94 



ELEMENTS OF WATER BACTERIOLOGY 



enteritidis and B. coli. Organisms of the first division 

 ferment neither dextrose, lactose nor saccharose; those 

 of the second ferment dextrose but not lactose; and 

 those of the B. coli division form gas in both these 

 sugars. The relationship of the commonest species 

 is indicated in tabular form below: 



BACTERIA OF THE COLON-TYPHOID GROUP 



In the typhoid division, B. alcaligenes and B. dysen- 

 teriae are the best-known forms, besides B. typhi itself. 

 B. alcaligenes stands at the lower end of the whole 

 series in fermentative power. B. typhi forms a slight 

 initial acidity in milk and a slight acidity in dextrose 

 broth, while the reaction of B. alcaligenes in sugar 

 media is always alkaline. B. dysenteriae, on the other 

 hand, differs from B. typhi in the direction of the B. 

 enteritidis group, producing a well-marked acid reac- 

 tion, but no gas in dextrose media. B. typhi and B. 

 dysenteriae are, of course, also distinguished by their 

 specific serum reactions. 



