THE SENSE OF HEARING. 389 



might thus be termed sense organs for the perception of noises. Evidence 

 will be adduced later (p. 407) for the belief that they are peripheral organs 

 for the preservation of static equilibrium. 



The hair-cells on the crista? of the ampullae of the semicircular canals seem 

 to have a special function in giving rise to sensations caused by changing the 

 position of the head ; they thus are organs concerned with the preservation of 

 the equilibrium of the body. 



Judgment of Direction and Distance. — The distance and direction from 

 which sounds come to the ear are not perceived directly, but our estimate of 

 them is a judgment based on the loudness and quality of the sound sensation, 

 combined with a power of reasoning from past experience. Thus, in seeking to 

 discover the direction whence a sound comes, it is usual for an observer to turn 



Fig. 197.-End-bulbs from human conjunctiva (from Quain, after Lonfrworth) : a, ramification of nerve- 

 fibres in the mucous membrane, and their termination in end-bulbs, as Been with a Lens; B, end-bulb, 

 highly magnified; a, nucleated capsule; b, core, the outlines of its component cells not seen; c, entering 

 nerve-fibre branching, its two divisions to end in the bulb at d. 



the head to the position in which the sound is heard loudest, and thus to form 

 an opinion as to the direction whence it comes. Errors of judgment as to the 

 direction are frequent, owing to the sound reflected from some object appearing 

 louder than that coming in a direct line from its source. It is said that when 

 there is total deafness in one ear every sound seems to have Its origin on the 

 side of the healthy ear. When the eyes are closed, sounds originating in 

 the median plane of the head are very imperfectly localized, but tend to be 

 projected upward, and somewhat in front, since this is the space from whirl) 

 most sounds come to us. 1 The quality as well as the loudness of a sound varies 

 according to the distance of its source. Thus the lower tones die away earliest 

 as a sound recedes, bringing the overtones into undue prominence. The art ot 



1 Seashore: hoc cit. 



