EXERCISE 90 



The skin, including the mucous lining of the mouth and nose, can perceive several kinds of sensa- 

 tions besides that of touch. Just as some parts of the skin are sensitive to heat and others to touch, 

 so different parts of the tongue are sensitive to the different kinds of taste, of which four are com- 

 monly distinguished sour, sweet, salt, and bitter. The sensitive elevations on the tongue are called 

 papillae. 



Problem. What is the location of the papillae which are sensitive to the different tastes ? 



What to use. Four very dilute solutions : salt, sugar, vinegar or citric acid, and quinine or aloes ; 

 glass tubes drawn to a fine point, rounded off ; water ; two students working together. 



What to do. With the subject blindfolded, place tiny drops of the different solutions on various 

 parts of the tongue, following a systematic plan, and have the subject tell what sensation is produced 

 by each drop. Occasionally introduce plain water. After the drop, have subject rinse mouth with 

 water ; rinse tip of tube if it comes in touch with the tongue. 



Record. Make a diagram of the tongue and locate the distribution of the different kinds of papillae, 

 using colored ink or crayon, or different symbols or letters, to distinguish the four kinds. 



Questions. 1. Is it possible to distinguish two or more tastes at the same time? 



2. Do substances of different taste ever interfere with our recognizing tastes ? 



3. How does the order in which different substances are placed in the mouth influence our 

 perception ? 



4. Under what conditions would it be possible to put a bit of salt or sugar in the mouth without 

 tasting it ? 



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