  The quark number susceptibility is expressed as an integral in terms of
dressed quark propagator and dressed vector vertex. It is then investigated
with the latter two- and three-point functions confronted with a
Dyson-Schwinger equation model which accommodates both finite temperature and
baryon chemical potential. The critical end point in the phase diagram is
identified and the behavior of the quark number susceptibility around the
critical end point is highlighted. The characteristic features found agree well
with recent lattice QCD simulation results.
