428 Avian Diphtheria and Chicken Pox. 



These variable results of the several oliservers preclude any specific 

 role of the bacteria found ; on the other hand, however, in view of 

 the positive inoculation results obtained with pure cultures the possi- 

 bility is by no means excluded that under certain conditions, especially 

 when the requirements for their propagation in the body of the fowl 

 are for any reason favorable, local diphtheritic inflammatory processes 

 may be caused or already existing processes be aggravated. When it is 

 considered that the disease of the mucous membrane may also be produced 

 by filtrates of disease products and by intravenous injection of such 

 filtrates the assumption or supposition can hardly be rejected that avian 

 diphtheria, as well as chicken pox, is primarily produced by the same 

 filterable virus, whereupon facultative pathogenic bacteria subsequently 

 settle on the mucous membranes and on their own part participate more 

 or less in the development of the clinical picture of the disease. 



According to Bollinger and Csokor the epithelioma contagiosnm of man is 

 identical with the epithelioma of birds, for material from the former, when inocvilated 

 into the comb of birds, gave rise to a disease identical with chicken pox. The close 

 relationship is indicated further by the fact that the virus of the disease is also 

 filterable (Juliusberg, Casagrandi, Serra, and others). 



Natural infection probably occurs in most cases by the 

 intermediation of exfoliated epithelial material or of exudate 

 discharged by the diseased animals while sneezing or cough- 

 ing, or otherwise. These, or the intestinal contents or 

 portions of internal organs of diseased or dead animals, may 

 come in contact with superficial abrasions on the skin or 

 mucous membranes. It is possible that infection may occur 

 also through the unimpaired mucosa, which is favored, no 

 doubt, by a preceding injury, and the frequent disease of the 

 eyes may be associated wdtli the habit chickens have of rubbing 

 the vicinity of the orbit with their feet (according to Megnin 

 older pigeons, wdiicli frequently show small caseated nodules 

 in the esophagus, may infect their young while feeding them). 



Healthy foAvls are usually infected by sick animals, con- 

 taminated drinking water, food, etc., serving as media of in- 

 fection. The disease is spread mostly through transportation 

 of fowls to markets and poultry exhibits; but free-flying birds 

 (pigeons, sparro\vs, etc.) may carry the infection for long dis- 

 tances to healthy poultry farms. 



Pigeons are most susceptible to the disease, chickens less 

 so, and water fowls to a considerable degree less. The sus- 

 ceptibility to infection is in general greater in young than in 

 older animals. 



An attack of the disease, no matter whether skin changes 

 or diphtheria of the mucous membranes was manifested, confers 

 immunity against subsequent infection, for chickens which have 

 recovered from the artificially produced disease, can not be re- 

 infected after two weeks. The immunity so acquired is, how- 

 ever, sometimes, only of short duration (Loewenthal). 



Anatomical changes. These may be confined to the skin, 

 or to the mucosa of the mouth and nose, but in the animals 



