CHAPTER XXVII. 



Bacteriological study of water— Methods employed — Precautions to be 

 observed— Apparatus used, and methods of using them— Methods of investi- 

 gating air and soil. 



The conditions that favor the epidemic outbreak of 

 ty;phoid 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 explan- 

 ation of the existence and dissemination of these dis- 

 eases, 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 presence of these diseases in epidemic form through 

 alterations in the soil resulting from fluctuations in the 

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

 either a very insignificant r^h, 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 appearance of these 

 diseases in a neighborhood, but that, as a rule, they 

 appear as a result of direct infection through the use of 

 waters that are contaminated with materials containing 

 the specific organisms known to be the cause of them. 



As a result of many observations on both sides of the 



