Final answer:
In their experiments, Avery, MacLeod, and McCarty concluded that DNA was the transforming agent by degrading DNA and observing the loss of transformation ability.
Step-by-step explanation:
Scientists Oswald Avery, Colin MacLeod, and Maclyn McCarty (1944) conducted experiments to identify the transforming principle first described by Griffith. They isolated the S strain from infected mice and isolated proteins and nucleic acids, including RNA and DNA, as potential candidates for the molecule of heredity. Through a systematic elimination study, they found that when DNA was degraded, the resulting mixture was no longer able to transform the bacteria, leading them to conclude that DNA was the transforming agent.