The monkeys examined by Heape menstruated throughout the year and yet seemed in the free state to have definite breeding times.
The human female, with but few exceptions, menstruates throughout the year and may breed at any time. The exceptions in the case of the human female are of interest. Dr. Frederick A. Cook,[3] ethnologist to the first Peary North Greenland Expedition, says of the Esquimaux living in the extreme north, from the seventy-sixth to the seventy-ninth parallels of latitude: “The passions of these people are periodical, and their courtship is usually carried on soon after the return of the sun; in fact, at this time they almost tremble from the intensity of their passions, and for several weeks most of their time is taken up in gratifying them. Naturally enough, then, the children are usually born at the beginning of the Arctic night.” In Queensland the natives are also said to have a special breeding season.
Menstruation usually begins in this country at the fourteenth year. The time of the first appearance of the process is influenced by race, climate, and environment. As a rule, it begins earlier in warm climates and later in cold climates. It is earlier in girls who lead luxurious, indolent lives than in girls of the working classes.
During the first year or two of menstrual life menstruation is often very irregular. It may be absent for several months after its first appearance, or recur at varying intervals before it becomes regularly established. Irregularity at this time calls for no treatment.
Precocious menstruation rarely occurs at a very early age. It has been known to begin, and to recur with regularity, from the time of birth. In such cases there is a corresponding premature development of the sexual organs.
The menstrual discharge consists of blood, mucous secretion from the uterus and vagina, and epithelial cells from the endometrium.
The normal duration of the flow is from two days to a week. The amount of fluid discharged is from 2 to 9 ounces. Menstruation occurs every twenty-eight days, counting from the beginning of one period to the beginning of another. The menstrual interval is subject to considerable individual variations, which appear to be within the limits of health. It sometimes occurs with regularity every two, three, or five weeks. When it occurs every two weeks, the alternate flows are often but small in amount. The occurrence of, or the attempt at, menstruation every two weeks, in a woman who had previously menstruated monthly, is sometimes a symptom of beginning uterine disease.
Menstruation commonly ceases at about the forty-fifth year, when the menopause appears.
Most of the disorders of menstruation have already been considered as symptoms of the various lesions of the genital organs that have been described in the previous pages.
There are some disorders of menstruation, however, often unaccompanied by discoverable lesions, which now demand consideration.