In his transformation experiments, what did Griffith observe?
a. Infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains.
b. Mice infected with a pathogenic strain of bacteria can spread the infection to other mice.
c. Mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic.
d. Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.
Answer: d. Mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form.