  We present a formalism for studying the influence of dispersive and absorbing
dielectric bodies on a radiating atom in the framework of quantization of the
phenomenological Maxwell equations for given complex permittivities of the
bodies. In Markov approximation, the rate of spontaneous decay and the line
shift associated with it can then be related to the complex permittivities and
geometries of the bodies via the dyadic Green function of the classical
boundary value problem of electrodynamics -- a result which is in agreement
with second-order calculations for microscopic model systems. The theory is
applied to an atom near a planar interface as well as to an atom in a spherical
cavity. The latter, also known as the real-cavity model for spontaneous decay
of an excited atom embedded in a dielectric, is compared with the
virtual-cavity model. Connections with other approaches are mentioned and the
results are compared.
