  It is shown that the nuclear effects playing a relevant role in Deep
Inelastic Scattering of polarized electrons by polarized $^3$He are mainly
those arising from the effective proton and neutron polarizations generated by
the $S'$ and $D$ waves in $^3$He. A simple and reliable equation relating the
neutron, $g_1^n$, and $^3$He, $g_1^3$, spin structure functions is proposed. It
is shown that the measurement of the first moment of the $^3$He structure
function can provide a significant check of the Bjorken Sum Rule.
