  We re-analyze data on deep inelastic polarized lepton-nucleon scattering,
with particular attention to testing the Bjorken sum rule and estimating the
quark contributions to the nucleon spin. Since only structure function data at
fixed $Q^2$ can be used to test sum rules, we use E142 asymmetry measurements
and unpolarized structure function data to extract $g_1^n$ at fixed $Q^2$ = 2
GeV$^2$. When higher-twist effects, which are important at low $Q^2$, are
included, both the E142 and SMC data are compatible with the Bjorken sum rule
within one standard deviation. Assuming validity of the Bjorken sum rule, we
estimate the quark contributions to the nucleon spin, finding that their total
net contribution is small, with the strange quark contribution non-zero and
negative. The quark spin content of the nucleon spin is in agreement with
Skyrme model.
