TASTE 



411 



Papillae. 



dividers, or by two pins. The tongue can feel that there are two 

 points when they are only 1 /25 of an inch apart; the finger tips, when 

 they are about Vi2 of an i ncn apart. The back, however, feels the two 

 points as one, even when they are I 1 / 2 or 2 inches apart. 



The sense of temperature is also in the skin and mucous mem- 

 brane. A chemist, in trying to find out whether a reaction causes a 

 rise of temperature, often holds to his lips the vessel with which he is 

 working, because the lips are especially sensitive to heat and cold. 



411. Taste. The nerves of taste end in the mucous 

 membrane of the tongue and the back of the mouth 

 (Fig. 297). Only liquids and dissolved substances can 

 be tasted (cf. 359); solids 

 cannot get to the afferent 

 taste neurons. Some parts 

 of the tongue are much more 

 sensitive to taste than others, 

 and different parts of the 

 tongue : recognize different 

 tastes. There are sweet and 

 bitter tastes, sour and salty 

 tastes, and combinations of 

 these. Some of the nerves 

 of taste end in special struc- 

 tures called taste buds. F j g ' 297 V 



The Tongue, showing Taste Papillae. 



The "buds" contain little 



cavities that open into the mouth; in the openings of the 

 cavities the "taste cells" come into very close contact 

 with the food solution. 



The sense of taste can be greatly developed by use. Professional 

 "tasters" of tea, coffee, foods, etc., become very skillful. A good 

 sense of taste is a valuable protection to us, for it enables us to judge 



