Abstract
The Newcastle Disease Virus (NDV) hemolysin is inactivated by a single antibody molecule per virus. Electron irradiation of NDV indicates that the rate of hemolysis of red blood cells depends on the number of intact hemolysin units per virus, whereas 18649-18662 IMMUNOLOGY[long dash]GENERAL AND BACTERIAL [Vol. 33] 1512 the ability to lyse red blood cells, given sufficient time, depends on the presence of only one intact hemolysin unit per virus.