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No abstract

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Females of strain BALB were maintained sterile for 13 to 20 months by the subcutaneous implantation of pellets containing 40% of 19-nor-progesterone. The life-span of the treated animals was not shorter than that of normal breeding females. Pregnancy can still take place when the pellet is removed after having caused sterility during 395 days, i.e. till the moment when, in normal animals, 98 % of the reproductive task has been fulfilled.The females emerging from a steroid-induced sterility of 395 days behaved as to reproduction like normal aged females: litter frequency and litter size were as small as in the latter.The sterilizing 19-nor-steroid produced ovarian tumours in a considerable percentage of animals. It is not probable that the reproductive activity after removal of the pellets was impaired by these tumours.The experimental conditions as established by the protracted administration of the sterilizing anti-ovulatory steroid represent, supposedly, the maximum sparing of oocytes hitherto obtained. The decline of fertility not being counteracted by this sparing, it would seem that the gerontological decline of fertility is not dependent on the diminished number of oocytes available in the senile ovary.It is not yet possible to locate the gerontological factor responsible for the decline of fertility, in the ovary, or in the hypophysis, or in any other part of the body.Recovery offertility in mice 101

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