Río-Hortega, P

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(b. Portillo, Valladolid province, Spain, 5 May 1882; d. Buenos Aires, Argentina, 1 June 1945)


Río-Hortega received his medical degree in 1905 from the University of Valladolid, where he became assistant professor of histology. In 1915, after two years of study in Paris and London, he returned to Madrid and joined the laboratory staff of Nicolás Achúcarro, the histologist known for his studies of neuroglia and whose team worked closely with that of Santiago Ramón y Cajal.

Between 1914 and 1916 Río-Hortega worked on various histological topics, including the structure of the ovary and the fine texture of cancer cells. He did not begin his major work on the insterstitial cells of the nervous system until 1916. Both Ramón y Cajal and Achúcarro had studied the cytology of neurons and astrocytes, but the nature of the cells that the former called “corpuscles without processes” or the “third element” remained unclear.

By 1918 Río-Hortega had developed a silver carbonate stain enabling him to explicate the fine structure of the “third element,” which he found to consist of two different cytological types: microglia, small cells of mesodermal origin with spiny processes, dispersed throughout the central nervous system; and interfascicular glia or oligodendroglia, cells of ectodermal origin that follow and surround the nerve fibers. Rio-Hortega’s demonstration that these cells do not lack processes—as Ramón y Cajal had thought—led to heated controversy that strained relations between the two researchers.

The next phase of Río-Hortega’s career unfolded at the National Institute of Cancer in Madrid, where he headed the research division from 1928 to 1936. There he produced the basic cytological descriptions necessary for the classification of gliomatous and other tumors of the central nervous system. Soon after the outbreak of the Spanish Civil War he left Spain to work in neuropathology laboratories in Paris and Oxford. In 1940 he removed to Argentina. There he organized a laboratory in Buenos Aires and founded the Archivos de histología normal y patológica, in which he published his last studies on the neuroglial character of the satellite cells surrounding the neurons of sensory ganglia.


An account of Río-Hortega’s writings in Spanish is in J. M. Ortiz Picón, “La obra histoneurológica del doctor Pío del Río-Hortega (1882–1945),” in Archivos de neurobiologia, 34 (1971), 39–70.

For the work on microglia, see Río-Hortcga, “Microgiia,” in Wilder Penfield, ed., Cytology and Cellular Pathology of the Nervous System, 3 vols. (New York, 1932), III, 483–534; Jorge Bullo, “Contribuciones de la escuela de Cajal sobre histopatologia de la neuroglia y microglia,” in Archivos de histologia normal y patológica, 2 (1945), 425–445; and the following articles by Penfield, an American disciple of Río-Hortega: “Oligodendroglia and Its Relation to Classical Neuroglia,” in Brain, 47 (1924), 430–452; “Microglia and the Process of Phagocytosis in Gliomas,” in American Journal of Pathology, 1 (1925), 77–89; and “Neuroglia: Normal and Pathological,” in Cytology and Cellular Pathology of the Nervous System, II, 423–479.

For biographical details, see the article by Ortiz Picón cited above and Penfield’s obituary in Archives of Neurology and Psychiatry, 54 (1945), 413–416. On Río-Hortega’s place in the school of Spanish histologists, see José María López: Piñero, “La contribución de la escuela histológica españoia a la ciencia universal,” in Tercer programa (Madrid), no, 5 (Apr.-June 1967), 39–59. His relationship with Achúcarro is discussed by several contributors to the memorial volume Nicolás Achúcarro. Su vida y su obra (Madrid, 1968), Elements of an unpublished autobiographical MS describing Río-Hortega’s relationship with Ramón y Cajal appear in Dorothy F. Cannon, Explorer of the Human Brain, The Life of Santiago Ramón y Cajal (New York, 1949).

Thomas F. Glick