04 Dec The miasma theory
Hippocrates (460-377 BC) was the first who tried to find a scientific explanation for disease with the theory of the four humors (yellow bile, black bile, phlegm and blood) in the body, which are in balance in healthy beings but out of balance in a sick person if there is an excess of one of the humors. Galen (129-216 AD) expanded on the humoral theory by examining the bodies of people who had suffered a violent death to determine whether they conformed to the theory. The miasma theory of contagion, particularly in cholera, plagues and malaria, is based on the humoral theory of Hippocrates and Galen. It was a commonly held belief for over 15 centuries that contracting one of these diseases, among others, was the result of an imbalance in the humors due to poisonous vapors (miasma) coming from decomposing organic material (waste, manure, cadavers, etc.). The air had to be purified in order to be cured, which is how the practice of burning flowers and aromatic unguents to purify the air became widespread. The miasma theory enjoyed widespread consensus during both the Roman era and the Middle Ages, and also among many doctors until the first half of the 19th century. The miasma theory provided a plausible explanation for the deteriorating hygiene in cities and fetid odors emanating from drains during the cholera outbreak at that time, especially because there were fewer cholera outbreaks in areas where the air was not fetid from drain vapors. The medical community was mistaken, however, because it was not the toxic vapors that spread cholera but water contaminated with cholera bacteria and poor hygiene. The miasma theory also caught hold Italy, where Filippo Pacini’s discovery of the cholera bacillus was largely ignored due to the steadfast belief in it. In Italy, the miasma theory was also associated with malaria, which takes its name from the “mala aria”, meaning bad air in Italian, from the marshes where mosquitos live and which are actually the vectors of the Plasmodium parasites that cause malaria.