REVIEW OF RESPONSE OF ISOTROPIC ORGANS 699 



an unreliability of which we shall further meet with many 

 glaring instances. 



An assumption more or less current is, that in order to 

 obtain response, there must be an antecedent current, by 

 whose negative variation it can be detected. Hence the 

 supposed necessity of a current of injury prior to response. 

 The real reason, however, for thus injuring one of the 

 contacts is so to depress its excitability that, on diffuse 

 stimulation, the excitatory response of the uninjured may 

 remain unbalanced, and therefore unannulled. That it is 

 this depression of excitability, and not the current of injury 

 as such, which is the essential condition for obtaining 

 resultant response, is seen from the fact that excitatory 

 response may still be obtained, even when the so-called 

 current of injury is zero, or reversed positive (fig. 116). 



