A plaque technique for the titration of yellow fever virus and antisera

Yellow fever virus may be titrated by a plaque technique in cultures of chick embryo fibroblasts. The cells are grown and maintained under agar in a medium buffered with Tris (hydroxymethyl) aminomethane, using a conventional laboratory incubator without added carbon dioxide. The sensitivity of the technique approaches that of the mouse intracerebral test and exceeds that test in precision. Yellow fever neutralizing antibodies may be detected by a plaque inhibition test. The technique may be applied to a number of other viruses.