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 fasces. 
Tins cannot, however, represent all the iron metabolised, for the iron of 
the haemoglobin 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 haemoglobin 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 hcema- 
togens. As this nuclein is the only iron-containing constituent of the 
yolk, it is clear that the haemoglobin of the developing red corpuscles of 
the chick must derive its iron from it. It has further been shown by 
Socin, working in Bimge'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-hamatogen, 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 haemoglobin 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 haemoglobin. 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 : — 
Pi - PPT. 
Milk of Bitch. 
A. 
B. 
.4. 
B. 
K„0 . 
Na a O 
CaO . 
MgO . . . 
Fe,0 3 
P„0 5 . 
CI" . 
11-42 
10-64 
29-52 
1-82 
0-72 
39-42 
8-35 
8-50 
8-20 
35-8 
1-60 
0-34 
39-80 
7-30 
14-98 
8-80 
27-24 
1-54 
0-12 
34-22 
16-90 
10-70 
610 
34-40 
1-50 
0-14 
37-50 
12-40 
1 Brit. Med. Jowrn., London, 1893, vol. i. pp. 881, 942 (contains the literature regard- 
ing iron absorption up to that date) ; Jowrn. Physiol., Cambridge and London, 1895, vol. 
xviii. p. 485 ; also, with Greig, ibid., 1897, vol. xxi. p. 55. 
2 Bunge, Ztschr. f. yihysiol. 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. Jowrn. Mier. Sc, London, vol. xxxviii. p. 175. This will 
probably account for the fact that the feces, 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. 
*Ibid., 1892, Bd. xvi. S. 177. 
s Ibid., 1SS6, Bd. x. S. 479 and 495. 
