A HARD-WORKING DIET. 355 



In the second place it is not for a moment to be 

 expected that any one succeeds in calculating out his 

 daily diet with the exactness of a scientific chemist 

 making an analysis of a food, or conducting ex- 

 periments on the amount of carbonic acid given off 

 during work of a particular kind. Even with the 

 most rigidly routine life any attempt to meet the 

 daily needs with exactness would be upset by changes 

 in the weather. The nearest approach to exactness 

 is perhaps in training for boat-racing, but every one 

 with any experience knows how a muggy day or 

 roughish water will " take it out of you," and make a 

 slight increase of food necessary. 



The practical utility of the experiments such as 

 those referred to at p. 350, which these figures summa- 

 rise is that they show this the more the muscular 

 work done, the more carbonic acid and water are given 

 off, and the more C and H must be taken into the 

 blood for oxidation. These figures C 4,900, and 

 N 300 give an average. (For N, see p. 358.) 



Knowing then the amounts of C, H, and N that From what 



sources can 



are needed, the next inquiry is the sources from our intakes be 

 which these can be obtained. Side by side with the 

 investigations mentioned above, many chemists were 

 engaged in examining the chemical composition of 

 many substances we use as (ood. 



Leaving out of consideration the various methods 

 of giving the results, as this does not affect our present 

 inquiry, the important point to look to is the total 

 amount of C, H and N. 



It has been found that there is so important a dif- 



2 A 2 



