BACTERIOLOGICAL STUDY OF WATER. 623 



OF WATER. The qualitative bacteriological analysis 

 of water entails much labor, as it requires not only 

 that all the different species of organisms found in the 

 water should be isolated, but that each representative 

 should be subjected to systematic study, and its patho- 

 genic or non-pathogenic properties determined. 



For this purpose a knowledge of the methods for the 

 isolation of individual species which have already been 

 described, and of the means of studying these species 

 when isolated, is 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 

 should be made as quickly as possible after collecting 

 the sample. 



When circumstances permit, all water analyses should 

 be made on the spot where the sample is taken, as it 

 is known that during transportation, unless the samples 

 are kept packed in ice, a multiplication of the organ- 

 isms contained in it always occurs. 



For the purpose of qualitative analysis it is necessary 

 that a small portion of the water one, two, three, five 

 drops should first be employed for making the plates. 



