The existence of the palatal chemoreceptors responding specifically to dilute solutions of salts with monovalent cations was demonstrated in carp. The distilled water effect (a response produced by the application of distilled water after chemoreceptors had been rinsed out with hypertonic salt solutions) was assigned to the activity of the same receptor. Intensity of the response to dilute solutions of salts depended on the valency of the anion: the larger the valency, the greater the response. Positively charged sites of the receptor responsive to dilute salt solutions were suggested by previous treatments with acid and alkali, and dye salts. Increase in the ionic strength of the stimulating solution by the addition of supporting electrolytes caused a depression of response. In particular, strong depression of response was caused by the addition of a supporting electrolyte with a divalent cation. Effects of polarizing current on the chemoreceptor activity were investigated. Based upon the findings in this paper, a hypothesis is presented, which explains mechanisms underlying chemoreceptor responses to dilute solutions of electrolytes in terms of an interfacial electrokinetic process.

J. KOSISHI and Y. ZOTTERYAS. Taste junctions in the carp. An electropt!ssiological stu4v on gustatorr jbrcs. Acta physiol. scand. 196 1. 52. 150-161. -The electrical responses of the taste fibres in carp (Cyprinus carjio (L.) j were recorded during thr application of various sapid sub-

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Despite many behavioural investigations, our knowledge of the chemoreceptive functions in fish is still meager. Following a pioneering study by HOAGLAND ('33), apparently no detailed investigation on taste function in fish has been carried out until recently in spite of the obvious need for information on chemoreception in purely aquatic vertebrates. Receptors of freshwater and marine fish are constantly exposed to hypo-and hypertonic environments respectively, and thus might be expected to exhibit an excitatory mechanism which is rather different from that of land-inhabiting animals. Quite recently some properties of the taste receptors of freshwater fish were analyzed by several workers (TATEDA, '61; KONISHI & ZOTTERMAN, '61a, '61b , '63). The electrical response from the palatine nerve supplying the palatal organ in the carp, situated in the roof of the mouth and having particularly dense taste buds on its surface, was found to be ideally suited for obtaining further information about the gustatory mechanisms in freshwater fish (KONISHI & ZOTTERMAN, '61a, '61b). One of the authors (J. K.) had noticed the peculiar phenomenon that the receptors of freshwater fish are highly sensitive to very weak salt solutions such as NaC1, whereas NaCl in higher concentration produced little response, in some cases even smaller than the response to distilled water (KONISHI & ZOTTERMAN, '63). This report presents the results of further experiments that provided more detailed information on this subject. METHODS The experiments were carried out on 106 carp (Cyprinus carpio (L.)), with an average body length of 48 cm. A most important condition for success of this experiment was the use of healthy fish maintained in good condition. After the fish was decapitated, the vagal lobe and medulla oblongata were destroyed to abrogate

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