CONSCIOUSNESS AND MOVEMENT.
=All consciousness is motor.= The reader will not have forgotten, in the
jungle of purely inward processes and products through which the last
chapters have borne him, that the final result of them all must be some
form of bodily activity due to the escape of the central excitement
through outgoing nerves. The whole neural organism, it will be
remembered, is, physiologically considered, but a machine for converting
stimuli into reactions; and the intellectual part of our life is knit up
with but the middle or 'central' part of the machine's operations. We
now go on to consider the final or emergent operations, the bodily
activities, and the forms of consciousness consequent thereupon.
Every impression which impinges on the incoming nerves produces some
discharge down the outgoing ones, whether we be aware of it or not.
Using sweeping terms and ignoring exceptions, _we might say that every
possible feeling produces a movement, and that the movement is a
movement of the entire organism, and of each and all its parts_. What
happens patently when an explosion or a flash of lightning startles us,
or when we are tickled, happens latently with every sensation which we
receive. The only reason why we do not feel the startle or tickle in the
case of insignificant sensations is partly its very small amount, partly
our obtuseness. Professor Bain many years ago gave the name of the Law
of Diffusion to this phenomenon of general discharge, and expressed it
thus: "According as an impression is accompanied with Feeling, the
aroused currents diffuse themselves over the brain, leading to a
general agitation of the moving organs, as well as affecting the
viscera."
There are probably no exceptions to the diffusion of every impression
through the _nerve-centres_. The _effect_ of a new wave through the
centres may, however, often be to interfere with processes already going
on there; and the outward consequence of such interference may be the
checking of bodily activities in process of occurrence. When this
happens it probably is like the siphoning of certain channels by
currents flowing through others; as when, in walking, we suddenly stand
still because a sound, sight, smell, or thought catches our attention.
But there are cases of arrest of peripheral activity which depend, not
on inhibition of centres, but on stimulation of centres which discharge
outgoing currents of an inhibitory sort. Whenever we are startled, for
example, our heart momentarily stops or slows its beating, and then
palpitates with accelerated speed. The brief arrest is due to an
outgoing current down the pneumogastric nerve. This nerve, when
stimulated, stops or slows the heart-beats, and this particular effect
of startling fails to occur if the nerve be cut.
In general, however, the stimulating effects of a sense-impression
proponderate over the inhibiting effects, so that we may roughly say, as
we began by saying, that the wave of discharge produces an activity in
all parts of the body. The task of tracing out _all_ the effects of any
one incoming sensation has not yet been performed by physiologists.
Recent years have, however, begun to enlarge our information; and we
have now experimental proof that the heart-beats, the arterial pressure,
the respiration, the sweat-glands, the pupil, the bladder, bowels, and
uterus, as well as the voluntary muscles, may have their tone and degree
of contraction altered even by the most insignificant sensorial stimuli.
In short, a _process set up anywhere in the centres reverberates
everywhere, and in some way or other affects the organism throughout,
making its activities either greater or less_. It is as if the
nerve-central mass were like a good conductor charged with electricity,
of which the tension cannot be changed at all without changing it
everywhere at once.
Herr Schneider has tried to show, by an ingenious zoölogical review,
that all the _special_ movements which highly evolved animals make are
differentiated from the two originally simple movements of contraction
and expansion in which the entire body of simple organisms takes part.
The tendency to contract is the source of all the self-protective
impulses and reactions which are later developed, including that of
flight. The tendency to expand splits up, on the contrary, into the
impulses and instincts of an aggressive kind, feeding, fighting, sexual
intercourse, etc. I cite this as a sort of evolutionary reason to add to
the mechanical _a priori_ reason why there _ought_ to be the diffusive
wave which _a posteriori_ instances show to exist.
I shall now proceed to a detailed study of the more important classes of
movement consequent upon cerebromental change. They may be enumerated
as--
1) Expressions of Emotion;
2) Instinctive or Impulsive Performances; and
3) Voluntary Deeds;
and each shall have a chapter to itself.