148 LABORATORY GUIDE IN BACTERIOLOGY 



EXERCISE 5. EXAMINATION OF RAIN WATER, SNOW, 

 AND ICE 



Secure samples of rain water or snow, and of ice. 

 Examine these samples, making dilutions up to i : i;000 

 in the manner directed. 



SECTION 3 



EXAMINATION OF SEWAGE 



1. Secure two samples of sewage. Place one of 

 these in an ice chest. Examine the other sample in 

 the same manner as directed for water, with this 

 exception, that dilutions of 1:1,000, 1:10,000, 1:100,- 

 000, and 1:1,000,000 are to be used for plating and 

 inoculation of fermentation tubes, omitting the lower 

 dilutions. 



2. Keep the first sample of sewage in your locker. 



3. After seven days examine both samples, i.e., the 

 one kept in the locker and the one kept in the ice chest, 

 in the same manner as the fresh sewage was examined. 

 Note the difference in the results of this examination 

 as compared to that of fresh sewage. 



4. Replace the samples in the locker and ice chest 

 and examine again after seven and after 14 days. 



Note. — If possible a chemical examination for free and albu- 

 minoid ammonia and for nitrites and nitrates should be made 

 simultaneously with the bacteriological examination. This will 

 help to give a clear understanding of the changes which have 

 talien place during the three weeks. 



