They worked on pneumo coccus strains. The purification procedure Avery undertook consisted of first killing the bacteria with heat and extracting saline soluble component. Next protein was precipitaed out using chloroform and the polysaccharide capsules were hydrolysed with an enzyme. An immulogical precipitate caused by type-specific antibodies were used to verify the complete destruction of the capsules. Then active protein was precipitated by alcohol fractionation resulting in fibrous strands that could be removed with a string rod. Chemical analysis showed that the propotions of C,H,N & P in this active portion were consistent with chemical composition of DNA. To show that DNA rather than small amount of RNA, protein or some other cell component that was responsible for transformation, Avery et al used a number of bio chemical test. They found that proteinaser and RNAase did not have any effect on it but DNA polymerase did affect it.