Stability of fibrin contiguous to intima of veins.

B Activators capable of bringing about conversiou of a proenzyme of blood, profibrinolysin (plasminogen), to the active proteolytic enzyme, fibnnolysin (plasmin), have been reported to be present in the tissues of veins. Astrup and coworkers' isolated a tissue activator from veins which promoted an in vitro activation of profibrinolysin. Studies in vivo by Kwaan et al." have indicated the presence of fibrinolytic activity in blood taken from vessels subjected to a variety of stimuli. More recently, Todd, using histoehemical techniques, has observed that fibrin undergoes dissolution when brought into intimate contact with ultra-thin slices of vein.