The Egyptians developed a rational theory of illness in the body based on their observations of the River Nile. They believed that the body was made up of channels running from the heart to the other organs and limbs. In the same way that crops could fail to grow if the River Nile became blocked by silt, the body would become ill if the channels were blocked and the blood unable to flow.
It was reasoned that some illnesses could be cured by unblocking the channels, so patients would be given emetics to make them vomit the contents of their stomachs or purgatives (laxatives) to make them excrete the contents of their bowels. Bleeding from the veins was also used to reduce the amount of blood and so increase the flow in the channels. Although this was a practical theory as to the cause of disease, treatment was still accompanied by religious ritual.
Bloodletting was commonplace even in Europe. It was believed that by removing the blood, many diseases or illnesses could be removed from the body; even since 400BC it was considered by the Greeks to be a remedy for the balancing of the four humors.