6io METABOLISM, NUTRITION AND DIETETICS 



Milk as a Food. Milk is a food rich in calcium and also in phos 

 phorus, a circumstance evidently related to the rapid development 

 of the skeleton in the young child. As in the other natural foods, 

 the calcium and phosphorus are partly in the form of organic com- 

 pounds, united with the proteins, the calcium especially with 

 caseinogen, and partly in the form of inorganic salts. Both of these 

 elements are more easily assimilated by the body in the organic 

 than in the inorganic form. The same is true of iron, which exists 

 in organic combination in the bran of wheat, in the haemoglobin of 

 the blood and of muscular fibres, in the nuclei of most cells, vegetable 

 and animal, and conspicuously in the nuclein compounds of the yolk 

 of the egg. Attempts have been made to increase the amount of 

 iron in hen's eggs by giving them food mixed with preparations of 

 iron e.g., iron citrate. An increase takes place, but only after a 

 long time. Thus in one experiment 100 grammes of egg-substance 

 contained 4-4 milligrammes of Fe2O 3 before the administration of 

 the iron was begun; after feeding with iron for three and a half 

 weeks the amount was 4-5 milligrammes, after more than two 

 months 7-4 milligrammes; and after a year only 7-3 milligrammes. 

 Although, as we have seen, inorganic iron can be absorbed, it is 

 certainly the case that under ordinary conditions all the iron that 

 the body receives or needs is taken in the form of organic com- 

 pounds, since there is no inorganic iron in the natural food sub- 

 stances. Stockman, from careful estimations of the quantity of iron 

 in a number of actual dietaries, finds that it only amounts to about 

 8 to 10 milligrammes a day. He concludes that the greater part of 

 it must be retained in the body and used over and over again. : 



Milk is poor in iron, but this does not hinder the development of 

 the young child, except when it is weaned too late, when it is apt to 

 become anaemic unless the milk is supplemented with a food rich 

 in iron, such as yolk of egg. The explanation is that the foetus, 

 especially in the last three months of intra-uterine life, accumulates 

 a store of iron in the liver and other organs; so that, in proportion 

 to its body-weight, it is at birth several times richer in iron than the 

 adult. This iron, of course, all comes from the mother, and the 

 loss is not exactly balanced by the excess of iron in her food ; certain 

 of her organs, the spleen, for instance, though not apparently the 

 liver, are impoverished as regards their content of iron. 



SECTION V. DIETETICS. 



There are two ways in which we can arrive at a knowledge of the 

 amount of the various food substances necessary for an average 

 man : (a) By considering the diet of large numbers of people doing 

 fairly definite work, and sufficiently, but not extravagantly, fed 

 e.g., soldiers, gangs of navvies, or plantation labourers; (b) by making 

 special experiments on one or more individuals. 



