Galen's experimental anatomy and physiology

The physician Asclepiades had taught that drink reaches the bladder as vapor, soaking through its wall as if it were a sponge. Galen answered that view with an animal. He opened the belly of a living animal, tied off the two ureters and bandaged the wound. When he reopened it the bladder was empty and the ureters were swollen almost to bursting; when he loosened the ties, the bladder filled with urine. He described the demonstration in On the Natural Faculties and invited anyone who doubted it to try it for himself.

Galen was born in Pergamon in Asia Minor in 129 CE, trained in Smyrna and Alexandria, and made his name as surgeon to the gladiators of Pergamon. He was called to Rome as physician to the emperor Marcus Aurelius and spent the rest of his life at court, writing an enormous body of medical works; the National Library of Medicine gives his death as 201 CE. He built on the Hippocratic theory of the humors, took in the anatomy of Alexandrians such as Herophilus, and studied the function of the kidneys and the spinal cord by experiment.

Much of his anatomy came from animals. According to NLM's history of Islamic medicine, he argued to a large extent by analogy with animal structures, and his claim that blood passes from the right side of the heart to the left through the wall between the ventricles was rejected by Ibn al-Nafis in the 13th century.

Hunayn ibn Ishaq and other translators put Galen into Arabic, and the anatomy sections of the major Arabic and Persian encyclopedias summarized his ideas. In Europe his theories hardened into dogma. At Bologna in the early 14th century, Mondino de Luzzi read Galen's text aloud while assistants cut, and findings that did not match were explained away. NLM dates the return of Galen's own call for observation and investigation to the mid-16th century.