have deduced
a selfconsistent set of equations for electrons in metals, taking
into
account some special features of the problem as the
 quasineutrality condition and the
neglection of the displacement current in Maxwell's eqs. The magnetic
permeability $\mu$ has also been taken constant ($\mu = 1$). These
approximations were good enough to develop
 the electron plasma hydrodynamics in crystalline
metals as well as to consider magnetohydrodynamic effects \cite{Klara}.
\par
The problem is more complicated in bad conductors and semiconductors, as well
as at higher frequences, when the displacement current cannot be neglected,
the quasineutrality condition does not hold and
$\epsilon$ and $\mu$ are functions of the
deformation. We give in this
work the solution of this general case.
The only assumption is
 that the constitute relations are linear, i.e.
$ D_i = {\hat \epsilon}_{ik} E_k$,
$ B_i = {\hat \mu}_{ik}H_k$.
\par

    In the present work we shall consider electrons
having in mind that the theory is valid for
arbitrary quasiparticles. We suppose for simplicity that the crystal considered
 is isotropic in its undeformed state. This means that $\epsilon$ and $\mu$ are
taken scalars, but their derivatives with respect to coordinates are matrices
and depend on the lattice symmetry. It is 