The phenomenon was first described in Griffith's experiment of 1928, which suggested DNA was the material of heredity. In this early experiment dead "Streptococcus pneumoniae" of the virulent strain type III-S, was injected along with living but non-virulent type II-R pneumococci. This resulted in a deadly infection of type III-S pneumococci. This meant the non-virulent strain had been transformed (changed) by something in the dead bacteria.