Snake poison

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 the 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 (树眼镜蛇) and the cobras (眼镜蛇) and their venom is called neurotoxic. Vipers (adders) and rattlesnakes (响尾蛇) 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.

saliva / səˈlaɪvə / Saliva is the watery liquid that forms in your mouth and helps you to chew and digest food. 唾液
defy / dɪˈfaɪ / If something defies description or understanding, it is so strange, extreme, or surprising that it is almost impossible to understand or explain. 使不可能 (理解或解释)
prey / preɪ / A creature’s prey are the creatures that it hunts and eats in order to live. 猎物
tussle / ˈtʌsəl / If one person tussles with another, or if they tussle, they get hold of each other and struggle or fight. 扭打
Carnivore 食肉类
vertebrate / ˈvɜːtɪˌbreɪt / A vertebrate is a creature that has a spine. Mammals, birds, reptiles, and fish are vertebrates. 脊椎动物
concoct / kənˈkɒkt / If you concoct something, especially something unusual, you make it by mixing several things together. 调制
potency / ˈpəʊtənsɪ / The potency of a drug, poison, or other chemical is its strength. (毒品、药品等的) 效力
arsenic / ˈɑːsənɪk / Arsenic is a very strong poison that can kill people. 砒霜
venom / ˈvɛnəm / The venom of a creature such as a snake or spider is the poison that it puts into your body when it bites or stings you. (蛇或蜘蛛等分泌的) 毒液
viper / ˈvaɪpə / A viper is a small poisonous snake found mainly in Europe. 蝰蛇
primitive / ˈprɪmɪtɪv / Primitive means belonging to a very early period in the development of an animal or plant. 原始的
how it came about that xxx
Over the periods 经过漫长时间
was converted into xxx 演化成xxx
xxx to a xxx is xxx xxx对xxx来说
it enables it to xxx 他使得xxx能够xxx
it would be an assistance to xxx 能够从中受益
a two-edged weapon 双刃剑
be that as it may 不过
xxx,however, xxx