Spread a sheet of thin leather with the ointment of ammoniacum with
mercury, and cut out a place for the mouth, eyes, and nostrils. This
forms what is called a mask, and, after anointing the eyelids with a
little blue ointment, it should be applied to the face, and allowed to
remain for three days for the distinct kind, and four days for the
running variety. _Apply before_ the spots fill with matter, although
it will answer sometimes even after they have become pustulous. It may
be applied to any part in the same way.