  The bulk macroscopic response of a system of particles or inclusions with
field-induced forces is studied. The susceptibilities and transport
coefficients in such a system are expressed as averages of a multiple
scattering expansion. A special diagrammatic method is developed to analyze the
structure of the expansion. The concept of irreducibility is discussed in
detail and shown to be crucial in obtaining macroscopic equations
characterizing the system response with coefficients depending solely on local
properties of the medium. Due to the representation of particles by lines in
diagrams, irreducibility is given a particularly simple topological
interpretation in the diagrammatic language. The method is illustrated by a
discussion of response problems in colloidal suspensions in presence of
hydrodynamic interactions.
