Usually blood does not stagnate nor clot in its vessels. Spasm in a vein or artery, constricting the wall or sphincter, seines and assembles the ingredients of a thrombus. It further leads to rupture of the vessel's wall, so extravascular glue can complete or augment the recipe. The mechanisms of blood clotting, include three prime factors, stasis, dessication and extravascular glue. Idiopathic disorders of the arteries and veins and similar to each other and to those in other systems and, e.g. analogous to paralytic ileus and intestinal obstruction. Dissecting, i.e. intralaminar hemorrhage in the pathogenesis of emboli, venous/arterial and vascular occlusion, merits more attention as do the sphincters and valves of the vascular system.