I0 6 THE VITAL PROCESSES 



elements, and the affinity of other elements for oxygen, 

 and for each other, resides in their atoms. 



Oxidation. The uniting of oxygen with other elements 

 is termed oxidation. This may take place slowly or 

 rapidly, the two rates being designated as slow oxidation 

 and rapid oxidation. Examples of slow oxidation are 

 found in certain kinds of decay and in the rusting of iron. 

 Combustion is an example of rapid oxidation. Slow and 

 rapid oxidation, while differing widely in their effects upon 

 surrounding objects, are alike in that both produce heat 

 and form compounds of oxygen. In slow oxidation, how- 

 ever, the heat may come off so gradually that it is not 

 observed. 



Movement of Oxygen through the Body. Oxygen has 

 been shown in the preceding chapters to pass from the 

 lungs into the blood and later to leave the blood and, pass- 

 ing through the lymph, to enter the cells. That oxygen 

 does not become a permanent constituent of the cells is 

 shown by the constancy of the body weight. Nearly two 

 pounds of oxygen per day are known to enter the cells of 

 the average-sized person. If this became a permanent 

 part of the cells, the body would increase in weight from 

 day to day. Since the body weight remains constant, or 

 nearly so, we must conclude that oxygen leaves the body 

 about as fast as it enters. Oxygen enters the body as a 

 free element. The form in which it leaves the body will 

 be understood when we realize the purpose which it serves 

 and the method by which it serves this purpose. 



Purpose of Oxygen in the Body. The question may be 

 raised : Is it possible for oxygen to serve a purpose in the 

 body without remaining in it? This, of course, depends 

 upon what the purpose is. That it is possible for oxygen 

 to serve a purpose and at the same time pass on through 



