CHAPTER VIII 



VARIETIES OF COLON BACILLI AND THEIR SPECIAL 

 SIGNIFICANCE 



Tests Used for Subdividing the Colon Group. The 

 group of colon bacilH as defined in Chapter VI includes 

 all aerobic Gram-negative baciUi which produce acid 

 and gas in dextrose and lactose media. By the applica- 

 tion of various tests, mainly bio-chemical, it may be 

 further spUt up, almost at will, into a great number of 

 varieties. The principal tests which have been used for 

 this purpose are as follows: 



1. MotiHty. 



2. Coagulation of milk. 



3. Production of indol. 



4. Liquefaction of gelatin. 



5. Reduction of nitrates. 



6. Reduction of neutral red. 



7. Fermentation of various carbohydrates other than 

 dextrose and lactose. 



8. Voges and Proskauer reaction. 



9. Character of colonies on various solid media. 



10. Aesculin reaction. 



11. Growth and fermentation at 46°. 



Motility is seldom determined in actual routine work 

 in this country from the general belief that its demon- 



174 



