预习案一、introduction: john snow(1813-1858)was born and worked as a doctor in great britain. he was originally(原本，起初）anaesthetist(麻醉师）.he was so famous that he became the personal doctor for queen victoria at the births of her many children. four outbreaks of cholera in the 1830s and 1840s killed many people in england, in 1854, the most terrible outbreak of cholera which ever occurred in the kingdom began. it was so violent and sudden that 127 people around broad street died in the first three days. john snow wanted to face the challenge and solve the problem.at first he suspected(怀疑）the theory which suggested that people absorbed this disease into their bodies with their meals was correct.after many days of hard work, finally he found that the water from the polluted river
