万物简史 第448期:小生物的世界(19)

 Anyway, getting sick is a sensible response to infection. 生病正是对感染的一种能感觉到的反应。

Sick people retire to their beds and thus are less of a threat to the wider community. 病人躺在病床上，因此减少了对更多人的威胁。

Because there are so many things out there with the potential to hurt you, 由于外界有许多东西可能会伤害你，

your body holds lots of different varieties of defensive¹ white cells—some ten million types in all, 因此你的身体拥有大量各种各样的白细胞——总共大约有1000万种之多，

each designed to identify and destroy a particular sort of invader². 每一种的职责分别识别和消灭某种特定的入侵者。

It would be impossibly inefficient³ to maintain ten million separate standing⁴ armies, 要同时维持1000万支不同的常备军，那是不可能的，也是无效率的，

so each variety of white cell keeps only a few scouts⁵ on active duty. 因此每种白细胞只留下几名哨兵在服现役。

When an infectious agent—what's known as an antigen—invades, 一旦哪个传染介体——即所谓的抗原——前来侵犯，

relevant scouts identify the attacker and put out a call for reinforcements of the right type. 有关的哨兵认出了入侵者，便向自己的援军发出请求。

While your body is manufacturing these forces, you are likely to feel wretched. 当你的身体制造那种部队的时候，你就可能会觉得很不舒服。

The onset⁶ of recovery begins when the troops finally swing into action. 而当那支部队终于投入战斗的时候，康复就开始了。

White cells are merciless and will hunt down and kill every last pathogen they can find. 白细胞是毫不留情的，会追击每个被发现的病原菌，直到把它们最后消灭。

To avoid extinction⁷, attackers have evolved two elemental strategies. 为了避免覆灭的命运，进攻者已经具有两种基本的策略。

Either they strike quickly and move on to a new host, as with common infectious illnesses like flu,  它们要么快速进攻，然后转移到一个新的寄主，就像感冒这样的常见的传染病发地样；

or they disguise themselves so that the white cells fail to spot them, as with HIV, the virus responsible for AIDS, 要么乔装打扮，使白细胞无法识别自己，就像导致艾滋病的人体免疫缺陷病毒那样。

which can sit harmlessly and unnoticed in the nuclei⁸ of cells for years before springing into action. 那种病毒可以在细胞核里无害地停留几年而不被发觉，然后突然之间投入行动。

1 defensive   

adj.防御的；防卫的；防守的

参考例句：

• Their questions about the money put her on the defensive.他们问到钱的问题，使她警觉起来。
• The Government hastily organized defensive measures against the raids.政府急忙布置了防卫措施抵御空袭。

2 invader   

n.侵略者，侵犯者，入侵者

参考例句：

• They suffered a lot under the invader's heel.在侵略者的铁蹄下，他们受尽了奴役。
• A country must have the will to repel any invader.一个国家得有决心击退任何入侵者。

3 inefficient   

adj.效率低的，无效的

参考例句：

• The inefficient operation cost the firm a lot of money.低效率的运作使该公司损失了许多钱。
• Their communication systems are inefficient in the extreme.他们的通讯系统效率非常差。

4 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

5 scouts   

侦察员[机，舰]( scout的名词复数 )； 童子军； 搜索； 童子军成员

参考例句：

• to join the Scouts 参加童子军
• The scouts paired off and began to patrol the area. 巡逻人员两个一组，然后开始巡逻这个地区。

6 onset   

n.进攻，袭击，开始，突然开始

参考例句：

• The drug must be taken from the onset of the infection.这种药必须在感染的最初期就开始服用。
• Our troops withstood the onset of the enemy.我们的部队抵挡住了敌人的进攻。

7 extinction   

n.熄灭，消亡，消灭，灭绝，绝种

参考例句：

• The plant is now in danger of extinction.这种植物现在有绝种的危险。
• The island's way of life is doomed to extinction.这个岛上的生活方式注定要消失。

8 nuclei   

n.核

参考例句：

• To free electrons, something has to make them whirl fast enough to break away from their nuclei. 为了释放电子，必须使电子高速旋转而足以摆脱原子核的束缚。
• Energy is released by the fission of atomic nuclei. 能量是由原子核分裂释放出来的。