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Image caption on page 95 of the book US National Library of Medicine: "Technological advances helped to streamline the production of the library's indexes of medical literature. Beginning in the 1950s, the Index Section staff created punch cards that could be machine-sorted to automate the production of the printed indexes. The glass wall was designed to muffle the sounds of the noisy machines. It remains a feature of the second-floor mezzanine of the library."
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