Fred Griffith studied two strains of Streptococcus pneumonia, one that causes a lethal infection when injected into mice, and a second that is harmless. He observed that pathogenic bacteria that have been killed by heating can no longer cause an infection. But when these heat-killed bacteria are mixed with live, harmless bacteria, this mixture is capable of infecting and killing a mouse. What did Griffith conclude from this experiment?
(a) The infectious strain cannot killed by heating.
(b) The heat-killed pathogenic bacteria "transformed" the harmless strain into a lethal one.
(c) The harmless strain somehow revived the heat-killed pathogenic bacteria.
(d) The mice had lost their immunity to infection with S. pneumoniae.
Answer: B