CHAPTER IV 



METABOLISM AND NUTRITION 



THE physiology of metabolism and nutrition 1 seeks to discover what sub- 

 stances are necessary for the maintenance and growth of the body, to deter- 

 mine the character and extent of the combustion taking place in its tissues 

 and fluids under different circumstances, and to understand the significance 

 of the different substances for these processes. 



The substances in question admit of division into three groups, namely: 

 (1) organic foodstuffs, substances which supply potential energy and serve 

 therefore to maintain the combustion in the body; (2) water and inorganic 

 foodstuffs, which must be taken to make good the constant loss from the body 

 of these constituents, without which profound and eventually fatal disturb- 

 ances in health may ensue; (3) oxygen necessary for the maintenance of 

 combustion. 



FIRST SECTION 



METABOLISM 



1. ON THE METHOD OF METABOLISM EXPERIMENTS 

 A. THE INGESTA 



Organic as well as inorganic foodstuffs, mixed together in varying pro- 

 portions and mixed with other substances not needed in the body, occur in 

 our common articles of food and in our meals prepared from them. Chemical 

 analysis of the foods has shown that the organic foodstuffs are chiefly of three 

 kinds, namely: (1) proteids and allied substances; (2) fats; (3) carbohy- 

 drates. To the inorganic foodstuffs, which are designated also as ash con- 

 stituents, belong numerous salts which we shall discuss more in detail later. 

 By chemical analysis of the food we learn its composition, both qualitatively 

 and quantitatively, and determine in this way precisely the intake of the 

 body. 



In analysis of the foods and the faeces, (1) the nitrogen is determined and 

 the proteid is calculated by multiplying this result by 6.25. Since, however, 



1 It may serve to differentiate the two divisions of the subject somewhat, if we define 

 metabolism as covering all those chemical transformations of the foodstuffs by which 

 energy is supplied to the cells, and nutrition as covering all the processes by which the 

 materials which the cells require are supplied. Obviously the two are inseparable and 

 represent merely different aspects of the same subject. We speak of the substances as 

 undergoing metabolism and of the organism as nourishing itself. ED. 



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