AVIAN DIPHTHERIA AND BIRD POX 103 
into a hard dry scab. After seven to nine days this scab may be 
easily removed leaving a whitish area only slightly elevated above 
the surface and usually pitted. The scabs retain the virus of the 
disease and when rubbed on the scarified skin or mucous membrane 
Fie. 9. Head of a turkey affected with epithelioma 
contagiosum (bird pox). (Klee) 
of the mouth, even after a period of five years, may reproduce typical 
lesions. 
Haring and Kofoid describe the microscopic structure of chicken 
pox tissue as follows: 
“The epithelial tumors are produced by a hyperplasia of the epithelium 
due to an increase both in the size and number of cells. The zone of 
growth is in the stratum of Malpighii, the principal region of prolifera- 
tion being in the outer edges from which the cells increase in both direc- 
tions. A proliferating epithelium forms cell nests surrounded by thick 
bands of connective tissue, which contain blood vessels with thickened 
walls. The rapidly proliferating peripheral cells of the Malpighian layer 
are seen thickly studded with granules. The nucleus contains deeply 
staining chromatin bodies which are in an active process of proliferation. 
Karyokinetic figures are common in this region. More deeply ‘in the 
epithelial tumor mass the cells are greatly increased in size and have rela- 
tively fewer granules. The nuclei are nale and show little evidence of 
cell division. In these cells, are large cell inclusions which are very strik- 
ing in appearance, and which Reischauer and others have thought to be 
protozoa. There is usually but one of these bodies in each cell. They 
vary in size from five to twenty microns, most of them are round, al- 
though some of them are quite irregular in shape. They are evidently 
fatty in structure as they stain black with osmic acid. When eosin and 
methylene blue are used, they stain a faint pink, resembling somewhat the 
Negri bodies found in the brain tissue of rabid animals, although they are 
