IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 261 
method of liberating the “ masked ” iron in this organism, it is 
uncertain whether the iron demonstrated after the use of 
sulphuric acid alcohol had the distribution it obtained in the 
living organism, or in the cytoplasm before it was treated 
with acid alcohol. Apart from these matters it seems to me 
quite certain that the results indicate the presence of iron in 
a “masked ” form in this organism. 
Cyanophycez.—These organisms, which are generally 
regarded as closely related to bacteria, offer, on account of 
their much larger size, fewer and less formidable difficulties 
to an investigation of the morphological and micro-chemical 
characters of their cells, and I have, therefore, endeavoured to 
give a careful attention to the question of the presence of 
assimilated iron in them. The determination of the relations 
of the iron compounds in these organisms has entailed also an 
investigation of the morphology of their cells, and I have, in 
consequence, obtained a very large number of results, the 
description of which is beyond the scope of the present paper. 
These, and a fuller account of the literature of the subject, I 
propose to detail on a future occasion, and I now deal with 
the ascertained facts relating to the iron compounds and, in 
so far as morphological characters are associated with these, 
with the structure of the cells themselves. 
The literature on the subject of the Cyanophycez has grown 
considerably in the last ten years, but as it is only within the 
last six that improved technical methods have been employed 
in the investigation of their structure, a short sketch of the 
more important publications, which have appeared in the latter 
period, will suffice for present purposes. 
Zacharias found that the cell is constituted of a coloured 
peripheral part, and an uncoloured central portion of a reticu- 
lated or granular structure. In the central portion he observed 
two substances, one exhibiting the characters of a plastin, the 
other, which he termed the “central substance” (Central- 
substanz), varying in amount in the different cells, and re- 
sembling nuclein in its chemical reactions. In the central 
portion he found granules destitute of nuclein, and related in 
