In 1593, Duke Louis of Würtemberg issued an instruction to the University of Tübingen which reads as follows: “Book-dealers must be cautioned under sufficient penalties, neither to print, to possess, nor to sell, heretical or pernicious books, such as the abominable writings of the Jesuits. The preachers are directed to warn their hearers against the unclean literature. In order, however, that the instructors and preachers should be able to secure knowledge of the arguments of their adversaries and of the nature of their calumnies, printer George Gruppenbach is ordered to secure two copies of each of such books as are available and to deliver the same to the university. The preachers whose erudition and good judgment can be trusted to keep them from being led astray by pernicious doctrines, are to be permitted to read these heretical and sectarian writings, in order that they may be in a position to defend the true Faith. The superintendent appointed for the purpose is to keep a record of the pernicious books so distributed and is to secure reports as to the use made of them. The copies themselves are in any case to be returned to the university authorities, so that they may not be used to pervert the people. All this is done ‘In order that the assaults of the hateful Satan (who in these last days has been permitted to work much evil upon the Church of God) shall be withstood, and that for the people in this principality the true Faith shall be preserved and their souls shall be kept clean.’”[77] Luther was, it should be remembered, thoroughly in accord with pope and with emperor in the belief that it was the duty of the faithful to destroy heresy. He only differed from the pope as to what constituted heresy. In 1525, we find him invoking the aid of the censorship regulations of Saxony and of Brandenburg for the purpose of stamping out the “pernicious doctrines” of the Anabaptists and of the followers of Zwingli. The Protestant princes were for the most part more than willing to establish and to maintain a censorship for the presses of their several localities, as such a system served in more ways than one to strengthen their authority, while it could be utilised also to head off undesirable criticism. In 1525, Luther decides that a censorship ought to be established in the Protestant States. He asks the Protestant princes to co-operate in instituting the machinery for the purpose. The regulations established by the princes interfered seriously with the operations of the printers in the larger places, but proved ineffectual for securing any uniformity of religious publishing throughout the States of North Germany.