Beast in the Blood Jean Denis and the “Transfusion Affair”

During the late 1660s in Paris, transfusing the blood of calves and lambs into human veins held the promise of renewed youth and vigour. Peter Sahlins explores Jean Denis’ controversial experiments driven by his belief in the moral superiority of animal blood: a substance that could help redeem the fallen state of humanity.


March 22, 2023

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Illustration of an early xenotransfusion from lamb to man, from Matthias Gottfried Purmann’s Grosser und gantz neugewundener Lorbeer-Krantz, oder Wund Artzney . . . Zum andern Mahl vermehrt heraus gegeben (1705) — Source.

Beginning in the spring of 1667, public opinion in Paris was rocked by a remarkable affair involving domesticated animals: the first practical experiments to transfuse animal blood into humans for therapeutic purposes. The experiments that came to be known as the “Transfusion Affair” were shrouded in the competing claims of a highly public controversy in which consensus and truth, alongside the animal subjects themselves, were the first victims. “There was never anything that divided opinion as much as we presently witness with the transfusions”, wrote the Parisian lawyer at Parlement, Louis de Basril, late in the affair, in February 1668. “It is a topic of the salons, an amusement at the court, the subject of philosophical dissertations; and doctors talk incessantly about it in all their consultations.”1

At the center of the controversy was the young Montpellier physician and “most able Cartesian philosopher” Jean Denis, recently established in Paris, who experimented with animal blood to cure sickness, especially madness, and to prolong life. With the talented surgeon Paul Emmerez, Denis transfused small amounts of blood from the carotid arteries of calves, lambs, and kid goats into the veins of five ailing human patients between June 1667 and January 1668. Two died, but three were purportedly cured and rejuvenated.2 The experiments divided the medical establishment and engaged a Parisian public avid for scientific discoveries, especially medical therapies to cure disease and to stay forever young.3

The Transfusion Affair took place in the shadow of Descartes. Not only was Jean Denis trained at the Montpellier Medical School in 1667, following a program receptive to the mechanistic physiology of Descartes, but he also carried out his experiments under the patronage of Henri-Louis Habert de Montmor, whose private scientific salon or “academy” had been receptive and deeply sympathetic to Cartesian mechanism in the 1650s. Descartes developed the idea of animal automatism in his 1637 Discours de la méthode, which opposed the ‘‘thinking substance’’ and the “corporeal and mechanical” body, thus denying reason, speech, and consciousness to animals. The soul of animals, which had survived as a “sensible” one in the tripartite scheme of Aristotle and Galen (nutritive, sensible, and rational), fell away. While Descartes admired the infinitely complex mechanisms of animal bodily functions, he expressed extreme skepticism about the interior life of animals and inevitably denied their moral exemplarity.

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David de Coninck, Peacock, Turkey and Rabbits in a Park Landscape, ca. 1657–1705 — Source.

Descartes’ animal automatism had generated a minor philosophical controversy in the 1640s, but it was not until after 1668 that a broader struggle opposed his acolytes to the members of literary salons within the polite society of Paris. In the political context, Descartes’ ideas (including his concept of the beast-machine) were banned at court, although in practice, many “Cartesians” worked for the king, while a form of Cartesian reasoning, a self-styled critical and skeptical thinking, permeated the salons of the Parisian elite. At this moment, in 1668, the debate over Descartes — and indeed, over animals more generally — found a proxy expression in the controversy over Jean Denis’ experiments with blood transfusion.

In less than a year, the Transfusion Affair generated a score of pamphlets and scientific reports, some mediocre poetry, and uncounted letters sent across Europe. Jean Denis (and his publicists and “students”) published epistolary accounts of his successful experiments and responded to his doubters and critics. The antitransfusionist party has been identified with the Paris Faculty of Medicine, with its sclerotic teaching based on Galen and Hippocrates, whose thought offered little justification for transfusion, if only because the faculty officially denied major blood circulation. William Harvey had definitively demonstrated circulation in his published work of 1628, although he did not abandon his Galen, which Descartes quickly eliminated in his mechanistic physiology. But it was only after 1668 that the Paris faculty acknowledged the circulation of blood, a fact that did not contradict the physicians’ resistance to Cartesian physiology, as well as their continued insistence on the therapy of phlebotomy, or bloodletting.4

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Seventeenth-century colored engraving of bloodletting in France, Les Remedes à tous maux (the remedies for all ills) — Source.

