The interactions of ultrarelativistic (\ensuremath{\ge} ${10}^{12}$ ev) primary cosmic-ray protons with nucleons in photographic plates observed thus far show that in the majority of the cases the secondaries are emitted isotropically from two centers; this fact and the observation that the average transverse momentum of the secondaries is independent both of the energy of the primary nucleon and of the energy of the secondaries themselves suggest the following empirical model. When a nucleon-nucleon collision takes place at these energies, two "bodies" are formed, that move in opposite directions with respect to the center of momentum of the system, together with the two original nucleons, stripped of the energy necessary to create the "bodies." Each "body" emits, in its own system of reference, about half of the total number of secondaries, each secondary having an average energy of \ensuremath{\sim}1 Bev, independent of its nature. The inelasticity of the collision is thus determined by the number of secondaries and by the velocity of each "body" in the center-of-momentum system of the two original nucleons. Accurate determinations of the energy, in the laboratory system, of the secondaries of these interactions could provide a sensitive test for the model, but at present there are too few measurements available.