8 



BIOLOGY AND HUMAN LIFE 



the health of human beings or of some species of plant. Many 

 of us get much satisfaction from the beauty of living things ; 

 and while enjoying the song of a bird or the fragrance of a 

 flower is not quite the same as studying biology, there is the 

 possibility of increasing our satisfaction by increasing our 

 knowledge of living things. Indeed, for many boys and girls 

 there is more of a thrill in solving a problem about the how of 

 living things than in almost any other kind of experience. Bi- 

 ology may be a great adventure of exploration into a wonderful 



Oxygen 65% 



Carbon ••:'■ 



Hydro- 

 gen 



10% 



K Na Hg 

 SCIFe 



[Gil 



WM 



Fig. 3. The chemical composition of the human body 



In addition to the elements named there are nitrogen (N), calcium (Ca), phosphorus 

 (P), potassium (K), sodium (Na), magnesium (Mg), sulfur (S), chlorin (CI), iron 

 (Fe), and traces of iodin, fluorin, and silicon. The same chemical elements are found 



in other living bodies 



world of which the largest part is still unknown. To many peo- 

 ple biology is interesting because it answers practical questions 

 about the relations of plants and animals to our business, our 

 health, our sources of timber and furs and other useful material, 

 our laws, and so on. 



6. How biology is studied. Everybody knows some biology, 

 even without having studied it. Whatever you know about tak- 

 ing care of the baby, or a pet animal, or a garden, or a potted 

 plant, whatever you know about taking care of yourself, is so 

 much practical biology, no matter where or how you learned it. 

 We are constantly picking up a great deal of reliable and useful 

 information, just as we are picking up a great deal of rumor or 

 gossip or superstition that is neither true nor useful. To get 



