Let's look at a real world example of
the scientific method. We'll use the Broad
Street pump cholera epidemic in order to
explore how the scientific method works.
First some background - cholera is a
bacterial infection of the small bowel
caused by the bacteria Vibrio cholerae.
The small bowel has water pumps that add
water to the intestinal contents. When
the food moves past, the pump shut
down.  The cholera bacteria makes a toxin that prevents the water pumps from
turning off - the victim rapidly loses a
massive amount of water through diarrhea
and may die from dehydration.  Cholera can kill a healthy human being in a matter
of hours.  Though primarily a disease of
third world countries today.
cholera was common in Europe and the
Americas in the eighteen hundreds. As
many as half of the Pawnee nation
and two thirds of the southern Cheyenne
died of Cholera between 1849 and 1852. 
President James K Polk is thought to
have died of cholera.
Jon Snow was a physician in London in
the eighteen fifties -
no not that Jon Snow ... this Jon Snow. At
that time people thought disease was the
result of miasmas - or bad air -  in
fact the word malaria is Italian for bad air.
 
This was before the germ theory was
established, so people thought living
near a swamp was dangerous because of
the bad odors emanating from it.
Dr. Snow made several observations of
how cholera spread and decided it could
not be spread by bad air-
He was soon able to test this idea. In
the eighteen fifties, Soho's population
increased rapidly. It became the most
densely populated area of London. In the
Soho district cesspools were overflowing
due to a large population increase.
Since this was accompanied by foul odors, the city officials were concerned that
the bad air would cause disease.
Their solution was to drain the human
waste into the river Thames.  This got rid
of the smell, but unfortunately the
source of London's drinking water was
the river Thames! A serious outbreak of
cholera occurred in the Soho area . In
just a few weeks 4,000 people
became ill and 500 people died.
The scientific method for problem
solving consists of observation
-looking closely at the world around us
hypothesis - proposing an explanation
or a solution to the problem, and
experiment  -performing a test under
controlled conditions to see if the
explanation is correct.
Dr. Snow made a map of the outbreak
showing where each of the homes in which
someone had contracted cholera was
located.
He noticed the outbreak clustered around
a water pump at the intersection of
Broad Street and Cambridge Street, shown here by the blue circle on the map.
He also realized that the brewery
workers near the pump did not become ill.
He discovered that the workers are
allotted a certain amount of beer each
day and that they did not drink from the
pump.
So he proposed an explanation -
A solution to the problem.   He thought the pump was the source of the outbreak
not bad air.  Dr. Snow persuaded the
authorities to simply remove the handle
from the pump.
This ended the outbreak.  It was later
discovered that the well that the pump
drew water from was dug right next to
a cesspit.  When they examined the cesspit
they discovered that soiled diapers from
a baby that had contracted cholera were
washed into the cesspit and had leaked
into the well.
So we see that making an observation,
Constructing a hypothesis and doing an
experiment allowed Dr. Snow to show that
cholera was due to contaminated water
not bad air.  This is how the
scientific method works.
Thank you for your attention.
