460 W. J. CROZIER 



these substances have upon surface colloidal conditions, and 

 thus upon cell permeabiUty (Spaeth, '16). Herlitzka ('10) 

 has discussed this question with reference to the taste of salts, 

 but measurements of the effect of acid on permeability (Oster- 

 hout, '14) have not considered the possibiUty that characteristi- 

 cally different results may follow from the action of diverse 

 acids; Osterhout's ('14) measurements deal only with hydrochloric 

 acid. 



V. There remains to be accounted for the production of a 

 unitary taste quaUty, the sourness of acid solutions. This must 

 be related to ionizable hydrogen (Kahlenberg, '98, Richards, 

 '98). But it has just been shown that hydrogen ions outside 

 the cell surface cannot be the effective agents, since stimulation 

 by these acids parallels so closely the peculiarities of their pene- 

 tration of the cell. The hydrogen ion must therefore act after 

 the acid has united with the ceptor surface. At least two 

 possibilities are obvious: (1) the presence of potentially ionizable 

 hydrogen within sufficiently concentrated undissociated mole- 

 cules is enough to produce the sour taste, or (2) the acids ionize 

 secondarily after entering. The first suggestion is not so far 

 fetched as it may at first seem, though it is not in accord with 

 current teaching. Numerous parallels could be drawn from 

 the taste of organic substances (Francis and Fortescue-Brick- 

 dale, '08, pp. 331 et seq.). I believe that this view is possibly 

 correct, although something could also be said for the hypothesis 

 of secondary ionization following some reaction involved in 

 gaining admission to the outer layer of the cell. It is in this 

 latter direction that the explanation (Beutner, '14) must be 

 sought for the source of electromotive effects accompanying 

 stimulation in general, which presumably occur also in taste 

 excitation.' This interpretation disposes of the difficulty (very 

 conspicuous in the case of taste) which is encountered by those 

 who would make the process of stimulation and the production 

 of electromotive effects completely identical in every case. 



^ A taste cell bathed by a stimulating solution is in a condition very similar 

 indeed to that of the various tissues experimented upon by Loeb and Beutner 

 (Loeb. '15). 



