440 BACTERIOLOGY. 



the specific organisms that are known to cause such 

 diseases. 



As a result of many observations ori both sides of the 

 question, the evidence is greatly in favor of the opinion 

 that polluted water is primarily the underlying cause of 

 these epidemics, and this too, very often, when the state 

 of the soil water, in the light of the " ground- water " 

 hypothesis, is just the reverse of what it should be in 

 order to render it answerable for them. It is manifest, 

 therefore, that the careful bacteriological study of water 

 intended for domestic use is of the greatest importance, 

 and should be a routine procedure in all communities 

 receiving their water supply from sources that are liable 

 to pollution. 



The object aimed at in such investigations should be 

 to determine if the water approaches constancy in the 

 number and kind of bacteria contained in it for all 

 waters, except deep ground water, contain bacteria ; if 

 sudden fluctuations in the number of bacteria occur in 

 these waters, and if so, to what they are due; and finally, 

 and most important, does the water contain constantly, 

 or at irregular periods, bacteria that can be traced to 

 human excrement, not of necessity pathogenic varieties, 

 but bacteria that are known to be present normally in 

 the intestinal canal? For, if conditions are favorable to 

 ,the presence of these varieties the same conditions would 

 favor the admission to the water of other forms of bac- 

 teria that are concerned in the production of diseases in 

 the intestines. 



In considering water from a bacteriological stand- 

 point, it must always be borne in mind that comparisons 

 with any general fixed standard are not of much value, 

 for just as normal waters from different sources are seen 



