176 A. B. MACALLUM. 
animal and vegetable cells may be demonstrated micro-chemi- 
cally, and I referred to the results then obtained with it as 
indicating, apparently, that iron is always a constituent element 
of this substance. The interest which the subject had for me 
led me to continue the investigation with improved methods of 
research, and I am now consequently in a position to describe 
a much more extensive series of observations in support of the 
generalisation, then somewhat tentatively advanced, that iron 
is a constant constituent of the nuclein substance proper. 
From the commencement of the investigation I have been 
fully aware of its difficulties, and I can, therefore, readily under- 
stand that view of the subject which led Gilson to remark that 
the solution of the question concerned is one “that seems to 
require more than a single man’s activity.”’! The difficulties 
encountered in the application of the micro-chemical method 
are, however, very much less formidable than those met with 
in the employment of the older. methods. Ihave pointed out, in 
my first paper on this subject, how impossible it is to be certain 
that the iron revealed by macro-chemical methods in isolated 
quantities of nuclein is not present through absorption from some 
other source, but due to a combination obtaining in unisolated 
living chromatin, and I have indicated that the only way in 
which the question could be settled definitely is by the employ- 
ment of micro-chemical methods. I have shown in the suc- 
ceeding pages of this paper that the acid alcohol upon which 
Bunge relied to extract the iron of inorganic and albuminate 
compounds from egg-yolk and other nuclein-holding substances, 
and leave intact the organic (nucleinic) iron, does not perform 
this function at all when the substance treated with it is in 
mass, while it removes the iron of all three classes of compounds 
from thin sections of tissues, if the time allowed for its action 
be prolonged. We have, consequently, in a macro-chemical 
investigation, no means whatever of distinguishing between 
organic iron on the one hand and the iron of inorganic and 
albuminate combinations on the other, and we are therefore 
1 “On the Affinity of Nuclein for Iron and other Substances,” ‘ Report 
British Association for the Advancement of Science,’ 1892, p. 778. 
