586 BACTERIOLOGY. 



contaminated with materials containing the specific or- 

 ganisms known to cause such diseases. 



As a result of numerous observations by the disciples 

 of both schools, the opinion is now general that polluted 

 water is primarily the underlying cause of these epi- 

 demics, and this too, very often, when the state of the 

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

 esis, is just the reverse of what it should be in order to 

 render it answerable for them. It is manifest, there- 

 fore, 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, whether the water contains 

 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, 



