RESPONSE OF ANIMAL AND VEGETAL SKINS 307 



excitable inner to the less excitable outer, even in those 

 cases where the normal direction of the resting-current had 

 been reversed, as an excitatory after-effect of preparation. 

 This fact is well illustrated in the following record, taken 

 with the skin of the neck of tortoise. As an after-effect of 

 preparation, the resting-current so called was here reversed, 

 flowing from inner to outer. But the excitatory responsive 

 current was nevertheless from the more excitable inner 

 to the less excitable outer (fig. 186). 



It was stated at the beginning of this chapter that the 

 resultant response from inner to outer merely expresses the 

 general fact that the 

 excitability of the inner 

 is greater than that of 

 the outer. And this will 

 still remain true, even 

 when the transformation 

 of the external layer is 

 not so great as actually 

 to reverse its individual 



FIG. 187. Isolated Responses of Upper and 



galvanometriC response Lower Surfaces of Skin of Tomato to Rotary 

 from negativity tO posi- Mechanical Stimulus 



Hvitv Thp evnpri (a) A ' ne g ative response of feeble intensity in 



' ll v* outer surface ; B, negative response of much 



mental results obtained greater intensity in inner surface ; (b) c, cur- 



. , , . . f rent of rest from outer to inner. Resultant 



Wltn trie Skin Ol ripe excitatory response from inner to outer, due 



tomato form a Case in to S reater induced galvanometric negativity 



of inner. 



point. 1 he natural 



current of rest is here, as usual, from the outer to the 

 inner, and the excitatory responsive current in the opposite 

 direction. But from the analysis of individual responses, 

 on the outer and inner surfaces, obtained by means of 

 the rotary apparatus for mechanical stimulation, it will be 

 seen (fig. 187) that both the surfaces alike give the 

 normal excitatory response of galvanometric negativity. 

 This responsive negativity of the inner, B, is, however, 

 very much greater than that of the outer. The resultant 

 response, then, representing as this does the difference in 



X 2 



