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. 



UHAPTER IX 



Purification op 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 90-9S 



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 op Water-supplies . . .99-102 



