In the 1950s I was working on the out islands of Newfoundland as a field engineer for a mining company. I lived with a fisherman's family. When the fishermen went to sea in small open boats to go cod jigging they invariably got very wet, and their rubber boots chafed against the gunwales. The skin would break down and get infected. Once they were back home, Mother would have a mouldy bread poultice handy to apply to the injury.
It was not until years later when I was in medical school that it dawned on me that they were treating the injury with penicillin.