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

Addition to the letter of the 27 January 1934.

Pauli expresses scepticism about the theory of holes, especially in view of a certain arbitrariness in Dirac's derivations.

Pauli makes some remarks on Dirac's theory, on the mass of the neutron and on the negative protons.

Pauli replies to Heisenberg's letter concerning e$^{2}$. He gives an outline of how far a future theory will have to differ from the present one in order to avoid infinities.

Pauli makes two further remarks on theory of holes and e$^{2}$/(h.c.), concerning "Vertauschungsrelationen".

Pauli discusses details of Heisenberg's last letter of the 11th December. He makes more remarks about nuclear magnetic moments and gives some ideas about the neutron.

Addition to the last letter (17 July) about hermitic operators. Pauli talks about the five dimentional formalism.

Pauli writes more about hermitic operators.

Pauli writes about the impossibility of half-integer spin in a theory with a four-vector Psi which is quantized according to Fermi statistics. He writes also of the five-dimensional theory and its prospects.