496 CONTAGIOUS EPITHELIOMA 
epithelial nodular form occurs more frequently in the south. The 
statement is quoted by Jowett that chicken pox is one of the most 
destructive diseases of chickens in Southern Africa. 
Etiology. Chicken pox seems to be due to a filterable virus. 
Rivolte considered the cause to be a protozoan parasite belonging to 
the Gregarinidia. 
Symptoms and morbid anatomy. The disease manifests itself by 
the formation of nodules composed of tissue of an epitheloid nature on 
the areas of the skin free or nearly so of feathers about the head. The 
nodules are formed often with a caseous center and usually remain 
discrete. At other times 
the contents may be of a 
flaky or coagulated ma- 
terial. When the lesions 
are in the mouth they 
resemble those of diph- 
theria. When the no- 
dules appear on the 
eyelids, the eyes may 
become closed and the 
fowl die of starvation. 
Prevention. Manteu- 
fel was the first to im- 
Fic. 119. HEAD OF FOWL SHOWING LESIONS munize fowls against 
ABOUT THE MouTH (Pickens). 
contagious epithelioma 
by vaccination. He succeeded by injecting into the circula- 
tion or subcutaneous tissue a substance prepared from scrap- 
ings of epithelial or mucous membranes mixed with salt solution. 
He also claimed that therapeutic results followed such injections. 
Later Hadley and Beach, Giltner and Mack reported success in 
vaccinating fowls with an emulsion prepared from the nodules. 
Mack grinds this carefully in a mortar with sand in a small quantity 
of salt solution. It is then filtered through cotton, diluted with nor- 
mal salt solution until it is moderately turbid and attenuated by 
heating in a water bath at 55° C. for one hour. Each fowl is then 
given 1 c.c. of the attenuated virus subcutaneously in an unfeathered 
area beneath the wing. He reports satisfactory results. 
