cular lines. It starts with mere criticism and with objections,
which go no further than saying that "in the meantime" we are still far
from having reached a physico-chemical solution of the riddle of life; it
may ascend through all stages up to an absolute rejection of the theory as
an idiosyncrasy of the time which impedes the progress of investigation,
and as an uncritical prejudice of the schools. It may remain at the level
of mere protest, and content itself with demonstrating the insufficiency
of the mechanical explanation, without attempting to formulate any
independent theory for the domain of the vital; or it may construct a
specifically biological theory, claiming independence amid other
disciplines, and basing this claim on the autonomy of vital processes; or
it may widen out deliberately into metaphysical study and speculation.
Taken at all these levels it presents such a complete section of the trend
of modern ideas and problems that it would be an attractive study even
apart from the special interest which attaches to it from the point of
view of religious and idealistic conceptions of the universe.

Both Liebig and Johannes Mueller remained vitalists, notwithstanding the
discovery of the synthesis of urea and the increasing number of organic
compounds which were built up artificially by purely chemical methods. It
was only about the middle of the last century that the younger generation,
under the leadership, in Germany, of Du Bois-Reymond in particular, went
over decidedly to the mechanistic side, and carried the doctrines of the
school to ever fresh victories. But opposition was not lacking from the
outset, though it was restrained and cautious.

Virchow's "Caution".

Here, as also in regard to "Darwinism," which was advanced about the same
time, the typical advocate of "caution" was Rudolf Virchow. His doubts and
reservations found utterance very soon after the theory itself had been
promulgated. In his "Cellular Pathologie,"(76) and in an essay on "The Old
Vitalism and the New,"(77) he puts in a word for a _vis vitalis_. The old
vitalism, he declared, had been false because it assumed, not a _vis_, but
a _spiritus vitalis_. The substances in animate and in inanimate bodies
have undoubtedly absolutely the same properties. Nevertheless, "we must at
once rid ourselves of the scientific prudery of regarding the processes of
life solely as the mechanical result of the molecular forces inherent in