Essentially, the ovary is a collection of follicles, nests of cells, acting as safe deposit vaults for the ova that are to become candidates for fertilization.  At birth, there are some 30,000 to 200,000 of these, of which a good many atrophy during childhood so that there are no more than about 30,000 left at puberty.  Of the 30,000, only an elite 400 actually mature between the ages of fifteen and forty-five.  About every twenty-eight days, one of the follicles swells, becomes filled with liquid, pushes or is pushed to the surface of the ovary, there to rupture and expel into the abdominal cavity the tiny ripe ovum.  The rest of the torn follicle makes itself over into a peculiar yellowish body, the true corpus luteum, should pregnancy occur.  If pregnancy and the consequent placenta do not occur, it shrinks and turns into a scar, the false corpus luteum.  The true corpus luteum resembles closely the adrenal cortex in make-up and staining reactions.  It seems as if, once successful impregnation has been achieved, the feminine organism adrenalizes itself, makes itself more masculine and less feminine, inhibiting the posterior pituitary and the adrenal medulla, as well as the ovaries.  Besides, the corpus luteum stimulates the thyroid to prepare for the heavy demands to be made upon it during pregnancy.

Before menstruation, there is a stage of preparation, a stir and twittering of the endocrines, the premenstrual state.  Currents of communication flow between the different glands, messages and replies pass to and fro.  When these are properly balanced, so that all goes well, the consciousness of the woman will be disturbed by no knowledge of them.  In some women abnormal sensations appear, a sense of fullness in the breasts, or of weight in the back or pelvis, or pain in the head.  The last is probably due to swelling of the pituitary beyond the capacity of its bony container.  In a good many women, nervous and mental phenomena herald the expected menstruation because of a complete upset of the balance between the internal secretions, with resulting disturbance of the nervous system.  Irritability, depression, excitability, melancholia, exaltations, restlessness, hysteria, loss of self-control, or even more marked mental aberrations may appear.  Following them, and roughly paralleling them, may come various abnormalities of menstruation itself.  The character, extent and duration of these furnish us the best clues to the endocrine stability or instability of the particular feminine organism.

Menstruation is simply the uterus saying:  well, not this time.  As the destined ovum within its nest, the follicle, grows, its fluid affects the interstitial cells to send their specific stuff into the blood.  There it circulates, hits this gland and that, makes some more active, others less, transforms the chemistry of the cells, and engorges the mucous membranes, most of all those of the nose and of the uterus.  It is all to welcome the mature ovum and its possible