Editing Frederick Griffith (section)

==Griffith's experiment==
{{Main|Griffith's experiment}}

[[File:Griffith experiment.svg|thumb|268px]]
Pneumococci has two general forms—''rough'' (R) and ''smooth'' (S).  The S form is more [[virulent]], and bears a [[Capsule (microbiology)|capsule]], which is a slippery [[polysaccharide]] coat—outside the [[peptidoglycan]] [[cell wall]] common among all classical bacteria—and prevents efficient [[phagocytosis]] by the host's [[innate immune system|innate immune cells]].  Injected [[Subcutaneous injection|subcutaneous]]ly with S form, mice succumbed to pneumonia and death within several days. However, the R form, lacking a capsule—its outer surface being cell wall—is relatively [[avirulent]], and does not cause pneumonia as often.

When Griffith injected heat-killed S into mice, as expected, no disease ensued. When mice were injected with a mixture of heat-killed S and live R, however, pneumonia and death ensued. The live R had transformed into S—and replicated as such—often characterized as Griffith's Experiment. More accurately, point six of Griffith's abstract reports that R tended to transform into S if a large amount of live R, alone, were injected, and that adding much heat-killed S made transformation ''reliable''<ref name=Griffith/> Griffith also induced some pneumococci to transform back and forth.<ref name = Griffith />

Griffith also reported transformation of [[serology|serological]] ''type''—bacterial [[antigenicity]]—distinct from presence or absence of a capsule. Bacteriologist [[Fred Neufeld]], of the [[Robert Koch Institute]] in [[Berlin]], Germany, had earlier identified the pneumococcal types, confirmed and expanded by [[Alphonse Dochez]] at Oswald Avery's laboratory in [[United States|America]] at The Rockefeller Hospital.<ref name=Lehrer/> Types I, II, and III were each a distinct antigenic grouping, whereas type IV was a catchall of varying antigenicities not matching other types.<ref name=Lehrer/>

Illustrating the plasticity of ''Streptococcus pneumoniae'', the abstract of Griffith's paper reports, "The S form of Type I has been produced from the R form of Type II, and the R form of Type I has been transformed into the S form of Type II".<ref name=Griffith/>