PART I 

 THE WORLD IN WHICH WE LIVE 



CHAPTER I 

 INTRODUCTION 



1. A new science. At the time of the American Revolution 

 the name biology, which means the " science of life," or the 

 " science of living things," had not been invented. And at 

 the time of the Civil War only a few men were engaged in the 

 study of the subject. At the present time, however, the subject 

 of biology has already come to be so important that everyone 

 should know something about it, for a variety of reasons. 



2. Biology related to health. In the first place, the people 

 of civilized countries have come to live in larger and larger 

 towns and cities and in closer and closer neighborhoods, so 

 that it is necessary to regulate our lives in many ways that 

 were not necessary when most people lived on farms or in 

 villages. Each person may now be a source of assistance and 

 comfort to more people than formerly ; but he may also, quite 

 unintentionally, become a source of danger to many people. 

 When each farm was all by itself, it did not matter very 

 much what became of the barnyard wastes, and most of the 

 kitchen refuse was eaten by the pigs and chickens. In a 

 city the garbage may furnish materials of great practical value, 

 but it may also breed flies and other insects that carry germs, 

 if proper disposition is not made of it. The water supply of 

 a city is a more difficult problem than that of a rural com- 

 munity, and the health of the city depends very largely upon 

 an abundant supply of the right kind of water. We have 



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