  Equations of motions and energy-momentum density tensors are obtained for a
dispersive and dissipative medium sustaining electric and magnetic
polarizations, using Lagrangian formalisms. A previous work on the subject by
the authors has been simplified by reduction in the Lagrangian of the number of
independent vector fields, with which the sink modes (associated with the
dissipation) interact. The paper also formulates the dynamics of the
electromagnetic field in the medium in a covariant (relativistic) manner. We
discuss (and compare) the results, especially from the point of view of the
positivity of the energy density.
