=Flat Files.= One of the filing systems still found in some offices is the flat, or box file. This file is made in the form of a box, with a hinged cover, as shown in Fig. 9. This box is of the right size to hold letters without folding, and is equipped with an _A_ to _Z_ index. Letters and other papers are filed between the index sheets in the order of their receipt. Sometimes an attempt is made to keep all of the correspondence of one person together but, since the letters are simply laid in the file, with no means of separating those of the several correspondents filed in one subdivision, it is very difficult to maintain this arrangement. Cabinets are also made with box drawers of wood, the number of drawers in a cabinet ranging from two to sixty. This permits of the use of a more finely subdivided index, and better classification of the contents. Each box in the cabinet is equipped with a spring compressor which holds the contents in place. To file or remove papers it is necessary to release this compressor. The index is removable, and when the drawer is full, the index and contents are placed in one of the box files referred to, which then becomes a transfer case. A new index is placed in the file, which is then ready for current correspondence. This style of cabinet was for long the best to be had, but when used for filing an extensive correspondence, its defects became apparent. Among the disadvantages of its use, one of the chief is the uneven filling up of the separate divisions. Where the alphabet is divided among several drawers, one may fill up in two months, while another is but half full at the end of a year. This means that the transferring must be done whenever a single drawer is filled, instead of transferring the contents of the entire file at one time, adding to the difficulty of locating correspondence at a given date. Other disadvantages are that correspondence is mixed together, making it difficult to locate all of the correspondence of one person; to remove a letter, the drawer must be taken from the file, and a search made through all of the letters in a given subdivision of the alphabet. Frequent transfers are necessary, resulting in an accumulation of transfer files which occupy valuable space in the office. =Vertical Filing.= The vertical system of filing takes its name from the fact that papers are filed vertically, on edge, instead of being laid flat in a drawer. Vertical filing is the result of a gradual evolution of filing methods.