| Every 4 weeks in | 77 women. |
| Every 3 weeks in | 17 women. |
| Every 2 weeks in | 1 woman. |
| Every 6 weeks in | 5 women. |
Foster instituted inquiries regarding this matter in 56 healthy women. In 380 periods, 45 recurred after an interval of 28 days, 225 after a shorter interval than this, 110 after a longer interval. The duration of the flow varied from 1 to 14 days; most commonly it lasted from 3 to 5 days.
A peculiar change in the type of menstruation sometimes manifests itself in this way, that in women in whom the regular four-weekly type of menstruation has prevailed, exactly in the middle of this four-weekly period the menstrual molimina, with or without menstrual discharge, make their appearance; the patient suffers from pain in the lower belly, sacrache, sensation of weight, and bearing-down pains. Courty, Dubois, and Pajot Négrier have described such cases of molimen utérin intermenstruel, which Tilt denotes by the term remittent menstruation.
From the earliest times the process of menstruation has attracted the attention of natural philosophers, and has led them to formulate hypotheses and to institute investigations, especially in order to ascertain whether the connection between ovulation and menstruation is one of temporal succession merely, or whether the relation is a causal one.
From Hippocrates and Galen downwards until well beyond the middle ages, the view of the father of medicine was generally accepted, that menstruation is a purificatory process by means of which materials harmful to the organism are eliminated from the body—a view which finds expression also in the religious and legal ordinances of all times.
A new epoch of scientific research into the nature of menstruation began with de Graaf’s discovery of the ovarian follicles (1672). This discovery did not, indeed, bring ovulation and menstruation into immediate relationship, but it certainly paved the way for the opinion expressed by Sintemma, a countryman of de Graaf, that the ova, even in virgins, leave the ovary spontaneously, and by their contact with the capillary terminations of the bloodvessels give rise to the menstrual bleeding (1728).
As a result of anatomical investigations, Négrier, in 1840, was the first to establish the thesis that in women suffering from congenital absence of the ovaries, menstruation never occurs; that after the loss of the ovaries, menstruation always ceases; that during pregnancy and lactation and during the climacteric period, ovulation ceases; and that a relation of temporal succession obtains between ovulation and menstruation. This close relation between the two processes was maintained also by Gendrin at about the same date. Later, Girdwood, by post mortem research, proved that the number of scars in the ovary coincides with the number of previous menstruations.
Brierre de Boismont, in his exhaustive work on Menstruation, lays stress on the view that the periodically recurring ovulation furnishes the impulse for the menstrual flow. First among German investigators, Bischoff upheld the opinion that maturation and discharge of ova are spontaneous processes occurring independently of sexual intercourse, and compared heat or rut in other animals to menstruation in women—a view shared by Pouchet and Coste. Ovulation occurs simultaneously with the menstrual flow, and the follicles burst toward the end of menstruation.
Pflüger, in his important work on the significance and cause of menstruation, has demonstrated the causal connection between menstruation and ovulation. The bleeding and the discharge of the ova are according to him joint effects of a common cause. It is not the bursting of the follicle, but the ripening of the follicle, that gives rise to the menstrual congestion. The pressure of the growing follicle on the surrounding ovarian tissue gives rise to a continued stimulation of the ovarian nerves; the summation of these stimuli, which after the lapse of a certain time attain always a certain degree of intensity, results in a reflex from the spinal cord taking the form of great congestion of the genital organs; this congestion leads, on the one hand, to hæmorrhage from the uterine mucous membrane, and, on the other hand, and as a rule simultaneously, to the bursting of the ovarian follicle. The swelling and granulation of the uterine mucous membrane at every menstrual period signifies nothing else than the commencement of the formation of the decidua.
Nägele already mentioned the view, that inasmuch as immediately after the first appearance of menstruation a woman has become capable of reproducing the species, each process of menstruation must be regarded as a renewal of the exhausted faculty for conception.