The Action of Tissue Extracts in the Coagu- Lation Of’ Blood.*

It has often been demonstrated that blood drawn from a vessel without contact with any injured tissue surface and kept in such a manner as to prevent destruction of the blood corpuscles, exhibits a considerable delay in its coagulation. Bird blood especially will remain fluid almost indefinitely when drawn and kept under such conditions. If, however, the escaping blood flows over an injured tissue surface, or the corpuscles are broken up as by whipping, it is found that the blood exhibits a much more prompt coagulation. The addition of saline extracts of tissues, especially such tissues as the lungs and brain, accelerates the clotting still further, it being possible thus to shorten the coagulation time to a small fraction of a minute. There is evidently then in tissues and cells in general a substance which possesses the property of quickening the clotting of the blood. This substance has been variously named. Wooldridge (l), who was the first to study the nature and action of it, held that it was a protein-phospholipin compound and that in the process of coagulation it reacted with the fibrinogen to form fibrin, an actual union occurring between the two substances with a loss of phospholipin. Since the tissue material entered into the formation of the fibrin, he termed it tissue fibrinogen. He also showed that there was a substance in the blood itself which was: practically identical with the tissue fibrinogen, and this he termed! A-fibrinogen. The reaction of this with the ordinary fibrinogen of the blood which he termed B-fibrinogen, resulted in the forma-