Catamenia (Gr. kaтa, according to, and unv, month), or Metises, a monthly flowing of sanguineous fluid, which occurs in the female economy. The function of menstruation generally commences at the age of puberty, and terminates at the "critical period," or "change of life," including a period of some 30 years, between the ages of 14 and 45. The blood of the catamenial flux is exuded from the vessels of the uterus, and escapes through the vagina; the flow generally returns every 28 days, and continues from 3 to 6 days. The amount discharged varies from 4 to 8 oz. in most cases. The first menstrual flow is generally preceded by languor, pains in the back, headache, chilliness, etc, which usually disappear when the discharge takes place. The after occurrences are often unaccompanied in healthy females by any premonitory or attendant symptoms. During the whole of a woman's menstrual life she is capable of bearing children. After it is closed, she ceases child-bearing. - The influence of climate in advancing or retarding the period of puberty and menstruation has been shown by recent observation to have been formerly much overrated, the average period being much the same all over the world, and exceptional cases about as numerous in one region as in another.

Mr. Robertson has shown, from statistical evidence, that menstruation does not occur more early in the negress than in the white female, and Dr. Vaigas affirms that precocious menstruation is more common in the white than in the colored races. Early marriages in Hindostan and other warm climates, then, do not depend on natural precocity, but on the habits and customs of the country. - The uterus is congested during the menstruation, and so are the ovaries and the Fallopian tubes; the tissues of the vagina are relaxed, and the os uteri is softened and swollen; these conditions disappear when the flow ceases, and the parts return to their natural state. During pregnancy and lactation the menses usually cease, and they may also be suppressed from other local causes. - Vicarious menstruation sometimes takes place as a means of obviating the ill effects of suppressed menstruation, by substituting a similar discharge from some other part. It occurs from the gums, the nostrils, the lungs, the stomach, or even from the eyes, and other parts of the body.