Yet the Paris faculty was divided: some of its members supported Denis, even if the majority opposed the experiments, some quite actively. According to the Parlement lawyer Louis de Basril, the Paris physicians paid a “little schoolboy”, the second-year medical student Guillaume Lamy, and a “charlatan” and “tooth-puller”, the royally licensed empiric Pierre-Martin de La Martinière, to rebut the claims of Denis. Their “secret intrigue” and “cowardly plot” produced a strange alliance and convergent arguments against the uses of animal blood, which reached reaching from the heights of the Paris Medical School and the newly founded Royal Academy of Sciences to the world of empirics and apothecaries who sold remedies under the Pont-Neuf bridge.5

The Affair of the Transfusions climaxed after the death of Madame de Sévigné’s ex-valet Antoine Mauroy de Saint-Amant in February 1668, who suffered from some form of dementia (perhaps caused by syphilis), following his third transfusion by Denis and Emmerez. The first two transfusions using the blood of lambs, performed just before Christmas 1667, had by Denis’ account gone well, and the patient, much to the relief of the gens de bien (the well-to-do), “received devotionally his Creator during the Jubilee”.6 Yet by the end of January, the madness of Mauroy had returned, and, by all accounts, things went awry. His wife, born Périne Pesson, pressured Denis incessantly to perform the transfusion, then quickly buried her husband’s body before an autopsy could be performed and immediately filed suit before the Paris courts. A dramatic cause célèbre ensued, the moral depths of which “Zola himself can hardly rival”, wrote historian Harcourt Brown.7 In April 1668, the Châtelet court exonerated Jean Denis, for the widow was found to have poisoned her husband with arsenic (possibly provided by La Martinière, at least according to Basril), and three unnamed doctors of the Paris Medical School were implicated in bribing Pesson to bring charges against Denis. On appeal, the Paris Parlement ruled in 1670 — on what basis we will never know — to ban doctors and surgeons from “exercising the transfusion of blood under penalty of corporeal punishment”, a sanction that lasted until after the French Revolution.8

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Frontispiece engraving to Georg Abraham Mercklin’s Tractatio med. curiosa, de ortu & occasu transfusionis sanguinis (1679), depicting animal-to-human transfusion (top) and human-to-human transfusion (bottom left and right) — Source.

The Transfusion Affair was the dramatic climax of an international rivalry for national scientific precedence, a veritable “blood race” between England and France, instigated by two kings at a moment when the “scientific community” was being built across political boundaries. In the aftermath of William Harvey’s publication of his proof of major blood circulation (1628), and René Descartes’ mechanistic and materialist appropriation of Harvey’s still-traditional idea of blood (1637 and after), blood became an object of competition for precedence. The Royal Society of London urgently undertook experimental blood research in 1665 when Richard Lower, Robert Boyle, and Thomas Coxe began to work feverishly “to transfer the unimpaired blood of an animal into a second by means of a tube”.9 Only in January 1667 did Louis XIV and his principal minister, Jean-Baptiste Colbert, direct the attention of the newly minted Royal Academy of Sciences to proceed, under the leadership of the physician Claude Perrault, with the similar transfusion experiments, although using different methods.10 Perrault’s experiments with dogs failed when all the animals died, and he finally abandoned his efforts in March 1667, becoming an implacable but unpublished enemy of blood transfusion.11 Meanwhile, Jean Denis began his work, and by June 1667, he had beaten the English to the punch. (Five months later, Edmund King of the London Royal Society transfused the “calming” blood of a lamb into the madman Arthur Coga’s “overheated” blood.12)

On March 3rd, 1667, Denis and Emmerez first claimed a successful allogeneic transfusion — among animals of the same species — using the blood of a donor “Spaniel bitch” to a recipient “short-haired dog, resembling a fox”. Denis and Emmerez then repeated the experiment on March 8th, and the results were published immediately (as letters) and reprinted in the Journal des sçavans, which quickly adopted a sympathetic stance and active role in publicizing Denis’ achievements.13 Building on the success of same-species transfusions (twenty animals, mostly dogs), Denis moved on to xeno-transfusion between animal species in early April.14 Denis gave the blood of four rams to a twenty-six-year-old horse “that recovered its force and appetite”, reported the Journal des sçavans.15 Denis and his apologists, including his own young “student” Claude Gadroys, published only positive results: the dogs and other animals were rejuvenated, they regained vital energy. At the end of this score of experiments, Denis declared that he had not caused the death of a single animal and that the “secondary effects” occasionally observed, including “black urine” among the recipients — what medical historians now understand as a classic hemoglobic reaction — passed quickly as the animals universally improved, while the condition of the donor dogs and other animals was barely mentioned.16

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Engravings of blood transfusion and intravenous injection from Johann Sigismund Elsholtz’s Clysmatica Nova (1667) — Source.

