Skip to main content

Full text of "Exercises in practical physiology. v.3"

See other formats


This is a digital copy of a book that was preserved for generations on library shelves before it was carefully scanned by Google as part of a project 

to make the world's books discoverable online. 

It has survived long enough for the copyright to expire and the book to enter the public domain. A public domain book is one that was never subject 

to copyright or whose legal copyright term has expired. Whether a book is in the public domain may vary country to country. Public domain books 

are our gateways to the past, representing a wealth of history, culture and knowledge that's often difficult to discover. 

Marks, notations and other maiginalia present in the original volume will appear in this file - a reminder of this book's long journey from the 

publisher to a library and finally to you. 

Usage guidelines 

Google is proud to partner with libraries to digitize public domain materials and make them widely accessible. Public domain books belong to the 
public and we are merely their custodians. Nevertheless, this work is expensive, so in order to keep providing tliis resource, we liave taken steps to 
prevent abuse by commercial parties, including placing technical restrictions on automated querying. 
We also ask that you: 

+ Make non-commercial use of the files We designed Google Book Search for use by individuals, and we request that you use these files for 
personal, non-commercial purposes. 

+ Refrain fivm automated querying Do not send automated queries of any sort to Google's system: If you are conducting research on machine 
translation, optical character recognition or other areas where access to a large amount of text is helpful, please contact us. We encourage the 
use of public domain materials for these purposes and may be able to help. 

+ Maintain attributionTht GoogXt "watermark" you see on each file is essential for in forming people about this project and helping them find 
additional materials through Google Book Search. Please do not remove it. 

+ Keep it legal Whatever your use, remember that you are responsible for ensuring that what you are doing is legal. Do not assume that just 
because we believe a book is in the public domain for users in the United States, that the work is also in the public domain for users in other 
countries. Whether a book is still in copyright varies from country to country, and we can't offer guidance on whether any specific use of 
any specific book is allowed. Please do not assume that a book's appearance in Google Book Search means it can be used in any manner 
anywhere in the world. Copyright infringement liabili^ can be quite severe. 

About Google Book Search 

Google's mission is to organize the world's information and to make it universally accessible and useful. Google Book Search helps readers 
discover the world's books while helping authors and publishers reach new audiences. You can search through the full text of this book on the web 

at |http: //books .google .com/I 














Third Edition. With J14 Illustrations, 8v0y i8s. 

An Introduction to Human 


In the Press. 

Lectures on Animal Electricity 

(Delivered at the Royal Institute of Qreat Britain). 





St. Maby's Hospital Medical School. 

May, 1897. 


The following pages form Part III. of a series of Exercises and 
Demonstrations to accompany ** An Introduction to Human 
Physiology," and are primarily intended to facilitate the class- 
work of this Laboratory, 

The Directions given in them are addressed to " advanced *' 
sticdents who have properly expended one year in the study of 

In some cases it will be found that an exercise may be carried 
out by each student working independently ; in others, that the 
student will require much assistance from a skilled demonstrator; 
in others stilly that the student will at most take som^ part in a 
carefully -prepared demons tration . 

A, D, Waller. 






LECTram 0.-. maou«i lo .t. «,«,. *.,.;., , 










1 Galvanic Cells ; Daniell, Leolanch6. 

2 Du Bois-Reymond Key ; Tumbler Key. 

3 Pohl*s Commutator ; Circular Commutator. 

4 The Galvanoscope or Current-Indicator. 

5 Du Bols-Beymond's Induction Apparatus. 

6 Principle of the Helmholtz* Modification. 

7 Demonstration of the Break Extra-Current. 

8 Demonstration of the Make Extra-Current. 

9 To cut out the Make or Break Current. 

10 Verification of Ohm's Law. 

11 Action of Rheostat as a Shunt. . 

12 The Bheochord ; the Monochord. 

13 Measurement of Resistance. 

14 Kelvin's Reflecting Galvanometers. 

15 Measurement of Potential by Compensation. 

16 Demonstration of Equipotential Lines. 

17 Excitation of Nerve by the -Condenser ; Minimum Energy of an 

Electrical Stimulus. 

18 Unipolar Stimulation. 

19 Unpolarisable Electrodes. 

20 Lippmann's Capillary Electrometer. 

21 Recording Apparatus. 

22 The Chronograph. 

23 Photo-galvanometric and Photo-electrometric Records. 

24 To Pith a Frog ; Decerebration. 

25 To Prepare a Muscle or a Netve-Muscle for Experiment. 

26 Action of Curare. 

27 Action of Veratrine. 

28 A Single Muscular Contraction. Efiect of Heat and Cold. 

29 Two Successive Contractions. 

80. Many Successive Contractions ; Clonus; Tetanus. 

31 Fatigue. 

82 Extensibility of Muscle. 

33 Electrotonic Alterations of Excitability. (Frog). 

84 Pfliiger*8 Law of Contractions. (Frog.) 

35 Law of Contractions. (Man). 

36 Electrotonic Alterations of J^xcitability. (Man). 

37 Measurement of the Velocity of Nervous Impulses. (Man.) 

38 Influence of Temperature upon the Excitability of Nerve. (Gotch.) 

39 Electrotonic Currents. 


10 The Paradoxical Contraction. 

41-2 Oalvani's Firet and Last Experiments with and without metalG. 

43 MuBcle-Currente. 

44 Nerve-CurrentB : the Current of Injury and itB Negative Variation. 

45 Action of AniBBthetics upon Isolated Nerve. Carbon Dioiide, 

Chlotolonn, and Ether. 

46 The Secondary Qpntraction. 

47 Secondiuy Contraction from the Heart. 

4S An Apparent Anomaly dne to Secondary Contraction. {Hering.) 

49 Secondary Excitation from Nerve to Nerve. 

CO OurrentB of Action oE Frog'a Heart 

fil Currents of Action of Mammalian Heart. 

62 Currents of Action of Human Heart. 

C3 Retinal Currents. (Frog.) 

G4 Sound is Produced during Muscular Contraction. 

66 Heat ia Produced during Muscular Contraction. 

66 Tendon-Reflex Time, (Man.) 

67 Tendon-Reflex Time, (Rabbit.) 

66 Function of Nerve-Roots. (Muller's Experiment.) 

59 " Overlap " of Nerve-Supply, (Sherrington.) 

60 Reflex Actions of Brainless Frog. jGoltz' Klopf-Verguch.) 

61 Inhibitory Action oi Superior upon Interior Centres. 

62 Time of Reflex Action. (Frog.) 

68 Action of Strychnia. (Frog.) 
64 Summation of Stimuli. (Frog. 
66 Reflex Winking Time. (Man.) 

66 Sensory Reaction -Timing. (Man. 

67 Discrimination Time. (Man.) 

68 Volition Time. (Man.) 


(1) Put up a galvanic cell ; you should first amalgamate 
the zinc and scrape the ends of 
all wires and terminal screws. 

The cells in ordinary use in 
this laboratory are the Daniell, 
the bi-chromate, and the Le- ^'"h^ 

clanche. Parauapot 

The Leclanche is the most "^^So" 

convenient, but must not be 
used too long in a circuit of low 
resistance {e.g., primary coil), 
and must never be left " short- 

Bemember that in all these cells the zinc is the positive 


element, the end of the wire from it is the negative electrode 
or kathode, and the direction of current is from anode to 
kathode; we shall habitually designate any kind of cell by 

the conventional figure ©. 

(2) Study the du Bois-Eeymond key and Pohl's commu- 
tator, in connection with a cell and a current indicator. 

The du Bois key can be employed — 

(a) To interrupt a circuit, the key being interposed in 
the course of one of the wires of the circuit, which is there- 
fore made by closing the key, broken by opening the key ; 

(6) To bridge a circuit, both wires from the cell being 
connected with the two sides of the key, and other two 
wires being connected with the electrodes ; the current is 
therefore made through the electrodes by opening the key, 
broken by closing the key. When used in the primary 
circuit of a coil, the key should be put up to break one 
wire (a), when used in the secondary circuit the key should 
be put up to bridge both wires (6) . 

We shall habitually designate any kind of key by the 
letter K, 

(a) Interrupting a circuit, thus — 

Fig. 2. 

(6) Bridging a circuit, thus — 

Fig. 3.— Du Bois-Beyhond's Friction Kesy. 
Put up so as to ** short-circuit " current when it is closed. 

For producing a "clean" make and break, this key is 
not suitable on account of friction, and a simple contact or 
spring key or a simple mercury key is preferable. 









lul, . 

■- r-. 

iJw Eiar !. 

»»I WlTt!^ ,. 

Th. . 1,1,, 

tl» hi-. 





this laboratory mercury apparatus are, as far as may 
• -placed by brass instruments. Spring keys are used 
eference to mercury keys, and Pohl's commutator is 
:ei by a reverser of the following pattern, 
wo semi-circular pieces of metal, each provided with 
minal ; a transverse piece of ebonite revolving horizon- 
round a vertical axis, and provided with two terminals 
•.'h rub firmly against the metal semicircles. Eeversal 
arrent as indicated in the figure. This key is used in 
•e of Pohl's commutator with cross wires. 

Fig. 6.— CiBCuiiAB Commutatob in its Two Fosrrioifs. 


If it is desired to turn a current into one or other of 
several circuits, or — what amounts to the same thing — ^to 
lead off from one or other of several circuits to a galvano- 
meter, or — as when " compensation " is made: — to conjoin two 
currents into one circuit, a convenient and simple apparatus 
is a keyboard on this principle, composed of a series of 
tumbler keys arranged as in fig. 7. 

Muddt' <^CL£va/no79tU€/L CoTryiendcitrr 

Fig* 7. 

When all the keys are closed, current is short-circuited ; 
when any key is opened current passes in the circuit connected 
with its two sides. 

A key-board of this character is represented in fig. 7. 

(4) The cnrrent-indicator or galvanoscope consists of a magne- 
tised needle surrounded by a coil of wire. It serves to show 
the passage of a current and its direction; a properly graduated 
instrument on this principle will serve to show further the 
magnitude of a current and is now a galvanometer, (Ex. 14.) 

Put up this circuit to verify the action of the commutator 
in reversing current through the galvanoscope. 

Fig. 8. 



(5) The induction apparatus of du Bois-Reymond consists of 
(a), a cell supplying current to (b), a primary or thick wire coil 
by which currents are induced in a secondary or thin wire coil. 
These secondary currents are those employed for excitation, 
and their strength is altered by altering the distance between 
secondary and primary coils. 

Connect the cell with the primary circuit, with a key to 
gap one of the wires. Connect the electrodes with the 
secondary circuit, with a second key to bridge the circuit. 
Test for the currents in the secondary circuit by placing the 
electrodes on the tongue or lips. 

Pig 9.— Dd Boia-RfiYMOBD'a Ibduction Apparatus, with Diagbahs < 


FoVB Kinds of Cdbbehts that uai 

N.B.— Figs, a and b are given for tha sake of sjatematic cleamesB. 
tise, however, the circuit of fig. 6 would lead to rapid polarisation 
aud weakening of the cell, especially if a Lectanch6 celt. To 
prevent too prolonged short-circuiting, a apring-key, Kj, had 
better be introduced on one of the battery wires, thus : — 

This oirouit ia a combination of a and 6. With K, open we 
have the circuit a made and broken by closing and opening K,. 
With Kj oloEed we have the circuit b made through the coil by 
opening K„ and broken by closing K,. ' 


The numbers 1 to 7 indicate the terminals and contact 
screws connected with the primary coil. 

For single shocks the two battery wires are to be connected 
with the terminals 4 and 5, which are at the two ends of the 
primary wire. 

(a) Ordinary shocks are obtained when a key is used to 
interrupt one of the wires. 

(6) Modified shocks are obtained when a key is used short- 
circuiting the primary wire. 

(c) For repeated shocks (ordinary) the two battery wires 
are to be inserted at 1 and 6. The circuit now includes the 
spring interrupter and the wire of the electro-magnet by which, 
the circuit is made and broken at the contact screw 3 ; the 
contact screw 7 is kept out of use by being lowered. 

(d) For repeated shocks {modified) the battery wires are left, 
as before, at 1 and 6. A short thick side wire is placed between 
2 and 4. The contact screw 3 is raised out of range of the 
spring, and the contact screw 7 is raised until it comes within 
range of the spring. This is known as the " Hehnholtz " 

* In ordinary coils the graduation is given in millimeters only. But mere 
distance gives no true idea of relative strength of stimulation ; e.g., with the coil 
at 10 cm., the strength is nothing like one half what it is at 5 cm. The better 
sort of coils are provided with a graduation in units of strength. Failing this 
graduation, it is useful to draw up a graduation in arbitrary units of strength by 
means of a reflecting galvanometer. Single induction shocks from the secondaiy 
coil at different distances from the primary, give galvanometer deflections nearly 
proportional with current strength; and from a series of such readings an 
arbitrary strength scale can be constructed on the coil opposite to the centi- 
meters of the distance scale. This should be done by the demonstrator. 

The accompanying table gives an example of such a graduation: 




































Note. — With an ungraduated coil an approximate scale is aflorded by taking 
the strength as varying inversely as the square of the distance. 







When you have become familiar with the four modes of 
connection described in connection with fig. 9, take a series 
of observations with tne electrodes on the tongue and observe — 

With (a) that the break induction shock is stronger than 
the make induction shock ; 

With (6) that both shocks are reduced, but especially so 
the break; 

With (c) and (d) that the efifect on the tongue is greater 
with (c) than with (d), with (c) than with (a), with (d) than 
with (6). 

Note in each case the greatest distance of secondary from 
primary coil at which you first feel the secondary make and 
break currents, and fill up the accompanying table with your 


Greatest distance 

at which shock 

is felt. 

At make 


Single Ordin. 

Single Hodif. 

Repeated Oidin. 

Repeated Modif. 

[Bemember that make and break currents in a secondary 
coil are altogether different from the make and break of a 
battery current.] 


(6) Principle of the Helmholtz' modification. — Not only does a 
current made or broken in one coil (primary) induce other currents 
in a second coil, but in any single coil every turn of wire has an 
inductive influence upon every other turn. This influence is termed 
self-induction, and the currents thus generated are termed extra- 
currents. The inequality between the ordinary make and the break 
shocks from the secondary coil is due to an extra-current in the 
primary coil ; the direction of an extra-current is against the battery 
current at make, with it at break, thus delaying the rise (but not 
delaying the fall, inasmuch as it does not pass at all, or, more 
strictly, inasmuch as it is non-existent, the circuit being broken). 
Therefore, if means can be provided for the break extra-current to 
exist, the break shock will be reduced and made more nearly equal 
to the make shock. This is done by the Helmholtz side-wire 
between the terminals 2 and 4 (fig. d), which keeps the primary 
circuit complete during variations of its current. Those variations 
are effected by a key or interrupter cutting out current by ** bridge " 
at the lower screw 7, instead of by " gap " at the upper screw 3 
(fig. 9). 

