Skin from the thigh of an unfortunate Philadelphia woman felled by a parasitic infection delicately lines the spines of three books in the Historical Medical Library of the College of Physicians of Philadelphia. Along with two other examples of books bound in human skin, theirs was officially confirmed as the country’s largest collection of anthropodermic bibliopegy, as the macabre practice is known.

The Historical Medical Library (HML), of which the Mütter Museum is a part, recently had its five books tested to assess their possible hominid origin. Last year Harvard University did similar testing on its purported human skin books, finding that two were sheepskin but a third — an 1880s copy of Arsène Houssaye’s Des destinées de l’ame (Destinies of the Soul) — was made from the skin of a French woman, possibly a mental patient.

Dr. Richard Hark of Juniata College extracted minuscule samples of the tanned flesh on the HML books. Those were then tested by conservation scientist Dr. Daniel Kirby. College of Physicians of Philadelphia Librarian Beth Lander explained the process on the HML’s new Fugitive Leaves blog:

Dr. Kirby used peptide mass fingerprinting (PMF), a method used “to identify mammalian sources of collagen.” PMF does not look at DNA; rather, “enzymatic digestion is used to cleave collagen at specific amino acid sites forming a mixture of peptides. The amino acid sequence of each protein is unique, thus the resultant mixture of peptides is unique.” Drs. Hark and Kirby presented their findings on September 29th at SciX, a conference dedicated “to the analytical sciences, instrumentation and unique applications,” at which they confirmed that the HML is home to five samples of anthropodermic bibliopegy, the largest such confirmed collection in the United States.

It’s only recently that these books have undergone such testing, but it’s likely that the HML’s collection is among the largest of its kind in the world — most institutions only have one or two examples. Their identification is often based on handwritten inscriptions or the particular way that flayed human skin appears when tanned: thinner than that of other mammals used in bookbinding. What’s even more unique about the HML books is that the library knows not just who had the morbid idea to bind the books this way, but also the human sources.

Lander relates how the thigh of Mary Lynch, a woman in her late 20s, was used to bind three books. After entering the Old Blockley almshouse in Philadelphia in 1868 with what was likely tuberculosis of the lungs, she got worse when her friends brought her pork products during the summer heat; they were contaminated with a parasitic roundworm. Six months later, on January 16, 1869, she died, and for reasons unclear, when one Dr. John Stockton Hough carried out the autopsy, he sliced off some of her skin, which he promptly tanned in an almshouse chamber pot. Two decades later, he used it for the spines of three books on women’s health. Despite the detailed inscriptions that led researchers back to Lynch, why Hough did this remains lost to history.

Heather Cole, Harvard University’s assistant curator of modern books and manuscripts, wrote on the Houghton Library blog that while “books bound in human skin are now objects of fascination and revulsion, the practice was once somewhat common.” She goes on to note that “the binding of books in human skin has occurred at least since the 16th century. The confessions of criminals were occasionally bound in the skin of the convicted, or an individual might request to be memorialized for family or lovers in the form of a book.”

Often the books were medical, such as an edition of Vesalius at Brown University’s John Hay Library, which also holds two of the memento mori variety. The Boston Athenaeum has the perhaps best-known human skin book: The Highwayman: Narrative of the Life of James Allen alias George Walton, bound with skin from Allen himself, reportedly for a copy to gifted to a man who outwitted his robbery attempt. Another notorious example is a pocket book made from the skin of murderer William Burke, who teamed up with William Hare to kill people and sell their bodies for dissection. Whether a reminder of mortality, a strange souvenir, or a punishment for a crime, the impetuses behind anthropodermic bibliopegy are as varied as the lives of their skin donors.

Read more about the Historical Medical Library of the College of Physicians of Philadelphia human skin books on their Fugitive Leaves blog.