大学英语四六级考试阅读提高的练习（21）
<p> <span word="At">At</span> <span word="the">the</span> <span word="time">time</span> <span word="of">of</span> <span word="Leeuwenhoek">Leeuwenhoek</span> <span word="the">the</span> <span word="microscope">microscope</span> <span word="was">was</span> <span word="not">not</span> <span word="well">well</span> <span word="developed">developed</span>, <span word="but">but</span> <span word="with">with</span> <span word="it">it</span> <span word="he">he</span> <span word="discovered">discovered</span> <span word="bacteria">bacteria</span>. <span word="The">The</span> <span word="study">study</span> <span word="of">of</span> <span word="these">these</span> <span word="tiny">tiny</span> <span word="forms">forms</span> <span word="of">of</span> <span word="life">life</span> <span word="which">which</span> <span word="looked">looked</span> <span word="like">like</span> <span word="specks">specks</span> <span word="to">to</span> <span word="him">him</span> <span word="was">was</span> <span word="not">not</span> <span word="practical">practical</span> <span word="until">until</span> <span word="more">more</span> <span word="than">than</span> 150 <span word="years">years</span> <span word="later">later</span>, <span word="when">when</span> <span word="microscopes">microscopes</span> <span word="were">were</span> <span word="much">much</span> <span word="improved">improved</span>. <span word="However">However</span>, <span word="the">the</span> <span word="discovery">discovery</span> <span word="led">led</span> <span word="some">some</span> <span word="medical">medical</span> <span word="men">men</span> <span word="at">at</span> <span word="the">the</span> <span word="time">time</span> <span word="to">to</span> <span word="think">think</span> <span word="that">that</span> <span word="contagious">contagious</span> <span word="diseases">diseases</span> <span word="were">were</span> <span word="due">due</span> <span word="to">to</span> <span word="germs">germs</span> <span word="passed">passed</span> <span word="from">from</span> <span word="the">the</span> <span word="sick">sick</span> <span word="to">to</span> <span word="the">the</span> <span word="well">well</span>.</p><p> <span word="Dr">Dr</span>. <span word="Edward">Edward</span> <span word="Jenner">Jenner</span>, <span word="a">a</span> <span word="young">young</span> <span word="English">English</span> <span word="physician">physician</span>, <span word="overheard">overheard</span> <span word="a">a</span> <span word="milkmaid">milkmaid</span> <span word="say">say</span> <span word="that">that</span> <span word="she">she</span> <span word="was">was</span> <span word="not">not</span> <span word="afraid">afraid</span> <span word="of">of</span> <span word="smallpox">smallpox</span> <span word="because">because</span> <span word="she">she</span> <span word="had">had</span> <span word="just">just</span> <span word="recovered">recovered</span> <span word="from">from</span> <span word="an">an</span> <span word="attack">attack</span> <span word="of">of</span> <span word="cowpox">cowpox</span>. <span word="This">This</span> <span word="gave">gave</span> <span word="Jenner">Jenner</span> <span word="the">the</span> <span word="clue">clue</span>, <span word="and">and</span> <span word="in">in</span> 1796 <span word="he">he</span> <span word="proved">proved</span> <span word="that">that</span> <span word="a">a</span> <span word="person">person</span> <span word="vaccinated">vaccinated</span> <span word="with">with</span> <span word="cowpox">cowpox</span> <span word="germs">germs</span> <span word="is">is</span> <span word="quite">quite</span> <span word="certain">certain</span> <span word="to">to</span> <span word="escape">escape</span> <span word="from">from</span> <span word="getting">getting</span> <span word="smallpox">smallpox</span>. <span word="At">At</span> <span word="this">this</span> <span word="time">time</span> <span word="smallpox">smallpox</span> <span word="was">was</span> <span word="so">so</span> <span word="common">common</span> <span word="that">that</span> <span word="about">about</span> <span word="only">only</span> <span word="one">one</span> <span word="person">person</span> <span word="in">in</span> <span word="a">a</span> <span word="hundred">hundred</span> <span word="escaped">escaped</span>.