Sendai virus is able to induce the fusion o f human erythrocytes. Bivalent cations or A T P are not essential for polyerythrocyte formation. High fusion indices were obtained when Sendai virus was added to cells incubated in the presence of both E D T A and iodoacetic acid. H u m a n erythrocyte ghosts prepared by gradual hemolysis still retain the potential to undergo virus-induced fusion. Fusion of human red blood cells without the addition of viruses was obtained by incubation of erythrocytes at p H 10.5 in the presence of Ca ++ (40 m M ) or by addition of phospholipase C Clostridium perfringens preparations to cells previously agglutinated or polylysine.

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Phospholipase-C preparations from Clostridium perfringens can induce hemolysis of chicken erythrocytes in the presence of EDTA. Under these conditions hydrolysis of membrane phospholipids does not take place. When Ca2+ is added to the incubation media both hemolysis and hydrolysis of phospholipids occur. However, when Mn2+ or U0,2+ is added, both the hemolysis and hydrolysis of membrane phospholipids are strongly inhibited. When phospholipase-C (Cl. perfringens) preparations are heated a t 56 "C in the presence of Ca2+, the hemolytic activity is inhibited while the hydrolytic activity of the enzyme is retained. Such non-hemolytic phospholipase-C barely hydrolyse phospholipids from intact chicken redblood cells. However, it readily hydrolyses phospholipids from erythrocyte ghosts. Thus it appears that membrane phospholipids are unavailable to the enzyme unless they are exposed by hemolysis. Enveloped viruses of the paramyxoviruses group can induce, under certain conditions, fusion of mammalian cells and form homo and hetero-polykaryons [i]. These viruses are able to hemolyse redblood cells, and concomitantly with the hemolytic reaction, they induce fusion of red-blood cells [a]. Previous work on the virus-induced fusion of both red-blood cells and Ehrlich's Ascites tumor cells, indicated that there is a correlation between the virus's hemolytic activity and the fusion reaction. Recently we have shown that lytic phospholipase-C preparations from Clostridium perfringens may also

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