第20课

旁白 neutral

How in came about that snakes manufactured poison is a mystery.

蛇是怎样产生毒液的，这至今仍是个谜。

旁白 neutral

Over the periods their saliva, a mild, digestive juice like our own, was converted into a poison that defies analysis even today.

经过漫长的岁月，它们的唾液——一种像我们人类唾液一样的温和的消化液——变成了毒液，这种毒液即使在今天也无法分析其成分。

旁白 neutral

It was not forced upon them by the survival competition;

毒液并不是由生存竞争强加给它们的；

旁白 neutral

they could have caught and lived on prey without using poison, just as the thousands of non-poisonous snakes still do.

它们本来可以不用毒液捕食猎物而生存下来，就像成千上万的无毒蛇今天仍然在做的那样。

旁白 neutral

Poison to a snake is merely a luxury;

对蛇来说，毒液只是一种奢侈品；

旁白 neutral

it enables it to get its food with very little effort, no more effort than one bite.

它能使蛇毫不费力地获取食物，一口咬下去便大功告成。

旁白 neutral

And why only snakes?

为什么只有蛇有毒液呢？

旁白 neutral

Cats, for instance, would be greatly helped;

拿猫来说，毒液对它们会大有帮助；

旁白 neutral

no running fights with large, fierce rats or tussles with grown rabbits--just a bite and no more effort needed.

它们不必和凶猛的大老鼠追逐撕打，也不必和长大的兔子扭斗——只需一口咬下去，便不必再费力气了。

旁白 neutral

In fact, it would be an assistance to all carnivores though it would be a two-edged weapon when they fought each other.

事实上，毒液对所有的食肉动物都会有帮助，尽管在它们互相搏斗时，毒液会变成一把双刃剑。

旁白 neutral

But, of the vertebrates unpredictable Nature selected only snakes (and one lizard).

但在脊椎动物中，变幻莫测的大自然只选择了蛇（和一种蜥蜴）。

旁白 neutral

One wonders also why Nature, with some snakes concocted poison of such extreme potency.

人们也想知道，为什么大自然让有些蛇产生如此剧烈的毒液。

旁白 neutral

In the conversion of saliva into poison, one might suppose that a fixed process took place. It did not;

在唾液变为毒液的过程中，人们可能会认为发生了一个固定的过程。但事实并非如此；

旁白 neutral

some snakes manufactured a poison different in every respect from that of others,

有些蛇产生的毒液与另一些蛇的毒液在各个方面都不同，

旁白 neutral

as different as arsenic is from strychnine, and having different effects.

就像砷和士的宁的区别一样大，而且有不同的效果。

旁白 neutral

One poison acts on the nerves, the other on the blood.

一种毒液作用于神经，另一种作用于血液。

旁白 neutral

The makers of the nerve poison include the mambas and the cobras and their venom is called neurotoxic.

产生神经毒液的包括曼巴蛇和眼镜蛇，它们的毒液被称为神经毒素。

旁白 neutral

Vipers (adders) and rattlesnakes manufacture the blood poison, which is known as haemolytic.

蝰蛇（蝮蛇）和响尾蛇产生血液毒液，这种毒液被称为溶血性毒素。

旁白 neutral

Both poisons are unpleasant, but by far the more unpleasant is the blood poison.

两种毒液都不好，但更不好的是血液毒液。

旁白 neutral

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.

据说神经毒液是两种毒液中较原始的一种，而血液毒液，可以说，是改进配方的新产品。

旁白 neutral

Be that as it may, the nerve poison does its business with man far more quickly than the blood poison.

话虽如此，神经毒液对人起作用的速度比血液毒液快得多。

旁白 neutral

This, however, means nothing.

然而，这并不说明什么。

旁白 neutral

Snakes did not acquire their poison for use against man but for use against prey such as rats and mice,

蛇获得毒液并不是为了对付人，而是为了对付像老鼠之类的小动物，

旁白 neutral

and the effects on these of viperine poison is almost immediate.

蝰蛇毒液对这些猎物几乎能立即见效。