IRLF

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TO THE

LIBRARY OF THE
MEDICAL DEPARTMENT

OF THE
UNIVERSITY OF CALIFORNIA

UNIVERSITY OF CALIFORNIA

MEDICAL CENTER LIBRARY

SAN FRANCISCO

'0/2.

GIFT OF

TO THE

LIBRARY OF THE
MEDICAL DEPARTMENT

OF THE
UNIVERSITY OF CALIFORNIA

UNIVERSITY OF CALIFORNIA

MEDICAL CENTER LIBRARY

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Practical Work in Physiology

T

Directions for Class
in Practical Physiology

o

ELEMENTARY PHYSIOLOGY OF MUSCLE AND

NERVE AND OF THE VASCULAR

AND NERVOUS SYSTEMS

— " BY

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

Professor of Physiology in the University of Edinburgh ; formerly
Jodrell Professor of Physiology in University College t London

WITH DIAGRAMS

LONGMANS, GREEN, AND CO

91 AND 93 FIFTH AVENUE. NEW YORK

COPYRIGHT, 1901, BY
LONGMANS, GREEN, AND CO.

All rights reserved

. J. .Little & Co.

c » * . •* c I1 I * «
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190'

PREFACE

THE following directions are based upon an ex-
perience of many years in University College, Lon-
don, where such a course of instruction was first
instituted by Professor Burdon-Sanderson. Al-
though they have long been in use I have now
had them printed for the convenience of my
Edinburgh students. There are several text-books
dealing with the same subject, but they are all
more elaborate, and concern themselves with many
problems which the average medical student can-
not be expected to investigate for himself. On
this account perfectly simple instructions dealing
only with such elementary exercises as can readily
be worked out by even a large class, may, it is
hoped, prove useful to other teachers and students
than those for whom they are primarily intended.

205

'

205

Practical Physiology

CHAPTER I.

Batteries. — A voltaic element or cell usually
consists of two metals— e.g., zinc and copper — im-
mersed in a fluid such as dilute sulphuric acid, and
the changes (movements of ions) which occur under
these circumstances in the fluid produce a disturb-
ance of electrical equilibrium 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 con-
nected with the copper or negative metal is
charged with positive electricity, and that connected
with the zinc or positive metal is charged with
negative electricity ; these ends are called the pos-
itive 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

PRACTICAL PHYSIOLOGY

the copper inside.1 The amount of this current
depends upon the difference of potential produced
within the cell. This is diminished by any in-
crease 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 1.079 volts.

Anode..

Copper,—

Kathode.

Zinc.

mmm .Dilute sulphuric acid.

FIG. i.— VOLTAIC COUPLE.

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.

If electricity be generated simply by immersing
plates of zinc and copper into acid the chemical
action which ensues causes bubbles of hydrogen

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.

PRACTICAL PHYSIOLOGY

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

gas to form on the copper, and this not only intro-
duces 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

Copper pot.

Zinc.

Porous pot containing
dilute sulphuric acid.

-Sulphate of copper
(saturated solution).

FIG. 3.— DANIELL CELL.

PRACTICAL PHYSIOLOGY

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 im-
mersed. The zinc then dissolves in the acid, dis-
placing hydrogen ; the hydrogen in its turn dis-
places copper from the copper sulphate, and the

Zinc

Carbon.

Manganese dioxide
in porous pot.

Ammonium chloride
solution.

FIG. 4. — LECLANCHE CELL.

displaced 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 " by rubbing its
surface with mercury after it has been cleaned by
dipping into acid.

PRACTICAL PHYSIOLOGY 5

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 parti-
tion ; that of Bunsen, which is similar to Grove's,
but with a negative plate of carbon ; that of Le-
clanche (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
then termed the electrodes.1- They are often made

1 The term electrode means literally the ' ' path " of the electric cur-
rent, 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).

PRACTICAL PHYSIOLOGY

of platinum set in a vulcanite holder; but a pair
of pins with fine wires soldered to their heads,
which can on occasion be passed through a small
cork, with their points projecting for a few milli-
metres, constitute a readily improvised and efficient

FIG. 5.— PAIR OF ELECTRODES IN CORK OR VULCANITE HOLDER.

pair of electrodes for most class purposes. Like
the plates of the battery itself, such metallic elec-
trodes 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 ex-
periments it is necessary to obviate this
polarisation of electrodes and to employ
electrodes 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 modelling clay moistened
with salt solution, filling the tube with
saturated solution of zinc sulphate, and

. . A

plunging an amalgamated zinc rod (to
which one of the wires of the circuit is soldered
or otherwise attached) in the zinc sulphate.

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

PRACTICAL PHYSIOLOGY

Saturated solution of
zinc sulphate.

moistened with starch so-
lution containing iodide
of potassium. Iodine is
set free at the anode and
turns the starch blue.
Feeble differences of elec-
trical potential are de-
termined and estimated
by other methods (gal-
vanometer, electrometer),
which will be studied
later.

Keys. — Any apparatus
which is used for inter-
rupting or diverting the
course of a current is

called a key or switch. The keys used in physio-
logical experiments are arranged to close and open

Clay plug, moistened
with salt solution.

FlG. 7. — NON-POLARISABLE ELEC-
TRODE.

Zinc wire.

-Clay plug in small glass
tube.

-Zinc sulphate solution.

FIG. 8.— SANDERSON'S PATTERN OF NON-POLARISABLE ELECTRODE.

8

PRACTICAL PHYSIOLOGY

the circuit (make and break the current) by con-
necting the wires together either through a pool of
mercury (inercury key — Fig. 9) ; or by contact be-

FIG. 9. — MERCURY KEY IN A BATTERY CIRCUIT.

tween a platinum plate and platinum point (contact
key — Fig. 10), as in the Morse key ; or by friction
contact between two brass surfaces {friction

FIG. 10. — CONTACT KEY IN A BATTERY CIRCUJT.

as in that known as du Bois-Reymond's (Fig. n),
and in the ordinary electric-light switches. They
are used in two ways, viz. : either to simply close

FIG. ii. — FRICTION KEY IN A BATTERY CIRCUIT; DIRECT METHOD OF USE.

or open the circuit (direct method} ; or by bridg-
ing across a part of the circuit a passage with very
little resistance is offered through the key, and the
current is thus diverted from the main circuit and

PRACTICAL PHYSIOLOGY O

from the electrodes (short-circuit met hod — Fig. 12).
For this purpose du Bois-Reymond's key is espe-
cially well suited. A key which is constructed so
as to cause a current to flow either in one direc-
tion or in the reverse direction in a circuit is called
a reverser or commutator. One of the most con-

FIG. 12.— FRICTION KEY ; SHORT-CIRCUIT METHOD OF USE.

venient is Pohl's commutator (Fig. 13), which con-
sists of a square plate of vulcanite or other non-
conducting material in which are six cups of
mercury connected with terminals. Four of the
cups are joined diagonally, two and two, by crossed
wires. A rocking double bridge of copper serves,
on being moved to one side or the other, to effect
the reversal.

FIG. 13. — POHL'S COMMUTATOR.

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. 14).

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

10

PRACTICAL PHYSIOLOGY

shall pass through the experimental circuit. It
usually consists of a german-silver or platinum-
iridium wire of a certain known resistance (e.g.,

FIG. 14. — POHL'S COMMUTATOR USED AS SWITCH (CROSS WIRES REMOVED).

20 ohms), to the ends (Fig. 15, a and b) of which
the battery poles are connected ; a certain differ-
ence of potential is thereby produced at the two

FIG. 15.— DIAGRAM OF RHEOCHORD.

ends of the wire. With one of these ends (a) an-
other wire is connected ; this forms part of the ex-
perimental circuit through which a portion of the
battery current is to be conducted ; this circuit is

PRACTICAL PHYSIOLOGY II

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 — this difference de-
pending upon the E.M.F. of the battery and the
resistance of the rheochord wire — is operative in
producing a current through the experimental cir-
cuit. 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 dis-

FIG. 16. — DOUBLE-WIRE RHEOCHORD.

tance between a and r as compared with the whole
length of the wire. Thus if the wire be 100 centi-
metres long and r be placed at one centimetre
from a only T^ of the total difference of potential
will be operative and a proportional current will
be diverted into the experimental circuit. When
this form of rheochord is to be used, the resistance
of the experimental circuit must always be very
great : this is invariably the case in physiological
experiments.

In another form of rheochord (Poggendorff's)
the wire is doubled on itself, and a rider (r) bridges
across and forms a short circuit between the two

12 PRACTICAL PHYSIOLOGY

parts of the wire (Fig. 16). The battery circuit
and the experimental circuit are both connected
with the ends of the wire. When the rider is
brought in contact with these ends the battery
'current is completely short-circuited, but when the
rider is moved away from the ends a gradually in-
creasing resistance is inserted into the short circuit
formed by the rheochord and its rider, and propor-
tionally 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, in the one 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.

