two ways. On the one hand, it is a record of the exact determination and approximative analysis of the electric phenomena presented by living beings. Viewed from this standpoint, it represents a significant advance in biological knowledge. Du Bois-Reymond built up this branch of science, by inventing or improving methods, by devising new instruments of observation, or by adapting old ones. On the other hand, the volumes in question contain an exposition of a theory of bioelectricity. In them Du Bois-Reymond put forward a general conception that a living tissue, such as muscle, might be regarded as composed of a number of electric molecules, and that the electric behavior of the muscle was the product of these elementary units. We now know that these are sodium, potassium and other ions, the gradients of which are responsible for maintaining membrane potentials in excitable cells. His theory was soon criticized by several contemporary physiologists, such as Ludimar Hermann, who maintained that intact living tissue such as muscle does not generate electric currents unless it has suffered injury. The subsequent controversy was ultimately resolved in 1902 by du Bois-Reymond's student Julius Bernstein, who incorporated parts of both theories into an ionic model of action potential. Thus, du Bois-Reymond's work focused on animal electricity, although he made other physiological inquiries — such as could be studied by physical methods — concerning the phenomena of diffusion, the muscular production of lactic acid, and the development of shocks by electric fishes. Du Bois-Reymond exerted great influence as a teacher. In 1858, upon the death of Johannes Müller, the professorship of anatomy and physiology at the University of Berlin was divided into a professorship of human and comparative anatomy, which was given to Karl Bogislaus Reichert (1811–1883), and a professorship of physiology, which was given to du Bois-Reymond. This he held until his death, performing research for many years without adequate accommodation. In 1877, the Prussian government granted his wish and provided the university with a modern physiological laboratory. In 1851 he was admitted to the Academy of Sciences of Berlin, and in 1876 he became its perpetual secretary. Like his friend Hermann von Helmholtz, who had also studied under Johannes Peter Müller, du Bois-Reymond was known throughout Germany. He used his influence for the advancement of science, introducing the theories of thermodynamics and Darwin to students at the University of Berlin. He owed the largest part