310 COMPARATIVE ELECTRO-PHYSIOLOGY 



The result which I have described namely, a greater 

 responsive negativity of the inner than of the outer, giving 

 rise to a resultant responsive current from inner to outer is 

 that which occurs in the majority of cases with tomato. 

 But, as establishing a continuity between this response and 

 that of grape-skin, I may mention the interesting fact that 

 in a few instances I obtained records in which, while the 

 inner surface on excitation exhibited a strong negativity, 

 the outer, under the same stimulus, exhibited a feeble 

 positivity. 



The normal response of skin is sometimes, however, 

 found to be reversed, and no explanations have yet been 



FIG. 190. Photographic Record of Series of Normal Responses 

 in Skin of Gecko 



Responsive current from inner to outer surface. 



offered to account for this. But I have shown two definite 

 conditions of universal application, which are liable to bring 

 about the reversal of normal response. These are, on the 

 one hand, sub-tonicity, and, on the other, fatigue. Should 

 the condition, in a given case, be the former of these, then 

 the impact of stimulus will of itself, by raising the tonic 

 condition, restore the normal response. Thus in a case of 

 abnormal positive response due to sub-tonicity, an inter- 

 vening period of tetanisation will tend to convert the ab- 

 normal response to normal. An abnormal positive will thus 

 pass into diphasic, and thence into the normal negative. 



