Pauli writes about the difficulties of the theory of holes, as far as physical interpretation is concerned.

Heisenberg replies to two letters from Pauli about empirical data of nuclear moments. He writes about the rule of Fermi and Segrè. He talks about Pauli's idea of the existence of two kinds of neutrons and on the possible types of nuclear forces, about Ehrenfest's death and about Planck's philosophy of science.

Heisenberg writes more about the theory of holes and about another method for the elimination of an infinite charge density.

Pauli gives further critical comments on Heisenberg's formalism. He writes of Bloch's report on a theory of Beta-desintegration by Fermi.

Pauli talks about the solution he found for the matrix problem.

In connection with a note by De Broglie, published in: comptes rendus: (1934) Bd. 198, Heft Nr. 2, S. 135, Pauliremarks that the main problem is the correct formulation of the interaction terms of neutrino and electrons.

Appendix to the letter of the same date, entitled: "Ueber die quanten-elektrodynamische Formulierung der Löcher-theorie".

Heisenberg asks some questions in connection with Pauli's letter. One of Heisenberg's assumptions for space-like vectors is incompatible with the differential form of the conservation laws, and the latter has to be renounced which makes sense. He gives some remarks about Fermi's paper and the interaction introduced by him.

Addition to the letter of the 27 January 1934.