METABOLISM, NUTRITION AND DIETETICS 543 



organic than in the inorganic form. And 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 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 

 Fe 2 O s 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 compounds, since there 

 is no inorganic iron in the natural food substances. 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 milli- 

 grammes 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 develop- 

 ment 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 im- 

 poverished as regards their content of iron. 



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 ex- 

 travagantly, fed e.g., soldiers, gangs of navvies, or plantation 

 labourers ; (b) by making special experiments on one or more 

 individuals. 



Voit, bringing together a large number of observations, con- 

 cluded that an ' average workman,' weighing 70 to 75 kilos, 

 and working ten hours a day, required in the twenty-four hours 



