  We study Barut's covariant equations describing the electromagnetic
interactions between N spin-1/2 particles. In the covariant formulation each
particle is described by a Dirac spinor. It is assumed that the interactions
between the particles are not mediated by a bosonic field (direct
interactions). Within this formulation, using the Lagrangian formalism, we
derive the approximate (semirelativistic) Breit equation for two interacting
spin-1/2 particles.
