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1、 Antigen and Antibody（抗原和抗体） The human body is quick to (1) recognize foreign organism that enter it. ”Foes” must be attacked or otherwise got rid of. （人体能迅速辨认出进入的外来生物。这些外来的“敌人”一定会受到攻击或被用其他方式摆脱。）The most common of these foes are (2) viruses, bacteria, and other microscopic organisms . The body recog
2、nizes these foes by the chemicals within them called antigens.（最常见的这些敌人是病毒、细菌和微生物。人体通过它们内部称为抗原的化学物质来辨认它们） To (3)counteract there foreign invaders, body produces its own chemicals , protein molecules called (4) antibodies. Each kind of antigen causes the production of a specific kind of antibody .Ant
3、ibodies appear in the 5）body fluids such as blood and lymph and in the bodys cells .（为了抵御外来的入侵者，机体产生自身的化学物质，一种称为抗体的蛋白质分子。每一种抗原导致人体产生一种特殊的抗体，抗体出现在体液中，比如血液和淋巴液，也出现在身体的细胞里。） Doctors learned to make use of the antibody system for defense long before they had any idea that antibodies exist.（医生在发现抗体之前很久就学
4、会了利用抗体系统来防御疾病。） As early as 1796 , Edward Jenner ,an English country doctor , discovered that if he gave people a (6)case of mild disease cowpox , he prevented them from (7)getting the serious disease smallpox .（早在1796年，一个叫爱德华*詹纳的英国乡村医生发现如果他让人患上比较轻的牛痘，他们就不会患上严重的天花疾病。）What Jenner did not know is that
5、 the diseases are caused by (8)closely related viruses . They are so closely related that the cowpox antibody will counteract the smallpox antigen .（詹纳不知道的是这两种疾病是由密切相关的病毒引起的，它们如此密切相关以至于牛痘抗体可以消灭天花病毒。） Injecting an antigen to (9) start the production of antibodies is now called vaccination. (It is one
6、 kind of immunizationmaking person (10) immune .)（注射抗原使机体产生抗体现在被称为接种。这是免疫接种的一种，使人具有免疫力）The antigen injected is a (11) vaccine . These terms are based on vacca, the Latin word for “cow” ,because Jenners vaccine was made from the cowpox virus .（注射的抗原是一种疫苗。这些专业术语都是基于拉丁语中的“牛”的词语vacca，因为詹纳的疫苗是从牛痘病毒制成的。）
7、Today doctors know of several ways that people become immune to diseases . Some people (12)inherit a natural resistance to certain diseases .（今天，医生知道许多方法让人对疾病有免疫力。有些人继承了对某些疾病的抵抗性） Over the years they build up an immunity that keeps them from ever getting certain diseases. But most antibodies are (13
8、) acquired only after the body has been (14) exposed to a known antigen. （多年来，他们建立起来的免疫力让他们远离曾经患过的疾病。但大多数抗体只有在人体暴露于已知的抗原中后才获得。）The antigen may be carried by some organism that enters the body (15) on its own, or the antigen may be artificially (16) injected with a needle .（抗原可以由自主进入人体的生物携带，也可以用针进行人工
9、注射） Both antigens and antibodies are large molecules . Scientists believe that the antibody molecule combines with a particular antigen molecule , the two(17) fitting like a key and a lock . In the chemical reaction that takes place, the antigen (18) loses its power to cause the disease（抗原和抗体都是大分子。科学家认为抗体只与特定的抗原结合，他们两个就像钥匙和锁。当这个化学反应发生，抗原就会失去引起疾病的能力。）