第一单元·1原文：

　　JohnSnowwasafamousdoctorinLondon-soexpert,indeed,thatheattendedQueenVictoriaasherpersonalphysician.Buthebecameinspiredwhenhethoughtabouthelpingordinarypeopleexposedtocholera.Thiswasthedeadlydiseaseofitsday.Neitheritscausenoritscurewasunderstood.Somanythousandsofterrifiedpeoplediedeverytimetherewasanoutbreak.JohnSnowwantedtofacethechallengeandsolvethisproblem.Heknewthatcholerawouldneverbecontrolleduntilitscausewasfound.

　　Hebecameinterestedintwotheoriesthatpossiblyexplained

　　howcholerakilledpeople.Thefirstsuggestedthatcholeramultipliedintheair.Acloudofdangerousgasfloatedarounduntilitfounditsvictims.Thesecondsuggestedthatpeopleabsorbedthisdiseaseintotheirbodieswiththeirmeals.Fromthestomachthediseasequicklyattackedthebodyandsoontheaffectedpersondied.

　　JohnSnowsuspectedthatthesecondtheorywascorrectbutheneededevidence.SowhenanotheroutbreakhitLondonin1854,hewasreadytobeginhisenquiry.Asthediseasespreadquicklythroughpoorneighbourhoods,hebegantogatherinformation.Intwoparticularstreets,thecholeraoutbreakwassoseverethatmorethan500peoplediedintendays.Hewasdeterminedtofindoutwhy.

　　Firsthemarkedonamaptheexactplaceswhereallthedeadpeoplehadlived.Thisgavehimavaluableclueaboutthecauseofthedisease.ManyofthedeathswerenearthewaterpumpinBroadStreet(especiallynumbers16,37,38and40).Healsonoticedthatsomehouses(suchas20and21BroadStreetand8and9CambridgeStreet)hadhadnodeaths.Hehadnotforeseenthis,sohemadefurtherinvestigations.Hediscoveredthatthesepeopleworkedinthepubat7CambridgeStreet.Theyhadbeengivenfreebeerandsohadnotdrunkthewaterfromthepump.Itseemedthatthewaterwastoblame.

　　Next,JohnSnowlookedintothesourceofthewaterforthesetwostreets.HefoundthatitcamefromtheriverpollutedbythedirtywaterfromLondon.HeimmediatelytoldtheastonishedpeopleinBroadStreettoremovethehandlefromthepumpsothatitcouldnotbeused.Soonafterwardsthediseasesloweddown.Hehadshownthatcholerawasspreadbygermsandnotinacloudofgas.

　　InanotherpartofLondon,hefoundsupportingevidencefromtwootherdeathsthatwerelinkedtotheBroadStreetoutbreak.Awoman,whohadmovedawayfromBroadStreet,likedthewaterfromthepumpsomuchthatshehaditdeliveredtoherhouseeveryday.Bothsheandherdaughterdiedofcholeraafterdrinkingthewater.WiththisextraevidenceJohnSnowwasabletoannouncewithcertaintythatpollutedwatercarriedthevirus.

　　Topreventthisfromhappeningagain,JohnSnowsuggestedthatthesourceofallthewatersuppliesbeexamined.Thewatercompanieswereinstructednottoexposepeopletopollutedwateranymore.Finally"KingCholera"wasdefeated.