  An integral-differential equation is derived for the self-consistent
(effective) field in the medium consisting of many small bodies randomly
distributed in some region. Acoustic and electromagnetic fields are considered
in such a medium. Each body has a characteristic dimension $a\ll\lambda$, where
$\lambda$ is the wavelength in the free space.
  The minimal distance $d$ between any of the two bodies satisfies the
condition $d\gg a$, but it may also satisfy the condition $d\ll\lambda$. Using
Ramm's theory of wave scattering by small bodies of arbitrary shapes, the
author derives an integral-differential equation for the self-consistent
acoustic or electromagnetic fields in the above medium.