As a general rule the Helmholtz modification of the coil 
should be adopted when induced currents are applied to nerve 
or muscle. By this precaution, the risk of two possible fallacies 
is greatly diminished, viz., (1) an undesirable predominance of 
currents in one direction, i.e., in that of the break ; (2) unipolar 




/kM^of/ ^^ 7n.abikcafio7i 

Pig. 10. — To Illustbatb Induction Gubbents and theib Modification by 


In the primary coil at make the current rises gradually to a maximum, being 
delayed by the opposed extra-current, at break it suddenly falls to zero, undelayed 
by extra- current, inasmuch as the circuit is now broken. The make and break 
currents induced in the secondary coil are indicated by the unbroken line ; they 
are of opposite directions, and the break is of greater intensity than the make 

The several currents, as modified by the side wire, are shown by dotted lines. 
The total current variation at make and break in the primary circuit is smaller 
than before, and the break extra-current can now take effect^ inasmuch as a circuit 
is preserved through the side-wire. The fall of current in the primary wire is 
thereby delayed, and the break current in the secondary coil is much reduced. 
Obviously, as the primary current variation is smaller, the secondary make 
current must also be slightly reduced. 


(7) The existence of a break extra-current is demonstrated 
as follows : — 

A cell is connected with the primary coil of an inductorimn 
(the secondary coil having been removed) as shown in the 

lo ^hO'JIu }T(ff}{%^ 

Fig. 11. 

One key Ki bridges the coil, the other Kg bridges the elec- 
trodes, which are applied to the tongue. Close K^, i.e., cut out 
the coil, and while K^ is closed, open and close Kg, i.e., make 
and break the battery current through the tongue ; little or 
nothing is felt. 

Now open K^ so as to put the coil into circuit, and while K^ 
is open, open and close Kg ; as Kg is opened the current through 
the coil is suddenly reduced, and a smart twinge is felt» which 
is the effect of a break extra-current. Nothing is felt when 
Kg is closed, for the make extra-current then passes in the 
metallic circuit across the bridge Kg. 


(8) To demonstrate the make extra-current, a nerve-muscle 
preparation must be used, and a rheostat to diminish the 
battery current. Connections as per diagram. 



FiQ. 12. 

With Kg open, opening and closing either K^ in the principal 
circuit or K. in the nerve circuit, makes and breaks a branch 
current in the latter circuit independently of any self-induction 
in the coil sufficient to excite the nerve. By means of the 
rheostat the current is now reduced until K^ gives no effect at 
make or break. 

(1) Opening and closing K^ (with Kg open so as to send 
current through coil, and Kg closed) cause contractions by the 
break and the make extra-currents, whereas opening and closing 
K3 are ineffectual. 

(2) Or (with K^ and Kg closed) while closing Kg has no 
effect (the break extra-current then produced being bridged 
through Kg), opening Kg so as to make current through the 
coil gives contraction. In the first case we have demonstrated 
the effect of the make and of the break extra-currents, in the 
second case that of the make extra-current alone. 


(9) To cut off the Make or Break Shock. — It is sometimes 
desirable to use only make shocks ^ to test the excitability of 
nerve or muscle, in which case the break shock must be cut 
out. This can be done as follows : — 

Jo cut of£. ItuL ovuvH^ o^lPuL hxA}{ mhtcut cu/i^um^ 

Fig. 13. 

Ki is a gap key in the primary circuit, K2 is a bridge key 
in the secondary circuit. 

To cut out the make shock, the two keys are worked in this 
order : — close Kg, then close K^ (the make is bridged at Kg) ; 
then successively open Kg and K^ (the brpak passes through 
the electrodes). 

To cut out the break shock, open Kg, close Kj (the make 
passes through the electrodes), then successively close Kg and 
open Ki (the break is bridged at Kg). 

But to attend to these details during experiment is incon- 
venient, nor would it be possible to obtain a rapid succession 
of only one kind of shock. 

It is convenient to use an automatic " cutting out " 
interrupter in the two circuits. 

Automatic "cutter out." — The armature of an electro- 
magnet in the primary circuit is attracted at make, tilts the 
lever a b, so as to make contact at the mercury cup a, which 
forms a " bridge " to the secondary and electrode circuit. But 
before the contact has been made at a, the make shock has 
taken effect. The break induction shock passes while the con- 

* With the ordinary arrangement of the coil, the make induction shook is 
far more uniform in strength than the break induction shock. The latter is in 
reality a double current partly due to the break of the battery current, partly 
due to the sudden make and break of the extra-current which sparks across at 
the interrupter in a varying manner. 



Fig. 14. 

tact at a is still unbroken. Care must be taken that the wire 
plunges well into and out of the mercury, so that the secondary 
coil is bridged at a a^ break in the primary circuit, i.e., the break 
induction shock is cut off from the electrode circuit. There is 
no short circuit at a at make in the primary circuit, i,e,, the 
make induction shock passes to the electrodes. 

The apparatus can be connected up in various other ways, 
cutting out the make or the break by bridge or by gap at a or 
at b. 

Double Keys. — It is sometimes desired to simultaneously 
make or break two currents in two separate circuits (e.g,, to 
simultaneously excite and signal the excitation) and a double 
key is easily improvised for this purpose. HelmhoUz' Key, by 
which a " make " in one circuit is simultaneous with a " break " 
in another circuit, will occasionally be found useful. 




Fig. 15. Hblmholtz' Key. 

By depressing the handle at a, a circuit is made at a, and another circuit is 
simultaneously broken at &• 



(10) Verify Oliin's law (c«, 

A rheostat ie a set of resistance coils, gradtiated in ohms, 
by means of which more or less resistance can, at will, be put 
into a, circuit. 

^]||2^) using for the purpose 
1, 2, or 3 Leclanche cells, 
key, rheostat and galvano- 

Set up the cells "in series," 
in circuit with a rheostat, 
galvanometer and key. Ad- 
just the resistance by means 
of the plugs to give a con- 
venient deflection of the gal- 
vanometer magnet (say 10 
milliamperes) with the three 
cells in circuit, as shown in 
the diagram. 

A. Keeping one of the 
wires (say from the zinc) in 
position, shift the other wire 
from the copper of the third 
cell to that of the second and 
then to that of the first, and 
note the deflection obtained with one, two and three cells in 
circuit. Observe that the current varies with the electromotive 

B. In the preliminary adjustment you have had occasion to 
observe that the current varies inversely as the resistance. 
Take readings of the current strength unplugging the rheostat 
to give resistances between, say, 1,CK)0 and 1(X) ohms. Plot 
out the results on millimeter paper. 

Fio. 16. 

Wires ol definite resistance unite the 
metal blocks a, b, c, d, e, wluch can be 
connected and dUconnectod by inserting 
or removing tnetal plugs. If sJl the plugs 
are inserted the resistance is practically 
zero ; if a plug is remoyed (as shown in 
fignrej.resiBtftaoe in aoircuitia increased; 
if the four wires in the t>ox have resist- 
ances of 1, S, 3, andlohms, removal of all 
the plugs would give a resistance of 10 


Note. — An exact verification of Ohm's law is not sought for 
in this exercise, but only a verification of the principle. The 
graduation of the galvanometer is comparatively rough, and 
the resistance in circuit is not only that of the rheostat, but 
also the resistance of the galvanometer, and wires, and the 
internal resistance of the cells. 



(11) Action of a rheostat arranged as a shnnt. — Put up a 
divided circuit with a Leclanche cell, key, two rheostats, 
and galvanometer, as per diagram, one rheostat, Ei, being used 

Pig. 18. 

to adjust the current to a convenient strength, the other 
rheostat. Eg, being disposed as a " shunt " or short-circuit to the 

Make E^ = say 100 ohms. Then take readings of the 
galvanometer with variation of Eg from 1 to 10 ohms. Observe 
that as the resistance is increased and diminished in this 
'* shunt *' the galvanometer deflection is increased and 

The circuit branches at Eg current passes through Eg, 
and through the galvanometer; if Eg has little resistance 
a greater fraction of current passes through Eg, and a lesser 
fraction of current through the galvanometer ; as Eg is 
increased a greater fraction of current is diverted into the 

Notice that rheostat Ej, being on the path of the undivided 
current, gives greater deflection when its resistance is dimin- 
ished, smaller deflection when it is increased — as in the 
previous exercise. 


(12) A rheochord is a wire and slider so disposed that a very 
low but variable resistance can be offered as a deriving or 
'* shunt ** circuit by the side of a principal circuit of higher 
resistance. It affords means of dividing a current into two 
parts, and of thus obtaining any desired small fraction of the 
current of a single cell, the larger part passing through the 
rheochord, which is of low resistance, the smaller part pass- 
ing through the principal circuit, which is of high resistance. 
If, for instance, the current of a cell is made to branch (a) 
through a rheochord with a resistance of 1 ohm, (b) through a 
nerve with a resistance of 9999 ohms, then the current in the 
shunting or rheochord circuit will be ^nfxny> ^^^ current in the 
nerve circuit will be only Yishrsis o^ ^^^ entire current of the 
cell. The rheochord, as a deriving circuit, is to the prin- 
cipal circuit what the galvanometer shunt is to a galvano- 
meter (E2 in fig. 18) ; by means of a slider the resistance of 
the deriving circuit, and, consequently, the magnitude of the 
current diverted into the principal circuit, can be increased or 
diminished at will. 


Fig. 19. 

Put up a circuit similar to that of Exercise 11, but substituting 
a rheochord r r, for Bg, acting like it as a shunt ; and adjusting 
El to give any convenient deflection with the slider midway 
between its two extreme positions. Observe that as the metal 
slider s s is moved further from and nearer to the rheochord 
terminals r r (to which both the battery and the galvanometer 
wires are attached), more and less current is diverted into the 
galvanometer in accordance with the greater and smaller length 
(and therefore resistance) of the shunting path r s s r. 



The monochord is in principle a rheochord, but with a 
slightly different system of connections, as should be verified 
in accordance with this diagram. 

Fig. 20. 

As the slider s is moved further from and nearer to r, the 
resistance r s (and therefore the proportion of current diverted 
into the galvanometer) is increased and diminished. The 
resistance box E may be set at about 10 ohms, and is con- 
venient for the purpose of reducing the current to a convenient 

As may be understood from the above description, a rheo- 
chord is a means of obtaining a small electromotive pressure. 
One of its chief practical applications is to the measurement or 
neutralisation of " currents of injury " by compensation. (See 
Exercise 44.) A monochord is easily improvised by stretching 
a wire between two terminals fixed in a board with a brass 
spring clip and attached wire to serve as a slider. 


(13) Measnrement of Resistance. Dem. — Use a Leclanche 
cell, two spring keys, Wheatstone bridge and galvanometer. 

Principle. — The two points b ft^ are at the same potential, 
i.e,, there is no current through a wire (and galvanometer), 
joining these points when the resistance A is to the resistance B 

A X 

as the resistance x is to the resistance C; viz., when :^ = 7^, 

or a; = :^, that is = C X 4 

Jt> ±) 

Therefore, with the three known resistances adjusted until 
there is no deflection of the galvanometer and the unknown 
resistance a;, this last is determined by resolving the equation 

aj = C X g. 

Fig. 21. 

If A and B are equal, a; = C; ifA = t^B, a; = ^C; if 
A = 10 B, a; = 10 C, &c. 

In practice, we shall as nearly as possible have the four 
resistances of the same order of magnitude, i.e., in the tens, 
hundreds or thousands of ohms. But with x very large we 
shall adjust A = 10 B or = 100 B ; and with x very small we 
shall put A = ^ B, or = ^^ B. 

The " no current " state will be found by subsequent adjust- 
ment of C, the final value of C being taken as the mean be- 
tween the ** just too much '* and ** just too little," as shown by 
the slightest possible galvanometer deflection first in one then 


in the opposite direction. In the first rough trial we note in 
which direction the magnet swings when C is evidently too 
great and evidently too small. In testing for the current first 
close the battery key K^, and then keeping K^ closed, close the 
galvanometer key Kg. The connections of the Wheatstone 
box put into your hands are figured below. 

Note. — The small galvanometers placed in your hands 
will serve only for resistances not exceeding 1000 ohms. For 
measuring higher resistances a Kelvin's reflecting galvanometer 
must be used. This instrument cannot be put into the hands 
of students who have not previously worked in a physical 
laboratory, until they have become familiar with the use of the 
small galvanometer. 



(14) Kelvin's Reflecting Oalvanometers. — A galvanometer is an 
indicator of the presence, direction and magnitude of a galvanic 
current. In principle it consists of a coil of wire surrounding 
a suspended freely-swinging magnet, which becomes deflected 
from its position of rest when current passes through the wire. 
In practice (i.e., in Kelvin's reflecting galvanometer), a sus- 
pended system of magnets is used, with poles so disposed as to 
make the system not far from ** astatic," i.e., not to set too 
strongly in a position of rest pointing to the magnetic pole, and 
further controllable by an indepen- 
dent large magnet, by which the 
** set," and therefore the sensitive- 
ness, of the suspended system may 
be modified. The distance of this 
magnet from (and therefore its effect 
upon) the suspended system can be 
altered at will, and its poles may be 
turned so that the ** set " is increased 
or diminished. In the former case 
the magnet is said to be '* friendly," 
the set is increased, the suspended 
system is less sensitive, and bringing 
the magnet closer increases the set. 
In the latter case (marked end point- 
ing north) the magnet is said to be 
** unfriendly," the set is diminished, ^ ^ 

the sensitiveness is increased, and Fig. 22. 

bringing the magnet closer diminishes Astatic couple of magnets n s, 
the set (up to a certain limit, beyond sn, suspended by a silk fibre and 

1 • 1 i 1 ^ • J \ mu carrying a mirror (indicated by 

which the set IS reversed). The the dotted circle); the surround 
movements of the suspended system ing line and arrows indicate the 

of magnets are shown greatly magni- disposition of the coils ; n s is the 
fied by means of a Ught mirror which ^^1^*^^^,^ ^? ^' controUing mag- 

^ 1. A r T 1-j. J. r. • ^®*- AH these parts are repre- 

reflects a spot of light on to a hori- sented as if viewed by an observer 

zontal scale. (If desired, the varying standing west, i.e., in the posi- 
positions of this spot can be recorded ^^^^ ^^ *^® ^*°^P ^ *^® ^^^xt fig. 
photographically. See p. 40.) 

