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 entries of these are written in, they are immovable; even if they are made movable by one of the devices to be described later on, they will, in the case of prolific authors and subjects of growing importance, inevitably overflow the allotted space. It should be remembered that these "accession titles" will practically include such titles already in the catalogue as require to have their position changed owing to the discovery of printers' or cataloguers' errors. All these changes, of course, are effected with the greatest ease in a card-catalogue. Few libraries, again, have more than a single copy of their card-catalogues. In a much-frequented library this must inevitably retard the work both of staff and readers, and if at any time it were decided to print the catalogue, would involve a partial cessation of work for both. The general verdict appears to be that the card-catalogue is most serviceable for all libraries but the largest, i.e. those of which the catalogues have to be printed in the interests of knowledge.

The almost universal employment of card-catalogues in the United States has been attended by some interesting developments. The influence of the American Library Association has led to uniformity in the size and shape of the cards employed, the structure of the boxes used for displaying them, and in devices for arrangement. Upon this has followed a scheme for "co-operative cataloguing"