DIGESTION OF FOOD: THE MOUTH 



79 



Opening 



structure, growing up from shallow pits in the tongue's surface- 

 More numerous than these and scattered over the remainder 

 of the tongue are two types, the filiform and the fungiform 

 papillae. As the terms indicate, the former are slender and 

 thread-like; the latter are short, pillar-like growths. In the 

 tissues of the circumvallate and fungiform papillae are located 

 the organs of taste, the so-called taste buds. The cells making 

 up these buds are elongate, arranged in a more or less spherical 

 mass. The cells in the middle of this mass come close to the 

 surface and are affected by the 

 food which touches them; Fig. 39. 

 From them the stimulus passes 

 through nerves to the brain. 



There is a kind of taste geog- 

 raphy mapped out on the tongue's 

 surface. Bitter tastes are noticed 

 at the back of the tongue, acid on 

 the sides, salt and sweet toward 

 the front. None of these tastes can 

 be perceived if the tongue be wiped 

 dry. In other words, all material 

 to be tasted must be in solution. 1 

 Electric stimuli applied to the 

 tongue produce the same impres- 

 sion as dissolved foods. Thus 

 arises the popular contention that 

 electricity is sweet, for the wires are usually applied to that 

 portion in which the sweet-perceiving nerve endings are 

 located. 



The Palate. The roof of the mouth toward the front is 

 called the hard palate and contains a bony partition between 

 the mouth and nose chambers. This bony partition, however, 

 soon ends, and the palate continues backward toward the 

 throat as a soft membrane; Fig. 40. This soft palate extends 



1 Students should prove these statements by experiments at home. 



FlG. 39. A TASTE BUD FROM 



THE TONGUE 



Highly magnified, showing the 

 taste cells. 



