150 THE HOUSE 1 LIVE IN. 



and is represented in the cut by two white 

 lines approaching each other, but not quite 

 coming together. When we look at the eye 

 of a living person, this curtain is sometimes 

 light blue ; in other persons it is gray, hazel or 

 black. When this curtain called the iris is 

 blue, the person is said to have blue eyes ; 

 when black, he is said to have black eyes, &ic. 



The hole in the middle of the iris is called 

 the pupil of the eye. It is larger or smaller in 

 proportion as the iris is shrunk more or less ; 

 for the iris will shrink or contract, a little like 

 the muscles. The greater the light before the 

 eye, the smaller is the pupil. When we are 

 in the dark, it is very large, as if the iris shrunk 

 back in order to let as many rays of light pass 

 through the pupil, to the optic nerve, at the 

 back part of the eye, as possible. 



All the rest of the eye ball, besides the 

 coverings which I have described, consists of a 

 substance which I told you had some resem- 

 blance to the white of an egg, or that ropy but 

 clear fluid in which the yolk swims. Anato- 

 mists, however, say that the greater part of it 

 resembles melted glass, which I suppose few 

 of you have seen ; but as we have called the 



