Experimental physiology / by E.A. Schäfer.

  • Edward Albert Sharpey-Schäfer
Date:
1912
Catalogue details

Licence: Public Domain Mark

Credit: Experimental physiology / by E.A. Schäfer. Source: Wellcome Collection.

    114/128 page 102
    EXPERIMENTS ON THE DIOPTRIC MECHANISM / An eye (ox, sheep, or pig) is to be dissected. (1) After cleaning away from the globe all remains of muscles, fat, etc., cut a window out from the back, removing the sclera and choroid and exposing the retina. Notice that when the cornea is turned to the window an inverted image of this is formed upon the retina. (2) Cut away a small portion of the sclera at the edge of the cornea. A grey¬ looking ring of plain muscular tissue is exposed, the fibres passing from the corneo-sclerotic junction backwards over and into the choroid. This is the ciliary muscle. (3) Cut the eye in two at its equator. Notice, in the posterior half, from which the jelly-like vitreous humour flows away, the retina—usually somewhat opaque and crumpled after death—spreading out from the entrance of the optic nerve; in the anterior half the lens within its capsule, the suspensory ligament around the margin of the lens, the radiating ciliary processes. (4) Snip through the suspensory ligament all round the lens, which can be removed within its capsule; the iris is now seen projecting into the anterior chamber. Accommodation; Change in shape of the lens.—That the lens bulges forward in accommodation is shown in various ways. 1. Stand at the side of another person and let him fix his vision on a distant object, looking beyond a near object such as a needle or pencil held a few inches from the eye. Notice his iris which can be seen through the edge of the cornea lying against the front of the lens. Now let the subject look at the near object. His iris is seen to advance, being pushed forwards by the bulging lens ; the pupil at the same time contracts. 2. Sanson’s images.—In a dark room hold a candle at one side of the eye of a subject, and, standing on the other side, observe the reflected images—a bright one from the front of the cornea, a less bright one from the front of the lens, and a duller, small, and inverted image—difficult to see—from the back of the lens. The subject as before is to have his vision fixed at first on a distant object, and is then to transfer his gaze to a near object in the same line. The image reflected from the front of the lens becomes smaller and moves nearer to that reflected from the front of the cornea ; the other
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