FOOD 47 



of the activity of plants or of animals, or of their de- 

 composition. This apparently leads to a deadlock which 

 we shall try to explain later. Here we must try to find 

 out how food properly so called can be a store of energy. 



We must remember that every organism, if alive, is 

 constantly doing work, whether this work be external 

 and visible, or internal and invisible. For this work 

 energy must be expended, and this naturally means that 

 there is a source of energy. Now energy occurs in two 

 states, potential and kinetic. By potential energy we 

 mean that a body is capable of doing work, although 

 at the time it is not so doing. Physicists tell us that 

 energy may be recognised in several different forms 

 chemical energy, thermal energy, electrical energy, and 

 so on, and by chemical energy they mean that form of 

 energy that is exhibited when the necessary units or 

 atoms combine to form a molecule. Thus in the forma- 

 tion of a molecule of carbon dioxide, in which there is 

 one atom of carbon and two of oxygen, there is a linking 

 up of the various atoms, and in this process energy is 

 set free. 



Again, we are told that the various forms of energy 

 are reducible to one, and that each may be changed, and 

 in Nature is constantly being changed, into another. 

 Yet in spite of all these changes the sum total of all the 

 energies in the Universe is a constant quantity. The 

 best way to measure the amount of energy expended in 

 a day by a living organism is to measure it in terms of 

 heat, and when this is done we find that a considerable 

 number of heat-units or calories has been expended. 

 Now the only possible place where this energy can 

 have been stored is in the food. 



