Development and morphology of trachoma agent in the yolk sac cell as revealed by electron microscopy

Abstract

The trachoma agent cultivated in the yolk sac of the chick embryo was examined by electron microscopy. A reticulated matrix is seen as a precursor of viral forms in the cytoplasm of the yolk sac cell 18 hours after inoculation. The matrix consists of fine filaments 100 A in width, which resemble chromosome fibrils. The matrix has no limiting membrane and no inner particles. In the next few hours the matrix is surrounded by a double membrane and forms a giant body (plaque by light microscopy) 1–5 μ in diameter. An inclusion cavity develops surrounding the giant body. The cavity is separated from the cytoplasm by a membrane. Forty-eight hours after inoculation large bodies (initial bodies by light microscopy) 0.5–1 μ in diameter predominate in the inclusion cavity. Each large body has a double outer membrane and a reticulated inner substance with slightly higher electron density than the giant body. Some internal structure is suggested in the reticulated substance. Seventy-two hours after inoculation elementary bodies 0.3–0.5 μ in diameter predominate. Each elementary body has a single membrane, a nucleoid, and a viroplasm. The nucleoid consists of coiled filaments 50 A in width which resemble DNA filaments in bacterial nucleoplasm. The mode of the development of the trachoma agent seems to be similar to viral replication. Elementary bodies seem to result from developmental forms by subdivision of the latter, but the subdivision seems to be different from bacterial binary fission.