Circulus was a socioeconomics doctrine devised by nineteenth-century French utopian socialist Pierre Leroux (1797–1871), who proposed that human excrement be collected by the state in the form of a tax and used as fertiliser, thereby increasing agricultural production sufficiently to prevent Malthusian catastrophe.
[1] Leroux posits the existence of a natural law dependent on the circulation of human excrement back through the agricultural process and which maintains a necessary balance between soil fertility and inexorable population growth.
Chacun recueillerait religieusement son fumier pour le donner à l'état, c'est-à-dire au percepteur, en guise d'impôt ou de contribution personelle.
[5] Despite public ridicule,[6] Leroux held firm to his theory in the decades that followed and, while living in exile in Jersey after the fall of the Second Republic, he carried out experiments using his own excrement as fertiliser in an attempt to persuade the local authorities to adopt the doctrine of circulus.
[10] But in practical terms, rather than by Leroux's vision of individual members of society willingly paying a tax in their own excrement for the sake of the common weal, Hugo's collector sewers were sooner inspired by the ideas of English social reformer Edwin Chadwick, who proposed that human waste be pumped from cities to the countryside to provide fertiliser for crops to feed those very cities, thereby completing "the circle and [realising] the Egyptian type of eternity by bringing as it were the serpent's tail into the serpent's mouth".