Aelius Galenus or Claudius Galenus (September AD 129 – 199 / 217; Greek: Γαληνός, Galēnos, from adjective "γαληνός", "calm"), better known as Galen of Pergamon (modern day Bergama, Turkey), was a prominent Roman (of Greek ethnicity) physician, surgeon and philosopher. Arguably the most accomplished of all medical researchers of antiquity, Galen contributed greatly to the understanding of numerous scientific disciplines including anatomy, physiology, pathology, pharmacology, and neurology, as well as philosophy, and logic.

The son of Aelius Nicon, a wealthy architect with scholarly interests, Galen received a comprehensive education that prepared him for a successful career as a physician and philosopher. He traveled extensively, exposing himself to a wide variety of medical theories and discoveries before settling in Rome, where he served prominent members of Roman society and eventually was given the position of personal physician to several emperors.

Galen's understanding of anatomy and medicine were principally influenced by the then current theory of humorism, as advanced by many ancient Greek physicians such as Hippocrates. His theories dominated and influenced Western medical science for nearly two millennia. His anatomical reports, based mainly on dissection of monkeys and pigs, remained uncontested until 1543, when printed descriptions and illustrations of human dissections were published in the seminal work De humani corporis fabrica by Andreas Vesalius where Galen's physiological theory was accommodated to these new observations. Galen's theory of the physiology of the circulatory system endured until 1628, when William Harvey published his treatise entitled De motu cordis, in which he established that the blood circulates with the heart acting as a pump. Medical students continued to study Galen's writings until well into the 19th century. Galen conducted many nerve ligation experiments that supported the theory, which is still believed today, that the brain controls all the motions of the muscles by means of the cranial and peripheral nervous systems.

Galen saw himself as being both a physician and a philosopher, as he wrote in his treatise entitled That the Best Physician is also a Philosopher. Galen was very interested in the debate between the rationalist and empiricist medical sects, and his use of direct observation, dissection and vivisection represents a complex middle ground between the extremes of those two viewpoints. Many of his works have been preserved and / or translated from the original Greek, although many were destroyed and some credited to him are believed to be spurious. Although there is some debate over the date of his death, he was no younger than seventy when he died.

Galen describes his early life in On the affections of the mind. He was born in September 129 AD; his father Aelius Nicon was a wealthy patrician, an architect and builder, with eclectic interests including philosophy, mathematics, logic, astronomy, agriculture and literature. Galen describes his father as a "highly amiable, just, good and benevolent man". At that time Pergamon was a major cultural and intellectual center, noted for its library (Eumenes II), second only to that in Alexandria and attracted both Stoic and Platonic philosophers, to whom Galen was exposed at age 14. His studies also took in each of the principal philosophical systems of the time, including Aristotelian and Epicurean. His father had planned a traditional career for Galen in philosophy or politics and took care to expose him to literary and philosophical influences. However Galen states that in around 145 AD, his father had a dream in which the god Asclepius (Aesculapius) appeared and commanded Nicon to send his son to study medicine. Again, no expense was spared, and following his earlier liberal education, at 16 he began studies at the prestigious local sanctuary or Asclepieum dedicated to Asclepius, god of medicine, as a θεραπευτής (therapeutes, or attendant) for four years. There he came under the influence of men like Aeschrion of Pergamon, Stratonicus and Satyrus. Asclepiea functioned as spas or sanitoria to which the sick would come to seek the ministrations of the priesthood. The temple at Pergamon was eagerly sought by Romans in search of a cure. It was also the haunt of notable people such as Claudius Charax the historian, Aelius Aristides the orator, Polemo the sophist, and Cuspius Rufinus the Consul.

