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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  So, the idea developed that it might be a wise measure to
  于是人们就慢慢有了一个想法
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  induce a mild case of smallpox artificially,
  或许以人为方式植入温和化的天花病
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  to protect a person, or especially a child,
  可以保护一个人 尤其是孩子
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  from the risk of acquiring a naturally occurring but severe
  不受自然获得的严重致残致命版
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  and life-threatening or maiming case.
  天花病的威胁
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  And the practice that resulted was called variously
  从而得出的方法被称为接芽
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  inoculation, variolation, or,
  种人痘
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  in a gardening metaphor, engrafting.
  或者用园艺的语言说 就是移植
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  There were variations, but the major technique was
  移植的方法多样 不过主要环节都是
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  that liquid material from a smallpox pustule--
  取天花病人脓包中的液体
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  you saw those last time--
  上次你们见过的那种液体
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  of a patient selected for having a
  液体要适量 不能超过温和化的天花病