342 APPLIED PHYSIOLOGY 



Eyes may become sore and run matter ; or pimples may come on 

 the edges of the lids. The soreness is usually caused by disease germs 

 which enter the eye with dust and dirt. Some eye diseases are caused 

 by using towels or handkerchiefs on which other persons have wiped 

 their sore eyes, or by rubbing the eyes with dirty fingers which have 

 touched the matter from the sore eyes of another person. Babies often 

 have sore eyes because their eyes are not kept clean, or because flies 

 are allowed to crawl over them. We should wash our eyes with clean 

 water as often as we wash our faces, and should remove all scales and 

 dried matter from the edges of the lids. If the eyes are red and tender, 

 they should be washed with boiled water to which borax has been added, 

 so as to kill the germs. In granulated lids the conjunctiva becomes 

 red and roughened. A dangerous form of granulated lids, called 

 trachoma, is catching, and often spreads among school children. Every 

 person who has trachoma should be required to take treatment so as to 

 prevent the spread of the disease. 



623. Illusions of sight. Irritating the optic nerve ex- 

 cites the sensation of light. A blow upon the head causes 

 a sensation of seeing bright stars. Pressure upon the 

 eyeball causes a sensation of a ring of light. 



In dreams, sight memories return to consciousness with 

 all the vividness with which they were first made. A 

 crazy man may imagine the face of the clock to be a man's 

 face mocking him, and so he may attack and destroy it. 

 To insane persons of a religious turn of mind, a cloud 

 may seem to be an angel urging them on to some inspired 

 mission. 



624. Effects of alcohol and tobacco. Alcohol weakens 

 the optic nerves, and tends to cause dimness of vision 

 while the eyes may appear healthy. Tobacco has a still 

 greater effect upon the optic nerve. 



625. X rays. In December, 1895, a kind of light pro- 

 duced by electricity was discovered which can penetrate 

 wood, flesh, and other substances. By means of it photo- 

 graphs can be taken. Although it makes no impression 



