The Sympathoadrenal System and Homeostasis: Coping With Changes in the Internal and External Environment
Lewis Landsberg, M.D. Diane R. Krieger, M.D. Beth Israel Hospital and Harvard Medical School
This kind of independence shown by the organism in the external environment comes from the fact that, in the living being, the tissues are, in reality, removed from direct external influences and protected by a true internal environment (milieu interieur) mostly constituted by the fluid circulating in the body.
The constancy of the internal environment is the condition for free and independent life, the mechanism that makes it possible is that which assures the maintenance within the internal environment of all the conditions necessary for . . . life . . . . The constancy of the environment presupposes a perfection of the organism such that external variations are at every instant compensated and brought into balance. The conditions necessary for the life of the elements which must be brought together and maintained constant in the internal environment, for the exercise of free life, are those that we know already: water, oxygen, heat, and chemical substances or reserves.
These are the same conditions as those which are necessary for life in the simple beings, except in the more perfect animals with independent life the nervous system is called upon to regulate the harmony among all these conditions.
-- Claude Bernard, 1857, 1878 ( Langley, 1973)
Biologists have long been impressed by the ability of living beings to maintain their own stability . . . . The coordinated physiological reactions which maintain most of the steady states in the body are so complex, and are so peculiar to the living organism, that it has been