“The Roman pontiffs, to whom, in the person of S. Peter the chief of the Apostles, that great duty was committed of feeding the universal flock of Christ, have all been constant in preserving whole and inviolate the most precious deposit of the Faith, and in nourishing the Christian peoples of the world with the food of sound doctrine. Hence the fervent and provident care continually taken by them that, as good grain from tares, so sound and excellent books may be separated from the alloyed, the apocryphal, and the hurtful, lest Christian men, by using them incautiously or daringly, may injure the integrity of their faith and morals. Under this head, the pontiffs themselves or the councils have been ever careful to provide remedies suitable to the evils, changing these to suit the changes of time. When the invention, in the 15th century, of the new art of printing caused a great increase in the number of books and also a great spread of the pest of evil heresies, it was everywhere deemed necessary to take severe notice of evil writings, both to forestall danger and to repair evil already done. Therefore the Fathers of the Council of Trent, to whom our predecessor Pius IV had entrusted the matter, deemed that the great contagion of heretical books, or of books suspected of the crime of heresy, or of books hurtful to piety and morals, should be attacked in two ways: First, the scholars and theologians, chosen for this purpose by the authority of the same synod, made certain general rules so that it might be easier to decide of what books in general the faithful should beware; and secondly, they compiled an accurate and absolute exposition or Index of books of improper contents. When the synod adjourned, by its own decree, this Index, with the rules above mentioned, was shown to our predecessor, Pius IV, that it might, before publication, receive the support of the Apostolic sanction. The pontiff approved it after it had been worked over again with great diligence, and ordered its observance by all. “In the nature of the case, his Index required additions as in the course of time new wicked and hurtful books appeared, and every one knows that the Apostolic Chair has attended to this again and again with zealous care. Thus Clement VIII and later Alexander VII and Benedict XIV, our predecessors, by the specification of those books which the popes had proscribed, by Apostolic letters, by the Roman Congregations, and chiefly by the Congregations of the Inquisition and the Index, revised and reshaped the Index proper so that it constituted practically a new compilation. Since (the issue of Benedict) there has been a long interval, almost a hundred and forty years, and the conditions seemed to call for something more comprehensive and more efficient for the present needs....