Mad Scientists and Blood Transfusion Experiments

Every medical breakthrough has a history. Sometimes that history is inspiring—dedicated researchers working tirelessly in laboratories, making careful observations, conducting ethical studies. Sometimes it’s the result of war-time necessity or brilliant insights that change everything overnight.

And sometimes, that history is horrifying.

Today, blood transfusions are routine, safe, and life-saving. We understand blood types, compatibility, screening, and storage. We have protocols, regulations, and ethical oversight. But we didn’t start here. We got here through a long, dark road of experimentation that would be unthinkable today—experiments conducted by physicians who were equal parts scientist and showman, who injected bizarre substances into living animals, who transfused animal blood into humans, and who sometimes treated their human subjects more like carnival attractions than patients.

In the spirit of spooky month, I want to tell you about the mad scientists of early blood transfusion research. These stories are real. The experiments happened. And while we learned valuable lessons that eventually led to modern transfusion medicine, those lessons came at a terrible cost.

The Royal Society: When Scientists Injected Wine and Opium into Dogs’ Veins

Before anyone attempted blood transfusion, they had to figure out if it was even possible to inject substances directly into the bloodstream. In the 1650s and 1660s, members of the British Royal Society—some of the most respected scientists of their time—began experimenting on living animals.

Christopher Wren (yes, the famous architect) was among the first. At Royal Society meetings, he and his colleagues would demonstrate their experiments on dogs, birds, and other animals. They would inject various fluids directly into the animals’ veins: water, milk, wine, beer, broth, and even opium.

The results were treated as entertainment. Animals were purged, made to vomit, intoxicated, killed, or sometimes revived by these injections. The scientists would bleed dogs nearly to death, then attempt to revive them by injecting blood from another animal. Sometimes it worked. Often it didn’t.

This wasn’t careful, systematic research with proper controls and ethical consideration. This was spectacle. This was “let’s see what happens when we inject ale into a dog’s vein” and watching the results in front of an audience.

But it established something important: you could inject substances directly into the bloodstream, and sometimes the animal survived. That knowledge—gained through horrible animal cruelty—paved the way for blood transfusion experiments.

Richard Lower: Dog-to-Dog Transfusions

English physician Richard Lower took the experiments further. He reasoned that if you could inject various fluids into veins, you should be able to transfer blood from one living creature directly into another.

Lower began with dogs. He would connect the artery of one dog to the vein of another using tubes and perform direct blood transfusions. He bled one dog “until its strength was nearly gone,” then tried to revive it with blood from a large mastiff.

The experiments were sometimes successful—the dogs survived. This encouraged Lower to believe that blood transfusion could work in humans. He was on the verge of attempting the first animal-to-human transfusion when news came from France that someone had beaten him to it.

That someone was Jean-Baptiste Denis. And his experiments would make Lower’s work look positively restrained.

Jean-Baptiste Denis: The Carnival Barker of Blood Transfusion

If there’s a villain in the history of blood transfusion—or at least someone who embodies the “mad scientist” archetype—it’s Jean-Baptiste Denis.

Denis was a physician and self-promoter who saw blood transfusion as his ticket to fame and glory across Europe. He wasn’t content to conduct quiet experiments in a laboratory. He wanted spectacle. He wanted publicity. He wanted to be the first, the most famous, the most celebrated transfusionist in the world.

And he was willing to use anyone—human or animal—to get there.

The Theory: Animal Blood is Better Than Human Blood

Denis had a theory that seems laughably wrong now, but that he genuinely believed: animal blood would be superior to human blood for transfusions.

His reasoning? Human blood was corrupted by human vices—anger, jealousy, sin, moral failings. Animals, being innocent and pure, had blood uncorrupted by these human weaknesses. By transfusing animal blood into humans, Denis believed he could cure not just physical ailments, but moral and mental problems as well.

He thought lamb’s blood, from such a gentle and innocent creature, would have a calming effect. Calf’s blood would be similarly pure and restorative. The blood of these innocent animals could cleanse and heal corrupted human blood.

It’s a theory that reveals just how little they understood about blood, immunity, and physiology. But Denis was convinced. And he was determined to prove it.

The Public Spectacle

Unlike the English scientists who conducted their experiments in the somewhat controlled environment of the Royal Society, Denis took his work public. He performed experiments on the banks of the Seine River in Paris, turning blood transfusion into entertainment for crowds.

Witnesses described a carnival atmosphere. Denis wasn’t just trying to help patients—he was putting on a show, conducting demonstrations for audiences of curious onlookers and potential patrons. Every successful experiment was immediately publicized through letters to scientific journals and announcements to the European scientific community.