In 148, when he was 19, his father died, leaving him independently wealthy. He then followed the advice he found in Hippocrates' teaching and traveled and studied widely including Smyrna (now Izmir), Corinth, Crete, Cilicia (now Çukurova), Cyprus and finally the great medical school of Alexandria, exposing himself to the various schools of thought in medicine. In 157, aged 28, he returned to Pergamon as physician to the gladiators of the High Priest of Asia, one of the most influential and wealthiest men in Asia. The High Priest chose Galen over other physicians after Galen claims he eviscerated an ape and challenged other physicians to repair the damage. When they refused, Galen did the surgery himself and in doing so won himself the favor of the High Priest of Asia. Over the four years there he learnt the importance of diet, fitness, hygiene and preventive measures, as well as living anatomy, and the treatment of fractures and severe trauma, referring to their wounds as "windows into the body". Only five deaths occurred while he held the post, compared to sixty in his predecessor's time, generally ascribed to his attention to their wounds. At the same time he pursued studies in theoretical medicine and philosophy.

Galen went to Rome in 162 AD and made his mark as a practicing physician. His impatience brought him into conflict with other doctors and he felt menaced by them. His demonstrations there antagonized the less able and original physicians in the city. They plotted against him and he feared he might be driven away or poisoned so he left the city.

Rome then engaged in the foreign wars in 161 AD. Marcus Aurelius and his colleague Lucius Verus were in the north fighting the Marcomanni. During the autumn of 169 AD when Roman troops were returning to Aquileia, the great plague broke out and the emperor summoned Galen back to Rome. He was ordered to accompany Marcus and Verus to Germany as the court physician. In the following spring Marcus was persuaded to release Galen after receiving a report that Asclepius was against the project. He was left behind to act as physician to the imperial heir Commodus. It was here in court that Galen wrote extensively on medical subjects. Ironically, Lucius Verus died in 169, and Marcus Aurelius himself died in 180, both victims of the plague.

Galen was the physician to Commodus for much of the emperor’s life and treated his common illnesses. According to Dio Cassius, in about 189 AD, under Commodus’ reign, a pestilence occurred, the largest of which he had knowledge, in which 2,000 people died in Rome each day. It is most likely that this was the same plague that struck Rome during Marcus Aurelius’ reign.

Galen became physician to Septimius Severus during his reign in Rome. Galen compliments Septimius and Caracalla on keeping a supply of drugs for their friends and mentions three cases in which they had been of use in 198 AD.

The Antonine Plague was named after Marcus Aurelius’ family name of Antoninus. It was also known as the Plague of Galen and holds an important place in medicinal history because of its association with Galen. Galen had first hand knowledge of the disease. He was in Rome when it struck in 166 AD, and was also present in the winter of 168 - 9 during an outbreak among troops stationed at Aquileia. He had experience with the epidemic, referring to it as very long lasting, and describes its symptoms and his treatment of it. Unfortunately, his references to the plague are scattered and brief. Galen was not trying to present a description of the disease so that it could be recognized in future generations; he was more interested in the treatment and physical effects of the disease. For example, in his writings about a young man afflicted with the plague, he concentrated on the treatment of internal and external ulcerations. According to Niebuhr "this pestilence must have raged with incredible fury; it carried off innumerable victims. The ancient world never recovered from the blow inflected upon it by the plague which visited it in the reign of M. Aurelius." The mortality rate of the plague was 7 - 10 percent; the outbreak in 165 - 6 - 168 would have caused approximately 3.5 to 5 million deaths. Otto Seek believes that over half the population of the empire perished. J.F. Gilliam believes that the Antonine plague probably caused more deaths than any other epidemic during the empire before the mid 3rd century. It is believed that the Antonine Plague was smallpox, because though his description is incomplete, Galen gave enough information to enable a firm identification of the disease.

Galen notes that the exanthema covered the victim’s entire body and was usually black. The exanthem became rough and scabby where there was no ulceration. He states that those who were going to survive developed a black exanthem. According to Galen, it was black because of a remnant of blood putrefied in a fever blister that was pustular. His writings state that raised blisters were present in the Antonine plague, usually in the form of a blistery rash. Galen states that the skin rash was close to the one Thucydides described. Galen describes symptoms of the alimentary tract via a patient’s diarrhea and stools. If the stool was very black, the patient died. He says that the amount of black stools varied. It depended on the severity of the intestinal lesions. He observes that in cases where the stool was not black, the black exanthum appeared. Galen describes the symptoms of fever, vomiting, fetid breath, catarrh, cough and ulceration of the larynx and trachea.

