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120 DENTAL MEDICINE.
tense in one spot, gradually fading as it recedes, until lost in the
surrounding healthy tissue; in other cases the redness has an
abrupt boundary, and is of equal intensity over its entire area.
The bright hue usually attends ordinary active inflammation j the
dark or purplish hue that form of inflammation proceeding from
some specific cause, or associated with a gangrenous tendency,
and indicates stasis. The redness of inflammation is caused by
the increased amount of blood entering the vessels of the part,
and remaining there for a longer time than is natural under other
conditions.
The Heat of an inflamed part is also caused by the unusual
quantity of red blood present, and also by an increase of that vital
action upon which the evolution of heat depends, namely, super-
oxidation of the affected tissues, resulting in their decomposition.
It is more marked at the focus of the inflamed area. The in-
crease of temperature is generally more sensible to the suff^erer
than to the observer, though it may often be detected by the
hand, and is very evident by the use of the clinical thermometer;
it is also verified by comparison with other unaffected parts ; but
is never beyond the temperature of the internal organs.
The Swelling of an inflamed tissue is caused in part by the
unusual quantity of blood present in the dilated vessels,—the en-
gorgement of the blood vessels of the part, and also by the mat-
ters, both liquid and solid, which exude into the affected tissue
through the walls of the dilated vessels, and also to extravasation
resulting from rupture of these walls; for as the vessels are dis-
tended their walls become thinner, and permit the blood plasma
to escape through them in greater quantity than is required for
hence inflamed tissue becomes
mere nourishment ; the infil-
trated with this plasma, the consequence of which is an increase
of thickness or swelling. The swell of a part, however, without
other symptoms is not an evidence of inflammation, as this phe-
nomenon may occur from other causes. Swelling may also be
absent when the other symptoms of inflammation are present, an
example of which is afforded in inflammation of mucous mem-
branes, before exudation has occurred in the connective tissue
beneath. The swelling is soft in acute inflammations, and hard