Griffith observed two strains of Streptococcus pneumoniae - smooth shiny colony called S type - virulent with capsule, The other R type rough colony non virulent.
Live S type ---->injected into mice --->mice died.
Live R type ---> injected into mice ----> no infection.
Heat killed S type ----> injected into mice ----> no infection.
Heat killed S type + Live R type ----> injected into mice ---->mice died.
S type bacteria were isolated from the dead mice.
Griffith concluded that the genetic material of heat killed S type could transform R type into virulent S type.
He concluded that 'R' strain bacteria had been transformed by the heat - killed 'S' strain bacteria.