TASTE FUNCTIONS IN FISH 



231 



several powerful sapid substances are interesting in connection with the 

 following two points : (1) resemblance in molecular structures between the 

 gustatory active lipid-like substances and the structural complex of the 

 receptor membrane (2) saliva stimulates sweet fibres and the specific re- 

 ceptors responding to saliva, both of which were easily impaired by the 



■■■■ 



Time imin.) 



Fig. 13. Effect of sodium cholatc (0.3 per cent) on the responses of the taste 

 nerve endings of the carp to the appHcation of various sapid solutions. Abscissa: 

 Time after administration of sodium cholate. Series of lower records showing 

 gradual shift in the response to the application of 0.5 m NaCl. Records from 

 left to right are taken before application of sodium cholate, T 30", 3' 30", 5', 

 6' 30" and 15' thereafter. 



treatment of sodium cholate which probably acts mainly on the Hpid layer 

 of the membrane. It is especially noteworthy as is shown in Fig. 13 that 

 there is a temporal enhancement of the responses to acid and salt before 

 the endings are paralysed. This was not observed in the response to sugar 

 and saliva. Strong resistance of the salt receptors to lytic agents was also 

 observed in the treatment by silver nitrate. Although we have no direct 

 evidence so far regarding the mechanism involved in this temporal enhance- 

 ment, it seems possible that the lytic agents may loosen the structural 

 complex of the receptor membrane resulting in a higher degree of excit- 

 ability. 



SUMMARY 



1. Chemoceptive fibres of the palatine nerves innervating the palatal 

 organ of carp were found to respond to a great variety of sapid solutions. 



