302 



COMPARATIVE ELECTRO-PHYSIOLOGY 



be subsequently reversed to positive once more. Such phasic 

 changes, moreover, may be repeated. They find visible 

 indications in appropriate shiftings of the base line of the 

 record. Similar effects are also shown in the differential 

 response as seen in the records given in fig. 182 ; this feature 



is very noticeable. We here ob- 

 tain the resultant response of the 

 two surfaces of grape-skin, from 

 the inner to the outer. As the 

 result of the series of stimuli 

 applied, the existing current of 



FlG. 182. Photographic Re- 

 cord of Electrical Responses 

 of Grape-skin to Stimula- 

 tion by Equi-alternating 

 Electrical Shocks at In- 

 tervals of a Minute 



Responsive current from inner 

 to outer. Note periodic 

 variation of resting-current, 

 causing shifting of base-line, 

 down and up. 



FIG. 183. Photographic Record of Series 

 of Electrical Responses of Frog's Skin to 

 Equi-alternating Electrical Shocks applied 

 at Intervals of One Minute 



Direction of responsive current from inner to 

 outer. Note also variation of base-line. 



rest undergoes a periodic variation. If this had remained 

 constant, the base-line would have been horizontal. In the 

 present case, the original current of rest was from outside 

 to inside. This, at first, underwent an increase ; then a 

 decrease ; to be followed, later, by another increase. Thus, 

 in the course of about ten minutes, it exhibited an alterna- 

 tion of almost one whole cycle. 



In the next figure (fig. 1 83) I give a series of results obtained 



