Claude Bernard (1813 –1878), “one of the greatest of all men of science,” originated the term milieu intérieur, and furthered the concept of homeostasis. After an early high school and college education, he become an assistant in a druggist’s shop and contemplated becoming a writer, but was persuaded to study medicine and became an intern at the Hôtel-Dieu hospital in Paris. Working under the direction of the great physiologist François Magendie, he became his deputy in 1847 and succeeded him as full professor in 1855. In 1864 Napoleon III built him a laboratory at the National Museum of Natural History. He first worked on the function of the pancreas, then on the glycogenic function of the liver as the seat of an internal secretion and its role in the causation of diabetes. He also showed that the arterial system was under the control of vasodilator and vasoconstrictor impulses generated by the sympathetic system. He originated the concept that the cells of the body needed to live in a stable environment, the milieu interior, and advocated a disciplined approach to research that included using controls and carrying out animal experiments.