Soils accelerate clotting of plasma, dependent on FXII. (A) Clot times of human normal and FXII-depleted plasma by soils and kaolinite clay. (B) Onset of thrombin generation in human plasma by soils with CTI (FXIIa inhibited) or without CTI (FXIIa active). (C) Clot times with increasing concentration of soil and kaolinite, measured by thromboelastography. n = 8-9 (A-B), n = 5 (C). *P < .01; **P < .001. Error bars represent SEM.