Pauli talks of technicalities about a visit to Copenhagen in spring. Heisenberg agrees with Källén's results and yet he wants to retain the dipole ghosts. He writes about experimental results with oriented nuclear spin in Co58 by Mrs. Wu.

Pauli asks Källén to tell Gustafson that he cannot come to Sweden before his trip to Berkeley. He talks about Jost's example which showed that Källén representation's by retarded functions cannot be derived. He also writes on Thirring's model.

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 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?"

Pauli wants to write first to Lee before the proposed paper by Pauli and Källén is written. He writes on a definition of a "ghost state". He expresses doubts about the Tamm-Dancoff approximation in the case of more general systems. He makes some mathematical remarks.