The occurrence of bleeding is usually a sign of disease. Bleeding from the nose or of the lungs or intestines or kidneys is an indication of disease more or less serious. Discharge of blood from the female reproductive organs may also be an indication of disease, as for instance when due to tumours of the uterus. The only exception to the rule is the periodic flow in the case of women, by which they lose hundreds of grammes of blood (100 to 600 gr.). There is something paradoxical in such a physiological occurrence, and it deserves minute consideration. These periodic losses, unlike the possession of a hymen, are not a peculiarity of the human female. “Heat” in lower animals is analogous, although in that case the chief indications are swellings of the mucous membrane with a slight discharge of fluid, hardly tinged with blood. The state indicates the awakening of the sexual instinct and readiness for coition.[100] Among monkeys there has been observed a flow much more closely resembling that of woman. In the case of macaques and cercopitheci, it has been observed even that the flow is monthly. Heape,[101] while in British India, took advantage of a valuable opportunity for making observations on this subject. Among two hundred and thirty females of _Macacus rhesus_ of which the greater number were adult or nearly so, seventeen displayed signs of menstruation, consisting of a swelling of the genitalia accompanied by the discharge of a pale and viscid fluid. Usually the flow assumed a pale rose tint, due to the presence in it of blood corpuscles, but cases where it was highly coloured were rare. Although they are distinctly analogous to the menstrual flows of women, these occurrences in monkeys are distinguished by the predominance of the swelling of the genitalia, the viscid character of the discharge, and the relative absence of blood. They present a condition intermediate between the “heat” of lower animals and the human phenomena. In anthropoid apes a similar menstruation has been observed. Bolau, Ehlers, and Hermes, record it in the case of the chimpanzee. “At this period,” wrote Hartmann,[102] “swelling and reddening of the genitalia occurred. The labiæ majores, which are usually inconspicuous, enlarged greatly, and a similar increase took place in the labiæ minores and the clitoris.” In the case of women swelling of the genitalia is very slightly marked, and the chief occurrence is the flow of blood. It is plain, then, that something new has been acquired in the menstruation of women.