What advances were made in medicine during the Renaissance?

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:

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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.