THE BACILLUS OF AXTHRAX. 



425 



temperature of 20 to 38 C. Development ceases at temperatures 

 below 12 C. or above 45 C. 



This bacillus grows best in neutral or slightly alkaline media, and 

 its development is arrested by a decidedly acid reaction of the cul- 

 ture medium. It may be cultivated in infusions of flesh or of vari- 

 ous vegetables, in diluted urine, in milk, etc. 



In gelatin plate cultures small, white, opaque colonies are devel- 

 oped in from twenty-four to thirty-six hours, which under the micro- 

 scope are seen to be somewhat irregular in outline and of a greenish 

 tint ; later the colonies spread out upon the surface of the gelatin, 

 and the darker central portion is surrounded by a brownish mass of 

 wavy filaments, which are associated in tangled bundles. Mycelial- 

 like outgrowths from the periphery of 

 the colony may often be seen extending 

 into the surrounding gelatin. At the 

 end of two or three days liquefaction of 

 the gelatin commences, and the colony 

 is soon surrounded by the liquefied me- 

 dium, upon the surface of which it floats 

 as an irregular white pellicle. In gela- 

 tin stab cultures growth occurs all 

 along the line of puncture as a white cen- 

 tral thread, from which lateral thread- 

 like ramifications extend into the culture 

 medium. At the end of two or three 

 days liquefaction of the culture medium 

 commences near the surface, where the 

 development has been most abundant. 

 At first a pasty, white mass is formed, 

 but as liquefaction progresses the upper 

 part of the liquefied gelatin becomes 

 transparent from the subsidence of the 

 motionless bacilli, and these are seen 

 upon the surface of the non-liquefied 

 portion of the medium in the form of 

 cloudy, white masses, while below the line of liquefaction the charac- 

 teristic branching growth may still be seen along the line of puncture. 



In agar plate cultures, in the incubating oven at 35 to 37 C., 

 colonies are developed within twenty-four hours, which under the 

 microscope are seen to be made up of interlaced filaments and are 

 very characteristic and beautiful. Upon the surface of nutrient agar 

 a grayish-white layer is formed, which may be removed in ribbon-like 

 strips ; and in stick cultures in this medium a branching growth is 

 seen, like that in gelatin, but without liquefaction. The addition of 



FIG. 100. Culture of Bacillus an- 

 thracis in nutrient gelatin : a, end 

 of four days ; 6, end of eight days. 

 ( Baumgarten.) 



