ease 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 to one hundred
single acts in the year.[394] Forel advises two or three times a week for
a man in the prime of manhood, but he adds that for some healthy and
vigorous men once a month appears to be excess.[395] Mantegazza, in his
_Hygiene of Love_, also states that, for a man between twenty and thirty,
two or three times a week represents the proper amount of intercourse, and
between the ages of thirty and forty-five, twice a week. Guyot recommends
every three days.[396]

It seems, however, quite unnecessary to lay down any general rules
regarding the frequency of coitus. Individual desire and individual
aptitude, even within the limits of health, vary enormously. Moreover, if
we recognize that the restraint of desire is sometimes desirable, and
often necessary for prolonged periods, it is as