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andsolvethisproblem.Heknewthatcholerawouldneverbecontrolleduntilitscausewasfound.Hebecameinterestedintwotheoriesthatpossiblyexplainedhowcholerakilledpeople.Thefirstsuggestedthatcholeramultipliedintheair.Acloudofdangerousgasfloatedarounduntilitfounditsvictims.Thesecondsuggestedthatpeopleabsorbedthisdiseaseintotheirbodieswiththeirmeals.Fromthestomachthediseasequicklyattackedthebodyandsoontheaffectedpersondied.JohnSnowsuspectedthatthesecondtheorywascorrectbutheneededevidence.SowhenanotheroutbreakhitLondonin1845,hewasreadytobeginhisenquiry.Asthediseasespreadquicklythroughpoorneighborhoods,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.Thewater
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