BOOK V 



CHAPTER XXXVII 

 GENERAL METABOLISM AND DIETETICS 



METABOLISM and reproduction are the* chief characteristics of 

 living matter. We know that complex bodies such as proteins, fats, 

 and carbohydrates, are constantly taken into the "body, and that 

 each undergoes its own special metabolism. As the result of these 

 reactions chemical energy is transformed into heat and mechanical 

 work; waste products, such as carbon dioxide and urea are formed, 

 and excreted from the body. 



The study of general metabolism concerns the intake and output 

 of energy by, and the processes of building up and breaking down 

 which occur in, the body as a whole; while the study of the special 

 metabolisms deals with the exact chemical changes undergone by the 

 various foodstuffs, and with the localization of such changes in the 

 body. 



General Metabolism: Methods. The general metabolism of a 

 man or animal may be investigated by two means: (1) Directly, 

 by ascertaining the heat value of the foodstuffs taken in, and 

 then measuring the heat given off, either as such or as work, the 

 work performed being subsequently calculated as heat. (2) Indirectly, 

 by drawing up a balance-sheet between the intake (the amount of 

 food and amount of oxygen taken in) and the output (the amount of 

 the various bodies excreted in the breath, urine, faeces, and sweat), 

 and from these calculating the energy exchange. Of these, the second 

 method demands a less difficult technique and is more generally 

 employed. For very exact work a combination of the methods is 

 used. 



The body is to be looked upon as a machine capable of performing 

 work and liberating heat. In the living as in the inanimate world, 

 there is no such thing as a loss of energy. All such apparent losses 

 are merely transformations of energy, the chief transformation in 

 the body being that of the chemical energy of the foodstuffs into 

 work and heat. 



It is not possible, however, to account for the operations that go 

 on in the human machine on the supposition that man is a thermo- 

 dynamic engine. 



