The poison idea, in a lab coat

Middle ages – 1970s

Pliny's list survived in European folk belief essentially intact and remarkably specific: a menstruating woman could not make bread rise, could not set jam, would spoil milk or wine, should not sow seed or handle preserved meat. These are not vague superstitions — they are the same claims, transmitted for eighteen hundred years.

What happened next is the part that ought to be uncomfortable for medicine.

Menotoxin, 1920

The paediatrician Béla Schick — the same Schick of the Schick test for diphtheria immunity — observed that roses handled by a menstruating maid wilted overnight, and concluded that menstruating women secrete a toxic substance through the skin. He published in 1920. Others tested blood, saliva, sweat, tears and breast milk against seedlings and cut flowers, with conflicting results that were read as supportive.

The idea did not quietly die. It was still being argued in The Lancet in 1974, where the correspondence was ended by an epidemiologist pointing out that a photograph of a wilted daisy from 1924 and one dead Italian tree were not sufficient evidence for a claim in 1974. Further experiments were still being run in 1977.

There is a simple argument against the whole edifice that nobody appears to have made loudly enough at the time: if the lining of the uterus were toxic, embryos could not implant in it.