Fortunately, for an ORN with a simple structure, which reaches a steady state without exhibiting oscillatory or dispersive behavior, we can show that such a steady state is stable against fluctuation, as can be expected from the foregoing argument. That is to say, whether an ORN reaches a steady state or not depends on particular reactions in the ORN, but for an ORN which is certain to reach a steady state, the steady state is stable against fluctuation. This argument becomes easier to understand by considering a function fDOB given by the sum of the absolute values of dCi /dt: