BACTERIOLOGICAL ANALYSIS OF SEWAGE 233 



organisms. What is the significance in sanitary water anal- 

 ysis of a large number of liquefying organisms? 



18. If acid colonies are not present in twenty-four to 

 forty-eight hours on litmus lactose agar plates, and acid 

 and gas are evident within this time either in the agar 

 shake or lactose bile fermentation tubes, make dilution 

 plates from either of these in litmus lactose agar, incubate 

 at 37 C. for twenty-four hours and fish acid colonies, 

 placing them on the different media for differentiating 

 B. coli. 



19. Compare the cultures isolated with the pure culture 

 of B. coli in every case. Also make comparisons with 

 Bad. aerogenes and B. typhosus. 



20. Isolate several different colonies and record the cultural, 

 etc., characteristics of each organism on the record sheet 

 furnished. Were any of the types of organisms in this 

 sample present in the first sample? Would you expect to 

 find this the case? Give reason. 



21. The data and conclusions in the above should be 

 given in detail. Point out also any practical applications. 



REFERENCES 



Standard Methods of Water Analysis, 1913 edition, pp. 79-82, 87-88, 



92, 95-102. 

 PRESCOTT and WINSLOW: Water Bacteriology, 3d. ed., pp. 61-201, 



228-265. 



SAVAGE: Bacteriological Examination of Water Supplies, pp. 27-69. 

 MARSHALL: Microbiology, pp. 97, 108, 162, 182, 204, 212, 221, 



323-324. 