In order to multiply the inductive effect the two
circuits always take the form of closely coiled
wires (Fig. 1 7) (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

PRACTICAL PHYSIOLOGY 13

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. For multiple induced shocks
most coils are fitted with an apparatus for auto-

Secondary

coil. „

_ —-Mercury key

bnort-cir- \ t*y / /° in primary

cuit key -*— *JLJ-

FIG. 17. — INDUCTION COIL ARRANGED FOR SINGLE SHOCKS.

matically breaking and making the primary circuit
(Neef's hammer). This will be understood from
the diagram (Fig. 18). 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
the current passes from the spring, which has a
plate of platinum upon it, to the platinum point of
a screw, S*, and thence through the primary coil.
Before passing back to the battery it is conducted
through a small electro-magnet, M; the electro-

14 PRACTICAL PHYSIOLOGY

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 electro-magnet is no
longer active, the bar springs up again, and con-
tact is re-established between the spring and screw;
this produces a make induced current in the sec-
ondary coil. Thus the spring vibrates to and fro,
and break and make induced currents are set up in

Short-cir-
cuit key

Electrodes +\ v Mercury

key.

FIG. 18. — INDUCTION COIL ARRANGED FOR AUTOMATIC INTERRUPTION OF PRIMARY

CIRCUIT.

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 (see below) which is self-induced within
the primary coil, and which diminishes the make
effect. This inequality is, however, got over by
a modification introduced by Helmholtz. In this
arrangement (Fig. 19) a wire, W , connects the
terminals, 7\ T3 ; the screw S* is raised alto-

PRACTICAL PHYSIOLOGY 15

gether away from the spring, and the screw S2 is
brought nearly up to the spring. The battery cur-
rent passes by the wire, W, from the terminal, T\
directly to T\ thence through the primary coil
and through the electro-magnet, Mt which draws
down the iron bar and brings the spring in contact
with the screw, S2. A large part of the battery cur-
rent now goes directly back to the battery through
this contact, and is diverted from the primary coil
and electro-magnet. This greatly weakens the

FIG. 19. — HELMHOLTZ'S ARRANGEMENT OF INDUCTION COIL.

current through the primary coil, and the equiva-
lent 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 produc-
ing 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-cir-
cuiting 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,

1 6 PRACTICAL PHYSIOLOGY

and so on automatically. It will be observed that
the primary circuit is never actually broken, but
only short-circuited.

The above-described apparatus having been
studied, the following experiments are to be per-
formed :

1. Connect up a cell with a pair of wires, intro-
ducing a simple key into the circuit (Fig. 9). Place
the free ends of the wires on the tongue, and close
and open the key.

2. Repeat this experiment, but use a short-cir-
cuiting key (Fig. 12). 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 com-
mutator, as shown in Fig. 13. Determine with
pole-reaction 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, T*,
T2, of the primary coil of the inductorium, intro-
ducing 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. 17).
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.

PRACTICAL PHYSIOLOGY 17

This is partly due to the fact that as the current of
the primary circuit is made and broken induced cur-
rents (extra currents) are formed in its own coils ;
the make extra current of closure being in the op-
posite direction to the battery current diminishes
the make induced current in the secondary circuit,
while the break extra current is cut off by the open-
ing of the primary circuit. 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 the closure.

Primary coil

FIG. 20.— EXPERIMENT TO SHOW BREAK "EXTRA" CURRENT.

5. To show the existence of the " extra "cur-
rents remove the secondary coil altogether and
connect up the primary coil by T1 and T* with a
battery and keys in the way shown in Fig. 20.
Place the electrodes on the tongue. Make and
break the battery circuit by closing and opening
the key, K\ If this is done when the pri-
mary coil is included in the circuit (i.e., with K*
open) the effect is greatly enhanced by the " extra "
current, but if the coil is shunted out by clos-

1 8 PRACTICAL PHYSIOLOGY

ing K* the stimulus is hardly perceptible to the
tongue.

6. Instead of placing the simple key in the pri-
mary circuit place it in a side circuit (Fig. 21). On
closing and opening the key, shocks are still pro-
duced in the secondary circuit, although the current
through the primary coil is not made and broken,
but only strengthened and weakened. The make
and break shocks in the secondary coil are now
more uniform, but are both weaker.

7. Take the secondary coil out and place it across

FIG. 21. — INDUCTION EFFECTS OF CLOSING AND OPENING A SIDE CIRCUIT CONNECTED
WITH PRIMARY COIL.

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 coils are again parallel.

8. Connect up the battery with the terminals,
7"3, 7"4, of the induction coil (as in Fig. 18), intro-
ducing a simple key into the circuit. Set the

PRACTICAL PHYSIOLOGY 19

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 key, K*, being closed).

9. Unipolar induction. — 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. It is on account
of this possibility of stimulating through only one
pole that a simple key is never used in the second-
ary circuit, but always a short-circuiting key, which
is introduced in the manner shown in Fig. 18. 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 must always be
used ; were a short-circuiting key placed here the
battery would rapidly run down.

10. Connect up a battery with the induction coil,
using Helmholtz's modification (Fig. 19). As in
experiment 8, find the distance of the secondary
from the primary coil at which the induced shocks

20 PRACTICAL PHYSIOLOGY

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.

CHAPTER II.

Nerve-muscle preparation. — Pith a frog by
cutting through the spinal cord at the occipito-
atlantoid ligament and passing a blanket pin or
wire into the skull and down the cord. Notice
that the muscles of the trunk and limbs are thrown
into contraction when the cord is being destroyed.
Make a circular incision round the middle of the
trunk through the skin only, and strip off the skin
from both hind limbs. Lay the frog on its back on
the frog-plate, and open the abdomen and thorax
freely but carefully. Notice the viscera (Fig. 22)—
heart and lungs, liver, stomach, intestines, 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,
cutting through the middle of the vertebral column
with strong scissors, remove the fore part of the
trunk and the viscera. Lay the hind part on the
frog-plate, and note the several muscles which are
seen on the front and back of the lower limbs (Figs.
23, 24). The gastrocnemius is generally used for

22 PRACTICAL PHYSIOLOGY

experiments. Tie a thread round its tendon (tendo
Achillis K and 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.

Fiu. ».— V]

«A or Faoc. THZ Lrrat B
PATTS GcwexAUEix ET rf AID

I . . : T -._ : -------

Next prepare the sciatic nerve. Separate the
muscles at the back of the thigh by the aid of two
pairs of forceps, keeping to the inner of the two
chief intermuscular septa, and the nerve will be
seen, accompanied by the femoral vessels. Do not
touch the nerve, but separate the muscles from it
as low down and as high up as possible.

PRACTICAL PHYSIOLOGY

Adductor brevis
Adductor ma gnus

Gracilis

Gastrocnemhs.

TibiaHs posticns
Tendo AchiTIis.

FIG. 23.— MUSCLES OF FROG'S LEG; YEN-TEAL ASPECT

Next seize the urostyle with forceps, and cut it
and the muscles attached to it entirely away with
scissors. The nerves previously seen behind the

Gl

Rectus anterior. .
Vastus externns. _

^Coccjg-eo-iliacus.

"T ' """ " S ^ JL fc'JLS

.Ter; . .-..:- ift

FIG. 24.— MUSCLES OF FKOG'S LEG ; DOSSAL ASPECT (ECKE*>.

24 PRACTICAL PHYSIOLOGY

kidneys are now exposed from the back; they are
continuous with the sciatic nerve. To completely
isolate this nerve along its whole length sever the
attachment of the ilium to the sacrum. Split the
end of the spinal column longitudinally, and, hold-
ing one-half with forceps, lift it and the nerves
issuing from it up, and then gradually dissect the
nerves from above down by snipping their lateral
branches wth scissors (without touching the main
nerve) until the knee is nearly reached. Notice that
as each branch is snipped the muscles which it sup-
plies contract. Lay the sciatic nerve thus isolated
upon the gastrocnemius muscle. Lastly, cut
through the middle of the femur, after clearing the
muscles away from its lower end ; you now have a
nerve-muscle preparation. Place a piece of blotting
paper wetted with normal salt solution1 or Ringer's
solution on the frog-plate, and the preparation
upon this, laying the nerve out upon the wet blot-
ting paper. Fix a pair of electrodes so that the
nerve lies across them. Perform the following
experiments, which are, for the most part, similar
to those already performed upon the tongue :

i. Determine that making or breaking the circuit
of a constant battery is a stimulus to the nerve,
whereas the passage of the current usually2 pro-
duces no obvious effect.

1 Normal salt solution is made by dissolving six grammes of com-
mon salt in a litre of tap-water. Ringer's solution is an improved salt
solution made by saturating one litre of the above with calcium
phosphate and adding ten milligrammes of potassium chloride.

