Illustration of the experiment reported in 1928 by British bacteriologist Frederick Griffith (1879-1941). This experiment was the first to suggest that bacteria can transfer genetic information through a process called transformation. Two types of pneumococcus bacteria were used in the experiment: an S type (smooth) that was harmful (virulent) and an R type (rough) that was safe (nonvirulent). The mice were infected with both types of bacteria. The results showed that the R type (blue) did not kill the mouse, while the S type (red) did kill the mouse. The heat-killed S type (yellow) did not kill the mouse. However, when the R type and heat-killed S type (the two non-fatal forms mixed together) were given to the mouse, it died. This led to the conclusion that the R type bacteria had been transformed into the lethal S type. Even though the S type bacteria had been heat-killed, their DNA (deoxyribonucleic acid) had survived the heating process and had been taken up by the R type. With these new genes, the formerly safe R type bacteria could now kill the mouse. This concept is now known as the 'transforming principle'.