Psellos answered three questions from Ioannes Doukas the kaisar: prosagoge is gradual treatment, e.g. of heat by cold; the diaphragm divides respiratory and alimentary systems; patriarchal matter is so called because of a connection with the Father. In another letter, Psellos recalled that Trajans army when attacked by forest animals was saved by magicians. To defend his crops against caterpillars, Psellos told Ioannes, like Proklos, to slit a viper lengthways when Hydros rose and tie it to string around the plants