ANTHRAX 



253 



in a gelatin plate in about thirty hours, and in two to 

 three days appear as small, roundish, cream-coloured 

 pasty masses in little pits in the gelatin, due to its lique- 

 faction. Microscopically the colonies are somewhat char- 

 acteristic ; each consists of a mass of wavy, tangled 

 filaments like a tiny wad of 

 cotton- wool. In gelatin streak- 

 cultures development is slow, 

 and in four or five days a 

 creamy, pasty growth forms 

 in a trough of liquefaction. In 

 a gelatin stab- culture (prefer- 

 ably 5 per cent, gelatin) lateral 

 branches spread from the cen- 

 tral growth, longer in the upper 

 layers, shorter below, so that 

 at the end of a week the cul- 

 ture is like an inverted fir tree 

 (Fig. 36), and the gelatin be- 

 comes gradually liquefied from 

 above downwards. The colonies 

 on an agar plate develop in 

 twenty hours at 37 C. as cream- 

 coloured points. The surface 

 colonies microscopically consist 

 of little masses of wavy, tangled 

 filaments (Plate V. a and b) ; 

 " they are not circular but run to a point in two or three 

 directions, with gracefully curved margins " (Reichel), and 

 the growth is sticky. The young deep agar colonies, which 

 Eurich x considers most characteristic, consist of interlacing 

 knotted coils of fine filaments. On an agar surface culture 

 at 37 C. there is a copious development in eighteen hours 

 of a thick, cream-coloured, slimy growth, which at this 

 1 Journ. Path, and Bact., xvii, 1912, p. 249. 



FIG. 36. Anthrax. Gelatin 

 stab-culture. Seven days 

 old. 



