IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS, 205 
days and then transferring them to a quantity of a concen- 
trated solution of potassium hydrate for an hour, after which 
interval the sections give abundant evidence of the presence of 
iron. That not a trace of iron is left in the sections by 
Bunge’s fluid may be shown by incinerating some of the 
sections so treated and examining micro-chemically the ash 
for the presence of iron. Were one able to obtain the reagent 
absolutely free from iron, its employment for this purpose, 
limited as it must be through its drastic action on cellular 
structures, would, however, still be open to objection on the 
score that it dissolves and redistributes the iron of the 
tissues. 
III. GeneRAL OBSERVATIONS ON THE DISTRIBUTION OF 
ASSIMILATED IRON IN HIGHLY SPECIALISED ANIMAL AND 
VEGETABLE CELLS. 
The greater part, and sometimes the whole, of the assimi- 
lated iron in the cells of the higher forms of animal life is 
held in the nucleus, in the chromatin of which it is chiefly 
found. The chromatin fibrille, the chromatin granules, the 
nodal points of the chromatin network, all exhibit, after the 
employment of the methods described above, the clearest 
evidence of the presence of iron. Though no definite com- 
parison is possible, yet, judging by the depth of colour result- 
ing from the Prussian blue reaction in a large number of 
animal nuclei, one may say that the amount of iron thus 
demonstrated appears to correspond in all cases with the 
amount of chromatin present. This is probably best seen 
after the use of sulphuric acid alcohol, followed by treatment 
with an acid ferrocyanide solution, the sections thus prepared 
being compared with others simply stained with a reagent like 
Ehrlich’s hematoxylin so employed as to affect the chromatin 
only. In this case the hematoxylin stain in the chromatin 
is always found to correspond in intensity, in the object stained 
and in the general distribution of the stain, with the blue re- 
action obtained in the other sections. If, further, sections 
