Until perhaps the early 20th century, many people believed that miasma, some sort of corrupt air, was the cause of all sorts of diseases, especially the bubonic plague. In this post, I discussed some examples from the literature.
Yesterday, I read a 1673 paper from the Philosophical Transactions* that attempted to explain why there were frequent outbreaks of the plague in the 17th century Constantinople (present day Istanbul). The anonymous author offered 3 possibilities. The 1st was the large number of slaves that were brought to the city by ship from the Black Sea; the 2nd was the locals' habit of eating cucumbers and melons in the summer. Here is the 3rd possibility given the most weight:
But the Physitians generally conclude, That the Air of Constantinople is infected by the North-East winds, which blow commonly for 3 months, beginning about the Summer-solstice arising from unwholesome Marshes in Tartary and Muscovy, and passing over the Black Sea, (a place known to abound with Fogs,) bring with them certain dispositions tending to corruption; which working upon bodies already prepared by bad diet, may well be judged, they say to be the cause of this distemper.What exactly miasma was in general is not clear to me. It couldn't have a been just a wind, because wind is a very common and more often than not a benign atmospheric phenomenon. Miasma proper seems to have been associated with a visible change in air quality, such as a fog. Before a physical explanation for fog was developed**, it was probably seen as a mysterious, ominous happening; it often came at night and decreased visibility. The association of miasma with fog was natural (also see the previous post).
Interestingly, from our present-day perspective, the first 2 explanations given for the supposed prevalance of plague in Constantinople make more medical sense than the blowing of bad air over the city. The delivery of large numbers of slaves, many of whom were probably sick with various infectious diseases, must indeed have raised the incidences of the same diseases in the city, if not of the plague. At the same time, if the groundwater and the streams in and around the city were contaminated with human and animal wastes, then the consumption any produce watered with them, including cucumbers and melons, could cause gastrointestinal illness. In any case, many of the illnesses reported as cases of the plague back then may well have been other diseases.
*Anonymous. 1673. Some communications out of Turky, by persons residing there. Philosophical Transactions 8:6017.
**I don't know when that happened and even then most laypeople may have not understood it.