Hippocrates developed many key ideas with regard to medicine and many of his key ideas survived for many hundreds of years after his life as they were preserved in books by the church. The main idea put forward by Hippocrates was the idea of the four humours. This key idea was that the body was made up of four humours, blood, yellow bile, black bile and phlegm. Hippocrates believed that it was important to keep the humours balanced and in order to do so Hippocrates introduced the idea of regular exercise and healthy eating. It can be said that this method was seen as successful as it was maintained for several years and the idea was even further developed by Galen when he introduced the theory of opposites.