HOW LINNAEUS INVENTED THE INDEX CARD. This article by Jonathan Schifman on the Popular Mechanics website gives a short history of the index card. Kids, the index card played an important part in the life of a researcher until it was replaced by the computer. (Schifman says: “Index cards are mostly obsolete nowadays.”)
Your mother researched her dissertation with index cards.
I was surprised to learn that it was a great scholar—Linnaeus—who invented the index card. This wikipedia entry on index cards says that: “Using cards to create an index was the brainchild of 18th-century naturalist Carl Linnaeus, for his work on categorizing species. He needed a system for organizing data that was expandable and able to be rearranged easily, so he kept each datum on individual sheets and could add new sheets and reorganize simply.” This wikipedia entry on Linnaeus gives an idea of the usefulness of an open ended system: “The first edition of Systema Naturae was printed in the Netherlands in 1735. It was a twelve-page work. By the time it reached its 10th edition in 1758, it classified 4,400 species of animals and 7,700 species of plants.”
In addition to his system, Linnaeus invented the index card 30 years later when he put all of the organisms and minerals on smaller, thicker pieces of paper—index cards.