There are two theories concerning the etiology of measles, both of which are founded on actual laboratory and clinical experiments. The theory that the disease is caused by a filtrable virus not yet identified is based on work carried out previous to 1925 by Hektoen,1 Anderson and Goldberger,2 Blake and Trask3 and others. These workers undoubtedly reproduced the disease experimentally, in either the human being or the animal, from filtered blood or filtered nasopharyngeal washings obtained from patients during the early stages of the disease. None of these investigators, however, was able to isolate or to make a culture of the virus from the filtered blood or washings or from the animal into which these body fluids or washings had been injected.
The other theory, constructed from the work reported later by Tunnicliff,4 Ferry and Fisher,5 Hibbard and Duval6 and Cary and Day,7