  The neutron spin structure function, $g_{1n}$, has been of considerable
interest recently in connection with the Bjorken sum rule and the proton spin
crisis. Work on this problem has concentrated on measurements at low-$x$. We
recall the important, non-perturbative physics to be learnt by going instead to
larger values of $x$ and especially from a determination of the place where the
expected sign change occurs. Of course, in order to obtain neutron data one
must use nuclear targets and apply appropriate corrections. In this regard, we
review recent progress concerning the various nuclear corrections that must be
applied to measurements on polarised $^3$He.
