The involuntary muscular fibres of the uterus appear, like those of the ureter or of the frog's heart, to possess the power of rhythmical contraction, and may contract when entirely separated from the general nervous system. They are, however, controlled by the higher nerve-centres. There appears to be one centre, situated in the lumbar portion of the spinal cord, which is of itself sufficient to regulate all the movements, for they go on normally, even when the spinal cord has been completely divided above it. This centre may be reflexly stimulated and contractions of the uterus induced by irritation of the ovarian, crural, or sciatic nerves. It may be also stimulated by the action upon it of drugs circulating in the blood, as ergotin, picrotoxine, or strychnine, or by great venosity of the blood, due to asphyxia.

There appears, however, also to be a second centre for the uterus, as for the male genital organs, in the brain (vide p. 448), by which the lumbar centre may be excited, and in consequence of this, stimulation of the cerebellum, crura cerebri, corpora striata, and optic thalami, also gives rise to uterine contractions.

Von Basch and Hofmann consider that the impulses pass to the uterus from the central nervous system, along two sets of nerves. One is composed of nerves passing from the inferior mesenteric ganglion to the hypogastric plexus. Stimulation of these causes circular contraction of the uterus, descent of the cervix and dilatation of the os. The other consists of branches passing from the sacral nerves across the pelvis to the hypogastric plexus, and representing the nervi erigentes. On stimulation of these the uterus contracts longitudinally; the cervix ascends and the os closes.

The mode of action of ecbolics has not been satisfactorily ascertained. Ammonia injected into the circulation appears to cause contraction of the muscular fibres, for it causes contraction of the uterus even when all nervous connections have been divided. Ergot possibly acts in the same way, but it is possible also that it acts on the spinal centre.

The chief ecbolics are :Ergot.

Hydrastis.

Quinine.

Savin.

Thuja.

Uses. - Ecbolics are used to accelerate the expulsion of the child when the passages are free but expulsive power is deficient, and to cause firm contraction of the uterus and so prevent haemorrhage after delivery.

Adjuncts. - Compression of the uterus by kneading, pressure over it by a pad, the hand dipped in cold water laid over the uterus, or a cold pad. Sternutatories have been used to supplement the expulsive power of the uterus, and when necessary, operative interference must be had recourse to.

The injection of hot water into the vagina, as hot as can be borne, is a great aid in causing firm contraction of the uterus, and thus stopping post partem haemorrhage. Some of the liquid probably enters the cervix through the flaccid os (vide p. 351).