A week or so after the Congress, Pauling attended the International Phage Colloquium at the centuries-old Abbey of Royaumont outside Paris, where he heard the American microbiologist Alfred Hershey describe an ingenious experiment that had everyone talking. In an attempt to settle the question of whether DNA or protein was the genetic material, Hershey and a coworker, Martha Chase, had found a way to tag the DNA and protein of a bacterial virus with separate radioactive labels.

By tracking the labels, they were able to show persuasively that the protein did nothing. DNA alone directed the replication of new viruses. While Oswald Avery's work had been presented tentatively and made little impact, the "Waring blender experiment," as it became known, after a piece of decidedly nontechnical machinery that was used in the experiment, clearly showed that DNA was the genetic material. What worked with viruses might well work with higher organisms as well, and as word of the Hershey-Chase experiment spread, phage researchers, geneticists, and biochemists interested in replication began to switch their focus from protein to DNA.

Pauling, too, quickly realized that he had been on the wrong track. It was clear now that the genetic master molecule, the one that directed the making of proteins, was DNA.