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.

For some years I have been making as scientific and detailed a study as possible of this extremely complex problem. Owing to the frank and scientific attitude of a number of women, and the ready and intimate confidence of many more, I have obtained a number of most interesting facts from which I think it is already possible to deduce a generalisation which is illuminating, and may be of great medical and sociological value. A detailed statement of this will be given in a scientific publication, but as it bears very intimately on the subject of the present chapter, a short and simple account of my conclusions must be given here.

It is first necessary to consider several other features of woman's life, however.

The obvious moon-month rhythm in woman, so obvious that it cannot be overlooked, has been partially studied in its relation to some of the ordinary functions of her life. Experiments have been made to show its influence on the rate of breathing, the muscular strength, the temperature, the keenness of sight, etc.,. and these results have even been brought together and pictured in a single curved diagram supposed to show the variability in woman's capacities at the different times in her twenty-eight-day cycle.

But it brings home to one how little original work even in this field has yet been done, that the same identical diagram is repeated from book to book, and in Marshall's Physiology it is " taken from Sellheim," in Havelock Ellis " from Von Ott," and in other books is re-copied and attributed to still other sources, but it is always the same old diagram.

This diagram is reproduced by one learned authority after another, yet nearly every point on which this curve is based appears to have been disputed.

According to this curve,- woman's vitality rises during the few days before menstruation, sinks to its lowest ebb during menstruation and rises shortly after, and then runs nearly level till it begins to rise again before the next menstrual period. This simple curve may or may not be true for woman's temperature, muscular strength, and the other relatively simple things which have been investigated. My work and observations on a large number of women all go to show that this curve does not represent the waves of woman's sex-vitality.

The whole subject is so complex and so little studied that it is difficult to enter upon it at all without going into many details which may seem remote or dull to the general reader. Even a question which we must all have asked, and over which we have probably pondered in vain--namely, what is menstruation?--cannot yet be answered. To the lay mind it would seem that this question should be answerable at once by any doctor; but many medical men are still far from being able to reply to it even approximately correctly. (See also Appendix, note 2.)

There are a good many slight variations among us, ranging from a three to a five weeks "month," but the majority of the women of our race have a moon-month of twenty-eight days, once during which comes the flow of menstruation. If we draw out a chart with succeeding periods of twenty-eight days each, looking on each period as a unit: When in this period is it that a normal healthy woman feels desire or any up-welling of her sex-tides ?

The few statements which are made in general medical and physiological literature on the subject of sex feeling in women are generally very guarded and vague. Marshall ("Physiology of Reproduction," p. 138), for instance, says: "The period of most acute sexual feeling is generally just after the close of the menstrual period." Ellis speaks of desire being stronger before and sometimes also after menstruation, and appears to lean to the view that it is natural for desire to coincide with the menstrual flow.

After the most careful inquiries I have come to the conclusion that the general confusion regarding this subject is due partly to the great amount of variation which exists between different individuals, and partly to the fact that very few women have any idea of taking any scientific interest in life, and partly to the fact that the more profound, fundamental rhythm of sex desire which I have come to the conclusion exists or is potential in every normal woman, is covered over or masked by the more superficial and temporary influences due to a great variety of stimuli or inhibitions in modern life. For the present consideration I have tried to disentangle the profound and natural rhythm from the more irregular surface waves.

The chart given opposite may assist in making graphically clear what has been said in these last few pages. It is compounded from a number of individual records, and shows a fair average chart of the rhythmic sequence of superabundance and flagging in woman's sex-vitality. The tops of the wave-crests come with remarkable regularity, so that there are two wave-crests in each twenty-eight-day month, The one comes on the two or three days just before menstruation, the other after; but after menstruation has ceased there is a nearly level interyal, bringing the next wave-crest to the two 6r three days which come about eight or nine days after the close of menstruation--that is, just round the fourteen days, or half the moon month, since the last wave-crest. If this is put in its simplest way, one may say that there are fortnightly periods of desire, arranged so that one period comes always just before each menstrual flow. According to her vitality at'the time, and the general health of the woman, the length of each desire-period, or, as we might say, the size and complexity of each wave-crest, depends. Sometimes for the whole of as much as, or even more than three days, she may be ardently and quite naturally stimulated, while at another time the same woman, if she is tired and over-worked, may be conscious of desire for only a few hours, or even less.