346 AGEICULTUEAL AND INDUSTEIAL BACTERIOLOGY 



teurella suiseptica and of bubonic plague in man caused by 

 Pasteurella pestis will be considered. 



The organisms causing hemorrhagic septicemia in the 

 lower animals and birds, as already mentioned, are so much 

 alike that a description of one is satisfactory as a descrip- 

 tion for all except for pathogenic characteristics. 



The Hemorrhagic Septicemias 



It is probable that organisms belonging to this genus are 

 in some cases nonpathogenic and that there has developed 

 in literature some difficulty because of confusion of such 

 nonpathogenic forms with the disease producers. 



Pathology. — The pasteurellas are nonmotile rods, usu- 

 ally about 0.5 X !/"• The usual aniline dyes, particularly 

 when the organisms are stained from body fluid, as blood, 

 generally cause more intensive staining at the poles, the 

 central portion of the cell scarcely staining if at all. Some 

 forms when grown in culture media show frequently great 

 variation in size and appearance, and the polar staining is 

 much more difficult to demonstrate from such cultures than 

 from tissues. • The bacteria are Gram-negative and do not 

 produce spores. 



Cultural Characters. — These bacteria are readily culti- 

 vated in artificial media, producing upon gelatin and agar 

 round, flat and grayish colonies, finally becoming grayish 

 white and opaque. They do not grow well upon potato. In 

 broth they may produce clouding with clearing by sedi- 

 mentation; frequently a pellicle develops. There is no 

 appreciable change in milk. The organisms show very 

 slight fermentative powers. There has been an attempt to 

 differentiate species on the basis of acid production from 

 certain sugars, but this has not proved entirely successful. 



Physiological Characters. — The organisms grow best at 

 blood heat, but fairly well at room temperatures. They are 

 aerobic, gas is never formed, but volatile acids may be. 



