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听写训练营Day41

听写训练营Day41

作者: 葉鴻 | 来源:发表于2019-04-01 22:33 被阅读0次

    Let's have a quick look at a bit of history, the discovery of vaccination to boost the body's immune system by making it sensitive to particular disease causing bacteria was made by an eighteenth-century English doctor called Edward Jeanne, he noticed that survivors of smallpox, a common but extremely dangerous disease, never contracted the disease a second time. In other words, they were immune, he studied a similar disease in cows called cowpox and realized that people in contact with the infected cows became ill with symptoms resembling smallpox. However, this disease was quite mild by comparison and those who contracted cowpox were then immune to smallpox, he conducted an experiment by injecting a child with a small amount of pus taken from a cowpox pustule. The child subsequently became ill but soon recovered,  later, he injected the child with pus from a smallpox pustule and the child did not get sick, he had developed immunity to the more dangerous disease, then antibodies produced to fight the cowpox bacteria had been able to fight off the smallpox bacteria.

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