2 APPLIED PHYSIOLOGY 



the facts which have been ascertained to the problems of 

 clinical medicine so far, at least, as such application is 

 at present possible. 



Metabolism has two great purposes to fulfil : (1) the 

 maintenance unimpaired of the substance of the tissues ; 

 (2) the conservation of bodily energy. The former con- 

 sists in the replacement of the waste of tissue substance 

 which the stress and strain of vital activity entails ; it 

 is therefore essentially anabolic in nature. The conser- 

 vation of bodily energy, on the other hand, is achieved 

 by the breaking down of food compounds and the libera- 

 tion of their potential energy in the form of heat and 

 work, and is therefore preponderatingly katabolic. 



We may regard these two aspects of metabolism 

 either from the point of view of the total amount of 

 chemical change which takes place (quantitative meta- 

 bolism), or from that of the intimate nature of the 

 chemical processes which they involve (qualitative meta- 

 bolism). As the former point of view is the simpler, it 

 will be best to consider it first. 



QUANTITATIVE METABOLISM.* 

 1. The Conservation of Tissue Substance. 



As protein is the only constituent of the food which is 

 able to repair tissue waste, it is obvious that this aspect 

 of metabolism when looked at quantitatively resolves 



* In order to appreciate the relative mass of the various tissues 

 which compose the 'vital machine' and take part in metabolism, 

 it should be remembered that, of the total body-weight, about 40 per 

 cent, is made up of muscle, 5 per cent, of blood, 2 per cent, of 

 brain, whilst the other internal organs and the skeleton make up 

 the remainder. 



