How Cholera Was Beat

The title of Steven Johnson's book -- The Ghost Map -- was what prompted me to pick it up. I love maps, and this promised to be about a historical map.

Instead, it turned out to be the story of Dr. John Snow, considered the greatest doctor of all time. He created the world's first dosage manual -- for the use of chloroform and ether as anaesthetics during surgery -- after realizing that the dosage of a gas needed to depend on the ambient temperature. His obituary mentioned only his work on chloroform. But what he's remembered for now is for his work in tracking down the cause of cholera.

A part of the map referred to in the book title is on the left. Snow created the map to fight then-current misconceptions about cholera -- that it was spread through the air. The map shows the relationship between an infected water source (the pump) and the walking (not aerial) distance to the pump. He was also able to show that clumps of deaths far away from the pump were because someone in the household had a drink from the Broad Street pump. John Snow is now regarded the world's first epidemiologist.

The map was published in one of the two official reports of the cholera outbreak. The other report continued to blame the general stink of the neighborhood.

A couple of great vignettes from the book:

1. Because cholera was thought to be caused by the stink of cesspools, the urban reformers of the day built sewers to drain the cesspools directly into the Thames. Steven Johnson notes that this remedy actually made cholera outbreaks more likely because it was a guaranteed way to infect the entire populace with fecal matter. No bioterrorist, he says, could have come up with a more nefarious plan.

2. The waterborne theory of cholera did not win out immediately -- people continued to cling to the theory that it was due to bad air ("miasma"). When a second cholera outbreak happened a couple decades later, Snow was dead. But a convert to his theory named Whitehead was able to show that this second outbreak was due to an impure water supply from the Thames. At a parliament hearing on the subject, Whitehead fingered commercial interests for fighting the waterborne theory. Why? Because air was free, it could be blamed with impunity. But water delivery was commercial, and so the water corporations would try to muddy the scientific consensus. Interesting parallels to today's battles (on tobacco and on carbon-pollution) ...

But London did act, with one of the greatest engineering feats in history. London's sewer system was built, to flush the sewage indirectly into the sea. And there were no more cholera outbreaks. There's a wonderful book (by Stephen Halliday) about this feat and the brilliant engineer Bazalgette who brought it about. But I wasn't blogging when I read that book, so no summary to point you to.

Read the two books and you'll never think of big cities the same way again.

No comments:

Post a Comment