PHYSIOLOGY OF GUSTATION 137 



taste, that the sour taste of the acid solution cannot be 

 due to its chlorine ions but must be occasioned by its only- 

 other constituent, the hydrogen ions. Kahlenberg, there- 

 fore, concluded that these ions are accountable for the 

 sour taste. 



This view is supported by the fact that the sourness 

 of all acid solutions is the same, for instance, it is impos- 

 sible to distinguish by taste hydrochloric add from nitric 

 or sulphuric acid. So far as the sensations are concerned 

 all these reagents produce identical results, the one qual- 

 ity of sourness. There has been some tendency to sepa- 

 rate astringency from sourness, but it is generally 

 conceded that astringency is merely sourness near the 

 vanishing point.' With hydrochloric and other mineral 

 acids this occurs in molar solutions at about 0.00125 to 

 0.001 below which the acid solutions cannot be distin- 

 guished from pure water. 



From this standpoint sour taste might be regarded 

 as due directly to hydrogen ions and the intensity of this 

 taste to depend upon the concentration of such ions. 

 But the question is not so simple as this. Although solu- 

 tions of most mineral acids agree well among themselves 

 so far as sourness and hydrogen ion concentration are 

 concerned, organic acids are not necessarily so related. 

 Most organic acids are much less dissociated in aqueous 

 solution than are inorganic acids and contain, therefore, 

 in normal solution, fewer hydrogen ions per unit volume, 

 than inorganic acids do. Nevertheless Richards (1898) 

 found that tartaric, citric, and especially acetic acids were 

 more sour than would have been expected from the hydro- 

 gen ion concentration of their solutions. According to 

 Richards acetic acid is about as sour as a solution of 



