Thrombosis

Thrombosis (Gr. thrombos, 'a clot of blood'), an affection of the blood-vessels (either veins or arteries), which essentially consists in a coagulation of blood (forming a true clot) at a certain fixed spot. Under certain morbid conditions the blood has a tendency to coagulate in its vessels during life on the least provocation. Thus, slight pressure on the side of a vein will sometimes induce this coagulation, while in other cases it is due to inflammation of the tissues which surround a vein, or laceration of a vein (as when the placenta is expelled from the uterus). A clot thus formed in a vessel may increase and extend from one to another, till it reaches and finally fills a large vessel.