Curve showing the Periodicity of Recurrence of natural desire in healthy causes make slight irregularities in the position, size and duration of th< but the general rhythmic sequence is apparent.

Chart II

Curve showing the depressing effects on the " wave-crests" of fatigue and over-work. Crest a represented only by a feeble and transient up-welling. Shortly before and during ■-he time of the crest d Alpine air restored the vitality of the subject. The increased vitality is shown by the height and number of the apices of this wave-crest.

The effects of fatigue, city life, bad feeding, and, indeed, of most outward circumstances may be very marked, and may for years, or all her life, so reduce her vitality that a woman may never have experienced any spontaneous sex-impulse at all.

The effects of fatigue, which reduces the vital energy, even in a normal, strongly sexed woman, can be seen in the second curve opposite, where at a the intermediate wave-crest is very much reduced. This is not a generalised chart, but a detailed record of an actual individual case.

Curves similar to those shown facing page 32 represent in general terms a simplified view of what my research leads me to believe to be the normal, spontaneous sex tide in women of our rage. As one young married woman confided to me, her longing for bodily union with her husband, as distinct from her longing for his daily companionship, seemed to well up naturally like "clockwork," and this during his long absence. But human beings vary remarkably in every particular, and just as no two people have the same features, so no two people would have absolutely identical curves were they recorded in sufficient detail. Many a woman is particularly conscious of only one sex-impulse in each moon-month* Of such women, some feel the period which comes before menstruation, and some feel the one which follows it. In those who generally feel only one, the second period is sometimes felt when they are particularly well, or only when they read exciting novels, or meet the man they love at a time coinciding with the natural, but suppressed, time of desire. There are a few women, who seem to be really a little abnormal, who feel the strongest desire actually during the menstrual flow.

If anyone who reads this thinks to test my view by questioning a number of women, the result will probably appear very conflicting, partly because it is not often that women will tell the truth about such a thing, and partly because in the larger number of women either one or the other period is the more acute and is the one they observe in themselves--if they have observed anything. But a delicate and more accurate investigation of such cases will often bring to light the existence of the second crest of vitality. Once the fundamental idea is grasped, much that appeared obscure or of no significance becomes plain and full of meaning. One lady doctor with whom I discussed my view at once said that it illuminated many observations she had made on her patients, but had not brought together or explained.

There is but little evidence to be found in scientific works on sex, but an interesting instance is mentioned by Forel ("The Sexual Question," Engl. Transl. page 92) in another connection. He says: " A married woman confessed to me, when I reproached her for being unfaithful to her husband, that she desired coitus at least once a fortnight, and that when her husband was not there she took the first comer." Forel did not see any law in this. We may perhaps all see in her want of self-control a grievous moral abnormality, but in her fortnightly periods of desire she fits perfectly into the physiological law which, it appears to me, governs the normal sex tides of our race.

In this connection it is of interest to note the decrees of the Mosaic Law regarding marriage intercourse. Not only was all intercourse with a woman during her menstruation period very heavily punished (see Leviticus xx. 18 : " If a man lie with a woman having her sickness . . .• both of them shall be cut off from among their people "), but the Mosaic Law provided that women should be protected from intercourse for some days after each such period. The results obtained by my independent investigation thus find some support in this ancient wisdom of the East. Modern writers are inclined to deride the Mosaic Law on the ground that it prohibits intercourse just at the time when they think sex feeling should be strongest. But it does not appear on what grounds they make the latter statement, nor do they give any scientific data in support of it. Thus Galabin in his Manual of Midwifery says: " In the Jewish law women are directed to abstain* from coitus during menstruation and for seven days after its cessation. Strict observers of the law are said to go beyond what is commanded in Leviticus, and even if discharge lasts only for an hour or two, to observe five days during which the discharge might last, for the period itself and add to these seven clear days, making twelve in all. It is much to be doubted whether a whole nation was ever induced to practise abstinence at the period of most acute sexual feeling." But, as will readily be recognised, the old Jewish plan of having twelve clear days after the beginning of menstruation before the next union is in almost exact harmony with the Law of Periodicity of Recurrence of women's desire shown in my charts, pp. 32, 33.

* Note.--In Leviticus xv. it is the man who is directed to abstain from touching the woman at this period, and who is rendered unclean if he does. ---M. C. S.

These comparatively simple curves represent what I would postulate as the normal spontaneous up-welling of natural desire in woman. These are the foundations on which the edifice of the physical expression of love may be built. It must not be forgotten, however, that, particularly in modern luxurious life, there are innumerable excitements which may stimulate sexual feeling, just as there are many factors in our life which tend to inhibit or retard it. A woman may be, like a man, so swayed by a great love that there is not a day in the whole month when her lover's touch, his voice, the memory of his smile, does not stir her into the thrilling longing for the uttermost union. Hence it is often difficult, particularly for a woman dwelling with the man she loves, to recognise this rhythm in herself, for she may be perpetually stimulated by her love and by his beiiig.

I am convinced, however, that ordinarily, whether she recognises it by outward signs or not, a fortnightly rhythm profoundly influences the average woman, and hence that it fundamentally affects the marriage relation in every way. The burning magnificence of an overpowering life-long love is not given to many, and a husband who desires lasting and mutual happiness in his marriage will carefully study his wife, observe how far she has a normal rhythm, and in what she has little personal traits. He will then endeavour to adapt his demands on her so that they are in harmony with her nature.

This mutual adaptation is not an entirely simple matter, and will be considered in the next chapter.