The Experimental Induction of Prenatal Mortality and the Subsequent Elimination of the Dead Embryos in Rabbits

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Abstract
1. All the embryos in utero in pregnant rabbits were killed in a few hours by 5 mg. of stilboestrol administered subcutaneously. Experiments were performed on fourteen animals at 11 days, twelve animals at 15¾ days and three animals at 19-20 days post-coitum. 2. Embryos killed with stilboestrol administered at 11 or 15¾ days post-coitum were invariably reabsorbed. Abortion occurred when the embryos were killed by stilboestrol at 19-20 days. 3. Some or all of the embryos were killed in sixteen animals at 16 days and in five animals at 19-20 days post-coitum by perforating the uterus, membranes and embryos with a needle at laparotomy. Many of the embryons survived this treatment. 4. Abortion occurs as a rule, but not invariably, when all the embryos are killed by surgical means. In the 16-day-series abortion is probably preceded by an initial period of autolysis. In the 20-day-series one animal reabsorbed but the others aborted. 5. Destruction of some only of the embryos at 16 or 20 days post-coitum by surgical means usually results in reabsorption of the dead embryos and the maintenance of pregnancy, but may result in abortion. 6. The occurrence of abortion may depend on the stage of development attained by the placenta. 7. Abortion occcurred at 19½-25 days post-coitum. There was no evidence that abortion occurred before the 19th day. 8. The speed at which reabsorption proceeds varies with the stage of development of the embryos at the time of death, the manner of death, and whether some or all the embryos die. Reabsorption proceeds much more quickly after stilboestrol administration than after surgical interference. The dead embryos are much more persistent when others survive and the mother remains pregnant than when all are killed surgically. It is uncertain whether the greater rapidity of removal, when all embryos die, is due to more rapid autolysis or is due to the curtailment of reabsorption by abortion.