  We use the Nambu-Jona-Lasinio model as an effective quark theory to
investigate the medium modifications of the nucleon electromagnetic form
factors. By using the equation of state of nuclear matter derived in this
model, we discuss the results based on the naive quark-scalar diquark picture,
the effects of finite diquark size, and the meson cloud around the constituent
quarks. We apply this description to the longitudinal response function for
quasielastic electron scattering. RPA correlations, based on the
nucleon-nucleon interaction derived in the same model, are also taken into
account in the calculation of the response function.
