VARIETIES OF COLON BACILLI 



195 



Group IV. Of 280 colonies isolated during dry periods, 

 37 belonged to Group I, 22 to Group III and 221 to 

 Group IV. When the forces of self-purification had 

 been at work, Group II (B. coli) entirely disappeared 

 and Group IV (B. cloacae and B. coscoroba) was pre- 

 dominant. B. Griinthal was the commonest of the 

 Group I forms. B. cloacae was especially prevalent 

 in bottom samples. 



A study of a number of rivers in Bengal gave the 

 results tabulated below. 



RELATIVE PREVALENCE OF CERTAIN LACTOSE- 

 FERMENTING TYPES IN BENGAL RIVERS 



There are many irregularities in Dr. Clemesha's 

 results. For example, B. aerogenes, as well as the other 

 representatives of Group IV, was more abundant in Red 

 Hills Lake during dry periods than at times of rain. 

 On the whole, however, it does seem clear that his 

 results justify a general classification of the lactose- 

 fermenting organisms into three main groups accord- 

 ing to resistance. B. coli communis and B. oxytocus 

 perniciosus (representing MacConkey's Groups II and 

 III, both fermenting dulcite) are sensitive organisms 

 found in numbers only where pollution is fresh. B. lactis- 

 aerogenes, representing the subgroup of MacConkey's 



