Heisenberg replies to Pauli's problem of the mirror-world. He writes on new problems in connection with the eigenvalue question.

Pauli gives some more suggestions for formulation of their results.

Pauli expresses satisfaction over Gürsey's idea to make the neutrino rather than the vacuum responsible for strangeness. He discusses several difficulties connected with the spinor-model.

Heisenberg resents the publicity given by the press to their work. He sends him by same mail an amended copy of the manuscript.

Pauli replies to some issues raised in de Shalit's letter of 6 March, including: strangeness; the role of particles with rest mass zero for the decrease in symmetry (group-invariance); the ^-conjugation formalism; and a "philosophical" problem.

Pauli says that the spinor model may be wrong, but Källén's considerations do not yet prove this as Pauli undertakes to demonstrate.