Reoviruses are ether-resistant icosahedral viruses 60 to 75 mp in diameter which contain ribonucleic acid. They have been recovered from man and lower animals and are ubiquitous in their geographic distribution. At present, the importance of these viruses as a cause of human or animal disease is still largely unknown. As a result of having a number of unusual characteristics, reoviruses have attracted the attention of many workers in the relatively short time since they were first recogniz...