ements into three classes, voluntary,
reflex and mechanical. We may illustrate the distinction by a quotation
from William James ("Psychology," i, 12):

"If I hear the conductor calling 'all aboard' as I enter the depot, my
heart first stops, then palpitates, and my legs respond to the air-waves
falling on my tympanum by quickening their movements. If I stumble as I
run, the sensation of falling provokes a movement of the hands towards
the direction of the fall, the effect of which is to shield the body
from too sudden a shock. If a cinder enter my eye, its lids close
forcibly and a copious flow of tears tends to wash it out.

"These three responses to a sensational stimulus differ, however, in
many respects. The closure of the eye and the lachrymation are quite
involuntary, and so is the disturbance of the heart. Such involuntary
responses we know as 'reflex' acts. The motion of the arms to break the
shock of falling may also be called reflex, since it occurs too quickly
to be deliberately intended. Whether it be instinctive or whether it
result from the pedestrian education of childhood may be doubtful; it
is, at any rate, less automatic than the previous acts, for a man might
by conscious effort learn to perform it more skilfully, or even to
suppress it altogether. Actions of this kind, with which instinct and
volition enter upon equal terms, have been called 'semi-reflex.' The
act of running towards the train, on the other hand, has no instinctive
element about it. It is purely the result of education, and is preceded
by a consciousness of the purpose to be attained and a distinct mandate
of the will. It is a 'voluntary act.' Thus the animal's reflex and
voluntary performances shade into each other gradually, being connected
by acts which may often occur automatically, but may also be modified by
conscious intelligence.

"An outside observer, unable to perceive the accompanying consciousness,
might be wholly at a loss to discriminate between the automatic acts and
those which volition escorted. But if the criterion of mind's existence
be the choice of the proper means for the attainment of a supposed
end, all the acts alike seem to be inspired by intelligence, for
APPROPRIATENESS characterizes them all alike."

There is one movement, among those that James mentions at first, which
is not subsequently classified, namely, the stumbling. This is the
kind of movement which may be called "mechanical"; it is evidently