SOME REASONS FOR STUDYING BIOLOGY 17 



pear from the world." His prophecy is gradually being fulfilled, 

 and it may be the lot of some boys or girls who read this book to 

 do their share in helping to bring this condition of affairs about. 



The Relation of Animals to Man. — Animals also play an im- 

 portant part in the world in causing and carrying disease. Ani- 

 mals that cause disease are usually tiny, and live in other 

 animals as parasites ; that is, they get their living from their hosts 

 on which they feed. Among the diseases caused by parasitic 

 animals are malaria, yellow fever, the sleeping sickness, and the 

 hookworm disease. Animals also carry disease, especially the 

 flies and mosquitoes ; rats and olj^ier animals are also well known 

 as spreaders of disease. 



From a money standpoint, animals called insects do much harm. 

 It is estimated that in this country alone they are annually re- 

 sponsible for $800,000,000 worth of damage by eating crops, forest 

 trees, stored food, and other material wealth. 



The Uses of Animals to Man. — We all know the uses man 

 has made of the domesticated animals for food and as beasts of 

 burden. But many other uses are found for animal products, 

 and materials made from animals. Wool, furs, leather, hides, 

 feathers, and silk are examples. The arts make use of ivory, tor- 

 toise shell, corals, and mother-of-pearl ; from animals come per- 

 fumes and oils, glue, lard, and butter; animals produce honey, 

 wax, milk, eggs, and various other commodities. 



The Conservation of our Natural Resources. — Still another 

 reason why we should study biology is that we may work under- 

 standingly for the conservation of our natural resources, especially 

 of our forests. The forest, aside from its beauty and its health- 

 giving properties, holds water in the earth. It keeps the water 

 from drying out of the earth on hot days and from running off on 

 rainy days. Thus a more even supply of water is given to our 

 rivers, and thus freshets are prevented. Countries that have been 

 deforested, such as China, Italy, and parts of France, are now sub- 

 ject to floods,~^nd are in many places barren. On the forests 

 depend our supply of timber, our future Avater power, and the 

 future commercial importance of cities which, like New York, are 

 located at the mouths of our navigable rivers. 



HUNTER. CIV. BI. — 2 