2 For exceptions see Chapter VII.

PRACTICAL PHYSIOLOGY 25

2. That an induction shock is a stimulus, and
that the break induction shock is a far stronger
stimulus than the make induction shock. Get the
minimal effect of each by sliding the secondary
coil to the necessary distance from the primary,
and make notes as to the respective positions of
the secondary coil.

3. That 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. It is best for

FIG. 25. — STIMULATION OF NERVE BY CONDENSER DISCHARGE.

this experiment to place the secondary coil at zero
and to make use of the automatic interrupter (Fig.
1 8). The nerve should be raised up from the wet
blotting paper.

4. That the discharge of a condenser through a
nerve also acts as a stimulus. Arrange the appa-
ratus as shown in Fig. 25, in which C is a condenser
made by covering a sheet of glass with tinfoil on
both sides. The sheets of tinfoil are first connected
with a battery, and then, by turning the switch, are

26 PRACTICAL PHYSIOLOGY

connected with the nerve, the battery being cut off
by the same movement.

5. That the nerve can be stimulated by mechan-
ical means — e.g., by tapping it gently or by allowing
mercury to drop upon it from a height of three or
four inches. The effect of a mechanical stimulus is
also seen whenever a nerve is cut or pinched, but
such severe injury abolishes its conducting func-
tions.

6. That the nerve is stimulated if it be touched
with a hot wire.

7. That it can be stimulated by chemical means,
as by placing wet salt or strong glycerine upon a
freshly cut end.

8. That drying acts as a stimulus to the nerve.
If it be raised off the wet blotting paper and begin
to dry, the muscle will be observed to begin to
twitch. The salt and glycerine in the last experi-
ment probably also act by abstracting water.

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 attach-
ment. 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

PRACTICAL PHYSIOLOGY

isolated. Its uppermost part contains no nerve
fibres, and can be used to show that, independently
of nerve, muscle also responds to all forms of
stimulation (electrical, mechanical, thermal, and
chemical).

CHAPTER III.

Kecord of muscular contraction (muscle-
twitch). — Muscular contractions are recorded
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 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 a
lever (myograph lever), which may be straight, but
which may also very conveniently take the crank
form (Sanderson's myograph). In this form of
myograph the lever is fixed at the end of a frog-
cork, to which the muscle is fastened by a pin
passed through the knee joint ; the tendon is
attached to the short arm of the lever by means of
a thread and hook. The lever should be weighted
with a ten-gramme weight, attached to it near the
fulcrum, and should be so adjusted that when nearly
horizontal, but with the point a little lower than
the fulcrum, the muscle is stretched by the weight
and the connecting thread is taut. Arrange the
drum in the primary circuit of the induction coil
(Fig. 26), so that, as it revolves, a pin which pro-

PRACTICAL PHYSIOLOGY

29

jects from it, by striking against a spring fixed out-
side, instantaneously makes and breaks the circuit
at each revolution. Although two induction shocks
are thereby produced in the secondary circuit, they
follow one another so closely as to act as a single
stimulus.1 Either attach a pair of electrodes to the
muscle itself or lay the nerve upon them. The elec-

Muscle.

Spring.

. Drum.

FIG. 26. — GRAPHIC RECORD OF MUSCLE-TWITCH. THE HYOGLOSSUS (TONGUE OF FROG)
is REPRESENTED IN THIS DIAGRAM INSTEAD OF THE GASTROCNEMIUS. THE MUSCLE
AND LEVER SHOULD BE ON THE RIGHT SIDE OF THE DRUM (WHICH MUST REVOLVE
FROM RIGHT TO LEFT) ; NOT ON THE LEFT SIDE, AS HERE REPRESENTED.

trodes are connected through a short-circuit key
with the secondary coil. Before the lever is allowed
actually to touch the cylinder determine that the
apparatus is all in working order, and at what dis-

JIt is also possible to employ a single induction shock as the stim-
ulus by introducing a break key into the primary circuit and mak-
ing the pin open this key as the drum revolves ; but this is not neces-
sary, since it is easy with the arrangement above described to slide
the secondary coil at such a distance from the primary that, even if
the drum is revolving slowly, only the break shock is effective.

-l B.R A»'i

,}

30 PRACTICAL PHYSIOLOGY

tance of the secondary from the primary the break
shock produces its full effect — i.e., causes a full con-
traction— when the drum is made to revolve. Do
not allow the muscle to be fatigued by many excita-
tions before recording its contraction.

Now bring the lever point so as lightly to touch
the blackened paper, using the stop of the myo-
graph stand to prevent the possibility of the point
pressing too hard against the paper. When the
stop is used in this 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 therefore absolutely essential
to make use of the stop in all recording experi-
ments 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 contracted ; immediately
afterwards remove the lever point from the drum
before this has had time to perform another revolu-
tion. 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 spring where contact is
made ; 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

PRACTICAL PHYSIOLOGY 31

moment when the stimulus was put into the
nerve, and the rise of the curve, which indicates
the commencement of the contraction of the mus-
cle, 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 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, for a second
only against the drum. Cut through the paper
and remove it carefully from the drum. Lay it
on the table, and write upon it date and descrip-
tion. 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 heat and. cold on muscle contrac-
tion.— 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 tempera-
ture.

2. A simple curve after warming the muscle by
placing over it for two or three minutes a saddle-
shaped brass block which has been warmed to
about 30° C. Or warmed salt solution may be
dropped upon the muscle.

3. A simple curve after cooling the muscle for

32 PRACTICAL PHYSIOLOGY

two or three minutes with a brass block at the tem-
perature of ice (or by placing a piece of ice in
contact with the muscle).

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.

Effect of fatigue on muscular contraction.—
The same or a similar nerve-muscle preparation
may be used as in the last experiments, but if the
same it should be allowed to resume the normal
temperature of the room. Make a new abscissa,
and mark, as usual, upon it the point of stimula-
tion. Take a normal curve. Remove the writing
point from the drum, which is allowed to revolve
continuously and to stimulate the muscle with each
revolution. After about twenty of such excita-
tions 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 about twenty excitations,
and repeat the above procedure a number of times
until the fatigue curves are very pronounced.
Notice the effects of fatigue upon contraction,
prolonging the latency period, diminishing the
amount and slowing the course of the contraction,
and greatly delaying, and at length even prevent-
ing, the relaxation of the muscle.

A fatigue curve or series of curves can also be
obtained by recording every contraction — that is, by

PRACTICAL PHYSIOLOGY 33

leaving the lever point in contact with the cylinder
during the whole course of the experiment ; but
the individual curves in a tracing so obtained are
very numerous, and tend somewhat to obscure one
another.

CHAPTER IV.

Action of curari. — Destroy the brain of a frog
by passing a sharp splinter of wood through the
occipital foramen after cutting through the occipito-
atlantoid ligament. Ligature the blood-vessels of
one leg, taking care to avoid injuring the accom-
panying sciatic nerve. Or the whole leg can be
tightly tied round with a tape so as to stop the
circulation in it. A drop of one per cent, solution
of curari is now injected under the skin of the back,
and the frog is left for about an hour. The drug
will have penetrated to all parts except the liga-
tured leg. The following observations and experi-
ments are to be made upon the curarized animal :

(1) Notice that all the muscles are paralyzed
except those of the ligatured limb.

(2) On tapping any of the paralyzed parts the
foot on the ligatured side is moved.

(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 difference of effect. Excitation
of the nerve of the limb which has been exposed
to the poison produces no contraction of its
muscles ; excitation of the nerve of the ligatured
limb produces the usual effect. Now stimulate
the muscles of the two limbs, applying the elec-

PRACTICAL PHYSIOLOGY 35

trodes directly to them. The muscles of the
poisoned limb react like those of the normal limb,
but the liminal stimulation1 is greater. Determine
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 connection
between the motor nerve fibres and the muscle
fibres, probably at the end-plates.

Muscle wave. — Separate the adductor muscles
(gracilis and semimembranosus ; see Figs. 23, 24)
of a frog's leg (which has been poisoned with curari
so as to eliminate the intramuscular nerves) from the
remaining thigh muscles, leaving their 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
effect 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 be-
tween these threads, and fasten the threads by a
couple of pins to the frog-cork. Allow a light
muscle-lever to rest across the muscles near one
end. The movements of the lever are recorded
upon a rapidly revolving drum, and curves are to
be obtained of the swelling of the muscle during

'The stimulation which is just effective—/.*., just produces a
response.

36 PRACTICAL PHYSIOLOGY

its contraction in the same manner as the curves of
shortening of the gastrocnemius were obtained in
previous experiments.

