Page:Proceedings of the Royal Society of London Vol 69.djvu/186

172 made upon a freshly killed animal, affords a very convenient means of class-demonstration of the fundamental fact. The response is elicited by stimulation of the sciatic nerve after the latter has ceased to pro- voke muscular contraction, and can then be most conveniently demon- strated (and recorded) without resort to the curarisation and artificial respiration necessary in the case of the living animal. The method and its results will be made sufficiently apparent by the following experiments and figures :

Experiment 1. Electrical Response of the Skin to Indirect Excitation through the Sciatic Nerve.

Cat decapitated -Both sciatics exposed and cut Large pad of each hind foot led off to galvanometer by unpolarisable electrodes Tetanic excitation of peripheral end of one or other sciatic for 5 seconds at intervals of 5 minutes Berne coil at 1000 units supplied by two Leclanches.

Deflection + signifies that the skin of the right side is electro- positive, i.e., that it is traversed by an ingoing current (directed from left side to right through the galvanometer).

Remarks.

Muscles contract.

Do.

Do.

Do. faintly. No contraction.

Do.

Do.

Do.

Do.

The effect of excitation was thus in each instance an ingoing current of the skin of the excited side.

Experiment 2. Similar Experiment. Excitation of Right Sciatic at

Time after

Deflection by excitation of

Deflection by excitation of

decapitation.

left sciatic.

right sciatic.

Mins.

Volt.

15

-o-oioo

20

-0-0150

25

-0-0110

-

30

+ 0-0050

35 and 36

-o-oioo

+ 0-0160

40 and 41

-0-0060

+ 0-0100

45 and 46

-o-ooio

+ 0-0060

50 and 51

Nil

+ 0-0010

55 and 56

Nil

Nil

Time, mins.

20

30

40

50

60

70

Intervals of 10 minutes. Deflection. Remarks.

+ 0-0050 + 0-0045 + 0-0035 + 0-0020 + 0-0005 Nil

Faint contraction. No contraction.

Do.

Do.

Do.