2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/6433Many gravitationally lensed quasars exhibit flux ratio "anomalies" that cannot be explained under the hypothesis that the lensing potential is smooth on scales smaller than one kpc. Micro-lensing by stars is a natural source of granularity in the lens potential. The character of the expected fluctuations due to micro-lensing depends sensitively on the relative surface densities of micro-lenses (stars) and smoothly distributed (dark) matter. Observations of flux ratios may therefore be used to infer the ratio of stellar to dark matter along the line of sight -- typically at impact parameters 1.5 times the half light radius. Several recently discovered systems have anomalies that would seem to be explained by micro-lensing only by demanding that 70-90% of the matter along the line of sight be smoothly distributed.6 pages, 3 figures, uses newpasp.sty. Contributed paper to be published in IAU Symposium No. 220: Dark Matter in Galaxies, eds. S. Ryder, D.J. Pisano, M. Walker, and K. FreemanAstrophysicstext