 A major breakthrough came in 1931, when the American pathologist Ernest William Goodpasture grew influenza and several other viruses in fertilised chickens' eggs.Hirst identified an enzymic activity associated with the virus particle, later characterised as the neuraminidase, the first demonstration that viruses could contain enzymes.Frank Macfarlane Burnet showed in the early 1950s that the virus recombines at high frequencies, and Hirst later deduced that it has a segmented genome.