6o 



ANIMAL ELECTRICITY. LECTURE III. 



Bois-Reymond, and the hardly less typical after-effect 

 is the positive after - variation of Hering. The 

 electrical state of nerve after excitation is for a short 

 period the reverse of that obtaining during excitation ; 

 and if we call the latter " negative," v^e must call the 

 former ''positive." Here, for example, recorded by a 

 quite dead-beat galvanometer, is a typical series of 

 negative followed by positive after-effects, the former 



Fig. 22 (2177). 



undiminishing, the latter progressively diminishing. 

 That progressive diminution of the positive after-effect 

 will presently be clear to us as a characteristic change 

 produced by carbonic acid — but I anticipate. 



The positive after-effect presents itself more or less 

 obviously — more so as a rule in nerve that is becoming 

 a little stale, or that has been trifled with by previous 

 experiments. Sometimes the positive after-effect is so 

 pronounced as greatly to exceed the negative effect 

 that precedes it. As a matter of convenience I 

 distinguish such nerve as beint/ in the second stage, 



