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Network of nerve cells. Illustration of nervous system cells in a continuous network, as proposed by the reticular theory. This theory was put forward by the German anatomist Joseph von Gerlach (1820-1896) in 1871 and popularised by the Italian physician Camillo Golgi (1843-1926). The theory was discredited in the late 19th century by the Spanish neuroscientist Santiago Ramon y Cajal (1852-1934), who showed that the nervous system is composed of discrete cells. From Traite d'Anatomie Humaine by Leo Testut (1905). (KEYSTONE/SCIENCE PHOTO LIBRARY/COLLECTION ABECASIS/SCIENCE PHOTO LIBRARY)