  In the context of Modified Newtonian Dynamics (MOND), we study how
perturbation of a spherically symmetric system would affect the gravitational
field. In particular, we study systems of perturbed and unperturbed spherical
shells. For a single perturbed shell, we show that the field inside the shell
is much smaller than what would be expected from a naive scaling formula. The
strength of the perturbation field within the shell is screened by the
spherically symmetric component of the mass, and is reduced as the spherically
symmetric component is increased. For a two-shell system, we again show that
the perturbed field is screened by the shells, no matter which shell's mass
distribution is perturbed. The field within the inner shell is most suppressed
when the inner and outer shells coincide. However, for a very light inner
shell, the perturbation to the field can be enhanced. The enhancement is
typically larger for smaller inner shells, and the perturbed field can be
amplified by almost a factor of 2. The relevance to the effect of external
fields on galaxy dynamics is discussed.
