Every theory of love, from Plato down, teaches that each individual loves in the other sex what he lacks in himself.

The years from about eight to twelve constitute a unique period of human life.

Abundance and vigor of automatic movements are desirable, and even a considerable degree of restlessness is a good sign in young children.

Being an only child is a disease in itself.

Muscles are in a most intimate and peculiar sense the organs of the will.

Adolescence as the time when an individual 'recapitulates' the savage stage of the race's past.