A protective mechanism that prevents excessive blood from being lost after an injury. In the clotting process, a mesh of tight fibers of the protein fibrin coagulates at the site of injury through a series of chemical reactions. This mesh traps blood cells to form a clot, which dries to forma scab. This prevents further loss of blood, and also prevents bacteria getting into the wound. Normal clotting takes place within five minutes. In some diseases, such as hemophilia, the clotting mechanism is impaired.