Brains of mice infected with the street rabies virus were observed by the electron microscope and by the light microscope for aiming to elucidate the origin of the Negri body. Adjacent thin (ca 0.05μ) and thick (ca 1.0μ) sections were prepared from Epon embedded blocks of the nerve cell band of Ammon's horn in the hippocampus where Negri bodies are apt to be abundant and by mapping the sections could be identified the same nerve cells including Negri bodies under both electron and light microscope.
The Negri bodies were recognizable by light microscopy as lightly colored cytoplasmic inclusions containing few dark granules after toluidine blue staining. Electron micrographs of the consecutive sections revealed that the ground substance of the Negri body was identical with the matrix which was commonly related to rabies virus replication of both street and fixed strains. This evidence follows the conclusion that the degree of capability to produce Negri bodies depends upon the formation of numerous and extensive foci of virus synthesis.
It might appear that Negri bodies increase in their volume by coherence of neighbouring small Negri bodies within the same cytoplasm, resulting in varied positions of inner bodies within large Negri bodies. The inner body, an important constituent of the Negri body, being surrounded by the ground substance of this inclusion was composed of virus particles associated with some amount of cytoplasmic constituents.
