This phenomenon seems to be one of the indications of the immense organic significance of the sexual relations.  Woman’s part in the world is less obtrusively active than man’s, but there is a moment when nature cannot dispense with energy and mental vigor in women, and that is during the reproductive period.  The languidest woman must needs be alive when her sexual emotions are profoundly stirred.  People often marvel at the infatuation which men display for women who, in the eyes of all the world, seem commonplace and dull.  This is not, as we usually suppose, always entirely due to the proverbial blindness of love.  For the man whom she loves, such a woman is often alive and transformed.  He sees a woman who is hidden from all the world.  He experiences something of that surprise and awe which Dostoieffsky felt when the seemingly dull and brutish criminals of Siberia suddenly exhibited gleams of exquisite sensibility.

In women, it must further be said, the sexual impulse shows a much more marked tendency to periodicity than in men; not only is it less apt to appear spontaneously, but its spontaneous manifestations are in a very pronounced manner correlated with menstruation.  A woman who may experience almost overmastering sexual desire just before, during, or after the monthly period may remain perfectly calm and self-possessed during the rest of the month.  In men such irregularities of the sexual impulse are far less marked.  Thus it is that a woman may often appear capricious, unaccountable, or cold, merely because her moments of strong emotion have been physiologically confined within a limited period.  She may be one day capable of audacities of which on another the very memory might seem to have left her.

Not only is the intensity of the sexual impulse in women, as compared to men, more liable to vary from day to day, or from week to week, but the same greater variability is marked when we compare the whole cycle of life in women to that of men.  The stress of early womanhood, when the reproductive functions are in fullest activity, and of late womanhood, when they are ceasing, produces a profound organic fermentation, psychic as much as physical, which is not paralleled in the lives of men.  This greater variability in the cycle of a woman’s life as compared with a man’s is indicated very delicately and precisely by the varying incidence of insanity, and is made clearly visible in a diagram prepared by Marro showing the relative liability to mental diseases in the two sexes according to age.[180] At the age of 20 the incidence of insanity in both sexes is equal; from that age onward the curve in men proceeds in a gradual and equable manner, with only the slightest oscillation, on to old age.  But in women the curve is extremely irregular; it remains high during all the years from 20 to 30, instead of falling like the masculine curve;