Oswald Avery, Canadian physician and bacteriologist, found that the agent responsible for genetic transferring is the nucleic acid DNA and not protein as most biochemists theorized at the time. In 1944 Avery and his coworkers, McCarty and MacLeod, discovered the "transforming principle."

The Experiment

• First they treated the bacteria with centafugation, which eliminates large cellular pieces. The result: bacteria still transformed
• Added protease, which removes all proteins
  The result: bacteria still transformed
• Treated the bacteria with deoxyribonuclease, which eliminates all DNA
  The result: no transformation in the bacteria

The trio concluded that DNA is the cause of transformation, where in this experiment virulence is inherited.