单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,Lesson 20 Snake poison,How,it,came about that,snakes manufactured poison,is a mystery,Over the periods,经过很长时间，在,期间，在,过程中,their saliva,a mild,digestive juice like our own,was converted into,改变成,a poison that defies analysis even today,The solar cell can convert the energy of sunlight into electric energy.,It was not,forced upon,把,强加给某人,them by the survival competition;,they could have caught and,lived on,（,注：,live on,后面不可跟,sb.live off,后面可以跟,sb,或,sth,，意思分别是“靠什么人养活”和“靠什么活着”。）,prey,without using poison,含蓄条件句,just as,方式状语从句,the thousands of non-poisonous snakes still do,Poison to a snake is merely a luxury;,it,enables,it,to get,itsfood,with very little effort,no more effort than one bite,同位语,And why only snakes?,Cats,for instance,（省略,if they had poison,，含蓄条件句）,would be greatly helped;,no running fights with large,fierce rats or tussles with grown rabbits,-just a bite and no more effort needed,rat,In fact,it would be an assistance to all carnivores,though it would be,a two-edged weapon,一把双刃剑（也可说成,double-edged sword,）,when they fought each other,例句：,Scientific development may be a two-edged weapon,on one hand it lifts peoples living standard,on the other hand it poses potential threats to the environment.,But,of,（,among,）,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,（某种可能性）,that a fixed process took place,It did not;some snakes manufactured a poison different,in every respect,在各个方面,from that of others,（,as different as arsenic is from strychnine,and having different effects,）,arsenic,Poisnous,effect of arsenic,Arsenic occurs in many minerals,mainly combined with sulfur,硫磺,and metals,and also naturally in the native(elemental)state.,Strychnine is a very toxic,colorless crystalline,alkaloid,lklid,n.,生物碱,),used as a,pesticide,particularly for killing small,vertebrates,such as,birds,and,rodents,啮齿动物,.,One poison acts on the nerves,the other,（,act,）,on the blood,act on,，对,起作用；遵照。,If a force or substance acts on someone or something,it has a certain effect on them.,例句：,These medical herbs are said to act on the heart.,The makers of the nerve poison include the mambas and the cobras and their venom is called,neurotoxic,If you act on advice or information,you do what has been advised or suggested.,例句：,A patient will usually listen to the,doctorsadvice,and act on it.,Vipers(adders)and rattlesnakes manufacture the blood poison,which is known as,haemolytic,Viper/adder,rattlesnake,Neurotoxic,poison effect,Haemolytic,poison effect,Both poisons are unpleasant,but,by far,（,得多，显然：修饰比较级或者最高级）,the more unpleasant,is the blood poison,例句：,It is quicker by far to go by train.,It is said that the nerve poison is the more primitive of the two,that the blood poison is,so to speak“,可以这样说”，“打个比方说”,a newer product from an improved formula,Be that as it may,倒装的让步状语从句，相当于,however that may be,，可译成“尽管如此”,the nerve poison,does its business with man,在人的身上发挥作用，要人的命,far more quickly than the blood poison,do ones business,产生效果，完成某人的工作,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.,