Menstruation seems to give a disposition to the female organs of generation to be acted upon by the male semen so as to fit them for impregnation, as women seldom, if ever, bear children before they have menstruated, and few or none ever become pregnant after the total cessation of this discharge.

An ingenious solution of the problem, why nature should have doomed the human female to the menstrual discharge, has been offered by the late Mr. Abernethy. "It can only be solved," he remarks, " by supposing that it relieves uterine irritation, and mitigates the extreme of sexual desire, thus enabling a woman to conform to the laws of morality, and the social compacts that are established between us."

In warm climates menstruation takes place at a much earlier period of life than in cold ones, as in the former it often makes its appearance at the age of ten or eleven years; whereas, in the latter it is seldom to be observed before fifteen or sixteen. It also ceases much sooner with women who reside in warm climates than it does with those who are inhabitants of cold ones; as, in the former, menstruation is not often found after the age of forty: whereas, in the latter it seldom stops before forty-five, and is in many instances extended to fifty years.

Some women begin to menstruate without any previous indisposition; but with most of them the first appearance of the discharge is preceded by a swelling or enlargement of the breasts, together with a sense of fulness at the lower region of the belly, pains in the back and the lower limbs, and some slight hysteric affections, all of which cease as soon as the flow of blood or menstrual secretion takes place.

For the first two or three times of its appearing it is apt to be somewhat irregular both as to the quantity of blood which is discharged and the period of its return; but, after these it usually observes stated times, and nearly the same quantity is lost at each visitation, unless some irregularity ensues. The quantity varies in different women, and greatly depends on the constitution. Those of a delicate habit and lax fibre have a more copious and longer continued discharge than women of a robust constitution. In general, however, the discharge continues to flow from four to six days, and the quantity of blood discharged is about five ounces.

Pregnant women, and those that suckle children, do not usually menstruate during those periods.