134 CONSCIOUS NERVOUS OPERATIONS 



but our judgment as to position in space of sound-pro- 

 ducing bodies, and of directions of sound, are indirect and 

 not always reliable. 



181. Differences in Sound Perception. The ears of differ- 

 ent persons vary greatly in power to distinguish differ- 

 ences in sound and in pitch, or the number of vibrations 

 in a given time. All are limited in the perception of 

 high-pitched notes. The ear may become wearied in 

 respect to sound of a particular pitch, much as the eye is 

 soon fatigued in respect to a particular color. 



182. Care of the Ear. A cold which causes inflamma- 

 tion of the throat often affects the lining membrane of 

 the Eustachian tube and that of the middle ear, causing 

 temporary partial deafness. If the cause often recurs, 

 one or both ears may be permanently impaired. Some- 

 times repeated attacks of inflammation in the ear as 

 from abscesses result in perforation of the membrane 

 of the tympanum and great injury to the hearing. 



Generally the wax which is secreted in the external 

 canal of the ear needs no attention, and should not be 

 picked out. Occasionally, however, it accumulates and 

 hardens upon the membrane of the tympanum so as to 

 interfere with its vibrations and impair the hearing. In 

 such a case it should be removed by a surgeon. 



Warm or tepid water should be used for washing the 

 ears never very cold water. Before going to baths 

 in cold water or in salt water the ears should be filled 

 with soft absorbent cotton. 



A sudden very loud noise, as from a gun or cannon, 

 has been known to rupture the eardrum, and a sudden 

 shout close to a child's ear has been known to make it 

 deaf. Insects sometimes crawl into the canal of the ear, 

 in spite of the wax and the hairs there which usually 



