On the occurrence of the œstrous cycle after X-ray sterilisation. Part IV.–Irradiation of the adult during pregnancy and lactation; and general summary

In the first two parts of this series (2, 3) it was shown that the complete destruction of Graafian follicles as organised units by irradiation of the young female does not inhibit the appearance of the œstrous cycle when puberty is subsequently reached, while in Part III (4) the cycle in the non-mated adult was shown to persist unchanged after sterilisation. The clear deduction from these results is that neither follicles nor corpora lutea are essential to the main­ tenance of the œstrous cycle in the unmated animal. Extensive investigation was first made on the sterilisation of young animals, because preliminary experiments had shown that irradiation of the adult, during the functional life of the persistent corpus luteum at any rate, resulted in the permanent histological survival of corpora lutea vera, and it was desired in the first place to investigate the œstrous cycle after sterilisation in the absence of such a com­plication. This anticipation was not altogether realised, because in certain cases the young follicles, sent into atresia by irradiation, produced corpora lutea atretica. In the majority of cases, however, the ovaries from animals sterilised at birth or at weaning time were free from tissue of follicular derivation. Since it seemed possible that the removal of follicular competition might cause the persistent corpus luteum to function for an abnormally long period, experiments on this question have been carried out, and the present paper deals with the irradiation of the adult during the functional life of the persistent corpus luteum (i. e ., irradiation during pregnancy and lactation), which results in the permanent histological survival of the orpora lutea vera, and with the effects of these structures on the recurrence of the œstrous cycle. The histology of the ovaries of the animals discussed in this paper is essentially similar to that found in the ovaries of non-parous adults after irradiation, and is con­sidered in collaboration with Dr. Brambell elsewhere.