380 BACTERIOLOGY. 



seen to lie parallel side by side or are twisted in strands 

 like those of a rope sometimes they have a plaited 

 arrangement. (See Fig. 81.) These bundles twist about 

 and cross in all directions, and eventually disappear at 

 the periphery of the colony, At the extreme periphery 

 of the colonies it is sometimes possible to trace single 

 bundles of these threads for long distances across the 

 surface of the agar-agar. The colony itself is not cir- 

 cumscribed in its appearance, but is more or less irregu- 

 larly 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 bouillon the growth is characterized 

 by the formation of flaky masses, which also have very 

 much the appearance of bits of raw cotton. Microscopic 



