Carl Pyrdum points indirectly at how things these days have gone to hell—just like they always have. In this case, “Oh My God, They Got Medieval On South Park! You Bastards!”:

But back to the horrible sacrilege of the actual South Park episode. I couldn’t find any examples of the Virgin’s menstrual blood being venerated in the Middle Ages, unfortunately, though not for lack of trying.**** The closest I could get was to her menstrual cave. As all good Christians know–especially those at the Catholic League of Stuff and Things–the Bible is very specific about menstruating. At that time of the month, a woman should remain in a cave in order to keep from making things unclean, and since Mary was a good Jew, she retired to a cave with a handy mikveh, or purification bath, which you can still visit in Nazareth today. The best part is, the whole site is under the control of French Franciscans for some reason. I imagine there was some kind of draft for holy artifacts around the time of the Reformation. The Templars got the number one first round pick, on account of having been completely eradicated, and they drafted the Holy Grail. The Franciscans had unwisely traded away most of their picks for miracles-to-be-named-later, and so the menstrual cave was just all that was left by the time they got to go.