There is evidently a close relation between the functions of the breasts and of the uterus and accordingly involution is likely to progress more satisfactorily in women who nurse their babies than in those who do not. The so-called “after-pains,” also, are affected by nursing, being more severe, as a rule, when the baby is at the breast than at other times. These pains are caused by alternate contractions and relaxations of the uterine muscles and are more common in women who have had other children than after the first baby. These pains usually subside after the first twenty-four hours, though they may persist for three or four days. In connection with the changes that take place in the uterus, the discharge called _lochia_ should be mentioned. This is quite profuse and bloody at first but if the uterus involutes normally the discharge gradually decreases in amount and fades in color, until by the end of the puerperium it has entirely disappeared. =The Production of Milk.= During the first two or three days after the baby is born, the breasts secrete a small amount of yellowish fluid called _colostrum_, which differs somewhat from the milk that comes later. About the third day the meager amount of colostrum is replaced by milk and as this increases rapidly in amount, the breasts usually become tense and swollen and sometimes painful; but this discomfort generally subsides in a day or two. The production of milk is definitely stimulated by the baby’s suckling and will not continue for more than a few days without this stimulation, a fact to be remembered if, for any reason, it is desirable to dry up the breasts. The end earnestly to be desired is for the breasts to produce a quantity and quality of milk which will adequately nourish the baby during the first eight or ten months of his life, and with proper care and effort this ideal can nearly always be realized. But if the mother becomes pregnant while nursing her baby—and this sometimes occurs as early as a few weeks after childbirth—the quality of her milk is likely to suffer. The return of menstruation, however, does not necessarily affect the milk unfavorably, as is so generally believed. It is true that in the ideal course of events, the mother does not menstruate while nursing her baby, that is, for eight or ten months, but it is probable that about one-third of all nursing mothers begin to menstruate about two months after confinement and half of those who do not nurse their babies begin to menstruate in six weeks. A nursing mother may menstruate once and then not again for several months or a year; or she may menstruate regularly and still nurse her baby satisfactorily.