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新概念第四册Lesson 20 Snake poison

2021-07-12 16:06:00来源：网络

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　　Lesson 20

　　Snake poison

　　蛇毒

　　What are the two different ways in which snake poison acts?

　　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 manufacture 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.

　　JOHN CROMPTON The snake

　　New words and expressions 生词与短语

　　saliva

　　n. 唾液

　　digestive

　　adj. 助消化的

　　defy

　　v. 使不可能

　　analysis

　　n. 分析

　　prey

　　n. 被捕食的动物

　　fierce

　　adj. 凶猛的

　　tussle

　　n. 扭打

　　carnivore

　　n. 食肉动物

　　vertebrate

　　n. 脊椎动物

　　lizard

　　n. 蜥蜴

　　concoct

　　v. 调制

　　potency

　　n. 效力

　　conversion

　　n. 转变

　　arsenic

　　n. 砒霜

　　strychnine

　　n. 马钱子碱

　　mamba

　　n. 树眼镜蛇

　　cobra

　　n. 眼镜蛇

　　venom

　　n. 毒液

　　neurotoxic

　　adj. 毒害神经的

　　viper

　　n. 蝰蛇

　　adder

　　n. 蝮蛇

　　rattlesnake

　　n. 响尾蛇

　　haemolytic

　　adj. 溶血性的

　　viperine

　　adj. 毒蛇

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