ZOOLOGY. 299 



greeable medicine lias its origin in this peculiar relation of these two 

 senses. 



We have now to consider the exact locality of the sensations pro- 

 duced by these four classes of stimuli. Experiments have been tried 

 by various physiologists with entirely different results, which may be 

 attributed to want of care and to not recognizing the fact that allyfa- 

 vors should be excluded from the investigation. All agree, however, 

 in this that, to be tasted, a substance must be brought to the sen- 

 sitive part in solution, inasmuch as insoluble substances have no taste. 

 In the experiments performed by the writer, solutions of white sugar, 

 tartaric acid, common salt, and sulphate of quinine, were carefully ap- 

 plied to various parts of the mouth and fauces by means of a camel's- 

 hair pencil, pains being taken that no excess of fluid should be used, 

 which might diffuse itself over other parts than that directly under ob- 

 servation. The following results were uniformly obtained on six differ- 

 ent individuals, they all being unaware of the substances used in each 

 experiment. 



1. The upper surface, tip, and edges of the tongue, as far back as 

 ^lo include the circumvallate papilla, are the only parts concerned in 

 the sense of taste ; the hard and soft palate, tonsils, pharynx, lips, 

 gums, and under surface of the tongue, being entirely destitute of this 

 sense. 



2. The circumvallate papillae are far the most sensitive portion of 

 the organ. They perceive, at once, very minute quantities of any one 

 of the four substances used, and are particularly sensitive to bitter. Ir- 

 ritation of these papillae by pressure, or placing a drop of cold water 

 on them, excites decided sensations of bitterness. 



3. The central portion of the dorsum of the tongue, to within half 

 an inch of the edge, is the least sensitive portion. Substances are dis- 

 tinguished with difficulty, or not at all, when applied to it. 



4. The edees and tip of the tongue ar3 quite sensitive, the edges be- 

 coming less so as we come forward. They recognize all the four classes 

 of substances. The tip detects bitter with great difficulty, but is par- 

 ticularly sensitive to sweet. A sweet sensation, sometimes mingled 

 with sour or saL, is produced by gently tapping it with any insipid soft 

 substance. 



The tongue possesses ordinary sensibility to a marked degree, espe- 

 cially at its tip, and in this way detects the size, shape, and texture of 

 substances. It is in the same way that the qualities of pungency and 

 astringency are perceived, which fact is proved by their being nearly 

 as perceptible to the conjunctiva, or any other mucous membrane pos- 

 sessing ordinary sensibility, as to the mouth. A solution of tannin, 

 applied to the circumvallate papillas, gives the sensation of extreme 

 bitterness, while at the tip it produces a slight sweetish taste, espe- 

 ,cially after it has been washed off by the saliva. These sensations are 

 entirely distinct from tne puckering, which, as just said, is perceived 

 by other mucous membranes. The application of a solution of potassa 

 gives nearly the same result, proving that there is no such thing as a 

 distinct alkaline taste. 



Certain substances have been observed to produce sensations, pain- 

 ful or otherwise, when applied to perfectly sound teeth. As it has 

 been ascertained that fluids are readily and rapidly absorbed by the 



