Soils accelerate clotting of plasma from humans but not from dolphins or a bird. (A) Clot times of normal, PK-depleted, or FXII-depleted plasma by soils. (B) Western blot analysis of plasma, supplemented with or without CTI, after incubation with soil B. Full-length (FL) HK was fully converted to light chain fragment (LCF) after 30 minutes. No HK or LCF is seen in the lane with HK-depleted plasma. (C) Quantifying data in panel E, using densitometry of bands of FL and LCF. (D) Activation of purified PK and HK by soil. Dashed lines represent fully converted FXIIa and kallikrein activity after activation of PK by purified FXIIa. (E) Clot times with an antibody that inhibits FXI activation by FXIIa (14E11). (F) Clot times of plasma, comparing FXII-deficient vertebrates with humans. n = 5. *P < .01; **P < .001. Error bars represent SEM.