272 ELEMENTARY PHYSIOLOGY less. 



and 2,300 grammes of water the total waste is about 

 balanced thus : — 



Nitrogen. Carbon 



Proteins 130 grammes (4i oz.) contain 20 graninics (J oz.) TO granniies (2J oz.) 



Foods as previously explained (p. 226) never consist, 

 except perhaps in the case of fats and oils, of one kind of 

 food-stuff only ; each article of food contains at most an 

 excess of some one kind of food-stuff, and no two foods 

 are exactly alike. Hence the selection of such foods as 

 will supply the amount of proteids, fats, and carbo- 

 hydrates re<iuired by the above statement opens up the 

 possibility of an almost indefinite choice. But the 

 composition of the more commonly used articles of food 

 as regards the amounts of the several kinds of food-stuffs 

 they contain, has l)een very carefully determined, so 

 that we may now proceed to select a meal such as will 

 give us the desired quantities of proteins, fats, and 

 carbohydrates. 



Suppose, for instance, that we select lean meat, bread, 

 potatoes, milk, and fat, such as butter or dripping, as our 

 food. We may obtain all that we require from the 

 amounts of each food shown in the table on the following 

 page. 



The amounts of the several foods shown in the above 

 table suffice to cover the waste shown in the table on j). 270 

 and constitute what is ordinarily known as a diet. But tlie 

 data thus given are to be taken rather as an illustration 

 of how the balance-sheet between food and waste is drawn 

 up, than as an example of exactly what a man ought to 

 eat in the way of food. As already pointed out, foods are 

 many, and vary in the relative amounts of the several 

 food-stuffs they contain, so that it is possible to draw up 



