THE SENSE OF SIGHT. 299 



towel. By not observing this rule certain contagious dis- 

 eases of the eyes often spread rapidly. 



13. Consult a Reliable Oculist. If there is any con- 

 tinuous trouble with the eyes, consult a reliable oculist. 

 Many headaches are due to eye-strain, the real cause being 

 unsuspected. If a child has frequent headaches, it is well 

 to have the eyes examined. Many persons injure their 

 eyes by not wearing suitable glasses. On the other hand, 

 do not buy glasses of peddlers nor of any but reliable 

 specialists. One may ruin the eyes by wearing glasses 

 when they are not needed. Sight is priceless. 



Effects of Alcohol and of Tobacco on Sight. Impaired 

 vision is a frequent result of the use of either tobacco or 

 alcoholic drink, of tener of both combined. A peculiar dis- 

 ease known as the " cigarette eye " has been described as 

 a dimness and film-like gathering over the eye, which ap- 

 pears and disappears at intervals. It can only be cured by 

 long treatment and entire disuse of tobacco. The Belgian 

 government once made an investigation into the cause of the 

 prevailing color-blindness, and the testimony of experts was 

 that the use of tobacco was one of the principal causes. 



READING. Sight, Le Conte. 



Summary. I . Sight, like hearing, acts through space, outstripping 

 the "contact senses" of touch, taste, and smell. 



2. The eye is protected by its bony surroundings, lids, lashes, tears, 

 sensitiveness of the conjunctiva, etc. 



3. The eye is moved by muscles under nerve control. 



4. The eye has three coats, sclerotic, choroid, and retina. 



5. The pupil is a hole in the iris, and varies in size to regulate the 

 amount of light admitted. 



6. The refracting media of the eye are the cornea, aqueous humor, 

 lens, and vitreous humor. 



