Frederick Griffith heat-killed a culture of pathogenic bacteria. He split the sample and injected half of it into mice. The mice lived. He then mixed the other half of the sample with a living, nonpathogenic bacteria strain and injected the mixture into mice. The mice died. Which of the following describes a treatment that would help clarify interpretation of these data?
A) injecting another population of mice with the original, heat-killed pathogenic bacteria B) heat killing the mixed sample and injecting it into mice C) examining tissue from the dead mice (injected with mixed sample) for the presence of pathogenic bacteria D) culturing bacteria from blood isolated from the living mice (injected with heat-killed pathogenic bacteria)