</p><p> <span word="In">In</span> <span word="Aristotles">Aristotles</span> <span word="days">days</span>, <span word="it">it</span> <span word="was">was</span> <span word="the">the</span> <span word="common">common</span> <span word="belief">belief</span> <span word="that">that</span> <span word="air">air</span> <span word="caused">caused</span> <span word="foods">foods</span> <span word="to">to</span> <span word="spoil">spoil</span>. <span word="People">People</span> <span word="believed">believed</span> <span word="that">that</span> <span word="this">this</span> <span word="was">was</span> <span word="true">true</span> <span word="until">until</span> <span word="the">the</span> <span word="seventeenth">seventeenth</span> <span word="century">century</span>. <span word="In">In</span> 1800, <span word="Napoleon">Napoleon</span> <span word="offered">offered</span> <span word="a">a</span> <span word="prize">prize</span> <span word="for">for</span> <span word="the">the</span> <span word="successful">successful</span> <span word="invention">invention</span> <span word="of">of</span> <span word="a">a</span> <span word="container">container</span> <span word="which">which</span> <span word="would">would</span> <span word="keep">keep</span> <span word="foods">foods</span> <span word="from">from</span> <span word="spoiling">spoiling</span> <span word="in">in</span> <span word="war">war</span> <span word="times">times</span>. <span word="The">The</span> <span word="prize">prize</span> <span word="was">was</span> <span word="won">won</span> <span word="by">by</span> <span word="Francois">Francois</span> <span word="Appert">Appert</span>, <span word="who">who</span> <span word="had">had</span> <span word="worked">worked</span> <span word="all">all</span> <span word="his">his</span> <span word="life">life</span> <span word="on">on</span> <span word="this">this</span> <span word="problem">problem</span>. <span word="He">He</span> <span word="packed">packed</span> <span word="foods">foods</span> <span word="in">in</span> <span word="glass">glass</span> <span word="or">or</span> <span word="china">china</span> <span word="jars">jars</span>, <span word="poured">poured</span> <span word="in">in</span> <span word="enough">enough</span> <span word="water">water</span> <span word="to">to</span> <span word="cover">cover</span> <span word="the">the</span> <span word="food">food</span>, <span word="corked">corked</span> <span word="and">and</span> <span word="sealed">sealed</span> <span word="them">them</span>, <span word="then">then</span> <span word="placed">placed</span> <span word="the">the</span> <span word="jars">jars</span> <span word="in">in</span> <span word="a">a</span> <span word="container">container</span> <span word="of">of</span> <span word="water">water</span> <span word="which">which</span> <span word="was">was</span> <span word="gradually">gradually</span> <span word="heated">heated</span> <span word="to">to</span> <span word="the">the</span> <span word="boiling">boiling</span> <span word="point">point</span>. <span word="He">He</span> <span word="thought">thought</span>, <span word="however">however</span>, <span word="that">that</span> <span word="it">it</span> <span word="was">was</span> <span word="air">air</span> <span word="that">that</span> <span word="caused">caused</span> <span word="the">the</span> <span word="foods">foods</span> <span word="to">to</span> <span word="spoil">spoil</span>. <span word="It">It</span> <span word="was">was</span> <span word="not">not</span> <span word="until">until</span> <span word="fifty">fifty</span> <span word="years">years</span> <span word="later">later</span> <span word="that">that</span> <span word="Louis">Louis</span> <span word="Pasteur">Pasteur</span> <span word="proved">proved</span> <span word="that">that</span> <span word="it">it</span> <span word="was">was</span> <span word="not">not</span> <span word="air">air</span> <span word="that">that</span> <span word="spoiled">spoiled</span> <span word="foods">foods</span>, <span word="but">but</span> <span word="tiny">tiny</span> <span word="living">living</span> <span word="organisms">organisms</span> <span word="that">that</span> <span word="float">float</span> <span word="about">about</span> <span word="in">in</span> <span word="the">the</span> <span word="air">air</span>. <span word="The">The</span> <span word="first">first</span> <span word="tin">tin</span>-<span word="can">can</span> <span word="container">container</span> <span word="was">was</span> <span word="made">made</span> <span word="in">in</span> 1807 <span word="by">by</span> <span word="Peter">Peter</span> <span word="Durand">Durand</span>. <span word="The">The</span> <span word="canning">canning</span> <span word="industry">industry</span> <span word="in">in</span> <span word="the">the</span> <span word="United">United</span> <span word="States">States</span> <span word="began">began</span> <span word="in">in</span> 1819 <span word="when">when</span> <span word="salmon">salmon</span>, <span word="lobster">lobster</span>, <span word="and">and</span> <span word="oysters">oysters</span> <span word="were">were</span> <span word="first">first</span> <span word="canned">canned</span>.</p>
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