Pauli talks about Springer concerning the Handbuch article. He writes more on Thirring's model.

Pauli gives the result of his thoughts about Heisenberg's Lee model and sends a detailed discussion on infinite metric and complex energy values. He writes on possible generalization of Heisenberg's formalism.

Pauli writes about the conference in Geneva, saying that the mirror-problem remains unsolved, and that it seems clear that the masses of elementary particles are certain eigenvalues. He is disappointed with the results of Heisenberg's school. He needs help in the mathematics of these eigenvalue problems and wants to hear Källén's opinion on several points. He hopes that Källén's generation will produce constructive models of elementary particles.

Pauli adds an extract from a letter by Weisskopf about the Geneva conference . He has a positive attitude to Schwinger's last paper. He talks about a spinor-model by Gürsey where the neutrino and not the vacuum creates strangeness.

Pauli thanks Källén for his manuscript and letter. He makes a comparison of Källén's and Yang's results. He talks about results by Rohrlich for the case of charged scalar mesons in interaction with the quantized electromagnetic field. He also talks about results by Peasler and Kiroshita and about nu mber for charged vector mesons.

Pauli talks about identical results in papers by Thirring and by Hurst. He writes on the evaluation of a certain integral and on Peierl's method for the quantization of the form factor theory.

Pauli talks about a confusion in Källén's calculations in the last letter.

Pauli has more thoughts about the Lee model. He asks Källén to work out the free-of-infinities formalism and gives an indication how to do it. He asks about a generalization of the method of Cauchy's integral-proposition for quantum electrodynamics.

Pauli writes on a question about the S-matrix in Lee's model. "Is it unitary?"