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INFLAMMATION. HJ

soon arrested, owing to its benign form, by the particles of
lacerated tissue being carried away by the blood and the subse-
quent liquid exudation, while those that remain undergo lique-
faction and absorption by the lymphatics; hence, when the cut
surfaces are brought and retained in proper apposition, speedy
union, by the '' Jirst intention^'' results. Union by " first in-
"
tention is induced by such changes as cell-proliferation, the
formation of new capillaries, and the generation of cicatricial
tissue. It is only when the vitality of the tissue is destroyed and
foreign matters left in the wound, especially a punctured one,
caused by a rough or rusty instrument, that there are complica-
tions. The tissues themselves, when they lose their vitality, be-
come irritants, even when the dead matter is very minute. A
boil furnishes an example, the core of which is composed mainly
of yellow, elastic fibres with some leucocytes or pus cells in the
meshes. This mass becomes dead, and while the white fibrous
element liquefies and mingles with the pus, the yellow fibres re-
main unchanged and constitute the irritant body, to the presence
of which is due the suppurative inflammation. The presence
of a clot of blood in a wound may prevent union, and cause pus
formation.
Chemical Irritants excite inflammation by first causing in-
creased redness, which steadily extends and becomes more intense
until a considerable diameter is attained. There is also increased
heat and fullness of the part affected, and an eschar forms as the
result of the action of the chemical agent upon the epidermis in
the case of the skin, or the corium in the case of mucous mem-
brane, the depth of the action depending upon the nature of the
chemical irritant. After one or two days the narrow circle of
redness disappears, and, after one or two weeks, the eschar sepa-
rates, disclosing an area of smooth cicatricial tissue. When the
action of such irritants is slight, repair soon follows, without the
formation of an eschar ; but when their action is severe enough
to devitalize the tissue, the sloughs are thrown off without sup-
puration, if the parts have been protected from the air, or anti-
septic applications have been made.
Mineral irritants^ such as mercury and arsenic, for example.