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 writes in order to proceed with electrodynamics. One has to know the consequences of the present formalism. He asks for Pauli's opinion.

Heisenberg writes on Bohr's forthcoming reply to Einstein's thought experiment (screen and two diaphragms) concerning causality and quantum theory. He talks of his own plans for a paper on nuclear physics.

Heisenberg does not agree with Pauli about the identical situation of quantum electrodynamics and Fermi's theory, because the latter contains a universal constant of nature. He says that for high energies one has to expect completely different results. He writes that is the shower-formation is as an important consequence of Fermi's theory.

Heisenberg agrees with Pauli that the mathematical problems should be approached by a limiting process from the lattice-world. He gives some suggestion for a Hamiltonian scalar theory. He talks about a common trip to Copenhagen.

Heisenberg believes that Pauli's proof of the infinity of eigenvalues is not cogent.

Heisenberg reports on the results of his investigation on the mathematical properties of Pauli's lattice world. He believes that further investigation on this model is worthwhile.

Heisenberg agrees now with Pauli that their model does not lead to the existence of showers, and cites qualitative arguments for this conjecture. He also writes about recent experimental results in nuclear physics.

Heisenberg comments on Bhabha's and Heitler's paper which leads to agreement with Heisenberg's data about cross-section for genuine showers. There is a difference between Bhabha's and Heisenberg's conception regarding cosmic radiation at great depths. He writes on an experiment deciding between both conceptions: measurement of electron energies at great depths.

Heisenberg revokes his former statement about the relativistic invariance of the cut-off-method.