Extravasation

Extravasation is the escape of any of the fluids of the living body from their proper vessels (vas) through a rupture or injury in their walls. Excrementitious matter thus sometimes escapes into the abdomen through a wound or ulceration of the bowels. But the term is oftenest used in speaking of the escape of blood from injured blood-vessels. Extravasation is distinguished from exudation by this, that in the last the vessels remain entire, and the effusion takes place by filtration through their walls; nor does more than a part of the blood so escape, the coloured blood-corpuscles being retained, while in extravasation perfect blood is effused. Many kinds of extravasation are rapidly fatal, such as that of urine or of the contents of the intestines into the abdomen, or of blood from the vessels of the brain in cases of apoplexy. The dark colour resulting from a bruise is owing to extravasated blood from ruptured capillary or larger vessels.