  Gas cloud models taking into account the recently disclosed fractal structure
of cold gas are set up, showing that large errors in the classical gas mass
determination based on smooth cloud models can easily follow if the gas is in
reality fractal. Fractal clouds must present both optically thin and optically
thick clumps in any single wavelength observations. The observed fractal
dimension of the cold ISM suggests that mass underestimates by a factor 10 or
more are typical. Due to its low temperature (around 3 K), and its condensed
fractal structure, together with its low metallicity, the outer gas would be
almost invisible for usual detectors. (A&A paper (in press) and figures
available by anonymous ftp at obssd8.unige.ch in /pub/fractal as postscript
file: dm_paper_II.ps (251k) and FIG*.ps, or papers I & II + figures as a
compressed tar file dm_papers.Z.tar (2.1 Mb)).
