1. Griffith's Experiment...(background)

In 1928 Fredrick Griffith identified the presence of a "transforming factor" while working with rough and smooth types of pneumonia bacteria. The smooth bacteria have a polysaccharide coating giving them a smooth appearance. This coat that encompasses the bacteria protects it from the hosts immune system, therefore the S strain is infectious. The graphic below outlines Griffith's experiment:


The S strain of bacteria that Griffith used was virulent meaning that when injected into the mouse, the mouse would die from pneumonia  The R strain was nonvirulent and did not result in the death of the mouse. When Griffith injected mice with a dead S strain of pneumatic bacteria the mice remained healthy. This showed that once killed the S strain bacteria that was once deathly to the mouse had no harmful effects. Griffith then combined the dead S strain bacteria with living R strain bacteria (nonvirulent). This injection resulted in the death of the mouse. Griffith was able to conclude that some sort of material from the harmful, but dead, S strain bacteria was able to transfer to the nonvirulent R strain of bacteria turning it into live S strain bacteria, ultimately resulting in the death of the mouse. However, he was unsure what this "transforming factor" was specifically. 


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