  The large discrepancy between the amount of baryons that were synthesized in
Big-Bang and that we detect at $z=0$ locked in stars inside galaxies and in
hot/cold gas in galaxies. goup and clusters, is a well known crucial issue for
present day cosmology. It is also thought that this riddle is at the backbone
of how the ordinary matter has formed, inside dark potential wells, the
structures we see today. Then, it is useful to reprint, by means of this
archive, the first (pre- astro-ph era) published work in which the amount of
"luminous" baryons was actually and suitably computed and the disagreement with
the BBN predictions strongly claimed. This because 12 years after the method
and the results are still up-to-date, and above all, people are occasionally
found to know only later works (appeared on astro-ph) that were meant to be
just (ours or other's) follow ups of the present paper.
