According to O. Avery, Mc Leod and Mc Carty, one of the following events is correct.

 When heat-killed "S" cells was mixed with live "R" cells and injected them into mice, the mice died, and live pathogenic bacteria were recovered from their bodies. This indicated that something from the heat-killed "S" cells had transformed the live "R" cells into pathogenic "S" cells.

To determine if it was the DNA in the heat-killed "S" cells that was responsible for the transformation, the heat-killed "S" cell extract was treated with DNase, an enzyme that specifically digests DNA, before mixing it with live "R" cells and injecting them into mice.

When the DNA was digested with DNase, the transformation did not occur, and the mice survived. This result showed that the destruction of DNA in the heat-killed "S" cells prevented the transformation of live "R" cells into pathogenic cells.

This experiment provided strong evidence that DNA was the molecule responsible for carrying genetic information because the destruction of DNA eliminated the transforming ability of the heat-killed "S" cells. It reinforced the idea that genetic material is contained within DNA and laid the foundation for our understanding of DNA's central role in genetics and heredity.