BACILLUS ANTHRACIS AND ANTHRAX 567 



It may be cultivated also upon hay infusion, various other vegetable 

 media, sugar solutions, and urine. While moderate acidity of the 

 medium does not prevent the growth of this bacillus, the most favorable 

 reaction for media is neutrality or slight alkalinity. 



On gelatin plates, colonies develop within twenty-four to forty-eight 

 hours as opaque, white disks, pin-head in size, irregularly round and 

 rather flat. As the colonies increase in size their outlines become less 

 regular and under the microscope they are seen to be made up of a 

 hair-like tangle of threads spreading in thin wavy layers from a more 

 compact central knot. The microscopic appearance of these colonies 

 has been aptly described as resembling a Medusa head. Fragments of a 



Fig. 123.— Anthrax Colony on Gelatin. (After Giinther.) 



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 fluidified. 



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

 along the course of the puncture. From this, growth proceeds in 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 fiUed with an, opaque mixture of bacilli and fluid. 



