His great zoological work, "Historiae animalium", appeared in 4 vols. (quadrupeds, birds, fish) folio, 1551–1558, at Zürich, a fifth (snakes) being issued in 1587. This work is the starting-point of modern zoology. Not content with such vast works, Gessner put forth in 1555 his book entitled "Mithridates de differentis linguis", an account of about 130 known languages, with the "Lord's Prayer" in twenty-two languages, while in 1556 appeared his edition of the works of Claudius Aelianus.