Beflecting galvanometers in ordinary use in a physiological 
laboratory are of two kinds, viz., of high resistance (5,000 to 
20,000 ohms), and of low resistance (1 ohm or less). The 


former are used for currents of muscle and nerve, the latter 
for thermo-electric currents. 

In connection with a high-resista-noe galvanometer, a 
'■shunt" is frequently employed; this serves to reduce the 
sensitiveness when desired by carrying off ^5 or ^ or -^^ of 
any given current (the coils in the shunt having respectively 
^ or ^ or ^5 of the resistance of the galvanometer coils), 
thus leaving to pass through the galvanometer tfe or j^ or 
ttAto of the total current. As ordinarily used this galvanometer 
is an indicator of current, but by adopting the method of 
compensation it becomes an indicator of potential or pressure, 
being in this case used to indicate equality of opposite poten- 
tials by absence of current. (See next exercise 15), 

Fio. 23. — SiDB View of GALVAxoicB'rBB and Shubt, Lamp atsd Scale. 

The galvanometer and scale are placed eaat and west, and appear as if viewed 
by an obBervec standing on the north side; the path of light is indicated by dotted 
lines. The essential pojis concealed by the galvanometer case are di^ranunati' 
colly given in fig. 23. 

The suspended system of magnets of an ordinary galva- 
nometer, after it has been set in movement, comes to rest by a 
series of diminishing oscillations above and below its position 
of rest. In such case the instrument is said to be "un- 
damped" or "partially damped," and an instrument in which 
the unavoidable damping to the resistance of the air is made 
as small as possible is called a ballistic galvanometer. If, on 



the contrary, the damping is increased — as by a light vane 
turning in a confined air-space — the movement is rendered 
'^dead-beat'* or ** aperiodic^** i.e., the oscillations are sup- 
pressed, so that the magnet (or system of magnets) does not 
swing beyond its steady deflection by a current, nor beyond its 
zero with cessation of current. In such case the movement 
by which the magnet takes up a new position of rest occurs 
more slowly than is the case with an undamped magnet, and 
with a gradually increasing slowness; the time occupied by 
this movement is called the ''falling-time" oi the magnet. 
With an undamped magnet the time occupied by one oscilla- 
tion to and fro is its ** period,*' and the relation between the 
magnitudes of two successive operations is the ** decrement.'* 

Fig. 2 . 

Deflection of a dead-beat galvano- 
Falling time = 15 sees. 

Deflection of a partially damped 

Period =8'5 sees. 
Decrement ~ about 2. 


Fio. 25. — Mbasubbmbnt of Potential by Compensation. Dbh. 

(15) A Daniell cell is connected with the two ends of a rheo* 
stat, divided into two parts, one of lower resistance, r, the other 
of higher resistance, E. With the high external resistance, the 
P.D. (" Potential Difference ") at the two terminals is practically 
equal to the full E.M.F. of the cell (i.e., 1 Dan. or about 1*1 
volt), and the P.D. at any two points of the circuit varies 
directly as the resistance between these points. Thus the P.D. 
at two points of a muscle is ascertained by finding the resist- 
ance, r, at which it is balanced (i.e., no current through the 

galvanometer) ; it is then equal to .p . For example, if the 

balance is obtained with r = 260 ohms, and r + 'R = 7500 


ohms, the muscle potential is tf^F^, or '033 Dan. 


(16) Xqoipotential Lines. Dem, 

A Daniell cell, a du Bois key, galvanometer, a large flat 
dish of zinc sulphate, two pairs of amalgamated zinc elec- 

Fix the leadiog-in electrodes at + — ; place one leading-oflf 
electrode midway between them. 

(1) Determine the equator by shifting the other lead- 
ing-off electrode to positions at which no current passes the 
galvanometer on closure of the key. 

(2) Shift the electrode towards +, and on closure of the 
key observe a current through the galvanometer from S to N, 
indicating + potential at this point. 

(3) Shift the electrode towards — , and on closure of the 
key, observe a deflection from N to S, indicating — potential at 
that point. 


(4) Shift the first leading-off electrode nearer to — , and by 
successive trials of shifting the second lead-oflf, find several 
equipotential points, from which construct a curve. 

(5) Repeat the observation with the first leading-oflf electrode 
nearer to +. (Vide " Human Physiology," p. 306). 

(6) Find equipotential curves near and far from one of the 
poles, place the leading-off electrodes on any two points of 
each of these curves, and observe the galvanometer on closure 
of the key ; or, more simply, take a pair of leading-off electrodes 
at a fixed distance from each other, and find positions in the 
field at which more or less current passes in one or other 



(17) Excitation of nerve by the Condeneer. 

A condenser in its simplest form is a pair of metallic 
surfaces separated by a thin layer of air, glass, paraflSn, mica, 
&c., that are charged by being brought into metallic connection 
with points of different electrical pressure, such as the copper 



Fig. 27. 

and zinc of a Daniell cell, and discharged when connected by 
a sufficient conductor. Either the charge or the discharge 
may be made through a nerve. 

Connect the middle pair of pools of a commutator vnthout 
cross wires to the terminals of a "condenser," connect the 
two lateral pairs with a cell and with the nerve of a nerve- 
muscle preparation as in fig. 27. 

With the cradle of the commutator as shown in the 
diagram, the condenser is connected with the cell and 
"charged." When the cradle is turned over, the charged 
condenser is disconnected from the cell and connected with 
the nerve through which it is "discharged," provoking a 
single twitch of the attached muscle. 



Minimum energy of stimulus. Dem. 

With stimulation by the discharge (or charge) of a con- 
denser we can express in terms of energy the value of the 
electrical stimulus. 

WoTic J^UJ 

Pig. 28. 

Charge from + through hce* ep* p\iO — when contact is made at h by depres- 
sing the Morse key (and broken at a) viz., ascending in the nerve. 

Discharge from p' through ee^c a to p when contact is made at a by recoil of 
the Morse key (and broken at b) viz., descending in the nerve. 

The bridging key is for the purpose of cutting out from the nerve either the 
charge or the discharge. If desired this may be effected without the bridging 
key by the circuits 1 and 2 of fig. 29, substituting the exciting electrodes e e' for 
the galvonometer SN. 

Put up connections in accordance with fig. 28, using a 
condenser of 0*10 microfarad, subdivided into parts = O'Ol. 

Determine by adjustment of the rheostats r, E, the smallest 
fraction of a volt that will excite the nerve of a nerve-muscle 
preparation : — 

(A) with the condenser at 0*10 microfarad ; 

(B) with the condenser at 0*01 microfarad ; 

and calculate in the two cases the quantity and the energy of 
such a minimal electrical stimulus. 

(C) with a convenient fraction (say O'l of a volt) 
find the minimum effective condenser value (between 001 and 
0*10 microfarad) and calculate as before. 

N.B. — ^You may expect the energy value of a minimal 
effective stimulus to come out at something like O'OOl erg., 
viz., 1 millierg. 


Note. — Eecollect the difference between "quantity" and 
"energy" of an electrical charge (or discharge) — (1) that 
quantity varies directly as capacity and as pressure ; (2) that 
energy varies directly as capacity and as pressure squared. 
Identical quantities may be of very different energies ; a given 
energy may be derived from very different quantities, e,g, : — 





O'Ol microfarad 



0*001 microcoulomb 

00006 erg. 







00020 „ 







00046 „ 







00080 „ 







00126 „ 







000006 „ 







000020 „ 







000045 „ 







000080 „ 







000125 „ 







00006 „ 







00010 „ 







00016 „ 







00020 „ 






00025 „ 


In accordance with the formulse : — 

Q = FV 

(in microcoulombs) (in microfarads and in volts) 

E = 6 PV« 

(in ergs) (in microfarads and in volts.) 

A sufficient approximation may be arrived at from the following data : 

Taking a fresh Leclanch^ cell (of which the E.M.F. = 1*47 volt) as the source 
of pressure, make the total resistance r + B = 14700 ohms, when 10, 100, 1000 
ohms in r will give at its two ends pressures of 0*001, 0*01, 0*1 volt. 

In order to preserve a constant value of the total resistance r + B when r is 
increased, the simplest plan is to arrange the two rheostats so that for each plug 
removed in r, an equivalent plug can be inserted in B ; resistance- is thus 
diminished in B by as much as it is increased in r, and the total value of r + B 
is kept constant. 

E.g,i to obtain a series of pressures from a Leclanch6 cell in decimal parts of 
a volt, we may arrange to unplug r and plug B as follows :— 





+ 1000 



+ 2000 



+ 3000 

14700 3000 


+ 4360 



+ 100 



+ 200 



+ 300 



With a fresh DanieU cell r + B should be made 11000 ohms. 



Before putting up the condenser circuit in connection with a nerve-muscl& 
it should he put up in connection with a galvanometer (or a capillary electro- 
meter), and the action of the Morse key verified in the cases 1, 2, and 3 (fig. 29). 
In case 3 the circuit is identical with that of fig. 29. 

•a c > 

Ckw»5cvu.Cac|L*(LX , 


Fig. 29. 



(18) Unipolar stimulation. — Lay the nerve across a single 
electrode connected by a single wire with the secondary coil. 

Carefully insulate the frog or nerve-muscle preparation on 
a dry glass plate, also the coil in the same way. If the in- 
sulation is perfect, no contraction occurs when the coil is set 
in action. But if the insulation be destroyed, contractions 
occur although only one pole is connected with the nerve. 

Note that unipolar contraction is most apt to occur at the 
break shock with the ordinary arrangement of the coil. This 
is one reason for using the Helmholtz modification ; also for 
using a key as a bridge when it is desired to cut off the 
secondary current from a nerve. 


(19) TTnpolaiiBable eleotrodee are constructed eis follows. A 
carefolly amalgamated' zinc rod dips into a saturated solution 
of zinc sulphate, which in turn communicates with & plug of 
china clay made up into a paste with normal saline; a glass 
tube shaped according to requirements and fixed in a suitable 
holder. Such an electrode has the following qualities : it is 
unpolarisable by weak cnrrents, it is not itself a source of 
electromotive force, it is of high resistance, it can be applied 
to living tissues without appreciably injuring them. A pair 
of unpolarisable electrodes should be tested before use by 
bringing their plugs into contact while they are connected 
with the galvanometer; they should then give little or no 
current. Another form of unpolarisable electrode is that 
of d'Arsonval ; it consistB of a silver rod coated with fused 
silver chloride dipping into a tube filled vnth normal saline. 

Fifl. 30.— Sevkbal Models of Usfolaeisabu; Eikctrodes. 

1 and 2, du BoiB-ReymoEd'a ; 3, Burdon- Sanderson's ; i, von FlBiaohl'B ; 
5, d'ArsoQval's. 

Id 1, 2, 3, and i the component parts are nine, zinc- sulphate, and saline clay 
ID 5 a silver rod coated with fused silver chloride dipping in normal ssJine con- 
tiiined in the tube from which a thread projects. 

' AmalgamalAng fluid for unpolarisable electrodes. Dissolve 3 c.o. of mercury 
in 50 c.c. HNO, + 150 c.o. HCl. Add 10 per cent. HCl. to make up 1000 c.c. 



(20) The capillary electrometer may be used instead of the 
galvanometer for the demonstration of muscle and nerve 
currents; it is more suitable than the galvanometer for tlie 
electrical variations of the frog's heart, and it is the only 
instrument by which the electrical variations of the human 
heart can be demonstrated. The galvanometer indicates 
electrical current, the electrometer indicates electrical pres- 
sure, being, in fact, an extremely delicate electrical manometer, 
by which minute differences of potential between any two 
points of muscle, nerve or other tissue can be exhibited. 

, The apparatus consists essentially in a glass tube drawn 
out at one end to a fine bore (20 to 30 fj) filled with clean 
mercury, and in air connection with a pressure apparatus. 
The capillary end dips into a tube containing 10 per cent, 
sulphuric acid, and is viewed through a microscope magnifying 
60 to 3(K) diameters or more.^ Two platinum wires establish 
connection with the mercury and the sulphuric acid respec- 
tively. By means of the pressure apparatus mercury is forced 
along the capillary (which tapers slightly towards its end) up 
to a certain point, according to the pressure used, and the 
meniscus is adjusted in the field of the microscope. The sur- 
face of the mercury meniscus is in a state of tension, which is 
very easily altered by variations of electrical pressure, sach 
alterations causing the mercury to advance or to recede in 
the capillary. AdLce or retreat of the mercury siguifies rise 
or fall of potential at its electrode. 

N.B. — In putting up the instrument for the first time be 
careful to use clean mercury and filling pipettes ; do not allow 
the mercury in the glass tube to come in contact with india- 
rubber tubing, nor with mercury from the pressure apparatus. 

In testing a new instrument see that the mercury moves 
freely (1) to slight variations of pressure, (2) to slight electrical 
variations caused by touching the electrodes, (3) to the electrical 
variations accompanying the action of your own heart. (Ex. 
61). If it responds to this third test, it is more than sufficiently 
sensitive for the exposed heart of a frog or manunal. 

When you have done with the instrument lower the pres- 
sure bulb nearly to, but not below zero, and close the short- 

> With the higher powers the definition of the edge of the menisous is much 
improved by using a drop of water between the tube and objective, thus oonverting 
the latter into an immersion lens. 



(1) Pressure appamtus and mioroBOope on the stand of which tha eapillajy 
tuba is fixed. 

(2) Capillary tube dipping into H,SO, In & surronnding tnbe, and in oonneo- 
tion with pressure apparatus (the meroui7 in the lower port of the surrounding 
tabe serves onlyto establish oonneotion with the platinum wire). 

(3) The capillary tnbe and colnma of mercury as seen in the field of the 
microscope, (Scale in i^gths mm.) 

circuiting key, to which the electrometer wires are attached. 
The two defects to which a capillary is moat liable are : (1) 
stickiness of the tube, causing the mercury to move in jerka 
instead of araoothly with variations of pressure, (2) blocking of 
the tube by (?) sulphate of mercury. A block may sometimes 
be got rid of by applying considerable pressure (two metres of 
mercury) ; but, in general, it saves time to reject a faulty tube 
at once and put up a new one. A tube in good working order 
may be so kept for months or years ; it should be kept short- 
circuited, and the sulphuric acid replenished from time to time 
so that the capillary is never dry. 


