2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/61724We give a systematic presentation of relations between lattice gas models with hard-core interactions, enumeration of directed-site animals, and the algebra of formal power-series in the partially commutative case, along the work of X.G.Viennot. We present a complete and simplified solution, using this algebra, of the directed animals enumeration problem in two dimensions, including a fast program for random generation of such animals (with uniform distribution) and images produced by this program.French, 49 pages, see http://dept-info.labri.u-bordeaux.fr/~betrema/animaux/CombinatoricsStatistical Mechanicstext