Ring Worm

This eruption, which generally appears on the head, in a circular form, attended with painful itching, is sometimes removed by rubbing it with black ink, or mushroom ketchup. The following preparation is also recommended. Wash some roots of sorrel quite clean, bruise them in a mortar, and steep them in white wine vinegar for two or three days. Then rub the liquor on the ring worm three or four times a day, till it begin to disappear.

Source: The Cook And Housekeeper’s Complete and Universal Dictionary, Mary Eaton