(21) Becording Apparatus. 

The recording apparatus in use in this laboratory are :— 

(1) A cylinder fitting either the hour or the minute axis of 
an American clock; speed 25 mm., and 300 mm. per hour. 
Used for e.g., fatigue of muscle, action of drugs on frog'a 
heart, temperature records on man, respiration records on 

(2) Cylinders driven by a water motor; ordinary speeda 
between 10 and 100 mm. per second. 

(3) The spring myograph. 

(4) The pendulum myograph. 

(5) The railway myograph. 

For all ordinary purposes (sphygmograms, cardiograms,, 
myograms, latent period, rate of nerve-impulse, reaction times, 
&c.), the cylinder is sufficient. For the higher speed phe-^ 
nomena (latent period, rate of nerve-impulse), the spring or 
pendulum myograph is more convenient ; the railway myo- 
graph consists essentially in a vertical smoked plate carried 
horizontally across the field of a lantern, and is used only for 

In the spring -myograph a smoked glass plate is fixed in a 
metal frame which is shot along wire guides by the release of 
a spring. The speed of movement can be varied by varying 
the strength of the spring, and it is indicated by means of a 
vibrating reed (100 per sec.) that is set in movement by the 
release of the spring. One (or two) trigger keys are set so 
as to be struck open by the carrier in its passage, and the 
instant of stimulation is marked in the usual way by bringing 
the carrier slowly up to each key and then marking the 
position of the recording lever. 

In the pendulum myograph a smoked glass is fixed in a 
frame at the end of a pendulum, which is allowed to swing from 
one clutch to another clutch, adjusted so that the pendulum, 
when released from th-e first, swings so as to be just caught by 
the second. The frame and plate sweep past the myographic 
and chronographic levers and strike open one or more trigger 
keys ; the levers are adjusted so as to come into Ught contact 
with the plate, and the instant or instants of stimulation are 
marked in the usual way. The speed of movement can be 
varied by varying the amplitude of swing with alteration of the 
position of the clutches ; but a convenient speed having once 
l^^en obtained, it is best to let well alone. 


With these two instruments the usual and convenient 
speeds are such that r^th sec. measures 5 to 10 millimeters. 

The ** railway myograph,'' consisting of a miniature truck 
slowly moved along rails, and carrying a smoked glass plate, is 
very convenient for the demonstration of experiments in which 
changes are gradually developed, e,g., fatigue, action of drugs 
on heart. The apparatus is arranged so that the smoked plate, 
against which the lever is writing, is slowly carried across the 
field of a lantern by which the magnified tracing is projected 
on a screen. 

The trigger key and peg fixed respectively to the clock, 
or cylinder or plate-carrier, are for the purpose of obtaining a 
break induction shock by the revolution of the cylinder at a 
definite point. The key is placed in the primary circuit, left 
open until the cylinder is at full speed, then closed so that the 
next time the peg comes round, the trigger is knocked over and 
the contact broken. It is used, 6.^., to measure the latent 
period or the rapidity of transmission of a nerve-impulse. The 
lever indicating muscular contraction begins to rise a small 
space {i.e.y time; after the point corresponding with the knock 
down of the trigger. To determine this correspondence on the 
stationary cylinder or plate bring the peg very slowly against 
the trigger, and mark the point on the cylinder by a touch on 
the lever ; having done this, do not disturb the lever before 
taking your observation, and verify the correspondence at its 

The principle upon which the use of these instruments is 
based will at once be realised by one or two simple experi- 
ments ; of these the easiest is a determination of the latent 
period — 

(a) By a break induction shock applied to an isolated 
gastrocnemius muscle of the frog. 

(6) By make of a constant current to muscles of the hiunan 

(c) By break of a constant current to muscles of the human 

In a, 6 and c, the latent periods should come out re- 
spectively at about 0*01, 0*02. and 0*05 sec, but, except in the 
last case, the latent period is more apparent than real. 

* A slip of flexible metaJ (e.g., a piece of watoh spring), fixed to the cylinder 
80 as to strike against a pin at each revolution, will answer the same purpose as 
the more complicated trigger key. 


(22) The rate of movement of a smrface upon which a record 
is or hae been taken, ib ascertained by means of some form of 
time-marker or chronograph. 


CompoBsd of battery, vibrating reed (Page's), signal (Pfeil'a). 

For slowly travelling surfaces, e.g., a cylinder revolving 
once in twelve hoars, or once in one hour, or once in oue 
minute, it will be sufficient to arrange a lever against the 
smoked surface, and to make a mark with it by hand at each 
hoar, or at each minute, or at each second. The circumference 
of the cylinders in ordinary use is 300 to 600 millimeters ; 
therefore at once per twelve hours, 25 to 50 mm. represent 
one hour; at once per hour 5 to 10 mm. represent one minute; 
at once per minute 5 to 10 mm. represent one second. 

In most experiments on muscle and nerve, time has to 
be measured in small fractions of a second — hundredths or 
thousandths, and the recording surface is used at higher speeds 
— 50 to 1000 mm. per second. 

A tuning-fork vibrating 100 times per second carrying a 
style that marks the vibrations against the smoked suriiace is 
the simplest instrument by which to obtain a time record of 
hundredths of a second. 

For convenience' sake it is more usual to employ some form 
of electrical chronograph. Its essential components are : a 
battery, a vibrating reed and a marker. These three portiooB 
of apparatus are set up in a single circuit, the reed being 


arranged so as to give a succession to interruptions by vibrat- 
ing in and out of a mercury pool in the circuit. The makes 
and breaks of current thus produced act as makes and breaks 
of two electro-magnets A and B ; A keeps up the vibrations 
of the reed, B gives corresponding vibrations of the recording 

Take chronograms. 

(a) With a 100 tuning fork. Arrange the fork close to 
but not touching the cylinder ; start the clock, and when the 
cylinder is at full speed, set the fork in vibration by a smart 
blow, and make its vibrating style come into contact with the 
revolving surface. Stop the cylinder. The fork has vibrated 
100 times per sec. ; with a slowly revolving surface you will be 
unable to distinguish the vibrations. With speeds at or above 
50 mm. per sec. they will be visible as separate teeth — 2 per 
mm. at 50 mm. per sec, 1 per mm. at a speed of 100 mm. per 
sec, 1 per 2*5 mm. at a speed of 250 mm. per sec By this 
means you ascertain the time values of distances traversed 
by the revolving cylinder. 

(6) With an electrical chronograph. Set up the chrono- 
graph as per diagram. See that the reed-points and mercury 
surface are clean. By raising or lowering the mercury cup 
and the two electro-magnets A and B by the two milled 
head screws (a) and (6), find such an adjustment of parts 
that the reed shall continue vibrating automatically when once 
its vibrations are started by a twinge or tap. 

Take as neatly as you can for future reference the following 
series of chronograms : 

20 per sec reed on fast, medium and slow rates. 
50 per sec. reed on fast and medium rates. 
100 per sec. reed on fast and medium rates. 
100 tuning-fork on fast and medium rates. 

Finally, put up a Marey tympanum and closed india rubber 
tube connected with it, and mark seconds on the three rates 
by pressing the tube in time with the ticking of a watch. 


(23) Fboto-aalvanometric and Photo-Eleetrometric Records. 

The value of galvanometric and electrometric indications is 
greatly increased when they are photographically recorded. 
Thia can be done by very simple apparatus, of which the 
essential part is a sensitive plate moved by clockwork. For 
most galvanometer experiments it will be found convenient to 
use "ordinary photographic quarter-plates" let down behind a 
screen with a horizontal slit, about 0'6 mm. broad, at a speed 
of 10 to 20 cm, per hoar, by means of a wheel fixed to the 
minute axis of an American clock ; the spot of light being 
formed by an ordinary paraf&n lamp at a distance of about 50 
cm. from the galvanometer, and focussed upon the slit by a 
lens of about + 5 D. 

For most electrometer experiments, a more sensitive plate 
and a greater speed of movement, i.e., 1 to 10 cm. per sec, will 
be found suitable. 

The recording apparatus must be used in a dark chamber — 
which may be a simple box, or preferably a dark room. The 
photographic plates are developed and fixed by any of the usual 
methods; in this laboratory the " hydroquinone developer" is 
usually employed. 




Galvanometer Eecohds. — The vertical apot of light from 
the lamp ib reflected to cross the horizontal slit S M in the 
front of a dark box, within which a sensitive plate is let down 
vertically by clock-work. The spot of light deflected to right 
and left between S and N yields a black line on the developed 
plate, and thus records the movements of the galvanometric 
magnet and mirror. 


Fio. 35. — Simultaaeous record of (M) ooutractioDs of musole and (N) electrieaj 
irve, taken by the apparatuB of Fig. 34. 


To obtain a simultajieous record of, e.g., the negative varia- 
tion of nerve and the contraction of the supplied muscle, half 
the slit (and plate) left obscured is used for the record of the 
galvanometer spot, and the other half, illuminated by a candle, 
is used for the record of the muscular contraction, by means of 
the lever and small screen, as shown in fig. 34. 

Electrometer Eecobds. — The image of the vertical 
column of mercury is made to cover the lower portion of a 
narrow vertical slit in a screen behind which a sensitive plate 
travels horizontally, drawn by a falling weight, and restrained 

Fic. 36. — Becobdiho Elecirometeb. 

by clockwork. Light passes through the upper portion of the 
vertical slit, and blackens the upper portion of the developed 
plate ; the lower portion of the slit is screened from hght by 
the mercury, so that the lower portion of the developed plate 
comes out white or grey, rising and falling with rise and fall of 
the column. The rate of movement of the plate is recorded 
by the horizontal shadow of a chronograph lever (not repre- 
sented in the figure) across the upper part of the vertical slit ; 
on the' developed plate the time-record comes out white on 
black. In a similar manner, i.e., by means of a horizontal 
lever moved by a muscle or by a heart, a record of mechanical 
movement (white on black) may be taken above that of elec- 
trical change. 



Fio. 87.— PBoa'a Heabt. Diphasic Vabiatiou. 
Simultaneom phatograjn of a single beat (black line) and of the M:compaiiy' 
ing Qlectrioal ohauge, indioated b; the level of the black area, which shows the 
varying level of mercury in a capillary eleotromeler. The base of the ventricle 
U oonnectod with the mercury. I. First phase, base negative to apex. II. 
Second phase, apex negative to base, {N.B. — The figure, as printed, is a 
poBitive of the original negative, i^e., black here represents white, and vice versa. 



(24) To Pith a Frog; Deeerebration. 


Insert one blade of a strong pair of scissors into the mouth 
as far back as it will go, and cat o£f the top of the head. The 
brain (hemispheres and optic lobes) will thus be removed, or 
ut least exposed at the first scissor cut; in any case, all 
sensibility is at once abolished by "shock." Thoroughly 
destroy the brain, bulb, and cord by means of a stout wire 
pushed several times down the spinal canal. The frog is now 
thoroughly " pithed," and should remain permanently flaccid 
and motionless ; any movements of the limbs signify that the 
spinal cord has not been thoroughly destroyed. 

For certain experiments it is necessary to only decerebrate 
the frog — i.«., to destroy only the hemispheres or the hemi- 
spheres and optic lobes. In this case, the scissor cut must 
not be made quite so far back, and the brain carefully 

In some experiments, again, it is desirable to decerebrate 
the frog with as little haemorrhage as possible. In this case 
the occipito-atlantoid space should be felt for by the finger nail 

with the frog's head bent forward, opened 
with the point of a scalpel, and a small 
piece of wood (a sharpened match) forced 
through the opening into the cranial cavity 
so as to destroy the brain. The complete 
destruction of the brain is best assured by 
raking out the cranial cavity with a stout wire. 

. ^Hemispheres 

^Optic Lobes 

Fig. 38. 


(25) To Prepare a Muscle or a Nerve-Musole for Experiment* 

Proceed in the following order : — ^Pith a frog ; expose the 
tendon of the gastrocnemius muscle and tie a thread or fine 
wire round it; expose the sciatic nerve, tearing aside the 
muscles and keeping them open by pins ; cut through the 
ileo-coccygeus and remove the urostyle; cut through the spinal 
column and use the bit to handle the nerve by; raise the 
nerve and set it free ; clear the lower end of the femur, pass a 
pin through the joint, or cut the femur if you are about to use 
a muscle clamp ; cut through the tibia below the joint. 

Put up the muscle or the nerve-muscle according to what 
you want to do. For elasticity, single and double contraction,, 
tetanus, you do not need the nerve, and should use direct 



(26; Action of Curare. 

Draw out one or two capillary pipettes in the blow-pipe 
flame, break the ends and fill a pipette with 1 per cent, solution 
of curare. 

Decerebrate a frog with as little hemorrhage as possible ; 
push one end of the filled pipette beneath the skin of the back 
and inject the curare solution by blowing into the other end. 

(a) When the frog li^s flaccid and motionless expose the 
gastrocnemius muscle and the sciatic nerve; cut the nerve 
and test the muscle and nerve successively. If the curarisation 
is complete you will get contraction by excitation of muscle, 
no contraction by excitation of nerve. 

(6) To prove that curare acts at the periphery, the experi- 
ment may be repeated on a frog with one limb protected from 
the curare by a ligature tied round the thigh, with the excep- 
tion of the nerve,^ before the injection of the drug. On the 
protected side both nerve and muscle respond to excitation, 
when on the unprotected side only the muscle responds and 
not the nerve. 

(c) To prove that curare has no distinct action on afferent 
nerves or on nerve-centres, proceed as follows : a drop of dilute 
strychnia solution (1 in 1,000) is applied to the skin, and when 
absorbed will enhance the excitability of the spinal cord. One 
limb is protected and curare injected as before. A pinch (i.^., 
a sensificatory stimulus) of the unprotected motionless limb 
will cause reflex contraction of the protected limb. 

By (a) you have learned that after curarisation muscle 
remains excitable when the excitation of its nerve fails to set it 
in movement ; by (6) you have learned that the action of 
curare is peripheral ; by (c) you have learned that curare 
does not appreciably affect sensificatory nerve-ends, afferent 
fibres, nerve-centres, or efferent fibres. From which you con- 
<5lude that curare paralyses the junction between efferent fibres 
and muscle, i.e., the motor end-plates. 

