102 The American Naturalist. [February, 
to itself. Obviously, however, the most striking differences 
are manifested in the character of the so-called secondary con- 
stituents of the cell protoplasm, i. e. the katabolie products 
of the cell’s activity, such as the different enzymes or their an- 
tecedents, the albuminoids, pigments, fat, glycogen, etc., to 
which must be added the substratum of dead food material 
for the nutrition of the cell. From this very diversity in the 
character of the katabolic products of protoplasmic activity, 
we might easily argue corresponding differences in the charac- 
ter of the primary constituents of the cell protoplasm, which 
in turn would imply fundamental differences in the nature of 
the anabolic processes by which the cell protoplasm is 
formed. 
It will be seen from what has just been said that it is notan 
easy matter to discriminate between the primary constituents 
of a cell and the so-called secondary constituents, or such as 
arise from the katabolie activity of the primary bodies. 
Furthermore, it is an extremely difficult matter to isolate from 
a given tissue or organ the active cells entering into its struc- 
ture, or to collect together a sufficient number of unicellular 
organisms free from impurities or admixtures. When, bow- 
ever, this has been accomplished and we are ready to analyze 
the isolated cells, we are at once confronted with the limita- 
tions attending this kind of work, especially the fact that any 
ordinary method of separation or analysis, even the initiatory 
steps in the process, immediately transforms the living matter 
into dead matter, which transformation may be accompan! 
by cleavage or other chemical changes of more or less com- 
plexity ; so that the bodies we identify as components of the 
cell protoplasm may be simply alteration products, oF frag- 
ments of the larger and more complex molecules resident 12 
the living matter. | 
From microscopical examination we have evidence that 
protoplasm is far from being homogeneous, that it is loade 
with granules and pervaded by a mesh-work of irregu®” 
arrangement. These various forms of protoplasmic diferet" 
tiation have, as you know, been variously named by different 
investigators, as the spongioplasm, paraplasm, h yaloplasm, ete, 