When Peripatetic philosopher Eudemus became ill with Quartan fever, Galen felt obliged to treat him "since he was my teacher and I happened to live nearby." Galen wrote: "I return to the case of Eudemus. He was thoroughly attacked by the three attacks of quartan ague, and the doctors had given him up, as it was now mid winter." Some Roman physicians criticized Galen for his use of the prognosis in his treatment of Eudemus. This practice conflicted with the then current standard of care, which relied upon divination and mysticism. Galen retaliated against his detractors by defending his own methods. Garcia - Ballester quotes Galen as saying: "In order to diagnose, one must observe and reason. This was the basis of his criticism of the doctors who proceeded alogos and askeptos." However, Eudemus warned Galen that engaging in conflict with these physicians could lead to his assassination. "Eudemus said this, and more to the same effect; he added that if they were not able to harm me by unscrupulous conduct they would proceed to attempts at poisoning. Among other things he told me that, some ten years before, a young man had come to the city and had given, like me practical demonstrations of the resources of our art; this young man was put to death by poison, together with two servants who accompanied him."

Garcia - Ballester says the following of Galen’s use of prognosis: "In modern medicine, we are used to distinguishing between the diagnostic judgment (the scientific knowledge of what a patient has) and the prognostic judgment (the conjecture about what will happen to him.) Galen, like the Hippocratics, was not. For him, to understand a clinical case technically, ‘to diagnose’, was among other things, to know with greater or lesser certainty the outcome fore the patient, ‘to prognosticate’. Prognosis, then, is one of the essential problems and most important objectives of Galenic diagnosis. Galen was concerned to distinguish it from divination or prophecy, both to improve diagnosis technically and to enhance the physician’s reputation."

The 11th century Suda lexicon states that Galen died at the age of 70, therefore about the year 199. However, there is a reference in Galen's treatise "On Theriac to Piso" (which may however be spurious) to events of 204. There are also statements in Arabic sources that he died at 87, after 17 years studying medicine and 70 practicing it, therefore about 217. Nutton believes that "On Theriac to Piso" is genuine, the Arabic sources are correct and that the Suda has erroneously interpreted the 70 years of Galen's career in the Arabic tradition as referring to his whole lifespan. Boudon - Millot more or less concurs and favors a date of 216.

Galen contributed a substantial amount to the Hippocratic understanding of pathology. Under Hippocrates’ bodily humors theory, differences in human moods come as a consequence of imbalances in one of the four bodily fluids: blood, yellow bile, black bile, and phlegm. Galen advanced this theory, creating a typology of human temperaments. An imbalance of each humor corresponded with a particular human temperament (blood  -sanguine, black bile - melancholic, yellow bile - choleric, and phlegm - phlegmatic). Individuals with sanguine temperaments are extroverted and social. Choleric people have energy, passion and charisma. Melancholics are creative, kind and considerate. Phlegmatic temperaments are characterized by dependability, kindness, and affection.

Galen’s principal interest was in human anatomy, but Roman law had prohibited the dissection of human cadavers since about 150 BC. Because of this restriction, Galen performed anatomical dissections on living (vivisection) and dead animals, mostly focusing on pigs and primates. This work turned out to be particularly useful because in most cases, the anatomical structures of these animals closely mirror those of humans. Galen clarified the anatomy of the trachea and was the first to demonstrate that the larynx generates the voice. Galen may have understood the importance of artificial ventilation, because in one of his experiments he used bellows to inflate the lungs of a dead animal.

