  The next-to-leading order chiral pion-nucleon Lagrangian contains seven
finite low-energy constants. Two can be fixed from the nucleon anomalous
magnetic moments and another one from the quark mass contribution to the
neutron-proton mass splitting. We find a set of nine observables, which to one
loop order do only depend on the remaining four dimension two couplings. These
are then determined from a best fit. We also show that their values can be
understood in terms of resonance exchange related to $\Delta$ excitation as
well as vector and scalar meson exchange. In particular, we discuss the role of
the fictitious scalar-isoscalar meson. We also investigate the chiral expansion
of the two P-wave scattering volumes $P_1^-$ and $P_2^+$ as well as the
isovector S-wave effective range parameter $b^-$. The one-loop calculation is
in good agreement with the data. The difference $P_1^- - P_2^+$ signals chiral
loop effects in the $\pi N$ P-waves. The calculated D- and F-wave threshold
parameters compare well with the empirical values.
