'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,
[T H Pennington Listerism, its decline and its persistence: the introduction of aseptic surgical techniques in three British teaching hospitals, 1890-99.Med Hist. 1995 January; 39(1): 35–60.] 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.
References