Biological modeling with variable compartmental structure

Many biological processes such as water balance and temperature regulation may be modeled by a variable-structure compartmental system of ordinary differential equations. In some cases the system is naturally bilinear, and in others the bilinear system may be a valid approximation of a complex nonlinear process. Tracer dynamics and associated methodology, which can be used to realize certain properties of the system, are analyzed. The theory is applied to tracer experiments for the development of a mammalian water-balance model.