  Several attempts to construct theories of gravity with variable mass are
considered. The theoretical impacts of allowing the rest mass to vary with
respect to time or an appropriate curve parameter are examined in the framework
of Newtonian and Einsteinian gravity theories. In further steps, scalar-tensor
theories are examined with respect to their relation to the variation of the
mass and in an ultimate step, an additional coordinate is introduced and its
possible relation to the mass is examined, yielding a five dimensional
space-time-matter theory.
