a . ceva we mney | ; z . mn ul -

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these are now known to be derived from longer rods broken in the preparation of
the sample for microscopy. How homogeneous was a population of virus
particles? Lauffer, analyzing the spreading of a sedimenting boundary of
tomato busy stunt virus, concluded that the diameters of the particles could
deviate from the mean by no more than 1%. In an exuberant moment, Lauffer
referred to "living molecules."

Nevertheless, it is of considerable interest that neither group tested the
infectivity of viral RNA before 1956. Despite the availability of appropriate
viral RNA after 1936 and inactivating crystalline ribonuclease in 1940, despite

the demonstration of DNA as Pneumococcal transforming agent in 1944 and the

apparent infectivity of phage DNA, aecepred by the community of phage workers a
i j iscé l ick the thought that om

viral RNA might be the genetic element of this virus was not tested before

 

 

 

 

 

 

 

 

 

 

1956.

In 1940 E, Pfankuch et al. had studied X-ray induced mutations of the ~
virus and had attributed differences in the phosphorus contents of the parent Jen
and mutant strains to irradiation-induced alterations in the nucleic acid. part
of the virus. These data were not considered convincing in 1941 by C.A. Knight
and Stanley who had found differences in the amino acid compositions of various
strains. They had concluded that "the chemical differences between strains
probably lies not in the nucleic acid but rather in the protein part of the v
virus molecule." They apparently did not consider the possibility that the | a

ae
w ; ; nucleic acid might determine the composition of the protein. Following this Pe
w \ fe

voce oS Pe . “ line of thought, Miller and Stanley modified amino acid residues with a variety
of reagents but found that, although many groups could be modified without loss
of biological activity, the virus propagated was normal virus. At this point

in the work, early in the entrance of the United States into World War II, the

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