The chief difficulty in the application of any censorship regulation within the Lutheran States was the existence of different schools of belief, the controversies between which soon became active. The control of the censorship machinery for any one State fell into the hands first of one set of controversialists and then of another, according to the activity of the respective leaders and to the influence brought to bear upon the local ruler. In the Lutheran States, such as Saxony, the prohibition against papistical writings was accompanied by an equally sweeping condemnation of the writings of the Calvinists; while the Calvinistic authorities of States like Brandenburg were prompt on their side to take similar measures for the protection of their own special tenets. This continued conflict between the several groups of reformers had the necessary effect of bringing into disrepute and ineffectiveness the larger portion of the attempts at censorship control. Some attempts were made towards a more tolerant and a more practicable policy. Zwingli, for instance, insisted that his fellow-believers in Essling should follow the Christian example of the church in Zürich, which refused to interfere with the sale even of Anabaptist writings; but in Zürich itself this tolerant spirit was not long permitted to control. The Elector of Saxony[75] prohibited, under a penalty of three thousand gulden, the printing of the _Corpus Doctrinae_ of Melanchthon, and Frederick II of Denmark prohibited preachers and instructors, under penalty of the loss of their positions and (for persistency in misdoing) of further punishments, the use of the formula of the _Concordia_. Again, in 1574, the Elector of Saxony compelled the members of the University of Wittenberg to subscribe to an oath that they would neither purchase nor read the writings of the Sacramentists or of the Vermigli. In 1439, Nicholas Wohlrab, who had, under the instructions of Duke George of Saxony and the Magistracy of Leipsic, brought into print the _Postille_ of Wicels, was put into prison by Duke Henry, acting at the instance of the Elector John Frederick. Before he could secure his release, Wohlrab was obliged to take oath to bring no further works into print or into sale until these had received the censorship and the approval of the magistrates. The three other book-dealers of Leipsic were forbidden to print or to sell any books that had not secured approval of the censor appointed by the magistrates, and two deputy magistrates were detached to make a weekly inspection of the printing-offices and assure themselves that nothing was printed antagonistic to the teachings of the Gospel.[76] There were from time to time schemes for a Protestant Index. In 1579, Duke Julius of Brunswick brought out a scheme for charging a general synod with the duty of compiling an Index of heretical books and of instituting measures for the censorship of the press; but the plan was not put into execution.