In the middle of the 16th century, a talented young anatomist named Andreas
Vesalius made a shocking discovery: the most famous human anatomy texts in
the world were wrong. They not only failed to account for many
details of the human body, they also described the organs of apes
and other mammals. While Vesalius knew he was right, announcing these errors would mean
challenging Galen of Pergamon– the most renowned physician
in medical history. But who was this towering figure? And why did doctors working more than
1,300 years later so revere and fear him? Born in 129 CE, Galen left home as a teen to scour the
Mediterranean for medical wisdom. He returned home a gifted surgeon with a
passion for anatomy and a penchant for showmanship. He gleefully entered public anatomy
contests, eager to show up his fellow physicians. In one demonstration, he caused a pig to lose its voice by tying
off one of its nerves. In another, he disemboweled a monkey and
challenged his colleagues to repair it. When they couldn’t, he did. These grizzly feats won him a position as
surgeon to the city’s gladiators. Eventually, he would leave the arena
to become the personal physician to four Roman Emperors. While his peers debated symptoms and
their origins, Galen obsessively studied anatomy. He was convinced that each organ had a
specific function. Since the Roman government largely
prohibited working with human cadavers, Galen conducted countless dissections
of animals instead. Even with this constraint, his exhaustive investigations yielded
some remarkably accurate conclusions. One of Galen’s most important
contributions was the insight that the brain,
not the heart, controlled the body. He confirmed this theory by opening the
cranium of a living cow. By applying pressure to different
parts of the brain, he could link various regions
to specific functions. Other experiments allowed him to
distinguish sensory from motor nerves, establish that urine was
made in the kidneys, and deduce that respiration was
controlled by muscles and nerves. But these wild experiments also produced
extraordinary misconceptions. Galen never realized that blood cycles
continuously throughout the body. Instead, he believed the liver constantly
produces an endless supply of blood, which gets entirely depleted on its
one-way trip to the organs. Galen is also credited with solidifying
the popular theory of the Four Humours. Introduced by Hippocrates
centuries earlier, this misguided hypothesis attributed most
medical problems to an imbalance in four bodily fluids
called humours. To correct the balance of these fluids,
doctors employed dangerous treatments like bloodletting and purging. Informed by his poor understanding
of the circulatory system, Galen was a strong proponent
of these treatments, despite their sometimes lethal
consequences. Unfortunately, Galen’s ego
drove him to believe that all his discoveries were
of the utmost importance. He penned treatises on everything from
anatomy to nutrition to bedside manner, meticulously cataloguing his writings
to ensure their preservation. Over the next 13 centuries, Galen’s prolific collection dominated
all other schools of medical thought. His texts became the standard works
taught to new generations of doctors, who in turn, wrote new essays extolling
Galen’s ideas. Even doctors who actually dissected
human cadavers would bafflingly repeat Galen’s mistakes, despite seeing clear evidence
to the contrary. Meanwhile, the few practitioners bold
enough to offer conflicting opinions were either ignored or ridiculed. For 1,300 years, Galen’s legacy
remained untouchable– until renaissance anatomist Vesalius
spoke out against him. As a prominent scientist and lecturer, his authority influenced many young
doctors of his time. But even then, it took another
hundred years for an accurate description
of blood flow to emerge, and two hundred more for the theory
of the Four Humours to fade. Hopefully, today we can reap the benefits
of Galen’s experiments without attributing equal credence
to his less accurate ideas. But perhaps just as valuable is the reminder that science is an
ever-evolving process, which should always place
evidence above ego.