BACILLUS OF BUBONIC PLAGUE. 607 



rhagic cases and shortly before death. It also occurs 

 in the feces of men and animals. 



Morphology. Short thick rods, with rounded ends, 

 frequently occurring in short chains and often sur- 

 rounded by a capsule. When obtained from cultures 

 the bacilli present considerable spherical enlargement 

 (Fig. 82). 



Stains readily with the ordinary aniline dyes, the 

 ends being usually more deeply colored than the central 

 portion; does not stain by Gram's method. 



Biological Characters. An aerobic, non-motile bacil- 

 lus. Does not form spores. Grows on the usual culture 

 media. Does not liquefy gelatin. Grows best on blood- 

 serum in the incubator, the growth appearing on the 

 surface after twenty-four to forty-eight hours, in the 

 form of white, moist, transparent and iridescent col- 

 onies. It grows rapidly on glycerin-agar, forming a 

 grayish-white surface growth. In bouillon a very char- 

 acteristic appearance is produced, the culture medium 

 remaining clear while a granular or grumous deposit 

 forms on the walls and on the bottom of the tube. 



Pathogenesis. This bacillus is pathogenic for rats, 

 mice, guinea-pigs, monkeys, rabbits, flies, and other 

 insects, which usually die within two or three days 

 after inoculation. Then at the point of inoculation is 

 found a somewhat hemorrhagic infiltration and rcdema, 

 with enlargements of the neighboring lymph-glands, 

 hemorrhages into the peritoneal cavity and parenchy- 

 matous congestion of the organs. The spleen sometimes 

 shows minute nodules resembling miliary tubercles. 

 Microscopically the bacilli are found in all the organs 

 and in the blood. The disease is rapidly communicated 

 from one animal to another, and thus its extension is 



