458 



ELECTRO-PHYSIOLOGY 



CHAP. 



shooting trigger successively opens three contacts. The first of 

 these (Fig. 280, SJ opens the circuit of the primary coil of a 

 sliding apparatus, the second, $ 2 , abolishes the shunt to the galvano- 

 meter, which can only then be affected by the current from the organ- 

 preparation; and, finally, the third, /S^, opens the galvanometer circuit 

 again, so that the effect in the galvanometer can only last for the 

 interval between the opening of S 2 and that of g . This interval, in 

 Gotch's first experiments, was 0'02 sec. If $ 2 is shifted close to $ 1} 

 so that the shunt to the galvanometer is opened almost simul- 

 taneously with the inducing circuit, the former will exhibit the 



Fio. 280. 



same intensity with both homodromous and heterodromous direc- 

 tion. This result can obviously be referred only to the fact that 

 the galvanometer circuit was closed in Gotch's experiments for a 

 very short time after the moment of stimulation, while in du 

 Bois-Eeymond's method, not merely the exciting current, but also 

 the whole after-current of the preparation, passes through the 

 galvanometer. In the first case, therefore, the homodromous 

 after-current (positive polarisation, in du Bois-Eeymond's sense) 

 can add nothing to the homodromous induction -shock which 

 produces it, since, according to Gotch, it is not developed for 

 0-05 sec. 



Gotch subsequently extended his operations (I.e.), making the 



