390 PATHOGENIC BACTERIA. 



The bacillus is rather variable culturally, and is some- 

 what polymorphic. Probably both size and form depend 

 to a certain extent upon the culture-medium on which 

 it grows. On the average, it measures 1-3 X 0.4-0. y/A 

 It usually occurs in the form of short rods, but very 

 short coccus-like elements and quite elongate forms are 

 often found in the same culture. The individual bacilli 

 are frequently isolated or in pairs. Chains are the ex- 

 ception. They are provided with flagella, which are 

 very variable in number, generally from four to a dozen, 

 though there may be more. It forms no spores. 



The bacillus stains well with the ordinary aqueous 

 solutions of the anilin dyes, but does not retain the stain 

 after immersion in Gram's solution. 



The bacillus is motile, though in this particular it is 

 subject to irregularity, the organisms from some cultures 





FlG. no. Bacillus coli communis: superficial colony two days old upon a 

 gelatin plate; x 21 (Ileim). 



always swimming actively, even when the culture is 

 some days old, others being exceedingly sluggish even 

 when voting and actively growing, and a few cultures 

 seem to consist of bacilli that do not move at all. Fresh 

 cultures which, when grown at incubation temperature, 

 consist of entirely non-motile bacteria are probably Bacil- 

 lus coli iwmohilis, not Bacillus coli communis. 



The bacillus is readily cultivated upon the ordinary 



