  We use nucleon-nucleon phase shifts obtained from experimental data, together
with the chiral expansion for the long-distance part of the NN interaction, to
obtain information about the short-distance piece of the NN potential that is
at work in the 1S0 channel. We find that if the scale R that defines the
separation between "long-" and "short-" distance is chosen to be \lsim 1.8 fm
then the energy dependence produced by short-distance dynamics is well
approximated by a two-term polynomial for Tlab < 200 MeV. We also find that a
quantitative description of NN dynamics is possible, at least in this channel,
if one treats the long-distance parts of the chiral NN potential in
perturbation theory. However, in order to achieve this we have to choose a
separation scale R that is larger than 1.0 fm.
