RESPONSE OF ANIMAL AND VEGETAL SKINS 309 



these we see the normal response of galvanometric negativity, 

 followed by recovery, without evidence of any antagonistic 

 process, such as might give rise to subsequent positivity. 

 The difference between these two responses lies simply in 

 their time-relations. On simultaneous excitation of the two, 

 the predominant negativity of the inner gives the first half 

 of the negative response. The persistence of the excitatory 

 reaction of the outer, on the other hand, after the subsidence 

 of the effect on the inner, gives rise to the apparently 



FIG. 189. A Single Response of Skin of Tomato to Equi-alternating 

 Shock recorded on Faster Moving Drum 



positive after-effect. Thus, here the supposed tug-of-war 

 between two opposite processes of assimilation and dis- 

 similation is, in reality, between two normal responses 

 having different time-relations. It is from a failure to 

 recognise the fact that the excitatory reaction is not con- 

 fined to one, but takes place on both surfaces, that such 

 erroneous assumptions as that referred to have often been 

 occasioned. 



