Galen
Galen, (130?–201? A.D.), a Greek physician. Galen was one of the greatest physicians of ancient times and is considered the father of experimental physiology. Dissection of human bodies was not practiced in his time, but he made many excellent observations based on his dissections of animals. His teachings were accepted without question in Europe until the 16th century—a fact that discouraged original work and hampered medical progress.
Galen was born in Asia Minor. He moved to Rome about 164 A.D., and for a time was physician to Emperor Marcus Aurelius' children. At least 83 of Galen's medical works have survived.
Galen correctly explained the mechanism of respiration. He identified the kidneys as the source of urine and was the first to describe the flow of urine through the ureters to the bladder. He described in detail the backbone and its divisions, and examined the nerves connecting the spinal cord and brain. He showed that the arteries contain blood, not air as was widely believed. Galen's errors also had great influence on medicine. He accepted the view that illness results from an imbalance of four “humors” —blood, phlegm, black bile, and yellow bile. Doctors of the Renaissance who opposed the use of new drugs called themselves “Galenists.”