250 



OUR BODIES AND HOW WE LIVE 



The sensations of the tongue are very complex. They 

 are really combinations of the sensations of touch and 

 taste. Strictly speaking, we can tell by the sense of taste 

 only whether anything is bitter, sweet, sour, or salt. We 

 detect the flavor of food and drink by the sense of smell. 



Experiment 71. Wipe the tongue dry and lay on its tip a few 

 grains of granulated sugar. It is not tasted until it is dissolved. 

 Apply a few grains of sugar to the tip, and a few more to the back, 

 of the tongue. The sweet taste is more pronounced at the tip. 



Experiment 72. Prepare a solution of sulphate of quinine by dis- 

 solving a small quinine pill in a tablespoonful of hot water. It is 

 scarcely tasted at the tip, but is tasted immediately on the back part 

 of the tongue. 



343. Smell. The sense of smell is located in the mem- 

 brane which lines the cavities of the nose. This delicate 

 membrane, over which the fibers of 

 the olfactory nerves, or the nerves of 

 smell, are distributed, is kept con- 

 tinually moist by the mucus which 

 it secretes. At the beginning of a 

 cold in the head it becomes dry and 

 swollen, and the sense of smell may 

 be greatly lessened. 



It is in the upper parts of the 

 nasal cavities that the sense of smell 



FIG. 153. Nasal Cavities, is most ^^^ Hence, when we 

 seen from Below. wish to detect a faint odor we sniff 



1 The sense of smell varies very much in different individuals. Among 

 civilized people it is often defective, while in savage races it is notably 

 acute. We are told that the South American Indians can detect the 

 approach of a stranger, even on a dark night, by their sense of smell, and 

 can also tell whether he is white or black. Many animals are more highly 

 endowed with this sense than man. Thus, a dog will smell the footsteps 



