The additive quark model revisited: hadron and photon induced   cross-sections
  The standard additive quark model and the ensuing counting rules are modified to take into account the quark-gluonic content of the Pomeron and of the secondary Reggeons. The result is that a much improved description of $pp, \pi p, \gamma p$ and $\gamma \gamma$ cross-sections is achieved. 
P. Desgrolard, M. Giffon, E. Martynov, E. Predazzi