Connect two pairs of pin electrodes with a com-
mutator, the cross wires of which are removed so
that it is used merely as a switch. The commutator
is placed in the secondary circuit. One pair of elec-
trodes is used to stimulate the muscles close to the
lever, the other at the far end of the muscular mass ;
the electrodes must be securely fixed into the frog-
cork. Describe an abscissa, and mark the point of
stimulation as in previous experiments, making use
of the stop. Then take two tracings of the contrac-
tion of the muscle, firstly when stimulated close to
the lever, secondly when stimulated at the further
end of the muscle. In the latter case the latency
period is prolonged, and the second curve, there-
fore, occurs later than the other. The interval
between the two curves 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 points which were successively
stimulated. Take a tuning-fork tracing, and meas-
ure this time, and from it and the length of muscle
traversed by the wave calculate the rate of propa-
gation of the muscle wave per second.

It is essential for the success of this experiment
that the muscles used should have their fibres run-
ning longitudinally and parallel with one another.
If the frogs are large the two sartorius muscles
may be used with advantage instead of the adduc-
tor preparation described.

PRACTICAL PHYSIOLOGY 37

Action of veratrin on muscular contraction.

— The hyoglossus muscle — i.e., the frog's tongue-
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 connect
with the muscle lever (Fig. 26). Fix the prepara-
tion to the myograph cork by inserting pin elec-
trodes on either side and immediately in front of
the hyoid bone so that induction shocks will stimu-
late all the fibres of the hyoglossus muscles.

Take a muscle curve in the usual way. If the
speed of the drum is the same as before (one
revolution per second), the curve is more pro-
longed than that of the gastrocnemius — i.e., the
contraction is slower. It is better, however, for
investigating the action of veratrin to use a less
rapid rate of cylinder, since this drug enormously
delays the relaxation of muscle. The cylinder
therefore should be arranged to revolve once in
about four or five 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 few drops of veratrin acetate
solution (one per thousand) under the mucous
membrane of the tongue, so that the drug is
brought into contact with the fibres of the hyo-
glossus. After a minute or two take another mus-
cle curve. Describe a tuning-fork tracing below
the abscissa. If the preparation is excited repeat-
edly, it will be found that the contractions grad-
ually lose their prolonged character, which, how-
ever, returns after a period of rest.

CHAPTER V.

Effect of two successive stimuli upon a mus-
cle-nerve preparation. A. Summation. — Make
a muscle-nerve preparation and fix it upon the
myograph in the usual way, so that the muscle writes
its contractions upon a cylinder revolving about
once in two or three seconds. Place the secondary
coil at such a distance from the primary that the con-
traction produced is minimal. Now by means of a
second pin projecting from the drum quite close
to the first, allow two shocks of the same minimal
intensity to affect the nerve in rapid succession.
If the two pins are sufficiently near one another
a simple muscle curve will again be described,
but the contraction will be more complete than
with the single minimal stimulus. If the stimulus
used is subminimal — i.e., ineffective — the effect
of its repetition may be to produce an effective
stimulus.

B. Superposition. — Place the secondary coil at
such a distance from the primary that the excita-
tion produced by a single projecting pin striking
the spring in its revolution is maximal, and de-
scribe 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;

PRACTICAL PHYSIOLOGY

39

viz., (a) during the rise of the first curve, (d) 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 ; teta-
nus.— For studying the effect on a nerve-muscle
preparation of a rapid succession of stimuli a vibrat-
ing steel reed is used to make or break the primary

FIG. 27. — TETANUS OF MUSCLE.

circuit of the induction coil by allowing a wire at-
tached to its end to dip into and out of a cup of
mercury. The rate of vibration of the reed de-
pends upon its length, which can be varied by
clamping it at different places ; it is marked at
points for producing vibrations of ten, fifteen,
twenty, and thirty per second (Fig. 27). The
secondary coil should be placed at such a distance
from the primary that only the break shock is
effective. The drum may revolve at only a mod-
erate speed (one revolution in four or five seconds.)

40 PRACTICAL PHYSIOLOGY

Attach the muscle to the lever of the myograph
in the usual way ; place the nerve upon the elec-
trodes ; describe an abscissa ; set the reed vibrat-
ing ; open the key in the secondary circuit for
about a second ; take the 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.

FIG. 28. — TRANSMISSION MYOGRAPH OF MAREV. F, FORCEPS FOR GRASPING THE MUS-
CLE THE CONTRACTION OF WHICH is TO BE RECORDED. THE Two BLADES OF THE
FORCEPS ARE DRAWN TOGETHER BY AN INDIA-RUBBER BAND. 7", RECEIVING TAM-
BOUR, THE AlR IN WHICH IS COMPRESSED BY THE SWELLING OF THE MUSCLE, AND

FROM WHICH THE PRESSURE IS TRANSMITTED BY AN INDIA-RUBBER TUBE TO T't
THE RECORDING TAMBOUR, THE LEVER OF WHICH WRITES ON A REVOLVING DRUM.

Record of voluntary contraction. — A volun-
tary muscular contraction, say of the finger-muscles,
may be recorded in the same way as the contraction
of a frog's muscle, by resting the hand upon the frog-
plate and tying a thread to one of the fingers, the
other end of the thread being attached to the lever ;
this should, however, either be furnished with a
moderately heavy weight or held down by a strong
spring or elastic band. On abducting the finger

PRACTICAL PHYSIOLOGY 41

the lever is raised, and a curve is described which
bears a close resemblance to a tetanus produced
by ten or twelve vibrations per second.

Another method of obtaining such a curve is by
the use of the transmission myograph (Fig. 28),
which consists of two tambours connected by india-
rubber tubing. The first or receiving tambour is
so arranged against the muscles of the ball of the
thumb that when these muscles are made to con-
tract voluntarily the air within it is compressed,
and the differences of pressure are transmitted to
the second or recording tambour, which writes
against the revolving drum.

Sound of a voluntarily contracting muscle. —
Place the tips of the middle fingers in the ears,
and contract the muscles of the arm strongly. A
rumbling sound is heard which is generally as-
sumed to be caused by the successive contractions
of the fibres, and to indicate the rate of vibration
of the voluntary tetanus. The sound heard is,
however, probably a harmonic of the actual note
produced, the perception of notes of so low a pitch
being modified by resonance within the ear.

CHAPTER VI.

Work of muscle ; extensibility of muscle. —

The experiments to be performed on this subject
are recorded upon a stationary drum which must
be moved onwards for about five millimetres by
hand after each record.

Make a muscle preparation, preferably the sarto-
rius (p. 26), place it on the myograph, and arrange
that it shall be stimulated by induction shocks. The
lever should have a light scale pan suspended from
it near the fulcrum ; 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 grammes), of a gradual
increase of the strength of the stimulus from mini-
mal to maximal.

2. The amount of work which the muscle performs
in lifting different weights, the stimulus being con-
stant and maximal. 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.

Another result is yielded in this experiment ;
viz., the effect of gradually increasing weights in
producing extension of muscle in the resting and
contracted conditions respectively. For it is ob-
vious that the lowermost point of any ordinate
described by a contracting muscle represents the

PRACTICAL PHYSIOLOGY 43

length to which the resting 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 curve of extension of the contract-
ing 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.

3. The effect of after-loading. Take a series of
contraction ordinates, using a maximal stimulus
and a constant weight (say about thirty grammes).
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 some-
what slackened. Under these circumstances the
muscle will not begin to raise the weight until its
contraction has proceeded to a certain extent ; this
is termed after-loading. Describe a series of con-
traction ordinates with a gradual increase of after-
load. Estimate the amount of work done under
these conditions, and compare with that performed
by the free-weighted muscle.

These experiments on muscle work and exten-
sion can be performed either with single make or
break shocks, or by. tetanisation by means of the
Neef s hammer of the induction coil.

CHAPTER VII.

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 com-
mutator 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. 29).

Two muscle curves are now taken with a fast
rate of cylinder and a maximal stimulus ; this is to
be applied to the nerve, firstly, close to the muscle,
and, secondly, close to the vertebral column. The
muscle curves are to be taken in exactly the same
way, and with exactly the same precautions as to
the use of the stop, etc., as detailed in Chapter III.,
and the two curves are to be traced upon one ab-
scissa, and a time tracing written beneath this. It
will be found that the curves are not coincident,
but that one succeeds the other by a very small
interval, this interval representing the time occu-
pied by the transmission of the nerve impulse

PRACTICAL PHYSIOLOGY

45

along the length of nerve between the two pairs of
electrodes. The interval is relatively small com-
pared with the total latency period of the muscle-
nerve preparation ; it can be rendered more evident
if the nerve (not the muscle) be cooled. But to
measure it accurately a very fast rate of movement
and a longer nerve must be taken. This is usually
done by the use of the pendulum myograph, upon

FIG. 29. — EXPERIMENT TO DETERMINE THE RATE OF CONDUCTION ALONG A MOTOR
NERVE. THE MUSCLE AND LEVER SHOULD BE ON THE RIGHT-HAND SIDE OF THE
DRUM ; NOT ON THE LEFT SIDE, AS REPRESENTED IN THE DIAGRAM.

which the contraction of the thumb muscles in man
is recorded, the electrodes being applied over the
median nerve at the elbow and over the brachial
plexus above the clavicle respectively ; the length of
nerve thus investigated may be a foot or more. The
muscle-contraction is recorded by means of tambours.
Conduction in both directions ; Kulme's ex-
periment.— 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

46 PRACTICAL PHYSIOLOGY

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. The middle part of the muscle can be
entirely cut away 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,
chemically (salt), or mechanically (by snipping with
scissors), both pieces contract.

