IRON COMPOUNDS IN ANIMAL AND VEGETABLE CELLS, 241 
the antecedent of the ferments is, in this class also, an iron- 
holding chromatin.! 
Euglena viridis is a form whose position, whether as a 
vegetable or as an animal organism, has not by any means 
been definitely determined, but the distribution of assimilated 
iron in its interior appears to indicate that if it does not be- 
long to the animal kingdom, its physiological processes pos- 
sibly resemble those of the Protozoan cell, and it is for this 
reason that I deal with it in this place. Examples of this 
organism free from inorganic compounds of iron may be ob- 
tained readily, and when hardened in alcohol, they may be 
subjected to the action of the glycerine and sulphide mixture 
for twenty-four hours, without manifesting a reaction for iron, 
but when the application is extended for three days or longer, 
a reaction for iron is obtained in the nucleus and cytoplasm. 
The chromatin network is usually so affected by the reagent 
that its nodal points only manifest the reaction, while the 
nucleolus exhibits a less intense dark-green colour. The 
cytoplasmic trabecule separating the “ amylaceous ” corpuscles 
from each other develop a dark-green reaction, which is found 
to be most intense at the nodal points. All these features are 
more clearly seen in specimens which have been hardened in 
alcohol, then treated for two days with sulphuric acid alcohol, 
and finally, after being acted on with the acid ferrocyanide 
mixture to produce the Prussian blue reaction, mounted in 
balsam (fig. 49). In these preparations the iron revealed in 
the cytoplasm is most abundant in its nodal points, which, with 
the reticulum of the nucleus, are thereby rendered most pro- 
minent. The nucleolus, separated from the other elements 
by a clear zone, in which the light blue observed is derived 
from the nuclear elements above and below the focal plane, 
gives a less intense reaction than one of the much smaller 
nodal points of the nuclear network. If the preparation has 
also been stained with eosin the nucleolus alone appears to be 
1 The ferment or ferments, according to M. Greenwood (‘Journal of Physio- 
logy,’ vol. viii, 1887, p. 263), pass into the fluid surrounding the ingested 
matter, 
