THE COLON, TYPHOID AND DYSENTERY BACILLI 325 



o.7M wide and i to 6/1 long, with rounded ends, usually single but 

 sometimes occurring in threads. It is motile but not very active^ 

 and many cells, even in young cultures, may be motionless. 



There are four to eight peritrichous flagella. Spores have 

 not been observed. The bacillus stains readily and is Gram- 

 negative. 



Cultures develop rapidly at 37 C. on all ordinary media. 

 The colony is white, opaque, often somewhat heaped up in the 

 center and thinner near the edge. It may be round with smooth 

 outline or the border may be lobulated. Under the low-power 



FIG. 131. Bacillus coli. Superficial colony on a gelatin plate two days old. X 21. 

 (From McFarland after Heim.) 



lens the colony appears brown, finely granular near the periphery 

 and more coarsely granular near the center. It is soft and moist, 

 easily removed from the medium and easily suspended as a dif- 

 fuse cloud in water. Gelatin is not liquefied. B. coli ferments 

 dextrose and lactose with the production of gas as well as acid. 

 It coagulates milk in 24 to 48 hours at 37 C. and renders it acid, 

 produces considerable indol in pepton solution and grows abun- 

 dantly on potato, often producing a brown color. 



Intraperitoneal injection of cultures into guinea-pigs and rats 

 causes fatal peritonitis. Subcutaneous injection may also cause 

 death but frequently results in a local abscess. 



