Summary
Tissue thromboplastin injected into the femoral vein of anesthetized rabbits produced
intravascular clotting in the vessels through which the thromboplastin flowed. In
the systemic arteries macroscopically visible clots were never observed. No trace
of tissue thromboplastin could be demonstrated in blood drawn from the carotid artery
following infusion of tissue thromboplastin into the femoral vein. The slight, transient
enhancement of coagulation of the arterial blood following tissue thromboplastin infusion
was caused by a serum effect. After intravenous injection of serum, enhanced activation
of coagulation could be observed for a period of up to 2 hrs. It is concluded that
tissue thromboplastin, intravenously injected, is removed from the blood during its
passage from the femoral vein to the systemic arteries, probably in the capillaries
of the lung. True hypercoagulability appears to be due to a serum effect or caused
by partial activation of the intrinsic coagulation system. The levels of coagulation
precursors in blood are of minor significance.