SENSATIONS OF SMELL 



757 



The stimulation for the hot and cold spots does not depend upon the 

 absolute temperature, but on the relative temperature. Insert the hand in 

 water that feels lukewarm. Place the same hand in a cup of quite warm 

 water for a moment, then reinsert it in the lukewarm water. This will now 

 feel cold. 



4. Sensations of Taste. The distribution of taste organs in the tongue 

 is shown in figure 481. Examine your own tongue for organs of sweet, 

 acid, saline, and bitter, using solutions of i to 2 per cent, salt, 10 per cent, 

 sugar, i to 2 per cent, sulfuric acid, or 5 per cent, acetic acid, and o.i per 

 cent, quinine. 



ft. 



FIG. 481. Localization of Taste. Bitter ; acid ; salt, ; sweet ; T, 



tonsils; FC, foramen cecum; CF, circumvallate papillae; FP, fungiform papillae. (Hall.) 



Wipe the tongue dry and apply the solution named from the tip of a glass 

 rod. The best form of rod is about 15 cm. long by o. 5 cm. in diameter, and 

 has one end drawn out to a slender pencil-shaped tip and of a size which 

 will suspend a very small drop. Too large a drop diffuses over too great an 

 area of the tongue. Occasionally small crystals of sugar, salt, etc., give 

 more satisfactory results. 



Perform the experiments on yourself before a mirror and map the re- 

 sults as shown in figure 481. 



If the experiments are done with care certain papillae will be found which 

 give one or two of the taste sensations, but not all. 



5. Sensations of Smell. Quantitative experiments on the sense 

 of smell are difficult to determine. Inhale vapor of ammonia so dilute that 

 it can just be detected. Note that the sensation is strongest at the moment 

 of drawing the vapor into the nostril. Fill the nostrils with the diluted vapor 

 and close the external opening; the sensation quickly disappears. Keeping 



