SILOS, ENSILAGE AND SIl^GE. 57 



formed from protoplasm. As heat is liberated in the 

 manufacture of starch from the more complex molecules 

 of protoplasm, it will be seen that starch has less poten- 

 tial energy than the protoplasm from which it is formed. 



The stored-up energy of organic substances may also 

 be transformed into heat by the process of combustive oxi- 

 dation, as well as by the metabolism of the living cells. 

 " The heat which is given out by burning the organic 

 substance is but the conversion into kinetic energy of the 

 potential energy stored up in the substance. The heat, 

 for instance, which is given out by burning wood, or coal, 

 represents the kinetie energy, derived principally from 

 the sun's rays, by which were effected the processes of 

 constructive metabolism of which the wood, or coal, was 

 the product."* 



When a healthy balance is maintained between the con- 

 structive and the destructive metabolism of the cell, its 

 activities are vigorously carried on, if other conditions are 

 favorable ; but with a lowering or loss of cell vitality, an 

 invasion by the true, or organic ferments cannot be 

 resisted, and these in their turn become the leading 

 factors in the changes which follow. And here we have 

 a further illustration of the law of the conservation of 

 energy. The heat evolved in the processes of fermenta- 

 tion and putrefaction has the same origin as that devel- 

 oped in the metabolism of plants and animals. The 

 microbes that cause fermentation do not produce the heat 

 observed, but they feed upon the fermentable materials, 

 and among the results which follow, the stored-up ener- 

 gy of these organic substances is liberated in the form of 

 heat. It will be seen, moreover, that when this heat is 

 not dissipated by conduction or radiation it may be suf- 

 ficient to prove fatal to the organisms that are concerned 

 in liberating it. 



The phenomena usually included in the general term 



*Encycl. Brit. 9tb ed. vol xix p. 56. 



