_Formation of the bag of the liquor amnii._ When the os uteri has dilated more or less, a quantity of liquor amnii begins to collect between the head and the membranes, so that when a pain comes on they form a tense, elastic, and conical bag, which presses firmly against the os uteri, and protrudes through it into the vagina, and from its form and elastic nature greatly facilitates the speedy dilatation of it. If the edge of the os uteri be still thin, it will become so tense during the pain, and the bag of membranes will press so firmly against it, that we shall have some difficulty for the moment in distinguishing the one from the other. As the labour advances, the intervals between the pains become shorter, whereas the pains themselves are of longer duration and more effective. In this way pain succeeds pain until the os uteri, at length, attains its full degree of dilatation; if the membranes have not yet ruptured, we may now expect them to burst with every succeeding pain. _Rigour at the end of the first stage._ At this moment the patient is occasionally seized with a sudden and violent fit of shivering, so much so as to make the teeth chatter, and even communicate a tremulous motion to the bed itself; this is not the result of cold, nor is it relieved by the application of external warmth; and, in many cases, the patient will express her surprise that she should shiver thus violently, and yet not feel cold. It appears to be a modification of convulsive action, excited by sympathy between the os uteri on its becoming fully dilated, and certain muscles in other parts of the body. _Show._ On examination at this stage of the process, streaks of blood will be found in the mucus which soils the finger, and sometimes it amounts to a slight discharge of blood: this appearance is called by midwives "_a show_," as it usually indicates that the os uteri is nearly or fully dilated. It is produced by a separation of the membranes from the vicinity of the os uteri, and consequent rupture of any little vascular twigs which may have passed from the uterus to them. The full dilatation of the os uteri terminates the _first stage_ of labour. During this stage, the action of the pains does not appear to have been so much for the expulsion of the child, as for preparing it as well as the passages for this purpose, viz. by so arranging and regulating the different forces of the uterus, and at the same time by giving the child such a position (_i. e._ with its long axis parallel to that of the uterus,) and the os uteri such a degree of dilatation, as shall ensure its expulsion with the greatest possible ease and safety.