Consider the example of the weapon salve. This was a famous, or notorious, magical ointment developed and promoted by the Paracelsians... It was an ointment that could cure wounds incurred in battle by applying the ointment to the weapon that caused the wound... If, as seems likely, the weapon was not available, then the ointment was applied to a bandage or piece of cloth that had been soaked in blood from the wound but which was then kept away from the injury. This proved to be much more successful than the standard means of treating wounds... To understand this you just need to know what the standard method of treatment was.
Since time immemorial, healers had noticed that wounds run with yellow matter, pus, before they heal. We are speaking, of course, of the days before antiseptics - indeed before anybody ever dreamed there were such things as invisible germs and before any concomitant ideas of the need for hygiene in this regard. Formation of pus in a wound seemed, therefore, to be part of the healing process. Here, then, we have a perfectly reasonable conclusion based on often-repeated observational evidence. This was the medical theory ... of ‘laudable pus’: pus is a good thing, a sign that healing is taking place. Accordingly, doctors and surgeons throughout the ages would pack wounds with irritating substances - ground up egg-shells, sand, coarse feathers and the like - in order deliberately to stimulate the formation of pus and thereby, as they thought, accelerate the healing process. In the case of serious wounds they would often bandage the packed wound really tightly to increase the irritation, and would arrange a goose quill (or some other tube), emerging from the dressing, to act as an outlet pipe to drain off the pus as it formed.
By contrast, in the case of treatment by the weapon salve, the wound would simply be kept clean and dry, perhaps with a light dressing ... while the doctors concentrated on smearing their obnoxious potions on a sword or a blood-stained cloth. It's easy to see, therefore, why the weapon salve was so successful as a cure for wounds... The theory of laudable pus was so strongly held that on-lookers concluded not that the theory of laudable pus must be wrong, but that somehow the weapon salve had an occult power of curing wounds without the formation of pus...
From
Knowledge is Power: How Magic, the Government and an Apocalyptic Vision Helped Francis Bacon to Create Modern Science by John Henry. Under current circumstances, I should clarify this cite has no allegorical meaning, that I’m aware of.