Whether procured from plant, animal, or human sources, in one form or another fat has been an important element in the European pharmacopoeia since ancient times. For reasons that are not quite clear, a medicinal interest in human fat was especially pronounced in the 16th and 17th centuries. In 1543, the physician Andreas Vesalius instructed anatomists who boiled bones for the study of skeletons to carefully collect the layer of fat “for the benefit of the masses, who ascribe to it a considerable efficacy in obliterating scars and fostering the growth of nerves and tendons.” Vesalius knew what he was talking about. At the time, human fat was widely considered—and not just by “the masses”—to be efficacious in healing wounds, and was typically harvested from the recently deceased. In October 1601, after a particularly bloody battle during the Siege of Ostend, Dutch surgeons descended upon the battlefield to return with “bags full of human fat,” presumably to treat their own soldiers’ wounds.

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If the fat of warriors was efficacious, that of executed criminals was easier to lay one’s hands on. What was called “poor sinner’s fat” was rendered from the bodies of the recently executed and used to treat sprains, broken bones, and arthritis. Beyond such uses, human fat was also prescribed as a painkiller or to treat sciatica and rheumatism, while dead men’s sweat was collected for the treatment of hemorrhoids. Until the mid-18th century, executioners in the city of Munich, who often prescribed and administered homemade remedies from the corpses of their doomed clients, had a lucrative trade in the fat they delivered to physicians by the pound.

Knowing what would become of their corpses was a source of great anguish for the condemned, many of whom believed in the Christian doctrine of the resurrection of bodies and were not consoled by the thought that their fat, flesh, blood, and bones might be parceled out for the benefit of others. Still, business was business, and against the wishes of donors, executioners continued to supply fat, blood, and other body parts to those willing to buy them. And it wasn’t just ordinary people buying such things. The wise druggist kept large supplies of human fat (Axungia hominis) on hand alongside numerous other solids and liquids derived from human corpses, a class of materia medica known as “mummy.” If fortune smiled on the fat trade when the rate of executions increased, it would have been positively beaming during the Terror days of the French Revolution. According to some reports, certain Parisian butchers started offering their customers an exciting new item: graisse de guillotiné, supposedly procured from the corpses of the freshly executed.

What was it about human fat that made it so sought-after? And what was so special about the fat of slain criminals in particular? The practice no doubt echoes the Catholic cult of holy relics, whereby saints were considered to be fully present in their bodies after death, as well as in the objects they touched. Yet this mystical appreciation explains only so much, and most executed criminals were no saints. Rather, the use of fat for medical purposes was perceived as a natural practice rather than a magical one, and thus was based on assumptions about the physical properties of the substance itself. Despite the apparent obsolescence of many of these beliefs, the claim that fat could heal wounds was not entirely misguided. Physicians today know that adipose tissue is highly “angiogenic,” meaning that it promotes the growth of new blood vessels from preexisting ones.