20 · 蛇毒
Snake Poison
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时代语境：本课关于毒液、血清和动物种类的概括反映成文年代；此处训练解释与比较的读法，不把课文中的分类或处理描述当作现代医学、生物学的完整结论。
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How it came about that snakes manufactured poison is a mystery. Over the periods their saliva, a mild, digestive juice like our own, was converted into a poison that defies analysis even today. It was not forced upon them by the survival competition; they could have caught and lived on prey without using poison, just as the thousands of non-poisonous snakes still do. Poison to a snake is merely a luxury; it enables it to get its food with very little effort, no more effort than one bite. And why only snakes? Cats, for instance, would be greatly helped; no running fights with large, fierce rats or tussles with grown rabbits—just a bite and no more effort needed. In fact, it would be an assistance to all carnivores though it would be a two-edged weapon when they fought each other. But, of the vertebrates, unpredictable Nature selected only snakes and one lizard. One wonders also why Nature, with some snakes, concocted poison of such extreme potency.
In the conversion of saliva into poison, one might suppose that a fixed process took place. It did not; some snakes manufactured a poison different in every respect from that of others, as different as arsenic is from strychnine, and having different effects. One poison acts on the nerves, the other on the blood.
The makers of the nerve poison include the mambas and the cobras and their venom is called neurotoxic. Vipers adders and rattlesnakes manufacture the blood poison, which is known as haemolytic. Both poisons are unpleasant, but by far the more unpleasant is the blood poison. It is said that the nerve poison is the more primitive of the two, that the blood poison is, so to speak, a newer product from an improved formula. Be that as it may, the nerve poison does its business with man far more quickly than the blood poison. This, however, means nothing. Snakes did not acquire their poison for use against man but for use against prey such as rats and mice, and the effects on these of viperine poison is almost immediate.
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整篇课文
How it came about that snakes manufactured poison is a mystery. Over the periods their saliva, a mild, digestive juice like our own, was converted into a poison that defies analysis even today. It was not forced upon them by the survival competition; they could have caught and lived on prey without using poison, just as the thousands of non-poisonous snakes still do. Poison to a snake is merely a luxury; it enables it to get its food with very little effort, no more effort than one bite. And why only snakes? Cats, for instance, would be greatly helped; no running fights with large, fierce rats or tussles with grown rabbits—just a bite and no more effort needed. In fact, it would be an assistance to all carnivores though it would be a two-edged weapon when they fought each other. But, of the vertebrates, unpredictable Nature selected only snakes and one lizard. One wonders also why Nature, with some snakes, concocted poison of such extreme potency.
In the conversion of saliva into poison, one might suppose that a fixed process took place. It did not; some snakes manufactured a poison different in every respect from that of others, as different as arsenic is from strychnine, and having different effects. One poison acts on the nerves, the other on the blood.
The makers of the nerve poison include the mambas and the cobras and their venom is called neurotoxic. Vipers adders and rattlesnakes manufacture the blood poison, which is known as haemolytic. Both poisons are unpleasant, but by far the more unpleasant is the blood poison. It is said that the nerve poison is the more primitive of the two, that the blood poison is, so to speak, a newer product from an improved formula. Be that as it may, the nerve poison does its business with man far more quickly than the blood poison. This, however, means nothing. Snakes did not acquire their poison for use against man but for use against prey such as rats and mice, and the effects on these of viperine poison is almost immediate.
蛇究竟是怎样产生毒液的，至今还是个谜。经过漫长的岁月，它们原本像人的唾液一样温和、具有消化作用的液体，变成了即使今天也难以分析透彻的毒液。这并不是生存竞争迫使它们发生的变化；不使用毒液，它们照样能捕食并生存，就像今天成千上万的无毒蛇一样。毒液对蛇来说，只是一种奢侈品：它让蛇几乎不费力就能获得食物，只需咬一口。可为什么偏偏是蛇呢？比如，猫如果有毒液，就会省事得多：不用追着又大又凶的老鼠搏斗，也不用与成年兔子厮打，只咬一口，就不必再费力。其实，所有食肉动物都能从中获益，尽管彼此争斗时，毒液会成为双刃剑。然而，难以捉摸的大自然，在脊椎动物中偏偏只选择了蛇和一种蜥蜴。人们也不免疑惑，为什么大自然让有些蛇拥有如此猛烈的毒液。
人们也许会以为，唾液转化为毒液经历的是同一种固定过程。事实并非如此。有些蛇产生的毒液，与另一些蛇的毒液在各方面都不同，就像砒霜与马钱子碱截然不同，产生的作用也不一样：一种作用于神经，另一种作用于血液。
产生神经毒液的蛇包括曼巴蛇和眼镜蛇，这类毒液被称为神经毒性毒液。蝰蛇、蝮蛇和响尾蛇产生的则是作用于血液的毒液，称为溶血性毒液。两类毒液都很可怕，但后者可怕得多。据说，神经毒液较为原始；打个比方，血液毒液像是根据改良配方制成的新产品。不管怎样，神经毒液作用于人体的速度，比血液毒液快得多。不过，这一点并不重要。蛇获得毒液，不是为了对付人，而是为了对付大小鼠类等猎物；蝰蛇的毒液对这些猎物几乎立即就能起效。
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译文依据整理稿，由本站按中文表达重新校订；解析据吴应时整理资料及首轮审校稿；词伙与练习提示为本站学习设计。原PDF第80—83页，2022年2月第2版。