604 APPLICATION OF METHODS OP 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 opinion is now general 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 bac- 

 teriological 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 



