On the Secrets of Women.

...and concerning the earthy [type], because their menstrual fluid is livid—that is, black. For the earth is black, and because their menstrual fluid is highly earthy original: "summe terrestre", it therefore follows the color of the earth. For color is a secondary quality secondary quality: a property like color or smell that arises from the interaction of primary qualities like heat, cold, moisture, and dryness, left behind by the primary qualities. For example, just as we see when heat acts upon moisture and does not sufficiently consume that moisture, a green color remains, as is seen in pears and apples. And if cold predominates, the color is white; but if heat predominates, a black color is left behind, as is evident in pepper; and so it is with other similar things.

The second doubt can be whether the menstrual fluid flows through the anus original: "anum", in the manner of a bowel movement original: "secessus", or through the vulva, in the manner of the discharge of urine? To this it must be briefly said that it flows through the vulva in the form of raw and thin blood.

Here the author poses the second doubt, as is evident in the text. And it is answered regarding this doubt that in women who are greatly corrupted original: "corruptis"; likely referring to physical trauma, such as severe tearing during childbirth or an obstetric fistula, whose anus and vulva are a single opening, the menses nonetheless flow through the anus; however, as long as health and good digestion persist, then they do not flow through the anus, but through the vulva.

Thirdly, it is doubted why menstrual fluids—which are a superfluity superfluity: an excess byproduct of the body's "digestion" of food that must be expelled of nourishment—flow in women, but in men sperm original: "sperma"—which is also a superfluity of nourishment—does not flow in the same way? To this doubt it must be said that a woman is cold and moist by nature, whereas a man is hot and dry. It is the nature of moisture to flow, according to the 4th book of the Metaphysics Referring to the works of Aristotle, the foundational authority for medieval science, and the moisture that is in women is especially watery.