A similar experiment can be made with the sar-
torius, the nerve fibres of which branch as they pass
into the upper end of the muscle, so that if this end
is split down the middle, and the nerve fibres in
either half are stimulated, the other half of the split
part contracts. It will be remembered, however,
that there are no nerve fibres at the very end of
this muscle, so that to get the desired result — i.e.,
contraction of both halves — the muscle must be
stimulated a short distance from this end.

Effect of CO2 on conduction in nerve. — Take
a nerve-muscle preparation and lay the nerve across
and partly imbedded in a ring of soft modelling
clay placed upon a glass slide, to which a tube is
cemented so that a current of CO2 can be conducted
over the nerve. The ring is covered by a cover
glass, and the end of the nerve projects beyond
it and rests upon a pair of electrodes (Fig. 30).

Find the minimal stimulus which will produce
contraction of the muscle; then pass a current of
CO2 over the intervening nerve, and determine the

PRACTICAL PHYSIOLOGY

47

effect upon the conducting power of .the nerve.
Remove the CO2 by a current of air, and repeat
the observation.

Another experiment may subsequently be made
with ether vapour instead of CO2.

Electrotonic effects of constant current on
nerve excitability. — Make a pair of non-polari-
sable electrodes by plugging one end of each of two
short glass tubes with modelling clay moistened
with normal saline solution, filling the tubes with

FIG. 30. — EFFECT OF CARBON DIOXIDE ON CONDUCTION IN NERVE.

saturated solution of zinc sulphate, and placing in
this solution an amalgamated zinc wire (Figs. 7, 8).
To these electrodes is led the current of a galvanic
battery consisting of at least two cells (Fig. 31).
Insert a rheochord, a mercury key, and a commuta-
tor into this circuit {polarising circuit) ; by means
of these the polarising current can be varied in
strength and in direction, or can be cut off or put
in at will. Another circuit (exciting circuit) must
also be put up, and must include an induction coil
with a mercury key in the primary circuit ; the

48

PRACTICAL PHYSIOLOGY

secondary circuit is to have a short-circuit key, with
which a pair of ordinary metallic electrodes are
connected ; these electrodes are brought in contact
with the nerve of a muscle-nerve preparation near
the muscle. The non-polarisable electrodes are
fixed to the myograph cork, and the upper part of
the nerve is laid upon them. The record of the
muscular contractions obtained is made on a sta-
tionary drum. Be careful to keep the nerve moist.

FIG. 31. — To TEST THE POLAR EFFECTS OF A CONSTANT CURRENT ON NERVE
EXCITABILITY.

Place the secondary coil at such a distance from
the primary coil that the break induction shock
just produces a contraction. Now put in the polar-
ising current first in an ascending and secondly in
a descending direction, and determine the effect of
its poles in diminishing or increasing the excitabil-
ity of the nerve as tested by the submaximal stim-
ulus employed.

Closing and opening tetanus; Pfliiger's law
of contraction. — Using the same apparatus (but

PRACTICAL PHYSIOLOGY

49

with the omission of the induction coil and its
accessories), test the so-called law of contraction, or,
in other words, the conditions of excitation of a
motor nerve by the making or breaking of a con-
stant current. The rheochord is employed as
before to vary the strength of the current, the com-
mutator to vary its direction up or down the ijerve.
It will have been observed in the last experiment
that the closing or opening of the polarising cur-
rent itself acts as a stimulus to the nerve, the result

FIG. 32. — To TEST PFLUGER'S " LAW OF CONTRACTION."

varying with the direction and strength of the cur-
rent. The conditions of this excitation, so far as
regards strength and direction of current, are now
to be worked out. Beginning with a very weak
current, the rider of the rheochord being brought
near to the end b of the rheochord wire (see Fig.
15), determine the effect upon the nerve, as indi-
cated by the contraction of the muscle, of making
and breaking the current when it is (i) 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 a of the

50 PRACTICAL PHYSIOLOGY

wire. Finally, the effect of a strong current is to be
studied by eliminating the rheochord altogether,
and, if necessary, adding more cells to the battery.
If the nerve be very excitable1 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 con-
siderable time after the removal of a strong ascend-

Glass rod.

-Curarized sartorius.

FIG. 33. — POLAR EFFECTS OF CONSTANT CURRENT UPON MUSCLE.

ing current (Ritters opening tetanus). If Ritter's
tetanus is obtained the nerve may be cut between
the electrodes. The tetanus instantly ceases be-
cause the point where the stimulus occurs (the
original anode) is cut off.

That in closing a constant current the excitation

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

PRACTICAL PHYSIOLOGY 51

occurs at the kathode, in opening at the anode, can
be shown upon a curarized sartorius laid upon a
pair of non-polarisable electrodes (Fig. 33). 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 the
current. On the other hand, on opening the cir-
cuit the twitch begins near the anode, and may again
be followed by a prolonged contraction. These
prolonged contractions correspond to the closing

FIG. 34.— EFFECT OF A CONSTANT CURRENT ON NERVE CONDUCTION.

and opening tetanus obtained through a motor
nerve. They 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.

Effect of a constant current on conduction in
nerve. — Place the spinal ends of the two sciatic
nerves of a frog upon a single pair of stimulating
electrodes, and on one of the nerves between the
point to be stimulated and the muscle place a pair
of non-polarisable electrodes connected through a

52 PRACTICAL PHYSIOLOGY

key to a constant battery of moderate strength
(Fig. 34). Throw in an ascending current, and then
faradize both nerves by the automatic interrupter.
Whilst the muscle in the one case will be tetanized
and speedily fatigued, in the other case the ner-
vous impulses will be blocked by the constant cur-
rent, and there will be no contraction, while on
removing the constant current the second muscle
is at once tetanized by the faradization of its nerve.
This experiment was devised by Bernstein to dem-
onstrate the fact that a nerve may be stimulated
indefinitely without showing fatigue — i.e., without
its excitability and conductivity being affected.

CHAPTER VIII.

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 pos-
sible. Place the central cut end of this branch
upon the electrodes from a secondary coil, and
faradize by rapid induced currents (Fig. 35). The
calf muscles are thrown into tetanus by reason of

FIG. 35. — PARADOXICAL CONTRACTION.

the electrotonic changes which are produced in the
sciatic nerve trunk.

Secondary contraction. — Take a nerve-muscle
preparation, and lay its nerve over the muscles of
another leg, the nerve of which is placed upon the
electrodes (Fig. 36). Tetanize these muscles ;
the nerve of the first-named preparation will be
stimulated by the electrical variations which accom.
pany the contraction of the tetanized muscles. A
nerve-muscle preparation thus used in place of a

54

PRACTICAL PHYSIOLOGY

galvanometer to indicate electrical variations is
known as a rheoscopic preparation.

Secondary contraction from the heart. — Lay

FIG. 36. — SECONDARY CONTRACTION.

the nerve of a muscle-nerve preparation upon the
beating heart. If the preparation is very excit-
able the muscle will be seen to twitch with each
beat of the ventricle. If the heart beat and twitch
are both recorded 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.

Contraction without metals ;
Galvani's experiment. — By means
of a glass rod loop up the nerve of a
nerve-muscle preparation, and allow FIG. 37.-coNTRAc-
its cut end to come in contact either M^liIlTf°
with the surface of its own muscle
(Fig. 37) or with other muscles. If the nerve is
very excitable there will be a contraction of its
muscle each time that the end of the nerve is
brought in contact with the muscle. This excita-
tion is caused by the closing through the nerve of
the demarcation current of the muscle.

PRACTICAL PHYSIOLOGY 55

Capillary electrometer. — The capillary elec-
trometer consists essentially of mercury, which is
forced by pressure from behind for a certain dis-
tance into a glass tube drawn out to a capillary
termination ; the free end of the capillary is filled
with dilute sulphuric acid and dips into a vessel
containing the same fluid. The capillary is ob-
served 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 extent of movement of the meniscus being,
roughly speaking, proportioned to the difference
of potential. From the direction and extent of
the movement the direction and electromotive
force of the current can therefore be gauged.

Join a pair of non-polarisable electrodes up in
circuit with a capillary electrometer and Daniell
cell through a rheochord and commutator in the
manner shown in the diagram (Fig. 38), 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 shut
at first so that the electrometer is short-circuited,
and the battery key 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

PRACTICAL PHYSIOLOGY

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 corresponding movement of the mercury. Note

Sulphuric acid __

Meniscus of
mercury

Tube for trans-
mitting pres-
sure to mercury

Mercury passing
into capillary

Dilute sulphuric
acid .

