s essentially an automaton or machine, a configuration of
material particles, which, like an engine or a piece of clockwork,
owes its mode of operation to its physical and chemical construction?
It is not open to doubt that the living body _is_ a machine. It is a
complex chemical engine that applies the energy of the food-stuffs to
the performance of the work of life. But is it something more than a
machine? If we may imagine the physico-chemical analysis of the body
to be carried through to the very end, may we expect to find at last
an unknown something that transcends such analysis and is neither a
form of physical energy nor anything given in the physical or chemical
configuration of the body? Shall we find anything corresponding to the
usual popular conception--which was also along the view of
physiologists--that the body is "animated" by a specific "vital
principle," or "vital force," a dominating "archaeus" that exists only
in the realm of organic nature? If such a principle exists, then the
mechanistic hypothesis fails and the fundamental problem of biology
becomes a problem _sui generis_.

In its bearing on man's place in nature this question is one of the
most momentous with which natural science has to deal, and it has
occupied the attention of thinking men in every age. I cannot trace
its history, but it will be worth our while to place side by side the
words of three of the great leaders of modern scientific and
philosophic thought. The saying has been attributed to Descartes,
"Give me matter and I will construct the world"--meaning by this the
living world as well as the non-living; but Descartes specifically
excepted the human mind. I do not know whether the great French
philosopher actually used these particular words, but they express the
essence of the mechanistic hypothesis that he adopted. Kant utterly
repudiated such a conception in the following well known passage: "It
is quite certain that we cannot become adequately acquainted with
organized creatures and their hidden potentialities by means of the
merely mechanical principles of nature, much less can we explain them;
and this is so certain that we may boldly assert that it is absurd for
man even to make such an attempt or to hope that a Newton may one day
arise who will make the production of a blade of grass comprehensible
to us according to natural laws that have not been ordered by design.
Such an insight we must absolutely deny to man." Stil