^.J3. — Obviously if frogs are scarce, the whole series of 
data can be obtained from a single frog by experiment (c), 
omitting (a) and (6). 

* By a thick ligature moderately tight round the intact limb the circulatioa 
^an be arrested, if desired, without interruption of nerve-conduction. 


(27) Action of Veratrine. 

Proceed as before (Ex. 26) by using a 1 per cent, solution 
of veratrine. 

On the slowest axis of the cylinder take a record of a normal 
twitch, and of the twitch of a veratrinised muscle. Make a 
time tracing (in seconds) below the latter curve. Write a de- 
scription of the alteration. 

(28) Take a tracing of a single contraction of frog's gastroc- 
nemius on the cylinder or on the swing, or on the shooter. 
Mark the latent period. Do not forget to put in a time tracing 
(100 fork or reed). Take note of the temperature of the room 
at the time of the experiment, it will probably be between 12° 
and 18°. 

Take a similiar tracing with the mascle put up in the hot 
and cold air chamber. 

(6) With raised temperature. 

(c) With lowered temperature. 

Sufl&ciently well-marked effects will be produced by using 
for the former a heated poker held not too near the muscle, and 
for the latter a lump of ice. 



(29) Superposition of two contractions. — Use either the 
pendulum or the spring myograph with two coils and two 
keys. Connections as follows : — 

Fig. 39. 

Set the keys and myograph lever so that the record will 
come well on the plate. Adjust the coils to give a stimulus of 
suitable strength. 

Take a single contraction with K^ only, then with K2 only, 
then with K^ and Kg. 

(30) Composition of Tetanus. 

Arrange a spring to interrupt the primary circuit more or 
less frequently by vibrating in and out of a mercury pool, 
according to diagram. The spring is to be held firmly in a 
clamp, and the vibrating portion taken long or short, according 
as less or more frequent interruptions are desired. Take a 
muscle record (a), with the spring as long as possible (6), with the 
spring moderately long (c), with the spring short, viz., to give 
less or more frequent interruptions. Observe that with lower 
frequency tetanus is incomplete {= clonus), and at higher fre- 
quency complete. 



F . 40. 


(31) Fatigue (and Recovery). — Put up a frog's gastrocnemius 
in connection with a lever to record its movements, against a 
smoked cylinder. 

(1) First take a record of a series of contractions on a slow 
cylinder, stimulating the muscle by break induction shocks at 
1 sec. intervals, by means of a spring key in the primary cir- 
cuits, rhythming yourself by aid of the clock sounds, and having 
found a strength of stim. such that the break gives maximal 
effects, the make nothing. Take two such records with the 
two gastrocnemii, one with the ordinary (isotonic) lever, and 
an after-load of ten grammes, the other with the spring 
(isometric) lever. Observe in each case the gradual decline 
of the record, i.e., muscular fatigue. Keep on stimulating 
until the muscle is quite or nearly exhausted, then pause 
for two minutes and begin again. Observe that the muscle 
has recovered power. 

(2) With a fresh gastrocnemius take a record of a series of 
contractions (by either isotonic or isometric method) on a 
rapid cylinder (250 mm. per sec), using a trigger-key or other 
contact fixed to the clock in the primary circuit (p. 37). Each 
revolution takes about 1*5 sec. Keep on stimulating thus 
until the muscle is nearly exhausted, then stop the cylinder. 


A. — 0/ Voluntary Muscular Efforts. 

With the dynamograph and bIow clock take series ot 
maximum voluntary grasps of the hand at some regular 
rhythm, timing yourself by the clock tick. Make the volun- 
tary efforts in some such rhythm as the following : — Each 
contraction lasting 2 sec. ; interval between each two con- 
tractions, 2 eec. ; a group of 30 
such contractions will therefore 
take 2 minutes. Take two or 
more such groups of 30 maximal 
efforts, interposing between each 
two groups a period of rest of 
say 1 min. Be as attentive as 
possible to make the voluntary 
efforts as regular and as great 
as possible, and do not look at 
the tracing until the series is 
finished. If bo inclined, you 
may further examine the effects 
of variations of rhythm upon 
the rate of fatigue. 

Fig. 42.— Dyhauoqbaph. 

Fia. 13.— Bthuioobafh Becobd, 


B. — Of Electrically Excited Muscular Contractions. 

With the hghter dynamograph and slow clock take seriea 
of muscular tetani of the muscles of the forearm, put into 
contraction at some regular rhythm by direct excitation,, 
placing one electrode from the induction coil on the muscles, 
of the forearm, the other on any convenient part of the body 
{e,g,, the calf of the leg). 

If so inclined, you may test the effect of voluntary muscular 
action upon the muscle itself, by taking series of electrically 
excited contractions before and after a series of voluntary 
muscular contractions. 


(32) Extensibility of Muscle. — Isolate the gastrocnemius 
muscle of a pithed frog : tie a strong thread securely to the 
tendon, divide the femur, and fix the lower end firmly in a 
clamp. Tie the end of the thread from the tendon to a light, 
long lever, and to the same thread attach a light scale-pan to 
receive a succession of weights (pennies, which weigh about 
10 grammes each, are convenient for the purpose of the experi- 

Make the point of the lever touch a smoked cylinder or plate, 
which is to be moved on by hand by an equal space as each 
equal increment of weight has been made. Carefully place in 
the scale-pan 1, 2, 3, &c., pennies, and move the recording 
surface as just directed. Observe that fche successive incre- 
ments of length of muscle, caused by successive equal incre- 
ments of extending weight, form a diminishing series, forming 
a curve convex towards the abscissa. Eemove the weights one 
by one, and observe the converse series of elastic shortenings 
of the progressively unloaded muscle. Repeat a similar experi- 
ment with a rather strong piece of elastic substituted for the 
muscle, and observe that successive equal increments of weight 
produce successive equal increments of length. 


(33) Electrotonic Alterations of Excitability. (Frog.) 

Apparatus, — Battery, cell and coil, wires, rheochord, 2 
unpolarisable electrodes, moist chamber, myograph, 2 keys> 

First prepare the unpolarisable electrodes and arrange 
them close to a pair of ordinary electrodes in the moist 
chamber, ready for the nerve to be laid upon them, and so 
that the ordinary electrodes shall be nearer to the muscle. 
Connect the unpolarisable electrodes with the battery, for the 
"polarising current"; and the ordinary electrodes with the 
coil for the testing current. Place an interrupting key and a 
commutator in the polarising circuit, and mark what direction 
the current has in the nerve according as the cradle is turned 
right or left. Arrange a key in the testing current for single 

Then make a nerve-muscle preparation (Ex. 25); lay the 
nerve across the electrodes, and attach the tendon of the 
muscle to the lever of the myograph. 

{A) Find a distance of secondary &om primary coil such 
that a break induction shock just fails to cause contraction. 

Now let the polarising current pass through the nerve in 
the descending direction, i.e., so that the pole near the testing 
electrodes is its kathode, and observe that the previously 
ineffectual stimulus now causes a contraction, proving that 
the excitability is increased near the kathode. 

(B) Find a distance of secondary from primary coil such 
that a break induction shock is rather more than sufficient to 
give a contraction. 

I/et the polarising current pass in an ascending direction 
so that the pole near the testing electrodes in itn nnode, and 


observe that the previoasly effectual Btimalus is now ineffec- 
tual, proving that the excitability ia diminished in the neigh- 
bourhood of the anode. 

(G) Arrange the coil for tetanising currents, and repeat 
experiments A and B with this test, finding just ineffectual 
stimuli rendered effectual near a polarising kathode, i.e., giving 
a tetanus, and effectual stimnli rendered ineffectual neEir a 
polarising anode, i.e., giving a remission of tetanus. 


(2) Remove the rheochord, bringing the battery wires 
•straight to the commutator, but keeping the key in. 

Test as before, and observe with this stronger current that 
a contraction occurs at make and at break of the ascending and 
of the descending current. 

(3) Use a stronger electromotive force, i.e., more cells. 
Test as before, and find such a strength of current that con- 
traction shall occur at break of the ascending and at make of 
the descending current, but no contraction at make of the 
ascending nor at break of the descending current. 

You have now verified Pfliiger's law of contractions : — 

Make. Break. 

Hake. Break. 

I. — Weak current 

II. — Medium current . . 

III.— Strong current . . 


.. - 

From the previous exercise you have learned that excitability 
is increased at and near the kathode, diminished at and near 
the anode during the passage of a current. Taking this into 
account, together with the facts (1) that the immediate after- 
effect of a current is diminished excitability at and near the 
kathode, increased excitability at and near the anode, and (2) 
that the kathodic increase is more eflicacious than the after 
anodic increase, you may understand the meaning of the 
results you have obtained. Considering the position of kathode 
and anode in the nerve rather than actual direction of current, 
you see (1) that CO. CO. illustrates the greater efficacy of the 
kathode as compared with the after anode ; (2) that C.C.C.C 
illustrates the efficacy of both kathode and after-anode in that 
O.C illustrates blocking of a kathodic (make) stimulus by an 
anodic diminution lower down the nerve, and CO. blocking of 
an after-anodic (break) stimulus by an after-kathodic diminu- 
tion lower down the nerve. 



(35) Law of Contractions. (Man.) 

Apply one electrode of a galvanic battery (of say thirty^ 
Leclanche cells) to any indifferent part of the body. Use the: 
other as a testing electrode, applying it as close as possible to- 
some superficial nerve such as the ulnar or median at the 
elbow, or the peroneal at the head of the fibula. Test on such 
nerve the effect as regards muscular contraction of make and 
of break of the kathode and anode, gradually increasing the- 
number of cells in use by means of the collecting dial on the 

Observe (1) that the first effect is obtained with kathodic 
closure ; (2) that the next to appear is the anodic closure, or 
the anodic opening contraction ; and (3) that (unless an exces- 
sively strong current is used) kathodic opening produces na 
effect. Note in each case the smallest number of cells with 
which an effect is visible, or preferably put into the circuit the 
galvanoscope mentioned on p. 6, and note in each case the 
smallest deflection with which an effect is visible. [N.B. — 
The graduation of the galvanoscope is supposed to indicate: 



(36) Electrotonic Alterations of Excitability. (Man) .—(A) Tested 

by Break Induction Shocks. 

Put up a circuit in accordance with the accompanying 
diagram, so that an exciting current from the secondary coil of 
a du Bois' apparatus can be applied in the absence or in 
the presence of a polarising current from a galvanic battery (of 
say 30 Leclanche cells). In the latter case, i.6., when the 
exciting current is superposed upon a polarising current, their 
coincidence is secured, inasmuch as both currents enter or leave 
the body by the same electrodes. Apply the testing electrode 
to the median nerve at the bend of the elbow, or to the peroneal 
nerve at the head of the fibula. The commutators, as shown 

Trim.: S^ 

Fig. 46. 

The commutators C, C, with cross wires serve to reverse the direction of 
current from the battery and from the coil independently of each other. The 
commutator O, without cross wires, but with a junctional vnre as shown in 
diagram, is used for cutting out the battery without short-circuiting it, and 
without breaking the secondary circuit. (N.B. — The cradles of the three com- 
mutators are omitted for the sake of distinction.) 

in diagram, enable you to make the testing electrode either 
kathode or anode of the make or break induction current, with 
or without either kathode or anode of the galvanic polarising 
current. Leaving out of account the make induction current 
by cutting it out, or by taking such a distance of coil that 
has no effect) you may now proceed to compare the effects of — 



(1) The coil Kathode with and without the battery Kathode. 

(2) „ Anode „ „ „ Anode. 

(3) „ Kathode ,, „ „ Anode. 

(4) „ Anode „ „ „ Kathode. 

You will find that in cases (1) and (2) the effect of the 
excitation is increased daring polarisation, in cases (3) and 
(4) diminished during polarisation. The increase in (1) and the 
diminution in (3) (being effected in the polar region) are 
respectively more considerable than the increase in (2) and the 
diminution in (4) (being effected in the peripolar region). In 
case (4) you may notice that the make induction shock 
becomes effective during polarisation, unless means have been 
taken to cut it out. (J. ET. P., pp. 364, 372; Phil. Trans. 
B. S.y 1882, p, 961.) 

(B) Tested by Make and Break of a Constant Current. 

Put up a circuit in accordance with the accompanying 
diagram, so that an exciting current from the testing battery, 
T.b., can be made and broken in the absence or in the presence 
of a polarising current from a second battery, P.b. Both 
currents have, as before, the same electrodes to and from the 
body; the testing electrode may be applied to the median or 
to the peroneal nerve. The switches, C^, Cg, C3, serve the 
same purpose as in the previous exercise. Recording apparatus 
as there described. 

Fig. 47. 


The keys, K^, Kg* ^® introduced in order to allow the test- 
ing current from T.b. to be made and broken without affecting 
the circuit of the polarising current from P.b., K^ being used 
as a short-circuiting key that breaks the test current when 
closed, a»nd makes it, when opened ; Kg being used as a guard 
key to save the battery from remaining short-circuited when K, 
is closed ; to this end E« must be opened directly after K^^ 
is closed, for a test break ; K, must be closed directly before K^ 
is opened, for a test make. 

The comparisons that are to be made with this disposition 
of apparatus are the effects of — 

(1) K.C.C. alone and K.C.C. upon a Kathodic current. 

(2) A.C.C. alone and A.C.C. upon an Axiodic current. 

(3) A.O.C. alone and A.O.C. from an Anodic current. 

(1) K.C.C. alone and K.C.C. during Kathodic polarisation. 

(2) A.C.C. alone and A.C.C. during Anodic polarisation. 

(3) A.O.C. alone and during Anodic polarisation. 

Observe that — 

(1) K.C.C. is increased during Kathodic polarisation. 

(2) A.C.C. is increased during Anodic polarisation. 

(3) The increase of K.C.C. in (1) is greater than the 
increase of A.C.C. in (2) ; i.e., in (1) the increase is effected in 
the polar region, in (2) it is effected in the peripolar region. 

(4) A.O.C. is diminished during Anodic polarisation; in 
this case the diminution is effected in the peripolar region. 

With regard to the strengths of current to be used for test- 
ing and for polarising, no numerical directions are given ; the 
most suitable numbers of cells to be used in each case are to be 
ascertained by trial. If a galvanometer is used (and properly it 
should be) it is to be placed on the course of the wire joining 
the reversers, C^, Cg. 

