oxygen

选自英语文摘，难度系数较高。

Can Oxygen Be Toxic?
In order for us to live we must have oxygen, so how can it be bad for us? Today we explain how oxygen can be toxic.
Toxic? Really?
Unbeknown to most people, too much oxygen can be toxic. After several days of breathing nothing but pure oxygen, you’d begin to experience nausea, dizziness, muscle twitches, and convulsions. You might even die.

Ironically, too much oxygen actually inhibits ventilation and ends up slowing down the delivery of oxygen to your body’s tissues. Another problem is that certain tissues, like the lining of the lungs and the walls of the arteries, are very sensitive to oxygen. The cornea is also very sensitive to oxygen; you may have heard of people who have gone blind because, as newborns, the oxygen levels in their incubators were too high.

Oxygen Molecules
Scientists aren’t really sure why oxygen affects the body this way. Some think it has to do with a special form of the oxygen molecule which bonds with the proteins and membranes in the lining of the lungs, and ends up destroying them. In other words, with too much oxygen around, your insides begin to oxidize. 

氧气有毒吗？
氧气是我们生存所必需的，所以它怎么会对我们有害呢？今天我们来解释为什么说氧气有毒。

有毒？真的？
多数人都不知道，过多的氧气是有毒的。只呼吸纯氧几天之后，你会觉得恶心，头昏眼花，肌肉痉挛，抽搐。甚至你可能会死亡。

讽刺的是，过多的氧气实际上会阻止空气流通，最终会减慢氧气在身体组织中的输送速度。另一个问题是，特定的组织，例如肺粘膜，动脉壁都对氧气很敏感。眼角膜也对氧气很敏感，你或许听说过有人在婴儿时期因为恒温箱中的氧气量过高而失明的事情。

氧气分子
科学家们不是很确定为什么氧气会这样影响身体。一些认为氧气分子以特殊的形式与肺粘膜上的蛋白质和细胞膜结合，最终破坏它们。换句话说，周围的氧气过多，身体内部会开始氧化。