“In 1636, the educated world didn’t know that foxgloves had medicinal powers. Gerard said they had “…a certaine kinde of clensing qualitie joyned therewith; yet are they of no use, neither have they any place amongst medicines, according to the Antients.”
Among the unlettered holders of knowledge, though, foxglove was probably already in place as a heart remedy. In the hundred years before Gerard, there had been a wholesale murdering of healers and herbalists by the Church. They were called witches and heretics, and were burned at the stake, tortured, drowned. In this way, the Church acquired the accused witches’ property, plus sovereignty over the healing arts, a domain they awarded to the academically trained doctors. The era that we call the Renaisance had its evil side; progress often seems to involve wholesale slaughter. At least in Western European civilization.
Witch-killing still wasn’t over by 1636, so it’s likely that anyone who knew how to use foxglove kept pretty quiet, especially around lettered men, educated in church-run schools. Foxglove was used in ointments or poultices for swellings, old sores, and scrofulous swellings: that use was known. Though it might not have worked for everybody: some people are sensitive to the touch of foxglove leaves on bare skin, and come up with rashes, headaches, and nausea.
Foxglove’s use internally, as a heart remedy, was for a long time a secret, partly because it was something that took a lot of skill. Foxglove’s active ingredients make the heart constrict and blood pressure rise rapidly. Getting the dose right is essential: if you don’t the patient dies. It’s also tricky: the strength of the active ingredients varies from plant to plant, some people have much higher tolerance to drugs than others, and a person’s individual response varies as fast as internal chemistry, which is to say, from mood to mood. Getting a dose right under such circumstances – and without scientific measuring technology – required skill and insight.”