in THE SENSE OF TASTE 145 



V. What is the physical or chemical property that confers 

 upon certain bodies the capacity of stimulating the taste organs ? 

 Why do some of them arouse a sensation of sweet, others of 

 bitter, others of acid, others lastly of salt ? Why do other 

 substances that are equally soluble and diffusible remain inert as 

 regards taste ? These are 'the fundamental questions that arise 

 when we attempt to determine the relations between chemical 

 structure and the sense of taste. 



At first sight it does not seem difficult to discover a series of 

 correlations between the chemical composition of bodies and their \ 

 taste. Almost all acids have a sour taste, many salts a salt taste, j 

 a large number of alkaloids are bitter, many carbohydrates are 

 sweet. It might reasonably be supposed that some of the 

 properties which enable us to classify these substances into 

 definite and distinct chemical groups represent the cause or 

 constitute the origin of their respective flavours. But this 

 correlation is more apparent than real, because not all compounds 

 chemically known as acids give an acid taste, not all salts a salt 

 taste, not all alkaloids are bitter, nor are all sugars sweet. There 

 are bodies of very different constitution from the sugars which 

 arouse a sensation of sweetness, such as the glucosides, saccharine, 

 chloroform, and certain mineral salts, as lead acetate and salts of 

 beryllium. On the other hand, it is interesting to note that one 

 sugar, ^-mannose, has a bitter taste, while many other mineral 

 and organic substances of varying chemical composition which do 

 not belong to the alkaloids have the same bitter taste. Lastly, 

 there are compounds of closely allied chemical composition, with 

 different tastes. Such are the two asparagines (Piutti), of which the 

 dextro-rotatory is sweet, and the laevo-rotatory tasteless, although 

 they do not differ chemically, but only in their optical properties. 

 These enigmatical facts have so far received no interpretation. 



The first advance in the correlation of chemical structure and 

 taste was made by the researches of Gley and Kichet (1885), who 

 compared the liminal values, as taste stimuli, of the chlorides, 

 bromides, and iodides of different alkaline metals lithium, sodium, 

 potassium, rubidium the atomic weights of which differ in the 

 relations of 7, 23, 39, 87, although their chemical properties are 

 very similar. They found that equimolecular solutions were 

 required for liminal excitation of the taste organs, i.e. such as 

 contained approximately the same number of molecules of the 

 twelve ; different alkaline salts, whatever the absolute weight of- 

 these molecules. Hence, according to Gley and Kichet, it is 

 legitimate to conclude that their physiological action on the ; 

 organs of taste is a chemical effect, because it takes place according 

 to the laws of ordinary chemical action. 



Another interesting series of researches into the gustatory 

 property of acids was made by Corin (1888). He employed 



VOL. IV L 



