In the two decades since the introduction of the cascade and waterfall models of blood coagulation 1,2, the investigative emphasis has been on the “intrinsic” system of coagulation. In this system, coagulation is initiated by Hageman factor, which is presumably activated by virtue of an interaction with a “surface”, and proceeds by way of several intermediate steps to form thrombin. Although each of these papers explicitly recognized that tissue factor and factor VII markedly accelerated clotting, neither included this step in the coagulation scheme. Put differently, neither model included a step in which the interaction of blood with damaged tissues was viewed as a stimulus for initiating coagulation.