n experience, however, I am inclined to believe that these
movements are not unconscious, but merely unattended to, in other
words, we have a narrowing down of the apperceived content within
certain limits, but not a narrowing down of consciousness, (much
less a "splitting" of consciousness or of personality as the thing
unfortunately has sometimes been called). In order, however, not to
be guilty of premature judgment, I have avoided the terms
"unconscious" and "unattended to," and chose expressions which leave
these finer distinctions untouched.]

The next question that arises is: why did only a few persons receive
responses regularly from Hans, whereas the greater number were favored
only occasionally? What was the selective principle involved? The answer
is, that the successful person had to belong to a certain type, which
embodied the following essential characteristics.

1. A certain measure of ability and tact in dealing with the horse. As
in the case of dealing with wild animals, such as the lion, etc., Hans
must not be made uneasy by timidity in the questioner, but must be
approached with an air of quiet authority.

2. The power of intense concentration, whether in expectation of a
certain sensory impression (the final tap), or in fixing attention upon
some idea-content ("yes", "no", etc.). It is only when expectancy and
volition are very forceful, that a sufficient release of tension can
ensue. This release of tension is accompanied by a change in innervation
and results in a perceptible movement. And it was only when the thought
of "yes", or "up", etc., was very vivid, that the nervous energy would
spread to the motor areas and thence to the efferent fibers, and thus
result in the head-movement of the questioner. From infancy we are
trained to keep all of our voluntary muscles under a certain measure of
control. During the state of concentration just described, this control
is relaxed, and our whole musculature becomes the instrument for the
play of non-voluntary impulses. The stronger the customary control, the
stronger must the stimuli be which can overcome it. The steady
unremitting fixation, which resulted in the horse's selection of the
cloths, also involves a high degree of concentration.

3. Facility of motor discharge. Great concentration was necessary of
course, but not sufficient. Persons in whom the flow of nervous energy
tended to drain off over the nerves leadin