154 METABOLISM 



general lines: (l) A consideration of the dietaries of various 

 groups of people; (2) by special experiments on man. By 

 the first method Voit concluded that an average workman of 

 70 to 75 kilos, working ten hours a day, required in twenty- 

 four hours 118 grams of protein, 56 grams of fat, and 500 grams 

 of carbohydrate. The very many figures obtained by numerous 

 experimenters vary within considerable limits, Chittenden, 

 for instance, having recently determined that the average 

 man eats at least twice as much protein as he really requires. 

 Although there are peoples and animals who for long periods 

 of time may live on a diet of flesh alone, it has been found, 

 both by experience and experiment, that for civilized man a 

 mixture of the three main foodstuffs is necessary for health. 

 From a physiological point of view, for a man of 70 kilos the 

 following may be put down as the solids of a normal daily 

 diet: 95 grams of proteins, 80 grams of fat, 310 grams of 

 carbohydrates, and 30 grams of salts. Knowing, as the result 

 of analysis, the composition of various foods, a selection of 

 foods can be made giving the proper proportions of foodstuffs. 

 The protein and carbohydrate should be present in such 

 amounts that there is one part of nitrogen for every fifteen 

 parts of carbon. Oatmeal and wheat flour contain nearly the 

 proper proportions. 



A growing child needs, relative to weight, far more food 

 than does a man. In the first place, it requires more food 

 because it is growing. In the second place, the expenditure of 

 an organism is determined by the surface rather than by mass. 

 Roughly, when the weight is doubled the surface becomes 

 only one and one-half times as great. During the first seven 

 months an infant should receive nothing but milk, for careful 

 observations on the carbon dioxide and nitrogen excreted by 

 a child have shown that the assimilation of milk is very com- 

 plete, 91 per cent, of the total energy being utilized. In an 

 adult maintaining nitrogen equilibrium on milk, only 84 per 

 cent, of the energy is utilized. Human milk contains about 

 2 per cent, of protein, 3 per cent, of fat, 5 or 6 per cent, of 

 carbohydrate 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, salts. When cow's 



