Simple applications of the Zweig rule can fix some chiral-symmetry-breaking parameters in the quark-gluon theory of strong interactions. Using a bare-quark-mass ratio of $\frac{2m_s}{(m_u+m_d)}=25\mathrm{}$, we find ${{\sigma }^{\pi \pi }}_{\mathrm{NN}}=32\mathrm{}\pm 8$ MeV. This is in disagreement (by a factor of 2) with dispersion-relation calculations based on the new $\pi N$ phase shifts. Implications of this discrepancy are discussed.

• Received 29 September 1975

DOI:https://doi.org/10.1103/PhysRevD.13.2161