( F.Griffith) used Streptococcus pneumoniae ( bacterium responsible for pneumonia) , S- strain ( producing shiny colonies) when injected into mice the mice develop pneumonia and die , R- strain( producing rough colonies) when injected into mice the mice do not develop pneumonia,Griffith killed S-strain with heat and injected into mice & mice live, he then mixed heat killed S-strain with live R strain and mice die,recovered living S-bacteria from dead mice concluding that R-strain had been transformed by heat killed S-strain
