INFECTIONS OF THE DIGESTIVE TRACT 7 



and here are confronted with immense numbers of the 

 chief obligate race of bacteria of the digestive tract 

 the representatives of the B. coli type. Another group 

 of obligate organisms closely allied to B. coli, B. lactis 

 aerogenes, is present in the upper part of the small 

 intestine and becomes gradually less abundant with its 

 descent into the colon and finally appears in relatively 

 small numbers in the fa3ces, if at all. As the bacteria 

 of the B.lactis aerogenes type grow less numerous, the 

 representatives of the B. coli group grow more abundant 

 and beyond the ileocaecal valve largely dominate the 

 intestinal flora. 



Exactly what happens when the accidental, sapro- 

 phytic forms of bacterial life the "wild races/' as 

 the French call them come to close quarters with 

 the " obligate/' well-adapted parasitic forms of the 

 intestine, we do not at present know. There are, how- 

 ever, numerous facts which point to well-defined bio- 

 logical antagonisms between the "wild" forms and the 

 representatives of the B. coli group. 



ON THE ANTAGONISM BETWEEN B. Coli COmmunis AND 

 OTHER MICROORGANISMS 



The members of the B. coli group are organisms of 

 varying morphology, characterized by a certain hardiness 

 in growth on ordinary media, by the free production of 

 gas and acid on various sugars, by the coagulation of 

 milk, and usually by the formation of indol, and by a 

 sluggish motility in some fully grown forms and active 



