14 



CELL HEREDITY 



SIII 



Virulent strain 



(a) 



Dead 



Living 



(b) 



SIII 



Virulent .^ 



strain, U 



heat-killed 



Living 



D^ 



(0 



Rll 



Nonvirulent qq'q 



e 



^-^_ 



-j^— »-.. 



FIGURE 1.4. Diagram of Griffith's experiment. 



(a). Mice injected with a virulent strain of pneumococcus, SIII, die of bacteremia. 



(b). Mice do not die when injected with a nonvirulent strain, Rll, which does not 

 possess a capsule but comes from a virulent, encapsulated strain, Sll. 



(c). Mice do not die when injected with the virulent strain, SIII, which has been 

 heat-killed. 



id). When mice are injected with a mixture of heat-killed SIII and nonvirulent Rll, 

 they die of bacteremia, and living virulent SIII organisms are found in their bodies. 



