gusts to drive the rain in over a high
doorsill, so must any stimulus--an idea or a sensation--come with
sufficient force to get over the obstructions at the doorway of
consciousness. These psychic thresholds do not maintain a constant
level. They are raised or lowered at will by a hidden and automatic
machinery, which is dependent entirely on the ideas already in
consciousness, by the interest bestowed upon the newcomer. The
intensity of the stimuli cannot be controlled, but the interest we
feel in them and the welcome given them are very largely a matter of
choice.

[Footnote 59: Sidis: _Foundations of Normal and Abnormal Psychology_,
Chap. XXX.]

Each organism has a wide field of choice as to which ideas and which
physical stimuli it shall welcome and which it shall shut out. We may
raise our thresholds, build up a bulwark of indifference to a whole
class of excitations, shut our mental doors, and pull down the shades;
or we may lower the thresholds so that the slightest flicker of an
idea or the smallest pin-prick of a sensation finds ready access to
the center of attention.

=Thresholds and Character.= There are certain thresholds made to shift
frequently and easily. When one is hungry any food tastes good, for
the threshold is low; but the food must be most tempting to be
acceptable just after a hearty meal. On the other hand, a fairly
constant threshold is maintained for many different kinds of stimuli.
These stimuli are always bound together in groups, and make appeal
depending upon the predominating interest. As anything pertaining to
agriculture is noticed by a farmer, or any article of dress by a
fashionable woman, so any stimulus coming from a "warm" group is
welcomed, while any from a "cold" group is met by a high threshold.
The kind of person one is depends on what kind of things are "warm"
to him and what kind are "cold." The superman is one who has gained
such conscious control of his psychic thresholds that he can raise and
lower them at will in the interests of the social good.

=Thresholds and Sensations.= The importance of these principles is
obvious. The next chapter will show more of their influence on ideas
and emotions; but for the present we will consider their lessons in
the sphere of the physical. Psychology speaks here in no uncertain
terms to physiology. Whoever becomes fascinated by the processes of
his own body is bound to magnify the sensations from those processes,
until the most