Abstract
The quantum field dynamics outlined in part I is developed in detail for an arbitrary system of interacting fields. The theory is proved to be covariant, and its formal consistency is made to depend on the integrability conditions given by Dirac. These are discussed in an appendix. It is shown that each system may be described by its Lagrangian, because there is a general order for the operators in the corresponding Hamiltonian function which ensures that the integrability conditions are satisfied. The Dyson
S
-matrix is expressed in terms of the interaction Hamiltonian function, but may be evaluated with the help of the interaction Lagrangian. The reason for the appearance of the more complicated interaction Hamiltonian function is explained.