Contents xi 



CHAPTER VIII 



Pages 



CONTAMINATION OF STREAMS AND LAKES 61-76 



Soils contain bacteria The character of the bacteria in 

 water The number of bacteria in water Causes affect- 

 ing the increase or decrease of bacteria in water The 

 supply of food Temperature Sunlight Animalcules 

 injurious to bacteria Sedimentation Dilution The 

 contamination of drinking-water by sewage. 



CHAPTER IX 



PURIFICATION OF RIVER AND LAKE SUPPLIES . ... 77-89 



The quality of organic matter Alkaline water 

 River-water and surface drainage Self-purification 

 of rivers The storing and filtration of river-water 

 Sand-filtration Other methods of water purification 

 The alum method The Clark process Purification by 

 finely divided solids The Woolf method Purification 

 by means of ozone Filters for domestic purposes 

 The waters of lakes and ponds. 



CHAPTER X 



BACTERIA IN WELLS, SPRINGS, TANKS AND ICE 90-98 



Bacteria and well-water Deep wells and springs 

 Driven wells Artesian wells Bacteria in the water of 

 cisterns and tanks. Bacteria in ice. 



CHAPTER XI 



THE SANITARY EXAMINATION OF WATER-SUPPLIES . . .99-102 



