Tells about a report by Schein at a meeting in New York on artificial meson production.

Pauli thanks Delbrück for the copy of his lecture. He hopes that biology will soon have a development analogous to that of physics from 1900 - 1905. He is interested in processes in living organisms which cannot be explained by quantum mechanics. There may exist in living organisms, besides statistical laws, an additional interdependence which might explain biological evolution.

Pauli expresses great doubts as to the correctness of Dirac's quantum-electrodynamical approach. He explains that it is possible that the way to describe the interaction of particles with an electromagnetic field could be fundamentally wrong.

Pauli makes some remarks on Dirac's theory, particularly on the problem of low-frequency photons.

Pauli quotes and comments parts of a letter of Eliezer. He also writes about a letter of Heitler whose method leads in the case of meson-fields to different results from those made by Dirac. He mentions two papers by Heisenberg and comments on his unitary S-matrix.

Pauli writes of another letter of Eliezer and encloses a copy of his answer to him and he adds some remarks.

Pauli expresses his enthusiasm over Dirac's Bakerian lecture and makes several comments on it.

Pauli thanks for a paper sent in honour of Bohr's 60th birthday. He cannot accept Dirac's theory from the standpoint of physics because it leads to results contradicting the required correspondence to the classical theory.

Pauli's letter deals with Dirac's new formulation of quantum electrodynamics. He objects to the fact that Einstein's radiation laws are not derived but introduced as additional assumptions and refers to

Pauli makes some new remarks on Dirac's theory on the occasion of sending him a copy of Pauli's paper on Dirac's method of field-quantization.