BACILLUS ANTHRACIS 



375 



of dead animals, or from the blood of an infected animal. Gelatin 

 is rapidly liquefied; colonies appear in gelatin plates within eighteen 

 hours after inoculation, which are from 1 to 2 mm. in diameter. They 

 are gray, opaque, and somewhat irregular in size. The organisms 

 develop rapidly, and liquefaction commences within thirty hours as a 

 rule. At this stage of development the edges of the colonies are com- 

 posed of tangled, radiating chains of bacilli which extend into the 

 surrounding medium, and the colony itself is composed of a mass of 

 twisted filaments which has been likened to a Medusa head. Few, 

 if any, pathogenic bacteria present such an appearance. The growth 

 in stab cultures in gelatin is also characteristic; the organisms grow 



FIG. 54. Bacillus anthracis, section from kidney, semi-diagrammatic. 

 (Kolle and Hetsch.) 



X 500. 



away from the line of inoculation into the medium as spikelets which 

 resemble an "inverted pine tree." Liquefaction soon takes place. 

 Milk is rendered acid, and the casein precipitated and slowly liquefied. 

 A pellicle forms upon the surface of broth which readily becomes 

 detached from the sides of the tube and settles to the bottom. No 

 turbidity is produced in fluid media. 



Bacillus anthracis is a strongly aerobic bacillus, but growth will 

 take place under anaerobic conditions. Growth is very slow at 18 

 C., and ceases below 15 C. The optimum is about 37 C., and 

 development does not take place at 45 C. 



The vegetative (asporeless) organisms are not resistant to heat or 

 drying. The spores are very resistant. Dried spores have remained 

 viable and virulent for eighteen years. 1 Fresh blood containing anthrax 



1 V. Szekely, Ztschr. f. Hyg., 1903, xliv, 363. 



