DISEASES PRODUCED BY ULTRA-MICROSCOPIC ORGANISMS 487 



of the subcutaneous tissues and of the serous membranes, and the 

 formation of a fibrous exudate upon the latter. 



Immunity. Practicable methods of immunization have not 

 been developed. 



Transmission. The disease is transmitted by the ingestion of 

 food soiled with the infective feces, nasal secretion, or blood of in- 

 fected birds. 



Virus of Epithelioma Contagiosum 



Disease Produced. Fowl pox, epithelioma contagiosum in 

 domestic fowls, sore head. 



Marx and Sticker, in 1902, determined the cause of fowl pox 

 to be a filterable virus. Several other investigators subsequently 

 confirmed their results. 



Distribution. The disease is known to occur in Europe, in the 

 United States, particularly the south, in California, and Hawaii. 



Nature of the Virus. Marx and Sticker showed that when an 

 epithelial nodule was triturated in physiological salt solution that 

 the fluid which passed through a Berkefeld filter was infective. 

 Some investigators have observed tiny spherical granules, less than 

 0.25 u. in diameter, in the emulsion of the virus, but it is by no 

 means certain that these are the disease-producing organisms. The 

 virus is relatively resistant to unfavorable conditions. The 

 nodules may be dried for weeks without losing their infectivity. 

 It is destroyed by heating to 60 for eight minutes. Mixed with 

 glycerin, it retains its infectivity for many weeks. It is easily 

 destroyed by disinfectants. 



Pathogenesis. The disease is a chronic, contagious infection, 

 characterized by an initial catarrh of the mucosa of the head, 

 followed by wart-like growths (epithelial hyperplasia) of the skin, 

 especially of the comb and naked skin of the head, sometimes 

 associated with a croupous diphtheritic condition of the mucosa 

 of the head. This latter condition is one of those grouped under 

 the general name of fowl diphtheria. The disease commonly 

 terminates favorably in three to five weeks. 



Immunity. No practicable method of immunization has been 

 devised. 



Transmission. The disease is transmitted by direct contact 

 with infected fowls. 



