Claude Bernard, The "Milieu Intérieur", and Regulatory Physiology

Claude Bernard's idea of the 'milieu intérieur' has been incorporated into modern physiology as a fundamental unifying concept. Bernard developed his conception, however, with a framework of nineteenth century concerns that differ in important ways from those of the present. This article summarizes the origins of Bernard's idea, the contemporary issues in physiology to which it was a response, and the gradual evolution of the idea in his thought up until the end of his career. Only in the late stages of development did Bernard make regulatory mechanisms central to the idea of the internal environment, even though he had himself much earlier made important discoveries concerning specific physiological regulatory systems. The paper discusses Bernard's views on physiological regulation, comparing them to the views of other pioneers in this field particularly those of Carl Bergmann.