458 A MANUAL OF BACTERIOLOGY 



or more. It is often so short that it is merely ovoid in 

 shape ; and, on the other hand, longer individuals and 

 involution forms occur 10 /x or more in length (Plate 

 XIV, a). It is feebly motile, and possesses flagella to 

 the number of three or four on an average, which are 

 shorter and straighter than those of the typhoid bacillus. 

 It is sometimes met with in diplococcoid form, which by 



FIG. 42. Colonies of the colon bacillus, superficial and deep. 



cultivation in ascitic fluid may become fixed. Capsulated 

 forms have been described. 



Spore-formation does not occur, but vacuolation may 

 sometimes be observed. The organism stains well by 

 the ordinary anilin dyes, but is Gram-negative. 



Cultural characters. The B. coli is aerobic and faculta- 

 tively anaerobic, and grows readily on the ordinary culture 

 media from 20 to 42 C. In gelatin plates the colonies 

 are visible in twenty-four to forty-eight hours. The deep 

 colonies are spherical, granular, and of a pale brownish 



