Physiology as a distinct discipline utilizing chemical, physical, and anatomical methods began to develop in the 19th century. Claude Bernard in France; Johannes Müller, Justus von Liebig, and Carl Ludwig in Germany; and Sir Michael Foster in England may be numbered among the founders of physiology as it now is known. At the beginning of the 19th century, German physiology was under the influence of the romantic school of Naturphilosophie. In France, on the other hand, romantic elements were opposed by rational and skeptical viewpoints. Bernard’s teacher, François Magendie, the pioneer of experimental physiology, was one of the first men to perform experiments on living animals

Müller and Bernard, however, recognized that the results of observations and experiments must be incorporated into a body of scientific knowledge and that the theories of natural philosophers must be tested by experimentation. Many important ideas in physiology were investigated experimentally by Bernard, who also wrote books on the subject. He recognized cells as functional units of life and developed the concept of blood and body fluids as the internal environment in which cells carry out their activities. This concept of physiological regulation of the internal enviornment occupies an important position in physiology and medicine