EAR. 387 



ighted apartments, counting-rooms, houses and shops in dark 

 alleys, or with insufficient windows, weaken the vision of 

 those who study, write, or work in them. 



907. The eyes suffer from protracted exertion in the same 

 way as the brain and the muscles. They become wearied, 

 and even sometimes disordered, from looking long at objects 

 that require minute attention, as reading fine print, engraving, 

 miniature portrait painting, sewing, &c. Those who are 

 employed in such things would do well to give their eyes 

 change of occupation and rest. 



EAR. 



CHAPTER XVIII. 



Composition. External Ear. Position. Not to be covered. 

 Ear- Wax. Membrane of the Tympanum. Eustachian Tube. 

 Bones of the Ear. Labyrinth. Nerve. Requisites of hearing. 

 Air. Healthy Ear. Attention. Deafness. Causes. Hear- 

 ing may be cultivated. Ear for Music. 



908. THE organ of hearing includes the external ear, which, 

 is on the outside of the head, the passage to the tympanum or 

 drum, and the internal ear, which is within the drum. 



909. The outer ear is composed principally of a somewhat 

 stiff cartilage, that retains it in its shape. 



The shape of the outer ear is that which is best adapted to 

 catch sounds and transmit them to the internal ear. This 

 form has been adopted by skilful mechanicians, to gather 

 sounds in rooms and transmit them to other and distant 

 places. 



The ears of the lower animals are differently shaped, accord- 

 ing to their different purposes. The human ear is scarcely 

 movable ; but, in some other animals it is moved to catch 

 rounds in different directions. 



