Three rare books dating from the 16th and 17th centuries have been found by scientists to be covered in a deadly poison.
The discovery in a university library has echoes of the novel and film The Name Of The Rose, which sees a string of monks in a 14th-century Italian monastery killed off by the toxic pages of a forbidden manuscript.
X-ray analysis of the books held by the University of Southern Denmark revealed a large concentration of arsenic on the covers.
The volumes were being studied because it had previously been discovered that mediaeval manuscript fragments had been used by bookbinders to make their covers.
In attempting to identify the Latin texts used, researchers found they were hard to read because of a heavy layer of green paint obscuring the letters.
The study of this green pigment layer revealed it to be arsenic – one of the most toxic substances in the world.
Kaare Lund Rasmussen, an associate professor at the University of Southern Denmark, told Fox News: "The moment we put the X-ray beam on the green surface we saw the fantastic high amounts of arsenic."
It is likely that it was applied to the books to protect them against insects and vermin.
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The three volumes are now stored with safety labels in a ventilated cabinet.
It is planned to digitise the content to reduce the handling of the books.