ORGANS OF SPECIAL SENSE THE EYE 350 



that which is sensitive to green, but smaller than that which is 

 sensitive to violet. Physiologists claim that red, green and 

 violet are the only colors perceived by the eye, and that other 

 colors are seen when two or more of these colors are stimulated 

 at the same time, in different degrees. 



Color blindness is a more common defect than is supposed. 

 It consists in inability to see any difference between two 

 colors which seem to most people very unlike and distinct. 

 The most common kind is that in which a person is unable to 

 distinguish between red and green. To such a person the 

 only difference between red apples and green leaves on the 



ime tree would be merely a difference in shape and brightness. 

 If one accepts the theory that the eye perceives only red, 

 jn and violet, then red color blindness would be explained 

 supposing that the red sensations were only imperfectly 

 leveloped, or perhaps altogether lacking. 



Persons who are color blind cannot obtain employment on 

 railroads or ships, for in such positions it is absolutely neces- 

 sary that one see clearly both red and green, since flags, 

 lights etc., used as signals are generally of these colors. 

 There is no known remedy for this defect. 



CARE OF THE EYES 



Probably no defects are so apt to escape attention and 

 proper treatment as imperfections in the eyes. Even in 

 cases where the eye is very defective, one may see fairly well 

 and so neglect to attend to the matter. The result is that 

 some part of the eye may be in a condition of strain, trying to 

 force the refractive surfaces into shape to produce a proper 

 focus upon the retina. This strain brings on fatigue of the 

 delicate muscles themselves and exhaustion of the nerves 

 that may lead to serious results, e. g. headaches, indigestion, 

 nausea and various nervous diseases. Any one of these out- 

 comes is sufficient practically to disable a person for hard 

 work and to cloud living with continuous pain. The mental 



