It may be remarked, in passing, that the estimates of the proper frequency of sexual intercourse may always be taken to assume that there is a cessation during the menstrual period.  This is especially the case as regards early periods of culture when intercourse at this time is usually regarded as either dangerous or sinful, or both. (This point has been discussed in the “Phenomena of Periodicity” in volume i of these Studies.) Under civilized conditions the inhibition is due to aesthetic reasons, the wife, even if she desires intercourse, feeling a repugnance to be approached at a time when she regards herself as “disgusting,” and the husband easily sharing this attitude.  It may, however, be pointed out that the aesthetic objection is very largely the result of the superstitious horror of water which is still widely felt at this time, and would, to some extent, disappear if a more scrupulous cleanliness were observed.  It remains a good general rule to abstain from sexual intercourse during the menstrual period, but in some cases there may be adequate reason for breaking it.  This is so when desire is specially strong at this time, or when intercourse is physically difficult at other times but easier during the relaxation of the parts caused by menstruation.  It must be remembered also that the time when the menstrual flow is beginning to cease is probably, more than any other period of the month, the biologically proper time for sexual intercourse, since not only is intercourse easiest then, and also most gratifying to the female, but it affords the most favorable opportunity for securing fertilization.

Schurig long since brought together evidence (Parthenologia, pp. 302 et seq.) showing that coitus is most easy during menstruation.  Some of the Catholic theologians (like Sanchez, and later, Liguori), going against the popular opinion, have distinctly permitted intercourse during menstruation, though many earlier theologians regarded it as a mortal sin.  From the medical side, Kossmann (Senator and Kaminer, Health and Disease in Relation to Marriage, vol. i, p. 249) advocates coitus not only at the end of menstruation, but even during the latter part of the period, as being the time when women most usually need it, the marked disagreeableness of temper often shown by women at this time, he says, being connected with the suppression, demanded by custom, of a natural desire.  “It is almost always during menstruation that the first clouds appear on the matrimonial horizon.”

In modern times the physiologists and physicians who have expressed any opinion on this subject have usually come very near to Luther’s dictum.  Haller said that intercourse should not be much more frequent than twice a week.[392] Acton said once a week, and so also Hammond, even for healthy men between the ages of twenty-five and forty.[393] Fuerbringer only slightly exceeds this estimate by advocating from fifty