560 APPLICATION OF METHODS OF BACTERIOLOGY 



sometimes they have a plaited arrangement. (See Fig. 96.) 

 These bundles twist and cross in all directions, and even- 

 tually 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 circumscribed in 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 and opaque, and granular and rough on the 

 surface. When touched with a sterilized needle one experi- 

 ences 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, 

 suggesting a tiny particle of moist blotting paper. 



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 

 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 formation 

 of flaky masses, which also have very much the appearance 

 of bits of raw cotton. Microscopic examination 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 of 



