Final answer:
Fredrick Griffith performed transformation experiments where he observed the effects of injecting different strains of a bacterium into mice. He discovered that a substance from the heat-killed S-strain bacteria transformed the harmless R-strain bacteria into a deadly form.
Step-by-step explanation:
Fredrick Griffith performed transformation experiments in the 1920s where he observed the effects of injecting different strains of a bacterium called R (rough) strain and S (smooth) strain into mice. He discovered that the S strain was virulent and killed the mice, while the R strain was non-virulent and did not harm the mice.
Additionally, when he mixed heat-killed S-strain bacteria with live R-strain bacteria and injected them, the mice died. From these experiments, Griffith concluded that a substance from the heat-killed S-strain bacteria transformed the harmless R-strain bacteria into a deadly form.