IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 2038 
water. When oil of cloves or oil of lavender was used all the 
preparations faded, for some reason at present unexplainable. 
The presence of safranin or eosin in the preparation does not 
influence, in any way, its chances of fading, but if the excess 
of the stain has not been removed it is apt, while the balsam 
is hardening, to diffuse, and thereby obscure the finer details 
of the preparation. That it is not difficult to keep Prussian 
blue preparations of animal and vegetable tissues, if carefully 
made, is shown by the fact that I have had now for over two 
years several hundred of such which retain unimpaired the 
original intensity of the reaction. 
I have always washed the sections with distilled water, before 
putting them in the acid ferrocyanide mixture, because the 
presence of acid alcohol, especially that containing nitric acid, 
causes decomposition of the ferrocyanide and a deposition of 
Prussian blue in parts of the preparation in which iron did not 
occur originally. The acid ferrocyanide mixture itself decom- 
poses after twenty minutes with the formation of Prussian 
blue, but that this is not, even in an infinitesimal part, the 
source of the blue that obtains in a section during the first 
five minutes after the mixture is made, was shown by the com- 
plete absence of a blue reaction in other sections of the same 
tissue (e.g. cartilage, muscle, ovary of Erythronium) placed 
in the mixture at the same time without having previously 
been treated with an acid alcohol. The distribution of the 
Prussian blue due to such a decomposition is quite different 
from that which one finds in preparations treated with acid 
alcohol, but in which this decomposition was avoided, for when 
one leaves sections of animal or vegetable tissue in the acid 
ferrocyanide mixture for two hours, the blue colour is uniformly 
diffused through the section, not localised as it is when the 
reaction is due to the iron of the tissue. 
In the permanent preparations made to illustrate the distribu- 
tion of iron, and on which no staining reagents were employed, 
the parts revealed by the transparent blue are not as sharply 
outlined as they would be if stained with hematoxylin for 
example, owing to the cytoplasmic parts, over or under the 
