Saliva triggers the coagulation of plasma. Human plasma containing vesicles (A) was incubated without (◇) or with saliva (●). Plasma depleted from endogenous vesicles before the addition of saliva (B-D) was incubated with (B) saliva (●), or without saliva (□), or with (C) saliva preincubated with antifactor XII (○) or antifactor VII (Δ). Coagulation/clot formation was initiated by addition of calcium chloride (t = 0) and monitored for 1 hour. (B-C) Graphs were obtained in a single experiment and are representative of 6 other independent experiments. (D) The effects of antifactor XII and antifactor VII on the saliva-induced shortening of the plasma clotting time have been summarized (n = 7).