and the diaphragm, respiration follows as a matter of
pneumatics. In all these cases there are indeed qualifica-
tions induced by more searching inquiry. Not all the
facts of circulation are explicable on the principles of the
common pump. When the dilatation and contraction of
the arteries, for example, are taken into account, we can no
longer think of the blood as circulating through a simple
system of elastic tubes. When all the facts are known
the phenomena of digestion are not found to correspond
accurately to the chemical laws of osmosis. Moreover,
in stating each of these processes in mechanical terms, we
have to assume certain forces which are not like those of
an ordinary inanimate mechanism. Nevertheless the
advocates of the mechanical theory of life point with
triumph to a series of successes. Time and again they
have reduced some mysterious process, which seemed
distinctive of living beings and explicable only by the
assumption of some vital force, to mechanical terms.
Their belief is that the residue which is at present
unreduced only requires further investigation to be set
upon the same basis. If we knew enough about the
structure of the heart and the nature of nerves and
muscular action, we should be able to state the law of its
pulsations in mechanical formulæ. A similar extension
of our knowledge would explain the adaptation of the
arteries to the fluctuating requirements of the body, the
control of the respiratory mechanism by the medullary
centre, the absorption of foodstuff by the cells lining
the alimentary canal, and so forth. Finally, a still more
perfect knowledge would enable us to reduce purposive
action, artistic creation, philosophic thought to a complex
of mechanical changes in nervous tissue. All would be
recognised as mechanism if we could only know the
whole of the intimate structure of the body.

In order to examine this theory and to decide what
part, if any, is played by Mind in modifying mechanical
processes, we must ask in general terms what is meant by
the mechanical and what sort of function we suppose
mind to introduce in the business of correlating vital
activities. Now if we take a confessedly inanimate

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