A review of the various factors in the blood that have to do with the promotion and the retardation of coagulation is presented.

Circulating blood seems to have within and about itself all the factors required to delay or to promote coagulation. The stability of blood (i.e., its tendency to remain fluid) depends on the extent of the dominance of the anticoagulant (fluidity-inducing) group of factors over the coagulant (coagulation-promoting) group.

Among the anticoagulant factors are the natural anticephalin activity of the plasma and the intact vascular endothelium; the latter is simulated by such contacting surfaces as collodion and paraffin films.

Alterations in the stability of blood result from uncompensated increases or decreases in one or more of the anticoagulant or coagulant factors.

The increased stability of hemophilic blood, due to an uncompensated excess of anticephalin activity, enables it to resist activation by cephalin or by contact with injured walls of blood vessels or with surfaces like glass. Blood obtained from normal individuals after severe hemorrhage has a decreased stability owing to an uncompensated diminution in anticephalin activity; such blood is readily clotted by cephalin and may not remain stable even when in contact with undamaged vascular endothelium or surfaces like collodion or paraffin.

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