More than 15 million pints of blood are donated each year in the US to be used in transfusions to over 5 million patients. So the idea of, like, putting blood into a person was a radical one when it was first attempted 350 years ago... and it was also dangerous... and really dumb!

The first ever documented human blood transfusion was conducted using the blood of a sheep. The year was 1667 and the patient was a 15 year old French boy... and somehow, he survived! Now, we gotta note here that for thousands of years, no one really understood what blood even was. The Romans and Greeks believed that the body was filled with four basic substances, or humors, one of which was blood. According to humorism, the liver turned food into blood, which was then distributed via veins to the rest of the organs to feed them. Hmm...

Despite Arabic physicians describing blood circulation as early as 1250 AD, the liver theory pretty much held up until the early 1600s, when English physician William Harvey, after years of measuring and calculating blood volume and velocity, said that it was impossible for the liver to produce enough blood based on our food intake. Blood must continuously circulate, he said, propelled by our beating heart.

Harvey's discovery set off a half-century of experimentation to learn more about the circulatory system, often at the expense of dogs, who were intravenously injected with various substances, including ale, wine, and opium. And in 1665, English physician Richard Lower became the first to successfully transfuse blood from one animal to another. Bleeding or exsanguinating a dog near to the point of death, and tying the artery off and then using a larger dog as a donor to "refill" the little one. Just over 2 years later, on June 15, 1667, French physician Jean-Baptiste Denys bled three ounces from a fifteen-year old boy and transfused nine ounces of blood from a lamb. Lower would perform a similar procedure on a 32-year old man less than six months later, using goose quills and silver pipes to carry the blood. Like the blood, the man survived.

Now, these early procedures were not intended as medically-necessary transfusions to replace lost blood. Rather, the idea was that the energy and personality of the blood donor would somehow seep into the recipient. The possibility of altering the mental state of a patient or restoring youth to the aged was what motivated Lower, Denys, and others. Denys himself said that the blood of docile animals such as the lamb could exert a calming influence on the troubled and deranged mind.

Given the misconceptions about blood in the 1660s, we can all agree that Lower and Denys got really lucky with their first animal to human blood transfusions. As modern scientists would later learn, there are many potentially-fatal reactions that can occur during a transfusions. From agglutination, or clumping, if the blood is exposed to even a tiny amount of oxygen, to hemolytic transfusion reactions would can cause the recipient's cells to destroy a donor's transfused blood cells, releasing substances toxic to the recipient's kidneys... so naturally it wasn't long before early experimenters ran out of luck, and patients began to die. Religious and political leaders, many of whom still believed that blood was the seat of the soul and that transfusion was blasphemy, quickly banned the practice. And it didn't help that even many physicians thought that transfusions could cause a change in species! It would be nearly 150 years before a new generation of scientists would pick up the needles that these seventeenth-century crazy pioneers put down.

In 1818, a British doctor named James Blundell performed the first human to human blood transfusion, a process that would take over 100 years to achieve regular success. The most important of these improvements was Karl Landsteiner's classification of ABO blood types at the beginning of the 20th century. Landsteiner recognized that different types of blood carried different types of antigens, A and/or B, each of which will set off a potentially deadly immune reaction in patients without that antigen. This knowledge allowed proper matching of donors and recipients. Scientists nowadays are working on ways to actually create blood from scratch, but at the moment, the only way for someone who needs it to get it, is to have someone else give it to them. And with millions in need of transfusions each year, I'll just remind you to donate whenever you're able.

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