Among Galen’s major contributions to medicine was his work on the circulatory system. He was the first to recognize that there were distinct differences between venous (dark) and arterial (bright) blood. Although his many anatomical experiments on animal models led him to a more complete understanding of the circulatory system, nervous system, respiratory system and other structures, his work was not without scientific inaccuracies. Galen believed that the circulatory system consisted of two separate one - way systems of distribution, rather than a single unified system of circulation. His understanding was that venous blood was generated in the liver, from where it was distributed and consumed by all organs of the body. He posited that arterial blood originated in the heart, from where it was distributed and consumed by all organs of the body. The blood was then regenerated in either the liver or the heart, completing the cycle. Galen also believed in the existence of a group of blood vessels he called the rete mirabile, near the back of the human brain. Both of these theories of the circulation of blood were later shown to be incorrect.

In his work De motu musculorum, Galen explained the difference between motor and sensory nerves, discussed the concept of muscle tone and explained the difference between agonists and antagonists.

Galen was also a highly skilled surgeon, and he performed surgical operations on human patients. Many of the procedures and techniques that he utilized would not be used again for centuries. Of particular note are procedures that Galen performed on patients’ brains and eyes. In order to correct cataracts in patients, Galen performed an operation that was similar to what is performed by contemporary ophthalmologists. Using a needle shaped instrument, Galen attempted to remove the cataract from behind the lens of the eye.

At first reluctantly, but then with increasing vigor, Galen promoted Hippocratic teaching including venesection and bloodletting, then unknown in Rome. This was sharply criticized by the Erasistrateans, who predicted dire outcomes, believing that it was not blood but pneuma that flowed in the veins. Galen however staunchly defended venesection in his three books on the subject, and in his demonstrations and public disputations.

Although the main focus of his work was on medicine, anatomy, and physiology, Galen also wrote about logic and philosophy. His writings were influenced by earlier Greek and Roman thinkers, including Plato, Aristotle, and the Stoics. Several schools of thought existed within the medical field during Galen’s lifetime, the main two being the Empiricists and Rationalists (also called Dogmatists or Philosophers), with the Methodists being a lesser, more moderate group. The Empiricists emphasized the importance of physical practice and experimentation, or "active learning" in the medical discipline. In direct opposition to the Empiricists were the Rationalists, who valued the study of established teachings in order to create new theories in the name of medical advancements. The Methodists formed somewhat of a middle ground, as they were not as experimental as the Empiricists, nor as theoretical as the Rationalists. The Methodists mainly utilized pure observation, showing greater interest in studying the natural course of ailments than making efforts to find remedies.

Galen was highly interested in the importance of combining philosophical thought with medical practice, an idea he expressed in his brief work "That the Best Physician is also a Philosopher." He refused to be placed into one particular school of thought, instead taking aspects from each group and combining them with his original thoughts to form his own unique approach to medicine. He was a proponent of medicine as a highly interdisciplinary field that was best practiced by utilizing theory, observation, and experimentation in conjunction to yield the most complete results. This attitude was largely a result of his pluralist education, which exposed him to the four major schools of thought (Platonists, Peripatetics, Stoics, Epicureans), and encouraged him to pick and choose aspects from each to adhere to. His early education also included instruction both from teachers who belonged to the Rationalist sect and from teachers who belonged to the Empiricist sect, allowing him to learn about the merits of both schools.

Galen may have produced more work than any author in antiquity, rivaling the quantity of work issued from Augustine of Hippo. So profuse was Galen's output that the surviving texts represent nearly half of all the extant literature from ancient Greece. It has been reported that Galen employed twenty scribes to write down his words. Galen may have written as many as 600 treatises, amounting to some 10 million words. Although his surviving works amount to some 3 million words, this is thought to represent less than a third of his complete writings. In AD 191, a fire in the Temple of Peace destroyed many of his works, particularly treatises on philosophy.

