Many basic dyestuffs are adsorbed by stainable substrates in two different shades of color, designated as the normal and the metachromatic color. As a model for a substrate stainable in the normal color, a 3y0 solution of nucleic acid at pH 4.6, is chosen; as a model for a substrate stainable in the metachromatic color a solution or gel of agar at PH 4.6 is chosen. These model substrates allow of spectrophotometric measurement of the absorption curve ...