Gesner makes a distinction between the Arabian camel with one hump and the Bactrian camel with two humps. In his etymology of the word "camelus," he traces its roots back to the Hebrew "gamal" and the Chaldaic "gamela." Historiae Animalium (Studies on Animals) is considered to be the first modern zoological work. This first attempt to describe many of the animals accurately is illustrated with hand-colored woodcuts drawn from personal observations by Gesner and his colleagues. Conrad Gesner (March 26, 1516 - December 13, 1565) was a Swiss naturalist and bibliographer. To his contemporaries he was best known as a botanist, but in 1551 he was the first to describe brown adipose tissue; and in 1565 the first to document the pencil. He died of the plague, at the age of 49, the year after his ennoblement.