306 TEE HUMAN BODY 



substances. About 300 grams (4620 grains) of water 

 (containing 33.3 grams (513 grains) of hydrogen are, how- 

 ever, formed in the Body by oxidation, and the hydrogen for 

 this purpose must be supplied in the form of some oxidiza- 

 ble foodstuff, whether proteid, fat, or carbohydrate. The 

 oxygen wanted is mainly received fi'm the air through the 

 lungs, but some is taken in the food. 



Since proteid foods contain carbon, nitrogen and hydro- 

 gen, life may be kept up on them alone, with the necessary 

 salts, water and oxygen; but such a form of feeding would 

 be anything but economical. Ordinary proteids contain in 

 100 parts (p. 10) about 52 of carbon and 15 of nitrogen, so 

 a man fed on them alone w r ould get about 3J parts of carbon 

 for every 1 of nitrogen. His daily losses are not in this 

 ratio, but about that of 274 grams (4220 grains) of carbon 

 to 20 grams (308 grains) of nitrogen, or as 13.7 to 1; and 

 so to get enough carbon from proteids far more than the 

 necessary amount of nitrogen must be taken. Of dry 

 proteids 527 grams (8116 grains) would yield the necessary 

 carbon, but would contain 79 grams (1217 grains) of 

 nitrogen; or four times more than is necessary to cover the 

 daily losses of that element from the Body. Fed on a 

 purely proteid diet a man would, therefore, have to digest a 

 vast quantity to get enough carbon, and in eating and 

 absorbing it, as well as in getting rid of the extra nitrogen 

 which is useless to him, a great deal of unnecessary labor 

 would be thrown upon the various organs of his Body. 

 Similarly, if a man were to live on bread alone he would 

 burden his organs with much useless work. For bread 

 contains but little nitrogen in proportion to its carbon, and 

 so, to get enough of the former, far more carbon than was 

 utilized would have to be eaten, digested, and eliminated 

 daily. 



Accordingly, we find that mankind in general employ a 

 mixed diet when they can get it, using richly proteid sub- 

 stances to supply the nitrogen needed, but deriving the 

 carbon mainly from non-nitrogenous foods of the fatty or 

 carbohydrate groups, and so avoiding excess of either. For 

 instance, lean beef contains about \ of its weight of dry 



