Radial plot of the transmission T, which is the fraction of incident light reaching us through the foreground galaxy. Solid points are the averaged radial profile of transmission, with error bars at each radius from the scatter in measurements (error of the mean in each case). Open symbols show inter-arm regions as identified in the transmission map (Fig. 2), in regions of high expected S/N. Solid lines are the intensity of light from foreground (UGC 3995B) and background (UGC 3995A) galaxies along the line between both nuclei (the orange line in Fig. 1), to the same but arbitrary scale.