424 BACTERIOLOGY. 



pollutions are possible are a constant menace to the 

 health of those who use them for domestic pur- 

 poses. 



A sudden variation from the normal, mean number 

 of bacteria, or from the normal chemical composition 

 of a water, calls at once for a thorough inspection of the 

 supply, while at the same time the characters of the 

 organisms present are to be subjected to the most careful 

 study. 



The Qualitative Bacteriological Analysis 

 OF Water. — The qualitative bacteriological analysis 

 of water entails much labor, as it requires not only that 

 all the different species of organism found in the water 

 should be isolated, but that each representative should 

 be subjected to systematic study, and its pathogenic or 

 non-pathogenic properties deternjined. 



For this purpose the methods for the isolation of 

 individual species, which have already been described, 

 and the means of studying these species when isolated, 

 are indispensable. 



For this analysis certain precautions essential to 

 accuracy are always to be observed. 



The sample is to be collected under the most rigid 

 precautions that will exclude organisms from sources 

 other than that under consideration. If drawn from a 

 spigot, it should never be collected until the water has 

 been flowing for .fifteen to twenty minutes in a full 

 stream. If obtained from a stream or a spring, it 

 should be collected, not from the surface, but rather 

 from about one foot beneath the surface. 



It should always be collected in vessels which have 

 previously been thoroughly freed from all dirt and 

 organic particles, and then sterilized. And the plates 



