Blood is an essential conduit for the immune system, hormonal messages, and fluid, and enables thermal homeostasis. The study of blood, or hematology, is a broad and evolving field of medicine that has fascinated physicians and scientists throughout the ages. Antonie van Leeuwenhoek’s discovery of blood cells, in 1674, and William Hewson’s description of the different cell types, in 1770, established the foundation on which the entire discipline of hematology has been built. Rudolf Virchow (1821–1902), the father of cellular pathology, was the first to recognize leukemia and to explain the mechanism of pulmonary thromboembolism. He documented that blood clots in the pulmonary artery can originate from venous thrombi, writing:
“…the detachment of larger or smaller fragments from the end of the softening thrombus which are carried along by the current of blood and driven into remote vessels. This gives rise to the very frequent process upon which I have bestowed the name of Embolia.” (Source: Thrombosis and Emboli, 1856.)
The subspecialty of hematology is said to have begun as a consequence of Max Wintrobe’s characterization of normal blood values in the late 1920s. He refined the hematocrit as a quantitative measure of red cells and was the first to characterize anemias on the basis of their size — microcytic, normocytic, and macrocytic. The advent of better diagnostic techniques has improved our understanding of the pathophysiology related to blood and shapes the field today.