LEEDING IS A highly visible manifestation of injury. Methods for hemorrhage control, including direct pressure, ligature, and suture to close injuries, were described in the Edwin Smith surgical papyrus from Egypt in 1600 BCE. 1 Cautery and the binding of wounds also were known to the ancients, with a classic Greek plate showing Achilles binding the wounded arm of Patroclus in a scene from the Trojan War. 2 Styptics, such as sulfur, and procoagulants, such as spider webs, were known and used in both folk and formal medicine. With the Renaissance, knowledge of anatomy and of the circulation of the blood led to the use of tourniquets and increasingly sophisticated amputation for the control of hemorrhage from extremity injuries. 3,4 Napoleon’s surgeon, Dominique Larrey, performed 200 amputations, including 11 at the shoulder, in the 24 hours after the battle of Borodino. 5 Blundell, who described the first successful human-tohuman transfusions in 1828, wrote that “States of the body really requiring the infusion of blood into the veins are probably rare; yet sometimes we meet with such cases in which the patient must die unless the procedure can be performed, …”. 6 Despite its obvious lifesaving potential, transfusion remained risky throughout the 19th century because of primitive and unsterile equipment and the lack of anticoagulants or knowledge of blood types. Nevertheless, modern understanding of coagulation started in the 19th century with the recognition that fibrin formed in standing rabbit blood, and that the fresh serum thus formed would clot hydrocele fluid. 7 This meant that the precursor of the fibrin—what now is called fibrinogen—was present in the hydrocele fluid, and the “fibrin ferment”—what is now called thrombin—was activated in the fresh serum and must exist in the blood in an inactive form that was activated when the blood was removed from the body or exposed to tissue other than the blood vessel. Late in the century, achromatic microscopes allowed the further recognition that platelets adhered to the walls of damaged blood vessels. 8 Advances in clinical chemistry allowed the identification of the salts in human blood and the development of blood volume replacement solutions such as Ringer’s solution. Early in the 20th century, Roger Lee confirmed the fibrinogen and thrombin model for human coagulation, identified citrate as an anticoagulant, and developed the Lee-White clotting time, the first coagulation test. 9 While serving in the Harvard Medical Unit in World War I, Lee arranged for his former student, Oswald Robertson, to collect “universal donor” whole blood in citrate in bottles, build the world’s first blood bank for the treatment of seriously injured battle casualties, and demonstrate the lifesaving capability of transfusion as an adjunct to surgical care. 10 In the same unit, Walter Cannon,