Samarium sulfide (SmS) is a nonmagnetic narrow-gap (0.06 eV) semiconductor that undergoes a transition to a metallic intermediate valence state at 6.5 kbar. Europium sulfide (EuS) is a ferromagnetic semiconductor with a Curie temperature of 16 K and a gap of 1.6 eV. Here we present a study of the lattice constant, magnetic susceptibility, and resistivity of the substitution series Sm1-xEuxS for 0 \u3c x \u3c 1. We observe a smooth interpolation of magnetic and transport behavior across the series, consistent with a virtual crystal scenario and Vegard\u27s law. Surprisingly, however, the lattice constant deviates below Vegard\u27s law in a manner that suggests parametric control of the Sm-Sm distance by the Eu moment in the manner of a magnetic polaron