Mercury .

. .Non-polarisable
electrodes.

FIG. 38.— ARRANGEMENT FOR EXAMINING MUSCLE CURRENT BY CAPILLARY ELECTRO-
METER. A, DIAGRAM OF ELECTROMETER; B, THE CAPILLARY AS SEEN WITH THE
MICROSCOPE.

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 direc-
tion through the electrodes — i.e., through any
preparation with which they may be connected.

PRACTICAL PHYSIOLOGY 57

Open the battery key and close the short-circuiting
key ; the meniscus should return to its original posi-
tion. Lay a muscle, which may have one end cut or
injured, upon the electrodes in place of the wet blot-
ting paper. Place it 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 affect the electrometer. From the direction of
movement of the mercury determine the direction
of the muscle current through the apparatus. 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 rheocord and commutator sending a current
through the circuit in a direction the reverse of the
demarcation current and of exactly such a strength
(as measured by the position of the rider on the
rheocord) as to bring the mercury back to zero.

G-alvaiiometer. — Substitute in the above experi-
ment a high-resistance galvanometer (Fig. 39) for
the electrometer, and repeat the above observa-
tions, using the movement of the needle as the
index instead of the mercury of the electrometer.

Having with either the electrometer or galvano-
meter determined the existence and direction of a
current in muscle, tetanize a muscle through its nerve
as it lies upon the non-polarisable electrodes, and no-
tice the diminution of the excursion of the mercury
or of the magnetic needle which occurs on stimula-
tion (negative variation of the demarcation current).

.The demarcation and excitation currents of nerve

58 PRACTICAL PHYSIOLOGY

are examined and measured in exactly the same
way as those of muscle.

Excitation current of heart muscle. — Con-
nect the non-polarisable electrodes of the electro-
meter with a beating frog-heart, which may either
be removed from the body and laid with the

Galvanometer. . -

FIG. 39. — ARRANGEMENT FOR EXAMINING MUSCLE CURRENT BY GALVANOMETER.

base of the ventricle upon one electrode and the
apex on the other, or left in situ and the elec-
trodes connected with apex and base of ventricle
by thick threads wetted with salt solution. Each
contraction of the ventricle is accompanied by a to
and fro movement of the mercury meniscus of the
electrometer, the direction of which may be noted
and the alterations in electrical potential of base
and apex deduced therefrom.1

1 An accurate record of changes in electrical potential can be ob-
tained by photographing the excursions of the mercury meniscus.

CHAPTER IX.

Involuntary muscle. — Cut a transverse strip
from the stomach of a recently fed frog, and attach
to a light muscle lever in exactly the same way as
with a voluntary muscle. Keep moist with Ringer's
solution. Allow the lever to write upon a very
slowly revolving drum. Place a pair of stimulating
electrodes in contact with the fixed end of the strip,
and excite by allowing the drum to make and break
a galvanic circuit. Record the resulting contraction
and determine its period of latency.

The strip will probably be found to contract
spontaneously and rhythmically after a time. Re-
cord these contractions.

The frog-heart.— Examine the contracting
heart of a pithed frog, cutting away the sternum
and ensiform cartilage and the front of the peri-
cardium. Gently raise the tip of the ventricle with
a blunt hook, and tie a thread to the pericardial liga-
ment which binds the ventricle to the back of the
pericardium. Cut the ligament beyond the thread
and raise the heart by the latter. Do not grasp
the heart with forceps.

Notice the sinus venosus receiving the two venae
cavae superiores and the vena cava inferior; the
double auricle ; the single ventricle ; and on the
front the bulbus aortse leaving the ventricle and

6o

PRACTICAL PHYSIOLOGY

dividing into two branches, each of which again
soon divides into three (Figs. 40, 41, and 43).

Right auricle .
Bulbusaortae

Left auricle.

Ventricle.

FIG. 40. — FROG'S HEART ; VENTRAL ASPECT (£CKER).

Effect of heat and cold on rate of beat. —

Count the number of beats per minute. Now apply,
first, a cooled and, second, a warmed wire (a) to
the ventricle, (<$) to the auricles, (r), by turning up
the heart, to the sinus. Count the rate immedi-

Left superior vena cava ...

Left auricle..
Opening from sinus into

right auricle.. _-

Sinus venosus cut open..---"

Pulmonary vein.
..Right superior vena cava.

. .Right auricle.

Ventricle.
Inferior vena cava.

FIG. 41. — FROG'S HEART; DORSAL ASPECT (ECKER).

ately after each application. If desired the effects
may be recorded in the manner described below.
Stannius' experiment. — Raise the ventricle

PRACTICAL PHYSIOLOGY

6l

carefully, and, passing a thread under the sinus,
tighten it round the sino-auricular junction, which
is marked by a whitish line (x in Fig. 43). The
sinus continues to beat as before, but the auricle
and ventricle come to a standstill in diastole, con-
tracting, however, each time they are stimulated,
whether electrically or mechanically (prick). Now
tie a second ligature round the auriculo-ventricu-
lar junction. The ventricle usually gives a few
beats, and then again comes to a permanent stand-

Olfactory lobes.

Cerebral hemispheres.
Thalamus with pineal gland.
Optic lobes.
-VTI lU_ Cerebellum.

Medulla oblongata.
Spinal cord.

FIG. 42. — BRAIN OF FROG in Situ, EXPOSED BY REMOVING THE ROOF OF THE CRANIUM.

still. It can, however, be made to beat by artificial
stimulation (prick, electric shock), and the curve
which is obtained, if it be recorded in the same way
as the record of an ordinary muscle twitch (i.e., by
attaching the ventricle-apex by means of a hook
and thread to a lever, as in Fig. 44), is similar to
the latter except that all parts of the curve, includ-
ing the period of latent stimulation, are much pro-
longed.

The following points can be made out in the Stan-
nius' preparation, viz.: (i) Any excitation of cardiac
muscle which is adequate to produce a contraction

62

PRACTICAL PHYSIOLOGY

produces a full contraction (all or none), (2) dur-
ing both the period of latency and the progress of
the contraction produced by one excitation the
muscle gives no response to a second excitation;
in other words, there is a prolonged refractory
period, (3) no superposition is produced by succes-
sive stimuli, and therefore no true tetanus, (4) after

PRACTICAL PHYSIOLOGY

a period of rest there is a slight increase in the ex-
tent of the first few succeeding contractions, the
second curve being a little higher than the first,
the third than the second, and so on (staircase phe-
nomenon of Bow ditch).

Cardiac nerves. — Destroy by a wire the spinal
cord of a frog, and also remove the cerebral hemi-
spheres ; this can be done without special dissec-

AA.

FIG. 44. — FROG CARDIOGRAPH. r

tion by cutting away the upper jaw and anterior
part of the skull at the level of the front of the
tympana (see Fig. 42). The posterior part of the
brain with the medulla oblongata must not be
injured. Fix a pair of pin electrodes passed
through a small cork into this part of the brain
and arrange for tetanization. , Lay the frog upon
its back on the frog-cork ; 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. 43). The var

64 PRACTICAL PHYSIOLOGY

gus gives off a small branch on each side, which runs
close along the superior vena cava to the sinus ve-
nosus. Place the vagus trunk upon a fine pair of
wire electrodes passed through a flat piece of cork
(which must itself be fixed securely by pins to the
frog-cork), and connect these electrodes, and also
those which are fixed into the brain, to a commu-
tator without cross wires so that the faradizing
shocks can be sent to one or other pair as may be
desired. Place the frog-cork upon the stand of a
frog cardiograph (Fig. 44), and by means of a
thread and fine steel hook attach the apex of the
ventricle to the light lever of the apparatus, and
record the contractions of the heart upon a very
slowly moving drum (one revolution in four or five
minutes). Be careful not to injure the heart more
than is absolutely necessary. It is well, in order
to fix the preparation securely, to pass a pin close
to the base of the heart through the vertebral
column into the frog-cork. The following experi-
ments may be performed upon this preparation :

1. Take a normal tracing of the beats during
about a minute.

2. Whilst this is proceeding stimulate not too
strongly the medulla oblongata, allowing the result
to be recorded.

3. Cut the vagi nerves near the skull and repeat
the above experiment. No effect should be obtained.

4. After the normal contractions are resumed
stimulate the vagus, and again record the result.
With weak stimulation of this nerve the heart
may beat faster and more strongly owing to exci-

PRACTICAL PHYSIOLOGY 65

tation of the sympathetic fibres which have joined
the vagus near the skull and are running with the
cardiac branches to the heart ; with stronger stimu-
lation the heart will beat more slowly and less
vigorously or may stop altogether.

5. Place a drop or two of a weak solution (0.2
per cent.) of nicotin upon the heart, and after a
minute or two again stimulate the vagus ; no
effect should be obtained, since nicotin blocks the
junction of the nerve fibres with the distributing
nerve cells within the heart. Wash away the
nicotin with salt solution, and the effect will re-
turn after a time.

