The Catoptrum Microcosmicum resembles a child’s flap book, in which you lift a flap showing a beach ball to discover a kitten. But this book, nearly 400 years old, is a multilayered map of the human body. Raise the skull flap to see the brain beneath the bone. Turn aside the belly flap to reveal the intestines. Some pages have up to 15 layers of anatomical structures—detailed engravings made from copper plates.

This 1613 version of the rare and precious anatomy text by German physician Johann Remmelin is among the treasures in the locked stacks of the Medical Historical Library. The collection includes handwritten manuscripts, among them the Paneth Codex, an early 14th-century compendium of texts. The codex includes works by Hippocrates, Galen and Avicenna. Also in the collection are 325 medical incunabula, materials produced during the infancy of printing from 1450 to 1500.

Items in the collection range from antique gynecologic instruments to 19th-century stereoscopic slides of skin ailments, with a viewer for seeing them in 3D. The collection also includes scores of public health posters in Farsi, Chinese and various Indian languages; 2,000 photographs, from daguerreotypes to modern digital images; and the Fry Collection of prints and drawings of medical and health-related subjects across five centuries.

The world-renowned historical collection comprises 130,000 books, bound manuscripts and pamphlets, along with several thousand medical and scientific instruments and weights and measures. “The Historical Library houses one of the world’s finest historical medical collections, and because of its wide variety of objects, poses large challenges to preservation,” said preservation librarian Sarah A. Burge, M.L.S.

Burge, hired as the first preservation librarian for the Cushing/Whitney Library in 2005, has begun a full preservation program for the collection. She devotes her time to the historic materials, which attract scholars from all |over the world. Many of the rare books came from the collections of surgeon Harvey W. Cushing, M.D., physiologist John F. Fulton, M.D., and tuberculosis specialist Arnold C. Klebs, M.D.—all bibliophiles—whose donations formed the backbone of the historical library founded in 1941. “They had a real appreciation of the book as an object and the book as content,” said Burge.

Some of Burge’s challenges are technical. For instance, because the health of the books depends on the right environmental conditions, Burge is working with the medical school’s heating and ventilation experts. Their dream: air temperature at 65 degrees Fahrenheit, humidity at 40 percent, no fluctuations. Other challenges are more abstract: Burge has helped draft policies to allow students and scholars to use the collection while protecting it from damage or the kind of theft that occurred at Yale’s Beinecke Rare Book and Manuscript Library in 2005, when dealer E. Forbes Smiley III stole several rare maps from the collection.

Paradoxically, many of Burge’s challenges result from the rise of literacy in the 1830s, when advances in papermaking put books in the hands of ordinary people. New steam-powered machines and a scarcity of linen transformed the paper industry. For the first time, paper was made primarily from wood pulp rather than cotton or linen fibers. And wood-pulp paper doesn’t last; it becomes brittle as a result of acid decay through a process known as slow fire.

“The brittle-book problem is what I’m fighting with our 19th-century materials,” said Burge, who studied book preservation at the University of Illinois at Urbana-Champaign. Embrittlement can be halted by a process called deacidification, while books too fragile for public use can be digitized or microfilmed. “The historical library’s long-standing mission includes the understanding that library materials will be used, and with use comes wear and tear,” said Burge. “Our goal is to keep our collections safe and in useable condition through preservation and conservation measures.”