Griffith tried to prepare a vaccine against pneumococcus, the causative agent of a form of pneumonia. The graffiti hoped that if a patient received a capsule-free or heat-encapsulated encapsulated form, his body would begin to produce antibodies that could protect against pneumonia. In a series of experiments, Griffith introduced mice to both forms of bacteria. When autopsies of dead mice were found, live encapsulated forms were found in them. Based on these results, Griffith concluded that from those killed by heating encapsulated forms to live capsule-free forms, obviously, some factor is transmitted that causes them to produce capsules and become virulent. However, the nature of this transforming factor remained unknown up to now.
Avery was engaged in the isolation and purification of molecules that make up the heat-killed encapsulated pneumococcal cells, and studied their ability to transform non-capsular cells. Removal of the polysaccharide capsule and protein fraction from cellular extracts did not affect this ability, but the addition of the deoxyribonuclease enzyme (DNase), the hydrolyzing DNA, prevented transformation. The ability of highly purified extracts of DNA from encapsulated cells to cause transformation showed that Griffith was DNA.