration of the narrowed part.

109

110 EXPERIMENTAL PHYSIOLOGY

The production of sounds by vibration of the vocal cords, and the dependence
of the pitch of sounds on the tension of the cords. — Take a sheep's larynx and
tie a glass tube into the trachea. Fix the larynx securely on a board, with the
dorsal surface downwards, by wires or strong pins through the cricoid cartilage
and epiglottis. Pass a string through the lower part of the thyroid cartilage.
When this string is pulled vertically upwards, the vocal cords are stretched in
proportion to the pull, and become approximated. If air is blown through the
tube in the trachea, their edges are set in vibration when thus approximated
and a sound is emitted, the pitch of which varies with the tension of the cords
(the blast of air should be of about the same strength throughout).

Analysis of sounds of musical instruments and of the voice. — The analysis
can be made by applying different Helmholtz resonators to the ear of the observer.
Konig's manometric flames, which are provided with these resonators and are
examined with the aid of vertical rotating mirrors, are also employed for this
purpose.

Determination of range of pitch for audition. — The highest and lowest notes
which can be appreciated are determined by the use of Galton's adjustable
whistle.

Conduction of sound by the bones of the skull. — Stop the ears with wool. Set
a small tuning-fork in vibration, and hold it with the base touching the top of
the skull. The sound is propagated to the cochlea by the bones of the skull.

Inspection of the tympanic membrane. — Using a mirror with a central aperture
fixed in front of the eye, throw the reflection of a lamp into the meatus of the
subject, whose external ear must be drawn somewhat backwards and upwards.

Propagation of sound to the internal ear. — The mode of transmission may be
st udied with the aid of a model showing the bones of the middle ear and their
attachments to the membrana tympani and the fenestra ovalis. The model
shows that when the tympanic membrane — to which the handle of the malleus
is attached — is driven in, the base of the stapes, which fits into the fenestra
ovalis, follows the movement : but when the tympanic membrane is forced
outwards beyond a certain point the stapes is not dragged after it owing to the
nature of the articulation between malleus and incus. The model also shows the
effect of the tensor tympani in pulling inwards the handle of the malleus and with
it the membrana tympani, and the effect of the stapedius in pulling the head of
the stapes backwards and causing the base to be tilted within the fenestra
ovalis, thus rendering tight the ligament which fixes it in that aperture.

Semicircular canals. — For demonstrating the effects of injury to semicircular
canals, a bird (pigeon) is employed. An opening is made in the side of the
.skull of the anaesthetised animal with a very small trephine, and through the
aperture a special instrument is introduced and passed underneath the dura
mater until one of the bony semicircular canals (which in the bird project above
the surface of the petrous bone) is met with ; the canal can then be broken across.

For observing the effects of stimulation of the canals a strong galvanic
current is passed from one side of the head to the other; pad electrodes wetted
with strong salt solution being applied in the neighbourhood of the ears : the
stimulation occurs on the side of the kathode.

CHAPTER XXX

TASTE AND SMELL

Taste. —(a) To test the localisation of taste, direct the subject to close his eyes
and put out his tongue. This organ is then dried, and different parts are touched
with a small brush or a glass rod moistened with the sapid substance in solution.
After each observation the mouth must be rinsed with water. The following
solutions may be used for testing the four qualities of taste, viz. : for bitter, 1
per cent, solution of quinine sulphate ; for sweet, 5 per cent, solution of sugar;

FIG. 83. — ZWAARDKMAKER'S OLFACTOMETEK. », NOSE PIECE ; SCT, SCREEX:

t, POROUS TUBE SLIDING OVER GRADUATED GLASS TUBE.

for acid, 2 per cent, solution of citric acid ; and for salt, 5 per cent, solution
of common salt. Notice the time which intervenes between the application
of the sapid substance and its effect. Record your results as regards localisation
upon an outline plan of the tongue.

(b) Chew a leaf of Gymnema sylvestris, or paint with cocaine solution, and
determine whether the taste of any of the varieties of sapid substances is affected.

(c) Test different parts of the tongue by applying closely-set electrodes arranged
to conduct a weak faradising current.

Smell. — The sense of smell is tested by Zwaardemaker's olfactometer, which
consists of a glass tube with one end adapted to the nostril, while over the other
end a tube constructed of, or impregnated with, the odoriferous substance,
slides ; so that a greater or less amount of its inner surface can be exposed to
the air which is passing through the glass tube into the nostril (fig. 83).

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