ix ELECTRICAL EXCITATION OF NERVE 201 



of excitation, the difference in effect being occasioned by the 

 central or peripheral end-organ, the fact that the two directions 

 of current call out different sensations by their excitatory action 

 on the nerve, or its end-organs in the tongue, is contradictory. 



Whether we assume, e.g., that the ascending current excites the 

 acid-reacting fibres only, or mainly (which is highly improbable), 

 or that the action of the ascending current in each fibre differs 

 from that of the descending, the law of specific energy is 

 inevitably contravened if it is construed in the preceding sense. 

 On the other hand, there is little difficulty in bringing facts into 

 line with theory, to which indeed they appear the inevitable 

 corollary, if the effects of polar excitation of the taste-nerves are 

 viewed as parallel with the antagonistic polar action of the 

 electrical current in other excitable substances (muscle, nerve). 

 There is only one point in which the consequences of the 

 electrical excitation of centrifugal nerves and muscles differ from 

 those in sensory nerves, viz. that in the last case the end-organs 

 (central ganglion-cells) react by qualitatively different (antagon- 

 istic) sensations to the changes produced at the kathode, as well as 

 at the anode, whence it follows that centripetal nerve-fibres must 

 transmit the two opposite kinds of alterations. 



According to the view developed by Hering it may be 

 presumed that a sensory nerve gives rise to opposite sensations, 

 according as the dissimilatory or assimilatory process predominates 

 (Hermann, Pflugers Arch. xlix. p. 536). If we add that the 

 former is always developed persistently at the kathode, the 

 latter at the anode, the phenomena of electrical taste find a 

 simple explanation without prejudice to the law of specific energy. 

 Moreover, the phenomena consequent on the electrical stimulation 

 of other sense-organs will then be satisfactorily accounted for, since, 

 as Hermann pointed out (I.e. p. 537), there is no difficulty in 

 deriving opposite sensations from opposite directions of current. 

 In most cases the peripheral end-organs must be understood, since 

 these alone, as a rule, are perceptibly polarised under experimental 

 conditions. The ingoing current causes the assimilatory, the 

 outgoing current the dissimilatory change to preponderate ; but 

 it must always be assumed that the electropolar sensations 

 are mutually complementary, or (which amounts to the same 

 thing) stand in relation of contrast (Hermann, I.e.). 



This is even more plainly seen in the electrical excitation of 



