Doctors thought that there were four liquids in the body. These were blood, plegm (think of spit), black bile and yellow bile (the sort of stuff you squeeze from spots!)

These were called "the humours." It was thought that people became sick when they had too much of one humour.

An important part of the doctor's job was making sure that a patient's humours were all equal.

This could be done by making sure the patient lived properly. This meant not eating too much, not drinking too much alcohol and getting the proper amount of rest and exercise.

The doctor did have another way of treating this problem though...