  Results of a systematic study of fully integrated particle multiplicities in
central Au-Au and Pb-Pb collisions at beam momenta 1.7 A GeV, 11.6 A GeV
(Au-Au) and 158 A GeV (Pb-Pb) using a statistical-thermal model are presented.
The close similarity of the colliding systems makes it possible to study heavy
ion collisions under definite initial conditions over a range of centre-of-mass
energies covering more than one order of magnitude. We conclude that a thermal
model description of particle multiplicities, with additional strangeness
suppression, is possible for each energy. The degree of chemical equilibrium of
strange particles and the relative production of strange quarks with respect to
u and d quarks are higher than in e+e-, pp and pp(bar) collisions at comparable
and even at lower energies. The average energy per hadron in the comoving frame
is always close to 1 GeV per hadron despite the fact that the energy varies
more than 10-fold.
