218 A. B. MACALLUM, 
to decide whether the iron is contained in the granules or in 
the extra-granular substance, so intimately are these usually 
intermingled. The granules, whether of the large or of the 
punctiform variety, always contain an iron compound, while 
the substance in which they are shown is destitute of this 
element. In demonstrating this fact the acid alcohols are of 
the greatest service, the glycerine and sulphide mixture, owing 
to the large size of the vast majority of the spherules, not 
being as effective in liberating and demonstrating their iron, 
but in the smallest spherules the complete reaction may be 
obtained with the mixture in four or five days. In those 
spherules which contain, as described, granular and non- 
granular portions, the granules, closely aggregated as they 
usually are, appear very prominent by reason of the reaction 
for iron which they give with both methods of demonstration. 
In some of the “yellow” spherules also, after treatment 
with sulphurie acid alcohol, vesicles of different sizes were 
observed, each of which appeared to be enveloped by an iron- 
containing membrane-like structure. Their position near the 
centre of the spherule often rendered the occurrence of iron 
in the envelope obscure, owing to the light passing through so 
many iron-holding granules above and below these vesicles. 
What the latter contained it is not possible to say, for although 
fat globules of a similar size can be demonstrated in some 
spherules when these are subjected to the action of the chrom- 
osmio-acetic mixture for twenty-four hours, it cannot be 
demonstrated that the two classes of structures are connected 
in any way.! The difficulty lies in the fact that in order to 
show the occurrence of iron in the envelope, alcohol in some 
form must be used, and by this the fat is largely, if not wholly, 
removed ; while in those spherules treated only with osmic acid 
solutions the black reaction of the globules prevents a demon- 
stration by the Prussian blue reaction of any iron present. 
1 In another paper (‘‘On the Absorption of Iron in the Animal Body,” 
‘ Journ. of Physiol.,’ xvi, 1894, p. 268) I expressed the view that these vesicles 
contain fat. After a more extended study of these elements than I was able 
to make before that paper was published, I am doubtful of this interpretation 
of their structure. 
