268 MAN'S IMPROVEMENT OF HIS ENVIRONMENT 



NxiKvber o/ Colonies iiv. ccccK 



different waters to be tested. Suggested samples are as follows : 

 distilled water, rain water, bottled spring waters of various kinds, 

 city tap water, standing water from lakes or pools near your home, 

 river water thought to contain sewage, dilute sewage. After 

 inoculating the Petri dishes with the water to be tested, place all 



of the dishes contain- 

 ing the samples in a 

 moderately warm place. 

 Examine after two or 

 three days, and on suc- 

 cessive days for one 

 week. Tabulate the 

 results. 



Observations. In which Petri dishes does the most bacterial 

 growth take place? 



Conclusion. 1. Which of the examined samples of water are 

 free from bacteria ? 



2. Which of the samples are best for drinking purposes? Give 

 reasons for your answer. 



Problem 24O : To determine some of the problems of water 

 supply and sewage disposal for a city. 



Method. Visit the sanitation exhibit in a city museum. 



Observations. From information gained from maps in the 

 museum, or in some other way, trace the growth of the water 

 supply of your city since its beginning. Where did the city first 

 get its water? What is now the source of the water supply? 



What impurities are commonly found in water? What do 

 reservoirs do to a water supply ? State 1 several ways in which a 

 water supply becomes contaminated. How might contaminated 

 waters bounding a city affect the health of the citizens of that 

 city? 



How does the sewage of your city affect the waters surrounding 

 it? How is this contamination brought about? What methods 

 are there for sewage disposal ? Which would you choose for use in 

 your city? Why? How is sewage now disposed of? 



How do conditions of water supply and sewage disposal on a 



