Strangeness enhancement at mid--rapidity in Pb--Pb collisions at 158 $A$ GeV/c

K-S(0), Lambda, Xi, Omega and negative particle h(-) yields and transverse mass spectra, measured at central rapidity in p-Pb and Pb-Pb collisions at 158 A GeV/c, are presented and discussed, Yields are studied as a function of the number of nucleons participating in the collision N-part, which have been estimated using the Glauber model. From p-Pb to Pb-Pb collisions the particle yields per participant increase substantially. Such an enhancement is more pronounced for multiply strange particles, and reaches an order of magnitude for a. For a number of participants N-part > 100, however, all yields per participant appear to be constant.