  Spin longitudinal and transverse response function are studied by means of
the relativistic many-body theory. The spin response functions in the
relativistic theory are largely reduced from those in the non-relativistic
theory. The local density approximation with the eikonal approximation is
applied to the the nuclear absorption in the $(\vec{p},\vec{n})$ reactions on C
and Ca. We compare the calculated results with the recent experimental data.