Because Galen's works were not translated into Latin in the ancient period, and because of the collapse of the Roman Empire in the West, the study of Galen, along with the Greek medical tradition as a whole, went into decline in Western Europe during the Early Middle Ages, when very few Latin scholars could read Greek. However, Galen and the ancient Greek medical tradition generally continued to be studied and followed in the Eastern Roman Empire, commonly known as the Byzantine Empire. All of the extant Greek manuscripts of Galen were copied by Byzantine scholars. In the Abbasid period (after 750 AD) Arab Muslims began to be interested in Greek scientific and medical texts for the first time, and had some of Galen's texts translated into Arabic, often by Syrian Christian scholars. As a result some texts of Galen exist only in Arabic translation, while others exist only in medieval Latin translations of the Arabic. In some cases scholars have even attempted to translate from the Latin or Arabic back into Greek where the original is lost. For some of the ancient sources, such as Herophilus, Galen's account of their work is all that survives.

Even in his own time, forgeries and unscrupulous editions of his work were a problem, prompting him to write On his Own Books. Forgeries in Latin, Arabic or Greek continued until the Renaissance. Some of Galen's treatises have appeared under many different titles over the years. Sources are often in obscure and difficult to access journals or repositories. Although written in Greek, by convention the works are referred to by Latin titles, and often by merely abbreviations of those. No single authoritative collection of his work exists, and controversy remains as to the authenticity of a number of works attributed to Galen. Consequently research on Galen's work is fraught with hazard.

Various attempts have been made to classify Galen's vast output. For instance Coxe (1846) lists a Prolegomena, or introductory books, followed by 7 classes of treatise embracing Physiology (28 vols.), Hygiene (12), Aetiology (19), Semeiotics (14), Pharmacy (10), Blood letting (4) and Therapeutics (17), in addition to 4 of aphorisms, and spurious works. The most complete compendium of Galen's writings, surpassing even modern projects like the Corpus Medicorum Graecorum, is the one compiled and translated by Karl Gottlob Kühn of Leipzig between 1821 and 1833. This collection consists of 122 of Galen's treatises, translated from the original Greek into Latin (the text is presented in both languages). Over 20,000 pages in length, it is divided into 22 volumes, with 676 index pages. Many of Galen's works are included in the Thesaurus Linguae Graecae, a digital library of Greek literature started in 1972. Another useful modern source is the French Bibliothèque interuniversitaire de médicine (BIUM).

In his time, Galen's reputation as both physician and philosopher was legendary, the Emperor Marcus Aurelius describing him as "Primum sane medicorum esse, philosophorum autem solum" (first among doctors and unique among philosophers Praen 14: 660). Other contemporary authors in the Greek world confirm this including Theodotus the Shoemaker, Athenaeus and Alexander of Aphrodisias. The 7th century poet George of Pisida went so far as to refer to Christ as a second and neglected Galen. Galen continued to exert an important influence over the theory and practice of medicine until the mid 17th century in the Byzantine and Arabic worlds and Europe. Hippocrates and Galen form important landmarks of 600 years of Greek medicine. AJ Brock describes them as representing the foundation and apex respectively. A few centuries after Galen Palladius Iatrosophista in his commentary on Hippocrates, stated that Hippocrates sowed and Galen reaped.

Thus Galen summarized and synthesized the work of his predecessors, and it is in Galen's words (Galenism) that Greek medicine was handed down to subsequent generations, such that Galenism became the means by which Greek medicine was known to the world. Frequently this was in the form of restating and reinterpreting, such as in Magnus of Nisibis' 4th century work on urine, which was in turn translated into Arabic. Yet the full importance of his contributions was not appreciated till long after his death. Galen's rhetoric and prolificity were so powerful as to convey the impression that there was little left to learn. The term Galenism has subsequently taken on both a positive and pejorative meaning as one that transformed medicine in late antiquity yet so dominated subsequent thinking as to stifle further progress.

