At the end of pregnancy the mouth of the womb is small, too small, often, to admit an instrument as broad as a lead pencil. It is obvious, therefore, that very radical changes must be wrought before the infant can pass. The door, as it were, must be widely opened. This phenomenon, which we call dilatation of the womb, is brought about by involuntary contractions of the muscle fibers in its wall, every point of which they draw upward. Now, the top of the womb is directly opposite its mouth, consequently the contractions inevitably pull its lips wider and wider apart. Ordinarily another factor is concerned in this mechanism. To understand the whole process we must recall that a fluid surrounds the fetus, and that this fluid is contained within elastic membranes. The uterine contractions compress the fluid, drive the membranes, like a wedge, into the mouth of the womb and spread its lips apart. Thus, to the pulling effect just mentioned, a pushing force is added. After full dilatation has been accomplished and the membranes can serve no further purpose, they rupture; as the midwife puts it, "the bag of waters breaks." The quantity of fluid which escapes will vary. Occasionally, a huge gush will drench the patient's clothing; but more often what is lost at first amounts to only a few teaspoonfuls, though small quantities of fluid often dribble away with subsequent contractions. Although not the rule, it is by no means unusual for the membrane to rupture at the onset of labor, or at least before the mouth of the womb is fully dilated. Exceptionally, rupture occurs a few days before labor begins; and still longer intervals, though extremely rare, have been recorded. Whenever the membranes rupture prematurely, the pushing force of the uterine contractions becomes less effective, though the pulling force is never impaired. Under these circumstances, which occasion what is called a "dry labor," delivery is apt to proceed slowly, yet that does not follow necessarily, for the part of the fetus which happens to lie over the mouth of the womb may act as efficiently as the unruptured membrane would. During the first stage, the longest of the three, the patient is comfortable between the contractions and generally interests herself in some diverting occupation. The presence of the physician can be of no assistance then, and patients rarely demand it. Usually, they are satisfied to know he is ready to come when called. It is wrong to deceive patients with various recommendations from which they will vainly expect help during this stage; their welfare is best served when they are left alone. Generally the advice of well-meaning friends will be as harmless as it is futile, yet I must emphasize that during the first stage straining to expel the fetus is ill advised. Such effort will surely be ineffective then and may exhaust the patient; in that event it becomes harmful, for she will be fatigued when she most needs strength.