As an experimenter, Claude Bernard (1813–1878) enriched physiology by introducing numerous new concepts into the field. The most famous of these concepts is that of the French milieu intérieur or, loosely translated, the body’s “internal environment.” This means that the complex functions of the various organs are closely interrelated and are all directed to maintaining a constancy of the animal’s internal conditions, even with external changes. All internal cells exist in a combination of blood and lymph (thus, aqueous) environment that bathes the cells and provides a medium for the simple exchange of nutrients and waste material.