Osler's role in defining the third corpuscle,
or "blood plates"

Barry Cooper, MD

As a young microscopist in 1874, William Osler was probably the first physician to recognize platelets in blood as a single unit and their coalescence when blood was shed. He expounded on the earlier observations of Schultze, who in 1865 noted abundant, irregular masses of colorless globules in normal blood that were almost certainly platelets. The impact of Osler's initial observations were diminished by an unclear relation between this third blood particle and bacteria. Initial observers of this blood element were handicapped by the inadequacy of microscopes, the lack of anticoagulants and blood stains, and the tendency of platelets to clump and undergo morphologic change when blood is shed.