  The opacity of spiral galaxies is examined by modelling the dust and stellar
content of individual galaxies. The model is applied to five late-type spiral
galaxies (NGC 4013, IC 2531, UGC 1082, NGC 5529 and NGC 5907). Having analyzed
a total of seven galaxies thus far, the five galaxies mentioned above plus UGC
2048 and NGC 891 presented in (Xilouris et al. 1997, 1998), we are able to draw
some general conclusions, the most significant of which are: 1) The face-on
central optical depth is less than one in all optical bands indicating that
typical spiral galaxies like the ones that we have modelled would be completely
transparent if they were to be seen face-on. 2) The dust scaleheight is about
half that of the stars, which means that the dust is more concentrated near the
plane of the disk. 3) The dust scalelength is about 1.4 times larger than that
of the stars and the dust is more radially extended than the stars. 4) The dust
mass is found to be about an order of a magnitude more than previously measured
using the IRAS fluxes, indicating the existence of a cold dust component. The
gas-to-dust mass ratio calculated is close to the value derived for our Galaxy.
5) The derived extinction law matches quite well the Galactic extinction law,
indicating a universal dust behaviour.
