RESPONSE OF ANIMAL AND VEGETAL SKINS 



303 



with frog's skin in direct response to equi- alternating shocks. 

 Here we find the usual * up ' responses, showing that, as 

 before, the direction of the responsive current is from within 

 to without ; and here also we see the existing current of rest 

 undergoing a periodic change. 



It has now been fully demonstrated that the response 

 of skin is determined by the differential excitabilities of its 

 two surfaces, upper and lower, that of the lower being the 

 greater. That the resultant responsive current from lower to 

 upper, is in such cases brought about by the greater excit- 

 ability of the lower, has been fully shown, in a previous 

 chapter, by experiments on 

 the pulvinus of Mimosa. 

 I next made records of a 

 long series of responses 

 given by the last-named 

 specimen, with the object 

 of finding out whether or 

 not these also exhibited a 

 periodic variation of the 

 resting-current similar to 

 those just observed in the 

 anisotropic skins of grape 

 and of frog. Electrical 

 connections were made 

 with diametrically opposite 

 points on the upper and 

 lower surfaces of this 



organ, and they were subjected to equi-alternating shocks. 

 Owing to the conducting power of the tissues, it was 

 not now the upper and lower skin surfaces merely, but 

 the upper and lower halves of the organ that became 

 excited. And the responsive current was from the lower 

 to the upper, as already demonstrated. In the particular 

 record seen in fig. 184, the general resemblance to the 

 responses of skin is sufficiently obvious. The interesting 

 feature of this record is the periodic changes in the resting'- 



FIG. 184. Photographic Record of Trans- 

 verse Response of Pulvinus of Mimosa 

 to Equi-alternating Electrical Shocks 



The direction of the responsive current is 

 from the more excitable lower to the 

 less excitable upper. Note the cyclic 

 variation of the current of rest. 



