111 THE SENSE OF TASTE 149 



due to the- products of the chemical decomposition produced in 

 the tongue by the passage of the current. These divergent 

 opinions gave rise to two theories which for a century disputed 

 the effects of the electrical current on the organ of taste. 



Humboldt's explanation assumed a more definite form when 

 it became known that the passage of an electrical current through 

 a solution of alkaline salts (sucli as the buccal secretion) caused 

 its electrical decomposition, so that acid was liberated at the 

 anode and alkali at the kathode. This fact is sufficient of itself to 

 explain why, on passing a galvanic current through the part of the 

 tongue that is supplied with gustatory sensibility, there is an 

 acid taste on applying the anode (the kathode being placed on 

 the neck or some other part) ; when the kathode is applied to 

 the tongue there is, on the contrary, an alkaline taste. 



But this explanation is opposed by an ingenious experiment 

 ma,de by Volta and confirmed at a later date (1860) by Eosenthal. 

 If the tip of the tongue is dipped into a small tin vessel filled with 

 an alkaline solution, and held in the moist hands so as to pro- 

 duce a weak current, the acid taste is equally perceptible. If this 

 taste depended on electrolytic action it ought not to appear under 

 these conditions, because the acid would at once be neutralised by 

 the alkali in the vessel. 



Rosenthal adduced other experiments in support of Volta's 

 opinion. If two persons are in circuit by means of placing the 

 moist hand of one on the positive pole and of the other on the 

 negative pole of an electric battery, and the tips of their tongues 

 are brought into contact, the first will be aware of an acid taste, the 

 second of an alkaline. Both tongues are under identical conditions, 

 being separated only by a thin layer of buccal secretion, and the 

 sole difference is the direction of the current passing through 

 them. How then can there be an alkaline fluid on the one side 

 and an acid on the other at the point of contact of the two 

 tongues? Eosenthal also experimented on the stimulation of the 

 tongue by an electrode formed of red litmus paper, which became 

 blue on contact with the buccal fluid, before the passage of the 

 current. During the passage of the current when the paper 

 acted as anode, the subject perceived the characteristic acid taste, 

 but the paper did not turn red, showing that no perceptible 

 amount of acid was liberated at the anode. 



Hermann objected to the first two experiments that electrolytic 

 decomposition might take place in the depths of the lingual tissue 

 and not at its surface; for the third it was remarked by Valentin 

 that the taste-endings might lie more sensitive than litmus 

 paper. 



But there are other points in connection with the electrical 

 taste that claim attention. Bitter (1798) stated that on passing 

 an electrical current for a long time through the tongue, 



