Galen was born in Pergamum (modern-day Bergama, Greece) to an architect's family. His interests were eclectic - agriculture, architecture, astronomy, philosophy - until he concentrated on medicine.
By the age of 20 he had become a therapeutes ("attendant") of the god Asclepius in the local temple for four years. After his father's death in 148 or 149 he left to study abroad. He studied in Smyrna and Corinth and at Alexandria. He studied medicine for a total of twelve years. When he returned to Pergamum in 157, he worked as a physician in a gladiator school for three or four years. During this time he gained experience of trauma and wound treatment. He later regarded wounds as "windows into the body".
From 162 he lived in Rome where he wrote extensively, lectured and publicly demonstrated his knowledge of anatomy. He gained a reputation as an experienced physician and his practice had widespread clientele. One of them was consul Flavius Boethius who introduced him in court where he became a court physician to emperor Marcus Aurelius. Later he also treated Lucius Verus, Commodus and Septimius Severus. Reputedly he spoke mostly Greek, which was a more respected language of medicine than Latin at the time. He briefly returned to Pergamum in 166-169.
Galen spent the rest of his life in royal court, writing and experimenting. He performed vivisections of numerous animals to study the function of the kidneys and the spinal cord. His favorite subject was the barbary ape. Reportedly he employed 20 scribes to write down his words. In 191, fire in the Temple of Peace destroyed some of his records. He died in 203.
Galen transmitted Hippocratic medicine all the way to the renaissance. His On the Elements According to Hippocrates describes the philosopher's system of four bodily humours, which were identified with the four classical elements. He created his own theories from those principles. In turn, he mainly ignored Latin writings of Celsus.
Amongst Galen's own major works is a 17-volume On the Usefulness of the Parts of the Human Body. He also wrote about philosophy and philology. His collected works total 22 volumes.
Galen's own theories emphasized purposeful creation by a single Creator - a major reason why later Christian and Muslim scholars could accept his views. His fundamental principle of life was pneuma (air, breath) that later writers connected with the soul. Pneuma physicon (animal spirit) in the brain took care of movement, perception and senses. Pneuma zoticon (vital spirit) in the heart controlled blood and body temperature. Natural spirit in the liver handled nutrition and metabolism.
Galen expanded his knowledge by experimenting with live animals. One of his methods was to publicly dissect a living pig and cut its nerve bundles one at the time. Eventually he cut a laryngeal nerve (now also known as Galen's Nerve) and the pig stopped squealing. He tied the ureters of living animals to show that urine comes from the kidneys. He severed spinal cords to demonstrate paralysis.
From the modern viewpoint, Galen's knowledge was partially correct, partially flawed. He demonstrated that arteries carry blood, not air and made first studies about nerve functions, brain and heart. He might have begun the practice to check the patient's pulse. He also found that the mind was in the brain, not in the heart as Aristotle had claimed.
However, much of Galen's understanding is flawed from the modern point of view. He did not recognize blood circulation and thought that venous and arterial systems were separate. This view did not change before William Harvey in the 17th century. Since most of his knowledge of anatomy was based on dissection of pigs, dogs and Barbary apes, he also assumed that rete mirabile, a blood vessel plexus of ungulates, also existed in the human body. He also resisted the idea of tourniquets to stop bleeding and vigorously propagated blood letting as a treatment.
Galen's authority dominated medicine all the way to the 16th century. Experimenter's disciples did not bother to experiment and studies of physiology and anatomy stopped - Galen had already written about everything. Blood letting became a standard medical procedure. The first serious change in his hegemony was Vesalius.
Most of Galen's Greek writings were first translated to Syriac by Nestorian monks in the university of Jundi Shapur, Persia. Then muslim scholars translated them to Arabic, alongside many other Greek classics. They became one of the main sources for Persian scholars such as Avicenna and Rhazes.Life
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