  We show that the experimental data for the total virtual-photon proton cross
section, \sigma_{\gamma^*p} (W^2, Q^2), for x_{bj} \lsim 0.1 lie on a universal
curve, when plotted against \eta = (Q^2 + m^2_0)/ \Lambda^2(W^2), where
\Lambda^2 (W^2) = C_1 (W^2+W^2_0)^{C_2} is determined by the parameters m^2_0,
C_1, C_2 and W^2_0. The observed scaling law follows from the
generalized-vector-dominance/color-dipole picture of low-x deep inelastic
scattering.
