CHAPTER VI. 





 METHODS FOR THE ISOLATION OF THE COLON BACILLUS. 



THE Bacillus coli was first isolated by Escherich 

 (Escherich, 1884) from the feces of a cholera patient. 

 It was subsequently found to be a normal inhabitant of 

 the intestinal tract of man and many other animals, and 

 to occur regularly in their excreta, and on this account 

 it became of the highest interest and importance to sani- 

 tarians, since its presence in water-supplies was regarded 

 as direct evidence of sewage pollution. 



This organism may be described as a short, usually 

 motile rod, with diameter generally less than one micron 

 and exhibiting no spore formation. It forms thin irregu- 

 lar translucent films upon the surface of gelatin, called 

 " grape-leaf colonies" by the Germans, produces no 

 liquefaction, and gives a wire-nail-like growth in stick 

 cultures. It forms a white translucent layer of character- 

 istic appearance upon agar, produces a more or' less 

 abundant, moist, yellowish growth on potato, and tur- 

 bidity and some sediment in broth; it ferments dextrose 

 and lactose with the formation of gas of which the ratio is 



approximately, - = as ordinarily determined; a 

 CO 2 i, 



86 



