File:Physiology, hygiene and sanitation, an elementary textbook of physiology, with special attention given to hygiene and sanitation (1919) (14578761697).jpg

Identifier: physiologyhygien00heiz (find matches)
Title: Physiology, hygiene and sanitation, an elementary textbook of physiology, with special attention given to hygiene and sanitation
Year: 1919 (1910s)
Authors: Heizer, W. L. (W. Lucien), b. 1880
Subjects: Physiology Hygiene Sanitation
Publisher: Louisville, Ky., C.T. Dearing Printing Co., Incorporated
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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Eye Strain is the result of too long continued use ofthe eyes, or their use in a poor light, or while facing toostrong light. Reading on a train or in an automobile isinjurious because themotion of the car causesvarying distances be-tween the objects andthe eye, and the delicatemuscles of the lens areconstantly at work andon a strain to keep theimages properlyfocused. When a long periodis needed for work withthe eyes, it is wise torest for a few minutesso the muscles of theeye may relax and beready to resume workwith less fatigue. Read-ing while lying down isinjurious because toomuch blood flows to the head and the eyes become red-dened and eye strain with headache frequently results. Cross Eyes are sometimes due to a defect causing near-sight or farsight in one eye or the other. In such casesglasses fitted early may cause the eyes to become straight.In some cases it may become necessary to have a surgeonoperate upon the eye so that the muscles may pull theeye to its proper position.
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Fig-. 150.— Testing- the eye for defectsby reading- letters twenty feet dis-tant. 298 PHYSIOLOGY, HYGIENE AND SANITATION Summary The loss of the sense of sight is so terrible that greatcare should be used to protect its organs, the eyes, frominjury. The eyelids with their hairs and the tears protect theeyeball from foreign bodies. The eye is almost a sphere and moves freely by theaction of its six muscles in its bed of fat, muscles, andconnective tissue. The cornea is the transparent windowin front through which the iris and its opening, the pupil,may be seen. The lens is transparent, and is so arranged that by theaction of its controlling muscles, it may change its shapeto bring the rays of light to a focus on the retina or nerveof sight in the back of the eyeball. The chamber backof the lens is filled with vitreous humor. Sight is a sensation perceived in the brain when its cellsare stimulated by impulses coming through the opticnerve from its end in the retina which has been stim

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