The Black Plague is caused by a bacterium, called yersinia pestis. It was discovered and named in the 1890s, during the third pandemic of bubonic plague.

Until the discovery of bacteria, physicians, and people in general, had very different ideas of what being sick meant, and therefore also what being healthy meant.

The prevalent ideas of what constituted health and disease originated in Ancient Greece and Rome, with Hippocrates and Galen.

These same ideas would remain dominant until the end of the 1800s, after the discovery of bacteria.

No matter how wrong these ideas might seem in the light of modern science, we cannot expect to understand how people of the past reasoned and acted, when confronted with something as disastrous as the plague, without examining how they perceived disease and health.

Humours

The main idea was, that the human body contained four essential liquids, which in a healthy person were in balance.

They were called humours, and they were blood, black bile, yellow bile and phlegm.

Physicians made various associations of the four humours with the four seasons, with the four basic elements in the ancient Greek world-view (earth, water, air and fire), with different internal organs and with types of personality, temperament or complexion.

For example, blood was considered hot and wet, associated with spring, air, the liver, and a sanguine disposition.

Disease

If something brought the four humours out of balance, disease and sickness followed.

Different diseases corresponded to different combinations of excess or deficiency of one or more of the four humours.

The main skill of a physician was to understand, based on the conditions of the patient, which humours were in excess or in deficiency, and to devise a treatment to restore the balance.

For example, a patient with a fever, and therefore sweaty, was hot and wet, which corresponded to an excess of blood. A possible cure was bloodletting with leaches, to restore the correct balance of blood with other humours.

Miasma

If a person had a wound or abscess, it was fairly easy to interpret what caused the imbalance of the humours. The cause was visible.

With contagious diseases, it wasn’t so simple, as persons could fall ill with no clearly visible cause.

What had then caused the imbalance of their humours?

This was explained by miasma, a Greek word which means impurity or pollution.

Miasma (sing. miasmata) were something invisible or imperceptible, which, if it entered the human body somehow, would cause an imbalance of the humours and therefore disease.

Different kinds of miasma caused different types of imbalances, and therefore different diseases.

Consequently, if a space — say, a house or a ship — was full of miasma, those who spent time there were likely to get the same illness. This explained how entire households or ship crews could come down with the same disease, even in the absence of directly physical contact between some of them.

In the model, contagion was seen more as a kind of environmental problem.

Naturally, the people of the past observed person-to-person contagion. They settled on the explanation that one person could pass a disease to another because the miasma had attached to the person’s body or to their clothes.

The origin of miasma

All this just led to the next question, of where did miasma come from? Why were they sometimes there, and sometimes not.

The accepted idea was, that miasma generated spontaneously in certain conditions.

The belief was that the miasma appeared in unburied cadavers in decomposition, in rotting rubbish, and more in general, in foul smelling places. Miasma were not considered a reproducing living organism, but rather something that spontaneously appeared if the conditions were right.

Consequently, the appearance of miasma became associated with things and places that smelled bad.

The disease of malaria, caused by a parasite which spread through mosquito bites, was common around swamps and wetlands, where mosquitoes could easily breed. Such swamps also smelled bad, so people named the illness mal aria — literally ‘bad air’.

An interesting aside is that within the theory of miasma, there is no contagion. The disease doesn’t move from one individual to another by some kind of transmission.

The image on the right is an illustration from a collection of medical writings, published in 1495.

The physician, dressed in red with wide sleeves, is holding a sponge soaked in vinegar in front of his nose and mouth, to protect himself from the miasma around the patient.

Two assistants are purifying the air with the fumes of long torches, burning incense, scented oils and wood of juniper and rosemary.

The spread of disease was an environmental problem because people get sick by exposure to miasma in a polluted environment. To prevent the disease, the environment had be purified.

Fighting miasma

If the miasma appears in foul smelling environments, how can such a place be purified?

On a very basic level, ventilation. Simply have the miasma blow away, by replacing smelly air with fresh air.

To prevent miasma from appearing, the sources of stench and foul smells were removed. Rotting rubbish were disposed of, and the corpses of the dead buried quickly, or taken away, as was common during outbreaks of the plague.

