34 
knowledge gained, we cannot repress a cer- 
tain sense of disappointment, partly that 
microscopical research should have fallen 
so far short of giving the insight for which 
we had hoped, but still more because of the 
failure of the best observers to reach any 
unanimity in the interpretation of what is 
actually visible under the microscope. In 
any consideration of the general subject, 
therefore, it is well to keep clearly in view 
the fact that such disagreement exists, and 
that we are not yet in a position to justify 
any very certain or far-reaching conclu- 
sions. 
I would like, at the outset, to express the 
opinion that, if we except certain highly 
specialized structures, the hope of finding 
in visible protoplasmic structure any ap- 
proach to an understanding of its physio- 
logical activity is growing more, instead of 
less, remote, and is giving way to a convic- 
tion that the way of progress lies rather in 
an appeal to the ultra-microscopical proto- 
plasmie organization and to the chemical 
processes through which this is expressed. 
Nevertheless, it is of very great importance 
to arrive at definite conclusions regarding 
the visible morphology of protoplasm, not 
only because of its intimate connection with 
all the problems of cell-morphology, but 
also in order to find the right framework, 
as it were, for our physiological conceptions, 
and thus to gain suggestions for further 
physiological and chemical inquiry. And 
this must be my excuse for reviewing a 
subject which is still so largely obscured 
by doubt, and of which the outcome gives, 
after all, so little satisfaction. 
It is especially important in this field of 
biological inquiry to distinguish clearly be- 
tween theory and observed fact, for theories 
of protoplasmic structure have always far 
outrun the actual achievements of observa- 
tion. From the time of Briicke (one of the 
first to insist that protoplasm must possess 
a far more complicated organization than 
SCIENCE. 
[N. S. Vou. X. No. 237. 
that visible under the microscope) specu- 
lation has gone steadily forward, to reach, 
perhaps, its most elaborate expression in 
Weismann’s interesting, but unconvincing, 
work on the germ-plasm—an_ elaborate 
speculative system built out of hypotheses 
which, for the most part, float in the air 
without visible means of support. We 
need not consider this side of the subject 
in extenso, but I will ask attention, for a 
moment, to what is the most characteristic 
and, to the morphologist, the most interest- 
ing point in these speculations, namely, the 
doctrine of genetic continuity as applied 
to the corpuscular, or micellar, theory of 
protoplasm. We are all familiar with the 
successive steps by which that doctrine 
gradually developed. Harvey’s celebrated 
formula, ex ovo omnia—or, as usually quoted, 
omne vivum ex ovo— took with Redi the far 
more philosophical form, omne vivum e vivo, 
thus expressing a truth which forms the very 
foundation of all biological teaching at the 
present day. The development of the cell- 
theory, long afterwards, enabled Virchow 
to pronounce the more specific aphorism, 
omnis cellula e cellula (1855), a statement 
involving the highly interesting conclusion 
that protoplasm is never formed de novo, 
but always arises from or through the ac- 
tivity of preéxisting protoplasm differenti- 
ated into the form of a cell. Still later a 
like conclusion was reached with respect to 
at least one of the structural components 
of the cell, namely, the nucleus, and the 
work especially of Flemming and Stras- 
burger justified the saying, omnis nucleus e 
nucleo. Not long afterwards, the researches 
of Schmitz, Schimper and others showed 
that in plant cells some, if not all, forms 
of plastids (for example, the chlorophyll- 
bodies) likewise arise by the division of 
preexisting bodies of the same kind. Thus 
the law of genetic continuity was gradually 
extended downwards from the grosser and 
more obvious characters of the organism 
