Bacilli Resembling the Typhoid Bacillus 617 



motile, and provided with fiagella, 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 Uquefied. 



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, sufhcient gas-production may occur to 

 break up the medium. The gelatin may become slightly clouded 

 but is not Hquefied. 



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 



