The breakthrough came in 1931 when Robert Shope, a veterinarian, transmitted the infectious agent of swine influenza from sick pigs, by filtering their virus-containing secretions, to healthy animals.7 Infectivity of the filtrate was subsequently confirmed by Smith, Andrewes, and Laidlaw,8 who used the ferret model of influenza infection to document transmissibility for both human and swine viruses -http://www.nejm.org/doi/full/10.1056/NEJMra0904322

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Pauling, “The Nature of the Chemical Bond. Application of Results Obtained from the Quantum Mechanics and from a Theory of Paramagnetic Susceptibility to the Structure of Molecules,” Journal of the American Chemical Society 53 (1931) 1367-1400. In January 2014 images of Pauling's original manuscript for this paper could be downloaded from Oregon State University's Pauling website.