He was building his brand, and his subjects—both animal and human—were props in his performance.

The First Human Experiments

On June 15, 1667, Denis performed his first animal-to-human blood transfusion. His subject was a 15-year-old boy who had been suffering from a chronic fever. The boy had already been subjected to the other popular “treatment” of the time: therapeutic bloodletting. He had been bled so many times by other physicians that he was weak from blood loss.

Denis saw an opportunity. With the help of surgeon Paul Emmerez, he drew three ounces of blood from the boy’s arm, then injected about nine ounces of blood from a lamb directly from the lamb’s artery into the boy’s vein.

The boy survived. He complained of a sensation of great heat in his arm, but he didn’t die. Denis declared it a triumph.

His second subject was a 45-year-old laborer—a healthy man who was paid to be a guinea pig. Denis transfused about twenty ounces of lamb’s blood into him. Again, except for the sensation of heat in the arm, no immediate ill effects were reported.

Denis was emboldened. Two successful experiments! Clearly, his theory about the superiority of animal blood was correct. He began publicizing his successes throughout Europe.

What Denis didn’t understand was that his “successful” patients had survived despite the animal blood, not because of it. They received small enough amounts that their immune systems could handle the attack. The sensation of heat they reported? That was their bodies mounting an immune response to foreign blood cells. They were lucky to have survived at all.

But Denis’s luck—and his patients’ luck—was about to run out.

Antoine Mauroy: The “Madman” Denis Tried to Cure

Antoine Mauroy was a well-known figure in Paris—a mentally ill man whose behavior was erratic and sometimes violent. Denis and his colleagues wondered: if animal blood was pure and uncorrupted, could it cure madness?

They decided to find out. And their approach to “treatment” was chilling.

In November 1667, Mauroy was abducted from the streets of Paris by guards working for Denis’s patron. He was tied to a chair in front of an audience of noblemen and transfused with calf’s blood as a public demonstration.

Mauroy’s reaction was immediate and horrifying. He experienced debilitating fever, nausea, diarrhea, nosebleeds, and urine that was described as “black as chimney soot.” He had tachycardia, abundant sweating, and severe pain.

These are classic symptoms of a hemolytic transfusion reaction—the body’s immune system attacking and destroying foreign blood cells. The black urine was from his kidneys trying to filter out the debris from destroyed red blood cells. Mauroy was experiencing organ damage in real time.

But somehow, miraculously, he survived that first transfusion. Denis took this as confirmation that his treatment was working. Days later, Mauroy seemed to have recovered.

His wife, Perrine, wasn’t convinced. When Mauroy’s mental state deteriorated again after he returned to drinking and smoking, she allowed Denis to perform a second transfusion. Again, Mauroy experienced terrible symptoms. Again, he survived.

When Denis proposed a third transfusion, Perrine initially agreed. But this time, Antoine Mauroy died.

The Murder Trial

Denis was charged with murder. The trial became a sensation in Paris. Denis argued that his transfusions were safe and that Mauroy must have died from some other cause. He brought forward other transfusion recipients who had survived to testify on his behalf.

The truth that eventually emerged was even more twisted than the transfusions themselves: Perrine Mauroy had been secretly poisoning her husband with arsenic. She had been bribed by physicians who opposed Denis—doctors who saw transfusion as dangerous and wanted to stop Denis before he killed more people.

So Denis was acquitted of murder. His transfusions hadn’t killed Mauroy—the arsenic had.

But the court had seen enough. Even though Denis wasn’t found guilty, the French court banned blood transfusions. The practice was too dangerous, too experimental, too likely to kill people even if it hadn’t killed Mauroy. The Catholic Church soon followed suit. The Royal Society in England banned it as well.

Blood transfusion, after just a few years of horrifying experiments, was effectively outlawed across Europe for the next 150 years.

What We Learned (And What It Cost)

Denis’s experiments were unethical by any modern standard. He subjected animals to invasive procedures. He transfused animal blood into humans despite warning signs that it was dangerous. He abducted a mentally ill man, tied him to a chair, and performed experimental medical procedures on him in front of an audience.

He prioritized publicity over patient welfare. He ignored his patients’ suffering. He pushed forward with increasingly dangerous experiments because he wanted fame, not because he had evidence his treatments were safe or effective.

And yet, we learned things from his experiments—terrible, valuable things that eventually led to safe blood transfusion:

What doesn’t work: Animal blood cannot be safely transfused into humans. The immune system will attack it. Recipients will experience fever, pain, organ damage, and often death.

What the symptoms mean: The fever, black urine, and kidney pain that Denis’s patients experienced? Those are signs of a hemolytic transfusion reaction. Understanding what was happening to Denis’s patients eventually helped physicians recognize incompatible transfusions in later human-to-human experiments.

