Isolation- of the Colon Bacillus. ill 



In general routine work there will scarcely be time to 

 carry out preliminary enrichment processes of this sort, 

 and cultures which fail to reduce nitrates or to form indol, 

 or which do not form sufficient acid in milk to coagulate 

 it, must be classed as atypical colon bacilli or " Paracolon " 

 bacilli. The interpretation of results of this kind will be 

 discussed in Chapter IX. It may be noted in passing that 

 the results of the test for B. coli will fall under four general 

 heads : If the preliminary dextrose tube or the litmus- . 

 lactose-agar plate fail to show fermentation, the test is 

 negative. If these are positive and gelatin is liquefied, 

 we are dealing with a member of the B. cloacae group. 

 If, on the other hand, gelatin is not liquefied, the organ- 

 'ism is a typical B. coli if it meets the standard require- 

 ments of the nitrate, indol, and milk tests. If not it 

 must be classed as an allied " atypical " form. 



