The Hippocratic Corpus
For many centuries explanations for disease were based not on science, but on religion, superstition, and myth.
The Hippocratic Corpus was an early attempt to think about diseases, not as punishment from the gods, but as an imbalance of man with the environment. Although it was unsophisticated by today's standards, it was an important step forward. By considering the possibility that disease was associated with environmental factors or imbalances in diet or personal behaviors, the Corpus also opened up the possibility of intervening to prevent disease or treat it.
The Corpus looked at disease as an imbalance in natural forces or an imbalance in humours (or fluids): melancholy, phlegm, bile, and blood. Health depended on a proper balance of these humours. While crude, this concept of humours provided some sort of rationale for understanding health and disease. Greek physicians prescribed changes in diet or lifestyle and sometimes concocted drugs or performed surgery. An excess of the humour blood, for example, became the rationale for bloodletting, a practice that was followed for centuries (without any evidence of its efficacy).
Despite the contributions of the Corpus, medical and scientific progress in Europe was arrested for several centuries. The population grew, and cities became densely populated, but there was little attention to waste disposal and sanitation.These factors set the stage for endemic disease and periodic epidemics.
Those with too much blood were sanguine. Those with too much phlegm were phlegmatic. Those with too much yellow bile were choleric, and those with too much black bile were melancholic. The idea of human personality based on humors contributed to the character comedies of Menander and, later, Plautus.