THE PHYSIOLOGY OF MUSCULAR WORK 249 



during a day of work, the time of labour being nine hours. In 

 the series of experiments when the man received food the figures 

 were 16'8 grms. during rest and 17' 1 grms. during work. There 

 is no increase in the discharge of nitrogen on the days following 

 the work, provided that the man started with stores of energy 

 in the form of glycogen and fat sufficient to prevent any demand 

 upon the protein of his tissues to supply the energy required for 

 the performance of the work. 



There is no doubt that the amount of food required by a man 

 depends upon the muscular work which he performs. So much 

 follows from our knowledge of the conservation of energy, but 

 that law gives us no guidance as to the relative amounts of protein, 

 carbohydrate, and fat which are required. To obtain evidence upon 

 these points we must examine the diets of men whose occupations 

 entail different amounts of manual labour. 



Atwater calculated the energy value of the dietaries of civilians 

 living under different conditions, and upon these data based his 

 well-known standards of diet. These are given in the table on 

 the following page, together with other dietaries for the sake of 

 comparison. 



Special importance must be attached to the dietaries of prisoners 

 both military and civil, for in these cases it was impossible for 

 the men to obtain extra food ; work was regularly performed, and 

 medical inspection and the weights of the men at different times 

 showed that their health was satisfactory. 



During the last two or three years special attention has been 

 directed to the question of diet. Chittenden's (* 8 ) experiments 

 and writings have given rise to much discussion, for he maintains 

 that most men eat too much protein and impair their health by 

 this extravagance. His contention is that the large amount of 

 protein consumed overtaxes the kidneys in their work of excreting 

 the waste products of digestion. For this he gives no evidence. 

 On the other hand it is well known that the body is overcompen- 

 sated and is able to adjust itself within certain limits to a wide 

 range of work. This capacity is no doubt shared by the kidneys, 

 for one kidney may for years efficiently remove the waste products 

 which are normally discharged by two kidneys. 



It is impossible here to examine fully Chittenden's experiments 

 and views, but it may be well to emphasise again the importance 

 of instinct and experience as guides to questions of food. Healthy 



