CHAPTER III 



If 



OXIDATION 



37. The nature of burning or oxidation. In addition to 

 the substances taken in as food, the body is continually 

 taking in oxygen by the breath. The air which is 

 breathed is four fifths nitrogen gas and one fifth 

 oxygen gas. When air is fed to fuel in the hot 



fire box of a boiler, burning takes place. Burn- 

 ing is a chemical process. Oxygen unites with 

 the carbon and the hydro- 

 gen of the wood, so that 

 both the wood and the 

 oxygen disappear. The 

 carbon and part of the 

 oxygen form carbonic acid 

 gas. The hydrogen and 

 the rest of the oxygen 

 form water. Both sub- 

 stances pass off in the smoke. What is left as ashes is 

 the mineral part of the wood. 



By the burning, heat and a flame are produced. The 

 heat can be used to make steam which will drive an 

 engine and do work. Burning is called oxidation. 



38. Oxidation within the body. The body also is an 

 engine, self-regulating and self-sustaining. The oxygen 

 which is breathed into the body slowly burns food and 

 the cells, just as it oxidizes the wood under the boiler of an 



ov. PHYSIOL. 3 33 



f_ 



Diagram of burning or oxidation in a 

 stove. 



