CHARACTERISTICS OF THE COLON-AEROGENES GROUP 103 



/>. cloacae may be considered as the stem from which the 

 other members of the group have sprung. By its vigorous 

 habits of growth, the wide range of substances from which 

 it is able to obtain its supply of carbon and its ability to ex- 

 crete proteolytic enzymes, it is able to thrive under the sapro- 

 phytic conditions in which it is found. B. aeroyenes has lost 

 the proteolytic ability and acquired semi-parasitic habits. 

 B. coli is still more parasitic in its habits, is more restricted 

 in its range of carbon suppl\~, and is further removed from 

 B. cloacae and B. aeroyenes by the loss of the carbinol reaction 

 and by the development of the ability to form indol. Still 

 more parasitic in their habits and correspondingly more re- 

 moved from B. cloacae by their physiological characters are 

 B. enteritides, B. typhosus and B. dysenteriae. Removed 

 from B. cloacae in the opposite direction is B. protens which 

 has developed the proteolytic ability but lost in the utilization 

 of carbohydrates both in the range of materials fermented and 

 in the extent of the fermentation. 



