418 BIOLOGY FOR BEGINNERS 



lined with a complicated set of nerve endings, which receive the 

 sound impressions. The semicircular canals, three in number, are 

 little loop-shaped tubes each at right angles to the other, and 

 have to do with maintaining the balance of the body. 



How We Hear. When a person speaks to you, he starts certain 

 air waves which are gathered in by the external ear, and conveyed 

 to the tympanum, which is thus made to vibrate. By means of the 

 bones of the middle ear, this vibration is communicated to the 

 fluid in the inner ear, and this in turn acts upon the nerve endings 

 of the cochlea. This disturbance of the nerve endings is trans- 

 mitted to the brain by way of the auditory nerves and we hear the 

 sound of words. 



The human ear can distinguish vibrations varying from sixteen 

 to forty thousand per second, but we have reason to believe that 

 insects can hear sounds of higher pitch. 



Care of the Ears. Fortunately this delicate and important 

 organ is deeply imbedded in the skull where little harm can reach 

 it, but care must be observed not to injure the tympanum by 

 probing with hard implements, ear spoons, etc., when trying to 

 clean the ear. In this connection it has been said that one ought 

 never to explore their ears with anything sharper than their elbow. 



Ear wax has a useful function in keeping out dirt and insects, 

 and excess can be properly removed by ordinary washing. Foreign 

 bodies should be washed out and never removed by " poking " 

 with hairpins and other implements. Water which .enters the 

 ears in diving does no harm, and can easily be shaken out. 



Ear ache or a discharge from the ear may indicate a serious con- 

 dition and should have immediate attention from a physician. 

 The brain and ear cavities are very close together at one point, 

 so that inflammation of the ear may reach the brain with fatal 

 results. 



. Temporary deafness may be caused by inflammation of the 

 eustachian tubes as a result of a cold. Permanent deafness may 

 be caused by a blow on the ear bursting the tympanum, or by 

 disease of the middle or inner ear. It is always a serious matter 

 and should never be treated by advertising quack doctors, whose 



