2 WHY AND HOW WE STUDY BIOLOGY 



once said, "It is within the power of man to cause all parasitic 

 diseases to disappear from the world." This prophecy is gradually 

 being fulfilled. It is estimated that from 75 to 90 per cent of all 

 sickness is preventable and that the economic loss in the United 

 States each year from disease and death is about $3,000,000,000. 

 This loss could be largely prevented if we were willing to use the 

 knowledge we now have in the methods of controlling and ex- 

 terminating disease. It may be the lot of some boys and girls 

 who read this book to do their share to bring about this condition 

 of affairs. 



The economic values of biology. There are other reasons why 

 we should know something about biology. Plants and animals 

 can live together on the earth only because food is supplied by 

 green plants. Probably many of us do not realize that if all 

 the green plants were gone from the earth there would be no 

 animals. We shall see later why this is true. We all know that 

 man's food supply is determined very largely by his ability to 

 grow and develop plants that produce food for him and for the 

 animals which he eats. 



Plants and animals are useful to man in other ways than for food. 

 He uses, for clothing and ornaments, animal products such as wool, 

 fur, leather, hides, ivory, coral, and mother-of-pearl. Plants also 

 provide him with many kinds of building materials. Much of his 

 clothing, and the thread with which he sews it, come from plant 

 fibers. In hundreds of ways plants are made use of in the arts and 

 trades. It is the duty of every boy and girl to know something of 

 these uses. 



The conservation of our natural resources. Still another reason 

 why we should study biology is that we may work intelligently for 

 the conservation of our natural resources, especially our forests. 

 The forest, aside from its beauty and its health-giving properties, 

 holds water in the earth. It keeps the water from evaporating 

 from the soil on hot days and from running off the surface on rainy 

 days. Regions that have been deforested, such as parts of China, 

 Italy, and France, are now subject to floods, and are in many 

 places barren. Our supply of timber and to a large extent our 

 future water power depend on the forests. 



