CHAPTER V 



NUTRITION 



When a muscle contracts glycogen disappears. Only part 

 of this glycogen is reinstated in the recovery phase of muscular 

 contraction, and probably an analogous phenomenon occurs, 

 as already indicated, in the case of ciliary and glandular activity. 

 It is necessary, therefore, that the supply of materials in the 

 effector organ should be replenished. In the case of growing 

 organisms, it is necessary also that a supply of the materials 

 concerned with the manufacture and growth of cells shall 

 be maintained. In this chapter we shall deal with the means 

 by which a supply of necessary material is ensured. 



It is more than a century since Lavoisier and Laplace 

 showed that the bodily heat of warm-blooded animals is a 

 form of slow combustion, and that the amount of oxygen 

 used up and of carbon dioxide liberated has a definite and 

 ascertainable relationship to the heat that is generated. By 

 applying the balance and the thermometer to the phenomena 

 of life, Lavoisier founded the modern science of nutrition. 

 By the middle of the following century Liebig had shown 

 that the three categories of organic compounds known as 

 proteins, carbohydrates and fats are the substances whose 

 decomposition and oxidation form the basis of those chemical 

 changes which occur under the influence of living cells and are 

 collectively referred to under the term *' metabolism." A signal 

 advance was made by the researches of Voit and others in the 

 ^sixties, when it was shown that muscular activity does not 

 increase protein metabolism (estimated by the nitrogenous 

 content of the urine) ; that the complete combustion of a given 

 weight of each class of compounds is associated with the 



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