File:An elementary physiology and hygiene for use in upper grammar grades (1910) (14802978143).jpg

Identifier: elementaryphysio00conn (find matches)
Title: An elementary physiology and hygiene for use in upper grammar grades
Year: 1910 (1910s)
Authors: Conn, Herbert William, 1859- (from old catalog)
Subjects: Physiology
Publisher: New York, Boston (etc.) Silver, Burdett and company
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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, and the sight be affected.The eyelids, by means of their long lashes and theirexceedingly quick motion, serve also to guard the eyeagainst accident. The hairs on the edges of the lids,called the eyelashes, assist in keeping out the dust. The Tear Gland. — The lids are aided in keeping theeyes clear by the tears. A small lachrymal gland, ortear gland, is lodged just above each eye, on the sideaway from the nose. This gland produces a wateryliquid, which flows down over the eye and keeps itssurface moist. The liquid flows over the eyeball tothe inner edge of the eye near the nose, where there isa tube, the tear duct, leading to the cavity inside thenose, as shown in Figure 72. The tears, after washingthe surface of the eye, pass through the duct into thenose and the throat, and are then swallowed. Usu-ally the gland produces just liquid enough to wash the 216 PHYSIOLOGY AND HYGIENE eyeballs and to pass easily down the lachrymal duct.But when a person cries, the tears are produced so
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Nerve Fig. 73. — The Eye, viewed from the Side.Showing its shape, the socket, and the attachment of muscles. rapidly that they cannot all pass through the duct intothe nose. They then overflow and run down the cheeks. The Eye Muscles. — Six small muscles are attached toeach eyeball to move it. One is on the top, one on thebottom, one on each side, and two others have an obliqueposition. Figure 73 shows the form and position ofthese muscles. By the contraction of the muscles theeyeball can be turned in any desired direction. Structure of the Eyeball. — If we examine a photog-raphers camera, we find that it has three chief parts.There is (1) a dark chamber, the box of the camera,closed so as to admit light only from the front. In theopening in front which admits the light there is (2) alens, which makes an image of the object to be photo- THE SENSES 217 graphed; at the back of the camera is (3) the sensitiveplate, upon which the picture is taken. The human eye is made upon much th

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