236 A. B. MACALLUM. 
holds an assimilated iron compound, for if small fragments of 
cells, hardened in alcohol, be subjected to the action of the 
warm glycerine and sulphide mixture for a week or more, they 
will manifest a dark-green reaction which, when the mixture is 
washed away and replaced by an acid ferrocyanide solution, is 
converted into that of Prussian blue. One may more readily 
obtain the demonstration of the iron in these cells by allowing 
sulphuric acid alcohol to act on the hardened gland for two 
days, when the cytoplasm of the secreting cells and the sub- 
stance of the thread (silk ?) in the lumen give evidence of the 
presence of this element. Whether the iron thus demonstrated 
in the substance of the thread belongs to the latter, or is 
derived by diffusion from the cytoplasm of the secreting cells 
during treatment with the acid alcohol, 1 am unable to say, 
since my experiments made to determine this question, by the 
use of the glycerine and sulphide mixture on isolated bits 
of the threads, turned out to be failures.! The substance 
forming the threads manifests a strong affinity for dyes, and 
should it eventually be ascertained that the iron demonstrated 
in it, after treatment with acid alcohol, is part of a “ masked ” 
compound contained in it, the facts will then all indicate that 
the iron-containing substance in the cytoplasm is the antece- 
dent of at least a portion of the substance of the thread in the 
lumen, and one will have then also a parallel of what was 
pointed out as obtaining in the pancreas and other ferment- 
secreting cells in Vertebrates. 
Protozoa.—I have selected the genera Stentor, Epis- 
tylis, Vorticella,and Param cecium for specially illustrating 
the distribution of the assimilated iron in unicellular animals. 
A very large number of other forms were used to confirm the 
results which a study of the named organisms gave, but owing 
1 Gilson (loc. cit.) has referred to the fact “that the silk of certain insects 
seems to possess a stronger aflinity for this metal (iron) than nuclein itself.” 
I have observed this peculiarity, but the iron absorbed is at once demonstrated 
on the application of any form of ammonium sulphide, a fact which shows that 
the iron so revealed does not enter into a “ masked ” condition, and ought not 
to be confused with that of “ masked” compounds. 