Scaling quickly from same-species transfusion to attempts among different species, Denis moved rapidly to the xenotransfusion of animal blood into humans. On June 15th, 1667, Denis and Emmerez completed the first documented xenotransfusion with a fifteen-year-old boy suffering from a chronic fever. Under the supervision of a Parisian physician, the patient had been bled twenty times in the previous two months “to assuage the excessive heat” and was in a condition of extreme lethargy with memory loss.17 According to Denis, after his patient received about eight ounces of blood from a lamb’s carotid artery, he felt a “very great heat along his arm” (likely an incompatible transfusion reaction) and then made a “startling” recovery. With “a clear and happy countenance”, he became gay and cheerful and subsequently ate and slept well.

Encouraged by the results, Denis and Emmerez completed a second operation a week later, admittedly “more by curiosity than necessity”, on a robust, healthy porter of forty-five to whom a fee was paid. Denis reported on his instant energetic response and cheerful nature. Far from being debilitated by the transfusion, the porter quickly got up and slaughtered, skinned, and dressed the donor lamb for consumption, after which he went out drinking in the local pub, returning the next day to volunteer for any further trials. And these renewed appetites were not limited to food. Christian Huygens wrote to his brother: “It is said that he performed marvelous feats that night with his wife, this last detail spreading among the ladies has made them favorable to the new practice, and one can only find too many who would want their husbands transfused.”18 But later that fall, Denis’ third transfusion attempt, on the Swedish Baron Bond, had fatal results, although even an opponent had to admit that his gangrene, discovered in the autopsy, would never have allowed him to live.19

Why did Jean Denis believe that the blood of certain animals could produce a renewed vitality, cure illness, and even prolong life? Perhaps a clue can be found in a curious biographical detail. Jean Denis, it turns out, was the son of Claude Denis, the royal fountain engineer and an aspiring poet. Denis père served under André Le Nôtre in the installation and maintenance of the Versailles garden infrastructure of pumps and canals, especially the Royal Menagerie and the waterworks of the animal fountains of the Royal Labyrinth.20 (He was also interested in the healing therapies of water, as is evident in the publication of a commissioned treatise that explained the science behind a “miraculous” fountain in Poland. It was the sulfur.21) The kinship of father and son perhaps influenced Jean Denis’ hydraulic model of the body, as did René Descartes.

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Poem and illustration from Le Labyrinthe de Versailles (ca. 1675), a book of etchings of the hydraulic sculptures in the labyrinth of Versailles by Sébastien Leclerc, illuminated by Jacques Bailly. The fountains and waterworks depicted were designed by a team of sculptors and engineers which included Claude Denis. — Source.

Claude Denis, the professional fountain engineer, was by avocation a composer of undistinguished and unpublished “heroic verse” about the gardens of Versailles, verse in which he poeticized the Royal Menagerie as a collection of peaceable, graceful, and beautiful birds displayed majestically in sun-lit courtyards radiating from an octagonal pavilion. The Versailles menagerie was for Claude Denis a model of civilité, grace, and harmony (even if, in real life, it was a place of noisy strife), and he seems to have shared a certain sensibility about animals with his son. For the younger Denis, it was not the exotic and domestic birds of the menagerie, but familiar comestible quadrupeds — calves and lambs and occasionally a kid goat — that could elevate humans, both physiologically and morally. Denis was convinced that the blood of these animals was in fact physiologically superior to human blood because it was morally less disordered, a point he elaborated in the published letter about the first xenotransfusion experiment:

It is easy to judge that the blood of animals must have less impurity than that of men, for debauchery and derangement in drinking and eating are not as common as among us. The sorrows, the worries, the fits, the melancholies, the anxiety, and generally all the passions that are so many causes of the troubled life of man corrupt the substance of his blood; instead, the life of the animal is much better regulated and less exposed to these miseries, the dreadful consequences of the sins of our first father [Adam].

Experience shows, he continued, that it is rare to find “bad blood” in animals, whereas human blood is inevitably corrupted, the result, he reiterated, of man’s fallen state.22 The text might have been written by Montaigne on a bad day.

Jean Denis was a “Modern” in his unquestioned belief in blood circulation and his Cartesian physiology, however underdeveloped. He was a mechanist who followed Descartes to the letter in his physics and his astronomy, as in his account of the great comet of 1665, composed with J. D. P. Monnier.23 In his desire to prolong life, too, Denis was an unswerving Cartesian. But Denis’ thinking and his experiments with animals ran directly counter to Descartes’ metaphysical dualism and to the philosopher’s understanding of animals as clockworks, machines, or fountains. For Denis, it was the moral and physiological superiority of animal blood that made transfusion a positive intervention. Moreover, in part to justify rhetorically his experiments, he consistently invoked not only the theological debasement of man, but also the moral purity, in the Christian tradition, of certain animals — notably lambs, with the implicit reference to the “lamb of God” and to the logic of the Eucharist as a source of eternal life. All this could not have been more anti-Cartesian, both in his understanding of animals and their passions and in the implicit Christian framing of xenotransfusion.

