IX ELECTRICAL EXCITATION OF NERVE 197 



more with rhythmical excitation at uniform direction of current. 

 A positive interpretation of these data is hardly possible without 

 further investigation ; in any case, LangendorfFs assumption that 

 "simple galvanic variations of current, and the passage of 

 the current, are merely inhibitory, while oscillatory variations 

 are excitatory in action "- and that " the excitation which pro- 

 ceeds from the lower, distal electrode implies a tetanising 

 element " needs further corroboration. 



Great theoretical interest attaches to experiments on the 

 polar excitation of the higher sensory nerves by the constant current, 

 sensation here serving as the excitatory reagent. The earlier 

 electricians collected a fund of experimental data in this depart- 

 ment, although the interpretation of their facts is very dubious. 

 Those relating to the taste-sense are the most obvious. Here, as in 

 all other cases, it must be noted that excitation of the isolated 

 sensory nerve involved is not possible, the peripheral end-organ 

 (sensory epithelium] being under all circumstances excited with it. 



The first and weightiest conclusion from the older experiments 

 is as follows : When an electrical current is passed through the 

 tongue, an acid taste is perceived at the point where current 

 enters (anode), and a different taste, usually described as alkaline, 

 at the point where it leaves (kathode). Volta, however, described 

 the latter as being merely somewhat alkaline, sharp, and rough, 

 approaching to bitter. These two sensations, one of which 

 (kathodic) is always much weaker than the other (anodic), 

 continue as long as the current is passing, and are perceptibly 

 reversed (as observed by Eitter) when the circuit is opened. 

 Eosenthal (47) was unable to discover this, finding merely that 

 the acid taste continued for a short time after breaking the 

 current, while the alkaline trace quickly disappeared. At the 

 same time v. Vintschgau (47) confirmed the observations of 

 Ritter the predominant acid being converted into a faintly 

 metallic taste at the moment of opening the current, when the 

 kathode was applied to the root of the tongue. 



As early as 1793 Pfaff discovered the relation between the 

 difference in electrical taste according to the disposition of the 

 metals on the tongue, and the difference in contraction according to 

 their distribution in nerve and muscle ; and the possibility at once 

 presents itself of direct comparison between the qualitatively 

 different, and in a certain sense antagonistic, polar effects, on excita- 



