CHAPTER XXYI. 



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 OF WATER. 



THE conditions that favor the epidemic outbreak 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 hypotheses that have been advanced in ex- 

 planation of the existence and dissemination of these 

 diseases, two stand pre-eminent and are worthy of con- 

 sideration. They are the "ground-water" theory of 

 von Pettenkofer and his pupils, and the " drinking- 

 water" theory of the school of bacteriologists of which 

 Koch stands at the head. 



The adherents to the "ground-water" view explain 

 the occurrence of these diseases in epidemic form through 

 alterations in the soil resulting from fluctuations in the 

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

 either a very insignificant role, or, as is most frequently 

 the case, ignore 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 the outbreak of these dis- 

 eases ; but that, as a rule, they appear as a result of 

 direct infection, through the use of waters contaminated 



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