What is menstruation?  It is easy to describe it, by its obvious symptoms, as a monthly discharge of blood from the uterus, but nearly as much as that was known in the infancy of the world.  When we seek to probe more intimately into the nature of menstruation we are still baffled, not merely as regards its cause, but even as regards its precise mechanism.  “The primary cause of menstruation remains unexplained”; “the cause of menstruation remains as obscure as ever”; so conclude two of the most thorough and cautious investigators into this subject.[95] It is, however, widely accepted that the main cause of menstruation is a rhythmic contraction of the uterus,—­the result of a disappointed preparation for impregnation,—­a kind of miniature childbirth.  This seems to be the most reasonable view of menstruation; i.e., as an abortion of a decidua.  Burdach (according to Beard) was the first who described menstruation as an abortive parturition.  “The hypothesis,” Marshall and Jolly conclude, “that the entire pro-oestrous process is of the nature of a preparation for the lodgment of the ovum is in accordance with the facts."[96] Fortunately, since we are here primarily concerned with its psychological aspects, the precise biological cause and physiological nature of menstruation do not greatly concern us.

There is, however, one point which of late years has been definitely determined, and which should not be passed without mention:  the relation of menstruation to ovulation.  It was once supposed that the maturation of an ovule in the ovaries was the necessary accompaniment, and even cause, of menstruation.  We now know that ovulation proceeds throughout the whole of life, even before birth, and during gestation,[97] and that removal of the ovaries by no means necessarily involves a cessation of menstruation.  It has been shown that regular and even excessive menstruation may take place in the congenital absence of a trace of ovaries or Fallopian tubes.[98] On the other hand, a rudimentary state of the uterus, and a complete absence of menstruation, may exist with well-developed ovaries and normal ovulation.[99] We must regard the uterus as to some extent an independent organ, and menstruation as a process which arose, no doubt, with the object, teleologically speaking, of cooperating more effectively with ovulation, but has become largely independent.[100]

It is sometimes stated that menstruation may be entirely absent in perfect health.  Few cases of this condition have, however, been recorded with the detail necessary to prove the assertion.  One such case was investigated by Dr. H.W.  Mitchell, and described in a paper read to the New York County Medical Society, February 22, 1892 (to be found in Medical Reprints, June, 1892).  The subject was a young, unmarried woman, 24 years of age.  She was born in Ireland, and, until her emigration, lived quietly at home with her parents.  Being then twenty years of age,