244 Life and Health 



^ 377. The Sense of Taste. The sense of taste is excited 

 by stimulation of the mucous membrane of the tongue 

 and of the palate, affecting the ends of the nerve fibers. 

 Taste is most acute in or near the circumvallate papillae. 

 The middle of the tongue is scarcely sensitive to taste, while 

 the edges and the tip are, as a rule, highly sensitive. 



Certain conditions are necessary that the sense of taste 

 may be excited. First, the substance to be tasted must 

 be in solution, or be soluble in the fluids of the mouth. 

 Insoluble substances are tasteless. If we touch our tongue 

 to a piece of rock crystal, there is a sensation of contact or 

 cold, but no sense of taste. On the other hand, when we 

 bring the tongue in contact with a piece of rock salt we 

 experience the sensations of contact, coolness, and saline 

 taste. 



Again, the mucous membrane of the mouth must be 

 moist. When the mouth is dry and receives substances 

 not already in solution there is no saliva ready to dissolve 

 them ; hence they are tasteless. This absence of taste is 

 common with the parched mouth during a fever. 



Experiment 106. Put a drop of vinegar on a friend's tongue, or on 

 your own. Notice how the papillae of the tongue start up. 



Experiment 107. Rub different parts of the tongue with the pointed 

 end of a piece of salt or gum aloes, to show that the back of the tongue 

 is most sensitive to salt and bitter substances. 



Experiment 108. Repeat the same w : th some sweet or sour sub- 

 stance, to show that the edges of the tongue are the most sensitive to 

 these substances. 



Experiment 109. We often fail to distinguish between the sense of 

 taste and that of smell. Chew some pure, roasted coffee, and it seems 

 to have a distinct taste. Pinch the nose hard while chewing it, and 

 there is little taste. Coffee has a powerful odor, but only a feeble 

 taste. The same is true of garlic, onions, and various spices. 



