Pauli discusses the problem of scattering of mesons and protons. He talks about the preparation for the next Solvay congress.

Pauli talks about de Broglie's report for the Solvay congress on the theory of the photon. Pauli does not believe in de Broglie's hypothesis that the rest mass of the photon is different from zero.

Pauli makes some remarks on Heisenberg's "Hilbert-space II", and replies to Heisenberg's criticism of Landeau's work.

Pauli comments on Heisenberg's formulation of field quantization and some questions on specified points.

Pauli replies to Heisenberg's letter of 1st January. He is not convinced that dipole-"ghosts" cannot appear in Lee's model and gives some reasons for this.

Pauli regards Heisenberg's letter of 31 January as showing new progress. He talks about the mathematical difficulties of the Lee model and a general charaterization of the class of models with indefinite metric.

Mathematical appendix to the last letter.

Pauli writes about the results of his discussion (with Källén) of the motion of V- and N-particles in the Lee model, and is now more optimistic about Heisenberg's interpretation. He has questions which still have to be clarified.

Pauli makes a few more remarks on Heisenberg's manuscript.