s a thing peculiar in itself; but it does not constitute a
diametrical, dualistic opposition to those laws; it is only a peculiar
species of motion. The motion itself is a mechanical one, for how
should we become cognisant of it if it were not based on the sensible
properties of bodies? The media of the motion are certain chemical
matters, for we recognise none but chemical matter in bodies. The
individual acts of motion reduce themselves to mechanical, or
physico-chemical, modifications of the constituent elements of the
organic unities, the cells and their equivalents." These and many
similar utterances in Virchow's earlier writings, and especially in
the essay I have mentioned, "On the Mechanical Conception of Life,"
leave no doubt that he formerly supported, with a clear conscience and
his utmost energy, in psychology as in the other collected departments
of physiology, that very mechanical standpoint which we to-day accept
as the essential basis of our monism, and which stands in
irreconcilable antagonism to the dualism of the vitalistic doctrine.
To none of my teachers am I so deeply indebted for my emancipation
from all the prejudices of the dualistic doctrine, and for my
conversion to the monistic, as to Rudolf Virchow; for it was his
superior guidance which most firmly convinced me, and many others, of
the exclusive importance of the mechanical view of nature. He led me
to a clear recognition of the fact that the nature of man, like every
other organism, can only be rightly understood as a united whole, that
this spiritual and corporeal being are inseparable, and that the
phenomena of the soul-life depend, like all other vital phenomena, on
material motion only--on mechanical (or physico-chemical)
modifications of cells. And it was in perfect agreement with my most
honoured master that I subscribed then, and at this day still
subscribe, to the proposition with which he, in September 1849, closed
the preface to the above-mentioned "Efforts at Unity." "It is possible
that I may have erred in details; in the future I shall be ready and
willing to acknowledge my mistakes and to rectify them, but I enjoy
this conviction, that I shall never find myself in the position of
denying the principle of the unity of the human nature with all its
consequences!"

To err is human! Who can say to what diametrical contradiction to his
firmest convictions man may not in the future be driven by his
adaptation to new relations in l