HEMOEEHAGIC SEPTICEMIAS AND PLAGUE 347 



Pathogenic Characteristics.— Practically all species of 

 the genus Pasteurella quickly prove fatal when injected 

 into the ear vein of a rabbit. The animal dies as a result of 

 a septicemia; small hemorrhages usually may be noted in 

 the membranes of the digestive tract. Practically all the 

 species are pathogenic to sparrows. The various races show 

 some differences in their ability to affect other species of 

 animals. For example, fowls, in general, will succumb to 

 various cultures of the organisms associated with swine 

 plague, but not of the organisms causing hemorrhagic 

 septicemia in cattle. 



Pasteurella cHOLEEiE-GALLiNAEUM 



S3nion3Tns. — Bacillus avisepticus, Bacillus cholerce-gal- 

 linarum, Bacillus cholerw, and Bacterium avicidum. 



This organism is the specific cause of the disease chicken 

 cholera. This disease has a wide distribution over Europe 

 and America. It was first studied by Pasteur in 1880. He 

 succeeded in growing the causal organism in artificial 

 media and made use of it in making studies on immuniza- 

 tion. By growing this organism in artificial media he suc- 

 ceeded in attenuating certain strains so that they might be 

 used as a vaccine. This work was of great historical im- 

 portance, as it marked the first step in the study of experi- 

 mental immunity, particularly the production of immunity 

 by means of injections of pure cultures of microorganisms. 



Apparently there are many different strains of the fowl 

 cholera organism, showing marked differences in virulence. 

 Some, when injected in considerable quantities into fowls, 

 cause the development of a high degree of immunity ; others 

 bring about practically no immunity. The pigeon is very 

 susceptible and is frequently used in a study of this organ- 

 ism in the laboratory. 



Fowls which have died of chicken cholera usually show 

 congestion of the heart and an accumulation of serum in 



