The most important occurrence of all, however, is the periodical occurrence of menstruation, whose most marked phenomenon is a sanguineous discharge from the genitals, normally occurring at intervals of a lunar month twenty eight days.
This menstruation signifies that the woman is capable of reproduction or child bearing. Beginning, on the average, soon after fourteen years of age, it continues until the "change of life", or "menopause", or "climacteric", i.e., until about forty four years of age, and it is, in health, interrupted only by pregnancy and lactation (suckling).
If menstruation begin earlier it ends earlier, and vice versa, so that the child-bearing period of a woman's life, or her distinctive sex life, lasts about thirty years, though in hot countries it is shorter.
Each woman usually has a definite periodicity in her menstruation, the common interval from the beginning of one menstrual period to the beginning of the next being the "twenty eight day type", though some menstruate every thirty days, a few every twenty one days, and fewer still every twenty seven days. When a girl starts to menstruate there is complete uncertainty as to what the type will be, though when once fully established it remains pretty constant.
The amount of blood lost averages from six to eight ounces, though sometimes it may normally be only two or three ounces, or sometimes twelve or fourteen ounces. The discharge usually lasts from two to six days, and is usually more profuse in blondes than in brunettes.
Menstruation is by no means merely a monthly flow of blood from the genitals. As Matthews Duncan of Edinburgh well said, "The red flag at the auctioneer's door shows that something more important is going on inside." And so also the flow of blood proves to be but an incident of menstruation, and not at all the important factor ovulation, or the formation of eggs, being the peculiar and interesting event.
In viviparous animals there is a condition similar to that of menstruation in women, but in them it is called the "heat" ("rutting" in deer). Usually this season of "heat" in animals occurs but once a year, and at other times the females neither admit the males, nor could they become pregnant if they did. Domestication with its artificialities of diet and temperature has made the recurrence of this phenomenon uncertain in some of our animals.
A woman when she is menstruating cannot be said to have a "mens sana in corpore sano", and is thus physically unfitted for the active pursuits followed by men. Before menstruation begins there is a feeling of mental irritation and lassitude, fatigue in the lower limbs, congestion in the back, loins and lower abdominal region, sensitiveness on pressure over the abdomen, feelings of heat and cold, disorders of appetite and digestion, and various other systemic disturbances.
The principal event in menstruation is the maturation and rupture of a Graafian follicle, the discharge of an ovum, or egg, from one of the ovaries, and its passage along one of the Fallopian tubes to the cavity of the uterus. If the ovum is fertilized by the male reproductive element, or spermatozoid, it finds lodgment in the uterus and develops into a foetus; if not fertilized, it passes off unnoticed in the menstrual discharge.
A woman is more liable to conceive immediately after her menstrual period has passed; but it is most important to remember that conception may occur at any time during the thirty years of her menstrual life, and that fornication can never be indulged in without the risk of impregnation. Each "monthly sickness" is in reality a sort of mimic parturition or missed pregnancy; childbirth being physiologically the aim and object of a woman's life, for which, though it may not be accomplished, Nature is nevertheless constantly striving. The sexual impress is thus seen to be stamped upon womankind as a much more powerful factor in their lives than in men's, though we must be careful to avoid confusing the word "sexual" with "sensual."
To bear in mind the tender graces of women, their beauty and delicacy, their susceptible and responsive mental natures, their trustful and confiding love, their mission of motherhood with the subsequent rearing of the children, their heavenly influence over our lives, their unfitness to meet us on a common level in the battle of life, must influence every warm-hearted man to ever treat them with chivalry and veneration, to protect their honor, and to oppose their degradation and downfall with all his power