Page:Proceedings of the Royal Society of London Vol 69.djvu/189

Rh If after exact compensation of this normal current a single induction shock is sent through the pad, either in the ingoing or in the outgoing direction, the effect or, properly speaking, the after-effect is in nearly every instance outgoing, as in the case of the frog's skin. The few instances in which I have witnessed an ingoing response have been in the case of fresh skin, taken soon after decapitation, and tested by comparatively weak induction shocks. (I find in my laboratory notes only one instance of a late ingoing response 3 days after decapitation.) In such cases the ingoing response has been of comparatively low voltage, and has given place to an outgoing re- sponse at the end of a few hours. From review of a considerable number of observations I conclude that outgoing response is the rule, ingoing response the exception. I have kept the former under systematic observation up to 60 hours post-mortem, but have found under the conditions of observation that it may disappear at an earlier period from the skin of ill-nourished animals.

The physiological action of the skin is indicated : 1, by its invariable direction with both directions of excitation ; 2, by its complete aboli- tion after immersion of the skin in hot water.

A series of responses provoked at short intervals exhibits summa- tion. Tetanisation by alternating induction shocks in both pairs of directions, excites a larger response than that aroused by a single induction shock.

These several points will be made sufficiently clear by the following experiments and figures :

Experiment 4. Direct Excitation. Same Cat as that of Experiment 2.

Large pad cut off and set up between unpolar electrodes 9 hours after

decapitation. Compensation. Direct Excitation in + (outgoing) and

- (ingoing) directions. Berne Coil. 8 Leclanche's in primary circuit.

10,000 units.

Time.

Excitation.

Response.

After immersion in hot water.

9 hours

Tetan.{7}

+ -0056 volt.

T> J" m -+l

Do. <, > \br.- j

+ '0100

24 hours

Single break +

+ 0-0025

trace.

+ -0032

+ trace.


 * {;}

+ 0-0175

+ -0004

{.1}

+ 0-0242

- 0-0004