When equilibrium is reached in a reaction system (containing an arbitrary number of components and reaction paths), as many atoms, in their respective molecular entities will pass forward, as well as backwards, along each individual path in a given finite time interval. Accordingly, the reaction path in the reverse direction must in every detail be the reverse of the reaction path in the forward direction (provided always that the system is at equilibrium). The principle of detailed balancing is a consequence for macroscopic systems of the principle of microscopic reversibility.