It is certainly true of women as they have been made by the inhibitions of modern conditions, that most of them are only fully awake to the existence of sex after marriage. As we are human beings, the social, intellectual, spiritual side of the love-choice have tended to mask the basic physiological aspect of women's sex-life. To find a woman in whom the currents are not all so entangled that the whole is inseparable into factors, is not easy, but I have found that wives (particularly happy wives whose feelings are not complicated by the stimulus of another love) who have been separated from their husbands for some months through professional or business duties--whose husbands, for instance, are abroad--are the women from whom the best and most definitive evidence of a fundamental rhythm of feeling can be obtained. Such women, yearning daily for the tender comradeship and nearness of their husbands, find, in addition, at particular times, an accession of longing for the close physical union of the final sex-act. Many such separated wives feel this; and those I have asked to keep notes of the dates, have, with remarkable unanimity, told me that these times came specially just before and some week or so after the close of menstruation, coming, that is, about every fortnight. It is from such women that I got the first clue to the knowledge of what I call the Law of Periodicity of Recurrence of desire in women. This law it is possible to represent graphically as a curved line; a succession of crests and hollows as in all wave-lines. Its simplest and most fundamental expression, however, is generally immensely complicated by other stimulations which may bring into it diverse series of waves, or irregular wave-crests. We have all, at some time, watched the regular ripples of the sea breaking against a sand-bank, and noticed that the influx of another current of water may send a second system of waves at right angles to the first, cutting athwart them, so that the two series of waves pass through each other. Woman is so sensitive and responsive an instrument, and so liable in our modern civilised world to be influenced by innumerable sets of stimuli, that it is perhaps scarcely surprising that the deep, underlying waves of her primitive sex-tides have been obscured, and entangled so that their regular sequence has been masked in the choppy turmoil of her sea, and their existence has been largely unsuspected, and apparently quite unstudied.