M ACROFORM ATIONS I39 



The structural complexity, even beauty, of this type of colony has tended 

 to produce the impression that there exists an intrinsic tendency towards the 

 formation of the structure, as in the case of a true, multicellular organism. 

 This is not so. A rough bacillus growing upon a frictionless surface, would 

 produce a straight, or slightly spiral thread of indefinite length. Upon an 

 agar plate, however, after the thread has grown a short way across the surface, 

 its rigidity is not sufficiently great to permit it to extend further in a straight 

 line. It therefore kinks, and because of its slightly spiral growth, tends to 

 form flat coils upon the surface of the plate. All portions of tliis primary 

 coil are growing simultaneously, and to accommodate this growth it produces 



(Reproduced from the Journal of Pathology 

 and Bacteriology.) 



Fig. 61 

 GROWTH OF A ROUGH COLONY 



Primary coil of a rough colony. Shigella flexneri, impression preparation < 7(»(). 



secondary loops and coils, and upon them still further and more complex 

 convolutions. The outer portions of the colony lie flat upon the medium, 

 and the internal coils ovcrhe one another to a small extent. 



The appearance and complexity of the colony vary with the rigidity of 

 the bacterial thread, and the resistance of the surface of the medium. Colonies 

 upon lactose-taurocholatc agar may be noticeably flat and widespread, 

 presumably in consequence of the high concentration of electrolytes and low 

 I surface-tension of such media. 