After the collapse of the Western Empire the study of Galen and other Greek works almost disappeared in the Latin West. In contrast, in the predominantly Greek speaking eastern half of the Roman empire (Byzantium), many commentators of the subsequent centuries, such as Oribasius, physician to the emperor Julian who compiled a Synopsis in the 4th century, preserved and disseminated Galen's works, making Galenism more accessible. Nutton refers to these authors as the "medical refrigerators of antiquity". In late antiquity medical writing veered increasingly in the direction of the theoretical at the expense of the practical, with many authors merely debating Galenism. Magnus of Nisibis was a pure theorist, as were John of Alexandria and Agnellus of Ravenna with their lectures on Galen's De Sectis. So strong was Galenism that other authors such as Hippocrates began to be seen through a Galenic lens, while his opponents became marginalized and other medical sects such as Asclepiadism slowly disappeared. Greek medicine was part of Greek culture, and Syrian Eastern Christians came in contact with it while the Eastern Roman Empire (Byzantium) ruled Syria and Western Mesopotamia, regions that were conquered from Byzantium in the 7th century by Arab Muslims. After 750 AD, Muslims had these Syrian Christians make the first translations of Galen into Arabic. From then on Galen and the Greek medical tradition in general became assimilated into the medieval and early modern Islamic Middle East.

The first major translator of Galen into Arabic was the Syrian Christian Hunayn ibn Ishaq. Hunayn translated (c.830 - 870) 129 works of "Jalinos" into Arabic. One of the Arabic translations, ‘Kitab ila Aglooqan fi Shifa al Amraz’, which is extant in the Library of Ibn Sina Academy of Medieval Medicine & Sciences, is a master piece of all literary works of Galen. It is a part of the Alexandrian compendium of Galen’s work. This manuscript of 10th century comprises two parts that include details regarding various types of fevers (Humyat) and different inflammatory conditions of the body. More importantly, it includes details of more than 150 single and compound formulations of both herbal and animal origin. The book provides an insight into understanding the traditions and methods of treatment in Greek (Unani) and Roman era. In addition, this book provides a direct source for the study of more than 150 single and compound drugs used during the Greco - Roman period.

Galen's insistence on a rational systematic approach to medicine set the template for Islamic medicine, which rapidly spread throughout the Arab Empire. Arabic sources, such as Rhazes (Muhammad ibn Zakarīya Rāzi 865 - 925 AD), continue to be the source of discovery of new or relatively inaccessible Galenic writings. As the title, Doubts on Galen by Rhazes implies, as well as the writings of physicians such as Ibn Zuhr (Avenzoar) and Ibn al-Nafis, the works of Galen were not taken on unquestioningly, but as a challengeable basis for further inquiry.

A strong emphasis on experimentation and empiricism led to new results and new observations, which were contrasted and combined with those of Galen by writers such as Rhazes, Ali ibn Abbas al-Majusi (Haly Abbas), Abu al-Qasim al-Zahrawi (Abulasis), Ibn Sina (Avicenna), Ibn Zuhr and Ibn al-Nafis. For example, the experiments carried out by Rāzi and Ibn Zuhr contradicted the Galenic theory of humorism, while Ibn al-Nafis' discovery of the pulmonary circulation contradicted the Galenic theory on the heart.

From the 11th century onwards, Latin translations of Islamic medical texts began to appear in the West, alongside the Salerno school of thought, and were soon incorporated into teaching at the universities of Naples and Montpellier. Galenism now took on a new unquestioned authority, Galen even being referred to as the "Medical Pope of the Middle Ages". Constantine the African was amongst those who carried out translations of both Hippocrates and Galen from Arabic. In addition to the more numerous translations of Arabic texts in this period, there were a few translations of Galenic works directly from the Greek, such as Burgundio of Pisa's translation of De complexionibus. Galen's works on anatomy and medicine became the mainstay of the medieval physician's university curriculum, alongside Ibn Sina's The Canon of Medicine which elaborated on Galen's works. Unlike pagan Rome, Christian Europe did not exercise a universal prohibition of the dissection and autopsy of the human body and such examinations were carried out regularly from at least the 13th century. However, Galen's influence, as in the Arab world, was so great that when dissections discovered anomalies in Galen's anatomy, the physicians often tried to fit these into the Galenic system. An example of this is Mondino de Liuzzi, who describes rudimentary blood circulation in his writings but still asserts that the left ventricle should contain air. Some cited these changes as proof that human anatomy had changed since the time of Galen.

