which result of frederick griffith's experiments led him to believe in a transforming principle?
Unfortunately, Griffith was not able to identify the chemical nature of this  transforming principle  beyond the fact that it was able to survive heat treatment. Looking back on Griffith's results, which were published in 1928, the interpretation seems obvious. Today, we know that DNA molecules can renature after heat treatment and that bacteria can take up foreign DNA from the environment by a process that we still refer to as transformation.