230 JIHEI KONISHI AND YNGVE ZOTTERMAN 



to Funakoshi (1962), the active substance in saliva may be a macromole- 

 cular one which is non-dialzyable through Cellophane membranes. 



It is thus most probable that there may be more than two kinds of gusta- 

 tory active lipid-like substances in the sapid materials which strongly 

 stimulate fish chemoceptors. The view that one of the active substances 

 in the pupa belong to the glycerophospholipid group is fortified by the 

 facts that (1) 0.5 per cent lecithine, both from yolk and soya bean, was a 

 strong stimulus (Fig. 12), and (2) the response to lecithine was remarkably 

 affected by the previous adaptation to the pupa fluid. Unfortunately, we 

 have not yet tested pure preparations of sphingolipid or the related lipid 

 from other sources, and it is thus difficult at present to make a final identi- 

 fication of the gustatory active components in the ether insoluble fraction 

 of the pupa as well as those in saliva. At any rate, it looks as if lipid-Hke 

 substances, except for fatty oils, are capable of stimulating strongly the fish 

 chemoceptors. It is of interest to note Hiyama's observation (1947) that 

 rice-chul, common freshwater fish in Japan, preferred the hook smeared 

 with the fat of pupa of a certain moth to a hook without the fat. The 

 results presented here in addition to the finding of specific fibres responding 

 to the saliva suggest the existence of highly differentiated specific receptors 

 that respond to specific substances, though they may not exist in other 

 animals. Furthermore the results give us the impression that the majority 

 of the substances which attract fish may mainly stimulate these receptors. 

 We only found a few specific fibres responding to saliva in the Swedish carp, 

 but many more such fibres may be detectable, especially in the Japanese 

 carp, because Japanese carp have higher sensitivity to saliva than Swedish 

 carp, despite their less sensitivity to sugar. 



The effects of lytic agents on the chemoceptor activity in the carp were 

 investigated. Digitonin had a strong influence on the chemoceptors, which 

 were impaired almost immediately even at as low a digitonin concentration 

 as 0.005 per cent. The action of sodium cholate was rather mild. Never- 

 theless it finally made the receptors almost inexcitable. It was found that 

 the sweet and saliva receptors were paralysed most quickly by the treatment 

 of 0.3 per cent sodium cholate ; the sweet receptors were affected almost 

 immediately while the salt and acid receptors were more resistant, all in 

 accordance with the action of gymnemic acid (Fig. 13). The quinine 

 receptors formed an intermediate group. The fact that digitonin, a typical 

 lytic agent, which probably acts exclusively on the lipid part of the cell 

 membrane (Danielli, 1951), could very quickly extinguish the chemoceptor 

 activity even at a very low concentration suggests that the chemoceptor 

 membrane in the fish may have a lipid layer in its molecular structure. 

 This layer may play an important role in gustatory excitation comparable 

 to excitation in nerve axon (Tobias, 1958) and in visual cells (Sjostrand, 

 1953). If that is the case, our study of the gustatory active components in 



