344 AGKICULTUEAL AND INDUSTBIAL BACTEEIOLOGT 



has caused some investigators to place the organism in the 

 genus Pasteurella. 



Cultural Characters. — The isolation and cultivation of 

 this organism are somewhat complicated by its peculiar 

 relationship to oxygen. When in shake culture in serum 

 agar, the organism grows in a layer several millimeters 

 below the surface, that is, while not a strict anaerobe, it does 

 not grow well (at least upon first cultivation) in the pres- 

 ence of an atmospheric pressure of oxygen ; in other words 

 it is micro-aerophilic. After cultivation for a time in the 

 laboratory, it may be grown readily in the presence of oxy- 

 gen in the ordinary laboratory media. It grows best with 

 the addition of serum to the medium. The colonies develop 

 at 37° as small, usually transparent dots. Growth is very 

 slow at room temperature. 



Pathogenesis. — Experiments have shown that this or- 

 ganism will cause abortion in pregnant cows, both by 

 injection and by feeding. Injection into the rabbit or into 

 guinea pigs is followed by specific changes in the liver and 

 spleen and by the development of arthritis. 



Immunity. — Cows that have aborted one or more times 

 frequently become immunized against disease. Various 

 methods of vaccination and serum treatment have been 

 attempted but have not been attended with general success. 



The organism is not infrequently present in milk from 

 infected cows. The disease is probably frequently trans- 

 mitted Jjy ingestion, perhaps also by coition. 



Ahoriin prepared in an analogous manner to tuberculin 

 has been used to some extent for diagnosis. More fre- 

 quently the agglutination test is used and has come to be 

 the recognized test for diseased animals. 



