THE SENSE OF TASTE 



519 



TABLE 6. Sweet Thresholds in Man (in Molar Concentrations) 



* a, Fabian & Blum (74); b, Biester & Wood (27); c, Schutz & Pilgrim (186), d, Janowitz & Grossman; e, Richter & Camp- 

 bell (179); f, von Skramlik (198); g, Warren, R. W. & C. Pfaffmann (unpublished observations). 

 t Detection threshold. 

 J Recognition threshold. 



TABLE 7. Possible Structural Basis for Sweet Taste* 



ferences in ta.ste. For example, of the homologues of 

 w-nitroaniline, which is sweet, only 2-nitro-p-toluidine 

 is sweet. 



Sweet 

 NO2 



Sweet 

 NO2 



Tasteless 



NH, 



NH., 



NO, 



NH., 



CH, 



CH3 



Very shghtly bitter 

 NH, 



NO, 



CH, 



Saccharin is one of the better known physiologi- 

 cally inert synthetic sweetening agents. The salts of 



saccharin, especially the sodium salt crystallose, are 

 sweet presumably due to the anion 



■N- 



-SO, 

 -CO 



Where substitution of the hydrogen in the imide 

 group occurs to form .^''-methyl saccharin, the com- 

 pound is tasteless presumably because ionization 

 cannot occur, 



CO. 



-SO, 



.NCH,. 



Several other intensely sweet substances are dulcin, 

 cyclamate (Sucaryl) and the 4-alkoxy-3-amino- 

 nitrobenzenes. The n propyl derivative of the latter 

 class, called P-4000, is said to be the sweetest known 

 compound but its use as a synthetic sweetening agent 

 is limited by its toxicity (29, 131). 



Stereoisomerism is of significance in taste as in 

 other physiological systems. In fact, one of the earlier 

 examples of the biological significance of optical 

 activity was provided by asparagine of which the 

 dextro forin is sweet, the levo form tasteless. Freshly 

 prepared solutions of alpha D glucose are sweeter 

 than beta D glucose which predominates in solution 

 after mutarotation has occurred (44). 



Mention has already been made of the selective 

 and reversible action of certain drugs like gymnemic 

 acid which reduces sensitivity to sweet and bitter but 



