Even this elementary fact of the sexual life has, however, been denied, and, strange to say, by two women doctors. Dr. Mary Putnam Jacobi, of New York, who furnished valuable contributions to the physiology of menstruation, wrote some years ago, in a paper on "The Theory of Menstruation," in reference to the question of the connection between oestrus and menstruation: "Neither can any such rhythmical alternation of sexual instinct be demonstrated in women as would lead to the inference that the menstrual crisis was an expression of this," i.e., of oestrus. Dr. Elizabeth Blackwell, again, in her book on _The Human Element in Sex_, asserts that the menstrual flow itself affords complete relief for the sexual feelings in women (like sexual emissions during sleep in men), and thus practically denies the prevalence of sexual desire in the immediately post-menstrual period, when, on such a theory, sexual feeling should be at its minimum. It is fair to add that Dr. Blackwell's opinion is merely the survival of a view which was widely held a century ago, when various writers (Bordeu, Roussel, Duffieux, J. Arnould, etc.), as Icard has pointed out, regarded menstruation as a device of Providence for safeguarding the virginity of women. FOOTNOTES: [75] Thaddeus L. Bolton, "Rhythm," _American Journal of Psychology_, January, 1894. [76] It is scarcely necessary to warn the reader that this statement does not prejudge the question of the inheritance of acquired characters, although it fits in with Semon's Mnemic theory. We can, however, very well suppose that the organism became adjusted to the rhythms of its environment by a series of congenital variations. Or it might be held, on the basis of Weismann's doctrine, that the germ-plasm has been directly modified by the environment. [77] Thus, the Papuans, in some districts, believe that the first menstruation is due to an actual connection, during sleep, with the moon in the shape of a man, the girl dreaming that a real man is embracing her. (_Reports Cambridge Expedition to Torres Straits_, vol. v, p. 206.) [78] Darwin, _Descent of Man_, p. 164. [79] While in the majority of women the menstrual cycle is regular for the individual, and corresponds to the lunar month of 28 days, it must be added that in a considerable minority it is rather longer, or, more usually, shorter than this, and in many individuals is not constant. Osterloh found a regular type of menstruation in 68 per cent, healthy women, four weeks being the most usual length of the cycle; in 21 per cent, the cycle was always irregular. See Näcke, "Die Menstruation und ihr Einfluss bei chronischen Psychosen," _Archiv für Psychiatrie_, 1896, Bd, 28, Heft 1.