  Guided by the experimental confirmation of the validity of the Effective
Momentum Approximation (EMA) in quasi-elastic scattering off nuclei, we have
re-examined the extraction of the longitudinal and transverse response
functions in medium-weight and heavy nuclei. In the EMA we have performed a
Rosenbluth separation of the available world data on $^{40}$Ca, $^{48}$Ca,
$^{56}$Fe, $^{197}$Au, $^{208}$Pb and $^{238}$U. We find that the longitudinal
response function for these nuclei is "quenched" and that the Coulomb sum is
not saturated, at odds with claims in the literature.
