198 ELECTRO-PHYSIOLOGY CHAP. 



tion of the sensitive lingual rnucosa, and those exhibited by so 

 many other excitable substances the more so since the contrast 

 between closing and opening effects finds complete analogy in the 

 law of polar current action. 



Further details of electrical sensations of taste are subjoined 

 from the recent investigations of Laserstein (47). Just as there 

 are individual differences in the sense of taste, so there are individual 

 variations in sensibility to the current, varying in the same person 

 at different times, and in different individuals. As might be ex- 

 pected from the greater intensity of the anodic acid taste, the 

 liminal value for the ingoing (acid) current lies considerably 

 lower than that for the outgoing current. With non-polarisable 

 electrodes, the liminal value of current for the acid taste was 

 about T l^ milli-ampere. This very low figure is undoubtedly 

 due to the high specific excitability of the organ of taste towards 

 constant currents, in which respect it far exceeds all other sense- 

 organs. Oscillations of current produce no visible augmentation 

 of gustatory sensations. 



The electrical taste has been very differently interpreted. 

 One question is of primary importance : Do the sensations of taste 

 arise from the direct stimulation of the taste-nerves 'by the current, or 

 are they caused indirectly by electrolytic decomposition of the fluids 

 in the mouth ? We know that when an electrical current passes 

 through a fluid containing salts of alkalies instance the fluids of 

 the mouth which are moistened by the lingual mucosa the salts 

 are decomposed ; the acids coming off freely at the anode, the 

 alkalies (which are immediately oxidised) at the kathode. The 

 presence of free acids at the positive, of free alkalies at the 

 negative pole, would thus very simply account for the acid taste 

 at the latter. Against this explanation it may be urged that the 

 sensations of electrical taste are also present when the current 

 does not enter and leave by metallic electrodes (in which case 

 electrolysis is inevitable), but is led through the tongue by other 

 electrolytes, or by non-polarisable electrodes ; this experiment 

 has been tried by Monro, Volta, and, more recently, by 

 Eosenthal (47). 



" Eosenthal brought two persons into contact by the tip of 

 their tongue, the one holding the positive, the other the negative 

 pole of a battery, with moist hands : the first person has an alka- 

 line, the second an acid taste. Here the two persons are under 



