How to keep well : a text-book of health for use in the lower grades of schools with special reference to the effects of alcholic drinks, tobacco and other narcotics on the bodily life . nking, protect the eyefrom insects and from dust. They are fringed with thedelicate hairs of the eyelashes, which are so sensitivethat the slightest touch gives warning, and the lidsclose. By means of little muscles the eye is moved up anddown, or rolled sideways. Sometimes these musclesdo not act properly; then the person is said to squint,or to be cross-eyed. At the upper and outer side of each eye is a litt
How to keep well : a text-book of health for use in the lower grades of schools with special reference to the effects of alcholic drinks, tobacco and other narcotics on the bodily life . nking, protect the eyefrom insects and from dust. They are fringed with thedelicate hairs of the eyelashes, which are so sensitivethat the slightest touch gives warning, and the lidsclose. By means of little muscles the eye is moved up anddown, or rolled sideways. Sometimes these musclesdo not act properly; then the person is said to squint,or to be cross-eyed. At the upper and outer side of each eye is a littlegland which is constantly forming a saltish kind offluid. Sometimes more of this fluid comes out of thelittle gland than can be carried away through the nose,and it flows over the eyelids down the cheeks, and iscalled tears. THE FIVE GATEWAYS OF KNOWLEDGE 163 Tears are constantly passing over the front of theeye, washing it clean, and keeping it moist; while theeyelid wipes it dry, as it were, by forcing the tears intoa little drain-pipe, which carries them off into the , however, kindly oils the edges of the eyelids,to prevent, to some extent, the overflow of 52. — Muscles of EyebalL 130. Color-Blindness.—Color-blindness is the in-ability to tell certain colors. It is sometimes producedby sickness, but generally exists at birth. This defectof sight is quite common. It is found that four or fiveout of every hundred people are color-blind. A personmay be color-blind, and not know it until the defect isaccidentally revealed, or a special test is made. It is a matter of the utmost practical importance tothose employed on railroads, vessels, and, other placeswhere colored signals are used. Some are only partiallycolor-blind, while others are wholly so. The mostcommon form of color-blindness is that in which onefails to distinguish red. 164 HOW TO KEEP WELL 131. How to take Care of the Eyes. — The eye is an exceedingly delicate and sensitive organ. I
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