Describe in detail Griffith's experiment on bacterial transformation.

(N/A) Based on the earlier discoveries of Gregor Mendel,Sutton,Morgan,and other scientists,it was clear that chromosomes in the nucleus carry genetic information,but the nature of the genetic material remained unclear.
The search for the mechanism of genetic inheritance reached the molecular level by $1926$.
In $1928$,Frederick Griffith performed a series of experiments with Streptococcus pneumoniae (pneumococcus) bacteria.
When Streptococcus pneumoniae bacteria are grown on a culture plate,some produce smooth,shiny colonies ($S$ strain),while others produce rough colonies ($R$ strain). This is because $S$ strain bacteria have a mucous (polysaccharide) coat,whereas $R$ strain bacteria do not. When mice were infected with the $S$ strain (virulent),they died from pneumonia infection. However,when mice were infected with the $R$ strain,they did not develop pneumonia.
$S$ strain $\longrightarrow$ Injection into mice $\longrightarrow$ Mice died.
$R$ strain $\longrightarrow$ Injection into mice $\longrightarrow$ Mice lived.
Griffith killed the bacteria by heating them. He observed that injecting heat-killed $S$ strain bacteria into mice did not cause death. When he injected a mixture of heat-killed $S$ strain and live $R$ strain into mice,the mice died. Furthermore,he recovered live $S$ bacteria from these dead mice.
$S$ strain (heat-killed) $\longrightarrow$ Injection into mice $\longrightarrow$ Mice lived.
$S$ strain (heat-killed) $+$ $R$ strain (live) $\longrightarrow$ Injection into mice $\longrightarrow$ Mice died.
Griffith concluded that the $R$ strain bacteria were transformed by the heat-killed $S$ strain bacteria.
Transformation Principle: Some transforming principle transferred from the heat-killed $S$ strain to the $R$ strain,causing the $R$ strain to develop a smooth polysaccharide coat,which made it virulent. This suggested that the genetic material itself had been transformed.