218 JIHEI KONISHI AND YNGVE ZOTTERMAN 



exceed those of acid and sucrose, whereas Japanese carp showed far higher 

 sensitivity to the sahva, earthworm-extract and milk as well as to extracts of 

 silkworm pupa which is an important bait for carp in Japan. 



The responses to sapid substances in the facial nerve from the barbel, and 

 also the branchial nerve, innervating the chemoceptors on the gill rakers in 

 this fish, were quite small. However, all taste substances which stimulated 

 the palatal organ were able to produce positive responses in these nerves. 

 On the other hand, tactile stimulation caused larger response than the 

 response to chemicals. 



A study of the records from single taste fibres in the palatine nerves re- 

 vealed that the individual fibres could be divided into seven groups accord- 

 ing to their response pattern. None of the taste fibres tested responded to 

 tactile stimulation of the palatal organ. The number of touch fibres seems 

 to be relatively small compared with the chemoceptive fibres. The charac- 

 teristic of the gustatory fibres in this fish may be caused by fi.bres which 

 respond to many taste substances in contrast to other animals such as the 

 cat. The existence of many fibres displaying a broad gustatory spectrum 

 draws attention to the possibility of a simple osmotic effect as the primary 

 mechanism for producing taste sensation in the fish. This possibility, 

 however, is ruled out because human saliva which is nearly isotonic to fish 

 body fluid was intensively stimulating. We found specific taste fibres for 

 salt and for acid (Fig. 5). It is especially noteworthy that among the 16 

 fibres of the salt fibre type so far studied, all except two were not stimulated 

 by acid at the concentration used. This is the only taste fibre type which 

 was insensitive to acid. Next to the fibre type displaying a broad gustatory 

 spectrum the " sweet fibre " was commonly found (Fig. 4). Sweet tasting 

 substances except for saccharine stimulated this fibre. It is particularly 

 remarkable that human saliva selectively stimulated these " sweet fibres " 

 as strongly as 0.5 M sucrose, and in some cases even more so. The salt, 

 quinine and acid fibres were not stimulated by saliva. Besides the " sweet 

 fibres " and the fibre displaying a broad gustatory spectrum, fibres which 

 showed a vigorous response exclusively to saliva were rarely found (Fig. 6). 

 The response pattern of individual palatine chemoceptive fibres are sum- 

 marized in Table 1 with the exception of rare cases. The fact that the great 

 majority of taste fibres running to the palatal organ of the carp display a 

 rather broad gustatory spectrum raises again the question, previously 

 brought up by Pfalfmann (1941) as well as by one of us (Zotterman, 1956), 

 whether a taste fibre might possess in its endings different receptors res- 

 ponding to diff'erent classes of gustatory stimuli. As it is difficult to find 

 any common denominator for the excitatory eff'ect of such stimuh as sugar, 

 salt, quinine and acid, it seems more hkely that the broad gustatory sen- 

 sitivity of these fibres is due to the existence of diff"erent chemosensitive 

 sites in the villi of the gustatory cells or the fine endings of the individual 



