INORGANIC SUBSTANCES. 



885 



shown that only about 10 mgrms. a day is ingested in an ordinary diet. 1 

 Of this amount, 1 mgrm.is egested by the urine, the remainder by the feces. 

 This cannot, however, represent all the iron metabolised, for the iron of 

 the hemoglobin of disintegrated blood corpuscles is retained, mainly by 

 the liver, and is no doubt again built up into blood pigment. The nuclei 

 of most cells, both animal and vegetable, contain appreciable quantities 

 of iron, and in this form, and in the hemoglobin of meat, it must occur in 

 most food. 2 In both these cases it forms an integral part of the molecule 

 of the proteid or nucleo-proteid, and under ordinary circumstances there 

 is no inorganic iron, nor any iron salt of organic acid present in the diet. 

 Such compounds of iron as are contained in nucleins such, for instance, 

 as the nuclein of the yolk of the egg have been termed by Bunge Jicema- 

 togens. As this nuclein is the only iron-containing constituent of the 

 yolk, it is clear that the hemoglobin of the developing red corpuscles of 

 the chick must derive its iron from it. It has further been shown by 

 Socin, working in Bunge's laboratory, 3 that in mammals also haemoglobin 

 is manufactured when the only iron contained in the food is in the form of 

 the same yolk-hematogen, and that the urine of animals (dogs) fed freely 

 with egg yolk shows a marked increase in the amount of iron present. 



It is noteworthy, as has been pointed out by Bunge, that the natural 

 food of the infant, namely, milk, contains mere traces of iron, although 

 the formation of hemoglobin is actively proceeding. This is accounted 

 for by the fact that the foetus lays up a store of iron (in its liver and else- 

 where) before birth, and gradually draws upon such store for the manufac- 

 ture of hemoglobin. Thus Bunge 4 found 18 '2 mgrms. iron per 100 grins, 

 body weight in a new-born rabbit, as compared with 3*2 mgrms. per 100 

 grms. in an animal twenty-four days old; and Zalesky, 5 four to nine times as 

 much iron in the liver of a new-born puppy as in that of a full-grown dog. 



In all other respects the composition of the ash of milk nearly 

 corresponds with the composition of the ash of the sucking animal, as 

 may be seen in the following table from Bunge, which gives the result 

 of two experiments : 



xviii. p. 485 ; also, with Greig, ibid., 1897, vol. xxi. p. 55. 



2 Bunge, Ztschr. f. physiol. Chem., Strassburg, 1885, Bd. ix. S. 49. For the micro- 

 chemical evidence of the presence of iron in cell-nuclei, see Macallum, Proc. Roy. Soc. London, 

 1891, vol. 1. p. 277 ; and Quart. Journ. Micr. Sc., London, vol. xxxviii. p. 175. This will 

 probably account for the fact that the faeces, which includes many disintegrated cells of the 

 alimentary passages, sometimes shows a greater percentage of iron than is present in the 

 food, although the secretions poured into the intestines only contain iron in minute amounts. 



3 Ztschr. f. physiol. Chem., Strassburg, 1891, Bd. xv. S. 93 and 133. 



4 Ibid., 1892, Bd. xvi. S. 177. 



5 Ibid., 1886, Bd. x. S. 479 and 495. 



