152 MASAYASU SATO 



linear relationship was observed between temperature of stimulating solu- 

 tions and change in surface temperature of the tongue. After flowing a 

 solution over the tongue a mean change of 5.4 C in the tongue temperature 

 was produced when there was a difference of IOC between temperature of 

 the solution and that of the tongue. 



For the stimulation we have employed sodium chloride, saccharine 

 sodium, hydrochloric acid, quinine hydrochloride and distilled water, 

 quinine and acid being dissolved in Ringer's solution. Temperature of 

 these solutions was changed from 5'C to 45 C, which resulted in lowering 

 of the tongue temperature to about 15 C and raising it to 40'C. Ringer's 

 solution was also employed for stimulating thermoreceptors only. 



As already shown by a number of investigators (Cohen, Hagiwara and 

 Zotterman, 1955 ; Appelberg, 1958), the tongue of cats hardly responds 

 to sweet substances. It was also found in our experiments that the threshold 

 for saccharine was 1/8 m and response to saccharine was nearly the same 

 as that to NaCl. It seemed that chemoreceptors of cats respond to sac- 

 charine as sodium salts. 



RESPONSE FROM THE WHOLE CHORDA TYMPANI 



An example of the integrated response from the whole chorda tympani 

 to Ringer's solution, NaCl and water of varying temperatures is shown in 

 Fig. 1. in general, the response attains its maximum within 1-2 sec and 

 decays thereafter. The time course of decay is slower when temperature 

 is lower. The maximum amplitude of the response was measured and 

 taken as the response magnitude. 



As shown in Fig. 1, no response was observed to Ringer's solution at 

 30°C, while warm or cold Ringer's solution produced a response. Similarly 

 the response to NaCl is small at 30 C, but it is increased with a rise or fall 

 of the temperature. This is more clearly shown in Fig. 2, in which magni- 

 tude of the response to various kinds of solutions is plotted against the 

 temperature of solutions. All the responses are minimal at 30 C and are 

 increased with a rise or fall of the temperature. 



The response to warm or cold Ringer's solution may result from the 

 response of thermoreceptors. In order to compare the response of the 

 chorda tympani to warming or cooling of the tongue with that of the 

 lingual nerve, which does not mediate taste information, we recorded the 

 response of the lingual nerve when the tongue was stimulated with solu- 

 tions of varying temperatures. It is easily seen in Fig. 3 that the lingual 

 nerve contains only fibres mediating cold, and it is clear from Fig. 2 that 

 the chorda tympani contains fibres mediating warm and cold sensations. 

 This finding is consistent with earlier findings by Zotterman (1954). 



Since it is supposed that the response of the chorda tympani to solutions 



