A Card from the Past

The other day, at the  OldCornerBooks.com storage facility, Marash Girl's young assistant Ethan found a 3"x5" card inside of one of the books he was shelving.  "What's this?"  he asked.  Marash Girl started laughing.  "That's a library catalogue card.  In the old days (not so old), every library had rooms filled with cases filled with drawers filled with thousands of those cards, several cards for every book in the library -- filed once under the author's last name, once under the title, once or twice or thrice under the subject heading -- oh, and the number?  That's a number in the Dewey Decimal System, an internationally used system that allows you to find that book in any library in the world that uses that system -- if, of course, the library has the book. If you wanted to find a book, you'd have to let your feet do the walking through the room full of card catalogue cases, so that your fingers could do the walking through the alphabetically arranged cards in the drawers of the cases of the catalogue, and the walk through the library until to find the number on the book that you seek.  When the card is slipped inside of the book, it indicates that that book has been withdrawn from the library.  

"Really?" laughed Ethan.