14 ELEMENTARY BIOLOGY 



we are most familiar cannot be kept up under water. Yet we 

 know that rusting of iron can go on under water, and this 

 rusting is really a roundabout oxidation process. 



In the common animals, including ourselves, a large part of 

 the activities which we usually notice have to do with getting 

 materials that can be oxidized. And a large part of the inter- 

 nal activities, which we do not notice, have to do with bringing 

 the fuel and oxygen together and with removing the oxids 

 resulting from oxidation. 



The conclusion of this matter is that living beings do their 

 work through energy set free from fuel by oxidation, which 

 requires oxygen in addition to food, and that we can under- 

 stand the organism's need for food and air in the same way 

 that we understand the requirements of an engine for fuel 

 and draft. 



