PHYSIOLOGY OF GUSTATION 135 



the like (Kahlenberg, 1898). The metallic taste of a 

 0.0005 molar solution of silver nitrate is very pronounced 

 and is discernible even at the greater dilution, 0.0002. 

 Since the nitrate ions are incapable of exciting taste at 

 such slight concentrations, it follows that stimulation 

 must depend upon the silver ions. In a similar way mer- 

 cury ions in normal solutions of 0.001 to 0.0005 of mercu- 

 ric chloride have been shown to excite the so-called 

 metallic taste. This taste, however, has been declared 

 to be a complex of other tastes such as sour and sweet, 

 and Herhtzka (1808) has gone so far as to maintain that 

 it is not a true taste but an olfactory phenomenon. 



The alkaline tastes so-called are excited by the appli- 

 cation to the tongue of dilute solutions of such caustic 

 alkalis as sodium or potassium hydrate. Kahlenberg 

 (1898) has shown that the stimulating material in such 

 mixtures is the hydroxylion which is effective in solutions 

 as weak as 0.0025 molar. In the alkaline taste, as in the 

 metallic taste, the results have been variously explained. 

 Oehrwall (1891) regarded the so-called alkaline taste as 

 a mixture of sensations due to a simultaneous combina- 

 tion of several tastes and touch. Hober and Kiesow 

 (1898) pointed out that weak alkalis produce a sweetish 

 taste, but von Frey (1910) showed that these reagents 

 act on the tongue in such a way as to produce odorous 

 materials that he believed to be the occasion of the so- 

 called alkaline taste. He, therefore, relegated these as- 

 sumed tastes to olfaction. 



Insipidity, such as is characteristic of distilled water, 

 is probably real tastelessness. Oehrwall (1891) attributed 

 it to the absence of small amounts of carbon dioxide from 

 such waters and this is probably true, for tastelessness 



