At the periods of interstitial cell hyperactivity, when a wave of radicalism in the blood sweeps through the tissues, the other endocrines are tested, and their latent stability or instability is made manifest. Even before puberty, cyclic variations of health and conduct may be observed in boys and girls which undoubtedly depend upon currents among the internal secretions. Children, who, in the best of circumstances, habitually are attacked by a wanderlust and run away from home, or suffer from fits of naughtiness, are samples of such endocrine lability. Children specialists have found that at about the end of the second year their charges begin to individuate. In a certain percentage, sex traits appear pretty early. But the fact of the matter is that it is rather the minority of girls who spontaneously exhibit the traditional stigmata of the natural girl. The doll-cherishing, housekeeping imitator of mother is another story. At puberty arise the most exquisite cases of life crisis dependent upon hormonic crisis. The boy becomes restless, irritable and quick-tempered when his thyroid and adrenals respond to the call of the interstitial cells. If they do not, he will become dull, heavy, lazy and listless. The girl correspondingly is transformed into a vivacious, gay, nervous and apprehensive butterfly, or a sedate, dreamy, bashful, or even morose moth. It is interesting to note that poise, mental equilibrium, is not established until physical growth ceases, marked by a cessation of growth of the long bones known as ossification of the epiphyses. Poise seems to be controlled by the ante-pituitary. The growth of the long bones is also dominated by the ante-pituitary. It would seem as if, its secretion dedicated to the one function, could not be available for the other. So it happens that those in whom growth ceases early (probably because of an earlier and more vigorous invasion of the internal secretion system by the interstitial cell product), develop mental maturity more rapidly and possess more of it than those in whom growth continues. The acumen and salacity of certain dwarfs is proverbial. The puberty phenomena teach that sex crises of every sort are dependent fundamentally upon fluctuations, periodic or aperiodic, of the sex index, as we have defined it. THE DETERMINING FACTORS OF SEX LIFE The material summarized in the preceding paragraphs furnish some slight inkling of the vast dominion of Sex, in all its relations, somatic and spiritual, over which the glands of internal secretions rule. The founder of modern pathology, Virchow, said that woman is woman because of her ovaries. He meant that woman is a woman, the sort of woman she specifically is, because of her internal secretions. But no divine decree has laid down a line of cleavage between man and woman. There are fundamental constitutional differences between man and woman. But it is just as true that man is man because of _his_ internal secretions.