mind holds opinions tentatively and is always ready to reexamine, modify
or discard as new evidence comes to light.

Naturally in a book of this sort there are many references to the human
mind and its activities. In most books, whether scientific or not, the
mind has generally been more closely associated with the brain than any
other portion of the body. As a rule I have assumed that this view of
mind and brain is correct. Often I have referred to it as a matter of
course. I am aware that the latest investigations seem to establish the
mind more as a function of the nervous system and the vital organs than
of the brain. Whether the brain is like a telephone exchange and is only
concerned with automatically receiving and sending out messages to the
different parts of the body, or whether it registers impressions and
compares them and is the seat of consciousness and thought, is not
important in this discussion. Whatever mind may be, or through whatever
part of the human system it may function, can make no difference in the
conclusions I have reached.

The physical origin of such abnormalities of the mind as are called
"criminal" is a comparatively new idea. The whole subject has long been
dealt with from the standpoint of metaphysics. Man has slowly banished
chance from the material world and left behavior alone outside the realm
of cause and effect. It has not been long since insanity was treated as
a moral defect. It is now universally accepted as a functional defect of
the human structure in its relation to environment.

My main effort is to show that the laws that control human behavior are
as fixed and certain as those that control the physical world. In fact,
that the manifestations of the mind and the actions of men are a part of
the physical world.