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; then it falls rapidly to considerably below the masculine curve, rising again considerably above the masculine level during the climacteric years from 40 to 50, after which age the two sexes remain fairly close together to the end of life. Thus, as measured by the test of insanity, the curve of woman's life, in the sudden rise and sudden fall of its sexual crisis, differs from the curve of man's life and closely resembles the minor curve of her menstrual cycle. The general tendency of this difference in sexual life and impulse is to show a greater range of variation in women than in men. Fairly uniform, on the whole, in men generally and in the same man throughout mature life, sexual impulse varies widely between woman and woman, and even in the same woman at different periods. FOOTNOTES: [169] Ovid remarks (_Ars Amatoria_, bk. i) that, if men were silent, women would take the active and suppliant part. [170] Ferrand, _De la Maladie d'Amour_, 1623, ch. ii. [171] Tarde, _Archives d'Anthropologie Criminelle_, May 15, 1897. Marro, who quotes this observation (_Pubertà_, p. 467; in French edition, p. 61), remarks that his own evidence lends some support to Lombroso's conclusion that under ordinary circumstances woman's sensory acuteness is less than that of man. He is, however, inclined to impute this to defective attention; within the sexual sphere women's attention becomes concentrated, and their sensory perceptions then go far beyond those of men. There is probably considerable truth in this subtle observation.