CULTURAL CHARACTERISTICS 167 



sporangium wall persist for some little time at either end of the 

 spores. Spores are oval to cylindrical 1.0 to 1.6 by 2 to 2.5 /j, often 

 in fairly long chains. 



"Cultural Characteristics. Growth in broth vigorous, flocculent, 

 with no persistent surface growth. Gelatin colonies rapidly liquefy- 

 ing, filamentous to rhizoid. Growth on agar streak rhizoid, mostly 

 beneath the surface of the medium. 



"Physiology. The typical group number is B. 121.23230?2. It 

 shows less variation than does the group number of B. megatherium, 

 probably because B. mycoides grows better in the media used for 

 making the tests. The same acid reactions are obtained in broth 

 culture and on litmus agar. 



"B. cereus Frankland, 1887. --This type can be distinguished 

 from B. megatherium by the smaller size of its spores and by its 

 more vigorous growth in liquid media, and from B. mycoides by the 

 absence of rhizoid growth on agar. 



o o 



FIG. 26. B. cereus. X 1000 diameters. (After Conn) 



"Morphology. In morphology it is scarcely to be distinguished 

 from B. mycoides. Young rods are 0.8 to 1.3 by 2. to 6 /* form- 

 ing long chains, but unlike B. mycoides they are very actively 

 motile and are easily shown to be surrounded with numerous flagella. 

 Older rods are often swollen and contain unstained globules. Oval 

 to cylindrical spores, 1.2 to 1.6 by 2. to 2.5 /x, are produced cen- 

 trally, retain the remnants of the sporangium wall for a short time 

 and often cling together in chains. 



"Cultural Characteristics. Growth in broth vigorous, with uniform 

 turbidity, sediment and a surface pellicle. Gelatin colonies quite 

 large, ordinarily round, with entire margin, and covered with a 

 pellicle that generally shows concentric rings, although under some 

 conditions the colonies are filamentous and resemble those of B. 

 mycoides. Growth on agar streak raised, ordinarily rugose, soft 

 to membranous, generally dull; never rhizoid or beneath the surface 



