  The Lagrangian description of fluid flow in relativistic cosmology is
extended to the case of flow accelerated by pressure. In the description, the
entropy and the vorticity are obtained exactly for the barotropic equation of
state. In order to determine the metric, the Einstein equation is solved
perturbatively, when metric fluctuations are small but entropy inhomogeneities
are large. Thus, the present formalism is applicable to the case when the
inhomogeneities are small in the large scale but locally nonlinear.
