CHAPTER n 

 SOME RELATIONS BETWEEN WATER AND LIFE 



You have seen that in order to understand the great 

 "cycle of nature" that permits us to live, you must study 

 the following things: air, water, heat, light, soil, plants, and 

 animals. You must study especially the ways in which 

 these things work together in producing the conditions that 

 permit us to live. 



We might begin with the study of any one of these 

 topics, and as we studied it we should find ourselves study- 

 ing all the others, so closely are they related. We will 

 begin with water, because water is the simplest. 



Water. As you look at water in a glass it seems a 

 very simple thing, easy to understand. But when you be- 

 gin to study the way that water behaves, and the many 

 effects it has upon our lives, you soon find that this is a 

 very large subject indeed. Three-fourths of the surface 

 of the earth is covered with water, and more than three- 

 fourths of the bodies of all living things are composed of 

 water. This suggests the idea that life began in the water, 

 and slowly spread from there over the land and into the 

 air. There are many land animals, including man, in 

 which, when they are very young, structures appear that 

 suggest ancestors that lived in the water. However that 

 may have been, it is very certain that water is one of the 

 largest factors in life to-day, and to get a pure water- 