(C) Tested by Mechanical Excitation, 

This is the simplest and most unobjectionable mode of 
demonstrating kathodic augmentation and anodic diminution of 
excitability. It is best made on the ulnar nerve ; the apparatus 
required being a battery, a reverser, electrodes, and a mallet. 
As before, the object aimed at is coincidence of test excitation,, 
and of polarisation in a nerve. 


A.pplying the testing-electrode against the uhiar nerve, find, 
by tapping it with the mallet, a force of blow sufficient to make 
the fingers twitch slightly. While taps are being applied 
at regular intervals, giving regular finger twitches, make a 
polarising current, kathodic, through the test-electrode, and 
observe that the twitches are strengthened ; then make a 
polarising current, anodic, through the test-electrode, and 
observe that the twitches are weakened or abolished. The 
augmentation and diminution are effected in the polar region of 
the current passing through the nerve. 


<37) Measurement of the Velocity of Transmission of Nerve- 
Impulses in the Motor Nerves of Man. 

Use the pendulum myograph, or a spring-myograph. Pre- 
3)are also (1) a small, thick-walled india-rubber bag, connected 
by tubing with a Marey's tympanum ; (2) a cell, induction coil, 
and electrodes (one large flat electrode, and one small electrode, 
-fixed to a handle) ; (3) a tuning-fork (100 per sec.) 

Put up the circuit as follows : primary circuit to include a 
fixed ** snap ** key, which is struck open by the plate-carrier of 
the myograph ; secondary circuit in connection with yourself, 
by strapping the flat electrode to one leg, and using the small 
electrode to excite the brachial nerves. Assure yourself that 
the contact at the snap key is not loose when the key is closed. 

Hold the india-rubber bag between the middle finger and 
thumb of the left hand, and taking the small electrode in the 
right hand, press it against the nerves (A), above the left 
clavicle (B), at the bend of the forearm. Find the best points 
of application by trial stimuli (these should be made by an 
assistant, by a simple key in the primary circuit.) 

All being ready (i.e., plate ready to let off, electrodes 
applied, primary circuit closed, india-rubber ball in hand, lever 
of tympanum just touching the recording surface) the plate is 
let off. In its passage the plate-carrier strikes open the key, 
giving a break induction shock, by which the nerves at A are 
excited, the flexor muscles pinch the bag, and cause a sharp 
rise of the tympanum-lever. 

A second observation is taken with the small electrode 
applied at B, great care being taken in re-setting the plate- 
•carrier not to disturb the position of the tympanum. 

It will be found that the contraction caused by distal excita- 
tion (at A) commences to rise from the base-line a little earlier 
than that caused by proximal excitation (at B). For measur- 
ing purposes a pair of contractions should be selected which 
are as equal as possible. 

The time-value of the interval between the two rises ia 
ascertained by the tuning-fork. 

The velocity of impulse is calculated firom this time- value, 
and from the length of nerve between A and B. It will be 
found to be about 50 metres per second. 


(38) Influence of Temperature upon the Excitability of H erve» 
Dem. Tested (a) by indnction currentd; (b) by make of the 
constant current. (Gotch.) 

Preliminaries. — Arrange two beakers, tubing and clips, to 
deliver a flow of hot, or of cold water through a thin glass tube 
across which the nerve is to be laid. 

Prepare a cell and rheochord to obtain a weak constant 
current by a small fraction of a volt. Wire rheostats, as 
shown in fig. 16, had better not be used, on account of the 
possibility of induction ; a short zinc rheostat, as figured below, 
is preferable. 

Put up the induction apparatus, using a spring key E^ 
in the primary circuit, and a short-circuiting key Kg in the 
secondary circuit. 

Connect the coil and the rheochord respectively with the 
two sides of a commutator without cross-wires, and lead off 
the exciting (unpolarisable) electrodes from the two middle 
pools (or in place of the commutator use two short-circuiting 
keys, connected as in fig. 7); make the connections so as to 
have current descending in the nerve. 

Put up the nerve-muscle preparation, laying the nerve across 
the water-tube (and upon short, rather stiff cords), moistened 
with saline, projecting from the clay ends of the exciting elec- 
trodes. Let the water-tube be as close as possible to the 
electrode nearest the muscle. 

Experiments. — Find the minimum stimulus to : 

(a) A descending induced cur- 

Do. Do. 

(&) Make of descending con- 
stant current 

Do. Do. 

with warm water passing 
through the tube. 

with cold water. 

with warm water. 

with cold water. 

or, having found a moderately effective strength of stimulation 
at ordinary room-temperature (about IS''), make stimuli at 
regular intervals (conveniently so by a metronome) and test the 
effect of warming and cooling upon : — 

(a) the effects of induction shocks ; 

(b) the effects of make of the constant current. 



The general tenour of your results will be : — 

(a) Augmented and diminished excitability of the nerve 
tested by induction shocks at high and low temperatures 

(b) Augmented and diminished excitability of the nerve 
tested by make of a constant current, at low and high tempera- 
tures respectively. 

(N.B. — The electrical conductivity of nerve, and therefore 
the strength of exciting current, increase and diminish with 
rising and falling temperature ; this disturbing influence may 
be diminished by placing large resistance of 100,000 ohms in 
the exciting circuit. Drying of the nerve and of the electrodes 
augment the resistance. Strictly speaking, the current-strength 
should be observed by a galvanometer, but in an ordinary 
demonstration this precaution must be neglected.) 


Fig. 48. 


KXE.jb^izxM.i Msnp ^mx- 

V»e d'Araonval's galvanomexer to wiiness the extra-polar 
currents prr^dnced by the current of a Danieu led into Her- 
mann's modeL 

Fig. 49. 

01m» tube with short rertical branches, filled with satuiated solokion of zinc 
«ialph*te, PUtinnm wire in centre stretched between two corks. Amalgamated 
;$inc wiroH inserted in branches, bent so as to dip into fluid, but not touch central 
wire, one pair for leading in polarising current, one pair for leading off the extra- 
polar current. 

Observe : — 

(1) Direction of extra-polar current. 

(2) Direction with reversal of polarising current. 

(3) Htrength of extra-polar current near and far from 
polarising current. 

(4) Modifications of extra-polar current with various 
Htronglhs of polarising current. 

The results are similar to those obtained on nerve, but are 
not HUpproBsod by anesthetics. 



(40) The Paradoxical Contraction. 

Dissect out one of the two main divisions of the 
sciatic, and divide it as far as possible from its 
origin. Galvanic excitation of the central end of 
the divided branch gives rise to contraction of 
the muscles supplied by the other branch. The 
second nerve is stimulated by the electrotonic 
alteration of the first nerve. Apply the ligature 
test for current dififusion. 

Fig. 60. 

Fig. 61. — Galvani's 
Experiment with 

(41) Galvani's Experiment. 

Connect tvsro dissimilar wires, e,g.f zinc 
and copper, and apply their points to a 
nerve, or one point to a nerve, the other to 
any part of the frog ; contraction occurs at 
each application (make cui^^rent), or if the 
preparation is very excitable, at each appli- 
cation and removal (make and break cur- 
rents) . 

(42) The Contraction without Metals. 

Prepare a nerve-muscle preparation, choosing a vigorous 
and lively frog. Allow the nerve to fall on the muscles of the 
lower limb stripped of its skin. The muscle of the preparation 
contracts because different parts of the surface with which 
the nerve is suddenly brought into contact are at different 

Fig. 52. — Galvani's Experiment without Metals . 


(43) Current of Injury of Muscle. {A) Its Measurement. (B) Its 

'^Negative Variation." Dem. 

Set up the galvanometer, shunt, lamp, and scale ; see that 
the suspended system of magnets swings freely; adjust it 
by means of the controlling magnet until the spot of light, 
when at rest, is at the middle of the scale. 

Put up the circuit containing : Dahiell cell, low resistance 
rheostat r, high resistance rheostat E, galvanometer G, shunt 
s (and muscle), as per diagram — 


FiQ. 63. 

Arrange a cell and coil for tetanisation (fig. 40) ; assure 
yourself that current passes through the exciting electrodes. 

Prepare unpolarisable electrodes for leading off. Expose 
and isolate a gastrocnemius muscle; tie one thread to the 
tendon and another to the femur, fixing the two threads to 
two large pins, between which the muscle is slightly stretched 
on, but not touching, a sheet of cork. 

(A) Bring the leading off electrodes into contact with the 
tendon and the belly of the muscle ; close Kg to see whether 
in this comparatively ** uninjured *' state there is any deflection 
of the spot of light, i.e., any muscle-current. Determine its 
direction, and, if need be, take only a fraction of it by using 
the shunt. 


Compensate this current. Take E =1,000 ohms., and find 
the value of r at which, with the Daniell current against the 
muscle current, the spot of light is brought back to zero, i.e., 
the two opposed currents balance. Calculate the value of 
the muscle current. The latter is equal to the following 
fraction of a Daniell, viz : ~-r. If, e.g., the muscle current 
is balanced withr = 50, its value in terms of a Daniell = xi^. 

Now injure the belly of the muscle by a scissor cut, re- 
moving and then replacing the leading ofif electrode. Observe 
direction and magnitude of current as before. Compensate 
and calculate as above directed. 

(JB) Make a nerve-muscle preparation, bring the leading off 
electrodes into contact with the muscle as before; lay the 
nerve across the exciting electrodes in connection with the 
coil. Compensate. 

Now tetanise the muscle by sending induction currents 
through the exciting electrodes ; observe the deflection of the 
spot of light ; this is in an opposite direction to that of th^ 
current of injury, i.e., a negative variation. 

^.jB. — To be sure that the deflection is really by the 
muscle, and not a fallacy due to coil magnetism, see that the 
starting the coil alone does not produce it. In any case, use 
long wires, placing the coil several yards distant from the 


(44) Nerve-currents ; the Carrent of. Injury and its Negative 

Variation. Dem. 

Same apparatus and preparations as for the analogous 
experiments on muscle. Connections as in fig. 53, an excised 
sciatic nerve enclosed in a moist chamber (fig. 48) taking the 
place of the muscle. 

Having assured yourself that all parts of the apparatus are 
in working order, isolate and excise a frog's sciatic, and lay it 
upon the exciting and leading-oflf electrodes ; let the cut end 
of the nerve rest upon one of the latter. 

Close the galvanometer key ; observe the deflection, and 
trace the current from longitudinal to transverse section 
through the galvanometer, viz., transverse section or injured 
part negative to longitudinal surface. 

Measure this current of injury by compensation, as in the 
case of muscle. 

Now tetanise the nerve for five to ten seconds by sending 
induction currents through the exciting electrodes. Observe 
the deflection, which is opposed to that caused by the current 
of injury, i.e., a negative variation. 

Bepeat the tetanisation with the direction of the exciting 
currents reversed, and observe that the negative variation is 
unchanged in direction. 

[N.B. — ^You may repeat this experiment an indefinite 
number of times without any diminution of the variation 
becoming apparent; you will be tired out before the nerve 
shows any signs of fatigue, provided you do not injure it by 
currents of excessive strength. The fallacies of current- 
escape and of electrotonic current have been met by the 
reversal of the exciting current ; that of unipolar excitation 
can be tested by detaching one of the wires from the secondary 
coil ; any magnetic effect of the coil has been tested for at the 


(45) Action of AnsBsthetics upon Isolated Nerve. Carbon Dioxide, 

Chloroform, and Ether. Dem. 

Tetanise the nerve during regular periods at regular 
intervals and observe that the negative deflections are of 
regular magnitude. To do this, time yourself by the seconds' 
hand of a watch, tetanising during say five or ten seconds at 
minute intervals.^ 

(a) Having assured yourself of the regularity of the de- 
flections, blow a little strong ether vapour into the nerve 
chamber, and continue to tetanise at minute intervals ; observe 
that the deflection is abolished. Clear out the ether vapour, 
and observe that the deflection returns. 

(6) Bepeat the experiment with strong chloroform vapour. 
The results are similar; the difference, if any, being to the 
effect that the abolition is more prompt, the return more 

(c) Send a stream of CO2 gas through the nerve chamber 
for two or three minutes, then blow it out. The deflection is 
diminished or abolished during the passage of CO2, and subse- 
quently greatly augmented. 

(dy e,f) If the three preceding experiments are. made with 
weaker reagents — with, e.g., a very slow stream of COj, or 
with one per cent, ether or one per cent, chloroform in the 
wash bottle, a primary stimulant instead of a primary de- 
pressant effect will be obtained, i.e., the deflection will be 
augmented while the nerve is under the influence of the 

[N.B. — Strong chloroform and ether vapour clear off very 
slowly, and should be used last if it is intended to show each 
of the six experiments above described. The best order then 
isd, 6,/, c, a, b.] 

' It is convenient, but not indispensable, to stimulate automatically. The 
Himplest means to this end is an ordinary clock with a platinum wire soldered to 
the seconds* wheel, arranged to complete a circuit once a minute for say seven 
and a half seconds by passing through a mercury pool. 


(46) The Secondary Contraction. — Pith a frog. Make two 
nerve-muscle preparations. Lay the nerve of II. across the 
muscle of I. Tetanise the nerve of I., and observe that the 
muscle of II., as well as that of I., enters into contraction. 

Test for current escape by crushing or ligaturing the nerve 
of II. If tetanisation of nerve I. still gives a contraction of 
muscle II., there has been current escape. A true secondary 
contraction (abolished by ligature) is due to excitation of nerve 
II. by a negative variation of the current of muscle I. 

Fig. 54. — The Sbcondaby Contbaction. 

(47) Secondary Contraction from the Heart. 

Excise the heart ; lay the nerve of a fresh nerve-muscle 

preparation upon it as per dia- 
gram. The muscle contracts 
at each beat of the heart, being 
excited by the electrical cur- 
^^' ^ • rent which accompanies each 


(48) An Apparent Anomaly due to Secondary Contraction. 
(Hering.) — ^After the foregoing experiments have been per- 
formed, the following simple and striking experiment by Hering 
may be undertaken without arousing misconception. 

A frog is pithed, and the urostyle removed, exposing on 
both sides the long nerve roots lying on the ileo-coccygeal 
muscle, and which form the sciatic nerve. These are to be 
cleanly divided by scissors on both sides, at or about the middle 
of their exposed length. The motor nerve roots above are now 
exposed, or a pair of stiff wire electrodes are pushed down the 
spinal canal so as to come in contact with them. 


On weak tetanisation of these roots the limbs are tetauised. 

The result is due to contraction of the coccygeal muscles 
(supplied by nerves arising above the point of division) which 
excites the peripheral ends of the divided sciatic roots. 

