ix ELECTRICAL EXCITATION OF NERVE 199 



identical conditions, except as to the direction of the current in 

 the tongue. This is opposite in the two subjects, so that they 

 have opposite sensations, although their tongues are in contact, 

 and the same capillary layer of fluid covers the one as well as 

 the other. Eosenthal, moreover, sent the current of 14 Dan. 

 through the body and tip of the tongue, both poles consisting of 

 zinc plates dipping into two vessels of zinc sulphate : these were 

 connected by siphon-shaped tubes with two other vessels, one 

 filled with saturated salt solution, the other with distilled water. 

 A pad of filter-paper, also soaked with distilled water, projected 

 from the latter. On dipping one hand into the saline and 

 touching the pad of filter-paper with the tip of the tongue, the 

 current either passed from tongue to pad, or vice versa as regulated 

 by a reverser in the circuit. A strip of red litmus-paper was 

 laid on the pad so that both were in contact with the tongue. 

 The red paper turned faintly blue when touched by the alkaline 

 fluid of the mouth blue remained unaltered. On closing the 

 current there was a distinct sensation of taste, but the colour 

 of the two papers remained unchanged with either direction of 

 the current " (v. Vintschgau, I.e.). 



Against the cogency of these experiments there is good 

 evidence to indicate that the electrical taste depends not upon 

 electrolysis of the fluids in the mouth, but upon direct excitation 

 of the taste-nerves. It must in the first place be remembered, 

 as pointed out by du Bois-Eeymoud, that polarisation occurs at 

 the interface of dissimilar electrolytes (Gfes. Abh. I. p. 1), so that 

 under given conditions there may be a separation into acids and 

 alkalies (Hermann, 48). There is no reason why the electrical 

 taste should not be derived from electrolytic processes within 

 the lingual tissues, the direction of current being indifferent. 

 From this point of view, Volta's experiment with a tin beaker 

 filled with lime (34, iii. 2, p. 185) loses all point; as also, 

 according to Hermann (I.e.), the second of Eosenthal's experiments, 

 as cited above. Neither, however, is the electrolytic theory 

 tenable, as appears from electrically exciting other sense-organs, 

 and also from the opposite after-sensations on breaking the 

 current when the tongue is stimulated. Hermann pointed to this 

 last difficulty (I.e. p. 538) when he remarked that an ingoing 

 depolarising current was discharged in the polarised organ at 

 the moment of breaking an outgoing current ; this current is 



