Beuttner, Centralblatt für Gynäkologie, No. 49, 1893; summarized in British Medical Journal, December, 1893. Many cases show that pregnancy may occur in the absence of menstruation. See, e.g., Nouvelles Archives d'Obstétrique et de Gynécologie, 25 Janvier, 1894, supplement, p. 9.
It is still possible, and even probable, that the primordial cause of both phenomena is the same. Heape (Transactions Obstetrical Society of London, 1898, vol. xl, p. 161) argues that both menstruation and ovulation are closely connected with and influenced by congestion, and that in the primitive condition they are largely due to the same cause. This primary cause he is inclined to regard as a ferment, due to a change in the constitution of the blood brought about by climatic influences and food, which he proposes to call gonadin. (W. Heape, Proceedings of Royal Society, 1905, vol. B. 76, p. 266.) Marshall, who has found that in the ferret and other animals, ovulation may be dependent upon copulation, also considers that ovulation and menstruation, though connected and able to react on each other, may both be dependent upon a common cause; he finds that in bitches and rats heat can be produced by injection of extract from ovaries in the œstrous state (F. H. A. Marshall, Philosophical Transactions, 1903, vol. B. 196; also Marshall and Jolly, id., 1905, B. 198). Cf. C. J. Bond, "An Inquiry Into Some Points in Uterine and Ovarian Physiology and Pathology in Rabbits," British Medical Journal, July 21, 1906.
Pouchet, Théorie de l'Ovulation Spontanée, 1847. As Blair Bell and Pontland Hick remark ("Menstruation," British Medical Journal, March 6, 1909), the repeated œstrus of unimpregnated animals (once a fortnight in rabbits) is surely comparable to menstruation.