[Superficially regarded, the result appears as if division of 
nerve has not interfered with the conduction of impulses ; but 
equally obviously (1896) this is absurd.] 

(49) Secondary Excitation from Nerve to Nerve. (Hering.) — 
A frog is pithed, a sciatic nerve is exposed from hip to knee, 
ligatured at the knee, divided beyond the knee, and isolated 
from knee to hip. 

By means of the thread, the distal part of this central end 
is laid across electrodes and tested by weak tetanisation. A 
strength of current is thus found at which the muscles of the 
thigh are made to contract. 

This contraction is not augmented, but, on the contrary, 
disappears when the electrodes are slipped higher up the nerve, 
i.e., nearer to rest of the frog. Therefore the contraction is not 
due to current-escape. For the same reason it cannot be a 
** paradoxical contraction '* — an excitation of centrifugal nerve- 
fibres to thigh muscles by electrotonic currents aroused in ad- 
jacent nerve-fibres. Therefore, by exclusion, it is due to the 
excitation of nerve-fibres to the thigh by the action-currents of 
adjacent nerve-fibres, i.e., a true secondary excitation of nerve 
by nerve. 

[N.B. — This experiment goes best with ** cold frogs,*' i.e.> 
frogs kept in the cold — 0° to 2° — and left for a few hours before 
use at room temperature, about 15°. On beginning to test the 
distal end of the nerve, vary the direction of excitation by 
turning the electrodes one way or the other, and continue to 
test with the electrodes in the more favourable direction (which 
will be such that the kathode of the break shock is distal to the 

The "paradoxical contraction" itself is, in certain cases, 
attributable to action-currents ; in such case it diminishes as 
the electrodes are slipped upwards from the distal end ; when 
it increases with this changed situation of the electrodes, it is 
of electrotonic origin (or, it may be by reason of current- 


. (50) Electrical Variations of the Frog's Heart. 

Arrange the capillary electrometer under a low power of 
the microscope, and assure yourself that the mercury moves 
freely (Ex. 20). Connect a pair of silver electrodes with the 
two sides of its short-circuiting key. 

(1) Pith a frog and expose the heart. Bring the electrodes 
in contact with apex and base of the beating ventricle, using 
bits of moist wool tied to the ends of the electrodes, as the 
connecting links between electrodes and ventricle, so as to 
avoid shifting of contacts. Open the key, and, if necessary, 
readjust the pressure apparatus so as to bring the mercury 
into field. See whether the mercury pulsates with the pulsa- 
tion of the heart, and if it does, note the order and direction 
of its movements, and interpret their significance.^ 

(2) Arrest the heart by a Stannius' ligature. Excise it, and 
place it on a moist slip of wood. Bring the wool ends of the 
electrodes in contact with the apex and base of the ventricle. 
Observe the effect of a beat provoked by exciting the ventricle 
with a needle-touch (a) near the base, (6) near the apex. 

(3) Separate the ventricle from the rest of the heart by a 
«cissor cut through the auriculo-ventricular junction. Connect 
the electrodes with base and apex of ventricle, and note the 
effects on electrometer (a) of spontaneous beats, if such occur ; 
(ft) of beats provoked by a needle-touch, if the ventricle is not 
beating spontaneously. 

* With the heart in situ, the movements of the mercury are not always easy 
to interpret ; they may apparently be mono-, di-, tri-, or poly-phasic, according 
to various circumstances, and in consequence of auricle, or sinus, or bulb con- 
tributing to the main effect which is of the ventricle. 

With a stanniused heart, the effect of a beat excited by a needle touch is 

normally diphasic, being | ^ ^tj, ^?,* when excitation is applied to the base, 

I 2 2a!s« n«fll w^®^^ excitation is applied to the apex. But here again the 

variation may be complicated by an effect from the bulbus arteriosus. 

With a ventricle preparation, it will be noted, that the injured base becomes 
strongly negative, and that the main, or, it may be, the sole variation with each 
beat, whether spontaneous or provoked, is such as to indicate a'gex neg,- 



(51a) Electrical Variations of the Mammalian HeariL Dem. (Cat.) 

Decapitate a cat or kitten. Eapidly expose 
the heart, and connect it with the electrometer, 
as in the previous exercise. Note the variations 
that accompany the spontaneous beat of the 
heart in situ. 

Excise the heart, connect again with the 
electrometer, and note the variations (a) of the 
spontaneous beat, (b) of beats excited by needle- 
pricks applied to the base and to the apex. 

{61b) Electrical Variations of the Heart of an 
Uniigured Mammal. Dem. (Cat, Dog, or Horse.) 

Silver electrodes of the following shape, fixed 
by elastic garters to the limbs of a large dog or 
of a horse, serve as leads-off to a capillary 
electrometer. The mercury pulsates or does 
not pulsate, according as the electrodes are in 
** favourable" or in ** unfavourable'* combina- 
tion. The two anterior extremities or the two 
posterior extremities form an unfavourable com- 
bination, the two leads-off being then on the 
same side of the equator. An anterior and a 
posterior extremity form a favourable combina- 
tion, the two leads-off being then on opposite 
sides of the equator. Large animals are most 
suitable to this demonstration on account of 
their low pulse frequency. 

Qtiadruped (Gat). 
— Nearly trans- 
verse equator. The 
two anterior ex- 
tremities form 
therefore an ** un^ 
favourable " com- 


(52) Electiioal VariationB of the Human Heart. Dem. 

Plat electrodes, fixed by elastic garters, as in the previous 
experiment, may be used as leads-off. Or, in order to c^uickly 
contrast a favourable with an unfavourable combination, one 
electrode dips into a dish of salt solution, into which the 
fingers of the right or of the left hand ate plunged, while the 
other electrode is held in the mouth or fixed to the forehead. 
'■'Favourable" combinations, i.e., with the two electrodes on 
opposite sides of the equator, are : — 

Head and Left Ann. Left Arm and Biglit Arm. 

Head and Left Leg. Right Arm and Left Leg. 

Bead luid Right Leg. Right Arm and Right Leg. 

" Unfavourable " combinations, i.e., with the two electrodes 
on the same side of the equator, are : — 

Head and Bight Arm. Left Arm and Bight Leg. 

Left Arm and Left L^. Left Leg and Right Leg. 

Verify these several statements. 



(53) Retinal Currents. Dem. (Frog.) 

Make unpolarisable electrodes : one U shaped to receive the 
eyeball ; the other straight, with a thread projecting from it, 
to be brought into contact with it from above. Connect the 
electrodes with the galvanometer (and compensator, if you 
wish to measure the E.M.F.). 

Eemove the eyeball of a pithed frog with as httle injury as 
possible, using scissors to remove the surrounding skin and 
bone. Place it upon an unpolarisable electrode, with the 
cornea upwards, and bring the moist thread of the second 
electrode in contact with the cornea. 

Close the galvanometer circuit, and observe a deflection 
indicating current in that circuit from cornea to fundus, i.e., 
that the fundus is negative to the cornea. This is an ordinary 
injury current, owing to the divided optic nerve. 

Fio 68. 


Having brought the spot to mid-Bcale, either by the com- 
penBator or by the controlhng magnet, cover the electrodes 
with an opaque box, taking all care not to shift wires or shake 
the electrode stand. 

Observe a deflection in the same direction as the current of 
injury, i.e., a, positive variation. 

Kemove the box, observe again a positive variation- 
Leaving the box on or off lor a few minutes, observe that 
the spot occupies a more positive poeition during illumination, 
a less positive position during obscurity. 

N.B. — It will save ambiguity to adopt the following dis- 
position : — 

Cornea to south terminal of galvanometer. 

Nerve to north terminal of galvanometer. 

The current of injury will deflect the spot north, the varia- 
tions at the beginning and end of illumination will be north, 
and the position of the spot will be further north during 
illumination than during obscurity. 


(54) Sound is Produced during Muscular Contraction. 

(A) With Voluntary Contraction. — ^Place the junction of 
the hand and wrist against the ear, and alternately clench and 
relax the fist ; a low rumbling sound is heard throughout, 
which is much intensified during contraction. The less in- 
tense rumbling heard while the fist is relaxed is due to muscles 
by which the arm is raised to the ear. During the more 
intense rumbling heard while the fist is clenched, an overtone 
an octave above the rumbling sound may become audible. 

With an ordinary stethoscope auscultate the flexor muscles 
in the forearm of a second person, who alternately clenches and 
relaxes the fist. 

(B) With Contraction by Faradisation, — Arrange a battery, 
induction coil, and interrupter in one room, and connect the 
secondary coil by long wires with a Du Bois key in another 
room in which the vibrations of the interrupter are not 
audible. Use Page*s reeds as the interrupter, and tetanise the 
muscles of the forearm at frequencies of 20, 50, and 100 per 
second, auscultating as before. A note of corresponding pitch 
will be plainly audible. 

N.B, — You may compare this muscular note with that of 
the interrupter by means of a telephone introduced into the 
secondary circuit. 

(C) During Galvanotonus, — Use a strong galvanic current 
to tetanise the muscles, applying the exciting electrode over 
the median nerve at the bend of the elbow, and auscultate 
as before. The pitch of the muscle-sound heard during 
galvanotonus is identical with that of the sound heard with 
voluntary contraction. 

Note. — ^You may with reason doubt whether the pitch of 
the sounds heard in experiments A and C is due to muscular 
vibrations, and not simply a resonation tone of your own ear . 


(55) Heat is produced during Muscular Contraction. 

A. — With the Excised Muscles of a Frog. Dem. 

Apparatus and preparations, — Low resistance galvanometer. 
Two thermo-electric needles. Cell, coil, keys, and two pairs 
ordinary electrodes. Commutator without cross wires, arranged 
to turn the secondary current to one or other pair of electrodes. 
See that the apparatus is in good working order before pro- 
ceeding further. Note in what direction the spot of light 
moves when one or other of the two thermo-electric needles 
is touched. 

Pith the frog, expose and isolate both sciatic nerves, and 
both gastrocnemii ; insert each of the two needles longitudinally 
into each of the two muscles, and lay each of the two nerves 
across a pair of electrodes. Wait till the galvanometer spot is 

Now tetanise one of the muscles for, say one minute, and 
watch the spot for the next few minutes ; it should move in a 
direction indicating greater heat of the contracting muscle. 

After a short interval, turn the commutator so that the 
other nerve shall be excited when the key in the secondary cir- 
cuit is raised. Eepeat the excitation on that side and watch 
the spot, which should move in the opposite direction to its 
movement in the first experiment, indicating however, as 
before, greater heat of contracting muscle. 

N,B, — The galvanometer, and all other terminals, should 
be protected from draughts of air by wadding, to guard against 
accidental effects of temperature changes at adventitious 
junctions of dissimilar metals. 


B. — With th€ Normal Museles of a Man. Dem. 

Apparatus and preparatioTU. — Air thermometer or thermo- 
graph. Dynamograph. Cell, coil, and keys. 

The essential part of the apparatus is a hollow metal cap- 
sule, to be strapped to the muscles o£ the forearm or other part, 
in air-commnnication throngh a flexible tube with an indicator. 
Two forms of indicator may be used: — 


(1) For the purpose of demonstration, a small water-mano- 
meter in which the level of water can be watched directly, or 
projected on a screen, by placing the manometer in the magic 

(2) For the purpose of recording the variations, a piston- 
recorder, the lever of which is adjusted above that of the 
d3mamograph,on the same cylinder. 

Whichever form of indicator be adopted, it should be 
graduated in tenths of a degree, by immersing the capsule 
in a vessel of cooling water by the side of a mercury ther- 

When the apparatus is first applied to the skin it should be 
left in situ, with the side tap open until it is in temperature 
equilibrium. This is known by the lever or manometer re- 
maining stationary with the side tap closed. This occurs with 
less delay, i.e., in about say five min., if the capsule is warmed 
between the hands or kept in a pocket against the body before 

While an observation is in progress, the side-tap is kept 
shut, the object being to record variations of temperature, and 
not absolute values. These variations should not exceed 1'5°, 
if they do, the indicator should be zeroed, by opening the tap. 

Using the piston-recorder on the forearm, and the dynamo- 
graph, take a record of — 

(1) The effect of, say 30 grasps of 20 kilos, of 2 sec. duration, 
with 2 sec. intervals. 

{a) With normal circulation. 

(6) With the circulation arrested by an elastic bandage 
apphed tightjy round the arm. 

Notice the effectjin (a), i.e., that the temperature of the fore- 
arm is raised, and tUe much smaller effect in (6), i.e., that the rise 
is in greatest part que to an augmented circulation of blood. 

(2) Compare thd effect of 30 with that of 15 similar grasps 
of 20 kilos at 2"— 2r rhythm. 

(3) Compare th6 effect of 30 grasps of 20 kilos at 2"— 2" 
rhythm with that of 30 grasps of 10 kilos at the same rhythm. 

(4) Compare the effect of 30 voluntary grasps of 10 kilos at 
2" — 2" rhythm with that of 30 similar grasps provoked by 
faradisation of the muscles. Notice that the temperature 
effect is greater in the former case than in the latter. 


(56) Tendon-Reflex Time. (Man.) 

The subject of experiment is seated on a table, so that the 
leg hangs freely. An elastic bag, fixed by a strap round the 
middle of the thigh, serves as the explorer ; the explorer is 
connected by tubing with a Marey's tympanum, the lever of 
which marks against the smoked cylinder (speed of revolution 
about 250 mm. per sec). 

(a) Start the clock, and when the cylinder has reached its 
full speed, smartly tap the ligamentum patellae with the back 
of a thin book or a round ruler. Stop the clock, and examine 
the line ; if the ligament has been struck rightly, so that the 
muscles of the thigh have responded sharply, the line will 
present two elevations — (1) A small preliminary wavelet, which 
was caused by the mechanical jar of the blow on the ligament, 
and serves therefore to signal the moment of excitation ; (2) 
a more prolonged elevation, which was caused by the con- 
traction of the muscles of the thigh. Put a time-tracing of a 
100 per sec. tuning-fork under the best of your tracings, and 
take as the time of response the interval between the middle 
of the wavelet and the beginning of the main elevation. 

