Griffith observed two strains of the bacterium—one forming smooth shiny colonies ( -type) with capsule, while other forming rough colonies (R-type) without capsule. He injected live -type cells into live mice and observed that they due to pneumonia. He then injected live R-type cells into live mice and observed that they survived. When he injected heat-** -type cells into live mice, they survived and there were no symptoms of pnuemonia and when heat- -type cells were mixed with live R-type cells and injected into mice, they due to unexpected symptoms of pneumonia. He thus, concluded that heat-** -type bacteria caused a transformation of the R-type bacteria into -type bacteria but he was not able to understand the cause of this bacterial transformation.
