Scientists have found significant quantities of penicillin in cobwebs............
I found this on The Virginian Pilot (University Libraries, Virginia Tech) in Norfolk, Virginia, USA: "Farmers in central Europe used to prevent infection by packing open wounds with fistfuls of cobwebs laced with fungus-grown penicillin."
The healing cells (granulocytes and others) migrate into the middle of the wound, usually under a scab which forms over top to protect the site. In fact wounds heal much better if they are kept clean and moist and there is some sort of fabric for the cells to migrate along.