The discovery of the chemical nature of tobacco mosaic virus.
The path to arrive at the elucidation of the chemical nature of plant viruses was greatly facilitated by the availability of Tobacco mosaic virus (TMV) as biological tool. The first hypothesis on the chemical nature of TMV was advanced in 1899 by the American Albert Wood, who suggested an enzyme nature. This hypothesis, severely questioned by Harry Hallard in 1915, was re-proposed by several virologists. In 1926, the American Maurice Mulvania concluded that the virus might be a protein with the biological characteristics of an autocatalytic enzyme. Before arriving at the experimental evidence it was necessary to resolve two questions: the estimation of virus infectivity in quantitative terms, performed by Francis Holmes in 1928, and the purification of the virus, performed by Carl George Vinson between 1927 and 1934. Vinson gave a conclusive contribution to solve the question of the chemical nature of TMV by settling the protocol of TMV purification. He put forward the hypothesis of the protein nature in the early 1930s but had not the required firm belief to gave the final experimental evidence of it. Who first arrived at the experimental evidence of the protein nature of the virus was the American Wendell Meredith Stanley, in 1935. His celebrated work, a classic of the fundamental Virology, was followed by several papers in which this result was firmly reaffirmed. The heuristic value of Stanley's discovery held out a year: the decisive evidence of the actual chemical nature of TMV was offered in the late 1936 by an English group under the leadership of Frederick Charles Bawden. In their short paper, Bawden and co-operators demonstrated that TMV had a ribonucleoprotein nature, a result that was confirmed in the following years for several TMV strains and other viruses. Stanley and his group did accept this result only after a year of reticence and contradictions. The conversion to the ribonucleoprotein nature raised a dignified protest by Bawden and the sarcasm of his closest co-operator, Norman Wingate Pirie, because Stanley proved to be very reluctant to recognize the merit of the English group. The world of Virology continues to consider Stanley as the first scientist who elucidated the actual nature of a virus, and this eminent scientist was awarded the Nobel Prize for Chemistry, in 1946. By examining the papers Stanley published from 1937 to 1945, one can however find proof of his ambiguity, a fact that justifies the bitterness of Bawden and the sarcastic comments of Pirie.