Hemolytic interaction of Newcastle disease virus and chicken erythrocytes. I. Quantitative comparison procedure.

The extent to which erythrocytes are hemolyzed by Newcastle disease virus is a function of the relative concentrations of both virus and erythrocytes. Under proper conditions, the interaction of a single virus particle with an erythrocyte is sufficient to cause lysis. The extent of hemolysis is directly proportional to virus concentration only when the virus-erythrocyte ratio is very low. At the higher virus-erythrocyte ratios usually employed in hemolysis experiments, the extent of hemolysis is proportional to the logarithm of the virus concentration. Thus, quantitative comparisons of hemolytic activities of different virus preparations cannot be made by directly comparing the extent of hemolysis. Relative hemolytic activities must be determined by comparing virus concentrations which yield equivalent amounts of hemolysis (the quantitative comparison procedure).