6. Disconnect the electrodes which are at-
tached to the skull from the commutator, and use
them to stimulate the heart itself 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 other-
wise.) The heart again comes to a standstill in
diastole. Record this effect also.

Notice that in each case there is an after-effect
of a nature contrary to the immediate effect.

7. Drop a very small quantity of dilute solution
of muscarin upon the sinus, recording the effect
produced upon the rate and force of the beat.
After a short time the heart will probably come
to a standstill in diastole. Now wash away the
muscarin with two or three drops of solution of
atropin sulphate (i in 300). Notice the gradual
restoration of the rate and force of the beats.
Notice further that no inhibition can now be

5

66 PRACTICAL PHYSIOLOGY

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
vagus.

CHAPTER X.

Perfusion of frog-heart. — Expose the heart of
a large pithed frog ; remove the pericardium and
cut through the pericardial ligament. Raise the
apex of the ventricle with a blunt hook ; make a
free cut with scissors into the auricles thus ex-
posed, near to the sino-auricular junction ; insert
the scissors into the auricles and snip through
their septum. Wash all blood away with salt
solution. Place a loop of cotton around the auri-
cles near to their junction with the ventricles ; in-
sert the double perfusion cannula of the heart
plethysmograph (Fig. 45) through the auricles

4 _- Perfusion cannula
("natural size).

Beaker for overflow

Perfusion cannula

Heart tied on perfusion

cannula

FIG. 45.— FROG-HEART PLETHYSMOGRAPH.

68 PRACTICAL PHYSIOLOGY

and into the ventricle, and tie it in firmly by means
of the ligature round the auricles ; cut through
the sinus, and remove the heart upon the cannula.
Now place the heart in the plethysmograph, which
must be full of oil, both stop-cocks being closed ;
then open the one belonging to the bent tube. The
inlet tube of the perfusion cannula is connected to a
reservoir containing Ringer's solution, and the out-
let tube conducts to a receptacle into which the fluid
may flow after passing through the heart. If the
reservoir of Ringer's fluid be at a height of three
or four inches above the heart the ventricle will
presently begin to beat, and its changes in volume
will cause a movement of the oil to and fro in the
open tube. If this be now closed and the one con-
taining the piston opened the piston will move to
and fro, and its movements can be recorded on a very
slowly rotating horizontal drum. (See diagram.)

The influence of various salts, such as chloride
of calcium and chloride of potassium, and of drugs,
such as veratrin, can be studied by adding definite
amounts of them to the Ringer's solution used for
perfusion.

Perfusion through vessels. — Tie a small simple
glass cannula into the aorta of a large pithed frog ;
it can either be passed directly into the cut aorta
or more easily through a cut in the ventricle. The
cannula must be filled with Ringer's solution, and
connected through an india-rubber tube with a
reservoir of the same fluid. Suspend the frog by
a pin through the jaw, and fix the reservoir a short
distance above the head so that the fluid flows

PRACTICAL PHYSIOLOGY 69

into the vessels by gravitation. Make a cut into
the sinus venosus so that the Ringer's fluid may
flow freely out after it has traversed the blood-ves-
sels of the body ; the escaping fluid will drop from
the toes. Count the number of drops per minute,
and repeat the counting two or three times ; it will
be found that the flow is fairly regular.

To test the effect of drugs upon the muscular
tissue of the arterioles the drug to be tested is
added in known quantity to the circulating fluid,
and by again counting the number of drops per
minute it can be determined whether the arterioles
are becoming dilated or contracted as the effect of
the drug. This experiment may be tried with a
decoction of suprarenal capsule.

CHAPTER XI.

Study of the chief vascular and respiratory
mechanisms: 1. 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. Apply the ear directly or
through a stethoscope over this spot, and make out
the two cardiac sounds.1 Whilst listening to the
sounds of the heart feel the pulse of the subject, and
determine that the first sound is systolic — t.e.t is
synchronous with the rise of pressure in the artery
due to the contraction of the ventricle. Next
apply the button of a cardiograph 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 may be held
whilst the tracing is taken, so as to eliminate the
movements caused by respiration.

2. Methods of determining the pressure and
velocity of the blood in the arteries. — The chief
methods used can be studied upon a system of india-
rubber tubes through which water is pumped by a
Higginson syringe. With this system mercurial and
other manometers and the stromuhr and other in-

1 The second is heard most distinctly over the second right
costo-sternal articulation.

PRACTICAL PHYSIOLOGY 71

struments for measuring or estimating velocity can
be successively connected by means of T-tubes.

3. The pulse in the arteries. — Feel the pulse in
the radial artery and determine (i) its rate, (2) its
quality, whether hard or soft, bounding, readily
compressible, etc. ; then apply a sphygmograph,
either Marey's original pattern or the modification
devised by Dudgeon. Use such a 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 employed ; varnish and preserve.

4. Arterial pressure in man. — The pressure of
the blood within the human arteries can be deter-
mined by applying over any artery, such as the
radial, the sphygmoscope of Hill or the sphygmo-
dynamometer of Oliver. Both these instruments
are adapted for showing the variations in pressure
which accompany the pulse, and it is found that
these fluctuations are best indicated when the pres-
sure of the instrument upon the artery is the same
as the average pressure of the blood within the
vessel. The point, therefore, around which the
largest fluctuations oscillate indicates the average
blood pressure.

5. The respiratory movements in man. — Ex-
amine the chest during quiet respiration, and notice
the parts in which most movement is evident ; the
same with forced respiration. Observe the altera-
tion in obliquity "and other changes in position of

72 PRACTICAL PHYSIOLOGY

the ribs, rib cartilages, sternum, and epigastrium.
Apply the ear directly or through a stethoscope to
the :hest wall, and listen to the vesicular murmur.
Lastly apply a stethograph (Marey's or Sander-
son's) to the chest, and register the movements of
respiration by means of a recording tambour upon
a slowly moving drum.

CHAPTER XII.

Reflex action. — A decerebrate frog is sus-
pended by the lower jaw. The following experi-
ments are to be made upon it :

1. 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, and there may also be a move-
ment of the upper limbs (spread of excitation).

2. Stimulate the toe (a) with single and (<5) with
interrupted induced currents. Determine at what
distance of the secondary coil from the primary
the reflex response is elicited in each case (effect
of summation).

3. Touch one flank with a glass rod 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 {purposeful actio^i) .

4. Having washed off the acetic acid and allowed
the frog to become quiescent allow the extremity
of the toes to dip into dilute sulphuric acid (i per
1,000). Count the time in half-seconds which
elapses between the application of the acid and the
withdrawal of the toe. Wash the acid off immedi-
ately after the withdrawal. Repeat this observation
at intervals of a few minutes, and take the average
time of response (Turc&s method).

74 PRACTICAL PHYSIOLOGY

Next place a crystal of chloride of sodium upon
the optic lobes, and again determine the time of
response after application of the dilute sulphuric
acid to the toes. It will probably be found to be
decidedly longer (inhibition of reflex by descending
excitation ; Setschenows experiment}.

5. Lay the frog upon the frog-cork ; open the
abdomen and draw out a loop of intestine ; the
heart is also to be sufficiently exposed for its beats
to be observed. Now excite the intestine strongly,
either by induction shocks or mechanically by a
pinch or blow. The effect will be to produce a
slowing or complete stoppage of the heart, which
will, however, soon recommence beating (reflex in-
hibition of heart).

6. Inject a very small dose of strychnin (i drop
of a i per 1,000 solution) under the skin of a
decerebrate frog, and wait for a few minutes until
it is absorbed into and distributed by the circula-
tion. It will then be found that the slightest touch
of the skin produces not a simple purposeful reflex
action, but convulsive contractions of all the mus-
cles in the body.

Reaction time in man. — The reaction time in
man may be determined by an arrangement of
electric signals, but is done more simply by Wal-
ler's apparatus. This consists of two wooden lev-
ers lying across a piece of india-rubber tube,
one end of which is closed, the other being con-
nected with a tambour which writes upon a drum,
the speed of which should be moderate. A screen
is used to hide the movements of the experimenter

PRACTICAL PHYSIOLOGY 75

from the person experimented on. The latter sits
at the table with one finger resting lightly on one of
the levers. He is to respond by pressing the lever
the instant he (a) feels a tap on that finger, his eyes
being shut ; (fr) hears a tap on the second lever ; (c)
sees the movement 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 impart-
ing the stimulus and the other that made by the
observed person in responding. The interval be-
tween the two marks, which can be accurately
measured by the aid of a tuning-fork tracing, indi-
cates 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 a
large number of observations must be made with
each method of stimulation and the average time
taken.

Discrimination time. — For the measurement of
this the observed person places one finger upon
the end of 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.

