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 radiatirg 

 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. 



