  The absorptive part of the $WW\gamma$ vertex induced by massive fermion loops
is considered for different kinematical configurations. We show that the axial
part of this vertex is different from zero not only when massive fermions are
involved but also for massless fermion loops, if one of the W bosons is
space-like and the other is time-like. We also discuss in what sense Low's soft
photon theorem is satisfied.
