BACILLUS AEROGENES CAPSULATUS 489 



oval, somewhat less in diameter than the vegetative form of the 

 organism, and are usually situated near one end of the rod. But one 

 spore is found in a single organism. Spores are apparently not formed 

 in the tissues of the body. The organism stains readily with ordinary 

 anilin dyes. It is Gram-positive,_although old cultures on artificial 

 media exhibit irregularities in staining, probably due to beginning 

 degeneration. 



Isolation and Culture. The organism is an obligate anaerobe. It 

 grows well in all ordinary media containing dextrose or lactose. From 

 tissues it is best obtained on anaerobic agar plates, where the colonies 

 are round, semi-translucent and colorless, and not characteristic. 

 Many strains hemolyze blood and on blood agar the colonies are sur- 

 rounded by a rather narrow zone of hemolysis. From the intestinal 



; 



FIG. 66. Bacillus aerogenes capsulatus from pure milk culture. X 1000. 



contents the organism is best isolated in milk. A thin suspension of 

 feces is emulsified in milk (whole milk) after the milk has been boiled 

 and rapidly cooled to remove all oxygen. The milk is heated to 80 

 C. for twenty minutes to kill vegetative organisms, and then it is 

 incubated at body temperature for eighteen to twenty-four hours. 

 At the end of that time the milk exhibits a characteristic stormy fer- 

 mentation. The casein is reduced in amount and the residual casein 

 is full of holes and is usually slightly pink in color. The whey is usually 

 colorless, gas bubbles are seen at the top of it, and there is character- 

 istically an odor of rancid butter butyric acid. The organism may be 

 obtained from the milk culture directly by plating anaerobically on 

 agar, or it may be obtained by injecting some of the whey into the 

 ear vein of a rabbit, killing the animal after five minutes and incubating 



