  In a previous work, assuming that the nucleus can be treated as a perfect
fluid, we have studied the propagation of perturbations in the baryon density.
For a given equation of state we have derived a Korteweg - de Vries (KdV)
equation from Euler and continuity equations in non-relativistic hydrodynamics.
Here, using a more general equation of state, we extend our formalism to
relativistic hydrodynamics.
