438 AGEICULTUBAL AND INDUSTEIAL BACTERIOLOGY 



Streams which entered the sink. Such springs are apt to 

 be muddy following rainy weather, showing the surface 

 communication. Springs of this character, of course, are 

 dangerous. 



Water from cisterns carefully protected from dirt and 

 adequately filtered is usually satisfactory for domestic use. 

 There is very little opportunity in most cases for human 

 excretions to reach such water. 



Wells constitute the source of water supply for most 

 rural communities and for farms. Studies which have been 

 made upon the water in farm wells in different parts of the 

 United States would seem to indicate that in general their 

 character is relatively poor. In one survey made in Iowa, 

 for example, about sixty per cent of samples secured from 

 well water supplies were found to contain Bacterium coli. 

 An examination of the surroundings of wells shown thus 

 to be polluted will usually reveal the manner in which the 

 contamination reaches the well. Many wells are located in 

 barnyards and are not satisfactorily protected from surface 

 water. It will be recalled that Bacterium coli is abundant 

 in animal excretions as well as in human dejecta. The 

 presence of such an organism in a farm water, therefore, 

 does not necessarily mean that human excreta are finding 

 their way into the supply, but that barnyard manure is 

 gaining access. There is no reason to suppose that water 

 containing diluted barnyard manure will produce disease 

 in man unless it also contains human excretions. Any one 

 who has had experience upon a farm will know, however, 

 that water receiving drainage from the barnyard will con- 

 tain not only organisms derived from animal sources but 

 from human sources as well. In other words, while a water 

 containing large numbers of Bacteriupi coli because of sur- 

 face drainage from the barnyard, may be used for years 

 without causing disease, nevertheless, inasmuch as it is 

 subject to contamination, it is a source of constant danger. 



