Galen was born in Pergamon (modern day Bergama, Turkey) which at the time was a very lively intellectual center. The city boasted a fine library which had been greatly expanded by King Eumenes II, and it was only bettered by the famous library in Alexandria. Galen’s father was a well-educated and affluent man who had high hopes that his son would continue in his own philosophical traditions. However a remarkable event narrated by Galen was that when he was about 16, he had a dream in which the god Asclepius urged his father to have his son study medicine. His father agreed and Galen was initially a student in Pergamon which was a famous medical center and attracted many sick people who could afford to get the best treatment. Three years later his father died leaving him wealthy, and he was able to travel widely and visit the most important medical centers including the outstanding medical school in Alexandria.

At the age of 28 Galen returned to Pergamon where he became a physician to the gladiators. This institution was run by the High Priest of Asia who was enormously influential. Galen spent 4 years treating the gladiators for their wounds and also emphasizing their training, fitness and hygiene. It is said that during his period, there were only five deaths among the gladiators while he was in charge, and this was an enormous improvement over the previous period when many gladiators died of their wounds. There is an interesting recent article on head injuries of gladiators whose bodies were exhumed from a cemetery in Ephesus, Turkey [9]. A feature was the large number of extensive fractures of the skull in spite of the fact that most gladiators are believed to have worn helmets. Perhaps the blows were delivered after the victims had received other serious injuries in order to put them out of their misery.

When he was 33 Galen went to Rome, then the center of the civilized Western world. However he recounted that he fell out with some of the prominent physicians there and, fearing that he might be harmed, he moved away from the city. A few years later he was recalled by the Roman emperors Marcus Aurelius and Lucius Verus, who ruled together, to serve in the army. A great plague broke out in Rome at that time and large numbers of patients developed severe skin lesions and many died. It is now thought that the disease was smallpox. Galen remained in Rome for the rest of his life and there has been much discussion on when he died. However many historians now believe that his death occurred in about 216 when his age was 87. This was an exceptionally long life in those times.

As indicated above, Galen and his school were much influenced by earlier Greek thinking. Students of today often find it difficult to see the relevance of many of these developing ideas and there is some reluctance to grapple with them. However many vestiges of early Greek thinking remained in the work of the Galenical school, for example the notion of how four humors determine the medical status of an individual, and it is interesting to review how such concepts developed.

Historians often chose to start the beginnings of early Greek physiology with the work of Anaximenes (ca. 570 BC). He argued that “pneuma” (πνεύμα, Greek for breath or spirit) was essential for life. This is hardly surprising because death is often signaled by a cessation of respiration. However Anaximenes expanded the idea of pneuma which was seen as an all-pervading property that was essential for life everywhere. For example he stated “As our soul, being air, sustains us, so pneuma and air pervade the whole world” [20].

About a hundred years later, Empedocles (490–430 BC) wrote about the movement of blood, and he developed the idea that this ebbed and flowed from the heart in a reciprocating manner. A related notion was “innate heat” which was seen as a life-giving principle and was distributed by the blood throughout the body. Empedocles was also one of the first philosophers to suggest that all things are made up of four essential elements: earth, air, fire and water. This notion evolved into the philosophy of the four humors which persisted in different forms right up to the European Renaissance. Earth, air, fire, and water represented the concepts of solidity, volatility, energy, and liquidity. This idea was taken up a hundred years later by Aristotle (384–322 BC) and was still part of physiological dogma 2000 years later.

Hippocrates (c. 460–360 BC) was one of the giants of the ancient Greek period. His school produced an enormous volume of work known as the Hippocratic Corpus which was studied extensively until the European Renaissance. The emphasis here was on the practice of medicine rather than its physiological principles. For example this was the origin of the Hippocratic Oath which sets out ethical principles for physicians and is still often used in one form or another for graduating medical students.

Many clinical signs that are still taught to medical students can be found in the Hippocratic Corpus. For example there is a description of the succussion splash, that is the sound that can be heard if a patient with air and fluid in the pleural cavity or an abdominal viscus such as the stomach is moved from side to side. Another sign included in the Corpus is the pleural friction rub. This is the sound heard through a stethoscope, or the ear applied directly to the chest, when there is disease of the pleural membranes, and they move over each other during breathing with a rasping sound like sandpaper. Hippocrates also described some of the clinical features of pulmonary tuberculosis which was rife at the time. For example he stated that the disease was associated with fever, the coughing up of blood, and that it was usually fatal [8].

