Studies on the histopathology and pathogenesis of Newcastle disease of fowls in South Africa, with special reference to the lymphoid tissue. A preliminary report.

1. Newcastle Disease, after intramuscular inoculation of virulent virus, was characterised by pathognomonic lesions in the spleen, the gastro-intestinal tract, and the nervous system. 2. In the Spleen degenerative changes in the cells of the lymphoid sheath were noted in early deaths. In some of them flake-like granules were observed. There were depletion of lymphocytic cells in the follicle, increase in the number of plasmacytes, and proliferation of reticulum cells. In cases with a more protracted course, hyperplasia of the lymphoid tissue was apparent. 3. In the gastro-intestinal tract the chief changes were observed in the Proventriculus, the Small Intestine, and Caecal Tonsils. In early cases, this was of the nature of a localised necrosis with haemorrhage. The changes in the lymphoid tissue were of a similar nature as those observed in the spleen. 4. The Nervous system in the majority of cases revealed a hyperaemia, and in some, small haemorrhages. The changes in the small blood vessels were of the nature of a so-called "endotheliosis" with an infiltration of the walls with lymphocytes, and other cells of the blood. In some of these vessels the presence of plasma, mononuclears and red cells was noted within the lumen. In some cases chromatolysis and slight gliosis were seen. 5. More information is desired about the depots, morphology, and function of the lymphoid tissue of the fowl. It would, however, appear that lymphocytes and plasmacytes have an independent origin, and that they are probably implicated in the propagation of the virus and antibody mechanism. At this stage it is not possible to indicate what the nature is of the flake-like granules in some of the cells of the lymphoid tissue. Further investigations are indicated to clarify some of the problems raised in this preliminary study.