I have not been able to satisfy myself of distinct benefit from mercurial frictions in pleuritic or pericardial effusions, though they have been considered useful by others: in hydrocele in children Kock uses an ointment of the cyanide (1 part in 4), rubbing a very small quantity into the scrotum daily for three to six weeks unless erythema supervene: in such cases I have sometimes successfully employed, as a paint, a 2 to 10 per cent. solution of the oleate.