680 BACTERIOLOGY. 



with materials containing the specific organisms known 

 to cause such diseases. 



As a result of numerous observations by the disciples 

 of both schools, the evidence is now 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 

 liable to pollution. 



The object aimed at in such investigations should be 

 to determine the number and kind of bacteria con- 

 stantly present in the water — for all waters, except 

 deep ground-water, contain bacteria ; if sudden fluctua- 

 tions in the number and kind 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 continuously favorable to pollution of the water 

 by the normal constituents of the intestinal canal, the 

 same conditions would allow of the occasional pollution 

 of such water by infective matters from the bowels of 

 persons suffering from specific disease of the intestines. 



In considering water from a bacteriological stand- 

 point it must always be borne in mind that com- 

 parisons with fixed standards are not of much value. 



