670 THE SENSES 



sensation of warmth or cold. Examine a given small area of the back of 

 the hand with the thermoesthesiometer. Certain points will give stronger 

 sensation of heat than others. Map these out carefully. Examine the same 

 area for the cold. A large number of cold spots will be found and they will 

 not coincide with the warm spots, figure 421. 



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

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



fp. 



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



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



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, 2 to 5 per cent acid, 5 per cent acetic acid, and o.i per cent quinine. 



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 0.5 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 



