Fierz discusses the representation of the neutrino by spinor or pseudospinor and the implications of rest mass for the concept of anti-particle.

Fierz writes on various papers dealing with the limes photon mass = 0. He adds to this letter some observations on the physical difficulties of quantum electrodynamics.

Fierz asks some questions connected with the two-component theory of Lee and Yang.

Fierz replies to a letter by Pauli on interactions and the limitations of linear theories.

Fierz makes a short remark on an impending lecture by Lee on rigid spheres and on an experiment by Deutsch which would refute the two component theory.

Fierz writes on further calculations concerning fields with spin. He makes some remarks on Heisenberg's treatment of the Lee-model.

Fierz gives a schematic description of the parity experiments. He makes theoretical comments on the Lee model.

Fierz briefly replies to Pauli's New Year letter.

Frauenfelder gives a detailed description of a new experiment for parity measurement.

Frauenfelder refers in detail to several experiments whose results do not contradict the 2-component theory.