During the Renaissance the prevailing theory on medicine was that of Greek physician Galen. Galen believed that the body was made up of four humors: blood, phlegm, yellow bile and black bile. Each person has a mixture of humors but one is dominant. The determination of the dominant humor was based upon that persons temperament; blood – sanguine or cheerful, phlegmatic – slow, melancholic – sad; relating to black bile; choleric – angry relating to yellow bile. Treatment would be the opposite of the dominant humor. Physicians would make observations and then prescribe diet, rest, sleep, exercise, or baths; or they could administer emetics and purgatives or bleed the patient.
The doctrines of the humors are even evident in the literature of the time. Chaucer described the physician in Canterbury Tales as:
Well could he guess the ascending of the star
Wherein his patient’s fortunes settled were.
He knew the course of every malady,
Were it of cold or heat or moist or dry.
The emphasis of Renaissance art became the most important advance to modern medicine as artists made drawings of human bodies. Raphael, Albrecht Dürer, and Michelangelo were integrating their knowledge of anatomy into their paintings. The painter Leonardo da Vinci even made drawings of the body systems from the cadavers he dissected. For the first time physicians had detailed and accurate drawings of the human body. The information was disseminated with the invention of the printing press which led to the creations of thousands of copies of the books.
The microscope was another very important invention which occurred during the Renaissance. Although mentioned as far back as the first century, Anthony van Leeuwenhoek was able to develop magnification up to 270x and see micro-organisms.
Andreas Vesalius made vital advances and contributions in the study of human anatomy. In 1543 Vesalius published De humani corporis fabrics. Vesalius contradicted Galen on a number of details. For instance, he established that the liver does not have five lobes as Galen contended.
English anatomist William Harvey discovered the circulatory system. He was the first to use previous studies to show the circulation of the blood through the body. Harvey established that the heart acts like a muscle when it contracts. He also pointed out flaws in Galen's description of the cardiovascular (heart and veins) system.