CHEMICAL STRUCTURE AND STIMULATION 175 



the sugar receptor cell. Hodgson (1957) reported preliminary experiments 

 to this end, but his methods were inadequate. He assayed a number of 

 sugars, but they were always dissolved in a NaCl solution. It has been 

 shown that some ions influence the response of the sugar receptor (Evans, 

 1958 ; Tateda and Morita, 1959), as might very well have been expected. 

 Furthermore, since he believed there were only two spike types in record- 

 ings from the preparation, when in reality there are potentially four (Evans 

 and Mellon, 1962a) or more, his counts of the " sugar spikes " cannot 

 be taken at face value, and should be repeated using methods that permit 

 assignment of a given spike in a record to a particular sensory cell. 



When appropriate quantitative electrophysiological studies are made, 

 the mechanism of stimulation by polyols may be elucidated. If as is 

 purported, the reaction of sugar with receptor site does not involve 

 chemical changes in the molecule, the mechanism promises to be a unique 

 neural process. While potential changes of membrane produced by fat 

 soluble molecules and ions are familiar, depolarization of a membrane 

 by a highly specific physical combination with un-ionized, water-soluble 

 sugar molecules promises to involve interesting processes. Since indi- 

 vidual mammalian taste bud cells respond to an array of chemical species 

 even broader than those which elicit a sweet taste (Kimura and Beidler, 

 1961), the sugar receptor cell of insects is the more advantageous prepara- 

 tion for this purpose. 



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