Avery, MacLeod, and McCarty isolated the transforming principle by centrifugation to collect the cells, followed by heat-killing and extraction of macromolecules.

This filtrate is capable of transformation.

Inactivating or removing the polysaccharides, proteins and RNA left the filtrate still capable of transformation.

Adding DNase (an enzume that digests DNA) to the filtrate stops the inactivated transformation, proving that the "active factor" is DNA.