  We explore the effects of dust in cosmologically distributed intervening
galaxies on the high redshift universe using a generalised model where dust
content evolves with cosmic time. The absorbing galaxies are modelled as
exponential disks which form coevally, maintain a constant space density and
evolve in dust content at a rate that is uniform throughout. We find that the
inclusion of moderate to moderately weak amounts of evolution consistent with
other studies can reduce the mean observed $B$-band optical depth to redshifts
$z \simgt 1$ by at least 60% relative to non-evolving models. Our predictions
imply that intervening galactic dust is unlikely to bias the optical counts of
quasars at high redshifts and their evolution in space density derived
therefrom.
