  We derive a representation for the pion nucleon scattering amplitude that is
valid to the fourth order of the chiral expansion. To obtain the correct
analytic structure of the singularities in the low energy region, we have
performed the calculation in a relativistic framework (infrared
regularization). The result can be written in terms of functions of a single
variable. We study the corresponding dispersion relations and discuss the
problems encountered in the straightforward nonrelativistic expansion of the
infrared singularities. As an application, we evaluate the corrections to the
Goldberger-Treiman relation and to the low energy theorem that relates the
value of the amplitude at the Cheng-Dashen point to the \sigma-term. While
chiral symmetry does govern the behaviour of the amplitude in the vicinity of
this point, the representation for the scattering amplitude is not accurate
enough to use it for an extrapolation of the experimental data to the
subthreshold region. We propose to perform this extrapolation on the basis of a
set of integral equations that interrelate the lowest partial waves and are
analogous to the Roy equations for \pi\pi scattering.
