  Recent work by the author in collaboration with S. Narison and G. Veneziano
on the EMC-SMC-SLAC `proton spin' effect is reviewed. This uses a novel
approach to deep inelastic scattering in which the matrix elements arising from
the OPE are factorised into composite operator propagators and proper vertices.
For polarised $\mu p$ scattering, the composite operator propagator is equated
to the square root of the first moment of the QCD topological susceptibility,
$\sqrt{\chi^\prime(0)}$. We evaluate $\chi^\prime(0)$ using QCD spectral sum
rules and find a significant suppression relative to its OZI expectation. This
is identified as the source of the violation of the Ellis-Jaffe sum rule for
the first moment of the polarised proton structure function $g_1^p$. Our
predictions, $\int_0^1 dx g_1^p(x;Q^2=10GeV^2) = 0.143\pm 0.005$ and
$\Delta\Sigma =0.353\pm 0.052$, are in excellent agreement with the new SMC
data. This supports our earlier conjecture that the suppression in the flavour
singlet component of the first moment of $g_1^p$ is a target-independent
feature of QCD related to the $U(1)$ anomaly and is not a special property of
the proton structure.
