84 LABORATORY GUIDE IN BACTERIOLOGY 



SECTION 4 



BACTERIOLOGICAL EXAMINATION OF WATER, AIR 

 AND MILK 



EXERCISE I. BACTERIOLOGICAL ANALYSIS OF WATER 

 References 



Prescott and Winslow, Elements of Water Bacteriology, New 



York, 1914. 



Savage, The Bacteriological Examination of Water Supplies, 

 London, 1906. 



A bacteriological examination of water is made for 

 the purpose of determining 



1. Bacterial numbers. 



2. Bacterial species. 



3. Sewage pollution. 



Collection of samples. Procure wide-mouthed, 

 glass-stoppered bottles, having a capacity of at least 

 100 c.c. After cleaning and drying, tie lead foil or 

 filter paper over the stopper, wrap the bottles indi- 

 vidually in paper and sterilize in the hot-air oven for i 

 hour at 160 C. ; then deposit them in a metal or wooden 

 case. The samples from surface waters should be taken 

 at least one foot below the surface, to avoid contamina- 

 tion with organisms from the air. If possible, samples 

 should be plated on the spot or in the laboratory within 

 an hour at the latest. But when a greater interval of 

 time must occur, the samples should be taken to the 

 laboratory packed in ice, despite the probability of 

 thus partially altering the bacterial flora. 



Method of examination. A number of pipettes of 

 various sizes (i c.c., 2 c.c., 5 c.c., and 10 c.c.) are plugged 



