Branch of medicine concerned with the nature, function, and diseases of the blood. It covers the cellular and serum composition of blood, the coagulation process, blood-cell formation, hemoglobin synthesis, and disorders of all these. Marcello Malpighi, in the 17th century, was the first to examine red blood cells (erythrocytes). In the 18th century, the British physiologist William Hewson (1739–74) examined the lymphatic system and blood clotting. In the 19th century, the bone marrow was recognized as the site of blood-cell formation, and diseases of the blood such as anemia and leukemia were identified. In the early 20th century, the ABO blood-group system was discovered and the role of nutrition in blood formation was studied. Post-World War II studies have delved further into the nature of blood diseases and improved treatments and have examined hemoglobin synthesis and the role of platelets in blood coagulation.