Medical ideas in the Middle Ages were heavily influenced by the ancient Greeks and Romans, particularly Hippocrates and Galen. Although Galen was not a Christian he was accepted by the Church because he believed that humans have a soul and in his books he often referred to the Creator. To question Galen, therefore, was to challenge the Church’s teachings.
The four humours were:
If the humours stayed in balance then a person remained healthy, but if there was too much of one humour then illness occurred.
It was important to keep the patient’s body in balance. They did this by removing excess fluid:
Medieval doctors also used astrology, as they believed that the movement of the stars affected people’s health. The modern word "influenza" comes from a medieval Italian word meaning "the influence" of the planets.
Each part of the body was associated with an astrological sign and procedures such as bleeding would only be carried out when the moon was in the correct position. Physicians therefore needed knowledge of astrology as well as medicine to treat patients.
According to the medieval chart of Zodiac Man, each part of the body associated with a star sign. Physicians consulted a book called the Valemecum which contained charts to decide when to bleed patients or carry out other procedures.
Even medicinal plants were thought to be under the influence of the heavens. As late as the 17th century Nicholas Culpeper, a famous London herbalist wrote this advice about dandelion in his herbal.
VULGARLY called Piss-a-Beds
It is under the dominion of Jupiter... It is of an opening and cleansing quality and therefore very effectual for obstructions of the liver…It openeth the passages of the urine in both young and old.
In some ways, therefore, knowledge went into reverse in medieval Europe. Much of the knowledge of the Greeks and Romans was lost and was replaced by superstition.
Not only did doctors use astrology before treating patients, but kings thought that by touching people suffering from scrofula, the 'King's Evil', they could cure them.
Peasants turned to the priest or visited the dynion hysbys for help.
The Church forbad dissection of corpses and discouraged experiments. However, it did encourage people to go on Crusades to the Holy Land, where they came into contact with the Muslim world. Muslim doctors were more knowledgeable than their European counterparts and this brought some improvements in medical knowledge.