The Renaissance and fall of the Byzantine Empire (1453) was accompanied by an influx of Greek scholars and manuscripts to the West, allowing direct comparison between the Arabic commentaries and the original Greek texts of Galen. This New Learning and the Humanist movement, particularly the work of Thomas Linacre, promoted literae humaniores including Galen in the Latin scientific canon, De Naturalibus Facultatibus appearing in London in 1523. Debates on medical science now had two traditions, the more conservative Arabian and liberal Greek. The more extreme liberal movements began to challenge the role of authority in medicine, as exemplified by Paracelsus symbolically burning the works of Avicenna and Galen at his medical school in Basle. Nevertheless Galen's pre-eminence amongst the great thinkers of the millennium is exemplified by a 16th century mural in the refectory of the Great Lavra of Mt Athos. This depicts pagan sages at the foot of the Tree of Jesse, with Galen between the Sibyl and Aristotle.

Galenism's final defeat came from a combination of the negativism of Paracelsus and the constructivism of the Italian Renaissance anatomists, such as Vesalius in the 16th century. In the 1530s, Flemish anatomist and physician Andreas Vesalius took on a project to translate many of Galen's Greek texts into Latin. Vesalius' most famous work, De humani corporis fabrica, was greatly influenced by Galenic writing and form. Seeking to examine critically Galen's methods and outlook, Vesalius turned to human cadaver dissection as a means of verification. Galen's writings were shown to describe details present in monkeys but not in humans by Vesalius, who demonstrated Galen's limitations through books and hands - on demonstrations, despite fierce opposition from pro-Galenist orthodoxy, such as Jacobus Sylvius. Since Galen states that he is using observations of monkeys (human dissection was prohibited) to give an account of what the body looks like, Vesalius could portray himself as using Galen's approach of description of direct observation to create a record of the exact details of the human body, since he worked in a time when human dissection was allowed. Galen argued that monkey anatomy was close enough to humans for physicians to learn anatomy with monkey dissections and then make observations of similar structures in the wounds of their patients, rather than trying to learn anatomy only from wounds in human patients as students being trained by the Empiricist medical sect would. The examinations of Vesalius also disproved medical theories of Aristotle and Mondino de Liuzzi. One of the best known examples of Vesalius' overturning of Galenism was his demonstration that the interventricular septum of the heart was not permeable, as Galen had taught. However, this had been revealed 2 years before by Michael De Villeneuve (Michael Servetus) in his fatidique "Christianismi restitutio" (1553).

Michael De Villanueva (Michael Servetus), Vesalius' fellow student, was the best galenist at the University of Paris, according to Johann Winter von Andernach, who taught both. In the galenism of the Rennaisance, editions of the Opera Omnia by Galen were very important. It was begun in Venice in 1541 - 1542 by the Guinta. There were fourteen editions of the book from that date until 1625. Just one edition was produced from Lyon, between 1548 - 1551. The Lyon edition has commentaries on breathing and blood streaming, that correct the work of earlier renowned authors such as Vesalius, Caius or Janus Cornarius . Michael De Villeneuve had contracts with Jean Frellon for that work, and the Servetus scholar - researcher Francisco Javier González Echeverría presented research that became an accepted communication in the International Society for the History of Medicine which concluded that Michael De Villeneuve (Michael Servetus) is the author of the commentaries of this edition of Frellon, in Lyon.

Another convincing case where understanding of the body was extended beyond where Galen had left it came from these demonstrations of the nature of the circulation and the subsequent work of Andrea Cesalpino, Fabricio of Acquapendente and William Harvey. Some Galenic teaching, such as his emphasis on bloodletting as a remedy for many ailments, however remained influential until well into the 19th century.

Galenic scholarship remains an intense and vibrant field, following renewed interest in his work, dating from the Realencyclopädie der Classischen Altertumswissenschaft.