Labor is caused by involuntary contractions of the uterus and abdominal muscles. By their force the liquor amnii flows out, the head of the fœtus is engaged in the pelvis, it goes through it, and soon passes out by the valve, the folds of which disappear. These different phenomena take place in succession, and continue a certain time: they are accompanied with pains more or less severe, with swelling and softening of the soft parts of the pelvis and external genital parts, and with an abundant mucous secretion in the cavity of the vagina. All these circumstances, each in its own way, favor the passage of the fœtus.
The precursory signs of labor are as follows: Two or three days before it is to commence, a flow of mucus takes place from the vagina, and the external genital parts swell and become softer: it is the same with the ligaments that unite the bones of the pelvis; the mouth of the womb flattens, its opening is enlarged, its edges become thinner, and slight pains, known under the name of _flying pains_, are felt in the loins and abdomen. At the next stage pains begin to be felt in the lower part of the back, or lumbar region, and tend towards the womb, or the rectum: these occur at intervals of fifteen to thirty minutes, and each is accompanied with contraction of the womb, and tension of its neck, which begins to open. If a finger is now introduced into the vagina, a considerable tumor may be felt, which is a protrusion of the membrane coverings of the fœtus, containing the first waters. The pains gradually become stronger up to the time when the membranes break, and labor actually begins.
The uterus now contracts on itself, and is applied to the surface of the fœtus. Soon the pains and contractions of the uterus increase considerably, and are accompanied by the contraction of the abdominal muscles. The woman should favor this state of things by making all the muscular efforts in her power, (straining.) As the labor progresses, her pulse will become stronger and more frequent; her face becomes animated; her eyes grow brighter; her whole body is in extreme agitation; perspiration flows in abundance; until the head of the child descends into the lower strait of the pelvis.