VISION 499 



VISION 



Mapping the Blind Spot. Fasten a rod fifteen 

 inches from the table. Beneath the rod place 

 a well-lighted sheet of wnite paper (a page of 

 the laboratory note-book will serve). Make a 

 small black cross near the left margin. Eest 

 the chin upon the rod in such a way that the 

 right eye shall look directly down at the cross. 

 Place the hand over the other eye. A straw 

 bearing a black pin-head will be drawn by an 

 assistant from the cross along the horizontal 

 meridian toward the temporal side of the eye 

 under observation. The assistant will mark the 

 point where the black object ceases to be visible, 

 and the point at which it reappears. These are 

 the boundaries of the blind spot of the right 

 eye in the horizontal meridian. Determine the 

 boundaries in other meridians. Obtain similarly 

 the outlines of the blind spot of the left eye. 



Yellow Spot. Close the eyes for half a 

 minute, and then look at the clear sky or a 

 brightly lighted surface through a solution of 

 chrome alum in a glass bottle with parallel 

 sides. The yellow spot will appear rose-colored 



