[1] slow at first to abandon the idea

1 On a summer’s day in 1854, as thousands of
Londoners were fleeing their homes to escape a deadly outbreak of cholera, English
doctor John Snow risked his life by deliberately walking into the center of the
outbreak. His aim was to gather data about the epidemic, and to prove his
theory about its cause.


2 By the mid-nineteenth century, London had grown
to become the world’s largest city, with over two million inhabitants. But
there was a downside: it was a city of inequality, with thousands of poor
people living in terrible conditions, especially in the crowded inner-city
areas. Many people lived alongside pigs, cows, and other livestock; raw sewage
was common on the streets and in the river. Cholera epidemics were frequent, including
two outbreaks in 1832 and 1849 that killed over 14,000 people. At that time,
people thought that the causes of cholera had to do with “bad air.” However, John
Snow proposed a different theory: he believed the disease was actually spread
through water.

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3 With the help of a minister who was
well-connected to local residents, Snow conducted interviews and gathered
information. He recorded the deaths and where they occurred. He then used the data
to create a map that showed the number of deaths, according to their location. He
drew black lines to represent deaths at each address. Looking at the map, a
pattern was immediately clear—a large number of deaths had occurred in one area,
and nearly all of them were located near a particular water pump.


4 With this evidence, Snow managed to convince
local government officials to close the pump, helping bring the epidemic to an
end. He later found out that the pump was extremely close to an area used for
sewage, and that the sewage had started to contaminate the well water. This
supported the statistics he had compiled that showed a connection between the
number of cholera cases and the quality of water sources.


5 The government was slow at first to abandon the
idea that cholera came from bad air. Gradually, however, more and more officials
came to believe in Snow’s theory. By the time the next cholera outbreak
occurred in 1866, most officials were convinced. The government instructed
people in the affected area to boil their water, and the outbreak stopped. There
has not been a cholera outbreak in London since.


6 Snow’s legacy lives on today. Because of his
work, basic improvements were made in the water systems of London, benefitting
all the city’s residents. His ideas also led to improvements in public health
around the world. In addition, Snow helped change people’s opinions of cities. In
his lifetime, most people believed that the problems of bad sanitation, overcrowding,
and disease were impossible to control in cities with large populations. However,
Snow showed that even serious urban problems could be solved using a reasoned
approach and objective data. Thanks to him, people around the world now take it
for granted that cities can safely support many millions of people.