_Mittelschmerz_ is a condition of pain occurring about the middle of the intermenstrual period, either alone or accompanied by a slight sanguineous discharge, or, more frequently, a non-sanguineous discharge. (In a case described by Van Voornveld, the manifestation was confined to a regularly occurring rise of temperature.) The phenomenon varies, but seems usually to occur about the fourteenth day, and to last two or three days. Laycock, in 1840 (_Nervous Diseases of Women_, p. 46), gave instances of women with an intermenstrual period. Depaul and Guéniot (_Dictionnaire Encyclopédique des Sciences Médicales_, Art., "Menstruation," p. 694) speak of intermenstrual symptoms, and even actual flow, as occurring in women who are in a perfect state of health, and constituting genuine "_règles surnuméraries_." The condition is, however, said to have been first fully described by Valleix; then, in 18725 by Sir William Priestley; and subsequently by Fehling, Fasbender, Sorel, Halliday Croom, Findley, Addinsell, and others. (See, for instance, "Mittelschmerz," by J. Halliday Croom, _Transactions of Edinburgh Obstetrical Society_, vol. xxi, 1896. Also, Krieger, _Menstruation_, pp. 68-69.) Fliess (_Die Beziehungen zwischen Nase und weiblichen Geschlechts-Organen_, p. 118) goes so far as to assert that an intermenstrual period of menstrual symptoms--which he terms _Nebenmenstruation_--is "a phenomenon well known to most healthy women." Observations are at present too few to allow any definite conclusions, and in some of the cases so far recorded a pathological condition of the sexual organs has been found to exist. Rosner, of Cracow, however, found that only in one case out of twelve was there any disease present (_La Gynécologie_, June, 1905), and Storer, who has met with twenty cases, insists on the remarkable and definite regularity of the manifestations, wholly unlike those of neuralgia (_Boston Medical and Surgical Journal_, April 19, 1900). There is no agreement as to the cause of _Mittelschmerz_. Addinsell attributed it to disease of the Fallopian tubes. This, however, is denied by such competent authorities as Cullingworth and Bland Sutton. Others, like Priestley, and subsequently Marsh (_American Journal of Obstetrics_, July, 1897), have sought to find the explanation in the occurrence of ovulation. This theory is, however, unsupported by facts, and eventually rests on the exploded belief that ovulation is the cause of menstruation. Rosner, following Richelet, vaguely attributes it to the diffused hyperæmia which is generally present. Van de Velde also attributes it to an abnormal fall of vascular tone, causing passive congestion of the pelvic viscera. Others again, like Armand Routh and MacLean, in the course of an interesting