BACTERIA OF WATEE AND SEWAGE 51 



SECTION XI 

 BACTERIA OF WATER AND SEWAGE 



Nearly aU bodies of natural waters contain varying numbers 

 of bacteria. ^lany bacteria are introduced from the atmosphere 

 or from organic substances comiug iuto the water, but the larger 

 number are washed in from the soU. Those bacteria survive and 

 multiply which are best suited to the physical environment of 

 the water iuto which they are brought. There comes to be a 

 characteristic group of organisms in water, which may be re- 

 garded as " normal " bacteria. 



The bacteriology of waters is of importance from the stand- 

 point of sanitary Hving, and has received much study. A chem- 

 ical determination of the chlorides, nitrates, nitrites, albuminoid 

 ammonia, and the hardness of the water is required for complete 

 investigation of the water sample. 



HoKKOCKS. The Bacteriological Examination of Water. London, 1901. 

 KiN-sicuTT, "WixsLOw, and Pratt. Sewage Disposal. Xew York, 1910. 

 Pkescott and Wisslow. Elements of Water Bacteriology. New York, 1908. 

 Masox. Examination of Water. Xew York, 1909. 



Exercise 73. Collecting Samples of Water 



1. Tie pieces of filter paper or tin foil over five glass-stop- 

 pered bottles of 150-2-50 cc. capacity. The bottles, which should 

 be perfectly clean, are sterilized in the dry sterilizer at 140° C. 

 for two hours. 



2. At the time of taking samples from surface waters, re- 

 move the paper cap, then withdraw the stopper, touching only 

 the top of it with the fingers. Hold the bottle by the base in 

 the other hand and plunge it mouth downward into the water. 

 When about 12 in. beneath the surface, turn the bottle mouth 

 upwards and allow it to fill. Whenever any current exists, the 

 mouth of the bottle should be directed against it, in order to 

 carry away any bacteria from the fingers. If there is no current, 

 a similar effect can be produced by turning the bottle under 

 water and giving it a quick forward motion. Remove the bottle 



