  Isoscalar collective modes in a relativistic meson-nucleon system are
investigated in the framework of the time-dependent Thomas-Fermi method. The
energies of the collective modes are determined by solving consistently the
dispersion relations and the boundary conditions. The energy weighted sum rule
satisfied by the model allows the identification of the giant ressonances. The
percentage of the energy weighted sum rule exhausted by the collective modes is
in agreement with experimental data, but the energies come too high.
