I
The mechanistic theory of life--the theory that all living things can be
explained and fully accounted for on purely physico-chemical
principles--has many defenders in our day. The main aim of the foregoing
chapters is to point out the inadequacy of this view. At the risk of
wearying my reader I am going to collect under the above heading a few
more considerations bearing on this point.
A thing that grows, that develops, cannot, except by very free use of
language, be called a machine. We speak of the body as a machine, but we
have to qualify it by prefixing the adjective living--the living
machine, which takes it out of the mechanical order of things
fabricated, contrived, built up from without, and puts it in the order
we call vital, the order of things self-developed from within, the order
of things autonomous, as contrasted with things automatic. All the
mechanical principles are operative in the life processes, but they have
been vitalized, not changed in any way but in the service of a new order
of reality. The heart with its chambers and valves is a pump that
forces the blood through the system, but a pump that works itself and
does not depend upon pneumatic pressure--a pump in which vital energy
takes the place of gravitational energy. The peristaltic movement in the
intestines involves a mechanical principle, but it is set up by an
inward stimulus, and not by outward force. It is these inward stimuli,
which of course involve chemical reactions, that afford the motive power
for all living bodies and that put the living in another order from the
mechanical. The eye is an optical instrument,--a rather crude one, it is
said,--but it cannot be separated from its function, as can a mere
instrument--the eye sees as literally as the brain thinks. In breathing
we unconsciously apply the principle of the bellows; it is a bellows
again which works itself, but the function of which, in a very limited
sense, we can inhibit and control. An artificial, or man-made, machine
always implies an artificer, but the living machine is not made in any
such sense; it grows, it arises out of the organizing principle that
becomes active in matter under conditions that we only dimly understand,
and that we cannot reproduce.
The vital and the mechanical coöperate in all our bodily functions.
Swallowing our food is a mechanical process, the digestion of it is a
chemical process and the assimilation and elimination of it a vital
process. Inhaling and exhaling the air is a mechanical process, the
oxidation of the blood is a chemical process, and the renewal of the
corpuscles is a vital process. Growth, assimilation, elimination,
reproduction, metabolism, and secretion, are all vital processes 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, coördinates, 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.