Al had no trace of Delbrück's almost evangelical charisma or of Luria's candid assertiveness and never welcomed the need to travel and expose his ideas to a wide audience. He framed his experiments to convince himself, not others, that he was on the right track. Then he could enjoy what he called Hershey Heaven, doing experiments that he understood would give the same answer upon repetition. Although both he and Luria had independently demonstrated that phages upon multiplying give rise to stable variants (mutants), it was Hershey, then in St. Louis, who in 1948 showed that their genetic determinants (genes) were linearly linked to each other like the genes along chromosomes of higher organisms.

His most famous experiment, however, occurred soon after he moved to the Department of Genetics of the Carnegie Institution of Washington in Cold Spring Harbor on Long Island. There, in 1952, with his assistant, Martha Chase, he showed that phage DNA, not its protein component, contains the phage genes. After a tadpole-shaped phage particle attaches to a bacterium, its DNA enters through a tiny hole while its protein coat remains outside. Key to Hershey's success was showing that viral infection is not affected by violent agitation in a kitchen blender, which removes the empty viral protein shells from the bacterial surface.

Although there was already good evidence from the 1944 announcement of Avery, MacLeod, and McCarty at the Rockefeller Institute that DNA could genetically alter the surface properties of bacteria, its broader significance was unknown. The Hershey-Chase experiment had a much stronger impact than most confirmatory announcements and made me ever more certain that finding the three-dimensional structure of DNA was biology's next most important objective. The finding of the double helix by Francis Crick and me came only 11 months after my receipt of a long Hershey letter describing his blender experiment results. Soon afterward, I brought it to Oxford to excitedly read aloud before a large April meeting on viral multiplication.

Hershey's extraordinary experimental acumen was last demonstrated through his 1965 finding that the DNA molecule (chromosome) of bacteriophage l had 20-base-long single-stranded tails at each end. The base sequences of these tails were complementary, allowing them to find each other and circular l DNA molecules. This was a bombshell result, because circular molecules had 2 years before been hypothesized as an intermediate in the integration of l DNA molecules into bacterial chromosomes.

Key to the esprit of the phage group was its annual late summer meeting at Cold Spring Harbor. It was not for amateurs, and the intellects then exposed had no equal in biology then or even now, in the hurly burly rush of genetic manipulation of today where perhaps a quarter-million individuals think about DNA in the course of their daily lives. Logic, never emotion or commercial consideration, set the tone in those days, and it was always with keen expectation that we awaited Al's often hour-long concluding remarks. Tightly constructed, his summaries struck those of us aware of his acute taciturnity as containing more words than he might have spoken to outsiders over the course of the past year.

By 1970, the base features of l DNA replication and functioning, both in its more conventional lytic phase and in its prophage stage, had become known, and a book was needed for their presentation to a broader biological audience. Because of his stature and honest impartiality, everyone wanted Al to be the editor and to see that the 52 different papers said what they should and no more. Through Al's ruthless cutting of unneeded verbiage, the book's length was kept in check and the final volume not painful to hold in one's hands. Working hard to make the changes that Al suggested, the young Harvard star, Mark Ptashne, noted with pleasure that Al had made no further changes in his revised manuscript's first ten pages. Then on page 11, Al wrote, "Start here." Only Al could be so direct and so admired.

This was his last scientific hurrah. Although he was only 63, he soon chose to retire. It bothered me that a mind so focused and inventive would willingly stop doing science, but he lived to his own standards, and the pursuit of new ideas was never easy. New moments of Hershey Heaven never lasted long, and his long summers sailing on Georgian Bay were out of place as the number of new scientists seeking gene secrets increased. In retrospect, he did not get out too soon. Recombinant DNA was but 2 years away, and soon there would have been competitors on all sides.

Retirement saw him first expanding his garden, and I could exchange words with him on my walks past his home. Later, when he became absorbed with computers, he was inside and I never thought I had something important enough for an excuse to interrupt. I now regret my lack of courage. Al always appreciated others trying to move ahead. In his last month, now 88 and much curved over by arthritis, Al drove his wife to my house for a small gathering. In asking about our daily lives at the lab, Al likely knew that this would be the last time we saw him. The time to go was at hand, and he stopped eating. No one among his friends ever expects to see another who so pushed science to that level of human endurance.

James D. Watson
November 10, 1997

An abridged version of this essay appeared in the
New York Times Magazine on January 4, 1998.