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  • In the 1500s and 1600s, the work of Copernicus and Galileo, among many others, reshaped how

  • natural philosophers in western Europe thought about the question, where are we?

  • But there's another question to consider that's at least equally daunting, what is

  • life?

  • And to try to answer that question, three tools stand out as being especially useful:

  • ...a really long book full of beautifully grotesque illustrations based on dissected

  • bodies… ...experiments about blood pumping through

  • living animals… ...and the microscope.

  • [Intro Music Plays]

  • You could call Andreas Vesalius the Copernicus

  • of anatomy: his name has become synonymous with a revolution of its own, and his major

  • book even came out in 1543, the same year as De rev.

  • Vesalius was born in Brussels in 1514.

  • He studied at the Universities of Leuven, Paris, and Padua.

  • He wrote his thesis about al-Rāzī, the famous and prolific medieval physician who wrote

  • Doubts About Galen.

  • And Vesalius did some Galen-doubting of his own.

  • After conducting years of medical research, Vesalius wrote up his findings in a gigantic,

  • seven-volume book with 273 illustrations.

  • It was published in 1543 under the name De Humani corporis fabrica, or On the Fabric

  • of the Human Body.

  • And it redefined the long HippocraticGalenicArabicPersian medical tradition.

  • It didn't just tweak Galen's ideas.

  • Fabrica was a new way of doing medicine—a new paradigm.

  • The seven books of Fabrica cover the bones and cartilage, the ligaments and muscles,

  • the veins and arteries, the nerves, the heart, the brain, andthe organs of nutrition and generation”—meaning

  • most of the stuff in the body.

  • And along the way, it brims with observations that were new to Vesalius's world.

  • Vesalius accurately described the sternum, the bones of the arm, the skull, and the entire

  • muscular system.

  • Importantly, he also wrote that the brain and nerves are the center of the mind.

  • This overturned the Aristotelian idea that the heart was the center of thought and feeling.

  • And, despite possible religious objections, Vesalius disproved the belief that men had

  • one rib fewer than women.

  • He even disproved the idea, from Galen, that men have more teeth than women.

  • Seems like fairly easy things to do!

  • No one had thought to look inside of a woman's mouth.

  • That's just way too weird!

  • How are you gonna study a woman??? Where are they?

  • In fact, Vesalius realized that many of Galen's observations, made back in Roman timeswhen

  • human dissection was illegalhad actually been observations of animals, not humans.

  • Galen incorrectly thought the human lower jaw was made of two bones, like it is in some animals.

  • He thought the major blood vessels started in the liver.

  • And he thought the human body had a network of blood vessels at the base of the brain,

  • called a rete mirable, that are actually found in dolphins and sheep.

  • But Vesalius was able to correct a lot of this misconceptions, thanks to the big innovation

  • he used in his lectur-at Padua: dissection.

  • Instead of hiring a surgeon to do his dirty work, Vesalius—a scholarconducted dissections himself.

  • Thought Bubble, Show us the wonder of hands-on medical observation.

  • Fabrica is written as a sort of guide to dissecting someone.

  • Vesalius clearly explains the order in which you have to dissect a body to observe each muscle.

  • He lets you know what tools you need.

  • So Fabrica shows how important instruments are to scientific knowledge-making.

  • And over the course of its thousands of pages, you see that Vesalius began to think about

  • the human body as a composite of physical, mechanical, interlocking systemsand not

  • a bag of humors.

  • In some ways, “anatomyin the modern sense begins with Fabrica.

  • The book wasn't just an encyclopedia of diseases and treatments.

  • It was a guide for seeing the body anatomically instead of humorally.

  • And Vesalius wanted others to see what he saw.

  • His book's illustrations were made possible by advances in artistic techniques and the

  • improvement of detailed woodcut engraving as ahtechnology.

  • And Vesalius supervised the whole process carefully.

  • He wrote out such specific instructions for his printer that the printer included them

  • in the text.

