Last we left John Snow, he had failed to convince the leading scientific
minds of his time that cholera was transmitted through fluid,
rather than through a miasma in the air. But he was far from done.
In 1850, he became one of the founding members of the
Epidemiological Society of London.
This was one of the first scientific medical societies to explicitly look
not only for a cure to a disease or a way to treat its symptoms,
but also to study the disease itself.
How is it transmitted? How does it propagate? What environmental factors
cause the disease to break out? In understanding these things, they could
help not only to cure a disease, but also to contain it.
Or perhaps even prevent it from happening in the first place.
So when cholera once a again returned to London in 1854, John Snow planned
to use all the tools his prodigious powers of logic availed him of
to finally and definitively show that this disease, which he had fought
all of his life, could be contained simply by keeping people away
from contaminated water.
But when the cholera outbreak of 1854 struck London, it appeared to follow
no rhyme or reason. It was a primal force.
It struck all over the city and it struck across the class divide.
So many in London, perhaps everybody in London except John Snow,
thought it to be random. Some trick of the constitution or some
predisposition caused those who fell ill to fall ill
and those who didn't to stay well. It had to be an act of fate or just dumb luck.
But Snow had a hypothesis and he planned to test it in one of the
grandest statistical experiments done to that day.
You see, he had his theory, the theory that cholera was transmitted through
water. But even though he'd proven it to HIS satisfaction, with his previous
experiment regarding houses on opposite sides of the street,
he knew he'd need further proof to convince the medical world.
So he began to look. He needed commonalities.
He needed something to link the seemingly random spread of the disease with water.
Then while going through municipal records, he found it. Eureka!
There it was! Just sitting in the books in front of him, staring him in the face.
The district he worked in, had its water supplied by two water companies:
the Southwark & Vauxhall water company and the Lambeth water company.
Both of them drew their water from the Thames river, but S&V and Lambeth had
one key dissimilarity that would make all the difference in the world.
One that may have been costing thousands of lives,
but one we could barely conceive of today.
You see, at the time, London not only had cesspools below houses
and household waste running through the streets, but also a sewer system
that flushed all of this waste to the nearest source of running water:
the Thames. All of the city's sewage was pumped right into the river
running through the middle of the city.
The river where most of its occupants got their drinking water from.
In a few years time, this would get so bad, that the smell of the river
would be unceremoniously labeled: "The Great Stink".
Which leads us right back to difference between Southwark & Vauxhall and
Lambeth. What was it that John Snow saw right there in those books
that caused his eureka moment? Well, S&V was getting their water
from downstream of where the sewage emptied into the Thames,
while Lambeth had recently moved their facilities above the sewage outflows.
He had the perfect case-study, the perfect A/B test.
If he was right about the mode of communication of cholera, all he'd
have to do is compare the infection rate from those served by S&V
to those served by Lambeth. He wrote:
"People of both sexes, of every age and occupation and of every rank and station,
from gentlefolks down to the very poor were divided into two groups
without their choice and in most cases without their knowledge.
One group being supplied with water containing the sewage of London
and amongst it, whatever might have come from the cholera patients.
The other group having water quite free from such impurity."
So, Snow began to canvas two of London's districts that had recently
been hit hard by the epidemic. At first he thought it would be simple:
He would go door-to-door, asking if anybody from that residence
had been afflicted and what water company they used.
Simple! But nothing is ever that simple.
Most residence didn't know what company they used.
They were just tenants, they hadn't contracted the water for their place.
Hm, what could he do? Ah! The landlords would know!
Armed with this thought, he traced the tenants back to their landlords
then used official documents to trace the landlords back to their homes
scattered throughout London. He madly dashed about the city, knocking on doors
standing in the hallways of the rich and powerful asking mad questions
about water companies and properties they didn't even remember they owned.
He was closer, but he needed more. Hm, what about the water itself?
Could the water tell him where it came from?
Perhaps now he was a mad man possessed of his errant, trying to make water talk.
But talk it did. He ran a chemical analysis on water samples from each
of the companies and found that S&V water contained 4 times as much salt
as the water from Lambeth. He raced back to all the houses whose
water source he couldn't yet ascertain and surely seeming mad,
asked them for a thimbleful of water, which he then put in a test tube
and brought back to his lab. And with that, he had it.
His records were complete. 38 of the 44 deaths that had occurred in that month,
had come from the S&V water.
You were 933% more likely to die just by having the wrong water company
pipe water to your house. There it was, that was the answer.
And that's what he would have found out if he had just had a few more weeks
to analyze his samples and tabulate his data.
But he was a doctor and his old foe wasn't gonna let him rest that easily.
Cholera struck again. At first it was a rumor,
then a few isolated cases he might be able to ignore.
Then on Tuesday morning the 4th of September,
He opened the paper and read these words:
In Broad street on Monday evening, when the hearses came round to
to remove the dead, the coffins were so numerous that they were put
on top of the hearses as well as the inside.
Such a spectacle has not been witnessed in London since the time of the Plague.
He was needed in a place called "Broad street".