12 



V. G. DETHIER 



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ALCOHOLS IN WATER 



O ALCOHOLS IN GLYCOL 



• ALCOHOLS IN MINERAL OIL 



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LOG NUMBER OF C ATOMS 



Fig. 9. Rejection thresholds of aqueous, glycol, and oil solutions of primary alco- 

 hols by the blowfly Plwrmia (Dethier, 1951a). 



Mechanism of Action of Sugars 



With the foregoing information derived from studies of various mammals 

 and insects, and without losing sight of the fact that there are pronounced spe- 

 cific differences which eventually require explanation, we can attempt to draw 

 some conclusions regarding the nature of the interaction between taste stimuli 

 and chemoreceptors. First of all, since there is good evidence that there are 

 specific types of receptors, it would seem intelligent to consider each apart. 

 There is no reason to believe that all act similarly. It is certainly apparent that 

 the sugar receptors of insects and the sugar bitter receptors of mammals are 

 basically different from non-sugar receptors. Some of the outstanding differ- 

 ences are these: (1) the sugar receptors are sensitive to highly specific chemical 

 configurations; the other receptors react to an extremely wide variety of com- 

 pounds; (2) the reaction of sugar receptors is slow compared to that of the other 

 receptors; (3) the magnitude of electrical response of sugar receptors appears 

 to be less than that of other receptors; (4) the amplitude of the potential in the 

 sugar fibers is smaller than that of other fibers. 



The really striking difference between the sugar receptor and all others is its 