  • Chances are you've seen some of the dissection-inspired woodcuts from Fabrica: flayed human bodies

  • traipse through a stylized Italian countryside, making dance-like motions, demonstrating how

  • their muscles and bones connect, and lookingnot too bad for people with no skin.

  • Thanks Thought Bubble, Where Vesalius helped readers of his book

  • see the human body differently, they would still have had many questions about what life

  • is and how it functions.

  • William Harvey answered one of the big oneshow does blood work?

  • Harvey was born in Kent, England, in 1578.

  • He studied in Italy, was a fellow of the Royal College of Physicians in London, gave popular

  • lectures on anatomy, and served as physician to King James the First.

  • He also was a major skeptic when it came to witchcraft, which was the source of much freaking

  • out at the time.

  • So, as an official examiner of witches, which was a thing you could be back then, he acquitted the accused

  • rather than having them burned alive.

  • But William Harvey is most famous for his theory of blood circulation, which Galen and

  • Vesalius both got wrong.

  • Like Vesalius, Harvey learned a lot about bodies through careful observation, AKA getting gettin' all gross.

  • He did this specifically through vivisection, or cutting open live animals.

  • He watched their hearts slow down and finally stop beating as they died, and he estimated

  • the amount of blood that left those exposed hearts.

  • And he used those measurements for a reason: to help him formulate medicines.

  • In doing so, Harvey helped bring the the idea of rigorous measurement to medical investigation.

  • And by 1618, Harvey had arrived at the conclusion that arterial and venous blood vessels form

  • a single, connected, closed circulatory system.

  • This was a brand new idea!

  • Harvey published his findings in 1628, in another Latin-language classic which sounds

  • a little bit like you're casting a spell when you say it:

  • Exercitatio Anatomica de Motu Cordis et Sanguinis in Animalibus, or On the Motion of the Heart

  • and Blood.

  • Which historians tend to shorten to De Motu Cordis.

  • Which is the name of my new metal band.

  • De Motu Cordis was, again, a revolt against the old AristotelianGalenic system.

  • It's also a great early example of comparative anatomy:

  • Harvey compared the hearts and arteries of many cold-blooded animals in order to understand

  • the basics of how a heart pumps bloodor, really, that heart does pump at all -- as

  • opposed to the blooddiffusingthrough the system as Galen thought.

  • Through his quantitative experiments, Harvey disproved the Galenic idea that the liver

  • creates the blood found in veins.

  • And Harvey figured out that blood flows in one direction at a time, thanks to valves.

  • Also not part of Galen's system.

  • But, while Harvey's De Motu Cordis was a more accurate theory of how blood circulates

  • than Galen's, Harvey also fudged his data in order to make his point.

  • When he measured a heart, Harvey estimated the volume of liquid it could hold, how much

  • blood it moved each time it beat, and the number of beats it made in half an hour.

  • And Harvey made each of these estimates intentionally low, so that people could easily see how wrong

  • Galen's liver-based system was.

  • The liver simply couldn't make enough blood, fast enough, for the diffusion theory to work.

  • But he made sure that the numbers didn't come close.

  • Now, still, to his credit, Harvey did all of that observational and experimental work

  • without a critical instrument that would soon be developed over in the Low Countriesthe

  • microscope.

  • Anton Philips van Leeuwenhoek was born in Delft, in what was then the Dutch Republic,

  • in 1632.

  • The inventor of the microscope became the so-calledfatherof microbiology, because

  • you can't have a “microbiologywithout a microscope -- another example of the importance

  • of instrumentation to scientific knowledge-making.

  • We don't have all the details of what process Van Leeuwenhoek used to create his invention.

  • But we do know he made hundreds of magnifying lenses and at least twenty-five proper microscopes.

  • Somewhere along the line, Van Leeuwenhoek told a doctor friend about his investigation

  • of the very small, and that friend told the Royal Society over in England.

