The Check and Drive systems, with the adrenals and thyroid opposed, are one of the best instances of their antagonisms. All these poses, of course, have supplied not an iota to an understanding of the foundations of the problems of sex, biologically considered. The womb must surrender some of that blood, the glands return to their routine, and a sex diastole of the whole organism succeeds. In general, the major endocrines, the pituitary, the adrenals, and the thyroid should hypertrophy and hyperfunction during pregnancy. When the activity of a ductless gland rises above a certain minimum, its hormones in the blood sensitize, as a photographic plate is sensitized, a group of brain cells, to respond to a message from the outside world, with a definite line of conduct. With a fortunate combination, he develops into a progressive winning fighter, arriving at the top in the long run every time.
An increase in size, a broadening, together with a greater mental tranquillity and stability, accompany the adaptation. Intense mental occupation, concentration as the popular term has it, acts as a patent excitor of the attack. Just as Napoleon was transformed by the mutations of his pituitary, so was the Saint with the Lamp. Slitting the genital duct of the other testis, causing its interstitial cells to hypertrophy and multiply, repeats the effects of the first experiment. Beginning with the traits and qualities which distinguish the sexes, grouped as the secondary sex characters, he showed that they are correlated with the special sexual function of the species in which they occur.