_Causes._ Premature expulsion may be induced by a great variety of causes, which may be brought under the two following heads: those which act indirectly, by destroying the life of the embryo, and those which act directly on the uterus itself. These various causes may be general or local; the process of nutrition for the growth and development of the embryo may be defective and scanty, from general debility or disease: hence, whatever depresses the tone of the patient's health renders her liable to abortion by causing the death of the embryo. Thus, dyspepsia and derangement of the chylopoietic viscera; debilitating evacuations; depressing passions of the mind; bad or insufficient nourishment; intense pain, as in toothach; severe suffering from existing disease, especially where the health is much broken down by some chronic affection; syphilis, and febrile attacks, all act as indirect causes of abortion.[62] Salivation from mercury not unfrequently has a similar effect; in some instances, however, febrile affections appear to act much more directly, stimulating the uterus to powerful contractions and rapid expulsion of its contents. The symptoms which indicate the death of the child have already been detailed in the chapter upon that subject. The period which may elapse between the death and the expulsion of the embryo varies exceedingly: in the early months the one usually follows the other pretty quickly, owing probably to the slight attachment of the ovum to the uterus; during the middle third of pregnancy the interval may be of considerable duration, and cases every now and then occur where the foetus is retained, not only several weeks, but even some months after its death; whereas, during the latter third of pregnancy, expulsion follows the death of the child after a short interval, seldom exceeding two or three days; for now the weight of the dead foetus speedily irritates the uterus to contraction, and, as has been observed by Smellie, the membranes, running gradually into putrefaction, and being now unable to bear the weight of the liquor amnii, burst, and expulsion soon follows.