Here's the breakdown:
* Griffith's experiment (1928) showed that a substance from heat-killed virulent bacteria could transform harmless bacteria into virulent ones. He called this substance the "transforming principle." However, he didn't identify the substance itself.
* Avery, MacLeod, and McCarty's experiment (1944) built on Griffith's work. They used a series of experiments to isolate and purify the transforming principle. They systematically destroyed different components of the heat-killed bacteria (proteins, lipids, carbohydrates, and DNA) and observed whether the transforming ability remained. They found that only when DNA was destroyed, the transforming ability was lost. This led them to conclude that DNA was the transforming principle and therefore the genetic material.
So, while Griffith's experiment provided the initial evidence of a transforming factor, Avery, MacLeod, and McCarty were the ones who definitively identified DNA as the genetic material.