64 PLAIN FACTS FOR OLD AND YOUNG 



2. The amount of intelligence which an animal is 

 able to exhibit, depends upon the size of the thinking 

 portion of the brain in proportion to its body. Man 

 is the most intelligent of all animals, simply because 

 he has more cells capable of thinking than any other 

 animal. There are animals which possess a larger 

 brain than man, but none in which the thinking por- 

 tion of the brain is so great, in proportion to the size 

 of the body. It is also observed that men whose brains 

 are largest in proportion to their body, other things 

 being equal, possess the greatest intelligence. For ex- 

 ample, a man who has a four-pound brain is more likely 

 to be a philosopher, or to be distinguished for great 

 mental powers, than a man whose brain has only the 

 average weight of three pounds; while a man whose 

 brain weighs but two pounds, is certain to be an 

 idiot. 



Our Eyes.— Nearly all animals possess certain 

 nerves which are sensitive to light. Even the jelly- 

 fish, which has hardly any nerves, and certainly has 

 no eyes, seems happiest in the sunlight, and is dis- 

 turbed whenever a cloud passes over the sun. 



Did you ever see a leech, — one of those curious 

 creatures which the doctor sometimes applies to draw 

 away a little blood from an inflamed part? If you 

 should examine one of these strange animals, you 

 would find, close to the little opening which constitutes 

 its mouth, a circular row of minute red spots. These 

 are its eyes. By examining one of these red spots 

 with a microscope, it is found to consist of a little dark 

 pigment, or coloring matter, over which is spread a 

 thin, transparent skin. Between the colored and the 

 transparent layers is placed a very delicate membrane, 

 which contains the nerves of sight. These nerves pass 



