IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 189 
extent, it was my practice to allow the section to lie in the 
glycerine and sulphide mixture for a few minutes before teasing 
it out, the iron of these forms of combination giving an imme- 
diate reaction on the penetration of the reagent. The removal 
of all iron of this description is necessary, since its presence 
may give confusing results in teased-out cells. For this 
purpose I have used Bunge’s fluid, in which the sections were 
kept for about an hour with the reagent at a temperature of 
55° C., the subsequent treatment with alcohol and ammonium 
hydrogen sulphide in all cases showing that the inorganic and 
albuminate iron had been thereby removed.! Sections so 
treated were teased out and mounted in the glycerine and 
sulphide mixture in the usual way. 
The disadvantages connected with the use of ammonium 
hydrogen sulphide to demonstrate the presence of ‘ masked” 
iron are that it effects, in the animal cell at least, structural 
changes, that it is not successful on large nuclei or on nuclei 
of large cells, and that it requires a great expenditure of time. 
In regard to the structural changes it is obvious that, however 
well hardened or well fixed cellular elements may be through 
the action of alcohol, ammonium hydrogen sulphide or diam- 
monium sulphide must, when heat is applied, sometimes alter, 
to a greater or less degree, the structure of the cell, and 
especially ofits nucleus. This is quite evident when we compare 
such preparations with others in which the “ masked” iron has 
been liberated by the use of sulphuric acid alcohol, and sub- 
sequently treated with the sulphide. Figs. 23 and 24 illustrate 
the differences obtained with the two methods, the former 
representing liver-cells of Necturus lateralis treated for 
ten days at 55° C. with the glycerine and sulphide mixture, 
while the latter was drawn from a section of the same material 
after it had been acted on by sulphuric acid alcohol for seven 
hours at 85° C., and then with the glycerine and sulphide 
mixture. The first difference to be noted between the 
1 In regard to the capacity of Bunge’s fluid for extracting iron of all forms 
of combination, see the description of the properties of hydrochloric acid 
alcohol as given below. 
