  Event-by-event multiplicity fluctuations in nucleus-nucleus collisions are
studied within the HSD and UrQMD transport models. The scaled variances of
negative, positive, and all charged hadrons in Pb+Pb at 158 AGeV are analyzed
in comparison to the data from the NA49 Collaboration. We find a dominant role
of the fluctuations in the nucleon participant number for the final hadron
multiplicity fluctuations. This fact can be used to check different scenarios
of nucleus-nucleus collisions by measuring the final multiplicity fluctuations
as a function of collision centrality. The analysis reveals surprising effects
in the recent NA49 data which indicate a rather strong mixing of the projectile
and target hadron production sources even in peripheral collisions.
