THE SENSE OF HEARING. 



227 



by placing his little finger in his ear, and then opening and 

 closing the mouth. This is, no doubt, one reason why a 

 person stands with his mouth open when he is listening at- 

 tentively. This tube being constantly open, is liable to the 

 entrance of foreign bodies, such as dust, insects, and the 

 like. But, like the eye, it is not left without means of de- 

 fence, for on its inside, there are numerous fine bristles, 

 which interlace and prevent the entrance of any thing but 

 sound ; while between the roots of these hairs, there are 

 numerous little glands, which secrete a nauseous bitter wax, 

 which by its ofFensiveness, either deters insects from enter- 

 ing, or if they do, entangles them, and thus prevents any 

 further advance. This wax often becomes hard, and ob. 

 structs the tube, causing more or less deafness. This form 

 of deafness is easily cured, although it may have existed 

 even for years. When the ear is dry, from a deficiency of 

 wax, the hearing also becomes imperfect, as also when it ia 

 thin and purulent^ 



Fig. 2. 





General sectional view of the structure of the ear ; a, th? meatus 



