CHAPTER XXII 



THE COLON BACILLUS 



(BACILLUS COLI) 



The colon bacillus is a normal inhabitant of the intestinal canal of man and 

 many animals, including all the domestic animals. A large portion of the entire 

 bulk of f eces is composed of colon bacilli. The colon bacillus has been found in 

 abundance upon plants and in water of regions barren of animal life. 



The colon bacillus is commonly present in air, dust and soil and in water pol- 

 luted with sewage. From these sources contamination of milk and foodstuffs 

 often occurs. 



FIG. 20. BACILLUS COLI. STAINED WITH METHYLENE BLUE. 

 (4 X eyepiece and M2 oil immersion objective.) 



Morphology. The colon bacillus is a straight, round-end bacillus, 2 to 3 ju 

 long and 0.5 to 0.8 fj. wide. It has from four to eight lateral flagella, which are 

 about 4 n long, and is actively motile. Colon bacilli are arranged irregularly, in 

 groups, singly, sometimes in pairs, end to end, and in long filaments. 



Staining. The colon bacillus stains readily with all the usual anilin dyes 

 and is Gram negative. 



Growth. The colon bacillus is aerobic and to a degree anaerobic. It grows 

 at temperatures between 4C. and 46C., best at 37C. 



Plain Bouillon incubated at 37C. begins to show cloudiness in about 12 

 hours. A light, whitish sediment forms in 24 to 48 hours, which increases in 

 amount for several days. Eventually, if undisturbed, the entire growth pre- 

 cipitates, leaving the fluid clear. 



. 103 



