bject of instruction; for the cell itself is
not a certain and undoubted fact, but only an abstraction, a
philosophical idea.

Nothing more clearly shows what a complete change Virchow has
undergone in his most important principles, and what an utter
metapsychosis in this special province, than his famous axiom,
uttered in 1855--"Omnis cellula e cellula." That is unquestionably the
boldest generalisation to which the youthful, independent Virchow ever
attained, and one on which he justly prided himself not a little. He
himself repeatedly compared it with Harvey's saying, which marked an
epoch--"Omne vivum ex ovo." But neither of these axioms is universally
correct. On the contrary, we now know that every cell does not
necessarily originate from a cell, any more than that every organic
individual originates from an ovum. In many cases true nucleated cells
proceed from un-nucleated cytods, as in the Gregarinae, Myxomycetae and
others. Nay more, the primordial organic cells could only have
originated in the first instance from non-cellular plastides or monads
by their homogeneous plasson resolving itself into an internal nucleus
and an external protoplasm. Thus, as we subsequently learnt to know
most of the exceptions to this generalisation of Virchow, it appeared
all the bolder; the more so as we were at that time far from being
able to refer all the different tissues of the higher animals with any
certainty to cells, and as not a few experiments seemed to point to
the hypothesis of free cell-formation. That guiding axiom, which so
powerfully furthered the cell-theory, Virchow, from his present
standpoint, must wholly condemn as a crime against exact science, and
he surely can never forgive himself for having propounded this
hypothesis--which was afterwards found to be not universally true--as
an important doctrinal axiom.

We shall indeed find much worse sins against his own principles of
to-day if we turn to Virchow's own special department of science,
namely, pathological anatomy and physiology, the most important
division of theoretic medicine. The great and incomparable services
which Virchow here effected do not depend on the numerous independent
new facts which he discovered, but on the theories and hypotheses by
which, like an inspired pioneer, he sought to open a way through the
dead waste of pathological knowledge and to form it into a living
science. These new theories and the hypotheses on which they were
f