ABSTRACT
The Frenchman Claude Bernard (1813-1878) noticed a remarkable constancy in the internal environment (milieu inte´rieur) of a living organism, despite changing conditions in the external environment. He wrote “The constancy of the internal environment is the condition for a free and independent life” (La fixite´ du milieu inte´rieur est la condition d’une vie libre et inde´pendante). A living body, as he explained, is relatively independent of the surrounding environment. This independence derives from the fact that the tissues are protected by a veritable internal environment which is constituted by the fluids circulating in the body.