The next step was to replace the bad smells with something more pleasant. The fumes of fires were commonly used, which was called ‘per-fuming’, hence the word perfume.

Other means of replacing foul smells were incense, vinegar, ambergris, herbs, scents of all kinds, and what we would call perfumes today.

The medicines of the time, such as theriac — or Venice treacle — were made of substances with strong smells and flavours.

Ventilation and fumigation

For us, with our baggage of modern science and technology, the idea of miasma might sound ridiculous, but that is entirely on our arrogance.

The people of the past weren’t stupid. They had to deal with existential problems like the plague without our scientific knowledge, and they very often did quite a good job. The main proof of that is that we’re here.

The Venetians created the procedures used in the lazzaretti — and in the city during outbreaks — from the concept of miasma, especially for cleansing the merchandise from infected ships.

Many of the procedures the Venetians applied in the lazzaretti actually worked, at least to some extent.

For example, the main building on the Lazzaretto Nuovo, called the Tezon Grando (the big warehouse) was a building with open arches all along the sides, so the wind could blow straight through. Ventilation served to keep the air inside clean and healthy for workers who had to do the dangerous job of washing and cleaning objects from infected ships.

Often they would make bonfires of juniper and rosemary just outside the building, and have the fumes waft through the inside of the building, again to purify the environment both to assist the cleansing of the merchandise and to keep the workers safe.

In Venice, it was common for shops to have a bowl of vinegar on the counter, where the coins would be cleansed.

The use of incense in some church rites is also related to the ideas of miasma.

Did it work?

Yes, it did, at least partly.

The plague could spread through airborne particles, so ventilation would have an effect.

Cotton, silk and the resulting threads, fabrics and clothes were a substantial part of Venetian trade. The fleas, which are part of one way of transmission of the bacteria, can live in such goods. Fumigating the goods will cause the fleas to scamper. Exposing the textiles to sunlight would also help, as ultraviolet light kills germs.

A procedure of fumigation, applied to the empty ship, would cause the rats on board to flee. Consequently, the ship would be safer afterwards, which could be observed.

The plague stricken houses in Venice were systematically fumigated.

Likewise, treating metallic objects with vinegar will have a positive effect. Not because vinegar has a pleasant smell, but because it is a natural disinfectant.

This was, for example, how persons in quarantine on the Lazzaretto Nuovo could pay for better food or accommodation. They would drop their coins in a bowl of vinegar, whence the guards could then retrieve the coins.

Doctors would hold a sponge soaked in vinegar up to their face when seeing patients suspected of having the plague, thus keeping their hands and face disinfected.

Right result, but …

It is sometimes possible to get to a ‘correct’ result by a ‘wrong’ method.

The Venetians of the past, based on their perceived truth (the belief in miasma), drew some logical conclusions, acted accordingly, and observed that sometimes it had a positive effect. It is then only natural to feel confirmed that the point of departure, the belief in miasma as the cause of disease, was, in fact, correct.

Not every conclusion drawn from faulty premises will be correct.

The archaeological digs on the Lazzaretto Nuovo have yielded a huge number of ancient pipes. Smoking tobacco offers some gratification on a biological level, but for believers in miasma it also offers protection from disease by purifying the air, not only for the smoker but also for those around them.

The idea helped the Republic of Venice protect itself against the plague.

Western medicine today

The belief in miasma persisted until the end of the 1800s, and it helped healthcare progress in many ways. Florence Nightingale, for example, used it to promote better hygiene in hospitals.

Western medicine was based on these ideas for two millennia, and such ancient beliefs don’t die easy. The paradigm lingered until the early 1900s, but as vaccines and antibiotics offered much better treatments, and within the scientific world, the belief in miasma disappeared.

Not necessarily so in popular culture, where these ideas still persist, even in less evident forms.

Many such misconceptions linger. Plenty of people still believe you can ‘catch a cold’ by exposure to freezing air, when the common cold is actually a virus infection.

Illustrations

The illustrations above are from Brunschwig (1500), Brunschwig (1500) and Iohannes de Ketham (1495).

---