216 



ELECTRO-PHYSIOLOGY 



CHAP. 



travels up as well as downwards (Hermann, 34, p. 109). All 

 observations hitherto made on this point refer exclusively to 

 experiments with two electrical stimuli. The results of this 

 method, which have been variously diagnosed as summation, or 

 as interference effects, are by no means free from ambiguity. In 

 using electrical stimuli, i.e., we must take into consideration not 

 merely the combination of two independent processes of excitation, 



FIG. '200. Schema for simultaneous excitation of a nerve by induction shocks at different 

 points. (Werigo.) 



but also (owing to the nature of the electrical stimulus) alterations 

 in the conductivity of the nerve, which are unfavourable to the 

 integrity of the experiment. 



Griinhagen (58), in order to obtain the absolutely simultaneous 

 action of two or more distinct currents upon different points of 

 a nerve, devised the method of leading the current from a 

 sufficiently strong battery through two or more primary induction 

 coils, with as many corresponding secondary coils. Every closure 



