268 



OUR BODIES AND HOW WE LIVE 



are used. The most common forms of color blindness are 

 those in which one fails to distinguish red from green. 



368. Near Sight. Near sight is a common defect of 

 vision. In the healthy eye the rays of light are brought 

 to a focus on the retina. But in some eyes the image is 

 blurred ; the outer coat bulges backward, making the eye- 

 ball a little too long, thus 

 bringing the rays of light to 

 a focus before they reach the 

 retina. A person is said to 

 be nearsighted because he 

 can see near objects better 

 than those at a distance. 



Nearsightedness may exist 

 at birth and is often heredi- 

 tary. It is sometimes ac- 

 quired by overstraining the 

 eyes in reading too fine print, 

 by reading by a dim or im- 

 perfect light, and in many 

 other ways. This defect is 

 common with those who use 



FIG. 167. Lachrymal Gland and 

 Ducts. 



A, lachrymal gland, the size of a small 

 almond, lodged in the upper and outer 



part of the orbit ; B, lachrymal ducts, their eyes much in reading, 



which form a row >f openings into the writing and studv> Sailors, 

 conjunctival fold. * 



farmers, and others who 

 work outdoors are rarely nearsighted. 



There has been found to be a steady increase of near- 

 sightedness, especially among school children. This defect 

 of vision calls for skillful advice and careful treatment. 



369. Long or Far Sight. A farsighted person is so 

 called because he can see distant objects more easily than 

 those near by. In a long-sighted person the eyeball is too 



