TASTE SENSATIONS. 



1241 



It is a matter of common experience that bitter substances are tasted 

 best at the back of the tongue, and on that account no one would think 

 of sipping a glass of beer. Sweet substances are tasted best by the tip 

 and sides of the tongue, and so perhaps are salines and acids. All parts 

 of the tongue are, however, sensitive to all four tastes, and bitter if it 

 is strong enough — as quinine powder, for instance — can be tasted on 

 the front of the tongue. The difference appears, therefore, to be one of 

 degree, and suggests that for each taste there are special end-organs 

 present, and that they are unequally distributed over the tongue. We 

 may suppose, for instance, that there are many end-organs for bitter 

 sensations towards the back of the tongue, and very few at the front. 

 In support of this view much evidence is forthcoming. Let us take 

 first the reaction time for the various sensations. M. v. Vintschgau 

 and Honigschmied x give the following reaction times in seconds for 

 the base as compared with the tip of the tongue : — 



The most outstanding fact in the above table is the difference 

 between the reaction time of quinine at the base and tip of the tongue. 

 This corresponds with the observable difference of sensitiveness of these 

 parts, the less sensitive one requiring a longer application of the 

 stimulus to produce an appreciable result in sensation. This result is 

 verified by Ohrwall, 2 who finds that the reaction time of bitter sub- 

 stances is long at the front of the tongue, while at the base it is the 

 same as for other substances. 



Ohrwall, in the same paper, has described the effects of stimuli 

 applied to individual papillae. He used porous points soaked in sapid 

 substances, and with these he was able to apply stimuli to a single 

 papilla, to the exclusion of the rest. Ohrwall found that the filiform 

 papillae are insensitive to taste, not so the fungiform papilla?. Of 125 

 papillae, tested by him, twenty-seven reacted neither to acid, bitter, nor 

 sweet; sixty reacted to all three; and of the remaining thirty-eight, some 

 reacted to acid and sweet but not to bitter, others to bitter and acid 

 and not to sweet, and others to sweet, but not to bitter and acid. On 

 placing an electrode in contact with a papilla, and passing through it a 

 constant electrical current, an acid papilla discharged an acid, and a 

 sweet papilla discharged a sweet taste. These results are again con- 

 sistent with the separate existence of bitter, sweet, etc, end-organs. 

 Some papillae are devoid of any end-organs, others possess them all, and 

 others again possess one or two varieties. 



Action of drugs.— By the action of drugs we can abolish certain 

 tastes more than others, so as to leave the mouth practically insensible 

 to certain stimuli. This again suggests the presence of different kinds 

 of end-organs, some of which are more affected than others. Cocaine 



1 Arch. f. d. gcs. Physiol., Bonn, 1875, Bel. x. S. 1 ; and v. Vintschgau, ibid., 1879, 

 Bd. xx. 



2 Skandin. Arch. f. Physiol,, Leipzig, 1890, Bd. ii. S. 1. 



