268 A. B. MACALLUM. 
GENERAL REMARKS. 
The facts described in the preceding pages appear to indi- 
cate that a substance, in which iron is firmly held, is a constant 
constituent of the nucleus, animal and vegetable, of the cyto- 
plasm of non-nucleated organisms and those possessed of 
apparently rudimentary nuclei, and that, further, a similar 
iron-containing substance obtains in the cytoplasm of ferment- 
forming cells. This substance, to which cytologists apply the 
term chromatin, cannot, on theoretical grounds, be regarded as 
constant in its molecular structure, even in the same organism, 
and its most marked characteristic, apart from the iron in its com- 
position, is the occurrence in it of nuclein or nucleinic acid. 
Beyond the fact that the iron is firmly held, it is difficult 
to say how it is disposed in the molecular structure of the 
nuclein or nucleinic acid. It is, possibly, united directly to 
the carbon of the latter. The acid alcohols liberate it as a 
ferric salt, but this fact cannot be held to indicate that it is 
combined in the nuclein or nucleinic acid in a ferric state, 
since from solutions of potassium ferrocyanide, in which the 
iron is contained in a ferrous state, acids liberate the iron in a 
ferric condition,! as evidenced by the formation of ferric ferro- 
cyanide or Prussian blue. 
It is also difficult to say whether there is, in the way in 
which the iron is held in the animal cell, anything different 
from that obtaining in the vegetable organism. I have, as 
a rule, found it easier, in the case of the vegetable cell than in 
that of the animal cell, to liberate the iron with ammonium 
hydrogen sulphide; but upon this no conclusion may be 
founded, since the same reagent liberates the iron of free 
hematin readily, while it does not affect the iron of hematin 
in hemoglobin, and it is possible that in the animal cell the 
1 The iron immediately on liberation may be in the ferrous state, but it 
quickly assumes the ferric form. Similarly, the iron liberated in the chro- 
matin may at first be a ferrous compound which, with the continued action of 
the liberating reagent and under the conditions obtaining in the hardened 
tissues, may further undergo a conversion into a ferric salt. 
