CHEMORECEPTOR MECHANISMS 11 



trical recordings of Hodgson et al. (1955) and similar ones obtained in our lab- 

 oratory (Fig. 15) show clearly that compounds such as salts, alcohols, etc., fire 

 one of the two fibers while sugars fire the other. Thus, by choice of stimulus one 

 has available a single-receptor preparation. In contrast to the situation as it 

 exists in mammalian tongues, there appear to be only two specific receptors in 

 flies, one for sugar, the other for acids, salts, and various organic compounds. 

 Of course, further extensive exploration is necessary, especially with reference 

 to the role of the third neuron. 



Studies have been started (Dethier, 1955) which show that most of the in- 

 formation regarding the nature and effects of stimuli as applied to receptor 

 fields in the fly can be extrapolated to the single receptor. Thus, for example, 

 the order of stimulating efficiency of cation series appears to be the same for 

 the single receptor as for the animal as a whole, and the series resembles in many 

 respects that found in certain mammals. The logarithmic decrease of threshold 

 of homologous aliphatic compounds with the chain length, as recorded for the 

 whole animal, applies also to single receptors. And, finally, the high degree of 

 specificity for sugars is as characteristic of the single receptor as of populations 

 of receptors. 





-3 -2 



LOG SOLUBILITY GRAM MOLES PER LITER 



Fig. 8. Correlation between concentration required for stimulation and solubility 

 of compounds at 25-27°C. in water. Each of the 46 points represents a different ali- 

 phatic compound. The vertical lines represent the fiducial limits of the error of esti- 

 mate of each determination at the 0.01 probabilitv level (Dethier and Chadwick, 

 1950.) 



