554 APPLICATION OF METHODS OF BACTERIOLOGY 



greenish or yellowish-green color, sharply outlined, and 

 not perfectly round. (See a, Fig. 90.) As growth progresses 

 this homogeneous granular appearance is replaced by an 

 irregular lobulation, and ultimately the sharply-cut margin 

 of the colony becomes dentated or scalloped. (See b and c, 

 Fig. 90.) After forty-eight hours (and frequently sooner) 

 liquefaction of the gelatin has taken place to such an extent 

 that the appearance of the colony is entirely altered. Under 

 a magnifying glass the colony proper is now seen to be 

 ragged about its edges, while here and there shreds of the 

 colony can.be detected scattered through the liquid into 

 which it is sinking. These shreds evidently represent 

 portions of the colony that became detached from its margin 

 as it gradually sank into the liquefied area. 



At d, in Fig. 90, is seen a representation of the several 

 appearances afforded by the colonies at this stage. At the 

 end of the second, or during the early part of the third day, 

 the sinking of the colonies into the liquefied pits resulting 

 from their growth is about complete, and under a low-power 

 lens they now appear as dense, granular masses, surrounded 

 by an area of liquefaction through which can be seen 

 granular prolongations of the colony, usually extending 

 irregularly between the periphery and the central mass. 

 (See e, Fig. 90.) If the periphery be examined, it will be seen 

 to be fringed with delicate, cilia-like lines that radiate from 

 it in much the same way that cilia radiate from the ends 

 of the columnar epithelial cells lining the air-passages. 



These are the more marked phases through which the 

 colonies of this organism pass in their development on 

 gelatin plates. In some cultures the various phases here 

 given pass in succession more quickly, while in cultures 

 from other sources they may be somewhat retarded. 



