  A general formulation of spinor fields in Riemannian space-time is given
without using vierbeins. The space-time dependence of the Dirac matrices
required by the anticommutation relation
{\gamma_{\mu},\gamma_{\nu}}=2g_{\mu\nu} determines the spin connection. The
action is invariant under any local spin base transformations in the 32
parameter group Gl(4,c) and not just under local Lorentz transformations. The
Dirac equation and the energy-momentum tensor are computed from the action.
