IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS. 259 
central portion described by Biitschli, and I am inclined to re- 
gard the structure observed in the exceptional cases as due to 
shrinkage caused by the method of preparation. In some of 
the comma-shaped elements the hematoxylin stain demon- 
strates granules like those which were observed to manifest an 
iron reaction in the glycerine and sulphide preparations, The 
use of Loffler’s solution of methylene blue, followed by that of 
a saturated solution of bismarck brown, as recommended by 
Ernst, stains similar granules in the “ comma” elements, and 
in a few of the spirilla only ; but it is doubtful if these may be 
classed with the “sporogenous”’ granules of other bacteria 
revealed in the same way. I have not found that there are any 
granules in the spirilla which contain ‘ masked” iron, although 
there is the possibility that spirilla, containing granules, were 
not present in the preparations made with the glycerine and 
sulphide mixture or with acid alcohol. 
The diffusion of the ‘‘ masked” iron throughout the cyto- 
plasm of Beggiatoa corresponds, on the whole, with what was 
observed in the other bacteria, but the interpretation of 
the results in the latter has an element of obscurity in it, It 
is evident that the iron-holding compound is not, as a rule, 
localised in granules or in special structures; and although 
the distribution of this compound, in Beggiatoa alba at least, 
corresponds with that of the substance which stains with 
hematoxylin and other dyes, it is uncertain whether the two 
compounds are identical. It is possible that experiments with 
some of the larger forms, as, e. g., Beggiatoa mirabilis or 
Crenothrix Kihniana, may result in determining a solu- 
tion of the question. Unfortunately I had no opportunity of 
studying the distribution of iron in such large forms. 
I did, however, obtain a few preparations of a form which is 
possibly allied to Crenothrix, and whose size (2°8—3:2 x 
6'4—8 yw) rendered it favourable for such observations as I 
had an opportunity of making, This organism grew on the 
surface of some sewage water collected in the fall of 1898, in 
which also myriads of examples of Euglena viridis throve. 
It multiplied by fission. Some of them exhibited rounded 
