METABOLISM OF BACTERIA 169 



Coal represents stored-up energy, but we must transform .the 

 latent energy that is imprisoned in the coal into the active 

 energy of motion before it becomes available. This is done by 

 combustion, or oxidation, and by placing the coal under con- 

 ditions where the affinity of the carbon for oxygen will be 

 satisfied and the kinetic energy will be released in heat. The 

 food consumed by all organisms functions like coal, and the 

 process by which it is oxidized is known as respiration. It 

 was formerly thought that oxygen in a free state was neces- 

 sary, but it is now known that it is not. The oxygen may be 

 obtained from organic compounds, as in the case of the 

 anaerobes, but the amount of energy obtained when the oxy- 

 gen is derived in this way is much less than when the free 

 oxygen is used. For example, when 1000 grams of sugar 

 are oxidized to carbon dioxide and water 3939 calories of heat 

 are obtained, but when the same amount of sugar is oxidized 

 to butyric acid, hydrogen, and carbon dioxide, only 414 calories 

 are obtained. As a result of the process of respiration carbon 

 dioxide is universally produced, as well as water. In addition 

 to this, energy is dissipated in the form of heat, light, and 

 motion. In the case of the bacteria the heat formed during 

 the process of respiration is not apparent or easily measured 

 except in certain conditions where a high degree of heat is 

 produced. For instance, in certain fermenting masses the 

 temperature may be raised to 60 or 70 C. and the bacteria 

 have some relation to the spontaneous combustion of hay, 

 cotton waste, etc. Energy is sometimes given off in the form 



