Boracic lint was a type of medical dressing made from surgical lint that was soaked in a hot, saturated solution of boracic acid and glycerine and then left to dry.
It has been in use since at least the 19th century, but is now less commonly used.
The term boracic lint, or often just "boracic", pronounced "brassic", is also used as Cockney rhyming slang for having no money - "boracic lint" → "skint."