118 PHYSIOLOGY FOR THE LABORATORY. 



II. THE IMAGE ON THE RETINA. 



Materials. The eye of an albino rabbit. Care should be taken to 

 have it freshly excised, with the cornea still clear, or the experiment 

 will fail. A piece of black paper about six inches square. A candle. 



Roll the black paper into the form of a tube, and place 

 the rabbit's eye in it with the cornea directed forwards. 

 Hold the eye in front of a candle-flame, and look for the 

 image of the flame shining through the retina, choroid, and 

 sclerotic coats. Move the flame and watch the image. 



D. Accommodation. 



Close one eye and hold up both forefingers, the one 

 about six inches, the other about eighteen inches, from 

 the open eye. Look steadily at the nearer finger. Is the 

 image of it clear or indistinct? Do you see clearly the 

 finger farther away ? Look steadily at the finger farther 

 away. Is its image distinct? How is the image of the 

 nearer finger? Can you focus on the nearer finger with- 

 out an effort? 



E. Defects in Vision. 



Materials. Siiellen's cards of test-types including the card for 

 astigmatism. 



I. NEAKSIGHT AND FABSIGHT. 



With the aid of Snellen's test-types, examine your 

 own eyes and determine if they are normal. You should 

 be able to read type of this size ^ at a distance of 

 sixteen feet. ^ 



What is nearsightedness, or myopia ? What is farsight- 

 edness, or hypermetropia ? How may each be corrected 

 by the use of glasses? 



