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.