(6) This time should be compared with the lost time 
between excitation and contraction of the same muscles under 
the same conditions of observation, but with a single break 
induction shock as the stimulus. To this end put up an 
induction coil and electrodes, using one electrode as the in- 
different electrode (ex. 35). Arrange the trigger-key of the 
clock in the primary circuit. Find, by preliminary trial, a 
point of application of the testing electrode, and a distance of 
coil such that the muscles of the thigh contract sharply when 
the trigger-key is opened. Having done this, start the clock, 
and when the cylinder is at full speed close the key. After the 
key has been struck over, stop the clock, reclose the key, and 
find the time between excitation and contraction in the usual 
way (ex. 28). 

^.J5. — The time in this experiment may appear to be 
excessively long for a latent period by direct excitation. The 
length is due in part to lost time in the transmitting apparatus, 
in part to the inertia of the large muscular mass explored. 

>«l » . r. I 


The lost time in the transmitting apparatus can be deter- 
mined as follows: — The explorer is arranged on a firm base 
under a lever, the point of which is adjusted against the cylinder 
xmder the point of the tympanum lever. With the cylinder 
at full speed, the lower lever is tapped ; both levers record the 
movement, the tympanum lever beginning to move slightly 
after the explorer lever. The difference between the) initial 
points of the two elevations gives the lost time in the trans- 
mission of movement from explorer to recorder. To measure 
this difference at all accurately, these initial points should be 
measured from "corresponding points," i.e., pairs of points 
on the abscissae of the two levers marked by tapping the 
explorer lever with the cylinder stationary. 

(57) Tendon-Beflex Time. Dem. (Babbit.) 

A rabbit laid on its back in a shallow wooden trough, 
unrestrained by any ligature, will remain quiet for an in- 
definite time in an attitude that is convenient for the study of 
** tendon-reflex " and its comparison with other movements. 

(a) Connect the leg of a rabbit so disposed by a fine thread 
to a light lever touching the smoked cylinder. Start the 
clock, and when the cylinder is at full speed tap the lig. 
patellsB with the edge of a paper-knife. A record is obtained, 
on which the tap and the response can be identified, and the 
interval of time between them measured. 

(6) This time should be compared with the time of a true 
reflex action of the same muscles under the same conditions 
of observation. To this end it is sufficient to smartly tap the 
table or rabbit trough with a slip of wood, while the cylinder 
revolves past the recording lever. A rabbit in this state of 
slight hj^nosis gives at each tap a slight reflex start withotit 
otherwise agitating itself. The excitatory tap and the muscular 
response are easily identified on the tracing, and the interval 
of time between them measured as before. 

(c) (If desired, the lost time of direct excitation of the 
same muscles by a break induction shock may be taken, the 
electrical apparatus being arranged as in exp. 56 b). 


(58) Timotioii of Nerve-roots. (Miiller's experiment.) 

The spinal eolumn of a decerebrated frog is exposed by a 
median incision and cleared of the muscles on each side of the 
spinous processes ; the cord is then exposed by a pair of saw- 
cnts on each side, fine bone-forceps or stout scissors being 
used to complete the exposure of the nerve-roots. 

The three posterior roots of the 7th, 8th, and 9th nerves, 
lying upon the corresponding anterior roots, are now to be 
isolated by a fine seeker. A posterior root is ligatured and 
divided as far as possible from the cord ; electrical or mechani- 
cal excitation of its central end gives rise to general (reflex) 
movement. Another posterior root is ligatured and divided as 
near the cord as possible; excitation of its peripheral end pro- 
duces no effect. 

A similar pair of experiments is then made upon two of the 
underlying anterior roots. Excitation of a central end pro- 
duces no effect ; excitation of a peripheral end produces move- 
ment of the corresponding limb. 

With a little care, the demonstration may be made as 
follows :— The three posterior roots are divided on one side (say 
the left) ; on the other side the posterior roots are carefully 
turned aside and the three anterior roots divided. On touching 
the skin of the left leg with a drop of acid, nothing happens ; 
on touching the right leg with a drop of acid, general (reflex) 
movements are elicited, with the exception of that leg. The 
left leg is deprived of sensation, the right leg of motion. 


(59) Overlap of Distribution of Spinal Nerves in Skin and in 

Muscles. Dem. (Sherrington.) 

Exercise. — A frog, freshly killed ; the brain and the upper 
part of the spinal cord have been destroyed by " pithing." 

Bemov^ the coccyx with its surrounding tissues (by seizing 
the tip with forceps and somewhat lifting it, then cutting from 
behind, forward with strong scissors). By raising the lips of 
the opening thus made each sciatic plexus is brought in view. 
This plexus consists of the seventh, eighth and ninth spinal 
nerves joining to form the sciatic trunk. On one side cut 
through these nerves except the eighth, on the other except 
the ninth. 

Hang up the preparation by a thread so that it is free from 
contact with anything except the thread. 

With fine forceps pinch a toe of one foot. A movement is 
provoked ; this is *' reflex ; " it proves the persistence of an 
afferent channel between the toe and the spinal cord, although 
two nerves out of the three have been cut through. 

Pinch the corresponding toe of the opposite foot. A reflex 
again ensues, proving similarly existence of an afferent path 
from it to the cord. The spinal nerve uncut on one side is not 
the one left uncut on the other : either the distributions of 
the spinal nerves right and left are asymmetrical, or the 
stimulated toe receives sensory fibres from two segmental 
nerves. As the segmental nerves are symmetrically distributed, 
the latter alternative must be the explanation. 

Bepeat the observation on other toes and on the planta and 
dorsum of the feet, applying the stimuli to right and left 
alternately, and placing them as symmetrically as possible. It 
will be found that the skin of the foot contains sensory nerve- 
endings all over it from each of the two spinal nerves. 

Take the preparation down and pith it now completely. 
Fix the lower end of each tibia with a pin to the cork of the 
frog-board in such a way as to let the foot hang over the edge 
of the board. Slit up the skin over the pre-tibial and post- 
tibial muscles. Place the preparation in a good light so that 
any twitching of the post and pre-tibial muscles can be seen. 


Place a thick cotton thread round the nncut nerve, both 
right and left. Draw the ligature tight slowly whilst observing 
the exposed muscles. It will be found that all the muscles of 
the pre- and post-tibial groups twitch while the ligatures 
tightened^ both left and right. 

Each of the muscles of these groups is therefore supplied 
with motor nerve- fibres by each of the two roots excited. 

The contractions can, if desired, be studied, of course, 
^graphically by the myograph. 


(60) Reflex Actions of the BrainleBs Frog. (Qoltz.) 

 ' ' . . ' ' 

Expose the cranial cavity of a firog, by a scissor cuti.witibi 

difie blade in the month as far back as it will go, and the pther 

blade over the top of the heart. 

Remove the brain^ (hemispheres and optic ]obe8)| and 
observe that the frog placed at liberty assumes a normal 
attitude, springs when stimulated, resumes its normal attitude 
if turned over, avoids obstacles in springing. ' t 

Hang the frog up and touch the side of the skin with, a 
glass rod dipped in strong acid ; the frog raises the leg of tiie 
6am6 side and wipes the irritated spot, and if that leg be held 
it irepeats the manoeuvre with the other leg. All these highly 
€o-otdinated mov^nents are reflex movements effected by tlie 
bulboHspinal centres, and not, involving sensation. Open' the 
«bdomen and draw but a loop of intestine. Expose the hearty 
and while its movements are under observation, strike or 
pinch the intestine ; the heart is temporarily arrested (Golts'a 
*' Elopfversuch ")• If you divide the vagi or destroy the spinal 
m^ulla and repeat the stimulus, the arrest does not occiix« 

Or instead of the intestine you may employ strong stimolar 
tion of a limb by the sudden tightening of a string round it. 
The heart will stop, and the body of the frog will become 
inert and flaccid, and will not respond to cutaneous stimuli. 
The bulbo-spinal axis is in a state of " shock.'* > 

(Ql) Inhibitory Action of Superior upon Inferior Centres. (Frog.) 

Prepare a couple of beakers, one containing one per cent. 
H,804, ^^® other saline solution. 

Prepare a frog as before, removing only the hemispheres. 
Hang the frog up by the lower maxilla, and when it has come 
to rest raise the vessel of acid until the longest toe o£ one 
limb just touches the surface. Count the number of seconds 
elapsing between the stimulus and the retractation of the 
limb. Place a crystal of sodium chloride upon the exposed 
optic lobes, and measure the stimulus-to-reaction interval ala 
before. The interval is longer in the second than in the first 
instance, because the excitability of the spinal cord upon which 
the ceaction depends has been interfered with — " inhibited " — 
by atLB excitation of the optic lobes (Setschenow). 

' Yon ^nU probably h&ve xemoved the brain at the fizst Boissor cak 

IN THB FHrnoiiO^ir or «nn mnrroos snTsac. 89- 

(62) Time of Beflez Aeiion. (Frog.) 

The stimulas-to-reaiction intenral obtained by the above- 
deiacribed acid method (Tiirck's) is apt » true '' time of reflex 
iK^tion " ; the former is many seconds, the latter is only a 
ionali fraction of a second. 

To measure it you must employ recording apparatus, myo- 
^^raph, and electric signal, measuring the interval of time 
between the application of a single induction shock to the 
skin and the response of the gastrocnemius muscle. 

Use a decerebrated frog as above,, adjust electrodes from a 
aepcmdary coil to touch a toe, expose a gastrocnemius muscle, 
and connect its tendon with a bell-crank myograph, arrange a 
(^rqiiograph or a trigger-key in the, primaiy mrcuit. Tou may 
boieasure the reiiex on the same side as the stimulus, or on the 
opposite side (crossed reflex). 

(63) Action of Strydmine on Sirinal Oord. 

(a) Proceed as in experiment on curare, using a 1 per 
IkOOO solution of strychnia. Note the gradual incidence of the 
effeots, and write out a description of them. 

(b) Take a tracing (on the slow axis) of a strychnia con- 

(o) Measure the time of reflex action, using the muscle of 
one limb as your indicator, and stimulating the central end of 
tba other limb by a single shock through the trigger-key fik!i^ 
to the clock (p. 37). 

(d) Pass electrodes under the exposed, but undivided^ 
nerves of a frog before and after the intoxication by strychnia. 
Note in each case the minimum distance at which direct and 
reflex effects are obtained. ^ 

(64) Sammation. 

Take the same occasion to recognise the effeots of Qmn- 
mation of stimuli. Excite with single shocks, and with a 
secies of shocks, the central end of one nerve before and after 
akcycdininisation, and note the minimum distance at which 
reflex effects are observed in the opposite limb. (No need 
to use recording apparatus.) . . 

Demonstration. — Comparison of the reflex times of atrychni* 
niaed frog in limb excited opposite limb, and limb above ; by 
means of the double myograph. 


(65) Reflex Winking Time. (Man.) 

' Fix a fine thread to the eyelid and to the lever of A'bell 
crank myograph. 

From the secondary coil take a wire to a large electrode 
fixed to any convenient part of the body, and for the second 
electrode take a silver chloride silver wire covered with chamois 
leather and moistened with salt solution. 

Use the cylinder on the quickest axis, or else use a shooting 
myograph, placing the trigger-key in the primary circuit. 

Press the silver electrode against the conjunctiva of the 
lower Hd ; select by trial a suitable strength of shock ; see that 
the thread from the upper eyelid is kept taut, and that the 
trigger-key is shut ; let off the apparatus, and measure the 
interval between, the moment when the conjunctiva is stimu- 
lated and the moment when the upper eyelid moves, 

(66) Sensory Reaction-Timing. (Man.) 

Two persons co-operate in such experiments — (a) the 
examiner, (6) the examinee. 

The simple reaction-timer consists of a wooden lever resting 
across a closed india-rubber tube connected with a Marey's 
tympanum, marking against a smoked cylinder on the middle 
axis of the ordinary physiological clock. (Speed = something 
under 50 mm. per sec, but must be carefully measured hdske 

beginning). The butt-end of the lever is painted white to sei^e 
AS a visual stimulus. 

(a) Touch. — The examinee, blind-folded, rests a finger lightly 
on a lever of the ** timer." The examiner taps the finger. The 
examinee responds by pressing the lever down as soon as lie 
feels the tap. The instant of the tap, and that of the response, 
are thus marked on the revolving cylinder, and the interval 
between them gives the reaction time to a tactile stimulus^ e.g,, 
with the speed given above, an interval of 10 mm. indicates a 
reaction time of 20 hundredths of a second. 

(6) Hearing, — The examinee, blindfolded, holds the ha^d 
ready to press down the lever. The examiner strikes the 
lever so as to make a sharp sound, and signal it at the same 
instant. The examinee responds by pressing his lever down as 
soon as he hears the sound. The interval measured as before 
givQS the reaction-time to an auditory stimulus. (The exan^inee 


must be careful not to have his hand in contact with the lever 
when the sonnding^tap is made, as in this case there would be 
nothing to show whether the reaction is auditory or tactile.) 

(c) Sight — ^A screen through which the white end of the 
lever protrudes is placed so as to conceal the rest of the appa- 
ratu8» and the examiner &om the examinee, who watches the 
white end, with his hand ready to strike it as soon as he sees it 
move. Beaction-time determined as before. 

Take an average of 10 observations in each of the three 
preceding cases. 

(67) The Discrimination Time. 

A timer with a double lever is now used ; the end of one 
lever is painted white. Both levers rest across the same tube, 
so that the question and the answer signals are made by one 

(a) Totich. — The examinee places a finger of each hand on 
each lever, it being agreed that he is to react to a touch on one 
side, but not to a touch on the other. Sometimes one and 
sometimes the other finger is tapped by the examiner. 

Take the averages of the responses made in succession 
without mistake. 

(6) Hearing. — The sigpal is struck either with a bell or with 
a ruler. The examinee, blind-folded, has to answer only to one 
or other of these sounds. Take average as before. 

(c) Sight. — With a screen arranged as in ex. 66 c, the 
subject has to signal when he sees one of the levers move, 
but not when he sees the other. Average as before. 

The result in these three cases = the sensory reactioaEi- 
time + the discrimination-time ; the latter, is therefore 
roughly known by subtracting the results of ex. 66 from 
those of ex. 67. 

(68) The Volition or Choice-time. 

Bepeat the previous trio of observations with the double 
" timer," but with the understanding that the left hand is to 
be used to signal touch, sound, or sight connected with the 
left hand lever, and the right hand for the stimuli connected 
with the right hand lever. Take averages as before. 

The result = sensory reaction-time + discrimination- 
time + volition-time ; the latter is therefore roughly known 
by subtracting the results of 67 from those of 68. 



To avoid fine, this book should be returned on 
or before the date last stamped below. 

I'44 Wallr, A.D.