28 BACILLUS ANTHRACIS 



becomes older and spore formation advances, the 

 cohesion between the cells grows less, and finally 

 disappears when the spores are mature and free, so 

 that shaking then produces a general turbidity of 

 the fluid containing the growth. 



The dull grey blanket-like growth of the young 

 agar culture similarly betrays the microscopic 

 structure. 



In gelatine stab-culture (Fig. 18) the growth is 

 very characteristic, and produces with its radiating 

 filaments starting from the line of inoculation, 

 longest near the surface, and gradually diminishing 

 as the depth in the gelatine increases, an appear- 

 ance which has been compared to that of an 

 inverted fir-tree. Liquefaction slowly takes place, 

 commencing at the surface ; and in the liquefied 

 portion the growth acquires the usual cotton-wool 

 appearance characteristic of young cultures in fluid 

 media. 



In gelatine plate cultures the appearance of the 

 colonies differs as the growth occurs on the sur- 

 face or in the depth of the medium. An impression 

 preparation of a surface colony (Fig. 19) shows it 

 to consist of a series of beautifully regular parallel 

 lines of bacilli concentrically arranged, and resulting 

 in a roughly circular growth with a waved margin. 



