Bacilli Resembling the Typhoid Bacillus 617 



motile, and provided with flagella, which are variable in number, 

 usually from four to a dozen. The organisms from some cultures 

 swim actively, even when the culture is some days old; others are 

 sluggish even when young and actively growing, and still other 

 cultures consist of bacilli that scarcely move at all. It forms no 

 endospores. 



Staining. The bacillus stains well with the aqueous solutions of 

 the anilin dyes, but not by Gram's method. 



Cultivation. It is readily cultivated upon the ordinary media. 



Colonies. Upon gelatin plates the colonies are visible in twenty- 

 four hours. Those situated below the surface appear round, yellow- 

 brown, and homogeneous. As they increase in size they become 

 opaque. The superficial colonies are larger and spread out upon the 



Fig. 255. Bacillus coli communis; superficial colony two days old upon a gelatin 

 plate. X 21 (Heim). 



surface. The edges are dentate and slightly resemble grape-vine 

 leaves, often showing radiating ridges suggestive of the veins of a 

 leaf. They may have a slightly concentric appearance. The col- 

 onies rapidly increase in size and become more and more opaque. The 

 gelatin is not liquefied. 



Gelatin Punctures. Development in gelatin punctures occurs 

 upon the surface, and also in the needle's track, causing the forma- 

 tion of a nail-like growth. The head of the nail may reach the walls 

 of the test-tube. No gas is formed in ordinary gelatin, but should 

 any dextrose be present, sufficient gas-production may occur to 

 break up the medium. The gelatin may become slightly clouded 

 but is not liquefied. 



Agar-agar. Upon agar-agar, along the line of inoculation, a gray- 

 ish-white, translucent, smeary growth, devoid of any characteristics, 

 takes place. The entire surface of the culture-medium is never cov- 

 ered, the growth remaining confined to the inoculation line, except 



