John Snow was a famous doctor in London-so expert,indeed,that he attended Queen Victoria as her personal physician.But he became inspired when he thought about helping ordinary people exposed to cholera.This was the deadly disease of its day.Neither its cause nor its cure was understood.So many thousands of terrified people died every time there was an outbreak.John Snow wanted to face the challenge and solve this problem.He knew that cholera would never be controlled until its cause was found.
He became interested in two theories that possibly explained
how cholera killed people.The first suggested that cholera multiplied in the air.A cloud of dangerous gas floated around until it found its victims.The second suggested that people absorbed this disease into their bodies with their meals.From the stomach the disease quickly attacked the body and soon the affected person died.
John Snow suspected that the second theory was correct but he needed evidence.So when another outbreak hit London in 1854,he was ready to begin his enquiry.As the disease spread quickly through poor neighbourhoods,he began to gather information.In two particular streets,the cholera outbreak was so severe that more than 500 people died in ten days. He was determined to find out why.
First he marked on a map the exact places where all the dead people had lived. This gave him a valuable clue about the cause of the disease.Many of the deaths were near the water pump in Broad Street(especially numbers 16,37,38and40).He also noticed that some houses(such as 20 and 21 Broad Street and 8and 9 Cambridge Street)had had no deaths.He had not foreseen this,so he made further investigations.He discovered that these people worked in the pub at 7 Cambridge Street.They had been given free beer and so had not drunk the water from the pump.It seemed that the water was to blame.
Next,John Snow looked into the source of the water for these two streets.He found that it came from the river polluted by the dirty water from London.He immediately told the astonished people in Broad Street to remove the handle from the pump so that it could not be used.Soon afterwards the disease slowed down.He had shown that cholera was spread by germs and not in a cloud of gas.
In another part of London,he found supporting evidence from two other deaths that were linked to the Broad Street outbreak.A woman,who had moved away from Broad Street,liked the water from the pump so much that she had it delivered to her house every day. Both she and her daughter died of cholera after drinking the water.With this extra evidence John Snow was able to announce with certainty that polluted water carried the virus.
To prevent this from happening again,John Snow suggested that the source of all the water supplies be examined.The water companies were instructed not to expose people to polluted water any more.Finally "King Cholera"was defeated.