collodion (one ounce containing thirty grains of salicylic acid) may
be painted, night and morning for several days, on the callus, and
then, after soaking for some time in hot water, the surface should be
scraped off with a dull knife and the process repeated as often as
necessary to effect a cure. Fissure or cracks of the skin caused by
callus are treated in the same manner: by prolonged soaking in hot
water, paring away the edges, and applying diachylon ointment or cold
cream to the part. Inflammation about callus must be cared for as
recommended above for inflamed corns.

=BOILS.=--A boil is a circumscribed inflammatory process, caused by
the entrance of pus-producing germs into the skin either through the
pores (the mouths of the sweat glands) or along the shafts of the
hair, and in this way invading the glands which secrete a greasy
material (sebaceous glands). In either case the pus germs set up an
inflammation of the sweat or sebaceous glands, and the surrounding
structures of the skin, and a small, red, itching pimple results.
Rarely, after a few days, the redness and swelling disappear, and the
pus, if any, dries and the whole process subsides. This is called a
"blind boil." But usually the boil increases in size for several days,
until it may be as large as a pigeon's egg. It assumes a bright-red
sharply defined, rounded shape, with a conical point, and is at first
hard and then softens as pus or "matter" forms. There is severe pain
of a throbbing, boring character, which is worse at night, and
destroys the patient's sleep and appetite. There may be some fever.
The glands in the neighborhood may be enlarged and tender, owing to
some of the pus germs' escaping from the boil and lodging in the
glands.

If the boil is not lanced, it reaches its full development in seven to
ten days with the formation of a central "core" of dead tissue and
some pus, which gives to the center of the boil a whitish or
yellowish-brown appearance. The boil then breaks down spontaneously in
one or more places (usually only one) and discharges some pus, and,
with a little pressure, also the white, central core of dead tissue.
The remaining wound closes in and heals in a week or two. Boils occur
singly or in numbers, and sometimes in successive crops. When this
happens it is because the pus germs from the previous boils have
invaded fresh areas of skin.

=Causes.=--Boils are thus contagious, the pus germs being communicated
to n