Medieval men looked down on menstruation as something unnatural and unclean. In a word, they considered it monstrous -- to the point that "menstrum" is often written as "monstrum" in the 15th century gynecological treatise "Secreta Mulierum." According to historian Bettina Bildhauer, the same text also dropped this bombshell: Jewish men experience a monthly menstrual flow too.
Let's unpack that idea, shall we?
As Bildhauer points out in "Blood, Jews and Monsters," this particular slice of antisemitism stems from a host of physiological to the theological notions. The overarching purpose, of course, is to portray Jews as not only cultural others but monstrous others and feminine others.
Remember that "Secreta Mulierum" was written in the wake of the 1475 Simon of Trent blood libel, which saw an entire Jewish community tortured over the death of a 2-year-old Christian boy in Trento, Italy. The event resulted in the tragic execution of 15 men, all falsely charged with the ritual murder of the boy. Antisemitic violence surged throughout Europe as a result.*
But of course men are men, and surely even a particularly daft antisemite would realize that males lack the basic equipment necessary for menstruation. According to Willis Johnson in his excellent paper "The myth of Jewish male menses," the notion of menstruating male Jews ties back to centuries-older beliefs that God punished the wicked with bleeding anuses.
After all, Judus' belly burst when he hanged himself and third-century heretic Arius died of prolapse in an Alexandrian toilet. As it was common to blame the death of Christ on Jews, the notion emerged that God placed such a curse on them as well. Just as Christians were redeemed by blood at Easter, Jews were said to be plagued by it.
If this weren't enough, modern medical theories of the day seemed to back this up. Medical theorist Galen (AD 129-216) argued that menstrual blood and hemorrhoid blood were both a natural process of unhealthy humors leaving the body. As the recovered works of Galen and Plato spread through the medieval world, the notion melded with an older understanding: that incontinence was rooted in moral failing.
Johnson closes by asking why the mythical Jewish flux was never attributed to anal sex. After all, homosexuality was a frequent charge when it came to heresies and witchcraft -- and some even theorized that the devil had entered Judas through the anus. But, Johnson points out, to contemplate sodomite Jews and a sodomite Judas may have "forced a re-reading of the relationship between Judas and Jesus himself."
It reminds me of witchcraft treatises that spared nothing in the way of heterosexual congress between demons and humans, but steered away from the notion of anything gay.
Such were the times...
* Simon of Trent, the 2-year-old, was also eventually declared a saint and remained so in Catholic tradition till 1965.