The importance of careful observation: Denis at least documented his experiments and the reactions his patients experienced. His detailed descriptions of symptoms—however horrifying—provided data that future researchers could learn from.

The need for ethical oversight: The ban on transfusions that followed Denis’s work wasn’t just about safety. It was a recognition that medical experimentation needed limits, oversight, and protection for vulnerable subjects.

But we paid for those lessons with human suffering. Mauroy experienced excruciating symptoms from transfusions that never should have been performed. The 15-year-old boy and the paid laborer were subjected to dangerous experiments without informed consent or understanding of the risks. Denis’s patients were guinea pigs in a public spectacle.

The 150-Year Pause

After Denis’s trial, blood transfusion went silent for a century and a half. The bans stayed in place. The experiments stopped. Medicine moved on to other treatments (many of which were also dangerous and ineffective, but that’s another story).

When physicians finally returned to blood transfusion in the early 1800s, they at least had the wisdom not to use animal blood. They tried human-to-human transfusions instead. Many patients still died—because we didn’t yet understand blood types—but at least no one was injecting lamb’s blood into humans anymore.

It would take until 1900, when Karl Landsteiner discovered blood types, before transfusions could be performed safely and reliably. But by then, Denis had been dead for nearly 200 years.

Other Mad Scientist Moments in Blood History

Denis wasn’t the only physician to conduct horrifying experiments:

James Blundell - In the 1810s-1820s, this British obstetrician performed about 10 human-to-human blood transfusions. Only about half of his patients survived because he had no way of knowing he was sometimes transfusing incompatible blood types.

Nazi Medical Experiments - During World War II, Nazi physicians conducted forced blood transfusion experiments on concentration camp prisoners, among many other horrific medical experiments. These experiments contributed nothing to medical knowledge and represented pure evil masquerading as science.

Arkansas Prison Blood Program - In the 1980s, Arkansas prisons ran a blood plasma program that collected blood from inmates under questionable conditions, leading to contamination of the blood supply with hepatitis and HIV.

Early HIV Blood Contamination - The failure to screen blood for HIV in the early 1980s infected thousands of hemophiliacs and transfusion recipients. Some have argued that blood banks moved too slowly to implement safety measures even after the risk was known.

A Phlebotomist’s Perspective

When I draw blood today, I’m working within a system built on centuries of trial and error—and a lot of error. Every safety protocol I follow, every test I run, every label I carefully apply exists because people died when we didn’t have these safeguards.

Denis’s experiments horrify me, but they also remind me why my job matters. I’m not just collecting samples. I’m participating in a practice that took hundreds of years to get right. Every blood draw I perform safely and correctly is a small victory over the ignorance and recklessness of the past.

But I also wonder: what are we doing now that physicians 200 years from now will look back on with horror? What practices that seem reasonable today will be revealed as dangerous or unethical? Medicine is always evolving, and we’re not done learning.

The difference, I hope, is that we now have ethical frameworks that Denis never had. We have informed consent. We have institutional review boards. We have regulations that protect research subjects. We have learned—painfully, slowly, incompletely—that the ends don’t justify the means when those means involve human suffering.

Denis wanted glory. He wanted to be remembered. He got his wish—but not in the way he intended. He’s remembered as a cautionary tale about the dangers of prioritizing ambition over ethics, publicity over patient welfare, and personal fame over human dignity.

Putting It All Together

Blood transfusion is one of modern medicine’s greatest achievements. It saves countless lives every day. But we didn’t get here through noble, ethical research. We got here through spectacle, suffering, and experimentation that would be criminal today.

Denis and his contemporaries were products of their time, when ethical standards for medical research didn’t exist. They genuinely believed they were helping people, even as their patients experienced agony from incompatible transfusions. They were wrong—catastrophically wrong—but they moved the field forward, even if only by showing what didn’t work.

The lesson isn’t to condemn them from our modern perspective. The lesson is to remember that medical progress has a price, and we should never forget the people who paid it.

This Halloween, as you think about mad scientists and horrifying experiments, remember that some of the real ones were wearing physician’s robes. Remember that good intentions combined with ignorance can be just as dangerous as malice. And remember that the routine medical care you receive today was built on a foundation of failure and hard-won lessons.

I’m grateful to work in an era where we finally got it right. Where we understand blood types and compatibility. Where we screen for diseases and follow protocols. Where we treat patients with dignity.

But I never forget how we got here.

Happy October from your friendly neighborhood phlebotomist, who promises to never transfuse lamb’s blood into anyone, no matter how pure and innocent that lamb might be.

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