RESPONSE OF ANIMAL AND VEGETAL SKINS 



299 



were subjected to excitation. It was now found that the 

 responses of the inner surface were normal that is to say, of 

 galvanometric negativity. I give here (fig. 178, a) records 

 of two successive sets of responses obtained from the external 

 and internal points A and B. These records clearly demon- 

 strate that the resultant up-response, on simultaneous exci- 

 tation of the outer and inner surfaces, is brought about 

 by the induced galvanometric positivity of the outer added 

 to the induced negativity of the inner surface. As the resist- 

 ance of the circuit in the two successive experiments was 

 maintained approxi- 

 mately the same, the 

 amplitude of these re- 

 sponses gives a fairly 

 accurate idea of the 

 relative electrical effects 

 induced on the two sur- 

 faces. The positive or 

 ' outgoing ' effect of the 

 outer surface is here 

 slightly greater than the 

 ' ingoing ' effect. The 

 diagram in fig. 178, , 

 shows how the individual effects conspire to give rise to a 

 responsive current from the inner to the outer. 



In order to test the reality of the correspondence between 

 this response of the grape skin and that of the frog, I now 

 repeated these experiments, employing the same apparatus 

 for mechanical stimulation, on the skin of the frog. From 

 the records given in fig. 179 it will be seen that the isolated 

 response of the outer surface is positive, or * outgoing,' that 

 of the inner being negative, or ' ingoing.' The amplitude 

 of the former was, however, much greater than that of the 

 latter. These responses disappeared altogether when the 

 tissue had been killed by immersion in boiling water. From 

 isolated responses obtained by means of induction shocks, 

 Dr. Waller had been led to regard the outer surface of frog's 



FIG. 178. Electrical Response of Grape- 

 skin to Rotary Mechanical Stimulation 



(a) A, positive response of outer surface ; 

 B, negative response of inner surface ; 

 (b] c, current of rest, from outer to inner ; 

 R, excitatory response from inner to outer, 

 consisting of summated results of positive 

 response of outer with negative response 

 of inner. 



