Sight is one of the greatest blessings we have. Think how dreadful it is to be blind. If you take care of your eyes, there is no reason why you should be blind; but if you do not take care of your eyes, there is a possibility that you may lose your sight. Most of the blind people in the world became blind because their eyes were not given proper care, and most of this lack of care happened when these people were babies. [Illustration: FIGS. 30 and 31. The roller towel is a common source of infection of eyes in schools; every school should have properly constructed wash-rooms, with individual towels.] [Sidenote: How germs get into the eyes] Many of the diseases that affect the eyes are catching. They are not carried through the air, but are transmitted by the use of a towel or handkerchief used by someone who had the disease. Never use the towel or handkerchief that another has used. Germs may be rubbed into the eyes. Keep your hands away from your eyes. Your hands may have disease germs on them, and when you rub your eyes you may put the disease germs into them. [Sidenote: How eyes are overworked] Many boys and girls ruin their eyes by making them do too much work. They do this by reading in a poor light, by reading where the light strikes into the eyes, or by reading in a bad position, as when in bed or lying down. When you are reading, drawing, or doing any work with the eyes, always have the best light possible, which means that the light should fall on your book or work over your left shoulder. If you are only reading, it does not make much difference which shoulder the light comes over, provided it comes from behind. If you are writing or drawing, and the light comes over your right shoulder, it makes the shadow of your hand fall just where you want to see. [Illustration: FIGS. 32 and 33. Correct positions for reading and writing.] Another way of working your eyes too much is by trying to see when the eyes are not focused right. Sometimes people are said to be near-sighted, because they cannot see very well at a distance. This is due to the fact that the eyeball is too long, so that the lens does not cause the rays of light to focus on the retina. Some people are called far-sighted. This means that they can see well at a distance, but that it is hard for them to see things close to them. Far-sighted children can usually see things near by, but they do this by making the muscle that rules the lens of the eye work too hard. [Sidenote: Method of testing the eyes]