Ernst von Fleischl-Marxow, also Ernst Fleischl von Marxow (5 August 1846, Vienna – 22 October 1891, Vienna), son of Karl Fleischl Edlem von Marxow and his wife Ida (née Marx) was an Austrian physiologist and physician who became known for his important investigations on the electrical activity of nerves and the brain. He was also a creative inventor of new devices which were widely adopted in clinical medicine and physiological research. Marxow studied medicine in the University of Vienna, Austria. He started his scientific career as a research assistant in the laboratory of Ernst Wilhelm von Brücke (1819–1892), and later as an assistant, in the same university, to the eminent pathologist Carl von Rokitansky (1804–1878). However, an accident while he was dissecting a cadaver injured his thumb, which became infected and had to be amputated, interrupting his activities in anatomical pathology. Thus, he had to turn to physiology, and he came back to von Brücke's laboratory in Vienna after studying for a year with Carl Ludwig (1816–1895), another famous physiologist at the University of Leipzig, Germany, obtaining his doctoral degree in medicine in 1874. In the first phase of his career in neurophysiology, Marxow dedicated himself to electrophysiology of nerves and muscles, then a research field of increasing prestige, after the pioneering investigations of Emil du Bois-Reymond (1818–1896), who had discovered the action potentials of axons. This field highly benefited from the technical developments occurring in the physical sciences, particularly new devices which were invented to work with small electric potentials and currents. Since biological tissues have extremely low levels of electrical activity (in the range of microvolts), neurophysiology's progress had to wait for them. Like many German physiologists of his time, Marxow had a good knowledge and ability with physics, and invented a number of devices for the purpose of his studies, particularly the reonome (a kind of rheostat, or variable resistor used to control finely the intensity of an electrical stimulus). He also adapted the Lippmann's capillary electrometer in order to use it for measuring subtle bioelectrical phenomena. From the bioelectricity of nerves, Marxow turned his attention, from 1876 on, to the global electrical activity of the cerebral hemispheres. Neuroanatomists had already determined at the time that its nervous tissue was also composed of cells (the neurons), with their bodies mainly located in the gray matter, and filamentary prolongations, the dendrites and the axons. Thus, it was only