  In continuum physics is presupposed that general-relativistic balance
equations are valid which are created from the Lorentz-covariant ones by
application of the equivalence principle. Consequently, the question arises,
how to make these general-covariant balances compatible with Einstein's field
equations. The compatibility conditions are derived by performing a modified
Belinfante-Rosenfeld symmetrization for the non-symmetric and not
divergence-free general-relativistic energy-momentum tensor. The procedure
results in the Mathisson-Papapetrou equations.
