The specific detection of the antigens of vaccine virus in cultured human cells by means of fluorescent antibody is reported. The antigenic material occurred in the cytoplasm in progressively increasing amounts and in the early stages was in close contact with the nuclear membrane. The antigens were present in a finely particulate form, either as foci or loosely spread out, up to late stages of infection, at which time the staining assumed a homogeneous form due either to close packing of the particles or to soluble antigen, or both. In late stages, homogeneous collections of antigen were observed in the nucleus. They may have resulted from diffusion of soluble antigen through the nuclear membrane. The antigens were observed in situations which suggest a new method of spread from one to another of these cells, namely by transmission through cytoplasmic connections.

This content is only available as a PDF.