Pneumococci has two general forms—
rough (R) and
smooth (S). The S form is more
virulent, and bears a
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 cells. Injected
subcutaneously 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 Griffith also induced some pneumococci to transform back and forth. Griffith also reported transformation of
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
America at The Rockefeller Hospital. Types I, II, and III were each a distinct antigenic grouping, whereas type IV was a catchall of varying antigenicities not matching other types. 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". ==Impact of Griffith's discovery==