  Using the Nambu-Jona-Lasinio model to describe the nucleon as a quark-diquark
state, we discuss the stability of nuclear matter in a hybrid model for the
ground state at finite nucleon density. It is shown that a simple extension of
the model to simulate the effects of confinement leads to a scalar
polarizability of the nucleon. This, in turn, leads to a less attractive
effective interaction between the nucleons, helping to achieve saturation of
the nuclear matter ground state. It is also pointed out that that the same
effect naturally leads to a suppression of ``Z-graph'' contributions with
increasing scalar potential.
