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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  susceptible adults who could fall ill of the disease.
  易得病的成人越来越多
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  It was also true that European cities in the early modern era
  早期现代欧洲城市的运作
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  were so unhealthy
  都非常不健康
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  that they sustained or expanded their population,
  以至于他们得靠大量外来人口涌入
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  not by growth from within,
  而不是自身人口增长
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  but by a constant influx of people from without.
  来保持及扩大人口数量
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  Peasants driven off the land,
  农民也许由于饥饿或战乱
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  perhaps by hunger or warfare,
  寻求工作或田地收成不好
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  or the search for work, failed harvests.
  而离开自家的土地
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  And these newcomers, in large numbers,
  而那些大量的新移民
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  to use contemporary medical jargon,
  用当代医学术语来说
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  were immunologically naive.
  他们免疫力一片空白