It seems amazing that the basic functions of the heart, circulatory system, and other bodily organs remained such a mystery to humans for so long, since they are so close to us and so vital to our very existence. However, early doctors faced serious obstacles in determining those functions. Religious taboos seriously limited the amount of human dissections taking place. Surgery's low status and primitive state is seen by the fact that barbers would typically double as surgeons, since they had the necessary cutting tools. Another major limitation was the lack of anesthetics to kill the pain. Heavy doses of liquor or a blow to the head were the closest thing to painkillers that doctors had before the 1800's.
As a result, people would rarely submit to surgery except in the most extreme circumstances (e.g., amputation for gangrene). And by then it was often too late. Without willing patients, surgery was rarely performed and could not advance. And without such advances, few people would risk operations. Caught in this vicious cycle, doctors had to resort to the dissection of animals. However, inferences made from animal dissections about human anatomy were often incorrect. Also, the practice of dissecting animals bled to death led to the misconception that only air flowed through the arteries and left side of the heart. This plus Aristotle's theory of four terrestrial elements led to various conclusions about human biology as seen in the theories of the dominant medical authority since the second century, the Greek physician Galen.
While Galen did clear up the misconception that only air flowed through the arteries, he also passed on several misconceptions. For one thing, he said that air passes directly from the lungs to cool the heart, which is the seat of the soul, a furnace to heat the body, and the source of the blood in the arteries, while the liver is the source of blood in the veins. His second contention was that blood then flows out to the body, which absorbs the blood and does not recirculate it. Third, Galen said that air mixes with the blood to form a spirituous substance called pneuma . There are three kinds of pneuma, formed in the liver, heart, and brain, and controlling such things as the passions, senses, and consciousness. According to Galen, pneuma is the main source of the life process and consciousness in an organism. Finally, drawing upon Aristotle's theory of four terrestrial elements, there was the theory of the four humours (blood, bile, black bile, and phlegm), which must be in balance in order for one to be healthy.
These incorrect conclusions about human biology in turn led to two major misconceptions about disease. First of all, scholars saw sickness as a sign of an imbalance of the four humours that should be treated by bloodletting or other forms of purging. This supposedly would rid the body of imbalanced humours and cause it to restore the balance. This tied in closely with the second misconception: that disease is purely a result of internal balance, not external factors. Therefore, each person's disease was seen as a purely individual matter having no relationship to anyone else's disease, no matter how similar the symptoms may be
Despite the Church's support of Galen and feelings against dissection, problems started to arise with Galen's theories over time just through normal observations. This and two other factors, both leading out of the Renaissance, led to new research to figure out what the nature of the heart was. For one thing, the Renaissance artists placed increased emphasis on accurate representation of nature and human anatomy. Leonardo da Vinci's notebooks are the best-known examples of this emphasis on realism. Also, the printing press helped publicize and popularize these ideas within the medical community.
Second, in biology, as in physics and astronomy, the Renaissance oftentimes was not so important for breeding new ideas as for discovering other ancient authors that contradicted the accepted authority, thus forcing scholars to seek the truth for themselves. Interestingly enough, the opposing authority was Aristotle, who differed with Galen on several points, claiming the life process was the product of all the various organs in the body, not of pneuma. This helped open up discussion on the life process and the nature of disease.
As with Aristotle, the combination of these factors generated a cycle that both undermined Galen and slowed down the creation of a new set of theories. New observations would be made that seemed to contradict his theories. This would lead to new explanations, once again framed in the context of the old beliefs, thus patching up the system. However, more observations would take place, leading to more patching of the old system, and so on. Eventually, the system would be so full of holes that someone would take the new data and synthesize it into a new set of theories that more accurately explained the universe.
