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.

Enz writes on his theory on renormalization of photon-electron coupling constant.

Enz writes about a student's diploma work and about a discussion he had with R Jost on "associated production" of $\mu$ -mesons.