Poliomyelitis, for example, emerged as an epidemic in the United States in the twentieth century; by then, modern sanitation was able to delay exposure to polio until adolescence or adulthood, at which time polio infection produced paralysis. Previously, infection had occurred during infancy, when it typically provided lifelong immunity without paralysis.
这句话前面和后面都看得懂，就是by then到paralysis之间，怎么看不懂到底说的是什么意思。请教NN给翻译一下。多谢！作者: himba 时间: 2004-7-19 09:31
A这是一个比较,in the twentieth century,直到成人才会被感染，而previously,在婴儿时期就被感染了作者: kuuiytt 时间: 2004-7-19 09:35
In analyzing the latter, scientists have discovered the importance of social and ecological factors to epidemics.。。。Another example is Lyme disease, which is caused by bacteria that are transmitted by deer ticks. It occurred only sporadically during the late nineteenth century but has recently become prevalent in parts of the United States, largely due to an increase in the deer population that occurred simultaneously with the growth of the suburbs and increased outdoor recreational activities in the deer’s habitat.
这是文中的另一个例子，说过去的程度没有现在的程度重，这与卫生条件是不相关的，看我贴的文章的第一句，说社会和生态是importance.
当然，delay exposure to polio 我也不是很理解，但是，按照作者的意思，肯定是现在比过去严重的。作者: ppp1 时间: 2004-7-19 09:38
