  The data on average hadron multiplicities in central A+A collisions measured
at CERN SPS are analysed with the ideal hadron gas model. It is shown that the
full chemical equilibrium version of the model fails to describe the
experimental results. The agreement of the data with the off-equilibrium
version allowing for partial strangeness saturation is significantly better.
The freeze-out temperature of about 180 MeV seems to be independent of the
system size (from S+S to Pb+Pb) and in agreement with that extracted in e+e-,
pp and p{\bar p} collisions. The strangeness suppression is discussed at both
hadron and valence quark level. It is found that the hadronic strangeness
saturation factor gamma_S increases from about 0.45 for pp interactions to
about 0.7 for central A+A collisions with no significant change from S+S to
Pb+Pb collisions. The quark strangeness suppression factor lambda_S is found to
be about 0.2 for elementary collisions and about 0.4 for heavy ion collisions
independently of collision energy and type of colliding system