The Hippocratic Corpus also continued the belief, earlier enunciated by Empedocles, that the heart is the origin of innate heat and that the primary purpose of respiration is to cool this fiery process. Plato (428–348 BC) expanded on these views in his book Timaeus where he stated “As the heart might be easily raised to too high a temperature by hurtful irritation, the genii placed the lungs in its neighbourhood, which adhere to it and fill the cavity of the thorax, in order that their air vessels might moderate the great heat of that organ, and reduce the vessels to an exact obedience” [15].

Aristotle was not only the most eminent biologist of Greek antiquity but many would say that he deserved this accolade up to the time of the European Renaissance. He was a pupil of Plato, and incidentally also tutored Alexander the Great (356–323 BC). Aristotle had an inexhaustible curiosity and his writings on various animals give pleasure even today. One of his great strengths was in the classification of animals. It is said that he described 540 different species. Aristotle’s colorful text De Partibus Animalium (On the Parts of Animals) [1] still makes enjoyable reading. For example here is his description of the elephant trunk. “Just then as divers are sometimes provided with instruments for respiration, through which they can draw air from above the water, and thus may remain for a long time under the sea, so also have elephants been furnished by nature with their lengthened nostril; and, whenever they have to traverse the water, they lift this up above the surface and breathing [sic] through it” [1]. It could be argued that Aristotle’s contributions to systematizing biology were not equaled until the time of Carl Linnaeus (1707–1778). Aristotle’s three great books on biology were History of Animals, Parts of Animals, and The Generation of Animals. His contributions include a diagram of the “ladder of nature” (scala naturae) shown in Fig. 1.2.

However although Aristotle had such remarkable insights into the diversity of nature, his footing in physiology was not always secure. For example although it had previously been concluded by others that the brain was the seat of intelligence, Aristotle made a backward step and elevated the heart to this status. As we saw, Empedocles had initiated this idea many years before. Also strangely, Aristotle believed that the arteries normally contained air. This error resulted from the fact that in preparing some animals for dissection by strangulation, the arteries were left virtually empty. Another interesting feature of Aristotle’s beliefs was that living creatures were fundamentally different from inanimate objects because there was a special principle essential for life. This notion, known as vitalism, has recurred many times in the history of physiology, and it could be argued that it survived until Claude Bernard (1813–1878) finally put it to rest. Having said that, even the great British physiologist J.S. Haldane (1860–1936) believed that the lung secreted oxygen and his arguments supporting this were associated with a nod towards vitalism [5].

Erasistratus (c. 304–250 BC) was one of the last, and some would say the greatest Greek physiologist prior to Galen. He is credited with promulgating the pneumatic theory of respiration. This recognized the critical importance of inspired air but was curious in that it taught that air from the lungs passed by way of the pulmonary circulation to the left ventricle where it was endowed with “vital spirit”. This was distributed by air-filled arteries to the various tisssues. Some of the vital spirit found its way to the brain where it was changed to “animal spirit” and then distributed via the hollow nerves to the muscles. Venous blood was believed to contain products of food, and this was modified by the liver and delivered to the right heart. As we shall see, a variant of this scheme was adopted by the Galenical school and dominated cardiorespiratory physiology for some 1300 years.

The teachings of the Galenical school were based on those of the ancient Greeks especially Hippocrates for whom Galen had enormous admiration, but also Aristotle, Plato and Erasistratus. Two major areas of teaching stand out. The first was the dominating effects of the four humors emanating from the four bodily fluids: blood, yellow bile, black bile and phlegm. This tradition closely followed the work of Hippocrates. Health was seen as a situation where the humors were equally balanced. An imbalance resulted in a particular type of temperament or disease. For example an overemphasis of blood led to a sanguine personality, too much black bile made the subject melancholic, an excess of yellow bile resulted in a choleric temperament, and too much phlegm caused the subject to become phlegmatic. We can easily see how the present use of these terms reflects the supposed pathological basis. People with a sanguine temperament were happy, optimistic, extraverted, and generally good company. We could wish we were all like that. People with a superabundance of yellow bile had excessive energy and were likely to have short tempers. By contrast, an excess of black bile resulted in melancholy, a subdued temperament, and perhaps a bipolar personality with periods of depression. Finally the phlegmatic personality was on a more even keel but perhaps with a tendency to occasional depression. On the other hand these people were affectionate.