ELECTROPHYSIOLOGICAL RESPONSES TO SUGARS 



185 



much the same, our analysis of the functional single fibres have revealed 

 some detailed, new information. 



It will be remembered that some of the fibres studied were activated by all 

 of the sugars tested (Fig. 6). All of these fibres exhibited the largest res- 

 ponse to D-fructose and next to sucrose. However, we also noted fibres 

 which displayed electrical activity only after stimulation with these two 

 sugars. The sweet receptors, therefore, appear to have different threshold 

 values, and consequently, D-fructose and sucrose elicit their large responses 

 from the whole chorda tympani not only by activating the individual fibres 

 to discharge with a higher frequency than the other sugars do, but also 

 by activating more fibres. 



The marked diff'erences in stimulating ability displayed by the various 

 sugars is certainly a result of differences in chemical and physical pro- 

 perties. One very interesting observation may be made by comparing the 

 molecular configurations and sweet stimulating ability of the three di- 

 saccharides used, and those of the three monosaccharides which participate 

 in the molecules of these disaccharides : Among the monosaccharides the 

 stimulating ability decreases in the following order, D-fructose >D-glucose 

 >D-galactose. The corresponding rating for the disaccharides is sucrose > 

 maltose>lactose. In all of these three disaccharides D-glucose constitutes 

 one half of the molecule, the other component being D-fructose, D-glucose 

 and D-galactose, respectively (Fig. 1). Hence, the following rule appears to 

 hold for the six sugars considered : Since all of the disaccharides have 

 D-glucose in common as one half of the molecule, their relative sweetness 

 and stimulating power may be determined by the second constituent 

 monosaccharide, and in such a way that each of the disaccharides is less 

 powerful in its sweet stimulating abihty than an equimolar solution of that 

 monosaccharide participating in its molecule which is not common to the 

 other two disaccharides. For these six sugars we should consequently have 

 the following rating of decreasing potency : D-fructose >sucrose >d- 

 glucose>maltose>D-galactose>lactose. The discussion is summarized in 

 the following scheme : 



D-fructose > D-glucose >D-galactose 



Sucrose >Maltose>Lactose 



and 



D-fructose >sucrose >D-glucose >maltose >D-galactose >lactose 



