terialist theory, however, are perhaps less confident than their
predecessors of the last century, for the solution in this direction
has to face not only the problem of organic co-ordination already
referred to, but also that of consciousness and mind. For although the
study of psychology on physiological lines has made similar progress to
that of other branches of physiology, it seems to approach little nearer
to a discovery of the nature of the relation between consciousness in
its various aspects and the material body with which it is associated.
So long as this gulf remains unbridged, the possibility of a
satisfactory mechanistic explanation of life seems far away.

On the other hand, there has been a revival of the ancient tendency
towards what is called a vitalistic solution. A certain number of
biologists, impressed by the apparent similarity between the control and
co-ordination exercised by the organism over its functions and the
conscious control of voluntary activity with which we are familiar in
ourselves, have supposed that these things are not merely superficially
similar but have a real and fundamental affinity. This does not mean
that organic control is always conscious, but that there is a
controlling entity, non-material in nature, which is similar in kind to
the 'ego' of a self-conscious human being. They suppose that the
organism is not simply material, but is a material mechanism controlled
by a non-material entity the nature of which is more akin to what we
mean by the word spirit than anything else of which we are accustomed to
think. They are in fact dualists, and divide reality into the material
and spatial on the one hand, and non-material principle or entity which
may fairly be called spiritual on the other.

And, in the third place, there are those who seek a solution which
denies the truth of both the preceding, and which is metaphysically
idealist or monist in character. To them, if the present writer
understands their attitude, matter and spirit are different aspects of
one reality. In the inorganic and non-living, phenomena appear which are
generalized under the laws of physics and chemistry, but the phenomena
of life fall into a different category which includes the conception of
co-ordination or individuality, while a still higher category is
required to include the phenomena of consciousness and mind.

It is evident from this brief review that Biology in the period
considered has pa