Sylvius was not only an eloquent professor, but also a demonstration teacher. He was the first professor to teach anatomy of a human corpse, in France. His biggest intellectual flaw was his blind reverence for the ancient authors. He treated the writings of Galen as if they were wholly sacred, he would believe that if a corpse showed structures different from those described by Galen, the error was not in the texts, but in the corpse, or the structure of the human body that had changed over the centuries. In one of his works, "Ordo et Ratio Ordinis Legendis Hippocratis et Galeni Libris", Sylvius says that the anatomy of Galen was infallible, that his treatise
De Usu Partium was divine and that further progress in anatomy would have been impossible.
Andreas Vesalius, who was his (frustrated) pupil, states that his manner of teaching was calculated neither to advance the science nor to rectify the mistakes of his predecessors. A human body was never seen in Dubois' anatomical theatre. The carcasses of dogs and other animals were the materials from which he taught. It was so difficult to obtain human bones, that Vesalius and his fellow-students had to collect them themselves from the
Cimetière des Innocents and other cemeteries. Without these, they must have committed numerous errors in acquiring the first principles. Though
Jean Riolan (1577–1657) contradicted these comments and accused Vesalius of ingratitude, it is certain that the frustrations that Vesalius experienced were the basis for which he later traveled to
Padua and became a famous anatomist himself. Only in Italy were the opportunities of inspecting the human body frequent enough as to facilitate the study of the science.
Charles Estienne also attacked his old teacher and assured that Sylvius was greedy. Some other pupils of Sylvius defended his teaching and work, specially Louis Vasse and
Michel de Villeneuve, the latter being considered by
Johann Winter von Andernach (colleague and friend of Sylvius) the best galenist of Paris and second anatomist after
Vesalius. Louis Vassé denounced the attacks of Vesalius and Estienne, and affirmed they had learnt all they knew by Sylvius' lessons. Vasse explains the nature of Sylvius' influence over his unruly audience this way:
"This depended not so much on his splendid use of the Latin tongue as upon the exceptional clarity of his thought. He was, moreover, never tired of teaching and so taught that none of his students ever tired of learning. He had an astonishing power of enabling them to grasp and see quite clearly that which a moment before had seemed impenetrable and terribly involved." This period was a time of fierce debate between
Galenists and the new body of thought on anatomy. The conservative Riolan attacked
William Harvey with equal fervour. ==Contributions to anatomy==