30 BACTERIOLOGICAL EXAMINATION OF WATER. 



Egger counted only four organisms per c.c. in the artesian 

 wells in Mainz, and Hueppe found only 4 bacteria per c.c. in 

 the deep wells in Wiesbaden. Heraeus, C. Frankel, and Maschek 

 made numerous studies of wells after they had been at rest for 

 some time and after pumping. Heraeus found 5000 organisms 

 in a well which had been at rest for 36 hours, but, after the well 

 had been emptied by continuous pumping, a sample collected 

 showed only 35 bacteria per c.c. Frankel and Maschek obtained 

 similar results. 



Springs are closely allied to deep wells as regards their 

 bacterial contents. Cramer found in Zurich springs 9, 17, 17, 

 31, 36, 182, 15, 25 and 45 bacteria per c.c. Frommelt counted 

 in the water supply of the town of Altenburg, which was derived 

 from springs, only 28, 35, and 25 bacteria per c.c. Buchner 

 found the springs in a garden at Brunnthal to contain only 

 from 4 to 35 colonies per c.c. 



A brief consideration of these results shows that, with the 

 exception of deep wells and springs, it is impossible to decide 

 from the quantitative examination alone whether a water supply 

 has been polluted or not. This is due to the fact that the 

 great variations in the results are attributable not only to 

 possible sewage contamination, but also to the influence of the 

 physical and chemical conditions of the supply, which operate 

 sometimes so as to increase the number of micro-organisms 

 present, and at other times lead to a rapid disappearance of 

 the microbes. It is also evident that the general standards 

 given by many observers cannot be used for all waters. Mace 

 certainly says that the number of micro-organisms present does 

 not give any accurate information as to the value of a water ; 

 at the same time he suggests the following classification, which 

 gives the mean results of a long series of examinations : 



Very good waters contain from 0-50 rnicro-organisms per c c. 



Good 50-500 



Mediocre 500-3,000 



Bad 3,000-10,000 



Very bad 10,000-100,000 



The only sound way to judge a supply is to examine each 

 source separately at different times of the year, especially 

 before and after rain, in summer and in winter ; in this way 



