“It happened sometimes that the first volume or volumes of a work were placed in the Index, the later volumes of which followed the publication of the prohibition; or that periodicals were proscribed which continued afterwards to be published; also that all the works of an author were proscribed, who, after the publication of the decree, produced other works. In all these cases, the volumes or numbers published after the latest special decree, although not mentioned in that special decree, are nevertheless held suspicious and are justly presumed to fall under the prohibition of some general decree, unless there is evidence of the author’s change of heart. “It remains to indicate in a few words, for the readier use of the Index, the method used in arranging and describing books. In order that the issue of Leo might be more correct than its predecessors, and that all corruptions might be eliminated which, in the course of so many editions, (some of them prepared by private authority) had crept in, much zealous labour has been given to the investigation of the records of the Congregation of the Index and of the Inquisition, both Roman and general; and of libraries in Rome and abroad. Books whose authorship is declared in their titles are entered under their titles in alphabetical order, the author’s name being subjoined when possible. These names are always entered in full, lest the omission of a syllable should lead to the confusion of similar ones. Assumed or fraudulent names included in titles are treated on the same basis as real names. “Italian names prefixed by the syllable _De_, _Del_, _Di_, etc., which appears to be part of the name, always begin with that syllable in this catalogue. The same applies to _Van_ etc., in Dutch names, and to _Des_, etc., and _St._ in French names; but names beginning with the two syllables _De la_ are entered under _La_. When the syllable _De_ alone begins a French name, it is placed after the name in this catalogue unless the name begins with a vowel.[156]...” There follow certain further bibliographical details. The Preface bears the signature of “Fr. Thomas Esser, Ord. Praed. S. Indicis Congregationis a Secretis.” THE CONSTITUTION OF POPE LEO XIII, CONCERNING THE PROHIBITION AND CENSORSHIP OF BOOKS