PHYSIOLOGY OF GUSTATION 159 



sodium chloride, sodium iodide, and sodium bromide, 

 though much the same are still characteristically diif erent. 

 And he has further maintained that the mixed tastes so- 

 called cannot be imitated by real mixtures; thus the 

 bitter-saline taste of magnesium chloride cannot be repro- 

 duced, he believes, by a mixture of sodium chloride and 

 bitter aloes. But all such statements imply that the 

 conception of the receptive independence of tastes neces- 

 sarily involves the further view that a gustatory stimulus 

 is limited to one category of receptors. That some sub- 

 stances, such as parabrombenzoic sulphinide, stimulate 

 two categories of receptors has already been made clear 

 and though most stimulating materials influence in a 

 vigorous way only one set of end-organs, it is more than 

 probable that they all affect at least to a slight degree 

 other such sets. The taste of any substance then is not 

 necessarily one of the four tastes and this alone, but one 

 of these qualified by traces of other tastes excited slightly 

 and simultaneously by the same stimulating agent. 

 Hence any substance such as sodium chloride, or sodium 

 bromide, may perfectly well have a somewhat individual 

 taste without doing violence to the hypothesis that there 

 are four separate tastes, and the success with which 

 mixed tastes so-called may be imitated is rather a matter 

 of skill than despair. 



It is true that gustation is a strikingly unified oper- 

 ation, but when this unity is looked into, it is seen to 

 depend upon simultaneousness of action rather than on 

 interdependence of activities. Smell is related to taste 

 in much the same way that one taste is related to another. 

 On the whole it would seem more consistent with fact to 

 speak of the sour sense, the saline, the sweet, and the 



