However, in 1928, Fred Griffith, a leader in public-health research in Britain, demonstrated that the conversion of one strain to another could happen in vivo in mice. Shortly after the publication of his results, they were confirmed in several quarters, including Avery's lab. The analysis relied on serotyping: it was known that phenotypic differentiation of pneumoccocal groups could be diagnosed by their reactions with specific antisera, already recognized to reflect chemically distinct capsular polysaccharides. Griffith had neither the resources nor the inclination to purify and identify the responsible agent in pneumococcal extracts that induced the changes of serotype. But the phenomenon of transformation was at least vaguely understood to comprise an alteration of what we would now call genetic factors.