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and solve this problem. He knew that cholera would never be controlled until its cause was found. He became interest ed 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 1845, he was ready to begin his enquiry. As the disease spread quickly through poor neighborhoods, he began to gather information. In two particular streets, the cholera out break 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. Th is gave him a valuable clue about the cause of the disease. Many of the d eaths were near the water pump in Broad Street (especially numbers 16,37, 38 and 40) . He also noticed that some houses ( such as 20 and 21 Broad Street and 8 and 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. Th ey 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 s ource 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 ...