Canadian-American physician who obtained his medical degree from Columbia University in 1904 and joined the Rockefeller Institute in 1913. Avery studied a curious phenomenon that had been observed in pneumococci (pneumonia-causing bacteria) with a smooth coat (S) and those with a rough coat (R). It seemed that the R strain lacked an enzyme needed to make the carbohydrate capsule encasing the smooth strain. When a nonliving extract of the S strain was mixed with live R strains an injected into a mouse, it was found that that mouse's tissue would eventually contain live S bacteria, thus indicating that the S strain contained some factor containing an enzyme necessary to convert the R strain into the S strain.

It was believed that the factor must be a protein, but in 1944, Avery and his coworkers discovered that it was pure DNA with no protein present. This marked a turning point in the understanding of genetics, since DNA had previously been believed to by a minor player among proteins involved in passing genetic characteristics, and essentially amounted to demonstrating that DNA itself was the unit of genetic inheritance known as the gene.

Chargaff, Crick, Watson (James)