File:A treatise on physiology and hygiene for educational institutions and general readers (1884) (14590525397).jpg

Identifier: treatiseonphysi00hutc (find matches)
Title: A treatise on physiology and hygiene for educational institutions and general readers ..
Year: 1884 (1880s)
Authors: Hutchison, Joseph C. (Joseph Chrisman), 1822-1887
Subjects: Physiology
Publisher: New York, Clark & Maynard
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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of Breslau, published theresults of the examination of the eyes of 10,060 scholars. His examinationscovered the entire range of school-life. He found that 1,750 of the 10,060children had defective vision—about seventeen per cent. He also examined,without selection, 410 of the 964 students of the Breslau University, and foundthat not one-third had normal eyes.—Dr. C. R. Agnew. 82. What is stated in connection with the opera-glass ? Experiment with pencil and dis-tant object? 83. Function of accommodation? In what does it consist? How is the functionexplained ? THE SPECIAL SENSES. 25i own elasticity, and partly through the action of the ciliary muscle.When the eye is at rest—that is, when accommodated for a distantobject—the lens is flatter and its curvature diminished (see Fig. 62) ;but when strongly accommodated for near vision, the lens becomesthicker, its curvature increases, and the image on the retina is mademore sharp and distinct. Since a strong light is not required in
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Fig. 62.—The Function of Accommodation. The right half of the diagram shows the eye at rest. The left half shows the lensaccommodated for near vision. viewing near objects, the pupil contracts, as is shown in the left-hand half of the diagram. 84. Old-sight, OP Presbyopia.—But this niarvelously beautifulmechanism becomes worn with use: or, more strictly speaking, thelens, like other structures of the body, becomes harder with the ap-proach of old age. The material composing the lens becomes lesselastic, the power to increase its curvature is gradually lost, and as aconsequence, the person is obliged to hold the book further awaywhen reading, and to seek a stronger light. In a word, the functionof accommodation begins to fail, and is about the first evidence thatmarks the decline of life. By looking at the last preceding dia-gram, and remembering that the increased curvature of the lenscannot take place, it will be at once understood why old-sight isbenefited in near vision by the

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