348 ELEMENTS OF PHYSIOLOGY 



solids in the middle ear, and liquids in the inner ear. The 

 vibrations of the liquid start nerve impulses in the fibers 

 of the auditory nerve, and when these impulses are re- 

 ceived and interpreted in the brain, 

 the miracle of the conversion of 

 the external sound wave into the 

 sensation of sound is complete. 



628. The Equilibrium Sense. 

 It is now believed that the semi- 

 circular canals of the inner ear 

 FIG. 226. The inner Ear, or are not concerned in hearing. The 

 Labyrinth. weight of the liquid they contain 



g t vestibule; /", snail shell; k, semi- .-i ^-i 



circular canals. pressing Upon the HQVVQ fibers 



located in them and exerting a 



varying pressure according to the position of the body, 

 gives us the "equilibrium sense," which enables us to know 

 the position of the body at all times, that we may preserve 

 its equilibrium. Sight and the muscular sense also prob- 

 ably contribute to maintain the equilibrium. 



629. Care of the Ear. The meatus is self-cleansing ; 

 the wax changes into dry scales, which fall out. The 

 external ear should be washed, but when we reach the 

 passage, we should go no deeper than we can easily reach 

 with the tip of the finger covered with a damp cloth ; espe- 

 cially the finger should not be forced into the tender ears 

 of children. A blow with the flat hand upon the ear may 

 force the air in and injure the tympanum. Picking the ear 

 with hard or sharp objects is dangerous to the tympanum. 



630. Sometimes the wax collects in a lump near the 

 drum, causing deafness. The remedy is to syringe the 

 meatus with warm water until the lump is softened and 

 comes away. The bitter wax is a protection against 

 insects. Quinine often does great damage to the hearing. 

 Chronic cold in the throat reaching the ear through the 

 Eustachian tube sometimes injures the hearing. 



