Griffith wanted to develop a vaccine against pneumonia but during his experiments he identified the genetic material.
In his experiments, he used two strands of Streptococcus pneumoniae bacteria:
R strain- colonies with rough appearance; nonvirulent
S strain - rounded and smooth colonies; virulent (those bacteria had protein coat that protected them from mice immune system, so when they were injected in mice, mice developed pneumonia and died).
Then in the next steps of his experiment:
• Griffith injected mice with heat-killed S bacteria which did not cause disease;
• R bacteria were combined with heat-killed S bacteria and injected into a mouse. Mice developed pnenumonia and die, but also Griffith found that the mice contained living S bacteria.
He concluded that the R-strain bacteria must have taken up something from the heat-killed S bacteria, which allowed them to "transform" and become virulent. Today, we now it is genetic material.
