METABOLISM, NUTRITION AND DIETETICS 549 



live, lives in order not to eat, consumes, according to Voit, 68 

 grammes protein, 1 1 grammes fat, and 469 grammes carbo-hydrates ; 

 but manual labour is a part of the discipline of the brotherhood, 

 and this must be still above the lowest subsistence diet. 



The question whether it is best to derive the proteins (and fats) 

 of the food mainly from plants or mainly from animals is one which 

 is never left to physiology alone to decide. But it has been definitely 

 proved that vegetable proteins and vegetable fats are (when properly 

 prepared) digested and absorbed as completely as those of animal 

 origin, and play the same part in the metabolism of the body. 



A growing child needs far more food than its weight alone 

 would indicate ; for, in the first place, its income must exceed 

 its expenditure so that it may grow ; and, in the second place, 

 the expenditure of an organism is pretty nearly proportional, 

 not to its mass, but to its surface. Now, speaking roughly, the 

 cube of the surface of an animal varies as the square of the 

 mass ; when the weight is doubled, the surface only becomes 

 V4, or one and a half times as great. The surface of a boy 

 of six to nine years, with a body-weight of 18 to 24 kilos, is 

 two-fifths to one-half that of a man of 70 kilos ; and he should 

 have about half as much food as the man. A child of four 

 months, weighing 5-3 kilos, consumed per diem food containing 

 0-6 gramme nitrogen per kilo of body- weight, or 3-18 grammes 

 nitrogen altogether, as against a daily consumption of only 

 0-275 gramme nitrogen per kilo in a man of 71 kilos (Voit). 



An infant for the first seven months should have nothing 

 except milk. Up to this age vegetable food is unsuited to it ; 

 it is a purely carnivorous animal. By careful observations on 

 the amount of carbon dioxide and nitrogen excreted by a child 

 nine weeks old, fed exclusively on its mother's milk, it has been 

 shown that the absorption and assimilation of milk in the infant 

 is very complete, over 91 per cent, of the total energy being 

 utilized ; while an adult, taking as much milk as is necessary for 

 the maintenance of nitrogenous equilibrium, does not utilize 

 at most more than 84 per cent. Human milk contains about 

 2 per cent, of protein (mainly caseinogen), 3 per cent, of fat, 

 5 or 6 per cent of carbo-hydrate (lactose or milk-sugar), and 

 from 0-2 to 0-3 per cent, of salts. Cow's milk contains about 

 4 per cent, of protein, 4 to 6 per cent, of fat, 4 per cent, of lactose, 

 and 0-7 per cent, of salts. When given to infants it should, as 

 a general rule, be diluted with water, and some sugar should be 

 added to it. Ass's milk has about the same amount of protein, 

 lactose, and salts as human milk, but less than half as much fat. 

 It is very well borne and very completely absorbed. 



As to the place of water and inorganic salts in diet, it is 

 neither necessary nor practicable to lay down precise rules. 

 In most well-settled countries they cost little or nothing ; very 



