Källén proves a mathematical identity and he dicusses the properties of a function.

Källén replies to two letters and questions about dipole ghosts. He talks about his own work.

Källén replies to Pauli's last letter. The normal pertubation theory cannot be used in the case mentioned by Pauli.

Kröner's reply to Fierz's letter. He writes about the relation between physics and the physicist, and speaks about the concept of wholeness.

Kröner's reply to Pauli's letter of 5 Feb. He speaks about the classification of cognition in Plato. He makes some remarks on Leibniz's philosophy and scholasticism.

Landé defines the meaning of a "filter" in his work. He distinguishes it from a potential barrier.