Cantharides, or Spanish flies, when used internally, are diuretic and
stimulant; and epispastic and rubefacient when applied externally.
_Mode of application._--A portion of the blistering plaster is spread
with the thumb upon brown paper, linen, or leather, to the size
required; its surface then _slightly_ moistened with olive oil and
sprinkled with camphor, and the plaster applied by a _light_ bandage:
or it is spread on adhesive plaster, and attached to the skin by the
adhesive margin of the plaster.
_Caution._--If a blister is to be applied to the head, shave it at
least ten hours before it is put on; it is better to place a thin
piece of gauze, wetted with vinegar, between the skin and the blister.
If a distressing feeling be experienced about the bladder, give warm
and copious draughts of linseed tea, milk, or decoction of quince
seeds, and apply warm fomentations of milk and water to the blistered
surface. The _period required_ for a _blister_ to remain on varies
from eight to ten hours for adults, and from twenty minutes to two
hours for children: as soon as it is removed, if the blister is not
raised, apply a "spongio-piline" poultice, and it will then rise
properly. When it is required to act as a rubefacient, the blister
should remain on from one to three hours for adults, and from fifteen
to forty minutes for children.
_To dress a blister._--Cut the bag of cuticle containing the scrum at
the lowest part, by snipping it with the scissors, so as to form an
opening like this--V; and then apply a piece of calico, spread with
spermaceti or some other dressing. Such is the ordinary method; but a
much better and more expeditious plan, and one that prevents all pain
and inconvenience in the healing, is, after cutting the blister as
directed above, to immediately cover it with a warm bread and water
poultice for about an hour and a half, and on the removal of the
poultice to dust the raw surface with violet powder; apply a
handkerchief to retain the powder, and lastly dust the part every two
hours. It will be healed in twelve hours.
_Caution._--Never attempt to take cantharides internally, except under
the advice of a medical man, as it is a poison, and requires extreme
caution in its use.