  In this paper we study the gravitational instability in presence of
viscosity. In particular, the standard Jeans Mechanism is analyzed taking into
account bulk-viscosity effects in the first-order Newtonian dynamics. We show
how the perturbation evolution is damped by dissipative processes and the
top-down fragmentation mechanism is suppressed for strong viscous effects. The
critical value of the Jeans Mass remains unchanged also in presence of bulk
viscosity.
