We thought smells made you sick, so we cleaned up the wrong things
You wouldn’t want to have lived in 19th century London. In the 1830s, epidemics of typhoid, influenza, and particularly cholera decimated the city. According to London’s Science Museum, it was so bad that even the upper class started to sit up and take notice of the squalor that the city’s poor were living in. Behind it all was the miasma theory of disease transmission, which basically meant that it was the bad-smelling air that was making people sick and dead. That was completely wrong, of course. But this misunderstanding actually had an incredibly positive impact on the world as a whole.
The miasma theory led London to make improvements in sanitation, drainage, and ventilation, and that’s important stuff for a civilized society. It didn’t happen overnight — 1858 was the year of the Great Stink, and we’ll leave that to your imagination — but there was still a problem. After the cleanup, people wouldn’t accept that bad smells didn’t make you sick.
In the 1850s, an anaesthetist named John Snow theorized that the cholera that killed so many citizens wasn’t a stink, but actually a water-borne contagion. But the miasma theory was so widely accepted that no one believed him. He died in 1858, and people were still stamping their feet and firmly insisting that it was the air.
The miasma theory hung in there until 1892, and according to Buckinghamshire Chilterns University College lecturer Stephen Halliday, it wasn’t until a cholera outbreak in Hamburg, Germany, didn’t spread to London — in spite of London’s still-somewhat stinky air — that people started thinking that maybe Snow had been onto something after all.