THE SENSES 967 



against the entrance of food in deglutition (Wilson). Epithelial 

 buds, different from the olfactory elements, also occur in the olfactory 

 region of the nasal mucous membrane. It is possible that the 

 so-called nasal taste- -e. g., the sweet taste caused by chloroform 

 when aspirated in not too small an amount through the nose 

 depends upon these buds. 



As to the properties in virtue of which sapid substances are 

 enabled to stimulate the gustatory nerve-endings, we know that 

 they must be soluble in the liquids of the mouth, and there our 

 knowledge ends. An attempt has been made by various authors 

 to connect the taste of such bodies with their chemical composi- 

 tion, but researches of this kind have not hitherto yielded much 

 fruit. The number of distinct qualities of taste sensation is con- 

 siderable, but by no means so great as the number of qualities of 

 olfactory sensations, and they are more easily reduced to a few 

 primary or fundamental sensations.- Sapid substances have 

 generally been divided into four classes, as regards the funda- 

 mental sensations produced by them viz. : (i) Sweet, (2) acid, 

 (3) bitter, (4) saline. All taste sensations seem to be combina- 

 tions of these, or combinations of one or more of them with 

 olfactory sensations, or with sensations due to excitation of the 

 ordinary sensory nerves of the tongue. 



Sweet and acid tastes are best appreciated by the tip, and 

 bitter tastes by the base, of the tongue. Differences have been 

 detected between individual papillae in their power of reaction 

 to sapid substances which produce one or other of the funda- 

 mental sensations. Of 125 fungiform papillae tested with solu- 

 tions of tartaric acid, sugar, and quinine, 27 gave no sensation 

 of taste. Tartaric acid evoked its acid taste in 91 of the remain- 

 ing 98, sugar its sweet taste in 79, and quinine its bitter taste 

 in 71 ; 12 reacted only to tartaric acid, and 3 only to sugar 

 (Ohrwall). Such facts indicate, although they do not definitely 

 prove, the existence of specific receptors for each of the funda- 

 mental taste sensations i.e., gustatory end-organs, which are 

 easily excited by an adequate stimulus (acid, e.g., in the case of 

 an ' acid ' taste-bud), with difficulty or not at all by an in- 

 adequate stimulus. 



The form of inadequate stimulation most investigated is that 

 produced when a constant current is passed through the tongue. An 

 acid taste is experienced at the positive, and an alkaline or bitter 

 taste at the negative, pole ; and this is the case even when the current 

 is conducted to and from the tongue by unpolarizable combinations, 

 which prevent the deposition of electrolytic products on the mucous 

 membrane (p. 625). The sensations are due to stimulation of the 

 gustatory end-organs and not of the nerve-trunks. 



Normal lymph, which bathes these end-organs, does not excite 

 any sensation of taste, but when the composition of the blood 

 is altered in disease or by the introduction of foreign substances, 



