V. G. DETHIER 



EASto^ 



I 



Fig. 2. Integrated electrical response of chorda tympani to various 0.1 M salt 

 solutions flowed over tongue of rat: NH 4 C1, LiCl, NaCl, KC1, CaCl 2 , NaCl, RbCl, 

 CsCl, NaCl. Test solutions are interspaced with water rinses. Time scale: 1 large 

 division = 20 sec. (Redrawn from Beidler, 1953). 



cerned with few-fiber preparations or with total-fiber integrated response 

 (Fig. 2) (Beidler, 1953). Information derived from these approaches has revealed 

 facts of the following sort. 



There is general agreement insofar as the acid taste is concerned that an im- 

 portant constituent of the stimulus is the hydrogen ion. However, if this ion 

 were the sole factor, all acids would be expected to taste equally sour at the 

 same pH, and this is not so. Some workers feel that the discrepancy is to be 

 accounted for on the basis of interaction with saliva; others do not agree (Pfaff- 

 mann, 1951, Beidler, 1952). It is clear that there is no simple correlation with 

 pH, and, by analogy with the salts, it is not at all unlikely that the anion may 

 have a contributory effect. In the case of insects, where there exist acid receptors 

 unencumbered with saliva, there is again no simple correlation with pH (Chad- 

 wick and Dethier, 1947). Furthermore, as Beidler (1952) has pointed out, ex- 

 periments with buffered solutions, designed to isolate the effect of the hydrogen 

 ion, are confounded by the existence of receptors which are sensitive to salts as 

 well as to acid. 



Practically all salts are stimulating. Their stimulating efficiency in a variety 

 of animals has been expressed as series of values based upon threshold measure- 

 ments, saltiness of taste, etc. There are serial differences from one species of 

 animal to the next and differences depending upon the criterion of response 

 which is chosen. With regard to species differences, Beidler, Fishman, and Hard- 

 iman (1955) have reported the results of recording electrically the response of 

 the chorda tympani to chemical stimulation of the tongue of rats, guinea pigs, 

 rabbits, cats, dogs, hamsters, and racoons. Marked differences exist in the abil- 

 ity of the taste receptor-units (= a group of cells innervated by one 

 single chorda typani fiber) to respond to a number of substances. The rodents 

 respond well to NaCl compared to KC1, whereas the opposite is true with the 

 carnivores. Animals of both orders respond well to NH 4 C1. The hamster and 

 guinea pig are easily stimulated by sucrose, whereas the cat is not. 



For many species the cations can be arranged in increasing order of stimulat- 



