492 



COMPARATIVE ELECTRO-PHYSIOLOGY 



at the responding point E. 



of conductivity than of responsivity. In respect of conduc- 

 tivity and responsivity, therefore, the effects of these two 

 drugs, KI and Nal, are seen to be opposite. 



In order to observe the effect of alcohol on nervous tissue, 

 by means of the conductivity balance, I first experimented 

 on the nerve of frog. A 5 per cent, solution was applied 



This is seen (fig. 301) to induce 

 a depression of responsivity. 

 A more dilute solution generally 

 induces a preliminary exaltation 

 followed by depression. 



We said in the previous 

 chapter that when alcohol 

 vapour was passed into the 

 chamber of the vegetable nerve 

 the responses underwent a rapid 

 abolition. This result, however, 



FIG. 300. RESPONSIVITY versus 

 CONDUCTIVITY under Nal 



The formula in this case is E' Na iC N ai. 

 Photographic record shows an 

 effect opposite to that of KI as 

 previously described, there being 

 now a relatively greater de- 

 pression of conductivity than of 

 responsivity. 



FIG. 301. Effect of Alcohol on 

 the Responsivity of Frog's 

 Nerve 



Upsetting of the balance in the 

 downward direction shows 

 depression. 



was due to the joint action of the variations of receptivity, 

 conductivity, and responsivity, some of which may possibly 

 have been in the positive and others in the negative 

 direction. In order to determine the effect of each of these 

 we must, then, perform separate experiments. Such a deter- 

 mination I have made, using the method of the so-called 

 'negative variation,' in which the proximal galvanometric 



