  Using a relativistic Dirac-Brueckner analysis the pion contribution to the
ground state energy of nuclear matter is studied. Evidence is presented that
the role of the tensor force in the saturation mechanism is substantially
reduced compared to its dominant role in a usual non-relativistic treatment.
The reduction of the pion contribution in nuclear matter is due to many-body
effects present in a relativistic treatment. In particular, we show that the
damping of OPEP is actually due to the decrease of $M^*/M$ with increasing
density.
