When nerve surgeon Dr Susan Mackinnon needed help to finish an operation, she reached, as she often does, for a mid-20th Century book of anatomy.
Thanks to the complex hand-drawn illustrations – showing the human body peeled back layer by layer – Dr Mackinnon, from Washington University in St Louis, was able to complete the procedure.
The book she had used, the innocuous-sounding Pernkopf Topographic Anatomy of Man, is widely considered to be the best example of anatomical drawings in the world. It is richer in detail and more vivid in colour than any other.
Skin, muscle, tendons, nerves, organs and bone are revealed in graphic detail. It's not for the faint-hearted.
But the book, often referred to as Pernkopf's Atlas, is no longer in print and a second-hand set – there are several volumes – can sell for thousands of pounds online.
Yet despite its hefty asking price, few would proudly display it in their clinic, library or home.
That's because the book's findings came from the bodies of hundreds of people killed by the Nazis. It is their bodies – cut up and dissected – that are shown across thousands of pages.
Critics say the book is tainted by its dark past and scientists have grappled with the ethics involved in its use.
Dr Mackinnon says she feels uncomfortable with its origin, but using the book is a crucial part of being an "ethical surgeon" – and that she could not do her job without it.
Rabbi Joseph Polak – a Holocaust survivor and professor of health law – believes the book is a "moral enigma" because it is derived from "real evil, but can be used in the service of good".
The book was a 20-year project of a prominent Nazi and doctor, Eduard Pernkopf, who rose through the academic ranks in Austria thanks to his support for Adolf Hitler's party.
His colleagues described him as an "ardent" National Socialist who, from 1938, wore a Nazi uniform to work every day.
When he was made dean of the medical school at the University of Vienna, he sacked all the Jewish members of the faculty, including three Nobel laureates.
In 1939, a new Third Reich law ensured the bodies of all executed prisoners were immediately sent to the nearest department of anatomy for research and teaching purposes.
During this period Pernkopf worked 18-hour days dissecting corpses, while a team of artists created images for his book. Sometimes the anatomy institute was so full, executions had to be postponed.
Dr Sabine Hildebrandt, from Harvard Medical School, says at least half of the 800 images in the atlas came from political prisoners. They included gay men and lesbians, gypsies, political dissidents and Jews./BBC news