Though menstruation in women is analogous to the rut or “heat” of other animals, yet there are some points of difference: The lower mammals breed only at times of “heat,” and these times of “heat” occur in the wild state only at certain periods of the year, which are dependent upon climatic conditions, the young being born at the season of the year best suited for their survival. Some domestic animals, like the cow, probably as a result of domestication, have no regular breeding time. In the lower mammals “heat” and ovulation appear to be coincident, and these are the only periods during which the female seems normally to have any sexual desire. 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.