Investigations on Plasmin. III. On the Formation of Plasmin from Plasminogen.

Abstract
It was observed that the activity of plasmin solns. after a preliminary period of decrease, suddenly increased and then decreased normally. This could not be explained by a mechanism of transformation of plasminogen to plasmin, but by the presence of antiplasminogen that prevented the transformation of plasminogen to plasmin, and which must first be broken down by the plasmin before the transformation could take place.