A protein solution is confined between two solid ultrasmooth mica surfaces of an automated surface force apparatus (SFA). When the surfaces are slowly brought closer to each other (v less than or equal to 0.2 nm.s(-1)), the ordering and displacement of the molecular layers in the compressed protein solution can be observed by continuous recording of the refractive index of the medium between the mica surfaces of the SFA. At a pH near the protein pH(i), an increase of the ionic strength in the medium induces an accumulation of the protein molecules against the imposed compression stress, and the mica surfaces recede. The refractive index of the medium, constant when the adsorbed layers are ordered, decreases step by step from a mean high value (around 1.55) to an intermediary value (1.45). We discuss this behavior in terms of growth of multiple nucleation centers.