Nucleic acids are molecules that contain information and are also capable of replication. It refuted the once held claim that only protein was capable of carrying genetic information that can be transferred because of its structural diversity. Oswald Avery of the Rockefeller institute in the city of New York presented evidence that showed nucleic acids rather than proteins were responsible for carrying genetic information.
The bacteria that causes pneumonia, pneomococcus , exists in two distinct forms— the capsulated and the non capsulated forms. The capsulated forms have their cells surrounded by a thick capsule while the non capsulated form has this thick capsule completely missing. Oswald Avery and his colleagues then prepared a medium of disrupted capsulated bacteria which did not contain any living bacteria cells but only the chemicals extracted from them. He introduced non-capsulated bacteria into this medium and allowed it to grow. He found quite remarkable that the non-capsulated bacteria developed capsules.
The conclusion here is that a chemical component in the extract of the capsulated bacteria was capable of bringing about a permanent and inheritable change in the non-capsulated strains. What then is this chemical component? Avery later conducted several other experiments on the medium by systematically isolating and purifying the different chemical constituents and him and his colleagues were able to show and confirm that nucleic acids were the active agent!