262 VETERINARY BACTERIOLOGY 



The differences may be summarized as follows: the organisms 

 of subgroup I. ferment both dextrose and lactose, with formation 

 of both acid and gas; those of subgroup II. form acid and gas from 

 dextrose, but not from lactose; and those of subgroup III. may or 

 may not form acid from dextrose, but never from lactose, and gas 

 from neither of the sugars. 



The fermentations of other carbohydrates and related com- 

 pounds are used to differentiate species and varieties from each 

 other. A few can be satisfactorily differentiated only by the ag- 

 glutination reaction. For a study of the fermentative power of 

 the organisms 1 per cent, solutions of the sugars to be studied are 

 made in sugar-free broth and placed in fermentation tubes, and 

 sterilized by the discontinuous process to prevent decomposition. 

 Those organisms which produce gas grow in both the open and 

 closed arm, as do those which produce acid, and those which do 

 not ferment the sugar are usually confined to the open arm. 

 The composition of the gas, that is, the relative proportion of 

 CO 2 and H 2 , is also of diagnostic value. 



The organisms to be considered belonging to the colon sub- 

 group are Bacillus coli, B. lactis aerogenes, and B. pneumonia?. 

 Those of the intermediate group, Bacillus enteritidis, B. cholera 

 suis, B. psittacosis, B. paratyphosus, B. typhi murium, bacillus of 

 Danysz, and B. pullorum. The most important forms of the 

 third subgroup are Bacillus typhosus, B. dysenteries, and B. 

 fceqalis alkaligenes. 



The growth reactions of the various members of the intestinal 

 group, and more particularly of the colon subgroup, are of con- 

 siderable sanitary significance, as they furnish our most efficient 

 means of securing evidence of the suitability of water for drinking 

 purposes, and of its contamination by sewage. The topics of 

 .water analysis, sewage disposal, and water purification are so 

 intimately connected with the discussion of the members of the 

 intestinal group that they are included in the same chapter. 



SUBGROUP I COLON SUBGROUP 



Bacillus coli 



Synonyms. ^Bacillus coli communis; B. neapolitanus ; B. 

 pyogenes fcetidus ; Bacterium coli (commune); colon bacillus. 



