Paul Ehrlich and the Early History of Granulocytes

Paul Ehrlich's techniques, published between 1879 and 1880, for staining blood films using coal tar dyes, and his method of differential blood cell counting, ended years of speculation regarding the classification of white cells. Acidic and basic dyes had allowed him to recognize eosinophil and basophil granules, respectively, work that was a direct continuation of his discovery of the tissue mast cell described in his doctoral thesis. Ehrlich went on to develop neutral dyes that identified epsilon granules in neutrophils ("cells with polymorphous nuclei"). He also speculated, for the most part correctly, on the formation, function, and fate of blood neutrophils and eosinophils. Before Ehrlich, a number of important observations had been made on white cells and their role in health and disease. Among the most notable were William Hewson's studies of blood and lymph; the early descriptions of leukemia by Alfred Donné, John Hughes Bennett, Rudolf Virchow, and others; as well as seminal observations on inflammation by William Addison, Friedrich von Recklinghausen, and Julius Cohnheim. Eosinophils were almost certainly recognized previously by others. In 1846, Thomas Wharton Jones (1808-1891) described "granule blood-cells" in several species including humans. The term "granule cell" had also been used by Julius Vogel (1814-1880), who had previously observed similar cells in inflammatory exudates. Vogel, in turn, was aware of the work of Gottlieb Gluge (1812-1898), who had observed "compound inflammatory globules" in pus and serum that resembled eosinophils. Almost 20 years before Ehrlich developed his staining methods, Max Johann Schultze (1825-1874) performed functional experiments on fine and coarse granular cells using a warm stage microscopic technique and showed they had amoeboid movement and phagocytic abilities. Despite these earlier observations, it was Ehrlich's use of stains that heralded the modern era of studies of leukocyte biology and pathology.