62 rOODS AND NUTRITION 



transformed into kinetic energy or actual heating when the 

 coal is burned. Further, heat is transformed into poten- 

 tial energy or the power to expand, that steam has when 

 it is not actually expanding. 



Third. Kinetic energy can be transformed from one 

 kind of kinetic energy into another. Thus heat is trans- 

 formed into expansion, expansion into thrusting, thrust- 

 ing into rotation, rotation into sawing, etc. Careful 

 experiment has demonstrated that when energy is trans- 

 formed from one form to another no energy is lost or 

 created. The law which expresses this fact is called the 

 law of the conservation of energy, and applies to all cases 

 where the production of energy is concerned. It is usually 

 stated as follows: Energy can be transformed from one 

 kind to another, but can never be increased, diminished, 

 destroyed, or created from nothing. 



Fourth. The source of energy in a steam engine is the 

 oxidation of fuel. That is to say, the energy of an engine 

 is derived fundamentally from the oxidation of certain 

 chemical compounds. Such oxidation is simply a chem- 

 ical change, and chemical changes are the sources of most 

 forms of energy. 



In the light of this example let us examine again our 

 body as a machine for the transformation of energy. Just 

 as in the steam engine, we find that its source of energy is 

 to be foimd in the oxidation of fuel. Such fuel is found 

 in the carbon compounds known as carbohydrates and 

 fats which form part of our food. The energy liberated 

 by the oxidation of these compounds in the body takes 

 many forms, such as heat, muscular activity, secretion, 

 etc., and one form may be transformed into another, 

 since the law of conservation holds here just as every- 



