=303.= Everything that comes into the library or goes out of it, except the actual books, will fit into such a classification, and may be numbered and indexed by it. All correspondence is marked boldly with the number of the division to which it belongs, and is filed in the folders which bear the number. The folders are numbered on the projecting edge of the broader flap, as shown in Fig. 114, and are arranged numerically according to the notation order. It may be objected that this method separates letters from one correspondent who may write at various times or on various subjects; but experience proves that except in few cases, such as are provided for under 55, where general correspondence is arranged alphabetically under the names of the writers, the questions the file is required to answer are not answered in terms of names of correspondents; moreover, the alphabetical name index, which is an indispensable accompaniment of the method, brings together all references to letters from any given correspondent. The index should be on cards, and should give the name and address of the correspondent, the classification number of the subject, and the dates of the letters received or dispatched (see Fig. 116). Not only does this index serve as a key to the correspondence file (Section 302); it may contain, without prejudice to its value, all addresses which the librarian deems it expedient to keep, with telephone numbers, telegraphic addresses, and cable codes where necessary. It will be obvious that a classified file of this kind will accommodate all other documents and lists--book-lists, reports made on subjects or departments, minutes, and in fact any miscellaneous papers whatsoever. =304.= The effectiveness, and indeed safety, of any individual indexing or filing system depends upon the care with which it is manipulated in order that misplacements of papers or cards may not occur. The fear of carelessness or ignorance on the part of assistants has caused some librarians to prefer an alphabetical system of filing. When this is so it should be alphabetical by subjects, except in the case of general correspondence which deals with no particular subjects. Library communications are frequently of this general nature, but the vital letters are upon subjects; for example, Exhibitions, Lectures, Readings, Story Hours, are headings taken at random for which folders would be included. In arranging courses of lectures, for example, a librarian may write and receive any number of letters; and he wants them together as a rule and not in the alphabetical order of correspondents. This alphabetical-subject system requires an index to such folders as do not come under general correspondence; folders coming under the latter would be most useful in a sequence separate from the subject folders, but such separation is not essential.