  The matrix element of the isoscalar axial vector current,
$\bar{u}\gamma_\mu\gamma_5u + \bar{d}\gamma_\mu\gamma_5d $, between nucleon
states is computed using the external field QCD sum rule method. The external
field induced correlator, $<0|\bar{q}\gamma_\mu\gamma_5q|0>$, is calculated
from the spectrum of the isoscalar axial vector meson states. Since it is
difficult to ascertain, from QCD sum rule for hyperons, the accuracy of
validity of flavour SU(3) symmetry in hyperon decays when strange quark mass is
taken into account, we rely on the empirical validity of Cabbibo theory to
dertermine the matrix element $\bar{u}\gamma_{\mu}\gamma_5 u +
\bar{d}\gamma_{\mu}\gamma_5 d - 2 \bar{s}\gamma_{\mu}\gamma_5 s$ between
nucleon states. Combining with our calculation of $\bar{u}\gamma_{\mu}\gamma_5
u + \bar{d}\gamma_{\mu}\gamma_5 d$ and the well known nucleon $\beta$-decay
constant allows us to determine $< p,s| {4/9}\bar{u}\gamma_{\mu}\gamma_5 u +
{1/9}\bar{d}\gamma_{\mu}\gamma_5 d + {1/9}\bar{s}\gamma_{\mu}\gamma_5 s |p, s>$
occuring in the Bjorken sum rule. The result is in reasonable agreement with
experiment. We also discuss the role of the anomaly in maintaining flavour
symmetry and validity of OZI rule.
