346 BACTERIOLOGY. 



It is motile and has but a single flagellum attached to 

 one of its ends. It liquefies gelatin more rapidly than 

 does Koch's organism. It possesses no characteristic 

 grouping, as can be seen in impression cover-slips of its 

 colonies. It does not form spores. On gelatin plates 

 its colonies develop very rapidly as saucer-shaped 

 depressions ; after twenty-four hours they vary from 

 1 to 4 mm. in transverse diameter. To the naked 

 eye they are almost transparent and are usually marked 

 by a denser centre and peripheral zone, the space 

 between being quite clear. They are not regularly 

 round in all cases. A peculiar aromatic odor accom- 

 panies their growth on gelatin. Under a low magnify- 

 ing power the smallest colonies are irregularly round 

 in outline, their borders being often rough and broken, 

 and the body of the colony is frequently marked by 

 creases or ridges that give to it a lobulated appearance 

 The larger colonies under the same lens appear as 



/ 



\. 



Fig. 68. 



Colopy of spirillum, tyrogenum on gelatin, twenty-four hours old. 



granular patches, a little denser at the periphery and 

 centre than at the intermediate portions. The periphery 

 gradually fades away and no distinct circumference 

 can be made out. (See Fig. 68.) The colonies of an 

 intermediate size in which liquefaction is just beginning 



