358 BODY CONTROL AND HABIT FORMATION 



Taste Cells 



^Supporting 

 ' Cells 



c 



A, isolated taste bud, 

 from whose upper free 

 end project the ends of 

 the taste cells ; B, sup- 

 porting or protecting 

 cell ; C, sensory cell. 



Taste Organs. — The surface of the tongue is folded into a number of 

 Httle projections known as papillae. These may be more easily found on 

 your own tongue if a drop of vinegar is placed on its broad surface. In the 



folds, between these projections on the top and 

 back part of the tongue, are located the organs of 

 taste. These organs are called taste buds. 



Each taste bud consists of a collection of 

 spindle-shaped neurones, each cell tipped at its 

 outer end with a hairlike projection. These cells 

 send inward fibers to other cells, the fibers from 

 which ultimately reach the brain. The sensory 

 cells are surrounded by a number of projecting 

 cells which are arranged in layers about them. 

 Thus the organ in longitudinal section looks 

 somewhat like an onion cut lengthwise. 



How we Taste. — Four kinds of substances 

 may be distinguished by the sense of taste. These 

 are sweet, sour, bitter, and salt. Certain taste cells located near the 

 back of the tongue are stimulated only by a bitter taste. Sweet sub- 

 stances are perceived by cells near the tip of the tongue, sour substances 

 along the sides, and salt about equally all over the surface. A substance 

 must be dissolved in fluid in order to be tasted. Many things which 

 we beheve we taste are in reality perceived by the sense of smell. Such 

 are spicy sauces and flavors of meats and vegetables. This may easily 

 be proved by holding the nose and chewing, with closed eyes, several 

 different substances, such as an apple, an onion, and a raw potato. 



Smell. — The sense of smell is located in the membrane hning the upper 

 part of the nose. Here are found a large number of rod-shaped cells wliich 

 are connected with the brain by means of the olfactory nerve. In order 

 to perceive odors, it is necessary to have them diffused in the air ; hence 

 we sniff so as to draw in more air over the olfactory ceUs. 



The Organ of Hearing. — The organ of hearing is the ear. The outer 

 ear consists of a funnel-like organ composed largely of cartilage which is 

 of use in collecting sound waves. This part of the ear incloses the audi- 

 tory canal, which is closed at the irmer end by a tightly stretched mem- 

 brane, the tympajiic membrane or ear drum. The function of the tym- 

 panic membrane is to receive sound waves, for all sound is caused by 

 vibrations in the air, these vibrations being transmitted, by the means 

 of a comphcated apparatus found in the middle ear, to the real organ of 

 hearing located in the inner ear. 



