200 ANATOMY AND PHYSIOLOGY. 



the mouth. A large proportion, however, of the feelings conveyed 

 by the tongue, are little more than different degrees of pungency, 

 which we may almost conceive capable of being felt by the ends of 

 the fingers, had their cuticle been fine enough. The flavor of 

 bodies, generally included when we speak of their taste, is a sensa- 

 tion entirely owing to the action of their vapor on the back part of 

 the nostrils ; so that, when the membrane that lines these is inflamed, 

 pr otherwise diseased, whiskey, vinegar, mustard, and many other 

 substances, can with some difficulty be distinguished from each 

 other. Any onre may easily satisfy himself of the indefinite nature 

 of the sensation of taste, by pushing out the tongue, accurately 

 closing the mouth and nostrils, and then applying it to different 

 substances. 



In the savage state, the sense of smell is much used, and becomes 

 proportionately acute. The American Indians, it is said, can 

 easily distinguish different tribes and nations by the odor of their 

 bodies. The blind and deaf boy, James Mitchell, whose history 

 has" been recorded by Mr. Wardrop and Professor Dugald Stewart, 

 knew his friends, and at once detected strangers in a room by this 

 sense. 



These senses are very acute in some of the lower animals, and 

 particularly in the carnivorous Vertebrata. The olfactory nerves 

 of most birds are small. In the duck and similar tribes, however, 

 they are large, and are much used. The nostrils of fishes do not 

 communicate with the mouth, and smell becomes with them more 

 like taste, from the substance being dissolved in water instead of 

 air. 



HEARING. 



The sense of hearing results from vibrations in an elastic sub- 

 stance, such as air or water, being communicated to the ear. When 

 a bell is shaken in the exhausted receiver of an air-pump, no sound 

 is heard, because the air which usually carries the vibrations to the 

 ear is absent. Sound travels through the air at the rate of about 

 twelve and a half miles in a minute ; through water its velocity is 

 four or five times greater ; and ice and other solid bodies are known 

 to transmit it even more quickly. 



. The organ of hearing in man may be divided into external, mid- 

 dle, and internal parts. The external consist of the gristle of the 

 ear (c), of use in most animals for collecting the sounds ; and of a 

 funnel-shaped canal (m), which leads to the middle part or drum (t). 



