Toxicity of blood clotting factors.

Pure bovine thrombin was separated from autoprothrombin C, and the lethal intravenous dose for mice weighing 25 g was 0.4 ml of a solution containing 50 units of thrombin per milliliter. Autoprothrombin C was not toxic alone, but with crude cephalin it was fatal. The clotting time of human plasma was only slightly accelerated by autoprothrombin C alone; the clotting time was as short as 5 seconds with a combination of autoprothrombin C and cephalin.