Q.Why was the conclusion of Avery, MacLeod and McCarty's 1944 experiment not immediately and universally accepted by the scientific community, even though it was a rigorous biochemical proof?

Avery, MacLeod and McCarty (1944) identified the chemical nature of Griffith's 'transforming principle' through a purely biochemical approach. They purified the transforming principle from heat-killed S-strain bacteria and treated separate samples with three different classes of enzyme: protease (which digests protein), RNase (which digests RNA), and DNase (which digests DNA). Treatment with protease or RNase left the transforming activity completely intact — transformation of R bacteria into S bacteria still occurred — ruling out both protein and RNA as the transforming principle. Treatment with DNase, however, completely destroyed transforming activity, showing that DNA — and DNA alone — was responsible. This was the first purely biochemical, molecule-by-molecule proof that …