Dna from one type of bacterium genetically transforms another type. When he looked at blood from these mice he found living bacteria with characteristics of virulent s strain. Some of the r strain had been transformed into the virulent s strain, because they were in the presence of the dead bacteria. Therefore when you put r strain and heat killed s strained together it yields the same transformation. A chemical transforming principle from the dead s strain can cause a heritable change in the affected r cells. Oswald avery was the one that found the transforming principle. Dna was not as genetically variant like protein could be. Did not know if bacteria even contained dna. Viral replication experiments confirmed that dna is the genetic material. Proteins contain more sulphur not present in dna grew bacteriophage in the presence sulphur. Dna is rich with phosphorus not present in dna grew another batch of bacteriophage in the presence of phosphorus.