Our conception is that of a theory about the system in an inertial state... if the organism is a system in an inertial state, as our law expresses it… - Ludwig von Bertalanffy

Animal growth can be considered as a result of a counteraction of synthesis and destruction, of the anabolism and catabolism of the building materials of the body. There will be growth so long as building up prevails over breaking down.

Conventional physics deals only with closed systems, i.e. systems which are considered to be isolated from their environment... However, we find systems which by their very nature and definition are not closed systems. Every living organism is essentially an open system. It maintains itself in a continuous inflow and outflow, a building up and breaking down of components, never being, so long as it is alive, in a state of chemical and thermodynamic equilibrium but maintained in a so-called steady state which is distinct from the latter.

If the variables are continuous, this definition [Ashby’s fundamental concept of machine] corresponds to the description of a dynamic system by a set of ordinary differential equations with time as the independent variable. However, such representation by differential equations is too restricted for a theory to include biological systems and calculating machines where discontinuities are ubiquitous.