308 



A MANUAL OF BACTERIOLOGY 



end of a week the culture is like an inverted fir tree 

 (Fig. 37), and the gelatin becomes 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 direc- 

 tions, with gracefully curved 

 margins " (Reichel), and the 

 growth is sticky. The young 

 deep agar colonies, which Eurich 1 

 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 early stage has a 

 finely granular, ground - glass 

 appearance. On blood-serum a 

 thick creamy layer forms, with 

 slow liquefaction of the medium. 

 On potato the organism grows 

 Seven days f ree iy as a (j r y greyish layer, 



with an abundant formation of 

 spores. In broth it forms a somewhat scanty flocculent 

 deposit, the broth remaining clear and giving the indole 

 reaction. 



In old cultures various involution forms are met with ; 

 the rods lose their regular shape and become swollen, 

 producing the so-called torula forms, while the homo- 



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



FIG. 37. Anthrax 

 stab - culture, 

 old. 



Gelatin 



