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128 DENTAL MEDICINE.

This thinning and weakening of the surface is caused by the
stretching and obstruction of the blood vessels, which convey the
nutritive supply from beneath, by the pressure of the enlarging
abscess to such a degree that the surface integument is de-
prived of its blood and slowly dies by minute particles, the dead
material being added to the contents of the abscess.
An abscess unattended with such symptoms as pain, heat, and
redness, is termed a cold abscess^ and its presence depends upon a
low degree of vitality. Such an abscess presents the same
phenomena of pus formation as the acute form, but resembles
more the growth of a tumor, as all the symptoms mav be absent
except the swelling. The formation of pus on the surface of a
tissue, such as mucous membrane, is not so serious as that in an
abscess, as the conversion of the leucocytes into pus requires
but little more increased activity than in cell germination. The
exudation takes place from the network of capillaries which exist
beneath every mucous membrane, and which furnishes nourish-
ment for the constant renewal of the epithelium, and any injury
received causes a fluxion of blood to the capillaries, which in-
creases the cell proliferation. The effect is, then, to promote an
increased discharge from the surface of the membrane, in the
form of pus. Suppuration from mucous membrane usually
causes pain, heat, imcreased redness, and swelling of the in-
flamed surface, owing to the exudation into the meshes of the
connective tissue beneath, and recovery is characterized by di-
minished fluxion of blood to the affected part, and consequent
lessening of cell production ; the cells resume their function of
producing epithelial tissue, the pus becomes thin and more
fluid, and finally ceases when the normal conditions again appear.
Hectic fever is a symptom of destructive inflammation, and is a
persistent, low form of continued fever, characterized by remis-
sion and exacerbation morning and night. This form of fever is
caused by absorption into the blood of some of the products of
inflammation, in such quantities and so gradually as not to produce
an immediate fatal result, and inducing a regular succession of
chill, fever, and perspiration during the space of every twenty-
four hours. Its effect is progressive emaciation and a tendency