来自《耶鲁大学开放课程：1600年后西方社会的流行病 第7集 第7集》

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  an Act of 1840 that
  1840年法案
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  provided for free infant vaccination.
  为婴儿提供免费接种
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  And from that time, the annual toll from smallpox
  从那以后 每年因天花而死亡的人数
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  began to plummet, despite the fact that the
  开始直线下降 即便在十九世纪
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  nineteenth century provided conditions that would have been
  各种环境都适宜天花病的传播泛滥
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  favorable to promoting the disease: improved and speedy
  改善的快速交通
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  transport, with steamships,
  比如蒸汽船
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  canals and the railroads; crowding with a population that
  加上运河和铁路 大量流动性强
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  was ever more mobile, massive growth and urbanization
  增长快速的人口 城市化
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  and large cities.
  还有许多大城市
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  And those changes and
  这些变化
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  advances were reproduced across Europe
  和进步在欧洲和北美