  Numerical evaluation of the path integral for QCD on a discrete space-time
lattice has been used to calculate ground state matrix elements specifying
moments of quark density and spin distributions. This talk will explain how
these matrix elements have been calculated in full QCD using dynamical quarks,
show how physical extrapolation to the chiral limit including the physics of
the pion cloud resolves previous apparent conflicts with experiment, and
describe the computational resources required for a definitive comparison with
experiment.
