148 COMPARATIVE ELECTRO-PHYSIOLOGY 



allowed to return to the surrounding temperature of the room, 

 records of the response being taken meanwhile, at intervals 

 of one minute. It will be seen how, by means of the gradual 

 restoration of the original excitability of A, the resultant 

 response changes gradually from negative to zero, and then 

 again from zero back to positive, indicating the restoration 

 of the naturally greater excitability of A (fig. 103). 



We have thus studied two different methods, both of 

 which depend on interference, for the determination of the 

 variations of excitability induced by different external agents. 

 In a subsequent chapter we shall study a modification of this 

 method, by means of which it is possible to demonstrate the 

 variations not only of excitability but also of conductivity 

 under various reagents. 



