126 THE HUMAN BODY. 



in getting rid of the excess nitrogen which is useless to 

 him, a great deal of unnecessary labor would be thrown 

 upon the digestive and excretory organs. Similarly, if a 

 man were to live on bread alone he would throw much un- 

 necessary work on his body. For bread contains but little 

 nitrogen in proportion to its carbon, and so to get enough 

 nitrogen far more carbon than could be utilized would 

 have to be eaten, digested, and excreted 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 kinds, and so avoiding excess of either nitrogen 

 or carbon. For instance, lean beef contains about of its 

 weight of dry proteid, which proteid contains 15 per cent 

 of nitrogen. Consequently 1 pound 3 ounces of lean meat 

 would supply the nitrogen needed to compensate for a day's 

 losses. But the proteid contains 52 per cent of carbon, so 

 the amount of it in the above weight of fatless meat would 

 be 1070 grains (69 grams) or nearly 2 ounces, leaving 3150 

 grains (205 grams) or rather more than seven ounces, to 

 be got either from fats or carbohydrates. The necessary 

 amount would be contained in 3940 grains (256 grams) or 

 about 9 ounces of ordinary fats, or in 7080 grains (460 

 grams), a little over a pound, of starch; hence either of these 

 with the above quantity of lean meat, would form a far bet- 

 ter diet both for the purse and the system than meat alone. 



As already pointed out, nearly all common foods contain 

 s. Good butcher's meat, for example,contains 



Explain why bread by itself would afford a bad diet. 



Why do men use a mixed diet? Explain why lean meat alone 

 would not be a good food. How could the deficient carbon of lean 

 beef be supplied? 



Give illustrations of the fact that most foods contain more than 

 one foodstuff. 



