CHAP, v.] NUTRITION. 845 



initial weight of 45 kilos, and a daily nitrogenous metabolism, 

 calculated as 28 grm. proteid, reached in the course of about 

 50 days a weight of 60 kilos, the daily nitrogenous metabolism 

 being raised on one occasion to 182 grm. proteid, with an average 

 on the whole period of 150 grm. During the treatment no less 

 than 8420 grm. of proteid were taken as food. 



557. With regard to labour, since as we have seen the 

 energy expended as work done is not taken out of and away from 

 the amount set free as heat, the two forms of energy being so 

 related that an increase of work done is accompanied by a greater 

 or less increase of heat set free, it is obvious that a man who is 

 doing a hard day's muscular work needs a larger income of energy 

 for the day than does an idle man. What we have learnt 

 concerning muscular metabolism further shews us that the 

 additional energy needed is not necessarily to be supplied by 

 an increase in the proteid components of the diet ; the energy of 

 muscular contraction does not come as was once thought from 

 proteid metabolism ( 529). The fact that it is the carbon 

 metabolism which is augmented in muscular work may suggest 

 that the extra food for extra work should be exclusively carbon 

 compounds ; and if, as seems probable, the carbohydrates are 

 more readily and directly available for the functional metabolism 

 of muscle than are the fats, we might be further led to recom- 

 mend an increase in carbohydrates to form a diet especially 

 suited for labour. But several considerations should make us 

 hesitate before we come to such a conclusion. A muscle is not 

 a machine within the body which can be loaded and fired off 

 irrespective of the rest of the body. In the performance of 

 muscular labour, the condition of the muscle, the amount of 

 energy available in the muscle itself, is of course of prime im- 

 portance ; but, and this perhaps especially holds good in severe 

 labour, of great importance also, we might almost say of no less 

 importance, is as we have urged ( 390) the power of the body 

 as a whole to avail itself of the energy latent in the muscle. 

 The power of doing work hangs not on the muscle alone, but on 

 the heart, the lungs, the nervous system and indeed on the whole 

 body. It is very doubtful whether we ever, even in supreme 

 efforts, draw upon more than a portion of the capital of energy 

 lodged in the muscle itself ; fatigue is far more a nervous than a 

 muscular condition, and even the distinctly muscular fatigue is as 

 we have seen ( 86) partly at least the result of the accumulation 

 of products and not alone the using up of available energy. In 

 choosing a diet for muscular labour we must have in view not the 

 muscle itself but the whole organism. And though it is possible 

 that future research may suggest minor changes in the various 

 components of a normal diet such as would lessen the strain during 

 labour on this or that part of the body, on the muscles as well as 

 on other organs, our present knowledge would rather lead us to 



