In addition to climate, nationality, and the age at which menstruation begins, the sexual activity of women also exercises an influence on the duration of their sexual life, and of especial importance in this connection are the number of children born, and exercise or neglect of the function of lactation. From my own observations on this matter it appears, that in women who are healthy and of powerful constitution, whose reproductive organs have been sufficiently exercised, who have given birth to several children and have suckled these children themselves, the duration of menstrual activity is in general notably longer than in women whose circumstances have been just the opposite in these respects. Among the women in my own series of cases in whom menstrual activity lasted longest, of the 177 women in whom menstruation ceased between the forty-fifth and the fiftieth year of life, 1 only was unmarried, 2 were married but childless, 32 married with 1 or 2 children only, and 142 married and with more than 2 children; of the 89 women in whom menstruation ceased between the fiftieth and the fifty-fifth year of life, none were either unmarried or childless, 19 were married with 1 or 2 children, 17 married and with more than 2 children; of the 17 women in whom menstruation ceased later than the fifty-fifth year of life, there were 2 only with less than 2 children, but 10 who had each given birth to from 6 to 8 children. A similar influence is exercised by the function of lactation. Among 40 women who had not suckled their children, the average duration of menstrual activity was 4 years less than the general mean. As regards the conditions of life, _L. Mayer_ affirms that the duration of sexual activity among well-to-do women is on the average a year and a half longer than among women of the working classes. _Metschnikoff_ has drawn attention to the remarkable disharmony in the development of three of the phases of the sexual life of woman, inasmuch as the sexual impulse, the union of the sexes, and the capacity for procreation, which, considering their nature and purpose, might have been expected to be attuned so as to act in harmony, exhibit as a matter of fact no such relation; the different factors of the sexual function develop independently and unharmoniously. In a child not yet fitted to fulfil the function of procreation, the sexual impulse will none the less make its appearance, and be liable to misuse. In the girl the pelvis does not attain that complete development which fits it for the process of parturition until toward the age of twenty, whilst puberty occurs at the age of sixteen. “A girl of ten is capable of aspiring to play the part of a woman, but not before the age of sixteen is she fitted to play that part, nor indeed fitted to become a mother before the age of twenty.”