Like Caligula, Nero seemed to grow gradually more insane as his reign progressed. Pliny devoted much of his time to writing on the comparatively safe subjects of grammar and rhetoric. He published a three-book, six-volume educational manual on rhetoric, entitled "Studiosus", "The Student". Pliny the Younger says of it: "The orator is trained from his very cradle and perfected." It was followed by eight books entitled "Dubii sermonis", "Of Doubtful Phraseology". These are both now lost works. His nephew relates: "He wrote this under Nero, in the last years of his reign, when every kind of literary pursuit which was in the least independent or elevated had been rendered dangerous by servitude."