The Christian frame, not coincidentally, was taken up by the first, anonymous illustrator of the affair, who published a copy of Denis’ letter describing the first xenotransfusion in June 1667, republished in Amsterdam in 1671.24 The illustration is misleading on many different fronts, including the fact that it was the blood of a dog which was transfused, but seems significantly marked by a near Christ-like appearance of the recipient, the true hero of this image, whose servant (to the right) is the apostle-like figure of Jean Denis.

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Illustration from Johannes Scultetus’ Armamentarium chirurgicum (1693) of Jean Denis performing a xenotransfusion from dog to man. The image was originally published by an anonymous illustrator in 1667 — Source.

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Detail of the Adoration of the Mystic Lamb from the Ghent Altarpiece by Jan van Eyck and Hubert van Eyck, 1432 — Source.

Denis’ own moralization of animal blood clearly partook of Renaissance humanimalism and the theriophiliac tradition of the “Happy Beast” that informed a corpus of philosophical, literary, and scientific thinking in the sixteenth and seventeenth centuries and that upheld the moral superiority of animals against the debased condition of humans. By the middle of the seventeenth century, theriophilia had become a widely accepted doctrine among the educated classes, from erudite libertines, to natural philosophers, to theologians. Animals were seen as not only linked to humans by kinship and proximity, but also as moral exemplars, less subjected to destructive passions that marked the fallen condition of man. René Descartes, and Classical naturalism more generally, challenged this Renaissance humanimalism and all its theriophiliac expressions. For Descartes and the Cartesians, animal bodies could be thought of as infinitely complex machines, elaborate bodily mechanisms devoid of consciousness, but subject to the laws of physics and mathematics and, without soul, language, or consciousness, hardly suitable as exemplars of human virtue.

Jean Denis was far more doubtful about human-to-human blood transfusions, and not only because of his belief in the superiority of animal blood. Rather, he was concerned to avoid unnecessary “cruelty”. The question of cruelty appears with surprising frequency in the debate — but only concerning experiments on dogs, not on the animals that could otherwise serve as foodstuffs. The physician-poet Claude-Denis Dufour de La Crespelière supported transfusions, even if he complained satirically in a poem about “cruel men” who had used the poet’s own dog in a transfusion experiment and who would certainly not get into “Dog Heaven”.25 Jean Denis’ reasons for not using human blood unintentionally exposed the cost in animal lives that his experiments had produced. For although he claimed that all the recipient dogs and other animals that received the fresh blood flourished, he did not disclose in his extensive accounts that the technique he had “perfected” of taking blood from a femoral curial artery resulted more often than not in severe hemorrhaging, leading to the death of the donor animal. The proof is his own claim that to cure a human recipient of blood at the expense of a human donor would be a “highly barbarous operation to prolong the life of some while abridging that of others”. The statement reveals at the very least the high mortality risks of the donors, including the animals.26 Animal blood may have been more pure, less contaminated by the vices of human frailty, and thus usefully transfused in small amounts, but the animals from which it came were ultimately more expendable than humans.

Medical historians have long been interested in Denis’ contribution to the history of blood transfusion, universally condemned as a failure born of ignorance. Over the course of the nineteenth century, experiments in life-saving blood transfusions led physiologists toward proof of the incompatibility of heterologous blood, resulting in an exclusive focus on allogeneic blood transfusion between humans, especially after the identification of human blood types in 1901.27 But recent hematological work in “transfusion studies” has reopened the question of xenotransfusion in pursuit of a pure, unlimited, and affordable therapeutic blood supply from animals (using porcine red blood cells, for example), despite the great challenges of antigen body reactions.28 As a result, medical accounts of the early xenotransfusion experiments have evolved from mere vignettes in medical history to sustained analyses about the challenges of transfusion and of xenotransfusion in particular.29 Three hundred and fifty years after the first animal-to-human blood transfusions in Paris, the transfusion affair is more relevant than ever.

The essay was adapted and excerpted from 1668: The Year of the Animal in France (Brooklyn: Zone Books, 2017). © 2017 Peter Sahlins. All Rights Reserved.

Peter Sahlins is Professor of History Emeritus at the University of California, Berkeley. He is the author of five books including Boundaries: The Making of France and Spain in the Pyrenees (1989) and Unnaturally French: Foreign Citizens in Old Regime France and After (2004). He currently lives in Paris where he is researching a book on Neanderthal culture and consults for museums and non-profits.

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