200 ELECTRO-PHYSIOLOGY CHAP. 



only capable of neutralising the alkali present, and not of 

 forming acid, so that there should be no acid after-taste at the 

 kathode which does, notwithstanding, make its appearance. 



If we attempt to determine the phenomena in question as 

 the consequences of direct polar excitation of nervous organs, we 

 meet with an initial difficulty in deciding which portion is 

 primarily excited by the current flowing in alternate directions. 

 Laserstein has contributed to the solution of the question in the 

 communication above quoted. It is known that cocaine has the 

 property of abolishing the excitability of most peripheral sensory 

 nerve-endings, the sense of taste not excepted. In Laserstein 

 himself this was not fully abolished by cocaine disappearing 

 first for bitter and sweet, then for salts, but not entirely for 

 acids, though enormously reduced for these also. A trace of 

 acid electrical taste remained with an ingoing current, but the 

 full strength of a Dan. was then required, whereas previous to 

 the application a current with 5000 ohms principal, and 210 

 deriving, resistance was sufficient. For Hermann, cocaine abolished 

 all taste, including the electrical. This experiment proves 

 essentially that the structures, upon alteration of which by 

 current depends the sensation of taste, are situated in the extreme 

 periphery. The strength of current that produces these sensations, 

 as compared with other physiological persistent effects of stimula- 

 tion, is so low that its density can only be adequate immediately 

 beneath the electrode. 



If the trunk of the nerve also were traversed, there would 

 each time be other sensations in the region of the cervical nerves. 

 Moreover, there can only be a question of orientated passage of 

 current through nerve-fibres or end-organs immediately under 

 the electrode, and it thus becomes intelligible that when 

 both electrodes are applied to the tongue there should be an 

 acid taste under the one, an alkaline taste under the other. 

 The electrical taste therefore depends exclusively upon passage of 

 current through the end-organs, or the ultimate nerve-endings 

 radiating in the mucosa. According to the law of specific energy, 

 by which each sensory nerve, wherever and however excited, 

 produces but one and the same specific sensation, the results 

 from electrical excitation of the tongue seem to coincide with and 

 witness to this principle. But if the law is strictly adhered to, 

 all nerve-fibres being regarded merely as indifferent conductors 



