Radical as the bodily changes in progress at this time are, the lying-in period is not a period of illness. But there is, perhaps, no other time in a woman's life when she may cross the boundary between sickness and health so easily; for here nature tolerates no trifling. Not infrequently puerperal patients who are feeling well attempt too much, and suffer a more or less serious set-back; it is an all- important duty of the obstetrician, therefore, to restrain them from harmful activity. In my experience patients yield to restraint most readily, and secure the best results, if I explain to them the anatomical facts which should guide the management of the lying-in period. THE CHANGES IN THE UTERUS.--Since of all the organs the uterus undergoes during pregnancy the most extensive development, it also holds the place of prominence during the lying-in period. Immediately after delivery the womb weighs two pounds and measures some eight inches in height, five in breadth, and four in thickness. In the course of a few days it begins to dwindle in size, gradually sinking in the abdomen until it lies entirely within the pelvic cavity. Toward the end of five or six weeks it resumes the position occupied before conception, regains approximately its original dimensions, and weighs two ounces. We speak of the process which leads to these results as the _involution_ of the uterus. Since a great deal depends upon the rapidity with which involution progresses, we must understand just what it is and how it may be influenced. The muscle of the womb, to which this property of involution belongs, is an aggregation of thousands of individual fibers. In response to excellent nutrition during pregnancy, these fibers have grown thick and strong, in order that they may furnish the power needed at the time of labor. When this purpose has been fulfilled each fiber becomes smaller and gradually passes into a resting stage the better to preserve its vigor. It is the shrivelling of the individual fibers, therefore, which accounts for the total reduction in the size of the womb.