In 1924 he graduated as a Doctor of Arts and was named, by request of his students, as assistant professor in the Faculty of Arts, teaching a course on Psychology and Logic which he completely rewrote based on his studies and academic experiences in North America. After his death, a letter from the amazed and intrigued British philosopher Bertrand Russell reached Lima, congratulating him on the contents of his doctoral thesis and asking him if the Peruvian philosophical movement was at the same level. Zulen only published two works during his lifetime, his university theses, while two further texts were published posthumously by his mother and Dora Mayer. Apart from these books there were also innumerable newspaper articles on indigenous rights, decentralisation and university reform - Zulen himself had tried on two occasions to publish a selection of these in Spain (under the title of "Gamonalismo y centralismo" or "Exploitation and Centralism"), but without success.