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In
1928 Fred Griffith, working with the Dipplococcus pneumonia
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bacteria
found that there was a virulent and nonvirulent form of the
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bacterium. When injected into mice the virulent
bacteria caused death
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while
the mice injected with a non virulent bacteria remained healthy.
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He
next went on to heat kill the virulent bacteria and showed that they
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could
no longer kill the mice. However, if
mixed with nonvirulent
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bacteria
the mice again died. Furthermore,
bacteria isolated from these
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mice
were virulent having now become virulent.
Griffith, postulated
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that
there was a transforming factor which survived heating in the
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virulent
bacteria which could then be transferred to the nonvirulent a
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bacteria.
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