The Bizarre Saga Of The Guy Who Got A Sheep's Blood Transfusion And Became Convinced He Was A Sheep

Medical advances often take steps back before they reach a breakthrough – and that's exactly what happened in 1667, when one man claimed that a medical experiment turned him into a sheep. 

The story starts in the 1660s, when French and English scientists raced to perform the first successful blood transfusion into a human. But instead of taking blood from another person, these scientists used animal blood. In 1667, English scientists performed a sheep’s blood transfusion on Arthur Coga. Who was Arthur Coga? He started as a Cambridge-educated man, but by the end of his transfusions, he claimed to be Arthur Coga the Sheep Man, transformed into an animal after receiving too much sheep's blood.

Did something go terribly wrong in this 17th century blood transfusion? Did the sheep to human blood transfusion change something vital about Arthur Coga’s identity? The scientists at the Royal Society worried that they had done something crazy, or that they had gone too far in their drive to be first. They had certainly made progress, but in the process, they created a man who honestly believed he was an animal.


  • Many Medical Experiments At The Time Were Deadly

    Many Medical Experiments At The Time Were Deadly
    Photo: Wellcome Images / Wikimedia Commons / CC BY 4.0

    In the 17th century, scientists experimented with all sorts of things. Galileo performed experiments on falling weights, Newton used prisms to understand light, and in London, the Royal Society tried to understand how blood worked.

    In the 1620s, William Harvey had proved that blood circulated through the body rather than being generated by the liver and burned up by the heart. Harvey’s groundbreaking work meant that it was theoretically possible to transfer blood between two bodies. And that’s exactly what the scientists in London’s Royal Society decided to test. 

    Rather than starting with human transfusions, the Royal Society began experimenting on animals.

  • Scientists Tested Theories About Blood Circulation On Animals

    Scientists Tested Theories About Blood Circulation On Animals
    Photo: Wellcome Images / Wikimedia Commons / CC BY 4.0

    Scientists in the 17th century frequently experimented on animals. The father of the scientific method, Francis Bacon, argued that you must carefully examine, even torture, nature to understand its secrets. And in the mid-1600s, that meant performing experiments on dogs.

    In 1656, Christopher Wren, best known as the designer of St. Paul’s Cathedral in London, injected wine and ale into the veins of a dog. Wren observed that the dog became very drunk. This experiment confirmed Harvey’s theory that the veins could transmit materials throughout the body.

    A decade later, Richard Lower, an Oxford physician, tried transferring blood between various dogs. He was somewhat successful in his experiments, though the dogs all eventually died as a result of the gruesome tests.

  • Tests On Animals Were Grotesque And Deadly

    Tests On Animals Were Grotesque And Deadly
    Photo: Wellcome Images / Wikimedia Commons / CC BY 4.0

    In 1665, Richard Lower successfully transferred blood between dogs. His success spurred a race for blood transfusions, with the ultimate goal being human transfusion. The French put sheep’s blood into horses and goats. The English put calf’s blood into sheep. The Italians performed transfusions on horses and cows. They claimed this medical breakthrough would not only save lives, but it could also improve foods; the Royal Society Fellows put milk and sugar into a sheep and claimed it made the meat sweeter.

    These experiments were incredibly harmful for the animals. In nearly every case, the animal “donating” blood died, and many of the receiving animals also didn’t survive. Dogs alone have 13 different blood types, and mixing blood types can be deadly.

  • Once Scientists Perfected Animal Blood Transfusions, They Turned To Humans

    Once Scientists Perfected Animal Blood Transfusions, They Turned To Humans
    Photo: Wellcome Images / Wikimedia Commons / CC BY 4.0

    In June 1667, Jean-Baptiste Denis, a French physician, became the first person to transfuse an animal's blood into a human. Denis transfused lamb’s blood into a 15-year-old who suffered from fevers. After the transfusion, Denis declared the boy was cured.

    Denis believed that blood transfusion was a powerful medical tool that could cure a range of ailments. But he ruled out using human blood for the transfusions because it was too dangerous. Denis explained, “I am persuaded that it will be much more expedient to make use of the blood of other animals.” 

    But why didn’t the transfusions kill Denis’s patients? They had the era's limited technology to thank: physicians were only able to transfer a few ounces of blood into a human’s body, which is not a high enough dose to be fatal.

  • People Believed New Blood Might Change Someone's Identity

    People Believed New Blood Might Change Someone's Identity
    Photo: Wellcome Images / Wikimedia Commons / CC BY 4.0

    In the 17th century, everyone agreed that your environment, including what you ate, affected your temperament. Samuel Pepys recorded a story in his diary about a very old man who lived on breast milk. Pepys reported, "While he fed upon the milk of an angry, fretful woman, [he] was so himself; and then, being advised to take it of a good-natured, patient woman, he did become so, beyond the common temper of his age."

    Blood, too, was linked to a person's very essence, their vital spirit. Robert Boyle, famous for his experiments on gas, questioned whether transfusing the blood of a cowardly dog into a fierce dog would turn it tame, or if a dog’s fur might change color after a blood transfusion. Would a dog trained in retrieving ducks lose that skill if given blood from an untrained dog? And what might happen if a person received new blood?

  • Coga Was An Ideal Experimental Patient

    Coga Was An Ideal Experimental Patient
    Photo: Wellcome Images / Wikimedia Commons / CC BY 4.0

    When news of Jean-Baptiste Denis's experiments reached London, Richard Lower decided it was time to find his own human recipient. He selected Arthur Coga, a Cambridge-educated man whose brain was "a little too warm." The Royal Society Fellows argued that the transfusion would cool Coga’s blood, curing his mental instability. If Denis could only cure fevers, the English scientists would prove they were better by tackling a more challenging ailment. Also, Coga was educated and able to speak Latin, so he could reliably report on the transfusion's effects on his body.

    When the men approached Coga and offered him money in exchange for serving as a test subject in a medical experiment, Coga agreed. He would become only the third man in the world to receive a blood transfusion directly into his arteries. Coga was paid 20 shillings – about $225 in today's dollars – to serve as a human test subject.