Discovery
In 1928 it was discovered by Frederick Griffith in an experiment generally known as transformation.
Experiment
In his experiment he considered two strains of streptococus pneumonia, one was R-type which was non-virulent and cause no disease in mice, other was virulent and S-type which cause disease and at last death of mice.
This experiment was comprised of four steps which are as follow:
Step 1:
First he injected living strain of S into mice, after sometime mouce died.
Step 2:
He injected living strain of R into mice, the mice alive as he did not got any disease.
Step 3:
He injected heat killed strain of S into mice and mice remain alive.
Step 4:
He mixed living R strain with heat killed S strain and then inject into mice. As a result the mice died.
Conclusion:
It was found that genetic material from heat killed S stain were transferred to living R (non-virulent) strain, as a result R become virulent and cause the death of mice.
