Such books as are still missing at the end of any given period, together with those that have been discarded as worn out, and those that have been lost by borrowers, should be properly marked on the shelf-list, and should have an entry in the accession book, stating what has become of them.
If they are not replaced, it will be advisable to withdraw the cards representing them from the card catalog, or to write on the cards the fact of withdrawal and the cause.
Keep a record of all books withdrawn from the library for whatever reason..