104 DISEASES OF DOMESTICATED BIRDS 
usually much larger. They seem to have no definite internal structure, 
being usually homogeneous in appearance. Deeper in the epithelial mass 
the cells are very large and show evidence of degeneration, here the cyto- 
plasm stains poorly and has but few granules. Burnett has called this con- 
dition hydropic. In the center of the older epithelial cell masses, the cells 
are so degenerated that they form a necrotic mass. The nucleus of the 
cell first degenerates. The cause of this degeneration is probably due to 
the fact that the cell nests increase in size by multiplication at the peri- 
phery. The outside cells consume all the nutriment at the expense of the 
central ones and cause their degeneration. The central necrosis rapidly 
extends, involving the greater part of the tumor mass.” 
The cell inclusions characteristic of pox have been studied ex- 
tensively and the interpretation of their nature and significance has 
been the subject of much discussion. Some observers see in them, 
stages in the life of a protozoan, while others regard them as products 
of degeneration of the cell. 
In the early stage of false membrane formation, the external layer 
of the mucosa is principally involved. There is an exfoliation of 
the cells, which become swollen and amorphous. The cell proto- 
plasm early loses its identity, while the nuclei disintegrate more 
slowly and appear as independent bodies showing different degrees 
of degeneration. Mucous exudates which have undergone coagula- 
tion, together with the epithelial cells, enclose leucocytes in various 
stages of degeneration. An edematous area is formed around the 
membrane, and wandering leucocytes are observed in the Malpighian 
layer of the mucosa. During this stage there is a well marked line 
of differentiation between the morbid area and the comparatively 
unaffected base. As the pseudo membranes are extended, the under- 
lying tissues are more deeply involved. The deeper epithelial cells 
become infiltrated and exhibit cloudy swelling. A fibrinous exudate 
accumulates which holds the cell elements in a compact tenacious 
mass. In this may be observed numerous organisms, principally of 
the bacterial type, which are to be considered as secondary invaders. 
Protozoal organisms may also be present including flagellates, amebas, 
coccidia and other forms. Some investigators have attributed the 
origin of avian diphtheria to certain of these protozoa. However, the 
evidence brought out has not been sufficient to establish these organ- 
isms as specific causes. The course of development of filterable 
viruses in the animal system is a problem which has not been satis- 
factorily solved, and until this is accomplished, it is unsafe to give 
etiologic significance to organisms or cell inclusions which may he 
‘found associated with certain morbid conditions. 
