VISION. 223 



) Pur kinje- Sans orfs images. 



(6) In a dark room, light a candle and hold it to one 

 side of the observed eye and on a level with it. Ask 

 the person to accommodate for a distant object, and 

 look into his eye from the side opposite to the candle, 

 and three reflected images will be seen. At the 

 margin of the pupil, and superficially, one sees a small 

 bright erect image of the candle flame reflected from 

 the anterior surface of the cornea. In the middle of 

 the pupil there is a second less brilliant and not 

 sharply defined erect image, which, of all the three 

 images, appears to lie most posteriorly. It is reflected 

 from the anterior surface of the lens. The third image 

 lies toward the opposite margin of the pupil, is the 

 smallest of the three, and is a sharp inverted image, 

 from the posterior surface of the lens. Ask the person 

 to accommodate for a near object, and observe that 

 the pupil contracts, and the middle image that from 

 the anterior surface of the lens becomes smaller and 

 comes nearer to the corneal image. This shows that 

 the anterior surface of the lens undergoes a change in 

 its curvature during accommodation. 



(7) Place in a convenient position on a table a large 

 convex lens, supported on a stand. Standing in front 

 of it, hold a watch glass in the left hand in front of 

 the lens and a few inches from it. Move a lighted 

 candle at the side of this arrangement, and observe 

 the three images described above. Substitute a con- 

 vex lens of shorter focus, and observe how the images 

 reflected from the lens become smaller. [Practical 

 Physiology Stirling.] 



(8) Explain the phenomena, using drawings. 

 The blind spot. 



(9) Marriotte's experiment. On a white card make a black 



