[From Sex, Society and Medieval Women by N. M. Heckel]
De Secretis Mulierum: On The Signs of Chastity (Ch. X):
The signs of chastity are as follows: shame, modesty, fear, a faultless gait and speech, casting eyes down before men and the acts of men. Some women are so clever, however, that they know how to resist detection by these signs, and in this case a man should turn to their urine. The urine of virgins is clear and lucid, sometimes white, sometimes sparkling. . . . Corrupted women have a muddy urine because of the rupture of the aforementioned skin, and male sperm appear at the bottom of this urine.
There are still other ways to tell if a virgin has been corrupted. If a girl's breasts point downwards, this is a sign that she has been corrupted, because at the moment of impregnation the menses move upwards to the breasts and the added weight causes them to sag. If a man has sexual intercourse with a woman and experiences no sore on his penis and no difficulty of entry, this is a sign that she was first corrupted. However, a true sign of the woman's virginity is if it is difficult to perform the act and it causes a sore on his member.
Pseudo-Albertus Magnus. De Secretis Mulierum (On the Secrets of Women). Trans. Helen Rodnite Lemay. Albany, NY: State University of New York, 1992.