1. G. Cocconi:Phys. Rev.,111, 1699 (1958);P. Ciok, T. Coghen, J. Gierula, R. Hołyński, A. Jurak, M. Miesowicz, T. Saniewska andJ. Pernegr:Nuovo Cimento,10, 741 (1958);M. Good andW. D. Walker:Phys. Rev.,120, 1857 (1960). For the latest developments of this line of models, see, for instance: Japanese and Brazilian Emulsion Chamber Group:Chacaltaya Emulsion Chamber Experiment; Notas de Fìsica, Vol.17, No. 1 (1971) and references therein.
2. R. Hagedorn andJ. Ranft:Suppl. Nuovo Cimento,6, 169 (1968);R. Adair:Phys. Rev.,172, 1370 (1968);Phys. Rev. D,5, 1105 (1972);J. Benecke, T. Chou, C. N. Yang andE. Yen:Phys. Rev.,188, 2159 (1969);G. Ranft andJ. Ranft:Phys. Lett.,32 B, 207 (1970);E. L. Berger andA. Krzywichi:Phys. Lett.,36 B, 380 (1971);R. Hwa:Phys. Rev. Lett.,26, 1143 (1971);R. Hagedorn andJ. Ranft:Nucl. Phys.,48 B, 157 (1972);M. Jacob andR. Slansky:Phys. Rev. D,5, 1847 (1972);Y. Hama:Phys. Rev. D,6, 3306 (1972);E. L. Feinberg:Phys. Rep.,5 C, 238 (1972);M. Abud andY. Hama:Lett. Nuovo Cimento,7, 659 (1973);J. Kripfganz, G. Ranft andJ. Ranft:Nucl. Phys.,56 B, 205 (1973);G. Ranft andJ. Ranft:Phys. Lett.,45 B, 43 (1973);P. Pirilä andS. Pokorski:Phys. Lett.,43 B, 502 (1973);Lett. Nuovo Cimento,8, 141 (1973);A. Białas, K. Fiałkowski andK. Zalewski:Phys. Lett.,45 B, 337 (1973);C. Quigg andG. H. Thomas:Phys. Rev. D,7, 2752 (1973);E. L. Berger andG. C. Fox:Phys. Lett.,47 B, 162 (1973);E. L. Berger, G. C. Fox andA. Krzywicki:Phys. Lett.,43 B, 132 (1973);C. B. Chiu andK. H. Wang:Phys. Rev. D,8, 2929 (1973);D. Lévy:Nucl. Phys.,59 B, 583 (1973);M. Le Bellac, H. I. Miettinen andR. G. Roberts:Phys. Lett.,48 B, 115 (1974);F. Hayot andA. Morel: Saclay preprints D. Ph. T/73/58 and D. Ph. T/73/61 (1973);S. Pokorski andL. Van Hove: CERN preprint Th 1772 (1973);G. Ranft andJ. Ranft: CERN preprint Th 1838 (1974).
3. A. Ballestrero andE. Predazzi: Torino preprint IFTT 201 (1973);
4. A. Ballestrero: Torino preprint IFTT 202 (1973).
5. E. Predazzi andG. Veneziano:Lett. Nuovo Cimento,2, 749 (1971).