little subject to change. It represents the earlier adjustments of the
race, crystallized into habit. It takes no account of the differences
between the present and the past. It knows no culture, no reason, no
lately acquired prudence. It is all energy and can only wish, or urge
toward action. But since only those race-memories became instincts
which had proved needful to the race in the long run, they are on the
whole beneficent forces, working for the good of the race and the good
of the individual, if he learns how to handle them aright and to adapt
them to present conditions.

This instinctive urge toward action arouses in the individual an
organic response that is felt as a tension or craving and is mainly
dependent upon its own chemical constitution at the moment. Hunger is
the sensation caused by the little muscular contractions in the
stomach when the body is low in its food supply. Sudden fright is felt
as an all-gone sensation "at the pit of the stomach." What really
happens is a tightening up of the circular muscles of the
blood-vessels lying in the network of the solar plexus, and a spasm of
the muscles of the digestive tract. The hungry stomach impels to
action until satisfied; the physical discomfort in fear impels toward
measures of safety. The apparatus that is made use of by the
subconscious in carrying out this instinctive urge is called the
autonomic nervous system.[19] It regulates all the functions of
living, not only under the stress of emotion, but during every moment
of waking or sleeping.

[Footnote 19: Kempf: "The Tonus of Automatic Segments as a Cause of
Abnormal Behavior," _Journal of Nervous and Mental Diseases_, January,
1921.]