the Edge of Chaos
. . . . the old controversies about the reducibility of biological facts to physico-chemical facts are now seen to be unnecessary if we realise that we have to deal with regularities which occur at each of these levels. . . .
-- J. Needham, Biochemical Aspects of Form and Growth
The modern era of physiology is usually considered to begin with the recognition by nineteenth-century physicians that the human body has mechanisms whereby it regulates its fundamental processes independently of external influences. This maintainenance of internal conditions was called homeostasis by the great French physiologist Claude Bernard in his classic text of 1878, Lefons sur les PhU+00noménes de la Vie Commun aux Animaux et aux Végétaux. He recognized that the internal environment of the body, measured by such variables as temperature, blood sugar, salts, and acid-base balance (pH), are maintained at constant values despite changes in the individual's behavior and in external conditions. The body has a remarkable degree of autonomy, sustaining within narrow limits the internal conditions required for life despite long intervals without eating or drinking, and while engaged in the most diverse activities, from sleeping to climbing Mont Blanc.
Working out the details of the interactions between the different body systems that underlie this basic phenomenon occupied