224 



MICROBIOLOGY 



Cultivation. The anthrax bacterium is an aerobic, facul- 

 tative anaerobic organism. While it may develop slowly and 

 sparsely under anaerobic conditions, free oxygen is required 

 to permit its luxuriant and characteristic growth. 



The optimum temperature for its cultivation is about 

 37.5 C. It is not, however, delicately susceptible to moderate 

 variations of temperature and growth is not entirely checked 

 until temperatures as low as 12 C. or as high as 45 C. are 

 reached. By continuous cultivation at a temperature near 

 either the higher or the lower of these limits, it may become 

 well adapted to the new environment and attain a luxuriant 

 growth. It may be cultivated on all of the usual artificial 

 media. It grows in hay infusion and on various other vege- 



Fig. 51. Fig. 52. 



Fig. 51. Photograph of colonies of anthrax bacteria on agar plate 



culture. (Reduced one-half.) 

 Fig. 52. Photograph of a colony on agar of anthrax bacteria. X 6. 



table media. A neutral or slightly alkaline medium is the 

 most favorable for its growth. 



Agar. On agar plates, growth at 37.5 C. is vigorous and 

 colonies appear within twelve to twenty- four hours. They are. 

 irregular in outline, slightly wrinkled, and give under the 

 microscope a characteristic tangled-thread appearance. The 

 colonies are slightly glistening and tough in consistency. 



On inclined agar, the colonies usually become confluent, 



