BACTERIOLOGICAL ANALYSIS OF WATER 227 



isms developing on the agar and gelatin plates. Explain 

 why your results vary on different media. 



29. Does one medium seem more favorable to the 

 development of a larger number of organisms? If so, 

 which? Give reasons for answers. 



30. If the gelatin count is less than 100 organisms per 

 cubic centimeter the water is good, 200 per cubic centimeter 

 will pass but if many more, i.e., 500, 1000 or over, the water 

 is suspicious and effort should be made to determine the 

 presence of B. coli. 



31. Read the statements on pp. 41-43 and 62-64, et al, 

 in Prescott and Winslow's Elements of Water Bacteriol- 

 ogy and compare with those on p. 77, Standard Methods 

 of Water Analysis. After experiments 1 and 2 are com- 

 pleted, draw your own conclusions from the above and give 

 reasons for statements you make. 



32. Each student must know the morphological and cul- 

 tural characteristics of B. coli, Bad. aerogenes and B. typho- 

 sus. 



Read about and comment on the methods used in other 

 countries, giving references to the literature read. 



33. What other methods are employed to determine 

 the potability of water? Discuss these. 



REFERENCES 



Standard Methods of Water Analysis, American Public Health Asso- 

 ciation (1913), pp. 77-80, 88-96, el al. 



PRESCOTT and WINSLOW: Elements of Water Bacteriology, 3d Ed., 

 pp. 1-51, 215-228. 



MARSHALL: Microbiology, pp. 192-204. 



SAVAGE: Bacteriological Examination of Water Supplies (1906), 

 pp. 192-193, 194-264. 



THRESH: Examination of Waters and Water Supplies, 2d Ed. (1913), 

 pp. 184-271, 488-524. 



DON and CHISHOLM: Modern Methods of Water Purification (1911), 

 pp. 260-271, 



