14 SOME REASONS FOR THE STUDY OF BIOLOGY 



animals with their food. Even the meat-eating animals feed in 

 the long run upon those that feed upon plants. How the plants 

 manufacture this food and the relation they have to animals will 

 be discussed in later chapters. Plants furnish man with the 

 greater part of his food in the form of grains and cereals, fruits 

 and nuts, edible roots and leaves ; they provide his domesticated 

 animals with food ; they give him timber for his houses and wood 

 and coal for his fires ; they provide him with pulp wood, from 

 which he makes his paper, and oak galls, from which he obtains 

 ink. Much of man's clothing and the thread with which they 

 are sewed together come from fiber-producing plants. Most medi- 

 cines, beverages, flavoring extracts, and spices are plant products, 

 while plants are made use of in hundreds of ways in the useful 

 arts and trades, producing varnishes, dyestuffs, rubber, and other 

 useful products. 



Bacteria in their Relation to Man. In still another way, cer- 

 tain plants vitally affect mankind. These tiny plants, so small 

 that millions can exist in a single drop of fluid, are called bacteria 

 or germs. Existing almost everywhere about us, in water, soil, 

 food, and the air, they play a tremendous part in shaping the 

 destiny of man on the earth. They help him in that they act as 

 scavengers, causing things to decay ; they help make cheese and 

 butter ; they assist the tanner ; and the farmer could not do with- 

 out them; but they likewise spoil our meat and fish, and our 

 vegetables and fruits; they sour our milk, and make our canned 

 goods spoil. More than this, they cause diseases, among others 

 tuberculosis, a disease so harmful as to be called the " white 

 plague." Fully one half of all yearly deaths are caused by these 

 plants. So important are the bacteria that a subdivision of biol- 

 ogy, called bacteriology, has been named after them, and hundreds 

 of scientists are devoting their lives to the study of germs and 

 their control. The greatest of all bacteriologists, Louis Pasteur, 

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

 diseases (diseases mostly caused by bacteria) to disappear 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- 



