In the latter part of the puerperium there may be doubt as to whether a discharge is menstrual or lochial; though, if necessary, an examination of the interior of the womb would always settle the question, for structural changes in the uterine mucous membrane form the most characteristic feature of menstruation. If, therefore, small bits of this tissue are removed and studied under the microscope, a definite conclusion can be reached. Physicians may resort to such an examination when the significance of a discharge is not clear without it; but other evidence usually enables them to decide the matter. The secretion of milk often exerts an influence upon the reestablishment of menstruation. Under ideal circumstances the mother does not menstruate while she nurses her infant; whereas, if the breasts are not in use, the menstrual function returns six to eight weeks after delivery. Other pertinent clinical facts also lend weight to the opinion that the activity of the breasts, more technically called lactation, should not only prevent menstruation but also hinder the ripening of egg-cells in the ovary. Thus, the nursing infant has a potent influence upon the reproductive function of its mother, enabling it to preserve its food supply; for in the event of conception the milk usually decreases in amount or becomes of an inferior quality. To secure this protective influence should prove a strong incentive for the mother to nurse her child; in barely half the cases, however, is it effective throughout a year. One-third of nursing mothers, statistics indicate, begin to menstruate about two months after delivery, and month by month the proportion gradually increases. Since menstruation appears so frequently during lactation, it cannot be considered abnormal. It does not follow that the function will become permanently reestablished after a patient has menstruated once; in many instances several months elapse before there is another period, and in a few cases there will be only one period during the year the child suckles. Nevertheless, when the function has once made its appearance extraordinary precaution should be exercised to avert a return, and about the time its reappearance would be expected the woman should go to bed for several days. Although this measure may prove futile, we know of no other so likely to prove successful. Menstruation is more apt to return prematurely after the birth of the first child than of later ones. This may be due in part to a kind of accommodation of the maternal organism to the reproductive process as one pregnancy follows another; but I am convinced that it is also due in part to the greater physical and mental composure of experienced mothers. Until a woman has learned the unwelcome consequences she is apt to take over household duties before she is equal to the task, or she may engage in too strenuous amusements; and most mothers err in a too energetic care of the baby.