416 BACTERIOLOGY. 



iu strands like those of a rope — sometimes they have a 

 plaited arrangement. (See Fig. 88.) These bundles 

 twist about and cross in all directions, and eventually 

 disappear at the periphery of the colony. At the ex- 

 treme periphery of the colonies it is sometimes possible 

 to trace single bundles of these threads for long dis- 

 tances across the surface of the agar-agar. The colony 

 itself is not circumscribed iu its appearance, but is more 

 or less irregularly fringed or ragged, or scalloped. To 

 the naked eye they look very much like minute pellicles 

 of raw cotton that have been pressed into the surface 

 of the agar-agar. 



As the colonies continue to grow they become more 

 and more dense, opaque, and granular and rough on the 

 surface. When touched with a sterilized needle one 

 experiences a sensation that suggests, somewhat, the 

 matted structure of these colonies. The bit that may 

 thus be taken from a colony is always more or less 

 ragged. 



Gelatin. — The colonies on gelatin at the earliest 

 stages also present the same wavy appearance; but this 

 characteristic soon becomes in part destroyed by the 

 liquefaction of the gelatin which is produced by the 

 growing organisms. This allows them to sink to the 

 bottom of the fluid, where they lie as an irregular mass. 



Through the fluid portion of the gelatin may be seen 

 small clumps of growing bacilli, which look very much 

 like bits of cotton-wool. 



Bouillon. — In bonillon the growth is characterized 

 by the formation of flaky masses, which also have very 

 much the appearance of bits of raw cotton. Micro- 

 scopic examination of one of these flakes reveals the 

 twisted and plaited arrangement of the long threads. 



