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By maintaining L cells in a balanced salt solution of inorganic salts and glucose (BSS) for 2 days or more, they are rendered incapable of supporting the growth of psittacosis virus (6BC), though it infects such cells and is present intracellularly for as long as 3 days in a non-infectious phase. The addition of an enriched medium to such a culture of cells at any time up to 4 days after infection results in the appearance of infectious virus within these cells, which multiplies and is released from the cells, providing the entire period of exposure of such cells to the BSS does not exceed 6 days, following which the cells die. A latent infection with psittacosis virus in a non-infectious phase has been established in a pure line of cells which possess properties of malignancy.

Chick embryo fibroblasts infected in vitro with Rous sarcoma virus have properties similar to tumor cells when injected into virus-immune chickens. When such virus-transformed fibroblasts are injected into normal chickens, they apparently participate in the production of tumors independent of their release of virus and are thus apparently malignant in vivo.

Hemolysis of chicken red blood cells by mumps virus is associated with the release of sphingomyelin from the stromal lipoprotein and the destruction of 65 per cent of the sphingomyelin of the red cell stroma. However, the virus had no effect on isolated phosphatides extracted from the erythrocytes. The hemolytic action of the virus and changes in sphingomyelin content of the erythrocytes fail to occur at a pH of 6.0. The viral hemolysis of human erythrocytes is not associated with similar alterations in their content of sphingomyelin. The absence of lecithin from sheep erythrocytes, which are also lysed by mumps virus, is additional evidence that a viral lecithinase is not associated with the hemolytic property of mumps virus. Mumps virus concentrated from the amniotic fluid of viral infected chick embryos contains about 7 per cent phosphatide, 60 per cent of which is sphingomyelin.

The conditions for the production of extra-embryonic fluids with hemolytic activity from chick embryos infected with mumps virus have been investigated. Infected fluids with strong hemolytic activity can be obtained by harvesting the fluids of 6- to 8-day-old chick embryos inoculated by the amniotic route after 5 to 6 days' incubation at 35 degrees C. Under such circumstances, the hemolytic capacity of amniotic fluids is usually much higher than that of the allantoic fluids. The hemolytic activity and infectivity of the virus have been found to be reduced or destroyed by heat, formaldehyde, and ultraviolet irradiation under conditions which leave the hemagglutinating capacity practically unchanged. Ultraviolet irradiation appeared to have a greater deleterious effect on the infectivity of the virus than on its hemolytic capacity. The marked reduction or destruction of hemolytic activity of the virus produced by certain treatments with these various agencies was not accompanied by loss of the ability of the virus to elute following its adsorption on red blood cells during the process of hemagglutination. This test for hemolytic activity, which measures a more labile property of the virus than do determinations of virus hemagglutination or virus elution, may be useful in detecting changes which occur early during degradation of the virus.

The chick embryo fibroblast infected by Rous sarcoma virus in vitro acquires the capacity to produce the acid mucopolysaccharides which are found in the tumors caused by this virus and which are also produced by tumor cells in vitro. The transformed cell acquires synthetic as well as morphologic, metabolic, and proliferative properties characteristic of Rous sarcoma tumor cells in vivo and in vitro and the transformed cell may be analogous to the tumor cell produced by virus infection in vivo.