io GENERAL SCIENCE 



Great as the value of a good set of teeth may be in the appearance 

 of a person, their primary purpose is their use for the digestion of food. 

 To go through life with teeth made more or less worthless by neglect 

 in childhood is a serious handicap upon health and length of life. 



THE EYE 



The human eyes when one stands erect command a wide 

 range of vision without turning the head. 



The eye is seldom perfect as an optical instrument. Its 

 defects, even when serious, may often easily be remedied by 

 glasses fitted after an examination of the eye by a competent 

 oculist. The eyes of people whose general health is good 

 give a lifetime of excellent service when they have not been 

 subjected to abuse. It is the utmost folly not to give the 

 eyes intelligent care especially during school days. When 

 once the sight is destroyed a person is shut away from much 

 that is in the world about him. His knowledge then be- 

 comes limited largely to what he can hear and touch. 



To understand how it is that we can know of objects far 

 distant from us, and beyond our reach, requires the study of 

 light as given in Physics. Through the transparent interior 

 of the eyeball light reaches the optic nerve. Its terminal 

 fibres are spread out over the interior of the rear wall of the 

 eyeball and form the retina. 



Any transparent medium with a curved surface is a lens. 

 Those used in telescopes and microscopes, and in spectacles, 

 are of glass. In the eye the soft, elastic crystalline lens 

 serves to form images on the retina just as the lens of the 

 photographer's camera forms an image on the chemically 

 prepared plate. The cornea (kor'-ne-ah) , the vitreous humor, 

 and the aqueous humor of the eyeball also refract light, 

 i.e., bend it from a straight line course as it passes into and 

 then out of them. 



An ample supply of blood is furnished to the eyeball, but 

 the humors, lens, and cornea are nourished without dimming 



