Introduction.-Physiological organization, like gravitation, is a" stubborn fact," and it is one task of theoretical physiology to find quantitative laws which describe organization in its various aspects. Just as the laws of thermodynamics were known before the kinetic theory of gases was developed, so it is not impossible that some quantitative generalizations may be arrived at in physiology which are independent of the discrete mechanisms in living things, but which apply to organic systems considered statistically. One such generalization is the principle of the maintenance of steady states-a principle which furnishes definite equations (of the type indicating equality of intake and output of elementary substances) applicable to the hypothetical normal individual. The purpose of these studies is to discuss the possible application of a second principle, the principle of minimum work, to problems concerning the operation of physiological systems.

The concept of adaptation has been treated in a quantitative manner by experimental morphologists, students of growth and form, who have shown again and again the tendency toward perfect fitness between structure and function in all sorts of plants and animals. Only rarely, however, has the concept of fitness been used as a premise for physiological deductions. The beginnings of theoretical or deductive physiology are to be found in the works of Galileo'and of Borelli, 2 who argued from the principle of similitude, as others havedone since. Thompson's fascinat-ing book3 contains a wealth of material on this subject. Henderson's classic essay4 covers the history of the teleological problem, and pre-sents his own proof that the teleological aspect ofnature (until Darwin's time associated with the minutiae of biological adaptations, and in the latter part of the last century associated with primitive theological doc-trine) has its real roots in the properties of matter and in the laws of physics and chemistry. Thus it may be seen that organization is a legitimate field for scientific inquiry and not an" affair of the reflective judgment."