CHAPTER XXXIV 

 TASTE, SMELL, AND HEARING 



588. Touch. Touch is a special sense. Its sensations 

 are aroused without the need of any special organ. So 

 the discussion of sensory nerves is really a discussion of 

 the special sense of touch. (See p. 269.) 



589. Taste. Taste is a special sense which is located 

 in the tongue, palate, and pharynx. All these parts are 

 endowed with a delicate sense of touch, but in addition 

 two pairs of cranial nerves carry special sensations of taste. 

 The impulses are aroused by the direct action of sub- 

 stances upon the nerves. The motions of chewing and a 

 good flow of saliva aid the sense of taste by bringing food 

 in contact with the nerves, while a dry substance, or one 

 which will not dissolve in water, can have no taste. All 

 tastes are some combination of sweet, sour, bitter, and salt 

 tastes. Sweetness and sourness are recognized mainly by 

 the front part of the tongue, and bitterness and saltness 

 by the back parts and pharynx. 



Taste is greatly influenced by the sense of smell. The 

 real taste of coffee is greatly changed by the odor which 

 reaches the back part of the nose as it is swallowed. 



590. Use of taste. Taste enables a man to detect 

 spoiled or unwholesome food. The sense is capable of 

 great education. The prices of different grades of tea are 

 determined by expert tea tasters, who devote their whole 

 time to tasting different samples. Alcohol and tobacco 



323 



