776 PATHOGENIC MICROORGANISMS 



Medusa head. Fragments of a colony examined on a slide with a 

 higher power show the individual threads to be made up of parallel 

 chains of bacilli. 



After a day or two of further growth, the gelatin about the 

 colonies becomes liquefied. 



In gelatin stab cultures, growth appears at first as a thin white line 

 along the course of the puncture. From this, growth proceeds in 



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FIG. 79. BACILLUS ANTHRACIS. In section of kidney of animal dead of anthrax. 



thin spicules or filaments diverging from the stab, more abundantly 

 near the top than near the bottom of the stab, owing to more active 

 growth in well oxygenated environment. The resulting picture 

 is that of a small inverted "Christmas tree." Fluidification begins 

 at the top, at first a shallow depression filled with an opaque mixture 

 of bacilli and fluid. Later the bacilli sink to tlic bottom of the flat 

 depression, leaving a clear supernatant fluid of poptonizod gelatin. 

 In broth, growth takes place rapidly, but does not lead to an even, 

 general clouding. There is usually an initial pellicle formation at 



