Spatial optical solitons can be observed in bulk nematic-liquid-crystal cells with an entrance window and a bias voltage applied over the cell to enhance the optical nonlinear effect of laser-induced molecular reorientation. The soliton-induced waveguide is observed in transmission by use of a second light source and crossed polarizers. This set-up allows us to investigate the time dependence of the molecular reorientation that sustains the soliton-like beam propagation. Results from a numerical simulation are in good agreement with the experimental results, which confirms the validity of our model.