ABSTRACT
From a standpoint of individual personality, the postnatal development and differentiation are modified by progressive experiences to an extent of serious importance. The definite changes in form and disposition which occur at clearly accented periods of life are of peculiar interest in the process of postnatal human development. The periodic changes in structure associated with the reproductive apparatus and the final attainment of sexual maturity are thought to be brought about through growth-stimulating substances which arise in the germ-glands, the testis and ovary. The recognition of the personality changes resulting from modifications in the gonadal secretions serves to impress us with the fact that more or less marked responses to other chemical changes and varying hormonal relations are constantly arising within the body during the growth and development of the postnatal animal. The new environment is freer and more extensive in its possibilities than the prenatal surroundings, and the young animal must react to it in far more complex ways.
