346 



COMPARATIVE ELECTRO-PHYSIOLOGY 



external surface. After an intervening period of tetanisation, 

 however, the responses are seen to be reversed (fig. 212). 



The next record has been selected for the purpose of 

 showing the gradual process of transition from the normal 

 negative to the reversed positive response. The specimen 

 taken was frog's stomach. At the commencement of the 

 experiment the galvanometer spot was quiescent, but when 

 the specimen was subjected to a single strong thermal shock, 

 a prolonged series of multiple responses was initiated, per- 

 sisting for more than an hour. Of this series I here re- 

 produce four different 

 portions (fig. 213). The 

 first of these (a) con- 

 sists of pulses of gal- 

 vanometric negativity 

 of the internal surface. 

 The recoveries are here 

 incomplete, and the 

 base-line shifts upwards, 

 showing an increasing 

 negativity of that sur- 

 face. The negative 

 pulses are then reversed 

 to positive, through an 

 intermediate di-phasic 

 (). In the first part 

 of this pronouncedly 



positive response (c) the base line is horizontal. It then 

 begins to shift downwards (d\ thus exhibiting a decreasing 

 negativity or increasing positivity of the internal surface. 

 In this periodic variation of the electrical condition we have 

 a significant parallel to the records which we have already 

 seen in Nepenthe and in Drosera (figs. 203, 205, 208, and 209). 

 It has already been pointed out that, in view of the 

 functional peculiarities of the digestive organ, it might be ex- 

 pected that the alternate reactions of secretion and absorption 

 would neither of them be single and spasmodic, but each long- 



FIG. 212. Photographic Record of Normal 

 Response in Stomach of Gecko to Equi- 

 alternating Shocks, seen to be reversed after 

 Tetanisation 



