This article reviews Fraenkel-Conrat's research on the genetic code of tobacco mosaic virus. The reviewer, Bolton Davidheiser, points out that the complexity of the RNA code of the virus was unexpected by researchers. He also discusses how Fraenkel-Conrat used nitrous acid to induce mutations in the virus and studied these mutations in an effort to understand the nucleotide arrangements associated with specific protein synthesis. The reviewer highlights the point that evolutionists use the term "natural selection" in two different ways and provides an example of how the concept is used to explain the frequency of certain amino acid exchanges in the virus shell.