The fine structure and composition of mature herpes virus have been investigated in thin sections by electron microscopy. The virus was grown in cultured HeLa cells and was collected with them. Tests for the biological activity of the infected cultures were included in the first half of the work. Preparations were fixed with both osmium and permanganate, and were embedded either in methacrylate or in aquon, a water-miscible fraction of a commercially available epoxy resin. In further experiments material fixed with permanganate was subjected to the action of specific nucleases or control medium before embedding.

All the preparations showed numerous uniform particles around and between the cells and this was paralleled by considerable biological activity where tests were made on samples of the culture fluids.

Mature herpes virus has been found to be round and to measure, when dehydration shrinkage is avoided, about 165 mµ in diameter. The particle contained an eccentric round-ended rod-shaped, electron-opaque nucleoid lying in an inner zone of low density. A dense outer zone or viroplasm surrounded this, no membrane being present between the two zones. After permanganate fixation the particle was found to have an outer limiting membrane showing a triple-layered structure morphologically indistinguishable from that of the plasma membrane of the HeLa cells.

The results of the digestion experiments show that herpes virus contains nucleic acid of deoxyribose type and that this is localized in the dense nucleoid.

Both the findings and the methods used are discussed.

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