Propagation of fowl plague and of Newcastle disease viruses in cultures of embryonic human lung.

could be observed around each explant. Cultures of varying ages were used for the experiments. Virus was added in appropriate dilutions to the medium. Passages were made into fresh cultures by the inoculation of the fluid medium from infected cultures in dilutions of 10-1 to 10-3. Coverslips were stained by May-Grunwald-Giemsa according to the nethod described by Jacobson and Webb (1952). Virus multiplication was estimated by egg infectivity and haemagglutination tests of the culture fluids. Egg infectivity titrations were carried out by allantoic inoculation of 0-05 ml. of tenfold dilutions of the virus preparations into groups of 4 ten-day embryonated eggs. The end points were calculated by the method of Reed and Muench (1938) and the results given as the number of 50 per cent infectivity doses (EID50) per ml. Haemagglutination tests were performed by the pattern technique using 0-2 ml. of twofold dilutions of the culture material and an equal volume of a 0-5 per cent suspension of chicken red cells.