st
injury, and to regenerate lost parts? All this is done by living
organisms, all this is the expression in them of "Life." What is it?
Whence comes it? And how can it be explained?

The problem of the nature of life, of the principle of vitality, is almost
as old as philosophy itself, and from the earliest times in which men
began to ponder over the problem, the same antitheses have been apparent
which we find to-day. Disguised under various catchwords and with the
greatest diversities of expression, the antitheses remain essentially the
same through the centuries, competing with one another, often mingling
curiously, so that from time to time one or other almost disappears, but
always crops up again, so that it seems as if the conflict would be a
never-ending one--the antitheses between the mechanical and the
"vitalistic" view of life. On the one side there is the conviction that
the processes of life may be interpreted in terms of natural processes of
a simple and obvious kind, indeed directly in terms of those which are
most general and most intelligible--namely, the simplest movements of the
smallest particles of matter, which are governed by the same laws as
movement in general. And associated with this is the attempt to take away
any special halo from around the processes of life, to admit even here no
other processes but the mechanical ones, and to explain everything as the
effect of material causes. On the opposite side is the conviction that
vital phenomena occupy a special and peculiar sphere in the world of
natural phenomena, a higher platform; that they cannot be explained by
merely physical or chemical or mechanical factors, and that, if
"explaining" means reducing to terms of such factors, they do in truth
include something inexplicable. These opposing conceptions of the living
and the organic have been contrasted with one another, in most precise
form and exact expression, by Kant in certain chapters of the Kritik der
Urteilskraft, which must be regarded as a classic for our subject.(56) But
as far as their general tendency is concerned, they were already
represented in the nature-philosophies of Democritus on the one hand, and
of Aristotle on the other.

All the essential constituents of the modern mechanical theories are
really to be found in Democritus, the causal interpretation, the denial of
any operative purposes or formative principles, the admission and
assertion of quantitative explanations al