Galen believed that a doctor needed to treat an excess of one humour with its exact opposite
If the patient suffered from a fever, he taught that cold treatment should be given, such as ice packs.
If the patient was deemed to have an excess of phlegm, which was cold and moist, something hot and dry would be prescribed, such as a spoonful of hot pepper.
Galen’s ideas were adopted and promoted by the Christian Church. They strongly defended Galen’s teachings from any criticism.
Galen's ideas fitted with the Christian belief. For example, Galen believed that the parts of the human body fitted together perfectly and that they were like a well-designed machine. The Bible said that God created man in his own image
Galen used animal dissections to justify his research on human anatomy basing his research on the anatomy of pigs, monkeys and dogs.
The Church’s support of Galen’s work prevented any real progress in medicine at the time. Those who dared to question him were seen as challenging the Church.
The work of Galen was also preserved in the Middle East at a time when much of medieval Britain was warring, pillaging and burning their books.
Galen had been right about various aspects of human anatomy but he was wrong about his descriptions of the liver, sternum, jaw, bile duct and uterus.
Galen’s errors can be explained by the fact that human dissection was strictly prohibited in his time.