

SENSATIONS OF TASTE 485 



It is impossible to classify the gustatory impressions any further. For 

 example, if we use solutions of HC1. HN0 3 H 2 S0 4 , acetic, tartaric and oxalic 

 acids of such strength as to produce sensations of the same intensity, they 

 all taste alike. The same is true of bitter substances like strychnin, quinin, 

 morphin and picric acid, and of sweet substances such as milk sugar, grape 

 sugar, cane sugar. On the base of the tongue we can distinguish all the taste 

 qualities, but on the tip there are considerable differences in this respect in 

 different individuals, v. Vintschgau recognizes four groups of individuals: 



(1) those who distinguish with the tip of the tongue all the four qualities; 



(2) those who distinguish sweet, salt and acid readily, but bitter less easily; 



(3) those who distinguish none of the qualities easily; (4) those who have 

 no sense of taste at all on the tip of the tongue. 



Moreover, the same substance placed on different parts of the tongue may 

 have a different taste. Thus according to Howell and Castle brom-saccharin 

 tastes bitter on the base of the tongue, but sweet on the tip. Shore found 

 that a five-per-cent solution of MgS0 4 has a faintly sweetish taste on the 

 tip of the tongue followed by an acid taste, an acid and bitter taste on the edge 

 and a pure bitter taste on the base. 



By means of cocaine the sensibility of the tongue to gustatory stimuli can be 

 considerably reduced. But the effect is different for the different taste qualities. 

 A five-per-cent solution of cocaine acts most markedly on the sense of bitter, 

 then on sweet and acid, while it is entirely without effect on salt (Shore, 

 Kiesow). The faintly toxic substance eucain has approximately the same effect. 

 Gymnemic acid obtained from Gymnema sylvestre placed on the tongue in a 

 sufficiently concentrated form obliterates every trace of sensitiveness for sweet 

 (Edgeworth) ; it acts secondarily on bitter and to a much less degree "on salt 

 and acid (Shore, Kiesow). 



It is very probable, from such observations as those just mentioned, that 

 the different taste qualities are mediated by different nerves, just as in the 

 case with the different qualities of the temperature sense. This inference 

 has been directly confirmed by Ohrwall. 



By means of a very fine brush he placed solutions of sugar, quinin and 

 tartaric acid on different fungiform papillae, and found that out of 125 such 

 papilla? on the anterior part of the tongue 27 (21.6 per cent) did not react 

 to either of these substances. Of the remaining 98, 12 reacted only to tartaric 

 acid, 3 only to sugar, 12 only to tartaric acid and sugar, 7 only to quinin 

 and tartaric acid, 4 only to sugar and quinin. No definite results were ob- 

 tained with reference to the sensitivity of different papillae for salt. Kiesow 

 has reached similar conclusions. 



Hoeber and Kiesow have discussed the significance of electrolytes as gusta- 

 tory excitants, and have reached the conclusion that the specific sensations are 

 aroused in part by ions. For example, the salty taste of KC1 NaCl, MgCl 2 , 

 NaBr, Nal, Na,SO 4 is caused by the electronegative ions (Cl, Br, etc.) ; the 

 threshold stimulus is given by a concentration of 0.020-0.025 g. of the ion per 

 liter; a sweet taste produced by a very weak solution is caused by the OH-ions, 

 the threshold value of the stimulus being given by 0.006-0.009 g. ions per liter. 



The acid taste produced by the anode of a constant current is probably due 

 to electrolytic dissociation of the saliva. 



