It is necessary, therefore, to distinguish between the sex instinct and the maternal instinct. For different glands of internal secretion have been found responsible for them. A distinct difference in the quality and amount of the two instincts may be observed in the same person. A strong maternal instinct may be seen again and again to dominate a woman with but little or no sex urge or passion. Numerous physiologically frigid women have lived successful and happy married lives because of contented maternity. Other women, with normal or exaggerated sex instinct who welcome and stimulate the sex life, may have no wish for children, no functioning maternal instinct at all, and if sterile, will accept their fate with indifference or even exultation. These variations occur because of a difference in chemical source and determination of the two instincts. While the ovary, stimulated by the thyroid and the adrenal medulla, is the chief determinant of the sex instinct, to the posterior pituitary must be credited the chief hormone of the maternal instinct. The interactions of the two glands, the ovary and the posterior pituitary, modified by accessory influences, determine the relative intensity of the two instincts. In a sense, the two glands may be said to be antagonistic and yet one stimulates and complements the other. THE TRANSFIGURATIONS OF CHILD-BEARING Though what happens at puberty, what happens all through life through the agencies of the endocrines is amazing enough, what occurs during the period of child-bearing is perhaps the most amazing of all. As emphasized, pregnancy is the time, among the internal secretions, of a great uprooting and stirring, of fundamental and cataclysmic changes in the most intimate chemistry of the cells. It is as if a dictator, inspired by his country's danger, its enemies at the gates of its capitol, were to draft and mobilize everyone, man woman and child from everyday activities to the necessities of defense. Or rather it is as if there appeared within the heart of our civilization a common purpose and intelligence, now so palpably lacking, which magnetized and drew to itself all the streams of individual self-aggrandizing effort. Imagine that possibility and how it would change the face of the earth and the entire basic constitution of human life and society. So do the profound tides of the hormones, centering around the new creature being made in the womb, transfigure the face and constitution of the child-bearing woman.