  We compute the baryonic mass function (BMF) of disc galaxies using the best
LFs and baryonic M/L ratios reliable for this goal. For baryonic masses (M_b)
ranging between 10^8 and 10^{11} solar masses, the BMF is featureless, i.e. it
scales as M_b^{-1/2}. Outside this mass range, the BMF is a strong inverse
function of M_b. The contributions to the baryon density Omega_b from objects
of different mass highlight a characteristic mass scale of spirals at about
2x10^{11} solar masses, around which >50% of the total baryonic mass is
concentrated. The integral value, Omega_b= 1.4x10^{-3}, confirms, to a higher
accuracy, previous evidence (Persic & Salucci 1992) that the fraction of BBN
baryons locked in disc galaxies is negligible and matches that of high-z Damped
Lyman Alpha systems (DLAs). We investigate the scenario where DLAs are the
progenitors of present-day spirals, and find a simple relationship between
their masses and HI column densities by which the DLA mass function closely
matches the spiral BMF.
