264 THE WONDERFUL HOUSE THAT JACK HAS 



canal grows outward, carrying with it any worn-out 

 skin and superfluous earwax. Consequently, the ordi- 

 nary daily washing of the auricle and the outer opening 

 of the auditory canal is sufficient. Trying to swab or 

 dig out more of the wax may do injury by packing it in 

 or by wounding the drumhead. The auditory canal is 

 slightly curved. On this account an insect or a flying 

 missile cannot go straight against the drumhead. 



The latter is the partition between the auditory 

 canal and the middle ear or drum, and is commonly 

 spoken of as the "ear-drum." However, it is no more 

 entitled to that name than is a part of anything to be 

 called by the name of the whole. The drumhead is 

 circular, about one-fourth of an inch in diameter, and 

 extremely thin. The cavity of the middle ear or drum 

 is about half an inch in height and width, and from one- 

 twelfth to one-sixth of an inch deep. It contains the 

 three tiniest bones of the body, which join together so 

 as to form a chain or bridge from the drumhead to the 

 inner ear. In the front part of the drum cavity is an 

 opening into a little passage, called the Eustachian 

 tube, leading to the throat. This tube is of great im- 

 portance, for through it the middle ear gets its supply 

 of air. The inner ear is a shell-shaped hollow in one 

 of the bones of the skull. It contains a fluid and has 

 a lining from which float delicate nerve endings. 



Now let us consider how we hear. When anything 

 has been set into vibration, at a certain rate of rapidity, 

 waves of sound travel from it just as ripples of water 



