494 BACTERIOLOGY. 



appear 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 in 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 and opaque, and granular and rough on 

 the surface. When touched with a sterilized needle 

 one experiences a sensation that suggests somewhat 

 their matted structure. They are never moist or 

 creamy. The bit that is taken up with the needle is 

 always more or less ragged. 



The colonies on gelatin at the earliest stages also pre- 

 sent the same wavy appearance ; but this characteristic 

 soon becomes in part destroyed by the liquefaction of 

 the gelatin which is preduced by the growing organisms. 

 This allows them to sink to the bottom of the fluid, 

 where they lie as irregular masses. Through the fluid 

 portion of the gelatin may be seen small clumps of 

 growing bacteria, which look very much like bits of 

 cotton-wool. 



In bouillon the growth is characterized by the forma- 

 tion of flaky masses, which also have very much the ap- 

 pearance of bits of raw cotton. Microscopic examina- 

 tion of one of these flakes reveals the twisted and plaited 

 arrangement of the long threads. 



On potato it develops rapidly as a dull, dry, granular, 

 whitish mass, which is more or less limited to the point 



