THE SENSE OF TASTE ^2 1 



- 0.075 



E 0.050 



S 0.025 



0.050 075 100 



Gram-mol per cent 



0125 



0150 



FIG. 13. Curves showing the concentrations at which different substances taste as sweet as various 

 concentrations of sucrose. Gram-mol per cent is ' fo the value of the molar concentration. [From 

 Cameron C44).j 



TABLE 8. Bitter Thresholds in Man (in Molar Concentrations) 



Substance 

 Quinine sulphate 

 Quin ine hydrochloride 

 Strychine inonohydrochloride 

 Nicotine 

 Caffeine 

 Phenyl thiourea (PTC) 



tasters 



nontastcrs 

 Urea 

 Magnesium sulfate 



(Epsom salt) 



* a, Blakeslee (28); b, Hanig (96); c, Harris (99); d, Hartmann (of. 48); e, Harris & Kalmus (100); f, Kiesow (118); g, Parker 

 & Stabler (154); h, Richter & Clisby (180); i, Schutz & Pilgrim (186); j, Setterfield, Schottl & Snyder (cf. 48): k, von Skram- 

 lik (198). 



t Modes. 



2, =N, =N= — SH, — S— , — S— S— , and — CS— . 

 Some typical threshold values for the human are 

 shown in table 8. 



The importance of structure and specific chemical 

 grouping is shown by the phenomenon of 'taste blind- 

 ness,' a specific relative insensitivity to a number of 



S 



substances possessing the y NC — group. Phenylthio- 



carbamide (PTC) is widely used as a test for 'taste 

 blindness.' The actual distribution of taste-blind 

 individuals found depends upon the manner of ad- 

 ministering the PTC;, the percentages of 'nontasters' 

 in Caucasians having been variously reported to be 

 between 3 per cent and 40 per cent. A graded series 



of solutions yields no sharp cutoff at one threshold 

 concentration but rather a bimodal distribution. 



This deficiency is inherited as a Mendelian reces- 

 sive characteristic. Evidence for such taste defects 

 were found in anthropoid apes (28, 48, too). Rats, 

 however, rejected PTC solutions with no evidence of 

 the defect. PTC is intensely toxic to the rat when 

 administered by stomach tube. This property was 

 utilized in the preparation of a rat poison "Antu' 

 from a chemically related but tasteless compound 

 C178, 180). 



S 



\ " 

 The inability to taste y NC — may be overridden 



by other chemical groups as in thiourea, NH2CSNH.2, 



