Heisenberg writes on a talk Heisenberg had with Bohr about the theory of holes. The reason why an arbitrary small value of e$^{2}$/(h.c.) is not realized in nature is given by two deviations from Maxwell's theory which are identical in principle that dependent on pair production and that connected with the deviation from linearity and connected with finite self-energy. He talks on further considerations by Heisenberg. One Hamilton - electron and photon.

Heisenberg uses Dirac's method for the calculation of certain quantities. The concept of polarization of vacuum is not defined according to this theory.

Heisenberg does not think that substraction physics makes sense. He writes about what he has learned of nuclear physics in Copenhagen, about the order of magnitude of exchange forces, and Bethe's suggestion to replace Fermi's relation for interaction by another. He writes about the explanation of all mass defects by a plausible exchange force and he belives that the theory of the positron and quantum electrodynamics should be brought in order before attacking nuclear problems.

Heisenberg replies to Pauli's letter. He is now satisfied with the state of the theory of holes. There are two problems. The first is what kind of Schrödinger equation characterizes the theory of holes and what are at any moment the expectation values for current and charge-density. The second problem is what are the expectation values for the energy-density. He discusses the solutions for both problems. If Pauli agrees, he would like to publish the theory of holes in the present form. He is grateful for Pauli's criticism of his attempts to solve the self-energy question.

Heisenberg talks of more progress about e$^{2}$(h.c.). He also writes of a solution of the Schrödinger equation in the present theory of holes by a power-series of e$^{2}$(h.c.).