  We use the existing catalog of Damped Lyman-Alpha (DLA) systems to place
constraints on the amount of evolution in the baryonic content of galaxies and
on the value of the cosmological constant. The density of cold gas at redshifts
z=3+-1 is obtained from the mean HI column density of DLAs per cosmological
path length. This path length per unit redshift is in turn a sensitive function
of the vacuum density parameter, Omega_v. We compare the total inferred mass of
cold gas at high redshifts to that observed in stars today for flat
cosmologies. We define "eta" to be net fraction of the baryonic content of
local galaxies which was expelled since z=3, and use Bayesian inference to
derive confidence regions in the (eta, Omega_v) plane. In all cosmologies we
find that eta<0.4 with at least 95% confidence if <25% of the current stellar
population formed before z=3. The most likely value of eta is negative,
implying a net increase by several tens of percent in the baryonic mass of
galaxies since z=3+-1. On the other hand, recent observations of high metal
abundances in the intracluster medium of rich clusters (Loewenstein & Mushotzky
1996) require that metal-rich gas be expelled from galaxies in an amount
approximately equal to the current mass in stars. Based on our results and the
low metallicity observed in DLAs at z>2, we infer that more than half of the
baryonic mass processed through galaxies must have been assembled and partly
expelled from galaxies after z=2. We expect our constraints to improve
considerably as the size of the DLA sample will increase with the forthcoming
Sloan Digital Sky Survey.
