An ill wind indeed

The Black Plague, which wiped out perhaps a third of the population of Europe, demanded an explanation, and the medical establishment of the time responded as well as it could.

The most popular conjectures about the pestilence were variations on the miasmic theory of disease, an idea that went back at least to the ancient Greeks — that disease was essentially bad air. ("Miasma" was the Greek word for pollution.)

Hundreds of treatises about the epidemic survive, many of them written in the mid-14th century, when the plague was at its height. One written by members of the faculty at the medical school at the University of Paris, in response to a request from their king, Philip VI, mixed humoral and miasmic theories: The planets had aligned in such a way as to poison the air.

Another theory held that a series of earthquakes in Europe had released corrupt air from the middle of the earth. A third had the plague wafting in on noxious winds from the equator.

The cause of the plague was actually Yersinia pestis, a murderous bacterium spread by the bite of rodent fleas in the primary, "bubonic" phase, characterized by swollen lymph nodes and other symptoms. The plague can also be spread by infected droplets exhaled by its victims in a less common but deadlier "pneumonic" phase.

The plague was a catastrophe for Europe, but it did usher in reforms. It pushed the medical community toward a more professional approach to its practice, an increased emphasis on public health and the establishment of hospitals that would treat the sick, rather than merely warehouse them away from the healthy population, according to The Black Death: Natural and Human Disaster in Medieval Europe, by Robert S. Gottfried.

Frustration with the utter failure of the medical establishment to discern the pandemic's cause, stop its spread or treat it effectively helped create an environment from which the scientific method emerged.

The Black Plague and the siege of Caffa

The Black Death came to Europe in the 14th century, probably mostly aboard merchant ships from the Crimean peninsula in the Black Sea, though soldiers returning from late, intermittent Crusade-type forays likely contributed to the pandemic as well.

One early episode in this notorious outbreak of plague demonstrates that its victims had the misfortune to learn firsthand that the disease could be transmitted from person to person.

In 1346, a Tartar army laid seige to Caffa, a port in Crimea, now an autonomous republic just south of Ukraine. Caffa, now called Feodosija, was then held by Genoa, a mighty Italian city-state and commercial power. The seige lasted three years, and the residents and refugees in Caffa were in a bad way by the end. But then the Tartars began to die in great numbers from a horrific disease, and the tide appeared to be turning.

The remaining Tartars got the idea of catapulting the rotting corpses of their plague victims into the walled city of Caffa. Apparently, the Tartars' hope was that the "intolerable stench would kill everyone inside," according to an account by the Italian notary and writer Gabriele de’ Mussi. At the time, "miasmas," or noxious airs from rotting organic matter, were thought to be one source of disease.

Soon, even though the cadavers were dumped into the sea, people began to die in the besieged city. And then, the survivors began to flee.

De' Mussi writes:

Among those who escaped from Caffa by boat were a few sailors who had been infected with the poisonous disease. Some boats were bound for Genoa, others went to Venice and to other Christian areas. When the sailors reached these places and mixed with the people there, it was as if they had brought evil spirits with them: every city, every settlement, every place was poisoned by the contagious pestilence, and their inhabitants, both men and women, died suddenly. And when one person had contracted the illness, he poisoned his whole family even as he fell and died, so that those preparing to bury his body were seized by death in the same way.

De' Mussi was not an eye-witness to the events in Caffa. However, his account preserved not only the details of what has been remarked upon as an early instance of biological warfare, but also what the survivors learned about how diseases can be transmitted.