462 BACTERIOLOGY. 



has taken place to such an extent that the appearance 

 of the colony is entirely altered. Under a magnify- 

 ing 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 repre- 

 sent portions of the colony that became detached from 

 its margin as it gradually sank into the liquefied area. 



At d, in Fig. 77, 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 lique- 

 faction through which can be seen granular prolonga- 

 tions of the colony, usually extending irregularly be- 

 tween the periphery and the central mass. (See e, Fig. 

 77.) 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 re- 

 tarded. 



On plates of nutrient agar-agar the appearance of the 

 colonies is not characteristic. They appear as round or 

 oval patches of growth that are moist and moderately 

 transparent. The colonies on this medium at 37 C. 



