CHAPTER XXVIII 



INTESTINAL OR COLON-TYPHOID GROUP. WATER ANALYSIS 



THE organisms belonging to this group may be characterized 

 as plump, gram-negative rods, frequently though not always 

 motile; they produce no spores, do not liquefy gelatin, and in most 

 cases ferment certain sugars, with acid- and sometimes gas- 

 production. The group contains many undoubted species that 

 may be easily differentiated, but there are many intergrading 

 types and forms showing similar morphologic and cultural char- 

 acters, but differing considerably in kind and in degree of virulence. 

 These latter make a systematic presentation of the group as a 

 whole difficult. Exactly what amount of difference is necessary 

 to constitute a distinct species is always a difficult problem, but 

 nowhere more so than with these forms. The group name is 

 given because of their prominence in the intestinal flora in disease 

 and health in both man and animals. They are, therefore, abun- 

 dant in sewage and water contaminated thereby, and in soil, par- 

 ticularly that which has received additions of barn-yard manure. 

 They are uncommon in virgin soil and in uncontaminated water. 



The members of this group are divided, for convenience in 

 study, into three subgroups. This arrangement seems to repre- 

 sent evident relationships. The fermentative powers of the 

 organisms are used as a basis upon which to make the groupings. 

 The first of these is known as the colon bacillus subgroup, the 

 second as the intermediate, hog-cholera, or enteritidis subgroup, 

 and the third as the typhoid-dysentery subgroup. The principal 

 points of difference between these subgroups may be summarized 

 in the following chart, giving the fermentation reactions in dex- 

 trose and lactose broth. 



Subgroup I. Subgroup II. Subgroup III. 



Colon subgroup. Intermediate subgroup. Typhoid-dysentery sub- 

 group. 

 Acid. Gas. Acid. Gas. Acid. Gas. 



Dextrose -*- 4- Dextrose 4- 4- Dextrose 



Lactose 4- 4- Lactose - . Lactose 



261 



