  Instantons are the natural mechanism in non-perturbative QCD to remove
helicity from valence quarks and transfer it to gluons and quark-antiquark
pairs. To understand the extent to which instantons explain the so-called "spin
crisis" in the nucleon, we calculate moments of spin-dependent structure
functions in quenched QCD and compare them with the results obtained with
cooled configurations from which essentially all gluon contributions except
instantons have been removed. Preliminary results are presented.
