452 MAN BECOMES THE CONQUEROR OF THE WORLD 



IV. We see (16) by means of the retina which receives the light 

 images ; (17) in the brain and not in the eye ; (18) because the retina 

 transforms the stimulus caused by the light waves and transmits them 

 by the optic nerve to the brain ; (19) because our eye is like a camera 

 — the eye becoming deeper or more shallow as we focus ; (20) when 

 through a change of shape the lens is focused on an object. 



V. The sense organs of man (21) are the nose, tongue, eyes, and 

 skin ; (22) are all external ; (23) are connected by nerves with the central 

 nervous system ; (24) are made up of sensory cells ; (25) are not deli- 

 cate enough to need protection, and so do not have any. 



VI. Instincts (26) are actions that are performed without having 

 first been learned ; (27) are behaviors which are useful because they 

 help preserve the race; (28) are acts that are carefully thought out 

 before they are performed; (29) may be modified or conditioned 

 through teaching ; (30) serve to avoid dangers. 



VII. Habits (31) may be either harmful or useful ; (32) are learned 

 activities ; (33) may be mental or physical ; (34) make up a large part 

 of our life activities ; (35) cannot easily be learned by young people. 



VIII. The following are good rules for forming desirable habits : 

 (36) never use will power; (37) allow no exceptions to occur; 

 (38) never make a strong start; (39) have a real desire to build the 

 habit ; (40) act on every opportunity to make the desired reaction. 



Achievement Test 



1. How can you demonstrate what a tropism is and how it causes 

 a living thing to react ? 



2. What are the different stimuli that affect the lives of plants and 

 animals ? 



3. What is meant by the method of trial and error? 



4. How can you demonstrate a reflex act? 



5. Locate the parts of your nervous system, and tell the uses of 

 each part. 



6. How do we taste, touch, and feel hot or cold objects? 



7. How do we hear? 



8. How do we see? How can we compare the human eye to a 

 camera ? 



9. How would you define instinct? 



10. Wliat is meant by a " conditioned " reflex? 



