CHAPTER LXIV 

 ENERGY CHANGES IN ORGANISMS 



From what has been stated previously it is clear that a living organism 

 may be looked upon as representing a store of potential energy, while 

 the organization which it possesses may be regarded as a system for the 

 transformation of energy. During the carrying on of life activities 

 energy is constantly being changed from potential to kinetic form. 

 Kinetic energy is dissipated and thus the body will run down unless an 

 additional amount of potential energy is continually being supplied to it. 

 That additional amount is secured from the food for the most part, the 

 small amount of kinetic energy received by the animal organism directly 

 from the light and heat of the sun and the heat of the earth being quite 

 insufficient to maintain life. 



496. • Chemical Changes in the Body. — For the most part the chemical 

 changes which occur in the body are of the nature of oxidations. These 

 occur in all tissues but to a greater degree in the more active ones. The 

 food taken in is, after digestion, circulated to various parts of the body 

 and built into the organization of the living cells. Oxygen also enters 

 the body and is circulated so as to reach every cell. Then, within the 

 cell, and under the influence of enzymes known as oxidases, the oxygen 

 is caused to unite with the food, which has now become part of the 

 protoplasm. Later, when the complex compound thus produced is 

 broken down and simpler compounds are formed, kinetic energy is 

 liberated. These simpler compounds, now waste products of the cells 

 which produced them, have to be carried from these cells to some point 

 where they can be eliminated from the body. It is probable that no food 

 is oxidized in the body until after it has been added to the living matter. 

 In some cases, as we have seen, the waste may temporarily serve some 

 purpose in the body, in which case it is known as a secretion. Among 

 such substances are the hormones and those which themselves stimulate 

 other chemical changes, as, for instance, the digestive enzymes. 



497. Organism Compared to a Fire.— Since life involves constant 

 oxidation, it was pointed out nearly two centuries ago by the French 

 chemist, Lavoisier, that life might be considered combustion taking 

 place under certain peculiar and complicated circumstances. Fire is 

 usually thought of as combustion, or oxidation, taking place rapidly 

 with the appearance of flame, but slow burning involves exactly the 

 same chemical changes and leads to the same result. The correspond- 



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