COMPARATIVE ELECTRO-PHYSIOLOGY 



degree between two negativities, is still from inner to 

 outer, owing to the greater excitatory reaction of the 

 inner. 



That the direction of the resultant response is actually 

 from the inner to the outer is seen in the series of records 

 given in fig. 188. The stimulus consisted of equi-alter- 

 nating electrical shocks, applied at intervals of one minute. 

 The record shows negative responses, followed appa- 

 rently by the positive after-effect. In order to observe the 

 peculiarities of this response in greater detail, the record 

 was taken on a faster-moving drum (fig. 189). From this 



figure it will be seen that 

 there was a short latent period 

 of no responsive reaction. 

 Response then rose to a 

 maximum, and again sub- 

 sided. After now reaching 

 the zero position, the record 

 proceeded in the positive 

 direction, and again reverted 

 back to zero. In similar 

 records, the occurrence of 

 this latent period, and posi- 

 tive after-variation, has been 

 adduced by certain physio- 

 logists as affording visible 

 demonstration of the exist- 

 ence of opposite processes of assimilation and dissimilation. 

 It has been supposed that the various features of the response 

 were the outcome of a sort of tug-of-war between the two 

 opposed forces, the preliminary pause being the expression 

 of a short-lived balance, while the subsequent negative and 

 positive variations were to be regarded as indicating the 

 predominance, now of the one process, and then of the other. 

 That in the present case such an assumption is unwarranted 

 will be evident when we observe the isolated responses of the 

 upper and lower surfaces separately (fig. 187). In each of 



FIG. 1 88. Photographic Record of 

 Series of Responses in Skin of 

 Tomato under Equi-alternating 

 Electrical Shocks applied at In- 

 tervals of One Minute 



Direction of resultant current from 

 inner to outer followed by feeble 

 opposite after-effect. 



