2p6 DISTRIBUTION OF BACTERIA 



affecting the potableness (drinkableness) of the water. Other 

 kinds of bacteria make their way into the water and usually 

 quickly disappear. Those which are most important in this 

 connection are from sewage in general, and human sewage in 

 particular. Among these sewage bacteria which get into water 

 are B. coli, B. typhosus, B. dysenteriae, and Msp. comma. 

 Bacillus coli is the common inhabitant of the human intestine. 

 It is also found in the intestine of other animals, particularly 

 those which are domesticated. Its presence in surface waters 

 in very small numbers, for example, less than one to a cubic 

 centimeter, may possibly be accounted for by the presence 

 of the excreta of animals not closely associated with man. 

 But when present in greater numbers than indicated above, 

 they constitute, by practically common consent, evidence 

 of dangerous sewage contamination. The presence of B. coli 

 in water may, then, be regarded as an indication of pollution. 

 In fact, its presence or absence in water, as determined by an 

 analysis, is used very largely in forming an opinion in regard to 

 the potableness of a water supply. Not infrequently, the dis- 

 ease-producing bacteria mentioned above, B. typhosus, B. dys- 

 enteriae and Msp. comma, get into sewage-polluted waters, 

 and very serious epidemics are frequently traced to sewage- 

 polluted waters. In the case of typhoid fever, probably at 

 least sixty per cent of the cases are water-borne. One of the 

 first typhoid epidemics to be carefully studied was that which 

 occurred in Lawsen, Switzerland, in 1872. Here, from August 

 to October, a hundred and thirty cases of typhoid fever 



