1890-1957

American physician who is known for his discovery of the anticoagulant, or non-blood clotting substance, that later became known as heparin. As a medical student at Johns Hopkins University, McLean studied under William Howell, who was studying blood coagulation with a clotting substance from the brain. McLean, while comparing similar substances from the liver, discovered that the liver substance did not clot blood. This substance is now widely used in surgery and medicine for its anticoagulant properties.