  The role of chiral transformations in effective theories modeling Quantum
Chromo Dynamics is reviewed. In the context of the Nambu--Jona--Lasinio model
the hidden gauge and massive Yang--Mills approaches to vector mesons are
demonstrated to be linked by a special chiral transformation which removes the
chiral field from the scalar--pseudoscalar sector. The role of this
transformation in the presence of a topologically non--trivial chiral field is
illuminated. The fermion determinant for such a field configuration is
evaluated by summing the discretized eigenvalues of the Dirac Hamiltonian. This
discretization is accomplished by demanding certain boundary conditions on the
quark fields leaving a finite model space. The properties of two sets of
boundary conditions are compared. When the topologically non-trivial chiral
transformation is applied to the meson fields the associated transformation of
the boundary conditions is shown to be indispensable. A constructive procedure
for transforming the boundary conditions is developed.
