CHAPTER XXVIII. 



Bacteriological study of water Methods employed Precautions to 

 be observed Apparatus employed, and methods of using it- 

 Methods of investigating air and soil Bacteriological study of 

 milk Methods employed. 



BACTERIOLOGICAL STUDY OP WATER. 



THE conditions that favor epidemic outbreaks of 

 typhoid fever, Asiatic cholera, and other maladies of 

 which these may be taken as types, have served as a 

 subject for discussion by sanitarians for a long time. 



Of the opinions that have been advanced in explana- 

 tion of the existence and dissemination of these diseases, 

 two should be considered : one, the ground- water doctrine 

 of von Pettenkofer, because of its historic interest; the 

 other, the belief that the diseases are disseminated by 

 specifically polluted waters, because it is the view now 

 prevalent among modern sanitarians. 



The advocates of the "ground- water" view explained 

 the occurrence of these diseases in epidemic form through 

 alterations in the soil resulting from fluctuations in the 

 level of the soil-water; and assigned to drinking-water 

 either a very insignificant role, or ignored it entirely. 

 On the other hand, those who have been instrumental 

 in developing the drinking-water hypothesis claim that 

 alterations in the soil play little or no part in favoring 

 epidemic outbreaks ; but that, as a rule, they appear as 

 a result of direct infection, through the use of waters 



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