I recall an interview with an interdisciplinary team of medical scientists and historians that was looking at medieval European spell books and found that a lot of the healing spells were not the hogwash they'd been trained to expect, but in fact were healing in medically recognizable ways, if you parse the spells right.
The one I recall in particular was one to fight infections in which many ingredients were called for (you know - mouse feet, old piece of leather, dried buckthorn, tooth of a newborn, that kind of thing) and left somewhere for several days. Thing is, among the many ingredients was bread - which, when the team followed the recipe, accumulated penicillium mold exactly as they expected. Previous readers had looked at this spell and, because of all the extraneous ingredients as well as their own biases, had put this off as mere medieval mumbo-jumbo. But in fact, if you did use this spell as written, you'd basically be making medieval penicillin, and it absolutely would fight infection.
Their research also suggested that when the spells said things like "chant this formula four times while walking eastward," or "then say the Hail Mary fourteen times," this was often quite important because it was a way of timing the application. "Fourteen Hail Marys" was, at the time, about as precise and accessible a way of saying "X amount of minutes" as you could come up with.