FlemingrecountedthatthedateofhisbreakthroughwasonthemorningofFriday,September28,1928.Itwasafortuitousaccident:inhislaboratoryinthebasementofSt.Mary'sHospitalinLondon(nowpartofImperialCollege),FlemingnoticedapetridishcontainingStaphylococcusplateculturehehadmistakenlyleftopen,whichwascontaminatedbyblue-greenmould.Therewasahaloofinhibitedbacterialgrowtharoundit.Flemingconcludedthatthemouldwasreleasingasubstancethatwasrepressingthegrowthandlysingthebacteria.HegrewapurecultureanddiscoveredthatitwasaPenicilliummould,nowknowntobePenicilliumnotatum.CharlesThom,anAmericanspecialistworkingattheU.S.DepartmentofAgriculture,wastheacknowledgedexpert,andFlemingreferredthemattertohim.Flemingcoinedtheterm"penicillin"todescribethefiltrateofabrothcultureofthePenicilliummould.Evenintheseearlystages,penicillinwasfoundtobemosteffectiveagainstGram-positivebacteria,andineffectiveagainstGram-negativeorganismsandfungi.Heexpressedinitialoptimismthatpenicillinwouldbeausefuldisinfectant,beinghighlypotentwithminimaltoxicitycomparedtoantisepticsoftheday,andnoteditslaboratoryvalueintheisolationof"Bacillusinfluenzae"(nowHaemophilusinfluenzae).Afterfurtherexperiments,Flemingwasconvincedthatpenicillincouldnotlastlongenoughinthehumanbodytokillpathogenicbacteria,andstoppedstudyingitafter1931.Herestartedclinicaltrialsin1934,andcontinuedtotrytogetsomeonetopurifyituntil1940.