APPENDIX II
Reading edition
Since the chapter on Human Fecundity was set up in type my attention has been called to a paper by Siegel (Münchener Medizinische Wochenschrift, 1916, p. 748). Though much has been said as to the supposed influence of the time of copulation with reference to the sexual cycle upon fertility, no definite information has been forthcoming. This paper, however, contains important data which bear upon this point. Owing to the fact that married soldiers only had occasional leave from the army during the war and then only for two or three days at a time, it has been possible to obtain information as to the period in the sexual cycle in which between two and three hundred children were conceived. Siegel finds that the likelihood of fertilization increases from the beginning of menstruation, reaches the highest point six days later, remains almost at the same height until the twelfth or thirteenth day, and then declines to the twenty-second day, after which there is absolute sterility.
If these data are confirmed, then those customs which encouraged copulation immediately after menstruation (as among the ancient Jews) or discourage it (as among the Hindus) must have an important bearing upon fertility.
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