110 Bacteria in Relation to Country Life 



more or less complicated and difficult by the fact tliat 

 the rivers and lakes used as a source of water-supply 

 by some communities receive the sewage of other com- 

 munities. Progressive legislation in this respect in some 

 states has contributed much towards a rational solution 

 of the problem. . The pollution of rivers by sewage is 

 prohibited in some states, exception being made only 

 in the case of rivers already much polluted before enter- 

 ing the boundaries of the state. 



It is unnecessary to add proof of the growing realiza- 

 tion of the importance of proper sewage-disposal, and 

 of the awakened public interest in the matter, as ex- 

 pressed in recent legislation. The work is, nevertheless, 

 still in its very beginning. 



The source, composition and quantity of sewage. — City 

 sewage consists of human and animal excreta, refuse 

 from the kitchen and laundry, various manufacturing 

 wastes, and the dust and dirt of streets and roads, dis- 

 tributed in a greater or slighter quantity of water. Some 

 cities provide a separate system for storm water, thus 

 facilitating the purification of the sewage, when this 

 is found necessary. For instance, in the city of Paris, 

 where the sewage is utilized for irrigation purposes, a 

 large portion of the water used for flushing the streets 

 finds its way back to the Seine without previous puri- 

 fication. 



The composition of sewage is variable. Variations 

 in sewage of the same town occur at different periods in 

 the day. The sewage that is produced in the forenoon 

 and afternoon shows the influence of human activities 

 in the greater volume and in the greater amount of 



