638 APPLICATION OF METHODS OF BACTERIOLOGY 



with materials containing the specific organisms known to 

 cause such diseases. 



As a result of evidence now known to everyone it is the 

 general belief that polluted water is primarily the under- 

 lying cause of most widespread epidemics of intestinal 

 infections 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 constantly 

 present in the water for all waters, except deep ground- 

 water, contain bacteria; if sudden fluctuations 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 standpoint it 

 must always be borne in mind that comparisons with fixed 

 standards are not of much value, for just as normal waters 

 from different sources are seen to present variations in their 



