One of the important unsolved problems in gynecology is the cause and treatment of so-called primary or essential dysmenorrhea. This condition is responsible, in the aggregate, for much human suffering and invalidism. Its great frequency, the inadequacy of all the many theories of its causation which have been offered and the general unsatisfactoriness of its treatment have made it one of the bugbears of gynecology. And yet investigation of the problem has received comparatively little attention, much less than its importance would seem to justify. The menstrual pain in cases of this type occurs frequently in patients whose pelvic organs are quite normal from an anatomic standpoint. Most characteristically, the pain begins a day or two before the onset of the menstrual bleeding, and is commonly, though not always, of a colicky, spasmodic character. Usually it disappears after the menstrual bleeding has been well established. The clinical aspects of this