Galen (c. 129–c. 200)

Greek physician and anatomist whose ideas dominated Western medicine for almost 1,500 years. Central to his thinking were the threefold circulation of the blood and the theory of humours (blood, phlegm, choler/yellow bile, and melancholy/black bile) that contributed to mental and physical state. His On Anatomical Procedures, a detailed description of animal dissections when work on human corpses was forbidden, became a standard text on anatomy when rediscovered in Western Europe in the 16th century. He remained the highest medical authority until Andreas Vesalius and William Harvey exposed the fundamental errors of his system.

Galen postulated a circulation system in which the liver produced the natural spirit, the heart the vital spirit, and the brain the animal spirit. He also wrote about philosophy and believed that Nature expressed a divine purpose, a belief that became increasingly popular with the rise of Christianity (Galen himself was not a Christian). This helped to account for the enormous influence of his ideas.

On Anatomical Procedures, Galen's most important work on anatomy, contained descriptions of his work on pigs, monkeys, and dogs. He also explained that detailed dissection was essential to knowledge of anatomy, and stated that his inability to dissect human corpses had hindered his work. The book was lost to Europe after the fall of the Roman Empire in AD 476, but it was preserved in the Middle East in Arabic translation, and became a source for Islamic medicine. Europeans rediscovered the text in 1531 when Johannes Guinter, a professor of medicine at the University of Paris, translated it into Latin. On Anatomical Procedures became the standard text for dissection and anatomy until Vesalius and others refuted his ideas in the late 16th century.

Galen was born in Pergamum in Asia Minor and studied medicine there and at Smyrna (now Izmir), Corinth in Greece, and Alexandria in Egypt, after which he returned home to become chief physician to the gladiators at Pergamum. In 161 he went to Rome, where he became a society physician and attended the Roman emperor Marcus Aurelius Antoninus. Although Galen made relatively few discoveries and relied heavily on the teachings of Hippocrates, he wrote a large number of books, more than 100 of which are known.

The dissection of human beings was then regarded as taboo and Galen made inferences about human anatomy from his many dissections of animals. His detailed descriptions of bones and muscles, many of which he was the first to identify, are particularly good; he also noted that many muscles are arranged in antagonistic pairs. In addition he performed several vivisection experiments; for example, to show that urine passes from the kidneys down the ureters to the bladder. More important, he demonstrated that arteries carry blood, not air, thus disproving Erasistratus' view, which had been taught for some 500 years.