A novel model of biological organisms is advanced, treating an organism as a
self-consistent system subject to a pathogen flux. The principal novelty of the
model is that it describes not some parts, but a biological organism as a
whole. The organism is modeled by a five-dimensional dynamical system. The
organism homeostasis is described by the evolution equations for five
interacting components: healthy cells, ill cells, innate immune cells, specific
immune cells, and pathogens. The stability analysis demonstrates that, in a
wide domain of the parameter space, the system exhibits robust structural
stability. There always exist four stable stationary solutions characterizing
four qualitatively differing states of the organism: alive state, boundary
state, critical state, and dead state.Comment: Latex file, 12 pages, 4 figure
