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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  this procedure took
  这种技术只会
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  infective material only from very mild cases.
  从非常温和的病例身上提取感染性液体
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  That was--the selection then of cases
  也就是说 对于病例的谨慎选择
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  was one reason behind its success.
  是其成功之处之一
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  The infective matter also was made to enter the body through
  这些感染性的物质提取出来后也是
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  the skin, in a way that doesn't happen in
  穿过皮肤进入体内 这再自然情况下是
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  nature, and,
  不大可能发生的
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  for reasons that aren't understood,
  而且因为不知名的原因
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  attenuates the virulence of the virus.
  这会使病毒的病毒性减弱
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  So, the portal of entry into the body
  也就是说 进入身体的入口
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  also seems to have made a difference.
  似乎也影响了这种技术的效果
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  And lastly, for all that one knows,
  最后 据我们所知