Etiology 



Evidence obtained by our experiments indicates that a filtra- 

 ble virus is the primary causative agent, and that more or less 

 severe complicating conditions are induced by secondary infec- 

 tion, of which a bacillus, probably the bacillus diphtheriae col- 

 umbarum of Loeffler seems to be the most important. 



Pathogenesis 



Transmission of this disease is not very difficult. Usually 

 about 70% of healthy birds will show symptoms of the disease 

 after associating with an affected one for a short time. Actual 

 contact is not necessary, as is shown by the spread of the dis- 

 ease at poultry shows. When using an infecting bird with 

 mucous membrane lesions, a few of our experimental birds 

 would show cutaneous lesions, and if a bird with the cutaneous 

 form was used the mucous membrane lesions were in excess. 



Emulsions of scrapings from either cutaneous or mucous 

 membrane lesions injected subcutaneously, submucously or ap- 

 plied to scarified areas on the skin, would in some cases produce 

 the generalized form of the disease. Similar results were pro- 

 duced by using an emulsion of a 24-hour agar growth of cul- 

 tures taken from lesions and injected subcutaneously. 



It is possible at times by scarifying the mucous membrane 

 of apparently healthy birds to produce at the point of injury 

 local lesions not unlike those of this disease, but they disappear 

 in a few days without manifestation of general symptoms. In- 

 complete experiments by using the blood of sick birds in an 

 attempt to produce the disease gave negative results, which is 

 contrary to that claimed by a few other investigators. 



Natural Infection 



There are a variety of ways by which natural infection takes 

 place. Cohabitation is one of the most common methods, an 

 infected bird introducing the disease into an entire flock. The 

 exfoliated membranes, or the exudate given off while sneezing 

 or coughing, act as intermediary carriers to the healthy birds. 

 The infection in this way will find lodgment on the skin where 

 there are slight abrasions, or on the mucosa of the eyes or 

 mouth, where it develops either to form the pox lesions or the 

 various other forms found on the mucous membranes. 



