Is it possible to have too much blood? Ancient doctors thought so.
Bloodletting was once such a common practice that it was prominently featured in numerous paintings and drawings before the 20th century. You’ve likely seen the images: A woman drooping in a chair with a languid expression on her face, and a few drops of blood leaking from her inner elbow into a cup or bucket.
Today, historians believe the concept behind bloodletting wasn’t just inaccurate, but it actually stalled medical advancements for centuries. To understand why anyone would believe ridding the body of “extra blood” could cure just about any illness, you have to start by learning the theory of the four humors.
How the Four Humors Shaped Medical Thought
If you’ve ever wondered where the phrase “in a bad humor” comes from, you can thank the theory of humorism. Humor, in this instance, refers to bodily fluids. However, these bodily fluids were associated with a number of human traits, including mood, personality, maturity, and—of course—disease.
Ancient physicians believed adequate health required just the right balance of the four humors. The humors, or bodily fluids, were meant to be the human version of the four elements: earth, water, fire, and air.
Blood: This humor was associated with the heart, and is the counterpart to air. It has a hot and moist quality and is more prominent during spring and adolescence. It was said to cause an optimistic personality.
Phlegm: This humor was linked to the brain, and it’s the counterpart to water. Being connected to the brain, it’s not surprising that it’s associated with maturity and a stoic personality. It has a cold and moist quality and is more prominent during the fall season.
Black bile: This humor was associated with the spleen, and is the counterpart to earth. It has a cold and dry quality and is more prominent during winter and old age. It was believed to create melancholy.
Yellow bile: This humor was linked to the gallbladder, and it’s the counterpart to fire. It has a hot and dry quality, and it’s more prominent in the summer and during childhood. The theory claims this humor creates an irritable personality.
Physicians believed the four humors naturally fluctuated throughout the lifespan, and even throughout the year as the seasons changed. For example, during winter, it would not be unusual for black bile to become excessive, resulting in a melancholy mood—according to the theory.
Humorism could be used to explain just about anything, but one way it was used was to diagnose and treat illnesses. The physician’s job was to determine which bodily fluid was in excess, and then to force the elimination of that fluid using sweating, urination, laxatives, vomiting, or bloodletting.
The Era of Bloodletting
There’s a reason you’ve only ever heard of bloodletting (and not the forced excretion of yellow bile). Around the 2nd century, a Greek physician known as Galen of Pergamon claimed in one of his many writings that blood was the dominant humor. (Find out how Galen contributed to the understanding of migraines.)
After Galen’s claim, bloodletting became the remedy of choice—and remained that way for hundreds of years, although methods of bloodletting evolved over time and varied from physician to physician.
Some physicians preferred simply cutting the skin and letting blood drip into a receptacle; this was called venesection. Often—as portrayed in many paintings over the years—the vein at the inside of the elbow was used. This is the same vein used today for blood tests, as it is close to the surface and thus easily accessible.
Another common method used leeches. One physician in particular—François Broussais—highly favored leeches for bloodletting. In the early 19th century, this French doctor proposed the theory that fever was caused by inflammation of specific organs. He would place the leech over the area of the supposedly inflamed organ.
The theory took hold in Europe. In Paris alone, around 5 to 6 million leeches were used annually during the 1800s, according to Gerry Greenstone, MD, family physician and medical historian.
Bloodletting became particularly aggressive in its final years. Many physicians were known for removing vast quantities of blood at once. For example, former president George Washington died after a physician removed nearly two pints of blood to treat his inflamed throat.
The Downfall of Bloodletting
Dr. Broussais may have had a huge impact on the use of bloodletting, but it would be short lived. By the end of the 19th century, the practice was being heavily questioned. Bloodletting had been embraced for thousands of years—so what changed?
Toward the end of the 19th century, Louis Pasteur pushed forward the idea of germ theory, proving that many diseases were caused by viral, bacterial, or fungal infections. (Other physicians had proposed the idea centuries earlier but were mocked and never taken seriously.)
Additionally, doctors became more familiar with how blood circulated throughout the body. The dissection of human bodies hadn’t always been allowed during various time periods and in certain cultures, which stunted the understanding of disease.
As the medical community became more knowledgeable about how infections were spread from person to person, and how the body worked, it caused a significant paradigm shift. It became increasingly difficult to justify humorism with this new logic—although some stubborn doctors clung to bloodletting for years afterwards, causing feuds among the medical community.
Surprisingly, bloodletting is still used today in a practice known as phlebotomy therapy, but only for rare blood disorders. Besides for these specific instances, you’re unlikely to see a doctor bring a knife to your elbow anytime soon.
Arikha N. Passions and tempers: a history of the humours. Noga Arikha, 2007.
Greenstone G. The history of bloodletting. BCMJ. 2010 Jan-Feb;52(1):12-14.
Kim KH, Oh KY. Clinical applications of therapeutic phlebotomy. J Blood Med. 2016;7:139-144.
Smith KA. Louis Pasteur, the father of immunology? Front Immunol. 2012;3:68.The world of Shakespeare’s humors. Washington, DC: U.S. National Library of Medicine. (Accessed on December 30, 2021 at https://www.nlm.nih.gov/exhibition/shakespeare/fourhumors.html.)