IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 239 
iron compounds, were, after being hardened in alcohol and 
after treatment with ammonium sulphide, isolated from those 
more or less impregnated with iron salts, the large size of the 
organisms enabling one to do this readily. One of such, after 
treatment for fourteen days with the warm glycerine and sul- 
phide mixture, is represented in fig. 25. In this no distinct 
reaction was obtained during the first two days, definitely 
showing that no inorganic iron was present. In the interior 
of the spherical elements constituting the nucleus there 
appeared eventually a diffuse iron reaction, as well as one 
localised in granules, and the cytoplasm gave a diffuse reaction 
like that given by the cytoplasm in Epistylis and Vorticella. 
I do not think that in this case the reaction had developed to 
the fullest extent of which it was capable, for I found other 
examples in which the nuclear and cytoplasmic elements gave 
amore intense one; but it is usually difficult in such large 
cells to obtain the best effects of the réagent, since in two 
weeks’ time it is apt to undergo decomposition, when the 
development of the iron reaction ceases. In order to ascer- 
tain how abundant the assimilated iron is, 1 employed acid 
alcohols to liberate it, and, after the removal of the acid, 
treated the preparation with ammonium sulphide.  Sul- 
phuric acid alcohol is the best reagent for the purpose, since 
with it there is less iron diffused from the parts in which it is 
liberated; but, in order to get the most exact results, the 
examples of Stentor used should be free from inorganic iron 
compounds, a point of which one may be certain by putting the 
hardened examples in ammonium sulphide for a few minutes, 
when, if they pass this test, they may be washed in alcohol to 
remove all traces of the reagent and placed in the acid alcohol 
for one or two days. I have represented in fig. 26 an example 
of S. polymorphus, in the wall of the funnel-shaped ceso- 
phagus of which was found the only inorganic iron compound 
present, and in this, after it had been treated as described, the 
ribbon-like nucleus appeared intensely greenish-black, while the 
cytoplasm gave a deeper reaction than was obtained in any 
specimen simply by prolonged treatment of it with the warm 
VOL. 38, PART 2.—NEW SER. Q 
