RESPIRATION 33 



example of what is going on in every part, and the 

 essential feature of all is movement. 



5. If kinetic energy is displayed as movement, it Modification 

 need not be of a gross or visible character. Much of of energy 

 it takes the form of heat, which we may be able to feel, 



but cannot see. It may appear as light, even in the 

 living animal, such as the glowworm (a beetle), which 

 produces a bright light with amazingly little expendi- 

 ture of energy. Or again, it may be represented by 

 nerve impulses, conveying messages to and from the 

 brain ; or by muscular contractions, enabling us to 

 work in the more ordinary sense of that word. The 

 oxidation process therefore provides the power which 

 runs the machine, and without it life activities 

 cease. 



6. When we try to define oxidation, the first ob- Combustion 

 vious thought is that it is combustion. When coal 



burns in air, the carbon and oxygen unite, carbon 

 dioxid is formed, and energy is liberated to warm us or 

 to run an engine. In modern chemistry the matter 

 is more closely defined, and the term oxidation has 

 come to include a certain type of reaction, no matter 

 whether oxygen is present or not. It is a reaction in 

 which there appears to be a transfer of electrical 

 particles or electrons, and thus we come back to the 

 alternation of electric states as the source of the dy- 

 namic properties of the living substance. At this point 

 we are near the limit of our present knowledge, and 

 proceeding thence, science will probably make nota- 

 ble gains in the not distant future. 



7. When oxidation takes place, something is oxidized Oxidation 

 or burnt. The source of the oxidized material is the 



food, but not necessarily directly and as such. When 

 yeast causes alcoholic fermentation, grape sugar 



