1899

First discovery of a virus: Discovery of yellow fever virus by Walter Reed, studied by Lewis and five other Rockefeller scientists who themselves got infected and died of the disease. But the discovery was based on “an argument by exclusion”: the scientists did not know that a virus is simply a bundle of genes, in the form of DNA or RNA, wrapped in a coating of proteins and lipids. They could isolate it via fine sieve with holes small enough to trap every known microorganism. But the viruses tiny enough to pass through the filter, isolated in this way, infected animals. So they knew there was super-small infectious agent in the filtered fluid (Kolata, 71).