An American Text-Book of Physiology Volume 2

An American Text-Book of Physiology Volume 2

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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1901 edition. Excerpt: ...for distance--let the person who is under observation be now requested to direct his eye to a near object lying in the same direction. When this is done the corneal image and that reflected from the posterior surface of the lens will remain unchanged,1 1 A very slight diminution in size may sometimes be observed in the image reflected from the posterior surface of the lens. while that reflected from the anterior surface of the lens will become smaller and move toward the corneal image. This change in the size and position of the reflected image can only mean that the surface from which the reflection takes place has become more convex and has moved forward. Coincident with this change a contraction of the pupil will be observed. An apparatus for making observations of this sort is known as the phakoscope of Helmholtz (Fig. 130). The eye in which the changes due to accommodation are to be observed is placed at an opening in the back of the instrument at C, and directed alternately to a needle placed in the opening D and li to a distant object lying in the same direction. Two K prisms at B and B' serve fo throw the light of a candle on to the observed eye, and the eye of an observer at A sees the three reflected images, each if' as w0 sma scluare spots of light. The movement and the change of size of the image reflected from the anterior surface of the lens can be thus much better observed than when a candle-flame is used. The course of the rays of light in this experiment is shown diagrammatically in Figure 131. The observed eye is directed to the point A, while the candle and the eye of the observer are placed symmetrically on either side. The images of the candle reflected from the various surfaces of the eye will be seen projected on the dark...show more

Product details

  • Paperback | 312 pages
  • 189 x 246 x 17mm | 558g
  • Rarebooksclub.com
  • Miami Fl, United States
  • English
  • black & white illustrations
  • 1236543114
  • 9781236543110