In his transformation experiments, what did griffith observe? 6) a. mixing a heat-killed nonpathogenic strain of bacteria with a living pathogenic strain makes the pathogenic strain nonpathogenic. b. mixing a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form. c. mice infected with a pathogenic strain of bacteria can spread the infection to other mice. d. mutant mice were resistant to bacterial infections. e. infecting mice with nonpathogenic strains of bacteria makes them resistant to pathogenic strains.