which
cannot be described in terms of physics and chemistry. All our bodily
movements--lifting, striking, walking, running--are mechanical, but
seeing, hearing, and tasting, are of another order. And that which
controls, directs, cooerdinates, and inhibits our activities belongs to a
still higher order, the psychic. The world of thoughts and emotions
within us, while dependent upon and interacting with the physical world
without us, cannot be accounted for in terms of the physical world. A
living thing is more than a machine, more than a chemical laboratory.

We can analyze the processes of a tree into their mechanical and
chemical elements, but there is besides a kind of force there which we
must call vital. The whole growth and development of the tree, its
manner of branching and gripping the soil, its fixity of species, its
individuality--all imply something that does not belong to the order of
the inorganic, automatic forces. In the living animal how the psychic
stands related to the physical or physiological and arises out of it,
science cannot tell us, but the relation must be real; only philosophy
can grapple with that question. To resolve the psychic and the vital
into the mechanical and chemical and refuse to see any other factors at
work is the essence of materialism.

II

Any contrivance which shows an interdependence of parts, that results in
unity of action, is super-mechanical. The solar system may be regarded
as a unit, but it has not the purposive unity of a living body. It is
one only in the sense that its separate bodies are all made of one
stuff, and obey the same laws and move together in the same direction,
but a living body is a unit because all its parts are in the service of
one purposive end. An army is a unit, a flock of gregarious birds, a
colony of ants or bees, is a unit because the spirit and purpose of one
is the spirit and purpose of all; the unity is psychological.

Only living bodies are adaptive. Adaptation, of course, has its physics
or its chemistry, because it is a physical phenomenon; but there is no
adaptation of a rock or a clay-bank to its environment; there is only
mechanical and chemical adjustment. The influence of the environment may
bring about chemical and physical changes in a non-living body, but they
are not purposive as in a living body. The fat in the seeds of plants in
northern countries is liquid and solid at a lower temperature than in
tropical climates. Liv