LIFE AND MECHANISM 107

he confesses that we have " only a surface know-
ledge"; "only the manifestations come within the
range of our intelligence while that which is mani-
fested lies beyond it"; " the order existing among
the actions which living things exhibit remains the
same whether we know or do not know the nature
of that from which the actions originate." This
seems to us to sound a more modest note than is
heard in the sentence: " The interpretation of all
phenomena in terms of Matter, Motion and Force, is
nothing more than the reduction of our complex
symbols of thought to the simplest symbols."

Life and Mechanism.—But are not all biologists
confronted with the difficulty that gave Herbert
Spencer pause ? Physiological analysis has done
much in revealing chains of sequence within the
organism, but no vital phenomenon has as yet been
redescribed in terms of chemistry and physics.
Again and again some success in discovering physico-
chemical chains of sequence has awakened the
expectation that the dawn of a mechanical theory of
life was drawing nigh, but the dawn seems further
off than ever. The residual phenomena left unin-
terpreted by mechanical categories loom out more
persistently than they did a century ago. As Bunge
once said " the more thoroughly and conscientiously
we endeavour to study biological problems, the more
are we convinced that even those processes which we
have already regarded as explicable by chemical and
physical laws, are in reality infinitely more complex,
and at present defy any attempt at a mechanical
explanation." As Dr J. S. Haldane puts it: " If we
look at the phenomena which are capable of beingour of even the simplest organism,