procedures with which you could visualize individual virus particles;
I mean you could put them on a plate with a lawn of bacteria, and the
next morning every virus particle would have eaten a macroscopic one-
millimeter hole in the lawn. You could hold up the plate and count the
plaques. This seemed to me just beyond my wildest dreams of doing sim-
ple experiments on something like atoms in biology.Soon World War II was consuming Europe, and Delbriick remained in
the United States, settling in Nashville, Tennessee, where he taught
physics at Vanderbilt University and conducted research with E. coli
and bacteriophages.
A bacteriophage virus was known to be composed only of pro-
teins and nucleic acids (DNA or RNA). In animal and plant cells,
chromosomes appeared to be the locus of genetic information, and
chromosomes were also composed of proteins and nucleic acids.
Thus, if genes are molecules, it must be the case that they consist
of either proteins or nucleic acids. In the early 1940s, given these
choices, it was generally assumed that genes must be made of pro-
teins. After all, proteins are hundreds of amino acids in length, and
each of these amino acids may be one of twenty different types. This
allows for enormous variability and complexity among proteins, the
kind of complexity that surely would be needed to encode the vast
amount of information required to build an organism. In contrast,
nucleic acids were known to be composed of only four different kinds
of units—adenine, thymine, guanine, and cytosine in the case of DNA
—and thus were presumably far less able to code complex informa-
tion. Some folks even referred to DNA as a “stupid substance.” What-
ever genes were, they must surely be made of protein—so everyone
believed.
Then, in 1944, Oswald Avery (1877-1955) of the Rockefeller Insti-