Activation time of blood platelets.

Blood platelets react rapidly in their hemostatic function. Determination of the reaction or activation time of individual platelets is difficult because it requires that physical and/or chemical effectors of activation are nonlimiting. Analysis of experimental conditions shows that the best estimate of mean activation time comes from in vivo measurements. Thus, the constancy of height-to-length ratio of a growing thrombus, and its change with flow rate, provide additional evidence for the activation time hypothesis.