It is external only in those whose higher brain centres are either undeveloped or diseased.  These constitute the criminal classes.  Their motor impulses are unrestrained.  They offer a low or reduced resistance to temptation.

Weak or absent resistance in the face of a normal motor impulse whose expression injuriously affects another, is crime, and a criminal is one whose power of resistance to motor impulses has been reduced by disease, hereditary or acquired, or is absent through arrested development.

A confirmed criminal is one in whom the frequent recurrence of an unrestrained impulse injurious to others has induced habit.

Auto-inhibition is defective or absent, and society must in her own interest provide external restraint, and this we call law.

Criminals are, therefore, mental defectives, and may be defined for sociological purposes as those in whom legal punishment for the second time, for the same offence, has failed to act as a deterrent.

M. Boies, in “Prisoners and Paupers,” says that conviction for the third time for an offence, is proof of hereditary criminal taint.

The existence of motor impulses in the human animal is normal.  They vary in strength and force.  We cannot eradicate, we can only control them.

They may become less assertive under the constant control of a highly cultivated inhibition, but it is only in this way that they can be affected at all.  They may be controlled, either by the individual himself or by the State.  Our reformatories are peopled by young persons whose distinguishing characteristic is that inhibition is undeveloped or defective.  This defect may be due to want of education, but it is more often hereditary.

Two things only can be done for them.  This faculty of inhibition can be trained by education, or external restraint can be provided by law.

But the distinguishing characteristic of all defectives, within or without our public institutions, is defective inhibition,—­they are unable to control the spontaneous impulses that continually arise, and which may indeed be normal.

Impulses may be abnormal from hereditary predisposition, as e.g. the impulse to drink, but only through strengthening inhibition can these impulses be controlled,—­their existence must be accepted.

But whether the defect is an abnormal impulse, or a normal impulse abnormally strong, or an abnormally weak or defective inhibition, the condition is hereditary, and such defectives propagate their kind.

It has been shown that they are more fertile than any other classes because of the very defect that makes them a danger to society.

The defective restraint that allows them to commit offences against person and property, also allows their procreative impulse unrestrained activity.

Defectives, therefore, are not only fertile, but they propagate their kind, and a few examples will serve to show to some extent the fertility, and to an enormous extent the hereditary tendencies, of the unfit.