Volitional time. — Similar observations are
made, but with the understanding that it is only
the hand on the side which receives the stimulus

76 PRACTICAL PHYSIOLOGY

which is to be used for the response. The reac-
tion 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.

A List of Works in Medicine and Surgery

PUBLISHED BY

LONGMANS, GREEN, & CO.

ASHBY, WRIGHT and NORTHRUP.
The Diseases of Children, Medical and
Surgical. By HENRY ASHBY, M.D.
(Lond.), F.R.C.P., Physician to the Gen-
eral Hospital for Sick Children, Manchester,
and G. A. WRIGHT, B.A., M.B. (Oxon.),
F.R.C.S. (Eng.), Assistant Surgeon to the
Manchester Royal Infirmary and Surgeon
to the Children's Hospital. Fourth Edi-
tion. Edited for American Students by
WILLIAM PERRY NORTHRUP, A.M., M.D.,
Professor of Pediatrics, Bellevue Hospital
Medical College, Attending Physician New
York Foundling, Willard Parker, and Pres-
byterian Hospitals, etc. With about 200
Illustrations. 8vo. $5.00*

ASHBY. Works by HENRY ASHBY, M.D.
(Lond.), Physician to the General Hospital
for Sick Children, Manchester ; formerly
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Summary of Contents : Introduction. Chapter I. — Collection and Removal. II. Sewer-
age. III. The Flow of Liquid in Pipes and Open Channels. IV. Hydraulic Memoranda —
Hydraulic Tables. V. Application of Formulae of Durcy and Bazin, and also of Ganguillet
and Kutter. VI. Construction and Materials. VII. Ventilation. VIII. Traps. IX. Appa-
ratus, Latrines and W. C.'s. X. Apparatus (continued), Urinals, Lavatory Fittings, etc.
XI. Surface Water Collection. XII. Subsoil Drainage. XIII. Sanitary Notes. XIV.
Sewage Disposal. XV. Disposal of Sludge and House Refuse.

The following are some of the leading features of this important work :

a. The entirely new and extended series of tables of velocity and discharge of circular and

egg-shape sewers, etc. This is the first published series of such tables, based upon
Kutter's formula and they have been specially calculated for the work.

b. The full manner in which all sections of the subject are illustrated, both by lithographic

plates and smaller illustrations in the text.

c.. The special descriptions, with illustrations of important works of Sewerage and Sewage
Disposal and the valuable information on the Disposal and Destruction of House
Refuse and Sludge.

d. The important information on the flow of water in Pipes and Open Channels.

e. The extensive series of Hydraulic and other Tables beyond those just mentioned.

Considering the grave importance of Sanitary Engineering, it is remarkable that no book
dealing with the subject in a thorough and comprehensive manner has hitherto been published.

In the preparation of the work Colonel Moore has availed himself of valuable information
furnished by leading specialists in particular branches of the subject, one of whom is the late
Colonel Waring, whose work in the disposal of sewage and garbage is described at length.

OPINIONS OF THE PRESS.

" No engineer can afford to be without a copy of this comprehensive manual of sanitary engineering. . . .

" The book is ... full and complete epitome of the latest practice in sanitary engineering ; a glance at the
list of authorities quoted at the commencement of the work will show how thorough and how painstaking Colonel
Moore has been. . . . As a book of reference it is simply indispensable." — The Public Health Engineer.

" Few departments of applied science can show greater or more dangerous errors than are revealed in the
history of sanitation, but a volume like this shows the immense progress which has been made, and leads us to
think that at last we are on firm ground ... a great book, involving almost infinite labor on the part of the
author, and can be recommended as undoubtedly the standard work on the subject. . . . The type is ex-
cellent, the misprints remarkably few, the illustrations in the text most clearly drawn and reproduced, and the
folding plates are models of what such plates ought to be." — The Builder.

" It is the only book yet received by The Engineering Record which presents a good description of the
various biological systems of sewage disposal now attracting so much attention. It contains a large number of new
hydraulic tables of undoubted value as time and labor-saving aids in computations. Its illustrations of sewer de-
tails are numerous and well chosen. The subject of disposal in general is treated in an interesting manner, and
the information on British systems of refuse cremation it will be difficult to secure elsewhere in so convenient a
form. . . . The book is very good from beginning to end, and will be a valuable addition to the library of any
one who wishes to learn the general theory and practice of so much of sanitary engineering practice in Great
Britain as is embraced in its scope. The discussion of various theories of the flow in sewers, and the tables to
assist in applying them, is a feature which is alone worth the price of the volume."

—Engineering Record, New York.

Longmans, Green, & Co., 91 and 93 Fifth Ave., New York.

A List of Works in Medicine and Surgery.

A Dictionary of Applied Chemistry

BY

T. E. THORPE, B.Sc. (ViCT.), PH.D., D.Sc. (DUEL.), F.R.S,

PROFESSOR OF CHEMISTRY IN THE ROYAL COLLEGE OF SCIENCE, LONDON.

ASSISTED BY EMINENT CONTRIBUTORS.

PUBLISHED IN THREE VOLUMES.

VOL. I. (A— DY.) With 236 Illustrations. Pp. 724, 8vo, $15. oo

VOL. II. (E — NU.) With 240 Illustrations. Pp. 722, 8vo, 15.00

VOL. III. (O— Z.) With 352 Illustrations. Pp. 1,066, 8vo, 20.00

ADVERTISEMENT.

This Work is essentially a Dictionary of Chemistry in its Applications to the Arts and Manufactures ; hence
it deals but sparingly with the purely scientific aspects of Chemistry, unless these have some direct and immediate
bearing upon the business of the technologist. For all such matters reference is made to the New Edition of
" Watt's Dictionary of Chemistry," by Dr. Forster Morley and Mr. Pattison Muir, to which, indeed, the present
Work may be said to be complementary. In order to facilitate such reference the general plan and method ol
arrangement of the two Dictionaries are similar, and the nomenclature and notation adopted are practically
identical. It has, however, not been thought desirable, even if it had been found possible, to make use of the same
elaborate system of abbreviation and contracted expression as that employed in the companion Work, in which the
variety and complexity of the subject-matter are necessarily much greater.

Although the two Works are, in a broad general sense, complementary, it is practically impossible to avoid a
certain amount of overlapping, and therefore a certain degree of independence. Hence in the present Work the
Chemical history of a product of technical importance, so far as it is known, has often been completed, although its
derivatives have, at present, no applications in the Arts. Moreover, such subjects as the ATMOSPHERE, WATER,
FERMENTATION, the CHEMISTRY OF THE HYDROCARBONS, the VEGETO- ALKALOIDS, GLUCOSIDES, etc., etc., all of
which are dealt with in the other Work, find also a place in this Dictionary by reason of their relations to Tech-
nology or to Medicine and Sanitation. In all cases, however, these subjects are treated from the stand-point of
practical application.

The Editor has been fortunate in securing the co-operation of a large number of gentlemen, not only in the
United Kingdom, but also in America, Germany, Switzerland, Russia, and France, as contributors on subjects
with which they are specially qualified to deal. A list of these, with the titles of their contributions, is prefixed to
each volume. Their names and standing are a sufficient guarantee that no pains have been spared to make the
Work a faithful record of the present condition of Chemistry in its relations to the Arts and Manufactures. Special
attention has been paid to the bibliography of the subjects, and in certain cases to the compilation of trustworthy
patent-lists.

SOME OPINIONS OF THE PRESS.

" Should be in the hands of every manufacturer who
wishes to be well posted in the subjects with which he
has to do." — Iron and Steel Trades Journal.

" The list of the names of contributors and the selec-
tion of their subjects inspires confidence at once." —
Journal of Society of Chemical Industry.

"Will be universally appreciated by technical and
manufacturing chemists. . . . Dr. Thorpe's great
work carries with it its own emphatic recommendation.
It must prove most valuable, not merely to chemists and
chemical manufacturers, but to all merchants who have
to deal with chemical products." — Chemical Nevus.

' ' The completion of this important work places at the
service of manufacturers and others a complete encyclo-
paedia treating of industrial operations which in any-
way involve a knowledge of chemistry, and it cannot
fail to prove a valuable source of information for all who
are interested in the productive arts. . . . We feel
confident that those who may desire to keep abreast of
the progress made in chemical industries, and to pos-
sess a trustworthy source of information concerning
modern chemical arts and operations, cannot do bet-
ter than provide themselves with a copy of Professor
Thorpe's admirable ' -

try.' " —

Dictionary of Applied Chemis-
— Pharmaceutical Journal.

A Prospectus of the work with Specimen Pages may be had, post free, of the Publishers.

Longmans, Green, & Co., 91 and 93 Fifth Ave., New York.

UNIVERSITY OF CALIFORNIA MEDICAL SCHOOL LIBRARY

THIS BOOK IS DUE ON THE LAST DATE
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UNIVERSITY OF CALIFORNIA MEDICAL SCHOOL LIBRARY