  • In 1673, the Philosophical Transactions of the Royal Society published van Leeuwenhoek's

  • microscope-enabled observations.

  • A few years of debate ensued about whether van Leeuwenhoek was pulling everyone's collective

  • naturalphilosophical chain, but members of the Royal Society eventually confirmed

  • his findings.

  • Using his invention, van Leeuwenhoek discovered an entire world of amazing forms in miniature.

  • He found single-celled organisms living their best lives at an entirely different

  • scale than our own.

  • He called theseanimalculesorlittle animals‚” many of which aren't actually

  • animals.

  • For example, in 1677, van Leeuwenhoek observed spermatozoa.

  • And in 1682, he observed muscle fibers.

  • Over the years, he wrote hundreds of letters to the Royal Society and similar institutions

  • to share his observations.

  • But he never divulged the secret of his microscope-manufacturing.

  • ...Jerk!

  • Another Dutch natural philosopher combined the work of van Leeuwenhoek and Vesalius.

  • Jan Swammerdam was born in Amsterdam, in the Dutch Republic, in 1637.

  • And, yes, I said that without laughing.

  • He delicately dissected animal and plant tissues under a microscope, learning in the process

  • about both the structure and the development of life.

  • This was a critical turn in the life sciences.

  • Swammerdam observed, for example, how an insect changes from an egg into a wriggly larva,

  • then a hibernating pupa, and finally an adult, often capable of flight.

  • Four different bodies from one animal!

  • Swammerdam also experimented on muscle contraction.

  • And, in 1658, he was the first to observe red blood cells.

  • All told, seventeenth-century Holland was a rad time to be a natural philosopher, asking

  • what is life?”

  • As long as you can get your hands on one of Van Leeuwenhoek's microscopes... which apparently only 26 people could.

  • But perhaps the greatest early microscopist was the English polymath Robert Hooke, born

  • on the Isle of Wight in 1635.

  • Hooke became the curator of experiments of the Royal Society and did a whole bunch of

  • amazing work in science that we'll have to explore some other time.

  • For now, just googleMicrographia.”

  • This is the book Hooke published in 1665, which was the first book of microscope-enabled

  • observations of the natural world, and arguably the first scientific bestseller.

  • It's also the first instance of the wordcellbeing used to describe a single

  • chamber within a living tissuelike the cell, or small, confined quarters inhabited

  • by a monk.

  • Like Vesalius, who was obsessed with woodcuts, and van Leeuwenhoek, who was a manic letter

  • writer, Hooke wanted others to see the living world how he saw it.

  • So Micrographia is full of beautiful, tattoo-worthy illustrations, including a famous one of the

  • homely flea.

  • In fact, it's so beautiful that it's easy to forget that, even though it was a scientific

  • rendering, it was still highly subjective.

  • After all, seeing nature through a device like a microscope or telescope doesn't make

  • you free from your biases.

  • And the microscope raised more questions than the slightly older telescope, because it required

  • even more subjective interpretation.

  • With only a few good microscopes around in Hooke's day, most readers of Micrographia

  • couldn't have confirmed the accuracy of Hooke's drawing of a flea, or of anything

  • else in that book.

  • They just had to trust in the authority of the professional scientistone of the first

  • in his society.

  • Next timewe'll follow so-calledexplorersfrom Eurasia as they travel throughout the

  • Americas and Africa, pillaging, classifying, andmostly pillaging.

  • Stay tuned!

  • Crash Course History of Science is filmed in the Dr. Cheryl C. Kinney studio in Missoula, Montana and it's made with the help of all this nice people

  • and our animation team is Thought Cafe.

  • Crash Course is a Complexly production. If you wanna keep imagining the world complexly with us,

  • you can check out some of our other channels like Healthcare Triage, How to Adult, and Scishow Psych.

  • And, if you'd like to keep Crash Course free for everybody, forever, you can support the series at Patreon;

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In the 1500s and 1600s, the work of Copernicus and Galileo, among many others, reshaped how

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