Much of this research was done at the University of Padua, which was one of the main centers of research and new theories in the 1500's and 1600's. Being controlled by Venice, which had a bit of an anti-clerical tradition, the University of Padua encouraged more of the intellectual freedom needed to develop new theories that better explained nature. Copernicus and Galileo, had both worked there, as did most of the men who discredited Galen's theory and formed the modern theory of circulation. Two men in particular opened the way for challenging the old theories: Vesalius and Paracelsus.
Paracelsus (1493-1541) never received a medical degree, but he continued to teach, write about, and practice medicine. However, he taught from his own experiences, not Galen's books, and he taught in the vernacular. This was contrary to the Hippocratic Oath by which doctors were supposed to teach in Latin to prevent any trade secrets from getting into the wrong hands and being popularized. Paracelsus' actions made him an outsider to the medical community and caused him to challenge many of its most honored (and mistaken) theories and practices. One thing he claimed was that disease was the result of outside forces acting on the body, not an internal imbalance. Although he had no concept of germ theory, this idea opened the way for a new approach to diagnosing and treating disease. Paracelsus was reviled by the medical establishment of his day, but became something of a folk hero to later generations and inspired further challenges to Galen.
Vesalius (1514-64) also took steps in overthrowing Galen and opening the way for a new theory on the heart and circulatory system. Unlike most medical scholars, who had assistants do the actual dissection while they read the appropriate passages from Galen, Vesalius did his own dissections and saw things for himself. He even saw things he was not looking for and that disagreed with Galen. He had a hard time believing that what his eyes saw was true and that Galen could be wrong. Nevertheless, in 1543, the same year that Copernicus (who also worked at Padua) published his book proposing a heliocentric universe, Vesalius published De Fabrica. This book, which was illustrated by the great artist Titian's own art students, provided anatomical drawings of unprecedented accuracy for medical manuals and set the standard for years to come. It also proved many of Galen's anatomical descriptions to be completely wrong.
Thanks to Vesalius and Paracelsus, more evidence kept coming in to cast doubts on Galen. In 1559, one of Vesalius' students, Colombo, published a description of how blood went from the right side of the heart to the lungs and then to the left ventricle. However, he still kept the traditional view that blood flowed out of the heart through both the arteries and veins. In 1574, Fabricius published a work describing valves in the veins preventing the outward flow of blood from the heart. Still, he refused to see that this meant the blood flowed from the veins to the heart. Instead he said the purpose of the valves was to keep too much blood from flowing to the veins from the heart. In 1606, Cesalpino observed blood flowing from the arteries to the veins and toward the heart. However, he also failed to grasp the meaning of this. As obvious as it should have been that Galen's system was not working, scientists' minds were too rigidly set to admit it. Finally, a man came along whose genius, like that of Newton and Mendeleev, was to synthesize the recent evidence into a new system that shattered the old views. That man was William Harvey, an Englishman also working at Padua.
Harvey, who was influenced by Fabricius' work on valves in the veins, developed very modern methods of observation and experimentation. In 1628, nine years after his experiments confirmed his suspicions about Galen's system, Harvey published his findings in De Motu Cordis (Concerning the Motion of the Heart). The wealth of evidence it brought to bear effectively shattered Galen's theory forever.
Harvey showed that blood did not seep through a septum and that blood passes through the lungs to be refreshed, although he was not aware of oxygenation. He pointed out that animals without lungs also had no right ventricle and, that in developing embryos, the blood took a shorter route from the right to left side of the heart. Harvey's most important and astounding contribution was the calculation that, in one hour, the heart pumps more than the body's weight in blood. This could only mean one thing: that the blood circulated from the left side of the heart, through the body, then to the right side of the heart, and from there through the lungs and back to the left side of the heart.
It took nearly half a century for Harvey's work to be accepted by the medical community. Once it was accepted, it provided a much better framework for studying the rest of the body. With the mysteries of the circulatory system unraveled, the respiratory and digestive systems could be better understood. And with those in place, other functions of the body could be figured out. Thanks to Harvey's brilliant synthesis, the way to modern biology was opened.