EXERCISES 423 



In near-sight the light rays are brought to a focus too far in front 

 of the retina. The remedy is concave glasses. 



In far-sight the light rays are not brought to a focus at all. The 

 focus would be behind the retina, if this were possible. The remedy 

 is convex glasses. 



The eyes should not be strained by being used in too bright a light, 

 too dim a light, or in awkward positions. If defective, they should be 

 cared for by a competent oculist. 



420. Exercises. 



1 . Name as many sensations as you can, and tell what impulses 

 produce them. 



2. "Saccharine" is a white solid having several hundred times the 

 sweetening power of sugar. A tiny amount, placed on the tongue, is 

 sweet; a larger amount is intensely bitter. Can you suggest a 

 reason? 



3. How would you set about cultivating your sense of smell, so 

 as to make it acute? What do you think would happen in the 

 olfactory cells, if you were to do this? In the brain? 



4. Name the organs through which a sound must travel before it 

 reaches the auditory nerve. 



5. Stand before a mirror, in the dark, for a minute, and then sud- 

 denly turn on a light; what is the condition of the pupils of your eyes? 

 What happens as the light shines into your eyes? Tell why we are 

 dazed when we first come from the dark into a bright light. Why can 

 we not see so well when we first go into a dark room as we can after we 

 have been in it for a time? 



6. Name all the structures through which a ray of light must go to 

 reach the optic nerve. 



7. Read about the "compound" eyes of insects, and describe 

 them. 



8. If it is true that the image on the retina is inverted, why do we 

 not see objects upside down? 



9. A fly held near the eye looks as large as a man who is down the 

 street; how do we know it is not really as large? 



